FP441ABSENCE OF VDR SOLELY IN VSMCs IMPEDES ARTERIAL CALCIFICATION IN CKD THROUGH TARGETING miR-145a AND miR-155

INTRODUCTION: Vascular calcification (VC) is a highly prevalent complication of chronic kidney disease (CKD) and, when present, is associated with the higher morbidity and mortality in CKD patients. Vitamin D receptor (VDR) has been identified as a risk factor for VC, suggesting a direct effect of VDR on the osteoblastic differentiation of vascular smooth muscle cells (VSMCs). The potential of VDR to influence widespread microRNAs (miRNAs) expression, as well as a myriad of miRNAs present in VSMCs drew attention to these small molecules as important regulators of VSMC differentiation and phenotypic modulation. The aim of this study was to evaluate the effect of VDR deficiency on vascular calcification in CKD and the possible involvement of miR-145a and miR-155 in this process. METHODS: VSMC-VDR conditional knockout mice (Cre+ VDR lox/lox) and their counterparts (Cre+ VDR wt/wt) were subjected to a 5/6 reduction of renal mass and fed a high phosphorus diet (0,9% P and 0,6% Ca) alongside the calcitriol treatment (500 ng/kg; three days per week during two months) - (5/6Nx+P+Ca; model of advanced CKD with hyperphosphatemia). Serum Ca2+, P and BUN were determined using standard clinical methods. Arterial calcium content was measured by o-cresolphthalein complexone method (mg Ca/mg protein), whilst calcium deposits in aortic sections were visualized by Alizarin red staining. The levels of osteopontin mRNA, as well as the expression of selected miRNAs were quantified by qPCR. RESULTS: Cre+ VDR wt/wt and Cre+ VDR lox/lox mice subjected to 5/6Nx+P+Ca showed evident signs of CKD with increased serum BUN, as well as equally high levels of serum Ca2+ and P. Cre+ VDRwt/wt animals demonstrated a significant increase of arterial calcium content compared with Cre+ VDRlox/lox mice (Cre+ VDR wt/wt: 522,89 µg Ca/mg protein ± 196,71; Cre+ VDR lox/lox: 93,42 µg Ca/mg protein ± 26,31), alongside higher levels of Alizarin red staining and higher osteopontin mRNA expression. Cre+ VDR wt/wt mice affected by CKD and VC showed lower levels of arterial miR-145a and higher levels of miR-155, compared to mice with targeted deletion of VDR in VSMCs (Cre+ VDR lox/lox). Levels of both miRNAs showed significant correlation with the expression of osteopontin mRNA. CONCLUSIONS: We conclude that VSMC’s VDR has a direct role in the progression of vascular calcification in CKD through targeting miR-145a and miR-155.