Epitranscriptomic Reader YTHDF2 Regulates SEK1( MAP2K4 )-JNK-cJUN Inflammatory Signaling in Astrocytes during Neurotoxic Stress

As the most abundant glial cells in the CNS, astrocytes dynamically respond to neurotoxic stress, however, the key molecular regulators controlling the inflammatory status of these sentinels during neurotoxic stress have remained elusive. Herein, we demonstrate that the m6A epitranscriptomic mRNA modification tightly regulates the pro-inflammatory functions of astrocytes. Specifically, the astrocytic neurotoxic stresser, manganese (Mn), downregulated the m6A reader YTHDF2 in human and mouse astrocyte cultures and in the mouse brain. Functionally, YTHDF2 knockdown augmented, while its overexpression dampened, neurotoxic stress induced proinflammatory response, suggesting YTHDF2 serves as a key upstream regulator of inflammatory responses in astrocytes. Mechnistically, YTHDF2 RIP-sequencing identified MAP2K4 ( MKK4; SEK1) mRNA as a YTHDF2 target influencing inflammatory signaling. Our target validation revealed Mn-exposed astrocytes mediates proinflammatory response by activating the phosphorylation of SEK1, JNK, and cJUN signaling. Collectively, YTHDF2 serves a key upstream 'molecular switch' controlling SEK1( MAP2K4 )-JNK-cJUN proinflammatory signaling in astrocytes.

Aggregation-Inhibiting scFv-Based Therapies Protect Mice against AAV1/2-Induced A53T-α-Synuclein Overexpression

To date, there is no cure for Parkinson's disease (PD). There is a pressing need for anti-neurodegenerative therapeutics that can slow or halt PD progression by targeting underlying disease mechanisms. Specifically, preventing the build-up of alpha-synuclein (αSyn) and its aggregated and mutated forms is a key therapeutic target. In this study, an adeno-associated viral vector loaded with the A53T gene mutation was used to induce rapid αSyn-associated PD pathogenesis in C57BL/6 mice. We tested the ability of a novel therapeutic, a single chain fragment variable (scFv) antibody with specificity only for pathologic forms of αSyn, to protect against αSyn-induced neurodegeneration, after unilateral viral vector injection in the substantia nigra. Additionally, polyanhydride nanoparticles, which provide sustained release of therapeutics with dose-sparing properties, were used as a delivery platform for the scFv. Through bi-weekly behavioral assessments and across multiple post-mortem immunochemical analyses, we found that the scFv-based therapies allowed the mice to recover motor activity and reduce overall αSyn expression in the substantia nigra. In summary, these novel scFv-based therapies, which are specific exclusively for pathological aggregates of αSyn, show early promise in blocking PD progression in a surrogate mouse PD model.

Advances in DNA, histone, and RNA methylation mechanisms in the pathophysiology of alcohol use disorder

Alcohol use disorder (AUD) has a complex, multifactorial etiology involving dysregulation across several brain regions and peripheral organs. Acute and chronic alcohol consumption cause epigenetic modifications in these systems, which underlie changes in gene expression and subsequently, the emergence of pathophysiological phenotypes associated with AUD. One such epigenetic mechanism is methylation, which can occur on DNA, histones, and RNA. Methylation relies on one carbon metabolism to generate methyl groups, which can then be transferred to acceptor substrates. While DNA methylation of particular genes generally represses transcription, methylation of histones and RNA can have bidirectional effects on gene expression. This review summarizes one carbon metabolism and the mechanisms behind methylation of DNA, histones, and RNA. We discuss the field's findings regarding alcohol's global and gene-specific effects on methylation in the brain and liver and the resulting phenotypes characteristic of AUD.

Microglial immune regulation by epigenetic reprogramming through histone H3K27 acetylation in neuroinflammation

Epigenetic reprogramming is the ability of innate immune cells to form memories of environmental stimuli (priming), allowing for heightened responses to secondary stressors. Herein, we explored microglial epigenetic marks using the known inflammagen LPS as a memory priming trigger and Parkinsonian-linked environmental neurotoxic stressor manganese (Mn) as the secondary environmental trigger. To mimic physiological responses, the memory priming trigger LPS treatment was removed by triple-washing to allow the cells' acute inflammatory response to reset back before applying the secondary insult. Our results show that after the secondary Mn insult, levels of key proinflammatory markers, including nitrite release, iNOS mRNA and protein expression, Il-6, Il-α and cytokines were exaggerated in LPS-primed microglia. Our paradigm implies primed microglia retain immune memory that can be reprogrammed to augment inflammatory response by secondary environmental stress. To ascertain the molecular underpinning of this neuroimmune memory, we further hypothesize that epigenetic reprogramming contributes to the retention of a heightened immune response. Interestingly, Mn-exposed, LPS-primed microglia showed enhanced deposition of H3K27ac and H3K4me3 along with H3K4me1. We further confirmed the results using a PD mouse model (MitoPark) and postmortem human PD brains, thereby adding clinical relevance to our findings. Co-treatment with the p300/H3K27ac inhibitor GNE-049 reduced p300 expression and H3K27ac deposition, decreased iNOS, and increased ARG1 and IRF4 levels. Lastly, since mitochondrial stress is a driver of environmentally linked Parkinson's disease (PD) progression, we examined the effects of GNE-049 on primary trigger-induced mitochondrial stress. GNE-049 reduced mitochondrial superoxide, mitochondrial circularity and stress, and mitochondrial membrane depolarization, suggesting beneficial consequences of GNE-049 on mitochondrial function. Collectively, our findings demonstrate that proinflammatory primary triggers can shape microglial memory via the epigenetic mark H3K27ac and that inhibiting H3K27ac deposition can prevent primary trigger immune memory formation and attenuate subsequent secondary inflammatory responses.

Environmental neurotoxic pesticide exposure induces gut inflammation and enteric neuronal degeneration by impairing enteric glial mitochondrial function in pesticide models of Parkinson's disease: Potential relevance to gut-brain axis inflammation in Parkinson's disease pathogenesis

Despite the growing recognition that gastrointestinal (GI) dysfunction is prevalent in Parkinson's disease (PD) and occurs as a major prodromal symptom of PD, its cellular and molecular mechanisms remain largely unknown. Among the various types of GI cells, enteric glial cells (EGCs), which resemble astrocytes in structure and function, play a critical role in the pathophysiology of many GI diseases including PD. Thus, we investigated how EGCs respond to the environmental pesticides rotenone (Rot) and tebufenpyrad (Tebu) in cell and animal models to better understand the mechanism underlying GI abnormalities. Both Rot and Tebu induce dopaminergic neuronal cell death through complex 1 inhibition of the mitochondrial respiratory chain. We report that exposing a rat enteric glial cell model (CRL-2690 cells) to these pesticides increased mitochondrial fission and reduced mitochondrial fusion by impairing MFN2 function. Furthermore, they also increased mitochondrial superoxide generation and impaired mitochondrial ATP levels and basal respiratory rate. Measurement of LC3, p62 and lysosomal assays revealed impaired autolysosomal function in ECGs during mitochondrial stress. Consistent with our recent findings that mitochondrial dysfunction augments inflammation in astrocytes and microglia, we found that neurotoxic pesticide exposure also enhanced the production of pro-inflammatory factors in EGCs in direct correlation with the loss in mitochondrial mass. Finally, we show that pesticide-induced mitochondrial defects functionally impaired smooth muscle velocity, acceleration, and total kinetic energy in a mixed primary culture of the enteric nervous system (ENS). Collectively, our studies demonstrate for the first time that exposure to environmental neurotoxic pesticides impairs mitochondrial bioenergetics and activates inflammatory pathways in EGCs, further augmenting mitochondrial dysfunction and pro-inflammatory events to induce gut dysfunction. Our findings have major implications in understanding the GI-related pathogenesis and progression of environmentally linked PD.

Emerging Roles of N6-Methyladenosine (m6A) Epitranscriptomics in Toxicology

Epitranscriptomics, the study of chemically modified RNAs, is a burgeoning field being explored in a variety of scientific disciplines. Of the currently known epitranscriptomic modifications, N6-methyladenosine (m6A) methylation is the most abundant. The m6A modification is predominantly regulated by 3 tiers of protein modulators classified as writers, erasers, and readers. Depending upon cellular needs, these proteins function to deposit, remove, or read the methyl modifications on cognate mRNAs. Many environmental chemicals including heavy metals, pesticides, and other toxic pollutants, are all known to perturb transcription and translation machinery to exert their toxic responses. As such, we herein review how the m6A modification may be affected under different toxicological paradigms. Furthermore, we discuss how toxicants can affect the 3 tiers of regulation directly, and how these effects influence the m6A-modified mRNAs. Lastly, we highlight the disparities between published findings and theories, especially those concerning the m6A reader tier of regulation. In the far-reaching field of toxicology, m6A epitranscriptomics provides another enticing avenue to explore new mechanisms and therapies for a diverse range of environmentally linked disorders and diseases.

Kv1.3 modulates neuroinflammation and neurodegeneration in Parkinson's disease

Characterization of the key cellular targets contributing to sustained microglial activation in neurodegenerative diseases, including Parkinson's disease (PD), and optimal modulation of these targets can provide potential treatments to halt disease progression. Here, we demonstrated that microglial Kv1.3, a voltage-gated potassium channel, was transcriptionally upregulated in response to aggregated α-synuclein (αSynAgg) stimulation in primary microglial cultures and animal models of PD, as well as in postmortem human PD brains. Patch-clamp electrophysiological studies confirmed that the observed Kv1.3 upregulation translated to increased Kv1.3 channel activity. The kinase Fyn, a risk factor for PD, modulated transcriptional upregulation and posttranslational modification of microglial Kv1.3. Multiple state-of-the-art analyses, including Duolink proximity ligation assay imaging, revealed that Fyn directly bound to Kv1.3 and posttranslationally modified its channel activity. Furthermore, we demonstrated the functional relevance of Kv1.3 in augmenting the neuroinflammatory response by using Kv1.3-KO primary microglia and the Kv1.3-specific small-molecule inhibitor PAP-1, thus highlighting the importance of Kv1.3 in neuroinflammation. Administration of PAP-1 significantly inhibited neurodegeneration and neuroinflammation in multiple animal models of PD. Collectively, our results imply that Fyn-dependent regulation of Kv1.3 channels plays an obligatory role in accentuating the neuroinflammatory response in PD and identify Kv1.3 as a potential therapeutic target for PD.

Molecular Signatures of Neuroinflammation Induced by αSynuclein Aggregates in Microglial Cells

Alpha-synuclein (αSyn_Agg) are pathological hallmarks of Parkinson's disease (PD) and other synucleinopathies that induce microglial activation and immune-mediated neurotoxicity, but the molecular mechanisms of αSyn_Agg-induced immune activation are poorly defined. We performed quantitative proteomics by mass spectrometry coupled with PCR, immunohistochemical and functional validations studies to define the molecular characteristics of alpha synuclein mediated microglial activation. In mouse microglia, αSyn_Agg induced robust pro-inflammatory activation (increased expression of 864 genes including Irg1, Ifit1, and Pyhin) and increased nuclear proteins involved in RNA synthesis, splicing, and anti-viral defense mechanisms. Conversely, αSyn_Agg decreased expression several proteins (including Cdc123, Sod1, and Grn), which were predominantly cytosolic and involved in metabolic, proteasomal and lysosomal mechanisms. Pathway analyses and confirmatory in vitro studies suggested that αSyn_Agg partly mediates its effects via Stat3 activation. As predicted by our proteomic findings, we verified that αSyn_Agg induces mitochondrial dysfunction in microglia. Twenty-six proteins differentially expressed by αSyn_Agg were also identified as PD risk genes in genome-wide association studies (upregulated: Brd2, Clk1, Siglec1; down-regulated: Memo1, Arhgap18, Fyn, and Pgrn/Grn). We validated progranulin (PGRN) as a lysosomal PD-associated protein that is downregulated by αSyn_Agg in microglia in-vivo and is expressed by microglia in post-mortem PD brain, congruent with our in vitro findings. Conclusion: Together, proteomics approach both reveals novel molecular insights into αSyn-mediated neuroinflammation in PD and other synucleinopathies.

Manganese activates NLRP3 inflammasome signaling and propagates exosomal release of ASC in microglial cells

Chronic, sustained inflammation underlies many pathological conditions, including neurodegenerative diseases. Divalent manganese (Mn²⁺) exposure can stimulate neurotoxicity by increasing inflammation. In this study, we examined whether Mn²⁺ activates the multiprotein NLRP3 inflammasome complex to promote neuroinflammation. Exposing activated mouse microglial cells to Mn²⁺ substantially augmented NLRP3 abundance, caspase-1 cleavage, and maturation of the inflammatory cytokine interleukin-1β (IL-1β). Exposure of mice to Mn²⁺ had similar effects in brain microglial cells. Furthermore, Mn²⁺ impaired mitochondrial ATP generation, basal respiratory rate, and spare capacity in microglial cells. These data suggest that Mn-induced mitochondrial defects drove the inflammasome signal amplification. We found that Mn induced cell-to-cell transfer of the inflammasome adaptor protein ASC in exosomes. Furthermore, primed microglial cells exposed to exosomes from Mn-treated mice released more IL-1β than did cells exposed to exosomes from control-treated animals. We also observed that welders exposed to manganese-containing fumes had plasma exosomes that contained more ASC than did those from a matched control group. Together, these results suggest that the divalent metal manganese acts as a key amplifier of NLRP3 inflammasome signaling and exosomal ASC release.

Characterization and comparative analysis of a new mouse microglial cell model for studying neuroinflammatory mechanisms during neurotoxic insults

Microglia are the first responders of the central nervous system, acting as the key modulators of neuroinflammation observed during neurotoxic insults as well as in the pathophysiology of several neurodegenerative disorders including Alzheimer's (AD), Parkinson's (PD), and Huntington's diseases (HD). The number of publications on microglia has increased steadily throughout the past decade because of immense interests in the neuroinflammation that precedes the neurodegenerative process. To study microglial biology and its role in modulating neuroinflammation, immortalized microglial cell lines derived from mice, rats, and humans have been developed. Among these, the BV2 mouse microglial cell line is the most well characterized and widely used cell culture model. However, even unstimulated BV2 cells exhibit an amoeboid, hypertrophied morphology, indicating a highly activated and inflammatory state compared to primary microglia, thus making them less than ideal for studying the low-dose effects of toxicants on microglial activation. Therefore, we performed an in-depth characterization of a recently developed mouse microglial cell (MMC) line, which we compared with primary mouse microglia (PMG) and BV2s to identify which cell line was best suited for studying the microglial response to neurotoxicants. Comparative analyses reveal that MMCs are strikingly more similar to PMGs in basal activity, morphology, and sensitivity, than are BV2s. Furthermore, basal nitrite and inflammatory cytokine levels are significantly higher in BV2s compared to MMCs. BV2 cells are also less reactive to the inflammagen LPS compared to MMCs, due to the higher basal activation state of BV2s. Collectively, our in-depth analyses of morphology, basal activity, and responsivity to two different stimuli (LPS, aggregated α-synuclein) demonstrate that MMCs closely mimic neonatal PMGs, and are discernibly more suitable than BV2s for studying the neuroinflammatory mechanisms of neurotoxicants.

Mitochondrial impairment in microglia amplifies NLRP3 inflammasome proinflammatory signaling in cell culture and animal models of Parkinson's disease

The NLRP3 inflammasome signaling pathway is a major contributor to the neuroinflammatory process in the central nervous system. Oxidative stress and mitochondrial dysfunction are key pathophysiological processes of many chronic neurodegenerative diseases, including Parkinson’s disease (PD). However, the inter-relationship between mitochondrial defects and neuroinflammation is not well understood. In the present study, we show that impaired mitochondrial function can augment the NLRP3 inflammasome-driven proinflammatory cascade in microglia. Primary mouse microglia treated with the common inflammogen LPS increased NLRP3 and pro-IL-1β expression. Interestingly, exposure of LPS-primed microglial cells to the mitochondrial complex-I inhibitory pesticides rotenone and tebufenpyrad specifically potentiated the NLRP3 induction, ASC speck formation and pro-IL-1β processing to IL-1β in a dose-dependent manner, indicating that mitochondrial impairment heightened the NLRP3 inflammasome-mediated proinflammatory response in microglia. The neurotoxic pesticide-induced NLRP3 inflammasome activation was accompanied by bioenergetic defects and lysosomal dysfunction in microglia. Furthermore, the pesticides enhanced mitochondrial ROS generation in primary microglia, while amelioration of mitochondria-derived ROS by the mitochondria-targeted antioxidant mito-apocynin completely abolished IL-1β release, indicating mitochondrial ROS drives potentiation of the NLRP3 inflammasome in microglia. Exposure to conditioned media obtained from mitochondrial inhibitor-treated, LPS-primed microglial cells, but not unprimed cells, induced dopaminergic neurodegeneration in cultured primary mesencephalic and human dopaminergic neuronal cells (LUHMES). Notably, our in vivo results with chronic rotenone rodent models of PD further support the activation of proinflammatory NLRP3 inflammasome signaling due to mitochondrial dysfunction. Collectively, our results demonstrate that mitochondrial impairment in microglia can amplify NLRP3 inflammasome signaling, which augments the dopaminergic neurodegenerative process.

A team of American researchers demonstrate that disruption of mitochondria in microglia contributes to inflammation and neurodegeneration. Anumantha G. Kanthasamy at Iowa State University in Ames, IA and colleagues examined the effect of pesticides known to impair mitochondrial function on proinflammatory signaling pathways in microglia, the brain’s immune cells. They found that both rotenone and tebufenpyrad specifically stimulated the NLRP3 inflammasome, a multi-protein complex implicated in neuroinflammatory processes. The pesticide-treated microglia were able to cause more damage to neuronal cells than the untreated ones, indicating that mitochondrial dysfunction in microglia augments neurodegeneration. The authors also show that in rodents chronically exposed to rotenone, which causes many of the features of Parkinson’s disease (PD), the NLRP3 inflammasome is activated. These findings contribute to better understand the mechanisms driving chronic neuroinflammation in PD.

Manganese exposure induces neuroinflammation by impairing mitochondrial dynamics in astrocytes

Chronic manganese (Mn) exposure induces neurotoxicity, which is characterized by Parkinsonian symptoms resulting from impairment in the extrapyramidal motor system of the basal ganglia. Mitochondrial dysfunction and oxidative stress are considered key pathophysiological features of Mn neurotoxicity. Recent evidence suggests astrocytes as a major target of Mn neurotoxicity since Mn accumulates predominantly in astrocytes. However, the primary mechanisms underlying Mn-induced astroglial dysfunction and its role in metal neurotoxicity are not completely understood. In this study, we examined the interrelationship between mitochondrial dysfunction and astrocytic inflammation in Mn neurotoxicity. We first evaluated whether Mn exposure alters mitochondrial bioenergetics in cultured astrocytes. Metabolic activity assessed by MTS assay revealed an IC₅₀ of 92.68μM Mn at 24h in primary mouse astrocytes (PMAs) and 50.46μM in the human astrocytic U373 cell line. Mn treatment reduced mitochondrial mass, indicative of impaired mitochondrial function and biogenesis, which was substantiated by the significant reduction in mRNA of mitofusin-2, a protein that serves as a ubiquitination target for mitophagy. Furthermore, Mn increased mitochondrial circularity indicating augmented mitochondrial fission. Seahorse analysis of bioenergetics status in Mn-treated astrocytes revealed that Mn significantly impaired the basal mitochondrial oxygen consumption rate as well as the ATP-linked respiration rate. The effect of Mn on mitochondrial energy deficits was further supported by a reduction in ATP production. Mn-exposed primary astrocytes also exhibited a severely quiescent energy phenotype, which was substantiated by the inability of oligomycin to increase the extracellular acidification rate. Since astrocytes regulate immune functions in the CNS, we also evaluated whether Mn modulates astrocytic inflammation. Mn exposure in astrocytes not only stimulated the release of proinflammatory cytokines, but also exacerbated the inflammatory response induced by aggregated α-synuclein. The novel mitochondria-targeted antioxidant, mito-apocynin, significantly attenuated Mn-induced inflammatory gene expression, further supporting the role of mitochondria dysfunction and oxidative stress in mediating astrogliosis. Lastly, intranasal delivery of Mn in vivo elevated GFAP and depressed TH levels in the olfactory bulbs, clearly supporting the involvement of astrocytes in Mn-induced dopaminergic neurotoxicity. Collectively, our study demonstrates that Mn drives proinflammatory events in astrocytes by impairing mitochondrial bioenergetics.

Rapid and Refined CD11b Magnetic Isolation of Primary Microglia with Enhanced Purity and Versatility

Microglia are the primary responders to central nervous system insults; however, much remains unknown about their role in regulating neuroinflammation. Microglia are mesodermal cells that function similarly to macrophages in surveying inflammatory stress. The classical (M1-type) and alternative (M2-type) activations of macrophages have also been extended to microglia in an effort to better understand the underlying interplay these phenotypes have in neuroinflammatory conditions such as Parkinson's, Alzheimer's, and Huntington's Diseases. In vitro experimentation utilizing primary microglia offers rapid and reliable results that may be extended to the in vivo environment. Although this is a clear advantage over in vivo experimentation, isolating microglia while achieving adequate yields of optimal purity has been a challenge. Common methods currently in use either suffer from low recovery, low purity, or both. Herein, we demonstrate a refinement of the column-free CD11b magnetic separation method that achieves a high cell recovery and enhanced purity in half the amount of time. We propose this optimized method as a highly useful model of primary microglial isolation for the purposes of studying neuroinflammation and neurodegeneration.

Off-Target drug effects resulting in altered gene expression events with epigenetic and "Quasi-Epigenetic" origins

This review synthesizes examples of pharmacological agents who have off-target effects of an epigenetic nature. We expand upon the paradigm of epigenetics to include "quasi-epigenetic" mechanisms. Quasi-epigenetics includes mechanisms of drugs acting upstream of epigenetic machinery or may themselves impact transcription factor regulation on a more global scale. We explore these avenues with four examples of conventional pharmaceuticals and their unintended, but not necessarily adverse, biological effects. The quasi-epigenetic drugs identified in this review include the use of beta-lactam antibiotics to alter glutamate receptor activity and the action of cyclosporine on multiple transcription factors. In addition, we report on more canonical epigenome changes associated with pharmacological agents such as lithium impacting autophagy of aberrant proteins, and opioid drugs whose chronic use increases the expression of genes associated with addictive phenotypes. By expanding our appreciation of transcriptomic regulation and the effects these drugs have on the epigenome, it is possible to enhance therapeutic applications by exploiting off-target effects and even repurposing established pharmaceuticals. That is, exploration of "pharmacoepigenetic" mechanisms can expand the breadth of the useful activity of a drug beyond the traditional drug targets such as receptors and enzymes.