AbstractThe long saphenous vein (LSV) is commonly used as a conduit in coronary artery bypass grafting (CABG); however, long term patency remains limited by the development of intimal hyperplasia and superimposed atherosclerosis. Upon engraftment of the LSV, there is a necessity to accommodate a vastly increased flow rate and wall shear stress, the effect of which, remains poorly defined. Venous endothelial cell (vEC) activation induced by vein harvest and the acutely altered shear stress rates (or acute high shear stress (AHSS) at 12dyn/cm2) is thought to be pivotal for development of later-stage pathologies, but little is known about the signalling pathways involved. In this thesis, the involvement of two transcription factors, NF-κB and Nrf2, in vEC activation were assessed in the context of AHSS.
Firstly, NF-kB was activated in the LSV endothelium and HUVECs, in response to AHSS. This was further supported by the detection of AHSS-induced NF-kB target inflammatory genes including MCP-1, which was reduced with NF-kB inhibition prior to the onset of AHSS. Additionally, AHSS enhanced monocyte adhesion to the endothelium, in vitro and ex vivo, and reduced endothelial cell-cell contacts, both of which were reversed with NF-kB inhibition prior to the onset of AHSS. The second aim was to promote cellular defence prior to the onset of AHSS, through activation of the Nrf2-Keap1 antioxidant regulatory system. In response to AHSS in vitro, there was an Nrf2 target gene transcriptional response; however, not induced by increased Nrf2 translocation, but rather, increased dissociation from and nuclear export of Keap1. When Nrf2 was pre-activated, however, far from preventing the pro-inflammatory response to AHSS, the inflammatory response of venous ECs was increased. This contradictory finding appears to be mediated in part by the dysregulation of Keap1 under AHSS, suggesting that this cellular defence system is not a suitable target in the treatment acute vein graft inflammation.
Pharmacological modulation of vein graft patency has proven to be exceedingly difficult, with the identification of suitable targets providing the primary hurdle, due to the complex disease aetiology and multicellular pathology. This thesis, provides evidence that inhibition of acute EC activation and inflammation as a result of AHSS may represent an exciting and unexplored strategy for improving vein graft outcome, with the NF-κB transcription factor emerging as a potential target for localised inhibition prior to grafting.
|Date of Award||25 Sep 2018|
|Supervisor||Sarah J George (Supervisor) & Mustafa Zakkar (Supervisor)|