MicroRNA-451 from Human Umbilical Cord-Derived Mesenchymal Stem Cell Exosomes Inhibits Alveolar Macrophage Autophagy via Tuberous Sclerosis Complex 1/Mammalian Target of Rapamycin Pathway to Attenuate Burn-Induced Acute Lung Injury in Rats*

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Abstract
Objective Our previous studies established that microRNA (miR)-451 from human umbilical cord mesenchymal stem cell-derived exosomes (hUC-MSC-Exos) alleviates acute lung injury (ALI). This study aims to elucidate the mechanisms by which miR-451 in hUC-MSC-Exos reduces ALI by modulating macrophage autophagy. Methods Exosomes were isolated from hUC-MSCs. Severe burn-induced ALI rat models were treated with hUC-MSC-Exos carrying the miR-451 inhibitor. Hematoxylin-eosin staining evaluated inflammatory injury. Enzyme-linked immunosorbnent assay measured lipopolysaccharide (LPS), tumor necrosis factor alpha, and interleukin-1 beta levels. qRT-PCR detected miR-451 and tuberous sclerosis complex 1 (TSC1) expressions. The regulatory role of miR-451 on TSC1 was determined using a dual-luciferase reporter system. Western blotting determined TSC1 and proteins related to the mammalian target of rapamycin (mTOR) pathway and autophagy. Immunofluorescence analysis was conducted to examine exosomes phagocytosis in alveolar macrophages and autophagy level. Results hUC-MSC-Exos with miR-451 inhibitor reduced burn-induced ALI and promoted macrophage autophagy. MiR-451 could be transferred from hUC-MSCs to alveolar macrophages via exosomes and directly targeted TSC1. Inhibiting miR-451 in hUC-MSC-Exos elevated TSC1 expression and inactivated the mTOR pathway in alveolar macrophages. Silencing TSC1 activated mTOR signaling and inhibited autophagy, while TSC1 knockdown reversed the autophagy from the miR-451 inhibitor-induced. Conclusion miR-451 from hUC-MSC exosomes improves ALI by suppressing alveolar macrophage autophagy through modulation of the TSC1/mTOR pathway, providing a potential therapeutic strategy for ALI.

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