Posts Tagged ‘Organoids’

Tumor Organoids Used to Speed Cancer Treatment

Reporter: Irina Robu, PhD

Collecting cancer cells from patients and growing them into 3-D mini tumors could make it possible to quickly screen large numbers of potential drugs for ultra-rare cancers. Preliminary success with a new high-speed, high-volume approach is already guiding treatment decisions for some patients with recurring hard-to-treat cancers.

A London-based team labelled how a “tumor-in-a-dish” approach positively forecasted drug responses in cancer patients who previously took part in clinical trials. That study was a major development in a new research area focused on “organoids” — tiny 3-D versions of the brain, gut, lung and other organs grown in the lab to probe basic biology or test drugs.

UCLA cancer biologist Alice Soragni and her colleagues developed a high-volume, automated method to rapidly study drug responses in tumor organoids grown from patient cells. By studying mini tumors grown on a plate with 96 tiny test tubes, her team can screen hundreds of compounds at once and classify promising candidates within a time frame that is therapeutically actionable. According to Dr. Soragni, the method seemed to work for various kinds of ovarian cancer. It was shown that the lab-grown organoids mimicked how tumors in the body look and behave. And even in cases when mini tumors had a hard time growing in a dish, scientists still acknowledged potential drug candidates.
Up to now, the UCLA team has produced organoids from 35 to 40 people with various types of sarcoma which will allow them to classify tumors that won’t respond to conventional therapy. This proves useful for people with recurrent metastases, where it’s not clear if we’re doing anything for their overall survival or giving them more toxicity.



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Functioning Human Neural Networks Grown in 3-D from Stem Cells

Reporter: Irina Robu, PhD


Researchers at Tuffs University developed three-dimensional human tissue model that mimics structural and functional features of the brain and were able to demonstrate sustained neural activity over several months. The 3D brain tissue models were the result of a collaborative effort between researchers from Tufts University School of Engineering, Tufts University School of Medicine, the Sackler School of Graduate Biomedical Sciences at Tufts, and the Jackson Laboratory.


These tissue models have the ability to populate a 3D matrix of silk protein and collagen with cells from patients with Parkinson’s disease, Alzheimer’s disease and the ability to

  • explore cell interactions,
  • disease progression and
  • response to treatment.

The 3D brain tissue models overcome a crucial challenge of previous models which is the availability of human source neurons due to the fact that neurological tissues are rarely removed from

  • healthy patients, and are usually available
  • post-mortem from diseased patients.

The 3D tissue models are populated with human induced pluripotent stem cells (iPSCs) that can be derived from several sources, including patient skin. The iPSCs are generated by turning back the clock on cell development to their embryonic-like precursors. They can then be dialed forward again to any cell type, including neurons. The porous structure of the 3D tissue cultures labeled in the research delivers sufficient oxygenation, access for nutrients and measurement of cellular properties. A clear window in the center of each 3D matrix allows researchers to visualize the

  • growth,
  • organization and
  • behavior of individual cells.

According to David L. Kaplan, “the silk-collagen scaffolds provide the right environment to produce cells with the genetic signatures and electrical signaling found in native neuronal tissues”. Compared to growing and culturing cells in two dimensions, the three-dimensional matrix yields a knowingly extra complete mix of cells found in neural tissue, with the appropriate morphology and expression of receptors and neurotransmitters. Other researchers have used iPSCs to create brain-like organoids, but can still make it difficult figuring out what individual cells are doing in real time. Likewise, cells in the center of the organoids may not obtain enough oxygen or nutrients to function in a native state.

However, the researchers can see a great advantage of the 3D tissue models with advanced imaging techniques, and the addition of cell types such as

  • microglia and
  • endothelial cells,

to create a more complete model of the brain environment and the complex interactions that are involved in

  • signaling,
  • learning and plasticity, and
  • degeneration.



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Colon cancer and organoids

Larry H. Bernstein, MD, FCAP, Curator





Guts and Glory

An open mind and collaborative spirit have taken Hans Clevers on a journey from medicine to developmental biology, gastroenterology, cancer, and stem cells.

By Anna Azvolinsky

Ihave had to talk a lot about my science recently and it’s made me think about how science works,” says Hans Clevers. “Scientists are trained to think science is driven by hypotheses, but for [my lab], hypothesis-driven research has never worked. Instead, it has been about trying to be as open-minded as possible—which is not natural for our brains,” adds the Utrecht University molecular genetics professor. “The human mind is such that it tries to prove it’s right, so pursuing a hypothesis can result in disaster. My advice to my own team and others is to not preformulate an answer to a scientific question, but just observe and never be afraid of the unknown. What has worked well for us is to keep an open mind and do the experiments. And find a collaborator if it is outside our niche.”

“One thing I have learned is that hypothesis-driven research tends not to be productive when you are in an unknown territory.”

Clevers entered medical school at Utrecht University in The Netherlands in 1978 while simultaneously pursuing a master’s degree in biology. Drawn to working with people in the clinic, Clevers had a training position in pediatrics lined up after medical school, but then mentors persuaded him to spend an additional year converting the master’s degree to a PhD in immunology. “At the end of that year, looking back, I got more satisfaction from the research than from seeing patients.” Clevers also had an aptitude for benchwork, publishing four papers from his PhD year. “They were all projects I had made up myself. The department didn’t do the kind of research I was doing,” he says. “Now that I look back, it’s surprising that an inexperienced PhD student could come up with a project and publish independently.”

Clevers studied T- and B-cell signaling; he set up assays to visualize calcium ion flux and demonstrated that the ions act as messengers to activate human B cells, signaling through antibodies on the cell surface. “As soon as the experiment worked, I got T cells from the lab next door and did the same experiment. That was my strategy: as soon as something worked, I would apply it elsewhere and didn’t stop just because I was a B-cell biologist and not a T-cell biologist. What I learned then, that I have continued to benefit from, is that a lot of scientists tend to adhere to a niche. They cling to these niches and are not that flexible. You think scientists are, but really most are not.”

Here, Clevers talks about promoting a collaborative spirit in research, the art of doing a pilot experiment, and growing miniature organs in a dish.

Clevers Creates

Re-search? Clevers was born in Eindhoven, in the south of The Netherlands. The town was headquarters to Philips Electronics, where his father worked as a businessman, and his mother took care of Clevers and his three brothers. Clevers did well in school but his passion was sports, especially tennis and field hockey, “a big thing in Holland.” Then in 1975, at age 18, he moved to Utrecht University, where he entered an intensive, biology-focused program. “I knew I wanted to be a biology researcher since I was young. In Dutch, the word for research is ‘onderzoek’ and I knew the English word ‘research’ and had wondered why there was the ‘re’ in the word, because I wanted to search but I didn’t want to do re-search—to find what someone else had already found.”

Opportunity to travel. “I was very disappointed in my biology studies, which were old-fashioned and descriptive,” says Clevers. He thought medicine might be more interesting and enrolled in medical school while still pursuing a master’s degree in biology at Utrecht. For the master’s, Clevers had to do three rotations. He spent a year at the International Laboratory for Research on Animal Diseases (ILRAD) in Nairobi, Kenya, and six months in Bethesda, Maryland, at the National Institutes of Health. “Holland is really small, so everyone travels.” Clevers saw those two rotations more as travel explorations. In Nairobi, he went on safaris and explored the country in Land Rovers borrowed from the institute. While in Maryland in 1980, Clevers—with the consent of his advisor, who thought it was a good idea for him to get a feel for the U.S.—flew to Portland, Oregon, and drove back to Boston with a musician friend along the Canadian border. He met the fiancé of political activist and academic Angela Davis in New York City and even stayed in their empty apartment there.

Life and lab lessons. Back in Holland, Clevers joined Rudolf Eugène Ballieux’s lab at Utrecht University to pursue his PhD, for which he studied immune cell signaling. “I didn’t learn much science from him, but I learned that you always have to create trust and to trust people around you. This became a major theme in my own lab. We don’t distrust journals or reviewers or collaborators. We trust everyone and we share. There will be people who take advantage, but there have only been a few of those. So I learned from Ballieux to give everyone maximum trust and then change this strategy only if they fail that trust. We collaborate easily because we give out everything and we also easily get reagents and tools that we may need. It’s been valuable to me in my career. And it is fun!”

Clevers Concentrates

On a mission. “Once I decided to become a scientist, I knew I needed to train seriously. Up to that point, I was totally self-trained.” From an extensive reading of the immunology literature, Clevers became interested in how T cells recognize antigens, and headed off to spend a postdoc studying the problem in Cox Terhorst’s lab at Dana-Farber Cancer Institute in Boston. “Immunology was young, but it was very exciting and there was a lot to discover. I became a professional scientist there and experienced how tough science is.” In 1988, Clevers cloned and characterized the gene for a component of the T-cell receptor (TCR) called CD3-epsilon, which binds antigen and activates intracellular signaling pathways.

On the fast track in Holland. Clevers returned to Utrecht University in 1989 as a professor of immunology. Within one month of setting up his lab, he had two graduate students and a technician, and the lab had cloned the first T cell–specific transcription factor, which they called TCF-1, in human T cells. When his former thesis advisor retired, Clevers was asked, at age 33, to become head of the immunology department. While the appointment was high-risk for him and for the department, Clevers says, he was chosen because he was good at multitasking and because he got along well with everyone.

Problem-solving strategy. “My strategy in research has always been opportunistic. One thing I have learned is that hypothesis-driven research tends not to be productive when you are in an unknown territory. I think there is an art to doing pilot experiments. So we have always just set up systems in which something happens and then you try and try things until a pattern appears and maybe you formulate a small hypothesis. But as soon as it turns out not to be exactly right, you abandon it. It’s a very open-minded type of research where you question whether what you are seeing is a real phenomenon without spending a year on doing all of the proper controls.”

Trial and error. Clevers’s lab found that while TCF-1 bound to DNA, it did not alter gene expression, despite the researchers’ tinkering with promoter and enhancer assays. “For about five years this was a problem. My first PhD students were leaving and they thought the whole TCF project was a failure,” says Clevers. His lab meanwhile cloned TCF homologs from several model organisms and made many reagents including antibodies against these homologs. To try to figure out the function of TCF-1, the lab performed a two-hybrid screen and identified components of the Wnt signaling pathway as binding partners of TCF-1. “We started to read about Wnt and realized that you study Wnt not in T cells but in frogs and flies, so we rapidly transformed into a developmental biology lab. We showed that we held the key for a major issue in developmental biology, the final protein in the Wnt cascade: TCF-1 binds b-catenin when b-catenin becomes available and activates transcription.” In 1996, Clevers published the mechanism of how the TCF-1 homolog in Xenopus embryos, called XTcf-3, is integrated into the Wnt signaling pathway.

Clevers Catapults


3DCrypt building and colon cancer.

Clevers next collaborated with Bert Vogelstein’s lab at Johns Hopkins, linking TCF to Wnt signaling in colon cancer. In colon cancer cell lines with mutated forms of the tumor suppressor gene APC, the APC protein can’t rein in b-catenin, which accumulates in the cytoplasm, forms a complex with TCF-4 (later renamed TCF7L2) in the nucleus, and caninitiate colon cancer by changing gene expression. Then, the lab showed that Wnt signaling is necessary for self-renewal of adult stem cells, as mice missing TCF-4 do not have intestinal crypts, the site in the gut where stem cells reside. “This was the first time Wnt was shown to play a role in adults, not just during development, and to be crucial for adult stem cell maintenance,” says Clevers. “Then, when I started thinking about studying the gut, I realized it was by far the best way to study stem cells. And I also realized that almost no one in the world was studying the healthy gut. Almost everyone who researched the gut was studying a disease.” The main advantages of the murine model are rapid cell turnover and the presence of millions of stereotypic crypts throughout the entire intestine.

Against the grain. In 2007, Nick Barker, a senior scientist in the Clevers lab, identified the Wnt target gene Lgr5 as a unique marker of adult stem cells in several epithelial organs, including the intestine, hair follicle, and stomach. In the intestine, the gene codes for a plasma membrane protein on crypt stem cells that enable the intestinal epithelium to self-renew, but can also give rise to adenomas of the gut. Upon making mice with adult stem cell populations tagged with a fluorescent Lgr5-binding marker, the lab helped to overturn assumptions that “stem cells are rare, impossible to find, quiescent, and divide asymmetrically.”

On to organoids. Once the lab could identify adult stem cells within the crypts of the gut, postdoc Toshiro Sato discovered that a single stem cell, in the presence of Matrigel and just three growth factors, could generate a miniature crypt structure—what is now called an organoid. “Toshi is very Japanese and doesn’t always talk much,” says Clevers. “One day I had asked him, while he was at the microscope, if the gut stem cells were growing, and he said, ‘Yes.’ Then I looked under the microscope and saw the beautiful structures and said, ‘Why didn’t you tell me?’ and he said, ‘You didn’t ask.’ For three months he had been growing them!” The lab has since also grown mini-pancreases, -livers, -stomachs, and many other mini-organs.

Tumor Organoids. Clevers showed that organoids can be grown from diseased patients’ samples, a technique that could be used in the future to screen drugs. The lab is also building biobanks of organoidsderived from tumor samples and adjacent normal tissue, which could be especially useful for monitoring responses to chemotherapies. “It’s a similar approach to getting a bacterium cultured to identify which antibiotic to take. The most basic goal is not to give a toxic chemotherapy to a patient who will not respond anyway,” says Clevers. “Tumor organoids grow slower than healthy organoids, which seems counterintuitive, but with cancer cells, often they try to divide and often things go wrong because they don’t have normal numbers of chromosomes and [have] lots of mutations. So, I am not yet convinced that this approach will work for every patient. Sometimes, the tumor organoids may just grow too slowly.”

Selective memory. “When I received the Breakthrough Prize in 2013, I invited everyone who has ever worked with me to Amsterdam, about 100 people, and the lab organized a symposium where many of the researchers gave an account of what they had done in the lab,” says Clevers. “In my experience, my lab has been a straight line from cloning TCF-1 to where we are now. But when you hear them talk it was ‘Hans told me to try this and stop this’ and ‘Half of our knockout mice were never published,’ and I realized that the lab is an endless list of failures,” Clevers recalls. “The one thing we did well is that we would start something and, as soon as it didn’t look very good, we would stop it and try something else. And the few times when we seemed to hit gold, I would regroup my entire lab. We just tried a lot of things, and the 10 percent of what worked, those are the things I remember.”

Greatest Hits

  • Cloned the first T cell–specific transcription factor, TCF-1, and identified homologous genes in model organisms including the fruit fly, frog, and worm
  • Found that transcriptional activation by the abundant β-catenin/TCF-4 [TCF7L2] complex drives cancer initiation in colon cells missing the tumor suppressor protein APC
  • First to extend the role of Wnt signaling from developmental biology to adult stem cells by showing that the two Wnt pathway transcription factors, TCF-1 and TCF-4, are necessary for maintaining the stem cell compartments in the thymus and in the crypt structures of the small intestine, respectively
  • Identified Lgr5 as an adult stem cell marker of many epithelial stem cells including those of the colon, small intestine, hair follicle, and stomach, and found that Lgr5-expressing crypt cells in the small intestine divide constantly and symmetrically, disproving the common belief that stem cell division is asymmetrical and uncommon
  • Established a three-dimensional, stable model, the “organoid,” grown from adult stem cells, to study diseased patients’ tissues from the gut, stomach, liver, and prostate
 Regenerative Medicine Comes of Age   
“Anti-Aging Medicine” Sounds Vaguely Disreputable, So Serious Scientists Prefer to Speak of “Regenerative Medicine”
  • Induced pluripotent stem cells (iPSCs) and genome-editing techniques have facilitated manipulation of living organisms in innumerable ways at the cellular and genetic levels, respectively, and will underpin many aspects of regenerative medicine as it continues to evolve.

    An attitudinal change is also occurring. Experts in regenerative medicine have increasingly begun to embrace the view that comprehensively repairing the damage of aging is a practical and feasible goal.

    A notable proponent of this view is Aubrey de Grey, Ph.D., a biomedical gerontologist who has pioneered an regenerative medicine approach called Strategies for Engineered Negligible Senescence (SENS). He works to “develop, promote, and ensure widespread access to regenerative medicine solutions to the disabilities and diseases of aging” as CSO and co-founder of the SENS Research Foundation. He is also the editor-in-chief of Rejuvenation Research, published by Mary Ann Liebert.

    Dr. de Grey points out that stem cell treatments for age-related conditions such as Parkinson’s are already in clinical trials, and immune therapies to remove molecular waste products in the extracellular space, such as amyloid in Alzheimer’s, have succeeded in such trials. Recently, there has been progress in animal models in removing toxic cells that the body is failing to kill. The most encouraging work is in cancer immunotherapy, which is rapidly advancing after decades in the doldrums.

    Many damage-repair strategies are at an  early stage of research. Although these strategies look promising, they are handicapped by a lack of funding. If that does not change soon, the scientific community is at risk of failing to capitalize on the relevant technological advances.

    Regenerative medicine has moved beyond boutique applications. In degenerative disease, cells lose their function or suffer elimination because they harbor genetic defects. iPSC therapies have the potential to be curative, replacing the defective cells and eliminating symptoms in their entirety. One of the biggest hurdles to commercialization of iPSC therapies is manufacturing.

  • Building Stem Cell Factories

    Cellular Dynamics International (CDI) has been developing clinically compatible induced pluripotent stem cells (iPSCs) and iPSC-derived human retinal pigment epithelial (RPE) cells. CDI’s MyCell Retinal Pigment Epithelial Cells are part of a possible therapy for macular degeneration. They can be grown on bioengineered, nanofibrous scaffolds, and then the RPE cell–enriched scaffolds can be transplanted into patients’ eyes. In this pseudo-colored image, RPE cells are shown growing over the nanofibers. Each cell has thousands of “tongue” and “rod” protrusions that could naturally support rod and cone cells in the eye.

    “Now that an infrastructure is being developed to make unlimited cells for the tools business, new opportunities are being created. These cells can be employed in a therapeutic context, and they can be used to understand the efficacy and safety of drugs,” asserts Chris Parker, executive vice president and CBO, Cellular Dynamics International (CDI). “CDI has the capability to make a lot of cells from a single iPSC line that represents one person (a capability termed scale-up) as well as the capability to do it in parallel for multiple individuals (a capability termed scale-out).”

    Minimally manipulated adult stem cells have progressed relatively quickly to the clinic. In this scenario, cells are taken out of the body, expanded unchanged, then reintroduced. More preclinical rigor applies to potential iPSC therapy. In this case, hematopoietic blood cells are used to make stem cells, which are manufactured into the cell type of interest before reintroduction. Preclinical tests must demonstrate that iPSC-derived cells perform as intended, are safe, and possess little or no off-target activity.

    For example, CDI developed a Parkinsonian model in which iPSC-derived dopaminergic neurons were introduced to primates. The model showed engraftment and enervation, and it appeared to be free of proliferative stem cells.

    • “You will see iPSCs first used in clinical trials as a surrogate to understand efficacy and safety,” notes Mr. Parker. “In an ongoing drug-repurposing trial with GlaxoSmithKline and Harvard University, iPSC-derived motor neurons will be produced from patients with amyotrophic lateral sclerosis and tested in parallel with the drug.” CDI has three cell-therapy programs in their commercialization pipeline focusing on macular degeneration, Parkinson’s disease, and postmyocardial infarction.

    • Keeping an Eye on Aging Eyes

      The California Project to Cure Blindness is evaluating a stem cell–based treatment strategy for age-related macular degeneration. The strategy involves growing retinal pigment epithelium (RPE) cells on a biostable, synthetic scaffold, then implanting the RPE cell–enriched scaffold to replace RPE cells that are dying or dysfunctional. One of the project’s directors, Dennis Clegg, Ph.D., a researcher at the University of California, Santa Barbara, provided this image, which shows stem cell–derived RPE cells. Cell borders are green, and nuclei are red.

      The eye has multiple advantages over other organ systems for regenerative medicine. Advanced surgical methods can access the back of the eye, noninvasive imaging methods can follow the transplanted cells, good outcome parameters exist, and relatively few cells are needed.

      These advantages have attracted many groups to tackle ocular disease, in particular age-related macular degeneration, the leading cause of blindness in the elderly in the United States. Most cases of age-related macular degeneration are thought to be due to the death or dysfunction of cells in the retinal pigment epithelium (RPE). RPE cells are crucial support cells for the rods, cones, and photoreceptors. When RPE cells stop working or die, the photoreceptors die and a vision deficit results.

      A regenerated and restored RPE might prevent the irreversible loss of photoreceptors, possibly via the the transplantation of functionally polarized RPE monolayers derived from human embryonic stem cells. This approach is being explored by the California Project to Cure Blindness, a collaborative effort involving the University of Southern California (USC), the University of California, Santa Barbara (UCSB), the California Institute of Technology, City of Hope, and Regenerative Patch Technologies.

      The project, which is funded by the California Institute of Regenerative Medicine (CIRM), started in 2010, and an IND was filed early 2015. Clinical trial recruitment has begun.

      One of the project’s leaders is Dennis Clegg, Ph.D., Wilcox Family Chair in BioMedicine, UCSB. His laboratory developed the protocol to turn undifferentiated H9 embryonic stem cells into a homogenous population of RPE cells.

      “These are not easy experiments,” remarks Dr. Clegg. “Figuring out the biology and how to make the cell of interest is a challenge that everyone in regenerative medicine faces. About 100,000 RPE cells will be grown as a sheet on a 3 × 5 mm biostable, synthetic scaffold, and then implanted in the patients to replace the cells that are dying or dysfunctional. The idea is to preserve the photoreceptors and to halt disease progression.”

      Moving therapies such as this RPE treatment from concept to clinic is a huge team effort and requires various kinds of expertise. Besides benefitting from Dr. Clegg’s contribution, the RPE project incorporates the work of Mark Humayun, M.D., Ph.D., co-director of the USC Eye Institute and director of the USC Institute for Biomedical Therapeutics and recipient of the National Medal of Technology and Innovation, and David Hinton, Ph.D., a researcher at USC who has studied how actvated RPE cells can alter the local retinal microenvironment.

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Organoid Development

Curator: Larry H Bernstein, MD, FCAP



Thyroid Organoids Made from Stem Cells Treat Thyroid-Deficient Mice

Their gut lining regrew onto the scaffold and functioned normally to absorb water from the colon. Within weeks, the scaffolding dissolved and was replaced with normal connective tissue. “The scaffold was well tolerated and promoted healing by recruiting stem cells,” Hackam says. “[The dogs] had a perfectly normal lining after 8 weeks.”

Sourced through from:


Stem Cells Dev. 2015 Oct 1. [Epub ahead of print]
Zfp553 is essential for maintenance and acquisition of pluripotency.

Pluripotent cells are promising tools in the arena of regenerative medicine. For many years, research efforts have been directed towards uncovering the underlying mechanisms that govern the pluripotent state and this involves identifying new pluripotency associated factors. Zinc finger protein 553 (Zfp553) has been hypothesized to be one such factor due to its predominant expression in inner cell mass of the mouse early embryo. In this study, we have identified Zfp553 as a regulator of pluripotency. Zfp553 knockdown down-regulates pluripotency markers and triggers differentiation in mouse embryonic stem cells (mESCs). Further investigation revealed that Zfp553 regulates pluripotency in mESCs via the transcriptional activation of Pou5f1 and Nanog. Microarray results revealed that depletion of Zfp553 down-regulates many pluripotency genes, as well as genes associated with metabolism related processes. ChIP-seq depicted the genomic binding sites of Zfp553 in mESCs and its binding motif. In addition, we found that depletion of Zfp553 could impair somatic cell reprogramming, evidenced by reduced reprogramming efficiency and cell viability. Together, our preliminary findings provide novel insights to a newly identified pluripotency factor Zfp553 and its role in pluripotency regulation.


Mesenchymal stem cells use extracellular vesicles to outsource mitophagy and shuttle microRNAs

Donald G. PhinneyMichelangelo Di GiuseppeJoel NjahErnest SalaSruti ShivaClaudette M. St CroixDonna B. StolzSimon C. WatkinsY. Peter DiGeorge D. LeikaufJay Kolls,… , & Luis A. Ortiz

Nature Communications 07 Oct 2015; 6(8472)

Mesenchymal stem cells (MSCs) and macrophages are fundamental components of the stem cell niche and function coordinately to regulate haematopoietic stem cell self-renewal and mobilization. Recent studies indicate that mitophagy and healthy mitochondrial function are critical to the survival of stem cells, but how these processes are regulated in MSCs is unknown. Here we show that MSCs manage intracellular oxidative stress by targeting depolarized mitochondria to the plasma membrane via arrestin domain-containing protein 1-mediated microvesicles. The vesicles are then engulfed and re-utilized via a process involving fusion by macrophages, resulting in enhanced bioenergetics. Furthermore, we show that MSCs simultaneously shed micro RNA-containing exosomes that inhibit macrophage activation by suppressing Toll-like receptor signalling, thereby de-sensitizing macrophages to the ingested mitochondria. Collectively, these studies mechanistically link mitophagy and MSC survival with macrophage function, thereby providing a physiologically relevant context for the innate immunomodulatory activity of MSCs.


MSCs undergo mitophagy in response to oxidative stress

Human MSCs shed from their surface a diverse subpopulation of vesicles. To characterize these vesicles, we performed electron microscopy on those recovered from MSC-conditioned medium by differential ultracentrifugation (100,000g for 18h). This analysis demonstrated the presence of 50–100-nm vesicles that are morphologically consistent with exosomes (Fig. 1a, left). Flotation of the 100,000g pellets on sucrose gradients followed by western blot and fluorescent activated cell sorting (FACS) further demonstrated that these vesicles expressed the exosomal markers’ milk fat globule factor 8 (Mfge8) and the tetraspanins CD9 and CD63, respectively (Supplementary Fig. 1A). Centrifugation of conditioned medium at low speeds (10,000g) revealed the presence of larger vesicles (>100nm) that contain subcellular mitochondrial structures including outer and inner membranes and cristae, and expressed the mitochondria-specific protein ATP synthase as evidenced by immuno-gold labelling (Fig. 1a, centre and Supplementary Fig. 1B). MSCs also release larger multivesicular bodies containing lysosome-like vesicles and entire mitochondria, suggesting that these organelles were selected for mitophagy by targeting to autophagosomes (Fig. 1a, right).

Figure 1: MSC-derived MVs contain depolarized mitochondria.

MSC-derived MVs contain depolarized mitochondria.

(a) Left panel, electron microscopy of vesicles isolated from sucrose densities of 1.11 and 1.14gml−1 and purified using differential ultracentrifugation (100,000g per 18h) reveal a typical exosome morphology. Middle panel, MVs over 100nm in size recovered from human MSC-conditioned medium following low-speed (10,000g per 1h) centrifugation contain structures conforming to the morphology of mitochondria. Right panel, MVs contain closely packed-vesicles and entire mitochondria (multivesicular body (MVB)) representing autophagosomes. (b) Left panel, flow cytometric analysis of MitoSOX Red-stained human MSCs expanded in 5 or 21% oxygen for 7 days. Right panel, quantification of the flow cytometric data. Plotted values (mean±s.e.m.) represent four replicates for each sample using three distinct replicate cultures from each experimental group. (c) Mitochondrial membrane potential of human MSCs from bdetermined using JC-1 staining. Expansion in 21% oxygen results in partial depolarization of mitochondria as evidenced by accumulation of JC-1 monomers (*P<0.005, Student’s-t test versus MSCs in 5%oxygen). (d) Western blot analysis (Supplementary Fig. 1) of cytoplasmic or mitochondrial extracts prepared from human MSCs expanded in 21% oxygen for the indicated passage numbers (P1 or P4) reveals Parkin mitochondrial translocation and Pink1 kinase activation in human MSCs but not human dermal fibroblasts. Data are representative of a single experiment repeated five times.

To determine whether culture expansion of MSCs impairs mitochondrial function, we expanded cells under physiological oxygen levels (5% O2) or standard culture conditions (21% O2) and quantified mtROS levels and mitochondrial membrane potential by staining with MitoSOX Red and JC-1, respectively37. FACS analysis of stained cells confirmed that exposure to 21% oxygen resulted in a significant increase in mtROS (Fig. 1b) and a concomitant decrease in mitochondrial membrane potential as demonstrated by the accumulation of JC-1 monomers (Fig. 1c). Moreover, western blot analysis revealed that prolonged exposure to 21% oxygen activated the Pink1/Parkin-mediated pathway of mitophagy in MSCs but not in human fibroblasts cultured under identical conditions (Fig. 1d). Herein, increased mitochondrial expression of Parkin and Pink1 kinase was accompanied by Pink1 kinase activation as evidenced by the presence of lower molecular weight moieties of the protein and reduced Miro levels in mitochondrial extracts from P4 versus P1 MSCs (Fig. 1c and Supplementary Fig. 1C). Importantly, Pink1 targets Miro for degradation, thereby severing the connection of the mitochondria to the cytoskeleton and facilitating its incorporation into the phagosome38. Consistent with these results, western blot analysis also revealed that mitochondria-containing MVs expressed microtubule-associated protein 1 light chain 3 (LC3) and autophagy-related protein 12, which are highly enriched in MVs as compared with whole-cell extracts (Supplementary Fig. 1D). Therefore, these MVs are characteristic of autophagosomes39.

MSCs package mitochondria in MVs for cellular transfer

To examine mitophagy in MSCs in more detail, MSCs were infected with baculoviruses encoding green fluorescent protein (GFP) fused to the E1alpha pyruvate dehydrogenase leader peptide, which drives transport to the mitochondria, and LC3 fused to a red fluorescent protein (RFP) to allow tracking to the phagophore39, 40. Fluorescent microscopy confirmed that the GFP-labelled mitochondrial network is in close proximity to RFP-LC3-labelled phagosomes (Fig. 2a). Live cell imaging further revealed that mitochondria are loaded in the cytoplasm into LC3-containing vesicles, which migrate towards the cell periphery and are incorporated into outward budding blebs in the plasma membrane (Fig. 2b–d and Supplementary Movie 1). Western blot analysis further revealed that RFP-LC3-MVs also expressed the endosomal sorting complex required for transport (ESCRT)-associated proteins’ tumour suppressor gene 101 (TSG101) and arrestin domain-containing protein 1 (ARRDC1)11, 41 (Supplementary Fig. 1D). Collectively, these results indicate that MSCs employ the release of ARMMs to extrude mitochondria at their cell surface. Moreover, MSCs exhibited marked increases in apoptosis when treated with Bafilomycin A1 or low concentrations (3–5μM) of chloroquine, which block the mitophagy flux, indicating that this process is critical for MSC survival (Supplementary Movie 2).

Figure 2: MSC outsource mitophagy to macrophages.

MSC outsource mitophagy to macrophages.

(ad) Differential interference contrast (DIC) fluorescence overlay of live human MSCs expressing fluorescent proteins that target mitochondria (green) and phagosomes (red) shows mitochondria being loaded into phagosomes (arrows), which are then shuttled to the plasma membrane for extrusion (also seeSupplementary Movie 1). (eh) Inset shows a representative macrophage interacting with a human MSC. This interaction is shown as a time sequence (5min intervals) in the lower images and in Supplementary Movie 3. The inset demarcates the area in the human MSC plasma membrane where the membrane blebs outwards and accumulates vesicles. Macrophages nibble the surface of human MSCs and uptake mitochondrial laden phagosomes from blebs budding (arrows) from the plasma membrane of the human MSCs. Scale bars, 10μ.



Next, we co-cultured GFP-labelled human MSCs from above with primary human or mouse macrophages. Live cell imaging revealed that macrophages nibble the plasma membrane of MSCs, establishing cell contact at areas where membrane blebs are enriched in RFP-labelled vesicles, which are subsequently stripped by the macrophage (Fig. 2e–h and Supplementary Movie 3). This activity was also observed between mouse macrophages and primary human MSCs (Fig. 3a and Supplementary Movies 4 and 5) but was not evident when macrophages were co-cultured with mouse or human fibroblasts (Supplementary Fig. 2). In a subsequent experiment, we co-cultured the macrophage cell line RAW 264.7 with human MSCs containing RFP-labelled mitochondria (10:1 ratio) for 4h and recovered macrophages using FACS after staining with antibodies that recognize macrophage epitopes (that is, F4/80) not expressed by MSCs. Sorted macrophages were cultured for up to 2 weeks in RPMI media, which do not support MSC expansion and survival. Fluorescent microscopy of these macrophages revealed clear evidence of cell-associated RFP derived from human MSCs (Fig. 3b). To confirm these findings, we demonstrated using PCR amplification that these macrophages expressed the mitochondrial specific transcript human cytochrome c oxidase I (MT-COX I), which was confirmed on the basis of the restriction fragment pattern obtained after digestion of the PCR product with Bfa1 (Fig. 3b). This PCR product was not detected in mouse macrophages because of limited sequence homology between the two genes30 but was detected in human MSC-derived MVs as expected (Fig. 3c and Supplementary Fig. 3A). Lastly, we co-cultured Cy5-labelled human MSCs with macrophages that were pre-incubated with or without dextran sulfate (100μgml−1), a nonspecific inhibitor of phagocytosis. Live cell imaging showed phagocytosis of MVs by macrophages over a period of 18min, and confocal microscopy confirmed that the engulfed Cy5-labelled vesicles resided within the cell body of the macrophage (Supplementary Movie 6). However, MV uptake was blocked in macrophages pre-treated with dextran sulfate as evidenced by the accumulation of Cy5-labelled MVs on the macrophage surface (Supplementary Movie 7).

Figure 3: MSC transfer mitochondria to macrophages and lung tissues.

MSC transfer mitochondria to macrophages and lung tissues.

(a) Top panel is DIC fluorescent overlay at time 0 of primary human MSCs infected with Organelle Lights to label mitochondria (green) and co-cultured with mouse (RAW 264.7) macrophages. Lower panels, time sequence at 45min intervals showing transfer of green-labelled mitochondria from the a MSC to a macrophage (red arrow, see Supplementary Movie 4 for transfer of mitochondria in filamentous form, andSupplementary Movie 5 in which GFP signal is compensated to allow the tracking of the transferred mitochondria into macrophages). (b) Left panel, photomicrograph of FACS-sorted mouse macrophages that were co-cultured with mitochondria-labelled (RFP) human MSCs clearly show retention of RFP label. Right panel, electrophoretic pattern of human COX I PCR product treated with or without Bfa1 after amplification from the indicated cell sources. (c) MSC-derived exosomes and MVs express the Bfa1-sensitive 228-bp COX I mtDNA PCR product detected in human MSCs (b). (d) Left panel, electrophoretic pattern of Bfa1-digested human COX1 PCR product amplified from mouse lung DNA isolated 14 days after the intravenous administration of human MSCs, human MSC-derived MVs or exosomes. Right panel, human GAPDH and human COX1 relative expression levels quantified by RT–PCR in mouse lung (3–28 days) after a single (intratracheal (IT) or intravenous (IV)) injection of human MSCs, human MSC-derived exosomes or human fibroblasts. *P<0.001, #P<0.001 by ANOVA compared with untreated mouse lung. Plotted values (mean±s.e.m.) are from experiments repeated four times. Scale bars, 20μ.


To track the in vivo transfer of mitochondria, we systemically administered RFP-labelled human MSCs into C57BL/6 mice expressing a GFP reporter under control of the endothelial specific Tie2 promoter. At 24h post injection, GFP-labelled endothelial cells, epithelial cells and macrophages that contained RFP-labelled mitochondria were visible (Supplementary Fig. 3B). Bfa1 digestion of mouse lung DNA following intravenous administration of human MSCs, exosomes or MVs yielded a pattern of restriction similar to those observed in RAW 264.7 macrophages (Fig. 3d). To follow the fate of viable human MSCs in the mouse lung, we measured the abundance of human-specific GAPDH transcripts via reverse transcriptase–PCR (RT–PCR)42. Human GAPDH mRNA was not detected in the lung tissue of untreated mice but was detected at 3 days post injection of human MSCs or human fibroblasts (Fig. 3d). However, expression rapidly declined and was no longer evident by 14 or 28 days post transplant, consistent with the clearance rate of cells from lung tissue. Expression of human COXI mRNA in mouse lung mirrored that of human GAPDH following injection of human fibroblasts and was detected at 3 days but not 14 or 28 days post transplant. In contrast, human COXI transcripts were detected up to 28 days post injection of human MSCs, indicating that mouse lung tissue retained mtDNA long after the disappearance of viable human MSCs (Fig. 3d). Thus, MSC-derived vesicles constitute an effective mechanism to transfer mtDNA into the mouse lung.


MSC extracellular vesicles enhance macrophage energetics

To study the effect of MVs on macrophage bioenergetics, we analysed oxygen consumption rates (OCRs) using the SeaHorse technology. Human macrophages exhibit higher basal OCR than human MSCs or human fibroblasts (Fig. 4a). Co-culture of macrophages with human MSCs (Mac+hMSC) or MSC-derived exosomes (Mac+Exo) but not human fibroblasts (Mac+Fibro) significantly (analysis of variance (ANOVA) followed by Student–Neuman Keuls (SNK) post-hocpairwise comparisons) increased their OCR, suggesting that MSCs or MSC-derived exosomes alter macrophage bioenergetics (Fig. 4a). Next, we repeated these measurements after treatment of cells with oligomycin A, an inhibitor of ATP synthase, which is required for the oxidative phosphorylation of ADP to ATP. These conditions differentiate ATP-linked respiration from the proton leak. Macrophages exhibited a higher level of proton leak as compared with human MSCs and fibroblasts, and proton leak was significantly (ANOVA followed by SNK post hoc pairwise comparisons) reduced following co-culture with human Mac+Exo but not Mac+Fibro (Fig. 4a). Co-culture with human MSCs (Mac+hMSC) also significantly (ANOVA followed by SNK post hocpairwise comparisons) reduced proton leak in macrophages. We also repeated the OCR measurements following treatment of cells with the uncoupling agent carbonyl cyanide 4-(trifluoromethoxy) phenylhydraone (FCCP) to determine how cells respond to an increase in ATP demand. All three cell types responded to FCCP treatment with increased OCR, and the magnitude of the response was greater in macrophages as compared with human MSCs and fibroblasts. Moreover, OCR was significantly increased in FCCP-treated macrophages following co-culture with human MSCs (Mac+hMSC) or human Mac+Exo but not Mac+Fibro (Fig. 4a).

Figure 4: MSCs enhance macrophage bioenergetics.

MSCs enhance macrophage bioenergetics.

(a) Mitochondrial respiration of human macrophages, human MSCs or human fibroblasts was measured as OCR using the XF technology. Macrophages were co-cultured with or without human MSCs or fibroblasts (1:10 ratio) or treated with human MSC-derived exosomes (40μg per protein) in the presence or absence of Oligomycin A and FCCP to differentiate ATP-linked respiration from the proton leak. Plotted data (mean±s.e.m.) were performed using six replicates per sample and repeated three times. (b) Pseudocoloured photomicrographs (0–240min) of MitoSOX Red-stained macrophages that were non-stimulated (upper panel), or treated with silica (20μgcm−2, lower panel) or silica plus human MSC-derived exosomes (added 10min after silica, middle panel). Scale bars, 50μ. (c) Time course of MitoSOX Red emission by human macrophages treated as in b. Figure is representative of five exposures (nine stages positions per test and 6 cells per stage). (d) OCR as in a of silica-exposed macrophages treated with or without human MSCs, human MSC-derived exosomes or human fibroblasts. Plotted values (mean±s.e.m.) are from experiments repeated three times, *P<0.05 as compared to control, #P<0.05 as compared to silica treated macrophages, as determined by Student’s t-test.


To examine the effect of MSC or exosomes on macrophage bioenergetics under conditions of altered homeostasis, we exposed macrophages to silica particles. Silica exposure results in a burst of mtROS production as evidenced by changes in MitoSOX Red fluorescence intensity; however, this effect is largely mitigated in macrophages incubated with human MSC-derived exosomes (Fig. 4b,c). Silica exposure also decreased macrophage OCR, but this decrease was reversed by co-culture with human MSCs or human MSC-derived exosomes but not with human fibroblasts (Fig. 4d). The fact that transfer of partially depolarized mitochondria from MSCs to macrophages enhances that macrophage bioenergetics appears paradoxical. However, loss of mitochondrial membrane potential as a result of MSC expansion is not absolute as mitochondria exhibit residual membrane potential as evidenced by the concentration of JC-1 aggregates (Fig. 1c). This indicates that the mitochondrial membrane is not collapsed and the mitochondria are still capable of undergoing fusion. To determine whether these mitochondria are recycled in macrophages by fusion, we co-cultured human MSCs with macrophages after labelling cells with two different MitoTracker dyes (Red and Green)43. Live cell imaging clearly demonstrated the transfer and subsequent fusion (yellow colour in merged images) of RFP-labelled, human MSC-derived mitochondria with GFP-labelled mitochondria within human macrophages (Fig. 5). These data indicate that under oxidative stress MSCs outsource mitophagy to macrophages to unload partially depolarized mitochondria, which are recycled via fusion by macrophages thereby enhancing their bioenergetics.

Figure 5: Mitochondrial transfer from human MSCs is followed by fusion inside macrophages.

Mitochondrial transfer from human MSCs is followed by fusion inside macrophages.

Human MSCs and human macrophages (1 × 105) were infected separately with Organelle Lights to label human MSC mitochondria (red) and macrophage mitochondria (green). Twenty-four hours following infection, macrophages were harvested and co-incubated with the human MSCs for 2h. Images were collected using an inverted Nikon TiE fluorescent microscope equipped with a × 60 oil immersion optic and NIS Elements Software. Organelle Lights were excited using a Lumencor diode-pumped light engine and detected using an ORCA-Flash4.0 sCMOS camera. (a,b) DIC images of two separate fields within the same dish. (c) A zoomed image of the outlined section within b (scale bars, 20μ). The fluorescence-based images for each field appear in the panels below the DIC images, with df showing macrophage mitochondria (green); gi showing human MSC mitochondria (red); and jl showing the overlay with yellow indicative of colocalization of human MSC and macrophage mitochondria. Not every macrophage was shown to take up human MSC mitochondria (a,d,g, j).


MSC-derived exosomes are enriched in microRNAs

Exosomes transfer RNAs between cells8. We hypothesized that this process may be exploited by MSCs to tolerize macrophages against mitochondrial transfer. To explore this possibility, we analysed the RNA content of human MSC-derived exosomes. Using microRNA microarray analysis, we identified 156 (45 increased; 111 decreased) microRNAs that differed (log2>1.0,P<0.05 (ANOVA followed by Holm–Sidak post hoc pairwise comparisons) in abundance between exosomes compared with their parent MSCs. The 10 microRNAs that exhibited the greatest increase included miR451a (316-fold), miR1202 (45-fold), miR630 (40-fold) and miR638 (28-fold), while microRNAs that exhibited the greatest decrease in exosomes and were enriched in MSCs included miR125b (148-fold) and miR21 (91-fold; Fig. 6a,b). This pattern of microRNA expression was conserved in MSC-derived exosomes obtained from five human donors (Fig. 6c,d).

Figure 6: RNA expression profile in human MSCs and their exosomes.

RNA expression profile in human MSCs and their exosomes.

(a) Heatmap illustrating the 10 microRNAs most highly enriched in human MSCs versus their corresponding exosomes. Every row represents a microRNA and every column a cell or exosome, and yellow and purple represent increased or decreased expression, respectively. (b) Plotted values represent the means log 2 fold enrichment of exosomal versus human MSC microRNAs (n=5 microarrays of different MSCs cell lines; P<0.05, ANOVA followed by Holm–Sidak post hoc pairwise comparisons). (c) Data in b show distribution of differentially expressed microRNAs between samples based on the –log base 10 significant P value (<0.05) and with a relative fold change of >2 (in log base 2). Green and red squares represent increasingly and decreasingly expressed microRNAs, respectively, in exosomes versus human MSCs. (d) Computational analysis of human MSCs and exosomes from five donors demonstrates that microRNAs isolated in exosomes cluster among different donors.


MSC-derived exosomes inhibit TLR signalling in macrophages

Mitochondrial uptake can induce inflammation via activation of pattern recognition receptors34. Therefore, given the presence of mtDNA and microRNAs in MSC-derived MVs and exosomes, respectively, we hypothesized that exposure to these vesicles would tolerize macrophages to mitochondrial transfer by inducing changes in TLR expression. Subsequently, we profiled the expression of 84 TLR-associated transcripts in mouse macrophages. We contrasted these results with those observed in macrophages that were co-cultured with mouse or human MSCs, human MSC-derived exosomes or silica particles, which when phagocytized induce macrophage activation44. Co-culture of macrophages with MSC-derived exosomes induced nuclear translocation of the transcription factor NF-κB (Fig. 7a) resulting in significant changes (>2.5-fold increase or decrease) in expression of 50 of the 84 TLR-associated transcripts (Fig. 7b). For example, compared with silica-exposed macrophages those treated with exosomes exhibited significant (>2.5-fold) increases in transcripts associated with cytokine signalling including interleukin (IL)-1β, prostaglandin endoperoxide synthase 2 (PTGS2, aka COX2), granulocyte colony-stimulating factor 3 (CSF3), IL-10, chemokine (C–C motif) ligand 2 (CCL2, aka MCP-1), NF-κB-chemokine (C–X–C motif) ligand 10 (CXCL10), tumour necrosis factor (TNF) and reticuloendotheliosis oncogene (Rel; Fig. 7b). In contrast, transcripts encoding proteins involved in MyD88-dependent signalling (MyD88, TLR 1,4,5,7,8 and 9, IRAK1 and TRAF6), TRIF-dependent signalling (TLR adaptor molecule 1 (TICAM1) and TICAM2) and TLR-related signalling (CD80, CD86, IL-2, IL-12, Interferon gamma, PGLYRP1 and CSF2) were downregulated.

Figure 7: MSC-derived MVs inhibit TLR signalling in macrophages.

MSC-derived MVs inhibit TLR signalling in macrophages.

(a) Upper panels, confocal microscopy showing intracellular localization of Cy5-labelled exosomes within macrophages 18min post administration. Lower panel, nuclear localization of NF-κB in macrophages 2h post administration of exosomes. Scale bars, 15μ. (b) Partial heatmap illustrating mRNA levels of 84 TLR-associated transcripts in macrophages at 8h post treatment with silica (20mgcm−2), human or mouse MSCs (1:10 ratio) or human MSC-derived exosomes (40μg protein). Transcript order is highest (top) to lowest (bottom), and each row represents a gene and each column a specific treatment. Red and green illustrates increased or decreased gene expression, respectively. Experiments were repeated four times. (c) Effect of exosome treatment on PGE2, TNF and IL-10 secretion in macrophages from the indicated mouse strains. Plotted data (mean±s.e.m.) were from experiments repeated five times. *P<0.05 compared with C57BL/6J or BALB/CJ macrophages as determined by ANOVA). (d) Upper panel, western blot illustrating the time-dependent effect of silica or human MSC-derived exosomes on expression of TLR7 in macrophages. Lower panel, fold change in expression of the indicated transcripts in macrophages RT–PCR demonstrating the negative regulation of exosomes on macrophage expression of TLR genes. Plotted data (mean±s.e.m.) are from experiments repeated four times. *P<0.05 compared with baseline.#P<0.05 compared with native exosomes by Student’ t-test. P<0.05 compared with the effect of native exosomes and indomethacin (Indo) treated by Student’s t-test.


MSCs secrete PGE2 that acts on prostaglandin receptors of LPS-stimulated macrophages to enhance their production of the anti-inflammatory cytokine IL-10 (ref. 45). However, this effect of MSCs was abrogated in macrophages from TLR4, MyD88, TNFR1 or COX2-deficient mice45. Consistent with these results, exosome treatment of non-stimulated macrophages augmented secretion of PGE2, TNF, IL-10 and IL-1-receptor antagonist (Fig. 7c), which may reprogramme macrophages3. These responses recapitulate those observed when macrophages are exposed to intact human or mouse MSCs, except that IL-6, CSF2 and IL-1 receptor 1 were increased more following exposure to mouse MSCs (Fig. 7b).

Subsequently, we treated TLR-signalling-deficient macrophages (TLR4−/−, TLR9−/−, MyD88−/−) or scavenger receptor-deficient macrophages (MARCO−/−) with MSC-derived exosomes. As shown inFig. 7c, PGE2 production was similar following exosome treatment in all signalling-deficient macrophages as compared with wild-type cells from strain-matched C57BL/6J or BALB/CJ mice. In contrast, secretion of TNF and IL-10 was significantly (ANOVA followed by SNK post hoc pairwise comparisons) reduced in TLR4−/− and MYD88−/− macrophages as compared with wild-type cells following exosome treatment, and IL-10 secretion was also significantly reduced in macrophages from TLR9−/− mice (Fig. 7c). These data confirm the importance of TLRs and in particular MyD88-dependent pathways in mediating exosome-induced effects on macrophage function. Lastly, we showed that pre-incubation with dextran sulfate significantly (ANOVA followed by SNK post hocpairwise comparisons) reduced the release of PGE2, TNF and IL-10 by exosome-treated macrophages, confirming the need for phagocytosis of MSC-derived vesicles in this process (Supplementary Fig. 4A).

To examine the role of microRNAs in macrophage tolerization, we treated RAW 264.7 cells, which use TLRs to recruit autophagy proteins in phagosomes to degrade its cargo46, with exosomes derived from human MSCs transfected with or without an short-hairpin RNA (shRNA) designed to inhibit DICER expression in the presence or absence of indomethacin, a cyclooxygenase inhibitor (Supplementary Fig. 4B). Treatment of naive RAW 264.7 macrophages with native exosomes enhanced TNF and reduced TLRs and MyD88 mRNA expression over 24h (Fig. 7c), while treatment of silica-exposed macrophages with exosomes ameliorated TLR7 induction following silica exposure (Fig. 7c). Pre-incubation of RAW 264.7 macrophages with indomethacin before treatment with native exosomes, or treatment with exosomes from DICER knockout MSCs significantly (ANOVA followed by SNK post hoc pairwise comparisons) reduced the observed effects on TLR mRNA expression (Fig. 7c) and reduced secretion of proteins such as TNF, MIP, MCP1, KC and IP-10 associated with macrophage activation (Supplementary Fig. 4B,C). The inhibitory effects of indomethacin were restricted to TLR4 and MyD88 mRNA, while the effects of DICER-deficient exosomes were of greater magnitude and also involved negative regulation of TLR 7 and 9 (Fig. 7c). Concomitant treatment with indomethacin and exosomes from DICER-deficient exosomes demonstrated additive effects (Fig. 7c).

Importantly, miR-451 is one of the most abundantly expressed microRNAs in MSC-derived exosomes, but its maturation occurs independent of DICER47. Therefore, its expression is not altered in exosomes from DICER knockdown MSCs. MiR-451 negatively regulates cytokine production in dendritic cells infected with influenza virus48. Consistent with these results, transfection of RAW 264.7 macrophages with a miR-451 mimic significantly (Student’s t-test) decreased TNF mRNA expression in non-stimulated macrophages, and inhibited mRNA expression and protein release in silica-exposed macrophages (Supplementary Fig. 4D). In contrast, treatment of cells with a miR-451 antagomir yielded the opposite result. These data confirm a role of exosome-derived microRNAs in regulating cytokine expression in macrophages.


MSC exosomes attenuate monocyte activation and silicosis

Circulating MVs enter the bone marrow and reprogramme cells to express proteins of the tissue of vesicle origin49. Ly6Chi monocytes are recruited from the bone marrow into the lung in response to injury and play an important role in the pathogenesis of lung fibrosis50, 51. Therefore, we investigated whether MSC or their exosomes are capable of altering the lung recruitment and cytokine production of Ly6Chi monocytes in mice following silica exposure. As shown in Fig. 8a, FACS identified a limited number of Ly6Chi monocytes in the normal mouse lung, which was significantly (ANOVA followed by SNK post hoc pairwise comparisons) increased by 72h post exposure to silica. Moreover, high expression of CCR2 and release of inflammatory (TNF, CCL2 and CXCL1) and fibrotic (transforming growth factor β (TGFβ) and IL-10) mediators indicate that these monocytes are activated (Fig. 8b). In contrast, intravenous administration of human MSCs (500,000 cells) or freshly isolated human MSC-derived exosomes (~3 × 1011 exosomes containing 40μg protein) at 24h post-silica exposure (0.2g·kg−1) significantly reduced the extent of Ly6Chimonocyte infiltration into the lung and secreted levels of inflammatory mediators (Fig. 8a,b).

Figure 8: Human MSCs and their exosomes prevent the accumulation of Ly6Chimonocytes in the lungs of silica-exposed mice.

Human MSCs and their exosomes prevent the accumulation of Ly6Chi monocytes in the lungs of silica-exposed mice.

(a) Upper panel, absolute number of F4/80/CD11b- and Ly6C/CCR2-expressing cells in lung tissue of mice 72h post administration of saline (50μl), silica (0.2gkg−1) or silica plus human MSC-derived exosomes (~3 × 1011 exosomes containing 40μg protein). *P<0.05 compared with saline by t-test). Lower panel, representative histograms of flow cytometric data analysed in a showing the phenotype and frequency of cells recovered from lung tissue after enzymatic digestion. (b) Mulitplex ELISA of inflammatory (TNF, MCP1 and KC) and fibrotic (TGFβ and IL-10) mediators secreted by cultured F4/80/CD11b/ and Ly6C/CCR2 cells from a. Plotted values (mean±s.e.m.) are from experiments usingN=5 animals per group and repeated three times. *P<0.05 compared with saline, #P<0.001 compared with silica-treated monocytes by ANOVA.


Silica induces inflammation and collagen deposition in peri-bronchiolar, silicotic nodule and peri-vascular regions of the lung (Fig. 9a). These lesions are associated with enhanced numbers of inflammatory cells (although the percentage of macrophages decreases, there is an increase in neutrophils and lymphocytes) in bronchoalveolar lavage fluid (BALF, Fig. 9b), significant deposition of lung collagen as measured by hydroxyproline (Fig. 9c) and enhanced expression of pro-inflammatory cytokines (TNF and IL-6) and fibrotic mediators (IL-10 and α(I) collagen) by 14 and 28 days after silica exposure (Fig. 9d). Intravenous administration of human MSCs or exosomes 3 days after silica exposure reduced the size of the silicotic nodules (Fig. 9a), the total number of white blood cells in BALF (Fig. 9b) and expression of inflammatory and pro-fibrotic genes in the lung (Fig. 9d). Administration of exosomes significantly (ANOVA followed by SNK post hocpairwise comparisons) reduced the accumulation of neutrophils and lymphocytes in BALF, while MSCs only reduced the accumulation of neutrophils and induced a slight (<1%) increase in eosinophil count (Fig. 9b). In contrast, the intravenous administration of human fibroblasts significantly exacerbated the inflammatory and fibrotic responses to silica (Fig. 9a–c). Exosomes, but not MSC or fibroblast administration, reduced the accumulation of hydroxyproline in lung tissue 28 days after silica (Fig. 9c).

Figure 9: Human MSCs and their exosomes ameliorate experimental silicosis.

Human MSCs and their exosomes ameliorate experimental silicosis.

(a) Photomicrographs of lung sections stained with haematoxylin and eosine from mice 28 days after intratracheal administration of silica (0.2gkg−1) alone or followed 3 days later with an intravenous injection of human MSCs, human MSC-derived exosomes (~3 × 1011 exosomes containing 40μg protein) or human fibroblasts (scale bars, 500μ). (b) Upper panel, photomicrographs of Diff-Quick-stained cytospins of BAL from mice in a. Lower panel, differential cell counts showing counts of total cells (left) and percentage of macrophages, lymphocytes, neutrophils and eosinophils (right panels). *P<0.05 compared with control, P<0.05 compared with fibroblasts treated mice by Student’s t-test. (c) Hydroxyproline content of lung tissue from animals treated as in a. *P<0.001 compared with saline by Student’s t-test.P<0.05 compared with silica, human MSC or fibroblast by ANOVA. (d) Quantification of mouse TNF, IL-6, IL-10 and Col1α1 levels in lung tissue from mice in a at 14 and 28 d post treatment. Plotted values (mean±s.e.m.) are representative of experiments using 15 animals per group and repeated three times.*P<0.001 compared with saline by Student’s t-test, P<0.05 compared with silica by ANOVA.



MSCs modulate macrophage function by a variety of mechanisms, and this crosstalk contributes to their anti-inflammatory activity but the physiological relevance of this crosstalk remains obscure particularly as it relates to the survival and function of MSCs. In this study, we report that during their ex vivo culture MSCs transfer partially depolarized mitochondria to macrophages as a pro-survival mechanism in response to oxidative stress and that these mitochondria are repurposed via a process involving fusion to increase macrophage bioenergetics. Moreover, we show that MSCs also desensitize macrophages to mitochondrial transfers by repressing TLR-signalling. Our data indicate that MSCs employ two different types of MVs to achieve these goals. MSCs load mitochondria in the cytoplasm into LC3 containing MVs that are recovered from cell culture media with low-speed centrifugation. These MVs express the ESCRT-I-associated proteins TSG101 and ARRDC1 and are extruded from cells in ARMMs11, which bud outwards directly from the plasma membrane where they are identified by macrophages. MSCs also shed exosomes that modulate TLR signalling and cytokine secretion in macrophages, in part, by transfer of regulatory microRNAs.

Previous reports indicate that mitochondria transferred by MSCs improve the energetic activity of the alveolar epithelium of LPS-treated mice30, 31, 32, 33 and animal models of rotenone-induced airway injury52. However, the beneficial effects of mitochondria were limited to acceptor cells almost completely deficient of mitochondrial function30, 53. Therefore, it is unclear whether rescue is because of the transfer of mitochondria, mtDNA or release of other mediators by MSCs33. Importantly, the bone marrow niche contains few, if any, epithelium, so the physiological relevance of this is unclear.

Our data suggest that mitochondrial transfer by MSCs is not altruistic but rather may serve to enhance MSCs’ cell survival by unloading partially depolarized mitochondria. Elimination of depolarized mitochondria is a priority for MSCs that experience high mtROS generation when cultured under atmospheric oxygen tension28 since inhibitors of the mitophagy flux induce MSC apoptosis. Unexpectedly, MV-mediated mitochondrial transfer augments macrophage function by improving mitochondrial bioenergetics. As reported for the alveolar epithelial cells, recovery of the energetic function of macrophages is characterized by an increased ability to generate ATP under conditions in which the cells exhibit mitochondrial uncoupling or an enhanced proton leak, and involves protection of the macrophage by reducing mtROS generation. This outcome is consistent with data indicating that transfer of mitochondria, even if partially depolarized, is followed by fusion inside the acceptor macrophage. Notably, several studies have reported that transfer of only a few mitochondria is sufficient to rescue cells depleted of mtDNA by culture in ethidium bromide30, 54,55. Furthermore, the current study confirms evidence that exosomes, which do not carry mitochondria, contain nucleic acids56, including mtDNA that can be transferred, long term, in vivoto the lung. Presence of mtDNA inside exosomes is not surprising as mtDNAs are dispersed throughout the mitochondrial network as histone-free nucleoids with an average size in mammals under 100nm, and contain a single copy of mtDNA per nucleoid57. However, we cannot completely exclude the possibility that the exosome preparations could be contaminated by apoptotic bodies.

Accumulation of mtDNA that escapes mitophagy induces TLR 9-mediated inflammation that in the case of cardiac muscle is associated with heart failure35 and mice transplanted with cells harbouring allogeneic mtDNA trigger MyD88 responses to reject these cells36. Therefore, silencing TLR responses in macrophages is likely necessary to induce tolerance to transferred mitochondria. Consistent with this hypothesis, we demonstrate that uptake of MSC-derived exosomes represses TLR signalling in macrophages and the production of inflammatory mediators by targeting pathways (TLRs and NF-κB) central to inflammation.

Interestingly, microRNAs present in MSC-derived exosomes are highly conserved between human MSC donors. One such microRNA, miR-451, is highly abundant in exosomes but is expressed at low levels in macrophages and dendritic cells where it regulates cytokine production58, 59, 60. Mir-451 is known to suppress TNF, and macrophage migration inhibitory factor, which inhibits the anti-inflammatory effects of glucocorticoids and negatively regulates p38 MAPK signalling to protect from diabetic nephropathy48, 58, 59, 60. Indeed, ectopic expression of a mir-451 mimic in macrophages inhibits TNF secretion in response to silica. Consistent with these findings, MSC-derived exosomes prevent the recruitment of Ly6Chi monocytes and reduces secretion of pro-fibrotic IL-10 and TGFβ by these cells in the lung of silica-exposed mice. Therefore, these data suggest that, as tested in vitro, immunomodulatory activities may have evolved, in part, as a mechanism by which MSCs survive oxidative stress and serendipitously confers on cells the ability to suppress inflammation, in lung injury models. Indeed, our data illustrate a physiological role for the innate immune regulatory activity of MSCs, and in doing so further highlights the important association between MSCs and macrophages in vivo.





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Mini-kidney organoids re-create disease in lab dishes

Reported by :Irina Robu, PhD

Kidney disease affects about 700 million people worldwide and the costs are tremendous. Dialysis and kidney transplantation are the only options of kidney failure which can cause harmful side effects and poor quality-of-life.

To re-create human disease, Freedman and his colleagues used the gene-editing technique called CRISPR. They engineered mini-kidneys with genetic changes linked to two common kidney diseases, polycystic kidney disease and glomerulonephritis. The mini-kidney organoids are grown using genome editing to recreate human kidney disease in petri dishes. The achievement  is published on Nature Communications, today October 23 and it paves the way for personalized drug discovery for kidney disease.

Pluripotent stem cells are used to grow the mini-kidney organoids. When treated with a chemical cocktail, the stem cell matured into structures that resemble miniature kidneys. The organoids contain  filtering cells, blood vessel cells and tubules and developed characteristics of these diseases. Those with mutations in polycystic kidney disease genes formed balloon like, fluid filled sacks, called cysts, from kidney tubules. The organoids with mutations in podocalyxin, a gene linked to glomerulonephritis, lost connections between filtering cells.


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