Characterization of the proteins released from activated platelets leads to localization of novel platelet proteins in human atherosclerotic lesions

Calumenin, a multiple EF-hands Ca2+-binding protein, interacts with ryanodine receptor-1 in rabbit skeletal sarcoplasmic reticulum

Calumenin is a multiple EF-hand Ca2+-binding protein located in endo/sarcoplasmic reticulum of mammalian tissues. In the present study, we cloned two rabbit calumenin isoforms (rabbit calumenin-1 and -2, GenBank Accession Nos. SY225335 and AY225336, respectively) by RT-PCR. Both isoforms contain a 19 aa N-terminal signal sequence, 6 EF-hand domains, and a C-terminal ER/SR retrieval signal, HDEF. Both calumenin isoforms exist in rabbit cardiac and skeletal muscles, but calumenin-2 is the main isoform in skeletal muscle. Presence of calumenin in rabbit sarcoplasmic reticulum (SR) was identified by Western blot analysis. GST-pull down and co-immunoprecipitation experiments showed that ryanodine receptor 1 (RyR1) interacted with calumenin-2 in millimolar Ca2+ concentration range. Experiments of gradual EF-hand deletions suggest that the second EF-hand domain is essential for calumenin binding to RyR1. Adenovirus-mediated overexpression of calumenin-2 in C2C12 myotubes led to increased caffeine-induced Ca2+ release, but decreased depolarization-induced Ca2+ release. Taken together, we propose that calumenin-2 in the SR lumen can directly regulate the RyR1 activity in Ca2+-dependent manner.

Antiplatelet Therapy after Percutaneous Coronary Intervention

There is intense interest in the relationship between inflammation, thrombosis, platelet aggregation, and hyperlipidemia in patients with coronary artery disease. The specific role of inflammation with its linkage to the coagulation cascade has been well studied. A number of inflammatory markers have been identified which can be used for risk stratification in patients with acute coronary syndromes. Patients with acute coronary syndromes at the time of presentation often have an underlying inflammatory state which needs therapy with antiplatelet regimens including now increasingly frequently clopidogrel in addition to the standard of aspirin. In those patients who are treated medically for their acute coronary syndromes, long-term treatment with dual antiplatelet therapy has been documented to be associated with improved outcome. In patients who undergo an invasive approach with placement of intracoronary stents, the importance of dual antiplatelet therapy is increased. Drug-eluting stents are now used in approximately 90% of all interventional procedures. There is evidence to suggest that while these patients have improved outcome in terms of a decreased need for subsequent procedures to treat restenosis, there is the potential for late subacute stent thrombosis. When late subacute stent thrombosis occurs, it results in mortality or infarction in 40-60% of patients. Dual antiplatelet therapy is therefore recommended for an increasingly longer time in this patient group. At the present time, protocols indicate 3 months for one of the drug-eluting stents and 6 months for the other. However, increasingly longer antiplatelet therapy is being used clinically. Assessment of platelet function during follow-up is as yet early. There are issues about which specific test to use and the definition of platelet hyperreactivity. In the future, more individually targeted therapy may be possible if we can more adequately assess the degree of hyperreactivity and underlying inflammation.

Platelet depletion in mice increases mortality after thermal injury

Platelets play a fundamental role in maintaining hemostasis and have been shown to participate in innate and adaptive immunity. However, the role of platelets in the immune response to injury remains undefined. We tested the importance of platelets in the host response to serious injury in a newly developed platelet-deficient mouse model. Wild-type and platelet-depleted C57BL/6J mice underwent a 25% full-thickness total body surface area thermal or sham injury. Platelet-deficient mice showed survival of 51% at 48 hours after injury compared with 94% to 100% survival in experimental control mice (P < .001). Necropsy and histology ruled out hemorrhage and hypovolemia as causes of death. Percentages of peripheral blood monocytes (P < .01) and neutrophils (P < .05) were increased between 36 and 48 hours after thermal injury in platelet-deficient mice compared with control mice. Plasma levels of TNFalpha (P < .001), IL-6 (P < .001), and MCP-1 (P < .05) were also elevated by 24 hours whereas levels of TGFbeta(1) were reduced between 24 and 36 hours following injury in platelet-depleted mice (P < .001) compared with control mice. Our findings demonstrate for the first time that platelets play a critical protective role during the host response to injury. Moreover, our findings suggest that platelets and, more importantly, platelet-derived TGFbeta(1) modulate the systemic inflammatory response occurring after injury.

Platelets in inflammation and atherogenesis

Platelets represent an important linkage between inflammation, thrombosis, and atherogenesis. Inflammation is characterized by interactions among platelets, leukocytes, and ECs. These interactions trigger autocrine and paracrine activation processes that lead to leukocyte recruitment into the vascular wall. Platelet-induced chronic inflammatory processes at the vascular wall result in development of atherosclerotic lesions and atherothrombosis. This Review highlights the molecular machinery and inflammatory pathways used by platelets to initiate and accelerate atherothrombosis.

Minding the gaps to promote thrombus growth and stability

Efforts to understand the role of platelets in hemostasis and thrombosis have largely focused on the earliest events of platelet activation, those that lead to aggregation. Although much remains to be learned about those early events, this Review examines a later series of events: the interactions between platelets that can only occur once aggregation has begun, bringing platelets into close contact with each other, creating a protected environment in the gaps between aggregated platelets, and fostering the continued growth and stability of the hemostatic plug.

Platelet genomics and proteomics in human health and disease

Proteomic and genomic technologies provide powerful tools for characterizing the multitude of events that occur in the anucleate platelet. These technologies are beginning to define the complete platelet transcriptome and proteome as well as the protein-protein interactions critical for platelet function. The integration of these results provides the opportunity to identify those proteins involved in discrete facets of platelet function. Here we summarize the findings of platelet proteome and transcriptome studies and their application to diseases of platelet function.

Pharmacological targeting of catalyzed protein folding: the example of peptide bond cis/trans isomerases

Peptide bond isomerases are involved in important physiological processes that can be targeted in order to treat neurodegenerative disease, cancer, diseases of the immune system, allergies, and many others. The folding helper enzyme class of Peptidyl-Prolyl-cis/trans Isomerases (PPIases) contains the three enzyme families of cyclophilins (Cyps), FK506 binding proteins (FKBPs), and parvulins (Pars). Although they are structurally unrelated, all PPIases catalyze the cis/trans isomerization of the peptide bond preceding the proline in a polypeptide chain. This process not only plays an important role in de novo protein folding, but also in isomerization of native proteins. The native state isomerization plays a role in physiological processes by influencing receptor ligand recognition or isomer-specific enzyme reaction or by regulating protein function by catalyzing the switch between native isomers differing in their activity, e.g., ion channel regulation. Therefore elucidating PPIase involvement in physiological processes and development of specific inhibitors will be a suitable attempt to design therapies for fatal and deadly diseases.

New Surgical Treatments for Osteochondritis Dissecans and Subchondral Bone Cysts

Osteochondritis dissecans (OCD) and subchondral bone cysts (SBCs) occur commonly and at many different locations in equine limbs and can lead to secondary osteoarthritis when left untreated. Depending on the location and extent of the lesion, arthroscopic surgical debridement may be an effective treatment for returning a horse to athletic soundness. In many cases, however, additional techniques to improve the healing response in bone and cartilage are needed so as to preserve articular function. Methods for improving cartilage repair (ie, restoration of damaged cartilage)or regeneration (ie, reformation or recreation of new articular cartilage) in select cases of OCD and SBCs are discussed.

Applying proteomics technology to platelet research

Platelets are small enucleated cells that circulate in the blood, where they play a key role in hemostasis and contribute to the formation of vascular plugs. Pathologically, they are involved in thrombosis and heart disease. Because platelets do not have a nucleus, proteomics offers a powerful way to approach their biology. Proteomics technology is based on the huge analytical power offered by mass spectrometry in combination with several separation techniques, such as two-dimensional gel electrophoresis (2DGE) or multidimensional liquid chromatography. Proteomics provides information about the complete set of proteins present in platelets, the platelet proteome, including post-translational variants. Over the last years, several research groups have applied proteomics to platelet research. A detailed analysis of the general proteome and signaling cascades in human platelets will improve our knowledge of platelet function, and thereby aid the development of new therapeutic agents to treat thrombotic diseases. This review presents the major advances in mass spectrometry-based proteomics techniques and their application to platelet research, and analyzes in detail the most relevant contributions to the field.

Correlation of probioticLactobacillus salivariusgrowth phase with its cell wall-associated proteome

Lactobacillus salivarius subsp. salivarius UCC118 is a probiotic bacterium that was originally isolated from human intestinal tissues and was subsequently shown in a pilot study to alleviate symptoms associated with mild-moderate Crohn's disease. Strain UCC118 can adhere to animal and human intestinal tissue, and to both healthy and inflamed ulcerative colitis mucosa, irrespective of location in the gut. In this study, an enzymatic technique has been combined with proteomic analysis to correlate bacterial growth phase with the presence of factors present in the cell wall of the bacterium. Using PAGE electrophoresis, it was determined that progression from lag to log to stationary growth phases in vitro correlated with increasing prominence of an 84kD protein associated with in vitro adherence ability. Isolated proteins from the 84kD band region were further separated by two-dimensional electrophoresis, resolving this band into 20 individual protein spots at differing isoelectric points. The protein moieties were excised, trypsin digested and subjected to tandem mass spectrometry. The observed proteins are analogous to those reported to be associated with the Listeria monocytogenes cell-wall proteome, and include DnaK, Ef-Ts and pyruvate kinase. These data suggest that at least some of the beneficial attributes of probiotic lactobacilli, and in particular this strain, may be due to nonpathogenic mimicry of pathogens and potentially be mediated through a form of attenuated virulence.

Quest for novel cardiovascular biomarkers by proteomic analysis

Atherosclerosis, and the resulting coronary heart disease and stroke, is the most common cause of death in developed countries. Atherosclerosis is an inflammatory process that results in the development of complex lesions or plaques that protrude into the arterial lumen. Plaque rupture and thrombosis result in the acute clinical complications of myocardial infarction (MI) and stroke. Although certain risk factors (dyslipidemias, diabetes, hypertension) and humoral markers of plaque vulnerability (C-reactive protein, interleukin-6, 10 and 18, CD40L) have been identified, a highly sensitive and specific biomarker or protein profile, which could provide information on the stability/vulnerability of atherosclerotic lesions, remains to be identified. In this review, we report several proteomic approaches which have been applied to circulating or resident cells, atherosclerotic plaques or plasma, in the search for new proteins that could be used as cardiovascular biomarkers. First, an example using a differential proteomic approach (2-DE and MS) comparing the secretome from control mammary arteries and atherosclerotic plaques is displayed. Among the different proteins identified, we showed that low levels of HSP-27 could be a potential marker of atherosclerosis. Second, we have revised several studies performed in cells involved in the pathogenesis of atherosclerosis (foam cells and smooth muscle cells). Another approach consists of performing proteomic analysis on circulating cells or plasma, which will provide a global view of the whole body response to atherosclerotic aggression. Circulating cells can bear information reflecting directly an inflammatory or pro-coagulant state related to the pathology. As an illustration, we report that circulating monocytes and plasma in patients with acute coronary syndromes has disclosed that mature Cathepsin D is increased both in the plasma and monocytes of these patients. Finally, the problems of applying proteomic approach directly to plasma will be discussed. The purpose of this review is to provide the reader with an overview of different proteomic approaches that can be used to identify new biomarkers in vascular diseases.

The human platelet proteome mapped by peptide-centric proteomics: a functional protein profile

Several studies have been published in which holistic approaches were used to characterise the proteome and transcriptome of human platelets. The key intent being that a deeper understanding of the normal and aberrant physiological functions of platelets can only be achieved if most biomolecular building blocks are mapped. Here we present the application of recently developed novel technologies that overcome some of the shortcomings of gel-based proteomics. Central in our approach is the so-called combined fractional diagonal chromatography (COFRADIC)-technology in which sets of representative peptides are sorted in a diagonal RP chromatographic system through a specific modification of their side chain. In this study we combined three different COFRADIC sorting techniques to analyse the proteome of human platelets. Methionyl, cysteinyl and amino terminal peptides were isolated and analysed by MS/MS. Merging the peptide identifications obtained after database searching resulted in a core set of 641 platelet proteins, which comprises the largest set identified today. In comparison to previously published platelet proteomes, we identified 404 novel platelet proteins containing a high number of hydrophobic membrane proteins and hypothetical proteins. Furthermore we discuss the observed characteristics and potential benefits of each of the different COFRADIC technologies for proteome analysis and highlight important issues that need to be considered when searching sequence databases using data obtained in peptide-centric, non-gel proteomics studies.

Recent advances in blood-related proteomics

Blood is divided in two compartments, namely, plasma and cells. The latter contain red blood cells, leukocytes, and platelets. From a descriptive medical discipline, hematology has evolved towards a pioneering discipline where molecular biology has permitted the development of prognostic and diagnostic indicators for disease. The recent advance in MS and protein separation now allows similar progress in the analysis of proteins. Proteomics offers great promise for the study of proteins in plasma/serum, indeed a number of proteomics databases for plasma/serum have been established. This is a very complex body fluid containing lipids, carbohydrates, amino acids, vitamins, nucleic acids, hormones, and proteins. About 1500 different proteins have recently been identified, and a number of potential new markers of diseases have been characterized. Here, examples of the enormous promise of plasma/serum proteomic analysis for diagnostic/prognostic markers and information on disease mechanism are given. Within the blood are also a large number of different blood cell types that potentially hold similar information. Proteomics of red blood cells, until now, has not improved our knowledge of these cells, in contrast to the major progresses achieved while studying platelets and leukocytes. In the future, proteomics will change several aspects of hematology.

Platelet Toll-like receptor expression modulates lipopolysaccharide-induced thrombocytopenia and tumor necrosis factor-alpha production in vivo

Toll-like receptors (TLRs) play a critical role in stimulating innate immunity by recognizing pathogen-associated molecular patterns (PAMPs) on invading microorganisms. Platelets also play a role in innate immunity, and we studied whether they express TLR. Results show that human and murine platelets variably expressed TLR2, TLR4, and TLR9 by flow cytometry and Western blotting. TLR4 expression was confirmed by demonstrating murine platelet binding to lipopolysaccharide (LPS). Thrombin activation of the platelets significantly enhanced the expression of TLR9, suggesting that at least some TLRs may derive from intracellular compartments. When LPS was administered to LPS-sensitive C3H/HeN and LPS-resistant C3H/HeJ mice, functional TLR4 expression in vivo was shown to be responsible for LPS-induced thrombocytopenia. However, when the C3H/HeN mice were first rendered thrombocytopenic by an antiplatelet antibody and then administered LPS, a significant reduction occurred in their ability to produce TNF-alpha. The decreased cytokine production in the thrombocytopenic mice was restored with platelet transfusion. These results suggest that platelets express various TLRs and that the functional significance of one of these, TLR4, appears to be a role in the modulation of LPS-induced thrombocytopenia and TNF-alpha production. This work implicates platelets as important mediators of innate immune responses against invading microorganisms.

Mapping the platelet proteome: a report of the ISTH Platelet Physiology Subcommittee

Proteomic technology has the potential to transform the way we analyze platelet biology, through the determination of platelet protein composition and its modification upon stimulation and with disease. We are a considerable way from achieving these goals, however, because of significant limitations in current methodology. It is therefore important to consider the extent to which these aims can be met and the way that proteomic data should be presented and used. These issues are discussed in the present paper by the Platelet Physiology Subcommittee of the ISTH Scientific Standardisation Committee (SSC). It is recommended that proteomic information be combined with data from other experimental approaches to establish a database on protein expression and function in platelets.

Two-dimensional Blue Native/sodium dodecyl sulfate gel electrophoresis for analysis of multimeric proteins in platelets

Two-dimensional (2-D) Blue Native/SDS gel electrophoresis combines a first-dimensional separation of monomeric and multimeric proteins in their native state with a second denaturing dimension. These high-resolution 2-D gels aim at identifying multiprotein complexes with respect to their subunit composition. We applied this method for the first time to analyze two human platelet subproteomes: the cytosolic and the microsomal membrane protein fraction. Solubilization of platelet membrane proteins was achieved with the nondenaturing detergent n-dodecyl-beta-D-maltoside. To validate native solubilization conditions, we demonstrated the correct assembly of the Na,K-ATPase, a functional multimeric transmembrane protein, when expressed in Xenopus oocytes. We identified 63 platelet proteins after in-gel tryptic digestion of 58 selected protein spots and liquid chromatography-coupled tandem mass spectrometry. Nine proteins were detected for the first time in platelets by a proteomic approach. We also show that this technology efficiently resolves several known membrane and cytosolic multiprotein complexes. Blue Native/SDS gel electrophoresis is thus a valuable procedure to analyze specific platelet subproteomes, like the membrane(-bound) protein fraction, by mass spectrometry and immunoblotting and could be relevant for the study of protein-protein interactions generated following platelet activation.

Mechanisms of thrombopoiesis

Megakaryocytes (MKs) expand and differentiate over several days in response to thrombopoietin (Tpo) before releasing innumerable blood platelets. The final steps in platelet assembly and release represent a unique cellular transformation that is orchestrated by a range of transcription factors, signaling molecules, and cytoskeletal elements. Here we review recent advances in the physiology and molecular basis of MK differentiation. Genome-wide approaches, including transcriptional profiling and proteomics, have been used to identify novel platelet products and differentiation markers. The extracellular factors, stromal-derived factor (SDF)-1 chemokine and fibroblast growth factor (FGF)-4 direct MK interactions with the bone marrow stroma and regulate cytokine-independent cell maturation. An abundance of bone marrow MKs induce pathologic states, including excessive bone formation and myelofibrosis, and the basis for these effects is now better appreciated. We review the status of transcription factors that control MK differentiation, with special emphasis on nuclear factor-erythroid 2 (NF-E2) and its two putative target genes, beta1-tubulin and 3-beta-hydroxysteroid reductase. MKs express steroid receptors and some estrogen ligands, which may constitute an autocrine loop in formation of proplatelets, the cytoplasmic protrusions within which nascent blood platelets are assembled. Finally, we summarize our own studies on cellular and molecular facets of proplatelet formation and place the findings within the context of outstanding questions about mechanisms of thrombopoiesis.

Measurement of adhesion of human platelets in plasma to protein surfaces in microplates

INTRODUCTION

Platelet adhesion is an initial, crucial and complex event for inhibiting blood loss upon vascular injury. Activation and adhesion of platelets also play a fundamental role in the development of thrombosis. A combination of exposed extracellular matrix proteins in the vascular wall and release of activating compounds from the participating cells activate the platelets. New potent anti-platelet agents are in progress but there is a shortage of methods that measure the concerted action of adhesive surfaces and soluble compounds upon platelet adhesion in vitro. The aim of this work was to develop a method to measure adhesion of platelets in plasma with standard laboratory equipment.

METHODS

Platelet-rich plasma from healthy humans was used in studies to optimise the conditions of the present assay. Different proteins were coated in microplate wells and various soluble platelet activators and inhibitors were added to establish the ability of the current method to detect increased as well as decreased platelet adhesion. The amount of platelet adhesion was measured by the reaction between p-nitrophenyl phosphate and the intracellular enzyme acid phosphatase.

RESULTS

Adhesion of platelets in plasma to microplate wells coated with albumin, collagen, fibrinogen and activated plasma showed significant surface dependency. The known soluble platelet activators adenosine diphosphate, adrenaline and ristocetin enhanced the levels of adhesion. Available anti-platelet agents such as prostacyclin, forskolin, acetylsalicylic acid and RGD containing peptides caused dose-dependent inhibition of platelet adhesion.

DISCUSSION

This report describes a further development of a previously described method and offers the advantage to use platelets in plasma to measure platelet adhesion to protein surfaces. The assay is simple and flexible and is suitable in basic research for screening and characterisation of platelet adhesion responsiveness.

Using proteomics to identify potential therapeutic targets in platelets

Proteomics has provided powerful new insights into the complex events of the anucleate platelet and has revealed many potential protein targets in the search for suitable agents for thrombotic disease. In the present study, we summarize recent proteomic approaches to analyse specific platelet subproteomes, such as the platelet releasate, the platelet phosphotyrosine proteome and characterization of the proteins associated with membrane lipid rafts.

From proteomics to biomarker discovery in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly. AD is an invariably fatal neurodegenerative disorder with no effective treatment or definitive antemortem diagnostic test. Little is known about the changes in the brain preceding or accompanying initiation of the disease. Understanding the biological processes, which occur during AD onset and/or progression, will improve the diagnosis and treatment of the disease. As we will discuss in this review article, using high-throughput cDNA microarray we identified candidate genes whose expression is altered in the brain of cases at risk for AD dementia. However, it is possible that the use of the cDNA microarray technology alone may underestimate post-transcriptional modifications and therefore provides only a partial view of the biological problem of interest. As such, the combination of cDNA and protein arrays may provide a more global picture of the biological processes being studied. Based on this hypothesis, we initiated a series of high-throughput proteomic studies and found that the expressions of proteins involved in synaptic plasticity are selectively altered in the brain of cases at high risk to develop AD dementia (mild cognitive impairment; MCI). This is consistent with our cDNA microarray evidence showing that the expression of a-type synapsins is selectively altered in the brain of MCI cases. Collectively, these studies support the feasibility and usefulness of high-throughput cDNA microarray and proteomics techniques to study the sequential changes of distinctive gene expression patterns in the brain as a function of the progression of AD dementia.

New horizons in the analysis of circulating cell-derived microparticles

Analysis of circulating cell-derived microparticles (MP) is becoming more refined and clinically useful. This review, stemming from lectures given at Tokyo late 2003, does not repeat prior reviews but focuses on new horizons. A major theme is the rising recognition of platelets and their MP (PMP) as key mediators of inflammation/immunity. Among the major concepts developed are that (i) many so-called soluble markers of inflammation are in reality MP-bound; (ii) PMP and other MP appear to serve important signaling and immune functions including antigen presentation. In conclusion, MP analysis is poised to enter the mainstream of clinical testing, measuring specific antigens rather than gross levels. However, more research is needed to decisively establish their functions, and international standards are needed to allow comparing results from different laboratories.

Pathobiology and cell interactions of platelets in diabetes

Diabetes is a well-recognised risk factor for atherosclerotic cardiovascular disease and in fact most diabetic patients die from vascular complications. The Diabetes Control and Complications Trial (DCCT) and the U.K. Prospective Diabetes Study (UKPDS) indicate a consistent relationship between hyperglycaemia and the incidence of chronic vascular complications in patients with diabetes. Platelets are essential for haemostasis, and abnormalities of platelet function may cause vascular disease in diabetes. Diabetic patients have hyperreactive platelets with exaggerated adhesion, aggregation and thrombin generation. In summary, the entire coagulation cascade is dysfunctional in diabetes. This review provides a comprehensive overview of the physiological role of platelets in maintaining haemostasis and of the pathophysiological processes that contribute to platelet dysfunction in diabetes and associated cardiovascular diseases, with special emphasis on proteomic approaches and leukocyte-platelet cross-talk.

Application of proteomics to the study of platelet regulatory mechanisms

Newly developed proteomic technologies now permit the routine identification of hundreds or even thousands of proteins in a single experiment. However, the global study of any proteome has unique challenges that set it apart from comprehensive studies of genes and transcripts. The detection of low-abundance, biologically relevant proteins poses a particular challenge, especially given that the dynamic range of proteins in cells is estimated to be > or =10(6). Nevertheless, the incorporation of proteomics into functional biochemical and biologic investigation has proved to be a powerful tool when applied to platelet biology. This review highlights recent proteomic approaches to the characterization of the proteins released from activated platelets and to the identification of integrin-associated regulators of platelet function. Also described are efforts to link platelet-proteomic and platelet-transcriptional data.

Platelet Proteomics: Identification of Potential Therapeutic Targets

The integration of proteomics into biochemical and biological investigation has proved a powerful tool in understanding the anucleate platelet. Over the past few years, various approaches have been used to document platelet proteins and here, we describe our efforts to analyse specific platelet subproteomes so as to capture biologically relevant proteins of low abundance. These include characterisation of the phosphotyrosine proteome, the platelet releasate and more recently, the proteome of membrane lipid rafts. These approaches have revealed a wealth of relevant platelet proteins, which may in the future prove suitable as therapeutic targets in atherothrombosis.

The physiology of vitamin K nutriture and vitamin K-dependent protein function in atherosclerosis

Recent advances in the discovery of new functions for vitamin K-dependent (VKD) proteins and in defining vitamin K nutriture have led to a substantial revision in our understanding of vitamin K physiology. The only unequivocal function for vitamin K is as a cofactor for the carboxylation of VKD proteins which renders them active. While vitamin K was originally associated only with hepatic VKD proteins that participate in hemostasis, VKD proteins are now known to be present in virtually every tissue and to be important to bone mineralization, arterial calcification, apoptosis, phagocytosis, growth control, chemotaxis, and signal transduction. The development of improved methods for analyzing vitamin K has shed considerable insight into the relative importance of different vitamin K forms in the diet and their contribution to hepatic vs. non-hepatic tissue. New assays that measure the extent of carboxylation in VKD proteins have revealed that while the current recommended daily allowance for vitamin K is sufficient for maintaining functional hemostasis, the undercarboxylation of at least one non-hemostatic protein is frequently observed in the general population. The advances in defining VKD protein function and vitamin K nutriture are described, as is the potential impact of VKD proteins on atherosclerosis. Many of the VKD proteins contribute to atherogenesis. Recent studies suggest involvement in arterial calcification, which may be influenced by dietary levels of vitamin K and by anticoagulant drugs such as warfarin that antagonize vitamin K action.

Gene expression analysis in platelets from a single donor: evaluation of a PCR-based amplification technique

BACKGROUND

Genetic analysis of platelet mRNA may facilitate the diagnosis of disorders affecting the megakaryocytic-platelet lineage. Its use, however, is limited by the exceptionally small yield of platelet mRNA and the risk of leukocyte contamination during platelet preparation.

METHODS

We depleted platelet suspensions of leukocytes by filtration and used a PCR-based RNA amplification step [switching mechanism at the 5' end of RNA templates (SMART)]. We tested the reliability and precision of the RNA amplification procedure by use of real-time PCR to measure quantities of specific transcripts: von Willebrand factor (vWF), A-subunit of coagulation factor XIII (F13A), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Microarray analysis was performed on platelet RNA with and without amplification.

RESULTS

Microgram quantities of platelet-specific cDNAs were produced from as little as 50 ng of total platelet RNA or 40 mL of whole blood. At cycle numbers <16, amplification of all transcripts tested was exponential with slightly more efficient amplification of low-abundance transcripts. Expression profiling of 9850 genes gave identical results for 9815 genes (1576 positive/8239 negative). Eight transcripts failed to be amplified by the SMART procedure. Expression of vWF, F13A, and GAPDH transcripts showed only minor day-to-day variations in three healthy individuals.

CONCLUSION

The proposed protocol makes extremely small amounts of platelet RNA available for gene expression analysis in single patients.

Interactions between the megakaryocyte/platelet-specific beta1 tubulin and the secretory leukocyte protease inhibitor SLPI suggest a role for regulated proteolysis in platelet functions

Platelet-restricted beta1 tubulin is required for optimal thrombopoiesis and discoid cell shape. To identify interacting factors, we used the divergent beta1-tubulin C-terminus as the bait in a yeast 2-hybrid screen of megakaryocyte (MK) cDNAs. We isolated secretory leukocyte protease inhibitor (SLPI), a serine protease antagonist characterized principally as a secreted factor with multiple roles in inflammation. SLPI is expressed in MKs and platelets in 2 discrete compartments. One pool resides in punctate cytoplasmic structures, whereas a significant fraction localizes along peripheral microtubules (MTs) and is lost with cold-induced MT disruption or in beta1 tubulin(-/-) platelets. These findings reveal unexpected interaction between a prominent cytoskeletal protein and an inhibitor of proteolysis. SLPI(-/-) mice show intact proplatelet formation, platelet numbers and shape, and marginal MT bands; thus, SLPI is not essential for thrombopoiesis. However, SLPI is released upon platelet activation, which also reverses its association with the resting marginal band. Platelet SLPI inhibits neutrophil elastase, an activity that is reduced when beta1 tubulin is absent. We conclude that SLPI localizes in part along the MK and platelet MT cytoskeleton by virtue of specific interactions with beta1 tubulin. SLPI may thus have unanticipated roles in MK and platelet functions, including regulated proteolysis after activation.

Transgenic mice overexpressing cyclophilin A are resistant to cyclosporin A-induced nephrotoxicity via peptidyl-prolyl cis–trans isomerase activity

Cyclosporin A (CsA) suppresses immune reaction by inhibiting calcineurin activity after forming complex with cyclophilins and is currently widely used as an immunosuppressive drug. Cyclophilin A (CypA) is the most abundantly and ubiquitously expressed family member of cyclophilins. We previously showed that CsA toxicity is mediated by ROS generation as well as by inhibition of peptidyl-prolyl cis-trans isomerase (PPIase) activity of CypA in CsA-treated myoblasts [FASEB J. 16 (2002) 1633]. Since CsA-induced nephrotoxicity is the most significant adverse effect in its clinical utilization, we here investigated the role of CsA inhibition of CypA PPIase activity in its nephrotoxicity using transgenic mouse models. Transgenic mice of either wild type (CypA/wt) or R55A PPIase mutant type (CypA/R55A), a dominant negative mutant of CypA PPIase activity, showed normal growth without any apparent abnormalities. However, CsA-induced nephrotoxicity was virtually suppressed in CypA/wt mice, but exacerbated in CypA/R55A mice, compared to that of littermates. Also, life expectancy was extended in CypA/wt mice and shortened in CypA/R55A mice during CsA administration. Besides, CsA-induced nephrotoxicity was inversely related to the levels of catalase expression and activity. In conclusion, our data provide in vivo evidence that supplement of CypA PPIase activity allows animal's resistance toward CsA-induced nephrotoxicity.

Integration of proteomics and genomics in platelets: a profile of platelet proteins and platelet-specific genes

Platelets, while anucleate, contain RNA, some of which is translated into protein upon activation. Hypothesising that the platelet proteome is reflected in the transcriptome, we identified 82 proteins secreted from activated platelets and compared these, as well as published proteomic data, to the transcriptional profile. We also compared the transcriptome of platelets to other tissues to identify platelet-specific genes and used ontology to determine gene categories over-represented in platelets. RNA was isolated from highly pure platelet preparations for hybridization to Affymetrix oligonucleotide arrays. We identified 2,928 distinct messages as being present in platelets. The platelet transcriptome was compared with the proteome by relating both to UniGene clusters. Platelet proteomic data correlated well with the transcriptome, with 69% of secreted proteins detectable at the mRNA level, and similar concordance was obtained using two published datasets. While many of the most abundant mRNAs are for known platelet proteins, messages were detected for proteins not previously reported in platelets. Some of these may represent residual megakaryocyte messages; however, proteomic analysis confirmed the expression of many previously unreported genes in platelets. Transcripts for well-described platelet proteins are among the most platelet-specific messages. Ontological categories related to signal transduction, receptors, ion channels, and membranes are over-represented in platelets, while categories involved in protein synthesis are depleted. Despite the absence of gene transcription, the platelet proteome is mirrored in the transcriptome. Conversely, transcriptional analysis predicts the presence of novel proteins in the platelet. Transcriptional analysis is relevant to platelet biology, providing insights into platelet function and the mechanisms of platelet disorders.