The role of tumor necrosis factor alpha in down-regulation of osteoblast Phex gene expression in experimental murine colitis.
OBJECTIVE
Reduced bone mass is a common complication of inflammatory bowel disease (IBD), although the mechanisms that contribute to osteopenia are not completely understood. Tumor necrosis factor alpha (TNF-alpha) is up-regulated in patients with IBD and has detrimental effects on osteoblasts. Phex gene is expressed predominantly in osteoblasts, and its disruption results in defective bone mineralization. The aim of this study was to evaluate whether TNF-alpha regulates Phex gene expression thus contributing to the abnormal bone metabolism observed in IBD.


METHODS
Phex gene expression was evaluated in calvaria of 6-7-week-old mice administered with trinitrobenzene sulfonic acid (TNBS) with or without neutralizing anti-TNF-alpha antibody, dietary curcumin, or systemically with recombinant TNF-alpha. TNF-alpha-treated UMR-106 osteoblasts were also examined. Phex promoter activity was assayed in transiently transfected TNF-alpha-treated UMR-106 cells.


RESULTS
Compared with control animals, Phex messenger RNA (mRNA) expression decreased by 40%-50% in both TNBS colitis and TNF-alpha-injected mice. Dietary curcumin and anti-TNF-alpha antibody counteracted the detrimental effect of TNBS on Phex gene expression. TNF-alpha-treated UMR-106 cells showed a concentration-dependent and transcriptionally mediated decrease in Phex mRNA and gene promoter activity, with the -133 to -74 bp region of the Phex promoter likely involved in the mechanism of TNF-alpha action. Coinciding with decreased Phex protein level, TNF-alpha drastically reduced mineralization in UMR-106 osteoblasts.


CONCLUSIONS
Acute colitis and TNF-alpha decrease Phex mRNA and protein expression via a transcriptional mechanism. TNF-alpha-mediated reduction in Phex protein is at least in part responsible for inhibition of osteoblast mineralization, and the described mechanism may contribute to the abnormal bone metabolism associated with IBD.
Uno
Jennifer K
JK
Department of Pediatrics, Steele Children's Research Center, University of Arizona Health Sciences Center, Tucson, Arizona 85724, USA.
Kolek
Olga I
OI
Hines
Eric R
ER
Xu
Hua
H
Timmermann
Barbara N
BN
Kiela
Pawel R
PR
Ghishan
Fayez K
FK
D000818:Animals; D049109:Cell Proliferation; D002478:Cells, Cultured; D003092:Colitis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000187:drug effects*; D015151:Immunoblotting; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D008666:Metalloendopeptidases / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D010006:Osteoblasts / Q000378:metabolism*; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D008666:Metalloendopeptidases; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506232:Phex protein, mouse; C506229:Phex protein, rat