Gene expression of isoformic enzymes in arachidonate cyclooxygenase pathway and the regulation by tumor necrosis factor α during life cycle of adipocytes

Abstract

Adipocytes serve not only as a storage depot of fats but also as endocrine cells secreting adipocytokines including tumor necrosis factor α (TNFα). Using preadipogenic 3T3-L1 cells, we attempt to determine the response of adipocytes at different stages of the life cycle to TNFα with respect to the gene expression of the arachidonate cyclooxygenase (COX) pathway and the role of endogenous prostaglandins (PGs). The gene expression analysis of the COX pathway revealed the marked increase in mRNA and protein levels of COX-2 in response to TNFα in preadipocytes, whereas COX-1 was expressed constitutively. Moreover, the cells at different cycle stages exhibited the specific gene expression of isoformic enzymes of prostaglandin (PG) synthases for PGs of the D 2, E 2, and F 2α series upon exposure to TNFα. The treatment of preadipocytes with TNFα along with calcium ionophore A23187 resulted in the stimulated formation of PGE 2 and PGF 2α, attenuating the apoptotic cell death induced by TNFα alone. The response of adipocytes to synthesize these PGs declined during the differentiation and maturation phases. The cells during the differentiation phase were the most sensitive to TNFα in terms of the decrease in adipogenesis without the mediation of endogenous PGs. TNFα was also effective in suppressing adipogenesis during the maturation process. Taken together, TNFα can control cell number of preadipocytes as well as the size of fat storage in mature adipocytes. The action of TNFα on preadipocytes can be modulated by the production of endogenous PGs through the induction of COX-2.