Involvement of c-Abl Kinase in Microglial Activation of NLRP3 Inflammasome and Impairment in Autolysosomal System

Pharmaceutical-mediated neuroimmune modulation in psychiatric/psychological adverse events

The therapeutic use of many pharmaceuticals, including small molecules and biological therapies, has been associated with the onset of psychiatric and psychological adverse events (PPAEs), posing substantial concerns to patients' health and safety. These events, which encompass mood (e.g., depression, schizophrenia, suicidal ideation) and cognitive changes (e.g., learning and memory impairment, dementia) often remain undetected until advanced stages of clinical trials or pharmacovigilance, mostly because the mechanisms underlying the onset of PPAEs remain poorly understood. In recent years, the role of neuroimmune modulation (comprising an intricate interplay between various cell types and signaling pathways) in PPAEs has garnered substantial interest. Indeed, understanding these complex interactions would substantially contribute to increase the ability to predict the potential onset of PPAEs during preclinical stages of a new drug's R&D. This review provides a comprehensive summary of the most recent advances in neuroimmune modulation-related mechanisms contributing to the onset of PPAEs and their association with specific pharmaceuticals. Reported data strongly support an association between neuroimmune modulation and the onset of PPAEs. Pharmaceuticals may target specific molecular pathways and pathway elements (e.g., cholinergic and serotonergic systems), which in turn may directly or indirectly impact the inflammatory status and the homeostasis of the brain, regulating inflammation and neuronal function. Also, modulation of the peripheral immune system by pharmaceuticals that do not permeate the blood-brain barrier (e.g., monoclonal antibodies) may alter the neuroimmunomodulatory status of the brain, leading to PPAEs. In summary, this review underscores the diverse pathways through which drugs can influence brain inflammation, shedding light on potential targeted interventions.

An update on novel and emerging therapeutic targets in Parkinson's disease

Parkinson's Disease (PD) remains a significant focus of extensive research aimed at developing effective therapeutic strategies. Current treatments primarily target symptom management, with limited success in altering the course of the disease. This shortfall underscores the urgent need for novel therapeutic approaches that can modify the progression of PD.This review concentrates on emerging therapeutic targets poised to address the underlying mechanisms of PD. Highlighted novel and emerging targets include Protein Abelson, Rabphilin-3 A, Colony Stimulating Factor 1-Receptor, and Apelin, each showing promising potential in preclinical and clinical settings for their ability to modulate disease progression. By examining recent advancements and outcomes from trials focusing on these targets, the review aims to elucidate their efficacy and potential as disease-modifying therapies.Furthermore, the review explores the concept of multi-target approaches, emphasizing their relevance in tackling the complex pathology of PD. By providing comprehensive insights into these novel targets and their therapeutic implications, this review aims to guide future research directions and clinical developments toward more effective treatments for PD and related neurodegenerative disorders.

Intravenous Injection of Na Ions Aggravates Ang II-Induced Hypertension-Related Vascular Endothelial Injury by Increasing Transmembrane Osmotic Pressure

Introduction

Extracellular protein nanoparticles (PNs) and ions perform synergistical functions in the control of transmembrane osmotic pressure (OP) under isotonic conditions. Intravenous injection may disrupt the ion balance and alter PN levels in blood plasma, changing transmembrane OP and damaging vascular endothelial cells.

Methods

Na ions were injected into AngII-induced HUVECs to simulate cell injury in vitro, and tail vein infusion of Na ions into hypertensive rats was performed to assess vascular damage. Optical measurements using an intermediate filament (IF) tension probe were conducted to detect indicators related to transmembrane OP. Immunofluorescence, Western blotting and small interfering RNA (siRNA) transfection were employed to investigate inflammasomes and the relationship between Abl2 and inflammation.

Results

Electrolyte injections with sodium ions (but not glucose and hydroxyethyl starch) induced the production of ASC and NLRP3 inflammasomes in Ang II-induced HUVECs; this in turn resulted in the disorder of calcium signals, and changes in transmembrane OP and cell permeability. Moreover, injection of Na ions into Ang II-induced HUVECs activated the mechanosensitive protein Abl2, involved in inflammation-induced transmembrane OP changes. A drug combination was identified that could induce OP recovery and block hyperpermeability induced by cytoplasmic inflammatory corpuscles in vivo and in vitro.

Conclusion

Changes in extracellular PNs and ions following chemical stimuli (Ang II) participate in the regulation of transmembrane OP. Furthermore, injection of Na ions causes vascular endothelial injury in Ang II-induced cells in vitro and hypertension rats in vivo, suggesting it is not safe for hypertensive patients, and we propose a new drug combination as a solution.

Biotin rescues manganese-induced Parkinson's disease phenotypes and neurotoxicity

Occupational exposure to manganese (Mn) induces manganism and has been widely linked as a contributing environmental factor to Parkinson's disease (PD), featuring dramatic signature overlaps between the two in motor symptoms and clinical hallmarks. However, the molecular mechanism underlying such link remains elusive, and for combating PD, effective mechanism-based therapies are lacking. Here, we developed an adult Drosophila model of Mn toxicity to recapitulate key parkinsonian features, spanning behavioral deficits, neuronal loss, and dysfunctions in lysosome and mitochondria. We performed global metabolomics on flies at an early stage of toxicity and identified metabolism of the B vitamin, biotin (vitamin B 7 ), as a master pathway underpinning Mn toxicity with systemic, body-brain increases in Mn-treated groups compared to the controls. Using Btnd RNAi mutant flies, we show that biotin depletion exacerbates Mn-induced neurotoxicity, parkinsonism, and mitochondrial dysfunction; while in Mn-exposed wild-type flies, biotin feeding dramatically ameliorates these pathophenotypes. We further show in human induced stem cells (iPSCs)- differentiated midbrain dopaminergic neurons that the supplemented biotin protects against Mn-induced neuronal loss, cytotoxicity, and mitochondrial dysregulation. Finally, human data profiling biotin-related proteins show for PD cases elevated circulating levels of biotin transporters but not of metabolic enzymes compared to healthy controls, suggesting humoral biotin transport as a key event involved in PD. Taken together, our findings identified compensatory biotin pathway as a convergent, systemic driver of Mn toxicity and parkinsonian pathology, providing new basis for devising effective countermeasures against manganism and PD.

Significance Statement

Environmental exposure to manganese (Mn) may increase the risk for Parkinson's disease (PD); however, the mechanistic basis linking the two remains unclear. Our adult fruit fly ( Drosophila ) model of Mn toxicity recapitulated key Parkinson's hallmarks in vivo spanning behavioral deficits, neuronal loss, and mitochondrial dysfunction. Metabolomics identified the biotin (vitamin B 7 ) pathway as a key mediator, featuring systemic biotin increases in the flies. Rescue trials leveraging biotin-deficient flies, wild-type flies, and human iPSC-derived dopaminergic neurons determined biotin as a driver of manganism, with the parkinsonian phenotypes dramatically reversed through biotin supplementation. Our findings, in line with overexpressed circulating biotin transporters observed in PD patients, suggest compensatory biotin pathway as a key to untangle the Mn-PD link for combating neurodegenerative disease.

Development of 18F-Labeled PET Tracer Candidates for Imaging of the Abelson Non-receptor Tyrosine Kinase in Parkinson's Disease

Activated Abelson non-receptor tyrosine kinase (c-Abl) plays a harmful role in neurodegenerative conditions such as Parkinson's disease (PD). Inhibition of c-Abl is reported to have a neuroprotective effect and be a promising therapeutic strategy for PD. We have previously identified a series of benzo[d]thiazole derivatives as selective c-Abl inhibitors from which one compound showed high therapeutic potential. Herein, we report the development of a complementary positron emission tomography (PET) tracer. In total, three PET tracer candidates were developed and eventually radiolabeled with fluorine-18 for in vivo evaluation studies in mice. Candidate [18F]3 was identified as the most promising compound, since it showed sufficient brain uptake, good washout kinetics, and satisfactory metabolic stability. In conclusion, we believe this tracer provides a good starting point to further validate and explore c-Abl as a target for therapeutic strategies against PD supported by PET.

Imatinib Attenuates Pentylenetetrazole Kindled and Pilocarpine Induced Recurrent Spontaneous Seizures in Mice

c-Abl is a non-receptor tyrosine kinase that promotes intracellular apoptotic signaling in prolonged epileptic seizures. PTZ and pilocarpine-induced continuous epileptic convulsions cause neuronal death and gliosis. C-Abl is linked to oxidative stress, neuronal hyperexcitability, mitochondrial malfunction, and subsequent seizures. We investigated the involvement of c-Abl in epileptogenesis by employing its selective inhibitor Imatinib (1 & 3 mg/kg; i.p.) together with conventional medication valproate (110 mg/kg; i.p.) tends to be effective in decreasing seizures threshold provoked by PTZ for 15 days and pilocarpine for 37 days. Further, Imatinib was effective in preventing epileptic seizures arbitrated oxidative stress injury. Oxidative stress has been linked to excitotoxicity that is considered to pathogenic factor in epileptic brain damage. As ELIZA and biochemical estimations showed the high level of c-Abl as an indicator of neuronal oxidative and apoptosis under chronic PTZ & pilocarpine epileptic seizures marked by decreased antioxidants and elevated levels of caspase-3 that were successfully prevented with Imatinib treatment same as valproate (standard drug). Further, the aberrant c-Abl activation is also linked with neuroinflammation that is also predisposing factor in the development of seizures. Selective inhibition of c-Abl by Imatinib also showed anti-inflammatory activity marked with suppressed levels of NF-kB and pro-inflammatory mediators (TNF-alpha, IL-1β, and IL-6) suggesting the neuroprotective effect of Imatinib same as valproate (standard drug) in epilepsy. Therefore, the current study provides preclinical evidence of Imatinib as a potential treatment for seizures, as well as an understanding of potential role of c-Ablin epilepsy.

FDA-Approved Kinase Inhibitors in Preclinical and Clinical Trials for Neurological Disorders

Cancers and neurological disorders are two major types of diseases. We previously developed a new concept termed "Aberrant Cell Cycle Diseases" (ACCD), revealing that these two diseases share a common mechanism of aberrant cell cycle re-entry. The aberrant cell cycle re-entry is manifested as kinase/oncogene activation and tumor suppressor inactivation, which are hallmarks of both tumor growth in cancers and neuronal death in neurological disorders. Therefore, some cancer therapies (e.g., kinase inhibition, tumor suppressor elevation) can be leveraged for neurological treatments. The United States Food and Drug Administration (US FDA) has so far approved 74 kinase inhibitors, with numerous other kinase inhibitors in clinical trials, mostly for the treatment of cancers. In contrast, there are dire unmet needs of FDA-approved drugs for neurological treatments, such as Alzheimer's disease (AD), intracerebral hemorrhage (ICH), ischemic stroke (IS), traumatic brain injury (TBI), and others. In this review, we list these 74 FDA-approved kinase-targeted drugs and identify those that have been reported in preclinical and/or clinical trials for neurological disorders, with a purpose of discussing the feasibility and applicability of leveraging these cancer drugs (FDA-approved kinase inhibitors) for neurological treatments.

Impact of Environmental Risk Factors on Mitochondrial Dysfunction, Neuroinflammation, Protein Misfolding, and Oxidative Stress in the Etiopathogenesis of Parkinson's Disease

As a prevalent progressive neurodegenerative disorder, Parkinson's disease (PD) is characterized by the neuropathological hallmark of the loss of nigrostriatal dopaminergic (DAergic) innervation and the appearance of Lewy bodies with aggregated α-synuclein. Although several familial forms of PD have been reported to be associated with several gene variants, most cases in nature are sporadic, triggered by a complex interplay of genetic and environmental risk factors. Numerous epidemiological studies during the past two decades have shown positive associations between PD and several environmental factors, including exposure to neurotoxic pesticides/herbicides and heavy metals as well as traumatic brain injury. Other environmental factors that have been implicated as potential risk factors for PD include industrial chemicals, wood pulp mills, farming, well-water consumption, and rural residence. In this review, we summarize the environmental toxicology of PD with the focus on the elaboration of chemical toxicity and the underlying pathogenic mechanisms associated with exposure to several neurotoxic chemicals, specifically 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat (PQ), dichloro-diphenyl-trichloroethane (DDT), dieldrin, manganese (Mn), and vanadium (V). Our overview of the current findings from cellular, animal, and human studies of PD provides information for possible intervention strategies aimed at halting the initiation and exacerbation of environmentally linked PD.

Microglial ion channels: Key players in non-cell autonomous neurodegeneration

Neuroinflammation is a critical pathophysiological hallmark of neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and traumatic brain injury (TBI). Microglia, the first responders of the brain, are the drivers of this neuroinflammation. Microglial activation, leading to induction of pro-inflammatory factors, like Interleukin 1-β (IL-1β), Tumor necrosis factor-α (TNFα), nitrites, and others, have been shown to induce neurodegeneration. Non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the risk of developing PD, but the mechanism underlying the microglial activation is still under active research. Recently, microglial ion channels have come to the forefront as potential drug targets in multiple neurodegenerative disorders, including AD and PD. Microglia expresses a variety of ion channels, including potassium channels, calcium channels, chloride channels, sodium channels, and proton channels. The diversity of channels present on microglia is responsible for the dynamic nature of these immune cells of the brain. These ion channels regulate microglial proliferation, chemotaxis, phagocytosis, antigen recognition and presentation, apoptosis, and cell signaling leading to inflammation, among other critical functions. Understanding the role of these ion channels and the signaling mechanism these channels regulate under pathological conditions is an active area of research. This review will be focusing on the roles of different microglial ion channels, and their potential role in regulating microglial functions in neurodegenerative disorders.

Enhancing autophagy in Alzheimer's disease through drug repositioning

Alzheimer's disease (AD) is one of the biggest human health threats due to increases in aging of the global population. Unfortunately, drugs for treating AD have been largely ineffective. Interestingly, downregulation of macroautophagy (autophagy) plays an essential role in AD pathogenesis. Therefore, targeting autophagy has drawn considerable attention as a therapeutic approach for the treatment of AD. However, developing new therapeutics is time-consuming and requires huge investments. One of the strategies currently under consideration for many diseases is "drug repositioning" or "drug repurposing". In this comprehensive review, we have provided an overview of the impact of autophagy on AD pathophysiology, reviewed the therapeutics that upregulate autophagy and are currently used in the treatment of other diseases, including cancers, and evaluated their repurposing as a possible treatment option for AD. In addition, we discussed the potential of applying nano-drug delivery to neurodegenerative diseases, such as AD, to overcome the challenge of crossing the blood brain barrier and specifically target molecules/pathways of interest with minimal side effects.

Inflammasome Signaling in the Aging Brain and Age-Related Neurodegenerative Diseases

Inflammasomes are intracellular protein complexes, members of the innate immune system, and their activation and regulation play an essential role in maintaining homeostatic conditions against exogenous and endogenous stimuli. Inflammasomes occur as cytosolic proteins and assemble into a complex during the recognition of pathogen-associated or danger-associated molecular patterns by pattern-recognition receptors in host cells. The formation of the inflammasome complex elicits signaling molecules of proinflammatory cytokines such as interleukin-1β and interleukin 18 via activation of caspase-1 in the canonical inflammasome pathway whereas caspase-11 in the case of a mouse and caspase-4 and caspase-5 in the case of humans in the non-canonical inflammasome pathway, resulting in pyroptotic or inflammatory cell death which ultimately leads to neuroinflammation and neurodegenerative diseases. Inflammasome activation, particularly in microglial cells and macrophages, has been linked to aging as well as age-related neurodegenerative diseases. The accumulation of abnormal/ misfolded proteins acts as a ligand for inflammasome activation in neurodegenerative diseases. Although recent studies have revealed the inflammasomes' functionality in both in vitro and in vivo models, many inflammasome signaling cascade activations during biological aging, neuroinflammation, and neurodegeneration are still ambiguous. In this review, we comprehensively unveil the cellular and molecular mechanisms of inflammasome activation during neuronal aging and age-related neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, prion disease, and amyotrophic lateral sclerosis.

Roles for c-Abl in postoperative neurodegeneration

The nonreceptor tyrosine kinase c-Abl is inactive under normal conditions. Upon activation, c-Abl regulates signaling pathways related to cytoskeletal reorganization. It plays a vital role in modulating cell protrusion, cell migration, morphogenesis, adhesion, endocytosis and phagocytosis. A large number of studies have also found that abnormally activated c-Abl plays an important role in a variety of pathologies, including various inflammatory diseases and neurodegenerative diseases. c-Abl also plays a crucial role in neurodevelopment and neurodegenerative diseases, mainly through mechanisms such as neuroinflammation, oxidative stress (OS), and Tau protein phosphorylation. Inhibiting expression or activity of this kinase has certain neuroprotective and anti-inflammatory effects and can also improve cognition and behavior. Blockers of this kinase may have good preventive and treatment effects on neurodegenerative diseases. Cognitive dysfunction after anesthesia is also closely related to the abovementioned mechanisms. We infer that alterations in the expression and activity of c-Abl may underlie postoperative cognitive dysfunction (POCD). This article summarizes the current understanding and research progress on the mechanisms by which c-Abl may be related to postoperative neurodegeneration.

Environmental neurotoxicants and inflammasome activation in Parkinson's disease - A focus on the gut-brain axis

Inflammasomes are multi-protein complexes expressed in immune cells that function as intracellular sensors of environmental, metabolic and cellular stress. Inflammasome activation in the brain, has been shown to drive neuropathology and disease progression by multiple mechanisms, making it one of the most attractive therapeutic targets for disease modification in Parkinson's Disease (PD). Extensive inflammasome activation is evident in the brains of people with PD at the sites of dopaminergic degeneration and synuclein aggregation. While substantial progress has been made on validating inflammasome activation as a therapeutic target for PD, the mechanisms by which inflammasome activation is triggered and sustained over the disease course remain poorly understood. A growing body of evidence point to environmental and occupational chemical exposures as possible triggers of inflammasome activation in PD. The involvement of the gastrointestinal system and gut microbiota in PD pathophysiology is beginning to be elucidated, especially the profound link between gut dysbiosis and immune activation. While large cohort studies confirmed specific changes in the gut microbiota in PD patients compared to age-matched healthy controls, recent research suggest that synuclein pathology could be initiated in the gastrointestinal tract. In this review, we present a summarized perspective on current understanding on inflammasome activation and the gut-brain-axis link during PD pathophysiology. We discuss multiple environmental toxicants that are implicated as the etiological agents in causing idiopathic PD and their mechanistic underpinnings during neuroinflammatory events. We additionally present future directions that needs to address the research questions related to the gut-microbiome-brain mechanisms in PD.

A Novel, Selective c-Abl Inhibitor, Compound 5, Prevents Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects movement. The nonreceptor tyrosine kinase c-Abl has shown a potential role in the progression of PD. As such, c-Abl inhibition is a promising candidate for neuroprotection in PD and α-synucleinopathies. Compound 5 is a newly synthesized blood-brain barrier penetrant c-Abl inhibitor with higher efficacy than existing inhibitors. The objective of the current study was to demonstrate the neuroprotective effects of compound 5 on the α-synuclein preformed fibril (α-syn PFF) mouse model of PD. Compound 5 significantly reduced neurotoxicity, activation of c-Abl, and Lewy body pathology caused by α-syn PFF in cortical neurons. Additionally, compound 5 markedly ameliorated the loss of dopaminergic neurons, c-Abl activation, Lewy body pathology, neuroinflammatory responses, and behavioral deficits induced by α-syn PFF injection in vivo. Taken together, these results suggest that compound 5 could be a pharmaceutical agent to prevent the progression of PD and α-synucleinopathies.

Activation of NLRP3 Inflammasome and Onset of Alzheimer's Disease

The nucleotide-binding domain leucine-rich repeat and pyrin domain containing receptor protein 3 (NLRP3) is an important pattern recognition receptor in human innate immunity. Activation of the NLRP3 inflammasome play a key role in the pathogenesis of Alzheimer’s disease (AD). Theories explaining activation of the NLRP3 inflammasome include the reactive oxygen species theory, the lysosomal damage theory and the mitochondrial DNA theory. The NLRP3 activation promotes occurrence of AD by producing IL-1β, IL-18 and other cytokines, and then by affecting the deposition of Aβ and tau proteins. Over-activated NLRP3 inflammasome often impair cell function and induces immune-related diseases. Some mechanisms have been found to negatively regulate activation of the NLRP3 inflammasome, which may be through receptor binding blocking mechanism, autophagy related mechanism, abnormal cytokine secretion mechanism, or interference related gene expression regulation mechanism. In this review, we summarize the possible mechanisms by which the activation of NLRP3 inflammasomes affects the pathogenesis of AD, and the recent advances in the prevention and treatment of AD by controlling the activation of NLRP3 inflammasomes. By researching the activation or inactivation of NLRP3 inflammasome, it is possible to reveal the pathogenesis of AD from a new perspective and provide a new idea for the prevention and treatment of AD.

Roles of PRR-Mediated Signaling Pathways in the Regulation of Oxidative Stress and Inflammatory Diseases

Oxidative stress is a major contributor to the pathogenesis of various inflammatory diseases. Accumulating evidence has shown that oxidative stress is characterized by the overproduction of reactive oxygen species (ROS). Previous reviews have highlighted inflammatory signaling pathways, biomarkers, molecular targets, and pathogenetic functions mediated by oxidative stress in various diseases. The inflammatory signaling cascades are initiated through the recognition of host cell-derived damage associated molecular patterns (DAMPs) and microorganism-derived pathogen associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs). In this review, the effects of PRRs from the Toll-like (TLRs), the retinoic acid-induced gene I (RIG-I)-like receptors (RLRs) and the NOD-like (NLRs) families, and the activation of these signaling pathways in regulating the production of ROS and/or oxidative stress are summarized. Furthermore, important directions for future studies, especially for pathogen-induced signaling pathways through oxidative stress are also reviewed. The present review will highlight potential therapeutic strategies relevant to inflammatory diseases based on the correlations between ROS regulation and PRRs-mediated signaling pathways.

Genetic Imaging of Neuroinflammation in Parkinson's Disease: Recent Advancements

Parkinson's disease (PD) is one of the most prevalent neurodegenerative aging disorders characterized by motor and non-motor symptoms due to the selective loss of midbrain dopaminergic (DA) neurons. The decreased viability of DA neurons slowly results in the appearance of motor symptoms such as rigidity, bradykinesia, resting tremor, and postural instability. These symptoms largely depend on DA nigrostriatal denervation. Pharmacological and surgical interventions are the main treatment for improving clinical symptoms, but it has not been possible to cure PD. Furthermore, the cause of neurodegeneration remains unclear. One of the possible neurodegeneration mechanisms is a chronic inflammation of the central nervous system, which is mediated by microglial cells. Impaired or dead DA neurons can directly lead to microglia activation, producing a large number of reactive oxygen species and pro-inflammatory cytokines. These cytotoxic factors contribute to the apoptosis and death of DA neurons, and the pathological process of neuroinflammation aggravates the primary morbid process and exacerbates ongoing neurodegeneration. Therefore, anti-inflammatory treatment exerts a robust neuroprotective effect in a mouse model of PD. Since discovering the first mutation in the α-synuclein gene (SNCA), which can cause disease-causing, PD has involved many genes and loci such as LRRK2, Parkin, SNCA, and PINK1. In this article, we summarize the critical descriptions of the genetic factors involved in PD's occurrence and development (such as LRRK2, SNCA, Parkin, PINK1, and inflammasome), and these factors play a crucial role in neuroinflammation. Regulation of these signaling pathways and molecular factors related to these genetic factors can vastly improve the neuroinflammation of PD.

PKC Delta Activation Promotes Endoplasmic Reticulum Stress (ERS) and NLR Family Pyrin Domain-Containing 3 (NLRP3) Inflammasome Activation Subsequent to Asynuclein-Induced Microglial Activation: Involvement of Thioredoxin-Interacting Protein (TXNIP)/Thioredoxin (Trx) Redoxisome Pathway

A classical hallmark of Parkinson's disease (PD) pathogenesis is the accumulation of misfolded alpha-synuclein (αSyn) within Lewy bodies and Lewy neurites, although its role in microglial dysfunction and resultant dopaminergic (DAergic) neurotoxicity is still elusive. Previously, we identified that protein kinase C delta (PKCδ) is activated in post mortem PD brains and experimental Parkinsonism and that it participates in reactive microgliosis; however, the relationship between PKCδ activation, endoplasmic reticulum stress (ERS) and the reactive microglial activation state in the context of α-synucleinopathy is largely unknown. Herein, we show that oxidative stress, mitochondrial dysfunction, NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, and PKCδ activation increased concomitantly with ERS markers, including the activating transcription factor 4 (ATF-4), serine/threonine-protein kinase/endoribonuclease inositol-requiring enzyme 1α (p-IRE1α), p-eukaryotic initiation factor 2 (eIF2α) as well as increased generation of neurotoxic cytokines, including IL-1β in aggregated αSyn_agg-stimulated primary microglia. Importantly, in mouse primary microglia-treated with αSyn_agg we observed increased expression of Thioredoxin-interacting protein (TXNIP), an endogenous inhibitor of the thioredoxin (Trx) pathway, a major antioxidant protein system. Additionally, αSyn_agg promoted interaction between NLRP3 and TXNIP in these cells. In vitro knockdown of PKCδ using siRNA reduced ERS and led to reduced expression of TXNIP and the NLRP3 activation response in αSyn_agg-stimulated mouse microglial cells (MMCs). Additionally, attenuation of mitochondrial reactive oxygen species (mitoROS) via mito-apocynin and amelioration of ERS via the eIF2α inhibitor salubrinal (SAL) reduced the induction of the ERS/TXNIP/NLRP3 signaling axis, suggesting that mitochondrial dysfunction and ERS may act in concert to promote the αSyn_agg-induced microglial activation response. Likewise, knockdown of TXNIP by siRNA attenuated the αSyn_agg-induced NLRP3 inflammasome activation response. Finally, unilateral injection of αSyn preformed fibrils (αSyn_PFF) into the striatum of wild-type mice induced a significant increase in the expression of nigral p-PKCδ, ERS markers, and upregulation of the TXNIP/NLRP3 inflammasome signaling axis prior to delayed loss of TH⁺ neurons. Together, our results suggest that inhibition of ERS and its downstream signaling mediators TXNIP and NLRP3 might represent novel therapeutic avenues for ameliorating microglia-mediated neuroinflammation in PD and other synucleinopathies.

Mechanism of Gene-Environment Interactions Driving Glial Activation in Parkinson's Diseases

PURPOSE OF REVIEW

Parkinson's disease (PD) is the most prevalent motor disorder and is characterized by loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) region of the brain. Though the pathology of PD is well established, the cause of this neuronal loss is not well understood. Approximately 90% of PD cases are sporadic, and the environment plays a significant role in disease pathogenesis. The etiology of PD is highly complex, with neuroinflammation being one of the most critical factors implicated in PD. However, the signaling mechanisms underlying neuroinflammation and its interaction with environmental factors are unclear.

RECENT FINDINGS

Astroglia and microglia are the two principal cells that play an essential role in maintaining neuronal health in many ways, including through immunological means. Exposure to environmental stressors from various sources affects these glial cells leading to chronic and sustained inflammation. Recent epidemiological studies have identified an interaction among environmental factors and glial genes in Parkinson's disease. Mechanistic studies have shown that exposure to pesticides like rotenone and paraquat, neurotoxic metals like manganese and lead, and even diesel exhaust fumes induce glial activation by regulating various key inflammatory pathways, including the inflammasomes, NOX pathways, and others. This review aims to discuss the recent advances in understanding the mechanism of glial induction in response to environmental stressors and discuss the potential role of gene-environment interaction in driving glial activation.

Neuromelanin Modulates Heterocyclic Aromatic Amine-Induced Dopaminergic Neurotoxicity

Heterocyclic aromatic amines (HAAs) are mutagens and potential human carcinogens. Our group and others have demonstrated that HAAs may also produce selective dopaminergic neurotoxicity, potentially relevant to Parkinson's disease (PD). The goal of this study was to elucidate mechanisms of HAA-induced neurotoxicity through examining a translational biochemical weakness of common PD models. Neuromelanin is a pigmented byproduct of dopamine metabolism that has been debated as being both neurotoxic and neuroprotective in PD. Importantly, neuromelanin is known to bind and potentially release dopaminergic neurotoxicants, including HAAs (eg, β-carbolines such as harmane). Binding of other HAA subclasses (ie, aminoimidazoaazarenes) to neuromelanin has not been investigated, nor has a specific role for neuromelanin in mediating HAA-induced neurotoxicity been examined. Thus, we investigated the role of neuromelanin in modulating HAA-induced neurotoxicity. We characterized melanin from Sepia officinalis and synthetic dopamine melanin, proposed neuromelanin analogs with similar biophysical properties. Using a cell-free assay, we demonstrated strong binding of harmane and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to neuromelanin analogs. To increase cellular neuromelanin, we transfected SH-SY5Y neuroblastoma cells with tyrosinase. Relative to controls, tyrosinase-expressing cells exhibited increased neuromelanin levels, cellular HAA uptake, cell toxicity, and oxidative damage. Given that typical cellular and rodent PD models form far lower neuromelanin levels than humans, there is a critical translational weakness in assessing HAA-neurotoxicity. The primary impacts of these results are identification of a potential mechanism by which HAAs accumulate in catecholaminergic neurons and support for the need to conduct neurotoxicity studies in systems forming neuromelanin.

α-synuclein aggregates induce c-Abl activation and dopaminergic neuronal loss by a feed-forward redox stress mechanism

Oxidative stress and α-synuclein aggregation both drive neurodegeneration in Parkinson's disease, and the protein kinase c-Abl provides a potential amplifying link between these pathogenic factors. Suppressing interactions between these factors may thus be a viable therapeutic approach for this disorder. To evaluate this possibility, pre-formed α-synuclein fibrils (PFFs) were used to induce α-synuclein aggregation in neuronal cultures. Exposure to PFFs induced oxidative stress and c-Abl activation in wild-type neurons. By contrast, α-synuclein - deficient neurons, which cannot form α-synuclein aggregates, failed to exhibit either oxidative stress or c-Abl activation. N-acetyl cysteine, a thiol repletion agent that supports neuronal glutathione metabolism, suppressed the PFF - induced redox stress and c-Abl activation in the wild-type neurons, and likewise suppressed α-synuclein aggregation. Parallel findings were observed in mouse brain: PFF-induced α-synuclein aggregation in the substantia nigra was associated with redox stress, c-Abl activation, and dopaminergic neuronal loss, along with microglial activation and motor impairment, all of which were attenuated with oral N-acetyl cysteine. Similar results were obtained using AAV-mediated α-synuclein overexpression as an alternative means of driving α-synuclein aggregation in vivo. These findings show that α-synuclein aggregates induce c-Abl activation by a redox stress mechanism. c-Abl activation in turn promotes α-synuclein aggregation, in a feed-forward interaction. The capacity of N-acetyl cysteine to interrupt this interaction adds mechanistic support its consideration as a therapeutic in Parkinson's disease.

Nilotinib Improves Bioenergetic Profiling in Brain Astroglia in the 3xTg Mouse Model of Alzheimer's Disease

Current treatments targeting amyloid beta in Alzheimer's disease (AD) have minimal efficacy, which results in a huge unmet medical need worldwide. Accumulating data suggest that brain mitochondrial dysfunction play a critical role in AD pathogenesis. Targeting cellular mechanisms associated with mitochondrial dysfunction in AD create a novel approach for drug development. This study investigated the effects of nilotinib, as a selective tyrosine kinase inhibitor, in astroglia derived from 3xTg-AD mice versus their C57BL/6-controls. Parameters included oxygen consumption rates (OCR), ATP, cytochrome c oxidase (COX), citrate synthase (CS) activity, alterations in oxidative phosphorylation (OXPHOS), nuclear factor kappa B (NF-κB), key regulators of mitochondrial dynamics (mitofusin (Mfn1), dynamin-related protein 1 (Drp1)), and mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator1-alpha (PGC-1α), calcium/calmodulin-dependent protein kinase II (CaMKII), and nuclear factor (erythroid-derived 2)-like 2 (Nrf2)). Nilotinib increased OCR, ATP, COX, Mfn1, and OXPHOS levels in 3xTg astroglia. No significant differences were detected in levels of Drp1 protein and CS activity. Nilotinib enhanced mitochondrial numbers, potentially through a CaMKII-PGC1α-Nrf2 pathway in 3xTg astroglia. Additionally, nilotinib-induced OCR increases were reduced in the presence of the NF-κB inhibitor, Bay11-7082. The data suggest that NF-κB signaling is intimately involved in nilotinib-induced changes in bioenergetics in 3xTg brain astroglia. Nilotinib increased translocation of the NF-κB p50 subunit into the nucleus of 3xTg astroglia that correlates with an increased expression and activation of NF-κB. The current findings support a role for nilotinib in improving mitochondrial function and suggest that astroglia may be a key therapeutic target in treating AD.

Baicalein Exerts Anti-Neuroinflammatory Effects by Inhibiting the TLR4-ROS /NF-κB-NLRP3 Inflammasome

Emerging evidence indicates that NOD-like receptor protein 3 (NLRP3) inflammasome-induced inflammation plays a critical role in the pathogenesis of Parkinson’s disease (PD). Baicalein has been considered as a possible option for PD treatment based on its anti-neuroinflammatory effects. However, no studies have elucidated the precise mechanisms underlying the anti-neuroinflammatory activity of baicalein, particularly inflammasome-mediated effects. In this present study, rotenone-induced PD mice and BV2 microglia were used to investigate the anti-neuroinflammatory effects of baicalein and explore its underlying mechanism in vivo and in vitro. The results demonstrated that baicalein alleviated motor impairments and attenuated several inflammatory responses in rotenone-induced PD mice. Also, baicalein inhibited the expression of NLRP3 and activated caspase-1 in brain tissues. Correspondingly, baicalein prominently suppressed the inflammatory response in BV2 microglia induced by rotenone. Furthermore, in vitro data showed that baicalein suppressed the expression of NLRP3 and activated caspase-1 by abrogating the upregulation of ROS, as well as by inhibiting the TLR4/NF-κB signaling cascade. Overall, the results of the present study indicated that baicalein exerted anti-neuroinflammatory effects partly by inhibiting activation of the NLRP3 inflammasome, and targeting NLRP3 inflammasome signaling offers a novel therapeutic strategy for PD treatment.

Timely Inhibitory Circuit Formation Controlled by Abl1 Regulates Innate Olfactory Behaviors in Mouse

More than one-half of the interneurons in a mouse olfactory bulb (OB) develop during the first week after birth and predominantly connect to excitatory tufted cells near the superficial granule cell layer (sGCL), unlike late-born interneurons. However, the molecular mechanisms underlying the temporal specification are yet to be identified. In this study, we determined the role of Abelson tyrosine-protein kinase 1 (Abl1) in the temporal development of early-born OB interneurons. Lentiviral knockdown of Abl1 disrupts the sGCL circuit of early-born interneurons through defects in function and circuit integration, resulting in olfactory hyper-sensitivity. We show that doublecortin (Dcx) is phosphorylated by Abl1, which contributes to the stabilization of Dcx, thereby regulating microtubule dynamics. Finally, Dcx overexpression rescues Abl1 knockdown-induced anatomic or functional defects. In summary, specific signaling by Abl1-Dcx in early-born interneurons facilitates the temporal development of the sGCL circuit to regulate innate olfactory functions, such as detection and sensitivity.

Plasma-borne indicators of inflammasome activity in Parkinson's disease patients

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms and loss of dopaminergic neurons of the substantia nigra. Inflammation and cell death are recognized aspects of PD suggesting that strategies to monitor and modify these processes may improve the management of the disease. Inflammasomes are pro-inflammatory intracellular pattern recognition complexes that couple these processes. The NLRP3 inflammasome responds to sterile triggers to initiate pro-inflammatory processes characterized by maturation of inflammatory cytokines, cytoplasmic membrane pore formation, vesicular shedding, and if unresolved, pyroptotic cell death. Histologic analysis of tissues from PD patients and individuals with nigral cell loss but no diagnosis of PD identified elevated expression of inflammasome-related proteins and activation-related “speck” formation in degenerating mesencephalic tissues compared with controls. Based on previous reports of circulating inflammasome proteins in patients suffering from heritable syndromes caused by hyper-activation of the NLRP3 inflammasome, we evaluated PD patient plasma for evidence of inflammasome activity. Multiple circulating inflammasome proteins were detected almost exclusively in extracellular vesicles indicative of ongoing inflammasome activation and pyroptosis. Analysis of plasma obtained from a multi-center cohort identified elevated plasma-borne NLRP3 associated with PD status. Our findings are consistent with others indicating inflammasome activity in neurodegenerative disorders. Findings suggest mesencephalic inflammasome protein expression as a histopathologic marker of early-stage nigral degeneration and suggest plasma-borne inflammasome-related proteins as a potentially useful class of biomarkers for patient stratification and the detection and monitoring of inflammation in PD.

Therapeutic role of inflammasome inhibitors in neurodegenerative disorders

Neuroinflammation, characterized by the activation of glial cells, is a hallmark in several neurological and neurodegenerative disorders. Inadequate inflammation cannot eliminate the infection of pathogens, while excessive or hyper-reactive inflammation can cause chronic or systemic inflammatory diseases affecting the central nervous system (CNS). In response to a brain injury or pathogen invasion, the pathogen recognition receptors (PRRs) expressed on glial cells are activated via binding to cellular damage-associated molecular patterns (DAMPs) or pathogen-associated molecular patterns (PAMPs). This subsequently leads to the activation of NOD (nucleotide-binding oligomerization domain)-like receptor proteins (NLRs). In neurodegenerative diseases such as HIV-1-associated neurocognitive disorders (HAND), Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS), chronic inflammation is a critical contributing factor for disease manifestation including pathogenesis. Emerging evidence points to the involvement of "inflammasomes", especially the nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing (NLRP) complex in the development of these diseases. The activated NLRP3 results in the proteolytic activation of caspase-1 that facilitates the cleavage of pro-IL-1β and the secretion of IL-1β and IL-18 proinflammatory cytokines. Accordingly, these and other seminal findings have led to the development of NLRP-targeting small-molecule therapeutics as possible treatment options for neurodegenerative disorders. In this review, we will discuss the new advances and evidence-based literature concerning the role of inflammasomes in neurodegenerative diseases, its role in the neurological repercussions of CNS chronic infection, and the examples of preclinical or clinically tested NLRP inhibitors as potential strategies for the treatment of chronic neurological diseases.

New Insights into Immune-Mediated Mechanisms in Parkinson's Disease

The immune system has been increasingly recognized as a major contributor in the pathogenesis of Parkinson’s disease (PD). The double-edged nature of the immune system poses a problem in harnessing immunomodulatory therapies to prevent and slow the progression of this debilitating disease. To tackle this conundrum, understanding the mechanisms underlying immune-mediated neuronal death will aid in the identification of neuroprotective strategies to preserve dopaminergic neurons. Specific innate and adaptive immune mediators may directly or indirectly induce dopaminergic neuronal death. Genetic factors, the gut-brain axis and the recent identification of PD-specific T cells may provide novel mechanistic insights on PD pathogenesis. Future studies to address the gaps in the identification of autoantibodies, variability in immunophenotyping studies and the contribution of gut dysbiosis to PD may eventually provide new therapeutic targets for PD.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Neuromelanin formation exacerbates HAA-induced mitochondrial toxicity and mitophagy impairments

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is a major public health concern due in part to prevalence, debilitating symptoms, and links to environmental exposures. Much research has focused on environmental factors that may lead to dopaminergic neurotoxicity that occurs in PD. In the study of neuronal uptake and neurotoxicity, critical species differences have been observed. For example, neuromelanin is a molecule formed in part by the breakdown products of dopamine metabolism, along with lipid and protein components. Interestingly, human catecholaminergic neurons contain readily detectable amounts of neuromelanin, while rodent models form far lower levels of neuromelanin that is barely detectable. This discrepancy is potentially an important translational weakness. Recently, we showed that neuromelanin formation modulates heterocyclic aromatic amine (HAA)-induced neurotoxicity in cellular models. HAAs are dietary toxins that have primarily been studied as carcinogens, with emergent literature on selective neurotoxicity. The goal of the present study was to identify whether mitochondria in neuromelanin forming cells may be especially sensitive to HAAs. Here, we exposed galactose-supplemented SH-SY5Y cells to HAAs and tested mitochondrial function and mitophagy. The ectopic formation of neuromelanin was found to increase mitochondrial oxidative stress, decrease membrane potential, increase mitochondrial bioenergetic impairments, and impair mitophagy relative to HAA-treated cells that do not form neuromelanin. These results suggest that neuromelanin has a critical role in HAA toxicity and adverse effects on mitochondria. The data also further cement the need to conduct both mechanistic and risk assessment studies on PD-relevant neurotoxicity in models that form neuromelanin.

c-Abl Inhibition Activates TFEB and Promotes Cellular Clearance in a Lysosomal Disorder

The transcription factor EB (TFEB) has emerged as a master regulator of lysosomal biogenesis, exocytosis, and autophagy, promoting the clearance of substrates stored in cells. c-Abl is a tyrosine kinase that participates in cellular signaling in physiological and pathophysiological conditions. In this study, we explored the connection between c-Abl and TFEB. Here, we show that under pharmacological and genetic c-Abl inhibition, TFEB translocates into the nucleus promoting the expression of its target genes independently of its well-known regulator, mammalian target of rapamycin complex 1. Active c-Abl induces TFEB phosphorylation on tyrosine and the inhibition of this kinase promotes lysosomal biogenesis, autophagy, and exocytosis. c-Abl inhibition in Niemann-Pick type C (NPC) models, a neurodegenerative disease characterized by cholesterol accumulation in lysosomes, promotes a cholesterol-lowering effect in a TFEB-dependent manner. Thus, c-Abl is a TFEB regulator that mediates its tyrosine phosphorylation, and the inhibition of c-Abl activates TFEB promoting cholesterol clearance in NPC models.

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c-Abl is a TFEB regulator that mediates its tyr phosphorylation

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c-Abl inhibition promotes TFEB activity independently of mTORC1

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c-Abl inhibition reduces cholesterol accumulation in NPC1 models

Tumor Necrosis Factor-Like Weak Inducer of Apoptosis (TWEAK) Enhances Activation of STAT3/NLRC4 Inflammasome Signaling Axis through PKCδ in Astrocytes: Implications for Parkinson's Disease

Astrocytic dysfunction has been implicated in Parkinson's disease (PD) pathogenesis. While the Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 signaling axis is known to play a role in PD-like neuropathology, the molecular mechanisms that govern this process remain poorly understood. Herein, we show that TWEAK levels are elevated in PD serum compared to controls. Moreover, using both U373 human astrocyte cells and primary mouse astrocytes, we demonstrate that TWEAK induces mitochondrial oxidative stress as well as protein kinase C delta (PKCδ) and signal transducer and activator of transcription 3 (STAT3) activation, accompanied by NLRC4 inflammasome activation and upregulation and release of proinflammatory cytokines, including IL-1β, TNF-α, and IL-18. Mechanistically, TWEAK-induced PKCδ activation enhances the STAT3/NLRC4 signaling pathway and other proinflammatory mediators through a mitochondrial oxidative stress-dependent mechanism. We further show that PKCδ knockdown and mito-apocynin, a mitochondrial antioxidant, suppress TWEAK-induced proinflammatory NLRC4/STAT3 signaling and cellular oxidative stress response. Notably, we validated our in vitro findings in an MPTP mouse model of PD and in mice receiving intrastriatal administration of TWEAK. These results indicate that TWEAK is a key regulator of astroglial reactivity and illustrate a novel mechanism by which mitochondrial oxidative stress may influence dopaminergic neuronal survival in PD.

Emodin Attenuates Severe Acute Pancreatitis via Antioxidant and Anti-inflammatory Activity

There is no specific drug to treat severe acute pancreatitis (SAP), which induces substantial medical and social burden. Many studies have reported the beneficial effects of emodin against SAP in vivo and in vitro. However, the underlying mechanism has been unclear. This paper described the design and implementation of anti-inflammatory and antioxidant activity of emodin. Emodin restored the pathological damage of SAP and simultaneously decreased the high levels of serum amylase, lipase, TNF-α, and IL-18 in the peripheral blood of SAP rat. Emodin reversed reactive oxygen species (ROS) in neutrophils derived from SAP rat. The levels of voltage-dependent anion channel 1 (VDAC1), NOD-like receptor protein 3 (NLRP3), caspase-1, and IL-18 were examined to analyze the change of inflammasome-related mediators between SAP and emodin treatment. These findings suggest that emodin plays its protective role on SAP against oxidative stress and inflammasome signals.

NLRP3 inflammasome and glia maturation factor coordinately regulate neuroinflammation and neuronal loss in MPTP mouse model of Parkinson's disease

Neuroinflammation plays an active role in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease (PD). Earlier studies from this laboratory showed that glia maturation factor (GMF), a proinflammatory mediator; is up-regulated in the brain in neurodegenerative diseases and that deficiency of GMF showed decreased production of IL-1β and improved behavioral abnormalities in mouse model of PD. However, the mechanisms linking GMF and dopaminergic neuronal death have not been completely explored. In the present study, we have investigated the expression of NLRP3 inflammasome and caspase-1 in the substantia nigra (SN) of human PD and non-PD brains by immunohistochemistry. Wild-type (WT) and GMF^-/- (GMF knock-out) mice were treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine (MPTP) and the brains were isolated for neurochemical and morphological examinations. NLRP3 and caspase-1 positive cells were found significantly increased in PD when compared to non-PD control brains. Moreover, GMF co-localized with α-Synuclein within reactive astrocytes in the midbrain of PD. Mice treated with MPTP exhibit glial activation-induced inflammation, and nigrostriatal dopaminergic neurodegeneration. Interestingly, increased expression of the inflammasome components in astrocytes and microglia observed in the SN of MPTP-treated WT mice were significantly reduced in GMF^-/- mice. Additionally, we show that NLRP3 activation in microglia leads to translocation of GMF and NLRP3 to the mitochondria. We conclude that downregulation of GMF may have beneficial effects in prevention of PD by modulating the cytotoxic functions of microglia and astrocytes through reduced activation of the NLRP3 inflammasome; a major contributor of neuroinflammation in the CNS.

Drp1, a potential therapeutic target for Parkinson's disease, is involved in olfactory bulb pathological alteration in the Rotenone-induced rat model

Olfaction is often affected in parkinsonian patients and its disturbances precede the classical cognitive and locomotor dysfunction. The olfactory bulb might be the region of onset in Parkinson's disease (PD) pathogenesis, evidenced by the presence of disease-related protein aggregates and disturbed olfactory information processing. However, the underlying molecular mechanism that governs the olfactory bulb impairments remains unclear. This study was designed to investigate the relationship between olfactory bulb and inflammatory pathological alterations and the potential mechanisms. Here we found that rotenone led to typical parkinsonian symptoms and decreased tyrosine hydroxylase (TH)-positive neurons in the olfactory bulb. Additionally, increased NF-κB nuclear translocation and NLRP3 inflammasome components expressions caused by rotenone injection were observed accompanied by the activation of microglia and astrocytes in the olfactory bulb. Rotenone also triggered Drp1-mediated mitochondrial fission and this in turn caused mitochondrial damage. Furthermore, Mdivi-1(a selective Drp1 inhibitor) markedly ameliorated the morphologic disruptions of mitochondria and Drp1 translocation, inhibited the nuclear translocation of NF-κB, eventually blocked the downstream pathway of the NLRP3/caspase-1/IL-1β axis and expression of iNOS. Overall, these findings suggest that Drp1-dependent mitochondrial fission induces NF-κB nuclear translocation and NLRP3 inflammasome activation that may further contribute to olfactory bulb disturbances.

Molecular Signatures of Neuroinflammation Induced by αSynuclein Aggregates in Microglial Cells

Alpha-synuclein (αSyn_Agg) are pathological hallmarks of Parkinson's disease (PD) and other synucleinopathies that induce microglial activation and immune-mediated neurotoxicity, but the molecular mechanisms of αSyn_Agg-induced immune activation are poorly defined. We performed quantitative proteomics by mass spectrometry coupled with PCR, immunohistochemical and functional validations studies to define the molecular characteristics of alpha synuclein mediated microglial activation. In mouse microglia, αSyn_Agg induced robust pro-inflammatory activation (increased expression of 864 genes including Irg1, Ifit1, and Pyhin) and increased nuclear proteins involved in RNA synthesis, splicing, and anti-viral defense mechanisms. Conversely, αSyn_Agg decreased expression several proteins (including Cdc123, Sod1, and Grn), which were predominantly cytosolic and involved in metabolic, proteasomal and lysosomal mechanisms. Pathway analyses and confirmatory in vitro studies suggested that αSyn_Agg partly mediates its effects via Stat3 activation. As predicted by our proteomic findings, we verified that αSyn_Agg induces mitochondrial dysfunction in microglia. Twenty-six proteins differentially expressed by αSyn_Agg were also identified as PD risk genes in genome-wide association studies (upregulated: Brd2, Clk1, Siglec1; down-regulated: Memo1, Arhgap18, Fyn, and Pgrn/Grn). We validated progranulin (PGRN) as a lysosomal PD-associated protein that is downregulated by αSyn_Agg in microglia in-vivo and is expressed by microglia in post-mortem PD brain, congruent with our in vitro findings. Conclusion: Together, proteomics approach both reveals novel molecular insights into αSyn-mediated neuroinflammation in PD and other synucleinopathies.

Small molecule modulator of aggrephagy regulates neuroinflammation to curb pathogenesis of neurodegeneration

Background

Plethora of efforts fails to yield a single drug to reverse the pathogenesis of Parkinson's disease (PD) and related α-synucleopathies.

Methods

Using chemical biology, we identified a small molecule inhibitor of c-abl kinase, PD180970 that could potentially clear the toxic protein aggregates. Genetic, molecular, cell biological and immunological assays were performed to understand the mechanism of action. In vivo preclinical disease model of PD was used to assess its neuroprotection efficacy.

Findings

In this report, we show the ability of a small molecule inhibitor of tyrosine kinases, PD180970, to induce autophagy (cell lines and mice midbrain) in an mTOR-independent manner and ameliorate the α-synuclein mediated toxicity. PD180970 also exerts anti-neuroinflammatory potential by inhibiting the release of proinflammatory cytokines such as IL-6 (interleukin-6) and MCP-1 (monocyte chemoattractant protein-1) through reduction of TLR-4 (toll like receptor-4) mediated NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activation. In vivo studies show that PD180970 is neuroprotective by degrading the toxic protein oligomers through induction of autophagy and subsiding the microglial activation.

Interpretation

These protective mechanisms ensure the negation of Parkinson's disease related motor impairments.

Fund

This work was supported by Wellcome Trust/DBT India Alliance Intermediate Fellowship (500159-Z-09-Z), DST-SERB grant (EMR/2015/001946), DBT (BT/INF/22/SP27679/2018) and JNCASR intramural funds to RM, and SERB, DST (SR/SO/HS/0121/2012) to PAA, and DST-SERB (SB/YS/LS-215/2013) to JPC and BIRAC funding to ETA C-CAMP.

Dasatinib regulates LPS-induced microglial and astrocytic neuroinflammatory responses by inhibiting AKT/STAT3 signaling

Background

The FDA-approved small-molecule drug dasatinib is currently used as a treatment for chronic myeloid leukemia (CML). However, the effects of dasatinib on microglial and/or astrocytic neuroinflammatory responses and its mechanism of action have not been studied in detail.

Methods

BV2 microglial cells, primary astrocytes, or primary microglial cells were treated with dasatinib (100 or 250 nM) or vehicle (1% DMSO) for 30 min or 2 h followed by lipopolysaccharide (LPS; 200 ng/ml or 1 μg/ml) or PBS for 5.5 h. RT-PCR, real-time PCR; immunocytochemistry; subcellular fractionation; and immunohistochemistry were subsequently conducted to determine the effects of dasatinib on LPS-induced neuroinflammation. In addition, wild-type mice were injected with dasatinib (20 mg/kg, intraperitoneally (i.p.) daily for 4 days or 20 mg/kg, orally administered (p.o.) daily for 4 days or 2 weeks) or vehicle (4% DMSO + 30% polyethylene glycol (PEG) + 5% Tween 80), followed by injection with LPS (10 mg/kg, i.p.) or PBS. Then, immunohistochemistry was performed, and plasma IL-6, IL-1β, and TNF-α levels were analyzed by ELISA.

Results

Dasatinib regulates LPS-induced proinflammatory cytokine and anti-inflammatory cytokine levels in BV2 microglial cells, primary microglial cells, and primary astrocytes. In BV2 microglial cells, dasatinib regulates LPS-induced proinflammatory cytokine levels by regulating TLR4/AKT and/or TLR4/ERK signaling. In addition, intraperitoneal injection and oral administration of dasatinib suppress LPS-induced microglial/astrocyte activation, proinflammatory cytokine levels (including brain and plasma levels), and neutrophil rolling in the brains of wild-type mice.

Conclusions

Our results suggest that dasatinib modulates LPS-induced microglial and astrocytic activation, proinflammatory cytokine levels, and neutrophil rolling in the brain.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1561-x) contains supplementary material, which is available to authorized users.

Inflammasomes: An Emerging Mechanism Translating Environmental Toxicant Exposure Into Neuroinflammation in Parkinson's Disease

Evidence indicates that complex gene-environment interactions underlie the incidence and progression of Parkinson's disease (PD). Neuroinflammation is a well-characterized feature of PD widely believed to exacerbate the neurodegenerative process. Environmental toxicants associated with PD, such as pesticides and heavy metals, can cause cellular damage and stress potentially triggering an inflammatory response. Toxicant exposure can cause stress and damage to cells by impairing mitochondrial function, deregulating lysosomal function, and enhancing the spread of misfolded proteins. These stress-associated mechanisms produce sterile triggers such as reactive oxygen species (ROS) along with a variety of proteinaceous insults that are well documented in PD. These associations provide a compelling rationale for analysis of sterile inflammatory mechanisms that may link environmental exposure to neuroinflammation and PD progression. Intracellular inflammasomes are cytosolic assemblies of proteins that contain pattern recognition receptors, and a growing body of evidence implicates the association between inflammasome activation and neurodegenerative disease. Characterization of how inflammasomes may function in PD is a high priority because the majority of PD cases are sporadic, supporting the widely held belief that environmental exposure is a major factor in disease initiation and progression. Inflammasomes may represent a common mechanism that helps to explain the strong association between exposure and PD by mechanistically linking environmental toxicant-driven cellular stress with neuroinflammation and ultimately cell death.

Role of c-Abl-GSK3β Signaling in MPP+-Induced Autophagy-Lysosomal Dysfunction

Impairment in autophagy-lysosomal pathway (ALP) results in accumulation of misfolded proteins and dysfunctional organelles, which is the hallmark of neurodegenerative diseases including Parkinson's disease (PD). Recent studies revealed activated nonreceptor tyrosine kinase Abelson (c-Abl) in PD models and brain specimen of PD patients. Inhibition of c-Abl through pharmacological inhibitors has been shown to enhance ALP function and provide neuroprotective effects in cells and animal models of PD. However, the molecular mechanisms of neuroprotective effects underlying c-Abl inhibition remain elusive. In this study, STI-571, a c-Abl inhibitor, rescued the ALP function through facilitating the nuclear translocation of TFEB and protected against MPP+-induced neuronal cell death. Furthermore, siRNA-mediated knock-down or pharmacological inhibition of GSK3β mitigated the MPP+-induced neuronal cell death, which was achieved through promoting TFEB nuclear localization and subsequently reversing the function of ALP. Intriguingly, either DPH, c-Abl activator, or MPP+ led to the activation of GSK3β, which is a negative regulator of TFEB. In addition, c-Abl directly interacted with GSK3β and catalyzed its phosphorylation at tyrosine 216, and their interaction was enhanced under MPP+ treatment. In contrast, STI-571 abrogated phosphorylation of GSK3β-Tyr216 induced by MPP+ in SN4741 cells and in primary midbrain neurons. Taken together, these results demonstrate that GSK3β is a novel c-Abl substrate, and c-Abl-GSk3β pathway mediates MPP+-induced ALP defects and neuronal cell death, which may represent a potential therapeutic target for PD.

Astragaloside IV ameliorates motor deficits and dopaminergic neuron degeneration via inhibiting neuroinflammation and oxidative stress in a Parkinson's disease mouse model

Oxidative stress and neuroinflammation are the key and early events during the pathological process of Parkinson's disease (PD). Thus, therapeutic intervention to regulate oxidative stress and neuroinflammation would be an effective strategy to alleviate the progression of PD. Astragaloside IV, the main active component isolated from Astragalus membranaceus, has been shown to possess anti-inflammatory and anti-oxidant properties in neurodegeneration diseases, however, the molecular mechanisms of Astragaloside IV in the pathology of PD are still unclear. In this study, we explored the mechanisms of Astragaloside IV of PD on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice model and lipopolysaccharide (LPS)-induced BV2 microglia cells. Our results showed Astragaloside IV significantly alleviated behavioral impairments and dopaminergic neuron degeneration induced by MPTP. Also, Astragaloside IV inhibited microglia activation and reduced the oxidative stress of MPTP mouse model. In addition, Astragaloside IV significantly inhibited NFκB mediated NLRP3 inflammasome activation and activated Nrf2 both in vivo and in vitro. Furthermore, Astragaloside IV lessened reactive oxygen species (ROS) generation in LPS-induced BV2 microglia cells remarkably. These findings demonstrate that Astragaloside IV protects dopaminergic neuron from neuroinflammation and oxidative stress which are largely dependent upon activation of the Nrf2 pathways and suppression of NFκB/NLRP3 inflammasome signaling pathway. Therefore, Astragaloside IV is a promising neuroprotective agent that should be further developed for neurodegeneration diseases.

α-Synuclein in Parkinson's disease: causal or bystander?

Parkinson's disease (PD) comprises a spectrum of disorders with differing subtypes, the vast majority of which share Lewy bodies (LB) as a characteristic pathological hallmark. The process(es) underlying LB generation and its causal trigger molecules are not yet fully understood. α-Synuclein (α-syn) is a major component of LB and SNCA gene missense mutations or duplications/triplications are causal for rare hereditary forms of PD. As typical sporadic PD is associated with LB pathology, a factor of major importance is the study of the α-syn protein and its pathology. α-Syn pathology is, however, also evident in multiple system atrophy (MSA) and Lewy body disease (LBD), making it non-specific for PD. In addition, there is an overlap of these α-synucleinopathies with other protein-misfolding diseases. It has been proven that α-syn, phosphorylated tau protein (pτ), amyloid beta (Aβ) and other proteins show synergistic effects in the underlying pathogenic mechanisms. Multiple cell death mechanisms can induce pathological protein-cascades, but this can also be a reverse process. This holds true for the early phases of the disease process and especially for the progression of PD. In conclusion, while rare SNCA gene mutations are causal for a minority of familial PD patients, in sporadic PD (where common SNCA polymorphisms are the most consistent genetic risk factor across populations worldwide, accounting for 95% of PD patients) α-syn pathology is an important feature. Conversely, with regard to the etiopathogenesis of α-synucleinopathies PD, MSA and LBD, α-syn is rather a bystander contributing to multiple neurodegenerative processes, which overlap in their composition and individual strength. Therapeutic developments aiming to impact on α-syn pathology should take this fact into consideration.

A Bcr-Abl Inhibitor GNF-2 Attenuates Inflammatory Activation of Glia and Chronic Pain

GNF-2 is an allosteric inhibitor of Bcr-Abl. It was developed as a new class of anti-cancer drug to treat resistant chronic myelogenous leukemia. Recent studies suggest that c-Abl inhibition would provide a neuroprotective effect in animal models of Parkinson’s disease as well as in clinical trials. However, the role of c-Abl and effects of GNF-2 in glia-mediated neuroinflammation or pain hypersensitivity has not been investigated. Thus, in the present study, we tested the hypothesis that c-Abl inhibition by GNF-2 may attenuate the inflammatory activation of glia and the ensuing pain behaviors in animal models. Our results show that GNF-2 reduced lipopolysaccharide (LPS)-induced nitric oxide and pro-inflammatory cytokine production in cultured glial cells in a c-Abl-dependent manner. The small interfering ribonucleic acid (siRNA)-mediated knockdown of c-Abl attenuated LPS-induced nuclear factor kappa light chain enhancer of activated B cell (NF-κB) activation and the production of pro-inflammatory mediators in glial cell cultures. Moreover, GNF-2 administration significantly attenuated mechanical and thermal hypersensitivities in experimental models of diabetic and inflammatory pain. Together, our findings suggest the involvement of c-Abl in neuroinflammation and pain pathogenesis and that GNF-2 can be used for the management of chronic pain.

Interplay between Mitophagy and Inflammasomes in Neurological Disorders

Mitophagy and inflammasomes have a pivotal role in the development of neuropathology. Molecular mechanisms behind mitophagy and inflammasomes are well-understood, but lacunae prevail in understanding the crosstalk between them in various neurological disorders. As mitochondrial dysfunction is the prime event in neurodegeneration, the clearance of impaired mitochondria is one of the main tasks for maintaining cell integrity in the majority of neuropathologies. Along with it, inflammasome activation also plays a major role, which is usually followed by mitochondrial dysfunction. The present review highlights basics of autophagy, mitophagy, and inflammasomes and the molecular mechanisms involved, and more importantly, it tries to elaborate the interplay between mitophagy and inflammasomes in various neurological disorders. This will help in upgrading the reader's understanding in exploring the link between mitophagy and inflammasomes, which has dealt with limitations in past studies.

Environmental neurotoxicant-induced dopaminergic neurodegeneration: a potential link to impaired neuroinflammatory mechanisms

With the increased incidence of neurodegenerative diseases worldwide, Parkinson's disease (PD) represents the second-most common neurodegenerative disease. PD is a progressive multisystem neurodegenerative disorder characterized by a marked loss of nigrostriatal dopaminergic neurons and the formation of Lewy pathology in diverse brain regions. Although the mechanisms underlying dopaminergic neurodegeneration remain poorly characterized, data from animal models and postmortem studies have revealed that heightened inflammatory responses mediated via microglial and astroglial activation and the resultant release of proinflammatory factors may act as silent drivers of neurodegeneration. In recent years, numerous studies have demonstrated a positive association between the exposure to environmental neurotoxicants and the etiology of PD. Although it is unclear whether neuroinflammation drives pesticide-induced neurodegeneration, emerging evidence suggests that the failure to dampen neuroinflammatory mechanisms may account for the increased vulnerability to pesticide neurotoxicity. Furthermore, recent studies provide additional evidence that shifts the focus from a neuron-centric view to glial-associated neurodegeneration following pesticide exposure. In this review, we propose to summarize briefly the possible factors that regulate neuroinflammatory processes during environmental neurotoxicant exposure with a focus on the potential roles of mitochondria-driven redox mechanisms. In this context, a critical discussion of the data obtained from experimental research and possible epidemiological studies is included. Finally, we hope to provide insights on the pivotal role of exosome-mediated intercellular transmission of aggregated proteins in microglial activation response and the resultant dopaminergic neurodegeneration after exposure to pesticides. Collectively, an improved understanding of glia-mediated neuroinflammatory signaling might provide novel insights into the mechanisms that contribute to neurodegeneration induced by environmental neurotoxicant exposure.

The c-Abl inhibitor, Radotinib HCl, is neuroprotective in a preclinical Parkinson's disease mouse model

Accumulating evidence suggests that the non-receptor tyrosine kinase c-Abl plays an important role in the progression of Parkinson’s disease (PD) and c-Abl inhibition could be neuroprotective in PD and related α-synucleinopathies. Nilotinib, a c-Abl inhibitor, has shown improved motor and cognitive symptoms in PD patients. However, issues concerning blood–brain barrier (BBB) penetration, lack of selectivity and safety still remain. Radotinib HCl is a selective Bcr-Abl kinase inhibitor that not only effectively access the brain, but also exhibits greater pharmacokinetic properties and safety profiles compared to Nilotinib and other c-Abl inhibitors. Here, we show the neuroprotective efficacy of Radotinib HCl, a brain penetrant c-Abl inhibitor, in a pre-clinical model of PD. Importantly, in vitro studies demonstrate that the treatment of Radotinib HCl protects the α-synuclein preformed fibrils (PFF)-induced neuronal toxicity, reduces the α-synuclein PFF-induced Lewy bodies (LB)/Lewy neurites (LN)-like pathology and inhibits the α-synuclein PFF-induced c-Abl activation in primary cortical neurons. Furthermore, administration of Radotinib HCl inhibits c-Abl activation and prevents dopaminergic neuron loss, neuroinflammation and behavioral deficits following α-synuclein PFF-induced toxicity in vivo. Taken together, our findings indicate that Radotinib HCl has beneficial neuroprotective effects in PD and provides an evidence that selective and brain permeable c-Abl inhibitors can be potential therapeutic agents for the treatment of PD and related α-synucleinopathies.

Manganese activates NLRP3 inflammasome signaling and propagates exosomal release of ASC in microglial cells

Chronic, sustained inflammation underlies many pathological conditions, including neurodegenerative diseases. Divalent manganese (Mn²⁺) exposure can stimulate neurotoxicity by increasing inflammation. In this study, we examined whether Mn²⁺ activates the multiprotein NLRP3 inflammasome complex to promote neuroinflammation. Exposing activated mouse microglial cells to Mn²⁺ substantially augmented NLRP3 abundance, caspase-1 cleavage, and maturation of the inflammatory cytokine interleukin-1β (IL-1β). Exposure of mice to Mn²⁺ had similar effects in brain microglial cells. Furthermore, Mn²⁺ impaired mitochondrial ATP generation, basal respiratory rate, and spare capacity in microglial cells. These data suggest that Mn-induced mitochondrial defects drove the inflammasome signal amplification. We found that Mn induced cell-to-cell transfer of the inflammasome adaptor protein ASC in exosomes. Furthermore, primed microglial cells exposed to exosomes from Mn-treated mice released more IL-1β than did cells exposed to exosomes from control-treated animals. We also observed that welders exposed to manganese-containing fumes had plasma exosomes that contained more ASC than did those from a matched control group. Together, these results suggest that the divalent metal manganese acts as a key amplifier of NLRP3 inflammasome signaling and exosomal ASC release.

Kinase-Based Taming of Brain Microglia Toward Disease-Modifying Therapy

Microglia are the primary immune cells residing in the central nervous system (CNS), where they play essential roles in the health and disease. Depending on the CNS inflammatory milieu, they exist in either resting or activated states. Chronic neuroinflammation mediated by activated microglia is now considered to be a common characteristic shared by many neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis, which currently pose a significant socioeconomic burden to the global healthcare system. Accumulating evidence has indicated protein kinases (PKs) as important drug targets for therapeutic interventions of these detrimental diseases. Here, we review recent findings suggesting that selected PKs potentially participate in microglia-mediated neuroinflammation. Taming microglial phenotypes by modulating the activity of these PKs holds great promise for the development of disease-modifying therapies for many neurodegenerative diseases.