Pulmonary endogenous progenitor stem cell subpopulation: Physiology, pathogenesis, and progress.

Lungs are structurally and functionally complex organs consisting of diverse cell types from the proximal to distal axis. They have direct contact with the external environment and are constantly at risk of various injuries. Capable to proliferate and differentiate, pulmonary endogenous progenitor stem cells contribute to the maintenance of lung structure and function both under homeostasis and following injuries. Discovering candidate pulmonary endogenous progenitor stem cell types and underlying regenerative mechanisms provide insights into therapeutic strategy development for lung diseases. In this review, we reveal their compositions, roles in lung disease pathogenesis and injury repair, and the underlying mechanisms. We further underline the advanced progress in research approach and potential therapy for lung regeneration. We also demonstrate the feasibility and prospects of pulmonary endogenous stem cell transplantation for lung disease treatment.

SOX9 maintains human foetal lung tip progenitor state by enhancing WNT and RTK signalling.

The balance between self-renewal and differentiation in human foetal lung epithelial progenitors controls the size and function of the adult organ. Moreover, progenitor cell gene regulation networks are employed by both regenerating and malignant lung cells, where modulators of their effects could potentially be of therapeutic value. Details of the molecular networks controlling human lung progenitor self-renewal remain unknown. We performed the first CRISPRi screen in primary human lung organoids to identify transcription factors controlling progenitor self-renewal. We show that SOX9 promotes proliferation of lung progenitors and inhibits precocious airway differentiation. Moreover, by identifying direct transcriptional targets using Targeted DamID, we place SOX9 at the centre of a transcriptional network, which amplifies WNT and RTK signalling to stabilise the progenitor cell state. In addition, the proof-of-principle CRISPRi screen and Targeted DamID tools establish a new workflow for using primary human organoids to elucidate detailed functional mechanisms underlying normal development and disease.

Pathogenesis of ventilator-induced lung injury: metabolomics analysis of the lung and plasma.

INTRODUCTION: Nowadays,the mechanical ventilation (MV) aims to rest the respiratory muscles while providing adequate gas exchange, and it has been a part of basic life support during general anesthesia as well as in critically ill patients with and without respiratory failure. However, MV itself has the potential to cause or worsen lung injury, which is also known as ventilator-induced lung injury (VILI). Thus, the early diagnosis of VILI is of great importance for the prevention and treatment of VILI. OBJECTIVE: This study aimed to investigate the metabolomes in the lung and plasma of mice receiving mechanical ventilation (MV). METHODS: Healthy mice were randomly assigned into control group; (2) high volume tidal (HV) group (30 ml/kg); (3) low volume tidal (LV) group (6 ml/kg). After ventilation for 4 h, mice were sacrificed and the lung tissue and plasma were collected. The lung and plasma were processed for the metabolomics analysis. We also performed histopathological examination on the lung tissue. RESULTS: We detected moderate inflammatory damage with alveolar septal thickening in the HV group compared with the normal and LV groups.The metabolomics analysis results showed MV altered the metabolism which was characterized by the dysregulation of γ-amino butyric acid (GABA) system and urea cycle (desregulations in plasma and lung guanidinosuccinic acid, argininosuccinic acid, succinic acid semialdehyde and lung GABA ), Disturbance of citric acid cycle (CAC) (increased plasma glutamine and lung phosphoenol pyruvate) and redox imbalance (desregulations in plasma and/or lung ascorbic acid, chenodeoxycholic acid, uric acid, oleic acid, stearidonic acid, palmitoleic acid and docosahexaenoic acid). Moreover, the lung and plasma metabolomes were also significantly different between LV and HV groups. CONCLUSIONS: Some lung and plasma metabolites related to the GABA system and urea cycle, citric acid cycle and redox balance were significantly altered, and they may be employed for the evaluation of VILI and serve as targets in the treatment of VILI.

[Establishment of a three-dimensional organoid culture system for mouse type 2 alveolar epithelial cells].

The purpose of this study was to establish a three-dimensional (3D) organoid culture system for type 2 alveolar epithelial (AT2) cells in mice. AT2 cells were isolated from ICR mouse lung and purified by enzymatic digestion and MicroBeads sorting. The purity of AT2 cells was determined by immunofluorescence (IF) staining using an antibody against proSPC. The AT2 differentiation was examined by IF staining with proSPC/HopX and proSPC/T1α antibodies, and proliferation of AT2 cells was assessed by EdU incorporation assays after two-dimensional (2D) culture for 8 days. In addition, AT2 cells were co-cultured with mouse lung fibroblasts (Mlg) in three-dimensional (3D) culture system. After 13 days of co-culture, the organoids were fixed in 2% paraformaldehyde for histological analysis and IF staining. The results showed that the purity of the AT2 cells was over 95%, as assessed by proSPC staining. 2D cultured AT2 cells were negative for EdU staining, which indicates that no proliferation occurs. proSPC expression was gradually disappeared, whereas T1α and HopX expression was gradually increased after 3, 5 and 8 days of culture. In 3D culture system, the alveolar organoids were formed after co-culturing AT2 cells with Mlg for 4 days. Histological analysis showed that alveolar organoids displayed a hollow morphology. proSPC was highly expressed in the peripheral cells, whereas type 1 alveolar epithelial (AT1) cells transdifferentiated from AT2 cells expressing HopX were mainly located in the interior of organoid bodies after 13 days. Some of the proSPC-positive AT2 cells located in the outer circle of alveolar organoids were stained positive for both proSPC and EdU, indicating that the AT2 cells in the alveolar organoids were proliferative. These results showed that the 3D organoid culture system of mouse AT2 cells was successfully established.

Upregulation of Matrix Metalloproteinase-9 Protects against Sepsis-Induced Acute Lung Injury via Promoting the Release of Soluble Receptor for Advanced Glycation End Products.

Dysregulation of matrix metalloproteinase- (MMP-) 9 is implicated in the pathogenesis of acute lung injury (ALI). However, it remains controversial whether MMP-9 improves or deteriorates acute lung injury of different etiologies. The receptor for advanced glycation end products (RAGE) plays a critical role in the pathogenesis of acute lung injury. MMPs are known to mediate RAGE shedding and release of soluble RAGE (sRAGE), which can act as a decoy receptor by competitively inhibiting the binding of RAGE ligands to RAGE. Therefore, this study is aimed at clarifying whether and how pulmonary knockdown of MMP-9 affected sepsis-induced acute lung injury as well as the release of sRAGE in a murine cecal ligation and puncture (CLP) model. The analysis of GEO mouse sepsis datasets GSE15379, GSE52474, and GSE60088 revealed that the mRNA expression of MMP-9 was significantly upregulated in septic mouse lung tissues. Elevation of pulmonary MMP-9 mRNA and protein expressions was confirmed in CLP-induced mouse sepsis model. Intratracheal injection of MMP-9 siRNA resulted in an approximately 60% decrease in pulmonary MMP-9 expression. It was found that pulmonary knockdown of MMP-9 significantly increased mortality of sepsis and exacerbated sepsis-associated acute lung injury. Pulmonary MMP-9 knockdown also decreased sRAGE release and enhanced sepsis-induced activation of the RAGE/nuclear factor-κB (NF-κB) signaling pathway, meanwhile aggravating sepsis-induced oxidative stress and inflammation in lung tissues. In addition, administration of recombinant sRAGE protein suppressed the activation of the RAGE/NF-κB signaling pathway and ameliorated pulmonary oxidative stress, inflammation, and lung injury in CLP-induced septic mice. In conclusion, our data indicate that MMP-9-mediated RAGE shedding limits the severity of sepsis-associated pulmonary edema, inflammation, oxidative stress, and lung injury by suppressing the RAGE/NF-κB signaling pathway via the decoy receptor activities of sRAGE. MMP-9-mediated sRAGE production may serve as a self-limiting mechanism to control and resolve excessive inflammation and oxidative stress in the lung during sepsis.

Elevated angiotensin II induces platelet apoptosis through promoting oxidative stress in an AT1R-dependent manner during sepsis.

Thrombocytopenia is independently related with increased mortality in severe septic patients. Renin-angiotensin system (RAS) is elevated in septic subjects; accumulating studies show that angiotensin II (Ang II) stimulate the intrinsic apoptosis pathway by promoting reactive oxygen species (ROS) production. However, the mechanisms underlying the relationship of platelet apoptosis and RAS system in sepsis have not been fully elucidated. The present study aimed to elucidate whether the RAS was involved in the pathogenesis of sepsis-associated thrombocytopenia and explore the underlying mechanisms. We found that elevated plasma Ang II was associated with decreased platelet count in both patients with sepsis and experimental animals exposed to lipopolysaccharide (LPS). Besides, Ang II treatment induced platelet apoptosis in a concentration-dependent manner in primary isolated platelets, which was blocked by angiotensin II type 1 receptor (AT1R) antagonist losartan, but not by angiotensin II type 2 receptor (AT2R) antagonist PD123319. Moreover, inhibiting AT1R by losartan attenuated LPS-induced platelet apoptosis and alleviated sepsis-associated thrombocytopenia. Furthermore, Ang II treatment induced oxidative stress level in a concentration-dependent manner in primary isolated platelets, which was partially reversed by the AT1R antagonist losartan. The present study demonstrated that elevated Ang II directly stimulated platelet apoptosis through promoting oxidative stress in an AT1R-dependent manner in sepsis-associated thrombocytopenia. The results would helpful for understanding the role of RAS system in sepsis-associated thrombocytopenia.

DRD1 downregulation contributes to mechanical stretch-induced lung endothelial barrier dysfunction.

Rationale: The lung-protective effects of dopamine and its role in the pathology of ventilator-induced lung injury (VILI) are emerging. However, the underlying mechanisms are still largely unknown. Objective: To investigate the contribution of dopamine receptor dysregulation in the pathogenesis of VILI and therapeutic potential of dopamine D1 receptor (DRD1) agonist in VILI. Methods: The role of dopamine receptors in mechanical stretch-induced endothelial barrier dysfunction and lung injury was studied in DRD1 knockout mice, in isolated mouse lung vascular endothelial cells (MLVECs), and in lung samples from patients who underwent pulmonary lobectomy with mechanical ventilation for different time periods. Measurements and Main Results: DRD1 was downregulated in both surgical patients and mice exposed to mechanical ventilation. Prophylactic administration of dopamine or DRD1 agonist attenuated mechanical stretch-induced lung endothelial barrier dysfunction and lung injury. By contrast, pulmonary knockdown or global knockout of DRD1 exacerbated these effects. Prophylactic administration of dopamine attenuated mechanical stretch-induced α-tubulin deacetylation and subsequent endothelial hyperpermeability through DRD1 signaling. We identified that cyclic stretch-induced glycogen-synthase-kinase-3ß activation led to phosphorylation and activation of histone deacetylase 6 (HDAC6), which resulted in deacetylation of α-tubulin. Upon activation, DRD1 signaling attenuated mechanical stretch-induced α-tubulin deacetylation and subsequent lung endothelial barrier dysfunction through cAMP/exchange protein activated by cAMP (EPAC)-mediated inactivation of HDAC6. Conclusions: This work identifies a novel protective role for DRD1 against mechanical stretch-induced lung endothelial barrier dysfunction and lung injury. Further study of the mechanisms involving DRD1 in the regulation of microtubule stability and interference with DRD1/cAMP/EPAC/HDAC6 signaling may provide insight into therapeutic approaches for VILI.

Downregulation of R-Spondin1 Contributes to Mechanical Stretch-Induced Lung Injury.

OBJECTIVES: The R-spondin family attenuates tissue damage via tightening endothelium and preventing vascular leakage. This study aims to investigate whether R-spondins protect against mechanical stretch-induced endothelial dysfunction and lung injury and to reveal the underlying mechanisms. DESIGN: Randomized controlled study. SETTING: University research laboratory. SUBJECTS: Patients scheduled to undergo surgery with mechanical ventilation support. Adult male Institute of Cancer Research mice. Primary cultured mouse lung vascular endothelial cells. INTERVENTIONS: Patients underwent a surgical procedure with mechanical ventilation support of 3 hours or more. Mice were subjected to mechanical ventilation (6 or 30 mL/kg) for 0.5-4 hours. Another group of mice were intraperitoneally injected with 1 mg/kg lipopolysaccharide, and 12 hours later subjected to mechanical ventilation (10 mL/kg) for 4 hours. Mouse lung vascular endothelial cells were subjected to cyclic stretch for 4 hours. MEASUREMENTS AND MAIN RESULTS: R-spondin1 were downregulated in both surgical patients and experimental animals exposed to mechanical ventilation. Intratracheal instillation of R-spondin1 attenuated, whereas knockdown of pulmonary R-spondin1 exacerbated ventilator-induced lung injury and mechanical stretch-induced lung vascular endothelial cell apoptosis. The antiapoptotic effect of R-spondin1 was mediated through the leucine-rich repeat containing G-protein coupled receptor 5 in cyclic stretched mouse lung vascular endothelial cells. We identified apoptosis-stimulating protein of p53 2 as the intracellular signaling protein interacted with leucine-rich repeat containing G-protein coupled receptor 5. R-spondin1 treatment decreased the interaction of apoptosis-stimulating protein of p53 2 with p53 while increased the binding of apoptosis-stimulating protein of p53 2 to leucine-rich repeat containing G-protein coupled receptor 5, therefore resulting in inactivation of p53-mediated proapoptotic pathway in cyclic stretched mouse lung vascular endothelial cells. CONCLUSIONS: Mechanical ventilation leads to down-regulation of R-spondin1. R-spondin1 may enhance the interaction of leucine-rich repeat containing G-protein coupled receptor 5 and apoptosis-stimulating protein of p53 2, thus inactivating p53-mediated proapoptotic pathway in cyclic stretched mouse lung vascular endothelial cells. R-spondin1 may have clinical benefit in alleviating mechanical ventilator-induced lung injury.

Salidroside Attenuates Ventilation Induced Lung Injury via SIRT1-Dependent Inhibition of NLRP3 Inflammasome.

BACKGROUND: Salidroside (SDS) is the main effective ingredient of Rhodiola rosea L with a variety of pharmacologic properties. We aim to investigate the effects of SDS on ventilation induced lung injury (VILI) and explore the possible underlying molecular mechanism. METHODS: Lung injury was induced in male ICR mice via mechanical ventilation (30 ml/kg) for 4h. The mice were divided in four groups:(1) Control group; (2) Ventilation group; (3) SDS group; (4) Ventilation with SDS group. SDS (50 mg/kg) was injected intraperitoneally 1h before operation. Mouse lung vascular endothelial cells (MLVECs) were subjected to cyclic stretch for 4h. RESULTS: It was found that SDS attenuated VILI as shown in HE staining, cell count and protein content levels in BAL fluid, W/D and Evans blue dye leakage into the lung tissue. SDS treatment inhibited the activation of NLRP3 inflammasome and subsequent caspase-1 cleavage as well as interleukin (IL)-1ß secretion both in vivo and in vitro. Moreover, SDS administration up-regulated SIRT1 expression. Importantly, knockdown of SIRT1 reversed the inhibitory effect of SDS on NLRP3 inflammasome activation. CONCLUSIONS: Taken together, these findings indicate that SDS may confer protection against ventilation induced lung injury via SIRT1-de-pendent inhibition of NLRP3 inflammasome activation.