Microglia and Astrocytes Dysfunction and Key Neuroinflammation-Based Biomarkers in Parkinson's Disease

PET, SPECT, and MRI imaging for evaluation of Parkinson's disease

This review assesses the primary neuroimaging techniques used to evaluate Parkinson's disease (PD) - a neurological condition characterized by gradual dopamine-producing nerve cell degeneration. The neuroimaging techniques explored include positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI). These modalities offer varying degrees of insights into PD pathophysiology, diagnostic accuracy, specificity by way of exclusion of other Parkinsonian syndromes, and monitoring of disease progression. Neuroimaging is thus crucial for diagnosing and managing PD, with integrated multimodal approaches and novel techniques further enhancing early detection and treatment evaluation.

Single-cell sequencing insights into the transcriptional landscape of Parkinson's disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disorder, with an unknown etiology and no specific treatment. Emerging single-cell and single-nucleus RNA sequencing (sc/snRNA-seq) technologies have become instrumental in unravelling cellular heterogeneity and characterizing molecular signatures at single-cell resolution. Single-cell T cell receptor sequencing (scTCR-seq) and single-cell B cell receptor sequencing (scBCR-seq) technologies provide unprecedented opportunities to explore the immune repertoire diversity. These state-of-the-art technologies have been increasingly applied in PD research in the last five years, offering novel insights into the cellular susceptibilities and complex molecular mechanisms underlying PD pathogenesis. Herein we review recent advances in the applications of sc/snRNA-seq, scTCR-seq and scBCR-seq technologies in various PD models. Moreover, we focus on degenerative neurons, activated neuroglial cells, as well as pro-inflammatory immune cells, exploring their unique transcriptional landscapes in PD, as revealed by single-cell sequencing technologies. Finally, we highlight important challenges and the future directions of single-cell experiments in PD research.

Nrf2 pathways in neuroprotection: Alleviating mitochondrial dysfunction and cognitive impairment in aging

Mitochondrial dysfunction and cognitive impairment are widespread phenomena among the elderly, being crucial factors that contribute to neurodegenerative diseases. Nuclear factor erythroid 2-related factor 2 (Nrf2) is an important regulator of cellular defense systems, including that against oxidative stress. As such, increased Nrf2 activity may serve as a strategy to avert mitochondrial dysfunction and cognitive decline. Scientific data on Nrf2-mediated neuroprotection was collected from PubMed, Google Scholar, and Science Direct, specifically addressing mitochondrial dysfunction and cognitive impairment in older people. Search terms included "Nrf2", "mitochondrial dysfunction," "cognitive impairment," and "neuroprotection." Studies focusing on in vitro and in vivo models and clinical investigations were included to review Nrf2's therapeutic potential comprehensively. The relative studies have demonstrated that increased Nrf2 activity could improve mitochondrial performance, decrease oxidative pressure, and mitigate cognitive impairment. To a large extent, this is achieved through the modulation of critical cellular signalling pathways such as the Keap1/Nrf2 pathway, mitochondrial biogenesis, and neuroinflammatory responses. The present review summarizes the recent progress in comprehending the molecular mechanisms regarding the neuroprotective benefits mediated by Nrf2 through its substantial role against mitochondrial dysfunction and cognitive impairment. This review also emphasizes Nrf2-target pathways and their contribution to cognitive function improvement and rescue from mitochondria-related abnormalities as treatment strategies for neurodegenerative diseases that often affect elderly individuals.

Experimental peri-implantitis induces neuroinflammation: An exploratory study in rats

PURPOSE

Cumulating evidence supports the close association between periodontal diseases, neuroinflammation and neurodegenerative pathologies, except for peri-implantitis (PI). Thus, this study explored the association between experimental PI and neuropathological changes in the rat brain.

MATERIALS AND METHODS

After bilateral first molars extraction, experimental PI was induced at titanium implants placed in the maxillae by lipopolysaccharide injections and ligature placement. Following 28-weeks of disease progression, the maxillae and brains were retrieved from 6 rats. Healthy brains from 3 rats were used as control. Brains were analyzed by immunohistochemistry to detect signs of neuroinflammation (interleukin (IL)-6 and tumor necrosis factor (TNF)-α)), microglial activation (IBA-1) and astrogliosis (GFAP). To explore signs of neurodegeneration, hematoxylin/eosin and Nissl stainings were used. Also, four different antibodies against amyloid beta (Aβ 1-42) were tested.

RESULTS

Chronic PI lesions showed peri-implant bone resorption accompanied by large inflammatory infiltrates. IL-6+ and TNF-α+ cells were found within the CA1 and Dentate Gyrus regions of the hippocampus of the PI-affected group, while almost no immune-positivity was detected in the control (p < 0.05). Detection of activated GFAP+ microglia and IBA-1+ astrocytes surface were significantly higher at the CA areas, and cerebral cortex of the PI-affected group, in comparison with control (p < 0.05). Shrunk neurons with pyknotic nuclei were inconsistently found among the PI-affected group, and these were almost not detected in control. No positive Aβ reactivity was detected in any of the samples.

CONCLUSION

Chronic experimental PI lesions led to an increased detection of IL-6 and TNF-α, GFAP+ microgliosis and IBA-1+ astrocytosis, and in some cases, neurodegeneration, in the rat brain.

Astrocyte-Mediated Neuroinflammation in Neurological Conditions

Astrocytes are one of the key glial types of the central nervous system (CNS), accounting for over 20% of total glial cells in the brain. Extensive evidence has established their indispensable functions in the maintenance of CNS homeostasis, as well as their broad involvement in neurological conditions. In particular, astrocytes can participate in various neuroinflammatory processes, e.g., releasing a repertoire of cytokines and chemokines or specific neurotrophic factors, which result in both beneficial and detrimental effects. It has become increasingly clear that such astrocyte-mediated neuroinflammation, together with its complex crosstalk with other glial cells or immune cells, designates neuronal survival and the functional integrity of neurocircuits, thus critically contributing to disease onset and progression. In this review, we focus on the current knowledge of the neuroinflammatory responses of astrocytes, summarizing their common features in neurological conditions. Moreover, we highlight several vital questions for future research that promise novel insights into diagnostic or therapeutic strategies against those debilitating CNS diseases.

Motor deficits and brain pathology in the Parkinson's disease mouse model hA53Ttg

Background

Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons and the accumulation of α-synuclein (α-syn) aggregates. The A53T missense point mutation occurs in autosomal dominant familial PD and has been found to promote the aggregation of α-syn. To investigate the role of the A53T mutation in PD, researchers have developed various mouse models with this mutation.

Objective

We therefore conducted a comprehensive characterization of the tg(THY1-SNCA*A53T)M53Sud mouse model (hA53Ttg mice) for its motor and pathological features.

Methods

hA53Ttg mice were tested for motor impairments in a series of motor tests at 2, 4 or 6 months of age. Human α-syn and α-syn pSer129, as well as GFAP and Iba1 signal were labeled and quantified in the cortex, hippocampus, and brainstem. Neurofilament light chain (NF-L) levels were measured in the cerebrospinal fluid (CSF) and plasma. Ex vivo analyses were performed at the age of 2, 4, 6, and 10 months.

Results

Behavioral tests revealed early muscle weakness and motor impairments that progressed with age. Immunohistochemical analyses demonstrated elevated levels of human α-syn and α-syn pSer129 in all evaluated brain regions. α-syn pSer129 labeling further revealed fiber-like structures in the cortex of older animals. Neuroinflammation was observed in an age-dependent manner. Biochemical evaluation revealed elevated NF-L levels in the plasma and CSF. Overall, our findings highlight the value of hA53Ttg mice in modeling PD-associated pathologies that closely resemble those observed in PD patients.

Conclusion

Our results thus suggest that hA53Ttg mice are a useful tool for studying the underlying mechanisms of PD.

Emerging insights into Lipocalin-2: Unraveling its role in Parkinson's Disease

Parkinson's disease (PD) ranks as the second most prevalent neurodegenerative disorder globally, marked by a complex pathogenesis. Lipocalin-2 (LCN2) emerges as a crucial factor during the progression of PD. Belonging to the lipocalin family, LCN2 is integral to several biological functions, including glial cell activation, iron homeostasis regulation, immune response, inflammatory reactions, and oxidative stress mitigation. Substantial research has highlighted marked increases in LCN2 expression within the substantia nigra (SN), cerebrospinal fluid (CSF), and blood of individuals with PD. This review focuses on the pathological roles of LCN2 in neuroinflammation, aging, neuronal damage, and iron dysregulation in PD. It aims to explore the underlying mechanisms of LCN2 in the disease and potential therapeutic targets that could inform future treatment strategies.

Golexanolone reduces glial activation in the striatum and improves non-motor and some motor alterations in a rat model of Parkinson's disease

Background

Parkinson's disease (PD) affects more than 6 million people worldwide. Along with motor impairments, patients and animal models exhibiting PD symptoms also experience cognitive impairment, fatigue, anxiety, and depression. Currently, there are no drugs available for PD that alter the progression of the disease. A body of evidence suggests that increased GABA levels contribute to the reduced expression of tyrosine hydroxylase (TH) and accompanying behavioral deficits. TH expression may be restored by blocking GABAA receptors. We hypothesized that golexanolone (GR3027), a well-tolerated GABAA receptor-modulating steroid antagonist (GAMSA), may improve Parkinson's symptoms in a rat model of PD.

Objectives

The aims of this study were to assess whether golexanolone can ameliorate motor and non-motor symptoms in a rat model of PD and to identify some underlying mechanisms.

Methods

We used the unilateral 6-OHDA rat model of PD. The golexanolone treatment started 4 weeks after surgery. Motor symptoms were assessed using Motorater and CatWalk tests. We also analyzed fatigue (using a treadmill test), anhedonia (via the sucrose preference test), anxiety (with an open field test), and short-term memory (using a Y maze). Glial activation and key proteins involved in PD pathogenesis were analyzed using immunohistochemistry and Western blot.

Results

Rats with PD showed motor incoordination and impaired locomotor gait, increased fatigue, anxiety, depression, and impaired short-term memory. Golexanolone treatment led to improvements in motor incoordination, certain aspects of locomotor gait, fatigue, anxiety, depression, and short-term memory. Notably, golexanolone reduced the activation of microglia and astrocytes, mitigated TH loss at 5 weeks after surgery, and prevented the increase of α-synuclein levels at 10 weeks.

Conclusions

Golexanolone may be useful in improving both motor and non-motor symptoms that adversely affect the quality of life in PD patients, such as anxiety, depression, fatigue, motor coordination, locomotor gait, and certain cognitive alterations.

Insights into Calpain Activation and Rho-ROCK Signaling in Parkinson's Disease and Aging

Parkinson's disease (PD), a progressive neurodegenerative disease, has no cure, and current therapies are not effective at halting disease progression. The disease affects mid-brain dopaminergic neurons and, subsequently, the spinal cord, contributing to many debilitating symptoms associated with PD. The GTP-binding protein, Rho, plays a significant role in the cellular pathology of PD. The downstream effector of Rho, Rho-associated kinase (ROCK), plays multiple functions, including microglial activation and induction of inflammatory responses. Activated microglia have been implicated in the pathology of many neurodegenerative diseases, including PD, that initiate inflammatory responses, leading to neuron death. Calpain expression and activity is increased following glial activation, which triggers the Rho-ROCK pathway and induces inflammatory T cell activation and migration as well as mediates toxic α-synuclein (α-syn) aggregation and neuron death, indicating a pivotal role for calpain in the inflammatory and degenerative processes in PD. Increased calpain activity and Rho-ROCK activation may represent a new mechanism for increased oxidative damage in aging. This review will summarize calpain activation and the role of the Rho-ROCK pathway in oxidative stress and α-syn aggregation, their influence on the neurodegenerative process in PD and aging, and possible strategies and research directions for therapeutic intervention.

Gastrointestinal dysmotility in rodent models of Parkinson's disease

Multiple studies describe prodromal, nonmotor dysfunctions that affect the quality of life of patients who subsequently develop Parkinson's disease (PD). These prodromal dysfunctions comprise a wide array of autonomic issues, including severe gastrointestinal (GI) motility disorders such as dysphagia, delayed gastric emptying, and chronic constipation. Indeed, strong evidence from studies in humans and animal models suggests that the GI tract and its neural, mainly vagal, connection to the central nervous system (CNS) could have a major role in the etiology of PD. In fact, misfolded α-synuclein aggregates that form Lewy bodies and neurites, i.e., the histological hallmarks of PD, are detected in the enteric nervous system (ENS) before clinical diagnosis of PD. The aim of the present review is to provide novel insights into the pathogenesis of GI dysmotility in PD, focusing our attention on functional, neurochemical, and molecular alterations in animal models.

Polymeric nanocomposite electrode for enhanced electrochemical detection of α-lipoic acid: Application in neuroinflammation prevention and clinical analysis

Using poly (vanillin-co-chitosan)/functionalized MWCNTs/GCE (PV-CS/f-MWCNTs/GCE) as a polymeric nanocomposite modified electrode, the present investigation has been conducted on the electrochemical detection of α-lipoic acid (α-LA) to prevent the activation of microglia inflammation of the nervous system. The manufacture of modified polymeric nanocomposite electrodes was carried out using the established electropolymerization process. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analyses of structure revealed that the electropolymerization of poly (vanillin-co-chitosan) on the surface of the f-MWCNTs modified electrode was successful. Vanillin-co-chitosan electropolymerization on f-MWCNTs as electroactive sheets can enhance the signal for α-LA electrochemical sensors, according to research on the electrochemical characteristics utilizing cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methodologies. The PV-CS/f-MWCNTs/GCE demonstrated that it had a sensitivity of 0.04664 μA/μM, a detection limit of 0.012 μM, and an excellent response, linear range, and wide linear range to α-LA from 0 to 3000 μM. The results of the application of PV-CS/f-MWCNTs/GCE for determining the concentration of α-LA in a prepared real sample of human serum by DPV and human lipoic acid ELISA Kit analyses via standard addition method illustrated the substantial conformity between the findings of both assays. The results of the DPV analyses resulted in acceptable recovery values (97.60%-99.10%) and appropriate values of the Relative Standard Deviation (RSD) (3.58%-5.07%), which demonstrated the great applicability and accuracy of the results of PV-CS/f-MWCNTs/GCE for determining α-LA concentration in biological fluids and pharmaceutical specimens.

Nicotinic Acetylcholine Receptors in Glial Cells as Molecular Target for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by resting tremor, bradykinesia, rigidity, and postural instability that also includes non-motor symptoms such as mood dysregulation. Dopamine (DA) is the primary neurotransmitter involved in this disease, but cholinergic imbalance has also been implicated. Current intervention in PD is focused on replenishing central DA, which provides remarkable temporary symptomatic relief but does not address neuronal loss and the progression of the disease. It has been well established that neuronal nicotinic cholinergic receptors (nAChRs) can regulate DA release and that nicotine itself may have neuroprotective effects. Recent studies identified nAChRs in nonneuronal cell types, including glial cells, where they may regulate inflammatory responses. Given the crucial role of neuroinflammation in dopaminergic degeneration and the involvement of microglia and astrocytes in this response, glial nAChRs may provide a novel therapeutic target in the prevention and/or treatment of PD. In this review, following a brief discussion of PD, we focus on the role of glial cells and, specifically, their nAChRs in PD pathology and/or treatment.

The interplay between neuroinflammatory pathways and Parkinson's disease

Parkinson's disease, a progressive neurodegenerative disorder predominantly affecting elderly, is marked by the gradual degeneration of the nigrostriatal dopaminergic pathway, culminating in neuronal loss within the substantia nigra pars compacta (SNpc) and dopamine depletion. At the molecular level, neuronal loss in the SNpc has been attributed to factors including neuroinflammation, impaired protein homeostasis, as well as mitochondrial dysfunction and the resulting oxidative stress. This review focuses on the interplay between neuroinflammatory pathways and Parkinson's disease, drawing insights from current literature.

Rubusoside mitigates neuroinflammation and cellular apoptosis in Parkinson's disease, and alters gut microbiota and metabolite composition

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative condition characterized by the progressive loss of dopaminergic neurons within the substantia nigra. Neuroinflammation plays a pivotal role in the pathogenesis of PD, involving the activation of microglia cells, heightened production of proinflammatory cytokines, and perturbations in the composition of the gut microbiota. Rubusoside (Ru), the principal steviol bisglucoside present in Rubus chingii var. suavissimus (S.K.Lee) L.T.Lu (Rosaceae), has been documented for its anti-inflammatory properties in diverse disease models. Nonetheless, there is an imperative need to comprehensively assess and elucidate the protective and anti-inflammatory attributes of Ru concerning PD, as well as to uncover the underlying mechanism involved.

OBJECTIVE

The aim of this study is to evaluate the neuroprotective and anti-inflammatory effects of Ru on PD and investigate its potential mechanisms associated with microbes.

RESEARCH DESIGN AND METHODS

We pre-treated mice and cell lines with Ru in order to simulate the progression of PD and the neuroinflammatory state. The mouse model was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), SN4741 cells were induced by 1-methyl-4-phenylpyridine (mpp+), and BV-2 cells were induced by lipopolysaccharide (LPS). We assessed the impact of Ru on motor function, neuroinflammation, neuron apoptosis, the composition of gut microbes, and their metabolites.

RESULTS

Ru treatment reduces the release of pro-inflammatory mediators by inhibiting microglia activation. It also prevents neuronal apoptosis, thereby safeguarding dopaminergic neurons and ameliorating motor dysfunction. Furthermore, it induces alterations in the fecal microbiota composition and metabolites profile in PD mice. In vitro experiments have demonstrated that Ru inhibits neuronal apoptosis in SN4741 cells induced by mpp+, suppresses the production of pro-inflammatory mediators, and activates the c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase (p38 MAPK), and nuclear factor kappa-B (NF-κB) signaling pathways.

CONCLUSION

Ru exhibits inhibitory effects on the MPTP-induced PD model by mitigating neuroinflammation and neuronal apoptosis while also inducing changes in the gut microbiota and metabolite composition.

Brain FADE syndrome: the final common pathway of chronic inflammation in neurological disease

Importance

While the understanding of inflammation in the pathogenesis of many neurological diseases is now accepted, this special commentary addresses the need to study chronic inflammation in the propagation of cognitive Fog, Asthenia, and Depression Related to Inflammation which we name Brain FADE syndrome. Patients with Brain FADE syndrome fall in the void between neurology and psychiatry because the depression, fatigue, and fog seen in these patients are not idiopathic, but instead due to organic, inflammation involved in neurological disease initiation.

Observations

A review of randomized clinical trials in stroke, multiple sclerosis, Parkinson's disease, COVID, traumatic brain injury, and Alzheimer's disease reveal a paucity of studies with any component of Brain FADE syndrome as a primary endpoint. Furthermore, despite the relatively well-accepted notion that inflammation is a critical driving factor in these disease pathologies, none have connected chronic inflammation to depression, fatigue, or fog despite over half of the patients suffering from them.

Conclusions and relevance

Brain FADE Syndrome is important and prevalent in the neurological diseases we examined. Classical "psychiatric medications" are insufficient to address Brain FADE Syndrome and a novel approach that utilizes sequential targeting of innate and adaptive immune responses should be studied.

Differential profiles of serum cytokines in Parkinson's disease according to disease duration

OBJECTIVE

Neurodegeneration and neuroinflammation are two intertwined mechanisms contributing to the pathophysiology of Parkinson's disease. Whether circulating biomarkers reflecting those two processes differ according to disease duration remains to be established. The present study was conducted to characterize the biomarkers individuals with PD with short (≤5 years) or long disease duration (>5 years).

METHODS

We consecutively enrolled 104 patients with Parkinson's disease and evaluated them using validated clinical scales (MDS-UPDRS, Hoehn and Yahr staging, MMSE). Serum samples were assayed for the following biomarkers: neurofilament light chain (NfL), brain-derived neurotrophic factor (BDNF), interleukin (IL-) 1β, 4, 5, 6, 10, 17, interferon-γ, and tumor necrosis factor α.

RESULTS

Mean age of participants was 66.0 ± 9.6 years and 45 (34%) were women. The average disease duration was 8 ± 5 years (range 1 to 19 years). Patients with short disease duration (≤ 5 years) showed a pro-inflammatory profile, with significantly higher levels of pro-inflammatory IL-1β and lower concentrations of IL-5, IL-10 and IL-17 (p < 0.05). NfL serum levels showed a positive correlation with disease duration and age (respectively rho = 0.248, p = 0.014 and rho = 0.559, p < 0.001) while an opposite pattern was detected for BDNF (respectively rho -0,187, p = 0.034 and rho = -0.245, p = 0.014).

CONCLUSIONS

Our findings suggest that a pro-inflammatory status may be observed in PD patients in the early phases of the disease, independently from age.

Microglia in Neurodegenerative Diseases

Neurodegenerative diseases are manifested by a progressive death of neural cells, resulting in the deterioration of central nervous system (CNS) functions, ultimately leading to specific behavioural and cognitive symptoms associated with affected brain regions. Several neurodegenerative disorders are caused by genetic variants or mutations, although the majority of cases are sporadic and linked to various environmental risk factors, with yet an unknown aetiology. Neuroglial changes are fundamental and often lead to the pathophysiology of neurodegenerative diseases. In particular, microglial cells, which are essential for maintaining CNS health, become compromised in their physiological functions with the exposure to environmental risk factors, genetic variants or mutations, as well as disease pathology. In this chapter, we cover the contribution of neuroglia, especially microglia, to several neurodegenerative diseases, including Nasu-Hakola disease, Parkinson's disease, amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease, infectious disease-associated neurodegeneration, and metal-precipitated neurodegeneration. Future research perspectives for the field pertaining to the therapeutic targeting of microglia across these disease conditions are also discussed.

Role of Astrogliosis in the Pathogenesis of Parkinson's Disease: Insights into Astrocytic Nrf2 Pathway as a Potential Therapeutic Target

Recently, Parkinson's disease (PD) has become a remarkable burden on families and society with an acceleration of population aging having several pathological hallmarks such as dopaminergic neuronal loss of the substantia nigra pars compacta, α-synucleinopathy, neuroinflammation, autophagy, last but not the least astrogliosis. Astrocyte, star-shaped glial cells perform notable physiological functions in the brain through several molecular and cellular mechanisms including nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway. It has been well established that the downregulation of the astrocytic Nrf2 signaling pathway plays a crucial role in the pathogenesis of PD because it is a master regulator of cellular defense mechanism along with a regulator of numerous detoxifying and antioxidant enzymes gene expression. Fascinatingly, upregulation of the astrocytic Nrf2 signaling pathway attenuates the degeneration of nigrostriatal neurons, restores neuronal proliferation, rejuvenates astrocytic functions, and exhibits neuroprotective effects via numerous cellular and molecular mechanisms in the PD-like brain of the experimental animal. Here, we discuss the numerous in-vitro and in-vivo studies that evaluate the neuroprotective potential of the astrocytic Nrf2 signaling pathway against experimentally-induced PD-like manifestation. In conclusion, based on available preclinical reports, it can be assumed that the astrocytic Nrf2 signaling pathway could be an alternative target in the drug discovery process for the prevention, management, and treatment of PD.

Sevoflurane-induced hypotension causes cognitive dysfunction and hippocampal inflammation in mice

Sevoflurane commonly adopted for anesthetic in clinical practice, however, its influences on cerebral blood flow and cognitive function remain controversial. Herein, the sevoflurane-induced hypotension on arterial blood pressure, cerebral blood flow, cognitive function, and hippocampal inflammation was investigated in mice. A significant decrease in arterial blood pressure and cerebral blood flow was indicated by the sevoflurane anesthesia treatment. Moreover, sevoflurane-induced hypotension was associated with the impaired cognitive function and the increased levels of NLRP3 inflammasome activation and oxidative stress in hippocampus. These findings suggest that sevoflurane-induced hypotension may lead to the cognitive dysfunction and hippocampal inflammation.