Platelet gene expression and function in patients with COVID-19.

Coagulopathy in COVID-19.

The blood-brain barrier (BBB) is a highly complex and dynamic barrier. It is formed by an interdependent network of brain capillary endothelial cells, endowed with barrier properties, and perivascular cells (astrocytes and pericytes) responsible for inducing and maintaining those properties. One of the primary properties of the BBB is a strict regulation of paracellular permeability due to the presence of junctional complexes (tight, adherens and gap junctions) between the endothelial cells. Alterations in junction assembly and function significantly affect BBB properties, particularly barrier permeability. However, such alterations are also involved in remodeling the brain endothelial cell surface and regulating brain endothelial cell phenotype. This review summarizes the characteristics of brain endothelial tight, adherens and gap junctions and highlights structural and functional alterations in junctional proteins that may contribute to BBB dysfunction.

https://www.tandfonline.com/doi/pdf/10.1080/21688370.2016.1154641

Junctional proteins of the blood-brain barrier: New insights into function and dysfunction

Platelets are anucleate cells produced by megakaryocytes. In recent years, a robust body of literature supports the evolving role of platelets as key sentinel and effector cells in infectious diseases, especially critical in bridging hemostatic, inflammatory, and immune continuums. Upon intravascular pathogen invasion, platelets can directly sense viral, parasitic, and bacterial infections through pattern recognition receptors and integrin receptors or pathogen: immunoglobulin complexes through Fc and complement receptors-although our understanding of these interactions remains incomplete. Constantly scanning for areas of injury or inflammation as they circulate in the vasculature, platelets also indirectly respond to pathogen invasion through interactions with leukocytes and the endothelium. Following antigen recognition, platelets often become activated. Through a diverse repertoire of mechanisms, activated platelets can directly sequester or kill pathogens, or facilitate pathogen clearance by activating macrophages and neutrophils, promoting neutrophil extracellular traps (NETs) formation, forming platelet aggregates and microthrombi. At times, however, platelet activation may also be injurious to the host, exacerbating inflammation and promoting endothelial damage and thrombosis. There are many gaps in our understandings of the role of platelets in infectious diseases. However, with the emergence of advanced technologies, our knowledge is increasing. In the current review, we mainly discuss these evolving roles of platelets under four different infectious pathogen infections, of which are dengue, malaria, Esterichia coli (E. coli) and staphylococcus aureus S. aureus, highlighting the complex interplay of these processes with hemostatic and thrombotic pathways.

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The Era of Thromboinflammation: Platelets Are Dynamic Sensors and Effector Cells During Infectious Diseases.

Sepsis is a systemic inflammatory response syndrome caused by infection. The core mechanism underlying sepsis is immune dysfunction, with macrophages, as important cells of the innate immune system, playing an essential role. Autophagy has been shown to be closely related to inflammation and immunity, and autophagy enhancement in sepsis can play a protective role by negatively regulating abnormal macrophage activation, modulating macrophage polarization phenotype, reducing activation of the inflammasome and release of inflammatory factors, and affecting macrophage apoptosis. However, excessive autophagy may also lead to autophagic death of macrophages, which further aggravates the inflammatory response. The mechanisms underlying these functions are relatively complex and remain unclear, but may be related to a variety of signaling pathways such as NF-κB, mTOR, and PI3K/AKT. The administration of drugs to assist in the regulation of macrophage autophagy has become a novel treatment for sepsis. The present review focuses on the role and the potential mechanisms of macrophage autophagy in sepsis.

Review: the Role and Mechanisms of Macrophage Autophagy in Sepsis.

Dengue virus (DENV) infection, the most common mosquito-transmitted viral infection, can cause a range of diseases from self-limiting dengue fever to life-threatening dengue hemorrhagic fever and shock syndrome. Thrombocytopenia is a major characteristic observed in both mild and severe dengue disease and is significantly correlated with the progression of dengue severity. Previous studies have shown that DENV nonstructural protein 1 (NS1), which can be secreted into patients' blood, can stimulate immune cells via Toll-like receptor 4 (TLR4) and can cause endothelial leakage. However, it is unclear whether DENV NS1 can directly induce platelet activation or cause thrombocytopenia during DENV infection. In this study, we first demonstrated that DENV but not Zika virus cell culture supernatant could induce P-selectin expression and phosphatidylserine (PS) exposure in human platelets, both of which were abolished when NS1 was depleted from the DENV supernatant. Similar results were found using recombinant NS1 from all four serotypes of DENV, and those effects were blocked in the presence of anti-NS1 F(ab')2, anti-TLR4 antibody, a TLR4 antagonist (Rhodobacter sphaeroides lipopolysaccharide, LPS-Rs) and a TLR4 signaling inhibitor (TAK242), but not polymyxin B (an LPS inhibitor). Moreover, the activation of platelets by DENV NS1 promoted subthreshold concentrations of adenosine diphosphate (ADP)-induced platelet aggregation and enhanced platelet adhesion to endothelial cells and phagocytosis by macrophages. Finally, we demonstrated that DENV-induced thrombocytopenia and hemorrhage were attenuated in TLR4 knockout and wild-type mice when NS1 was depleted from DENV supernatant. Taken together, these results suggest that the binding of DENV NS1 to TLR4 on platelets can trigger its activation, which may contribute to thrombocytopenia and hemorrhage during dengue infection.

Dengue virus nonstructural protein 1 activates platelets via Toll-like receptor 4, leading to thrombocytopenia and hemorrhage.

Vascular leakage is one of the salient characteristics of severe dengue. Nonstructural protein 1 (NS1) of dengue virus (DENV) can stimulate endothelial cells to secrete endothelial hyperpermeability factor, macrophage migration inhibitory factor (MIF), and the glycocalyx degradation factor heparanase 1 (HPA-1). However, it is unclear whether MIF is directly involved in NS1-induced glycocalyx degradation. In this study, we observed that among NS1, MIF and glycocalyx degradation-related molecules, the HPA-1, metalloproteinase 9 (MMP-9) and syndecan 1 (CD138) serum levels were all increased in dengue patients, and only NS1 and MIF showed a positive correlation with the CD138 level in severe patients. To further characterize and clarify the relationship between MIF and CD138, we used recombinant NS1 to stimulate human cells in vitro and challenge mice in vivo. Our tabulated results suggested that NS1 stimulation could induce human endothelial cells to secrete HPA-1 and immune cells to secrete MMP-9, resulting in endothelial glycocalyx degradation and hyperpermeability. Moreover, HPA-1, MMP-9, and CD138 secretion after NS1 stimulation was blocked by MIF inhibitors or antibodies both in vitro and in mice. Taken together, these results suggest that MIF directly engages in dengue NS1-induced glycocalyx degradation and that targeting MIF may represent a possible therapeutic approach for preventing dengue-induced vascular leakage.

/pdf/macrophage-migration-inhibitory-factor-is-critical-for-1e7xxtv1vu.pdf

Macrophage migration inhibitory factor is critical for dengue NS1-induced endothelial glycocalyx degradation and hyperpermeability.

Vascular leakage is an important feature of acute inflammatory shock, which currently has no effective treatment. Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine that can induce vascular leakage and plays an important role in the pathogenesis of shock. However, the mechanism of MIF-induced vascular leakage is still unclear. In this study, using recombinant MIF (rMIF), we demonstrated that MIF induced disorganization and degradation of junction proteins and increased the permeability of human endothelial cells in vitro. Western blotting analysis showed that rMIF treatment induced LC3 conversion and p62 degradation. Inhibition of autophagy with a PI3K inhibitor (3-MA), a ROS scavenger (NAC) or autophagosomal-lysosomal fusion inhibitors (bafilomycin A1 and chloroquine) rescued rMIF-induced vascular leakage, suggesting that autophagy mediates MIF-induced vascular leakage. The potential involvement of other signaling pathways was also studied using different inhibitors, and the results suggested that MIF-induced vascular leakage may occur through the ERK pathway. In conclusion, we showed that MIF triggered autophagic degradation of endothelial cells, resulting in vascular leakage. Inhibition of MIF-induced autophagy may provide therapeutic targets against vascular leakage in inflammatory shock.

/pdf/macrophage-migration-inhibitory-factor-induces-vascular-48eqf1614g.pdf

Macrophage migration inhibitory factor induces vascular leakage via autophagy.

Inhibition of autophagy protects against sepsis by concurrently attenuating the cytokine storm and vascular leakage.

Vascular leakage contributes to the high morbidity and mortality associated with sepsis. Exposure of the endothelium to inflammatory mediators, such as thrombin and cytokines, during sepsis leads to hyperpermeability. We recently observed that autophagy, a cellular process for protein turnover, is involved in macrophage migration inhibitory factor (MIF)-induced endothelial hyperpermeability. Even though it is known that thrombin induces endothelial cells to secrete MIF and to increase vascular permeability, the possible role of autophagy in this process is unknown. In this study, we proposed and tested the hypothesis that MIF-induced autophagy plays an important role in thrombin-induced endothelial hyperpermeability. We evaluated the effects of thrombin on endothelial permeability, autophagy induction, and MIF secretion in vitro using the human microvascular endothelial cell line-1 and human umbilical vein endothelial cells. Several mechanisms/read outs of endothelial permeability and autophagy formation were examined. We observed that blocking autophagy attenuated thrombin-induced endothelial hyperpermeability. Furthermore, thrombin-induced MIF secretion was involved in this process because MIF inhibition reduced thrombin-induced autophagy and hyperpermeability. Finally, we showed that blocking MIF or autophagy effectively alleviated vascular leakage and mortality in endotoxemic mice. Thus, MIF-induced autophagy may represent a common mechanism causing vascular leakage in sepsis.

Chiao Hsuan Chao

Papers

Dengue virus nonstructural protein 1 activates platelets via Toll-like receptor 4, leading to thrombocytopenia and hemorrhage.

Macrophage migration inhibitory factor is critical for dengue NS1-induced endothelial glycocalyx degradation and hyperpermeability.

Macrophage migration inhibitory factor induces vascular leakage via autophagy.

Inhibition of autophagy protects against sepsis by concurrently attenuating the cytokine storm and vascular leakage.

Macrophage Migration Inhibitory Factor-Induced Autophagy Contributes to Thrombin-Triggered Endothelial Hyperpermeability in Sepsis.