No abstract

Blood coagulation is thought to be initiated by plasma protease factor VIIa in complex with the membrane protein tissue factor. In contrast, coagulation factor XII (FXII)–mediated fibrin formation is not believed to play an important role for coagulation in vivo. We used FXII-deficient mice to study the contributions of FXII to thrombus formation in vivo. Intravital fluorescence microscopy and blood flow measurements in three distinct arterial beds revealed a severe defect in the formation and stabilization of platelet-rich occlusive thrombi. Although FXII-deficient mice do not experience spontaneous or excessive injury-related bleeding, they are protected against collagen- and epinephrine-induced thromboembolism. Infusion of human FXII into FXII-null mice restored injury-induced thrombus formation. These unexpected findings change the long-standing concept that the FXII-induced intrinsic coagulation pathway is not important for clotting in vivo. The results establish FXII as essential for thrombus formation, and identify FXII as a novel target for antithrombotic therapy.

Formation of fibrin is critical for limiting blood loss at a site of blood vessel injury (hemostasis), but may also contribute to vascular thrombosis. Hereditary deficiency of factor XII (FXII), the protease that triggers the intrinsic pathway of coagulation in vitro, is not associated with spontaneous or excessive injury-related bleeding, indicating FXII is not required for hemostasis. We demonstrate that deficiency or inhibition of FXII protects mice from ischemic brain injury. After transient middle cerebral artery occlusion, the volume of infarcted brain in FXII-deficient and FXII inhibitor–treated mice was substantially less than in wild-type controls, without an increase in infarct-associated hemorrhage. Targeting FXII reduced fibrin formation in ischemic vessels, and reconstitution of FXII-deficient mice with human FXII restored fibrin deposition. Mice deficient in the FXII substrate factor XI were similarly protected from vessel-occluding fibrin formation, suggesting that FXII contributes to pathologic clotting through the intrinsic pathway. These data demonstrate that some processes involved in pathologic thrombus formation are distinct from those required for normal hemostasis. As FXII appears to be instrumental in pathologic fibrin formation but dispensable for hemostasis, FXII inhibition may offer a selective and safe strategy for preventing stroke and other thromboembolic diseases.

Proteins of the Enabled/vasodilator-stimulated phosphoprotein (Ena/VASP) family link signal transduction pathways to actin cytoskeleton dynamics. VASP is substrate of cAMP-dependent, cGMP-dependent and AMP-activated protein kinases that primarily phosphorylate the sites S157, S239 and T278, respectively. Here, we systematically analyzed functions of VASP phosphorylation patterns for actin assembly and subcellular targeting in vivo and compared the phosphorylation effects of Ena/VASP family members. Methods used were the reconstitution of VASP-null cells with `locked' phosphomimetic VASP mutants, actin polymerization of VASP mutants in vitro and in living cells, site-specific kinase-mediated VASP phosphorylation, and analysis of the endogenous protein with phosphorylation-status-specific antibodies. Phosphorylation at S157 influenced VASP localization, but had a minor impact on F-actin assembly. Phosphorylation of the S157-equivalent site in the Ena/VASP family members Mena and EVL had no effect on the ratio of cellular F-actin to G-actin. By contrast, VASP phosphorylation at S239 (and the equivalent site in Mena) or T278 impaired VASP-driven actin filament formation. The data show that VASP functions are precisely regulated by differential phosphorylation and provide new insights into cytoskeletal control by serine/threonine kinase-dependent signaling pathways.

Calcium and Ca 2؉ -dependent signals play a crucial role in sperm motility and mammalian fertilization, but the molecules and mechanisms underlying these Ca 2؉ -dependent pathways are incompletely understood. Here we show that homozygous male mice with a targeted gene deletion of isoform 4 of the plasma membrane calcium/ calmodulin-dependent calcium ATPase (PMCA), which is highly enriched in the sperm tail, are infertile due to severely impaired sperm motility. Furthermore, the PMCA inhibitor 5-(and-6)-carboxyeosin diacetate succinimidyl ester reduced sperm motility in wild-type animals, thus mimicking the effects of PMCA4 deficiency on sperm motility and supporting the hypothesis of a pivotal role of the PMCA4 on the regulation of sperm function and intracellular Ca 2؉ levels.Successful fertilization requires the sperm to travel long distances and undergo capacitation prior to reaching the female egg. After reaching their target, the sperm must interact with the extracellular matrix of the egg, including proteins of the zona pellucida, and release acrosomal material. Calcium is considered to exert a function on most, if not all, of these processes. In this field, most of the work on Ca 2ϩ signaling has focused on Ca 2ϩ entry mechanisms, especially on the role of Ca 2ϩ channels (1-4). For example, gene ablation of the cation channel of sperm (CatSper) leads to impaired sperm motility and male infertility (5), and mice lacking the mitochondrial voltage-dependent anion channel type 3 (VDAC3) are also infertile due to immotile sperm (6). These results show that tight regulation of ion entry by ion channels is critical to sperm function. Although there is little doubt as to the importance of calcium homeostasis in sperm motility and fertilization (7-12), the function of the plasma membrane Ca 2ϩ /calmodulin-dependent Ca 2ϩ ATPase (PMCA) 1 during this process remained enigmatic.PMCA represents a family of enzymes that extrude calcium from the cytosol across the plasma membrane of eukaryotic cells. Since their initial identification in erythrocytes (13), four different isoforms have been identified, and multiple splice forms of these isoforms have been described. The well defined tissue-specific expression pattern of different isoforms and splice variants of the pump in various mammalian tissues (14) and the regulated expression pattern during mouse development (15) strongly suggest a specific physiological function for each isoform and splice variant (reviewed in Strehler and Zacharias (16)). The identification of physical and functional interaction partners of the Ca 2ϩ pump has given insights into the putative functions of PMCAs as regulators of Ca 2ϩ -dependent signal transduction processes (17-21). Interaction of PMCA2 and -4 "b" splice variants was shown to be mediated by the PDZ-(PSD-95/Dlg/ZO-1) domain of the corresponding interaction partner and the C termini of the PMCA isoform (which harbors a typical PDZ domain binding motif (17)). Both modes of interaction with PDZ domain-containing proteins, specific and...

Directed cortical actin assembly is the driving force for intercellular adhesion. Regulated by phosphorylation, vasodilator-stimulated phosphoprotein (VASP) participates in actin fiber formation. We screened for endothelial proteins, which bind to VASP, dependent on its phosphorylation status. Differential proteomics identified αII-spectrin as such a VASP-interacting protein. αII-Spectrin binds to the VASP triple GP5-motif via its SH3 domain. cAMP-dependent protein kinase–mediated VASP phosphorylation at Ser157 inhibits αII-spectrin–VASP binding. VASP is dephosphorylated upon formation of cell–cell contacts and in confluent, but not in sparse cells, αII-spectrin colocalizes with nonphosphorylated VASP at cell–cell junctions. Ectopic expression of the αII-spectrin SH3 domain at cell–cell contacts translocates VASP, initiates cortical actin cytoskeleton formation, stabilizes cell–cell contacts, and decreases endothelial permeability. Conversely, the permeability of VASP-deficient endothelial cells (ECs) and microvessels of VASP-null mice increases. Reconstitution of VASP-deficient ECs rescues barrier function, whereas αII-spectrin binding-deficient VASP mutants fail to restore elevated permeability. We propose that αII-spectrin–VASP complexes regulate cortical actin cytoskeleton assembly with implications for vascular permeability.

In recent years, the myocardium has been rediscovered under the lenses of immunology, and lymphocytes have been implicated in the pathogenesis of cardiomyopathies with different etiologies. Aging is an important risk factor for heart diseases, and it also has impact on the immune system. Thus, we sought to determine whether immunological activity would influence myocardial structure and function in elderly mice. Morphological, functional, and molecular analyses revealed that the age-related myocardial impairment occurs in parallel with shifts in the composition of tissueresident leukocytes and with an accumulation of activated CD4 + Foxp3 − (forkhead box P3) IFN-γ + T cells in the heart-draining lymph nodes. A comprehensive characterization of different aged immune-deficient mouse strains revealed that T cells significantly contribute to age-related myocardial inflammation and functional decline. Upon adoptive cell transfer, the T cells isolated from the mediastinal lymph node (med-LN) of aged animals exhibited increased cardiotropism, compared with cells purified from young donors or from other irrelevant sites. Nevertheless, these cells caused rather mild effects on cardiac functionality, indicating that myocardial aging might stem from a combination of intrinsic and extrinsic (immunological) factors. Taken together, the data herein presented indicate that heart-directed immune responses may spontaneously arise in the elderly, even in the absence of a clear tissue damage or concomitant infection. These observations might shed new light on the emerging role of T cells in myocardial diseases, which primarily affect the elderly population.T he myocardial cellular composition has been revisited in recent years, and leukocyte subsets residing in the healthy heart have been described (1-10). Cardiac-resident macrophages exhibiting an M2-like gene expression profile were found to be distributed in close association with the coronary vascular bed (3), and niches for dendritic cells (CD11c + MHC-II high CD80/86 low ) were found near the cardiac valves of the intact heart (1). It was also demonstrated that cardiac-resident MHCII + cells process and present myosin heavy chain-alpha-derived peptides under steady-state conditions (11, 12) and prime T cells ex vivo (1). However, whether lymphocytes can seed the intact myocardium and whether T-cell priming with myocardial antigens can occur in the absence of an infection or autoimmune myocarditis remain elusive.More recently, accumulating evidence indicated that noninfectious myocardial diseases are modulated by T cells. During the last couple of years, our group demonstrated that ischemic, sterile myocardial injuries can elicit lymphocyte activation directed against cardiac antigens (13-16). Our previous data, showing for the first time that CD4 + T cells reactive to cardiac components can foster the healing process that takes place after myocardial infarction, were corroborated by several other reports (13,15,(17)(18)(19)(20). However, these autoreactive T cells can also b...

Two major subtypes of cardiac β-adrenergic receptors (β−ARs) modulate the effects of catecholamines on excitation-contraction coupling. The predominantly G s -coupled β 1 -AR is evenly distributed across the sarcolemma and stimulates Brief UltraRapid Communication© 2015 American Heart Association, Inc. Objective: To directly visualize alterations in β-adrenergic receptor-associated cAMP and cGMP microdomain signaling in early cardiac disease. Methods and Results:Unexpectedly, measurements of cell shortening revealed augmented β-adrenergic receptorstimulated cardiomyocyte contractility by atrial natriuretic peptide/cGMP signaling in early cardiac hypertrophy after transverse aortic constriction, which was in sharp contrast to well-documented β-adrenergic and natriuretic peptide signaling desensitization during chronic disease. Real-time cAMP analysis in β 1 -and β 2 -adrenergic receptor-associated membrane microdomains using a novel membrane-targeted Förster resonance energy transfer-based biosensor transgenically expressed in mice revealed that this unexpected atrial natriuretic peptide effect is brought about by spatial redistribution of cGMP-sensitive phosphodiesterases 2 and 3 between both receptor compartments. Functionally, this led to a significant shift in cGMP/cAMP cross-talk and, in particular, to cGMP-driven augmentation of contractility in vitro and in vivo. The online-only Data Supplement is available with this article at http://circres.ahajournals.org/lookup/suppl Conclusions: