084 MICE OVER-EXPRESSING SALMON CALCITONIN HAVE STRONGLY ATTENUATED BONE AND CARTILAGE CHANGES AFTER DESTABILIZATION OF THE MEDIAL MENISCUS

Abstract

Purpose: The pathogenesis of osteoarthritis (OA) involves both bone and cartilage changes. The peptide hormone calcitonin is produced by the thyroidal C-cells and is well-known for its inhibitory actions on bone resorbing osteoclasts. We investigated the effect on the articular cartilage and subchondral bone, after destabilization of the medial meniscus (DMM) in mice over-expressing salmon calcitonin (sCT) compared to control littermates. Methods: Mice over-expressing salmon calcitonin behind the liver ApoE promoter and wild-type littermate control were used for the experiments. Phenotype determination was performed by evaluating circulating serum levels of salmon calcitonin by specific ELISA. Northern Blot expression analysis was carried out to investigate the liver-specific expression of the transgene. Noncalcified plastic embedded vertebrae from mice of 6 and 12 month of age were used for histomophometric investigations. Serum samples were collected for osteocalcin measurements and urine for Dpd/creatinine measurements. In a preliminary experiment 10 week old mice were subjected to microsurgery to introduce DMM or sham operated, after which bone and cartilage degradation was monitored. After 7 weeks the study was terminated and the knee joints isolated for histological analysis by safranin’O staining. Results: Characterization of the transgenic mice was carried out by Northern Blot expression analysis and serum levels of sCT were about 8-times higher than endogenous CT levels in transgenic mice. Transgenic mice had >1000 pg/mL serum sCT and wild-type mice had no detectable levels. Von Kossa staining revealed an increase in trabecular bone volume (BV/TV) 100% after 6 month and 150% after 12 month in sCT mice when compared to controls (P<0.05). Trabecular number and thickness increased significantly (P<0.05) in transgenic mice at 6 and 12 months of age, and trabecular separation decreased in transgenic mice (P<0.05). Additionally, the osteoblasts number and bone formation rate were quantified by histomorphometry and together with the measurements of osteocalcin revealed that bone formation was not affected in transgenic mice. Mice having their medial meniscus transected for 7 weeks had major damage to cartilage and subchondral bone, which were visualized by histology. Sham operated animals, wild-type and transgenic mice, had maximum 8% erosion of the articular cartilage surface of both femur and tibia combined. DMM-operated wild-type mice had collapse of the trabecular structure and thickening of the subchondral bone and complete loss of articular cartilage in the medial tibial plateau of the joint compartment. These degenerative changes in the entire joint were however hampered in transgenic mice. The cartilage degradation comprised only 38% of the tibial plateau and 10% of the femoral chondyle and the subchondral bone and trabecular structure of the underlying bone were comparable to sham operated animals. Conclusions: Salmon calcitonin over-expressing mice had higher bone volume compared to wild-type. Mice over-expressing salmon calcitonin were protected against cartilage erosion, collapse of the subchondral compartment and bone thickening compared to wildtype litter mate controls. This data suggest that salmon calcitonin may have positive effects on the pathogenesis of OA however more studies are necessary to confirm these preliminary results.