Date of Graduation
12-2015
Document Type
Dissertation (PhD)
Program Affiliation
Biomedical Sciences
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Yong-Jian Geng M.D Ph.D
Committee Member
Mikael Akesson-Wassler Ph.D
Committee Member
Karen Uray Ph.D
Committee Member
Jianping Jin Ph.D
Committee Member
Melvin Klegerman Ph.D
Abstract
Atherosclerosis is a chronic arterial disease which impacts systemically the function of organs and tissues by causing inflammation and disruption of blood supply. During atherogenesis, lipid deposits, inflammation, and cells accumulate within the walls of arteries, ultimately leading to a buildup of fatty plaques and occlusion of the arterial lumen. In a multifactorial disease like atherosclerosis there are complex interplays between environmental, genetic and epigenetic risk factors. The epigenetics of atherosclerosis involving DNA methylation has been progressing from single gene to genome wide analyses. Although these epistudies have provided evidence that DNA methylation exists within certain genes during atherogenesis, the presence and effects of DNA methylation and hydroxymethylation are not fully understood and their impact on vascular cell signal transduction and proliferation may prove to be critically important.
Hypothesis and Aims. The central hypothesis of this project is that an imbalance between DNA methylation and demethylation occurs in the lesions of atherosclerosis, which leads to changes in vascular gene expression, in particular those coding for growth factor receptors. The long term goal of this research is to elucidate the epigenetic mechanisms, mainly DNA methylation and hydroxymethylation, and their contribution to the progression or reprogression of atherogenesis.
The specific aims are to use in vitro and in vivo models of atherosclerosis to examine the functional role of, and the mechanisms contributing to, DNA methylation and hydroxymethylation in insulin-like growth factor 1 receptor (IGF-1R) expression during atherogenesis triggered by genetic knockout of ApoE and/or the addition of high fat.
Methods and Results. Atherosclerosis is a chronic arterial disease systemically impacting the function of organs and tissues by causing inflammation and disruption of blood supply. The presence and effects of DNA methylation and hydroxymethylation during atherogenesis are not fully understood and their impact on vascular cell signal transduction and proliferation may prove to be critically important. Here we seek to examine the functional role of DNA methylation and hydroxymethylation in insulin-like growth factor 1 receptor (IGF-1R) expression during atherogenesis triggered by genetic knockout of ApoE and/or the addition of high fat. Using cultured vascular smooth muscle cells (VSMCs) and murine models of atherosclerosis, high fat diet feeding augments the inhibitory effect of ApoE deficiency on DNA methylation and hydroxymethylation in the aortas with severe plaques. Interestingly, the same induction of atherosclerosis causes a decrease in hydroxymethylation but an increase in methylation within the promoter region of the IGF-1R gene. Results detail the identification of TET2 as an epigenetic regulator that acts upstream of IGF-1R during atherogenesis through demethylation of the promoter area. We further show that TET2 mRNA and protein were found to be regulated by the mTORC1 signaling pathway, and selective rapamycin-induced inhibition of mTOR can reactivate IGF-1R expression through up-regulation of TET2 and hydroxymethylation of the IGF-1R promotor.
Conclusion. Identification of altered DNA methylation/hydroxymethylation in the arterial wall during atherosclerosis and its contribution to the down-regulation of IGF-1R during atherosclerosis may lend itself to altering key components of the mTOR-TET2-5-hmC pathway and thereby lead to novel therapeutic targets for treating disease.
Keywords
Epigenetic, DNA methylation, DNA hydroxymethylation, IGF-1R