Role of CDA1 In Vascular Diseases

Atherosclerosis is a major cause of mortality and morbidity globally. It is a complex chronic disease involving inflammatory and fibrotic processes. Diabetes is considered a risk factor for atherosclerosis development due to its promotion of inflammatory and fibrotic pathways.

Our group had previously discovered elevated levels of CDA1 (Cell division autoantigen 1) in atherosclerotic aortas from diabetic ApoE knockout mice. Further investigation revealed the ability of CDA1 to regulate extracellular matrix production through modulation of TGFb/Smad2,3 signalling in VSMCs. These studies indicated that CDA1 may play a role in regulating vascular fibrosis in atherosclerosis. To extend our understanding of the potential role of CDA1 in atherosclerosis, this study investigated the role of CDA1 on another important atherosclerotic factor, inflammation, particularly in endothelial cells. In addition, mechanisms regulating CDA1 were also explored in this study.

To achieve the study goals described as above, a series of in vitro and in vivo studies were conducted. The in vitro studies involved the use of normal endothelial cells, as well as endothelial cells in which approaches were used to knockdown CDA1 under conditions of hypoxia, TNFa, VEGF and its inhibitor V1. The in vivo arm of the study involved the generation of a unique ApoE/CDA1 dKO (double knockout) mouse strain which was rendered diabetic by Streptozotocin (STZ), and used as a model of diabetes accelerated atherosclerosis.

In vitro results showed significantly increased CDA1 mRNA and protein levels in human umbilical vein endothelial cells under hypoxic conditions and VEGF treatment. The VEGF inhibitor, V1 was able to attenuate these increases in CDA1 expression in human endothelial cells. Retrovirus delivery of a specific siRNA (shRNA) to knockdown CDA1 in the endothelial cell line EA.hy926 cells attenuated the expression of TNF-α stimulated inflammatory markers such as MCP-1 and VCAM-1 by ~50%. Knockdown of CDA1 also resulted in reduced monocyte adhesion to TNF-α treated EA.hy926 cells.

In vivo studies revealed that diabetic CDA1/ApoE double knockout mice (dKO) had enhanced atherosclerosis despite reduced extracellular matrix (ECM) production and accumulation including Collagen I, III and IV in the aortas when compared to diabetic ApoE KO mice. There was increased atherosclerotic plaque development in the aorta, as well as the development of aortic aneurysms in the diabetic CDA1/ApoE dKO mice (10 out of 25 mice). There was also increased matrix metalloproteinases activity, aggressive immune cell infiltration from the adventitial to the medial layer of the aorta, and elastin depletion at sites of aneurysm in diabetic CDA1/ApoE dKO mice. To explore the potential clinical relevance of these findings, real time PCR revealed reduced CDA1 mRNA level (~70%) in human abdominal aortic aneurysm (AAA) biopsy samples when compared to the aorta from healthy controls.

In conclusion, CDA1 is regulated by hypoxia and VEGF stimulation. While the pro-fibrotic role of CDA1 in atherosclerosis is confirmed, its role in inflammation in atherosclerosis requires further investigation. Interestingly, CDA1 deficiency increased the risk of aneurysm development in diabetic CDA1/ApoE dKO mice due to enhanced matrix degeneration as a result of increased activity of MMPs and an aggressive local inflammatory response. The discovery of reduced CDA1 expression in human AAAs further suggests a potentially protective role of CDA1 against aneurysms. Further research to better understand CDA1’s role in aneurysm development may provide valuable knowledge in developing therapeutics to target CDA1 for the treatment of aneurysms.