title: Post-translational loss of renal TRPV5 calcium channel expression, Ca(2+) wasting, and bone loss in experimental colitis.
abstract: OBJECTIVE
  Dysregulated Ca(2+) homeostasis likely contributes to the etiology of inflammatory bowel disease-associated loss of bone mineral density. Experimental colitis leads to decreased expression of Klotho, a protein that supports renal Ca(2+) reabsorption by stabilizing the transient receptor potential vanilloid 5 (TRPV5) channel on the apical membrane of distal tubule epithelial cells.
  
  
  METHODS
  Colitis was induced in mice via administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) or transfer of CD4(+)interleukin-10(-/-) and CD4(+), CD45RB(hi) T cells. We investigated changes in bone metabolism, renal processing of Ca(2+), and expression of TRPV5.
  
  
  RESULTS
  Mice with colitis had normal serum levels of Ca(2+) and parathormone. Computed tomography analysis showed a decreased density of cortical and trabecular bone, and there was biochemical evidence for reduced bone formation and increased bone resorption. Increased fractional urinary excretion of Ca(2+) was accompanied by reduced levels of TRPV5 protein in distal convoluted tubules, with a concomitant increase in TRPV5 sialylation. In mouse renal intermedullary collecting duct epithelial (mIMCD3) cells transduced with TRPV5 adenovirus, the inflammatory cytokines tumor necrosis factor, interferon-γ, and interleukin-1β reduced levels of TRPV5 on the cell surface, leading to its degradation. Cytomix induced interaction between TRPV5 and UBR4 (Ubiquitin recoginition 4), an E3 ubiquitin ligase; knockdown of UBR4 with small interfering RNAs prevented cytomix-induced degradation of TRPV5. The effects of cytokines on TRPV5 were not observed in cells stably transfected with membrane-bound Klotho; TRPV5 expression was preserved when colitis was induced with TNBS in transgenic mice that overexpressed Klotho or in mice with T-cell transfer colitis injected with soluble recombinant Klotho.
  
  
  CONCLUSIONS
  After induction of colitis in mice via TNBS administration or T-cell transfer, tumor necrosis factor and interferon-γ reduced the expression and activity of Klotho, which otherwise would protect TRPV5 from hypersialylation and cytokine-induced TRPV5 endocytosis, UBR4-dependent ubiquitination, degradation, and urinary wasting of Ca(2+).
authors.affiliation: Department of Pediatrics, University of Arizona Health Sciences Center, Tucson, AZ, USA.
authors.forename: Vijayababu M
authors.initials: VM
authors.lastname: Radhakrishnan
authors.forename: Rajalakshmy
authors.initials: R
authors.lastname: Ramalingam
authors.forename: Claire B
authors.initials: CB
authors.lastname: Larmonier
authors.forename: Robert D
authors.initials: RD
authors.lastname: Thurston
authors.forename: Daniel
authors.initials: D
authors.lastname: Laubitz
authors.forename: Monica T
authors.initials: MT
authors.lastname: Midura-Kiela
authors.forename: Rita-Marie T
authors.initials: RM
authors.lastname: McFadden
authors.forename: Makoto
authors.initials: M
authors.lastname: Kuro-O
authors.forename: Pawel R
authors.initials: PR
authors.lastname: Kiela
authors.forename: Fayez K
authors.initials: FK
authors.lastname: Ghishan
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D015519:Bone Density; D015496:CD4-Positive T-Lymphocytes / Q000637:transplantation; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D003092:Colitis / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism*; D005966:Glucuronidase / Q000378:metabolism; D007371:Interferon-gamma / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D000090265:Klotho Proteins; D051379:Mice; D008822:Mice, Transgenic; D011499:Protein Processing, Post-Translational; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050916:TRPV Cation Channels / Q000378:metabolism*; D014057:Tomography, X-Ray Computed; D014302:Trinitrobenzenesulfonic Acid; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D015415:Biomarkers; D015220:Calcium Channels; D050916:TRPV Cation Channels; C492240:Trpv5 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D014302:Trinitrobenzenesulfonic Acid; D005966:Glucuronidase; D000090265:Klotho Proteins; D002118:Calcium
keywords: 2,4,6-trinitrobenzenesulfonic acid; ARE; AU-rich elements; BMD; FECa(2+); IBD; IFN; IL; Mouse Model; Osteoporosis; TNBS; TNF; TRPV5; UC; Ub; Ulcerative Colitis; bone mineral density; eGFP; enhanced green flourescent protein; fractional excretion of Ca(2+); inflammatory bowel disease; interferon; interleukin; mIMCD3; mRNA; messenger RNA; mouse renal intermedullary collecting duct epithelial cells; siRNA; small interfering RNA; transient receptor potential vanilloid 5; tumor necrosis factor; ubiquitin