title: Functional TRPV6 channels are crucial for transepithelial Ca2+ absorption.
abstract: TRPV6 is considered the primary protein responsible for transcellular Ca2+ absorption. In vitro studies demonstrate that a negatively charged amino acid (D) within the putative pore region of mouse TRPV6 (position 541) is critical for Ca2+ permeation of the channel. To elucidate the role of TRPV6 in transepithelial Ca2+ transport in vivo, we functionally analyzed a TRPV6D541A/D541A knockin mouse model. After weaning, mice were fed a regular (1% wt/wt) or Ca2+-deficient (0.02% wt/wt) diet and housed in metabolic cages. Blood was sampled for Ca2+ measurements, and the expression of Ca2+ transport proteins was analyzed in kidney and duodenum. Intestinal 45Ca2+ uptake was measured in vivo by an absorption assay. Challenging the mice with the Ca2+-deficient diet resulted in hypocalcemia in wild-type and TRPV6D541A/D541A mice. On a low-Ca2+ diet both mouse strains displayed increased expression of intestinal TRPV6, calbindin-D(9K), and renal TRPV5. TRPV6D541A/D541A mice showed significantly impaired intestinal Ca2+ uptake compared with wild-type mice, and duodenal TRPV5 expression was increased in TRPV6D541A/D541A mice. On a normal diet, serum Ca2+ concentrations normalized in both mouse strains. Under these conditions, intestinal Ca2+ uptake was similar, and the expression levels of renal and intestinal Ca2+ transport proteins were not affected. We demonstrate that TRPV6D541A/D541A mice exhibit impaired transcellular Ca2+ absorption. Duodenal TRPV5 expression was increased in TRPV6D541A/D541A mice, albeit insufficient to correct for the diminished Ca2+ absorption. Under normal conditions, when passive Ca2+ transport is predominant, no differences between wild-type and TRPV6D541A/D541A mice were observed. Our results demonstrate a specific role for TRPV6 in transepithelial Ca2+ absorption.
authors.affiliation: Department of Physiology, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.
authors.forename: Titia E
authors.initials: TE
authors.lastname: Woudenberg-Vrenken
authors.forename: Anke L
authors.initials: AL
authors.lastname: Lameris
authors.forename: Petra
authors.initials: P
authors.lastname: Weißgerber
authors.forename: Jenny
authors.initials: J
authors.lastname: Olausson
authors.forename: Veit
authors.initials: V
authors.lastname: Flockerzi
authors.forename: René J M
authors.initials: RJ
authors.lastname: Bindels
authors.forename: Marc
authors.initials: M
authors.lastname: Freichel
authors.forename: Joost G J
authors.initials: JG
authors.lastname: Hoenderop
mesh_terms: D000818:Animals; D064026:Calbindins; D002118:Calcium / Q000097:blood / Q000493:pharmacokinetics; D015220:Calcium Channels / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D004032:Diet / Q000009:adverse effects / Q000379:methods; D006996:Hypocalcemia / Q000378:metabolism; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000502:physiology; D007668:Kidney / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D057900:Transcytosis
chemical_list: D064026:Calbindins; D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D064030:S100 Calcium Binding Protein G; D050916:TRPV Cation Channels; C120776:TRPV6 channel; C492240:Trpv5 protein, mouse; D002118:Calcium