Reprogramming human macrophages in symptomatic carotid stenosis: stabilization of atherosclerotic carotid plaques

Background and Aims: Inflammation is a precursor to atherosclerotic plaque destabilisation, leading to ischaemic events like stroke. Since macrophage phenotypes can be influenced by their microenvironment, we aimed to stabilise plaques and reduce the risk of recurrent ischaemic events using clinically relevant anti-inflammatory agents.

Methods: Thirteen carotid plaques from stroke/Transient Ischaemic Attack (TIA) patients undergoing carotid endarterectomy were analysed using immunofluorescence stain to identify macrophage markers (CD68, CD86, MRC1). An in vitro model of human blood-derived macrophages was used to evaluate the effects of statins and glucocorticoids on macrophage-specific markers using RT-qPCR, Western Blot, and immunofluorescence staining. The physiological effects of dexamethasone on macrophages and human carotid plaques were further studied ex vivo.

Results: The macrophage population (CD68+) in the carotid plaques was dominated by “double-positive” (CD86+MRC1+) macrophages (67.8 %), followed by “M1-like” (CD86+MRC1-) (16.5 %), “M2-like” (CD86-MRC1+) (8.7 %) and “double-negative” (CD86-MRC1-) (7.0 %) macrophages. M1-like macrophages were more prevalent in unstable plaque sections than stable ones (p = 0.0022). Exposure to dexamethasone increased macrophage MRC1 gene expression in vitro and ex vivo. It also reduced the expression of the Oxidised Low-Density Lipoprotein Receptor 1 (OLR1) gene and protein, leading to reduced oxLDL uptake in foam cell assays.

Conclusions: Clinically relevant concentrations of glucocorticoids may shift human macrophages to a less inflammatory state, thus reducing their ability for oxidised LDL uptake. In contrast, this anti-inflammatory mechanism was not observed in response to statins. These findings suggest that glucocorticoids could help prevent ischemic events in patients with advanced atherosclerosis.