MPTP-driven NLRP3 inflammasome activation in microglia plays a central role in dopaminergic neurodegeneration

iTRAQ-Based Quantitative Proteomics Indicated Nrf2/OPTN-Mediated Mitophagy Inhibits NLRP3 Inflammasome Activation after Intracerebral Hemorrhage

Intracerebral hemorrhage- (ICH-) induced secondary brain injury (SBI) is a very complex pathophysiological process. However, the molecular mechanisms and drug targets of SBI are highly intricate and still elusive, yet a clear understanding is crucial for the treatment of SBI. In the current study, we aimed to confirm that nuclear factor-E2-related factor 2 (Nrf2)/Optineurin- (OPTN-) mediated mitophagy alleviated SBI by inhibiting nucleotide-binding oligomerization domain-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation based on the isobaric tag for relative and absolute quantization (iTRAQ) quantification proteomics. Human ICH brain specimens were collected for iTRAQ-based proteomics analysis. Male Nrf2 wild-type (WT) and knockout (KO) mice were employed to establish ICH murine models. The survival rate, hematoma volume, neurofunctional outcomes, blood-brain barrier (BBB) permeability, brain edema, spatial neuronal death, NLRP3 inflammasome, inflammatory response, mitochondrial function, and mitophagy level were evaluated after ICH. The iTRAQ quantification analysis showed that the differentially expressed proteins (DEPs), Nrf2 and NLRP3, were closely associated with the initiation and development of SBI after ICH. The Nrf2 KO mice had a significantly lower survival rate, bigger hematoma volume, worse neurological deficits, and increased BBB disruption, brain edema, and neuronal death when compared with the Nrf2 WT mice after ICH. Furthermore, Nrf2 KO enhanced NLRP3 inflammasome activation and neuroinflammation as evidenced by the NF-κB activation and various proinflammatory cytokine releases following ICH. Moreover, Nrf2 could interact with and modulate the mitophagy receptor OPTN, further mediating mitophagy to remove dysfunctional mitochondria after ICH. Furthermore, OPTN small interfering RNA (siRNA) increased the NLRP3 inflammasome activation by downregulating mitophagy level and enhancing mitochondrial damage in the Nrf2 WT mice after ICH. Together, our data indicated that Nrf2/OPTN inhibited NLRP3 inflammasome activation, possibly via modulating mitophagy, therefore alleviating SBI after ICH.

Anti-inflammatory and neuroprotective effects of natural cordycepin in rotenone-induced PD models through inhibiting Drp1-mediated mitochondrial fission

Accumulating evidences suggest that inflammation-mediated neurons dysfunction participates in the initial and development of Parkinson's disease (PD), whereas mitochondria have been recently recognized as crucial regulators in NLRP3 inflammasome activation. Cordycepin, a major component of cordyceps militaris, has been shown to possess neuroprotective and anti-inflammatory activity. However, the effects of cordycepin in rotenone-induced PD models and the possible mechanisms are still not fully understood. Here, we observed that motor dysfunction and dopaminergic neurons loss induced by rotenone exposure were ameliorated by cordycepin. Cordycepin also reversed Drp1-mediated aberrant mitochondrial fragmentation through increasing AMPK phosphorylation and maintained normal mitochondrial morphology. Additionally, cordycepin effectively increased adenosine 5'-triphosphate (ATP) content, mitochondrial membrane potential (MMP), and reduced mitochondrial ROS levels, as well as inhibited complex 1 activity. More importantly, cordycepin administration inhibited the expression of NLRP3 inflammasome components and the release of pro-inflammatory cytokine in rotenone-induced rats and cultured neuronal PC12 cells. Moreover, we demonstrated that the activation of NLRP3 inflammasome within neurons could be suppressed by the mitochondrial division inhibitor (Mdivi-1). Collectively, the present study provides evidence that cordycepin exerts neuroprotective effects partially through preventing neural NLRP3 inflammasome activation induced by Drp1-dependent mitochondrial fragmentation in rotenone-injected PD models.

Neuroprotective Effects of a GLP-2 Analogue in the MPTP Parkinson's Disease Mouse Model

BACKGROUND

Glucagon-like peptide 2 (GLP-2) is a peptide hormone derived from the proglucagon gene expressed in the intestines, pancreas and brain. Some previous studies showed that GLP-2 improved aging and Alzheimer's disease related memory impairments. Parkinson's disease (PD) is a progressive neurodegenerative disorder, and to date, there is no particular medicine reversed PD symptoms effectively.

OBJECTIVE

The aim of this study was to evaluate neuroprotective effects of a GLP-2 analogue in the 1-Methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) PD mouse model.

METHODS

In the present study, the protease resistant Gly(2)-GLP-2 (50 nmol/kg ip.) analogue has been tested for 14 days by behavioral assessment, transmission electron microscope, immunofluorescence histochemistry, enzyme-linked immunosorbent assay and western blot in an acute PD mouse model induced by MPTP. For comparison, the incretin receptor dual agonist DA5-CH was tested in a separate group.

RESULTS

The GLP-2 analogue treatment improved the locomotor and exploratory activity of mice, and improved bradykinesia and movement imbalance of mice. Gly(2)-GLP-2 treatment also protected dopaminergic neurons and restored tyrosine hydroxylase expression levels in the substantia nigra. Gly(2)-GLP-2 furthermore reduced the inflammation response as seen in lower microglia activation, and decreased NLRP3 and interleukin-1β pro-inflammatory cytokine expression levels. In addition, the GLP-2 analogue improved MPTP-induced mitochondrial dysfunction in the substantia nigra. The protective effects were comparable to those of the dual agonist DA5-CH.

CONCLUSION

The present results demonstrate that Gly(2)-GLP-2 can attenuate NLRP3 inflammasome-mediated inflammation and mitochondrial damage in the substantia nigra induced by MPTP, and Gly(2)-GLP-2 shows neuroprotective effects in this PD animal model.

Neuroimmune crosstalk and evolving pharmacotherapies in neurodegenerative diseases

Neurodegeneration is characterized by gradual onset and limited availability of specific biomarkers. Apart from various aetiologies such as infection, trauma, genetic mutation, the interaction between the immune system and CNS is widely associated with neuronal damage in neurodegenerative diseases. The immune system plays a distinct role in disease progression and cellular homeostasis. It induces cellular and humoral responses, and enables tissue repair, cellular healing and clearance of cellular detritus. Aberrant and chronic activation of the immune system can damage healthy neurons. The pro-inflammatory mediators secreted by chief innate immune components, the complement system, microglia and inflammasome can augment cytotoxicity. Furthermore, these inflammatory mediators accelerate microglial activation resulting in progressive neuronal loss. Various animal studies have been carried out to unravel the complex pathology and ascertain biomarkers for these harmful diseases, but have had limited success. The present review will provide a thorough understanding of microglial activation, complement system and inflammasome generation, which lead the healthy brain towards neurodegeneration. In addition to this, possible targets of immune components to confer a strategic treatment regime for the alleviation of neuronal damage are also summarized.

Neuroprotective effects of hydro-alcoholic extract of Eclipta alba against 1-methyl-4-phenylpyridinium-induced in vitro and in vivo models of Parkinson's disease

Pathogenesis of Parkinson's disease (PD) specifically involves the degeneration of dopaminergic neurons in the substantia nigra region, which mainly begun with the overwhelmed oxidative stress and neuroinflammation. Considering the antioxidant and other pharmacological properties, Eclipta alba needs to be exploited for its possible neuroprotective efficacy against PD and other neurological disorders. Therefore, the current study was conducted to exemplify the remedial effects of hydro-alcoholic extract of E. alba (EA-MEx) against MPP⁺-elicited in vitro and in vivo PD models. SH-SY5Y, a neuroblastoma cell culture and male Wistar rats were used to impersonate the hallmarks of PD. Qualitative and quantitative analyses of EA-MEx revealed the presence of quercetin, ellagic acid, catechin, kaempferol, and epicatechin at varying concentrations. EA-MEx was found to deliver considerable protection against MPP⁺-induced oxidative damages in SH-SY5Y cells. Furthermore, in vivo study also supported the neuroprotective efficacy of EA-MEx, with significant mitigation of behavioral deficits induced by intrastriatal injection of MPP⁺. Furthermore, the disturbed levels of cellular antioxidant machinery have been significantly improved with the pre-treatment of EA-MEx. Mechanistically, the expression of α-synuclein, tyrosine hydroxylase, and mortalin were also found to be improved with the prior treatment of EA-MEx. Hence, the study suggests Eclipta alba as a suitable candidate for the development of better neuropathological therapeutics.

α-Synuclein evokes NLRP3 inflammasome-mediated IL-1β secretion from primary human microglia

Synucleinopathies such as Parkinson's disease (PD) are hallmarked by α‐synuclein (α‐syn) pathology and neuroinflammation. This neuroinflammation involves activated microglia with increased secretion of interleukin‐1β (IL‐1β). The main driver of IL‐1β secretion from microglia is the NLRP3 inflammasome. A critical link between microglial NLRP3 inflammasome activation and the progression of both α‐syn pathology and dopaminergic neurodegeneration has been identified in various PD models in vivo. α‐Syn is known to activate the microglial NLRP3 inflammasome in murine models, but its relationship to this inflammasome in human microglia has not been established. In this study, IL‐1β secretion from primary mouse microglia induced by α‐syn fibrils was dependent on NLRP3 inflammasome assembly and caspase‐1 activity, as previously reported. We show that exposure of primary human microglia to α‐syn fibrils also resulted in significant IL‐1β secretion that was dependent on inflammasome assembly and involved the recruitment of caspase‐1 protein to inflammasome scaffolds as visualized with superresolution microscopy. While canonical IL‐1β secretion was clearly dependent on caspase‐1 enzymatic activity, this activity was less clearly involved for α‐syn‐induced IL‐1β secretion from human microglia. This work presents similarities between primary human and mouse microglia in the mechanisms of activation of the NLRP3 inflammasome by α‐syn, but also highlights evidence to suggest that there may be a difference in the requirement for caspase‐1 activity in IL‐1β output. The data represent a novel characterization of PD‐related NLRP3 inflammasome activation in primary human microglia and further implicate this mechanism in the pathology underlying PD.

Berberine Protects Against NLRP3 Inflammasome via Ameliorating Autophagic Impairment in MPTP-Induced Parkinson's Disease Model

The NLR family pyrin domain containing 3 (NLRP3) inflammasome was reported to be regulated by autophagy and activated during inflammatory procession of Parkinson’s disease (PD). Berberine (BBR) is well-studied to play an important role in promoting anti-inflammatory response to mediate the autophagy activity. However, the effect of Berberine on NLRP3 inflammasome in PD and its potential mechanisms remain unclear. Hence, in this study, we investigated the effects of BBR on 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice, by evaluating their behavioral changes, dopaminergic (DA) neurons loss, neuroinflammation, NLRP3 inflammasome and autophagic activity. BBR was also applied in BV2 cells treated with 1-methyl-4-pehnyl-pyridine (MPP+). The autophagy inhibitor 3-Methyladenine (3-MA) was administrated to block autophagy activity both in vivo and in vitro. In our in vivo studies, compared to MPTP group, mice in MPTP + BBR group showed significant amelioration of behavioral disorders, mitigation of neurotoxicity and NLRP3-associated neuroinflammation, enhancement of the autophagic process in substantia nigra (SN). In vitro, compared to MPP+ group, BBR significantly decreased the level of NLRP3 inflammasome including the expressions of NLRP3, PYD and CARD domain containing (PYCARD), cleaved caspase 1 (CASP1), and mature interleukin 1 beta (IL1B), via enhancing autophagic activity. Furthermore, BBR treatment increased the formation of autophagosomes in MPP+-treated BV2 cells. Taken together, our data indicated that BBR prevents NLRP3 inflammasome activation and restores autophagic activity to protect DA neurons against degeneration in vivo and in vitro, suggesting that BBR may be a potential therapeutic to treat PD.

Influenza Causes MLKL-Driven Cardiac Proteome Remodeling During Convalescence

RATIONALE

Patients with and without cardiovascular diseases have been shown to be at risk of influenza-mediated cardiac complications. Recent clinical reports support the notion of a direct link between laboratory-confirmed influenza virus infections and adverse cardiac events.

OBJECTIVE

Define the molecular mechanisms underlying influenza virus-induced cardiac pathogenesis after resolution of pulmonary infection and the role of necroptosis in this process.

METHODS AND RESULTS

Hearts from wild-type and necroptosis-deficient (MLKL [mixed lineage kinase domain-like protein]-KO) mice were dissected 12 days after initial influenza A virus (IAV) infection when viral titers were undetectable in the lungs. Immunofluorescence microscopy and plaque assays showed presence of viable IAV particles in the myocardium without generation of interferon responses. Global proteome and phosphoproteome analyses using high-resolution accurate mass-based LC-MS/MS and label-free quantitation showed that the global proteome as well as the phosphoproteome profiles were significantly altered in IAV-infected mouse hearts in a strain-independent manner. Necroptosis-deficient mice had increased survival and reduced weight loss post-IAV infection, as well as increased antioxidant and mitochondrial function, indicating partial protection to IAV infection. These findings were confirmed in vitro by pretreatment of human and rat myocytes with antioxidants or necroptosis inhibitors, which blunted oxidative stress and mitochondrial damage after IAV infection.

CONCLUSIONS

This study provides the first evidence that the cardiac proteome and phosphoproteome are significantly altered post-pulmonary influenza infection. Moreover, viral particles can persist in the heart after lung clearance, altering mitochondrial function and promoting cell death without active replication and interferon responses. Finally, our findings show inhibition of necroptosis or prevention of mitochondrial damage as possible therapeutic interventions to reduce cardiac damage during influenza infections. Graphic Abstract: A graphic abstract is available for this article.

Decoding Mast Cell-Microglia Communication in Neurodegenerative Diseases

Microglia, resident immune cells of the central nervous system (CNS), play a pivotal role in immune surveillance and maintenance of neuronal health. Mast cells are also important resident immune cells of the CNS but they are underappreciated and understudied. Both microglia and mast cells are endowed with an array of signaling receptors that recognize microbes and cellular damage. As cellular sensors and effectors in the CNS, they respond to many CNS perturbations and have been implicated in neuroinflammation and neurodegeneration. Mast cells contain numerous secretory granules packaged with a plethora of readily available and newly synthesized compounds known as 'mast cell mediators'. Mast cells act as 'first responders' to a pathogenic stimuli and respond by degranulation and releasing these mediators into the extracellular milieu. They alert other glial cells, including microglia to initiate neuroinflammatory processes that culminate in the resolution of injury. However, failure to resolve the pathogenic process can lead to persistent activation, release of pro-inflammatory mediators and amplification of neuroinflammatory responses, in turn, resulting in neuronal dysfunction and demise. This review discusses the current understanding of the molecular conversation between mast cells and microglia in orchestrating immune responses during two of the most prevalent neurodegenerative diseases, namely Alzheimer's disease and Parkinson's disease. Here we also survey the potential emerging therapeutic approaches targeting common pathways in mast cells and microglia to extinguish the fire of inflammation.

The Role of Mitochondria in Pyroptosis

Pyroptosis is a recently discovered aspartic aspart-specific cysteine protease (Caspase-1/4/5/11) dependent mode of gene-regulated cell death cell death, which is represented by the rupture of cell membrane perforations and the production of proinflammatory mediaters like interleukin-18(IL-18) and interleukin-1β (IL-1β). Mitochondria also play an important role in apoptotic cell death. When it comes to apoptosis of mitochondrion, mitochondrial outer membrane permeabilization (MOMP) is commonly known to cause cell death. As a downstream pathological process of apoptotic signaling, MOMP participates in the leakage of cytochrome-c from mitochondrion to the cytosol and subsequently activate caspase proteases. Hence, targeting MOMP for the sake of manipulating cell death presents potential therapeutic effects among various types of diseases, such as autoimmune disorders, neurodegenerative diseases, and cancer. In this review, we highlights the roles and significance of mitochondria in pyroptosis to provide unexplored strategies that target the mitochondria to regulate cell death for clinical benefits.

The NLRP3 inflammasome: Multiple activation pathways and its role in primary cells during ventricular remodeling

Inflammasomes are a group of multiprotein signaling complexes located in the cytoplasm. Several inflammasomes have been identified, including NLRP1, NLRP2, NLRP3, AIM2, and NLRC4. Among them, NLRP3 was investigated in most detail, and it was reported that it can be activated by many different stimuli. Increased NLRP3 protein expression and inflammasome assembly lead to caspase-1 mediated maturation and release of IL-1β, which triggers inflammation and pyroptosis. The activation of the NLRP3 inflammasome has been widely reported in studies of tumors and neurological diseases, but relatively few studies on the cardiovascular system. Ventricular remodeling (VR) is an important factor contributing to heart failure (HF) after myocardial infarction (MI). Consequently, delaying VR is of great significance for improving heart function. Studies have shown that the NLRP3 inflammasome plays an essential role in the process of VR. Here, we reviewed the latest studies on the activation pathway of the NLRP3 inflammasome, focusing on the effects of the NLRP3 inflammasome in primary cells during VR, and finally discuss future research directions in this field.

Inhibiting NLRP3 inflammasome activation prevents copper-induced neuropathology in a murine model of Wilson's disease

Wilson’s disease (WD) is an inherited disorder characterized by excessive accumulation of copper in the body, particularly in the liver and brain. In the central nervous system (CNS), extracellular copper accumulation triggers pathological microglial activation and subsequent neurotoxicity. Growing evidence suggests that levels of inflammatory cytokines are elevated in the brain of murine WD models. However, the mechanisms associated with copper deposition to neuroinflammation have not been completely elucidated. In this study, we investigated how the activation of NLR family pyrin domain containing 3 (NLRP3) inflammasome contributes to copper-mediated neuroinflammation in an animal model of WD. Elevated levels of interleukin-1β, interleukin-18, interleukin-6, and tumor necrosis factor-α were observed in the sera of WD patients and toxic milk (TX) mice. The protein levels of inflammasome adaptor molecule apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), cleaved caspase-1, and interleukin-1β were upregulated in the brain regions of the TX mice. The NLRP3 inflammasome was activated in the TX mice brains. Furthermore, the activation of NLRP3 inflammasome was noted in primary microglia treated with CuCl₂, accompanied by the increased levels of cleaved caspase-1, ASC, and interleukin-1β. Blocking NLRP3 inflammasome activation with siNlrp3 or MCC950 reduced interleukin-1β and interleukin-18 production, thereby effectively mitigating cognitive decline, locomotor behavior impairment, and neurodegeneration in TX mice. Overall, our study demonstrates the contribution of copper overload-mediated activation of NLRP3 inflammasome to progressive neuropathology in the CNS of a murine model of WD. Therefore, blockade of the NLRP3 inflammasome activation could be a potential therapeutic strategy for WD.

The Mitochondrial Permeability Transition: Nexus of Aging, Disease and Longevity

The activity of the mitochondrial permeability transition pore, mPTP, a highly regulated multi-component mega-channel, is enhanced in aging and in aging-driven degenerative diseases. mPTP activity accelerates aging by releasing large amounts of cell-damaging reactive oxygen species, Ca²⁺ and NAD⁺. The various pathways that control the channel activity, directly or indirectly, can therefore either inhibit or accelerate aging or retard or enhance the progression of aging-driven degenerative diseases and determine lifespan and healthspan. Autophagy, a catabolic process that removes and digests damaged proteins and organelles, protects the cell against aging and disease. However, the protective effect of autophagy depends on mTORC2/SKG1 inhibition of mPTP. Autophagy is inhibited in aging cells. Mitophagy, a specialized form of autophagy, which retards aging by removing mitochondrial fragments with activated mPTP, is also inhibited in aging cells, and this inhibition leads to increased mPTP activation, which is a major contributor to neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. The increased activity of mPTP in aging turns autophagy/mitophagy into a destructive process leading to cell aging and death. Several drugs and lifestyle modifications that enhance healthspan and lifespan enhance autophagy and inhibit the activation of mPTP. Therefore, elucidating the intricate connections between pathways that activate and inhibit mPTP, in the context of aging and degenerative diseases, could enhance the discovery of new drugs and lifestyle modifications that slow aging and degenerative disease.

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.

Role of Microgliosis and NLRP3 Inflammasome in Parkinson's Disease Pathogenesis and Therapy

Parkinson's disease (PD) is a neurodegenerative disorder marked primarily by motor symptoms such as rigidity, bradykinesia, postural instability and resting tremor associated with dopaminergic neuronal loss in the Substantia Nigra pars compacta (SNpc) and deficit of dopamine in the basal ganglia. These motor symptoms can be preceded by pre-motor symptoms whose recognition can be useful to apply different strategies to evaluate risk, early diagnosis and prevention of PD progression. Although clinical characteristics of PD are well defined, its pathogenesis is still not completely known, what makes discoveries of therapies capable of curing patients difficult to be reached. Several theories about the cause of idiopathic PD have been investigated and among them, the key role of inflammation, microglia and the inflammasome in the pathogenesis of PD has been considered. In this review, we describe the role and relation of both the inflammasome and microglial activation with the pathogenesis, symptoms, progression and the possibilities for new therapeutic strategies in PD.

Targeting microglial autophagic degradation in NLRP3 inflammasome-mediated neurodegenerative diseases

Neuroinflammation is considered as a detrimental factor in neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), etc. Nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3), the most well-studied inflammasome, is abundantly expressed in microglia and has gained considerable attention. Misfolded proteins are characterized as the common hallmarks of neurodegenerative diseases due to not only their induced neuronal toxicity but also their effects in over-activating microglia and the NLRP3 inflammasome. The activated NLRP3 inflammasome aggravates the pathology and accelerates the progression of neurodegenerative diseases. Emerging evidence indicates that microglial autophagy plays an important role in the maintenance of brain homeostasis and the negative regulation of NLRP3 inflammasome-mediated neuroinflammation. The excessive activation of NLRP3 inflammasome impairs microglial autophagy and further aggravates the pathogenesis of neurodegenerative diseases. In this review article, we summarize and discuss the NLRP3 inflammasome and its specific inhibitors in microglia. The crucial role of microglial autophagy and its inducers in the removal of misfolded proteins, the clearance of damaged mitochondria and reactive oxygen species (ROS), and the degradation of the NLRP3 inflammasome or its components in neurodegenerative diseases are summarized. Understanding the underlying mechanisms behind the sex differences in NLRP3 inflammasome-mediated neurodegenerative diseases will help researchers to develop more targeted therapies and increase our diagnostic and prognostic abilities. In addition, the superiority of the combined use of microglial autophagy inducers with the specific inhibitors of the NLRP3 inflammasome in the inhibition of NLRP3 inflammasome-mediated neuroinflammation requires further preclinical and clinical validations in the future.

Andrographolide suppresses NLRP3 inflammasome activation in microglia through induction of parkin-mediated mitophagy in in-vitro and in-vivo models of Parkinson disease

Cellular communication linking microglia activation and dopaminergic neuronal loss play an imperative role in the progression of Parkinson's disease (PD); however, underlying molecular mechanisms are not precise and require further elucidation. NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome activation is extensively studied in context to microglial activation and progressive dopaminergic neuronal loss in PD. Several pathophysiological factors such as oxidative stress, mitochondrial dysfunction impaired mitophagy plays a crucial role in activating NLRP3 inflammasome complex. Hence, regulation of microglial activation through mitophagy could be a valuable strategy in controlling microglia mediated neurodegeneration. In this study we have developed a model of inflammasome activation by combining LPS with a mitochondrial complex-I inhibitor MPP⁺. The idea of using MPP⁺ after priming mouse microglia with LPS was to disrupt mitochondria and release reactive oxygen species, which act as Signal 2 in augmenting NLRP3 assembly, thereby releasing potent inflammatory mediators such as active interleukin-1 beta (IL-1β) and IL-18. LPS-MPP⁺ combination was seen to impaired the mitophagy by inhibiting the initial step of autophagosome formation as evidenced by protein expression and confocal imaging data. Treatment with Andrographolide promoted the parkin-dependent autophagic flux formation in microglia; resulting in the removal of defective mitochondria which in turn inhibit NLRP3 inflammasome activation. Additionally, the neuroprotective role of Andrographolide in inhibiting NLRP3 activation together with salvage ATP level via promoting parkin-dependent mitophagy was seen in the substantial nigra par compacta (SNpc) region of mice brain. Furthermore, Andrographolide rescued the dopaminergic neuron loss and improved the behavioural parameters in animal model. Collectively, our results reveal the role of mitophagy in the regulation of NLRP3 inflammasome by removing defective mitochondria. In addition, andrographolide was seen to abate NLRP3 inflammasome activation in microglia and rescue dopaminergic neuron loss.

2,5-hexanedione induces NLRP3 inflammasome activation and neurotoxicity through NADPH oxidase-dependent pathway

Chronic exposure to n-hexane causes sensorimotor neuropathy, which is mediated by 2,5-hexanedione (HD), a toxic metabolite of n-hexane. Activation of the nucleotide-binding and oligomerization domain, leucine-rich repeat, and pyrin domain-containing 3 (NLRP3) inflammasome is involved in multiple neurodegenerative diseases. However, whether the NLRP3 inflammasome contributes to HD-induced neurotoxicity remains unclear. In this study, the effects of HD on NLRP3 inflammasome activation and the underlying mechanisms were determined by using HD-treated rat and cell culture models. Increased NLRP3 expression, caspase-1 activation and interleukin-1β production were observed in both the brain and spinal cord of HD-treated rats. Double-immunofluorescence staining showed that ASC speck formation and caspase-1 expression were mainly localized in microglia. HD-induced activation of the NLRP3 inflammasome was further mirrored in BV2 microglial cells and was associated with NADPH oxidase activation. Interestingly, inhibition of NADPH oxidase by apocynin or specific siRNAs significantly mitigated HD-induced NLRP3 inflammasome activation. Furthermore, apocynin suppressed activation of the MAPK and NF-κB signaling pathways. Blocking activation of p38-MAPK and NF-κB significantly reduced HD-induced capase-1 activation and interleukin-1β maturation, indicating a critical role of NADPH oxidase and downstream MAPK and NF-κB pathways in regulating activation of NLRP3 inflammasome, in HD-treated microglia. Finally, we found that inhibition of microglial NLRP3 inflammasome and NADPH oxidase activation abrogated HD-induced microglial activation and neurodegeneration in both SHSY5Y neuronal cells and primary cortical neuron-glia cultures. Altogether, our findings suggest that NADPH oxidase-dependent activation of microglial NLRP3 inflammasome contributes to HD-induced neurotoxicity, providing novel insight into the mechanisms of this solvent-induced neuropathy.

Impaired autophagy in microglia aggravates dopaminergic neurodegeneration by regulating NLRP3 inflammasome activation in experimental models of Parkinson's disease

Microglia-mediated inflammation plays an important role in the pathogenesis of several neurodegenerative diseases including Parkinson's disease (PD). Recently, autophagy has been linked to the regulation of the inflammatory response. However, the potential role of microglial autophagy in the context of PD pathology has not been characterized. In the present study, we investigated whether impaired microglial autophagy would affect dopaminergic neurodegeneration and neuroinflammation both in vivo and in vitro. In vitro, BV2 microglial cells were exposed to LPS in the presence or absence of autophagy-related gene 5 (Atg5) small interference RNA (Atg5-siRNA). For in vivo study, microglial Atg5 conditional knockout (Atg5^flox/flox; CX3CR1-Cre) mice and their wild-type littermates (Atg5^flox/flox) were intraperitoneally injected with MPTP to induce experimental PD model. Our results revealed that disruption of autophagy by Atg5-siRNA aggravated LPS-induced inflammatory responses in BV2 cells and caused greater apoptosis in SH-SY5Y cells treated with BV2 conditioned medium. In mice, impaired autophagy in microglia exacerbated dopaminergic neuron loss in response to MPTP. The mechanism by which the deficiency of microglial autophagy promoted neuroinflammation and dopaminergic neurodegeneration was related to the regulation of NLRP3 inflammasome activation. These findings demonstrate that impairing microglial autophagy aggravates pro-inflammatory responses to LPS and exacerbates MPTP-induced neurodegeneration by modulating NLRP3 inflammasome responses. We anticipate that enhancing microglial autophagy may be a promising new therapeutic strategy for PD.

Nutraceutical Strategies for Suppressing NLRP3 Inflammasome Activation: Pertinence to the Management of COVID-19 and Beyond

Inflammasomes are intracellular protein complexes that form in response to a variety of stress signals and that serve to catalyze the proteolytic conversion of pro-interleukin-1β and pro-interleukin-18 to active interleukin-1β and interleukin-18, central mediators of the inflammatory response; inflammasomes can also promote a type of cell death known as pyroptosis. The NLRP3 inflammasome has received the most study and plays an important pathogenic role in a vast range of pathologies associated with inflammation-including atherosclerosis, myocardial infarction, the complications of diabetes, neurological and autoimmune disorders, dry macular degeneration, gout, and the cytokine storm phase of COVID-19. A consideration of the molecular biology underlying inflammasome priming and activation enables the prediction that a range of nutraceuticals may have clinical potential for suppressing inflammasome activity-antioxidants including phycocyanobilin, phase 2 inducers, melatonin, and N-acetylcysteine, the AMPK activator berberine, glucosamine, zinc, and various nutraceuticals that support generation of hydrogen sulfide. Complex nutraceuticals or functional foods featuring a number of these agents may find utility in the prevention and control of a wide range of medical disorders.

Mitochondrial dysfunction in the development and progression of neurodegenerative diseases

In addition to ATP synthesis, mitochondria are highly dynamic organelles that modulate apoptosis, ferroptosis, and inflammasome activation. Through executing these varied functions, the mitochondria play critical roles in the development and progression of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Friedreich ataxia, among others. Impaired mitochondrial biogenesis and abnormal mitochondrial dynamics contribute to mitochondrial dysfunction in these diseases. Additionally, dysfunctional mitochondria play critical roles in signaling for both inflammasome activation and ferroptosis. Therapeutics are being developed to circumvent inflammasome activation and ferroptosis in dysfunctional mitochondria. Targeting these aspects of mitochondrial dysfunction may present viable therapeutic strategies for combatting the neurodegenerative diseases. This review aims to summarize the role of the mitochondria in the development and progression of neurodegenerative diseases and to present current therapeutic approaches that target mitochondrial dysfunction in these diseases.

Anti-inflammatory effects of vinpocetine in LPS-stimulated microglia via activation of AMPK

Microglia are the resident immune cells in the central nervous system (CNS), which play important roles in the repair of neuroinflammatory injury. The present study investigated the anti-neuroinflammatory effects of vinpocetine induced by lipopolysaccharide (LPS) in BV2 microglia. BV2 microglia were pretreated with vinpocetine, and then stimulated with LPS (100 ng/mL). The cytotoxicity of BV2 microglia was assessed by MTT assay. The expression levels of nitrite oxide were measured by Griess assay. Proinflammatory cytokines and mediators were determined by Western blot, ELISA, or quantitative real-time PCR. Vinpocetine significantly decreased the generation of nitric oxide-inducible nitric oxide synthase (iNOS), cyclooxygenase- (COX-) 2 in a dose-dependent manner. In addition, vinpocetine decreased the production of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-6 and IL-1β. Furthermore, it was observed that phosphorylation levels of AMPK (Thr-172) decreased in LPS-stimulated BV2 microglia. Vinpocetine treatment increased AMPK phosphorylation in LPS-stimulated BV2 microglia. AMPK inhibition by siRNA blocked the anti-inflammatory effects of vinpocetine induced by LPS in BV2 microglia. The overall results demonstrate that vinpocetine has anti-inflammatory effects on LPS-stimulated BV2 microglia via inducing phosphorylation of AMPK, suggesting that vinpocetine is a potential therapeutic agent in neuroinflammatory injury.

Ellagic Acid Protects Dopamine Neurons via Inhibition of NLRP3 Inflammasome Activation in Microglia

Neuroinflammation plays a crucial role in the pathological process of Parkinson's disease (PD). Nod-like receptor protein 3 (NLRP3) inflammasome was highly located in microglia and involved in the process of neuroinflammation. Activation of the NLRP3 inflammasome has been confirmed to contribute to the progression of PD. Thus, inhibition of NLRP3 inflammasome activation could be an important breakthrough point on PD therapy. Ellagic acid (EA) is a natural polyphenol that has been widely found in soft fruits, nuts, and other plant tissues with anti-inflammatory, antioxidant, and neuroprotective properties. However, the mechanisms underlying EA-mediated anti-inflammation and neuroprotection have not been fully elucidated. In this study, a lipopolysaccharide- (LPS-) induced rat dopamine (DA) neuronal damage model was performed to determine the effects of EA on the protection of DA neurons. In addition, the DA neuronal MN9D cell line and microglial BV-2 cell line were employed to explore whether EA-mediated neuroprotection was through an NLRP3-dependent mechanism. Results indicated that EA ameliorated LPS-induced DA neuronal loss in the rat substantia nigra. Further, inhibition of microglial NLRP3 inflammasome signaling activation was involved in EA-generated neuroprotection, as evidenced by the following observations. First, EA reduced NLRP3 inflammasome signaling activation in microglia and subsequent proinflammatory cytokines' excretion. Second, EA-mediated antineuroinflammation and further DA neuroprotection from LPS-induced neurotoxicity were not shown upon microglial NLRP3 siRNA treatment. In conclusion, this study demonstrated that EA has a profound effect on protecting DA neurons against LPS-induced neurotoxicity via the suppression of microglial NLRP3 inflammasome activation.

From inflammasome to Parkinson's disease: Does the NLRP3 inflammasome facilitate exosome secretion and exosomal alpha-synuclein transmission in Parkinson's disease?

A pivotal neuropathological manifestation of synucleinopathies, like Parkinson's disease (PD), is the aggregation of α-synuclein. In a recent cell-to-cell transmission model of α-synuclein, α-synuclein propagation was demonstrated to resemble that of prion proteins in the central nervous system. Furthermore, exosomes, as biomolecule carriers, have been shown to transmit α-synuclein from neuron to neuron. However, the mechanisms underlying exosomal α-synuclein transmission have not been well understood. The NLR family pyrin domain containing 3 protein (NLRP3) inflammasome activation in microglia, and the subsequent release of proinflammatory cytokines, are two crucial pathological events involved in neuroinflammation and PD progression. Research has revealed that the NLRP3 inflammasome may facilitate the secretion of extracellular vesicles, as well as exosomal transmission of proteins like aggregated α-synuclein. However, only a few reports have evaluated these pathogenic mechanisms. Herein we evaluate for the first time the current evidence for the involvement of the NLRP3 inflammasome in microvesicle generation by microglial cells, and the various mechanisms regarding the production, shedding, and content of exosomes in relation to α-synuclein transmission from neuron to neuron. Furthermore, we propose a model of microglial NLRP3 inflammasome-dependent exosome secretion and exosomal α-synuclein transmission in PD. This knowledge may lead to the identification of novel potential targets for drug development and stimulate further research in PD.

JNK/c-Jun-driven NLRP3 inflammasome activation in microglia contributed to retinal ganglion cells degeneration induced by indirect traumatic optic neuropathy

BACKGROUND

Indirect traumatic optic neuropathy (ITON) is a major cause of permanent loss of vision after blunt head trauma. Neuroinflammation plays a crucial role in neurodegenerative diseases. The present study concentrated on JNK/c-Jun-driven NLRP3 inflammasome activation in microglia during the degeneration of retinal ganglion cells (RGCs) in ITON.

METHODS

An impact acceleration (IA) model was employed to induce ITON, which could produce significant neurodegeneration in the visual system. Pharmacological approaches were employed to disrupt JNK and to explore whether JNK and the microglial response contribute to RGC death and axonal degeneration.

RESULTS

Our results indicated that the ITON model induced significant RGC death and axonal degeneration and activated JNK/c-Jun signaling, which could further induce the microglial response and NLRP3 inflammasome activation. Moreover, JNK disruption is sufficient to suppress NLRP3 inflammasome activation in microglia and to prevent RGC death and axonal degeneration.

CONCLUSIONS

ITON could promote JNK/c-Jun signaling, which further activates the NLRP3 inflammasome in microglia and contributes to the degeneration of axons and death of RGCs. JNK inhibition is able to suppress the inflammatory reaction and improve RGC survival. Although further work is needed to determine whether pharmacological inhibition of the NLRP3 inflammasome can prevent ITON, our findings indicated that such intervention could be promising for translational work.

The Dichotomous Role of Inflammation in the CNS: A Mitochondrial Point of View

Innate immune response is one of our primary defenses against pathogens infection, although, if dysregulated, it represents the leading cause of chronic tissue inflammation. This dualism is even more present in the central nervous system, where neuroinflammation is both important for the activation of reparatory mechanisms and, at the same time, leads to the release of detrimental factors that induce neurons loss. Key players in modulating the neuroinflammatory response are mitochondria. Indeed, they are responsible for a variety of cell mechanisms that control tissue homeostasis, such as autophagy, apoptosis, energy production, and also inflammation. Accordingly, it is widely recognized that mitochondria exert a pivotal role in the development of neurodegenerative diseases, such as multiple sclerosis, Parkinson's and Alzheimer's diseases, as well as in acute brain damage, such in ischemic stroke and epileptic seizures. In this review, we will describe the role of mitochondria molecular signaling in regulating neuroinflammation in central nervous system (CNS) diseases, by focusing on pattern recognition receptors (PRRs) signaling, reactive oxygen species (ROS) production, and mitophagy, giving a hint on the possible therapeutic approaches targeting mitochondrial pathways involved in inflammation.

Primate differential redoxome (PDR) - A paradigm for understanding neurodegenerative diseases

Despite different phenotypic manifestations, mounting evidence points to similarities in the molecular basis of major neurodegenerative diseases (ND). CNS has evolved to be robust against hazard of ROS, a common perturbation aerobic organisms are confronted with. The trade-off of robustness is system's fragility against rare and unexpected perturbations. Identifying the points of CNS fragility is key for understanding etiology of ND. We postulated that the 'primate differential redoxome' (PDR), an assembly of proteins that contain cysteine residues present only in the primate orthologues of mammals, is likely to associate with an added level of regulatory functionalities that enhanced CNS robustness against ROS and facilitated evolution. The PDR contains multiple deterministic and susceptibility factors of major ND, which cluster to form coordinated redox networks regulating various cellular processes. The PDR analysis revealed a potential CNS fragility point, which appears to associates with a non-redundant PINK1-PRKN-SQSTM1(p62) axis coordinating protein homeostasis and mitophagy.

NLRP3 inflammasome mediates 2,5-hexanedione-induced neurotoxicity through regulation of macrophage infiltration in rats

Currently, whether nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation contributes to neuropathy induced by 2,5-Hexanedione (HD), the toxic metabolite of n-hexane, remains unknown. In this study, we found that HD intoxication elevated NLRP3 expression, caspase-1 activation and interleukin-1β production in sciatic nerve of rats, indicating activation of NLRP3 inflammasome. The increased cleavage of gasdermin D (GSDMD) protein, an important mediator of pyroptosis, and axon degeneration were also observed in sciatic nerves of HD-intoxicated rats. Interestingly, glybenclamide, a widely used inhibitor of NLRP3 inflammasome, significantly reduced NLRP3 inflammasome activation, which was associated with decreased GSDMD cleavage and axon degeneration as well as improved motor performance of HD-intoxicated rats. Subsequently, we found that inhibition of NLRP3 inflammasome by glybenclamide attenuated macrophage infiltration, activation and M1 polarization in sciatic nerves of HD-intoxicated rats. Furthermore, decreased malondialdehyde (MDA) contents and increased glutathione (GSH) level and total anti-oxidative capacity were also observed in sciatic nerves of rats treated with combined glybenclamide and HD compared with HD alone group. Altogether, our findings suggest that NLRP3 inflammasome activation contributes to HD-induced neurotoxicity by enhancing macrophage infiltration and activation as well as oxidative stress, providing a novel mechanism of neuropathy induced by this neurotoxicant.

NLRP3 Inflammasomes in Parkinson's disease and their Regulation by Parkin

Chronic inflammation might correlate with the formation of α-synuclein oligomers, subsequently leading to dopaminergic (DA) neuronal death in Parkinson's disease (PD). As major components of chronic inflammation, NOD-like receptor protein 3 (NLRP3) inflammasomes play a crucial role in PD via caspase 1 activation, primarily induced by mitochondrial damage. NLRP3 binds to apoptosis-associated speck-like protein containing a CARD (PYCARD/ASC), and forms inflammasomes in the brain. Inflammasomes act as a platform for caspase 1 to induce interleukin 1 Beta (IL1β) maturation, leading to neuronal pyroptosis. Furthermore, alpha-synuclein, whose abnormal aggregation is the main pathogenesis of PD, also activates NLRP3 inflammasomes. Mutations to PRKN (encoding Parkin) are the most common cause of autosomal recessive familial and sporadic early-onset PD. Evidence has confirmed a relationship between Parkin and NLRP3 inflammasomes. In this review, we summarize the current understanding of NLRP3 inflammasomes and their role in PD progression, and discuss their regulation by Parkin.

Baicalein Attenuates Neuroinflammation by Inhibiting NLRP3/caspase-1/GSDMD Pathway in MPTP Induced Mice Model of Parkinson's Disease

BACKGROUND

Inflammasome-induced neuroinflammation is a major pathogenic mechanism underlying the degeneration of nigral dopaminergic neurons in Parkinson's disease (PD). Baicalein is a flavonoid isolated from the traditional Chinese medicinal herbal Scutellaria baicalensis Georgi with known anti-inflammatory and neuroprotective efficacy in models of neurodegenerative diseases, including PD. However, its effects on inflammasome-induced neuroinflammation during PD remain unclear.

METHODS

We used N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to induce PD-like pathology in mice. Behavioral assessments including the pole test, rotarod test and open filed test were conducted to evaluate the effects of baicalein on MPTP-induced motor dysfunction. The efficacies of baicalein against MPTP-induced dopaminergic neuron loss and glial cell activation in the substantia nigra compact (SNc) were examined by immunohistochemistry, effects on proinflammatory cytokines by qPCR and enzyme-linked immunosorbent assay (ELISA), effects on inflammasome pathway activation by immunoblotting and flow cytometry.

RESULTS

Administration of baicalein reversed MPTP-induced motor dysfunction, loss of dopaminergic neurons, and pro-inflammatory cytokine elevation. Baicalein also inhibited NLRP3 and caspase-1 activation and suppressed gasdermin D (GSDMD)-dependent pyroptosis. Additionally, baicalein inhibited the activation and proliferation of disease-associated proinflammatory microglia.

CONCLUSIONS

These findings suggest that baicalein can reverse MPTP-induced neuroinflammation in mice by suppressing NLRP3/caspase-1/GSDMD pathway. Our study provides potential insight of baicalein in PD therapy.

TRP Channels Role in Pain Associated With Neurodegenerative Diseases

Transient receptor potential (TRP) are cation channels expressed in both non-excitable and excitable cells from diverse tissues, including heart, lung, and brain. The TRP channel family includes 28 isoforms activated by physical and chemical stimuli, such as temperature, pH, osmotic pressure, and noxious stimuli. Recently, it has been shown that TRP channels are also directly or indirectly activated by reactive oxygen species. Oxidative stress plays an essential role in neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases, and TRP channels are involved in the progression of those diseases by mechanisms involving changes in the crosstalk between Ca2+ regulation, oxidative stress, and production of inflammatory mediators. TRP channels involved in nociception include members of the TRPV, TRPM, TRPA, and TRPC subfamilies that transduce physical and chemical noxious stimuli. It has also been reported that pain is a complex issue in patients with Alzheimer's and Parkinson's diseases, and adequate management of pain in those conditions is still in discussion. TRPV1 has a role in neuroinflammation, a critical mechanism involved in neurodegeneration. Therefore, some studies have considered TRPV1 as a target for both pain treatment and neurodegenerative disorders. Thus, this review aimed to describe the TRP-dependent mechanism that can mediate pain sensation in neurodegenerative diseases and the therapeutic approach available to palliate pain and neurodegenerative symptoms throughout the regulation of these channels.

Key Mechanisms and Potential Targets of the NLRP3 Inflammasome in Neurodegenerative Diseases

Neurodegenerative diseases are neuronal disorders characterized by the loss of a large number of neurons in the human brain. Innate immunity-mediated neuroinflammation actively contributes to the onset and progression of neurodegenerative diseases. Inflammasomes are involved in the progression of the innate immune response and are responsible for the maturation of caspase-1 and inflammatory cytokines during neuroinflammation. The nucleotide-binding oligomerization domain leucine-rich repeat and pyrin domain-containing protein 3 (NLRP3) inflammasome, which is one of the most intensively investigated inflammasomes, has been reported to play a key role in neurodegenerative diseases. Here, we reviewed the mechanisms, role, and latest developments regarding the NLRP3 inflammasome with respect to three neurodegenerative diseases: Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Patient and animal model studies have found that abnormal protein aggregation of Aβ, synuclein, or copper–zinc superoxide dismutase-1 (SOD1), which are the main proteins expressed in the three diseases, respectively, can activate microglial cells, induce increased interleukin-1β (IL-1β) release, and activate the NLRP3 pathway, leading to neurodegeneration. In contrast, a deficiency of the components of the NLRP3 pathway may inhibit Aβ, synuclein, or SOD1-induced microglial activation. These studies indicate a positive correlation between NLRP3 levels and abnormal protein aggregation. However, in the case of ALS, not only microglia but also astrocytes express increased NLRP3 levels and contribute to activation of the NLRP3 pathway. In addition, in this review article, we also focus on the therapeutic implications of targeting novel inhibitors of the NLRP3 inflammasome or of novel drugs that mediate the NLRP3 pathway, which could play a role via NLRP3 in the treatment of neurodegenerative diseases.

The NLRP3 inflammasome as a bridge between neuro-inflammation in metabolic and neurodegenerative diseases

Evidence increasingly suggests that type 2 diabetes mellitus (T2DM) is a risk factor for neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD) and Parkinson's disease (PD). These diseases share many pathological processes, including oxidative stress, local inflammation/neuroinflammation and chronic, low-grade (systemic) inflammation, which are exacerbated by aging, a common risk factor for T2DM and NDDs. Here, we focus on the link between chronic inflammation driven by peripheral metabolic disease and how this may impact neurodegeneration in AD and PD. We review the relationship between these common pathological processes in AD and PD from the perspective of the "pro-inflammatory" signaling of the nucleotide-binding oligomerization domain (NOD)-, leucine-rich repeat- (LRR)-, and pyrin domain-containing protein 3 (NLRP3) inflammasome complex. Since the need for effective disease-modifying therapies in T2DM, AD and PD is significant, the relationship between these diseases is important as a positive clinical impact on one may benefit the others. We briefly consider how novel strategies may target neuro-inflammation and provide potential therapies for AD and PD.

Slc6a3-dependent expression of a CAPS-associated Nlrp3 allele results in progressive behavioral abnormalities and neuroinflammation in aging mice

BACKGROUND

An association between neuroinflammation and age-related neurologic disorders has been established but the molecular mechanisms and cell types involved have not been thoroughly characterized. Activity of the proinflammatory NLRP3 inflammasome is implicated in Alzheimer's and Parkinson's disease and our recent studies in patients suggest that dopaminergic neurons within the degenerating mesencephalon express NLRP3 throughout the progression of PD. Here, we directly test the impact of enhanced inflammasome activity in mesencephalic neurons by characterizing motor function, tissue integrity, and neuroinflammation in aging mice harboring hyperactivating mutations within the endogenous murine Nlrp3 locus, enabled only in cells expressing the dopaminergic neuron-specific Slc6a3 promoter.

METHODS

We compared mice harboring inducible alleles encoding the cryopyrin-associated periodic syndrome activating mutations Nlrp3A350V and Nlrp3L351P inserted into the endogenous mouse Nlrp3 locus. Tissue specific expression was driven by breeding these animals with mice expressing Cre recombinase under the control of the dopaminergic neuron-specific Slc6a3 promoter. The experimental mice, designed to express hyperactive NLRP3 only when the endogenous mouse Nlrp3 promotor is active in dopaminergic neurons, were analyzed throughout 18 months of aging using longitudinal motor function assessments. Biochemical and histologic analyses of mesencephalic tissues were conducted in 1- and 18-month-old animals.

RESULTS

We observed progressive and significant deficits in motor function in animals expressing Nlrp3L351P, compared with animals expressing Nlrp3WT and Nlrp3A350V. Age-dependent neuroinflammatory changes in the mesencephalon were noted in all animals. Analysis of GFAP-immunoreactive astrocytes in the substantia nigra revealed a significant increase in astrocyte number in animals expressing Nlrp3L351P compared with Nlrp3WT and Nlrp3A350V. Further analysis of Nlrp3L351P striatal tissues indicated genotype specific gliosis, elevated Il1b expression, and both morphologic and gene expression indicators of proinflammatory A1 astrocytes.

CONCLUSIONS

Dopaminergic neurons have the potential to accumulate NLRP3 inflammasome activators with age, including reactive oxygen species, dopamine metabolites, and misfolded proteins. Results indicate the Nlrp3 locus is active in dopaminergic neurons in aging mice, and that the hyperactive Nlrp3L351P allele can drive neuroinflammatory changes in association with progressive behavioral deficits. Findings suggest neuronal NLRP3 inflammasome activity may contribute to neuroinflammation observed during normal aging and the progression of neurologic disorders.

Rojo A, Manda G, Boscá L, Cuadrado A. Inflammation in Parkinson's Disease: Mechanisms and Therapeutic Implications

Parkinson's disease (PD) is a common neurodegenerative disorder primarily characterized by the death of dopaminergic neurons that project from the substantia nigra pars compacta. Although the molecular bases for PD development are still little defined, extensive evidence from human samples and animal models support the involvement of inflammation in onset or progression. However, the exact trigger for this response remains unclear. Here, we provide a systematic review of the cellular mediators, i.e., microglia, astroglia and endothelial cells. We also discuss the genetic and transcriptional control of inflammation in PD and the immunomodulatory role of dopamine and reactive oxygen species. Finally, we summarize the preclinical and clinical approaches targeting neuroinflammation in PD.

Neuroinflammatory Responses and Parkinson' Disease: Pathogenic Mechanisms and Therapeutic Targets

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorders of the central nervous system, which mainly impairs the motor system. However, the pathogenic mechanisms are still unclear. Gene-environment complex interaction leads to selective dopaminergic neuron death in PD. Growing evidences supports that neuroinflammatory responses are involved in the pathogenesis of PD. This review critically discusses current studies on the inflammatory response of the pathological process of PD. The mechanisms and strategies of modifying inflammatory responses would be potential treatments for neurodegenerative diseases. Graphical abstract Activated microglia canpromote the damage ofdopaminergic neurons, which inturn aggravates the activation ofmicroglia in the process of PD. Atthe same time, microglia canactivate astrocytes throughproliferation and secretion ofinflammatory factors. The role ofastrocytes on the loss ofdopaminergic neurons is stillcontroversial in PD. (Nonsteroidalanti-inflammatory drugs,NSAIDs. adiposed-derived stemcells, ADSCs.nicotinamideadenine dinucleotide phosphate,NADPH. signal transducers andactivators of transcription,STAT.DJ-1,Aliases forPARK7.mesencephalic astrocytederivedneurotrophic factor,MANF.Ciliary neurotrophicfactor,CNTF.glial cell linederivedneurotrophic factor,GDNF.Wnt Family Member1,Wnt1). Graphical abstract Mitochondrial dysfunction causes neuroinflammation throughDAMPs and a series of factors such as oxidative stress andinflammatory bodies in PD. (Damage-associated molecular patterns,DAMPs. reactive oxygen species, ROS). Graphical abstract Various mechanismsparticipate in NLRP3 activation,causing microglia activation inPD. ( -synuclein, -syn.) TolllikeReceptor 2, TLR2. Toll-likeReceptor 4, TLR4. TumorNecrosis Factor, TNF.Apoptosisassociated speck like proteincontaining a CARD, ASC).

Integrin CD11b mediates locus coeruleus noradrenergic neurodegeneration in a mouse Parkinson's disease model

BACKGROUND

The loss of locus coeruleus noradrenergic (LC/NE) neurons in the brainstem is reported in multiple neurodegenerative disorders, including Parkinson's disease (PD). However, the mechanisms remain unclear. Strong evidence suggested that microglia-mediated neuroinflammation contributes to neurodegeneration in PD. We recently recognized integrin CD11b, the α-chain of macrophage antigen complex-1 (Mac-1, also called CR3), as a key regulator for microglial activation. However, whether CD11b is involved in LC/NE neurodegeneration in PD remains to be investigated.

METHODS

LC/NE neurodegeneration and microglial activation were compared between wild type (WT) and CD11b KO mice after treated with paraquat and maneb, two pesticides that widely used to create PD model. The role of NLRP3 inflammasome in CD11b-mediated microglial dysfunction and LC/NE neurodegeneration was further explored. LC/NE neurodegeneration, microglial phenotype, and NLRP3 inflammasome activation were determined by using Western blot, immunohistochemistry, and RT-PCR technologies.

RESULTS

Paraquat and maneb co-exposure elevated the expressions of CD11b in the brainstem of mice, and CD11b knockout significantly reduced LC/NE neurodegeneration induced by paraquat and maneb. Mitigated microglial activation and gene expressions of proinflammatory cytokines were also observed in paraquat and maneb-treated CD11b^-/- mice. Mechanistically, CD11b-mediated NLRP3 inflammasome activation contributes to paraquat and maneb-induced LC/NE neurodegeneration. Compared with WT controls, CD11b deficiency reduced paraquat and maneb-induced NLRP3 expression, caspase-1 activation, and interleukin-1β production in mice. Furthermore, inhibition of NLRP3 inflammasome by glybenclamide, a sulfonylurea inhibitor of NLRP3 inflammasome, was found to be able to suppress microglial proinflammatory activation and nuclear factor-κB activation induced by paraquat and maneb. Moreover, reduced reactive oxygen species production, NADPH oxidase, and inducible nitric oxide synthase expressions as well as 4-hydroxynonenal and malondialdehyde levels were detected in combined glybenclamide and paraquat and maneb-treated mice compared with paraquat and maneb alone group. Finally, we found that glybenclamide treatment ameliorated LC/NE neurodegeneration and α-synuclein aggregation in paraquat and maneb-treated mice.

CONCLUSION

Our findings suggested that CD11b mediates LC/NE neurodegeneration through NLRP3 inflammation-dependent microglial proinflammatory activation in a two pesticide-induced mouse PD model, providing a novel insight into the immune pathogenesis of LC/NE neuronal damage in related disorders.

Cardioprotective Role of Melatonin in Acute Myocardial Infarction

Melatonin is a pleiotropic, indole secreted, and synthesized by the human pineal gland. Melatonin has biological effects including anti-apoptosis, protecting mitochondria, anti-oxidation, anti-inflammation, and stimulating target cells to secrete cytokines. Its protective effect on cardiomyocytes in acute myocardial infarction (AMI) has caused widespread interest in the actions of this molecule. The effects of melatonin against oxidative stress, promoting autophagic repair of cells, regulating immune and inflammatory responses, enhancing mitochondrial function, and relieving endoplasmic reticulum stress, play crucial roles in protecting cardiomyocytes from infarction. Mitochondrial apoptosis and dysfunction are common occurrence in cardiomyocyte injury after myocardial infarction. This review focuses on the targets of melatonin in protecting cardiomyocytes in AMI, the main molecular signaling pathways that melatonin influences in its endogenous protective role in myocardial infarction, and the developmental prospect of melatonin in myocardial infarction treatment.

The onjisaponin B metabolite tenuifolin ameliorates dopaminergic neurodegeneration in a mouse model of Parkinson's disease

Onjisaponin B (OB) is the main active ingredient of the traditional Chinese medicinal herb polygala, which is effective against neurodegenerative disorders. However, the target of OB is currently unknown. Neuroinflammation and oxidative stress are both risk factors for the pathogenesis and progression of Parkinson's disease (PD). Here, we used a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced subacute mouse model of PD to explore the efficacy and neuroprotective mechanism of OB in PD. Immunohistochemistry was used to mark dopaminergic (DA) neurons and microglia in the substantia nigra pars compact. Administration of OB (20 and 40 mg/kg) prevented the degeneration of DA neurons and improved motor impairment in the rotarod test. Furthermore, OB attenuated microglia over-activation and reduced the secretion of inflammatory factors including tumor necrosis factor-alpha, interleukin-1 beta (IL-1β) and interleukin-6 (IL-6), as determined by ELISA. Meanwhile, the activities of superoxide dismutase and malondialdehyde were used to measure the level of oxidative stress in brain homogenates and suppression of excessive lipid epoxidation and increased antioxidant enzyme activity were found in OB-treated PD mice. Finally, OB inhibits the expression of the p65 subunit of NF-κB in the nucleus and attenuated expression of the RhoA and ROCK2 proteins in PD mice. Consequently, our results show that OB ameliorates DA neurodegeneration in a MPTP-induced mouse model of PD through anti-oxidant and anti-inflammatory activities mediated via the RhoA/ROCK2 signaling pathway. This finding demonstrates that OB may be a promising drug for DA neuron degeneration, which may provide a new therapeutic agent for future discovery of drugs for PD.See video abstract: http://links.lww.com/WNR/A580.

Pharmacological Inhibition of HDAC6 Attenuates NLRP3 Inflammatory Response and Protects Dopaminergic Neurons in Experimental Models of Parkinson's Disease

Aim

To investigate the role of histone deacetylase 6 (HDAC6) deacetylation activity in nucleotide-binding oligomerization domain and leucine-rich repeat pyrin 3 domain (NLRP3) inflammatory response and explore the effects of pharmacological inhibition of HDAC6 with tubastatin A (TBA) on dopaminergic injury.

Methods

Using 6-OHDA-induced Parkinson's disease (PD) models, we examined the effects of TBA on NLRP3 activation and cell injury in SH-SY5Y cells. We also investigated the effects of TBA on NLRP3 inflammatory responses and dopaminergic injury in the nigrostriatal system in mice and analyzed the acetylation levels of peroxiredoxin2 (Prx2) and oxidative stress.

Results

TBA inhibited 6-OHDA-induced NLRP3 activation, as demonstrated by decreased expressions of NLRP3 and matured caspase-1 and IL-1β, and also alleviated glial proliferation and dopaminergic neuronal degeneration. Notably, TBA recovered acetylation levels of Prx2 and reduced oxidative stress.

Conclusion

Our findings indicate that pharmacological inhibition of HDAC6 with TBA attenuates NLRP3 inflammation and protects dopaminergic neurons, probably through Prx2 acetylation. This study suggests that the deacetylase catalytic domain of HDAC6 is a potential target for PD treatment.

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.

Neurodegenerative Susceptibility During Maternal Nutritional Programing: Are Central and Peripheral Innate Immune Training Relevant?

Maternal overnutrition modulates body weight, development of metabolic failure and, potentially, neurodegenerative susceptibility in the offspring. Overnutrition sets a chronic pro-inflammatory profile that integrates peripheral and central immune activation nodes, damaging neuronal physiology and survival. Innate immune cells exposed to hypercaloric diets might experience trained immunity. Here, we address the role of maternal overnutrition as a trigger for central and peripheral immune training and its contribution to neurodegeneration and the molecular nodes implicated in the Nod-like receptor protein 3 (NLRP3) inflammasome pathway leading to immune training. We propose that maternal overnutrition leads to peripheral or central immune training that favor neurodegenerative susceptibility in the offspring.

Through Reducing ROS Production, IL-10 Suppresses Caspase-1-Dependent IL-1β Maturation, thereby Preventing Chronic Neuroinflammation and Neurodegeneration

Chronic neuroinflammation contributes to the pathogenesis of Parkinson’s disease (PD). However, cellular and molecular mechanisms by which chronic neuroinflammation is formed and maintained remain elusive. This study aimed to explore detailed mechanisms by which anti-inflammatory cytokine interleukin-10 (IL-10) prevented chronic neuroinflammation and neurodegeneration. At 24 h after an intranigral injection of lipopolysaccharide (LPS), levels of NLRP3, pro-caspase-1, pro-IL-1β, active caspase-1, and mature IL-1β in the midbrain were much higher in IL-10^−/− mice than wildtype mice. Mechanistically, IL-10^−/− microglia produced more intracellular reactive oxygen species (iROS) and showed more profound activation of NADPH oxidase (NOX2) than wildtype microglia. Meanwhile, suppression of NOX2-derived iROS production blocked LPS-elicited caspase-1 activation and IL-1β maturation in IL-10^−/− microglia in vitro and in vivo. One month after intranigral LPS injection, IL-10^−/− mice revealed more profound microglial activation and dopaminergic neurodegeneration in the substantia nigra than wildtype mice. Importantly, such PD-like pathological changes were prevented by IL-1β neutralization. Collectively, IL-10 inhibited LPS-elicited production of NOX2-derived iROS thereby suppressing synthesis of NLRP3, pro-caspase-1 and pro-IL-1β and their activation and cleavage. By this mechanism, IL-10 prevented chronic neuroinflammation and neurodegeneration. This study suggested boosting anti-inflammatory effects of IL-10 and suppressing NLRP3 inflammasome activation could be beneficial for PD treatment.

Systemic activation of NLRP3 inflammasome and plasma α-synuclein levels are correlated with motor severity and progression in Parkinson's disease

Background

Emerging evidence indicates that inflammasome-induced inflammation plays a crucial role in the pathogenesis of Parkinson’s disease (PD). Several proteins including α-synuclein trigger the activation of NLRP3 inflammasome. However, few studies examined whether inflammasomes are activated in the periphery of PD patients and their possible value in the diagnosis or tracking of the progress of PD. The aim of this study was to determine the association between inflammasome-induced inflammation and clinical features in PD.

Methods

There were a total of 67 participants, including 43 patients with PD and 24 controls, in the study. Participants received a complete evaluation of motor and non-motor symptoms, including Hoehn and Yahr (H-Y) staging scale. Blood samples were collected from all participants. The protein and mRNA expression levels of inflammasomes subtypes and components in peripheral blood mononuclear cells (PBMCs) were determined using western blotting and RT-qPCR. We applied Meso Scale Discovery (MSD) immunoassay to measure the plasma levels of IL-1β and α-synuclein.

Results

We observed increased gene expression of NLRP3, ASC, and caspase-1 in PBMCs, and increased protein levels of NLRP3, caspase-1, and IL-1β in PD patients. Plasma levels of IL-1β were significantly higher in patients with PD compared with controls and have a positive correlation with H-Y stage and UPDRS part III scores. Furthermore, plasma α-synuclein levels were also increased in PD patients and have a positive correlation with both UPDRS part III scores and plasma IL-1β levels.

Conclusions

Our data demonstrated that the NLRP3 inflammasome is activated in the PBMCs from PD patients. The related inflammatory cytokine IL-1β and total α-synuclein in plasma were increased in PD patients than controls, and both of them presented a positive correlation with motor severity in patients with PD. Furthermore, plasma α-synuclein levels have a positive correlation with IL-1β levels in PD patients. All these findings suggested that the NLRP3 inflammasome activation-related cytokine IL-1β and α-synuclein could serve as non-invasive biomarkers to monitor the severity and progression of PD in regard to motor function.

Novel approaches to counter protein aggregation pathology in Parkinson's disease

The primary neuropathological characteristics of the Parkinsonian brain are the loss of nigral dopamine neurons and the aggregation of alpha synuclein protein. Efforts to development potentially disease-modifying treatments have largely focused on correcting these aspects of the condition. In the last decade treatments targeting protein aggregation have entered the clinical pipeline. In this chapter we provide an overview of ongoing clinical trial programs for different therapies attempting to reduce protein aggregation pathology in Parkinson's disease. We will also briefly consider various novel approaches being proposed-and being developed preclinically-to inhibit/reduce aggregated protein pathology in Parkinson's.

Fiery Cell Death: Pyroptosis in the Central Nervous System

Pyroptosis ('fiery death') is an inflammatory type of regulated cell death (RCD), which occurs downstream of inflammasome activation. Pyroptosis is mediated directly by the recently identified family of pore-forming proteins known as gasdermins, the best characterized of which is gasdermin D (GSDMD). Recent investigations implicate pyroptosis in the pathogenesis of multiple neurological diseases. In this review, we discuss molecular mechanisms that drive pyroptosis, evidence for pyroptosis within the CNS, and emerging therapeutic strategies for its inhibition in the context of neurological disease.

The NLRP3 inflammasome: a new player in neurological diseases

Inflammasomes are supramolecular protein complexes implicated in the detection of pathogens or danger-associated molecules and are responsible for mounting the first line of innate immune response to counteract these signals and restore tissue homeostasis. Among different inflammasomes identified so far, NLRP3 is of main interest since mutations in Nlrp3 gene are associated with autoinflammatory diseases such as Muckle–Wells syndrome, neonatal onset multisystem inflammatory disease, and familial cold urticaria/autoinflammatory syndrome. On the other hand, whereas other inflammasomes are mainly detectors of specific molecular motifs, NLRP3 is acting as a general sensor of cellular perturbations including potassium efflux, lysosomal damage, and ROS production. Besides this central role of NLRP3 in inflammation, recent publications show that the NLRP3 inflammasome is also involved in the physiopathology of several neurological disorders including Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. This review gives an overview of the established functions of the NLRP3 inflammasome in mediating inflammation in macrophages and describes its recently discovered roles in neurological disorders in promoting neuroinflammation, as well as modulating key proteins mediating the disorders. Finally, we discuss the targeting of NLRP3 in neurological diseases and present some examples of NLRP3 inhibitors that could be used in neurological disorder treatments.

Diet in Parkinson's Disease: Critical Role for the Microbiome

Background: Parkinson's disease (PD) is the most common movement disorder affecting up to 1% of the population above the age of 60 and 4–5% of those above the age of 85. Little progress has been made on efforts to prevent disease development or halt disease progression. Diet has emerged as a potential factor that may prevent the development or slow the progression of PD. In this review, we discuss evidence for a role for the intestinal microbiome in PD and how diet-associated changes in the microbiome may be a viable approach to prevent or modify disease progression.

Methods: We reviewed studies demonstrating that dietary components/foods were related to risk for PD. We reviewed evidence for the dysregulated intestinal microbiome in PD patients including abnormal shifts in the intestinal microbiota composition (i.e., dysbiosis) characterized by a loss of short chain fatty acid (SCFA) bacteria and increased lipopolysaccharide (LPS) bacteria. We also examined several candidate mechanisms by which the microbiota can influence PD including the NLRP3 inflammasome, insulin resistance, mitochondrial function, vagal nerve signaling.

Results: The PD-associated microbiome is associated with decreased production of SCFA and increased LPS and it is believed that these changes may contribute to the development or exacerbation of PD. Diet robustly impacts the intestinal microbiome and the Western diet is associated with increased risk for PD whereas the Mediterranean diet (including high intake of dietary fiber) decreases PD risk. Mechanistically this may be the consequence of changes in the relative abundance of SCFA-producing or LPS-containing bacteria in the intestinal microbiome with effects on intestinal barrier function, endotoxemia (i.e., systemic LPS), NLRP3 inflammasome activation, insulin resistance, and mitochondrial dysfunction, and the production of factors such as glucagon like peptide 1 (GLP-1) and brain derived neurotrophic factor (BDNF) as well as intestinal gluconeogenesis.

Conclusions: This review summarizes a model of microbiota-gut-brain-axis regulation of neuroinflammation in PD including several new mechanisms. We conclude with the need for clinical trials in PD patients to test this model for beneficial effects of Mediterranean based high fiber diets.