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 April 3, 2017
Citation Information: J Clin Invest. 2017;127(4):1405-1413. doi:10.1172/JCI89452.
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Categories: Research Article Hematology Stem cells

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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Rraga is required for maintaining proper progenitor differentiation and...

Figure 1

Rraga is required for maintaining proper progenitor differentiation and mature hematopoietic lineage cells.

(A) Quantitative PCR (qPCR) on cDNA was performed to measure levels of mRNA of Rraga (normalized to Gapdh) from the indicated cell populations from mice induced with pIpC 1 to 1.5 months previously (+/+, WT; Δ/Δ, induced Rragafl/fl MxCre; n = 2–4). (B) The frequency of LSKCD34–FLT3– gated CD150+CD48– cells in BM of mice of the indicated genotypes is shown with representative FACS plot (n = 5). Additional HSPC populations in BM (left panel) and spleen (right panel) from the mice of the indicated genotypes 1 to 1.5 months after pIpC (n = 7 for BM and n = 6–7 for spleen). HSC, Lin–7AAD–CD127–Sca1+cKit+CD34–FLT3–; STRC, Lin–7AAD–CD127–Sca1+cKit+CD34+FLT3–; LMPP, Lin–7AAD–CD127–Sca1+cKit+CD34+FLT3+. (C) The frequency of committed progenitors is shown from BM (left panel) and spleen (right panel) of mice of the indicated genotypes 1 to 1.5 months after pIpC (n = 6–7). (D) Types and total number of colonies produced in M3434 media from cells of mice are indicated (n = 3). G, granulocyte; M, macrophage/monocyte; E, erythroid; GEMM, GEM-megakaryocyte; MEG, megakaryocyte-EG. (E) The frequencies of B cells (B220), T cells (CD3), and myeloid cells (monocytes [Mac1+Gr1lo] and granulocytes [Mac1+Gr1+]) in the BM and spleen from mice of the indicated Rraga genotype 1 to 1.5 months after deletion are shown (n = 3–4). (F) Ter119/CD71 staining was performed from BM and spleen to assess erythroid fractions (F1–FIV) in control and Rraga-deleted mice 1 to 1.5 months after deletion (n = 3). See Supplemental Figure 1F for gating scheme. Error bars indicate SEM. *P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001.