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Transcriptomic analysis of the effect of ASO-mediated (50ug/day) CD33 knock-down on the microglial gene network in an APP/PS1 mouse model of Alzheimer’s disease. [LNA-012]

ABSTRACT: Microglia, the resident innate immune cells of the central nervous system (CNS), are increasingly recognized as critical for normal CNS function as well as for the pathophysiology of CNS disorders, including Alzheimer's disease (AD). Advances in transcriptomic analyses, such as weighted gene co-expression network analysis, reveal that the most perturbed gene networks identified in AD brains fall squarely within microglial pathways and these findings are consistent with genetic and epigenetic genome-wide association studies linking specific microglial genes to AD risk. Increased expression of full-length CD33 increases AD risk and CD33 is a component of the microglial gene network, yet relatively little is known about the significance of CD33 in this gene network or in microglial biology. To gain further insight into these questions, we first identified and characterized locked nucleic acid (LNA) antisense oligonucleotides (ASOs) as tools to knock down CD33 in APP/PS1 mice in vivo. We report here that CD33 LNA ASO results in robust knockdown of CD33 mRNA the frontal cortex and hippocampus of APP/PS1 mice and that this knockdown causes changes to the AD-associated microglial gene network. This work suggests that CD33 may be a viable therapeutic target in AD.

ORGANISM(S): Mus musculus

PROVIDER: GSE74438 | GEO | 2016/09/30

SECONDARY ACCESSION(S): PRJNA300425

REPOSITORIES: GEO

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Project description:Background Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer’s disease (AD). In vitro, microglia preferentially upregulate iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of knocking down microglial iron import gene, Slc11a2, on AD-related cognitive decline and microglial transcriptional phenotype. Methods In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1Cre-ERT2;Slc11a2flfl;APP/PS1+ or – mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b+ microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted. Results DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2KD APP/PS1 females displayed significant increases in genes Enpp2, Ttr, and iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2KD cells from APP/PS1 females also exhibited decreased expression of markers related to disease-associated microglia (DAMs), such as Apoe, Ctsb, Csf1, and Hif1α. Conclusions This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in female microglia and cognitive deficits in Slc11a2KD APP/PS1 mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

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Transcriptomic analysis of the effect of ASO-mediated (50ug/day) CD33 knock-down on the microglial gene network in an APP/PS1 mouse model of Alzheimer’s disease. [LNA-012]

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