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. Author manuscript; available in PMC: 2013 May 22.
Published in final edited form as: Nat Rev Rheumatol. 2009 May 26;5(7):365–372. doi: 10.1038/nrrheum.2009.102

Figure 1.

Figure 1

PPARγ regulates bone mass in bone marrow milieu. First step of regulation resides in the determination of lineage allocation of mesenchymal stem cells. Several transcription factors including PPARγ and C/EBPs govern adipogenesis, while transcription factors such as Runx2 and Osx are necessary for osteoblastogenesis. PPARγ favors adipogenesis, and suppresses osteoblastogenesis partly through inhibiting Runx2 function, resulting in the reduction of osteoblast pool in bone marrow. Second, PPARγ stimulates osteoclastogenesis by enhancing c-fos expression in osteoclast precursor cell. Third, secretory factors including inflammatory, leptin, adipsin, adiponectin and resistin are also produced by marrow adipocytes. These cytokines are possibly acting on osteoblasts in a paracrine manner and suppressing osteoblast function and/or differentiation in pathogenic conditions. PPAR: peroxisome proliferative activated receptors, C/EBP: CCAAT/enhancer binding proteins; RUNX: runt-related transcription factor, Osx: osterix, RANKL: receptor activator of nuclear transcription factor κB ligand, OPG: osteoprotegerin, MSC: mesenchymal stem cell, HSC: hematopoietic stem cell.