Exogenous gene transfer of Rab8 small GTPase ameliorates aberrant lung surfactant homeostasis in Ruby rats.

Background: Rab8 small GTPase regulates intracellular transport in melanocytes and alveolar type II epithelial cells. Ruby rats carrying Rab8 and other gene mutations exhibit oculocutaneous albinism, bleeding diathesis, and hence, are a rat model of human Hermansky-Pudlak syndrome (HPS). We previously showed that Long Evans Cinnamon (LEC) rats, one strain of the Ruby rats, developed aberrant lung surfactant homeostasis with remarkably enlarged lamellar bodies in alveolar type II cells.

Methods: A replication-deficient recombinant adenovirus expressing rat Rab8 (Ad-Rab8) was constructed. Alveolar type II cells were isolated from the LEC rats and tested for lung surfactant phosphatidylcholine secretion. The rats were also examined whether exogenous expression of Ad- Rab8 could rescue the altered lung surfactant homeostasis in the lungs.

Results: Isolated type II cells infected with Ad-Rab8 exhibited improved secretion patterns of [H]phosphatidylcholine, i.e. increased basal hyposecretion and decreased agonist-induced hypersecretion. Endobronchial administration of Ad-Rab8 improved the morphology of type II cells and lamellar bodies, reducing their sizes close to those of wild-type rats. The increased amounts of phosphatidylcholine and surfactant protein B in the lamellar body fractions were decreased in the Ad-Rab8 infected lungs.

Conclusions: These results provide strong evidence that the aberrant lung surfactant homeostasis in the LEC rats is caused by Rab8 deficit, and suggest that endobronchial delivery of the responsive transgene could be an effective method to ameliorate the abnormal lung phenotype in the animal model of HPS.