Histone deacetylase‐dependent control of lung alveolar fluid clearance

Abstract

TGF‐β mediates acute lung injury (ALI) by impacting alveolar ion transport and thereby promoting pulmonary edema. The Na,K‐ATPase regulates ion transport and fluid balance and Na,K‐ATPase function is perturbed in ALI. It was hypothesized that TGF‐β impacts Na,K‐ATPase activity by altering subunit stoichiometry. Na,K‐ATPase activity and surface abundance were reduced in primary alveolar type II and A549 cells treated with TGF‐β, assessed by 86Rb+ uptake and cell surface biotinylation. The ATP1B1 subunit regulates surface stability, and hence alveolar fluid clearance (AFC) activity of the Na,K‐ATPase. PCR analysis revealed repression of ATP1B1 gene expression in lungs from ALI patients, in mice with bleomycin‐induced ALI model and in TGF‐β‐treated A549 cells. A Dual‐luciferase reporter assay revealed decreased ATP1B1 promoter activity in response to TGF‐ β. Enzyme inhibition and siRNA approaches demonstrated that ATP1B1 gene repression was mediated by epigenetic mechanisms and relied on HDAC2. TGF‐β induced phosphorylation of HDAC2 at S394 while chromatin immunoprecipitation confirmed binding of the HDAC2 to the ATP1B1 promoter. HDAC inhibition abrogated repression of the Atp1b1 gene in bleomycin‐induced ALI and drove edema resolution. In sum, HDAC2 mediated repression of the ATP1B1 gene, impairing Na,K‐ATPase function and AFC in ALI.German Research Foundation.