Idiopathic pulmonary fibrosis (IPF) pathogenesis has been postulated to involve a variety of mechanisms associated with the aging process, including loss of protein homeostasis (proteostasis). Heat shock proteins are cellular chaperones that serve a number of vital maintenance and repair functions, including the regulation of proteostasis. Previously published data have implicated heat shock protein 70 (Hsp70) in the development of pulmonary fibrosis in animal models. We sought to identify alterations in Hsp70 expression in IPF lung. Hsp70 mRNA and protein were decreased in primary fibroblasts cultured from IPF versus normal donor lung tissue. In addition to cultured fibroblasts, Hsp70 expression was decreased in intact IPF lung, a stressed environment in which upregulation of protective heat shock proteins would be anticipated. In support of a mechanistic association between decreased Hsp70 and fibrosis, cultured primary lung fibroblasts deficient in Hsp70 secreted increased extracellular matrix proteins. Treatment of primary normal human lung fibroblasts in vitro with either of the profibrotic molecules IGFBP5 (insulin-like growth factor-binding protein 5) or transforming growth factor-β1 downregulated Hsp70, suggesting Hsp70 is a downstream target in the fibrotic cascade. Hsp70-knockout mice subjected to an inhalational bleomycin model of pulmonary fibrosis demonstrated accelerated fibrosis versus wild-type control animals. We therefore conclude that reduced Hsp70 protein contributes to fibrosis and that interventions aimed at restoring normal expression of Hsp70 represent a novel therapeutic strategy for pulmonary fibrosis.
Keywords: heat shock protein 70; idiopathic pulmonary fibrosis; proteostasis; transforming growth factor-β.