Muscle mass, function, and tissue repair after injury decrease with aging in skeletal muscle. Autophagy appears to play a critical role, but what the effects might be are still controversial. Confounding factors are the multiple types of cells present in the muscle (e.g. muscle fibers, satellite cells, macrophages), which may have different autophagy requirements, and how the autophagy machinery targets specific organelle types (e.g. mitochondria or lipid droplets). It is not known how autophagy changes in coexisting cell types in the aging skeletal muscle, how prevalent are organelle-specific autophagy, and whether there is coordination between organelle-specific autophagy types. Techniques to pinpoint to the molecular and cellular pathways behind the changes observed in complex tissues and co-existing forms of autophagy are not readily available. In order to address some of the current technological limitations, this application proposes the development and use of mass cytometry to carry out single cell proteomics and individual organelle capillary electrophoresis to investigate organelle populations of autophagy in aging skeletal muscle.
The aims of this proposal are: (1) Establish mass cytometry strategies to monitor at the single cell level autophagy-related molecular changes in muscle fibers, macrophages, and satellite cells. (2) Establish individual-organelle capillary electrophoretic strategies that selectively describe lipophagy and mitophagy in muscle fibers, macrophages, and satellite cells. (3) Define changes in lipophagy, mitophagy and global autophagy in a murine model of aging under basal and tissue injury/repair conditions using the methodologies developed under Aims 1 and 3. Completion of the proposed work will provide new technological advances to fine tune the characterization of autophagy and will provide more concrete answers to the controversial role of autophagy in the aging of the skeletal muscle system.
Loss of muscle mass and function that occurs in aging compromises physical performance, lifestyle, and recovery after injury for half of those in their late seventies or older. Autophagy (degradation of cellular components) appears to play a role in the changes observed in the muscle system. This application proposes the development of new methodologies to understand the cell types involved in those changes and define in those cells how the degradation of their cellular components is affected by aging.
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