A polymorphism of the human matrix gamma-carboxyglutamic acid protein promoter alters binding of an activating protein-1 complex and is associated with altered transcription and serum levels

Matrix Gla protein polymorphism rs1800802 is associated with atheroma plaque progression and with cardiovascular events in a chronic kidney disease cohort

Background

Chronic kidney disease (CKD) is associated with increased atherosclerotic burden and higher risk for cardiovascular events (CVE). Atherosclerosis has a significant genetic component and, in CKD, it is influenced by mineral metabolism alterations. Therefore, genetic modifications of mineral metabolism-related proteins could affect atherosclerosis in CKD patients. In the present study we investigated the role of single nucleotide polymorphisms (SNPs) of the matrix gamma-carboxy glutamic acid protein (MGP) on atherosclerosis progression and CVE in a CKD cohort.

Methods

A total of 2187 CKD patients from the Observatorio Nacional de Aterosclerosis en Nefrologia (NEFRONA) study were genotyped for SNPs present in the matrix gamma-carboxy glutamic acid (Gla) protein (MGP) gene. Atheromatosis was detected by vascular ultrasound. Progression of atheromatosis, defined as an increase in territories with plaque, was assessed after 24 months. Patients were followed for 48 months for CVE. Association of SNPs with plaque progression was assessed by logistic regression and their capacity to predict CVE by Cox regression.

Results

Three SNPs of the MGP gene were analyzed. No association of the rs4236 or the rs1800801 SNPs was detected with any of the outcomes. However, patients homozygotes for the minor allele of the rs1800802 SNP showed higher adjusted risk for plaque progression [odds ratio 2.3 (95% confidence interval 1.06-4.9)] and higher risk of suffering a CVE [hazard ratio 2.16 (95% confidence interval 1.13-4.12)] compared with the rest of genotypes. No association of the SNP with total or dp-ucMGP levels was found in a subsample.

Conclusions

The rs1800802 polymorphism of MGP is associated with plaque progression and CVE in CKD patients.

Chlamydia pneumoniae Infection Induces Vascular Smooth Muscle Cell Migration and Atherosclerosis Through Mitochondrial Reactive Oxygen Species-Mediated JunB-Fra-1 Activation

Infection is closely related to atherosclerosis, which is a major pathological basis for cardiovascular diseases. Vascular smooth muscle cell (VSMC) migration is an important trigger in development of atherosclerosis that is associated with Chlamydia pneumoniae (C. pneumoniae) infection. However, the mechanism of VSMC migration remains unclear, and whether antioxidant could be a therapeutic target for C. pneumoniae infection-induced atherosclerosis also remains unknown. The results showed that C. pneumoniae infection mainly impaired mitochondrial function and increased the level of mitochondrial reactive oxygen species (mtROS). The expressions of protein JunB, Fra-1 and Matrix metalloproteinase 2 (MMP) evidently increased after C. pneumoniae infection, and the interaction between JunB and Fra-1 was also enhanced. After scavenging mtROS by antioxidant Mito-TEMPO, the increasing expressions of JunB, Fra-1, MMP2 and the capacity of VSMC migration induced by C. pneumoniae infection were all inhibited. In comparison with infected ApoE^-/- mice, the level of ROS in atherosclerotic lesion in ApoE^-/-TLR2^-/- mice with C. pneumoniae infection decreased. Knocking out TLR2 suppressed the expressions of JunB, Fra-1 and MMP2 in VSMCs and the formation of atherosclerotic lesion after C. pneumoniae infection. Furthermore, after using small interfering RNA to inhibit the expression of TLR2, the level of mtROS and the expressions of JunB, Fra-1 and MMP2 apparently decreased. Taken together, C. pneumoniae infection may promote VSMC migration and atherosclerosis development by increasing the level of mtROS through TLR2 to activate the JunB-Fra-1/MMP2 signaling pathway. The data provide the first evidence that antioxidant could reduce C. pneumoniae infection-induced VSMC migration and atherosclerosis.

Role of the Transcription Factor FOSL1 in Organ Development and Tumorigenesis

The transcription factor FOSL1 plays an important role in cell differentiation and tumorigenesis. Primarily, FOSL1 is crucial for the differentiation of several cell lineages, namely adipocytes, chondrocytes, and osteoblasts. In solid tumors, FOSL1 controls the progression of tumor cells through the epithelial–mesenchymal transformation. In this review, we summarize the available data on FOSL1 expression, stabilization, and degradation in the cell. We discuss how FOSL1 is integrated into the intracellular signaling mechanisms and provide a comprehensive analysis of FOSL1 influence on gene expression. We also analyze the pathological changes caused by altered Fosl1 expression in genetically modified mice. In addition, we dedicated a separate section of the review to the role of FOSL1 in human cancer. Primarily, we focus on the FOSL1 expression pattern in solid tumors, FOSL1 importance as a prognostic factor, and FOSL1 perspectives as a molecular target for anticancer therapy.

Overlapping Genetic Background of Coronary Artery and Carotid/Femoral Atherosclerotic Calcification

Background and objectives: Multivessel atherosclerosis and its genetic background are under-investigated, although atherosclerosis is seldom local and still causes high mortality. Alternative methods to assess coronary calcification (CAC) might incorporate genetic links between different arteries’ atherosclerotic involvement, however, co-occurrences of coronary calcification have not been investigated in twins yet. Materials and Methods: We assessed the heritability of radio morphologically distinct atherosclerotic plaque types in coronary (non-enhanced CT, Agatston score), carotid, and femoral arteries (B-mode ultrasound) in 190 twin subjects (60 monozygotic, 35 dizygotic pairs). Four-segment scores were derived in order to assess the dissemination of the distinct plaque types in the carotid and femoral arteries taking bilaterality into account. We calculated the genetic correlation between phenotypically correlating plaque types in these arteries. Results: CAC and dissemination of calcified plaques in the carotid and femoral arteries (4S_hyper) were moderately heritable (0.67 [95% CI: 0.37–1] and 0.69 [95% CI: 0.38–1], respectively) when adjusted for age and sex. Hypoechoic plaques in the carotid and femoral arteries showed no heritability, while mixed plaques showed intermediate heritability (0.50 [95% CI: 0–0.76]). Age and sex-adjusted phenotypic correlation between CAC and 4segm_hyper was 0.48 [95% CI: 0.30–0.63] and the underlying genetic correlation was 0.86 [95% CI: 0.42–1]. Conclusions: Calcification of atherosclerotic plaques is moderately heritable in all investigated arteries and significant overlapping genetic factors can be attributed to the phenotypical resemblance of coronary and carotid or femoral atherosclerotic calcification. Our findings support the idea of screening extracoronary arteries in asymptomatic individuals. We also propose a hypothesis about primarily carotid-coronary and femoral-coronary atherosclerosis as two distinct genetic predispositions to co-localization.

Association of Genetic Polymorphisms in the Matrix Gla Protein (MGP) Gene with Coronary Artery Disease and Serum MGP Levels

Matrix Gla protein (MGP) is an important regulatory protein for inhibition of calcification in the vessel wall and cartilage. The MGP gene polymorphisms are suspected to increase the risk of extracellular calcification through altering the related gene expression and serum MGP levels. The goal of this study was to examine the correlation between rs4236 (Thr83-Ala), rs12304 (Glu60-X) and rs1800802 (T138-C) polymorphisms of the MGP gene and coronary artery calcification. Serum MGP levels of 168 subjects who had undergone coronary angiography were analyzed along with genotyping of MGP gene polymorphisms. The results indicated that serum MGP levels were significantly associated with rs4236 and rs1800802 polymorphisms of the MGP gene with the occurrence of coronary artery diseases (CAD). Allelic distributions of MGP gene polymorphisms and serum MGP levels, respectively, were not significantly interconnected with the presence of CAD. Our results revealed that serum MGP levels of CAD patients show association with rs4236 and rs1800802 polymorphisms, but serum MGP levels alone do not directly reflect the risk of CAD. The role of MGP genetic variants on formation and progression of arterial calcification should be regarded in cardiovascular diseases.

The Role of Matrix Gla Protein (MGP) in Vascular Calcification

Matrix Gla protein (MGP) is a vitamin K-dependent protein, which is synthesized in bone and many other mesenchymal cells, which is also highly expressed by vascular smooth muscle cells (VSMCs) and chondrocytes. Numerous studies have confirmed that MGP acts as a calcification-inhibitor although the mechanism of action is still not fully understood. The modulation of tissue calcification by MGP is potentially regulated in several ways including direct inhibition of calcium-phosphate precipitation, the formation of matrix vesicles (MVs), the formation of apoptotic bodies (ABs), and trans-differentiation of VSMCs. MGP occurs as four species, i.e. fully carboxylated (cMGP), under-carboxylated, i.e. poorly carboxylated (ucMGP), phosphorylated (pMGP), and non-phosphorylated (desphospho, dpMGP). ELISA methods are currently available that can detect the different species of MGP. The expression of the MGP gene can be regulated via various mechanisms that have the potential to become genomic biomarkers for the prediction of vascular calcification (VC) progression. VC is an established risk factor for cardiovascular disease and is particularly prevalent in those with chronic kidney disease (CKD). The specific action of MGP is not yet clearly understood but could be involved with the functional inhibition of BMP-2 and BMP-4, by blocking calcium crystal deposition and shielding the nidus from calcification.

Association of the Inactive Circulating Matrix Gla Protein with Vitamin K Intake, Calcification, Mortality, and Cardiovascular Disease: A Review

Matrix Gla Protein (MGP), a small Gla vitamin K-dependent protein, is the most powerful natural occurring inhibitor of calcification in the human body. To become biologically active, MGP must undergo vitamin K-dependent carboxylation and phosphorylation. Vitamin K deficiency leads to the inactive uncarboxylated, dephosphorylated form of MGP (dpucMGP). We aimed to review the existing data on the association between circulating dpucMGP and vascular calcification, renal function, mortality, and cardiovascular disease in distinct populations. Moreover, the association between vitamin K supplementation and serum levels of dpucMGP was also reviewed.

Polymorphism related to cardiovascular risk in hemodialysis subjects: a systematic review

Cardiovascular disease (CVD) is one of the leading causes of mortality in hemodialysis (HD) subjects. In addition to the traditional risk factors that are common in these individuals, genetic factors are also involved, with emphasis on single nucleotide polymorphs (SNPs). In this context, the present study aims to systematically review the studies that investigated the polymorphisms associated with cardiovascular risk in this population. In general, the SNPs present in HD individuals are those of genes related to inflammation, oxidative stress and vascular calcification, also able of interfering in the cardiovascular risk of this population. In addition, polymorphisms in genes related to recognized risk factors for CVD, such as dyslipidemia, arterial hypertension and left ventricular hypertrophy, also influence cardiovascular morbidity and mortality.

Status of Single Nucleotide Polymorphism of Matrix Gla Protein Gene (rs4236) in Nephrolithiasis: A Preliminary Study in Indian Population

Background:

Urine is a supersaturated solution with solutes in very high concentration. Matrix gla protein (MGP) is one of the proteins involved in inhibition of extracellular calcification. Among the various polymorphisms studied, polymorphism of SNP rs4236 in the MGP gene is found to have association with nephrolithiasis. We evaluated the significance of SNP rs4236 polymorphism in nephrolithiasis among the Indian population.

Materials and Methods:

The study was conducted in 2013 and 2014 among fifty participants. Twenty-five of them were patients with documented symptomatic stone disease and the 25 controls had no history of stone disease and ultrasonogram was normal. Serum creatinine was estimated in all patients. DNA was isolated from the blood sample and amplified by polymerase chain reaction using defined primers. Single strand conformational polymorphism was done to identify abnormal bands and the same was sequenced.

Results:

The patients and controls were matched in age and sex. The serum creatinine levels were similar in both groups. The predominant change in SNP rs4236 in patients was a G to A nucleotide change, resulting in AA homozygous genotype. This was found in 60% of patients. The rest (40%) of patients and all (100%) controls had heterozygous AG genotype. This corresponds to a stone disease with an odds ratio (OR) of 75 (P < 0.003).

Conclusion:

This first study in Indian population shows that genotype AA polymorphism of SNP rs4236 of MGP gene was found to be significant risk factor for renal stone disease. Studies with larger sample size may be needed to confirm this finding and elucidate the exact OR.

Matrix Gla protein T-138C polymorphism is associated with carotid intima media thickness and predicts mortality in patients with diabetic nephropathy

AIMS

We sought to determine the predictive value of Matrix Gla Protein MGP T-138C polymorphism in relation to all-cause mortality, cardiovascular mortality and cardiovascular events in patients with diabetic nephropathy (DN).

METHODS

MGP T-138C polymorphism was assessed in 40 diabetic patients without nephropathy and 118 patients at different stages of DN, including patients on hemodialysis. Measurement of carotid intima-media thickness (cIMT) was performed using real-time B-mode ultrasonography. Plasma levels of dephoshorylated uncarboxylated Matrix Gla Protein (dp-ucMGP) were determined in a subgroup of 67 patients by ELISA. Mortality and cardiovascular events were assessed during a 7year follow-up.

RESULTS

TT homozygotes for the MGP T-138C polymorphism had higher values of cIMT compared to combined TC and CC genotypes (P=0.006) whereas no association was observed between cIMT and dp-ucMGP levels. MGP T-138C polymorphism was a strong independent predictor of cIMT (P<0.0001), after adjustment for several well-known atherosclerosis risk factors. Patients with TT genotype presented a significantly higher all-cause and cardiovascular mortality risk compared to patients with TC and CC genotypes (P=0.01 and P=0.04 respectively), after adjustment for several traditional risk factors.

CONCLUSIONS

MGP T-138C polymorphism is a strong and independent predictor of increased cIMT as well as all-cause and cardiovascular mortality in DN patients.

Association of Matrix Gla protein gene (rs1800801, rs1800802, rs4236) polymorphism with vascular calcification and atherosclerotic disease: a meta-analysis

Association between the MGP gene rs1800801, rs1800802, rs4236 polymorphisms and vascular calcification and atherosclerotic disease was inconsistent. To clarify precise association, we performed this meta-analysis. Medline, Embase and China Knowledge Resource Integrated Database were systematically searched through December 2016. A total of 23 case-control studies, consisting of 5280 cases and 5773 controls, were included. The overall results suggested that the -7A polymorphism was associated with an increased risk for vascular calcification and atherosclerotic disease in the recessive model (OR = 1.50, 95% CI 1.01-2.24, P = 0.045). Subgroup analyses of Caucasians showed significant associations in the allelic model, recessive model, and homozygote model: allelic model (OR = 1.19, 95% CI 1.06-1.34, P = 0.004), recessive model (OR = 1.60, 95% CI 1.26-2.03, P < 0.001), homozygote model (OR = 1.83, 95% CI 1.18-2.81, P = 0.006). Subgroup analysis of the Asian population did not demonstrate any significant associations in any of the genetic models. No significant association was found in any genetic model amongst the rs1800802 and rs4236 polymorphisms. The findings of this meta-analysis indicate that the MGP gene rs1800801 polymorphism is significantly associated with vascular calcification and atherosclerotic disease, especially in the Caucasian population.

GRECOS Project (Genotyping Recurrence Risk of Stroke): The Use of Genetics to Predict the Vascular Recurrence After Stroke

BACKGROUND AND PURPOSE

Vascular recurrence occurs in 11% of patients during the first year after ischemic stroke (IS) or transient ischemic attack. Clinical scores do not predict the whole vascular recurrence risk; therefore, we aimed to find genetic variants associated with recurrence that might improve the clinical predictive models in IS.

METHODS

We analyzed 256 polymorphisms from 115 candidate genes in 3 patient cohorts comprising 4482 IS or transient ischemic attack patients. The discovery cohort was prospectively recruited and included 1494 patients, 6.2% of them developed a new IS during the first year of follow-up. Replication analysis was performed in 2988 patients using SNPlex or HumanOmni1-Quad technology. We generated a predictive model using Cox regression (GRECOS score [Genotyping Reurrence Risk of Stroke]) and generated risk groups using a classification tree method.

RESULTS

The analyses revealed that rs1800801 in the MGP gene (hazard ratio, 1.33; P=9×10^-03), a gene related to artery calcification, was associated with new IS during the first year of follow-up. This polymorphism was replicated in a Spanish cohort (n=1.305); however, it was not significantly associated in a North American cohort (n=1.683). The GRECOS score predicted new IS (P=3.2×10^-09) and could classify patients, from low risk of stroke recurrence (1.9%) to high risk (12.6%). Moreover, the addition of genetic risk factors to the GRECOS score improves the prediction compared with previous Stroke Prognosis Instrument-II score (P=0.03).

CONCLUSIONS

The use of genetics could be useful to estimate vascular recurrence risk after IS. Genetic variability in the MGP gene was associated with vascular recurrence in the Spanish population.

Matrix-Gla Protein rs4236 [A/G] gene polymorphism and serum and GCF levels of MGP in patients with subgingival dental calculus

AIM

Matrix-Gla Protein (MGP) is one of the major Gla-containing protein associated with calcification process. It also has a high affinity for Ca2+ and hydroxyapatite. In this study we aimed to evaluate the MGP rs4236 [A/G] gene polymorphism in association with subgingival dental calculus. Also a possible relationship between MGP gene polymorphism and serum and GCF levels of MGP were examined.

MATERIAL AND METHODS

MGP rs4236 [A/G] gene polymorphism was investigated in 110 patients with or without subgingival dental calculus, using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) techniques. Additionally, serum and GCF levels of MGP of the patients were compared according to subgingival dental calculus.

RESULTS

Comparison of patients with and without subgingival dental calculus showed no statistically significant difference in MGP rs4236 [A/G] gene polymorphism (p=0.368). MGP concentrations in GCF of patients with subgingival dental calculus were statistically higher than those without subgingival dental calculus (p=0.032). However, a significant association was not observed between the genotypes of AA, AG and GG of the MGP rs4236 gene and the serum and GCF concentrations of MGP in subjects.

CONCLUSION

In this study, it was found that MGP rs4236 [A/G] gene polymorphism was not to be associated with subgingival dental calculus. Also, that GCF MGP levels were detected higher in patients with subgingival dental calculus than those without subgingival dental calculus independently of polymorphism, may be the effect of adaptive mechanism to inhibit calculus formation.

SNP haplotyping technique for evaluation of MGP 5' UTR power in osteoblast cells

Matrix Gla protein (MGP) is involved in calcium trafficking and arterial calcification. The aim of study was to investigate the role of three polymorphisms within the MGP gene promoter region on reporter gene (luciferase) expression level. The fragments containing rs1800799 (C/T), rs1800802 (T/C), and rs1800801 (G/A) sites were constructed and transferred into human G292 osteoblast cells using pGL3-Basic plasmid. The reporter gene expression was calculated for the high and low frequency polymorphic haplotypes (CTG and TCA, respectively). Results showed that the reporter gene expression levels are not statistically different (p > 0.3). We concluded that the investigated polymorphic sites are not able to change the gene expression pattern in human G292 osteoblast cells.

Unified theory on the pathogenesis of Randall's plaques and plugs

Kidney stones develop attached to sub-epithelial plaques of calcium phosphate (CaP) crystals (termed Randall's plaque) and/or form as a result of occlusion of the openings of the Ducts of Bellini by stone-forming crystals (Randall's plugs). These plaques and plugs eventually extrude into the urinary space, acting as a nidus for crystal overgrowth and stone formation. To better understand these regulatory mechanisms and the pathophysiology of idiopathic calcium stone disease, this review provides in-depth descriptions of the morphology and potential origins of these plaques and plugs, summarizes existing animal models of renal papillary interstitial deposits, and describes factors that are believed to regulate plaque formation and calcium overgrowth. Based on evidence provided within this review and from the vascular calcification literature, we propose a "unified" theory of plaque formation-one similar to pathological biomineralization observed elsewhere in the body. Abnormal urinary conditions (hypercalciuria, hyperoxaluria, and hypocitraturia), renal stress or trauma, and perhaps even the normal aging process lead to transformation of renal epithelial cells into an osteoblastic phenotype. With this de-differentiation comes an increased production of bone-specific proteins (i.e., osteopontin), a reduction in crystallization inhibitors (such as fetuin and matrix Gla protein), and creation of matrix vesicles, which support nucleation of CaP crystals. These small deposits promote aggregation and calcification of surrounding collagen. Mineralization continues by calcification of membranous cellular degradation products and other fibers until the plaque reaches the papillary epithelium. Through the activity of matrix metalloproteinases or perhaps by brute physical force produced by the large sub-epithelial crystalline mass, the surface is breached and further stone growth occurs by organic matrix-associated nucleation of CaOx or by the transformation of the outer layer of CaP crystals into CaOx crystals. Should this theory hold true, developing an understanding of the cellular mechanisms involved in progression of a small, basic interstitial plaque to that of an expanding, penetrating plaque could assist in the development of new therapies for stone prevention.

Matrix Gla protein (MGP) promoter polymorphic variants and its serum level in stenosis of coronary artery

Although the role of matrix Gla protein (MGP) is not completely known but, its expression within subendothelial macrophages and vascular smooth muscle cells is suggested to be involved in vascular calcification. In this study, we investigated the associations between the serum MGP levels and the MGP promoter high minor allele frequency (MAF) variants with the development of stenosis in coronary arteries. Moreover, we evaluated the allele changes within predicted transcription factor elements with bioinformatics tools. 182 subjects were recruited from who underwent coronary angiography. The MGP promoter rs1800801, rs1800802 and rs1800799 genotypes and haplotypes were detected by ARMS-RFLP PCR techniques. The serum MGP concentration was measured using ELISA method. Jaspar profiles were used for scoring the polymorphic variations within the transcription factor elements. The genotype and two-allelic haplotype distributions were not significant between the patient and control groups (P > 0.05). The serum MGP levels had not significant differences between the genotypes (P > 0.1) and haplotypes (P > 0.4). Based on the prediction studies, we did not observe significant differences between the polymorphic scores in the predicted elements (P > 0.05). We concluded that the genotype and haplotype distributions of the MGP promoter high-MAF polymorphisms, as confirmed in the prediction studies and the serum MGP level are not significantly associated with the coronary artery disease. Based on the study results, the MGP protein did not play an important role in the development of stenosis of coronary arteries.

Calcium oxalate nephrolithiasis and expression of matrix GLA protein in the kidneys

OBJECTIVES

Polymorphism of the gene for matrix GLA protein (MGP), a calcification inhibitor, is associated with nephrolithiasis. However, experimental investigations of MGP role in stone pathogenesis are limited. We determined the effect of renal epithelial exposure to oxalate (Ox), calcium oxalate (CaOx) monohydrate (COM) or hydroxyapatite (HA) crystal on the expression of MGP.

METHODS

MDCK cells in culture were exposed to 0.3, 0.5 or 1 mM Ox and 33, 66 or 133-150 μg/cm(2) of COM/HA for 3-72 h. MGP expression and production were determined by Western blotting and densitometric analysis. Enzyme-linked immunosorbent assay was performed to determine MGP release into the medium. Hyperoxaluria was induced in male Sprague-Dawley rats by feeding hydroxyl-L-proline. Immunohistochemistry was performed to detect renal MGP expression.

RESULTS

Exposure to Ox and crystals led to time- and concentration-dependent increase in expression of MGP in MDCK cells. Cellular response was quicker to crystal exposure than to the Ox, expression being significantly higher after 3-h exposure to COM or HA crystals and more than 6 h of exposure to Ox. MGP expression was increased in kidneys of hyperoxaluric rats particularly in renal peritubular vessels.

CONCLUSION

We demonstrate increased expression of MGP in renal tubular epithelial cells exposed to Ox or CaOx crystals as well as the HA crystals. The most significant finding of this study is the increased staining seen in renal peritubular vessels of the hyperoxaluric rats, indicating involvement of renal endothelial cells in the synthesis of MGP.

Polymorphism in the human matrix Gla protein gene is associated with the progression of vascular calcification in maintenance hemodialysis patients

BACKGROUND

Matrix Gla protein (MGP) is one of the important proteins inhibiting vascular calcification (VC). Single nucleotide polymorphisms (SNPs) located in the promoter and coding regions of the MGP gene affect the transcriptional activity. In this study, we investigated the relationship between the SNPs and progression of VC in patients undergoing maintenance hemodialysis (MHD).

METHODS

This was a retrospective, longitudinal cohort study of 134 MHD patients whose VC could be followed by multi-detector computed tomography (MDCT) examinations. MGP-SNPs (T-138C, rs1800802 and G-7A, rs1800801) were determined. The progression speed of VC was examined by plotting the abdominal aortic calcium volume scores.

RESULTS

The progression speed of VC of patients with the CC genotype of T-138C was significantly slower than that of patients with the CT or TT genotype. Multiple regression analysis showed that CT/TT genotype, greater age at the beginning of MHD, male sex, high levels of calcium × phosphate, low levels of high-density lipoprotein cholesterol, high levels of low-density lipoprotein cholesterol, low levels of ferritin and non-use of angiotensin II receptor blockers were significantly associated with progression of VC.

CONCLUSIONS

The MGP-138CC genotype may be associated with slower progression of VC in MHD patients. The genotype of the MGP gene will be a genomic biomarker that is predictive of VC progression.

Common genetic variants of MGP are associated with calcification on the arterial wall but not with calcification present in the atherosclerotic plaques

BACKGROUND

Two endophenotypes of arterial calcification, calcification on arterial wall and calcification in atherosclerotic plaques, are associated with different types of cardiovascular events. Mgp-deficient mice showed matrix Gla protein (MGP) is strongly associated with calcification on arterial wall without atherosclerotic plaques, and MGP variants were not significantly associated with myocardial infarction. MGP may play different roles in the 2 endophenotypes.

METHODS AND RESULTS

We analyzed the associations of MGP variants rs4236, rs1800801, and rs1800802 with the 2 endophenotypes determined by multidetector computed tomography angiography. A total of 585 with calcification on coronary artery wall, 675 with calcification in coronary atherosclerotic plaques, 454 with calcification on aortic wall, and 725 controls were enrolled. After Bonferroni correction, rs4236 and rs1800801 were still associated with calcification on arterial wall, the odds ratios were 0.708 (95% confidence interval, 0.540-0.928) for rs4236 and 0.652 (95% confidence interval, 0.479-0.888) for rs1800801 in coronary artery wall calcification, and 0.699 (95% confidence interval, 0.525-0.931) for rs4236 and 0.650 (95% confidence interval, 0.467-0.905) for rs1800801 in aortic wall calcification, respectively. The variants were correlated with calcification severity by ln(CAC Agatston score+1) in coronary artery wall calcification but not in atherosclerotic plaque calcification. In accordance with their associations with calcification on arterial wall, rs4236C and rs1800801A were associated with higher MGP plasma levels, whereas rs1800802C was associated with lower MGP levels in normal controls. Because of the role of calcification in plaque vulnerability, their associations with acute myocardial infarction were also determined in 771 controls and 752 patients, no association was found.

CONCLUSIONS

MGP genetic variants showed association with calcification on arterial wall but not with calcification in atherosclerotic plaques.

No association between MGP rs1800802 polymorphism and stenosis of the coronary artery

BACKGROUND AND OBJECTIVES

Matrix Gla protein (MGP) was originally isolated from bone but it is known to be expressed in several tissues including kidney, lung, heart, cartilage and vascular smooth muscle cells (VSMC) of the blood vessel wall. Since it inhibits calcification in subendothelial space of vessels thus, we evaluated the association of rs1800802(T > C) polymorphism and stenosis of the coronary artery.

DESIGN AND SETTING

Cross-sectional case-control.

SUBJECTS AND METHODS

One hundred eighty two subjects recruited on the basis of study protocol from who underwent coronary angiography. The controls (n=70) had normal coronary arteries (up to 5% stenosis). The patients (n=112) subdivided into three subgroups; single-vessel disease (SVD), two-vessel disease (2VD) and three-vessel disease (3VD) based on the number of stenosed coronary vessels (at least 50% stenosis). rs1800802 (T > C) polymorphism was determined by PCR-RFLP technique.

RESULTS

Genotype distribution was not significant between control and patient groups. In addition, there were no significant differences between rs1800802 (T > C) frequency and gender (P=.092), and also patient subgroups (one-, two- and three vessel disease) (P=.840).

CONCLUSION

We concluded that rs1800802 (T > C) polymorphism within the MGP promoter is not related to stenosis of the coronary artery.

Matrix gla protein gene polymorphism is associated with increased coronary artery calcification progression

OBJECTIVE

Matrix gla protein (MGP) inhibits arterial and cartilaginous calcification. A threonine to alanine (Thr83Ala) polymorphism (codon 83) in MGP is associated with myocardial infarction and femoral artery calcification. We examined the association of the MGP Thr83Ala polymorphism with quantity and progression of coronary artery calcification (CAC), a noninvasive measure of subclinical coronary atherosclerosis.

METHODS AND RESULTS

In 605 participants of the Epidemiology of Coronary Artery Calcification Study, generalized linear mixed models were fit to determine the association of MGP Thr83Ala with CAC quantity and progression. There was a significant additive relation between MGP Thr83Ala and CAC progression (P=0.001). In the fully adjusted model, every 1 Ala83 allele increase was associated with an estimated 1.9% (95% confidence interval, 0.7%-3.0%) per year since baseline larger increase in CAC quantity. A proxy single nucleotide polymorphism for MGP Thr83Ala (rs6488724) was similarly associated with CAC progression in an independent cohort from the Genetic Epidemiology Network of Arteriopathy (GENOA) study.

CONCLUSIONS

Increased risk of myocardial infarction associated with MGP ThrAla83 genotype observed elsewhere may be related to faster progression of subclinical coronary atherosclerosis. MGP genotype could be a potential candidate for identifying individuals at increased risk of atherosclerotic disease who would benefit from aggressive primary prevention strategies.

Computational prediction and analysis of protein γ-carboxylation sites based on a random forest method

The glutamate γ-carboxylation plays a pivotal part in a number of important human diseases. However, traditional protein γ-carboxylation site detection by experimental approaches are often laborious and time-consuming. In this study, we initiated an attempt for the computational prediction of protein γ-carboxylation sites. We developed a new method for predicting the γ-carboxylation sites based on a Random Forest method. As a result, 90.44% accuracy and 0.7739 MCC value were obtained for the training dataset, and 89.83% accuracy and 0.7448 MCC value for the testing dataset. Our method considered several features including sequence conservation, residual disorder, secondary structures, solvent accessibility, physicochemical/biochemical properties and amino acid occurrence frequencies. By means of the feature selection algorithm, an optimal set of 327 features were selected; these features were considered as the ones that contributed significantly to the prediction of protein γ-carboxylation sites. Analysis of the optimal feature set indicated several important factors in determining the γ-carboxylation and a possible consensus sequence of the γ-carboxylation recognition site (γ-CRS) was suggested. These may shed some light on the in-depth understanding of the mechanisms of γ-carboxylation, providing guidelines for experimental validation.

Vitamin K status and vascular calcification: evidence from observational and clinical studies

Vascular calcification occurs when calcium accumulates in the intima (associated with atherosclerosis) and/or media layers of the vessel wall. Coronary artery calcification (CAC) reflects the calcium burden within the intima and media of the coronary arteries. In population-based studies, CAC independently predicts cardiovascular disease (CVD) and mortality. A preventive role for vitamin K in vascular calcification has been proposed based on its role in activating matrix Gla protein (MGP), a calcification inhibitor that is expressed in vascular tissue. Although animal and in vitro data support this role of vitamin K, overall data from human studies are inconsistent. The majority of population-based studies have relied on vitamin K intake to measure status. Phylloquinone is the primary dietary form of vitamin K and available supplementation trials, albeit limited, suggest phylloquinone supplementation is relevant to CAC. Yet observational studies have found higher dietary menaquinone, but not phylloquinone, to be associated with less calcification. Vascular calcification is highly prevalent in certain patient populations, especially in those with chronic kidney disease (CKD), and it is plausible vitamin K may contribute to reducing vascular calcification in patients at higher risk. Subclinical vitamin K deficiency has been reported in CKD patients, but studies linking vitamin K status to calcification outcomes in CKD are needed to clarify whether or not improving vitamin K status is associated with improved vascular health in CKD. This review summarizes the available evidence of vitamin K and vascular calcification in population-based studies and clinic-based studies, with a specific focus on CKD patients.

Understanding the genetics of coronary artery disease through the lens of noninvasive imaging

Coronary artery disease is a common condition with a known heritable component that has spurred interest in genetic research for decades, resulting in a handful of candidate genes and an appreciation for the complexity of its genetic contributions. Recent advances in sequencing technologies have resulted in large-scale association studies, possibly adding to our current understanding of the genetics of coronary artery disease. Sifting through the statistical noise, however, requires the selection of effective phenotypic markers. New imaging technologies have improved our ability to detect subclinical atherosclerosis in a safe and reproducible manner in large numbers of patients. In this article, we propose that advances in imaging technology have generated improved phenotypic markers for genetic association studies of coronary artery disease.

Gene-drug interaction in stroke

Stroke is the third cause of mortality and one of most frequent causes of long-term neurological disability, as well as a complex disease that results from the interaction of environmental and genetic factors. The focus on genetics has produced a large number of studies with the objective of revealing the genetic basis of cerebrovascular diseases. Furthermore, pharmacogenetic research has investigated the relation between genetic variability and drug effectiveness/toxicity. This review will examine the implications of pharmacogenetics of stroke; data on antihypertensives, statins, antiplatelets, anticoagulants, and recombinant tissue plasminogen activator will be illustrated. Several polymorphisms have been studied and some have been associated with positive drug-gene interaction on stroke, but the superiority of the genotype-guided approach over the clinical approach has not been proved yet; for this reason, it is not routinely recommended.

Genetics in arterial calcification: pieces of a puzzle and cogs in a wheel

Artery calcification reflects an admixture of factors such as ectopic osteochondral differentiation with primary host pathological conditions. We review how genetic factors, as identified by human genome-wide association studies, and incomplete correlations with various mouse studies, including knockout and strain analyses, fit into "pieces of the puzzle" in intimal calcification in human atherosclerosis, and artery tunica media calcification in aging, diabetes mellitus, and chronic kidney disease. We also describe in sharp contrast how ENPP1, CD73, and ABCC6 serve as "cogs in a wheel" of arterial calcification. Specifically, each is a minor component in the function of a much larger network of factors that exert balanced effects to promote and suppress arterial calcification. For the network to normally suppress spontaneous arterial calcification, the "cogs" ENPP1, CD73, and ABCC6 must be present and in working order. Monogenic ENPP1, CD73, and ABCC6 deficiencies each drive a molecular pathophysiology of closely related but phenotypically different diseases (generalized arterial calcification of infancy (GACI), pseudoxanthoma elasticum (PXE) and arterial calcification caused by CD73 deficiency (ACDC)), in which premature onset arterial calcification is a prominent but not the sole feature.

Arterial calcification in chronic kidney disease: key roles for calcium and phosphate

Vascular calcification contributes to the high risk of cardiovascular mortality in chronic kidney disease (CKD) patients. Dysregulation of calcium (Ca) and phosphate (P) metabolism is common in CKD patients and drives vascular calcification. In this article, we review the physiological regulatory mechanisms for Ca and P homeostasis and the basis for their dysregulation in CKD. In addition, we highlight recent findings indicating that elevated Ca and P have direct effects on vascular smooth muscle cells (VSMCs) that promote vascular calcification, including stimulation of osteogenic/chondrogenic differentiation, vesicle release, apoptosis, loss of inhibitors, and extracellular matrix degradation. These studies suggest a major role for elevated P in promoting osteogenic/chondrogenic differentiation of VSMC, whereas elevated Ca has a predominant role in promoting VSMC apoptosis and vesicle release. Furthermore, the effects of elevated Ca and P are synergistic, providing a major stimulus for vascular calcification in CKD. Unraveling the complex regulatory pathways that mediate the effects of both Ca and P on VSMCs will ultimately provide novel targets and therapies to limit the destructive effects of vascular calcification in CKD patients.

Assessment of matrix Gla protein, Klotho gene polymorphisms, and oxidative stress in chronic kidney disease

Increased vascular calcification and oxidative stress are considered as extra renal risk factors at the pathogenesis cardiovascular events in chronic kidney disease (CKD). We investigated matrix Gla protein (MGP) (T-138C, Glu60X, Thr83Ala) and Klotho (Cys370Ser) gene polymorphisms, serum MGP levels, and oxidative stress status of 84 CKD patients and 37 healthy controls. The MGP gene Glu60X and Thr83Ala polymorphisms were significantly associated with CKD. The correlation between T-138C genotype of MGP gene, Cys370Ser genotype of Klotho gene, and CKD was not significant (p > 0.05). At the haplotype analysis, the combination of the X allele of Glu60X and the Thr allele of Thr83Ala showed a significantly increased risk of CKD (p < 0.05). X allele, Thr allele, and C allele of T-138C were associated with diabetes mellitus and CKD phenotypes occurring concurrently (p < 0.01). Serum zinc levels were significantly low in end-stage renal disease (ESRD) patients (p = 0.0001). The total comet score frequency of ESRD patients was higher than that of control group (p < 0.05). The urinary 8-hydroxy-2'-deoxyguanosine levels were significantly high in CKD patients (p < 0.05). According to this study, analyzing the distribution of MGP gene and oxidative stress status would be very informative in order to detect their role at CKD.

CD40-1C>T polymorphism (rs1883832) is associated with brain vessel reocclusion after fibrinolysis in ischemic stroke

AIMS

To find genetic predictors of reocclusion after successful fibrinolytic therapy during the acute phase of ischemic stroke.

PATIENTS & METHODS

This was a case-case prospective study analyzing 236 polymorphisms in a cohort of 222 patients treated with tissue plasminogen activator, from which 16 patients suffered a reocclusion event (7.2%). A predictive scale was generated using independent polymorphisms with a dominant/recessive model and tandem occlusion, weighted by their beta-coefficients in logistic regression.

RESULTS

Using a dominant/recessive model, the rs1800801 SNP from the MGP gene (odds ratio [OR]: 15.25; 95% CI: 2.23-104.46; adjusted p = 0.006) and the rs1883832 SNP from CD40 gene (OR: 0.077; 95% CI: 0.009-0.66; adjusted p = 0.019) were independently associated with reocclusion after logistic regression adjustment by clinical predictors. In an additive model, only the rs1883832 SNP (OR: 4.43; 95% CI: 1.62-12.15; adjusted p = 0.004) was related to reocclusion occurrence. The predictive model that was generated stratified the reocclusion risk from less than 1% to more than 70%. Reocclusions were associated with neurological worsening at 24 h (patients with reocclusion: 26.7%, versus patients without reocclusion: 4.9%; p = 0.002), as it was seen for MGP -7A>G (AA: 17.2% vs AG+GG: 4.5%; p = 0.027), but not for CD40 1C>T (CC: 4.5% vs CT+TT: 7.7%; p = 0.565). There was an association between CD40 -1C>T genotype and CD40 transcriptional activity in peripheral blood mononuclear cells (median expression values TT: 65.75%, CT: 70.80%, CC: 96.00%; p = 0.023). However, CD40 soluble fraction was not a useful biomarker of reocclusion status.

CONCLUSION

An association was found between MGP -7A>G and CD40 -1C>T polymorphisms, and reocclusion risk. The predictive scale that was generated permits the stratification of patients by their reocclusion risk with higher accuracy than clinical parameters alone.

FIAT, the factor-inhibiting ATF4-mediated transcription, also represses the transcriptional activity of the bZIP factor FRA-1

FIAT is a leucine zipper protein whose name was coined for its interaction with ATF4 and subsequent blockage of ATF4-directed osteocalcin gene transcription. FIAT lacks a basic DNA-binding domain but contains three leucine zippers; it heterodimerizes with ATF4 to prohibit binding to DNA. FIAT could also potentially interact with additional basic domain-leucine zipper transcriptional regulators of osteoblast activity, such as FRA-1. We have found that FIAT inhibits transcriptional activation by a FRA-1/c-JUN heterodimer without affecting transcription mediated by a c-JUN homodimer. The repressor effect of FIAT on FRA-1-dependent transcription was measured using reporter constructs for the natural FRA-1 targets, Mmp-9 and Mgp. The FIAT-FRA-1 interaction is mediated through the second leucine zipper of FIAT. These data confirm an additional target of the FIAT transcriptional repressor activity and suggest that FIAT can both modulate early osteoblast activity by interacting with ATF4 and regulate later osteoblast function through inhibition of FRA-1.

Functional impact of a single-nucleotide polymorphism in the OPRD1 promoter region

The δ-opioid receptor mediates rewarding effects of many substances of abuse. We reported an increased frequency of the minor G-allele of single nucleotide polymorphism (SNP) rs569356 [the only variant identified so far in the promoter region of the δ-opioid receptor gene (OPRD1)] in subjects with opioid dependence. In this study, we examined the functional significance of this variant. OPRD1 promoter region harboring SNP rs569356 was amplified by polymerase chain reaction (PCR) and inserted into a firefly luciferase reporter vector. HEK293 cells were co-transfected with these constructs and a renilla luciferase vector to control for transfection efficiency. Expression of firefly luciferase (driven by the OPRD1 promoter) was measured by a dual luciferase reporter assay and normalized by renilla luciferase expression. Moreover, alleles altering expression were further assessed for binding of human brain nuclear proteins by electrophoretic mobility shift assay (EMSA). The minor G-allele was associated with significantly greater expression levels of firefly luciferase than the major A-allele of SNP rs569356 (P=0.003). EMSA also showed specific gel shift bands, suggesting that SNP rs569356 is situated in the binding site of potential transcription factors. These results suggest that the minor G-allele of SNP rs569356 may enhance transcription factor binding and increase OPRD1 expression.

Dual transcriptional regulation by runx2 of matrix Gla protein in Xenopus laevis

Matrix Gla protein (MGP) is an extracellular mineral-binding protein expressed in several tissues but it only accumulates in bone and calcified cartilage under physiological conditions. Available evidence indicates that it acts as a physiological inhibitor of mineralization. Runx2 is a transcription factor essential for bone formation in mammals, affecting osteoblast and chondrocyte differentiation by regulating key genes crucial for bone and cartilage development. Being an important cartilage-associated gene, MGP is a potential target for Runx2, and thus we have investigated the possible functional interactions between them. In A6 cells, Runx2 was found to modulate MGP transcription and deletion analysis of MGP distal and proximal promoter-luciferase constructs identified cis-regulatory regions. Interestingly, we have also identified a runx2-binding site that mediates transcriptional repression of XlMGP. Mutation of this element, located between -54 and +33 bp, results in 18-fold up-regulation of transcription. Furthermore, and in addition to the previously reported Xlrunx2 types I and II, we have identified three transcripts encoding novel, truncated Xlrunx2 isoforms. Although only type I and type II could transactivate XlMGP, the truncated isoforms identified in this study, which result from alternative splicing, could be involved in negative regulation of MGP expression, as described for other RUNX2 truncated isoforms acting in other target genes. In vivo microinjection of XlMGP promoter constructs and runx2 mRNA confirmed that those promoters are targets for this transcription factor. These data also indicate that MGP is under dual regulation by runx2 through the use of various isoforms and context-dependent formation of transcriptional complexes.

Phosphate-dependent regulation of MGP in osteoblasts: role of ERK1/2 and Fra-1

Inorganic phosphate (Pi) and the matrix Gla protein (MGP) are key regulators of bone formation. We have recently shown that Pi upregulates MGP in growth plate chondrocytes, which may represent a negative feedback loop for the control of mineralization. Osteoblasts from Fra-1-deleted mice express low levels of MGP, whereas the expression of MGP is elevated in Fra-1 transgenic osteoblasts, suggesting a role for Fra-1 in MGP expression and bone formation. In this study, we aimed at deciphering the relationships between Pi and MGP in osteoblasts to determine the molecular mechanisms involved in the Pi-dependent regulation of MGP. In MC3T3-E1 cells and primary calvaria-derived osteoblasts, Pi increased MGP and Fra-1 expression at both the mRNA and protein levels. We also found that Pi enhanced the phosphorylation of ERK1/2. U0126 (MEK1/2 inhibitor) suppressed Pi-stimulated MGP and Fra-1 expression, indicating that ERK1/2 is required for Pi-dependent regulation of MGP and Fra-1. In addition, using in vitro DNA binding and chromatin immunoprecipitation assays, we showed that Fra-1 interacts with the MGP promoter in response to Pi in MC3T3-E1 cells. Finally, we found that in fra-1 knockdown MC3T3-E1 osteoblasts, the level of MGP expression is no more significantly upregulated by Pi. We further showed that primary osteoblasts from Fra-1-deficient mice failed to exhibit a Pi-dependent stimulation of MGP expression. These data show, for the first time, that Pi regulates MGP expression in osteoblasts through the ERK1/2-Fra-1 pathway.

Roles for vitamin K beyond coagulation

Recent interest in vitamin K has been motivated by evidence of physiological roles beyond that of coagulation. Vitamin K and vitamin K-dependent (VKD) proteins may be involved in regulation of calcification, energy metabolism, and inflammation. However, the evidence for many of these proposed roles in the maintenance of health is equivocal. There is also an emerging viewpoint that the biochemical function of vitamin K may extend beyond that of a cofactor for the VKD carboxylation of glutamyl residues (Glus) to carboxylated Glus in VKD proteins.

Individual susceptibility and genotoxicity in workers exposed to hazardous materials like lead

The present study was undertaken to investigate lead-induced toxicity in occupationally exposed humans and to evaluate whether genetic damage can be correlated with the known clinical indicators of lead poisoning. For this purpose, genotoxicity biomarkers along with some clinical indices of lead poisoning were determined in blood samples of battery plant workers and compared with healthy control subjects. Workers had significantly increased chromosomal aberrations, micronuclei and DNA damage compared to the controls. Increased blood lead levels (BLLs), decreased hemoglobin, PCV and symptoms of lead poisoning were used as clinical indices of lead toxicity. In addition gene polymorphisms in ALAD and MGP gene were investigated and correlated with BLL and hemoglobin content. Our results showed no significant effects of the ALAD G177C polymorphism on BLL concentrations and BLL concentrations varied to levels much above the normal reference ranges independent of the genotype. Although, significance could not be achieved, ALAD 1-2/2-2 type subjects had numerically higher BLLs (76.2-89.1 microg/dl), compared to ALAD 1-1 volunteers (21.8-79.1 microg/dl). Similarly, this study also aimed to identify the relation of some SNPs with emphasis on lead toxicity and since MGP gene is an important biomarker associated with calcium metabolism; it was hypothesized that it may be associated with lead toxicity. However, we did not find any significant association of MGP T-138C and lead poisoning. Further studies on the role of gene polymorphisms over a larger population along with genotoxicity parameters and biochemical analyses may serve to understand lead toxicity.

Phylogenetic analysis of ALAD and MGP genes related to lead toxicity

Experimental studies in our laboratory have established the role of delta-aminolevulinic acid dehydratase (ALAD) and matrix gamma-carboxyglutamic acid (MGP) gene polymorphisms in the etiology of lead toxicity. Polymorphisms in these genes influenced the levels of lead in subjects exposed to this metal. In extension to our studies, we aimed to investigate the possible role of these proteins in evolution by studying the phylogenetic relationship and divergence of ALAD and MGP genes using computational phylogenetic methods. The human ALAD and MGP protein sequences from various species were retrieved from Swiss-Prot database and were compared using Basic Local Alignment Search Tool. Multiple sequence alignment was carried out using ClustalW with defaults, and phylogenetic trees for both the genes were built using neighbor-joining method as in Mega software. Our study indicated that ALAD is a highly conserved protein with the same metal binding site distributed in all the phyla (from archaea to chordates). Phylogenetic analysis of MGP gene revealed that it had an important role in the evolution of endogenous skeleton in contrast to exoskeleton of insects. Occurrence of these genes in evolution with conserved metal binding sites strengthens the role of ALAD and MGP genes in regulating heme biosynthesis and mineralization, respectively, in evolution and helps in better understanding of lead poisoning.

Association of kidney function and uncarboxylated matrix Gla protein: data from the Heart and Soul Study

BACKGROUND

Vascular calcification is highly prevalent in persons with chronic kidney disease (CKD) and predicts cardiovascular disease (CVD) events. Matrix Gla protein (MGP) is a potent inhibitor of vascular calcification, and lower levels of its precursor-uncarboxylated MGP (ucMGP)--are associated with vascular calcification and atherosclerosis. Whether mild to moderate decrements in kidney function are associated with lower serum ucMGP is unknown.

METHODS

In a cross-sectional study among 842 outpatients with stable CVD, estimated glomerular filtration rate (eGFR), serum cystatin-C and urine albumin-to-creatinine ratio (ACR) were measured and serum ucMGP levels were determined by ELISA. Multivariate linear regression evaluated the association of each kidney function measure with serum ucMGP levels.

RESULTS

The mean eGFR was 76 +/- 23 mL/min/1.73 m(2), and 186 subjects (22%) had moderate CKD (eGFR <60 mL/min/1.73 m(2)). The mean +/- SD ucMGP level was 3289 +/- 1177 nM. In unadjusted analysis, each 10 mL/ min/1.73 m(2) lower eGFR was associated with 101 nM lower ucMGP level. This association was only minimally attenuated in final multivariate models wherein each 10 mL/ min/1.73 m(2) lower eGFR was associated with 79 nM lower ucMGP (95% confidence interval [CI]; 44 to 115; P < 0.001) after adjustment for age, sex, race, body mass index, blood pressure, smoking, hypertension, diabetes; and serum albumin, calcium, phosphorus, and fetuin-A levels. Similarly, in models adjusted for identical covariates, each 0.1 mg/L higher cystatin-C was associated with 39 nM lower ucMGP (95% CI 23 to 55; P < 0.001). In contrast, no significant association was observed between ACR and ucMGP in either unadjusted or adjusted analyses (adjusted P = 0.17). All associations were similar among subjects with or without diabetes (P-values for interaction > 0.50).

CONCLUSIONS

Among outpatients with stable CVD, a reduced glomerular filtration rate is associated with a decreased serum ucMGP level. In contrast, ACR is not associated with ucMGP levels. Whether ucMGP is a useful marker of vascular calcification and CVD event risk in persons with CKD deserves future study.

Sp proteins and Runx2 mediate regulation of matrix gla protein (MGP) expression by parathyroid hormone

As part of its catabolic action in bone, parathyroid hormone (PTH) inhibits extracellular matrix mineralization. We previously showed that PTH dose-dependently induces matrix gla protein (MGP) expression in osteoblasts and this induction is at least partially responsible for PTH-mediated inhibition of mineralization. Recently, we identified PKA and ERK/MAPK as the key signaling pathways involved in PTH regulation of MGP expression. The goal of this study was to further characterize the mechanism by which PTH stimulates expression of MGP. Deletion analysis of the murine Mgp gene promoter identified a PTH-responsive region between -173 bp and-49 bp. Using gel-mobility shift assays we found that Sp1/Sp3, and Runx2 bind to distinct sites within this region. Mutation of either the Sp or the Runx2 site reduced MGP induction by PTH, while mutation of both sites completely abolished PTH responsiveness. Overexpression of Runx2 or Sp1 activated the Mgp reporter, while Sp3 was a dose-dependent repressor of Sp1 and PTH-induced MGP expression. Collectively, these data show that PTH regulates MGP gene transcription in osteoblasts through altered activities of Sp and Runx2 transcription factors.

Polymorphisms in MGP gene and their association with lead toxicity

Matrix gamma-carboxy glutamic acid protein (MGP) is a 10-kDa secreted protein containing five residues of the vitamin K-dependent calcium binding amino acid gamma-carboxyglutamic acid (Gla). This study was carried out to examine the effects of MGP gene promoter polymorphism (T-138C) on blood lead levels (BLL) and hematological parameters in 113 battery manufacturing unit workers occupationally exposed to lead and 102 controls. Genotypes for the MGP T-138C polymorphism were determined by PCR and restriction fragment length digestion. BLL were determined by Anode Stripping Voltammetry using ESA Model 3010B Lead analyzer. Complete blood picture (CBP) was analyzed using ADVIA Cell counter for each sample. The frequencies of MGP-TT, CT and CC genotypes in our population were 38.6%, 44.3%, and 17.2%, respectively. The frequencies for T and C alleles were 0.612 and 0.386, respectively. Although BLL did not differ significantly among genotypes; they were higher in workers with TT/CT genotype compared to CC genotype subjects (76-88 microg/dL vs 22-45 microg/dL, p > 0.05). About 29.2% of volunteers (n = 33) from the occupationally exposed group had hemoglobin levels below 10.0 gms/dl. There was no significant difference in total white cell count and platelet count between occupational and non-exposed groups. The possible role of SNPs in the promoter region of MGP gene with relation to lead toxicity was investigated for the first time in the Indian population; although significance could not be achieved in this study, further assessments over a larger population size may help in better understanding of the consequences of lead exposure.

Matrix Gla protein polymorphisms are associated with coronary artery calcification in men

Matrix Gla protein (MGP) is a key regulator of vascular calcification. Genetic variation at the MGP locus could modulate the development of coronary artery calcification (CAC). Our aim was to examine the cross-sectional association between MGP single nucleotide polymorphisms (SNPs) [rs1800802 (T-138C), rs1800801 (G-7A), and rs4236 (Ala102Thr)] and CAC. CAC was measured by multidetector computed tomography (MDCT), in older men and women of European descent, (n=386; 60 to 80 y of age). Serum MGP was measured by radioimmunoassay. Linear, Tobit and Ordinal regression analyses all revealed that in men, homozygous carriers of the minor allele of rs1800802, rs1800801, or rs4236 (minor allele frequency: 21, 38, and 40%, respectively) were associated with a decreased quantity of CAC, relative to major allele carriers. This association was not found in women. Although genetic variation in MGP was associated with serum MGP concentrations, there were no associations between serum MGP and CAC. The results of this study suggest a role for MGP genetic variants in coronary atherosclerosis among men that is not reflected in serum MGP concentrations.

JunB as a potential mediator of PTHrP actions: new gene targets Ephrin B1 and VCAM-1

Parathyroid hormone-related protein (PTHrP) is an integral mediator of physiologic and pathologic processes and has demonstrated actions in the periodontium. PTHrP functions via AP-1, and specifically through JunB. This study identified JunB-dependent downstream mediators of PTHrP using OCCM cementoblastic transfectants with JunB over- or reduced expression. Over-expressing cells showed an increase in proliferation, while the opposite was seen in siRNA transfected cells. Microarray analysis of over-expressing cells revealed more than 1000 regulated genes. Three genes were investigated in more detail. The PTH/PTHrP receptor (PTHR1) and ephrin B1 (EfnB1) were down-regulated, and vascular cell adhesion molecule-1 (VCAM-1) was up-regulated with JunB over-expression. JunB siRNA transfectants had increased PTHR1, but reduced ephrin B1 and unaltered VCAM-1 in vitro. To validate these targets, parental OCCM cells and primary osteoblasts were treated with PTHrP, resulting in reduced PTHR1 and ephrin B1, and increased VCAM-1. Cell transfectants were implanted subcutaneously in vivo, and microarray analysis and RT-PCR performed. Over-expression of JunB down-regulated PTHR1 and ephrin B1, and increased VCAM-1. JunB siRNA transfectant implants had increased PTHR1 and ephrin B1, but no altered VCAM-1. These data highlight new gene targets for PTHrP and indicate JunB is a critical mediator of PTHrP actions.

Baicalein stimulates osteoblast differentiation via coordinating activation of MAP kinases and transcription factors

The identification of anabolic agents that directly stimulate bone formation has recently attracted greater interest. Here, baicalein was identified as a natural compound that stimulates the differentiation of mouse osteoblastic MC3T3-E1 subclone 4 cells. Baicalein induced the activation of NF-kappaB in the initiation stage of osteoblast differentiation, and it activated the MAP kinase/NF-kappaB signaling pathway and induced the expression of osteoblast differentiation markers in the early stage. In the late stage, baicalein stimulated the calcium deposition with the activation of MAP kinases and AP-1 family members such as Fra-1 and Fra-2. Another transcription factor, NFATc1, was slightly induced by baicalein in the late stage. Thus, baicalein could stimulate the osteoblast differentiation via the activation of complexly coordinated signaling pathways that include MAP kinases and transcription factors such as NF-kappaB, AP-1, and NFATc1.

Renal handling of matrix Gla-protein in humans with moderate to severe hypertension

Vascular calcifications are common among patients with hypertension. The vitamin K-dependent protein matrix Gla-protein plays an important role in preventing arterial calcification. Since a decrease in renal clearance is a prevalent clinical problem in patients with hypertension, we aimed to study the renal clearance of matrix Gla-protein from the circulation in these patients having a wide range of creatinine clearances. Ninety moderate to severe hypertensive patients who were scheduled for renal angiography were enrolled in the study. In these patients, renal arterial and renal venous blood was sampled prior to the administration of contrast material in order to determine the total renal and single kidney clearance of matrix Gla-protein. The average renal fractional extraction of matrix Gla-protein was 12.8%. There was no significant correlation between creatinine clearance (range 26-154) and renal fractional extraction of matrix Gla-protein in this population. The extraction of matrix Gla-protein was not influenced by the presence of a renal artery stenosis. In conclusion, we demonstrate that the kidney is able to extract matrix Gla-protein from the plasma at a constant level of 12.8%, independent of renal function in hypertensive subjects.

Vitamin K-dependent proteins, warfarin, and vascular calcification

Vitamin K-dependent proteins (VKDPs) require carboxylation to become biologically active. Although the coagulant factors are the most well-known VKDPs, there are many others with important physiologic roles. Matrix Gla Protein (MGP) and Growth Arrest Specific Gene 6 (Gas-6) are two particularly important VKDPs, and their roles in vascular biology are just beginning to be understood. Both function to protect the vasculature; MGP prevents vascular calcification and Gas-6 affects vascular smooth muscle cell apoptosis and movement. Unlike the coagulant factors, which undergo hepatic carboxylation, MGP and Gas-6 are carboxylated within the vasculature. This peripheral carboxylation process is distinct from hepatic carboxylation, yet both are inhibited by warfarin administration. Warfarin prevents the activation of MGP and Gas-6, and in animals, induces vascular calcification. The relationship of warfarin to vascular calcification in humans is not fully known, yet observational data suggest an association. Given the high risk of vascular calcification in those patients with chronic kidney disease, the importance of understanding warfarin's effect on VKDPs is paramount. Furthermore, recognizing the importance of VKDPs in vascular biology will stimulate new areas of research and offer potential therapeutic interventions.

Circulating calcification inhibitors and vascular properties in children after renal transplantation

Pediatric transplant patients are known to have vascular abnormalities. The calcification inhibitors matrix Gla protein (MGP) and fetuin-A play an important role in the pathophysiology of vascular calcification. In the cross-sectional study reported here, we examined the circulating levels of fetuin-A and MGP in children after renal transplantation compared to healthy children and the association of these factors with vascular properties of the carotid artery. Levels of MGP and fetuin-A together with vascular properties of the carotid artery were determined in 29 pediatric renal transplant recipients and 54 healthy controls. The level of fetuin-A was decreased in the transplant group relative to the control group (P=0.005), whereas the level of MGP (both non-phosphorylated MGP and non-carboxylated MGP) did not differ between groups. The intima-media thickness (P<0.001) and the elasticity (P=0.002) of the carotid artery were significantly increased in children after renal transplantation compared to healthy children. No associations between vascular parameters and calcification inhibitors were found in either group. Circulating levels of MGP and fetuin-A could not be identified as independent predictors of vascular stiffness or other carotid artery parameters in pediatric renal transplant recipients. Future prospective studies in pediatric ESRD and transplant patients are needed to learn more about the role of calcification inhibitors in relation to the prevention of vascular damage.