Crosstalk Between the NLRP3 Inflammasome/ASC Speck and Amyloid Protein Aggregates Drives Disease Progression in Alzheimer's and Parkinson's Disease

Treating amyotrophic lateral sclerosis with allogeneic Schwann cell-derived exosomal vesicles: a case report

Schwann cells are essential for the maintenance and function of motor neurons, axonal networks, and the neuromuscular junction. In amyotrophic lateral sclerosis, where motor neuron function is progressively lost, Schwann cell function may also be impaired. Recently, important signaling and potential trophic activities of Schwann cell-derived exosomal vesicles have been reported. This case report describes the treatment of a patient with advanced amyotrophic lateral sclerosis using serial intravenous infusions of allogeneic Schwann cell-derived exosomal vesicles, marking, to our knowledge, the first instance of such treatment. An 81-year-old male patient presented with a 1.5-year history of rapidly progressive amyotrophic lateral sclerosis. After initial diagnosis, the patient underwent a combination of generic riluzole, sodium phenylbutyrate for the treatment of amyotrophic lateral sclerosis, and taurursodiol. The patient volunteered to participate in an FDA-approved single-patient expanded access treatment and received weekly intravenous infusions of allogeneic Schwann cell-derived exosomal vesicles to potentially restore impaired Schwann cell and motor neuron function. We confirmed that cultured Schwann cells obtained from the amyotrophic lateral sclerosis patient via sural nerve biopsy appeared impaired (senescent) and that exposure of the patient's Schwann cells to allogeneic Schwann cell-derived exosomal vesicles, cultured expanded from a cadaver donor improved their growth capacity in vitro. After a period of observation lasting 10 weeks, during which amyotrophic lateral sclerosis Functional Rating Scale-Revised and pulmonary function were regularly monitored, the patient received weekly consecutive infusions of 1.54 × 10 12 (×2), and then consecutive infusions of 7.5 × 10 12 (×6) allogeneic Schwann cell-derived exosomal vesicles diluted in 40 mL of Dulbecco's phosphate-buffered saline. None of the infusions were associated with adverse events such as infusion reactions (allergic or otherwise) or changes in vital signs. Clinical lab serum neurofilament and cytokine levels measured prior to each infusion varied somewhat without a clear trend. A more sensitive in-house assay suggested possible inflammasome activation during the disease course. A trend for clinical stabilization was observed during the infusion period. Our study provides a novel approach to address impaired Schwann cells and possibly motor neuron function in patients with amyotrophic lateral sclerosis using allogeneic Schwann cell-derived exosomal vesicles. Initial findings suggest that this approach is safe.

Therapeutic Targets in Innate Immunity to Tackle Alzheimer's Disease

There is an urgent need for effective disease-modifying therapeutic interventions for Alzheimer's disease (AD)-the most prevalent cause of dementia with a profound socioeconomic burden. Most clinical trials targeting the classical hallmarks of this disease-β-amyloid plaques and neurofibrillary tangles-failed, showed discrete clinical effects, or were accompanied by concerning side effects. There has been an ongoing search for novel therapeutic targets. Neuroinflammation, now widely recognized as a hallmark of all neurodegenerative diseases, has been proven to be a major contributor to AD pathology. Here, we summarize the role of neuroinflammation in the pathogenesis and progression of AD and discuss potential targets such as microglia, TREM2, the complement system, inflammasomes, and cytosolic DNA sensors. We also present an overview of ongoing studies targeting specific innate immune system components, highlighting the progress in this field of drug research while bringing attention to the delicate nature of innate immune modulations in AD.

Mechanism of flavonoids in the treatment of gouty arthritis (Review)

The present review expounds the advancements in the application and mechanisms of flavonoids in gouty arthritis, highlighting their significance in managing the disease. Gouty arthritis is among the most common and severe inflammatory diseases, caused by hyperuricemia and the deposition of sodium urate crystals in the joints and surrounding tissues, posing a serious threat to human life and health. Flavonoids, extracted from various herbs, have attracted significant attention due to their efficacy in improving gouty arthritis. The present study systematically reviews the in vivo studies and in vitro animal studies on flavonoids from herbal medicines for the treatment of gouty arthritis that have been previously published in the PubMed, ScienceDirect, Google Scholar and China National Knowledge Infrastructure databases between 2000 and 2023. The review of the literature indicated that flavonoids can improve gouty arthritis through multiple mechanisms. These include lowering xanthine oxidase activity, inhibiting uric acid (UA) synthesis, regulating UA transporters to promote UA excretion, reducing the inflammatory response and improving oxidative stress. These mechanisms predominantly involve regulating the NOD‑like receptor 3 inflammasome, the Toll‑like receptor 4/myeloid differentiation factor 88/nuclear factor‑κB signaling pathway, and the levels of UA transporter proteins, namely recombinant urate transporter 1, glucose transporter 9, organic anion transporter (OAT)1 and OAT3. Various flavonoids used in traditional Chinese medicine hold therapeutic promise for gouty arthritis and are anticipated to pave the way for novel pharmaceuticals and clinical applications.

Targeting NLRP3 Inflammasomes: A Trojan Horse Strategy for Intervention in Neurological Disorders

Recently, a growing focus has been on identifying critical mechanisms in neurological diseases that trigger a cascade of events, making it easier to target them effectively. One such mechanism is the inflammasome, an essential component of the immune response system that plays a crucial role in disease progression. The NLRP3 (nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 3) inflammasome is a subcellular multiprotein complex that is widely expressed in the central nervous system (CNS) and can be activated by a variety of external and internal stimuli. When activated, the NLRP3 inflammasome triggers the production of proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18) and facilitates rapid cell death by assembling the inflammasome. These cytokines initiate inflammatory responses through various downstream signaling pathways, leading to damage to neurons. Therefore, the NLRP3 inflammasome is considered a significant contributor to the development of neuroinflammation. To counter the damage caused by NLRP3 inflammasome activation, researchers have investigated various interventions such as small molecules, antibodies, and cellular and gene therapy to regulate inflammasome activity. For instance, recent studies indicate that substances like micro-RNAs (e.g., miR-29c and mR-190) and drugs such as melatonin can reduce neuronal damage and suppress neuroinflammation through NLRP3. Furthermore, the transplantation of bone marrow mesenchymal stem cells resulted in a significant reduction in the levels of pyroptosis-related proteins NLRP3, caspase-1, IL-1β, and IL-18. However, it would benefit future research to have an in-depth review of the pharmacological and biological interventions targeting inflammasome activity. Therefore, our review of current evidence demonstrates that targeting NLRP3 inflammasomes could be a pivotal approach for intervention in neurological disorders.

The Inflammasome Adaptor Protein ASC in Plasma as a Biomarker of Early Cognitive Changes

Dementia is a group of symptoms including memory loss, language difficulties, and other types of cognitive and functional impairments that affects 57 million people worldwide, with the incidence expected to double by 2040. Therefore, there is an unmet need to develop reliable biomarkers to diagnose early brain impairments so that emerging interventions can be applied before brain degeneration. Here, we performed biomarker analyses for apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), and amyloid-β 42/40 (Aβ42/40) ratio in the plasma of older adults. Participants had blood drawn at baseline and underwent two annual clinical and cognitive evaluations. The groups tested either cognitively normal on both evaluations (NN), cognitively normal year 1 but cognitively impaired year 2 (NI), or cognitively impaired on both evaluations (II). ASC was elevated in the plasma of the NI group compared to the NN and II groups. Additionally, Aβ42 was increased in the plasma in the NI and II groups compared to the NN group. Importantly, the area under the curve (AUC) for ASC in participants older than 70 years old in NN vs. NI groups was 0.81, indicating that ASC is a promising plasma biomarker for early detection of cognitive decline.

Virus-like particle (VLP)-based vaccine targeting tau phosphorylated at Ser396/Ser404 (PHF1) site outperforms phosphorylated S199/S202 (AT8) site in reducing tau pathology and restoring cognitive deficits in the rTg4510 mouse model of tauopathy

Tauopathies, including Alzheimer's disease (AD) and Frontotemporal Dementia (FTD), are histopathologically defined by the aggregation of hyperphosphorylated pathological tau (pTau) as neurofibrillary tangles in the brain. Site-specific phosphorylation of tau occurs early in the disease process and correlates with progressive cognitive decline, thus serving as targetable pathological epitopes for immunotherapeutic development. Previously, we developed a vaccine (Qβ-pT181) displaying phosphorylated Thr181 tau peptides on the surface of a Qβ bacteriophage virus-like particle (VLP) that induced robust antibody responses, cleared pathological tau, and rescued memory deficits in a transgenic mouse model of tauopathy. Here we report the characterization and comparison of two additional Qβ VLP-based vaccines targeting the dual phosphorylation sites Ser199/Ser202 (Qβ-AT8) and Ser396/Ser404 (Qβ-PHF1). Both Qβ-AT8 and Qβ-PHF1 vaccines elicited high-titer antibody responses against their pTau epitopes. However, only Qβ-PHF1 rescued cognitive deficits, reduced soluble and insoluble pathological tau, and reactive microgliosis in a 4-month rTg4510 model of FTD. Both sera from Qβ-AT8 and Qβ-PHF1 vaccinated mice were specifically reactive to tau pathology in human AD post-mortem brain sections. These studies further support the use of VLP-based immunotherapies to target pTau in AD and related tauopathies and provide potential insight into the clinical efficacy of various pTau epitopes in the development of immunotherapeutics.

Sirtuin 6 Deacetylates Apoptosis-Associated Speck-Like Protein (ASC) to Inhibit Endothelial Cell Pyroptosis in Atherosclerosis

Endothelial cell dysfunction is the main pathology of atherosclerosis (AS). Sirtuin 6 (SIRT6), a deacetylase, is involved in AS progression. This study aimed to investigate the impacts of SIRT6 on the pyroptosis of endothelial cells and its underlying mechanisms. ApoE-/- mice were fed a high-fat diet (HFD) to establish the AS mouse model, atherosclerotic lesions were evaluated using oil red O staining, and blood lipids and inflammatory factors were measured using corresponding kits. Human umbilical vein endothelial cells (HUVECs) were treated with oxidized low-density lipoprotein (ox-LDL) to establish the cell model, and pyroptosis was evaluated by flow cytometry, ELISA, and western blot. Immunoprecipitation (IP), co-IP, western blot, and immunofluorescence were used to detect the molecular mechanisms. The results showed that SIRT6 expression was downregulated in the blood of HFD-induced mice and ox-LDL-induced HUVECs. Overexpression of SIRT6 reduced atherosclerotic lesions, blood lipids, and inflammation in vivo and suppressed pyroptosis of HUVECs in vitro. Moreover, SIRT6 interacted with ASC to inhibit the acetylation of ASC, thus, reducing the interaction between ASC and NLRP3. Moreover, SIRT6 inhibits endothelial cell pyroptosis in the aortic roots of mice by deacetylating ASC. In conclusion, SIRT6 deacetylated ASC to inhibit its interaction with NLRP3 and then suppressed pyroptosis of endothelial cells, thus, decelerating the progression of AS. The findings provide new insights into the function of SIRT6 in AS.

Virus-like particle (VLP)-based vaccine targeting tau phosphorylated at Ser396/Ser404 (PHF1) site outperforms phosphorylated S199/S202 (AT8) site in reducing tau pathology and restoring cognitive deficits in the rTg4510 mouse model of tauopathy

Tauopathies, including Alzheimer's disease (AD) and Frontotemporal Dementia (FTD), are histopathologically defined by the aggregation of hyperphosphorylated pathological tau (pTau) as neurofibrillary tangles in the brain. Site-specific phosphorylation of tau occurs early in the disease process and correlates with progressive cognitive decline, thus serving as targetable pathological epitopes for immunotherapeutic development. Previously, we developed a vaccine (Qβ-pT181) displaying phosphorylated Thr181 tau peptides on the surface of a Qβ bacteriophage virus-like particle (VLP) that induced robust antibody responses, cleared pathological tau, and rescued memory deficits in a transgenic mouse model of tauopathy. Here we report the characterization and comparison of two additional Qβ VLP-based vaccines targeting the dual phosphorylation sites Ser199/Ser202 (Qβ-AT8) and Ser396/Ser404 (Qβ-PHF1). Both Qβ-AT8 and Qβ-PHF1 vaccines elicited high-titer antibody responses against their pTau epitopes. However, only Qβ-PHF1 rescued cognitive deficits, reduced soluble and insoluble pathological tau, and reactive microgliosis in a 4-month rTg4510 model of FTD. Both sera from Qβ-AT8 and Qβ-PHF1 vaccinated mice were specifically reactive to tau pathology in human AD post-mortem brain sections. These studies further support the use of VLP-based immunotherapies to target pTau in AD and related tauopathies and provide potential insight into the clinical efficacy of various pTau epitopes in the development of immunotherapeutics.

Cerebral organoids with chromosome 21 trisomy secrete Alzheimer's disease-related soluble aggregates detectable by single-molecule-fluorescence and super-resolution microscopy

Understanding the role of small, soluble aggregates of beta-amyloid (Aβ) and tau in Alzheimer's disease (AD) is of great importance for the rational design of preventative therapies. Here we report a set of methods for the detection, quantification, and characterisation of soluble aggregates in conditioned media of cerebral organoids derived from human iPSCs with trisomy 21, thus containing an extra copy of the amyloid precursor protein (APP) gene. We detected soluble beta-amyloid (Aβ) and tau aggregates secreted by cerebral organoids from both control and the isogenic trisomy 21 (T21) genotype. We developed a novel method to normalise measurements to the number of live neurons within organoid-conditioned media based on glucose consumption. Thus normalised, T21 organoids produced 2.5-fold more Aβ aggregates with a higher proportion of larger (300-2000 nm2) and more fibrillary-shaped aggregates than controls, along with 1.3-fold more soluble phosphorylated tau (pTau) aggregates, increased inflammasome ASC-specks, and a higher level of oxidative stress inducing thioredoxin-interacting protein (TXNIP). Importantly, all this was detectable prior to the appearance of histological amyloid plaques or intraneuronal tau-pathology in organoid slices, demonstrating the feasibility to model the initial pathogenic mechanisms for AD in-vitro using cells from live genetically pre-disposed donors before the onset of clinical disease. Then, using different iPSC clones generated from the same donor at different times in two independent experiments, we tested the reproducibility of findings in organoids. While there were differences in rates of disease progression between the experiments, the disease mechanisms were conserved. Overall, our results show that it is possible to non-invasively follow the development of pathology in organoid models of AD over time, by monitoring changes in the aggregates and proteins in the conditioned media, and open possibilities to study the time-course of the key pathogenic processes taking place.

The role of inflammasomes in human diseases and their potential as therapeutic targets

Inflammasomes are large protein complexes that play a major role in sensing inflammatory signals and triggering the innate immune response. Each inflammasome complex has three major components: an upstream sensor molecule that is connected to a downstream effector protein such as caspase-1 through the adapter protein ASC. Inflammasome formation typically occurs in response to infectious agents or cellular damage. The active inflammasome then triggers caspase-1 activation, followed by the secretion of pro-inflammatory cytokines and pyroptotic cell death. Aberrant inflammasome activation and activity contribute to the development of diabetes, cancer, and several cardiovascular and neurodegenerative disorders. As a result, recent research has increasingly focused on investigating the mechanisms that regulate inflammasome assembly and activation, as well as the potential of targeting inflammasomes to treat various diseases. Multiple clinical trials are currently underway to evaluate the therapeutic potential of several distinct inflammasome-targeting therapies. Therefore, understanding how different inflammasomes contribute to disease pathology may have significant implications for developing novel therapeutic strategies. In this article, we provide a summary of the biological and pathological roles of inflammasomes in health and disease. We also highlight key evidence that suggests targeting inflammasomes could be a novel strategy for developing new disease-modifying therapies that may be effective in several conditions.

Association of region-specific hippocampal reduction of neurogranin with inflammasome proteins in post mortem brains of Alzheimer's disease

INTRODUCTION

Neurogranin (Ng) is considered a biomarker for synaptic dysfunction in Alzheimer's disease (AD). In contrast, the inflammasome complex has been shown to exacerbate AD pathology.

METHODS

We investigated the protein expression, morphological differences of Ng, and correlated Ng to hyperphosphorylated tau in the post mortem brains of 17 AD cases and 17 age- and sex-matched controls. In addition, we correlated the Ng expression with two different epitopes of apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC).

RESULTS

We show a reduction of Ng immunopositive neurons and morphological differences in AD compared to controls. Ng immunostaining was negatively correlated with neurofibrillary tangles, humanized anti-ASC (IC100) positive neurons and anti-ASC positive microglia, in AD.

DISCUSSION

The finding of a negative correlation between Ng and ASC speck protein expression in post mortem brains of AD suggests that the activation of inflammasome/ASC speck pathway may play an important role in synaptic degeneration in AD.

Highlights

We show the role that neurogranin plays on post-synaptic signaling in specific hippocampal regions.We demonstrate that there could be clinical implications of using neurogranin as a biomarker for dementia.We describe the loss of plasticity and neuronal scaffolding proteins in the present of AD pathology.We show the response of neuroinflammation when tau proteins phosphorylate in hippocampal neurons.We show that there is a potential therapeutic target for the inflammasome, and future studies may show that IC100, a humanized monoclonal antibody directed against ASC, may slow the progression of neurodegeneration.

Traumatic brain injury derived pathological tau polymorphs induce the distinct propagation pattern and neuroinflammatory response in wild type mice

The misfolding and aggregation of the tau protein into neurofibrillary tangles constitutes a central feature of tauopathies. Traumatic brain injury (TBI) has emerged as a potential risk factor, triggering the onset and progression of tauopathies. Our previous research revealed distinct polymorphisms in soluble tau oligomers originating from single versus repetitive mild TBIs. However, the mechanisms orchestrating the dissemination of TBI brain-derived tau polymorphs (TBI-BDTPs) remain elusive. In this study, we explored whether TBI-BDTPs could initiate pathological tau formation, leading to distinct pathogenic trajectories. Wild-type mice were exposed to TBI-BDTPs from sham, single-blast (SB), or repeated-blast (RB) conditions, and their memory function was assessed through behavioral assays at 2- and 8-month post-injection. Our findings revealed that RB-BDTPs induced cognitive and motor deficits, concurrently fostering the emergence of toxic tau aggregates within the injected hippocampus. Strikingly, this tau pathology propagated to cortical layers, intensifying over time. Importantly, RB-BDTP-exposed animals displayed heightened glial cell activation, NLRP3 inflammasome formation, and increased TBI biomarkers, particularly triggering the aggregation of S100B, which is indicative of a neuroinflammatory response. Collectively, our results shed light on the intricate mechanisms underlying TBI-BDTP-induced tau pathology and its association with neuroinflammatory processes. This investigation enhances our understanding of tauopathies and their interplay with neurodegenerative and inflammatory pathways following traumatic brain injury.

A detailed molecular network map and model of the NLRP3 inflammasome

The NLRP3 inflammasome is a key regulator of inflammation that responds to a broad range of stimuli. The exact mechanism of activation has not been determined, but there is a consensus on cellular potassium efflux as a major common denominator. Once NLRP3 is activated, it forms high-order complexes together with NEK7 that trigger aggregation of ASC into specks. Typically, there is only one speck per cell, consistent with the proposal that specks form - or end up at - the centrosome. ASC polymerisation in turn triggers caspase-1 activation, leading to maturation and release of IL-1β and pyroptosis, i.e., highly inflammatory cell death. Several gain-of-function mutations in the NLRP3 inflammasome have been suggested to induce spontaneous activation of NLRP3 and hence contribute to development and disease severity in numerous autoinflammatory and autoimmune diseases. Consequently, the NLRP3 inflammasome is of significant clinical interest, and recent attention has drastically improved our insight in the range of involved triggers and mechanisms of signal transduction. However, despite recent progress in knowledge, a clear and comprehensive overview of how these mechanisms interplay to shape the system level function is missing from the literature. Here, we provide such an overview as a resource to researchers working in or entering the field, as well as a computational model that allows for evaluating and explaining the function of the NLRP3 inflammasome system from the current molecular knowledge. We present a detailed reconstruction of the molecular network surrounding the NLRP3 inflammasome, which account for each specific reaction and the known regulatory constraints on each event as well as the mechanisms of drug action and impact of genetics when known. Furthermore, an executable model from this network reconstruction is generated with the aim to be used to explain NLRP3 activation from priming and activation to the maturation and release of IL-1β and IL-18. Finally, we test this detailed mechanistic model against data on the effect of different modes of inhibition of NLRP3 assembly. While the exact mechanisms of NLRP3 activation remains elusive, the literature indicates that the different stimuli converge on a single activation mechanism that is additionally controlled by distinct (positive or negative) priming and licensing events through covalent modifications of the NLRP3 molecule. Taken together, we present a compilation of the literature knowledge on the molecular mechanisms on NLRP3 activation, a detailed mechanistic model of NLRP3 activation, and explore the convergence of diverse NLRP3 activation stimuli into a single input mechanism.

The Inflammasome-Dependent Dysfunction and Death of Retinal Ganglion Cells after Repetitive Intraocular Pressure Spikes

The dysfunction and selective loss of retinal ganglion cells (RGCs) is a known cause of vision loss in glaucoma and other neuropathies, where ocular hypertension (OHT) is the major risk factor. We investigated the impact of transient non-ischemic OHT spikes (spOHT) on RGC function and viability in vivo to identify cellular pathways linking low-grade repetitive mechanical stress to RGC pathology. We found that repetitive spOHT had an unexpectedly high impact on intraocular homeostasis and RGC viability, while exposure to steady OHT (stOHT) of a similar intensity and duration failed to induce pathology. The repetitive spOHT induced the rapid activation of the inflammasome, marked by the upregulation of NLRP1, NLRP3, AIM2, caspases -1, -3/7, -8, and Gasdermin D (GSDMD), and the release of interleukin-1β (IL-1β) and other cytokines into the vitreous. Similar effects were also detected after 5 weeks of exposure to chronic OHT in an induced glaucoma model. The onset of these immune responses in both spOHT and glaucoma models preceded a 50% deficit in pattern electroretinogram (PERG) amplitude and a significant loss of RGCs 7 days post-injury. The inactivation of inflammasome complexes in Nlrp1-/-, Casp1-/-, and GsdmD-/- knockout animals significantly suppressed the spOHT-induced inflammatory response and protected RGCs. Our results demonstrate that mechanical stress produced by acute repetitive spOHT or chronic OHT is mechanistically linked to inflammasome activation, which leads to RGC dysfunction and death.

Antiplatelet drugs: Potential therapeutic options for the management of neurodegenerative diseases

The blood platelet plays an important role but often remains under-recognized in several vascular complications and associated diseases. Surprisingly, platelet hyperactivity and hyperaggregability have often been considered the critical risk factors for developing vascular dysfunctions in several neurodegenerative diseases (NDDs) like Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In addition, platelet structural and functional impairments promote prothrombotic and proinflammatory environment that can aggravate the progression of several NDDs. These findings provide the rationale for using antiplatelet agents not only to prevent morbidity but also to reduce mortality caused by NDDs. Therefore, we thoroughly review the evidence supporting the potential pleiotropic effects of several novel classes of synthetic antiplatelet drugs, that is, cyclooxygenase inhibitors, adenosine diphosphate receptor antagonists, protease-activated receptor blockers, and glycoprotein IIb/IIIa receptor inhibitors in NDDs. Apart from this, the review also emphasizes the recent developments of selected natural antiplatelet phytochemicals belonging to key classes of plant-based bioactive compounds, including polyphenols, alkaloids, terpenoids, and flavonoids as potential therapeutic candidates in NDDs. We believe that the broad analysis of contemporary strategies and specific approaches for plausible therapeutic treatment for NDDs presented in this review could be helpful for further successful research in this area.

The role of dopamine in NLRP3 inflammasome inhibition: Implications for neurodegenerative diseases

In the Central Nervous System (CNS), neuroinflammation orchestrated by microglia and astrocytes is an innate immune response to counteract stressful and dangerous insults. One of the most important and best characterized players in the neuroinflammatory response is the NLRP3 inflammasome, a multiproteic complex composed by NOD-like receptor family Pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC) and pro-caspase-1. Different stimuli mediate NLRP3 activation, resulting in the NLRP3 inflammasome assembly and the pro-inflammatory cytokine (IL-1β and IL-18) maturation and secretion. The persistent and uncontrolled NLRP3 inflammasome activation has a leading role during the pathophysiology of neuroinflammation in age-related neurodegenerative diseases such as Parkinson's (PD) and Alzheimer's (AD). The neurotransmitter dopamine (DA) is one of the players that negatively modulate NLRP3 inflammasome activation through DA receptors expressed in both microglia and astrocytes. This review summarizes recent findings linking the role of DA in the modulation of NLRP3-mediated neuroinflammation in PD and AD, where early deficits of the dopaminergic system are well characterized. Highlighting the relationship between DA, its glial receptors and the NLRP3-mediated neuroinflammation can provide insights to novel diagnostic strategies in early disease phases and new pharmacological tools to delay the progression of these diseases.

ASC specks exacerbate α‑synuclein pathology via amplifying NLRP3 inflammasome activities

BACKGROUND

Inflammasome activation has a pathogenic role in Parkinson's disease (PD). Up-regulated expressions of inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC) and assembly of ASC specks have been observed in postmortems of human PD brains and experimental PD models. Extracellular ASC specks behave like danger signals and sustain prolonged inflammasome activation. However, the contribution of ASC specks in propagation of inflammasome activation and pathological progression in PD has not been fully established.

METHODS

Herein, we used human A53T mutant α-synuclein preformed fibrils (PFFs)-stimulated microglia in vitro and unilateral striatal stereotaxic injection of PFFs-induced mice model of PD in vivo, to investigate the significance of ASC specks in PD pathological progression. Rotarod and open-field tests were performed to measure motor behaviors of indicated mice. Changes in the molecular expression were evaluated by immunofluorescence and immunoblotting (IB). Intracellular knockdown of the ASC in BV2 cells was performed using si-RNA. Microglial and neuronal cells were co-cultured in a trans-well system to determine the effects of ASC knockdown on cytoprotection.

RESULTS

We observed a direct relationship between levels of ASC protein and misfolded α‑synuclein aggregates in PD mice brains. ASC specks amplified NLRP3 inflammasome activation driven by α-synuclein PFFs stimulation, which aggravated reactive microgliosis and accelerated α‑synuclein pathology, dopaminergic neurodegeneration and motor deficits. Endogenous ASC knockdown suppressed microglial inflammasome activation and neuronal α‑synuclein aggregation.

CONCLUSIONS

In conclusion, our study elucidated that ASC specks contribute to the propagation of inflammasome activation-associated α‑synuclein pathology in PD, which forms the basis for targeting ASC as a potential therapy for PD.

Uncoupled pyroptosis and IL-1β secretion downstream of inflammasome signaling

Inflammasomes are supramolecular platforms that organize in response to various damage-associated molecular patterns and pathogen-associated molecular patterns. Upon activation, inflammasome sensors (with or without the help of ASC) activate caspase-1 and other inflammatory caspases that cleave gasdermin D and pro-IL-1β/pro-IL-18, leading to pyroptosis and mature cytokine secretion. Pyroptosis enables intracellular pathogen niche disruption and intracellular content release at the cost of cell death, inducing pro-inflammatory responses in the neighboring cells. IL-1β is a potent pro-inflammatory regulator for neutrophil recruitment, macrophage activation, and T-cell expansion. Thus, pyroptosis and cytokine secretion are the two main mechanisms that occur downstream of inflammasome signaling; they maintain homeostasis, drive the innate immune response, and shape adaptive immunity. This review aims to discuss the possible mechanisms, timing, consequences, and significance of the two uncoupling preferences downstream of inflammasome signaling. While pyroptosis and cytokine secretion may be usually coupled, pyroptosis-predominant and cytokine-predominant uncoupling are also observed in a stimulus-, cell type-, or context-dependent manner, contributing to the pathogenesis and development of numerous pathological conditions such as cryopyrin-associated periodic syndromes, LPS-induced sepsis, and Salmonella enterica serovar Typhimurium infection. Hyperactive cells consistently release IL-1β without LDH leakage and pyroptotic death, thereby leading to prolonged inflammation, expanding the lifespans of pyroptosis-resistant neutrophils, and hyperactivating stimuli-challenged macrophages, dendritic cells, monocytes, and specific nonimmune cells. Death inflammasome activation also induces GSDMD-mediated pyroptosis with no IL-1β secretion, which may increase lethality in vivo. The sublytic GSDMD pore formation associated with lower expressions of pyroptotic components, GSDMD-mediated extracellular vesicles, or other GSDMD-independent pathways that involve unconventional secretion could contribute to the cytokine-predominant uncoupling; the regulation of caspase-1 dynamics, which may generate various active species with different activities in terms of GSDMD or pro-IL-1β, could lead to pyroptosis-predominant uncoupling. These uncoupling preferences enable precise reactions to different stimuli of different intensities under specific conditions at the single-cell level, promoting cooperative cell and host fate decisions and participating in the pathogen "game". Appropriate decisions in terms of coupling and uncoupling are required to heal tissues and eliminate threats, and further studies exploring the inflammasome tilt toward pyroptosis or cytokine secretion may be helpful.

Identification of inflammasome signaling proteins in neurons and microglia in early and intermediate stages of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that destroys memory and cognitive function. Inflammasome activation has been suggested to play a critical role in the neuroinflammatory response in AD progression, but the cell-type expression of inflammasome proteins in the brain has not been fully characterized. In this study, we used samples from the hippocampus formation, the subiculum, and the entorhinal cortex brain from 17 donors with low-level AD pathology and 17 intermediate AD donors to assess the expression of inflammasome proteins. We performed analysis of hippocampal thickness, β-amyloid plaques, and hyperphosphorylated tau to ascertain the cellular pathological changes that occur between low and intermediate AD pathology. Next, we determined changes in the cells that express the inflammasome sensor proteins NOD-like receptor proteins (NLRP) 1 and 3, and caspase-1. In addition, we stained section with IC100, a humanized monoclonal antibody directed against the inflammasome adaptor protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and a commercially available anti-ASC antibody. Our results indicate that hippocampal cortical thickness did not significantly change between low and intermediate AD pathology, but there was an increase in pTau and β-amyloid clusters in intermediate AD cases. NLRP3 was identified mainly in microglial populations, whereas NLRP1 was seen in neuronal cytoplasmic regions. There was a significant increase of ASC in neurons labeled by IC100, whereas microglia in the hippocampus and subiculum were labeled with the commercial anti-ASC antibody. Caspase-1 was present in the parenchyma in the CA regions where amyloid and pTau were identified. Together, our results indicate increased inflammasome protein expression in the early pathological stages of AD, that IC100 identifies neurons in early stages of AD and that ASC expression correlates with Aβ and pTau in postmortem AD brains.

Interaction between autophagy and the NLRP3 inflammasome in Alzheimer’s and Parkinson’s disease

Autophagy degrades phagocytosed damaged organelles, misfolded proteins, and various pathogens through lysosomes as an essential way to maintain cellular homeostasis. Autophagy is a tightly regulated cellular self-degradation process that plays a crucial role in maintaining normal cellular function and homeostasis in the body. The NLRP3 inflammasome in neuroinflammation is a vital recognition receptor in innate cellular immunity, sensing external invading pathogens and endogenous stimuli and further triggering inflammatory responses. The NLRP3 inflammasome forms an inflammatory complex by recognizing DAMPS or PAMPS, and its activation triggers caspase-1-mediated cleavage of pro-IL-1β and pro-IL-18 to promote the inflammatory response. In recent years, it has been reported that there is a complex interaction between autophagy and neuroinflammation. Strengthening autophagy can regulate the expression of NLRP3 inflammasome to reduce neuroinflammation in neurodegenerative disease and protect neurons. However, the related mechanism is not entirely clear. The formation of protein aggregates is one of the standard features of Neurodegenerative diseases. A large number of toxic protein aggregates can induce inflammation. In theory, activation of the autophagy pathway can remove the potential toxicity of protein aggregates and delay the progression of the disease. This article aims to review recent research on the interaction of autophagy, NLRP3 inflammasome, and protein aggregates in Alzheimer’s disease (AD) and Parkinson’s disease (PD), analyze the mechanism and provide theoretical references for further research in the future.

Based on molecular structures: Amyloid-β generation, clearance, toxicity and therapeutic strategies

Amyloid-β (Aβ) has long been considered as one of the most important pathogenic factors in Alzheimer’s disease (AD), but the specific pathogenic mechanism of Aβ is still not completely understood. In recent years, the development of structural biology technology has led to new understandings about Aβ molecular structures, Aβ generation and clearance from the brain and peripheral tissues, and its pathological toxicity. The purpose of the review is to discuss Aβ metabolism and toxicity, and the therapeutic strategy of AD based on the latest progress in molecular structures of Aβ. The Aβ structure at the atomic level has been analyzed, which provides a new and refined perspective to comprehend the role of Aβ in AD and to formulate therapeutic strategies of AD.