Adenoviral SERCA1 overexpression triggers an apoptotic response in cultured neonatal but not in adult rat cardiomyocytes.

Although adenoviral SERCA gene transfer improves cardiac function in the failing heart, there is controversy regarding the cytotoxic effect of such overexpression. We sought to examine the effect of SERCA1 overexpression on neonatal (NRCMs) and adult rat cardiomyocytes (ARCMs). Cultured NRCMs and ARCMs were infected with adenoviral vector expressing EGFP (Ad.EGFP) or SERCA1 (Ad.SERCA1). Gel electrophoresis and microarray analysis were performed to examine DNA fragmentation and apoptosis-related genes, respectively. Northern and western blot were used to examine the expression level of SERCA. The optimal viral titer for Ad.EGFP was found to be 2-5 pfu/cell in NRCMs and 100 pfu/cell in ARCMs. Infection of NRCMs with 4 pfu/cell of Ad.SERCA1 resulted in loss of cells and DNA fragmentation, while no apoptosis was detected in Ad.EGFP-infected cells. Gene array analysis also revealed that Ad.SERCA1 induced expression of apoptosis-related genes in NRCMs. However, neither loss of cell viability nor DNA fragmentation and induction of apoptosis-related genes was observed in ARCMs infected with 100 pfu/cell of Ad.SERCA1. Following the optimal infection, the SERCA1 expression level in NRCMs was 4-fold higher than that in ARCMs. Interestingly, the endogenous SERCA2 protein in NRCMs was completely replaced by exogenous SERCA1 protein. Furthermore, the activity of Ca2+ ATPase was increased by 4-fold in NRCMs but only by 1.5-fold in ARCMs. Our results indicate that adenoviral SERCA1 gene transfer has appreciably different effects on NRCMs and ARCMs. SERCA1 overexpression triggers an apoptotic response in NRCMs but not in ARCMs.