Effect of insulin-like-growth factor and its receptors regarding lung development in fetal mice

A prenatally disrupted airway epithelium orchestrates the fetal origin of asthma in mice

BACKGROUND

Prenatal challenges such as maternal stress perception increase the risk and severity of asthma during childhood. However, insights into the trajectories and targets underlying the pathogenesis of prenatally triggered asthma are largely unknown. The developing lung and immune system may constitute such targets.

OBJECTIVE

Here we have aimed to identify the differential sex-specific effects of prenatal challenges on lung function, immune response, and asthma severity in mice.

METHODS

We generated bone marrow chimeric (BMC) mice harboring either prenatally stress-exposed lungs or a prenatally stress-exposed immune (hematopoietic) system and induced allergic asthma via ovalbumin. Next-generation sequencing (RNA sequencing) of lungs and assessment of airway epithelial barrier function in ovalbumin-sensitized control and prenatally stressed offspring was also performed.

RESULTS

Profoundly enhanced airway hyperresponsiveness, inflammation, and fibrosis were exclusively present in female BMC mice with prenatally stress-exposed lungs. These effects were significantly perpetuated if both the lungs and the immune system had been exposed to prenatal stress. A prenatally stress-exposed immune system alone did not suffice to increase the severity of these asthma features. RNA sequencing analysis of lungs from prenatally stressed, non-BMC, ovalbumin-sensitized females unveiled a deregulated expression of genes involved in asthma pathogenesis, tissue remodeling, and tight junction formation. It was also possible to independently confirm a tight junction disruption. In line with this, we identified an altered perinatal and/or postnatal expression of genes involved in lung development along with an impaired alveolarization in female prenatally stressed mice.

CONCLUSION

Here we have shown that the fetal origin of asthma is orchestrated by a disrupted airway epithelium and further perpetuated by a predisposed immune system.

Genome-wide enrichment of damaging de novo variants in patients with isolated and complex congenital diaphragmatic hernia

Congenital Diaphragmatic Hernia (CDH) is a common and often lethal birth defect characterized by diaphragmatic structural defects and pulmonary hypoplasia. CDH is isolated in 60% of newborns, but may also be part of a complex phenotype with additional anomalies. We performed whole exome sequencing (WES) on 87 individuals with isolated or complex CDH and on their unaffected parents, to assess the contribution of de novo mutations in the etiology of diaphragmatic and pulmonary defects and to identify new candidate genes. A combined analysis with 39 additional trios with complex CDH, previously published, revealed a significant genome-wide burden of de novo variants compared to background mutation rate and 900 control trios. We identified an increased burden of likely gene-disrupting (LGD, i.e. nonsense, frameshift, and canonical splice site) and predicted deleterious missense (D-mis) variants in complex and isolated CDH patients. Overall, an excess of predicted damaging de novo LGD and D-mis variants relative to the expected frequency contributed to 21% of complex cases and 12% of isolated CDH cases. The burden of de novo variants was higher in genes expressed in the developing mouse diaphragm and heart. Some overlap with genes responsible for congenital heart defects and neurodevelopmental disorders was observed in CDH patients within our cohorts. We propose that de novo variants contribute significantly to the development of CDH.

Involvement of Igf1r in Bronchiolar Epithelial Regeneration: Role during Repair Kinetics after Selective Club Cell Ablation

Regeneration of lung epithelium is vital for maintaining airway function and integrity. An imbalance between epithelial damage and repair is at the basis of numerous chronic lung diseases such as asthma, COPD, pulmonary fibrosis and lung cancer. IGF (Insulin-like Growth Factors) signaling has been associated with most of these respiratory pathologies, although their mechanisms of action in this tissue remain poorly understood. Expression profiles analyses of IGF system genes performed in mouse lung support their functional implication in pulmonary ontogeny. Immuno-localization revealed high expression levels of Igf1r (Insulin-like Growth Factor 1 Receptor) in lung epithelial cells, alveolar macrophages and smooth muscle. To further understand the role of Igf1r in pulmonary homeostasis, two distinct lung epithelial-specific Igf1r mutant mice were generated and studied. The lack of Igf1r disturbed airway epithelial differentiation in adult mice, and revealed enhanced proliferation and altered morphology in distal airway club cells. During recovery after naphthalene-induced club cell injury, the kinetics of terminal bronchiolar epithelium regeneration was hindered in Igf1r mutants, revealing increased proliferation and delayed differentiation of club and ciliated cells. Amid airway restoration, lungs of Igf1r deficient mice showed increased levels of Igf1, Insr, Igfbp3 and epithelial precursor markers, reduced amounts of Scgb1a1 protein, and alterations in IGF signaling mediators. These results support the role of Igf1r in controlling the kinetics of cell proliferation and differentiation during pulmonary airway epithelial regeneration after injury.

Transcriptome analysis in prenatal IGF1-deficient mice identifies molecular pathways and target genes involved in distal lung differentiation

Background

Insulin-like Growth Factor 1 (IGF1) is a multifunctional regulator of somatic growth and development throughout evolution. IGF1 signaling through IGF type 1 receptor (IGF1R) controls cell proliferation, survival and differentiation in multiple cell types. IGF1 deficiency in mice disrupts lung morphogenesis, causing altered prenatal pulmonary alveologenesis. Nevertheless, little is known about the cellular and molecular basis of IGF1 activity during lung development.

Methods/Principal Findings

Prenatal Igf1^−/− mutant mice with a C57Bl/6J genetic background displayed severe disproportional lung hypoplasia, leading to lethal neonatal respiratory distress. Immuno-histological analysis of their lungs showed a thickened mesenchyme, alterations in extracellular matrix deposition, thinner smooth muscles and dilated blood vessels, which indicated immature and delayed distal pulmonary organogenesis. Transcriptomic analysis of Igf1^−/− E18.5 lungs using RNA microarrays identified deregulated genes related to vascularization, morphogenesis and cellular growth, and to MAP-kinase, Wnt and cell-adhesion pathways. Up-regulation of immunity-related genes was verified by an increase in inflammatory markers. Increased expression of Nfib and reduced expression of Klf2, Egr1 and Ctgf regulatory proteins as well as activation of ERK2 MAP-kinase were corroborated by Western blot. Among IGF-system genes only IGFBP2 revealed a reduction in mRNA expression in mutant lungs. Immuno-staining patterns for IGF1R and IGF2, similar in both genotypes, correlated to alterations found in specific cell compartments of Igf1^−/− lungs. IGF1 addition to Igf1^−/− embryonic lungs cultured ex vivo increased airway septa remodeling and distal epithelium maturation, processes accompanied by up-regulation of Nfib and Klf2 transcription factors and Cyr61 matricellular protein.

Conclusions/Significance

We demonstrated the functional tissue specific implication of IGF1 on fetal lung development in mice. Results revealed novel target genes and gene networks mediators of IGF1 action on pulmonary cellular proliferation, differentiation, adhesion and immunity, and on vascular and distal epithelium maturation during prenatal lung development.

miRNA regulated pathways in late stage murine lung development

Background

MicroRNAs play important roles in regulating biological processes, including organ morphogenesis and maturation. However, little is known about specific pathways regulated by miRNA during lung development. Between the canalicular and saccular stages of the developing lung several important cellular events occur, including the onset of surfactant synthesis, microvascular remodeling and structural preparation for subsequent alveolarization. The miRNAs that are actively regulated, and the identity of their targets during this important developmental interval in the lung remain elusive.

Results

Using TLDA low density real-time PCR arrays, the expression of 376 miRNAs in male and female fetal mouse lungs of gestational days E15 – E18 were profiled. Statistical analyses identified 25 and 37 miRNAs that changed significantly between sexes and with gestation, respectively. In silico analysis using Ingenuity Pathway Analysis (IPA) identified specific pathways and networks known to be targets of these miRNAs which are important to lung development. Pathways that are targeted by sex regulated miRNAs include retinoin, IGFR1, Tp53 and Akt. Pathways targeted by gestation-regulated miRNAs include VEGFA and mediators of glucose metabolism.

Conclusion

MiRNAs are differentially regulated across time and between sexes during the canalicular and saccular stages of lung development. Sex-associated differential miRNA expression may regulate the differences in structural and functional male and female lung development, as shown by networks generated using in silico analysis. These data provide a valuable resource to further enhance the understanding of miRNA control of lung development and maturation.

Knockout of insulin-like growth factor-1 receptor impairs distal lung morphogenesis

Background

Insulin-like growth factors (IGF-I and -II) are pleiotropic regulators of somatic growth and development in vertebrate species. Endocrine and paracrine effects of both hormones are mediated by a common IGF type 1 receptor (IGF-1R). Lethal respiratory failure in neonatal IGF-1R knockout mice suggested a particular role for this receptor in pulmonary development, and we therefore investigated the consequences of IGF-1R inactivation in lung tissue.

Methods and Findings

We first generated compound heterozygous mutant mice harboring a hypomorphic (Igf1r^neo) and a null (Igf1r⁻) allele. These IGF-1R^neo/− mice express only 22% of normal IGF-1R levels and are viable. In adult IGF-1R^neo/− mice, we assessed lung morphology and respiratory physiology and found normal histomorphometric characteristics and normal breathing response to hypercapnia. We then generated homozygous IGF-1R knockout mutants (IGF-1R^−/−) and analyzed their lung development during late gestation using histomorphometric and immunohistochemical methods. IGF-1R^−/− embryos displayed severe lung hypoplasia and markedly underdeveloped diaphragms, leading to lethal neonatal respiratory distress. Importantly, IGF-1R^−/− lungs from late gestation embryos were four times smaller than control lungs and showed markedly thickened intersaccular mesenchyme, indicating strongly delayed lung maturation. Cell proliferation and apoptosis were significantly increased in IGF-1R^−/− lung tissue as compared with IGF-1R^+/+ controls. Immunohistochemistry using pro-SP-C, NKX2-1, CD31 and vWF as markers revealed a delay in cell differentiation and arrest in the canalicular stage of prenatal respiratory organ development in IGF-1R^−/− mutant mice.

Conclusions/Significance

We found that low levels of IGF-1R were sufficient to ensure normal lung development in mice. In contrast, complete absence of IGF-1R significantly delayed end-gestational lung maturation. Results indicate that IGF-1R plays essential roles in cell proliferation and timing of cell differentiation during fetal lung development.

Prenatal administration of retinoic acid upregulates insulin-like growth factor receptors in the nitrofen-induced hypoplastic lung

BACKGROUND

Pulmonary hypoplasia (PH) is the main cause of mortality in newborns with congenital diaphragmatic hernia (CDH). Prenatal administration of retinoic acid (RA) stimulates alveologenesis in the nitrofen-induced pulmonary hypoplasia. Insulin-like growth factor receptors (IGFRs) play a crucial role in alveologenesis during lung development. We recently demonstrated that IGFRs were downregulated in later stages of lung development in the nitrofen CDH model. Several studies suggest the ability of RA to regulate insulin-like growth factor signaling. We hypothesized that IGFRs pulmonary gene expression is upregulated after the administration of RA in the nitrofen-induced CDH model.

METHODS

Pregnant rats were exposed to either olive oil or nitrofen on day 9 (D9) of gestation. RA was given intraperitoneally on days D18, D19, and D20. Fetal lungs were dissected on D21 and divided into control, control + RA, CDH, and CDH + RA group. IGFRs gene and protein expression were determined using RT-PCR and immunohistochemistry.

RESULTS

mRNA expression levels of IGFRs were significantly increased in control + RA and CDH + RA compared with CDH group. Immunoreactivity of IGFRs was markedly increased in control + RA and CDH + RA compared with CDH lungs.

CONCLUSIONS

Upregulation of pulmonary gene and protein expression of IGFRs after prenatal RA treatment in the nitrofen model suggests that RA may promote lung growth by stimulating IGFRs mediated alveologenesis.

Effect of insulin-like growth factors on lung development in a nitrofen-induced CDH rat model

PURPOSE

Both the mortality and morbidity associated with congenital diaphragmatic hernia (CDH) are mainly caused by pulmonary hypoplasia and persistent pulmonary hypertension. A previous study revealed that insulin-like growth factors (IGFs) play important roles in fetal lung development. The aim of this study was to investigate the effect of IGF-1 and IGF-2 on tissue cultures of fetal hypoplastic lungs obtained from nitrofen-induced CDH model rats.

METHODS

Pregnant rats were exposed to nitrofen on day 9 of gestation (D9). Fetuses were harvested on D18 by caesarian section. Lung specimens of the CDH (+) fetus were divided into three groups; control, IGF-1, and IGF-2. The specimens from the control group were cultured in culture medium without IGFs. The IGF-1 group specimens were cultured with IGF-1 (500 ng/ml), and those in the IGF-2 group were cultured with IGF-2 (500 ng/ml). The mRNA expression of TTF-1, T1α and α-SMA were analyzed in each group using real-time RT-PCR after 24 and 48 h of incubation. Immunohistochemical staining of these markers was also assessed for each of the cultured specimens.

RESULTS

There was a significant increase in the expression of both TTF-1 and T1α mRNA in the IGF-2 group, in comparison to the control group after 48 h of culture. Immunohistochemical staining revealed that the cell morphology was changed from cuboidal to squamous type in the IGF-2 group.

CONCLUSIONS

An increased mRNA expression of the markers related to type 1 and 2 alveolar epithelial cells, and morphological changes in the epithelial cells were observed in the IGF-2 group. The administration of IGF-2 to nitrofen-induced hypoplastic lungs might lead to alveolar maturation, which thus results in their improved development.

Congenital diaphragmatic hernia: an overview of the etiology and current management

AIM

To review provide an overview of the etiology and current strategies in the management of congenital diaphragmatic hernia (CDH).

METHODS

We did a comprehensive review of research trends, evidence based studies and epidemiologic studies.

RESULTS

CDH is a life-threatening pathology in infants, and a major cause of death due to the pulmonary hypoplasia and pulmonary hypertension. There is much research related to elucidating the etiology of CDH and developing management strategies to improve the outcomes in these infants.

CONCLUSION

An early diagnosis with increased understanding of this disease is a crucial factor for a timely approach to managing the critically ill infant, and to offer the potential for improved outcomes and substantial reductions in morbidity.