Instituto de Histologia e Embriologia, Faculdade de Medicina, Universidade de Coimbra; Centro Hospitalar e Universitário de Coimbra.
Department of Chemical Engineering, University of Coimbra.
Eur J Histochem. 2020 May 6;64(2):3124. doi: 10.4081/ejh.2020.3124.
Sialic acids, particularly N-acetylneuraminic acid (Neu5Ac), are present as terminal components of rich and complex oligosaccharide chains, which are termed glycans, and are exhibited on the cell surfaces, especially on epithelial cells. Crucial in the 'social behavior' of the cell, sialic acids play vital roles in many physiological and pathological phenomena. The aim of the present study was to separate, identify, and quantify Neu5Ac in purified lung membranes from 4-, 14-, and 21-day-old animals, followed by the statistical analysis of these results with our previously reported data (0-day-old and adult results). Complementary, ultrastructural methodologies were used. The differences in the Neu5Ac values obtained across the examined postnatal-lung development relevant ages studied were found to be statistically significant. A substantial increase in the mean level of this compound was found during the period of 'bulk' alveolarization, which takes place from postnatal day 4 to 14 (P4-P14). The comparison of the mean levels of Neu5Ac, during microvascular maturation (mainly between P12 and P21), reveals that the difference, although statistically significant, is the least significant difference among all the pair-wise differences between the developmental stages. The presence of sub-terminal N-acetylgalactosamine (GalNAc)/Galactose (Gal) residues with terminal sialic acids on the bronchioloalveolar cell surfaces was confirmed using lung ultra-thin sections of adult and 0-day-old animals. These results showed that, although Neu5Ac levels increase throughout postnatal lung development, this sialic acid was substantially added to epithelial cell surfaces during the "bulk" alveolarization period, while its presence was less important during the microvascular maturation period. Bearing in mind that sialic acids are negatively charged and create charge repulsions between adjacent cells, we hypothesized that they can substantially contribute to postnatal alveolar formation and maturation.
唾液酸，特别是 N-乙酰神经氨酸（Neu5Ac），作为丰富而复杂的寡糖链的末端成分存在，这些寡糖链被称为聚糖，并展示在细胞表面，特别是在上皮细胞表面。唾液酸在细胞的“社交行为”中起着至关重要的作用，在许多生理和病理现象中发挥着重要作用。本研究的目的是分离、鉴定和定量来自 4 天、14 天和 21 天龄动物的纯化肺膜中的 Neu5Ac，然后对这些结果与我们之前报告的数据（0 天龄和成年结果）进行统计分析。同时使用了补充的超微结构方法。在所研究的出生后肺发育相关年龄中，发现 Neu5Ac 值的差异具有统计学意义。在“大量”肺泡化期间（从出生后第 4 天到第 14 天，即 P4-P14），发现该化合物的平均水平显著增加。在微血管成熟期间（主要在 P12 和 P21 之间）比较 Neu5Ac 的平均水平，尽管差异具有统计学意义，但与所有发育阶段之间的两两差异中，该差异是最不显著的差异。使用成年和 0 天龄动物的肺超薄切片证实了在细支气管肺泡细胞表面上存在带有末端唾液酸的亚末端 N-乙酰半乳糖胺（GalNAc）/半乳糖（Gal）残基。这些结果表明，尽管 Neu5Ac 水平在出生后肺发育过程中增加，但这种唾液酸在“大量”肺泡化期间大量添加到上皮细胞表面，而在微血管成熟期间其存在不太重要。考虑到唾液酸带负电荷并在相邻细胞之间产生电荷排斥，我们假设它们可以为出生后肺泡的形成和成熟做出重大贡献。
