Spontaneous cartilage repair has recently been recognized as proof of concept in man. This team will delineate the unknown mechanisms by which mesenchymal stem cells (MSCs) in the context of the intraarticular milieu are involved in this repair activity.
Upon distraction it suggested that MSC number initially decline in the synovial fluid (SF) (figure 1A-B). MSCs present in the SF showed changes in their gene expression profile upon KJD, most clearly observed during the treatment (3 weeks; figure 1C).
GDF5 and Grem1 presented with a statistically significant increased expression (p<0.05) during treatment while FAB4 expression was decreased. ACAN, PTH1R, and DDR expression had the tendency to increase over time. ADAMTS4, SOX9 and PTHLH expression showed a trend to decrease over time.
Preliminary proteomics analysis on the SF samples of the first 5 patients indicate a clear difference can be seen in the samples before vs during and after distraction (see figure 2). Exact interpretation needs further analyses of the remaining patients. In parallel to this study we have analyzed (in collaboration with Oxford) the synovial fluid of joint distraction patients (additional group in addition to this project) for mechano-sensitive de/regenerative markers. Of the 10 markers studied 4 were significant elevated (IL-6, TGF-B, MCP-1, FGF-2), 2 significant downregulated (Activin-A, LTBP-2) and 4 were not changed (IL-8, MMP-3, TIMP-1, TSG-6). These results can give further guidance to the analyses performed in Paris.
This explorative study provides for the first-time data on changes in SF MSC number and their gene and protein expression profiles upon knee joint distraction. As such, first clues are provided for the involvement of MSCs in the regenerative process induced by joint distraction for end-stage knee OA. Final results are expected this summer. Further studies are necessary to unravel the processes involved
Worldwide, the general opinion is that OA joint cartilage cannot repair itself, as it has a limited number of cells in an abundant amount of extracellular matrix that is not vascularized. Working against this dogma, it was demonstrated that application of unloading by knee joint distraction (6 wks) leads to prolonged (>5 up to 9 yrs) intrinsic cartilage repair in combination with meaningful clinical efficacy. As this intrinsic cartilage repair activity is unique, this provides for the first time the opportunity to unravel and identify the mechanisms that are essential for this cartilage repair. The present project identified cells and metabolites that are present or induced by joint distraction to better understand and further refine joint distraction treatment.
It was studied whether intrinsic mesenchymal stem cell (MSC) activity plays a role in the observed cartilage repair activity. Synovial fluid (SF) in OA contains MSCs, of which the number is elevated in the early stages of OA. The discovery of this resident population of highly proliferative MSCs in SF whereby such cells have reproducibly good chondrogenic activity supports the concept that such MSCs, having a direct access to the damaged cartilage areas, and so may be key players in the reparative process as a result of joint distraction. A collaboration (UK/NL) has already shown that SF resident MSCs adhere to sites of cartilage injury in the canine OA model.
Pilot data (UK) using human OA joints showed an increased MSC proliferative response in subchondral bone areas directly adjacent to the denuded cartilage. Moreover, the in vitro pilot (UK) work demonstrated that the SF biochemical composition influences MSC cartilage adherence. Several mediators (cytokines, growth factors, lubricants, etc) as well as inflammatory cell subsets are changed by joint distraction as well. Within the consortium extensive expertise on delineating these ‘soluble’ and ‘inflammatory’ components of joint distraction in the OA joint (Fr) exist. A first impression is that these components are influenced by the distraction. Further analyses need to be performed to determine details. Using an animal model, we demonstrated for the first time that during the joint distraction the process is initiated but the actual repair process is most likely started after the treatment period once the joint is normally loaded again.
Although significant progress was made not all data is yet available. Additional research is necessary to enhance our understanding of the changes observed and to relate to clinical changes observed after knee joint distraction. Several follow-up studies are already initiated.