Molecular determinants of stem cell fate during hPSC differentiation into skeletal muscle
Facioscapulohumeral muscular dystrophy (FSHD) is the third most common of the major muscular dystrophies affecting 1 in 20,000 individuals. In most cases, FSHD is associated with a reduction in the number of repeat sequences on human chromosome (hchr) 4q. Loss of DNA organization in the region is thought to affect expression of nearby genes causing FSHD. The gene encoding the transcription factor REX-1 is located in this region. The role of REX-1 in the etiology of FSHD or skeletal muscle development has not been fully explored. The hypothesis to be tested is that over-expression of REX-1 affects muscle development and/or regeneration, and contributes to the pathology observed in FSHD. To determine whether REX-1 could be a key regulator of muscle development it will be necessary to assay REX-1 expression through all stages of muscle development. But many stages of human muscle development that occur during embryonic and fetal development are inaccessible. Therefore, to examine embryonic and fetal stages of muscle development we will use a novel approach taking advantage of newly developed methods for modeling muscle development by isolating muscle precursors from human embryonic stem cells (ESCs). The results of the studies proposed here will delineate the role of REX-1 in muscle development and its role in regulating a signaling pathway required in muscle development. To test the novel hypothesis that inappropriate expression of REX-1 during development of skeletal muscle contributes to the pathology observed in FSHD, we will also make use of induced pluripotent stem (iPSCs) made from FSHD and control fibroblasts and myoblasts. These cells will then be induced to differentiate to compare muscle development and gene expression in FSHD to that of normal controls. To further test whether REX-1 over-expression contributes to FSHD pathology, we will reduce REX-1 expression in FSHD iPS cells to attempt to normalize FSHD pathology and increase REX-1 expression in control iPS cells to test the idea that REX-1 contributes to FSHD pathology. Determination that REX-1 regulates muscle development and altered expression of REX-1 causes muscle pathology would be a major step forward in our understanding of a molecular mechanism underlying cellular differentiation and human disease. FSHD iPSCs will also provide an important reagent to fill vital gaps in our knowledge of the molecular mechanism of the disease as well as provide a novel reagent to identify drugs to treat FSHD.
Facioscapulohumeral muscular dystrophy (FSHD) is third most common type of muscular dystrophy affecting about 1 in 20,000 individuals. The age of onset is about age 20. The disease begins with weakness and wasting of muscles around the eyes, mouth, shoulder blades and upper arms and progresses relatively slowly spreading to the legs and abdominal region. In most cases, affected individuals have a normal life span. The impact of this disease on affected individuals and their families is significant and long-lived, both financially and emotionally. The cost to the state of California directly is equally long-lived. At the present time, an effective treatment does not exist, in part, because even after many years of investigation, the disease mechanism is still unknown. This lack of understanding of the disease mechanism has made development of effective treatments difficult. The studies in this proposal will fill vital gaps in our knowledge of the molecular mechanisms that control muscle development and how these mechanisms could go awry in neuromuscular diseases such as FSHD. We will use human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) to dissect the molecular pathways that regulate muscle development. These pluripotent cells differentiate into all cells in the body providing a unique tool to identify, isolate and characterize specific muscle precursor populations in human development. The results of our studies could constitute a major step forward in our understanding of a molecular mechanism underlying cellular differentiation and human disease. In addition, the FSHD iPSCs generated in this study will provide an important reagent to develop drugs to treat FSHD.