S-Nitrosylation of PINK1 Attenuates PINK1/Parkin-Dependent Mitophagy in hiPSC-Based Parkinson's Disease Models

Furin inhibits HSCs activation and ameliorates liver fibrosis by regulating PTEN-L/PINK1/parkin mediated mitophagy in mouse

Hepatic Stellate cells (HSCs) play an important role during liver fibrosis progression; more and more evidence indicates that mitophagy greatly regulates HSCs activation. HSCs mitophagy mainly depends on the classical PINK1/Parkin pathway, which can be strongly regulated by phosphatase PTEN-long (PTEN-L). PTEN-L can be cleaved by Furin that leading to functional changes in the tumor regulation process. However, the impact of the interaction between Furin and PTEN-L on HSCs mitophagy remains unclear. Therefore, this study aims to explore the role of Furin in HSCs activation and liver fibrosis and its potential mechanisms. Our results revealed that Furin expression was obviously up-regulated during HSCs activation and mice liver fibrogenesis. We also found that the activation of primary HSCs can be inhibited by Furin treatment in vitro. Besides, functional studies showed that LX-2 cell proliferation and migration were obviously inhibited by Furin treatment. Further studies showed that mitochondrial membrane potential (MMP) was significantly reduced by Furin treatment, and the knockdown of PTEN-L expression caused similar effects. These results demonstrated the role of Furin in promoting HSCs mitophagy but leading to inhibition of HSCs persistent activation. Furthermore, we constructed a liver fibrosis mouse model by CCl4-induced method and found that forced expression of Furin caused alleviation of liver fibrosis in CCl4-induced mice. Our findings provide a new clue for understanding liver fibrogenesis and highlight the therapeutic potential of Furin for hepatic fibrosis.

Current Development of iPSC-Based Modeling in Neurodegenerative Diseases

Over the past two decades, significant advancements have been made in the induced pluripotent stem cell (iPSC) technology. These developments have enabled the broader application of iPSCs in neuroscience, improved our understanding of disease pathogenesis, and advanced the investigation of therapeutic targets and methods. Specifically, optimizations in reprogramming protocols, coupled with improved neuronal differentiation and maturation techniques, have greatly facilitated the generation of iPSC-derived neural cells. The integration of the cerebral organoid technology and CRISPR/Cas9 genome editing has further propelled the application of iPSCs in neurodegenerative diseases to a new stage. Patient-derived or CRISPR-edited cerebral neurons and organoids now serve as ideal disease models, contributing to our understanding of disease pathophysiology and identifying novel therapeutic targets and candidates. In this review, we examine the development of iPSC-based models in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease.

Modulation of autophagy by melatonin and its receptors: implications in brain disorders

Autophagy plays a crucial role in maintaining neuronal homeostasis and function, and its disruption is linked to various brain diseases. Melatonin, an endogenous hormone that primarily acts through MT1 and MT2 receptors, regulates autophagy via multiple pathways. Growing evidence indicates that melatonin's ability to modulate autophagy provides therapeutic and preventive benefits in brain disorders, including neurodegenerative and affective diseases. In this review, we summarize the key mechanisms by which melatonin affects autophagy and explore its therapeutic potential in the treatment of brain disorders.

Stem Cell-Based Approaches in Parkinson's Disease Research

Parkinson's disease (PD) is a neurodegenerative condition characterized by the loss of midbrain dopaminergic neurons, leading to motor symptoms. While current treatments provide limited relief, they don't alter disease progression. Stem cell technology, involving patient-specific stem cell-derived neurons, offers a promising avenue for research and personalized regenerative therapies. This article reviews the potential of stem cell-based research in PD, summarizing ongoing efforts, their limitations, and introducing innovative research models. The integration of stem cell technology and advanced models promises to enhance our understanding and treatment strategies for PD.

Rethinking 'rare' PINK1 Parkinson's disease: A meta-analysis of geographical prevalence, phenotypic diversity, and α-synuclein pathology

PTEN-induced kinase 1 (PINK1)-related Parkinson's disease (PD) is traditionally considered a rare autosomal recessive form of early-onset PD (EOPD), lacking classical Lewy body pathology. However, this characterization underestimates and oversimplifies PINK1-PD, largely due to a lack of extensive studies in diverse ethnic populations. This review and meta-analysis explores considerable variations in PINK1 variant rates and the wide heterogeneity influenced by patient- and variant-specific factors, delineating a more precise disease profile. Our findings reveal that PINK1-PD is more common than previously thought, with geographic 'hotspots' where up to 9% of EOPD cases are linked to PINK1 variants, including the pathogenic p.Leu347Pro variant affecting 1 in 1300 West Polynesians. Homozygous PINK1-PD typically manifests around age 35, predominantly affecting the lower limbs, with an excellent response to levodopa. Heterozygous PINK1-PD presents an 'intermediate' phenotype, with a later onset age (around 43 years) than homozygous PINK1-PD but earlier than idiopathic PD (typically after age 65). The severity of the phenotype is influenced by variant zygosity and pathogenicity, interacting with genetic and environmental factors to push some individuals beyond the disease threshold. Notably, females with PINK1-PD have earlier onset age than males, particularly in homozygous cases and when variants occur in the first half of PINK1's kinase domain. Contrary to traditional views, α-synuclein pathology is present in 87.5% of PINK1-PD postmortem cases across ages and variants. We challenge conventional views on PINK1-PD, highlighting distinct phenotypes influenced by zygosity, sex, and a role for α-synuclein pathology, urging for increased recognition and research of this not-so-rare disease.

Nitric Oxide in Parkinson's Disease: The Potential Role of Dietary Nitrate in Enhancing Cognitive and Motor Health via the Nitrate-Nitrite-Nitric Oxide Pathway

BACKGROUND/OBJECTIVES

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta, leading to motor symptoms such as tremor, rigidity, and bradykinesia. The pathological hallmarks of PD include Lewy bodies and mechanisms like oxidative/nitrosative stress, chronic inflammation, and mitochondrial dysfunction. Nitric oxide (NO), produced by nitric oxide synthase (NOS) isoforms, plays a dual role in neuroprotection and neurodegeneration. Excessive NO production exacerbates neuroinflammation and oxidative/nitrosative damage, contributing to dopaminergic cell death. This review explores NO's role in PD pathogenesis and investigates dietary nitrate as a therapeutic strategy to regulate NO levels.

METHODS

A literature review of studies addressing the role of NO in PD was conducted using major scientific databases, including PubMed, Scopus, and Web of Science, using keywords such as "nitric oxide", "NOSs", "Parkinson's disease", and "nitrate neuroprotection in PD". Studies on nitrate metabolism via the nitrate-nitrite-NO pathway and its effects on PD hallmarks were analyzed. Studies regarding the role of nitrosamine formation in PD, which are mainly formed during the nitrification process of amines (nitrogen-containing compounds), often due to chemical reactions in the presence of nitrite or nitrate, were also examined. In particular, nitrate has been shown to induce oxidative stress, affect the mitochondrial function, and contribute to inflammatory phenomena in the brain, another factor closely related to the pathogenesis of PD.

RESULTS

Excessive NO production, particularly from iNOS and nNOS, was strongly associated with neuroinflammation and oxidative/nitrosative stress, amplifying neuronal damage in PD. Dietary nitrate was shown to enhance NO bioavailability through the nitrate-nitrite-NO pathway, mitigating inflammation and oxidative/nitrosative damage.

CONCLUSIONS

Dysregulated NO production contributes significantly to PD progression via inflammatory and oxidative/nitrosative pathways. Dietary nitrate, by modulating NO levels, offers a promising therapeutic strategy to counteract these pathological mechanisms. Further clinical trials are warranted to establish its efficacy and optimize its use in PD management.

Redox regulation, protein S-nitrosylation, and synapse loss in Alzheimer's and related dementias

Redox-mediated posttranslational modification, as exemplified by protein S-nitrosylation, modulates protein activity and function in both health and disease. Here, we review recent findings that show how normal aging, infection/inflammation, trauma, environmental toxins, and diseases associated with protein aggregation can each trigger excessive nitrosative stress, resulting in aberrant protein S-nitrosylation and hence dysfunctional protein networks. These redox reactions contribute to the etiology of multiple neurodegenerative disorders as well as systemic diseases. In the CNS, aberrant S-nitrosylation reactions of single proteins or, in many cases, interconnected networks of proteins lead to dysfunctional pathways affecting endoplasmic reticulum (ER) stress, inflammatory signaling, autophagy/mitophagy, the ubiquitin-proteasome system, transcriptional and enzymatic machinery, and mitochondrial metabolism. Aberrant protein S-nitrosylation and transnitrosylation (transfer of nitric oxide [NO]-related species from one protein to another) trigger protein aggregation, neuronal bioenergetic compromise, and microglial phagocytosis, all of which contribute to the synapse loss that underlies cognitive decline in Alzheimer's disease and related dementias.

Mitochondrial Mechanisms in Immunity and Inflammatory Conditions: Beyond Energy Management

Significance: The growing importance of mitochondria in the immune response and inflammation is multifaceted. Unraveling the different mechanisms by which mitochondria have a relevant role in the inflammatory response beyond the energy management of the process is necessary for improving our understanding of the host immune defense and the pathogenesis of various inflammatory diseases and syndromes. Critical Issues: Mitochondria are relevant in the immune response at different levels, including releasing activation molecules, changing its structure and function to accompany the immune response, and serving as a structural base for activating intermediates as NLRP3 inflammasome. In this scientific journey of dissecting mitochondrial mechanisms, new questions and interesting aspects arise, such as the involvement of mitochondrial-derived vesicles in the immune response with the putative role of preventing uncontrolled situations. Recent Advances: Researchers are continuously rethinking the role of mitochondria in acute and chronic inflammation and related disorders. As such, mitochondria have important roles as centrally positioned signaling hubs in regulating inflammatory and immune responses. In this review, we present the current understanding of mitochondrial mechanisms involved, beyond the largely known mitochondrial dysfunction, in the onset and development of inflammatory situations. Future Directions: Mitochondria emerge as an interesting and multifaceted platform for studying and developing pharmaceutical and therapeutic approaches. There are many ongoing studies aimed to describe the effects of specific mitochondrial targeted molecules and treatments to ameliorate the consequences of exacerbated inflammatory components of pathologies and syndromes, resulting in an open area of increasing research interest.

Melatonin regulates microglial M1/M2 polarization via AMPKα2-mediated mitophagy in attenuating sepsis-associated encephalopathy

BACKGROUND

Sepsis-associated encephalopathy (SAE) is a disease characterized by neuroinflammation and cognitive dysfunction caused by systemic infection. Inflammation-induced microglial activation is closely associated with neuroinflammation in SAE. It is widely understood that melatonin has strong anti-inflammatory and immunomodulatory properties beneficial for sepsis-related brain damage. However, the mechanism of melatonin action in SAE has not been fully elucidated.

METHODS

The SAE cell model and SAE mouse model were induced by lipopolysaccharide (LPS). Behavioral tests were performed to analyze cognitive function. Microglial markers and M1/M2 markers were measured by immunofluorescence. Mitophagy was assessed by western blot, mt-Keima and transmission electron microscopy experiments. Immunoprecipitation and co-immunoprecipitation assays investigated the interactions between AMP-activated protein kinase α2 (AMPKα2) and PTEN-induced putative kinase 1 (PINK1).

RESULTS

Melatonin suppresses LPS-induced microglia M1 polarization by enhancing mitophagy, thereby attenuating LPS-induced neuroinflammation and behavioral deficits. However, inhibition or knockdown of AMPKα2 can inhibit the enhancement of melatonin on mitophagy, then weaken its promotion of microglia polarization towards M2 phenotype, and eliminate its protective effect on brain function. Furthermore, melatonin enhances mitophagy through activating AMPKα2, promotes PINK1 Ser495 site phosphorylation, and ultimately regulates microglial polarization from M1 to M2.

CONCLUSIONS

Our findings demonstrate that melatonin facilitates microglia polarization towards M2 phenotype to alleviate LPS-induced neuroinflammation, primarily through AMPKα2-mediated enhancement of mitophagy.

Protein modification in neurodegenerative diseases

Posttranslational modifications play a crucial role in governing cellular functions and protein behavior. Researchers have implicated dysregulated posttranslational modifications in protein misfolding, which results in cytotoxicity, particularly in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease. These aberrant posttranslational modifications cause proteins to gather in certain parts of the brain that are linked to the development of the diseases. This leads to neuronal dysfunction and the start of neurodegenerative disease symptoms. Cognitive decline and neurological impairments commonly manifest in neurodegenerative disease patients, underscoring the urgency of comprehending the posttranslational modifications' impact on protein function for targeted therapeutic interventions. This review elucidates the critical link between neurodegenerative diseases and specific posttranslational modifications, focusing on Tau, APP, α-synuclein, Huntingtin protein, Parkin, DJ-1, and Drp1. By delineating the prominent aberrant posttranslational modifications within Alzheimer disease, Parkinson disease, and Huntington disease, the review underscores the significance of understanding the interplay among these modifications. Emphasizing 10 key abnormal posttranslational modifications, this study aims to provide a comprehensive framework for investigating neurodegenerative diseases holistically. The insights presented herein shed light on potential therapeutic avenues aimed at modulating posttranslational modifications to mitigate protein aggregation and retard neurodegenerative disease progression.

The interplay between mitochondrial dysfunction and NLRP3 inflammasome in multiple sclerosis: Therapeutic implications and animal model studies

Multiple sclerosis (MS) is a complex autoimmune disorder that impacts the central nervous system (CNS), resulting in inflammation, demyelination, and neurodegeneration. The NOD-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome, a multiprotein complex of the innate immune system, serves an essential role in the pathogenesis of MS by regulating the production of pro-inflammatory cytokines (IL-1β & IL-18) and the induction of pyroptotic cell death. Mitochondrial dysfunction is one of the main potential factors that can trigger NLRP3 inflammasome activation and lead to inflammation and axonal damage in MS. This highlights the importance of understanding how mitochondrial dynamics modulate NLRP3 inflammasome activity and contribute to the inflammatory and neurodegenerative features of MS. The lack of a comprehensive understanding of the pathogenesis of MS and the urge for the introduction of new therapeutic strategies led us to review the therapeutic potential of targeting the interplay between mitochondrial dysfunction and the NLRP3 inflammasome in MS. This paper also evaluates the natural and synthetic compounds that can improve mitochondrial function and/or inhibit the NLRP3 inflammasome, thereby providing neuroprotection. Moreover, it summarizes the evidence from animal models of MS that demonstrate the beneficial effects of these compounds on reducing inflammation, demyelination, and neurodegeneration. Finally, this review advocates for a deeper investigation into the molecular crosstalk between mitochondrial dynamics and the NLRP3 inflammasome as a means to refine therapeutic targets for MS.

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.

The Role of Protein S-Nitrosylation in Mitochondrial Quality Control in Central Nervous System Diseases

S-Nitrosylation is a reversible covalent post-translational modification. Under physiological conditions, S-nitrosylation plays a dynamic role in a wide range of biological processes by regulating the function of substrate proteins. Like other post-translational modifications, S-nitrosylation can affect protein conformation, activity, localization, aggregation, and protein interactions. Aberrant S-nitrosylation can lead to protein misfolding, mitochondrial fragmentation, synaptic damage, and autophagy. Mitochondria are essential organelles in energy production, metabolite biosynthesis, cell death, and immune responses, among other processes. Mitochondrial dysfunction can result in cell death and has been implicated in the development of many human diseases. Recent evidence suggests that S-nitrosylation and mitochondrial dysfunction are important modulators of the progression of several diseases. In this review, we highlight recent findings regarding the aberrant S- nitrosylation of mitochondrial proteins that regulate mitochondrial biosynthesis, fission and fusion, and autophagy. Specifically, we discuss the mechanisms by which S-nitrosylated mitochondrial proteins exercise mitochondrial quality control under pathological conditions, thereby influencing disease. A better understanding of these pathological events may provide novel therapeutic targets to mitigate the development of neurological diseases.

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

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

Role of Autophagy and Mitophagy in Neurodegenerative Disorders

Autophagy is a self-destructive cellular process that removes essential metabolites and waste from inside the cell to maintain cellular health. Mitophagy is the process by which autophagy causes disruption inside mitochondria and the total removal of damaged or stressed mitochondria, hence enhancing cellular health. The mitochondria are the powerhouses of the cell, performing essential functions such as ATP (adenosine triphosphate) generation, metabolism, Ca2+ buffering, and signal transduction. Many different mechanisms, including endosomal and autophagosomal transport, bring these substrates to lysosomes for processing. Autophagy and endocytic processes each have distinct compartments, and they interact dynamically with one another to complete digestion. Since mitophagy is essential for maintaining cellular health and using genetics, cell biology, and proteomics techniques, it is necessary to understand its beginning, particularly in ubiquitin and receptor-dependent signalling in injured mitochondria. Despite their similar symptoms and emerging genetic foundations, Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) have all been linked to abnormalities in autophagy and endolysosomal pathways associated with neuronal dysfunction. Mitophagy is responsible for normal mitochondrial turnover and, under certain physiological or pathological situations, may drive the elimination of faulty mitochondria. Due to their high energy requirements and post-mitotic origin, neurons are especially susceptible to autophagic and mitochondrial malfunction. This article focused on the importance of autophagy and mitophagy in neurodegenerative illnesses and how they might be used to create novel therapeutic approaches for treating a wide range of neurological disorders.

Biochemical study of the effect of mesenchymal stem cells-derived exosome versus L-Dopa in experimentally induced Parkinson's disease in rats

Parkinson's disease (PD) is a chronic and ongoing neurological condition. Unfortunately, as the dopaminergic terminals continue to deteriorate, the effectiveness of anti-Parkinson therapy decreases. This study aimed to examine the effects of BM-MSCs-derived exosomes in rats induced with Parkinson's disease. The goal was to determine their potential for neurogenic repair and functional restoration. Forty male albino rats were divided into four groups: control (group I), PD (group II), PD-L-Dopa (group III), and PD-exosome (group IV). Motor tests, histopathological examinations, and immunohistochemistry for tyrosine hydroxylase were performed on brain tissue. The levels of α-synuclein, DJ-1, PARKIN, circRNA.2837, and microRNA-34b were measured in brain homogenates. Rotenone induced motor deficits and neuronal alterations. Groups (III) and (IV) showed improvement in motor function, histopathology, α-synuclein, PARKIN, and DJ-1 compared to group (II). Group (IV) showed improvement in microRNA-34b and circRNA.2837 compared to groups (III) and (II). MSC-derived exosomes showed a greater suppression of neurodegenerative disease (ND) compared to L-Dopa in Parkinson's patients.

S-Nitrosylation at the intersection of metabolism and autophagy: Implications for cancer

Metabolic plasticity, which determines tumour growth and metastasis, is now understood to be a flexible and context-specific process in cancer metabolism. One of the major pathways contributing to metabolic adaptations in eucaryotic cells is autophagy, a cellular degradation and recycling process that is activated during periods of starvation or stress to maintain metabolite and biosynthetic intermediate levels. Consequently, there is a close association between the metabolic adaptive capacity of tumour cells and autophagy-related pathways in cancer. Additionally, nitric oxide regulates protein function and signalling through S-nitrosylation, a post-translational modification that can also impact metabolism and autophagy. The primary objective of this review is to provide an up-to-date overview of the role of S-nitrosylation at the intersection of metabolism and autophagy in cancer. First, we will outline the involvement of S-nitrosylation in the metabolic adaptations that occur in tumours. Then, we will discuss the multifaceted role of autophagy in cancer, the interplay between metabolism and autophagy during tumour progression, and the contribution of S-nitrosylation to autophagic dysregulation in cancer. Finally, we will present insights into relevant therapeutic aspects and discuss prospects for the future.

Comparison of the Nitric Oxide Synthase Interactomes and S-Nitroso-Proteomes: Furthering the Case for Enzymatic S-Nitrosylation

Aims: S-nitrosylation of proteins is the main mechanism through which nitric oxide (NO) regulates cellular function and likely represents the archetype redox-based signaling system across aerobic and anaerobic organisms. How NO generated by different nitric oxide synthase (NOS) isoforms leads to specificity of S-nitrosylation remains incompletely understood. This study aimed to identify proteins interacting with, and whose S-nitrosylation is mediated by, human NOS isoforms in the same cellular system, thereby illuminating the contribution of individual NOSs to specificity. Results: Of the hundreds of proteins interacting with each NOS, many were also S-nitrosylated. However, a large proportion of S-nitrosylated proteins (SNO-proteins) did not associate with NOS. Moreover, most NOS interactors and SNO-proteins were unique to each isoform. The amount of NO produced by each NOS isoform was unrelated to the numbers of SNO-proteins. Thus, NOSs promoted S-nitrosylation of largely distinct sets of target proteins. Different signaling pathways were enriched downstream of each NOS. Innovation and Conclusion: The interactomes and SNOomes of individual NOS isoforms were largely distinct. Only a small fraction of SNO-proteins interacted with their respective NOS. Amounts of S-nitrosylation were unrelated to the amount of NO generated by NOSs. These data argue against free diffusion of NO or NOS interactions as being necessary or sufficient for S-nitrosylation and favor roles for additional enzymes and/or regulatory elements in imparting SNO-protein specificity. Antioxid. Redox Signal. 39, 621-634.

Targeting calcium homeostasis and impaired inter-organelle crosstalk as a potential therapeutic approach in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta, leading to motor symptoms such as tremors, rigidity, and bradykinesia. Current therapeutic strategies for PD are limited and mainly involve symptomatic relief, with no available treatment for the underlying causes of the disease. Therefore, there is a need for new therapeutic approaches that target the underlying pathophysiological mechanisms of PD. Calcium homeostasis is an essential process for maintaining proper cellular function and survival, including neuronal cells. Calcium dysregulation is also observed in various organelles, including the endoplasmic reticulum (ER), mitochondria, and lysosomes, resulting in organelle dysfunction and impaired inter-organelle communication. The ER, as the primary calcium reservoir, is responsible for folding proteins and maintaining calcium homeostasis, and its dysregulation can lead to protein misfolding and neurodegeneration. The crosstalk between ER and mitochondrial calcium signaling is disrupted in PD, leading to neuronal dysfunction and death. In addition, a lethal network of calcium cytotoxicity utilizes mitochondria, ER and lysosome to destroy neurons. This review article focused on the complex role of calcium dysregulation and its role in aggravating functioning of organelles in PD so as to provide new insight into therapeutic strategies for treating this disease. Targeting dysfunctional organelles, such as the ER and mitochondria and lysosomes and whole network of calcium dyshomeostasis can restore proper calcium homeostasis and improve neuronal function. Additionally targeting calcium dyshomeostasis that arises from miscommunication between several organelles can be targeted so that therapeutic effects of calcium are realised in whole cellular territory.

Primary and Secondary Coordination Sphere Effects on the Structure and Function of S-Nitrosylating Azurin

Much progress has been made in understanding the roles of the secondary coordination sphere (SCS) in tuning redox potentials of metalloproteins. In contrast, the impact of SCS on reactivity is much less understood. A primary example is how copper proteins can promote S-nitrosylation (SNO), which is one of the most important dynamic post-translational modifications, and is crucial in regulating nitric oxide storage and transportation. Specifically, the factors that instill CuII with S-nitrosylating capabilities and modulate activity are not well understood. To address this issue, we investigated the influence of the primary and secondary coordination sphere on CuII-catalyzed S-nitrosylation by developing a series of azurin variants with varying catalytic capabilities. We have employed a multidimensional approach involving electronic absorption, S and Cu K-edge XAS, EPR, and resonance Raman spectroscopies together with QM/MM computational analysis to examine the relationships between structure and molecular mechanism in this reaction. Our findings have revealed that kinetic competency is correlated with three balancing factors, namely Cu-S bond strength, Cu spin localization, and relative S(ps) vs S(pp) contributions to the ground state. Together, these results support a reaction pathway that proceeds through the attack of the Cu-S bond rather than electrophilic addition to CuII or radical attack of SCys. The insights gained from this work provide not only a deeper understanding of SNO in biology but also a basis for designing artificial and tunable SNO enzymes to regulate NO and prevent diseases due to SNO dysregulation.

Chemical mitophagy modulators: Drug development strategies and novel regulatory mechanisms

Maintaining mitochondrial homeostasis is a potential therapeutic strategy for various diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic disorders, and cancer. Selective degradation of mitochondria by autophagy (mitophagy) is a fundamental mitochondrial quality control mechanism conserved from yeast to humans. Indeed, small-molecule modulators of mitophagy are valuable pharmaceutical tools that can be used to dissect complex biological processes and turn them into potential drugs. In the past few years, pharmacological regulation of mitophagy has shown promising therapeutic efficacy in various disease models. However, with the increasing number of chemical mitophagy modulator studies, frequent methodological flaws can be observed, leading some studies to draw unreliable or misleading conclusions. This review attempts (a) to summarize the molecular mechanisms of mitophagy; (b) to propose a Mitophagy Modulator Characterization System (MMCS); (c) to perform a comprehensive analysis of methods used to characterize mitophagy modulators, covering publications over the past 20 years; (d) to provide novel targets for pharmacological intervention of mitophagy. We believe this review will provide a panorama of current research on chemical mitophagy modulators and promote the development of safe and robust mitophagy modulators with therapeutic potential by introducing high methodological standards.

Targeting neuronal mitophagy in ischemic stroke: an update

Cerebral ischemia is a neurological disorder associated with complex pathological mechanisms, including autophagic degradation of neuronal mitochondria, or termed mitophagy, following ischemic events. Despite being well-documented, the cellular and molecular mechanisms underlying the regulation of neuronal mitophagy remain unknown. So far, the evidence suggests neuronal autophagy and mitophagy are separately regulated in ischemic neurons, the latter being more likely activated by reperfusional injury. Specifically, given the polarized morphology of neurons, mitophagy is regulated by different neuronal compartments, with axonal mitochondria being degraded by autophagy in the cell body following ischemia-reperfusion insult. A variety of molecules have been associated with neuronal adaptation to ischemia, including PTEN-induced kinase 1, Parkin, BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (Bnip3), Bnip3-like (Bnip3l) and FUN14 domain-containing 1. Moreover, it is still controversial whether mitophagy protects against or instead aggravates ischemic brain injury. Here, we review recent studies on this topic and provide an updated overview of the role and regulation of mitophagy during ischemic events.

Mitophagy regulation in aging and neurodegenerative disease

Mitochondria are the primary cellular energy generators, supplying the majority of adenosine triphosphate through oxidative phosphorylation, which is necessary for neuron function and survival. Mitophagy is the metabolic process of eliminating dysfunctional or redundant mitochondria. It is a type of autophagy and it is crucial for maintaining mitochondrial and neuronal health. Impaired mitophagy leads to an accumulation of damaged mitochondria and proteins leading to the dysregulation of mitochondrial quality control processes. Recent research shows the vital role of mitophagy in neurons and the pathogenesis of major neurodegenerative diseases. Mitophagy also plays a major role in the process of aging. This review describes the alterations that are being caused in the mitophagy process at the molecular level in aging and in neurodegenerative diseases, particularly Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis, also looks at how mitophagy can be exploited as a therapeutic target for these diseases.

Sepsis-like Energy Deficit Is Not Sufficient to Induce Early Muscle Fiber Atrophy and Mitochondrial Dysfunction in a Murine Sepsis Model

Sepsis-induced myopathy is characterized by muscle fiber atrophy, mitochondrial dysfunction, and worsened outcomes. Whether whole-body energy deficit participates in the early alteration of skeletal muscle metabolism has never been investigated. Three groups were studied: "Sepsis" mice, fed ad libitum with a spontaneous decrease in caloric intake (n = 17), and "Sham" mice fed ad libitum (Sham fed (SF), n = 13) or subjected to pair-feeding (Sham pair fed (SPF), n = 12). Sepsis was induced by the intraperitoneal injection of cecal slurry in resuscitated C57BL6/J mice. The feeding of the SPF mice was restricted according to the food intake of the Sepsis mice. Energy balance was evaluated by indirect calorimetry over 24 h. The tibialis anterior cross-sectional area (TA CSA), mitochondrial function (high-resolution respirometry), and mitochondrial quality control pathways (RTqPCR and Western blot) were assessed 24 h after sepsis induction. The energy balance was positive in the SF group and negative in both the SPF and Sepsis groups. The TA CSA did not differ between the SF and SPF groups, but was reduced by 17% in the Sepsis group compared with the SPF group (p < 0.05). The complex-I-linked respiration in permeabilized soleus fibers was higher in the SPF group than the SF group (p < 0.05) and lower in the Sepsis group than the SPF group (p < 0.01). Pgc1α protein expression increased 3.9-fold in the SPF mice compared with the SF mice (p < 0.05) and remained unchanged in the Sepsis mice compared with the SPF mice; the Pgc1α mRNA expression decreased in the Sepsis compared with the SPF mice (p < 0.05). Thus, the sepsis-like energy deficit did not explain the early sepsis-induced muscle fiber atrophy and mitochondrial dysfunction, but led to specific metabolic adaptations not observed in sepsis.

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.

A Mouse Model to Test Novel Therapeutics for Parkinson's Disease: an Update on the Thy1-aSyn ("line 61") Mice

Development of neuroprotective therapeutics for Parkinson's disease (PD) is facing a lack of translation from pre-clinical to clinical trials. One strategy for improvement is to increase predictive validity of pre-clinical studies by using extensively characterized animal models with a comprehensive set of validated pharmacodynamic readouts. Mice over-expressing full-length, human, wild-type alpha-synuclein under the Thy-1 promoter (Thy1-aSyn line 61) reproduce key features of sporadic PD, such as progressive loss of striatal dopamine, alpha-synuclein pathology, deficits in motor and non-motor functions, and elevation of inflammatory markers. Extensive work with this model by multiple laboratories over the past decade further increased confidence in its robustness and validity, especially for analyzing pathomechanisms of alpha-synuclein pathology and down-stream pathways, and for pre-clinical drug testing. Interestingly, while postnatal transgene expression is widespread in central and peripheral neurons, the extent and progression of down-stream pathology differs between brain regions, thereby replicating the characteristic selective vulnerability of neurodegenerative diseases. In-depth characterization of these readouts in conjunction with behavioral deficits has led to more informative endpoints for pre-clinical trials. Each drug tested in Thy1-aSyn line 61 enhances knowledge on how molecular targets, pathology, and functional behavioral readouts are interconnected, thereby further optimizing the platform towards predictive validity for clinical trials. Here, we present the current state of the art using Thy1-aSyn line 61 for drug target discovery, validation, and pre-clinical testing.

Cellular mitophagy: Mechanism, roles in diseases and small molecule pharmacological regulation

Cellular mitophagy means that cells selectively wrap and degrade damaged mitochondria through an autophagy mechanism, thus maintaining mitochondria and intracellular homeostasis. In recent years, mitophagy has received increasing attention as a research hotspot related to the pathogenesis of clinical diseases, such as neurodegenerative diseases, cardiovascular diseases, cancer, metabolic diseases, and so on. It has been found that the regulation of mitophagy may become a new direction for the treatment of some diseases. In addition, numerous small molecule modulators of mitophagy have also been reported, which provides new opportunities to comprehend the procedure and potential of therapeutic development. Taken together, in this review, we summarize current understanding of the mechanism of mitophagy, discuss the roles of mitophagy and its relationship with diseases, introduce the existing small-molecule pharmacological modulators of mitophagy and further highlight the significance of their development.

S-Glutathionylation and S-Nitrosylation in Mitochondria: Focus on Homeostasis and Neurodegenerative Diseases

Redox post-translational modifications are derived from fluctuations in the redox potential and modulate protein function, localization, activity and structure. Amongst the oxidative reversible modifications, the S-glutathionylation of proteins was the first to be characterized as a post-translational modification, which primarily protects proteins from irreversible oxidation. However, a growing body of evidence suggests that S-glutathionylation plays a key role in core cell processes, particularly in mitochondria, which are the main source of reactive oxygen species. S-nitrosylation, another post-translational modification, was identified >150 years ago, but it was re-introduced as a prototype cell-signaling mechanism only recently, one that tightly regulates core processes within the cell’s sub-compartments, especially in mitochondria. S-glutathionylation and S-nitrosylation are modulated by fluctuations in reactive oxygen and nitrogen species and, in turn, orchestrate mitochondrial bioenergetics machinery, morphology, nutrients metabolism and apoptosis. In many neurodegenerative disorders, mitochondria dysfunction and oxidative/nitrosative stresses trigger or exacerbate their pathologies. Despite the substantial amount of research for most of these disorders, there are no successful treatments, while antioxidant supplementation failed in the majority of clinical trials. Herein, we discuss how S-glutathionylation and S-nitrosylation interfere in mitochondrial homeostasis and how the deregulation of these modifications is associated with Alzheimer’s, Parkinson’s, amyotrophic lateral sclerosis and Friedreich’s ataxia.

Cell Biology of Parkin: Clues to the Development of New Therapeutics for Parkinson's Disease

Parkinson's disease is the second most prevalent neurodegenerative disease and contributes significantly to morbidity globally. Currently, no disease-modifying therapies exist to combat this disorder. Insights from the molecular and cellular pathobiology of the disease seems to indicate promising therapeutic targets. The parkin protein has been extensively studied for its role in autosomal recessive Parkinson's disease and, more recently, its role in sporadic Parkinson's disease. Parkin is an E3 ubiquitin ligase that plays a prominent role in mitochondrial quality control, mitochondrial-dependent cell death pathways, and other diverse functions. Understanding the numerous roles of parkin has introduced many new possibilities for therapeutic modalities in treating both autosomal recessive Parkinson's disease and sporadic Parkinson's disease. In this article, we review parkin biology with an emphasis on mitochondrial-related functions and propose novel, potentially disease-modifying therapeutic approaches for treating this debilitating condition.

Mitochondrial dysfunction of induced pluripotent stem cells-based neurodegenerative disease modeling and therapeutic strategy

Neurodegenerative diseases (NDDs) are disorders in which neurons are lost owing to various factors, resulting in a series of dysfunctions. Their rising prevalence and irreversibility have brought physical pain to patients and economic pressure to both individuals and society. However, the pathogenesis of NDDs has not yet been fully elucidated, hampering the use of precise medication. Induced pluripotent stem cell (IPSC) modeling provides a new method for drug discovery, and exploring the early pathological mechanisms including mitochondrial dysfunction, which is not only an early but a prominent pathological feature of NDDs. In this review, we summarize the iPSC modeling approach of Alzheimer’s disease, Parkinson’s disease, and Amyotrophic lateral sclerosis, as well as outline typical mitochondrial dysfunction and recapitulate corresponding therapeutic strategies.

Prospects for the Development of Pink1 and Parkin Activators for the Treatment of Parkinson's Disease

Impaired mitophagy is one of the hallmarks of the pathogenesis of Parkinson's disease, which highlights the importance of the proper functioning of mitochondria, as well as the processes of mitochondrial dynamics for the functioning of dopaminergic neurons. At the same time, the main factors leading to disruption of mitophagy in Parkinson's disease are mutations in the Pink1 and Parkin enzymes. Based on the characterized mutant forms, the marked cellular localization, and the level of expression in neurons, these proteins can be considered promising targets for the development of drugs for Parkinson's therapy. This review will consider such class of drug compounds as mitophagy activators and these drugs in the treatment of Parkinson's disease.

Autophagy and Its Association with Genetic Mutations in Parkinson Disease

Parkinson disease is the second most common neurodegenerative disorder, affecting 0.1-0.2% of the general population. It is a progressive debilitating disorder caused by degeneration of dopaminergic neurons in the substantia nigra pars compacta. It is characterized by motor and non-motor symptoms. Parkinson disease can be caused by mutations in genes that encode proteins involved in the autophagic process, resulting in impaired autophagy. Indeed, autophagy has been implicated in the pathogenesis of Parkinson disease, particularly because its impairment causes the buildup of proteins. Thus, this review aims to provide an overview of Parkinson disease-related genetic mutations and their association with autophagy impairment in Parkinson disease, which can be helpful in improving the understanding of the pathogenesis of Parkinson disease, illustrating the potential therapeutic implications of agents that can enhance autophagy in Parkinson disease. Additionally, we will highlight the essential need for the development of highly sensitive and specific assays for gene-based diagnostic biomarkers. Finally, we will provide an overview on the potential gene-based therapeutic approaches for Parkinson disease, which have been most advanced and are associated with the most common targets being alpha-synuclein (SNCA), leucine-rich repeat kinase-2 (LRRK2), and glucocerebrosidase (GBA).

S-Nitrosylation of cathepsin B affects autophagic flux and accumulation of protein aggregates in neurodegenerative disorders

Protein S-nitrosylation is known to regulate enzymatic function. Here, we report that nitric oxide (NO)-related species can contribute to Alzheimer's disease (AD) by S-nitrosylating the lysosomal protease cathepsin B (forming SNO-CTSB), thereby inhibiting CTSB activity. This posttranslational modification inhibited autophagic flux, increased autolysosomal vesicles, and led to accumulation of protein aggregates. CA-074Me, a CTSB chemical inhibitor, also inhibited autophagic flux and resulted in accumulation of protein aggregates similar to the effect of SNO-CTSB. Inhibition of CTSB activity also induced caspase-dependent neuronal apoptosis in mouse cerebrocortical cultures. To examine which cysteine residue(s) in CTSB are S-nitrosylated, we mutated candidate cysteines and found that three cysteines were susceptible to S-nitrosylation. Finally, we observed an increase in SNO-CTSB in both 5XFAD transgenic mouse and flash-frozen postmortem human AD brains. These results suggest that S-nitrosylation of CTSB inhibits enzymatic activity, blocks autophagic flux, and thus contributes to AD pathogenesis.

Mitochondrial Distress in Methylmalonic Acidemia: Novel Pathogenic Insights and Therapeutic Perspectives

Mitochondria are highly dynamic, double-membrane-enclosed organelles that sustain cellular metabolism and, hence, cellular, and organismal homeostasis. Dysregulation of the mitochondrial network might, therefore, confer a potentially devastating vulnerability to high-energy-requiring cell types, contributing to a broad variety of hereditary and acquired diseases, which include inborn errors of metabolism, cancer, neurodegeneration, and aging-associated adversities. In this Review, we highlight the biological functions of mitochondria-localized enzymes, from the perspective of understanding the pathophysiology of the inherited disorders destroying mitochondrial homeostasis and cellular metabolism. Using methylmalonic acidemia (MMA) as a paradigm of mitochondrial dysfunction, we discuss how mitochondrial-directed signaling pathways sustain the physiological homeostasis of specialized cell types and how these may be disturbed in disease conditions. This Review also provides a critical analysis of molecular underpinnings, through which defects in the autophagy-mediated quality control and surveillance systems contribute to cellular dysfunction, and indicates potential therapeutic strategies for affected tissues. These insights might, ultimately, advance the discovery and development of new therapeutics, not only for methylmalonic acidemia but also for other currently intractable mitochondrial diseases, thus transforming our ability to modulate health and homeostasis.

Mitophagy: A Potential Target for Pressure Overload-Induced Cardiac Remodelling

The pathological mechanisms underlying cardiac remodelling and cardiac dysfunction caused by pressure overload are poorly understood. Mitochondrial damage and functional dysfunction, including mitochondrial bioenergetic disorder, oxidative stress, and mtDNA damage, contribute to heart injury caused by pressure overload. Mitophagy, an important regulator of mitochondrial homeostasis and function, is triggered by mitochondrial damage and participates in the pathological process of cardiovascular diseases. Recent studies indicate that mitophagy plays a critical role in the pressure overload model, but evidence on the causal relationship between mitophagy abnormality and pressure overload-induced heart injury is inconclusive. This review summarises the mechanism, role, and regulation of mitophagy in the pressure overload model. It also pays special attention to active compounds that may regulate mitophagy in pressure overload, which provide clues for possible clinical applications.

The role of oxidative stress in the development of knee osteoarthritis: A comprehensive research review

Knee osteoarthritis (KOA) is one of the most common degenerative diseases, and its core feature is the degeneration and damage of articular cartilage. The cartilage degeneration of KOA is due to the destruction of dynamic balance caused by the activation of chondrocytes by various factors, with oxidative stress playing an important role in the pathogenesis of KOA. The overproduction of reactive oxygen species (ROS) is a result of oxidative stress, which is caused by a redox process that goes awry in the inherent antioxidant defence system of the human body. Superoxide dismutase (SOD) inside and outside chondrocytes plays a key role in regulating ROS in cartilage. Additionally, synovitis is a key factor in the development of KOA. In an inflammatory environment, hypoxia in synovial cells leads to mitochondrial damage, which leads to an increase in ROS levels, which further aggravates synovitis. In addition, oxidative stress significantly accelerates the telomere shortening and ageing of chondrocytes, while ageing promotes the development of KOA, damages the regulation of redox of mitochondria in cartilage, and stimulates ROS production to further aggravate KOA. At present, there are many drugs to regulate the level of ROS, but these drugs still need to be developed and verified in animal models of KOA. We discuss mainly how oxidative stress plays a part in the development of KOA. Although the current research has achieved some results, more research is needed.

GSNOR deficiency attenuates MPTP-induced neurotoxicity and autophagy by facilitating CDK5 S-nitrosation in a mouse model of Parkinson's disease

The S-nitrosoglutathione reductase (GSNOR) is a key denitrosating enzyme that regulates protein S-nitrosation, a process which has been found to be involved in the pathogenesis of Parkinson's disease (PD). However, the physiological function of GSNOR in PD remains unknown. In a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model, we found that GSNOR expression was significantly increased and accompanied by autophagy mediated by MPTP-induced cyclin dependent kinase 5 (CDK5), behavioral dyskinesias and dopaminergic neuron loss. Whereas, knockout of GSNOR, or treatment with the GSNOR inhibitor N6022, alleviated MPTP-induced PD-like pathology and neurotoxicity. Mechanistically, deficiency of GSNOR inhibited MPTP-induced CDK5 kinase activity and CDK5-mediated autophagy by increasing S-nitrosation of CDK5 at Cys83. Our study indicated that GSNOR is a key regulator of CDK5 S-nitrosation and is actively involved in CDK5-mediated autophagy induced by MPTP.

Nitrosative stress in Parkinson's disease

Parkinson’s Disease (PD) is a neurodegenerative disorder characterized, in part, by the loss of dopaminergic neurons within the nigral-striatal pathway. Multiple lines of evidence support a role for reactive nitrogen species (RNS) in degeneration of this pathway, specifically nitric oxide (NO). This review will focus on how RNS leads to loss of dopaminergic neurons in PD and whether RNS accumulation represents a central signal in the degenerative cascade. Herein, we provide an overview of how RNS accumulates in PD by considering the various cellular sources of RNS including nNOS, iNOS, nitrate, and nitrite reduction and describe evidence that these sources are upregulating RNS in PD. We document that over 1/3 of the proteins that deposit in Lewy Bodies, are post-translationally modified (S-nitrosylated) by RNS and provide a broad description of how this elicits deleterious effects in neurons. In doing so, we identify specific proteins that are modified by RNS in neurons which are implicated in PD pathogenesis, with an emphasis on exacerbation of synucleinopathy. How nitration of alpha-synuclein (aSyn) leads to aSyn misfolding and toxicity in PD models is outlined. Furthermore, we delineate how RNS modulates known PD-related phenotypes including axo-dendritic-, mitochondrial-, and dopamine-dysfunctions. Finally, we discuss successful outcomes of therapeutics that target S-nitrosylation of proteins in Parkinson’s Disease related clinical trials. In conclusion, we argue that targeting RNS may be of therapeutic benefit for people in early clinical stages of PD.

Mitochondrial function and dynamics in neural stem cells and neurogenesis: Implications for neurodegenerative diseases

Mitochondria have been largely described as the powerhouse of the cell and recent findings demonstrate that this organelle is fundamental for neurogenesis. The mechanisms underlying neural stem cells (NSCs) maintenance and differentiation are highly regulated by both intrinsic and extrinsic factors. Mitochondrial-mediated switch from glycolysis to oxidative phosphorylation, accompanied by mitochondrial remodeling and dynamics are vital to NSCs fate. Deregulation of mitochondrial proteins, mitochondrial DNA, function, fission/fusion and metabolism underly several neurodegenerative diseases; data show that these impairments are already present in early developmental stages and NSC fate decisions. However, little is known about mitochondrial role in neurogenesis. In this Review, we describe the recent evidence covering mitochondrial role in neurogenesis, its impact in selected neurodegenerative diseases, for which aging is the major risk factor, and the recent advances in stem cell-based therapies that may alleviate neurodegenerative disorders-related neuronal deregulation through improvement of mitochondrial function and dynamics.

Induced pluripotent stem cells: a tool for modeling Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder. Among its pathologies, progressive loss of dopaminergic (DA) neurons in the substantia nigra is characteristic and contributes to many of the most severe symptoms of PD. Recent advances in induced pluripotent stem cell (iPSC) technology have made it possible to generate patient-derived DA neuronal cell culture and organoid models of PD. These models have contributed to understanding disease mechanisms and the identification of novel targets and therapeutic candidates. Still needed are better ways to model the age-related aspects of PD, as well as a deeper understanding of the interactions among disease-modifying genes and between genetic and environmental contributions to the etiology and progression of PD.

The multifaceted regulation of mitophagy by endogenous metabolites

Owing to the dominant functions of mitochondria in multiple cellular metabolisms and distinct types of regulated cell death, maintaining a functional mitochondrial network is fundamental for the cellular homeostasis and body fitness in response to physiological adaptations and stressed conditions. The process of mitophagy, in which the dysfunctional or superfluous mitochondria are selectively engulfed by autophagosome and subsequently degraded in lysosome, has been well formulated as one of the major mechanisms for mitochondrial quality control. To date, the PINK1-PRKN-dependent and receptors (including proteins and lipids)-dependent pathways have been characterized to determine the mitophagy in mammalian cells. The mitophagy is highly responsive to the dynamics of endogenous metabolites, including iron-, calcium-, glycolysis-TCA-, NAD+-, amino acids-, fatty acids-, and cAMP-associated metabolites. Herein, we summarize the recent advances toward the molecular details of mitophagy regulation in mammalian cells. We also highlight the key regulations of mammalian mitophagy by endogenous metabolites, shed new light on the bidirectional interplay between mitophagy and cellular metabolisms, with attempting to provide a perspective insight into the nutritional intervention of metabolic disorders with mitophagy deficit.Abbreviations: acetyl-CoA: acetyl-coenzyme A; ACO1: aconitase 1; ADCYs: adenylate cyclases; AMPK: AMP-activated protein kinase; ATM: ATM serine/threonine kinase; BCL2L1: BCL2 like 1; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; Ca2+: calcium ion; CALCOCO2: calcium binding and coiled-coil domain 2; CANX: calnexin; CO: carbon monoxide; CYCS: cytochrome c, somatic; DFP: deferiprone; DNM1L: dynamin 1 like; ER: endoplasmic reticulum; FKBP8: FKBP prolyl isomerase 8; FOXO3: forkhead box O3; FTMT: ferritin mitochondrial; FUNDC1: FUN14 domain containing 1; GABA: γ-aminobutyric acid; GSH: glutathione; HIF1A: hypoxia inducible factor 1 subunit alpha; IMMT: inner membrane mitochondrial protein; IRP1: iron regulatory protein 1; ISC: iron-sulfur cluster; ITPR2: inositol 1,4,5-trisphosphate type 2 receptor; KMO: kynurenine 3-monooxygenase; LIR: LC3 interacting region; MAM: mitochondria-associated membrane; MAP1LC3: microtubule associated protein 1 light chain 3; MFNs: mitofusins; mitophagy: mitochondrial autophagy; mPTP: mitochondrial permeability transition pore; MTOR: mechanistic target of rapamycin kinase; NAD+: nicotinamide adenine dinucleotide; NAM: nicotinamide; NMN: nicotinamide mononucleotide; NO: nitric oxide; NPA: Niemann-Pick type A; NR: nicotinamide riboside; NR4A1: nuclear receptor subfamily 4 group A member 1; NRF1: nuclear respiratory factor 1; OPA1: OPA1 mitochondrial dynamin like GTPase; OPTN: optineurin; PARL: presenilin associated rhomboid like; PARPs: poly(ADP-ribose) polymerases; PC: phosphatidylcholine; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PPARG: peroxisome proliferator activated receptor gamma; PPARGC1A: PPARG coactivator 1 alpha; PRKA: protein kinase AMP-activated; PRKDC: protein kinase, DNA-activated, catalytic subunit; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT: ras homolog family member T; ROS: reactive oxygen species; SIRTs: sirtuins; STK11: serine/threonine kinase 11; TCA: tricarboxylic acid; TP53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VDAC1: voltage dependent anion channel 1.

S-Nitrosylation of p62 Inhibits Autophagic Flux to Promote α-Synuclein Secretion and Spread in Parkinson's Disease and Lewy Body Dementia

Dysregulation of autophagic pathways leads to accumulation of abnormal proteins and damaged organelles in many neurodegenerative disorders, including Parkinson's disease (PD) and Lewy body dementia (LBD). Autophagy-related dysfunction may also trigger secretion and spread of misfolded proteins, such as α-synuclein (α-syn), the major misfolded protein found in PD/LBD. However, the mechanism underlying these phenomena remains largely unknown. Here, we used cell-based models, including human induced pluripotent stem cell-derived neurons, CRISPR/Cas9 technology, and male transgenic PD/LBD mice, plus vetting in human postmortem brains (both male and female). We provide mechanistic insight into this pathologic pathway. We find that aberrant S-nitrosylation of the autophagic adaptor protein p62 causes inhibition of autophagic flux and intracellular buildup of misfolded proteins, with consequent secretion resulting in cell-to-cell spread. Thus, our data show that pathologic protein S-nitrosylation of p62 represents a critical factor not only for autophagic inhibition and demise of individual neurons, but also for α-syn release and spread of disease throughout the nervous system.SIGNIFICANCE STATEMENT In Parkinson's disease and Lewy body dementia, dysfunctional autophagy contributes to accumulation and spread of aggregated α-synuclein. Here, we provide evidence that protein S-nitrosylation of p62 inhibits autophagic flux, contributing to α-synuclein aggregation and spread.

Albumin binds to uncoupler CCCP to diminish depolarization of mitochondria

Mitochondria are at the core of cellular energy metabolism and are also involved in the oxidative stress response and programmed cell death pathways. Mitochondrial dysfunction is found to be associated with many disease conditions like metabolic syndrome, neurodegenerative disorders, coronary artery diseases, cancer, etc. This has generated considerable interest in the scientific community over the assessment of mitochondrial function and mitochondrial damage. One of the most common methodologies in these studies is by analysing the mitochondrial activity in the presence of mitochondrial substrates, inhibitors and uncouplers. Apart from the specific effects of these molecules on mitochondria, their interactions with the components of the experimental system could interfere with the results derived. Therefore, the role some specific experimental conditions would have on the outcome should be carefully elucidated. Fetal Bovine Serum or Bovine Serum Albumin (BSA); routinely used in in vitro experiments for their growth promoting and surfactant properties; can have profound impact on the pharmacokinetics of chemical compounds as albumin residue can bind to and affect their bioavailability. In the present study, we demonstrate that Carbonyl cyanide 3-chlorophenylhydrazone (CCCP) induced mitochondrial depolarization is hindered in the presence of albumin due to the molecular interaction between CCCP and albumin.

Mitochondrial Phenotypes in Parkinson's Diseases-A Focus on Human iPSC-Derived Dopaminergic Neurons

Established disease models have helped unravel the mechanistic underpinnings of pathological phenotypes in Parkinson’s disease (PD), the second most common neurodegenerative disorder. However, these discoveries have been limited to relatively simple cellular systems and animal models, which typically manifest with incomplete or imperfect recapitulation of disease phenotypes. The advent of induced pluripotent stem cells (iPSCs) has provided a powerful scientific tool for investigating the underlying molecular mechanisms of both familial and sporadic PD within disease-relevant cell types and patient-specific genetic backgrounds. Overwhelming evidence supports mitochondrial dysfunction as a central feature in PD pathophysiology, and iPSC-based neuronal models have expanded our understanding of mitochondrial dynamics in the development and progression of this devastating disorder. The present review provides a comprehensive assessment of mitochondrial phenotypes reported in iPSC-derived neurons generated from PD patients’ somatic cells, with an emphasis on the role of mitochondrial respiration, morphology, and trafficking, as well as mitophagy and calcium handling in health and disease. Furthermore, we summarize the distinguishing characteristics of vulnerable midbrain dopaminergic neurons in PD and report the unique advantages and challenges of iPSC disease modeling at present, and for future mechanistic and therapeutic applications.

Mitochondrial disease, mitophagy, and cellular distress in methylmalonic acidemia

Mitochondria—the intracellular powerhouse in which nutrients are converted into energy in the form of ATP or heat—are highly dynamic, double-membraned organelles that harness a plethora of cellular functions that sustain energy metabolism and homeostasis. Exciting new discoveries now indicate that the maintenance of this ever changing and functionally pleiotropic organelle is particularly relevant in terminally differentiated cells that are highly dependent on aerobic metabolism. Given the central role in maintaining metabolic and physiological homeostasis, dysregulation of the mitochondrial network might therefore confer a potentially devastating vulnerability to high-energy requiring cell types, contributing to a broad variety of hereditary and acquired diseases. In this Review, we highlight the biological functions of mitochondria-localized enzymes from the perspective of understanding—and potentially reversing—the pathophysiology of inherited disorders affecting the homeostasis of the mitochondrial network and cellular metabolism. Using methylmalonic acidemia as a paradigm of complex mitochondrial dysfunction, we discuss how mitochondrial directed-signaling circuitries govern the homeostasis and physiology of specialized cell types and how these may be disturbed in disease. This Review also provides a critical analysis of affected tissues, potential molecular mechanisms, and novel cellular and animal models of methylmalonic acidemia which are being used to develop new therapeutic options for this disease. These insights might ultimately lead to new therapeutics, not only for methylmalonic acidemia, but also for other currently intractable mitochondrial diseases, potentially transforming our ability to regulate homeostasis and health.

Redox metabolism: ROS as specific molecular regulators of cell signaling and function

Redox reactions are intrinsically linked to energy metabolism. Therefore, redox processes are indispensable for organismal physiology and life itself. The term reactive oxygen species (ROS) describes a set of distinct molecular oxygen derivatives produced during normal aerobic metabolism. Multiple ROS-generating and ROS-eliminating systems actively maintain the intracellular redox state, which serves to mediate redox signaling and regulate cellular functions. ROS, in particular hydrogen peroxide (H₂O₂), are able to reversibly oxidize critical, redox-sensitive cysteine residues on target proteins. These oxidative post-translational modifications (PTMs) can control the biological activity of numerous enzymes and transcription factors (TFs), as well as their cellular localization or interactions with binding partners. In this review, we describe the diverse roles of redox regulation in the context of physiological cellular metabolism and provide insights into the pathophysiology of diseases when redox homeostasis is dysregulated.

Protein S-nitrosylation and oxidation contribute to protein misfolding in neurodegeneration

Neurodegenerative disorders like Alzheimer's disease and Parkinson's disease are characterized by progressive degeneration of synapses and neurons. Accumulation of misfolded/aggregated proteins represents a pathological hallmark of most neurodegenerative diseases, potentially contributing to synapse loss and neuronal damage. Emerging evidence suggests that misfolded proteins accumulate in the diseased brain at least in part as a consequence of excessively generated reactive oxygen species (ROS) and reactive nitrogen species (RNS). Mechanistically, not only disease-linked genetic mutations but also known risk factors for neurodegenerative diseases, such as aging and exposure to environmental toxins, can accelerate production of ROS/RNS, which contribute to protein misfolding - in many cases mimicking the effect of rare genetic mutations known to be linked to the disease. This review will focus on the role of RNS-dependent post-translational modifications, such as S-nitrosylation and tyrosine nitration, in protein misfolding and aggregation. Specifically, we will discuss molecular mechanisms whereby RNS disrupt the activity of the cellular protein quality control machinery, including molecular chaperones, autophagy/lysosomal pathways, and the ubiquitin-proteasome system (UPS). Because chronic accumulation of misfolded proteins can trigger mitochondrial dysfunction, synaptic damage, and neuronal demise, further characterization of RNS-mediated protein misfolding may establish these molecular events as therapeutic targets for intervention in neurodegenerative diseases.

Emerging hiPSC Models for Drug Discovery in Neurodegenerative Diseases

Neurodegenerative diseases affect millions of people worldwide and are characterized by the chronic and progressive deterioration of neural function. Neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), represent a huge social and economic burden due to increasing prevalence in our aging society, severity of symptoms, and lack of effective disease-modifying therapies. This lack of effective treatments is partly due to a lack of reliable models. Modeling neurodegenerative diseases is difficult because of poor access to human samples (restricted in general to postmortem tissue) and limited knowledge of disease mechanisms in a human context. Animal models play an instrumental role in understanding these diseases but fail to comprehensively represent the full extent of disease due to critical differences between humans and other mammals. The advent of human-induced pluripotent stem cell (hiPSC) technology presents an advantageous system that complements animal models of neurodegenerative diseases. Coupled with advances in gene-editing technologies, hiPSC-derived neural cells from patients and healthy donors now allow disease modeling using human samples that can be used for drug discovery.

Methamphetamine-induced dopaminergic neurotoxicity as a model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with a high prevalence, approximately 1 % in the elderly population. Numerous studies have demonstrated that methamphetamine (MA) intoxication caused the neurological deficits and nigrostriatal damage seen in Parkinsonian conditions, and subsequent rodent studies have found that neurotoxic binge administration of MA reproduced PD-like features, in terms of its symptomatology and pathology. Several anti-Parkinsonian medications have been shown to attenuate the motor impairments and dopaminergic damage induced by MA. In addition, it has been recognized that mitochondrial dysfunction, oxidative stress, pro-apoptosis, proteasomal/autophagic impairment, and neuroinflammation play important roles in inducing MA neurotoxicity. Importantly, MA neurotoxicity has been shown to share a common mechanism of dopaminergic toxicity with that of PD pathogenesis. This review describes the major findings on the neuropathological features and underlying neurotoxic mechanisms induced by MA and compares them with Parkinsonian pathogenesis. Taken together, it is suggested that neurotoxic binge-type administration of MA in rodents is a valid animal model for PD that may provide knowledge on the neuropathogenesis of PD.