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Ammonia-induced autophagy is independent of ULK1/ULK2 kinases.

ABSTRACT: Autophagy, a lysosome-mediated catabolic process, contributes to maintenance of intracellular homeostasis and cellular response to metabolic stress. In yeast, genes essential to the execution of autophagy have been defined, including autophagy-related gene 1 (ATG1), a kinase responsible for initiation of autophagy downstream of target of rapamycin. Here we investigate the role of the mammalian Atg1 homologs, uncoordinated family member (unc)-51-like kinase 1 and 2 (ULK1 and ULK2), in autophagy by generating mouse embryo fibroblasts (MEFs) doubly deficient for ULK1 and ULK2. We found that ULK1/2 are required in the autophagy response to amino acid deprivation but not for autophagy induced by deprivation of glucose or inhibition of glucose metabolism. This ULK1/2-independent autophagy was not the simple result of bioenergetic compromise and failed to be induced by AMP-activated protein kinase activators such as 5-aminoimidazole-4-carboxamide riboside and phenformin. Instead we found that autophagy induction upon glucose deprivation correlated with a rise in cellular ammonia levels caused by elevated amino acid catabolism. Even in complete medium, ammonia induced autophagy in WT and Ulk1/2(-/-) MEFs but not in Atg5-deficient MEFs. The autophagy response to ammonia is abrogated by a cell-permeable form of pyruvate resulting from the scavenging of excess ammonia through pyruvate conversion to alanine. Thus, although ULK1 and/or ULK2 are required for the autophagy response following deprivation of nitrogenous amino acids, the autophagy response to the enhanced amino acid catabolism induced by deprivation of glucose or direct exposure to ammonia does not require ULK1 and/or ULK2. Together, these data suggest that autophagy provides cells with a mechanism to adapt not only to nitrogen deprivation but also to nitrogen excess.

SUBMITTER: Cheong H

PROVIDER: S-EPMC3131371 | biostudies-literature | 2011 Jul

REPOSITORIES: biostudies-literature

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Ammonia-induced autophagy is independent of ULK1/ULK2 kinases.

Cheong Heesun H Lindsten Tullia T Wu Junmin J Lu Chao C Thompson Craig B CB

Proceedings of the National Academy of Sciences of the United States of America 20110620 27

Autophagy, a lysosome-mediated catabolic process, contributes to maintenance of intracellular homeostasis and cellular response to metabolic stress. In yeast, genes essential to the execution of autophagy have been defined, including autophagy-related gene 1 (ATG1), a kinase responsible for initiation of autophagy downstream of target of rapamycin. Here we investigate the role of the mammalian Atg1 homologs, uncoordinated family member (unc)-51-like kinase 1 and 2 (ULK1 and ULK2), in autophagy b ...[more]

PMID: 21690395

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Project description:Impairments in macroautophagy/autophagy, which degrades dysfunctional organelles as well as long-lived and aggregate proteins, are associated with several cardiomyopathies; however, the regulation of cardiac autophagy remains insufficiently understood. In this regard, ULK1 and ULK2 are thought to play primarily redundant roles in autophagy initiation, but whether their function is developmentally determined, potentially having an impact on cardiac integrity and function remains unknown. Here, we demonstrate that perinatal loss of ULK1 or ULK2 in cardiomyocytes (cU1-KO and cU2-KO mice, respectively) enhances basal autophagy without altering autophagy machinery content while preserving cardiac function. This increased basal autophagy is dependent on the remaining ULK protein given that perinatal loss of both ULK1 and ULK2 in cU1/2-DKO mice impaired autophagy causing age-related cardiomyopathy and reduced survival. Conversely, adult loss of cardiac ULK1, but not of ULK2 (i.e., icU1-KO and icU2-KO mice, respectively), led to a rapidly developing cardiomyopathy, heart failure and early death. icU1-KO mice had impaired autophagy with robust deficits in mitochondrial respiration and ATP synthesis. Trehalose ameliorated autophagy impairments in icU1-KO hearts but did not delay cardiac dysfunction suggesting that ULK1 plays other critical, autophagy-independent, functions in the adult heart. Collectively, these results indicate that cardiac ULK1 and ULK2 are functionally redundant in the developing heart, while ULK1 assumes a more unique, prominent role in the adult heart.Abbreviations: ATG4: autophagy related 4, cysteine peptidase; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG9: autophagy related 9; ATG13: autophagy related 13; CYCS: Cytochrome C; DNM1L, dynamin 1-like; MAP1LC3A: microtubule-associated protein 1 light chain 3 alpha; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; MFN1: mitofusin 1; MFN2: mitofusin 2; MT-CO1: mitochondrially encoded cytochrome c oxidase I; MYH: myosin, heavy polypeptide; NBR1: NBR1 autophagy cargo receptor; NDUFA9: NADH:ubiquinone oxidoreductase subunit A9; OPA1: OPA1, mitochondrial dynamin like GTPase; PPARGC1A, peroxisome proliferator activated receptor, gamma, coactivator 1 alpha; SDHA: succinate dehydrogenase complex, subunit A, flavoprotein (Fp); SQSTM1: sequestosome 1; ULK1: unc-51 like kinase 1; ULK2: unc-51 like kinase 2; UQCRC1: ubiquinol-cytochrome c reductase core protein 1.

Dataset Information

Ammonia-induced autophagy is independent of ULK1/ULK2 kinases.

Publications

Ammonia-induced autophagy is independent of ULK1/ULK2 kinases.

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