A steady-state competition model describes the modulating effects of thrombomodulin on thrombin inhibition by plasminogen activator inhibitor-1 in the absence and presence of vitronectin

Arc Regulates Transcription of Genes for Plasticity, Excitability and Alzheimer’s Disease

The immediate early gene Arc is a master regulator of synaptic function and a critical determinant of memory consolidation. Here, we show that Arc interacts with dynamic chromatin and closely associates with histone markers for active enhancers and transcription in cultured rat hippocampal neurons. Both these histone modifications, H3K27Ac and H3K9Ac, have recently been shown to be upregulated in late-onset Alzheimer’s disease (AD). When Arc induction by pharmacological network activation was prevented using a short hairpin RNA, the expression profile was altered for over 1900 genes, which included genes associated with synaptic function, neuronal plasticity, intrinsic excitability, and signalling pathways. Interestingly, about 100 Arc-dependent genes are associated with the pathophysiology of AD. When endogenous Arc expression was induced in HEK293T cells, the transcription of many neuronal genes was increased, suggesting that Arc can control expression in the absence of activated signalling pathways. Taken together, these data establish Arc as a master regulator of neuronal activity-dependent gene expression and suggest that it plays a significant role in the pathophysiology of AD.

Vitronectin--master controller or micromanager?

The concept that the mammalian glycoprotein vitronectin acts as a biological 'glue' and key controller of mammalian tissue repair and remodelling activity is emerging from nearly 50 years of experimental in vitro and in vivo data. Unexpectedly, the vitronectin-knockout (VN-KO) mouse was found to be viable and to have largely normal phenotype. However, diligent observation revealed that the VN-KO animal exhibits delayed coagulation and poor wound healing. This is interpreted to indicate that VN occupies a role in the earliest events of thrombogenesis and tissue repair. VN is the foundation upon which the thrombus grows in an organised structure. In addition to sealing the wound, the thrombus also serves to protect the underlying tissue from oxidation, is a reservoir of mitogens and tissue repair mediators, and provides a provisional scaffold for the repairing tissue. In the absence of VN (e.g., VN-KO animal), this cascade is disrupted before it begins. A wide variety of biologically active species associate with VN. Although initial studies were focused on mitogens, other classes of bioactives (e.g., glycosaminoglycans and metalloproteinases) are now also known to specifically interact with VN. Although some interactions are transient, others are long-lived and often result in multi-protein complexes. Multi-protein complexes provide several advantages: prolonging molecular interactions, sustaining local concentrations, facilitating co-stimulation of cell surface receptors and thereby enhancing cellular/biological responses. We contend that these, or equivalent, multi-protein complexes facilitate VN polyfunctionality in vivo. It is also likely that many of the species demonstrated to associate with VN in vitro, also associate with VN in vivo in similar multi-protein complexes. Thus, the predominant biological function of VN is that of a master controller of the extracellular environment; informing, and possibly instructing cells 'where' to behave, 'when' to behave and 'how' to behave (i.e., appropriately for the current circumstance).

Plasminogen activator inhibitor type 1 gene polymorphism and sepsis

Plasminogen activator inhibitor type 1 (PAI-1) is a 50-kilodalton glycoprotein of the serine protease inhibitor family. The primary role of PAI-1 in vivo is the inhibition of both tissue- and urokinase-type plasminogen activators. In addition to this function, PAI-1 acts as an acute-phase protein during acute inflammation. PAI-1 is a pivotal player in the pathogenesis of sepsis, a complex clinical syndrome that results from a systemic inflammatory response. In patients with sepsis, the levels of PAI-1 are positively related to poor outcome, increased severity of disease, and increased levels of various cytokines, acute-phase proteins, and coagulation parameters. The 4G/5G insertion/deletion promoter polymorphism, which leads to differences in PAI-1 production, has been demonstrated to affect the risk of developing severe complications and dying from sepsis during meningococcal infection and multiple trauma.

Protease nexin-1 interacts with thrombomodulin and modulates its anticoagulant effect

The endothelial cell membrane glycoprotein thrombomodulin (TM) plays a critical role in the regulation of coagulation. TM is an essential cofactor in protein C activation by thrombin, and a direct inhibitor of thrombin-induced platelet activation and fibrinogen clotting. Protease nexin-1 (PN-1) is a serpin synthesized and secreted by a variety of cells including endothelial cells. PN-1 bound to the cell surface through interactions with glycosaminoglycans, is an efficient inhibitor of thrombin and controls thrombin-induced cell responses. An investigation of the interaction of PN-1 with TM using purified proteins and cultured human aortic endothelial cells was performed. Purified PN-1 was observed to bind to purified TM in a concentration-dependent manner. Double immunofluorescence studies indicated that PN-1 and TM were colocalized at the endothelial cell surface from which they were coprecipitated. Pretreatment of the cells with chondroitinase ABC greatly decreased the amount of the PN-1 associated to TM at the cell surface demonstrating the involvement of the TM chondroitin-sulfate chain in the formation of complexes. The inhibitory activity of the PN-1/TM complexes on the catalytic activity of thrombin, and on thrombin-induced fibrinogen clotting, was markedly enhanced when compared with the inhibitory activity of each partner. PN-1-overexpressing human aortic endothelial cells and PN-1-underexpressing human aortic endothelial cells exhibited respectively a significantly reduced ability and enhanced capacity to activate protein C. Furthermore, PN-1 decreased the cofactor activity of TM on thrombin activable fibrinolysis inhibitor activation by thrombin. These data show for the first time that PN-1 forms complexes with TM and modulates its anticoagulant activity.

Survey of the year 2003 commercial optical biosensor literature

In the year 2003 there was a 17% increase in the number of publications citing work performed using optical biosensor technology compared with the previous year. We collated the 962 total papers for 2003, identified the geographical regions where the work was performed, highlighted the instrument types on which it was carried out, and segregated the papers by biological system. In this overview, we spotlight 13 papers that should be on everyone's 'must read' list for 2003 and provide examples of how to identify and interpret high-quality biosensor data. Although we still find that the literature is replete with poorly performed experiments, over-interpreted results and a general lack of understanding of data analysis, we are optimistic that these shortcomings will be addressed as biosensor technology continues to mature.