Alex CY Chang1,2,3, Gaspard Pardon3,4,5, Andrew CH Chang1,2,3, John W Day4, Joseph C Wu2,3, Beth Pruitt3,5,6, Helen M Blau1,3
1 Baxter Laboratory for Stem Cell Biology, Microbiology and Immunology, Stanford, CA; 2 Cardiovascular Medicine, Stanford, CA; 3 Stanford Cardiovascular Institute, Medicine, Stanford, CA; 4 Department of Neurology, Medicine, Stanford, CA ; 5 Department of Bioengineering at Stanford University, Stanford, CA; 6 Department of Mechanical Engineering at Stanford University, Stanford, CA
Introduction: Duchenne muscular dystrophy (DMD) is a lethal X-linked recessive disease that results from mutations in the dystrophin gene and is the most common myopathic disease in humans with a prevalence of one in every 3500 males. Dystrophin is crucial for the formation of a dystrophin-glycoprotein complex, which connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix in both skeletal and cardiac muscles. In the heart, loss of dystrophin leads to increased fibrosis and death in the third decade of life due to dilated cardiomyopathy. Previously we showed that cardiomyocytes in patients with DMD had telomeres 50% the length of unaffected controls. Notably, shortening was not observed in smooth muscle cells.
Hypothesis: We hypothesize that contractile defects due to dystrophin deficiency drive telomere shortening and result in metabolic compromise and cell death due to inhibition of mitochondrial function and biogenesis.
Method: To study telomere shortening in the course of disease progression, we differentiated DMD human induced pluripotent stem cell line into beating cardiomyocytes (hiPSC-CMs) as a model.
Results: We observed aberrant calcium handling and decreased contractility using bioengineered micropatterned hydrogel traction force microscopy. Here we present new evidence where aberrant contraction results in telomere deprotection and resection in in non-dividing hiPSC-CMs. Induction of DNA damage response culminated in mitochondrial dysfunction and apoptosis.
Conclusions: Patient hiPSC-CMs recapitulate in 30 days the telomere shortening that occurs in 30 years of life in DMD patients and this technology enables the study of cause and effect and tests of interventions.