Expression of 25-hydroxyvitamin D-3-1 alpha-hydroxylase along the nephron:new insights into renal vitamin D metabolism

Renal synthesis of the active form of vitamin D, 1,25-dihydroxyvitamin Dg [ 1,25(OH)(2)D-3], is a pivotal step in calcium and phosphate homeostasis. Pr oduction of 1,25(OH)(2)D-3 is catalyzed by the mitchondrial cytochrome P450 , 25-hydroxyvitamin D-3-1 alpha-hydroxylase (1 alpha-HYD). As a consequence of the tight regulation of vitamin D metabolism during normal physiology, studies of the expression and regulation of 1 alpha-HYD have proved remarka bly difficult, However, the recent cloning of the gene for 1 alpha-HYD has enabled a more comprehensive analysis of the tissue distribution of 1 alpha -HYD, as well as the mechanisms involved in controlling 1,25(OH)(2)D-3 prod uction. In particular, an understanding of site-specific expression and reg ulation of 1 alpha-HYD along the nephron might help to elucidate a more ver satile role for 1,25(OH)(2)D-3 in renal physiology. Curr Opin Nephrol Hyper tens 9:17-22. (C) 2000 Lippincott Williams & Wilkins.