Low-density lipoprotein receptor-related protein (LRP)-mediated clearance of activated blood coagulation co-factors and proteases: clearance mechanism or regulation?

The role of endogenous tissue-type plasminogen activator in neuronal survival after ischemic stroke: friend or foe?

Endogenous protease tissue-type plasminogen activator (tPA) has highly efficient fibrinolytic activity and its recombinant variants alteplase and tenecteplase are established as highly effective thrombolytic drugs for ischemic stroke. Endogenous tPA is constituted of five functional domains through which it interacts with a variety of substrates, binding proteins and receptors, thus having enzymatic and cytokine-like effects to act on all cell types of the brain. In the past 2 decades, numerous studies have explored the clinical relevance of endogenous tPA in neurological diseases, especially in ischemic stroke. tPA is released from many cells within the brain parenchyma exposed to ischemia conditions in vitro and in vivo, which is believed to control neuronal fate. Some studies proved that tPA could induce blood-brain barrier disruption, neural excitotoxicity and inflammation, while others indicated that tPA also has anti-excitotoxic, neurotrophic and anti-apoptotic effects on neurons. Therefore, more work is needed to elucidate how tPA mediates such opposing functions that may amplify tPA from a therapeutic means into a key therapeutic target in endogenous neuroprotection after stroke. In this review, we summarize the biological characteristics and pleiotropic functions of tPA in the brain. Then we focus on possible hypotheses about why and how endogenous tPA mediates ischemic neuronal death and survival. Finally, we analyze how endogenous tPA affects neuron fate in ischemic stroke in a comprehensive view.

Potential roles of metalloproteinases of endometrium-derived exosomes in embryo-maternal crosstalk during implantation

During embryo implantation, crosstalk between the endometrial epithelium and the blastocyst, especially the trophoblasts, is a prerequisite for successful implantation. During this crosstalk, various molecular and functional changes occur to promote synchrony between the embryo and the endometrium as well as the uterine cavity microenvironment. In the past few years, growing evidence has shown that endometrium-derived exosomes play pivotal roles in the embryonic-maternal crosstalk during implantation, although the exact mechanism of this crosstalk has yet to be determined. The presence of metalloproteinases has been reported in endometrium-derived exosomes, implying the importance of these enzymes in exosome-based crosstalk. Thus, in this review, we describe the potential roles of the metalloproteinases of endometrium-derived exosomes in promoting embryo attachment and implantation. This study could provide a better understanding of the potential roles of exosomal metalloproteinases in embryo implantation and pave the way for developing novel exosome-based regulatory agents to support early pregnancy.

Impact of alcohol consumption on the outcome of ischemic stroke and thrombolysis: role of the hepatic clearance of tissue-type plasminogen activator

BACKGROUND AND PURPOSE

Tissue-type plasminogen activator (tPA) is the only acute treatment for ischemic stroke. Unfortunately, the benefit of tPA-driven thrombolysis is not systematic, and understanding the reasons for this is mandatory. The balance between beneficial and detrimental effects of tPA might explain the limited overall efficiency of thrombolysis. Here, we investigated whether this balance could be influenced by excessive alcohol intake.

METHODS

We used a murine model of thromboembolic stroke, coupled to an array of biochemical assays, near-infrared or magnetic resonance imaging scans, 2-photon microscopy, hydrodynamic transfections, and immunohistological techniques.

RESULTS

We found that 6 weeks of alcohol consumption (10% in drinking water) worsens ischemic lesions and cancels the beneficial effects of tPA-induced thrombolysis. We accumulate in vivo and in vitro evidence showing that this aggravation is correlated with a decrease in lipoprotein receptor-related protein 1-mediated hepatic clearance of tPA in alcohol-exposed mice.

CONCLUSIONS

An efficient liver-driven clearance of tPA might influence the safety of thrombolysis after stroke.

Low-density lipoprotein receptor-related protein-1: role in the regulation of vascular integrity

Low-density lipoprotein receptor-related protein-1 (LRP1) is a large endocytic and signaling receptor that is widely expressed. In the liver, LRP1 plays an important role in regulating the plasma levels of blood coagulation factor VIII (fVIII) by mediating its uptake and subsequent degradation. fVIII is a key plasma protein that is deficient in hemophilia A and circulates in complex with von Willebrand factor. Because von Willebrand factor blocks binding of fVIII to LRP1, questions remain on the molecular mechanisms by which LRP1 removes fVIII from the circulation. LRP1 also regulates cell surface levels of tissue factor, a component of the extrinsic blood coagulation pathway. This occurs when tissue factor pathway inhibitor bridges the fVII/tissue factor complex to LRP1, resulting in rapid LRP1-mediated internalization and downregulation of coagulant activity. In the vasculature LRP1 also plays protective role from the development of aneurysms. Mice in which the lrp1 gene is selectively deleted in vascular smooth muscle cells develop a phenotype similar to the progression of aneurysm formation in human patient, revealing that these mice are ideal for investigating molecular mechanisms associated with aneurysm formation. Studies suggest that LRP1 protects against elastin fiber fragmentation by reducing excess protease activity in the vessel wall. These proteases include high-temperature requirement factor A1, matrix metalloproteinase 2, matrix metalloproteinase-9, and membrane associated type 1-matrix metalloproteinase. In addition, LRP1 regulates matrix deposition, in part, by modulating levels of connective tissue growth factor. Defining pathways modulated by LRP1 that lead to aneurysm formation and defining its role in thrombosis may allow for more effective intervention in patients.

A single-species approach considering additional physiological information for prediction of hepatic clearance of glycoprotein derivate therapeutics

BACKGROUND AND OBJECTIVES

Existing methods for the prediction of human clearance of therapeutic proteins involve the use of allometry approaches. In general, these approaches have concentrated on the role of body weight, with only occasional attention given to more specific physiological parameters. The objective of this study was to develop a mechanism-based model of hepatic clearance (CL(H)), which combines a single-species scaling approach with liver physiology, for predicting CL(H) of selected glycoprotein derivate therapeutics, and to compare the outcome of this novel method with those of two empirical methods obtained from the literature - namely, the single-exponent theory and multiple-species allometry. Thus, this study was designed as an explanatory study to verify if the addition of physiological information is of benefit for extrapolating clearance of selected therapeutic proteins from one species to another.

METHODS

Five glycoprotein derivate therapeutics that are known to be principally eliminated by asialoglycoprotein receptors (ASGPRs) under in vivo conditions were selected. It was assumed that the interspecies differences in CL(H) reported for these compounds are reflected by the interspecies differences in the abundance of these receptors. Therefore, key scaling factors related to these differences were integrated into one model. Fourteen extrapolation (prediction) scenarios across species were used in this study while comparing the single-species model, based on physiology, with the single-exponent theory. In addition, the physiological model was compared with multiple-species allometry for three proteins.

RESULTS

In general, the novel physiological model is superior to the derived allometric methods. Overall, the physiological model produced a predicted CL(H) value with levels of accuracy of 100% within 3-fold, 100% within 2-fold and about 82% within 1.5-fold, compared with the observed values, whereas the levels of accuracy decreased to 93%, 77% and 53%, respectively, for allometry. The proposed physiological model is also superior to allometry on the basis of the root mean square error and absolute average fold error values.

CONCLUSIONS

It has been demonstrated that interspecies differences in the abundance of ASGPRs principally govern interspecies variations in CL(H) of compounds that are principally eliminated by ASGPRs. Overall, the proposed physiological model is an additional tool, which should facilitate investigation and prediction of human CL(H) of specific glycoproteins solely on the basis of clearance data determined in a single preclinical species.

Low-density lipoprotein receptor-related protein 1: new functions for an old molecule

The low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional cell surface receptor member of the low-density lipoprotein (LDL)-receptor family. As LRP1 plays an important role in endocytosis and regulation of signalling pathways, it is implicated in a number of physiologic processes, including the regulation of lipid metabolism, the proliferation of vascular smooth muscle cells and in neuro-development. More recently, LRP1 has been implicated in the catabolism of factor VIII and regulation of its plasma concentrations. The pathophysiology of the role of LRP1 in hemostasis will be summarized in this review.

Lipoprotein receptors--an evolutionarily ancient multifunctional receptor family

The evolutionarily ancient low-density lipoprotein (LDL) receptor gene family represents a class of widely expressed cell surface receptors. Since the dawn of the first primitive multicellular organisms, several structurally and functionally distinct families of lipoprotein receptors have evolved. In accordance with the now obsolete 'one-gene-one-function' hypothesis, these cell surface receptors were originally perceived as mere transporters of lipoproteins, lipids, and nutrients or as scavenger receptors, which remove other kinds of macromolecules, such as proteases and protease inhibitors from the extracellular environment and the cell surface. This picture has since undergone a fundamental change. Experimental evidence has replaced the perception that these receptors serve merely as cargo transporters. Instead it is now clear that the transport of macromolecules is inseparably intertwined with the molecular machinery by which cells communicate with each other. Lipoprotein receptors are essentially sensors of the extracellular environment that participate in a wide range of physiological processes by physically interacting and coevolving with primary signal transducers as co-regulators. Furthermore, lipoprotein receptors modulate cellular trafficking and localization of the amyloid precursor protein (APP) and the β-amyloid peptide (Aβ), suggesting a role in the pathogenesis of Alzheimer's disease. Moreover, compelling evidence shows that LDL receptor family members are involved in tumor development and progression.

Factor VIII and von Willebrand factor interaction: biological, clinical and therapeutic importance

The interaction of factor VIII (FVIII) with von Willebrand Factor (VWF) is of direct clinical significance in the diagnosis and treatment of patients with haemophilia A and von Willebrand disease (VWD). A normal haemostatic response to vascular injury requires both FVIII and VWF. It is well-established that in addition to its role in mediating platelet to platelet and platelet to matrix binding, VWF has a direct role in thrombin and fibrin generation by acting as a carrier molecule for the cofactor FVIII. Recent studies show that the interaction affects not only the biology of both FVIII and VWF, and the pathology of haemophilia and VWD, but also presents opportunities in the treatment of haemophilia. This review details the mechanisms and the molecular determinants of FVIII interaction with VWF, and the role of FVIII-VWF interaction in modulating FVIII interactions with other proteases, cell types and cellular receptors. The effect of defective interaction of FVIII with VWF as a result of mutations in either protein is discussed.

Membrane type 1-matrix metalloproteinase: substrate diversity in pericellular proteolysis

Enzymes in the matrix metalloproteinase (MMP) family have been linked to key events in developmental biology for almost 50 years. Biochemical, cellular and in vivo analyses have established that pericellular proteolysis contributes to numerous aspects of ontogeny including ovulation, fertilization, implantation, cellular migration, tissue remodeling and repair. Surface anchoring of proteinase activity provides spatial restrictions on substrate targeting. This review will utilize membrane type 1 MMP (MT1-MMP) as an example to highlight substrate diversity in pericellular proteolysis catalyzed by a membrane anchored MMP.

Inhibition of PDGF-BB by Factor VII-activating protease (FSAP) is neutralized by protease nexin-1, and the FSAP-inhibitor complexes are internalized via LRP

FSAP (Factor VII-activating protease) can inhibit neointima formation and VSMC (vascular smooth-muscle cell) proliferation by cleavage of PDGF-BB (platelet-derived growth factor-BB). Negatively charged polyanions lead to autoactivation of the FSAP, but no information is available concerning the potential regulation of FSAP activity and its metabolism in the vessel wall. In the present study, we demonstrate that the enzymatic activity of FSAP can be inhibited by the serine protease inhibitor, PN-1 (protease nexin-1), that is found in the vasculature. This leads to the loss of the inhibitory effect of FSAP on PDGF-BB-mediated DNA synthesis and mitogen-activated protein kinase phosphorylation in VSMCs. The FSAP-PN-1 complexes bind to the LRP (low-density lipoprotein receptor-related protein) and are subsequently internalized. This binding is inhibited by receptor-associated protein, an antagonist of LRP, as well as heparin. While PDGFbetaR (PDGFbeta receptor) is internalized by an LRP-dependent mechanism after stimulation of cells by PDGF-BB, the FSAP-PN-1 complex neither influenced PDGF-BB-mediated phosphorylation of PDGFbetaR nor its internalization via LRP. Hence, PN-1 inhibits the enzymatic activity of FSAP and neutralizes its effect on PDGF-BB-mediated VSMC proliferation. The FSAP-inhibitor complexes are internalized via LRP without influencing the PDGF-BB signal transduction pathway.