The Key Role of Akt Protein Kinase in Metabolic-Inflammatory Pathways Cross-Talk: TNF-α Down-Regulation and Improving of Insulin Resistance in HepG2 Cell Line

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Author(s): Iraj Alipourfard, Salar Bakhtiyari*, Ali Gheysarzadeh, Laura Di Renzo, Antonio De Lorenzo, David Mikeladze, Atefeh Khamoushi

Journal Name: Current Molecular Medicine

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Abstract:

Background: Elevation of plasma free fatty acids as a principal aspect of type 2 diabetes maintains etiologically insulin insensitivity in target cells. TNF-α inhibitory effects on key insulin signaling pathway elements remain to be verified in insulin-resistant hepatic cells. Thus, TNF-α knockdown effects on the key elements of insulin signaling were investigated in the palmitate-induced insulin-resistant hepatocytes. The Akt serine kinase, a key protein of the insulin signaling pathway, phosphorylation was monitored to understand the TNF-α effect on probable enhancing of insulin resistance.

Methods: Insulin-resistant HepG2 cells were produced using 0.5 mM palmitate treatment and shRNA-mediated TNF-α gene knockdown and its down-regulation confirmed using ELISA technique. Western blotting analysis used to assess the Akt protein phosphorylation status.

Results: Palmitate-induced insulin resistance caused TNF-α protein overexpression 1.2-, 2.78, and 2.25- fold as compared to the control cells at post-treatment times of 8 h, 16 h, and 24 h, respectively. In the presence of palmitate, TNF-α expression showed around 30% reduction in TNF-α knockdown cells as compared to normal cells. In the TNF-α down-regulated cell, Akt phosphorylation was approximately 62% more than control cells after treatment with 100 nM insulin in conjugation with 0.5 mM palmitate.

Conclusions: The obtained data demonstrated that TNF-α protein expression reduction improved insulin-stimulated Akt phosphorylation in the HepG2 cells and decreased lipid-induced insulin resistance of the diabetic hepatocytes.

Keywords: Insulin resistance, TNF-α, Akt kinase, Palmitate, HepG2 cell, diabetes

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(E-pub Ahead of Print)
DOI: 10.2174/1566524020666200427102209
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