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Posts Tagged ‘pluripotent cells’


Stem Cell Therapy for Coronary Artery Disease (CAD)

Author and Curator: Larry H. Bernstein, MD, FCAP

and

Curator: Aviva Lev-Ari, PhD, RN

 

There is great interest and future promise for stem cell therapy in ischemic heart disease.  This is another report for the active work in cardiology with stem cell therapy by MA Gaballa and associates at University of Arizona.

Stem Cell Therapy for Coronary Heart Disease

Julia N. E. Sunkomat and Mohamed A. Gaballa

The University ofArizona Sarver Heart Center, Section of Cardiology, Tucson, Ar
Cardiovascular Drug Reviews 2003: 21(4): 327–342

Keywords: Angiogenesis — Cardiac therapy — Coronary heart disease — Heart failure — Myoblasts — Myocardial ischemia — Myocardial regenera­tion — Stem cells

ABSTRACT

Coronary artery disease (CAD) remains the leading cause of death in the Western world. The high impact of its main sequelae, acute myocardial infarction and congestive heart failure (CHF), on the quality of life of patients and the cost of health care drives the search for new therapies. The recent finding that

stem cells contribute to neovascularization and possibly improve cardiac function after myocardial infarction makes stem cell therapy the most highly active research area in cardiology. Although the concept of stem cell therapy may revolutionize heart failure treatment, several obstacles need to be ad­dressed. To name a few:

  1.  Which patient population should be considered for stem cell therapy?
  2.  What type of stem cell should be used?
  3.  What is the best route for cell de­livery?
  4.  What is the optimum number of cells that should be used to achieve functional effects?
  5.  Is stem cell therapy safer and more effective than conventional therapies?

The published studies vary significantly in design, making it difficult to draw conclusions on the efficacy of this treatment. For example, different models of

  1. ischemia,
  2. species of donors and recipients,
  3. techniques of cell delivery,
  4. cell types,
  5. cell numbers and
  6. timing of the experiments

have been used. However, these studies highlight the landmark concept that stem cell therapy may play a major role in treating cardiovascular diseases in the near future. It should be noted that stem cell therapy is not limited to the treatment of ischemic cardiac disease.

  • Non-ischemic cardiomyopathy,
  • peripheral vascular disease, and
  • aging may be treated by stem cells.

Stem cells could be used as vehicle for gene therapy and eliminate the use of viral vectors. Finally, stem cell therapy may be combined with phar­macological, surgical, and interventional therapy to improve outcome. Here we attempt a systematic overview of the science of stem cells and their effects when transplanted into ischemic myocardium.

INTRODUCTION

Background

Congestive heart failure (CHF) is the leading discharge diagnosis in patients over the age of 65 with estimates of $24 billion spent on health care in the US (1,11). The number one cause of CHF is coronary artery diseases (CAD). Coronary care units, reperfusion therapy (lytic and percutaneous coronary intervention) and medical therapy with anti-pla­telet agents, statins, ACE-inhibitors and â-adrenoceptor antagonists all significantly reduce morbidity and mortality of CAD and CHF (9), but it is very difficult to regenerate new viable myocardium and new blood vessels.

Identification of circulating endothelial progenitor cells in peripheral blood that incor­porated into foci of neovascularization in hindlimb ischemia (4) and the successful engraftment of embryonic stem cells into myocardium of adult dystrophic mice (31) intro­duced a new therapeutic strategy to the field of cardiovascular diseases: tissue regeneration. This approach is supported by the discovery of primitive cells of extracardiac origin in cardiac tissues after sex-mismatched transplants suggesting that an endogenous repair mechanism may exist in the heart (35,45,54). The number of recruited cells varied significantly from 0 (19) to 18% (54), but the natural course of ischemic cardiomyopathy implies that cell recruitment for tissue repair in most cases is insufficient to prevent heart failure. Therefore, investigational efforts are geared towards

  • augmenting the number of multipotent stem cells and endothelial and myocardial progenitor cells at the site of ischemia to induce clinically significant angiogenesis and potentially myogenesis.

Stem and Progenitor Cells

Stem cells are defined by their ability to give rise to identical stem cells and progenitor cells that continue to differentiate into a specific tissue cell phenotype (23,33). The po­tential of mammalian stem cells varies with stage of development and age (Table 1).

In mammals, the fertilized oocyte and blastomere cells of embryos of the two to eight cell stage can generate a complete organism when implanted into the uterus; they are called totipotent stem cells. After the blastocyst stage, embryonic stem cells retain the ability to differentiate into all cell types, but

  • cannot generate a complete organism and thus are denoted pluripotent stem cells.

Other examples of pluripotent stem cells are embryo­nic germ cells that are derived from the gonadal ridge of aborted embryos and embryonic carcinoma cells that are found in gonadal tumors (teratocarcinomas) (23,33). Both these cell types can also differentiate into cells of all three germ layers, but are not as well inves­tigated as embryonic stem cells.

It is well established that embryonic stem cells can differentiate into cardiomyocytes (7,10,13,14,31,37,76), endothelial cells (55), and smooth muscle cells (5,22,78) in vitro, but it is unclear whether

  • pure populations of embryonic stem cell-derived cardiomyocytes can integrate and function appropriately in the heart after transplantation.
  • one study reported arrhythmogenic potential of embryonic stem cell-derived cardiomyocytes in vitro (80).

Adult somatic stem cells are cells that have already committed to one of the three germ layers: endoderm, ectoderm, or mesoderm (76). While embryonic stem cells are defined by their origin (the inner cell mass of the blastocyst), the origin of adult stem cells in mature tissues is still unknown. The primary role of adult stem cells in a living organism is thought to be maintaining and repairing the tissue in which they reside. They are the source of more identical stem cells and cells with a progressively more distinct phenotype of specialized tissue cells (progenitor and precursor cells) (Fig. 1). Until recently adult stem cells were thought to be lineage-specific, meaning that they can only differentiate into the cell-type of their original tissue. This concept has now been challenged with the discovery of multipotent stem and progenitor cells (26, 50, 51).

The presence of multipotent stem and progenitor cells in adult mammals has vast im­plications on the availability of stem cells to research and clinical medicine. Recent publi­cations, however, have questioned whether the adaptation of a phenotype in those dogma-challenging studies is really a result of trans-differentiation or rather a result of cell and nuclear fusion (60,68,75,79). Spontaneous fusion between mammalian cells was first re­ported in 1961 (8), but how frequently fusion occurs and whether it occurs in vivo is not clear.

The bone marrow is a known source of stem cells. Hematopoietic stem cells are fre­quently used in the field of hematology. Surface receptors are used to differentiate hematopoietic stem and progenitor cells from mature cells. For example, virtually all

  • hematopoietic stem and progenitor cells express the CD34+ glycoprotein antigen on their cell membrane (73),

though a small proportion of primitive cells have been shown to be CD34 negative (58).

The function of the CD34+ receptor is not yet fully understood. It has been suggested that it may act as a regulator of hematopoietic cell adhesion in the bone marrow microenvironment. It also appears to be involved in the maintenance of the hematopoietic stem/progenitor cell phenotype and function (16,21). The frequency of immature CD34+ cells in peripheral circulation diminishes with age.

  • It is the highest (up to 11%) in utero (69) and decreases to 1% of nucleated cells in term cord blood (63).
  • This equals the per­centage of CD34+ cells in adult bone marrow.
  • The number of circulating stem cells in adult peripheral blood is even lower at 0.1% of nucleated cells.

Since hematopoietic stem cells have been identified as endothelial progenitor cells (29,30,32) their low density in adult bone marrow and blood could explain the inadequacy of endogenous recruitment of cells to injured organs such as an ischemic heart. The bone marrow is also home to another stem cell population the so-called mesenchymal stem cells. These may constitute a subset of the bone marrow stromal cells (2,43). Bone marrow stromal cells are a mixed cell popu­lation that generates

  1. bone,
  2. cartilage,
  3. fat,
  4. connective tissue, and
  5. reticular network that sup­ports cell formation (23).

Mesenchymal stem cells have been described as multipotent (51,52) and as a source of myocardial progenitor cells (41,59). They are, however, much less defined than the hematopoietic stem cells and a characteristic antigen constellation has not yet been identified (44).

Another example of an adult tissue containing stem cells is the skeletal muscle. The cells responsible for renewal and growth of the skeletal muscle are called satellite cells or myoblasts and are located between the sarcolemma and the basal lamina of the muscle fiber (5). Since skeletal muscle and cardiac muscle share similar characteristics such as they both are striated muscle cells, satellite cells are considered good candidates for the repair of damaged myocardium and have been extensively studied (20,25,38–40,48,56, 64–67). Myoblasts are particularly attractive, because they can be autotransplanted, so that issues of donor availability, ethics, tumorigenesis and immunological compatibility can be avoided. They also have been shown to have a high growth potential in vitro and a strong resistance to ischemia in vivo (20). On the down side

  • they may have more arrhythmogenic potential when transplanted into myocardium than bone marrow or peripheral blood de­rived stem cells and progenitor cells (40).

Isolation of Cells Prior to Transplantation

Hematopoietic stem and progenitor cells are commonly identified by the expression of a profile of surface receptors (cell antigens). For example, human hematopoietic stem cells are defined as CD34+/CD59+/Thy-1+/CD38low//c-kit/low/lin, while mouse hema-topoietic stem cells are defined as CD34low//Sca-1+/Thy-1+/low/CD38+/c-kit+/lin (23). Additional cell surface receptors have been identified as markers for subgroups of hema-topoietic stem cells with the ability to differentiate into non-hematopoetic tissues, such as endothelial cells (57,78). These can be specifically targeted by isolation methods that use the receptors for cell selection (positive selection with antibody coated magnetic beads or fluorescence-activated cell sorting, FACS). Other stem cell populations are identified by their behavior in cell culture (mesenchymal stem cells) or dye exclusion (SP cells). Finally, embryonic stem cells are isolated from the inner cell mass of the blastocyst and skeletal myoblasts are mechanically and enzymatically dissociated from an easily acces­sible skeletal muscle and expanded in cell culture.

FIG. 1. Maturation process of adult stem cells: with acquisition of a certain phenotype the cell gradually loses its self-renewal capability.  (unable to transfer)

METHODICAL APPROACHES 

j.1527-3466.2003.tb00125.x  fig stem cell

FIG. 2. Intramyocardial injection:

the cells are injected directly into the myocardium through the epicardium. Usually a thoracotomy or sternotomy is required. Transendocardial injection: access can be gained from the ar­terial vasculature. Cells are injected through the endocardium into the myocardium, ideally after identifying the ischemic myocardium by perfusion studies and/or electromechanical mapping. Intracoronary injection: the coronary artery is accessed from the arterial vasculature. Stem cells are injected into the lumen of the coronary artery. Proximal washout is prevented by inflation of a balloon. Cells are then distributed through the capillary system. They eventually cross the endothelium and migrate towards ischemic areas.

The intracoronary delivery of stem cells (Fig. 2) and distribution through the coronary system has also been explored (6,62,74). This approach was pioneered by Robinson et al. (56), who demonstrated successful engraftment within the coronary distribution after intracoronary delivery of genetically labeled skeletal myoblasts. The risk of intracoronary injection is comparable to that of a coronary angiogram and percutaneous transluminal coronary angioplasty (PTCA) (62), which are safe and clinically well established.

RESULTS IN ANIMAL STUDIES AND HUMAN TRIALS

Dif­ferentiation into cardiomyocytes was observed after transplantation of embryonic stem cells, mesenchymal stem cells, lin/c-kit+ and SP cells. The induction of angiogenesis was observed after transplantation of embryonic stem cells, mesenchymal stem cells, bone marrow-derived mononuclear cells, circulating endothelial progenitor cells, SP cells and lin/c-kit+ cells.

The use of embryonic stem cells in ischemia was examined in two studies (42,43). These studies demonstrated that mice embryonic stem cells transplanted into rat myo­cardium exhibited cardiomyocyte phenotype at 6 weeks after transplantation. In addition, generation of myocardium and angiogenesis were observed at 32 weeks after allogenic transplantation in rats. In these two studies no arrhythmias or cardiac tumors were reported.

Several studies have shown retardation of LV remodeling and improvement of cardiac function after administration of bone marrow-derived mononuclear cells. For example, decreases in infarct size, and increase in ejection fraction (EF), and left ventricular (LV) time rate change of pressure (dP/dtmax) were observed after direct injection of bone marrow-derived mononuclear cells 60 min after ischemia in swine (28). In humans, intra-coronary delivery and transendocardial injection of mononuclear cells leads to a decrease in LV dimensions and improvement of cardiac function and perfusion (49,62). A decrease in end systolic volume (ESV) and an increase in EF as well as regional wall motion were observed following intracoronary administration of CD34+/CD45+ human circulating en­dothelial cells (6). Injection of circulating human CD34+/CD117+ cells into infarcted rat myocardium induced neoangiogenesis and improved cardiac function (32). This study suggests that the improvement in LV remodeling after infarction appears to be in part me­diated by a decrease in apoptosis within the noninfarcted myocardium. Two other studies reported increased fractional shortening, improved regional wall motion and decreased left ventricular dimensions after transplantation of human CD34+ cells (29,30). Improved global left ventricular function and infarct perfusion was demonstrated after intramyo-cardial injection of autologous endothelial progenitor cells in humans (61).

DISCUSSION AND OUTLOOK

The idea of replacing damaged myocardium by healthy cardiac tissue is exciting and has received much attention in the medical field and the media. Therefore, it is important for the scientist to know what is established and what is based on premature conclusions. Currently, there are data from animal studies and human trials (Table 2). However, some of these data are not very concrete. For example,

  • many animal studies do not report the level of achieved neoangiogenesis and/or regeneration of myocardium.
  • In studies where the numbers of neovessels and new cardiomyocytes are specified, these numbers are often very low.

While these experiments confirm the concept that bone marrow and peripheral blood-derived stem and progenitor cells can differentiate into cardiomyocytes and endo­thelial cells when transplanted into ischemic myocardium, they also raise the question how effective this treatment is.

The results of the clinical trials that have been conducted are encouraging, but they need to be interpreted with caution. The common endpoints of these studies include left ventricular dimensions, perfusion, wall motion and hemodynamic function. While all studies report improvement after mononuclear cell, myoblast or endothelial progenitor cell transplantation, it is difficult to separate the effects of stem cell transplantation from the effects of the state-of-the art medical care that the patients typically received.

CONCLUSION

While the majority of studies demonstrate neoangiogenesis and some studies also show regeneration of myocardium after stem/progenitor cell transplantation, it remains unclear whether the currently achieved level of tissue regeneration is sufficient to affect clinical outcome. Long-term follow-up of patients that received stem/progenitor cells in clinical trials will provide important information on the potential risks of neoplasm and arrhythmias and, therefore, safety of this treatment. Ultimately, postmortem histological confirmation of scar tissue repair by transplanted cells and randomized placebo control trials with long-term follow-up are required to prove efficacy of this treatment.

REFERENCES (10)

1. American Heart Association Disease and Stroke Statistics-2003 Update, Dallas TX, American Heart Associ­ation; 2002 http://http://www.americanheart.org/downloadable/heart/10461207852142003HDSStatsBook.pdf

2. Arai A, Sheikh F, Agyeman K, et al. Lack of benefit from cytokine mobilized stem cell therapy for acute myocardial infarction in nonhuman primates. J Am Coll Cardiol 2003;41(Suppl 6A):371.

3. Asahara T, Masuda H, Takahashi T, et al. Bone marrow origin of endothelial progenitor cells responsible for postnatal vasculogenesis in physiological and pathological neovascularization. Circ Res 1999;85:221–228.

4. Asahara T, Murohara T, Sullivan A, et al. Isolation of putative progenitor endothelial cells for angiogenesis. Science 1997;275:964–967.

5. Asakura A, Seale P, Girgis-Gabardo A, Rudnicki M. Myogenic specification of side population cells in skeletal muscle. J Cell Biol 2002;159(1):123–134.

6. Assmus B, Schaechinger V, Teupe C, et al. Transplantation of progenitor cells and regeneration en­hancement in acute myocardial infarction (TOPCARE-AMI). Circulation 2002;106:r53–r61.

7. Bader A, Al-Dubai H, Weitzer G. Leukemia inhibitory factor modulates cardiogenesis in embryoid bodies in opposite fashions. Circ Res 2000;86(7):787–794.

8. Barski G, Sorieul S, Cornefert F. “Hybrid” type cells in combined cultures of two different mammalian cell strains. J Natl Cancer Inst 1961;26:1269–1291.

9. Boersma E, Mercado N, Poldermans D, Gardien M, Vos J, Simoons M. Acute myocardial infarction. Lancet 2003;361:847–58.

  1. 10.          Boheler K, Czyz J, Tweedie D, Yang H, Anisimov S, Wobus A. Differentiation of pluripotent embryonic stem cells into cardiomyocytes. Circ Res 2002;91:189–201.

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Reporter: Ritu Saxena, Ph.D.

Diabetes currently affects more than 336 million people worldwide, with healthcare costs by diabetes and its complications of up to $612 million per day in the US alone.  The islets of Langerhans, miniature endocrine organs within the pancreas, are essential regulators of blood glucose homeostasis and play a key role in the pathogenesis of diabetes.  Islets of Langerhans are composed of several types of endocrine cells.  The α- and β-cells are the most abundant and also the most important in that they secrete hormones (glucagon and insulin, respectively) crucial for glucose homeostasis (Bosco D, et al, Diabetes, May 2010;59(5):1202-10).

Diabetes is a ‘bihormonal’ disease, involving both insulin deficiency and excess glucagon.  For decades, insulin deficiency was considered to be the sole reason for diabetes; however, recent studies emphasize excess glucagon as an important part of diabetes etiology.  Thus, insulin-secreting β cells and glucagon-secreting α cells maintain physiological blood glucose levels, and their malfunction drives diabetes development.  Increasing the number of insulin-producing β cells while decreasing the number of glucagon-producing α cells, either in vitro in donor pancreatic islets before transplantation into type 1 diabetics or in vivo in type 2 diabetics, is a promising therapeutic avenue.  A huge leap has been taken in this direction by the researchers at the University of Pennsylvania (Philadelphia, PA) in collaboration with Oregon Health and Science University (Portland, OR), USA by demonstrating that α to β cell reprogramming could be promoted by manipulating the histone methylation signature of human pancreatic islets.  In fact, the treatment of cultured pancreatic islets with a histone methyltransferase inhibitor leads to colocalization of both glucagon and insulin and glucagon and insulin promoter factor 1 (PDX1) in human islets and colocalization of both glucagon and insulin in mouse islets.  The research findings were published in the Journal of Clinical Investigation.

Study design: First step was to study and analyze the epigenetic and transcriptional landscape of human pancreatic human pancreatic α, β, and exocrine cells using ChIP and RNA sequencing.  Study design for determination of the transcriptome and differential histone marks included the dispersion and FACS to of human islets to obtain cell populations highly enriched for α, β, and exocrine (duct and acinar) cells.  Then, chromatin was prepared for ChIP analysis using antibodies for histone modifications, H3K4me3 (represents gene activation) and H3K27me3 (represents gene repression).  RNA-Sequencing analysis was then performed to determine mRNA and lncRNA.  Sample purity was confirmed using qRT-PCR of insulin and glucagon expression levels of the individual α and β cell population revealing high sample purity.

Results:

  • Long noncoding transcripts: Long noncoding RNA molecules have been implicated as important developmental regulators, cell lineage allocators, and contributors to disease development.  The authors discovered 12 cell–specific and 5 α cell–specific noncoding (lnc) transcripts, indicative of the valuable research resource represented from transcriptome data.  Recently discovered lncRNA molecules in islets are regulated during development and dysregulated in type 2 diabetic islets.
  • Monovalent histone modification landscapes shared among three cell types:  Monovalent H3K4me3-enriched regions, indicative of gene activation, were identified and compared in α, β, and exocrine cells.  Strikingly, the vast majority of monovalently H3K4me3-marked genes were shared among the 3 pancreatic cell lineages (83%–95%), reflecting both their related function in protein secretion and common embryonic descent. Similarly, a high degree of overlap was observed in H3K27me3 modification patterns in all the three cell types (73%–83%).
  • Bivalent histone modifications (H3K4me3 and H3K27me3) were high in α cells: Bernstein colleagues observed bivalent marks to be common in undifferentiated cells, such as ES cells and pluripotent progenitor cells, and in most cases, one of the histone modification marks was lost during differentiation, accompanying lineage specification (Bernstein BE, et al, Cell, 21 Apr 2006; 125(2):315-26).  α cells exhibited many more genes bivalently marked, followed by β cells and exocrine cells.  Bivalent state was remarkably similar to that of hESC, suggesting a more plastic epigenomic state for α cells.
  • Monovalent histone modifications were high in β cells: Thousands of the genes that were in bivalent state in α cells were in a monovalent state, carrying only the activating or repressing mark.
  • Inhibition of histone methyltransferases led to partial cell-fate conversion: Adenosine dialdehye (Adox), a drug that interferes with histone methylation and decreases H3K27me3, when administered in human islet tissue, led to decrease of H3K27me3 enrichment at the 3 gene loci that are originally expressed bivalently in α cells and monovalently in β cells:  MAFA, PDX1 and ARX.  Adox resulted in the occasional cooccurrence of glucagon and insulin granules within the same islet cell, which was not observed in untreated islets.  Thus, inhibition of histone methyltransferases leads to partial endocrine cell-fate conversion.

Conclusion:  α cells have been reprogrammed into β cell fate in various mouse models.  The reason, as proposed by the authors, might be the presence of more bivalently marked genes that confers a more plastic epigenomic state of the cells that probably drives them to the β cell fate.  Therefore, using epigenomic information of different cell types in pancreatic islets and harnessing it for subsequent manipulation of their epigenetic signature could be utilized to reprogram cells and hence provide a path for diabetes therapy.

Source: Bramswig NC, et al, Epigenomic plasticity enables human pancreatic α to β cell reprogramming. J Clin Invest, 22 Feb 2013. pii: 66514.

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