Conflicts with diarrheal pathogens trigger rapid evolution of an intestinal signaling axis

Carey, Clayton M.; Apple, Sarah E.; Hilbert, Zoё A.; Kay, Michael S.; Elde, Nels C.

The pathogenesis of infectious diarrheal diseases is largely attributed to enterotoxin proteins that disrupt intestinal water absorption, causing severe dehydration. Despite profound health consequences, the impacts of diarrhea-causing microbes on the evolutionary history of host species are largely unknown. We investigated patterns of genetic variation in mammalian Guanylate Cyclase-C (GC-C), an intestinal receptor frequently targeted by bacterial enterotoxins, to determine how hosts might adapt in response to diarrheal infections. Under normal conditions, GC-C interacts with endogenous guanylin peptides to promote water secretion in the intestine, but signaling can be hijacked by bacterially-encoded heat-stable enterotoxins (STa) during infection, which leads to overstimulation of GC-C and diarrhea. Phylogenetic analysis in mammals revealed evidence of recurrent positive selection in the GC-C ligand-binding domain in primates and bats, consistent with selective pressures to evade interactions with STa. Using in vitro assays and transgenic intestinal organoids to model STa-mediated diarrhea, we show that GC-C diversification in these lineages results in substantial variation in toxin susceptibility. In bats, we observe a unique pattern of compensatory coevolution in the endogenous GC-C ligand uroguanylin, reflecting intense bouts of positive selection at the receptor-ligand interface. These findings demonstrate control of water physiology as a previously unrecognized interface for genetic conflict and reveal diarrheal pathogens as a source of selective pressure among diverse mammals.