Hyaluronan Signaling Ameliorates the Epithelial Injury Response and Barrier Disruption After Ozone Exposure

Airway pollutants, like the reactive oxygen species ozone, cause significant lung injury, which can lead to the development or exacerbation of lung diseases like asthma and chronic obstructive pulmonary disease (COPD), and drives worldwide morbidity and mortality. Altered epithelial function is a hallmark and trigger of ozone-induced lung injury, but its precise mechanisms are incompletely known. The extracellular matrix, and specifically its major component, hyaluronan (HA), plays a crucial role in cellular injury responses. We hypothesized that HA signaling mediates epithelial responses to ozone-induced injury. We exposed human and murine differentiated primary epithelia to ozone in vitro and evaluated epithelial integrity and transcriptomic responses. We used genetically deficient cells for cognate HA receptors cluster of differentiation 44 (CD44) and receptor for HA-mediated motility (RHAMM), and innate immune receptors toll-like receptor 4 (TLR4) and TLR5 to study signaling pathways, and evaluated high molecular weight HA (HMWHA) as a potential treatment for ozone-induced epithelial injury. In vitro ozone exposure caused significant reduction in epithelial integrity and very similar inflammatory changes in human and murine cells. CD44 deficiency led to decreased inflammation, while RHAMM deficiency exacerbated cell injury. HMWHA protected against ozone-induced epithelial injury, mediated by TLR4 and TLR5 but not CD44 or RHAMM. Our results identify novel contributions of HA signaling to ozone-induced epithelial injury and suggest that HMWHA protects epithelia via innate immune activation of TLR4 and TLR5.