Surfactant protein h is part of the tear film, lowers surface tension, is increased in dry eye disease and accelerates corneal wound healing

Abstract

Purpose : Surfactant proteins (SP) are well known from human lung and have also been described in tears. Recently, we characterized a new surfactant-associated protein termed SFTA3 or SP-H. The objective of this study was to determine the possible expression of SP-H at the ocular surface and in tears and to analyze possible functional aspects. Methods : Ocular tissues, human corneal (HCE) and conjunctival (HCjE) epithelial cell lines as well as tear fluid from volunteers and patients with different forms of dry eye disease (DED) were analyzed by means of RT-PCR, western blot, immunohistochemistry, and ELISA. A possible role of recombinat SP-H in corneal wound healing was investigated in an in vitro scratch assay. Tear film regulatory properties were analyzed with the spinning drop method. Regulation of SP-H transcripts was studied in HCE and HCjE after incubation with proinflammatory cytokines as well as typical ocular pathogens by real-time RT-PCR and ELISA. Results : Lacrimal gland epithelial cells, corneal epithelium and endothelium, conjunctival epithelium, meibocytes and secretory cells of glands of Moll all expressed SP-H which also could be detected at low concentrations in tears of healthy volunteers. Tears from patients with DED revealed significantly increased SP-H levels (evaporative forms more than aqueous deficient forms). In vitro wounding of cultured HCE cells that were treated with recombinant SP-H revealed an significantly increased wound closure rate compared to control. Moreover, recombinant SP-H reduced the surface tension of tear fluid from healthy volunteers compared to water or BSA. In vitro experiments with HCE cells revealed that stimulation with distinct pro-inflammatory cytokines or bacterial supernatants had no significant effect on the SP-H expression rate. Conclusions : The results indicate that SP-H is part of the tear film. There, it is involved in wound healing and lowering surface tension but has seemingly no immunomodulatory functions with regard to the investigated pro-inflammatory cytokines or bacterial supernatants. Moreover, it seems to have a role in DED as it is significantly upregulated in aqueous and evaporative forms of DED.