CYP27B1 null mice with LacZreporter gene display no 25-hydroxyvitamin D3-1α-hydroxylase promoter activity in the skin

摘要

The hormonally active form of vitamin D3,1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], is synthesized in the kidney through a tightly regulated reaction catalyzed by 25-hydroxyvitamin D3-1α-hydroxylase (1α-hydroxylase), the product of the CYP27B1 gene. Through gene targeting in embryonic stem cells, we engineered a mouse strain in which the coding region of the 1α-hydroxylase gene is replaced by the genes for β-galactosidase (lacZ) and neomycin resistance. Null mice produced no detectable 1α-hydroxylase transcript. The mice grew normally when maintained on a balanced diet containing 1,25(OH)2D3 but rapidly developed rickets when phosphorus and 1,25(OH)2D3 were restricted. Rickets was curable through administration of 1,25(OH)2D3 but not its biological precursor, 25-hydroxyvitamin D3. Upon administration of a diet low in calcium and devoid of any form of vitamin D3, β-galactosidase activity was detected in the kidneys of the –/– and +/– mice and in placentas harvested from –/– females bred with –/– males. No β-galactosidase activity was detected in skin sections or in primary keratinocyte cultures from –/– animals. Our results demonstrate we have generated 1α-hydroxylase null mice that display phenotypes characteristic of vitamin D-dependency rickets type I. From the histochemical analysis of reporter gene expression in these mice, we conclude that acute 1,25(OH)2D3 deficiency in otherwise healthy animals does not stimulate local production of 1,25(OH)2D₃ in the skin. These findings stand in contrast to previously published reports of 1,25(OH)₂D₃ production in keratinocytes.