Cited by 110Neuroinflammation and Neurodegeneration MechanismsPhagocytosis and Immune RegulationInflammation biomarkers and pathways

Distinct Signaling Pathways Regulate TREM2 Phagocytic and NFκB Antagonistic Activities

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Yao, Hailan, Coppola, Kyle, Schweig, Jonas Elias, Crawford, Fiona, Mullan, Michael, Paris, Daniel·2019·Frontiers in Cellular Neuroscience

Abstract

Several genetic variants of the Triggering Receptor Expressed on Myeloid Cells-2 (TREM2) have been shown to increase the risk of developing Alzheimer's disease (AD) supporting a role of microglia and immune cells in the pathobiology of AD. We have employed an ectopic model of TREM2 and DAP12 expression in HEK293 cells to study selectively TREM2 dependent signaling and phagocytic functions and evaluated the effects of some of the TREM2 mutations associated with AD. We show that shedding of the TREM2 N-terminal domain does not affect the inhibition of NFκB activation induced by TREM2 while it completely blocks phagocytosis suggesting that TREM2 anti-inflammatory properties can be mediated by the TREM2 C-terminal fragment while the phagocytic activity requires the full-length receptor. In addition, we confirm in that model that apolipoprotein E (APOE) is a ligand for TREM2 and triggers TREM2 signaling. In particular, we show that APOE4 stimulates spleen tyrosine kinase (SYK) activation more potently than APOE2 in a TREM2 dependent manner. Interestingly, TREM2 appears to antagonize NFκB activation induced by phorbol ester but is unable to prevent TNFα induction of NFκB activation suggesting that TREM2 antagonizes inflammatory events triggered downstream of PKC. TREM2 mutations drastically impact TREM2 phagocytosis as well as its ability to antagonize NFκB activation and notably prevent the activation of the PI3K/AKT pathway observed with wild-type TREM2. Overall our data suggest that TREM2 dependent phagocytosis requires an activation of the SYK/PI3K/AKT/PLCγ pathways while the suppression of NFκB activation by TREM2 is independent of SYK, PI3K, and PLCγ activities. This model of ectopic TREM2-DAP12 co-expression appears suitable to study TREM2 signaling as several biological functions of TREM2 and TREM2 mutations that have been previously described in myeloid and microglial cells were also replicated in this model.

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Crossref · 10.3389/fncel.2019.00457

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  • SYK is the central kinase that instructs signaling and effector functions downstream of TREM2, CD33, and CD22 receptors.

    “In addition, SYK has been identified as the central kinase that instructs signaling and effector functions downstream of TREM2, CD33, and CD22 receptors (Clark and Giltiay, 2018; Wissfeld et al., 2021; Yao et al., 2019).”

    From SYK coordinates neuroprotective microglial responses in neurodegenerative disease (2022) · cites this paper as Yao et al., 2019

    The Introduction (page unavailable) describes SYK as a proposed key kinase in TREM2 signaling. The Results section on SYK-dependent phagocytosis (page unavailable) finds that SYK only partially mediates TREM2 phagocytosis and is not required for its suppression of NFκB activation. The paper does not establish the claimed role downstream of CD33 or CD22. (LLM, conf=0.90)

    Experimental — accuracy not yet measured
  • Previous in vitro studies have shown that TREM2 activation can provoke SYK signaling.

    “Though previous in vitro studies have shown that TREM2 activation can provoke SYK signaling (Yao et al., 2019)”

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Authors
Yao, H., Coppola, K., Schweig, J. E., Crawford, F., Mullan, M., & Paris, D.
Affiliations
James A. Haley Veterans' Hospital (US)
Corresponding author
Yao, Hailan
Venue
Frontiers in Cellular Neuroscience
Published
2019-10-10
Volume
13
Pages
457-457
ISSN
1662-5102 (ISSN-L)
OpenAlex
W2979963278
Cited by
110
References
86
Citations by year
2026: 14 · 2025: 22 · 2024: 21 · 2023: 17 · 2022: 17 · 2021: 13 · 2020: 6
FWCI
3.96
Type
journal article
Language
en
Open access
Locations
  • Frontiers in Cellular Neuroscience (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
U.S. Department of Veterans Affairs
Topics
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Immunology and Microbiology › Immunology › Phagocytosis and Immune Regulation
  • Life Sciences › Immunology and Microbiology › Immunology › Inflammation biomarkers and pathways
Keywords
TREM2, Alzheimer's disease, phagocytosis, NF-κB signaling, DAP12, Syk, apolipoprotein E, APOE ε4, PI3K/Akt signaling, phospholipase C-gamma, microglia, anti-inflammatory signaling, TNF-α

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