Release of acidic store calcium is required for effective priming of the NLRP3 inflammasome

The lysosome is a dynamic signaling organelle that is critical for cell functioning. It is a regulated calcium store that can contribute to Ca 2+ -regulated processes via both local calcium release and more globally by influencing ER Ca 2+ release. Here, we provide evidence from studies of an authentic mouse model of the lysosomal storage disease Niemann-Pick Type C (NPC) that has reduced lysosomal Ca 2+ levels, and genetically modified mice in which the two-pore lysosomal Ca 2+ release channel family are deleted that lysosomal Ca 2+ signaling is required for normal pro-inflammatory responses. We demonstrate that production of the pro-inflammatory cytokine IL-1β via the NLRP3 inflammasome is significantly reduced in murine Niemann-Pick Type C, the inhibition is selective because secretion of TNFα is not diminished and it is a consequence of inefficient inflammasome priming. Synthesis of precursor ProIL-1β is significantly reduced in macrophages genetically deficient in the lysosomal protein Npc1, which is mutated in most clinical cases of NPC, and in wild type cells in which Npc1 activity is pharmacologically inhibited. Comparable reductions in ProIL-1β generation were measured in vitro and in vivo by macrophages (MΦ) genetically altered to lack expression of the two-pore lysosomal Ca 2+ release channels Tpcn1 or Tpcn2 . These data demonstrate a requirement for lysosome-dependent Ca 2+ signaling in the generation of specific pro-inflammatory responses.