Suppression of discoidin domain receptor 1 expression enhances the chondrogenesis of adipose-derived stem cells

Effectively directing the chondrogenesis of adipose-derived stem cells (ADSCs) to engineer articular cartilage represents an important challenge in ADSC-based articular cartilage tissue engineering. The discoidin domain receptor 1 (DDR1) has been shown to affect cartilage homeostasis; however, little is known about the roles of DDR1 in ADSC chondrogenesis. In this study, we used the three-dimensional culture pellet culture model system with chondrogenic induction to investigate the roles of DDR1 in the chondrogenic differentiation of human ADSCs (hADSCs). Real-time polymerase chain reaction and Western blot were used to detect the expression of DDRs and chondrogenic genes. Sulfated glycosaminoglycan (sGAG) was detected by Alcian blue and dimethylmethylene blue (DMMB) assays. Terminal deoxy-nucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining was used to assess cell death. During the chondrogenesis of hADSCs, the expression of DDR1 but not DDR2 was significantly elevated. The depletion of DDR1 expression in hADSCs using short hairpin RNA increased the expression of chondrogenic genes (SOX-9, collagen type II, and aggrecan) and cartilaginous matrix deposition (collagen type II and sGAG) and only slightly increased cell death (2-8%). DDR1 overexpression in hADSCs decreased the expression of chondrogenic genes (SOX-9, collagen type II, and aggrecan) and sGAG and enhanced hADSC survival. Moreover, DDR1-depleted hADSCs showed decreased expression of the terminal differentiation genes runt-related transcription factor 2 (Runx2) and matrix metalloproteinase 13 (MMP-13). These results suggest that DDR1 suppression may enhance ADSC chondrogenesis by enhancing the expression of chondrogenic genes and cartilaginous matrix deposition. We proposed that the suppression of DDR1 in ADSCs may be a candidate strategy of genetic modification to optimize ADSC-based articular cartilage tissue engineering.