Endothelial RSPO3 mediates pulmonary endothelial regeneration by LGR4-dependent activation of ß-catenin and ILK signaling pathways after inflammatory vascular injury.

Endothelial repair is essential for restoring tissue fluid homeostasis following lung injury. R-spondin3 (RSPO3), a secreted protein mainly produced by endothelial cells (ECs), has shown its protective effect on endothelium. However, the specific mechanisms remain unknown. To explore whether and how RSPO3 regulates endothelial regeneration after inflammatory vascular injury, the role of RSPO3 in sepsis-induced pulmonary endothelial injury was investigated in EC-specific RSPO3 knockdown, inducible EC-specific RSPO3 deletion mice, EC-specific RSPO3 overexpression mice, systemic RSPO3-administration mice, in isolated mouse lung vascular endothelial cells (MLVECs), and in plasma from septic patients. Here we show that plasma RSPO3 levels are decreased in septic patients and correlated with endothelial injury markers and PaO2/FiO2 index. Both pulmonary EC-specific knockdown of RSPO3 and inducible EC-specific RSPO3 deletion inhibit pulmonary ECs proliferation and exacerbate ECs injury, whereas intra-pulmonary EC-specific RSPO3 overexpression promotes endothelial recovery and attenuates ECs injury during endotoxemia. We show that RSPO3 mediates pulmonary endothelial regeneration by a LGR4-dependent manner. Except for ß-catenin, integrin-linked kinase (ILK)/Akt is also identified as a novel downstream effector of RSPO3/LGR4 signaling. These results conclude that EC-derived RSPO3 mediates pulmonary endothelial regeneration by LGR4-dependent activation of ß-catenin and ILK signaling pathways after inflammatory vascular injury.

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.

Upregulation of sphingosine kinase 1 contributes to ventilator-associated lung injury in a two-hit model.

Ventilator­associated lung injury (VALI) remains a significant medical problem in intensive care units. The present study aimed to investigate the role of sphingosine kinase 1 (SPHK1) in VALI using a two­hit model and explore the potential underlying molecular mechanism. Mice were divided into five groups: i) Non­ventilated group; ii) non­ventilated + lipopolysaccharide (LPS) group; iii) ventilated group; iv) ventilated + LPS group; and v) ventilated + LPS + SPHK1 inhibitor group. Mice were administered LPS (1 mg/kg) via an intraperitoneal injection. After 12 h, the mice were anesthetized and connected to a ventilator (10 ml/kg at 150 breaths/min) for 4 h. SPHK1 inhibitor (50 mg/kg) was injected intraperitoneally 1 h prior to ventilation. Mouse lung vascular endothelial cells were treated with LPS and SPHK1 inhibitor, and then subjected to cyclic stretch for 4 h. The present results suggested that the expression of SPHK1 and sphingosine 1 phosphate was upregulated in the two­hit model of VALI; SPHK1 inhibitor could attenuate VALI in the two­hit model as observed by hematoxylin and eosin staining, and affected the cell count and the protein content levels in the bronchoalveolar lavage fluid. In addition, treatment with SPHK1 inhibitor reduced the wet­to­dry ratio of the lungs and suppressed Evans blue dye leakage into the lung tissue. Furthermore, SPHK1 inhibitor exhibited protective effects on the two­hit model of VALI by inhibiting the Ras homolog family member a­mediated phosphorylation of myosin phosphatase target subunit 1 (MYPT­1) and endothelial hyperpermeability. Additionally, mice were divided into five additional groups: i) Non­ventilated group; ii) non­ventilated + LPS group; iii) ventilated group; iv) ventilated + LPS group; and v) ventilated + LPS + Rho­associated coiled­coil forming protein kinase (ROCK)1 inhibitor group. ROCK1 inhibitor (10 mg/kg) was injected intraperitoneally 1 h prior to ventilation. The present results suggested that ROCK1 inhibitor could attenuate mechanical stretch­induced lung endothelial injury and the phosphorylation of MYPT­1 in vivo and in vitro. Collectively, the present findings indicated that upregulation of SPHK1 may contribute to VALI in a two­hit model.

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.