Desmin deficiency affects the microenvironment of the cardiac side population and Sca1⁺ stem cell population of the adult heart and impairs their cardiomyogenic commitment

The heart's limited regenerative capacity raises the need for novel stem cell-based therapeutic approaches for cardiac regeneration. However, the use of stem cells is restrictive due to poor determination of their properties and the factors that regulate them. Here, we investigated the role of desmin, the major muscle-specific intermediate filament protein, in the characteristics and differentiation capacity of cardiac side population (CSP) and Sca1⁺ stem cells of adult mice. We found that desmin deficiency affects the microenvironment of the cells and leads to increased numbers of CSP but not Sca1⁺ cells; CSP subpopulation composition is altered, the expression of the senescence marker p16^INK4a in Sca1⁺ cells is increased, and early cardiomyogenic commitment is impaired. Specifically, we found that mRNA levels of the cardiac transcription factors Mef2c and Nkx2.5 were significantly reduced in des^-/- CSP and Sca1⁺ cells, while differentiation of CSP and Sca1⁺ cells demonstrated that in the absence of desmin, the levels of Nkx2.5, Mef2c, Tnnt2, Hey2, and Myh6 mRNA are differentially affected. Thus, desmin deficiency restricts the regenerative potential of CSP and Sca1⁺ cells, both directly and indirectly through their microenvironment.