Background Nearly-universal cardiomyopathy in Duchenne muscular dystrophy (DMD) contributes to heart failure and death. As DMD patients show myocardial fibrosis well before functional impairment, we postulated that earlier treatment using drugs with anti-fibrotic effect may be beneficial. Methods and Results Three groups of 10 utrn+/−;mdx or “het” mice with skeletal myopathy and cardiomyopathy that closely mimics clinical DMD were studied. One het group received spironolactone and lisinopril starting at 8 weeks-of-life (het-treated-8), a second received the same starting at 4 weeks-of-life (het-treated-4), and the third het group was untreated. At 20 weeks, all mice had normal EFs though circumferential strain rate was abnormal (−0.21±0.08) in untreated hets. This improved to −0.40±0.07 in het-treated-8 mice (p=0.003), and further improved to −0.56±0.10 in het-treated-4 mice (p=0.014 for het-treated-4 vs. het-treated-8). Treated mice showed less cardiomyocyte damage, with a 44% reduction in intra-cardiomyocyte serum IgG localization in het-treated-8 mice (p<0.0001), and further 53% reduction in het-treated-4 mice (p=0.0003 vs. het-treated-8); matrix metalloproteinases were similarly reduced. Cardiac, limb and diaphragm function by ex vivo muscle testing remained at 80% of normal with early treatment compared to a decline to 40% of normal skeletal muscle function without treatment. Conclusions These findings offer clinically-available medications with proven anti-fibrotic effect as a new therapeutic strategy in DMD. Early initiation greatly attenuated myocardial disease and, for the first time with these drugs, improved skeletal myopathy. Thus, early initiation of such agents warrants further clinical evaluation to maintain ambulatory, respiratory and cardiac function for DMD and related myopathies.

SUMMARYAmyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that, for ~80% of patients, is fatal within five years of diagnosis. To better understand ALS, animal models have been essential; however, only rodent models of ALS exhibit the major hallmarks of the disease. Here, we report the generation of transgenic zebrafish overexpressing mutant Sod1. The construct used to generate these lines contained the zebrafish sod1 gene and ~16 kb of flanking sequences. We generated lines expressing the G93R mutation, as well as lines expressing wild-type Sod1. Focusing on two G93R lines, we found that they displayed the major phenotypes of ALS. Changes at the neuromuscular junction were observed at larval and adult stages. In adulthood the G93R mutants exhibited decreased endurance in a swim tunnel test. An analysis of muscle revealed normal muscle force, however, at the end stage the fish exhibited motoneuron loss, muscle atrophy, paralysis and premature death. These phenotypes were more severe in lines expressing higher levels of mutant Sod1 and were absent in lines overexpressing wild-type Sod1. Thus, we have generated a vertebrate model of ALS to complement existing mammal models.

Rationale Duchenne muscular dystrophy (DMD) is a severe inherited form of muscular dystrophy caused by mutations in the reading frame of the dystrophin gene disrupting its protein expression. Dystrophic cardiomyopathy is a leading cause of death in DMD patients and currently no effective treatment exists to halt its progression. Recent advancement in genome editing technologies offers a promising therapeutic approach in restoring dystrophin protein expression. However, the impact of this approach on DMD cardiac function has yet to be evaluated. Therefore, we assessed the therapeutic efficacy of CRISPR (clustered regularly interspaced short palindromic repeats)-mediated genome editing on dystrophin expression and cardiac function in mdx/Utr+/− mice after a single systemic delivery of recombinant adeno-associated virus (AAV). Objective To examine the efficiency and physiological impact of CRISPR-mediated genome editing on cardiac dystrophin expression and function in dystrophic mice. Methods and Results Here we packaged SaCas9/gRNA constructs into an AAV vector and systemically delivered them to mdx/Utr+/− neonates. We showed that CRIPSR-mediated genome editing efficiently excised the mutant exon 23 in dystrophic mice and immunofluorescence data supported the restoration of dystrophin protein expression in dystrophic cardiac muscles to a level approaching 40%. Moreover, there was a noted restoration in the architecture of cardiac muscle fibers and a reduction in the extent of fibrosis in dystrophin deficient hearts. The contractility of cardiac papillary muscles was also restored in CRISPR-edited cardiac muscles compared to untreated controls. Furthermore, our targeted deep sequencing results confirmed that our AAV-CRISPR-Cas9 strategy was very efficient in deleting the ~23 kb of intervening genomic sequences. Conclusions This study provides evidence for using CRISPR-based genome editing as a potential therapeutic approach for restoring dystrophic cardiomyopathy structurally and functionally.

Duchenne muscular dystrophy (DMD) is characterized by progressive skeletal muscle dysfunction leading to premature death by the third decade of life. The mdx mouse, the most widely used animal model of DMD, has been extremely useful to study disease mechanisms and to screen new therapeutics. However, unlike patients with DMD, mdx mice have a very mild motor function deficit, posing significant limitations for its use as a platform to assess the impact of treatments on motor function. It has been suggested that an mdx variant, the mdx(5cv) mouse, might be more severely affected. Here, we compared the motor activity, histopathology, and individual muscle force measurements of mdx and mdx(⁵cv) mice. Our study revealed that mdx(⁵cv) mice showed more severe exercise-induced fatigue, Rotarod performance deficits, and gait anomalies than mdx mice and that these deficits began at a younger age. Muscle force studies showed more severe strength deficits in the diaphragm of mdx(⁵cv) mice compared to mdx mice, but similar force generation in the extensor digitorum longus. Muscle histology was similar between the two strains. Differences in genetic background (genetic modifiers) probably account for these functional differences between mdx strains. Overall, our findings indicate that the mdx and mdx(⁵cv) mouse models of DMD are not interchangeable and identify the mdx(⁵cv) mouse as a valuable platform for preclinical studies that require assessment of muscle function in live animals.

Deterioration of diaphragm function is one of the prominent factors that contributes to the susceptibility of serious respiratory infections and development of respiratory failure in patients with Duchenne Muscular Dystrophy (DMD). The NF-κB signaling pathway has been implicated as a contributing factor of dystrophic pathology, making it a potential therapeutic target. Previously, we demonstrated that pharmacological inhibition of NF-κB via a small NEMO Binding Domain (NBD) peptide was beneficial for reducing pathological features of mdx mice. Now, we stringently test the effectiveness and clinical potential of NBD by treating mdx mice with various formulations of NBD and use diaphragm function as our primary outcome criteria. We found that administering DMSO-soluble NBD rescued 78% of the contractile deficit between mdx and wild-type (WT) diaphragm. Interestingly, synthesis of a GLP NBD peptide as an acetate salt permitted its solubility in water, but as a negative consequence, also greatly attenuated functional efficacy. However, replacing the acetic acid counterion of the NBD peptide with trifluoroacetic acid retained the peptide's water solubility and significantly restored mdx diaphragm contractile function and improved histopathological indices of disease in both diaphragm and limb muscle. Together, these results support the feasibility of using a mass-produced, water-soluble NBD peptide for clinical use.

Alternative NF-κB signaling modulates the activity of PGC-1β to promote oxidative metabolism in skeletal muscle.

Cross-bridge cycling rate is an important determinant of cardiac output, and its alteration can potentially contribute to reduced output in heart failure patients. Additionally, animal studies suggest that this rate can be regulated by muscle length. The purpose of this study was to investigate cross-bridge cycling rate and its regulation by muscle length under near-physiological conditions in intact right ventricular muscles of nonfailing and failing human hearts. We acquired freshly explanted nonfailing (n = 9) and failing (n = 10) human hearts. All experiments were performed on intact right ventricular cardiac trabeculae (n = 40) at physiological temperature and near the normal heart rate range. The failing myocardium showed the typical heart failure phenotype: a negative force-frequency relationship and β-adrenergic desensitization (P < 0.05), indicating the expected pathological myocardium in the right ventricles. We found that there exists a length-dependent regulation of cross-bridge cycling kinetics in human myocardium. Decreasing muscle length accelerated the rate of cross-bridge reattachment (ktr) in both nonfailing and failing myocardium (P < 0.05) equally; there were no major differences between nonfailing and failing myocardium at each respective length (P > 0.05), indicating that this regulatory mechanism is preserved in heart failure. Length-dependent assessment of twitch kinetics mirrored these findings; normalized dF/dt slowed down with increasing length of the muscle and was virtually identical in diseased tissue. This study shows for the first time that muscle length regulates cross-bridge kinetics in human myocardium under near-physiological conditions and that those kinetics are preserved in the right ventricular tissues of heart failure patients.

Pharmacologic strategies have provided modest improvement in the devastating muscle-wasting disease, Duchenne muscular dystrophy (DMD). Pre-clinical gene therapy studies have shown promise in the mdx mouse model; however, studies conducted after disease onset fall short of fully correcting muscle strength or protecting against contraction-induced injury. Here we examine the treatment effect on muscle physiology in aged dystrophic mice with significant disease pathology by combining two promising therapies: micro-dystrophin gene replacement and muscle enhancement with follistatin, a potent myostatin inhibitor. Individual treatments with micro-dystrophin and follistatin demonstrated marked improvement in mdx mice but were insufficient to fully restore muscle strength and response to injury to wild-type levels. Strikingly, when combined, micro-dystrophin/follistatin treatment restored force generation and conferred resistance to contraction-induced injury in aged mdx mice. Pre-clinical studies with miniature dystrophins have failed to demonstrate full correction of the physiological defects seen in mdx mice. Importantly, the addition of a muscle enhancement strategy with delivery of follistatin in combination with micro-dystrophin gene therapy completely restored resistance to eccentric contraction-induced injury and improved force. Eccentric contraction-induced injury is a pre-clinical parameter relevant to the exercise induced injury that occurs in DMD patients, and herein, we demonstrate compelling evidence for the therapeutic potential of micro-dystrophin/follistatin combinatorial therapy.