Activation of CD137 signaling accelerates vascular calcification in vivo and vitro.

Objectives: Vascular calcification is a characteristic feature of atherosclerosis and is considered as an independent predictor of cardiovascular risk. CD137 signaling has previously shown to be involved in atherosclerosis. However, the possible role of CD137 signaling in regulation of vascular calcification has not been reported. In the present study, we investigated the effect of CD137 signaling on vascular calcification in ApoE ^-/- mice and in vascular smooth muscle cells (VSMCs) of mice.
Methods: Calcium deposition and muscle fibers in vivo or vitro were identified by von-Kossa and Masson's trichrome staining respectively. Alkaline phosphatase (ALP) activity was measured by the ALP assay Kit. The presence of bone morphogenic protein 2 (BMP2) and runt-related transcription factor 2 (Runx2) was detected by real-time PCR, Western blot and immunofluorescence in vitro or vivo.
Results: Our data shows that activation of CD137 signaling by intraperitoneal injection of agonist-CD137 antibody increased the areas of vascular calcification. Activation of CD137 signaling also increased the expression of BMP2 and Runx2 in the atherosclerotic plaques. In vitro, activation of CD137 signaling also aggravated VSMC calcification, while blocking CD137 signaling could alleviate agonist-CD137 induced VSMC calcification. In addition, the levels of calcium, BMP2 and Runx2, indicators of calcification, were all significantly elevated in agonist-CD137 group in VSMCs.
Conclusion: Our data revealed a previously unrecognized role of CD137 signaling in vascular calcification in vivo and vitro and provides a novel target for prevention and treatment of atherosclerosis in the future.
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