Microvascular endothelial cells remodel cultured adult cardiomyocytes and increase their survival

We investigated the paracrine effect of cardiac microvascular endothelial c ells (MVEC) on cultured adult rat cardiomyocytes (ARC). ARC were exposed fo r 8 days to serum-free medium (CM)conditioned by MVEC. Controls were grown in FCS or FCS-free medium. Protein synthesis of CM-stimulated ARC increased twofold versus 5% FCS-stimulated cells until day 8. Seventy-nine percent o f CM-treated myocytes survived, whereas only twenty-four percent of FCS-fre e ARC retained viability. The phenotype of myocytes exposed to CM was diffe rent from control. Analysis by confocal laser microscopy of CM-stimulated m yocytes showed actin staining throughout the whole cell body up to the peri pheral extensions, with concomitant appearance of myomesin in a cross-stria ted pattern. The reexpression of fetal a-smooth muscle actin determined imm unohistochemically and by Western blot increased from day 6 in CM-treated c ells, whereas ARC grown in up to 20% serum were negative. These effects cou ld not be mimicked by any of the other cardioactive substances tested here, indicating a novel trophic factor in CM.