Reciprocal stabilization of coagulation factor XIII-A and -B subunits is a determinant of plasma FXIII concentration.

ABSTRACT: Transglutaminase factor XIII (FXIII) is essential for hemostasis, wound healing, and pregnancy maintenance. Plasma FXIII is composed of A and B subunit dimers synthesized in cells of hematopoietic origin and hepatocytes, respectively. The subunits associate tightly in circulation as FXIII-A2B2. FXIII-B2 stabilizes the (pro)active site-containing FXIII-A subunits. Interestingly, people with genetic FXIII-A deficiency have decreased FXIII-B2, and therapeutic infusion of recombinant FXIII-A2 (rFXIII-A2) increases FXIII-B2, suggesting FXIII-A regulates FXIII-B secretion, production, and/or clearance. We analyzed humans and mice with genetic FXIII-A deficiency and developed a mouse model of rFXIII-A2 infusion to define mechanisms mediating plasma FXIII-B levels. Like humans with FXIII-A deficiency, mice with genetic FXIII-A deficiency had reduced circulating FXIII-B2, and infusion of FXIII-A2 increased FXIII-B2. FXIII-A-deficient mice had normal hepatic function and did not store FXIII-B in liver, indicating FXIII-A does not mediate FXIII-B secretion. Transcriptional analysis and polysome profiling indicated similar F13b levels and ribosome occupancy in FXIII-A-sufficient and -deficient mice and in FXIII-A-deficient mice infused with rFXIII-A2, indicating FXIII-A does not induce de novo FXIII-B synthesis. Unexpectedly, pharmacokinetic/pharmacodynamic modeling of FXIII-B antigen after rFXIII-A2 infusion in humans and mice suggested FXIII-A2 slows FXIII-B2 loss from plasma. Accordingly, comparison of free FXIII-B2 vs FXIII-A2-complexed FXIII-B2 (FXIII-A2B2) infused into mice revealed faster clearance of free FXIII-B2. These data show FXIII-A2 prevents FXIII-B2 loss from circulation and establish the mechanism underlying FXIII-B2 behavior in FXIII-A deficiency and during rFXIII-A2 therapy. Our findings reveal a unique, reciprocal relationship between independently synthesized subunits that mediate an essential hemostatic protein in circulation. This trial was registered at www.ClinicalTrials.com as #NCT00978380.

Insulin Elevates ID2 Expression in Trophoblasts and Aggravates Preeclampsia in Obese ASB4-Null Mice.

Obesity is a risk factor for preeclampsia. We investigated how obesity influences preeclampsia in mice lacking ankyrin-repeat-and-SOCS-box-containing-protein 4 (ASB4), which promotes trophoblast differentiation via degrading the inhibitor of DNA-binding protein 2 (ID2). Asb4-/- mice on normal chow (NC) develop mild preeclampsia-like phenotypes during pregnancy, including hypertension, proteinuria, and reduced litter size. Wild-type (WT) and Asb4-/- females were placed on a high-fat diet (HFD) starting at weaning. At the age of 8-9 weeks, they were mated with WT or Asb4-/- males, and preeclamptic phenotypes were assessed. HFD-WT dams had no obvious adverse outcomes of pregnancy. In contrast, HFD-Asb4-/- dams had significantly more severe preeclampsia-like phenotypes compared to NC-Asb4-/- dams. The HFD increased white fat weights and plasma leptin and insulin levels in Asb4-/- females. In the HFD-Asb4-/- placenta, ID2 amounts doubled without changing the transcript levels, indicating that insulin likely increases ID2 at a level of post-transcription. In human first-trimester trophoblast HTR8/SVneo cells, exposure to insulin, but not to leptin, led to a significant increase in ID2. HFD-induced obesity markedly worsens the preeclampsia-like phenotypes in the absence of ASB4. Our data indicate that hyperinsulinemia perturbs the timely removal of ID2 and interferes with proper trophoblast differentiation, contributing to enhanced preeclampsia.

Performance of acoustic radiation force impulse ultrasound imaging for carotid plaque characterization with histologic validation.

OBJECTIVE: Stroke is commonly caused by thromboembolic events originating from ruptured carotid plaque with vulnerable composition. This study assessed the performance of acoustic radiation force impulse (ARFI) imaging, a noninvasive ultrasound elasticity imaging method, for delineating the composition of human carotid plaque in vivo with histologic validation. METHODS: Carotid ARFI images were captured before surgery in 25 patients undergoing clinically indicated carotid endarterectomy. The surgical specimens were histologically processed with sectioning matched to the ultrasound imaging plane. Three radiologists, blinded to histology, evaluated parametric images of ARFI-induced peak displacement to identify plaque features such as necrotic core (NC), intraplaque hemorrhage (IPH), collagen (COL), calcium (CAL), and fibrous cap (FC) thickness. Reader performance was measured against the histologic standard using receiver operating characteristic curve analysis, linear regression, Spearman correlation (ρ), and Bland-Altman analysis. RESULTS: ARFI peak displacement was two-to-four-times larger in regions of NC and IPH relative to regions of COL or CAL. Readers detected soft plaque features (NC/IPH) with a median area under the curve of 0.887 (range, 0.867-0.924) and stiff plaque features (COL/CAL) with median area under the curve of 0.859 (range, 0.771-0.929). FC thickness measurements of two of the three readers correlated with histology (reader 1: R2 = 0.64, ρ = 0.81; reader 2: R2 = 0.89, ρ = 0.75). CONCLUSIONS: This study suggests that ARFI is capable of distinguishing soft from stiff atherosclerotic plaque components and delineating FC thickness.

α(1,3)-Fucosyltransferases FUT4 and FUT7 control murine susceptibility to thrombosis.

The α(1,3)-fucosyltransferases, types IV and VII (FUT4 and FUT7, respectively), are required for the synthesis of functional selectin-type leukocyte adhesion molecule ligands. The selectins and their ligands modulate leukocyte trafficking, and P-selectin and its ligand, P-selectin glycoprotein ligand-1, can modulate hemostasis and thrombosis. Regulation of thrombosis by FUT4 and/or FUT7 activity was examined in mouse models of carotid artery thrombosis and collagen/epinephrine-induced thromboembolism. Mice lacking both FUT4 and FUT7 (Fut(-/-) mice) had a shorter time to occlusive thrombus formation in the injured carotid artery and a higher mortality due to collagen/epinephrine-induced pulmonary thromboemboli. Mice lacking P-selectin or P-selectin glycoprotein ligand-1 did not have a prothrombotic phenotype. Whole blood platelet aggregation was enhanced, and plasma fibrinogen content, clot weight, and clot strength were increased in Fut(-/-) mice, and in vitro clot lysis was reduced compared with wild type. Fut4(-/-), but not Fut7(-/-), mice had increased pulmonary thromboembolism-induced mortality and decreased thromboemboli dissolution in vivo. These data show that FUT4 and FUT7 activity regulates thrombosis in a P-selectin- and P-selectin glycoprotein ligand-1-independent manner and suggest that FUT4 activity is important for thrombolysis.

Functional redundancy of SWI/SNF catalytic subunits in maintaining vascular endothelial cells in the adult heart.

RATIONALE: Mating type switching/sucrose non-fermenting (SWI/SNF) chromatin-remodeling complexes utilize either BRG1 or BRM as a catalytic subunit to alter nucleosome position and regulate gene expression. BRG1 is required for vascular endothelial cell (VEC) development and embryonic survival, whereas BRM is dispensable. OBJECTIVE: To circumvent embryonic lethality and study Brg1 function in adult tissues, we used conditional gene targeting. To evaluate possible Brg1-Brm redundancy, we analyzed Brg1 mutant mice on wild-type and Brm-deficient backgrounds. METHODS AND RESULTS: The inducible Mx1-Cre driver was used to mutate Brg1 in adult mice. These conditional-null mutants exhibited a tissue-specific phenotype and unanticipated functional compensation between Brg1 and Brm. Brg1 single mutants were healthy and had a normal lifespan, whereas Brg1/Brm double mutants exhibited cardiovascular defects and died within 1 month. BRG1 and BRM were required for the viability of VECs but not other cell types where both genes were also knocked out. The VEC phenotype was most evident in the heart, particularly in the microvasculature of the outer myocardium, and was recapitulated in primary cells ex vivo. VEC death resulted in vascular leakage, cardiac hemorrhage, secondary death of cardiomyocytes due to ischemia, and ventricular dissections. CONCLUSIONS: BRG1-catalyzed SWI/SNF complexes are particularly important in cardiovascular tissues. However, in contrast to embryonic development, in which Brm does not compensate, Brg1 is required in adult VECs only when Brm is also mutated. These results demonstrate for the first time that Brm functionally compensates for Brg1 in vivo and that there are significant changes in the relative importance of BRG1- and BRM-catalyzed SWI/SNF complexes during the development of an essential cell lineage.

Bmper inhibits endothelial expression of inflammatory adhesion molecules and protects against atherosclerosis.

OBJECTIVE: Bone morphogenetic proteins (Bmps) are important mediators of inflammation and atherosclerosis, though their mechanism of action is not fully understood. To better understand the contribution of the Bmp signaling pathway in vascular inflammation, we investigated the role of Bmper (Bmp endothelial cell precursor-derived regulator), an extracellular Bmp modulator, in an induced in vivo model of inflammation and atherosclerosis. METHODS AND RESULTS: We crossed apolipoprotein E-deficient (ApoE(-/-)) mice with mice missing 1 allele of Bmper (Bmper(+/-) mice used in the place of Bmper(-/-) mice that die at birth) and measured the development of atherosclerosis in mice fed a high-fat diet. Bmper haploinsufficiency in ApoE(-/-) mice (Bmper(+/-);ApoE(-/-) mice) led to a more severe phenotype compared with Bmper(+/+);ApoE(-/-) mice. Bmper(+/-);ApoE(-/-) mice also exhibited increased Bmp activity in the endothelial cells in both the greater and lesser curvatures of the aortic arch, suggesting a role for Bmper in regulating Bmp-mediated inflammation associated with laminar and oscillatory shear stress. Small interfering RNA knockdown of Bmper in human umbilical vein endothelial cells caused a dramatic increase in the inflammatory markers intracellular adhesion molecule 1 and vascular cell adhesion molecule 1 at rest and after exposure to oscillatory and laminar shear stress. CONCLUSIONS: We conclude that Bmper is a critical regulator of Bmp-mediated vascular inflammation and that the fine-tuning of Bmp and Bmper levels is essential in the maintenance of normal vascular homeostasis.

Comparing Focused-Tracked and Plane Wave-Tracked ARFI Log(VoA) In Silico and in Application to Human Carotid Atherosclerotic Plaque, Ex Vivo.

A significant risk factor for ischemic stroke is carotid atherosclerotic plaque that is susceptible to rupture, with rupture potential conveyed by plaque morphology. Human carotid plaque composition and structure have been delineated noninvasively and in vivo by evaluating log(VoA), a parameter derived as the decadic log of the second time derivative of displacement induced by an acoustic radiation force impulse (ARFI). In prior work, ARFI-induced displacement was measured using conventional focused tracking; however, this requires a long data acquisition period, thereby reducing framerate. We herein evaluate if ARFI log(VoA) framerate can be increased without a reduction in plaque imaging performance using plane wave tracking instead. In silico, both focused- and plane wave-tracked log(VoA) decreased with increasing echobrightness, quantified as signal-to-noise ratio (SNR), but did not vary with material elasticity for SNRs below 40 dB. For SNRs of 40-60 dB, both focused- and plane wave-tracked log(VoA) varied with SNR and material elasticity. Above 60 dB SNR, both focused- and plane wave-tracked log(VoA) varied with material elasticity alone. This suggests that log(VoA) discriminates features according to a combination of their echobrightness and mechanical property. Further, while both focused- and plane-wave tracked log(VoA) values were artifactually inflated by mechanical reflections at inclusion boundaries, plane wave-tracked log(VoA) was more strongly impacted by off-axis scattering. Applied to three excised human cadaveric carotid plaques with spatially aligned histological validation, both log(VoA) methods detected regions of lipid, collagen, and calcium (CAL) deposits. These findings support that plane wave tracking performs comparably to focused tracking for log(VoA) imaging and that plane wave-tracked log(VoA) is a viable approach to discriminating clinically relevant atherosclerotic plaque features at a 30-fold higher framerate than by focused tracking.

Sent to destroy: the ubiquitin proteasome system regulates cell signaling and protein quality control in cardiovascular development and disease.

The ubiquitin proteasome system (UPS) plays a crucial role in biological processes integral to the development of the cardiovascular system and cardiovascular diseases. The UPS prototypically recognizes specific protein substrates and places polyubiquitin chains on them for subsequent destruction by the proteasome. This system is in place to degrade not only misfolded and damaged proteins, but is essential also in regulating a host of cell signaling pathways involved in proliferation, adaptation to stress, regulation of cell size, and cell death. During the development of the cardiovascular system, the UPS regulates cell signaling by modifying transcription factors, receptors, and structural proteins. Later, in the event of cardiovascular diseases as diverse as atherosclerosis, cardiac hypertrophy, and ischemia/reperfusion injury, ubiquitin ligases and the proteasome are implicated in protecting and exacerbating clinical outcomes. However, when misfolded and damaged proteins are ubiquitinated by the UPS, their destruction by the proteasome is not always possible because of their aggregated confirmations. Recent studies have discovered how these ubiquitinated misfolded proteins can be destroyed by alternative "specific" mechanisms. The cytosolic receptors p62, NBR, and histone deacetylase 6 recognize aggregated ubiquitinated proteins and target them for autophagy in the process of "selective autophagy." Even the ubiquitination of multiple proteins within whole organelles that drive the more general macro-autophagy may be due, in part, to similar ubiquitin-driven mechanisms. In summary, the crosstalk between the UPS and autophagy highlight the pivotal and diverse roles the UPS plays in maintaining protein quality control and regulating cardiovascular development and disease.

Anaplasma phagocytophilum infects mast cells via alpha1,3-fucosylated but not sialylated glycans and inhibits IgE-mediated cytokine production and histamine release.

Mast cells are sentinels for infection. Upon exposure to pathogens, they release their stores of proinflammatory cytokines, chemokines, and histamine. Mast cells are also important for the control of certain tick-borne infections. Anaplasma phagocytophilum is an obligate intracellular tick-transmitted bacterium that infects neutrophils to cause the emerging disease granulocytic anaplasmosis. A. phagocytophilum adhesion to and infection of neutrophils depend on sialylated and α1,3-fucosylated glycans. We investigated the hypotheses that A. phagocytophilum invades mast cells and inhibits mast cell activation. We demonstrate that A. phagocytophilum binds and/or infects murine bone marrow-derived mast cells (BMMCs), murine peritoneal mast cells, and human skin-derived mast cells. A. phagocytophilum infection of BMMCs depends on α1,3-fucosylated, but not sialylated, glycans. A. phagocytophilum binding to and invasion of BMMCs do not elicit proinflammatory cytokine secretion. Moreover, A. phagocytophilum-infected cells are inhibited in the release of tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), IL-13, and histamine following stimulation with IgE or antigen. Thus, A. phagocytophilum mitigates mast cell activation. These findings potentially represent a novel means by which A. phagocytophilum usurps host defense mechanisms and shed light on the interplay between mast cells and vector-borne bacterial pathogens.

Disruption of tissue-specific fucosyltransferase VII, an enzyme necessary for selectin ligand synthesis, suppresses atherosclerosis in mice.

A hallmark feature of atherosclerosis is that circulating mononuclear cells adhere to the endothelium and migrate into the subendothelial space. This adhesion is mediated by molecules such as selectins that are expressed on the surfaces of both leukocytes and endothelial cells. In this study, we have determined the role of tissue-specific fucosyltransferase VII (FucT-VII), an enzyme necessary for selectin ligand synthesis, in the development of atherosclerosis. We adopted a scheme of transplanting either FucT-VII(-/-)GFP(+) bone marrow into lethally irradiated low-density lipoprotein receptor low density lipoprotein receptor mice or FucT-VII(+/+) GFP(+) bone marrow into FucT-VII(-/-), low density lipoprotein receptor double-mutant mice to evaluate the roles of E- and P-selectin ligands versus L-selectin ligands, respectively, in diet-induced atherosclerosis. GFP was used to track the transplanted cells. Our results indicate that, compared with controls, selective disruption of E- and P-selectin ligand synthesis resulted in a significant reduction in atherosclerosis. Selective disruption of L-selectin ligand production did not reduce atherosclerosis as robustly as disruption of E- and P-selectin ligands. In both groups, however, there was a significant reduction in the accumulation of macrophages in the lesion. These studies indicate that selectin ligands, particularly those for E- and P-selectins, play an important role in the pathogenesis of atherosclerosis by regulating macrophage accumulation in atherosclerotic lesions.

Conditional deletion of focal adhesion kinase leads to defects in ventricular septation and outflow tract alignment.

To examine a role for focal adhesion kinase (FAK) in cardiac morphogenesis, we generated a line of mice with a conditional deletion of FAK in nkx2-5-expressing cells (herein termed FAKnk mice). FAKnk mice died shortly after birth, likely resulting from a profound subaortic ventricular septal defect and associated malalignment of the outflow tract. Additional less penetrant phenotypes included persistent truncus arteriosus and thickened valve leaflets. Thus, conditional inactivation of FAK in nkx2-5-expressing cells leads to the most common congenital heart defect that is also a subset of abnormalities associated with tetralogy of Fallot and the DiGeorge syndrome. No significant differences in proliferation or apoptosis between control and FAKnk hearts were observed. However, decreased myocardialization was observed for the conal ridges of the proximal outflow tract in FAKnk hearts. Interestingly, chemotaxis was significantly attenuated in isolated FAK-null cardiomyocytes in comparison to genetic controls, and these effects were concomitant with reduced tyrosine phosphorylation of Crk-associated substrate (CAS). Thus, it is possible that ventricular septation and appropriate outflow tract alignment is dependent, at least in part, upon FAK-dependent CAS activation and subsequent induction of polarized myocyte movement into the conal ridges. Future studies will be necessary to determine the precise contributions of the additional nkx2-5-derived lineages to the phenotypes observed.

Mice with heterozygous deficiency of lipoic acid synthase have an increased sensitivity to lipopolysaccharide-induced tissue injury.

Alpha-lipoic acid (1, 2-dithiolane-3-pentanoic acid; LA), synthesized in mitochondria by LA synthase (Lias), is a potent antioxidant and a cofactor for metabolic enzyme complexes. In this study, we examined the effect of genetic reduction of LA synthesis on its antioxidant and anti-inflammatory properties using a model of LPS-induced inflammation in Lias+/- mice. The increase of plasma proinflammatory cytokine, TNF-alpha, and NF-kappaB at an early phase following LPS injection was greater in Lias+/- mice compared with Lias+/+ mice. The circulating blood white blood cell (WBC) and platelet counts dropped continuously during the initial 4 h. The counts subsequently recovered partially in Lias+/+ mice, but the recovery was impaired totally in Lias+/- mice. Administration of exogenous LA normalized the recovery of WBC counts in Lias+/- mice but not platelets. Enhanced neutrophil sequestration in the livers of Lias+/- mice was associated with increased hepatocyte injury and increased gene expression of growth-related oncogene, E-selectin, and VCAM-1 in the liver and/or lung. Lias gene expression in tissues was 50% of normal expression in Lias+/- mice and reduced further by LPS treatment. Decreased Lias expression was associated with diminished hepatic LA and tissue oxidative stress. Finally, Lias+/- mice displayed enhanced mortality when exposed to LPS-induced sepsis. These data demonstrate the importance of endogenously produced LA for preventing leukocyte accumulation and tissue injury that result from LPS-induced inflammation.

Carotid Plaque Fibrous Cap Thickness Measurement by ARFI Variance of Acceleration: In Vivo Human Results.

This study evaluates the performance of an acoustic radiation force impulse (ARFI)-based outcome parameter, the decadic logarithm of the variance of acceleration, or log(VoA), for measuring carotid fibrous cap thickness. Carotid plaque fibrous cap thickness measurement by log(VoA) was compared to that by ARFI peak displacement (PD) in patients undergoing clinically indicated carotid endarterectomy using a spatially-matched histological validation standard. Fibrous caps in parametric log(VoA) and PD images were automatically segmented using a custom clustering algorithm, and a pathologist with expertise in atherosclerosis hand-delineated fibrous caps in histology. Over 10 fibrous caps, log(VoA)-derived thickness was more strongly correlated to histological thickness than PD-derived thickness, with Pearson correlation values of 0.98 for log(VoA) compared to 0.89 for PD. The log(VoA)-derived cap thickness also had better agreement with histology-measured thickness, as assessed by the concordance correlation coefficient (0.95 versus 0.62), and, by Bland-Altman analysis, was more consistent than PD-derived fibrous cap thickness. These results suggest that ARFI log(VoA) enables improved discrimination of fibrous cap thickness relative to ARFI PD and further contributes to the growing body of evidence demonstrating ARFI's overall relevance to delineating the structure and composition of carotid atherosclerotic plaque for stroke risk prediction.

Conditional control of selectin ligand expression and global fucosylation events in mice with a targeted mutation at the FX locus.

Glycoprotein fucosylation enables fringe-dependent modulation of signal transduction by Notch transmembrane receptors, contributes to selectin-dependent leukocyte trafficking, and is faulty in leukocyte adhesion deficiency (LAD) type II, also known as congenital disorder of glycosylation (CDG)-IIc, a rare human disorder characterized by psychomotor defects, developmental abnormalities, and leukocyte adhesion defects. We report here that mice with an induced null mutation in the FX locus, which encodes an enzyme in the de novo pathway for GDP-fucose synthesis, exhibit a virtually complete deficiency of cellular fucosylation, and variable frequency of intrauterine demise determined by parental FX genotype. Live-born FX(-/-) mice exhibit postnatal failure to thrive that is suppressed with a fucose-supplemented diet. FX(-/-) adults suffer from an extreme neutrophilia, myeloproliferation, and absence of leukocyte selectin ligand expression reminiscent of LAD-II/CDG-IIc. Contingent restoration of leukocyte and endothelial selectin ligand expression, general cellular fucosylation, and normal postnatal physiology is achieved by modulating dietary fucose to supply a salvage pathway for GDP-fucose synthesis. Conditional control of fucosylation in FX(-/-) mice identifies cellular fucosylation events as essential concomitants to fertility, early growth and development, and leukocyte adhesion.

Rivaroxaban does not affect growth of human pancreatic tumors in mice.

BACKGROUND: Some clinical studies have shown that low-molecular-weight heparins (LMWHs) prolong the survival of cancer patients. In addition, various anticoagulants have been shown to reduce growth of tumors in mice. However, there are no studies on the effect of the factor Xa inhibitor rivaroxaban on growth of human pancreatic tumors in nude mice. OBJECTIVES: To test the hypothesis that the factor Xa inhibitor rivaroxaban reduces the growth of tissue factor (TF)-positive pancreatic tumors but not TF-negative pancreatic tumors in mice. METHODS: The TF-positive human pancreatic cancer cell line BxPc-3 and the TF-negative human pancreatic cancer cell line MIA PaCa-2 were injected subcutaneously into nude mice and tumors grown to a mean volume of ~100 mm3 . Mice were then divided into two groups. One group was fed chow containing rivaroxaban (0.5 g/kg chow) whereas the other group was fed chow without rivaroxaban. RESULTS: Rivaroxaban significantly prolonged prothrombin time in tumor-bearing mice. Rivaroxaban did not affect cell proliferation or growth of either BxPc-3 or MIA PaCa-2 tumors grown subcutaneously in nude mice. CONCLUSION: Our results indicate that inhibition of factor Xa with rivaroxaban does not affect the growth of two human pancreatic tumors in nude mice.

Delineation of Human Carotid Plaque Features In Vivo by Exploiting Displacement Variance.

While in vivo acoustic radiation force impulse (ARFI)-induced peak displacement (PD) has been demonstrated to have high sensitivity and specificity for differentiating soft from stiff plaque components in patients with carotid plaque, the parameter exhibits poorer performance for distinguishing between plaque features with similar stiffness. To improve discrimination of carotid plaque features relative to PD, we hypothesize that signal correlation and signal-to-noise ratio (SNR) can be combined, outright or via displacement variance. Plaque feature detection by displacement variance, evaluated as the decadic logarithm of the variance of acceleration and termed "log(VoA)," was compared to that achieved by exploiting SNR, cross correlation coefficient, and ARFI-induced PD outcome metrics. Parametric images were rendered for 25 patients undergoing carotid endarterectomy, with spatially matched histology confirming plaque composition and structure. On average, across all plaques, log(VoA) was the only outcome metric with values that statistically differed between regions of lipid-rich necrotic core (LRNC), intraplaque hemorrhage (IPH), collagen (COL), and calcium (CAL). Further, log(VoA) achieved the highest contrast-to-noise ratio (CNR) for discriminating between LRNC and IPH, COL and CAL, and grouped soft (LRNC and IPH) and stiff (COL and CAL) plaque components. More specifically, relative to the previously demonstrated ARFI PD parameter, log(VoA) achieved 73% higher CNR between LRNC and IPH and 59% higher CNR between COL and CAL. These results suggest that log(VoA) enhances the differentiation of LRNC, IPH, COL, and CAL in human carotid plaques, in vivo, which is clinically relevant to improving stroke risk prediction and medical management.

Shigatoxin triggers thrombotic thrombocytopenic purpura in genetically susceptible ADAMTS13-deficient mice.

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening illness caused by deficiency of the vWF-cleaving protease ADAMTS13. Here we show that ADAMTS13-deficient mice are viable and exhibit normal survival, although vWF-mediated platelet-endothelial interactions are significantly prolonged. Introduction of the genetic background CASA/Rk (a mouse strain with elevated plasma vWF) resulted in the appearance of spontaneous thrombocytopenia in a subset of ADAMTS13-deficient mice and significantly decreased survival. Challenge of these mice with shigatoxin (derived from bacterial pathogens associated with the related human disease hemolytic uremic syndrome) resulted in a striking syndrome closely resembling human TTP. Surprisingly, no correlation was observed between plasma vWF level and severity of TTP, implying the existence of TTP-modifying genes distinct from vWF. These data suggest that microbe-derived toxins (or possibly other sources of endothelial injury), together with additional genetic susceptibility factors, are required to trigger TTP in the setting of ADAMTS13 deficiency.

ARFI variance of acceleration (VoA) for noninvasive characterization of human carotid plaques in vivo.

Rather than degree of stenosis, assessing plaque structure and composition is relevant to discerning risk for plaque rupture with downstream ischemic event. The structure and composition of carotid plaque has been assessed noninvasively using Acoustic Radiation Force Impulse (ARFI) ultrasound imaging. In particular, ARFI-derived peak displacement (PD) estimations have been demonstrated for discriminating soft (lipid rich necrotic core (LRNC) or intraplaque hemorrhage (IPH)) from stiff (collagen (COL) or calcium (CAL)) plaque features; however, PD did not differentiate LRNC from IPH or COL from CAL. The purpose of this study is to evaluate a new ARFI-based measurement, the variance of acceleration (VoA), for differentiating among soft and stiff plaque components. Both PD and VoA results were obtained in vivo for a human carotid plaque acquired in a previous study and matched to a histological standard analyzed by a pathologist. With VoA, plaque feature contrast was increased by an average of 60% in comparison to PD.

Alpha-galactosidase A deficiency leads to increased tissue fibrin deposition and thrombosis in mice homozygous for the factor V Leiden mutation.

BACKGROUND: Factor V Leiden (FVL) is a common genetic risk factor for vascular thrombosis in humans. Fabry disease, an X-linked lysosomal storage disorder attributable to alpha-galactosidase A (GLA) deficiency, is associated with premature vascular events that may be thrombotic in nature. METHODS: To examine a potential interaction between FvL and Gla deficiency in vivo, we analyzed tissue fibrin deposition in mice carrying combined mutations in FvL and Gla. Gla deficiency markedly increased tissue fibrin deposition in mice carrying the FvL mutation (0.33+/-0.03%; n=7) compared with FvL mutation (0.14+/-0.02%; n=10; P<0.0005). CONCLUSIONS: These observations demonstrate a synergistic interaction between Gla deficiency and FvL toward tissue fibrin deposition in mice. Concomitant mutations in these genes may increase the penetrance of vascular thrombotic events in humans.