The effect of repeated umbilical cord occlusions on pulmonary surfactant protein mRNA levels in the ovine fetus

Evolution, Development, and Function of the Pulmonary Surfactant System in Normal and Perturbed Environments

Surfactant lipids and proteins form a surface active film at the air-liquid interface of internal gas exchange organs, including swim bladders and lungs. The system is uniquely positioned to meet both the physical challenges associated with a dynamically changing internal air-liquid interface, and the environmental challenges associated with the foreign pathogens and particles to which the internal surface is exposed. Lungs range from simple, transparent, bag-like units to complex, multilobed, compartmentalized structures. Despite this anatomical variability, the surfactant system is remarkably conserved. Here, we discuss the evolutionary origin of the surfactant system, which likely predates lungs. We describe the evolution of surfactant structure and function in invertebrates and vertebrates. We focus on changes in lipid and protein composition and surfactant function from its antiadhesive and innate immune to its alveolar stability and structural integrity functions. We discuss the biochemical, hormonal, autonomic, and mechanical factors that regulate normal surfactant secretion in mature animals. We present an analysis of the ontogeny of surfactant development among the vertebrates and the contribution of different regulatory mechanisms that control this development. We also discuss environmental (oxygen), hormonal and biochemical (glucocorticoids and glucose) and pollutant (maternal smoking, alcohol, and common "recreational" drugs) effects that impact surfactant development. On the adult surfactant system, we focus on environmental variables including temperature, pressure, and hypoxia that have shaped its evolution and we discuss the resultant biochemical, biophysical, and cellular adaptations. Finally, we discuss the effect of major modern gaseous and particulate pollutants on the lung and surfactant system.

Expression of lung surfactant proteins SP-B and SP-C and their modulating factors in fetal lung of FGR rats

This study investigated the expression of lung surfactant proteins SP-B and SP-C, and their modulating factors TTF-1 and PLAGL2 in the fetal lung of rats with fetal growth restriction (FGR). The rat FGR model was established by prenatal hypoxia in the first stage of pregnancy, 180 rats for experiment served as hypoxia group, and 197 healthy rats served as normal control group. The FGR incidence in hypoxia was compared with that in normal control group. The histological changes in the fetal lung were observed under the light microscope and electronic microscope in two groups. The SP-B, SP-C, TTF-1 and PLAGL2 proteins were determined in the fetal lung of two groups immunohistochemically. The expression levels of SP-B, SP-C, TTF-1 and PLAGL2 protein and mRNA in the fetal lung of two groups were detected by using Western blotting and RT-PCR respectively. The FGR rat model was successfully established by using hypoxia. Pathologically the fetal lung developed slowly, and the expression levels of SP-B, SP-C, TTF-1 and PLAGL2 protein and mRNA in the fetal lung were significantly reduced in hypoxia group as compared with those in normal control group. It was suggested that maternal hypoxia in the first stage of pregnancy could induce FGR, and reduce the expression of SP-B and SP-C, resulting in the disorder of fetal lung development and maturation.

Prenatal hypoxia downregulates the expression of pulmonary vascular endothelial growth factor and its receptors in fetal mice

BACKGROUND

Previous reports showed that prenatal hypoxia delays the process of lung maturation. Vascular endothelial growth factor (VEGF) and its receptors were important for lung development. However, the role of VEGF and VEGF receptors in altered fetal lung development and maturation induced by prenatal hypoxia remains unknown.

OBJECTIVES

To elucidate the role of VEGF and VEGF receptors in altered fetal lung development and maturation induced by prenatal hypoxia.

METHODS

Lung sections of control and maternal hypoxic fetal mice were used for the determination of lung development and total RNA isolated from lung homogenates were used for determination of the expression patterns of VEGF, Flt-1, Flk-1, hypoxia-inducible factor (HIF)-1α, HIF-2α, surfactant protein (SP)-A, SP-B, SP-C, and SP-D by quantitative real-time RT-PCR.

RESULTS

Prenatal hypoxia resulted in fetal mice body weight gain impairment, delayed fetal pulmonary aeration and maturation. Pulmonary SP-A, SP-B, SP-C, and SP-D mRNA were all decreased in the prenatal hypoxia group. In addition, we demonstrated that prenatal hypoxia inhibited the developmental increase of pulmonary HIF-1α and HIF-2α expression and resulted in decreasing VEGF and its receptors (Flt-1 and Flk-1) at the mRNA expression level and VEGF protein level in fetal lungs. These inhibitory effects persisted and progressed even when the dams were returned to air.

CONCLUSIONS

We suggest that prenatal hypoxia insults, at least in late gestation, influence pulmonary VEGF and VEGF receptor expression through the down-regulation of HIF pathways and impair fetal lung growth and maturation.

Intrauterine growth restriction delays surfactant protein maturation in the sheep fetus

Pulmonary surfactant is synthesized by type II alveolar epithelial cells to regulate the surface tension at the air-liquid interface of the air-breathing lung. Developmental maturation of the surfactant system is controlled by many factors including oxygen, glucose, catecholamines, and cortisol. The intrauterine growth-restricted (IUGR) fetus is hypoxemic and hypoglycemic, with elevated plasma catecholamine and cortisol concentrations. The impact of IUGR on surfactant maturation is unclear. Here we investigate the expression of surfactant protein (SP) A, B, and C in lung tissue of fetal sheep at 133 and 141 days of gestation (term 150 +/- 3 days) from control and carunclectomized Merino ewes. Placentally restricted (PR) fetuses had a body weight <2 SD from the mean of control fetuses and a mean gestational Pa(O(2)) <17 mmHg. PR fetuses had reduced absolute, but not relative, lung weight, decreased plasma glucose concentration, and increased plasma cortisol concentration. Lung SP-A, -B, and -C protein and mRNA expression was reduced in PR compared with control fetuses at both ages. SP-B and -C but not SP-A mRNA expression and SP-A but not SP-B or -C protein expression increased with gestational age. Mean gestational Pa(O(2)) was positively correlated with SP-A, -B, and -C protein and SP-B and -C mRNA expression in the younger cohort. SP-A and -B gene expression was inversely related to plasma cortisol concentration. Placental restriction, leading to chronic hypoxemia and hypercortisolemia in the carunclectomy model, results in significant inhibition of surfactant maturation. These data suggest that IUGR fetuses are at significant risk of lung complications, especially if born prematurely.