Available online 19 January 2024, 103917

Author links open overlay panelAbstract

Triggering receptor expressed on myeloid cells 2 (TREM2) is a membrane glycoprotein that plays a crucial role in the regulation of microglial survival, activation, phagocytosis, as well as in the maintenance of brain homeostasis and the inflammatory response to injury or neurodegeneration. This review provides a comprehensive overview of TREM2 structure and functions, highlighting the role of its variants in the development and progression of Alzheimer's disease (AD), a devastating neurodegenerative disease that affects millions of people worldwide. Additionally, the article discusses the potential of TREM2 as a therapeutic target in AD, analyzing the current state of research and future prospects. Given the significant challenges associated with the activation of TREM2, particularly due to its diverse isoforms and the delicate balance required to modulate the immune response without triggering hyperactivation, this review aims to enhance our understanding of TREM2 in AD and inspire further research into this promising yet challenging therapeutic target.

Section snippetsTREM2 structure and functions

TREM2 (Triggering receptor expressed on myeloid cells 2) is a ∼ 40-kDa type I membrane glycoprotein that in the CNS is believed to be exclusively expressed on microglia (Dhandapani et al., 2022; Schmid et al., 2002). The TREM2 protein is encoded by the TREM2 gene consisting of five exons with a total length of 4681 base pairs located on human chromosome 6p21.1 (“GeneCards,” n.d.). The TREM2 undergoes alternative splicing, and it has been reported that there are at least three TREM2 transcripts:

The role of TREM2 in Alzheimer's disease

Alzheimer's disease (AD) is an age-dependent, complex, and devastating neurodegenerative disease that affects millions of individuals worldwide (Li et al., 2022). It is characterized by progressive cognitive decline and memory loss. The neuropathologic hallmarks of AD are the widespread deposition of amyloid β (Aβ) plaques in the neocortex and hierarchically organized pattern of neurofibrillary tangles (composed of aggregated and hyperphosphorylated forms of tau protein) in limbic and cortical

Impact of TREM2 signalling disruptions on microglial functions

In the literature, can be found numerous, although sometimes contraindicatory, results regarding the effects of wild-type, R47H and KO of TREM2 on the most important function of microglia: phagocytosis. Hall-Roberts et al., comparing the R47H homozygous TREM2 variant with TREM2 KO in human microglia-like iPSC macrophages, reported that altered gene expression in R47H overlapped by 90 % with TREM2 KO. The dysregulated genes were involved in immune response, proliferation, activation, and

Benefits and limitations of TREM2 activation

In the development of new treatment strategies based on modulation of TREM2 activity, it is crucial to determine whether it is more advantageous to increase TREM2 activity or, conversely, to inhibit it.

Okuzono et al. (Okuzono et al., 2021), using anti-TREM2-specific agonistic antibody and pluripotent stem cell-derived microglia-like cells, identified 300 upregulated and 251 downregulated differentially expressed genes (DEGs) following TREM2 activation. As presented in Table 1, activation of

Conclusions and future perspectives

The role of TREM2 and its precise function in AD is still a subject of ongoing research. Some studies have suggested that TREM2 dysfunction, caused by the mutations or reduced expression, may be associated with an increased risk of AD and can contribute to the development of this disease. This may result from an impaired ability of CNS to regulate the immune response, leading to overproduction of proinflammatory cytokines and thus increased inflammation. Therefore, some researchers have

Funding

This work was supported by NCN (National Science Centre, Poland) MINIATURA grant number DEC-2021/05/X/NZ3/01074.

CRediT authorship contribution statement

Emilia Zgorzynska: Conceptualization, Funding acquisition, Writing – original draft, Writing – review & editing.

Uncited references

Frank et al., 2008

Lue et al., 2015

Declaration of competing interest

The author has no relevant financial or non-financial interests to disclose.

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