15502-m-pleumeekers

ABSTRACT Combining mesenchymal stem cells (MSCs) and chondrocytes has great potential for cell- based cartilage repair. However, there is much debate regarding the mechanisms behind this concept. We aimed to clarify the mechanisms that lead to chondrogenesis (chondrocyte driven MSC-differentiation versus MSC driven chondro-induction) and whether their effect was dependent on MSC-origin. Therefore, chondrogenesis of human adipose-tissue-derived MSCs ( h AMSCs) and bone-marrow-derived MSCs ( h BMSCs) combined with bovine articular chondrocytes ( b ACs) was compared. h AMSCs or h BMSCs were combined with b ACs in alginate and cultured in vitro or implanted subcutaneously in mice. Cartilage formation was evaluated with biochemical, histological and biomechanical analyses. To further investigate the interactions between b ACs and h MSCs, (1) co-culture, (2) pellet, (3) Transwell® and (4) conditioned media studies were conducted. The presence of h MSCs - either h AMSCs or h BMSCs - increased chondrogenesis in culture; deposition of sGAG was most evidently enhanced in h BMSC/ b ACs. This effect was similar when h MSCs and b AC were combined in pellet culture, in alginate culture or when conditioned media of h MSCs were used on b AC. Species-specific gene-expression analyses demonstrated that aggrecan was expressed by b ACs only, indicating a predominantly trophic role for h MSCs. Collagen-10 -gene expression of b ACs was not affected by h BMSCs, but slightly enhanced by h AMSCs. After in-vivo implantation, h AMSC/ b ACs and h BMSC/ b ACs had similar cartilage matrix production, both appeared stable and did not calcify. This study demonstrates that replacing 80% of b ACs by either h AMSCs or h BMSCs does not influence cartilage matrix production or stability. The remaining chondrocytes produce more matrix due to trophic factors produced by h MSCs. 84 CHAPTER 5