Extracellular Adenosine 5′-Triphosphate Modulates Interleukin-6 Production by Human Thyrocytes through Functional Purinergic P2 Receptors

We investigated the presence of P2 receptors (P2Rs) in human thyrocytes and their possible involvement in the modulation of cytokine release. P2Rs expression was assessed by RT-PCR and, when possible, by immunoblotting. Human primary thyrocytes express the mRNA for the following P2X and P2Y subtypes: P2X3, P2X5, P2X6, P2X7, and P2Y1, P2Y2, P2Y4, and P2Y11. Stimulation with extracellular nucleotides of fura-2-loaded thyrocytes triggered an intracellular Ca2+ signal, suggesting expression of functional receptors. Thyrocytes spontaneously released the proinflammatory cytokine IL-6. The ATP-hydrolyzing enzyme apyrase reduced basal IL-6 release, whereas extracellular ATP dose-dependently increased IL-6 secretion. Uridine 5′-triphosphate was also an effective stimulus, whereas benzoyl-ATP was ineffective, suggesting a P2Y- rather than P2X-modulated response. Finally, TSH reduced both the intracellular Ca2+ ([Ca2+]i) rise and IL-6 release triggered by P2Rs stimulation. In conclusion, we provide functional, pharmacological, and biochemical evidence that human primary thyrocytes express P2YR and P2XR subtypes, coupled to increases in ([Ca2+]i) and secretion of IL-6. P2R-dependent modulation of IL-6 release from human thyrocytes suggests a novel mechanism whereby an inflammatory and/or immune-mediated damage can be initiated and amplified in the thyroid.