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TRB3 Regulates Protein Turnover in Mouse Skeletal Muscle
Author(s) -
Choi Ran Hee,
McConahay Abigail,
Hardee Justin P,
Carson James A,
Hirshman Michael F,
Goodyear Laurie J,
Koh HoJin
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.1021.5
Subject(s) - skeletal muscle , denervation , medicine , endocrinology , protein kinase b , muscle atrophy , protein turnover , pi3k/akt/mtor pathway , protein degradation , insulin resistance , genetically modified mouse , biology , phosphorylation , chemistry , insulin , transgene , signal transduction , microbiology and biotechnology , protein biosynthesis , biochemistry , gene
Skeletal muscle atrophy is a critical condition associated with several diseases, including cancer cachexia, diabetes, and cardiac failure. Skeletal muscle mass loss is related to disrupted protein turnover involving increased protein degradation and suppressed protein synthesis. The IGF1/PI3K/Akt pathway has emerged as a major signaling cascade of protein turnover through mTOR (protein synthesis) and FOXOs (protein degradation) signaling, and is activated by anabolic signals such as insulin. Recently, TRB3, a mammalian homologue of Drosophila Tribbles 3 , has been found in multiple tissues, including liver, fat, pancreas, and skeletal muscle, and negatively regulates Akt via direct binding to its phosphorylation sites (S 473 and T 308 ). Although increased TRB3 expression has been associated with insulin resistance in in vitro and in vivo models, its role in the regulation of skeletal muscle mass is not known. Here, we tested the hypothesis that TRB3 negatively regulates skeletal muscle mass in denervation‐induced atrophy. We performed denervation of the sciatic nerve in one leg while the contralateral leg served as a control. At 9 days post‐denervation, there was a robust increased in TRB3 mRNA (12.2‐fold) and protein expression (16.2‐fold) compared to the control. In addition, skeletal muscle weight was reduced by 20–30% after 9 days of denervation, and insulin‐stimulated IRS1 Y 612 (23%, P<0.01) and Akt T 308 (22%, P<0.001) phosphorylation was attenuated. Muscle‐specific transgenic mice overexpressing TRB3 (TRB3TG) exhibited reduced skeletal muscle mass compared to wild type (TA; 10%, P=0.056, Gas; 20%, P=0.079), with substantially elevated mRNA expression of skeletal muscle specific‐ubiquitin ligases, Atrogin‐1 (WT:1.00±0.33, TG: 1.6±0.16, A.U.; P=0.073) and MURF‐1 (WT: 1.00±0.1, TG: 1.7±0.2, A.U.; P<0.01). We then examined if skeletal muscle TRB3 overexpression would affect protein synthesis measured by assessing the incorporation of puromycin into nascent peptide chains. Muscle protein synthesis in TRB3TG mice was reduced by 60%. Grip strength was also decreased by 15% in TRB3TG mice when compared to wild type. However, muscle‐specific TRB3 overexpression did not accelerate or inhibit denervation‐induced atrophy. In contrast, whole body TRB3 knockout mice (TRB3KO) displayed a 90% decrease in Atrogin‐1 protein expression compared to wild type (WT:1.00±0.03, KO: 0.1±0.01, A.U.; P<0.001). Furthermore, TRB3KO mice that received denervation for 9 days tended to prevent increasing of Atrogin‐1 (WT: 2.27±0.6; KO:1.39±0.07, A.U.; P=0.33) and MURF‐1 (WT: 2.6±0.5; KO: 1.72±0.23, A.U; P=0.093) protein expression compared to wild type. These data suggest that TRB3 could be a critical regulator of skeletal muscle mass under atrophic conditions and could be a target for therapeutic treatment.