Investigation of the roles of calcium-dependent proteases in muscle damage and disease

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Muscle strength is important to the health and well-being of everyone. Skeletal muscle weakening occurs as a result of certain disease states, aging and prolonged inactivity due to illness-injury-surgery. This can result in the loss of normal activity and mobility and an increased incidence of falls and accidents, which impact considerably on health care costs. There is a family of proteins called calpains that have been linked to a number of factors affecting muscle function, however it is not known how they are involved. Calpains are proteases, ie. they destroy other proteins, and they are regulated by the concentration of calcium inside a cell. The calcium concentration increases dramatically inside a muscle cell when it contracts. Inside a muscle cell it is important that there is tight regulation of the calpains to avoid them being activated inappropriately during normal use and causing muscle damage. In certain disease states, such as types of muscular dystrophy, it is known that the calcium concentration within resting muscle fibres is increased compared with healthy muscle fibres. We propose that as a consequence of this, the calpains will be less regulated and will cause damage to the muscle, which contributes to the muscle weakness seen in these diseases. Whilst calpains have been implicated with symptoms associated with muscle dystrophies, the role they play is certainly unclear. The objectives of our research proposal are to understand what factors influence i) where the calpains are located and ii) when and how much they are activated, within muscle fibres. We will compare this in healthy muscle and muscle from mdx mice, an animal model of Duchenne muscular dystrophy.