Intramitochondrial proteostasis is directly coupled to α-synuclein and amyloid β1-42 pathologies

Mitochondrial dysfunction has long been implicated in the neurodegenerative disorder Parkinson's disease (PD); however, it is unclear how mitochondrial impairment and α-synuclein pathology are coupled. Using specific mitochondrial inhibitors, EM analysis, and biochemical assays, we report here that intramitochondrial protein homeostasis plays a major role in α-synuclein aggregation. We found that interference with intramitochondrial proteases, such as HtrA2 and Lon protease, and mitochondrial protein import significantly aggravates α-synuclein seeding. In contrast, direct inhibition of mitochondrial complex I, an increase in intracellular calcium concentration, or formation of reactive oxygen species, all of which have been associated with mitochondrial stress, did not affect α-synuclein pathology. We further demonstrate that similar mechanisms are involved in amyloid-β 1-42 (Aβ42) aggregation. Our results suggest that, in addition to other protein quality control pathways, such as the ubiquitin–proteasome system, mitochondria per se can influence protein homeostasis of cytosolic aggregation-prone proteins. We propose that approaches that seek to maintain mitochondrial fitness, rather than target downstream mitochondrial dysfunction, may aid in the search for therapeutic strategies to manage PD and related neuropathologies.

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Cytosolic Quality Control of Mitochondrial Protein Precursors—The Early Stages of the Organelle Biogenesis

International Journal of Molecular Sciences ◽

10.3390/ijms23010007 ◽

2021 ◽

Vol 23 (1) ◽

pp. 7

Author(s):

Anna M. Lenkiewicz ◽

Magda Krakowczyk ◽

Piotr Bragoszewski

Keyword(s):

Quality Control ◽

Protein Import ◽

Mitochondrial Protein ◽

Ubiquitin Proteasome System ◽

Vital Role ◽

Protein Homeostasis ◽

Organelle Biogenesis ◽

Mitochondrial Protein Import ◽

Ubiquitin Proteasome ◽

Cellular Pathways

With few exceptions, proteins that constitute the proteome of mitochondria originate outside of this organelle in precursor forms. Such protein precursors follow dedicated transportation paths to reach specific parts of mitochondria, where they complete their maturation and perform their functions. Mitochondrial precursor targeting and import pathways are essential to maintain proper mitochondrial function and cell survival, thus are tightly controlled at each stage. Mechanisms that sustain protein homeostasis of the cytosol play a vital role in the quality control of proteins targeted to the organelle. Starting from their synthesis, precursors are constantly chaperoned and guided to reduce the risk of premature folding, erroneous interactions, or protein damage. The ubiquitin-proteasome system provides proteolytic control that is not restricted to defective proteins but also regulates the supply of precursors to the organelle. Recent discoveries provide evidence that stress caused by the mislocalization of mitochondrial proteins may contribute to disease development. Precursors are not only subject to regulation but also modulate cytosolic machinery. Here we provide an overview of the cellular pathways that are involved in precursor maintenance and guidance at the early cytosolic stages of mitochondrial biogenesis. Moreover, we follow the circumstances in which mitochondrial protein import deregulation disturbs the cellular balance, carefully looking for rescue paths that can restore proteostasis.

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Skeletal Phenotypes Due to Abnormalities in Mitochondrial Protein Homeostasis and Import

International Journal of Molecular Sciences ◽

10.3390/ijms21218327 ◽

2020 ◽

Vol 21 (21) ◽

pp. 8327

Author(s):

Tian Zhao ◽

Caitlin Goedhart ◽

Gerald Pfeffer ◽

Steven C Greenway ◽

Matthew Lines ◽

...

Keyword(s):

Mitochondrial Dysfunction ◽

Mitochondrial Disease ◽

Protein Import ◽

Mitochondrial Protein ◽

Membrane Lipid ◽

Disease Genes ◽

Protein Homeostasis ◽

Inner Mitochondrial Membrane ◽

Mitochondrial Functions ◽

Insight Into

Mitochondrial disease represents a collection of rare genetic disorders caused by mitochondrial dysfunction. These disorders can be quite complex and heterogeneous, and it is recognized that mitochondrial disease can affect any tissue at any age. The reasons for this variability are not well understood. In this review, we develop and expand a subset of mitochondrial diseases including predominantly skeletal phenotypes. Understanding how impairment ofdiverse mitochondrial functions leads to a skeletal phenotype will help diagnose and treat patients with mitochondrial disease and provide additional insight into the growing list of human pathologies associated with mitochondrial dysfunction. The underlying disease genes encode factors involved in various aspects of mitochondrial protein homeostasis, including proteases and chaperones, mitochondrial protein import machinery, mediators of inner mitochondrial membrane lipid homeostasis, and aminoacylation of mitochondrial tRNAs required for translation. We further discuss a complex of frequently associated phenotypes (short stature, cataracts, and cardiomyopathy) potentially explained by alterations to steroidogenesis, a process regulated by mitochondria. Together, these observations provide novel insight into the consequences of impaired mitochondrial protein homeostasis.

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Mitochondrial Protein Quality Control Mechanisms

Genes ◽

10.3390/genes11050563 ◽

2020 ◽

Vol 11 (5) ◽

pp. 563 ◽

Cited By ~ 4

Author(s):

Pooja Jadiya ◽

Dhanendra Tomar

Keyword(s):

Quality Control ◽

Protein Import ◽

Protein Quality ◽

Current Knowledge ◽

Mitochondrial Protein ◽

Protein Quality Control ◽

Redox Balance ◽

Ubiquitin Proteasome System ◽

Control Mechanisms ◽

Mitochondrial Proteome

Mitochondria serve as a hub for many cellular processes, including bioenergetics, metabolism, cellular signaling, redox balance, calcium homeostasis, and cell death. The mitochondrial proteome includes over a thousand proteins, encoded by both the mitochondrial and nuclear genomes. The majority (~99%) of proteins are nuclear encoded that are synthesized in the cytosol and subsequently imported into the mitochondria. Within the mitochondria, polypeptides fold and assemble into their native functional form. Mitochondria health and integrity depend on correct protein import, folding, and regulated turnover termed as mitochondrial protein quality control (MPQC). Failure to maintain these processes can cause mitochondrial dysfunction that leads to various pathophysiological outcomes and the commencement of diseases. Here, we summarize the current knowledge about the role of different MPQC regulatory systems such as mitochondrial chaperones, proteases, the ubiquitin-proteasome system, mitochondrial unfolded protein response, mitophagy, and mitochondria-derived vesicles in the maintenance of mitochondrial proteome and health. The proper understanding of mitochondrial protein quality control mechanisms will provide relevant insights to treat multiple human diseases.

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Mitochondrial quality control by the ubiquitin–proteasome system

Biochemical Society Transactions ◽

10.1042/bst0391509 ◽

2011 ◽

Vol 39 (5) ◽

pp. 1509-1513 ◽

Cited By ~ 124

Author(s):

Eric B. Taylor ◽

Jared Rutter

Keyword(s):

Quality Control ◽

Ubiquitin Ligase ◽

Protein Quality ◽

Mitochondrial Protein ◽

Ubiquitin Proteasome System ◽

Degradation Pathway ◽

Outer Mitochondrial Membrane ◽

Mitochondrial Quality Control ◽

Ubiquitinated Proteins ◽

Ubiquitin Proteasome

Mitochondria perform multiple functions critical to the maintenance of cellular homoeostasis and their dysfunction leads to disease. Several lines of evidence suggest the presence of a MAD (mitochondria-associated degradation) pathway that regulates mitochondrial protein quality control. Internal mitochondrial proteins may be retrotranslocated to the OMM (outer mitochondrial membrane), multiple E3 ubiquitin ligases reside at the OMM and inhibition of the proteasome causes accumulation of ubiquitinated proteins at the OMM. Reminiscent of ERAD [ER (endoplasmic reticulum)-associated degradation], Cdc48 (cell division cycle 42)/p97 is recruited to stressed mitochondria, extracts ubiquitinated proteins from the OMM and presents ubiquitinated proteins to the proteasome for degradation. Recent research has provided mechanistic insights into the interaction of the UPS (ubiquitin–proteasome system) with the OMM. In yeast, Vms1 [VCP (valosin-containing protein) (p97)/Cdc48-associated mitochondrial-stress-responsive 1] protein recruits Cdc48/p97 to the OMM. In mammalian systems, the E3 ubiquitin ligase parkin regulates the recruitment of Cdc48/p97 to mitochondria, subsequent mitochondrial protein degradation and mitochondrial autophagy. Disruption of the Vms1 or parkin systems results in the hyper-accumulation of ubiquitinated proteins at mitochondria and subsequent mitochondrial dysfunction. The emerging MAD pathway is important for the maintenance of cellular and therefore organismal viability.

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Cytosolic aggregation of mitochondrial proteins disrupts cellular homeostasis by stimulating other proteins aggregation

10.1101/2021.05.02.442342 ◽

2021 ◽

Author(s):

Urszula Nowicka ◽

Piotr Chroscicki ◽

Karen Stroobants ◽

Maria Sladowska ◽

Michal Turek ◽

...

Keyword(s):

Protein Import ◽

Mitochondrial Protein ◽

Amyloid Β ◽

Mitochondrial Proteins ◽

Protein Homeostasis ◽

Mitochondrial Protein Import ◽

Protein Levels ◽

Proteotoxic Stress ◽

Encoded Proteins ◽

Related Proteins

Mitochondria are organelles with their own genomes but rely on the import of nuclear-encoded proteins synthesized by cytosolic ribosomes. Therefore, it is important to understand whether failures in the mitochondrial uptake of these nuclear-encoded proteins may cause proteotoxic stress, and to identify which response mechanisms may be in place to respond to it. Here, we report that upon mitochondrial protein import impairment, high-risk precursor and immature forms of mitochondrial proteins form aberrant deposits in the cytosol. In turn, these deposits cause further cytosolic accumulation of other mitochondrial and disease-related proteins, including α-synuclein and amyloid β. This aberrant accumulation triggers a cytosolic protein homeostasis imbalance that is accompanied by specific molecular chaperone responses, both at the transcriptomic and protein levels. Our results provide evidence that mitochondrial dysfunction, and specifically protein import defects, can contribute to protein homeostasis impairment, thus revealing a possible molecular mechanism for mitochondrial involvement in neurodegenerative diseases.

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Cytosolic aggregation of mitochondrial proteins disrupts cellular homeostasis by stimulating the aggregation of other proteins

eLife ◽

10.7554/elife.65484 ◽

2021 ◽

Vol 10 ◽

Author(s):

Urszula Nowicka ◽

Piotr Chroscicki ◽

Karen Stroobants ◽

Maria Sladowska ◽

Michal Turek ◽

...

Keyword(s):

Protein Import ◽

Mitochondrial Protein ◽

Amyloid Β ◽

Mitochondrial Proteins ◽

Protein Homeostasis ◽

Mitochondrial Protein Import ◽

Protein Levels ◽

Proteotoxic Stress ◽

Encoded Proteins ◽

Related Proteins

Mitochondria are organelles with their own genomes, but they rely on the import of nuclear-encoded proteins that are translated by cytosolic ribosomes. Therefore, it is important to understand whether failures in the mitochondrial uptake of these nuclear-encoded proteins can cause proteotoxic stress and identify response mechanisms that may counteract it. Here, we report that upon impairments in mitochondrial protein import, high-risk precursor and immature forms of mitochondrial proteins form aberrant deposits in the cytosol. These deposits then cause further cytosolic accumulation and consequently aggregation of other mitochondrial proteins and disease-related proteins, including α-synuclein and amyloid β. This aggregation triggers a cytosolic protein homeostasis imbalance that is accompanied by specific molecular chaperone responses at both the transcriptomic and protein levels. Altogether, our results provide evidence that mitochondrial dysfunction, specifically protein import defects, contributes to impairments in protein homeostasis, thus revealing a possible molecular mechanism by which mitochondria are involved in neurodegenerative diseases.

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Intra-mitochondrial proteostasis is directly coupled to alpha-synuclein and Amyloid β 1-42 pathology

10.1101/561134 ◽

2019 ◽

Author(s):

Janin Lautenschläger ◽

Sara Wagner-Valladolid ◽

Amberley D. Stephens ◽

Ana Fernández-Villegas ◽

Colin Hockings ◽

...

Keyword(s):

Calcium Concentration ◽

Protein Import ◽

Mitochondrial Protein ◽

Amyloid Β ◽

Alpha Synuclein ◽

Protein Homeostasis ◽

Oxygen Species ◽

Direct Inhibition ◽

Mitochondrial Protein Import ◽

Alpha Synuclein Aggregation

AbstractMitochondria have long been implicated in Parkinson’s disease (PD), however, it is not clear how mitochondrial impairment and alpha-synuclein pathology are coupled. We report here that intra-mitochondrial protein homeostasis plays a major role in alpha-synuclein fibril elongation, as interference with intra-mitochondrial proteases and mitochondrial protein import significantly aggravate alpha-synuclein aggregation. In contrast, direct inhibition of mitochondrial complex I, increase in intracellular calcium concentration or formation of reactive oxygen species (ROS), all of which have been associated with mitochondrial stress, did not affect alpha-synuclein pathology. We further demonstrate that similar mechanisms are involved in Amyloid β 1-42 (Aβ42) aggregation, suggesting that mitochondria are directly capable of influencing cytosolic protein homeostasis of aggregation-prone proteins.

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A conserved quality-control pathway that mediates degradation of unassembled ribosomal proteins

eLife ◽

10.7554/elife.19105 ◽

2016 ◽

Vol 5 ◽

Cited By ~ 75

Author(s):

Min-Kyung Sung ◽

Tanya R Porras-Yakushi ◽

Justin M Reitsma ◽

Ferdinand M Huber ◽

Michael J Sweredoski ◽

...

Keyword(s):

Quality Control ◽

Ribosomal Protein ◽

Ubiquitin Ligase ◽

Ribosomal Proteins ◽

Protein Quality ◽

Ubiquitin Proteasome System ◽

Protein Homeostasis ◽

System Quality ◽

Ubiquitin Proteasome ◽

E2 Enzymes

Overproduced yeast ribosomal protein (RP) Rpl26 fails to assemble into ribosomes and is degraded in the nucleus/nucleolus by a ubiquitin-proteasome system quality control pathway comprising the E2 enzymes Ubc4/Ubc5 and the ubiquitin ligase Tom1. tom1 cells show reduced ubiquitination of multiple RPs, exceptional accumulation of detergent-insoluble proteins including multiple RPs, and hypersensitivity to imbalances in production of RPs and rRNA, indicative of a profound perturbation to proteostasis. Tom1 directly ubiquitinates unassembled RPs primarily via residues that are concealed in mature ribosomes. Together, these data point to an important role for Tom1 in normal physiology and prompt us to refer to this pathway as ERISQ, for excess ribosomal protein quality control. A similar pathway, mediated by the Tom1 homolog Huwe1, restricts accumulation of overexpressed hRpl26 in human cells. We propose that ERISQ is a key element of the quality control machinery that sustains protein homeostasis and cellular fitness in eukaryotes.

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Neuronal mitochondrial dysfunction in sporadic amyotrophic lateral sclerosis is developmentally regulated

Scientific Reports ◽

10.1038/s41598-021-97928-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Tanisha Singh ◽

Yuanyuan Jiao ◽

Lisa M. Ferrando ◽

Svitlana Yablonska ◽

Fang Li ◽

...

Keyword(s):

Amyotrophic Lateral Sclerosis ◽

Mitochondrial Dysfunction ◽

Motor Neurons ◽

Protein Import ◽

Neurodegenerative Disorder ◽

Mitochondrial Protein ◽

Neural Progenitors ◽

Developmentally Regulated ◽

Sporadic Als ◽

Lateral Sclerosis

AbstractAmyotrophic lateral sclerosis is an adult-onset neurodegenerative disorder characterized by loss of motor neurons. Mitochondria are essential for neuronal survival but the developmental timing and mechanistic importance of mitochondrial dysfunction in sporadic ALS (sALS) neurons is not fully understood. We used human induced pluripotent stem cells and generated a developmental timeline by differentiating sALS iPSCs to neural progenitors and to motor neurons and comparing mitochondrial parameters with familial ALS (fALS) and control cells at each developmental stage. We report that sALS and fALS motor neurons have elevated reactive oxygen species levels, depolarized mitochondria, impaired oxidative phosphorylation, ATP loss and defective mitochondrial protein import compared with control motor neurons. This phenotype develops with differentiation into motor neurons, the affected cell type in ALS, and does not occur in the parental undifferentiated sALS cells or sALS neural progenitors. Our work demonstrates a developmentally regulated unifying mitochondrial phenotype between patient derived sALS and fALS motor neurons. The occurrence of a unifying mitochondrial phenotype suggests that mitochondrial etiology known to SOD1-fALS may applicable to sALS. Furthermore, our findings suggest that disease-modifying treatments focused on rescue of mitochondrial function may benefit both sALS and fALS patients.

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Expression of Mutant Ubiquitin and Proteostasis Impairment in Kii Amyotrophic Lateral Sclerosis/Parkinsonism-Dementia Complex Brains

Journal of Neuropathology & Experimental Neurology ◽

10.1093/jnen/nlaa056 ◽

2020 ◽

Vol 79 (8) ◽

pp. 902-907

Author(s):

Bert M Verheijen ◽

Satoru Morimoto ◽

Ryogen Sasaki ◽

Kiyomitsu Oyanagi ◽

Yasumasa Kokubo ◽

...

Keyword(s):

Amyotrophic Lateral Sclerosis ◽

Neurodegenerative Disorder ◽

Neuronal Loss ◽

Ubiquitin Proteasome System ◽

Postmortem Brain ◽

Protein Homeostasis ◽

Postmortem Brain Tissue ◽

Ubiquitin Proteasome ◽

Variable Combination ◽

Lateral Sclerosis

Abstract Kii amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS/PDC) is a progressive neurodegenerative disorder that is endemic to the Kii peninsula of Japan. The disorder is clinically characterized by a variable combination of parkinsonism, dementia, and motor neuron symptoms. Despite extensive investigations, the etiology and pathogenesis of ALS/PDC remain unclear. At the neuropathological level, Kii ALS/PDC is characterized by neuronal loss and tau-dominant polyproteinopathy. Here, we report the accumulation of several proteins involved in protein homeostasis pathways, that is, the ubiquitin-proteasome system and the autophagy-lysosome pathway, in postmortem brain tissue from a number of Kii ALS/PDC cases (n = 4). Of particular interest is the presence of a mutant ubiquitin protein (UBB+1), which is indicative of disrupted ubiquitin homeostasis. The findings suggest that abnormal protein aggregation is linked to impaired protein homeostasis pathways in Kii ALS/PDC.

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