Effect Of Chronic Intermittent Hypoxia On The Expression Of BACE1 In Rat Carotid Body And Adrenal Gland

BackgroundChronic Intermittent Hypoxia（CIH）is a pathological feature of obstructive sleep apnea（OSA）.CIH enhances the hypoxic ventilation response,sympathetic nerve activity and leads to hypertension,which results from the enhanced reflection of hypoxia from the carotid body and adrenal medulla.βsite amyloid precursor protein cleaving enzyme 1（BACE1）not only mediates the production ofβ-amyloid in Alzheimer’s Disease,but also participates in the regulation of peripheral synaptic plasticity.Electron microscopy showed that CIH induced reversible damage of carotid body synapses,but the mechanism was unclear.Based on it,we investigate the expression and localization of BACE1 in the carotid body and adrenal gland,and the effect of CIH on BACE1 level.ObjectiveTo elucidate the expression and localization of BACE1 in the carotid body and adrenal gland,and to investigate the effect of CIH on the expression level of BACE1.MethodsOxycycler A84 was used to establish the CIH rat model,and treated with reactive oxygen species（ROS）scavenger MnTMPyP,normal saline（NS）or reoxygenation（ReOx）.Following:for the control group,the rats were injected compressed air in the incubator for2 weeks.For the CIH group,rats were placed in an incubator（3 min of 10%O₂ followed by 1 min 21%O₂,8 h/d,2 weeks）.For the CIH plus MnTMPyP（CIH+MnTMPyP）group,MnTMPyP at a dose of 5 mg/kg/day was administered via intraperitoneal injection into the rats before daily exposed to CIH.For the CIH plus NS group,the CIH rats were administered with saline instead of MnTMPyP via intraperitoneal injection before daily exposed to CIH.For the CIH plus reoxygenation（CIH+ReOx）group,the rats were returned to room air for 2 weeks after an initial 2 weeks of CIH exposure.Firstly,RT-PCR,immunohistochemistry and immunofluorescence double labeled staining were used to detect the expression,distribution and cell localization of BACE1 in rat carotid body.Secondly,immunohistochemical staining was used to detect the expression level of BACE1 in the carotid body of the above 5 groups of rats,and the effect of CIH,MnTMPyP and reoxygenation on the level of BACE1 protein in the carotid body were observed.Finally,RT-PCR was used to detect the effect of CIH on BACE1 mRNA level in the carotid body.In addition,the expression,distribution and cell localization of BACE1 in rat adrenal gland were detected;the effect of CIH on the BACE1 protein level in the adrenal medulla was detected by western blot.Results1.BACE1 mRNA and protein were expressed in rat carotid body;glial fibrillary acidic protein（GFAP）positive carotid body type II cells and neurofilament（NF）positive nerve fibers showed immunofluorescence co-localized staining with BACE1,while tyrosine hydroxylase（TH）positive carotid body type I cells and aminopeptidase P（AP）positive vascular endothelium showed no BACE1 fluorescence staining;CIH reduced the expression of BACE1 in carotid body,and MnTMPyP or reoxygenation prevented the reduction of BACE1 level caused by CIH;CIH down-regulated the BACE1 mRNA level and up-regulated the PGC-1?mRNA level of carotid body.2.BACE1 mRNA and protein were expressed in rat adrenal gland;AP-positive vascular endothelium and NF-positive nerve fibers showed immunofluorescence co-localized staining with BACE1,while TH-positive chromaffin cells and NF-positive neurons showed no BACE1 fluorescence staining;CIH reduced the level of BACE1protein in the adrenal medulla.ConclusionsBACE1 is expressed in rat carotid body and adrenal gland,and CIH reduces the expression level of BACE1.