Einleitung Neben Tumorzellen stellen auch Zellen in der Tumorumgebung wie Thrombozyten Immuncheckpoint (IC)-Moleküle her. Die Bedeutung dieser zellulären Blutbestandteile für die Regulation von Immunzellantworten in bösartigen Tumoren ist unklar.
Microvascular immunothrombotic dysregulation is a critical process in the pathogenesis of severe systemic inflammatory diseases. The mechanisms controlling immunothrombosis in inflamed microvessels, however, remain poorly understood. Here, we report that under systemic inflammatory conditions the matricellular glycoproteinvitronectin (VN) establishes an intravascular scaffold, supporting interactions of aggregating platelets with immune cells and the venular endothelium. Blockade of the VN receptor glycoprotein (GP)IIb/IIIa interfered with this multicellular interplay and effectively prevented microvascular clot formation. In line with these experimental data, particularly VN was found to be enriched in the pulmonary microvasculature of patients with non-infectious (pancreatitis-associated) or infectious (coronavirus disease 2019 (COVID-19)-associated) severe systemic inflammatory responses. Targeting the VN-GPIIb/IIIa axis hence appears as a promising, already feasible strategy to counteract microvascular immunothrombotic dysregulation in systemic inflammatory pathologies.
Neutrophil infiltration of the postischemic tissue considerably contributes to organ dysfunction on ischemia/reperfusion injury. Beyond its established role in fibrinolysis, tissue-type plasminogen activator (tPA) has recently been implicated in nonfibrinolytic processes. The role of this serine protease in the recruitment process of neutrophils remains largely obscure.Using in vivo microscopy on the postischemic cremaster muscle, neutrophil recruitment and microvascular leakage, but not fibrinogen deposition at the vessel wall, were significantly diminished in tPA(-/-) mice. Using cell transfer techniques, leukocyte and nonleukocyte tPA were found to mediate ischemia/reperfusion-elicited neutrophil responses. Intrascrotal but not intra-arterial application of recombinant tPA induced a dose-dependent increase in the recruitment of neutrophils, which was significantly higher compared with stimulation with a tPA mutant lacking catalytic activity. Whereas tPA-dependent transmigration of neutrophils was selectively reduced on the inhibition of plasmin or gelatinases, neutrophil intravascular adherence was significantly diminished on the blockade of mast cell activation or lipid mediator synthesis. Moreover, stimulation with tPA caused a significant elevation in the leakage of fluorescein isothiocyanate dextran to the perivascular tissue, which was completely abolished on neutrophil depletion. In vitro, tPA-elicited macromolecular leakage of endothelial cell layers was abrogated on the inhibition of its proteolytic activity.Endogenously released tPA promotes neutrophil transmigration to reperfused tissue via proteolytic activation of plasmin and gelatinases. As a consequence, tPA on transmigrating neutrophils disrupts endothelial junctions allowing circulating tPA to extravasate to the perivascular tissue, which, in turn, amplifies neutrophil recruitment through the activation of mast cells and release of lipid mediators.
The alkaloid narciclasine has been characterized extensively as an anticancer compound. Accumulating evidence suggests that narciclasine has anti-inflammatory potential; however, the underlying mechanism remains poorly understood. We hypothesized that narciclasine affects the activation of endothelial cells (ECs), a hallmark of inflammatory processes, which is a prerequisite for leukocyte-EC interaction. Thus, we aimed to investigate narciclasine's action on this process in vivo and to analyze the underlying mechanisms in vitro. In a murine peritonitis model, narciclasine reduced leukocyte infiltration, proinflammatory cytokine expression, and inflammation-associated abdominal pain. Moreover, narciclasine decreased rolling and blocked adhesion and transmigration of leukocytes in vivo. In cultured ECs, narciclasine inhibited the expression of cell adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin and blocked crucial steps of the NF-κB activation cascade: NF-κB promotor activity, p65 nuclear translocation, inhibitor of κB α (IκBα) phosphorylation and degradation, and IκBα kinase β and TGF-β-activated kinase 1 phosphorylation. Interestingly, these effects were based on the narciclasine-triggered loss of TNF receptor 1 (TNFR1). Our study highlights narciclasine as an interesting anti-inflammatory compound that effectively inhibits the interaction of leukocytes with ECs by blocking endothelial activation processes. Most importantly, we showed that the observed inhibitory action of narciclasine on TNF-triggered signaling pathways is based on the loss of TNFR1.-Stark, A., Schwenk, R., Wack, G., Zuchtriegel, G., Hatemler, M. G., Bräutigam, J., Schmidtko, A., Reichel, C. A., Bischoff, I., Fürst, R. Narciclasine exerts anti-inflammatory actions by blocking leukocyte-endothelial cell interactions and down-regulation of the endothelial TNF receptor 1.
Recent evidence points to a critical role of the time‐of‐day in the regulation of leukocyte recruitment to tissues. Using in vivo quantitative imaging analyses across the day in inflammatory scenarios, we observed circadian (~24h) leukocyte recruitment in arteries and veins of the macro‐ and microvasculature. Interestingly however, while in arteries the number of adherent cells peaked in the morning, in veins it peaked at night. These differences were functionally associated with a vessel‐type‐specific oscillatory pattern in the expression of the adhesion molecule ICAM‐1 but not of other promigratory molecules or clock genes. ICAM‐1‐deficient mice lacked rhythmic leukocyte adhesion in both arteries and veins, which was also observed in studies using functional ICAM‐1‐blocking antibodies. Since the sympathetic nervous system (SNS) is an important orchestrator of rhythmicity in peripheral tissues, we disrupted the SNS systemically by 6‐OHDA treatment. This resulted in a lack of oscillations in both arteries and veins. To assess the functional role of direct sympathetic innervation in this process, we surgically denervated sympathetic input to vessels locally by unilaterally cutting the superior cervical ganglion. While the contralateral, nerve‐intact sides still exhibited rhythmicity in both leukocyte adhesion and ICAM‐1 expression, local denervation resulted in a loss of oscillations. Similar results were obtained by administration of beta adrenergic receptor antagonists. Interestingly, when using Ng2Cre x Bmal1 flox/flox mice, in which the core clock gene Bmal1 and thus rhythmicity was selectively deleted in arteriolar Ng2 + ‐pericytes, an ablation of the oscillations was observed in both arteries and veins. Thus, using pharmacological, surgical and genetic approaches, our data point to an important role of arteries in regulating rhythmic leukocyte recruitment to veins. Support or Funding Information Funded by the German Research Foundation (Emmy Noether SCHE 1645/2‐1 and SFB914 projects B09 and Z03) and the European Research Council (CIRCODE, 635872)
