Low Molecular Weight Hyaluronan Inhibits Lung Epithelial Ion Channels by Activating Calcium-Sensing Receptor
Herein, we tested the hypothesis low molecular weight hyaluronan (LMW-HA) inhibits lung epithelial ion transport in-vivo, ex-vivo, and in-vitro by activating the calcium-sensing receptor (CaSR). Intranasal instillation of LMW-HA (150g/ml) to C57BL/6 mice inhibited their alveolar fluid clearance (AFC) by 75%, increased the epithelial lining fluid (ELF) thickness threefold, and lung wet/dry (W/D) ratio by 20% 24hrs later. Incubation of lung slices from mouse and human lungs with 150g/ml LMW-HA decreased the open probability (Po) of ENaC in ATII cell by more than 50% in 4hrs, inhibited amiloride sensitive short circuit current (SCC) 4hrs post exposure, and Cl- current through CFTR by more than 70%, and Na,K-ATPase current by 66% at 24hrs. In all cases the inhibitory effect of LMW-HA on lung epithelial ion transport in vivo, ex vivo, and in vitro preparations were reversed by the administration of 1M of NPS2143, a CaSR inhibitor, or 150g/ml HMW-HA. In HEK-293 cells co-transfected with CaSR and the calcium sensitive Cl- channel TMEM16-A, LMW-HA activated an inward Cl- current. These data are the first demonstration of the inhibitory effects of LMW-HA on lung epithelial ion and water transport, and are due to the activation of CaSR and its downstream signaling cascades.