The mechanisms through which bone marrow adipocytes might influence differentiation and function of osteoblasts are not completely understood. To investigate the direct effects of bone marrow fat cells on osteoblast function, an ex vivo co-culture system was utilized comprising either primary fat cells or differentiated 3T3-L1 adipocytes and osteoblastic cells on transwells. In co-culture, both adipocytes and osteoblastic cells were differentiated into adipocytes or osteoblasts, respectively, before culturing on transwells. Co-culture with either primary fat cells or fully differentiated 3T3-L1 adipocytes significantly decreased mRNA and protein expression of runt-related transcription factor 2 (Runx2) in osteoblastic cells. An increase in mRNA and protein expression of peroxisome proliferator-activated receptor ? (PPAR?) occurred concomitantly with the reduction of Runx2 expression. Adiponectin concentration was increased in the media by co-culture. In addition, co-culture with conditioned media from fat cells increased PPAR? promoter activity and decreased Runx2 promoter activity. Knockdown of PPAR? or adiponectin receptor 1 in osteoblastic cells by siRNA prevented the down-regulation of mRNA expression of Runx2 in osteoblastic cells cultured with fully differentiated 3T3-L1 cells. Furthermore, co-transfection with PPAR? decreased Runx2 promoter activity. A marker of osteogenesis, alkaline phosphatase activity in osteoblastic cells was significantly decreased by co-culture. Annexin V/propidium iodide staining showed that co-culture did not induce apoptosis in osteoblastic cells. Thus, we conclude that adipocytes modulate key metabolic functions of osteoblasts through the release of secretory products. PPAR? plays a key role in mediating the effects of adipocytes on osteoblasts.
View details for DOI 10.1002/jcp.22291
View details for Web of Science ID 000284191100024
View details for PubMedID 20589837