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The HLA-B27 transgenic rat, a model of spondyloarthritis, has decreased bone mineral density and increased RANKL to osteoprotegerin mRNA ratio.
OBJECTIVEBone metabolism in spondyloarthritis (SpA) is not well elucidated. We investigated alterations in bone in the HLA-B27 transgenic rat, a model of SpA.
METHODSFemur, tibia, and lumbar vertebral bodies of disease-prone HLA-B27 transgenic, healthy HLA-B7 transgenic, and nontransgenic control rats were used for bone histomorphometric and dual energy x-ray absorptiometry (DEXA) analysis. Serum levels of type I collagen C-telopeptides (CTX), N-terminal propeptide of type I procollagen (P1NP), and osteocalcin, as well as receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG), were measured. RNA was isolated from the bone tissue of the femura to analyze gene expression of RANKL, OPG, and osteocalcin.
RESULTSHistomorphometric analysis indicated a significant decrease in bone volume as well as trabecular number and thickness in the HLA-B27 rats. Trabecular separation was increased. Numbers of osteoblasts, osteoclasts, and osteoid volume were not altered significantly. The decrease in bone mineral density was confirmed using DEXA. Levels of RANKL mRNA were significantly increased in the bone tissue of HLA-B27 transgenic rats, resulting in an increased RANKL to OPG ratio. Osteocalcin mRNA expression was also significantly elevated in bone of HLA-B27 rats. Serum levels of CTX, RANKL, OPG, P1NP, and osteocalcin did not differ significantly.
CONCLUSIONOur data indicate that, similarly to SpA in humans, HLA-B27 transgenic rats show a reduced bone mass, and suggest an involvement of the RANKL/OPG system in the mechanism of bone loss in this disease. This model may be adequate to study osteoporosis in SpA.
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The Journal of rheumatology 36:1 2009 Jan pg 120-6
Disease Models, Animal
Rats, Inbred F344
Pub Type(s)Journal Article
Research Support, Non-U.S. Gov't