Procoagulant platelets promote immune evasion in triple-negative breast cancer.

ABSTRACT: Triple-negative breast cancer (TNBC) is an aggressive tumor entity in which immune checkpoint (IC) molecules are primarily synthesized in the tumor environment. Here, we report that procoagulant platelets bear large amounts of such immunomodulatory factors and that the presence of these cellular blood components in TNBC relates to protumorigenic immune-cell activity and impaired survival. Mechanistically, tumor-released nucleic acids attract platelets to the aberrant tumor microvasculature, where they undergo procoagulant activation, thus delivering specific stimulatory and inhibitory IC molecules. This concomitantly promotes protumorigenic myeloid leukocyte responses and compromises antitumorigenic lymphocyte activity, ultimately supporting tumor growth. Interference with platelet-leukocyte interactions prevented immune cell misguidance and suppressed tumor progression, nearly as effective as systemic IC inhibition. Hence, our data uncover a self-sustaining mechanism of TNBC by using platelets to misdirect immune-cell responses. Targeting this irregular multicellular interplay may represent a novel immunotherapeutic strategy for TNBC without the adverse effects of systemic IC inhibition.

A transcriptomic pan-cancer signature for survival prognostication and prediction of immunotherapy response based on endothelial senescence.

BACKGROUND: The microvascular endothelium inherently controls nutrient delivery, oxygen supply, and immune surveillance of malignant tumors, thus representing both biological prerequisite and therapeutic vulnerability in cancer. Recently, cellular senescence emerged as a fundamental characteristic of solid malignancies. In particular, tumor endothelial cells have been reported to acquire a senescence-associated secretory phenotype, which is characterized by a pro-inflammatory transcriptional program, eventually promoting tumor growth and formation of distant metastases. We therefore hypothesize that senescence of tumor endothelial cells (TEC) represents a promising target for survival prognostication and prediction of immunotherapy efficacy in precision oncology. METHODS: Published single-cell RNA sequencing datasets of different cancer entities were analyzed for cell-specific senescence, before generating a pan-cancer endothelial senescence-related transcriptomic signature termed EC.SENESCENCE.SIG. Utilizing this signature, machine learning algorithms were employed to construct survival prognostication and immunotherapy response prediction models. Machine learning-based feature selection algorithms were applied to select key genes as prognostic biomarkers. RESULTS: Our analyses in published transcriptomic datasets indicate that in a variety of cancers, endothelial cells exhibit the highest cellular senescence as compared to tumor cells or other cells in the vascular compartment of malignant tumors. Based on these findings, we developed a TEC-associated, senescence-related transcriptomic signature (EC.SENESCENCE.SIG) that positively correlates with pro-tumorigenic signaling, tumor-promoting dysbalance of immune cell responses, and impaired patient survival across multiple cancer entities. Combining clinical patient data with a risk score computed from EC.SENESCENCE.SIG, a nomogram model was constructed that enhanced the accuracy of clinical survival prognostication. Towards clinical application, we identified three genes as pan-cancer biomarkers for survival probability estimation. As therapeutic perspective, a machine learning model constructed on EC.SENESCENCE.SIG provided superior pan-cancer prediction for immunotherapy response than previously published transcriptomic models. CONCLUSIONS: We here established a pan-cancer transcriptomic signature for survival prognostication and prediction of immunotherapy response based on endothelial senescence.

The RonchAP® palatinal device: A conservative approach in treating obstructive sleep apnea syndrome-a randomized, controlled study.

PURPOSE: The aim of the present study was to assess the efficacy of the Ronch®AP palatal device in treating patients with moderate and severe forms of obstructive sleep apnea syndrome. METHODS: In a randomized controlled trial 22 patients were examined with the Ronch®AP palatal device after 4 weeks of usage. Their results were compared to a control group of 30 patients who did not receive any treatment during this time. All patients included did not tolerate CPAP therapy. Among other parameters the apnea-hypopnea index (AHI) was measured using nocturnal cardiorespiratory polysomnography. Daytime sleepiness was assessed using Epworth Sleepiness Scale. Pittsburgh Sleep Quality Index was used to analyze sleep quality. RESULTS: Using the Ronch®AP palatal device AHI was reduced from an average of 35.34 ± 14.9/h to 19.18 ± 14.93/h, whereas the control group only showed a minimal mean reduction from 31.32 ± 12.76/h to 29.37 ± 17.11/h. The difference in reduction between the two randomized groups was highly significant (d = - 14.2, 95% CI 5.9-22.6, t = 3.4, df = 49.9, p = 0.001). Epworth Sleepiness Scale score was lowered from 9.18 ± 4.73 to 7.82 ± 4.14 on average and sleep quality improved by - 1.91 ± 2.31. Both changes were also statistically relevant (p < 0.005). CONCLUSIONS: The Ronch®AP device is an effective alternative treatment option for patients suffering from moderate and severe forms of obstructive sleep apnea syndrome and not tolerating CPAP therapy. TRIAL REGISTRATION NUMBER: 407-16 with approval from the local ethical committee (Ethikkommission der Medizinischen Fakultät der LMU München).

Vitronectin stabilizes intravascular adhesion of neutrophils by coordinating ß2 integrin clustering.

The recruitment of neutrophils from the microvasculature to the site of injury or infection represents a key event in the inflammatory response. Vitronectin (VN) is a multifunctional macromolecule abundantly present in blood and extracellular matrix. The role of this glycoprotein in the extravasation process of circulating neutrophils remains elusive. Employing advanced in vivo/ex vivo imaging techniques in different mouse models as well as in vitro methods, we uncovered a previously unrecognized function of VN in the transition of dynamic to static intravascular interactions of neutrophils with microvascular endothelial cells. These distinct properties of VN require the heteromerization of this glycoprotein with plasminogen activator inhibitor-1 (PAI- 1) on the activated venular endothelium and subsequent interactions of this protein complex with the scavenger receptor low-density lipoprotein receptor-related protein-1 on intravascularly adhering neutrophils. This induces p38 mitogen-activated protein kinases-dependent intracellular signaling events which, in turn, regulates the proper clustering of the b2 integrin lymphocyte function associated antigen-1 on the surface of these immune cells. As a consequence of this molecular interplay, neutrophils become able to stabilize their adhesion to the microvascular endothelium and, subsequently, to extravasate to the perivascular tissue. Hence, endothelial-bound VN-PAI-1 heteromers stabilize intravascular adhesion of neutrophils by coordinating b2 integrin clustering on the surface of these immune cells, thereby effectively controlling neutrophil trafficking to inflamed tissue. Targeting this protein complex might be beneficial for the prevention and treatment of inflammatory pathologies.

Platelets Guide Leukocytes to Their Sites of Extravasation.

Effective immune responses require the directed migration of leukocytes from the vasculature to the site of injury or infection. How immune cells "find" their site of extravasation remains largely obscure. Here, we identified a previously unrecognized role of platelets as pathfinders guiding leukocytes to their exit points in the microvasculature: upon onset of inflammation, circulating platelets were found to immediately adhere at distinct sites in venular microvessels enabling these cellular blood components to capture neutrophils and, in turn, inflammatory monocytes via CD40-CD40L-dependent interactions. In this cellular crosstalk, ligation of PSGL-1 by P-selectin leads to ERK1/2 MAPK-dependent conformational changes of leukocyte integrins, which promote the successive extravasation of neutrophils and monocytes to the perivascular tissue. Conversely, blockade of this cellular partnership resulted in misguided, inefficient leukocyte responses. Our experimental data uncover a platelet-directed, spatiotemporally organized, multicellular crosstalk that is essential for effective trafficking of leukocytes to the site of inflammation.

Plasminogen Activator Inhibitor-1 Promotes Neutrophil Infiltration and Tissue Injury on Ischemia-Reperfusion.

OBJECTIVE: Ischemia-reperfusion (I/R) injury significantly contributes to organ dysfunction and failure after myocardial infarction, stroke, and transplantation. In addition to its established role in the fibrinolytic system, plasminogen activator inhibitor-1 has recently been implicated in the pathogenesis of I/R injury. The underlying mechanisms remain largely obscure. APPROACH AND RESULTS: Using different in vivo microscopy techniques as well as ex vivo analyses and in vitro assays, we identified that plasminogen activator inhibitor-1 rapidly accumulates on microvascular endothelial cells on I/R enabling this protease inhibitor to exhibit previously unrecognized functional properties by inducing an increase in the affinity of ß2 integrins in intravascularly rolling neutrophils. These events are mediated through low-density lipoprotein receptor-related protein-1 and mitogen-activated protein kinase-dependent signaling pathways that initiate intravascular adherence of these immune cells to the microvascular endothelium. Subsequent to this process, extravasating neutrophils disrupt endothelial junctions and promote the postischemic microvascular leakage. Conversely, deficiency of plasminogen activator inhibitor-1 effectively reversed leukocyte infiltration, microvascular dysfunction, and tissue injury on experimental I/R without exhibiting side effects on microvascular hemostasis. CONCLUSIONS: Our experimental data provide novel insights into the nonfibrinolytic properties of the fibrinolytic system and emphasize plasminogen activator inhibitor-1 as a promising target for the prevention and treatment of I/R injury.

Aged neutrophils contribute to the first line of defense in the acute inflammatory response.

Under steady-state conditions, aged neutrophils are removed from the circulation in bone marrow, liver, and spleen, thereby maintaining myeloid cell homeostasis. The fate of these aged immune cells under inflammatory conditions, however, remains largely obscure. Here, we demonstrate that in the acute inflammatory response during endotoxemia, aged neutrophils cease returning to the bone marrow and instead rapidly migrate to the site of inflammation. Having arrived in inflamed tissue, aged neutrophils were found to exhibit a higher phagocytic activity as compared with the subsequently recruited nonaged neutrophils. This distinct behavior of aged neutrophils under inflammatory conditions is dependent on specific age-related changes in their molecular repertoire that enable these "experienced" immune cells to instantly translate inflammatory signals into immune responses. In particular, aged neutrophils engage Toll-like receptor-4- and p38 MAPK-dependent pathways to induce conformational changes in ß2 integrins that allow these phagocytes to effectively accomplish their mission in the front line of the inflammatory response. Hence, ageing in the circulation might represent a critical process for neutrophils that enables these immune cells to properly unfold their functional properties for host defense.

In situ targeting of dendritic cells sets tolerogenic environment and ameliorates CD4+ T-cell response in the postischemic liver.

CD4+ T cells recruited to the liver play a key role in the pathogenesis of ischemia/reperfusion (I/R) injury. The mechanism of their activation during alloantigen-independent I/R is not completely understood. We hypothesized that liver-resident dendritic cells (DCs) interact with CD4+ T cells in the postischemic liver and that modulation of DCs or T-cell-DC interactions attenuates liver inflammation. In mice, warm hepatic I/R (90/120-240 min) was induced. Tolerogenic DCs were generated in situ by pretreatment of animals with the vitamin D analog paricalcitol. A mAb-CD44 was used for blockade of CD4+ T-cell-DC interactions. As shown by 2-photon in vivo microscopy as well as confocal microscopy, CD4+ T cells were closely colocalized with DCs in the postischemic liver. Pretreatment with paricalcitol attenuated I/R-induced maturation of DCs (flow cytometry), CD4+ T-cell recruitment into the liver (intravital microscopy), and hepatocellular/microvascular damage (intravital microscopy, alanine aminotransferase/aspartate aminotransferase, histology). However, interruption of T-cell-DC interaction increased proinflammatory DC maturation and even enhanced tissue damage. Simultaneous treatment with an anti-CD44mAb completely abolished the beneficial effect of paricalcitol on T-cell migration and tissue injury. Our study demonstrates for the first time that hepatic DCs interact with CD4+ T cells in the postischemic liver in vivo; modulation of DCs and/or generation of tolerogenic DCs attenuates intrahepatic CD4+ T-cell recruitment and reduces I/R injury; and interruption of CD44-dependent CD4+ T-cell-DC interactions enhances tissue injury by preventing the modulatory effect of hepatic DCs on T cells, especially type 1 T helper effector cells. Thus, hepatic DCs are strongly involved in the promotion of CD4+ T-cell-dependent postischemic liver inflammation.-Funken, D., Ishikawa-Ankerhold, H., Uhl, B., Lerchenberger, M., Rentsch, M., Mayr, D., Massberg, S., Werner, J., Khandoga, A. In situ targeting of dendritic cells sets tolerogenic environment and ameliorates CD4+ T-cell response in the postischemic liver.

Endothelial Dysfunction, and A Prothrombotic, Proinflammatory Phenotype Is Caused by Loss of Mitochondrial Thioredoxin Reductase in Endothelium.

OBJECTIVE: Although the investigation on the importance of mitochondria-derived reactive oxygen species (ROS) in endothelial function has been gaining momentum, little is known on the precise role of the individual components involved in the maintenance of a delicate ROS balance. Here we studied the impact of an ongoing dysregulated redox homeostasis by examining the effects of endothelial cell-specific deletion of murine thioredoxin reductase 2 (Txnrd2), a key enzyme of mitochondrial redox control. APPROACH AND RESULTS: We analyzed the impact of an inducible, endothelial cell-specific deletion of Txnrd2 on vascular remodeling in the adult mouse after femoral artery ligation. Laser Doppler analysis and histology revealed impaired angiogenesis and arteriogenesis. In addition, endothelial loss of Txnrd2 resulted in a prothrombotic, proinflammatory vascular phenotype, manifested as intravascular cellular deposits, as well as microthrombi. This phenotype was confirmed by an increased leukocyte response toward interleukin-1 in the mouse cremaster model. In vitro, we could confirm the attenuated angiogenesis measured in vivo, which was accompanied by increased ROS and an impaired mitochondrial membrane potential. Ex vivo analysis of femoral arteries revealed reduced flow-dependent vasodilation in endothelial cell Txnrd2-deficient mice. This endothelial dysfunction could be, at least partly, ascribed to inadequate nitric oxide signaling. CONCLUSIONS: We conclude that the maintenance of mitochondrial ROS via Txnrd2 in endothelial cells is necessary for an intact vascular homeostasis and remodeling and that Txnrd2 plays a vitally important role in balancing mitochondrial ROS production in the endothelium.

Multiphoton Microscopy of Nonfluorescent Nanoparticles In Vitro and In Vivo.

Nanotechnology holds great promise for a plethora of potential applications. The interaction of engineered nanomaterials with living cells, tissues, and organisms is, however, only partly understood. Microscopic investigations of nano-bio interactions are mostly performed with a few model nanoparticles (NPs) which are easy to visualize, such as fluorescent quantum dots. Here the possibility to visualize nonfluorescent NPs with multiphoton excitation is investigated. Signals from silver (Ag), titanium dioxide (TiO2 ), and silica (SiO2 ) NPs in nonbiological environments are characterized to determine signal dependency on excitation wavelength and intensity as well as their signal stability over time. Ag NPs generate plasmon-induced luminescence decaying over time. TiO2 NPs induce photoluminescent signals of variable intensities and in addition strong third harmonic generation (THG). Optimal settings for microscopic detection are determined and then applied for visualization of these two particle types in living cells, in murine muscle tissue, and in the murine blood stream. Silica NPs produce a THG signal, but in living cells it cannot be discriminated sufficiently from endogenous cellular structures. It is concluded that multiphoton excitation is a viable option for studies of nano-bio interactions not only for fluorescent but also for some types of nonfluorescent NPs.

Spatiotemporal expression dynamics of selectins govern the sequential extravasation of neutrophils and monocytes in the acute inflammatory response.

OBJECTIVE: Leukocyte recruitment to the site of inflammation is a key event in a variety of cardiovascular pathologies. Infiltrating neutrophils constitute the first line of defense that precedes a second wave of emigrating monocytes reinforcing the inflammatory reaction. The mechanisms initiating this sequential process remained largely obscure. APPROACH AND RESULTS: Using advanced in vivo microscopy and in vitro/ex vivo techniques, we identified individual spatiotemporal expression patterns of selectins and their principal interaction partners on neutrophils, resident/inflammatory monocytes, and endothelial cells. Coordinating the intraluminal trafficking of neutrophils and inflammatory monocytes to common sites of extravasation, selectins assign different sites to these immune cells for their initial interactions with the microvascular endothelium. Whereas constitutively expressed leukocyte L-selectin/CD62L and endothelial P-selectin/CD62P together with CD44 and P-selectin glycoprotein ligand-1/CD162 initiate the emigration of neutrophils, de novo synthesis of endothelial E-selectin/CD62E launches the delayed secondary recruitment of inflammatory monocytes. In this context, P-selectin/CD62P and L-selectin/CD62L together with P-selectin glycoprotein ligand-1/CD162 and CD44 were found to regulate the flux of rolling neutrophils and inflammatory monocytes, whereas E-selectin/CD62E selectively adjusts the rolling velocity of inflammatory monocytes. Moreover, selectins and their interaction partners P-selectin glycoprotein ligand-1/CD162 and CD44 differentially control the intraluminal crawling behavior of neutrophils and inflammatory monocytes collectively enabling the sequential extravasation of these immune cells to inflamed tissue. CONCLUSIONS: Our findings provide novel insights into the mechanisms initiating the sequential infiltration of the perivascular tissue by neutrophils and monocytes in the acute inflammatory response and might thereby contribute to the development of targeted therapeutic strategies for prevention and treatment of cardiovascular diseases.

Matrix metalloproteinases modulate ameboid-like migration of neutrophils through inflamed interstitial tissue.

In vitro studies suggest that leukocytes locomote in an ameboid fashion independently of pericellular proteolysis. Whether this motility pattern applies for leukocyte migration in inflamed tissue is still unknown. In vivo microscopy on the inflamed mouse cremaster muscle revealed that blockade of serine proteases or of matrix metalloproteinases (MMPs) significantly reduces intravascular accumulation and transmigration of neutrophils. Using a novel in vivo chemotaxis assay, perivenular microinjection of inflammatory mediators induced directional interstitial migration of neutrophils. Blockade of actin polymerization, but not of actomyosin contraction abolished neutrophil interstitial locomotion. Multiphoton laser scanning in vivo microscopy showed that the density of the interstitial collagen network increases in inflamed tissue, thereby providing physical guidance to infiltrating neutrophils. Although neutrophils locomote through the interstitium without pericellular collagen degradation, inhibition of MMPs, but not of serine proteases, diminished their polarization and interstitial locomotion. In this context, blockade of MMPs was found to modulate expression of adhesion/signaling molecules on neutrophils. Collectively, our data indicate that serine proteases are critical for neutrophil extravasation, whereas these enzymes are dispensable for neutrophil extravascular locomotion. By contrast, neutrophil interstitial migration strictly relies on actin polymerization and does not require the pericellular degradation of collagen fibers but is modulated by MMPs.

Tissue plasminogen activator promotes postischemic neutrophil recruitment via its proteolytic and nonproteolytic properties.

OBJECTIVE: 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. APPROACH AND RESULTS: 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. CONCLUSIONS: 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.

C-C motif chemokine CCL3 and canonical neutrophil attractants promote neutrophil extravasation through common and distinct mechanisms.

Initial observations suggested that C-C motif chemokines exclusively mediate chemotaxis of mononuclear cells. In addition, recent studies also implicated these chemotactic cytokines in the recruitment of neutrophils. The underlying mechanisms remained largely unknown. Using in vivo microscopy on the mouse cremaster muscle, intravascular adherence and subsequent paracellular transmigration of neutrophils elicited by the chemokine (C-C motif) ligand 3 (CCL3, synonym MIP-1α) were significantly diminished in mice with a deficiency of the chemokine (C-C motif) receptor 1 (Ccr1(-/-)) or 5 (Ccr5(-/-)). Using cell-transfer techniques, neutrophil responses required leukocyte CCR1 and nonleukocyte CCR5. Furthermore, neutrophil extravasation elicited by CCL3 was almost completely abolished on inhibition of G protein-receptor coupling and PI3Kγ-dependent signaling, while neutrophil recruitment induced by the canonical neutrophil attractants chemokine (C-X-C motif) ligand 1 (CXCL1, synonym KC) or the lipid mediator platetelet-activating factor (PAF) was only partially reduced. Moreover, Ab blockade of ß(2) integrins, of α(4) integrins, or of their putative counter receptors ICAM-1 and VCAM-1 significantly attenuated CCL3-, CXCL1-, or PAF-elicited intravascular adherence and paracellular transmigration of neutrophils. These data indicate that the C-C motif chemokine CCL3 and canonical neutrophil attractants exhibit both common and distinct mechanisms for the regulation of intravascular adherence and transmigration of neutrophils.

Carbon-based nanomaterials accelerate arteriolar thrombus formation in the murine microcirculation independently of their shape.

Although carbon-based nanomaterials (CBNs) have been shown to exert prothrombotic effects in microvessels, it is poorly understood whether CBNs also have the potential to interfere with the process of leukocyte-endothelial cell interactions and whether the shape of CBNs plays a role in these processes. Thus, the aim of this study was to compare the acute effects of two differently shaped CBNs, fiber-shaped single-walled carbon nanotubes (SWCNT) and spherical ultrafine carbon black (CB), on thrombus formation as well as on leukocyte-endothelial cell interactions and leukocyte transmigration in the murine microcirculation upon systemic administration in vivo. Systemic administration of both SWCNT and CB accelerated arteriolar thrombus formation at a dose of 1 mg kg(-1) body weight, whereas SWCNT exerted a prothrombotic effect also at a lower dose (0.1 mg kg(-1) body weight). In vitro, both CBNs induced P-selectin expression on human platelets and formation of platelet-granulocyte complexes. In contrast, injection of fiber-shaped SWCNT or of spherical CB did not induce leukocyte-endothelial cell interactions or leukocyte transmigration. In vitro, both CBNs slightly increased the expression of activation markers on human monocytes and granulocytes. These findings suggest that systemic administration of CBNs accelerates arteriolar thrombus formation independently of the CBNs' shape, but does not induce leukocyte-endothelial cell interactions or leukocyte transmigration.

Endogenous and exogenous pentraxin-3 limits postischemic acute and chronic kidney injury.

Ischemia-reperfusion activates innate immunity and sterile inflammation, resulting in acute kidney injury. Since pentraxin 3 (PTX3) regulates multiple aspects of innate immunity and tissue inflammation, we tested whether PTX3 would be involved in renal ischemia-reperfusion injury. Renal pedicle clamping increased PTX3 serum levels, as well as PTX3 expression, inside the kidney but predominantly in CD45/CD11c(+) cells, a subpopulation of intrarenal mononuclear phagocytes. Lack of PTX3 aggravated postischemic acute kidney injury as evidenced by massive tubular necrosis, and TNF and IL-6 release, as well as massively increased neutrophil and macrophage infiltrates at 24 h. This was followed by tubular atrophy, interstitial fibrosis, and kidney shrinking 10 weeks later. In vivo microscopy uncovered increased leukocyte adhesion and transmigration in postischemic microvessels of Ptx3-deficient mice. Furthermore, injection of recombinant PTX3 up to 6 h after reperfusion prevented renal leukocyte recruitment and postischemic kidney injury. Thus, local PTX3 release from a subpopulation of intrarenal mononuclear phagocytes or delayed PTX3 treatment limits postischemic renal inflammation. Conversely, Ptx3 loss-of-function mutations predispose to postischemic acute kidney injury and subsequent chronic kidney disease.

Histones from dying renal cells aggravate kidney injury via TLR2 and TLR4.

In AKI, dying renal cells release intracellular molecules that stimulate immune cells to secrete proinflammatory cytokines, which trigger leukocyte recruitment and renal inflammation. Whether the release of histones, specifically, from dying cells contributes to the inflammation of AKI is unknown. In this study, we found that dying tubular epithelial cells released histones into the extracellular space, which directly interacted with Toll-like receptor (TLR)-2 (TLR2) and TLR4 to induce MyD88, NF-κB, and mitogen activated protein kinase signaling. Extracellular histones also had directly toxic effects on renal endothelial cells and tubular epithelial cells in vitro. In addition, direct injection of histones into the renal arteries of mice demonstrated that histones induce leukocyte recruitment, microvascular vascular leakage, renal inflammation, and structural features of AKI in a TLR2/TLR4-dependent manner. Antihistone IgG, which neutralizes the immunostimulatory effects of histones, suppressed intrarenal inflammation, neutrophil infiltration, and tubular cell necrosis and improved excretory renal function. In summary, the release of histones from dying cells aggravates AKI via both its direct toxicity to renal cells and its proinflammatory effects. Because the induction of proinflammatory cytokines in dendritic cells requires TLR2 and TLR4, these results support the concept that renal damage triggers an innate immune response, which contributes to the pathogenesis of AKI.

A novel OSA-related model of intermittent hypoxia in endothelial cells under flow reveals pronounced inflammatory pathway activation.

Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder characterized by recurrent episodes of upper airway obstruction and subsequent hypoxia. In patients with OSA, severity and number of these hypoxic events positively correlate with the extent of associated cardiovascular pathology. The molecular mechanisms underlying intermittent hypoxia (IH)-driven cardiovascular disease in OSA, however, remain poorly understood-partly due to the lack of adequate experimental models. Here, we present a novel experimental approach that utilizes primary human endothelial cells cultivated under shear stress. Oxygen partial pressure dynamics were adopted in our in vitro model according to the desaturation-reoxygenation patterns identified in polysomnographic data of severe OSA patients (n = 10, with 892 severe desaturations, SpO2<80%). Using western blot analysis, we detected a robust activation of the two major inflammatory pathways ERK and NF-κB in endothelial cells, whereas no HIF1α and HIF2α protein stabilization was observed. In line with these findings, mRNA and protein expression of the pro-inflammatory adhesion and signaling molecule ICAM-1 and the chemokine CCL2 were significantly increased. Hence, we established a novel in vitro model for deciphering OSA-elicited effects on the vascular endothelium. First data obtained in this model point to the endothelial activation of pro-inflammatory rather than hypoxia-associated pathways in OSA. Future studies in this model might contribute to the development of targeted strategies against OSA-induced, secondary cardiovascular disease.

Vitronectin promotes immunothrombotic dysregulation in the venular microvasculature.

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.

Urokinase-type plasminogen activator promotes paracellular transmigration of neutrophils via Mac-1, but independently of urokinase-type plasminogen activator receptor.

BACKGROUND: Urokinase-type plasminogen activator (uPA) has recently been implicated in the pathogenesis of ischemia-reperfusion (I/R) injury. The underlying mechanisms remain largely unclear. METHODS AND RESULTS: Using in vivo microscopy on the mouse cremaster muscle, I/R-elicited firm adherence and transmigration of neutrophils were found to be significantly diminished in uPA-deficient mice and in mice treated with the uPA inhibitor WX-340, but not in uPA receptor (uPAR)-deficient mice. Interestingly, postischemic leukocyte responses were significantly reduced on blockade of the integrin CD11b/Mac-1, which also serves as uPAR receptor. Using a cell transfer technique, postischemic adherence and transmigration of wild-type leukocytes were significantly decreased in uPA-deficient animals, whereas uPA-deficient leukocytes exhibited a selectively reduced transmigration in wild-type animals. On I/R or stimulation with recombinant uPA, >90% of firmly adherent leukocytes colocalized with CD31-immunoreactive endothelial junctions as detected by in vivo fluorescence microscopy. In a model of hepatic I/R, treatment with WX-340 significantly attenuated postischemic neutrophil infiltration and tissue injury. CONCLUSIONS: Our data suggest that endothelial uPA promotes intravascular adherence, whereas leukocyte uPA facilitates the subsequent paracellular transmigration of neutrophils during I/R. This process is regulated via CD11b/Mac-1, and does not require uPAR. Pharmacological blockade of uPA interferes with these events and effectively attenuates postischemic tissue injury.