Subsets of telocytes: the progenitor cells in the human endocardial niche.

Abstract

We used cardiac samples from 10 human adult donor cadavers. Endocardial endothelial cells expressed CD146, alpha-smooth muscle actin (α-SMA), smooth muscle myosin (SMM), nestin and, scarcely, neurofilaments. Within atrial and ventricular samples, we found an endocardial discontinuous smooth muscle layer expressing, similar to pericytes and vascular smooth muscle cells, α-SMA, nestin, SMM, and CD146. We assessed a similar phenotype in the subendocardial muscle layer, which also expressed neuron-specific enolase. The expression of nestin and CD146 strongly indicates a progenitor phenotype, which, in turn, supports the hypothesis that, in humans, an endocardial stem niche supplied by an endothelial-mesenchymal transition should be considered, although it mimics a primitive supply from the cardiac neural crest with dormant cardiac side population progenitor cells. Nevertheless, the endocardial niche could indeed harbor precursor cells that are morphologically similar to TCs.