Exosomal MicroRNA let-7 Modulates Lipid Metabolism and Inflammation in Foamy Macrophages of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) involves persistent inflammation and dysregulated lipid metabolism, with foamy macrophages playing a central role in disease progression. Exosomes—vesicles transporting microRNAs (miRNAs)—mediate intercellular communication, but their contribution to foamy macrophage-driven COPD remains unclear. This study investigates the role of exosomal miRNAs, particularly let-7, in modulating lipid metabolism and inflammation in foamy macrophages. Bone marrow-derived macrophages (BMDMs) were treated with oxidized low-density lipoprotein (oxLDL) and lipopolysaccharide (LPS) to induce foamy macrophage formation. Exosomal miRNA profiles were analyzed, and the function of let-7c-3p was assessed via transfection. Foamy macrophages released significantly more exosomes (392.7 × 10⁷ particles) than controls (284.9–302.5 × 10⁷), without differences in exosome size or molecular content. The miRNA sequencing and qRT-PCR confirmed downregulation of exosomal let-7c-3p in foamy macrophages, correlating with increased RNF8 and decreased RXR expression—markers of disrupted PPAR/RXR signaling. Pathway analysis implicated let-7c-3p in regulating PPAR/RXR, WNT/β-catenin, and pulmonary fibrosis pathways. Transfection with let-7 mimics reduced lipid accumulation (52% to 19%), suppressed RNF8, restored RXR, and lowered IL-6 and TNF-α levels, indicating strong anti-inflammatory and lipid-modulating effects. Loss of exosomal let-7c-3p aggravates lipid dysregulation and inflammation in COPD by impairing PPAR/RXR signaling. Restoring let-7 expression reverses these effects, highlighting its potential as a diagnostic biomarker and therapeutic target.