Mass Cytometry to Delineate the Human Muscle Stem Cell Hierarchy and Dysfunction in Aging
Aging is characterized by a decline in skeletal muscle mass and strength (sarcopenia), coupled with an accumulation of fat tissue, impairing mobility and quality of life in 45% of individuals over 65 years of age. In aged mice, the regeneration defect arises in part from a diminished regenerative capacity of resident muscle stem cells (MuSCs). The goal of this proposal is to characterize muscle stem cell subsets residing in human skeletal muscle tissue and investigate the mechanisms responsible for their regenerative defects in aging. We will capitalize on two cutting edge technologies, single-cell bioengineered stem cell niches, which will allow tracking individual muscle cell fates, and multi-dimensional single-cell mass cytometry, which will allow resolution of the molecular characteristics of skeletal muscle cells from aged humans with detail previously unattainable. We expect that this combined approach will elucidate the functional defects observed in aged MuSC populations and therefore facilitate the development of a therapeutic agent to target muscle stem cells for the treatment muscle weakness in aged humans.
The state of California is the front-runner in stem cell research, having gathered not only private investments, as demonstrated by the numerous biotechnology companies that are developing innovative tools, but also extensive public funds via Prop 71, that allows the state, through CIRM, to sponsor stem cell research in public and private institutions. In order to preserve its leadership position and encourage research on stem cells, the CIRM is calling for research proposals that could lead to significant breakthroughs or the development of technologies useful for studying stem cells in order to improve human health. Aging is characterized by a decline in tissue function and regenerative capacity that leads to degeneration and loss of muscle mass and strength (sarcopenia). Muscle stem cells (MuSCs), also known as satellite cells, are responsible for the maintenance and regeneration of skeletal muscle mass. Several studies have shown a decrease in MuSC function in aged mice. However, the mechanisms responsible for their reduced function are not yet defined. The work we propose here focuses on human muscle and discerning differences among subsets of muscle stem cells. The results will facilitate the development of targets to augment a muscle stem cell based therapy to treat muscle weakness in aged humans.
Aging is characterized by a decline in skeletal muscle mass and strength, coupled with accumulation of fat tissue, impairing mobility and quality of life in 45% of individuals over 65 years of age. While muscle stem cells (MuSCs) have a remarkable capacity to maintain and repair skeletal muscle throughout adulthood, they decline in regenerative capacity during aging. The goal of this proposal is to elucidate dysregulated functions of MuSCs in human aged tissues and identify pharmacological targets to enhance the function of dysfunctional subsets or amplify the residual functional subsets. During the first 12 months of this grant period we have made significant advances toward the aims that will allow us to address the remaining aspects of the goals of the grant.
We have, for the first time, achieved:
Identification of novel subsets within the human muscle stem/progenitor cell population using multidimensional single-cell mass cytometry (CyTOF);
Prospective isolation of a fully functional human muscle stem cell population;
Demonstration that human muscle stem cells regenerate injured muscle fibers following transplantation into NSG mice;
Verification that engrafted human muscle stem cells home to the stem cell niche and respond to muscle injury, thereby constituting a stem cell reservoir to meet future needs for regeneration;
Observed that the number of human muscle stem cells decrease in aged muscle tissue.