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Friedrich P Paulsen, Felix Rausch, Christina Jakobi, Ulrike Hampel, Lars Bräuer, Martin Schicht; Surfactant Protein-H (SFTA 3), a novel regulatory surfactant protein at the ocular surface and in the tear film. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1305.
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© ARVO (1962-2015); The Authors (2016-present)
To detect and characterize a novel surfactant protein at the ocular surface. Surfactant proteins (SP) are well known from human lung. These proteins assist the formation of a monolayer of surface- active phospholipids at the liquid-air interface of the alveolar lining, play a major role in lowering the surface tension of interfaces, and have functions in innate and adaptive immune defense. During recent years it became obvious that SPs are also part of other tissues and fluids such as saliva, kidney or also tear fluid. Recently, a putative new surfactant protein (SFTA3 or SP-H) was identified, which has no sequence or structural identity to the already know surfactant proteins.
In this work, computational chemistry and molecular-biological methods were combined to localize and characterize SP-H. With the help of a protein structure model, specific antibodies were obtained which allowed the detection of SP-H. SP-H expression was analyzed by Western-blot analysis, ELISA as well as immunohistochemistry in different tissues of the ocular surface and in tear fluid. The activation and regulation of SP-H transcription was studied in human cornea (HCE) and conjunctiva (HCjE) epithelial cell lines after incubation with ocular pathogens by real-time RT-PCR. Furthermore, the protein concentration of SP-H was measured by ELISA in tears from patients suffering from dry eye disease (DED) in comparison to healthy volunteers.
The localization of SP-H in cornea, eye lid, lacrimal gland and meibomian gland, sequence based prediction tools for posttranslational modifications and molecular dynamic simulations revealed that SP-H has physicochemical properties similar to the already known surfactant proteins B and C. This includes also the possibility of interactions with lipid systems and with that, a potential surface-regulatory feature of SP-H. Stimulation experiments in HCE and HCjE with pathogens showed an increased expression of SP-H. In tears from DES patients SP-H concentration was increased compared to controls.
In conclusion, the results indicate SP-H as a novel surfactant protein of the ocular surface and tear film which represents an until now unknown surfactant protein class. SP-H seems to have surface tension-regulatory features and is upregulated under experimental inflammatory conditions and in cases of DED indicating further immune modulatory functions.
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