Profiling of the secreted proteins during 3T3-L1 adipocyte differentiation leads to the identification of novel adipokines

Adipose tissue is an endocrine organ capable of secreting a number of adipokines with a role in the regulation of adipose tissue and whole-body metabolism. We used two-dimensional gel electrophoresis combined with mass spectrometry to profile the secreted proteins from (pre)adipocytes. The culture medium of 3T3-L1 cells during adipocyte differentiation was screened, and 41 proteins that responded to blocking of secretion by 20°C treatment and/or brefeldin A treatment were identified. Prohibitin, stress-70 protein, and adhesion-regulating molecule 1 are reported for the first time as secreted proteins. In addition, procollagen C-proteinase enhancer protein, galectin-1, cyclophilin A and C, and SF20/IL-25 are newly identified as adipocyte secreted factors. Secretion profiles indicated a dynamic environment including an actively remodeling extracellular matrix and several factors involved in growth regulation.Received 15 June 2004; received after revision 26 July 2004; accepted 2 August 2004     

Protein profiling of 3T3-L1 adipocyte differentiation and (tumor necrosis factor α-mediated) starvation

The increased incidence of obesity and related disorders in Western societies requires a thorough understanding of the adipogenic process. Data at the protein level of this process are scarce. Therefore we performed a proteome analysis of differentiating and starving 3T3-L1 cells using two-dimensional gel electrophoresis combined with mass spectrometry. Effects of different starvation conditions were examined by subjecting 3T3-L1 adipocytes to caloric restriction, either in the absence or the presence of the lipolysis inducer tumor necrosis factor-. Ninety-three differentially expressed proteins were found during differentiation and starvation of 3T3-L1 cells, 50 of which were identified. GenMAPP/MAPP-finder software revealed a non-reciprocal regulation of the glycolytic pathway during 3T3-L1 differentiation followed by starvation. Furthermore, proteins involved in growth regulation, cytoskeletal rearrangements and protein modification, 16 of which have not been described before in 3T3-L1 cells, were identified. In conclusion, our data provide valuable information for further understanding of the adipogenic process.Received 9 November 2004; received after revision 21 December 2004; accepted 28 December 2004     

Adipocyte extracellular matrix composition, dynamics and role in obesity

The central role of the adipose tissue in lipid metabolism places specific demands on the cell structure of adipocytes. The protein composition and dynamics of the extracellular matrix (ECM) is of crucial importance for the functioning of those cells. Adipogenesis is a bi-phasic process in which the ECM develops from a fibrillar to a laminar structure as cells move from the commitment phase to the growth phase characterized by storage of vast amounts of triglycerides. Mature adipocytes appear to spend a lot of energy on the maintenance of the ECM. ECM remodeling is mediated by a balanced complement of constructive and destructive enzymes together with their enhancers and inhibitors. ECM remodeling is an energy costing process regulated by insulin, by the energy metabolism, and by mechanical forces. In the obese, overgrowth of adipocytes may lead to instability of the ECM, possibly mediated by hypoxia.