IL-6 is a pleiotropic cytokine expressed in a variety of cells mediating proliferation, growth, differentiation, survival and apoptosis signals. It can activate various cell types carrying the membrane bound IL-6R as well as IL-6R- gp130 + cells via the soluble IL-6R. IL-6 signaling involves the Jak/STAT-3, the Ras/Erk and PI-3K/Akt pathways. Increased circulating and intracardiac levels of IL-6 have been associated with chronic heart failure and myocardial infarction, and recent studies suggest that IL-6 signalling can be involved in the modulation of the compensatory hypertrophy by influencing remodelling processes and inducing Protein kinase C (PKC)-dependent apoptosis. Nevertheless, its role in cardiomyoblast differentiation remain unexplored.Purpose
To analyze the possible role of IL-6 in inducing terminal differentiation of embryonic cardiomyoblasts, as well as its downstream intracellular signalling pathways.Methods
H9C2 cells were cultured in medium supplemented with 1% FBS in presence of IL-6 (10 ng/ml) up to three days.Results
In presence of IL-6 embryonic cardiomyoblasts underwent morphological modifications characterized by cells elongation and fusion into multinucleated tubes. This process was accompanied by the nuclear translocation of Nkx2.5 (a myocardial development transcription factor), an upregulation and spatial reorganization of α-myosin heavy chain (α-MHC; terminal cardiac differentiation marker) and a modulation and sub-cellular redistribution of gp130. The IL-6 signal was mainly mediated by a prompt involvement of PI3K that determined downstream a PKCzeta activation and a PTEN dependent Akt de-phosphorylation. These data were confirmed by the transient transfection of H9C2 cells with a catalytically active form of PKCzeta that induced cell fusion, Nkx2.5 nuclear translocation and upregulation of α-MHC expression. The IL-6 differentiating effect was abolished when the PKCzeta activity was blocked with a specific pseudo-substrate. No early modification in Erk1 and Erk2 expression or phosphorylation levels were detected in response to IL-6 treatment.Conclusion
Our data evidence that IL-6 induces a terminal differentiation of embryonic cardiomyocytes through the activation of PI3K-PKCzeta pathway and that IL-6 may contribute to regenerative capacity of myocardium by inducing resident progenitor cells differentiation.