Expression analysis of asthma candidate genes during human and murine lung development

Background: Premature infants, who require high O2, often develop bronchopulmonary dysplasia, a neonatal chronic lung disease, characterized by a reduced alveolarization. Prior studies showed that lung growth arrest is linked to reduced Kruppel-like factor 4 (Klf4), a transcription factor regulating cell pluripotency and survival. Aim: To study (1) spatiotemporal expression of Klf4 in type II alveolar epithelial cells (ATII) in human and murine lung development; (2) if hyperoxia-induced lung injury is linked to reduced Klf4 in ATII cells. Methods: (1) Investigation of human fetal and murine lungs. (2) Newborn mice or cultured murine ATII cells (MLE-12) were exposed to 85% O2 (HYX) or room air (NOX). Klf4 was overexpressed in MLE-12 using sleeping beauty transposon system. Results: (1) Klf4 was localized in CDH1 or surfactant protein C (SfptC) positive cells during human and murine lung development, respectively, by immunofluorescence. (2) Decreased SftptC and aquaporin 5 coupled with reduced radial alveolar count and increased mean linear intercept after HYX was related to diminished lung Klf4 gene and protein expression. Lower cell survival of MLE-12 and increased markers of epithelial-mesenchymal transition after HYX were linked to reduced Klf4 mRNA and protein abundance. Overexpression of Klf4, however, aggravated the anti-proliferative effect of HYX on MLE-12. Conclusion: Our study does not only identify Klf4 in epithelial cells during murine and human lung development, but also as a potential novel regulator of AECII homeostasis in hyperoxia-induced lung injury, and thereby also as a target to enable lung regeneration.

Current understanding of the molecular regulation of lung development is limited and derives mostly from animal studies. To define global patterns of gene expression during human lung development. Genome-wide expression profiling was used to measure the developing lung transcriptome in RNA samples derived from 38 normal human lung tissues at 53 to 154 days post conception. Principal component analysis was used to characterize global expression variation and to identify genes and bioontologic attributes contributing to these variations. Individual gene expression patterns were verified by quantitative reverse transcriptase-polymerase chain reaction analysis. Gene expression analysis identified attributes not previously associated with lung development, such as chemokine-immunologic processes. Lung characteristics attributes (e.g., surfactant function) were observed at an earlier-than-anticipated age. We defined a 3,223 gene developing lung characteristic subtranscriptome capable of describing a majority of the process. In gene expression space, the samples formed a time-contiguous trajectory with transition points correlating with histological stages and suggesting the existence of novel molecular substages. Induction of surfactant gene expression characterized a pseudoglandular "molecular phase" transition. Individual gene expression patterns were independently validated. We predicted the age of independent human lung transcriptome profiles with a median absolute error of 5 days, supporting the validity of the data and modeling approach. This study extends our knowledge of key gene expression patterns and bioontologic attributes underlying early human lung developmental processes. The data also suggest the existence of molecular phases of lung development.

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) are thought to be involved in lung development because they play an important role in the turnover of the extracellular matrix. Although limited data on MMP and TIMP expression are available from animal studies during prenatal pulmonary development, little is known about their expression during human fetal lung development. The aim of this study was to investigate the expression of MMP-1, -2, -9, TIMP-1, -2 and -3 in human fetal lungs from 9 to 42 weeks of gestation. Forty-five normal human fetal lung samples were analysed by immunohistochemistry. MMP-1, -9, TIMP-1, -2 and -3, but not MMP-2, were expressed in the epithelium at all gestational ages. The endothelium of all vessels and the arterial smooth muscle cells expressed MMP-1, -2, -9, TIMP-2 and -3, but not TIMP-1, at all developmental stages. The extensive distribution of MMPs and TIMPs throughout all stages of human lung development suggests that they play a significant role in the remodelling that occurs in the interstitium and epithelial basement membrane during lung development and in pulmonary vascular development. These data will serve as a base line for comparison with neonatal lung pathology, including pulmonary hypertension.

Tandem exposure to cannabinoids and nicotine during pregnancy poses significant risks to fetal development and health including low birth weight, preterm birth, and perinatal death. However, the effect of co-exposure with the most prominent cannabinoids found in Cannabis sativa (Trans-Δ-9- tetrahydrocannabinol (THC) and cannabidiol (CBD)) alongside nicotine on fetal lung development is not well understood. This study aims to investigate the combinatorial impact of CBD, THC, and nicotine, on human lung development through investigating cellular senescence and the potential role of senolytics in alleviating these effects. Human fetal lung explants from 10 to 16 weeks gestation were cultured on air-liquid interface and treated with various concentrations of nicotine (1µM), CBD, and THC (5µM, or 2.5µM each when used in combination), for 72 hours. To assess the effect of senolytics, the explants were also treated for 48 hours with a combination of CBD, THC, and nicotine. Subsequently, senolytics, Dasatinib (D, 250nM) and Quercetin (Q, 375nM), were added or not for an additional 24 hours. After the 72-hour treatment, explants were collected and either fixed for immunofluorescence staining (IF) analyses or used for RNA extraction and quantitative reverse transcription PCR (qRT-PCR). Additionally, the supernatants were used to evaluate the expression of the senescence-associated secretory phenotype (SASP), conducted by Eve Technologies Corporation-Canada. This study used Luminex xMAP technology for multiplexed quantification of 96 Human cytokines, chemokines, and growth factors. Our results demonstrated that co-exposure to CBD, THC, and nicotine increases the expression of the senescence markers CDKN1A (0.1163±0.02384, p=0.0094, n=8) and CDKN2A (0.005793±0.002157, p=0.0516, n=8) encoding P21 and P16 respectively. Moreover, the IF staining showed increased expression of the DNA damage marker γH2A.X following treatment with CBD+THC+nicotine (7.375±2.154% vs 2.245±0.8329%, p=0.0604, n=6). Furthermore, the lung explants treated with cannabinoids and nicotine released cytokines and chemokines involved in immune responses and inflammation among others IL-6, IL-8, M-CSF, MCP-3, MIP-1β, TNFα, MIP-3β, and TSLP (p<0.05). The addition of D+Q reduced SASP secretion and showed a decreasing trend in expression of the senescence genes CDKN1A and CDKN2A compared to the triple treatment. Taken together, our results showed that the combinatorial exposure to CBD, THC, and nicotine increases senescence, DNA damage, and the senescence-associated secretory phenotypes (SASP) secretion. The use of senolytics (D+Q) may prove to be a promising therapeutic option, alleviating several of the negative effects induced by the different substances. RO1HL171915-01A1 RO!HL155104 RO1HL158532-03 ROIHL160570 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Introduction: The lung is an important and complicated organ that has profound impacts on the entire body when impacted by disease or illness. Due to its complexity, the human lung is difficult to study; lung models that can mimic this organ are key to better understanding and treating lung diseases. Various lung models have been developed over the years, but one important and recent model is the lung organoid model. Here we review human lung organoid models, including the main characteristics and potentials and their current and future applications for modelling lung development and diseases. Method: For the selection of literature cited, we used MEDLINE/Pubmed database. The keywords used in the MEDLINE research were: human lung development, lung organoids, lung stem cells, lung disease and repair, bioengineering lung. Results: Lung organoids, in layman's terms referred to as “mini lungs in a dish”, are 3D tissues that recapitulate the endogenous functions of the lungs. Lung organoids currently represent the closest model to the human pulmonary system. Human-derived three-dimensional (3D) models have been generated, allowing for a deeper understanding of cell-to-cell communication. They have also allowed researchers to better understand how diseases affect the lungs and determine potential treatment methods. Conclusions: Although the area of research using lung organoids is still relatively new, much has been learned from this model, and much more will continue to be learned. There is an urgent need to develop more complex organoid models containing mesenchymal tissues and vasculature to better understand lung diseases.KeywordsLungOrganoidStem cellRepair and regenerationLung diseases

The lung develops by epithelial tubes budding and branching into a flexible mesenchyme. This growth is associated with the remodelling of the epithelial basement membrane, of which laminin is a major component. Both the synthesis and expression of laminin were studied in the human lung between 10 and 31 weeks of gestation, using in situ hybridization and immunohistochemistry. The synthesis of the beta chain was active in the epithelial and surrounding mesenchymal cells. The mRNAs coding for the gamma chain were less abundant and mainly found in the epithelium. The synthesis of these two chains continued throughout gestation, and no significant difference in the density of hybridization grains could be detected between the tips of the expanding buds and the proximal portions. Immunohistochemical localization of laminin showed important modifications of the basement membrane during gestation. In the first part of the pseudoglandular stage the epithelial basement membrane stained continuously for laminin. Later, the basement membrane was labelled in a graded fashion: at the apex of the growing buds the staining became weak with focal disruptions. Both epithelial and mesenchymal synthesis of laminin remained active, while the polypeptide was undetectable using immunohistochemistry. These findings suggest that the remodelling of the basement membrane during human lung morphogenesis is probably not related to a decreasing synthesis of laminin, but to either a proteolytic degradation or the assembly of an inadequate complex undetectable with the polyclonal antibody antilaminin.

BackgroundDuring pseudoglandular stage of the human lung development the primitive bronchial buds are initially conformed by simple tubules lined by endoderm-derived epithelium surrounded by mesenchyme, which will progressively branch into airways and start to form distal epithelial saculles. For first time alveolar type II (AT2) pneumocytes appears. This study aims to characterize the genes and microRNAs involved in this differentiation process and decipher its role in the starting alveolar differentiation.MethodsGene and microRNA profiling was performed in human embryonic lungs from 7 to 12 post conception weeks (pcw). Protein expression location of candidate genes were analyzed by immunofluorescense in embryonic lung tissue sections. mRNA/miRNA target pairs were identified using computational approaches and their expression was studied in purified epithelial/mesenchymal cell populations and in isolated tips and stalks from the bronchial tree. Additionally, silencing experiments in human embryonic lung mesenchymal cells and in human embryonic tip-derived lung organoids were performed, as well as organoid differentiation studies. AT2 cell markers were studied by qRT-PCR and by immunofluorescence. The TGFB-β phosphorylated pathways was analyzed with membrane protein arrays. Lung explants were cultured in air/liquid interface with/without peptides.ResultsWe identified 88 differentially expressed genes, including IGFBP3. Although IGFBP3 mRNA was detected in both epithelial and mesenchymal populations, the protein was restricted to the epithelium, indicating post-transcriptional regulation preventing IGFBP3 protein expression in the mesenchyme. MicroRNA profiling identified miR-34a as an IGFBP3 regulator. miR-34a was up-regulated in mesenchymal cells, and its silencing in human embryonic lung mesenchymal cells increased IGFBP3 levels. Additionally, IGFBP3 expression showed a marked downregulation from 7 to 12 pcw, suggesting its involvement in the differentiation process. The differentiation of human tip-derived lung embryonic organoids showed a drastic reduction in IGFBP3, supported by the scRNAseq data. IGFBP3 silencing in organoids activated an alveolar-like differentiation process characterized by stem cell markers downregulation and upregulation of AT2 markers. This process was mediated by TGFβ signalling inhibition and BMP pathway activation.ConclusionsThe IGFBP3/miR-34a axis restricts IGFBP3 expression in the embryonic undifferentiated lung epithelium, and the progressive downregulation of IGFBP3 during the pseudoglandular stage is required for alveolar differentiation.Graphical abstract

The lung is formed from a bud that grows and divides in a dichotomous way. A bud is a new growth center which is determined by epithelial-mesenchymal interactions where proteins of the extracellular matrix (ECM) might be involved. To understand this protein participation during human lung development, we examined the expression and distribution of proteoglycans in relation to the different types of collagens during the period in which the air conducting system is installed. Using light microscopy and immunohistochemistry we evaluate the expression of collagens (I, III and VI) and proteoglycans (decorin, biglycan and lumican) between 8 to 10 weeks post fertilization and 11 to 14 weeks of gestational age of human embryo and fetus lungs. We show that decorin, lumican and all the collagen types investigated were expressed at the epithelium-mesenchymal interface, forming a sleeve around the bronchiolar ducts. In addition, biglycan was expressed in both the endothelial cells and the smooth muscle of the blood vessels. Thus, the similar distribution pattern of collagen and proteoglycans in the early developmental stages of the human lung may be closely related to the process of dichotomous division of the bronchial tree. This study provides a new insight concerning the participation of collagens and proteoglycans in the epithelial-mesenchymal interface during the period in which the air conducting system is installed in the human fetal lung.

Catalase, superoxide dismutase and glutathione peroxidase activities of lung and liver during human development

The complex interplay between cells and extracellular matrix (ECM) proteins is critical for lung development. Integrins are key modulators of this interaction. The integrin subunit alpha 8 associates with the beta(1)-subunit to form an RGD-binding integrin. We previously showed that, in adult lung, alpha 8 is expressed in contractile interstitial cells and smooth muscle cells and is upregulated in lung injury. To gain insight into the function of alpha 8 during lung development, we examined the spatiotemporal expression of alpha 8 throughout murine lung development. We compared the distribution of alpha 8 with alpha-smooth muscle actin (alpha SMA), fibronectin (alpha 8 ligand), and cytokeratin. alpha 8 co-localized with alpha SMA and fibronectin in the peribronchial and perivascular regions. In all stages, alpha 8 immunoreactivity was detected diffusely in the mesenchyme except for cells surrounding distal, newly forming airways. alpha 8, alpha SMA, and fibronectin co-localized at tips of secondary septae in the alveolar stage. We conclude that alpha 8 is marker for lung mesenchymal cells starting early in development. alpha 8 is also a marker for smooth muscle cells, expressed as early as alpha SMA. Co-localization of alpha 8 with fibronectin suggests a role in branching morphogenesis. Furthermore, alpha 8 may participate in secondary septation by modulating signals from the extracellular matrix to alveolar myofibroblasts.

Surfactant protein A (SP-A) is the most abundant of the surfactant-associated proteins. SP-A is involved in the formation of tubular myelin, the modulation of the surface tension-reducing properties of surfactant phospholipids, the metabolism of surfactant phospholipids, and local pulmonary host defense. We hypothesized that elimination of SP-A would alter the regulation of SP-B gene expression and the formation of tubular myelin. Midtrimester human fetal lung explants were cultured for 3-5 days in the presence or absence of an antisense 18-mer phosphorothioate oligonucleotide (ON) complementary to SP-A mRNA. After 3 days in culture, SP-A mRNA was undetectable in antisense ON-treated explants. After 5 days in culture, levels of SP-A protein were also decreased by antisense treatment. SP-B mRNA levels were not affected by the antisense SP-A ON treatment. However, there was decreased tubular myelin formation in the antisense SP-A ON-treated tissue. We conclude that selective elimination of SP-A mRNA and protein results in a decrease in tubular myelin formation in human fetal lung without affecting SP-B mRNA. We speculate that SP-A is critical to the formation of tubular myelin during human lung development and that the regulation of SP-B gene expression is independent of SP-A gene expression.

Organoids as a model system for studying human lung development and disease

Empowering human lung development.

The number and severity of diseases affecting human lung development and adult respiratory function has stimulated great interest in new in vitro models to study the human lung. This review summarizes the most recent breakthroughs deriving lung lineages in a dish by directing the differentiation of human pluripotent stem cells. A variety of culturing platforms have been developed, including two-dimensional and three-dimensional (organoid) culture platforms, to derive specific cell types and structures of the lung. These stem cell-derived lung models will further our understanding of human lung development, disease, and regeneration.

Human embryonic stem cell (hESC) derived 3D human lung organoids (HLOs) provide a promising model to study human lung development and disease. HLOs containing proximal or/and immature distal airway epithelial cells have been successfully generated in vitro, such as early staged alveolar type 2 (AT2) cells (SPC+/SOX9+) and immature alveolar type 1 (AT1) cells (HOPX+/SOX9+). When HLOs were transplanted into immunocompromised mice for further differentiation in vivo, only few distal epithelial cells could be observed. In this study, we transplanted different stages of HLOs into immunocompromised mice to assess whether HLOs could expand and mature in vivo. We found that short-term transplanted HLOs contained lung progenitor cells (NKX2.1+, SOX9+, and P63+), but not SPC+ AT2 cells or AQP5+ AT1 cells. Meanwhile, long-term engrafted HLOs could differentiate into lung distal bipotent progenitor cells (PDPN+/SPC+/SOX9+), AT2 cells (SPC+, SPB+), and immature AT1 cells (PDPN+, AQP5-). However, HLOs at late in vitro stage turned into mature AT1-like cells (AQP5+/SPB-/SOX9-) in vivo. Immunofluorescence staining and transmission electron microscopy (TEM) results revealed that transplanted HLOs contained mesenchymal cells (collagen I+), vasculature (ACTA2+), neuroendocrine-like cells (PGP9.5+), and nerve fiber structures (myelin sheath structure). Together, these data reveal that hESC-derived HLOs would be useful for human lung development modeling, and transplanted HLOs could mimic lung organ-like structures in vivo by possessing vascular network and neuronal network.