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Divergent effects of DHA treatment and AMPK activation on protein synthesis rate and signaling in palmitate‐treated skeletal muscle
Author(s) -
Perry Ben Douglas,
Rahnert Jill A,
Xie Yang,
Zhang Peng,
Espinosa Daniel,
Price S. Russ
Publication year - 2017
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.31.1_supplement.694.8
Subject(s) - p70 s6 kinase 1 , ampk , docosahexaenoic acid , medicine , skeletal muscle , endocrinology , phosphorylation , protein kinase a , amp activated protein kinase , chemistry , insulin resistance , ribosomal protein s6 , polyunsaturated fatty acid , protein kinase b , insulin , biochemistry , biology , fatty acid
Circulating levels of saturated fatty acids, such as palmitate (PA), are elevated in type II diabetes mellitus. In skeletal muscle, PA impairs insulin sensitivity, induces ER stress and impairs protein synthesis. Both insulin resistance and ER stress are reversed with treatment of n‐3 polyunsaturated fatty acids like docosahexaenoic acid (DHA). However, it remains unclear whether DHA reverses the PA‐induced impairment in protein synthesis. This study investigated the effects of PA and DHA on protein synthesis and related signaling proteins, including eukaryotic initiation factor 2α (eIF2α) and p70 S6K in skeletal muscle cells. Due to its potential role in reducing ER stress and altering protein synthesis through mTOR signaling, we also investigated the effects of 5′ AMP‐activated protein kinase (AMPK) on these processes. C 2 C 12 myotubes were treated with vehicle (2% BSA), DHA (100 μM), PA (500 μM) or co‐treated with PA+DHA. Protein synthesis was inhibited after 6h (−34.7%) and 24h (−40.8%) of treatment with PA and co‐treatment with DHA restored protein synthesis to the control level; DHA alone increased protein synthesis. PA treatment for 6–24 h also increased eIF2α phosphorylation, a response that reduces protein translation; co‐treatment with DHA prevented the responses. Surprisingly, the phosphorylation of p70 S6K was increased after 6 h of PA treatment but restored to normal levels after 24 h. Moreover, AMPK phosphorylation was also increased after treatment with PA for 6 h but reduced after 24 h; in both cases, DHA co‐treatment normalized AMPK phosphorylation. Co‐treating myotubes with PA plus metformin, an activator of AMPK, caused a drastic decrease in protein synthesis and p70 S6K phosphorylation after 24 h. In summary, PA induced a global reduction in protein synthesis rate that was prevented by co‐treatment with DHA. Changes in the phosphorylation of eIF2α, but not p‐p70 S6K coincided with those in protein synthesis after both 6 and 24 h. Despite the widely reported beneficial effects of AMPK activation in PA‐treated cells, impaired protein synthesis and increased p‐eIF2α preceded the PA‐induced reduction in AMPK. Support or Funding Information Supported by NIH RO1 DK95610, NIH T32 DK007656 and VA Merit I01BX001456