Conclusion
Our study demonstrated a critical role of repeated UCMSCs dosing on preserving SFCs function, cartilage structure and inhibiting synovitis during OA progression, and thus provided mechanistic proof of evidence for the use of UCMSCs on OA patients in the future. The translational potential of this article: UCMSCs are a relatively "young" stem cell, and noninvasively collectible. In our study, we clearly demonstrated that it could effectively delay OA progression, possibly through reserving SFCs function and inhibiting synovitis. Therefore, it could be a new promising therapeutic cell source for OA after further clinical trials.
Methods
Intra-articular injection of 0.3 mg MIA in 50 μL saline was performed on the left knee of the 200 g weight male Sprague-Dawley rat to induce rat knee OA. A single dose of 2.5 × 105 undifferentiated UCMSCs one day after MIA or three-time intra-articular injection of 2.5 × 105 UCMSCs on Days 1, 7 and 14 were given, respectively. Four weeks after MIA, joints were harvested and processed for paraffin sections. Safranine-O staining, haematoxylin and eosin staining and immunohistochemistry of MMP-13, ADAMTS-5, Col-2, CD68 and CD4 were performed to observe cartilage erosion and synovium. For in vitro studies, migration ability of cartilage superficial layer cells (SFCs) by UCMSCs were accessed by transwell assay. Furthermore, catabolism change of MIA-induced SFCs by UCMSCs was performed by real-rime polymerase chain reaction of Col-X and BCL-2 genes. CCK-8 assay was performed to check proliferation ability of SFCs by UCMSCs-conditioned media. Result: In this study, we locally injected human UCMSCs, which is highly proliferative and noninvasively collectible, into MIA-induced rat knee OA. An important finding is on obviously ameliorated cartilage erosion and decreased OA Mankin score by repeated UCMSCs injection after MIA injection compared with single injection, both of which attenuated OA progression compared with vehicle. Interestingly, we observed significantly increased number of SFCs on the articular cartilage surface, probably related to elevated proliferation, mobilisation and inhibited catabolism marker: Col-X and BCL-2 gene expression of cultured SFCs by UCMSCs-conditioned media treatment in vitro. In addition to the change of unique SFCs, catabolism markers of ADAMTS-5 and MMP-13 were substantially upregulated in the whole cartilage layer chondrocytes as well. Strikingly, MIA-induced inflammatory cells infiltration, on both CD4+ Th cells and CD68+ macrophages, and hyperplasia of the synovium, which was alleviated by repeated UCMSCs injection.