The oxidation state of DJ-1 regulates its chaperone activity toward alpha-synuclein

Mechanisms of ubiquitin-independent proteasomal degradation and their roles in age-related neurodegenerative disease

Neurodegenerative diseases are characterized by the progressive breakdown of neuronal structure and function and the pathological accumulation of misfolded protein aggregates and toxic protein oligomers. A major contributor to the deterioration of neuronal physiology is the disruption of protein catabolic pathways mediated by the proteasome, a large protease complex responsible for most cellular protein degradation. Previously, it was believed that proteolysis by the proteasome required tagging of protein targets with polyubiquitin chains, a pathway called the ubiquitin-proteasome system (UPS). Because of this, most research on proteasomal roles in neurodegeneration has historically focused on the UPS. However, additional ubiquitin-independent pathways and their importance in neurodegeneration are increasingly recognized. In this review, we discuss the range of ubiquitin-independent proteasome pathways, focusing on substrate identification and targeting, regulatory molecules and adaptors, proteasome activators and alternative caps, and diverse proteasome complexes including the 20S proteasome, the neuronal membrane proteasome, the immunoproteasome, extracellular proteasomes, and hybrid proteasomes. These pathways are further discussed in the context of aging, oxidative stress, protein aggregation, and age-associated neurodegenerative diseases, with a special focus on Alzheimer's Disease, Huntington's Disease, and Parkinson's Disease. A mechanistic understanding of ubiquitin-independent proteasome function and regulation in neurodegeneration is critical for the development of therapies to treat these devastating conditions. This review summarizes the current state of ubiquitin-independent proteasome research in neurodegeneration.

Development and use of DJ-1 affinity microcolumns to screen and study small drug candidates for Parkinson's disease

BACKGROUND

DJ-1 is a protein whose mutation causes rare heritable forms of Parkinson's disease (PD) and is of interest as a target for treating PD and other disorders. This work used high performance affinity microcolumns to screen and examine the binding of small molecules to DJ-1, as could be used to develop new therapeutics or to study the role of DJ-1 in PD. Non-covalent entrapment was used to place microgram quantities of DJ-1 in an unmodified form within microcolumns, which were then used in multiple studies to analyze binding by model compounds and possible drug candidates to DJ-1.

RESULTS

Several factors were examined in optimizing the entrapment method, including the addition of a reducing agent to maintain a reduced active site cysteine residue in DJ-1, the concentration of DJ-1 employed, and the entrapment times. Isatin was used as a known binding agent (dissociation constant, ∼2.0 μM) and probe for DJ-1 activity. This compound gave good retention on 2.0 cm × 2.1 mm inner diameter DJ-1 microcolumns made under the final entrapment conditions, with a typical retention factor of 14 and elution in ∼8 min at 0.50 mL/min. These DJ-1 microcolumns were used to evaluate the binding of small molecules that were selected in silico to bind or not to bind DJ-1. A compound predicted to have good binding with DJ-1 gave a retention factor of 122, an elution time of ∼15 min at 0.50 mL/min, and an estimated dissociation constant for this protein of 0.5 μM.

SIGNIFICANCE

These chromatographic tools can be used in future work to screen additional possible binding agents for DJ-1 or adapted for examining drug candidates for other proteins. This work represents the first time protein entrapment has been deployed with DJ-1, and it is the first experimental confirmation of binding to DJ-1 by a small lead compound selected in silico.

Interaction of α-synuclein with DJ-1 in homodimer and L166P mutant monomer forms in Parkinson's disease: a molecular dynamics study

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is characterized by the formation of Lewy bodies, which are primarily composed of misfolded α-Synuclein (α-Syn). DJ-1 is a crucial protein involved in the correct folding of α-Syn, and mutations impairing its function are associated with the onset of PD. One such mutation, the L166P substitution in DJ-1, which has been linked to early-onset PD and results in the loss of DJ-1's homodimer structure. Recent studies have shown the presence of DJ-1 in Lewy bodies, but its interaction with α-Syn is unknown. Therefore, in this study, we investigated the interaction between α-Syn and DJ-1 in both its wild-type (wDJ-1: homodimer) and L166P mutant (mDJ-1: monomer) forms using molecular dynamics simulation. Our results indicated that α-Syn binds more tightly to mDJ-1 than to wDJ-1. Gibbs free energy landscape analysis showed that the bonded α-Syn to mDJ-1 complex represents a stable conformation, whereas only a partial connection of α-Syn to wDJ-1 was observed. Generally, it appears that the monomer form of DJ-1 resulting from the L166P mutation can form a stable complex with α-Syn, potentially intensifying the formation of Lewy bodies. Thus, the identification of aggregated α-Syn with DJ-1 may serve as a potential biomarker for PD.

DJ-1 as a Novel Therapeutic Target for Mitigating Myocardial Ischemia-Reperfusion Injury

Ischemic heart disease (IHD) remains one of the most prominent causes of mortality and morbidity globally, and the risk of ischemia-reperfusion injury is becoming more severe and constant. This underscores the need to develop new methods to protect the heart from damage. DJ-1 is a multifunctional intracellular protein encoded by the PARK7 gene that plays roles in processes including the control of autophagy, the preservation of mitochondrial integrity, the prevention of apoptosis, and the elimination of oxidative stress. DJ-1 has recently been the focus of growing interest as a target molecule relevant to treating myocardial ischemia-reperfusion injury due to its protective properties and its role in cellular response mechanisms. Consistently, DJ-1-related interventions, such as its exogenous administration or the use of pharmacological agents, have been demonstrated to help protect the myocardium from ischemia-reperfusion injury and associated adverse outcomes. This review provides an overview of DJ-1 and its therapeutic relevance in the myocardium in the setting of ischemia and reperfusion.

The hunt for transnitrosylase

The biochemical interplay between antioxidants and pro-oxidants maintains the redox homeostatic balance of the cell, which, when perturbed to moderate or high extents, has been implicated in the onset and/or progression of chronic diseases such as diabetes mellitus, cancer, and neurodegenerative diseases. Thioredoxin, glutaredoxin, and lipoic acid-like thiol oxidoreductase systems constitute a unique ensemble of robust cellular antioxidant defenses, owing to their indispensable roles as S-denitrosylases, S-deglutathionylases, and disulfide reductants in maintaining a reduced free thiol state with biological relevance. Thus, in cells subjected to nitrosative stress, cellular antioxidants will S-denitrosylate their cognate S-nitrosoprotein substrates, rather than participate in trans-S-nitrosylation via protein-protein interactions. Researchers have been at the forefront of vaguely establishing the concept of 'transnitrosylation' and its influence on pathophysiology with experimental evidence from in vitro studies that lack proper biochemical logic. The suggestive and reiterative use of antioxidants as transnitrosylases in the scientific literature leaves us on a cliffhanger with several open-ended questions that prompted us to 'hunt' for scientific logic behind the trans-S-nitrosylation chemistry. Given the gravity of the situation and to look at the bigger picture of 'trans-S-nitrosylation', we aim to present a novel attempt at justifying the hesitance in accepting antioxidants as capable of transnitrosylating their cognate protein partners and reflecting on the need to resolve the controversy that would be crucial from the perspective of understanding therapeutic outcomes involving such cellular antioxidants in disease pathogenesis. Further characterization is required to identify the regulatory mechanisms or conditions where an antioxidant like Trx, Grx, or DJ-1 can act as a cellular transnitrosylase.

Peptide Activator Stabilizes DJ-1 Structure and Enhances Its Activity

DJ-1 is a vital enzyme involved in the maintenance of mitochondrial health, and its mutation has been associated with an increased risk of Parkinson's disease (PD). Effective regulation of DJ-1 activity is essential for the well-being of mitochondria, and DJ-1 is thus a potential target for PD drug development. In this study, two peptides (15EEMETIIPVDVMRRA29 and 47SRDVVICPDA56) were utilized with the aim of enhancing the activity of DJ-1. The mechanisms underlying the activity enhancement by these two peptides were investigated using hydrogen/deuterium exchange mass spectrometry (HDXMS). The HDXMS results revealed distinct mechanisms. Peptide 1 obstructs the access of solvent to the dimer interface and stabilizes the α/β hydrolase structure, facilitating substrate binding to a stabilized active site. Conversely, peptide 2 induces a destabilization of the α/β hydrolase core, enhancing substrate accessibility and subsequently increasing DJ-1 activity. The binding of these two peptides optimizes the activity site within the dimeric structure. These findings offer valuable insights into the mechanisms underlying the activity enhancement of DJ-1 by the two peptides, potentially aiding the development of new drugs that can enhance the activity of DJ-1 and, consequently, advance PD treatment.

DJ-1 regulates mitochondrial function and promotes retinal ganglion cell survival under high glucose-induced oxidative stress

Purpose

This study aimed to investigate the antioxidative and neuroprotective effects of DJ-1 in mitigating retinal ganglion cell (RGC) damage induced by high glucose (HG).

Methods

A diabetic mouse model and an HG-induced R28 cell model were employed for loss- and gain-of-function experiments. The expression levels of apoptosis and oxidative stress-related factors, including Bax, Bcl-2, caspase3, Catalase, MnSOD, GCLC, Cyto c, and GPx-1/2, were assessed in both animal and cell models using Western blotting. Retinal structure and function were evaluated through HE staining, electroretinogram, and RGC counting. Mitochondrial function and apoptosis were determined using JC-1 and TUNEL staining, and reactive oxygen species (ROS) measurement.

Results

In the mouse model, hyperglycemia resulted in reduced retinal DJ-1 expression, retinal structural and functional damage, disrupted redox protein profiles, and mitochondrial dysfunction. Elevated glucose levels induced mitochondrial impairment, ROS generation, abnormal protein expression, and apoptosis in R28 cells. Augmenting DJ-1 expression demonstrated a restoration of mitochondrial homeostasis and alleviated diabetes-induced morphological and functional impairments both in vivo and in vitro.

Conclusion

This study provides novel insights into the regulatory role of DJ-1 in mitochondrial dynamics, suggesting a potential avenue for enhancing RGC survival in diabetic retinopathy.

The origin of esterase activity of Parkinson's disease causative factor DJ-1 implied by evolutionary trace analysis of its prokaryotic homolog HchA

DJ-1, a causative gene for hereditary recessive Parkinsonism, is evolutionarily conserved across eukaryotes and prokaryotes. Structural analyses of DJ-1 and its homologs suggested the 106th Cys is a nucleophilic cysteine functioning as the catalytic center of hydratase or hydrolase activity. Indeed, DJ-1 and its homologs can convert highly electrophilic α-oxoaldehydes such as methylglyoxal into α-hydroxy acids as hydratase in vitro, and oxidation-dependent ester hydrolase (esterase) activity has also been reported for DJ-1. The mechanism underlying such plural activities, however, has not been fully characterized. To address this knowledge gap, we conducted a series of biochemical assays assessing the enzymatic activity of DJ-1 and its homologs. We found no evidence for esterase activity in any of the Escherichia coli DJ-1 homologs. Furthermore, contrary to previous reports, we found that oxidation inactivated rather than facilitated DJ-1 esterase activity. The E. coli DJ-1 homolog HchA possesses phenylglyoxalase and methylglyoxalase activities but lacks esterase activity. Since evolutionary trace analysis identified the 186th H as a candidate residue involved in functional differentiation between HchA and DJ-1, we focused on H186 of HchA and found that an esterase activity was acquired by H186A mutation. Introduction of reverse mutations into the equivalent position in DJ-1 (A107H) selectively eliminated its esterase activity without compromising α-oxoaldehyde hydratase activity. The obtained results suggest that differences in the amino acid sequences near the active site contributed to acquisition of esterase activity in vitro and provide an important clue to the origin and significance of DJ-1 esterase activity.

Protein Oxidative Modifications in Neurodegenerative Diseases: From Advances in Detection and Modelling to Their Use as Disease Biomarkers

Oxidation-reduction post-translational modifications (redox-PTMs) are chemical alterations to amino acids of proteins. Redox-PTMs participate in the regulation of protein conformation, localization and function, acting as signalling effectors that impact many essential biochemical processes in the cells. Crucially, the dysregulation of redox-PTMs of proteins has been implicated in the pathophysiology of numerous human diseases, including neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. This review aims to highlight the current gaps in knowledge in the field of redox-PTMs biology and to explore new methodological advances in proteomics and computational modelling that will pave the way for a better understanding of the role and therapeutic potential of redox-PTMs of proteins in neurodegenerative diseases. Here, we summarize the main types of redox-PTMs of proteins while providing examples of their occurrence in neurodegenerative diseases and an overview of the state-of-the-art methods used for their detection. We explore the potential of novel computational modelling approaches as essential tools to obtain insights into the precise role of redox-PTMs in regulating protein structure and function. We also discuss the complex crosstalk between various PTMs that occur in living cells. Finally, we argue that redox-PTMs of proteins could be used in the future as diagnosis and prognosis biomarkers for neurodegenerative diseases.

Oxidized DJ-1 activates the p-IKK/NF-κB/Beclin1 pathway by binding PTEN to induce autophagy and exacerbate myocardial ischemia-reperfusion injury

Patients with myocardial infarction have a much worse prognosis when they have myocardial ischemia-reperfusion (I/R) injury. Further research into the molecular basis of myocardial I/R injury is therefore urgently needed, as well as the identification of novel therapeutic targets and linkages to interventions. Three cysteine residues are present in DJ-1 at amino acids 46, 53, and 106 sites, with the cysteine at position 106 being the most oxidation-prone. This study sought to understand how oxidized DJ-1(C106) contributes to myocardial I/R damage. Rats' left anterior descending branches were tied off to establish a myocardial I/R model in vivo. A myocardial I/R model in vitro was established via anoxia/reoxygenation (A/R) of H9c2 cells. The results showed that autophagy increased after I/R, accompanied by the increased expression of oxidized DJ-1 (ox-DJ-1). In contrast, after pretreatment with NAC (N-acetylcysteine, a ROS scavenger) or Comp-23 (Compound-23, a specific antioxidant binding to the C106 site of DJ-1), the levels of ox-DJ-1, autophagy and LDH release decreased, and cell survival rate increased. Furthermore, the inhibition of interaction between ox-DJ-1 and PTEN could increase PTEN phosphatase activity, inhibit the p-IKK/NF-κB/Beclin1 pathway, reduce injurious autophagy, and alleviate A/R injury. However, BA (Betulinic acid, a NF-κB agonist) was able to reverse the protective effects produced by Comp-23 pretreatment. In conclusion, ox-DJ-1 could activate detrimental autophagy through the PTEN/p-IKK/NF-κB/Beclin1 pathway and exacerbate myocardial I/R injury.

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.

Disruption of lysosomal proteolysis in astrocytes facilitates midbrain organoid proteostasis failure in an early-onset Parkinson's disease model

Accumulation of advanced glycation end products (AGEs) on biopolymers accompanies cellular aging and drives poorly understood disease processes. Here, we studied how AGEs contribute to development of early onset Parkinson's Disease (PD) caused by loss-of-function of DJ1, a protein deglycase. In induced pluripotent stem cell (iPSC)-derived midbrain organoid models deficient for DJ1 activity, we find that lysosomal proteolysis is impaired, causing AGEs to accumulate, α-synuclein (α-syn) phosphorylation to increase, and proteins to aggregate. We demonstrated these processes are at least partly driven by astrocytes, as DJ1 loss reduces their capacity to provide metabolic support and triggers acquisition of a pro-inflammatory phenotype. Consistently, in co-cultures, we find that DJ1-expressing astrocytes are able to reverse the proteolysis deficits of DJ1 knockout midbrain neurons. In conclusion, astrocytes' capacity to clear toxic damaged proteins is critical to preserve neuronal function and their dysfunction contributes to the neurodegeneration observed in a DJ1 loss-of-function PD model.

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.

Protein Persulfidation: Recent Progress and Future Directions

Significance: Hydrogen sulfide (H2S) is considered to be a gasotransmitter along with carbon monoxide (CO) and nitric oxide (NO), and is known as a key regulator of physiological and pathological activities. S-sulfhydration (also known as persulfidation), a mechanism involving the formation of protein persulfides by modification of cysteine residues, is proposed here to explain the multiple biological functions of H2S. Investigating the properties of protein persulfides can provide a foundation for further understanding of the potential functions of H2S. Recent Advances: Multiple methods have been developed to determine the level of protein persulfides. It has been demonstrated that protein persulfidation is involved in many biological processes through various mechanisms including the regulation of ion channels, enzymes, and transcription factors, as well as influencing protein-protein interactions. Critical Issues: Some technical and theoretical questions remain to be solved. These include how to improve the specificity of the detection methods for protein persulfidation, why persulfidation typically occurs on one or a few thiols within a protein, how this modification alters protein functions, and whether protein persulfidation has organ-specific patterns. Future Directions: Optimizing the detection methods and elucidating the properties and molecular functions of protein persulfidation would be beneficial for current therapeutics. In this review, we introduce the detailed mechanism of the persulfidation process and discuss persulfidation detection methods. In addition, this review summarizes recent discoveries of the selectivity of protein persulfidation and the regulation of protein functions and cell signaling pathways by persulfidation. Antioxid. Redox Signal. 39, 829-852.

Parkinson's Disease: From Genetics and Epigenetics to Treatment, a miRNA-Based Strategy

Parkinson's disease (PD) is one of the most common neurodegenerative disorders, characterized by an initial and progressive loss of dopaminergic neurons of the substantia nigra pars compacta via a potentially substantial contribution from protein aggregates, the Lewy bodies, mainly composed of α-Synuclein among other factors. Distinguishing symptoms of PD are bradykinesia, muscular rigidity, unstable posture and gait, hypokinetic movement disorder and resting tremor. Currently, there is no cure for PD, and palliative treatments, such as Levodopa administration, are directed to relieve the motor symptoms but induce severe side effects over time. Therefore, there is an urgency for discovering new drugs in order to design more effective therapeutic approaches. The evidence of epigenetic alterations, such as the dysregulation of different miRNAs that may stimulate many aspects of PD pathogenesis, opened a new scenario in the research for a successful treatment. Along this line, a promising strategy for PD treatment comes from the potential exploitation of modified exosomes, which can be loaded with bioactive molecules, such as therapeutic compounds and RNAs, and can allow their delivery to the appropriate location in the brain, overcoming the blood-brain barrier. In this regard, the transfer of miRNAs within Mesenchymal stem cell (MSC)-derived exosomes has yet to demonstrate successful results both in vitro and in vivo. This review, besides providing a systematic overview of both the genetic and epigenetic basis of the disease, aims to explore the exosomes/miRNAs network and its clinical potential for PD treatment.

Oxime blot: A novel method for reliable and sensitive detection of carbonylated proteins in diverse biological systems

Oxidative stress and oxidative protein damage occur in various biological processes and diseases. The carbonyl group on amino acid side chains is the most widely used protein oxidation biomarker. Carbonyl groups are commonly detected indirectly through their reaction with 2,4-dinitrophenylhydrazine (DNPH) and subsequent labeling with an anti-DNP antibody. However, the DNPH immunoblotting method lacks protocol standardization, exhibits technical bias, and has low reliability. To overcome these shortcomings, we have developed a new blotting method in which the carbonyl group reacts with the biotin-aminooxy probe to form a chemically stable oxime bond. The reaction speed and the extent of the carbonyl group derivatization are increased by adding a p-phenylenediamine (pPDA) catalyst under neutral pH conditions. These improvements are crucial since they ensure that the carbonyl derivatization reaction reaches a plateau within hours and increases the sensitivity and robustness of protein carbonyl detection. Furthermore, derivatization under pH-neutral conditions facilitates a good SDS-PAGE protein migration pattern, avoids protein loss by acidic precipitation, and is directly compatible with protein immunoprecipitation. This work describes the new Oxime blot method and demonstrates its use in detecting protein carbonylation in complex matrices from diverse biological samples.

DJ-1 Molecular Chaperone Activity Depresses Tau Aggregation Propensity through Interaction with Monomers

Tau aggregate-bearing lesions are pathological markers and potential mediators of tauopathic neurodegenerative diseases, including Alzheimer's disease. The molecular chaperone DJ-1 colocalizes with tau pathology in these disorders, but it has been unclear what functional link exists between them. In this study, we examined the consequences of tau/DJ-1 interaction as isolated proteins in vitro. When added to full-length 2N4R tau under aggregation-promoting conditions, DJ-1 inhibited both the rate and extent of filament formation in a concentration-dependent manner. Inhibitory activity was low affinity, did not require ATP, and was not affected by substituting oxidation incompetent missense mutation C106A for wild-type DJ-1. In contrast, missense mutations previously linked to familial Parkinson's disease and loss of α-synuclein chaperone activity, M26I and E64D, displayed diminished tau chaperone activity relative to wild-type DJ-1. Although DJ-1 directly bound the isolated microtubule-binding repeat region of tau protein, exposure of preformed tau seeds to DJ-1 did not diminish seeding activity in a biosensor cell model. These data reveal DJ-1 to be a holdase chaperone capable of engaging tau as a client in addition to α-synuclein. Our findings support a role for DJ-1 as part of an endogenous defense against the aggregation of these intrinsically disordered proteins.

Is Disrupted Mitophagy a Central Player to Parkinson's Disease Pathology?

Whilst the pathophysiology at a cellular level has been defined, the cause of Parkinson's disease (PD) remains poorly understood. This neurodegenerative disorder is associated with impaired dopamine transmission in the substantia nigra, and protein accumulations known as Lewy bodies are visible in affected neurons. Cell culture models of PD have indicated impaired mitochondrial function, so the focus of this paper is on the quality control processes involved in and around mitochondria. Mitochondrial autophagy (mitophagy) is the process through which defective mitochondria are removed from the cell by internalisation into autophagosomes which fuse with a lysosome. This process involves many proteins, notably including PINK1 and parkin, both of which are known to be coded on genes associated with PD. Normally in healthy individuals, PINK1 associates with the outer mitochondrial membrane, which then recruits parkin, activating it to attach ubiquitin proteins to the mitochondrial membrane. PINK1, parkin, and ubiquitin cooperate to form a positive feedback system which accelerates the deposition of ubiquitin on dysfunctional mitochondria, resulting in mitophagy. However, in hereditary PD, the genes encoding PINK1 and parkin are mutated, resulting in proteins that are less efficient at removing poorly performing mitochondria, leaving cells more vulnerable to oxidative stress and ubiquitinated inclusion bodies, such as Lewy bodies. Current research that looks into the connection between mitophagy and PD is promising, already yielding potentially therapeutic compounds; until now, pharmacological support for the mitophagy process has not been part of the therapeutic arsenal. Continued research in this area is warranted.

DJ-1 Alleviates Neuroinflammation and the Related Blood-Spinal Cord Barrier Destruction by Suppressing NLRP3 Inflammasome Activation via SOCS1/Rac1/ROS Pathway in a Rat Model of Traumatic Spinal Cord Injury

DJ-1 has been shown to play essential roles in neuronal protection and anti-inflammation in nervous system diseases. This study aimed to explore how DJ-1 regulates neuroinflammation after traumatic spinal cord injury (t-SCI). The rat model of spinal cord injury was established by the clamping method. The Basso, Beattie, Bresnahan (BBB) score and the inclined plane test (IPT) were used to evaluate neurological function. Western blot was then applied to test the levels of DJ-1, NLRP3, SOCS1, and related proinflammatory factors (cleaved caspase 1, IL-1β and IL-18); ROS level was also examined. The distribution of DJ-1 was assessed by immunofluorescence staining (IF). BSCB integrity was assessed by the level of MMP-9 and tight junction proteins (Claudin-5, Occludin and ZO-1). We found that DJ-1 became significantly elevated after t-SCI and was mainly located in neurons. Knockdown of DJ-1 with specific siRNA aggravated NLRP3 inflammasome-related neuroinflammation and strengthened the disruption of BSCB integrity. However, the upregulation of DJ-1 by Sodium benzoate (SB) reversed these effects and improved neurological function. Furthermore, SOCS1-siRNA attenuated the neuroprotective effects of DJ-1 and increased the ROS, Rac1 and NLRP3. In conclusion, DJ-1 may alleviate neuroinflammation and the related BSCB destruction after t-SCI by suppressing NLRP3 inflammasome activation by SOCS1/Rac1/ROS pathways. DJ-1 shows potential as a feasible target for mediating neuroinflammation after t-SCI.

DJ-1 is not a deglycase and makes a modest contribution to cellular defense against methylglyoxal damage in neurons

Human DJ‐1 is a cytoprotective protein whose absence causes Parkinson's disease and is also associated with other diseases. DJ‐1 has an established role as a redox‐regulated protein that defends against oxidative stress and mitochondrial dysfunction. Multiple studies have suggested that DJ‐1 is also a protein/nucleic acid deglycase that plays a key role in the repair of glycation damage caused by methylglyoxal (MG), a reactive α‐keto aldehyde formed by central metabolism. Contradictory reports suggest that DJ‐1 is a glyoxalase but not a deglycase and does not play a major role in glycation defense. Resolving this issue is important for understanding how DJ‐1 protects cells against insults that can cause disease. We find that DJ‐1 reduces levels of reversible adducts of MG with guanine and cysteine in vitro. The steady‐state kinetics of DJ‐1 acting on reversible hemithioacetal substrates are fitted adequately with a computational kinetic model that requires only a DJ‐1 glyoxalase activity, supporting the conclusion that deglycation is an apparent rather than a true activity of DJ‐1. Sensitive and quantitative isotope‐dilution mass spectrometry shows that DJ‐1 modestly reduces the levels of some irreversible guanine and lysine glycation products in primary and cultured neuronal cell lines and whole mouse brain, consistent with a small but measurable effect on total neuronal glycation burden. However, DJ‐1 does not improve cultured cell viability in exogenous MG. In total, our results suggest that DJ‐1 is not a deglycase and has only a minor role in protecting neurons against methylglyoxal toxicity.

PARK7/DJ-1 as a Therapeutic Target in Gut-Brain Axis Diseases

It is increasingly known that Parkinson's (PD) and Alzheimer's (AD) diseases occur more frequently in patients with inflammatory gastrointestinal diseases including inflammatory bowel (IBD) or celiac disease, indicating a pathological link between them. Although epidemiological observations suggest the existence of the gut-brain axis (GBA) involving systemic inflammatory and neural pathways, little is known about the exact molecular mechanisms. Parkinson's disease 7 (PARK7/DJ-1) is a multifunctional protein whose protective role has been widely demonstrated in neurodegenerative diseases, including PD, AD, or ischemic stroke. Recent studies also revealed the importance of PARK7/DJ-1 in the maintenance of the gut microbiome and also in the regulation of intestinal inflammation. All these findings suggest that PARK7/DJ-1 may be a link and also a potential therapeutic target in gut and brain diseases. In this review, therefore, we discuss our current knowledge about PARK7/DJ-1 in the context of GBA diseases.

Parkinson's disease protein PARK7 prevents metabolite and protein damage caused by a glycolytic metabolite

Reactive compounds cause cellular damage that is suspected to contribute to aging and neurodegenerative diseases. Oxidative stress and environmental factors likely contribute to this. Here we report that an enzyme mutated in Parkinson’s disease can prevent damage of metabolites and proteins caused by a metabolite from the central pathway of sugar metabolism. Inactivation of this enzyme in model systems, ranging from flies to human cells, leads to the accumulation of a wide range of damaged metabolites and proteins. Thus, this enzyme represents a highly conserved strategy to prevent damage in cells that metabolize sugars. Overall, we discovered a fundamental link between carbohydrate metabolism and a type of cellular damage that might contribute to the development of Parkinson’s disease.

Cells are continuously exposed to potentially dangerous compounds. Progressive accumulation of damage is suspected to contribute to neurodegenerative diseases and aging, but the molecular identity of the damage remains largely unknown. Here we report that PARK7, an enzyme mutated in hereditary Parkinson’s disease, prevents damage of proteins and metabolites caused by a metabolite of glycolysis. We found that the glycolytic metabolite 1,3-bisphosphoglycerate (1,3-BPG) spontaneously forms a novel reactive intermediate that avidly reacts with amino groups. PARK7 acts by destroying this intermediate, thereby preventing the formation of proteins and metabolites with glycerate and phosphoglycerate modifications on amino groups. As a consequence, inactivation of PARK7 (or its orthologs) in human cell lines, mouse brain, and Drosophila melanogaster leads to the accumulation of these damaged compounds, most of which have not been described before. Our work demonstrates that PARK7 function represents a highly conserved strategy to prevent damage in cells that metabolize carbohydrates. This represents a fundamental link between metabolism and a type of cellular damage that might contribute to the development of Parkinson’s disease.

Mitochondrial Function and Parkinson's Disease: From the Perspective of the Electron Transport Chain

Parkinson’s disease (PD) is known as a mitochondrial disease. Some even regarded it specifically as a disorder of the complex I of the electron transport chain (ETC). The ETC is fundamental for mitochondrial energy production which is essential for neuronal health. In the past two decades, more than 20 PD-associated genes have been identified. Some are directly involved in mitochondrial functions, such as PRKN, PINK1, and DJ-1. While other PD-associate genes, such as LRRK2, SNCA, and GBA1, regulate lysosomal functions, lipid metabolism, or protein aggregation, some have been shown to indirectly affect the electron transport chain. The recent identification of CHCHD2 and UQCRC1 that are critical for functions of complex IV and complex III, respectively, provide direct evidence that PD is more than just a complex I disorder. Like UQCRC1 in preventing cytochrome c from release, functions of ETC proteins beyond oxidative phosphorylation might also contribute to the pathogenesis of PD.

The role of intra and inter-molecular disulfide bonds in modulating amyloidogenesis: A review

All proteins have the inherent ability to undergo transformation from their native structure to a β sheet rich fibrillar structure, called amyloid when subjected to specific conditions. Proteins with a high propensity to form amyloid fibrils have been implicated in a variety of disorders like Alzheimer's disease, Parkinson's disease, Type II diabetes, Amyotrophic Lateral Sclerosis (ALS) and prion diseases. Among the various critical factors that modulate the process of amyloid formation, disulfide bonds have been identified as one of the key determinants of amyloid propensity in proteins. Studies have shown that intra-molecular disulfide bonds impart stability to the native structure of a protein and decrease the tendency for amyloid aggregation, whereas intermolecular disulfide bonds aid in the process of aggregation. In this review, we will analyze the varying effects of both intra as well as inter-molecular disulfide bonds on the amyloid aggregation propensities of a few proteins associated with amyloid disorders.

Impacts of oxidants and antioxidants on the emergence and progression of Alzheimer's disease

The brain shows a high sensitivity to oxidative stress (OS). Thus, the maintenance of homeostasis of the brain regarding the reduction-oxidation (redox) situation is crucial for the regular function of the central nervous systems (CNS). The imbalance between the reactive oxygen species (ROS) and the cellular mechanism might lead to the emergence of OS, causing profound cell death as well as tissue damages and initiating neurodegenerative disorders (NDDs). Characterized by the cytoplasmic growth of neurofibrillary tangles and extracellular β-amyloid plaques, Alzheimer's disease (AD) is a complex NDD that causes dementia in adult life with severe manifestations. Nuclear factor erythroid 2-related factor 2 (NRF2) is a key transcription factor that regulates the functional expression of OS-related genes and the functionality of endogenous antioxidants. In the case of oxidative damage, NRF2 is transferred to the nucleus and attached to the antioxidant response element (ARE) that enhances the sequence to initiate transcription of the cell-protecting genes. This review articulates various mechanisms engaged with the generation of active and reactive species of endogenous and exogenous oxidants and focuses on the antioxidants as a body defense system regarding the NRF2-ARE signaling path in the CNS.

A New Insight into an Alternative Therapeutic Approach to Restore Redox Homeostasis and Functional Mitochondria in Neurodegenerative Diseases

Neurodegenerative diseases are accompanied by oxidative stress and mitochondrial dysfunction, leading to a progressive loss of neuronal cells, formation of protein aggregates, and a decrease in cognitive or motor functions. Mitochondrial dysfunction occurs at the early stage of neurodegenerative diseases. Protein aggregates containing oxidatively damaged biomolecules and other misfolded proteins and neuroinflammation have been identified in animal models and patients with neurodegenerative diseases. A variety of neurodegenerative diseases commonly exhibits decreased activity of antioxidant enzymes, lower amounts of antioxidants, and altered cellular signalling. Although several molecules have been approved clinically, there is no known cure for neurodegenerative diseases, though some drugs are focused on improving mitochondrial function. Mitochondrial dysfunction is caused by oxidative damage and impaired cellular signalling, including that of peroxisome proliferator-activated receptor gamma coactivator 1α. Mitochondrial function can also be modulated by mitochondrial biogenesis and the mitochondrial fusion/fission cycle. Mitochondrial biogenesis is regulated mainly by sirtuin 1, NAD⁺, AMP-activated protein kinase, mammalian target of rapamycin, and peroxisome proliferator-activated receptor γ. Altered mitochondrial dynamics, such as increased fission proteins and decreased fusion products, are shown in neurodegenerative diseases. Due to the restrictions of a target-based approach, a phenotype-based approach has been performed to find novel proteins or pathways. Alternatively, plasma membrane redox enzymes improve mitochondrial function without the further production of reactive oxygen species. In addition, inducers of antioxidant response elements can be useful to induce a series of detoxifying enzymes. Thus, redox homeostasis and metabolic regulation can be important therapeutic targets for delaying the progression of neurodegenerative diseases.

DJ-1 Acts as a Scavenger of α-Synuclein Oligomers and Restores Monomeric Glycated α-Synuclein

Glycation of α-synuclein (αSyn), as occurs with aging, has been linked to the progression of Parkinson’s disease (PD) through the promotion of advanced glycation end-products and the formation of toxic oligomers that cannot be properly cleared from neurons. DJ-1, an antioxidative protein that plays a critical role in PD pathology, has been proposed to repair glycation in proteins, yet a mechanism has not been elucidated. In this study, we integrate solution nuclear magnetic resonance (NMR) spectroscopy and liquid atomic force microscopy (AFM) techniques to characterize glycated N-terminally acetylated-αSyn (glyc-ac-αSyn) and its interaction with DJ-1. Glycation of ac-αSyn by methylglyoxal increases oligomer formation, as visualized by AFM in solution, resulting in decreased dynamics of the monomer amide backbone around the Lys residues, as measured using NMR. Upon addition of DJ-1, this NMR signature of glyc-ac-αSyn monomers reverts to a native ac-αSyn-like character. This phenomenon is reversible upon removal of DJ-1 from the solution. Using relaxation-based NMR, we have identified the binding site on DJ-1 for glycated and native ac-αSyn as the catalytic pocket and established that the oxidation state of the catalytic cysteine is imperative for binding. Based on our results, we propose a novel mechanism by which DJ-1 scavenges glyc-ac-αSyn oligomers without chemical deglycation, suppresses glyc-ac-αSyn monomer–oligomer interactions, and releases free glyc-ac-αSyn monomers in solution. The interference of DJ-1 with ac-αSyn oligomers may promote free ac-αSyn monomer in solution and suppress the propagation of toxic oligomer and fibril species. These results expand the understanding of the role of DJ-1 in PD pathology by acting as a scavenger for aggregated αSyn.

Protein Transnitrosylation Signaling Networks Contribute to Inflammaging and Neurodegenerative Disorders

Significance: Physiological concentrations of nitric oxide (NO^•) and related reactive nitrogen species (RNS) mediate multiple signaling pathways in the nervous system. During inflammaging (chronic low-grade inflammation associated with aging) and in neurodegenerative diseases, excessive RNS contribute to synaptic and neuronal loss. "NO signaling" in both health and disease is largely mediated through protein S-nitrosylation (SNO), a redox-based posttranslational modification with "NO" (possibly in the form of nitrosonium cation [NO⁺]) reacting with cysteine thiol (or, more properly, thiolate anion [R-S^-]). Recent Advances: Emerging evidence suggests that S-nitrosylation occurs predominantly via transnitros(yl)ation. Mechanistically, the reaction involves thiolate anion, as a nucleophile, performing a reversible nucleophilic attack on a nitroso nitrogen to form an SNO-protein adduct. Prior studies identified transnitrosylation reactions between glyceraldehyde-3-phosphate dehydrogenase (GAPDH)-nuclear proteins, thioredoxin-caspase-3, and X-linked inhibitor of apoptosis (XIAP)-caspase-3. Recently, we discovered that enzymes previously thought to act in completely disparate biochemical pathways can transnitrosylate one another during inflammaging in an unexpected manner to mediate neurodegeneration. Accordingly, we reported a concerted tricomponent transnitrosylation network from Uch-L1-to-Cdk5-to-Drp1 that mediates synaptic damage in Alzheimer's disease. Critical Issues: Transnitrosylation represents a critical chemical mechanism for transduction of redox-mediated events to distinct subsets of proteins. Although thousands of thiol-containing proteins undergo S-nitrosylation, how transnitrosylation regulates a myriad of neuronal attributes is just now being uncovered. In this review, we highlight recent progress in the study of the chemical biology of transnitrosylation between proteins as a mechanism of disease. Future Directions: We discuss future areas of study of protein transnitrosylation that link our understanding of aging, inflammation, and neurodegenerative diseases. Antioxid. Redox Signal. 35, 531-550.

The Parkinson's Disease-Associated Protein DJ-1 Protects Dictyostelium Cells from AMPK-Dependent Outcomes of Oxidative Stress

Mitochondrial dysfunction has been implicated in the pathology of Parkinson’s disease (PD). In Dictyostelium discoideum, strains with mitochondrial dysfunction present consistent, AMPK-dependent phenotypes. This provides an opportunity to investigate if the loss of function of specific PD-associated genes produces cellular pathology by causing mitochondrial dysfunction with AMPK-mediated consequences. DJ-1 is a PD-associated, cytosolic protein with a conserved oxidizable cysteine residue that is important for the protein’s ability to protect cells from the pathological consequences of oxidative stress. Dictyostelium DJ-1 (encoded by the gene deeJ) is located in the cytosol from where it indirectly inhibits mitochondrial respiration and also exerts a positive, nonmitochondrial role in endocytosis (particularly phagocytosis). Its loss in unstressed cells impairs endocytosis and causes correspondingly slower growth, while also stimulating mitochondrial respiration. We report here that oxidative stress in Dictyostelium cells inhibits mitochondrial respiration and impairs phagocytosis in an AMPK-dependent manner. This adds to the separate impairment of phagocytosis caused by DJ-1 knockdown. Oxidative stress also combines with DJ-1 loss in an AMPK-dependent manner to impair or exacerbate defects in phototaxis, morphogenesis and growth. It thereby phenocopies mitochondrial dysfunction. These results support a model in which the oxidized but not the reduced form of DJ-1 inhibits AMPK in the cytosol, thereby protecting cells from the adverse consequences of oxidative stress, mitochondrial dysfunction and the resulting AMPK hyperactivity.

DJ-1 Protein and Its Role in the Development of Parkinson's Disease: Studies on Experimental Models

DJ-1, also known as Parkinson's disease protein 7, is a multifunctional protein ubiquitously expressed in cells and tissues. Interacting with proteins of various intracellular compartments, DJ-1 plays an important role in maintaining different cellular functions. Mutant DJ-1 forms containing amino acid substitutions (especially L166P), typical of Parkinson's disease, are characterized by impaired dimerization, stability, and folding. DJ-1 exhibits several types of catalytic activity; however, in the enzyme classification it exists as protein deglycase (EC 3.5.1.124). Apparently, in different cell compartments DJ-1 exhibits catalytic and non-catalytic functions, and their ratio still remains unknown. Oxidative stress promotes dissociation of cytoplasmic DJ-1 dimers into monomers, which are translocated to the nucleus, where this protein acts as a coactivator of various signaling pathways, preventing cell death. In mitochondria, DJ-1 is found in the synthasome, where it interacts with the β ATP synthase subunit. Downregulation of the DJ-1 gene under conditions of experimental PD increases sensitivity of the cells to neurotoxins, and introduction of the recombinant DJ-1 protein attenuates manifestation of this pathology. The thirteen-membered fragment of the DJ-1 amino acid sequence attached to the heptapeptide of the TAT protein penetrating into the cells exhibited neuroprotective properties in various PD models both in cell cultures and after administration to animals. Low molecular weight DJ-1 ligands also demonstrate therapeutic potential, providing neuroprotective effects seen during their incubation with cells and administration to animals.

Bis-isatin derivatives: design, synthesis, and biological activity evaluation as potent dimeric DJ-1 inhibitors

The PARK7 gene (encode DJ-1 protein) was first discovered as an oncogene and later found to be a causative gene for autosomal recessive early onset Parkinson's disease. DJ-1 has been proposed as a potential therapeutic anticancer target due to its pivotal role in tumorigenesis and cancer progression. Based on the homodimer structure of DJ-1, a series of bis-isatin derivatives with different length linkers were designed, synthesized, and evaluated as dimeric inhibitors targeting DJ-1 homodimer. Among them, DM10 with alkylene chain of C10 displayed the most potent inhibitory activity against DJ-1 deglycase. We further demonstrated that DM10 bound covalently to the homodimer of DJ-1. In human cancer cell lines H1299, MDA-MB-231, BEL7402, and 786-O, DM10 (2.5-20 μM) inhibited the cell growth in a concentration-dependent manner showing better anticancer effects compared with the positive control drug STK793590. In nude mice bearing H1299 cell xenograft, intratumor injection of DM10 (15 mg/kg) produced significantly potent tumor growth inhibition when compared with that caused by STK793590 (30 mg/kg). Moreover, we found that DM10 could significantly enhance N-(4-hydroxyphenyl)retinamide-based apoptosis and erastin-based ferroptosis in H1299 cells. In conclusion, DM10 is identified as a potent inhibitor targeting DJ-1 homodimer with the potential as sensitizing agent for other anticancer drugs, which might provide synergistical therapeutic option for cancer treatment.

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.

Phenotypic manifestation of α-synuclein strains derived from Parkinson's disease and multiple system atrophy in human dopaminergic neurons

α-Synuclein is critical in the pathogenesis of Parkinson's disease and related disorders, yet it remains unclear how its aggregation causes degeneration of human dopaminergic neurons. In this study, we induced α-synuclein aggregation in human iPSC-derived dopaminergic neurons using fibrils generated de novo or amplified in the presence of brain homogenates from Parkinson's disease or multiple system atrophy. Increased α-synuclein monomer levels promote seeded aggregation in a dose and time-dependent manner, which is associated with a further increase in α-synuclein gene expression. Progressive neuronal death is observed with brain-amplified fibrils and reversed by reduction of intraneuronal α-synuclein abundance. We identified 56 proteins differentially interacting with aggregates triggered by brain-amplified fibrils, including evasion of Parkinson's disease-associated deglycase DJ-1. Knockout of DJ-1 in iPSC-derived dopaminergic neurons enhance fibril-induced aggregation and neuronal death. Taken together, our results show that the toxicity of α-synuclein strains depends on aggregate burden, which is determined by monomer levels and conformation which dictates differential interactomes. Our study demonstrates how Parkinson's disease-associated genes influence the phenotypic manifestation of strains in human neurons.

Neurodegeneration: Impact of S-nitrosylated Parkin, DJ-1 and PINK1 on the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is one of the fastest-growing neurodegenerative disorders of increasing global prevalence. It represents the second most common movement disorder after tremor and the second most common neurodegenerative disorder after Alzheimer's disease. The incidence rate of idiopathic PD increases steadily with age, however, some variants of autosomal recessive inheritance are present with an early age-at-onset (ARPD). Approximately 50 percent of ARPD cases have been linked to bi-allelic mutations in genes encoding Parkin, DJ-1, and PINK1. Each protein has been implicated in maintaining proper mitochondrial function, which is particularly important for neuronal health. Aberrant post-translational modifications of these proteins may disrupt their cellular functions and thus contributing to the development of idiopathic PD. Some post-translational modifictions can be attributed to the dysregulation of potentially harmful reactive oxygen and nitrogen species inside the cell, which promote oxidative and nitrosative stress, respectively. Unlike oxidative modifications, the covalent modification by Nitric Oxide under nitrosative stress, leading to S-nitrosylation of Parkin, DJ-1; and PINK1, is less studied. Here, we review the available literature on S-nitrosylation of these three proteins, their implications in the pathogenesis of PD, and provide an overview of currently known, denitrosylating systems in eukaryotic cells.

Mitochondrial LonP1 protease is implicated in the degradation of unstable Parkinson's disease-associated DJ-1/PARK 7 missense mutants

DJ-1/PARK7 mutations are linked with familial forms of early-onset Parkinson's disease (PD). We have studied the degradation of untagged DJ-1 wild type (WT) and missense mutants in mouse embryonic fibroblasts obtained from DJ-1-null mice, an approach closer to the situation in patients carrying homozygous mutations. The results showed that the mutants L10P, M26I, A107P, P158Δ, L166P, E163K, and L172Q are unstable proteins, while A39S, E64D, R98Q, A104T, D149A, A171S, K175E, and A179T are as stable as DJ-1 WT. Inhibition of proteasomal and autophagic-lysosomal pathways had little effect on their degradation. Immunofluorescence and biochemical fractionation studies indicated that M26I, A107P, P158Δ, L166P, E163K, and L172Q mutants associate with mitochondria. Silencing of mitochondrial matrix protease LonP1 produced a strong reduction of the degradation of the mitochondrial-associated DJ-1 mutants A107P, P158Δ, L166P, E163K, and L172Q but not of mutant L10P. These results demonstrated a mitochondrial pathway of degradation of those DJ-1 missense mutants implicated in PD pathogenesis.

The cell biology of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder resulting from the death of dopamine neurons in the substantia nigra pars compacta. Our understanding of PD biology has been enriched by the identification of genes involved in its rare, inheritable forms, termed PARK genes. These genes encode proteins including α-syn, LRRK2, VPS35, parkin, PINK1, and DJ1, which can cause monogenetic PD when mutated. Investigating the cellular functions of these proteins has been instrumental in identifying signaling pathways that mediate pathology in PD and neuroprotective mechanisms active during homeostatic and pathological conditions. It is now evident that many PD-associated proteins perform multiple functions in PD-associated signaling pathways in neurons. Furthermore, several PARK proteins contribute to non-cell-autonomous mechanisms of neuron death, such as neuroinflammation. A comprehensive understanding of cell-autonomous and non-cell-autonomous pathways involved in PD is essential for developing therapeutics that may slow or halt its progression.

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.

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.

Identification of Disease-Associated Variants by Targeted Gene Panel Resequencing in Parkinson's Disease

Background: Recent advanced technologies, such as high-throughput sequencing, have enabled the identification of a broad spectrum of variants. Using targeted-gene-panel resequencing for Parkinson's disease (PD)-associated genes, we have occasionally found several single-nucleotide variants (SNVs), which are thought to be disease-associated, in PD patients. To confirm the significance of these potentially disease-associated variants, we performed genome association analyses, using next-generation target resequencing, to evaluate the associations between the identified SNVs and PD. Methods: We obtained genomic DNA from 766 patients, who were clinically diagnosed with PD, and 336 healthy controls, all of Japanese origin. All data were analyzed using Ion AmpliSeq panel sequences, with 29 PD- or dementia-associated genes in a single panel. We excluded any variants that did not comply with the Hardy-Weinberg equilibrium in the control group. Variant frequencies in the PD and control groups were compared using PLINK. The identified variants were confirmed to a frequency difference of P < 0.05, after applying the Benjamini-Hochberg procedure using Fisher's exact test. The pathogenicity and prevalence of each variant were estimated based on a public gene database. Results: We identified three rare variants that were significantly associated with PD: rs201012663/rs150500694 in SYNJ1 and rs372754391 in DJ-1, which are intronic variants, and rs7412 in ApoE, which is an exonic variant. The variants in SYNJ1 and ApoE were frequently identified in the control group, and rs201012663/rs150500694 in SYNJ1 may play a protective role against PD. The DJ-1 variant was frequently identified in the PD group, with a high odds ratio of 2.2. Conclusion: The detected variants may represent genetic modifiers or disease-related variants in PD. Targeted-gene-panel resequencing may represent a useful method for detecting disease-causing variants and genetic association studies in PD.

Small Substrate or Large? Debate Over the Mechanism of Glycation Adduct Repair by DJ-1

Glycation, the term for non-enzymatic covalent reactions between aldehyde metabolites and nucleophiles on biopolymers, results in deleterious cellular damage and diseases. Since Parkinsonism-associated protein DJ-1 was proposed as a novel deglycase that directly repairs glycated adducts, it has been considered a major contributor to glycation damage repair. Recently, an interesting debate over the mechanism of glycation repair by DJ-1 has emerged, focusing on whether the substrate of DJ-1 is glycated adducts or the free small aldehydes. The physiological significance of DJ-1 on glycation defense also remains in question. This debate is complicated by the fact that glycated biomolecular adducts are in rapid equilibrium with free aldehydes. Here, we summarize experimental evidence for the two possibilities, highlighting both consistencies and conflicts. We discuss the experimental complexities from a mechanistic perspective, and suggest classes of experiments that should help clarify this debate.

Association between a DJ-1 polymorphism and the risk of Parkinson's disease: a PRISMA-compliant systematic review and meta-analysis

Objective

In recent years, a number of case–control studies have focused on the association between the DJ-1 g.168_185del polymorphism and the risk of Parkinson's disease (PD). However, the results have been conflicting. To estimate the relationship between the DJ-1 g.168_185del polymorphism and PD susceptibility, a comprehensive meta-analysis was performed.

Methods

Eligible studies concerning the DJ-1 g.168_185del polymorphism and PD susceptibility were searched for in the PubMed, Web of Science, Embase, Wanfang, CNKI, and VIP databases. Odds ratios and 95% confidence intervals were calculated to estimate the strength of the associations. In total, 11 studies were included in this meta-analysis, including 13 case–control studies with 2890 cases and 3043 controls.

Results

This meta-analysis revealed that DJ-1 g.168_185del variants are associated with PD susceptibility in the non-Asian population, but not in the Asian population.

Conclusions

Our meta-analysis suggests that DJ-1 gene variants are not associated with the risk of PD in the overall population.

Role of DJ-1 in Immune and Inflammatory Diseases

The DJ-1 protein, known as an oxidative stress sensor, participates in the onset of oxidative stress-related diseases such as cancer, neurodegenerative disorders, type 2 diabetes, and male infertility. Although DJ-1 has been extensively studied for more than two decades, evidence has only recently emerged that it plays a key role in immune and inflammatory disorders. The immune regulatory function of DJ-1 is achieved by modulating the activation of several immune cells including macrophages, mast cells, and T cells via reactive oxygen species (ROS)-dependent and/or ROS-independent mechanisms. This review describes the current knowledge on DJ-1, focusing on its immune and inflammatory regulatory roles, and highlights the significance of DJ-1 as a novel therapeutic target for immune and inflammatory diseases.

Extreme Environmental Stress-Induced Biological Responses in the Planarian

Planarians are bilaterally symmetric metazoans of the phylum Platyhelminthes. They have well-defined anteroposterior and dorsoventral axes and have a highly structured true brain which consists of all neural cell types and neuropeptides found in a vertebrate. Planarian flatworms are famous for their strong regenerative ability; they can easily regenerate any part of the body including the complete neoformation of a functional brain within a few days and can survive a series of extreme environmental stress. Nowadays, they are an emerging model system in the field of developmental, regenerative, and stem cell biology and have offered lots of helpful information for these realms. In this review, we will summarize the response of planarians to some typical environmental stress and hope to shed light on basic mechanisms of how organisms interact with extreme environmental stress and survive it, such as altered gravity, temperature, and oxygen, and this information will help researchers improve the design in future studies.

Redox-dependent regulation of mitochondrial dynamics by DJ-1 paralogs in Saccharomyces cerevisiae

Mitochondria are indispensable organelles that perform critical cellular functions, including energy metabolism, neurotransmission, and synaptic maintenance. Mitochondrial dysfunction and impairment in the organellar homeostasis are key hallmarks implicated in the progression of neurodegenerative disorders. The members of DJ-1/ThiJ/PfpI family are highly conserved, and loss of DJ-1 (PARK7) function in humans results in the impairment of mitochondrial homeostasis, which is one of the key cellular etiology implicated in the progression of Parkinson's Disease. However, the underlying molecular mechanism involved in mitochondrial maintenance and other cellular processes by DJ-1 paralogs is poorly understood. By utilizing genetic approaches from S. cerevisiae, we uncovered intricate mechanisms associated with the mitochondrial phenotypic variations regulated by DJ-1 paralogs. The deletion of DJ-1 paralogs led to respiratory incompetence and the accumulation of enhanced functional mitochondrial mass. The lack of DJ-1 paralogs also displayed enriched mitochondrial interconnectivity due to upregulation in the fusion-mediating proteins, facilitated by the elevation in the basal cellular ROS and oxidized glutathione levels. Intriguingly, these mitochondrial phenotypes variations cause cell size abnormalities, partially suppressed by reestablishing redox balance and upregulation of fission protein levels. Besides, in the absence of DJ-1 paralogs, cells exhibited a significant delay in the cell-cycle progression in the G2/M phase, attributed to mitochondrial hyperfusion and partial DNA damage. Additionally, the aberrations in mitochondrial dynamics and cell-cycle induce cell death mediated by apoptosis. Taken together, our findings first-time provide evidence to show how DJ-1 family members regulate mitochondrial homeostasis and other intricate cellular processes, including cell cycle and apoptosis.

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Lack of DJ-1 members causes respiratory incompetence and elevated basal ROS levels.

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Enhanced ROS and GSSG levels promote increased mitochondrial mass and hyperfusion.

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Mitochondrial hyperfusion together with ROS-induced DNA damage cause G2/M arrest.

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Impairment in cell cycle progression triggers apoptotic cell death in yeast.

The pROS of Autophagy in Neuronal Health

Autophagy refers to a set of catabolic pathways that together facilitate degradation of superfluous, damaged and toxic cellular components. The most studied type of autophagy, called macroautophagy, involves membrane mobilisation, cargo engulfment and trafficking of the newly formed autophagic vesicle to the recycling organelle, the lysosome. Macroautophagy responds to a variety of intra- and extra-cellular stress conditions including, but not limited to, pathogen intrusion, oxygen or nutrient starvation, proteotoxic and organelle stress, and elevation of reactive oxygen species (ROS). ROS are highly reactive oxygen molecules that can interact with cellular macromolecules (proteins, lipids, nucleic acids) to either modify their activity or, when released in excess, inflict irreversible damage. Although increased ROS release has long been recognised for its involvement in macroautophagy activation, the underlying mechanisms and the wider impact of ROS-mediated macroautophagy stimulation remain incompletely understood.

We therefore discuss the growing body of evidence that describes the variety of mechanisms modulated by ROS that trigger cytoprotective detoxification via macroautophagy. We outline the role of ROS in signalling upstream of autophagy initiation, by increased gene expression and post-translational modifications of transcription factors, and in the formation and nucleation of autophagic vesicles by cysteine modification of conserved autophagy proteins including ATG4B, ATG7 and ATG3. Furthermore, we review the effect of ROS on selective forms of macroautophagy, specifically on cargo recognition by autophagy receptor proteins p62 and NBR1 (neighbour of BRCA1) and the recycling of mitochondria (mitophagy), and peroxisomes (pexophagy). Finally, we highlight both, the standalone and mutual contributions of abnormal ROS signalling and macroautophagy to the development and progression of neurodegenerative diseases.

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ROS are messengers that modify protein activity by PTMs.

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ROS-mediated PTMs regulate activity and specificity of autophagy proteins.

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Increase in autophagy mediates rapid clearance of oxidised cargo and ROS sources.

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The importance of ROS-mediated autophagy is highlighted in neurodegeneration.

DJ-1 can form β-sheet structured aggregates that co-localize with pathological amyloid deposits

The loss of native function of the DJ-1 protein has been linked to the development of Parkinson's (PD) and other neurodegenerative diseases. Here we show that DJ-1 aggregates into β-sheet structured soluble and fibrillar aggregates in vitro under physiological conditions and that this process is promoted by the oxidation of its catalytic Cys106 residue. This aggregation resulted in the loss of its native biochemical glyoxalase function and in addition oxidized DJ-1 aggregates were observed to localize within Lewy bodies, neurofibrillary tangles and amyloid plaques in human PD and Alzheimer's (AD) patients' post-mortem brain tissue. These findings suggest that the aggregation of DJ-1 may be a critical player in the development of the pathology of PD and AD and demonstrate that loss of DJ-1 function can happen through DJ-1 aggregation. This could then contribute to AD and PD disease onset and progression.