Increased glutamine catabolism mediates bone anabolism in response to WNT signaling
Courtney M. Karner, … , Bruce W. Patterson, Fanxin Long
Courtney M. Karner, … , Bruce W. Patterson, Fanxin Long
Published December 22, 2014
Citation Information: J Clin Invest. 2015;125(2):551-562. https://doi.org/10.1172/JCI78470.
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Research Article Bone biology

Increased glutamine catabolism mediates bone anabolism in response to WNT signaling

Abstract

WNT signaling stimulates bone formation by increasing both the number of osteoblasts and their protein-synthesis activity. It is not clear how WNT augments the capacity of osteoblast progenitors to meet the increased energetic and synthetic needs associated with mature osteoblasts. Here, in cultured osteoblast progenitors, we determined that WNT stimulates glutamine catabolism through the tricarboxylic acid (TCA) cycle and consequently lowers intracellular glutamine levels. The WNT-induced reduction of glutamine concentration triggered a general control nonderepressible 2–mediated (GCN2-mediated) integrated stress response (ISR) that stimulated expression of genes responsible for amino acid supply, transfer RNA (tRNA) aminoacylation, and protein folding. WNT-induced glutamine catabolism and ISR were β-catenin independent, but required mammalian target of rapamycin complex 1 (mTORC1) activation. In a hyperactive WNT signaling mouse model of human osteosclerosis, inhibition of glutamine catabolism or Gcn2 deletion suppressed excessive bone formation. Together, our data indicate that glutamine is both an energy source and a protein-translation rheostat that is responsive to WNT and suggest that manipulation of the glutamine/GCN2 signaling axis may provide a valuable approach for normalizing deranged protein anabolism associated with human diseases.

Authors

Courtney M. Karner, Emel Esen, Adewole L. Okunade, Bruce W. Patterson, Fanxin Long

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Figure 2

WNT induces Gln-dependent anaplerosis during osteoblast differentiation.

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WNT induces Gln-dependent anaplerosis during osteoblast differentiation....
(A) Relative intracellular Gln levels in response to WNT3A determined by mass spectrometry. Welch’s 2-sample t test. n = 5. Box denotes upper and lower quartiles, while line denotes the median. The whiskers denote the maximum and minimum values of the distribution. (B and C) Measurements of Gln uptake from the medium in response to WNT3A without (B) or with Torin1 (C). Error bars indicate SD. *P < 0.05, Student’s t test. n = 3. (D) Effect of WNT3A on GLS protein levels at 6 hours. Fold change ± SD from 3 independent experiments. (E) Effect of WNT3A on GLS activity by measuring the conversion of 3H[2,3,4] Gln to glutamate (Glu). 3H cpm ± SD. *P < 0.05, Student’s t test. n = 5. (F) Graphical depiction of Gln-dependent anaplerosis into the TCA cycle. Red circles indicate 13C, whereas black and green circles denote 12C and 14N, respectively. [U-13C5] glutamine–derived αKG generates [13C4] citrate (M+4) through oxidation, but [13C5] citrate (M+5) via reductive carboxylation.