Syncytin-1/HERV-W envelope is an early activation marker of leukocytes and is upregulated in multiple sclerosis patients.

Syncytin-1 is the envelope protein of the human endogenous retrovirus W (HERV-W). It has been related to multiple sclerosis (MS) but its role in cellular immunity and its pathogenic mechanism in the autoimmune context are not fully understood. We analyzed syncytin-1 levels in peripheral blood mononuclear cells (PBMC) subsets from healthy donors, MS patients in relapse or remission, and patients with acute infections by flow cytometry. PBMC cultures were also prepared to analyze protein expression kinetics. MS patients had higher levels of syncytin-1 levels than controls. We found that syncytin-1 is elevated in monocytes during MS relapses and infections. Cells expressing syncytin-1, including monocytes, T and B lymphocytes, and NKs presented mainly an activated phenotype and, upon stimulation with LPS, its levels increased rapidly on antigen-presenting cells. Syncytin-1 ligation promoted the activation of monocytes, as demonstrated by the upregulation of CD80 and the nonclassical subset CD14low CD16+ . Our results suggest an important role for syncytin-1 in the activation of leukocytes. Given that the expression of syncytin-1 is upregulated in MS patients, this protein might be contributing to the autoimmune cascade in the disease.

Lipocalin-2 deficiency or blockade protects against aortic abdominal aneurysm development in mice.

AIMS: To study the role of lipocalin-2 (Lcn2) and the effect of Lcn2 blockade via anti-Lcn2 antibody in the development of abdominal aortic aneurysm (AAA). METHODS AND RESULTS: Expression mRNA and protein levels of Lcn2 and its human orthologue neutrophil gelatinase-associated lipocalin (NGAL) in aortic wall samples from experimental mouse and human AAA samples, respectively, were analysed by real-time PCR and immunohistochemistry. Experimental AAA was induced by aortic elastase perfusion in wild-type mice (WT) and Lcn2-deficient mice (Lcn2-/-). NGAL/Lcn2 mRNA and protein levels in human and murine AAA samples were increased compared with healthy aortas. Decreased AAA incidence and reduced aortic expansion were observed in Lcn2-/- mice or mice preoperative treated with a polyclonal anti-Lcn2 antibody compared with WT mice or mice treated with control IgG, respectively, at Day 14 after elastase perfusion. Moreover, immunohistochemical analysis of AAA tissues from Lcn2-/- or anti-Lcn2-treated mice showed diminished elastin damage, reduced microvessels and polymorphonuclear neutrophil (PMN) infiltration, and enhanced preservation of vascular smooth muscle cells compared with WT aortas. Fluorescent molecular tomography revealed decreased MMP activity in AAA of Lcn2-/- mice compared with WT controls. Therapeutic administration of anti-Lcn2 antibody to WT mice 3 days after elastase perfusion decreased aortic dilatation and PMN infiltration compared with WT mice treated with control IgG. CONCLUSION: Either Lcn2 deficiency or anti-Lcn2 antibody blockade limits AAA expansion in mice by decreasing PMN infiltration in the aorta. Lcn2 modulation may therefore be a viable new therapeutic option for the treatment of AAA.

A functional variant that affects exon-skipping and protein expression of SP140 as genetic mechanism predisposing to multiple sclerosis.

Several variants in strong linkage disequilibrium (LD) at the SP140 locus have been associated with multiple sclerosis (MS), Crohn's disease (CD) and chronic lymphocytic leukemia (CLL). To determine the causal polymorphism, we have integrated high-density data sets of expression quantitative trait loci (eQTL), using GEUVADIS RNA sequences and 1000 Genomes genotypes, with MS-risk variants of the high-density Immunochip array performed by the International Multiple Sclerosis Genetic Consortium (IMSGC). The variants most associated with MS were also correlated with a decreased expression of the full-length RNA isoform of SP140 and an increase of an isoform lacking exon 7. By exon splicing assay, we have demonstrated that the rs28445040 variant was the causal factor for skipping of exon 7. Western blots of peripheral blood mononuclear cells from MS patients showed a significant allele-dependent reduction of the SP140 protein expression. To confirm the association of this functional variant with MS and to compare it with the best-associated variant previously reported by GWAS (rs10201872), a case-control study including 4384 MS patients and 3197 controls was performed. Both variants, in strong LD (r(2) = 0.93), were found similarly associated with MS [P-values, odds ratios: 1.9E-9, OR = 1.35 (1.22-1.49) and 4.9E-10, OR = 1.37 (1.24-1.51), respectively]. In conclusion, our data uncover the causal variant for the SP140 locus and the molecular mechanism associated with MS risk. In addition, this study and others previously reported strongly suggest that this functional variant may be shared with other immune-mediated diseases as CD and CLL.

Identification of novel biomarkers of abdominal aortic aneurysms by 2D-DIGE and MALDI-MS from AAA-thrombus-conditioned media.

In the search for novel biomarkers, noncandidate-based proteomic strategies open up new opportunities to gain a deeper insight into disease processes regarding their molecular mechanisms, the risk factors involved, and the monitoring of disease progression. To carry out these complex analyses, the combined use of gel electrophoresis with mass spectrometry (MS) represents a powerful choice. In addition, the introduction of protein dye labeling has notably improved the reliability of differential expression studies by increasing the statistical significance of the protein candidates. Here, we describe a strategy where different layers (luminal/abluminal) from the intraluminal thrombus (ILT) of human abdominal aortic aneurysm (AAA) patients were incubated in protein-free medium. Then, the levels of the proteins released were compared by two-dimensional differential in-gel electrophoresis (2D-DIGE) and the proteins of interest identified by MS. We consider that the use of tissue-conditioned media could offer a substantial advantage in the analytical study of biological fluids, as they provide a source of proteins to be released to the bloodstream, which could serve as potential circulating biomarkers.

Unraveling biomarkers of abdominal aortic aneurisms by iTRAQ analysis of depleted plasma.

Abdominal aortic aneurysm (AAA) is a significant health problem in Western countries. The diameter of AAA is a surrogate marker of its growth rate that reflects the magnitude of the degenerative process in the vascular wall, although most AAAs show discontinuous growth patterns and alternate periods of stability and nongrowth with periods of acute expansion and occasionally ruptures. Thus, the identification of biomarkers of AAA in plasma could aid in the diagnosis, prognosis, and therapy of AAA progression. However, owing to the complex composition of plasma, depletion methods must be applied before the analytical approaches for detecting low-abundant plasma protein components. In the present work, we describe a proteomic study on MARS 14-depleted plasma based on mass spectrometry (MS) which combines peptide labelling (isobaric tagging for relative and absolute quantification, iTRAQ) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). This quantitative approach revealed altered levels of several proteins related to the complement system in AAA patients.

Erythrocytes, leukocytes and platelets as a source of oxidative stress in chronic vascular diseases: detoxifying mechanisms and potential therapeutic options.

Oxidative stress is involved in the chronic pathological vascular remodelling of both abdominal aortic aneurysm and occlusive atherosclerosis. Red blood cells (RBCs), leukocytes and platelets present in both, aneurysmal intraluminal thrombus and intraplaque haemorraghes, could be involved in the redox imbalance inside diseased arterial tissues. RBCs haemolysis may release the pro-oxidant haemoglobin (Hb), which transfers heme to tissue and low-density lipoproteins. Heme-iron potentiates molecular, cell and tissue toxicity mediated by leukocytes and other sources of reactive oxygen species (ROS). Polymorphonuclear neutrophils release myeloperoxidase and, along with activated platelets, produce superoxide mediated by NADPH oxidase, causing oxidative damage. In response to this pro-oxidant milieu, several antioxidant molecules of plasma or cell origin can prevent ROS production. Free Hb binds to haptoglobin (Hp) and once Hp-Hb complex is endocytosed by CD163, liberated heme is converted into less toxic compounds by heme oxygenase-1. Iron homeostasis is mainly regulated by transferrin, which transports ferric ions to other cells. Transferrin-bound iron is internalised via endocytosis mediated by transferrin receptor. Once inside the cell, iron is mainly stored by ferritin. Other non hemo-iron related antioxidant enzymes (e.g. superoxide dismutase, catalase, thioredoxin and peroxiredoxin) are also involved in redox modulation in vascular remodelling. Oxidative stress is a main determinant of chronic pathological remodelling of the arterial wall, partially linked to the presence of RBCs, leukocytes, platelets and oxidised fibrin within tissue and to the imbalance between pro-/anti-oxidant molecules. Understanding the complex mechanisms underlying redox imbalance could help to define novel potential targets to decrease atherothrombotic risk.

Cell stress proteins in atherothrombosis.

Cell stress proteins (CSPS) are a large and heterogeneous family of proteins, sharing two main characteristics: their levels and/or location are modified under stress and most of them can exert a chaperon function inside the cells. Nonetheless, they are also involved in the modulation of several mechanisms, both at the intracellular and the extracellular compartments. There are more than 100 proteins belonging to the CSPs family, among them the thioredoxin (TRX) system, which is the focus of the present paper. TRX system is composed of several proteins such as TRX and peroxiredoxin (PRDX), two thiol-containing enzymes that are key players in redox homeostasis due to their ability to scavenge potential harmful reactive oxygen species. In addition to their main role as antioxidants, recent data highlights their function in several processes such as cell signalling, immune inflammatory responses, or apoptosis, all of them key mechanisms involved in atherothrombosis. Moreover, since TRX and PRDX are present in the pathological vascular wall and can be secreted under prooxidative conditions to the circulation, several studies have addressed their role as diagnostic, prognostic, and therapeutic biomarkers of cardiovascular diseases (CVDs).

Metabolomic study of plasma of patients with abdominal aortic aneurysm.

Abdominal aortic aneurysm (AAA) is an important health problem, both because of AAA rupture and death and because of increased cardiovascular mortality. Identification of new biomarkers of AAA may suggest novel pathological mechanisms and targets for new medical treatments to slow AAA progression. Metabolic changes in AAA patients were mainly related to carbohydrate and lipid metabolism and many of these changes can be associated with a situation of insulin resistance (which can be related to metabolic syndrome) together with altered amino acid metabolism. For the first time, metabolites that can be associated with differential metabolism by the gut microflora of AAA patients have also been found. Moreover, aminomalonic acid in plasma has been shown to be the metabolite with the biggest difference between patients suffering from large aneurysm (>5 cm) and controls.

Increased plasma levels of NGAL, a marker of neutrophil activation, in patients with abdominal aortic aneurysm.

OBJECTIVE: Neutrophil gelatinase-associated lipocalin (NGAL) plasma concentrations have been associated with cardiovascular diseases. We aimed to assess the association of NGAL with abdominal aortic aneurysm (AAA). METHODS: NGAL concentrations were analyzed by Western blotting in conditioned medium of polymorphonuclear neutrophils (PMNs) from AAA patients (n=22) and controls (n=11), and also in aortic biopsies from AAA patients and healthy controls (n=10). Plasma NGAL concentrations were measured by ELISA in three groups of subjects from France (n=60), Spain (n=75) and Australia (n=100) and associated with AAA presence and growth. RESULTS: PMNs isolated from AAA patients secreted significantly greater amounts of NGAL than PMNs from controls. Luminal thrombus released large amounts of NGAL compared to abluminal AAA thrombus, AAA wall and healthy aortic media. Plasma NGAL concentrations were significantly higher in patients with AAA than controls from France [115 (78-200) vs. 94 (72-114) ng/ml, p<0.001]. NGAL plasma concentrations in AAA patients from Spain correlated with other markers of thrombus activity (plasmin-antiplasmin complexes and D-dimer). Furthermore, a positive correlation between plasma NGAL and retrospective AAA growth (rho=0.4, p=0.01) was observed, which remained significant after adjusting for other risk factors. Plasma NGAL was only weakly associated with prospective growth in both Spanish and Australian patients. CONCLUSIONS: NGAL is released by PMNs and by the luminal part of AAA thrombus. NGAL plasma levels were increased in AAA patients compared with healthy subjects and correlated with retrospective AAA growth. Further studies in larger subjects groups are needed to confirm the association between NGAL and AAA presence and growth.

Proteomic analysis of polymorphonuclear neutrophils identifies catalase as a novel biomarker of abdominal aortic aneurysm: potential implication of oxidative stress in abdominal aortic aneurysm progression.

OBJECTIVE: Polymorphonuclear neutrophils (PMNs) play a main role in abdominal aortic aneurysm (AAA) progression. We have analyzed circulating PMNs isolated from AAA patients and controls by a proteomic approach to identify proteins potentially involved in AAA pathogenesis. METHODS AND RESULTS: PMNs from 8 AAA patients (4 large AAA >5 cm and 4 small AAA 3-5 cm) and 4 controls were analyzed by 2D differential in-gel electrophoresis. Among differentially expressed spots, several proteins involved in redox balance were identified by mass spectrometry (eg, cyclophilin, thioredoxin reductase, catalase). Diminished catalase expression and activity were observed in PMNs from AAA patients compared with controls. In contrast, PMNs from AAA patients displayed higher H(2)O(2) and myeloperoxidase levels than PMNs from controls. Moreover, a significant decrease in catalase mRNA levels was observed in PMNs after phorbol 12-myristate 13-acetate incubation. Catalase plasma levels were also decreased in large (n=47) and small (n=56) AAA patients compared with controls (n=34). We observed catalase expression in AAA thrombus and thrombus-conditioned medium, associated with PMN infiltration. Furthermore, increased H(2)O(2) levels were observed in AAA thrombus-conditioned medium compared with the media layer. CONCLUSIONS: Diminished catalase levels in circulating PMNs and plasma are observed in AAA patients, supporting an important role of oxidative stress in AAA evolution.

Identification of peroxiredoxin-1 as a novel biomarker of abdominal aortic aneurysm.

OBJECTIVE: In the search of novel biomarkers of abdominal aortic aneurysm (AAA) progression, proteins released by intraluminal thrombus (ILT) were analyzed by a differential proteomic approach. METHODS AND RESULTS: Different layers (luminal/abluminal) of the ILT of AAA were incubated, and the proteins released were analyzed by 2-dimensional difference in-gel electrophoresis. Several differentially expressed proteins involved in main AAA pathological mechanisms (proteolysis, oxidative stress, and thrombosis) were identified by mass spectrometry. Among the proteins identified, peroxiredoxin-1 (PRX-1) was more released by the luminal layer compared with the abluminal layer of the ILT, which was further validated by Western blot, ELISA, and immunohistochemistry. We demonstrated increased PRX-1 serum levels in AAA patients compared with healthy subjects and also positive correlation among PRX-1 and AAA diameter, plasmin-antiplasmin, and myeloperoxidase levels. Finally, a prospective study revealed a positive correlation between PRX-1 serum levels and AAA expansion rate. Moreover, the combination of PRX-1 and AAA size had significantly additive value in predicting growth. CONCLUSIONS: Several proteins associated with AAA pathogenesis have been identified by a proteomic approach in ILT-conditioned medium. Among them, PRX-1 serum levels are increased in AAA patients and correlate with AAA size and growth rate, suggesting the potential use of PRX-1 as a biomarker for AAA evolution.

Proteomic and metabolomic profiles in atherothrombotic vascular disease.

Atherothrombosis remains a major cause of morbidity and mortality in the western world. The underlying processes associated with clinical expression of atherothrombosis include oxidative stress and proteolysis in relation to neovascularisation and intraplaque hemorrhages, leading to immuno-inflammatory response, cell death, and extracellular matrix breakdown. The complex biological multifactorial nature of atherothrombosis requires the development of novel technologies that allow the analysis of cellular and molecular processes responsible for the transition to disease phenotypes and the discovery of new diagnostic and prognostic biomarkers. In the present article, we have reviewed recent advances in the application of proteomic and metabolomic techniques to the study of atherothrombosis. We have focused on recent studies analyzing cells involved in hemo-thrombus formation (platelets, red blood cells, and polymorphonuclear cells), as well as tissues, tissue-conditioned media, and plasma of atherothrombotic patients. In the future, the application of these high-throughput technologies, along with imaging techniques, in systems biology approaches will help to individualize medicine.

Heat shock protein 90 inhibitors attenuate inflammatory responses in atherosclerosis.

AIMS: Heat shock protein 90 (HSP90) is a ubiquitous chaperone involved in the folding, activation, and assembly of many proteins. HSP90 inhibitors [17-allylamino-17-demethoxygeldamycin (17-AAG)/17-dimethyl aminothylamino-17-demethoxygeldanamycin hydrochloride (17-DMAG)] bind to and inactivate HSP90, increasing the heat shock response and suppressing different signalling pathways. We aim to investigate the effect of HSP90 inhibitors in the modulation of inflammatory responses during atherogenesis. METHODS AND RESULTS: In human atherosclerotic plaques, HSP90 immunostaining was increased in inflammatory regions and in plaques characterized by lower cap thickness. In cultured human macrophages and vascular smooth muscle cells, treatment with either 17-AAG or 17-DMAG increased HSP70 expression and reduced transcription factor [signal transducers and activators of transcription (STAT) and nuclear factor-kappaB (NF-kappaB)] activation and chemokine expression induced by proinflammatory cytokines. In vivo, hyperlipidaemic ApoE(-/-) mice were randomized to 17-DMAG (2 mg/kg every 2 days, n = 11) or vehicle injected (n = 9) during 10 weeks. Atherosclerotic plaques of mice treated with 17-DMAG displayed increased HSP70 expression and diminished NF-kappaB and STAT activation, along with decreased lesion, lipid, and macrophage content, compared with vehicle-injected mice. In addition, treatment with 17-DMAG significantly reduced monocyte chemoattractant protein-1 levels, both in plaques and in plasma. CONCLUSION: HSP90 expression is associated with features of plaque instability in advanced human lesions. HSP90 inhibitors reduce inflammatory responses in atherosclerosis, suggesting that HSP90 could be a novel therapeutic target in atherosclerosis.

Las proteínas de choque térmico (heat shock proteins) como potenciales dianas terapéuticas en aterosclerosis / Heat shock proteins as potential therapeutic targets in atherosclerosis

Las heat shock proteins (HSP) son una familia de proteínas que se producen en grandes cantidades por la mayoría de las células como respuesta al estrés. Las HSP se localizan tanto en arterias sanas, como en placas ateroscleróticas, aunque su papel en la aterosclerosis está aún por definir. En el presente estudio, nuestro objetivo fue analizar el efecto de la modulación de las HSP en procesos involucrados en la formación de la placa de ateroma, como el estrés oxidativo, la inflamación y la apoptosis. Para ello, hemos usado un inhibidor de la HSP90 (17-AAG), el cual es capaz de inducir un aumento en los valores de expresión de la HSP70/HSP27. Inicialmente, hemos observado que el tratamiento con 17-AAG es capaz de reducir la actividad de la NAD(P)H oxidasa inducida por factor de necrosis tumoral alfa. Asimismo, el tratamiento moduló distintas vías de señalización proliferativas (p. ej., MAPK), así como la activación del factor nuclear kappa B (NF-κB) inducidas por un cócktail de citocinas (interferón gamma/interleucina 6 [IL-6]). En estas condiciones, se observó una disminución en los niveles de citocinas proinflamatorias (p. ej., IL-6). Por último, mientras el tratamiento con 17-AAG provocó una disminución en la apoptosis después de la incubación con diversos estímulos proapoptóticos, la inhibición de la HSP27 mediante transfección con un siARN específico aumentó la apoptosis celular inducida por elastasa. Estos resultados indican que la modulación de los valores de ciertas HSP puede representar una nueva aproximación terapéutica en el tratamiento de enfermedades inflamatorio-proliferativas como la aterosclerosis (AU)

Heat shock proteins (HSP) are a family of proteins present in the majority of cells and are produced as a cell protection mechanism against adverse conditions. HSP are present in both atherosclerotic plaques and healthy arteries, although their role in atherosclerosis remain to be defined. Our objective was to investigate the effect of HSP90 inhibitors in the modulation of the different processes involved in atherogenesis. We have used an HSP90 inhibitor (17-AAG), which is able to increase the heat shock response. Treatment of monocytes and vascular smooth muscle cells with 17-AAG increased HSP70 expression. Under these conditions, 17-AAG was able to decrease NADPH oxidase activity induced by TNF-α. Stimulation of cells with cytokines induced the activation of different signalling pathways (e.g. MAPKs and NF-κB) and increased the levels of cytokines such as IL-6, which was diminished by HSP90 inhibitors. Finally, while treatment with 17-AAG prevented the apoptosis of cells induced proapoptotic stimuli, HSP27 silencing increased apoptosis induced by elastase. HSP90 inhibitors decrease pro-atherogenic processes, suggesting that these drugs may have beneficial effects in the treatment of atherosclerosis (AU)

Pravastatin increases the expression of the tissue inhibitor of matrix metalloproteinase-1 and the oncogene Bax in human aortic abdominal aneurysms.

The effect of pravastatin on matrix metalloproteinase-9 (MMP-9) and the level of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 was studied in explants of human abdominal aortic aneurysm (AAA) obtained from 13 patients. The effect of pravastatin on the apoptotic status of human AAA explants was also examined. Total MMP-9 content did not differ in human AAA explants incubated in vitro in the presence or absence of pravastatin (10-6 mol/L) for 48 h. TIMP-1 levels were significantly increased in pravastatin-incubated AAA explants, but TIMP-2 production was not modified by pravastatin. Western blot experiments showed that, whereas Bax expression was increased in pravastatin-incubated AAA explants, the expression of Bcl-2 was not modified. On the other hand, the ratio of the expression of Bax to Bcl-2, an apoptotic index, was not modified by pravastatin. In the human AAA explants, the increase in Bax expression, but not the increase in TIMP-1 expression elicited by pravastatin, was reversed by L-mevalonate, a downstream HMG-CoA reductase metabolite, suggesting that the expression of Bax and TIMP-1 followed HMG-CoA reductase-dependent and -independent pathways, respectively. In conclusion, pravastatin increases both TIMP-1 and Bax expression in human AAA explants without changes in either MMP-9 activity or the apoptotic status.

Modifications by Olmesartan medoxomil treatment of the platelet protein profile of moderate hypertensive patients.

Olmesartan medoxomil is a new angiotensin II receptor blockers (ARB) which exhibits pleiotropic effects that are not fully understood. Our aims were: i) to determine the effect of Olmesartan medoxomil on blood pressure, lipid profile and renal functionality in moderately hypertensive patients with non-controlled blood pressure, ii) to determine if Olmesartan medoxomil may exert anti-inflammatory effects and modify the expression profile of platelet proteins. Thirteen moderate hypertensive patients with non-controlled systolic blood pressure (SBP) and renal function classified as Kidney Disease Outcome Quality Initiative stage 2-3 were included. Patients were treated with Olmesartan medoxomil (20 mg/day) for 6 months. SBP, proteinuria and the plasma levels of cholesterol and low density lipoprotein (LDL)-cholesterol were reduced after the treatment. Olmesartan medoxomil did not modify the circulating plasma levels of a number of proteins associated with inflammation, but reduced the expression level of different platelet proteins including tropomyosin-ß chain isotypes 3 and 4, serotransferrin isotypes 1 to 5, the leukocyte elastase inhibitor and the chloride intracellular channel-protein isotype 1. The expression of the gelsolin precursor isotype 4 was increased in the platelets after the treatment. In summary, Olmesartan medoxomil reduced SBP, total and LDL-cholesterol plasma levels and urinary protein excretion and induced changes in the expression of platelet proteins which may be related to some action of the drug at the megakaryocyte level.

Effect of parathyroid-hormone-related protein on human platelet activation.

Evidence suggests that PTHrP [PTH (parathyroid hormone)-related protein] can act as an inflammatory mediator in several pathological settings including cardiovascular disease. The aim of the present study was to determine whether PTHrP might be involved in human platelet activation. We used a turbidimetric method to determine platelet aggregation. The expression of PTH1R (PTH type 1 receptor) in human platelets was analysed by Western blot and flow cytometry analyses. PTHrP-(1-36) (10(-7) mol/l) by itself failed to modify the activation of platelets. However, it significantly enhanced ADP-induced platelet activation, and also increased the ability of other agonists (thrombin, collagen and arachidonic acid) to induce platelet aggregation. H89 (10(-6) mol/l) and 25 x 10(-6) mol/l Rp-cAMPS (adenosine 3',5'-cyclic monophosphorothioate Rp-isomer), two protein kinase A inhibitors, and 25 x 10(-9) mol/l bisindolylmaleimide I, a protein kinase C inhibitor, partially decreased the enhancing effect of PTHrP-(1-36) on ADP-induced platelet activation. Meanwhile, 10(-6) mol/l PTHrP-(7-34), a PTH1R antagonist, as well as 10(-5) mol/l PD098059, a MAPK (mitogen-activated protein kinase) inhibitor, or a farnesyltransferase inhibitor abolished this effect of PTHrP-(1-36). Moreover, 10(-7) mol/l PTHrP-(1-36) increased (2-fold over control) MAPK activation in human platelets. PTH1R was detected in platelets, and the number of platelets expressing it on their surface in patients during AMI (acute myocardial infarction) was not different from that in a group of patients with similar cardiovascular risk factors without AMI. Western blot analysis showed that total PTH1R protein levels were markedly higher in platelets from control than those from AMI patients. PTH1R was found in plasma, where its levels were increased in AMI patients compared with controls. In conclusion, human platelets express the PTH1R. PTHrP can interact with this receptor to enhance human platelet activation induced by several agonists through a MAPK-dependent mechanism.