| Abstrakt: |
Background: Upregulation of complement genes in Alzheimer's disease (AD) mouse models is associated with inflammation and cognitive decline. Genetic ablation of C5aR1 reduces loss of neuronal complexity and cognition in the Arctic mouse model. Inhibition of C5aR1 with PMX205 has shown success in preclinical studies of AD, reducing recruitment of reactive glia and amyloid deposition in the Tg2576 AD model. However, the molecular and cellular mechanisms underlying this neuroprotection are unclear. Thus, we used single cell RNA‐seq to interrogate gene pathways involved in C5aR1‐mediated deficits in the Arctic mouse model. Method: WT and Arctic mice were treated with PMX205 or vehicle via drinking water (20 µg/mL, equivalent to ∼5 mg/kg/day, consistent with previous studies) from 7.5 to 10 months of age. Effects of PMX205 on long‐ and short‐term memory were tested with object location memory (OLM) with a 24hr inter‐trial interval (ITI) and y‐maze spatial reference memory test with a 1hr ITI, respectively. Hippocampi were dissected and immediately prepared for microglial isolation and fixation. The single cell whole transcriptome kit (Parse Biosciences) was used to prepare single cell microglia libraries for RNA‐seq. Libraries were sequenced using NextSeq 2000. Parse Bioscience split‐pipe v0.7.6 was used to demultiplex reads into single‐cells, Scrublets to remove doublets, and Seurat for quality control, normalization, and clustering. Result: PMX205 protected against short‐, but not long‐, term memory deficits. Arctic‐PMX205 mice spent more time in the novel arm (44%) than Arctic‐vehicle mice (30%) in Y‐maze. Microglial single cell RNA‐seq identified 7 microglial clusters. Within these clusters, we probed for genes previously described as homeostatic, DAM1, and DAM2. DAM1 (Tyrobp, Apoe, Trem2) and DAM2 (Cst7, Itgax) genes were enriched in Arctic‐vehicle mice compared to WT mice, and expression was downregulated with PMX205 treatment in Arctic mice, most notably in DAM1 genes. Conclusion: Pharmacological C5aR1 inhibition confers some protective function even when treatment is initiated months after amyloid pathology onset in this aggressive mouse model of AD, and alters microglial polarization, suppressing detrimental inflammation. These findings complement previous data from genetic ablation of C5aR1, and suggest that C5aR1 may be a viable therapeutic target for individuals with an AD diagnosis. [ABSTRACT FROM AUTHOR] |
