Abstract 19838: The Atypical Cadherin Fat1 Suppresses Vascular Smooth Muscle Mesenchymal Markers and Limits Atherosclerosis

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Introduction: Fat1 controls vascular smooth muscle cell (SMC) growth and migration. In recent studies, we found increased Fat1 expression in atherosclerotic lesions from apoE -/- (KO) mice, and identified vimentin, an intermediate filament protein and mesenchymal marker, as a novel Fat1 interactor also expressed in SMCs. Hypothesis: Fat1 regulation of SMCs limits atherosclerosis, at least in part via Fat1 effects on vimentin. Methods: We generated fat1 SMC-KO ; apoE double knockout (DKO) mice, fed them a high fat diet for 24 weeks, and assessed atherosclerosis analyzing aortic roots and brachiocephalic arteries (BCA) for lesion area, immunohistochemical features, and gene expression. Results: DKO mice (N=10) exhibited larger lesions at the aortic root (80837.0±7942.4) and BCA (36017.2±10496.4) compared to KO controls (64190.2±6539.1 and 19462.9±5246.3, respectively, p<0.05). DKO lesions had larger fibrous caps (40.6±5.5%, N=7) and necrotic cores (30.3±3.2%, N=8) compared to KO samples (26.3±2.9 and 21.6±2.2%, respectively, p<0.05), plus a trend towards increased cellularity (+24%, N=7, p=0.0573). Macrophage number was not different, but SMC area (staining for SM22α) was larger in DKO lesions (1.15±0.25, vs. KO, 0.37±0.08, N=9, p<0.01). Proliferation (phospho-histone H3 staining) was also higher (DKO, 52.6±13.3 vs. KO, 31.4±10.1, N=7 p<0.05). Fat1 and vimentin expression colocalized within fibrous caps, and Fat1-deficient SMCs and lesions expressed more vimentin (>3-fold, p<0.05 by immunoblotting). By co-immunoprecipitation, Fat1 interacted with vimentin and limited its abundance in SMCs; knockdown studies suggested that increased proliferation of Fat1-deficient SMCs depends on vimentin. In addition, Fat1-deficient SMCs showed evidence of E- to N-cadherin switching and upregulation of the Snail1 transcription factor. Conclusions: Our in vivo data support a role for Fat1 in control of SMC proliferation during atherogenesis, and suggest that Fat1-vimentin interaction is important for this regulation. These findings are reminiscent of the epithelial-mesenchymal transition (EMT) program described in proper epithelial cells, suggest that components of this regulatory network are operative in SMCs, and are controlled by Fat1.