Hepatocyte Growth Factor Protects Pulmonary Endothelial Barrier Against Oxidative Stress and Mitochondria-Dependent Apoptosis
Acute respiratory distress syndrome (ARDS) is a severe condition characterized by high mortality and dyspnea, often resulting from damage to the pulmonary microvascular endothelial cells (PMVECs) and the destruction of the endothelial barrier. Previous research has highlighted the protective role of hepatocyte growth factor (HGF), secreted by bone marrow mesenchymal stem cells, in reducing endothelial apoptosis. This study delves into the mechanisms by which HGF exerts its protective effects against oxidative stress and mitochondria-dependent apoptosis in lipopolysaccharide (LPS)-induced endothelial barrier dysfunction and ARDS.
The study begins by establishing the context of ARDS and the critical role of PMVECs in its pathogenesis. It then introduces HGF as a potential therapeutic agent, given its known effects on endothelial apoptosis. The primary focus is to investigate whether the mammalian target of rapamycin (mTOR) and signal transducer and activator of transcription 3 (STAT3) signaling pathways are involved in the protective effects of HGF against oxidative stress and mitochondria-dependent apoptosis.
To explore this, the researchers employed LPS-induced PMVECs treated with HGF. They used specific inhibitors, rapamycin for mTOR and S3I-201 for STAT3, to inhibit these signaling pathways. Additionally, lentivirus vector-mediated knockdown of mTORC1 (Raptor) and mTORC2 (Rictor) genes was performed to evaluate the roles of these complexes in the protective effects of HGF. Various assays were conducted to measure calcium levels, reactive oxygen species (ROS) production, mitochondrial membrane potential, cell proliferation, apoptosis, and endothelial junction proteins.
The results demonstrated that HGF significantly protects the endothelium by suppressing ROS production and intracellular calcium uptake. This leads to increased mitochondrial membrane potential, elevated levels of specific mitochondrial proteins (such as complex I), and increased anti-apoptotic mRNA levels (B-cell lymphoma 2 and Bcl-xL). Furthermore, HGF treatment enhanced the expression of endothelial junction proteins (VE-cadherin and occludin), which are crucial for maintaining endothelial barrier integrity.
Interestingly, the study found that inhibition of mTOR with rapamycin and STAT3 with S3I-201 reversed the protective effects of HGF, leading to increased oxidative stress and mitochondria-dependent apoptosis even in the presence of HGF. This suggests that both mTOR and STAT3 pathways are integral to the protective mechanisms of HGF. The knockdown experiments further confirmed that both mTORC1 and mTORC2 complexes play significant roles in protecting against mitochondrial damage and apoptosis.
In vivo experiments using an ALI mouse model corroborated these findings. HGF treatment increased mitochondrial structural integrity in the pulmonary endothelium, and this effect was mediated through the mTOR/STAT3 pathway. Electron microscopy observations revealed that inhibition of mTOR and STAT3 signaling resulted in increased mitochondrial damage in the ALI model.
The discussion section of the study provides a comprehensive analysis of the findings. It highlights the importance of calcium homeostasis and ROS production in mitochondrial function and endothelial cell survival. The study underscores the role of mTOR and STAT3 signaling in maintaining mitochondrial integrity and preventing apoptosis. It also discusses the implications of these findings for the treatment of ARDS and other conditions characterized by endothelial barrier dysfunction.
In conclusion, the study reveals that HGF protects the pulmonary endothelial barrier against oxidative stress and mitochondria-dependent apoptosis through the mTOR/STAT3 signaling pathway. This protective effect is achieved by suppressing ROS production and intracellular calcium uptake, enhancing mitochondrial membrane potential, and increasing the expression of anti-apoptotic proteins and endothelial junction proteins. These findings provide valuable insights into the therapeutic potential of HGF in treating ARDS and other conditions involving endothelial barrier dysfunction.
doi.org/10.1097/CM9.0000000000001916
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