Previous studies have demonstrated the beneficial effects of apple polyphenol (AP) intake on muscle endurance. Since mitochondria are critical for muscle endurance, we investigated mitochondrial ...enzyme activity, biogenesis, degradation and protein quality control. Twenty‐four Wistar rats were randomly fed a 5% AP diet (5% AP group, n = 8), a 0.5% AP diet (0.5% AP group, n = 8), or a control diet (control group, n = 8). After a 4‐week feeding period, the expression level of peroxisome proliferator‐activated receptor γ coactivator‐1α, a mitochondrial biosynthetic factor, did not increase, whereas that of transcription factor EB, another regulator of mitochondrial synthesis, significantly increased. Moreover, the mitochondrial count did not differ significantly between the groups. In contrast, mitophagy‐related protein levels were significantly increased. The enzymatic activities of mitochondrial respiratory chain complexes II, III and IV were significantly higher in the AP intake group than in the control group. We conclude that AP feeding increases the activity of respiratory chain complex enzymes in rat skeletal muscles. Moreover, mitochondrial biosynthesis and degradation may have increased in AP‐treated rats.
What is the central question of this study?
Does the administration of apple polyphenols (AP) affect mitochondrial respiratory chain complex enzyme activity, biogenesis, degradation and protein quality control in rat skeletal muscles?
What is the main finding and its importance?
AP feeding increases respiratory chain complex enzyme activity in rat skeletal muscle. Moreover, AP administration increases transcription factor EB activation, and mitophagy may be enhanced to promote degradation of dysfunctional mitochondria, but mitochondrial protein quality control was not affected.
Key points
Traumatic nerve injury or nerve disease leads to denervation and severe muscle atrophy. Recent evidence shows that mitochondrial loss could be a key mediator of skeletal muscle atrophy.
...Here, we show that daily heat stress treatment rescues denervation‐induced loss of mitochondria and concomitant muscle atrophy.
We also found that denervation‐activated autophagy‐dependent mitochondrial clearance (mitophagy) was suppressed by daily heat stress treatment. The molecular basis of this observation is explained by our results showing that heat stress treatment attenuates the increase of key proteins that regulate the tagging step for mitochondrial clearance and the intermediate step of autophagosome formation in denervated muscle.
These findings contribute to the better understanding of mitochondrial quality control in denervated muscle from a translational perspective and provide a mechanism behind the attenuation of muscle wasting by heat stress.
Traumatic nerve injury or motor neuron disease leads to denervation and severe muscle atrophy. Recent evidence indicates that loss of mitochondria and the related reduction in oxidative capacity could be key mediators of skeletal muscle atrophy. As our previous study showed that heat stress increased the numbers of mitochondria in skeletal muscle, we evaluated whether heat stress treatment could have a beneficial impact on denervation‐induced loss of mitochondria and subsequent muscle atrophy. Here, we report that daily heat stress treatment (mice placed in a chamber with a hot environment; 40°C, 30 min day−1, for 7 days) rescues the following parameters: (i) muscle atrophy (decreased gastrocnemius muscle mass); (ii) loss of mitochondrial content (decreased levels of ubiquinol–cytochrome c reductase core protein II, cytochrome c oxidase subunits I and IV and voltage‐dependent anion channel protein); and (iii) reduction in oxidative capacity (reduced maximal activities of citrate synthase and 3‐hydroxyacyl‐CoA dehydrogenase) in denervated muscle (produced by unilateral sciatic nerve transection). In order to gain a better understanding of the above mitochondrial adaptations, we also examined the effects of heat stress on autophagy‐dependent mitochondrial clearance (mitophagy). Daily heat stress normalized denervation‐activated induction of mitophagy (increased mitochondrial microtubule‐associated protein 1A/1B‐light chain3‐II (LC3‐II) with and without blocker of autophagosome clearance). The molecular basis of this observation was explained by the results that heat stress attenuated the denervation‐induced increase in key proteins that regulate the following steps: (i) the tagging step of mitochondrial clearance (increased mitochondrial Parkin, ubiquitin‐conjugated, P62/sequestosome 1 (P62/SQSTM1)); and (ii) the elongation step of autophagosome formation (increased Atg5–Atg12 conjugate and Atg16L). Overall, our results contribute to the better understanding of mitochondrial quality control and the mechanisms behind the attenuation of muscle wasting by heat stress in denervated skeletal muscle.
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Recently, non-spherical particles for inhalation have attracted attention. In the previous study, we reported non-spherical nanocomposite particles suitable for transpulmonary ...administration using amino acids I. Takeuchi et. al., Colloids Surf. A 529 (2017) 387–393. In this study, to apply this nanocomposite particle preparation method using amino acid to microparticles for inhalation, the influence of l-leucine on small fine particle fraction (FPF) values of poly(lactic-co-glycolide) (PLGA) microparticles and their phagocytotic ratio of alveolar macrophages was investigated. We prepared non-spherical rifampicin-loaded PLGA microparticles for inhalation using l-leucine and l-aspartic acid. The amino acids were added in aqueous phase, and the microparticles were prepared using a spray dryer via emulsion. Spherical rifampicin-loaded PLGA microparticles were also prepared using a conventional spray drying method for comparison. The FPF below 4.7μm of microparticles prepared using an aqueous phase with a leucine concentration of 0.2% (w/v) increased to 6.9 times (43.4±5.7%) that of conventional microspheres (6.3±4.0%). From the measurement result of the tap density, it was found that the shape of the particle had a large effect on the FPF value in this study. To evaluate the effectiveness of this particle in treating tuberculosis, microparticles phagocytotic ratio of alveolar macrophages (rat alveolar macrophage-derived NR8383 cells) was studied. The phagocytotic ratio of the microparticles prepared using an aqueous phase with a leucine concentration of 0.2% (w/v) was significantly higher than the spherical microparticles, and 0.34±0.16μg/mL of rifampicin concentration in alveolar macrophages was obtained.
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder characterized by progressive muscular weakness because of the loss of dystrophin. Extracellular Ca2+ flows into the ...cytoplasm through membrane tears in dystrophin-deficient myofibers, which leads to muscle contracture and necrosis. Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) takes up cytosolic Ca2+ into the sarcoplasmic reticulum, but its activity is decreased in dystrophic muscle. Here, we show that an allosteric SERCA activator, CDN1163, ameliorates dystrophic phenotypes in dystrophin-deficient mdx mice. The administration of CDN1163 prevented exercise-induced muscular damage and restored mitochondrial function. In addition, treatment with CDN1163 for 7 weeks enhanced muscular strength and reduced muscular degeneration and fibrosis in mdx mice. Our findings provide preclinical proof-of-concept evidence that pharmacological activation of SERCA could be a promising therapeutic strategy for DMD. Moreover, CDN1163 improved muscular strength surprisingly in wild-type mice, which may pave the new way for the treatment of muscular dysfunction.
Endothelial cells acquire different phenotypes to establish functional vascular networks. Vascular endothelial growth factor (VEGF) signaling induces endothelial proliferation, migration, and ...survival to regulate vascular development, which leads to the construction of a vascular plexuses with a regular morphology. The spatiotemporal localization of angiogenic factors and the extracellular matrix play fundamental roles in ensuring the proper regulation of angiogenesis. This review article highlights how and what kinds of extracellular environmental molecules regulate angiogenesis. Close interactions between the vascular and neural systems involve shared molecular mechanisms to coordinate developmental and regenerative processes. This review article focuses on current knowledge about the roles of angiogenesis in peripheral nerve regeneration and the latest therapeutic strategies for the treatment of peripheral nerve injury.
Abstract The forced turnout has a perceived risk of development of hallux valgus (HV) in ballet dancers. We determined how the forced turnout affects the sagittal mobility of the first ...tarsometatarsal (TMT) joint, which is one of the pathogenic factors of HV development. Seventeen female ballet dancers (body mass index: 18.2 ± 1.8 kg/m 2 ) were included and performed demi-plié in control, functional turnout, and forced turnout conditions. Ultrasound imaging synchronized with a three-dimensional motion analysis system was used for measuring the vertical locations of the first metatarsal and medial cuneiform (MC) to evaluate the first TMT joint mobility. Plantar displacement of MC and the first TMT joint mobility in the forced turnout were the greatest among the 3 conditions. Multiple regression analysis indicated that the greater extent of the forcing angle might increase the displacement of MC and the first TMT joint mobility. Evaluating the sagittal mobility of the first TMT joint in the forced turnout can assist in understanding the association between inappropriate techniques including the forced turnout and HV development in ballet dancers. Since the excessive mobility of the first TMT joint is a factor in HV development, the acquirement of adequate active turnout may have the potential to prevent HV development in ballet dancers.
Belt electrode skeletal muscle electrical stimulation (B-SES) can simultaneously contract multiple muscle groups. Although the beneficial effects of B-SES in clinical situations have been elucidated, ...its molecular mechanism remains unknown. In this study, we developed a novel rodent B-SES ankle stimulation system to test whether low-frequency stimulation prevents denervation-induced muscle atrophy. Electrical stimulations (7‒8 Hz, 30 min) with ankle belt electrodes were applied to Sprague-Dawley rats daily for one week. All animals were assigned to the control (CONT), denervation-induced atrophy (DEN), and DEN + electrical stimulation (ES) groups. The tibialis anterior (TA) and gastrocnemius (GAS) muscles were used to examine the effect of ES treatment. After seven daily sessions of continuous stimulation, muscle wet weight (n = 8-11), and muscle fiber cross-sectional area (CSA, n = 4-6) of TA and GAS muscles were lower in DEN and DEN + ES than in CON. However, it was significantly higher in DEN than DEN + ES, showing that ES partially prevented muscle atrophy. PGC-1α, COX-IV, and citrate synthase activities (n = 6) were significantly higher in DEN + ES than in DEN. The mRNA levels of muscle proteolytic molecules, Atrogin-1 and Murf1, were significantly higher in DEN than in CONT, while B-SES significantly suppressed their expression (p < 0.05). In conclusion, low-frequency electrical stimulation of the bilateral ankles using belt electrodes (but not the pad electrodes) is effective in preventing denervation-induced atrophy in multiple muscles, which has not been observed with pad electrodes. Maintaining the mitochondrial quantity and enzyme activity by low-frequency electrical stimulation is key to suppressing muscle protein degradation.
A recent study demonstrated that heat stress induces mitochondrial biogenesis in C2C12 myotubes, thereby implying that heat stress may be an effective treatment to enhance endurance training-induced ...mitochondrial adaptations in skeletal muscle. However, whether heat stress actually induces mitochondrial adaptations in skeletal muscle in vivo is unclear. In the present study, we report the novel findings that 1) whole body heat stress produced by exposure of ICR mice to a hot environment (40°C, 30 min/day, 5 days/wk, 3 wk) induced mitochondrial adaptations such as increased mitochondrial enzyme activity (citrate synthase and 3-hydroxyacyl CoA dehydrogenase) and respiratory chain protein content (complexes I-V) in skeletal muscle in vivo and 2) postexercise whole body heat stress additively enhanced endurance training-induced mitochondrial adaptations (treadmill running, 25 m/min, 30 min/day, 5 days/wk, 3 wk). Moreover, to determine the candidate mechanisms underlying mitochondrial adaptations, we investigated the acute effects of postexercise whole body heat stress on the phosphorylation status of cellular signaling cascades that subsequently induce mitochondrial gene transcription. We found that whole body heat stress boosted the endurance exercise-induced phosphorylation of p38 MAPK, increased the phosphorylation status of p70S6K, a biomarker of mammalian target of rapamycin complex 1 activity, and unexpectedly dephosphorylated AMP-activated protein kinase and its downstream target acetyl-CoA carboxylase in skeletal muscle. Our present observations suggest that heat stress can act as an effective postexercise treatment. Heat stress treatment appeared to be clinically beneficial for people who have difficulty participating in sufficient exercise training, such as the elderly, injured athletes, and patients.
Belt electrode-skeletal muscle electrical stimulation (B-SES) involves the use of belt-shaped electrodes to contract multiple muscle groups simultaneously. Twitch contractions have been demonstrated ...to protect against denervation-induced muscle atrophy in rats, possibly through mitochondrial biosynthesis. This study examined whether inducing tetanus contractions with B-SES suppresses muscle atrophy and identified the underlying molecular mechanisms. We evaluated the effects of acute (60 Hz, 5 min) and chronic (60 Hz, 5 min, every alternate day for one week) B-SES on the tibialis anterior (TA) and gastrocnemius (GAS) muscles in Sprague-Dawley rats using belt electrodes attached to both ankle joints. After acute stimulation, a significant decrease in the glycogen content was observed in the left and right TA and GAS, suggesting that B-SES causes simultaneous contractions in multiple muscle groups. B-SES enhanced p70S6K phosphorylation, an indicator of the mechanistic target of rapamycin complex 1 activity. During chronic stimulations, rats were divided into control (CONT), denervation-induced atrophy (DEN), and DEN + electrically stimulated with B-SES (DEN + ES) groups. After seven days of treatment, the wet weight (n = 8-11 for each group) and muscle fiber cross-sectional area (CSA, n = 6 for each group) of the TA and GAS muscles were reduced in the DEN and DEN + ES groups compared with that in the CON group. The DEN + ES group showed significantly higher muscle weight and CSA than those in the DEN group. Although RNA-seq and pathway analysis suggested that mitochondrial biogenesis is a critical event in this phenomenon, mitochondrial content showed no difference. In contrast, ribosomal RNA 28S and 18S (n = 6) levels in the DEN + ES group were higher than those in the DEN group, even though RNA-seq showed that the ribosome biogenesis pathway was reduced by electrical stimulation. The mRNA levels of the muscle proteolytic molecules atrogin-1 and MuRF1 were significantly higher in DEN than those in CONT. However, they were more suppressed in DEN + ES than those in DEN. In conclusion, tetanic electrical stimulation of both ankles using belt electrodes effectively reduced denervation-induced atrophy in multiple muscle groups. Furthermore, ribosomal biosynthesis plays a vital role in this phenomenon.
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