The Opto-inflammasome in zebrafish: a tool to study cell and tissue responses to speck formation and cell death

Abstract

The inflammasome is a conserved system for the intracellular detection of danger or pathogen signals. By forming a large intracellular multiprotein signaling platform, it activates downstream effectors that initiate a rapid necrotic programmed cell death (PCD) termed pyroptosis and activation and secretion of pro-inflammatory cytokines to warn and activate surrounding cells. However, inflammasome activation is difficult to control on a single-cell level using canonical triggers. We constructed Opto-Asc, a light-responsive form of the inflammasome adaptor protein ASC (Apoptosis-Associated Speck-Like Protein Containing a CARD) which allows tight control of inflammasome formation in vivo. We introduced a cassette of this construct under the control of a heat shock element into zebrafish in which we can now induce Asc inflammasome (speck) formation in single cells of the skin. We find that cell death resulting from Asc speck formation is morphological distinct from apoptosis in periderm but not in basal cells. Asc induced PCD in can lead to apical or basal extrusion from the periderm. The apical extrusion in periderm cells depends on Caspb but and triggers a strong Ca2+ signaling response in nearby cells.

Optogenetically controlled inflammasome activation demonstrates two phases of cell swelling during pyroptosis

“…Similar approaches have coupled optogenetic modules to different cell death effectors (CDEs) to compare, in vivo, the impact of different cell death modes on tissues, to GSDMD-truncated protein to assess the regulation of GSDMD pore formation, or to chimeric antigen receptor T cell to promote cell death, reinforcing the usefulness of these approaches to dissecting specific signaling pathways (36)(37)(38). Moreover, in zebrafish, the introduction of an opto-ASC construct revealed that cells undergoing pyroptosis are extruded from the tissue, an observation that is consistent with the ones made with opto-CASP1 (36,39). However, no optogenetic approach has been designed to control inflammasome assembly in mammalian cells.…”