title: Villin promoter-mediated transgenic expression of transient receptor potential cation channel, subfamily V, member 6 (TRPV6) increases intestinal calcium absorption in wild-type and vitamin D receptor knockout mice.
abstract: Transient receptor potential cation channel, subfamily V, member 6 (TRPV6) is an apical membrane calcium (Ca) channel in the small intestine proposed to be essential for vitamin D-regulated intestinal Ca absorption. Recent studies have challenged the proposed role for TRPV6 in Ca absorption. We directly tested intestinal TRPV6 function in Ca and bone metabolism in wild-type (WT) and vitamin D receptor knockout (VDRKO) mice. TRPV6 transgenic mice (TG) were made with intestinal epithelium-specific expression of a 3X Flag-tagged human TRPV6 protein. TG and VDRKO mice were crossed to make TG-VDRKO mice. Ca and bone metabolism was examined in WT, TG, VDRKO, and TG-VDRKO mice. TG mice developed hypercalcemia and soft tissue calcification on a chow diet. In TG mice fed a 0.25% Ca diet, Ca absorption was more than three-fold higher and femur bone mineral density (BMD) was 26% higher than WT. Renal 1α hydroxylase (CYP27B1) mRNA and intestinal expression of the natural mouse TRPV6 gene were reduced to <10% of WT but small intestine calbindin-D(9k)  expression was elevated >15 times in TG mice. TG-VDRKO mice had high Ca absorption that prevented the low serum Ca, high renal CYP27B1 mRNA, low BMD, and abnormal bone microarchitecture seen in VDRKO mice. In addition, small intestinal calbindin D(9K)  mRNA and protein levels were elevated in TG-VDRKO. Transgenic TRPV6 expression in intestine is sufficient to increase Ca absorption and bone density, even in VDRKO mice. VDR-independent upregulation of intestinal calbindin D(9k)  in TG-VDRKO suggests this protein may buffer intracellular Ca during Ca absorption. © 2012 American Society for Bone and Mineral Research.
authors.affiliation: Department of Nutrition Science, Purdue University, West Lafayette, IN 47907-2059, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Cui
authors.forename: Qiang
authors.initials: Q
authors.lastname: Li
authors.forename: Robert
authors.initials: R
authors.lastname: Johnson
authors.forename: James C
authors.initials: JC
authors.lastname: Fleet
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000378:metabolism; D018938:Caco-2 Cells; D064026:Calbindins; D002118:Calcium / Q000097:blood / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D007408:Intestinal Absorption; D007413:Intestinal Mucosa / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000235:genetics*; D009928:Organ Specificity; D010641:Phenotype; D011401:Promoter Regions, Genetic / Q000235:genetics*; D018167:Receptors, Calcitriol / Q000172:deficiency* / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D050916:TRPV Cation Channels / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D019076:Transgenes / Q000235:genetics*; D055114:X-Ray Microtomography
chemical_list: D064026:Calbindins; D015220:Calcium Channels; D008840:Microfilament Proteins; D018167:Receptors, Calcitriol; D064030:S100 Calcium Binding Protein G; D050916:TRPV Cation Channels; C422827:TRPV6 protein, human; C026615:villin; D002118:Calcium