Mechanism of circRNA_SMG6 mediating lung macrophage ECM degradation via miR-570-3p in microplastics-induced emphysema

Microplastics (MPs) are plastic particles < 5 mm in diameter, of which polystyrene microplastics (PS-MPs) are representative type. The extracellular matrix (ECM) degradation of macrophages is associated with the development of emphysema. Additionally, circular RNAs (circRNAs) have a regulatory role in epigenetic mechanisms related to lung disease. However, the mechanisms of the ECM degradation and circRNAs in MPs-induced emphysema are still unclear. In our study, Sprague-Dawley (SD) rats were treated with 0, 0.5, 1.0 and 2.0 mg/m³ 100 nm PS-MPs for 90 days in an inhalation experiment. PS-MPs-exposed rats showed elevated airway resistance and pulmonary dysfunction. Lung histopathology exhibited inflammatory cell infiltration, septal thickening and alveolar dilatation. Exposure to PS-MPs was able to induce elevated levels of ECM degradation-related markers MMP9 and MMP12, as well as reduced levels of elastin in rat lung tissues. CircRNA_SMG6 is a non-coding RNA (ncRNA) with a homologous circular structure in human, rat and mouse. The expression level of circRNA_SMG6 was decreased in both rat lung tissues exposed to PS-MPs and PS-MPs-treated THP-1 cells. The luciferase reporter gene demonstrated that circRNA_SMG6 combined with miR-570-3p and co-regulated PTEN, the target gene of miR-570-3p. Moreover, overexpression of circRNA_SMG6 or inhibition of miR-570-3p attenuated PS-MPs-induced ECM degradation in THP-1 cells. Taken together, circRNA_SMG6 may have a significant function in the deterioration of emphysema caused by PS-MPs-induced macrophage ECM degradation by regulating miR-570-3p. Our findings reveal a novel mechanism of emphysema caused by PS-MPs and provide valuable information for assessing the health risks of MPs.