Abstract
Human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have been shown as the most potential stem cell source for articular cartilage repair. In this study, we aimed to develop a method for long-term coculture of human articular chondrocytes (hACs) and hUCB-MSCs at low density in vitro to determine if the low density of hACs could enhance the hUCB-MSC chondrogenic differentiation as well as to determine the optimal ratio of the two cell types. Also, we compared the difference between direct coculture and indirect coculture at low density. Monolayer cultures of hUCB-MSCs and hACs were investigated at different ratios, at direct cell-cell contact groups for 21 days. Compared to direct coculture, hUCB-MSCs and hACs indirect contact culture significantly increased type II collagen (COL2) and decreased type I collagen (COL1) protein expression levels. SRY-box 9 (SOX9) mRNA levels and protein expression were highest in indirect coculture. Overall, these results indicate that low density direct coculture induces fibrocartilage. However, indirect coculture in conditioned chondrocyte cell culture medium can increase expression of chondrogenic markers and induce hUCB-MSCs differentiation into mature chondrocytes. This work demonstrates that it is possible to promote chondrogenesis of hUCB-MSCs in combination with hACs, further supporting the concept of novel coculture strategies for tissue engineering.
Highlights
Repair of cartilage defects represents a significant orthopedic challenge due to the limited healing capacity of mature cartilage; the development of new tissue engineering strategies is of major importance for cartilage repair [1]
The flow cytometry analysis revealed that the isolated hUCB-MSC population had high expression of CD105 and CD73 and low expression of CD34 and CD45. These cells had acquired the fibroblastic morphology that is characteristic of mesenchymal stem cells, confirming the existence of mesenchymal stem cells in human umbilical cord blood
The loss of phenotypic functions during chondrocyte expansion in monolayer culture has led to the search for an alternative cell source for cartilage tissue engineering
Summary
Repair of cartilage defects represents a significant orthopedic challenge due to the limited healing capacity of mature cartilage; the development of new tissue engineering strategies is of major importance for cartilage repair [1]. Use of autologous chondrocytes has disadvantages that limit potential clinical applications, including donor site morbidity and dedifferentiation of the harvested chondrocytes after ex vivo monolayer expansion [3]. Recent studies have shifted focus from ACI to mesenchymal stem cell (MSC) therapy, which has been shown as effective for articular cartilage repair [4,5,6,7,8,9,10,11]. Human umbilical cord bloodderived MSCs (hUCB-MSCs) could serve as a promising cell source for in vivo repair of cartilage defects due to advantages of noninvasive collection, high proliferative potential, lower immunogenicity, and chondrogenic potential in vitro [15,16,17]
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