Duchenne muscular dystrophy (DMD) is a progressive muscle disease that results in muscle wasting, wheelchair dependence, and eventual death due to cardiac and respiratory complications. In addition to muscle fragility, dystrophin deficiency also results in multiple secondary dysfunctions, which may lead to the accumulation of unfolded proteins causing endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The purpose of this investigation was to understand how ER stress and the UPR are modified in muscle from D2-mdx mice, an emerging DMD model, and from humans with DMD. We hypothesized that markers of ER stress and the UPR are upregulated in D2-mdx and human dystrophic muscles compared to their healthy counterparts. Immunoblotting in diaphragms from 11-month-old D2-mdx and DBA mice indicated increased ER stress and UPR in dystrophic diaphragms compared to healthy, including increased relative abundance of ER stress chaperone CHOP, canonical ER stress transducers ATF6 and pIRE1α S724, and transcription factors that regulate the UPR such as ATF4, XBP1s, and peIF2α S51. The publicly available Affymetrix dataset (GSE38417) was used to analyze the expression of ER stress and UPR-related transcripts and processes. Fifty-eight upregulated genes related to ER stress and the UPR in human dystrophic muscles suggest pathway activation. Further, based on analyses using iRegulon, putative transcription factors that regulate this upregulation profile were identified, including ATF6, XBP1, ATF4, CREB3L2, and EIF2AK3. This study adds to and extends the emerging knowledge of ER stress and the UPR in dystrophin deficiency and identifies transcriptional regulators that may be responsible for these changes and be of therapeutic interest.

Noncommunicable diseases are chronic diseases that contribute to death worldwide, but these diseases can be prevented and mitigated with regular exercise. Exercise activates signaling molecules and the transcriptional network to promote physiological adaptations, such as fiber type transformation, angiogenesis, and mitochondrial biogenesis. AMP-activated protein kinase (AMPK) is a master regulator that senses the energy state, promotes metabolism for glucose and fatty acid utilization, and mediates beneficial cellular adaptations in many vital tissues and organs. This review focuses on the current, integrative understanding of the role of exercise-induced activation of AMPK in the regulation of system metabolism and promotion of health benefits.

Significance Here, we present unequivocal evidence of physical association of AMPK holoenzymes with mitochondrial reticulum (mitoAMPK) across multiple mouse tissues with evidence of conservation in human skeletal muscle and heart. We demonstrate that mitoAMPK is activated heterogeneously across the mitochondrial reticulum by mitochondrial energetic stress. Finally, we present evidence that suggests activation of mitoAMPK in skeletal muscle is required for mitophagy. We propose that mitoAMPK responds to mitochondrial microenvironment cues to maintain energetic homeostasis through mitochondrial quality control.

Duchenne muscular dystrophy (DMD) is a fatal, progressive muscle disease caused by the absence of functional dystrophin protein. Previous studies in mdx mice, a common DMD model, identified impaired autophagy with lysosomal insufficiency and impaired autophagosomal degradation as consequences of dystrophin deficiency. Thus, we hypothesized that lysosomal abundance would be decreased and degradation of autophagosomes would be impaired in muscles of D2-mdx mice. To test this hypothesis, diaphragm and gastrocnemius muscles from 11 month-old D2-mdx and DBA/2J (healthy) mice were collected. Whole muscle protein from diaphragm and gastrocnemius muscles, and protein from a cytosolic fraction (CF) and a lysosome-enriched fraction (LEF) from gastrocnemius muscles, were isolated and used for western blotting. Initiation of autophagy was not robustly activated in whole muscle protein from diaphragm and gastrocnemius, however, autophagosome formation markers were elevated in dystrophic muscles. Autophagosome degradation was impaired in D2-mdx diaphragms but appeared to be maintained in gastrocnemius muscles. To better understand this muscle-specific distinction, we investigated autophagic signaling in CFs and LEFs from gastrocnemius muscles. Within the LEF we discovered that the degradation of autophagosomes was similar between groups. Further, our data suggest an expanded, though impaired, lysosomal pool in dystrophic muscle. Notably, these data indicate a degree of muscle specificity as well as model specificity with regard to autophagic dysfunction in dystrophic muscles. Stimulation of autophagy in dystrophic muscles may hold promise for DMD patients as a potential therapeutic, however, it will be critical to choose the appropriate model and muscles that most closely recapitulate findings from human patients to further develop these therapeutics.

Extracellular superoxide dismutase (EcSOD) is the only extracellular scavenger of superoxide anion (O2.-) with unique binding capacity to cell surface and extracellular matrix through its heparin-binding domain. Enhanced EcSOD activity prevents oxidative stress and damage, which are fundamental in a variety of disease pathologies. In this review we will discuss the findings in humans and animal studies supporting the benefits of EcSOD induced by exercise training in reducing oxidative stress in various tissues. In particularly, we will highlight the importance of skeletal muscle EcSOD, which is induced by endurance exercise and redistributed through the circulation to the peripheral tissues, as a molecular transducer of exercise training to confer protection against oxidative stress and damage in various disease conditions.

Duchenne muscular dystrophy (DMD) is caused by the absence of functional dystrophin protein and results in progressive muscle wasting. Dystrophin deficiency leads to a host of dysfunctional cellular processes including impaired autophagy. Autophagic dysfunction appears to be due, at least in part, to decreased lysosomal abundance mediated by decreased nuclear localization of transcription factor EB (TFEB), a transcription factor responsible for lysosomal biogenesis. PGC-1 alpha overexpression decreased disease severity in dystrophin-deficient skeletal muscle and increased PGC-1 alpha has been linked to TFEB activation in healthy muscle. The purpose of this study was to determine the extent to which PGC-1 alpha overexpression increased nuclear TFEB localization, increased lysosome abundance, and increased autophagosome degradation. We hypothesized that overexpression of PGC-1 alpha would drive TFEB nuclear translocation, increase lysosome biogenesis, and improve autophagosome degradation. To address this hypothesis, we delivered PGC-1 alpha via adeno-associated virus (AAV) vector injected into the right limb of 3-week-old mdx mice and the contralateral limbs received a sham injection. At 6 weeks of age, this approach increased PGC-1 alpha transcript by 60-fold and increased TFEB nuclear localization in gastrocnemii from PGC-1 alpha treated limbs by twofold compared to contralateral controls. Furthermore, lamp2, a marker of lysosome abundance, was significantly elevated in muscles from limbs overexpressing PGC-1 alpha. Lastly, increased LC3II and similar p62 in PGC-1 alpha overexpressing-limbs compared to contralateral limbs are supportive of increased degradation of autophagosomes. These data provide mechanistic insight into PGC-1 alpha-mediated benefits to dystrophin-deficient muscle, such that increased TFEB nuclear localization in dystrophin-deficient muscle leads to increased lysosome biogenesis and autophagy.

Progressive muscle injury and weakness are hallmarks of Duchenne muscular dystrophy. We showed previously that quercetin (Q) partially protected dystrophic limb muscles from disease-related injury. As quercetin activates PGC-1α through Sirtuin-1, an NAD+-dependent deacetylase, the depleted NAD+ in dystrophic skeletal muscle may limit quercetin efficacy; hence, supplementation with the NAD+ donor, nicotinamide riboside (NR), may facilitate quercetin efficacy. Lisinopril (Lis) protects skeletal muscle and improves cardiac function in dystrophin-deficient mice; therefore, it was included in this study to evaluate the effects of lisinopril used with quercetin and NR. Our purpose was to determine the extent to which Q, NR, and Lis decreased dystrophic injury. We hypothesized that Q, NR, or Lis alone would improve muscle function and decrease histological injury and when used in combination would have additive effects. Muscle function of 11-mo-old DBA (healthy), D2-mdx (dystrophin-deficient), and D2-mdx mice was assessed after treatment with Q, NR, and/or Lis for 7 mo. To mimic typical pharmacology of patients with Duchenne muscular dystrophy, a group was treated with prednisolone (Pred) in combination with Q, NR, and Lis. At 11 mo of age, dystrophin deficiency decreased specific tension and tetanic force in the soleus and extensor digitorum longus muscles and was not corrected by any treatment. Dystrophic muscle was more sensitive to contraction-induced injury, which was partially offset in the QNRLisPred group, whereas fatigue was similar between all groups. Treatments did not decrease histological damage. These data suggest that treatment with Q, NR, Lis, and Pred failed to adequately maintain dystrophic limb muscle function or decrease histological damage.NEW & NOTEWORTHY Despite a compelling rationale and previous evidence to the contrary in short-term investigations, quercetin, nicotinamide riboside, or Lisinopril, alone or in combination, failed to restore muscle function or decrease histological injury in dystrophic limb muscle from D2-mdx mice after long-term administration. Importantly, we also found that in the D2-mdx model, an emerging and relatively understudied model of Duchenne muscular dystrophy dystrophin deficiency caused profound muscle dysfunction and histopathology in skeletal muscle.

Duchenne muscular dystrophy is a severe muscle wasting disease caused by the absence of functional dystrophin protein. We have previously established that increased peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) pathway activity is therapeutic in dystrophic muscle. The purpose of this study was to determine the extent to which increased PGC‐1α pathway activity increased nuclear localization and activity of transcription factor EB (TFEB), a transcription factor that leads to lysosomal biogenesis. We hypothesized that increased PGC‐1α pathway activity would increase TFEB nuclear migration, lysosome abundance, and the restoration of impaired autophagosome degradation. To address this hypothesis, 3‐week‐old mdx mice were injected in one limb with an adeno‐associated virus that drives PGC‐1α gene expression and the other limb was injected with an empty capsid. Animals were sacrificed at 6 weeks of age and the gastrocnemii were harvested. PGC‐1α overexpression was confirmed by qPCR. Total TFEB protein abundance was similar between groups, however, nuclear TFEB was significantly increased in PGC‐1α treated limbs consistent with our hypothesis. We also discovered that Lamp2, a lysosomal marker, was significantly elevated in PGC‐1α treated muscle. Finally, abundance of autophagy‐related proteins were compared between treated and control gastrocnemii of mdx mice as well as to gastrocnemii from adult C57 mice. LC3 II, an indicator of autophagosome formation, was significantly elevated in PGC‐1α‐treated limbs compared to both the C57 and mdx‐control muscles. However, p62, an inverse correlate of autophagosome degradation, was similar between groups suggesting elevated degradation of autophagosomes in PGC‐1α treated limbs. These data suggest increased PGC‐1α pathway activity increased lysosomal degradation of autophagosomes in dystrophic muscle, likely through a TFEB‐mediated mechanism.Support or Funding InformationSupported by the American Physiological Society.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Progressive muscle injury and weakness are hallmarks of Duchenne muscular dystrophy (DMD), which is caused by the absence of functional dystrophin protein. Likewise, chronic muscle injuries are common in military personnel. We have previously shown PGC‐1α‐mediated protection of dystrophic muscle via gene transfer approaches, however, investigations using quercetin (Q) to activate the PGC‐1α pathway have been equivocal. Quercetin activates PGC‐1α through Sirtuin‐1, an NAD+‐dependent deacetylase, however, NAD+ may be depleted in dystrophic skeletal muscle. Therefore, the purpose of this investigation was to determine the extent to which supplementation with Q and nicotinamide riboside (NR), an NAD+ precursor, alone and in combination, improved function of dystrophic skeletal muscle. We hypothesized that the addition of Q or NR would improve diaphragm, soleus and extensor digitorum longus (EDL) muscle function, and when given in combination would cause synergistic effects. To address this hypothesis, muscle function from DBA (healthy), D2‐mdx (dystrophin deficient), and D2‐mdx mice fed Q (0.2% of diet), NR (400 mg/kg/d), and Q/NR was assessed. In addition, to mimic typical pharmacology of DMD patients an additional group was fed Q/NR and treated with prednisone (10 mg/L; Pred) and lisinopril (66 mg/L: Lis). Treatment was started at 4 mo of age under blinded conditions and ended upon tissue collection at 11 mo of age. Dystrophin deficiency impaired diaphragm specific tension and was not corrected by treatments, nor was fatigue resistance improved. In the EDL, dystrophin deficiency decreased resistance to contraction‐induced injury that was partially restored in the Q/NR/Lis/Pred group compared to untreated D2‐mdx. Specific tension in the EDL and soleus was decreased in dystrophic muscle and was not altered by treatments. Interestingly, Q, NR, and Q/NR increased soleus fatigue resistance through 1 min of a fatigue protocol compared to untreated dystrophic controls, but was similar thereafter (10 min). Fatigue resistance was increased throughout the fatigue protocol in the Q/NR/Lis/Pred group compared to D2‐mdx. This finding suggests that Q, NR or Q/NR may improve soleus glycolytic capacity resulting in sustained force production for the first minute of exercise and that the addition of Lis and Pred augments these effects. In total these data suggest that treatment with Q, NR, and Q/NR provide limited protection to dystrophic muscle that is enhanced by the addition of Lis/Pred. As many activities of daily living are completed within 1 min, increased fatigue resistance demonstrated herein, while modest, may decrease disease burden in DMD patients and in other chronic muscle injury conditions.Support or Funding InformationSupported by Parent Project Muscular Dystrophy, Ryan's Quest and Michael's Cause.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Introduction Duchenne muscular dystrophy (DMD) is a neuromuscular disease caused by a dystrophin protein deficiency. Dystrophin functions to stabilize and protect the muscle fiber during muscle contraction; thus, the absence of functional dystrophin protein leads to muscle injury. DMD patients experience progressive muscle necrosis, loss of function, and ultimately succumb to respiratory failure or cardiomyopathy. Exercise is known to improve muscle health and strength in healthy individuals as well as positively affect other systems. Because of this, exercise has been investigated as a potential therapeutic approach for DMD. Methods This review aims to provide a concise presentation of the exercise literature with a focus on dystrophin-deficient muscle. Our intent was to identify trends and gaps in knowledge with an appreciation of exercise modality. Results After compiling data from mouse and human studies, it became apparent that endurance exercises such as a swimming and voluntary wheel running have therapeutic potential in limb muscles of mice and respiratory training was beneficial in humans. However, in the comparatively few long-term investigations, the effect of low-intensity training on cardiac and respiratory muscles was contradictory. In addition, the effect of exercise on other systems is largely unknown. Conclusions To safely prescribe exercise as a therapy to DMD patients, multisystemic investigations are needed including the evaluation of respiratory and cardiac muscle.

Dystrophinopathies are caused by a mutation in the dystrophin gene, which can result in dystrophin protein insufficiency (Becker muscular dystrophy) and more commonly a dystrophin protein deficiency (Duchenne muscular dystrophy). These diseases are frequently modeled by the mdx mouse or the Golden Retriever Muscular Dystrophy model. Albeit useful, these models are not optimal for translational research due to inherent limitations. The purpose of this research was to determine the extent to which skeletal muscle is damaged by dystrophin insufficiency in a spontaneously occurring pig muscular dystrophy model. We hypothesized that dystrophin insufficiency would result in progressive muscle injury to skeletal muscle. To test this hypothesis, diaphragm from male pigs affected by dystrophin insufficiency and healthy male littermates were harvested at 3 months and 12 months of age and frozen for subsequent histological analysis. Sections were stained with hematoxylin and eosin and 3–5 random images were taken of each section. Central nucleation, a marker of skeletal muscle degeneration/regeneration, was similar between groups at 3 months of age, however, at 12 months of age central nucleation was increased by 42% in affected pigs compared to healthy pigs. When considering changes over time central nucleation increased in healthy pigs by 5‐fold (3 mo – 1.5%; 12 mo – 8%; p<0.05) and by 8‐fold in affected pigs (3 mo – 1.8%; 12 mo – 14%; p<0.05). These data indicate that the porcine diaphragm undergoes an increasing rate of central nucleation with normal aging. Importantly, this rate is dramatically increased with dystrophin insufficiency suggestive of an elevated pathological degeneration and regeneration. Interestingly, extracellular nuclei, which are associated with immune cell infiltration, and total muscle cells per area changed as a function of time but were similar between healthy and affected pigs at both 3 and 12 months of age. These data suggest that dystrophin insufficiency in diaphragm muscle increased muscle damage, which is consistent with disease‐related injury. Support or Funding Information Supported by NIH R21 NS079603

Dystrophinopathies are caused by mutations in the dystrophin gene leading to a dystrophin deficiency (Duchenne muscular dystrophy) or insufficiency (Becker muscular dystrophy). These diseases are commonly modeled by the mdx mouse or other related mouse models as well as the Golden Retriever Muscular Dystrophy model. While these models have been useful, inherent limitations necessitate continued development of novel large animal models. The purpose of this investigation was to determine the extent to which a spontaneous dystrophin mutation would impair locomotion in a pig dystrophinopathy model. We performed a monthly gait analysis from 3–12 months of age in male pigs with a dystrophin mutation causing an insufficiency and healthy male littermates using a Zeno gait analysis system. This system consists of a 5 m pad with approximately 50,000 integrated force transducers, which allows sensitive detection of pressure during the gait cycle as the pig walks across the pad. Pigs were euthanized at 3 and 12 months of age and tissues collected for histological analyses. Histological quantifications revealed a 2‐fold increase (p<0.05) in centralized nuclei in affected pigs at 12 months of age and a 2‐fold increase (p<0.05) in centralized nuclei in affected pigs over time at 12 months compared to 3 months of age suggesting progressive disease‐related injury. By 9 months of age affected pigs developed a distinct walking gait. When considering movement in the front limbs, stride length was shortened by 6–10 cm (p<0.05) and by 12 months of age stride width was increased by 7 cm (p<0.05) in affected pigs compared to healthy pigs. In addition to a wider and shorter gait, the swing phase was decreased by 14% and the mean single support center of pressure distance was also decreased at 9 months of age by 36%. Similar results were discovered when measuring movement in the hind limbs and when comparing same side limbs and contralateral limbs. In total, these pigs appear to be moving with a shorter, wider gait with a slower march‐like movement pattern. This unique gait shares similarities with patients affected by dystrophinopathies who also have notable gait changes as the disease progresses. These data suggest that pigs affected with a spontaneously occurring dystrophin insufficiency develop a progressive muscle pathology that ultimately impacts locomotion, consistent with changes in dystrophinopathy patients. These data also contribute to a growing body of literature supporting the utility of this human‐sized model that accurately recapitulates the human disease. Support or Funding Information This work supported by NIH grant R21 NS079603.

Dystrophinopathies are muscle diseases caused by mutations in the dystrophin gene resulting in insufficiency or absence of functional dystrophin protein. A deficiency of functional dystrophin results in membrane instability, mitochondrial dysfunction and metabolic abnormalities. Autophagy functions to remove damaged organelles, proteins and other cellular components and is emerging as an important process in dystrophic skeletal muscle, though the role of autophagy in dystrophic myocardium is currently unknown. The purpose of this investigation is to determine the extent to which autophagy is affected by disease progression in cardiac muscle. We hypothesized that dystrophin deficiency would result in progressive autophagic dysfunction in the heart. To address this hypothesis protein abundances from 7 week and 17 months old mdx mice were compared to C57 age‐matched controls. Surprisingly, measures of autophagic initiation, phosphorylated AMPK T172, phosphorylated UNC‐51‐like kinase 1 (ULK1) and Beclin‐1, were similar between all groups. In addition, autophagy‐related gene 5 (ATG5) and the ATG 12/5 complex, proteins indicative of autophagosome formation, were similar between groups. Furthermore, LC3I and the LC3I lipidation product, LC3II, were similar to age‐matched controls and markers of autophagic flux, the LC3II/I ratio and p62, were also similar between groups. To confirm that autophagy was independent of disease progression, heart tissue from a novel porcine dystrophinopathy model was also evaluated. Hearts were collected from healthy and affected male littermates at 3 and 12 months of age. This porcine model is dystrophin insufficient with necrotic lesions apparent at 12 months but not at 3 months of age. Consistent with our findings in the mdx mouse, protein abundances of phosphorylated ULK1, Beclin, ATG12/5 complex formation, LC3I, and p62 were similar between all groups. LC3II and the LC3II/I ratio were decreased as a function of age but did not differ with dystrophin deficiency. These data suggest that disease progression does not cause autophagic dysfunction in dystrophic myocardium. Support or Funding Information This work was supported in part by NIH R21 NS079603 and the Duchenne Alliance.

Duchenne muscular dystrophy (DMD) impacts 1 : 3500 boys and leads to muscle dysfunction culminating in death due to respiratory or cardiac failure. There is an urgent need for effective therapies with the potential for immediate application for this patient population. Quercetin, a flavonoid with an outstanding safety profile, may provide therapeutic relief to DMD patients as the wait for additional therapies continues. This study evaluated the capacity of orally administered quercetin (0.2%) in 2 month old mdx mice to improve respiratory function and end-point functional and histological outcomes in the diaphragm following 12 months of treatment. Respiratory function was protected for the first 4-6 months of treatment but appeared to become insensitive to quercetin thereafter. Consistent with this, end-point functional measures were decreased and histopathological measures were more severe in dystrophic muscle compared to C57 and similar between control-fed and quercetin-fed mdx mice. To better understand the transient nature of improved respiratory function, we measured PGC-1 alpha pathway activity, which is suggested to be up-regulated by quercetin supplementation. This pathway was largely suppressed in dystrophic muscle compared to healthy muscle, and at the 14 month time point dietary quercetin enrichment did not increase expression of downstream effectors. These data support the efficacy of quercetin as an intervention for DMD in skeletal muscle, and also indicate the development of age-dependent quercetin insensitivity when continued supplementation fails to drive the PGC-1 alpha pathway. Continued study is needed to determine if this is related to disease severity, age or other factors.

Overexpression of PGC‐1α has been shown to attenuate disuse atrophy and reduce disease severity caused by dystrophin deficiency. Effective therapeutics for atrophy caused by prolonged exposure to microgravity and dystrophin deficiency will require long‐term interventions as these are persistent perturbations of skeletal muscle. Quercetin, a naturally occurring flavonoid, is predicted to activate the PGC‐1α pathway via SIRT‐1, which ultimately results in a shift toward a slow, oxidative muscle phenotype. We demonstrated that a 0.2% quercetin enriched diet attenuated respiratory dysfunction in mdx mice, a model of Duchenne muscular dystrophy caused by dystrophin deficiency, for 4–8 months during a 12 month study in 14 month old mice. The purpose of this investigation was to determine the extent to which chronic dietary quercetin enrichment maintained elevated PGC‐1α pathway activity in diaphragms of 14 month old mdx mice fed quercetin for 12 months. Relative protein abundance of the upstream PGC‐1α pathway regulator phosphorylated (p‐) AMPK T172, was decreased 7.1‐fold (p<0.05) in mdx compared to C57, however, quercetin increased p‐AMPK T172 3.5‐fold compared to mdx. SIRT‐1 and SIRT‐1 activity, measured by histone 3 lysine 9 acetylation, increased over 2.0‐ (p<0.05) and 3.0‐fold (p<0.05), respectively, in mdx compared to C57, but were unaltered with quercetin treatment. PGC‐1α protein abundance was increased by 1.8‐fold in mdx and 1.3‐fold in mdxQ mice compared to C57. Protein abundance of downstream pathway components leading to an oxidative phenotype, ERRα, NRF‐1 and TFAM, were increased 1.7‐fold, decreased 1.4‐fold, and decreased 6.0‐fold, respectively, in dystrophic muscle compared to C57 and were not altered by the quercetin diet. Consistent with these findings, protein abundance of cytochrome c and succinate dehydrogenase A decreased 1.7‐fold in mdx compared to C57; cytochrome c oxidase IV was not detectable in dystrophic muscle. Mitochondrial markers were similar between mdx and mdxQ. The PGC‐1α pathway also leads to a slow muscle phenotype. We found that GABPA was decreased 1.6‐fold (p<0.05) in mdx mice while utrophin and type I myosin heavy chain were increased 30‐fold (p<0.05) and 2.0‐fold (p<0.05), respectively. Relative protein abundance of GABPA, utrophin, and type I myosin heavy chain was not altered with quercetin treatment. These data suggest that following 12 months of dietary quercetin enrichment PGC‐1α pathway activity was depressed in dystrophic diaphragms compared to C57 and was similar between untreated and quercetin‐treated mdx mice. This finding is consistent with our previous functional data and supports the postulate that the transient nature of quercetin‐mediated protection of respiratory function is due to the development of quercetin insensitivity. This inhibitory mechanism will need to be characterized and overcome if quercetin is to be a successful therapy for Duchenne muscular dystrophy and atrophy caused by long‐term exposure to microgravity. Support or Funding Information This work was supported by the Duchenne Alliance Research Foundation and its member foundations.

Duchenne muscular dystrophy (DMD) results from a genetic lesion in the dystrophin gene and leads to progressive muscle damage. PGC-1α pathway activation improves muscle function and decreases histopathological injury. We hypothesized that mild disease found in the limb muscles of mdx mice may be responsive to quercetin-mediated protection of dystrophic muscle via PGC-1α pathway activation. To test this hypothesis muscle function was measured in the soleus and EDL from 14 month old C57, mdx, and mdx mice treated with quercetin (mdxQ; 0.2% dietary enrichment) for 12 months. Quercetin reversed 50% of disease-related losses in specific tension and partially preserved fatigue resistance in the soleus. Specific tension and resistance to contraction-induced injury in the EDL were not protected by quercetin. Given some functional gain in the soleus it was probed with histological and biochemical approaches, however, in dystrophic muscle histopathological outcomes were not improved by quercetin and suppressed PGC-1α pathway activation was not increased. Similar to results in the diaphragm from these mice, these data suggest that the benefits conferred to dystrophic muscle following 12 months of quercetin enrichment were underwhelming. Spontaneous activity at the end of the treatment period was greater in mdxQ compared to mdx indicating that quercetin fed mice were more active in addition to engaging in more vigorous activity. Hence, modest preservation of muscle function (specific tension) and elevated spontaneous physical activity largely in the absence of tissue damage in mdxQ suggests dietary quercetin may mediate protection.