Pannexin-1 Is Required for ATP Release during Apoptosis but Not for Inflammasome Activation

TLDR

Apoptosis and the rapid pyroptotic death of innate immune cells are key for development, immune homeostasis, and pathogen clearance, and the hemichannel pannexin‑1 has been implicated in both processes. This study characterizes pannexin‑1‑deficient mice to determine the channel’s role in cell death and immune signaling. Panx1‑deficient macrophages activate caspase‑1 and secrete IL‑1β/IL‑18 normally, but Panx1‑null thymocytes fail to release ATP during early apoptosis, impairing macrophage recruitment, indicating pannexin‑1 is required for ATP‑mediated “find‑me” signals but not for inflammasome assembly.

Abstract

Apoptotic cell death is important for embryonic development, immune cell homeostasis, and pathogen elimination. Innate immune cells also undergo a very rapid form of cell death termed pyroptosis after activating the protease caspase-1. The hemichannel pannexin-1 has been implicated in both processes. In this study, we describe the characterization of pannexin-1-deficient mice. LPS-primed bone marrow-derived macrophages lacking pannexin-1 activated caspase-1 and secreted its substrates IL-1β and IL-18 normally after stimulation with ATP, nigericin, alum, silica, flagellin, or cytoplasmic DNA, indicating that pannexin-1 is dispensable for assembly of caspase-1-activating inflammasome complexes. Instead, thymocytes lacking pannexin-1, but not the P2X7R purinergic receptor, were defective in their uptake of the nucleic acid dye YO-PRO-1 during early apoptosis. Cell death was not delayed but, unlike their wild-type counterparts, Panx1(-/-) thymocytes failed to recruit wild-type peritoneal macrophages in a Transwell migration assay. These data are consistent with pannexin-1 liberating ATP and other yet to be defined "find me" signals necessary for macrophage recruitment to apoptotic cells.