Alveolarization genes modulated by fetal tracheal occlusion in the rabbit model for congenital diaphragmatic hernia: a randomized study.

BACKGROUND: The mechanisms by which tracheal occlusion (TO) improves alveolarization in congenital diaphragmatic hernia (CDH) are incompletely understood. Therefore transcriptional and histological effects of TO on alveolarization were studied in the rabbit model for CDH. The question of the best normalization strategy for gene expression analysis was also addressed. METHODS: Fetal rabbits were randomized for CDH or sham operation on gestational day 23/31 and for TO or sham operation on day 28/31 resulting in four study groups. Untouched littermates were added. At term and before lung harvest, fetuses were subjected to mechanical ventilation or not. Quantitative real-time PCR was performed on lungs from 4-5 fetuses of each group with and without previous ventilation. Stability of ten housekeeping genes (HKGs) and optimal number of HKGs for normalization were determined, followed by assessment of HKG expression levels. Expression levels of eleven target genes were studied in ventilated lungs, including genes regulating elastogenesis, cell-environment interactions, and thinning of alveolar walls. Elastic staining, immunohistochemistry and Western blotting completed gene analysis. RESULTS: Regarding HKG expression, TO increased ß-actin and ß-subunit of ATP synthase. Mechanical ventilation increased ß-actin and ß2-microglobulin. Flavoprotein subunit of succinate dehydrogenase and DNA topoisomerase were the most stable HKGs. CDH lungs showed disorganized elastin deposition with lower levels for tropoelastin, fibulin-5, tenascin-C, and α6-integrin. After TO, CDH lungs displayed a normal pattern of elastin distribution with increased levels for tropoelastin, fibulin-5, tenascin-C, α6-integrin, ß1-integrin, lysyl oxidase, and drebrin. TO increased transcription and immunoreactivity of tissue inhibitor of metalloproteinase-1. CONCLUSIONS: Experimental TO might improve alveolarization through the mechanoregulation of crucial genes for late lung development. However part of the transcriptional changes involved genes that were not affected in CDH, raising the question of TO-induced disturbances of alveolar remodeling. Attention should also be paid to selection of HKGs for studies on mechanotransduction-mediated gene expressions.

Signaling molecules in the fetal rabbit model for congenital diaphragmatic hernia.

RATIONALE AND OBJECTIVES: Little is known about molecular changes in lungs of fetal rabbits with surgically induced diaphragmatic hernia (DH). Therefore, we examined in this model gene expressions of pivotal molecules for the developing lung. METHODS: At day 23 of gestation, DH was created in 12 fetuses from 4 does. Both lungs from six live DH fetuses and from six unoperated controls were harvested and weighed at term. Transcription of 15 genes involved in alveolarization, angiogenesis, regulation of vascular tone, or epithelial maturation was investigated by real-time quantitative polymerase chain reaction. MAIN RESULTS: DH decreased lung-to-body weight ratio (P < 0.001). A bilateral downregulation was seen for genes encoding for tropoelastin (P < 0.01), lysyl oxidase (P < 0.05), fibulin 5 (P < 0.05), and cGMP specific phosphodiesterase 5 (P < 0.05). Lower mRNA levels for endothelial nitric oxide synthase occurred in the ipsilateral lung (P < 0.05). CONCLUSIONS: Experimental DH in fetal rabbits disrupted transcription of genes implicated in lung growth and function. Similarities with the human disease make this model appropriate for investigation of new prenatal therapies.

A longer tracheal occlusion period results in increased lung growth in the nitrofen rat model.

OBJECTIVE: Prenatal tracheal occlusion (TO) promotes lung growth and is applied clinically in fetuses with severe congenital diaphragmatic hernia. Limited data are available regarding the effect of duration of TO on lung development. Our objective was to evaluate the effects of long (2 and 2.5 days) versus short (1 day) TO on lung development in rats with nitrofen-induced diaphragmatic hernia. METHOD: Nitrofen was administered on embryonic day (ED) 9 and fetal TO performed either on ED18.5, 19 or 20 (term = 22 days). Sham-operated and untouched littermates served as controls. On ED21, lungs were harvested and only fetuses with a left-sided diaphragmatic defect were included in further analyses. RESULTS: Lung-body-weight ratio incrementally increased with the duration of TO. Increased proliferation following long TO was confirmed by immunohistochemistry and qRT-PCR for the proliferation marker Ki-67. Irrespective of duration, TO induced more complex airway architecture. Medial wall thickness of pulmonary arteries was thinner after long rather than short TO. CONCLUSION: In the nitrofen rat model of congenital diaphragmatic hernia, a longer period of TO leads to enhanced lung growth and less muscularized pulmonary arteries.

Morphologic changes and methodological issues in the rabbit experimental model for diaphragmatic hernia.

Fetal lung development may be impaired by some congenital anomalies or in utero events. Animal models are used to understand the pathophysiology of these diseases and explore therapeutic strategies. Our group has an interest in the prenatal management of congenital diaphragmatic hernia (CDH). Isolated CDH remains associated with a 30% mortality because of lung hypoplasia and pulmonary hypertension. On day 23 of gestation (pseudoglandular stage) CDH was created in both ovarian-end fetuses (n= 28) in 14 time-mated pregnant white rabbits (hybrid of Dendermonde and New-Zealand White). At term (day 30) all survived operated fetuses and size-matched controls were harvested. Fetuses/lungs were assigned randomly to formalin fixation either under pressure of 25 cm H2O (CDH25 n=5; CTR25 n=5) or without (0 cm H2O (CDH0 n=7; CTR0 n=7). Fetuses and lungs were first weighed, and then the lungs were processed for morphometry. Pulmonary development was evaluated by lung-to-body weight ratio (LBWR) and airway and vascular morphometry. Surgical induction of CDH does reduce the LBWR to hypoplastic levels. The contralateral lung weight is 81% of what is expected, whereas the ipsilateral lung is only 46% of the normal. This was accompagnied by a loss of conducting airway generations, precisely, terminal bronchioles (TB), which were surrounded by less alveoli. The ipsilateral CDH lung demonstrated a thickened media in the peripheral arteries as well. As a result, in the severely hypoplastic ipsilateral lung, an airway fixation pressure of 25 H2O has no significant effect on the morphometric indices. The contralateral lung has a normal amount of alveoli around a single TB, which also behave like alveoli of the normal lung, i.e. expand under pressure fixation. The present study on severely hypoplastic lungs that never respirated, shows that in contrast to normal lungs, the morphometric indices are not significantly influenced by a difference in fixation pressure. Increasing fixation pressure seems to expand the lung only when sufficient alveolated parenchyma is present.

The effect of maternal betamethasone and fetal tracheal occlusion on pulmonary vascular morphometry in fetal rabbits with surgically induced diaphragmatic hernia: a placebo controlled morphologic study.

OBJECTIVES: We studied the vascular effects of betamethasone (BM) and/or tracheal occlusion (TO) in fetal rabbits with surgically induced congenital diaphragmatic hernia (CDH). METHODS: At day 23 (pseudoglandular phase; term = 31 d), 54 ovarian-end fetuses from 27 does underwent induction of CDH. Thirteen did receive either 0.05 mg/kg BM, on days 28 and 29 with a 24-h interval, or 14 saline [controls (CTR)]. At day 28, one ovarian-end fetus underwent TO and harvesting was at term. In total, we compared (ANOVA) lung-to-body weight ratio (LBWR) and vascular morphometric indices in survivors from the following groups (n - number alive at delivery): CDH (9); CDH + TO (10); unoperated controls (14); CDH + BM (10); CDH + TO (9); controls CTR + BM (13). RESULTS: Maternal BM had no effect on LBWR. LBWR was comparable to normal in CDH fetuses undergoing TO. Both TO and BM have an effect on medial thickening due to CDH which is larger when both interventions are combined. CONCLUSIONS: Both TO and BM lessen peripheric muscularization present in CDH lungs and their effect is cumulative.

Effects of betamethasone on peripheral arterial development in term fetal rabbit.

Glucocorticoids are given antenatally to promote pulmonary epithelial maturation and prevent respiratory distress syndrome in premature newborns. In contrast to airway changes, effects on vessels are less documented. We hypothesized that antenatal betamethasone (BM) administration promotes vascular development. Does received either a course of BM = 0.05 mg/kg/day (18 does, 70 fetuses), BM = 0.1 mg/kg/day (20 does, 75 fetuses), or saline (11 does, 92 fetuses) starting on d25, 26 (canalicular stage), d27, d28 (saccular stage), and d29 (alveolar stage) of gestation. In total 236 fetuses from 49 does were examined at term (d31) in terms of vascular development. Lung specimens were weighed and formalin fixed for morphometry. We determined differences in fetal body, liver and lung weight, proportionate medial thickness, muscularization of intra-acinar vessels, number of vessels under 100 microm, as well as immunoreactivity to Flk-1 in vascular smooth muscle and endothelial cells. A dose-dependent reduction in neonatal body and organ weight was observed in fetuses exposed to BM at d25. In contrast, term liver weight increased after late administration of BM (d28, 29). There was a dose- and time-dependent thinning of the pulmonary arterial media, which coincided with a decreased proportion of intra- and pre-acinar muscularized arteries (ED

Effect of maternal administration of betamethasone on peripheral arterial development in fetal rabbit lungs.

OBJECTIVES: Glucocorticoids promote lung maturation and reduce the incidence of respiratory distress syndrome in premature newborns. We hypothesized that betamethasone (BM), which is known to induce thinning of the alveolar walls, would also thin the arterial media and adventitia of intra-parenchymatic vessels in developing rabbit lungs. STUDY DESIGN: 112 fetuses from 21 time-mated, pregnant, giant white rabbits received maternal injections of BM at either 0.05 or 0.1 mg/kg/day on days 25-26 of gestational age. Controls received either saline (10 does, 56 fetuses) or no injection (10 does, 59 fetuses). Fetuses were harvested from day 27 onwards until term (day 31). 44 additional fetuses (8 does) were harvested between days 23 and 26. Endpoints were wet lung-to-body weight ratio, vascular morphometric indices and immunohistochemistry staining for alpha-smooth muscle actin, Flk-1, vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). ANOVA (Tukey's test) and independent t test (p < 0.05) were used for comparison between BM and saline groups. RESULTS: Maternal BM injected on days 25-26 to pregnant rabbits induced a significant decrease in fetal body and lung weight and the lung-to-body weight ratio in the preterm pups shortly after injection. BM led to a dose-dependent thinning of the arterial media and adventitia (pulmonary arteries with an external diameter (ED) of <100 microm), to an increase in the percentage of non-muscularized peripheral vessels (ED <60 microm), in eNOS and VEGF immunoreactivity of the endothelial and smooth muscle cells in the pulmonary vessels and to an increase in Flk-1-positive pulmonary epithelial cell density. CONCLUSIONS: Maternal administration of BM caused thinning of the arterial wall of pulmonary vessels (ED <100 microm) and a decrease in muscularization in peripheral vessels (ED <60 microm). This coincided with increased expression of Flk-1 in the endothelium and smooth muscle cells of the pulmonary arteries. All the effects studied were dose-dependent.

Effect of tracheal occlusion on peripheric pulmonary vessel muscularization in a fetal rabbit model for congenital diaphragmatic hernia.

OBJECTIVE: This study was undertaken to evaluate the effects on peripheric pulmonary vessel muscularization by tracheal occlusion (TO) performed at different gestational ages in fetal rabbits with surgically induced diaphragmatic hernia. STUDY DESIGN: In 23 New Zealand white does, both ovarian end fetuses underwent surgical creation of diaphragmatic hernia at 23 days of gestation (pseudoglandular phase). At 26, 27, or 28 days 1 fetus underwent TO, the contralateral one underwent a sham operation for a total of 46 fetuses. At 30 days (alveolar phase), fetuses were harvested together with 1 nonoperated internal control. Lungs were processed for vascular morphometry. Proportionate medial thickness and muscularization of intra-acinar vessels were evaluated. RESULTS: Late TO (day 28; saccular phase) normalizes the lung-to-body weight ratio and causes significant medial thinning in vessels up to 35 microm diameter. CONCLUSION: Tracheal occlusion decreases muscularization of intra-acinar pulmonary vessels in a gestational age-dependent fashion, with maximal effect when TO is performed at 28 days.