Upregulation of alveolar fluid clearance is not sufficient for Na+,K+-ATPase β subunit-mediated gene therapy of LPS-induced acute lung injury in mice

Acute Lung Injury/Acute Respiratory Distress Syndrome (ALI/ARDS) is characterized by diffuse alveolar damage and significant edema accumulation, which is associated with impaired alveolar fluid clearance (AFC) and alveolar-capillary barrier disruption, leading to acute respiratory failure. Our previous data showed that electroporation-mediated gene delivery of the Na+, K+-ATPase beta 1 subunit not only increased AFC, but also restored alveolar barrier function through upregulation of tight junction proteins, leading to treatment of LPS-induced ALI in mice. More importantly, our recent publication showed that gene delivery of MRCK alpha, the downstream effector of beta 1 subunit-mediated signaling towards upregulation of adhesive junctions and epithelial and endothelial barrier integrity, also provided therapeutic potential for ARDS treatment in vivo but without necessarily accelerating AFC, indicating that for ARDS treatment, improving alveolar capillary barrier function may be of more benefit than improving fluid clearance. In the present study, we investigated the therapeutical potential of beta 2 and beta 3 subunits, the other two beta isoforms of Na+, K+-ATPase, for LPS-induced ALI. We found that gene transfer of either the beta 1, beta 2, or beta 3 subunits significantly increased AFC compared to the basal level in naive animals and each gave similar increased AFC to each other. However, unlike that of the beta 1 subunit, gene transfer of the beta 2 or beta 3 subunit into pre-injured animal lungs failed to show the beneficial effects of attenuated histological damage, neutrophil infiltration, overall lung edema, or increased lung permeability, indicating that beta 2 or beta 3 gene delivery could not treat LPS induced lung injury. Further, while beta 1 gene transfer increased levels of key tight junction proteins in the lungs of injured mice, that of either the beta 2 or beta 3 subunit had no effect on levels of tight junction proteins. Taken together, this strongly suggests that restoration of alveolar-capillary barrier function alone may be of equal or even more benefit than improving AFC for ALI/ARDS treatment.