**2.3. Anti-fibrotic and proangiogenic effects**

**2.2. Cardiac differentiation**

*Reproduced from Cao Y et al., JCI, 2015.*

148 Stromal Cells - Structure, Function, and Therapeutic Implications

tion remains unclear.

Cardiomyogenic differentiation of MSCs is of key interest for cardiac regenerative medicine, particularly ischemic and non-ischemic cardiomyopathy [40, 67, 68]. Treating MSCs with 5-azacytidine produces spontaneous, synchronous beating cells in culture with ventricular myocyte-like potentials, suggesting that MSCs are able to transdifferentiate into cardiomyocytes [43]. Alternative and potentially safer factors that induce differentiation into a cardiomyocyte phenotype include conditioned media containing bone morphogenetic protein-2 (BMP-2) and FGF-4 [69] as well as insulin, dexamethasone, and ascorbic acid [70]. The combination of these factors induces overexpression of cardiomyocyte-specific proteins, leading to cardiomyogenic differentiation for possible use in disease processes of injured myocardium [69–72]. Indeed, expression of myotubules, α-actinin, SERCA2 and other cardiac-related proteins in transdifferentiated cells may serve to attenuate cardiac infarct size and enhance perfusion, and regional function as suggested by early *in vivo* studies [73, 74]. Co-culture of mouse or rat MSCs with rat neonatal ventricular myocytes also stimulates MSC transdifferentiation into cardiomyocytes [75, 76]. The necessity of cell-to-cell contact [1, 75] versus secreted factors within the cardiac microenvironment [76] as a requirement for cardiomyogenic differentia-

**Figure 4.** Regulation of adipogenesis-osteogenesis by MSCs. GSNOR deficiency with ensuing elevated levels of S-nitrosylated PPAR-γ leads to a decrease in PPAR- γ transcriptional activity and binding affinity to FABP4 promoter. This results in increased osteogenesis and decreased adipogenesis, which has strong implications in bone disease.

MSC therapy promotes cardiomyogenesis not only by direct cardiomyocyte differentiation, but also by stimulating endogenous c-kit+ cardiac progenitors (CPCs) to proliferate, undergo lineage commitment, and form transient amplifying cells [1, 28, 29, 77–79]. We demonstrated The hypothesis that exogenously delivered stem cells would promote organ regeneration through transdifferentiation into tissue-specific cells sparked interest in stem cell research and cell-based therapy and was originally supported by studies in the heart [82] where MSCs become cardiomyocyte-like cells and endothelial cells [40, 41, 43]. However, subsequent studies have revealed that the MSC-mediated regenerative process is more complex than was initially envisioned, and that several mechanisms underlie the ability of MSCs to reduce scar size and improve left ventricular structure and function after myocardial injury [33, 83, 84]. MSCs engraft and persist for several months in myocardium when delivered by transendocardial injection [1, 33, 40] and they reduce cardiac fibrosis and promote neovascularization and cardiomyogenesis [40, 77, 85, 86]. Importantly, cardiac magnetic resonance imaging (MRI) documented a reduction of infarct size, improvement in left ventricular shape (measured as sphericity index of the left ventricle), and improvement in tissue perfusion and regional contractility [87]. Together, these preclinical studies support the anti-fibrotic and proangiogenic role of MSCs in the repair of the injured myocardium.
