Cytoplasmic anchorage of L-selectin controls leukocyte capture and rolling by increasing the mechanical stability of the selectin tether

L-selectin is a leukocyte lectin that mediates leukocyte capture and rolling in the vasculature. The cytoplasmic domain of L-selectin has been shown to regulate leukocyte rolling. In this study, the regulatory mechanisms by which this domain controls L-selectin adhesiveness were investigated. We report that an L-selectin mutant generated by truncation of the COOH-terminal 11 residues of L-selectin tail, which impairs association with the cytoskeletal protein α-actinin, could capture leukocytes to glycoprotein L-selectin ligands under physiological shear flow. However, the conversion of initial tethers into rolling was impaired by this partial tail truncation, and was completely abolished by a further four-residue truncation of the L-selectin tail. Physical anchorage of both cell-free tail-truncated mutants within a substrate fully rescued their adhesive deficiencies. Microkinetic analysis of full-length and truncated L-selectin–mediated rolling at millisecond temporal resolution suggests that the lifetime of unstressed L-selectin tethers is unaffected by cytoplasmic tail truncation. However, cytoskeletal anchorage of L-selectin stabilizes the selectin tether by reducing the sensitivity of its dissociation rate to increasing shear forces. Low force sensitivity (reactive compliance) of tether lifetime is crucial for selectins to mediate leukocyte rolling under physiological shear stresses. This is the first demonstration that reduced reactive compliance of L-selectin tethers is regulated by cytoskeletal anchorage, in addition to intrinsic mechanical properties of the selectin–carbohydrate bond

Effect of water composition on perchlorate removal from polluted ground- water using Ion Exchange Membrane Bioreactor

Perchlorate contamination of ground water is a worldwide concern. At several sites in Israel\u27s coastal aquifer, hundreds of ppm of perchlorate was found accompanied with significant concentrations of nitrate and chlorate, consequently preventing water production from wells in the area. The IEMB hybrid process [1] allows safe treatment of high perchlorate (and nitrate and chlorate) contaminated groundwater. The Donnan dialysis process removes the perchlorate from the water compartment using an anion exchange membrane (AEM) to the bio-compartment where it undergoes microbial degradation to much safer components such as chloride. The AEM acts as a barrier and keeps both compartments completely separate. Glycerol is used as an exogenous carbon and electron source for the biodegradation process [2]. This arrangement keeps the carbon source, reaction byproducts and bacteria confined in the bio-reactor thus preventing the contamination of the treated water. The present study examines the performance of the IEMB in removing perchlorate and other anions (nitrate and chlorate) at levels of hundreds mg L-1 from polluted ground water from the Ramat HaSharon (RHGW) contaminated site. The IEMB removal of the polluting anions was studied initially for synthetic and actual ground water fed to the water side while feeding 0.1 N of NaCl to the bio-compartment. We further studied the effect of adding bacteria and bio-media to the bio-compartment. In all experiment setups it is obvious that perchlorate dominates the flux across the AEM. Even though perchlorate concentration is considerably lower than nitrate and chlorate, its flux is greater than the sum of the other anion fluxes. At an effective driving force (EDF) value above 0.7 [mM] perchlorate had a negative effect on the other anions transport across the membrane. Adding bacteria to bio-compartment side fed with RHGW and bio-media increased anions total flux by 15%-23% at the first two runs. A thick biofilm has developed on the membrane bio-side during the following two runs, resulting in a total flux decline of 18%-22% when compared to the pure Donnan dialysis experiment. Throughout all the bio-degradation experiment regardless of the anion load to the bio-compartment the bio-degradation efficiency of the trace anions was above 99%. This study is the first to treat highly polluted complex ground water in an IEMB. It further established the perchlorate strong interaction with the AEM, consequently affecting the flux of other anions in the treatment process. This research is the basis for upscaling the IEMB technology into the field Please click Additional Files below to see the full abstract

Trust Dies in Darkness: Shedding Light on Samsung\u27s TrustZone Keymaster Design

ARM-based Android smartphones rely on the TrustZone hardware support for a Trusted Execution Environment (TEE) to implement security-sensitive functions. The TEE runs a separate, isolated, TrustZone Operating System (TZOS), in parallel to Android. The implementation of the cryptographic functions within the TZOS is left to the device vendors, who create proprietary undocumented designs. In this work, we expose the cryptographic design and implementation of Android\u27s Hardware-Backed Keystore in Samsung\u27s Galaxy S8, S9, S10, S20, and S21 flagship devices. We reversed-engineered and provide a detailed description of the cryptographic design and code structure, and we unveil severe design flaws. We present an IV reuse attack on AES-GCM that allows an attacker to extract hardware-protected key material, and a downgrade attack that makes even the latest Samsung devices vulnerable to the IV reuse attack. We demonstrate working key extraction attacks on the latest devices. We also show the implications of our attacks on two higher-level cryptographic protocols between the TrustZone and a remote server: we demonstrate a working FIDO2 WebAuthn login bypass and a compromise of Google’s Secure Key Import. We discuss multiple flaws in the design flow of TrustZone based protocols. Although our specific attacks only apply to the $\approx$100 million devices made by Samsung, it raises the much more general requirement for open and proven standards for critical cryptographic and security designs

Avidity enhancement of L-selectin bonds by flow: shear-promoted rotation of leukocytes turn labile bonds into functional tethers

L-selectin is a key lectin essential for leukocyte capture and rolling on vessel walls. Functional adhesion of L-selectin requires a minimal threshold of hydrodynamic shear. Using high temporal resolution videomicroscopy, we now report that L-selectin engages its ligands through exceptionally labile adhesive bonds (tethers) even below this shear threshold. These tethers share a lifetime of 4 ms on distinct physiological ligands, two orders of magnitude shorter than the lifetime of the P-selectin–PSGL-1 bond. Below threshold shear, tether duration is not shortened by elevated shear stresses. However, above the shear threshold, selectin tethers undergo 14-fold stabilization by shear-driven leukocyte transport. Notably, the cytoplasmic tail of L-selectin contributes to this stabilization only above the shear threshold. These properties are not shared by P-selectin– or VLA-4–mediated tethers. L-selectin tethers appear adapted to undergo rapid avidity enhancement by cellular transport, a specialized mechanism not used by any other known adhesion receptor

beta 2 Integrin Signaling Cascade in Neutrophils : More Than a Single Function

Neutrophils are the most prevalent leukocytes in the human body. They have a pivotal role in the innate immune response against invading bacterial and fungal pathogens, while recent emerging evidence also demonstrates their role in cancer progression and anti-tumor responses. The efficient execution of many neutrophil effector responses requires the presence of beta 2 integrins, in particular CD11a/CD18 or CD11b/CD18 heterodimers. Although extensively studied at the molecular level, the exact signaling cascades downstream of beta 2 integrins still remain to be fully elucidated. In this review, we focus mainly on inside-out and outside-in signaling of these two beta 2 integrin members expressed on neutrophils and describe differences between various neutrophil stimuli with respect to integrin activation, integrin ligand binding, and the pertinent differences between mouse and human studies. Last, we discuss how integrin signaling studies could be used to explore the therapeutic potential of targeting beta 2 integrins and the intracellular signaling cascade in neutrophils in several, among other, inflammatory conditions in which neutrophil activity should be dampened to mitigate disease.Peer reviewe

Subgraphs and network motifs in geometric networks

Many real-world networks describe systems in which interactions decay with the distance between nodes. Examples include systems constrained in real space such as transportation and communication networks, as well as systems constrained in abstract spaces such as multivariate biological or economic datasets and models of social networks. These networks often display network motifs: subgraphs that recur in the network much more often than in randomized networks. To understand the origin of the network motifs in these networks, it is important to study the subgraphs and network motifs that arise solely from geometric constraints. To address this, we analyze geometric network models, in which nodes are arranged on a lattice and edges are formed with a probability that decays with the distance between nodes. We present analytical solutions for the numbers of all 3 and 4-node subgraphs, in both directed and non-directed geometric networks. We also analyze geometric networks with arbitrary degree sequences, and models with a field that biases for directed edges in one direction. Scaling rules for scaling of subgraph numbers with system size, lattice dimension and interaction range are given. Several invariant measures are found, such as the ratio of feedback and feed-forward loops, which do not depend on system size, dimension or connectivity function. We find that network motifs in many real-world networks, including social networks and neuronal networks, are not captured solely by these geometric models. This is in line with recent evidence that biological network motifs were selected as basic circuit elements with defined information-processing functions.Comment: 9 pages, 6 figure

Nuclear Deformation During Neutrophil Migration at Sites of Inflammation

Cell migration is indispensable for various biological processes including angiogenesis, wound healing, and immunity. In general, there are two different migration modes described, the mesenchymal migration mode and the amoeboid migration mode. Neutrophils rapidly migrate toward the sites of injury, infection, and inflammation using the amoeboid migration mode which is characterized by cell polarization and a high migration velocity. During site-directed trafficking of neutrophils from the blood stream into the inflamed tissue, neutrophils must first withstand shear stress while migrating on the 2-dimensional endothelial surface. Subsequently, they have to cross different physical barriers during the extravasation process including the squeezing through the compact endothelial monolayer that comprises the blood vessel, the underlining basement membrane and then the 3-dimensional meshwork of extracellular matrix (ECM) proteins in the tissue. Therefore, neutrophils have to rapidly switch between distinct migration modes such as intraluminal crawling, transmigration, and interstitial migration to pass these different confinements and mechanical barriers. The nucleus is the largest and stiffest organelle in every cell and is therefore the key cellular element involved in cellular migration through variable confinements. This review highlights the importance of nuclear deformation during neutrophil crossing of such confinements, with a focus on transendothelial migration and interstitial migration. We discuss the key molecular components involved in the nuclear shape changes that underlie neutrophil motility and squeezing through cellular and ECM barriers. Understanding the precise molecular mechanisms that orchestrate these distinct neutrophil migration modes introduces an opportunity to develop new therapeutic concepts for controlling pathological neutrophil-driven inflammation