Regulation Of Hypoxia On The Gene Expression Patterns Of CRH, CRHR1, CRHR2 In Rat Brain And Pituitary

Background and ObjectiveCorticotropin releasing factor (CRF or CRH) is a critical integrator of the hypothalamic-pituitary-adrenal (HPA) axis in response to stress. The neuroendocrine aspect of the mammalian stress response is initiated by the release of CRH from hypothalamic neurons into the pituitary portal system. In the anterior pituitary, CRH receptor activation stimulates adrenocorticotrophic hormone (ACTH) release from corticotropes, followed by adrenal secretion of glucocorticoids, and the subsequent physiological changes associated with the classic stress response. CRH exerts its action through two major receptors, corticotropin-releasing factor receptor 1(CRHR1) and corticotropin-releasing factor receptor 2 (CRHR2). Our laboratory previous work showed the increase of HPA axis activity in hypobaric hypoxia that simulates the high altitude situation, and clarified CRHR1 played key roles in regulating progress in hypoxia stress. In our laboratory, we investigated stress and adaptation to high altitude hypoxia and its mechanism from systematic, cell and subcellular level by simulating altitude hypoxia in low pressure chamber. To study the stability of brain-endocrine-immune network and the role of regulating physiological function by the hypoxic activation of HPA axis. This study reports the different regulation of hypoxia on the gene expression patterns of CRH, CRFR1, CRFR2 in rat brain and pituitary.Research design and MethodsIn this research, rats were exposed to 2km (16.0% O2,79.97 kPa),5 km(10.8% O2,54.02 kPa) and 7km (7.8% O2,41.83 kPa) hypoxia for 8h. Using real-time RT-PCR, this study reports the expression of CRH, CRHR1 and CRHR2 genes in different cerebral nuclei and pituitary, and the expression of hypoxia-inducible factor 1 alpha (HIF-la)gene in rat brain and pituitary. We also predicted AP-1,P53,GR,NF-κB and HIF-1a binding sites in promoter of CRHR1 and CRHR2, then analyze the regulation patterns of HIF-1 on CRHR1 gene.Results1. During hypobaric hypoxia 2km,5km and 7km, the level of CRH mRNA in cortex, hippocampus and PVN significantly increased, and the level of CRH mRNA in CeA only increased in 5km and 7km. The increase of CRH mRNA expression in brain has shown an obviously positive linear correlation with the intensity of hypoxia.2. During hypobaric hypoxia 2km,5km and 7km, the level of CRHR1 mRNA in cortex, hippocampus, PVN, LC and pituitary significantly increased.and the level of CRHR1 mRNA in CeA only increased in 5km and 7km. The increase of CRHR1 mRNA expression in brain has shown a positive linear correlation with the intensity of hypoxia.3. CRHR2 mRNA in cortex and CeA remarkably reduced in 5km and 7km, and the level of CRHR2 mRNA in hippocampus did not change evidently. The expression of CRHR2 in PVN significantly increased in 2km,5km and 7km, and CRHR2 mRNA in LC remarkably increased in 2km and 5km. The expression of CRHR2 significantly reduced in 7km. The increase of CRHR2 mRNA expression in cortex, CeA has shown a negative linear correlation with the intensity of hypoxia while the increase of CRHR2 mRNA expression in PVN negative, and the increase of CRHR2 mRNA expression in hippocampus has shown no correlation with the intensity of hypoxia4. HIF-la mRNA expressionin cortex, hippocampus and pituitary remarkably increased in 5km and 7km hypoxia. The increase of HIF-1a mRNA expression in brain has shown a positive linear correlation with the intensity of hypoxia.ConclusionsThe regulation of hypoxia on the gene expression of of CRH and CRHR1 mRNA significantly increased in the intensity-dependent manner. The increase was related to the intensity of hypoxia. The expression of CRHR2 mRNA in PVN showed a positive correlation with the intensity of hypoxia while CRHR2 mRNA in CeA and cortex negative.One possible reason of the different expression patterns of CRHR1 and CRHR2 is the different transcription factor binding sites in their promoter and their opposite roles in activing HPA axis. The level of HIF-la mRNA in cortex, hippocampus and pituitary significantly increased, that suggests the role of HIF-1a in the transcriptional regulation of CRH, CRHR1 and CRHR2 genes.