Increased hypothalamic microglial activation after viral-induced pneumococcal lung infection is associated with excess serum amyloid A production

Biological agents and the aging brain: glial inflammation and neurotoxic signaling

Neuroinflammation is a universal characteristic of brain aging and neurological disorders, irrespective of the disease state. Glial inflammation mediates this signaling, through astrocyte and microglial polarization from neuroprotective to neurotoxic phenotypes. Glial reactivity results in the loss of homeostasis, as these cells no longer provide support to neurons, in addition to the production of chronically toxic pro-inflammatory mediators. These glial changes initiate an inflammatory brain state that injures the central nervous system (CNS) over time. As the brain ages, glia are altered, including increased glial cell numbers, morphological changes, and either a pre-disposition or inability to become reactive. These alterations induce age-related neuropathologies, ultimately leading to neuronal degradation and irreversible damage associated with disorders of the aged brain, including Alzheimer's Disease (AD) and other related diseases. While the complex interactions of these glial cells and the brain are well studied, the role additional stressors, such as infectious agents, play on age-related neuropathology has not been fully elucidated. Both biological agents in the periphery, such as bacterial infections, or in the CNS, including viral infections like SARS-CoV-2, push glia into neuroinflammatory phenotypes that can exacerbate pathology within the aging brain. These biological agents release pattern associated molecular patterns (PAMPs) that bind to pattern recognition receptors (PRRs) on glial cells, beginning an inflammatory cascade. In this review, we will summarize the evidence that biological agents induce reactive glia, which worsens age-related neuropathology.

Decoding the neurocircuitry of gut feelings: Region-specific microbiome-mediated brain alterations

Research in the last decade has unveiled a crucial role for the trillions of microorganisms that reside in the gut in influencing host neurodevelopment across the lifespan via the microbiota-gut-brain axis. Studies have linked alterations in the composition, complexity, and diversity of the gut microbiota to changes in behaviour including abnormal social interactions, cognitive deficits, and anxiety- and depressive-like phenotypes. Moreover, the microbiota has been linked with neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. Interestingly, there appears to be specific brain regions governing the neurocircuitry driving higher cognitive function that are susceptible to influence from manipulations to the host microbiome. This review will aim to elucidate the region-specific effects mediated by the gut microbiota, with a focus on translational animal models and some existing human neuroimaging data. Compelling preclinical evidence suggests disruption to normal microbiota-gut-brain signalling can have detrimental effects on the prefrontal cortex, amygdala, hippocampus, hypothalamus, and striatum. Furthermore, human neuroimaging studies have unveiled a role for the microbiota in mediating functional connectivity and structure of specific brain regions that can be traced back to neurocognition and behavioural output. Understanding these microbiota-mediated changes will aid in identifying unique therapeutic targets for treating neurological disorders associated with these regions.

Inflammation and the role of infection: Complications and treatment options following neurotrauma

Traumatic brain injury can have devastating consequences for patients and extended hospital stays and recovery course. Recent data indicate that the initial insult causes profound changes to the immune system and leads to a pro-inflammatory state. This alteration in homeostasis predisposes patients to an increased risk of infection and underlying autoimmune conditions. Increased emphasis has been placed on understanding this process both in the clinical and preclinical literature. This review highlights the intrinsic inflammatory conditions that can occur within the initial hospital stay, discusses long-term immune consequences, highlights emerging treatment options, and delves into important pathways currently being investigated with preclinical models.

Peripheral Pathways to Neurovascular Unit Dysfunction, Cognitive Impairment, and Alzheimer’s Disease

Alzheimer’s disease (AD) is the most common form of dementia. It was first described more than a century ago, and scientists are acquiring new data and learning novel information about the disease every day. Although there are nuances and details continuously being unraveled, many key players were identified in the early 1900’s by Dr. Oskar Fischer and Dr. Alois Alzheimer, including amyloid-beta (Aβ), tau, vascular abnormalities, gliosis, and a possible role of infections. More recently, there has been growing interest in and appreciation for neurovascular unit dysfunction that occurs early in mild cognitive impairment (MCI) before and independent of Aβ and tau brain accumulation. In the last decade, evidence that Aβ and tau oligomers are antimicrobial peptides generated in response to infection has expanded our knowledge and challenged preconceived notions. The concept that pathogenic germs cause infections generating an innate immune response (e.g., Aβ and tau produced by peripheral organs) that is associated with incident dementia is worthwhile considering in the context of sporadic AD with an unknown root cause. Therefore, the peripheral amyloid hypothesis to cognitive impairment and AD is proposed and remains to be vetted by future research. Meanwhile, humans remain complex variable organisms with individual risk factors that define their immune status, neurovascular function, and neuronal plasticity. In this focused review, the idea that infections and organ dysfunction contribute to Alzheimer’s disease, through the generation of peripheral amyloids and/or neurovascular unit dysfunction will be explored and discussed. Ultimately, many questions remain to be answered and critical areas of future exploration are highlighted.

House Dust Mite Aeroallergen Suppresses Leukocyte Phagocytosis and Netosis Initiated by Pneumococcal Lung Infection

Asthmatics are highly susceptible to developing lower respiratory tract infections caused by Streptococcus pneumoniae (SPN, the pneumococcus). It has recently emerged that underlying allergic airway disease creates a lung microenvironment that is defective in controlling pneumococcal lung infections. In the present study, we examined how house dust mite (HDM) aeroallergen exposure altered immunity to acute pneumococcal lung infection. Alveolar macrophage (AM) isolated from HDM-exposed mice expressed alternatively activated macrophage (AAM) markers including YM1, FIZZ1, IL-10, and ARG-1. In vivo, prior HDM exposure resulted in accumulation of AAMs in the lungs and 2-log higher bacterial titres in the bronchoalveolar (BAL) fluid of SPN-infected mice (Day 2). Acute pneumococcal infection further increased the expression of IL-10 and ARG1 in the lungs of HDM-exposed mice. Moreover, prior HDM exposure attenuated neutrophil extracellular traps (NETs) formation in the lungs and dsDNA levels in the BAL fluid of SPN-infected mice. In addition, HDM-SPN infected animals had significantly increased BAL fluid cellularity driven by an influx of macrophages/monocytes, neutrophils, and eosinophils. Increased lung inflammation and mucus production was also evident in HDM-sensitised mice following acute pneumococcal infection, which was associated with exacerbated airway hyperresponsiveness. Of note, PCV13 vaccination modestly reduced pneumococcal titres in the BAL fluid of HDM-exposed animals and did not prevent BAL inflammation. Our findings provide new insights on the relationship between pneumococcal lung infections and allergic airways disease, where defective AM phagocytosis and NETosis are implicated in increased susceptibility to pneumococcal infection.

Continuous humidification enhances postoperative recovery in laryngeal cancer patients undergoing tracheotomy

OBJECTIVE

To investigate the effects of perioperative continuous humidification on patients with laryngeal cancer undergoing tracheotomy.

METHODS

Eighty patients with laryngeal cancer underwent tracheotomy in our hospital were selected as the subjects and divided into the observation group and the control group according to random table method. Patients in the control group were given routine tracheotomy care, including regular open endotracheal suction, tracheotomy nursing, oral care, dietary intervention, etc., while those in the observation group were given continuous airway humidification on the basis of the control group. The differences in sputum pH, viscosity, comfort, cough frequency, and respiratory ventilation were compared between the two groups at three postoperative time points. The incidence of complications such as pulmonary infection, bloody sputum and sputum crust, and the improvement of clinical symptoms were compared between the two groups.

RESULTS

The sputum pH of patients in the observation group was higher than that in the control group at the 4th and 7th postoperative days (P<0.001). The observation group showed significantly lower percentage of grade 3 viscous sputum and higher comfort scores than the control group at the 7th postoperative day (P=0.020, P<0.001). The observation group showed lower cough frequency and higher airway patency than the control group at the 4th and 7th postoperative days (P<0.001, P<0.001, P<0.001, P=0.007).

CONCLUSION

Perioperative continuous airway humidification in patients with laryngeal cancer undergoing tracheotomy could reduce sputum consistency and cough frequency, improve comfort and respiratory patency of patients, and has positive significance in accelerating their postoperative rehabilitation.

Long-term diet-induced obesity does not lead to learning and memory impairment in adult mice

Obesity arising from excessive dietary fat intake is a risk factor for cognitive decline, dementia and neurodegenerative diseases, including Alzheimer’s disease. Here, we studied the effect of long-term high-fat diet (HFD) (24 weeks) and return to normal diet (ND) on behavioral features, microglia and neurons in adult male C57BL/6J mice. Consequences of HFD-induced obesity and dietary changes on general health (coat appearance, presence of vibrissae), sensory and motor reflexes, learning and memory were assessed by applying a phenotypic assessment protocol, the Y maze and Morris Water Maze test. Neurons and microglia were histologically analyzed within the mediobasal hypothalamus, hippocampus and frontal motor cortex after long-term HFD and change of diet. Long periods of HFD caused general health issues (coat alterations, loss of vibrissae), but did not affect sensory and motor reflexes, emotional state, memory and learning. Long-term HFD increased the microglial response (increased Iba1 fluorescence intensity, percentage of Iba1-stained area and Iba1 gene expression) within the hypothalamus, but not in the cortex and hippocampus. In neither of these regions, neurodegeneration or intracellular lipid droplet accumulation was observed. The former alterations were reversible in mice whose diet was changed from HFD to ND. Taken together, long periods of excessive dietary fat alone do not cause learning deficits or spatial memory impairment, though HFD-induced obesity may have detrimental consequences for cognitive flexibility. Our data confirm the selective responsiveness of hypothalamic microglia to HFD.

Aspirin-Triggered Resolvin D1 Reduces Proliferation and the Neutrophil to Lymphocyte Ratio in a Mutant KRAS-Driven Lung Adenocarcinoma Model

Simple Summary

Aspirin-triggered resolvin D1 (AT-RvD1) is biosynthesised by leukocytes as a mechanism to resolve inflammation during infection and/or injury. Emerging studies reveal that AT-RvD1 also has anti-cancer properties associated with stimulating macrophage-mediated clearance of tumour debris. No study to date has investigated how AT-RvD1 influences the neutrophil to lymphocyte ratio (NLR) in lung cancer, an established marker of poor prognosis. The biosynthesis of AT-RvD1 is dependent on the ALOX5 gene, and we reveal that ALOX5 mRNA expression was markedly reduced in lung adenocarcinoma tumours. We next utilised an oncogenic Kras^G12D lung adenocarcinoma mouse model to investigate the efficacy of AT-RvD1 in vivo. We show for the first time that AT-RvD1 reduces tumour growth in the lungs of Kras^G12D mice and alters the immune landscape in tumours by reducing the NLR.

Abstract

Tumour-associated neutrophils (TANs) can support tumour growth by suppressing cytotoxic lymphocytes. AT-RvD1 is an eicosanoid that can antagonise neutrophil trafficking instigated by ALX/FPR2 ligands such as serum amyloid A (SAA). We aimed to establish whether SAA and ALOX5 expression associates with TANs and investigate the immunomodulatory actions of AT-RvD1 in vivo. MPO-positive neutrophils were quantified in tumour blocks from lung adenocarcinoma (n = 48) and control tissue (n = 20) by IHC. Tumour expression of SAA and ALOX5 were analysed by RTqPCR and an oncogenic Kras^G12D lung adenocarcinoma mouse model was used to investigate the in vivo efficacy of AT-RvD1 treatment. ALOX5 expression was markedly reduced in lung adenocarcinoma tumours. The SAA/ALOX5 ratio strongly correlated with TANs and was significantly increased in tumours harbouring an oncogenic KRAS mutation. AT-RvD1 treatment reduced tumour growth in Kras^G12D mice, which was accompanied by suppressed cellular proliferation within parenchymal lesions. In addition, AT-RvD1 significantly reduced the neutrophil to lymphocyte ratio (NLR), an established prognostic marker of poor survival in adenocarcinoma. This study identifies a novel molecular signature whereby elevated levels of SAA relative to ALOX5 favour accumulation of TANs. Furthermore, the ALOX5/5-LO enzymatic product, AT-RvD1, markedly reduced the NLR and suppressed tumour growth in Kras^G12D mice.

Role of microbiota-gut-brain axis dysfunctions induced by infections in the onset of anorexia nervosa

Anorexia nervosa (AN) is an eating disorder characterized by low food intake, severe body weight loss, intense fear of gaining weight, and dysmorphophobia. This chronic disease is associated with both psychiatric and somatic comorbidities. Over the years, clinical studies have accumulated evidence that viral or bacterial infections may promote the onset of eating disorders such as AN. This review aims to describe how infections and the subsequent immune responses affect food intake regulation in the short term and also how these processes may lead to long-term intestinal disorders, including gut barrier disruption and gut microbiota dysbiosis, even after the clearance of the pathogens. We discuss in particular how infection-mediated intestinal dysbiosis may promote the onset of several AN symptoms and comorbidities, including appetite dysregulation, functional gastrointestinal disorders, and mood disorders.

Serum Amyloid A Aggravates Lipopolysaccharide-Induced Injury of BEAS-2B Cells by Activating Toll-Like Receptor 2/Activator Protein-1 Signaling

The serum amyloid A (sAA) is a common sensitive indicator for the diagnosis of infectious diseases, and sAA levels are increased in pneumonia. However, the detailed molecular mechanism is unknown. Previous studies have demonstrated the participation of Toll-like receptor (TLR) 2 and its downstream protein activator protein-1 (AP-1) in inflammatory lung injury. This study aimed to investigate the effect of sAA on LPS-induced BEAS-2B cells injury and uncover the possible mechanism. The human bronchial epithelial cell line BEAS-2B was exposed to sAA with or without lipopolysaccharide (LPS) treatment, then cell viability, inflammation and apoptosis were evaluated. The effects of TLR2 knockout on sAA + LPS-treated BEAS-2B cells were also determined. Results revealed that sAA treatment reduced cell viability in a concentration-dependent manner and the effect of 500 nM sAA on cell viability was approximately equivalent to LPS. The levels of inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-8, monocyte chemotactic protein (MCP)-1 and IL-6 as well as cell apoptosis and expression of proteins related to apoptosis were significantly increased upon sAA or LPS stimulation. The expression of TLR2 and AP-1 was also elevated in cells challenged with sAA or LPS. Besides, sAA and LPS co-treatment further enhanced the actions of LPS. However, the knockdown of TLR2 obviously blunted the effects of LPS and sAA co-treatment on cell viability, inflammation and apoptosis. Taken together, our results revealed that sAA could exert an enhanced effect on LPS-induced BEAS-2B cells injury via promoting TLR2/AP-1 expression.

Pulmonary arterial hypertension-associated changes in gut pathology and microbiota

Emerging evidence implicates an interplay among multiple organs such as brain, vasculature, gut and lung in the development of established pulmonary arterial hypertension (PAH). This has led us to propose that activated microglia mediated-enhanced sympathetic activation contributes to PAH pathophysiology. Since enhanced sympathetic activity is observed in human PAH and the gut is highly innervated by sympathetic nerves that regulate its physiological functions, we hypothesized that PAH would be associated with gut pathophysiology. A monocrotaline rat model of PAH was utilized to investigate the link between gut pathology and PAH. Haemodynamics, histology, immunocytochemistry and 16S RNA gene sequencing were used to assess cardiopulmonary functions, gut pathology and gut microbial communities respectively. Monocrotaline treatment caused increased right ventricular systolic pressure, haemodynamics and pathological changes associated with PAH. PAH animals also showed profound gut pathology that included increased intestinal permeability, increased muscularis layer, decreased villi length and goblet cells. These changes in gut pathology were associated with alterations in microbial communities, some unique to PAH animals. Furthermore, enhanced gut-neural communication involving the paraventricular nucleus of the hypothalamus and increased sympathetic drive were observed. In conclusion, our data show the presence of gut pathology and distinct changes in gut microbiota and increased sympathetic activity in PAH. They suggest that dysfunctional gut-brain crosstalk could be critical in PAH and considered a future therapeutic target for PAH.

Excessive Reactive Oxygen Species Inhibit IL-17A+ γδ T Cells and Innate Cellular Responses to Bacterial Lung Infection

Aims: Excessive reactive oxygen species (ROS) are detrimental to immune cellular functions that control pathogenic microbes; however, the mechanisms are poorly understood. Our aim was to determine the immunological consequences of increased ROS levels during acute bacterial infection. Results: We used a model of Streptococcus pneumoniae (Spn) lung infection and superoxide dismutase 3-deficient (SOD3^-/-) mice, as SOD3 is a major antioxidant enzyme that catalyses the dismutation of superoxide radicals. First, we observed that in vitro, macrophages from SOD3^-/- mice generated excessive phagosomal ROS during acute bacterial infection. In vivo, there was a significant reduction in infiltrating neutrophils in the bronchoalveolar lavage fluid and reduced peribronchial and alveoli inflammation in SOD3^-/- mice 2 days after Spn infection. Annexin V/propidium iodide staining revealed enhanced apoptosis in neutrophils from Spn-infected SOD3^-/- mice. In addition, SOD3^-/- mice showed an altered macrophage phenotypic profile, with markedly diminished recruitment of monocytes (CD11c^lo, CD11b^hi) in the airways. Further investigation revealed significantly lower levels of the monocyte chemokine CCL-2, and cytokines IL-23, IL-1β, and IL-17A in Spn-infected SOD3^-/- mice. There were also significantly fewer IL-17A-expressing gamma-delta T cells (γδ T cells) in the lungs of Spn-infected SOD3^-/- mice. Innovation: Our data demonstrate that SOD3 deficiency leads to an accumulation of phagosomal ROS levels that initiate early neutrophil apoptosis during pneumococcal infection. Consequent to these events, there was a failure to initiate innate γδ T cell responses. Conclusion: These studies offer new cellular and mechanistic insights into how excessive ROS can regulate innate immune responses to bacterial infection.

Interleukin-6 Expression by Hypothalamic Microglia in Multiple Inflammatory Contexts: A Systematic Review

Interleukin-6 (IL-6) is a unique cytokine that can play both pro- and anti-inflammatory roles depending on the anatomical site and conditions under which it has been induced. Specific neurons of the hypothalamus provide important signals to control food intake and energy expenditure. In individuals with obesity, a microglia-dependent inflammatory response damages the neural circuits responsible for maintaining whole-body energy homeostasis, resulting in a positive energy balance. However, little is known about the role of IL-6 in the regulation of hypothalamic microglia. In this systematic review, we asked what types of conditions and stimuli could modulate microglial IL-6 expression in murine model. We searched the PubMed and Web of Science databases and analyzed 13 articles that evaluated diverse contexts and study models focused on IL-6 expression and microglia activation, including the effects of stress, hypoxia, infection, neonatal overfeeding and nicotine exposure, lipopolysaccharide stimulus, hormones, exercise protocols, and aging. The results presented in this review emphasized the role of "injury-like" stimuli, under which IL-6 acts as a proinflammatory cytokine, concomitant with marked microglial activation, which drive hypothalamic neuroinflammation. Emerging evidence indicates an important correlation of basal IL-6 levels and microglial function with the maintenance of hypothalamic homeostasis. Advances in our understanding of these different contexts will lead to the development of more specific pharmacological approaches for the management of acute and chronic conditions, like obesity and metabolic diseases, without disturbing the homeostatic functions of IL-6 and microglia in the hypothalamus.

Development and validation of a simplified method to generate human microglia from pluripotent stem cells

BACKGROUND

Microglia, the principle immune cells of the brain, play important roles in neuronal development, homeostatic function and neurodegenerative disease. Recent genetic studies have further highlighted the importance of microglia in neurodegeneration with the identification of disease risk polymorphisms in many microglial genes. To better understand the role of these genes in microglial biology and disease, we, and others, have developed methods to differentiate microglia from human induced pluripotent stem cells (iPSCs). While the development of these methods has begun to enable important new studies of microglial biology, labs with little prior stem cell experience have sometimes found it challenging to adopt these complex protocols. Therefore, we have now developed a greatly simplified approach to generate large numbers of highly pure human microglia.

RESULTS

iPSCs are first differentiated toward a mesodermal, hematopoietic lineage using commercially available media. Highly pure populations of non-adherent CD43⁺ hematopoietic progenitors are then simply transferred to media that includes three key cytokines (M-CSF, IL-34, and TGFβ-1) that promote differentiation of homeostatic microglia. This updated approach avoids the prior requirement for hypoxic incubation, complex media formulation, FACS sorting, or co-culture, thereby significantly simplifying human microglial generation. To confirm that the resulting cells are equivalent to previously developed iPSC-microglia, we performed RNA-sequencing, functional testing, and transplantation studies. Our findings reveal that microglia generated via this simplified method are virtually identical to iPS-microglia produced via our previously published approach. To also determine whether a small molecule activator of TGFβ signaling (IDE1) can be used to replace recombinant TGFβ1, further reducing costs, we examined growth kinetics and the transcriptome of cells differentiated with IDE1. These data demonstrate that a microglial cell can indeed be produced using this alternative approach, although transcriptional differences do occur that should be considered.

CONCLUSION

We anticipate that this new and greatly simplified protocol will enable many interested labs, including those with little prior stem cell or flow cytometry experience, to generate and study human iPS-microglia. By combining this method with other advances such as CRISPR-gene editing and xenotransplantation, the field will continue to improve our understanding of microglial biology and their important roles in human development, homeostasis, and disease.

Commentary on the 2018 Named Series on blood-brain interfaces: Roles of neuroimmunomodulation in health and disease

This year's 2018 Named Series on blood-brain interfaces highlights the importance of brain barriers as mediators of neuroimmune communication and regulators of neurological function. The term "brain interfaces" reflects our growing understanding that brain barriers such as the blood-brain barrier (BBB) and blood-CSF barrier (BCSFB) are not only gatekeepers, but facilitators of bidirectional communication between the brain and periphery. There is also an emerging appreciation that CNS sites that are exposed to blood-borne immune molecules and cells, such as the leptomeninges and circumventricular organs, may also be considered brain interfaces with important homeostatic and pathological functions. The work featured in this Series covers novel aspects of brain interface functions that focus on mechanisms regulating barrier integrity and transporter activities, downstream consequences of neurovascular injury, peripheral organ infection/injury, and clearance of pathogenic proteins. Results of these studies have emphasized new mechanisms by which brain interface dysfunction could contribute to neuroinflammation and CNS damage in eclampsia, fetal and adult hypoxic/ischemic injury, traumatic brain injury, Helicobacter infections, acute lung injury, multiple sclerosis, and Alzheimer's disease. This body of work emphasizes that brain interfaces may themselves be important therapeutic targets for a variety of CNS diseases that are associated with immune dyshomeostasis. Future works are warranted to further investigate brain interface functions in health and disease.

Resolving Viral-Induced Secondary Bacterial Infection in COPD: A Concise Review

Chronic obstructive pulmonary disease (COPD) is a leading cause of disability and death world-wide, where chronic inflammation accelerates lung function decline. Pathological inflammation is worsened by chronic bacterial lung infections and susceptibility to recurrent acute exacerbations of COPD (AECOPD), typically caused by viral and/or bacterial respiratory pathogens. Despite ongoing efforts to reduce AECOPD rates with inhaled corticosteroids, COPD patients remain at heightened risk of developing serious lung infections/AECOPD, frequently leading to hospitalization and infection-dependent delirium. Here, we review emerging mechanisms into why COPD patients are susceptible to chronic bacterial infections and highlight dysregulated inflammation and production of reactive oxygen species (ROS) as central causes. This underlying chronic infection leaves COPD patients particularly vulnerable to acute viral infections, which further destabilize host immunity to bacteria. The pathogeneses of bacterial and viral exacerbations are significant as clinical symptoms are more severe and there is a marked increase in neutrophilic inflammation and tissue damage. AECOPD triggered by a bacterial and viral co-infection increases circulating levels of the systemic inflammatory marker, serum amyloid A (SAA). SAA is a functional agonist for formyl peptide receptor 2 (FPR2/ALX), where it promotes chemotaxis and survival of neutrophils. Excessive levels of SAA can antagonize the protective actions of FPR2/ALX that involve engagement of specialized pro-resolving mediators, such as resolvin-D1. We propose that the anti-microbial and anti-inflammatory actions of specialized pro-resolving mediators, such as resolvin-D1 should be harnessed for the treatment of AECOPD that are complicated by the co-pathogenesis of viruses and bacteria.