Amino acid–insensitive mTORC1 regulation enables nutritional stress resilience in hematopoietic stem cells
Demetrios Kalaitzidis, … , David M. Sabatini, David T. Scadden
Demetrios Kalaitzidis, … , David M. Sabatini, David T. Scadden
Published March 20, 2017
Citation Information: J Clin Invest. 2017;127(4):1405-1413. https://doi.org/10.1172/JCI89452.
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Research Article Hematology

Amino acid–insensitive mTORC1 regulation enables nutritional stress resilience in hematopoietic stem cells

Abstract

The mTOR pathway is a critical determinant of cell persistence and growth wherein mTOR complex 1 (mTORC1) mediates a balance between growth factor stimuli and nutrient availability. Amino acids or glucose facilitates mTORC1 activation by inducing RagA GTPase recruitment of mTORC1 to the lysosomal outer surface, enabling activation of mTOR by the Ras homolog Rheb. Thereby, RagA alters mTORC1-driven growth in times of nutrient abundance or scarcity. Here, we have evaluated differential nutrient-sensing dependence through RagA and mTORC1 in hematopoietic progenitors, which dynamically drive mature cell production, and hematopoietic stem cells (HSC), which provide a quiescent cellular reserve. In nutrient-abundant conditions, RagA-deficient HSC were functionally unimpaired and upregulated mTORC1 via nutrient-insensitive mechanisms. RagA was also dispensable for HSC function under nutritional stress conditions. Similarly, hyperactivation of RagA did not affect HSC function. In contrast, RagA deficiency markedly altered progenitor population function and mature cell output. Therefore, RagA is a molecular mechanism that distinguishes the functional attributes of reactive progenitors from a reserve stem cell pool. The indifference of HSC to nutrient sensing through RagA contributes to their molecular resilience to nutritional stress, a characteristic that is relevant to organismal viability in evolution and in modern HSC transplantation approaches.

Authors

Demetrios Kalaitzidis, Dongjun Lee, Alejo Efeyan, Youmna Kfoury, Naema Nayyar, David B. Sykes, Francois E. Mercier, Ani Papazian, Ninib Baryawno, Gabriel D. Victora, Donna Neuberg, David M. Sabatini, David T. Scadden

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Figure 2

HSC were preserved from the Rraga-deficient setting under transplantation stress.

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HSC were preserved from the Rraga-deficient setting under transplantatio...
(A) A 1:1 mixture of CD45.2 test cells (indicated) were transplanted with CD45.1 competitor cells. At the indicated time points, mice were treated with pIpC and PB was collected and analyzed for CD45.2 chimerism (n = 4–8). (B) The frequencies of B cells (B220), T cells (CD3), and myeloid cells (monocytes [Mac1+Gr1lo] and granulocytes [Mac1+Gr1+]) from the PB of transplant recipients from A are shown (n = 4–8). (C) BM HSC (CD48–CD150+LSK gate) chimerism was assessed 19 to 20 weeks after pIpC in mice receiving cells of the indicated genotypes (n = 7). (D) The percentage of chimerism in each cell type of the indicated genotypes is shown at 19 to 20 weeks after pIpC. HSC, Lin–Sca1+cKit+CD150+CD48– (n = 7); HPC, Lin–Sca1+cKit+CD48+ (n = 7); whole BM (WBM, n = 4). (E) The contribution to indicated progenitors from mice of the indicated genotypes was assessed in the Lin–Sca1–cKit+ gate (n = 3). GMP, Lin–Sca1–cKit+CD34+CD16/32+; CMP, Lin–Sca1–cKit+CD34+CD16/32–; MEP, Lin–Sca1–cKit+CD34–CD16/32–. (F) The relative levels of Rraga mRNA were assessed from sorted BM CD45.2 LSK cells from mice of the indicated genotypes 20 weeks after pIpC (n = 3). (G) The frequencies of B cells (B220), T cells (CD3), and myeloid cells (monocytes [Mac1+Gr1lo] and granulocytes [Mac1+Gr1+]) are shown at 19 to 20 weeks after pIpC (n = 4) in the BM of mice receiving cells of the indicated genotype. Error bars indicate SEM. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.