Co-regulation of the Cytochrome P450 24A1 gene in a model of kidney fibrosis by 1,25-dihydroxyvitamin D3 and growth factors
Hadi Dastjerdi, Sara
MetadataShow full item record
Renal fibrosis is a dominant pathological characteristic of progressive Chronic Kidney Disease (CKD). Epithelial-to-Mesenchymal-Transition (EMT), triggered by tissue damage, caused by renal inflammation, initiates and expands interstitial renal fibrosis. Renal fibrosis can, in turn, cause abnormalities in vitamin D and mineral metabolism, and therefore CKD patients are often vitamin D- deficient and hyperphosphatemic. Treatment of CKD patients with 1,25-dihydroxyvitamin D3 (1,25D3, the active form of vitamin D) has been shown to ameliorate fibrosis, but it can also cause hypercalcemia and possibly exacerbate vascular and soft tissue calcification. We have hypothesized that, due to the longer half-life of calcifediol, or 25-hydroxyvitamin D3 (25D3), and the feedback-controlled activation of this prohormone, treatment of renal fibrosis in a murine Unilateral Ureteral Obstruction (UUO) model would suppress renal inflammation and fibrosis without inducing hypercalcemia. We have treated UUO mice by subcutaneous injection of 25D3 and 1,25D3, and compared their effects on suppression of renal fibrosis, using histological and molecular parameters, for one or two weeks, and monitored various markers of fibrosis and inflammation. Treatment of UUO mice kept on a normal diet with 25D3 significantly suppressed the expression level of the major fibrotic and inflammatory markers without inducing hypercalcemia. If the animals were kept on a vitamin D-deficient diet, the expected anti-fibrotic effects of vitamin D treatment were not achievable. Also, through in vitro studies, the regulatory effect of the inflammatory and fibrotic factors TGFβ1, TNFα, and FGF23 in the presence and absence of 1,25D3, on the expression level as well as regulation of Cyp24a1 (the vitamin D catabolizing enzyme) promoter construct were examined. These studies revealed that TGFβ1 and FGF23 in the presence of vitamin D could induce synergistic upregulation of the Cyp24a1 mRNA, and Tnfα in the presence of vitamin D abrogated upregulation of the enzyme with 1,25D3. Further mutational analysis of the hCYP24A1 promoter confirmed the significant role of major DNA binding elements for the transcriptional effects of TGFβ1 and FGF23.