Neutrophils promote venular thrombosis by shaping the rheological environment for platelet aggregation.

In advanced inflammatory disease, microvascular thrombosis leads to the interruption of blood supply and provokes ischemic tissue injury. Recently, intravascularly adherent leukocytes have been reported to shape the blood flow in their immediate vascular environment. Whether these rheological effects are relevant for microvascular thrombogenesis remains elusive. Employing multi-channel in vivo microscopy, analyses in microfluidic devices, and computational modeling, we identified a previously unanticipated role of leukocytes for microvascular clot formation in inflamed tissue. For this purpose, neutrophils adhere at distinct sites in the microvasculature where these immune cells effectively promote thrombosis by shaping the rheological environment for platelet aggregation. In contrast to larger (lower-shear) vessels, this process in high-shear microvessels does not require fibrin generation or extracellular trap formation, but involves GPIbα-vWF and CD40-CD40L-dependent platelet interactions. Conversely, interference with these cellular interactions substantially compromises microvascular clotting. Thus, leukocytes shape the rheological environment in the inflamed venular microvasculature for platelet aggregation thereby effectively promoting the formation of blood clots. Targeting this specific crosstalk between the immune system and the hemostatic system might be instrumental for the prevention and treatment of microvascular thromboembolic pathologies, which are inaccessible to invasive revascularization strategies.

Artery-Associated Sympathetic Innervation Drives Rhythmic Vascular Inflammation of Arteries and Veins.

BACKGROUND: The incidence of acute cardiovascular complications is highly time-of-day dependent. However, the mechanisms driving rhythmicity of ischemic vascular events are unknown. Although enhanced numbers of leukocytes have been linked to an increased risk of cardiovascular complications, the role that rhythmic leukocyte adhesion plays in different vascular beds has not been studied. METHODS: We evaluated leukocyte recruitment in vivo by using real-time multichannel fluorescence intravital microscopy of a tumor necrosis factor-α-induced acute inflammation model in both murine arterial and venous macrovasculature and microvasculature. These approaches were complemented with genetic, surgical, and pharmacological ablation of sympathetic nerves or adrenergic receptors to assess their relevance for rhythmic leukocyte adhesion. In addition, we genetically targeted the key circadian clock gene Bmal1 (also known as Arntl) in a lineage-specific manner to dissect the importance of oscillations in leukocytes and components of the vessel wall in this process. RESULTS: In vivo quantitative imaging analyses of acute inflammation revealed a 24-hour rhythm in leukocyte recruitment to arteries and veins of the mouse macrovasculature and microvasculature. Unexpectedly, although in arteries leukocyte adhesion was highest in the morning, it peaked at night in veins. This phase shift was governed by a rhythmic microenvironment and a vessel type-specific oscillatory pattern in the expression of promigratory molecules. Differences in cell adhesion molecules and leukocyte adhesion were ablated when disrupting sympathetic nerves, demonstrating their critical role in this process and the importance of ß2-adrenergic receptor signaling. Loss of the core clock gene Bmal1 in leukocytes, endothelial cells, or arterial mural cells affected the oscillations in a vessel type-specific manner. Rhythmicity in the intravascular reactivity of adherent leukocytes resulted in increased interactions with platelets in the morning in arteries and in veins at night with a higher predisposition to acute thrombosis at different times as a consequence. CONCLUSIONS: Together, our findings point to an important and previously unrecognized role of artery-associated sympathetic innervation in governing rhythmicity in vascular inflammation in both arteries and veins and its potential implications in the occurrence of time-of-day-dependent vessel type-specific thrombotic events.

Vitronectin promotes the vascularization of porous polyethylene biomaterials.

Rapid implant vascularization is a prerequisite for successful biomaterial engraftment. Vitronectin (VN) is a matricellular glycoprotein well known for its capability to interact with growth factors, proteases, and protease inhibitors/receptors. Since such proteins are highly relevant for angiogenic processes, we hypothesized that VN contributes to the tissue integration of biomaterials. Employing different in vivo and ex vivo microscopy techniques, engraftment of porous polyethylene (PPE) implants was analyzed in the dorsal skinfold chamber model in wild-type (WT) and VN-/- mice. Upon PPE implantation, vascularization of this biomaterial was severely compromised in animals lacking this matricellular protein. Proteome profiling revealed that VN deficiency does not cause major changes in angiogenic protein composition in the implants suggesting that VN promotes PPE vascularization via mechanisms modulating the activity of angiogenic factors rather than by directly enriching them in the implant. Consequently, surface coating with recombinant VN (embedded in Matrigel®) accelerated implant vascularization in WT mice by enhancing the maturation of a vascular network. Thus, VN contributes to the engraftment of PPE implants by promoting the vascularization of this biomaterial. Surface coating with VN might provide a promising strategy to improve the vascularization of PPE implants without affecting the host's integrity. STATEMENT OF SIGNIFICANCE: Porous polyethylene (PPE) is a biomaterial frequently used in reconstructive surgery. The proper vascularization of PPE implants is a fundamental prerequisite for its successful engraftment in host tissue. Although the overall biocompatibility of PPE is good, there are less favorable application sites for its use in tissue reconstruction mostly characterized by low blood supply. Employing advanced in vivo microscopy methods and proteomic analyses in genetically engineered mice, we here describe a previously unrecognized function of vitronectin (VN) that enables this abundantly present glycoprotein to particularly promote the vascularization of PPE biomaterial. These properties of VN specifically facilitate the formation of a dense vessel network within the implant which relies on modulating the activity of angiogenic mediators rather than on the enrichment of these factors in the implant. Consequently, surface coating with this matricellular protein effectively accelerated and intensified implant vascularization which might be beneficial for its implementation at unfavorable sites for implantation without affecting the host's integrity.

[The Value of Endoscopic Decompression in Surgical Therapy of Carpal Tunnel Syndrome]. / Stellenwert der endoskopischen Karpaltunneldekompression.

Carpal tunnel syndrome is one of the most common diseases in hand surgery. The gold standard in therapy is the surgical release of the carpal tunnel. We provide a brief update on the relevant pathogenesis, diagnosis and therapy and discuss questions related to minimal invasive decompression of the median nerve. Together with a review of the current literature, we report on our experiences in minimally invasive carpal tunnel release via a monoportal endoscopic access in over 700 cases. In conclusion, the endoscopic technique provides superior convalescence and patient safety is comparable to open methods. In addition, advantages and disadvantages of the various techniques are discussed.

Components of the plasminogen activation system promote engraftment of porous polyethylene biomaterial via common and distinct effects.

Rapid fibrovascularization is a prerequisite for successful biomaterial engraftment. In addition to their well-known roles in fibrinolysis, urokinase-type plasminogen activator (uPA) and tissue plasminogen activator (tPA) or their inhibitor plasminogen activator inhibitor-1 (PAI-1) have recently been implicated as individual mediators in non-fibrinolytic processes, including cell adhesion, migration, and proliferation. Since these events are critical for fibrovascularization of biomaterial, we hypothesized that the components of the plasminogen activation system contribute to biomaterial engraftment. Employing in vivo and ex vivo microscopy techniques, vessel and collagen network formation within porous polyethylene (PPE) implants engrafted into dorsal skinfold chambers were found to be significantly impaired in uPA-, tPA-, or PAI-1-deficient mice. Consequently, the force required for mechanical disintegration of the implants out of the host tissue was significantly lower in the mutant mice than in wild-type controls. Conversely, surface coating with recombinant uPA, tPA, non-catalytic uPA, or PAI-1, but not with non-catalytic tPA, accelerated implant vascularization in wild-type mice. Thus, uPA, tPA, and PAI-1 contribute to the fibrovascularization of PPE implants through common and distinct effects. As clinical perspective, surface coating with recombinant uPA, tPA, or PAI-1 might provide a novel strategy for accelerating the vascularization of this biomaterial.

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.