Rewiring of glucose metabolism defines trained immunity induced by oxidized low-density lipoprotein

Abstract

Stimulation of monocytes with microbial and non-microbial products, including oxidized low-density lipoprotein (oxLDL), induces a protracted pro-inflammatory, atherogenic phenotype sustained by metabolic and epigenetic reprogramming via a process called trained immunity. We investigated the intracellular metabolic mechanisms driving oxLDL-induced trained immunity in human primary monocytes and observed concomitant upregulation of glycolytic activity and oxygen consumption. In two separate cohorts of healthy volunteers, we assessed the impact of genetic variation in glycolytic genes on the training capacity of monocytes and found that variants mapped to glycolytic enzymes PFKFB3 and PFKP influenced trained immunity by oxLDL. Subsequent functional validation with inhibitors of glycolytic metabolism revealed dose-dependent inhibition of trained immunity in vitro. Furthermore, in vivo administration of the glucose metabolism modulator metformin abrogated the ability for human monocytes to mount a trained response to oxLDL. These findings underscore the importance of cellular metabolism for oxLDL-induced trained immunity and highlight potential immunomodulatory strategies for clinical management of atherosclerosis. Key messages & Brief stimulation of monocytes to oxLDL induces a prolonged inflammatory phenotype. & This is due to upregulation of glycolytic metabolism. & Genetic variation in glycolytic genes modulates oxLDL-induced trained immunity. & Pharmacological inhibition of glycolysis prevents trained immunity.

β-Glucan-Induced Trained Immunity in Dogs

“…Notably, the marks on these pro-inflammatory cytokine genes returned to baseline when inhibitors of glycolysis were used. Therefore, while immune training is required to alter cell metabolism, these metabolic changes in turn seem to be necessary to maintain a trained phenotype ( 16 , 35 ).…”

Immunometabolic control of trained immunity

“…First, the KDM5 family of histone demethylases, which are responsible for demethylation of H3K4 appears critical for trained immunity: β-glucan training of monocytes resulted in decreased biological activity of KDM5 demethylases on day 6 after training, which was regulated by changes in intracellular fumarate, which will be discussed later ( Arts et al, 2016 ). More recently, the lysine methyltransferase Set7, which writes H3K4me1 marks, was identified as key enzyme necessary for β-glucan-induced trained immunity in vitro and in vivo ( Keating, Groh, van der Heijden, et al, 2020 ).…”

“…Also for training with oxLDL, an increased glycolytic activity is essential for the development of the trained immune phenotype: oxLDL-trained macrophages are characterized by an increased extracellular acidification rate using Seahorse technology, and pharmacological inhibition of glycolysis (either by 2-DG or by inhibition of the inducible PFK-2/FBPase isozyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3)) prevents trained immunity ( Keating et al, 2020 ). In addition, genetic variation in genes encoding PFKFB3 and PFKP were associated with the potentiation of TNF-α and IL-6 production upon training with oxLDL ex vivo ( Keating et al, 2020 ).…”

“…There is a close bilateral relationship between the upregulation of glycolytic metabolism and epigenetic reprogramming. Glycolysis is essential for the induction of cytokine production capacity which is mediated by enrichment of the promoters of these genes by activating histone modifications, including H3K4me3 ( Keating et al, 2020 ) ( Arts et al, 2016 ; Cheng et al, 2014 ). One mechanism that links glycolytic activation to epigenetic reprogramming is the dependency of the sirtuin family of histone deacytelases (HDACs) on the intracellular NAD + concentration ( Anderson et al, 2017 ).…”

“…Indeed, the NAD+/NADP ratio is increased in trained macrophages ( Cheng et al, 2014 ) and the induction of cytokine production capacity by β-glucan is blunted by co-administration of the HDAC inhibitor resveratrol ( Cheng et al, 2014 ). Conversely, the increased expression of glycolytic enzymes is mediated by activating histone modifications itself, and co-administration of epigenetic inhibitors, such as the nonspecific methyltransferase inhibitor methylthioadenosine or the Set7 methyltransferase inhibitor cyproheptadine, prevents the upregulation of glycolysis by β-glucan on day 6, whereas it does not affect the lactate production in the first 24 h of exposure to β-glucan ( Cheng et al, 2014 ; Keating, Groh, van der Heijden, et al, 2020 ). Interestingly, oxLDL-trained macrophages are characterized by an enrichment of H3K4me3 on the promoters of PFKFB3 and HK2, which is attenuated by pharmacological inhibition of glycolysis, pointing to a self-perpetuating epigenetic activation of glycolysis ( Keating et al, 2020 ).…”