Partial loss of actin nucleator actin-related protein 2/3 activity triggers blebbing in primary T lymphocytes

T lymphocytes utilize amoeboid migration to navigate effectively within complex microenvironments. The precise rearrangement of the actin cytoskeleton required for cellular forward propulsion is mediated by actin regulators, including the actin‐related protein 2/3 (Arp2/3) complex, a macromolecular machine that nucleates branched actin filaments at the leading edge. The consequences of modulating Arp2/3 activity on the biophysical properties of the actomyosin cortex and downstream T cell function are incompletely understood. We report that even a moderate decrease of Arp3 levels in T cells profoundly affects actin cortex integrity. Reduction in total F‐actin content leads to reduced cortical tension and disrupted lamellipodia formation. Instead, in Arp3‐knockdown cells, the motility mode is dominated by blebbing migration characterized by transient, balloon‐like protrusions at the leading edge. Although this migration mode seems to be compatible with interstitial migration in three‐dimensional environments, diminished locomotion kinetics and impaired cytotoxicity interfere with optimal T cell function. These findings define the importance of finely tuned, Arp2/3‐dependent mechanophysical membrane integrity in cytotoxic effector T lymphocyte activities

Autoregulation of von Willebrand factor function by a disulfide bond switch

Force-dependent binding of platelet glycoprotein Ib (GPIb) receptors to plasma von Willebrand factor (VWF) plays a key role in hemostasis and thrombosis. Previous studies have suggested that VWF activation requires force-induced exposure of the GPIb binding site in the A1 domain that is autoinhibited by the neighboring A2 domain. However, the biochemical basis of this “mechanopresentation” remains elusive. From a combination of protein chemical, biophysical, and functional studies, we find that the autoinhibition is controlled by the redox state of an unusual disulfide bond near the carboxyl terminus of the A2 domain that links adjacent cysteine residues to form an eight-membered ring. Only when the bond is cleaved does the A2 domain bind to the A1 domain and block platelet GPIb binding. Molecular dynamics simulations indicate that cleavage of the disulfide bond modifies the structure and molecular stresses of the A2 domain in a long-range allosteric manner, which provides a structural explanation for redox control of the autoinhibition. Significantly, the A2 disulfide bond is cleaved in ~75% of VWF subunits in healthy human donor plasma but in just ~25% of plasma VWF subunits from heart failure patients who have received extracorporeal membrane oxygenation support. This suggests that the majority of plasma VWF binding sites for platelet GPIb are autoinhibited in healthy donors but are mostly available in heart failure patients. These findings demonstrate that a disulfide bond switch regulates mechanopresentation of VWF

Illustrated State-of-the-Art Capsules of the ISTH 2019 Congress in Melbourne, Australia : Plasminogen in wound healing

The 27th Congress of the International Society of Thrombosis and Haemostasis (ISTH) is an international conference held July 6-10, 2019, in Melbourne, the capital of the state of Victoria, Australia. The ISTH congress has previously been held every other year, with the Scientific and Standardization Committee (SSC) meeting held annually, until 2019 when it became one combined annual meeting of the ISTH and SSC. The conference covers clinical and basic aspects of hemostasis and thrombosis, and this year includes 5 Plenary lectures and >50 State of Art (SOA) lectures, presented by internationally recognized speakers, as well as numerous oral session and poster presentations selected from submitted abstracts, including many early career and reach the world support recipients. This SOA review article in RPTH contains concise Illustrated Review Articles or 'Capsules' consisting of short text, three references and a figure, with topics including stroke, cancer-associated thrombosis, hemophilia, coagulation, the interface between infection and inflammation, and in the experimental and discovery areas, megakaryocyte biology and platelet production, structure-function of key receptors and coagulation factors, and emerging new roles for thrombotic/hemostatic factors. Together, these articles highlight novel findings which will advance knowledge and with the potential to change clinical practice and improve outcomes. It is hoped that conference attendees and followers will enjoy utilizing the images for ongoing education and during the conference for live tweeting during sessions, to assist in the broadcasting and promotion of the science to those unable to attend, or who have chosen to attend a concurrent session. Use #IllustratedReview and #ISTH2019 on social media

Illustrated State-of-the-Art Capsules of the ISTH 2019 Congress in Melbourne, Australia

The 27th Congress of the International Society of Thrombosis and Haemostasis (ISTH) is an international conference held July 6-10, 2019, in Melbourne, the capital of the state of Victoria, Australia. The ISTH congress has previously been held every other year, with the Scientific and Standardization Committee (SSC) meeting held annually, until 2019 when it became one combined annual meeting of the ISTH and SSC. The conference covers clinical and basic aspects of hemostasis and thrombosis, and this year includes 5 Plenary lectures and >50 State of Art (SOA) lectures, presented by internationally recognized speakers, as well as numerous oral session and poster presentations selected from submitted abstracts, including many early career and reach the world support recipients. This SOA review article in RPTH contains concise Illustrated Review Articles or 'Capsules' consisting of short text, three references and a figure, with topics including stroke, cancer-associated thrombosis, hemophilia, coagulation, the interface between infection and inflammation, and in the experimental and discovery areas, megakaryocyte biology and platelet production, structure-function of key receptors and coagulation factors, and emerging new roles for thrombotic/hemostatic factors. Together, these articles highlight novel findings which will advance knowledge and with the potential to change clinical practice and improve outcomes. It is hoped that conference attendees and followers will enjoy utilizing the images for ongoing education and during the conference for live tweeting during sessions, to assist in the broadcasting and promotion of the science to those unable to attend, or who have chosen to attend a concurrent session. Use #IllustratedReview and #ISTH2019 on social media.status: publishe