Metabolic rewiring during bone development underlies tRNA m7G–associated primordial dwarfism
Qiwen Li, Shuang Jiang, Kexin Lei, Hui Han, Yaqian Chen, Weimin Lin, Qiuchan Xiong, Xingying Qi, Xinyan Gan, Rui Sheng, Yuan Wang, Yarong Zhang, Jieyi Ma, Tao Li, Shuibin Lin, Chenchen Zhou, Demeng Chen, Quan Yuan
Qiwen Li, Shuang Jiang, Kexin Lei, Hui Han, Yaqian Chen, Weimin Lin, Qiuchan Xiong, Xingying Qi, Xinyan Gan, Rui Sheng, Yuan Wang, Yarong Zhang, Jieyi Ma, Tao Li, Shuibin Lin, Chenchen Zhou, Demeng Chen, Quan Yuan
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Research Article Bone biology Metabolism

Metabolic rewiring during bone development underlies tRNA m7G–associated primordial dwarfism

Abstract

Translation of mRNA to protein is tightly regulated by transfer RNAs (tRNAs), which are subject to various chemical modifications that maintain structure, stability, and function. Deficiency of tRNA N7-methylguanosine (m7G) modification in patients causes a type of primordial dwarfism, but the underlying mechanism remains unknown. Here we report that the loss of m7G rewires cellular metabolism, leading to the pathogenesis of primordial dwarfism. Conditional deletion of the catalytic enzyme Mettl1 or missense mutation of the scaffold protein Wdr4 severely impaired endochondral bone formation and bone mass accrual. Mechanistically, Mettl1 knockout decreased abundance of m7G-modified tRNAs and inhibited translation of mRNAs relating to cytoskeleton and Rho GTPase signaling. Meanwhile, Mettl1 knockout enhanced cellular energy metabolism despite incompetent proliferation and osteogenic commitment. Further exploration revealed that impairment of Rho GTPase signaling upregulated the level of branched-chain amino acid transaminase 1 (BCAT1) that rewired cell metabolism and restricted intracellular α-ketoglutarate (αKG). Supplementation of αKG ameliorated the skeletal defect of Mettl1-deficient mice. In addition to the selective translation of metabolism-related mRNAs, we further revealed that Mettl1 knockout globally regulated translation via integrated stress response (ISR) and mammalian target of rapamycin complex 1 (mTORC1) signaling. Restoring translation by targeting either ISR or mTORC1 aggravated bone defects of Mettl1-deficient mice. Overall, our study unveils a critical role of m7G tRNA modification in bone development by regulation of cellular metabolism and indicates suspension of translation initiation as a quality control mechanism in response to tRNA dysregulation.

Authors

Qiwen Li, Shuang Jiang, Kexin Lei, Hui Han, Yaqian Chen, Weimin Lin, Qiuchan Xiong, Xingying Qi, Xinyan Gan, Rui Sheng, Yuan Wang, Yarong Zhang, Jieyi Ma, Tao Li, Shuibin Lin, Chenchen Zhou, Demeng Chen, Quan Yuan

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Figure 6

Supplementation of αKG ameliorates the skeletal defects of Prrx1Cre Mettl1fl/fl mice.

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Supplementation of αKG ameliorates the skeletal defects of Prrx1Cre Mett...
(A) Measurement of intracellular αKG level in WT and Prrx1Cre Mettl1fl/fl limb mesenchymal progenitors. n = 6. (B) Representative images of newborn WT and Prrx1Cre Mettl1fl/fl mice treated with vehicle or αKG. (C) Representative skeletal staining of WT and Prrx1Cre Mettl1fl/fl mouse forelimbs at P0, treated with vehicle or αKG. Scale bar: 2 mm. (D) Quantification of forelimb stylopod and zeugopod length. n = 8. (E) Representative Alcian blue staining of WT and Prrx1Cre Mettl1fl/fl mouse humerus at P0, treated with vehicle or αKG. Magnified images show growth plate hypertrophic zone of the proximal humerus. Scale bars: 200 μm (top) and 50 μm (bottom). (F) Growth curve of WT and Prrx1Cre Mettl1fl/fl chondrocytes, treated with vehicle or αKG. n = 3. (G) Quantitative reverse transcriptase PCR (qRT-PCR) analyses of the expression of Col2a1, Col10a1, and Mmp13 in WT and Prrx1Cre Mettl1fl/fl chondrocytes, treated with vehicle or αKG. n = 3 from independent experiments. (H) qRT-PCR analyses of the expression of Mettl1, Runx2, Sp7, and Bglap in Ad-gfp– and Ad-Cre–infected Mettl1fl/fl SSCs, treated with vehicle or αKG. n = 3 from independent experiments. (I and J) Representative images and quantification of ALP staining of WT and Prrx1Cre Mettl1fl/fl SSCs, treated with vehicle or αKG. n = 3 from independent experiments. (K and L) Representative images and quantification of ARS staining of WT and Prrx1Cre Mettl1fl/fl SSCs, treated with vehicle or αKG. n = 3 from independent experiments. Data are expressed as mean ± SEM; *P < 0.05, **P < 0.01, ***P < 0.001 by 1-way ANOVA with Tukey’s post hoc test.