The past two decades of research into the pathogenesis of Alzheimer disease (AD) have been driven largely by the amyloid hypothesis; the neuroinflammation that is associated with AD has been assumed ...to be merely a response to pathophysiological events. However, new data from preclinical and clinical studies have established that immune system-mediated actions in fact contribute to and drive AD pathogenesis. These insights have suggested both novel and well-defined potential therapeutic targets for AD, including microglia and several cytokines. In addition, as inflammation in AD primarily concerns the innate immune system - unlike in 'typical' neuroinflammatory diseases such as multiple sclerosis and encephalitides - the concept of neuroinflammation in AD may need refinement.
Infection by the new corona virus strain SARS-CoV-2 and its related syndrome COVID-19 has been associated with more than two million deaths worldwide. Patients of higher age and with preexisting ...chronic health conditions are at an increased risk of fatal disease outcome. However, detailed information on causes of death and the contribution of pre-existing health conditions to death yet is missing, which can be reliably established by autopsy only. We performed full body autopsies on 26 patients that had died after SARS-CoV-2 infection and COVID-19 at the Charité University Hospital Berlin, Germany, or at associated teaching hospitals. We systematically evaluated causes of death and pre-existing health conditions. Additionally, clinical records and death certificates were evaluated. We report findings on causes of death and comorbidities of 26 decedents that had clinically presented with severe COVID-19. We found that septic shock and multi organ failure was the most common immediate cause of death, often due to suppurative pulmonary infection. Respiratory failure due to diffuse alveolar damage presented as immediate cause of death in fewer cases. Several comorbidities, such as hypertension, ischemic heart disease, and obesity were present in the vast majority of patients. Our findings reveal that causes of death were directly related to COVID-19 in the majority of decedents, while they appear not to be an immediate result of preexisting health conditions and comorbidities. We therefore suggest that the majority of patients had died of COVID-19 with only contributory implications of preexisting health conditions to the mechanism of death.
Alzheimer's disease is characterized not only by extracellular amyloid plaques and neurofibrillary tangles, but also by microglia‐mediated neuroinflammation. Recently, autophagy has been linked to ...the regulation of the inflammatory response. Thus, we investigated how an impairment of autophagy mediated by BECN1/Beclin1 reduction, as described in Alzheimer's disease patients, would influence cytokine production of microglia. Acutely stimulated microglia from Becn1+/− mice exhibited increased expression of IL‐1beta and IL‐18 compared to wild‐type microglia. Becn1+/−APPPS1 mice also contained enhanced IL‐1beta levels. The investigation of the IL‐1beta/IL‐18 processing pathway showed an elevated number of cells with inflammasomes and increased levels of NLRP3 and cleaved CASP1/Caspase1 in Becn1+/− microglia. Super‐resolation microscopy revealed a very close association of NLRP3 aggregates and LC3‐positive vesicles. Interestingly, CALCOCO2 colocalized with NLRP3 and its downregulation increased IL‐1beta release. These data support the notion that selective autophagy can impact microglia activation by modulating IL‐1beta and IL‐18 production via NLRP3 degradation and thus present a mechanism how impaired autophagy could contribute to neuroinflammation in Alzheimer's disease.
Synopsis
Decreased autophagy in microglia, the resident immune cells of the CNS, modulates production of the proinflammatory cytokines IL‐1 beta and IL‐18 by selective degradation of NLRP3.
Primary microglia from Becn1+/− mice release a higher amount of IL‐1 beta and IL‐18 compared to wild‐type microglia upon a proinflammatory stimulus.
Microglia from Becn1+/− mice display an increase in crucial components of the NLRP3 inflammasome.
Super‐resolution microscopy (SIM) reveals the presence of NLRP3 aggregates in autophagosomes indicating their degradation.
The putative autophagic linker protein murine CALCOCO2 but not the established autophagic adaptor p62/SQSTM1 colocalizes with NLRP3 and its downregulation increases IL‐1 beta release from stimulated microglia.
Inflammasome degradation to curb production of IL‐1beta and IL‐18 cytokines indicates a brain immune cell role for autophagy, whose loss in Alzheimer's disease may contribute to neuropathology.
In this issue of Neuron, Griciuc et al. (2013) investigate the Alzheimer’s disease risk gene, CD33. AD brains have increased CD33 and CD33-positive microglia. Mice lacking CD33 have less AD pathology ...suggesting a role of microglia for Aβ clearance and development of future therapies.
Individual reports suggest that the central nervous system (CNS) contains multiple immune cell types with diverse roles in tissue homeostasis, immune defense, and neurological diseases. It has been ...challenging to map leukocytes across the entire brain, and in particular in pathology, where phenotypic changes and influx of blood-derived cells prevent a clear distinction between reactive leukocyte populations. Here, we applied high-dimensional single-cell mass and fluorescence cytometry, in parallel with genetic fate mapping systems, to identify, locate, and characterize multiple distinct immune populations within the mammalian CNS. Using this approach, we revealed that microglia, several subsets of border-associated macrophages and dendritic cells coexist in the CNS at steady state and exhibit disease-specific transformations in the immune microenvironment during aging and in models of Alzheimer’s disease and multiple sclerosis. Together, these data and the described framework provide a resource for the study of disease mechanisms, potential biomarkers, and therapeutic targets in CNS disease.
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•High-dimensional cytometry reveals diverse immune cells in the steady-state CNS•CD38 and MHCII distinguish CNS border-associated macrophage (BAM) subsets•A subset of microglia responds to aging and neurodegeneration•All microglia are homogenously affected in neuroinflammatory disease
It has been challenging to map leukocytes in the brain, particularly during pathology. Mrdjen et al. combine high-dimensional single-cell cytometry with fate mapping to capture the immune landscape of the brain. They identify different subsets of myeloid cells and the phenotypic changes in CNS immune cells during aging and in models of Alzheimer’s disease and multiple sclerosis.
Microglial cells closely interact with senile plaques in Alzheimer's disease and acquire the morphological appearance of an activated phenotype. The significance of this microglial phenotype and the ...impact of microglia for disease progression have remained controversial. To uncover and characterize putative changes in the functionality of microglia during Alzheimer's disease, we directly assessed microglial behavior in two mouse models of Alzheimer's disease. Using in vivo two-photon microscopy and acute brain slice preparations, we found that important microglial functions - directed process motility and phagocytic activity - were strongly impaired in mice with Alzheimer's disease-like pathology compared to age-matched non-transgenic animals. Notably, impairment of microglial function temporally and spatially correlated with Aβ plaque deposition, and phagocytic capacity of microglia could be restored by interventionally decreasing amyloid burden by Aβ vaccination. These data suggest that major microglial functions progressively decline in Alzheimer's disease with the appearance of Aβ plaques, and that this functional impairment is reversible by lowering Aβ burden, e.g. by means of Aβ vaccination.
Myalgia, increased levels of creatine kinase, and persistent muscle weakness have been reported in patients with COVID-19.
To study skeletal muscle and myocardial inflammation in patients with ...COVID-19 who had died.
This case-control autopsy series was conducted in a university hospital as a multidisciplinary postmortem investigation. Patients with COVID-19 or other critical illnesses who had died between March 2020 and February 2021 and on whom an autopsy was performed were included. Individuals for whom informed consent to autopsy was available and the postmortem interval was less than 6 days were randomly selected. Individuals who were infected with SARS-CoV-2 per polymerase chain reaction test results and had clinical features suggestive of COVID-19 were compared with individuals with negative SARS-CoV-2 polymerase chain reaction test results and an absence of clinical features suggestive of COVID-19.
Inflammation of skeletal muscle tissue was assessed by quantification of immune cell infiltrates, expression of major histocompatibility complex (MHC) class I and class II antigens on the sarcolemma, and a blinded evaluation on a visual analog scale ranging from absence of pathology to the most pronounced pathology. Inflammation of cardiac muscles was assessed by quantification of immune cell infiltrates.
Forty-three patients with COVID-19 (median interquartile range age, 72 16 years; 31 men 72%) and 11 patients with diseases other than COVID-19 (median interquartile range age, 71 5 years; 7 men 64%) were included. Skeletal muscle samples from the patients who died with COVID-19 showed a higher overall pathology score (mean SD, 3.4 1.8 vs 1.5 1.0; 95% CI, 0-3; P < .001) and a higher inflammation score (mean SD, 3.5 2.1 vs 1.0 0.6; 95% CI, 0-4; P < .001). Relevant expression of MHC class I antigens on the sarcolemma was present in 23 of 42 specimens from patients with COVID-19 (55%) and upregulation of MHC class II antigens in 7 of 42 specimens from patients with COVID-19 (17%), but neither were found in any of the controls. Increased numbers of natural killer cells (median interquartile range, 8 8 vs 3 4 cells per 10 high-power fields; 95% CI, 1-10 cells per 10 high-power fields; P < .001) were found. Skeletal muscles showed more inflammatory features than cardiac muscles, and inflammation was most pronounced in patients with COVID-19 with chronic courses. In some muscle specimens, SARS-CoV-2 RNA was detected by reverse transcription-polymerase chain reaction, but no evidence for a direct viral infection of myofibers was found by immunohistochemistry and electron microscopy.
In this case-control study of patients who had died with and without COVID-19, most individuals with severe COVID-19 showed signs of myositis ranging from mild to severe. Inflammation of skeletal muscles was associated with the duration of illness and was more pronounced than cardiac inflammation. Detection of viral load was low or negative in most skeletal and cardiac muscles and probably attributable to circulating viral RNA rather than genuine infection of myocytes. This suggests that SARS-CoV-2 may be associated with a postinfectious, immune-mediated myopathy.
Microglia actions in Alzheimer’s disease Prokop, Stefan; Miller, Kelly R.; Heppner, Frank L.
Acta neuropathologica,
10/2013, Volume:
126, Issue:
4
Journal Article
Peer reviewed
The identification of microglia-associated, neurological disease-causing mutations in patients, combined with studies in mouse models has highlighted microglia, the brain’s intrinsic myeloid cells, ...as key modulators of pathogenesis and disease progression in neurodegenerative diseases. In Alzheimer’s disease (AD) in particular, the activation and accumulation of microglial cells around β-Amyloid (Aβ) plaques has long been described and is believed to result in chronic neuroinflammation—a term that, despite being commonly used, lacks a precise definition. This seemingly directed response of microglia to amyloid deposits conflicts with the fact that the increasing buildup of Aβ plaques is not inhibited by these cells during disease progression. While recent evidence suggests that microglia lose their intrinsic beneficial function during the course of AD and may even acquire a “toxic” phenotype over time, Aβ may also simply not be an appropriate trigger to induce phagocytosis and degradation by microglia in vivo. As recent experimental evidence has indicated the importance of the microglia in AD pathogenesis, future efforts aimed at tackling this disease via utilization or modulation of microglia or factors therefrom appear to be an exciting and challenging research front.
The newly identified severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19, a pandemic respiratory disease. Moreover, thromboembolic events throughout the body, including in ...the CNS, have been described. Given the neurological symptoms observed in a large majority of individuals with COVID-19, SARS-CoV-2 penetrance of the CNS is likely. By various means, we demonstrate the presence of SARS-CoV-2 RNA and protein in anatomically distinct regions of the nasopharynx and brain. Furthermore, we describe the morphological changes associated with infection such as thromboembolic ischemic infarction of the CNS and present evidence of SARS-CoV-2 neurotropism. SARS-CoV-2 can enter the nervous system by crossing the neural-mucosal interface in olfactory mucosa, exploiting the close vicinity of olfactory mucosal, endothelial and nervous tissue, including delicate olfactory and sensory nerve endings. Subsequently, SARS-CoV-2 appears to follow neuroanatomical structures, penetrating defined neuroanatomical areas including the primary respiratory and cardiovascular control center in the medulla oblongata.
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