Angiotensinogen gene promoter haplotype and microangiopathy-related cerebral damage: results of the Austrian Stroke Prevention Study

Epigenetic and transcriptional regulation of the human angiotensinogen gene by high salt

Hypertension is caused by a combination of genetic and environmental factors. Angiotensinogen (AGT) is a component of RAAS, that regulates blood pressure. The human angiotensinogen (hAGT) gene has -6A/-6G polymorphism and -6A variant is associated with human hypertension. In this study, we have investigated the epigenetic regulation of the hAGT. To understand transcriptional regulation of the hAGT, we have made transgenic animals containing -6A. We show that HS affects DNA methylation and modulates transcriptional regulation of this gene in liver and kidney. High salt (HS) increases hAGT gene expression in -6A TG mice. We have observed that the number of CpG sites in the hAGT promoter is decreased after HS treatment. In the liver, seven CpG sites are methylated whereas after HS treatment, only three CpG sites remain methylated. In the kidney, five CpG sites are methylated, whereas after HS treatment, only three CpG sites remain methylated. These results suggest that HS promotes DNA demethylation and increasing AGT gene expression. RT-PCR and immunoblot analysis show that hAGT gene expression is increased by HS. Chip assay has shown that transcription factors bind strongly after HS treatment. RNA-Seq identified differentially expressed genes, novel target genes associated with hypertension, top canonical pathways, upstream regulators. One of the plausible mechanisms for HS induced up-regulation of the hAGT gene is through IL-6/JAK/STAT3/AGT axis.

A polymorphism in intron I of the human angiotensinogen gene (hAGT) affects binding by HNF3 and hAGT expression and increases blood pressure in mice

Angiotensinogen (AGT) is the precursor of one of the most potent vasoconstrictors, peptide angiotensin II. Genome-wide association studies have shown that two A/G polymorphisms (rs2493134 and rs2004776), located at +507 and +1164 in intron I of the human AGT (hAGT) gene, are associated with hypertension. Polymorphisms of the AGT gene result in two main haplotypes. Hap-I contains the variants -217A, -6A, +507G, and +1164A and is pro-hypertensive, whereas Hap-II contains the variants -217G, -6G, +507A, and +1164G and does not affect blood pressure. The nucleotide sequence of intron I of the hAGT gene containing the +1164A variant has a stronger homology with the hepatocyte nuclear factor 3 (HNF3)-binding site than +1164G. Here we found that an oligonucleotide containing +1164A binds HNF3β more strongly than +1164G and that Hap-I-containing reporter gene constructs have increased basal and HNF3- and glucocorticoid-induced promoter activity in transiently transfected liver and kidney cells. Using a knock-in approach at the hypoxanthine-guanine phosphoribosyltransferase locus, we generated a transgenic mouse model containing the human renin (hREN) gene and either Hap-I or Hap-II. We show that transgenic animals containing Hap-I have increased blood pressure compared with those containing Hap-II. Moreover, the transcription factors glucocorticoid receptor, CCAAT enhancer-binding protein β, and HNF3β bound more strongly to chromatin obtained from the liver of transgenic animals containing Hap-I than to liver chromatin from Hap-II-containing animals. These findings suggest that, unlike Hap-II variants, Hap-I variants of the hAGT gene have increased transcription rates, resulting in elevated blood pressure.

Decreased Number of Mitochondria in Leukoaraiosis

BACKGROUND AND AIMS

Leukoaraiosis (LA), one of the most frequent causes of an age-associated cognitive decline, can be associated with a poor quality of life, leading overall to far-reaching public health problems. Chronic hypoxia of the white matter of the brain may be a factor triggering this entity. LA may develop as a consequence of chronically insufficient cellular energy production and the accumulation of free radicals.

METHODS

In this context, after hypothesizing that the number of healthy mitochondria can be crucial in this complex process, a case-control LA study was carried out in which we analyzed the numbers of deleted and non-deleted mitochondria (the common D-loop deletion) per white blood cell. A total of 234 patients with LA and 123 MRI alteration-free subjects served as a control group.

RESULTS

Interestingly, it emerged that the ratio of deleted relative to non-deleted mitochondria is strongly associated with the risk of LA. The calculated K ratio in the LA group was significantly lower than the K ratio in the controls (LA: K 0.37 95% CI 0.05; controls: K 0.48, 95% CI 0.076, p < 0.001).

CONCLUSIONS

Our study suggests that the ratio of the dmDNA and mDNA can be of great importance in the pathogenesis of LA.

Neuromarkers of the common angiotensinogen polymorphism in healthy older adults: A comprehensive assessment of white matter integrity and cognition

The common angiotensinogen (AGT) M268T polymorphism (rs699; historically referred to as M235T) has been identified as a significant risk factor for cerebrovascular pathologies, yet it is unclear if healthy older adults carrying the threonine amino acid variant have a greater risk for white matter damage in specific fiber tracts. Further, the impact of the threonine variant on cognitive function remains unknown. The present study utilized multiple indices of diffusion tensor imaging (DTI) and neuropsychological assessment to examine the integrity of specific white matter tracts and cognition between individuals with homozygous genotypes of M268T (MetMet n=27, ThrThr n=27). Differences in subcortical hyperintensity (SH) volume were also examined between groups. Results indicated that the threonine variant was associated with significantly reduced integrity in the superior longitudinal fasciculus (SLF) and the cingulate gyrus segment of the cingulum bundle (cingulum CG) compared to those with the methionine variant, and poorer cognitive performance on tests of attention/processing speed and language. Despite these associations, integrity of these tracts did not significantly mediate relationships between cognition and genetic status, and SH did not differ significantly between groups. Collectively our results suggest that the threonine variant of M268T is a significant risk factor for abnormalities in specific white matter tracts and cognitive domains in healthy older adults, independent of SH burden.

Renin-angiotensin system genetic polymorphisms and brain white matter lesions in older Australians

BACKGROUND

White matter lesions (WMLs), seen as hyperintensities on T2-weighted magnetic resonance imaging brain scans, are common in the brains of healthy older individuals. They are thought to be related to cerebral small vessel disease and to have a genetic component to their aetiology, and hypertension is thought to be an important risk factor. Genetic polymorphisms in hypertension-related genes may therefore be associated with the formation of WMLs.

METHODS

In this study, a sample of 445 Australians aged 60-65 years was drawn from a larger longitudinal epidemiological study, the Personality and Total Health Through Life Project. The associations of single nucleotide polymorphisms (SNPs) in the genes encoding angiotensinogen (AGT, rs699), angiotensin-converting enzyme (ACE, rs4362), and angiotensin II receptor type 1 (AGTR1, rs5182) with WMLs were examined.

RESULTS

No individual SNPs showed a significant association with WMLs for the whole sample. When the cohort was stratified by sex, ACE rs4362 and AGT rs699 showed significant associations with WMLs in men only (P = 0.01 and P = 0.03, respectively), and remained significant after controlling for hypertension. Although the AGTR1 SNP did not show any association with WMLs, the interaction of the AGT rs699 and AGTR1 rs5182 SNPs with WMLs was significant before (P = 0.03) and after adjustment for hypertension (P = 0.045).

CONCLUSIONS

The results provide evidence for association of polymorphisms in the renin-angiotensin system genes with WMLs, independent of hypertension. Male-only associations with WMLs were found for the AGT rs699 and ACE rs362 polymorphisms. Moreover, for the entire sample an interaction between AGT and AGTR1 rs5182 genotypes on WMLs was observed.

Human angiotensinogen +11525 C/A polymorphism modulates its gene expression through microRNA binding

Hypertension is a serious risk factor for cardiovascular disease. Like other complex disease, hypertension is caused by a combination of genetic and environmental factors. The renin-angiotensin system plays an important role in the regulation of blood pressure. Angiotensinogen (AGT) gene is associated with essential hypertension in Caucasians, Japanese, and Asian-Indian subjects. AGT gene may also be associated with cardiac hypertrophy, coronary atherosclerosis, and microangiopathy related cerebral damage. Human AGT gene has a C/A polymorphism at nucleoside 11525 (rs7079) that is located in the 3'-untranslated region (3'-UTR) and is modestly associated with increased blood pressure. We show here that miR-31 and miR-584 bind strongly to the hAGT 3'-UTR containing 11525C allele compared with 11525A allele. We also show that transfection of miR-31 and miR-584 downregulates the hAGT mRNA and protein levels in human liver cells. These studies may provide new therapeutic approach to reduce hypertension.

Allele-specific expression of angiotensinogen in human subcutaneous adipose tissue

The angiotensinogen gene is genetically linked with hypertension, but the mechanistic basis for association of sequence variants in the promoter and coding region of the gene remains unclear. An E-box at position -20 has been hypothesized to control the level of angiotensinogen expression, but its mechanistic importance for angiotensinogen expression in human tissues is uncertain. We developed an allele-specific polymerase chain reaction-based assay to distinguish between angiotensinogen mRNA derived from variants at the -20 position (rs5050) in the angiotensinogen promoter in adipose tissues obtained during surgery. The assay takes advantage of linkage disequilibrium between the rs5050 (located in the promoter) and rs4762 (located in the coding region) single nucleotide polymorphisms. This strategy allowed us to assess the level of allele-specific expression in A-20C heterozygous subjects comparing the relative proportion of each allele with the total, thus eliminating the problem of variability in the level of total angiotensinogen mRNA among subjects. We show that angiotensinogen mRNA derived from the -20C allele is expressed significantly higher than that derived from the -20A allele in subcutaneous adipose tissue, and increased expression correlates with enriched chromatin binding of upstream stimulatory factor-2 to the -20C E-box compared with -20A. This may be depot selective because we were unable to detect these differences in omental adipose. This provides the first data directly comparing expression of angiotensinogen mRNA and differential transcription factor binding derived from 2 variant alleles in human tissue where the ratio of expression of one allele to another can be accurately determined.

Genetics of age-related white matter lesions from linkage to genome wide association studies

White matter lesions are a frequent phenomenon in the elderly and contribute to the development of disability. The mechanisms underlying these brain lesions are still not fully understood with age and hypertension being the most well established risk factors. The heritability of white matter lesions is consistently high in different populations. Candidate gene studies strongly support the role of genes involved in the renin–angiotensin system, as well as Notch3 signaling. The recent genome wide association study by the CHARGE consortium identified a novel locus on chromosome 17q25 harboring several genes such as TRIM65 and TRIM47 which pinpoint to possible novel mechanisms leading to white matter lesions.

Genetics of subcortical vascular dementia

Subcortical vascular dementia or cerebral small vessel disease is a common cause of disability in the elderly. On magnetic resonance imaging the disease is manifested as white matter lesions, lacunes and microbleeds. Its etiology is complex, with age and hypertension as established risk factors. The heritability of white matter lesions is constantly high over different populations. Linkage studies identified several loci for these lesions however no genes responsible for the linkage signals had been identified so far. Results from genetic association studies using the candidate gene approach support the role of APOE, the renin-angiotensin system, as well as the Notch3 signaling pathway in the development of subcortical vascular dementia. The recent genomegenome wide association study on white matter lesions identified a novel locus on chromosome 17q25 harboring several genes such as TRIM65 and TRIM47 which pinpoints to possible novel mechanisms leading to these lesions.

Promoter polymorphism G-6A, which modulates angiotensinogen gene expression, is associated with non-familial sick sinus syndrome

BACKGROUND

It is well known that familial sick sinus syndrome (SSS) is caused by functional alterations of ion channels and gap junction. Limited information is available on the mechanism of age-related non-familial SSS. Although evidence shows a close link between arrhythmia and the renin-angiotensin system (RAS), it remains to be determined whether the RAS is involved in the pathogenesis of non-familial SSS.

METHODS

In this study, 113 patients with documented non-familial SSS and 125 controls were screened for angiotensinogen (AGT) and gap junction protein-connexin 40 (Cx40) promoter polymorphisms by gene sequencing, followed by an association study. A luciferase assay was used to determine the transcriptional activity of the promoter polymorphism. The interaction between nuclear factors and the promoter polymorphism was characterized by an electrophoretic mobility shift assay (EMSA).

RESULTS

Association study showed the Cx40 -44/+71 polymorphisms are not associated with non-familial SSS; however, it indicated that four polymorphic sites at positions -6, -20, -152, and -217 in the AGT promoter are linked to non-familial SSS. Compared to controls, SSS patients had a lower frequency of the G-6A AA genotype (OR 2.88, 95% CI 1.58-5.22, P = 0.001) and a higher frequency of the G allele at -6 position (OR 2.65, 95% CI 1.54-4.57, P = 0.0003). EMSA and luciferase assays confirmed that nucleotide G at position -6 modulates the binding affinity with nuclear factors and yields a lower transcriptional activity than nucleotide A (P<0.01).

CONCLUSION

G-6A polymorphism, which modulates the transcriptional activity of the AGT promoter, may contribute to non-familial SSS susceptibility.

Genetic variants of the NOTCH3 gene in the elderly and magnetic resonance imaging correlates of age-related cerebral small vessel disease

Cerebral small vessel disease-related brain lesions such as white matter lesions and lacunes are common findings of magnetic resonance imaging in the elderly. These lesions are thought to be major contributors to disability in old age, and risk factors that include age and hypertension have been established. The radiological, histopathologic and clinical phenotypes of age-related cerebral small vessel disease remarkably resemble autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy, which is caused by mutations in NOTCH3. We hypothesized that genetic variations in NOTCH3 also play a role in age-related cerebral small vessel disease. We directly sequenced all 33 exons, the promoter and 3'-untranslated region of NOTCH3 in 195 participants with either coalescent white matter lesions or lacunes and compared the results to 82 randomly selected participants with no focal changes on magnetic resonance images in the Austrian Stroke Prevention Study. We detected nine common and 33 rare single nucleotide polymorphisms, of which 20 were novel. All common single nucleotide polymorphisms were genotyped in the entire cohort (n = 888), and four of them, rs1043994, rs10404382, rs10423702 and rs1043997, were associated significantly with both the presence and progression of white matter lesions. The association was confined to hypertensives, a result which we replicated in the Cohorts for Heart and Ageing Research in Genomic Epidemiology Consortium on an independent sample of 4773 stroke-free hypertensive elderly individuals of European descent (P = 0.04). The 33 rare single nucleotide polymorphisms were scattered over the NOTCH3 gene with three being located in the promoter region, 24 in exons (18 non-synonymous), three in introns and three in the 3'-untranslated region. None of the single nucleotide polymorphisms affected a cysteine residue. Sorting Intolerant From Tolerant, PolyPhen2 analyses and protein structure simulation consistently predicted six of the non-synonymous single nucleotide polymorphisms (H170R, P496L, V1183M, L1518M, D1823N and V1952M) to be functional, with four being exclusively or mainly detected in subjects with severe white matter lesions. In four individuals with rare non-synonymous single nucleotide polymorphisms, we noted anterior temporal lobe hyperintensity, hyperintensity in the external capsule, lacunar infarcts or subcortical lacunar lesions. None of the observed abnormalities were specific to cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy. This is the first comprehensive study investigating (i) the frequency of NOTCH3 variations in community-dwelling elderly and (ii) their effect on cerebral small vessel disease related magnetic resonance imaging phenotypes. We show that the NOTCH3 gene is highly variable with both common and rare single nucleotide polymorphisms spreading across the gene, and that common variants at the NOTCH3 gene increase the risk of age-related white matter lesions in hypertensives. Additional investigations are required to explore the biological mechanisms underlying the observed association.

Transgenic mice with -6A haplotype of the human angiotensinogen gene have increased blood pressure compared with -6G haplotype

Hypertension is a serious risk factor for cardiovascular disease, and the angiotensinogen (AGT) gene locus is associated with human essential hypertension. The human AGT (hAGT) gene has an A/G polymorphism at -6, and the -6A allele is associated with increased blood pressure. However, transgenic mice containing 1.2 kb of the promoter with -6A of the hAGT gene show neither increased plasma AGT level nor increased blood pressure compared with -6G. We have found that the hAGT gene has three additional SNPs (A/G at -1670, C/G at -1562, and T/G at -1561). Variants -1670A, -1562C, and -1561T almost always occur with -6A, and variants -1670G, -1562G, and -1561G almost always occur with -6G. Therefore, the hAGT gene may be subdivided into either -6A or -6G haplotypes. We show that these polymorphisms affect the binding of HNF-1α and glucocorticoid receptor to the promoter, and a reporter construct containing a 1.8-kb hAGT gene promoter with -6A haplotype has 4-fold increased glucocorticoid-induced promoter activity as compared with -6G haplotype. In order to understand the physiological significance of these haplotypes in an in vivo situation, we have generated double transgenic mice containing either the -6A or -6G haplotype of the hAGT gene and the human renin gene. Our ChIP assay shows that HNF-1α and glucocorticoid receptor have stronger affinity for the chromatin obtained from the liver of transgenic mice containing -6A haplotype. Our studies also show that transgenic mice containing -6A haplotype have increased plasma AGT level and increased blood pressure as compared with -6G haplotype. Our studies explain the molecular mechanism involved in association of the -6A allele of the hAGT gene with hypertension.

The genetics of white matter lesions

White matter lesions (WMLs), commonly seen as hyperintensities on T2-weighted MRI scans of healthy elderly individuals, are considered to be related to small vessel disease in the brain, and are often associated with subtle cognitive and functional impairments. WMLs also show a strong correlation with a wide range of neurodegenerative and neuropsychiatric disorders. Although a number of vascular risk factors for WMLs have been identified, genetic factors are also important with twin and family studies reporting high heritability. Mutations in several genes have been described that lead to monogenic disorders manifesting WMLs, such as Fabry disease and CADASIL. Because most individuals with WMLs do not have Mendelian disorders, most of the focus has been on single nucleotide polymorphisms as genetic risk markers for WMLs, either directly or through their interactions with other genes or medical risk factors. Candidate genes examined to date include those involved in cholesterol regulation and atherosclerosis, hypertension, neuronal repair, homocysteine levels, and oxidative stress pathways. In addition, although there have been a few genome-wide linkage studies, only one genome-wide association study has been performed. The majority of the genetic findings need independent replication, and studies need to be extended to other candidate genes. Collaborative efforts to examine genome-wide associations in large samples of both sexes of a broad age range using longitudinal studies are necessary. The identification of individuals genetically at risk of developing white matter lesions will have important implications for recognizing the etiology of WMLs and thereby developing clinical intervention strategies for their prevention.

Evaluation of asymmetric dimethylarginine and homocysteine in microangiopathy-related cerebral damage

BACKGROUND

Microangiopathy-related cerebral damage (MARCD) is an entity of cerebrovascular disease based on arteriosclerosis in deep white matter, which includes lacunar infarction and white matter hyperintensity (WMH). As asymmetric dimethylarginine (ADMA), an endogenous inhibitor of the nitric oxide (NO) synthases, and homocysteine are both potential risk factors for arteriosclerosis, the plasma levels of these two substances were evaluated in individuals with MARCD.

METHODS

Consecutive participants of a health examination (401 males and 311 females) were recruited for this cross-sectional study. All participants received an magnetic resonance imaging examination, and those with either lacunar infarction or WMH (grade > or =2) were classified into MARCD (+) (N = 146). The plasma ADMA concentration was measured with high performance liquid chromatography. The total homocysteine (tHcy) concentration was measured using a commercial kit.

RESULTS

The ADMA level (P < 0.001), symmetric dimethylarginine (SDMA) level (P < 0.05) and L-arginine (Arg)/ADMA ratio (P < 0.01) differed significantly between MARCD (+) and (-) according to nonparametric Wilcoxon test, while the tHcy level did not (P = 0.37). Classic risk factors such as age, blood pressure, and the presence of hypertension differed significantly between the two groups as well. In the logistic analysis, the association of Arg/ADMA with MARCD remained significant (odds ratio and 95% confidence interval, 0.19 (0.05, 0.73), P < 0.05) even after adjusting for the effects of age and hypertension.

CONCLUSIONS

ADMA and tHcy levels were studied in 712 subjects with or without MARCD. The Arg/ADMA ratio was suggested to be an independent risk factor for MARCD. A large-scale prospective study is warranted to confirm the causal relationship between Arg/ADMA and MARCD.

Pathomechanism of leukoaraiosis: a molecular bridge between the genetic, biochemical, and clinical processes (a mitochondrial hypothesis)

Ischemic demyelination in the white matter of the brain is a frequent clinical entity. In neuroimaging terms, it is referred to as leukoaraiosis (LA). LA can reflect a broad public health problem, which is caused by a cognitive impairment ranging from mild slowness of thinking to full-blown subcortical dementia. One-quarter of subjects aged 65 yr or over are affected by some degree of white matter changes. There are a number of genetic factors that can be associated with circulatory disturbances of the white matter of the brain. A slight chronic hypoperfusion or an endothelial dysfunction associated with unfavorable genetic variations such as methylenetetrahydrofolate reductase C677T variation and angiotensin-converting enzyme I/D polymorphism then may lead indirectly to a malfunction of the molecular cross-talk between the nucleus and the mitochondria. This results in a decrease in the production of energy in the glia cells and thereby the beginning of demyelination. From another aspect, the presence of either the apolipoprotein E 2 or 4 alleles may cause an increased vulnerability to a slight chronic hypoperfusion of the white matter by reducing the range of mechanical and chemical flexibility of the glial cytoskeleton. In consequence of the chronic hypoperfusion, the functionally damaged kinesin protein gives rise also to the disturbances of the trafficking of the myelin basic protein mRNAs in the oligodendrocytes. On the basis of the current knowledge on LA, this article suggests a hypothetical molecular bridge between the genetic, biochemical, and clinical processes.

Genetic profile of ischemic cerebrovascular disease and carotid stenosis

OBJECTIVES

Carotid artery stenosis (CS) is a major risk factor for ischemic cerebrovascular disease (ICVD) and is therefore of interest in genetic investigating. Here we report the distribution of 100 polymorphisms in 47 suspected susceptibility genes for ICVD and its risk factors.

MATERIALS AND METHODS

Previously published markers in suspected susceptibility genes were genotyped in ICVD patients and controls (928/602). Genotyping was performed using multiplex polymerase chain reaction (PCR) and linear immobilized probe array assays. ICVD cases were subtyped according to Trial of Org 10172 in Acute Stroke Treatment (TOAST) or subdivided into CS and non-CS patients by ultrasonography in a separate analysis.

RESULTS

Three polymorphisms located in the lipoprotein lipase (LPL), angiotensinogen (AGT) and guanine nucleotide-binding protein beta-3 (GNB3) genes were significantly associated with ICVD after correction for age and gender. The strongest association was found for the protective LPL Ser447Term polymorphism. All the significant markers showed varying frequencies in different subphenotypes of ICVD. Factor VII, apolipoprotein E and two renin polymorphisms were differentially frequent in patients with evidence of CS compared with non-CS patients.

CONCLUSIONS

We have found that some previously described susceptibility polymorphisms are weakly associated with ICVD and that subdivision of patients into CS and non-CS groups may help to identify new candidate polymorphisms.

Genetics of ischaemic stroke

Ischaemic stroke is a heterogeneous multifactorial disorder. Epidemiological data provide substantial evidence for a genetic component to the disease, but the extent of predisposition is unknown. Large progress has been made in single-gene disorders associated with ischaemic stroke. The identification of NOTCH3 mutations in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leucoencephalopathy (CADASIL) has led to new insights on lacunar stroke and small-vessel disease. Studies of sickle-cell disease have drawn attention to the importance of modifier genes and of gene-gene interactions in determining stroke risk. They have further highlighted a potential role of genetics in predicting stroke risk. Little is known about the genes associated with complex multifactorial stroke. There are probably many alleles with small effect sizes. Genetic-association studies on a wide range of candidate pathways, such as the haemostatic and inflammatory system, homocysteine metabolism, and the renin-angiotensin aldosterone system, suggest a weak but significant effect for several at-risk alleles. Genome-wide linkage studies in extended pedigrees from Iceland led to the identification of PDE4D and ALOX5AP. Specific haplotypes in these genes have been shown to confer risk for ischaemic stroke in the Icelandic population, but their role in other populations is unclear. Advances in high-throughput genotyping and biostatistics have enabled new study designs, including genome-wide association studies. Their application to ischaemic stroke requires the collaborative efforts of multiple centres. This approach will contribute to the identification of additional genes, novel pathways, and eventually novel therapeutic approaches to ischaemic stroke.

The renin-angiotensin-aldosterone system in cerebral small vessel disease

INTRODUCTION

Cerebral small vessel disease (SVD) appears on magnetic resonance imaging (MRI) as leukoaraiosis (LA), état criblé (EC), and multiple lacunar infarctions (MLI). Although the pathophysiology of SVD is poorly understood, there is evidence of a genetic contribution. We sought to analyze the influence of the renin-angiotensin-aldosterone system (RAAS) on SVD in symptomatic patients from the Génétique de l'Infarctus Cérébral (GENIC) study, including RAAS polymorphisms and circulating angiotensin converting enzyme (ACE).

METHODS

Caucasian patients (n=510) with acute brain infarction (BI) were recruited and MRIs were evaluated for SVD, including LA, EC, and MLI. We considered ACE levels and several polymorphisms, including ACE, angiotensinogen, aldosterone synthase CYP11B2, and angiotensin II receptor type I.

RESULTS

Among the polymorphisms, there were marginal negative associations between aldosterone synthase CYP11B2 -344C against severe EC (adjusted OR, 0.57; 95% CI, 0.31-1.05) and severe LA (adjusted OR, 0.54; 95% CI, 0.30-0.95), both considering -344C dominant. In addition, the frequency of -344C decreased with the number of SVD abnormalities (p=0.016). Mean plasma ACE was elevated in patients with MLI, but not with LA or EC. The risk of MLI increased gradually with increasing plasma ACE (adjusted OR, 1.25; 95% CI, 1.02-1.53).

CONCLUSIONS

This exploratory study found no strong evidence for RAAS involvement in severe SVD in this population. The whole spectrum of SVD, including EC, MLI, and LA, can be considered as phenotypes for genetic studies.

White matter hyperintensities in mid-adult life

PURPOSE OF REVIEW

White matter hyperintensities on T2-weighted magnetic resonance imaging are frequent incidental findings in the brains of elderly individuals. Recent studies have reported that they may also be common in middle-aged individuals, and their systematic evaluation in younger populations is necessary.

RECENT FINDINGS

Incidental white matter hyperintensities are common in brains of healthy individuals in their 60s and may be seen as early as the 30s and 40s. They are associated with subtle functional impairment and higher prevalence of neuropsychiatric disorders. While cerebrovascular risk factors such as hypertension, diabetes, high homocysteine, and so forth, are known risk factors for white matter hyperintensities, a significant proportion of the variance is unexplained. Genetic factors, alone or in interaction with environmental factors, appear to be important. There is a slight excess of white matter hyperintensities in women, the basis for which is not understood. Longitudinal studies show that those with baseline lesions have a greater progression over time.

SUMMARY

New imaging techniques present an opportunity to examine white matter pathology in great detail in younger populations. Standardized methods to examine such pathology and its determinants will help inform strategies for their prevention, which is an important component of a healthy ageing agenda.

The brain-derived neurotrophic factor VAL66MET polymorphism and cerebral white matter hyperintensities in late-life depression

OBJECTIVE

In animal models, brain-derived neurotrophic factor (BDNF) appears to protect against cerebral ischemia. The authors examined whether the BDNF Val66Met polymorphism, which affects BDNF distribution, was associated with greater volumes of hyperintense lesions as detected on magnetic resonance imaging in a cohort of depressed and nondepressed elders.

DESIGN

Subjects completed cross-sectional assessments, including clinical evaluation and a brain magnetic resonance imaging scan, and provided blood samples for Val66Met genotyping.

SETTING

The study was conducted at a university-based academic hospital.

PARTICIPANTS

Participants included 199 depressed and 113 nondepressed subjects aged 60 years or older.

MEASUREMENT

Hyperintensity lesion volumes were measured using a semiautomated segmentation procedure. Statistical models examined the relationship between genotype and lesion volume while controlling for depression, presence of hypertension, age, and sex.

RESULTS

After controlling for covariates, Met66 allele carriers exhibited significantly greater white matter hyperintensity volumes (F(1,311) = 4.09, p = 0.0442). This effect was independent of a diagnosis of depression or report of hypertension. Genotype was not significantly related to gray matter hyperintensity volume (F(1,311) = 1.14, p = 0.2871).

CONCLUSIONS

The BDNF Met66 allele is associated with greater white matter hyperintensity volumes in older individuals. Further work is needed to determine how this may be associated with other clinically relevant findings in late-life depression.

A genetic variant in cytoskeleton motors amplifies susceptibility to leukoaraiosis in hypertensive smokers: gene-environmental interactions behind vascular white matter demyelinization

One of the most frequent causes of an age-associated cognitive decline is the vascular white matter demyelinization of the brain referred to as leukoaraiosis (LA). The wide range of severity of the cognitive decline caused by LA can have numerous deleterious effects on the quality of life, leading overall to far-reaching public health problems. Besides clinical risk factors such as hypertension and advanced age, genetic susceptibility factors are presumed to be of great importance in the development of LA. The protein kinesin, which is the main motor protein in the trafficking system of the mitochondria, can undergo functional damage under the circumstances of chronic hypoxia. This may give rise to a slowly developing metabolic crisis in the glia cells, a phenomenon hypothesized to account for the evolution of LA. Setting out from this assumption, we examined how the kinesin light-chain 1 (KNS2) G56836C single nucleotide polymorphism in intron 13 affects the susceptibility to LA. This genetic variant was found to be associated with cognitive disturbances and neurodegeneration, and it was presumed to affect the function of kinesin. The association analysis of the above genetic variant was performed in 229 patients with LA and 264 neuroimaging alteration-free controls. The KNS2 56836CC variant increased the risk of LA 7.76-fold in hypertensive smokers as compared with those not carrying this variant. This finding may be useful in everyday clinical practice by indicating the need for stricter preventive measures in CC carriers.

Genes, endothelial function and cerebral small vessel disease in man

Cerebral small vessel disease results from ischaemia in the perforating arteries supplying the white matter and deep grey matter nuclei. It results in both focal lacunar infarction and more diffuse areas of chronic ischaemia (leukoaraiosis). Two subtypes may exist. One subtype (isolated lacunar infarction) is associated with single or a few larger lacunar infarcts without leukoaraiosis, and may result from microatheroma in the larger perforating arteries. The second subtype (ischaemic leukoaraiosis) results in multiple small lacunar infarcts with leukoaraiosis secondary to a diffuse arteriopathy affecting the smaller perforating arteries, usually occurring in the presence of hypertension. In this subtype, chronic hypoperfusion and impaired cerebral autoregulation have been reported. A number of lines of evidence support a pathogenic role of endothelial activation and dysfunction. Genetic predisposition has also been implicated. Associations with genes involved in endothelial function, including those regulating the renin-angiotensin system, endothelial nitric oxide and homocysteine levels, have been reported. However, not all results have been replicated and there are few robust replicable associations. Larger studies are required to determine definitively which associations represent important risk factors.

Evaluation of the roles of the A185C and C406T kinesin light-chain 1 variants in the development of leukoaraiosis

Vascular white matter demyelinization of the brain is referred to as leukoaraiosis (LA). This frequent age-associated entity leads to a cognitive decline or dementia. The background of LA has been hypothesized to be a chronic hypoxia-induced functional cytoskeleton malfunction. Setting out from this assumption, we earlier found that the kinesin light-chain 1 (KNS2) cytoskeleton motor protein 56836CC single nucleotide polymorphism conferred a risk of LA in hypertensive smokers. The aim of the present study was to extend our observations as to how the KNS2 A185C and C406T single nucleotide polymorphisms in the 5'-untranslated sequence region affect the susceptibility to LA. These two latter variants were presumed to influence the transcription of the KNS2 mRNA by locating in a function-enhancer region. An association analysis of these genetic variants was conducted on 242 patients with LA and 251 neuroimaging alteration-free controls. The KNS2 AA185-406TT haplotype increased the risk of LA 3.56-fold in hypertensive smokers as compared with those not carrying the KNS2 AA185-406TT genotype, which was similar to our previous findings for the KNS2 56836CC intron variant. Moreover, the three homozygous KNS2 variants (56936CC-AA185-406TT) coincided to an extent of 82.2%. Overall, although the 56836CC intron variant appears to be the most important of the three kinesin variants as regards the development of LA, the contribution of the AA185-406TT haplotype to the unfavorable phenotype of LA cannot be ruled out. The present finding supports the involvement of the cytoskeleton in the development of vascular white matter damage, thereby opening up novel fields in the research into LA.

Polymorphisms of the renin-angiotensin system are associated with blood pressure, atherosclerosis and cerebral white matter pathology

BACKGROUND

The renin-angiotensin system is involved in the development of hypertension, atherosclerosis and cardiovascular disease. We studied the association between the M235T polymorphism of the angiotensinogen gene (AGT) and the C573T polymorphism of the angiotensin II type 1 receptor (AT1R) and blood pressure, carotid atherosclerosis and cerebrovascular disease.

METHODS

We genotyped over 6000 subjects from the Rotterdam Study and more than 1000 subjects from the Rotterdam Scan Study. We used logistic regression and univariate analyses, adjusting for age and sex with, for AGT, the MM and, for AT1R, the TT genotype as reference.

RESULTS

We found that AGT-235T increased systolic (p for trend = 0.03) and diastolic blood pressure (p for trend = 0.04). The prevalence of carotid plaques was increased 1.25-fold (95% CI 1.02-1.52) in AGT-TT carriers. There was a significant increase in mean volume deep subcortical white matter lesions (WML) for AGT-TT carriers (1.78 ml vs 1.09 ml in the reference group; p = 0.008). A significant interaction was found between AGT and AT1R, further increasing the effect on periventricular and subtotal WML (p for interaction = 0.02). We found a non-significant increased risk of silent brain infarction for AGT-TT carriers and AT1R-CC carriers, but no effect on stroke.

CONCLUSION

We found an association between AGT and blood pressure, atherosclerosis and WML. Also, we found synergistic effects between AGT and AT1R on the development of WML. These findings raise the question of whether the renin-angiotensin system may be a therapeutic target for the prevention of cerebral white matter pathology.

Effect of the angiotensinogen genotype on experimental hypertension in mice

Polymorphisms of the angiotensinogen (Agt) gene may affect blood pressure. We used a mouse model to test for the role of the Agt genotype in low-renin or high-renin forms of hypertension. Mice bearing one, two, three, or four copies of the Agt gene underwent renal artery clipping to induce high-renin two-kidney, one-clip renovascular hypertension (2K1C), or uninephrectomy, salt loading, and application of deoxycorticosterone-acetate (DOCA) pellets to induce low-renin mineralocorticoid hypertension. Appropriate control animals were also studied. Blood pressure was measured by tail cuff as well as by direct intra-arterial recordings. There was a small effect of the Agt genotype on baseline blood pressure before induction of hypertension. The extent of 2K1C hypertension was not affected by the genotype. In contrast, there was a marked gene-dose effect on DOCA-hypertension (21.2 mmHg over all genotypes). Treatment of DOCA mice with the angiotensin II type 1 receptor antagonist abolished the genotype effect on blood pressure and left ventricular hypertrophy. There was a trend towards less suppression of endogenous aldosterone by DOCA treatment with increasing number of Agt gene copies. We conclude that the Agt genotype exerts a marked effect on blood pressure in a low-renin form of hypertension but no effect in the face of stimulated renin, at least in mice.

Progression of cerebral white matter lesions -- clinical and radiological considerations

More than half of all elderly have some degree of white matter lesions (WML) on MRI of the brain. Until recently, the rate of progression of WML was unknown. Recent work within several population based large scale studies was devoted to tackle this question, to identify factors related to WML progression and to establish a relationship with clinical variables and cognitive changes. There is converging evidence that at least a subset of WML demonstrates considerable progression over time. Increases in WML volume have been correlated with increased loss of brain volume and decline in cognitive and motor performance, indicating that progression of WML harbors clinical relevance. Correlative MRI-histopathologic studies and the clustering of vascular risk factors in subjects with progressive WML support a vascular aetiology of WML, particularly in "confluent" MRI phenotypes. Although specific rating scales have been proposed to detect WML progression, quantitative measurements appear superior given their objective and reproducible nature and regarding possibilities of statistical analyses. Measuring changes in the progression of WML may provide a valid surrogate marker in future clinical trials on cerebral small-vessel disease. Power calculations based on quantitative data of the Austrian Stroke Prevention Study (ASPS) suggest that such studies would be feasible.

Methodology for measuring cerebrovascular disease burden

Biological aging of the brain is partly attributable to aging of the cerebrovascular circulation and the effects of these vascular changes on the brain. A variety of techniques ranging from simple, clinical scores to complex radiological techniques have been used in an attempt to understand, describe and quantify this process. Simultaneously attempts have been made to relate these changes to cognitive and physical changes and the risk of dementia and stroke associated with brain aging. The most frequently used clinical scores are the Framingham Stroke Risk Profile and the Hachinski Ischemic Score for vascular dementia. Radiological techniques to estimate cerebrovascular burden include many varieties of ultrasonographic, computerized tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine techniques. The radiological techniques evaluate the nature and extent of disease in the vessels supplying the brain and the pattern and extent of radiological evidence of damage to the brain both on static and dynamic imaging and are briefly outlined in this review. There are several studies using these techniques to study 'normal' aging populations, and the techniques used in the most widely known of these studies are briefly highlighted in this review.

Family-based association study of matrix metalloproteinase-3 and -9 haplotypes with susceptibility to ischemic white matter injury

Susceptibility to ischemic damage to the subcortical white matter of the brain has a strong genetic basis. Dysregulation of matrix metalloproteinases (MMPs) contributes to loss of cerebrovascular integrity and white matter injury. We investigated whether sequence variation in the genes encoding MMP3 and MMP9 is associated with variation in leukoaraiosis volume, determined by magnetic resonance imaging, in non-Hispanic whites and African-Americans using family-based association tests. Seven hundred and fifty-six white and 671 African-American individuals from sibships ascertained through two or more siblings with hypertension were genotyped for 7 and 8 haplotype-tagging polymorphisms in the MMP3 and MMP9 genes, respectively. MMP3 sequence variation was significantly associated with variation in leukoaraiosis volume in Whites. Two common haplotypes with opposing relationships to leukoaraiosis volume were identified. MMP9 sequence variation was also significantly associated with variation in leukoaraiosis volume in both African-Americans and Whites. Different haplotypes contributed to these associations in the two racial groups. These findings add to the growing body of evidence from animal models and human clinical studies suggesting a role of MMPs in ischemic white matter injury. They provide the basis for further investigation of the role of these genes in susceptibility and/or progression to clinical disease.

Antihypertensive medications for risk reduction of first and recurrent ischemic stroke

It is increasingly clear that even a small reduction in blood pressure results in a substantial risk reduction of vascular events including ischemic stroke. Recently, several comparative prospective trials of angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers have demonstrated that, for equivalent reductions in blood pressure, these drugs may confer a greater effect on the prevention of primary and recurrent ischemic stroke compared with other antihypertensive medications. Given this information from prospective randomized trials, it appears that this class of drugs should be the first-line treatment for hypertension in patients at risk of a first or recurrent ischemic stroke. This review will critically assess the scientific basis and rationale of the use of angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers in primary and secondary stroke prevention.

Epidemiology of white matter lesions

This is an overview of the prevalence of, and risk factors for white matter lesions in older persons. The prevalence of white matter lesions is high and increases with age. Most risk factors that have been examined in association with white matter lesions are similar to those for cardiovascular disease, including elevated blood pressure, diabetes atherosclerosis, homocysteine levels, and markers of oxidative stress. The genetic contributions to white matter lesions are also reviewed.

Specific APO E genotypes in combination with the ACE D/D or MTHFR 677TT mutation yield an independent genetic risk of leukoaraiosis

OBJECTIVE

Ischaemic demyelination of the white matter of the brain is a frequent clinical entity. In the neuroimaging terms, it is referred to as leukoaraiosis. We earlier found that the co-occurrence of the homozygous methylenetetrahydrofolate reductase (MTHFR) 677TT and angiotensin-converting enzyme D/D (ACE D/D) genotypes yielded a highly significant moderate risk of leukoaraiosis. On the assumption of further genetic interactions, we have now investigated whether the different apolipoprotein E (APO E) genotypes, in pairwise combinations with the MTHFR 677TT or ACE D/D mutation, could lead to an increased risk of leukoaraiosis.

MATERIAL AND METHODS

We analysed the occurrence of the APO E genotypes in pairwise combinations with the MTHFR 677TT or ACE D/D mutation in 315 consecutive Caucasian patients with leukoaraiosis. A total of 646 neuroimaging-free subjects acted as a control group.

RESULTS

The APO E 2/2 and 2/3 or APO E 4/4 and 4/3 genotypes in combination with the MTHFR 677TT or ACE D/D mutation exhibited independent genetic risks of leukoaraiosis.

CONCLUSION

The interactions of certain unfavourable genetic mutations can contribute to the evolution of leukoaraiosis.

Microangiopathy-related cerebral damage and angiotensinogen gene: from epidemiology to biology

Microangiopathy-related cerebral damage (MARCD) is a common finding in the elderly. It may lead to cognitive impairment and gait disturbances. Arterial hypertension and age are the best accepted risk factors for MARCD. Genes involved in blood pressure regulation, like genes encoding the proteins of the renin-angiotensin system (RAS) therefore represents good candidate genes for MARCD. Plasma angiotensinogen level is a major determinant of the RAS activity. Positive correlation between angiotensinogen gene expression and RAS activity, as well as blood pressure were observed. Common mutations described in the AGT promoter were able to alter AGT expression in cell culture. We described that 4 frequent mutations at the AGT promoter are combined in 5 haplotypes coded as A (-6:g, -20:a, -152:g, -217:g), B (-6:a, -20:c, -152:g, -217:g), C (-6:a, -20:c, -152:a, -217:g), D (-6:a, -20:a, -152:g, -217:g), and E (-6:a, -20:a, -152:g, -217:a). The B haplotype was significantly associated with MARCD in the cohort of the Austrian Stroke Prevention Study (p = 0.005). The association was independent of hypertension, which pinpointed to a possible role of the local RAS in this relationship. Investigation of the promoter activity of the AGT gene in astrocytes suggests that expression of this gene may be modulated by the haplotype.

Epidemiology of white-matter lesions

White-matter lesions (WML) detected on MRI may reflect different pathologies, but, in older persons, are thought to be mainly of ischemic origin. WML increase in prevalence with age. Several cardiovascular risk factors and cognitive, emotional, and physical function consequences of WML have been identified. These are reviewed briefly in this report.

The natural course of MRI white matter hyperintensities

The rate and extent of progression of white matter hyperintensities (WMH) over time in elderly subjects is yet unclear. These abnormalities may represent an early form of subcortical vascular dementia. As to whether such changes could be used, as a surrogate marker for this subtype of vascular dementia remains to be determined. So far there exists only a very limited number of studies determining the rate, clinical predictors and cognitive consequences of WMH evolution. There is evidence that these changes do progress over time, however the results of the different studies cannot be compared due to methodological differences. The Austrian Stroke Prevention Study reported that 17.9% of normal individuals show progression over time. The only published quantitative data demonstrated an absolute increase of 1.1 cm(3) over an observational period of 4 years in healthy subjects. Diastolic blood pressure, early confluent or confluent WMH at baseline and genetic variants in the angiotensinogen gene are so far the only known predictors of WMH progression. The Austrian Stroke Prevention Study did not find an association between the evolution of WMH and cognitive functioning but the statistical power of this analysis was small and the relationship needs to be further explored.

Evaluation of the roles of common genetic mutations in leukoaraiosis

OBJECTIVES

Leukoaraiosis, a relatively frequent neuroimaging entity, is presumed to be primarily a vascular problem. However, it can be explained only in part by vascular risk factors. With the assumption of genetic susceptibility, the roles of common genetic polymorphisms and mutations in leukoaraiosis were examined in this study.

MATERIAL AND METHODS

A detailed clinical scrutiny of 843 Hungarian neurological patients with mild cognitive-like complaints revealed 229 subjects with leukoaraiosis that was probably vascular in origin: 143 with leukoaraiosis alone (group 1), and 86 with leukoaraiosis plus cerebral infarction (group 2). In all 229 patients, the methylenetetrahydrofolate reductase C677T (MTHFR C677T) mutation and angiotensin-converting enzyme (ACE I/D) polymorphism were examined by means of the PCR technique. The prevalences of the different genotypes for the examined mutations in the 2 groups were analysed in comparison with the data on 362 neuroimaging alteration-free subjects as controls.

RESULTS

The ACE D/D genotype (38.37%, P<0.0005; OR 2.46, 95% CI, 1.49-4.08) and ACE D allele (61%; P<0.001) were more frequent in group 2 than in the control group (20.17%; 47%). Neither the homozygous nor the heterozygous MTHFR C677T mutation alone was found to be a risk factor for leukoaraiosis. The homozygous MTHFR C677T mutation combined with the ACE D/D genotype was significantly more frequent in group 1 (11.89%, P<0.0005; OR 4.75, 95% CI, 2.12-10.65), in group 2 (12.79%, P<0.0005; OR 5.16, 95% CI, 2.12-12.6) and in combined group 1+2 (12.23%, P<0.0005; OR 4.9, 95% CI, 2.33-10.3) than in the control group (2.76%).

CONCLUSION

These data indicate that the contributions of the ACE D/D genotype and the homozygous MTHFR C677T mutation to leukoaraiosis should be taken into consideration not as major, but as additive factors. These findings draw attention to the fact that genetic polymorphisms that alone are insignificant can be risk factors for leukoaraiosis if they cluster in the same subjects.