Purpose: Recent progresses in the field of mesenchymal stem cells (MSCs) have brought us to apply them for clinical applications. In the autologous MSC transplantation therapy, the selection of donor tissues for the isolation of MSCs is quite important to obtain better clinical outcomes and to reduce patient's physical burden. We have started clinical trials to regenerate intra-articular cartilagenous tissues using MSCs derived from autologous synovial membrane (Syn-MSCs). In these trials, patients must suffer synovial biopsy to prepare autologous MSCs before transplantation. We considered that synovial fluid can be another good supplier for autologous MSCs for cartilage regeneration therapy since arthrocentesis is usually performed during the normal medical examinations in the consultation rooms. We have isolated MSCs from synovial fluid (SF-MSCs) and reported that these cells also have great potential to differentiate into chondrocytic lineage in vitro. However, it is still unrevealed whether SF-MSCs have comparable potential in cartilagenous tissue regeneration with those of Syn-MSCs. This study was aimed to compare proliferation and differentiation capacity of SF-MSCs and Syn-MSCs from the same patient. Methods: Synovial membrane (Syn) and synovial fluid (SF) were harvested from the same patient who underwent total knee arthroplasty at our hospital with approval and permission (n = 14, male = 1, female = 13, average 73.0 year-old). Isolated cells were maintained upto passage 10 to compare their proliferation ability. In vitro differentiation assay was performed using passage 3 cells. Flowcytometric analyses were performed to detect distinct surface antigen expression profiles between Syn- and SF-MSCs (FACS Verse, BD Bioscience). In order to compare the cartilage repair ability of SF-MSCs and Syn-MSCs, MSCs from the same patient were transplanted to osteochondral defects created in the trochlear groove of the femur of 10-week-old Lewis Rat, and histological assessments were performed at 4 weeks and 8 weeks. Results: Proliferation rate of SF-MSCs was much slower than that of Syn-MSC, however, they continued proliferating by 70 days in culture and needed for almost 3 weeks (passage 3) to become 1 × 107 cells, which is currently required for clinical application. In vitro differentiation assays indicated that there were subtle differences in chondrogenic-, osteogenic-, and adipogenic- differentiation ability between SF- and Syn-MSCs. Flowcytometric analyses indicated that the expression of MSC-related surface antigens (CD73, CD90, and CD105) was comparable between the groups. In contrast, expressions of certain sets of cell adhesion molecules (CD51/61) and growth factor receptors (CD140a) tended to decrease in SF-MSCs. In in vivo study, there was no significant difference in ICRS score (respectively SF 3.4, Syn 3.4 at 4weeks (P = 1.0), SF 6.8, Syn 5.4 at 8weeks (P = 0.798). Both MSCs groups showed good cartilage repair and there was no significant difference in histological grading scale modified from that of Pineda et al, and Wakitani et al(respectively SF 9.8, Syn 10.2 at 4weeks (P = 0.854), SF 7.4, Syn 7.4 at 8weeks (P = 0.446)). Conclusions: In this study, we showed that SF-MSCs could be the replacement of Syn-MSCs for cartilagenous tissue regeneration therapy. Surface antigen expression analyses and in vitro differentiation assays indicated that phenotypes of SF-MSCs are quite similar with those of Syn-MSCs and have characteristics of MSCs. However, proliferation rate was lower in SF-MSCs if compared to that of Syn-MSCs (n = 12). We consider that the down-regulation of cell adhesion molecules (CD51/61; Integrin alpha v/beta 3) and a growth factor receptor (CD140a/PDGFR alpha) might be possible reasons for that (n = 2). In spite of the less proliferation ability in vitro, cartilagenous tissue regeneration ability was quite comparable between SF-MSCs and Syn-MSCs. Since arthrocentesis is less invasive than synovial biopsy, it is much advantageous to reduce patient's physical burden in transplantation therapy.
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