Mechanisms by Which the MBD2/miR-301a-5p/CXCL12/CXCR4 Pathway Regulates Acute Exacerbations of Chronic Obstructive Pulmonary Disease

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is characterized by irreversible expiratory airflow obstruction, and its chronic course is worsened by recurrent acute exacerbations. Our previous microarray assay identified microRNA (miR)-301a-5p as being associated with progression of acute exacerbation of COPD (AE-COPD); however, the mechanism underlying COPD pathogenesis remains unknown. METHODS: Samples of serum and peripheral blood mononuclear cells (PBMCs) were isolated from healthy control subjects and patients with stable COPD (R-COPD) or with an acute exacerbation of COPD (AE-COPD). Human HULEC-5a and human bronchial epithelial (HBE) cells were transfected with methyl-CpG-binding domain protein 2 (MBD2), sh-MBD2, miR-301a-5p mimics or an inhibitor, and then stimulated with cigarette smoke extract (CSE). Conditioned medium co-culture assays were performed by adding the supernatant of medium derived from HULEC-5a cells transfected with miR-301a-5p mimics or inhibitor into wells containing si-c-x-c motif chemokine receptor 4 (CXCR4)-transfected-lung fibroblasts or human leukemic THP-1 cell line macrophages. Transwell assays were performed to analyze cell migration. RESULTS: Our analysis of clinical samples showed that decreased miR-301a-5p levels in patients with AE-COPD were positively correlated with levels of MBD2 expression, but negatively correlated with levels of chemokine ligand C-X-C motif chemokine ligand 12 (CXCL12) expression. MBD2 overexpression significantly promoted miR-301a-5p production, but suppressed CXCL12 production in HULEC-5a and HBE cells. CXCL12 was confirmed to be a direct target of miR-301a-5p. CXCR4 knockdown significantly enhanced the suppressive effect of miR-301a-5p mimics and attenuated the promotional effects of the miR-301a-5p inhibitor on the migration of circulating fibroblasts and macrophages, as well as the expression levels of phospho-mitogen-activated protein kinase (p-MEK) and phospho-protein kinase B (p-AKT). CONCLUSION: In summary, the MBD2/miR-301a-5p/CXCL12/CXCR4 pathway was shown to affect the migration of lung fibroblasts and monocyte-derived macrophages, which may play an important role during COPD exacerbations.