Welcome to the AD/PD™ 2022 Interactive Program
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THERAPEUTIC TARGETING OF MICROGLIAL FUNCTIONS
Abstract
Abstract Body
Triggering receptor expressed on myeloid cells 2 (TREM2) is essential for the transition of homeostatic microglia to a disease-associated microglial state. To enhance TREM2 activity, we sought to selectively increase the full-length protein on the cell surface via reducing its proteolytic shedding by A Disintegrin And Metalloproteinase (i.e., a-secretase) 10/17. We screened a panel of monoclonal antibodies against TREM2, with the aim to selectively compete for α-secretase-mediated shedding. Monoclonal antibody 4D9, which has a stalk region epitope close to the cleavage site, demonstrated dual mechanisms of action by stabilizing TREM2 on the cell surface and reducing its shedding, and concomitantly activating phospho-SYK signaling. 4D9 stimulated survival of macrophages and increased microglial uptake of myelin debris and amyloid β-peptide in vitro. In vivo target engagement was demonstrated in cerebrospinal fluid, where nearly all soluble TREM2 was 4D9-bound. Moreover, in a mouse model for Alzheimer’s disease related pathology, 4D9 reduced amyloidogenesis, enhanced microglial TREM2 expression, and reduced a homeostatic marker, suggesting a protective function by driving microglia toward a disease-associated state.
HIGHER SOLUBLE TREM2 IN CEREBROSPINAL FLUID IS ASSOCIATED WITH SLOWER AGE-RELATED HIPPOCAMPAL ATROPHY AND COGNITIVE DECLINE IN PRECLINICAL ALZHEIMER’S DISEASE
Abstract
Aims
Higher soluble TREM2 (sTREM2) in cerebrospinal fluid (CSF) has previously been linked with attenuated longitudinal brain atrophy and cognitive decline when assessed primarily among individuals with clinical MCI and AD. However, whether sTREM2 is associated with a protective effect preclinically is not known. Thus, the objective of this study was to assess whether higher baseline sTREM2 predicted slower age-related hippocampal atrophy and cognitive decline in preclinical AD.
Methods
Cognitively unimpaired participants with available lumbar puncture and longitudinal MRI and/or cognitive testing were considered preclinical and selected for analysis based on amyloid positivity as indexed by CSF amyloid-beta42/40 ratio. CSF sTREM2 was determined using a robust prototype assay as part of the Roche NeuroToolKit research platform. Linear mixed effects models with a random intercept tested whether higher baseline sTREM2 attenuated age-associated declines in ICV-adjusted hippocampal volume (N=80) as well as Rey Auditory Verbal Learning Test (RAVLT) total and long-delay recall scores (N=86), controlling for gender and years of education.
Results
See Figure 1. Results indicated significant sTREM2 x age interactions, whereby individuals with higher baseline sTREM2 had slower age-related decline in mean hippocampal volume (p = .033) as well as total (p = .009) and long-delay RAVLT scores (p = .027).
Conclusions
These findings support prior studies suggesting that higher sTREM2 levels may attenuate clinical progression in AD and extend previous findings by examining the impact of sTREM2 among cognitively unimpaired individuals with AD pathologic change. sTREM2, even in preclinical stages, may be associated with resilience to the deleterious impacts of amyloid accumulation.
UNDERSTANDING HUMAN TREM2-DEPENDENT MICROGLIAL RESPONSES TO ALZHEIMER’S DISEASE PATHOLOGY IN VIVO WITH CHIMERIC MICE
Abstract
Aims
Genome wide association studies have identified many Alzheimer’s disease (AD) risk genes that are highly expressed by microglia. Loss-of-function mutations in one such gene, TREM2 (Triggering receptor expressed on myeloid cells-2) have been shown to increase Late-onset AD risk by 2-4-fold. Studies of TREM2 knockout mice have provided consistent evidence that TREM2 is critically involved in the ability of microglia to sense and respond to beta-amyloid plaques. Yet many questions remain regarding whether human TREM2 knockout microglia exhibit similar or perhaps additional functional deficits.
Methods
To further examine the impact of TREM2 deletion on human microglia, we used CRISPR to generate TREM2-knockout (TREM2-KO) induced pluripotent stem cells (iPSCs). Isogenic wildtype and TREM2-KO iPSCs were differentiated into hematopoietic progenitors (HPCs) and transplanted into postnatal immunodeficient AD mice (hCSF1-5xFAD). Six months later, human microglia were isolated from chimeric mice brains and examined via single-cell RNA sequencing and bulk proteomic analysis.
Results
Analysis of RNA sequencing and proteomic datasets reveals significant and novel impacts of TREM2 deletion on the response of human microglia to beta-amyloid pathology. Examination of these complementary datasets identified both immune- and synapse-related co-expression networks that are significantly altered between TREM2 genotypes in AD mice. RNA sequencing further reveals distinct changes in disease associated microglia (DAM) and regulators of G protein signaling (RGS) cell populations with varying TREM2 genotypes.
Conclusions
Taken together, these data reveal important new information about the transcriptional and proteomic changes that occur within human microglia in response to amyloid pathology and loss of TREM2 expression.
COMPARATIVE ANALYSIS OF CRYOPRESERVED ISOGENIC IPSCS DERIVED I TREM2 WT, ENGINEERED TREM2HZ, TREM2 HO AND DONOR-DERIVED R47H MICROGLIA FROM FOR DISEASE MODELLING APPLICATIONS
Abstract
Aims
Recent GWAS have shown that sequence variants in the gene encoding the triggering receptor expressed on myeloid cells 2 (TREM2) are associated with an increased risk for AD. TREM2 senses lipids and mediates myelin phagocytosis. Loss-of-function (LOF) variants of TREM2, have been associated with an increased amyloid plaque seeding, reduced amyloid clustering and impairment of Microglia function. Cryopreserved microglia from engineered and patient derived iPSC provide an in vitro tool to model complex interactions to mimic neurogenerative diseases (Abud et al. 2017).
Methods
Episomally reprogrammed iPSCs were subjected to nuclease-mediated homologous recombination to generate TREM2 Heterozygous (TREM2HZ), homozygous iPSC line (TREM2HO) as well as R47H expressing donor derived Microglia. Parental, TREM2 HZ, TREM2 HO and R47H iPSCs were differentiated to microglia under defined conditions.
Results
Comparative analysis of TREM2HZ, TREM2HO and WT isogenic microglia identified different pathways altered by partial or complete loss of TREM2 function. TREM2HZ displayed enhanced down-regulation of SREBF2, the master regulator of cholesterol biosynthesis resulting in a decrease in the cholesterol and fatty acid synthesis, coinciding with increased lipid efflux. The role of TREM2 on the downregulation of in Gas6/Axl axis, Siglec11 expression, GPCRs, ion channels, transport proteins, soluble TREM2, neuroinflammatory cytokines and chemokines, phagocytic function to amyloid beta and a direct link between TREM2 with COMT, NRXN2 and SST expression is critical to understand the role of TREM2 in the onset of AD.
Conclusions
iPSC-derived microglia with TREM2 variants co-cultured with astrocyte and neurons can be used to mimic the onset of AD in a dish.
SINGLE-NUCLEI TRANSCRIPTOMIC ANALYSES OF HEALTHY AND ALZHEIMER’S DISEASE (AD) HUMAN BRAINS REVEAL CHANGES IN NEURON-MICROGLIA CELLULAR CROSSTALK PATTERNS
Abstract
Aims
Investigate changes in brain cellular crosstalk patterns between healthy and AD individuals.
Methods
We generated single-nuclei transcriptomic profiles (snRNA-seq) of parietal lobes from 67 donors, representing neuropathological-free controls and AD cases from pre-symptomatic, early, mid and late disease stages. We estimated cellular crosstalk patterns among the brain cell types based on the expression of known ligand-receptor pairs.
Results
We analyzed ~294K high-quality nuclei and identified six major cell populations. We observed changes in cellular crosstalk patterns between healthy and AD individuals, with the largest involving microglial interactions (increased in AD, OR=1.31, p=8.94e-11). Cellular interactions directly involving AD-related genes as either the receptor or the ligand were enriched for neuron-microglia pairs (OR=2.74, p=4.41e-15), and the majority (64.9%) codified for microglial cell membrane receptors, supporting the role for these cells in AD. We observed an increase in the frequency of a subset of AD-related interactions involving microglia when comparing pre-symptomatic and AD individuals, including TREM2-semaphorin (neuron-microglia, 4.38-fold increase), suggesting correlation with pathological burden. Another subset of microglia interactions, including HLADPB1-TNFSF13B (astrocyte-microglia, 4.67-fold increase), had increased frequency only in AD-risk variants carriers, suggesting these variants lead to pathological upregulation of these interactions. We compared interactions involving AD genes to interactions involving genes prioritized by GWAS for five neurological conditions. We identified shared and specific cellular crosstalk patterns across neurological conditions, consistent with distinct disease mechanisms.
Conclusions
Our work reveals the role of cellular crosstalk in AD biology and identifies disruptions in neuron-microglia interactions as an important component of AD pathology.
PRE-RECORDED: AMYLOID-INDUCED TAU SEEDING/SPREADING: ROLE OF MICROGLIA, TREM2, AND APOE
Abstract
Abstract Body
In Alzheimer disease (AD) models, microglia appear to influence amyloid-β (Aβ) linked tau seeding and spreading. We have been studying the effects of microglia, genes expressed by microglia, and genes expressed by microglia and other cells on Aβ-linked tau seeding and spreading. In the context of Aβ depositon, we asked whether microglial removal as well as removal with repopulation decreased Aβ driven tau seeding and spreading. We found that both TREM2 KO and microglial ablation dramatically enhance tau seeding and spreading around plaques. Interestingly, although repopulated microglia clustered around plaques, they had a reduction in disease associated microglia (DAM) gene expression and elevated tau seeding/spreading. Together, these data suggest that TREM2-dependent activation of the DAM phenotype is essential in delaying Aβ-induced pathological tau propagation. We are in the process of determining the role of apoE generally and apoE specifically deposited in plaques on Aβ-induced tau seeding and spreading.