The pathogenesis of chronic obstructive pulmonary disease (COPD) involves aberrant responses to cellular stress caused by chronic cigarette smoke (CS) exposure. However, not all smokers develop COPD and the critical mechanisms that regulate cellular stress responses to increase COPD susceptibility are not understood. Because microRNAs are well-known regulators of cellular stress responses, we evaluated microRNA expression arrays performed on distal parenchymal lung tissue samples from 172 subjects with and without COPD. We identified miR-24-3p as the microRNA that best correlated with radiographic emphysema and validated this finding in multiple cohorts. In a CS exposure mouse model, inhibition of miR-24-3p increased susceptibility to apoptosis, including alveolar type II epithelial cell apoptosis, and emphysema severity. In lung epithelial cells, miR-24-3p suppressed apoptosis through the BH3-only protein BIM and suppressed homology-directed DNA repair and the DNA repair protein BRCA1. Finally, we found BIM and BRCA1 were increased in COPD lung tissue, and BIM and BRCA1 expression inversely correlated with miR-24-3p. We concluded that miR-24-3p, a regulator of the cellular response to DNA damage, is decreased in COPD, and decreased miR-24-3p increases susceptibility to emphysema through increased BIM and apoptosis.

RATIONALEChronic obstructive pulmonary disease (COPD) is characterized by gradual destruction of alveolar architecture and subsequent airflow obstruction. Advancing age and significant exposure to cigarette smoke (CS) are common risk factors, yet the pathologic manifestations of COPD are heterogenous and the biologic risk factors for COPD are unclear. MIF is an important regulator of innate immunity, cellular homeostasis and survival. We previously reported that circulating MIF was lower in smokers with COPD compared with smokers without COPD. Others have confirmed these findings and correlated decreased MIF protein with greater radiologic/functional evidence of emphysema in patients.METHODSGene expression microarray analysis was performed on lung tissue from individuals with/without COPD (n=262), and endothelial cell (Ec) CD74 expression was analyzed in single‐cell RNA‐seq (control=19, COPD=29). CD74 expression was determined by immunohistochemistry in human lung. CS extract (CSE) treated to HUVEC along with the following recombinant‐MIF (rMIF), MIF‐siRNA, neutralizing anti‐MIF monoclonal antibody (anti‐MIF mAb), MIF098 (MIF antagonist), or MIF20 (MIF agonist). U0126 (ERK inhibitor) was treated 1 hour prior to MIF20 treatment. MIF‐KO mice were treated with a control or MIF expressing lentiviral‐vector. Ec were isolated via MACS sorting. AKR/J mice were exposed to CS (4 months), and MIF20 was administered orally (3 mg/mouse) to mice every day for the final 2 months of CS exposure. Pressure‐Volume (PV) loops were measured by FlexiVent.RESULTSCD74 expression was increased in COPD patients especially in lung Ec. CSE increased p16 and p21 mRNA expression in HUVEC. This increase was attenuated by rMIF or MIF20, while augmented by anti‐MIF mAb or MIF98. CSE increased SA‐β‐gal activity and MIF20 attenuated it. The protective effect of MIF20 against CS‐induced Ec senescence was abolished by ERK signaling inhibitor. MIF‐KO mice showed an upshift of PV loop and increased Ec p21 expression, which were attenuated by restoration of MIF expression. CS induced upshift of PV loop, increased p16 and p21 expression, which were attenuated by MIF20.CONCLUSIONSThe expression of CD74, the cognate receptor for MIF, was increased in COPD. Senescence was induced in Ec by CS, an important causative factor for COPD. MIF20, a novel small molecule MIF agonist, attenuated CS‐induced senescence via ERK signaling, which is known to support cell survival and proliferation. Furthermore, MIF20 prevented CS‐induced lung emphysema. These data suggest that therapeutic modulation of MIF targeting in lung Ec is feasible represents a novel strategy to protect against senescence‐induced COPD.Support or Funding InformationM.S. is supported by NIH/NHLBI K08HL135402 and FAMRI YCSA 142017. P.J.L. is supported by NIH/NHLBI R01 HL138386, VAORD11858595, US Department of Defense PR150809, and FAMRI 150074.

ABSTRACT Activation of the DNA damage response (DDR) due to chronic exposure to cigarette smoke (CS) is implicated in the pathogenesis of Chronic Obstructive Pulmonary Disease (COPD). However, not all smokers develop COPD and the pathologic consequences of CS exposure are heterogenous. Cellular mechanisms that regulate the DDR and contribute to disease progression in susceptible individuals are poorly understood. Because microRNAs are well known regulators of the DDR, we evaluated microRNA expression arrays performed on lung samples from 172 subjects with and without COPD. We identified miR-24-3p as the microRNA best correlated with radiographic emphysema (ρ=-0.353, P=1.3e-04) and validated this finding in multiple cohorts. In a CS-exposure mouse model, miR-24-3p inhibition increased emphysema severity. In human airway epithelial cells, miR-24-3p suppressed apoptosis through the BH3-only protein BIM and suppressed homology-directed DNA repair and the DNA repair protein BRCA1. Finally, we found BIM and BRCA1 were increased in COPD lung tissue and inversely correlated with miR-24-3p expression. We concluded that decreased miR-24-3p expression increases COPD susceptibility and potentiates the DDR through BIM and BRCA1.