Neuroinflammation Upregulated Neuronal Toll-Like Receptors 2 and 4 to Drive Synucleinopathy in Neurodegeneration

Proteomic analysis of P. gingivalis-Lipopolysaccharide induced neuroinflammation in SH-SY5Y and HMC3 cells

Chronic periodontitis and its keystone pathogen, Porphyromonas gingivalis, have increasingly been linked with Alzheimer's disease (AD). However, P.gingivalis-lipopolysaccharide (LPS) mediated release of neuroinflammatory proteins contributes to AD remains underexplored. In this study, we utilized data-independent acquisition mass spectrometry to characterize P.gingivalis-LPS induced profile of differentially expressed proteins associated with the neuroinflammatory response in human neuroblastoma (SH-SY5Y) and human microglial (HMC3) cells. We reported a set of 124 proteins in SH-SY5Y cells and 96 proteins in HMC3 cells whose levels were significantly upregulated or downregulated by exposure to P. gingivalis-LPS. Our findings demonstrate that P. gingivalis-LPS contributed to the elevated expressions of dementia biomarkers and pro-inflammatory cytokines that include APP, Aβ1-42, Aβ1-40, T-Tau, p-Tau, VEGF, TGF-β, IL-1β, IL-6 and TNF-α through 2 distinct pathways of extracellular sensing by cell surface receptors and intracellular cytosolic receptors. Interestingly, intracellular signaling proteins activated with P. gingivalis-LPS transfection using Lipofectamine™ 2000 had significantly higher fold change protein expression compared to the extracellular signaling with P. gingivalis-LPS treatment. Additionally, we also explored P. gingivalis-LPS mediated activation of caspase-4 dependent non canonical inflammasome pathway in both SH-SY5Y and HMC3 cells. In summary, P. gingivalis-LPS induced neuroinflammatory protein expression in SH-SY5Y and HMC3 cells, provided insights into the specific inflammatory pathways underlying the potential link between P. gingivalis-LPS infection and the pathogenesis of Alzheimer's disease and related dementias.

Glymphatic System Pathology and Neuroinflammation as Two Risk Factors of Neurodegeneration

The key to the effective treatment of neurodegenerative disorders is a thorough understanding of their pathomechanism. Neurodegeneration and neuroinflammation are mutually propelling brain processes. An impairment of glymphatic system function in neurodegeneration contributes to the progression of pathological processes. The question arises as to how neuroinflammation and the glymphatic system are related. This review highlights the direct and indirect influence of these two seemingly independent processes. Protein aggregates, a characteristic feature of neurodegeneration, are correlated with glymphatic clearance and neuroinflammation. Glial cells cannot be overlooked when considering the neuroinflammatory processes. Astrocytes are essential for the effective functioning of the glymphatic system and play a crucial role in the inflammatory responses in the central nervous system. It is imperative to acknowledge the significance of AQP4, a protein that exhibits a high degree of polarization in astrocytes and is crucial for the functioning of the glymphatic system. AQP4 influences inflammatory processes that have not yet been clearly delineated. Another interesting issue is the gut-brain axis and microbiome, which potentially impact the discussed processes. A discussion of the correlation between the functioning of the glymphatic system and neuroinflammation may contribute to exploring the pathomechanism of neurodegeneration.

Phosphorylated α-synuclein deposited in Schwann cells interacting with TLR2 mediates cell damage and induces Parkinson's disease autonomic dysfunction

Despite the significant frequency of autonomic dysfunction (AutD) in Parkinson's disease (PD) patients, its pathogenesis and diagnosis are challenging. Here, we aimed to further explore the mechanism of phosphorylated α-synuclein (p-α-syn) deposited in vagus nerve Schwann cells (SCs) causing SCs damage and PD AutD. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 20 mg/kg) was administrated to C57BL/6 mice twice a week for 35 days. Following the final injection, locomotor functions, gastrointestinal symptoms, urine functions, and cardiovascular system functions were evaluated. Meanwhile, we examined p-α-syn deposited in vagus nerve SCs, Toll-like receptor 2 (TLR2) activation, and SCs loss using immunofluorescence, western blot, and Luxol fast blue staining. In vitro, the rat SCs line RSC96 cells were exposed to α-synuclein preformed fibril (α-syn PFF), and cell viability was detected by CCK8. Co-IP was used to identify the interaction between p-α-syn and TLR2. Furthermore, the role of TLR2 in p-α-syn-mediated SCs damage was confirmed by the administration of CU-CPT22, a specific blocker of TLR2. In vivo, apart from dyskinesia, MPTP mice exhibited constipation, urinary dysfunction, and cardiovascular failure, which were associated with the deposition of p-α-syn in vagus nerve SCs, TLR2 activation, and vagus nerve demyelination. In vitro, stimulation of α-syn PFF induced a time-dependent loss of viability, and p-α-syn deposited in RSC96 cells induced a cellular inflammatory response by interacting with TLR2, resulting in cell dysfunction and apoptosis. However, both SCs inflammatory response and cell viability were alleviated after inhibition of TLR2. Furthermore, 1 h fecal pellets and water content, the frequency of 1 h urine, blood pressure, heart rate, and heart rate variability of mice in the MPTP + CU-CPT22 group were also improved. Our results support the perspective that p-α-syn interacts with TLR2 induced SCs damage and is involved in PD AutD, which sheds fresh light on the mechanism of PD AutD and indicates a promising treatment for PD AutD targeting SCs p-α-syn/ TLR2 signaling pathway.

Role of microglia autophagy and mitophagy in age-related neurodegenerative diseases

Microglia, characterized by responding to damage, regulating the secretion of soluble inflammatory mediators, and engulfing specific segments in the central nervous system (CNS), function as key immune cells in the CNS. Emerging evidence suggests that microglia coordinate the inflammatory responses in CNS system and play a pivotal role in the pathogenesis of age-related neurodegenerative diseases (NDDs). Remarkably, microglia autophagy participates in the regulation of subcellular substances, which includes the degradation of misfolded proteins and other harmful constituents produced by neurons. Therefore, microglia autophagy regulates neuronal homeostasis maintenance and process of neuroinflammation. In this review, we aimed at highlighting the pivotal role of microglia autophagy in the pathogenesis of age-related NDDs. Besides the mechanistic process and the co-interaction between microglia autophagy and different kinds of NDDs, we also emphasized potential therapeutic agents and approaches that could be utilized at the onset and progression of these diseases through modulating microglia autophagy, including promising nanomedicines. Our review provides a valuable reference for subsequent studies focusing on treatments of neurodegenerative disorders. The exploration of microglia autophagy and the development of nanomedicines greatly enhances current understanding of NDDs.

Gender differences in microRNA expression in levodopa-naive PD patients

Gender is an important factor influencing epidemiological and clinical features of Parkinson's disease (PD). We aimed to evaluate gender differences in the expression of a panel of miRNAs (miR-34a-5p, miR-146a, miR-155, miR-29a, miR-106a) possibly involved in the pathophysiology or progression of disease. Serum samples were obtained from 104 PD patients (58 men and 46 women) never treated with levodopa. We measured levels of miRNAs using quantitative PCR. Correlations between miRNA expression and clinical data were assessed using the Spearman's correlation test. We used STRING to evaluate co-expression relationship among target genes. MiR-34a-5p was significantly upregulated in PD male patients compared to PD female patients (fc: 1.62; p < 0.0001). No correlation was found with age, BMI, and disease severity, assessed by UPDRS III scale, in male and female patients. MiR-146a-5p was significantly upregulated in female as compared to male patients (fc: 3.44; p < 0.0001) and a significant correlation was also observed between disease duration and mir-146a-5p. No differences were found in the expression of miR-29a, miR-106a-5p and miR-155 between genders. Predicted target genes for miR-34a-5p and miR-146-5p and protein interactions in biological processes were reported. Our study supports the hypothesis that there are gender-specific differences in serum miRNAs expression in PD patients. Follow-up of this cohort is needed to understand if these differences may affect disease progression and response to treatment.

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.

The Role of Bacteria-Mitochondria Communication in the Activation of Neuronal Innate Immunity: Implications to Parkinson's Disease

Mitochondria play a key role in regulating host metabolism, immunity and cellular homeostasis. Remarkably, these organelles are proposed to have evolved from an endosymbiotic association between an alphaproteobacterium and a primitive eukaryotic host cell or an archaeon. This crucial event determined that human cell mitochondria share some features with bacteria, namely cardiolipin, N-formyl peptides, mtDNA and transcription factor A, that can act as mitochondrial-derived damage-associated molecular patterns (DAMPs). The impact of extracellular bacteria on the host act largely through the modulation of mitochondrial activities, and often mitochondria are themselves immunogenic organelles that can trigger protective mechanisms through DAMPs mobilization. In this work, we demonstrate that mesencephalic neurons exposed to an environmental alphaproteobacterium activate innate immunity through toll-like receptor 4 and Nod-like receptor 3. Moreover, we show that mesencephalic neurons increase the expression and aggregation of alpha-synuclein that interacts with mitochondria, leading to their dysfunction. Mitochondrial dynamic alterations also affect mitophagy which favors a positive feedback loop on innate immunity signaling. Our results help to elucidate how bacteria and neuronal mitochondria interact and trigger neuronal damage and neuroinflammation and allow us to discuss the role of bacterial-derived pathogen-associated molecular patterns (PAMPs) in Parkinson's disease etiology.

Effects of eugenol on the behavioral and pathological progression in the MPTP-induced Parkinson's disease mouse model

Parkinson's disease (PD) is the world's second most common neurological disorder. Oxidative stress and neuroinflammation play a crucial role in the pathogenesis of PD. Eugenol is a phytochemical with potent antioxidant and anti-inflammatory activity. The present investigation is aimed to study the effect of eugenol in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced mouse model of PD and its relationship to antioxidant effect. The effects of seven days of oral pre-treatment and post-treatment with three doses of eugenol (25, 50 and 100 mg/kg/day) were investigated against the MPTP-induced PD mouse model. In addition to the assessment of behavioural parameters using various tests (actophotometer, beam walking test, catalepsy, rearing, rotarod), biochemical parameters including lipid peroxidation and reduced glutathione levels in brain tissues, were also estimated in this study. The binding mode of eugenol in the human myeloid differentiation factor-2 (hMD-2) was also studied. Results showed that MPTP administration in mice resulted in the development of motor dysfunction (impaired motor coordination and hypo locomotion) similar to that of PD in different behavioural studies. Pre-treatment with eugenol reversed motor dysfunction caused by MPTP administration while post-treatment with eugenol at a high dose aggravated the symptoms of akinesia associated with MPTP administration. MPTP resulted in increased lipid peroxidation while decreased reduced glutathione levels in the brains of mice. MPTP-induced increased lipid peroxidation and attenuated levels of reduced glutathione were found to be alleviated with eugenol pre-treatment while augmented with eugenol post-treatment. Eugenol showed a binding affinity of -6.897 kcal/mol against the MD2 coreceptor of toll-like receptor-4 (TLR4). Biochemical, as well as neurobehavioral studies, showed that eugenol is having a protective effect, but does not have a curative effect on PD.

Gut microenvironmental changes as a potential trigger in Parkinson's disease through the gut-brain axis

Parkinson's disease (PD) is the second most common neurodegenerative disease attributed to the synergistic effects of genetic risk and environmental stimuli. Although PD is characterized by motor dysfunction resulting from intraneuronal alpha-synuclein accumulations, termed Lewy bodies, and dopaminergic neuronal degeneration in the substantia nigra, multiple systems are involved in the disease process, resulting in heterogenous clinical presentation and progression. Genetic predisposition to PD regarding aberrant immune responses, abnormal protein aggregation, autophagolysosomal impairment, and mitochondrial dysfunction leads to vulnerable neurons that are sensitive to environmental triggers and, together, result in neuronal degeneration. Neuropathology studies have shown that, at least in some patients, Lewy bodies start from the enteric nervous system and then spread to the central dopaminergic neurons through the gut-brain axis, suggesting the contribution of an altered gut microenvironment in the pathogenesis of PD. A plethora of evidence has revealed different gut microbiomes and gut metabolites in patients with PD compared to unaffected controls. Chronic gut inflammation and impaired intestinal barrier integrity have been observed in human PD patients and mouse models of PD. These observations led to the hypothesis that an altered gut microenvironment is a potential trigger of the PD process in a genetically susceptible host. In this review, we will discuss the complex interplay between genetic factors and gut microenvironmental changes contributing to PD pathogenesis.