UC San Diego

Mesenchymal stem cells (MSCs) have been considered as a promising cell source for cartilage tissue regeneration owing to their intrinsic musculoskeletal differentiation potential. A successful MSC-derived hyaline cartilage tissue should be structurally and functionally similar to native cartilage. During embryonic development morphogens have been shown to play a critical role in cartilage tissue formation. In this study we thus investigated the effect of chondrocyte-MSC interactions in the form of soluble morphogens on chondrogenic differentiation of MSCs using a co-culture system, wherein the hMSCs-laden hydrogels and chondrocytes were not in physical contact but can still exchange cell secreted factors. Healthy chondrocytes and osteoarthritic (OA) chondrocytes were able to induce chondrogenesis of hMSCs as analyzed by biochemical assays, gene analysis, and histology. We further explored the role of PTHrP and TGF-\[beta\]1 on chondrogenesis of hMSCs and found that in their combined presence, hMSCs had an upregulated expression of cartilage specific markers such as collagen type II and aggrecan and enhanced extracellular matrix production. Even in the absence of TGF-\[beta\]1 co-culture could induce chondrogenesis. A detailed analysis indicated that TGF- \[beta\]1 promotes proliferation and chondrogenic differentiation of MSCs, while PTHrP regulates hypertrophy. Mass spectrometry analysis underlined the crucial role of cross-talk on cell secreted morphogens. Extracellular histones inducing growth hormone production formed a major part of the morphogens unique to a co- culture system which is known to promote chondrogenesis. Our experimental observations along with numerical analysis indicated the crucial role of diffusion-mediated morphogenic concentration on chondrogenesis of MSCs.