Hyaluronan Directs Alveolar Type II Cell Response to Acute Ozone Exposure in Mice

Becoming more frequent because of climate change, ozone (O₃) exposures can cause lung injury. Alveolar type 2 (AT2) cells and hyaluronan (HA), a matrix component, are critical to repairing lung injury and restoring homeostasis. Here, we define the impact of HA on AT2 cells after acute O₃ exposure. C57BL/6J mice were exposed to filtered air or O₃ (2 ppm) for 3 hours. HA was measured in BAL and lung tissue; HAS (HA synthase) 1, 2, and 3 and HYAL (hyaluronidase) 1, 2, and 3 mRNA were measured in lung tissue and BAL cells. At 48 to 72 hours after O₃ exposure, HA increased in BAL fluid by ELISA and lung tissue by immunohistochemistry, with new HA deposition localized to the alveolar ducts. This was associated with increased whole-lung HAS2 mRNA expression. Using an AT2 lineage reporter (Sftpc-CreER;Rosa-Tm) mouse strain, we noted that proliferating AT2 cells colocalized with O₃-induced HA deposition in the alveolar duct region. In addition, AT2-to-AT1 cell differentiation after O₃ was noted. To determine whether O₃-induced HA alters AT2 cell function, we inhibited HA-AT2 interaction with a synthetic inhibitor (Pep-1), which diminished AT2 proliferation. Mice treated with Pep-1 after O₃ exposure demonstrated increased BAL albumin concentration compared with filtered air exposure, suggesting that inhibition of HA-AT2 cell interactions resulted in persistent alveolar-capillary permeability and diminished resolution of O₃-induced lung injury. Overall, the findings suggest that HA increases in the alveolar duct after acute O₃ exposure and that HA-AT2 cell interactions are required for resolution of acute O₃-induced lung injury.