HIF-1α and PFKFB3 Mediate a Tight Relationship Between Proinflammatory Activation and Anerobic Metabolism in Atherosclerotic Macrophages

Abstract

Objective While it is accepted that macrophage glycolysis is up-regulated under hypoxic conditions, it is not known whether this is linked to a similar increase in macrophage pro-inflammatory activation and whether specific energy demands regulate cell viability in the atheromatous plaque. Approach and Results We studied the interplay between macrophage energy metabolism, polarization and viability in the context of atherosclerosis. Cultured human and murine macrophages and an in vivo murine model of atherosclerosis were used to evaluate the mechanisms underlying metabolic and inflammatory activity of macrophages in the different atherosclerotic conditions analyzed. We observed that macrophage energetics and inflammatory activation are closely and linearly related, resulting in dynamic calibration of glycolysis to keep pace with inflammatory activity. Additionally, we show that macrophage glycolysis and proinflammatory activation mainly depend on hypoxia-inducible factor (HIF) and on its impact on glucose uptake, and on the expression of hexokinase II and ubiquitous 6-phosphofructo-2-kinase (PFKFB3). As a consequence, hypoxia potentiates inflammation and glycolysis mainly via these pathways. Moreover, when macrophages’ ability to increase glycolysis through PFKFB3 is experimentally attenuated, cell viability is reduced if subjected to proinflammatory and/or hypoxic conditions, but unaffected under control conditions. In addition to this, GM-CSF enhances anaerobic glycolysis while exerting a mild pro-inflammatory activation. Conclusions These findings, in human and murine cells and in an animal model, show that hypoxia potentiates macrophage glycolytic flux in concert with a proportional up-regulation of pro-inflammatory activity, in a manner that is dependent on both HIF-1α and PFKFB3.

Hypoxia-Inducible Factor-1α Expression in Macrophages Promotes Development of Atherosclerosis

“…62 Thus, this effect of HIF-1α was paralleled by a shift in the inflammatory phenotype of the macrophages. Inos mRNA expression was dramatically induced by hypoxia, and the induction was almost abolished in HIF-1α-null cells.…”

“…Glucose metabolism is a critical component in the proinflammatory response of macrophages, 61,62 and HIF-1α is an important mediator in these processes. 62 Thus, this effect of HIF-1α was paralleled by a shift in the inflammatory phenotype of the macrophages.…”

Hypoxia-inducible factors: key regulators of myeloid cells during inflammation

“…Myeloid HIF-1α is also a critical regulator of both glycolytic metabolism and proinflammatory activation of macrophages, and is stabilized by cues in the atherosclerotic microenvironment, such as hypoxia and cytokines. HIF-1α increases transcription of the gene encoding 6-phospho fructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), a key enzyme in the glycolytic pathway, leading to (a) increased glycolytic flux, (b) increased proinflammatory cytokine production (e.g., TNF-α), and (c) maintenance of macrophage viability (124). Together, these studies reveal that HIF-αs are crucial components in determining macrophage proatherosclerotic functions.…”

Macrophages

“…47,48 Hypoxia promotes glucose uptake by macrophages and potentiates glycolysis in parallel with the development of a proinflammatory M1 phenotype (essentially increased NOS2), dependent on HIF1α expression and 6-phosphofructo-2-kinase. 47,49 Deletion of HIF1α in murine myeloid cells (granulocytes and macrophages) does not affect the development of early atherosclerotic lesions 48 but significantly limits the accumulation of M1-like macrophages and reduces the development of advanced atherosclerosis. 47 This contrasts with the role of HIF1α in CD11c + antigen-presenting cells where it seems to limit proatherogenic Th1 cells through STAT3-dependent inhibition of interleukin-12 (IL-12) production.…”