Presence of N-acetylgalactosamine/galactose residues on bronchioloalveolar cells during rat postnatal development

Abstract

In mammals, the alveolarization process develops predominantly after birth. Airway cells display a complex assemblage of glycans on their surface. These glycans, particularly terminal glycan extensions, are important effective carriers of information that change during the differentiation process. Nevertheless, few systematic data are reported about the cell surface sugar residue content during post-natal lung development. In the present work, we aimed to identify and semi-quantify N-acetylgalactosamine (GalNAc)/galactose (Gal) residues on the bronchioloalveolar cell surface in rat lung sections from 1-, 4-, 8- day old and adult animals and link these data with the lung glycocalyx composition. Horseradish peroxidase-conjugated lectin from Glycine max (soybean agglutinin, SBA) was used, and light microscopy methodologies were performed. SBA labelling intensity was studied before and after sialidase pre-treatment, at one-, four- and eight-day-old animals and adult animals. For semi-quantitative evaluation of SBA binding intensity, two investigators performed the analysis independently, blinded to the type of experiment. Reactivity of the lectin was assessed in bronchiolar and respiratory portion/alveolar epithelial cell surfaces. We evidenced a stronger positive reaction when lung sections were pre-treated with neuraminidase before incubation with the lectin in one- and four-day-old animals and adult animals. These results were not so manifest in eight-day-old animals. This binding pattern, generally points towards the presence of terminal but mainly sub-terminal GalNAc/Gal residues probably capped by sialic acids on the rat bronchiolar/respiratory tract epithelial cells. As this glycan extension is common in O- and N-glycans, our results suggest that these glycan classes can be present in bronchioloalveolar cells immediately after birth and exist during the postnatal period. The results observed in eight-day-old rat lung sections may be due to the dramatic lung morphologic changes and the possible underlying biological mechanisms that occur during this age-moment.

Figure 1.

An increase in SBA binding is evident in sialidase pre-treated sections (arrows in B and D) when compared with non-pre-treated sections (arrowheads in A and C) from 1-day-old (A and B) and from 4-day-old (B and C). This increase is not so evident in sections from 8-day-old rat tissue sections (arrowheads in E and arrows in F).

Figure 2.

Adult rat lung sections show a stronger positive reaction on the surface of ciliated and non-ciliated cells when we compare sections pre-treated with neuraminidase (arrows in B), with the ones non-pre-treated (arrowheads in A). The surface of the alveoli shows the same labelling pattern (arrowheads in C and arrows in D).

Figure 3.

No staining is present when the lectin was pre-incubated with GalNAc. 1-dayold rat lung section.