Skeletal muscle mitochondrial adaptations induced by long-term cigarette smoke exposure

Because patients with chronic obstructive pulmonary disease (COPD) are often physically inactive, it is still unclear whether the lower respiratory capacity in the locomotor muscles of these patients is due to cigarette smoking per se or is secondary to physical deconditioning. Accordingly, the purpose of this study was to examine mitochondrial alterations in the quadriceps muscle of 10 mice exposed to 8 mo of cigarette smoke, a sedentary mouse model of emphysema, and 9 control mice, using immunoblotting, spectrophotometry, and high-resolution respirometry in permeabilized muscle fibers. Mice exposed to smoke displayed a twofold increase in the oxidative stress marker, 4-HNE, (P < 0.05) compared with control mice. This was accompanied by significant decrease in protein expression of UCP3 (65%), ANT (58%), and mitochondrial complexes II-V (∼60%-75%). In contrast, maximal ADP-stimulated respiration with complex I and II substrates (CON: 23.6 ± 6.6 and SMO: 19.2 ± 8.2 ρM·mg-1·s-1) or octanoylcarnitine (CON: 21.8 ± 9.0 and SMO: 16.5 ± 6.6 ρM·mg-1·s-1) measured in permeabilized muscle fibers, as well as citrate synthase activity, were not significantly different between groups. Collectively, our findings revealed that sedentary mice exposed to cigarette smoke for 8 mo, which is typically associated with pulmonary inflammation and emphysema, exhibited a preserved mitochondrial respiratory capacity for various substrates, including fatty acid, in the skeletal muscle. However, the mitochondrial adaptations induced by cigarette smoke favored the development of chronic oxidative stress, which can indirectly contribute to augment the susceptibility to muscle fatigue and exercise intolerance.NEW & NOTEWORTHY It is unclear whether the exercise intolerance and skeletal muscle mitochondrial dysfunction observed in patients with COPD is due to cigarette smoke exposure, per se, or if they are secondary consequences to inactivity. Herein, while long-term exposure to cigarette smoke induces oxidative stress and an altered skeletal muscle phenotype, cigarette smoke does not directly contribute to mitochondrial dysfunction. With this evidence, we demonstrate the critical role of physical inactivity in cigarette smoke-related skeletal muscle dysfunction.

Relative lipid oxidation associates directly with mitochondrial fusion phenotype and mitochondria-sarcoplasmic reticulum interactions in human skeletal muscle

Disturbances in skeletal muscle lipid oxidation might induce ectopic fat deposition and lipotoxicity. Nevertheless, the cellular mechanisms that regulate skeletal muscle lipid oxidation have not been fully determined. We aimed to determine whether there was an association between relative whole body lipid oxidation and mitochondrial size or mitochondria-sarcoplasmic reticulum interactions in the skeletal muscle. Twelve healthy men were included [mean (standard deviation), 24.7 (1.5) yr old, 24.4 (2.6) kg/m²]. The respiratory quotient (RQ) was used to estimate relative lipid oxidation at rest and during exercise (50% maximal oxygen consumption, 600 kcal expended). A skeletal muscle biopsy was obtained from the vastus lateralis at rest. Transmission electron microscopy was used to determine mitochondrial size and mitochondria-sarcoplasmic reticulum interactions (≤50 nm of distance between organelles). Protein levels of fusion/fission regulators were measured in skeletal muscle by Western blot. Resting RQ and exercise RQ associated inversely with intermyofibrillar mitochondrial size (r = -0.66 and r = -0.60, respectively, P < 0.05). Resting RQ also associated inversely with the percentage of intermyofibrillar mitochondria-sarcoplasmic reticulum interactions (r = -0.62, P = 0.03). Finally, intermyofibrillar mitochondrial size associated inversely with lipid droplet density (r = -0.66, P = 0.01) but directly with mitochondria fusion-to-fission ratio (r = 0.61, P = 0.03). Our results show that whole body lipid oxidation is associated with skeletal muscle intermyofibrillar mitochondrial size, fusion phenotype, and mitochondria-sarcoplasmic-reticulum interactions in nondiabetic humans.

Super-Resolution Reconstruction for Two- and Three-Dimensional LA-ICP-MS Bioimaging

The resolution of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) elemental bioimaging is usually constrained by the diameter of the laser spot size and is often not adequate to explore in situ subcellular distributions of elements and proteins in biological tissue sections. Super-resolution reconstruction is a method typically used for many imaging modalities and combines multiple lower resolution images to create a higher resolution image. Here, we present a super-resolution reconstruction method for LA-ICP-MS imaging by ablating consecutive layers of a biological specimen with offset orthogonal scans, resulting in a 10× improvement in resolution for quantitative measurement of dystrophin in murine muscle fibers. Layer-by-layer image reconstruction was also extended to the third dimension without the requirement of image registration across multiple thin section specimens. Quantitative super-resolution reconstruction, combined with Gaussian filtering and application of the Richardson-Lucy total variation algorithm, provided superior image clarity and fidelity in two- and three-dimensions.

Adult expression of PGC-1α and -1β in skeletal muscle is not required for endurance exercise-induced enhancement of exercise capacity

Exercise has been shown to be the best intervention in the treatment of many diseases. Many of the benefits of exercise are mediated by adaptions induced in skeletal muscle. The peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family of transcriptional coactivators has emerged as being key mediators of the exercise response and is considered to be essential for many of the adaptions seen in skeletal muscle. However, the contribution of the PGC-1s in skeletal muscle has been evaluated by the use of either whole body or congenital skeletal muscle-specific deletion. In these models, PGC-1s were never present, thereby opening the possibility to developmental compensation. Therefore, we generated an inducible muscle-specific deletion of PGC-1α and -1β (iMyo-PGC-1DKO), in which both PGC-1α and -β can be deleted specifically in adult skeletal muscle. These iMyo-PGC-1DKO animals were used to assess the role of both PGC-1α and -1β in adult skeletal muscle and their contribution to the exercise training response. Untrained iMyo-PGC-1DKO animals exhibited a time-dependent decrease in exercise performance 8 wk postdeletion, similar to what was observed in the congenital muscle-specific PGC-1DKOs. However, after 4 wk of voluntary training, the iMyo-PGC-1DKOs exhibited an increase in exercise performance with a similar adaptive response compared with control animals. This increase was associated with an increase in electron transport complex (ETC) expression and activity in the absence of PGC-1α and -1β expression. Taken together these data suggest that PGC-1α and -1β expression are not required for training-induced exercise performance, highlighting the contribution of PGC-1-independent mechanisms.

[Effects of electroacupuncture with manifestation-root acupoint combination on ultrastructure and biosynthesis in mitochondrial of quadriceps femoris in rats with insulin resistance]

OBJECTIVE

To explore the mechanism of electroacupuncture on improving insulin resistance of rat from aspects of morphology and function of mitochondrial in quadriceps femoris.

METHODS

Forty-eight 8-week Wistar rats (female and male in half) were randomly divided into a normal group (16 rats, group A), a model control group (16 rats, group B), a model plus electroacupuncture (EA) group (8 rats, group C) and a model plus sham acupoint EA group (8 rats, group D). Group A was given with basic diet while high-fat diet was applied in the group B, group C and group D for 8 weeks to establish model of insulin resistance. After the model establishment, "Guanyuan" (CV 4), "Zhongwan" (CV 12), "Zusanli" (ST 36) and "Fenglong" (ST 30) were selected according to acupoint combination of manifestation-root in the group C, while four points in non-meridian area where 1 to 2 mm next to the acupoints used in group C were selected in the group D. The treatment was given 15 min per time with 1 mA of intensity and 2 Hz in frequency, 5 times per week for totally 8 weeks. The transmission electron microscope was adopted to observe mitochondria structure, and chemical colorimetry was used to test the activity of adenosine triphosphate (ATP) synthase and phosphomolybdic acid colorimetry was applied to measure the content of ATP.

RESULTS

After the treatment, the body mass was (401.63 +/- 109.81) g in the group B, which was significantly higher than (305.88 +/- 62.72) g in the group A (P < 0.05); morphological structure of mitochondrion was damaged, showing swelling and deformation; the activity of ATP synthase was decreased (P < 0.05) and the content of ATP in tissue of quadriceps femoris was also obviously lowered (P < 0.05). The body mass was (294.13 +/- 53.78) g in the group C, which was significantly lower than that in the group B (P < 0.05); the damaged mitochondrion was restored and merged among each other; the activity of ATP synthase was increased (P < 0.05); the content of ATP in tissue of quadriceps femoris was obviously lifted (P < 0.05). The results in group D were not different from those in group B.

CONCLUSION

The electroacupuncture with manifestation-root acupoint combination could improve the recovery of damaged structure of mitochondrion and promote the merge among each other, which could enhance oxidizing capacity, lower body mass and improve synthetic rate of ATP.

Endurance training modulates intramyocellular lipid compartmentalization and morphology in skeletal muscle of lean and obese women

CONTEXT

The accumulation of intramyocellular lipids (IMCLs) and mitochondrial dysfunction in skeletal muscle have been associated with insulin resistance in obesity. Endurance training (ET) increases mitochondrial content/activity and IMCL content in young, active men and women. We have previously shown that ET alters the size, number, and physical juxtaposition of IMCLs and mitochondria.

OBJECTIVE

The purpose of this study was to determine the effects of obesity and ET on mitochondrial function, IMCL content, and IMCL-mitochondria juxtaposition in sedentary lean and obese women. DESIGN, SETTING, SUBJECTS, INTERVENTION, AND MAIN OUTCOME MEASURES: Obese (n = 11) and lean (n = 12), sedentary women were recruited using local advertisements and underwent 12 weeks of ET in our training facility at McMaster University. Blood and muscle biopsy samples (vastus lateralis) were collected before and after ET to measure IMCL and mitochondrial ultrastructure, mitochondrial oxidative capacity, lipid oxidation capacity, and lipid metabolism by-products.

RESULTS

Obese women were insulin resistant (homeostasis model assessment of insulin resistance) compared with lean women. ET did not change body weight but increased mitochondrial oxidative and β-oxidation capacity in both groups. ET mediated reorganization of the muscle architecture, whereby IMCL content in the subsarcolemmal region was reduced with a concomitant increase in intermyofibrillar IMCLs. ET increased the percentage of IMCLs in direct contact with mitochondria and did not alter diacylglycerol and ceramide content in either group.

CONCLUSIONS

ET mediated positive changes in mitochondrial function and lipid oxidation and induced intracellular IMCL reorganization, which is reflective of greater IMCL turnover capacity in both lean and obese women.

Association between ultrasound measurements of muscle thickness, pennation angle, echogenicity and skeletal muscle strength in the elderly

The increase of elderly in our society requires simple tools for quantification of sarcopenia in inpatient and outpatient settings. The aim of this study was to compare parameters determined with musculoskeletal ultrasound (M-US) with muscle strength in young and elderly patients. In this prospective, randomised and observer blind study, 26 young (24.2 ± 3.7 years) and 26 old (age 67.8 ± 4.8 years) patients were included. Muscle thickness, pennation angle and echogenicity of all muscles of musculus quadriceps were measured by M-US and correlated with isometric maximum voluntary contraction force (MVC) of musculus quadriceps. Reproducibility of M-US measurements as well as simple and multiple regression models were calculated. Of all measured M-US variables the highest reproducibility was found for measurements of thickness (intraclass correlation coefficients, 85-97%). Simple regression analysis showed a highly significant correlation of thickness measurements of all muscles of musculus quadriceps with MVC in the elderly and in the young. Multiple regression analysis revealed that thickness of musculus vastus medialis had the best correlation with MVC in the elderly. This study showed that measurement of muscle thickness, especially of musculus vastus medialis, by M-US is a reliable, bedside method for monitoring the extent of sarcopenia.

Mitochondrial fusion, fission, and biogenesis in prolonged critically ill patients

CONTEXT

Critical illness induces swelling, enlargement, and dysfunction of mitochondria, which in liver, but not in muscle, is aggravated by excessive hyperglycemia. We previously demonstrated impaired autophagic clearance of damaged mitochondria in fed prolonged critically ill patients. Impaired fusion/fission-mediated repair and/or renewal through biogenesis may further accentuate mitochondrial abnormalities.

OBJECTIVE

We studied mitochondrial fusion/fission and biogenesis and how these are affected by preventing hyperglycemia with insulin during critical illness.

DESIGN AND SETTING

Patients admitted to a university hospital surgical/medical intensive-care unit participated in a randomized study.

PATIENTS

We studied adult prolonged critically ill patients vs. controls.

INTERVENTION

Tolerating hyperglycemia up to 215 mg/dl was compared with intensive insulin therapy targeting normoglycemia (80-110 mg/dl).

MAIN OUTCOME MEASURES

In liver and skeletal muscle, we quantified levels of several proteins involved in mitochondrial fusion/fission and biogenesis.

RESULTS

Key players in mitochondrial fusion/fission and biogenesis were up-regulated in postmortem liver (1.4- to 3.7-fold) and rectus abdominis (1.2- to 4.2-fold) but not in in vivo or postmortem vastus lateralis biopsies of critically ill patients. Maintaining normoglycemia with insulin attenuated the hepatic response in the mitochondrial fusion/fission process but did not affect the markers of mitochondrial biogenesis in liver or muscle.

CONCLUSIONS

Our observations suggest tissue-dependent attempts of compensatory activation of mitochondrial repair mechanisms during critical illness. Considering the previously observed persistent mitochondrial damage, this activation may be insufficient and contribute to mitochondrial dysfunction. Suppressed activation of fusion/fission when excessive hyperglycemia is prevented with insulin may reflect reduced need for diluting (less) damage during normoglycemia or, alternatively, a suppressive effect of insulin on repair.

Danon disease: a novel Lamp-2 gene mutation in a family with four affected members

This is a report of a family with four members affected with Danon disease and variable clinical presentations, including cardiomyopathy, skeletal muscle pathology, and hepatopathy. Analysis by electron microscopy of the quadriceps muscle from the proband and his brother showed abnormal mitochondria, and immunohistochemistry revealed no expression of LAMP-2 protein. This defect is due to a yet undescribed mutation located at the second nucleotide in the intron 8 of the Lamp-2 gene (c.1093+2 T>A) that generated exon 8 skipping confirmed at RNA level in the proband.

A new form of childhood onset, autosomal recessive spinocerebellar ataxia and epilepsy is localized at 16q21-q23

Childhood ataxias are a complex set of inherited disorders. Ataxias associated with generalized tonic-clonic epilepsy are usually included with the progressive myoclonus epilepsies (PME). Five disease entities, Unverricht-Lundborg disease, Lafora's disease, neuronal ceroid lipofuscinoses, myoclonic epilepsy with ragged red fibres and sialidoses, account for the majority of PME cases. Two rare forms of ataxia plus epilepsy, sensory ataxic neuropathy, dysarthria and ophthalmoparesis, and infantile onset spinocerebellar ataxia were described recently and found to be caused by defective mitochondrial proteins. We report here a large consanguineous family from Saudi Arabia with four affected children presenting with generalized tonic-clonic epilepsy, ataxia and mental retardation, but neither myoclonus nor mental deterioration. MRI and muscle biopsy of one patient revealed, respectively, posterior white matter hyperintensities and vacuolization of the sarcotubular system. We localized the defective gene by homozygosity mapping to a 19 Mb interval in 16q21-q23 between markers D16S3091 and D16S3050. Linkage studies in this region will allow testing for homogeneity of this novel ataxia-epilepsy entity.

Characterization of pre- and post-treatment pathology after enzyme replacement therapy for Pompe disease

In Pompe disease, a genetic deficiency of lysosomal acid alpha-glucosidase, glycogen accumulates abnormally in the lysosomes of skeletal, cardiac and smooth muscle, and contributes to clinically progressive and debilitating muscle weakness. The present study involved 8 infantile-onset Pompe patients, treated weekly with 10 mg/kg of recombinant human acid alpha-glucosidase (rhGAA). Muscle biopsies were obtained at baseline, 12 and 52 weeks post-treatment to establish an indicator of efficacy. Several histologic strategies were employed to characterize changes in pre- and post-treatment samples, including high-resolution light microscopy and digital histomorphometry, electron microscopy, capillary density and fiber type analysis, and confocal microscopy for satellite cell activation analysis. Histomorphometric analysis was performed on muscle samples to assess glycogen depletion in response to enzyme replacement therapy (ERT). The extent of glycogen clearance varied widely among these patient samples, and correlated well with clinical outcome. Low glycogen levels, mild ultrastructural damage, a high proportion of type I fibers, and young age at baseline were all features associated with good histologic response. There was no correlation between capillary density and glycogen clearance, and activated satellite cell levels were shown to be higher in post-treatment biopsies with poor histologic responses. This histopathologic study of infantile Pompe disease provides detailed insight into the cellular progression of the disease and its response to therapy while highlighting a number of methodologies which may be employed to assess regression or progression of the associated pathology. As enzyme replacement therapy becomes more prevalent for the treatment of lysosomal storage diseases, such evaluation of post-treatment pathology will likely become a more common occurrence in the daily practice of pathologists.

Secondary mitochondrial dysfunction in propionic aciduria: a pathogenic role for endogenous mitochondrial toxins

Mitochondrial dysfunction during acute metabolic crises is considered an important pathomechanism in inherited disorders of propionate metabolism, i.e. propionic and methylmalonic acidurias. Biochemically, these disorders are characterized by accumulation of propionyl-CoA and metabolites of alternative propionate oxidation. In the present study, we demonstrate uncompetitive inhibition of PDHc (pyruvate dehydrogenase complex) by propionyl-CoA in purified porcine enzyme and in submitochondrial particles from bovine heart being in the same range as the inhibition induced by acetyl-CoA, the physiological product and known inhibitor of PDHc. Evaluation of similar monocarboxylic CoA esters showed a chain-length specificity for PDHc inhibition. In contrast with CoA esters, non-esterified fatty acids did not inhibit PDHc activity. In addition to PDHc inhibition, analysis of respiratory chain and tricarboxylic acid cycle enzymes also revealed an inhibition by propionyl-CoA on respiratory chain complex III and alpha-ketoglutarate dehydrogenase complex. To test whether impairment of mitochondrial energy metabolism is involved in the pathogenesis of propionic aciduria, we performed a thorough bioenergetic analysis in muscle biopsy specimens of two patients. In line with the in vitro results, oxidative phosphorylation was severely compromised in both patients. Furthermore, expression of respiratory chain complexes I-IV and the amount of mitochondrial DNA were strongly decreased, and ultrastructural mitochondrial abnormalities were found, highlighting severe mitochondrial dysfunction. In conclusion, our results favour the hypothesis that toxic metabolites, in particular propionyl-CoA, are involved in the pathogenesis of inherited disorders of propionate metabolism, sharing mechanistic similarities with propionate toxicity in micro-organisms.

Expression of myoferlin in skeletal muscles of patients with dysferlinopathy

Myoferlin is a novel protein of unknown function with high homology to dysferlin, the gene mutations of which cause limb girdle muscular dystrophy type 2B and Miyoshi myopathy. The myoferlin gene seems to be a candidate for the modifier, and because of the high homology to dysferlin myoferlin may work as a compensator for the absence of dysferlin in dysferlinopathy. This hypothesis is based on the observation that utrophin, which has 80% homology with dystrophin, is overexpressing in the dystrophin deficient myofibers. To test this hypothesis, we investigated the myoferlin expression by immunoblot and immunohistochemical analysis in muscles of five patients with dysferlinopathy. For this aim, we generated a myoferlin specific antibody that does not cross react with dysferlin, and performed the immunoblot, immunohistochemical and immunoelectron microscopic studies. Immunohistochemical analysis showed that the antibodies against myoferlin and dysferlin clearly stained the normal human myofiber surface membranes. The electron microscopy of single immunogold labeled samples for myoferlin showed the presence of the molecular signal along the normal muscle cell membrane. Immunoblot analysis showed that the intensity of 230-kDa myoferlin band of dysferlinopathy muscle extracts was similar to that of normal muscle extracts. The immunostaining of dysferlinopathy muscles with anti-myoferlin antibody revealed a weak immunoreactivity along the muscle cell surface. Thus, the compensatory overexpression of myoferlin was not detected in muscles with dysferlinopathy.

Endurance training modulates the muscular transcriptome response to acute exercise

We hypothesized that in untrained individuals (n=6) a single bout of ergometer endurance exercise provokes a concerted response of muscle transcripts towards a slow-oxidative muscle phenotype over a 24-h period. We further hypothesized this response during recovery to be attenuated after six weeks of endurance training. We monitored the expression profile of 220 selected transcripts in muscle biopsies before as well as 1, 8, and 24 h after a 30-min near-maximal bout of exercise. The generalized gene response of untrained vastus lateralis muscle peaked after 8 h of recovery (P=0.001). It involved multiple transcripts of oxidative metabolism and glycolysis. Angiogenic and cell regulatory transcripts were transiently reduced after 1 h independent of the training state. In the trained state, the induction of most transcripts 8 h after exercise was less pronounced despite a moderately higher relative exercise intensity, partially because of increased steady-state mRNA concentration, and the level of metabolic and extracellular RNAs was reduced during recovery from exercise. Our data suggest that the general response of the transcriptome for regulatory and metabolic processes is different in the trained state. Thus, the response is specifically modified with repeated bouts of endurance exercise during which muscle adjustments are established.