Selection and structural characterization of anti-TREM2 scFvs that reduce levels of shed ectodomain

Microglia and TREM2

TREM2 is a membrane receptor solely expressed on microglia in normal brain. In this review we outline recent advances in TREM2 biology and its implications for microglial function, with particular emphasis on findings from iPSC-derived microglia (iMG) expressing TREM2 loss-of-function mutations. Alterations in receptor proximal and distal signalling underlie TREM2 risk variants linked to neurodegenerative disease, principally NH-linked FTD, and late-onset AD, but emerging data suggest roles for TREM2 in PD, MS and ALS. TREM2 downstream functions include phagocytosis of myelin debris, amyloid beta peptides, and phosphatidylserine-expressing cells (resulting from damage or stress). Microglial survival, migration, DAMP signalling, inflammasome activation, and intercellular signalling including tau spreading via exosomes, as well as roles for sTREM2 in protection and as a biomarker are discussed. The role of TREM2 in metabolic homeostasis, and immunometabolic switching are discussed regarding microglial responses to damage and protection. The use of iPSC models to investigate the role of TREM2 in AD, PD, MS, ALS, and other neurodegenerative diseases could prove invaluable due to their ability to recapitulate human pathology, allowing a full understanding of TREM2 and microglial involvement in the underlying disease mechanisms and progression. This article is part of the Special Issue on "Microglia".

Multimerization of TREM2 is impaired by Alzheimer's disease-associated variants

INTRODUCTION

The immune receptor triggering receptor expressed on myeloid cells 2 (TREM2) is among the strongest genetic risk factors for Alzheimer's disease (AD) and is a therapeutic target. TREM2 multimers have been identified in crystallography and implicated in the efficacy of antibody therapeutics; however, the molecular basis for TREM2 multimerization remains poorly understood.

METHODS

We used molecular dynamics simulations and binding energy analysis to determine the effects of AD-associated variants on TREM2 multimerization and validated with experimental results.

RESULTS

TREM2 trimers remained stably bound, driven primarily by salt bridge between residues D87 and R76 at the interface of TREM2 units. This salt bridge was disrupted by the AD-associated variants R47H and R98W and nearly ablated by the D87N variant. This decreased binding among TREM2 multimers was validated with co-immunoprecipitation assays.

DISCUSSION

This study uncovers a molecular basis for TREM2 forming stable trimers and unveils a novel mechanism by which TREM2 variants may increase AD risk by disrupting TREM2 oligomerization to impair TREM2 normal function.

HIGHLIGHTS

Triggering receptor expressed on myeloid cells 2 (TREM2) multimerization could regulate TREM2 activation and function. D87-R76 salt bridges at the interface of TREM2 units drive the formation of stable TREM2 dimers and trimers. Alzheimer's disease (AD)-associated R47H and R98W variants disrupt the D87-R76 salt bridge. The AD-associated D87N variant leads to complete loss of the D87-R76 salt bridge.

Decoding sTREM2: its impact on Alzheimer's disease - a comprehensive review of mechanisms and implications

Soluble Triggering Receptor Expressed on Myeloid Cells 2 (sTREM2) plays a crucial role in the pathogenesis of Alzheimer's disease (AD). This review comprehensively examines sTREM2's involvement in AD, focusing on its regulatory functions in microglial responses, neuroinflammation, and interactions with key pathological processes. We discuss the dynamic changes in sTREM2 levels in cerebrospinal fluid and plasma throughout AD progression, highlighting its potential as a therapeutic target. Furthermore, we explore the impact of genetic variants on sTREM2 expression and its interplay with other AD risk genes. The evidence presented in this review suggests that modulating sTREM2 activity could influence AD trajectory, making it a promising avenue for future research and drug development. By providing a holistic understanding of sTREM2's multifaceted role in AD, this review aims to guide future studies and inspire novel therapeutic strategies.

Artificial intelligence for drug discovery and development in Alzheimer's disease

The complex molecular mechanism and pathophysiology of Alzheimer's disease (AD) limits the development of effective therapeutics or prevention strategies. Artificial Intelligence (AI)-guided drug discovery combined with genetics/multi-omics (genomics, epigenomics, transcriptomics, proteomics, and metabolomics) analysis contributes to the understanding of the pathophysiology and precision medicine of the disease, including AD and AD-related dementia. In this review, we summarize the AI-driven methodologies for AD-agnostic drug discovery and development, including de novo drug design, virtual screening, and prediction of drug-target interactions, all of which have shown potentials. In particular, AI-based drug repurposing emerges as a compelling strategy to identify new indications for existing drugs for AD. We provide several emerging AD targets from human genetics and multi-omics findings and highlight recent AI-based technologies and their applications in drug discovery using AD as a prototypical example. In closing, we discuss future challenges and directions in AI-based drug discovery for AD and other neurodegenerative diseases.

sTREM2 in the prognostic evaluation of acute lung injury after cardiac surgery in infants

BACKGROUND

Previous studies have shown that TREM2 plays a protective role in acute lung injury (ALI). This prospective study aimed to investigate the role of sTREM2 as a forecasting factor for ALI in infants after pediatric cardiac surgery undergoing cardiopulmonary bypass (CPB).

METHODS

Seventy-five consecutive patients younger than 1 year who underwent cardiac surgery were enrolled in this study. Sixty-one fulfilled the inclusion criteria and had been divided into ALI and non-ALI groups. Children's demographic characteristics and clinical data were collected. Perioperative sTREM2 levels were analyzed at five timepoints.

RESULTS

In this study, children in the ALI group were younger, lighter, with higher RACHS-1 scores and underwent significantly longer CPB time. Post-CPB ALI had an impact on clinical outcomes, which contributed to a longer duration of mechanical ventilation, ICU and hospital stay than non-ALI group. Significant differences were manifested off-CPB, 1 h/6 h after CPB, and day 1 after surgery between the two groups. Binary logistic models revealed that off-CPB sTREM2 was significantly associated with the incidence of post-CPB ALI after adjustment. ROC analysis showed that the AUC of off-CPB sTREM2 level was 0.791, and the optimal cutoff value was 788.6 pg/ml.

CONCLUSIONS

The off-CPB sTREM2 level was an independent prognostic factor for post-CPB ALI in infants.

IMPACT

Plasma sTREM2 works together with downstream TREM2 to regulate inflammation response by binding the receptor to other cells. Previous studies have shown that TREM2 plays a protective role in ischemia-reperfusion and has anti-inflammatory effects on acute lung injury (ALI). This study analyzed the risk factors of post-cardiopulmonary bypass (CPB) ALI. We found that weight and off-CPB sTREM2 level were independent prognostic factors for post-CPB ALI. Plasma sTREM2 may serve as an early biomarker in the prognostic evaluation of acute lung injury after cardiac surgery in infants.

The biology of TREM receptors

Triggering receptors expressed on myeloid cells (TREMs) encompass a family of cell-surface receptors chiefly expressed by granulocytes, monocytes and tissue macrophages. These receptors have been implicated in inflammation, neurodegenerative diseases, bone remodelling, metabolic syndrome, atherosclerosis and cancer. Here, I review the structure, ligands, signalling modes and functions of TREMs in humans and mice and discuss the challenges that remain in understanding TREM biology.

Serum soluble triggering receptor levels expressed on myeloid cells2 identify early acute kidney injury in infants and young children after pediatric cardiopulmonary bypass

Background

Acute kidney injury (AKI) is a potential complication after cardiopulmonary bypass (CPB) of pediatric cardiac surgery and contributes to a certain amount of perioperative mortality. Serum soluble triggering receptor expressed on myeloid cells2 (sTREM2) is an inflammation-associated cytokine in circulation. Alterations of sTREM2 level have been reported in Alzheimer's disease, sepsis, and some other pathologic conditions. This study aimed to investigate the role of sTREM2 as a forecasting factor for AKI in infants and young children and other factors associated with early renal injury after pediatric CPB.

Methods

A prospective cohort study with consecutive infants and young children ≤ 3 years old undergoing CPB from September 2021 to August 2022 was conducted in an affiliated university children's hospital. These patients were divided into an AKI group (n = 10) and a non-AKI group (n = 60). Children's characteristics and clinical data were measured. Perioperative sTREM2 levels were analyzed with enzyme-linked immunosorbent assay (ELISA).

Results

In children developing AKI, the sTREM2 levels significantly decreased at the beginning of CPB compared to the non-AKI group. Based on binary logistic regression analysis and multivariable regression analysis, risk-adjusted classification for congenital heart surgery (RACHS-1), operation time, and the s-TREM2 level at the beginning of CPB (AUC = 0.839, p = 0.001, optimal cut-off value: 716.0 pg/ml) had predictive value for post-CPB AKI. When combining the sTREM2 level at the beginning of CPB and other indicators together, the area under the ROC curve enlarged.

Conclusions

Operation time, RACHS-1 score, and sTREM2 level at the beginning of CPB were independent prognosis factors of post-CPB AKI in infants and young children ≤ 3 years old. Decreased sTREM2 identified post-CPB AKI, and ultimately hampered the outcomes. Our findings indicated that sTREM2 may be a protective factor for AKI after CPB in infants and young children ≤ 3 years old.

TREM2 dependent and independent functions of microglia in Alzheimer's disease

Microglia are central players in brain innate immunity and have been the subject of extensive research in Alzheimer's disease (AD). In this review, we aim to summarize the genetic and functional discoveries that have advanced our understanding of microglia reactivity to AD pathology. Given the heightened AD risk posed by rare variants of the microglial triggering receptor expressed on myeloid cells 2 (TREM2), we will focus on the studies addressing the impact of this receptor on microglia responses to amyloid plaques, tauopathy and demyelination pathologies in mouse and human. Finally, we will discuss the implications of recent discoveries on microglia and TREM2 biology on potential therapeutic strategies for AD.

Soluble TREM2: Innocent bystander or active player in neurological diseases?

Triggering receptor expressed on myeloid cells 2 (TREM2) is an innate immune receptor expressed by macrophages and microglia in the central nervous system (CNS). TREM2 has attracted a lot of interest in the past decade for its critical role in modulating microglia functions under homeostatic conditions and in neurodegenerative diseases. Genetic variation in TREM2 is sufficient to cause Nasu-Hakola disease, a rare pre-senile dementia with bone cysts, and to increase risk for Alzheimer's disease, frontotemporal dementia, and other neurodegenerative disorders. Beyond the role played by TREM2 genetic variants in these diseases, TREM2 engagement is a key step in microglia activation in response to different types of tissue injury (e.g. β-Amyloid deposition, demyelination, apoptotic cell death) leading to enhanced microglia metabolism, phagocytosis, proliferation and survival. TREM2 also exists as a soluble form (sTREM2), generated from receptor shedding or alternative splicing, which is detectable in plasma and cerebrospinal fluid (CSF). Genetic variation, physiological conditions and disease status impact CSF sTREM2 levels. Clinical and preclinical studies suggest that targeting and/or monitoring sTREM2 could have clinical and therapeutic implications. Despite the critical role of sTREM2 in neurologic disease, its function remains poorly understood. Here, we review the current literature on sTREM2 regarding its origin, genetic variation, and possible functions as a biomarker in neurological disorders and as a potential active player in CNS diseases and target for therapies.

Exciting new tools for studying TREM2 in dementia

TREM2 has long been implicated as an Alzheimer's disease (AD) risk gene. In this issue of Structure, Szykowska et al. (2021) generate antibody single-chain variable fragments (scFvs) to the immunoglobulin(Ig)-like domain of human TREM2. They present two co-crystalized structures and characterize the functional impact of these scFvs on TREM2.