Synovitis has been shown to play a role in pathophysiology of OA promoting cartilage destruction and pain. Synovium is mainly composed of synovial fibroblast (SF) and macrophage (SM) that guide synovial inflammation. Adipose stromal cells (ASC) promising candidate for cell therapy in OA are able to counteract inflammation. Two different subsets of macrophages have been described showing a pro-inflammatory (M1) and an anti-inflammatory (M2) phenotype. Macrophage markers: CD68, CD80 (M1-like) and CD206 (M2-like) were evaluated in osteoarthritic synovial tissue. GMP-clinical grade ASC were isolated from subcutaneous adipose tissue and M1-macrophages were differentiated from CD14+ obtained from peripheral blood of healthy donors. ASC were co-cultured in direct and indirect contact with activated (GM-CSF+IFNγ)-M1 macrophages for 48h. At the end of this co-culture we analyzed IL1β, TNFα, IL6, MIP1α/CCL3, S100A8, S100A9, IL10, CD163 and CD206 by qRT-PCR or immunoassay. PGE2 blocking experiments were performed. In moderate grade OA synovium we found similar percentages of CD80 and CD206. M1-activated macrophage factors IL1β, TNFα, IL6, MIP1α/CCL3, S100A8 and S100A9 were down-modulated both co-culture conditions. Moreover, ASC induced the typical M2 macrophage markers IL10, CD163 and CD206. Blocking experiments showed that TNFα, IL6, IL10, CD163 and CD206 were significantly modulated by PGE2. We confirmed the involvement of PGE2/COX2 also in CD14+ OA synovial macrophages. In conclusion we demonstrated that ASC are responsible for the switching of activated-M1-like to a M2-like anti-inflammatory phenotype, mainly through PGE2. This suggested a specific role of ASC as important determinants in therapeutic dampening of synovial inflammation in OA.

Bone formation proceeds through two distinct processes. One involves the deposition of bone by osteoblasts (intramembranous ossification) and another through the remodeling of an intermediate cartilaginous matrix formed by chondrogenic differentiation of mesenchymal stem/stromal cells (MSCs) aggregates – a process called endochondral ossification (EO). EO is responsible for formation of long bones during development and most prevalent during facture repair upon callus formation. In adult bone injuries MSCs from periosteum form bone via EO whereas MSCs from bone marrow are primarily differentiate to osteoblast in vivo. We hypothesized that the unique biophysical and biochemical properties of bone mineral phase has a role in programming MSCs. Using a biomimetic bone like apatite (BBHAp) as surrogate for bone mineral phase, we studied the chondrogenic differentiation of human marrow derived MSCs and observed that the BBHAp dictates MSCs fate and strictly dictates the pathway of bone formation in vivo. Through exhaustive dissection of the signaling pathways at play, a prominent role of PTH1R in modulating the effects imposed by the BBHAp has been unraveled. These fundamental insights gained in how bone microenvironment might alter fate of MSCs has important implications for bone repair and regeneration therapies.

Summary

Nasal Chondrocytes are safe and feasible for tissue engineering approaches in articular cartilage repair.

Summary Statement

This study reports that hMSC can be manipulated in order to engineer a bone organ, characterised by mature osseous and vascular components and capable to recruit, host and maintain functional HSCs.