Cardiomyopathy is currently the leading cause of death for patients with Duchenne muscular dystrophy (DMD), a severe neuromuscular disease affecting young boys. With no current cure, gene therapy is a promising solution, but supplementation with drug therapies is likely inevitable to fully address the pathology seen in older patients. The use of human-induced pluripotent stem cell (hiPSC) models for drug studies is beneficial due to the direct relevance to human physiology and the potential development of personalized care. Dystrophic hiPSC cardiomyocytes have been shown to exhibit calcium reuptake delays, higher resting calcium levels, and frequent arrhythmias. The Mack Lab previously conducted a preliminary drug screen on healthy and DMD-affected cardiomyocytes and found that certain L-type calcium channel blockers (CCBs) indicated a cardioprotective effect. These drug compounds (namely Nitrendipine and Nimodipine) have been shown to alleviate cardiac fibrosis in patients through vasodilation. In this project, I am validating the beneficial aspects of the drug compounds. I initially hypothesized that treatment of DMD hiPSC cardiomyocytes with L-type CCBs will rescue resting calcium levels and normalize relaxation kinetics. To assess this, I cultured mature hiPSC cardiomyocytes on a Microelectrode Array (MEA) system capable of maintaining physiological conditions while measuring properties of cardiac electrophysiology. The cells were then matured using lactate enrichment to attain further maturity and grown in culture prior to MEA experimentation. Using the MEA, I have found that the QT interval for DMD hiPSC cardiomyocytes was significantly longer than isogenic controls. In current experiments, I am using this platform to validate the effect of L-type CCB compounds of interest in relation to DMD cardiomyopathy. The development of this novel platform may not only have broader implications for DMD drug discoveries and targeted therapies, but it can potentially serve as a powerful preclinical model for other neuromuscular disorders.

Duchenne Muscular Dystrophy (DMD) is a severe muscle wasting disease caused by deficiency of the protein dystrophy and affects approximately 1/3500 boys. Patients have shortened life expectancy due to cardio-respiratory problems caused by the disease alongside impaired ambulatory function. Previous studies have described the “waddling” gait in patients with muscular dystrophy but not in the animal model of DMD. Here we present the characterization of exercise ability and quantified gait metrics in a novel DMDmdx model that better represents DMD in humans. We used the Noldus Catwalk XT motion capture system to identify different gait parameters between DMDmdx and wild-type rats at 14-15 weeks of age. Compared to wild-type rats, DMDmdx has a reduced stride length and swing time in both front paws and hind paws. Time to max contact in DMDmdx rats is 5% faster than wild-type, but max intensity at time of max paw contact is 15% lower in DMDmdx. The “waddling” gait is indicated by 13% higher uses of 3 and 4 paws supported by DMDmdx during a run compared to wild-type. Subsequently, this led to a higher abnormal step pattern as similarly observed in patients with muscular dystrophy due to hip muscle weakness, thus resulting in the “waddling” gait. Gait pattern of the novel DMDmdx rat model reflects the impaired ambulatory function commonly seen in patients with DMD, thus making this a potentially useful outcome for understanding disease progression, therapies, and development of exercise guidelines.