Abstract Background Atherosclerosis underlies major adverse cardiovascular events, and epidemiological studies signal an association between atherosclerosis and Alzheimer’s disease, including shared risk factors and predictive circulating cytokines. Both conditions are characterised by dysregulated accumulation of monocyte-derived macrophages. We have identified a distinct, deleterious pro-inflammatory macrophage subset within advanced mouse and human atherosclerotic plaques, which associates with ruptured plaques and is driven by GM-CSF signalling. Purpose This study aimed to investigate if subclinical plaque rupture associates with subsequent development of neuroinflammation within the hippocampus and the accumulation of a GM-CSF-directed macrophage subset. Methods A time-course study was conducted in eight-week-old female and male apolipoprotein E knockout (Apoe KO) mice (n=10/group), which were placed on high-fat diet (HFD) for up to 52 weeks. Bloods were collected for multiplex assessment of circulating cytokines alongside single-cell sequencing. After prefusion-fixation, brachiocephalic artery and brain were isolated for histological evaluation and digital spatial transcriptomics. An intervention study was undertaken in Apoe KO mice using a GM-CSF inhibitor (n=8/group). A validation study was performed utilising human hippocampus sections from patients with Alzheimer’s disease and control subjects (n=4/group). Results After 26- or 52-weeks of HFD, female and male Apoe KO mice displayed extensive atherosclerosis within their brachiocephalic arteries with evidence of previous plaque rupture. However, compared to 26-week HFD animals, the hippocampus of 52-week HFD mice displayed marked indicators of neuroinflammation, including number of CD68+ve cells (75%;p0.01) with elevated expression of activation markers (CD11c;73%;p0.01) alongside functional markers of GM-CSF polarised macrophages (MMP-12;80%;p0.01 and MMP-14;75%;p0.05). This was accompanied by increased signs of degeneration as evidenced through a decrease in the cross-sectional area of the hippocampus (25%; p0.05), area of the dentate gyrus (32%; p0.01), and granular layer cell density (13%; p0.05). Administration of a GM-CSF inhibitor for 14 weeks reversed MMP-12-positive macrophage numbers (28%;p0.01) and improved granular layer thickness (18%;p0.05) within the hippocampus of atherosclerotic Apoe KO mice, compared to control animals. Validation was confirmed in human brain samples, where we observed a marked increase in CD68 (38%;p0.05) and MMP-12 (34%;p0.05) positive cells within the hippocampus of Alzheimer’s patients compared to age/gender-matched healthy controls, as well as an increase in GM-CSF signalling (64%;p0.05). Conclusions Our results show accrual of a GM-CSF-driven macrophage subset in the hippocampus of atherosclerotic mice, which mimic macrophages observed in unstable plaques, and accompany neurodegeneration changes associated with Alzheimer’s disease.
Khalid et al. (Fri,) studied this question.