Wnt5a reverses the inhibitory effect of hyperoxia on transdifferentiation of alveolar epithelial type II cells to type I cells

Transformation of macrophages into myofibroblasts in fibrosis-related diseases: emerging biological concepts and potential mechanism

Macrophage-myofibroblast transformation (MMT) transforms macrophages into myofibroblasts in a specific inflammation or injury microenvironment. MMT is an essential biological process in fibrosis-related diseases involving the lung, heart, kidney, liver, skeletal muscle, and other organs and tissues. This process consists of interacting with various cells and molecules and activating different signal transduction pathways. This review deeply discussed the molecular mechanism of MMT, clarified crucial signal pathways, multiple cytokines, and growth factors, and formed a complex regulatory network. Significantly, the critical role of transforming growth factor-β (TGF-β) and its downstream signaling pathways in this process were clarified. Furthermore, we discussed the significance of MMT in physiological and pathological conditions, such as pulmonary fibrosis and cardiac fibrosis. This review provides a new perspective for understanding the interaction between macrophages and myofibroblasts and new strategies and targets for the prevention and treatment of MMT in fibrotic diseases.

Pulmonary Fibrosis as a Result of Acute Lung Inflammation: Molecular Mechanisms, Relevant In Vivo Models, Prognostic and Therapeutic Approaches

Pulmonary fibrosis is a chronic progressive lung disease that steadily leads to lung architecture disruption and respiratory failure. The development of pulmonary fibrosis is mostly the result of previous acute lung inflammation, caused by a wide variety of etiological factors, not resolved over time and causing the deposition of fibrotic tissue in the lungs. Despite a long history of study and good coverage of the problem in the scientific literature, the effective therapeutic approaches for pulmonary fibrosis treatment are currently lacking. Thus, the study of the molecular mechanisms underlying the transition from acute lung inflammation to pulmonary fibrosis, and the search for new molecular markers and promising therapeutic targets to prevent pulmonary fibrosis development, remain highly relevant tasks. This review focuses on the etiology, pathogenesis, morphological characteristics and outcomes of acute lung inflammation as a precursor of pulmonary fibrosis; the pathomorphological changes in the lungs during fibrosis development; the known molecular mechanisms and key players of the signaling pathways mediating acute lung inflammation and pulmonary fibrosis, as well as the characteristics of the most common in vivo models of these processes. Moreover, the prognostic markers of acute lung injury severity and pulmonary fibrosis development as well as approved and potential therapeutic approaches suppressing the transition from acute lung inflammation to fibrosis are discussed.

Mesenchymal stem cell-derived extracellular vesicles suppress hyperoxia-induced transdifferentiation of rat alveolar type 2 epithelial cells

Bronchopulmonary dysplasia (BPD) remains the most important respiratory morbidity of preterm infants with few effective preventive strategies. Administration of mesenchymal stem cells (MSC) was considered effective to prevent BPD via paracrine extracellular vesicles (EVs), while appropriate regimens of MSC-EVs and the mechanism remain unclear. Therefore, we established a hyperoxia-induced rat BPD model, and examined the effect of early intraperitoneal MSC-EVs with different doses on BPD. We found that MSC-EVs ameliorated hyperoxia-induced lung injury in a dose-dependent manner, and high dose MSC-EVs ameliorated alveolar simplification and fibrosis. Also, MSC-EVs showed its beneficial effects on vascular growth and pulmonary hypertension. Primary AT2 cells were observed to transdifferentiate into AT1 cells when exposure to hyperoxia in vitro. Administration of MSC-EVs at the first-day culture significantly delayed the transdifferentiation of AT2 cells induced by hyperoxia. We further found that exposure to hyperoxia led to elevated expression of WNT5a mRNA and protein, a key agent in AT2 transdifferentiation, while MSC-EVs administration decreased it. Further study is warranted that MSC-EVs may delay the transdifferentiation of AT2 cells via WNT5a. These studies provide key preclinical evidence of MSC-EVs therapeutics on BPD and highlight the effect of MSC-EVs on suppressing the transdifferentiation of AT2 cells and its possible mechanism through downregulation of WNT5a.

WNT5a-ROR Signaling Is Essential for Alveologenesis

WNT5a is a mainly “non-canonical” WNT ligand whose dysregulation is observed in lung diseases such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD) and asthma. Germline deletion of Wnt5a disrupts embryonic lung development. However, the temporal-specific function of WNT5a remains unknown. In this study, we generated a conditional loss-of-function mouse model (Wnt5a^CAG) and examined the specific role of Wnt5a during the saccular and alveolar phases of lung development. The lack of Wnt5a in the saccular phase blocked distal airway expansion and attenuated differentiation of endothelial and alveolar epithelial type I (AT1) cells and myofibroblasts. Postnatal Wnt5a inactivation disrupted alveologenesis, producing a phenotype resembling human bronchopulmonary dysplasia (BPD). Mutant lungs showed hypoalveolization, but endothelial and epithelial differentiation was unaffected. The major impact of Wnt5a inactivation on alveologenesis was on myofibroblast differentiation and migration, with reduced expression of key regulatory genes. These findings were validated in vitro using isolated lung fibroblasts. Conditional inactivation of the WNT5a receptors Ror1 and Ror2 in alveolar myofibroblasts recapitulated the Wnt5a^CAG phenotype, demonstrating that myofibroblast defects are the major cause of arrested alveologenesis in Wnt5a^CAG lungs. Finally, we show that WNT5a is reduced in human BPD lung samples, indicating the clinical relevance and potential role for WNT5a in pathogenesis of BPD.

Developmental pathways in the pathogenesis of lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and terminal lung disease with no known cure. IPF is a disease of aging, with median age of diagnosis over 65 years. Median survival is between 3 and 5 years after diagnosis. IPF is characterized primarily by excessive deposition of extracellular matrix (ECM) proteins by activated lung fibroblasts and myofibroblasts, resulting in reduced gas exchange and impaired pulmonary function. Growing evidence supports the concept of a pro-fibrotic environment orchestrated by underlying factors such as genetic predisposition, chronic injury and aging, oxidative stress, and impaired regenerative responses may account for disease development and persistence. Currently, two FDA approved drugs have limited efficacy in the treatment of IPF. Many of the genes and gene networks associated with lung development are induced or activated in IPF. In this review, we analyze current knowledge in the field, gained from both basic and clinical research, to provide new insights into the disease process, and potential approaches to treatment of pulmonary fibrosis.

SOX4 arrests lung development in rats with hyperoxia‑induced bronchopulmonary dysplasia by controlling EZH2 expression

Bronchopulmonary dysplasia (BPD) is currently the most common severe complication in premature infants and is characterized by the arrest of alveolar and vascular growth. Alveolar type II cells play an important role in the pathological foundation of BPD. An association of BPD with epithelial‑to‑mesenchymal transition (EMT) in type II cells exposed to hyperoxia was previously identified. SOX4, a transcription factor that is indispensable to embryogenesis, including lung development, participates in regulating EMT and cell survival, affecting tumorigenesis. The aim of the present study was to investigate the involvement of SOX4 in the occurrence of BPD, which, to the best of our knowledge, has not been previously determined. For this purpose, newborn rats were randomly divided into two treatment groups: The model group was exposed to hyperoxia (80-85% O2), while the control group was kept under normoxic conditions (21% O2). Lung tissues were collected on postnatal days 1, 3, 7, 14 and 21 and morphological changes in the lungs were examined by hematoxylin and eosin staining. The location of SOX4 in type II cells was detected by double immunofluorescence. The expression of SOX4 and enhancer of zeste homolog 2 (EZH2) in type II cells and lung tissues were detected by immunochemistry, western blotting and quantitative polymerase chain reaction analysis. The results demonstrated that, compared with the control group, the radial alveolar count decreased rapidly in the model group, accompanied by increased mean alveolar diameter and alveolar septal thickness. SOX4 and EZH2 were highly expressed in type II cells exposed to hyperoxia. However, in total lung tissues, SOX4 and EZH2 expression was profoundly decreased in the early stages and increased in the late stages following exposure to hyperoxia. The expression of the EZH2 protein was positively correlated with that of the SOX4 protein. In conclusion, at the alveolar stage, which is a critical period after birth for lung development, hyperoxia induced dysregulation of SOX4 and EZH2 in rat lungs, indicating that SOX4 may contribute to the disruption of lung development in BPD by regulating EZH2 expression.