Tracheal occlusion stimulates cell cycle progression and type I cell differentiation in lungs of fetal rats

Abstract

. Tracheal occlusion stimulates cell cycle progression and type I cell differentiation in lungs of fetal rats. Am J Physiol Lung Cell Mol Physiol 285: L344-L353, 2003. First published April 4, 2003 10.1152/ajplung.00281.2002 has been reported to stimulate lung growth but decreases number and maturation of type II cells, effects that vary with gestational age and duration of TO. We examined effects of a novel method of TO (unipolar microcautery to seal the trachea) produced at 19.5-20 days (d) of gestation in fetal rats; fetuses were delivered at term, 22 d. Controls were sham operated and unoperated littermates. TO increased wet lung weight but not dry lung weight or lung DNA and protein. To evaluate further the effects of TO, we examined the cell cycle regulators, cyclins D1 and A, in fetal lungs. Cyclin D1 increased with TO (P Ͻ 0.005). TO also increased expression of the type I epithelial cell marker RTI40 (mRNA and protein). TO decreased mRNA for surfactant proteins (SP)-A and -C but did not affect protein levels of SP-A and -B and of RTII70, a type II epithelial cell marker. We conclude that TO by microcautery, even of short duration, has diverse pulmonary effects including stimulating increased levels of cyclin D1 with probable cell cycle progression, type I cell differentiation, and possibly inhibiting type II cell function.cyclins; fetal lung development; lung growth; pulmonary epithelial differentiation; pulmonary surfactant LATE IN GESTATION, the fetal lung rapidly changes in appearance from an almost glandular tissue into a lacy, thin-walled organ capable of efficient gas exchange and surfactant production. During this period lung growth, septal thinning, maturation of the surfactant system, and differentiation of alveolar type I and type II cells occur. Normal fetal lung development is crucial for survival in extrauterine life, but factors that control these developmental processes and their interdependence have been incompletely defined.Lung growth and maturation of the surfactant system are the most widely studied aspects of late fetal lung development. Fetal lung growth is dependent on several mechanical factors, including adequate intrathoracic space, sufficient amniotic fluid volume, normal fetal breathing movements, and a positive transpulmonary distending pressure (21,27). In contrast, maturation of the surfactant system is highly dependent on endocrine factors (4, 50). There is relatively little information about factors that are responsible for differentiation of alveolar epithelial type I and type II cells in vivo.Several investigators have shown that occlusion of the trachea in experimental animals increases lung growth but has adverse affects on type II cell number and function (2,10,11,15,40). These changes occur when tracheal occlusion (TO) is produced relatively early in gestation and maintained for a prolonged period. In contrast, when TO is produced later in gestation for a relatively short period, lung growth is stimulated, and adverse affects on the type II cell population are di...

Changes in Fetal Lung Distension Alter Expression of Vascular Endothelial Growth Factor and Its Isoforms in Developing Rat Lung

“…On d 20 of gestation (presence of a vaginal plug indicated d 1), dams and fetuses were anesthetized. Through a maternal midline laparotomy, TO was performed on fetuses as previously described (51). Briefly, a section of uterine horn was exposed, a purse string suture (6 -0 polypropylene) was placed in the uterus near the fetal head, and the fetal head and neck were exteriorized through a small hysterotomy.…”

Traqueo-oclusão intra-útero: técnica cirúrgica associada à corticoterapia promove aumento nos receptores de VEGF (Vascular Endothelial Growth Factor) em pulmões de fetos de ratas

“…O efeito maturador da TO parece residir, sobretudo, na ação mecânica que exerce no parênquima pulmonar, consoante ao demonstrado que a aceleração do crescimento celular está diretamente relacionada ao aumento da pressão intratraqueal 13,14,15 . Esse estímulo físico, além de recuperar o espaço pulmonar perdido pela herniação na HDC e restabelecer a arquitetura pulmonar, estimula processos moleculares, culminando com maior transcrição gênica, maior produção protéica e conseqüentemente desenvolvimento e diferenciação celular confluindo para acelerar a maturação pulmonar 7,16 . O VEGF pode ser localizado nos pulmões, rins e ossos, sendo secretado por células endoteliais e outras como espermatozóides e pneumócitos, sendo considerado um mediador parácrino e autócrino.…”

“…Oue et al relata que houve aumento de VEGF no modelo de CDH induzido pelo nitrofen, mas esse aumento não pode ser excluído da própria ação tóxica do nitrofen, por outro lado, no mesmo modelo, Chang et al relatam diminuição do VEGF 18,19 . Os nossos achados mostram que a associação da TO com a corticoterapia induz maior produção dos receptores de VEGF, contribuindo para maturação vascular e maior distensibilidade pulmonar, com melhora funcional ao pulmão 6,16,26 . Em conclusão, os receptores de VEGF e os pneumócitos II são determinantes da maturação pulmonar e suas alterações contribuem para fisiopatologia da HDC com graves implicações clínicas.…”

Developmental Implications

“…Immunohistochemistry was performed on 3 m sections of fixed, cryoprotected rat lung using primary antibodies to PARP-1 and RTII 70 , a protein specific in the lung to the apical surface of rat type II cells (28). For PARP-1, sections were treated with 1% H 2 O 2 for 10 min at room temperature and washed with TBS.…”

“…Multiplex reverse transcriptase-polymerase chain reaction (RT-PCR) was used for the analysis of human PARP-1, rat SP-A, SP-B, and SP-C mRNA in combination with 18S rRNA using Competimer technology (Ambion, Austin, TX) as previously described (28). Total RNA was reverse transcribed using random primers.…”