Fig. 5: Myelin dysfunction induces a DAM-like state distinct to amyloid deposition as determined by snRNA-seq.
From: Myelin dysfunction drives amyloid-β deposition in models of Alzheimer’s disease
a, Experimental setup for studying microglia states associated with myelin disease (myelin-DAM) and amyloid-disease (amyloid-DAM) and in combination. Brain hemispheres were isolated from 6-month-old WT, Cnp−/−, 5×FAD and Cnp−/−;5×FAD mice and subjected to snRNA-seq. Cell types were identified on the basis of marker genes, and microglia were subset for further analysis. b,c, Uniform manifold approximation and projection (UMAP) visualization of microglia subsets coloured by genotypes (b) or subpopulations (c). d, Violin plots showing expression of microglia subpopulation marker genes. e, Bar plot showing the distribution of microglia subpopulations across genotypes. MyTE, myelin transcripts enriched. f, Differentially regulated genes between amyloid-DAM and myelin-DAM. g, Feature plots showing expression of Apoe, Abca1, Ms4a7 and Cst7 in microglia subpopulations. h, Representative example images of microglia distraction in Cnp−/−;5×FAD mice. The arrowhead in the bottom panel highlights an activated microglial cell that is engaged in myelin phagocytosis and does not react to nearby plaques. The same observations were made in five independent samples per mice per group. i, Left, amyloid and microglia immunostaining and single-molecule fluorescence in situ hybridization for the amyloid-DAM marker Cst7. Right, violin plots show the amount of Cst7 signal per microglia. Microglia were separated into groups according to their location in relation to amyloid plaques (plaque-proximal, plaque-distant and plaque-free regions). The following number of microglia were analysed: 5×FAD: plaque-proximal = 161, plaque-distant = 111, plaque-free = 128; Cnp−/−;5×FAD: plaque-proximal = 136, plaque-distant = 184, plaque-free = 184 from 3 mice per replicates per group (n = 3). For Cnp−/−, n = 61 and for WT, n = 63 from one animal each. Black lines indicate medians. Statistical analysis: two-sided, unpaired Student’s t-test (P values are indicated in the graphs) on biological replicate data. j, Scheme illustrating how myelin dysfunction acts as an AD risk factor. Upstream myelin defects cause microglia engagement and axonal transport problems. The two downstream pathologies are probably interrelated (dashed arrow). Axonal problems lead to endosome and lysosome accumulation and enhanced amyloid production. Simultaneously, microglia become increasingly engaged with defective myelin, which reduces their interaction with amyloid plaques. Both processes contribute to the enhanced deposition of amyloid.
