15502-m-pleumeekers

MSC-populations, AMSCs and BMSC seem both appropriate candidates for co-culture therapy in the head and neck area. However, only few studies have directly compared their behavior in co-cultures. [80, 246, 247] Unfortunately, these studies demonstrate conflicting outcomes and have never translated to animal or preclinical research. Acharya et al . demonstrated enhanced chondrocyte proliferation capacity and improved sGAG formation in pellets containing BMSC/chondrocytes compared to AMSC/chondrocytes. [80] Besides, 3 independent co- culture studies using AMSCs showed limited or decreased effects of AMSCs on chondrogenesis. [243-245] Such effect was hardly seen in co-culture studies using BMSCs, which may propose that, compared to BMSCs, AMSCs seem less efficient in co-culture. Although we could not find a general beneficial effect of human BMSCs in co-cultures compared to human AMSCs in chapter five , we did show that in vitro , BMSC/chondrocytes outperformed AMSC/chondrocytes and hypertrophic gene expression was lower in BMSC/chondrocytes. True dissimilarities between human AMSCs and BMSCs in co-culture are unfortunately hard to expose, as human MSC-cultures are highly heterogeneous and distinct population subsets probably interfere with the reciprocal communication pathways in co- culture. Therefore, the purification of distinct subsets of human MSCs might enhance the particular capability of AMSCs and BMSCs in co-culture by eliminating interfering cells with limited potential, or even cells with inhibitory activity. Unfortunately, in depth understanding of the cellular interaction pathways between MSCs and chondrocytes is under debate in literature. Numerous cellular communication pathways have been hypothesized in order to explain the beneficial effect in co-cultures [73]: (1) Chondrocyte-driven MSC-differentiation or (2) MSC-driven chondro-induction are considered the most plausible of them. [81] In recent years, the trophic and paracrine functions of MSCs appeared most critical in this process, rather than simple chondrogenic differentiation of MSCs alone as stated previously. [80, 253-262] In accordance to former research [74, 246, 263-268], we demonstrate ( chapter five and six ) that both AMSCs and BMSCs improve chondrocyte proliferation as well as ECM formation, which suggests a predominantly trophic role for MSCs in co-culture. We emphasize the importance of paracrine signaling pathways in co-culture comparatively to juxtacrine or gap-junctional signaling. The importance of direct cell-cell contact is still unclear in literature. [263] Nevertheless, in chapter five and six , such signaling pathways remained less important, as co-culture constructs were made of alginate hydrogel, impeding direct cell-cell contact. Moreover, in pellet culture no beneficial effect of direct cell-cell contact was observed. On the contrary, MSC-driven chondro-induction was less pronounced in Transwell® system and this effect was even further reduced by MSC-conditioned medium. Although direct cell-cell contact seems less significant than paracrine signaling, it seems correspondingly important to secure a certain cell-cell distance for optimal cell communication. The fact that MSCs full fill a trophic role in co-culture and have been demonstrated to be immune privileged, it seems no longer necessary to use autologous MSCs only. The use of allogeneic MSCs have already been used for the treatment of steroid-resistant graft-versus- host disease, acute respiratory distress syndrome and Crohn’s disease. [381] Even a few clinical trials have been commenced using allogeneic MSCs for cell-based cartilage repair in 182 CHAPTER 9