Sialic acids expression in newborn rat lungs: implications for pulmonary developmental biology.

Mammalian lung development proceeds during the postnatal period and continues throughout life. Intricate tubular systems of airways and vessels lined by epithelial cells are developed during this process. All cells, and particularly epithelial cells, carry an array of glycans on their surfaces. N-acetylneuraminic (Neu5Ac) and N-glycolylneuraminic (Neu5Gc) acids, two most frequently-occurring sialic acid residues, are essential determinants during development and in the homeostasis of cells and organisms. However, systematic data about the presence of cell surface sialic acids in the postnatal lung and their content is still scarce. In the present study, we addressed the histochemical localization of Neu5Ac > Neu5Gc in 0-day-old rat lungs. Furthermore, both residues were separated, identified and quantified in lung membranes isolated from 0-day-old rat lungs using high-performance liquid chromatography (HPLC) methodologies. Finally, we compared these results with those previously reported by us for adult rat lungs. The Neu5Ac > Neu5Gc residues were located on the surface of ciliated and non-ciliated cells and the median values for both residues in the purified lung membranes of newborn rats were 5.365 and 1.935 µg/mg prot., respectively. Comparing these results with those reported for the adults, it was possible to observe a significant difference between the levels of Neu5Ac and Neu5Gc (p < 0.001). A more substantial change was found for the case of Neu5Ac. The preponderance of Neu5Ac and its expressive increase during the postnatal development points towards a more prominent role of this residue. Bearing in mind that sialic acids are negatively charged molecules, the high content of Neu5Ac could contribute to the formation of an anion "shield" and have a role in pulmonary development and physiology.

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

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.