Overexpression of human truncated peroxisome proliferator-activated receptor a induces apoptosis in HL-1 cardiomyocytes

Aims Our goal was to analyse whether truncated peroxisome proliferator-activated receptor a (PPARa) overexpression induces apoptosis of cardiomyocytes. Methods and resultsWe constructed a recombinant vector of human truncated PPARa and a mammalian expression vector to transfect PPARa into a line of murine cardiomyocytes designated HL-1. Four hallmarks of apoptosis were measured in these transfected cells: depolarization of mitochondrial membrane, activation of caspase-3, phosphatidylserine (PS) externalization, and DNA fragmentation. Co-transfection with human cyclic adenosine monophosphate response element-binding protein (CREB) and human CREB binding protein (CBP) and analysis of apoptosis regulatory proteins, Bcl-2 and Bax, were also performed in truncated PPARa-transfected cells to determine the potential mechanisms by which truncated PPARa may influence apoptosis. Progressive depolarization of mitochondrial membrane, activation of caspase-3, PS externalization, DNA fragmentation, and cell death were observed in HL-1 cells upon increasing levels of transfected truncated PPARa. The expression of the antiapoptotic protein Bcl-2 decreased in transfected HL-1 cardiomyocytes, whereas no changes in the proapoptotic protein Bax were observed in these cells. Overexpression of CREB plus CBP abolished the inhibitory effect of truncated PPARa on Bcl-2 protein. Conclusion These results demonstrate that human truncated PPARa overexpression induces apoptosis in HL-1 cardiomyocytes. In addition, our findings suggest that truncated PPARa may induce cardiomyocyte apoptosis through the inhibition of the antiapoptotic protein, Bcl-2. It is proposed that competition with CREB for coactivators like CBP could be involved in this inhibitory effect.