Gα13 ablation reprograms myofibers to oxidative phenotype and enhances whole-body metabolism
Ja Hyun Koo, Tae Hyun Kim, Shi-Young Park, Min Sung Joo, Chang Yeob Han, Cheol Soo Choi, Sang Geon Kim
Ja Hyun Koo, Tae Hyun Kim, Shi-Young Park, Min Sung Joo, Chang Yeob Han, Cheol Soo Choi, Sang Geon Kim
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Research Article Metabolism Muscle biology

Gα13 ablation reprograms myofibers to oxidative phenotype and enhances whole-body metabolism

Abstract

Skeletal muscle is a key organ in energy homeostasis owing to its high requirement for nutrients. Heterotrimeric G proteins converge signals from cell-surface receptors to potentiate or blunt responses against environmental changes. Here, we show that muscle-specific ablation of Gα13 in mice promotes reprogramming of myofibers to the oxidative type, with resultant increases in mitochondrial biogenesis and cellular respiration. Mechanistically, Gα13 and its downstream effector RhoA suppressed nuclear factor of activated T cells 1 (NFATc1), a chief regulator of myofiber conversion, by increasing Rho-associated kinase 2–mediated (Rock2-mediated) phosphorylation at Ser243. Ser243 phosphorylation of NFATc1 was reduced after exercise, but was higher in obese animals. Consequently, Gα13 ablation in muscles enhanced whole-body energy metabolism and increased insulin sensitivity, thus affording protection from diet-induced obesity and hepatic steatosis. Our results define Gα13 as a switch regulator of myofiber reprogramming, implying that modulations of Gα13 and its downstream effectors in skeletal muscle are a potential therapeutic approach to treating metabolic diseases.

Authors

Ja Hyun Koo, Tae Hyun Kim, Shi-Young Park, Min Sung Joo, Chang Yeob Han, Cheol Soo Choi, Sang Geon Kim

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Figure 6

Rock2 associates with NFATc1 and inhibits its activity.

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Rock2 associates with NFATc1 and inhibits its activity. (A) NFATc1 trans...
(A) NFATc1 transcriptional activity assays (n = 3 each). Using C2C12 myotubes, NFAT activity luciferase- and NFATc1-expressing constructs were cotransfected with CA-RhoA or a control vector. Luciferase activity was assayed 48 hours after transfection. (B) Tissue distribution of Rho kinase (Rock) isoforms in RNA-seq and microarray data obtained from human samples. The data were extracted from GEO GSE30611 and GSE43346. (C) NFATc1 transcriptional activity assays (n = 3 each). An NFATc1 activity reporter construct was transfected into C2C12 myotubes with siRNAs against Rock1 or Rock2 (or with control siRNA) for 36 hours. The cells were then infected with adenovirus encoding LacZ or Gα13QL for another 36 hours. (D) GST pull-down assays. Recombinant GST or GST-NFATc1 fusion proteins were immobilized on glutathione-agarose beads and incubated with His-tagged recombinant human Rock2 fragment (5-554 residue). Silver staining and immunoblotting was performed to assess the interaction. (E) Immunoprecipitation assays. Left: HEK293 cells were transfected with HA-tagged NFATc1 and/or Flag-tagged Rock2. Right: Untransfected C2C12 cells were differentiated for 72 hours. Y-27632 (3 μM) was added 12 hours prior to the assay. (F) Schematic representation of N-terminal HA-tagged full-length NFATc1 (WT) along with its deletion mutants. Immunoprecipitation assays for HEK293 cells transfected with the indicated NFATc1 constructs along with Flag-tagged Rock2 for 24 hours; lysates were subjected to a pull-down assay. For A and C, data represent the mean ± SEM. **P < 0.01, by Student’s t test.