Metabolic adaptation of glucose-deprived macrophages involves partial gluconeogenesis

TL;DR

Macrophages adapt to low glucose by partially using gluconeogenesis, showing their metabolic flexibility in nutrient-poor environments like tumors.

Contribution

The study reveals that macrophages activate partial gluconeogenesis under glucose deprivation, a novel metabolic adaptation strategy.

Findings

Glucose-deprived macrophages reduce lactate production and increase glutamine usage.

Partial gluconeogenesis is activated, generating glycolytic intermediates and glycerol-3-phosphate.

PCK2 is expressed in lung and lung cancer macrophages, indicating its in vivo relevance.

Abstract

Macrophages are versatile immune cells which utilize glucose and other nutrients to fuel their metabolism. Mechanisms of adaptation of macrophages to a limited glucose supply, as present in the tumor microenvironment, are poorly understood. Using stable isotopic tracers, we found that upon glucose deprivation, macrophages reduce lactate production and enhance the usage of glutamine. Interestingly, initial steps of gluconeogenesis, the reverse pathway of glycolysis, were activated, generating cellular intermediates. Glucose deprivation only partially modulated functions of pro- or anti-inflammatory macrophages. The initial gluconeogenesis enzyme, phosphoenolpyruvate carboxykinase, was consistently expressed in human lung and lung cancer macrophages, suggesting its relevance in macrophages in vivo. Our findings show extensive metabolic flexibility of macrophages, involving the activation of partial gluconeogenesis upon glucose deprivation.

Macrophages are recruited to sites of infection contributing to the killing of bacteria, but also to malignant tumors, where they promote angiogenesis and suppress antitumor immune responses. The metabolic microenvironment in tumors is frequently depleted of important nutrients such as glucose. Here, we investigated metabolic adaptation strategies of macrophages to glucose deprivation using stable isotopic tracing. Lactate production was decreased, potentially indicating a reduction of glycolysis. In contrast, the contribution of glutamine to the tricarboxylic acid cycle via α-ketoglutarate and reductive carboxylation were increased. Moreover, gluconeogenesis, the reverse pathway of glycolysis, was activated in glucose-deprived macrophages, proceeding partially to the generation of glycolytic intermediates and glycerol-3-phosphate. The partial gluconeogenesis pathway was abrogated in human and murine macrophages lacking the initial gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PCK2, mitochondrial isoform). Partial gluconeogenesis was higher in anti-inflammatory, interleukin-4-stimulated compared to proinflammatory, interferon-γ/lipopolysaccharide-stimulated macrophages. Single-cell analysis and immunostaining revealed expression of PCK2 in macrophages from both lung cancer and normal lung. Low glucose conditions only partially modulated macrophage phenotypes, leading to reduced CD80 surface marker levels in proinflammatory, and enhanced vascular endothelial growth factor expression in anti-inflammatory macrophages. Our study reveals partial gluconeogenesis in glucose-deprived macrophages and shows that this versatile type of immune cells exhibits remarkable metabolic flexibility.

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