Neuroprotective Role Of Melanocortin Receptor-1 On Early Brain Injury In A Rat Model Of Subarachnoid Hemorrhage

Backgrounds AND purpose:Subarachnoid hemorrhage(SAH),which accounts for about 5%of all the stroke,is one of the most common emergency in neurosurgery department.The patients with SAH suffer from high mortality and morbidity.The mortality for the first onset of SAH is around 30%,while 8-20%of the rest survivors suffer from permanent disability.In recent years,the early brain injury(EBI)was reported to be the main reason leading to the poor prognosis of SAH patients.The underlying mechanisms include neuroinflammation,neuronal apoptosis,oxidative stress,and blood-brain barrier(BBB)disruption.The melanocortin receptor-1(MC1R)belongs to class A(rhodopsin-like)family of G-protein coupled receptors(GPCRs).MC1R has been reported to be highly expressed and plays important roles in the central nervous system(CNS),including feeding,hormone excretion,sexual activity,and so on.Recently,MC1R has been demonstrated to suppress inflammation and reduce cellular apoptosis.BMS-470539 was reported to be a selective and potent agonist of MC1R.However,the roles of MC1R and BMS-470539 have not been reported in SAH.Therefore,this study aims to explore whether the activation of MC1R with BMS-470539 could reduce EBI after SAH.Materials and methods:Totally,403 rats were used in this study.SAH model was induced by endovascular perforation.Peroxisome proliferator-activated receptor-y coactivator 1 a(PGC-la)small interfering RNA(siRNA)or scramble siRNA was intracerebroventricularly injected 48 h before SAH.MSG-606,MRT-68601 and selisistat were given 1 h before the induction of SAH.BMS-470539 was intra-nasal administrated 1 h after SAH.We evaluated brain water content,short-term(24 h)and long-term neurobehavior(21d)after SAH.Western blotting and immunofluorescence staining were utilized to assess the changes of protein levels(MC1R,phosphorylated adenosine monophosphate-activated protein kinase(p-AMPK),TBK1,NF-?B,sirtuin(SIRT1),PGC-la,Uncoupling protein 2(UCP2)and so on).DHE staining was performed to test the level of oxidative stress.Besides,terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay(TUNEL assay)and Fluoro-Jade staining were conducted to test cell death.Results:1.The neurological deficits,brain edema and the level of MC1R were significantly increased and reached a maximum point at 24 h after SAH.2.MC1R was extensively expressed in the brain and was colocalized with microglia,neurons,and astrocytes;3.The use of BMS-470539 significantly improved the neurological functions and alleviated brain edema after SAH;BMS-470539 significantly strengthened learning and memory abilities leading to improved long-term neurobehavior scores after SAH;4.The activation of MC1R showed neuroprotective effects by controlling microglia-mediated neuroinflammation following SAH,and these effects were at least partly mediated by the AMPK/TBK1/NF-?B signaling pathway.5.The activation of MC1R showed neuroprotective effects by reducing oxidative stress,improving mitochondrial functions and reducing neuronal apoptosis following SAH,and these effects were at least partly mediated by the AMPK/SIRT1/PGC-1? signaling pathway.Conclusions:The activation of MC1R with BMS-470539 improved short-term and long-term neurological functions by suppressing the neuroinflammation,promoting M2 transformation,and reducing neuronal apoptosis after SAH.The BMS-470539 could be a promising therapeutic drug in treating stroke in the future.