SARS-CoV-2 Spike triggers barrier dysfunction and vascular leak via integrins and TGF-β signaling

Severe COVID-19 is associated with epithelial and endothelial barrier dysfunction within the lung as well as in distal organs. While it is appreciated that an exaggerated inflammatory response is associated with barrier dysfunction, the triggers of this pathology are unclear. Here, we report that cell-intrinsic interactions between the Spike (S) glycoprotein of SARS-CoV-2 and epithelial/endothelial cells are sufficient to trigger barrier dysfunction in vitro and vascular leak in vivo, independently of viral replication and the ACE2 receptor. We identify an S-triggered transcriptional response associated with extracellular matrix reorganization and TGF-β signaling. Using genetic knockouts and specific inhibitors, we demonstrate that glycosaminoglycans, integrins, and the TGF-β signaling axis are required for S-mediated barrier dysfunction. Our findings suggest that S interactions with barrier cells are a contributing factor to COVID-19 disease severity and offer mechanistic insight into SARS-CoV-2 triggered vascular leak, providing a starting point for development of therapies targeting COVID-19 pathogenesis.

mTORC2 Activation Mediated by Mesenchymal Stem Cell-Secreted Hepatocyte Growth Factors for the Recovery of Lipopolysaccharide-Induced Vascular Endothelial Barrier

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is characterized by pulmonary microvascular endothelial barrier dysfunction. Mesenchymal stem cell-secreted hepatocyte growth factor (HGF) has positive effects of lipopolysaccharide- (LPS-) induced pulmonary endothelial barrier. Studies have exhibited the mammalian TORC1 (mTORC1) signaling is of potent angiogenesis effects. The mTOR protein kinase has two distinct multiprotein complexes mTORC1 and mTORC2 that regulate different branches of the mTOR network. However, detailed mTORC2 mechanisms of HGF protective effects remain poorly defined. Therefore, the aim of this study was to determine whether mTORC2 mediated protective effects of MSC-secreted HGF against LPS-induced pulmonary microvascular endothelial barrier dysfunction activated like mTORC1 activation. We introduced MSC-PMVEC coculture transwell system and recombinant murine HGF on LPS-induced endothelial cell barrier dysfunction in vitro and then explored potential mechanisms by lentivirus vector-mediated HGF, mTORC1 (raptor), and mTORC2 (rictor) gene knockdown modification. Endothelial paracellular and transcellular permeability, adherent junction protein (VE-Cadherin), cell proliferation, apoptosis, and mTOR-associated proteins were tested. These revealed that HGF could promote quick reestablishment of adherent junction VE-cadherin and decrease endothelial paracellular and transcellular permeability during LSP-induced endothelial dysfunction with the involvement of mTORC2 (rictor) and mTORC1 (raptor) pathways. Raptor and rictor knockdown in LPS-induced PMEVECs with stimulation of HGF increased apoptosis ratio, activated Cleaved-Caspase-3 expression, and downregulated cell proliferation. Moreover, mTORC2/Akt but not mTORC2/PKC had significance on HGF endothelial protective effects. Taken together, these highlight activation mTORC2 pathway could also contribute to vascular endothelial barrier recovery by MSC-secreted HGF in LPS stimulation.

Roles of VE-Cadherin in Hypoxia Induced Injury of Pulmonary Microvascular Endothelial Barrier

Background: Hypoxia induced injury of pulmonary microvascular endothelial barrier is closely related to the pathogenesis of acute lung injury after lung transplantation. VE-cadherin is an important structural molecule for pulmonary microvascular endothelial barrier. In this study, we aim to investigate the roles of VE-cadherin in hypoxia induced injury of pulmonary microvascular endothelial barrier. Methods: Rat model of hypoxia and cultured pulmonary microvascular endothelial cells (PMVECs) were utilized. Determination of PMVECs apoptosis, skeleton combination was conducted to verify the effects of hypoxia on injury of pulmonary microvascular endothelial barrier. In addition, VE-cadherin expression was modulated by administration of siRNA in order to investigate the roles of VE-cadherin in hypoxia induced PMVECs apoptosis and skeleton recombination. Results: Our data indicated that expression of VE-cadherin was down-regulated in hypoxia-exposed PMVECs. Whereas, in the cells treated using siRNA, down-regulation of VE-cadherin did not trigger PMVECs apoptosis, but it increased the sensitivity of PMVECs to the hypoxia induced apoptosis. In cases of hypoxia, the expression of VE-cadherin was significantly down-regulated, together with endothelial skeleton recombination and increase of permeability, which then triggered endothelial barrier dysfunction. Conclusions: These data verify that VE-cadherin expression played an important role in hypoxia induced PMVECs apoptosis and cellular skeletal recombination.

Salidroside Ameliorated Intermittent Hypoxia-Aggravated Endothelial Barrier Disruption and Atherosclerosis via the cAMP/PKA/RhoA Signaling Pathway

Background: Endothelial barrier dysfunction plays a key role in atherosclerosis progression. The primary pathology of obstructive sleep apnea-hypopnea syndrome is chronic intermittent hypoxia (IH), which induces reactive oxygen species (ROS) overproduction, endothelial barrier injury, and atherosclerosis. Salidroside, a typical pharmacological constituent of Rhodiola genus, has documented antioxidative, and cardiovascular protective effects. However, whether salidroside can improve IH-aggravated endothelial barrier dysfunction and atherosclerosis has not been elucidated.Methods and results: In normal chow diet-fed ApoE−/− mice, salidroside (100 mg/kg/d, p. o.) significantly ameliorated the formation of atherosclerotic lesions and barrier injury aggravated by 7-weeks IH (21%–5%–21%, 120 s/cycle). In human umbilical vein endothelial cells (HUVECs), exposure to IH (21%–5%–21%, 40 min/cycle, 72 cycles) decreased transendothelial electrical resistance and protein expression of vascular endothelial cadherin (VE-cadherin) and zonula occludens 1. In addition, IH promoted ROS production and activated ras homolog gene family member A (RhoA)/Rho-associated protein kinase (ROCK) pathway. All of these effects of IH were reversed by salidroside. Similar to salidroside, ROCK-selective inhibitors Y26732, and Fasudil protected HUVECs from IH-induced ROS overproduction and endothelial barrier disruption. Furthermore, salidroside increased intracellular cAMP levels, while the PKA-selective inhibitor H-89 attenuated the effects of salidroside on IH-induced RhoA/ROCK suppression, ROS scavenging, and barrier protection.Conclusion: Our findings demonstrate that salidroside effectively ameliorated IH-aggravated endothelial barrier injury and atherosclerosis, largely through the cAMP/PKA/RhoA signaling pathway.

Brefeldin A and Kifunensine modulate the LPS-induced lung endothelial hyperpermeability in human and bovine cells

Endothelial hyper-permeability is the hallmark of Acute Respiratory Distress Syndrome (ARDS). Laborious efforts in the investigation of the molecular pathways involved in the regulation of the vascular barrier, shall reveal novel therapeutic targets towards that respiratory disorder. Herein we investigate in vitro the effects of the alpha-1,2- mannosidase 1 inhibitor Kifunensine (KIF) and brefeldin A (BFA) in the LPS-induced endothelial breakdown. Our results suggest that BFA opposes the deteriorating effects of KIF (UPR suppressor) towards the lung microvasculature. Since KIF is an unfolded protein response (UPR) suppressor, and brefeldin A is a UPR inducer, we suggest that a carefully devised UPR manipulation may deliver novel therapeutic avenues in diseases related to endothelial barrier dysfunction (e.g. ARDS, sepsis).