Characterization of surfactant proteins in porcine Eustachian tube
1University of Oulu, Faculty of Medicine, Department of Paediatrics
2University of Oulu, Biocenter Oulu
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|Persistent link:|| http://urn.fi/urn:isbn:9514264673
|Publish Date:|| 2001-09-03
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic Dissertation to be presented with the assent of the Faculty of Medicine, University of Oulu, for public discussion in the Auditorium 12 of the University Hospital of Oulu, on October 12th, 2001, at 12 noon.
Docent Annika Laitinen
Docent Aaro Miettinen
The Eustachian tube (ET) connects the upper respiratory tract and the middle ear. It equilibrates the pressure in the middle ear and prevents the harmful impact of the airways. Middle ear infection, or otitis media, is one of the most common illnesses in childhood and affects nearly all children at least once. ET dysfunction is considered to be a major pathogenic factor in the development of otitis media.
Surfactant proteins A (SP-A) and D (SP-D) have an important role in the pulmonary host defence system, and interactions with bacteria that also cause middle ear infections raised a question about the expression of surfactant proteins in ET. The local defence system could be significant in preventing ear infections.
The purpose of the study was to increase our basic knowledge of the putative ET surfactant system. ET and lung epithelia are both of endodermal origin, and ET epithelium with its mucociliary system resembles that of the lower airways. The aim was to determine whether SP-A, SP-B and SP-D are expressed in ET. The expressions were characterized with reverse transcriptase polymerase chain reaction (RT-PCR), Northern hybridizations and in situ hybridizations. The surfactant proteins were localized using immunohistochemistry and immunoelectron microscopy. The proteins were characterized with Western analyses, and the properties of the ET surfactant were evaluated using electrospray ionization mass spectrometry and a pulsating bubble surfactometer.
SP-A, SP-B and SP-D were found to be expressed in porcine ET epithelium, and the cDNA sequences were homologous to those detected in lung tissue. The proteins were localized to specific ET epithelial cells, and their sizes were characteristic of lung SP-A, SP-B and SP-D. ET lavage fluid contained the surfactant proteins and phospholipid. However, the phospholipid molecular species and surface tension measurements showed the structure and function of the surfactant in ET to be different from lung surfactant, suggesting that a very low surface tension is not a critical determinant of ET surfactant function.
As a conclusion, surfactant proteins in ET are likely to be involved in the local host defence system and may contribute to the mucociliary function of the tube.
Acta Universitatis Ouluensis. D, Medica
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