Extracellullar matrix derived from cardiac fibroblasts is the optimal substrate for expansion of cardiac stem cells ex vivo.

Cardiac Stem Cells (CSCc) contributing to cell turnover have been recently described in adult heart. The expression of extracellular matrix (ECM) proteins changes in qualitative and quantitative manner during heart remodeling. However, the influence of these changes on CSCs biology awaits investigation. The scope of the study was to evaluate the influence of fibronectin, laminin-1 and -2, collagen IV and of the natural ECM (cardiogel), obtained by culturing cardiac fibroblasts (CFs) isolated from normal (n=7) and pathological (n=8) hearts, on the biology of normal CSCs. Proliferation of CSCs, evaluated by BrdU incorporation, was 6,3-fold higher in the presence of laminin-1 and only 2-fold higher on laminin-2 with respect to control albumin. Apoptosis, detected in TUNEL assay, was as low as 1,8±0,4% on laminin-1 and was 2,8-fold, 5,4-fold and 8,5-fold higher on laminin-2, fibronectin and collagen IV, respectively. As revealed by immunofluorescence and immunoblotting, normal CFs synthesized mainly laminin-2, while pathological CFs produced more laminin-1, fibronectin, collagen IV and tenascin C. Interestingly, proliferation rate of CSCs on pathological cardiogel was 5,7-fold higher than that in the presence of normal cardiogel. In the similar manner, components of ECM from pathological heart diminished apoptosis rate with respect to cardiogel from normal heart. To assess the role of ECM on CSCs biology, we investigated the expression of and the signaling mediated by integrins. Noticeably, CSCs expressed mainly alpha-6 and alpha-2 integrin when cultured on pathological cardiogel and beta-3 integrin on normal cardiogel and, when interfering with integrin-mediated signals by specific function blocking antibodies, alpha-2 and beta-3 integrin resulted implicated in the stimulation of CSCs proliferation, while alpha-6 and alpha-2 in the protection of CSCs from apoptosis. We conclude that the components of ECM, responding to the physiological changes during heart remodeling, have profound effects on CSCs. These results should be taken into consideration when planning stem cells transplantation in the diseased hearts, since the microenvironment may determine the fate of the injected cells.