Deficient nitric oxide signalling impairs skeletal muscle growth and performance: involvement of mitochondrial dysregulation

Abstract

BackgroundNitric oxide (NO), generated in skeletal muscle mostly by the neuronal NO synthases (nNOSμ), has profound effects on both mitochondrial bioenergetics and muscle development and function. The importance of NO for muscle repair emerges from the observation that nNOS signalling is defective in many genetically diverse skeletal muscle diseases in which muscle repair is dysregulated. How the effects of NO/nNOSμ on mitochondria impact on muscle function, however, has not been investigated yet.MethodsIn this study we have examined the relationship between the NO system, mitochondrial structure/activity and skeletal muscle phenotype/growth/functions using a mouse model in which nNOSμ is absent. Also, NO-induced effects and the NO pathway were dissected in myogenic precursor cells.ResultsWe show that nNOSμ deficiency in mouse skeletal muscle leads to altered mitochondrial bioenergetics and network remodelling, and increased mitochondrial unfolded protein response (UPRmt) and autophagy. The absence of nNOSμ is also accompanied by an altered mitochondrial homeostasis in myogenic precursor cells with a decrease in the number of myonuclei per fibre and impaired muscle development at early stages of perinatal growth. No alterations were observed, however, in the overall resting muscle structure, apart from a reduced specific muscle mass and cross sectional areas of the myofibres. Investigating the molecular mechanisms we found that nNOSμ deficiency was associated with an inhibition of the Akt-mammalian target of rapamycin pathway. Concomitantly, the Akt-FoxO3-mitochondrial E3 ubiquitin protein ligase 1 (Mul-1) axis was also dysregulated. In particular, inhibition of nNOS/NO/cyclic guanosine monophosphate (cGMP)/cGMP-dependent-protein kinases induced the transcriptional activity of FoxO3 and increased Mul-1 expression. nNOSμ deficiency was also accompanied by functional changes in muscle with reduced muscle force, decreased resistance to fatigue and increased degeneration/damage post-exercise.ConclusionsOur results indicate that nNOSμ/NO is required to regulate key homeostatic mechanisms in skeletal muscle, namely mitochondrial bioenergetics and network remodelling, UPRmt and autophagy. These events are likely associated with nNOSμ-dependent impairments of muscle fibre growth resulting in a deficit of muscle performance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13395-014-0022-6) contains supplementary material, which is available to authorized users.

Autophagy regulates satellite cell ability to regenerate normal and dystrophic muscles

“…Defective neuronal NO synthase signaling has been associated to DMD and other myopathies and affects muscle functions, performance, mitochondrial biogenesis and autophagy, 47 suggesting use of NO-donating drugs as candidate treatment for DMD. 48 Impaired nitrosylation is associated with deregulated activation of histone deacetylase2 (HDAC2) in mdx mice.…”

Muscular dystrophy in PTFR/cavin-1 null mice

“…Respiratory activity was assessed in soleus fiber bundles using an Oxygraph system (Hansatech Instruments) as described by De Palma et al (65). Fibers from soleus muscle were prepared in ice-cold BIOPS (50 mM K + -MES, 20 mM taurine, 0.5 mM dithiothreitol, 6.56 mM MgCl 2 , 5.77 mM ATP, 20 mM imidazole, 10 mM Ca-EGTA buffer, pH 7.1), and then permeabilized in 2 ml of BIOPS solution containing 50 μg/ml saponin by gentle agitation for 30 minutes at 4°C.…”

Nitric Oxide Regulates Skeletal Muscle Fatigue, Fiber Type, Microtubule Organization, and Mitochondrial ATP Synthesis Efficiency Through cGMP-Dependent Mechanisms

“…One other interesting result was that cGMP enhancement with sildenafil had no impact on total, subsarcolemmal, or intermyofibrillar mitochondrial content. This argues against compensatory biogenesis in the face of decreased efficiency and contrasts with reports showing that increases in NO or cGMP promote biogenesis (18,43,52,53). It is conceivable that PDE5 does not regulate biogenesis in muscle or that sildenafil did not produce a sufficient cGMP increase to induce biogenesis.…”

“…In skeletal muscle, NO is required for normal mitochondrial integrity and NO-cGMP signaling may regulate mitochondrial biogenesis, fission, and respiration in muscle cells (17,18,43,52,53,57). Supraphysiological PKG overexpression drives the biogenesis of giant mitochondria in vivo (49).…”

“…Because mitochondria are regulated by NO and play a central role in skeletal muscle contractile performance, we tested if mitochondrial oxidative phosphorylation was impacted by GC1 inhibition using in vivo metabolic spectroscopy (5,17,18,52,53,57,67). Mitochondrial ATP synthesis (Fig.…”