Pro‐ and Anti‐Inflammatory Macrophages Adjust UCP2 Protein Levels Based on Their Intrinsic Metabolism and Available Metabolites

Abstract

ABSTRACT The immune and metabolic responses of macrophages are closely linked. Mitochondrial uncoupling protein 2 (UCP2), proposed to facilitate metabolite transport, is involved in regulating inflammation and glucose metabolism in macrophages. However, its significance and regulatory mechanism in subsets of macrophages with distinct metabolic profiles remain unclear. In this study, we demonstrate that under physiological nutrient conditions, inflammatory stimuli in classically activated macrophages (via LPS) reduce UCP2 expression in line with decreased oxygen consumption rates, indicating mitochondrial suppression. In contrast, alternatively activated macrophages (via IL4) displayed higher UCP2 levels and enhanced respiration. Under glucose deprivation, LPS‐stimulated macrophages retained mitochondrial activity despite lower UCP2 levels. Blocking pyruvate entry into the mitochondria reduced UCP2 expression, highlighting the connection between glycolysis and mitochondrial metabolism. Mimicking the hypoxic milieu characteristic of LPS‐activated macrophages through CoCltreatment of IL‐4‐activated macrophages resulted in decreased UCP2 expression, suggesting that hypoxia broadly mediates UCP2 suppression in macrophages. Overall, our findings suggest that UCP2 protein levels are modulated by metabolic alterations in macrophages, with pyruvate acting as a key regulator of UCP2 abundance. This emphasizes the importance of UCP2 in linking glycolysis with mitochondrial metabolism, providing insights for developing therapeutic strategies for diseases involving immunometabolic dysregulation. LPS‐stimulated macrophages exhibit high glycolytic flux, with pyruvate preferentially converted to lactate even under normoglycemic conditions, limiting pyruvate availability for the tricarboxylic acid (TCA) cycle and reducing oxygen consumption rate (OCR). Glucose deprivation increases OCR; however, an innate hypoxic state is associated with low UCP2 levels in this phenotype. In contrast, under normal glucose conditions, IL4‐stimulated macrophages enhance mitochondrial pyruvate uptake, promoting TCA cycle activity and higher OCR. Elevated glutamine levels increase UCP2 expression, whereas hypoxia and high glucose suppress it. Overall, UCP2 levels are dynamically regulated by pyruvate availability, supporting its role in C4 metabolite transport and enabling metabolic flexibility in response to nutrient availability. eji70218-abs-0001 graphical