Lasp1 regulates adherens junction dynamics and fibroblast transformation in destructive arthritis.

The LIM and SH3 domain protein 1 (Lasp1) was originally cloned from metastatic breast cancer and characterised as an adaptor molecule associated with tumourigenesis and cancer cell invasion. However, the regulation of Lasp1 and its function in the aggressive transformation of cells is unclear. Here we use integrative epigenomic profiling of invasive fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and from mouse models of the disease, to identify Lasp1 as an epigenomically co-modified region in chronic inflammatory arthritis and a functionally important binding partner of the Cadherin-11/ß-Catenin complex in zipper-like cell-to-cell contacts. In vitro, loss or blocking of Lasp1 alters pathological tissue formation, migratory behaviour and platelet-derived growth factor response of arthritic FLS. In arthritic human TNF transgenic mice, deletion of Lasp1 reduces arthritic joint destruction. Therefore, we show a function of Lasp1 in cellular junction formation and inflammatory tissue remodelling and identify Lasp1 as a potential target for treating inflammatory joint disorders associated with aggressive cellular transformation.

The CellBorderTracker, a novel tool to quantitatively analyze spatiotemporal endothelial junction dynamics at the subcellular level.

Endothelial junctions are dynamic structures organized by multi-protein complexes that control monolayer integrity, homeostasis, inflammation, cell migration and angiogenesis. Newly developed methods for both the genetic manipulation of endothelium and microscopy permit time-lapse recordings of fluorescent proteins over long periods of time. Quantitative data analyses require automated methods. We developed a software package, the CellBorderTracker, allowing quantitative analysis of fluorescent-tagged cell junction protein dynamics in time-lapse sequences. The CellBorderTracker consists of the CellBorderExtractor that segments cells and identifies cell boundaries and mapping tools for data extraction. The tool is illustrated by analyzing fluorescent-tagged VE-cadherin the backbone of adherence junctions in endothelium. VE-cadherin displays high dynamics that is forced by junction-associated intermittent lamellipodia (JAIL) that are actin driven and WASP/ARP2/3 complex controlled. The manual segmentation and the automatic one agree to 90 %, a value that indicates high reliability. Based on segmentations, different maps were generated allowing more detailed data extraction. This includes the quantification of protein distribution pattern, the generation of regions of interest, junction displacements, cell shape changes, migration velocities and the visualization of junction dynamics over many hours. Furthermore, we demonstrate an advanced kymograph, the J-kymograph that steadily follows irregular cell junction dynamics in time-lapse sequences for individual junctions at the subcellular level. By using the CellBorderTracker, we demonstrate that VE-cadherin dynamics is quickly arrested upon thrombin stimulation, a phenomenon that was largely due to transient inhibition of JAIL and display a very heterogeneous subcellular and divers VE-cadherin dynamics during intercellular gap formation and resealing.

Actin filament dynamics and endothelial cell junctions: the Ying and Yang between stabilization and motion.

The vascular endothelium is a cellular interface between the blood and the interstitial space of tissue, which controls the exchange of fluid, solutes and cells by both transcellular and paracellular means. To accomplish the demands on barrier function, the regulation of the endothelium requires quick and adaptive mechanisms. This is, among others, accomplished by actin dynamics that interdependently interact with both the VE-cadherin/catenin complex, the main components of the adherens type junctions in endothelium and the membrane cytoskeleton. Actin filaments in endothelium are components of super-structured protein assemblies that control a variety of dynamic processes such as endo- and exocytosis, shape change, cell-substrate along with cell-cell adhesion and cell motion. In endothelium, actin filaments are components of: (1) contractile actin bundles appearing as stress fibers and junction-associated circumferential actin filaments, (2) actin networks accompanied by endocytotic ruffles, lamellipodia at leading edges of migrating cells and junction-associated intermittent lamellipodia (JAIL) that dynamically maintain junction integrity, (3) cortical actin and (4) the membrane cytoskeleton. All these structures, most probably interact with cell junctions and cell-substrate adhesion sites. Due to the rapid growth in information, we aim to provide a bird's eye view focusing on actin filaments in endothelium and its functional relevance for entire cell and junction integrity, rather than discussing the detailed molecular mechanism for control of actin dynamics.

Influence of growth hormone on maintenance of capillary-like structures in an in vitro model of stromal vascular tissue--results from morphometric analysis.

The in vitro development of a vascular stroma might be a solution for the engineering of vascularized tissues, however, in vitro stability of capillary-like structures is limited. In order to test the influence on maintenance of capillary-like structures, human growth hormone (hGH) was added in concentrations of 0.5, 5, 50, and 500 ng/mL in an in vitro model of stromal vascular tissue. The angiogenic response and maintenance of capillary-like structures were analyzed by means of confocal laser scanning microscopy (CLSM) and image analysis after 8, 16, and 32 days of culture. The highest angiogenic response was observed with a concentration of 50 ng/mL hGH. With the addition of 50 and 500 ng/mL, the length of capillary-like structures could be maintained on high levels up to the 32nd day of culture, whereas with 5 ng/mL values dropped to the level of the control group. The proposed technique of analysis allows quantification of capillary-like network formation and might be useful for tissue engineering applications.