Retinoic acid promotes primary fetal alveolar epithelial type II cell proliferation and differentiation to alveolar epithelial type I cells

Abnormal Fetal Lung of Hoxa1-/- Piglets Is Rescued by Maternal Feeding with All-Trans Retinoic Acid

Neonatal Hoxa1-/- piglets were characterized by dyspnea owing to the Hoxa1 mutation, and maternal administration with ATRA alleviated the dyspnea of neonatal Hoxa1-/- piglets. The purpose of this experiment was to explore how maternal ATRA administration rescued the abnormal fetal lungs of Hoxa1-/- piglets. Samples of the lungs were collected from neonatal Hoxa1-/- and non-Hoxa1-/- piglets delivered by sows in the control group, and from neonatal Hoxa1-/- piglets born by sows administered with ATRA at 4 mg/kg body weight on dpc 12, 13, or 14, respectively. These were used for the analysis of ELISA, histological morphology, immunofluorescence staining, immunohistochemistry staining, and quantitative real-time PCR. The results indicate that the Hoxa1 mutation had adverse impacts on the development of the alveoli and pulmonary microvessels of Hoxa1-/- piglets. Maternal administration with ATRA at 4 mg/kg body weight on dpc 14 rescued the abnormal lung development of Hoxa1-/- piglets by increasing the IFN-γ concentration (p < 0.05), airspace area (p < 0.01) and pulmonary microvessel density (p < 0.01); increasing the expression of VEGFD (p < 0.01), PDGFD (p < 0.01), KDR (p < 0.01), ID1 (p < 0.01), and NEDD4 (p < 0.01); and decreasing the septal wall thickness (p < 0.01) and the expression of SFTPC (p < 0.01) and FOXO3 (p < 0.01). Maternal administration with ATRA plays a vital role in rescuing the abnormal development of lung of Hoxa1-/- fetal piglets.

Retinoids stored locally in the lung are required to attenuate the severity of acute lung injury in male mice

Retinoids are potent transcriptional regulators that act in regulating cell proliferation, differentiation, and other cellular processes. We carried out studies in male mice to establish the importance of local cellular retinoid stores within the lung alveolus for maintaining its health in the face of an acute inflammatory challenge induced by intranasal instillation of lipopolysaccharide. We also undertook single cell RNA sequencing and bioinformatic analyses to identify roles for different alveolar cell populations involved in mediating these retinoid-dependent responses. Here we show that local retinoid stores and uncompromised metabolism and signaling within the lung are required to lessen the severity of an acute inflammatory challenge. Unexpectedly, our data also establish that alveolar cells other than lipofibroblasts, specifically microvascular endothelial and alveolar epithelial cells, are able to take up lipoprotein-transported retinoid and to accumulate cellular retinoid stores that are directly used to respond to an acute inflammatory challenge.

Serum vitamin A levels as a novel predictor for respiratory distress syndrome in neonates: is it beneficial?

BACKGROUND

Neonatal respiratory distress syndrome (RDS) is a very important dangerous disease in neonates and is accompanied by neonatal complications and death.

OBJECTIVE

Early determination of neonatal serum vitamin A levels as a possible novel predictor for neonatal RDS.

PATIENTS AND METHODS

A case-control study, with the identification number TCTR20210206001 was done on 100 neonates who were admitted to the neonatal intensive care unit (NICU) of Tanta University Hospital (TUH) suffering from RDS (patient group) and 100 healthy neonates (control group). Estimation of serum vitamin A (retinol) was occurred for all neonates of this study within the first four hours after birth before any nutrition or therapies.

RESULTS

Showed no significant difference between serums retinol (RT) levels in grade 1&2 RDS neonates (patient group) and the serum RT levels in the control group while there was significant difference between serums retinol levels in grade 3&4 RDS neonates (patient group) and the serum retinol levels in the control group where the P-value was 0.006, 0.002 respectively.

CONCLUSION

Serum vitamin A levels in neonates were decreased in RDS neonates and could be used as a predictor for the development and severity of RDS.

RECOMMENDATION

Routine estimation of serum vitamin A levels in neonates as a novel predictor for neonatal RDS.

Perinatal Undernutrition, Metabolic Hormones, and Lung Development

Maternal and perinatal undernutrition affects the lung development of litters and it may produce long-lasting alterations in respiratory health. This can be demonstrated using animal models and epidemiological studies. During pregnancy, maternal diet controls lung development by direct and indirect mechanisms. For sure, food intake and caloric restriction directly influence the whole body maturation and the lung. In addition, the maternal food intake during pregnancy controls mother, placenta, and fetal endocrine systems that regulate nutrient uptake and distribution to the fetus and pulmonary tissue development. There are several hormones involved in metabolic regulations, which may play an essential role in lung development during pregnancy. This review focuses on the effect of metabolic hormones in lung development and in how undernutrition alters the hormonal environment during pregnancy to disrupt normal lung maturation. We explore the role of GLP-1, ghrelin, and leptin, and also retinoids and cholecalciferol as hormones synthetized from diet precursors. Finally, we also address how metabolic hormones altered during pregnancy may affect lung pathophysiology in the adulthood.

The Evolution of Cholesterol-Rich Membrane in Oxygen Adaption: The Respiratory System as a Model

The increase in atmospheric oxygen levels imposed significant environmental pressure on primitive organisms concerning intracellular oxygen concentration management. Evidence suggests the rise of cholesterol, a key molecule for cellular membrane organization, as a cellular strategy to restrain free oxygen diffusion under the new environmental conditions. During evolution and the increase in organismal complexity, cholesterol played a pivotal role in the establishment of novel and more complex functions associated with lipid membranes. Of these, caveolae, cholesterol-rich membrane domains, are signaling hubs that regulate important in situ functions. Evolution resulted in complex respiratory systems and molecular response mechanisms that ensure responses to critical events such as hypoxia facilitated oxygen diffusion and transport in complex organisms. Caveolae have been structurally and functionally associated with respiratory systems and oxygen diffusion control through their relationship with molecular response systems like hypoxia-inducible factors (HIF), and particularly as a membrane-localized oxygen sensor, controlling oxygen diffusion balanced with cellular physiological requirements. This review will focus on membrane adaptations that contribute to regulating oxygen in living systems.

SENP1 has an important role in lung development and influences the differentiation of alveolar type 2 cells

Post-translational modification via small ubiquitin-like modifier (SUMO) is involved in the regulation of various important cellular processes. SUMO modification can be regulated at the level of conjugation, and can also be reversed by the SUMO-specific proteases (SENPs). However, current studies of the regulation and function of SENP in lung development remain limited. In this study, the expression levels of SENP1 and SUMO1 were assessed during lung development in rats. SUMO1 modification occurred during lung development and changes in SENP1 expression were consistent with the changes in the presence of free SUMO1. In order to investigate the function of SENP1, alveolar type (AT) 2 cells were transfected with SENP1-targeting small interfering RNA, and the proliferation, apoptosis and differentiation function of AT2 cells was subsequently evaluated. Marked upregulation of conjugated SUMO1 was observed following SENP1 inhibition. Furthermore, depletion of SENP1 resulted in increased apoptosis, decreased proliferation and impaired differentiation status of AT2 cells. Thus, the results support that SENP1 is an essential regulator of the balance between SUMOylation and deSUMOylation during lung development, specifically affecting the proliferation and differentiation status of AT2 cells.

Overexpressing dominant-negative FGFR2-IIIb impedes lung branching morphogenesis in pigs

Genetic studies with mouse models have shown that fibroblast growth factor receptor 2-IIIb (FGFR2-IIIb) plays crucial roles in lung development and differentiation. To evaluate the effect of FGFR2-IIIb in pig lung development, we employed somatic cell nuclear transfer (SCNT) technology to generate transgenic pig fetuses overexpressing the transmembrane (dnFGFR2-IIIb-Tm) and soluble (dnFGFR2-IIIb-HFc) forms of the dominant-negative human FGFR2-IIIb driven by the human surfactant protein C (SP-C) promoter, which was specifically expressed in lung epithelia. Eight dnFGFR2-IIIb-Tm transgenic and twelve dnFGFR2-IIIb-HFc transgenic pig fetuses were collected from three and two recipient sows, respectively. Repression of FGFR2-IIIb in lung epithelia resulted in smaller lobes and retardation of alveolarization in both forms of dnFGFR2-IIIb transgenic fetuses. Moreover, the dnFGFR2-IIIb-HFc transgenic ones showed more deterioration in lung development. Our results demonstrate that disruption of FGFR2-IIIb signaling in the epithelium impedes normal branching and alveolarization in pig lungs, which is less severe than the results observed in transgenic mice. The dnFGFR2-IIIb transgenic pig is a good model for the studies of blastocyst complementation as well as the mechanisms of lung development and organogenesis.

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.

A Role for the Liver in Parturition and Preterm Birth

Neither the mechanisms of parturition nor the pathogenesis of preterm birth are well understood. Poor nutritional status has been suspected as a major causal factor, since vitamin A concentrations are low in preterm infants. However, even large enteral doses of vitamin A from birth fail to increase plasma concentrations of vitamin A or improve outcomes in preterm and/or extremely low birthweight infants. These findings suggest an underlying impairment in the secretion of vitamin A from the liver, where about 80% of the vitamin is stored. Vitamin A accumulates in the liver and breast during pregnancy in preparation for lactation. While essential in low concentration for multiple biological functions, vitamin A in higher concentration can be pro-oxidant, mutagenic, teratogenic and cytotoxic, acting as a highly surface-active, membrane-seeking and destabilizing compound. Regarding the mechanism of parturition, it is conjectured that by nine months of gestation the hepatic accumulation of vitamin A (retinol) from the liver is such that mobilization and secretion are impaired to the point where stored vitamin A compounds in the form of retinyl esters and retinoic acid begin to spill or leak into the circulation, resulting in amniotic membrane destabilization and the initiation of parturition. If, however, the accumulation and spillage of stored retinoids reaches a critical threshold prior to nine months, e.g., due to cholestatic liver disease, which is common in mothers of preterm infants, the increased retinyl esters and/or retinoic acid rupture the fetal membranes, inducing preterm birth and its complications, including retinopathy, necrotizing enterocolitis and bronchopulmonary dysplasia. Subject to testing, the model suggests that measures taken prior to and during pregnancy to improve liver function could reduce the risk of adverse birth outcomes, including preterm birth.