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Introduction Autophagy is a fundamental catabolic and cytoprotective process. During autophagy, multiple lysosomes fuse with autophagosomes to form autolysosomes in which cellular debris is degraded (1). Lysosomes are critical for [...], The regulation of autophagy-dependent lysosome homeostasis in vivo is unclear. We showed that the inositol polyphosphate 5-phosphatase INPP5K regulates autophagic lysosome reformation (ALR), a lysosome recycling pathway, in muscle. INPP5K hydrolyzes phosphatidylinositol-4,5-bisphosphate [PI(4,5)[P.sub.2]] to phosphatidylinositol 4-phosphate [PI(4)P], and INPP5K mutations cause muscular dystrophy by unknown mechanisms. We report that loss of INPP5K in muscle caused severe disease, autophagy inhibition, and lysosome depletion. Reduced PI(4,5)[P.sub.2] turnover on autolysosomes in Inpp5K muscle suppressed autophagy and lysosome repopulation via ALR inhibition. Defective ALR in InppSkmyoblasts was characterized by enlarged autolysosomes and the persistence of hyperextended reformation tubules, structures that participate in membrane recycling to form lysosomes. Reduced disengagement of the PI(4,5)[P.sub.2] effector clathrin was observed on reformation tubules, which we propose interfered with ALR completion. Inhibition of PI(4,5)[P.sub.2] synthesis or expression of WT INPP5K but not INPP5K disease mutants in INPP5K-depleted myoblasts restored lysosomal homeostasis. Therefore, bidirectional interconversion of PI(4)P/PI(4,5)[P.sub.2] on autolysosomes was integral to lysosome replenishment and autophagy function in muscle. Activation of TFEB-dependent de novo lysosome biogenesis did not compensate for loss of ALR in InppSkmuscle, revealing a dependence on this lysosome recycling pathway. Therefore, in muscle, ALR is indispensable for lysosome homeostasis during autophagy and when defective is associated with muscular dystrophy.

DMD is the most severe form of muscular dystrophy; it affects about 1 in 3,500 live male births (1). Intracellular [Ca.sup.2+] regulation is compromised in dystrophic muscle fibres, which triggers [...], Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder caused by mutations in the dystrophin gene that result in the absence of the membrane-stabilizing protein dystrophin (1-3). Dystrophin-deficient muscle fibres are fragile and susceptible to an influx of [Ca.sup.2+], which activates inflammatory and muscle degenerative pathways (4-6). At present there is no cure for DMD, and existing therapies are ineffective. Here we show that increasing the expression of intramuscular heat shock protein 72 (Hsp72) preserves muscle strength and ameliorates the dystrophic pathology in two mouse models of muscular dystrophy. Treatment with BGP-15 (a pharmacological inducer of Hsp72 currently in clinical trials for diabetes) improved muscle architecture, strength and contractile function in severely affected diaphragm muscles in mdx dystrophic mice. In dko mice, a phenocopy of DMD that results in severe spinal curvature (kyphosis), muscle weakness and premature death (7,8), BGP-15 decreased kyphosis, improved the dystrophic pathophysiology in limb and diaphragm muscles and extended lifespan. We found that the sarcoplasmic/endoplasmic reticulum [Ca.sup.2+]-ATPase (SERCA, the main protein responsible for the removal of intracellular [Ca.sup.2+]) is dysfunctional in severely affected muscles of mdx and dko mice, and that Hsp72 interacts with SERCA to preserve its function under conditions of stress, ultimately contributing to the decreased muscle degeneration seen with Hsp72 upregulation. Treatment with BGP-15 similarly increased SERCA activity in dystrophic skeletal muscles. Our results provide evidence that increasing the expression of Hsp72 in muscle (through the administration of BGP-15) has significant therapeutic potential for DMD and related conditions, either as a self-contained therapy or as an adjuvant with other potential treatments, including gene, cell and pharmacological therapies.

Background: Duchenne muscular dystrophy (DMD) is a severe, genetic muscle wasting disorder characterised by progressive muscle weakness. DMD is caused by mutations in the dystrophin (dmd) gene resulting in very low levels or a complete absence of the dystrophin protein, a key structural element of muscle fibres which is responsible for the proper transmission of force. In the absence of dystrophin, muscle fibres become damaged easily during contraction resulting in their degeneration. DMD patients and mdx mice (an animal model of DMD) exhibit altered metabolic disturbances that cannot be attributed to the loss of dystrophin directly. We tested the hypothesis that glycogen metabolism is defective in mdx dystrophic mice. Results: Dystrophic mdx mice had increased skeletal muscle glycogen (79%, (P<0.01)). Skeletal muscle glycogen synthesis is initiated by glycogenin, the expression of which was increased by 50% in mdx mice (P<0.0001). Glycogen synthase activity was 12% higher (P<0.05) but glycogen branching enzyme activity was 70% lower (P<0.01) in mdx compared with wild-type mice. The rate-limiting enzyme for glycogen breakdown, glycogen phosphorylase, had 62% lower activity (P<0.01) in mdx mice resulting from a 24% reduction in PKA activity (P<0.01). In mdx mice glycogen debranching enzyme expression was 50% higher (P<0.001) together with starch-binding domain protein 1 (219% higher; P<0.01). In addition, mdx mice were glucose intolerant (P<0.01) and had 30% less liver glycogen (P<0.05) compared with control mice. Subsequent analysis of the enzymes dysregulated in skeletal muscle glycogen metabolism in mdx mice identified reduced glycogenin protein expression (46% less; P<0.05) as a possible cause of this phenotype. Conclusion: We identified that mdx mice were glucose intolerant, and had increased skeletal muscle glycogen but reduced amounts of liver glycogen. [ABSTRACT FROM AUTHOR]

Systemic administration of β2-adrenoceptor agonists (β2-agonists) can improve skeletal muscle regeneration after injury. However, therapeutic application of β2-agonists for muscle injury has been limited by detrimental cardiovascular side effects. Intramuscular administration may obviate some of these side effects. To test this hypothesis, the right extensor digitorum longus (EDL) muscle from rats was injected with bupivacaine hydrochloride to cause complete muscle fiber degeneration. Five days after injury, half of the injured muscles received an intramuscular injection of formoterol (100 µg). Muscle function was assessed at 7, 10, and 14 days after injury. A single intramuscular injection of formoterol increased muscle mass and force-producing capacity at day 7 by 17 and 91%, respectively, but this effect was transient because these values were not different from control levels at day 10. A second intramuscular injection of formoterol at day 7 prolonged the increase in muscle mass and force-producing capacity. Importantly, single or multiple intramuscular injections of formoterol did not elicit cardiac hypertrophy. To characterize any potential cardiovascular effects of intramuscular formoterol administration, we instrumented a separate group of rats with indwelling radio telemeters. Following an intramuscular injection of formoterol, heart rate increased by 18%, whereas systolic and diastolic blood pressure decreased by 31 and 44%, respectively. These results indicate that intramuscular injection can enhance functional muscle recovery after injury without causing cardiac hypertrophy. Therefore, if the transient cardiovascular effects associated with intramuscular formoterol administration can be minimized, this form of treatment may have significant therapeutic potential for muscle-wasting conditions. [ABSTRACT FROM AUTHOR]

Duchenne muscular dystrophy (DMD) is caused by a lack of dystrophin, a structural protein thought to confer stability to skeletal muscle fibers. A lack of dystrophin results in an increased susceptibility to contraction-induced (CI) injury. Insulin-like growth factor-I (IGF-I) therapy has beneficial effects on muscle function in mdx mice, a model of DMD. The actions of IGF-I are strongly modified by IGF binding proteins (IGFBPs). The IGF-I aptamer, NBI-31772, displaces IGFBPs from their interaction with IGF-I, releasing free biologically active IGF-I. We tested the hypothesis that disruption of IGF-I/IGFBP interactions using NBI-31772 would reduce the dystrophic pathology in mdx mice. NBI-31772 was administered to mdx mice (continuous infusion; ∼6 mg/kg/day) for 4 weeks via mini osmotic pump. Muscle contractile properties were examined in vitro. NBI-31772 treatment reduced the susceptibility of the EDL and diaphragm muscles to CI injury, concomitant with reduced fatigue resistance and lower citrate synthase activity. The findings indicate that displacing IGF-I from its binding proteins can protect dystrophic muscles from CI injury. [ABSTRACT FROM AUTHOR]

Systemic administration of beta(2)-adrenoceptor agonists (beta(2)-agonists) can improve skeletal muscle regeneration after injury. However, therapeutic application of beta(2)-agonists for muscle injury has been limited by detrimental cardiovascular side effects. Intramuscular administration may obviate some of these side effects. To test this hypothesis, the right extensor digitorum longus (EDL) muscle from rats was injected with bupivacaine hydrochloride to cause complete muscle fiber degeneration. Five days after injury, half of the injured muscles received an intramuscular injection of formoterol (100 mug). Muscle function was assessed at 7, 10, and 14 days after injury. A single intramuscular injection of formoterol increased muscle mass and force-producing capacity at day 7 by 17 and 91%, respectively, but this effect was transient because these values were not different from control levels at day 10. A second intramuscular injection of formoterol at day 7 prolonged the increase in muscle mass and force-producing capacity. Importantly, single or multiple intramuscular injections of formoterol did not elicit cardiac hypertrophy. To characterize any potential cardiovascular effects of intramuscular formoterol administration, we instrumented a separate group of rats with indwelling radio telemeters. Following an intramuscular injection of formoterol, heart rate increased by 18%, whereas systolic and diastolic blood pressure decreased by 31 and 44%, respectively. These results indicate that intramuscular injection can enhance functional muscle recovery after injury without causing cardiac hypertrophy. Therefore, if the transient cardiovascular effects associated with intramuscular formoterol administration can be minimized, this form of treatment may have significant therapeutic potential for muscle-wasting conditions.