Modulation of fear behavior and neuroimmune alterations in house dust mite exposed A/J mice, a model of severe asthma

House dust mite-induced asthma exacerbates Alzheimer's disease changes in the brain of the AppNL-G-F mouse model of disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by the accumulation of amyloid-β (Aβ) plaques, neuroinflammation, and neuronal death. Besides aging, various comorbidities increase the risk of AD, including obesity, diabetes, and allergic asthma. Epidemiological studies have reported a 2.17-fold higher risk of dementia in asthmatic patients. However, the molecular mechanism(s) underlying this asthma-associated AD exacerbation is unknown. This study was designed to explore house dust mite (HDM)-induced asthma effects on AD-related brain changes using the AppNL-G-F transgenic mouse model of disease. Male and female 8-9 months old C57BL/6J wild type and AppNL-G-F mice were exposed to no treatment, saline sham, or HDM extract every alternate day for 16 weeks for comparison across genotypes and treatment. Mice were euthanized at the end of the experiment, and broncho-alveolar lavage fluid (BALF), blood, lungs, and brains were collected. BALF was used to quantify immune cell phenotype, cytokine levels, total protein content, lactate dehydrogenase (LDH) activity, and total IgE. Lungs were sectioned and stained with hematoxylin and eosin, Alcian blue, and Masson's trichrome. Serum levels of cytokines and soluble Aβ1-40/42 were quantified. Brains were sectioned and immunostained for Aβ, GFAP, CD68, and collagen IV. Finally, frozen hippocampi and temporal cortices were used to perform Aβ ELISAs and cytokine arrays, respectively. HDM exposure led to increased levels of inflammatory cells, cytokines, total protein content, LDH activity, and total IgE in the BALF, as well as increased pulmonary mucus and collagen staining in both sexes and genotypes. Levels of serum cytokines increased in all HDM-exposed groups. Serum from the AppNL-G-F HDM-induced asthma group also had significantly increased soluble Aβ1-42 levels in both sexes. In agreement with this peripheral change, hippocampi from asthma-induced male and female AppNL-G-F mice demonstrated elevated Aβ plaque load and increased soluble Aβ 1-40/42 and insoluble Aβ 1-40 levels. HDM exposure also increased astrogliosis and microgliosis in both sexes of AppNL-G-F mice, as indicated by GFAP and CD68 immunoreactivity, respectively. Additionally, HDM exposure elevated cortical levels of several cytokines in both sexes and genotypes. Finally, HDM-exposed groups also showed a disturbed blood-brain-barrier (BBB) integrity in the hippocampus of AppNL-G-F mice, as indicated by decreased collagen IV immunoreactivity. HDM exposure was responsible for an asthma-like condition in the lungs that exacerbated Aβ pathology, astrogliosis, microgliosis, and cytokine changes in the brains of male and female AppNL-G-F mice that correlated with reduced BBB integrity. Defining mechanisms of asthma effects on the brain may identify novel therapeutic targets for asthma and AD.

Does the Farming Method Influence the Porcine Vomeronasal Organ Condition? A Histological Study

The vomeronasal organ (VNO) plays a key role in mammals, since it detects pheromones thus enabling social interactions between congeners. VNO inflammatory changes have been shown to severely impact animal life, leading to impaired social interactions in groups, such as in pigs. Environmental air is known to be strongly modified in farms, and it is suspected to be one of the causes of this alteration. This study aimed to compare via histology the VNOs of pigs housed in intensive conditions (n = 38) to those of pigs housed in free-range farming conditions (n = 35). VNO sections were stained in hematoxylin and eosin to assess the presence of nonsensory and sensory epithelium alterations and collagenolysis. The nonsensory epithelium was significantly more inflamed in animals in free-range farming conditions than those in intensive conditions (p < 0.0001) and was more strongly affected by signs of collagenolysis (p < 0.0001). The sensory epithelium seemed to be less altered by the different environmental conditions (p = 0.7267). These results suggest that species-typical pig behaviors, such as digging and rooting for food, could facilitate the presence of microparticles in the oral cavity and their entrance into the vomeronasal canals, leading to changes to the VNO.

Systemic Inflammation in Asthma: What Are the Risks and Impacts Outside the Airway?

Airway inflammation in asthma has been well recognized for several decades, with general agreement on its role in asthma pathogenesis, symptoms, propensity toward exacerbation, and decline in lung function. This has led to universal recommendation in asthma management guidelines to incorporate the use of inhaled corticosteroid as an anti-inflammatory therapy for all patients with persistent asthma symptoms. However, there has been limited attention paid to the presence and potential impact of systemic inflammation in asthma. Accumulating evidence from epidemiological observations and cohort studies points to a host of downstream organ dysfunction in asthma especially among patients with longstanding or more severe disease, frequent exacerbations, and underlying risk factors for organ dysfunction. Most studies to date have focused on cognitive impairment, depression/anxiety, metabolic syndrome, and cardiovascular abnormalities. In this review, we summarize some of the evidence demonstrating these abnormalities and highlight the proposed mechanisms and potential benefits of treatment in limiting these extrapulmonary abnormalities in patients with asthma. The goal of this commentary is to raise awareness of the importance of recognizing potential extrapulmonary conditions associated with systemic inflammation of asthma. This area of treatment of patients with asthma is a large unmet need.

Causal Association Between Allergic Diseases and Dementia: Evidence from Multivariate Mendelian Randomization Study

Background

The link between allergic diseases and dementia remains controversial, and the genetic causality of this link is unclear.

Objective

This study investigated the causal relationship between allergic diseases and dementia using univariate and multivariate Mendelian randomization (MR) methods.

Methods

We selected genome-wide association studies including 66,645 patients with allergic diseases and 12,281 patients with dementia, with statistical datasets derived from the FinnGen Consortium of European origin. After a rigorous screening process for single nucleotide polymorphisms to eliminate confounding effects, MR estimation was performed mainly using the inverse variance weighting method and the MR-Egger method. Sensitivity analyses were performed using Cochran's Q test, MR-PRESSO test, MR Pleiotropy residuals and leave-one-out analysis.

Results

Univariate and multivariate MR together demonstrated a causal relationship between atopic dermatitis and reduced vascular dementia (VaD) risk (OR = 0.89, 95% CI: 0.81-0.99, p = 0.031; OR = 0.85, 95% CI: 0.76-0.95, p = 0.003). MVMR confirmed asthma was associated with a reduction in the risk of Alzheimer's disease (AD) (OR = 0.82, 95% CI: 0.71-0.94, p = 0.005) and may be associated with a reduction in the risk of VaD (OR = 0.80, 95% CI: 0.65-0.99, p = 0.042); allergic rhinitis may be causally associated with an increased risk of AD (OR = 1.16, 95% CI: 1.00-1.35, p = 0.046) and VaD (OR = 1.29, 95% CI: 1.03-1.62, p = 0.027). In sensitivity analyses, these findings were reliable.

Conclusions

MR methods have only demonstrated that allergic rhinitis dementia is associated with an increased risk of developing dementia. Previously observed associations between other allergic diseases and dementia may be influenced by comorbidities and confounding factors rather than causality.

Molecular pathways underlying lung-brain axis signaling in asthma: Relevance for psychopathology and neuroinflammation

BACKGROUND

Accumulating evidence indicates that asthma has systemic effects and affects brain function. Although airway inflammation is proposed to initiate afferent communications with the brain, the signaling pathways have not been established.

OBJECTIVE

We sought to identify the cellular and molecular pathways involved in afferent lung-brain communication during airway inflammation in asthma.

METHODS

In 23 adults with mild asthma, segmental bronchial provocation with allergen (SBP-Ag) was used to provoke airway inflammation and retrieve bronchoalveolar lavage fluid for targeted protein analysis and RNA sequencing to determine gene expression profiles. Neural responses to emotional cues in nodes of the salience network were assessed with functional magnetic resonance imaging at baseline and 48 hours after SBP-Ag.

RESULTS

Cell deconvolution and gene coexpression network analysis identified 11 cell-associated gene modules that changed in response to SBP-Ag. SBP-Ag increased bronchoalveolar lavage eosinophils and expression of an eosinophil-associated module enriched for genes related to TH17-type inflammation (eg, IL17A), as well as cell proliferation in lung and brain (eg, NOTCH1, VEGFA, and LIF). Increased expression of genes in this module, as well as several TH17-type inflammation-related proteins, was associated with an increase from baseline in salience network reactivity.

CONCLUSIONS

Our results identify a specific inflammatory pathway linking asthma-related airway inflammation and emotion-related neural function. Systemically, TH17-type inflammation has been implicated in both depression and neuroinflammation, with impacts on long-term brain health. Thus, our data emphasize that inflammation in the lung in asthma may have profound effects outside of the lung that may be targetable with novel therapeutic approaches.

Brain structural and functional alterations related to anxiety in allergic asthma

Psychiatric disorders are common in patients with allergic asthma, and they can have a significant impact on their quality of life and disease control. Recent studies have suggested that there may be potential immune-brain communication mechanisms in asthma, which can activate inflammatory responses in different brain areas, leading to structural and functional alterations and behavioral changes. However, the precise mechanisms underlying these alterations remain unclear. In this paper, we comprehensively review the relevant research on asthma-induced brain structural and functional alterations that lead to the initiation and promotion of anxiety. We summarize the possible pathways for peripheral inflammation to affect the brain's structure and function. Our review highlights the importance of addressing neuropsychiatric disorders in the clinical guidelines of asthma, to improve the quality of life of these patients. We suggest that a better understanding of the mechanisms underlying psychiatric comorbidities in asthma could lead to the development of more effective treatments for these patients.

Altered Fear Behavior in Aeroallergen House Dust Mite Exposed C57Bl/6 Mice: A Model of Th2-skewed Airway Inflammation

There is a growing interest for studying the impact of chronic inflammation, particularly lung inflammation, on the brain and behavior. This includes asthma, a chronic inflammatory condition, that has been associated with psychiatric conditions such as posttraumatic stress disorder (PTSD). Although asthma is driven by elevated production of Th2 cytokines (IL-4, IL-5 and IL-13), which drive asthma symptomology, recent work demonstrates that concomitant Th1 or Th17 cytokine production can worsen asthma severity. We previously demonstrated a detrimental link between PTSD-relevant fear behavior and allergen-induced lung inflammation associated with a mixed Th2/Th17-inflammatory profile in mice. However, the behavioral effects of Th2-skewed airway inflammation, typical to mild/moderate asthma, are unknown. Therefore, we investigated fear conditioning/extinction in allergen house dust mite (HDM)-exposed C57Bl/6 mice, a model of Th2-skewed allergic asthma. Behaviors relevant to panic, anxiety, and depression were also assessed. Furthermore, we investigated the accumulation of Th2/Th17-cytokine-expressing cells in lung and brain, and the neuronal activation marker, ΔFosB, in fear regulatory brain areas. HDM-exposed mice elicited lower freezing during fear extinction with no effects on acquisition and conditioned fear. No HDM effect on panic, anxiety or depression-relevant behaviors was observed. While HDM evoked a Th2-skewed immune response in lung tissue, no significant alterations in brain Th cell subsets were observed. Significantly reduced ΔFosB+ cells in the basolateral amygdala of HDM mice were observed post extinction. Our data indicate that allergen-driven Th2-skewed responses may induce fear extinction promoting effects, highlighting beneficial interactions of Th2-associated immune mediators with fear regulatory circuits.

Impact of asthma on the brain: evidence from diffusion MRI, CSF biomarkers and cognitive decline

Chronic systemic inflammation increases the risk of neurodegeneration, but the mechanisms remain unclear. Part of the challenge in reaching a nuanced understanding is the presence of multiple risk factors that interact to potentiate adverse consequences. To address modifiable risk factors and mitigate downstream effects, it is necessary, although difficult, to tease apart the contribution of an individual risk factor by accounting for concurrent factors such as advanced age, cardiovascular risk, and genetic predisposition. Using a case-control design, we investigated the influence of asthma, a highly prevalent chronic inflammatory disease of the airways, on brain health in participants recruited to the Wisconsin Alzheimer's Disease Research Center (31 asthma patients, 186 non-asthma controls, aged 45-90 years, 62.2% female, 92.2% cognitively unimpaired), a sample enriched for parental history of Alzheimer's disease. Asthma status was determined using detailed prescription information. We employed multi-shell diffusion weighted imaging scans and the three-compartment neurite orientation dispersion and density imaging model to assess white and gray matter microstructure. We used cerebrospinal fluid biomarkers to examine evidence of Alzheimer's disease pathology, glial activation, neuroinflammation and neurodegeneration. We evaluated cognitive changes over time using a preclinical Alzheimer cognitive composite. Using permutation analysis of linear models, we examined the moderating influence of asthma on relationships between diffusion imaging metrics, CSF biomarkers, and cognitive decline, controlling for age, sex, and cognitive status. We ran additional models controlling for cardiovascular risk and genetic risk of Alzheimer's disease, defined as a carrier of at least one apolipoprotein E (APOE) ε4 allele. Relative to controls, greater Alzheimer's disease pathology (lower amyloid-β42/amyloid-β40, higher phosphorylated-tau-181) and synaptic degeneration (neurogranin) biomarker concentrations were associated with more adverse white matter metrics (e.g. lower neurite density, higher mean diffusivity) in patients with asthma. Higher concentrations of the pleiotropic cytokine IL-6 and the glial marker S100B were associated with more salubrious white matter metrics in asthma, but not in controls. The adverse effects of age on white matter integrity were accelerated in asthma. Finally, we found evidence that in asthma, relative to controls, deterioration in white and gray matter microstructure was associated with accelerated cognitive decline. Taken together, our findings suggest that asthma accelerates white and gray matter microstructural changes associated with aging and increasing neuropathology, that in turn, are associated with more rapid cognitive decline. Effective asthma control, on the other hand, may be protective and slow progression of cognitive symptoms.

Chronic allergic lung inflammation negatively influences neurobehavioral outcomes in mice

BACKGROUND

Asthma is a major public health problem worldwide. Emerging data from epidemiological studies show that allergies and allergic diseases may be linked to anxiety, depression and cognitive decline. However, little is known about the effect of asthma, an allergic lung inflammation, on cognitive decline/behavioral changes. Therefore, we investigated the hypothesis that allergic lung inflammation causes inflammation in the brain and leads to neurobehavioral changes in mice.

METHODS

Wild-type C57BL/6J female mice were sensitized with nasal house dust mite (HDM) antigen or control PBS for 6 weeks to induce chronic allergic lung inflammation. A series of neurocognitive tests for anxiety and/or depression were performed before and after the intranasal HDM administration. After the behavior tests, tissues were harvested to measure inflammation in the lungs and the brains.

RESULTS

HDM-treated mice exhibited significantly increased immobility times during tail suspension tests and significantly decreased sucrose preference compared with PBS controls, suggesting a more depressed and anhedonia phenotype. Spatial memory impairment was also observed in HDM-treated mice when assessed by the Y-maze novel arm tests. Development of lung inflammation after 6 weeks of HDM administration was confirmed by histology, bronchoalveolar lavage (BAL) cell count and lung cytokine measurements. Serum pro-inflammatory cytokines and Th2-related cytokines levels were elevated in HDM-sensitized mice. In the brain, the chemokine fractalkine was increased in the HDM group. The c-Fos protein, a marker for neuronal activity, Glial Fibrillary Acidic Protein (GFAP) and chymase, a serine protease from mast cells, were increased in the brains from mice in HDM group. Chymase expression in the brain was negatively correlated with the results of sucrose preference rate in individual mice.

CONCLUSIONS

6 weeks of intranasal HDM administration in mice to mimic the chronic status of lung inflammation in asthma, caused significant inflammatory histological changes in the lungs, and several behavioral changes consistent with depression and altered spatial memory. Chymase and c-Fos proteins were increased in the brain from HDM-treated mice, suggesting links between lung inflammation and brain mast cell activation, which could be responsible for depression-like behavior.

Asthma amplifies dementia risk: Evidence from CSF biomarkers and cognitive decline

Introduction

Evidence from epidemiology, neuroimaging, and animal models indicates that asthma adversely affects the brain, but the nature and extent of neuropathophysiological impact remain unclear.

Methods

We tested the hypothesis that asthma is a risk factor for dementia by comparing cognitive performance and cerebrospinal fluid biomarkers of glial activation/neuroinflammation, neurodegeneration, and Alzheimer's disease (AD) pathology in 60 participants with asthma to 315 non-asthma age-matched control participants (45-93 years), in a sample enriched for AD risk.

Results

Participants with severe asthma had higher neurogranin concentrations compared to controls and those with mild asthma. Positive relationships between cardiovascular risk and concentrations of neurogranin and α-synuclein were amplified in severe asthma. Severe asthma also amplified the deleterious associations that apolipoprotein E ε4 carrier status, cardiovascular risk, and phosphorylated tau181/amyloid beta42 have with rate of cognitive decline.

Discussion

Our data suggest that severe asthma is associated with synaptic degeneration and may compound risk for dementia posed by cardiovascular disease and genetic predisposition.

Highlights

Those with severe asthma showed evidence of higher dementia risk than controls evidenced by: higher levels of the synaptic degeneration biomarker neurogranin regardless of cognitive status, cardiovascular or genetic risk, and controlling for demographics.steeper increase in levels of synaptic degeneration biomarkers neurogranin and α-synuclein with increasing cardiovascular risk.accelerated cognitive decline with higher cardiovascular risk, genetic predisposition, or pathological tau.

Rates of and factors associated with atopy and allergies in posttraumatic stress disorder as compared to controls

OBJECTIVE

Several studies suggest a relationship between atopy and psychiatric disorders, but few have investigated the association between atopic conditions and posttraumatic stress disorder (PTSD). We sought to compare the rates of atopy and allergies in a South African case-control study of 220 patients with PTSD (mean age 41.7 years, SD = 11.7) and 196 trauma exposed controls (TEC, mean age 45.4 years, SD = 14.7) conducted in Cape Town, South Africa from May 2014 to June 2017.

METHODS

Self-reported atopic conditions and allergies were regressed on PTSD, as determined with the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5), in multivariate logistic regression models, controlling for age, gender, body mass index, physical activity, lifetime and childhood trauma, and time since index trauma.

RESULTS

Rates of lifetime atopy (p = 0.03), current asthma (p = 0.04), lifetime allergic rhinitis (p = 0.002), and current allergic rhinitis (p = 0.004) were significantly higher in patients than TEC on bivariate analysis. On multivariate analysis, rates of current atopy (Cohen's d = 0.26, p = 0.04) and current allergic rhinitis (Cohen's d = 0.34, p = 0.012) were significantly higher in patients with PTSD than in TEC. Current eczema (p = 0.24), current asthma (p = 0.26), and allergies (p = 0.59) were not associated with PTSD.

CONCLUSIONS

Rates of atopy are higher in participants with PTSD than TEC, and this effect is related to higher rates of allergic rhinitis. Further studies are needed to elucidate the pathways linking allergic rhinitis and PTSD.

Targeting the Adaptive Immune System in Depression: Focus on T Helper 17 Cells

There is a vital need to understand mechanisms contributing to susceptibility to depression to improve treatments for the 11% of Americans who currently suffer from this debilitating disease. The adaptive immune system, comprising T and B cells, has emerged as a potential contributor to depression, as demonstrated in the context of lymphopenic mice. Overall, patients with depression have reduced circulating T and regulatory B cells, "immunosuppressed" T cells, and alterations in the relative abundance of T cell subtypes. T helper (Th) cells have the capacity to differentiate to various lineages depending on the cytokine environment, antigen stimulation, and costimulation. Regulatory T cells are decreased, and the Th1/Th2 ratio and the Th17 cells are increased in patients with depression. Evidence for changes in each Th lineage has been reported to some extent in patients with depression. However, the evidence is strongest for the association of depression with changes in Th17 cells. Th17 cells produce the inflammatory cytokine interleukin (IL)-17A, and the discovery of Th17 cell involvement in depression evolved from the well established link that IL-6, which is required for Th17 cell differentiation, contributes to the onset, and possibly maintenance, of depression. One intriguing action of Th17 cells is their participation in the gut-brain axis to mediate stress responses. Although the mechanisms of action of Th17 cells in depression remain unclear, neutralization of IL-17A by anti-IL-17A antibodies, blocking stress-induced production, or release of gut Th17 cells represent feasible therapeutic approaches and might provide a new avenue to improve depression symptoms. SIGNIFICANCE STATEMENT: Th17 cells appear as a promising therapeutic target for depression, for which efficacious therapeutic options are limited. The use of neutralizing antibodies targeting Th17 cells has provided encouraging results in depressed patients with comorbid autoimmune diseases.

Anxiety, depression, and asthma: New perspectives and approaches for psychoneuroimmunology research

The field of psychoneuroimmunology has advanced the understanding of the relationship between immunology and mental health. More work can be done to advance the field by investigating the connection between internalizing disorders and persistent airway inflammation from asthma and air pollution exposure. Asthma is a prominent airway condition that affects about 10% of developing youth and 7.7% of adults in the United States. People who develop with asthma are at three times increased risk to develop internalizing disorders, namely anxiety and depression, compared to people who do not have asthma while developing. Interestingly, sex differences also exist in asthma prevalence and internalizing disorder development that differ based on age. Exposure to air pollution also is associated with increased asthma and internalizing disorder diagnoses. New perspectives of how chronic inflammation affects the brain could provide more understanding into internalizing disorder development. This review on how asthma and air pollution cause chronic airway inflammation details recent preclinical and clinical research that begins to highlight potential mechanisms that drive comorbidity with internalizing disorder symptoms. These findings provide a foundation for future studies to identify therapies that can simultaneously treat asthma and internalizing disorders, thus potentially decreasing mental health diagnoses in asthma patients.

Asthma and posttraumatic stress disorder (PTSD): Emerging links, potential models and mechanisms

Posttraumatic stress disorder (PTSD) is a highly prevalent, debilitating mental health condition. A better understanding of contributory neurobiological mechanisms will lead to effective treatments, improving quality of life for patients. Given that not all trauma-exposed individuals develop PTSD, identification of pre-trauma susceptibility factors that can modulate posttraumatic outcomes is important. Recent clinical evidence supports a strong link between inflammatory conditions and PTSD. A particularly strong association has been reported between asthma and PTSD prevalence and severity. Unlike many other PTSD-comorbid inflammatory conditions, asthma often develops in children, sensitizing them to subsequent posttraumatic pathology throughout their lifetime. Currently, there is a significant need to understand the neurobiology, shared mechanisms, and inflammatory mediators that may contribute to comorbid asthma and PTSD. Here, we provide a translational perspective of asthma and PTSD risk and comorbidity, focusing on clinical associations, relevant rodent paradigms and potential mechanisms that may translate asthma-associated inflammation to PTSD development.

Peri-adolescent asthma: Acute impacts on innate immune response, corticosterone, and microglia in mice

Asthma is highly comorbid with anxiety in youth. We investigated the hypothalamic-pituitary-adrenal (HPA) axis and microglia as mechanisms underlying asthma and anxiety comorbidity. We induced asthma symptoms in developing BALB/cJ mice with house dust mite (HDM) for airway inflammation and methacholine (MCH) for bronchoconstriction. On the last day of exposure, we analyzed samples at six timepoints. Lung IL-5 and IL-1β expression peaked 4 h after final HDM exposure. Circulating corticosterone was blunted in a sex- and treatment-specific temporal pattern. Hippocampal IL-1β expression and microglial area were marginally increased 24 h after MCH exposure. These results provide a foundation for further work investigating asthma-anxiety mechanisms.