DJ-1 cleavage by matrix metalloproteinase 3 mediates oxidative stress-induced dopaminergic cell death

Unlocking the Potential of Low-Molecular-Weight (Poly)phenol Metabolites: Protectors at the Blood-Brain Barrier Frontier

Neurodegenerative diseases (NDDs) are an increasing group of chronic and progressive neurological disorders that ultimately lead to neuronal cell failure and death. Despite all efforts throughout decades, their burden on individuals and society still casts one of the most massive socioeconomic problems worldwide. The neuronal failure observed in NDDs results from an intricacy of events, mirroring disease complexity, ranging from protein aggregation, oxidative stress, (neuro)inflammation, and even blood-brain barrier (BBB) dysfunction, ultimately leading to cognitive and motor symptoms in patients. As a result of such complex pathobiology, to date, there are still no effective treatments to treat/halt NDDs progression. Fortunately, interest in the bioavailable low molecular weight (LMW) phenolic metabolites derived from the metabolism of dietary (poly)phenols has been rising due to their multitargeted potential in attenuating multiple NDDs hallmarks. Even if not highly BBB permeant, their relatively high concentrations in the bloodstream arising from the intake of (poly)phenol-rich diets make them ideal candidates to act within the vasculature and particularly at the level of BBB. In this review, we highlight the most recent - though still scarce - studies demonstrating LMW phenolic metabolites' ability to modulate BBB homeostasis, including the improvement of tight and adherens junctional proteins, as well as their power to decrease pro-inflammatory cytokine secretion and oxidative stress levels in vitro and in vivo. Specific BBB-permeant LMW phenolic metabolites, such as simple phenolic sulfates, have been emerging as strong BBB properties boosters, pleiotropic compounds capable of improving cell fitness under oxidative and pro-inflammatory conditions. Nevertheless, further studies should be pursued to obtain a holistic overview of the promising role of LMW phenolic metabolites in NDDs prevention and management to fully harness their true therapeutic potential.

The role of reactive oxygen species in the regulation of the blood-brain barrier

The blood-brain barrier (BBB) regulates the exchange of metabolites and cells between the blood and brain, and maintains central nervous system homeostasis. Various factors affect BBB barrier functions, including reactive oxygen species (ROS). ROS can act as stressors, damaging biological molecules, but they also serve as secondary messengers in intracellular signaling cascades during redox signaling. The impact of ROS on the BBB has been observed in multiple sclerosis, stroke, trauma, and other neurological disorders, making blocking ROS generation a promising therapeutic strategy for BBB dysfunction. However, it is important to consider ROS generation during normal BBB functioning for signaling purposes. This review summarizes data on proteins expressed by BBB cells that can be targets of redox signaling or oxidative stress. It also provides examples of signaling molecules whose impact may cause ROS generation in the BBB, as well as discusses the most common diseases associated with BBB dysfunction and excessive ROS generation, open questions that arise in the study of this problem, and possible ways to overcome them.

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.

Nuclear and Mitochondrial Genome, Epigenome and Gut Microbiome: Emerging Molecular Biomarkers for Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is currently the second most common neurodegenerative disorder, burdening about 10 million elderly individuals worldwide. The multifactorial nature of PD poses a difficult obstacle for understanding the mechanisms involved in its onset and progression. Currently, diagnosis depends on the appearance of clinical signs, some of which are shared among various neurologic disorders, hindering early diagnosis. There are no effective tools to prevent PD onset, detect the disease in early stages or accurately report the risk of disease progression. Hence, there is an increasing demand for biomarkers that may identify disease onset and progression, as treatment-based medicine may not be the best approach for PD. Over the last few decades, the search for molecular markers to predict susceptibility, aid in accurate diagnosis and evaluate the progress of PD have intensified, but strategies aimed to improve individualized patient care have not yet been established.

CONCLUSIONS

Genomic variation, regulation by epigenomic mechanisms, as well as the influence of the host gut microbiome seem to have a crucial role in the onset and progress of PD, thus are considered potential biomarkers. As such, the human nuclear and mitochondrial genome, epigenome, and the host gut microbiome might be the key elements to the rise of personalized medicine for PD patients.

Multifunctional Nanoprobe for the Delivery of Therapeutic siRNA and Real-Time Molecular Imaging of Parkinson's Disease Biomarkers

Parkinson's disease (PD) has been recently associated with the excessive expression of matrix metalloproteinase 3 (MMP3). One of the major challenges in treating PD is to effectively detect and inhibit the early MMP3 activities to relieve the neural stress and inflammation responses. Previously, numerous upconversion nanoparticle (UCNP)-based nanoprobes have been designed for the detection of biomarkers in neurodegenerative diseases. To further improve the performance of the conventional nanoprobes, we introduced novel reporting units and integrated the therapeutic reagents to fabricate a theragnostic platform for PD and other neurodegenerative diseases. Here, we designed a multifunctional UCNP/aggregation-induced emission luminogen (AIEgen)-based nanoprobe to effectively detect the time-lapse MMP3 activities in the inflammatory catecholaminergic SH-SY5Y cells and simultaneously deliver the MMP3-siRNA into the stressed catecholaminergic SH-SY5Y cells, inhibiting the MMP3-induced inflammatory neural responses. The unique features of our UCNP/AIEgen-based nanoprobe platform shed light on the development of a novel theragnostic probe for the early diagnosis and cure of neurodegenerative diseases.

DJ-1 (Park7) affects the gut microbiome, metabolites and the development of innate lymphoid cells (ILCs)

The proper communication between gut and brain is pivotal for the maintenance of health and, dysregulation of the gut-brain axis can lead to several clinical disorders. In Parkinson’s disease (PD) 85% of all patients experienced constipation many years before showing any signs of motor phenotypes. For differential diagnosis and preventive treatment, there is an urgent need for the identification of biomarkers indicating early disease stages long before the disease phenotype manifests. DJ-1 is a chaperone protein involved in the protection against PD and genetic mutations in this protein have been shown to cause familial PD. However, how the deficiency of DJ-1 influences the risk of PD remains incompletely understood. In the present study, we provide evidence that DJ-1 is implicated in shaping the gut microbiome including; their metabolite production, inflammation and innate immune cells (ILCs) development. We revealed that deficiency of DJ-1 leads to a significant increase in two specific genera/species, namely Alistipes and Rikenella. In DJ-1 knock-out (DJ-1^-/-) mice the production of fecal calprotectin and MCP-1 inflammatory proteins were elevated. Fecal and serum metabolic profile showed that malonate which influences the immune system was significantly more abundant in DJ-1^−/− mice. DJ-1 appeared also to be involved in ILCs development. Further, inflammatory genes related to PD were augmented in the midbrain of DJ-1^−/− mice. Our data suggest that metabolites and inflammation produced in the gut could be used as biomarkers for PD detection. Perhaps, these metabolites and inflammatory mediators could be involved in triggering inflammation resulting in PD pathology.

Oxidative Stress-Mediated Blood-Brain Barrier (BBB) Disruption in Neurological Diseases

The blood-brain barrier (BBB), as a crucial gate of brain-blood molecular exchange, is involved in the pathogenesis of multiple neurological diseases. Oxidative stress is caused by an imbalance between the production of reactive oxygen species (ROS) and the scavenger system. Since oxidative stress plays a significant role in the production and maintenance of the BBB, the cerebrovascular system is especially vulnerable to it. The pathways that initiate BBB dysfunction include, but are not limited to, mitochondrial dysfunction, excitotoxicity, iron metabolism, cytokines, pyroptosis, and necroptosis, all converging on the generation of ROS. Interestingly, ROS also provide common triggers that directly regulate BBB damage, parameters including tight junction (TJ) modifications, transporters, matrix metalloproteinase (MMP) activation, inflammatory responses, and autophagy. We will discuss the role of oxidative stress-mediated BBB disruption in neurological diseases, such as hemorrhagic stroke, ischemic stroke (IS), Alzheimer’s disease (AD), Parkinson’s disease (PD), traumatic brain injury (TBI), amyotrophic lateral sclerosis (ALS), and cerebral small vessel disease (CSVD). This review will also discuss the latest clinical evidence of potential biomarkers and antioxidant drugs towards oxidative stress in neurological diseases. A deeper understanding of how oxidative stress damages BBB may open up more therapeutic options for the treatment of neurological diseases.

Metalloproteinases and their tissue inhibitors in Alzheimer's disease and other neurodegenerative disorders

As life expectancy increases worldwide, age-related neurodegenerative diseases will increase in parallel. The lack of effective treatment strategies may soon lead to an unprecedented health, social and economic crisis. Any attempt to halt the progression of these diseases requires a thorough knowledge of the pathophysiological mechanisms involved to facilitate the identification of new targets and the application of innovative therapeutic strategies. The metzincin superfamily of metalloproteinases includes matrix metalloproteinases (MMP), a disintegrin and metalloproteinase (ADAM) and ADAM with thrombospondin motifs (ADAMTS). These multigenic and multifunctional proteinase families regulate the functions of an increasing number of signalling and scaffolding molecules involved in neuroinflammation, blood-brain barrier disruption, protein misfolding, synaptic dysfunction or neuronal death. Metalloproteinases and their physiological inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), are therefore, at the crossroads of molecular and cellular mechanisms that support neurodegenerative processes, and emerge as potential new therapeutic targets. We provide an overview of current knowledge on the role and regulation of metalloproteinases and TIMPs in four major neurodegenerative diseases: Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease.

The Role of NADPH Oxidases and Oxidative Stress in Neurodegenerative Disorders

For a number of years, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) was synonymous with NOX2/gp91^phox and was considered to be a peculiarity of professional phagocytic cells. Over the last decade, several more homologs have been identified and based on current research, the NOX family consists of NOX1, NOX2, NOX3, NOX4, NOX5, DUOX1 and DUOX2 enzymes. NOXs are electron transporting membrane proteins that are responsible for reactive oxygen species (ROS) generation-primarily superoxide anion (O₂^●-), although hydrogen peroxide (H₂O₂) can also be generated. Elevated ROS leads to oxidative stress (OS), which has been associated with a myriad of inflammatory and degenerative pathologies. Interestingly, OS is also the commonality in the pathophysiology of neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). NOX enzymes are expressed in neurons, glial cells and cerebrovascular endothelial cells. NOX-mediated OS is identified as one of the main causes of cerebrovascular damage in neurodegenerative diseases. In this review, we will discuss recent developments in our understanding of the mechanisms linking NOX activity, OS and neurodegenerative diseases, with particular focus on the neurovascular component of these conditions. We conclude highlighting current challenges and future opportunities to combat age-related neurodegenerative disorders by targeting NOXs.

SheddomeDB: the ectodomain shedding database for membrane-bound shed markers

BACKGROUND

A number of membrane-anchored proteins are known to be released from cell surface via ectodomain shedding. The cleavage and release of membrane proteins has been shown to modulate various cellular processes and disease pathologies. Numerous studies revealed that cell membrane molecules of diverse functional groups are subjected to proteolytic cleavage, and the released soluble form of proteins may modulate various signaling processes. Therefore, in addition to the secreted protein markers that undergo secretion through the secretory pathway, the shed membrane proteins may comprise an additional resource of noninvasive and accessible biomarkers. In this context, identifying the membrane-bound proteins that will be shed has become important in the discovery of clinically noninvasive biomarkers. Nevertheless, a data repository for biological and clinical researchers to review the shedding information, which is experimentally validated, for membrane-bound protein shed markers is still lacking.

RESULTS

In this study, the database SheddomeDB was developed to integrate publicly available data of the shed membrane proteins. A comprehensive literature survey was performed to collect the membrane proteins that were verified to be cleaved or released in the supernatant by immunological-based validation experiments. From 436 studies on shedding, 401 validated shed membrane proteins were included, among which 199 shed membrane proteins have not been annotated or validated yet by existing cleavage databases. SheddomeDB attempted to provide a comprehensive shedding report, including the regulation of shedding machinery and the related function or diseases involved in the shedding events. In addition, our published tool ShedP was embedded into SheddomeDB to support researchers for predicting the shedding event on unknown or unrecorded membrane proteins.

CONCLUSIONS

To the best of our knowledge, SheddomeDB is the first database for the identification of experimentally validated shed membrane proteins and currently may provide the most number of membrane proteins for reviewing the shedding information. The database included membrane-bound shed markers associated with numerous cellular processes and diseases, and some of these markers are potential novel markers because they are not annotated or validated yet in other databases. SheddomeDB may provide a useful resource for discovering membrane-bound shed markers. The interactive web of SheddomeDB is publicly available at http://bal.ym.edu.tw/SheddomeDB/ .

Marine pharmacology: therapeutic targeting of matrix metalloproteinases in neuroinflammation

Alterations in matrix metalloproteinase (MMP) expression and activity are recognized as key pathogenetic events in several neurological disorders. This evidence makes MMPs possible therapeutic targets. The search for substances that can inhibit MMPs is moving progressively toward the screening of natural products. In particular, marine bioprospecting could be promising for the discovery of marine natural products with anti-MMP activities. Despite recent advances in this field, the possibility of using marine MMP inhibitors (MMPIs) for the treatment of neuroinflammation is still under-investigated. Here, we review the latest findings in this promising research field and the potential that marine MMPIs can have in the management and treatment of various neurological diseases.

The multifaceted role of metalloproteinases in physiological and pathological conditions in embryonic and adult brains

Matrix metalloproteinases (MMPs) are a large family of ubiquitous extracellular endopeptidases, which play important roles in a variety of physiological and pathological conditions, from the embryonic stages throughout adult life. Their extraordinary physiological "success" is due to concomitant broad substrate specificities and strict regulation of their expression, activation and inhibition levels. In recent years, MMPs have gained increasing attention as significant effectors in various aspects of central nervous system (CNS) physiology. Most importantly, they have been recognized as main players in a variety of brain disorders having different etiologies and evolution. A common aspect of these pathologies is the development of acute or chronic neuroinflammation. MMPs play an integral part in determining the result of neuroinflammation, in some cases turning its beneficial outcome into a harmful one. This review summarizes the most relevant studies concerning the physiology of MMPs, highlighting their involvement in both the developing and mature CNS, in long-lasting and acute brain diseases and, finally, in nervous system repair. Recently, a concerted effort has been made in identifying therapeutic strategies for major brain diseases by targeting MMP activities. However, from this revision of the literature appears clear that MMPs have multifaceted functional characteristics, which modulate physiological processes in multiple ways and with multiple consequences. Therefore, when choosing MMPs as possible targets, great care must be taken to evaluate the delicate balance between their activation and inhibition and to determine at which stage of the disease and at what level they become active in order maximize chances of success.

Matrix metalloproteinase-3 causes dopaminergic neuronal death through Nox1-regenerated oxidative stress

In the present study we investigated the interplay between matrix metalloproteinase 3 (MMP3) and NADPH oxidase 1 (Nox1) in the process of dopamine (DA) neuronal death. We found that MMP3 activation causes the induction of Nox1 via mitochondrial reactive oxygen species (ROS) production and subsequently Rac1 activation, eventually leading to Nox1-derived superoxide generation in a rat DA neuronal N27 cells exposed to 6-OHDA. While a MMP3 inhibitor, NNGH, largely attenuated mitochondrial ROS and subsequent Nox1 induction, both apocynin, a putative Nox inhibitor and GKT137831, a Nox1 selective inhibitor failed to reduce 6-OHDA-induced mitochondrial ROS. However, both inhibitors for MMP3 and Nox1 similarly attenuated 6-OHDA-induced N27 cell death. RNAi-mediated selective inhibition of MMP3 or Nox1 showed that knockdown of either MMP3 or Nox1 significantly reduced 6-OHDA-induced ROS generation in N27 cells. While 6-OHDA-induced Nox1 was abolished by MMP3 knockdown, Nox1 knockdown did not alter MMP3 expression. Direct overexpression of autoactivated MMP3 (actMMP3) in N27 cells or in rat substantia nigra (SN) increased expression of Nox1. Selective knockdown of Nox1 in the SN achieved by adeno-associated virus-mediated overexpression of Nox1-specific shRNA largely attenuated the actMMP3-mediated dopaminergic neuronal loss. Furthermore, Nox1 expression was significantly attenuated in Mmp3 null mice treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Together we established novel molecular mechanisms underlying oxidative stress-mediated dopaminergic neuronal death in which MMP3 activation is a key upstream event that leads to mitochondrial ROS, Nox1 induction and eventual dopaminergic neuronal death. Our findings may lead to the development of novel therapeutic approach.

Caspase-9 activation and Apaf-1 cleavage by MMP-3

We have previously demonstrated that matrix metalloprotease-3 (MMP-3) can act inside the cell to trigger apoptosis in response to various cell stresses in dopaminergic neuronal cells. However, the mechanism by which MMP-3 activity leads to caspase-3 activation in apoptotic signaling was not known. In the present study, we found that MMP-3 acts upstream of caspase-9. Overexpression of wild type MMP-3, but not mutant MMP-3, generated the enzymatically active 35kD caspase-9. The caspase-9 activation was absent in MMP-3 knockout cells, but was present when these cells were transfected with wild type MMP-3 cDNA. It was elevated in cells that were under a MMP-3-inducing ER stress condition, and this was attenuated by pharmacologic inhibition and gene knockdown of MMP-3. Incubation of recombinant catalytic domain of MMP-3 (cMMP-3) with procaspase-9 was not sufficient to cause caspase-9 activation, and an additional cytosolic factor was required. cMMP-3 was found to bind to the cytosolic protein Apaf-1, as determined by changes in surface plasmon resonance, and to cleave Apaf-1. Pharmacological inhibition, knockout, and knockdown of MMP-3 attenuated the cleavage. Taken together, the present study demonstrates that MMP-3 leads to caspase-9 activation and suggests that this occurs indirectly via a cytosolic protein, possibly involving Apaf-1.

Matrix metalloproteinases, new insights into the understanding of neurodegenerative disorders

Matrix metalloproteinases (MMPs) are a subfamily of zinc-dependent proteases that are responsible for degradation and remodeling of extracellular matrix proteins. The activity of MMPs is tightly regulated at several levels including cleavage of prodomain, allosteric activation, compartmentalization and complex formation with tissue inhibitor of metalloproteinases (TIMPs). In the central nervous system (CNS), MMPs play a wide variety of roles ranging from brain development, synaptic plasticity and repair after injury to the pathogenesis of various brain disorders. Following general discussion on the domain structure and the regulation of activity of MMPs, we emphasize their implication in various brain disorder conditions such as Alzheimer’s disease, multiple sclerosis, ischemia/reperfusion and Parkinson’s disease. We further highlight accumulating evidence that MMPs might be the culprit in Parkinson’s disease (PD). Among them, MMP-3 appears to be involved in a range of pathogenesis processes in PD including neuroinflammation, apoptosis and degradation of α-synuclein and DJ-1. MMP inhibitors could represent potential novel therapeutic strategies for treatments of neurodegenerative diseases.

Intracerebral administration of ultrasound-induced dissolution of lipid-coated GDNF microbubbles provides neuroprotection in a rat model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of dopaminergic neurons in the substantia nigra. Neurotrophic factors, such as glial cell derived neurotrophic factor (GDNF), have been shown to provide a neuroprotective effect in PD rats. We have previously reported that ultrasound-induced lipid-coated GDNF microspheres, which release GDNF in a sustained manner after low frequency ultrasound stimulation, can reduce hypoxic-ischemic injury in neonatal rats. In the present study, we investigated whether lipid-coated GDNF microspheres can provide a neuroprotective effect in a rat model of PD. After a rat model of PD was produced by 6-hydroxydompamine (6-OHDA) injections, lipid-coated GDNF microspheres (1.5mg/kg) were injected into the striatum of PD rats. We found that GDNF levels were increased in the striatum of PD rats after lipid-coated GDNF microspheres administration following low frequency ultrasound stimulation (20kHz, 5min per day, daily for 4 weeks). Moreover, GDNF microspheres reduced apomorphine-induced rotations, and increased striatal dopamine and nigral tyrosine hydroxylase (TH) levels in PD rats. Additionally, GDNF microspheres reduced caspase-3, tumor necrosis factor-alpha, matrix metalloproteinase 9 (MMP-9) and OX-6 levels induced by 6-OHDA injections in PD rats. These data indicated that lipid-coated GDNF microspheres can provide a neuroprotective effect in PD rats.

Matrix metalloproteinase-3 in the central nervous system: a look on the bright side

Matrix metalloproteinases (MMPs) are a large family of proteases involved in many cell-matrix and cell-cell signalling processes through activation, inactivation or release of extracellular matrix (ECM) and non-ECM molecules, such as growth factors and receptors. Uncontrolled MMP activities underlie the pathophysiology of many disorders. Also matrix metalloproteinase-3 (MMP-3) or stromelysin-1 contributes to several pathologies, such as cancer, asthma and rheumatoid arthritis, and has also been associated with neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and multiple sclerosis. However, based on defined MMP spatiotemporal expression patterns, the identification of novel candidate molecular targets and in vitro and in vivo studies, a beneficial role for MMPs in CNS physiology and recovery is emerging. The main purpose of this review is to shed light on the recently identified roles of MMP-3 in normal brain development and in plasticity and regeneration after CNS injury and disease. As such, MMP-3 is correlated with neuronal migration and neurite outgrowth and guidance in the developing CNS and contributes to synaptic plasticity and learning in the adult CNS. Moreover, a strict spatiotemporal MMP-3 up-regulation in the injured or diseased CNS might support remyelination and neuroprotection, as well as genesis and migration of stem cells in the damaged brain.

α-Synuclein and protein degradation systems: a reciprocal relationship

An increasing wealth of data indicates a close relationship between the presynaptic protein alpha-synuclein and Parkinson's disease (PD) pathogenesis. Alpha-synuclein protein levels are considered as a major determinant of its neurotoxic potential, whereas secreted extracellular alpha-synuclein has emerged as an additional important factor in this regard. However, the manner of alpha-synuclein degradation in neurons remains contentious. Both the ubiquitin-proteasome system (UPS) and the autophagy-lysosome pathway (ALP)-mainly macroautophagy and chaperone-mediated autophagy-have been suggested to contribute to alpha-synuclein turnover. Additionally, other proteases such as calpains, neurosin, and metalloproteinases have been also proposed to have a role in intracellular and extracellular alpha-synuclein processing. Both UPS and ALP activity decline with aging and such decline may play a pivotal role in many neurodegenerative conditions. Alterations in these major proteolytic pathways may result in alpha-synuclein accumulation due to impaired clearance. Conversely, increased alpha-synuclein protein burden promotes the generation of aberrant species that may impair further UPS or ALP function, generating thus a bidirectional positive feedback loop leading to neuronal death. In the current review, we summarize the recent findings related to alpha-synuclein degradation, as well as to alpha-synuclein-mediated aberrant effects on protein degradation systems. Identifying the factors that regulate alpha-synuclein association to cellular proteolytic pathways may represent potential targets for therapeutic interventions in PD and related synucleinopathies.

The caspase 6 derived N-terminal fragment of DJ-1 promotes apoptosis via increased ROS production

In pathological conditions, the amount of DJ-1 determines whether a cell can survive or engage a cell death program. This is exemplified in epithelial cancers, in which DJ-1 expression is increased, while autosomal recessive early onset Parkinson's disease mutations of DJ-1 generally lead to decreased stability and expression of the protein. We have shown previously that DJ-1 is cleaved by caspase-6 during induction of apoptosis. We demonstrate here that the N-terminal cleaved fragment of DJ-1 (DJ-1 Nt) is specifically expressed in the nucleus and promotes apoptosis in SH-SY5Y neuroblastoma cell lines. In addition, overexpression of DJ-1 Nt in different cell lines leads to a loss of clonogenic potential and sensitizes to staurosporin and 1-methyl-4-phenylpyridinium (MPP+)-mediated caspase activation and apoptosis. Importantly, inhibition of endogenous DJ-1 expression with sh-RNA or DJ-1 deficiency mimics the effect of DJ-1 Nt on cell growth and apoptosis. Moreover, overexpression of DJ-1 Nt increases reactive oxygen species (ROS) production, and sensitizes to MPP+-mediated apoptosis and DJ-1 oxidation. Finally, specific exclusion of DJ-1 Nt from the nucleus abrogates its pro-apoptotic effect. Taken together, our findings identify an original pathway by which generation of a nuclear fragment of DJ-1 through caspase 6-mediated cleavage induces ROS-dependent amplification of apoptosis.

Matrix metalloproteinase-3 is activated by HtrA2/Omi in dopaminergic cells: relevance to Parkinson's disease

Dopaminergic neurons in the substantia nigra are particularly vulnerable, and their degeneration leads to Parkinson's disease. We have previously reported that matrix metalloproteinase-3 (MMP-3) activity is involved in dopaminergic neurodegeneration by multiple mechanisms and that this requires activation of MMP-3 from proMMP-3 by an intracellular serine protease. HtrA2/Omi is a mitochondrial serine protease that has been shown in non-dopaminergic cells to translocate into the cytosol where it triggers apoptosis. In the present study we sought to determine whether HtrA2/Omi might cause activation of MMP-3 in dopaminergic neuronal cells using CATH.a cell line. Mitochondrial stress induced by rotenone led to MMP-3 activation and HtrA2/Omi translocation into the cytosol. The MMP-3 activation involved HtrA2/Omi, because both pharmacological inhibition and siRNA-induced knockdown of HtrA2/Omi attenuated the activation induced by rotenone or MPP+. Overexpression of mature HtrA2/Omi, but not mutant HtrA2/Omi, resulted in MMP-3 activity increase and cell death. Addition of recombinant and catalytically active HtrA2/Omi to lysate of untreated cells led to activation of the endogenous MMP-3, and incubation of the HtrA2/Omi with recombinant proMMP-3 caused cleavage of proMMP-3 to a 48kD protein, corresponding to the active form, which was accompanied by an increase in MMP-3 activity. Taken together, the data indicate that HtrA2/Omi, which normally exists in the mitochondria, can cause MMP-3 activation in the cytosol under a cell stress condition, which can ultimately lead to demise of dopaminergic neuronal cells.

Selective vulnerability of rat brain regions to unconjugated bilirubin

Hippocampus is one of the brain regions most vulnerable to unconjugated bilirubin (UCB) encephalopathy, although cerebellum also shows selective yellow staining in kernicterus. We previously demonstrated that UCB induces oxidative stress in cortical neurons, disruption of neuronal network dynamics, either in developing cortical or hippocampal neurons, and that immature cortical neurons are more prone to UCB-induced injury. Here, we studied if immature rat neurons isolated from cortex, cerebellum and hippocampus present distinct features of oxidative stress and cell dysfunction upon UCB exposure. We also explored whether oxidative damage and its regulation contribute to neuronal dysfunction induced by hyperbilirubinemia, considering neurite extension and ramification, as well as cell death. Our results show that UCB induces nitric oxide synthase expression, as well as production of nitrites and cyclic guanosine monophosphate in immature neurons, mainly in those from hippocampus. After exposure to UCB, hippocampal neurons presented the highest content of reactive oxygen species, disruption of glutathione redox status and cell death, when compared to neurons from cortex or cerebellum. In particular, the results indicate that cells exposed to UCB undertake an adaptive response that involves DJ-1, a multifunctional neuroprotective protein implicated in the maintenance of cellular oxidation status. However, longer neuronal exposure to UCB caused down-regulation of DJ-1 expression, especially in hippocampal neurons. In addition, a greater impairment in neurite outgrowth and branching following UCB treatment was also noticed in immature neurons from hippocampus. Interestingly, pre-incubation with N-acetylcysteine, a precursor of glutathione synthesis, protected neurons from UCB-induced oxidative stress and necrotic cell death, preventing DJ-1 down-regulation and neuritic impairment. Taken together, these data point to oxidative injury and disruption of neuritic network as hallmarks in hippocampal susceptibility to UCB. Most importantly, they also suggest that local differences in glutathione content may account to the different susceptibility between brain regions exposed to UCB.

Biomarker discovery and proteomic evaluation of cadmium toxicity on a collembolan species, Paronychiurus kimi (Lee)

The goal of this study was to identify promising new biomarkers of cadmium by identifying differentially expressed proteins in Paronychiurus kimi after exposure to cadmium. Through proteomic analysis of P. kimi using 1-D PAGE and nano-LC-MS/MS, 36 downregulated proteins and 40 upregulated proteins were found. Some of the downregulated and upregulated proteins were verified by LC-MS/MS analysis after 2-D PAGE. Downregulated proteins in response to cadmium exposure were involved in glycolysis and energy metabolism, chaperones, transcription, reproduction, and neuron growth. In contrast, proteins involved in glycolysis and energy production, neurogenesis, defense systems response to bacteria, and protein biosynthesis were upregulated in cadmium-treated collembolans. Cubulin may be a potential biomarker for the detection of cadmium in P. kimi since this biomarker was able to low levels (3.5 mg/kg) of cadmium. The 14-3-3 ζ was also found to be a potential biomarker for the detection of medium levels (14 mg/kg) of cadmium. Collembolans may be an alternative tool to humans because many collembolans proteins show a high homology to human proteins.

Role of matrix metalloproteinase 3-mediated alpha-synuclein cleavage in dopaminergic cell death

Evidence suggests that the C-terminal truncation of α-synuclein is equally important as aggregation of α-synuclein in Parkinson disease (PD). Our previous results showed that an endopeptidase, matrix metalloproteinase-3 (MMP3), was induced and activated in dopaminergic (DA) cells upon stress conditions. Here, we report that MMP3 cleaved α-synuclein in vitro and in vivo and that α-synuclein and MMP3 were co-localized in Lewy bodies (LB) in the postmortem brains of PD patients. Incubation of α-synuclein with the catalytic domain of MMP3 (cMMP3) resulted in generation of several peptides, and the peptide profiles of WT α-synuclein (WTsyn) and A53T mutant (A53Tsyn) were different. Combined analysis using mass spectrometry and N-terminal determination revealed that MMP3 generated C-terminally truncated peptides of amino acids 1-78, 1-91, and 1-93 and that A53Tsyn produced significantly higher quantities of these peptides. Similar sizes of peptides were detected in N27 DA cells under oxidative stress and RNA interference to knock down MMP3-attenuated peptide generation. Co-overexpression of cMMP3 with either WTsyn or A53Tsyn led to a reduction in Triton X-100-insoluble aggregates and an increase in protofibril-like small aggregates. In addition, overexpression of the 1-93-amino acid peptide in the substantia nigra led to DA neuronal loss without LB-like aggregate formation. The results strongly indicate that MMP3 digestion of α-synuclein in DA neurons plays a pivotal role in the progression of PD through modulation of α-synuclein in aggregation, LB formation, and neurotoxicity.

Role of matrix metalloproteinase-3 in neurodegeneration

Matrix metalloproteinase-3 (MMP-3) is a member of the class of zinc-dependent proteases known to degrade the extracellular matrix. MMP-3 activity is regulated at three different levels: gene expression, proteolytic activation of the zymogen, and inhibition by the endogenous tissue inhibitors of metalloproteinase. A line of evidence indicates a role of MMP-3 in neurodegeneration. In neuronal cells, MMP-3 expression is increased in response to cell stress, and the cleaved, active MMP-3 participates in apoptotic signaling. In the extracellular space, MMP-3 triggers microglia to produce proinflammatory and cytotoxic molecules as well as MMP-3, which in turn contribute to neuronal damage. MMP-3 is increased in various experimental models of Parkinson's disease that are produced by selective toxins and by inflammagen, and the neuronal death is attenuated by various ways that inhibit MMP-3. α-Synuclein, whose gene mutations are associated with familial forms of Parkinson's disease, is proteolyzed by MMP-3. Contribution of MMP-3 toward the pathogenesis of Alzheimer's disease and other neurodegenerative diseases has also been suggested. Thus, modulation of MMP-3 expression and/or activity could be of therapeutic value for neurodegenerative diseases.