MSX2-WNT SIGNALING IN CARDIOVASCULAR CALCIFICATION

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DESCRIPTION (provided by applicant): Arteriosclerosis is the chronic disease state characterized by thickening and hardening of arterial walls with loss of elasticity. Atherosclerosis, Monckeberg's medial calcific sclerosis, and arteriolosclerosis are the three histopathologic types of arteriosclerosis. With advancing age, impaired glucose tolerance, diabetes, and hypertension, the conduit arteries become increasingly arteriosclerotic, losing compliance necessary for smooth distal tissue perfusion. This Windkessel physiology is impaired by changes in vascular geometry, and by changes in vascular matrix material properties arising from fibrosis, cross-linking and mineralization. Arteriosclerosis- viz., medial calcific sclerosis - has emerged as a particularly important contributor to lower extremity (LE) amputation risk in type II diabetes (T2DM). A better understanding of signaling pathways that control arterial fibrosis, calcification, and compliance will lead to new strategies for diminishing arteriosclerotic disease burden. Recent data identify Wnt/ 2 -catenin signaling and Wnt7 /LRP6 interactions as important in vascular calcification and tissue fibrosis -- down-stream of TNF-, BMP2-, and Msx2- activated osteogenic mineralization. Thus, the specific aims of this proposal are: Aim 1: "To establish the contributions of cell-autonomous vascular smooth muscle cell (VSMC) 2-catenin actions to vascular calcification and mural fibrosis in diabetic arteriosclerosis, using SM22- Cre(+);Ctnnb1(flox/+);LDLR(-/-) mice as a model for study." We test whether genetic down- regulation of VSMC 2-catenin signaling alters initiation and progression of diabetic arteriosclerosis, including diet-induced reductions in LE blood flow in the LDLR-/- mouse. Aim 2: "To examine the role of VSMC LRP6 expression in mediating the pro-calcific actions of Msx2-Wnt signaling during cardiovascular calcification, using diabetic SM22- Cre(+);LRP6(fl/fl);LDLR(-/-) mice as a model for study." LRP6 mediates Wnt7-dependent osteogenic and fibrotic signals in culture via 2-catenin and NFATc-mediated transcription. In this aim, we determine in vivo the cell-autonomous roles of VSMC LRP6 to the initiation of vascular calcification in diabetic arteriosclerosis in vivo, and the impact upon diet-induced activation of aortic osteogenic gene programs. The outcomes of these aims will provide physiological rationale and validation for reducing VSMC 2-catenin levels and LRP6 signaling as a potential therapeutic strategy to ameliorate vascular calcification -- and thus reduce lower extremity amputation risk in type II diabetes PUBLIC HEALTH RELEVANCE: Arterial hardening in diabetes increases the risk for heart attacks & foot amputation. This occurs in part via metabolic & inflammatory signals that induce bone-like calcification in large arteries. We have identified that two proteins, LRP6 and 2-catenin, are activated with calcification, fibrosis, and hardening of the arteries in diabetic mice. We test whether regulation of these proteins reduces arterial hardening, decreases cardiac workload, and improves blood flow to the foot.