Abstract 555: The Atypical Cadherin Fat1 Interacts With the Intermediate Filament Vimentin in Vascular Smooth Muscle Cells and Limits Atherosclerosis

Abstract

Fat1 controls vascular smooth muscle cell (VSMC) growth and migration. In recent studies, we found that Fat1 expression colocalizes with VSMCs in atherosclerotic lesions from apoE -/- mice, and also identified the intermediate filament protein vimentin as a novel Fat1 interactor. Like Fat1, vimentin is expressed in VSMCs in atherosclerotic lesions and affects cell growth. We hypothesized that Fat1 regulation of VSMC activities limits atherosclerosis, and that the Fat1-vimentin interaction contributes to this regulation. To test this idea, we generated fat1 VSMC-KO ; apoE double knockout (DKO) mice and assessed atherosclerosis after 24 weeks on a high fat diet, analyzing aortic roots and brachiocephalic arteries (BCA) for lesion area and immunohistochemical features. DKO mice (N=10) exhibited larger lesions (p<0.05) at the aortic root (80837.0±7942.4μm 2 ) and BCA (36017.2±10496.4) compared to control (64190.2±6539.1 and 19462.9±5246.3, respectively). These lesions displayed significantly thicker fibrous caps (+54%, N=7, p<0.05) and larger necrotic cores (+40%, N=8) compared to control, with a trend towards increased cellularity in the DKO group (+24%, p=0.0573, N=7). To evaluate lesional macrophage and VSMC content, we stained for Mac-2 and SM22α, respectively. We found no difference in macrophage number, but greater SM22α-positive lesion area in DKO lesions (1.15±0.25μm 2 , vs. control, 0.37±0.08, p<0.01, N=9). Proliferation in plaques, assessed by phospho-histone H3 staining, was also higher (DKO, 52.6±13.3 cells/field vs. control, 31.4±10.1, p<0.05, N=7). Fat1 and vimentin expression colocalized within fibrous caps, and their physical interaction was validated by co-immunoprecipitation. In addition, Fat1-deficient VSMCs and lesions exhibited increased vimentin levels (>3-fold, p<0.05 by immunoblotting). Thus Fat1 interacts with vimentin and controls its abundance in VSMCs; preliminary knockdown studies suggest that the increased proliferation seen in Fat1-deficient VSMCs depends on vimentin. In summary, our in vivo data support a role for Fat1 in the regulation of VSMCs during atherogenesis, and suggest that the Fat1-vimentin interaction is important for this regulation.