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 8

Phosphorylation at Ser243 affects NFATc1 activity in vivo.

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Phosphorylation at Ser243 affects NFATc1 activity in vivo. (A) Immunoblo...
(A) Immunoblots for p-NFATc1 (Ser243). Twelve-week-old mice of each genotype were fasted overnight before sacrifice (n = 3 each). Each blot was obtained from samples run on parallel gels. (B and C) Immunoblots for p-NFATc1 (Ser243) and assays for Rock2 activity. A recombinant MYPT1 substrate peptide was used to determine the activity of Rock2 immunoprecipitated from tissue homogenates. (B) Mice were subjected to 1 hour of exercise and rested for 4 hours before sacrifice. Soleus muscles were used (n = 5 each). (C) Mice were fed a ND or a HFD for 13 weeks and were fasted overnight before sacrifice (n = 4–6 each). (D) Immunoblots and NFATc1 transcriptional activity assays. Left: C2C12 myotubes were transfected with mock or the plasmid encoding for WT NFATc1 or mutants, and subcellular fractions were collected 24 hours after transfection. Right: NFATc1-KO C2C12 myotubes were similarly cotransfected along with an NFAT reporter construct. Luciferase activity was assayed 48 hours after transfection (n = 4). (E) Immunostain images for myosin heavy chains and histochemical assays to determine SDH activity in tibialis anterior muscles, 14 days after electroporation-mediated gene delivery. Each mouse of the indicated genotype received a WT NFATc1 vector in 1 limb and a plasmid encoding S243A-mutant NFATc1 in the contralateral limb. Type 1 and 2a myofibers and those with high SDH activity were quantified. Scale bars: 200 μm. Data represent the mean ± SEM. *P < 0.05 and **P < 0.01, by Student’s t test.