Environmental hypoxia induces apoptosis in large yellow croaker Larimichthys crocea via both intrinsic and extrinsic pathways

Hypoxia has become an unfavorable factor affecting the sustainable development of the large yellow croaker Larimichthys crocea, an economically important mariculture fish in China. Apoptosis is a consequence of hypoxia on fish. However, the effects of hypoxia stress on apoptosis in L. crocea remain largely unknown. We investigated the effect of environmental hypoxia on apoptosis in L. crocea. Results show that hypoxia induced apoptosis in L. crocea both in vivo and in vitro. The mitochondrial membrane potential was significantly reduced in large yellow croaker fry (LYCF) cells. The expression levels of B-cell lymphoma/leukemia-2 (Bcl-2) mRNA and protein were also significantly decreased in the liver and LYCF cells during 96 h and 48 h of hypoxia stress, respectively, whereas the expression level of Bcl-2 associated X (Bax) mRNA, Casp3 mRNA, and activity of caspase-3/7/9 were significantly increased, indicating that hypoxia induced caspase-dependent intrinsic apoptosis in L. crocea. The expression level of the apoptosis-inducing factor (AIF) protein was significantly increased in the liver and LYCF cells. The level of AIF protein was significantly decreased in the cytoplasm but increased in the nuclei of L. crocea, demonstrating that hypoxia induced the AIF-mediated caspase-independent intrinsic apoptosis. In addition, the activity of caspase-8 was significantly increased, indicating that hypoxia stress induced extrinsic apoptosis in L. crocea. Therefore, hypoxia induced apoptosis in L. crocea through both the intrinsic and extrinsic pathways. The present study accumulated basic biological information to help elucidate the mechanism of hypoxia response in marine fish.