Critical role of macrophages in glucocorticoid driven vascular calcification in a mouse-model of atherosclerosis.

Objective: Macrophage-derived products are known to play a crucial role during atherogenesis and vascular calcification. Glucocorticoids (GC) are important modulators of immune cell functions, but their specific effects on macrophages behavior during plaque formation are not defined. The present study was therefore designed to investigate the effects of macrophage-specific deletion of the glucocorticoid receptor (GR(LysMCre)) on atherogenesis and vascular calcification in a hyperlipidemic mouse-model.
Methods and Results: Bone marrow was isolated from GR(LysMCre) mice and wild-type controls (GR(flox)) and subsequently transplanted into lethally irradiated LDL-receptor-deficient mice. Animals were fed a Western-type diet for 15 or 24 weeks, and atherosclerotic lesions within the aortic sinus were evaluated. At both time points, no significant difference in serum lipid and corticosterone concentrations, atherosclerotic lesion size and macrophage-content within the lesions could be observed. However, GR(LysMCre) mice showed less calcification as well as a significant reduction of RANKL, BMP2, and Msx2 expression within the vasculature. In vitro studies using conditioned media from macrophages which had been stimulated with dexamethasone demonstrated a dose-dependent increase in calcium deposition by vascular smooth muscle cells.
Conclusions: This study demonstrates that macrophage-specific glucocorticoid receptor inactivation reduces vascular calcification without affecting atherosclerotic lesion size in LDL receptor-deficient mice.