The vitronectin-binding domain of plasminogen activator inhibitor-1 plays an important functional role in lipopolysaccharide-induced lethality in mice

Plasminogen activator inhibitor 1 is not a major causative factor for exacerbation in a mouse model of SARS-CoV-2 infection

Coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains a global pandemic. Although several vaccines targeting SARS-CoV-2 spike proteins protect against COVID-19 infection, mutations affecting virus transmissibility and immune evasion potential have reduced their efficacy, leading to the need for a more efficient strategy. Available clinical evidence regarding COVID-19 suggests that endothelial dysfunction with thrombosis is a central pathogenesis of progression to systemic disease, in which overexpression of plasminogen activator inhibitor-1 (PAI-1) may be important. Here we developed a novel peptide vaccine against PAI-1 and evaluated its effect on lipopolysaccharide (LPS)-induced sepsis and SARS-CoV-2 infection in mice. Administration of LPS and mouse-adapted SARS-CoV-2 increased serum PAI-1 levels, although the latter showed smaller levels. In an LPS-induced sepsis model, mice immunized with PAI-1 vaccine showed reduced organ damage and microvascular thrombosis and improved survival compared with vehicle-treated mice. In plasma clot lysis assays, vaccination-induced serum IgG antibodies were fibrinolytic. However, in a SARS-CoV-2 infection model, survival and symptom severity (i.e., body weight reduction) did not differ between vaccine- and vehicle-treated groups. These results indicate that although PAI-1 may promote the severity of sepsis by increasing thrombus formation, it might not be a major contributor to COVID-19 exacerbation.

Intra- and extracellular plasminogen activator inhibitor-1 regulate effect of vitronectin against radiation-induced endothelial cell death

Plasminogen activator inhibitor-1 (PAI-1) is induced by radiation resulting in endothelial cell impairment, potentially leading to multiple organ failure. Vitronectin (VN) is a 75-kDa glycoprotein (VN₇₅) cleaved into two forms (VN₇₅ or VN_65/10) by furin, which is regulated by intracellular PAI-1. VN protects against radiation-induced endothelial cell death, but the mechanisms involved in VN processing and its interactions with intra- and extracellular PAI-1 remain unclear. We examined these processes in cells in vitro using recombinant proteins or overexpression of VN and PAI-1 genes, including furin-susceptible (T³⁸¹) and furin-resistant VN (A³⁸¹). VN processing was analyzed using a mutant PAI-1 with relatively weaker binding to VN. VN function was evaluated by survival of radiation-damaged endothelial cells. Wild-type, but not mutant PAI-1 inhibited furin-dependent VN processing. Gene transfer revealed that furin-susceptible VN was processed more than the furin-resistant form, but processing of both was inhibited by PAI-1 overexpression. Intracellular PAI-1 formed a complex with VN₇₅ (T³⁸¹) in cells and media, and the VN₇₅ form was secreted preferentially. Only VN₇₅ protected against radiation-induced endothelial cell death, in which its effect was abolished by wild-type but not mutant PAI-1. These findings indicate that intracellular PAI-1 inhibits VN processing and protects against radiation-induced endothelial cell death.

Abrogation of plasminogen activator inhibitor-1-vitronectin interaction ameliorates acute kidney injury in murine endotoxemia

Sepsis-induced acute kidney injury (AKI) contributes to the high mortality and morbidity in patients. Although the pathogenesis of AKI during sepsis is poorly understood, it is well accepted that plasminogen activator inhibitor-1 (PAI-1) and vitronectin (Vn) are involved in AKI. However, the functional cooperation between PAI-1 and Vn in septic AKI has not been completely elucidated. To address this issue, mice were utilized lacking either PAI-1 (PAI-1^−/−) or expressing a PAI-1-mutant (PAI-1^R101A/Q123K) in which the interaction between PAI-1 and Vn is abrogated, while other functions of PAI-1 are retained. It was found that both PAI-1^−/− and PAI-1^R101A/Q123K mice are associated with decreased renal dysfunction, apoptosis, inflammation, and ERK activation as compared to wild-type (WT) mice after LPS challenge. Also, PAI-1^−/− mice showed attenuated fibrin deposition in the kidneys. Furthermore, a lack of PAI-1 or PAI-1-Vn interaction was found to be associated with an increase in activated Protein C (aPC) in plasma. These results demonstrate that PAI-1, through its interaction with Vn, exerts multiple deleterious mechanisms to induce AKI. Therefore, targeting of the PAI-1-Vn interaction in kidney represents an appealing therapeutic strategy for the treatment of septic AKI by not only altering the fibrinolytic capacity but also regulating PC activity.

Effects of different types of fluid resuscitation on hepatic mitochondria and apoptosis

The aim of this study was to observe the effects of different types of fluid resuscitation on hepatic mitochondria and apoptosis in hemorrhagic shock, and the corresponding mechanisms. Forty rats were divided into five groups: Sham surgery (Sham group), shock (Shock group), Ringer's lactate resuscitation (RL group), hydroxyethyl starch resuscitation (HES group) and autologous blood resuscitation (BL group). A model of hemorrhagic shock was successfully induced in the latter four groups. The recovery objective was to maintain the mean arterial pressure (MAP) of the rats at 80 mmHg. Two hours after the end of the recovery experiment, fresh liver samples were examined in order to observe the changes in the morphology and mitochondrial membrane potential (ΔΨm). In addition, the levels of succinate dehydrogenase (SDH) activity were assessed, and a terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay was conducted to evaluate the level of apoptosis in the liver cells. In the Shock, RL, HES and BL groups, mitochondrial ultrastructural damage in the liver cells, significant reductions in liver cell function, liver ΔΨm and SDH activity, and the apoptosis of hepatocytes were more apparent compared with those in the Sham group. In the BL group, compared with the RL and HES groups, the injuries to the mitochondrial ultrastructure and liver cell function were significantly reduced, the hepatic ΔΨm and SDH activity were significantly increased and the hepatocyte apoptosis index (AI) was significantly reduced (P<0.05). In conclusion, in a rat model of hemorrhagic shock, different methods of fluid resuscitation may improve the liver cells with regard to mitochondrial ultrastructure and function, the stability of liver ΔΨm, the activity of SDH and the inhibition of liver cell apoptosis. The results indicate that infusion with autologous blood followed by RL solution is a preferable method of fluid resuscitation compared with HES.