Natural genetic variation determines microglia heterogeneity in wild-derived mouse models of Alzheimer’s disease

Abstract

Microglia are now considered drivers of Alzheimer's disease (AD) pathology. However, single-cell RNA-sequencing (scRNA-seq) of microglia in mice, a key preclinical model organsim, have shown mixed results regarding translatability to human studies. To address this, scRNA-seq of microglia from C57BL/6J (B6) and wild-derived strains WSB/EiJ, CAST/EiJ and PWK/PhJ carrying APP/PS1 was performed and demonstrated that genetic diversity significantly altered features and dynamics of microglia in baseline neuroimmune functions and in response to amyloidosis. There was significant variation in abundance of microglial subpopulations, including numbers of disease-associated microglia and interferon-responding microglia across the strains.Further, for each subpopulation, significant gene expression differences were observed between strains, and relative to B6 that included nineteen genes previously associated with human AD including Apoe, Trem2, Bin1 and Sorl1. This resource will be critical in the development of appropriately targeted therapeutics for AD and a range of other neurological diseases. 30 Introduction 31Alzheimer's disease (AD) is defined by the neuropathological accumulation of beta 32 amyloid plaques, neurofibrillary tangles of tau and widespread neuronal loss. AD is the 33 most common cause of adult dementia and is characterized by a wide range of 34 cognitive and behavioral deficits that severely impact quality of life and the ability to self-35 care. Recent work has re-focused the field towards the contribution of brain glial cells to 36 the initiation and spread of these disease-specific pathologies, and specifically on the 37 role of microglia as potentially a causative cell type in driving disease development and 38 progression. Human genome-wide association studies (GWAS) have identified more 39 than 25 variants near genes uniquely expressed in microglia that are predicted to 40 increase susceptibility for AD. In light of this complexity, the mouse represents a critical 41 model system to dissect the role of microglia and other glia in AD. 42 43There has been large debate regarding the alignment of mouse microglia to human 44 microglia in terms of identity, diversity and function. With the more widespread use of 45 single-cell sequencing technology, a number of groups have suggested that the species 46 difference is too great for conclusions drawn from mouse models to inform our 47 understanding of human microglia1,2. Central to this argument is the discovery and 48 description of a specific class of microglia in the mouse, disease-associated microglia 49 (DAM)3. Based upon the current data it is unclear whether the presence or absence of 50 DAM in human AD patients is the result of differences in tissue collection, extraction of 51 cells, genetic diversity of patients, sub-type of AD presented in donors or even the 52 relevant disease1,4. Recent work has demonstrated that single-nucleus RNA 53 sequencing of stored human tissue fails to detect differences in microglia activation 54 between AD and contro...

Amyloid-beta and tau pathologies are both necessary to induce novel stage-specific microglia subtypes during Alzheimer’s disease progression

“…1f). This observation is consistent with the previous report that accumulation of Aβ plaques leads to activation of the interferon pathway [27][28][29][30] . The expression of interferon pathway-related genes was robust in Tau4RΔK-AP microglia but was not observed in Tau4RΔK microglia, suggesting that both Aβ plaques and tau aggregation are necessary to fully induce EADAM differentiation.…”

“…LADAM continues to express classic DAM genes but also upregulates additional genes, including Cd74 and MHC Class II genes. These broad LADAM marker-expressing microglia (Cd74 and MHC Class II genes) have been previously shown in some amyloidosis mouse models at late stages (known as activated response microglia) [27][28][29] , but these genes are likely to be contributed by mild tau phosphorylation shown in these amyloidosis mouse models, based on our findings from Tau4RΔK (Fig. 2).…”

“…EADAM are characterized by many interferon-pathway-related genes (Ifit3, Ifit204, Ifit2) and interferon regulating transcription factors (Irf2/7/9) as well as inflammatory chemokines (Ccl12, Cxcl10, Ccl5, Ccl2). Some of the genes in EADAM have been observed in other mouse models of amyloidosis that show early AD-like pathology [27][28][29] , including APP;PS1 and 5xFAD. However, given that EADAM-enriched genes are expressed in much higher levels in our Tau4RΔK-AP microglia, this strongly supports the view that both Aβ and tau pathologies are required to induce disease stage-specific microglia subtypes in AD.…”

“…These datasets show that tau pathologies are sufficient to trigger the emergence of LADAM and that their amplification is Aβ plaque-dependent. However, since MHC class II genes that are expressed in LADAM, such as Cd74, H2-A2, H2-Eb1, and H2-Ab1 have also been previously observed in microglia in the CK-p25 neurodegeneration mouse model 31,32 and also in some mouse models of late stage amyloidosis [27][28][29] , LADAM may be induced at least in part by neuronal death.…”

Angiotensin II‐induced endothelial dysfunction: Impact of sex, genetic background, and rho kinase

“…Genetic variation, or differences in genetic background, can have a major influence on vascular biology (Bjorkegren & Lusis, 2022; De Silva, Modrick, et al, 2018; von Scheidt et al, 2017; Yang et al, 2021). Rather than basing all conclusions on a single genetic strain, we used mice on two very different genetic backgrounds.…”