Regulation of Muscle Stem Cells in Regeneration

Heterogeneity of stem cell populations

Skeletal muscle stem cells (MuSCs), or satellite cells, are essential for skeletal muscle growth, maintenance, and regeneration throughout life. MuSCs isolated from aged mice exhibit significant heterogeneity. We have discovered a dysfunctional MuSC subset arises with aging that through paracrine signaling impairs the proliferative potential of a resilient functional subset. CD47 is a marker on the MuSC membrane whose differential expression distinguishes dysfunctional and functional stem cells. Our current objectives are to characterize CD47 signaling during aging and understand how it arises. We are also developing a potential therapeutic designed to target the dysfunctional MuSC subset and enhance the resilient minority. Expanding an existing functional MuSC population rather than alteration of a dysfunctional population is a novel therapeutic approach and could benefit a wide variety of conditions.

Identification of stem cells and novel progenitor populations by CyTOF

Mapping the muscle stem cell niche

To understand the spatial relationships between the different cell types that make up the muscle, we have optimized multiplexed tissue imaging (CODEX). CODEX allows the identification of cellular neighborhoods. It is ideally suited to study signaling by secreted factors in the local microenvironment because it allows the identification of the cells upon which these factors act. Further, alterations in these relationships can be studied in response to perturbations such as injury, an antibody, or pharmacological intervention. We can visualize lo-calization of up to 60 proteins on single sections of skeletal muscle using antibodies labeled with unique DNA barcodes that are imaged three at time in an iterative process.

Iterative imaging of muscle by CODEX

Lineage tracing of stem cell fate decisions

MuSCs undergo asymmetric division.  The arsenal of fates a stem cell can access is used by tissues to maintain homeostasis and regenerate thanks to a tightly controlled network of biochemical and biophysical cues. We are developing a dynamic fluorescence time-lapse experiment to evaluate the effects of different conditions on MuSCs fate determination kinetics. Relying on quantified binary signal from the transcription factor Pax7, typical of MuSCs, and myogenin, characteristic of committed myogenic progenitors, we have monitored and classifed division in the three main types and and are comparing different cytokines’ effects on the fate determination scenarios of MuSCs.

Complete lineage tree of MuSC treated with PGE2