Aim:Severe gastrointestinal bleeding sometimes occurs in patients with aortic stenosis (AS), known as Heyde's syndrome. This syndrome is thought to be caused by acquired von Willebrand syndrome and is characterized by reduced large von Willebrand factor (vWF) multimers. However, the relationship between the severity of AS and loss of large vWF multimers is unclear. Methods: We examined 31 consecutive patients with severe AS. Quantitative evaluation for loss of large vWF multimers was performed using the conventional large vWF ratio and novel large vWF multimer index. This novel index was defined as the ratio of large multimers of patients to those of controls. Results: Loss of large vWF multimers, defined as the large vWF multimer index 80%, was detected in 21 patients (67.7%). The large vWF multimer ratio and the large vWF multimer index were inversely correlated with the peak aortic gradient (R 0.58, p 0.0007, and R 0.64, p 0.0001, respectively). Anemia defined as hemoglobin 9.0 g/dl was observed in 12 patients (38.7%), who were regarded as Heyde's syndrome. Aortic valve replacement was performed in 7 of these patients, resulting in the improvement of anemia in all patients from a hemoglobin concentration of 7.5 1.0 g/dl preoperatively to 12.4 1.3 g/dl postoperatively (p 0.0001). Conclusions: Acquired von Willebrand syndrome may be a differential diagnosis in patients with AS with anemia. The prevalence of AS-associated acquired von Willebrand syndrome is higher than anticipated.

The small GTPases RalA and RalB are multifunctional proteins regulating a variety of cellular processes. Like other GTPases, the activity of Ral is regulated by the opposing effects of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Although several RalGEFs have been identified and characterized, the molecular identity of RalGAP remains unknown. Here, we report the first molecular identification of RalGAPs, which we have named RalGAP1 and RalGAP2. They are large heterodimeric complexes, each consisting of a catalytic alpha1 or alpha2 subunit and a common beta subunit. These RalGAP complexes share structural and catalytic similarities with the tuberous sclerosis tumor suppressor complex, which acts as a GAP for Rheb. In vitro GTPase assays revealed that recombinant RalGAP1 accelerates the GTP hydrolysis rate of RalA by 280,000-fold. Heterodimerization was required for this GAP activity. In PC12 cells, knockdown of the beta subunit led to sustained Ral activation upon epidermal growth factor stimulation, indicating that the RalGAPs identified here are critical for efficient termination of Ral activation induced by extracellular stimuli. Our identification of RalGAPs will enable further understanding of Ral signaling in many biological and pathological processes.

We have previously demonstrated that Rab27 regulates dense granule secretion in platelets. Here, we analyzed the activation status of Rab27 using the thin layer chromatography method analyzing nucleotides bound to immunoprecipitated Rab27 and the pull-down method quantifying Rab27 bound to the GTPRab27-binding domain (synaptotagmin-like protein (Slp)-homology domain) of its specific effector, Slac2-b. We found that Rab27 was predominantly present in the GTP-bound form in unstimulated platelets due to constitutive GDP/GTP exchange activity. The GTP-bound Rab27 level drastically decreased due to enhanced GTP hydrolysis activity upon granule secretion. In permeabilized platelets, increase of Ca 2؉ concentration induced dense granule secretion with concomitant decrease of GTP-Rab27, whereas in non-hydrolyzable GTP analogue GppNHp (␤-␥-imidoguanosine 5-triphosphate)-loaded permeabilized platelets, the GTP (GppNHp)-Rab27 level did not decrease upon the Ca 2؉ -induced secretion. These data suggested that GTP hydrolysis of Rab27 was not necessary for inducing the secretion. Taken together, Rab27 is maintained in the active status in unstimulated platelets, which could function to keep dense granules in a preparative status for secretion.In eukaryotic cells, transport between distinct organelles is performed through vesicle trafficking. The final step of vesicle docking/fusion with target membrane is mediated by transsoluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) 3 complex bridging a vesicle and its target membrane (1). One of the key regulators for the SNARE complex formation is Rab GTPase (2, 3). So far, more than 60 members of Rab GTPases are identified in mammals, and they play critical roles in the specific transport pathways (2-4). Like other GTPases, the activity of Rab is regulated by its GDP/GTP cycle. Rab proteins have GTP-bound active and GDP-bound inactive forms. The activation process is performed by GDP/ GTP exchange mediated by the GDP/GTP exchange factor. GTP-bound Rabs execute their function by interaction with effector proteins. Then, GTP-Rab is inactivated into GDP-Rab by GTP hydrolysis that is mediated by the intrinsic GTPase activity and its enhancer, GTPase-activating protein. Furthermore, the Rab family has a unique regulatory protein named Rab GDP dissociation inhibitor (RabGDI), which extracts GDP-Rab from membrane into cytosol by forming a 1:1 complex and inhibits GDP/GTP exchange (3). RabGDI accompanies Rabs in cytosol to the correct organelles, where they are reactivated by the function of GDI dissociation factor (5-8).Although elucidation of the regulatory mechanism of the GDP/GTP cycle is crucial for understanding the functional mechanism of Rab GTPases, it has not been extensively investigated so far. Small GTPases belonging to Ras and Rho families are predominantly present in the GDP-bound forms under resting conditions and are transiently activated into GTPbound forms upon stimulation (9), indicating that these GTPases function as "switches" that transduce...

Aim:Obstructive sleep apnea (OSA) is a risk factor for cardiovascular diseases. Platelets play key roles in the development of atherothrombosis. Several studies assessing platelet activation in patients with OSA have been published; however, there have been only a few studies with a small number of patients with OSA investigating platelet aggregability, which evaluates platelet aggregation more directly than the platelet activation status. We aimed to investigate the effects of OSA and nasal continuous positive airway pressure (nCPAP) therapy, a well-established treatment for OSA, on platelet aggregability. Methods and Results: We examined 124 consecutive patients with snoring in whom the 3% oxygen desaturation index (3%ODI), a severity marker of OSA, and ADP-and collagen-induced platelet aggregability measured with the optical aggregometer were analyzed. ADP-induced platelet aggregability was increased more in patients with moderate-to-severe OSA (3%ODI 15) than in patients with non-to-mild OSA (p 0.029). In multiple linear models, 3%ODI significantly contributed to increased platelet aggregability induced by both ADP and collagen among 59 subjects with one or more risk factors for vascular diseases, such as smoking, hypertension, diabetes mellitus or hyperlipidemia. In 23 patients treated by nCPAP, collagen-induced platelet aggregability was ameliorated on Day 90, compared to at the baseline. Conclusion: The severity of OSA significantly contributed to platelet aggregability, which was improved by nCPAP treatment partially at three months.

The diaphanous-related formins are actin nucleating and elongating factors. They are kept in an inactive state by an intramolecular interaction between the diaphanous inhibitory domain (DID) and the diaphanous-autoregulatory domain (DAD). It is considered that the dissociation of this autoinhibitory interaction upon binding of GTP-bound Rho to the GTPase binding domain next to DID induces exposure of the FH1-FH2 domains, which assemble actin filaments. Here, we isolated two diaphanous-related formins, mDia1 and Daam1, in platelet extracts by GTP-RhoA affinity column chromatography. We characterized them by a novel assay, where beads coated with the FH1-FH2-DAD domains of either mDia1 or Daam1 were incubated with platelet cytosol, and the assembled actin filaments were observed after staining with rhodamine-phalloidin. Both formins generated fluorescent filamentous structures on the beads. Quantification of the fluorescence intensity of the beads revealed that the initial velocity in the presence of mDia1 was more than 10 times faster than in the presence of Daam1. The actin assembly activities of both FH1-FH2-DADs were inhibited by adding cognate DID domains. GTP-RhoA, -RhoB, and -RhoC, but not GTP-Rac1 or -Cdc42, bound to both mDia1 and Daam1 and efficiently neutralized the inhibition by the DID domains. The association between RhoA and Daam1 was induced by thrombin stimulation in platelets, and RhoA-bound endogenous formins induced actin assembly, which was inhibited by the DID domains of Daam1 and mDia1. Thus, mDia1 and Daam1 are platelet actin assembly factors having distinct efficiencies, and they are directly regulated by Rho GTPases.