OUR CURRENT RESEARCH PROGRAMS
1) Mechanisms of pathogenesis in muscular dystrophies.
Multiple muscular dystrophies are caused by mutations in any one of an interlinked group of proteins in the myofiber cell membrane and extracellular matrix. Examples include Congenital Muscular Dystrophy Type 1A (MDC1A, due to mutations in laminin-alpha-2), Ullrich and Bethlem dystrophies (collagen VI), and Limb-girdle Muscular Dystrophy Type 2D (LGMD2D, alpha-sarcoglycan). We have shown that aberrant activation of the Bax-mediated mitochondrial cell death pathway is a significant contributor to pathogenesis in MDC1A models. In addition, we identified the multi-functional protein Ku70 as an important regulator of this pathway. We are now testing the hypothesis that dysfunction in this pathway will underlie pathogenesis in additional diseases, and we are further analyzing upstream and downstream regulators of the pathway and how they respond to disease-causing mutations. We are using this knowledge to develop new therapeutic strategies.
2) Pathogenesis of facioscapulohumeral muscular dystrophy (FSHD).
Our FSHD studies focus on the regulation of expression and mechanism of action of a cytotoxic protein, DUX4-FL, that is aberrantly expressed in the skeletal muscles of FSHD patients. Many of our experiments use cultures of myogenic cells from FSHD patients or muscle biopsies. For example, we are analyzing how DUX4-FL expression leads to pathogenic changes in FSHD myotubes to determine how the diseased cells may differ from myoblasts obtained from healthy people and patients with non-FSHD muscle diseases. Our most recent work has shown that, while DUX4-FL overexpression can lead rapidly to myotube cell death, a lower level of expression, probably more representative of what occurs in muscle, can lead to more subtle pathological changes. In particular, DUX4-FL expression lead to inhibition of protein turnover (altered proteostasis) and nuclear aggregation of the key RNA-binding protein TDP-43. Our findings suggest that FSHD may share pathogenic mechanisms with other diseases (e.g., ALS, inclusion body myopathy) in which similar changes are found.
3) Mitochondria in neuromuscular disease.
Loss of normal mitochondrial function is a key event in many forms of cell death, and is important in neuromuscular disease as shown by our finding that inactivation of Bax, a protein that promotes cell death through the mitochondrial pathway, lessens pathology in models of Congenital Muscular Dystrophy. Accordingly, we have begun a new project designed to identify molecular mechanisms in mitochondrial dysfunction during disease, with a focus on identifying upstream signaling pathways that lead to activation of cell death in diseased nerve and muscle tissues. In addition, we are testing inhibitors of Bax-induced death as potential ameliorative therapies for some neuromuscular diseases.
4) Cell-based therapeutic screens.
Drug screening with human patients’ cells is one of our goals. To overcome the limitations on screening due to the restricted doubling capacity of human cells in culture, we have partnered with Dr. Woodring E. Wright (University of Texas Southwestern Medical School) to generate immortalized versions of laminin-alpha2-deficient human muscle cells. We have shown that these cells continue to show the pathological changes (e.g., aberrant induction of cell death) that are shown by primary cells in cultures. We are now in the process of developing automated screening assays based on reversal of pathology to identify potential therapeutics which can then be validated in additional models.