Injured tendons heal slowly and often result in the formation of mechanically and functionally inferior fibrotic scar tissue or fibrous adhesions. This study investigated the use of tendon-derived stem cells (TDSCs) for tendon repair in a rat patellar tendon window defect model. Fibrin glue constructs with or without GFP-TDSCs were transplanted into the window defect. The patellar tendons were harvested for histology, ex vivo fluorescent imaging and biomechanical test at various time points up to week 4. Our results showed that TDSCs significantly enhanced tendon healing as indicated by the increase in collagen production as shown by hematolxylin stain-ability of the tissue, improvement of cell alignment, collagen fiber alignment and collagen birefringence typical of tendon. The labeled cells were observed at weeks 1 and 2 and became almost undetectable at week 4. Both the ultimate stress and Young's modulus were significantly higher in the TDSCs group compared to those in the fibrin glue group at week 4. In conclusion, TDSCs promoted earlier and better repair in a rat patellar tendon window defect model.
This study aimed to investigate the effect of repetitive tensile loading on the expression of BMP-2 and the effect of BMP-2 on the osteogenic differentiation of tendon-derived stem cells (TDSCs) in vitro. Repetitive stretching was applied to TDSCs isolated from rat patellar tendon at 0%, 4%, and 8%, 0.5 Hz. The expression of BMP-2 was detected by Western blotting and qPCR. To study the osteogenic effects of BMP-2 on TDSCs, BMP-2 was added to the TDSC monolayer for the detection of ALP activity and calcium nodule formation in a separate experiment. TDSCs adhered, proliferated, and aligned along the direction of externally applied tensile force while they were randomly oriented in the control group. Western blotting showed increased expression of BMP-2 in 4% and 8% stretching groups but not in the control group. Up-regulation of BMP-2 mRNA was also observed in the 4% stretching group. BMP-2 increased the osteogenic differentiation of TDSCs as indicated by higher ALP cytochemical staining, ALP activity, and calcium nodule formation. Repetitive tensile loading increased the expression of BMP-2 and addition of BMP-2 enhanced osteogenic differentiation of TDSCs. Activation of BMP-2 expression in TDSCs during tendon overuse might provide a possible explanation of ectopic calcification in calcifying tendinopathy. Keywords: tendon-derived stem cells; calcifying tendinopathy; osteogenic differentiation; BMP-2; mechanical stimulation Calcifying tendinopathy is a tendon disorder with calcium deposits in the mid-substance presented with symptoms including chronic activity-related pain. It is a special case of tendinopathy and the presence of calcified deposits in calcifying tendinopathy worsens its clinical manifestations. Its underlying pathogenesis is poorly understood and treatment is usually symptomatic. Understanding the pathogenesis of calcifying tendinopathy is essential for its effective evidence-based management.Chondrocytes phenotype/markers were expressed in clinical samples of tendinopathy and calcifying tendinopathy.1,2 We reported the presence of chondrocyte phenotype and ectopic ossification in a calcifying tendinopathy model 3 and the expression of bone morphogenetic protein-2 (BMP-2) protein at those sites, 4 suggesting that BMP-2 might be involved in the pathogenesis. This was further supported by the ectopic overexpression of BMPs in the subacromial bursa of patients with chronic degeneration of rotator cuff. 5Tendons harbored stem cells (tendon-derived stem cells, TDSCs) that could differentiate into chondrocytes and osteoblasts. 6 As we observed earlier expression of BMP-2 mRNA and protein at week 2 in healing tendon cells, before the time of its appearance in chondrocyte-like cells and calcified deposits in our
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