The contraction of the cardiac muscle cell is generated by the relative sliding of actin-containing thin filaments and myosin-containing thick filaments driven by myosin motors. Until recently the acto-myosin interaction was thought to be regulated only by calcium-dependent structural changes in the thin filaments. However recent studies proposed that the thick filament acts as a mechanosensor that modulates the number of myosin motors in the ON and OFF states depending on the stress applied to the filament backbone and independently of calcium. This mechanosensing mechanism regulates the strength of contraction in each heartbeat and it might be disrupted in cardiac diseases and ageing. Currently, the molecular basis of thick filament mechanosensing has not been elucidated, limiting our understanding of the mechanisms responsible for muscle diseases and ageing.
The aims of the project are:
1. To investigate the myosin-based regulation of heart contractility in animal models, using a novel fluorescence microscopy approach that allows us to measure the changes in conformation of the myosin motors on the thick filament in the smallest contractile organelle of the cardiac muscle cells, called myofibrils.
2. To elucidate the regulation of the myosin motors in the human heart, applying the same microscopy technique to myofibrils isolated from human cardiac samples.
3. To study the changes in the myosin-based regulation associated with ageing, by comparing the regulation of the myosin motors in cardiac myofibrils isolated from young and old donors.
The student will use a combination of muscle mechanics at single-myofibril level and fluorescence microscopy techniques to investigate the mechanism of activation of the thick filament during active contraction and in response to the stretch of the muscle cell, which underpins the Frank-Starling Law of the Heart.
Year 1: The student will learn physiological methods to isolate cardiac myofibrils from the heart of animal models, in which the fluorescent proteins will be introduced for contractile and fluorescence measurements.
Year 2: The student will investigate the effect of calcium and force on the structure of the myosin motors on the thick filament, in the presence and in the absence of myosin-targeting drugs that are currently used for the treatment of heart failure in cardiomyopathies.
Year 3: Finally the student will transfer the methods developed in the previous years to the study of cardiac myofibrils isolated from human hearts from young and elderly donors.