Abstract
Introduction
DMD, an X-linked muscle degenerative fatal disease, is caused by mutations in the dystrophin gene. Dilated cardiomyopathy (DCM) is a major cause of morbidity and mortality in DMD patients. Treatments for DCM in DMD are limited to steroids and standard heart failure medications such as β-blockers and ACE-inhibitors, and therefore novel therapeutic modalities are urgently needed.
Purpose
We hypothesized that dystrophin mutations in DMD lead to cardiomyopathy-causing bioenergetic/metabolic impairments, which can be therapeutically targeted for improving cardiac function.
Methods
Induced Pluripotent Stem Cell-derived cardiomyocytes (iPSC-CMs) were generated from healthy volunteer and 3 DMD patients: young male (YM), adult male (AM) and adult female (AF). We investigated the bioenergetics, electrophysiology, mitochondrial and metabolic features of healthy and DMD iPSC-CMs using the Seahorse Flux analyzer, patch clamp, confocal fluorescence microscopy and Liquid chromatography mass spectrometry (LC-MS) technologies, respectively.
Results
To test the hypothesis, we measured respiration and glycolytic rates of healthy and DMD iPSC-CMs. Compared to healthy iPSC-CMs, in both AM and AF DMD, but not in YM DMD cardiomyocytes, there was a 75% decrease in ATP production, and 80% and 45% decrease in basal respiration, respectively. In agreement with the healthy-like bioenergetic status of YM, the iPSC-CMs showed no arrhythmias, in contrast to the prominent arrhythmias in AM and AF cardiomyocytes. To determine whether the impairment in the phosphorylation pathway (OXPHOS) affects glycolysis, we measured the cardiomyocytes' response to glycolytic stress test. These experiments showed that the glycolytic rates were similar in healthy and DMD iPSC-CMs. In agreement with impaired OXPHOS, mitochondrial activity measured by 3D life confocal microscopy was attenuated in the DMD male by 35%, compared to healthy cardiomyocytes. Furthermore, the metabolomic LC-MS analyses demonstrated significant differences in metabolite levels in YM, AM and AF DMD iPSC-CMs relative to healthy iPSC-CMs. For example, compared to healthy iPSC-CMs, there was a dramatic fall to undetected levels in phosphocreatine in both AM and AF, but not in YM DMD, indicating a dysfunctional phosphocreatine energy system.
Conclusions
DMD iPSC-CMs exhibit bioenergetic/metabolic impairments, which constitute novel targets for alleviating the cardiomyopathy in DMD patients.
Funding Acknowledgement
Type of funding source: Public grant(s) – National budget only. Main funding source(s): ISF - Israel Science Foundation
mTOR and differential activation of mitochondria orchestrate neutrophil chemotaxis
