Roles of Inflammatory Caspases during Processing of Zebrafish Interleukin-1β in Francisella noatunensis Infection

Abstract

The interleukin-1 family of cytokines are essential for the control of pathogenic microbes but are also responsible for devastating autoimmune pathologies. Consequently, tight regulation of inflammatory processes is essential for maintaining homeostasis. In mammals, interleukin-1 beta (IL-1␤) is primarily regulated at two levels, transcription and processing. The main pathway for processing IL-1␤ is the inflammasome, a multiprotein complex that forms in the cytosol and which results in the activation of inflammatory caspase (caspase 1) and the subsequent cleavage and secretion of active IL-1␤. Although zebrafish encode orthologs of IL-1␤ and inflammatory caspases, the processing of IL-1␤ by activated caspase(s) has never been examined. Here, we demonstrate that in response to infection with the fish-specific bacterial pathogen Francisella noatunensis, primary leukocytes from adult zebrafish display caspase-1-like activity that results in IL-1␤ processing. Addition of caspase 1 or pancaspase inhibitors considerably abrogates IL-1␤ processing. As in mammals, this processing event is concurrent with the secretion of cleaved IL-1␤ into the culture medium. Furthermore, two putative zebrafish inflammatory caspase orthologs, caspase A and caspase B, are both able to cleave IL-1␤, but with different specificities. These results represent the first demonstration of processing and secretion of zebrafish IL-1␤ in response to a pathogen, contributing to our understanding of the evolutionary processes governing the regulation of inflammation.

Systemic Response to Ultraviolet Radiation Involves Induction of Leukocytic IL-1β and Inflammation in Zebrafish

“…In vitro studies indicate that generation of reactive oxygen species, inflammasome formation, and IL-1b release are the initial events following UV exposure. In zebrafish, il-1b is upregulated postinfection with Yersinia ruckeri (44), and inflammasome formation and IL-1b release have been shown following Francisella noatunensis infection (31). Our data indicate involvement of caspase-1 in the signaling pathway that eventually leads to the transcriptional upregulation of IL-1b.…”

“…6A). YVAD has been reported to inhibit the activity of caspase-A, the zebrafish homolog of caspase-1 (31,32). Treatment with YVAD or the vehicle DMSO alone had no effect on mortality.…”

The zebrafish as a model to study the inflammasome

“…Nevertheless, it has been reported that infection of zebrafish leukocytes with Francisella noatunensis promotes caspase-1 activity, as demonstrated using a fluorogenic substrate for caspase-1, and the processing of IL-1β [22]. This study also showed that zebrafish inflammatory caspases A and B are able to process IL-1β in vitro.…”

Cellular Visualization of Macrophage Pyroptosis and Interleukin-1β Release in a Viral Hemorrhagic Infection in Zebrafish Larvae

“…In zebrafish, Caspa associates with the apoptosis-associated speck-like protein containing a CARD domain (ASC), an inflammasome adaptor (49). Moreover, it has recently been demonstrated that this caspase is able to cleave Il-1␤ in zebrafish (50). Using qPCR, we characterized the regulation of some important genes involved in the inflammatory response (Fig.…”