Palmitate-induced ER stress and inhibition of protein synthesis in cultured myotubes does not require Toll-like receptor 4

Abstract

Saturated fatty acids, such as palmitate, are elevated in metabolically dysfunctional conditions like type 2 diabetes mellitus. Palmitate has been shown to impair insulin sensitivity and suppress protein synthesis while upregulating proteolytic systems in skeletal muscle. Increased sarco/endoplasmic reticulum (ER) stress and subsequent activation of the unfolded protein response may contribute to the palmitate-induced impairment of muscle protein synthesis. In some cell types, ER stress occurs through activation of the Toll-like receptor 4 (TLR4). Given the link between ER stress and suppression of protein synthesis, we investigated whether palmitate induces markers of ER stress and protein synthesis by activating TLR4 in cultured mouse C2C12 myotubes. Myotubes were treated with vehicle, a TLR4-specific ligand (lipopolysaccharides), palmitate, or a combination of palmitate plus a TLR4-specific inhibitor (TAK-242). Inflammatory indicators of TLR4 activation (IL-6 and TNFα) and markers of ER stress were measured, and protein synthesis was assessed using puromycin incorporation. Palmitate substantially increased the levels of IL-6, TNF-α, CHOP, XBP1s, and ATF 4 mRNAs and augmented the levels of CHOP, XBP1s, phospho-PERK and phospho-eIF2α proteins. The TLR4 antagonist attenuated both acute palmitate and LPS-induced increases in IL-6 and TNFα, but did not reduce ER stress signaling with either 6 h or 24 h palmitate treatment. Similarly, treating myotubes with palmitate for 6 h caused a 43% decline in protein synthesis consistent with an increase in phospho-eIF2α, and the TLR4 antagonist did not alter these responses. These results suggest that palmitate does not induce ER stress through TLR4 in muscle, and that palmitate impairs protein synthesis in skeletal muscle in part by induction of ER stress.

İnsan kaynaklı karaciğer (HepG2) hücrelerinde palmitat ile oluşturulan yağlanmanın paraoksonaz-1 ve paraoksonaz-3 enzimlerine etkisi

“…Unchanged PON1 protein levels in palmitate-induced steatosis could have resulted from the incubation of cells with palmitate for a limited time. It is also known that palmitate induces endoplasmic reticulum stress and inhibits protein synthesis [34]. This may also be responsible from unchanged PON1 proteins and arylesterase activities in our study.…”

Whey Peptides Stimulate Differentiation and Lipid Metabolism in Adipocytes and Ameliorate Lipotoxicity-Induced Insulin Resistance in Muscle Cells

“…Palmitate is an inducer of ER stress and inflammation, both of which are implicated in insulin resistance [39,40]. Therefore, we examined whether whey peptides alter markers of palmitate-induced ER stress and inflammation.…”

Catestatin improves insulin sensitivity in diet-induced obese mice: in vivo and in silico validation

“…How does CST alleviate ER stress? Inflammation has been reported to influence ER stress (88,89). Conversely, ER stress has been implicated in several inflammatory diseases including obesity and diabetes, inflammatory bowel diseases, arthritis and spondyloarthropathies, neurodegenerative and neuromuscular inflammatory diseases, and numerous forms of respiratory inflammation (65,(90)(91)(92)(93)(94).…”