Gene Delivery of MRCKα Repairs the Alveolar‐Capillary Barrier and Rescues the Experimental Lipopolysaccharide‐Induced Acute Lung Injury

Abstract

Rationale Acute Respiratory Distress Syndrome (ARDS) is a devastating condition which is characterized by the pulmonary accumulation of protein-rich edema fluids and insufficient gas exchange, leading to acute hypoxemic respiratory failure. During ARDS, the net fluid clearance is undermined not only due to the impaired alveolar fluid clearance (AFC) which osmotically drives water following the ion gradient out of alveoli, but also the disrupted alveolar-capillary barrier. The previous data from our lab indicated that electroporation-mediated gene delivery of the β1 subunit of the Na+, K+-ATPase into mouse lungs treats LPS induced acute lung injury (ALI), showing significantly decreased lung edema, and improved overall outcome of lung injury. Overexpression of β1 increased AFC in healthy and injured murine lungs, and more importantly, gene delivery of β1 restored pulmonary barrier function, demonstrated by upregulated tight junction (TJ) proteins, and decreased lung permeability, total protein and cellularity in BAL fluid. MRCKα (CDC42 binding protein kinase alpha) was identified by our lab as an interacting partner of the β1 subunit through mass spectrometry. MRCKα is a Rho GTPase effector kinase, regulating diverse cell behaviors, including junction formation. Our previous in vitro data indicate that MRCKα mediated β1’s upregulation of TJ proteins and epithelial barrier integrity. Overexpression of MRCKα alone sufficiently increased the trans-epithelial electrical resistance (TEER) in cell culture. Thus, it is intriguing to investigate whether MRCKα has the therapeutic potential to treat LPS induced ALI by restoring pulmonary barrier function in vivo. This study tested whether electroporation-mediated gene transfer of MRCKα could upregulate TJ protein and barrier function and treat LPS induced ALI in mice. Methods ALI was induced by LPS intratracheal administration and 24 hours later, plasmids encoding MRCKα, β1- Na+, K+-ATPase, or nothing (control) were delivered individually or in combination to mouse lungs by oropharyngeal aspiration and electroporation. Two days after gene delivery, various endpoint assays were performed to evaluate lung edema, permeability, inflammation and histological injury. In addition, AFC was performed on mice with MRCKα overexpression to evaluate the fluid clearance. Results Gene transfer of MRCKα alone did not enhance AFC, but alone or in combination with β1- Na+, K+-ATPase attenuated LPS-increased Wet/Dry ratio, lung leakage, and BAL cellularity and protein concentration, restored TJ protein expression, and improved overall outcome of lung injury. Conclusions Gene delivery ofMRCKα repair alveolar capillary barrier integrity without promoting ion transport, and could benefit the pre-injured lungs by reducing pulmonary edema, restoring lung barrier function and reducing inflammation. Moreover, the data also suggest that improving barrier function alone may be of equal or even more benefit than improving alveolar fluid clearance in order to treat ALI/ARDS.