Effects of interleukin-1 on glucose uptake and energy homeostasis in lymphocytes

The research group in which this work was performed has shown that interleukin-1 (IL-1) induces a profound, long-lasting, and insulin-independent hypoglycemia, by mechanisms acting at peripheral and central levels. More recently, we reported that despite the concomitant hypoglycemia, IL-1 increases energetic activity in the brain in vivo and glucose uptake by neurons and astrocytes in vitro. The aim of this work was to study whether IL-1 can also affect glucose uptake by immune cells. For this purpose, murine spleen cells were stimulated with lipopolysaccharide (LPS) during 4 or 24 hours and endogenously produced IL-1 was neutralized with IL-1 receptor antagonist (IL-1Ra). Glucose incorporation was evaluated by uptake of the fluorescent glucose analog 2-(N-(7-Nitrobenz-2-oxa-1,3- diazol-4-yl)Amino)-2-Deoxyglucose (2-NBDG) and flow cytometry. The results showed that IL-1Ra decreases 2-NBDG uptake by LPS-stimulated cells to a degree comparable to that observed when glucose transporters are blocked with phloretin. Percentually, the decrease of 2-NBDG uptake in response to IL-1 blockade was larger in LPS-stimulated B cells than in unstimulated B cells after 24 h in vitro, suggesting an activation-dependent enhancement of glucose uptake by IL-1. Application of the agonist IL-1b during one hour increased 2-NBDG uptake by B cells, however, only to a comparably small extent, presumably because IL-1 receptors are already almost saturated under the in vitro conditions used in these studies. Neither Myeloid differentiation primary response 88 (MyD88), an innate immune signal adapter protein, nor the inward-rectifier potassium channel 6.2 (Kir6.2) seem to play a relevant role in the intracellular signaling pathway involved in the effect of IL-1 on glucose uptake. Pharmacological inhibition of AKT/PKB did not prevent the effect of IL-1 on glucose uptake in B cells, while the results in T cells were not clear. The effect of endogenously produced IL-1 on spleen cell energetic metabolism was also investigated. Using live cell real-time metabolic flux analysis, it was found that blockade of endogenous IL-1 resulted in a reduction of the oxygen consumption rate (OCR) that gradually recovered to the basal value after one hour. The decrease in OCR was of a magnitude comparable to the inhibition of mitochondrial ATP generation elicited by oligomycin. In the initial phase of IL-1Ra inhibition in non-stimulated spleen cells, the reduction of oxidative phosphorylation was paralleled by an increase in the extracellular acidification rate (ECAR), which is considered a marker of lactate production by glycolysis. The increase in ECAR induced by LPS stimulation could not be further augmented after IL-1Ra injection, probably because glycolysis could not be additionally accelerated. After the immediate effects of endogenous IL-1 blockade, which lasted for approximately 2 h, ECAR decreased below control values in both unstimulated and LPS-stimulated cells. The metabolic effects of IL-1 blockade were not MyD88-dependent. The results indicate that endogenously produced IL-1 can increase glucose uptake and energetic metabolism in immune cells and possibly contributes to the relocation of energy to the immune system.