Palmitate-induced ER stress and inhibition of protein synthesis in cultured myotubes does not require Toll-like receptor 4.
Level 5 - mechanism / opinion, no new human data
Bench research / in vitro cell culture experiment without human subjects.
PubMed 29329354 · doi:10.1371/journal.pone.0191313
What was done
Cultured mouse C2C12 myotubes were treated with vehicle, lipopolysaccharide (a TLR4 agonist), palmitate, or palmitate combined with the TLR4-specific inhibitor TAK-242 for 6 or 24 hours. Investigators measured inflammatory markers (IL-6 and TNF-α mRNA), endoplasmic reticulum (ER) stress markers (CHOP, XBP1s, and ATF4 mRNA; CHOP, XBP1s, phospho-PERK, and phospho-eIF2α protein), and rates of protein synthesis using puromycin incorporation.
What was found
Palmitate increased mRNA levels of IL-6, TNF-α, CHOP, XBP1s, and ATF4, and elevated CHOP, XBP1s, phospho-PERK, and phospho-eIF2α protein levels. The TLR4 antagonist TAK-242 attenuated palmitate- and LPS-induced increases in IL-6 and TNF-α mRNA, but had no effect on ER stress signaling markers at 6 or 24 hours. Palmitate treatment for 6 hours caused a 43% decline in protein synthesis alongside increased phospho-eIF2α, and TAK-242 did not prevent this decline. Exact baseline quantities and fold-changes beyond the 43% figure were not provided in the abstract.
Why it matters
This study shows that palmitate suppresses muscle protein synthesis and induces ER stress independently of TLR4 inflammatory signaling, clarifying lipid-induced metabolic pathways in skeletal muscle.
Limits
The study was conducted entirely in an immortalized mouse cell line (C2C12 myotubes) in vitro, which may not replicate in vivo human skeletal muscle physiology. Replicate numbers (n) and dose-response data were not reported in the abstract.
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