Expression of Prx1 and Tcf4 is decreased in the diaphragmatic muscle connective tissue of nitrofen-induced congenital diaphragmatic hernia

Background/purpose: Pleuroperitoneal folds (PPFs) are the source of the primordial diaphragm's muscle connective tissue (MCT), and developmental mutations have been shown to result in congenital diaphragmatic hernia (CDH). The protein paired-related homeobox 1 (Prx1) labels migrating PPF cells and stimulates expression of transcription factor 4 (Tcf4), a novel MCT marker that controls morphogenesis of the fetal diaphragm. We hypothesized that diaphragmatic Prx1 and Tcf4 expression is decreased in the nitrofen-induced CDH model. Methods: Time-mated rats were exposed to either nitrofen or vehicle on gestational day 9 (D9). Fetal diaphragms were microdissected on D13, D15, and D18, and divided into control and nitrofen-exposed specimens. Gene expression levels of Prx1 and Tcf4 were analyzed by qRT-PCR. Immunofluorescence double staining for Prx1 and Tcf4 was performed to evaluate protein expression and localization. Results: Relative mRNA expression of Prx1 and Tcf4 was significantly downregulated in PPFs (D13), developing diaphragms (D15) and fully muscularized diaphragms (D18) of nitrofen-exposed fetuses compared to controls. Confocal laser scanning microscopy revealed markedly diminished Prx1 and Tcf4 expression in diaphragmatic MCT of nitrofen-exposed fetuses on D13, D15, and D18 compared to controls. Conclusions: Decreased expression of Prx1 and Tcf4 in the fetal diaphragm may cause defects in the PPF-derived MCT, leading to development of CDH in the nitrofen model. Level of evidence: Level 2c (Centre for Evidence-Based Medicine, Oxford). (C) 2016 Elsevier Inc. All rights reserved.