Purpose of the study: Monolayer cultures of chondrocytes multiply and rapidly lose their chondrocyte phenotype, limiting their potential for tissue engineering. Mesenchymatous stem cells can preserve their phenotypic characteristics after several monolayer passages, offering a promising alternative for cartilage repair. The purpose of this work was to study the influence of transforming growth factor beta-1 (TGF-beta1) and bone morphogenic protein-2 (BMP2) and/or culture supplements (hyaluronic acid) on matrix synthesis and chondrocyte differentiation of human mesenchymatous stem cells (MSC) cultured on collagen sponges.

Material and methods: MSC were isolated from bone marrow harvested during hip arthroplsty. At the third passage in monolayer culture, the MSC were reseeded on collagen sponges and cultured in vitro for 28 days under seven differ conditions: insulin transferrin selenium (ITS), foetal calf serum (FCS), ITS+TGFbeta1, ITS+ hyaluronate, ITS+TGFbeta1+hyaluronate, ITS+TGFbeta1+BMP2, ITS +TGFbeta1+BMP2+hyaluronate. The phenotypic evolution was followed using the expression of different genes of interest with PCRq (collagen2, collagen1, collagen3, collagen10, agrecanne, versicanne, COMP, Sox9). Synthesis of matrix material was assessed histologically and immunohistochemically.

Results: Used alone, hyaluronic acid did not trigger chondrocyte differentiation of MSC. For the additives FCS, ITS, or hyaluronate, the synthesis of matrix material in the sponge was weak and poor in major constituents of cartilage. Conversely, the other conditions in presence of TGFbeta1±BMP2 induced important expression of collagen2, agrecanne and COMP as well as increased matrix synthesis with a strong content in proteoglycans and collagen.

Discussion: The usefulness of MSC is growing due to their pluripotent characteristics. The conditions leading to their differentiation into the chondrocyte phenotype remains a subject of discussion. Our results show the particular importance of TGFbeta1 in the process of differentiation.

Conclusion: Chondrogenic differentiation of MSC cultured in collagen sponges as well as the synthesis of the cartilaginous matrix requires the presence of TGFbeta1 in the culture medium and to a lesser extent BMP2. These results suggest the perspective of using MSC for guided cell therapy targeting cartilage.

Purpose: Section of the anterior cruciate ligament (ACL) is classically used to induce experimental joint degeneration in animal models (dog, rabbit, rat…), but the contribution of physical activity to the course of the cartilage damage observed in this model remains unknown. We studied the influence of moderate physical activity on the course of experimental knee joint degeneration induced by section of the ACL in the rat.

Material and methods: The right knee ACL was sectioned with and arthrotome in 60 male Wistar rats (180 g) under general anaesthesia. Full section of the ACL, performed with a fine lancet, was verified clinically by demonstrating anterior drawer. The non-operated knee served as a control. The rats were separated at random into two groups, with or without exercise. Exercise was calibrated on a treadmill running at constant speed (30 cm/s for 30 min, i.e. 15 km for 28 days). Rats were sacrificed on days 7, 14 and 28. Macroscopic inspection, histological analysis and immunohistochemistry tests (Caspase 3) were performed on each knee segment. NO was also assayed in the synovial fluid.

Results: No cartilage damage was observed in the non-operated knees after running 15 km. Marked synovitis was observed in the knees with a sectioned ACL starting on day 7, associated with fibrillary surface formations. The severity of the cartilage damage increased from day 14 to day 28, predominantly on the medial tibial plateau and to a lesser extent on the adjacent femoral condyle, in the weight-bearing zone. Damage was minimal on the patella. Chondrocyte apoptotic phenomena were also observed, reaching maximum on day 7 and sustained thereafter. Physical activity had a significant effect on these parameters showing an improvement in the macroscopic and histological lesions from day 14 to day 28, and improvement in chondrocyte apoptosis from day 7 to day 14 and to day 28.

Discussion: This novel work confirms the beneficial effect of moderate physical activity in an experimental joint degeneration rat model. Elsewhere, it has been well established experimentally that intense joint activity has a deleterious effect on chondral lesions after meniscectomy and/or section of the ACL. This unfavourable effect of intense physical activity has also been observed clinically in high-level athletes. Our experimental data suggest that moderate physical activity does not increase the risk of joint degeneration and could, under certain conditions, have a beneficial effect, as has been suggested by certain recent clinical data.