New insights into the complex role of mitochondria in Parkinson’s disease

Novel insights into Parkin-mediated mitochondrial dysfunction and neuroinflammation in Parkinson's disease

Mutations in PRKN cause the second most common genetic form of Parkinson's disease (PD)-a debilitating movement disorder that is on the rise due to population aging in the industrial world. PRKN codes for an E3 ubiquitin ligase that has been well established as a key regulator of mitophagy. Together with PTEN-induced kinase 1 (PINK1), Parkin controls the lysosomal degradation of depolarized mitochondria. But Parkin's functions go well beyond mitochondrial clearance: the versatile protein is involved in mitochondria-derived vesicle formation, cellular metabolism, calcium homeostasis, mitochondrial DNA maintenance, mitochondrial biogenesis, and apoptosis induction. Moreover, Parkin can act as a modulator of different inflammatory pathways. In the current review, we summarize the latest literature concerning the diverse roles of Parkin in maintaining a healthy mitochondrial pool. Moreover, we discuss how these recent discoveries may translate into personalized therapeutic approaches not only for PRKN-PD patients but also for a subset of idiopathic cases.

Understanding the involvement of innate immunity and the Nrf2-NLRP3 axis on mitochondrial health in Parkinson's disease

Parkinson's disease (PD), a multifactorial movement disorder, is interlinked with numerous molecular pathways, including neuroinflammation, which is a critical factor in the development and progression of PD. Microglia play a central role in driving neuroinflammation through activation and overexpression of the M1 phenotype, which has a significant impact on mitochondria. Multiple regulators converge together, and among these, the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasomes have been implicated in transmitting inflammatory and deleterious components to the mitochondria. Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the NLRP3 inflammasome and acts as the saviour of the mitochondria. Together, the NLRP3-Nrf2 axis functions in regulating mitochondrial function in the case of PD. It regulates fundamental processes such as oxidative stress, mitochondrial respiratory function, and mitochondrial dynamics. In this review, we discuss the contributions that a variety of miRNAs make to the regulation of the NLRP3 inflammasome and Nrf2, which can be used to target this important axis and contribute to the preservation of mitochondrial integrity. This axis may prove to be a crucial target for extending the lives of Parkinson's patients by deferring neuroinflammatory damage to mitochondria.

Neuroprotective and Antiherpetic Properties of Polyphenolic Compounds from Maackia amurensis Heartwood

In this study, we isolated a new isoflavanostilbene maackiapicevestitol (1) as a mixture of two stable conformers 1a and 1b as well as five previously known dimeric and monomeric stilbens: piceatannol (2), maackin (3), scirpusin A (4), maackiasine (5), and maackolin (6) from M. amurensis heartwood, using column chromatography on polyamide, silicagel, and C-18. The structures of these compounds were elucidated by NMR, HR-MS, and CD techniques. Maksar® obtained from M. amurensis heartwood and polyphenolics 1–6 possessed moderate anti-HSV-1 activity in cytopathic effect (CPE) inhibition and RT-PCR assays. A model of PQ-induced neurotoxicity was used to study the neuroprotective potential of polyphenolic compounds from M. amurensis. Maksar® showed the highest neuroprotective activity and increased cell viability by 18% at a concentration of 10 μg/mL. Maackolin (6) also effectively increased the viability of PQ-treated Neuro-2a cells and the value of mitochondrial membrane potential at concentrations up to 10 μΜ. Maksar® and compounds 1–6 possessed higher FRAP and DPPH-scavenging effects than quercetin. However, only compounds 1 and 4 at concentrations of 10 μM as well as Maksar® (10 μg/mL) statistically significantly reduced the level of intracellular ROS in PQ-treated Neuro-2a cells.

Redox Modulation of Mitochondrial Proteins in the Neurotoxicant Models of Parkinson's Disease

Significance: Mitochondrial proteins regulate the oxidative phosphorylation, cellular metabolism, and free radical generation. Redox modulation alters the mitochondrial proteins and instigates the damage to dopaminergic neurons. Toxicants contribute to Parkinson's disease (PD) pathogenesis in conjunction with aging and genetic factors. While oxidative modulation of a number of mitochondrial proteins is linked to xenobiotic exposure, little is known about its role in the toxicant-induced PD. Understanding the role of redox modulation of mitochondrial proteins in complex cellular events leading to neurodegeneration is highly relevant. Recent Advances: Many toxicants are shown to inhibit complex I or III and elicit free radical production that alters the redox status of mitochondrial proteins. Implication of redox modulation of the mitochondrial proteins makes them a target to comprehend the underlying mechanism of toxicant-induced PD. Critical Issues: Owing to multifactorial etiology, exploration of onset and progression and treatment outcomes needs a comprehensive approach. The article explains about a few mitochondrial proteins that undergo redox changes along with the promising strategies, which help to alleviate the toxicant-induced redox imbalance leading to neurodegeneration. Future Directions: Although mitochondrial proteins are linked to PD, their role in toxicant-induced parkinsonism is not yet completely known. Preservation of antioxidant defense machinery could alleviate the redox modulation of mitochondrial proteins. Targeted antioxidant delivery, use of metal chelators, and activation of nuclear factor erythroid 2-related factor 2, and combinational therapy that encounters multiple free radicals, could ameliorate the redox modulation of mitochondrial proteins and thereby PD progression.

Signaling pathways in Parkinson's disease: molecular mechanisms and therapeutic interventions

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, and its treatment remains a big challenge. The pathogenesis of PD may be related to environmental and genetic factors, and exposure to toxins and gene mutations may be the beginning of brain lesions. The identified mechanisms of PD include α-synuclein aggregation, oxidative stress, ferroptosis, mitochondrial dysfunction, neuroinflammation, and gut dysbiosis. The interactions among these molecular mechanisms complicate the pathogenesis of PD and pose great challenges to drug development. At the same time, the diagnosis and detection of PD are also one of obstacles to the treatment of PD due to its long latency and complex mechanism. Most conventional therapeutic interventions for PD possess limited effects and have serious side effects, heightening the need to develop novel treatments for this disease. In this review, we systematically summarized the pathogenesis, especially the molecular mechanisms of PD, the classical research models, clinical diagnostic criteria, and the reported drug therapy strategies, as well as the newly reported drug candidates in clinical trials. We also shed light on the components derived from medicinal plants that are newly identified for their effects in PD treatment, with the expectation to provide the summary and outlook for developing the next generation of drugs and preparations for PD therapy.

Mitochondria-Targeted Antioxidants, an Innovative Class of Antioxidant Compounds for Neurodegenerative Diseases: Perspectives and Limitations

Neurodegenerative diseases comprise a wide spectrum of pathologies characterized by progressive loss of neuronal functions and structures. Despite having different genetic backgrounds and etiology, in recent years, many studies have highlighted a point of convergence in the mechanisms leading to neurodegeneration: mitochondrial dysfunction and oxidative stress have been observed in different pathologies, and their detrimental effects on neurons contribute to the exacerbation of the pathological phenotype at various degrees. In this context, increasing relevance has been acquired by antioxidant therapies, with the purpose of restoring mitochondrial functions in order to revert the neuronal damage. However, conventional antioxidants were not able to specifically accumulate in diseased mitochondria, often eliciting harmful effects on the whole body. In the last decades, novel, precise, mitochondria-targeted antioxidant (MTA) compounds have been developed and studied, both in vitro and in vivo, to address the need to counter the oxidative stress in mitochondria and restore the energy supply and membrane potentials in neurons. In this review, we focus on the activity and therapeutic perspectives of MitoQ, SkQ1, MitoVitE and MitoTEMPO, the most studied compounds belonging to the class of MTA conjugated to lipophilic cations, in order to reach the mitochondrial compartment.

Phytochemicals and mitochondria: Therapeutic allies against gastric cancer

BACKGROUND

Mitochondria are the energy factories of cells with the ability to modulate the cell cycle, cellular differentiation, signal transduction, growth, and apoptosis. Existing drugs targeting mitochondria in cancer treatment have disadvantages of drug resistance and side effects. Phytochemicals, which are widely found in plants, are bioactive compounds that could facilitate the development of new drugs for gastric cancer. Studies have shown that some phytochemicals can suppress the development of gastric cancer.

METHODS

We searched for data from PubMed, China National Knowledge Infrastructure, Web of Science, and Embase databases from initial establishment to December 2021 to review the mechanism by which phytochemicals suppress gastric cancer cell growth by modulating mitochondrial function. Phytochemicals were classified and summarized by their mechanisms of action.

RESULTS

Phytochemicals can interfere with mitochondria through several mechanisms to reach the goal of promoting apoptosis in gastric cancer cells. Some phytochemicals, e.g., daidzein and tetrandrine promoted cytochrome c spillover into the cytoplasm by modulating the members of the B-cell lymphoma-2 protein family and induced apoptotic body activity by activating the caspase protein family. Phytochemicals (e.g., celastrol and shikonin) could promote the accumulation of reactive oxygen species and reduce the mitochondrial membrane potential. Several phytochemicals (e.g., berberine and oleanolic acid) activated mitochondrial apoptotic submission via the phosphatidylinositol-3-kinase/Akt signaling pathway, thereby triggering apoptosis in gastric cancer cells. Several well-known phytochemicals that target mitochondria, including berberine, ginsenoside, and baicalein, showed the advantages of multiple targets, high efficacy, and fewer side effects.

CONCLUSIONS

Phytochemicals could target the mitochondria in the treatment of gastric cancer, providing potential directions and evidence for clinical translation. Drug discovery focused on phytochemicals has great potential to break barriers in cancer treatment.

Irisin exhibits neuroprotection by preventing mitochondrial damage in Parkinson's disease

Exercise has been proposed as an effective non-pharmacological management for Parkinson's disease (PD) patients. Irisin, a recently identified myokine, is increased by exercise and plays pivotal roles in energy metabolism. However, it remains unknown whether irisin has any protective effects on PD. Here, we found that serum irisin levels of PD patients were markedly elevated after 12-week regular exercise, which had a positive correlation with improved balance function scored by Berg Balance Scale. Treatment with exogenous irisin could improve motor function, and reduce dopaminergic neurodegeneration in PD models. Meanwhile, irisin could reduce cell apoptosis by renovating mitochondrial function in PD models, which was reflected in decreased oxidative stress, increased mitochondrial complex I activity and mitochondrial content, increased mitochondrial biogenesis, and repaired mitochondrial morphology. Furthermore, irisin regulated the aforementioned aspects by upregulating downstream Akt signaling pathway and ERK1/2 signaling pathway through integrin receptors rather than directly targeting mitochondria. With the use of small-molecule inhibitors, it was found that irisin can reduce apoptosis, restore normal mitochondrial biogenesis, and improve mitochondrial morphology and dynamic balance in PD models by activating Akt signaling pathway and ERK1/2 signaling pathway. And irisin reduced oxidative stress via activating ERK1/2 signaling pathway. The results revealed that exogenous irisin conferred neuroprotection relieving apoptosis and oxidative stress, restraining mitochondrial fragmentation, and promoting mitochondrial respiration and biogenesis in PD models, and irisin exerted the aforementioned effects by activating Akt signaling pathway and ERK1/2 signaling pathway. Thus, peripherally delivered irisin might be a promising candidate for therapeutic targeting of PD.

H2S-based fluorescent imaging for pathophysiological processes

Hydrogen sulfide (H₂S), as an important endogenous signaling molecule, plays a vital role in many physiological processes. The abnormal behaviors of hydrogen sulfide in organisms may lead to various pathophysiological processes. Monitoring the changes in hydrogen sulfide is helpful for pre-warning and treating these pathophysiological processes. Fluorescence imaging techniques can be used to observe changes in the concentration of analytes in organisms in real-time. Therefore, employing fluorescent probes imaging to investigate the behaviors of hydrogen sulfide in pathophysiological processes is vital. This paper reviews the design strategy and sensing mechanisms of hydrogen sulfide-based fluorescent probes, focusing on imaging applications in various pathophysiological processes, including neurodegenerative diseases, inflammation, apoptosis, oxidative stress, organ injury, and diabetes. This review not only demonstrates the specific value of hydrogen sulfide fluorescent probes in preclinical studies but also illuminates the potential application in clinical diagnostics.

Proteomic profiling reveals the potential mechanisms and regulatory targets of sirtuin 4 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's mouse model

Introduction

Parkinson's disease (PD), as a common neurodegenerative disease, currently has no effective therapeutic approaches to delay or stop its progression. There is an urgent need to further define its pathogenesis and develop new therapeutic targets. An increasing number of studies have shown that members of the sirtuin (SIRT) family are differentially involved in neurodegenerative diseases, indicating their potential to serve as targets in therapeutic strategies. Mitochondrial SIRT4 possesses multiple enzymatic activities, such as deacetylase, ADP ribosyltransferase, lipoamidase, and deacylase activities, and exhibits different enzymatic activities and target substrates in different tissues and cells; thus, mitochondrial SIRT4 plays an integral role in regulating metabolism. However, the role and mechanism of SIRT4 in PD are not fully understood. This study aimed to investigate the potential mechanism and possible regulatory targets of SIRT4 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice.

Methods

The expression of the SIRT4 protein in the MPTP-induced PD mouse mice or key familial Parkinson disease protein 7 knockout (DJ-1 KO) rat was compared against the control group by western blot assay. Afterwards, quantitative proteomics and bioinformatics analyses were performed to identify altered proteins in the vitro model and reveal the possible functional role of SIRT4. The most promising molecular target of SIRT4 were screened and validated by viral transfection, western blot assay and reverse transcription quantitative PCR (RT-qPCR) assays.

Results

The expression of the SIRT4 protein was found to be altered both in the MPTP-induced PD mouse mice and DJ-1KO rats. Following the viral transfection of SIRT4, a quantitative proteomics analysis identified 5,094 altered proteins in the vitro model, including 213 significantly upregulated proteins and 222 significantly downregulated proteins. The results from bioinformatics analyses indicated that SIRT4 mainly affected the ribosomal pathway, propionate metabolism pathway, peroxisome proliferator-activated receptor (PPAR) signaling pathway and peroxisome pathway in cells, and we screened 25 potential molecular targets. Finally, only fatty acid binding protein 4 (FABP4) in the PPAR signaling pathway was regulated by SIRT4 among the 25 molecules. Importantly, the alterations in FABP4 and PPARγ were verified in the MPTP-induced PD mouse model.

Discussion

Our results indicated that FABP4 in the PPAR signaling pathway is the most promising molecular target of SIRT4 in an MPTP-induced mouse model and revealed the possible functional role of SIRT4. This study provides a reference for future drug development and mechanism research with SIRT4 as a target or biomarker.

Mitochondrial Modulators: The Defender

Mitochondria are widely considered the "power hub" of the cell because of their pivotal roles in energy metabolism and oxidative phosphorylation. However, beyond the production of ATP, which is the major source of chemical energy supply in eukaryotes, mitochondria are also central to calcium homeostasis, reactive oxygen species (ROS) balance, and cell apoptosis. The mitochondria also perform crucial multifaceted roles in biosynthetic pathways, serving as an important source of building blocks for the biosynthesis of fatty acid, cholesterol, amino acid, glucose, and heme. Since mitochondria play multiple vital roles in the cell, it is not surprising that disruption of mitochondrial function has been linked to a myriad of diseases, including neurodegenerative diseases, cancer, and metabolic disorders. In this review, we discuss the key physiological and pathological functions of mitochondria and present bioactive compounds with protective effects on the mitochondria and their mechanisms of action. We highlight promising compounds and existing difficulties limiting the therapeutic use of these compounds and potential solutions. We also provide insights and perspectives into future research windows on mitochondrial modulators.

Pulmonary hazard identifications of Graphene family nanomaterials: Adverse outcome pathways framework based on toxicity mechanisms

Graphene-family nanomaterials (GFNs) are revolutionary new nanomaterials that have attracted significant attention in the field of nanomaterials, but the ensuing problems lie in the potential threats to public health and the ecosystem caused by these nanomaterials. From the perspective of GFN-related health risk assessments, this study reviews the current status of GFN-induced pathological lung events with a focus on the damage caused to different biological moieties (molecular, cellular, tissue, and organ) and the mechanistic relationships between different toxic endpoints. These multiple sites of damage were matched with existing adverse outcome pathways (AOPs) in an online knowledge base to obtain available molecular initiation events (MIEs), key events (KEs), and adverse outcomes (AOs). Among them, the MIEs were discussed in combination with the structure-activity relationship due to the correlation between toxicity and physical and chemical properties of GFNs. Based on the collection of information regarding MIEs, Kes, and AOs in addition to upstream and downstream causal extrapolation, the AOP framework for GFN-induced pulmonary toxicity was developed, highlighting the possible mechanisms of GFN-induced lung damage. This review intended to combine AOP with classic toxicological methods with a view to rapidly and accurately establishing a nanotoxicology infrastructure so as to contribute to public health risk assessment strategies through iteration from and animal models up to the population level.

Mitochondrial Complex I, a Possible Sensible Site of cAMP Pathway in Aging

In mammals during aging, reactive oxygen species (ROS), produced by the mitochondrial respiratory chain, cause oxidative damage of macromolecules leading to respiratory chain dysfunction, which in turn increases ROS mitochondrial production. Many efforts have been made to understand the role of oxidative stress in aging and age-related diseases. The complex I of the mitochondrial respiratory chain is the major source of ROS production and its dysfunctions have been associated with several forms of neurodegeneration, other common human diseases and aging. Complex I-ROS production and complex I content have been proposed as the major determinants for longevity. The cAMP signal has a role in the regulation of complex I activity and the decrease of ROS production. In the last years, an increasing number of studies have attempted to activate cAMP signaling to treat age-related diseases associated with mitochondrial dysfunctions and ROS production. This idea comes from a long-line of studies showing a main role of cAMP signal in the memory consolidation mechanism and in the regulation of mitochondrial functions. Here, we discuss several evidences on the possible connection between complex I and cAMP pathway in the aging process.

On the Chemical and Biological Characteristics of Multifunctional Compounds for the Treatment of Parkinson's Disease

Protein aggregation, mitochondrial dysfunction, iron dyshomeostasis, increased oxidative damage and inflammation are pathognomonic features of Parkinson's disease (PD) and other neurodegenerative disorders characterized by abnormal iron accumulation. Moreover, the existence of positive feed-back loops between these pathological components, which accelerate, and sometimes make irreversible, the neurodegenerative process, is apparent. At present, the available treatments for PD aim to relieve the symptoms, thus improving quality of life, but no treatments to stop the progression of the disease are available. Recently, the use of multifunctional compounds with the capacity to attack several of the key components of neurodegenerative processes has been proposed as a strategy to slow down the progression of neurodegenerative processes. For the treatment of PD specifically, the necessary properties of new-generation drugs should include mitochondrial destination, the center of iron-reactive oxygen species interaction, iron chelation capacity to decrease iron-mediated oxidative damage, the capacity to quench free radicals to decrease the risk of ferroptotic neuronal death, the capacity to disrupt α-synuclein aggregates and the capacity to decrease inflammatory conditions. Desirable additional characteristics are dopaminergic neurons to lessen unwanted secondary effects during long-term treatment, and the inhibition of the MAO-B and COMPT activities to increase intraneuronal dopamine content. On the basis of the published evidence, in this work, we review the molecular basis underlying the pathological events associated with PD and the clinical trials that have used single-target drugs to stop the progress of the disease. We also review the current information on multifunctional compounds that may be used for the treatment of PD and discuss the chemical characteristics that underlie their functionality. As a projection, some of these compounds or modifications could be used to treat diseases that share common pathology features with PD, such as Friedreich's ataxia, Multiple sclerosis, Huntington disease and Alzheimer's disease.

Exposure to dithiocarbamate fungicide maneb in vitro and in vivo: Neuronal apoptosis and underlying mechanisms

Maneb, a widely-used dithiocarbamate fungicide, remains in the environment and exerts adverse health effects. Epidemiological evidence shows that maneb exposure is associated with a higher risk of Parkinson's disease (PD), one of the most common neurodegenerative diseases. However, the molecular mechanisms underlying maneb-induced neurotoxicity remain unclear. Here we investigated the toxic effects and the underlying mechanisms of maneb on the degeneration of dopaminergic cells and α-synuclein in A53T transgenic mice. In SH-SY5Y cells, exposure to maneb reduces cell viability, triggers neuronal apoptosis, induces mitochondrial dysfunction, and generates reactive oxidative species (ROS) in a dose-dependent manner. Furthermore, Western blot analysis found that the mitochondrial apoptosis pathway (Bcl-2, Bax, cytochrome c, activated caspase-3) and the PKA/CREB signaling pathway (PKA, PDE10A, CREB, p-CREB) were changed by maneb both in vitro and in vivo. In addition, the activation of the mitochondrial apoptosis pathway induced by maneb was attenuated by activating PKA. Therefore, these results suggest that the PKA/CREB signaling pathway is involved in maneb-induced apoptosis. This study provides novel insights into maneb-induced neurotoxicity and the underlying mechanisms, which may serve as a guide for further toxicological assessment and standard application of maneb.

UQCRC1 variants in early-onset and familial Parkinson's disease in a Taiwanese cohort

Background

A recent Taiwanese study reported variants of the ubiquinol-cytochrome c reductase core protein 1 (UQCRC1) gene linked to autosomal dominant parkinsonism with polyneuropathy. This study investigated the pathogenicity of UQCRC1 in a Taiwanese cohort of patients with Parkinson's disease (PD).

Method

This study involved 107 participants (98 with early-onset PD and nine with familial PD). All UQCRC1 coding exons and exon-intron boundaries were sequenced. The rarity and pathogenicity of the identified variants were analyzed. The carrier frequencies of our cohort and the Taiwan Biobank were compared through a Pearson's χ² or Fisher's exact test along with Bonferroni corrections.

Results

Three missense variants (c.643G > C, p.D215H; c.800C > G, p.P267R, and c.923A > G, p.N308S) and seven rare variants were identified. No significant differences in the missense-variant carrier frequency were noted between our cohort and individuals in the Taiwan Biobank. Furthermore, no significant associations were noted between the variants and the risk of PD.

Conclusions

Our study is not supporting a role of UQCRC1 variants in PD.

Secretome as neuropathology-targeted intervention of Parkinson’s disease

Parkinson’s disease (PD) is the second most common progressive neurodegenerative disease, characterized by apoptosis of dopaminergic neurons in substansia nigra pars compacta (SNpc) caused by ⍺-synuclein aggregation. The use of secretomes released by medicinal signaling cells (MSCs) is one the promising preventive approaches that target several mechanisms in the neuropathology of PD. Its components target the lack of neurotrophin factors, proteasome dysfunction, oxidative stress, mitochondrial dysfunction, and at last neuroinflammation via several pathways. The complex and obscure pathology of PD induce the difficulty of the search of potential preventive approach for this disease. We described the potential of secretome of MSC as the novel preventive approach for PD, especially by targeting the said major pathogenesis of PD.

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Secretome targets the major pathogenesis of PD.

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Secretome regulates inflammation by balancing pro- and anti-inflammatory cytokines.

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Secretome induces autophagy providing cytoprotective effects.

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Secretome has anti-oxidative, neuroprotective, and neurotrophic due to neurotrophic factors as its component.

Exposure to the environmentally toxic pesticide maneb induces Parkinson's disease-like neurotoxicity in mice: A combined proteomic and metabolomic analysis

Maneb is a typical dithiocarbamate fungicide that has been extensively used worldwide. Epidemiological evidence shows that exposure to maneb is an environmental risk factor for Parkinson's disease (PD). However, the mechanisms underlying maneb-induced neurotoxicity have yet to be elucidated. In this study, we exposed SH-SY5Y cells to maneb at environmentally relevant concentrations (0, 0.1, 5, 10 mg/L) and found that maneb dose-dependently decreased the cell viability. Furthermore, maneb (60 mg/kg) induced PD-like motor impairment in α-synuclein A53T transgenic mice. The results of tandem mass tag (TMT) proteomics and metabolomics studies of mouse brain and serum revealed significant changes in proteins and metabolites in the pathways involved in the neurotransmitter system. The omics results were verified by targeted metabolomics and Western blot analysis, which demonstrated that maneb induced disturbance of the PD-related pathways, including the phenylalanine and tryptophan metabolism pathways, dopaminergic synapse, synaptic vesicle cycle, mitochondrial dysfunction, and oxidative stress. In addition, the PD-like phenotype induced by maneb was attenuated by the asparagine endopeptidase (AEP) inhibitor compound #11 (CP11) (10 mg/kg), indicating that AEP may play a role in maneb-induced neurotoxicity. To the best of our knowledge, this is the first study to investigate the molecular mechanisms underlying maneb-induced PD-like phenotypes using multiomics analysis, which identified novel therapeutic targets for PD associated with pesticides and other environmental pollutants.

Molecular and Cellular Interactions in Pathogenesis of Sporadic Parkinson Disease

An increasing number of the population all around the world suffer from age-associated neurodegenerative diseases including Parkinson’s disease (PD). This disorder presents different signs of genetic, epigenetic and environmental origin, and molecular, cellular and intracellular dysfunction. At the molecular level, α-synuclein (αSyn) was identified as the principal molecule constituting the Lewy bodies (LB). The gut microbiota participates in the pathogenesis of PD and may contribute to the loss of dopaminergic neurons through mitochondrial dysfunction. The most important pathogenetic link is an imbalance of Ca²⁺ ions, which is associated with redox imbalance in the cells and increased generation of reactive oxygen species (ROS). In this review, genetic, epigenetic and environmental factors that cause these disorders and their cause-and-effect relationships are considered. As a constituent of environmental factors, the example of organophosphates (OPs) is also reviewed. The role of endothelial damage in the pathogenesis of PD is discussed, and a ‘triple hit hypothesis’ is proposed as a modification of Braak’s dual hit one. In the absence of effective therapies for neurodegenerative diseases, more and more evidence is emerging about the positive impact of nutritional structure and healthy lifestyle on the state of blood vessels and the risk of developing these diseases.

Rhus Coriaria L. Extract: Antioxidant Effect and Modulation of Bioenergetic Capacity in Fibroblasts from Parkinson’s Disease Patients and THP-1 Macrophages

Sumac, Rhus coriaria L., is a Mediterranean plant showing several useful properties, such as antioxidant and neuroprotective effects. Currently, there is no evidence about its possible neuroprotective action in Parkinson’s disease (PD). We hypothesized that sumac could modulate mitochondrial functionality in fibroblasts of familial early-onset PD patients showing PARK2 mutations. Sumac extract volatile profile, polyphenolic content and antioxidant activity have been previously characterized. We evaluated ROS and ATP levels on sumac-treated patients’ and healthy control fibroblasts. In PD fibroblasts, all treatments were effective in reducing H₂O₂ levels, while patients’ ATP content was modulated differently, probably due to the varying mutations in the PARK2 gene found in individual patients which are also involved in different mitochondrial phenotypes. We also investigated the effect of sumac extract on THP-1-differentiated macrophages, which show different embryogenic origin with respect to fibroblasts. In THP-1 macrophages, sumac treatment determined a reduction in H₂O₂ levels and an increase in the mitochondrial ATP content in M1, assuming that sumac could polarize the M1 to M2 phenotype, as demonstrated with other food-derived compounds rich in polyphenols. In conclusion, Rhus coriaria L. extracts could represent a potential nutraceutical approach to PD.

Exploring therapeutic potential of mitophagy modulators using Drosophila models of Parkinson’s disease

Parkinson’s disease (PD) is the second most popular age-associated neurodegenerative disorder after Alzheimer’s disease. The degeneration of dopaminergic neurons, aggregation of α-synuclein (α-syn), and locomotor defects are the main characteristic features of PD. The main cause of a familial form of PD is associated with a mutation in genes such as SNCA, PINK1, Parkin, DJ-1, LRKK2, and others. Recent advances have uncovered the different underlying mechanisms of PD but the treatment of PD is still unknown due to the unavailability of effective therapies and preventive medicines in the current scenario. The pathophysiology and genetics of PD have been strongly associated with mitochondria in disease etiology. Several studies have investigated a complex molecular mechanism governing the identification and clearance of dysfunctional mitochondria from the cell, a mitochondrial quality control mechanism called mitophagy. Reduced mitophagy and mitochondrial impairment are found in both sporadic and familial PD. Pharmacologically modulating mitophagy and accelerating the removal of defective mitochondria are of common interest in developing a therapy for PD. However, despite the extensive understanding of the mitochondrial quality control pathway and its underlying mechanism, the therapeutic potential of targeting mitophagy modulation and its role in PD remains to be explored. Thus, targeting mitophagy using chemical agents and naturally occurring phytochemicals could be an emerging therapeutic strategy in PD prevention and treatment. We discuss the current research on understanding the role of mitophagy modulators in PD using Drosophila melanogaster as a model. We further explore the contribution of Drosophila in the pathophysiology of PD, and discuss comprehensive genetic analysis in flies and pharmacological drug screening to develop potential therapeutic molecules for PD.

Mitophagy and reactive oxygen species interplay in Parkinson's disease

Mitophagy impairment and oxidative stress are cardinal pathological hallmarks in Parkinson's disease (PD), a common age-related neurodegenerative condition. The specific interactions between mitophagy and reactive oxygen species (ROS) have attracted considerable attention even though their exact interplay in PD has not been fully elucidated. We highlight the interactions between ROS and mitophagy, with a focus on the signalling pathways downstream to ROS that triggers mitophagy and draw attention to potential therapeutic compounds that target these pathways in both experimental and clinical models. Identifying a combination of ROS inhibitors and mitophagy activators to provide a physiologic balance in this complex signalling pathways may lead to a more optimal outcome. Deciphering the exact temporal relationship between mitophagy and oxidative stress and their triggers early in the course of neurodegeneration can unravel mechanistic clues that potentially lead to the development of compounds for clinical drug trials focusing on prodromic PD or at-risk individuals.

Novel therapeutic strategies targeting mitochondria as a gateway in neurodegeneration

In recent years, multiple disciplines have focused on mitochondrial biology and contributed to understanding its relevance towards adult-onset neurodegenerative disorders. These are complex dynamic organelles that have a variety of functions in ensuring cellular health and homeostasis. The plethora of mitochondrial functionalities confers them an intrinsic susceptibility to internal and external stressors (such as mutation accumulation or environmental toxins), particularly so in long-lived postmitotic cells such as neurons. Thus, it is reasonable to postulate an involvement of mitochondria in aging-associated neurological disorders, notably neurodegenerative pathologies including Alzheimer's disease and Parkinson's disease. On the other hand, biological effects resulting from neurodegeneration can in turn affect mitochondrial health and function, promoting a feedback loop further contributing to the progression of neuronal dysfunction and cellular death. This review examines state-of-the-art knowledge, focus on current research exploring mitochondrial health as a contributing factor to neuroregeneration, and the development of therapeutic approaches aimed at restoring mitochondrial homeostasis in a pathological setting.

Neuroprotective Effects of Sodium Butyrate and Monomethyl Fumarate Treatment through GPR109A Modulation and Intestinal Barrier Restoration on PD Mice

Research has connected Parkinson's disease (PD) with impaired intestinal barrier. The activation of G-protein-coupled receptor 109A (GPR109A) protects the intestinal barrier by inhibiting the NF-κB signaling pathway. Sodium butyrate (NaB), which is a GPR109A ligand, may have anti-PD effects. The current study's objective is to demonstrate that NaB or monomethyl fumarate (MMF, an agonist of the GPR109A) can treat PD mice induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) via repairing the intestinal barrier. Male C57BL/6J mice were divided into four groups randomly: control, MPTP + vehicle, MPTP + NaB, and MPTP + MMF. Modeling mice received MPTP (20 mg/kg/day, i.p.) for a week, while control mice received sterile PBS. Then, four groups each received two weeks of sterile PBS (10 mL/kg/day, i.g.), sterile PBS (10 mL/kg/day, i.g.), NaB (600 mg/kg/day, i.g.), or MMF (100 mg/kg/day, i.g.). We assessed the expression of tight junction (TJ) proteins (occludin and claudin-1), GPR109A, and p65 in the colon, performed microscopic examination via HE staining, quantified markers of intestinal permeability and proinflammatory cytokines in serum, and evaluated motor symptoms and pathological changes in the substantia nigra (SN) or striatum. According to our results, MPTP-induced defected motor function, decreased dopamine and 5-hydroxytryptamine levels in the striatum, decreased tyrosine hydroxylase-positive neurons and increased activated microglia in the SN, and systemic inflammation were ameliorated by NaB or MMF treatment. Additionally, the ruined intestinal barrier was also rebuilt and NF-κB was suppressed after the treatment, with higher levels of TJ proteins, GPR109A, and decreased intestinal permeability. These results show that NaB or MMF can remedy motor symptoms and pathological alterations in PD mice by restoring the intestinal barrier with activated GPR109A. We demonstrate the potential for repairing the compromised intestinal barrier and activating GPR109A as promising treatments for PD.

The Potential Role of Voltage-Dependent Anion Channel in the Treatment of Parkinson’s Disease

Parkinson’s disease (PD) is a neurodegenerative disease second only to Alzheimer’s disease in terms of prevalence. Previous studies have indicated that the occurrence and progression of PD are associated with mitochondrial dysfunction. Mitochondrial dysfunction is one of the most important causes for apoptosis of dopaminergic neurons. Therefore, maintaining the stability of mitochondrial functioning is a potential strategy in the treatment of PD. Voltage-dependent anion channel (VDAC) is the main component in the outer mitochondrial membrane, and it participates in a variety of biological processes. In this review, we focus on the potential roles of VDACs in the treatment of PD. We found that VDACs are involved in PD by regulating apoptosis, autophagy, and ferroptosis. VDAC1 oligomerization, VDACs ubiquitination, regulation of mitochondrial permeability transition pore (mPTP) by VDACs, and interaction between VDACs and α-synuclein (α-syn) are all promising methods for the treatment of PD. We proposed that inhibition of VDAC1 oligomerization and promotion of VDAC1 ubiquitination as an effective approach for the treatment of PD. Previous studies have proven that the expression of VDAC1 has a significant change in PD models. The expression levels of VDAC1 are decreased in the substantia nigra (SN) of patients suffering from PD compared with the control group consisting of normal individuals by using bioinformatics tools. VDAC2 is involved in PD mainly through the regulation of apoptosis. VDAC3 may have a similar function to VDAC1. It can be concluded that the functional roles of VDACs contribute to the therapeutic strategy of PD.

Mitochondria - Nucleus communication in neurodegenerative disease. Who talks first, who talks louder?

Mitochondria - nuclear coadaptation has been central to eukaryotic evolution. The dynamic dialogue between the two compartments within the context of multiorganellar interactions is critical for maintaining cellular homeostasis and directing the balance survival-death in case of cellular stress. The conceptualisation of mitochondria - nucleus communication has so far been focused on the communication from the mitochondria under stress to the nucleus and the consequent signalling responses, as well as from the nucleus to mitochondria in the context of DNA damage and repair. During ageing processes this dialogue may be better viewed as an integrated bidirectional 'talk' with feedback loops that expand beyond these two organelles depending on physiological cues. Here we explore the current views on mitochondria - nucleus dialogue and its role in maintaining cellular health with a focus on brain cells and neurodegenerative disease. Thus, we detail the transcriptional responses initiated by mitochondrial dysfunction in order to protect itself and the general cellular homeostasis. Additionally, we are reviewing the knowledge of the stress pathways initiated by DNA damage which affect mitochondria homeostasis and we add the information provided by the study of combined mitochondrial and genotoxic damage. Finally, we reflect on how each organelle may take the lead in this dialogue in an ageing context where both compartments undergo accumulation of stress and damage and where, perhaps, even the communications' mechanisms may suffer interruptions.

A Comprehensive Review on Beneficial Effects of Catechins on Secondary Mitochondrial Diseases

Mitochondria are the main sites for oxidative phosphorylation and synthesis of adenosine triphosphate in cells, and are known as cellular power factories. The phrase "secondary mitochondrial diseases" essentially refers to any abnormal mitochondrial function other than primary mitochondrial diseases, i.e., the process caused by the genes encoding the electron transport chain (ETC) proteins directly or impacting the production of the machinery needed for ETC. Mitochondrial diseases can cause adenosine triphosphate (ATP) synthesis disorder, an increase in oxygen free radicals, and intracellular redox imbalance. It can also induce apoptosis and, eventually, multi-system damage, which leads to neurodegenerative disease. The catechin compounds rich in tea have attracted much attention due to their effective antioxidant activity. Catechins, especially acetylated catechins such as epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), are able to protect mitochondria from reactive oxygen species. This review focuses on the role of catechins in regulating cell homeostasis, in which catechins act as a free radical scavenger and metal ion chelator, their protective mechanism on mitochondria, and the protective effect of catechins on mitochondrial deoxyribonucleic acid (DNA). This review highlights catechins and their effects on mitochondrial functional metabolic networks: regulating mitochondrial function and biogenesis, improving insulin resistance, regulating intracellular calcium homeostasis, and regulating epigenetic processes. Finally, the indirect beneficial effects of catechins on mitochondrial diseases are also illustrated by the warburg and the apoptosis effect. Some possible mechanisms are shown graphically. In addition, the bioavailability of catechins and peracetylated-catechins, free radical scavenging activity, mitochondrial activation ability of the high-molecular-weight polyphenol, and the mitochondrial activation factor were also discussed.

Mitochondrial DNA Repair in Neurodegenerative Diseases and Ageing

Mitochondria are the only organelles, along with the nucleus, that have their own DNA. Mitochondrial DNA (mtDNA) is a double-stranded circular molecule of ~16.5 kbp that can exist in multiple copies within the organelle. Both strands are translated and encode for 22 tRNAs, 2 rRNAs, and 13 proteins. mtDNA molecules are anchored to the inner mitochondrial membrane and, in association with proteins, form a structure called nucleoid, which exerts a structural and protective function. Indeed, mitochondria have evolved mechanisms necessary to protect their DNA from chemical and physical lesions such as DNA repair pathways similar to those present in the nucleus. However, there are mitochondria-specific mechanisms such as rapid mtDNA turnover, fission, fusion, and mitophagy. Nevertheless, mtDNA mutations may be abundant in somatic tissue due mainly to the proximity of the mtDNA to the oxidative phosphorylation (OXPHOS) system and, consequently, to the reactive oxygen species (ROS) formed during ATP production. In this review, we summarise the most common types of mtDNA lesions and mitochondria repair mechanisms. The second part of the review focuses on the physiological role of mtDNA damage in ageing and the effect of mtDNA mutations in neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. Considering the central role of mitochondria in maintaining cellular homeostasis, the analysis of mitochondrial function is a central point for developing personalised medicine.

NLRP3 inflammasomes: A potential target to improve mitochondrial biogenesis in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative condition for which no approved treatment exists to prevent collective neuronal death. There is ample evidence that mitochondrial dysfunction, reactive oxygen species (ROS), and associated caspase activity underlie the pathology observed. Neurons rely on mitochondrial activity since they have such high energy consumption. Therefore, it is not surprising that mitochondrial alterations favour neuronal degeneration. In particular, mitochondrial dysregulation contributes to PD, based on the observation that mitochondrial toxins can cause parkinsonism in humans and animal models. Also, it is known that inflammatory cytokine-mediated neuroinflammation is the key pathogenic mechanism in neuronal loss. In recent years, the research has focussed on mitochondria being the platform for nucleotide-binding oligomerization domain-like receptors 3 (NLRP3) inflammasome activation. Mitochondrial dysfunction and NLRP3 activation are emerging as critical players in inducing and sustaining neuroinflammation. Moreover, mitochondrial-derived ROS and mitochondrial DNA (mtDNA) could serve as the priming signal for forming inflammasome complexes responsible for the activation, maturation, and release of pro-inflammatory cytokines, including interleukin-1(IL-1) and interleukin-18 (IL-18). The current review takes a more comprehensive approach to elucidating the link between mitochondrial dysfunction and aberrant NLRP3 activation in PD. In addition, we focus on some inhibitors of NLRP3 inflammatory pathways to alleviate the progression of PD.

Neuroprotective Function of Rasagiline and Selegiline, Inhibitors of Type B Monoamine Oxidase, and Role of Monoamine Oxidases in Synucleinopathies

Synucleinopathies are a group of neurodegenerative disorders caused by the accumulation of toxic species of α-synuclein. The common clinical features are chronic progressive decline of motor, cognitive, behavioral, and autonomic functions. They include Parkinson’s disease, dementia with Lewy body, and multiple system atrophy. Their etiology has not been clarified and multiple pathogenic factors include oxidative stress, mitochondrial dysfunction, impaired protein degradation systems, and neuroinflammation. Current available therapy cannot prevent progressive neurodegeneration and “disease-modifying or neuroprotective” therapy has been proposed. This paper presents the molecular mechanisms of neuroprotection by the inhibitors of type B monoamine oxidase, rasagiline and selegiline. They prevent mitochondrial apoptosis, induce anti-apoptotic Bcl-2 protein family, and pro-survival brain- and glial cell line-derived neurotrophic factors. They also prevent toxic oligomerization and aggregation of α-synuclein. Monoamine oxidase is involved in neurodegeneration and neuroprotection, independently of the catalytic activity. Type A monoamine oxidases mediates rasagiline-activated signaling pathways to induce neuroprotective genes in neuronal cells. Multi-targeting propargylamine derivatives have been developed for therapy in various neurodegenerative diseases. Preclinical studies have presented neuroprotection of rasagiline and selegiline, but beneficial effects have been scarcely presented. Strategy to improve clinical trials is discussed to achieve disease-modification in synucleinopathies.

L-Ornithine L-Aspartate Restores Mitochondrial Function and Modulates Intracellular Calcium Homeostasis in Parkinson's Disease Models

The altered crosstalk between mitochondrial dysfunction, intracellular Ca²⁺ homeostasis, and oxidative stress has a central role in the dopaminergic neurodegeneration. In the present study, we investigated the hypothesis that pharmacological strategies able to improve mitochondrial functions might prevent neuronal dysfunction in in vitro models of Parkinson’s disease. To this aim, the attention was focused on the amino acid ornithine due to its ability to cross the blood–brain barrier, to selectively reach and penetrate the mitochondria through the ornithine transporter 1, and to control mitochondrial function. To pursue this issue, experiments were performed in human neuroblastoma cells SH-SY5Y treated with rotenone and 6-hydroxydopamine to investigate the pharmacological profile of the compound L-Ornithine-L-Aspartate (LOLA) as a new potential therapeutic strategy to prevent dopaminergic neurons’ death. In these models, confocal microscopy experiments with fluorescent dyes measuring mitochondrial calcium content, mitochondrial membrane potential, and mitochondrial ROS production, demonstrated that LOLA improved mitochondrial functions. Moreover, by increasing NCXs expression and activity, LOLA also reduced cytosolic [Ca²⁺] thanks to its ability to modulate NO production. Collectively, these results indicate that LOLA, by interfering with those mitochondrial mechanisms related to ROS and RNS production, promotes mitochondrial functional recovery, thus confirming the tight relationship existing between cytosolic ionic homeostasis and cellular metabolism depending on the type of insult applied.

Targeting Mitochondria as a Therapeutic Approach for Parkinson's Disease

Neurodegeneration is among the most critical challenges that involve modern societies and annually influences millions of patients worldwide. While the pathophysiology of Parkinson's disease (PD) is complicated, the role of mitochondrial is demonstrated. The in vitro and in vivo models and genome-wide association studies in human cases proved that specific genes, including PINK1, Parkin, DJ-1, SNCA, and LRRK2, linked mitochondrial dysfunction with PD. Also, mitochondrial DNA (mtDNA) plays an essential role in the pathophysiology of PD. Targeting mitochondria as a therapeutic approach to inhibit or slow down PD formation and progression seems to be an exciting issue. The current review summarized known mutations associated with both mitochondrial dysfunction and PD. The significance of mtDNA in Parkinson's disease pathogenesis and potential PD therapeutic approaches targeting mitochondrial dysfunction was then discussed.

C-terminal truncation modulates α-Synuclein's cytotoxicity and aggregation by promoting the interactions with membrane and chaperone

α-Synuclein (α-syn) is the main protein component of Lewy bodies, the major pathological hallmarks of Parkinson's disease (PD). C-terminally truncated α-syn is found in the brain of PD patients, reduces cell viability and tends to form fibrils. Nevertheless, little is known about the mechanisms underlying the role of C-terminal truncation on the cytotoxicity and aggregation of α-syn. Here, we use nuclear magnetic resonance spectroscopy to show that the truncation alters α-syn conformation, resulting in an attractive interaction of the N-terminus with membranes and molecular chaperone, protein disulfide isomerase (PDI). The truncated protein is more toxic to mitochondria than full-length protein and diminishes the effect of PDI on α-syn fibrillation. Our findings reveal a modulatory role for the C-terminus in the cytotoxicity and aggregation of α-syn by interfering with the N-terminus binding to membranes and chaperone, and provide a molecular basis for the pathological role of C-terminal truncation in PD pathogenesis.

Targeting NAAA counters dopamine neuron loss and symptom progression in mouse models of parkinsonism

The lysosomal cysteine hydrolase N-acylethanolamine acid amidase (NAAA) deactivates palmitoylethanolamide (PEA), a lipid-derived PPAR-α agonist that is critically involved in the control of pain and inflammation. In this study, we asked whether NAAA-regulated PEA signaling might contribute to dopamine neuron degeneration and parkinsonism induced by the mitochondrial neurotoxins, 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In vitro experiments showed that 6-OHDA and MPTP enhanced NAAA expression and lowered PEA content in human SH-SY5Y cells. A similar effect was observed in mouse midbrain dopamine neurons following intra-striatal 6-OHDA injection. Importantly, deletion of the Naaa gene or pharmacological inhibition of NAAA activity substantially attenuated both dopamine neuron death and parkinsonian symptoms in mice treated with 6-OHDA or MPTP. Moreover, NAAA expression was elevated in postmortem brain cortex and premortem blood-derived exosomes from persons with Parkinson's disease compared to age-matched controls. The results identify NAAA-regulated PEA signaling as a molecular control point for dopaminergic neuron survival and a potential target for neuroprotective intervention.

Peripheral Neuroprotective and Immunomodulatory Effects of 5α-Reductase Inhibitors in Parkinson's Disease Models

Gastrointestinal disorders in Parkinson's disease (PD) have been associated with neuronal alteration in the plexus of the gut. We previously demonstrated the immunomodulatory effect of female hormones to treat enteric neurodegeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. This study made the hypothesis of obtaining similar neuroprotection as with hormone treatments by affecting steroidogenesis with two 5α-reductase inhibitors, finasteride and dutasteride. These drugs are approved to treat benign prostatic hyperplasia and alopecia and display mitochondrial effects. In MPTP-treated mice, the dopaminergic and vasoactive intestinal peptide (VIP) neurons alteration was prevented by finasteride and dutasteride, while the increase in proinflammatory macrophages density was inhibited by dutasteride treatment but not finasteride. NF-κB response, oxidative stress, and nitric oxide and proinflammatory cytokines production in vitro were only prevented by dutasteride. In addition, mitochondrial production of free radicals, membrane depolarization, decreased basal respiration, and ATP production were inhibited by dutasteride, while finasteride had no effect. In conclusion, the present results indicate that dutasteride treatment prevents enteric neuronal damages in the MPTP mouse model, at least in part through anti-inflammatory and mitochondrial effects. This suggests that drug repurposing of dutasteride might be a promising avenue to treat enteric neuroinflammation in early PD.

Therapeutic application of quercetin in aging-related diseases: SIRT1 as a potential mechanism

Quercetin, a naturally non-toxic flavonoid within the safe dose range with antioxidant, anti-apoptotic and anti-inflammatory properties, plays an important role in the treatment of aging-related diseases. Sirtuin 1 (SIRT1), a member of NAD+-dependent deacetylase enzyme family, is extensively explored as a potential therapeutic target for attenuating aging-induced disorders. SIRT1 possess beneficial effects against aging-related diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), Depression, Osteoporosis, Myocardial ischemia (M/I) and reperfusion (MI/R), Atherosclerosis (AS), and Diabetes. Previous studies have reported that aging increases tissue susceptibility, whereas, SIRT1 regulates cellular senescence and multiple aging-related cellular processes, including SIRT1/Keap1/Nrf2/HO-1 and SIRTI/PI3K/Akt/GSK-3β mediated oxidative stress, SIRT1/NF-κB and SIRT1/NLRP3 regulated inflammatory response, SIRT1/PGC1α/eIF2α/ATF4/CHOP and SIRT1/PKD1/CREB controlled phosphorylation, SIRT1-PINK1-Parkin mediated mitochondrial damage, SIRT1/FoxO mediated autophagy, and SIRT1/FoxG1/CREB/BDNF/Trkβ-catenin mediated neuroprotective effects. In this review, we summarized the role of SIRT1 in the improvement of the attenuation effect of quercetin on aging-related diseases and the relationship between relevant signaling pathways regulated by SIRT1. Moreover, the functional regulation of quercetin in aging-related markers such as oxidative stress, inflammatory response, mitochondrial function, autophagy and apoptosis through SIRT1 was discussed. Finally, the prospects of an extracellular vesicles (EVs) as quercetin loading and delivery, and SIRT1-mediated EVs as signal carriers for treating aging-related diseases, as well as discussed the ferroptosis alleviation effects of quercetin to protect against aging-related disease via activating SIRT1. Generally, SIRT1 may serve as a promising therapeutic target in the treatment of aging-related diseases via inhibiting oxidative stress, reducing inflammatory responses, and restoring mitochondrial dysfunction.

Restorative therapy using microglial depletion and repopulation for central nervous system injuries and diseases

Microglia are important resident immune cells in the central nervous system (CNS) and play an important role in its development, homeostasis, and disease treatments. Activated microglia perform diverse functions in mouse models of CNS neurodegenerative diseases or deficits. In humans, microglia have been linked to various neurodegenerative diseases. Following brain or spinal cord injury, microglia express pro- and anti-inflammatory phenotypes at different stages of recovery. With the development of pharmacological and genetic tools for microglial depletion, studies have demonstrated that microglial depletion exerts both positive and negative effects in the treatment of CNS diseases. Notably, microglial depletion provides an empty niche that stimulates production of new microglia. Microglial depletion and repopulation can not only treat diseases by eliminating dysfunctional microglia but can also provide an indication of the molecular mechanisms of diseases. Although this approach has shown impressive results, its use is still in its infancy. In this review, we summarize the current pharmacological and genetic tools for microglial depletion and highlight recent advances in microglial repopulation therapy for the treatment and functional recovery of neurological diseases and deficits. Finally, we briefly discuss the therapeutic challenges and prospective uses of microglial repopulation therapy.

Hallmarks and Molecular Tools for the Study of Mitophagy in Parkinson’s Disease

The best-known hallmarks of Parkinson’s disease (PD) are the motor deficits that result from the degeneration of dopaminergic neurons in the substantia nigra. Dopaminergic neurons are thought to be particularly susceptible to mitochondrial dysfunction. As such, for their survival, they rely on the elaborate quality control mechanisms that have evolved in mammalian cells to monitor mitochondrial function and eliminate dysfunctional mitochondria. Mitophagy is a specialized type of autophagy that mediates the selective removal of damaged mitochondria from cells, with the net effect of dampening the toxicity arising from these dysfunctional organelles. Despite an increasing understanding of the molecular mechanisms that regulate the removal of damaged mitochondria, the detailed molecular link to PD pathophysiology is still not entirely clear. Herein, we review the fundamental molecular pathways involved in PINK1/Parkin-mediated and receptor-mediated mitophagy, the evidence for the dysfunction of these pathways in PD, and recently-developed state-of-the art assays for measuring mitophagy in vitro and in vivo.

Neuroprotective approaches to halt Parkinson's disease progression

One of the most significant threats in Parkinson's disease (PD) is neurodegeneration. Neurodegeneration at both nigral as well as non-nigral regions of the brain is considered responsible for disease progression in PD. The key factors that initiate neurodegeneration are oxidative stress, neuroinflammation, mitochondrial complex-1 inhibition, and abnormal α-synuclein (SNCA) protein aggregations. Nigral neurodegeneration results in motor symptoms (tremor, bradykinesia, rigidity, shuffling gait, and postural instability) whereas; non-nigral neurodegeneration is responsible for non-motor symptoms (depression, cognitive dysfunctions, sleep disorders, hallucination, and psychosis). The available therapies for PD aim at increasing dopamine levels. The medications such as Monoamine oxidase B (MAO-B) inhibitors, catechol o-methyltransferase (COMT) inhibitors, Dopamine precursor (Levodopa), dopamine agonists, and dopamine reuptake inhibitors drastically improve the motor symptoms and quality of life only in the early stages of the disease. However, dopa resistant motor symptoms (abnormality in posture, speech impediment, gait, and balance problems), dopa resistant non-motor signs (sleep problems, autonomic dysfunction, mood, and cognitive impairment, pain), and drug-related side effects (motor fluctuations, psychosis, and dyskinesias) are considered responsible for the failure of these therapies. Further, none of the treatments, alone or in combination, are capable of halting the disease progression in the long run. Therefore, there is a need to develop safe and efficient neuroprotective agents, which can slow or stop the disease progression for the better management of PD. In this review, an effort has been made to discuss the various mechanisms responsible for progressive neurodegeneration (disease progression) in PD and also multiple strategies available for halting disease progression.

Age-Associated Glia Remodeling and Mitochondrial Dysfunction in Neurodegeneration: Antioxidant Supplementation as a Possible Intervention

Aging induces substantial remodeling of glia, including density, morphology, cytokine expression, and phagocytic capacity. Alterations of glial cells, such as hypertrophy of lysosomes, endosomes and peroxisomes, and the progressive accumulation of lipofuscin, lipid droplets, and other debris have also been reported. These abnormalities have been associated with significant declines of microglial processes and reduced ability to survey the surrounding tissue, maintain synapses, and recover from injury. Similarly, aged astrocytes show reduced capacity to support metabolite transportation to neurons. In the setting of reduced glial activity, stressors and/or injury signals can trigger a coordinated action of microglia and astrocytes that may amplify neuroinflammation and contribute to the release of neurotoxic factors. Oxidative stress and proteotoxic aggregates may burst astrocyte-mediated secretion of pro-inflammatory cytokines, thus activating microglia, favoring microgliosis, and ultimately making the brain more susceptible to injury and/or neurodegeneration. Here, we discuss the contribution of microglia and astrocyte oxidative stress to neuroinflammation and neurodegeneration, highlight the pathways that may help gain insights into their molecular mechanisms, and describe the benefits of antioxidant supplementation-based strategies.

Neurogenesis in aging and age-related neurodegenerative diseases

Adult neurogenesis, the process by which neurons are generated in certain areas of the adult brain, declines in an age-dependent manner and is one potential target for extending cognitive healthspan. Aging is a major risk factor for neurodegenerative diseases and, as lifespans are increasing, these health challenges are becoming more prevalent. An age-associated loss in neural stem cell number and/or activity could cause this decline in brain function, so interventions that reverse aging in stem cells might increase the human cognitive healthspan. In this review, we describe the involvement of adult neurogenesis in neurodegenerative diseases and address the molecular mechanistic aspects of neurogenesis that involve some of the key aggregation-prone proteins in the brain (i.e., tau, Aβ, α-synuclein, …). We summarize the research pertaining to interventions that increase neurogenesis and regulate known targets in aging research, such as mTOR and sirtuins. Lastly, we share our outlook on restoring the levels of neurogenesis to physiological levels in elderly individuals and those with neurodegeneration. We suggest that modulating neurogenesis represents a potential target for interventions that could help in the fight against neurodegeneration and cognitive decline.

Single-cell sequencing of human midbrain reveals glial activation and a Parkinson-specific neuronal state

Idiopathic Parkinson's disease is characterized by a progressive loss of dopaminergic neurons, but the exact disease aetiology remains largely unknown. To date, Parkinson's disease research has mainly focused on nigral dopaminergic neurons, although recent studies suggest disease-related changes also in non-neuronal cells and in midbrain regions beyond the substantia nigra. While there is some evidence for glial involvement in Parkinson's disease, the molecular mechanisms remain poorly understood. The aim of this study was to characterize the contribution of all cell types of the midbrain to Parkinson's disease pathology by single-nuclei RNA sequencing and to assess the cell type-specific risk for Parkinson's disease using the latest genome-wide association study. We profiled >41 000 single-nuclei transcriptomes of post-mortem midbrain from six idiopathic Parkinson's disease patients and five age-/sex-matched controls. To validate our findings in a spatial context, we utilized immunolabelling of the same tissues. Moreover, we analysed Parkinson's disease-associated risk enrichment in genes with cell type-specific expression patterns. We discovered a neuronal cell cluster characterized by CADPS2 overexpression and low TH levels, which was exclusively present in idiopathic Parkinson's disease midbrains. Validation analyses in laser-microdissected neurons suggest that this cluster represents dysfunctional dopaminergic neurons. With regard to glial cells, we observed an increase in nigral microglia in Parkinson's disease patients. Moreover, nigral idiopathic Parkinson's disease microglia were more amoeboid, indicating an activated state. We also discovered a reduction in idiopathic Parkinson's disease oligodendrocyte numbers with the remaining cells being characterized by a stress-induced upregulation of S100B. Parkinson's disease risk variants were associated with glia- and neuron-specific gene expression patterns in idiopathic Parkinson's disease cases. Furthermore, astrocytes and microglia presented idiopathic Parkinson's disease-specific cell proliferation and dysregulation of genes related to unfolded protein response and cytokine signalling. While reactive patient astrocytes showed CD44 overexpression, idiopathic Parkinson's disease microglia revealed a pro-inflammatory trajectory characterized by elevated levels of IL1B, GPNMB and HSP90AA1. Taken together, we generated the first single-nuclei RNA sequencing dataset from the idiopathic Parkinson's disease midbrain, which highlights a disease-specific neuronal cell cluster as well as 'pan-glial' activation as a central mechanism in the pathology of the movement disorder. This finding warrants further research into inflammatory signalling and immunomodulatory treatments in Parkinson's disease.

Parkin Deficiency Impairs Mitochondrial DNA Dynamics and Propagates Inflammation

BACKGROUND

Mutations in the E3 ubiquitin ligase parkin cause autosomal recessive Parkinson's disease (PD). Together with PTEN-induced kinase 1 (PINK1), parkin regulates the clearance of dysfunctional mitochondria. New mitochondria are generated through an interplay of nuclear- and mitochondrial-encoded proteins, and recent studies suggest that parkin influences this process at both levels. In addition, parkin was shown to prevent mitochondrial membrane permeability, impeding mitochondrial DNA (mtDNA) escape and subsequent neuroinflammation. However, parkin's regulatory roles independent of mitophagy are not well described in patient-derived neurons.

OBJECTIVES

We sought to investigate parkin's role in preventing neuronal mtDNA dyshomeostasis, release, and glial activation at the endogenous level.

METHODS

We generated induced pluripotent stem cell (iPSC)-derived midbrain neurons from PD patients with parkin (PRKN) mutations and healthy controls. Live-cell imaging, proteomic, mtDNA integrity, and gene expression analyses were employed to investigate mitochondrial biogenesis and genome maintenance. To assess neuroinflammation, we performed single-nuclei RNA sequencing in postmortem tissue and quantified interleukin expression in mtDNA/lipopolysaccharides (LPS)-treated iPSC-derived neuron-microglia co-cultures.

RESULTS

Neurons from patients with PRKN mutations revealed deficits in the mitochondrial biogenesis pathway, resulting in mtDNA dyshomeostasis. Moreover, the energy sensor sirtuin 1, which controls mitochondrial biogenesis and clearance, was downregulated in parkin-deficient cells. Linking mtDNA disintegration to neuroinflammation, in postmortem midbrain with PRKN mutations, we confirmed mtDNA dyshomeostasis and detected an upregulation of microglia overexpressing proinflammatory cytokines. Finally, parkin-deficient neuron-microglia co-cultures elicited an enhanced immune response when exposed to mtDNA/LPS.

CONCLUSIONS

Our findings suggest that parkin coregulates mitophagy, mitochondrial biogenesis, and mtDNA maintenance pathways, thereby protecting midbrain neurons from neuroinflammation and degeneration. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Cerebroventricular Injection of Pgk1 Attenuates MPTP-Induced Neuronal Toxicity in Dopaminergic Cells in Zebrafish Brain in a Glycolysis-Independent Manner

Parkinson’s disease (PD) is characterized by the degeneration of dopaminergic neurons. While extracellular Pgk1 (ePgk1) is reported to promote neurite outgrowth, it remains unclear if it can affect the survival of dopaminergic cells. To address this, we employed cerebroventricular microinjection (CVMI) to deliver Pgk1 into the brain of larvae and adult zebrafish treated with methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a PD-like model. The number of dopamine-producing cells in ventral diencephalon clusters of Pgk1-injected, MPTP-treated embryos increased over that of MPTP-treated embryos. Swimming distances of Pgk1-injected, MPTP-treated larvae and adult zebrafish were much longer compared to MPTP-treated samples. The effect of injected Pgk1 on both dopamine-producing cells and locomotion was time- and dose-dependent. Indeed, injected Pgk1 could be detected, located on dopamine neurons. When the glycolytic mutant Pgk1, Pgk1-T378P, was injected into the brain of MPTP-treated zebrafish groups, the protective ability of dopaminergic neurons did not differ from that of normal Pgk1. Therefore, ePgk1 is functionally independent from intracellular Pgk1 serving as an energy supplier. Furthermore, when Pgk1 was added to the culture medium for culturing dopamine-like SH-SY5Y cells, it could reduce the ROS pathway and apoptosis caused by the neurotoxin MPP⁺. These results show that ePgk1 benefits the survival of dopamine-producing cells and decreases neurotoxin damage.

Neuronal SH2B1 attenuates apoptosis in an MPTP mouse model of Parkinson's disease via promoting PLIN4 degradation

The incidence of Parkinson's disease (PD) has increased tremendously, especially in the aged population and people with metabolic dysfunction; however, its underlying molecular mechanisms remain unclear. SH2B1, an intracellular adaptor protein, contributes to the signal transduction of several receptor tyrosine kinases and exerts beneficial metabolic effects for body weight regulation; however, whether SH2B1 plays a major role in pathological neurodegeneration in PD has not yet been investigated. This study aimed to investigate the effects of SH2B1 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)–induced PD mice with Sh2b1 deficiency or neuron-specific Sh2b1 overexpression. Cellular and molecular mechanisms were elucidated using human dopaminergic neuron SH-SY5Y cells analysed. We found that SH2B1 expression was confirmed to be downregulated in the blood samples of PD patients and in the brains of mice with MPTP-induced chronic PD. Sh2b1 deficiency caused marked exacerbation of behavioural defects and increased neuronal apoptosis in MPTP-treated mice, whereas restoration of neuron-specific Sh2b1 expression significantly reversed these effects. Similar results were observed in MPP ⁺ -treated SH-SY5Y cells. Mechanistically, upon binding to heat shock cognate 70 (HSC70), SH2B1 promotes HSC70-related recognition and PLIN4 lysosomal translocation and degradation, thus suppressing lipid peroxidation stress in the brains of PD mice. Adeno-associated virus-mediated rescue of neuronal HSC70 expression functionally alleviated the neuropathology of PD in wild-type but not in Sh2b1-deficient mice. This is the first study to examine the molecular underpinnings of SH2B1 against MPTP-induced neurodegeneration through cell autonomous promotion of neuronal survival in an in vivo PD model. Our findings reveal that SH2B1 antagonizes neurodegenerative pathology in PD via the SH2B1–HSC70–PLIN4 axis.

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Brain tissues, especially in TH⁺ neurons, of PD mice showed low SH2B1 expression.

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SH2B1 suppressed MPTP-induced neurodegeneration by inhibiting neuronal apoptosis.

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SH2B1 overexpression protected against MPP ⁺ -induced cell death via HSC70.

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SH2B1 interacts with HSC70 to form a complex that regulates PLIN4 degradation.