Comparative Effects of Tumor Necrosis Factor Alpha, Lipopolysaccharide, and Palmitate on Mitochondrial Dysfunction in Cultured 3T3-L1 Adipocytes

We have previously reported that dysregulated lipid metabolism and inflammation in 3T3-L1 adipocytes is attributed to tumor necrosis factor alpha (TNFα) rather than lipopolysaccharide (LPS) and palmitate (PA). In this study, we further compared the modulative effects of TNFα, LPS, and PA on mitochondrial function by treating 3T3-L1 adipocytes with TNFα (10 ng/mL), LPS (100 ng/mL), and PA (0.75 mM) individually or in combination for 24 h. Results showed a significant reduction in intracellular adenosine triphosphate (ATP) content, mitochondrial bioenergetics, total antioxidant capacity, and the mRNA expression of citrate synthase (Cs), sirtuin 3 (Sirt3), protein kinase AMP-activated catalytic subunit alpha 2 (Prkaa2), peroxisome proliferator-activated receptor gamma coactivator 1 alpha (Ppargc1α), nuclear respiratory factor 1 (Nrf1), and superoxide dismutase 1 (Sod1) in cells treated with TNFα individually or in combination with LPS and PA. Additionally, TNFα treatments decreased insulin receptor substrate 1 (Irs1), insulin receptor substrate 2 (Irs2), solute carrier family 2, facilitated glucose transporter member 4 (Slc2a4), and phosphoinositide 3 kinase regulatory subunit 1 (Pik3r1) mRNA expression. Treatment with LPS and PA alone, or in combination, did not affect the assessed metabolic parameters, while the combination of LPS and PA increased lipid peroxidation. These results show that TNFα but not LPS and PA dysregulate mitochondrial function, thus inducing oxidative stress and impaired insulin signaling in 3T3-L1 adipocytes. This suggests that TNFα treatment can be used as a basic in vitro model for studying the pathophysiology of mitochondrial dysfunction and related metabolic complications and screening potential anti-obesity therapeutics in 3T3-L1 adipocytes.