Distinct, Tissue-Specific Regulation of Vitamin D Receptor in the Intestine, Kidney, and Skin by Dietary Calcium and Vitamin D

We studied the effects of vitamin D deficiency and its correction by vitamin D or calcium-lactose supplementation on vitamin D receptor (VDR) expression in skin keratinocytes, kidney, and duodenum of adult rats. VDR messenger RNA (mRNA) was assayed by Northern blot, and VDR protein was determined immunocytochemically. In addition, four subpopulations of keratinocytes were isolated, characterized for their stages of differentiation, and analyzed for VDR expression. Vitamin D deficiency decreased VDR mRNA in all three tissues. Treatment with vitamin D or calcium-lactose reestablished the VDR mRNA content of the epidermis, but not that of the kidneys, and only the calcium-lactose diet increased duodenal VDR mRNA. The regulation of VDR mRNA in the epidermis was independent of cell differentiation, whereas VDR protein varied with differentiation. The VDR-positive cells in the control rats were at early and advanced states of differentiation. The expression of VDR was decreased by vitamin D deficiency and returned to control values after vitamin D or calcium supplementation. Vitamin D treatment, but not calcium, induced VDR expression in the normally immature population. Vitamin D and calcium, therefore, have distinct, tissue-specific effects on VDR. In epidermis, the posttranscriptional regulation of VDR expression is linked to cell differentiation. Calcium may be a key factor for VDR transcription, whereas both vitamin D and calcium seem to contribute to its posttranscriptional regulation.