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

Abstract

Background: 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.Objective: 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.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-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.Results: HIF-1α 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-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.Conclusion: 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.

Recent progress in the research of cold-inducible RNA-binding protein

“…In addition, CIRP is also upregulated upon UV radiation, mild hypoxia and glucose deprivation, but is decreased in response to heat stress and inflammatory cytokines including TNF-α and TGF-β [ 9 ], suggesting that CIRP is a more general stress responsive protein ( Figure 2 ). Although, CIRP is upregulated upon mild hypoxia, chronic hypoxia has been reported to depress CIRP expression [ 10 ]. The influence of H 2 O 2 on CIRP expression is controversial with some studies showing downregulation and others showing no change [ 3 , 11 , 6 ].…”

Extracellular CIRP (eCIRP) and inflammation

“…The genes induced by iCIRP are thought to be a function of the intensity (mild, moderate, or severe) and timing (early or late exposure) of the stressors. In a recent study, for example, the neuronal expression of iCIRP was increased in rats subjected to chronic hypoxia, which in turn inhibited HIF‐α and, thus, protected neuronal cells from apoptosis . Besides, its role in regulation of mRNA stability and translation in the cytoplasm, nuclear iCIRP has also been shown to play a role in posttranscriptional regulation of its targets by controlling alternative polyadenylation that leads to generating alternative mRNA transcripts .…”

“…The transcription factor specificity protein 1 (sp1) is induced by hypoxia and has been found to bind to the CIRP's cold responsive element, suggesting that it may mediate hypoxia‐induced CIRP transcription . Recently, the overexpression of miRNA‐23a has also been shown to induce the expression of CIRP during prolonged hypoxia condition, possibly through its binding to CIRP's transcriptional enhancer . A recent study also revealed that hypothermia increases intracellular calcium levels via TRPV4, which regulates CIRP's expression in response to cold stress .…”

The Transcriptomic Responses of Atlantic Salmon (Salmo salar) to High Temperature Stress Alone, and in Combination with Moderate Hypoxia

“…The abiotic factors temperature and water oxygen level have a profound in uence on the allocation of energy to maintenance versus growth in sh [3,38,143]. A reduction in metabolic processes can conserve energy during stressful conditions as imposed by thermal challenges [14,17,20,22,32,99,144,145] or hypoxia [25,28,146,147]. In this study, salmon exposed to the WN and WH conditions showed a suppression of genes related to a broad variety of cellular metabolic processes in the liver that were highly interconnected.…”