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

Abstract

<b>Rationale:</b> The relevance of hormones in idiopathic pulmonary fibrosis (IPF), a predominantly male lung disease, is unknown.<b>Objectives:</b> 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.<b>Methods:</b> ER expression in male lung tissue and myofibroblasts from control subjects (<i>n</i> = 6) and patients with IPF (<i>n</i> = 6), aging bleomycin (BLM)-treated mice (<i>n</i> = 7), and BLM-treated AF2ERKI mice (<i>n</i> = 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 (<i>ESR1</i>) with and without miRNA let-7 mimics or inhibitors or an estrogen response element-driven reporter construct (ERE) construct were conducted.<b>Measurements and Main Results:</b> ERα expression increased in IPF lung tissue, myofibroblasts, or BLM mice. <i>In vitro</i> 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.<b>Conclusions:</b> Our data show <i>1</i>) a critical role for ER and let-7 in lung fibrosis, and <i>2</i>) 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.