There is growing evidence that excessive microglial phagocytosis of neurons and synapses contributes to multiple brain pathologies. RNA‐seq and genome‐wide association (GWAS) studies have linked ...multiple phagocytic genes to neurodegenerative diseases, and knock‐out of phagocytic genes has been found to protect against neurodegeneration in animal models, suggesting that excessive microglial phagocytosis contributes to neurodegeneration. Here, we review recent evidence that microglial phagocytosis of live neurons and synapses causes neurodegeneration in animal models of Alzheimer's disease and other tauopathies, Parkinson's disease, frontotemporal dementias, multiple sclerosis, retinal degeneration and neurodegeneration induced by ischaemia, infection or ageing. We also review factors regulating microglial phagocytosis of neurons, including: nucleotides, frackalkine, phosphatidylserine, calreticulin, UDP, CD47, sialylation, complement, galectin‐3, Apolipoprotein E, phagocytic receptors, Siglec receptors, cytokines, microglial epigenetics and expression profile. Some of these factors may be potential treatment targets to prevent neurodegeneration mediated by excessive microglial phagocytosis of live neurons and synapses.
Microglia are the brain's main phagocytes and can phagocytose both live and dead neurons, as well as synapses, dendrites and axons. We review here how this microglial phagocytosis is regulated, and the evidence that microglial phagocytosis of live neurons and synapses may contribute to neurodegeneration. During neurodegenerative disease, neurons, dendrites or synapses may become stressed by aggregated proteins, neuroinflammation, oxidants, energy depletion or excitotoxicity, resulting in release of opsonins, find‐me and eat‐me signals, inducing their phagocytosis by activated microglia. Thus, blocking this signalling and phagocytosis may help prevent neurodegeneration.
Increasing evidence suggests that asthma is a heterogeneous disorder regulated by distinct molecular mechanisms. In a cross-sectional study of asthmatics of varying severity (n = 51), endobronchial ...tissue gene expression analysis revealed three major patient clusters: TH2-high, TH17-high, and TH2/17-low. TH2-high and TH17-high patterns were mutually exclusive in individual patient samples, and their gene signatures were inversely correlated and differentially regulated by interleukin-13 (IL-13) and IL-17A. To understand this dichotomous pattern of T helper 2 (TH2) and TH17 signatures, we investigated the potential of type 2 cytokine suppression in promoting TH17 responses in a preclinical model of allergen-induced asthma. Neutralization of IL-4 and/or IL-13 resulted in increased TH17 cells and neutrophilic inflammation in the lung. However, neutralization of IL-13 and IL-17 protected mice from eosinophilia, mucus hyperplasia, and airway hyperreactivity and abolished the neutrophilic inflammation, suggesting that combination therapies targeting both pathways may maximize therapeutic efficacy across a patient population comprising both TH2 and TH17 endotypes.
Triggering receptor on myeloid cells 2 (TREM2) is an innate immune receptor, upregulated on the surface of microglia associated with amyloid plaques in Alzheimer's disease (AD). Individuals ...heterozygous for the R47H variant of TREM2 have greatly increased risk of developing AD. We examined the effects of wild‐type (WT), R47H and knock‐out (KO) of human TREM2 expression in three microglial cell systems. Addition of mouse BV‐2 microglia expressing R47H TREM2 to primary mouse neuronal cultures caused neuronal loss, not observed with WT TREM2. Neuronal loss was prevented by using annexin V to block exposed phosphatidylserine, an eat‐me signal and ligand of TREM2, suggesting loss was mediated by microglial phagocytosis of neurons exposing phosphatidylserine. Addition of human CHME‐3 microglia expressing R47H TREM2 to LUHMES neuronal‐like cells also caused loss compared to WT TREM2. Expression of R47H TREM2 in BV‐2 and CHME‐3 microglia increased their uptake of phosphatidylserine‐beads and synaptosomes versus WT TREM2. Human iPSC‐derived microglia with heterozygous R47H TREM2 had increased phagocytosis of synaptosomes vs common‐variant TREM2. Additionally, phosphatidylserine liposomes increased activation of human iPSC‐derived microglia expressing homozygous R47H TREM2 versus common‐variant TREM2. Finally, overexpression of TREM2 in CHME‐3 microglia caused increased expression of cystatin F, a cysteine protease inhibitor, and knock‐down of cystatin F increased CHME‐3 uptake of phosphatidylserine‐beads. Together, these data suggest that R47H TREM2 may increase AD risk by increasing phagocytosis of synapses and neurons via greater activation by phosphatidylserine and that WT TREM2 may decrease microglial phagocytosis of synapses and neurons via cystatin F.
Main Points
R47H TREM2 variant, linked to Alzheimer's disease, increases neuronal loss and microglial phagocytosis likely via increased activation by phosphatidylserine.
TREM2 increases cystatin F expression which inhibits general microglial phagocytosis.
Despite increased clinician awareness, nonadherence to inhaled corticosteroid treatment presents a major challenge to successful asthma management and risks inappropriate treatment escalation, ...particularly in severe disease. In patients with Type-2 mediated biology, fractional exhaled nitric oxide (FeNO) has a role in assessment and monitoring of adherence to inhaled corticosteroids.
Asthmatic patients with elevated FeNO are at an increased risk of exacerbation. High FeNO is often secondary to suboptimal adherence to inhaled corticosteroid treatment, whether intentional or nonintentional. FENO-suppression can 'unmask' underlying adherence issues and is a useful test in the presence of Type-2 biology in the 'difficult-to-control' asthma population. Identification of nonadherence can improve asthma control and prevent inappropriate commencement of costly biologic therapies.
Assessment of adherence and FeNO response to monitored inhaled corticosteroid in Type-2 biomarker high asthmatic individuals may prevent unnecessary escalation to biologic therapy. Establishing an 'optimised' FeNO may alert clinicians to the possibility of underlying nonadherence at future clinical assessments.
Background The airway epithelium is exposed to a range of physical and chemical irritants in the environment that are known to trigger asthma. Transient receptor potential (TRP) cation channels play ...a central role in sensory responses to noxious physical and chemical stimuli. Recent genetic evidence suggests an involvement of transient receptor potential vanilloid 1 (TRPV1), one member of the vanilloid subfamily of TRP channels, in the pathophysiology of asthma. The functional expression of TRPV1 on airway epithelium has yet to be elucidated. Objective In this study we examined the molecular, functional, and immunohistochemical expression of TRPV1 in asthmatic and healthy airways. Methods Bronchial biopsy specimens and bronchial brushings were obtained from healthy volunteers (n = 18), patients with mild-to-moderate asthma (n = 24), and patients with refractory asthma (n = 22). Cultured primary bronchial epithelial cells from patients with mild asthma (n = 4), nonasthmatic coughers (n = 4), and healthy subjects (n = 4) were studied to investigate the functional role of TRPV1. Results Quantitative immunohistochemistry revealed significantly more TRPV1 expression in asthmatic patients compared with healthy subjects, with the greatest expression in patients with refractory asthma ( P = .001). PCR and Western blotting analysis confirmed gene and protein expression of TRPV1 in cultured primary bronchial epithelial cells. Patch-clamp electrophysiology directly confirmed functional TRPV1 expression in all 3 groups. In functional assays the TRPV1 agonist capsaicin induced dose-dependent IL-8 release, which could be blocked by the antagonist capsazepine. Reduction of external pH from 7.4 to 6.4 activated a capsazepine-sensitive outwardly rectifying membrane current. Conclusions Functional TRPV1 channels are present in the human airway epithelium and overexpressed in the airways of patients with refractory asthma. These channels might represent a novel therapeutic target for the treatment of uncontrolled asthma.
Calreticulin is a chaperone, normally found in the endoplasmic reticulum, but can be released by macrophages into the extracellular medium. It is also found in cerebrospinal fluid bound to amyloid ...beta (Aβ). We investigated whether brain cells release calreticulin, and whether extracellular calreticulin had any effects on microglia and neurons relevant to neuroinflammation and neurodegeneration. We found that microglia release nanomolar levels of calreticulin when inflammatory-activated with lipopolysaccharide, when endoplasmic reticulum stress was induced by tunicamycin, or when cell death was induced by staurosporine, and that neurons release calreticulin when crushed. Addition of nanomolar levels of extracellular calreticulin was found to chemoattract microglia, and activate microglia to release cytokines TNF-α, IL-6 and IL-1β, as well as chemokine (C-C motif) ligand 2. Calreticulin blocked Aβ fibrillization and modified Aβ oligomerization, as measured by thioflavin T fluorescence and transmission electron microscopy. Extracellular calreticulin also altered microglial morphology and proliferation, and prevented Aβ-induced neuronal loss in primary neuron-glial cultures. Thus, calreticulin is released by microglia and neurons, and acts: as an alarmin to recruit and activate microglia, as an extracellular chaperone to prevent Aβ aggregation, and as a neuroprotectant against Aβ neurotoxicity.
The rate of elongation and thickening of individual branches (shoots) varies across plant species. This variation is important for the outcome of competition and other plant–plant interactions. Here, ...we compared rates of shoot growth across 44 species from tropical, warm temperate and cool temperate forests of eastern Australia.
Shoot growth rate was found to correlate with a suite of traits including the potential height of the species, xylem‐specific conductivity, leaf size, leaf area per xylem cross‐section (LA/XA), twig diameter (at 40 cm length), wood density and modulus of elasticity.
Within this suite of traits, maximum plant height was the clearest correlate of growth rates, explaining 50%–67% of the variation in growth overall (p < .0001), and 23%–32% of the variation (p < .05) in growth when holding the influence of the other traits constant. Structural equation models suggest that traits associated with “hydraulics,” “biomechanics” and the “leaf economics spectrum” represent three clearly separated axes of variation, with the hydraulic axis exhibiting the strongest alignment with height and largest independent contribution to growth (in the case of branch thickening). However, most of the capacity of these axes to predict growth was also associated with maximum height, presumably reflecting coordinated selection on multiple traits that together influence life histories.
Growth rates were not strongly correlated with leaf nitrogen or leaf mass per unit leaf area.
Correlations between growth and maximum height arose both across latitude (47%, p < .0001) and from within‐site differences between species (30%, p < .0001). Covariation between growth and maximum height was driven in part by variation in irradiance across sites as well as among canopy positions within sites (23%, p < .0001). A significant fraction of this shared variation was independent of irradiance (45%, p < .0001), reflecting intrinsic differences across species and sites.
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Reduction in glucocorticoid exposure is the primary benefit of new biologic treatments in severe asthma, but there is currently no evidence that reduction in glucocorticoid exposure corresponds to a ...proportionate reduction in associated toxicity.
To use the validated Glucocorticoid Toxicity Index (GTI) to assess change in glucocorticoid toxicity after 12 months treatment with mepolizumab, and compare toxicity change to glucocorticoid reduction and change in patient-reported outcome measures (PROMs).
A longitudinal, real-world prospective cohort of 101 consecutive patients with severe asthma commenced on mepolizumab in a specialist UK regional severe asthma clinic. GTI toxicity assessment, cumulative glucocorticoid exposure and PROMs were recorded on commencing mepolizumab (V1), and after 12 months treatment (V2).
There was significant reduction in oral glucocorticoid exposure (V1 median 4280 mg prednisolone per year (interquartile range 3083-5475 mg)
V2 2450 mg prednisolone per year (1243-3360 mg), p<0.001). Substantial improvements in individual toxicities were observed, but did not correlate with oral glucocorticoid reduction. Mean±sd GTI aggregate improvement score (AIS) was -35.7±57.8 with a wide range in toxicity change at individual patient level (AIS range -165 to +130); 70% (71 out of 101) had a reduction in toxicity (AIS <0); 3% (three out of 101) had no change (AIS=0); and 27% (27 out of 101) an increase in overall toxicity. 62% (62 out of 101) of patients met the AIS minimally clinically important difference of ≤-10, but AIS did not correlate with glucocorticoid reduction or change in PROMs.
Mepolizumab resulted in substantial oral glucocorticoid reduction, but this did not correlate with reduction in oral glucocorticoid toxicity, which varies widely at the individual patient level. Oral glucocorticoid reduction is not a comprehensive measure of response to mepolizumab.
IMPORTANCE: To be considered for a kidney transplant, patients with advanced kidney disease must participate in a formal evaluation and selection process. Little is known about how this process ...proceeds in real-world clinical settings. OBJECTIVE: To characterize the transplant evaluation process among a representative national sample of US veterans with advanced kidney disease who were referred to a kidney transplant center. DESIGN, SETTING, AND PARTICIPANTS: This qualitative study was a thematic analysis of clinician notes in the electronic health records of US veterans referred for kidney transplant evaluation. In a random sample of 4000 patients with advanced kidney disease between January 1, 2004, and December 31, 2014, cared for in the US Department of Veterans Affairs (VA) health care system, there were 211 patients who were referred to a transplant center during the follow-up period. This group was included in the qualitative analysis and was followed up until their date of death or the end of the follow-up period on October 8, 2019. MAIN OUTCOMES AND MEASURES: Dominant themes pertaining to the kidney transplant evaluation and selection process identified through thematic analysis. RESULTS: Among 211 study patients, the mean (SD) age was 57.9 (9.5) years, and 202 patients (95.7%) were male. The following 4 dominant themes regarding the transplant evaluation process emerged: (1) far-reaching and inflexible medical evaluation, in which patients were expected to complete an extensive evaluation that could have substantial physical and emotional consequences, made little accommodation for their personal values and needs, and impacted other aspects of their care; (2) psychosocial valuation, in which the psychosocial component of the transplant assessment could be subjective and intrusive and could place substantial demands on patients’ family members; (3) surveillance over compliance, in which the patients’ ability and willingness to follow medical recommendations was an important criterion for transplant candidacy and their adherence to a wide range of recommendations and treatments was closely monitored; and (4) disempowerment and lack of transparency, in which patients and their local clinicians were often unsure about what to expect during the evaluation process or about the rationale for selection decisions. For the evaluation process to proceed, local clinicians had to follow transplant center requirements even when they believed the requirements did not align with best practices or the patients’ needs. CONCLUSIONS AND RELEVANCE: In this qualitative study of US veterans with advanced kidney disease evaluated for transplant, clinician documentation in the medical record indicated that, to be considered for a kidney transplant, patients were required to participate in a rigid, demanding, and opaque evaluation and selection process over which they and their local clinicians had little control. These findings highlight the need for a more evidence-based, individualized, and collaborative approach to kidney transplant evaluation.
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