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Inhibition of Toll‐like Receptor 4 does not prevent palmitate‐induced endoplasmic reticulum stress in cultured skeletal muscle cells
Author(s) -
Perry Ben Douglas,
Rahnert Jill A,
Zheng Bin,
Price Russ
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1245.12
Subject(s) - unfolded protein response , endoplasmic reticulum , medicine , xbp1 , endocrinology , skeletal muscle , tlr4 , atf6 , lipotoxicity , chop , chemistry , biology , receptor , microbiology and biotechnology , insulin resistance , biochemistry , insulin , rna , rna splicing , gene
Chronically elevated circulating saturated fatty acids (SFA), as seen in Type 2 Diabetes Mellitus, impairs insulin sensitivity, protein synthesis, and upregulates proteolytic pathways in skeletal muscle. The SFA‐induced impairment of muscle protein synthesis is due, in part, to increased endoplasmic reticulum (ER) stress and subsequent activation of the unfolded protein response. However, the upstream receptor(s) that initiate ER stress in response to SFA in skeletal muscle are not well delineated. This study investigated the role of TLR4, which is activated by SFA and induces pro‐inflammatory signaling, on markers of ER stress and protein synthesis signaling in cultured mouse muscle cells (C 2 C 12 ). C 2 C 12 myotubes were treated with either vehicle, a TLR4‐specific ligand (lipopolysaccharides; 100 ng/mL), palmitate (SFA; 500 μM), or a combination of palmitate and TLR4‐specific inhibitor (TAK‐242, 1 μM). After 24 hours, cells were harvested and analyzed for markers of ER stress and protein synthesis using RT PCR and western blotting. Palmitate treatment substantially increased the levels of CHOP, spliced XBP1, and ATF 4 mRNAs as well as the protein expression of p‐PERK/PERK and p‐eIF2α/eIF2α. The palmitate/TLR4 inhibitor treatment unexpectedly elevated both CHOP mRNA and protein expression of p‐eIF2α/eIF2α to levels greater than palmitate alone. Compared to control, the p‐p70S6k/p70S6k ratio was reduced to a similar extent with both palmitate and palmitate/TLR4 inhibitor treatments. These data suggest that in conditions involving lipotoxicity, activation of TLR4 in skeletal muscle is not responsible for palmitate‐induced ER stress. Instead, activation of TLR4 may induce signaling which is protective during heightened ER stress in muscle. Support or Funding Information Supported by NIH RO1 DK95610, NIH T32 DK007656 and VA Merit I01BX001456