Endocrine Abstracts

The active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25D3), is a potent regulator of the immune system and activation of the vitamin D receptor alters expression and secretion of cytokines, chemokines and cell adhesion factors. Initial studies suggested that 1,25D3 synthesis and metabolism are increased in renal epithelial cells by TNFα and IL-1β. Therefore, the aim of this study was to examine whether vitamin D alters the expression of immune activated molecules in the kidney. To investigate the regulation of intercellular adhesion molecule-1 (ICAM-1) and interleukin 8 (IL-8) by 1,25D3 we used a human proximal tubule cell line, HKC-8. HKC-8 cells were incubated with IL-1beta (1 ng/ml) and TNFα (10 ng/ml) for 24 h as positive controls, or 1,25D3 (10 nM) or 25-hydroxyvitamin D3 (25D3; 100 nM) for 4–24 h. mRNA expression was assessed by semi-quantitative RT-PCR and protein levels (ICAM-1) by Western blotting. Expression of IL-8 and ICAM-1 mRNA were increased by TNFα (6 and 3 fold respectively) and IL-1beta (10 and 2 fold respectively). IL8 mRNA was increased by 1,25D3 and 25D3 in a time dependent manner. The greatest increase was seen at 4 h (2.8 fold 1,25D3; 2.2 fold 25D3). ICAM-1 mRNA was also increased slightly by 1,25D3 and 25D3. ICAM-1 protein expression was significantly increased by both 1,25D3 and 25D3 at all time points (maximum 2 fold induction). TNFα and IL-1β induced ICAM-I protein expression by 7 and 2 fold respectively. Of particular interest is the ability of 25D3 to modulate IL-8 and ICAM-1 expression as this indicates that HKC-8 cells are able to hydroxylate 25D3 to 1,25D3, which then acts in a paracrine/autocrine manner. These results support the hypothesis that 1,25D3 synthesized by renal epithelial cells may influence immune responses in these cells and may be of clinical importance in certain renal diseases.