SYNOPSIS
Adipocytokines are a group of adipocyte-derived biologically active molecules, including adiponectin, leptin, tumor necrosis factor-α (TNF-α), resistin. A proteolytic cleavage product of adiponectin/Acrp30, gAcrp30, is found to circulate in plasma and to have a three-dimensional structure similar to that of TNF-α. In this study, we demonstrated the expression of adiponectin receptors in cultured pro-osteoblastic cells, and investigated the influences of gAcrp30 and TNF-α on osteoblast differentiation.
RT-PCR analysis demonstrated the expression of transcripts for both adiponectin receptors, AdipoR1 and AdipoR2, in murine pro-osteoblastic cell line, MC3T3-E1. Both gAcrp30 and TNF-α suppressed mRNA levels of type I collagen and RANKL compared with time-matched controls. Interestingly, gAcrp30 had no significant influence on the promotion of osteocalcin expression induced by the stimulation of ascorbic acid and β-glycerophosphate, although TNF-α inhibited the increase of osteocalcin expression.
These results indicated that adiponectin may not affect osteoblast differentiation but may suppress osteoclastogenesis in an endocrine manner, while TNF-α may inhibit the differentiation of pro-osteoblastic cells.

Key words: adiponectin, TNF-α, osteoblast