Nuclear respiratory factor 1 protects H9C2 cells against hypoxia-induced apoptosis via the death receptor pathway and mitochondrial pathway

Hypoxia-induced cardiomyocyte apoptosis is one of the leading causes of heart failure. Nuclear respiratory factor 1 (NRF-1) was suggested as a protector against cell apoptosis; However, the mechanism is not clear. Therefore, the aim of this study was to elucidate the role of NRF-1 in hypoxia-induced H9C2 cardiomyocyte apoptosis and to explore its effect on regulating the death receptor pathway and mitochondrial pathway. NRF-1 was overexpressed or knocked down in H9C2 cells, which were then exposed to a hypoxia condition for 0, 3, 6, 12, and 24 h. Changes in cell proliferation, cell viability, reactive oxygen species (ROS) generation, and mitochondrial membrane potential (MMP) were investigated. The activities of caspase-3, -8, and -9, apoptosis rate, and the gene and protein expression levels of the death receptor pathway and mitochondrial pathway were analyzed. Under hypoxia exposure, NRF-1 overexpression improved the proliferation and viability of H9C2 cells and decreased ROS generation, MMP loss, caspase activities, and the apoptosis rate. However, the NRF-1 knockdown group showed the opposite results. Additionally, NRF-1 upregulated the expression of antiapoptotic molecules involved in the death receptor and mitochondrial pathways, such as CASP8 and FADD-like apoptosis regulator, B-cell lymphoma 2, B-cell lymphoma-extra-large, and cytochrome C. Conversely, the expression of proapoptotic molecules, such as caspase-8, BH3-interacting domain death agonist, Bcl-2-associated X protein, caspase-9, and caspase-3 was downregulated by NRF-1 overexpression in hypoxia-induced H9C2 cells. These results suggest that NRF-1 functions as an antiapoptotic factor in the death receptor and mitochondrial pathways to mitigate hypoxia-induced apoptosis in H9C2 cardiomyocytes.