Presence of N-acetylglucosamine residues on the surface coating of bronchioloalveolar cells during rat postnatal development: What is their purpose?

Abstract

Mammalian lung development is a complex process that is partially accomplished during the postnatal period. Surface carbohydrates are crucial in many biological and pathological phenomena and are key partners during development. The outer surface of lung epithelial cells, which is rich in carbohydrate components, plays a pivotal role throughout the developmental process. However, systematic studies on the sugar residue content of the cell surface coating during postnatal rat lung development are scarce. The aim of the present study was to identify and determine the localization of N-acetylglucosamine residues on the bronchioloalveolar cell surface during rat lung development using light and pre-embedding transmission electron microscopy methodologies, and to associate these data with the components underlying postnatal lung growth. Strong binding sites for the lectin Triticum vulgare (common name Wheat Germ, WGA) are present on the luminal surface of adult rat bronchioloalveolar cells throughout the entire postnatal period and have been identified as N-acetylglucosamine residues. The consistent positive reaction observed on the surface coating of bronchioloalveolar lining cells before and after neuraminidase treatment suggests that aside from possible terminal sialic acids, the lectin specificity for N-acetylglucosamine residues is still evident. Our results also suggest a stronger positive reaction on the bronchioloalveolar cell surface when compared with endothelial cell surface. N-acetylglucosamine residues for lectin binding can be present in glycoproteins in the membrane and also within heparin sulfate chains of glycosaminoglycans, which are crucial for lung development. The work described here has sought to highlight the presence and possible importance of N-acetylglucosamine residues on the glycocalyx of bronchioloalveolar cells, during postnatal lung development.

Keywords: Glycans; Lung development; N-acetylglucosamine residues.