Abstract
Endothelial cell activation leading to leukocyte recruitment and adhesion plays an essential role in the initiation and progression of atherosclerosis. Vitamin D has cardioprotective actions, while its deficiency is a risk factor for the progression of cardiovascular damage. Our aim was to assess the role of basal levels of vitamin D receptor (VDR) on the early leukocyte recruitment and related endothelial cell-adhesion-molecule expression, as essential prerequisites for the onset of atherosclerosis. Knockdown of VDR in endothelial cells (shVDR) led to endothelial cell activation, characterized by upregulation of VCAM-1, ICAM-1 and IL-6, decreased peripheral blood mononuclear cell (PBMC) rolling velocity and increased PBMC rolling flux and adhesion to the endothelium. shVDR cells showed decreased IκBα levels and accumulation of p65 in the nucleus compared to shRNA controls. Inhibition of NF-κB activation with super-repressor IκBα blunted all signs of endothelial cell activation caused by downregulation of VDR in endothelial cells. In vivo, deletion of VDR led to significantly larger aortic arch and aortic root lesions in apoE-/- mice, with higher macrophage content. apoE-/-VDR-/-mice showed higher aortic expression of VCAM-1, ICAM-1 and IL-6 when compared to apoE-/-VDR+/+ mice. Our data demonstrate that lack of VDR signaling in endothelial cells leads to a state of endothelial activation with increased leukocyte-endothelial cell interactions that may contribute to the more severe plaque accumulation observed in apoE-/-VDR-/- mice. The results reveal an important role for basal levels of endothelial VDR in limiting endothelial cell inflammation and atherosclerosis.
Highlights
Vascular endothelium is considered to be a main regulator of blood vessel homeostasis, having not solely a barrier function, but exerting a number of vasoprotective roles
To further assess the role of vitamin D receptor (VDR) in endothelial cell activation, we analyzed the expression of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) in the same groups of cells
In our experimental model, downregulation of VDR led to a significant elevation of IL-6 mRNA, as well as of IL-6 secretion in shVDR cells compared with the corresponding controls (Fig 2E and 2F, respectively)
Summary
Vascular endothelium is considered to be a main regulator of blood vessel homeostasis, having not solely a barrier function, but exerting a number of vasoprotective roles. Due to its intrinsic ability to sense humoral and haemodynamic stimuli [1], the endothelium contributes to the local regulation of vascular tone and structure, controls the growth and migration of vascular smooth muscle cells (VSMCs), and regulates the adhesion and extravasation of leukocytes [2, 3]. Impairment of endothelial function is a major pathological mechanism predisposing to diseases like atherosclerosis [4]. Atherosclerosis is characterized by chronic inflammation of the vessel wall initiated by leukocyte recruitment and adhesion to the activated endothelium, and followed by their migration into the subendothelium with subsequent lipid accumulation within macrophages [5]. We explored the contribution of vitamin D receptor (VDR) in limiting vascular endothelial cell’s (EC) activation and inflammation. 1,25(OH)2D inhibits various aspects of inflammation [14], a well-known key pathogenic mechanism of atherosclerosis, and protects against myocardial cell hyperthrophy [15] and fibrosis [16], emerging as an important player in the protection against cardiovascular disease (CVD) mortality
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