Proteomics Reveals Context‐Dependent Activation of Rictor Signaling by TGFβ in Vascular Smooth Muscle Cells

Abstract

Aortic aneurysm describes abnormal growth and remodeling of the aorta and predisposes to fatal vascular dissection and rupture. Marfan syndrome (MFS) is a hereditary disorder caused by deficiency of extracellular fibrillin‐1, with multiple characteristic phenotypes including highly penetrant aneurysm. The discovery that deficiency of fibrillin‐1 lead to excessive activation of transforming growth factor β (TGFβ) signaling has led to major advances in the understanding of AA in MFS, though many details regarding the molecular mechanisms remain unclear. To describe molecular changes correlating with aneurysm development in a mouse model of MFS, proteomic analysis was performed on ascending aorta from young (10‐weeks; N=3 WT, N=3 MFS) and aged (12 months, N=3 WT, N=4 MFS) mice. We identified 425 proteins with altered abundance (e.g., Log2FC > |0.8| and < 1% FDR) in the MFS mice relative to WT, with 71 and 297 specific to young and aged mice, respectively, and 57 consistently altered at either age. Pathway analysis predicted TGFβ as a dominantly activated upstream regulator at both ages. Interestingly, in comparison to their WT counterparts, aged MFS mice showed markedly lower mitochondrial protein expression and a reversal in predicted activation status of the mTOR2 component rictor, with predicted inhibition in young MFS mice and strong activation in the aged MFS mice. Immunoblotting revealed increased phosphorylation of rictor and activation of its downstream signaling target Akt in aged MFS aorta. In cultured aortic vascular smooth muscle cells (VSMCs), TGFβ promoted both rictor and Akt phosphorylation, which could be blocked by inhibition of Integrin linked Kinase. Interrogation of integrin expression patterns implicated altered expression of integrin alpha v/beta 3 and its ligand vitronectin as uniquely upregulated in aged MFS aorta, leading to a hypothesis that the αv/β3 integrin may modulate TGFβ‐induced rictor signaling. Indeed, overexpression of ITβ3 enhanced while inhibition of ITβ3 blocked TGFβ‐induced rictor phosphorylation in cultured VSMCs. Altered physiology in ITβ3‐overexpressing VSMCs included increased migration/proliferation and altered TGFβ‐mediated effects on mitochondrial respiration. These results suggest that after additional in vivo validation, ITβ3 and/or mTOR2/Rictor signaling may represent novel targets for therapeutic intervention for aneurysm caused by MFS.Support or Funding Information1K99HL12878‐01A1 ‐ PI: Sarah ParkerThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.