A7.02 Protective effect of thrombospondin-4 expressing mesenchymal stem cells in osteoarthritis

Background and objectives Several members of the thrombospondin (THBS) family have been shown to play a role in cartilage homeostasis and physiopathology. While mesenchymal stem cells (MSCs) express different THBS members and exert a therapeutic effect in osteoarticular diseases, the role of THBS4 has been poorly investigated. We therefore evaluated the role of THBS4 deficient MSCs in osteoarthritic mice. Methods MSCs were isolated from the bone marrow of wild type C57BL6 and THBS4 knock-out C57BL6 mice and named wt and THBS4 -/- MSC, respectively. Osteoarthritis was induced in C57BL/6 mice by collagenase injections. On day 7, 200,000 MSCs were injected in the joint and on day 42, hind paws were processed for Safranin O-Fast green staining and scored. Tibiae were incubated in 30% of Hexabrix 320 contrast agent and scanned in a microCT scanner (SkyScan). Quantification of cartilage damage was then assessed after scanning the entire articular cartilage of tibiae with a confocal laser scanning microscope (CLSM; SP5 Leica). Results Histological analysis showed a significantly lower OA score in the joints of mice injected with wt MSCs as compared to control OA mice or mice that received THBS4 -/- MSCs. These results were confirmed by CLSM analysis of tibia plateau cartilages. Both the volume and thickness of articular cartilage were significantly lower in THBS4 -/- MSCs treated mice and in control OA mice than in mice treated with wt MSCs. Furthermore after incubation of tibiae with contrast agent, microCT analysis revealed a significant depletion of GAG content in the articular cartilage. Finally, microCT analysis of subchondral bone indicated a significant increase of bone surface degradation (increase of surface/volume ratio) as well as a significant decrease of bone mineral density and subchondral bone thickness in control OA mice and mice injected with THBS4 -/- MSCs as compared to wt MSCs treated mice. Conclusions In contrast to wt MSCs, THBS4 -/- MSCs were defective in their capacity to inhibit cartilage degradation in an osteoarthritic mouse model. Altogether, the data point out the role of the THBS4 pathway in the therapeutic effect of MSCs in osteo-articular diseases.