Our studies focus on understanding how muscle contraction is regulated at the level of the sarcomere in response to Ca2+ and how the regulation is altered in disease states. Most of our work has concentrated on two inherited heart disorders, hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), both of which can be caused by mutations in genes that encode components of the contractile apparatus. More recently, we have started to investigate novel post-translational mechanisms and have begun work on disease mechanisms in inherited skeletal muscle myopathies.
Structure-function approaches: We have investigated how HCM and DCM mutations affect contractile protein structure and function using recombinant proteins (both wild type and mutant) and a range of sensitive biochemical and biophysical assays. Our work has shown how HCM mutations in the thin filament regulatory proteins troponin and tropomyosin increase the Ca2+-sensitivity of regulation whereas DCM mutations in these same proteins cause a decrease. Thus these two different disease states are triggered by opposite changes in contractile regulation at the level of the sarcomere. Using a fluorescent probe attached to troponin C, we have demonstrated that these changes are the result of actual change in thin filament Ca2+ affinity.
Cardiomyocyte studies: To investigate further the impact of cardiomyopathy mutations, we are currently using adenoviral vectors to express mutant contractile proteins in adult cardiomyocyte cultures and assessing the effects on contractility and Ca2+ handling. This is allowing us to test our hypothesis that alteration of thin filament Ca2+ affinity by troponin and tropomyosin mutations will cause significant changes in Ca2+ dynamics which may in turn stimulate disease remodeling pathways.
Novel post-translational modification studies: Components of the myofilament regulatory mechanism, such as troponin I and myosin binding protein-C, are known to be the targets of certain protein kinases (e.g. PKA), and phosphorylation is an established mechanism for modulating contractile activity. We are currently investigating modification of sarcomeric proteins, both by additional protein kinases (e.g. AMPK) and novel post-translational modification mechanisms which may become altered in certain acquired disease states such as ischaemia and diabetes.
Analysis of mutations causing skeletal muscle disease: Mutations in the equivalent skeletal muscle proteins have been shown to cause a spectrum of different skeletal muscle disorders such as nemaline myopathy, distal arthrogryposis and cap disease. We are now assessing the impact of these mutations on contractility and protein structure, and examining whether correlations exist between the functional effect of mutation and the form of myopathy.