Mutations in the parkin gene cause autosomal recessive juvenile parkinsonism

Parkin R274W mutation affects muscle and mitochondrial physiology

Recessive mutations in the Parkin gene (PRKN) are the most common cause of young-onset inherited parkinsonism. Parkin is a multifunctional E3 ubiquitin ligase that plays a variety of roles in the cell including the degradation of proteins and the maintenance of mitochondrial homeostasis, integrity, and biogenesis. In 2001, the R275W mutation in the PRKN gene was identified in two unrelated families with a multigenerational history of postural tremor, dystonia and parkinsonism. Drosophila models of Parkin R275W showed selective and progressive degeneration of dopaminergic neuronal clusters, mitochondrial abnormalities, and prominent climbing defects. In the Prkn mouse orthologue, the amino acid R274 corresponds to human R275. Here we described an age-related motor impairment and a muscle phenotype in R274W +/+ mice. In vitro, Parkin R274W mutation correlates with abnormal myoblast differentiation, mitochondrial defects, and alteration in mitochondrial mRNA and protein levels. Our data suggest that the Parkin R274W mutation may impact mitochondrial physiology and eventually myoblast proliferation and differentiation.

Neurodegenerative disorders, metabolic icebergs, and mitohormesis

Neurodegenerative disorders are typically "split" based on their hallmark clinical, anatomical, and pathological features, but they can also be "lumped" by a shared feature of impaired mitochondrial biology. This leads us to present a scientific framework that conceptualizes Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD) as "metabolic icebergs" comprised of a tip, a bulk, and a base. The visible tip conveys the hallmark neurological symptoms, neurodegenerative regions, and neuronal protein aggregates for each disorder. The hidden bulk depicts impaired mitochondrial biology throughout the body, which is multifaceted and may be subdivided into impaired cellular metabolism, cell-specific mitotypes, and mitochondrial behaviours, functions, activities, and features. The underlying base encompasses environmental factors, especially modern industrial toxins, dietary lifestyles, and cognitive, physical, and psychosocial behaviours, but also accommodates genetic factors specific to familial forms of AD, PD, and ALS, as well as HD. Over years or decades, chronic exposure to a particular suite of environmental and genetic factors at the base elicits a trajectory of impaired mitochondrial biology that maximally impacts particular subsets of mitotypes in the bulk, which eventually surfaces as the hallmark features of a particular neurodegenerative disorder at the tip. We propose that impaired mitochondrial biology can be repaired and recalibrated by activating "mitohormesis", which is optimally achieved using strategies that facilitate a balanced oscillation between mitochondrial stressor and recovery phases. Sustainably harnessing mitohormesis may constitute a potent preventative and therapeutic measure for people at risk of, or suffering with, neurodegenerative disorders.

GALNT9 enrichment attenuates MPP+-induced cytotoxicity by ameliorating protein aggregations containing α-synuclein and mitochondrial dysfunction

BACKGROUND

GALNTs (UDP-GalNAc; polypeptide N-acetylgalactosaminyltransferases) initiate mucin-type O-GalNAc glycosylation by adding N-GalNAc to protein serine/threonine residues. Abnormalities in O-GalNAc glycosylation are involved in various disorders such as Parkinson's disease (PD), a neurodegenerative disorder. GALNT9 is potentially downregulated in PD patients.

METHODS

To determine whether GALNT9 enrichment ameliorates cytotoxicity related to PD-like variations, a pcDNA3.1-GALNT9 plasmid was constructed and transfected into SH-SY5Y cells to establish a GALNT9-overexpressing cell model.

RESULTS

Downregulation of GALNT9 and O-GalNAc glycosylation was confirmed in our animal and cellular models of PD-like variations. GALNT9 supplementation greatly attenuated cytotoxicity induced by MPP+ (1-Methyl-4-phenylpyridinium iodide) since it led to increased levels of tyrosine hydroxylase and dopamine, reduced rates of apoptosis, and significantly ameliorated MPP+-induced mitochondrial dysfunction by alleviating abnormal levels of mitochondrial membrane potential and reactive oxygen species. A long-lasting mPTP (mitochondrial permeability transition pores) opening and calcium efflux resulted in significantly lower activity in the cytochrome C-associated apoptotic pathway and mitophagy process, signifying that GALNT9 supplementation maintained neuronal cell health under MPP+ exposure. Additionally, it was found that glycans linked to proteins influenced the formation of protein aggregates containing α-synuclein, and GALNT9 supplement dramatically reduced such insoluble protein aggregations under MPP+ treatment. Glial GALNT9 predominantly appears under pathological conditions like PD-like variations.

CONCLUSIONS

GALNT9 enrichment improved cell survival, and glial GALNT9 potentially represents a pathogenic index for PD patients. This study provides insights into the development of therapeutic strategies for the treatment of PD.

Preserved striatal innervation maintains motor function despite severe loss of nigral dopaminergic neurons

Degeneration of dopaminergic neurons in the substantia nigra and their striatal axon terminals causes cardinal motor symptoms of Parkinson's disease. In idiopathic cases, high levels of mitochondrial DNA alterations, leading to mitochondrial dysfunction, are a central feature of these vulnerable neurons. Here we present a mouse model expressing the K320E variant of the mitochondrial helicase Twinkle in dopaminergic neurons, leading to accelerated mitochondrial DNA mutations. These K320E-TwinkleDaN mice showed normal motor function at 20 months of age, although ∼70% of nigral dopaminergic neurons had perished. Remaining neurons still preserved ∼75% of axon terminals in the dorsal striatum and enabled normal dopamine release. Transcriptome analysis and viral tracing confirmed compensatory axonal sprouting of the surviving neurons. We conclude that a small population of substantia nigra dopaminergic neurons is able to adapt to the accumulation of mitochondrial DNA mutations and maintain motor control.

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.

Dual-localized PPTC7 limits mitophagy through proximal and dynamic interactions with BNIP3 and NIX

PPTC7 is a mitochondrial-localized phosphatase that suppresses BNIP3- and NIX-mediated mitophagy, but the mechanisms underlying this regulation remain ill-defined. Here, we demonstrate that loss of PPTC7 upregulates BNIP3 and NIX post-transcriptionally and independent of HIF-1α stabilization. Loss of PPTC7 prolongs the half-life of BNIP3 and NIX while blunting their accumulation in response to proteasomal inhibition, suggesting that PPTC7 promotes the ubiquitin-mediated turnover of BNIP3 and NIX. Consistently, overexpression of PPTC7 limits the accumulation of BNIP3 and NIX protein levels, which requires an intact catalytic motif but is surprisingly independent of its targeting to mitochondria. Consistently, we find that PPTC7 is dual-localized to the outer mitochondrial membrane and the matrix. Importantly, anchoring PPTC7 to the outer mitochondrial membrane is sufficient to blunt BNIP3 and NIX accumulation, and proximity labeling and fluorescence co-localization experiments demonstrate that PPTC7 dynamically associates with BNIP3 and NIX within the native cellular environment. Collectively, these data reveal that a fraction of PPTC7 localizes to the outer mitochondrial membrane to promote the proteasomal turnover of BNIP3 and NIX, limiting basal mitophagy.

Clinical characteristics and pathophysiological properties of newly discovered LRRK2 variants associated with Parkinson's disease

Leucine-rich repeat kinase 2 (LRRK2) is the most common gene responsible for familial Parkinson's disease (PD). The gene product of LRRK2 contains multiple protein domains, including armadillo repeat, ankyrin repeat, leucine-rich repeat (LRR), Ras-of-complex (ROC), C-terminal of ROC (COR), kinase, and WD40 domains. In this study, we performed genetic screening of LRRK2 in our PD cohort, detecting sixteen LRRK2 rare variants. Among them, we selected seven variants that are likely to be familial and characterized them in terms of LRRK2 protein function, along with clinical information and one pathological analysis. The seven variants were S1120P and N1221K in the LRR domain; I1339M, S1403R, and V1447M in the ROC domain; and I1658F and D1873H in the COR domain. The kinase activity of the LRRK2 variants N1221K, S1403R, V1447M, and I1658F toward Rab10, a well-known phosphorylation substrate, was higher than that of wild-type LRRK2. LRRK2 D1873H showed enhanced self-association activity, whereas LRRK2 S1403R and D1873H showed reduced microtubule-binding activity. Pathological analysis of a patient with the LRRK2 V1447M variant was also performed, which revealed Lewy pathology in the brainstem. No functional alterations in terms of kinase activity, self-association activity, and microtubule-binding activity were detected in LRRK2 S1120P and I1339M variants. However, the patient with PD carrying LRRK2 S1120P variant also had a heterozygous Glucosylceramidase beta 1 (GBA1) L444P variant. In conclusion, we characterized seven LRRK2 variants potentially associated with PD. Five of the seven variants in different LRRK2 domains exhibited altered properties in kinase activity, self-association, and microtubule-binding activity, suggesting that each domain variant may contribute to disease progression in different ways.

Mitochondrial function in oral health and disease

Monitoring mitochondrial function and mitochondrial quality control in tissues is a crucial aspect of understanding cellular health and dysfunction, which may inform about the pathogenesis of several conditions associated with aging, including chronic inflammatory conditions, neurodegenerative disorders and metabolic diseases. This process involves assessing the functionality, integrity, and abundance of mitochondria within cells. Several lines of evidence have explored techniques and methods for monitoring mitochondrial quality control in tissues. In this review, we summarize and provide our perspective considering the latest evidence in mitochondrial function and mitochondrial quality control in oral health and disease with a particular focus in periodontal inflammation. This research is significant for gaining insights into cellular health and the pathophysiology of periodontal disease, a dysbiosis-related, immune mediated and age-associated chronic condition representing a significant burden to US elderly population. Approaches for assessing mitochondrial health status reviewed here include assessing mitochondrial dynamics, mitophagy, mitochondrial biogenesis, oxidative stress, electron transport chain function and metabolomics. Such assessments help researchers comprehend the role of mitochondrial function in cellular homeostasis and its implications for oral diseases.

Construct, Face, and Predictive Validity of Parkinson's Disease Rodent Models

Parkinson's disease (PD) is the second most common neurodegenerative disease globally. Current drugs only alleviate symptoms without halting disease progression, making rodent models essential for researching new therapies and understanding the disease better. However, selecting the right model is challenging due to the numerous models and protocols available. Key factors in model selection include construct, face, and predictive validity. Construct validity ensures the model replicates pathological changes seen in human PD, focusing on dopaminergic neurodegeneration and a-synuclein aggregation. Face validity ensures the model's symptoms mirror those in humans, primarily reproducing motor and non-motor symptoms. Predictive validity assesses if treatment responses in animals will reflect those in humans, typically involving classical pharmacotherapies and surgical procedures. This review highlights the primary characteristics of PD and how these characteristics are validated experimentally according to the three criteria. Additionally, it serves as a valuable tool for researchers in selecting the most appropriate animal model based on established validation criteria.

Excitotoxicity, Oxytosis/Ferroptosis, and Neurodegeneration: Emerging Insights into Mitochondrial Mechanisms

Mitochondrial dysfunction plays a pivotal role in the development of age-related diseases, particularly neurodegenerative disorders. The etiology of mitochondrial dysfunction involves a multitude of factors that remain elusive. This review centers on elucidating the role(s) of excitotoxicity, oxytosis/ferroptosis and neurodegeneration within the context of mitochondrial bioenergetics, biogenesis, mitophagy and oxidative stress and explores their intricate interplay in the pathogenesis of neurodegenerative diseases. The effective coordination of mitochondrial turnover processes, notably mitophagy and biogenesis, is assumed to be critically important for cellular resilience and longevity. However, the age-associated decrease in mitophagy impedes the elimination of dysfunctional mitochondria, consequently impairing mitochondrial biogenesis. This deleterious cascade results in the accumulation of damaged mitochondria and deterioration of cellular functions. Both excitotoxicity and oxytosis/ferroptosis have been demonstrated to contribute significantly to the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's Disease (HD), Amyotrophic Lateral Sclerosis (ALS) and Multiple Sclerosis (MS). Excitotoxicity, characterized by excessive glutamate signaling, initiates a cascade of events involving calcium dysregulation, energy depletion, and oxidative stress and is intricately linked to mitochondrial dysfunction. Furthermore, emerging concepts surrounding oxytosis/ferroptosis underscore the importance of iron-dependent lipid peroxidation and mitochondrial engagement in the pathogenesis of neurodegeneration. This review not only discusses the individual contributions of excitotoxicity and ferroptosis but also emphasizes their convergence with mitochondrial dysfunction, a key driver of neurodegenerative diseases. Understanding the intricate crosstalk between excitotoxicity, oxytosis/ferroptosis, and mitochondrial dysfunction holds potential to pave the way for mitochondrion-targeted therapeutic strategies. Such strategies, with a focus on bioenergetics, biogenesis, mitophagy, and oxidative stress, emerge as promising avenues for therapeutic intervention.

Capturing the catalytic intermediates of parkin ubiquitination

Parkin is an E3 ubiquitin ligase implicated in early-onset forms of Parkinson's disease. It catalyzes a transthiolation reaction by accepting ubiquitin (Ub) from an E2 conjugating enzyme, forming a short-lived thioester intermediate, and transfers Ub to mitochondrial membrane substrates to signal mitophagy. A major impediment to the development of Parkinsonism therapeutics is the lack of structural and mechanistic detail for the essential, short-lived transthiolation intermediate. It is not known how Ub is recognized by the catalytic Rcat domain in parkin that enables Ub transfer from an E2~Ub conjugate to the catalytic site and the structure of the transthiolation complex is undetermined. Here, we capture the catalytic intermediate for the Rcat domain of parkin in complex with ubiquitin (Rcat-Ub) and determine its structure using NMR-based chemical shift perturbation experiments. We show that a previously unidentified α-helical region near the Rcat domain is unmasked as a recognition motif for Ub and guides the C-terminus of Ub toward the parkin catalytic site. Further, we apply a combination of guided AlphaFold modeling, chemical cross-linking, and single turnover assays to establish and validate a model of full-length parkin in complex with UbcH7, its donor Ub, and phosphoubiquitin, trapped in the process of transthiolation. Identification of this catalytic intermediate and orientation of Ub with respect to the Rcat domain provides important structural insights into Ub transfer by this E3 ligase and explains how the previously enigmatic Parkinson's pathogenic mutation T415N alters parkin activity.

Unraveling the Triad: Hypoxia, Oxidative Stress and Inflammation in Neurodegenerative Disorders

The mammalian brain's complete dependence on oxygen for ATP production makes it highly susceptible to hypoxia, at high altitudes or in clinical scenarios including anemia or pulmonary disease. Hypoxia plays a crucial role in the development of various brain disorders, such as Alzheimer's, Parkinson's, and other age-related neurodegenerative diseases. On the other hand, a decrease in environmental oxygen levels, such as prolonged stays at high elevations, may have beneficial impacts on the process of ageing and the likelihood of death. Additionally, the utilization of controlled hypoxia exposure could potentially serve as a therapeutic approach for age-related brain diseases. Recent findings indicate that the involvement of HIF-1α and the NLRP3 inflammasome is of significant importance in the development of Alzheimer's disease. HIF-1α serves as a pivotal controller of various cellular reactions to oxygen deprivation, exerting influence on a multitude of physiological mechanisms such as energy metabolism and inflammatory responses. The NLRP3 plays a crucial role in the innate immune system by coordinating the initiation of inflammatory reactions through the assembly of the inflammasome complex. This review examines the information pertaining to the contrasting effects of hypoxia on the brain, highlighting both its positive and deleterious effects and molecular pathways that are involved in mediating these different effects. This study explores potential strategies for therapeutic intervention that focus on restoring cellular balance and reducing neuroinflammation, which are critical aspects in addressing this severe neurodegenerative condition and addresses crucial inquiries that warrant further future investigations.

Mitochondrial Parkinsonism: A Practical Guide to Genes and Clinical Diagnosis

BACKGROUND

Primary mitochondrial diseases (PMDs) are the most common inborn errors of energy metabolism, with a combined prevalence of 1 in 4300. They can result from mutations in either nuclear DNA (nDNA) or mitochondrial DNA (mtDNA). These disorders are multisystemic and mainly affect high energy-demanding tissues, such as muscle and the central nervous system (CNS). Among many clinical features of CNS involvement, parkinsonism is one of the most common movement disorders in PMDs.

METHODS

This review provides a pragmatic educational overview of the most recent advances in the field of mitochondrial parkinsonism, from pathophysiology and genetic etiologies to phenotype and diagnosis.

RESULTS

mtDNA maintenance and mitochondrial dynamics alterations represent the principal mechanisms underlying mitochondrial parkinsonism. It can be present in isolation, alongside other movement disorders or, more commonly, as part of a multisystemic phenotype. Mutations in several nuclear-encoded genes (ie, POLG, TWNK, SPG7, and OPA1) and, more rarely, mtDNA mutations, are responsible for mitochondrial parkinsonism. Progressive external opthalmoplegia and optic atrophy may guide genetic etiology identification.

CONCLUSION

A comprehensive deep-phenotyping approach is needed to reach a diagnosis of mitochondrial parkinsonism, which lacks distinctive clinical features and exemplifies the intricate genotype-phenotype interplay of PMDs.

Precision Medicine in Parkinson's Disease Using Induced Pluripotent Stem Cells

Parkinson's disease (PD) is one of the most devastating neurological diseases; however, there is no effective cure yet. The availability of human induced pluripotent stem cells (iPSCs) provides unprecedented opportunities to understand the pathogenic mechanism and identification of new therapy for PD. Here a new model system of PD, including 2D human iPSC-derived midbrain dopaminergic (mDA) neurons, 3D iPSC-derived midbrain organoids (MOs) with cellular complexity, and more advanced microphysiological systems (MPS) with 3D organoids, is introduced. It is believed that successful integrations and applications of iPSC, organoid, and MPS technologies can bring new insight on PD's pathogenesis that will lead to more effective treatments for this debilitating disease.

BL-918 activates PINK1/Parkin signaling pathway to ameliorate the progression of Parkinson's disease

The pathogenesis of Parkinson's disease (PD) has been associated with mitochondrial dysfunction. Given that the PINK1/Parkin pathway governs mitochondrial quality control by inducing mitophagy to remove damaged mitochondria, therapeutic approaches to activate PINK1/Parkin-mediated mitophagy have the potential in the treatment of PD. Here, we have identified a new small molecule, BL-918, as an inducer of mitophagy via activating the PINK1/Parkin pathway. BL-918 triggers PINK1 accumulation and Parkin mitochondrial translocation to initiate PINK1/Parkin-mediated mitophagy. We found that mitochondrial membrane potential and mitochondrial permeability transition pore were involved in BL-918-induced PINK1/Parkin pathway activation. Moreover, we showed that BL-918 mitigated PD progression in MPTP-induced PD mice in a PINK1-dependent manner. Our results unravel a new activator of the PINK1/Parkin signaling pathway and provide a potential strategy for the treatment of PD and other diseases with dysfunctional mitochondria.

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.

Diverse Functions of Parkin in Midbrain Dopaminergic Neurons

Parkinson's disease (PD) is characterized by preferential degeneration of midbrain dopaminergic neurons that contributes to its typical clinical manifestation. Mutations in the parkin gene (PARK2) represent a relatively common genetic cause of early onset PD. Parkin has been implicated in PINK1-dependent mitochondrial quantity control by targeting dysfunctional mitochondria to lysosomes via mitophagy. Recent evidence suggests that parkin can be activated in PINK1-independent manner to regulate synaptic function in human dopaminergic neurons. Neuronal activity triggers CaMKII-mediated activation of parkin and its recruitment to synaptic vesicles where parkin promotes binding of synaptojanin-1 to endophilin A1 and facilitates vesicle endocytosis. In PD patient neurons, disruption of this pathway on loss of parkin leads to defective recycling of synaptic vesicles and accumulation of toxic oxidized dopamine that at least in part explains preferential vulnerability of midbrain dopaminergic neurons. These findings suggest a convergent mechanism for PD-linked mutations in parkin, synaptojanin-1, and endophilin A1 and highlight synaptic dysfunction as an early pathogenic event in PD. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Interplay of Proteostasis Capacity and Protein Aggregation: Implications for Cellular Function and Disease

Eukaryotic cells are equipped with an intricate proteostasis network (PN), comprising nearly 3,000 components dedicated to preserving proteome integrity and sustaining protein homeostasis. This protective system is particularly important under conditions of external and intrinsic cell stress, where inherently dynamic proteins may unfold and lose functionality. A decline in proteostasis capacity is associated with the aging process, resulting in a reduced folding efficiency of newly synthesized proteins and a deficit in the cellular capacity to degrade misfolded proteins. A critical consequence of PN insufficiency is the accumulation of cytotoxic protein aggregates that underlie various age-related neurodegenerative conditions and other pathologies. By interfering with specific proteostasis components, toxic aggregates place an excessive burden on the PN's ability to maintain proteome integrity. This initiates a feed-forward loop, wherein the generation of misfolded and aggregated proteins ultimately leads to proteostasis collapse and cellular demise.

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.

New opportunities for antioxidants in amelioration of neurodegenerative diseases

This comprehensive review elucidates the critical role of antioxidants to mitigate oxidative stress, a common denominator in an array of neurodegenerative disorders. Oxidative stress-induced damage has been linked to the development of diseases such as Alzheimer's, Parkinson's, Huntington's disease and amyotrophic lateral sclerosis. This article examines a wide range of scientific literature and methodically delineates the several methods by which antioxidants exercise their neuroprotective benefits. It also explores into the complex relationship between oxidative stress and neuroinflammation, focusing on how antioxidants can alter signaling pathways and transcription factors to slow neurodegenerative processes. Key antioxidants, such as vitamins C and E, glutathione, and polyphenolic compounds, are tested for their ability to combat reactive oxygen and nitrogen species. The dual character of antioxidants, which operate as both direct free radical scavengers and regulators of cellular redox homeostasis, is investigated in terms of therapeutic potential. Furthermore, the study focuses on new antioxidant-based therapy techniques and their mechanisms including Nrf-2, PCG1α, Thioredoxin etc., which range from dietary interventions to targeted antioxidant molecules. Insights into ongoing clinical studies evaluating antioxidant therapies in neurodegenerative illnesses offer an insight into the translational potential of antioxidant research. Finally, this review summarizes our present understanding of antioxidant processes in neurodegenerative illnesses, providing important possibilities for future study and treatment development.

Pathological Impact of Redox Post-Translational Modifications

Oxidative stress is involved in the development of several pathologies. The different reactive oxygen species (ROS) produced during oxidative stress are at the origin of redox post-translational modifications (PTMs) on proteins and impact nucleic acids and lipids. This review provides an overview of recent data on cysteine and methionine oxidation and protein carbonylation following oxidative stress in a pathological context. Oxidation, like nitration, is a selective process and not all proteins are impacted. It depends on multiple factors, including amino acid environment, accessibility, and physical and chemical properties, as well as protein structures. Thiols can undergo reversible oxidations and others that are irreversible. On the contrary, carbonylation represents irreversible PTM. To date, hundreds of proteins were shown to be modified by ROS and reactive nitrogen species (RNS). We reviewed recent advances in the impact of redox-induced PTMs on protein functions and activity, as well as its involvement in disease development or treatment. These data show a complex situation of the involvement of redox PTM on the function of targeted proteins. Many proteins can have their activity decreased by the oxidation of cysteine thiols or methionine S-methyl thioethers, while for other proteins, this oxidation will be activating. This complexity of redox PTM regulation suggests that a global antioxidant therapeutic approach, as often proposed, is unlikely to be effective. However, the specificity of the effect obtained by targeting a cysteine or methionine residue to be able to inactivate or activate a particular protein represents a major interest if it is possible to consider this targeting from a therapeutic point of view with our current pharmacological tools. Antioxid. Redox Signal. 41, 152-180.

Global prevalence and incidence of Young Onset Parkinson's disease: A systematic review and meta-analysis

BACKGROUND

There is a lack of enough evidence regarding the epidemiology of Young-onset Parkinson's disease (YOPD) which is needed by clinicians and healthcare policymakers.

AIM

Herein, in this systematic review and meta-analysis, we aimed to estimate the global prevalence and incidence rates of YOPD.

METHODS

We searched the literature in PubMed, Scopus, and Web of Science in May 2022. We included retrospective, prospective, cross-sectional observational population-based studies that reported the prevalence or incidence of PD in individuals younger than 40 years with known diagnostic criteria.

RESULTS

After two-step screening, 50 studies were eligible to be included in our study. The age-standardized prevalence of YOPD was 10.2 per 100,000 persons globally while it was 14.7 per 100,000 population in European countries. Age-standardized prevalence estimates for 5-year age bands showed that the YOPD prevalence estimates varied from 6.1 per 100,000 population in the group aged 20-24 to 16.1 per 100,000 population in the group aged 35-39. Also, the age-standardized incidence of YOPD was 1.3 per 100,000 person-years population worldwide and 1.2 per 100,000 person-years in the European population.

CONCLUSION

Based on this systematic review and meta-analysis, the overall prevalence of YOPD is 10.2 per 100,000 population, although estimates of the prevalence and incidence in low-income countries remain scarce. To improve monitoring and certain diagnoses of YOPD, healthcare providers and policymakers should be aware that much more effective tools are required.

Parkin deficiency promotes liver cancer metastasis by TMEFF1 transcription activation via TGF-β/Smad2/3 pathway

Parkin (PARK2) deficiency is frequently observed in various cancers and potentially promotes tumor progression. Here, we showed that Parkin expression is downregulated in liver cancer tissues, which correlates with poor patient survival. Parkin deficiency in liver cancer cells promotes migration and metastasis as well as changes in EMT and metastasis markers. A negative correlation exists between TMEFF1 and Parkin expression in liver cancer cells and tumor tissues. Parkin deficiency leads to upregulation of TMEFF1 which promotes migration and metastasis. TMEFF1 transcription is activated by Parkin-induced endogenous TGF-β production and subsequent phosphorylation of Smad2/3 and its binding to TMEFF1 promotor. TGF-β inhibitor and TMEFF1 knockdown can reverse shParkin-induced cell migration and changes of EMT markers. Parkin interacts with and promotes the ubiquitin-dependent degradation of HIF-1α/HIF-1β and p53, which accounts for the suppression of TGF-β production. Our data have revealed that Parkin deficiency in cancer leads to the activation of the TGF-β/Smad2/3 pathway, resulting in the expression of TMEFF1 which promotes cell migration, EMT, and metastasis in liver cancer cells.

Control of mitophagy initiation and progression by the TBK1 adaptors NAP1 and SINTBAD

Mitophagy preserves overall mitochondrial fitness by selectively targeting damaged mitochondria for degradation. The regulatory mechanisms that prevent PTEN-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase Parkin (PINK1/Parkin)-dependent mitophagy and other selective autophagy pathways from overreacting while ensuring swift progression once initiated are largely elusive. Here, we demonstrate how the TBK1 (TANK-binding kinase 1) adaptors NAP1 (NAK-associated protein 1) and SINTBAD (similar to NAP1 TBK1 adaptor) restrict the initiation of OPTN (optineurin)-driven mitophagy by competing with OPTN for TBK1. Conversely, they promote the progression of nuclear dot protein 52 (NDP52)-driven mitophagy by recruiting TBK1 to NDP52 and stabilizing its interaction with FIP200. Notably, OPTN emerges as the primary recruiter of TBK1 during mitophagy initiation, which in return boosts NDP52-mediated mitophagy. Our results thus define NAP1 and SINTBAD as cargo receptor rheostats, elevating the threshold for mitophagy initiation by OPTN while promoting the progression of the pathway once set in motion by supporting NDP52. These findings shed light on the cellular strategy to prevent pathway hyperactivity while still ensuring efficient progression.

The Utility of Long-Read Sequencing in Diagnosing Genetic Autosomal Recessive Parkinson's Disease: a genetic screening study

Background

Mutations within the genes PRKN and PINK1 are the leading cause of early onset autosomal recessive Parkinson's disease (PD). However, the genetic cause of most early-onset PD (EOPD) cases still remains unresolved. Long-read sequencing has successfully identified many pathogenic structural variants that cause disease, but this technology has not been widely applied to PD. We recently identified the genetic cause of EOPD in a pair of monozygotic twins by uncovering a complex structural variant that spans over 7 Mb, utilizing Oxford Nanopore Technologies (ONT) long-read sequencing. In this study, we aimed to expand on this and assess whether a second variant could be detected with ONT long-read sequencing in other unresolved EOPD cases reported to carry one heterozygous variant in PRKN or PINK1.

Methods

ONT long-read sequencing was performed on patients with one reported PRKN/PINK1 pathogenic variant. EOPD patients with an age at onset younger than 50 were included in this study. As a positive control, we also included EOPD patients who had already been identified to carry two known PRKN pathogenic variants. Initial genetic testing was performed using either short-read targeted panel sequencing for single nucleotide variants and multiplex ligation-dependent probe amplification (MLPA) for copy number variants.

Results

48 patients were included in this study (PRKN "one-variant" n = 24, PINK1 "one-variant" n = 12, PRKN "two-variants" n = 12). Using ONT long-read sequencing, we detected a second pathogenic variant in six PRKN "one-variant" patients (26%, 6/23) but none in the PINK1 "one-variant" patients (0%, 0/12). Long-read sequencing identified one case with a complex inversion, two instances of structural variant overlap, and three cases of duplication. In addition, in the positive control PRKN "two-variants" group, we were able to identify both pathogenic variants in PRKN in all the patients (100%, 12/12).

Conclusions

This data highlights that ONT long-read sequencing is a powerful tool to identify a pathogenic structural variant at the PRKN locus that is often missed by conventional methods. Therefore, for cases where conventional methods fail to detect a second variant for EOPD, long-read sequencing should be considered as an alternative and complementary approach.

A-Syn(ful) MAM: A Fresh Perspective on a Converging Domain in Parkinson's Disease

Parkinson's disease (PD) is a disease of an unknown origin. Despite that, decades of research have provided considerable evidence that alpha-synuclein (αSyn) is central to the pathogenesis of disease. Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) are functional domains formed at contact sites between the ER and mitochondria, with a well-established function of MAMs being the control of lipid homeostasis within the cell. Additionally, there are numerous proteins localized or enriched at MAMs that have regulatory roles in several different molecular signaling pathways required for cellular homeostasis, such as autophagy and neuroinflammation. Alterations in several of these signaling pathways that are functionally associated with MAMs are found in PD. Taken together with studies that find αSyn localized at MAMs, this has implicated MAM (dys)function as a converging domain relevant to PD. This review will highlight the many functions of MAMs and provide an overview of the literature that finds αSyn, in addition to several other PD-related proteins, localized there. This review will also detail the direct interaction of αSyn and αSyn-interacting partners with specific MAM-resident proteins. In addition, recent studies exploring new methods to investigate MAMs will be discussed, along with some of the controversies regarding αSyn, including its several conformations and subcellular localizations. The goal of this review is to highlight and provide insight on a domain that is incompletely understood and, from a PD perspective, highlight those complex interactions that may hold the key to understanding the pathomechanisms underlying PD, which may lead to the targeted development of new therapeutic strategies.

Mitochondrial DNA Instability Supersedes Parkin Mutations in Driving Mitochondrial Proteomic Alterations and Functional Deficits in Polg Mutator Mice

Mitochondrial quality control is essential in mitochondrial function. To examine the importance of Parkin-dependent mechanisms in mitochondrial quality control, we assessed the impact of modulating Parkin on proteome flux and mitochondrial function in a context of reduced mtDNA fidelity. To accomplish this, we crossed either the Parkin knockout mouse or ParkinW402A knock-in mouse lines to the Polg mitochondrial mutator line to generate homozygous double mutants. In vivo longitudinal isotopic metabolic labeling was followed by isolation of liver mitochondria and synaptic terminals from the brain, which are rich in mitochondria. Mass spectrometry and bioenergetics analysis were assessed. We demonstrate that slower mitochondrial protein turnover is associated with loss of mtDNA fidelity in liver mitochondria but not synaptic terminals, and bioenergetic function in both tissues is impaired. Pathway analysis revealed loss of mtDNA fidelity is associated with disturbances of key metabolic pathways, consistent with its association with metabolic disorders and neurodegeneration. Furthermore, we find that loss of Parkin leads to exacerbation of Polg-driven proteomic consequences, though it may be bioenergetically protective in tissues exhibiting rapid mitochondrial turnover. Finally, we provide evidence that, surprisingly, dis-autoinhibition of Parkin (ParkinW402A) functionally resembles Parkin knockout and fails to rescue deleterious Polg-driven effects. Our study accomplishes three main outcomes: (1) it supports recent studies suggesting that Parkin dependence is low in response to an increased mtDNA mutational load, (2) it provides evidence of a potential protective role of Parkin insufficiency, and (3) it draws into question the therapeutic attractiveness of enhancing Parkin function.

Mechanism of human PINK1 activation at the TOM complex in a reconstituted system

Loss-of-function mutations in PTEN-induced kinase 1 (PINK1) are a frequent cause of early-onset Parkinson's disease (PD). Stabilization of PINK1 at the translocase of outer membrane (TOM) complex of damaged mitochondria is critical for its activation. The mechanism of how PINK1 is activated in the TOM complex is unclear. Here, we report that co-expression of human PINK1 and all seven TOM subunits in Saccharomyces cerevisiae is sufficient for PINK1 activation. We use this reconstitution system to systematically assess the role of each TOM subunit toward PINK1 activation. We unambiguously demonstrate that the TOM20 and TOM70 receptor subunits are required for optimal PINK1 activation and map their sites of interaction with PINK1 using AlphaFold structural modeling and mutagenesis. We also demonstrate an essential role of the pore-containing subunit TOM40 and its structurally associated subunits TOM7 and TOM22 for PINK1 activation. These findings will aid in the development of small-molecule activators of PINK1 as a therapeutic strategy for PD.

Exploring orphan GPCRs in neurodegenerative diseases

Neurodegenerative disorders represent a significant and growing health burden worldwide. Unfortunately, limited therapeutic options are currently available despite ongoing efforts. Over the past decades, research efforts have increasingly focused on understanding the molecular mechanisms underlying these devastating conditions. Orphan receptors, a class of receptors with no known endogenous ligands, emerge as promising druggable targets for diverse diseases. This review aims to direct attention to a subgroup of orphan GPCRs, in particular class A orphans that have roles in neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Multiple sclerosis. We highlight the diverse roles orphan receptors play in regulating critical cellular processes such as synaptic transmission, neuronal survival and neuro-inflammation. Moreover, we discuss the therapeutic potential of targeting orphan receptors for the treatment of neurodegenerative disorders, emphasizing recent advances in drug discovery and preclinical studies. Finally, we outline future directions and challenges in orphan receptor research.

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.

The mechanistic view of non-coding RNAs as a regulator of inflammatory pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra pars compacta, leading to motor and non-motor symptoms. Emerging evidence suggests that inflammation plays a crucial role in the pathogenesis of PD, with the NLRP3 inflammasome implicated as a key mediator. Nfon-coding RNAs (ncRNAs), including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), have recently garnered attention for their regulatory roles in various biological processes, including inflammation. This review aims to provide a mechanistic insight into how ncRNAs function as regulators of inflammatory pathways in PD, with a specific focus on the NLRP3 inflammasome. We discuss the dysregulation of miRNAs and lncRNAs in PD pathogenesis and their impact on neuroinflammation through modulation of NLRP3 activation, cytokine production, and microglial activation. Additionally, we explore the crosstalk between ncRNAs, alpha-synuclein pathology, and mitochondrial dysfunction, further elucidating the intricate network underlying PD-associated inflammation. Understanding the mechanistic roles of ncRNAs in regulating inflammatory pathways may offer novel therapeutic targets for the treatment of PD and provide insights into the broader implications of ncRNA-mediated regulation in neuroinflammatory diseases.

Pathological mechanisms and treatment of sporadic Parkinson's disease: past, present, and future

For a special issue, we review studies on the pathogenesis of nigral cell death and the treatment of sporadic Parkinson's disease (sPD) over the past few decades, with a focus on the studies performed by Prof. Mizuno and our group. Prof. Mizuno proposed the initial concept that mitochondrial function may be impaired in sPD. When working at Jichi Medical School, he found a decrease in complex I of the mitochondrial electron transfer complex in the substantia nigra of patients with Parkinson's disease (PD) and MPTP models. After moving to Juntendo University as a professor and chairman, he continued to study the mechanisms of cell death in the substantia nigra of patients with sPD. Under his supervision, I studied the relationships between PD and apoptosis, PD and iron involvement, mitochondrial dysfunction and apoptosis, and PD and neuroinflammation. Moving to Kitasato University, we focused on PD and the cytotoxicity of alpha synuclein (αSyn) as well as brain neuropathology. Eventually, I moved to Osaka University, where I continued working on PD and αSyn projects to promote therapeutic research. In this paper, we present the details of these studies in the following order: past, present, and future.

Current trends in basic research on Parkinson's disease: from mitochondria, lysosome to α-synuclein

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra and other brain regions. A key pathological feature of PD is the abnormal accumulation of α-synuclein protein within affected neurons, manifesting as Lewy bodies and Lewy neurites. Despite extensive research efforts spanning several decades, the underlying mechanisms of PD and disease-modifying therapies remain elusive. This review provides an overview of current trends in basic research on PD. Initially, it discusses the involvement of mitochondrial dysfunction in the pathogenesis of PD, followed by insights into the role of lysosomal dysfunction and disruptions in the vesicular transport system. Additionally, it delves into the pathological and physiological roles of α-synuclein, a crucial protein associated with PD pathophysiology. Overall, the purpose of this review is to comprehend the current state of elucidating the intricate mechanisms underlying PD and to outline future directions in understanding this disease.

Pathogenesis of Parkinson's disease: from hints from monogenic familial PD to biomarkers

Twenty-five years have passed since the causative gene for familial Parkinson's disease (PD), Parkin (now PRKN), was identified in 1998; PRKN is the most common causative gene in young-onset PD. Parkin encodes a ubiquitin-protein ligase, and Parkin is involved in mitophagy, a type of macroautophagy, in concert with PTEN-induced kinase 1 (PINK1). Both gene products are also involved in mitochondrial quality control. Among the many genetic PD-causing genes discovered, discovering PRKN as a cause of juvenile-onset PD has significantly impacted other neurodegenerative disorders. This is because the involvement of proteolytic systems has been suggested as a common mechanism in neurodegenerative diseases in which inclusion body formation is observed. The discovery of the participation of PRKN in PD has brought attention to the involvement of the proteolytic system in neurodegenerative diseases. Our research group has successfully isolated and identified CHCHD2, which is involved in the mitochondrial electron transfer system, and prosaposin (PSAP), which is involved in the lysosomal system, in this Parkin mechanism. Hereditary PD is undoubtedly an essential clue to solitary PD, and at least 25 or so genes and loci have been reported so far. This number of genes indicates that PD is a very diverse group of diseases. Currently, the diagnosis of PD is based on clinical symptoms and imaging studies. Although highly accurate diagnostic criteria have been published, early diagnosis is becoming increasingly important in treatment strategies for neurodegenerative diseases. Here, we also describe biomarkers that our group is working on.

Key genes and convergent pathogenic mechanisms in Parkinson disease

Parkinson disease (PD) is a neurodegenerative disorder marked by the preferential dysfunction and death of dopaminergic neurons in the substantia nigra. The onset and progression of PD is influenced by a diversity of genetic variants, many of which lack functional characterization. To identify the most high-yield targets for therapeutic intervention, it is important to consider the core cellular compartments and functional pathways upon which the varied forms of pathogenic dysfunction may converge. Here, we review several key PD-linked proteins and pathways, focusing on the mechanisms of their potential convergence in disease pathogenesis. These dysfunctions primarily localize to a subset of subcellular compartments, including mitochondria, lysosomes and synapses. We discuss how these pathogenic mechanisms that originate in different cellular compartments may coordinately lead to cellular dysfunction and neurodegeneration in PD.

A sporadic Parkinson's disease model via silencing of the ubiquitin-proteasome/E3 ligase component, SKP1A

Our and other's laboratory microarray-derived transcriptomic studies in human PD substantia nigra pars compacta (SNpc) samples have opened an avenue to concentrate on potential gene intersections or cross-talks along the dopaminergic (DAergic) neurodegenerative cascade in sporadic PD (SPD). One emerging gene candidate identified was SKP1A (p19, S-phase kinase-associated protein 1A), found significantly decreased in the SNpc as confirmed later at the protein level. SKP1 is part of the Skp1, Cullin 1, F-box protein (SCF) complex, the largest known class of sophisticated ubiquitin-proteasome/E3-ligases and was found to directly interact with FBXO7, a gene defective in PARK15-linked PD. This finding has led us to the hypothesis that a targeted site-specific reduction of Skp1 levels in DAergic neuronal cell culture and animal systems may result in a progressive loss of DAergic neurons and hopefully recreate motor disabilities in animals. The second premise considers the possibility that both intrinsic and extrinsic factors (e.g., manipulation of selected genes and mitochondria impairing toxins), alleged to play central roles in DAergic neurodegeneration in PD, may act in concert as modifiers of Skp1 deficiency-induced phenotype alterations ('dual-hit' hypothesis of neurodegeneration). To examine a possible role of Skp1 in DAergic phenotype, we have initially knocked down the expression of SKP1A gene in an embryonic mouse SN-derived cell line (SN4741) with short hairpin RNA (shRNA) lentiviruses (LVs). The deficiency of SKP1A closely recapitulated cardinal features of the DAergic pathology of human PD, such as decreased expression of DAergic phenotypic markers and cell cycle aberrations. Furthermore, the knocked down cells displayed a lethal phenotype when induced to differentiate exhibiting proteinaceous round inclusion structures, which were almost identical in composition to human Lewy bodies, a hallmark of PD. These findings support a role for Skp1 in neuronal phenotype, survival, and differentiation. The identification of Skp1 as a key player in DAergic neuron function suggested that a targeted site-specific reduction of Skp1 levels in mice SNpc may result in a progressive loss of DAergic neurons and terminal projections in the striatum. The injected LV SKP1shRNA to mouse SN resulted in decreased expression of Skp1 protein levels within DAergic neurons and loss of tyrosine hydroxylase immunoreactivity (TH-IR) in both SNpc and striatum that was accompanied by time-dependent motor disabilities. The reduction of the vertical movements, that is rearing, may be reminiscent of the early occurrence of hypokinesia and axial, postural instability in PD. According to the 'dual-hit' hypothesis of neurodegenerative diseases, it is predicted that gene-gene and/or gene-environmental factors would act in concert or sequentially to propagate the pathological process of PD. Our findings are compatible with this conjecture showing that the genetic vulnerability caused by knock down of SKP1A renders DAergic SN4741 cells especially sensitive to genetic reduction of Aldh1 and exposure to the external stressors MPP+ and DA, which have been implicated in PD pathology. Future consideration should be given in manipulation SKP1A expression as therapeutic window, via its induction genetically or pharmacological, to prevent degeneration of the nigra striatal dopamine neurons, since UPS is defective.

Catecholamines and Parkinson's disease: tyrosine hydroxylase (TH) over tetrahydrobiopterin (BH4) and GTP cyclohydrolase I (GCH1) to cytokines, neuromelanin, and gene therapy: a historical overview

The author identified the genes and proteins of human enzymes involved in the biosynthesis of catecholamines (dopamine, norepinephrine, epinephrine) and tetrahydrobiopterin (BH4): tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), dopamine β-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), and GTP cyclohydrolase I (GCH1). In Parkinson's disease (PD), the activities and levels of mRNA and protein of all catecholamine-synthesizing enzymes are decreased, especially in dopamine neurons in the substantia nigra. Hereditary GCH1 deficiency results in reductions in the levels of BH4 and the activities of TH, causing decreases in dopamine levels. Severe deficiencies in GCH1 or TH cause severe decreases in dopamine levels leading to severe neurological symptoms, whereas mild decreases in TH activity in mild GCH1 deficiency or in mild TH deficiency result in only modest reductions in dopamine levels and symptoms of DOPA-responsive dystonia (DRD, Segawa disease) or juvenile Parkinsonism. DRD is a treatable disease and small doses of L-DOPA can halt progression. The death of dopamine neurons in PD in the substantia nigra may be related to (i) inflammatory effect of extra neuronal neuromelanin, (ii) inflammatory cytokines which are produced by activated microglia, (iii) decreased levels of BDNF, and/or (iv) increased levels of apoptosis-related factors. This review also discusses progress in gene therapies for the treatment of PD, and of GCH1, TH and AADC deficiencies, by transfection of TH, AADC, and GCH1 via adeno-associated virus (AAV) vectors.

RAB32 Ser71Arg in autosomal dominant Parkinson's disease: linkage, association, and functional analyses

BACKGROUND

Parkinson's disease is a progressive neurodegenerative disorder with multifactorial causes, among which genetic risk factors play a part. The RAB GTPases are regulators and substrates of LRRK2, and variants in the LRRK2 gene are important risk factors for Parkinson's disease. We aimed to explore genetic variability in RAB GTPases within cases of familial Parkinson's disease.

METHODS

We did whole-exome sequencing in probands from families in Canada and Tunisia with Parkinson's disease without a genetic cause, who were recruited from the Centre for Applied Neurogenetics (Vancouver, BC, Canada), an international consortium that includes people with Parkinson's disease from 36 sites in 24 countries. 61 RAB GTPases were genetically screened, and candidate variants were genotyped in relatives of the probands to assess disease segregation by linkage analysis. Genotyping was also done to assess variant frequencies in individuals with idiopathic Parkinson's disease and controls, matched for age and sex, who were also from the Centre for Applied Neurogenetics but unrelated to the probands or each other. All participants were aged 18 years or older. The sequencing and genotyping findings were validated by case-control association analyses using bioinformatic data obtained from publicly available clinicogenomic databases (AMP-PD, GP2, and 100 000 Genomes Project) and a private German clinical diagnostic database (University of Tübingen). Clinical and pathological findings were summarised and haplotypes were determined. In-vitro studies were done to investigate protein interactions and enzyme activities.

FINDINGS

Between June 1, 2010, and May 31, 2017, 130 probands from Canada and Tunisia (47 [36%] female and 83 [64%] male; mean age 72·7 years [SD 11·7; range 38-96]; 109 White European ancestry, 18 north African, two east Asian, and one Hispanic] underwent whole-exome sequencing. 15 variants in RAB GTPase genes were identified, of which the RAB32 variant c.213C>G (Ser71Arg) cosegregated with autosomal dominant Parkinson's disease in three families (nine affected individuals; non-parametric linkage Z score=1·95; p=0·03). 2604 unrelated individuals with Parkinson's disease and 344 matched controls were additionally genotyped, and five more people originating from five countries (Canada, Italy, Poland, Turkey, and Tunisia) were identified with the RAB32 variant. From the database searches, in which 6043 individuals with Parkinson's disease and 62 549 controls were included, another eight individuals were identified with the RAB32 variant from four countries (Canada, Germany, UK, and USA). Overall, the association of RAB32 c.213C>G (Ser71Arg) with Parkinson's disease was significant (odds ratio [OR] 13·17, 95% CI 2·15-87·23; p=0·0055; I2=99·96%). In the people who had the variant, Parkinson's disease presented at age 54·6 years (SD 12·75, range 31-81, n=16), and two-thirds had a family history of parkinsonism. RAB32 Ser71Arg heterozygotes shared a common haplotype, although penetrance was incomplete. Findings in one individual at autopsy showed sparse neurofibrillary tangle pathology in the midbrain and thalamus, without Lewy body pathology. In functional studies, RAB32 Arg71 activated LRRK2 kinase to a level greater than RAB32 Ser71.

INTERPRETATION

RAB32 Ser71Arg is a novel genetic risk factor for Parkinson's disease, with reduced penetrance. The variant was found in individuals with Parkinson's disease from multiple ethnic groups, with the same haplotype. In-vitro assays show that RAB32 Arg71 activates LRRK2 kinase, which indicates that genetically distinct causes of familial parkinsonism share the same mechanism. The discovery of RAB32 Ser71Arg also suggests several genetically inherited causes of Parkinson's disease originated to control intracellular immunity. This shared aetiology should be considered in future translational research, while the global epidemiology of RAB32 Ser71Arg needs to be assessed to inform genetic counselling.

FUNDING

National Institutes of Health, the Canada Excellence Research Chairs program, Aligning Science Across Parkinson's, the Michael J Fox Foundation for Parkinson's Research, and the UK Medical Research Council.

Drug repurposing for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are neuronal problems that include the brain and spinal cord and result in loss of sensory and motor dysfunction. Common NDDs include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple Sclerosis (MS), and Amyotrophic Lateral Sclerosis (ALS) etc. The occurrence of these diseases increases with age and is one of the challenging problems among elderly people. Though, several scientific research has demonstrated the key pathologies associated with NDDs still the underlying mechanisms and molecular details are not well understood and need to be explored and this poses a lack of effective treatments for NDDs. Several lines of evidence have shown that NDDs have a high prevalence and affect more than a billion individuals globally but still, researchers need to work forward in identifying the best therapeutic target for NDDs. Thus, several researchers are working in the directions to find potential therapeutic targets to alter the disease pathology and treat the diseases. Several steps have been taken to identify the early detection of the disease and drug repurposing for effective treatment of NDDs. Moreover, it is logical that current medications are being evaluated for their efficacy in treating such disorders; therefore, drug repurposing would be an efficient, safe, and cost-effective way in finding out better medication. In the current manuscript we discussed the utilization of drugs that have been repurposed for the treatment of AD, PD, HD, MS, and ALS.

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.

Upregulated ECM genes and increased synaptic activity in Parkinson's human DA neurons with PINK1/ PRKN mutations

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease. Primary symptoms of PD arise with the loss of dopaminergic (DA) neurons in the Substantia Nigra Pars Compacta, but PD also affects the hippocampus and cortex, usually in its later stage. Approximately 15% of PD cases are familial with a genetic mutation. Two of the most associated genes with autosomal recessive (AR) early-onset familial PD are PINK1 and PRKN. In vitro studies of these genetic mutations are needed to understand the neurophysiological changes in patients' neurons that may contribute to neurodegeneration. In this work, we generated and differentiated DA and hippocampal neurons from human induced pluripotent stem cells (hiPSCs) derived from two patients with a double mutation in their PINK1 and PRKN (one homozygous and one heterozygous) genes and assessed their neurophysiology compared to two healthy controls. We showed that the synaptic activity of PD neurons generated from patients with the PINK1 and PRKN mutations is impaired in the hippocampus and dopaminergic neurons. Mutant dopaminergic neurons had enhanced excitatory post-synaptic activity. In addition, DA neurons with the homozygous mutation of PINK1 exhibited more pronounced electrophysiological differences compared to the control neurons. Signaling network analysis of RNA sequencing results revealed that Focal adhesion and ECM receptor pathway were the top two upregulated pathways in the mutant PD neurons. Our findings reveal that the phenotypes linked to PINK1 and PRKN mutations differ from those from other PD mutations, suggesting a unique interplay between these two mutations that drives different PD mechanisms.

Mitochondrial dysfunction: mechanisms and advances in therapy

Mitochondria, with their intricate networks of functions and information processing, are pivotal in both health regulation and disease progression. Particularly, mitochondrial dysfunctions are identified in many common pathologies, including cardiovascular diseases, neurodegeneration, metabolic syndrome, and cancer. However, the multifaceted nature and elusive phenotypic threshold of mitochondrial dysfunction complicate our understanding of their contributions to diseases. Nonetheless, these complexities do not prevent mitochondria from being among the most important therapeutic targets. In recent years, strategies targeting mitochondrial dysfunction have continuously emerged and transitioned to clinical trials. Advanced intervention such as using healthy mitochondria to replenish or replace damaged mitochondria, has shown promise in preclinical trials of various diseases. Mitochondrial components, including mtDNA, mitochondria-located microRNA, and associated proteins can be potential therapeutic agents to augment mitochondrial function in immunometabolic diseases and tissue injuries. Here, we review current knowledge of mitochondrial pathophysiology in concrete examples of common diseases. We also summarize current strategies to treat mitochondrial dysfunction from the perspective of dietary supplements and targeted therapies, as well as the clinical translational situation of related pharmacology agents. Finally, this review discusses the innovations and potential applications of mitochondrial transplantation as an advanced and promising treatment.

Exploring the neuroprotective role of artesunate in mouse models of anti-NMDAR encephalitis: insights from molecular mechanisms and transmission electron microscopy

BACKGROUND

The pathway involving PTEN-induced putative kinase 1 (PINK1) and PARKIN plays a crucial role in mitophagy, a process activated by artesunate (ART). We propose that patients with anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis exhibit insufficient mitophagy, and ART enhances mitophagy via the PINK1/PARKIN pathway, thereby providing neuroprotection.

METHODS

Adult female mice aged 8-10 weeks were selected to create a passive transfer model of anti-NMDAR encephalitis. We conducted behavioral tests on these mice within a set timeframe. Techniques such as immunohistochemistry, immunofluorescence, and western blotting were employed to assess markers including PINK1, PARKIN, LC3B, p62, caspase3, and cleaved caspase3. The TUNEL assay was utilized to detect neuronal apoptosis, while transmission electron microscopy (TEM) was used to examine mitochondrial autophagosomes. Primary hippocampal neurons were cultured, treated, and then analyzed through immunofluorescence for mtDNA, mtROS, TMRM.

RESULTS

In comparison to the control group, mitophagy levels in the experimental group were not significantly altered, yet there was a notable increase in apoptotic neurons. Furthermore, markers indicative of mitochondrial leakage and damage were found to be elevated in the experimental group compared to the control group, but these markers showed improvement following ART treatment. ART was effective in activating the PINK1/PARKIN pathway, enhancing mitophagy, and diminishing neuronal apoptosis. Behavioral assessments revealed that ART ameliorated symptoms in mice with anti-NMDAR encephalitis in the passive transfer model (PTM). The knockdown of PINK1 led to a reduction in mitophagy levels, and subsequent ART intervention did not alleviate symptoms in the anti-NMDAR encephalitis PTM mice, indicating that ART's therapeutic efficacy is mediated through the activation of the PINK1/PARKIN pathway.

CONCLUSIONS

At the onset of anti-NMDAR encephalitis, mitochondrial damage is observed; however, this damage is mitigated by the activation of mitophagy via the PINK1/PARKIN pathway. This regulatory feedback mechanism facilitates the removal of damaged mitochondria, prevents neuronal apoptosis, and consequently safeguards neural tissue. ART activates the PINK1/PARKIN pathway to enhance mitophagy, thereby exerting neuroprotective effects and may achieve therapeutic goals in treating anti-NMDAR encephalitis.

Long-read sequencing unravels the complexity of structural variants in PRKN in two individuals with early-onset Parkinson's disease

Background

PRKN biallelic pathogenic variants are the most common cause of autosomal recessive early-onset Parkinson's disease (PD). However, the variants responsible for suspected PRKN- PD individuals are not always identified with standard genetic testing.

Objectives

Identify the genetic cause in two siblings with a PRKN -PD phenotype using long-read sequencing (LRS).

Methods

The genetic investigation involved standard testing using successively multiple ligation probe amplification (MLPA), Sanger sequencing, targeted sequencing, whole-exome sequencing and LRS.

Results

MLPA and targeted sequencing identified one copy of exon four in PRKN but no other variants were identified. Subsequently, LRS unveiled a large deletion encompassing exon 3 to 4 on one allele and a duplication of exon 3 on the second allele; explaining the siblings' phenotype. MLPA could not identify the balanced rearrangement of exon 3.

Conclusions

This study highlights the potential utility of long-read sequencing in the context of unsolved typical PRKN- PD individuals.

Armcx1 Reduces Neurological Damage Via a Mitochondrial Transport Pathway Involving Miro1 After Traumatic Brain Injury

Armcx1 is a member of the ARMadillo repeat-Containing protein on the X chromosome (ARMCX) family, which is recognized to have evolutionary conserved roles in regulating mitochondrial transport and dynamics. Previous research has shown that Armcx1 is expressed at higher levels in mice after axotomy and in adult retinal ganglion cells after crush injury, and this protein increases neuronal survival and axonal regeneration. However, its role in traumatic brain injury (TBI) is unclear. Therefore, the aim of this study was to assess the expression of Armcx1 after TBI and to explore possible related mechanisms by which Armcx1 is involved in TBI. We used C57BL/6 male mice to model TBI and evaluated the role of Armcx1 in TBI by transfecting mice with Armcx1 small interfering RNA (siRNA) to inhibit Armcx1 expression 24 h before TBI modeling. Western blotting, immunofluorescence, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining, Nissl staining, transmission electron microscopy, adenosine triphosphate (ATP) level measurement, neuronal apoptosis analysis, neurological function scoring and the Morris water maze were performed. The results demonstrated that Armcx1 protein expression was elevated after TBI and that the Armcx1 protein was localized in neurons and astroglial cells in cortical tissue surrounding the injury site. In addition, inhibition of Armcx1 expression further led to impaired mitochondrial transport, abnormal morphology, reduced ATP levels, aggravation of neuronal apoptosis and neurological dysfunction, and decrease Miro1 expression. In conclusion, our findings indicate that Armcx1 may exert neuroprotective effects by ameliorating neurological injury after TBI through a mitochondrial transport pathway involving Miro1.

Alterations of PINK1-PRKN signaling in mice during normal aging

The ubiquitin kinase-ligase pair PINK1-PRKN identifies and selectively marks damaged mitochondria for elimination via the autophagy-lysosome system (mitophagy). While this cytoprotective pathway has been extensively studied in vitro upon acute and complete depolarization of mitochondria, the significance of PINK1-PRKN mitophagy in vivo is less well established. Here we used a novel approach to study PINK1-PRKN signaling in different energetically demanding tissues of mice during normal aging. We demonstrate a generally increased expression of both genes and enhanced enzymatic activity with aging across tissue types. Collectively our data suggest a distinct regulation of PINK1-PRKN signaling under basal conditions with the most pronounced activation and flux of the pathway in mouse heart compared to brain or skeletal muscle. Our biochemical analyses complement existing mitophagy reporter readouts and provide an important baseline assessment in vivo, setting the stage for further investigations of the PINK1-PRKN pathway during stress and in relevant disease conditions.

Basal activity of PINK1 and PRKN in cell models and rodent brain

The ubiquitin kinase-ligase pair PINK1-PRKN recognizes and transiently labels damaged mitochondria with ubiquitin phosphorylated at Ser65 (p-S65-Ub) to mediate their selective degradation (mitophagy). Complete loss of PINK1 or PRKN function unequivocally leads to early-onset Parkinson disease, but it is debated whether impairments in mitophagy contribute to disease later in life. While the pathway has been extensively studied in cell culture upon acute and massive mitochondrial stress, basal levels of activation under endogenous conditions and especially in vivo in the brain remain undetermined. Using rodent samples, patient-derived cells, and isogenic neurons, we here identified age-dependent, brain region-, and cell type-specific effects and determined expression levels and extent of basal and maximal activation of PINK1 and PRKN. Our work highlights the importance of defining critical risk and therapeutically relevant levels of PINK1-PRKN signaling which will further improve diagnosis and prognosis and will lead to better stratification of patients for future clinical trials.