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Mesenchymal stem cell-conditioned medium rescues LPS-impaired ENaC activity in mouse trachea via WNK4 pathway.

BACKGROUND
Airway epithelium plays an essential role in maintaining the homeostasis and function of respiratory system as the first line of host defense. Of note, epithelial sodium channel (ENaC) is one of the victims of LPS-induced airway injury. Regarding the great promise held by mesenchymal stem cells (MSCs) for regenerative medicine in the field of airway injury and the limitations of cell-based MSCs therapy, we focused on the therapeutic effect of MSCs conditioned medium (MSCs-CM) on the ENaC activity in mouse tracheal epithelial cells.


METHODS
Ussing chamber apparatus was applied to record the short-circuit currents in primary cultured mouse tracheal epithelial cells, which reflects the ENaC activity. Expressions of α and γ ENaC were measured at the protein and mRNA levels by western blot and real-time PCR, respectively. The expression of with-no-lysine-kinase-4 (WNK4) and ERK1/2 were measured at protein levels, and the relationship between WNK4 and ERK1/2 was determined by WNK4 knockdown.


RESULTS
MSCs-CM restored the LPS-impaired ENaC activity, as well as enhanced the mRNA and protein expressions of ENaC in primary cultured mouse tracheal epithelial cells. Meanwhile, WNK4 and ERK1/2, both negative-regulators of ENaC, are suppressed accordingly after the administration of MSCs-CM in LPS-induced airway injury. After WNK4 gene was knocked down by siRNA, the level of ERK1/2 phosphorylation decreased.


CONCLUSION
In light of the key role of ENaC in fluid reabsorption and the beneficial effects of MSCs-CM in the injury of airway epithelium, our results suggest that MSCs-CM is effective in alleviating LPS-induced ENaC dysfunction through WNK4-ERK1/2 pathway, which will provide a potent direction for the therapy of airway injury.