Expansive Vascular Remodeling and Increased Vascular Calcification Response to Cholecalciferol in a Murine Model of Obesity and Insulin Resistance.

Objective- We hypothesized that ob/ob mice develop expansive vascular remodeling associated with calcification. Approach and Results- We quantified and investigated mechanisms of vascular remodeling and vascular calcification in ob/ob mice after vitamin D3(VD) stimulation or PBS (control), compared with C57BL/6 mice. Both ob/ob (OBVD [VD-treated ob/ob mice]) and C57BL/6 (C57VD [VD-treated C57BL/6 mice]) received 8×103 IU/day of intraperitoneal VD for 14 days. Control ob/ob (OBCT [PBS-treated ob/ob mice]) and C57BL/6 (C57CT [PBS-treated C57BL/6 mice]) received intraperitoneal PBS for 14 days. Hypervitaminosis D increased the external and internal elastic length in aortae from OBVD, resulting in increased total vascular area and lumen vascular area, respectively, which characterizes expansive vascular remodeling. OBVD decreased the aortic wall thickness, resulting in hypotrophic vascular remodeling. We demonstrated increased collagen deposition, elastolysis, and calcification in aortae from OBVD. Our results showed a positive correlation between expansive vascular remodeling and vascular calcification in OBVD. We demonstrated increased serum calcium levels, augmented Bmp (bone morphogenetic protein)-2 and osteochondrogenic proteins expression in OBVD aortae. Furthermore, aortae from OBVD increased oxidative stress, coincidently with augmented in situ MMP (matrix metalloproteinase) activity and exhibited no VDR (VD receptor) inhibition after VD. Conclusions- Our data provide evidence that obese and insulin-resistant mice (ob/ob) developed expansive hypotrophic vascular remodeling correlated directly with increased vascular calcification after chronic VD stimulation. Positive hypotrophic vascular remodeling and vascular calcification in this mouse model is possibly mediated by the convergence of absence VDR downregulation after VD stimulation, increased reactive oxygen species generation, and MMP activation.

Msx2 is required for vascular smooth muscle cells osteoblastic differentiation but not calcification in insulin-resistant ob/ob mice.

BACKGROUND AND AIMS: Obesity and diabetes potentiate vascular calcification by increasing vascular smooth muscle cells osteoblastic differentiation mediated by the transcription factor Msx2 and bone morphogenetic protein-2 signaling. However, Bmp-2/Msx2 crosstalk to induce VSMC osteogenic phenotype transition and calcification is poorly understood in diabetes. We aimed to investigate mechanisms underlying Bmp-2-driven VSMC osteogenic differentiation and calcification in leptin-deficient ob/ob mice. METHODS: We incubated VSMC from ob/ob mice and wild type C57BL/6 littermates with or without Bmp-2. We used loss-of-function experiments to investigate the role of Msx2 in Bmp-2-induced ob/ob VSMC osteochondrogenic differentiation and calcification by transfecting Msx2 siRNA into VSMC. RESULTS: Baseline ob/ob VSMC and aorta showed increased Msx2, Runx2, alkaline phosphatase mRNA and protein expression, which further increased in Bmp-2-incubated ob/ob VSMC, therefore augmenting ob/ob VSMC calcification in comparison to wild type VSMC. Accordingly, signaling pathways to induce VSMC osteogenic differentiation, such as Smad1/5 phosphorylation increased in ob/ob versus wild type aorta. In comparison to wild type VSMC, Msx2 siRNA transfected VSMC decreased Bmp-2-dependent osteochondrogenic differentiation response by abrogating Msx2, Runx2, Alpl expression in ob/ob but not in wild type VSMC. Nonetheless, Msx2 inhibition did not decrease calcification in Bmp-2 stimulated ob/ob VSMC in vitro. CONCLUSIONS: Our data support a crucial role of Msx2 for ob/ob VSMC osteochondrogenic differentiation, however, Msx2 signaling alone is not sufficient for ob/ob VSMC calcification after Bmp-2 stimulation in vitro. These findings can be translated into novel perspectives for the understanding of the mechanisms and to provide therapeutic targets underlying vascular calcification in type 2 diabetes.