Mitochondrial Apoptotic Pathway Is Activated by H(2)O(2)-Mediated Oxidative Stress in BmN-SWU1 Cells from Bombyx mori Ovary

Apoptosis is a known regulator of morphogenetic events. In mammals, the critical role of oxidative stress-induced apoptosis has been well-studied; however, in insects the role of oxidative stress in apoptosis is not clear. In a previous study, we showed that apoptosis-related genes are present in the silkworm Bombyx mori, an important lepidopteran insect model. In this study, we evaluated the effect of H(2)O(2)-induced oxidative stress on apoptosis, reactive oxygen species (ROS) levels, mitochondrial response, cytochrome c release and apoptosis-related gene expression in the BmN-SWU1 cell line from B. mori ovaries. Our results showed that BmN-SWU1 cells exposed to H(2)O(2) showed cell protuberances, cytoplasmic condensation, apoptotic bodies, DNA ladder formation and caspase activities indicating apoptosis. H(2)O(2)-induced apoptosis also increased intracellular ROS level, changed mitochondrial distribution, reduced mitochondrial membrane potential and increased the release of cytochrome c from mitochondria. Furthermore, western blot analysis revealed a significant increase in p53 and cytochrome c expression, and a decrease in Bcl-2 expression compared to the controls. Moreover, quantitative real-time PCR (qRT-PCR) showed an increase in the transcript levels of BmICE, Bmapaf-1 and BmEndoG by 439.5%, 423.9% and 42.2%, respectively, after treatment with 1 μM H(2)O(2) for 24 h. However, the transcript levels of Bmbuffy declined by 41.4% after 24 h of exposure to 1 μM H(2)O(2). These results show that H(2)O(2) treatment induced apoptosis in BmN-SWU1 cells via the mitochondrial apoptotic pathway. Further, it appears that oxidative stress induced by H(2)O(2) activates both caspase-dependent and caspase-independent mitochondrial apoptotic pathways in silkworm cells. Taken together, these findings improve our knowledge of apoptosis in silkworm and the apoptotic pathways in insects.