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Int J Physiol Pathophysiol Pharmacol 2013;5(1):32-42

Original Article
Hyperhomocysteinemia during aortic aneurysm, a plausible role of epigenetics

Nithya Narayanan, Neetu Tyagi, Amy Shah, Sebastian Pagni, Suresh C Tyagi

Department of Physiology and Biophysics, University of Louisville School of Medicine, Louisville, Kentucky; Division of Thoracic and
Cardiovascular Surgery, University of Louisville, Louisville, Kentucky

Received November 28, 2012; Accepted January 29, 2013; Epub March 8, 2013; Published March 18, 2013

Abstract: Hyperhomocysteinemia is associated with aortic aneurysm, however, the mechanisms are unclear. We hypothesize that the
expression level of genes involved in extracellular matrix (ECM) remodeling, oxidative stress, and enzymes involved in homocysteine
metabolism pathway in aortic aneurysm and hyperhomocysteinemia are differentially regulated by DNA methylation. We studied the
mRNA levels of MTHFR, SAHH, MMP-1, -9, TIMP-1, -4, peroxiredoxin, NOX-2, -3 (NAPDH oxidase subunits), collagen and elastin in
normal and aortic aneurysm tissues from humans and aorta tissue from HHcy (Cystathionine beta synthase heterozygote knockout,
CBS+/-) mice treated with high methionine diet. The total RNA was extracted using Trizol method and RT-PCR was performed. Protein
expression of MTHFR, H3K9 (trimethyl) and TIMP4 were studied in mice using immunohistochemistry. MTHFR and TIMP4 expression
was seen to be increasing in both human aneurysm samples as well as HHcy CBS+/- mice. There was increased expression of
MMP9, peroxiredoxin and decreased expression of MMP1, Collagen I and IV was noted in thoracic aortic aneurysm samples. Increased
Collagen IV and decreased Collagen I levels were seen in CBS +/- HHcy mice compared to their wild type controls. Since DNA
methylation regulates gene expression of enzymes in Hcy metabolism pathway, we also measured the mRNA levels of DNMTs, MBD2
and H3K9. The results suggest an increase in the levels of DNMT1, 3a, MBD2 and H3K9 in CBS +/- aorta compared to their wild type
controls. Our findings suggest a possible role of methylation in regulation of expression of genes involved in matrix remodeling and
homocysteine metabolism. (IJPPP1211002)

Keywords: Homocysteine, aortic aneurysm, CBS, MTHFR, MMP, TIMP, collagen

Address correspondence to: Dr. Suresh C Tyagi, Department of Physiology & Biophysics, University of Louisville School of Medicine,
500 South Preston Street, Louisville, KY 40202. Phone: 502-852-3381; Fax: 502-852-6239; E-mail: s0tyag01@louisville.edu