Deep venous thrombosis (DVT) is one of the most common cardiovascular diseases, but its pathophysiology remains incompletely understood. Although sterile inflammation has recently been shown to boost coagulation during DVT, the underlying molecular mechanisms are not fully resolved, which could potentially identify new anti-inflammatory approaches to prophylaxis and therapy of DVT. Using a mouse model of venous thrombosis induced by flow reduction in the vena cava inferior, we identified blood-derived high-mobility group box 1 protein (HMGB1), a prototypical mediator of sterile inflammation, to be a master regulator of the prothrombotic cascade involving platelets and myeloid leukocytes fostering occlusive DVT formation. Transfer of platelets into Hmgb1^−/− chimeras showed that this cell type is the major source of HMGB1, exposing reduced HMGB1 on their surface upon activation thereby enhancing the recruitment of monocytes. Activated leukocytes in turn support oxidation of HMGB1 unleashing its prothrombotic activity and promoting platelet aggregation. This potentiates the amount of HMGB1 and further nurtures the accumulation and activation of monocytes through receptor for advanced glycation end products (RAGE) and Toll-like receptor 2, leading to local delivery of monocyte-derived tissue factor and cytokines. Moreover, disulfide HMGB1 facilitates formation of prothrombotic neutrophil extracellular traps (NETs) mediated by RAGE, exposing additional HMGB1 on their extracellular DNA strands. Eventually, a vicious circle of coagulation and inflammation is set in motion leading to obstructive DVT formation. Therefore, platelet-derived disulfide HMGB1 is a central mediator of the sterile inflammatory process in venous thrombosis and could be an attractive target for an anti-inflammatory approach for DVT prophylaxis. Publisher9s Note: There is an Inside Blood Commentary on this article in this issue. Key Points Sterile inflammation inducing venous thrombosis is coordinated by the damage-associated molecular pattern HMGB1 delivered by platelets. The effect of HMGB1 depends on the redox form, and disulfide HMGB1 induces NET formation, platelet aggregation, and monocyte activation.

Significance: Bacteria can communicate with each other by small diffusible molecules, a process termed quorum sensing. Many bacteria use acylated homoserine lactones (AHLs) as signals, which are sensed by so-called LuxR-type receptors. With the photopyrones from the insect pathogenic bacterium Photorhabdus luminescens , we recently identified the first quorum sensing molecules different from AHLs that are sensed by a LuxR-type receptor. Here we describe the second novel quorum sensing molecule sensed by a LuxR-type receptor of Photorhabdus species, PauR of the human pathogen Photorhabdus asymbiotica . We demonstrate that P. asymbiotica communicates via dialkylresorcinols (DARs) and cyclohexanediones (CHDs). As the synthesis pathway is widespread, and often present in human pathogens, we discuss DARs and CHDs as novel and widespread signaling molecules.

Summary: Proteins EI^Ntr, NPr and IIA^Ntr form a phosphoryl group transfer chain (Ntr‐PTS) working in parallel to the phosphoenolpyruvate:carbohydrate phosphotransferase system (transport‐PTS) in Escherichia coli. Recently, it was shown that dephosphorylated IIA^Ntr binds and inhibits TrkA, a low‐affinity potassium transporter. Here we report that the Ntr‐PTS also regulates expression of the high‐affinity K⁺ transporter KdpFABC, which rescues K⁺ uptake at limiting K⁺ concentrations. Transcription initiation at the kdpFABC promoter is positively controlled by the two‐component system KdpD/KdpE in response to K⁺ availability. We found that kdp promoter activity is stimulated by the dephosphorylated form of IIA^Ntr. Two‐hybrid data and biochemical analysis revealed that IIA^Ntr interacts with sensor kinase KdpD and stimulates kinase activity, resulting in increased levels of phosphorylated response regulator KdpE. The data suggest that exclusively dephosphorylated IIA^Ntr binds and activates KdpD. As there is cross‐talk between the Ntr‐PTS and the transport‐PTS, carbon source utilization affects kdpFABC expression. Expression is enhanced, when cells utilize preferred carbohydrates like glucose, which results in preferential dephosphorylation of the transport‐PTS and also of IIA^Ntr. Taken together, the data show that the Ntr‐PTS has an important role in maintaining K⁺ homeostasis and links K⁺ uptake to carbohydrate metabolism.

In Escherichia coli the Cpx sensor regulator system senses different kinds of envelope stress and responds by triggering the expression of periplasmic folding factors and proteases. It consists of the membrane-anchored sensor kinase CpxA, the response regulator CpxR, and the periplasmic protein CpxP. The Cpx pathway is induced in vivo by a variety of signals including pH variation, osmotic stress, and misfolded envelope proteins and is inhibited by overproduced CpxP. Because it is not clear how the Cpx pathway is able to recognize and correspond to so many different signals we overproduced, solubilized, purified, and incorporated the complete membrane-integral CpxA protein into proteoliposomes to analyze its biochemical properties in more detail. Autokinase and phosphotransfer activities of the reconstituted CpxA-His₆ protein were stimulated by KCl. NaCl also stimulated the activities but to a lesser extent. Other osmotic active solutes as glycine betaine, sucrose, and proline had no effect. The system was further characterized by testing for susceptibility to sensor kinase inhibitors. Among these, Closantel inhibited the activities of solubilized but not of the reconstituted CpxA-His₆ protein. We further analyzed the effect of CpxP on CpxA activities. Purified tagless CpxP protein reduced the phosphorylation status of CpxA to 50% but had no effect on CpxA phosphotransfer or phosphatase activities. As the in vitro system excludes the involvement of other factors our finding is the first biochemical evidence for direct protein-protein interaction between the sensor kinase CpxA and the periplasmic protein CpxP resulting in a down-regulation of the autokinase activity of CpxA.