Alveolar epithelial cell differentiation and surfactant protein expression after mild preterm birth in sheep

Abstract

As the transition to extrauterine life at birth alters the proportions of type I and II alveolar epithelial cells (AECs), our aim was to determine the effect of mild preterm birth on AECs and surfactant protein (SP) gene expression. Preterm lambs were born at ∼133 d of gestational age (DGA); controls were born at term (∼147 DGA). Lungs were collected from preterm lambs at term-equivalent age (TEA; ∼2 wk after preterm birth) and 6 wk post-TEA. Control lung tissue was collected from fetuses (at 132 DGA), as well as from lambs at ∼6 h (normal term) and 2, 6, and 8 wk of postnatal age (PNA). In controls, the proportion of type I AECs decreased from 65.1 ± 3.9% at term to 50.9 ± 3.3%, while the proportion of type II AECs increased from 33.7 ± 3.9% to 48.5 ± 3.3% at 6 wk PNA. At 2 wk after preterm birth, the proportions of type I and II AECs were similar in preterm lambs compared to 132-d fetal levels and term controls but differed from control values at 2 wk PNA; differences between control and preterm lambs persisted at 8 wk PNA. At ∼2 wk after preterm birth, SP-A and SP-B, but not SP-C, mRNA levels were significantly reduced in preterm lambs compared with term controls, but these differences did not persist at 2 and 6 wk PNA. We conclude that mild preterm birth alters the normal postnatal changes in type I and II cell proportions but does not severely affect SP gene expression. Copyright © 2005 International Pediatric Research Foundation, Inc.