title: TNF-α knockdown alleviates palmitate-induced insulin resistance in C2C12 skeletal muscle cells.
abstract: Insulin resistance is a cardinal feature of Type 2 Diabetes (T2D), which accompanied by lipid accumulation and TNF-α overexpression in skeletal muscle. The role of TNF-α in palmitate-induced insulin resistance remained to be elucidated. Here, we assessed effects of TNF-α knockdown on the components of insulin signaling pathway (IRS-1 and Akt) in palmitate-induced insulin resistant C2C12 skeletal muscle cells. To reduce TNF-α expression, C2C12 cells were transduced with TNF-α-shRNA lentiviral particles. Afterwards, the protein expression of TNF-α, IRS-1, and Akt, as well as phosphorylation levels of IRS-1 and Akt were evaluated by western blot. We also measured insulin-stimulated glucose uptake in the presence and absence of palmitate. TNF-α protein expression in C2C12 cells significantly increased by treatment with 0.75 mM palmitate (P < 0.05). In TNF-α knockdown cells, the protein expression level of TNF-α was significantly decreased by almost 70% (P < 0.01) compared with the control cells. Our results also revealed that, in control cells, palmitate treatment significantly reduced the insulin-induced phosphorylations of IRS-1 (Tyr632) and Akt (Ser473) by 60% and 66% (P < 0.01), respectively. Interestingly, these phosphorylations, even in the presence of palmitate, were not significantly reduced in TNF-α knockdown cells with respect to the untreated control cells (P > 0.05). Furthermore, palmitate significantly reduced insulin-dependent glucose uptake in control cells, however, it was not able to reduce insulin-stimulated glucose uptake in TNF-α knockdown cells in comparison with the untreated control cells (P < 0.01). These findings indicated that TNF-α down-regulation maintains insulin sensitivity, even in the presence of palmitate, therefore, TNF-α inhibition could be a good strategy for the treatment of palmitate-induced insulin resistance.
authors.affiliation: Department of Clinical Biochemistry, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran.
authors.forename: Karimeh
authors.initials: K
authors.lastname: Haghani
authors.affiliation: Student Research Committee, Ilam University of Medical Sciences, Ilam, Iran.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Pashaei
authors.affiliation: Department of Clinical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Sanaz
authors.initials: S
authors.lastname: Vakili
authors.affiliation: Department of Clinical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Gholamreza
authors.initials: G
authors.lastname: Taheripak
authors.affiliation: Department of Clinical Biochemistry, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran. Electronic address: bakhtiyaribio@gmail.com.
authors.forename: Salar
authors.initials: S
authors.lastname: Bakhtiyari
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D055785:Gene Knockdown Techniques; D007333:Insulin Resistance; D051379:Mice; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D019308:Palmitic Acid / Q000494:pharmacology*; D010766:Phosphorylation; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D014409:Tumor Necrosis Factor-alpha; D019308:Palmitic Acid
keywords: Insulin resistance; Knockdown; Palmitate; Short hairpin RNA; TNF-α