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.