Tauroursodeoxycholic acid inhibits TNF-α-induced lipolysis in 3T3-L1 adipocytes via the IRE-JNK-perilipin-A signaling pathway

The present study investigated the effects of tauroursodeoxycholic acid (TUDCA) on the lipolytic action of tumor necrosis factor (TNF)-alpha in 3T3-L1 adipocytes. Following treatment with TNF-alpha, cell viability was determined by MTT assay to select the optimum concentration and duration of TNF-alpha treatment in 3T3-L1 adipocytes. Intracellular lipid droplet dispersion and glycerin content in culture media were determined to evaluate the effect of TUDCA on TNF-alpha-induced lipolysis in 3T3-L1 adipocytes. Western blotting was performed to detect protein expression levels of perilipin-A and protein markers of endoplasmic reticulum stress: Immunoglobulin-binding protein (BiP), inositol-requiring enzyme (IRE), c-Jun N-terminal kinase (JNK), phosphorylated (p)-IRE and p-JNK. Following treatment with 50ng/ml TNF-alpha for 24 h, glycerin content increased significantly and lipid droplets were dispersed. Glycerin content was reduced significantly and dispersal of lipid droplets reduced following pretreatment of 3T3-L1 adipocytes with 1 mmol/l TUDCA. TNF-alpha additionally activated the expression of BiP, p-IRE and p-JNK in a time-dependent manner; following pretreatment of 3T3-L1 adipocytes with 1 mmol/l TUDCA, the expression levels of these three proteins decreased. Therefore, TUDCA may inhibit TNF-alpha-induced lipolysis in 3T3-L1 adipocytes and reduce production of free fatty acids. Its underlying molecular mechanisms are potentially associated with the inhibition of activation of the IRE-JNK signaling pathway, which influences perilipin-A expression levels.