Abstract P136: Dietary Salt and Non-Salt Components Have Substantial Effects on Genome-Wide DNA Methylation Patterns in Dahl SS Rats

Abstract

Epigenetic modifications of the genome play a key role in the regulation of gene expression. It has been reported that epigenetic modifications of several genes are associated with hypertension. To investigate the potential role of genome-wide changes in DNA methylation in salt-induced hypertension, experiments were performed on inbred Dahl SS rats obtained from two colonies maintained at the Medical College of Wisconsin (i.e. MCWSS) and Charles River Laboratory (CRLSS). The colonies are genetically identical, but CRLSS rats were maintained on a whole grain diet containing 1% NaCl (CRLSS_LS) while MCWSS rats were fed casein-based AIN-76A chow containing 0.4% NaCl (MCWSS_LS) until both colonies were switched to an AIN-76A chow containing 4% NaCl for 14 days starting at 6 weeks of age (CRLSS_HS and MCWSS_HS, respectively). Mean arterial pressure and albumin excretion rate in MCWSS_HS rats were significantly greater (142±14 mmHg and 100±16 mg/day, n=6) than in CRLSS_HS rats (118±2 mmHg and 20±2 mg/day, n=7). Reduced representation bisulfite genome sequencing (RRBS) measured 5-Methylcytosine levels at single-base resolution in the renal outer medulla in the above groups, each with four biological replicates. For genomic regions located within CpG islands (CGI’s) and exhibiting differential methylation between LS and HS in each colony, HS diet increased median methylation levels several-fold in both MCWSS (7.45% vs. 0.35% for MCWSS_HS vs. MCWSS_LS, respectively, p = 2.84E-31) and CRLSS rats (7.62% vs. 1.21% for CRLSS_HS vs. CRLSS_LS, respectively, p = 1.65E-32). For genomic regions exhibiting differential methylation between MCWSS and CRLSS, MCWSS_HS rats (which exhibited higher blood pressure) had higher median methylation levels than CRLSS_HS rats (7.56% vs. 2.75%, p = 2.12E-9). We observed 156 hypermethylated and 241 hypomethylated regions within CGI’s of MCWSS_LS compared to CRLSS_LS. Examples of differentially methylated genes include the serine protease Prss2 , the transcription factor E2f1 , and the matrix protein Spock2 . These results suggest that sodium-dependent and independent dietary components could induce changes in DNA methylation that may predispose and participate in the development of hypertension and renal damage.