Cardiovascular and Hemostatic Disorders: Role of STIM and Orai Proteins in Vascular Disorders.

Store-operated Ca2+ entry (SOCE) mediated by STIM and Orai proteins is a highly regulated and ubiquitous signaling pathway that plays an important role in various cellular and physiological functions. Endoplasmic reticulum (ER) serves as the major site for intracellular Ca2+ storage. Stromal Interaction Molecule 1/2 (STIM1/2) sense decrease in ER Ca2+ levels and transmits the message to plasma membrane Ca2+ channels constituted by Orai family members (Orai1/2/3) resulting in Ca2+ influx into the cells. This increase in cytosolic Ca2+ in turn activates a variety of signaling cascades to regulate a plethora of cellular functions. Evidence from the literature suggests that SOCE dysregulation is associated with several pathophysiologies, including vascular disorders. Interestingly, recent studies have suggested that STIM proteins may also regulate vascular functions independent of their contribution to SOCE. In this updated book chapter, we will focus on the physiological role of STIM and Orai proteins in the vasculature (endothelial cells and vascular smooth muscle cells). We will further retrospect the literature implicating a critical role for these proteins in vascular disease.

Cardiovascular and Hemostatic Disorders: SOCE and Ca2+ Handling in Platelet Dysfunction.

Among the Ca2+ entry mechanisms in platelets, store-operated Ca2+ entry (SOCE) plays a prominent role as it is necessary to achieve full activation of platelet functions and replenish intracellular Ca2+ stores. In platelets, as in other non-excitable cells, SOCE has been reported to involve the activation of plasma membrane channels by the ER Ca2+ sensor STIM1. Despite electrophysiological studies are not possible in human platelets, indirect analyses have revealed that the Ca2+-permeable channels involve Orai1 and, most likely, TRPC1 subunits. A relevant role for the latter has not been found in mouse platelets. There is a body of evidence revealing a number of abnormalities in SOCE or in its molecular regulators that result in qualitative platelet disorders and, as a consequence, altered platelet responsiveness upon stimulation with multiple physiological agonists. Platelet SOCE abnormalities include STIM1 and Orai1 mutations. This chapter summarizes the current knowledge in this field, as well as the disorders associated to platelet SOCE dysfunction.

Cardiovascular and Hemostatic Disorders: SOCE in Cardiovascular Cells: Emerging Targets for Therapeutic Intervention.

The discovery of the store-operated Ca2+ entry (SOCE) phenomenon is tightly associated with its recognition as a pathway of high (patho)physiological significance in the cardiovascular system. Early on, SOCE has been investigated primarily in non-excitable cell types, and the vascular endothelium received particular attention, while a role of SOCE in excitable cells, specifically cardiac myocytes and pacemakers, was initially ignored and remains largely enigmatic even to date. With the recent gain in knowledge on the molecular components of SOCE as well as their cellular organization within nanodomains, potential tissue/cell type-dependent heterogeneity of the SOCE machinery along with high specificity of linkage to downstream signaling pathways emerged for cardiovascular cells. The basis of precise decoding of cellular Ca2+ signals was recently uncovered to involve correct spatiotemporal organization of signaling components, and even minor disturbances in these assemblies trigger cardiovascular pathologies. With this chapter, we wish to provide an overview on current concepts of cellular organization of SOCE signaling complexes in cardiovascular cells with particular focus on the spatiotemporal aspects of coupling to downstream signaling and the potential disturbance of these mechanisms by pathogenic factors. The significance of these mechanistic concepts for the development of novel therapeutic strategies will be discussed.

Platelets: still a therapeutical target for haemostatic disorders.

Platelets are cytoplasmatic fragments from bone marrow megakaryocytes present in blood. In this work, we review the basis of platelet mechanisms, their participation in syndromes and in arterial thrombosis, and their potential as a target for designing new antithrombotic agents. The option of new biotechnological sources is also explored.

Prekallikrein deficiency in a dog.

Prekallikrein (PK) deficiency is an uncommon disorder in dogs. In this report, we describe a case of a dog that was referred for neurological defects and had a prolonged activated partial thromboplastin time (aPTT) and normal prothrombin time (PT) with no hemostatic defects. By using human PK-deficient plasma, the dog was diagnosed to have PK deficiency. The nucleotide sequence of normal canine PK cDNA was determined and compared with the genomic sequences of PK in the affected dog. The comparison revealed that the dog had a point mutation in exon 8 that leads to an amino acid substitution in the fourth apple domain of PK. This is the first report showing a point mutation of PK in a dog with PK deficiency.

[Hyperhomocysteinemia and the disturbance of haemostasis--facts and mythes]. / Hiperhomocysteinemia, a zaburzenia procesu hemostazy--fakty i mity.

The elevated concentration of homocysteine--Hcys (hyperhomocysteinemia) has been correlated with different pathologists, such as cardiovascular diseases. In the article, the some pathways of homocysteine metabolism (i.e. remethylation to methionine, formation of homocysteine thiolactone, and its enzymatic hydrolysis) and the actions of homocysteine and its metabolite--cyclic thioester--homocysteine thiolactone (HTL) on complex process of haemostasis, which regulates the flowing properties of blood, are described. Possible interaction of Hcys and HTL with endothelial cells, blood platelets, plasmatic fibrinogen and other coagulation factors, as the important major components of haemostasis are also discussed. The modification of haemostatic proteins (N-homocysteinylated or S-homocysteinylated proteins) induced by Hcys or its thiolactone, seem to be the main reason of biotoxicity of homocysteine in the disturbance of haemostasis and cardiovascular diseases.

Mouse carotid artery ligation induces platelet-leukocyte-dependent luminal fibrin, required for neointima development.

The relationship between platelet and leukocyte activation, coagulation, and neointima development was investigated in noninjured murine blood vessels subjected to blood stasis. The left common carotid artery of C57BL/6J mice was ligated proximal to the bifurcation. Tissue-factor expression in luminal leukocytes progressively increased over 2 weeks. On day 3 after ligation, in addition to infiltrated granulocytes, platelet microthrombi and platelet-covered leukocytes as well as tissue-factor-positive fibrin deposits lined the endothelium. Maximal neointima formation in carotid artery cross sections of control mice equaled 28+/-3.7% (n=11) and 42+/-5.1% (n=8) of the internal elastic lamina cross-sectional area 1 and 2 weeks after ligation. In FVIII(-/-) mice, stenosis was significantly lower 1 (11+/-3.6%, n=8) and 2 (21+/-4.7%, n=7) weeks after ligation (both P:<0.01 versus background-matched controls). In u-PA(-/-) mice, luminal stenosis was significantly higher 1 (38+/-7.0%, n=7) and 2 (77+/-5.6%, n=6) weeks after ligation (P:<0.05 and P:<0.01, respectively, versus matched controls). In alpha(2)-AP(-/-) mice, stenosis was lower at 1 week (14+/-2.6%, n=7, P:<0.01) but not at 2 weeks. Responses in tissue-type plasminogen activator or plasminogen activator inhibitor-1 gene-deficient mice equaled that in controls. Reducing plasma fibrinogen levels in controls with ancrod or inducing partial thrombocytopenia with busulfan resulted in significantly less neointima, but inflammation was inhibited only in busulfan-treated mice. We conclude that stasis induces platelet activation, leading to microthrombosis and platelet-leukocyte conjugate formation, triggering inflammation and tissue-factor accumulation on the carotid artery endothelium. Delayed coagulation then results in formation of a fibrin matrix, which is used by smooth muscle cells to migrate into the lumen.