Ethanol Induces Secretion of Proinflammatory Extracellular Vesicles That Inhibit Adult Hippocampal Neurogenesis Through G9a/GLP-Epigenetic Signaling

Impact of Neuroimmune System Activation by Adolescent Binge Alcohol Exposure on Adult Neurobiology

Adolescence is a conserved neurodevelopmental period encompassing maturation of glia and the innate immune system that parallels refinement of brain structures, neurotransmitter systems, and neurocircuitry. Given the vast neurodevelopmental processes occurring during adolescence, spanning brain structural and neurocircuitry refinement to maturation of neurotransmitter systems, glia, and the innate immune system, insults incurred during this critical period of neurodevelopment, could have profound effects on brain function and behavior that persist into adulthood. Adolescent binge drinking is common and associated with many adverse outcomes that may underlie the lifelong increased risk of alcohol-related problems and development of an alcohol use disorder (AUD). In this chapter, we examined the impact of adolescent binge drinking models using the adolescent intermittent ethanol (AIE) model on adult neurobiology. These studies implicate proinflammatory neuroimmune signaling across glia and neurons in persistent AIE-induced neuropathology. Some of these changes are reversible, providing unique opportunities for the development of treatments to prevent many of the long-term consequences of adolescent alcohol misuse.

Extracellular vesicles as modifiers of epigenomic profiles

Extracellular vesicles (EVs), emerging as novel mediators between intercellular communication, encapsulate distinct bioactive cargoes to modulate multiple biological events, such as epigenetic remodeling. In essence, EVs and epigenomic profiles are tightly linked and reciprocally regulated. Epigenetic factors, including histone and DNA modifications, noncoding RNAs, and protein post-translational modifications (PTMs) dynamically regulate EV biogenesis to contribute to EV heterogeneity. Alternatively, EVs actively modify DNA, RNA, and histone profiles in recipient cells by delivering RNA and protein cargoes for downstream epigenetic enzyme regulation. Moreover, EVs display great potential as diagnostic markers and drug-delivery vehicles for therapeutic applications. The combination of parental cell epigenomic modification with single EV characterization would be a promising strategy for EV engineering to enhance the epidrug loading efficacy and accuracy.

Microglia either promote or restrain TRAIL-mediated excitotoxicity caused by Aβ1-42 oligomers

BACKGROUND

Alzheimer's disease (AD) features progressive neurodegeneration and microglial activation that results in dementia and cognitive decline. The release of soluble amyloid (Aβ) oligomers into the extracellular space is an early feature of AD pathology. This can promote excitotoxicity and microglial activation. Microglia can adopt several activation states with various functional outcomes. Protective microglial activation states have been identified in response to Aβ plaque pathology in vivo. However, the role of microglia and immune mediators in neurotoxicity induced by soluble Aβ oligomers is unclear. Further, there remains a need to identify druggable molecular targets that promote protective microglial states to slow or prevent the progression of AD.

METHODS

Hippocampal entorhinal brain slice culture (HEBSC) was employed to study mechanisms of Aβ1-42 oligomer-induced neurotoxicity as well as the role of microglia. The roles of glutamate hyperexcitation and immune signaling in Aβ-induced neurotoxicity were assessed using MK801 and neutralizing antibodies to the TNF-related apoptosis-inducing ligand (TRAIL) respectively. Microglial activation state was manipulated using Gi-hM4di designer receptor exclusively activated by designer drugs (DREADDs), microglial depletion with the colony-stimulating factor 1 receptor (CSF1R) antagonist PLX3397, and microglial repopulation (PLX3397 withdrawal). Proteomic changes were assessed by LC-MS/MS in microglia isolated from control, repopulated, or Aβ-treated HEBSCs.

RESULTS

Neurotoxicity induced by soluble Aβ1-42 oligomers involves glutamatergic hyperexcitation caused by the proinflammatory mediator and death receptor ligand TRAIL. Microglia were found to have the ability to both promote and restrain Aβ-induced toxicity. Induction of microglial Gi-signaling with hM4di to prevent pro-inflammatory activation blunted Aβ neurotoxicity, while microglial depletion with CSF1R antagonism worsened neurotoxicity caused by Aβ as well as TRAIL. HEBSCs with repopulated microglia, however, showed a near complete resistance to Aβ-induced neurotoxicity. Comparison of microglial proteomes revealed that repopulated microglia have a baseline anti-inflammatory and trophic phenotype with a predicted pathway activation that is nearly opposite that of Aβ-exposed microglia. mTORC2 and IRF7 were identified as potential targets for intervention.

CONCLUSION

Microglia are key mediators of both protection and neurodegeneration in response to Aβ. Polarizing microglia toward a protective state could be used as a preventative strategy against Aβ-induced neurotoxicity.

Alcohol intake exacerbates experimental autoimmune prostatitis through gut microbiota driving cholesterol biosynthesis-mediated Th17 differentiation

BACKGROUND

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is very common worldwide, and alcohol consumption is a notable contributing factor. Researches have shown that gut microbiota can be influenced by alcohol consumption and is an important mediator in regulating Th17 cell immunity. However, it is still unclear the exact mechanism by which alcohol exacerbates the CP/CPPS and the role of gut microbiota in this process.

METHOD

We first constructed the most-commonly used animal model for CP/CPPS, the experimental autoimmune prostatitis (EAP) model, through immunoassay. Based on this, mice were divided into EAP group and alcohol-consuming EAP group. By 16S rRNA sequencing and non-targeted metabolomics analysis, differential gut microbiota and their metabolites between the two groups were identified. Subsequently, metabolomics detection targeting cholesterols was carried out to identify the exact difference in cholesterol. Furthermore, multiple methods such as flow cytometry and immunohistochemistry were used to detect the differentiation status of Th17 cells and severity of prostatitis treated with 27-hydroxycholesterol (the differential cholesterol) and its upstream regulatory factor-sterol regulatory element-binding protein 2 (SREBP2). Lastly, fecal transplantation was conducted to preliminary study on whether alcohol intake exacerbates EAP in immune receptor mice.

RESULTS

Alcohol intake increased the proportion of Th17 cells and levels of related inflammatory factors. It also led to an altered gut bacterial richness and increased gut permeability. Further metabolomic analysis showed that there were significant differences in a variety of metabolites between EAP and alcohol-fed EAP mice. Metabolic pathway enrichment analysis showed that the pathways related to cholesterol synthesis and metabolism were significantly enriched, which was subsequently confirmed by detecting the expression of metabolic enzymes. By targeting cholesterol synthesis, 27-hydroxycholesterol was significantly increased in alcohol-fed EAP mice. Subsequent mechanistic research showed that supplementation with 27-hydroxycholesterol could aggravate EAP and promote Th17 cell differentiation both in vivo and in vitro, which is regulated by SREBP2. In addition, we observed that fecal transplantation from mice with alcohol intake aggravated EAP in immunized recipient mice fed a normal diet.

CONCLUSION

Our study is the first to show that alcohol intake promotes Th17 cell differentiation and exacerbates EAP through microbiota-derived cholesterol biosynthesis.

Loss of neuronal lysosomal acid lipase drives amyloid pathology in Alzheimer's disease

Underlying drivers of late-onset Alzheimer's disease (LOAD) pathology remain unknown. However, multiple biologically diverse risk factors share a common pathological progression. To identify convergent molecular abnormalities that drive LOAD pathogenesis we compared two common midlife risk factors for LOAD, heavy alcohol use and obesity. This revealed that disrupted lipophagy is an underlying cause of LOAD pathogenesis. Both exposures reduced lysosomal flux, with a loss of neuronal lysosomal acid lipase (LAL). This resulted in neuronal lysosomal lipid (NLL) accumulation, which opposed Aβ localization to lysosomes. Neuronal LAL loss both preceded (with aging) and promoted (targeted knockdown) Aβ pathology and cognitive deficits in AD mice. The addition of recombinant LAL ex vivo and neuronal LAL overexpression in vivo prevented amyloid increases and improved cognition. In WT mice, neuronal LAL declined with aging and correlated negatively with entorhinal Aβ. In healthy human brain, LAL also declined with age, suggesting this contributes to the age-related vulnerability for AD. In human LOAD LAL was further reduced, correlated negatively with Aβ1-42, and occurred with polymerase pausing at the LAL gene. Together, this finds that the loss of neuronal LAL promotes NLL accumulation to impede degradation of Aβ in neuronal lysosomes to drive AD amyloid pathology.

Alcohol and Immunology: Mechanisms of multi-organ damage. Summary of the 2022 alcohol and Immunology research interest group (AIRIG) meeting

On October 26th, 2022 the annual Alcohol and Immunology Research Interest Group (AIRIG) meeting was held as a satellite symposium at the annual meeting of the Society for Leukocyte Biology in Hawaii. The 2022 meeting focused broadly on the immunological consequences of acute, chronic, and prenatal alcohol exposure and how these contribute to damage in multiple organs and tissues. These included alcohol-induced neuroinflammation, impaired lung immunity, intestinal dysfunction, and decreased anti-microbial and anti-viral responses. In addition, research presented covered multiple pathways behind alcohol-induced cellular dysfunction, including mitochondrial metabolism, cellular bioenergetics, gene regulation, and epigenetics. Finally, the work presented highlighted potential biomarkers and novel avenues of treatment for alcohol-induced organ damage.

Involvement of extracellular vesicles in the progression, diagnosis, treatment, and prevention of whole-body ionizing radiation-induced immune dysfunction

Acute radiation syndrome (ARS) develops after exposure to high doses of ionizing radiation and features immune suppression and organ failure. Currently, there are no diagnostics to identify the occurrence or severity of exposure and there are limited treatments and preventative strategies to mitigate ARS. Extracellular vesicles (EVs) are mediators of intercellular communication that contribute to immune dysfunction across many diseases. We investigated if EV cargo can identify whole body irradiation (WBIR) exposure and if EVs promote ARS immune dysfunction. We hypothesized that beneficial EVs derived from mesenchymal stem cells (MSC-EVs) would blunt ARS immune dysfunction and might serve as prophylactic radioprotectants. Mice received WBIR (2 or 9 Gy) with assessment of EVs at 3 and 7 days after exposure. LC-MS/MS proteomic analysis of WBIR-EVs found dose-related changes as well as candidate proteins that were increased with both doses and timepoints (34 total) such as Thromboxane-A Synthase and lymphocyte cytosolic protein 2. Suprabasin and Sarcalumenin were increased only after 9 Gy suggesting these proteins may indicate high dose/lethal exposure. Analysis of EV miRNAs identified miR-376 and miR-136, which were increased up to 200- and 60-fold respectively by both doses of WBIR and select miRNAs such as miR-1839 and miR-664 were increased only with 9 Gy. WBIR-EVs (9 Gy) were biologically active and blunted immune responses to LPS in RAW264.7 macrophages, inhibiting canonical signaling pathways associated with wound healing and phagosome formation. When given 3 days after exposure, MSC-EVs slightly modified immune gene expression changes in the spleens of mice in response to WBIR and in a combined radiation plus burn injury exposure (RCI). MSC-EVs normalized the expression of certain key immune genes such as NFκBia and Cxcr4 (WBIR), Map4k1, Ccr9 and Cxcl12 (RCI) and lowered plasma TNFα cytokine levels after RCI. When given prophylactically (24 and 3 hours before exposure), MSC-EVs prolonged survival to the 9 Gy lethal exposure. Thus, EVs are important participants in ARS. EV cargo might be used to diagnose WBIR exposure, and MSC-EVs might serve as radioprotectants to blunt the impact of toxic radiation exposure.

Microglia NLRP3 Inflammasome and Neuroimmune Signaling in Substance Use Disorders

During the last decade, substance use disorders (SUDs) have been increasingly recognized as neuroinflammation-related brain diseases. Various types of abused drugs (cocaine, methamphetamine, alcohol, opiate-like drugs, marijuana, etc.) can modulate the activation status of microglia and neuroinflammation levels which are involved in the pathogenesis of SUDs. Several neuroimmune signaling pathways, including TLR/NF-кB, reactive oxygen species, mitochondria dysfunction, as well as autophagy defection, etc., have been implicated in promoting SUDs. Recently, inflammasome-mediated signaling has been identified as playing critical roles in the microglia activation induced by abused drugs. Among the family of inflammasomes, NOD-, LRR-, and pyrin-domain-containing protein 3 (NLRP3) serves the primary research target due to its abundant expression in microglia. NLRP3 has the capability of integrating multiple external and internal inputs and coordinately determining the intensity of microglia activation under various pathological conditions. Here, we summarize the effects of abused drugs on NLRP3 inflammasomes, as well as others, if any. The research on this topic is still at an infant stage; however, the readily available findings suggest that NLRP3 inflammasome could be a common downstream effector stimulated by various types of abused drugs and play critical roles in determining abused-drug-mediated biological effects through enhancing glia-neuron communications. NLRP3 inflammasome might serve as a novel target for ameliorating the development of SUDs.

Microglia activation mediates circadian rhythm disruption-induced cognitive impairment in mice

Alzheimer's disease (AD) is the leading cause of dementia and there are no effective treatments for this disease currently. Circadian rhythm disruption (CRD) is a hallmark of modern society that appears to be on the rise. It is well reported that AD is associated with disrupted circadian functioning and CRD can impair cognitive function. However, the cellular mechanisms underlying CRD-associated cognitive decline remain elusive. In this study, we investigated whether microglia are involved in CRD-induced cognitive decline. We established experimental 'jet lag' (phase delay of the light/dark cycles)-induced CRD mouse model and observed significant impairment of spatial learning and memory function in these mice. In the brain, CRD resulted in neuroinflammation, which was characterized by microglia activation and increased pro-inflammatory cytokine production, impairments in neurogenesis and reduction of synaptic proteins in the hippocampus. Interestingly, elimination of microglia with the colony stimulating factor-1 receptor inhibitor PLX3397 prevented CRD-induced neuroinflammation, cognitive decline, impairment of neurogenesis and loss of synaptic proteins. These findings collectively suggest that microglia activation plays a key role in CRD-induced cognitive deficit most likely through neuroinflammation-mediated impairments in adult neurogenesis and synapses.

Targeting Persistent Changes in Neuroimmune and Epigenetic Signaling in Adolescent Drinking to Treat Alcohol Use Disorder in Adulthood

Studies universally find early age of drinking onset is linked to lifelong risks of alcohol problems and alcohol use disorder (AUD). Assessment of the lasting effect of drinking during adolescent development in humans is confounded by the diversity of environmental and genetic factors that affect adolescent development, including emerging personality disorders and progressive increases in drinking trajectories into adulthood. Preclinical studies using an adolescent intermittent ethanol (AIE) exposure rat model of underage binge drinking avoid the human confounds and support lifelong changes that increase risks. AIE increases adult alcohol drinking, risky decision-making, reward-seeking, and anxiety as well as reductions in executive function that all increase risks for the development of an AUD. AIE causes persistent increases in brain neuroimmune signaling high-mobility group box 1 (HMGB1), Toll-like receptor, receptor for advanced glycation end products, and innate immune genes that are also found to be increased in human AUD brain. HMGB1 is released from cells by ethanol, both free and within extracellular vesicles, that act on neurons and glia, shifting transcription and cellular phenotype. AIE-induced decreases in adult hippocampal neurogenesis and loss of basal forebrain cholinergic neurons are reviewed as examples of persistent AIE-induced pathology. Both are prevented and reversed by anti-inflammatory and epigenetic drugs. Findings suggest AIE-increased HMGB1 signaling induces the RE-1 silencing transcript blunting cholinergic gene expression, shifting neuronal phenotype. Inhibition of HMGB1 neuroimmune signaling, histone methylation enzymes, and galantamine, the cholinesterase inhibitor, both prevent and reverse AIE pathology. These findings provide new targets that may reverse AUD neuropathology as well as other brain diseases linked to neuroimmune signaling. SIGNIFICANCE STATEMENT: Adolescent underage binge drinking studies find that earlier adolescent drinking is associated with lifelong alcohol problems including high levels of lifetime alcohol use disorder (AUD). Preclinical studies find the underage binge drinking adolescent intermittent ethanol (AIE) model causes lasting changes in adults that increase risks of developing adult alcohol problems. Loss of hippocampal neurogenesis and loss of basal forebrain cholinergic neurons provide examples of how AIE-induced epigenetic and neuroimmune signaling provide novel therapeutic targets for adult AUD.