Salmonella enterica Infection of Murine and Human Enteroid-Derived Monolayers Elicits Differential Activation of Epithelium-Intrinsic Inflammasomes

ABSTRACT

Recent studies have determined that inflammasome signaling plays an important role in driving intestinal epithelial cell (IEC) responses to bacterial infections, such as Salmonella enterica serovar Typhimurium. There are two primary inflammasome pathways, canonical (involving caspase-1) and noncanonical (involving caspase-4 and -5 in humans and caspase-11 in mice). Prior studies identified the canonical inflammasome as the major pathway leading to interleukin-18 (IL-18) release and restriction of S. Typhimurium replication in the mouse cecum. In contrast, the human C2Bbe1 colorectal carcinoma cell line expresses little caspase-1 but instead utilizes caspase-4 to respond to S. Typhimurium infection. Intestinal enteroid culture has enabled long-term propagation of untransformed IECs from multiple species, including mouse and human. Capitalizing on this technology, we used a genetic approach to directly compare the relative importance of different inflammatory caspases in untransformed mouse and human IECs and transformed human IECs upon S. Typhimurium infection in vitro. We show that caspase-1 is important for restricting intracellular S. Typhimurium replication and initiating IL-18 secretion in mouse IECs but is dispensable in human IECs. In contrast, restriction of intracellular S. Typhimurium and production of IL-18 are dependent on caspase-4 in both transformed and untransformed human IECs. Notably, cytosolic replication in untransformed cells from both species was less pronounced than in transformed human cells, suggesting that transformation may impact additional pathways that restrict S. Typhimurium replication. Taken together, these data highlight the differences between mouse and human IECs and the utility of studying transformed and untransformed cells in parallel.