The G-protein coupled apelin receptor and its two endogenous peptide ligands, apelin and Elabela, have emerged as key regulators of cardiovascular development, physiology and disease. It has therefore been suggested that targeting the apelin receptor therapeutically may be beneficial for the treatment of a range of cardiovascular pathophysiologies. Despite this, there is a lack of a suitable human based in vitro system to investigate the cardiac apelin receptor. Human embryonic stem cells (hESCs) represent a powerful tool for modelling as they are amenable to genetic editing and can be induced to differentiate to any cell type. This study aimed to use hESC-derived cardiomyocytes to examine the role of the apelin receptor in cardiomyocyte development and function.

For the first time, hESC-derived cardiomyocytes were found to express the apelin receptor at similar levels to human hearts, indicating suitability for use as a model for investigating the apelin receptor. A novel apelin receptor inducible knockdown system was generated in hESCs. Inducing apelin receptor knockdown throughout differentiation reduced cardiomyocyte differentiation efficiency, and had functional consequences, including disrupted beating pattern and prolonged voltage sensing. Moreover, apelin receptor knockdown in differentiated cardiomyocytes, combined into 3D engineered heart tissues had detrimental effects on contractility, with decreased force generation and increased stiffness observed, accompanied by an increase in collagen deposition. An apelin receptor variant identified from the NIHR BioResource BRIDGE project and previously shown to affect ligand binding was also introduced into hESCs. Again, detrimental effects on hESC-derived cardiomyocyte differentiation and function were observed, similar to that seen with apelin receptor knockdown.

This thesis has characterised the expression of the apelin receptor in hESC-derived cardiomyocytes, and utilised genetic engineering to manipulate apelin receptor expression, identifying a key role for the apelin receptor in hESC-derived cardiomyocyte differentiation and function. This recapitulates what has previously been shown in animal models but in a more clinically relevant model, and offers a potential platform for further characterisation of apelin receptor function. It also offers a system for screening of novel pharmacological compounds for the treatment of heart failure and other cardiovascular diseases.