Stem Cells Regenerate Human Lens After Cataract Surgery, Restoring Vision

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Stem Cells Regenerate Human Lens After Cataract Surgery, Restoring Vision

March 10, 2016 by 2012pharmaceutical

Stem Cells Regenerate Human Lens After Cataract Surgery, Restoring Vision

Reporter: Aviva Lev-Ari, PhD, RN

SOURCE

http://ucsdnews.ucsd.edu/pressrelease/stem_cells_regenerate_human_lens_after_cataract_surgery_restoring_vision

March 09, 2016 | By Scott LaFee

Stem Cells Regenerate Human Lens After Cataract Surgery, Restoring Vision

Approach may have broad therapeutic implications on tissue and organ repair

The clouded lens of a cataract in human eye. Photo courtesy of Wikimedia

Researchers at University of California, San Diego School of Medicine and Shiley Eye Institute, with colleagues in China, have developed a new, regenerative medicine approach to remove congenital cataracts in infants, permitting remaining stem cells to regrow functional lenses.

The treatment, which has been tested in animals and in a small, human clinical trial, produced much fewer surgical complications than the current standard-of-care and resulted in regenerated lenses with superior visual function in all 12 of the pediatric cataract patients who received the new surgery.

The findings are published in the March 9 online issue of Nature.

Congenital cataracts – lens clouding that occurs at birth or shortly thereafter – is a significant cause of blindness in children. The clouded lens obstructs the passage of light to the retina and visual information to the brain, resulting in significant visual impairment. Current treatment is limited by the age of the patient and related complications. Most pediatric patients require corrective eyewear after cataract surgery.

“An ultimate goal of stem cell research is to turn on the regenerative potential of one’s own stem cells for tissue and organ repair and disease therapy,” said Kang Zhang, MD, PhD, chief of Ophthalmic Genetics, founding director of the Institute for Genomic Medicine and co-director of Biomaterials and Tissue Engineering at the Institute of Engineering in Medicine, both at UC San Diego School of Medicine.

In the new research, Zhang and colleagues relied upon the regenerative potential of endogenous stem cells. Unlike other stem cell approaches that involve creating stem cells in the lab and introducing them back into the patient, with potential hurdles like pathogen transmission and immune rejection, endogenous stem cells are stem cells already naturally in place at the site of the injury or problem. In the case of the human eye, lens epithelial stem cells or LECs generate replacement lens cells throughout a person’s life, though production declines with age.

Current cataract surgeries largely remove LECs within the lens; the lingering cells generate disorganized regrowth in infants and no useful vision. After confirming the regenerative potential of LECs in animal models, the researchers developed a novel minimally invasive surgery method that preserves the integrity of the lens capsule – a membrane that helps give the lens its required shape to function – and a way to stimulate LECs to grow and form a new lens with vision.

In subsequent tests in animals with cataracts and in a small human trial, they found the new surgical technique allowed pre-existing LECs to regenerate functional lenses. In particular, the human trial involved 12 infants under the age of 2 treated with the new method and 25 similar infants receiving current standard surgical care. The latter control group experienced a higher incidence of post-surgery inflammation, early-onset ocular hypertension and increased lens clouding.

The scientists reported fewer complications and faster healing among the 12 infants who underwent the new procedure and, after three months, a clear, regenerated biconvex lens in all of the patients’ eyes.

“The success of this work represents a new approach in how new human tissue or organ can be regenerated and human disease can be treated, and may have a broad impact on regenerative therapies by harnessing the regenerative power of our own body,” said Zhang, who also has an appointment at Veterans Affairs San Diego Healthcare System.

Zhang said he and colleagues are now looking to expand their work to treating age-related cataracts. Age-related cataracts is the leading cause of blindness in the world. More than 20 million Americans suffer from cataracts, and more than 4 million surgeries are performed annually to replace the clouded lens with an artificial plastic version, called an intraocular lens.

Despite technical advances, a large portion of patients undergoing surgery are left with suboptimal vision post-surgery and are dependent upon corrective eyewear for driving a car and/or reading a book. “We believe that our new approach will result in a paradigm shift in cataract surgery and may offer patients a safer and better treatment option in the future.”

Co-authors on the study include Haotian Lin, Hong Ouyang, Shan Huang, Zhenzhen Liu, Shuyi Chen, Xialin Liu, Lixia Luo, Baoxin Chen, Jiangna Chen, Fu Shang, Xuri Li, Yujuan Wang, Zheng Zhong, and senior author Yishi Liu, Sun Yat-sen University, China; Jie Zhu, Danni Lin, Sherrina Patel, Frances Wu, Christopher Chung, Cindy Wen, Jin Zhu, Austin Qiu, David Granet, Christopher Heichel, Michal Krawczyk, Dorota Skowronska-Krawczyk, Maryam Jafari, William Shi, Daniel Chen, Sheng Zhong, Liangfang Zhang, Jiayi Hou, and Shaochen Chen, UC San Diego; Guiqun Cao, Gen Li, Huimin Cai, and Yanxin Xu, Sichuan University, China; Rui Hou, Guangzhou KangRui Biological Pharmaceutical Technology Company, China; Robert A.J. Singer, Sean Morrison, Ying Zhang, and Richard L. Maas, University of Texas Southwestern Medical Center.

Funding for this research came, in part, from the 973 Program (National Basic Research Program of China); a Major International Joint Research Project (No. 81320108008); 863 Program (State High-Tech Development Plan of China); the National Natural Science Foundation of China; the State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yatsen University; Research to Prevent Blindness; and the Howard Hughes Medical Institute.

The repair and regeneration of tissues using endogenous stem cells represents an ultimate goal in regenerative medicine. To our knowledge, human lens regeneration has not yet been demonstrated. Currently, the only treatment for cataracts, the leading cause of blindness worldwide, is to extract the cataractous lens and implant an artificial intraocular lens. However, this procedure poses notable risks of complications. Here we isolate lens epithelial stem/progenitor cells (LECs) in mammals and show that Pax6 and Bmi1 are required for LEC renewal. We design a surgical method of cataract removal that preserves endogenous LECs and achieves functional lens regeneration in rabbits and macaques, as well as in human infants with cataracts. Our method differs conceptually from current practice, as it preserves endogenous LECs and their natural environment maximally, and regenerates lenses with visual function. Our approach demonstrates a novel treatment strategy for cataracts and provides a new paradigm for tissue regeneration using endogenous stem cells.

Characterization and differentiation of rabbit LECs.

a, LECs were positive for PAX6 (green) and SOX2 (red). b, Lentoid formation (green arrows) with positive αA-crystallin and β-crystallin staining on day 15 of LEC differentiation. c, Left panel, phase-contrast photograph of a lentoid bod…

Lens regeneration in macaque models after minimally invasive surgery.

a, Slit-lamp microscopy showed regenerating lens tissue grew from the peripheral to the central lens in a circular symmetrical pattern 2–3 months after surgery, reaching the centre at 5 months post-surgery. Five months after surgery, di…

Functional characteristics of regenerated human lenses

a, Lens thickness increased significantly 6 and 8 months after surgery (1.9 ± 0.3 and 3.7 ± 0.3 mm, respectively, *P < 0.01), n = 24. b, Lens refractive power increased significantly 6 and 8 months after surgery (5.1 ± 0.5 and 19.0 ± 0…

Conditional deletion of Bmi-1 led to decrease in Pax6⁺ and Sox2⁺ cells and cataract formation

A, Loss of Bmi-1 reduced the Pax6⁺ and Sox2⁺ LECs population. a, Representative images of haematoxylin and eosin-stained lens sections from Bmi1^fl/fl control mice andNestin-cre;Bmi1^fl/fl mice. b, Representative images of Bmi-1 (red) st…

Stem Cells Regenerate Human Lens After Cataract Surgery and Restore Vision

March 14, 2016 by mburatov

Collaboration between scientists from mainland China, the University of California, San Diego School of Medicine and Shiley Eye Institute have developed a new, stem cell-based technique that permits remaining stem cells to regrow functional lenses after the diseased lens was removed. This treatment was initially tested in laboratory animals, but it has now been tested in a small human clinical trial. This procedure produced far fewer surgical complications than the current standard-of-care. The real boost is that this regenerative procedure resulted in regenerated lenses that had superior visual qualities in all 12 of the pediatric cataract patients who served as subjects for this clinical trial.

Kang Zhang, MD, PhD, chief of Ophthalmic Genetics, founding director of the Institute for Genomic Medicine and co-director of Biomaterials and Tissue Engineering at the Institute of Engineering in Medicine, both at UC San Diego School of Medicine, said: “An ultimate goal of stem cell research is to turn on the regenerative potential of one’s own stem cells for tissue and organ repair and disease therapy.” Zhang and his colleagues published their work in the journal Nature.

Cataracts are cloudiness over the lens of the eye that blurs vision. The lens consists mostly of water and protein. When the protein aggregates, it clouds the lens and reduces the light that reaches the retina. This clouding may become severe enough to cause blurred vision. Most age-related cataracts develop from protein clumpings. You do not have to be older to suffer from cataracts. Congenital cataracts occur at birth or shortly after birth. Scarring of the retina or prenatal damage to the eye can cause congenital cataracts. Congenital cataracts are a significant cause of blindness in children. Current treatment for congenital cataracts is limited by the age of the patient. Most pediatric patients require corrective eyewear after cataract surgery.

To address this medical need, Zhang and colleagues examined the regenerative potential of endogenous stem cells on the lens. Unlike other stem cell approaches that involve creating stem cells in the lab and introducing them back into the patient, Zhang decided to use stem cells that are already in place at the site of the injury to do the heavy lifting. In the human eye, lens epithelial stem cells or LECs generate replacement lens cells throughout a person’s life, even though their production declines with age.

Unfortunately, current cataract surgeries essentially remove LECs within the lens. Whatever cells might be left over produce disorganized regrowth in infants and no useful vision. Zhang and his colleagues first confirmed that LECs had regenerative potential. To confirm this, they used laboratory animals. With that knowledge in hand, Zhang and his collaborators devised a novel, minimally invasive surgical procedure that removes the cloudy lens, but manages to maintain the integrity of the membrane that gives the lens its required shape (the lens capsule). With the lens capsule in place, the LECs were activated to replace the missing lens.

Once again, Zhang and his team ensured that their technique worked in animals before they ever tried it on a human patient. Animals with cataracts whose lenses were extirpated, but whose lens capsules were left intact, regenerated new lenses that were devoid of cataracts and provided excellent sight. With their technique honed and ready, Zhang and others tested their procedure on very young human infants in a small human trial. They discovered that their new surgical technique allowed pre-existing LECs to efficiently regenerate functional lenses. In particular, the human trial involved 12 infants under the age of 2 treated with the new method developed by Zhang and others, and 25 similar infants receiving current standard surgical care.

The results were stark: the control group experienced a higher incidence of post-surgery inflammation, early-onset ocular hypertension and increased lens clouding, but those infants who received Zhang’s new procedure showed fewer complications and faster healing. After three months, the 12 infants who underwent the new procedure had a clear, regenerated biconvex lens in all of their eyes.

Zhang indicated that he and his colleagues are now looking to apply what they learned in this project to tackling the issue of age-related cataracts. Age-related cataracts are the leading cause of blindness in the world. Over 20 million Americans suffer from cataracts, and more than 4 million surgeries are performed annually to replace the clouded lens with an artificial plastic lens (intraocular lens).

Lens stem cells may reside outside the lens capsule: an hypothesis

Susann G Remington Email author and Rita A Meyer

Theoret Biol and Med Modelling 2007; 4:22. http://dx.doi:/10.1186/1742-4682-4-22

In this paper, we consider the ocular lens in the context of contemporary developments in biological ideas. We attempt to reconcile lens biology with stem cell concepts and a dearth of lens tumors. Historically, the lens has been viewed as a closed system, in which cells at the periphery of the lens epithelium differentiate into fiber cells. Theoretical considerations led us to question whether the intracapsular lens is indeed self-contained. Since stem cells generate tumors and the lens does not naturally develop tumors, we reasoned that lens stem cells may not be present within the capsule. We hypothesize that lens stem cells reside outside the lens capsule, in the nearby ciliary body. Our ideas challenge the existing lens biology paradigm. We begin our discussion with lens background information, in order to describe our lens stem cell hypothesis in the context of published data. Then we present the ciliary body as a possible source for lens stem cells, and conclude by comparing the ocular lens with the corneal epithelium.

Lens background The vertebrate lens is a transparent cellular structure, specialized to focus and transmit light. The lens is composed of two cell types – epithelial cells that form a single cuboidal layer on the anterior surface, and elongated fiber cells that form the posterior bulk of the lens (Figure 1). A capsule of extracellular matrix components encompasses the lens.

The lens grows slowly throughout life, primarily via cell division in the germinative zone. The germinative zone is a narrow cellular region that rings the lens epithelium toward the periphery of the anterior lens surface. Newly formed cells within the germinative zone elongate and migrate along the inner capsular surface toward the lens equator, forming new lens fiber cells as they continue to elongate and migrate posteriorly beyond the equator. These new fiber cells add to the periphery of the existing fiber cell mass, displacing older fiber cells toward the interior of the expanding lens [1-3]. Central fiber cells are retained for life. Historically, the adult lens has been viewed as a closed system, in which all lens precursor cells or stem cells reside within the capsular confines.

Lens stem cells We use the following definition of lens stem cells – cells with prolonged self-renewing capacity, that produce one or more differentiated cell types with limited proliferative capabilities [4,5]. In general, stem cells are small, undifferentiated cells that reside in contact with a basement membrane in a protected location known as a stem cell niche.

Infrequent stem cell divisions result in one of two cell outcomes. The new cell either remains in its niche as a stem cell, or leaves as a progenitor cell that migrates from the niche to participate in cell differentiation events. Progenitor cells destined for differentiation increase in number through multiple, finite cell divisions as transit amplifying cells [5-7].

A lifetime of cell division in the lens implies the existence of a lens stem cell population. Typically stem cells reside in a protected niche, which for surface or exposed epithelia is a pigment protected and well vascularized location [8,9]. The lens lacks both pigment and a vascular system. An additional point is that tumors often arise from stem cells [10,11], yet the lens does not develop tumors [12,13]. How might these incongruities be reconciled? We hypothesize that the lens is not a closed system. Specifically, lens stem cells may reside outside the lens capsule. If the adult lens does not contain its own stem cell population, we asked where lens stem cells could exist. The pigmented, vascularized ciliary body lies in close proximity to the lens germinative zone, located outside of the lens capsule [14- 17]. We propose that the ciliary body could serve as a potential source of stem cells for the lens. We will discuss the ciliary body in more detail below.

Lens cell lineage If cell migration occurs within the anterior portions of the lens epithelium, the direction of this migration has not been conclusively determined. There is some circumstantial support (enumerated below) for transit amplifying cells of the germinative zone to supply precursors of new epithelial cells, as well as fiber cells. 1) As organisms age, the volume of the lens increases through new fiber cell addition at the lens equator. The growing lens maintains an epithelial cell monolayer over its expanding anterior surface area. While individual lens epithelial cells increase in average size with advancing age, some epithelial cell division is required to maintain the observed cell coverage [23]. New cells are needed in particular toward the periphery of the anterior epithelial region. Transit amplifying cells of the germinative zone are well positioned to fill this need. 2) Apoptosis of lens epithelial cells has been observed in normal and cataractous lenses [28,29]. Extrapolation of estimated apoptosis rates and cell division rates in the central epithelium suggests that replacement epithelial cells originate toward the lens epithelial periphery and migrate centripetally. 3) Injury of cells in the central lens epithelium resulted in increased DNA synthesis within 24 hours in the lens germinative zone. At later time points (four days), DNA synthesis was also observed in more central epithelial cells surrounding the wound [30]. One possible interpretation of these central epithelium wounding studies is that cells from the germinative zone may routinely migrate centripetally to replace damaged epithelial cells. By analogy, limbal cells are the recognized source of new corneal epithelial cells, and central corneal wounding was demonstrated to stimulate limbal cell proliferation [31-33]. 4) In vitro lens cell migration studies performed in an electric field provided indirect support for centripetal migration of lens epithelial cells in vivo [34]. 5) Several other researchers have proposed centripetal migration of lens epithelial cells based on their own diverse experimental observations [35-38].

If transit amplifying cells in the germinative zone provide replacement cells for the anterior epithelium, then cells of the germinative zone would possess differentiation potential for two different lens cell types – epithelial cells and fiber cells. Individual cells may have the potential to differentiate either as epithelial or fiber cells. Alternatively, two distinct precursor cell populations may reside within the lens germinative zone.

Lens stem cell hypothesis While circumstantial evidence implicates the germinative zone as the source of new cells for lens epithelium as well as for fiber cells, results from a recent study seem to contradict these ideas. …

Ciliary body, a possible source of lens stem cells If the encapsulated lens does not contain its own stem cell population, we asked where lens stem cells could reside. The ciliary body is a pigmented and vascularized tissue, that lies physically close to the lens germinative zone [14- 16,41]. The ciliary body represents the anterior extension of the choroid, and is situated between the choroid and the iris. The epithelium of the ciliary body consists of two cell layers, an inner non-pigmented epithelium, and an outer pigmented epithelium in intimate contact with capillaries [16]. The ciliary epithelial layers represent anterior extensions of the inner non-pigmented neural retina and the outer pigmented retinal epithelium, respectively. (The terms ‘inner’ and ‘outer’ are used in reference to the ocular globe interior.) A recognized stem cell population – the retinal stem cells – resides in the ciliary body [42-44]. …

Posterior capsule opacification If the continuity of the lens capsule is breached, however, extralenticular cell migration into the area delimited by the lens capsule likely occurs. Cataract extraction disrupts the lens capsule. Subsequent cell growth and migration on the remaining capsule lead to complications in 25% of adult patients (and nearly 100% of pediatric patients) that again compromise vision [71-73]. These complications, known as after-cataract or posterior capsule opacification, are believed to primarily involve proliferation and migration of lens epithelial cells left behind during cataract surgery [74-77]. There is also evidence that cells originating in non-lens ocular tissues participate in cell aggregates within the remaining capsule [78-80].

In posterior capsule opacification, the majority of aberrant cell growth is attributed to lens cells originating within the capsule. However, if our hypothesis is correct that lens stem cells normally reside outside the lens capsule, then much of this aberrant growth may actually arise from lens progenitor cells that migrate to the capsule after the cataract surgery.

Analogies to corneal epithelium If our lens literature summary seems contrived to explain an improbable lens stem cell hypothesis, consider the corneal epithelium. Like the lens, the corneal epithelium is a transparent, avascular ocular tissue, specialized to focus and transmit light [81]. One major difference between cornea and lens is that the cornea also provides a protective surface for the eye. In its protective role at the environment interface, the corneal epithelium has well developed tissue replacement capabilities to repair normal wear and minor injuries [82,83]. In contrast, lens cell division occurs on a more limited scale.

Conclusion In light of concepts that have evolved in stem cell literature in recent years, we re-examine the ocular lens in the context of features common to other biological tissues. Since the lens grows throughout life and does not naturally develop tumors, we ask whether lens stem cells could reside in a more typical stem cell niche, one that is pigmented and vascularized. We hypothesize that lens stem cells reside outside the lens capsule in nearby pigmented ocular tissue, the ciliary body. Here, we present our review of the lens literature from this novel perspective.

Ocular stem cells: a status update!

Kamesh Dhamodaran,^1,²Murali Subramani,¹Murugeswari Ponnalagu,¹Reshma Shetty,¹and Debashish Das^{1

Stem Cell Res Ther. 2014; 5(2): 56. 10.1186/scrt445}

Stem cells are unspecialized cells that have been a major focus of the field of regenerative medicine, opening new frontiers and regarded as the future of medicine. The ophthalmology branch of the medical sciences was the first to directly benefit from stem cells for regenerative treatment. The success stories of regenerative medicine in ophthalmology can be attributed to its accessibility, ease of follow-up and the eye being an immune-privileged organ. Cell-based therapies using stem cells from the ciliary body, iris and sclera are still in animal experimental stages but show potential for replacing degenerated photoreceptors. Limbal, corneal and conjunctival stem cells are still limited for use only for surface reconstruction, although they might have potential beyond this. Iris pigment epithelial, ciliary body epithelial and choroidal epithelial stem cells in laboratory studies have shown some promise for retinal or neural tissue replacement. Trabecular meshwork, orbital and sclera stem cells have properties identical to cells of mesenchymal origin but their potential has yet to be experimentally determined and validated. Retinal and retinal pigment epithelium stem cells remain the most sought out stem cells for curing retinal degenerative disorders, although treatments using them have resulted in variable outcomes. The functional aspects of the therapeutic application of lenticular stem cells are not known and need further attention. Recently, embryonic stem cell-derived retinal pigment epithelium has been used for treating patients with Stargardts disease and age-related macular degeneration. Overall, the different stem cells residing in different components of the eye have shown some success in clinical and animal studies in the field of regenerative medicine.

Pluripotency, the capacity to differentiate into multiple lineages, and proliferation are two characteristic attributes of stem cells. These cells are capable of replacing damaged or diseased cells under certain circumstances. Regenerative medicine or stem cell-based therapy has now reached a state where ocular tissues damaged by disease or injury can be repaired and/or regenerated. The ease of access for the therapeutic procedure as well as follow-up together with its immune-privileged status makes the eye an ideal organ for studying regenerative medicine. Such therapy involves various procedures where stem cells are injected into both the cellular and extracellular matrix microenvironments [1]. Corneal epithelial cell transplantation has been the most widely used stem cell-based therapy following bone marrow transplantation.

Stem cell-based treatment in ophthalmology follows either a cell replacement therapy strategy or a strategy involving trophic factor-based guidance cues. Throughout treatment, outcomes depend on our in-depth knowledge of the disease, the source of stem cells, the mode of treatment and the plausible mechanism driving the therapeutic outcome [2]. …

Cornea (limbus and stroma)

The cornea is at the outermost surface of the eye and safeguards transparency, which is crucial for vision. The corneal stem cell population is located in the periphery of the cornea, in the limbus; these cells are termed limbal epithelial stem cells (LESCs) [3–6]. Stroma comprises 90% of the volume of the cornea and, unlike the self-renewal of epithelia, the homeostasis of stroma is not based on a cycle of cell death and mitotic renewal.