Cardiac telocytes and fibroblasts in primary culture: different morphologies and immunophenotypes

Telocytes (TCs) are a peculiar type of interstitial cells with very long prolongations termed telopodes. TCs have previously been identified in different anatomic structures of the heart, and have also been isolated and cultured from heart tissues in vitro. TCs and fibroblasts, both located in the interstitial spaces of the heart, have different morphologies and functionality. However, other than microscopic observation, a reliable means to make differential diagnosis of cardiac TCs from fibroblasts remains unclear. In the present study, we isolated and cultured cardiac TCs and fibroblasts from heart tissues, and observed their different morphological features and immunophenotypes in primary culture. Morphologically, TCs had extremely long and thin telopodes with moniliform aspect, stretched away from cell bodies, while cell processes of fibroblasts were short, thick and cone shaped. Furthermore, cardiac TCs were positive for CD34/c-kit, CD34/vimentin, and CD34/PDGFR-β, while fibroblasts were only vimentin and PDGFR-β positive. In addition, TCs were also different from pericytes as TCs were CD34 positive and α-SMA weak positive while pericytes were CD34 negative but α-SMA positive. Besides that, we also showed cardiac TCs were homogenously positive for mesenchymal marker CD29 but negative for hematopoietic marker CD45, indicating that TCs could be a source of cardiac mesenchymal cells. The differences in morphological features and immunophenotypes between TCs and fibroblasts will provide more compelling evidence to differentiate cardiac TCs from fibroblasts.