The Effect And Mechanism Of PPARγ-mediated Phenotypic Transformation Of Smooth Muscle Cells In Subarachnoid Hemorrhage

THE MECHANISM OF BEXAROTENE INHIBITING PHENOTYPIC TRANSFORMATION OF VASCULAR SMOOTH MUSCLE CELLS AFTER SUBARACHNOID HEMORRHAGE IN SD RATS BY PPARΓ-MEDIATED PATHWAYBackground: Vascular smooth muscle cells(VSMCs)play an important role after a subarachnoid haemorrhage(SAH).The changes of VSMCs is unknown using bexarotene after SAH.The present study investigated potential role of bexarotene in phenotypically modulating VSMCs as well as the drug’s protective mechanism after SAH.Methods: The SAH model was established using an intravascular puncture model in adult male Sprague-Dawley rats.A modified Garcia score was used to determine neurological function.SAH grading,mortality and brain water content were used to assess the severity of brain injury after SAH.Laser speckle was used to measure cerebral cortical blood flow.Markers of the VSMC phenotype(α-SMA and Smemb)were detected using Western blot(WB)and immunofluorescence.The 5-lipoxygenaseactivating protein(FLAP)and peroxisome proliferator-activated receptor γ(PPARγ)expression were measured using Western blot andimmunofluorescence.Leukotriene B4(LTB4)was examined using enzyme-linked immunosorbent assay(ELISA).Bexarotene was used by intraperitoneal injection,and adenoviral vectors expressing scramble(control)or short hairpin RNA(shRNA)were used to interfere with PPARγ.GW9662 was used to suppress PPARγ,and MK886 was used to suppress FLAP,respectively.Results: Neurological impairment,decreased cerebral cortical blood flow and cerebral VSMC transformation from a contractile to a synthetic phenotype were observed after SAH.FLAP and LTB4 levels were increased.Bexarotene reduced neurological impairment,improved cerebral cortical blood flow,inhibited VSMC phenotypic transformation and suppressed the expression of FLAP and LTB4,which was partly reversed by GW9662-the inhibitor of PPARγ.Mechanically,sh-PPARγ mediated phenotypic transformation of VSMC was partially suppressed by MK886-the antagonist of FLAP.Conclusions: Bexarotene reduced neurological impairment,improved cerebral cortical blood flow and inhibited the VSMCs phenotypic transformation after SAH,which was achieved by activating PPARγmediated inhibition of FLAP/LTB4 in VSMCsMECHANISM OF PIOGLITAZONE ON THE SMOOTH MUSCLE PHENOTYPE TRANSFORMATION AFTER SUBARACHNOID HEMORRHAGE BY ACTIVATING ENDOTHELIAL CELL PPARΓBackground: Vascular smooth muscle cells,as an important member of the neurovascular network,participate in the pathophysiological processes of multiple subarachnoid hemorrhage.The phenotypic transformation of cerebral arterial smooth muscle cells is directly or indirectly involved in neurovascular damage after subarachnoid hemorrhage.As an important member of the cerebral arteries,endothelial cells interact with smooth muscle cells after subarachnoid hemorrhage,affecting the phenotypic transformation of smooth muscle cells,and thus affecting the function of neurovascular.However,the effect of cerebral artery endothelial cells on the phenotypic transformation of endothelin-1and endothelin receptor A-regulated smooth muscle cells after subarachnoid hemorrhage is unclear.Therefore,this study focused on the effect of endothelial cell PPARγ-mediated endothelin 1/endothelin receptor A on smooth muscle cell phenotype transformation and its underlying mechanism.Methods: Adult male Sprague-Dawley rats were used to establish a subarachnoid hemorrhage model using an intravascular puncture model.Intraperitoneal injection of pioglitazone was performed using a modified Garcia score to assess neurological impairment in rats,and brain water content was used to assess brain edema after subarachnoid hemorrhage.Laser Doppler is used to measure blood flow to the cerebral cortex.Markers of vascular smooth muscle cell phenotypes(α-SMA and Smemb)were detected using Western blot(WB)and immunofluorescence.Endothelin 1(ET-1)expression was detected using an enzyme-linked immunosorbent assay(ELISA).In the cell test,hemoglobin was used to stimulate endothelial cells and pioglitazone was applied to endothelial cells.The supernatant secreted by endothelial cells was applied to smooth muscle cells,and the expression of ET-1 secreted by endothelial cells was detected by ELISA.The expression of smooth muscle cell phenotype transformation markers and MAPK ERK and transcription factor KLF4 were detected by WB.Results: Pioglitazone reduced neurological deficits after subarachnoid hemorrhage in SD rats,improved cerebral cortical blood flow,inhibited phenotypic transformation of vascular smooth muscle cells,and inhibited ET-1 expression.Endothelial cells stimulated by hemoglobin may promote phenotypic transformation of smooth muscle cells by secreting ET-1.Pioglitazone activates PPARγ,inhibits the secretion of ET-1 by endothelial cells,and improves the phenotype of smooth muscle cells induced by ET-1.Conclusion: Pioglitazone inhibits the secretion of ET-1 in endothelial cells,thereby inhibiting ET-1 mediated smooth muscle cell phenotype transformation,which is partly achieved by the ERK/KLF4 pathway of smooth muscle cells.