Munchen Liu (Advisor: Chunru Lin, PhD)

Evaluation of myogenic differentiation potential of BMD iPSCs in vitro and the effect of ubiquitination inhibition on dystrophin stability in vivo

Background: Muscular dystrophies are heterogeneous groups of inherited diseases leading to progressive muscular weakness and degeneration. In the case of Becker muscular dystrophy (BMD), non-disrupting mutations of the DMD gene reading frame is the causative defect. By the age of 30s, about 60 to 70% of BMD patients develop cardiomyopathy, which is often lethal. Unfortunately, there is currently no cure for BMD. Meanwhile, improvement of dystrophin stability by repressing polyubiquitination is a promising strategy. The application of human iPSCs in tissue regeneration also serves as a potential therapeutic strategy. This study aimed to test the efficacy of selected drugs interfering with the dystrophin polyubiquitination using BMD iPSCs as the model system. The hypothesis is that myogenic differentiation of the BMD iPSC-derived myogenic progenitors can be improved after polyubiquitination inhibition.

Methods: The in vitro studies included evaluation of myogenic cell proliferation and differentiation using BMD and control iPSCs to identify affected phenotypes. These were done by measuring proliferation rate, myogenic marker quantification, gene expression profiling, and cell cycle analysis.  The in vivo studies were by transplanting BMD iPSC-derived myogenic progenitors into immune-deficient NSG mice with daily treatment of selected polyubiquitination inhibitors. Muscle cryosections will be studied for quantification of donor cell engraftment and dystrophin expression.

Results & Progress: The in vitro data indicates reduced myogenic potential of BMD-iPSCs, as well as defective cell cycle, proliferation, and differentiation, when compared to healthy iPSCs. In addition, Muscle sections from the BMD-iPSC engrafted mice treated with the selected ubiquitination inhibitors demonstrated significantly higher percentage of human cell engraftment expressing dystrophin, indicating the efficacy of the treatment.

Conclusions: Inhibition of ubiquitination significantly improves the BMD iPSC-derived myogenic engraftment with improved dystrophin expression. The study provides a new therapeutic strategy that utilizes human iPSCs transplantation and molecular medicine.

Advisory Committee:

• Chunru Lin, PhD, Chair
• Radbod Darabi, MD, PhD
• Ali Azhdarinia, PhD
• Xuelian Huang, PhD
• Hamed Jafar-Nejad, MD

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