Phenotypic Analysis of Human ES Cell-Derived Muscle Stem Cells
We study human muscle development, and are actively investigating potential cell-based therapies for the treatment of degenerative muscle diseases, such as muscle dystrophy. This project will define the pathway that muscle stem cells follow as they form new muscle, and identify which muscle stem cells are most useful for therapy. Our approach will be to examine human embryonic stem cells as they become muscle stem cells and mature muscle in culture, to define the stages of normal muscle development. We will then transplant these stem cells at various stages of development into the leg muscles of mice with muscular dystrophy, and study how these cells become new muscle tissue, how this impacts the animals’ ability to exercise, and the strength of the treated muscles. Our goal for this research is to fully understand the normal process of human muscle stem cell development, and to identify specific stem cells that provide therapeutic benefit when transplanted into dystrophic muscle.
Muscular dystrophies are profoundly debilitating disorders that affect more than 1 in 3,500 male births. They comprise a group of genetic diseases that cause progressive weakness and damage to skeletal muscle resulting from abnormal proteins critical to muscle health. These abnormal proteins are thought to predispose muscle to damage from normal activity, leading to premature depletion of normal muscle stem cells that maintain muscle health during normal use. This research will identify human embryonic stem cells that are able to repair damaged muscle, thereby providing a new approach to therapy for patients with muscle disease. The medical treatments developed as a result of these studies will not only benefit the health of Californians with muscular dystrophy and other degenerative muscle diseases, but also should result in significant savings in health care costs. This research will push the field of muscle regenerative medicine forward despite the paucity of federal funds for embryonic stem cell research, and better prepare us to utilize these funds when they become available in the future.
The overall goal of this project was to use hESCs to define the cellular and functional phenotypes of human muscle stem cells as they differentiate along the muscle lineage, and specifically evaluate their ability to augment tissue and function of dystrophic muscle. Toward this goal, we have evaluated one muscle-specific reporter hESC line, generated a second line using another muscle-specific promoter, developed three alternative methods for directing myoblast differentiation from hESCs in culture, and piloted injections of hESC-derived myogenic precursor cells into hind limb muscle of immunodeficient mice.
Muscle cells derived from human embryonic stem cell (hESC) can be potential source for cell therapy to regenerate muscular diseases. The focus of this grant has been to develop efficient methods for isolating muscle stem cells from hESCs that avoid animal products so that we can use these to both understand how muscle cells form, and determine which of these may be best for treating muscular dystrophy.
Our progress over the past year has significantly advanced the aims of this work: 1) Determine the cellular phenotypes of human muscle stem cells as they differentiate into myoblasts, and 2) Determine the ability of human muscle stem cells at different stages of development to engraft, proliferate and differentiate into muscle in a mouse model of muscular dystrophy, and determine their functional and myo-mechanical effects on dystrophic muscle. We now have a working system to derive early progenitor muscle cells from human embryonic stem cells. The differentiation protocol has been developed sufficiently such that skeletal muscle cells can be generated from human ES cells. We have identified points along the differentiation process at which muscle cells that are less mature and possibly more stem-like are prevalent. The data suggests that based on the genes the cells express at early stages, isolation and transplantation of cells at that stage but not further along will be most beneficial for transplantation and clinical application. This brings us a step closer to obtaining useful muscle cells that can be transplanted to treat muscle disorders. The current plan is to test these cells in muscle injury preclinical models to evaluate their capacity to regenerate injured muscle.