Hypoxia-Inducible Factor 1-alpha (HIF-1 alpha) Induces Apoptosis of Human Uterosacral Ligament Fibroblasts Through the Death Receptor and Mitochondrial Pathways

Background: Hypoxia induces cell apoptosis in the uterosacral ligaments of patients with pelvic organ prolapse by upregulation of hypoxia-inducible factor-1 alpha (HIF-1 alpha). This study aimed to investigate the effects of HIF-1 alpha on human uterosacral ligament fibroblasts (hUSLFs) following treatment with the chemical inducer of hypoxia, cobalt chloride (CoCl2), and to explore the underlying mechanisms. Material/Methods: Ten women who underwent hysterectomy for benign disease provided uterosacral ligament tissue for cell extraction. Following CoCl2 treatment, cell viability of isolated and cultured hUSLFs was evaluated by the MTT assay. JC-1 fluorescence mitochondria) imaging was used to study the change in mitochondria) membrane potential. Cell apoptosis and expression of apoptosis-associated proteins and collagen type I alpha 1 (COL1A1) were measured by flow cytometry, TUNEL and Western blot, respectively. Results: Hypoxia increased the expression of HIF-1 alpha and increased cell apoptosis, decreased cell viability and expres- sion levels of COL1A1. The JC-1 assay showed that the mitochondria) membrane potential was reduced and caspase-8, and -9 inhibitors partly reduced hUSLF apoptosis. HIF-1 alpha treatment downregulated the expression of cellular FLICE inhibitory protein (c-FLIP), decoy receptor 2 (DcR2), and the ratio of Bcl-2 to Bax, and upregulated the expression tumor necrosis factor related apoptosis-inducing ligand (TRAIL), death receptor 5 (DR5) or TRAIL-R2, Fas, Bcl-2 interacting protein 3 (BNIP3), and cytochrome C, and increased the activation of caspase-3, caspase-8, and caspase-9, all of which were reversed by knockdown of HIF-1 alpha. Conclusions: HIF-1 alpha significantly induced apoptosis of hUSLFs through both the cell death receptor and the mitochondrial-associated apoptosis pathways.