In vitro aging of 3T3-L1 mouse adipocytes leads to altered metabolism and response to inflammation

We used an in vitro model to evaluate the effects of cellular aging and inflammation on the gene expression and protein secretion profiles of adipocytes. 3T3-L1 mouse preadipocytes were cultured according to standard conditions and analyzed at different time points both at the basal state and after an acute stimulation with LPS. The mRNA levels of CCAAT/enhancer-binding protein (C/EBP)alpha, peroxisome proliferator-activated receptor (PPAR)gamma and S100A1 were maximal during adipocyte differentiation and then significantly decreased. The expression of the GLUT4 and IRS-1 genes peaked during differentiation and then decreased in aged cells. The mRNA levels and secretion of adiponectin, quickly rose as adipocytes matured and then declined. The mRNA levels of IL6, as well as its secretion, increased as preadipocytes matured and became old cells; a similar trend was also found for MCP-1. LPS decreased the mRNA levels of C/EBP alpha and PPAR gamma at all time points, as well as those of GLUT4, IRS-1 and adiponectin. LPS significantly increased the mRNA levels of IL-6, as well as its secretion, with a similar trend also observed for MCP-1. These data suggest that aging adipocytes in vitro show a decline in pro-adipogenic signals, in genes involved in glucose metabolism and cytoskeleton maintenance and in adiponectin. These changes are paralleled by an increase in inflammatory cytokines; inflammation seems to mimic and amplify the effects of cellular aging on adipocytes.