Involvement of TGF-β1 signaling in cardiomyocyte differentiation from P19CL6 cells

Stem cell-based therapy is being considered as an alternative treatment for cardiomyopathy. Hence understanding the basic molecular mechanisms of cardiomyocyte differentiation is important. Besides BMP or Wnt family proteins, TGF-β family members are thought to play a role in cardiac development and differentiation. Although TGF-β has been reported to induce cardiac differentiation in embryonic stem cells, the differential role of TGF-β isoforms has not been elucidated. In this study, employing the DMSO-induced cardiomyocyte differentiation system using P19CL6 mouse embryonic teratocarcinoma stem cells, we investigated the TGF-β-induced signaling pathway in cardiomyocyte differentiation. TGF-β1, but not the other two isoforms of TGF-β, was induced at the mRNA and protein level at an early stage of differentiation, and Smad2 phosphorylation increased in parallel with TGF-β1 induction. Inhibition of TGF-β1 activity with TGF-β1-specific neutralizing antibody reduced cell cycle arrest as well as expression of the CDK inhibitor p21^WAF1. The antibody also inhibited induction of the cardiac transcription factor Nkx2.5. Taken together, these results suggest that TGF-β1 is involved in cardiomyocyte differentiation by regulating cell cycle progression and cardiac gene expression in an autocrine or paracrine manner.