title: Intestinal resistance to 1,25 dihydroxyvitamin D in mice heterozygous for the vitamin D receptor knockout allele.
abstract: We tested the hypothesis that low vitamin D receptor (VDR) level causes intestinal vitamin D resistance and intestinal calcium (Ca) malabsorption. To do so, we examined vitamin D regulated duodenal Ca absorption and gene expression [transient receptor potential channel, vallinoid subfamily member 6 (TRPV6), 24-hydroxylase, calbindin D(9k) (CaBP) mRNA, and CaBP protein] in wild-type mice and mice with reduced tissue VDR levels [i.e. heterozygotes for the VDR gene knockout (HT)]. Induction of 24-hydroxylase mRNA levels by 1,25 dihydroxyvitamin D(3) [1,25(OH)(2) D(3)] injection was significantly reduced in the duodenum and kidney of HT mice in both time-course and dose-response experiments. TRPV6 and CaBP mRNA levels in duodenum were significantly induced after 1,25(OH)(2) D(3) injection, but there was no difference in response between wild-type and HT mice. Feeding a low-calcium diet for 1 wk increased plasma PTH, renal 1alpha-hydroxylase (CYP27B1) mRNA level, and plasma 1,25(OH)(2) D(3), and this response was greater in HT mice (by 88, 55, and 37% higher, respectively). In contrast, duodenal TRPV6 and CaBP mRNA were not higher in HT mice fed the low-calcium diet. However, the response of duodenal Ca absorption and CaBP protein to increasing 1,25(OH)(2) D(3) levels was blunted by 40% in HT mice. Our data show that low VDR levels lead to resistance of intestinal Ca absorption to 1,25(OH)(2) D(3), and this resistance may be due to a role for the VDR (and VDR level) in the translation of CaBP.
authors.affiliation: Interdepartmental Nutrition Program and Department of Foods and Nutrition, Purdue University, 700 West State Street, West Lafayette, IN 47906-2059, USA.
authors.forename: Yurong
authors.initials: Y
authors.lastname: Song
authors.forename: James C
authors.initials: JC
authors.lastname: Fleet
mesh_terms: D000818:Animals; D064026:Calbindins; D002117:Calcitriol / Q000008:administration & dosage / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D004032:Diet; D005260:Female; D007422:Intestines / Q000187:drug effects*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D018167:Receptors, Calcitriol / Q000235:genetics* / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D064026:Calbindins; D018167:Receptors, Calcitriol; D064030:S100 Calcium Binding Protein G; D002117:Calcitriol; D002118:Calcium