Nontranslational function of leucyl-tRNA synthetase regulates myogenic differentiation and skeletal muscle regeneration
Kook Son, … , Sunghoon Kim, Jie Chen
Kook Son, … , Sunghoon Kim, Jie Chen
Published April 15, 2019
Citation Information: J Clin Invest. 2019;129(5):2088-2093. https://doi.org/10.1172/JCI122560.
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Concise Communication Muscle biology Therapeutics

Nontranslational function of leucyl-tRNA synthetase regulates myogenic differentiation and skeletal muscle regeneration

Abstract

Aside from its catalytic function in protein synthesis, leucyl-tRNA synthetase (LRS) has a nontranslational function in regulating cell growth via the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) pathway by sensing amino acid availability. mTOR also regulates skeletal myogenesis, but the signaling mechanism is distinct from that in cell growth regulation. A role of LRS in myogenesis has not been reported. Here we report that LRS negatively regulated myoblast differentiation in vitro. This function of LRS was independent of its regulation of protein synthesis, and it required leucine-binding but not tRNA charging activity of LRS. Local knock down of LRS accelerated muscle regeneration in a mouse injury model, and so did the knock down of Rag or Raptor. Further in vitro studies established a Rag-mTORC1 pathway, which inhibits the IRS1-PI3K-Akt pathway, to be the mediator of the nontranslational function of LRS in myogenesis. BC-LI-0186, an inhibitor reported to disrupt LRS-Rag interaction, promoted robust muscle regeneration with enhanced functional recovery, and this effect was abolished by cotreatment with an Akt inhibitor. Taken together, our findings revealed what we believe is a novel function for LRS in controlling the homeostasis of myogenesis, and suggested a potential therapeutic strategy to target a noncanonical function of a housekeeping protein.

Authors

Kook Son, Jae-Sung You, Mee-Sup Yoon, Chong Dai, Jong Hyun Kim, Nidhi Khanna, Aditi Banerjee, Susan A. Martinis, Gyoonhee Han, Jung Min Han, Sunghoon Kim, Jie Chen

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Figure 4

An inhibitor of LRS-Rag interaction enhances muscle regeneration.

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An inhibitor of LRS-Rag interaction enhances muscle regeneration. (A) C2...
(A) C2C12 cells were induced to differentiate for 72 hours in the presence or absence of 4 μM BC-LI-0186 (0186) and subjected to measurement of differentiation index. Data were normalized to control (n = 3). (B) Mice were intraperitoneally injected with 0186 at 5 mg/kg body weight every 3 days. The first 0186 injection coincided with BaCl2 injection into TA muscles. Muscles were isolated on day 7 after injury (D7AI) and day 14 after injury (D14AI), and subjected to measurement of CSA of regenerating myofibers. Data were presented as the size distribution of all myofibers with average (avg.) CSA (n = 5–6). (C) TA muscles from mice treated as in B were isolated on day 4 after injury and subjected to Western blotting analysis (n = 3). (D, E) Mice were intraperitoneally injected with 0186 at 5 mg/kg body weight every 3 days and with triciribine (TCB) at 1 mg/kg body weight every day. The first injection of 0186 and TCB coincided with BaCl2 injection into TA muscles. Muscles were isolated on D14AI, weighed (D, n = 6–7), and subjected to measurement of CSA of regenerating myofibers (E, n = 6–7). (F–H) Mice treated as in B were subjected to in situ force measurements of regenerating TA muscles at D14AI (F, n = 7–8), followed by muscle weight measurement (G, n = 7–8). Maximum twitch force and tetanic force were converted to specific maximum twitch force and tetanic force as described in the Supplemental Methods (H, n = 7–8). All values were presented as relative to uninjured contralateral muscles. *P < 0.05, **P < 0.01 by 2-tailed paired t test (A) or 2-tailed unpaired t test (B, C, F–H). ††P < 0.001 (D), †P < 0.005 (E) by 2-way ANOVA. All error bars represent SEM.