Tumor necrosis factor-α promotes lipolysis and reduces insulin sensitivity by activating nuclear factor kappa B and c-Jun N-terminal kinase in primary bovine adipocytes

Abstract

Sustained lipolysis and insulin resistance increase the risk of metabolic dysfunction in dairy cows during the transition period. Proinflammatory cytokines are key regulators of adipose tissue metabolism in nonruminants, but biological functions of these molecules in ruminants are not well known. Thus, the objective of this study was to investigate whether tumor necrosis factor-α (TNF-α) could affect insulin sensitivity and lipolysis in bovine adipocytes as well as the underlying mechanisms. Bovine adipocytes (obtained from the omental and mesenteric adipose depots) isolated from 5 Holstein female calves (1 d old) with similar body weight (median: 36.9 kg, range: 35.5-41.2 kg) were differentiated and used for (1) treatment with different concentrations of TNF-α (0, 0.1, 1, or 10 ng/mL) for 12 h; (2) pretreatment with 10 μM lipolytic agonist isoproterenol (ISO) for 3 h, followed by treatment with or without 10 ng/mL TNF-α for 12 h; and (3) pretreatment with the c-Jun N-terminal kinase (JNK) inhibitor SP600125 (20 μM for 2 h) and nuclear factor kappa B (NF-κB) inhibitor BAY 11-7082 (10 μM for 1 h) followed by treatment with or without 10 ng/ mL TNF-α for 12 h. The TNF-α increased glycerol content in supernatant, decreased triglyceride content and insulin-stimulated phosphorylation of protein kinase B suggesting activation of lipolysis and impairment of insulin sensitivity. The TNF-α reduced cell viability, upregulated mRNA abundance of Caspase 3 (CASP3), an apoptosis marker, and increased activity of Caspase 3. In addition, increased phosphorylation of NF-κB and JNK, upregulation of mRNA abundance of interleukin-6 (IL-6), TNFA, and suppressor of cytokine signaling 3 (SOCS3) suggested that TNF-α activated NF-κB and JNK signaling pathways. Furthermore, ISO plus TNF-α-activated NF-κB and JNK signaling pathway to a greater extent than TNF-α alone. Combining TNF-α and ISO aggravated TNF-α-induced apoptosis, insulin insensitivity and lipolysis. In the absence of TNF-α, inhibition of NF-κB and JNK did not alter glycerol content in supernatant, triglyceride content or insulin-stimulated phosphorylation of protein kinase B. In the presence of TNF-α, inhibition of NF-κB and JNK alleviated TNF-α-induced apoptosis, insulin insensitivity and lipolysis. Overall, TNF-α impairs insulin sensitivity and induces lipolysis and apoptosis in bovine adipocytes, which may be partly mediated by activation of NF-κB and JNK. Thus, the data suggested that NF-κB and JNK are potential therapeutic targets for alleviating lipolysis dysregulation and insulin resistance in adipocytes.

Ceramide on the road to insulin resistance and immunometabolic disorders in transition dairy cows: driver or passenger?

“…A hallmark of an inflammatory state is the release of proinflammatory cytokines, which can result in various metabolic changes, such as anorexia, lipid mobilization, diminished insulin sensitivity, and decreased milk yield ( 88 ). For example, a recent study demonstrated that TNF-α can promote apoptosis, impair insulin sensitivity, and induces a lipolytic response in bovine adipocytes ( 89 ). In addition to playing a role in lipid storage and release, the metabolism of adipose tissue actively regulates homeostasis and the inflammatory response, making it crucial for studying sphingolipid biology ( 90 ).…”

Role of Dietary Factors on DNA Methylation Levels of TNF-Alpha Gene and Proteome Profiles in Obese Men

“…Abnormal FPG concentrations and the risk of insulin resistance related to TNF-α may involve the generation of reactive oxygen species and impairment of insulin signaling through serine phosphorylation, which leads to the development of type 2 diabetes mellitus [ 24 ]. Furthermore, TNF-α promotes lipolysis and reduces insulin sensitivity by activating nuclear factor kappa B and c-Jun N-terminal kinase [ 25 ].…”

Daily Injection of the β2 Adrenergic Agonist Clenbuterol Improved Muscle Glucose Metabolism, Glucose-Stimulated Insulin Secretion, and Hyperlipidemia in Juvenile Lambs Following Heat-Stress-Induced Intrauterine Growth Restriction

“…However, lipolytic responsiveness wanes after only a few days of sustained stimulation [ 59 , 60 ], and longer periods of stimulation ultimately produce anti-lipolytic effects [ 33 ]. Inflammatory cytokines also stimulate lipolysis [ 61 ], and thus the resolution of greater circulating TNFα and IL-6 in clenbuterol-treated IUGR lambs presumably further reduced circulating NEFA. Additionally, the anti-lipogenic effects of β2 pathways [ 62 ] may explain the concurrent increase of circulating triglycerides observed with clenbuterol, although this was independent of any IUGR effects.…”