Background:
The double hit of an increasingly sedentary lifestyle combined with an extended lifespan has led to a lengthened period of ill health in old age. A key contributor this is the loss of muscle mass and strength (sarcopenia), which drastically affects quality of life and increases risk of serious injury.
Perhaps the most promising treatment for muscle decline is exercise. Despite intensive research, the precise mechanisms underlying the benefits of exercise remain unclear. We recently published a study exploring a novel aspect of this problem: the effect of exercise on muscle nuclei. Nuclei are the parts of the cell that house the genome, the molecular instructions for making proteins that perform the major cellular functions.
Using inactivity as a paradigm of a sarcopenic trajectory in young and old humans we showed for the first-time aberrant changes of muscle nuclei in sedentary individuals compared to active counterparts. Specifically, muscle nuclei adopted more ovoidal shapes in young and old sedentary individuals. These nuclei also had alterations in arrangement of structural proteins and were less resistant to stretching. We probed these effects in mice, showing that exercise resulted in nuclei that were physically stiffer, analogous to our human findings.
Techniques:
Super-resolution imaging, isolation of muscle bundles, nanoindentation
Objective:
The overall objective of this proposal is to characterise novel alterations in muscle nuclei in individuals on sarcopenic vs. healthy trajectories and explore their functional relevance. To achieve this objective we propose the following:
Aims:
Aim 1: Using high-resolution microscopy we will reveal how various structural proteins surrounding the nucleus are altered. We will also assess changes deeper inside nuclei, since altered nuclear shape and structural proteins likely affects gene activation.
Aim 2: The physical properties of muscle nuclei will be probed in humans and sarcopenic mice. Muscle fibres will be isolated and the dynamics of nuclear shape will be measured during muscle contraction and relaxation.
Workplan:
Year 1: Isolation of muscle bundles and pilot imaging. Setup of mouse exercise training.
Year 2: Super-resolution imaging of human and mouse muscle fibres
Year 3: Nanoindentation of myonuclei in human muscle fibres
Year 4: Immunoblotting of muscle fibres and writing up thesis (6months).
Outline of rotation project: Isolation of muscle bundles and immunofluorescence staining
