Proteomics Reveals Rictor as a Non-Canonical TGFB Signaling Target During Aneurysm Progression in Marfan Mice
Objective. To (1) analyze the ascending aortic proteome within a mouse model of MFS (Fbn1C1041G/+) at early and late stages of aneurysm and subsequently to (2) test a novel hypothesis formulated based on this unbiased proteomic screen that links changes in integrin composition to TGFβ-dependent activation of the Rapamycin-Independent Component of TOR (Rictor) signaling pathway. Approach & Results. Ingenuity pathway analysis of over 1000 proteins quantified from in vivo MFS mouse aorta by data independent acquisition mass-spectrometry revealed a predicted upstream regulator, Rictor, that was selectively activated in aged MFS mice. We validated this pattern of Rictor activation in vivo by western blot for phosphorylation on Threonine-1135 in a separate cohort of mice, and showed in vitro that TGFβ-activates Rictor in an integrin linked kinase (ILK) dependent manner in cultured aortic VSMCs. Expression of Integrin Beta-3 (ITβ3) was upregulated in the aged MFS aorta relative to young MFS mice and WT mice. We showed that ITβ3 expression and activation modulated TGFβ-induced Rictor phosphorylation in vitro, and this signaling effect was associated with an altered VSMC proliferative / migratory, and metabolic in vitro phenotype which parallels the in vivo aneurysm phenotype in MFS. Conclusions. These results reveal that Rictor is a novel, context-dependent, non-canonical TGFβ-signaling effector with potential pathogenic implications in aortic aneurysm.