Receptor Tyrosine Kinase Axl Is Involved In The Pathogenesis Of Intracranial Aneurysms By Regulating The Phenotype Transformation Of Vascular Smooth Muscle Cells

Background:Intracranial aneurysm(IA)is one of the major cerebrovascular diseases that seriously endanger human health.At present,the pathogenesis of IA is not clear,but a large number of studies have shown that phenotype transformation of vascular smooth muscle cells(VSMC)is an important part of IA mechanism.Receptor tyrosine kinase Axl plays an important role in regulating vascular smooth muscle survival and apoptosis,but its role in IA has not been reported.In our previous work,we found that soluble Axl(sAxl)increased specifically in cerebrospinal fluid and plasma of patients with IA rupture,suggesting that the rise of sAxl may be related to IA rupture.Therefore,the purpose of this study is to explore the regulatory mechanism of Axl on phenotype transformation of VSMC and its role in the pathogenesis of IA.Methods:First of all,we used Elisa to measure the serum levels of sAxl in 102 patients with IA rupture and 138 patients without IA rupture,and analyzed the risk factors combined with clinical data;at the same time,we detected the level of Axl expression in the vascular tissue and peripheral blood mononuclear cells(PBMC)of IA patients.Then,we established the IA mouse model by ligating renal artery and carotid artery and injecting elastase into basal cistern.Elisa was used to detect the level of sAxl in the plasma of mice in different stages and grades of IA model.The expression of Axl mRNA and protein in IA tissues were analyzed by QT-PCR and Western blot.Finally,we further studied the effect of Axl on the expression of VSMC induced by angiotensin ?(Ang II)and the related signaling pathway in the primary culture of VSMC.Results:We found that in patients with IA rupture,the content of sAxl was significantly higher than that in patients without IA rupture(p<0.001),and hypertension,age and location were independent risk factors for IA rupture.In PBMC,the expression of Axl protein increased significantly in patients with IA rupture.Compared with normal vascular tissue,the expression of Axl in IA tissue of unruptured patients increased.However,there was no significant difference between normal and ruptured IA tissues.In the process of mice IA induction,the content of sAxl in the peripheral blood of mice increased with time and IA grade,and increased significantly in the late stage and IA rupture(p<0.05),which was consistent with the results in human peripheral blood.The mRNA expression of Axl and VSMC phenotype transformation related genes in IA tissues of mice increased.Different concentrations of Ang ? stimulated primary VSMC,10-7 M of Ang ? could induce VSMC phenotype transformation,and the ability of proliferation and migration was significantly enhanced.At this time,the expression of Axl and downstream regulatory protein PI3K increased,the phosphorylation level of Akt increased.After addition of R428(Axl specific inhibitor),the protein level of PI3K and phosphorylation level of Akt were significantly reduced,the proliferation and migration ability of VSMC was inhibited,and the phenotypic transformation of VSMC was inhibited.Conclusion:There is a significant correlation between the increase of sAxl in PBMC and IA rupture.Under pathological conditions,the expression level of Axl increased,which promoted the phenotype transformation of VSMC by activating PI3K/Akt signaling pathway,thus Axl plays an important role in IA.Axl may be a potential drug target to inhibit the occurrence and progress of IA.