Proteasome and p97 mediate mitophagy and degradation of mitofusins induced by Parkin

AAA+ ATPase chaperone p97/VCPFAF2 governs basal pexophagy

Peroxisomes are organelles that are central to lipid metabolism and chemical detoxification. Despite advances in our understanding of peroxisome biogenesis, the mechanisms maintaining peroxisomal membrane proteins remain to be fully elucidated. We show here that mammalian FAF2/UBXD8, a membrane-associated cofactor of p97/VCP, maintains peroxisomal homeostasis by modulating the turnover of peroxisomal membrane proteins such as PMP70. In FAF2-deficient cells, PMP70 accumulation recruits the autophagy adaptor OPTN (Optineurin) to peroxisomes and promotes their autophagic clearance (pexophagy). Pexophagy is also induced by p97/VCP inhibition. FAF2 functions together with p97/VCP to negatively regulate pexophagy rather than as a factor for peroxisome biogenesis. Our results strongly suggest that p97/VCPFAF2-mediated extraction of ubiquitylated peroxisomal membrane proteins (e.g., PMP70) prevents peroxisomes from inducing nonessential autophagy under steady state conditions. These findings provide insight into molecular mechanisms underlying the regulation of peroxisomal integrity by p97/VCP and its associated cofactors.

The effect of biocide chloromethylisothiazolinone/methylisothiazolinone (CMIT/MIT) mixture on C2C12 muscle cell damage attributed to mitochondrial reactive oxygen species overproduction and autophagy activation

The mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (CMIT/MIT) is a biocide widely used as a preservative in various commercial products. This biocide has also been used as an active ingredient in humidifier disinfectants in South Korea, resulting in serious health effects among users. Recent evidence suggests that the underlying mechanism of CMIT/MIT-initiated toxicity might be associated with defects in mitochondrial functions. The aim of this study was to utilize the C2C12 skeletal muscle model to investigate the effects of CMIT/MIT on mitochondrial function and relevant molecular pathways associated with skeletal muscle dysfunction. Data demonstrated that exposure to CMIT/MIT during myogenic differentiation induced significant mitochondrial excess production of reactive oxygen species (ROS) and a decrease in intracellular ATP levels. Notably, CMIT/MIT significantly inhibited mitochondrial oxidative phosphorylation (Oxphos) and reduced mitochondrial mass at a lower concentration than the biocide amount, which diminished the viability of myotubes. CMIT/MIT induced activation of autophagy flux and decreased protein expression levels of myosin heavy chain (MHC). Taken together, CMIT/MIT exposure produced damage in C2C12 myotubes by impairing mitochondrial bioenergetics and activating autophagy. Our findings contribute to an increased understanding of the underlying mechanisms associated with CMIT/MIT-induced adverse skeletal muscle health effects.

Mitochondria break free: Mitochondria-derived vesicles in aging and associated conditions

Mitophagy is the intracellular recycling system that disposes damaged/inefficient mitochondria and allows biogenesis of new organelles to ensure mitochondrial quality is optimized. Dysfunctional mitophagy has been implicated in human aging and diseases. Multiple evolutionarily selected, redundant mechanisms of mitophagy have been identified, but their specific roles in human health and their potential exploitation as therapeutic targets are unclear. Recently, the characterization of the endosomal-lysosomal system has revealed additional mechanisms of mitophagy and mitochondrial quality control that operate via the production of mitochondria-derived vesicles (MDVs). Circulating MDVs can be isolated and characterized to provide an unprecedented opportunity to study this type of mitochondrial recycling in vivo and to relate it to human physiology and pathology. Defining the role of MDVs in human physiology, pathology, and aging is hampered by the lack of standardized methods to isolate, validate, and characterize these vesicles. Hence, some basic questions about MDVs remain unanswered. While MDVs are generated directly through the extrusion of mitochondrial membranes within the cell, a set of circulating extracellular vesicles leaking from the endosomal-lysosomal system and containing mitochondrial portions have also been identified and warrant investigation. Preliminary research indicates that MDV generation serves multiple biological roles and contributes to restoring cell homeostasis. However, studies have shown that MDVs may also be involved in pathological conditions. Therefore, further research is warranted to establish when/whether MDVs are supporting disease progression and/or are extracting damaged mitochondrial components to alleviate cellular oxidative burden and restore redox homeoastasis. This information will be relevant for exploiting these vesicles for therapeutic purpose. Herein, we provide an overview of preclinical and clinical studies on MDVs in aging and associated conditions and discuss the interplay between MDVs and some of the hallmarks of aging (mitophagy, inflammation, and proteostasis). We also outline open questions on MDV research that should be prioritized by future investigations.

Pink1/Parkin deficiency alters circulating lymphocyte populations and increases platelet-T cell aggregates in rats

Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Pink1 and Parkin are proteins that function together in mitochondrial quality control, and when they carry loss-of-function mutations lead to familial forms of PD. While much research has focused on central nervous system alterations in PD, peripheral contributions to PD pathogenesis are increasingly appreciated. We report Pink1/Parkin regulate glycolytic and mitochondrial oxidative metabolism in peripheral blood mononuclear cells (PBMCs) from rats. Pink1/Parkin deficiency induces changes in the circulating lymphocyte populations, namely increased CD4 + T cells and decreased CD8 + T cells and B cells. Loss of Pink1/Parkin leads to elevated platelet counts in the blood and increased platelet-T cell aggregation. Platelet-lymphocyte aggregates are associated with increased thrombosis risk suggesting targeting the Pink1/Parkin pathway in the periphery might have therapeutic potential.

The role of PINK1-Parkin in mitochondrial quality control

Mitophagy mediated by the recessive Parkinson's disease genes PINK1 and Parkin responds to mitochondrial damage to preserve mitochondrial function. In the pathway, PINK1 is the damage sensor, probing the integrity of the mitochondrial import pathway, and activating Parkin when import is blocked. Parkin is the effector, selectively marking damaged mitochondria with ubiquitin for mitophagy and other quality-control processes. This selective mitochondrial quality-control pathway may be especially critical for dopamine neurons affected in Parkinson's disease, in which the mitochondrial network is widely distributed throughout a highly branched axonal arbor. Here we review the current understanding of the role of PINK1-Parkin in the quality control of mitophagy, including sensing of mitochondrial distress by PINK1, activation of Parkin by PINK1 to induce mitophagy, and the physiological relevance of the PINK1-Parkin pathway.

Iron chelators as mitophagy agents: Potential and limitations

Mitochondrial autophagy (mitophagy) is very important process for the maintenance of cellular homeostasis, functionality and survival. Its dysregulation is associated with high risk and progression numerous serious diseases (e.g., oncological, neurodegenerative and cardiovascular ones). Therefore, targeting mitophagy mechanisms is very hot topic in the biological and medicinal research. The interrelationships between the regulation of mitophagy and iron homeostasis are now becoming apparent. In short, mitochondria are central point for the regulation of iron homeostasis, but change in intracellular cheatable iron level can induce/repress mitophagy. In this review, relationships between iron homeostasis and mitophagy are thoroughly discussed and described. Also, therapeutic applicability of mitophagy chelators in the context of individual diseases is comprehensively and critically evaluated.

Is mitochondrial morphology important for cellular physiology?

Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

Ginsenoside Rg1 ameliorates cerebral ischemia-reperfusion injury by regulating Pink1/ Parkin-mediated mitochondrial autophagy and inhibiting microglia NLRP3 activation

OBJECTIVE

This study aimed to further elucidate the mechanism of ginsenoside Rg1 in the treatment of cerebral ischemia-reperfusion.

METHODS

In this study, we observed the apoptosis of RM cells (microglia) after oxygen-glucose deprivation/reoxygenation (OGD/R) modeling before and after Rg1 administration, changes in mitochondrial membrane potential, changes in the content of Reactive oxygen species (ROS) and inflammatory vesicles NLR Family Pyrin Domain Containing 3 (NLRP3), and the expression levels of autophagy-related proteins, inflammatory factors, and apoptosis proteins. We further examined the pathomorphological changes in brain tissue, neuronal damage, changes in mitochondrial morphology and mitochondrial structure, and the autophagy-related proteins, inflammatory factors, and apoptosis proteins expression levels in CI/RI rats before and after administration of Rg1 in vivo experiments.

RESULTS

In vitro experiments showed that Rg1 induced mitochondrial autophagy, decreased mitochondrial membrane potential, and reduced ROS content thereby inhibiting NLRP3 activation, decreasing secretion of inflammatory factors and RM cell apoptosis by regulating the PTEN induced putative kinase 1(Pink1) /Parkin signaling pathway. In vivo experiments showed that Rg1 induced mitochondrial autophagy, inhibited NLRP3 activation, improved inflammatory response, and reduced apoptosis by regulating the Pink1/Parkin signaling pathway, and Rg1 significantly reduced the area of cerebral infarcts, improved the pathological state of brain tissue, and attenuated the neuronal damage, thus improving cerebral ischemia/reperfusion injury in rats.

CONCLUSION

Our results suggest that ginsenoside Rg1 can ameliorate cerebral ischemia-reperfusion injury by modulating Pink1/ Parkin-mediated mitochondrial autophagy in microglia and inhibiting microglial NLRP3 activation.

The p97-UBXD8 complex maintains peroxisome abundance by suppressing pexophagy

Peroxisomes are vital organelles involved in key metabolic functions in eukaryotic cells. Their significance is highlighted by peroxisome biogenesis disorders; severe childhood diseases marked by disrupted lipid metabolism. One mechanism regulating peroxisome abundance is through selective ubiquitylation of peroxisomal membrane proteins that triggers peroxisome degradation via selective autophagy (pexophagy). However, the mechanisms regulating pexophagy remain poorly understood in mammalian cells. Here we show that the evolutionarily conserved AAA-ATPase p97 and its membrane embedded adaptor UBXD8 are essential for maintaining peroxisome abundance. From quantitative proteomic studies we reveal that loss of UBXD8 affects many peroxisomal proteins. We find depletion of UBXD8 results in a loss of peroxisomes in a manner that is independent of the known role of UBXD8 in ER associated degradation (ERAD). Loss of UBXD8 or inhibition of p97 increases peroxisomal turnover through autophagy and can be rescued by depleting key autophagy proteins or overexpressing the deubiquitylating enzyme USP30. Furthermore, we find increased ubiquitylation of the peroxisomal membrane protein PMP70 in cells lacking UBXD8 or p97. Collectively, our findings identify a new role for the p97-UBXD8 complex in regulating peroxisome abundance by suppressing pexophagy.

Analysis of the mitochondria-associated degradation pathway (MAD) in yeast cells

Mitochondria are critical for cellular function in health, disease and aging. Mitochondria-associated degradation (MAD), a pathway for quality control of the organelle, recognizes and ubiquitinates unfolded mitochondrial proteins, removes them from the organelle using a conserved segregase complex, which contains an AAA-ATPase Cdc48 and its cofactors, and degrades them using the ubiquitin-proteasome system (UPS). Here, we describe an approach to (1) study the turnover and ubiquitination of candidate MAD substrates, (2) assay retrotranslocation and export of MAD substrates from the mitochondrial matrix in vitro, and (3) study interactions between MAD substrates and Cdc48 using the budding yeast, Saccharomyces cerevisiae, as a model organism.

Investigating the interplay between mitophagy and diabetic neuropathy: Uncovering the hidden secrets of the disease pathology

Mitophagy, the cellular process of selectively eliminating damaged mitochondria, plays a crucial role in maintaining metabolic balance and preventing insulin resistance, both key factors in type 2 diabetes mellitus (T2DM) development. When mitophagy malfunctions in diabetic neuropathy, it triggers a cascade of metabolic disruptions, including reduced energy production, increased oxidative stress, and cell death, ultimately leading to various complications. Thus, targeting mitophagy to enhance the process may have emerged as a promising therapeutic strategy for T2DM and its complications. Notably, plant-derived compounds with β-cell protective and mitophagy-stimulating properties offer potential as novel therapeutic agents. This review highlights the intricate mechanisms linking mitophagy dysfunction to T2DM and its complications, particularly neuropathy, elucidating potential therapeutic interventions for this debilitating disease.

Role of AMBRA1 in mitophagy regulation: emerging evidence in aging-related diseases

Aging is a gradual and irreversible physiological process that significantly increases the risks of developing a variety of pathologies, including neurodegenerative, cardiovascular, metabolic, musculoskeletal, and immune system diseases. Mitochondria are the energy-producing organelles, and their proper functioning is crucial for overall cellular health. Over time, mitochondrial function declines causing an increased release of harmful reactive oxygen species (ROS) and DNA, which leads to oxidative stress, inflammation and cellular damage, common features associated with various age-related pathologies. The impairment of mitophagy, the selective removal of damaged or dysfunctional mitochondria by autophagy, is relevant to the development and progression of age-related diseases. The molecular mechanisms that regulates mitophagy levels in aging remain largely uncharacterized. AMBRA1 is an intrinsically disordered scaffold protein with a unique property of regulating the activity of both proliferation and autophagy core machineries. While the role of AMBRA1 during embryonic development and neoplastic transformation has been extensively investigated, its functions in post-mitotic cells of adult tissues have been limited due to the embryonic lethality caused by AMBRA1 deficiency. Recently, a key role of AMBRA1 in selectively regulating mitophagy in post-mitotic cells has emerged. Here we summarize and discuss these results with the aim of providing a comprehensive view of the mitochondrial roles of AMBRA1, and how defective activity of AMBRA1 has been functionally linked to mitophagy alterations observed in age-related degenerative disorders, including muscular dystrophy/sarcopenia, Parkinson diseases, Alzheimer diseases and age-related macular degeneration.Abbreviations: AD: Alzheimer disease; AMD: age-related macular degeneration; AMBRA1: autophagy and beclin 1 regulator 1; APOE4: apolipoprotein E4; ATAD3A: ATPase family AAA domain containing 3A; ATG: autophagy related; BCL2: BCL2 apoptosis regulator; BH3: BCL2-homology-3; BNIP3L/NIX: BCL2 interacting protein 3 like; CDK: cyclin dependent kinase; CHUK/IKKα: component of inhibitor of nuclear factor kappa B kinase complex; CRL2: CUL2-RING ubiquitin ligase; DDB1: damage specific DNA binding protein 1; ER: endoplasmic reticulum; FOXO: forkhead box O; FUNDC1: FUN14 domain containing 1; GBA/β-glucocerebrosidase: glucosylceramidase beta; HUWE1: HECT, UBA and WWE domain containing E3 ubiquitin protein ligase 1; IDR: intrinsically disordered region; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; MCL1: MCL1 apoptosis regulator, BCL2 family member; MFN2: mitofusin 2; MTOR: mechanistic target of rapamycin kinase; MSA: multiple system atrophy; MYC: MYC proto-oncogene, bHLH transcription factor; NUMA1: nuclear mitotic apparatus protein 1; OMM; mitochondria outer membrane; PD: Parkinson disease; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PTK2/FAK: protein tyrosine kinase 2; ROS: reactive oxygen species; RPE: retinal pigment epithelium; SAD: sporadic AD; SOCS3: suppressor of cytokine signaling 3; SRC, SRC proto-oncogene, non-receptor tyrosine kinase; STAT3: signal transducer and activator of transcription 3; STING1: stimulator of interferon response cGAMP interactor 1; SQSTM1/p62: sequestosome 1; TBK1: TANK binding kinase 1; TGFB/TGFβ: transforming growth factor beta; TOMM: translocase of outer mitochondrial membrane; TRAF6: TNF receptor associated factor 6; TRIM32: tripartite motif containing 32; ULK1: unc-51 like autophagy activating kinase 1.

Additional feedforward mechanism of Parkin activation via binding of phospho-UBL and RING0 in trans

Loss-of-function Parkin mutations lead to early-onset of Parkinson's disease. Parkin is an auto-inhibited ubiquitin E3 ligase activated by dual phosphorylation of its ubiquitin-like (Ubl) domain and ubiquitin by the PINK1 kinase. Herein, we demonstrate a competitive binding of the phospho-Ubl and RING2 domains towards the RING0 domain, which regulates Parkin activity. We show that phosphorylated Parkin can complex with native Parkin, leading to the activation of autoinhibited native Parkin in trans. Furthermore, we show that the activator element (ACT) of Parkin is required to maintain the enzyme kinetics, and the removal of ACT slows the enzyme catalysis. We also demonstrate that ACT can activate Parkin in trans but less efficiently than when present in the cis molecule. Furthermore, the crystal structure reveals a donor ubiquitin binding pocket in the linker connecting REP and RING2, which plays a crucial role in Parkin activity.

The interplay between mitochondrial dynamics and autophagy: From a key homeostatic mechanism to a driver of pathology

The complex relationship between mitochondrial dynamics and autophagy illustrates how two cellular housekeeping processes are intimately linked, illuminating fundamental principles of cellular homeostasis and shedding light on disparate pathological conditions including several neurodegenerative disorders. Here we review the basic tenets of mitochondrial dynamics i.e., the concerted balance between fusion and fission of the organelle, and its interplay with macroautophagy and selective mitochondrial autophagy, also dubbed mitophagy, in the maintenance of mitochondrial quality control and ultimately in cell viability. We illustrate how conditions of altered mitochondrial dynamics reverberate on autophagy and vice versa. Finally, we illustrate how altered interplay between these two key cellular processes participates in the pathogenesis of human disorders affecting multiple organs and systems.

Autophagy in aging-related diseases and cancer: Principles, regulatory mechanisms and therapeutic potential

Macroautophagy/autophagy is primarily accountable for the degradation of damaged organelles and toxic macromolecules in the cells. Regarding the essential function of autophagy for preserving cellular homeostasis, changes in, or dysfunction of, autophagy flux can lead to disease development. In the current paper, the complicated function of autophagy in aging-associated pathologies and cancer is evaluated, highlighting the underlying molecular mechanisms that can affect longevity and disease pathogenesis. As a natural biological process, a reduction in autophagy is observed with aging, resulting in an accumulation of cell damage and the development of different diseases, including neurological disorders, cardiovascular diseases, and cancer. The MTOR, AMPK, and ATG proteins demonstrate changes during aging, and they are promising therapeutic targets. Insulin/IGF1, TOR, PKA, AKT/PKB, caloric restriction and mitochondrial respiration are vital for lifespan regulation and can modulate or have an interaction with autophagy. The specific types of autophagy, such as mitophagy that degrades mitochondria, can regulate aging by affecting these organelles and eliminating those mitochondria with genomic mutations. Autophagy and its specific types contribute to the regulation of carcinogenesis and they are able to dually enhance or decrease cancer progression. Cancer hallmarks, including proliferation, metastasis, therapy resistance and immune reactions, are tightly regulated by autophagy, supporting the conclusion that autophagy is a promising target in cancer therapy.

Novel C. elegans models of Lewy body disease reveal pathological protein interactions and widespread miRNA dysregulation

Lewy body diseases (LBD) comprise a group of complex neurodegenerative conditions originating from accumulation of misfolded alpha-synuclein (α-syn) in the form of Lewy bodies. LBD pathologies are characterized by α-syn deposition in association with other proteins such as Amyloid β (Aβ), Tau, and TAR-DNA-binding protein. To investigate the complex interactions of these proteins, we constructed 2 novel transgenic overexpressing (OE) C. elegans strains (α-synA53T;Taupro-agg (OE) and α-synA53T;Aβ1-42;Taupro-agg (OE)) and compared them with previously established Parkinson's, Alzheimer's, and Lewy Body Dementia disease models. The LBD models presented here demonstrate impairments including uncoordinated movement, egg-laying deficits, altered serotonergic and cholinergic signaling, memory and posture deficits, as well as dopaminergic neuron damage and loss. Expression levels of total and prone to aggregation α-syn protein were increased in α-synA53T;Aβ1-42 but decreased in α-synA53T;Taupro-agg animals when compared to α-synA53T animals suggesting protein interactions. These alterations were also observed at the mRNA level suggesting a pre-transcriptional mechanism. miRNA-seq revealed that cel-miR-1018 was upregulated in LBD models α-synA53T, α-synA53T;Aβ1-42, and α-synA53T;Taupro-agg compared with WT. cel-miR-58c was upregulated in α-synA53T;Taupro-agg but downregulated in α-synA53T and α-synA53T;Aβ1-42 compared with WT. cel-miR-41-3p and cel-miR-355-5p were significantly downregulated in 3 LBD models. Our results obtained in a model organism provide evidence of interactions between different pathological proteins and alterations in specific miRNAs that may further exacerbate or ameliorate LBD pathology.

Cell life-or-death events in osteoporosis: All roads lead to mitochondrial dynamics

Mitochondria exhibit heterogeneous shapes and networks within and among cell types and tissues, also in normal or osteoporotic bone tissues with complex cell types. This dynamic characteristic is determined by the high plasticity provided by mitochondrial dynamics and is stemmed from responding to the survival and functional requirements of various bone cells in a specific microenvironments. In contrast, mitochondrial dysfunction, induced by dysregulation of mitochondrial dynamics, may act as a trigger of cell death signals, including common apoptosis and other forms of programmed cell death (PCD). These PCD processes consisting of tightly structured cascade gene expression events, can further influence the bone remodeling by facilitating the death of various bone cells. Mitochondrial dynamics, therefore, drive the bone cells to stand at the crossroads of life and death by integrating external signals and altering metabolism, shape, and signal-response properties of mitochondria. This implies that targeting mitochondrial dynamics displays significant potential in treatment of osteoporosis. Considerable effort has been made in osteoporosis to emphasize the parallel roles of mitochondria in regulating energy metabolism, calcium signal transduction, oxidative stress, inflammation, and cell death. However, the emerging field of mitochondrial dynamics-related PCD is not well understood. Herein, to bridge the gap, we outline the latest knowledge on mitochondrial dynamics regulating bone cell life or death during normal bone remodeling and osteoporosis.

The parkin V380L variant is a genetic modifier of Machado-Joseph disease with impact on mitophagy

Machado-Joseph disease (MJD) is an autosomal dominant neurodegenerative spinocerebellar ataxia caused by a polyglutamine-coding CAG repeat expansion in the ATXN3 gene. While the CAG length correlates negatively with the age at onset, it accounts for approximately 50% of its variability only. Despite larger efforts in identifying contributing genetic factors, candidate genes with a robust and plausible impact on the molecular pathogenesis of MJD are scarce. Therefore, we analysed missense single nucleotide polymorphism variants in the PRKN gene encoding the Parkinson's disease-associated E3 ubiquitin ligase parkin, which is a well-described interaction partner of the MJD protein ataxin-3, a deubiquitinase. By performing a correlation analysis in the to-date largest MJD cohort of more than 900 individuals, we identified the V380L variant as a relevant factor, decreasing the age at onset by 3 years in homozygous carriers. Functional analysis in an MJD cell model demonstrated that parkin V380L did not modulate soluble or aggregate levels of ataxin-3 but reduced the interaction of the two proteins. Moreover, the presence of parkin V380L interfered with the execution of mitophagy-the autophagic removal of surplus or damaged mitochondria-thereby compromising cell viability. In summary, we identified the V380L variant in parkin as a genetic modifier of MJD, with negative repercussions on its molecular pathogenesis and disease age at onset.

Developmental disruption of the mitochondrial fission gene drp-1 extends the longevity of daf-2 insulin/IGF-1 receptor mutant

The dynamic nature of the mitochondrial network is regulated by mitochondrial fission and fusion, allowing for re-organization of mitochondria to adapt to the cell's ever-changing needs. As organisms age, mitochondrial fission and fusion become dysregulated and mitochondrial networks become increasingly fragmented. Modulation of mitochondrial dynamics has been shown to affect longevity in fungi, yeast, Drosophila and C. elegans. Disruption of the mitochondrial fission gene drp-1 drastically increases the already long lifespan of daf-2 insulin/IGF-1 signaling (IIS) mutants. In this work, we determined the conditions required for drp-1 disruption to extend daf-2 longevity and explored the molecular mechanisms involved. We found that knockdown of drp-1 during development is sufficient to extend daf-2 lifespan, while tissue-specific knockdown of drp-1 in neurons, intestine or muscle failed to increase daf-2 longevity. Disruption of other genes involved in mitochondrial fission also increased daf-2 lifespan as did treatment with RNA interference clones that decrease mitochondrial fragmentation. In exploring potential mechanisms involved, we found that deletion of drp-1 increases resistance to chronic stresses. In addition, we found that disruption of drp-1 increased mitochondrial and peroxisomal connectedness in daf-2 worms, increased oxidative phosphorylation and ATP levels, and increased mitophagy in daf-2 worms, but did not affect their ROS levels, food consumption or mitochondrial membrane potential. Disruption of mitophagy through RNA interference targeting pink-1 decreased the lifespan of daf-2;drp-1 worms suggesting that increased mitophagy contributes to their extended lifespan. Overall, this work defined the conditions under which drp-1 disruption increases daf-2 lifespan and has identified multiple changes in daf-2;drp-1 mutants that may contribute to their lifespan extension.

Novel Insights into Parkin-Mediated Mitochondrial Dysfunction and "Mito-Inflammation" in α-Synuclein Toxicity. The Role of the cGAS-STING Signalling Pathway

The prevalence of age-related neurodegenerative diseases, such as Parkinson's disease (PD) and related disorders continues to grow worldwide. Increasing evidence links intracellular inclusions of misfolded alpha-synuclein (α-syn) aggregates, so-called Lewy bodies (LB) and Lewy neuritis, to the progressive pathology of PD and other synucleinopathies. Our previous findings established that α-syn oligomers induce S-nitrosylation and deregulation of the E3-ubiquitin ligase Parkin, leading to mitochondrial disturbances in neuronal cells. The accumulation of damaged mitochondria as a consequence, together with the release of mitochondrial-derived damage-associated molecular patterns (mtDAMPs) could activate the innate immune response and induce neuroinflammation ("mito-inflammation"), eventually accelerating neurodegeneration. However, the molecular pathways that transmit pro-inflammatory signals from damaged mitochondria are not well understood. One of the proposed pathways could be the cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) (cGAS-STING) pathway, which plays a pivotal role in modulating the innate immune response. It has recently been suggested that cGAS-STING deregulation may contribute to the development of various pathological conditions. Especially, its excessive engagement may lead to neuroinflammation and appear to be essential for the development of neurodegenerative brain diseases, including PD. However, the precise molecular mechanisms underlying cGAS-STING pathway activation in PD and other synucleinopathies are not fully understood. This review focuses on linking mitochondrial dysfunction to neuroinflammation in these disorders, particularly emphasizing the role of the cGAS-STING signaling. We propose the cGAS-STING pathway as a critical driver of inflammation in α-syn-dependent neurodegeneration and hypothesize that cGAS-STING-driven "mito-inflammation" may be one of the key mechanisms promoting the neurodegeneration in PD. Understanding the molecular mechanisms of α-syn-induced cGAS-STING-associated "mito-inflammation" in PD and related synucleinopathies may contribute to the identification of new targets for the treatment of these disorders.

A substrate-interacting region of Parkin directs ubiquitination of the mitochondrial GTPase Miro1

Mutations in the gene encoding for the E3 ubiquitin ligase Parkin have been linked to early-onset Parkinson's disease. Besides many other cellular roles, Parkin is involved in clearance of damaged mitochondria via mitophagy - a process of particular importance in dopaminergic neurons. Upon mitochondrial damage, Parkin accumulates at the outer mitochondrial membrane and is activated, leading to ubiquitination of many mitochondrial substrates and recruitment of mitophagy effectors. While the activation mechanisms of autoinhibited Parkin have been extensively studied, it remains unknown how Parkin recognises its substrates for ubiquitination, and no substrate interaction site in Parkin has been reported. Here, we identify a conserved region in the flexible linker between the Ubl and RING0 domains of Parkin, which is indispensable for Parkin interaction with the mitochondrial GTPase Miro1. Our results explain the preferential targeting and ubiquitination of Miro1 by Parkin and provide a biochemical explanation for the presence of Parkin at the mitochondrial membrane prior to activation induced by mitochondrial damage. Our findings are important for understanding mitochondrial homeostasis and may inspire new therapeutic avenues for Parkinson's disease.

Mechanisms and implications of podocyte autophagy in chronic kidney disease

Autophagy is a protective mechanism through which cells degrade and recycle proteins and organelles to maintain cellular homeostasis and integrity. An accumulating body of evidence underscores the significant impact of dysregulated autophagy on podocyte injury in chronic kidney disease (CKD). In this review, we provide a comprehensive overview of the diverse types of autophagy and their regulation in cellular homeostasis, with a specific emphasis on podocytes. Furthermore, we discuss recent findings that focus on the functional role of different types of autophagy during podocyte injury in chronic kidney disease. The intricate interplay between different types of autophagy and podocyte health requires further research, which is critical for understanding the pathogenesis of CKD and developing targeted therapeutic interventions.

Pink1/Parkin deficiency alters circulating lymphocyte populations and increases platelet-T cell aggregates in rats

Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Pink1 and Parkin are proteins that function together in mitochondrial quality control, and when they carry loss-of-function mutations lead to familial forms of PD. While much research has focused on central nervous system alterations in PD, peripheral contributions to PD pathogenesis are increasingly appreciated. We report Pink1/Parkin regulate glycolytic and mitochondrial oxidative metabolism in peripheral blood mononuclear cells (PBMCs) from rats. Pink1/Parkin deficiency induces changes in the circulating lymphocyte populations, namely increased CD4 + T cells and decreased CD8 + T cells and B cells. Loss of Pink1/Parkin leads to elevated platelet counts in the blood and increased platelet-T cell aggregation. Platelet-lymphocyte aggregates are associated with increased thrombosis risk, and venous thrombosis is a cause of sudden death in PD, suggesting targeting the Pink1/Parkin pathway in the periphery has therapeutic potential.

VCP activator reverses nuclear proteostasis defects and enhances TDP-43 aggregate clearance in multisystem proteinopathy models

Pathogenic variants in valosin-containing protein (VCP) cause multisystem proteinopathy (MSP), a disease characterized by multiple clinical phenotypes including inclusion body myopathy, Paget's disease of the bone, and frontotemporal dementia (FTD). How such diverse phenotypes are driven by pathogenic VCP variants is not known. We found that these diseases exhibit a common pathologic feature: ubiquitinated intranuclear inclusions affecting myocytes, osteoclasts, and neurons. Moreover, knock-in cell lines harboring MSP variants show a reduction in nuclear VCP. Given that MSP is associated with neuronal intranuclear inclusions comprised of TDP-43 protein, we developed a cellular model whereby proteostatic stress results in the formation of insoluble intranuclear TDP-43 aggregates. Consistent with a loss of nuclear VCP function, cells harboring MSP variants or cells treated with VCP inhibitor exhibited decreased clearance of insoluble intranuclear TDP-43 aggregates. Moreover, we identified 4 compounds that activate VCP primarily by increasing D2 ATPase activity, where pharmacologic VCP activation appears to enhance clearance of insoluble intranuclear TDP-43 aggregate. Our findings suggest that VCP function is important for nuclear protein homeostasis, that impaired nuclear proteostasis may contribute to MSP, and that VCP activation may be a potential therapeutic by virtue of enhancing the clearance of intranuclear protein aggregates.

Valosin-Containing Protein (VCP): A Review of Its Diverse Molecular Functions and Clinical Phenotypes

In this review we examine the functionally diverse ATPase associated with various cellular activities (AAA-ATPase), valosin-containing protein (VCP/p97), its molecular functions, the mutational landscape of VCP and the phenotypic manifestation of VCP disease. VCP is crucial to a multitude of cellular functions including protein quality control, endoplasmic reticulum-associated degradation (ERAD), autophagy, mitophagy, lysophagy, stress granule formation and clearance, DNA replication and mitosis, DNA damage response including nucleotide excision repair, ATM- and ATR-mediated damage response, homologous repair and non-homologous end joining. VCP variants cause multisystem proteinopathy, and pathology can arise in several tissue types such as skeletal muscle, bone, brain, motor neurons, sensory neurons and possibly cardiac muscle, with the disease course being challenging to predict.

PRKN-linked familial Parkinson's disease: cellular and molecular mechanisms of disease-linked variants

Parkinson's disease (PD) is a common and incurable neurodegenerative disorder that arises from the loss of dopaminergic neurons in the substantia nigra and is mainly characterized by progressive loss of motor function. Monogenic familial PD is associated with highly penetrant variants in specific genes, notably the PRKN gene, where homozygous or compound heterozygous loss-of-function variants predominate. PRKN encodes Parkin, an E3 ubiquitin-protein ligase important for protein ubiquitination and mitophagy of damaged mitochondria. Accordingly, Parkin plays a central role in mitochondrial quality control but is itself also subject to a strict protein quality control system that rapidly eliminates certain disease-linked Parkin variants. Here, we summarize the cellular and molecular functions of Parkin, highlighting the various mechanisms by which PRKN gene variants result in loss-of-function. We emphasize the importance of high-throughput assays and computational tools for the clinical classification of PRKN gene variants and how detailed insights into the pathogenic mechanisms of PRKN gene variants may impact the development of personalized therapeutics.

PARKIN is not required to sustain OXPHOS function in adult mammalian tissues

Loss-of-function variants in the PRKN gene encoding the ubiquitin E3 ligase PARKIN cause autosomal recessive early-onset Parkinson's disease (PD). Extensive in vitro and in vivo studies have reported that PARKIN is involved in multiple pathways of mitochondrial quality control, including mitochondrial degradation and biogenesis. However, these findings are surrounded by substantial controversy due to conflicting experimental data. In addition, the existing PARKIN-deficient mouse models have failed to faithfully recapitulate PD phenotypes. Therefore, we have investigated the mitochondrial role of PARKIN during ageing and in response to stress by employing a series of conditional Parkin knockout mice. We report that PARKIN loss does not affect oxidative phosphorylation (OXPHOS) capacity and mitochondrial DNA (mtDNA) levels in the brain, heart, and skeletal muscle of aged mice. We also demonstrate that PARKIN deficiency does not exacerbate the brain defects and the pro-inflammatory phenotype observed in mice carrying high levels of mtDNA mutations. To rule out compensatory mechanisms activated during embryonic development of Parkin-deficient mice, we generated a mouse model where loss of PARKIN was induced in adult dopaminergic (DA) neurons. Surprisingly, also these mice did not show motor impairment or neurodegeneration, and no major transcriptional changes were found in isolated midbrain DA neurons. Finally, we report a patient with compound heterozygous PRKN pathogenic variants that lacks PARKIN and has developed PD. The PARKIN deficiency did not impair OXPHOS activities or induce mitochondrial pathology in skeletal muscle from the patient. Altogether, our results argue that PARKIN is dispensable for OXPHOS function in adult mammalian tissues.

The role of mitophagy in the development of chronic kidney disease

Chronic kidney disease (CKD) represents a significant global health concern, with renal fibrosis emerging as a prevalent and ultimate manifestation of this condition. The absence of targeted therapies presents an ongoing and substantial challenge. Accumulating evidence suggests that the integrity and functionality of mitochondria within renal tubular epithelial cells (RTECs) often become compromised during CKD development, playing a pivotal role in the progression of renal fibrosis. Mitophagy, a specific form of autophagy, assumes responsibility for eliminating damaged mitochondria to uphold mitochondrial equilibrium. Dysregulated mitophagy not only correlates with disrupted mitochondrial dynamics but also contributes to the advancement of renal fibrosis in CKD. While numerous studies have examined mitochondrial metabolism, ROS (reactive oxygen species) production, inflammation, and apoptosis in kidney diseases, the precise pathogenic mechanisms underlying mitophagy in CKD remain elusive. The exact mechanisms through which modulating mitophagy mitigates renal fibrosis, as well as its influence on CKD progression and prognosis, have not undergone systematic investigation. The role of mitophagy in AKI has been relatively clear, but the role of mitophagy in CKD is still rare. This article presents a comprehensive review of the current state of research on regulating mitophagy as a potential treatment for CKD. The objective is to provide fresh perspectives, viable strategies, and practical insights into CKD therapy, thereby contributing to the enhancement of human living conditions and patient well-being.

Mitophagy and its regulatory mechanisms in the biological effects of nanomaterials

Mitophagy is a selective cellular process critical for the removal of damaged mitochondria. It is essential in regulating mitochondrial number, ensuring mitochondrial functionality, and maintaining cellular equilibrium, ultimately influencing cell destiny. Numerous pathologies, such as neurodegenerative diseases, cardiovascular disorders, cancers, and various other conditions, are associated with mitochondrial dysfunctions. Thus, a detailed exploration of the regulatory mechanisms of mitophagy is pivotal for enhancing our understanding and for the discovery of novel preventive and therapeutic options for these diseases. Nanomaterials have become integral in biomedicine and various other sectors, offering advanced solutions for medical uses including biological imaging, drug delivery, and disease diagnostics and therapy. Mitophagy is vital in managing the cellular effects elicited by nanomaterials. This review provides a comprehensive analysis of the molecular mechanisms underpinning mitophagy, underscoring its significant influence on the biological responses of cells to nanomaterials. Nanoparticles can initiate mitophagy via various pathways, among which the PINK1-Parkin pathway is critical for cellular defense against nanomaterial-induced damage by promoting mitophagy. The role of mitophagy in biological effects was induced by nanomaterials, which are associated with alterations in Ca2+ levels, the production of reactive oxygen species, endoplasmic reticulum stress, and lysosomal damage.

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

Lysosomal damage sensing and lysophagy initiation by SPG20-ITCH

Cells respond to lysosomal membrane permeabilization by membrane repair or selective macroautophagy of damaged lysosomes, termed lysophagy, but it is not fully understood how this decision is made. Here, we uncover a pathway in human cells that detects lipid bilayer perturbations in the limiting membrane of compromised lysosomes, which fail to be repaired, and then initiates ubiquitin-triggered lysophagy. We find that SPG20 binds the repair factor IST1 on damaged lysosomes and, importantly, integrates that with the detection of damage-associated lipid-packing defects of the lysosomal membrane. Detection occurs via sensory amphipathic helices in SPG20 before rupture of the membrane. If lipid-packing defects are extensive, such as during lipid peroxidation, SPG20 recruits and activates ITCH, which marks the damaged lysosome with lysine-63-linked ubiquitin chains to initiate lysophagy and thus triages the lysosome for destruction. With SPG20 being linked to neurodegeneration, these findings highlight the relevance of a coordinated lysosomal damage response for cellular homeostasis.

Chronic replication stress invokes mitochondria dysfunction via impaired parkin activity

Replication stress is a major contributor to tumorigenesis because it provides a source of chromosomal rearrangements via recombination events. PARK2, which encodes parkin, a regulator of mitochondrial homeostasis, is located on one of the common fragile sites that are prone to rearrangement by replication stress, indicating that replication stress may potentially impact mitochondrial homeostasis. Here, we show that chronic low-dose replication stress causes a fixed reduction in parkin expression, which is associated with mitochondrial dysfunction, indicated by an increase in mtROS. Consistent with the major role of parkin in mitophagy, reduction in parkin protein expression was associated with a slight decrease in mitophagy and changes in mitochondrial morphology. In contrast, cells expressing ectopic PARK2 gene does not show mtROS increases and changes in mitochondrial morphology even after exposure to chronic replication stress, suggesting that intrinsic fragility at PARK2 loci associated with parkin reduction is responsible for mitochondrial dysfunction caused by chronic replication stress. As endogenous replication stress and mitochondrial dysfunction are both involved in multiple pathophysiology, our data support the therapeutic development of recovery of parkin expression in human healthcare.

Regulation of PM2.5 on mitochondrial damage in H9c2 cells through miR-421/SIRT3 pathway and protective effect of miR-421 inhibitor and resveratrol

Fine particulate matter (PM2.5) exposure is associated with cardiovascular disease (CVD) morbidity and mortality. Mitochondria are sensitive targets of PM2.5, and mitochondrial dysfunction is closely related to the occurrence of CVD. The epigenetic mechanism of PM2.5-triggered mitochondrial injury of cardiomyocytes is unclear. This study focused on the miR-421/SIRT3 signaling pathway to investigate the regulatory mechanism in cardiac mitochondrial dynamics imbalance in rat H9c2 cells induced by PM2.5. Results illustrated that PM2.5 impaired mitochondrial function and caused dynamics homeostasis imbalance. Besides, PM2.5 up-regulated miR-421 and down-regulated SIRT3 gene expression, along with decreasing p-FOXO3a (SIRT3 downstream target gene) and p-Parkin expression and triggering abnormal expression of fusion gene OPA1 and fission gene Drp1. Further, miR-421 inhibitor (miR-421i) and resveratrol significantly elevated the SIRT3 levels in H9c2 cells after PM2.5 exposure and mediated the expression of SOD2, OPA1 and Drp1, restoring the mitochondrial morphology and function. It suggests that miR-421/SIRT3 pathway plays an epigenetic regulatory role in mitochondrial damage induced by PM2.5 and that miR-421i and resveratrol exert protective effects against PM2.5-incurred cardiotoxicity.

Charcot-Marie-tooth disease type 2A: An update on pathogenesis and therapeutic perspectives

Mutations in the gene encoding MFN2 have been identified as associated with Charcot-Marie-Tooth disease type 2A (CMT2A), a neurological disorder characterized by a broad clinical phenotype involving the entire nervous system. MFN2, a dynamin-like GTPase protein located on the outer mitochondrial membrane, is well-known for its involvement in mitochondrial fusion. Numerous studies have demonstrated its participation in a network crucial for various other mitochondrial functions, including mitophagy, axonal transport, and its controversial role in endoplasmic reticulum (ER)-mitochondria contacts. Considerable progress has been made in the last three decades in elucidating the disease pathogenesis, aided by the generation of animal and cellular models that have been instrumental in studying disease physiology. A review of the literature reveals that, up to now, no definitive pharmacological treatment for any CMT2A variant has been established; nonetheless, recent years have witnessed substantial progress. Many treatment approaches, especially concerning molecular therapy, such as histone deacetylase inhibitors, peptide therapy to increase mitochondrial fusion, the new therapeutic strategies based on MF1/MF2 balance, and SARM1 inhibitors, are currently in preclinical testing. The literature on gene silencing and gene replacement therapies is still limited, except for a recent study by Rizzo et al.(Rizzo et al., 2023), which recently first achieved encouraging results in in vitro and in vivo models of the disease. The near-future goal for these promising therapies is to progress to the stage of clinical translation.

Mitochondrial network dynamics in pulmonary disease: Bridging the gap between inflammation, oxidative stress, and bioenergetics

Once thought of in terms of bioenergetics, mitochondria are now widely accepted as both the orchestrator of cellular health and the gatekeeper of cell death. The pulmonary disease field has performed extensive efforts to explore the role of mitochondria in regulating inflammation, cellular metabolism, apoptosis, and oxidative stress. However, a critical component of these processes needs to be more studied: mitochondrial network dynamics. Mitochondria morphologically change in response to their environment to regulate these processes through fusion, fission, and mitophagy. This allows mitochondria to adapt their function to respond to cellular requirements, a critical component in maintaining cellular homeostasis. For that reason, mitochondrial network dynamics can be considered a bridge that brings multiple cellular processes together, revealing a potential pathway for therapeutic intervention. In this review, we discuss the critical modulators of mitochondrial dynamics and how they are affected in pulmonary diseases, including chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), acute lung injury (ALI), and pulmonary arterial hypertension (PAH). A dysregulated mitochondrial network plays a crucial role in lung disease pathobiology, and aberrant fission/fusion/mitophagy pathways are druggable processes that warrant further exploration. Thus, we also discuss the candidates for lung disease therapeutics that regulate mitochondrial network dynamics.

Mitophagy suppression by miquelianin-rich lotus leaf extract induces 'beiging' of white fat via AMPK/DRP1-PINK1/PARKIN signaling axis

BACKGROUND

Lotus (Nelumbo nucifera) leaf has been described to have anti-obesity activity, but the role of white fat 'browning' or 'beiging' in its beneficial metabolic actions remains unclear. Here, 3T3-L1 cells and high-fat-diet (HFD)-fed mice were used to evaluate the effects of miquelianin-rich lotus leaf extract (LLE) on white-to-beige fat conversion and its regulatory mechanisms.

RESULTS

Treatment with LLE increased mitochondrial abundance, mitochondrial membrane potential and NAD+ /NADH ratio in 3T3-L1 cells, suggesting its potential in promoting mitochondrial activity. qPCR and/or western blotting analysis confirmed that LLE induced the expression of beige fat-enriched gene signatures (e.g. Sirt1, Cidea, Dio2, Prdm16, Ucp1, Cd40, Cd137, Cited1) and mitochondrial biogenesis-related markers (e.g. Nrf1, Cox2, Cox7a, Tfam) in 3T3-L1 cells and inguinal white adipose tissue of HFD-fed mice. Furthermore, we found that LLE treatment inhibited mitochondrial fission protein DRP1 and blocked mitophagy markers such as PINK1, PARKIN, BECLIN1 and LC-3B. Chemical inhibition experiments revealed that AMPK/DRP1 signaling was required for LLE-induced beige fat formation via suppressing PINK1/PARKIN/mitophagy.

CONCLUSION

Our data reveal a novel mechanism underlying the anti-obesity effect of LLE, namely the induction of white fat beiging via AMPK/DRP1/mitophagy signaling. © 2023 Society of Chemical Industry.

ALS-related p97 R155H mutation disrupts lysophagy in iPSC-derived motor neurons

Mutations in the AAA+ ATPase p97 cause multisystem proteinopathy 1, which includes amyotrophic lateral sclerosis; however, the pathogenic mechanisms that contribute to motor neuron loss remain obscure. Here, we use two induced pluripotent stem cell models differentiated into spinal motor neurons to investigate how p97 mutations perturb the motor neuron proteome. Using quantitative proteomics, we find that motor neurons harboring the p97 R155H mutation have deficits in the selective autophagy of lysosomes (lysophagy). p97 R155H motor neurons are unable to clear damaged lysosomes and have reduced viability. Lysosomes in mutant motor neurons have increased pH compared with wild-type cells. The clearance of damaged lysosomes involves UBXD1-p97 interaction, which is disrupted in mutant motor neurons. Finally, inhibition of the ATPase activity of p97 using the inhibitor CB-5083 rescues lysophagy defects in mutant motor neurons. These results add to the evidence that endo-lysosomal dysfunction is a key aspect of disease pathogenesis in p97-related disorders.

Ubiquitin Ligase Parkin Regulates the Stability of SARS-CoV-2 Main Protease and Suppresses Viral Replication

The highly infectious coronavirus SARS-CoV-2 relies on the viral main protease (Mpro, also known as 3CLpro or Nsp5) to proteolytically process the polyproteins encoded by the viral genome for the release of functional units in the host cells to initiate viral replication. Mpro also interacts with host proteins of the innate immune pathways, such as IRF3 and STAT1, to suppress their activities and facilitate virus survival and proliferation. To identify the host mechanism for regulating Mpro, we screened various classes of E3 ubiquitin ligases and found that Parkin of the RING-between-RING family can induce the ubiquitination and degradation of Mpro in the cell. Furthermore, when the cells undergo mitophagy, the PINK1 kinase activates Parkin and enhances the ubiquitination of Mpro. We also found that elevated expression of Parkin in the cells significantly decreased the replication of SARS-CoV-2 virus. Interestingly, SARS-CoV-2 infection downregulates Parkin expression in the mouse lung tissues compared to healthy controls. These results suggest an antiviral role of Parkin as a ubiquitin ligase targeting Mpro and the potential for exploiting the virus-host interaction mediated by Parkin to treat SARS-CoV-2 infection.

Tom20 gates PINK1 activity and mediates its tethering of the TOM and TIM23 translocases upon mitochondrial stress

Mutations in PTEN-induced putative kinase 1 (PINK1) cause autosomal recessive early-onset Parkinson's disease (PD). PINK1 is a Ser/Thr kinase that regulates mitochondrial quality control by triggering mitophagy mediated by the ubiquitin (Ub) ligase Parkin. Upon mitochondrial damage, PINK1 accumulates on the outer mitochondrial membrane forming a high-molecular-weight complex with the translocase of the outer membrane (TOM). PINK1 then phosphorylates Ub, which enables recruitment and activation of Parkin followed by autophagic clearance of the damaged mitochondrion. Thus, Parkin-dependent mitophagy hinges on the stable accumulation of PINK1 on the TOM complex. Yet, the mechanism linking mitochondrial stressors to PINK1 accumulation and whether the translocases of the inner membrane (TIMs) are also involved remain unclear. Herein, we demonstrate that mitochondrial stress induces the formation of a PINK1-TOM-TIM23 supercomplex in human cultured cell lines, dopamine neurons, and midbrain organoids. Moreover, we show that PINK1 is required to stably tether the TOM to TIM23 complexes in response to stress such that the supercomplex fails to accumulate in cells lacking PINK1. This tethering is dependent on an interaction between the PINK1 N-terminal-C-terminal extension module and the cytosolic domain of the Tom20 subunit of the TOM complex, the disruption of which, by either designer or PD-associated PINK1 mutations, inhibits downstream mitophagy. Together, the findings provide key insight into how PINK1 interfaces with the mitochondrial import machinery, with important implications for the mechanisms of mitochondrial quality control and PD pathogenesis.

TNF-α-Induced KAT2A Impedes BMMSC Quiescence by Mediating Succinylation of the Mitophagy-Related Protein VCP

Regular quiescence and activation are important for the function of bone marrow mesenchymal stem cells (BMMSC), multipotent stem cells that are widely used in the clinic due to their capabilities in tissue repair and inflammatory disease treatment. TNF-α is previously reported to regulate BMMSC functions, including multilineage differentiation and immunoregulation. The present study demonstrates that TNF-α impedes quiescence and promotes the activation of BMMSC in vitro and in vivo. Mechanistically, the TNF-α-induced expression of KAT2A promotes the succinylation of VCP at K658, which inhibits the interaction between VCP and MFN1 and thus inhibits mitophagy. Furthermore, activated BMMSC exhibits stronger fracture repair and immunoregulation functions in vivo. This study contributes to a better understanding of the mechanisms of BMMSC quiescence and activation and to improving the effectiveness of BMMSC in clinical applications.

Mitochondrial dynamics and mitochondrial autophagy: Molecular structure, orchestrating mechanism and related disorders

Mitochondrial dynamics and autophagy play essential roles in normal cellular physiological activities, while abnormal mitochondrial dynamics and mitochondrial autophagy can cause cancer and related disorders. Abnormal mitochondrial dynamics usually occur in parallel with mitochondrial autophagy. Both have been reported to have a synergistic effect and can therefore complement or inhibit each other. Progress has been made in understanding the classical mitochondrial PINK1/Parkin pathway and mitochondrial dynamical abnormalities. Still, the mechanisms and regulatory pathways underlying the interaction between mitophagy and mitochondrial dynamics remain unexplored. Like other existing reviews, we review the molecular structure of proteins involved in mitochondrial dynamics and mitochondrial autophagy, and how their abnormalities can lead to the development of related diseases. We will also review the individual or synergistic effects of abnormal mitochondrial dynamics and mitophagy leading to cellular proliferation, differentiation and invasion. In addition, we explore the mechanisms underlying mitochondrial dynamics and mitochondrial autophagy to contribute to targeted and precise regulation of mitochondrial function. Through the study of abnormal mitochondrial dynamics and mitochondrial autophagy regulation mechanisms, as well as the role of early disease development, effective targets for mitochondrial function regulation can be proposed to enable accurate diagnosis and treatment of the associated disorders.

Cloflucarban Illuminates Specificity and Context-Dependent Activation of the PINK1-Parkin Pathway by Mitochondrial Complex Inhibition

The PTEN-induced kinase 1 (PINK1)-Parkin pathway plays a vital role in maintaining a healthy pool of mitochondria in higher eukaryotic cells. While the downstream components of this pathway are well understood, the upstream triggers remain less explored. In this study, we conducted an extensive analysis of inhibitors targeting various mitochondrial electron transport chain (ETC) complexes to investigate their potential as activators of the PINK1-Parkin pathway. We identified cloflucarban, an antibacterial compound, as a novel pathway activator that simultaneously inhibits mitochondrial complexes III and V, and V. RNA interference (RNAi) confirmed that the dual inhibition of these complexes activates the PINK1-Parkin pathway. Intriguingly, we discovered that albumin, specifically bovine serum albumin (BSA) and human serum albumin (HSA) commonly present in culture media, can hinder carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-induced pathway activation. However, cloflucarban's efficacy remains unaffected by albumin, highlighting its reliability for studying the PINK1-Parkin pathway. This study provides insights into the activation of the upstream PINK1-Parkin pathway and underscores the influence of culture conditions on research outcomes. Cloflucarban emerges as a promising tool for investigating mitochondrial quality control and neurodegenerative diseases.

Mechanism and role of mitophagy in the development of severe infection

Mitochondria produce adenosine triphosphate and potentially contribute to proinflammatory responses and cell death. Mitophagy, as a conservative phenomenon, scavenges waste mitochondria and their components in the cell. Recent studies suggest that severe infections develop alongside mitochondrial dysfunction and mitophagy abnormalities. Restoring mitophagy protects against excessive inflammation and multiple organ failure in sepsis. Here, we review the normal mitophagy process, its interaction with invading microorganisms and the immune system, and summarize the mechanism of mitophagy dysfunction during severe infection. We highlight critical role of normal mitophagy in preventing severe infection.

Mitochondrial entry gate as regulatory hub

Mitochondria import 1000-1300 different precursor proteins from the cytosol. The main mitochondrial entry gate is formed by the translocase of the outer membrane (TOM complex). Molecular coupling and modification of TOM subunits control and modulate protein import in response to cellular signaling. The TOM complex functions as regulatory hub to integrate mitochondrial protein biogenesis and quality control into the cellular proteostasis network.

Activation of Ca2+ phosphatase Calcineurin regulates Parkin translocation to mitochondria and mitophagy in flies

Selective removal of dysfunctional mitochondria via autophagy is crucial for the maintenance of cellular homeostasis. This event is initiated by the translocation of the E3 ubiquitin ligase Parkin to damaged mitochondria, and it requires the Serine/Threonine-protein kinase PINK1. In a coordinated set of events, PINK1 operates upstream of Parkin in a linear pathway that leads to the phosphorylation of Parkin, Ubiquitin, and Parkin mitochondrial substrates, to promote ubiquitination of outer mitochondrial membrane proteins. Ubiquitin-decorated mitochondria are selectively recruiting autophagy receptors, which are required to terminate the organelle via autophagy. In this work, we show a previously uncharacterized molecular pathway that correlates the activation of the Ca2+-dependent phosphatase Calcineurin to Parkin translocation and Parkin-dependent mitophagy. Calcineurin downregulation or genetic inhibition prevents Parkin translocation to CCCP-treated mitochondria and impairs stress-induced mitophagy, whereas Calcineurin activation promotes Parkin mitochondrial recruitment and basal mitophagy. Calcineurin interacts with Parkin, and promotes Parkin translocation in the absence of PINK1, but requires PINK1 expression to execute mitophagy in MEF cells. Genetic activation of Calcineurin in vivo boosts basal mitophagy in neurons and corrects locomotor dysfunction and mitochondrial respiratory defects of a Drosophila model of impaired mitochondrial functions. Our study identifies Calcineurin as a novel key player in the regulation of Parkin translocation and mitophagy.

Mitochondrial iron dyshomeostasis and its potential as a therapeutic target for Parkinson's disease

Abnormal iron accumulation has been implicated in the etiology of Parkinson's disease (PD). Understanding how iron damages dopaminergic neurons in the substantia nigra (SN) of PD is particularly important for developing targeted neurotherapeutic strategies for the disease. However, it is still not fully understood how excess iron contributes to the neurodegeneration of dopaminergic neurons in PD. There has been increased attention on mitochondrial iron dyshomeostasis, iron-induced mitochondrial dysfunction and ferroptosis in PD. Therefore, this review begins with a brief introduction to describe cellular iron metabolism and the dysregulation of iron metabolism in PD. Then we provide an update on how iron is delivered to mitochondria and induces the damage of dopaminergic neurons in PD. In addition, we also summarize new research progress on iron-dependent ferroptosis in PD and mitochondria-localized proteins involved in ferroptosis. This will provide new insight into potential therapeutic strategies targeting mitochondrial iron dysfunction.

Post-translational modification and mitochondrial function in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease with currently no cure. Most PD cases are sporadic, and about 5-10% of PD cases present a monogenic inheritance pattern. Mutations in more than 20 genes are associated with genetic forms of PD. Mitochondrial dysfunction is considered a prominent player in PD pathogenesis. Post-translational modifications (PTMs) allow rapid switching of protein functions and therefore impact various cellular functions including those related to mitochondria. Among the PD-associated genes, Parkin, PINK1, and LRRK2 encode enzymes that directly involved in catalyzing PTM modifications of target proteins, while others like α-synuclein, FBXO7, HTRA2, VPS35, CHCHD2, and DJ-1, undergo substantial PTM modification, subsequently altering mitochondrial functions. Here, we summarize recent findings on major PTMs associated with PD-related proteins, as enzymes or substrates, that are shown to regulate important mitochondrial functions and discuss their involvement in PD pathogenesis. We will further highlight the significance of PTM-regulated mitochondrial functions in understanding PD etiology. Furthermore, we emphasize the potential for developing important biomarkers for PD through extensive research into PTMs.

Arrestin-3 binds parkin and enhances parkin-dependent mitophagy

Arrestins were discovered for their role in homologous desensitization of G-protein-coupled receptors (GPCRs). Later non-visual arrestins were shown to regulate several signaling pathways. Some of these pathways require arrestin binding to GPCRs, the regulation of others is receptor independent. Here, we demonstrate that arrestin-3 binds the E3 ubiquitin ligase parkin via multiple sites, preferentially interacting with its RING0 domain. Identification of the parkin domains involved suggests that arrestin-3 likely relieves parkin autoinhibition and/or stabilizes the enzymatically active "open" conformation of parkin. Arrestin-3 binding enhances ubiquitination by parkin of the mitochondrial protein mitofusin-1 and facilitates parkin-mediated mitophagy in HeLa cells. Furthermore, arrestin-3 and its mutant with enhanced parkin binding rescue mitofusin-1 ubiquitination and mitophagy in the presence of the Parkinson's disease-associated R275W parkin mutant, which is defective in both functions. Thus, modulation of parkin activity via arrestin-3 might be a novel strategy of anti-parkinsonian therapy.

Sensitivity to targeted UBA1 inhibition in a myeloid cell line model of VEXAS syndrome

Somatic UBA1 mutations in hematopoietic cells are a hallmark of Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic (VEXAS) syndrome, which is a late-onset inflammatory disease associated with bone marrow failure and high mortality. The majority of UBA1 mutations in VEXAS syndrome comprise hemizygous mutations affecting methionine-41 (M41), leading to the expression of UBA1M41T, UBA1M41V, or UBA1M41L and globally reduced protein polyubiquitination. Here, we used CRISPR-Cas9 to engineer isogenic 32D mouse myeloid cell lines expressing hemizygous Uba1WT or Uba1M41L from the endogenous locus. Consistent with prior analyses of patients with VEXAS syndrome samples, hemizygous Uba1M41L expression was associated with loss of the UBA1b protein isoform, gain of the UBA1c protein isoform, reduced polyubiquitination, abnormal cytoplasmic vacuoles, and increased production of interleukin-1β and inflammatory chemokines. Vacuoles in Uba1M41L cells contained a variety of endolysosomal membranes, including small vesicles, multivesicular bodies, and multilamellar lysosomes. Uba1M41L cells were more sensitive to the UBA1 inhibitor TAK243. TAK243 treatment promoted apoptosis in Uba1M41L cells and led to preferential loss of Uba1M41L cells in competition assays with Uba1WT cells. Knock-in of a TAK243-binding mutation, Uba1A580S, conferred TAK243 resistance. In addition, overexpression of catalytically active UBA1b in Uba1M41L cells restored polyubiquitination and increased TAK243 resistance. Altogether, these data indicate that loss of UBA1b underlies a key biochemical phenotype associated with VEXAS syndrome and renders cells with reduced UBA1 activity vulnerable to targeted UBA1 inhibition. Our Uba1M41L knock-in cell line is a useful model of VEXAS syndrome that will aid in the study of disease pathogenesis and the development of effective therapies.

Post-Subfunctionalization Functions of HIF-1αA and HIF-1αB in Cyprinid Fish: Fine-Tuning Mitophagy and Apoptosis Regulation Under Hypoxic Stress

Hypoxia-inducible factor 1 (HIF-1) is a crucial transcriptional factor that can restore oxygen balance in the body by regulating multiple vital activities. Two HIF-1α copies were retained in cyprinid fish after experiencing a teleost-specific genome duplication. How the "divergent collaboration" of HIF-1αA and HIF-1αB proceeds in regulating mitophagy and apoptosis under hypoxic stress in cells of cyprinid fish remains unclear. In this study, zebrafish HIF-1αA/B expression plasmids were constructed and transfected into the epithelioma papulosum cyprini cells and were subjected to hypoxic stress. HIF-1αA induced apoptosis through promoting ROS generation and mitochondrial depolarization when cells were subjected to oxygen deficiency. Conversely, HIF-1αB was primarily responsible for mitophagy induction, prompting ATP production to mitigate apoptosis. HIF-1αA did not induce mitophagy in the mitochondria and lysosomes co-localization assay but it was involved in the regulation of different mitophagy pathways. Over-expression of HIF-1αA increased the expression of bnip3, fundc1, Beclin1, and foxo3, suggesting it has a dual role in mitochondrial autophagy and cell death. Each duplicated copy also experienced functional divergence and target shifting in the regulation of complexes in the mitochondrial electron transport chain (ETC). Our findings shed light on the post-subfunctionalization function of HIF-1αA and HIF-1αB in zebrafish to fine-tune regulation of mitophagy and apoptosis following hypoxia exposure.