Pro-fibrotic phenotype of human Hermansky-Pudlak syndrome lung fibroblasts

Abstract

Hermansky-Pudlak syndrome type 1 (HPS-1) is associated with highly prevalent pulmonary fibrosis. Patients with HPS-1 usually manifest with pulmonary fibrosis in middle-age and are typically younger than patients with idiopathic pulmonary fibrosis (IPF). Given the accelerated onset of pulmonary fibrosis in HPS-1, we hypothesized that lung fibroblasts from individuals with HPS-1 pulmonary fibrosis are constitutively activated and have an enhanced fibrotic response. To test this hypothesis, fibroblasts cultured from explanted lung tissue from patients with HPS-1 pulmonary fibrosis were analyzed and compared to lung fibroblasts from patients with IPF and normal controls. We found that HPS-1 lung fibroblasts express high levels of alpha-smooth muscle actin (a-SMA) transcript and protein compared to normal lung fibroblasts. Similarly, levels of connective tissue growth factor (CTGF) were increased in HPS-1 lung fibroblasts compared to normal cells. In contrast, no significant differences in a-SMA or CTGF protein levels were found in IPF and normal lung fibroblasts. Immunostaining of lung tissue showed prominent expression of a-SMA and CTGF in alveolar interstitial lung fibroblasts and myofibroblasts from patients with HPS-1 pulmonary fibrosis or IPF compared to normal lung. Levels of fibronectin, collagen type I α1, and collagen type I α2 transcripts were significantly higher in HPS-1 lung fibroblasts stimulated with transforming growth factor (TGF)-b compared to those in HPS-1 lung fibroblasts incubated with vehicle-only or normal lung fibroblasts stimulated with TGF-b. In conclusion, HPS-1 lung fibroblasts are constitutively activated and exhibit an exaggerated fibrotic response when stimulated with TGF-b.