Activated protein C reverses epigenetically sustained p66^Shc expression in plaque-associated macrophages in diabetes

Impaired activated protein C (aPC) generation is associated with atherosclerosis and diabetes mellitus. Diabetes-associated atherosclerosis is characterized by the hyperglycaemic memory, e.g., failure of disease improvement despite attenuation of hyperglycaemia. Therapies reversing the hyperglycaemic memory are lacking. Here we demonstrate that hyperglycaemia, but not hyperlipidaemia, induces the redox-regulator p66^Shc and reactive oxygen species (ROS) in macrophages. p66^Shc expression, ROS generation, and a pro-atherogenic phenotype are sustained despite restoring normoglycemic conditions. Inhibition of p66^Shc abolishes this sustained pro-atherogenic phenotype, identifying p66^Shc-dependent ROS in macrophages as a key mechanism conveying the hyperglycaemic memory. The p66^Shc-associated hyperglycaemic memory can be reversed by aPC via protease-activated receptor-1 signalling. aPC reverses glucose-induced CpG hypomethylation within the p66^Shc promoter by induction of the DNA methyltransferase-1 (DNMT1). Thus, epigenetically sustained p66^Shc expression in plaque macrophages drives the hyperglycaemic memory, which-however-can be reversed by aPC. This establishes that reversal of the hyperglycaemic memory in diabetic atherosclerosis is feasible.