Cholesterol accumulation-induced impairment of AKT signaling in LPS-stimulated macrophages play a dispensable role in suppressing HIF-1α-dependent glycolysis

Abstract

The formation of lipid-laden macrophages (M{varphi}s) is a hallmark of atherosclerosis, yet how the accumulation of cholesterol in M{varphi}s underlies the inflammatory process of atherogenesis remains unclear. It is well recognized that the reprogramming of metabolism in M{varphi}s is critical for supporting their inflammatory responses, which may shed light on how the metabolism of M{varphi} foam cells is linked to inflammation. Indeed, recent research has now revealed M{varphi}s that accumulate excess cholesterol adopt a distinct metabolic adaptation, a metabolic profile that is unexpectedly associated with a deactivated inflammatory response. Mechanistically, our group has previously shown that upon LPS stimulation, excess cholesterol accumulation in M{varphi}s impaired their induction of AKT-dependent early glycolytic reprogramming and HIF-1-dependent late glycolytic reprogramming. However, it remains unclear if these events are interconnected and synergistically contribute to the suppression of inflammation observed in these M{varphi}s. Here, we demonstrated that cholesterol loading of M{varphi}s impaired LPS-induced early glycolysis by reducing the phosphorylation of hexokinases, yet complete inhibition of AKT only modestly impaired HIF-1-dependent glycolytic reprogramming. On the other hand, we confirmed that HIF-1 degradation, but not its reduced synthesis, is the primary mechanism that underlies its impaired expression in cholesterol loaded M{varphi}s. Finally, we showed that cholesterol loading of M{varphi}s alone was sufficient to induce oxidative stress, such as the production of 4-HNE, and deplete the levels of reduced KEAP1 proteins. M{varphi}s lacking NRF2 resisted the effects of cholesterol loading on suppressing the expression of glycolytic and pro-inflammatory proteins.