Cardiac development is characterized by the active proliferation of different cardiac cell types, in particular cardiomyocytes and endothelial cells, that eventually build the beating heart. In mammals, these cells lose their regenerative potential early after birth, representing a major obstacle to our current capacity to restore the myocardial structure and function after an injury. Increasing evidence indicates that the cardiac extracellular matrix (ECM) actively regulates and orchestrates the proliferation, differentiation, and migration of cardiac cells within the heart, and that any change in either the composition of the ECM or its mechanical properties ultimately affect the behavior of these cells throughout one’s life. Thus, understanding the role of ECMs’ proteins and related signaling pathways on cardiac cell proliferation is essential to develop effective strategies fostering the regeneration of a damaged heart. This review provides an overview of the components of the ECM and its mechanical properties, whose function in cardiac regeneration has been elucidated, with a major focus on the strengths and weaknesses of the experimental models so far exploited to demonstrate the actual pro-regenerative capacity of the components of the ECM and to translate this knowledge into new therapies.

Shear stress induces atrial Ca²⁺ waves via connexin43 (Cx43)-mediated ATP release. Here, we examined whether ventricular myocytes release ATP under shear stress, and the underlying and regulatory mechanisms. A bioluminescence assay and the ‘sniffer patch’ were used to measure ATP release from multiple and single murine ventricular myocytes, respectively, in combination with laminar flow or micro-puffing. Shear stress (∼16 dyn/cm²) induced transient ATP release from myocyte batches, peaking at ~7 mol/cm²-membrane within 2 s. This response was abolished by the application of La³⁺ but was not affected by Gap19 treatment or zero external Ca²⁺. In addition, shear-induced ATP release was not different between control and cardiac-specific Cx43-conditional knockout (Cx43-cKO) ventricular cells, suggesting no role for Cx43. Shear-induced ATP release was suppressed by probenecid, low concentrations of carbenoxolone, or the pannexin (Panx) 1 inhibitory peptide ¹⁰Panx1 by 60−75%, suggesting a major role for Panx. Pharmacological screening further revealed a partial (30−40%) role of 9‐anthracenecarboxylic acid-sensitive, tamoxifen-insensitive Cl^- channels in ATP release. The sniffer patch, using a P2X7 receptor-overexpressing HEK293 cell positioned at a local region of the ventricular cell, showed a rapid development of shear-induced currents, approximated to be ∼1−10 μM ATP. The Cx43-cKO did not affect these sniffer cell currents. This shear response was suppressed by mitochondrial uncoupling or inhibition of the electron transport chain by 70-80% but was rather enhanced by Mito-TEMPO. Our data suggest that shear stress induces ATP release from murine ventricle cells mainly via Panx and that mitochondrial oxidative phosphorylation may be required for this response.