Microglial autophagy-associated phagocytosis is essential for recovery from neuroinflammation

Multiple sclerosis (MS) is a leading cause of incurable progressive disability in young adults caused by inflammation and neurodegeneration in the central nervous system (CNS). The capacity of microglia to clear tissue debris is essential for maintaining and restoring CNS homeostasis. This capacity diminishes with age, and age strongly associates with MS disease progression, although the underlying mechanisms are still largely elusive. Here, we demonstrate that the recovery from CNS inflammation in a murine model of MS is dependent on the ability of microglia to clear tissue debris. Microglia-specific deletion of the autophagy regulator Atg7, but not the canonical macroautophagy protein Ulk1, led to increased intracellular accumulation of phagocytosed myelin and progressive MS-like disease. This impairment correlated with a microglial phenotype previously associated with neurodegenerative pathologies. Moreover, Atg7-deficient microglia showed notable transcriptional and functional similarities to microglia from aged wild-type mice that were also unable to clear myelin and recover from disease. In contrast, induction of autophagy in aged mice using the disaccharide trehalose found in plants and fungi led to functional myelin clearance and disease remission. Our results demonstrate that a noncanonical form of autophagy in microglia is responsible for myelin degradation and clearance leading to recovery from MS-like disease and that boosting this process has a therapeutic potential for age-related neuroinflammatory conditions.Swedish Research CouncilSwedish Brain FoundationSwedish Association for Persons with Neurological DisabilitiesStockholm County Council (ALF project)AstraZeneca (AstraZeneca-Science for Life Laboratory collaboration)European Union Horizon 2020/European Research Council Consolidator Grant (Epi4MS)Knut and Alice Wallenbergs FoundationMargeretha af Ugglas FoundationAlltid Litt SterkereFoundation of Swedish MS researchNEURO SwedenKarolinska InstitutetAccepte

Myoclonus in comatose patients with electrographic status epilepticus after cardiac arrest:Corresponding EEG patterns, effects of treatment and outcomes

Objective: To clarify the significance of any form of myoclonus in comatose patients after cardiac arrest with rhythmic and periodic EEG patterns (RPPs) by analyzing associations between myoclonus and EEG pattern, response to anti-seizure medication and neurological outcome. Design: Post hoc analysis of the prospective randomized Treatment of ELectroencephalographic STatus Epilepticus After Cardiopulmonary Resuscitation (TELSTAR) trial. Setting: Eleven ICUs in the Netherlands and Belgium. Patients: One hundred and fifty-seven adult comatose post-cardiac arrest patients with RPPs on continuous EEG monitoring. Interventions: Anti-seizure medication vs no anti-seizure medication in addition to standard care. Measurements and Main Results: Of 157 patients, 98 (63%) had myoclonus at inclusion. Myoclonus was not associated with one specific RPP type. However, myoclonus was associated with a smaller probability of a continuous EEG background pattern (48% in patients with vs 75% without myoclonus, odds ratio (OR) 0.31; 95% confidence interval (CI) 0.16–0.64) and earlier onset of RPPs (24% vs 9% within 24 hours after cardiac arrest, OR 3.86;95% CI 1.64–9.11). Myoclonus was associated with poor outcome at three months, but not invariably so (poor neurological outcome in 96% vs 82%, p = 0.004). Anti-seizure medication did not improve outcome, regardless of myoclonus presence (6% good outcome in the intervention group vs 2% in the control group, OR 0.33; 95% CI 0.03–3.32). Conclusions: Myoclonus in comatose patients after cardiac arrest with RPPs is associated with poor outcome and discontinuous or suppressed EEG. However, presence of myoclonus does not interact with the effects of anti-seizure medication and cannot predict a poor outcome without false positives.</p

Longitudinal positron emission tomography and postmortem analysis reveals widespread neuroinflammation in SARS-CoV-2 infected rhesus macaques

BACKGROUND: Coronavirus disease 2019 (COVID-19) patients initially develop respiratory symptoms, but they may also suffer from neurological symptoms. People with long-lasting effects after acute infections with severe respiratory syndrome coronavirus 2 (SARS-CoV-2), i.e., post-COVID syndrome or long COVID, may experience a variety of neurological manifestations. Although we do not fully understand how SARS-CoV-2 affects the brain, neuroinflammation likely plays a role. METHODS: To investigate neuroinflammatory processes longitudinally after SARS-CoV-2 infection, four experimentally SARS-CoV-2 infected rhesus macaques were monitored for 7 weeks with 18-kDa translocator protein (TSPO) positron emission tomography (PET) using [18F]DPA714, together with computed tomography (CT). The baseline scan was compared to weekly PET-CTs obtained post-infection (pi). Brain tissue was collected following euthanasia (50 days pi) to correlate the PET signal with TSPO expression, and glial and endothelial cell markers. Expression of these markers was compared to brain tissue from uninfected animals of comparable age, allowing the examination of the contribution of these cells to the neuroinflammatory response following SARS-CoV-2 infection. RESULTS: TSPO PET revealed an increased tracer uptake throughout the brain of all infected animals already from the first scan obtained post-infection (day 2), which increased to approximately twofold until day 30 pi. Postmortem immunohistochemical analysis of the hippocampus and pons showed TSPO expression in cells expressing ionized calcium-binding adaptor molecule 1 (IBA1), glial fibrillary acidic protein (GFAP), and collagen IV. In the hippocampus of SARS-CoV-2 infected animals the TSPO+ area and number of TSPO+ cells were significantly increased compared to control animals. This increase was not cell type specific, since both the number of IBA1+TSPO+ and GFAP+TSPO+ cells was increased, as well as the TSPO+ area within collagen IV+ blood vessels. CONCLUSIONS: This study manifests [18F]DPA714 as a powerful radiotracer to visualize SARS-CoV-2 induced neuroinflammation. The increased uptake of [18F]DPA714 over time implies an active neuroinflammatory response following SARS-CoV-2 infection. This inflammatory signal coincides with an increased number of TSPO expressing cells, including glial and endothelial cells, suggesting neuroinflammation and vascular dysregulation. These results demonstrate the long-term neuroinflammatory response following a mild SARS-CoV-2 infection, which potentially precedes long-lasting neurological symptoms

Translocator protein is a marker of activated microglia in rodent models but not human neurodegenerative diseases

Microglial activation plays central roles in neuroinflammatory and neurodegenerative diseases. Positron emission tomography (PET) targeting 18 kDa Translocator Protein (TSPO) is widely used for localising inflammation in vivo, but its quantitative interpretation remains uncertain. We show that TSPO expression increases in activated microglia in mouse brain disease models but does not change in a non-human primate disease model or in common neurodegenerative and neuroinflammatory human diseases. We describe genetic divergence in the TSPO gene promoter, consistent with the hypothesis that the increase in TSPO expression in activated myeloid cells depends on the transcription factor AP1 and is unique to a subset of rodent species within the Muroidea superfamily. Finally, we identify LCP2 and TFEC as potential markers of microglial activation in humans. These data emphasise that TSPO expression in human myeloid cells is related to different phenomena than in mice, and that TSPO-PET signals in humans reflect the density of inflammatory cells rather than activation state.Published versionThe authors thank the UK MS Society for financial support (grant number: C008-16.1). DRO was funded by an MRC Clinician Scientist Award (MR/N008219/1). P.M.M. acknowledges generous support from Edmond J Safra Foundation and Lily Safra, the NIHR Senior Investigator programme and the UK Dementia Research Institute which receives its funding from DRI Ltd., funded by the UK Medical Research Council, Alzheimer’s Society, and Alzheimer’s Research UK. P.M.M. and D.R.O. thank the Imperial College Healthcare Trust-NIHR Biomedical Research Centre for infrastructure support and the Medical Research Council for support of TSPO studies (MR/N016343/1). E.A. was supported by the ALS Stichting (grant “The Dutch ALS Tissue Bank”). P.M. and B.B.T. are funded by the Swiss National Science Foundation (projects 320030_184713 and 310030_212322, respectively). S.T. was supported by an “Early Postdoc.Mobility” scholarship (P2GEP3_191446) from the Swiss National Science Foundation, a “Clinical Medicine Plus” scholarship from the Prof Dr. Max Cloëtta Foundation (Zurich, Switzerland), from the Jean et Madeleine Vachoux Foundation (Geneva, Switzerland) and from the University Hospitals of Geneva. This work was funded by NIH grants U01AG061356 (De Jager/Bennett), RF1AG057473 (De Jager/Bennett), and U01AG046152 (De Jager/Bennett) as part of the AMP-AD consortium, as well as NIH grants R01AG066831 (Menon) and U01AG072572 (De Jager/St George-Hyslop)

Visualising microglia in neurodegenerative diseases

Neuroinflammation in neuroinflammatory and neurodegenerative diseases is only one of the many complex multicellular processes that occurs behind the ‘closed borders’ within the central nervous system (CNS). Two important innate immune cells in the CNS that contribute to damage as well as repair are microglia and astrocytes. Given their importance in many diseases there is an urgent clinical need to monitor glial cell activity during disease as well as assess the impact of medical intervention on innate immune responses during diseases. Positron emission tomography (PET) is one of the modalities to monitor neuroinflammation and pathological changes in neurodegenerative diseases and experimental animal in vivo. PET has the advantage of being able to interrogate various disease mechanisms by quantifying specific molecular targets to directly study the CNS. In this thesis we examined the cellular distribution and the regulation of the translocator protein (TSPO) in CNS resident cells in neurodegenerative diseases and their respective animal models. TSPO is generally thought to be a marker of activated microglia and has been reported as such by many studies. Initial reports on animal models of neuroinflammatory diseases showed that TSPO is also expressed by other cell types than microglia but these findings have been largely ignored by PET studies, and the early human studies were qualitative rather than quantitative. Recently, it was shown in vitro that primary rodent microglia upregulate TSPO expression in a pro-inflammatory environment, while this is not the case in humans. Thus, findings of the triggers of TSPO, and the cellular expression of TSPO in the CNS in animal models may not translate to human disease. To investigate the cellular distribution and understand the triggers of TSPO we first performed in-depth studies of TSPO expression in MS to validate TSPO expression in glial cells and how the TSPO protein was regulated. Then we expanded our studies to other common neurodegenerative diseases such as AD and ALS and their respective animal models. In addition, we have utilised publicly available databases on TSPO regulation on multiple molecular levels. Another goal of the thesis was to investigate the role of microglia and astrocytes as innate immune cells of the CNS as they are becoming increasingly implicated in having diverse functions and heterogeneous states in many CNS diseases. While historically, microglia were considered as the phagocytes of the brain and astrocytes as responders to damage, the rise in advanced technologies such as single cell and single nucleus RNAseq, as well as detailed pathology studies made available by a plethora of antibodies and probes has shown that microglia and astrocytes have diverse and complex functions in the CNS. Together, these studies have allowed a more detailed understanding of the role of microglia and astrocytes as innate immune cells of the CNS

Visualising microglia in neurodegenerative diseases

Neuroinflammation in neuroinflammatory and neurodegenerative diseases is only one of the many complex multicellular processes that occurs behind the ‘closed borders’ within the central nervous system (CNS). Two important innate immune cells in the CNS that contribute to damage as well as repair are microglia and astrocytes. Given their importance in many diseases there is an urgent clinical need to monitor glial cell activity during disease as well as assess the impact of medical intervention on innate immune responses during diseases. Positron emission tomography (PET) is one of the modalities to monitor neuroinflammation and pathological changes in neurodegenerative diseases and experimental animal in vivo. PET has the advantage of being able to interrogate various disease mechanisms by quantifying specific molecular targets to directly study the CNS. In this thesis we examined the cellular distribution and the regulation of the translocator protein (TSPO) in CNS resident cells in neurodegenerative diseases and their respective animal models. TSPO is generally thought to be a marker of activated microglia and has been reported as such by many studies. Initial reports on animal models of neuroinflammatory diseases showed that TSPO is also expressed by other cell types than microglia but these findings have been largely ignored by PET studies, and the early human studies were qualitative rather than quantitative. Recently, it was shown in vitro that primary rodent microglia upregulate TSPO expression in a pro-inflammatory environment, while this is not the case in humans. Thus, findings of the triggers of TSPO, and the cellular expression of TSPO in the CNS in animal models may not translate to human disease. To investigate the cellular distribution and understand the triggers of TSPO we first performed in-depth studies of TSPO expression in MS to validate TSPO expression in glial cells and how the TSPO protein was regulated. Then we expanded our studies to other common neurodegenerative diseases such as AD and ALS and their respective animal models. In addition, we have utilised publicly available databases on TSPO regulation on multiple molecular levels. Another goal of the thesis was to investigate the role of microglia and astrocytes as innate immune cells of the CNS as they are becoming increasingly implicated in having diverse functions and heterogeneous states in many CNS diseases. While historically, microglia were considered as the phagocytes of the brain and astrocytes as responders to damage, the rise in advanced technologies such as single cell and single nucleus RNAseq, as well as detailed pathology studies made available by a plethora of antibodies and probes has shown that microglia and astrocytes have diverse and complex functions in the CNS. Together, these studies have allowed a more detailed understanding of the role of microglia and astrocytes as innate immune cells of the CNS

Visualising microglia in neurodegenerative diseases

Neuroinflammation in neuroinflammatory and neurodegenerative diseases is only one of the many complex multicellular processes that occurs behind the ‘closed borders’ within the central nervous system (CNS). Two important innate immune cells in the CNS that contribute to damage as well as repair are microglia and astrocytes. Given their importance in many diseases there is an urgent clinical need to monitor glial cell activity during disease as well as assess the impact of medical intervention on innate immune responses during diseases. Positron emission tomography (PET) is one of the modalities to monitor neuroinflammation and pathological changes in neurodegenerative diseases and experimental animal in vivo. PET has the advantage of being able to interrogate various disease mechanisms by quantifying specific molecular targets to directly study the CNS. In this thesis we examined the cellular distribution and the regulation of the translocator protein (TSPO) in CNS resident cells in neurodegenerative diseases and their respective animal models. TSPO is generally thought to be a marker of activated microglia and has been reported as such by many studies. Initial reports on animal models of neuroinflammatory diseases showed that TSPO is also expressed by other cell types than microglia but these findings have been largely ignored by PET studies, and the early human studies were qualitative rather than quantitative. Recently, it was shown in vitro that primary rodent microglia upregulate TSPO expression in a pro-inflammatory environment, while this is not the case in humans. Thus, findings of the triggers of TSPO, and the cellular expression of TSPO in the CNS in animal models may not translate to human disease. To investigate the cellular distribution and understand the triggers of TSPO we first performed in-depth studies of TSPO expression in MS to validate TSPO expression in glial cells and how the TSPO protein was regulated. Then we expanded our studies to other common neurodegenerative diseases such as AD and ALS and their respective animal models. In addition, we have utilised publicly available databases on TSPO regulation on multiple molecular levels. Another goal of the thesis was to investigate the role of microglia and astrocytes as innate immune cells of the CNS as they are becoming increasingly implicated in having diverse functions and heterogeneous states in many CNS diseases. While historically, microglia were considered as the phagocytes of the brain and astrocytes as responders to damage, the rise in advanced technologies such as single cell and single nucleus RNAseq, as well as detailed pathology studies made available by a plethora of antibodies and probes has shown that microglia and astrocytes have diverse and complex functions in the CNS. Together, these studies have allowed a more detailed understanding of the role of microglia and astrocytes as innate immune cells of the CNS

Imaging immune responses in neuroinflammatory diseases

Innate and adaptive immune responses in the central nervous system (CNS) play critical roles in the pathogenesis of neurological diseases. In the first of a two-part special issue, leading researchers discuss how imaging modalities are used to monitor immune responses in several neurodegenerative diseases and glioblastoma and brain metastases. While comparative studies in humans between imaging and pathology are biased towards the end stage of disease, animal models can inform regarding how immune responses change with disease progression and as a result of treatment regimens. Magnetic resonance imaging (MRI) and positron emission tomography (PET) are frequently used to image disease progression, and the articles indicate how one or more of these modalities have been applied to specific neuroimmune diseases. In addition, advanced microscopical imaging using two-dimensional photon microscopy and in vitro live cell imaging have also been applied to animal models. In this special issue (Parts 1 and 2), as well as the imaging modalities mentioned, several articles discuss biomarkers of disease and microscopical studies that have enabled characterization of immune responses. Future developments of imaging modalities should enable tracking of specific subsets of immune cells during disease allowing longitudinal monitoring of immune responses. These new approaches will be critical to more effectively monitor and thus target specific cell subsets for therapeutic interventions which may be applicable to a range of neurological diseases

Inflammation in CNS neurodegenerative diseases

Neurodegenerative diseases, the leading cause of morbidity and disability, are gaining increased attention as they impose a considerable socioeconomic impact, due in part to the ageing community. Neuronal damage is a pathological hallmark of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, Huntington's disease, spinocerebellar ataxia and multiple sclerosis, although such damage is also observed following neurotropic viral infections, stroke, genetic white matter diseases and paraneoplastic disorders. Despite the different aetiologies, for example, infections, genetic mutations, trauma and protein aggregations, neuronal damage is frequently associated with chronic activation of an innate immune response in the CNS. The growing awareness that the immune system is inextricably involved in shaping the brain during development as well as mediating damage, but also regeneration and repair, has stimulated therapeutic approaches to modulate the immune system in neurodegenerative diseases. Here, we review the current understanding of how astrocytes and microglia, as well as neurons and oligodendrocytes, shape the neuroimmune response during development, and how aberrant responses that arise due to genetic or environmental triggers may predispose the CNS to neurodegenerative diseases. We discuss the known interactions between the peripheral immune system and the brain, and review the current concepts on how immune cells enter and leave the CNS. A better understanding of neuroimmune interactions during development and disease will be key to further manipulating these responses and the development of effective therapies to improve quality of life, and reduce the impact of neuroinflammatory and degenerative diseases

Autophagy in white matter disorders of the CNS: mechanisms and therapeutic opportunities

Autophagy is a constitutive process that degrades, recycles and clears damaged proteins or organelles, yet, despite activation of this pathway, abnormal proteins accumulate in neurons in neurodegenerative diseases and in oligodendrocytes in white matter disorders. Here, we discuss the role of autophagy in white matter disorders, including neurotropic infections, inflammatory diseases such as multiple sclerosis, and in hereditary metabolic disorders and acquired toxic-metabolic disorders. Once triggered due to cell stress, autophagy can enhance cell survival or cell death that may contribute to oligodendrocyte damage and myelin loss in white matter diseases. For some disorders, the mechanisms leading to myelin loss are clear, whereas the aetiological agent and pathological mechanisms are unknown for other myelin disorders, although emerging studies indicate that a common mechanism underlying these disorders is dysregulation of autophagic pathways. In this review we discuss the alterations in the autophagic process in white matter disorders and the potential use of autophagy-modulating agents as therapeutic approaches in these pathological conditions