Aggregated alpha-synuclein transcriptionally activates pro-inflammatory canonical and non-canonical NF-κB signaling pathways in peripheral monocytic cells

Neuroinflammation in Parkinson's disease: focus on the relationship between miRNAs and microglia

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that affects the central nervous system (CNS). Neuroinflammation is a crucial factor in the pathological advancement of PD. PD is characterized by the presence of activated microglia and increased levels of proinflammatory factors, which play a crucial role in its pathology. During the immune response of PD, microglia regulation is significantly influenced by microRNA (miRNA). The excessive activation of microglia, persistent neuroinflammation, and abnormal polarization of macrophages in the brain can be attributed to the dysregulation of certain miRNAs. Additionally, there are miRNAs that possess the ability to inhibit neuroinflammation. miRNAs, which are small non-coding epigenetic regulators, have the ability to modulate microglial activity in both normal and abnormal conditions. They also have a significant impact on promoting communication between neurons and microglia.

Cerebrospinal fluid α-synuclein adds the risk of cognitive decline and is associated with tau pathology among non-demented older adults

BACKGROUND

The role of α-synuclein in dementia has been recognized, yet its exact influence on cognitive decline in non-demented older adults is still not fully understood.

METHODS

A total of 331 non-demented individuals were included in the study from the Alzheimer's Disease Neuroimaging Initiative (ADNI). Participants were divided into two distinct groups based on their α-synuclein levels: one with lower levels (α-synuclein-L) and another with higher levels (α-synuclein-H). Measurements included neuropsychiatric scales, cerebrospinal fluid (CSF) biomarkers, and blood transcriptomics. The linear mixed-effects model investigated the longitudinal changes in cognition. Kaplan-Meier survival analysis and the Cox proportional hazards model were utilized to evaluate the effects of different levels of α-synuclein on dementia. Gene set enrichment analysis (GSEA) was utilized to investigate the biological pathways related to cognitive impairment. Pearson correlation, multiple linear regression models, and mediation analysis were employed to investigate the relationship between α-synuclein and neurodegenerative biomarkers, and their potential mechanisms affecting cognition.

RESULTS

Higher CSF α-synuclein levels were associated with increased risk of cognitive decline and progression to dementia. Enrichment analysis highlighted the activation of tau-associated and immune response pathways in the α-synuclein-H group. Further correlation and regression analysis indicated that the CSF α-synuclein levels were positively correlated with CSF total tau (t-tau), phosphorylated tau (p-tau) 181, tumor necrosis factor receptor 1 (TNFR1) and intercellular cell adhesion molecule-1 (ICAM-1). Mediation analysis further elucidated that the detrimental effects of CSF α-synuclein on cognition were primarily mediated through CSF t-tau and p-tau. Additionally, it was observed that CSF α-synuclein influenced CSF t-tau and p-tau181 levels via inflammatory pathways involving CSF TNFR1 and ICAM-1.

CONCLUSIONS

These findings elucidate a significant connection between elevated levels of CSF α-synuclein and the progression of cognitive decline, highlighting the critical roles of activated inflammatory pathways and tau pathology in this association. They underscore the importance of monitoring CSF α-synuclein levels as a promising biomarker for identifying individuals at increased risk of cognitive deterioration and developing dementia.

The role of NF-κB signaling pathway in reactive astrocytes among neurodegeneration after methamphetamine exposure by integrated bioinformatics

BACKGROUND

Methamphetamine (METH) is a highly addictive stimulant that has become one of the top five risk substances cause deaths from substance abuse. METH exposure increases the risk of neurodegenerative disease (ND), such as Parkinson's disease (PD), leading to disability and death. Activation of reactive astrocytes is an essential factor in neurodegeneration, and their complex role in METH exposure remains unclear. This study explored the role of reactive astrocyte overactivation in neurodegeneration after METH exposure.

METHODS

METH bulk RNA sequencing data (GSE107015 and GSE98793) and single-cell RNA sequencing data (GSE119861) were obtained from the GEO database. We performed immune infiltration analysis on the bulk RNA data. After cell clustering using the single-cell RNA data, astrocytes were extracted for downstream analysis. Differentially expressed genes (DEGs) were identified from the bulk and single-cell RNA sequencing datasets, and GO, KEGG, and GSEA pathway analyses were performed. The PPI network and random forest methods were performed on the overlapping genes of the DEGs to screen hub genes. To explore the common ground between METH exposure and neurodegenerative diseases, we applied a random forest algorithm to PD chip data (GSE99039 and GSE72267) to establish a diagnostic model using the hub genes in METH. New object recognition and the Morris water maze were used to examine cognitive function in mice exposed to METH for 14 days in vivo. Astrocytes were cocultured with neurons for the detection of intercellular crosstalk.

RESULTS

DEGs in the METH group significantly enriched pathways related to NDs, inflammation, and the NF-κB signaling pathway. Immune infiltration analysis revealed significantly increased infiltration of monocytes, T cells, and NK cells and decreased infiltration of neutrophils in the METH group. An intersection of 44 hub genes was screened based on the PPI network and random forest algorithm. These genes suggest that there might be similar pathogenesis between METH exposure and PD. METH exposure resulted in learning memory impairment, hippocampal astrocyte activation, and upregulation of NF-κB expression in mice. Activation of reactive astrocytes cocultured with neurons causes neural damage.

CONCLUSIONS

This study explored the crosstalk between astrocytes and neurons in METH exposure, providing a potential pathogenesis to explore the altered immune microenvironment involving reactive astrocytes after METH exposure.

The interplay between monocytes, α-synuclein and LRRK2 in Parkinson's disease

The accumulation of aggregated α-synuclein in susceptible neurons in the brain, together with robust activation of nearby myeloid cells, are pathological hallmarks of Parkinson's disease (PD). While microglia represent the dominant type of myeloid cell in the brain, recent genetic and whole-transcriptomic studies have implicated another type of myeloid cell, bone-marrow derived monocytes, in disease risk and progression. Monocytes in circulation harbor high concentrations of the PD-linked enzyme leucine-rich repeat kinase 2 (LRRK2) and respond to both intracellular and extracellular aggregated α-synuclein with a variety of strong pro-inflammatory responses. This review highlights recent findings from studies that functionally characterize monocytes in PD patients, monocytes that infiltrate into cerebrospinal fluid, and emerging analyses of whole myeloid cell populations in the PD-affected brain that include monocyte populations. Central controversies discussed include the relative contribution of monocytes acting in the periphery from those that might engraft in the brain to modify disease risk and progression. We conclude that further investigation into monocyte pathways and responses in PD, especially the discovery of additional markers, transcriptomic signatures, and functional classifications, that better distinguish monocyte lineages and responses in the brain from other types of myeloid cells may reveal points for therapeutic intervention, as well as a better understanding of ongoing inflammation associated with PD.