Defective surfactant secretion in a mouse model of Hermansky-Pudlak syndrome
Hermansky-Pudlak syndrome (HPS) in humans represents a family of disorders of lysosome-related organelle biogenesis associated with severe, progressive pulmonary disease. Human case reports and a mouse model of HPS, the pale ear/pearl mouse (ep/pe), exhibit giant lamellar bodies (GLB) in type II alveolar epithelial cells. We examined surfactant proteins and phospholipid from ep/pe mice to elucidate the process of GLB formation. The 2.8-fold enrichment of tissue phospholipids in ep/pe mice resulted from accumulation from birth through adulthood. Tissue surfactant protein (SP)-B and -C were increased in adult ep/pe mice compared with wild-type mice (WT), whereas SP-A and -D were not different. Large aggregate surfactant (LA) from adult ep/pe mice had decreased phospholipid, SP-B, and SP-C, with no differences in SP-A and -D compared with WT. Although LA from ep/pe animals exhibited an increased total protein-to-total phospholipid ratio compared with WT, surface tension was not compromised. Phospholipid secretion from isolated type II cells showed that basal and stimulated secretion from ep/pe cells were approximately 50% of WT cells. Together, our data indicate that GLB formation is not associated with abnormal trafficking or recycling of surfactant material. Instead, impaired secretion is an important component of GLB formation in ep/pe mice.