We have found that long telomeres protect mice from genetic cardiac diseases analogous to those found in humans, such as Duchenne muscular dystrophy (DMD). Mice lacking dystrophin, similar to patients with DMD, exhibit only mild disease. In contrast, mice that lack dystrophin and have “humanized” telomere lengths (mdx 4cv /mTR G2 ) fully manifest both the severe human skeletal muscle wasting and cardiac failure typical of DMD. Remarkably, telomere shortening accompanies cardiac development even after cardiomyocyte division has ceased. This chronic proliferation-independent shortening in dystrophin-deficient cardiomyocytes is associated with induction of a DNA damage response, mitochondrial dysfunction, increased oxidative stress, and metabolic failure. Our findings highlight an interplay between telomere length and mitochondrial homeostasis in the etiology of dystrophic heart failure.

Abstract

Duchenne muscular dystrophy (DMD) is an incurable X-linked genetic disease that is caused by a mutation in the dystrophin gene and affects one in every 3,600 boys. We previously showed that long telomeres protect mice from the lethal cardiac disease seen in humans with the same genetic defect, dystrophin deficiency. By generating the mdx4cv/mTRG2 mouse model with “humanized” telomere lengths, the devastating dilated cardiomyopathy phenotype seen in patients with DMD was recapitulated. Here, we analyze the degenerative sequelae that culminate in heart failure and death in this mouse model. We report progressive telomere shortening in developing mouse cardiomyocytes after postnatal week 1, a time when the cells are no longer dividing. This proliferation-independent telomere shortening is accompanied by an induction of a DNA damage response, evident by p53 activation and increased expression of its target gene p21 in isolated cardiomyocytes. The consequent repression of Pgc1α/β leads to impaired mitochondrial biogenesis, which, in conjunction with the high demands of contraction, leads to increased oxidative stress and decreased mitochondrial membrane potential. As a result, cardiomyocyte respiration and ATP output are severely compromised. Importantly, treatment with a mitochondrial-specific antioxidant before the onset of cardiac dysfunction rescues the metabolic defects. These findings provide evidence for a link between short telomere length and metabolic compromise in the etiology of dilated cardiomyopathy in DMD and identify a window of opportunity for preventive interventions.