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

Embryology and anatomy of congenital diaphragmatic hernia

Prenatal and postnatal treatment modalities for congenital diaphragmatic hernia (CDH) continue to improve, however patients still face high rates of morbidity and mortality caused by severe underlying persistent pulmonary hypertension and pulmonary hypoplasia. Though the majority of CDH cases are idiopathic, it is believed that CDH is a polygenic developmental defect caused by interactions between candidate genes, as well as environmental and epigenetic factors. However, the origin and pathogenesis of these developmental insults are poorly understood. Further, connections between disrupted lung development and the failure of diaphragmatic closure during embryogenesis have not been fully elucidated. Though several animal models have been useful in identifying candidate genes and disrupted signalling pathways, more studies are required to understand the pathogenesis and to develop effective preventative care. In this article, we summarize the most recent litterature on disrupted embryological lung and diaphragmatic development associated with CDH.

TBX4 variants and pulmonary diseases: getting out of the 'Box'

PURPOSE OF REVIEW

In 2013, the association between T-Box factor 4 (TBX4) variants and pulmonary arterial hypertension (PAH) has first been described. Now - in 2020 - growing evidence is emerging indicating that TBX4 variants associate with a wide spectrum of lung disorders.

RECENT FINDINGS

TBX4 variants are enriched in both children and adults with PAH. The clinical phenotype associated with a TBX4 variant seems to be milder than that in other PAH-associated gene mutations. Further, TBX4 variants have increasingly been associated with a variety of clinical and histopathological phenotypes, including lethal developmental parenchymal lung diseases such as not only acinar dysplasia in neonates, but also less outspoken parenchymal lung diseases in children and adults.

SUMMARY

The clinical phenotype of a TBX4 variant has recently been recognised to expand from bone disorders to different types of lung diseases. Recent data suggest that variants of TBX4, a transcription factor known to be an important regulator in embryonic development, are not rare in both children and adults with PAH and/or developmental parenchymal lung diseases.

Recent advances in our understanding of the mechanisms of lung alveolarization and bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is the most common cause of morbidity and mortality in preterm infants. A key histopathological feature of BPD is stunted late lung development, where the process of alveolarization-the generation of alveolar gas exchange units-is impeded, through mechanisms that remain largely unclear. As such, there is interest in the clarification both of the pathomechanisms at play in affected lungs, and the mechanisms of de novo alveoli generation in healthy, developing lungs. A better understanding of normal and pathological alveolarization might reveal opportunities for improved medical management of affected infants. Furthermore, disturbances to the alveolar architecture are a key histopathological feature of several adult chronic lung diseases, including emphysema and fibrosis, and it is envisaged that knowledge about the mechanisms of alveologenesis might facilitate regeneration of healthy lung parenchyma in affected patients. To this end, recent efforts have interrogated clinical data, developed new-and refined existing-in vivo and in vitro models of BPD, have applied new microscopic and radiographic approaches, and have developed advanced cell-culture approaches, including organoid generation. Advances have also been made in the development of other methodologies, including single-cell analysis, metabolomics, lipidomics, and proteomics, as well as the generation and use of complex mouse genetics tools. The objective of this review is to present advances made in our understanding of the mechanisms of lung alveolarization and BPD over the period 1 January 2017-30 June 2019, a period that spans the 50th anniversary of the original clinical description of BPD in preterm infants.

Complex Compound Inheritance of Lethal Lung Developmental Disorders Due to Disruption of the TBX-FGF Pathway

Primary defects in lung branching morphogenesis, resulting in neonatal lethal pulmonary hypoplasias, are incompletely understood. To elucidate the pathogenetics of human lung development, we studied a unique collection of samples obtained from deceased individuals with clinically and histopathologically diagnosed interstitial neonatal lung disorders: acinar dysplasia (n = 14), congenital alveolar dysplasia (n = 2), and other lethal lung hypoplasias (n = 10). We identified rare heterozygous copy-number variant deletions or single-nucleotide variants (SNVs) involving TBX4 (n = 8 and n = 2, respectively) or FGF10 (n = 2 and n = 2, respectively) in 16/26 (61%) individuals. In addition to TBX4, the overlapping ∼2 Mb recurrent and nonrecurrent deletions at 17q23.1q23.2 identified in seven individuals with lung hypoplasia also remove a lung-specific enhancer region. Individuals with coding variants involving either TBX4 or FGF10 also harbored at least one non-coding SNV in the predicted lung-specific enhancer region, which was absent in 13 control individuals with the overlapping deletions but without any structural lung anomalies. The occurrence of rare coding variants involving TBX4 or FGF10 with the putative hypomorphic non-coding SNVs implies a complex compound inheritance of these pulmonary hypoplasias. Moreover, they support the importance of TBX4-FGF10-FGFR2 epithelial-mesenchymal signaling in human lung organogenesis and help to explain the histopathological continuum observed in these rare lethal developmental disorders of the lung.

Assessment of the nitrofen model of congenital diaphragmatic hernia and of the dysregulated factors involved in pulmonary hypoplasia

PURPOSE

To study pulmonary hypoplasia (PH) associated with congenital diaphragmatic hernia (CDH), investigators have been employing a fetal rat model based on nitrofen administration to dams. Herein, we aimed to: (1) investigate the validity of the model, and (2) synthesize the main biological pathways implicated in the development of PH associated with CDH.

METHODS

Using a defined strategy, we conducted a systematic review of the literature searching for studies reporting the incidence of CDH or factors involved in PH development. We also searched for PH factor interactions, relevance to lung development and to human PH.

RESULTS

Of 335 full-text articles, 116 reported the incidence of CDH after nitrofen exposure or dysregulated factors in the lungs of nitrofen-exposed rat fetuses. CDH incidence: 54% (27-85%) fetuses developed a diaphragmatic defect, whereas the whole litter had PH in varying degrees. Downregulated signaling pathways included FGF/FGFR, BMP/BMPR, Sonic Hedgehog and retinoid acid signaling pathway, resulting in a delay in early epithelial differentiation, immature distal epithelium and dysfunctional mesenchyme.

CONCLUSIONS

The nitrofen model effectively reproduces PH as it disrupts pathways that are critical for lung branching morphogenesis and alveolar differentiation. The low CDH rate confirms that PH is an associated phenomenon rather than the result of mechanical compression alone.

Genome-wide association study identifies loci and candidate genes for non-idiopathic pulmonary hypertension in Eastern Chinese Han population

BACKGROUND

Pulmonary hypertension (PH) is a rare disease characterized by proliferation and occlusion of small pulmonary arterioles, which has been associated with a high mortality rate. The pathogenesis of PH is complex and incompletely understood, which includes both genetic and environmental factors that alter vascular structure and function.

METHODS

Thus we aimed to reveal the potential genetic etiology of PH by targeting 143 tag SNPs of 14 candidate genes. Totally 208 individuals from Chinese Han population were enrolled in the present study, including 109 non-idiopathic PH patients and 99 healthy controls.

RESULTS

The data revealed that 2 SNPs were associated with PH overall susceptibility at p < 3×10^- 4 after Bonferroni correction. The top hit was rs6557421 (p = 4.5×10^- 9), located within Nox3 gene on chromosome 6. Another SNP rs3744439 located in Tbx4 gene, also showed evidence of association with PH susceptibility (p = 1.2×10^- 6). The distribution of genotype frequencies of rs6557421 and rs3744439 have dramatic differences between PH patients and controls. Individuals with rs6557421 TT genotype had a 10.72-fold/14.20-fold increased risk to develop PH when compared with GG or GG/GT carriers in codominant or recessive model, respectively (TT versus GG: 95%CI = 4.79-24.00; TT versus GG/GT: 95%CI = 6.65-30.33). As for rs3744439, AG genotype only occurred in healthy controls but has not been observed in PH patients. We further validated the result by using 26 different populations from five regions around the globe, including African (AFR), American (AMR), East Asian (EAS), European (EUR), and South Asian (SAS). In consistent with the present case-control study's results, significantly different genotype frequencies of the observed SNPs existed between PH patients and healthy individuals from all over the world.

CONCLUSIONS

The results suggested that rs6557421 variant in Nox3 and rs3744439 variant in Tbx4 might have potential effect on individual susceptibility to pulmonary hypertension, which could lead to therapeutic or diagnosis approaches in PH.

Effects of Simvastatin on Fetal Cardiac Impairment in the Diaphragmatic Experimental Hernia Model

BACKGROUND

Statins and sildenafil have been shown to exert beneficial effects in cardiac injury. We hypothesized that antenatal maternal administration of simvastatin and/or sildenafil might also promote benefits in cardiac remodeling of congenital diaphragmatic hernia (CDH). Therefore, we performed micro-CT image analysis and histology of the heart after antennal treatment in experimental nitrofen-induced CDH.

METHODS

At 9.5 days post conception (dpc), pregnant rats were exposed to nitrofen. At 16 and 20 dpc fetuses were treated with simvastatin and/or sildenafil. At 21 dpc postmortem micro-CT and autopsy were performed.

RESULTS

All nitrofen-treated fetuses had a lower birth weight compared to controls; in the simvastatin-treated group, a significant improvement in CDH was noted. Impairment of the lung and liver was also noted in CDH. Compared to controls, CDH rats showed lower ventricular mass, with greater left ventricular thickness; simvastatin decreased the ventricular mass and improved wall thickness. CDH rats exhibited myocardial hypotrophy, severe vascular depression in the left ventricle, and intense interstitial edema compared to controls and nitrofen-exposed animals without CDH. In CDH, the cardiac morphology appeared deformed with left ventricular wall verticalization. Simvastatin improved cardiac myocyte appearance and heart morphology.

CONCLUSION

The potential to treat CDH with antenatal simvastatin may improve the management of this malformation.

Recent advances in our understanding of the mechanisms of late lung development and bronchopulmonary dysplasia

The objective of lung development is to generate an organ of gas exchange that provides both a thin gas diffusion barrier and a large gas diffusion surface area, which concomitantly generates a steep gas diffusion concentration gradient. As such, the lung is perfectly structured to undertake the function of gas exchange: a large number of small alveoli provide extensive surface area within the limited volume of the lung, and a delicate alveolo-capillary barrier brings circulating blood into close proximity to the inspired air. Efficient movement of inspired air and circulating blood through the conducting airways and conducting vessels, respectively, generates steep oxygen and carbon dioxide concentration gradients across the alveolo-capillary barrier, providing ideal conditions for effective diffusion of both gases during breathing. The development of the gas exchange apparatus of the lung occurs during the second phase of lung development-namely, late lung development-which includes the canalicular, saccular, and alveolar stages of lung development. It is during these stages of lung development that preterm-born infants are delivered, when the lung is not yet competent for effective gas exchange. These infants may develop bronchopulmonary dysplasia (BPD), a syndrome complicated by disturbances to the development of the alveoli and the pulmonary vasculature. It is the objective of this review to update the reader about recent developments that further our understanding of the mechanisms of lung alveolarization and vascularization and the pathogenesis of BPD and other neonatal lung diseases that feature lung hypoplasia.