Ad-derived bone marrow transplant induces proinflammatory immune peripheral mechanisms accompanied by decreased neuroplasticity and reduced gut microbiome diversity affecting AD-like phenotype in the absence of Aβ neuropathology

Immune system dysfunction is increasingly recognized as a significant feature that contributes to Alzheimer's disease (AD) pathogenesis, reflected by alterations in central and peripheral responses leading to detrimental mechanisms that can contribute to the worsening of the disease. The damaging alterations in the peripheral immune system may disrupt the peripheral-central immune crosstalk, implicating the gut microbiota in this complex interaction. The central hypothesis posits that the immune signature inherently harbored in bone marrow (BM) cells can be transferred through allogeneic transplantation, influencing the recipient's immune system and modulating peripheral, gut, and brain immune responses. Employing a genetically modified mouse model to develop AD-type pathology we found that recipient wild-type (WT) mice engrafted with AD-derived BM, recapitulated the peripheral immune inflammatory donor phenotype, associated with a significant acceleration of cognitive deterioration in the absence of any overt change in AD-type amyloid neuropathology. Moreover, transcriptomic and phylogenetic 16S microbiome analysis evidence on these animals revealed a significantly impaired expression of genes associated with synaptic plasticity and neurotransmission in the brain and reduced bacteria diversity, respectively, compared to mice engrafted with WT BM. This investigation sheds light on the pivotal role of the peripheral immune system in the brain-gut-periphery axis and its profound potential to shape the trajectory of AD. In summary, this study advances our understanding of the complex interplay among the peripheral immune system, brain functionality, and the gut microbiome, which collectively influence AD onset and progression.

The role of the Toll like receptor 4 signaling in sex-specific persistency of depression-like behavior in response to chronic stress

Chronic stress is a major risk factor for Major Depressive Disorder (MDD), and it has been shown to impact the immune system and cause microglia activation in the medial prefrontal cortex (mPFC) involved in the pathogenesis of depression. The aim of this study is to further investigate cellular and molecular mechanisms underlying persistent depression behavior in sex specific manner, which is observed clinically. Here, we report that both male and female mice exhibited depression-like behavior following exposure to chronic stress. However, only female mice showed persistent depression-like behavior, which was associated with microglia activation in mPFC, characterized by distinctive alterations in the phenotype of microglia. Given these findings, to further investigate the underlying molecular mechanisms associated with persistent depression-like behavior and microglia activation in female mice, we used translating-ribosome affinity purification (TRAP). We find that Toll like receptor 4 (TLR4) signaling is casually related to persistent depression-like behavior in female mice. This is supported by the evidence that the fact that genetic ablation of TLR4 expression in microglia significantly reduced the persistent depression-like behavior to baseline levels in female mice. This study tentatively supports the hypothesis that the TLR4 signaling in microglia may be responsible for the sex differences in persistent depression-like behavior in female.

Dietary polyphenols drive dose-dependent behavioral and molecular alterations to repeated morphine

Opioid Use Disorder (OUD) is associated with tremendous morbidity and mortality. Despite this burden, current pharmacotherapies for OUD are ineffective or intolerable for many patients. As such, interventions aimed at promoting resilience against OUD are of immense clinical interest. Treatment with a Bioactive Dietary Polyphenol Preparation (BDPP) promotes resilience and adaptive neuroplasticity in multiple models of neuropsychiatric disease. Here, we assessed effects of BDPP treatment on behavioral and molecular responses to repeated morphine treatment in male mice. BDPP pre-treatment alters responses for both locomotor sensitization and conditioned place preference. Most notably, polyphenol treatment consistently reduced formation of preference at low dose (5 mg/kg) morphine but enhanced it at high dose (15 mg/kg). In parallel, we performed transcriptomic profiling of the nucleus accumbens, which again showed a dose × polyphenol interaction. We also profiled microbiome composition and function, as polyphenols are metabolized by the microbiome and can act as prebiotics. The profile revealed polyphenol treatment markedly altered microbiome composition and function. Finally, we investigated involvement of the SIRT1 deacetylase, and the role of polyphenol metabolites in behavioral responses. These results demonstrate polyphenols have robust dose-dependent effects on behavioral and physiological responses to morphine and lay the foundation for future translational work.

Inflammasome-Mediated Neuronal-Microglial Crosstalk: a Therapeutic Substrate for the Familial C9orf72 Variant of Frontotemporal Dementia/Amyotrophic Lateral Sclerosis

Intronic G₄C₂ hexanucleotide repeat expansions (HRE) of C9orf72 are the most common cause of familial variants of frontotemporal dementia/amyotrophic lateral sclerosis (FTD/ALS). G₄C₂ HREs in C9orf72 undergo non-canonical repeat-associated translation, producing dipeptide repeat (DPR) proteins, with various deleterious impacts on cellular homeostasis. While five different DPRs are produced, poly(glycine-arginine) (GR) is amongst the most toxic and is the only DPR to accumulate in the associated clinically relevant anatomical locations of the brain. Previous work has demonstrated the profound effects of a poly (GR) model of C9orf72 FTD/ALS, including motor impairment, memory deficits, neurodegeneration, and neuroinflammation. Neuroinflammation is hypothesized to be a driving factor in the disease course; microglia activation is present prior to symptom onset and persists throughout the disease. Here, using an established mouse model of C9orf72 FTD/ALS, we investigate the contributions of the nod-like receptor pyrin-containing 3 (NLRP3) inflammasome in the pathogenesis of FTD/ALS. We find that inflammasome-mediated neuroinflammation is increased with microglial activation, cleavage of caspase-1, production of IL-1β, and upregulation of Cxcl10 in the brain of C9orf72 FTD/ALS mice. Excitingly, we find that genetic ablation of Nlrp3 significantly improved survival, protected behavioral deficits, and prevented neurodegeneration suggesting a novel mechanism involving HRE-mediated induction of innate immunity. The findings provide experimental evidence of the integral role of HRE in inflammasome-mediated innate immunity in the C9orf72 variant of FTD/ALS pathogenesis and suggest the NLRP3 inflammasome as a therapeutic target.

Exposure to World Trade Center Dust Exacerbates Cognitive Impairment and Evokes a Central and Peripheral Pro-Inflammatory Transcriptional Profile in an Animal Model of Alzheimer's Disease

BACKGROUND

The terrorist attacks on September 11, 2001, on the World Trade Center (WTC) led to intense fires and a massive dense cloud of toxic gases and suspended pulverized debris. In the subsequent years, following the attack and cleanup efforts, a cluster of chronic health conditions emerged among First Responders (FR) who were at Ground Zero for prolonged periods and were repeatedly exposed to high levels of WTC particulate matter (WTCPM). Among those are neurological complications which may increase the risk for the development of Alzheimer's disease (AD) later in life.

OBJECTIVE

We hypothesize that WTCPM dust exposure affects the immune cross-talking between the periphery and central nervous systems that may induce brain permeability ultimately promoting AD-type phenotype.

METHODS

5XFAD and wild-type mice were intranasally administered with WTCPM dust collected at Ground Zero within 72 h after the attacks. Y-maze assay and novel object recognition behavioral tests were performed for working memory deficits and learning and recognition memory, respectively. Transcriptomic analysis in the blood and hippocampus was performed and confirmed by RT qPCR.

RESULTS

Mice exposed to WTCPM dust exhibited a significant impairment in spatial and recognition short and long-term memory. Furthermore, the transcriptomic analysis in the hippocampal formation and blood revealed significant changes in genes related to immune-inflammatory responses, and blood-brain barrier disruption.

CONCLUSION

These studies suggest a putative peripheral-brain immune inflammatory cross-talking that may potentiate cognitive decline, identifying for the first time key steps which may be therapeutically targetable in future studies in WTC FR.

COVID‐19 and Alzheimer’s disease: Meninges‐mediated neuropathology

Background

SARS‐CoV‐2 the causative agent of COVID‐19 displays a broad range of pathophysiology. Cytokine storms associated with COVID‐19 damage the blood‐brain barrier (BBB) and allow pro‐inflammatory factors to invade the brain, further promoting neurodegeneration. While SARS‐CoV‐2 viral RNA and proteins have been detected in brain tissues, the mechanisms of neuroinvasion remain unknown. COVID‐19 has had a disproportionate impact on those suffering from neurodegenerative disorders such as Alzheimer’s disease (AD). Understanding the mechanisms of SARS‐CoV‐2 neuroinvasion is crucial to study the long‐term neurocognitive effects of COVID‐19 on AD pathology. Viruses can infiltrate the brain through the meninges via infected immune cells. The meninges regulate the immune surveillance of the brain and play a key role in the efflux of pathogens from the brain. Meningeal dysfunction has been demonstrated to exacerbate amyloid‐beta pathogenesis. In this study, we explore the neuroinvasion pathway of SARS‐CoV‐2 through the meninges and its effect on AD pathology.

Method

5x FAD x hACE2 mice were inoculated intranasally with a sublethal dose of SARS‐CoV‐2. The mice were maintained for 2 weeks. Mouse brains and meninges were harvested. The tissue was stained and immunofluorescence imaging was conducted to study viral proliferation and immune responses. Histo‐cytometry was conducted for quantitative imaging analysis. Gene expression studies were done using Nanostring assays. All experiments involving the SARS‐Cov‐2 virus were carried out in a BSL3 facility.

Result

This ongoing study demonstrates the proliferation of the SARS‐CoV‐2 virus in the brain via meningeal lymphatics. SARS‐CoV‐2 infection resulted in increased neuroinflammation. Additionally, inflammatory responses induced meningeal dysfunction resulting in increased amyloid‐beta pathology and cerebrospinal fluid drainage.

Conclusion

Given the increasing evidence for a viral hypothesis of Alzheimer’s Disease it is extremely important to study the neurodegenerative effects of COVID‐19 which has affected millions worldwide. We demonstrate that SARS‐CoV‐2 infiltrates the brain via the meninges promoting neuroinflammation. Furthermore, amyloid‐beta pathologies are exacerbated by COVID‐19 in animal models providing preclinical evidence of the long‐term neurodegenerative effects of COVID‐19.

Anxiolytic effects of NLRP3 inflammasome inhibition in a model of chronic sleep deprivation

Sleep deprivation is a form of stress that provokes both inflammatory responses and neuropsychiatric disorders. Because persistent inflammation is implicated as a physiological process in anxiety disorders, we investigated the contributions of NLRP3 inflammasome signaling to anxiety and anxiolytic properties of flavanol diets in a model of chronic sleep deprivation. The results show a flavanol-rich dietary preparation (FDP) exhibits anxiolytic properties by attenuating markers of neuroimmune activation, which included IL-1β upregulation, NLRP3 signaling, and microglia activation in the cortex and hippocampus of sleep-deprived mice. Production of IL-1β and NLRP3 were critical for both anxiety phenotypes and microglia activation. Individual FDP metabolites potently inhibited IL-1β production from microglia following stimulation with NLRP3-specific agonists, supporting anxiolytic properties of FDP observed in models of sleep deprivation involve inhibition of the NLRP3 inflammasome. The study further showed sleep deprivation alters the expression of the circadian gene Bmal1, which critically regulated NLRP3 expression and IL-1β production.

Characterization of 3(3,4-dihydroxy-phenyl) propionic acid as a novel microbiome-derived epigenetic modifier in attenuation of immune inflammatory response in human monocytes

Recent studies suggest that microbiome derived 3(3,4-dihydroxy-phenyl) propionic acid (DHCA) attenuates IL-6 cytokine production through downregulation of the epigenetic modifier DNA Methyltransferase 1 (DNMT1) expression and inhibition of DNA methylation at the 5'-C-phosphate-G-3' (CpG)-rich IL6 sequence introns 1 and 3 in a mouse model of depression. In this study, we extended the investigation of DHCA epigenetic mechanisms in IL-6 expression in human peripheral blood mononuclear cells (PBMC). Using Lucia Luciferase reporter gene system we identified CpG-rich sequences in which of methylation is influenced by DHCA similar to what observed in response to treatment with the DNA methylation inhibitor 5-aza-2'-deoxycytidine. Correlation study showed that DNA methylation at select CpG motifs in the IL-6 promoter correlates with IL-6 gene expression. Our study suggests that DHCA is effective in reducing IL-6 expression in human PBMCs, in part, by regulation of methylation in the IL-6 promoter region.

Prophylactic effect of flavanol rich preparation metabolites in promoting resilience to a mouse model of social stress

Major depressive disorder (MDD) is a leading cause of disability, and there is an urgent need for new therapeutics. Stress-mediated induction of pro-inflammation in the periphery contributes to depression-like behaviors both in humans and in experimental models. Inflammatory cytokine interleukin-6 (IL-6) has emerged as a potential therapeutic target. Our studies demonstrated that metabolism of flavanol rich cocoa preparation (FRP) led to the accumulation of select phenolic acids that may contribute to its anti-inflammatory activity. Using a repeated social defeat stress (RSDS) model of depression, we showed that oral administration of FRP attenuates susceptibility to RSDS-mediated depression, supporting the further development of FRP as a novel therapeutic for the treatment of stress disorders and anxiety in humans.

The Innate Immune System and Inflammatory Priming: Potential Mechanistic Factors in Mood Disorders and Gulf War Illness

Gulf War Illness is a chronic multisystem disorder affecting approximately a third of the Veterans of the Gulf War, manifesting with physical and mental health symptoms such as cognitive impairment, neurological abnormalities, and dysregulation of mood. Among the leading theories into the etiology of this multisystem disorder is environmental exposure to the various neurotoxins encountered in the Gulf Theatre, including organophosphates, nerve agents, pyridostigmine bromide, smoke from oil well fires, and depleted uranium. The relationship of toxin exposure and the pathogenesis of Gulf War Illness converges on the innate immune system: a nonspecific form of immunity ubiquitous in nature that acts to respond to both exogenous and endogenous insults. Activation of the innate immune system results in inflammation mediated by the release of cytokines. Cytokine mediated neuroinflammation has been demonstrated in a number of psychiatric conditions and may help explain the larger than expected population of Gulf War Veterans afflicted with a mood disorder. Several of the environmental toxins encountered by soldiers during the first Gulf War have been shown to cause upregulation of inflammatory mediators after chronic exposure, even at low levels. This act of inflammatory priming, by which repeated exposure to chronic subthreshold insults elicits robust responses, even after an extended period of latency, is integral in the connection of Gulf War Illness and comorbid mood disorders. Further developing the understanding of the relationship between environmental toxin exposure, innate immune activation, and pathogenesis of disease in the Gulf War Veterans population, may yield novel therapeutic targets, and a greater understanding of disease pathology and subsequently prevention.

Mechanisms of Immune Activation by c9orf72-Expansions in Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative disorders with overlapping pathomechanisms, neurobehavioral features, and genetic etiologies. Individuals diagnosed with either disorder exhibit symptoms within a clinical spectrum. Symptoms of ALS involve neuromusculature deficits, reflecting upper and lower motor neurodegeneration, while the primary clinical features of FTD are behavioral and cognitive impairments, reflecting frontotemporal lobar degeneration. An intronic G₄C₂ hexanucleotide repeat expansion (HRE) within the promoter region of chromosome 9 open reading frame 72 (C9orf72) is the predominant monogenic cause of both ALS and FTD. While the heightened risk to develop ALS/FTD in response to C9orf72 expansions is well-established, studies continue to define the precise mechanisms by which this mutation elicits neurodegeneration. Studies show that G₄C₂ expansions undergo repeat-associated non-ATG dependent (RAN) translation, producing dipeptide repeat proteins (DRPs) with varying toxicities. Accumulation of DRPs in neurons, in particular arginine containing DRPs, have neurotoxic effects by potently impairing nucleocytoplasmic transport, nucleotide metabolism, lysosomal processes, and cellular metabolic pathways. How these pathophysiological effects of C9orf72 expansions engage and elicit immune activity with additional neurobiological consequences is an important line of future investigations. Immunoreactive microglia and elevated levels of peripheral inflammatory cytokines noted in individuals with C9orf72 ALS/FTD provide evidence that persistent immune activation has a causative role in the progression of each disorder. This review highlights the current understanding of the cellular, proteomic and genetic substrates through which G₄C₂ HREs may elicit detrimental immune activity, facilitating region-specific neurodegeneration in C9orf72 mediated ALS/FTD. We in particular emphasize interactions between intracellular pathways induced by C9orf72 expansions and innate immune inflammasome complexes, intracellular receptors responsible for eliciting inflammation in response to cellular stress. A further understanding of the intricate, reciprocal relationship between the cellular and molecular pathologies resulting from C9orf72 HREs and immune activation may yield novel therapeutics for ALS/FTD, which currently have limited treatment strategies.