Gain-of-Function Mutation in Filamin A Potentiates Platelet Integrin αIIbß3 Activation.

OBJECTIVE: Dominant mutations of the X-linked filamin A (FLNA) gene are responsible for filaminopathies A, which are rare disorders including brain periventricular nodular heterotopia, congenital intestinal pseudo-obstruction, cardiac valves or skeleton malformations, and often macrothrombocytopenia. APPROACH AND RESULTS: We studied a male patient with periventricular nodular heterotopia and congenital intestinal pseudo-obstruction, his unique X-linked FLNA allele carrying a stop codon mutation resulting in a 100-amino acid-long FLNa C-terminal extension (NP_001447.2: p.Ter2648SerextTer101). Platelet counts were normal, with few enlarged platelets. FLNa was detectable in all platelets but at 30% of control levels. Surprisingly, all platelet functions were significantly upregulated, including platelet aggregation and secretion, as induced by ADP, collagen, or von Willebrand factor in the presence of ristocetin, as well as thrombus formation in blood flow on a collagen or on a von Willebrand factor matrix. Most importantly, patient platelets stimulated with ADP exhibited a marked increase in αIIbß3 integrin activation and a parallel increase in talin recruitment to ß3, contrasting with normal Rap1 activation. These results are consistent with the mutant FLNa affecting the last step of αIIbß3 activation. Overexpression of mutant FLNa in the HEL megakaryocytic cell line correlated with an increase (compared with wild-type FLNa) in PMA-induced fibrinogen binding to and in talin and kindlin-3 recruitment by αIIbß3. CONCLUSIONS: Altogether, our results are consistent with a less binding of mutant FLNa to ß3 and the facilitated recruitment of talin by ß3 on platelet stimulation, explaining the increased αIIbß3 activation and the ensuing gain-of-platelet functions.

Loss of α1ß1 soluble guanylate cyclase, the major nitric oxide receptor, leads to moyamoya and achalasia.

Moyamoya is a cerebrovascular condition characterized by a progressive stenosis of the terminal part of the internal carotid arteries (ICAs) and the compensatory development of abnormal "moyamoya" vessels. The pathophysiological mechanisms of this condition, which leads to ischemic and hemorrhagic stroke, remain unknown. It can occur as an isolated cerebral angiopathy (so-called moyamoya disease) or in association with various conditions (moyamoya syndromes). Here, we describe an autosomal-recessive disease leading to severe moyamoya and early-onset achalasia in three unrelated families. This syndrome is associated in all three families with homozygous mutations in GUCY1A3, which encodes the α1 subunit of soluble guanylate cyclase (sGC), the major receptor for nitric oxide (NO). Platelet analysis showed a complete loss of the soluble α1ß1 guanylate cyclase and showed an unexpected stimulatory role of sGC within platelets. The NO-sGC-cGMP pathway is a major pathway controlling vascular smooth-muscle relaxation, vascular tone, and vascular remodeling. Our data suggest that alterations of this pathway might lead to an abnormal vascular-remodeling process in sensitive vascular areas such as ICA bifurcations. These data provide treatment options for affected individuals and strongly suggest that investigation of GUCY1A3 and other members of the NO-sGC-cGMP pathway is warranted in both isolated early-onset achalasia and nonsyndromic moyamoya.

von Willebrand factor mutation promotes thrombocytopathy by inhibiting integrin αIIbß3.

von Willebrand disease type 2B (vWD-type 2B) is characterized by gain-of-function mutations in von Willebrand factor (vWF) that enhance its binding to the glycoprotein Ib-IX-V complex on platelets. Patients with vWD-type 2B have a bleeding tendency that is linked to loss of vWF multimers and/or thrombocytopenia. In this study, we uncovered evidence that platelet dysfunction is a third possible mechanism for bleeding tendency. We found that platelet aggregation, secretion, and spreading were diminished due to inhibition of integrin αIIbß3 in platelets from mice expressing a vWD-type 2B-associated vWF (vWF/p.V1316M), platelets from a patient with the same mutation, and control platelets pretreated with recombinant vWF/p.V1316M. Impaired platelet function coincided with reduced thrombus growth. Further, αIIbß3 activation and activation of the small GTPase Rap1 were impaired by vWF/p.V1316M following exposure to platelet agonists (thrombin, ADP, or convulxin). Conversely, thrombin- or ADP-induced Ca2+ store release, which is required for αIIbß3 activation, was normal, indicating that vWF/p.V1316M acts downstream of Ca2+ release and upstream of Rap1. We found normal Syk phosphorylation and PLCγ2 activation following collagen receptor signaling, further implying that vWF/p.V1316M acts directly on or downstream of Ca2+ release. These data indicate that the vWD-type 2B mutation p.V1316M is associated with severe thrombocytopathy, which likely contributes to the bleeding tendency in vWD-type 2B.

Heterogeneity of platelet functional alterations in patients with filamin A mutations.

OBJECTIVE: We examined platelet functions in 4 unrelated patients with filaminopathy A caused by dominant mutations of the X-linked filamin A (FLNA) gene. METHODS AND RESULTS: Patients P1, P2, and P4 exhibited periventricular nodular heterotopia, heterozygozity for truncating FLNA mutations, and thrombocytopenia (except P2). P3 exhibited isolated thrombocytopenia and heterozygozity for a p.Glu1803Lys FLNA mutation. Truncated FLNA was undetectable by Western blotting of P1, P2, and P4 platelets, but full-length FLNA was detected at 37%, 82%, and 57% of control, respectively. P3 FLNA (p.Glu1803Lys and full-length) was assessed at 79%. All patients exhibited a platelet subpopulation negative for FLNA. Platelet aggregation, secretion, glycoprotein VI signaling, and thrombus growth on collagen were decreased for P1, P3, and P4, but normal for P2. For the 2 patients analyzed (P1 and P4), spreading was enhanced and, more markedly, in FLNA-negative platelets, suggesting that FLNA negatively regulates cytoskeleton reorganization. Platelet adhesion to von Willebrand factor under flow correlated with platelet full-length FLNA content: markedly reduced for P1 and P4 and unchanged for P2. Interestingly, von Willebrand factor flow adhesion was increased for P3, consistent with a gain-of-function effect enhancing glycoprotein Ib-IX-V/von Willebrand factor interaction. These results are consistent with a positive role for FLNA in platelet adhesion under high shear. CONCLUSIONS: FLNA mutation heterogeneity correlates with different platelet functional impacts and points to opposite regulatory roles of FLNA in spreading and flow adhesion under shear.

Aspirin alters arterial function in patients with chronic heart failure treated with ACE inhibitors: a dose-mediated deleterious effect.

BACKGROUND: By inhibiting prostaglandin synthesis, aspirin can interfere with both arterial functional and angiotensin-converting enzyme inhibitor (ACEI) properties and be deleterious in chronic heart failure (CHF). AIM: Our aim was to prospectively evaluate the effect of aspirin on arterial functional properties in CHF patients treated with ACEIs. METHODS AND RESULTS: Over three consecutive treatment periods of 7 days, 18 patients received placebo, followed by aspirin 100 mg/day, and then aspirin 325 mg/day. Single blind prospective assessment of reflected wave and time reflection by radial applanation tonometry; pulse wave velocity; blood pressure; thromboxane B2 (TxB2) and prostaglandins in plasma and urine was performed. Aspirin 325 mg/day induced a significant increase in augmentation index of reflected wave (P<0.0001 and P=0.0013 vs. placebo and aspirin 100 mg, respectively) and a significant decrease in reflected wave traveling times (P=0.0007 vs. placebo). Aspirin 100 mg/day produced a similar, though non-significant, trend in these parameters compared with placebo. Both aspirin treatments produced a statistically significant decrease in serum TxB2 (P<0.0001) but did not have an effect on the metabolite of prostaglandin I2 (P=0.136). CONCLUSION: This study demonstrates the existence of a dose-mediated deleterious effect of aspirin upon arterial functional properties in CHF patients treated with ACEI.