Inflammation is genetically implicated in Parkinson's disease

Parkinson's disease with anxiety: clinical characteristics and their correlation with oxidative stress, inflammation, and pathological proteins

OBJECTIVE

This study was performed to explore the differences in the clinical characteristics and oxidative stress indicators, inflammatory factors, and pathological proteins in serum between Parkinson's disease (PD) with anxiety (PD-A) and with no anxiety (PD-NA) patients, and further correlations among clinical characteristics and above variables were analyzed in PD-A and PD-NA groups.

METHODS

A total of 121 patients with PD were enrolled in this study and assessed by the Hamilton Anxiety Scale (14 items) (HAMA-14). These patients were divided into PD-A and PD-NA groups according to a cut-off point of 7 of HAMA-14. Demographic variables were collected, and clinical symptoms were assessed by multiple rating scales. The levels of free radicals, inflammatory factors, and pathological proteins in serum were measured by chemical colorimetric method and enzyme-linked immunosorbent assay (ELISA). The differences of above variables were compared between PD-A and PD-NA groups, and the correlations of clinical symptoms with the abovevariables were analyzed in PD-A and PD-NA groups.

RESULTS

The frequency of PD-A was 62.81%. PD-A group exhibited significantly impaired motor dysfunction and multiple non-motor symptoms, including fatigue, sleep behavior disorder, restless leg syndrome and autonomic dysfunction, and dramatically compromised activities of daily living compard with PD-NA group. PD-A group displayed prominently increasedlevels of hydroxyl radical (·OH) and tumor necrosis factor (TNF)-α, and a decreased nitric oxide (NO) level in serum compared with PD-NA group (P<0.001, P = 0.001, P= 0.027, respectively). ·OH, NO, and TNF-α were identified as the risk factors of PD-A (OR = 1.005, P = 0.036; OR = 0.956, P = 0.017; OR = 1.039, P = 0.033, respectively). In PD patients, HAMA-14 score was significantly and positively correlated with the levels of ·OH and TNF-α in serum (P<0.001, P = 0.002, respectively). In PD-A group, ·OH level was significantly and negatively correlated with Aβ1-42 level, while TNF-α level was significantly and positively correlated with P-tau (S396) level in serum.

CONCLUSIONS

The frequency of PD-A is high. PD-A patients present more severe motor dysfunction and multiple non-motor symptoms, and poorer activities of daily living. The increased levels of ·OH and TNF-α levels and the decreased NO level in serum are all associated with more severe anxiety in PD patients.Findings from this study may provide in-depth insights into the clinical characteristics, underlying mechanisms of PD-A, and potential correlations among anxiety, oxidative stress, inflammation, and cognitive decline in PD patients.

Single cell analysis reveals the roles and regulatory mechanisms of type-I interferons in Parkinson's disease

The pathogenesis of Parkinson's disease (PD) is strongly associated with neuroinflammation, and type I interferons (IFN-I) play a crucial role in regulating immune and inflammatory responses. However, the specific features of IFN in different cell types and the underlying mechanisms of PD have yet to be fully described. In this study, we analyzed the GSE157783 dataset, which includes 39,024 single-cell RNA sequencing results for five PD patients and six healthy controls from the Gene Expression Omnibus database. After cell type annotation, we intersected differentially expressed genes in each cell subcluster with genes collected in The Interferome database to generate an IFN-I-stimulated gene set (ISGs). Based on this gene set, we used the R package AUCell to score each cell, representing the IFN-I activity. Additionally, we performed monocle trajectory analysis, and single-cell regulatory network inference and clustering (SCENIC) to uncover the underlying mechanisms. In silico gene perturbation and subsequent experiments confirm NFATc2 regulation of type I interferon response and neuroinflammation. Our analysis revealed that microglia, endothelial cells, and pericytes exhibited the highest activity of IFN-I. Furthermore, single-cell trajectory detection demonstrated that microglia in the midbrain of PD patients were in a pro-inflammatory activation state, which was validated in the 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model as well. We identified transcription factors NFATc2, which was significantly up-regulated and involved in the expression of ISGs and activation of microglia in PD. In the 1-Methyl-4-phenylpyridinium (MPP+)-induced BV2 cell model, the suppression of NFATc2 resulted in a reduction in IFN-β levels, impeding the phosphorylation of STAT1, and attenuating the activation of the NF-κB pathway. Furthermore, the downregulation of NFATc2 mitigated the detrimental effects on SH-SY5Y cells co-cultured in conditioned medium. Our study highlights the critical role of microglia in type I interferon responses in PD. Additionally, we identified transcription factors NFATc2 as key regulators of aberrant type I interferon responses and microglial pro-inflammatory activation in PD. These findings provide new insights into the pathogenesis of PD and may have implications for the development of novel therapeutic strategies.

Causal association between atopic dermatitis and Parkinson's disease: A bidirectional Mendelian randomization study

BACKGROUND

Atopic dermatitis is one of the most common skin disorders. Evidence has suggested an association between skin disorders, such as atopic dermatitis, and Parkinson's disease (PD). However, whether atopic dermatitis has a causal effect on PD remains unknown.

METHODS

The study aimed to determine whether their association between atopic dermatitis and PD is causal, using a bidirectional two-sample Mendelian randomization method. Genetic variants from the public genome-wide association studies for atopic dermatitis (n = 10788 cases and 30047 controls) were selected to evaluate their causal effects on the risk of PD (33,674 cases and 449,056 controls). The inverse variance weighted (IVW) method was used as the primary analysis.

RESULTS

The IVW results indicated that atopic dermatitis was associated with decreased risk of PD {fixed effects: odds ratio [OR] [95% confidence interval (CI)]: .905 [.832-.986], p = .022; OR [95% CI]: .905 [.827-.991], p = .032}. However, we failed to detect the causal effects of PD on risk of atopic dermatitis in the reverse causation analysis.

CONCLUSION

This study indicated causal association of genetically proxied atopic dermatitis with the risk of PD. Future studies are warranted to explore the underlying mechanism and investigate the targeting effect of atopic dermatitis on PD.

Synaptic dysfunction and extracellular matrix dysregulation in dopaminergic neurons from sporadic and E326K-GBA1 Parkinson's disease patients

Parkinson's disease (PD) is a neurodegenerative disease with both genetic and sporadic origins. In this study, we investigated the electrophysiological properties, synaptic activity, and gene expression differences in dopaminergic (DA) neurons derived from induced pluripotent stem cells (iPSCs) of healthy controls, sporadic PD (sPD) patients, and PD patients with E326K-GBA1 mutations. Our results demonstrate reduced sodium currents and synaptic activity in DA neurons derived from PD patients with E326K-GBA1 mutations, suggesting a potential contribution to PD pathophysiology. We also observed distinct electrophysiological alterations in sPD DA neurons, which included a decrease in synaptic currents. RNA sequencing analysis revealed unique dysregulated pathways in sPD neurons and E326K-GBA1 neurons, further supporting the notion that molecular mechanisms driving PD may differ between PD patients. In agreement with our previous reports, Extracellular matrix and Focal adhesion pathways were among the top dysregulated pathways in DA neurons from sPD patients and from patients with E326K-GBA1 mutations. Overall, our study further confirms that impaired synaptic activity is a convergent functional phenotype in DA neurons derived from PD patients across multiple genetic mutations as well as sPD. At the transcriptome level, we find that the brain extracellular matrix is highly involved in PD pathology across multiple PD-associated mutations as well as sPD.

Cytokine activity in Parkinson's disease

The contribution of the immune system to the pathophysiology of neurodegenerative Parkinson's disease (PD) is increasingly being recognised, with alterations in the innate and adaptive arms of the immune system underlying central and peripheral inflammation in PD. As chief modulators of the immune response, cytokines have been intensely studied in the field of PD both in terms of trying to understand their contribution to disease pathogenesis, and if they may comprise much needed therapeutic targets for a disease with no current modifying therapy. This review summarises current knowledge on key cytokines implicated in PD (TNFα, IL-6, IL-1β, IL-10, IL-4 and IL-1RA) that can modulate both pro-inflammatory and anti-inflammatory effects. Cytokine activity in PD is clearly a complicated process mediated by substantial cross-talk of signalling pathways and the need to balance pro- and anti-inflammatory effects. However, understanding cytokine activity may hold promise for unlocking new insight into PD and how it may be halted.

Proof-of-Principle Study of Inflammasome Signaling Proteins as Diagnostic Biomarkers of the Inflammatory Response in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder marked by the death of dopaminergic neurons in the midbrain, the accumulation of α-synuclein aggregates, and motor deficits. A major contributor to dopaminergic neuronal loss is neuroinflammation. The inflammasome is a multiprotein complex that perpetuates neuroinflammation in neurodegenerative disorders including PD. Increases in inflammasome proteins are associated with worsened pathology. Thus, the inhibition of inflammatory mediators has the potential to aid in PD treatment. Here, we investigated inflammasome signaling proteins as potential biomarkers of the inflammatory response in PD. Plasma from PD subjects and healthy age-matched controls were evaluated for levels of the inflammasome protein apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), caspase-1, and interleukin (IL)-18. This was carried out using Simple Plex technology to identify changes in inflammasome proteins in the blood of PD subjects. The area under the curve (AUC) was obtained through calculation of the receiver operating characteristics (ROC) to obtain information on biomarker reliability and traits. Additionally, we completed a stepwise regression selected from the lowest Akaike information criterion (AIC) to assess how the inflammasome proteins caspase-1 and ASC contribute to IL-18 levels in people with PD. PD subjects demonstrated elevated caspase-1, ASC, and IL-18 levels when compared to controls; each of these proteins were found to be promising biomarkers of inflammation in PD. Furthermore, inflammasome proteins were determined to significantly contribute to and predict IL-18 levels in subjects with PD. Thus, we demonstrated that inflammasome proteins serve as reliable biomarkers of inflammation in PD and that inflammasome proteins provide significant contributions to IL-18 levels in PD.

Toll-like Receptor 4 Is Upregulated in Parkinson's Disease Patients and Co-Localizes with pSer129αSyn: A Possible Link with the Pathology

Growing evidence suggests a crucial role of neuroinflammation in the pathophysiology of Parkinson's disease (PD). Neuroinflammation is linked to the accumulation and aggregation of a-synuclein (αSyn), the primary pathological hallmark of PD. Toll-like receptors 4 (TLR4) can have implications in the development and progression of the pathology. In this study, we analyzed the expression of TLR4 in the substantia nigra (SN) and medial temporal gyrus (GTM) of well-characterized PD patients and age-matched controls. We also assessed the co-localization of TLR4 with pSer129 αSyn. Using qPCR, we observed an upregulation of TLR4 expression in the SN and GTM in PD patients compared to controls, which was accompanied by a reduction in αSyn expression likely due to the depletion of dopaminergic (DA) cells. Additionally, using immunofluorescence and confocal microscopy, we observed TLR4-positive staining and co-localization with pSer129-αSyn in Lewy bodies of DA neurons in the SN, as well as in pyramidal neurons in the GTM of PD donors. Furthermore, we observed a co-localization of TLR4 and Iba-1 in glial cells of both SN and GTM. Our findings provide evidence for the increased expression of TLR4 in the PD brain and suggest that the interaction between TLR4 and pSer129-αSyn could play a role in mediating the neuroinflammatory response in PD.

Therapeutic potential of autophagy in immunity and inflammation: current and future perspectives

Autophagy is recognized as a lysosomal degradation pathway important for cellular and organismal homeostasis. Accumulating evidence has demonstrated that autophagy is a paradoxical mechanism that regulates homeostasis and prevents stress under physiological and pathological conditions. Nevertheless, how autophagy is implicated in immune responses remains unclear. It is well established that autophagy bridges innate and adaptive immunity, while autophagic dysfunction is closely related to infection, inflammation, neurodegeneration, and tumorigenesis. Therefore, autophagy has attracted great attention from fundamental and translational fields due to its crucial role in inflammation and immunity. Inflammation is involved in the development and progression of various human diseases, and as a result, autophagy might be a potential target to prevent and treat inflammatory diseases. Nevertheless, insufficient autophagy might cause cell death, perpetrate inflammation, and trigger hereditary unsteadiness. Hence, targeting autophagy is a promising disease prevention and treatment strategy. To accomplish this safely, we should thoroughly understand the basic aspects of how autophagy works. Herein, we systematically summarized the correlation between autophagy and inflammation and its implication for human diseases.

Role of α-synuclein in microglia: autophagy and phagocytosis balance neuroinflammation in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease, and is characterized by accumulation of α-synuclein (α-syn). Neuroinflammation driven by microglia is an important pathological manifestation of PD. α-Syn is a crucial marker of PD, and its accumulation leads to microglia M1-like phenotype polarization, activation of NLRP3 inflammasomes, and impaired autophagy and phagocytosis in microglia. Autophagy of microglia is related to degradation of α-syn and NLRP3 inflammasome blockage to relieve neuroinflammation. Microglial autophagy and phagocytosis of released α-syn or fragments from apoptotic neurons maintain homeostasis in the brain. A variety of PD-related genes such as LRRK2, GBA and DJ-1 also contribute to this stability process.

OBJECTIVES

Further studies are needed to determine how α-syn works in microglia.

METHODS

A keyword-based search was performed using the PubMed database for published articles.

CONCLUSION

In this review, we discuss the interaction between microglia and α-syn in PD pathogenesis and the possible mechanism of microglial autophagy and phagocytosis in α-syn clearance and inhibition of neuroinflammation. This may provide a novel insight into treatment of PD.

Disease mechanisms as subtypes: Microbiome

Abnormalities in gut microbiota have been suggested to be involved in the pathophysiology and progression of Parkinson's disease (PD). Gastrointestinal nonmotor symptoms often precede the onset of motor features in PD, suggesting a role for gut dysbiosis in neuroinflammation and α-synuclein (α-syn) aggregation. In the first part of this chapter, we analyze critical features of healthy gut microbiota and factors (environmental and genetic) that modify its composition. In the second part, we focus on the mechanisms underlying the gut dysbiosis and how it alters anatomically and functionally the mucosal barrier, triggering neuroinflammation and subsequently α-syn aggregation. In the third part, we describe the most common alterations in the gut microbiota of PD patients, dividing the gastrointestinal system in higher and lower tract to examine the association between microbiota abnormalities and clinical features. In the final section, we report on current and future therapeutic approaches to gut dysbiosis aiming to either reduce the risk for PD, modify the disease course, or improve the pharmacokinetic profile of dopaminergic therapies. We also suggest that further studies will be needed to clarify the role of the microbiome in PD subtyping and of pharmacological and nonpharmacological interventions in modifying specific microbiota profiles in individualizing disease-modifying treatments in PD.

Genetic mechanism vs genetic subtypes: The example of GBA

Genetic variants in GBA, encoding the lysosomal enzyme glucocerebrosidase (GCase), are common risk factors for Parkinson's disease (PD). Genotype-phenotype studies have demonstrated that different types of GBA variants have differential effects on the phenotype. Variants could be classified as mild or severe depending on the type of Gaucher disease they cause in the biallelic state. It was shown that severe GBA variants, as compared to mild variants, are associated with higher risk of PD, earlier age at onset, and faster progression of motor and nonmotor symptoms. The observed difference in phenotype might be caused by a diversity of cellular mechanisms related to the particular variants. The lysosomal function of GCase is thought to play a significant role in the development of GBA-associated PD, and other mechanisms such as endoplasmic reticulum retention, mitochondrial dysfunction, and neuroinflammation have also been suggested. Moreover, genetic modifiers such as LRRK2, TMEM175, SNCA, and CTSB can either affect GCase activity or modulate risk and age at onset of GBA-associated PD. To achieve ideal outcomes with precision medicine, therapies will have to be tailored to individuals with specific variants, potentially in combination with known modifiers.

Non-Motor Symptoms of Parkinson's Disease: The Neurobiology of Early Psychiatric and Cognitive Dysfunction

Parkinson's disease (PD) is a progressive neurodegenerative disorder that has been recognized for over 200 years by its clinically dominant motor system impairment. There are prominent non-motor symptoms as well, and among these, psychiatric symptoms of depression and anxiety and cognitive impairment are common and can appear earlier than motor symptoms. Although the neurobiology underlying these particular PD-associated non-motor symptoms is not completely understood, the identification of PARK genes that contribute to hereditary and sporadic PD has enabled genetic models in animals that, in turn, have fostered ever deepening analyses of cells, synapses, circuits, and behaviors relevant to non-motor psychiatric and cognitive symptoms of human PD. Moreover, while it has long been recognized that inflammation is a prominent component of PD, recent studies demonstrate that brain-immune signaling crosstalk has significant modulatory effects on brain cell and synaptic function in the context of psychiatric symptoms. This review provides a focused update on such progress in understanding the neurobiology of PD-related non-motor psychiatric and cognitive symptoms.

Repositioning doxycycline for treating synucleinopathies: Evidence from a pre-clinical mouse model

BACKGROUND AND PURPOSE

Parkinson's disease remains orphan of valuable therapies capable to interfere with the disease pathogenesis despite the large number of symptomatic approaches adopted in clinical practice to manage this disease. Treatments simultaneously affecting α-synuclein (α-syn) oligomerization and neuroinflammation may counteract Parkinson's disease and related disorders. Recent data demonstrate that Doxycycline, a tetracycline antibiotic, can inhibit α-syn aggregation as well as neuroinflammation. We herein investigate, for the first time, the potential therapeutic properties of Doxy in a human α-syn A53T transgenic Parkinson's disease mouse model evaluating behavioural, biochemical and histopathological parameters.

EXPERIMENTAL APPROACH

Human α-syn A53T transgenic mice were treated with Doxycycline (10 mg/kg daily ip) for 30 days. The effect of treatment on motor, cognitive and daily live activity performances were examined. Neuropathological and neurophysiological parameters were assessed through immunocytochemical, electrophysiological and biochemical analysis of cerebral tissue.

KEY RESULTS

Doxy treatment abolished cognitive and daily life activity deficiencies in A53T mice. The effect on cognitive functions was associated with neuroprotection, inhibition of α-syn oligomerization and gliosis both in the cortex and hippocampus. Doxy treatment restored hippocampal long-term potentiation in association with the inhibition of pro-inflammatory cytokines expression. Moreover, Doxy ameliorated motor impairment and reduced striatal glial activation in A53T mice.

CONCLUSIONS AND IMPLICATIONS

Our findings promote Doxy as a valuable multi-target therapeutic approach counteracting both symptoms and neuropathology in the complex scenario of α-synucleinopathies.

Unraveling Parkinson's Disease Neurodegeneration: Does Aging Hold the Clues?

Aging is the greatest risk factor for Parkinson's disease (PD), suggesting that mechanisms driving the aging process promote PD neurodegeneration. Several lines of evidence support a role for aging in PD. First, hallmarks of brain aging such as mitochondrial dysfunction and oxidative stress, loss of protein homeostasis, and neuroinflammation are centrally implicated in PD development. Second, mutations that cause monogenic PD are present from conception, yet typically only cause disease following a period of aging. Third, lifespan-extending genetic, dietary, or pharmacological interventions frequently attenuate PD-related neurodegeneration. These observations support a central role for aging in disease development and suggest that new discoveries in the biology of aging could be leveraged to elucidate novel mechanisms of PD pathophysiology. A recent rapid growth in our understanding of conserved molecular pathways that govern model organism lifespan and healthspan has highlighted a key role for metabolism and nutrient sensing pathways. Uncovering how metabolic pathways involving NAD+ consumption, insulin, and mTOR signaling link to the development of PD is underway and implicates metabolism in disease etiology. Here, we assess areas of convergence between nervous system aging and PD, evaluate the link between metabolism, aging, and PD and address the potential of metabolic interventions to slow or halt the onset of PD-related neurodegeneration drawing on evidence from cellular and animal models.

Association between Parkinson's Disease and Diabetes Mellitus: From Epidemiology, Pathophysiology and Prevention to Treatment

Diabetes mellitus (DM) and Parkinson's disease (PD) are both age-related diseases of global concern being among the most common chronic metabolic and neurodegenerative diseases, respectively. While both diseases can be genetically inherited, environmental factors play a vital role in their pathogenesis. Moreover, DM and PD have common underlying molecular mechanisms, such as misfolded protein aggregation, mitochondrial dysfunction, oxidative stress, chronic inflammation, and microbial dysbiosis. Recently, epidemiological and experimental studies have reported that DM affects the incidence and progression of PD. Moreover, certain antidiabetic drugs have been proven to decrease the risk of PD and delay its progression. In this review, we elucidate the epidemiological and pathophysiological association between DM and PD and summarize the antidiabetic drugs used in animal models and clinical trials of PD, which may provide reference for the clinical translation of antidiabetic drugs in PD treatment.

The efficient generation of knockout microglia cells using a dual-sgRNA strategy by CRISPR/Cas9

Gene deletion in microglia has become an important and exciting approach for studying neuroinflammation, especially after the development of the CRISPR/Cas9 system for genome editing during the last decade. In this study, we described a protocol for the highly efficient generation of knockout microglia cells using a dual-short guide RNA (sgRNA) strategy by CRISPR/Cas9. Leucine-rich repeat kinase 2 (LRRK2), a pathogenic gene of Parkinson's disease (PD), has played versatile roles during the disease development. Despite many key insights into LRRK2 studies, the normal and disease-related functions of LRRK2 in microglia and neuroinflammation remain to be fully investigated. Given the importance of LRRK2 in PD pathogenesis, we designed and applied the protocol to target LRRK2. Specifically, we designed two sgRNAs targeting the N terminus of LRRK2, spanning the 5' untranslated region (UTR) and exon 1, and screened knockout cells by single-cell expansion. In practice, the dual-sgRNA system can facilitate in obtaining knockout cells in a more convenient, rapid, and accurate way. Candidate knockout cells can be easily distinguished by genomic PCR and running on agarose gels, based on the different band sizes. Successful knockouts were further verified by Sanger sequencing and Western blot. Using this protocol, we obtained an LRRK2-deficient microglia cell line, which was characterized by longer cellular processes, enhanced adhesion, and weakened migration capacity. The knockout microglia may further serve as an important cellular tool to reveal conserved and novel aspects of LRRK2 functions in the development and progression of PD. Our protocol using dual-sgRNA targeting guarantees > 60% targeting efficiency and could also be applied to targeting other genes/loci, especially non-coding RNAs and regulatory elements.

Role of the gut-microbiota-metabolite axis in the rotenone model of early-stage Parkinson's Disease

Gastrointestinal symptoms are common in the early-stage Parkinson's disease (PD), but its potential pathogenesis remains unclear. Therefore, in the present study, we used the 16S ribosomal RNA gene sequencing and gas chromatography coupled with mass spectrometry-based metabolomics to investigate the alterations of gut microbiome and serum amino acid levels in the early-stage PD mice model induced with rotenone. The results demonstrated that the microbial taxa at phylum, family and genus levels remarkably altered in rotenone-induced mice relative to vehicle-induced mice. The rotenone-induced mice had higher relative abundance of Flavobacteriaceae, Staphylococcaceae, and Prevotellaceae as well as lower relative abundance of Lachnospiraceae_UCG-001, Ruminiclostridium, and Prevotellaceae_NK3B31_group than vehicle-induced mice. The evaluation of serum amino acids revealed the alterations in several classes of amino acids, including L-proline, L-alanine, L-serine, L-asparagine, L-threonine, L-glutamine, L-methionine, and L-4-hydroxyproline. Notably, the altered serum amino acid levels were significantly associated with the abundance of gut microbiota, especially Ruminococcaceae and Ruminiclostridium. Our study explored the possible role of the gut-microbiota-metabolite axis in the early-stage PD and provided the possibility of prevention and treatment of PD by gut-microbiota-metabolite axis in the future.

Neuroprotective Function of Rasagiline and Selegiline, Inhibitors of Type B Monoamine Oxidase, and Role of Monoamine Oxidases in Synucleinopathies

Synucleinopathies are a group of neurodegenerative disorders caused by the accumulation of toxic species of α-synuclein. The common clinical features are chronic progressive decline of motor, cognitive, behavioral, and autonomic functions. They include Parkinson’s disease, dementia with Lewy body, and multiple system atrophy. Their etiology has not been clarified and multiple pathogenic factors include oxidative stress, mitochondrial dysfunction, impaired protein degradation systems, and neuroinflammation. Current available therapy cannot prevent progressive neurodegeneration and “disease-modifying or neuroprotective” therapy has been proposed. This paper presents the molecular mechanisms of neuroprotection by the inhibitors of type B monoamine oxidase, rasagiline and selegiline. They prevent mitochondrial apoptosis, induce anti-apoptotic Bcl-2 protein family, and pro-survival brain- and glial cell line-derived neurotrophic factors. They also prevent toxic oligomerization and aggregation of α-synuclein. Monoamine oxidase is involved in neurodegeneration and neuroprotection, independently of the catalytic activity. Type A monoamine oxidases mediates rasagiline-activated signaling pathways to induce neuroprotective genes in neuronal cells. Multi-targeting propargylamine derivatives have been developed for therapy in various neurodegenerative diseases. Preclinical studies have presented neuroprotection of rasagiline and selegiline, but beneficial effects have been scarcely presented. Strategy to improve clinical trials is discussed to achieve disease-modification in synucleinopathies.

Neuroinflammation represents a common theme amongst genetic and environmental risk factors for Alzheimer and Parkinson diseases

Multifactorial diseases are characterized by inter-individual variation in etiology, age of onset, and penetrance. These diseases tend to be relatively common and arise from the combined action of genetic and environmental factors; however, parsing the convoluted mechanisms underlying these gene-by-environment interactions presents a significant challenge to their study and management. For neurodegenerative disorders, resolving this challenge is imperative, given the enormous health and societal burdens they impose. The mechanisms by which genetic and environmental effects may act in concert to destabilize homeostasis and elevate risk has become a major research focus in the study of common disease. Emphasis is further being placed on determining the extent to which a unifying biological principle may account for the progressively diminishing capacity of a system to buffer disease phenotypes, as risk for disease increases. Data emerging from studies of common, neurodegenerative diseases are providing insights to pragmatically connect mechanisms of genetic and environmental risk that previously seemed disparate. In this review, we discuss evidence positing inflammation as a unifying biological principle of homeostatic destabilization affecting the risk, onset, and progression of neurodegenerative diseases. Specifically, we discuss how genetic variation associated with Alzheimer disease and Parkinson disease may contribute to pro-inflammatory responses, how such underlying predisposition may be exacerbated by environmental insults, and how this common theme is being leveraged in the ongoing search for effective therapeutic interventions.

12/15-Lipoxygenase Regulation of Diabetic Cognitive Dysfunction Is Determined by Interfering with Inflammation and Cell Apoptosis

This study aimed to discuss the role of 12/15-lipoxygenase (12/15-LOX) regulation involved in diabetes cognitive dysfunction. First, Mini Mental State Examination (MMSE) test was used to evaluate cognitive ability in diabetic patients and normal controls. The plasma test showed that the plasma level of 12/15-LOX in patients with MMSE scores below 27 was significantly increased compared with that of the normal group. Second, 12/15-LOX inhibitor was administered to diabetic rats. Behavioral tests, biochemistry, enzyme-linked immunosorbent assays, and Western blotting were used in this study. We found that the levels of fasting and random blood glucose increased rapidly in diabetic rats, the levels of triglycerides and total cholesterol in the diabetic group increased, and insulin levels decreased significantly. In the Morris water maze test, the escape latency was prolonged, and the crossing times decreased in the diabetic group. Under the microscope, the apoptosis of hippocampal neurons in diabetic rats increased significantly. The levels of TNF-α, IL-6 and 12-hydroxyindoleic acid (12(S)-HETE) significantly increased, and the protein expression of 12/15-LOX, p38 MAPK, Aβ_1-42, caspase-3, caspase-9 and cPLA2 increased, while that of Bcl-2 decreased. However, the use of 12/15-LOX inhibitor reversed these results. Third, 12/15-LOX shRNA and p38MAPK inhibitor were administered to HT22 cells in high-glucose medium. The results of the cell experiment were consistent with those of the animal experiment. Our results indicated that the 12/15-LOX pathway participates in diabetic brain damage by activating p38MAPK to promote inflammation and neuronal apoptosis, and intervention 12/15-LOX can improve diabetic cognitive dysfunction.

A guide to membrane atg8ylation and autophagy with reflections on immunity

The process of membrane atg8ylation, defined herein as the conjugation of the ATG8 family of ubiquitin-like proteins to membrane lipids, is beginning to be appreciated in its broader manifestations, mechanisms, and functions. Classically, membrane atg8ylation with LC3B, one of six mammalian ATG8 family proteins, has been viewed as the hallmark of canonical autophagy, entailing the formation of characteristic double membranes in the cytoplasm. However, ATG8s are now well described as being conjugated to single membranes and, most recently, proteins. Here we propose that the atg8ylation is coopted by multiple downstream processes, one of which is canonical autophagy. We elaborate on these biological outputs, which impact metabolism, quality control, and immunity, emphasizing the context of inflammation and immunological effects. In conclusion, we propose that atg8ylation is a modification akin to ubiquitylation, and that it is utilized by different systems participating in membrane stress responses and membrane remodeling activities encompassing autophagy and beyond.

WHOPPA Enables Parallel Assessment of Leucine-Rich Repeat Kinase 2 and Glucocerebrosidase Enzymatic Activity in Parkinson's Disease Monocytes

Both leucine-rich repeat kinase 2 (LRRK2) and glucocerebrosidase (GCase) are promising targets for the treatment of Parkinson’s disease (PD). Evidence suggests that both proteins are involved in biological pathways involving the lysosome. However, studies to date have largely investigated the enzymes in isolation and any relationship between LRRK2 and GCase remains unclear. Both enzymes are highly expressed in peripheral blood monocytes and have been implicated in immune function and inflammation. To facilitate the standardized measurement of these readouts in large cohorts of samples collected from persons with PD across the globe, we developed and optimized a sample collection and processing protocol with parallel flow cytometry assays. Assay parameters were first optimized using healthy control peripheral blood mononuclear cells (PBMCs), and then LRRK2 and GCase activities were measured in immune cells from persons with idiopathic PD (iPD). We tested the ability of this protocol to deliver similar results across institutes across the globe, and named this protocol the Wallings-Hughes Optimized Protocol for PBMC Assessment (WHOPPA). In the application of this protocol, we found increased LRRK2 levels and stimulation-dependent enzymatic activity, and decreased GBA index in classical iPD monocytes, as well as increased cytokine release in PD PBMCs. WHOPPA also demonstrated a strong positive correlation between LRRK2 levels, pRab10 and HLA-DR in classical monocytes from subjects with iPD. These data support a role for the global use of WHOPPA and expression levels of these two PD-associated proteins in immune responses, and provide a robust assay to determine if LRRK2 and GCase activities in monocytes have potential utility as reliable and reproducible biomarkers of disease in larger cohorts of subjects with PD.

The GBA1 D409V mutation exacerbates synuclein pathology to differing extents in two alpha-synuclein models

Heterozygous mutations in the GBA1 gene – encoding lysosomal glucocerebrosidase (GCase) – are the most common genetic risk factors for Parkinson's disease (PD). Experimental evidence suggests a correlation between decreased GCase activity and accumulation of alpha-synuclein (aSyn). To enable a better understanding of the relationship between aSyn and GCase activity, we developed and characterized two mouse models that investigate aSyn pathology in the context of reduced GCase activity. The first model used constitutive overexpression of wild-type human aSyn in the context of the homozygous GCase activity-reducing D409V mutant form of GBA1. Although increased aSyn pathology and grip strength reductions were observed in this model, the nigrostriatal system remained largely intact. The second model involved injection of aSyn preformed fibrils (PFFs) into the striatum of the homozygous GBA1 D409V knock-in mouse model. The GBA1 D409V mutation did not exacerbate the pathology induced by aSyn PFF injection. This study sheds light on the relationship between aSyn and GCase in mouse models, highlighting the impact of model design on the ability to model a relationship between these proteins in PD-related pathology.

Summary: Phenotyping data for two novel mouse models combining glucocerebrosidase (GCase) deficiencies and alpha-synuclein pathology reveal the extent to which alpha-synuclein pathology is exacerbated by GCase deficiency.

The Double-Faceted Role of Leucine-Rich Repeat Kinase 2 in the Immunopathogenesis of Parkinson’s Disease

Leucine-rich repeat kinase 2 (LRRK2) is one of the most common causative genes in Parkinson’s disease (PD). The complex structure of this multiple domains’ protein determines its versatile functions in multiple physiological processes, including migration, autophagy, phagocytosis, and mitochondrial function, among others. Mounting studies have also demonstrated the role of LRRK2 in mediating neuroinflammation, the prominent hallmark of PD, and intricate functions in immune cells, such as microglia, macrophages, and astrocytes. Of those, microglia were extensively studied in PD, which serves as the resident immune cell of the central nervous system that is rapidly activated upon neuronal injury and pathogenic insult. Moreover, the activation and function of immune cells can be achieved by modulating their intracellular metabolic profiles, in which LRRK2 plays an emerging role. Here, we provide an updated review focusing on the double-faceted role of LRRK2 in regulating various cellular physiology and immune functions especially in microglia. Moreover, we will summarize the latest discovery of the three-dimensional structure of LRRK2, as well as the function and dysfunction of LRRK2 in immune cell-related pathways.

"Reframing" dopamine signaling at the intersection of glial networks in the aged Parkinsonian brain as innate Nrf2/Wnt driver: Therapeutical implications

Dopamine (DA) signaling via G protein‐coupled receptors is a multifunctional neurotransmitter and neuroendocrine–immune modulator. The DA nigrostriatal pathway, which controls the motor coordination, progressively degenerates in Parkinson's disease (PD), a most common neurodegenerative disorder (ND) characterized by a selective, age‐dependent loss of substantia nigra pars compacta (SNpc) neurons, where DA itself is a primary source of oxidative stress and mitochondrial impairment, intersecting astrocyte and microglial inflammatory networks. Importantly, glia acts as a preferential neuroendocrine–immune DA target, in turn, counter‐modulating inflammatory processes. With a major focus on DA intersection within the astrocyte–microglial inflammatory network in PD vulnerability, we herein first summarize the characteristics of DA signaling systems, the propensity of DA neurons to oxidative stress, and glial inflammatory triggers dictating the vulnerability to PD. Reciprocally, DA modulation of astrocytes and microglial reactivity, coupled to the synergic impact of gene–environment interactions, then constitute a further level of control regulating midbrain DA neuron (mDAn) survival/death. Not surprisingly, within this circuitry, DA converges to modulate nuclear factor erythroid 2‐like 2 (Nrf2), the master regulator of cellular defense against oxidative stress and inflammation, and Wingless (Wnt)/β‐catenin signaling, a key pathway for mDAn neurogenesis, neuroprotection, and immunomodulation, adding to the already complex “signaling puzzle,” a novel actor in mDAn–glial regulatory machinery. Here, we propose an autoregulatory feedback system allowing DA to act as an endogenous Nrf2/Wnt innate modulator and trace the importance of DA receptor agonists applied to the clinic as immune modifiers.

Effect of LRRK2 protein and activity on stimulated cytokines in human monocytes and macrophages

Leucine-rich-repeat kinase 2 (LRRK2), a potential therapeutic target for the treatment of Parkinson's disease (PD), is highly expressed in monocytes and macrophages and may play a role in the regulation of inflammatory pathways. To determine how LRRK2 protein levels and/or its activity modulate inflammatory cytokine/chemokine levels in human immune cells, isogenic human induced pluripotent stem cells (iPSC) with the LRRK2-activating G2019S mutation, wild-type LRRK2, and iPSC deficient in LRRK2 were differentiated to monocytes and macrophages and stimulated with inflammatory toll-like receptor (TLR) agonists in the presence and absence of LRRK2 kinase inhibitors. The effect of LRRK2 inhibitors and the effect of increasing LRRK2 levels with interferon gamma on TLR-stimulated cytokines were also assessed in primary peripheral blood-derived monocytes. Monocytes and macrophages with the LRRK2 G2019S mutation had significantly higher levels of cytokines and chemokines in tissue culture media following stimulation with TLR agonists compared to isogenic controls. Knockout of LRRK2 impaired phagocytosis but did not significantly affect TLR-mediated cytokine levels. Interferon gamma significantly increased the levels of LRRK2 and phosphorylation of its downstream Rab10 substrate, and potentiated TLR-mediated cytokine levels. LRRK2 kinase inhibitors did not have a major effect on TLR-stimulated cytokine levels. Results suggest that the LRRK2 G2019S mutation may potentiate inflammation following activation of TLRs. However, this was not dependent on LRRK2 kinase activity. Indeed, LRRK2 kinase inhibitors had little effect on TLR-mediated inflammation under the conditions employed in this study.

Intranasal Administration of Self-Oriented Nanocarriers Based on Therapeutic Exosomes for Synergistic Treatment of Parkinson's Disease

The treatment of Parkinson's disease (PD) has been hindered by the complex pathologies and multiple membrane barriers during drug delivery. Although exosomes derived from mesenchymal stem cells (MSCs) have great potential for PD, MSC-derived exosomes alone could not fully meet the therapeutic requirements due to their limitation in therapy and delivery. Here, we develop a self-oriented nanocarrier called PR-EXO/PP@Cur that combines therapeutic MSC-derived exosomes with curcumin. PR-EXO/PP@Cur can be self-oriented across the multiple membrane barriers and directly release drugs into the cytoplasm of target cells after intranasal administration. With enhanced accumulation of drugs in the action site, PR-EXO/PP@Cur achieves three-pronged synergistic treatment to deal with the complex pathologies of PD by reducing α-synuclein aggregates, promoting neuron function recovery, and alleviating the neuroinflammation. After treatment with PR-EXO/PP@Cur, the movement and coordination ability of PD model mice are significantly improved. These results show that PR-EXO/PP@Cur has great prospects in treatment of PD or other neurodegenerative diseases.

Kaemperfol alleviates pyroptosis and microglia-mediated neuroinflammation in Parkinson's disease via inhibiting p38MAPK/NF-κB signaling pathway

The study aims to investigate whether kaemperfol (KAE) inhibits microglia pyroptosis and subsequent neuroinflammatory response to exert neuroprotective effects, along with the underlying mechanisms. The results showed KAE could ameliorate the behavioral deficits of Parkinson's disease (PD) rats, inhibit the activation of microglia and astrocytes, reduce the loss of TH-positive neurons, down-regulate levels of pyroptosis-related NOD-like receptor family pyrin domain containing 3 (NLRP3), GasderminD-N Term (GSDMD-NT), caspase1, apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), interleukin (IL)-1β, and IL-18, and decrease the levels of inflammatory molecules (inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2)) and p38 mitogen-activated protein kinase/nuclear factor-kappaB (p38MAPK/NF-κB) signaling pathway molecules (p38MAPK, p-p38MAPK, NF-κB, and p-NF-κB) in the substantia nigra of PD rats. Further in vitro study indicated that KAE reversed the activation of BV2 cells and down-regulated the expressions of pyrolytic proteins, inflammatory mediators and key molecules in p38MAPK/NF-κB signaling pathway. Collectively, KAE inhibits the microglia pyroptosis and subsequent neuroinflammatory response to exert neuroprotective effects on 6-hydroxydopamine (6-OHDA)-induced PD rats and lipopolysaccharide (LPS)-induced BV2 inflammatory cells through inhibiting p38MAPK/NF-κB signaling pathway.

Inorganic Nanomaterial for Biomedical Imaging of Brain Diseases

In the past few decades, brain diseases have taken a heavy toll on human health and social systems. Magnetic resonance imaging (MRI), photoacoustic imaging (PA), computed tomography (CT), and other imaging modes play important roles in disease prevention and treatment. However, the disadvantages of traditional imaging mode, such as long imaging time and large noise, limit the effective diagnosis of diseases, and reduce the precision treatment of diseases. The ever-growing applications of inorganic nanomaterials in biomedicine provide an exciting way to develop novel imaging systems. Moreover, these nanomaterials with special physicochemical characteristics can be modified by surface modification or combined with functional materials to improve targeting in different diseases of the brain to achieve accurate imaging of disease regions. This article reviews the potential applications of different types of inorganic nanomaterials in vivo imaging and in vitro detection of different brain disease models in recent years. In addition, the future trends, opportunities, and disadvantages of inorganic nanomaterials in the application of brain diseases are also discussed. Additionally, recommendations for improving the sensitivity and accuracy of inorganic nanomaterials in screening/diagnosis of brain diseases.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Chronic Stress Weakens Connectivity in the Prefrontal Cortex: Architectural and Molecular Changes

Chronic exposure to uncontrollable stress causes loss of spines and dendrites in the prefrontal cortex (PFC), a recently evolved brain region that provides top-down regulation of thought, action, and emotion. PFC neurons generate top-down goals through recurrent excitatory connections on spines. This persistent firing is the foundation for higher cognition, including working memory, and abstract thought. However, exposure to acute uncontrollable stress drives high levels of catecholamine release in the PFC, which activates feedforward calcium-cAMP signaling pathways to open nearby potassium channels, rapidly weakening synaptic connectivity to reduce persistent firing. Chronic stress exposures can further exacerbate these signaling events leading to loss of spines and resulting in marked cognitive impairment. In this review, we discuss how stress signaling mechanisms can lead to spine loss, including changes to BDNF-mTORC1 signaling, calcium homeostasis, actin dynamics, and mitochondrial actions that engage glial removal of spines through inflammatory signaling. Stress signaling events may be amplified in PFC spines due to cAMP magnification of internal calcium release. As PFC dendritic spine loss is a feature of many cognitive disorders, understanding how stress affects the structure and function of the PFC will help to inform strategies for treatment and prevention.

Extracellular Vesicles as Novel Diagnostic and Prognostic Biomarkers for Parkinson's Disease

The elderly population will significantly increase in the next decade and, with it, the proportion of people affected by age-related diseases. Among them, one of the most invalidating is Parkinson's disease (PD), characterized by motor- and non-motor dysfunctions which strongly impair the quality of life of affected individuals. PD is characterized by the progressive degeneration of dopaminergic neurons, with consequent dopamine depletion, and the accumulation of misfolded α-synuclein aggregates. Although 150 years have passed since PD first description, no effective therapies are currently available, but only palliative treatments. Importantly, PD is often diagnosed when the neuronal loss is elevated, making difficult any therapeutic intervention. In this context, two key challenges remain unanswered: (i) the early diagnosis to avoid the insurgence of irreversible symptoms; and (ii) the reliable monitoring of therapy efficacy. Research strives to identify novel biomarkers for PD diagnosis, prognosis, and therapeutic follow-up. One of the most promising sources of biomarkers is represented by extracellular vesicles (EVs), a heterogeneous population of nanoparticles, released by all cells in the microenvironment. Brain-derived EVs are able to cross the blood-brain barrier, protecting their payload from enzymatic degradation, and are easily recovered from biofluids. Interestingly, EV content is strongly influenced by the specific pathophysiological status of the donor cell. In this manuscript, the role of EVs as source of novel PD biomarkers is discussed, providing all recent findings concerning relevant proteins and miRNAs carried by PD patient-derived EVs, from several biological specimens. Moreover, the contribution of mitochondria-derived EVs will be dissected. Finally, the promising possibility to use EVs as source of markers to monitor PD therapy efficacy will be also examined. In the future, larger cohort studies will help to validate these EV-associated candidates, that might be effectively used as non-invasive and robust source of biomarkers for PD.

Mitochondrial Quality Control and Restraining Innate Immunity

Maintaining mitochondrial health is essential for the survival and function of eukaryotic organisms. Misfunctioning mitochondria activate stress-responsive pathways to restore mitochondrial network homeostasis, remove damaged or toxic proteins, and eliminate damaged organelles via selective autophagy of mitochondria, a process termed mitophagy. Failure of these quality control pathways is implicated in the pathogenesis of Parkinson's disease and other neurodegenerative diseases. Impairment of mitochondrial quality control has been demonstrated to activate innate immune pathways, including inflammasome-mediated signaling and the antiviral cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING)-regulated interferon response. Immune system malfunction is a common hallmark in many neurodegenerative diseases; however, whether inflammation suppresses or exacerbates disease pathology is still unclear. The goal of this review is to provide a historical overview of the field, describe mechanisms of mitochondrial quality control, and highlight recent advances on the emerging role of mitochondria in innate immunity and inflammation.

Glucocerebrosidase Activity is Reduced in Cryopreserved Parkinson's Disease Patient Monocytes and Inversely Correlates with Motor Severity

Background:

Reduced activity of lysosomal glucocerebrosidase is found in brain tissue from Parkinson’s disease patients. Glucocerebrosidase is also highly expressed in peripheral blood monocytes where its activity is decreased in Parkinson’s disease patients, even in the absence of GBA mutation.

Objective:

To measure glucocerebrosidase activity in cryopreserved peripheral blood monocytes from 30 Parkinson’s disease patients and 30 matched controls and identify any clinical correlation with disease severity.

Methods:

Flow cytometry was used to measure lysosomal glucocerebrosidase activity in total, classical, intermediate, and non-classical monocytes. All participants underwent neurological examination and motor severity was assessed by the Movement Disorders Society Unified Parkinson’s Disease Rating Scale.

Results:

Glucocerebrosidase activity was significantly reduced in the total and classical monocyte populations from the Parkinson’s disease patients compared to controls. GCase activity in classical monocytes was inversely correlated to motor symptom severity.

Conclusion:

Significant differences in monocyte glucocerebrosidase activity can be detected in Parkinson’s disease patients using cryopreserved mononuclear cells and monocyte GCase activity correlated with motor features of disease. Being able to use cryopreserved cells will facilitate the larger multi-site trials needed to validate monocyte GCase activity as a Parkinson’s disease biomarker.

Toll-like receptor 10 controls TLR2-induced cytokine production in monocytes from patients with Parkinson's disease

Peripheral inflammation, particularly mediated by monocytes, can cause neuroinflammation in Parkinson's disease (PD). We investigated the mechanism of TLR2-induced cytokine impairment in peripheral monocytes from PD patients and the association between the presence of CD14⁺ TLR10⁺ monocytes and PD severity. Peripheral blood mononuclear cells from PD patients and healthy individuals were evaluated for TLR expression on monocyte subsets (CD14 and CD16 expression) using flow cytometry. Moreover, cytokines were evaluated using flow cytometry after stimulation with Pam₃ Cys (TLR2/TLR1 agonist) in the absence or presence of neutralizing antibodies to TLR10. The severity of PD was assessed using the unified PD rating scale (UPDRS) and motor activity, anxiety (BAI), depression (BDI), and fatigue (PD Fatigue Scale-16) scales. The frequency of CD14⁺ TLR10⁺ monocytes and expression intensity of TLR2 and TLR10 were higher in patients with PD than healthy individuals. The frequency of intermediate monocytes (CD14⁺⁺ CD16⁺ ) was not significantly increased in patients with PD, but was the main monocyte subset expressing TLR10. The TLR2/TLR1-impaired cytokine production (IL-6, TNFα, IL-8, and IL-10) in PD patients was reversed by neutralizing TLR10. The high frequency of total CD14⁺ TLR10⁺ monocytes was associated with a reduction in the severity of PD according to the evaluation of motor and nonmotor symptoms. Peripheral monocytes from patients with PD showed phenotypic and functional alterations. The expression of TLR10 on monocytes can protect against PD by controlling TLR2-induced cytokine production. Furthermore, data suggested that a low frequency of CD14⁺ TLR10⁺ monocytes indicates the severity of PD. The results identified new opportunities for the development of novel PD neuroprotective therapies.

Microbial Infections Are a Risk Factor for Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, comprise a family of disorders characterized by progressive loss of nervous system function. Neuroinflammation is increasingly recognized to be associated with many neurodegenerative diseases but whether it is a cause or consequence of the disease process is unclear. Of growing interest is the role of microbial infections in inciting degenerative neuroinflammatory responses and genetic factors that may regulate those responses. Microbial infections cause inflammation within the central nervous system through activation of brain-resident immune cells and infiltration of peripheral immune cells. These responses are necessary to protect the brain from lethal infections but may also induce neuropathological changes that lead to neurodegeneration. This review discusses the molecular and cellular mechanisms through which microbial infections may increase susceptibility to neurodegenerative diseases. Elucidating these mechanisms is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of neurodegenerative diseases.

Small molecule therapeutics for neuroinflammation-mediated neurodegenerative disorders

Chronically activated microglia and the resulting cascade of neuroinflammatory mechanisms have been postulated to play a critical role in neurodegenerative disorders. Microglia are the main component of the brain's innate immune system and become activated by infection, injury, misfolded proteins or a multitude of other stimuli. Activated microglia release pro-inflammatory and cytotoxic factors that can damage neurons and transform astrocytes to become toxic to neurons as well. Therapeutic approaches aiming to modulate microglia activation may be beneficial to mitigate the progression of inflammatory-mediated neurodegenerative diseases. In this literature review, we provide an overview of recent progress on key microglia targets and discovery of small molecule compounds advancing in clinical trials to minimize neuroinflammation.

NPT520-34 improves neuropathology and motor deficits in a transgenic mouse model of Parkinson's disease

NPT520-34 is a clinical-stage, small molecule being developed for the treatment of Parkinson's disease and other neurodegenerative disorders. The therapeutic potential of NPT520-34 was first suggested by findings from cell-based assays of alpha-synuclein (ASYN) clearance. As reported here, NPT520-34 was subsequently evaluated for therapeutically relevant actions in a transgenic animal model of Parkinson's disease that overexpresses human ASYN and in an acute lipopolysaccharide (LPS)-challenge model using wild-type mice. Daily administration of NPT520-34 to mThy1-ASYN (Line 61) transgenic mice for one or three months resulted in reduced ASYN pathology, reduced expression of markers of neuroinflammation, and improvements in multiple indices of motor function. In an LPS-challenge model using wild-type mice, a single-dose of NPT520-34 reduced LPS-evoked increases in the expression of several pro-inflammatory cytokines in plasma. These findings demonstrate the beneficial effects of NPT520-34 on both inflammation and protein-pathology endpoints, with consequent improvements in motor function in an animal model of Parkinson's disease. These findings further suggest that NPT520-34 may have two complementary actions: (1) to increase the clearance of neurotoxic protein aggregates and (2) to directly attenuate inflammation. NPT520-34 treatment may thereby address two of the predominate underlying pathophysiological aspects of neurodegenerative disorders such as Parkinson's disease.

Neuronal autophagy and mitophagy in Parkinson's disease

Autophagy is the process by which cells can selectively or non-selectively remove damaged proteins and organelles. As the cell's main means of sequestering damaged mitochondria for removal, mitophagy is central to cellular function and survival. Research on autophagy and mitochondrial quality control has increased exponentially in relation to the pathogenesis of numerous disease conditions, from cancer and immune diseases to chronic neurodegenerative diseases like Parkinson's disease (PD). Understanding how components of the autophagic/mitophagic machinery are affected during disease, as well as the contextual relationship of autophagy with determining neuronal health and function, is essential to the goal of designing therapies for human disease. In this review, we will summarize key signaling molecules that consign damaged mitochondria for autophagic degradation, describe the relationship of genes linked to PD to autophagy/mitophagy dysfunction, and discuss additional roles of both mitochondrial and cytosolic pools of PTEN-induced kinase 1 (PINK1) in mitochondrial homeostasis, dendritic morphogenesis and inflammation.

High Inflammatory Tendency Induced by Malignant Stimulation Through Imbalance of CD28 and CTLA-4/PD-1 Contributes to Dopamine Neuron Injury

Background

Parkinson’s disease is a common neurodegenerative disease in the elderly. The incidence of various cancers in Parkinson’s disease patients is significantly lower than in healthy people. Parkinson’s disease patients are individuals with a high tendency for inflammation, whose peripheral immune system is represented in an activated state. We hypothesized that the hyperinflammatory predisposition of Parkinson’s disease patients is pathogenic.

Methods

DBA/1 mice were used to simulate “highly inflammatory individuals”, and the carcinogen DEN was used to induce malignancy. Hematoxylin & eosin (H&E) staining was used to observe the formation of lung tumors. Apoptosis of neurons was observed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Immunohistochemistry and flow cytometry were used to observe CD4, CD28, major histocompatibility complex II (MHCII), cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), and programmed death 1 (PD-1). The ionized calcium binding adaptor molecule-1 (IBA-1) + inducible nitric oxide synthase (iNOS) was used to label M1 microglia, and IBA-1 + arginase 1 (Arg1) was used to label M2 microglia by immunofluorescence. The expression of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and anti-inflammatory cytokines IL-10 and IL-4 was detected by ELISA.

Results

DBA/1 mice with high inflammatory tendency showed a continuous increase of peripheral inflammation, promoting intracranial inflammation, decreasing the tumor incidence and increasing the neurodegeneration under induction of malignant change. CD28 and CTLA-4/PD-1 reduced the T-cell-dominated inflammatory response, reduced the intracerebral inflammatory response, protected from neurodegeneration, and increased the incidence of tumor. Combination of CTLA-4 and PD-1 blocker can overactivate T cells, worsen peripheral and intracranial inflammation, reduce the incidence of tumor, cause damage to dopamine neurons, and promote the occurrence of neurodegeneration.

Conclusion

High inflammatory tendency induced by malignant stimulation through the imbalance of CD28 and CTLA-4/PD-1 leads to dopamine neuron injury.

Decreased glucocerebrosidase activity and substrate accumulation of glycosphingolipids in a novel GBA1 D409V knock-in mouse model

Multiple mutations have been described in the human GBA1 gene, which encodes the lysosomal enzyme beta-glucocerebrosidase (GCase) that degrades glucosylceramide and is pivotal in glycosphingolipid substrate metabolism. Depletion of GCase, typically by homozygous mutations in GBA1, is linked to the lysosomal storage disorder Gaucher’s disease (GD) and distinct or heterozygous mutations in GBA1 are associated with increased Parkinson’s disease (PD) risk. While numerous genes have been linked to heritable PD, GBA1 mutations in aggregate are the single greatest risk factor for development of idiopathic PD. The importance of GCase in PD necessitates preclinical models in which to study GCase-related mechanisms and novel therapeutic approaches, as well as to elucidate the molecular mechanisms leading to enhanced PD risk in GBA1 mutation carriers. The aim of this study was to develop and characterize a novel GBA1 mouse model and to facilitate wide accessibility of the model with phenotypic data. Herein we describe the results of molecular, biochemical, histological, and behavioral phenotyping analyses in a GBA1 D409V knock-in (KI) mouse. This mouse model exhibited significantly decreased GCase activity in liver and brain, with substantial increases in glycosphingolipid substrates in the liver. While no changes in the number of dopamine neurons in the substantia nigra were noted, subtle changes in striatal neurotransmitters were observed in GBA1 D409V KI mice. Alpha-synuclein pathology and inflammation were not observed in the nigrostriatal system of this model. In summary, the GBA1 D409V KI mouse model provides an ideal model for studies aimed at pharmacodynamic assessments of potential therapies aiming to restore GCase.

Protective mechanism of Syringic acid in an experimental model of Parkinson's disease

6-Hydroxydopamine (6-OHDA) is a widely used chemical to model Parkinson's disease (PD) in rats. Syringic acid (SA) is a polyphenolic compound which has antioxidant and anti-inflammatory properties. The present study aimed to evaluate the neuroprotective role of SA in a rat model of 6-OHDA-induced PD. Parkinson's disease was created by injection of 6-OHDA into the medial forebrain bundle via stereotaxic surgery. Syringic acid was administered daily by oral gavage, before or after surgery. All groups were tested for locomotor activity, rotarod performance and catatony. Dopamine levels in SN were determined by an optimized multiple reaction monitoring method using ultra-fast liquid chromatography coupled with tandem mass spectrometry (MS/MS). The immunoreactivities for tyrosine hydroxylase (TH) and inducible nitric oxide synthase (iNOS) were detected by immunohistochemistry in frozen substantia nigra (SN) sections. Nitrite/nitrate levels, iNOS protein, total oxidant (TOS) and total antioxidant (TAS) status were assayed in SN tissue by standard kits. Motor dysfunction, impaired nigral dopamine release, increased iNOS expression and elevated nitrite/nitrate levels induced by 6-OHDA were significantly restored by SA treatment. Syringic acid significantly improved the loss of nigral TH-positive cells, while increasing TAS capacity and reducing TOS capacity in SN of PD rats. These data conclude that SA is a potential therapeutic agent for the treatment of 6-OHDA-induced rat model of PD. Syringic acid reduced the progression of PD via its neuroprotective, antioxidant and anti-inflammatory effects.

Potential Effects of Leukotriene Receptor Antagonist Montelukast in Treatment of Neuroinflammation in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder where misfolded alpha-synuclein-enriched aggregates called Lewy bodies are central in pathogenesis. No neuroprotective or disease-modifying treatments are currently available. Parkinson’s disease is considered a multifactorial disease and evidence from multiple patient studies and animal models has shown a significant immune component during the course of the disease, highlighting immunomodulation as a potential treatment strategy. The immune changes occur centrally, involving microglia and astrocytes but also peripherally with changes to the innate and adaptive immune system. Here, we review current understanding of different components of the PD immune response with a particular emphasis on the leukotriene pathway. We will also describe evidence of montelukast, a leukotriene receptor antagonist, as a possible anti-inflammatory treatment for PD.

Imbalance between T helper 1 and regulatory T cells plays a detrimental role in experimental Parkinson's disease in mice

Objective

Parkinson’s disease (PD) is a degenerative disorder characterized by steady motor function loss. PD pathogenesis remains inconclusive, but aberrant immune responses might play important roles. We hypothesized that imbalance between T helper (Th) 1 and regulatory T (Treg) cells was essential in experimental PD.

Methods

Th1 and Treg cells from the blood of patients with PD and healthy volunteer blood were measured by flow cytometry. Experimental PD was induced in mice by peritoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Experimental PD severity was measured by open field test behavior assessments (distance moved, rearing, and grooming). Mice were administered neutralizing anti-tumor necrosis factor (TNF) α to inhibit Th1 effects. Treg cells were depleted by anti-CD25 neutralizing antibodies or isolated and transferred to experimental PD mice.

Results

Patients with PD had fewer Treg and more Th1 cells than healthy volunteers. Experimental PD mice exhibited fewer Treg and more Th1 cells. Treg cell depletion exacerbated experimental PD, whereas TNFα neutralization attenuated PD in mice. Treg transfer to experimental PD mice reduced PD severity. Mechanistically, anti-TNFα antibody administration and Treg transfer increased Treg and reduced Th1 cell abundance in the brain.

Conclusion

Th1 and Treg cell imbalance plays an essential role in mouse experimental PD pathogenesis.

Oxidative stress and regulated cell death in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide. Motor deficits usually associated with PD correlate with dopaminergic axonal neurodegeneration starting at the striatum, which is then followed by dopaminergic neuronal death in the substantia nigra pars compacta (SN), with both events occurring already at the prodromal stage. We will overview the main physiological characteristics responsible for the higher susceptibility of the nigrostriatal circuit to mitochondrial dysfunction and oxidative stress, as hinted by the acting mechanisms of the PD-causing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Then, we will present multiple lines of evidence linking several cell death mechanisms involving mitochondria and production of reactive oxygen species to neuronal loss in PD, namely intrinsic and extrinsic apoptosis, necroptosis, ferroptosis, parthanatos and mitochondrial permeability transition-driven necrosis. We will focus on gathered data from postmortem PD samples and relevant in vivo models, especially MPTP-based models.

Lipoprotein-Associated Phospholipase A2 Is a Risk Factor for Patients With Parkinson's Disease

Objective

To explore the association between lipoprotein-related phospholipase A2 (Lp-PLA2) and the risk of Parkinson's disease (PD).

Methods

A case-control study involving 58 hospitalized PD patients and 60 healthy controls was carried out. Serum Lp-PLA2 level was detected. According to the disease course and severity, PD patients were subdivided to analyze the clinical value of Lp-PLA2. Relationship between Lp-PLA2 and PD risk was analyzed by logistic regression. Diagnostic value of Lp-PLA2 in PD patients was investigated using receiver's operator characteristic curves.

Results

Lp-PLA2 level was significantly higher in the PD patients compared with the controls, and was significantly and positively correlated with the Hoehn-Yahr (H&Y) stage. The serum Lp-PLA2 level and H&Y stage of PD patients with a longer disease course were significantly higher than those with a shorter disease course. PD patients with milder conditions had significantly lower serum Lp-PLA2 levels than patients with severe conditions. Multivariable logistic regression analysis indicated higher Lp-PLA2 level was an independent risk factor of PD patients. Moreover, the area under the curve for Lp-PLA2 was 0.703, which was between those of homocysteine and serum amylase A.

Conclusion

To our knowledge, this is the first study to show that increased level of Lp-PLA2 is associated with the risk of PD. Lp-PLA2 may be used for early detection of PD, and provides an effective intervention target for clinical treatment of PD.