UCSF

The colonic epithelium provides an essential barrier against the environment that is critical for protecting the body and controlling inflammation. In response to injury or gut microbes, colonic epithelial cells produce extracellular hydrogen peroxide (H₂O₂), which acts as a potent signaling molecule affecting barrier function and host defense. In humans, impaired regulation of H₂O₂ in the intestine has been associated with early-onset inflammatory bowel disease and colon cancer. Here, we show that signal transduction by H₂O₂ depends on entry into the cell by transit through aquaporin-3 (AQP3), a plasma membrane H₂O₂-conducting channel. In response to injury, AQP3-depleted colonic epithelial cells showed defective lamellipodia, focal adhesions, and repair after wounding, along with impaired H₂O₂ responses after exposure to the intestinal pathogen Citrobacter rodentium Correspondingly, AQP3^-/- mice showed impaired healing of superficial wounds in the colon and impaired mucosal innate immune responses against C. rodentium infection, manifested by reduced crypt hyperplasia, reduced epithelial expression of IL-6 and TNF-α, and impaired bacterial clearance. These results elucidate the signaling mechanism of extracellular H₂O₂ in the colonic epithelium and implicate AQP3 in innate immunity at mucosal surfaces.