Murine TNF(DeltaARE) Crohn's disease model displays diminished expression of intestinal Ca2+ transporters.
BACKGROUND
Patients suffering from Crohn's disease (CD) show increased incidence of low bone mineral density. Investigating this complication is difficult because the exact etiology of CD remains elusive. Mice carrying a deletion in the tumor necrosis factor (TNF) AU-rich elements (ARE) are reported as a model for human CD and are characterized by elevated TNF-alpha levels and inflammations in the terminal ileum. To evaluate whether these mice have a Ca(2+) handling problem, this study analyzed the Ca(2+) homeostasis in heterozygous TNF(DeltaARE) mice (TNF(DeltaARE/+)) in comparison to wildtype littermates.


METHODS
Beside serum Ca(2+) and vitamin D levels, the expression of Ca(2+) transporters was analyzed in intestine, kidney and bone using quantitative real-time PCR, Western blot and immunohistochemistry. Bone scans were performed to measure bone parameters.


RESULTS
Ca(2+) transporters in duodenum (TRPV6, calbindin-D(9K), PMCA1b) and kidney (TRPV5, calbindin-D(28K), NCX1) showed significantly reduced mRNA expression levels in TNP(DeltaARE/+) mice, except for renal TRPV5. In bone, only calbindin-D(9K) mRNA displayed a significant down-regulation. These findings were supported by declined duodenal calbindin-D(9K) and renal calbindin-D(28K) protein values. Likely, this down-regulation of Ca(2+) transporters in TNP(DeltaARE/+) mice is mediated by the 58 +/- 9% reduction in serum 1,25(OH)(2)D(3) levels. Diminished expression of Ca(2+) transporters combined with unchanged serum Ca(2+) levels assumes Ca(2+) loss from bone to compensate for the body's overall Ca(2+) shortage. Indeed, microcomputed tomography scanning demonstrated reduced trabecular and corticol bone thickness and volume in TNF(DeltaARE/+) mice. This finding is further supported by increased total deoxypyridinoline in serum.


CONCLUSIONS
Our results imply that TNF(DeltaARE/+) mice have a disturbed Ca(2+) homeostasis characterized by reduced duodenal and renal Ca(2+) transporters, diminished 1,25(OH)(2)D(3) levels, and increased bone resorption associated with profound bone abnormalities.
Huybers
Sylvie
S
Department of Physiology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, The Netherlands.
Apostolaki
Maria
M
van der Eerden
Bram C J
BC
Kollias
George
G
Naber
Ton H J
TH
Bindels
René J M
RJ
Hoenderop
Joost G J
JG
D000818:Animals; D001862:Bone Resorption / Q000378:metabolism; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000378:metabolism*; D003424:Crohn Disease / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D006706:Homeostasis; D007413:Intestinal Mucosa / Q000378:metabolism*; D051379:Mice; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000097:blood / Q000235:genetics*
D014409:Tumor Necrosis Factor-alpha; D002117:Calcitriol; D002118:Calcium