Rationale: Vascular fibrosis and calcification contribute to diabetic arteriosclerosis, impairing Windkessel physiology necessary for distal tissue perfusion. Wnt family members, upregulated in arteries by the low-grade inflammation of "diabesity," stimulate type I collagen expression and osteogenic mineralization of mesenchymal progenitors via beta-catenin. Conversely, parathyroid hormone (PTH) inhibits aortic calcification in low-density lipoprotein receptor (LDLR)-deficient mice fed high fat diabetogenic diets (HFD).
Objective: We sought to determine the impact of vascular PTH receptor (PTH1R) activity on arteriosclerotic Wnt/beta-catenin signaling in vitro and in vivo. We generated SM-caPTH1R transgenic mice, a model in which the constitutively active PTH1R variant H223R (caPTH1R) is expressed only in the vasculature.
Methods and results: The caPTH1R inhibited Wnt/beta-catenin signaling, collagen production, and vascular smooth muscle cell proliferation and calcification in vitro. Transgenic SM-caPTH1R;LDLR(+/-) mice fed HFD develop diabesity, with no improvements in fasting serum glucose, cholesterol, weight, body composition, or bone mass versus LDLR(+/-) siblings. SM-caPTH1R downregulated aortic Col1A1, Runx2, and Nox1 expression without altering TNF, Msx2, Wnt7a/b, or Nox4. The SM-caPTH1R transgene decreased aortic beta-catenin protein accumulation and signaling in diabetic LDLR(+/-) mice. Levels of aortic superoxide (a precursor of peroxide that activates pro-matrix metalloproteinase 9 and osteogenic signaling in vascular smooth muscle cells) were suppressed by the SM-caPTH1R transgene. Aortic calcification, collagen accumulation, and wall thickness were concomitantly reduced, enhancing vessel distensibility.
Conclusions: Cell-autonomous vascular smooth muscle cell PTH1R activity inhibits arteriosclerotic Wnt/beta-catenin signaling and reduces vascular oxidative stress, thus limiting aortic type I collagen and calcium accrual in diabetic LDLR-deficient mice.