The prevalence of chronic kidney disease (CKD) is increasing worldwide. In the United States, over 20 million adults have CKD, and traditional cardiovascular risk factors do not account for this. Blood urea dissociates to form cyanate that may alter proteins including low-density lipoprotein (LDL) by a process known as carbamylation. Our recent studies demonstrate that cLDL has all of the biological effects relevant to atherosclerosis: (a) cLDL induces injury to human coronary artery endothelial cells;(b) it induces adhesion molecule expression and monocyte adhesion on human coronary artery endothelial cells;and (c) it causes proliferation of human coronary artery smooth muscle cells. In addition, we have demonstrated that elevated plasma cLDL concentration from either chronic kidney failure or chronic urea consumption results in the development of aortic atherosclerosis in mice. Our case-control study in uremic patients revealed a strong positive correlation between elevated cLDL and an increase in common carotid artery intima-media thickness (IMT), an accepted quantifiable marker of early atherosclerosis. One of the major events that occurs in response of cLDL exposure to endothelial cells is the induction of DNA fragmentation and cell death. The mechanisms by which cLDL induces endothelial cell injury, an early step in atherosclerosis, are not known. The central hypothesis of this proposal is that cLDL elevated by CKD induces endothelial cell injury by activating EndoG to promote atherosclerosis, and that inactivation of endothelial EndoG will blunt endothelial cell death and atherogenesis in uremic mice. Our preliminary studies show that endothelial cell death induced by cLDL depends on the expression of endonuclease G (EndoG), the nuclease associated with caspase-independent DNA fragmentation. Ex vivo experiments with primary endothelial cells isolated from wild-type (WT) and EndoG null knockout (KO) mice demonstrated that KO cells are partially protected against cLDL toxicity compared to WT cells. Our results showed increased number of floating endothelial cells after cLDL injection compared to nLDL in WT mice but not in KO mice. These data point to EndoG as an important mediator of cLDL toxicity to endothelial cells, and suggest that EndoG is a potential therapeutic target for cLDL cytotoxicity and, potentially, atherosclerosis. To study the cLDL-EndoG pathway, we plan:
Aim 1. Determine molecular and cellular targets of cLDL causing activation of EndoG in vitro and in vivo.
Aim 2. Evaluate the role of likely upstream regulators of EndoG in cLDL-induced endothelial cell death in vitro and in vivo.
Aim 3. Test whether genetic inactivation of EndoG or inhibition of mechanisms upregulating EndoG attenuate uremia/cLDL-induced endothelial cell injury and atherosclerosis. Recent studies showed that among veterans, traditional cardiovascular risk factors CVD and CKD are highly prevalent, and CKD is associated with an increased risk of baseline CVD and follow-up mortality. Our study is aimed to determine whether regulation of the cLDL mediator EndoG or its upstream mechanisms may be beneficial for protection against acute endothelial injury and atherosclerosis induced by cLDL. Therefore, the results of this study may eventually save human lives, improve the health and well being of veterans, and decrease the number of disabilities among veterans and in the general population.
In the United States, over 20 million adults, many of whom are veretans, have chronic kidney disease associated with chronic cardiovascular disease, and the reason for this is unknown. Our recent studies showed that a form of cholesterol called carbamylated low-density lipoprotein (cLDL) results from chronic kidney disease and induces cardiovascular disease. Our preliminary data additionally show that cLDL acts by causing death of endothelial cells, which cover blood vessles inside. In the proposed study, we plan to determine if cLDL causes endothelial cell death by activating DNA-degrading enzyme, endonuclease G (EndoG), and if an inactivation of EndoG may prevent from cardiovascular disease. The results of this study may eventually save human lives, improve the health and well being of veterans, and decrease the number of disabilities among veterans and in the general population.