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

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