ABSTRACT
In regenerative medicine using transplantation of mesenchymal stem cells (MSCs), the importance of regulating the quality of MSCs has been well recognized; however, there is little information concerning the relationship between the population doubling level (PDL) and the stemness of MSCs in equine medicine. In this study, we showed that the amount of glycosaminoglycan (GAG) secreted by bone marrow-derived MSCs (BMSCs) decreases with increase of PDL. Enzymatic digestion and two-dimensional electrophoresis revealed that a main component of GAG produced by BMSCs was hyaluronan with a small amount of chondroitin sulfate. Increase of PDL downregulated the expression of MSC CD markers, including CD44, CD73, CD90, CD105, and CD146, along with loss of differentiation capacity. Thus, the effect of hyaluronan supplement to the growth medium on both expression of CD markers and the tri-lineage potential of BMSCs was evaluated. Expression of CD73 and CD90 was preserved by continuous addition of hyaluronan to the growth medium, whereas mRNA levels corresponding to CD44, CD105 and CD146 were not preserved by supplementation of hyaluronan. BMSCs subcultured with hyaluronan-supplemented growth medium to PDL-12 showed osteogenic capacity, however adipogenic and chondrogenic activities at PDL-12 were not preserved by exogenous hyaluronan. These results suggest that downregulation of CD44, CD105 and CD146 might not affect the osteogenic capacity. Taken together, the results suggested that supplementation of hyaluronan to the growth medium might be effective at maintaining the osteogenic capacity of equine BMSCs.
ABSTRACT
Tenomodulin has been recognized as a biomarker for tendon differentiation, and its gene expression is regulated by several transcription factors including Scleraxis and Mohawk. In this study, we found a novel regulatory mechanism of tenomodulin expression. Equine bone marrow-derived mesenchymal stem cells (BMSCs) in monolayer culture showed a low mRNA level of tenomodulin in comparison with the level in the tendon. When cultured in collagen gel containing a glycogen synthase kinase-3 (GSK-3) inhibitor (BIO), expression of tenomodulin in BMSCs increased up to the level in the tendon. Participation of GSK-3 in its gene expression was further demonstrated by a gene silencing experiment with small interference RNA corresponding to GSK-3, suggesting that Wnt/ß-catenin signaling mediated expression of tenomodulin. These results were confirmed by nuclear translocation of ß-catenin in BIO-treated BMSCs cultured in collagen gel. Under this culture condition, expression of tenomodulin-related transcription factors including Scleraxis and Mohawk was not affected, suggesting that Wnt/ß-catenin signaling was independent from these transcription factors. Additionally, BIO strongly enhanced expression of type XIV collagen in collagen-embedded BMSCs up to the level in the tendon, and other tendon-related extracellular matrix components such as decorin and fibromodulin were also upregulated. Taken together, these results indicated that activation of Wnt/ß-catenin signaling could induce differentiation of BMSCs into tenomodulin-expressing tendon cells in collagen gel.
