Post-Subfunctionalization Functions of HIF-1αA and HIF-1αB in Cyprinid Fish: Fine-Tuning Mitophagy and Apoptosis Regulation Under Hypoxic Stress

Hypoxia-inducible factor 1 (HIF-1) is a crucial transcriptional factor that can restore oxygen balance in the body by regulating multiple vital activities. Two HIF-1 alpha copies were retained in cyprinid fish after experiencing a teleost-specific genome duplication. How the "divergent collaboration" of HIF-1 alpha A and HIF-1 alpha B proceeds in regulating mitophagy and apoptosis under hypoxic stress in cells of cyprinid fish remains unclear. In this study, zebrafish HIF-1 alpha A/B expression plasmids were constructed and transfected into the epithelioma papulosum cyprini cells and were subjected to hypoxic stress. HIF-1 alpha A induced apoptosis through promoting ROS generation and mitochondrial depolarization when cells were subjected to oxygen deficiency. Conversely, HIF-1 alpha B was primarily responsible for mitophagy induction, prompting ATP production to mitigate apoptosis. HIF-1 alpha A did not induce mitophagy in the mitochondria and lysosomes co-localization assay but it was involved in the regulation of different mitophagy pathways. Over-expression of HIF-1 alpha A increased the expression of bnip3, fundc1, Beclin1, and foxo3, suggesting it has a dual role in mitochondrial autophagy and cell death. Each duplicated copy also experienced functional divergence and target shifting in the regulation of complexes in the mitochondrial electron transport chain (ETC). Our findings shed light on the post-subfunctionalization function of HIF-1 alpha A and HIF-1 alpha B in zebrafish to fine-tune regulation of mitophagy and apoptosis following hypoxia exposure.