Neuropeptide Y Modulation of Interleukin-1β (IL-1β)-induced Nitric Oxide Production in Microglia

Given the modulatory role of neuropeptide Y (NPY) in the immune system, we investigated the effect of NPY on the production of NO and IL-1 beta in microglia. Upon LPS stimulation, NPY treatment inhibited NO production as well as the expression of inducible nitric-oxide synthase (iNOS). Pharmacological studies with a selective Y-1 receptor agonist and selective antagonists for Y-1, Y-2, and Y-5 receptors demonstrated that inhibition of NO production and iNOS expression was mediated exclusively through Y-1 receptor activation. Microglial cells stimulated with LPS and ATP responded with a massive release of IL-1 beta, as measured by ELISA. NPY inhibited this effect, suggesting that it can strongly impair the release of IL-1 beta. Furthermore, we observed that IL-1 beta stimulation induced NO production and that the use of a selective IL-1 receptor antagonist prevented NO production upon LPS stimulation. Moreover, NPY acting through Y1 receptor inhibited LPS-stimulated release of IL-1 beta, inhibiting NO synthesis. IL-1 beta activation of NF-kappa B was inhibited by NPY treatment, as observed by confocal microscopy and Western blotting analysis of nuclear translocation of NF-kappa B p65 subunit, leading to the decrease of NO synthesis. Our results showed that upon LPS challenge, microglial cells release IL-1 beta, promoting the production of NO through a NF-kappa B-dependent pathway. Also, NPY was able to strongly inhibit NO synthesis through Y1 receptor activation, which prevents IL-1 beta release and thus inhibits nuclear translocation of NF-kappa B. The role of NPY in key inflammatory events may contribute to unravel novel gateways to modulate inflammation associated with brain pathology.