Abnormal formation of new bone tissue has been observed in osteoarthritis (OA), a degenerative disease affecting joint, cartilage and bone. A series of events characterize OA, including degradation of cartilage matrix components associated with increased synthesis and activation of pro-inflammatory mediators and enhanced expression of bone erosion factors and up-regulation of bone remodeling proteins. Although, much is known about the pro-inflammatory and anti-inflammatory cytokines milieu contributing to bone remodeling and repair, the immune cell source of these factors and their reciprocal interaction are poorly understood. This is an important topic of investigation as several immune cell lineages were shown to regulate mesenchymal stem cell (MSC) migration and osteogenic capacity on one side and cartilage degradation on the other. We have documented that NK cells and neutrophils have a disease-promoting role in experimental OA. Since our preliminary observations indicate a role of NK cells in the repair phase of the disease, we hypothesized that NK cell interaction with other immune cells could affect the local growth factor environment, regulating osteogenesis and chondrogenesis.
This proposal is aimed to analyze the ability of NK cells to alter MSC chondrogenic/osteogenic potential in vitro. We will study how NK cells modulate the osteogenic vs chondrogenic differentiation of MSCs in normal conditions or in conditions guiding (i.e. by BMP-2, GDF-5 supplementation) MSC differentiation toward a specific cell lineage. We will investigate the contribution of CXCR3 in the migration of NK cells at the damage/remodeling phase of collagenase-induced OA and in MSC regenerative capacity. The study will provide novel facets on the NK cell-based mechanisms controlling bone/cartilage repair that will be of interest for regenerative medicine.
The proposed objectives will contribute to clarify the role of NK cells in growth factor-mediated differentiation of MSC, paving the way to in vivo analyses aimed at defining the role of immune cell-produced factor (i.e. IFN-gamma) in growth factor-mediated accelerated differentiation of MSC. We previously showed that CXCL10/CXCR3 chemokine/chemokine receptor axis is crucial for osteoarthritis disease establishment and progression, being CXCL10 increased in synovial fluid of CIOA mice and CXCR3-/- mice protected from disease development. CIOA CXCR3-/- mice had significantly reduced synovial NK cells and macrophages at day 3 after injury. Interestingly, our preliminary data point to a direct role of CXCR3 ligands on NK cell migration to CIOA synovium as in vitro migration to synovial fluids collected from CIOA mice joints was completely abrogated by CXCL10 blocking antibodies. Nevertheless, CXCR3/ligand interaction may exert a more complex role in vivo, as the protective effects promoted by CXCR3 deficiency were superior to the effects of NK cell depletion. New experiments will help to determine the contribution of the chemokine receptor CXCR3 in MSC differentiation potential. These set of data will be instrumental to determine the role of CXCR3 in MSC function and interaction with NK cells in the damaged joint.