Effects of hypoxia and ASIC3 on nucleus pulposus cells: From cell behavior to molecular mechanism

This study aimed to explore the effects of hypoxia and acid-sensing ion channel 3 (ASIC3) on nucleus pulposus cells from cell behavior to molecular mechanism. Primary rabbit nucleus pulposus cells were isolated and identified by HE, toluidine blue and immunohistochemical staining of collagen II. 2% O₂ and 48 h were screened as optimal oxygen concentration and effect time, respectively, by determining cell apoptosis and mRNA expression of ASIC3, hypoxia inducible factor-1α (HIF-1α) and aquaporin 3. FLuo-3 AM labeling showed that the Ca²⁺ concentration in cells increased under hypoxia condition. shRNA-ASIC3 and ASIC3 expression vector were transfected into cells. Subsequently, cells were divided into six groups: Control, 2% O₂, shRNA-NC+2% O₂, shRNA-ASIC3 + 2% O₂, Vector+2% O₂ and ASIC3 + 2% O₂. Flow cytometry, CCK-8 assay, transmission electron microscopy, immunofluorescent labeling, RT-PCR and western blot demonstrated that hypoxia and ASIC3 over-expression inhibited the proliferation, arrested cell cycle in G1 phase, promoted the apoptosis, initiated the autophagy and up-regulated the expression of ASIC3, HIF-1α, light chain 3, p-ERK1/2 and p-MAPK. However, ASIC3 silencing could significantly relieve these phenomena. Co-immunoprecipitation assay found ASIC3 was interacted with HIF-1α&ERK1/2. Evaluation of the effect of HIF-1αsilencing on ASIC3 expression showed that the high expression of ASIC3 induced by hypoxia was reduced significantly by HIF-1α silencing. In conclusion, hypoxia and ASIC3 changed the behavior of nucleus pulposus cells by activating the MAPK pathway. HIF-1α and ASIC3 could regulate each other in nucleus pulposus cells.