GABA, glucose and insulin orchestrate CD4+ T cells effector functions

Metabolic programs of immune cells are closely linked to their effector functions , where physiological molecules provide environmental cues and guidance. Exactly how it happens is still being unraveled. Insulin maintains normal blood glucose levels and glucose is themain source of energy and a precursor for many biomolecules in T cells, whereas γ-aminobutyric acid (GABA), best known as a neurotransmitter, is increasingly recognized as a regulatory molecule in the immune system. Here, we demonstrate that GABA-mediated reduction of metabolic activity and release of inflammatory molecules, including IFNγ and IL-10, was abolished in human CD4+ T cells, when the glucose concentration was elevated above normal levels. In a glucose concentration-dependent manner, insulin enhanced the GABAA receptors activated currents and GABA-dependent Ca2+ influx. GABA decreased, whereas insulin maintained glycolysis but in a SGLT (Na + -glucose transporter)-dependent manner, revealing expression of SGLTs in activated CD4+ T cells. The SGLTs antagonist phlorizin, alone or together with GABA, restored the inhibition of IFNγ and IL-10 release in presence of high glucose. This study exposes concerted effects of GABA, glucose and insulin on CD4+ T cells metabolic activity and release of inflammatory molecules, and identifies a role for SGLTs in CD4+ T cells function.