Julia Zimmer

Knockout mouse models of Hirschsprung’s disease

PurposeHirschsprung’s disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cell migration. Rodent animal models of aganglionosis have contributed greatly to our understanding of the genetic basis of HSCR. Several natural or target mutations in specific genes have been reported to produce developmental defects in neural crest migration, differentiation or survival. The aim of this study was to review the currently available knockout models of HSCR to better understand the molecular basis of HSCR.MethodsA review of the literature using the keywords “Hirschsprung’s disease”, “aganglionosis”, “megacolon” and “knockout mice model” was performed. Resulting publications were reviewed for relevant mouse models of human aganglionosis. Reference lists were screened for additional relevant studies.Results16 gene knockout mouse models were identified as relevant rodent models of human HSCR. Due to the deletion of a specific gene, the phenotypes of these knockout models are diverse and range from small bowel dilatation and muscular hypertrophy to total intestinal aganglionosis.ConclusionsMouse models of aganglionosis have been instrumental in the discovery of the causative genes of HSCR. Although important advances have been made in understanding the genetic basis of HSCR, animal models of aganglionosis in future should further help to identify the unknown susceptibility genes in HSCR.

Expression of T-box transcription factors 2, 4 and 5 is decreased in the branching airway mesenchyme of nitrofen-induced hypoplastic lungs.

PurposePulmonary hypoplasia (PH), characterized by smaller lung size and reduced airway branching, remains a major therapeutic challenge in newborns with congenital diaphragmatic hernia (CDH). T-box transcription factors (Tbx) have been identified as key components of the gene network that regulates fetal lung development. Tbx2, Tbx4 and Tbx5 are expressed throughout the mesenchyme of the developing lung, regulating the process of lung branching morphogenesis. Furthermore, lungs of Tbx2-, Tbx4- and Tbx5-deficient mice are hypoplastic and exhibit decreased lung branching, similar to PH in human CDH. We hypothesized that the expression of Tbx2, Tbx4 and Tbx5 is decreased in the branching airway mesenchyme of hypoplastic rat lungs with nitrofen-induced CDH.MethodsTime-mated rats received either nitrofen or vehicle on gestational day 9 (D9). Fetuses were killed on D15, D18 and D21, and dissected lungs were divided into control and nitrofen-exposed specimens. Pulmonary gene expression of Tbx2, Tbx4 and Tbx5 was investigated by quantitative real-time polymerase chain reaction. Immunofluorescence double staining for Tbx2, Tbx4 and Tbx5 was combined with the mesenchymal marker Fgf10 to assess protein expression and localization in branching airway tissue.ResultsRelative mRNA levels of Tbx2, Tbx4 and Tbx5 were significantly reduced in lungs of nitrofen-exposed fetuses on D15, D18 and D21 compared to controls. Confocal laser scanning microscopy showed markedly diminished immunofluorescence of Tbx2, Tbx4 and Tbx5 in mesenchymal cells surrounding branching airways of nitrofen-exposed fetuses on D15, D18 and D21 compared to controls.ConclusionDecreased expression of Tbx2, Tbx4 and Tbx5 in the pulmonary mesenchyme during fetal lung development may lead to a decrease or arrest of airway branching, thus contributing to PH in the nitrofen-induced CDH model.

Imbalance of NFATc2 and KV1.5 Expression in Rat Pulmonary Vasculature of Nitrofen-Induced Congenital Diaphragmatic Hernia.

Aim of the Study Nuclear factor of activated T‐cell (NFATc2), a Ca2+/calcineurin‐dependent transcription factor, is reported to be activated in human and animal pulmonary hypertension (PH). KV1.5, a voltage‐gated K+ (KV) channel, is expressed in pulmonary artery smooth muscle cells (PASMC) and downregulated in PASMC in patients and animals with PH. Furthermore, activation of NFATc2 downregulates expression of KV1.5 channels, leading to excessive PASMC proliferation. The aim of this study was to investigate the pulmonary vascular expression of NFATc2 and KV1.5 in rats with nitrofen‐induced congenital diaphragmatic hernia (CDH). Materials and Methods After ethical approval, time‐pregnant Sprague‐Dawley rats received nitrofen or vehicle on gestational day 9 (D9). When sacrificed on D21, the fetuses (n = 22) were divided into CDH and control groups. Using quantitative real‐time polymerase chain reaction and western blotting, we determined the gene and protein expression of NFATc2 and KV1.5. Confocal microscopy was used to detect both proteins in the pulmonary vasculature. Results Relative mRNA levels of NFATc2 were significantly upregulated and KV1.5 levels were significantly downregulated in CDH lungs compared with controls (p < 0.05). Western blotting confirmed the imbalanced pulmonary protein expression of both proteins. An increased pulmonary vascular expression of NFATc2 and a diminished expression of KV1.5 in CDH lungs compared with controls were seen in confocal microscopy. Conclusions This study demonstrates for the first time an altered gene and protein expression of NFATc2 and KV1.5 in the pulmonary vasculature of nitrofen‐induced CDH. Upregulation of NFATc2 with concomitant downregulation of KV1.5 channels may contribute to abnormal vascular remodeling resulting in PH in this model.

Increased c-kit and stem cell factor expression in the pulmonary vasculature of nitrofen-induced congenital diaphragmatic hernia

PURPOSE Persistent pulmonary hypertension(PPH) in congenital diaphragmatic hernia (CDH) is caused by increased vascular cell proliferation and endothelial cell (EC) dysfunction, thus leading to obstructive changes in the pulmonary vasculature. C-Kit and its ligand, stem cell factor(SCF), are expressed by ECs in the developing lung mesenchyme, suggesting an important role during lung vascular formation. Conversely, absence of c-Kit expression has been demonstrated in ECs of dysplastic alveolar capillaries. We hypothesized that c-Kit and SCF expression is increased in the pulmonary vasculature of nitrofen-induced CDH. METHODS Timed-pregnant rats received nitrofen or vehicle on gestational day 9(D9). Fetuses were sacrificed on D15, D18, and D21, and divided into control and CDH group. Pulmonary gene expression levels of c-Kit and SCF were analyzed by qRT-PCR. Immunofluorescence double staining for c-Kit and SCF was combined with CD34 to evaluate protein expression in ECs of the pulmonary vasculature. RESULTS Relative mRNA levels of c-Kit and SCF were significantly increased in lungs of CDH fetuses on D15, D18, and D21 compared to controls. Confocal laser scanning microscopy confirmed markedly increased vascular c-Kit and SCF expression in mesenchymal ECs of CDH lungs on D15, D18, and D21 compared to controls. CONCLUSION Increased expression of c-Kit and SCF in the pulmonary vasculature of nitrofen-induced CDH lungs suggest that increased c-Kit signaling during lung vascular formation may contribute to vascular remodeling and thus to PPH.

Follistatin-like 1 expression is decreased in the alveolar epithelium of hypoplastic rat lungs with nitrofen-induced congenital diaphragmatic hernia

BACKGROUND/PURPOSE Pulmonary hypoplasia (PH), characterized by incomplete alveolar development, remains a major therapeutic challenge associated with congenital diaphragmatic hernia (CDH). Follistatin-like 1 (Fstl1) is a crucial regulator of alveolar formation and maturation, which is strongly expressed in distal airway epithelium. Fstl1-deficient mice exhibit reduced airspaces, impaired alveolar epithelial cell differentiation, and insufficient production of surfactant proteins similar to PH in human CDH. We hypothesized that pulmonary Fstl1 expression is decreased during alveolarization in the nitrofen-induced CDH model. METHODS Timed-pregnant rats received nitrofen or vehicle on gestational day 9 (D9). Fetal lungs were harvested on D18 and D21 and divided into control-/nitrofen-exposed specimens. Alveolarization was assessed using morphometric analysis techniques. Pulmonary gene expression of Fstl1 was determined by qRT-PCR. Immunofluorescence-double-staining for Fstl1 and alveolar epithelial marker surfactant protein C (SP-C) was performed to evaluate protein expression/localization. RESULTS Radial alveolar count was significantly reduced in hypoplastic lungs of nitrofen-exposed fetuses with significant down regulation of Fstl1 mRNA expression on D18 and D21 compared to controls. Confocal-laser-scanning-microscopy revealed strikingly diminished Fstl1 immunofluorescence and SP-C expression in distal alveolar epithelium of nitrofen-exposed fetuses with CDH-associated PH on D18 and D21 compared to controls. CONCLUSIONS Decreased expression of Fstl1 in alveolar epithelium may disrupt alveolarization and pulmonary surfactant production, thus contributing to the development of PH in the nitrofen-induced CDH model. LEVEL OF EVIDENCE 2b (Centre for Evidence-Based Medicine, Oxford).

Leadership in Pediatric Surgery from a Trainee's Perspective

&NA; Role models are fundamental for anyone entering the field of medicine. Proper leadership is especially essential in surgical subspecialties to guide young doctors through their training, ensure surgical experience and skill development, and teach the values of professional and ethical behavior and team management. In the complex field of pediatric surgery, which is composed of a unique patient clientele and age‐dependent conditions, specialization, experience, and a strong executive are vital for patient care. Leaders in pediatric surgery are required to find a suitable balance between guidance and controlling a trainees actions to ensure correct medical and surgical treatment and provide young doctors with the opportunity to grow and gain independent experience. When teaching the present generation of trainees, current leaders need to consider the specific characteristics of the so‐called “Millennials” to avoid tension and frustration due to generation diversity. This article aims to assess leadership qualities, character traits, challenges, and expectations in pediatric surgery from a trainees perspective.

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 diaphragms 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).

Decreased expression of monocarboxylate transporter 1 and 4 in the branching airway epithelium of nitrofen-induced congenital diaphragmatic hernia.

BACKGROUND/PURPOSE Monocarboxylate transporters (MCTs) are crucial for the maintenance of intracellular pH homeostasis in developing fetal lungs. MCT1/4 is strongly expressed by epithelial airway cells throughout lung branching morphogenesis. Functional inhibition of MCT1/4 in fetal rat lung explants has been shown to result in airway defects similar to pulmonary hypoplasia (PH) in congenital diaphragmatic hernia (CDH). We hypothesized that pulmonary expression of MCT1/4 is decreased during lung branching morphogenesis in the nitrofen model of CDH-associated PH. METHODS Timed-pregnant rats received nitrofen or vehicle on gestational day 9 (D9). Fetuses were harvested on D15, D18, and D21, and divided into control and nitrofen-exposed group. Pulmonary gene expression levels of MCT1/4 were analyzed by qRT-PCR. Immunofluorescence staining for MCT1/4 was combined with E-cadherin in order to evaluate protein expression in branching airway tissue. RESULTS Relative mRNA levels of MCT1/4 were significantly reduced in lungs of nitrofen-exposed fetuses on D15, D18, and D21 compared to controls. Confocal laser scanning microscopy confirmed markedly decreased immunofluorescence of MCT1/4 in distal bronchial and primitive alveolar epithelium of nitrofen-exposed fetuses on D15, D18, and D21 compared to controls. CONCLUSION Decreased expression of MCT1/4 in distal airway epithelium may disrupt lung branching morphogenesis and thus contribute to the development of PH in the nitrofen-induced CDH model.

Fibrillin-1 Expression Is Decreased in the Diaphragmatic Muscle Connective Tissue of Nitrofen-Induced Congenital Diaphragmatic Hernia.

Introduction Diaphragmatic morphogenesis depends on proper formation of muscle connective tissue (MCT) and underlying extracellular matrix (ECM). Fibrillin‐1 is an essential ECM protein and crucial for the structural integrity of MCT in the developing diaphragm. Recently, mutations in the fibrillin‐1 gene (FBN1) have been identified in cases of congenital diaphragmatic hernia (CDH), thus suggesting that alterations in FBN1 gene expression may lead to diaphragmatic defects. We designed this study to investigate the hypothesis that the diaphragmatic expression of fibrillin‐1 is decreased in the MCT of nitrofen‐induced CDH. Materials and Methods Time‐mated rats were exposed to nitrofen or vehicle on gestational day 9 (D9). Fetal diaphragms (n = 72) were harvested on D13, D15, and D18, and divided into control and nitrofen‐exposed specimens. Laser‐capture microdissection was used to obtain diaphragmatic tissue cells. Gene expression levels of FBN1 were analyzed by qRT‐PCR. Immunofluorescence‐double‐staining for fibrillin‐1 and the mesenchymal marker Gata4 was performed to evaluate protein expression and localization. Results Relative mRNA expression of FBN1 was significantly decreased in pleuroperitoneal folds on D13 (3.39 ± 1.29 vs. 5.47 ± 1.92; p < 0.05), developing diaphragms on D15 (2.48 ± 0.89 vs. 4.03 ± 1.62; p < 0.05), and fully muscularized diaphragms on D18 (2.49 ± 0.69 vs. 3.93 ± 1.55; p < 0.05) of nitrofen‐exposed fetuses compared with controls. Confocal‐laser‐scanning microscopy revealed markedly diminished fibrillin‐1 immunofluorescence mainly in MCT, associated with a reduction of proliferating mesenchymal cells in nitrofen‐exposed fetuses on D13, D15, and D18 compared with controls. Conclusions Decreased expression of fibrillin‐1 during morphogenesis of the fetal diaphragm may disrupt mesenchymal cell proliferation, causing malformed MCT and thus resulting in diaphragmatic defects in the nitrofen‐induced CDH model.

The Role of Activin Receptor-Like Kinase 1 Signaling in the Pulmonary Vasculature of Experimental Diaphragmatic Hernia.

AIM The high morbidity and mortality in newborn infants diagnosed with congenital diaphragmatic hernia (CDH) is widely recognized to be due to pulmonary hypoplasia and persistent pulmonary hypertension (PH). The underlying structural and molecular pathomechanisms causing PH are not fully understood. Recently, activin receptor-like kinase 1 (ALK-1), an endothelial cell (EC) receptor, has been implicated in the pathogenesis of PH. ALK-1 transmits signals via a Smad pathway stimulating EC proliferation and migration leading to structural lung remodeling consecutively resulting in PH. Increased pulmonary expression of ALK-1 has been reported in patients with severe PH as well as in experimental models of PH. We designed this study to investigate the hypothesis that pulmonary ALK-1 expression is increased in nitrofen-induced CDH. METHODS Pregnant rats were exposed to nitrofen or vehicle on D9. Fetuses were sacrificed on D21 and divided into nitrofen (n = 16) and control group (n = 16). Quantitative real-time polymerase chain reaction, Western blotting, and confocal-immunofluorescence microscopy were performed to determine pulmonary gene and protein expression as well as vascular localization of expressed ALK-1. RESULTS Pulmonary gene expression levels of ALK-1 were significantly upregulated in nitrofen-treated lung tissue compared with controls. Western blotting showed increased pulmonary protein expression for ALK-1 in the CDH group when compared with control lung tissue. Confocal microscopy demonstrated markedly increased medial and adventitial thickness of pulmonary arteries in the CDH group and revealed increased ALK-1 protein expression of the pulmonary vasculature of CDH pups compared with controls. CONCLUSION Upregulated gene and increased protein expression of ALK-1 in the pulmonary vasculature of nitrofen-induced CDH suggest that increased expression of ALK-1 may play a crucial role in the molecular pathogenesis of vascular remodeling induced PH in experimental CDH.