The Effect Of Dexmedetomidine Preconditioning On The Expression Of GRP78 And CHOP After Cerebral Ischemia-Reperfusion In Rats

Background and ObjectiveStroke is one of the most common diseases in the world,usually referred to ischemic stroke which has high mortality and disability.It is the second leading causes of death in humans,only next to ischemic heart disease.Reperfusion therapy is the basic treatment of ischemic stroke.However,after a certain period of ischemia and hypoxia,the reperfusion will aggravate its original structural and functional damage,and even causes more serious complications.It is called cerebral ischemia-reperfusion injury?CIRI?.The mechanism of CIRI is complex and involves multiple mechanisms.Currently,the mechanism of CIRI includes the following theories:excitatory amino acid?EEA?toxicity;mitochondrial dysfunction,ATP depletion,acidosis theory;intracellular calcium overload,oxygen free radical damage theory;brain edema,vascular permeability changes and blood-brain barrier destruction inflammatory response theory;and the theory of apoptosis.After a certain period of ischemia and hypoxia in the brain tissue,infarcts will appear in the center of ischemia,and a penumbra will appear in the periphery.If the ischemia can not be corrected,the infarct area will be further enlarged,and the penumbra slowly develops into an infarct.The cell death in the area of penumbra is thought to be related to apoptosis.It is currently believed that the apoptotic pathway can be classified into the following three types,intrinsic pathway?mitochondrial pathway?,extrinsic pathway?death receptor pathway?,endoplasmic reticulum stress pathway,endoplasmic reticulum stress apoptosis pathway is currently the spot in research.Currently,the basic treatment for ischemic stroke is reperfusion therapy,ischemia-reperfusion injury is closely related to the mortality,disability and prognosis of stroke,so how to reduce ischemia-reperfusion injury becomes an urgent problem in the treating ischemic stroke.And the endoplasmic reticulum stress is an important part of ischemia-reperfusion injury.Allergic hypoxia,calcium overload,oxidative stress and other factors can induce endoplasmic reticulum stress?ERS?,causing unfolded or misfolded proteins to accumulate in the endoplasmic reticulum,triggering unfolded protein response?UPR?.Under the circumstances,the endoplasmic reticulum chaperone GRP78 dissociates from the transmembrane proteins PERK,ATF-6 and IRE-1,and activates the pathway to correct the disorder of the endoplasmic reticulum.The cells simultaneously up-regulates the expression of GRP78 protein which can relieve the ER stress by binding with unfolded/misfolded proteins.GRP78 also binds with cysteinyl aspartate specific proteinase?Caspase?,such as Caspsase-7,and Caspase-12,on the ER membrane,and regulates cell survival and apoptosis through these interactions.Therefore,the rapid upregulation of GRP78 is considered to be the most sensitive marker of endoplasmic reticulum stress.If ER-stress is too strong or lasts too long,UPR can not restore the endoplasmic reticulum homeostasis by itself,it will up-regulate the expression of Bcl-2 family pro-apoptotic proteins Bid,Bim,Noxa,Puma through the apoptosis regulator CHOP,and downregulates the expression of apoptotic factors Bcl-2 and Bcl-xL,leading to apoptosis through the mitochondrial pathway.CHOP and Caspase-3 are important apoptosis regulating and executing proteins.The expression of these proteins can reflect the stress state of the endoplasmic reticulum and apoptosis.Dexmedetomidine?Dex?is a highly selective?₂ receptor agonist with dose-dependent sedative,anxiolytic,antisympathetic,spinal cord analgesia,etc.,for its sedative effect is similar to physiologically sleep,it is easy to awake,and it barely causes respiratory depression.For these It is widely used for short-term sedation?less than 24 h?in critically ill patients and mechanically ventilated patients in ICU,and as an adjuvant for clinical anesthesia.With the wide application of clinical,Dex has been found to have other pharmacological effects.Many studies have shown that Dex can reduce the production of inflammatory factors,reduce the metabolic rate in brain,increase the perioperative urine volume and reduce perioperative shivering.Some animal ischemic models suggest that Dex can reduce lung and renal ischemia-reperfusion injury.It is speculated that Dex may have the effect of regulating endoplasmic reticulum stress and inhibiting apoptosis.In this study,the model of cereb0ral ischemia-reperfusion was established by occlusion of the middle cerebral artery?MCA?in rats.The Dex was given before ischemia and reperfusion in rats.After reperfusion for 24 hours,The rats were tested for neurological deficit score,brain infarct size,cerebral cortical endoplasmic reticulum stress and apoptosis related proteins GRP78,CHOP and Caspase3.To investigate the effect of Dex on cerebral ischemia-reperfusion injury and related apoptosis,and to clarify its related mechanisms.Material and MethodThirty adult male SD rats weighing 220-240 g were randomly divided into sham operation group?Sham group??S group,n=10?;cerebral ischemia-reperfusion group 24h?I/R group,n=10?In the dexmedetomidine group?Dex group,n=10?,the Middle Cerebral Artery Occlusion?MCAO?was established in both the I/R group and the Dex group.After ischemia for 2 hours,reperfusion was performed for 24 hours.The Sham group was the same as the Sham and I/R groups except for the line plug;the Dex group was given 50 ug/kg Dex intraperitoneal injection 30 min before reperfusion,and the I/R group was given the same amount of physiology.brine.After 24 hours of ischemia-reperfusion,a group of rats were subjected to Neurological Deficit Score?NDS?.2.The brain tissue of each group was stained with Triphenyl-tetrazolium chloride?TCC?.The digital infarct volume ratio?infarct size/total size?×100%was calculated by Image Pro Plus6.0 software after taking pictures from a digital camera.3.Western Blot was used to measure the cerebral cortex of ischemia-reperfusion side of each group.Expression of endoplasmic reticulum stress-related proteins GRP78,CHOP and Caspase3.Results1.After 24 hours of ischemia-reperfusion,neurological deficits were assessed in each group of rats.There was no neurological deficit behavior in the Sham group?NDS=0?;the rats in the I/R group and the Dex group showed different degrees of neurological behavior?the contralateral forelimb could not be straightened,and the left side when walking?,behavioral changes such as rotation or tilt).Compared with the Sham group,the NDS scores of the I/R group and the Dex group were significantly higher than those of the Sham group?P<0.01?.Compared with the I/R group,the neurological deficit scores of the Dex group were lower than those of the I/R group.?P<0.01?.2.Infarcts were not seen in the Sham group.TTC was reduced by normal tissue mitochondrial catalase,which induced dark red products and stained normal tissues.Infarcts of different degrees were observed in both I/R and Dex groups.White color was stained by TTC.Compared with I/R group,the infarct volume ratio of Dex group was significantly lower than that of I/R group?P<0.05?.3.GRP78,CHOP and Caspase-3 proteins were expressed in the cerebral cortex of each group.Compared with Sham group,the expression of GRP78 protein in I/R group and Dex group was increased?P<0.05?,and the expression of CHOP and Caspase-3protein was increased?P<0.01?.Compared with I/R group,Dex group The expression of GRP78 protein was higher than that in I/R group?P<0.05?.The expression of CHOP and Caspase-3 in Dex group was lower than that in I/R group?P<0.05?.Conclusion1.Intraperitoneal injection of Dex 50ug/kg 30 min before 24 h of cerebral ischemia-reperfusion can reduce the volume of infarction and the score of neurological deficit,suggesting that Dex preconditioning has protective effect on ischemia-reperfusion brain injury..2.Dex can reduce cerebral ischemia-reperfusion injury by up-regulating the expression of GRP78,and inhibiting the overexpression of CHOP and Caspase-3,attenuates the cerebral ischemia-reperfusion.