MicroRNA let-7 Downregulates Ligand-Independent Estrogen Receptor–mediated Male-Predominant Pulmonary Fibrosis

Abstract

Abstract Rationale The relevance of hormones in idiopathic pulmonary fibrosis (IPF), a predominantly male lung disease, is unknown. Objectives To determine whether the ER (estrogen receptor) facilitates the development of pulmonary fibrosis and is mediated in part through microRNA regulation of ERα and ERα-activated profibrotic pathways. Methods ER expression in male lung tissue and myofibroblasts from control subjects (n = 6) and patients with IPF (n = 6), aging bleomycin (BLM)-treated mice (n = 7), and BLM-treated AF2ERKI mice (n = 7) was determined. MicroRNAs that regulate ER and fibrotic pathways were assessed. Transfections with a reporter plasmid containing the 3′ untranslated region of the gene encoding ERα (ESR1) with and without miRNA let-7 mimics or inhibitors or an estrogen response element–driven reporter construct (ERE) construct were conducted. Measurements and Main Results ERα expression increased in IPF lung tissue, myofibroblasts, or BLM mice. In vitro treatment with let-7 mimic transfections in human myofibroblasts reduced ERα expression and associated fibrotic pathways. AF2ERKI mice developed BLM-induced lung fibrosis, suggesting a role for growth factors in stimulating ER and fibrosis. IGF-1 (insulin-like growth factor 1) expression was increased and induced a fourfold increase of an ERE construct. Conclusions Our data show 1) a critical role for ER and let-7 in lung fibrosis, and 2) that IGF may stimulate ER in an E2-independent manner. These results underscore the role of sex steroid hormones and their receptors in diseases that demonstrate a sex prevalence, such as IPF.