Establishment and characterization of a new and stable collagen-binding assay for the assessment of von Willebrand factor activity

Introduction

Laboratory diagnosis of von Willebrand disease (VWD) requires determination of both von Willebrand factor (VWF) protein levels and activity. Current VWF activity tests include the ristocetin cofactor assay and the collagen-binding assay (VWF:CB). The goal of this investigation is to characterize a new collagen-binding assay and to determine its effectiveness in identifying VWD.

Methods

Analytical studies were carried out to characterize the performance of a new VWF:CB ELISA. Additionally, samples from a normal population were tested as were well-characterized type 1 and type 2 VWD samples.

Results

Repeatability and within-laboratory precision studies resulted in coefficients of variation (CVs) of ≤11%. A linear range of 1–354% (0.01–3.54 IU/mL) was determined, along with a limit of detection and a lower limit of quantitation of 1.6% and 4.0% (0.016 and 0.04 IU/mL), respectively. Samples tested from apparently healthy individuals resulted in a normal range of 54–217% (0.54–2.17 IU/mL). Known VWD type 1 and type 2 samples were also analyzed by the ELISA, with 99% of samples having VWF:CB below the normal reference range and an estimated 96% sensitivity and 87% specificity using a VWF collagen-binding/antigen cutoff ratio of 0.50.

Conclusion

This new VWF:CB ELISA provides an accurate measure of collagen-binding activity that aids in the diagnosis and differentiation of type 1 from type 2 VWD.

Pathophysiology of β2-glycoprotein I in antiphospholipid syndrome

Since β2-glycoprotein I (β2GPI) was described as the major antigenic target for antiphospholipid antibodies, many studies have focused their attention to the physiological role of β2GPI and anti-β2GPI antibodies on autoimmune-mediated thrombosis. Studies reporting the physiological role of β2GPI have been numerous, but the exact mechanism of action(s) has yet to be completely determined. β2GPI’s epitopes for anti-β2GPI autoantibodies have been characterized, however, not all of the heterogeneous anti-β2GPI antibodies are pathogenic. The pathophysiologic role of β2GPI has been reported in the fields of coagulation, fibrinolysis, angiogenesis, and atherosclerosis. Our understanding of the impact of β2GPI, its metabolites and autoantibodies to β2GPI on these physiological functions may contribute to the development of better therapeutic strategies to treat and prevent autoimmune-mediated atherothrombotic vascular disease. Lupus (2010) 19, 379—384.

The biology of apoptosis

Apoptosis is a complex process that removes aging or injured cells from the body and occurs in a wide variety of organisms. Cell death has always been an integral aspect of the study of pathology, but only over the last 30 years or so has the interest in apoptosis gained appreciation in this field. This review analyzes pertinent aspects of apoptosis, from Virchow's initial descriptions of necrobiosis to more modern research, and reviews some of the key events and molecules involved in the process. Finally, the role of apoptosis in certain diseases and its importance in the clinical setting is addressed.

Early stages of p53-induced apoptosis are reversible

Apoptosis is a type of physiological cell death that occurs during development, normal tissue homeostasis, or as a result of different cellular insults. The phenotype of an apoptotic cell is relatively consistent in most cases of apoptosis and involves at least changes in the cell membrane, proteolysis of cytoplasmic and nuclear proteins, and eventual destruction of nuclear DNA. Our laboratory is interested in the reversibility of apoptosis. We have initial evidence that DNA repair is activated early in p53-induced apoptosis and may be involved in its reversibility. The present work further strengthens our proposition that p53-induced apoptosis is reversible. We show that p53 activation induces phosphatidylserine (PS) externalization early in apoptosis, and that these early apoptotic cells with externalized PS can be rescued and proliferate if the apoptotic stimulus is removed. In addition, we show that unscheduled DNA synthesis occurs in early apoptotic cells, and that if DNA repair is inhibited by aphidicolin, apoptosis is accelerated. These results confirm that early p53-induced apoptotic cells can be rescued from the apoptotic program, and that DNA repair can modulate that cell death process.

DNA repair is activated in early stages of p53-induced apoptosis

p53 is a complex molecule involved in apoptosis, cell cycle arrest, and DNA repair. Since apoptosis may play an important role in deletion of neoplastic cells, an understanding of the mechanism of p53-induced apoptosis may be critical for possible future therapeutic interventions. Recent evidence suggests that p53-induced apoptosis may involve members of the nucleotide excision repair (NER) family, linking these two cellular events. Our work using a temperature-sensitive p53 construct further analyzes p53-induced apoptosis in cultured murine mammary epithelial cells and also suggests that DNA repair plays a role in that process. Although p21 is induced in our system, apoptosis occurs without a detectable preceding G1 cell cycle arrest and independent of cellular alterations brought on by the temperature shift. In addition, clonogenic assays suggest that early stages of p53-induced apoptosis may be reversible upon removal of the apoptosis stimulus. As a possible explanation for this reversibility, our results show that general DNA repair activity increases early in p53-induced apoptosis. We also show that caspase-3 is activated at a timepoint when colony formation begins to drop, suggesting a possible mechanism for the point of no return in p53-induced apoptosis.

Isolation of cell death-associated cDNAs from involuting mouse mammary epithelium

Although apoptosis is important in determining cell fate and maintaining tissue homeostasis, the initiation and control of apoptotic cell death in epithelium is not well understood. Post-lactationai involution of the mammary gland provides both an important developmental process and a normal physiological setting for studying apoptosis of epithelium. We used a differential screening strategy, based on previous studies correlating morphology with gene expression and nucleic acid integrity during mammary gland involution, to isolate genes involved in the regulation and execution of apoptotic cell death in regressing mammary epithelium. This screening strategy yielded a large number of genes the expression of which is significantly altered during mammary gland involution. These include genes associated with cell death processes, tissue remodelling and mesenchymal differentiation. In addition, a number of novel genes have been isolated. We have used Northern analysis and in situ hybridisation to study the expression of a selection of these putative death-associated genes during post-lactational mouse mammary gland involution.

Use of the yeast two-hybrid system for identifying the cascade of protein interactions resulting in apoptotic cell death

Use of the yeast two-hybrid system allows rapid identification of interacting protein or proteins for a specific target protein. The technique is readily applied and allows immediate isolation of a cDNA encoding the interacting protein. One consideration might be to outline criteria for continued study of the interactors once they are identified. Our criterion for further study of an interactor is its presence in the mammary gland at a developmental time when the target protein is also present. Further characterization of interactors may involve immunoprecipitation, enzyme assays, or other techniques applicable to the specific protein.

Programmed cell death during mammary gland involution

Understanding the cascade of gene expression and subsequent protein interactions that result both in the death of secretory mammary epithelium and the remodeling and renewal of the mammary gland for another cycle of lactation poses significant challenges (see Chapters 7 and 8, this volume). The complexity of mammary gland involution warrants caution in sorting through the various potential regulators and executors of apoptotic cell death in the mammary gland. As demonstrated by the number of remodeling enzymes expressed during involution, the relationship between mammary epithelium and its related mesenchyme is important for maintenance of differentiated function (Barcellos-Hoff et al., 1989; Streuli et al., 1991). Components of the extracellular matrix may play the role of survival factors, or may provide a source of factors, as a reserve of matrix-bound growth factors, necessary for survival of the secretory epithelium. Perturbation of this interaction alters mammary-specific differentiation gene expression, for example, production of milk proteins (Parry et al., 1987; Strange et al., 1991; Talhouk et al., 1992). Thus, alteration of the interaction between epithelium and its associated mesenchyme, which is an integral part of mammary involution, may also play a role in epithelial cell death. However, the epithelial-mesenchymal interactions that are the determining features in either mediating or modulating this cell death are just beginning to be defined. Stimuli that alter differentiated function may also induce apoptotic cell death of the epithelium but may have no physiological correlate. They may, however, have significant application in prevention or control of breast neoplasia.

Biophysical characterization of a transit peptide directing chloroplast protein import

We have investigated the biophysical properties of a 35 amino acid peptide representing the entire length of a chloroplastic targeting sequence. The peptide, termed gamma-tp, corresponds in sequence to the transit peptide of the gamma subunit of the chloroplast ATP synthase from Chlamydomonas reinhardtii. We found that gamma-tp blocks the import of the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase into isolated pea chloroplasts (KI approximately 5 microM), suggesting that it interacts with higher plant plastids in a physiological manner. We also found the gamma-tp to have a high affinity for nonpolar environments, but not to cause a general disruption of membrane integrity. Hydrophobic moment analysis suggests that the gamma-tp can adopt an amphipathic beta structure. However, circular dichroism measurements indicate that the peptide is largely a random coil, in both the presence and absence of sodium laurylsulfate micelles. In the absence of a recognizable secondary structural targeting motif, we asked whether the presence of a transit peptide on a chloroplast protein increases the protein's overall affinity for nonpolar environments. Phase-partition experiments with Triton X-114 suggest that this is not the case. These results are discussed in relation to the mechanism of protein targeting to chloroplasts.