Cold Inducible RNA Binding Protein Is Involved in Chronic Hypoxia Induced Neuron Apoptosis by Down-Regulating HIF-1α Expression and Regulated By microRNA-23a

Background: Neuron apoptosis mediated by hypoxia inducible factor 1 alpha (HIF-1 alpha) in hippocampus is one of the most important factors accounting for the chronic hypobaric hypoxia induced cognitive impairment. As a neuroprotective molecule that is up-regulated in response to various environmental stress, CIRBP was reported to crosstalk with HIF-1 alpha under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. Objective: In this study, we tried to identify the role of CIRBP in HIF-1 alpha mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. Methods: We established a chronic hypobaric hypoxia rat model as well as a tissue culture model where SH-SY5Y cells were exposed to 1% hypoxia. Based on these models, we measured the expressions of HIF-1 alpha and CIRBP under hypoxia exposure and examined the apoptosis of neurons by TUNEL immunofluorescence staining and western blot analysis of apoptosis related proteins. In addition, by establishing HIF-1 alpha shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1 alpha in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1 alpha and neuron apoptosis in the process of exposure. Furthermore, we measured the expression of the reported hypoxia related miRNAs in both models and the influence of miRNAs' over-expression/ knock-down upon CIRBP in the process of HIF-1 alpha mediated neuron apoptosis. Results: HIF-1 alpha expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both in vivo and in vitro. CIRBP was induced in the early stage of exposure (3d/7d); however as the exposure was prolonged (21d), CIRBP level of the hypoxia group became significantly lower than that of control. In addition, HIF-1 alpha knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1 alpha may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1 alpha up-regulation in hypoxia and inhibited HIF-1 alpha mediated neuron apoptosis. Interestingly, miR-23a was also induced by hypoxia exposure and showed the same changing tendency with CIRBP (increasing in 3d/7d, decreasing in 21d). In addition, over-expressing miR-23a up-regulated CIRBP, down-regulated HIF-1 alpha and attenuated neuron apoptosis. Conclusion: Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1 alpha expression, and MiR-23a may be an important tool to maintain CIRBP level and function.