Alveolar epithelial cell (AEC) apoptosis and inadequate repair resulting from "exaggerated" lung aging and
mitochondrial dysfunction are critical determinants promoting lung
fibrosis. α-Klotho, which is an antiaging molecule that is expressed predominantly in the kidney and secreted in the blood, can protect lung epithelial cells against
hyperoxia-induced apoptosis. We reasoned that Klotho protects AEC exposed to oxidative stress in part by maintaining
mitochondrial DNA (
mtDNA) integrity and mitigating apoptosis. We find that Klotho levels are decreased in both serum and alveolar type II (AT2) cells from
asbestos-exposed mice. We show that oxidative stress reduces AEC Klotho
mRNA and
protein expression, whereas Klotho overexpression is protective while Klotho silencing augments AEC
mtDNA damage. Compared with wild-type, Klotho heterozygous hypomorphic allele (kl/+) mice have increased
asbestos-induced lung
fibrosis due in part to increased AT2 cell
mtDNA damage. Notably, we demonstrate that serum Klotho levels are reduced in wild-type but not mitochondrial
catalase overexpressing (MCAT) mice 3 wk following exposure to
asbestos and that
EUK-134, a MnSOD/
catalase mimetic, mitigates
oxidant-induced reductions in AEC Klotho expression. Using pharmacologic and genetic silencing studies, we show that Klotho attenuates
oxidant-induced AEC
mtDNA damage and apoptosis via mechanisms dependent on AKT activation arising from upstream
fibroblast growth factor receptor 1 activation. Our findings suggest that Klotho preserves AEC
mtDNA integrity in the setting of oxidative stress necessary for preventing apoptosis and
asbestos-induced lung
fibrosis. We reason that strategies aimed at augmenting AEC Klotho levels may be an innovative approach for mitigating age-related
lung diseases.