Role Of Hippo-YAP In Endothelial Activation And Atherogenic Responses To Disturbed Flow

Atherosclerosis has become one of the major death causes worldwide,which attributes to its severe complications such as acute myocardial infarction and stroke.As the interface between circulating blood and the vessel wall,ECs are constantly exposed to mechanical forces generated by blood flow.Atherosclerosis preferentially develops at branches and curvatures in the arterial tree where flow is disturbed.In contrast,the flow in straight parts of the arteries generates laminar shear stress?LSS?which is atheroprotective.Vascular endothelial cell?EC?activation acts as an initial step of atherosclerosis,which is responsive to various chemical and mechanical stimuli,including TNF?,LPS,and shear stress.Recent studies have revealed Hippo/YAP play a crucial role in atherosclerosis.However,the regulation of YAP by OSS and the underlying mechanism is largely unknown.The Hippo pathway plays an evolutionarily conserved fundamental role in controlling organ size in organisms.Core components of the mammalian hippo pathway content kinases cascade of Mst1/2 and Lats1/2.The transcription co-activator Yes-associated protein?YAP?is a major downstream effector of the Hippo pathway.LSS increases phosphorylation of YAP at Ser127,leading its retention in cytoplasm.LSS promotes integrin–G?13 interaction,leading to RhoA inhibition and YAP phosphorylation and suppression.YAP inhibition suppresses JNK signalling and downregulates pro-inflammatory genes expression,thereby reducing monocyte attachment and infiltration.In vivo endothelial-specific YAP overexpression exacerbates plaque formation in ApoE^-/-mice.Our previous studies showed that both integrin?5 activation and Yes-associated protein?YAP?nuclear translocation are involved in the endothelial atheroprone phenotypes induced by oscillatory shear stress?OSS?.We report here that integrin?5 heterozygous deficiency blocked YAP nuclear translocation and that YAP overexpression in ECs blunted the anti-atheroprone effect of an integrin-?5 blocking peptide in ApoE^-/-mice.OSS led to integrin?5 activation and strong,continuous nuclear translocation of YAP in ECs,as well as increased phosphorylation of YAP at Y357and a decreasing trend of that at S127 and S397.Blocking integrin?5 inhibited the OSS-induced YAP tyrosine phosphorylation at Y357 and nuclear translocation,but had minimal effect on the serine phosphorylation of YAP at S127 and S397.Mechanistic studies showed that both Src and c-Abl inhibitors abolished the FN-induced YAP tyrosine phosphorylation,with the effect of c-Abl inhibitor?Imatinib and Nilotinib?being more profound.Furthermore,the phosphorylation of c-Abl and YAP^Y357 was significantly increased in ECs in atherosclerotic vessels of mice induced by partial ligation and Western diet and in human plaques vs.normal vessels.Bosutinib,a Src and c-Abl dual inhibitor,markedly reduced the level of YAP^Y357357 and the development of atherosclerosis in ApoE^-/-mice.In conclusion,the activation of integrin?5 contributes to OSS-induced EC activation and atherosclerosis via a c-Abl/YAP^Y357 pathway,providing a potential therapeutic strategy for atherogenesis.