Chen Xiaoming, Liu Xinqin, Li Bin, Zhang Qian, Wang Jiye, Zhang Wenbin, Luo Wenjing, Chen Jingyuan
Department of Occupational and Environmental Health, the Ministry of Education Key Lab of Hazard Assessment and Control in Special Operational Environment, School of Public Health, Fourth Military Medical University, Xi'an, China.
Int J Biol Sci. 2017 Apr 10;13(4):518-531. doi: 10.7150/ijbs.17800. eCollection 2017.
Neuron apoptosis mediated by hypoxia inducible factor 1α (HIF-1α) 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-1α under cellular stress. However, its function under chronic hypobaric hypoxia remains unknown. In this study, we tried to identify the role of CIRBP in HIF-1α mediated neuron apoptosis under chronic hypobaric hypoxia and find a possible method to maintain its potential neuroprotective in long-term high altitude environmental exposure. 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-1α 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-1α shRNA and pEGFP-CIRBP plasmid transfected cells, we confirmed the role of HIF-1α in chronic hypoxia induced neuron apoptosis and identified the influence of CIRBP over-expression upon HIF-1α 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-1α mediated neuron apoptosis. HIF-1α expression as well as neuron apoptosis was significantly elevated by chronic hypobaric hypoxia both and . 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-1α knockdown significantly decreased neuron apoptosis under hypoxia, suggesting HIF-1α may be pro-apoptotic in the process of exposure. CIRBP over-expression significantly suppressed HIF-1α up-regulation in hypoxia and inhibited HIF-1α 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-1α and attenuated neuron apoptosis. Cold inducible RNA binding protein is involved in chronic hypoxia induced neuron apoptosis by down-regulating HIF-1α expression, and MiR-23a may be an important tool to maintain CIRBP level and function.
海马体中由缺氧诱导因子1α（HIF-1α）介导的神经元凋亡是导致慢性低压缺氧诱导认知障碍的最重要因素之一。作为一种在各种环境应激反应中上调的神经保护分子，据报道，CIRBP在细胞应激下与HIF-1α相互作用。然而，其在慢性低压缺氧下的功能仍不清楚。在本研究中，我们试图确定CIRBP在慢性低压缺氧下HIF-1α介导的神经元凋亡中的作用，并找到一种在长期高海拔环境暴露中维持其潜在神经保护作用的可能方法。我们建立了慢性低压缺氧大鼠模型以及将SH-SY5Y细胞暴露于1%低氧环境的组织培养模型。基于这些模型，我们测量了低氧暴露下HIF-1α和CIRBP的表达，并通过TUNEL免疫荧光染色和凋亡相关蛋白的蛋白质印迹分析检测神经元凋亡情况。此外，通过建立HIF-1α shRNA和pEGFP-CIRBP质粒转染细胞，我们证实了HIF-1α在慢性低氧诱导的神经元凋亡中的作用，并确定了CIRBP过表达在暴露过程中对HIF-1α和神经元凋亡的影响。此外，我们在两个模型中测量了报道的低氧相关miRNA的表达以及miRNA过表达/敲低在HIF-1α介导的神经元凋亡过程中对CIRBP的影响。慢性低压缺氧显著提高了HIF-1α的表达以及神经元凋亡水平。CIRBP在暴露早期（3天/7天）被诱导；然而，随着暴露时间延长（21天），低氧组的CIRBP水平显著低于对照组。此外，敲低HIF-1α显著降低了低氧条件下的神经元凋亡，表明HIF-1α在暴露过程中可能具有促凋亡作用。CIRBP过表达显著抑制了低氧条件下HIF-1α的上调，并抑制了HIF-1α介导的神经元凋亡。有趣的是，miR-23a也被低氧暴露诱导，并且表现出与CIRBP相同的变化趋势（3天/7天增加，21天减少）。此外，过表达miR-23a上调了CIRBP，下调了HIF-1α并减轻了神经元凋亡。冷诱导RNA结合蛋白通过下调HIF-1α表达参与慢性低氧诱导的神经元凋亡，并且miR-23a可能是维持CIRBP水平和功能的重要工具。
