Cancer associated thrombosis in everyday practice: perspectives from GARFIELD-VTE

Journal of Thrombosis and Thrombolysis - Venous thromboembolism (VTE) is common in cancer patients and is an important cause of morbidity and mortality. The Global Anticoagulant Registry in the...     

Vimentin intermediate filaments and filamentous actin form unexpected interpenetrating networks that redefine the cell cortex

The cytoskeleton of eukaryotic cells is primarily composed of networks of filamentous proteins, F-actin, microtubules, and intermediate filaments. Interactions among the cytoskeletal components are important in determining cell structure and in regulating cell functions. For example, F-actin and microtubules work together to control cell shape and polarity, while the subcellular organization and transport of vimentin intermediate filament (VIF) networks depend on their interactions with microtubules. However, it is generally thought that F-actin and VIFs form two coexisting but separate networks that are independent due to observed differences in their spatial distribution and functions. In this paper, we present a closer investigation of both the structural and functional interplay between the F-actin and VIF cytoskeletal networks. We characterize the structure of VIFs and F-actin networks within the cell cortex using structured illumination microscopy and cryo-electron tomography. We find that VIFs and F-actin form an interpenetrating network (IPN) with interactions at multiple length scales, and VIFs are integral components of F-actin stress fibers. From measurements of recovery of cell contractility after transient stretching, we find that the IPN structure results in enhanced contractile forces and contributes to cell resilience. Studies of reconstituted networks and dynamic measurements in cells suggest direct and specific associations between VIFs and F-actin. From these results, we conclude that VIFs and F-actin work synergistically, both in their structure and in their function. These results profoundly alter our understanding of the contributions of the components of the cytoskeleton, particularly the interactions between intermediate filaments and F-actin.

The cytoskeleton is a highly dynamic structure composed of multiple types of filamentous proteins. In eukaryotic cells, actin, microtubules, and intermediate filaments (IFs) each form intricate networks of entangled and cross-linked filaments. The organization of each individual network is precisely controlled to enable essential cellular functions. However, many core processes also require interactions among the different cytoskeletal components. For example, filamentous-actin (F-actin) and microtubules work together to control cell shape and polarity, which are critical for development, cell migration, and division. Close associations between microtubules and vimentin IFs (VIFs) have also been proposed based on similarities in their spatial distributions and the dependence of the organization of VIF networks on the microtubule-associated motors, kinesin and dynein (1–3). Indeed, there is some experimental evidence that microtubules can template VIF assembly and that VIFs can guide microtubules (4, 5), while VIFs stabilize microtubules in vitro (6). In addition, in stratified epithelial cells, a subplasmalemmal rim of keratin IFs can be localized just below the actin cortex, suggesting cooperativity of keratin and actin networks in regulating cell mechanics (7). Despite such interactions, VIFs and F-actin are generally thought to form two coexisting but separate networks. For example, fluorescence microscopy typically reveals the strongest signals for F-actin in the cell periphery, whereas the strongest signals for VIFs are near the nucleus in the bulk cytoplasm, suggesting that the two networks have little or no interaction. Furthermore, the functions of F-actin and VIFs appear to be largely contrasting: F-actin generates forces, whereas VIFs provide stability against these forces. Nevertheless, some evidence suggests there may be connections between vimentin and actin: for example, vimentin knockout cells are less motile and less contractile than their wild-type (WT) counterparts (8). Furthermore, some interactions have been observed between F-actin and VIFs (9–11) as well as the precursors to keratin, another IF system (12). These findings suggest that direct interactions or connections may exist between VIFs and F-actin. However, there have been no reports of direct observations of these interactions through imaging or other means, which would provide conclusive evidence of their significance. Such connections would belie our current understanding of the two independent cytoskeletal networks but could have a profound effect on the mechanical properties of cells. The possibility of such connections demands a closer investigation of both the structural and functional interplay between the F-actin and VIF cytoskeletal networks.Here we present evidence that VIFs and F-actin do work synergistically and form an interpenetrating network (IPN) structure within the cell cortex, defined as the cortical cytoplasm adjacent to the cell surface. We combine high-resolution structured illumination microscopy (SIM) and cryo-electron tomography (cryo-ET) to image mouse embryonic fibroblasts (MEFs) and observe coupling between F-actin and VIF structures within the cortex, contrary to the widely accepted view that they are each spatially segregated. In fact, the association of VIFs with cortical arrays of F-actin stress fibers occurs at multiple length scales. For example, VIFs run through and frequently appear to interconnect with adjacent stress fibers, forming meshworks that surround them. These organizational states are consistent with the formation of an IPN. We show that this IPN structure has important functional consequences in cells and can result in enhanced contractile forces. Moreover, our results indicate that specific associations exist between actin and vimentin proteins in the cytoplasmic environment, which may facilitate the formation of an IPN; the results also show that the VIF network can influence the diffusive behavior of actin monomers, which may, in turn, have downstream effects on other actin-driven processes. Thus, vimentin has a far more comprehensive role in cellular function than previously thought. These findings confirm the importance of the interplay between VIFs and F-actin, especially as it relates to the formation of IPNs and their consequences on the contractile nature of cells.     

Der Muskuläre Cyclus der Menschlichen Gebärmutter

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Pretest and change score intercorrelations in the validation of behavioral measures of openness

Two behavioral measures of openness (a miniature situations test and a structured self-disclosure interview), two self-report measures of openness (the Dogmatism Scale and the Experience Inventory), and the Ego-strength Scale were administered to 50 Ss on two different occasions spaced several weeks apart. One of the behavioral measures, the miniature situations test, correlated positively with the other measures of openness on the pretest. With regard to change scores across the two sessions, the behavioral measures correlated positively with each other and negatively with the self-report measures of openness and with the Ego-strength Scale. These results were interpreted as supporting the theoretical supposition that behavioral measures are most suitable for the measurement of short-term change in openness.     

Dabigatran attenuates thrombin generation to a lesser extent than warfarin: could this explain their differential effects on intracranial hemorrhage and myocardial infarction?

Compared with warfarin, dabigatran is associated with less intracranial hemorrhage, but an increased risk of myocardial infarction. To explore these phenomena, we compared their effects on thrombin generation. Thrombin generation in plasma from 10 patients taking therapeutic doses of warfarin (mean INR 2.6) was compared with that in plasma containing 250 ng/mL dabigatran. Although lag times were similar when thrombin generation was induced by recalcification or with a range of tissue factor concentrations, there was a greater reduction in peak thrombin generation and endogenous thrombin potential in plasma from warfarin-treated patients than in dabigatran-containing plasma. Similar results were obtained when thrombin generation was determined in plasma samples from 18 warfarin or 36 dabigatran treated patients entered into the RE-LY trial. Warfarin suppresses thrombin generation more efficiently than dabigatran. Greater suppression of normal hemostatic mechanisms in the brain and pathological thrombosis at sites of atherosclerotic plaque disruption may explain the higher rate of intracranial bleeding and lower rate of myocardial infarction with warfarin compared with dabigatran.