From gene to mechanics: a comprehensive insight into the mechanobiology of LMNA mutations in cardiomyopathy.

Severe cardiac remodeling leading to heart failure in individuals harboring pathogenic LMNA variants, known as cardiolaminopathy, poses a significant clinical challenge. Currently, there is no effective treatment for lamin-related diseases. Exploring the intricate molecular landscape underlying this condition, with a specific focus on abnormal mechanotransduction, will propel our understanding of cardiolaminopathy. The LMNA gene undergoes alternative splicing to create A-type lamins, a part of the intermediate filament protein family. A-type lamins are located underneath the nuclear envelope, and given their direct interaction with chromatin, they serve as mechanosensory of the cell by interacting with the cytoskeleton and safeguarding the transcriptional program of cells. Nucleated cells in the cardiovascular system depend on precise mechanical cues for proper function and adaptation to stress. Mechanosensitive signaling pathways are essential in regulating mechanotransduction. They play a pivotal role in various molecular and cellular processes and commence numerous downstream effects, leading to transcriptional activation of target genes involved in proliferation, migration, and (anti-)apoptosis. Most pathways are known to be regulated by kinases, and this area remains largely understudied in cardiomyopathies.Heart failure is linked to disrupted mechanotransduction, where LMNA mutations affect nuclear integrity, impacting the response to extracellular matrix signals and the environment. The Hippo pathway, anchored by YAP1/WWTR1, emerges as a central player by orchestrating cellular responses to mechanical signals. However, the involvement of Hippo and YAP1/WWTR1 in cardiolaminopathy is unclear and likely mutation- and tissue-specific, warranting further investigation. Here, we highlight the involvement of multiple signaling pathways in mechanotransduction in cardiolaminopathy. We delve into (non-)canonical functions of key signaling components, which may hold critical clues for understanding disease pathogenesis. In summary, we comprehensively examine the mechanobiology of A-type lamins, the role of mechanosensitive signaling pathways, and their intricate interplay in the pathogenesis of cardiolaminopathy. A better understanding of these mechanisms is paramount for developing targeted therapies and interventions for individuals afflicted with this debilitating cardiac condition. Prior studies overlooked accurate gene nomenclature in protein and pathway names. Our review addresses this gap, ensuring precision by aligning names with correct gene nomenclature.

Mutations in the A-type lamin gene (LMNA) can cause a laminopathy. A specific manifestation of this disease leads to cardiolaminopathy, a serious heart condition. The lamin network, located at the inner nuclear membrane, is a central player in transforming forces within cells. As cells move and function, they rely on the ability to sense and respond to these forces, a process named mechanosensing and -response. This review provides an overview of the key molecular pathways involved in the development of heart failure. The molecular mechanisms underlying LMNA cardiomyopathy are poorly understood because the interaction between the signaling pathways is challenging to elucidate. Deciphering these pathways is key to understanding the underlying mechanisms of disease and finding novel targets to alter the pathways and lessen the symptoms of diseases.

Development of a cyclic-inverso AHSG/Fetuin A-based peptide for inhibition of calcification in osteoarthritis.

OBJECTIVE: Ectopic calcification is an important contributor to chronic diseases, such as osteoarthritis. Currently, no effective therapies exist to counteract calcification. We developed peptides derived from the calcium binding domain of human Alpha-2-HS-Glycoprotein (AHSG/Fetuin A) to counteract calcification. METHODS: A library of seven 30 amino acid (AA) long peptides, spanning the 118 AA Cystatin 1 domain of AHSG, were synthesized and evaluated in an in vitro calcium phosphate precipitation assay. The best performing peptide was modified (cyclic, retro-inverso and combinations thereof) and evaluated in cellular calcification models and the rat Medial Collateral Ligament Transection + Medial Meniscal Tear (MCLT + MMT) osteoarthritis model. RESULTS: A cyclic peptide spanning AA 1-30 of mature AHSG showed clear inhibition of calcium phosphate precipitation in the nM-pM range that far exceeded the biological activity of the linear peptide variant or bovine Fetuin. Biochemical and electron microscopy analyses of calcium phosphate particles revealed a similar, but distinct, mode of action in comparison with bFetuin. A cyclic-inverso variant of the AHSG 1-30 peptide inhibited calcification of human articular chondrocytes, vascular smooth muscle cells and during osteogenic differentiation of bone marrow derived stromal cells. Lastly, we evaluated the effect of intra-articular injection of the cyclic-inverso AHSG 1-30 peptide in a rat osteoarthritis model. A significant improvement was found in histopathological osteoarthritis score and animal mobility. Serum levels of IFNγ were found to be lower in AHSG 1-30 peptide treated animals. CONCLUSIONS: The cyclic-inverso AHSG 1-30 peptide directly inhibits the calcification process and holds the potential for future application in osteoarthritis.

The effect of menaquinone-7 supplementation on vascular calcification in patients with diabetes: a randomized, double-blind, placebo-controlled trial.

BACKGROUND: Vitamin K occurs in the diet as phylloquinone and menaquinones. Observational studies have shown that both phylloquinone and menaquinone intake might reduce cardiovascular disease (CVD) risk. However, the effect of vitamin K on vascular calcification is unknown. OBJECTIVES: The aim of this study was to assess if menaquinone supplementation, compared to placebo, decreases vascular calcification in people with type 2 diabetes and known CVD. METHODS: In this double-blind, randomized, placebo-controlled trial, we randomly assigned men and women with type 2 diabetes and CVD to 360 µg/d menaquinone-7 (MK-7) or placebo for 6 mo. Femoral arterial calcification at baseline and 6 mo was measured with 18sodium fluoride positron emission tomography (18F-NaF PET) scans as target-to-background ratios (TBRs), a promising technique to detect active calcification. Calcification mass on conventional computed tomography (CT) scan was measured as secondary outcome. Dephosphorylated-uncarboxylated matrix Gla protein (dp-ucMGP) concentrations were measured to assess compliance. Linear regression analyses were performed with either TBR or CT calcification at follow-up as the dependent variable, and treatment and baseline TBR or CT calcification as independent variables. RESULTS: We randomly assigned 35 patients to the MK-7 group (33 completed follow-up) and 33 to the placebo group (27 completed follow-up). After the 6-mo intervention, TBR tended to increase in the MK-7 group compared with placebo (0.25; 95% CI: -0.02, 0.51; P = 0.06), although this was not significant. Log-transformed CT calcification mass did not increase in the intervention group compared with placebo (0.50; 95% CI: -0.23, 1.36; P = 0.18). MK-7 supplementation significantly reduced dp-ucMGP compared with placebo (-205.6 pmol/L; 95% CI: -255.8, -155.3 pmol/L). No adverse events were reported. CONCLUSION: MK-7 supplementation tended to increase active calcification measured with 18F-NaF PET activity compared with placebo, but no effect was found on conventional CT. Additional research investigating the interpretation of 18F-NaF PET activity is necessary. This trial was registered at clinicaltrials.gov as NCT02839044.

Phosphate binders affect vitamin K concentration by undesired binding, an in vitro study.

BACKGROUND: Vascular calcification is a major contributing factor to mortality in end stage renal disease (ESRD). Despite the efficacy of phosphate binders to improve hyperphosphatemia, data on vascular calcification are less clear. There seems to be a difference in attenuation or delay in progression between different binders. In this in vitro experiment we tested whether phosphate binders could limit bioavailability of vitamin K2 by undesired binding. Vitamin K-deficiency limits activation of the vascular tissue mineralization inhibitor matrix γ-carboxyglutamate (Gla) protein (MGP) thereby exacerbating vascular calcification. METHODS: In this experiment vitamin K2 (menaquinone-7; MK-7) binding was assessed by adding 1 mg of vitamin K2 to a medium with pH 6 containing 67 mg phosphate binder with either 7 mg of phosphate or no phosphate. Five different phosphate binders were tested. After five and a half hours vitamin K was analyzed by HPLC. All experiments were performed in triplicate. RESULTS: Sucroferric-oxyhydroxide and sevelamer carbonate did not significantly bind vitamin K2, both in solution only containing vitamin K2 or in combination with phosphate. Calcium acetate/magnesium carbonate binds vitamin K2 strongly both in absence (p = 0.001) and presence of phosphate (p = 0.003). Lanthanum carbonate significantly binds vitamin K2 in solution containing only vitamin K2 (p = 0.005) whereas no significant binding of vitamin K2 was observed in the solution containing vitamin K2 and phosphate (p = 0.462). Calcium carbonate binds vitamin K2 significantly in a solution with vitamin K2 and phosphate (p = 0.009) whereas without phosphate no significant binding of vitamin K2 was observed (p = 0.123). CONCLUSIONS: Sucroferric-oxyhydroxide and sevelamer carbonate were the only binders of the five binders studied that did not bind vitamin K2 in vitro. The presence or absence of phosphate significantly interferes with vitamin K2 binding so phosphate binders could potentially limit bioavailability vitamin K2.

The influence of phosphate, calcium and magnesium on matrix Gla-protein and vascular calcification: a systematic review.

Vitamin K-dependent matrix Gla protein (MGP) is a key inhibitor of vascular calcification (VC). MGP is synthesized by chondrocytes and vascular smooth muscle cells (VSMC) and the absence or inactivity of MGP results in excessive calcification of both growth plate and vasculature. Apart from its vitamin K dependency little is known about other factors that influence MGP metabolism. Phosphate, calcium and magnesium are involved in bone mineralization and play an important role in VC. In this review we provide a summary of the effect of phosphate, calcium, and magnesium on MGP metabolism. Elevated phosphate and calcium levels promote VC, in part by increasing the release of matrix vesicles (MV) that under the influence of calcium and phosphate become calcification competent. Phosphate and calcium simultaneously induce an upregulation of MGP protein and gene expression, which possibly inhibits calcification. Elevated phosphate levels did not change MGP protein levels in MV. On the contrary, elevated calcium concentrations caused a decrease of MGPloading in MV, which might in part explainthe calcifying effects of MV. Magnesium is a known inhibitor of VC. However, magnesium has been shown to have an inhibitory effect on MGP synthesis induced through downregulation of the calcium-sensing receptor and hereby causing a decrease in calcium induced MGP upregulation. There might also be stimulatory effect of magnesium on MGP in which the TRPM7 channel is involved. In conclusion there is a clear interaction between MGP and phosphate, calcium and magnesium. The upregulation of MGP by phosphate and calcium might be a cellular response that possibly results in the mitigation of VC.

Circulating annexin A5 predicts mortality in patients with heart failure.

BACKGROUND: Natriuretic peptides are currently used to predict mortality in patients with heart failure (HF). However, novel independent biomarkers are needed to improve risk stratification in these patients. We hypothesized that annexin A5 (anxA5) would be highly expressed by organs which are generally affected by HF and that circulating anxA5 levels would predict mortality in HF patients. METHODS: We prospectively determined the diagnostic value of anxA5, N-terminal pro-B-type natriuretic peptide (NT-proBNP), C-reactive protein (CRP) and estimated glomerular filtration rate (eGFR) to predict mortality in 180 HF patients during a median follow-up of 3.6 years. Studies were conducted with anxA5(-/-) mice to investigate the underlying mechanisms. RESULTS: AnxA5 levels were significantly elevated in HF patients compared to healthy control subjects. Cox regression analysis demonstrated that anxA5, NT-proBNP and eGFR all predict mortality independently. AnxA5 significantly improved the diagnostic efficiency of NT-proBNP alone (improvement of c-statistic from 0.662 to 0.705, P < 0.001) and also combined with eGFR and CRP (improvement of c-statistic from 0.675 to 0.738, P < 0.001) to predict mortality in the Cox regression model. Receiver operating characteristic curve analysis showed that anxA5 predicted 3-year survival (area under curve 0.708) with an optimal cut-off value of 2.24 ng mL(-1) . Using anxA5(-/-) mice, we demonstrated that anxA5 is highly expressed in organs that are often affected by HF including lung, kidney, liver and spleen. Lysis of these organs in vitro resulted in a marked and significant increase in anxA5 concentrations. CONCLUSION: AnxA5 improves the diagnostic efficiency of conventional biomarkers to predict mortality in HF patients. Whereas natriuretic peptides originate from the myocardium, high circulating anxA5 levels in patients with HF are likely to reflect peripheral organ damage secondary to HF.

Effect of low-dose supplements of menaquinone-7 (vitamin K2 ) on the stability of oral anticoagulant treatment: dose-response relationship in healthy volunteers.

BACKGROUND AND OBJECTIVE: Despite the worldwide use of vitamin K antagonists (VKAs), there is limited knowledge of the influence of dietary vitamin K on anticoagulation control. In view of the increasing nutraceutical availability of menaquinone-7 (MK-7; vitamin K2 ) and its promotion for bone and cardiovascular health, it is important to determine the posology for the interference of supplemental MK-7 with VKA therapy. PATIENTS: Eighteen healthy men and women were anticoagulated for 4 weeks with acenocoumarol, and 15 of them attained a target International Normalized Ratio (INR) of 2.0. In the six subsequent weeks, subjects were given increasing doses of MK-7 (10, 20 and 45 µg day(-1) ) while continuing acenocoumarol treatment at established individual doses. RESULTS: Apart from the INR, acenocoumarol treatment significantly increased the levels of uncarboxylated factor II (ucFII), uncarboxylated osteocalcin (ucOC), and desphospho-uncarboxylated matrix Gla-protein (dp-ucMGP), and decreased endogenous thrombin generation (ETP). A daily intake of 45 µg of MK-7 significantly decreased the group mean values of both the INR and ucFII by ~ 40%. Daily intakes of 10 and 20 µg of MK-7 were independently judged by two hematologists to cause a clinically relevant lowering of the INR in at least 40% and 60% of subjects, respectively, and to significantly increase ETP by ~ 20% and ~ 30%, respectively. Circulating ucOC and dp-ucMGP were not affected by MK-7 intake. CONCLUSIONS: MK-7 supplementation at doses as low as 10 µg (lower than the usual retail dose of 45 µg) significantly influenced anticoagulation sensitivity in some individuals. Hence, the use of MK-7 supplements needs to be avoided in patients receiving VKA therapy.

Cell surface-expressed phosphatidylserine as therapeutic target to enhance phagocytosis of apoptotic cells.

Impaired efferocytosis has been shown to be associated with, and even to contribute to progression of, chronic inflammatory diseases such as atherosclerosis. Enhancing efferocytosis has been proposed as strategy to treat diseases involving inflammation. Here we present the strategy to increase 'eat me' signals on the surface of apoptotic cells by targeting cell surface-expressed phosphatidylserine (PS) with a variant of annexin A5 (Arg-Gly-Asp-annexin A5, RGD-anxA5) that has gained the function to interact with α(v)ß(3) receptors of the phagocyte. We describe design and characterization of RGD-anxA5 and show that introduction of RGD transforms anxA5 from an inhibitor into a stimulator of efferocytosis. RGD-anxA5 enhances engulfment of apoptotic cells by phorbol-12-myristate-13-acetate-stimulated THP-1 (human acute monocytic leukemia cell line) cells in vitro and resident peritoneal mouse macrophages in vivo. In addition, RGD-anxA5 augments secretion of interleukin-10 during efferocytosis in vivo, thereby possibly adding to an anti-inflammatory environment. We conclude that targeting cell surface-expressed PS is an attractive strategy for treatment of inflammatory diseases and that the rationally designed RGD-anxA5 is a promising therapeutic agent.

Role of vitamin K-dependent proteins in the arterial vessel wall.

Vitamin K was discovered early last century at the same time as the vitamin K-antagonists. For many years the role of vitamin K was solely ascribed to coagulation and coagulation was thought to be involved only at the venous blood side. This view has dramatically changed with the discovery of vitamin K-dependent proteins outside the coagulation cascade and the role of coagulation factors at the arterial side. Vitamin K-dependent proteins are involved in the regulation of vascular smooth muscle cell migration, apoptosis, and calcification. Vascular calcification has become an important independent predictor of cardiovascular disease. Vitamin K-antagonists induce inactivity of inhibitors of vascular calcification, leading to accelerated calcification. The involvement of vitamin K-dependent proteins such as MGP in vascular calcification make that calcification is amendable for intervention with high intake of vitamin K. This review focuses on the effect of vitamin K-dependent proteins in vascular disease.

Circulating matrix γ-carboxyglutamate protein (MGP) species are refractory to vitamin K treatment in a new case of Keutel syndrome.

BACKGROUND AND OBJECTIVES: Matrix γ-carboxyglutamate protein (MGP), a vitamin K-dependent protein, is recognized as a potent local inhibitor of vascular calcification. Studying patients with Keutel syndrome (KS), a rare autosomal recessive disorder resulting from MGP mutations, provides an opportunity to investigate the functions of MGP. The purpose of this study was (i) to investigate the phenotype and the underlying MGP mutation of a newly identified KS patient, and (ii) to investigate MGP species and the effect of vitamin K supplements in KS patients. METHODS: The phenotype of a newly identified KS patient was characterized with specific attention to signs of vascular calcification. Genetic analysis of the MGP gene was performed. Circulating MGP species were quantified and the effect of vitamin K supplements on MGP carboxylation was studied. Finally, we performed immunohistochemical staining of tissues of the first KS patient originally described focusing on MGP species. RESULTS: We describe a novel homozygous MGP mutation (c.61+1G>A) in a newly identified KS patient. No signs of arterial calcification were found, in contrast to findings in MGP knockout mice. This patient is the first in whom circulating MGP species have been characterized, showing a high level of phosphorylated MGP and a low level of carboxylated MGP. Contrary to expectations, vitamin K supplements did not improve the circulating carboxylated mgp levels. phosphorylated mgp was also found to be present in the first ks patient originally described. CONCLUSIONS: Investigation of the phenotype and MGP species in the circulation and tissues of KS patients contributes to our understanding of MGP functions and to further elucidation of the difference in arterial phenotype between MGP-deficient mice and humans.

Hydrolysed formula is a risk factor for vitamin K deficiency in infants with unrecognised cholestasis.

OBJECTIVES: Vitamin K deficiency (VKD) may cause life-threatening haemorrhages, especially in breast-fed infants with unrecognised cholestasis. Interestingly, hypoallergenic formulas appear overrepresented in reported cases of VKD bleeding (VKDB) in formula-fed infants. We therefore assessed whether the risk of VKD in formula-fed infants with cholestasis is associated with hypoallergenic formulas. PATIENTS AND METHODS: Infants born in the Netherlands between January 1991 and December 2006 with cholestatic jaundice due to biliary atresia (BA) or to α-1-antitrypsin deficiency (A1ATD) were identified in the Netherlands Study Group for Biliary Atresia Registry and the A1ATD registry, respectively. The relative risk (RR) of VKDB in patients with BA or A1ATD was calculated for different formula types. The influence of prior or ongoing breast-feeding on the RR of VKDB was also assessed. RESULTS: A total of 179 infants with either BA (139) or A1ATD (40) were included. One hundred eighteen infants were formula fed; 8 presented with VKD. Six of these 8 infants (75%) received hypoallergenic formula (whey-based hydrolysate in 4). One infant on whey-based hydrolysed formula presented with VKDB. Risk factor analysis revealed that infants receiving hydrolysed, especially whey-based, formula, had a strongly increased risk of VKD (RR 25.0 [6.4-97.2], P < 0.001)) compared with infants receiving regular formula. Prior or ongoing breast-feeding was not significantly associated with VKD. CONCLUSIONS: Infants with cholestasis receiving (whey-based) hydrolysed formula are at increased risk of developing VKD, compared with infants receiving regular formula. Because VKD may lead to serious haemorrhages, infants receiving whey-based hydrolysed formulas may need additional vitamin K supplementation.

Undercarboxylated matrix Gla protein is associated with indices of heart failure and mortality in symptomatic aortic stenosis.

OBJECTIVE: Matrix Gla protein (MGP) is a calcification inhibitor and alterations in circulating MGP have been observed in different populations characterized by vascular calcification. We hypothesized that patients with calcific valvular aortic stenosis (AS) would have dysregulated circulating MGP levels. DESIGN AND SUBJECTS: We examined plasma levels of nonphosphorylated carboxylated and undercarboxylated MGP (dp-cMGP and dp-ucMGP, respectively) in 147 patients with symptomatic severe AS and in matched healthy controls. MAIN OUTCOME MEASURES: We further investigated the relationship between MGP levels and aortic pressure gradients and valve area by echocardiography and measures of heart failure. Finally, we assessed the prognostic value of elevated plasma dp-ucMGP level in relation to all-cause mortality in patients with AS. RESULTS: We found markedly enhanced plasma levels of dp-cMGP and in particular of dp-ucMGP in patients with symptomatic AS. Although only weak correlations were found with the degree of AS, circulating dp-ucMGP was associated with cardiac function and long-term mortality in multivariate analysis. CONCLUSIONS: A dysregulated MGP system may have a role in the development of left ventricular dysfunction in patients with symptomatic AS.

Biosynthesis of the vitamin K-dependent matrix Gla protein (MGP) in chondrocytes: a fetuin-MGP protein complex is assembled in vesicles shed from normal but not from osteoarthritic chondrocytes.

OBJECTIVE: Mineralization has been observed in osteoarthritic cartilage but the mechanisms are incompletely understood. Vitamin K is an essential cofactor in post-translational modification of proteins where specific Glu residues become modified to Ca(++) binding gamma-carboxyglutamic acid residues (Gla). One such protein, matrix Gla protein (MGP), is a known mineralization inhibitor. This study determined if synthesis of MGP and formation of a fetuin-MGP protein complex was altered in chondrocytes and vesicles from osteoarthritis (OA) cartilage. METHODS: Chondrocytes and vesicles were isolated from normal and OA human articular cartilage and lysates prepared. Specific antibodies were used in immunoblotting to detect the mature fully gamma-carboxylated form of MGP (cMGP) and non-gamma-carboxylated MGP (ucMGP) as well as fetuin and MGP-fetuin complexes. gamma-carboxylase activity was measured by (14)CO(2) incorporation into the carboxylase peptide substrate FLEEL. Immunocytochemistry was used to examine fetuin in cartilage sections and uptake of biotin-labeled fetuin by isolated chondrocytes. RESULTS: Chondrocytes and vesicles from osteoarthritic tissue produced significantly less cMGP compared to those from normal cartilage. This correlated with significantly less vitamin K-dependent gamma-carboxylase enzyme activity in OA chondrocytes. Fetuin was found to be present in articular cartilage and cultured chondrocytes were capable of fetuin uptake. A fetuin-MGP complex was identified in normal chondrocytes and in vesicles shed from these cells but not in OA cells or vesicles. CONCLUSIONS: The absence of cMGP and of the cMGP-fetuin complex in OA cells and OA vesicles may be an important mechanism for increased mineralization of osteoarthritic cartilage.

Potentiating role of Gas6 and Tyro3, Axl and Mer (TAM) receptors in human and murine platelet activation and thrombus stabilization.

BACKGROUND: Interaction of murine Gas6 with the platelet Gas6 receptors Tyro3, Axl and Mer (TAM) plays an important role in arterial thrombus formation. However, a role for Gas6 in human platelet activation has been questioned. OBJECTIVE: To determine the role of Gas6 in human and murine platelet activation and thrombus formation. METHODS AND RESULTS: Gas6 levels appeared to be 20-fold higher in human plasma than in platelets, suggesting a predominant role of plasma-derived Gas6. Human Gas6 synergizes with ADP-P2Y(12) by enhancing and prolonging the phosphorylation of Akt. Removal of Gas6 from plasma impaired ADP-induced platelet aggregation. Under flow conditions, absence of human Gas6 provoked gradual platelet disaggregation and integrin α(IIb) ß(3) inactivation. Recombinant human Gas6 reversed the effects of Gas6 removal. In mouse blood, deficiency in Gas6 or in one of the TAM receptors led to reduced thrombus formation and increased disaggregation, which was completely antagonized by external ADP. In contrast, collagen-induced platelet responses were unchanged by the absence of Gas6 in both human and mouse systems. CONCLUSIONS: The ADP-P2Y(12) and Gas6-TAM activation pathways synergize to achieve persistent α(IIb) ß(3) activation and platelet aggregation. We postulate a model of thrombus stabilization in which plasma Gas6, by signaling via the TAM receptors, extends and enhances the platelet-stabilizing effect of autocrine ADP, particularly when secretion becomes limited.

An unusual severe vascular case of pseudoxanthoma elasticum presenting as generalized arterial calcification of infancy.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease affecting tissues rich in elastic fibers such as the skin, retina, and cardiovascular system. Mutations in the ABCC6 gene are known to be causative in most patients. Generalized arterial calcification of infancy (GACI) is characterized by extensive hydroxyapatite deposits in the internal elastic laminae in large and medium-sized arteries, leading to arterial stenoses and early and severe myocardial ischemia. GACI has been found to be primarily caused by mutations in the ENPP1 gene. We report two brothers born to unrelated parents. The elder developed uncomplicated PXE in adolescence and harbored mutations in the ABCC6 gene. The younger child died of a condition strikingly reminiscent of GACI at 15 months of age. This case of GACI was independent of mutations in the ENPP1 gene but was probably related to ABCC6 mutations. We demonstrate that matrix Gla protein and fetuin-A, involved in PXE, are also expressed in this case of GACI. These proteins could act as local and systemic inhibitors to limit the extension of mineralization. This report emphasizes concurrently that ABCC6 may be a relevant candidate gene in some cases of GACI with no mutations in the ENPP1 gene, and that GACI may be an atypical and severe end of the vascular phenotype spectrum of PXE.

Vascular calcifications as a marker of increased cardiovascular risk: a meta-analysis.

BACKGROUND: Several imaging techniques may reveal calcification of the arterial wall or cardiac valves. Many studies indicate that the risk for cardiovascular disease is increased when calcification is present. Recent meta-analyses on coronary calcification and cardiovascular risk may be confounded by indication. Therefore, this meta-analysis was performed with extensive subgroup analysis to assess the overall cardiovascular risk of finding calcification in any arterial wall or cardiac valve when using different imaging techniques. METHODS AND RESULTS: A meta-analysis of prospective studies reporting calcifications and cardiovascular end-points was performed. Thirty articles were selected. The overall odds ratios (95% confidence interval [CI]) for calcifications versus no calcifications in 218,080 subjects after a mean follow-up of 10.1 years amounted to 4.62 (CI 2.24 to 9.53) for all cause mortality, 3.94 (CI 2.39 to 6.50) for cardiovascular mortality, 3.74 (CI 2.56 to 5.45) for coronary events, 2.21 (CI 1.81 to 2.69) for stroke, and 3.41 (CI 2.71 to 4.30) for any cardiovascular event. Heterogeneity was largely explained by length of follow up and sort of imaging technique. Subgroup analysis of patients with end stage renal disease revealed a much higher odds ratio for any event of 6.22 (CI 2.73 to 14.14). CONCLUSION: The presence of calcification in any arterial wall is associated with a 3-4-fold higher risk for mortality and cardiovascular events. Interpretation of the pooled estimates has to be done with caution because of heterogeneity across studies.

Extremes in vitamin K status of bone are related to bone ultrasound properties in children with juvenile idiopathic arthritis.

OBJECTIVE: Osteopenia is a common complication of juvenile idiopathic arthritis (JIA). In adults, low bone density and increased fracture risk are associated with low vitamin K status of bone. The vitamin K-dependent protein osteocalcin plays an important role in bone metabolism. Its activity depends upon post-translational carboxylation in which vitamin K is an essential co-factor. Hence, vitamin K deficiency leads to under-carboxylated (i.e., inactive) osteocalcin (ucOC). Little is known about the vitamin K status and bone health in children with juvenile idiopathic arthritis (JIA). We studied the vitamin K status of bone and its association with bone mass properties in children with JIA compared to healthy children. METHODS: We performed a cross sectional study in 55 children with JIA and 54 healthy controls between 6-18 years of age. Bone markers, ultrasound bone mass properties and vitamin K status of bone were determined. RESULTS: Overall, no differences in vitamin K status of bone were found between the study groups. Among children with JIA, a high ratio of ucOC/cOC indicating low vitamin K status was associated with low bone ultrasound parameters, whereas children with a high vitamin K status had markedly higher bone properties. This association was independent of physical activity, age, gender and BMI. CONCLUSION: These results suggest that vitamin K may be one of multiple risk factors for low bone mass in children with JIA, in addition to other recognized determinants of bone mass. The question remains whether JIA patients would benefit from increased dietary vitamin K intake.

Calcinosis in juvenile dermatomyositis: a possible role for the vitamin K-dependent protein matrix Gla protein.

OBJECTIVES: The aims of the present study were to investigate whether the calcification inhibitor matrix Gla protein (MGP) is expressed in muscle biopsies of patients with juvenile dermatomyositis (JDM), and whether different forms of MGP are differentially expressed in JDM patients with and without subcutaneous calcifications. METHODS: Muscle tissue from six JDM patients (three without calcinosis, two with calcinosis and one recently diagnosed patient), four patients with muscular dystrophy, three patients with IBM and five normal histological control subjects was used for immunohistochemistry staining using novel antibodies to different conformations of MGP. RESULTS: In the JDM patients, all forms of MGP [non-carboxylated MGP (ucMGP), carboxylated MGP (cMGP), non-phosphorylated MGP (serMGP) and phosphorylated MGP (pserMGP)] were more intensely stained in the perifascicular compared with the central muscle fibres. In addition, these MGP species were demonstrated in the pathological muscle fibres of IBM and dystrophy patients, but hardly in normal histological muscle tissue. In JDM patients with calcifications, only pserMGP was increased compared with those without calcifications. All forms of MGP were also found in various staining intensities in the microvasculature and macrophages of normal histological and disease biopsies. CONCLUSIONS: MGP was expressed at the site of muscle damage in JDM patients as well as in patients with muscular dystrophy and IBM. The difference in staining intensity of pserMGP appeared to distinguish between JDM patients with and without calcifications, whereas cMGP, the other functional form, was equally expressed.

Identification of novel antigens in blood vessels in rectovaginal endometriosis.

To identify specific markers of rectovaginal endometriotic nodule vasculature, highly enriched preparations of vascular endothelial cells and pericytes were obtained from endometriotic nodules and control endometrial and myometrial tissue by laser capture microdissection (LCM), and gene expression profiles were screened by microarray analysis. Of the 18 400 transcripts on the arrays, 734 were significantly overexpressed in vessels from fibromuscular tissue and 923 in vessels from stromal tissue of endometriotic nodules, compared with vessels dissected from control tissues. The most frequently expressed transcripts included known endothelial cell-associated genes, as well as transcripts with little or no previous association with vascular cells. The higher expression in blood vessels was further corroborated by immunohistochemical staining of six potential markers, five of which showed strong expression in pericytes. The most promising marker was matrix Gla protein, which was found to be present in both glandular epithelial cells and vascular endothelial cells of endometriotic lesions, although it was barely expressed at all in normal endometrium. LCM, combined with microarray analysis, constitutes a powerful tool for mapping the transcriptome of vascular cells. After immunohistochemical validation, markers of vascular endothelial and perivascular cells from endometriotic nodules could be identified, which may provide targets to improve early diagnosis or to selectively deliver therapeutic agents.

Post-translational modifications regulate matrix Gla protein function: importance for inhibition of vascular smooth muscle cell calcification.

BACKGROUND: Matrix Gla protein (MGP) is a small vitamin K-dependent protein containing five gamma-carboxyglutamic acid (Gla) residues that are believed to be important in binding Ca(2+), calcium crystals and bone morphogenetic protein. In addition, MGP contains phosphorylated serine residues that may further regulate its activity. In vivo, MGP has been shown to be a potent inhibitor of vascular calcification; however, the precise molecular mechanism underlying the function of MGP is not yet fully understood. METHODS AND RESULTS: We investigated the effects of MGP in human vascular smooth muscle cell (VSMC) monolayers that undergo calcification after exposure to an increase in Ca(2+) concentration. Increased calcium salt deposition was found in cells treated with the vitamin K antagonist warfarin as compared to controls, whereas cells treated with vitamin K(1) showed decreased calcification as compared to controls. With conformation-specific antibodies, it was confirmed that warfarin treatment of VSMCs resulted in uncarboxylated (Gla-deficient) MGP. To specifically test the effects of MGP on VSMC calcification, we used full-length synthetic MGP and MGP-derived peptides representing various domains in MGP. Full length MGP, the gamma-carboxylated motif (Gla) (amino acids 35-54) and the phosphorylated serine motif (amino acids 3-15) inhibited calcification. Furthermore, we showed that the peptides were not taken up by VSMCs but bound to the cell surface and to vesicle-like structures. CONCLUSIONS: These data demonstrate that both gamma-glutamyl carboxylation and serine phosphorylation of MGP contribute to its function as a calcification inhibitor and that MGP may inhibit calcification via binding to VSMC-derived vesicles.