Unique Associations of DNA Methylation Regions With 24-Hour Blood Pressure Phenotypes in Blacks

BACKGROUND

Epigenetic marks (eg, DNA methylation) may capture the effect of gene-environment interactions. DNA methylation is involved in blood pressure (BP) regulation and hypertension development; however, no studies have evaluated its relationship with 24-hour BP phenotypes (daytime, nighttime, and 24-hour average BPs).

METHODS

We examined the association of whole blood DNA methylation with 24-hour BP phenotypes and clinic BPs in a discovery cohort of 281 Blacks using reduced representation bisulfite sequencing. We developed a deep and region-specific methylation sequencing method, Bisulfite ULtrapLEx Targeted Sequencing and utilized it to validate our findings in a separate validation cohort (n=117).

RESULTS

Analysis of 38 215 DNA methylation regions (MRs), derived from 1 549 368 CpG sites across the genome, identified up to 72 regions that were significantly associated with 24-hour BP phenotypes. No MR was significantly associated with clinic BP. Two to 3 MRs were significantly associated with various 24-hour BP phenotypes after adjustment for age, sex, and body mass index. Together, these MRs explained up to 16.5% of the variance of 24-hour average BP, while age, sex, and BMI explained up to 11.0% of the variance. Analysis of one of the MRs in an independent cohort using Bisulfite ULtrapLEx Targeted Sequencing confirmed its association with 24-hour average BP phenotype.

CONCLUSIONS

We identified several MRs that explain a substantial portion of variances in 24-hour BP phenotypes, which might be excellent markers of cumulative effect of factors influencing 24-hour BP levels. The Bisulfite ULtrapLEx Targeted Sequencing workflow has potential to be suitable for clinical testing and population screenings on a large scale.

Abstract P175: Discovery And Validation Of Unique Associations Of DNA Methylation Regions With 24-hour Blood Pressure Phenotypes In African Americans

DNA methylation, an epigenetic mark, may reflect the interactions between DNA, environment, and lifestyle. It has been implicated in the development and progression of hypertension, a risk factor for cardiovascular disease. We hypothesize that regions of DNA methylation in blood cells can explain 24h BP phenotypes in African Americans. We performed Reduced Representation Bisulfite Sequencing (RRBS) in a discovery cohort of 281 African Americans. Several DNA methylation regions (MRs) were significantly associated with continuously monitored 24-h, daytime, or nighttime SBP, DBP, PP, and MAP after adjustments for covariates age, sex, and body mass index (False Discovery Rate (FDR) = 0.013 - 0.050). Each of these MRs explained a substantial portion of 24h BP variance, ranging from 6.5% - 9.4%. After FDR adjustment, there were no MRs significantly associated with clinic BPs (FDR > 0.1374), calculated by the average of 4 resting measurements (2 per arm) by sphygmomanometer. To interrogate specific regions of DNA methylation, our lab developed a potentially clinically applicable, deep, and targeted methylation sequencing method called Bisulfite-Specific PCR ULtrapLEx Targeted Sequencing (BULLET-Seq), and tested it in two reference samples for three MRs of interest. BULLET-Seq is able to accurately quantify the 10% changes in the dilution series when methylation rates ranged from ~40% to 90% (a chr19 methylation region; R 2 = 0.95 - 0.97) and can modestly measure these changes when rates range from ~2% to 4% (a chr5 region, R 2 = 0.82), and is questionable when methylation rates are below 2% (a chr13 region, R 2 = 0.03 - 0.27). Validation of the chr19 MR in an independent cohort (n=117) was performed in a single BULLET-Seq run. After covariate adjustment, the chr19 region was significantly associated with 24h BPs (SBP, DBP, and MAP; FDR < 0.05), confirming the findings from the discovery cohort. The MR accounted for up to 1.75% of BP variance in the 24h phenotypes. In conclusion, the reported DNA MRs have potential to be excellent markers for the cumulative effect of factors that influence 24h BPs and the BULLET-Seq workflow can be applied in clinical and population settings to screen up to thousands of patients.

Dietary Sodium Restriction Results in Tissue-Specific Changes in DNA Methylation in Humans

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Abstract 035: Unique Associations of DNA Methylation With 24-Hour Blood Pressure Phenotypes in African Americans

Blood pressure (BP) levels are influenced by genetic and environmental factors. Epigenome is the result of interactions between the DNA and the environment. Methylation is a naturally occurring epigenetic modification of genomic DNA and may influence BP levels. We examined the association of DNA methylation in whole blood with 24-hour and clinic BP phenotypes in 281 African Americans; fifty percent were women and fifty percent were hypertensive. Mean age of the participants was 44±7 years and mean body mass index (BMI) was 28±5 kg/m 2 . Clinic BP was obtained in duplicate from both arms and averaged using a standardized protocol as part of screening procedures for a 3-day inpatient clinical study. Blood was obtained for DNA at the time of screening visit. BP medications were discontinued for 1-week after the screening visit and prior to inpatient study. Detailed phenotyping and 24-hour BP measurements were performed during the in-patient study. DNA methylation profiles of these 281 subjects with 24-hour BP measurements were analyzed at single-base resolution with a modified reduced representation bisulfite sequencing (RRBS) method. Analysis of 38,216 DNA methylation regions, representing 1,549,368 CpG sites across the genome, identified up to 72 regions that were significantly associated with 24-hour, daytime or nighttime BPs. Considered jointly, these methylation regions explained up to 66.6% of the BP variance. Methylation regions associated with 24-hour, daytime or nighttime BPs or systolic, diastolic or mean arterial pressure or pulse pressure overlapped partially. No methylation region was significantly associated with clinic BP. Two to three methylation regions were significantly associated with 24-hour BP after adjustment for age, sex, and body mass index. These methylation regions, jointly, explained up to 16.5% of the variance of 24-hour BP, while age, sex and body mass index explained up to 11.0% of the variance. In summary, we have identified several DNA methylation regions in the whole blood that are associated with 24-hour, daytime or nighttime BPs, but not with clinic BP measured at a single point in time. DNA methylation appears to be an excellent marker for the cumulative effect of factors that influence 24-hour, daytime or nighttime BPs