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Shi Q, Gutierrez RA, Bhat MA. Microglia, Trem2, and Neurodegeneration. Neuroscientist 2024:10738584241254118. [PMID: 38769824 DOI: 10.1177/10738584241254118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/22/2024]
Abstract
Microglia are a specialized type of neuroimmune cells that undergo morphological and molecular changes through multiple signaling pathways in response to pathological protein aggregates, neuronal death, tissue injury, or infections. Microglia express Trem2, which serves as a receptor for a multitude of ligands enhancing their phagocytic activity. Trem2 has emerged as a critical modulator of microglial activity, especially in many neurodegenerative disorders. Human TREM2 mutations are associated with an increased risk of developing Alzheimer disease (AD) and other neurodegenerative diseases. Trem2 plays dual roles in neuroinflammation and more specifically in disease-associated microglia. Most recent developments on the molecular mechanisms of Trem2, emphasizing its role in uptake and clearance of amyloid β (Aβ) aggregates and other tissue debris to help protect and preserve the brain, are encouraging. Although Trem2 normally stimulates defense mechanisms, its dysregulation can intensify inflammation, which poses major therapeutic challenges. Recent therapeutic approaches targeting Trem2 via agonistic antibodies and gene therapy methodologies present possible avenues for reducing the burden of neurodegenerative diseases. This review highlights the promise of Trem2 as a therapeutic target, especially for Aβ-associated AD, and calls for more mechanistic investigations to understand the context-specific role of microglial Trem2 in developing effective therapies against neurodegenerative diseases.
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Affiliation(s)
- Qian Shi
- Department of Cellular and Integrative Physiology, Center for Biomedical Neuroscience, Joe R. and Teresa Lozano Long School of Medicine, University of Texas Health Science Center San Antonio, San Antonio, TX, USA
| | - Raul A Gutierrez
- Department of Cellular and Integrative Physiology, Center for Biomedical Neuroscience, Joe R. and Teresa Lozano Long School of Medicine, University of Texas Health Science Center San Antonio, San Antonio, TX, USA
| | - Manzoor A Bhat
- Department of Cellular and Integrative Physiology, Center for Biomedical Neuroscience, Joe R. and Teresa Lozano Long School of Medicine, University of Texas Health Science Center San Antonio, San Antonio, TX, USA
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2
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Rao Y, Peng B. Allogenic microglia replacement: A novel therapeutic strategy for neurological disorders. FUNDAMENTAL RESEARCH 2024; 4:237-245. [PMID: 38933508 PMCID: PMC11197774 DOI: 10.1016/j.fmre.2023.02.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2022] [Revised: 11/17/2022] [Accepted: 02/19/2023] [Indexed: 03/29/2023] Open
Abstract
Microglia are resident immune cells in the central nervous system (CNS) that play vital roles in CNS development, homeostasis and disease pathogenesis. Genetic defects in microglia lead to microglial dysfunction, which in turn leads to neurological disorders. The correction of the specific genetic defects in microglia in these disorders can lead to therapeutic effects. Traditional genetic defect correction approaches are dependent on viral vector-based genetic defect corrections. However, the viruses used in these approaches, including adeno-associated viruses, lentiviruses and retroviruses, do not primarily target microglia; therefore, viral vector-based genetic defect corrections are ineffective in microglia. Microglia replacement is a novel approach to correct microglial genetic defects via replacing microglia of genetic defects with allogenic healthy microglia. In this paper, we systematically review the history, rationale and therapeutic perspectives of microglia replacement, which would be a novel strategy for treating CNS disorders.
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Affiliation(s)
- Yanxia Rao
- Department of Laboratory Animal Science, MOE Frontiers Center for Brain Science, Fudan University, Shanghai 200032, China
| | - Bo Peng
- Department of Neurosurgery, Huashan Hospital, Institute for Translational Brain Research, State Key Laboratory of Medical Neurobiology, MOE Frontiers Center for Brain Science, MOE Innovative Center for New Drug Development of Immune Inflammatory Diseases, Fudan University, Shanghai 200000, China
- Co-Innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu 226001, China
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Xie M, Zhao S, Bosco DB, Nguyen A, Wu LJ. Microglial TREM2 in amyotrophic lateral sclerosis. Dev Neurobiol 2021; 82:125-137. [PMID: 34874625 DOI: 10.1002/dneu.22864] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Revised: 11/12/2021] [Accepted: 12/01/2021] [Indexed: 12/12/2022]
Abstract
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is an aggressive motor neuron degenerative disease characterized by selective loss of both upper and lower motor neurons. The mechanisms underlying disease initiation and progression are poorly understood. The involvement of nonmotor neuraxis emphasizes the contribution of glial cells in disease progress. Microglia comprise a unique subset of glial cells and are the principal immune cells in the central nervous system (CNS). Triggering receptor expressed on myeloid cell 2 (TREM2) is a surface receptor that, within the CNS, is exclusively expressed on microglia and plays crucial roles in microglial proliferation, migration, activation, metabolism, and phagocytosis. Genetic evidence has linked TREM2 to neurodegenerative diseases including ALS, but its function in ALS pathogenesis is largely unknown. In this review, we summarize how microglial activation, with a specific focus on TREM2 function, affects ALS progression clinically and experimentally. Understanding microglial TREM2 function will help pinpoint the molecular target for ALS treatment.
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Affiliation(s)
- Manling Xie
- Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.,Mayo Clinic Graduate School of Biomedical Sciences, Rochester, Minnesota, USA
| | - Shunyi Zhao
- Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA
| | - Dale B Bosco
- Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA
| | - Aivi Nguyen
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA
| | - Long-Jun Wu
- Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA.,Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, USA.,Department of Immunology, Mayo Clinic, Rochester, Minnesota, USA
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Siokas V, Aloizou AM, Liampas I, Tsouris Z, Mentis AFA, Nasios G, Papadimitriou D, Bogdanos DP, Hadjigeorgiou GM, Dardiotis E. Lack of association between TREM2 rs75932628 variant and amyotrophic lateral sclerosis. Mol Biol Rep 2021; 48:2601-2610. [PMID: 33826063 DOI: 10.1007/s11033-021-06312-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Accepted: 03/20/2021] [Indexed: 12/11/2022]
Abstract
Amyotrophic lateral sclerosis (ALS) is a multifactorial neurodegenerative disease. Inflammatory processes are among the mechanisms that are implicated in ALS pathogenesis. The TREM2 rs75932628 T variant may influence the regulatory effect of TREM2 on inflammation. Studies regarding the role of the rs75932628 variant in ALS have yielded inconsistent results, so far. To assess the role of TREM2 rs75932628 on ALS risk. We genotyped 155 patients with sporadic ALS and 155 healthy controls for TREM2 rs75932628. We also merged and meta-analyzed our data with data from previous studies (with a total of 7524 ALS cases and 14,675 controls), regarding TREM2 rs75932628 and ALS. No ALS or healthy subjects carried the TREM2 rs75932628-T variant. Results from meta-analyses (overall approach and sensitivity analyses) yielded no significant results for possible connection between TREM2 rs75932628-T variant and ALS. Based on our results, TREM2 rs75932628 does not seem to play a determining role to the pathophysiology of ALS.
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Affiliation(s)
- Vasileios Siokas
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece.,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece
| | - Athina-Maria Aloizou
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece.,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece
| | - Ioannis Liampas
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece.,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece
| | - Zisis Tsouris
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece.,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece
| | - Alexios-Fotios A Mentis
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece.,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece.,Public Health Laboratories, Hellenic Pasteur Institute, Athens, Greece
| | - Grigorios Nasios
- Department of Speech and Language Therapy, University of Ioannina, Ioannina, Greece
| | | | - Dimitrios P Bogdanos
- Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece.,Department of Rheumatology and Clinical Immunology, University General Hospital of Larissa, Larissa, Greece
| | - Georgios M Hadjigeorgiou
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece.,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece.,Department of Neurology, Medical School, University of Cyprus, Nicosia, Cyprus
| | - Efthimios Dardiotis
- Department of Neurology, Laboratory of Neurogenetics, University Hospital of Larissa, Larissa, Greece. .,Faculty of Medicine, School of Health Sciences, University of Thessaly, Biopolis, Mezourlo Hill, 41100, Larissa, Greece.
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Microglia Implicated in Tauopathy in the Striatum of Neurodegenerative Disease Patients from Genotype to Phenotype. Int J Mol Sci 2020; 21:ijms21176047. [PMID: 32842621 PMCID: PMC7503242 DOI: 10.3390/ijms21176047] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 08/19/2020] [Accepted: 08/20/2020] [Indexed: 12/12/2022] Open
Abstract
We found interactions between dopamine and oxidative damage in the striatum involved in advanced neurodegeneration, which probably change the microglial phenotype. We observed possible microglia dystrophy in the striatum of neurodegenerative brains. To investigate the interactions between oxidative damage and microglial phenotype, we quantified myeloperoxidase (MPO), poly (ADP-Ribose) (PAR), and triggering receptors expressed on myeloid cell 2 (TREM2) using enzyme-linked immunosorbent assay (ELISA). To test the correlations of microglia dystrophy and tauopathy, we quantified translocator protein (TSPO) and tau fibrils using autoradiography. We chose the caudate and putamen of Lewy body diseases (LBDs) (Parkinson’s disease, Parkinson’s disease dementia, and Dementia with Lewy body), Alzheimer’s disease (AD), and control brains and genotyped for TSPO, TREM2, and bridging integrator 1 (BIN1) genes using single nucleotide polymorphisms (SNP) assays. TREM2 gene variants were absent across all samples. However, associations between TSPO and BIN1 gene polymorphisms and TSPO, MPO, TREM2, and PAR level variations were found. PAR levels reduced significantly in the caudate of LBDs. TSPO density and tau fibrils decreased remarkably in the striatum of LBDs but increased in AD. Oxidative damage, induced by misfolded tau proteins and dopamine metabolism, causes microglia dystrophy or senescence during the late stage of LBDs. Consequently, microglia dysfunction conversely reduces tau propagation. The G allele of the BIN1 gene is a potential risk factor for tauopathy.
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Zhang B, Li R, Zhang Y, Gao X. Differential role of triggering receptors expressed on myeloid cells 2 R47H in 3 neurodegenerative diseases based on a systematic review and meta-analysis. Medicine (Baltimore) 2020; 99:e18921. [PMID: 32000403 PMCID: PMC7004756 DOI: 10.1097/md.0000000000018921] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Recent studies have suggested that the potential functional polymorphism R47H in triggering receptors expressed on myeloid cells 2 (TREM2) is associated with several neurodegenerative diseases, however, the results remain inconclusive. This meta-analysis aimed to investigate the association between TREM2 R47H and the risk for 3 typical neurodegenerative diseases: Alzheimer disease (AD), Parkinson disease (PD), and amyotrophic lateral sclerosis (ALS). METHODS A literature review was carried out using PubMed, Medline, and Embase. Data analysis was conducted using Stata 15.0 software. The pooled odds ratio (ORs) and 95% confidence interval (CIs) were calculated. RESULTS A total of 35 articles were identified as eligible: 22 on AD, 3 on ALS, 7 on PD, 2 on AD and ALS, and 1 on ALS and PD. The AD set included 23,092 cases and 30,920 controls, the ALS set included 7391 cases and 12,442 controls, and the PD set included 8498 patients and 9161 controls. We found that R47H was associated with an increased risk of AD in the total pooled population (P < .001, OR = 4.02, 95% CI = 3.15-5.13). However, this significant difference existed for Caucasian people (OR = 4.16, 95% CI = 3.24-5.33) but not for Asian or African people. Moreover, we did not find any significant differences in minor allele frequency distribution between the PD and control groups or between the ALS and control groups, not only for the total pooled population but also for the subgroups of different ethnicities. CONCLUSION Our study suggested that R47H in the TREM2 gene leads to an increased risk for developing AD, but not for ALS and PD, which adds evidence to the notion that diverse pathogenesis may be involved in different neurogenerative diseases.
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Affiliation(s)
- Bin Zhang
- Department of Neurology, the First Hospital of Yulin, Yulin, Shaanxi
| | - Rui Li
- Department of Neurology, the First Hospital of Yulin, Yulin, Shaanxi
| | - Yufan Zhang
- Department of Neurology, the First Hospital of Yulin, Yulin, Shaanxi
| | - Xia Gao
- Department of Geriatrics, Dazhou Central Hospital, Dazhou, Sichuan, China
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The Role of APOE and TREM2 in Alzheimer's Disease-Current Understanding and Perspectives. Int J Mol Sci 2018; 20:ijms20010081. [PMID: 30587772 PMCID: PMC6337314 DOI: 10.3390/ijms20010081] [Citation(s) in RCA: 106] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Revised: 12/19/2018] [Accepted: 12/21/2018] [Indexed: 12/12/2022] Open
Abstract
Alzheimer's disease (AD) is the leading cause of dementia worldwide. The extracellular deposits of Amyloid beta (Aβ) in the brain-called amyloid plaques, and neurofibrillary tangles-intracellular tau aggregates, are morphological hallmarks of the disease. The risk for AD is a complicated interplay between aging, genetic risk factors, and environmental influences. One of the Apolipoprotein E (APOE) alleles-APOEε4, is the major genetic risk factor for late-onset AD (LOAD). APOE is the primary cholesterol carrier in the brain, and plays an essential role in lipid trafficking, cholesterol homeostasis, and synaptic stability. Recent genome-wide association studies (GWAS) have identified other candidate LOAD risk loci, as well. One of those is the triggering receptor expressed on myeloid cells 2 (TREM2), which, in the brain, is expressed primarily by microglia. While the function of TREM2 is not fully understood, it promotes microglia survival, proliferation, and phagocytosis, making it important for cell viability and normal immune functions in the brain. Emerging evidence from protein binding assays suggests that APOE binds to TREM2 and APOE-containing lipoproteins in the brain as well as periphery, and are putative ligands for TREM2, thus raising the possibility of an APOE-TREM2 interaction modulating different aspects of AD pathology, potentially in an isoform-specific manner. This review is focusing on the interplay between APOE isoforms and TREM2 in association with AD pathology.
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The role of TREM2 in Alzheimer's disease and other neurodegenerative disorders. Lancet Neurol 2018; 17:721-730. [PMID: 30033062 DOI: 10.1016/s1474-4422(18)30232-1] [Citation(s) in RCA: 156] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/04/2018] [Accepted: 06/06/2018] [Indexed: 12/12/2022]
Abstract
Alzheimer's disease is a genetically complex disorder; rare variants in the triggering receptor expressed on myeloid cells 2 (TREM2) gene have been shown to as much as triple an individual's risk of developing Alzheimer's disease. TREM2 is a transmembrane receptor expressed in cells of the myeloid lineage, and its association with Alzheimer's disease supports the involvement of immune and inflammatory pathways in the cause of the disease, rather than as a consequence of the disease. TREM2 variants associated with Alzheimer's disease induce partial loss of function of the TREM2 protein and alter the behaviour of microglial cells, including their response to amyloid plaques. TREM2 variants have also been shown to cause polycystic lipomembranous osteodysplasia with sclerosing leukoencephalopathy and frontotemporal dementia. Although the low frequency of TREM2 variants makes it difficult to establish robust genotype-phenotype correlations, such studies are essential to enable a comprehensive understanding of the role of TREM2 in different neurological diseases, with the ultimate goal of developing novel therapeutic approaches.
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Let's make microglia great again in neurodegenerative disorders. J Neural Transm (Vienna) 2017; 125:751-770. [PMID: 29027011 DOI: 10.1007/s00702-017-1792-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2017] [Accepted: 09/18/2017] [Indexed: 12/12/2022]
Abstract
All of the common neurodegenerative disorders-Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and prion diseases-are characterized by accumulation of misfolded proteins that trigger activation of microglia; brain-resident mononuclear phagocytes. This chronic form of neuroinflammation is earmarked by increased release of myriad cytokines and chemokines in patient brains and biofluids. Microglial phagocytosis is compromised early in the disease process, obfuscating clearance of abnormal proteins. This review identifies immune pathologies shared by the major neurodegenerative disorders. The overarching concept is that aberrant innate immune pathways can be targeted for return to homeostasis in hopes of coaxing microglia into clearing neurotoxic misfolded proteins.
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Jay TR, von Saucken VE, Landreth GE. TREM2 in Neurodegenerative Diseases. Mol Neurodegener 2017; 12:56. [PMID: 28768545 PMCID: PMC5541421 DOI: 10.1186/s13024-017-0197-5] [Citation(s) in RCA: 256] [Impact Index Per Article: 36.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 07/20/2017] [Indexed: 12/12/2022] Open
Abstract
TREM2 variants have been identified as risk factors for Alzheimer's disease (AD) and other neurodegenerative diseases (NDDs). Because TREM2 encodes a receptor exclusively expressed on immune cells, identification of these variants conclusively demonstrates that the immune response can play an active role in the pathogenesis of NDDs. These TREM2 variants also confer the highest risk for developing Alzheimer's disease of any risk factor identified in nearly two decades, suggesting that understanding more about TREM2 function could provide key insights into NDD pathology and provide avenues for novel immune-related NDD biomarkers and therapeutics. The expression, signaling and function of TREM2 in NDDs have been extensively investigated in an effort to understand the role of immune function in disease pathogenesis and progression. We provide a comprehensive review of our current understanding of TREM2 biology, including new insights into the regulation of TREM2 expression, and TREM2 signaling and function across NDDs. While many open questions remain, the current body of literature provides clarity on several issues. While it is still often cited that TREM2 expression is decreased by pro-inflammatory stimuli, it is now clear that this is true in vitro, but inflammatory stimuli in vivo almost universally increase TREM2 expression. Likewise, while TREM2 function is classically described as promoting an anti-inflammatory phenotype, more than half of published studies demonstrate a pro-inflammatory role for TREM2, suggesting that its role in inflammation is much more complex. Finally, these components of TREM2 biology are applied to a discussion of how TREM2 impacts NDD pathologies and the latest assessment of how these findings might be applied to immune-directed clinical biomarkers and therapeutics.
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Affiliation(s)
- Taylor R. Jay
- Department of Neurosciences, Case Western Reserve University, School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106 USA
| | - Victoria E. von Saucken
- Department of Neurosciences, Case Western Reserve University, School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106 USA
- Stark Neurosciences Research Institute, Indiana University School of Medicine, 320 W 15th Street, Indianapolis, IN 46202 USA
| | - Gary E. Landreth
- Department of Neurosciences, Case Western Reserve University, School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106 USA
- Stark Neurosciences Research Institute, Indiana University School of Medicine, 320 W 15th Street, Indianapolis, IN 46202 USA
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