Mitophagy pathways in health and disease

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Abstract

Killackey et al. review recent advances and major questions in the field of mitophagy, as well as implications for mitophagy in disease.

Abstract

Mitophagy is an evolutionarily conserved process involving the autophagic targeting and clearance of mitochondria destined for removal. Recent insights into the complex nature of the overlapping pathways regulating mitophagy illustrate mitophagy’s essential role in maintaining the health of the mitochondrial network. In this review, we highlight recent studies that have changed the way mitophagy is understood, from initiation through lysosomal degradation. We outline the numerous mitophagic receptors and triggers, with a focus on basal and physiologically relevant cues, offering insight into why they lead to mitochondrial removal. We also explore how mitophagy maintains mitochondrial homeostasis at the organ and system levels and how a loss of mitophagy may play a role in a diverse group of diseases, including cardiovascular, metabolic, and neurodegenerative diseases. With disrupted mitophagy affecting such a wide array of physiological processes, a deeper understanding of how to modulate mitophagy could provide avenues for numerous therapies.

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AMPK and mTOR regulate autophagy through direct phosphorylation of Ulk1.

Joungmok Kim, Mondira Kundu, Benoit Viollet … (2011)

Autophagy is a process by which components of the cell are degraded to maintain essential activity and viability in response to nutrient limitation. Extensive genetic studies have shown that the yeast ATG1 kinase has an essential role in autophagy induction. Furthermore, autophagy is promoted by AMP activated protein kinase (AMPK), which is a key energy sensor and regulates cellular metabolism to maintain energy homeostasis. Conversely, autophagy is inhibited by the mammalian target of rapamycin (mTOR), a central cell-growth regulator that integrates growth factor and nutrient signals. Here we demonstrate a molecular mechanism for regulation of the mammalian autophagy-initiating kinase Ulk1, a homologue of yeast ATG1. Under glucose starvation, AMPK promotes autophagy by directly activating Ulk1 through phosphorylation of Ser 317 and Ser 777. Under nutrient sufficiency, high mTOR activity prevents Ulk1 activation by phosphorylating Ulk1 Ser 757 and disrupting the interaction between Ulk1 and AMPK. This coordinated phosphorylation is important for Ulk1 in autophagy induction. Our study has revealed a signalling mechanism for Ulk1 regulation and autophagy induction in response to nutrient signalling.

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Parkinson disease

Werner Poewe, Klaus Seppi, Caroline M Tanner … (2017)

Parkinson disease is the second-most common neurodegenerative disorder that affects 2-3% of the population ≥65 years of age. Neuronal loss in the substantia nigra, which causes striatal dopamine deficiency, and intracellular inclusions containing aggregates of α-synuclein are the neuropathological hallmarks of Parkinson disease. Multiple other cell types throughout the central and peripheral autonomic nervous system are also involved, probably from early disease onwards. Although clinical diagnosis relies on the presence of bradykinesia and other cardinal motor features, Parkinson disease is associated with many non-motor symptoms that add to overall disability. The underlying molecular pathogenesis involves multiple pathways and mechanisms: α-synuclein proteostasis, mitochondrial function, oxidative stress, calcium homeostasis, axonal transport and neuroinflammation. Recent research into diagnostic biomarkers has taken advantage of neuroimaging in which several modalities, including PET, single-photon emission CT (SPECT) and novel MRI techniques, have been shown to aid early and differential diagnosis. Treatment of Parkinson disease is anchored on pharmacological substitution of striatal dopamine, in addition to non-dopaminergic approaches to address both motor and non-motor symptoms and deep brain stimulation for those developing intractable L-DOPA-related motor complications. Experimental therapies have tried to restore striatal dopamine by gene-based and cell-based approaches, and most recently, aggregation and cellular transport of α-synuclein have become therapeutic targets. One of the greatest current challenges is to identify markers for prodromal disease stages, which would allow novel disease-modifying therapies to be started earlier.

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How mitochondria produce reactive oxygen species

Michael P. Murphy (2008)

The production of ROS (reactive oxygen species) by mammalian mitochondria is important because it underlies oxidative damage in many pathologies and contributes to retrograde redox signalling from the organelle to the cytosol and nucleus. Superoxide (O2 •−) is the proximal mitochondrial ROS, and in the present review I outline the principles that govern O2 •− production within the matrix of mammalian mitochondria. The flux of O2 •− is related to the concentration of potential electron donors, the local concentration of O2 and the second-order rate constants for the reactions between them. Two modes of operation by isolated mitochondria result in significant O2 •− production, predominantly from complex I: (i) when the mitochondria are not making ATP and consequently have a high Δp (protonmotive force) and a reduced CoQ (coenzyme Q) pool; and (ii) when there is a high NADH/NAD+ ratio in the mitochondrial matrix. For mitochondria that are actively making ATP, and consequently have a lower Δp and NADH/NAD+ ratio, the extent of O2 •− production is far lower. The generation of O2 •− within the mitochondrial matrix depends critically on Δp, the NADH/NAD+ and CoQH2/CoQ ratios and the local O2 concentration, which are all highly variable and difficult to measure in vivo. Consequently, it is not possible to estimate O2 •− generation by mitochondria in vivo from O2 •−-production rates by isolated mitochondria, and such extrapolations in the literature are misleading. Even so, the description outlined here facilitates the understanding of factors that favour mitochondrial ROS production. There is a clear need to develop better methods to measure mitochondrial O2 •− and H2O2 formation in vivo, as uncertainty about these values hampers studies on the role of mitochondrial ROS in pathological oxidative damage and redox signalling.

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Author and article information

Journal

Journal ID (nlm-ta): J Cell Biol

Journal ID (iso-abbrev): J Cell Biol

Journal ID (publisher-id): jcb

Title: The Journal of Cell Biology

Publisher: Rockefeller University Press

ISSN (Print): 0021-9525

ISSN (Electronic): 1540-8140

Publication date Collection: 02 November 2020

Publication date (Electronic): 14 September 2020

Volume: 219

Issue: 11

Electronic Location Identifier: e202004029

Affiliations

[1 ]Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada

[2 ]Department of Immunology, University of Toronto, Toronto, Ontario, Canada

Author notes

Correspondence to Samuel A. Killackey: sam.killackey@ 123456mail.utoronto.ca

Stephen E. Girardin: stephen.girardin@ 123456utoronto.ca

Author information

Samuel A. Killackey https://orcid.org/0000-0002-0622-9987

Dana J. Philpott https://orcid.org/0000-0003-3238-6254

Stephen E. Girardin https://orcid.org/0000-0001-9208-8879

Article

Publisher ID: jcb.202004029

DOI: 10.1083/jcb.202004029

PMC ID: 7594502

PubMed ID: 32926082

SO-VID: c04649ac-1043-4ff1-938f-a38f7d9201ae

License:

This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/).

History

Date received : 05 June 2020

Date revision received : 12 August 2020

Date accepted : 13 August 2020

Page count

Pages: 15

Funding

Funded by: Canadian Institutes of Health Research, DOI http://dx.doi.org/10.13039/501100000024;

Award ID: 000303157

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Mitophagy pathways in health and disease

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GLUT4 biology

Most cited references 185

AMPK and mTOR regulate autophagy through direct phosphorylation of Ulk1.

Parkinson disease

How mitochondria produce reactive oxygen species

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