CCN2 exerts direct cytoprotective actions in adult cardiac myocytes by activation of the PI3-kinase/Akt/GSK-3β signaling pathway

We recently reported that transgenic mice with cardiac-restricted overexpression of CCN2/CTGF have substantially increased tolerance towards ischemia/reperfusion injury. The purpose of this study was to investigate to what extent fully differentiated cardiac myocytes are direct targets of CCN2, and to resolve the signaling mechanisms that convey the cardioprotective actions of CCN2. Akt and GSK-3β were identified as putative intermediaries of intracellular signaling stimulated by recombinant human CCN2 (rhCCN2). Concentration-effect experiments revealed CCN2-stimulated phosphorylation of Akt (Ser473) and downstream GSK-3β (Ser9) with EC(50) ~250 nmol/L. CCN2-stimulated phosphorylation of Akt and GSK-3β was sensitive to inhibition of PI3-kinase (LY294002). Phosphorylation of GSK-3β was also sensitive to Akt-inhibition (API-2), demonstrating CCN2-engendered activation of a PI3-kinase/Akt/GSK-3β-signaling pathway. A C-terminal peptide fragment of CCN2 (11.2 kD) displayed partial agonist activity, while two short peptides derived from the Thrombospondin- and the IGFBP- homology domains of CCN2, respectively, additively inhibited rhCCN2-stimulated Akt-phosphorylation. The viability of cardiac myocytes subjected to hypoxia/reoxygenation injury or doxorubicin-induced oxidative stress was assessed by assays of adenylate kinase and lactate dehydrogenase released from dying cells. Cardiac myocytes exposed to CCN2 displayed increased tolerance towards hypoxia/reoxygenation and doxorubicin-induced oxidative stress, an effect that was abrogated by inhibition of PI3-kinase. The cytoprotective actions of CCN2 reflected in the transcriptome of CCN2-stimulated cardiac myocytes (anti-apoptosis, stress, and wound-response gene programs). In conclusion, this study discloses the novel findings that cardiac myocytes are CCN2 target cells in which CCN2 increases tolerance towards hypoxia and oxidative stress via PI3-kinase-dependent Akt/GSK-3β signaling.