INTERLEUKIN-10 INHIBITS TRANSFORMING GROWTH-FACTOR-BETA (TGF-BETA) SYNTHESIS REQUIRED FOR OSTEOGENIC COMMITMENT OF BONE-MARROW CELLS

Interleukin 10 (IL-10) suppressed TGF-beta synthesis in mouse bone mar row cultures. Coincidingly, IL-10 down-regulated the production of bon e proteins including alkaline phosphatase (ALP), collagen and osteocal cin, and the formation of mineralized extracellular matrix. The mAb 1D 11.16 which neutralizes TGF-beta 1 and TGF-beta 2, induced suppressive effects comparable to IL-10 when administered before the increase of cell proliferation in the culture. It appears that mainly TGF-beta 1 p lays a role in this system since (a) TGF-beta 2 levels were undetectab le in supernatants from osteogenic cultures, (b) no effect was observe d when the anti-TGF-beta 2 neutralizing mAb 4C7.11 was added and (c) t he suppressive effect of IL-10 could be reversed by adding exogenous T GF-beta 1. It is unlikely that TGF-beta 1 modulates osteogenic differe ntiation by changing the proliferative potential of marrow cells since 1D11.16 did not affect [H-3]thymidine ([H-3]TdR) incorporation or the number of fibroblast colony forming cells (CFU-F) which harbor the os teoprogenitor cell population. Furthermore, 1D11.16 did not alter [H-3 ]TdR uptake by the cloned osteoprogenitor cell lines MN7 and MC3T3. Li ght and scanning electron microscopy showed that IL-10 and 1D11.16 ind uced comparable morphological changes in the marrow cultures. Control cultures contained flat adherent cells embedded in a mineralized matri x. In contrast, IL-10 and 1D11.16 treated cultures were characterized by round non-adherent cells and the absence of a mineralized matrix. I n this study, the mechanism by which IL-10 suppresses the osteogenic d ifferentiation of mouse bone marrow was identified as inhibition of TG F-beta 1 production which is essential for osteogenic commitment of bo ne marrow cells.