alpha-Klotho protects against oxidative damage in pulmonary epithelia

摘要

alphaa-Klotho exerts pleiotropic biological actions. Heterozygous a-Klotho haplo-insufficient mice (kl/+) appear normal at baseline except for age-related changes in the lung, suggesting heightened pulmonary susceptibility to a-Klotho deficiency. We used in vivo and in vitro models to test whether a-Klotho protects lung epithelia against injury. Normally, a-Klotho is not expressed in the lung, but circulating a-Klotho levels are reduced —40% in kl/+ mice and undetectable in homozy-gous a-Klotho-deficient mice (kl/kl). kl/+ mice show distal air space enlargement at a given airway pressure, with elevated lung oxidative damage marker (8-hydroxydeoxyguanosine; 8-OHdG); these abnormalities are exacerbated in kl/kl mice. Studies were performed in A549 lung epithelial cells and/or primary culture of alveolar epithelial cells. Hyperoxia (95% O2) and high inorganic phosphate concentrations (Pi, 3-5 mM) additively caused cell injury (lactate dehydroge-nase release), oxidative DNA damage (8-OHdG), lipid oxidation (8-isoprostane), protein oxidation (carbonyl), and apoptosis (caspase-8 activity and TUNEL stain). Transfection of transmembrane or soluble a-Klotho, or addition of soluble a-Klotho-containing conditioned media, increased cellular antioxidant capacity (Cu- and Fe-based assays) via increased nuclear factor erythroid-derived 2-related factors 1 and 2 (Nrfl/2) transcriptional activity and ameliorated hyperoxic and phosphotoxic injury. To validate the findings in vivo, we injected a-Klotho-containing conditioned media into rat peritoneum before and during hyperoxia exposure and found reduced alveolar interstitial edema and oxidative damage. We conclude that circulating a-Klotho protects the lung against oxidative damage and apoptosis partly via increasing endogenous antioxidative capacity in pulmonary epithelia. Cytoprotection by a-Klotho may play an important role in degenerative diseases of the lung.