Urotensin II signalling pathway in cardiovascular disease

Abstract

Heart failure (HF) is a global health burden and its prevalence is increasing. Current pharmacological therapies for HF such as inhibitors of the reninangiotensin- system and beta-adrenoceptor antagonists have improved cardiac function and clinical outcomes. However, despite their usefulness, the cardiac remodelling process continues and cardiac hypertrophy and fibrosis ensues. Urotensin II (UII) is a neurohormone that is naturally produced in the body and has a primary role in regulating vascular tone. Circulating levels of UII in HF are significantly increased with reported deleterious effects on the heart and vasculature, thus contributing to the progression of this debilitating disease. However, the signalling pathways involved in mediating these effects have not been thoroughly investigated. Rho kinase (ROCK), soluble epoxide hydrolase (sEH), and reactive oxygen species (ROS) are intracellular mediators involved in the cardiac remodelling process that may translate these UII effects. Therefore, the aim of this thesis was to explore the intracellular pathways that are utilised by UII to exert its detrimental effects on the heart and vasculature. A series of studies were performed including 1) an in vivo study to evaluate the direct effects of chronic UII infusion on the heart, 2) ex vivo studies to examine UII pathways involved in aorta constriction with the use of specific inhibitors, 3) in vitro studies to explore the effects of UII on cardiac cells and the involvement of ROCK, sEH, and ROS. A final clinical study investigated the effect of UII and sEH inhibition on skin microvessel tone in healthy controls and HF patients. Chronic un infusion was shown to cause diastolic dysfunction in rats. Cardiac function was compromised, cardiomyocyte size was increased, and there was increased collagen deposition in the myocardium. These results suggest that chronic exposure to UII has a direct effect on the myocardium in relation to both structure and function, and is involved in the cardiac remodelling process. In vitro studies were performed to support the findings of the in vivo study and to examine potential intracellular pathways involved. Ull increased cardiomyocyte hypertrophy and fibroblast collagen synthesis supporting the in vivo findings. Utilising ROCK and sEH inhibitors, UlI's effects were ameliorated which suggest a role for both ROCK and sEH pathways downstream of UII in cardiac cells. Additional studies demonstrated that UII increased ROS production by these cells, which may contribute to the hypertrophy and fibrosis observed. ROS was reduced with ROCK and sEH inhibitors, suggesting a potentially important role for the ROCK and sEH pathway in the generation of ROS. Ex vivo organ bath studies demonstrated that potent vascular effects of UII on rat thoracic aorta may be mediated by ROCK but not sEH, suggesting a role for ROCK in the pathophysiology of vascular dysfunction leading to HF. Finally, a clinical study involving a cohort of healthy control subjects and HF patients investigated the effect of UII on skin microvessel tone using iontophoresis, a non-invasive technique to deliver drugs transdermally. Ull decreased flux in HF patients whilst administration of a sEH inhibitor significantly increased flux demonstrating the therapeutic potential of sEH inhibitors to overcome increased vascular tone. Together, this thesis demonstrates the direct contribution of UII to the cardiac remodelling process leading to HF. The intracellular signalling pathways involved in mediating these effects include ROCK, sEH, and ROS and may represent potential therapeutic targets for HF treatment.