Understanding the functional implications of differential integrin expression in cardiomyocytes

• Main Author: Hawkes, Will
• Format: Dissertation
• Language: English
• Published: King's College London 2020

Integrins are one of the major proteins that cells utilise to adhere to their extracellular matrix (ECM). Although integrins do not possess any catalytic capacity themselves, they facilitate and orchestrate the assembly of mechanically sensitive signalling hubs which provide essential cues to guide and inform cell behaviour. Within the heart, integrins are found in specialised adhesion structures called costameres which provide a physical link between the contractile sarcomere and the ECM. Via proteins such as vinculin and talin, integrin signalling has been reported to play a key role in developmental and diseased processes such as rigidity sensing and hypertrophy. Importantly, cardiomyocyte integrin expression is tightly regulated during development and diseased states where fibronectin binding integrin subtypes become dominant, whereas laminin binding subtypes are predominant in the healthy adult heart. Currently, the implications of this dynamic integrin expression profile for integrin signalling and cardiomyocyte behaviour is not well understood. Thus the aim of this thesis was to conduct a comparative investigation of cardiomyocyte spreading, morphology and contractility when cultured on fibronectin or laminin ligands. Initial investigations utilising PDMS substrates, nanopillar arrays and ligand micropatterning revealed that cardiomyocyte cultured on fibronectin exhibit greater spreading, contractility and vinculin enrichment than cells cultured on laminin. From these results, it was hypothesised that changes in integrin subtype expression may result in differential integrin signalling pathways. To understand the underpinning molecular mechanisms of these observations, we sought to investigate integrin clustering via the implementation of a DNA origami ligand nanopatterning platform. The results revealed key differences in the integrin clustering dynamics of fibronectin and laminin binding subtypes. This data provide new insights into the molecular mechanisms of integrin signalling in cardiomyocytes and advances our understanding of their role in development and disease.