Small Extracellular Vesicles Containing miR-34c Derived from Bone Marrow Mesenchymal Stem Cells Regulates Epithelial Sodium Channel via Targeting MARCKS.

Epithelial sodium channel (ENaC) is a pivotal regulator of alveolar fluid clearance in the airway epithelium and plays a key role in the treatment of acute lung injury (ALI), which is mainly composed of the three homologous subunits (α, β and γ). The mechanisms of microRNAs in small extracellular vesicles (sEVs) derived from mesenchymal stem cell (MSC-sEVs) on the regulation of lung ion transport are seldom reported. In this study, we aimed at investigating whether miR-34c had an effect on ENaC dysfunction induced by lipopolysaccharide and explored the underlying mechanism in this process. Primarily, the effect of miR-34c on lung edema and histopathology changes in an ALI mouse model was investigated. Then the uptake of PKH26-labeled sEVs was observed in recipient cells, and we observed that the overexpression of miR-34c in MSC-sEVs could upregulate the LPS-inhibited γ-ENaC expression. The dual luciferase reporter gene assay demonstrated that myristoylated alanine-rich C kinase substrate (MARCKS) was one of target genes of miR-34c, the protein expression of which was negatively correlated with miR-34c. Subsequently, either upregulating miR-34c or knocking down MARCKS could increase the protein expression of phospho-phosphatidylinositol 3-kinase (p-PI3K) and phospho-protein kinase B (p-AKT), implying a downstream regulation pathway was involved. All of the above suggest that miR-34c in MSC-sEVs can attenuate edematous lung injury via enhancing γ-ENaC expression, at least partially, through targeting MARCKS and activating the PI3K/AKT signaling pathway subsequently.