Endothelial PTP1B Deletion Promotes VWF Exocytosis and Venous Thromboinflammation

BACKGROUND

Endothelial activation promotes the release of procoagulant extracellular vesicles and inflammatory mediators from specialized storage granules. Endothelial membrane exocytosis is controlled by phosphorylation. We hypothesized that the absence of PTP1B (protein tyrosine phosphatase 1B) in endothelial cells promotes venous thromboinflammation by triggering endothelial membrane fusion and exocytosis.

METHODS

Mice with inducible endothelial deletion of PTP1B (End.PTP1B-KO) underwent inferior vena cava ligation to induce stenosis and venous thrombosis. Primary endothelial cells from transgenic mice and human umbilical vein endothelial cells were used for mechanistic studies.

RESULTS

Vascular ultrasound and histology showed significantly larger venous thrombi containing higher numbers of Ly6G (lymphocyte antigen 6 family member G)-positive neutrophils in mice with endothelial PTP1B deletion, and intravital microscopy confirmed the more pronounced neutrophil recruitment following inferior vena cava ligation. RT2 PCR profiler array and immunocytochemistry analysis revealed increased endothelial activation and adhesion molecule expression in primary End.PTP1B-KO endothelial cells, including CD62P (P-selectin) and VWF (von Willebrand factor). Pretreatment with the NF-κB (nuclear factor kappa B) kinase inhibitor BAY11-7082, antibodies neutralizing CD162 (P-selectin glycoprotein ligand-1) or VWF, or arginylglycylaspartic acid integrin-blocking peptides abolished the neutrophil adhesion to End.PTP1B-KO endothelial cells in vitro. Circulating levels of annexin V+ procoagulant endothelial CD62E+ (E-selectin) and neutrophil (Ly6G+) extracellular vesicles were also elevated in End.PTP1B-KO mice after inferior vena cava ligation. Higher plasma MPO (myeloperoxidase) and Cit-H3 (citrullinated histone-3) levels and neutrophil elastase activity indicated neutrophil activation and extracellular trap formation. Infusion of End.PTP1B-KO extracellular vesicles into C57BL/6J wild-type mice most prominently enhanced the recruitment of endogenous neutrophils, and this response was blunted in VWF-deficient mice or by VWF-blocking antibodies. Reduced PTP1B binding and tyrosine dephosphorylation of SNAP23 (synaptosome-associated protein 23) resulting in increased VWF exocytosis and neutrophil adhesion were identified as mechanisms, all of which could be restored by NF-κB kinase inhibition using BAY11-7082.

CONCLUSIONS

Our findings show that endothelial PTP1B deletion promotes venous thromboinflammation by enhancing SNAP23 phosphorylation, endothelial VWF exocytosis, and neutrophil recruitment.

Sterility testing of germ-free mouse colonies

In biomedical research, germ-free and gnotobiotic mouse models enable the mechanistic investigation of microbiota-host interactions and their role on (patho)physiology. Throughout any gnotobiotic experiment, standardized and periodic microbiological testing of defined gnotobiotic housing conditions is a key requirement. Here, we review basic principles of germ-free isolator technology, the suitability of various sterilization methods, and the use of sterility testing methods to monitor germ-free mouse colonies. We also discuss their effectiveness and limitations, and share the experience with protocols used in our facility. In addition, possible sources of isolator contamination are discussed and an overview of reported contaminants is provided.

Externalized histones fuel pulmonary fibrosis via a platelet-macrophage circuit of TGFβ1 and IL-27

Externalized histones erupt from the nucleus as extracellular traps, are associated with several acute and chronic lung disorders, but their implications in the molecular pathogenesis of interstitial lung disease are incompletely defined. To investigate the role and molecular mechanisms of externalized histones within the immunologic networks of pulmonary fibrosis, we studied externalized histones in human and animal bronchoalveolar lavage (BAL) samples of lung fibrosis. Neutralizing anti-histone antibodies were administered in bleomycin-induced fibrosis of C57BL/6 J mice, and subsequent studies used conditional/constitutive knockout mouse strains for TGFβ and IL-27 signaling along with isolated platelets and cultured macrophages. We found that externalized histones (citH3) were significantly (P < 0.01) increased in cell-free BAL fluids of patients with idiopathic pulmonary fibrosis (IPF; n = 29) as compared to healthy controls (n = 10). The pulmonary sources of externalized histones were Ly6G+CD11b+ neutrophils and nonhematopoietic cells after bleomycin in mice. Neutralizing monoclonal anti-histone H2A/H4 antibodies reduced the pulmonary collagen accumulation and hydroxyproline concentration. Histones activated platelets to release TGFβ1, which signaled through the TGFbRI/TGFbRII receptor complex on LysM+ cells to antagonize macrophage-derived IL-27 production. TGFβ1 evoked multiple downstream mechanisms in macrophages, including p38 MAPK, tristetraprolin, IL-10, and binding of SMAD3 to the IL-27 promotor regions. IL-27RA-deficient mice displayed more severe collagen depositions suggesting that intact IL-27 signaling limits fibrosis. In conclusion, externalized histones inactivate a safety switch of antifibrotic, macrophage-derived IL-27 by boosting platelet-derived TGFβ1. Externalized histones are accessible to neutralizing antibodies for improving the severity of experimental pulmonary fibrosis.

Animal and Cellular Models in Thrombosis and Hemostasis

STANDARDIZED IN VITRO AND IN VIVO MODEL SYSTEMS TO SIMPLIFY COMPLEXITY-THAT'S HOW WE LEARN: The discovery of new target molecules and translational progress in the development and refinement of antithrombotic therapies as well as the improved treatment of bleeding disorders strongly relies on standardized ex vivo and in vivo models that closely resemble the respective human pathologies. The standardization of these models requires sound training in specialized hemostasis and thrombosis research laboratories as well as a consistent daily routine. In this theme issue of Hämostaseologie-Progress in Haemostasis, four review articles cover key models that have proven instrumental to gain mechanistic insights on thrombogenesis and hemostatic processes. In recent decades, these models have moved our field forward and enabled translation across scales, from cell-based research to isolated flow chamber systems, to mouse thrombosis models reflecting the pathologic situations as observed in patients, to large animal models.

Gut Microbiota and the Microvasculature

The gut microbiota is increasingly recognized as an actuating variable shaping vascular development and endothelial cell function in the intestinal mucosa but also affecting the microvasculature of remote organs. In the small intestine, colonization with gut microbiota and subsequent activation of innate immune pathways promotes the development of intricate capillary networks and lacteals, influencing the integrity of the gut-vascular barrier as well as nutrient uptake. Since the liver yields most of its blood supply via the portal circulation, the hepatic microcirculation steadily encounters microbiota-derived patterns and active signaling metabolites that induce changes in the organization of the liver sinusoidal endothelium, influencing immune zonation of sinusoids and impacting on metabolic processes. In addition, microbiota-derived signals may affect the vasculature of distant organ systems such as the brain and the eye microvasculature. In recent years, this gut-resident microbial ecosystem was revealed to contribute to the development of several vascular disease phenotypes.

IL-17 Signaling in Keratinocytes Orchestrates the Defense against Staphylococcus aureus Skin Infection

Keratinocytes (KCs) form the outer epithelial barrier of the body, protecting against invading pathogens. Mice lacking the IL-17RA or both IL-17A and IL-17F develop spontaneous Staphylococcusaureus skin infections. We found a marked expansion of T17 cells, comprised of RORγt-expressing γδ T cells and T helper 17 cells in the skin-draining lymph nodes of these mice. Contradictory to previous suggestions, this expansion was not a result of a direct negative feedback loop because we found no expansion of T17 cells in mice lacking IL-17 signaling specifically in T cells. Instead, we found that the T17 expansion depended on the microbiota and was observed only when KCs were deficient for IL-17RA signaling. Indeed, mice that lack IL-17RA only in KCs showed an increased susceptibility to experimental epicutaneous infection with S. aureus together with an accumulation of IL-17A-producing γδ T cells. We conclude that deficiency of IL-17RA on KCs leads to microbiota dysbiosis in the skin, which triggers the expansion of IL-17A-producing T cells. Our data show that KCs are the primary target cells of IL-17A and IL-17F, coordinating the defense against microbial invaders in the skin.

Commensal bacteria weaken the intestinal barrier by suppressing epithelial neuropilin-1 and Hedgehog signaling

The gut microbiota influences intestinal barrier integrity through mechanisms that are incompletely understood. Here we show that the commensal microbiota weakens the intestinal barrier by suppressing epithelial neuropilin-1 (NRP1) and Hedgehog (Hh) signaling. Microbial colonization of germ-free mice dampens signaling of the intestinal Hh pathway through epithelial Toll-like receptor (TLR)-2, resulting in decreased epithelial NRP1 protein levels. Following activation via TLR2/TLR6, epithelial NRP1, a positive-feedback regulator of Hh signaling, is lysosomally degraded. Conversely, elevated epithelial NRP1 levels in germ-free mice are associated with a strengthened gut barrier. Functionally, intestinal epithelial cell-specific Nrp1 deficiency (Nrp1ΔIEC) results in decreased Hh pathway activity and a weakened gut barrier. In addition, Nrp1ΔIEC mice have a reduced density of capillary networks in their small intestinal villus structures. Collectively, our results reveal a role for the commensal microbiota and epithelial NRP1 signaling in the regulation of intestinal barrier function through postnatal control of Hh signaling.

Immunomodulation of neutrophil granulocyte functions by bacterial polyphosphates

Polyphosphates are highly conserved, linear polymers of monophosphates that reside in all living cells. Bacteria produce long chains containing hundreds to thousands of phosphate units, which can interfere with host defense to infection. Here, we report that intratracheal long-chain polyphosphate administration to C57BL/6J mice resulted in the release of proinflammatory cytokines and influx of Ly6G+ polymorphonuclear neutrophils in the bronchoalveolar lavage fluid causing a disruption of the physiologic endothelial-epithelial small airway barrier and histologic signs of lung injury. Polyphosphate-induced effects were attenuated after neutrophil depletion in mice. In isolated murine neutrophils, long-chain polyphosphates modulated cytokine release induced by lipopolysaccharides (LPS) from Gram-negative bacteria or lipoteichoic acid from Gram-positive bacteria. In addition, long-chain polyphosphates induced immune evasive effects in human neutrophils. In detail, long-chain polyphosphates downregulated CD11b and curtailed the phagocytosis of Escherichia coli particles by neutrophils. Polyphosphates modulated the migration capacity by inducing CD62L shedding resulting in CD62Llow and CD11blow neutrophils. The release of IL-8 induced by LPS was also significantly reduced. Pharmacologic blockade of PI3K with wortmannin antagonized long-chain polyphosphate-induced effects on LPS-induced IL-8 release. In conclusion, polyphosphates govern immunomodulation in murine and human neutrophils, suggesting polyphosphates as a therapeutic target for bacterial infections to restore innate immune defense.

Blood coagulation and beyond: Position paper from the Fourth Maastricht Consensus Conference on Thrombosis

The 4th Maastricht Consensus Conference on Thrombosis (MCCT), included the following themes: Theme 1: The "coagulome" as a critical driver of cardiovascular disease Blood coagulation proteins also play divergent roles in biology and pathophysiology, related to specific organs, including brain, heart, bone marrow and kidney. Four investigators shared their views on these organ-specific topics. Theme 2: Novel mechanisms of thrombosis Mechanisms linking factor XII to fibrin, including their structural and physical properties, contribute to thrombosis, which is also affected by variation in microbiome status. Virus infections associated-coagulopathies perturb the hemostatic balance resulting in thrombosis and/or bleeding. Theme 3: How to limit bleeding risks: insights from translational studies This theme included state of the art methodology for exploring the contribution of genetic determinants of a bleeding diathesis; determination of polymorphisms in genes that control the rate of metabolism by the liver of P2Y12 inhibitors, to improve safety of antithrombotic therapy. Novel reversal agents for direct oral anticoagulants are discussed. Theme 4: Hemostasis in extracorporeal systems: how to utilize ex vivo models? Perfusion flow chamber and nanotechnology developments are developed for studying bleeding and thrombosis tendencies. Vascularised organoids are utilized for disease modeling and drug development studies. Strategies for tackling extracorporeal membrane oxygenation (ECMO) associated coagulopathy are discussed. Theme 5: Clinical dilemmas in thrombosis and antithrombotic management Plenary presentations addressed controversial areas, ie thrombophilia testing, thrombosis risk assessment in hemophilia, novel antiplatelet strategies and clinically tested factor XI(a) inhibitors,both possibly with reduced bleeding risk. Finally, Covid-19 associated coagulopathy is revisited.

Bacterial polyphosphates induce CXCL4 and synergize with complement anaphylatoxin C5a in lung injury

Polyphosphates are linear polymers of inorganic phosphates that exist in all living cells and serve pleiotropic functions. Bacteria produce long-chain polyphosphates, which can interfere with host defense to infection. In contrast, short-chain polyphosphates are released from platelet dense granules and bind to the chemokine CXCL4. Here, we report that long-chain polyphosphates induced the release of CXCL4 from mouse bone marrow-derived macrophages and peritoneal macrophages in a dose-/time-dependent fashion resulting from an induction of CXCL4 mRNA. This polyphosphate effect was lost after pre-incubation with recombinant exopolyphosphatase (PPX) Fc fusion protein, demonstrating the potency of long chains over monophosphates and ambient cations. In detail, polyphosphate chains >70 inorganic phosphate residues were required to reliably induce CXCL4. Polyphosphates acted independently of the purinergic P2Y1 receptor and the MyD88/TRIF adaptors of Toll-like receptors. On the other hand, polyphosphates augmented LPS/MyD88-induced CXCL4 release, which was explained by intracellular signaling convergence on PI3K/Akt. Polyphosphates induced Akt phosphorylation at threonine-308. Pharmacologic blockade of PI3K (wortmannin, LY294002) antagonized polyphosphate-induced CXCL4 release from macrophages. Intratracheal polyphosphate administration to C57BL/6J mice caused histologic signs of lung injury, disruption of the endothelial-epithelial barrier, influx of Ly6G⁺ polymorphonuclear neutrophils, depletion of CD11c⁺SiglecF⁺ alveolar macrophages, and release of CXCL4. Long-chain polyphosphates synergized with the complement anaphylatoxin, C5a, which was partly explained by upregulation of C5aR1 on myeloid cells. C5aR1^-/- mice were protected from polyphosphate-induced lung injury. C5a generation occurred in the lungs and bronchoalveolar lavage fluid (BALF) of polyphosphate-treated C57BL/6J mice. In conclusion, we demonstrate that polyphosphates govern immunomodulation in macrophages and promote acute lung injury.

The Vitamin D Receptor–BIM Axis Overcomes Cisplatin Resistance in Head and Neck Cancer

Simple Summary

Treatment success of head and neck squamous cell carcinoma cancers (HNSCCs) is often hindered by cisplatin resistance. Vitamin D and its receptor (VDR) have been suggested to influence tumor pathobiology and therapy response. We found that VitD/analogs in combination with platinum-based drugs may help to fight therapy resistances in HNSCC. VitD/cisplatin combinations induced E-cadherin upregulation and killed cancer cells by increasing the expression of the pro-apoptotic protein BIM. By identifying the VDR/VitD/BIM axis, we here provide a molecular rationale for the anti-cancer activity of VitD/analogs in combination therapies, which should be further exploited in the clinics.

Abstract

Treatment success of head and neck squamous cell carcinoma (HNSCC) is often hindered by cisplatin resistance. As inherent and acquired therapy resistance counteracts improvement in long-term survival, novel multi-targeting strategies triggering cancer cell apoptosis are urgently required. Here, we identify the vitamin D receptor (VDR) as being significantly overexpressed in tumors of HNSCC patients (n = 604; p = 0.0059), correlating with tumor differentiation (p = 0.0002), HPV status (p = 0.00026), and perineural invasion (p = 0.0087). The VDR, a member of the nuclear receptor superfamily, is activated by its ligand vitamin D (VitD) and analogs, triggering multiple cellular responses. As we found that the VDR was also upregulated in our cisplatin-resistant HNSCC models, we investigated its effect on overcoming cisplatin resistance. We discovered that VitD/cisplatin combinations synergistically killed even cisplatin-resistant cells at clinically achievable levels. Similar results were obtained for the clinically used VitD analog Maxacalcitol. Moreover, VitD/cisplatin combinations inhibited tumor cell migration by E-cadherin upregulation. Signaling pathway analyses revealed that VitD co-treatments triggered cancer cell death by increasing the expression of the pro-apoptotic BCL-2 family protein BIM. BIM’s pro-apoptotic activity in HNSCC cells was confirmed by ectopic overexpression studies. Importantly, BIM expression is positively associated with HNSCC patients’ (n = 539) prognosis, as high expression correlated with improved survival (p = 0.0111), improved therapy response (p = 0.0026), and remission (p = 0.004). Collectively, by identifying, for the first time, the VDR/BIM axis, we here provide a molecular rationale for the reported anti-cancer activity of VitD/analogs in combination therapies. Our data also suggest its exploitation as a potential strategy to overcome cisplatin resistance in HNSCC and other malignancies by inducing additional pro-apoptotic pathways.

Conditional over-expression of heme-oxygenase 1 in myelomonocytic cells reduces hypertension and vascular inflammation

Background

Arterial hypertension is one of the most important modifiable risk factors for all-cause morbidity and mortality worldwide. Angiotensin II (Ang II) plays a pathogenic role in the development of hypertension, vascular dysfunction, inflammation and tissue damage. In the context of hypertension, heme-oxygenase 1 (HO-1) gene expression is upregulated as an antioxidant defense system in response to AngII through its action on heme catabolism, which generates carbon monoxide (CO), ferritin and biliverdin, which is reduced to bilirubin by biliverdin reductase A (BLVRA). Previous studies have shown the important role of HO-1 in the maturation and migration of immune cells. Myeloid HO-1 modulates macrophage polarization and protects against ischemia-reperfusion damage. However, the role of myeloid cell specific HO-1 in the detrimental effects of AngII induced vascular dysfunction has not yet been explored.

Objectives

To investigate the potential vascular protection of myeloid cell specific overexpression of HO-1 in AngII-induced arterial hypertension.

Methods

Hypertension was induced in 8–13 weeks old male mice with selective over-expression of HO-1 (HO-1indLysMcre) in myelomonocytic cells versus LysMCre/wt by AngII infusion (1mg/kg/d). Blood pressure was recorded by tail-cuff. Bilirubin levels were quantified in plasma by High Performance Liquid Chromatography (HPLC). The quantification of adherent and rolling leukocytes in carotid arteries was detected by intravital video microscopy (IVM). Endogenuos Thrombin potential (ETP) was measured in platelet rich plasma (PRP) and platelets poor plasma (PPP) by Calibrated Automated Thrombogram (CAT) assay. Endothelium-dependent vasodilation was assessed in isolated aortic rings by concentration-relaxation curves in response to acetylcholine (ACh).

Results

AngII-infused HO-1indLysMcre had decreased blood pressure values and improved endothelial function as compared to LysMcre controls. IVM revealed reduced leukocyte rolling and adhesion to the vascular endothelium in AngII infused HO-1indLysMcre mice compared to controls, paralleled by reduced expression of NOX-2 mediated oxidative stress and vascular inflammation in AngII-induced arterial hypertension by decreasing VCAM-1, CCR2 and MCP-1 expression. mRNA analysis revealed an increased expression of BLVRA in liver, spleen, heart and aortic tissues in response to AngII, which was higher in HO-1indLysMcre mice than in controls. By CAT assay we registered a decrease ETP in PPP and PRP in HO-1ind mice infused with AngII compatible with less abundance of inflammatory platelets, potentially regulated by BLVRA activity. This was supported by increased in bilirubin levels in response to AngII, which was higher in HO-1indLysMcre mice than in controls.

Conclusion

Myeloid cell specific overexpression of HO-1 confers anti-inflammatory protection to the vasculature in AngII induced hypertension. This effect is, at least in part, mediated by BLVRA.

Funding Acknowledgement

Type of funding sources: None.

Microbiota-derived tryptophan metabolites in vascular inflammation and cardiovascular disease

The essential amino acid tryptophan (Trp) is metabolized by gut commensals, yielding in compounds that affect innate immune cell functions directly, but also acting on the aryl hydrocarbon receptor (AHR), thus regulating the maintenance of group 3 innate lymphoid cells (ILCs), promoting T helper 17 (TH17) cell differentiation, and interleukin-22 production. In addition, microbiota-derived Trp metabolites have direct effects on the vascular endothelium, thus influencing the development of vascular inflammatory phenotypes. Indoxyl sulfate was demonstrated to promote vascular inflammation, whereas indole-3-propionic acid and indole-3-aldehyde had protective roles. Furthermore, there is increasing evidence for a contributory role of microbiota-derived indole-derivatives in blood pressure regulation and hypertension. Interestingly, there are indications for a role of the kynurenine pathway in atherosclerotic lesion development. Here, we provide an overview on the emerging role of gut commensals in the modulation of Trp metabolism and its influence in cardiovascular disease development.

Ethyl Hydroxyethyl Cellulose-A Biocompatible Polymer Carrier in Blood

The biocompatibility of carrier nanomaterials in blood is largely hampered by their activating or inhibiting role on the clotting system, which in many cases prevents safe intravascular application. Here, we characterized an aqueous colloidal ethyl hydroxyethyl cellulose (EHEC) solution and tested its effect on ex vivo clot formation, platelet aggregation, and activation by thromboelastometry, aggregometry, and flow cytometry. We compared the impact of EHEC solution on platelet aggregation with biocompatible materials used in transfusion medicine (the plasma expanders gelatin polysuccinate and hydroxyethyl starch). We demonstrate that the EHEC solution, in contrast to commercial products exhibiting Newtonian flow behavior, resembles the shear-thinning behavior of human blood. Similar to established nanomaterials that are considered biocompatible when added to blood, the EHEC exposure of resting platelets in platelet-rich plasma does not enhance tissue thromboplastin- or ellagic acid-induced blood clotting, or platelet aggregation or activation, as measured by integrin α_IIbβ₃ activation and P-selectin exposure. Furthermore, the addition of EHEC solution to adenosine diphosphate (ADP)-stimulated platelet-rich plasma does not affect the platelet aggregation induced by this agonist. Overall, our results suggest that EHEC may be suitable as a biocompatible carrier material in blood circulation and for applications in flow-dependent diagnostics.

A single-cell lung atlas of complement genes identifies the mesothelium and epithelium as prominent sources of extrahepatic complement proteins

To understand functional duality of the complement system in host defense and lung injury, a more comprehensive view of its localized production in the lung, and the impact of age on complement production are essential. Here, we explored the expression of complement genes through computational analysis of preexisting single cell RNA sequencing data from lung transcriptomes of healthy young (3 months) and old C57BL/6 mice (24 months), and humans. We characterized the distribution of 48 complement genes. Across 28 distinct immune and non-immune cell types in mice, mesothelial cells expressed the greatest number of complement genes (e.g., C1ra, C2, C3), and regulators (e.g., Serping1, Cfh). C5 was abundant in type II alveolar epithelial cells and C1q in interstitial lung macrophages. There were only moderate differences in gene expression between young and old mice. Among 57 human lung cell types, mesothelial cells showed abundant complement expression. A few differences in gene  expression (e.g., FCN1, CFI, C6, C7) were also evident between mice and human lung cells. Our findings present a novel perspective on the expression patterns of complement genes in normal lungs. These findings highlight the potential functions of complement in tissue-specific homeostasis and immunity and may foster a mechanistic understanding of its role in lung health and disease.

IL-27 Enhances γδ T Cell–Mediated Innate Resistance to Primary Hookworm Infection in the Lungs

IL-27 is a heterodimeric IL-12 family cytokine formed by noncovalent association of the promiscuous EBI3 subunit and selective p28 subunit. IL-27 is produced by mononuclear phagocytes and unfolds pleiotropic immune-modulatory functions through ligation to IL-27 receptor α (IL-27RA). Although IL-27 is known to contribute to immunity and to limit inflammation after various infections, its relevance for host defense against multicellular parasites is still poorly defined. Here, we investigated the role of IL-27 during infection with the soil-transmitted hookworm, Nippostrongylus brasiliensis, in its early host intrapulmonary life cycle. IL-27(p28) was detectable in bronchoalveolar lavage fluid of C57BL/6J wild-type mice on day 1 after s.c. inoculation. IL-27RA expression was most abundant on lung-invading γδ T cells. Il27ra^-/- mice showed increased lung parasite burden together with aggravated pulmonary hemorrhage and higher alveolar total protein leakage as a surrogate for epithelial-vascular barrier disruption. Conversely, injections of recombinant mouse (rm)IL-27 into wild-type mice reduced lung injury and parasite burden. In multiplex screens, higher airway accumulations of IL-6, TNF-α, and MCP-3 (CCL7) were observed in Il27ra^-/- mice, whereas rmIL-27 treatment showed a reciprocal effect. Importantly, γδ T cell numbers in airways were enhanced by endogenous or administered IL-27. Further analysis revealed a direct antihelminthic function of IL-27 on γδ T cells as adoptive intratracheal transfer of rmIL-27-treated γδ T cells during primary N. brasiliensis lung infection conferred protection in mice. In summary, this report demonstrates protective functions of IL-27 to control the early lung larval stage of hookworm infection.

Mechanistic Insights into Inorganic Nitrite-Mediated Vasodilation of Isolated Aortic Rings under Oxidative/Hypertensive Conditions and S-Nitros(yl)ation of Proteins in Germ-Free Mice

The prevalence and clinical importance of arterial hypertension are still growing. Inorganic nitrite (NO₂^-) represents an attractive dietary antihypertensive agent, but its metabolism and mode of action, which we aimed to investigate with the present study, are not completely understood. Isolated aortic rings from rats were treated ex vivo with oxidants, and rats were infused in vivo with angiotensin-II. Vascular responses to acetylcholine (ACh) and nitrite were assessed by isometric tension recording. The loss of vasodilatory potency in response to oxidants was much more pronounced for ACh as compared to nitrite ex vivo (but not in vivo with angiotensin-II). This effect may be caused by the redox regulation of conversion to xanthine oxidase (XO). Conventionally raised and germ-free mice were treated with nitrite by gavage, which did not improve ACh-mediated vasodilation, but did increase the plasma levels of S-nitros(yl)ated proteins in the conventionally-raised, but not in the germ-free mice. In conclusion, inorganic nitrite represents a dietary drug option to treat arterial hypertension in addition to already established pharmacological treatment. Short-term oxidative stress did not impair the vasodilatory properties of nitrite, which may be beneficial in cardiovascular disease patients. The gastrointestinal microbiome appears to play a key role in nitrite metabolism and bioactivation.

Targeting Cancer Chemotherapy Resistance by Precision Medicine-Driven Nanoparticle-Formulated Cisplatin

Therapy resistance is the major cause of cancer death. As patients respond heterogeneously, precision/personalized medicine needs to be considered, including the application of nanoparticles (NPs). The success of therapeutic NPs requires to first identify clinically relevant resistance mechanisms and to define key players, followed by a rational design of biocompatible NPs capable to target resistance. Consequently, we employed a tiered experimental pipeline from in silico to analytical and in vitro to overcome cisplatin resistance. First, we generated cisplatin-resistant cancer cells and used next-generation sequencing together with CRISPR/Cas9 knockout technology to identify the ion channel LRRC8A as a critical component for cisplatin resistance. LRRC8A's cisplatin-specificity was verified by testing free as well as nanoformulated paclitaxel or doxorubicin. The clinical relevance of LRRC8A was demonstrated by its differential expression in a cohort of 500 head and neck cancer patients, correlating with patient survival under cisplatin therapy. To overcome LRRC8A-mediated cisplatin resistance, we constructed cisplatin-loaded, polysarcosine-based core cross-linked polymeric NPs (NP_Cis, Ø ∼ 28 nm) with good colloidal stability, biocompatibility (low immunogenicity, low toxicity, prolonged in vivo circulation, no complement activation, no plasma protein aggregation), and low corona formation properties. 2D/3D-spheroid cell models were employed to demonstrate that, in contrast to standard of care cisplatin, NP_Cis significantly (p < 0.001) eradicated all cisplatin-resistant cells by circumventing the LRRC8A-transport pathway via the endocytic delivery route. We here identified LRRC8A as critical for cisplatin resistance and suggest LRRC8A-guided patient stratification for ongoing or prospective clinical studies assessing therapy resistance to nanoscale platinum drug nanoformulations versus current standard of care formulations.

The gut microbiota instructs the hepatic endothelial cell transcriptome

The gut microbiota affects remote organ functions but its impact on organotypic endothelial cell (EC) transcriptomes remains unexplored. The liver endothelium encounters microbiota-derived signals and metabolites via the portal circulation. To pinpoint how gut commensals affect the hepatic sinusoidal endothelium, a magnetic cell sorting protocol, combined with fluorescence-activated cell sorting, was used to isolate hepatic sinusoidal ECs from germ-free (GF) and conventionally raised (CONV-R) mice for transcriptome analysis by RNA sequencing. This resulted in a comprehensive map of microbiota-regulated hepatic EC-specific transcriptome profiles. Gene Ontology analysis revealed that several functional processes in the hepatic endothelium were affected. The absence of microbiota influenced the expression of genes involved in cholesterol flux and angiogenesis. Specifically, genes functioning in hepatic endothelial sphingosine metabolism and the sphingosine-1-phosphate pathway showed drastically increased expression in the GF state. Our analyses reveal a prominent role for the microbiota in shaping the transcriptional landscape of the hepatic endothelium.

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Germ-free mice show transcriptome differences in the liver sinusoidal endothelium

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Gut microbiota suppresses sphingolipid metabolism in the hepatic sinusoidal endothelium

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Cholesterol flux and angiogenesis in liver endothelium is microbiota-regulated

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Bacteroides thetaiotaomicron did not affect expression levels of the identified genes

Colonization with Altered Schaedler Flora Impacts Leukocyte Adhesion in Mesenteric Ischemia-Reperfusion Injury

The microbiota impacts mesenteric ischemia-reperfusion injury, aggravating the interaction of leukocytes with endothelial cells in mesenteric venules. The role of defined gut microbiomes in this life-threatening pathology is unknown. To investigate how a defined model microbiome affects the adhesion of leukocytes in mesenteric ischemia-reperfusion, we took advantage of gnotobiotic isolator technology and transferred altered Schaedler flora (ASF) from C3H/HeNTac to germ-free C57BL/6J mice. We were able to detect all eight bacterial taxa of ASF in fecal samples of colonized C57BL/6J mice by PCR. Applying qRT-PCR for quantification of species-specific 16S rDNA sequences of ASF bacteria, we found a major shift in the abundance of ASF 500, which was greater in C57BL/6J mice relative to the C3H/HeNTac founder breeding pair. Using high-speed epifluorescence intravital microscopy to visualize the venules of the small bowel mesentery, we found that gnotobiotic ASF-colonized mice showed reduced leukocyte adherence, both pre- and post-ischemia. Relative to germ-free mice, the counts of adhering leukocytes were increased pre-ischemia but did not significantly increase in ASF-colonized mice in the post-ischemic state. Collectively, our results suggest a protective role of the minimal microbial consortium ASF in mesenteric ischemia-reperfusion injury.

IL-17 controls central nervous system autoimmunity through the intestinal microbiome

Interleukin-17A- (IL-17A) and IL-17F-producing CD4⁺ T helper cells (T_H17 cells) are implicated in the development of chronic inflammatory diseases, such as multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). T_H17 cells also orchestrate leukocyte invasion of the central nervous system (CNS) and subsequent tissue damage. However, the role of IL-17A and IL-17F as effector cytokines is still confused with the encephalitogenic function of the cells that produce these cytokines, namely, T_H17 cells, fueling a long-standing debate in the neuroimmunology field. Here, we demonstrated that mice deficient for IL-17A/F lose their susceptibility to EAE, which correlated with an altered composition of their gut microbiota. However, loss of IL-17A/F in T_H cells did not diminish their encephalitogenic capacity. Reconstitution of a wild-type-like intestinal microbiota or reintroduction of IL-17A specifically into the gut epithelium of IL-17A/F-deficient mice reestablished their susceptibility to EAE. Thus, our data demonstrated that IL-17A and IL-17F are not encephalitogenic mediators but rather modulators of intestinal homeostasis that indirectly alter CNS-directed autoimmunity.

Co-option of Neutrophil Fates by Tissue Environments

Classically considered short-lived and purely defensive leukocytes, neutrophils are unique in their fast and moldable response to stimulation. This plastic behavior may underlie variable and even antagonistic functions during inflammation or cancer, yet the full spectrum of neutrophil properties as they enter healthy tissues remains unexplored. Using a new model to track neutrophil fates, we found short but variable lifetimes across multiple tissues. Through analysis of the receptor, transcriptional, and chromatin accessibility landscapes, we identify varying neutrophil states and assign non-canonical functions, including vascular repair and hematopoietic homeostasis. Accordingly, depletion of neutrophils compromised angiogenesis during early age, genotoxic injury, and viral infection, and impaired hematopoietic recovery after irradiation. Neutrophils acquired these properties in target tissues, a process that, in the lungs, occurred in CXCL12-rich areas and relied on CXCR4. Our results reveal that tissues co-opt neutrophils en route for elimination to induce programs that support their physiological demands.

Germ-free housing conditions do not affect aortic root and aortic arch lesion size of late atherosclerotic low-density lipoprotein receptor-deficient mice

The microbiota has been linked to the development of atherosclerosis, but the functional impact of these resident bacteria on the lesion size and cellular composition of atherosclerotic plaques in the aorta has never been experimentally addressed with the germ-free low-density lipoprotein receptor-deficient (Ldlr^-/- ) mouse atherosclerosis model. Here, we report that 16 weeks of high-fat diet (HFD) feeding of hypercholesterolemic Ldlr^-/- mice at germ-free (GF) housing conditions did not impact relative aortic root plaque size, macrophage content, and necrotic core area. Likewise, we did not find changes in the relative aortic arch lesion size. However, late atherosclerotic GF Ldlr^-/- mice had altered inflammatory plasma protein markers and reduced smooth muscle cell content in their atherosclerotic root plaques relative to CONV-R Ldlr^-/- mice. Neither absolute nor relative aortic root or aortic arch plaque size correlated with age. Our analyses on GF Ldlr^-/- mice did not reveal a significant contribution of the microbiota in late aortic atherosclerosis.

The Commensal Microbiota Enhances ADP-Triggered Integrin αIIbβ3 Activation and von Willebrand Factor-Mediated Platelet Deposition to Type I Collagen

The commensal microbiota is a recognized enhancer of arterial thrombus growth. While several studies have demonstrated the prothrombotic role of the gut microbiota, the molecular mechanisms promoting arterial thrombus growth are still under debate. Here, we demonstrate that germ-free (GF) mice, which from birth lack colonization with a gut microbiota, show diminished static deposition of washed platelets to type I collagen compared with their conventionally raised (CONV-R) counterparts. Flow cytometry experiments revealed that platelets from GF mice show diminished activation of the integrin α_IIbβ₃ (glycoprotein IIbIIIa) when activated by the platelet agonist adenosine diphosphate (ADP). Furthermore, washed platelets from Toll-like receptor-2 (Tlr2)-deficient mice likewise showed impaired static deposition to the subendothelial matrix component type I collagen compared with wild-type (WT) controls, a process that was unaffected by GPIbα-blockade but influenced by von Willebrand factor (VWF) plasma levels. Collectively, our results indicate that microbiota-triggered steady-state activation of innate immune pathways via TLR2 enhances platelet deposition to subendothelial matrix molecules. Our results link host colonization status with the ADP-triggered activation of integrin α_IIbβ₃, a pathway promoting platelet deposition to the growing thrombus.

ECITTS: An Integrated Approach to the Application of In Vitro Test Systems to the Hazard Assessment of Chemicals,

As a result of a workshop held at Täljöviken, Åkersberga, Sweden, on 27–29 May 1991, a multicentre collaborative research project was established, with the purpose of developing the concept of integrated in vitro toxicity testing. The first priority was the selection of tests within eight appropriate areas: basal cytotoxicity, irritancy, developmental toxicity, hepatotoxicity, nephrotoxicity, immunotoxicity, neurotoxicity and biokinetics. An ideal battery of tests for each area was identified. Since it was realised that it would not be feasible to include the full ideal list of tests in the project, a minimum test list was also agreed. For each area, ten calibration chemicals were selected. From these 80 compounds, 30 were selected for inclusion, together with 20 of the OECD test programme chemicals, in a first test set of chemicals. The toxicity of these 50 test set chemicals will be investigated in the minimum integrated test scheme.

The aim of the project is to employ non-animal methods to assess the toxicological properties of chemicals, and to improve this assessment through the use of knowledge about mechanisms of toxic action. The information produced will contribute to the establishment of a more-scientific and more-efficient toxicological procedure for hazard assessment. Questions concerning which parameters need to be investigated and combined to make hazard assessments, and which parameters relevant to in vivo toxicity can be determined in non-whole animal test systems, will also be addressed.

Bacterial polyphosphates interfere with the innate host defense to infection

Polyphosphates are linear polymers and ubiquitous metabolites. Bacterial polyphosphates are long chains of hundreds of phosphate units. Here, we report that mouse survival of peritoneal Escherichia coli sepsis is compromised by long-chain polyphosphates, and improves with bacterial polyphosphatekinase deficiency or neutralization using recombinant exopolyphosphatase. Polyphosphate activities are chain-length dependent, impair pathogen clearance, antagonize phagocyte recruitment, diminish phagocytosis and decrease production of iNOS and cytokines. Macrophages bind and internalize polyphosphates, in which their effects are independent of P2Y1 and RAGE receptors. The M1 polarization driven by E. coli derived LPS is misdirected by polyphosphates in favor of an M2 resembling phenotype. Long-chain polyphosphates modulate the expression of more than 1800 LPS/TLR4-regulated genes in macrophages. This interference includes suppression of hundreds of type I interferon-regulated genes due to lower interferon production and responsiveness, blunted STAT1 phosphorylation and reduced MHCII expression. In conclusion, prokaryotic polyphosphates disturb multiple macrophage functions for evading host immunity.

Gut Microbiota Restricts NETosis in Acute Mesenteric Ischemia-Reperfusion Injury

OBJECTIVE

Recruitment of neutrophils and formation of neutrophil extracellular traps (NETs) contribute to lethality in acute mesenteric infarction. To study the impact of the gut microbiota in acute mesenteric infarction, we used gnotobiotic mouse models to investigate whether gut commensals prime the reactivity of neutrophils towards formation of neutrophil extracellular traps (NETosis). Approach and Results: We applied a mesenteric ischemia-reperfusion (I/R) injury model to germ-free (GF) and colonized C57BL/6J mice. By intravital imaging, we quantified leukocyte adherence and NET formation in I/R-injured mesenteric venules. Colonization with gut microbiota or monocolonization with Escherichia coli augmented the adhesion of leukocytes, which was dependent on the TLR4 (Toll-like receptor-4)/TRIF (TIR-domain-containing adapter-inducing interferon-β) pathway. Although neutrophil accumulation was decreased in I/R-injured venules of GF mice, NETosis following I/R injury was significantly enhanced compared with conventionally raised mice or mice colonized with the minimal microbial consortium altered Schaedler flora. Also ex vivo, neutrophils from GF and antibiotic-treated mice showed increased LPS (lipopolysaccharide)-induced NETosis. Enhanced TLR4 signaling in GF neutrophils was due to elevated TLR4 expression and augmented IRF3 (interferon regulatory factor-3) phosphorylation. Likewise, neutrophils from antibiotic-treated conventionally raised mice had increased NET formation before and after ischemia. Increased NETosis in I/R injury was abolished in conventionally raised mice deficient in the TLR adaptor TRIF. In support of the desensitizing influence of enteric LPS, treatment of GF mice with LPS via drinking water diminished LPS-induced NETosis in vitro and in the mesenteric I/R injury model.

CONCLUSIONS

Collectively, our results identified that the gut microbiota suppresses NETing neutrophil hyperreactivity in mesenteric I/R injury, while ensuring immunovigilance by enhancing neutrophil recruitment.

Microbiota-Induced Type I Interferons Instruct a Poised Basal State of Dendritic Cells

Environmental signals shape host physiology and fitness. Microbiota-derived cues are required to program conventional dendritic cells (cDCs) during the steady state so that they can promptly respond and initiate adaptive immune responses when encountering pathogens. However, the molecular underpinnings of microbiota-guided instructive programs are not well understood. Here, we report that the indigenous microbiota controls constitutive production of type I interferons (IFN-I) by plasmacytoid DCs. Using genome-wide analysis of transcriptional and epigenetic regulomes of cDCs from germ-free and IFN-I receptor (IFNAR)-deficient mice, we found that tonic IFNAR signaling instructs a specific epigenomic and metabolic basal state that poises cDCs for future pathogen combat. However, such beneficial biological function comes with a trade-off. Instructed cDCs can prime T cell responses against harmless peripheral antigens when removing roadblocks of peripheral tolerance. Our data provide fresh insights into the evolutionary trade-offs that come with successful adaptation of vertebrates to their microbial environment.

Bacterial Polyphosphates Modulate Macrophage Responses to Infection

Polyphosphates are linear polymers of inorganic monophosphate residues (Pi) and these ancient metabolites exist in all living cells. In bacteria, polyphosphate kinases (PPK) and polyphosphatases (PPX) control the accumulation of polyphosphates from ATP as long chains (&gt;300–1000 Pi) for energy storage and prokaryotic homeostasis.

Here, we demonstrate that bacterial (long-chain) polyphosphates bound and were internalized by mouse macrophages. Long-chain polyphosphates modulated the expression of more than 1,800 LPS/TLR4-regulated genes in macrophages. This interference by polyphosphates included antagonism of hundreds of interferon-regulated genes as explained by reduced interferon-β release and responsiveness, reduced phosphorylation of STAT1 and diminished major histocompatibility complex II. Polyphosphates also prevented the LPS/TLR4-induced induction of NOS2 and M1 polarization. In C57BL/6J mice infected with live E. coli, PPK deficiency or polyphosphate neutralization using recombinant PPX resulted in better survival rates, amplified macrophage recruitment and improved pathogen clearance.

In conclusion, bacterial polyphosphate metabolites interfere with macrophage responses and the manipulation of such interactions could help to restore immunity to infection.

α-Linolenic Acid-Rich Diet Influences Microbiota Composition and Villus Morphology of the Mouse Small Intestine

α-Linolenic acid (ALA) is well-known for its anti-inflammatory activity. In contrast, the influence of an ALA-rich diet on intestinal microbiota composition and its impact on small intestine morphology are not fully understood. In the current study, we kept adult C57BL/6J mice for 4 weeks on an ALA-rich or control diet. Characterization of the microbial composition of the small intestine revealed that the ALA diet was associated with an enrichment in Prevotella and Parabacteroides. In contrast, taxa belonging to the Firmicutes phylum, including Lactobacillus, Clostridium cluster XIVa, Lachnospiraceae and Streptococcus, had significantly lower abundance compared to control diet. Metagenome prediction indicated an enrichment in functional pathways such as bacterial secretion system in the ALA group, whereas the two-component system and ALA metabolism pathways were downregulated. We also observed increased levels of ALA and its metabolites eicosapentanoic and docosahexanoic acid, but reduced levels of arachidonic acid in the intestinal tissue of ALA-fed mice. Furthermore, intestinal morphology in the ALA group was characterized by elongated villus structures with increased counts of epithelial cells and reduced epithelial proliferation rate. Interestingly, the ALA diet reduced relative goblet and Paneth cell counts. Of note, high-fat Western-type diet feeding resulted in a comparable adaptation of the small intestine. Collectively, our study demonstrates the impact of ALA on the gut microbiome and reveals the nutritional regulation of gut morphology.

A holobiont view on thrombosis: unravelling the microbiota's influence on arterial thrombus growth

The commensal microbiota has co-evolved with its host, colonizing all body surfaces. Therefore, this microbial ecosystem is intertwined with host physiology at multiple levels. While it is evident that microbes that reach the blood stream can trigger thrombus formation, it remains poorly explored if the wealth of microbes that colonize the body surfaces of the mammalian host can be regarded as a modifier of cardiovascular disease (CVD) development. To experimentally address the microbiota's role in the development of atherosclerotic lesions and arterial thrombosis, we generated a germ-free (GF) low-density lipoprotein receptor-deficient (Ldlr^−/−) atherosclerosis mouse model (Kiouptsi et al., mBio, 2019) and explored the role of nutritional composition on arterial thrombogenesis.

Physiological Roles of the von Willebrand Factor-Factor VIII Interaction

Von Willebrand factor (VWF) and coagulation factor VIII (FVIII) circulate as a complex in plasma and have a major role in the hemostatic system. VWF has a dual role in hemostasis. It promotes platelet adhesion by anchoring the platelets to the subendothelial matrix of damaged vessels and it protects FVIII from proteolytic degradation. Moreover, VWF is an acute phase protein that has multiple roles in vascular inflammation and is massively secreted from Weibel-Palade bodies upon endothelial cell activation. Activated FVIII on the other hand, together with coagulation factor IX forms the tenase complex, an essential feature of the propagation phase of coagulation on the surface of activated platelets. VWF deficiency, either quantitative or qualitative, results in von Willebrand disease (VWD), the most common bleeding disorder. The deficiency of FVIII is responsible for Hemophilia A, an X-linked bleeding disorder. Here, we provide an overview on the role of the VWF-FVIII interaction in vascular physiology.

Evaluation of blood collection methods and anticoagulants for platelet function analyses on C57BL/6J laboratory mice

The exploration of thrombotic mechanisms relies on the application of blood collection methods from laboratory mice with a minimal pre-activation of platelets and the clotting system. So far, very little is known on how the blood collection method and the anticoagulant used influence pre-activation of mouse platelets and coagulation. To determine the most suitable blood collection method, we systematically compared blood collection by heart puncture, Vena cava puncture, and puncture of the retro-orbital vein plexus and the use of citrate, heparin, and EDTA as frequently used anticoagulants with regard to platelet activation and whole blood clotting parameters. The activation of platelet-rich plasma diluted in Tyrode's buffer was analyzed by flow cytometry, analyzing the exposure of P-selectin and activated integrin α_IIbβ₃. Clotting of whole blood was profiled by thrombelastometry. Puncture of the retro-orbital vein plexus by plastic capillaries is not superior in terms of blood volume and platelet pre-activation, whereas heart puncture and Vena cava puncture resulted in similarly high blood volumes. Cardiac puncture and Vena cava puncture did not result in pre-activated platelets with citrate as an anticoagulant, but the use of EDTA resulted in increased levels of integrin α_IIbβ₃ activation. Puncture of the retro-orbital vein plexus by plastic capillaries resulted in increased platelet integrin α_IIbβ₃ activation, which could be prevented by soaking with citrate or coating with heparin. Further, activation of coagulation in citrated whole blood by puncture of the retro-orbital vein plexus using a blunt plastic capillary was observed by thromboelastometry. The use of citrate is the optimal anticoagulant in mouse platelet assays. Blood collections from the heart or Vena cava represent reliable alternatives to retro-orbital puncture of the vein plexus to avoid pre-activation of platelets and coagulation.

Protease-activated receptor signaling in intestinal permeability regulation

Protease-activated receptors (PARs) are a unique class of G-protein-coupled transmembrane receptors, which revolutionized the perception of proteases from degradative enzymes to context-specific signaling factors. Although PARs are traditionally known to affect several vascular responses, recent investigations have started to pinpoint the functional role of PAR signaling in the gastrointestinal (GI) tract. This organ is exposed to the highest number of proteases, either from the gut lumen or from the mucosa. Luminal proteases include the host's digestive enzymes and the proteases released by the commensal microbiota, while mucosal proteases entail extravascular clotting factors and the enzymes released from resident and infiltrating immune cells. Active proteases and, in case of a disrupted gut barrier, even entire microorganisms are capable to translocate the intestinal epithelium, particularly under inflammatory conditions. Especially PAR-1 and PAR-2, expressed throughout the GI tract, impact gut permeability regulation, a major factor affecting intestinal physiology and metabolic inflammation. In addition, PARs are critically involved in the onset of inflammatory bowel diseases, irritable bowel syndrome, and tumor progression. Due to the number of proteases involved and the multiple cell types affected, selective regulation of intestinal PARs represents an interesting therapeutic strategy. The analysis of tissue/cell-specific knockout animal models will be of crucial importance to unravel the intrinsic complexity of this signaling network. Here, we provide an overview on the implication of PARs in intestinal permeability regulation under physiologic and disease conditions.

Antibiotic Treatment Protocols and Germ-Free Mouse Models in Vascular Research

The gut microbiota influence host vascular physiology locally in the intestine, but also evoke remote effects that impact distant organ functions. Amongst others, the microbiota affect intestinal vascular remodeling, lymphatic development, cardiac output and vascular function, myelopoiesis, prothrombotic platelet function, and immunovigilance of the host. Experimentally, host-microbiota interactions are investigated by working with animals devoid of symbiotic bacteria, i.e., by the decimation of gut commensals by antibiotic administration, or by taking advantage of germ-free mouse isolator technology. Remarkably, some of the vascular effects that were unraveled following antibiotic treatment were not observed in the germ-free animal models and vice versa. In this review, we will dissect the manifold influences that antibiotics have on the cardiovascular system and their effects on thromboinflammation.

Flexure-tuned membrane-at-the-edge optomechanical system

We introduce a passively-aligned, flexure-tuned cavity optomechanical system in which a membrane is positioned microns from one end mirror of a Fabry-Perot optical cavity. By displacing the membrane through gentle flexure of its silicon supporting frame (i.e., to ∼80 m radius of curvature (ROC)), we gain access to the full range of available optomechanical couplings, finding also that the optical spectrum exhibits none of the abrupt discontinuities normally found in "membrane-in-the-middle" (MIM) systems. More aggressive flexure (3 m ROC) enables >15 μm membrane travel, milliradian tilt tuning, and a wavelength-scale (1.64 ± 0.78 μm) membrane-mirror separation. We also provide a complete set of analytical expressions for this system's leading-order dispersive and dissipative optomechanical couplings. Notably, this system can potentially generate orders of magnitude larger linear dissipative or quadratic dispersive strong coupling parameters than is possible with a MIM system. Additionally, it can generate the same purely quadratic dispersive coupling as a MIM system, but with significantly suppressed linear dissipative back-action (and force noise).