Development of the pulmonary pleura with special reference to the lung surface morphology: a study using human fetuses

Preterm birth affects both surfactant synthesis and lung liquid resorption actors in fetal sheep

INTRODUCTION

After birth, the lungs must resorb the fluid they contain. This process involves multiple actors such as surfactant, aquaporins and ENaC channels. Preterm newborns often exhibit respiratory distress syndrome due to surfactant deficiency, and transitory tachypnea caused by a delay in lung liquid resorption. Our hypothesis is that surfactant, ENaC and aquaporins are involved in respiratory transition to extrauterine life and altered by preterm birth. We compared these candidates in preterm and term fetal sheeps.

MATERIALS AND METHODS

We performed cesarean sections in 8 time-dated pregnant ewes (4 at 100 days and 4 at 140 days of gestation, corresponding to 24 and 36 weeks of gestation in humans), and obtained 13 fetal sheeps in each group. We studied surfactant synthesis (SP-A, SP-B, SP-C), lung liquid resorption (ENaC, aquaporins) and corticosteroid regulation (glucocorticoid receptor, mineralocorticoid receptor and 11-betaHSD2) at mRNA and protein levels.

RESULTS

The mRNA expression level of SFTPA, SFTPB and SFTPC was higher in the term group. These results were confirmed at the protein level for SP-B on Western Blot analysis and for SP-A, SP-B and SP-C on immunohistochemical analysis. Regarding aquaporins, ENaC and receptors, mRNA expression levels for AQP1, AQP3, AQP5, ENaCα, ENaCβ, ENaCγ and 11βHSD2 mRNA were also higher in the term group.

DISCUSSION

Expression of surfactant proteins, aquaporins and ENaC increases between 100 and 140 days of gestation in an ovine model. Further exploring these pathways and their hormonal regulation could highlight some new explanations in the pathophysiology of neonatal respiratory diseases.

The Intrapleural Bridge Connection is One of the Reasons for Unknown Localized Pleural Adhesion

Background

Simple signs of local pleural adhesion are often found in people during a physical examination. In the present study, we aimed to clarify whether the merely localized pleural adhesion was just caused by previous pleural inflammation or physiological variation.

Materials and Methods

Chest X-ray image materials were collected to analyze the incidence of simple pleural adhesions. Moreover, the causes of these simple pleural adhesions were further analyzed using thoracoscopy under direct vision and biopsy data.

Results

In all 2218 chest X-ray images, 68 cases were found to have pleural lesions (3.07%), including 15 cases of localized pleural adhesion only. Subsequently, we analyzed the characteristics of 70 cases of pleural lesions using thoracoscopy. In two lung cancer patients with pleural metastasis, we found an unusual pleural junction. This connective strip was smooth and free of inflammation, resembling the normal pleura.

Conclusion

Some of these purely localized pleural adhesions might be attributed to previous inflammation. However, there was still at least a possibility that there must be a physiological pleural junction, which could be the cause of the purely localized pleural adhesion shown in the chest radiograph.

Three-dimensional analysis of the segmental arrangement of lower lung lobes in human fetuses: is this arrangement a miniature version of adult morphology?

Knowledge of the lung segment system is essential for understanding human anatomy and has great clinical relevance. The arrangement of 11 segments, including the S* or subsuperior segment, and its individual variations, are considered to be the same in fetal and adult lungs. The present study assessed the topographical anatomy of lower segmental and subsegmental bronchi by computer-assisted three-dimensional imaging of serial sagittal sections of both lungs of 22 embryos and fetuses of gestational age 6-7 weeks (crown-rump length 15.0-28.5 mm). Long inferior courses of B8b (basal) and B10c (medial) were observed in sagittal sections of both lungs. B8a (lateral) and B10b (lateral) in the right lungs were consistently underdeveloped, with S9 occupying most of the lateral half of the lower lobe. In some samples, B6b (lateral) did not reach the lateral surface. The lateral dominance of S9 was also seen in the left lungs. Some B* candidates were present, but B7 candidates were absent. Lateral and posterior expansions of S6b, S8a and S10b to cover S9 were observed in additional midterm and near-term lung sections, indicating that the original S9 dominance was 'corrected' by an increase in lung volume. Delayed growth of the lower lateral subsegments might induce mechanical stress, resulting in aberrant notches or fissures, such as those separating an independent posterior lobe. The segmental arrangement of fetal lungs was not stable, but was altered over a long fetal period after the complete subsegmental division of the bronchi, except for the minor bronchi B* and B7.

Platelet CLEC-2 and lung development

In this article, the State of the Art lecture "Platelet CLEC-2 and Lung Development" presented at the ISTH congress 2019 is reviewed. During embryonic development, blood cells are often considered as porters of nutrition and oxygen but not as active influencers of cell differentiation. However, recent studies revealed that platelets actively facilitate cell differentiation by releasing biological substances during development. C-type lectin-like receptor 2 (CLEC-2) has been identified as a receptor for the platelet-activating snake venom rhodocytin. An endogenous ligand of CLEC-2 is the membrane protein podoplanin (PDPN), which is expressed on the surface of certain types of tumor cells and lymphatic endothelial cells (LECs). Deletion of CLEC-2 from platelets in mice results in death just after birth due to lung malformation and blood/lymphatic vessel separation. During development, lymphatic vessels are derived from cardinal veins. At this stage, platelets are activated by binding of CLEC-2 to LEC PDPN and release trandforming growth factor-β (TGF-β). This cytokine inhibits LEC migration and proliferation, facilitating blood/lymphatic vessel separation. TGF-β released upon platelet-expressed CLEC-2/LEC PDPN also facilitates differentiation of lung mesothelial cells into alveolar duct myofibroblasts (adMYFs) in the developing lung. AdMYFs generate elastic fibers inside the lung, so that the lung can be properly inflated. Thus, platelets act as an ultimate natural drug delivery system that enables biological substances to be specifically delivered to the target at high concentrations by receptor/ligand interactions during development.

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.