Formation of Human Myocardium in the Rat Heart from Human Embryonic Stem Cells

Abstract

Human embryonic stem cells (hESCs) offer the opportunity to replenish cells lost in the postinfarct heart. We explored whether human myocardium could be generated in rat hearts by injecting differentiated cardiac-enriched hESC progeny into the left ventricular wall of athymic rats. Although initial grafts were predominantly epithelial, noncardiac elements were lost over time, and grafts consisted predominantly of cardiomyocytes by 4 weeks. No teratomatous elements were observed. Engrafted cardiomyocytes were glycogen-rich and expressed expected cardiac markers including ␤-myosin heavy chain, myosin light chain 2v, and atrial natriuretic factor. Heat-shock treatment improved graft size approximately threefold. The cardiac implants exhibited substantial angiogenesis, both recipient and graft derived. Importantly, there was greater proliferation in human cardiomyocytes than previously seen in rodent-derived cardiomyocytes: 14.4% of graft cardiomyocytes expressed the proliferation marker Ki-67, and 2.7% incorporated the thymidine analog BrdU 4 weeks after transplantation. This proliferation was associated with a sevenfold increase in graft size over the 4-week interval. Thus, hESCs can form human myocardium in the rat heart, permitting studies of human myocardial development and physiology and supporting the feasibility of their use in myocardial repair.

Systems approaches to preventing transplanted cell death in cardiac repair

“…Several interventions are already known to enhance survival of transplanted cells in the heart, and these are summarized in Table 1. We identified heat shock as a potent strategy to enhance survival of neonatal cardiomyocyte grafts [44], and heat shock treatment has subequently been shown to be effective for skeletal myoblast survival [53,54] and hESC-derived cardiomyocytes [21,22]. Heat shock is typically achieved by heating cells to 43°C for 30-60 minutes one day before transplantation, and this results in induction of the heat shock proteins (hsps) 60, 70 and 90 [21,44].…”

“…We identified heat shock as a potent strategy to enhance survival of neonatal cardiomyocyte grafts [44], and heat shock treatment has subequently been shown to be effective for skeletal myoblast survival [53,54] and hESC-derived cardiomyocytes [21,22]. Heat shock is typically achieved by heating cells to 43°C for 30-60 minutes one day before transplantation, and this results in induction of the heat shock proteins (hsps) 60, 70 and 90 [21,44]. Of these, hsp70 has implicated by several groups [55,56] as limiting cell death by inhibiting pro-apoptotic signaling [57], acting as molecular chaperones for damaged proteins and during translation [58,59], or opposing oxidative stress [60].…”

“…Kutschka et al demonstrated that grafts were larger and ventricular function was improved in infarcted rats when human embryonic stem cell-derived cardiomyocytes were delivered with collagen matrices, including GelFoam and the basement membrane preparation, Matrigel [72]. As will be discussed below, Laflamme et al found that Matrigel significantly enhanced survival of hESC-derived cardiomyocytes in infarcted hearts of athymic rats [21,22].…”

“…These studies showed that a panoply of cells injected into the myocardium both can change the nature of the scar and improve post-infarction cardiac function. Skeletal myoblasts [6][7][8], fetal or neonatal cardiomyocytes [9][10][11], fibroblasts [12], smooth muscle cells [13], hematopoietic stem cells [14,15], mesenchymal stem cells [16], endothelial cells [17], resident cardiac progenitor cells [18,19], and derivatives of human embryonic stem cells [20][21][22][23][24] have all been transplanted into animal hearts. While it is clear that functional benefit is conferred from numerous cell types, the mechanism of action is unclear.…”

Adhesion Proteins, Stem Cells, and Arrhythmogenesis

“…For example, the TGF-beta family of secreted factors has been shown to induce mesodermal differentiation of ESC [63,64]. Therefore, sequential exposure of ESC to actinin A and BMP4 was shown to enhance cardiac differentiation 50 times more than serum induction alone [65]. Transplantation of these cells resulted in the "remuscularization" of the ischemic myocardium, with both echocardiograph and MRI studies showing improved diastolic and systolic function.…”