The Potential Role of DNA Methylation in Abdominal Aortic Aneurysms

Abstract

Abdominal aortic aneurysm (AAA) is a complex disorder that has a significant impact on the aging population. While both genetic and environmental risk factors have been implicated in AAA formation, the precise genetic markers involved and the factors influencing their expression remain an area of ongoing investigation. DNA methylation has been previously used to study gene silencing in other inflammatory disorders and since AAA has an extensive inflammatory component, we sought to examine the genome-wide DNA methylation profiles in mononuclear blood cells of AAA cases and matched non-AAA controls. To this end, we collected blood samples and isolated mononuclear cells for DNA and RNA extraction from four all male groups: AAA smokers (n = 11), AAA non-smokers (n = 9), control smokers (n = 10) and control non-smokers (n = 11). Methylation data were obtained using the Illumina 450k Human Methylation Bead Chip and analyzed using the R language and multiple Bioconductor packages. Principal component analysis and linear analysis of CpG island subsets identified four regions with significant differences in methylation with respect to AAA: kelch-like family member 35 (KLHL35), calponin 2 (CNN2), serpin peptidase inhibitor clade B (ovalbumin) member 9 (SERPINB9), and adenylate cyclase 10 pseudogene 1 (ADCY10P1). Follow-up studies included RT-PCR and immunostaining for CNN2 and SERPINB9. These findings are novel and suggest DNA methylation may play a role in AAA pathobiology.

Understanding the pathogenesis of abdominal aortic aneurysms

“…Furthermore, cigarette smoking has proven to be a powerful environmental modifier of DNA methylation and is a potential mechanism by which tobacco can affect gene expression [100]. In the face of the potential relationship between cigarette smoking, AAA formation and DNA methylation [101], it is surprising that only one study has been published about the direct role of DNA methylation in AAA [102]. This study analyzed genome-wide DNA methylation profiles of patients with AAA using peripheral blood mononuclear cells, which have been used for methylation studies in other inflammatory disorders [103].…”

“…This study analyzed genome-wide DNA methylation profiles of patients with AAA using peripheral blood mononuclear cells, which have been used for methylation studies in other inflammatory disorders [103]. Using isolated human mononuclear blood cells and controlling for smoking status, significant differences in DNA methylation at specific CpG islands that mapped to two genes were identified: CNN2 and SERPINB9 [102]. The first gene, CNN2 , which is also known as h2-calponin or calponin 2, is an actin-binding protein implicated in cytoskeletal organization and vascular development.…”

“…Moreover, SERPINB9 has been shown to inhibit apoptosis of human VSMCs, again a key process in AAA pathogenesis. These findings, while novel, come from a small patient cohort [102]. Hopefully, future research efforts will help to clarify the role of DNA methylation and epigenetic modification in the development of AAA.…”

Genetic and Epigenetic Regulation of Aortic Aneurysms

“…Ryer et al examined the genome-wide DNA methylation profiles of mononuclear cells isolated from 20 humans with AAA and 21 controls. Four genes with differential CpG methylation were identified: kelch-like family member 35 ( KLHL35 ), calponin 2 ( CNN2 ), serpin peptidase inhibitor clade B (ovalbumin) member 9 ( SERPINB9 ), and adenylate cyclase 10 pseudogene 1 (ADCY10P1) [47]. For three of these genes ( CNN2 , SERPINB9 , and ADCY10P1 ), methylation more closely correlated with the presence of AAA than with either age or smoking status and suggests that the methylation status of these genes may represent an independent and additive risk factor for AAA.…”

Disrupted regulation of serpinB9 in circulating T cells is associated with an increased risk for post-transplant skin cancer

“…This is comparable to findings by Ryer et al . , who identified higher methylation of the same region within SERPINB9 in PBMCs of patients with abdominal aortic aneurysm. Despite the differential DNA methylation, they also did not detect a difference in mRNA expression.…”