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  • 1
    Publication Date: 2012-12-25
    Description: The mechanistic target of rapamycin complex 1 (mTORC1) pathway regulates organismal growth in response to many environmental cues, including nutrients and growth factors. Cell-based studies showed that mTORC1 senses amino acids through the RagA-D family of GTPases (also known as RRAGA, B, C and D), but their importance in mammalian physiology is unknown. Here we generate knock-in mice that express a constitutively active form of RagA (RagA(GTP)) from its endogenous promoter. RagA(GTP/GTP) mice develop normally, but fail to survive postnatal day 1. When delivered by Caesarean section, fasted RagA(GTP/GTP) neonates die almost twice as rapidly as wild-type littermates. Within an hour of birth, wild-type neonates strongly inhibit mTORC1, which coincides with profound hypoglycaemia and a decrease in plasma amino-acid concentrations. In contrast, mTORC1 inhibition does not occur in RagA(GTP/GTP) neonates, despite identical reductions in blood nutrient amounts. With prolonged fasting, wild-type neonates recover their plasma glucose concentrations, but RagA(GTP/GTP) mice remain hypoglycaemic until death, despite using glycogen at a faster rate. The glucose homeostasis defect correlates with the inability of fasted RagA(GTP/GTP) neonates to trigger autophagy and produce amino acids for de novo glucose production. Because profound hypoglycaemia does not inhibit mTORC1 in RagA(GTP/GTP) neonates, we considered the possibility that the Rag pathway signals glucose as well as amino-acid sufficiency to mTORC1. Indeed, mTORC1 is resistant to glucose deprivation in RagA(GTP/GTP) fibroblasts, and glucose, like amino acids, controls its recruitment to the lysosomal surface, the site of mTORC1 activation. Thus, the Rag GTPases signal glucose and amino-acid concentrations to mTORC1, and have an unexpectedly key role in neonates in autophagy induction and thus nutrient homeostasis and viability.〈br /〉〈br /〉〈a href="" target="_blank"〉〈img src="" border="0"〉〈/a〉   〈a href="" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Efeyan, Alejo -- Zoncu, Roberto -- Chang, Steven -- Gumper, Iwona -- Snitkin, Harriet -- Wolfson, Rachel L -- Kirak, Oktay -- Sabatini, David D -- Sabatini, David M -- R01 AI047389/AI/NIAID NIH HHS/ -- R01 CA103866/CA/NCI NIH HHS/ -- R01 CA129105/CA/NCI NIH HHS/ -- R37 AI047389/AI/NIAID NIH HHS/ -- T32 GM007753/GM/NIGMS NIH HHS/ -- Howard Hughes Medical Institute/ -- England -- Nature. 2013 Jan 31;493(7434):679-83. doi: 10.1038/nature11745. Epub 2012 Dec 23.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, Massachusetts 02142, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acids/metabolism ; Animals ; Animals, Newborn/metabolism/*physiology ; Autophagy/*genetics ; Blood Glucose/metabolism ; GTP Phosphohydrolases/genetics/*metabolism ; *Gene Expression Regulation, Enzymologic ; Gene Knock-In Techniques ; Hypoglycemia/genetics ; Kaplan-Meier Estimate ; Mice ; Multiprotein Complexes/*genetics/*metabolism ; TOR Serine-Threonine Kinases/*genetics/*metabolism ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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