DJ-1 protects dopaminergic neurons against rotenone-induced apoptosis by enhancing ERK-dependent mitophagy

The autophagy-lysosome pathway: a potential target in the chemical and gene therapeutic strategies for Parkinson's disease

Parkinson's disease is a common neurodegenerative disease with movement disorders associated with the intracytoplasmic deposition of aggregate proteins such as α-synuclein in neurons. As one of the major intracellular degradation pathways, the autophagy-lysosome pathway plays an important role in eliminating these proteins. Accumulating evidence has shown that upregulation of the autophagy-lysosome pathway may contribute to the clearance of α-synuclein aggregates and protect against degeneration of dopaminergic neurons in Parkinson's disease. Moreover, multiple genes associated with the pathogenesis of Parkinson's disease are intimately linked to alterations in the autophagy-lysosome pathway. Thus, this pathway appears to be a promising therapeutic target for treatment of Parkinson's disease. In this review, we briefly introduce the machinery of autophagy. Then, we provide a description of the effects of Parkinson's disease-related genes on the autophagy-lysosome pathway. Finally, we highlight the potential chemical and genetic therapeutic strategies targeting the autophagy-lysosome pathway and their applications in Parkinson's disease.

A novel compound alleviates oxidative stress via PKA/CREB1-mediated DJ-1 upregulation

Oxidative stress is one of the major culprits causing dopaminergic neuron loss in Parkinson's disease (PD). DJ-1 is a protein with multiple actions against oxidative stress, apoptosis, neuroinflammation, etc. DJ-1 expression is decreased in sporadic PD, therefore increasing DJ-1 expression might be beneficial in PD treatment. However, drugs known to upregulate DJ-1 are still lacking. In this study, we identified a novel DJ-1-elevating compound called ChemJ through luciferase assay-based high-throughput compound screening in SH-SY5Y cells and confirmed that ChemJ upregulated DJ-1 in SH-SY5Y cell line and primary cortical neurons. DJ-1 upregulation by ChemJ alleviated MPP+-induced oxidative stress. In exploring the underlying mechanisms, we found that the transcription factor CREB1 bound to DJ-1 promoter and positively regulated its expression under both unstressed and 1-methyl-4-phenylpyridinium-induced oxidative stress conditions and that ChemJ promoted DJ-1 expression via activating PKA/CREB1 pathway in SH-SY5Y cells. Our results demonstrated that ChemJ alleviated the MPP+-induced oxidative stress through a PKA/CREB1-mediated regulation of DJ-1 expression, thus offering a novel and promising avenue for PD treatment.

Atox1 protects hippocampal neurons after traumatic brain injury via DJ-1 mediated anti-oxidative stress and mitophagy

Regulation of the oxidative stress response is crucial for the management and prognosis of traumatic brain injury (TBI). The copper chaperone Antioxidant 1 (Atox1) plays a crucial role in regulating intracellular copper ion balance and impacting the antioxidant capacity of mitochondria, as well as the oxidative stress state of cells. However, it remains unknown whether Atox1 is involved in modulating oxidative stress following TBI. Here, we investigated the regulatory role of Atox1 in oxidative stress on neurons both in vivo and in vitro, and elucidated the underlying mechanism through culturing hippocampal HT-22 cells with Atox1 mutation. The expression of Atox1 was significantly diminished following TBI, while mice with overexpressed Atox1 exhibited a more preserved hippocampal structure and reduced levels of oxidative stress post-TBI. Furthermore, the mice displayed notable impairments in learning and memory functions after TBI, which were ameliorated by the overexpression of Atox1. In the stretch injury model of HT-22 cells, overexpression of Atox1 mitigated oxidative stress by preserving the normal morphology and network connectivity of mitochondria, as well as facilitating the elimination of damaged mitochondria. Mechanistically, co-immunoprecipitation and mass spectrometry revealed the binding of Atox1 to DJ-1. Knockdown of DJ-1 in HT-22 cells significantly impaired the antioxidant capacity of Atox1. Mutations in the copper-binding motif or sequestration of free copper led to a substantial decrease in the interaction between Atox1 and DJ-1, with overexpression of DJ-1 failing to restore the antioxidant capacity of Atox1 mutants. The findings suggest that DJ-1 mediates the ability of Atox1 to withstand oxidative stress. And targeting Atox1 could be a potential therapeutic approach for addressing post-traumatic neurological dysfunction.

Mitochondrial function and gastrointestinal diseases

Mitochondria are dynamic organelles that function in cellular energy metabolism, intracellular and extracellular signalling, cellular fate and stress responses. Mitochondria of the intestinal epithelium, the cellular interface between self and enteric microbiota, have emerged as crucial in intestinal health. Mitochondrial dysfunction occurs in gastrointestinal diseases, including inflammatory bowel diseases and colorectal cancer. In this Review, we provide an overview of the current understanding of intestinal epithelial cell mitochondrial metabolism, function and signalling to affect tissue homeostasis, including gut microbiota composition. We also discuss mitochondrial-targeted therapeutics for inflammatory bowel diseases and colorectal cancer and the evolving concept of mitochondrial impairment as a consequence versus initiator of the disease.

Pathogenesis of DJ-1/PARK7-Mediated Parkinson's Disease

Parkinson's disease (PD) is a common movement disorder associated with the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Mutations in the PD-associated gene PARK7 alter the structure and function of the encoded protein DJ-1, and the resulting autosomal recessively inherited disease increases the risk of developing PD. DJ-1 was first discovered in 1997 as an oncogene and was associated with early-onset PD in 2003. Mutations in DJ-1 account for approximately 1% of all recessively inherited early-onset PD occurrences, and the functions of the protein have been studied extensively. In healthy subjects, DJ-1 acts as an antioxidant and oxidative stress sensor in several neuroprotective mechanisms. It is also involved in mitochondrial homeostasis, regulation of apoptosis, chaperone-mediated autophagy (CMA), and dopamine homeostasis by regulating various signaling pathways, transcription factors, and molecular chaperone functions. While DJ-1 protects neurons against damaging reactive oxygen species, neurotoxins, and mutant α-synuclein, mutations in the protein may lead to inefficient neuroprotection and the progression of PD. As current therapies treat only the symptoms of PD, the development of therapies that directly inhibit oxidative stress-induced neuronal cell death is critical. DJ-1 has been proposed as a potential therapeutic target, while oxidized DJ-1 could operate as a biomarker for PD. In this paper, we review the role of DJ-1 in the pathogenesis of PD by highlighting some of its key neuroprotective functions and the consequences of its dysfunction.

The reversible low-temperature instability of human DJ-1 oxidative states

DJ-1 is a homodimeric protein that is centrally involved in various human diseases including Parkinson disease (PD). DJ-1 protects against oxidative damage and mitochondrial dysfunction through a homeostatic control of reactive oxygen species (ROS). DJ-1 pathology results from a loss of function, where ROS readily oxidizes a highly conserved and functionally essential cysteine (C106). The over-oxidation of DJ-1 C106 leads to a dynamically destabilized and biologically inactivated protein. An analysis of the structural stability of DJ-1 as a function of oxidative state and temperature may provide further insights into the role the protein plays in PD progression. NMR spectroscopy, circular dichroism, analytical ultracentrifugation sedimentation equilibrium, and molecular dynamics simulations were utilized to investigate the structure and dynamics of the reduced, oxidized (C106-SO2 - ), and over-oxidized (C106-SO3 - ) forms of DJ-1 for temperatures ranging from 5°C to 37°C. The three oxidative states of DJ-1 exhibited distinct temperature-dependent structural changes. A cold-induced aggregation occurred for the three DJ-1 oxidative states by 5°C, where the over-oxidized state aggregated at significantly higher temperatures than both the oxidized and reduced forms. Only the oxidized and over-oxidized forms of DJ-1 exhibited a mix state containing both folded and partially denatured protein that likely preserved secondary structure content. The relative amount of this denatured form of DJ-1 increased as the temperature was lowered, consistent with a cold-denaturation. Notably, the cold-induced aggregation and denaturation for the DJ-1 oxidative states were completely reversible. The dramatic changes in the structural stability of DJ-1 as a function of oxidative state and temperature are relevant to its role in PD and its functional response to oxidative stress.

Cellular Exposure to Chloroacetanilide Herbicides Induces Distinct Protein Destabilization Profiles

Herbicides in the widely used chloroacetanilide class harbor a potent electrophilic moiety, which can damage proteins through nucleophilic substitution. In general, damaged proteins are subject to misfolding. Accumulation of misfolded proteins compromises cellular integrity by disrupting cellular proteostasis networks, which can further destabilize the cellular proteome. While direct conjugation targets can be discovered through affinity-based protein profiling, there are few approaches to probe how cellular exposure to toxicants impacts the stability of the proteome. We apply a quantitative proteomics methodology to identify chloroacetanilide-destabilized proteins in HEK293T cells based on their binding to the H31Q mutant of the human Hsp40 chaperone DNAJB8. We find that a brief cellular exposure to the chloroacetanilides acetochlor, alachlor, and propachlor induces misfolding of dozens of cellular proteins. These herbicides feature distinct but overlapping profiles of protein destabilization, highly concentrated in proteins with reactive cysteine residues. Consistent with the recent literature from the pharmacology field, reactivity is driven by neither inherent nucleophilic nor electrophilic reactivity but is idiosyncratic. We discover that propachlor induces a general increase in protein aggregation and selectively targets GAPDH and PARK7, leading to a decrease in their cellular activities. Hsp40 affinity profiling identifies a majority of propachlor targets identified by competitive activity-based protein profiling (ABPP), but ABPP can only identify about 10% of protein targets identified by Hsp40 affinity profiling. GAPDH is primarily modified by the direct conjugation of propachlor at a catalytic cysteine residue, leading to global destabilization of the protein. The Hsp40 affinity strategy is an effective technique to profile cellular proteins that are destabilized by cellular toxin exposure. Raw proteomics data is available through the PRIDE Archive at PXD030635.

Importance of DJ-1 in autophagy regulation and disease

Autophagy is a highly conserved biological process that has evolved across evolution. It can be activated by various external stimuli including oxidative stress, amino acid starvation, infection, and hypoxia. Autophagy is the primary mechanism for preserving cellular homeostasis and is implicated in the regulation of metabolism, cell differentiation, tolerance to starvation conditions, and resistance to aging. As a multifunctional protein, DJ-1 is commonly expressed in vivo and is associated with a variety of biological processes. Its most widely studied role is its function as an oxidative stress sensor that inhibits the production of excessive reactive oxygen species (ROS) in the mitochondria and subsequently the cellular damage caused by oxidative stress. In recent years, many studies have identified DJ-1 as another important factor regulating autophagy; it regulates autophagy in various ways, most commonly by regulating the oxidative stress response. In particular, DJ-1-regulated autophagy is involved in cancer progression and plays a key role in alleviating neurodegenerative diseases(NDS) and defective reperfusion diseases. It could serve as a potential target for the regulation of autophagy and participate in disease treatment as a meaningful modality. Therefore, exploring DJ-1-regulated autophagy could provide new avenues for future disease treatment.

Recent Advances in the Treatment of Genetic Forms of Parkinson's Disease: Hype or Hope?

Parkinson's disease (PD) is a multifarious neurodegenerative disease. Its pathology is characterized by a prominent early death of dopaminergic neurons in the pars compacta of the substantia nigra and the presence of Lewy bodies with aggregated α-synuclein. Although the α-synuclein pathological aggregation and propagation, induced by several factors, is considered one of the most relevant hypotheses, PD pathogenesis is still a matter of debate. Indeed, environmental factors and genetic predisposition play an important role in PD. Mutations associated with a high risk for PD, usually called monogenic PD, underlie 5% to 10% of all PD cases. However, this percentage tends to increase over time because of the continuous identification of new genes associated with PD. The identification of genetic variants that can cause or increase the risk of PD has also given researchers the possibility to explore new personalized therapies. In this narrative review, we discuss the recent advances in the treatment of genetic forms of PD, focusing on different pathophysiologic aspects and ongoing clinical trials.

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.

Role of mitophagy in the neurodegenerative diseases and its pharmacological advances: A review

Neurodegenerative diseases are a class of incurable and debilitating diseases characterized by progressive degeneration and death of cells in the central nervous system. They have multiple underlying mechanisms; however, they all share common degenerative features, such as mitochondrial dysfunction. According to recent studies, neurodegenerative diseases are associated with the accumulation of dysfunctional mitochondria. Selective autophagy of mitochondria, called mitophagy, can specifically degrade excess or dysfunctional mitochondria within cells. In this review, we highlight recent findings on the role of mitophagy in neurodegenerative disorders. Multiple studies were collected, including those related to the importance of mitochondria, the mechanism of mitophagy in protecting mitochondrial health, and canonical and non-canonical pathways in mitophagy. This review elucidated the important function of mitophagy in neurodegenerative diseases, discussed the research progress of mitophagy in neurodegenerative diseases, and summarized the role of mitophagy-related proteins in neurological diseases. In addition, we also highlight pharmacological advances in neurodegeneration.

Disuse-associated loss of the protease LONP1 in muscle impairs mitochondrial function and causes reduced skeletal muscle mass and strength

Mitochondrial proteolysis is an evolutionarily conserved quality-control mechanism to maintain proper mitochondrial integrity and function. However, the physiological relevance of stress-induced impaired mitochondrial protein quality remains unclear. Here, we demonstrate that LONP1, a major mitochondrial protease resides in the matrix, plays a role in controlling mitochondrial function as well as skeletal muscle mass and strength in response to muscle disuse. In humans and mice, disuse-related muscle loss is associated with decreased mitochondrial LONP1 protein. Skeletal muscle-specific ablation of LONP1 in mice resulted in impaired mitochondrial protein turnover, leading to mitochondrial dysfunction. This caused reduced muscle fiber size and strength. Mechanistically, aberrant accumulation of mitochondrial-retained protein in muscle upon loss of LONP1 induces the activation of autophagy-lysosome degradation program of muscle loss. Overexpressing a mitochondrial-retained mutant ornithine transcarbamylase (ΔOTC), a known protein degraded by LONP1, in skeletal muscle induces mitochondrial dysfunction, autophagy activation, and cause muscle loss and weakness. Thus, these findings reveal a role of LONP1-dependent mitochondrial protein quality-control in safeguarding mitochondrial function and preserving skeletal muscle mass and strength, and unravel a link between mitochondrial protein quality and muscle mass maintenance during muscle disuse.

Mitochondrial function is important for muscle maintenance and function, and mitochondrial proteolysis maintains mitochondrial integrity and function. Here the authors report that that loss of LONP1-dependent mitochondrial proteolysis in muscle causes reduced muscle mass and strength via activation of autophagy.

Serum DJ-1 Is a Biomarker of Colorectal Cancer and DJ-1 Activates Mitophagy to Promote Colorectal Cancer Progression

Simple Summary

Colorectal cancer is common cancer, and currently used serum markers for detecting colorectal cancer lack excellent diagnostic accuracy. In the present study, we collected matched tumor and adjacent normal tissues and serum from patients and cancer cells to demonstrate the clinical value of DJ-1 in colorectal cancer and the role of DJ-1-induced mitophagy in colorectal cancer progression. Our data indicate that DJ-1 might be clinically valuable as serum and tissue biomarkers for predicting the TNM (tumor-node-metastasis) stage in colorectal cancer patients. Besides, DJ-1 knockdown enhanced intracellular reactive oxygen species generation and damaged mitochondrial accumulation and mitophagy inhibition in metastatic colorectal adenocarcinoma cells. Since DJ-1-induced mitophagy promotes tumor progression, DJ-1 inhibition is a potential therapeutic strategy for colorectal cancer treatment.

Abstract

Colorectal cancer is the second most common cancer and the third cancer-associated death in Taiwan. Currently used serum markers for detecting colorectal cancer lack excellent diagnostic accuracy, which results in colorectal cancer being often recognized too late for successful therapy. Mitophagy is the selective autophagic degradation of damaged or excessive mitochondria. DJ-1 is an antioxidant protein that attenuates oxidative stress and maintains mitochondrial quality through activating mitophagy. Mitophagy activation contributes to anti-cancer drug resistance. However, the role of DJ-1-induced mitophagy in colorectal cancer progression remains unclear. In the present study, we collected matched tumor and adjacent normal tissues and serum from patients and cancer cells to demonstrate the clinical value and physiological function of DJ-1 in colorectal cancer. We found that DJ-1 increased in tumor tissues and serum; it was positively correlated with TNM (tumor-node-metastasis) stages of colorectal cancer patients. Through stable knockdown DJ-1 expression in metastatic colorectal adenocarcinoma cells SW620, DJ-1 knockdown inhibited cancer cell survival, migration, and colony formation. In SW620 cells, DJ-1 knockdown induced an incomplete autophagic response that did not affect ATP production; DJ-1 knockdown enhanced intracellular reactive oxygen species generation and damaged mitochondrial accumulation and mitophagy inhibition. It suggests that DJ-1 knockdown inhibits mitophagy that causes metastatic colorectal adenocarcinoma cells to be unable to remove damaged mitochondria and further enhance cancer cell apoptosis. Our data indicate that DJ-1 might be clinically valuable as serum and tissue biomarkers for predicting the TNM stage in colorectal cancer patients. Since DJ-1-induced mitophagy promotes tumor progression, DJ-1 inhibition is a potential therapeutic strategy for colorectal cancer treatment.

The translocator protein (TSPO) is prodromal to mitophagy loss in neurotoxicity

Dysfunctional mitochondria characterise Parkinson's Disease (PD). Uncovering etiological molecules, which harm the homeostasis of mitochondria in response to pathological cues, is therefore pivotal to inform early diagnosis and therapy in the condition, especially in its idiopathic forms. This study proposes the 18 kDa Translocator Protein (TSPO) to be one of those. Both in vitro and in vivo data show that neurotoxins, which phenotypically mimic PD, increase TSPO to enhance cellular redox-stress, susceptibility to dopamine-induced cell death, and repression of ubiquitin-dependent mitophagy. TSPO amplifies the extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) signalling, forming positive feedback, which represses the transcription factor EB (TFEB) and the controlled production of lysosomes. Finally, genetic variances in the transcriptome confirm that TSPO is required to alter the autophagy-lysosomal pathway during neurotoxicity.

DJ-1 in neurodegenerative diseases: Pathogenesis and clinical application

Neurodegenerative diseases (NDs) are one of the major health threats to human characterized by selective and progressive neuronal loss. The mechanisms of NDs are still not fully understood. The study of genetic defects and disease-related proteins offers us a window into the mystery of it, and the extension of knowledge indicates that different NDs share similar features, mechanisms, and even genetic or protein abnormalities. Among these findings, PARK7 and its production DJ-1 protein, which was initially found implicated in PD, have also been found altered in other NDs. PARK7 mutations, altered expression and posttranslational modification (PTM) cause DJ-1 abnormalities, which in turn lead to downstream mechanisms shared by most NDs, such as mitochondrial dysfunction, oxidative stress, protein aggregation, autophagy defects, and so on. The knowledge of DJ-1 derived from PD researches might apply to other NDs in both basic research and clinical application, and might yield novel insights into and alternative approaches for dealing with NDs.

Cytoprotective Mechanisms of DJ-1: Implications in Cardiac Pathophysiology

DJ-1 was originally identified as an oncogene product while mutations of the gene encoding DJ-1/PARK7 were later associated with a recessive form of Parkinson's disease. Its ubiquitous expression and diversity of function suggest that DJ-1 is also involved in mechanisms outside the central nervous system. In the last decade, the contribution of DJ-1 to the protection from ischemia-reperfusion injury has been recognized and its involvement in the pathophysiology of cardiovascular disease is attracting increasing attention. This review describes the current and gaps in our knowledge of DJ-1, focusing on its role in regulating cardiovascular function. In parallel, we present original data showing an association between increased DJ-1 expression and antiapoptotic and anti-inflammatory markers following cardiac and vascular surgical procedures. Future studies should address DJ-1's role as a plausible novel therapeutic target for cardiovascular disease.

Impact of DJ-1 and Helix 8 on the Proteome and Degradome of Neuron-Like Cells

DJ-1 is an abundant and ubiquitous component of cellular proteomes. DJ-1 supposedly exerts a wide variety of molecular functions, ranging from enzymatic activities as a deglycase, protease, and esterase to chaperone functions. However, a consensus perspective on its molecular function in the cellular context has not yet been reached. Structurally, the C-terminal helix 8 of DJ-1 has been proposed to constitute a propeptide whose proteolytic removal transforms a DJ-1 zymogen to an active hydrolase with potential proteolytic activity. To better understand the cell-contextual functionality of DJ-1 and the role of helix 8, we employed post-mitotically differentiated, neuron-like SH-SY5Y neuroblastoma cells with stable over-expression of full length DJ-1 or DJ-1 lacking helix 8 (ΔH8), either with a native catalytically active site (C106) or an inactive site (C106A active site mutation). Global proteome comparison of cells over-expressing DJ-1 ΔH8 with native or mutated active site cysteine indicated a strong impact on mitochondrial biology. N-terminomic profiling however did not highlight direct protease substrate candidates for DJ-1 ΔH8, but linked DJ-1 to elevated levels of activated lysosomal proteases, albeit presumably in an indirect manner. Finally, we show that DJ-1 ΔH8 loses the deglycation activity of full length DJ-1. Our study further establishes DJ-1 as deglycation enzyme. Helix 8 is essential for the deglycation activity but dispensable for the impact on lysosomal and mitochondrial biology; further illustrating the pleiotropic nature of DJ-1.

Mitophagy, a Form of Selective Autophagy, Plays an Essential Role in Mitochondrial Dynamics of Parkinson's Disease

Parkinson's disease (PD) is a severe neurodegenerative disorder caused by the progressive loss of dopaminergic neurons in the substantia nigra and affects millions of people. Currently, mitochondrial dysfunction is considered as a central role in the pathogenesis of both sporadic and familial forms of PD. Mitophagy, a process that selectively targets damaged or redundant mitochondria to the lysosome for elimination via the autophagy devices, is crucial in preserving mitochondrial health. So far, aberrant mitophagy has been observed in the postmortem of PD patients and genetic or toxin-induced models of PD. Except for mitochondrial dysfunction, mitophagy is involved in regulating several other PD-related pathological mechanisms as well, e.g., oxidative stress and calcium imbalance. So far, the mitophagy mechanisms induced by PD-related proteins, PINK1 and Parkin, have been studied widely, and several other PD-associated genes, e.g., DJ-1, LRRK2, and alpha-synuclein, have been discovered to participate in the regulation of mitophagy as well, which further strengthens the link between mitophagy and PD. Thus, in this view, we reviewed mitophagy pathways in belief and discussed the interactions between mitophagy and several PD's pathological mechanisms and how PD-related genes modulate the mitophagy process.

DJ-1 Regulates Microglial Polarization Through P62-Mediated TRAF6/IRF5 Signaling in Cerebral Ischemia-Reperfusion

The polarization of microglia/macrophage, the resident immune cells in the brain, plays an important role in the injury and repair associated with ischemia-reperfusion (I/R). Previous studies have shown that DJ-1 has a protective effect in cerebral I/R. We found that DJ-1 regulates the polarization of microglial cells/macrophages after cerebral I/R and explored the mechanism by which DJ-1 mediates microglial/macrophage polarization in cerebral I/R. Middle cerebral artery occlusion/reperfusion (MCAO/R) and oxygen and glucose deprivation/reoxygenation (OGD/R) models were used to simulate cerebral I/R in vivo and in vitro, respectively. DJ-1 siRNA and the DJ-1-based polypeptide ND13 were used to produce an effect on DJ-1, and the P62-specific inhibitor XRK3F2 was used to block the effect of P62. Enhancing the expression of DJ-1 induced anti-inflammatory (M2) polarization of microglia/macrophage, and the expression of the anti-inflammatory factors IL-10 and IL-4 increased. Interference with DJ-1 expression induced pro-inflammatory (M1) polarization of microglia/macrophage, and the expression of the proinflammatory factors TNF-α and IL-1β increased. DJ-1 inhibited the expression of P62, impeded the interaction between P62 and TRAF6, and blocked nuclear entry of IRF5. In subsequent experiments, XRK3F2 synergistically promoted the effect of DJ-1 on microglial/macrophage polarization, further attenuating the interaction between P62 and TRAF6.

The protective effect of biochanin A against rotenone-induced neurotoxicity in mice involves enhancing of PI3K/Akt/mTOR signaling and beclin-1 production

Rotenone is an insecticide that generates oxidative stress in the CNS and induces locomotor dysfunction and neurodegeneration in rodents. Biochanin A [BioA] is an isoflavone with antioxidant and anti-inflammatory actions. The antioxidant and the modulatory action of BioA on PI3K/Akt/mTOR signaling and autophagy were tested in rotenone-Parkinsonian mice. Mice were allocated into; Group I: oil control group, Group II: rotenone group [1-mg/kg/48h, subcutaneously], group III: rotenone and BioA [10-mg/kg]. Rotenone injection resulted in locomotor disturbances in mice, degeneration in dopaminergic neurons [tyrosine hydroxylase-immunoreactive cells], low striatal dopamine, increased malondialdehyde and decreased level of glutathione. Neuroinflammation was evidenced by upregulation of astrocytes [glia fibrillary acidic protein, GFAP] and elevated levels of cytokines. The phosphorylation of PI3K/Akt/mTOR and the autophagy-related protein, beclin-1, were decreased significantly as indicated by Western blot analysis. BioA treatment enhanced locomotor activity and afforded nigral neuroprotection. The mechanism by which BioA produced this effect includes increased antioxidant defenses, lessened proinflammatory cytokines, increased phosphorylation of PI3K/Akt/mTOR proteins and upregulated beclin-1. Importantly, BioA suppressed the striatal astrocyte marker [GFAP]. Overall, the currents study highlighted that BioA activates PI3K/Akt/mTOR signaling and enhances beclin-1 leading to neuroprotection for nigral dopaminergic neurons.

Autophagy and Redox Homeostasis in Parkinson's: A Crucial Balancing Act

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated primarily from endogenous biochemical reactions in mitochondria, endoplasmic reticulum (ER), and peroxisomes. Typically, ROS/RNS correlate with oxidative damage and cell death; however, free radicals are also crucial for normal cellular functions, including supporting neuronal homeostasis. ROS/RNS levels influence and are influenced by antioxidant systems, including the catabolic autophagy pathways. Autophagy is an intracellular lysosomal degradation process by which invasive, damaged, or redundant cytoplasmic components, including microorganisms and defunct organelles, are removed to maintain cellular homeostasis. This process is particularly important in neurons that are required to cope with prolonged and sustained operational stress. Consequently, autophagy is a primary line of protection against neurodegenerative diseases. Parkinson's is caused by the loss of midbrain dopaminergic neurons (mDANs), resulting in progressive disruption of the nigrostriatal pathway, leading to motor, behavioural, and cognitive impairments. Mitochondrial dysfunction, with associated increases in oxidative stress, and declining proteostasis control, are key contributors during mDAN demise in Parkinson's. In this review, we analyse the crosstalk between autophagy and redoxtasis, including the molecular mechanisms involved and the detrimental effect of an imbalance in the pathogenesis of Parkinson's.

Mitochondrial Translocation of DJ-1 Is Mediated by Grp75: Implication in Cardioprotection of Resveratrol Against Hypoxia/Reoxygenation-Induced Oxidative Stress

Resveratrol (Res) was recently reported to ameliorate hypoxia/reoxygenation (H/R)-caused oxidative stress in H9c2 cardiomyocytes through promoting the mitochondrial translocation of DJ-1 protein and subsequently preserving the activity of mitochondrial complex I. However, it is noteworthy that DJ-1 possesses no mitochondria-targeting sequence. Therefore, how Res induces DJ-1 mitochondrial translocation is an important and interesting question for further exploration. Glucose-regulated protein 75 (Grp75), whose N-terminus contains a 51-amino acid long mitochondrial-targeting signal peptide, is a cytoprotective chaperone that partakes in mitochondrial import of several proteins. Here, the contribution of Grp75 to mitochondrial import of DJ-1 by Res was investigated in a cellular model of H/R. Our results showed that Res upregulated the expression of DJ-1 protein, enhanced the interaction of DJ-1 and Grp75, and promoted DJ-1 translocation to mitochondria from cytosol in H9c2 cardiomyocytes undergoing H/R. Importantly, knockdown of Grp75 markedly reduced the interaction of DJ-1 with Grp75 and subsequent DJ-1 mitochondrial translocation induced by Res. Furthermore, Res pretreatment promoted the association of DJ-1 with ND1 and NDUFA4 subunits of complex I, preserved the activity of complex I, decreased mitochondria-derived reactive oxygen species production, and eventually ameliorated H/R-caused oxidative stress damage. Intriguingly, these effects were largely prevented also by small interfering RNA targeting Grp75. Overall, these results suggested that Grp75 interacts with DJ-1 to facilitate its translocation from cytosol to mitochondria, which is required for Res-mediated preservation of mitochondria complex I and cardioprotection from H/R-caused oxidative stress injury.

Adiponectin protects HL-1 cardiomyocytes against rotenone-induced cytotoxicity through AMPK activation

The relationship between mitochondrial dysfunction or ER stress with pathogenesis of cardiovascular disease is well documented, but the crosstalk between them in cardiovascular diseases is not clear. Adiponectin (APN) is reported to become a potential cardioprotective molecule, but whether and how APN regulates mitochondrial dysfunction and ER stress is not clear. In this study, we used rotenone-treated HL-1 atrial cardiomyocytes as an in vitro model of mitochondrial dysfunction to investigate the possible interactions between mitochondrial dysfunction and ER stress and explore the effects of APN on rotenone-induced cytotoxicity and the underlying mechanisms. It found that rotenone treatment significantly activated the ER stress PRK-like endoplasmic reticulum kinase (PERK)-dependent pathway, decreased autophagic flux and APN expression in a dose-dependent manner. Pretreatment of GSK2606414, an inhibitor of PERK kinase activity, attenuated the rotenone-induced decrease of APN expression. In return exogenous APN pretreatment inhibited rotenone-induced ER stress and activated autophagy via AMP-activated protein kinase (AMPK) activation and protected HL-1 cells against apoptosis and enhanced the viability after rotenone treatment. In conclusion, rotenone treatment induced significant cardiomyocyte cytotoxicity and ER stress, suppressed autophagy, and decreased APN expression in HL-1 cells. APN in return inhibited ER stress and activated autophagy through AMPK activation, thus alleviating rotenone induced HL-1 apoptosis.

The multi-faceted role of mitochondria in the pathology of Parkinson's disease

Mitochondria are essential for neuronal function. They produce ATP to meet energy demands, regulate homeostasis of ion levels such as calcium and regulate reactive oxygen species that cause oxidative cellular stress. Mitochondria have also been shown to regulate protein synthesis within themselves, as well as within the nucleus, and also influence synaptic plasticity. These roles are especially important for neurons, which have higher energy demands and greater susceptibility to stress. Dysfunction of mitochondria has been associated with several neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, Huntington's disease, Glaucoma and Amyotrophic Lateral Sclerosis. The focus of this review is on how and why mitochondrial function is linked to the pathology of Parkinson's disease (PD). Many of the PD-linked genetic mutations which have been identified result in dysfunctional mitochondria, through a wide-spread number of mechanisms. In this review, we describe how susceptible neurons are predisposed to be vulnerable to the toxic events that occur during the neurodegenerative process of PD, and how mitochondria are central to these pathways. We also discuss ways in which proteins linked with familial PD control mitochondrial function, both physiologically and pathologically, along with their implications in genome-wide association studies and risk assessment. Finally, we review potential strategies for disease modification through mitochondrial enhancement. Ultimately, agents capable of both improving and/or restoring mitochondrial function, either alone, or in conjunction with other disease-modifying agents may halt or slow the progression of neurodegeneration in Parkinson's disease.

Unique signatures of stress-induced senescent human astrocytes

Senescence was recently linked to neurodegeneration and astrocytes are one of the major cell types to turn senescent under neurodegenerative conditions. Senescent astrocytes were detected in Parkinson's disease (PD) patients' brains besides reactive astrocytes, yet the difference between senescent and reactive astrocytes is unclear. We aimed to characterize senescent astrocytes in comparison to reactive astrocytes and investigate differences and similarities. In a cell culture model of human fetal astrocytes, we determined a unique senescent transcriptome distinct from reactive astrocytes, which comprises dysregulated pathways. Both, senescent and reactive human astrocytes activated a proinflammatory pattern. Astrocyte senescence was at least partially depending on active mechanistic-target-of-rapamycin (mTOR) and DNA-damage response signaling, both drivers of senescence. To further investigate how PD and senescence connect to each other, we asked if a PD-linked environmental factor induces senescence and if senescence impairs midbrain neurons. We could show that the PD-linked pesticide rotenone causes astrocyte senescence. We further delineate, that the senescent secretome exaggerates rotenone-induced neurodegeneration in midbrain neurons differentiated from human induced pluripotent stem cells (hiPSC) of PD patients with alpha-synuclein gene (SNCA) locus duplication.

Mitophagy and Its Contribution to Metabolic and Aging-Associated Disorders

Significance: Mitochondria are the cellular powerhouses for ATP synthesis through oxidative phosphorylation, and the centers for fatty acid β-oxidation, metabolite synthesis, reactive oxygen species production, innate immunity, and apoptosis. To fulfill these critical functions, mitochondrial quality and homeostasis must be well maintained. Abnormal mitochondrial quality contributes to aging and age-related disorders, such as metabolic syndrome, cancers, and neurodegenerative diseases. Recent Advances: Mitophagy is a cellular process that selectively removes damaged or superfluous mitochondria by autolysosomal degradation and is regarded as one of the major mechanisms responsible for mitochondrial quality control. Critical Issues: To date, distinct mitophagy pathways have been discovered, including receptor-mediated mitophagy and ubiquitin-dependent mitophagy. Emerging knowledge of these pathways shows that they play important roles in sensing mitochondrial stress and signaling for metabolic adaptations. Future Directions: Here, we provide a review on the molecular mechanisms for mitophagy and its interplay with cellular metabolism, with a particular focus on its role in metabolic and age-related disorders.

Autophagy in Parkinson's Disease

Impaired protein homeostasis and accumulation of damaged or abnormally modified protein are common disease mechanisms in many neurodegenerative disorders, including Parkinson's disease (PD). As one of the major degradation pathways, autophagy plays a pivotal role in maintaining effective turnover of proteins and damaged organelles in cells. Several decades of research efforts led to insights into the potential contribution of impaired autophagy machinery to α-synuclein accumulation and the degeneration of dopaminergic neurons, two major features of PD pathology. In this review, we summarize recent pathological, genetic, and mechanistic findings that link defective autophagy with PD pathogenesis in human patients, animals, and cellular models and discuss current challenges in the field.

Galantamine Inhibits Aβ1-42-Induced Neurotoxicity by Enhancing α7nAChR Expression as a Cargo Carrier for LC3 Binding and Aβ1-42 Engulfment During Autophagic Degradation

Despite Alzheimer's disease (AD) being the most common neurodegenerative disorder worldwide, no FDA-approved disease-modifying treatments have been approved for this condition since 2003. Neuronal-type alpha7 nicotinic acetylcholine receptors (α7nAChRs) play an essential role in cognitive functions, binding with extracellular β-amyloid (Aβ plaques) and inhibiting Aβ-induced neurotoxicity. α7nAChRs are impaired early in the course of AD; drugs targeting α7nAChRs are being hotly pursued as a treatment of AD. Encenicline, a partial selective agonist of α7nAChR and modulator of acetylcholine, failed in phase III trials because of gastrointestinal side effects. We, therefore, evaluated the efficacy of galantamine, a positive allosteric modulator at α7nAChRs and an acetylcholinesterase inhibitor, that has been used since 2000 as first-line treatment of mild-to-moderate dementia. This study highlights an important new benefit with galantamine. We found that galantamine inhibits Aβ1-42-induced apoptosis by activating the JNK signaling pathway, thus enhancing α7nAChR expression, and also inhibits the Akt pathway, which further increases autophagosome biogenesis and autophagy. These effects can be reproduced by α7nAChR overexpression in the absence of galantamine. Importantly, the α7 subunit protein sequence of α7nAChRs contains 3 LC3-interacting regions; our immunoprecipitation data show that α7 binds with the autophagosomal marker protein LC3. This is the first report to provide evidence showing that the cell surface receptor α7nAChR acts as a cargo carrier for LC3 binding for Aβ1-42 sequestration to autophagosomes, suggesting a novel mechanism for the neuroprotective efficacy of galantamine in AD.

Antiapoptotic activity of Chlamydia trachomatis Pgp3 protein involves activation of the ERK1/2 pathway mediated by upregulation of DJ-1 protein

Chlamydia trachomatis has evolved strategies to prevent host cell apoptosis to evade the host immune defense. However, the precise mechanisms of antiapoptotic activity of C. trachomatis still need to be clarified. Pgp3, one of eight plasmid proteins of C. trachomatis, has been identified to be closely associated with chlamydial virulence. In this study, we attempted to explore the effects and the mechanisms of Pgp3 protein on apoptosis in HeLa cells; the results showed that Pgp3 increased Bcl-2/Bax ratio and prevented caspase-3 activation to suppress apoptosis induced by TNF-α and cycloheximide (CHX) through ERK1/2 pathway activation. Downregulation of DJ-1 with siRNA-DJ-1(si-DJ-1) reduced ERK1/2 phosphorylation and elevated apoptotic rate significantly in Pgp3-HeLa cells. However, inhibition of ERK1/2 signal pathway with ERK inhibitor PD98059 had little effect on DJ-1 expression. These findings confirm that plasmid protein Pgp3 contributes to apoptosis resistance through ERK1/2 signal pathway mediated by upregulation of DJ-1 expression. Therefore, the present study provided novel insights into the role of Pgp3 in apoptosis and suggested that manipulation of the host apoptosis response could be a new approach for the prevention and treatment of C. trachomatis infection.

Extracellular Signal-Regulated Kinase 1/2 Pathway Is Insufficiently Involved in the Neuroprotective Effect by Hydrogen Sulfide Supplement in Experimental Glaucoma

Purpose

Glaucoma is a neurodegenerative eye disease characterized by gradually impaired visual field and irreversible blindness due to retinal ganglion cell (RGC) loss. Our previous studies have confirmed that hydrogen sulfide (H2S) takes part in the glaucomatous process and contributes to RGC protection. The present study aimed to further investigate the role of extracellular signal-regulated kinase 1/2 (ERK 1/2) pathway underlying the impact of H2S, to better understand the mechanism through which H2S exerts neuroprotection in glaucoma.

Methods

An established rat glaucoma model was used and 168 rats were qualified to undergo sodium hydrosulfide (NaHS, a H2S donor)/PD98059 (an ERK inhibitor) treatment. Then the survival and apoptosis of RGC were evaluated through retrograde labeling and TUNEL staining, along with activity evaluations of ERK 1/2 pathway, intrinsic apoptotic pathway, glial activation, nuclear factor kappa B (NF-κB) pathway, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, autophagy, and TNF-α production through immunohistochemistry, Western blotting, and ELISA.

Results

The study demonstrated that NaHS suppressed ERK 1/2 pathway activity similarly to PD98059 in retinas of experimental glaucoma rats, while PD98059 also similarly suppressed glial activation, NF-κB pathway, NADPH oxidase, and TNF-α production. However, PD98059 did not affect RGC survival, apoptotic regulation, or autophagy as NaHS did.

Conclusions

Our study indicated that inhibition of ERK 1/2 pathway might partly contribute to the neuroprotection by H2S in experimental glaucoma; however, it was insufficient to initiate the therapeutic effect on its own.

Celastrol Inhibits Dopaminergic Neuronal Death of Parkinson's Disease through Activating Mitophagy

Parkinson’s disease (PD) is a neurodegenerative disease, which is associated with mitochondrial dysfunction and abnormal protein accumulation. No treatment can stop or slow PD. Autophagy inhibits neuronal death by removing damaged mitochondria and abnormal protein aggregations. Celastrol is a triterpene with antioxidant and anti-inflammatory effects. Up until now, no reports have shown that celastrol improves PD motor symptoms. In this study, we used PD cell and mouse models to evaluate the therapeutic efficacy and mechanism of celastrol. In the substantia nigra, we found lower levels of autophagic activity in patients with sporadic PD as compared to healthy controls. In neurons, celastrol enhances autophagy, autophagosome biogenesis (Beclin 1↑, Ambra1↑, Vps34↑, Atg7↑, Atg12↑, and LC3-II↑), and mitophagy (PINK1↑, DJ-1↑, and LRRK2↓), and these might be associated with MPAK signaling pathways. In the PD cell model, celastrol reduces MPP⁺-induced dopaminergic neuronal death, mitochondrial membrane depolarization, and ATP reduction. In the PD mouse model, celastrol suppresses motor symptoms and neurodegeneration in the substantia nigra and striatum and enhances mitophagy (PINK1↑ and DJ-1↑) in the striatum. Using MPP⁺ to induce mitochondrial damage in neurons, we found celastrol controls mitochondrial quality by sequestering impaired mitochondria into autophagosomes for degradation. This is the first report to show that celastrol exerts neuroprotection in PD by activating mitophagy to degrade impaired mitochondria and further inhibit dopaminergic neuronal apoptosis. Celastrol may help to prevent and treat PD.

Molecular Mechanism Underlying Hypoxic Preconditioning-Promoted Mitochondrial Translocation of DJ-1 in Hypoxia/Reoxygenation H9c2 Cells

DJ-1 was recently reported to be involved in the cardioprotection of hypoxic preconditioning (HPC) against hypoxia/reoxygenation (H/R)-induced oxidative stress damage, by preserving mitochondrial complex I activity and, subsequently, inhibiting mitochondrial reactive oxygen species (ROS) generation. However, the molecular mechanism by which HPC enables mitochondrial translocation of DJ-1, which has no mitochondria-targeting sequence, to preserve mitochondrial complex I, is largely unknown. In this study, co-immunoprecipitation data showed that DJ-1 was associated with glucose-regulated protein 75 (Grp75), and this association was significantly enhanced after HPC. Immunofluorescence imaging and Western blot analysis showed that HPC substantially enhanced the translocation of DJ-1 from cytosol to mitochondria in H9c2 cells subjected to H/R, which was mimicked by DJ-1 overexpression induced by pFlag-DJ-1 transfection. Importantly, knockdown of Grp75 markedly reduced the mitochondrial translocation of DJ-1 induced by HPC and pFlag-DJ-1 transfection. Moreover, HPC promoted the association of DJ-1 with mitochondrial complex I subunits ND1 and NDUFA4, improved complex I activity, and inhibited mitochondria-derived ROS production and subsequent oxidative stress damage after H/R, which was also mimicked by pFlag-DJ-1 transfection. Intriguingly, these effects of HPC and pFlag-DJ-1 transfection were also prevented by Grp75 knockdown. In conclusion, these results indicated that HPC promotes the translocation of DJ-1 from cytosol to mitochondria in a Grp75-dependent manner and Grp75 is required for DJ-1-mediated protection of HPC on H/R-induced mitochondrial complex I defect and subsequent oxidative stress damage.

Role of Autophagy in Parkinson's Disease

Autophagy is an essential catabolic mechanism that delivers misfolded proteins and damaged organelles to the lysosome for degradation. Autophagy pathways include macroautophagy, chaperone-mediated autophagy and microautophagy, each involving different mechanisms of substrate delivery to lysosome. Defects of these pathways and the resulting accumulation of protein aggregates represent a common pathobiological feature of neurodegenerative disorders such as Alzheimer, Parkinson and Huntington disease. This review provides an overview of the role of autophagy in Parkinson's disease (PD) by summarizing the most relevant genetic and experimental evidence showing how this process can contribute to disease pathogenesis. Given lysosomes take part in the final step of the autophagic process, the role of lysosomal defects in the impairment of autophagy and their impact on disease will also be discussed. A glance on the role of non-neuronal autophagy in the pathogenesis of PD will be included. Moreover, we will examine novel pharmacological targets and therapeutic strategies that, by boosting autophagy, may be theoretically beneficial for PD. Special attention will be focused on natural products, such as phenolic compounds, that are receiving increasing consideration due to their potential efficacy associated with low toxicity. Although many efforts have been made to elucidate autophagic process, the development of new therapeutic interventions requires a deeper understanding of the mechanisms that may lead to autophagy defects in PD and should take into account the multifactorial nature of the disease as well as the phenotypic heterogeneity of PD patients.

Salidroside Protects Dopaminergic Neurons by Enhancing PINK1/Parkin-Mediated Mitophagy

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the degeneration of nigrostriatal dopaminergic (DA) neurons. Our previous studies have suggested that salidroside (Sal) might play neuroprotective effects against PD by preserving mitochondrial Complex I activity. However, the exact mechanism of the neuroprotective effect of Sal remains unclear. Growing evidence indicates that PINK1/Parkin-mediated mitophagy is involved in the development of PD. In this study, we investigated whether Sal exerts a neuroprotective effect by modulating PINK1/Parkin-mediated mitophagy. Results showed that Sal alleviated MPTP-induced motor deficits in pole test. Moreover, Sal diminished MPTP-induced degeneration of nigrostriatal DA neurons as evidenced by upregulated TH-positive neurons in the substantia nigra, increased DAT expression, and high dopamine and metabolite levels in the striatum. Furthermore, in comparison with the MPP⁺/MPTP group, Sal considerably increased the mitophagosome and mitophagy flux. Moreover, in comparison with the MPP⁺/MPTP group, Sal evidently enhanced the mitochondrial expression of PINK1 and Parkin, accompanied by an increase in the colocalization of mitochondria with Parkin. However, transfection of MN9D cells with PINK1 siRNA reversed Sal-induced activated mitophagy and cytoprotective effect. In conclusion, Sal may confer neuroprotective effects by enhancing PINK1/Parkin-mediated mitophagy in MPP⁺/MPTP-induced PD models.

DJ-1 in Parkinson's Disease: Clinical Insights and Therapeutic Perspectives

Mutations in the protein DJ-1 cause autosomal recessive forms of Parkinson’s disease (PD) and oxidized DJ-1 is found in the brains of idiopathic PD individuals. While several functions have been ascribed to DJ-1 (most notably protection from oxidative stress), its contribution to PD pathogenesis is not yet clear. Here we provide an overview of the clinical research to date on DJ-1 and the current state of knowledge regarding DJ-1 characterization in the human brain. The relevance of DJ-1 as a PD biomarker is also discussed, as are studies exploring DJ-1 as a possible therapeutic target for PD and neurodegeneration.

Morinda citrifolia and Its Active Principle Scopoletin Mitigate Protein Aggregation and Neuronal Apoptosis through Augmenting the DJ-1/Nrf2/ARE Signaling Pathway

Given the role of oxidative stress in PD pathogenesis and off-target side effects of currently available drugs, several natural phytochemicals seem to be promising in the management of PD. Here, we tested the hypothesis that scopoletin, an active principle obtained from Morinda citrifolia (MC), efficiently quenches oxidative stress through DJ-1/Nrf2 signaling and ameliorates rotenone-induced PD. Despite reducing oxidative stress, the administration of MC extract (MCE) has lessened protein aggregation as evident from decreased levels of nitrotyrosine and α-synuclein. In vitro studies revealed that scopoletin lessened rotenone-induced apoptosis in SH-SY5Y cells through preventing oxidative injury. Particularly, scopoletin markedly upregulated DJ-1, which then promoted the nuclear translocation of Nrf2 and transactivation of antioxidant genes. Furthermore, we found that scopoletin prevents the nuclear exportation of Nrf2 by reducing the levels of Keap1 and thereby enhancing the neuronal defense system. Overall, our findings suggest that scopoletin acts through DJ-1-mediated Nrf2 signaling to protect the brain from rotenone-induced oxidative stress and PD. Thus, we postulate that scopoletin could be a potential drug to treat PD.

Mechanisms and roles of mitophagy in neurodegenerative diseases

Mitochondria are double‐membrane‐encircled organelles existing in most eukaryotic cells and playing important roles in energy production, metabolism, Ca²⁺ buffering, and cell signaling. Mitophagy is the selective degradation of mitochondria by autophagy. Mitophagy can effectively remove damaged or stressed mitochondria, which is essential for cellular health. Thanks to the implementation of genetics, cell biology, and proteomics approaches, we are beginning to understand the mechanisms of mitophagy, including the roles of ubiquitin‐dependent and receptor‐dependent signals on damaged mitochondria in triggering mitophagy. Mitochondrial dysfunction and defective mitophagy have been broadly associated with neurodegenerative diseases. This review is aimed at summarizing the mechanisms of mitophagy in higher organisms and the roles of mitophagy in the pathogenesis of neurodegenerative diseases. Although many studies have been devoted to elucidating the mitophagy process, a deeper understanding of the mechanisms leading to mitophagy defects in neurodegenerative diseases is required for the development of new therapeutic interventions, taking into account the multifactorial nature of diseases and the phenotypic heterogeneity of patients.

The deglycase activity of DJ-1 mitigates α-synuclein glycation and aggregation in dopaminergic cells: Role of oxidative stress mediated downregulation of DJ-1 in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with the degeneration of dopamine neurons of the substantia nigra pars compacta (SNpc) and the presence of intra-neuronal aggregates of α-synuclein and its post-translational products. Based on emerging reports on the association between glycated α-synuclein and PD; and the newly identified deglycase activity of DJ-1, we sought to find the relevance of deglycase activity of DJ-1 on glycation of α-synuclein and its plausible role in PD. Our results demonstrate that DJ-1 has a higher affinity towards the substrate methylglyoxal (MGO) (Km = 900 mM) as compared to its familial mutant, L166P (Km = 1900 mM). Also, CML α-synuclein (CML-syn) served as a substrate for the deglycase activity of DJ-1. Treatment of cells with Parkinsonian mimetic, 1-methyl-4-phenylpyridinium ion (MPP⁺); oxidants, such as H₂O₂ and methylglyoxal (MGO) lead to a dose-dependent decrease in the levels of DJ-1 with a concomitant increase in CML-syn. Also, MGO induced cytosolic α-synuclein aggregates in cells which stained positive with the anti-CML antibody. Further, unilateral stereotaxic administration of MGO into the SNpc of mice induced α-synuclein aggregates and CML-syn with a concomitant reduction in the number of TH positive neurons, protein levels of TH and DJ-1 at the site of injection. Interestingly, overexpression of DJ-1 enhanced the clearance of preformed CML-syn in cells, mitigated MGO induced CML-syn and intracellular α-synuclein aggregates. Overall, the findings of our present study demonstrate that DJ-1 plays a pivotal role in the glycation and aggregation of α-synuclein. Reduced DJ-1 activity due to mutations or oxidative stress may lead to the accumulation of glycated α-synuclein and its aggregates.

Resveratrol attenuates myocardial hypoxia/reoxygenation-induced cell apoptosis through DJ-1-mediated SIRT1-p53 pathway

Resveratrol, a multi-functional phytoalexin, has been well indicated to exert cardioprotective effects by weakening ischemia/reperfusion (I/R) injury, and cell apoptosis is a vital way in I/R injury. SIRT1-p53 pathway has strong significance in regulating cell apoptosis. DJ-1 can directly bind to SIRT1 and stimulate the activity of SIRT1-p53. Therefore, the current study was determined whether Resveratrol attenuates hypoxia/reoxygenation (H/R)-induced cell apoptosis, and whether DJ-1-mediated SIRT1 activation involves in the cardioprotective effects of Resveratrol. The results showed that remarkable decrease in the number of apoptotic cells along with reduction of lactate dehydrogenase release and restoration of cell viability emerged when Resveratrol was applied in the H9c2 cells exposed to H/R. Moreover, Resveratrol increased DJ-1 expression and promoted the interaction of DJ-1 with SIRT1, which further contributed to subsequent restoration of SIRT1 activity and decrease of acetylation level of p53. However, above cardioprotective effects of Resveratrol were abrogated by DJ-1 siRNA and SIRT1 specific inhibitor Sirtinol. In conclusion, the current study demonstrated that Resveratrol suppressed H/R-induced cell apoptosis, which may be conducted by up-regulating DJ-1, and later activating SIRT1 activity and subsequently inhibiting p53 acetylation level in the H9c2 cells.

p38 Inhibitor Protects Mitochondrial Dysfunction by Induction of DJ-1 Mitochondrial Translocation After Subarachnoid Hemorrhage

p38 mitogen-activated protein kinase (MAPK) is a major player in mitochondrial dysfunction after subarachnoid hemorrhage (SAH). Moreover, DJ-1, which responds to oxidative stress and translocates to mitochondria, maintains mitochondrial homeostasis. Although a few studies have demonstrated that DJ-1 indirectly regulates p38 activation, the relationship between DJ-1 and p38 in mitochondrial dysfunction after SAH has not been delineated. Using an in vitro SAH model, alterations in p38, p-p38, DJ-1, and autophagic-related protein expression were detected. As expected, p38 inhibitor significantly blocked excessive expression of p38 and p-p38 after SAH, whereas total DJ-1 expression and mitochondrial DJ-1 were up-regulated. Further analysis showed that p38 inhibitor significantly blocked oxyhemoglobin (OxyHb) induced mitochondrial dysfunction, including mitochondrial membrane potential depolarization and reactive oxygen species (ROS) release. In addition, p38 inhibitor restored OxyHb-induced abnormal autophagic flux at the initiation and formation stage by regulating Atg5, beclin-1, the ratio of LC3-II/LC3-I, and p62 expression. This study suggested that overexpression of p38 induced the accumulation of mitochondrial dysfunction partly due to abnormal activation of autophagy, which largely relied on DJ-1 mitochondrial translocation.

Discovery and Optimization of Inhibitors of the Parkinson's Disease Associated Protein DJ-1

DJ-1 is a Parkinson's disease associated protein endowed with enzymatic, redox sensing, regulatory, chaperoning, and neuroprotective activities. Although DJ-1 has been vigorously studied for the past decade and a half, its exact role in the progression of the disease remains uncertain. In addition, little is known about the spatiotemporal regulation of DJ-1, or the biochemical basis explaining its numerous biological functions. Progress has been hampered by the lack of inhibitors with precisely known mechanisms of action. Herein, we have employed biophysical methodologies and X-ray crystallography to identify and to optimize a family of compounds inactivating the critical Cys106 residue of human DJ-1. We demonstrate these compounds are potent inhibitors of various activities of DJ-1 in vitro and in cell-based assays. This study reports a new family of DJ-1 inhibitors with a defined mechanism of action, and contributes toward the understanding of the biological function of DJ-1.

Targeting mTORs by omega-3 fatty acids: A possible novel therapeutic strategy for neurodegeneration?

Neurodegenerative diseases (NDs) such as Parkinson's (PD), Alzheimer's (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) cause significant world-wide morbidity and mortality. To date, there is no drug of cure for these, mostly age-related diseases, although approaches in delaying the pathology and/or giving patients some symptomatic relief have been adopted for the last few decades. Various studies in recent years have shown the beneficial effects of omega-3 poly unsaturated fatty acids (PUFAs) through diverse mechanisms including anti-inflammatory effects. This review now assesses the potential of this class of compounds in NDs therapy through specific action against the mammalian target of rapamycin (mTOR) signaling pathway. The role of mTOR in neurodegenerative diseases and targeted therapies by PUFAs are discussed.

Astrocyte-specific DJ-1 overexpression protects against rotenone-induced neurotoxicity in a rat model of Parkinson's disease

DJ-1 is a redox-sensitive protein with several putative functions important in mitochondrial physiology, protein transcription, proteasome regulation, and chaperone activity. High levels of DJ-1 immunoreactivity are reported in astrocytes surrounding pathology associated with idiopathic Parkinson's disease, possibly reflecting the glial response to oxidative damage. Previous studies showed that astrocytic over-expression of DJ-1 in vitro prevented oxidative stress and mitochondrial dysfunction in primary neurons. Based on these observations, we developed a pseudotyped lentiviral gene transfer vector with specific tropism for CNS astrocytes in vivo to overexpress human DJ-1 protein in astroglial cells. Following vector delivery to the substantia nigra and striatum of adult Lewis rats, the DJ-1 transgene was expressed robustly and specifically within astrocytes. There was no observable transgene expression in neurons or other glial cell types. Three weeks after vector infusion, animals were exposed to rotenone to induce Parkinson's disease-like pathology, including loss of dopaminergic neurons, accumulation of endogenous α-synuclein, and neuroinflammation. Animals over-expressing hDJ-1 in astrocytes were protected from rotenone-induced neurodegeneration, and displayed a marked reduction in neuronal oxidative stress and microglial activation. In addition, α-synuclein accumulation and phosphorylation were decreased within substantia nigra dopaminergic neurons in DJ-1-transduced animals, and expression of LAMP-2A, a marker of chaperone mediated autophagy, was increased. Together, these data indicate that astrocyte-specific overexpression of hDJ-1 protects neighboring neurons against multiple pathologic features of Parkinson's disease and provides the first direct evidence in vivo of a cell non-autonomous neuroprotective function of astroglial DJ-1.

Cholesterol impairs autophagy-mediated clearance of amyloid beta while promoting its secretion

Macroautophagy/autophagy failure with the accumulation of autophagosomes is an early neuropathological feature of Alzheimer disease (AD) that directly affects amyloid beta (Aβ) metabolism. Although loss of presenilin 1 function has been reported to impair lysosomal function and prevent autophagy flux, the detailed mechanism leading to autophagy dysfunction in AD remains to be elucidated. The resemblance between pathological hallmarks of AD and Niemann-Pick Type C disease, including endosome-lysosome abnormalities and impaired autophagy, suggests cholesterol accumulation as a common link. Using a mouse model of AD (APP-PSEN1-SREBF2 mice), expressing chimeric mouse-human amyloid precursor protein with the familial Alzheimer Swedish mutation (APP695swe) and mutant presenilin 1 (PSEN1-dE9), together with a dominant-positive, truncated and active form of SREBF2/SREBP2 (sterol regulatory element binding factor 2), we demonstrated that high brain cholesterol enhanced autophagosome formation, but disrupted its fusion with endosomal-lysosomal vesicles. The combination of these alterations resulted in impaired degradation of Aβ and endogenous MAPT (microtubule associated protein tau), and stimulated autophagy-dependent Aβ secretion. Exacerbated Aβ-induced oxidative stress in APP-PSEN1-SREBF2 mice, due to cholesterol-mediated depletion of mitochondrial glutathione/mGSH, is critical for autophagy induction. In agreement, in vivo mitochondrial GSH recovery with GSH ethyl ester, inhibited autophagosome synthesis by preventing the oxidative inhibition of ATG4B deconjugation activity exerted by Aβ. Moreover, cholesterol-enrichment within the endosomes-lysosomes modified the levels and membrane distribution of RAB7A and SNAP receptors (SNAREs), which affected its fusogenic ability. Accordingly, in vivo treatment with 2-hydroxypropyl-β-cyclodextrin completely rescued these alterations, making it a potential therapeutic tool for AD.

Autophagy Disruptions Associated With Altered Optineurin Expression in Extranigral Regions in a Rotenone Model of Parkinson's Disease

The motor features of Parkinson's disease (PD) primarily result from a lesion to the nigrostriatal dopamine system. Numerous non-motor symptoms occur in PD, many of which are postulated to stem from pathology outside of the nigrostriatal dopamine system. Perturbations to protein trafficking, disruption of mitochondrial integrity, and impaired autophagy have repeatedly been implicated in dopaminergic neuron cell death. Previously, we demonstrated that multiple markers of autophagy are disrupted in a rotenone model of PD, with alterations occurring prior to an overt lesion to the nigrostriatal dopamine system. Whether these events occur in extra-nigral nuclei in PD and when relative to a lesion in the nigrostriatal dopamine system are generally unknown. The primary goal of these studies was to determine whether autophagy disruptions, in non-dopaminergic neuronal populations occur in an environmental model of PD utilizing a mitochondrial toxin. Here, we utilized the rat rotenone PD model, with sampling time-points before and after an overt lesion to the nigrostriatal dopamine system. In analyzing autophagy changes, we focused on optineurin (OPTN) and the autophagy marker, LC3. OPTN is an autophagy cargo adapter protein genetically linked to amyotrophic lateral sclerosis and glaucoma. In the present study, we observed OPTN enrichment in all PD-relevant brain regions examined. Further, alterations in OPTN and LC3 expression and colocalized puncta suggest specific impairments to autophagy that will inform future mechanistic studies. Thus, our data suggest that autophagy disruptions may be critical to PD pathogenesis in non-dopaminergic neurons and the onset of non-motor symptoms.

Mitochondrial dynamics in Parkinson's disease: a role for α-synuclein?

The distinctive pathological hallmarks of Parkinson's disease are the progressive death of dopaminergic neurons and the intracellular accumulation of Lewy bodies enriched in α-synuclein protein. Several lines of evidence from the study of sporadic, familial and pharmacologically induced forms of human Parkinson's disease also suggest that mitochondrial dysfunction plays an important role in disease progression. Although many functions have been proposed for α-synuclein, emerging data from human and animal models of Parkinson's disease highlight a role for α-synuclein in the control of neuronal mitochondrial dynamics. Here, we review the α-synuclein structural, biophysical and biochemical properties that influence relevant mitochondrial dynamic processes such as fusion-fission, transport and clearance. Drawing on current evidence, we propose that α-synuclein contributes to the mitochondrial defects that are associated with the pathology of this common and progressive neurodegenerative disease.

Summary: The authors review the α-synuclein structural, biophysical and biochemical properties that influence relevant mitochondrial physiological processes such as fusion-fission, transport and clearance, and propose that α-synuclein contributes to the mitochondrial defects that are associated with Parkinson's disease.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.