Role Of Hippo-YAP Pathway In Abdominal Aortic Aneurysm

Aortic aneurysm,a common cardiovascular disease,is a leading cause of mortality due to the rupture induced by the expansion of vascular wall.It contains thoracic aortic aneurysms?TAA?and abdominal aortic aneurysms?AAA?etc.The infrarenal abdominal and ascending aortic regions are highly susceptible in aneurysm.Gender,aging,smooking and inheritance are the crucial risk factors.The pathogenesis of AAA includes chronic inflammatory cells infiltration,vascular smooth muscle cell?VSMC?phenotype switch,migration and proliferation,following the extracellular matrix degradation,and the imbalance of VSMC homeostasis.At last the AAA expansion and ultimately rupture may occurs.Therefore,VSMCs play an important role in AAA formation.Hippo pathway controls organ size by regulating cell survival,proliferation and apoptosis.The mammalian core components of Hippo pathway includes Mst1/2,Lats1/2,signaling downstream effector YAP and TAZ.Many studies have revealed that Hippo-YAP pathway contributes to VSMC phenotype switch and cardiovascular diseases?CVDs?.However,its underlying mechanism in AAA are still unclear.Therefore,the purpose of this study is to determine whether VSMC YAP play a role in the development of AAA.In the current study,we assessed YAP expression in human VSMCs.As compared with nonaneurysmal vessels,human vessels from AAA patients showed decreased protein level of YAP.To investigate the role of VSMC YAP in the development of AAA,we performed SMC-YAP^tgApoE^-/-transgenic mice,which were subsequently treated with AngII infusion and CaCl₂ to induce AAA.Results showed that SMC-YAP^tgApoE^-/-mice alleviated AAA formation,as well as reduced aortic diameter and elastin degradation in both AAA models.RNA-sequencing analysis showed YAP/TAZ activation could promote TGF-?signaling activation in SMC-YAP^tgApoE^-/-mice,and indicated that YAP may participate in TGF-?signaling regulation.In vitro,YAP overexpression in VSMCs upregulated the expression of a panel of genes,which involved in TGF-?/Smad and activin signaling and induced Smad2phosphorylation to prolong its retention time in VSMCs.Proteomic and co-immunoprecipitation results showed that PPM1B,a protein phosphatase,directly interacted with YAP both in the cytoplasm and in nucleus.More importantly,PPM1B protein level was decreased by YAP overexpression in a dose-dependently manner.Further more PPM1B downregulated the phosphorylation of Smad2 and then inhibited TGF-?pathway.Hence,YAP maintained the activation of Smad2 and TGF-?signaling pathway through restraining PPM1B level.The apoptosis of VSMC plays a prominent role in AAA.In this study,we found SMC-YAP^tg mice had fewer apoptotic VSMCs compared with YAP^flox mice in both AAA models.In vitro,after using hydrogen peroxide to induce VSMCs apoptosis,we found YAP overexpression reduced cleaved-Caspase3 protein level,while YAP knockdown obtained corresponding results.In conclusion,YAP maintained Smad2 phosphorylation via degrading PPM1B,which increased the stability of ECM by TGF-?pathway activation.At the same time,we also found YAP inhibited VSMC apoptosis.This work provides fresh insights into the protective role of YAP in AAA and suggests a potential therapeutic strategy for AAA.