Glial epigenetics in neuroinflammation and neurodegeneration

Epigenetic age acceleration is associated with occupational exposures, sex, and survival in amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is linked to ageing and genetic and environmental risk factors, yet underlying mechanisms are incompletely understood. We aimed to evaluate epigenetic age acceleration (EAA), i.e., DNA methylation (DNAm) age acceleration, and its association with ALS case status and survival.

METHODS

In this study, we included 428 ALS and 288 control samples collected between 2011 and 2021. We calculated EAA using the GrimAge residual method from ALS and control blood samples and grouped participants with ALS into three ageing groups (fast, normal, slow). We associated EAA with ALS case status and survival, stratified by sex, and correlated it with environmental and biological factors through occupational exposure assessments, immune cell proportions, and transcriptome changes.

FINDINGS

Participants with ALS had higher average EAA by 1.80 ± 0.30 years (p < 0.0001) versus controls. Participants with ALS in the fast ageing group had a hazard ratio of 1.52 (95% confidence interval 1.16-2.00, p = 0.0028) referenced to the normal ageing group. In males, this hazard ratio was 1.55 (95% confidence interval 1.11-2.17, p = 0.010), and EAA was positively correlated with high-risk occupational exposures including particulate matter (adj.p < 0.0001) and metals (adj.p = 0.0087). Also, in male participants with ALS, EAA was positively correlated with neutrophil proportions and was negatively correlated with CD4+ T cell proportions. Pathways dysregulated in participants with ALS with fast ageing included spliceosome, nucleocytoplasmic transport, axon guidance, and interferons.

INTERPRETATION

EAA was associated with ALS case status and, at least in males, with shorter survival after diagnosis. The effect of EAA on ALS was partially explained by occupational exposures and immune cell proportions in a sex-dependent manner. These findings highlight the complex interactions of ageing and exposures in ALS.

FUNDING

NIH, CDC/National ALS Registry, ALS Association, Dr. Randall Whitcomb Fund for ALS Genetics, Peter Clark Fund for ALS Research, Sinai Medical Staff Foundation, Scott L. Pranger ALS Clinic Fund, NeuroNetwork Therapeutic Discovery Fund, NeuroNetwork for Emerging Therapies.

Genomic and transcriptomic advances in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder and the most common motor neuron disease. ALS shows substantial clinical and molecular heterogeneity. In vitro and in vivo models coupled with multiomic techniques have provided important contributions to unraveling the pathomechanisms underlying ALS. To date, despite promising results and accumulating knowledge, an effective treatment is still lacking. Here, we provide an overview of the literature on the use of genomics, epigenomics, transcriptomics and microRNAs to deeply investigate the molecular mechanisms developing and sustaining ALS. We report the most relevant genes implicated in ALS pathogenesis, discussing the use of different high-throughput sequencing techniques and the role of epigenomic modifications. Furthermore, we present transcriptomic studies discussing the most recent advances, from microarrays to bulk and single-cell RNA sequencing. Finally, we discuss the use of microRNAs as potential biomarkers and promising tools for molecular intervention. The integration of data from multiple omic approaches may provide new insights into pathogenic pathways in ALS by shedding light on diagnostic and prognostic biomarkers, helping to stratify patients into clinically relevant subgroups, revealing novel therapeutic targets and supporting the development of new effective therapies.

Ogt-mediated O-GlcNAcylation inhibits astrocytes activation through modulating NF-κB signaling pathway

Previous studies have shown that Ogt-mediated O-GlcNAcylation is essential for neuronal development and function. However, the function of O-GlcNAc transferase (Ogt) and O-GlcNAcylation in astrocytes remains largely unknown. Here we show that Ogt deficiency induces inflammatory activation of astrocytes in vivo and in vitro, and impairs cognitive function of mice. The restoration of O-GlcNAcylation via GlcNAc supplementation inhibits the activation of astrocytes, inflammation and improves the impaired cognitive function of Ogt deficient mice. Mechanistically, Ogt interacts with NF-κB p65 and catalyzes the O-GlcNAcylation of NF-κB p65 in astrocytes. Ogt deficiency induces the activation of NF-κB signaling pathway by promoting Gsk3β binding. Moreover, Ogt depletion induces the activation of astrocytes derived from human induced pluripotent stem cells. The restoration of O-GlcNAcylation inhibits the activation of astrocytes, inflammation and reduces Aβ plaque of AD mice in vitro and in vivo. Collectively, our study reveals a critical function of Ogt-mediated O-GlcNAcylation in astrocytes through regulating NF-κB signaling pathway.

Effects of Suberoylanilide Hydroxamic Acid (SAHA) on the Inflammatory Response in Lipopolysaccharide-Induced N9 Microglial Cells

INTRODUCTION

Epigenetics has shown promising results for understanding the different behaviors of microglia under the context of neuroinflammation. However, to our knowledge, the results of this complex mechanism with novel pharmacological agents such as histone deacetylase inhibitors (HDACis) are still missing. In this study, we aimed to investigate the effects of suberoylanilide hydroxamic acid (SAHA), a pan-HDACi, on the lipopolysaccharide (LPS)-induced neuroinflammation model in the N9 microglial cells.

METHODS

Microglial cells were treated with SAHA (0.25, 0.5, 1.0, 1.25, 1.5 µM) and LPS (100 ng/mL) for 24 hours. Then, levels of the pro/anti-inflammatory cytokines interleukin-1 beta (IL-1β), IL-6, tumor necrosis factor alpha (TNF-α), and IL-10 were determined by the enzyme-linked immunosorbent assay. The total cellular HDAC activity was determined by colorimetric analysis. Additionally, the expression levels of nuclear factor kappa-B (NF-κB) were quantified via western blotting.

RESULTS

SAHA (1.0 and 1.25 µM) attenuated the LPS-induced inflammatory response of microglial cells via decreasing NF-κB expression and pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) in the N9 microglial cells. Moreover, SAHA treatment improved IL-10 levels and prevented the LPS-induced increase in the HDAC activity in the microglial cells.

CONCLUSION

Our results suggest SAHA attenuates the LPS-induced inflammatory response in the N9 microglial cells, and regulation of histone acetylation with HDACis might be a rational approach for the treatment of neuroinflammation.

Multifaceted role of polyphenols in the treatment and management of neurodegenerative diseases

Neurodegenerative diseases (NDDs) are conditions that cause neuron structure and/or function to deteriorate over time. Genetic alterations may be responsible for several NDDs. However, a multitude of physiological systems can trigger neurodegeneration. Several NDDs, such as Huntington's, Parkinson's, and Alzheimer's, are assigned to oxidative stress (OS). Low concentrations of reactive oxygen and nitrogen species are crucial for maintaining normal brain activities, as their increasing concentrations can promote neural apoptosis. OS-mediated neurodegeneration has been linked to several factors, including notable dysfunction of mitochondria, excitotoxicity, and Ca2+ stress. However, synthetic drugs are commonly utilized to treat most NDDs, and these treatments have been known to have side effects during treatment. According to providing empirical evidence, studies have discovered many occurring natural components in plants used to treat NDDs. Polyphenols are often safer and have lesser side effects. As, epigallocatechin-3-gallate, resveratrol, curcumin, quercetin, celastrol, berberine, genistein, and luteolin have p-values less than 0.05, so they are typically considered to be statistically significant. These polyphenols could be a choice of interest as therapeutics for NDDs. This review highlighted to discusses the putative effectiveness of polyphenols against the most prevalent NDDs.

Impact of dietary polyphenols on neuroinflammation-associated disorders

Neurodegenerative disorders like Alzheimer's, Parkinson's, and associated dementia typically originate with altered protein folding and aggregation of their β structures in the neurons. This self-aggregation leads to glial activation in the brain, causing neuroinflammation and leads to neuronal death. According to statistics provided by WHO, there are around 50 million people with dementia worldwide and every year, 10 million more cases are projected to increase. Also, around 5-8 percentage of people who are aged above 60 globally has dementia or associated disorders. Over 82 million in 2030 and 152 in 2050 are expected to have dementia. Most of these patients fall into low-middle-income countries which makes it even more essential to find an affordable and effective treatment method. Polyphenols of different origin are studied for their potential role as anti-neuro-inflammatory molecules. This review would summarize recent advances in three widely researched dietary polyphenols projected as potential therapeutic agents for disorders like Alzheimer's, Parkinson's, etc. They are Resveratrol, Catechins, and Tannins. The review would discuss the recent advances and challenges in using these polyphenols using specific examples as potential therapeutic agents against neuroinflammation associated disorders. An abstract of neuroinflammation-associated events and the effects by selected polyphenols.

Epigenetics in blood-brain barrier disruption

The vessels of the central nervous system (CNS) have unique barrier properties. The endothelial cells (ECs) which comprise the CNS vessels contribute to the barrier via strong tight junctions, specific transporters, and limited endocytosis which combine to protect the brain from toxins and maintains brain homeostasis. Blood-brain barrier (BBB) leakage is a serious secondary injury in various CNS disorders like stroke, brain tumors, and neurodegenerative disorders. Currently, there are no drugs or therapeutics available to treat specifically BBB damage after a brain injury. Growing knowledge in the field of epigenetics can enhance the understanding of gene level of the BBB and has great potential for the development of novel therapeutic strategies or targets to repair a disrupted BBB. In this brief review, we summarize the epigenetic mechanisms or regulators that have a protective or disruptive role for components of BBB, along with the promising approaches to regain the integrity of BBB.

SAHA attenuates rotenone-induced toxicity in primary microglia and HT-22 cells

Rotenone is an industrial and environmental toxicant that has been strongly associated with neurodegeneration. It is clear that rotenone induces inflammatory and oxidative stress; however, information on the role of histone acetylation in neurotoxicity is limited. Epigenetic alterations, neuroinflammation, and oxidative stress play a role in the progression of neurodegeneration and can be caused by exposure to environmental chemicals, such as rotenone. Histone modifications, such as methylation and acetylation, play an important role in mediating epigenetic changes. Therefore, we here investigated the effects of histone acetylation on rotenone-induced inflammation and oxidative stress in both primary mouse microglia and hippocampal HT-22 cells using the pan-histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA). Our results showed that SAHA suppressed the inflammatory response by decreasing nuclear factor kappa B and inducible nitric oxide synthase expression. Additionally, SAHA inhibited the rotenone-induced elevation of interleukin 6 and tumor necrosis factor α levels in both cell lines. Furthermore, SAHA improved the rotenone-induced antioxidant status by mitigating the decrease in cellular glutathione levels. Additionally, SAHA prevented the rotenone-induced increase in the HDAC activity in microglial and hippocampal HT-22 cells. Together, our results showed that SAHA reduced rotenone-induced inflammatory and oxidative stress, suggesting a role for histone deacetylation in environmental-related neurotoxicity.

Astrocyte Crosstalk in CNS Inflammation

Astrocytes control multiple processes in the nervous system in health and disease. It is now clear that specific astrocyte subsets or activation states are associated with specific genomic programs and functions. The advent of novel genomic technologies has enabled rapid progress in the characterization of astrocyte heterogeneity and its control by astrocyte interactions with other cells in the central nervous system (CNS). In this review, we provide an overview of the multifaceted roles of astrocytes in the context of CNS inflammation, highlighting recent discoveries on astrocyte subsets and their regulation. We explore mechanisms of crosstalk between astrocytes and other cells in the CNS in the context of neuroinflammation and neurodegeneration and discuss how these interactions shape pathological outcomes.

Suppression of histone deacetylases by SAHA relieves bone cancer pain in rats via inhibiting activation of glial cells in spinal dorsal horn and dorsal root ganglia

BACKGROUND

Robust activation of glial cells has been reported to occur particularly during the pathogenesis of bone cancer pain (BCP). Researchers from our group and others have shown that histone deacetylases (HDACs) play a significant role in modulating glia-mediated immune responses; however, it still remains unclear whether HDACs are involved in the activation of glial cells during the development of BCP.

METHODS

BCP model was established by intra-tibia tumor cell inoculation (TCI). The expression levels and distribution sites of histone deacetylases (HDACs) in the spinal dorsal horn and dorsal root ganglia were evaluated by Western blot and immunofluorescent staining, respectively. Suberoylanilide hydroxamic acid (SAHA), a clinically used HDAC inhibitor, was then intraperitoneally and intrathecally injected to rescue the increased expression levels of HDAC1 and HDAC2. The analgesic effects of SAHA administration on BCP were then evaluated by measuring the paw withdrawal thresholds (PWTs). The effects of SAHA on activation of glial cells and expression of proinflammatory cytokines (TNF-α, IL-1β, and IL-6) in the spinal dorsal horn and dorsal root ganglia of TCI rats were further evaluated by immunofluorescent staining and Western blot analysis. Subsequently, the effects of SAHA administration on tumor growth and cancer cell-induced bone destruction were analyzed by hematoxylin and eosin (HE) staining and micro-CT scanning.

RESULTS

TCI caused rapid and long-lasting increased expression of HDAC1/HDAC2 in glial cells of the spinal dorsal horn and dorsal root ganglia. Inhibiting HDACs by SAHA not only reversed TCI-induced upregulation of HDACs but also inhibited the activation of glial cells in the spinal dorsal horn and dorsal root ganglia, and relieved TCI-induced mechanical allodynia. Further, we found that SAHA administration could not prevent cancer infiltration or bone destruction in the tibia, which indicated that the analgesic effects of SAHA were not due to its anti-tumor effects. Moreover, we found that SAHA administration could inhibit GSK3β activity in the spinal dorsal horn and dorsal root ganglia, which might contributed to the relief of BCP.

CONCLUSION

Our findings suggest that HDAC1 and HDAC2 are involved in the glia-mediated neuroinflammation in the spinal dorsal horn and dorsal root ganglia underlying the pathogenesis of BCP, which indicated that inhibiting HDACs by SAHA might be a potential strategy for pain relief of BCP.

Epigenetic Signaling in Glia Controls Presynaptic Homeostatic Plasticity

Epigenetic gene regulation shapes neuronal fate in the embryonic nervous system. Post-embryonically, epigenetic signaling within neurons has been associated with impaired learning, autism, ataxia, and schizophrenia. Epigenetic factors are also enriched in glial cells. However, little is known about epigenetic signaling in glia and nothing is known about the intersection of glial epigenetic signaling and presynaptic homeostatic plasticity. During a screen for genes involved in presynaptic homeostatic synaptic plasticity, we identified an essential role for the histone acetyltransferase and deubiquitinase SAGA complex in peripheral glia. We present evidence that the SAGA complex is necessary for homeostatic plasticity, demonstrating involvement of four new genes in homeostatic plasticity. This is also evidence that glia participate in presynaptic homeostatic plasticity, invoking previously unexplored intercellular, homeostatic signaling at a tripartite synapse. We show, mechanistically, SAGA signaling regulates the composition of and signaling from the extracellular matrix during homeostatic plasticity.

Epigenetic Regulation Of Axon Regeneration and Glial Activation in Injury Responses

Injury to the nervous system triggers a multicellular response in which epigenetic mechanisms play an important role in regulating cell type-specific transcriptional changes. Here, we summarize recent progress in characterizing neuronal intrinsic and extrinsic chromatin reconfigurations and epigenetic changes triggered by axonal injury that shape neuroplasticity and glial functions. We specifically discuss regeneration-associated transcriptional modules comprised of transcription factors and epigenetic regulators that control axon growth competence. We also review epigenetic regulation of neuroinflammation and astroglial responses that impact neural repair. These advances provide a framework for developing epigenetic strategies to maximize adaptive alterations while minimizing maladaptive stress responses in order to enhance axon regeneration and achieve functional recovery after injury.

Astrocytes and Aging

By 2050, the aging population is predicted to expand by over 100%. Considering this rapid growth, and the additional strain it will place on healthcare resources because of age-related impairments, it is vital that researchers gain a deeper understanding of the cellular interactions that occur with normal aging. A variety of mammalian cell types have been shown to become compromised with age, each with a unique potential to contribute to disease formation in the aging body. Astrocytes represent the largest group of glial cells and are responsible for a variety of essential functions in the healthy central nervous system (CNS). Like other cell types, aging can cause a loss of normal function in astrocytes which reduces their ability to properly maintain a healthy CNS environment, negatively alters their interactions with neighboring cells, and contribute to the heightened inflammatory state characteristic of aging. The goal of this review article is to consolidate the knowledge and research to date regarding the role of astrocytes in aging. In specific, this review article will focus on the morphology and molecular profile of aged astrocytes, the consequence of astrocyte dysfunction on homeostatic functions during aging, and the role of astrocytes in age-related neurodegenerative diseases.

Recent advances in the mechanisms of neuroinflammation and their roles in neurodegeneration

Neuroinflammation is associated with the pathogenesis of many neurological disorders including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington disease. Current studies in this area have advanced the mechanism of neuroinflammation and its role in neurodegeneration. Studies from epidemiologic, clinical and animal models also contributed in the various new mechanisms of neuroinflammation. In this line, activation of monocytes is an important emerging mechanism that has a, profound role in neuroinflammation and neurodegeneration. Ion channels, matrix metalloproteases and microRNAs are also found to be the key players in the pathogenesis of neuroinflammation. In particular, microRNA-32 regulates microglia-mediated neuroinflammation and thus neurodegeneration. Notably, some important studies describe the role of Th17 cells in neuroinflammation, but, very little knowledge is available about their mechanism of action. Particularly, the role of autophagy gets emphasized, which plays a very critical role in protein aggregation and neurodegeneration. In this review, we highlight and discuss the mechanisms of these mediators of inflammation by which they contribute to the disease progression. In conclusion, we focus on the various newer molecular mechanisms that are associated with the basic understanding of neuroinflammation in neurodegeneration.

Microglia at center stage: a comprehensive review about the versatile and unique residential macrophages of the central nervous system

Microglia cells are the unique residential macrophages of the central nervous system (CNS). They have a special origin, as they derive from the embryonic yolk sac and enter the developing CNS at a very early stage. They play an important role during CNS development and adult homeostasis. They have a major contribution to adult neurogenesis and neuroinflammation. Thus, they participate in the pathogenesis of neurodegenerative diseases and contribute to aging. They play an important role in sustaining and breaking the blood-brain barrier. As innate immune cells, they contribute substantially to the immune response against infectious agents affecting the CNS. They play also a major role in the growth of tumours of the CNS. Microglia are consequently the key cell population linking the nervous and the immune system. This review covers all different aspects of microglia biology and pathology in a comprehensive way.

The analgesic effects of triptolide in the bone cancer pain rats via inhibiting the upregulation of HDACs in spinal glial cells

Background

Bone cancer pain (BCP) severely compromises the quality of life, while current treatments are still unsatisfactory. Here, we tested the antinociceptive effects of triptolide (T10), a substance with considerable anti-tumor efficacies on BCP, and investigated the underlying mechanisms targeting the spinal dorsal horn (SDH).

Methods

Intratibial inoculation of Walker 256 mammary gland carcinoma cells was used to establish a BCP model in rats. T10 was intrathecally injected, and mechanical allodynia was tested by measuring the paw withdrawal thresholds (PWTs). In mechanism study, the activation of microglia, astrocytes, and the mitogen-activated protein kinase (MAPK) pathways in the SDH were evaluated by immunofluorescence staining or Western blot analysis of Iba-1, GFAP, p-ERK, p-p38, and p-JNK. The expression and cellular localization of histone deacetylases (HDACs) 1 and 2 were also detected to investigate molecular mechanism.

Results

Intrathecal injection of T10 inhibited the bone cancer-induced mechanical allodynia with an ED₅₀ of 5.874 μg/kg. This effect was still observed 6 days after drug withdrawal. Bone cancer caused significantly increased expression of HDAC1 in spinal microglia and neurons, with HDAC2 markedly increased in spinal astrocytes, which were accompanied by the upregulation of MAPK pathways and the activation of microglia and astrocytes in the SDH. T10 reversed the increase of HDACs, especially those in glial cells, and inhibited the glial activation.

Conclusions

Our results suggest that the upregulation of HDACs contributes to the pathological activation of spinal glial cells and the chronic pain caused by bone cancer, while T10 help to relieve BCP possibly via inhibiting the upregulation of HDACs in the glial cells in the SDH and then blocking the neuroinflammation induced by glial activation.

Brainstem cytokine changes in healthy ageing and Motor Neurone Disease

Neuroinflammation is linked to healthy ageing, but its role in the development of age-related neurodegenerative diseases is unclear. In this pilot study we used a multiplex assay approach to compare 27 cytokines in 6 young adult and 6 ageing control brainstems with those in 6 MND brainstems. We report that healthy ageing is associated with significantly increased brainstem levels of IL-1β, IP-10 and MIP-1β which co-localise immunocytochemically to astrocytes. MND brainstem is also characterised by a general increase in both pro- and anti-cytokine levels, but fails to show the expected age-related increase in MIP-1β and IP-10. This pilot study is the first to show that MND is associated with a failure of specific features of the normal age-related neuroinflammatory process. We suggest that our pilot data indicates that neuroinflammation during healthy ageing may not always be detrimental to motoneuronal survival and that age-related neurodegenerative diseases, such as MND, may instead result from defective neuroinflammation.

Amyotrophic lateral sclerosis: mechanisms and therapeutics in the epigenomic era

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of the motor neurons, which results in weakness and atrophy of voluntary skeletal muscles. Treatments do not modify the disease trajectory effectively, and only modestly improve survival. A complex interaction between genes, environmental exposure and impaired molecular pathways contributes to pathology in patients with ALS. Epigenetic mechanisms control the hereditary and reversible regulation of gene expression without altering the basic genetic code. Aberrant epigenetic patterns-including abnormal microRNA (miRNA) biogenesis and function, DNA modifications, histone remodeling, and RNA editing-are acquired throughout life and are influenced by environmental factors. Thus, understanding the molecular processes that lead to epigenetic dysregulation in patients with ALS might facilitate the discovery of novel therapeutic targets and biomarkers that could reduce diagnostic delay. These achievements could prove crucial for successful disease modification in patients with ALS. We review the latest findings regarding the role of miRNA modifications and other epigenetic mechanisms in ALS, and discuss their potential as therapeutic targets.