Epithelial Gasdermin D shapes the host-microbial interface by driving mucus layer formation

Abstract

Goblet cells and their main secretory product, mucus, play crucial roles in orchestrating the colonic host-microbe interactions that help maintain gut homeostasis. However, the precise intracellular machinery underlying this goblet cell–induced mucus secretion remains poorly understood. Gasdermin D (GSDMD) is a recently identified pore-forming effector protein that causes pyroptosis, a lytic proinflammatory type of cell death occurring during various pathophysiological conditions. Here, we reveal an unexpected function of GSDMD in goblet cell mucin secretion and mucus layer formation. Specific deletion of Gsdmd in intestinal epithelial cells (Δ IEC ) led to abrogated mucus secretion with a concomitant loss of the mucus layer. This impaired colonic mucus layer in Gsdmd Δ IEC mice featured a disturbed host-microbial interface and inefficient clearance of enteric pathogens from the mucosal surface. Mechanistically, stimulation of goblet cells activates caspases to process GSDMD via reactive oxygen species production; in turn, this activated GSDMD drives mucin secretion through calcium ion–dependent scinderin-mediated cortical F-actin disassembly, which is a key step in granule exocytosis. This study links epithelial GSDMD to the secretory granule exocytotic pathway and highlights its physiological nonpyroptotic role in shaping mucosal homeostasis in the gut.

Novel pyroptosis-independent functions of gasdermins

“…In addition, Rana et al identified methotrexate as a non-inflammatory stimulus capable of upregulating GSDMB, and Zhang et al successfully established an in vitro colon organoid culture system by three-dimensional printing. 1 , 2 These findings provide strong support for the further development of drugs targeting GSDMs and optimization of therapeutic strategies for the treatment of IBD. It is worth noting that more and more studies have been conducted on the pyroptosis-independent functions of GSDMs.…”

“…Recently, Rana et al and Zhang et al published two studies illustrating the important regulatory roles of gasdermin B (GSDMB) and -D (GSDMD) in inflammatory bowel disease (IBD) and intestinal immune homeostasis maintenance, respectively. 1 , 2 Their findings collectively indicate that the gasdermins (GSDMs) can play a crucial role in restoring epithelial barrier function and shaping gut mucosal homeostasis. Moreover, neither of the functions of GSDMs revealed by these two studies are related to pyroptosis, which may provide new insights into the non-pyroptosis-dependent functions of GSDM proteins.…”

“…Using a GSDMD-deficient human colonic goblet cell line, investigators showed that GSDMD pores are required for Ca 2+ influx, which can drive scinderin function. Scinderin, in turn, drives F-actin disassembly, which ultimately promotes the efflux of mucus vesicles and the formation of the intestinal mucus layer 2 (Fig. 1 ).…”

“…Zhang et al also showed that GSDMD uses a common membrane-targeting mechanism to form pores which lead to lytic cell death, membrane repair, or granule exocytosis in different physiological contexts. 2 This raises a crucial and intriguing question of how different cell types respond to these structurally similar GSDMD pores in different ways. Zhang et al hypothesized that differences in the number and size of GSDMD pores between different cell types and populations may be the cause.…”

No longer married to inflammasome signaling: the diverse interacting pathways leading to pyroptotic cell death

“…The release of granule stored neutrophil elastase into the cytosol can also act on GSDMD to generate a N-terminal pore-forming fragment which, in this case, was associated with neutrophil death and, therefore, the loss of GSDMD increased neutrophil levels and the hosts ability to combat extracellular E. coli infection [ 13 ]. More recently, intestinal epithelial cell GSDMD was shown to mediate goblet cell mucin secretion independent of cell death, and as such GSDMD was important in the formation of the mucus layer [ 87 ]. Therefore, GSDMD pores may serve several purposes beyond cell death and IL-1β release.…”