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Mol Neurodegener. 2019 Jan 10;14(1):1. doi: 10.1186/s13024-018-0301-5.

Early increase of CSF sTREM2 in Alzheimer's disease is associated with tau related-neurodegeneration but not with amyloid-β pathology.

Author information

1
Chair of Metabolic Biochemistry, Biomedical Center (BMC), Faculty of Medicine, Ludwig-Maximilians-Universität München, Munich, Germany. msuarez@barcelonabeta.org.
2
German Center for Neurodegenerative Diseases (DZNE) Munich, Munich, Germany. msuarez@barcelonabeta.org.
3
Barcelonaβeta Brain Research Center (BBRC), Pasqual Maragall Foundation, Barcelona, Catalonia, Spain. msuarez@barcelonabeta.org.
4
German Center for Neurodegenerative Diseases (DZNE) Munich, Munich, Germany.
5
Department of Neurology, Institut d'Investigacions Biomèdiques, Hospital de la Santa Creu i Sant Pau, Universitat Autònoma de Barcelona, Barcelona, Catalonia, Spain.
6
Chair of Metabolic Biochemistry, Biomedical Center (BMC), Faculty of Medicine, Ludwig-Maximilians-Universität München, Munich, Germany.
7
Munich Cluster for Systems Neurology (SyNergy), Munich, Germany.
8
Institute for Stroke and Dementia Research, Klinikum der Universität München, Ludwig-Maximilians-Universität München, Munich, Germany.
9
Izmir International Biomedicine and Genome Institute Dokuz Eylul University, Izmir, Turkey.
10
Department of Neuroscience, Institute of Health Sciences, Dokuz Eylul University, Izmir, Turkey.
11
Department of Neurology, Ludwig-Maximilians-Universität München, Munich, Germany.
12
Department of Psychiatry, Washington University School of Medicine, Saint Louis, MO, USA.
13
Department of Neurology, Washington University School of Medicine, St. Louis, MO, USA.
14
Hope Center for Neurological Disorders, Washington University in St. Louis, St. Louis, MO, USA.
15
Knight Alzheimer's Disease Research Center, Washington University in St. Louis, St. Louis, MO, USA.
16
Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
17
Center for Neurodegenerative Disease Research, Institute on Aging, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
18
University of California at San Francisco, San Francisco, CA, USA.
19
Chair of Metabolic Biochemistry, Biomedical Center (BMC), Faculty of Medicine, Ludwig-Maximilians-Universität München, Munich, Germany. christian.haass@mail03.med.uni-muenchen.de.
20
German Center for Neurodegenerative Diseases (DZNE) Munich, Munich, Germany. christian.haass@mail03.med.uni-muenchen.de.
21
Munich Cluster for Systems Neurology (SyNergy), Munich, Germany. christian.haass@mail03.med.uni-muenchen.de.

Abstract

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 β-peptide (Aβ) 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 Aβ1-42 (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 Aβ pathology (A+) but no tau pathology or neurodegeneration (TN-), is present.

CONCLUSIONS:

Aβ 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, Aβ pathology in the absence of downstream tau-related neurodegeneration is associated with a decrease in CSF sTREM2.

KEYWORDS:

Alzheimer’s disease; Biomarkers; Microglia; Neurodegeneration; Neuroinflammation; Shedding; TREM2

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