Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement
Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.
F-Spondin (spondin-1) Null Mice Exhibit Increased Bone Formation.
Attur1, Mukundan, Palmer1, Glyn, Liu1, James, Qing2, Yang, Rifkin2, Daniel, Beier3, Frank, Abramson1, Steven B.
We have previously reported that F-spondin (spondin-1), a neuroregulatory protein, is upregulated by chondrocytes in osteoarthritis. These studies showed that spondin-1, a member of the TSR (thrombospondin) type I class super family, activated latent TGF-b, which appeared to account for selected in vitro effects, including induction of the hypertrophic chondrocyte phenotype. In this study we generated Spon1 knockout mice to investigate in vivo the role of spondin-1 on skeletal maturation.
Total TGFb-1 was detected using R & D ELISA kit. MicroCt was performed on the Scanco mCT 35 system on proximal tibia and femurs bone evaluation. Values represent the average of 4 WT and 5 KO mice.
Spondin-1 knockout mice (Spon1-/-) were generated by targeted deletion of exon 1 in C57BL/6 mice. Exon 1 deletion was confirmed using Southern blot analysis and PCR using probes specific for wild type (WT) and mutant loci. Spon1-/- null mice were viable and initial macroscopic observations revealed no overt differences in size and body weight compared with WT (mice up to 6 months). Since we previously reported spondin-1 to regulate TGF-b and MMP activities, we measured their levels in adult mutant mice. Relative to WT mice, Spon1 deletion reduced serum levels of total TGFb-1 (82 ± 20 ng/ml vs. 30 ± 25.0 ng/ml; p<0.002) and increased serum total MMP activity (48 ± 15 RFU to 84 ± 18.0 RFU; p<0.061). Cultured chondrocytes isolated from the rib cages of 5 day old Spon1-/- mice also produced significantly less TGF-b (30%) compared to WT controls (p<0.01). To determine whether Spon1 deletion affected bone phenotype, we performed microCT of tibia and femurs in mutant and WT mice aged 16 months. Relative to WT mice, Spon1-/- exhibited increased bone formation at 6 months, evidenced by, a) increased trabecular and cortical bone volume fraction (Bone volume/Total volume: 0.27 ± 0.03 versus 0.15 ± 0.04, p<0.005; Fig 1), b) decreased trabecular spacing (0.14 ± 0.02 versus 0.2 ± 0.04, p<0.03); and c) increased trabecular number (7.8 ± 1.2, versus 5.0 ± 1.5, p<0.014). Interestingly, no significant changes were observed at 1 or 3 months, suggesting that spondin-1 effects are age-dependent.
Our studies indicate that F-spondin or spondin-1, a latent TGF-b activating ECM protein, over-expressed in OA bone and cartilage, regulates bone metabolism in aging male mice. Spon1 -/- male mice exhibit increased trabecular and cortical bone formation. Together these data suggest that a primary function of spondin-1 in skeletal tissue is the regulation of bone mass via latent TGF-b activation. Further studies are in progress regarding the potential of spondin-1 as a drugable target in future therapy of osteoporosis or osteoarthritis.
To cite this abstract, please use the following information:
Attur, Mukundan, Palmer, Glyn, Liu, James, Qing, Yang, Rifkin, Daniel, Beier, Frank, et al; F-Spondin (spondin-1) Null Mice Exhibit Increased Bone Formation. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :2434