Role of Sulf2 in Alveolar Epithelial Injury and Repair

Abstract

Alveolar epithelial cell injury and dysfunction have been proposed to be etiopathogenic factors in the development of idiopathic pulmonary fibrosis (IPF). We have shown previously that heparan sulfate (HS) 6-O-endosulfatase 2 (Sulf2) is overexpressed and specifically localized to the hyperplastic type II alveolar epithelial cells (AECs) in IPF lungs. By removing 6-O-sulfates from specific HS intrachain sites, Sulf2 has been shown to modulate the functions of many growth factors and cytokines including the fibroblast growth factors (FGFs), Wnt ligands, and transforming growth factor (TGF)-β1. We hypothesize in this study that Sulf2 plays a regulatory role in alveolar epithelial injury and repair in the development of IPF. We examined Sulf2 expression and localization in the bleomycin injury/fibrosis model in mice, using quantitative real-time PCR and immunohistochemistry. Consistent with the findings from human IPF lungs, bleomycin treatment in mice resulted in a twofold increase in Sulf2 mRNA expression in whole lung extracts, and Sulf2 protein was localized to the type II AECs, using immunohistochemistry on lung sections. In cultured primary murine type II AECs, bleomycin induced Sulf2 expression at both the mRNA and protein levels. To study the role of Sulf2 in alveolar epithelial injury and repair in vivo, we generated a doxycycline-inducible type II AEC-specific Sulf knockout mouse line. Deletion of Sulf2 was confirmed in freshly isolated type II AECs from these mice after doxycycline administration. We compared bleomycin-induced AEC injury in wild-type and type II AEC–specific Sulf knockout mice. Our results suggest that deletion of Sulf2 in type II AECs exacerbated bleomycin-induced epithelial injury as shown by increased lactate dehydrogenase levels in bronchoalveolar lavage fluid and increased epithelial apoptosis in type II AEC-Sulf knockout mice. We conclude from this study that Sulf2 promotes type II AEC survival after alveolar epithelial injury.