RESUMEN
Sequence variants of the microglial expressed TREM2 (triggering receptor expressed on myeloid cells 2) are a major risk factor for late onset Alzheimer's disease. TREM2 requires a stable interaction with DAP12 in the membrane to initiate signaling, which is terminated by TREM2 ectodomain shedding and subsequent intramembrane cleavage by γ-secretase. To understand the structural basis for the specificity of the intramembrane cleavage event, we determined the solution structure of the TREM2 transmembrane helix (TMH). Caused by the presence of a charged amino acid in the membrane region, the TREM2-TMH adopts a kinked structure with increased flexibility. Charge removal leads to TMH stabilization and reduced dynamics, similar to its structure in complex with DAP12. Strikingly, these dynamical features match with the site of the initial γ-secretase cleavage event. These data suggest an unprecedented cleavage mechanism by γ-secretase where flexible TMH regions act as key determinants of substrate cleavage specificity.
Asunto(s)
Enfermedad de Alzheimer/metabolismo , Secretasas de la Proteína Precursora del Amiloide/metabolismo , Membrana Celular/metabolismo , Glicoproteínas de Membrana/química , Glicoproteínas de Membrana/metabolismo , Receptores Inmunológicos/química , Receptores Inmunológicos/metabolismo , Proteínas Adaptadoras Transductoras de Señales/química , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Enfermedad de Alzheimer/enzimología , Enfermedad de Alzheimer/genética , Secretasas de la Proteína Precursora del Amiloide/genética , Dicroismo Circular , Células HEK293 , Humanos , Espectroscopía de Resonancia Magnética , Glicoproteínas de Membrana/genética , Proteínas de la Membrana/química , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Microglía/metabolismo , Simulación del Acoplamiento Molecular , Simulación de Dinámica Molecular , Mutación , Conformación Proteica en Hélice alfa , Dominios Proteicos , Receptores Inmunológicos/genética , Factores de Riesgo , Transducción de Señal/genéticaRESUMEN
Atherosclerosis is a chronic inflammatory condition of our arteries and the main underlying pathology of myocardial infarction and stroke. The pathogenesis is age-dependent, but the links between disease progression, age, and atherogenic cytokines and chemokines are incompletely understood. Here, we studied the chemokine-like inflammatory cytokine macrophage migration inhibitory factor (MIF) in atherogenic Apoe-/- mice across different stages of aging and cholesterol-rich high-fat diet (HFD). MIF promotes atherosclerosis by mediating leukocyte recruitment, lesional inflammation, and suppressing atheroprotective B cells. However, links between MIF and advanced atherosclerosis across aging have not been systematically explored. We compared effects of global Mif-gene deficiency in 30-, 42-, and 48-week-old Apoe-/- mice on HFD for 24, 36, or 42 weeks, respectively, and in 52-week-old mice on a 6-week HFD. Mif-deficient mice exhibited reduced atherosclerotic lesions in the 30/24- and 42/36-week-old groups, but atheroprotection, which in the applied Apoe-/- model was limited to lesions in the brachiocephalic artery and abdominal aorta, was not detected in the 48/42- and 52/6-week-old groups. This suggested that atheroprotection afforded by global Mif-gene deletion differs across aging stages and atherogenic diet duration. To characterize this phenotype and study the underlying mechanisms, we determined immune cells in the periphery and vascular lesions, obtained a multiplex cytokine/chemokine profile, and compared the transcriptome between the age-related phenotypes. We found that Mif deficiency promotes lesional macrophage and T-cell counts in younger but not aged mice, with subgroup analysis pointing toward a role for Trem2+ macrophages. The transcriptomic analysis identified pronounced MIF- and aging-dependent changes in pathways predominantly related to lipid synthesis and metabolism, lipid storage, and brown fat cell differentiation, as well as immunity, and atherosclerosis-relevant enriched genes such as Plin1, Ldlr, Cpne7, or Il34, hinting toward effects on lesional lipids, foamy macrophages, and immune cells. Moreover, Mif-deficient aged mice exhibited a distinct plasma cytokine/chemokine signature consistent with the notion that mediators known to drive inflamm'aging are either not downregulated or even upregulated in Mif-deficient aged mice compared with the corresponding younger ones. Lastly, Mif deficiency favored formation of lymphocyte-rich peri-adventitial leukocyte clusters. While the causative contributions of these mechanistic pillars and their interplay will be subject to future scrutiny, our study suggests that atheroprotection due to global Mif-gene deficiency in atherogenic Apoe-/- mice is reduced upon advanced aging and identifies previously unrecognized cellular and molecular targets that could explain this phenotype shift. These observations enhance our understanding of inflamm'aging and MIF pathways in atherosclerosis and may have implications for translational MIF-directed strategies.
Asunto(s)
Aterosclerosis , Factores Inhibidores de la Migración de Macrófagos , Placa Aterosclerótica , Animales , Ratones , Factores Inhibidores de la Migración de Macrófagos/genética , Factores Inhibidores de la Migración de Macrófagos/metabolismo , Aterosclerosis/metabolismo , Quimiocinas , Envejecimiento , Apolipoproteínas E/metabolismo , Ratones Noqueados , Ratones Endogámicos C57BL , Glicoproteínas de Membrana , Receptores InmunológicosRESUMEN
The triggering receptor expressed on myeloid cells 2 (TREM2) is a multifunctional surface protein that affects survival, migration, and phagocytic capacity of myeloid cells. Soluble TREM2 levels were found to be increased in early stages of sporadic and familial Alzheimer's disease (AD) probably reflecting a defensive microglial response to some initial brain damage. The disintegrin and metalloproteases (ADAM) 10 and 17 were identified as TREM2 sheddases. We demonstrate that meprin ß is a direct TREM2 cleaving enzyme using ADAM10/17 deficient HEK293 cells. LC-MS/MS analysis of recombinant TREM2 incubated with meprin ß revealed predominant cleavage between Arg136 and Asp137, distant to the site identified for ADAM10/17. We further demonstrate that the metalloprotease meprin ß cleaves TREM2 on macrophages concomitant with decreased levels of soluble TREM2 in the serum of Mep1b-/- mice compared to WT controls. Isolated BMDMs from Mep1b-/- mice showed significantly increased full-length TREM2 levels and enhanced phagocytosis efficiency compared to WT cells. The diminished constitutive shedding of TREM2 on meprin ß deficient macrophages could be rescued by ADAM stimulation through LPS treatment. Our data provide evidence that meprin ß is a TREM2 sheddase on macrophages and suggest that multiple proteases may be involved in the generation of soluble TREM2.
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Macrófagos/fisiología , Glicoproteínas de Membrana/metabolismo , Metaloendopeptidasas/fisiología , Fagocitosis , Receptores Inmunológicos/metabolismo , Animales , Arginina/metabolismo , Ácido Aspártico/metabolismo , Macrófagos/citología , Masculino , Glicoproteínas de Membrana/genética , Ratones , Ratones Noqueados , Receptores Inmunológicos/genéticaRESUMEN
Riboswitches are cis-acting gene-regulatory RNA elements that can function at the level of transcription, translation and RNA cleavage. The commonly accepted molecular mechanism for riboswitch function proposes a ligand-dependent conformational switch between two mutually exclusive states. According to this mechanism, ligand binding to an aptamer domain induces an allosteric conformational switch of an expression platform, leading to activation or repression of ligand-related gene expression. However, many riboswitch properties cannot be explained by a pure two-state mechanism. Here we show that the regulation mechanism of the adenine-sensing riboswitch, encoded by the add gene on chromosome II of the human Gram-negative pathogenic bacterium Vibrio vulnificus, is notably different from a two-state switch mechanism in that it involves three distinct stable conformations. We characterized the temperature and Mg(2+) dependence of the population ratios of the three conformations and the kinetics of their interconversion at nucleotide resolution. The observed temperature dependence of a pre-equilibrium involving two structurally distinct ligand-free conformations of the add riboswitch conferred efficient regulation over a physiologically relevant temperature range. Such robust switching is a key requirement for gene regulation in bacteria that have to adapt to environments with varying temperatures. The translational adenine-sensing riboswitch represents the first example, to our knowledge, of a temperature-compensated regulatory RNA element.
Asunto(s)
Regulación Bacteriana de la Expresión Génica , ARN Bacteriano/química , Riboswitch , Adenina/metabolismo , Secuencia de Bases , Ligandos , Magnesio/química , Datos de Secuencia Molecular , Conformación de Ácido Nucleico , ARN Bacteriano/metabolismo , Temperatura , Vibrio vulnificus/genéticaRESUMEN
The central hallmark of prion diseases is the misfolding of cellular prion protein (PrP(C)) into a disease-associated aggregated isoform known as scrapie prion protein (PrP(Sc)). NMR spectroscopy has made many essential contributions to the characterization of recombinant PrP in its folded, unfolded and aggregated states. Recent studies reporting on de novo generation of prions from recombinant PrP and infection of animals using prion aerosols suggest that adjustment of current biosafety measures may be necessary, particularly given the relatively high protein concentrations required for NMR applications that favor aggregation. We here present a protocol for the production of recombinant PrP under biosafety level 2 conditions that avoids entirely exposure of the experimenter to aerosols that might contain harmful PrP aggregates. In addition, we introduce an NMR sample tube setup that allows for safe handling of PrP samples at the spectrometer that usually is not part of a dedicated biosafety level 2 laboratory.
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Aerosoles , Resonancia Magnética Nuclear Biomolecular , Priones/química , Proteínas Recombinantes/metabolismo , Algoritmos , Secuencia de Aminoácidos , Aminoácidos/química , Simulación por Computador , Datos de Secuencia Molecular , Proteínas Recombinantes/químicaRESUMEN
We report here an in-depth characterization of the aptamer domain of the transcriptional adenine-sensing riboswitch (pbuE) by NMR and fluorescence spectroscopy. By NMR studies, the structure of two aptamer sequences with different lengths of the helix P1, the central element involved in riboswitch conformational switching, was characterized. Hydrogen-bond interactions could be mapped at nucleotide resolution providing information about secondary and tertiary structure, structure homogeneity and dynamics. Our study reveals that the elongation of helix P1 has pronounced effects not only on the local but on the global structure of the apo aptamer domain. The structural differences induced by stabilizing helix P1 were found to be linked to changes of the ligand binding affinity as revealed from analysis of kinetic and thermodynamic data obtained from stopped-flow fluorescence studies. The results provide new insight into the sequence-dependent fine tuning of the structure and function of purine-sensing riboswitches.
Asunto(s)
Adenina/metabolismo , Aptámeros de Nucleótidos/metabolismo , ARN Bacteriano/química , ARN Bacteriano/metabolismo , Riboswitch , Emparejamiento Base , Ligandos , Magnesio/metabolismo , Modelos Moleculares , Resonancia Magnética Nuclear Biomolecular , Conformación de Ácido Nucleico , Estabilidad del ARN , ARN Bacteriano/genética , TermodinámicaRESUMEN
Outer retinal degenerations, including age-related macular degeneration (AMD), are characterized by photoreceptor and retinal pigment epithelium (RPE) atrophy. In these blinding diseases, macrophages accumulate at atrophic sites, but their ontogeny and niche specialization remain poorly understood, especially in humans. We uncovered a unique profile of microglia, marked by galectin-3 upregulation, at atrophic sites in mouse models of retinal degeneration and human AMD. In disease models, conditional deletion of galectin-3 in microglia led to phagocytosis defects and consequent augmented photoreceptor death, RPE damage, and vision loss, indicating protective roles. Mechanistically, Trem2 signaling orchestrated microglial migration to atrophic sites and induced galectin-3 expression. Moreover, pharmacologic Trem2 agonization led to heightened protection but in a galectin-3-dependent manner. In elderly human subjects, we identified this highly conserved microglial population that expressed galectin-3 and Trem2. This population was significantly enriched in the macular RPE-choroid of AMD subjects. Collectively, our findings reveal a neuroprotective population of microglia and a potential therapeutic target for mitigating retinal degeneration.
Asunto(s)
Galectina 3 , Glicoproteínas de Membrana , Receptores Inmunológicos , Degeneración Retiniana , Anciano , Animales , Humanos , Ratones , Atrofia , Galectina 3/genética , Macrófagos , Glicoproteínas de Membrana/genética , Microglía , Receptores Inmunológicos/genéticaRESUMEN
Atherosclerosis is a chronic disease of the vascular wall driven by lipid accumulation and inflammation in the intimal layer of arteries, and its main complications, myocardial infarction and stroke, are the leading cause of mortality worldwide [1], [2]. Recent studies have identified Triggering receptor expressed on myeloid cells 2 (TREM2), a lipid-sensing receptor regulating myeloid cell functions [3], to be highly expressed in macrophage foam cells in experimental and human atherosclerosis [4]. However, the role of TREM2 in atherosclerosis is not fully known. Here, we show that hematopoietic or global TREM2 deficiency increased, whereas TREM2 agonism decreased necrotic core formation in early atherosclerosis. We demonstrate that TREM2 is essential for the efferocytosis capacities of macrophages, and to the survival of lipid-laden macrophages, indicating a crucial role of TREM2 in maintaining the balance between foam cell death and clearance of dead cells in atherosclerotic lesions, thereby controlling plaque necrosis.
RESUMEN
Prion protein oligomerization: Despite the crucial role of oligomers during prion protein (PrP) pathogenesis the molecular mechanism of their formation has remained largely elusive. A 2D time-resolved NMR study which made it possible to characterize the oligomerization kinetics with unprecedented site-specificity is reported.
Asunto(s)
Priones/química , Cinética , Espectroscopía de Resonancia Magnética , Estructura Molecular , Conformación ProteicaRESUMEN
Neurodegenerative disorders, including Alzheimer's disease, are associated with microgliosis. Microglia have long been considered to have detrimental roles in Alzheimer's disease. However, functional analyses of genes encoding risk factors that are linked to late-onset Alzheimer's disease, and that are enriched or exclusively expressed in microglia, have revealed unexpected protective functions. One of the major risk genes for Alzheimer's disease is TREM2. Risk variants of TREM2 are loss-of-function mutations affecting chemotaxis, phagocytosis, lipid and energy metabolism, and survival and proliferation. Agonistic anti-TREM2 antibodies have been developed to boost these protective functions in patients with intact TREM2 alleles. Several anti-TREM2 antibodies are in early clinical trials, and current efforts aim to achieve more efficient transport of these antibodies across the blood-brain barrier. PET imaging could be used to monitor target engagement. Data from animal models, and biomarker studies in patients, further support a rationale for boosting TREM2 functions during the preclinical stage of Alzheimer's disease.
Asunto(s)
Enfermedad de Alzheimer , Animales , Humanos , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Microglía/metabolismo , Mutación , Anticuerpos/genética , Anticuerpos/metabolismo , Modelos Animales de Enfermedad , Glicoproteínas de Membrana/genética , Receptores Inmunológicos/genéticaRESUMEN
Degenerative diseases of the outer retina, including age-related macular degeneration (AMD), are characterized by atrophy of photoreceptors and retinal pigment epithelium (RPE). In these blinding diseases, macrophages are known to accumulate ectopically at sites of atrophy, but their ontogeny and functional specialization within this atrophic niche remain poorly understood, especially in the human context. Here, we uncovered a transcriptionally unique profile of microglia, marked by galectin-3 upregulation, at atrophic sites in mouse models of retinal degeneration and in human AMD. Using disease models, we found that conditional deletion of galectin-3 in microglia led to defects in phagocytosis and consequent augmented photoreceptor death, RPE damage and vision loss, suggestive of a protective role. Mechanistically, Trem2 signaling orchestrated the migration of microglial cells to sites of atrophy, and there, induced galectin-3 expression. Moreover, pharmacologic Trem2 agonization led to heightened protection, but only in a galectin-3-dependent manner, further signifying the functional interdependence of these two molecules. Likewise in elderly human subjects, we identified a highly conserved population of microglia at the transcriptomic, protein and spatial levels, and this population was enriched in the macular region of postmortem AMD subjects. Collectively, our findings reveal an atrophy-associated specialization of microglia that restricts the progression of retinal degeneration in mice and further suggest that these protective microglia are conserved in AMD.
RESUMEN
AIMS: Macrophages have a critical and dual role in post-ischaemic cardiac repair, as they can foster both tissue healing and damage. Multiple subsets of tissue resident and monocyte-derived macrophages coexist in the infarcted heart, but their precise identity, temporal dynamics, and the mechanisms regulating their acquisition of discrete states are not fully understood. To address this, we used multi-modal single-cell immune profiling, combined with targeted cell depletion and macrophage fate mapping, to precisely map monocyte/macrophage transitions after experimental myocardial infarction. METHODS AND RESULTS: We performed single-cell transcriptomic and cell-surface marker profiling of circulating and cardiac immune cells in mice challenged with acute myocardial infarction, and integrated single-cell transcriptomes obtained before and at 1, 3, 5, 7, and 11 days after infarction. Using complementary strategies of CCR2+ monocyte depletion and fate mapping of tissue resident macrophages, we determined the origin of cardiac macrophage populations. The macrophage landscape of the infarcted heart was dominated by monocyte-derived cells comprising two pro-inflammatory populations defined as Isg15hi and MHCII+Il1b+, alongside non-inflammatory Trem2hi cells. Trem2hi macrophages were observed in the ischaemic area, but not in the remote viable myocardium, and comprised two subpopulations sequentially populating the heart defined as Trem2hiSpp1hi monocyte-to-macrophage intermediates, and fully differentiated Trem2hiGdf15hi macrophages. Cardiac Trem2hi macrophages showed similarities to 'lipid-associated macrophages' found in mouse models of metabolic diseases and were observed in the human heart, indicating conserved features of this macrophage state across diseases and species. Ischaemic injury induced a shift of circulating Ly6Chi monocytes towards a Chil3hi state with granulocyte-like features, but the acquisition of the Trem2hi macrophage signature occurred in the ischaemic tissue. In vitro, macrophages acquired features of the Trem2hi signature following apoptotic-cell efferocytosis. CONCLUSION: Our work provides a comprehensive map of monocyte/macrophage transitions in the ischaemic heart, constituting a valuable resource for further investigating how these cells may be harnessed and modulated to promote post-ischaemic heart repair.
Asunto(s)
Macrófagos , Infarto del Miocardio , Ratones , Humanos , Animales , Macrófagos/metabolismo , Infarto del Miocardio/metabolismo , Monocitos/metabolismo , Miocardio/metabolismo , Fagocitosis , Ratones Endogámicos C57BLRESUMEN
Loss-of-function variants of TREM2 are associated with increased risk of Alzheimer's disease (AD), suggesting that activation of this innate immune receptor may be a useful therapeutic strategy. Here we describe a high-affinity human TREM2-activating antibody engineered with a monovalent transferrin receptor (TfR) binding site, termed antibody transport vehicle (ATV), to facilitate blood-brain barrier transcytosis. Upon peripheral delivery in mice, ATV:TREM2 showed improved brain biodistribution and enhanced signaling compared to a standard anti-TREM2 antibody. In human induced pluripotent stem cell (iPSC)-derived microglia, ATV:TREM2 induced proliferation and improved mitochondrial metabolism. Single-cell RNA sequencing and morphometry revealed that ATV:TREM2 shifted microglia to metabolically responsive states, which were distinct from those induced by amyloid pathology. In an AD mouse model, ATV:TREM2 boosted brain microglial activity and glucose metabolism. Thus, ATV:TREM2 represents a promising approach to improve microglial function and treat brain hypometabolism found in patients with AD.
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Enfermedad de Alzheimer , Células Madre Pluripotentes Inducidas , Humanos , Animales , Ratones , Microglía , Barrera Hematoencefálica , Distribución Tisular , Anticuerpos , Encéfalo , Modelos Animales de Enfermedad , Glicoproteínas de Membrana , Receptores Inmunológicos/genéticaRESUMEN
BACKGROUND: Therapeutic modulation of TREM2-dependent microglial function might provide an additional strategy to slow the progression of Alzheimer's disease. Although studies in animal models suggest that TREM2 is protective against Alzheimer's pathology, its effect on tau pathology and its potential beneficial role in people with Alzheimer's disease is still unclear. Our aim was to study associations between the dynamics of soluble TREM2, as a biomarker of TREM2 signalling, and amyloid ß (Aß) deposition, tau-related pathology, neuroimaging markers, and cognitive decline, during the progression of autosomal dominant Alzheimer's disease. METHODS: We did a longitudinal analysis of data from the Dominantly Inherited Alzheimer Network (DIAN) observational study, which includes families with a history of autosomal dominant Alzheimer's disease. Participants aged over 18 years who were enrolled in DIAN between Jan 1, 2009, and July 31, 2019, were categorised as either carriers of pathogenic variants in PSEN1, PSEN2, and APP genes (n=155) or non-carriers (n=93). We measured amounts of cleaved soluble TREM2 using a novel immunoassay in CSF samples obtained every 2 years from participants who were asymptomatic (Clinical Dementia Rating [CDR]=0) and annually for those who were symptomatic (CDR>0). CSF concentrations of Aß40, Aß42, total tau (t-tau), and tau phosphorylated on threonine 181 (p-tau) were measured by validated immunoassays. Predefined neuroimaging measurements were total cortical uptake of Pittsburgh compound B PET (PiB-PET), cortical thickness in the precuneus ascertained by MRI, and hippocampal volume determined by MRI. Cognition was measured using a validated cognitive composite (including DIAN word list test, logical memory delayed recall, digit symbol coding test [total score], and minimental status examination). We based our statistical analysis on univariate and bivariate linear mixed effects models. FINDINGS: In carriers of pathogenic variants, a high amyloid burden at baseline, represented by low CSF Aß42 (ß=-4·28â×â10-2 [SE 0·013], p=0·0012), but not high cortical uptake in PiB-PET (ß=-5·51â×â10-3 [0·011], p=0·63), was the only predictor of an augmented annual rate of subsequent increase in soluble TREM2. Augmented annual rates of increase in soluble TREM2 were associated with a diminished rate of decrease in amyloid deposition, as measured by Aß42 in CSF (r=0·56 [0·22], p=0·011), in presymptomatic carriers of pathogenic variants, and with diminished annual rate of increase in PiB-PET (r=-0·67 [0·25], p=0·0060) in symptomatic carriers of pathogenic variants. Presymptomatic carriers of pathogenic variants with annual rates of increase in soluble TREM2 lower than the median showed a correlation between enhanced annual rates of increase in p-tau in CSF and augmented annual rates of increase in PiB-PET signal (r=0·45 [0·21], p=0·035), that was not observed in those with rates of increase in soluble TREM2 higher than the median. Furthermore, presymptomatic carriers of pathogenic variants with rates of increase in soluble TREM2 above or below the median had opposite associations between Aß42 in CSF and PiB-PET uptake when assessed longitudinally. Augmented annual rates of increase in soluble TREM2 in presymptomatic carriers of pathogenic variants correlated with decreased cortical shrinkage in the precuneus (r=0·46 [0·22]), p=0·040) and diminished cognitive decline (r=0·67 [0·22], p=0·0020). INTERPRETATION: Our findings in autosomal dominant Alzheimer's disease position the TREM2 response within the amyloid cascade immediately after the first pathological changes in Aß aggregation and further support the role of TREM2 on Aß plaque deposition and compaction. Furthermore, these findings underpin a beneficial effect of TREM2 on Aß deposition, Aß-dependent tau pathology, cortical shrinkage, and cognitive decline. Soluble TREM2 could, therefore, be a key marker for clinical trial design and interpretation. Efforts to develop TREM2-boosting therapies are ongoing. FUNDING: German Research Foundation, US National Institutes of Health.
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Enfermedad de Alzheimer , Disfunción Cognitiva , Glicoproteínas de Membrana , Adulto , Enfermedad de Alzheimer/diagnóstico por imagen , Enfermedad de Alzheimer/genética , Péptidos beta-Amiloides , Biomarcadores , Cognición/fisiología , Disfunción Cognitiva/diagnóstico por imagen , Disfunción Cognitiva/genética , Humanos , Glicoproteínas de Membrana/líquido cefalorraquídeo , Glicoproteínas de Membrana/genética , Persona de Mediana Edad , Receptores Inmunológicos/genética , Estados UnidosRESUMEN
Proregenerative responses are required for the restoration of nervous-system functionality in demyelinating diseases such as multiple sclerosis (MS). Yet, the limiting factors responsible for poor CNS repair are only partially understood. Here, we test the impact of a Western diet (WD) on phagocyte function in a mouse model of demyelinating injury that requires microglial innate immune function for a regenerative response to occur. We find that WD feeding triggers an ageing-related, dysfunctional metabolic response that is associated with impaired myelin-debris clearance in microglia, thereby impairing lesion recovery after demyelination. Mechanistically, we detect enhanced transforming growth factor beta (TGFß) signalling, which suppresses the activation of the liver X receptor (LXR)-regulated genes involved in cholesterol efflux, thereby inhibiting phagocytic clearance of myelin and cholesterol. Blocking TGFß or promoting triggering receptor expressed on myeloid cells 2 (TREM2) activity restores microglia responsiveness and myelin-debris clearance after demyelinating injury. Thus, we have identified a druggable microglial immune checkpoint mechanism regulating the microglial response to injury that promotes remyelination.
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Enfermedades Desmielinizantes/inmunología , Enfermedades Desmielinizantes/metabolismo , Dieta , Inmunidad Innata/inmunología , Factor de Crecimiento Transformador beta/metabolismo , Envejecimiento/metabolismo , Animales , Colesterol/metabolismo , Dieta Occidental , Receptores X del Hígado , Lisofosfatidilcolinas/farmacología , Glicoproteínas de Membrana/metabolismo , Ratones , Ratones Endogámicos C57BL , Microglía/metabolismo , Vaina de Mielina/metabolismo , Fagocitos/metabolismo , Receptores Inmunológicos/metabolismoRESUMEN
Alzheimer's disease (AD) is currently untreatable, and therapeutic strategies aimed to slow cognitive decline have not yet been successful. Many of these approaches have targeted the amyloid cascade, indicating that novel treatment strategies are required. Recent genome-wide association studies (GWASs) have identified a number of risk factors in genes expressed in microglia, underscoring their therapeutic potential in neurodegeneration. In this review, we discuss how the recently defined functions of these AD risk genes can be targeted therapeutically to modulate microglial cell state and slow the progression of AD. Antibody-mediated stimulation of the triggering receptor of myeloid cells 2 (TREM2) is on the forefront of these candidate therapeutic approaches based on a combination of compelling human genetics and emerging preclinical data. This and other approaches to modify microglial function are a topic of intensive study and provide an opportunity for innovative AD treatments, which may be applied alone or potentially in combination with classical anti-amyloid therapies.
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Enfermedad de Alzheimer/inmunología , Enfermedad de Alzheimer/terapia , Encéfalo/inmunología , Terapia Genética/tendencias , Inmunoterapia/tendencias , Microglía/inmunología , Enfermedad de Alzheimer/genética , Animales , Anticuerpos Monoclonales/farmacología , Anticuerpos Monoclonales/uso terapéutico , Encéfalo/efectos de los fármacos , Estudio de Asociación del Genoma Completo/tendencias , Humanos , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/inmunología , Glicoproteínas de Membrana/uso terapéutico , Microglía/efectos de los fármacos , Receptores Inmunológicos/genética , Receptores Inmunológicos/inmunología , Receptores Inmunológicos/uso terapéuticoRESUMEN
Triggering receptor expressed on myeloid cells 2 (TREM2) is essential for the transition of homeostatic microglia to a disease-associated microglial state. To enhance TREM2 activity, we sought to selectively increase the full-length protein on the cell surface via reducing its proteolytic shedding by A Disintegrin And Metalloproteinase (i.e., α-secretase) 10/17. We screened a panel of monoclonal antibodies against TREM2, with the aim to selectively compete for α-secretase-mediated shedding. Monoclonal antibody 4D9, which has a stalk region epitope close to the cleavage site, demonstrated dual mechanisms of action by stabilizing TREM2 on the cell surface and reducing its shedding, and concomitantly activating phospho-SYK signaling. 4D9 stimulated survival of macrophages and increased microglial uptake of myelin debris and amyloid ß-peptide in vitro. In vivo target engagement was demonstrated in cerebrospinal fluid, where nearly all soluble TREM2 was 4D9-bound. Moreover, in a mouse model for Alzheimer's disease-related pathology, 4D9 reduced amyloidogenesis, enhanced microglial TREM2 expression, and reduced a homeostatic marker, suggesting a protective function by driving microglia toward a disease-associated state.
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Anticuerpos Monoclonales/farmacología , Glicoproteínas de Membrana/inmunología , Microglía , Mieloma Múltiple , Receptores Inmunológicos/inmunología , Péptidos beta-Amiloides , Animales , Línea Celular Tumoral , Femenino , Macrófagos , Ratones , Microglía/patología , Ratas , Ratas WistarRESUMEN
BACKGROUND: TREM2 is a transmembrane receptor that is predominantly expressed by microglia in the central nervous system. Rare variants in the TREM2 gene increase the risk for late-onset Alzheimer's disease (AD). Soluble TREM2 (sTREM2) resulting from shedding of the TREM2 ectodomain can be detected in the cerebrospinal fluid (CSF) and is a surrogate measure of TREM2-mediated microglia function. CSF sTREM2 has been previously reported to increase at different clinical stages of AD, however, alterations in relation to Amyloid ß-peptide (Aß) deposition or additional pathological processes in the amyloid cascade (such as tau pathology or neurodegeneration) remain unclear. In the current cross-sectional study, we employed the biomarker-based classification framework recently proposed by the NIA-AA consensus guidelines, in combination with clinical staging, in order to examine the CSF sTREM2 alterations at early asymptomatic and symptomatic stages of AD. METHODS: A cross-sectional study of 1027 participants of the Alzheimer's Disease Imaging Initiative (ADNI) cohort, including 43 subjects carrying TREM2 rare genetic variants, was conducted to measure CSF sTREM2 using a previously validated enzyme-linked immunosorbent assay (ELISA). ADNI participants were classified following the A/T/N framework, which we implemented based on the CSF levels of Aß1-42 (A), phosphorylated tau (T) and total tau as a marker of neurodegeneration (N), at different clinical stages defined by the clinical dementia rating (CDR) score. RESULTS: CSF sTREM2 differed between TREM2 variants, whereas the p.R47H variant had higher CSF sTREM2, p.L211P had lower CSF sTREM2 than non-carriers. We found that CSF sTREM2 increased in early symptomatic stages of late-onset AD but, unexpectedly, we observed decreased CSF sTREM2 levels at the earliest asymptomatic phase when only abnormal Aß pathology (A+) but no tau pathology or neurodegeneration (TN-), is present. CONCLUSIONS: Aß pathology (A) and tau pathology/neurodegeneration (TN) have differing associations with CSF sTREM2. While tau-related neurodegeneration is associated with an increase in CSF sTREM2, Aß pathology in the absence of downstream tau-related neurodegeneration is associated with a decrease in CSF sTREM2.