Functional morphology of the bronchial mucociliary transport system in rats during postnatal ontogenesis

BACKGROUND: Age-related remodeling of the mucociliary transport system (MCTS) of the airways plays a significant role in the pathogenesis of respiratory diseases. However, the available published data lacks studies of the structural and functional parameters of bronchial epithelial lining throughout postnatal development conducted under standardized conditions and using unified methodological approaches, which highlights the relevance of further research in this area. AIM: The work aimed to investigate age-related patterns of postnatal morphogenesis of the bronchial mucociliary transport system in rats based on structural and functional analysis of the respiratory epithelium components. METHODS: The work utilizes in vivo measurement of ciliary activity, light and electron microscopy, immunohistochemistry (using antibodies against the proliferation marker Ki-67), and morphometry. The research material consisted of respiratory epithelium from the main, lobar, and segmental bronchi of Wistar rats (n = 76) at ages of 1, 8, 14 days, and 1, 3, 6, 14, 20, and 26 months, 6–9 animals per time point. RESULTS: In newborn rats, the bronchial tree is lined with a single-layer epithelium composed predominantly of undifferentiated cells (59%–62%) and a few ciliated cells (21%–26%). During the first postnatal month, MCTS elements undergo the most intensive and asynchronous differentiation: in the first two weeks, active ciliogenesis predominates, with the number of ciliated cells increasing by 2.2–2.7 times (p 0.001); between days 14 and 30; goblet cell subpopulations are formed. Ciliary apparatus development proceeds faster in segmental bronchi, whereas glandular element formation occurs primarily in the main bronchi. Ciliary beat frequency is the highest in newborns (25.0–25.9 Hz), decreasing to 14.9–18.6 Hz by one month of age (p 0.001), and subsequently stabilizing at 13.2–16.2 Hz. The formation of the typical structure of the respiratory epithelium is completed during puberty; starting from 3 months of age and throughout the entire reproductive period (6–14 months), its main structural and functional characteristics remain largely unchanged. In aging (20 months) and old (26 months) animals, the number of ciliated and goblet cells reaches its maximum, and ciliary apparatus activity is preserved. However, there is a decrease in proliferative cell count, an increase in hypertrophic ciliated cells, and the appearance of ultrastructural signs of epithelial cell damage. CONCLUSION: Postnatal morphogenesis of the bronchial MCTS in rats continues throughout life, with the most pronounced histogenetic changes occurring during the first month after birth. Subsequent age-related changes in the mature epithelial structure are aimed at maintaining stable mucociliary clearance.