The activation of P2X7 receptor induces cathepsin Dadependent production of a 20akDa form of ILa1I2 under acidic extracellular pH in LPSaprimed microglial cells

The potent pro-inflammatory cytokine, interleukin-1 beta (IL-1 beta ), is synthesized as an inactive 33-kDa precursor (pro-IL-1 beta ) and is processed by caspase 1 into the bioactive 17-kDa mature form. The P2X7 receptor, an ATP-gated cation channel, plays an essential role in caspase 1 activation, production and release of mature bioactive 17-kDa form. We recently reported ATP induces the release of an unconventional 20-kDa form of IL-1 beta (p20-IL-1 beta ) from lipopolysaccharide-primed microglial cells. Emerging evidence suggests physiological relevance for p20-IL-1 beta ; however, the underlying mechanisms for its production and release remain unknown. Here, we investigated the pathways involved in the ATP-induced production of p20-IL-1 beta using lipopolysaccharide-primed mouse microglial cells. The activation of P2X7 receptor by ATP triggered p20-IL-1 beta production under acidic extracellular conditions. ATP-induced p20-IL-1 beta production was blocked by pepstatin A, a potent inhibitor of the lysosomal protease, cathepsin D. The removal of extracellular Ca2+ inhibited the p20-IL-1 beta production as well as ATP-induced cathepsin D release via lysosome exocytosis. The acidic extracellular pH also facilitated the dilatation of membrane pore after ATP stimulation. Since facilitation of pore dilatation results in cytolysis accompanied with cytoplasmic pro-IL-1 beta leakage, our data suggest the leaked pro-IL-1 beta is processed into p20-IL-1 beta by cathepsin D released after ATP stimulation under acidic extracellular conditions.Original Abstract: J. Neurochem. (2011) 117, 712-723.