Chondroitin sulfate microparticles modulate TGF-B1-induced chondrogenesis in human mesenchymal stem cell spheroids

Due to the limited intrinsic healing ability of mature cartilage tissue, stem cell therapies offer the potential to restore cartilage lost due to trauma or arthritis. Mesenchymal stem cells (MSCs) are a promising cell source due to their ability to differentiate into various adult tissues under specific biochemical and physical cues. Current MSC chondrogenic differentiation strategies employ large pellets, however, we have previously developed a high-throughput technique to form small MSC aggregates (500-1,000 cells) that may reduce diffusion barriers while maintaining a multicellular structure that is analogous to cartilaginous condensations. The objective of this study was to examine the effects on chondrogenesis of incorporating chondroitin sulfate methacrylate (CSMA) microparticles (MPs) within these small MSC spheroids when cultured in the presence of transforming growth factor-β1 (TGF-β1) over 21 days. Spheroids +MP induced earlier increases in collagen II and aggrecan gene expression (chondrogenic markers) than spheroids -MP, although no large differences in immunostaining for these matrix molecules were observed by day 21. Collagen I and X was also detected in the ECM of all spheroids by immunostaining. Interestingly, histology revealed that CSMA MPs clustered together near the center of the MSC spheroids and induced circumferential alignment of cells and ECM around the material core. Because chondrogenesis was not hindered by the presence of CSMA MPs, this study demonstrates the utility of this culture system to further examine the effects of matrix molecules on MSC phenotype, as well as potentially direct differentiation in a more spatially controlled manner that better mimics the architecture of specific target tissues.M.S