Paracrine effects of transplanted myoblasts and relaxin on post‐infarction heart remodelling

Abstract

In the post-infarcted heart, grafting of precursor cells may partially restore heart function but the improvement is modest and the mechanisms involved remain to be elucidated. Here, we explored this issue by transplanting C2C12 myoblasts, genetically engineered to express enhanced green fluorescent protein (eGFP) or eGFP and the cardiotropic hormone relaxin (RLX) through coronary venous route to swine with experimental chronic myocardial infarction. The rationale was to deliver constant, biologically effective levels of RLX at the site of cell engraftment. One month after engraftment, histological analysis showed that C2C12 myoblasts selectively settled in the ischaemic scar and were located around blood vessels showing an activated endothelium (ICAM-1-,VCAM-positive). C2C12 myoblasts did not trans-differentiate towards a cardiac phenotype, but did induce extracellular matrix remodelling by the secretion of matrix metalloproteases (MMP) and increase microvessel density through the expression of vascular endothelial growth factor (VEGF). Relaxin-producing C2C12 myoblasts displayed greater efficacy to engraft the post-ischaemic scar and to induce extracellular matrix re-modelling and angiogenesis as compared with the control cells. By echocardio-graphy, C2C12-engrafted swine showed improved heart contractility compared with the ungrafted controls, especially those producing RLX. We suggest that the beneficial effects of myoblast grafting on cardiac function are primarily dependent on the paracrine effects of transplanted cells on extracellular matrix remodelling and vascularization. The combined treatment with myoblast transplantation and local RLX production may be helpful in preventing deleterious cardiac remodelling and may hold therapeutic possibility for post-infarcted patients.

Relaxin remodels fibrotic healing following myocardial infarction

“…While relaxin's major mode of action in the infarct model appeared to be its antifibrotic capability, its added capacity to reduce cardiomyocyte apoptosis, while promoting blood vessel growth suggests that relaxin may hold promise as an agent for the treatment of coronary artery disease including MI. Specifically, relaxin's effects seen in the infarct model might also be complementary to cell-based therapies in this setting, which is consistent with the recent findings of Bani and colleagues in pig 14 and rat 42 models of MI, demonstrating that transplanted myoblasts genetically engineered to express relaxin at the site of cell engraftment reduced post-infarct collagen density, while increasing markers of vascularization and cardiac function. Progress in cell-based therapies has been hampered by a very low viability of implanted stem cells, insufficient nourishment and fibrotic environment of the host, poor functional coupling with viable host cardiomyocytes, and incomplete differentiation.…”

“…The relaxin-induced remodeling of scar healing in this model are also consistent with its anti-fibrotic effects demonstrated in larger experimental models, 14 and with the progressive cardiac fibrosis phenotype demonstrated in ageing relaxin-deficient mice, with resultant ventricular diastolic dysfunction. 21 The anti-apoptotic effects of relaxin in the infarcted murine heart are also consistent with its effects in a porcine model of MI, 36 and its ability to protect cardiomyocytes from apoptosis in vitro; 16 while its pro-angiogenic Relaxin remodels post-infarct fibrotic healing CS Samuel et al effects are in keeping with that observed in the pig model of MI.…”

“…21 The anti-apoptotic effects of relaxin in the infarcted murine heart are also consistent with its effects in a porcine model of MI, 36 and its ability to protect cardiomyocytes from apoptosis in vitro; 16 while its pro-angiogenic Relaxin remodels post-infarct fibrotic healing CS Samuel et al effects are in keeping with that observed in the pig model of MI. 14 The rationale for Glut-1 staining was based on previous studies using endothelial expression of Glut-1 as a marker of active de novo capillary formation; where 75% of Glut-1 expression in the heart was localized to the capillary endothelium. 23 The morphological assessment of its expression was used as a surrogate marker of relaxin's pro-angiogenic properties, and to supplement the a-SMA staining of larger vessels.…”

“…[6][7][8][9][10] Relaxin has been shown to inhibit the collagen-promoting actions of transforming growth factor-b1 (TGF-b1) and angiotensin II in rat cardiac fibroblasts, 11 and was more recently shown to inhibit TGF-b1 signaling through stimulation of the nitric oxide (NO) pathway to inhibit Smad2 phosphorylation. 12 Of further significance are the findings that relaxin also stimulates vasodilation and coronary flow via NO signaling, increases angiogenesis by upregulating vascular endothelial growth factor and basic fibroblast growth factor [6][7][8][13][14][15] and inhibits cardiomyocyte apoptosis by altering the Bcl2/Bax ratio; 16 promoting its therapeutic potential.…”

A stromal cell-derived factor-1 releasing matrix enhances the progenitor cell response and blood vessel growth in ischaemic skeletal muscle

“…It is now believed that functional improvement results from neovascularisation and the restoration of blood fl ow to ischaemic muscle, and that this phenomenon is initiated, maintained, and enhanced by paracrine factors and secondary recruitment of progenitor cells (Cho et al, 2007;Formigli et al, 2007).…”