Interactions between monthly training volume, frequency and running distance per workout on marathon time.

PURPOSE: This study attempted to clarify the relationships between marathon time and monthly training volume, training frequency and the longest (LRD) or average running distance per workout (ARD), as well as their interactions. METHODS: Male recreational runners (n = 587) participating in the Hokkaido Marathon 2017 completed a questionnaire before the race; of these, 494 finished the race. We assessed age, running career, body height, body weight, body mass index (BMI), monthly training volume, training frequency, the LRD and the ARD. These indicators were each divided into 4 or 5 homogeneous subgroups to determine whether the other indicators in each subgroup predicted marathon time. RESULTS: In the training frequency subgroups, there were significant correlations between monthly training volume, the LRD or the ARD and marathon time, except for the subgroup that trained 2 times per week or less; in this subgroup, the relationship between the ARD and marathon time was not significant. In all monthly training volume subgroups, there were no significant relationships between training frequency, the LRD or the ARD and marathon time. In the ≥ 21 km LRD and ≥ 10 km ARD subgroups, there were significant correlations between monthly training volume and marathon time (all P < 0.01); these correlations were not significant in the 1-20 km LRD and < 10 km ARD subgroups. CONCLUSION: These results indicate that monthly training volume is the most important factor in predicting marathon time and that the influence of monthly training volume is only significant if the running distance per workout exceeded a certain level.

Secreted protein acidic and rich in cysteine (SPARC) improves glucose tolerance via AMP-activated protein kinase activation.

During exercise, skeletal muscles release cytokines, peptides, and metabolites that exert autocrine, paracrine, or endocrine effects on glucose homeostasis. In this study, we investigated the effects of secreted protein acidic and rich in cysteine (SPARC), an exercise-responsive myokine, on glucose metabolism in human and mouse skeletal muscle. SPARC-knockout mice showed impaired systemic metabolism and reduced phosphorylation of AMPK and protein kinase B in skeletal muscle. Treatment of SPARC-knockout mice with recombinant SPARC improved glucose tolerance and concomitantly activated AMPK in skeletal muscle. These effects were dependent on AMPK-γ3 because SPARC treatment enhanced skeletal muscle glucose uptake in wild-type mice but not in AMPK-γ3-knockout mice. SPARC strongly interacted with the voltage-dependent calcium channel, and inhibition of calcium-dependent signaling prevented SPARC-induced AMPK phosphorylation in human and mouse myotubes. Finally, chronic SPARC treatment improved systemic glucose tolerance and AMPK signaling in skeletal muscle of high-fat diet-induced obese mice, highlighting the efficacy of SPARC treatment in the management of metabolic diseases. Thus, our findings suggest that SPARC treatment mimics the effects of exercise on glucose tolerance by enhancing AMPK-dependent glucose uptake in skeletal muscle.-Aoi, W., Hirano, N., Lassiter, D. G., Björnholm, M., Chibalin, A. V., Sakuma, K., Tanimura, Y., Mizushima, K., Takagi, T., Naito, Y., Zierath, J. R., Krook, A. Secreted protein acidic and rich in cysteine (SPARC) improves glucose tolerance via AMP-activated protein kinase activation.

The influence of isoflavone for denervation-induced muscle atrophy.

PURPOSE: Decrease in activity stress induces skeletal muscle atrophy. A previous study showed that treatment with a high level (20%) of isoflavone inhibits muscle atrophy after short-term denervation (at 4 days) in mice. The present study was designed to elucidate whether the dietary isoflavone aglycone (AglyMax) at a 0.6% prevents denervation-mediated muscle atrophy, based on the modulation of atrogin-1- or apoptosis-dependent signaling. METHODS: Mice were fed either a normal diet or 0.6% AglyMax diet. One week later, the right sciatic nerve was cut. The wet weight, mean fiber area, amount of atrogin-1 and cleaved caspase-3 proteins, and the percentages of apoptotic nuclei were examined in the gastrocnemius muscle at 14 days after denervation. RESULTS: The 0.6% AglyMax diet significantly attenuated denervation-induced decreases in fiber atrophy but not the muscle wet weight. In addition, dietary isoflavone suppressed the denervation-induced apoptosis in spite of there being no significant changes in the amount of cleaved caspase-3 protein. In contrast, the 0.6% AglyMax diet did not significantly modulate the protein expression of atrogin-1 in the denervated muscle of mice. CONCLUSIONS: The isoflavone aglycone (AglyMax) at a 0.6% significantly would modulate muscle atrophy after denervation in mice, probably due to the decrease in apoptosis-dependent signaling.

Recent advances in pharmacological, hormonal, and nutritional intervention for sarcopenia.

Sarcopenia, the age-related loss of skeletal muscle mass, is characterized by a deterioration of muscle quantity and quality leading to a gradual slowing of movement, a decline in strength and power, increased risk of fall-related injury, and often frailty. This review focuses on the recent advances of pharmacological, hormonal, and nutritional approaches for attenuating sarcopenia. The article is composed of the data reported in many basic and some clinical studies for mammalian muscles. Resistance training combined with amino acid-containing supplements is the gold standard to prevent sarcopenia. Supplementation with proteins (amino acids) only did not influence sarcopenic symptoms. A myostatin-inhibiting strategy is the most important candidate to prevent sarcopenia in humans. Milder caloric restriction (CR, 15-25%) would also be effective for age-related muscle atrophy in humans. Supplementation with ursolic acid and ghrelin is an intriguing candidate to combat sarcopenia, although further systematic and fundamental research is needed on this treatment.

Resveratrol attenuates denervation-induced muscle atrophy due to the blockade of atrogin-1 and p62 accumulation.

Decrease in activity stress induces skeletal muscle atrophy. A previous study showed that treatment with resveratrol inhibits muscular atrophy in mdx mice, a model of DMD. However, almost all studies using resveratrol supplementation have only looked at adaptive changes in the muscle weight. The present study was designed to elucidate whether the resveratrol-inducing attenuation of skeletal muscle actually reflects the adaptation of muscle fibers themselves, based on the modulation of atrogin-1- or p62-dependent signaling. Mice were fed either a normal diet or 0.5% resveratrol diet. One week later, the right sciatic nerve was cut. The wet weight, mean fiber area, and amount of atrogin-1 and p62 proteins were examined in the gastrocnemius muscle at 14 days after denervation. The 0.5% resveratrol diet significantly prevented denervation-induced decreases in both the muscle weight and fiber atrophy. In addition, dietary resveratrol suppressed the denervation-induced atrogin-1 and p62 immunoreactivity. In contrast, 0.5% resveratrol supplementation did not significantly modulate the total protein amount of atrogin-1 or p62 in the denervated muscle of mice. Resveratrol supplementation significantly prevents muscle atrophy after denervation in mice, possibly due to the decrease in atrogin-1 and p62-dependent signaling.

Drugs of Muscle Wasting and Their Therapeutic Targets.

Muscle wasting and weakness such as cachexia, atrophy, and sarcopenia are characterized by marked decreases in the protein content, myonuclear number, muscle fiber size, and muscle strength. This chapter focuses on the recent advances of pharmacological approach for attenuating muscle wasting.A myostatin-inhibiting approach is very intriguing to prevent sarcopenia but not muscular dystrophy in humans. Supplementation with ghrelin is also an important candidate to combat sarcopenia as well as cachexia. Treatment with soy isoflavone, trichostatin A (TSA), and cyclooxygenase 2 (Cox2) inhibitors seems to be effective modulators attenuating muscle wasting, although further systematic research is needed on this treatment in particular concerning side effects.

Molecular mechanism of sarcopenia and cachexia: recent research advances.

Skeletal muscle provides a fundamental basis for human function, enabling locomotion and respiration. Muscle loss occurs as a consequence of several chronic diseases (cachexia) and normal aging (sarcopenia). Although many negative regulators (atrogin-1, muscle ring finger-1, nuclear factor-kappaB (NF-κB), myostatin, etc.) have been proposed to enhance protein degradation during both sarcopenia and cachexia, the adaptation of these mediators markedly differs within both conditions. Sarcopenia and cachectic muscles have been demonstrated to be abundant in myostatin-linked molecules. The ubiquitin-proteasome system (UPS) is activated during rapid atrophy model (cancer cachexia), but few mediators of the UPS change during sarcopenia. NF-κB signaling is activated in cachectic, but not in sarcopenic, muscle. Recent studies have indicated the age-related defect of autophagy signaling in skeletal muscle, whereas autophagic activation occurs in cachectic muscle. This review provides recent research advances dealing with molecular mediators modulating muscle mass in both sarcopenia and cachexia.

Current understanding of sarcopenia: possible candidates modulating muscle mass.

The world's elderly population is expanding rapidly, and we are now faced with the significant challenge of maintaining or improving physical activity, independence, and quality of life in the elderly. Sarcopenia, the age-related loss of skeletal muscle mass, is characterized by a deterioration of muscle quantity and quality leading to a gradual slowing of movement, a decline in strength and power, increased risk of fall-related injury, and often, frailty. Since sarcopenia is largely attributed to various molecular mediators affecting fiber size, mitochondrial homeostasis, and apoptosis, the mechanisms responsible for these deleterious changes present numerous therapeutic targets for drug discovery. Muscle loss has been linked with several proteolytic systems, including the ubuiquitin-proteasome, lysosome-autophagy, and tumor necrosis factor (TNF)-α/nuclear factor-kappaB (NF-κB) systems. Although many factors are considered to regulate age-dependent muscle loss, this gentle atrophy is not affected by factors known to enhance rapid atrophy (denervation, hindlimb suspension, etc.). In addition, defects in Akt-mammalian target of rapamycin (mTOR) and serum response factor (SRF)-dependent signaling have been found in sarcopenic muscle. Intriguingly, more recent studies indicated an apparent functional defect in autophagy- and myostatin-dependent signaling in sarcopenic muscle. In this review, we summarize the current understanding of the adaptation of many regulators in sarcopenia.

A novel myokine, secreted protein acidic and rich in cysteine (SPARC), suppresses colon tumorigenesis via regular exercise.

OBJECTIVE: Several epidemiological studies have shown that regular exercise can prevent the onset of colon cancer, although the underlying mechanism is unclear. Myokines are secreted skeletal muscle proteins responsible for some exercise-induced health benefits including metabolic improvement and anti-inflammatory effects in organs. The purpose of this study was to identify new myokines that contribute to the prevention of colon tumorigenesis. METHODS: To identify novel secreted muscle-derived proteins, DNA microarrays were used to compare the transcriptome of muscle tissue in sedentary and exercised young and old mice. The level of circulating secreted protein acidic and rich in cysteine (SPARC) was measured in mice and humans that performed a single bout of exercise. The effect of SPARC on colon tumorigenesis was examined using SPARC-null mice. The secretion and function of SPARC was examined in culture experiments. RESULTS: A single bout of exercise increased the expression and secretion of SPARC in skeletal muscle in both mice and humans. In addition, in an azoxymethane-induced colon cancer mouse model, regular low-intensity exercise significantly reduced the formation of aberrant crypt foci in wild-type mice but not in SPARC-null mice. Furthermore, regular exercise enhanced apoptosis in colon mucosal cells and increased the cleaved forms of caspase-3 and caspase-8 in wild-type mice but not in SPARC-null mice. Culture experiments showed that SPARC secretion from myocytes was induced by cyclic stretch and inhibited proliferation with apoptotic effect of colon cancer cells. CONCLUSIONS: These findings suggest that exercise stimulates SPARC secretion from muscle tissues and that SPARC inhibits colon tumorigenesis by increasing apoptosis.

Mitochondria as a potential regulator of myogenesis.

Recent studies have shown that mitochondria play a role in the regulation of myogenesis. Indeed, the abundance, morphology, and functional properties of mitochondria become altered when the myoblasts differentiate into myotubes. For example, mitochondrial mass/volume, mtDNA copy number, and mitochondrial respiration are markedly increased after the onset of myogenic differentiation. Besides, mitochondrial enzyme activity is also increased, suggesting that the metabolic shift from glycolysis to oxidative phosphorylation as the major energy source occurs during myogenic differentiation. Several lines of evidence suggest that impairment of mitochondrial function and activity blocks myogenic differentiation. However, yet little is known about the molecular mechanisms underlying the regulation of myogenesis by mitochondria. Understanding how mitochondria are involved in myogenesis will provide a valuable insight into the underlying mechanisms that regulate the maintenance of cellular homeostasis. Here, we will summarize the current knowledge regarding the role of mitochondria as a potential regulator of myogenesis.

Current Nutritional and Pharmacological Approaches for Attenuating Sarcopenia.

Sarcopenia is characterized by a gradual slowing of movement due to loss of muscle mass and quality, decreased power and strength, increased risk of injury from falls, and often weakness. This review will focus on recent research trends in nutritional and pharmacological approaches to controlling sarcopenia. Because nutritional studies in humans are fairly limited, this paper includes many results from nutritional studies in mammals. The combination of resistance training with supplements containing amino acids is the gold standard for preventing sarcopenia. Amino acid (HMB) supplementation alone has no significant effect on muscle strength or muscle mass in sarcopenia, but the combination of HMB and exercise (whole body vibration stimulation) is likely to be effective. Tea catechins, soy isoflavones, and ursolic acid are interesting candidates for reducing sarcopenia, but both more detailed basic research on this treatment and clinical studies in humans are needed. Vitamin D supplementation has been shown not to improve sarcopenia in elderly individuals who are not vitamin D-deficient. Myostatin inhibitory drugs have been tried in many neuromuscular diseases, but increases in muscle mass and strength are less likely to be expected. Validation of myostatin inhibitory antibodies in patients with sarcopenia has been positive, but excessive expectations are not warranted.

Pathophysiology of cachexia and characteristics of dysphagia in chronic diseases.

Cachexia is a condition characterized by skeletal muscle loss, weight loss, and anorexia. It is a complication of many diseases, not only cancer, and is characterized by chronic systemic inflammation. Cachexia and sarcopenia share common factors. The various symptoms observed in cachexia may be caused by multiple factors and inflammatory cytokines secreted by a tumor. Essentially, sarcopenia develops with aging, but it can occur at younger ages in the presence of cachexia, malnutrition, and disuse syndrome. In a recent study, dysphagia was found to be closely associated with malnutrition and sarcopenia. Factors specific to chronic diseases may influence the clinical outcome of dysphagia. Elderly people frequently exhibit dysphagia, but no research has been reported on whether cachexia is directly linked with dysphagia. Dysphagia is an important clinical problem, leading to aspiration pneumonia, suffocation, dehydration, malnutrition, and death. In addition to treating the patient, the degree of dysphagia needs to be accurately assessed. This review focuses on the pathogenesis of cachexia and the prevalence of dysphagia-related diseases, methods of assessment, and their impact on clinical outcomes.

Association of Oral Function and Dysphagia with Frailty and Sarcopenia in Community-Dwelling Older Adults: A Systematic Review and Meta-Analysis.

Studies investigating the associations of oral function and dysphagia with frailty and sarcopenia in community-dwelling older adults are increasing; however, they have not been systematically summarized. We conducted a systematic review to investigate these associations. We searched electronic databases and synthesized relevant data using conventional (frequentist-style) and Bayesian meta-analyses. Twenty-four studies were found to be eligible for our review, including 20 cross-sectional and four prospective cohort studies. Older adults with frailty or sarcopenia had lower tongue pressure, according to the results of conventional meta-analysis (mean difference [95% confidence interval or credible interval]: -6.80 kPa [-10.22 to -3.38] for frailty and -5.40 kPa [-6.62 to -4.17] for sarcopenia) and Bayesian meta-analysis (-6.90 kPa [-9.0 to -4.8] for frailty, -5.35 kPa [-6.78 to -3.89] for sarcopenia). People with frailty had a higher odds ratio (OR) for dysphagia according to the results of conventional meta-analysis (3.99 [2.17 to 7.32]) and Bayesian meta-analysis (1.38 [0.77 to 1.98]). However, the results were inconclusive for people with sarcopenia. A prospective association could not be determined because of the lack of information and the limited number of studies. Decreased oral function and dysphagia can be important characteristics of frailty and sarcopenia in community-dwelling older adults.

The recent understanding of the neurotrophin's role in skeletal muscle adaptation.

This paper summarizes the various effects of neurotrophins in skeletal muscle and how these proteins act as potential regulators of the maintenance, function, and regeneration of skeletal muscle fibers. Increasing evidence suggests that this family of neurotrophic factors influence not only the survival and function of innervating motoneurons but also the development and differentiation of myoblasts and muscle fibers. Muscle contractions (e.g., exercise) produce BDNF mRNA and protein in skeletal muscle, and the BDNF seems to play a role in enhancing glucose metabolism and may act for myokine to improve various brain disorders (e.g., Alzheimer's disease and major depression). In adults with neuromuscular disorders, variations in neurotrophin expression are found, and the role of neurotrophins under such conditions is beginning to be elucidated. This paper provides a basis for a better understanding of the role of these factors under such pathological conditions and for treatment of human neuromuscular disease.

The functional role of calcineurin in hypertrophy, regeneration, and disorders of skeletal muscle.

Skeletal muscle uses calcium as a second messenger to respond and adapt to environmental stimuli. Elevations in intracellular calcium levels activate calcineurin, a serine/threonine phosphatase, resulting in the expression of a set of genes involved in the maintenance, growth, and remodeling of skeletal muscle. In this review, we discuss the effects of calcineurin activity on hypertrophy, regeneration, and disorders of skeletal muscle. Calcineurin is a potent regulator of muscle remodeling, enhancing the differentiation through upregulation of myogenin or MEF2A and downregulation of the Id1 family and myostatin. Foxo may also be a downstream candidate for a calcineurin signaling molecule during muscle regeneration. The strategy of controlling the amount of calcineurin may be effective for the treatment of muscular disorders such as DMD, UCMD, and LGMD. Activation of calcineurin produces muscular hypertrophy of the slow-twitch soleus muscle but not fast-twitch muscles.

Age-related reductions in expression of serum response factor and myocardin-related transcription factor A in mouse skeletal muscles.

The molecular signaling pathways linking the atrophy of skeletal muscle during aging have not been identified. Using reverse transcription (RT)-PCR, Western blotting, and immunofluorescence microscopy, we investigated whether the amounts of RhoA, RhoGDI, SRF, MRTF-A, and MyoD in the triceps brachii and quadriceps muscles change with aging in mice. Young adult (3 mo) and aged (24 mo) C57BL/6J mice were used. Senescent mice possessed many fibers with central nuclei in the quadriceps muscle. Western blotting using a homogenate of whole muscle or the cytosolic fraction clearly showed that the amount of SRF protein was significantly decreased in the aged skeletal muscles. Immunofluorescence labeling indicated more SRF-positive muscle fibers in young mice. Both young and old mice possessed SRF immunoreactivity in some satellite cells expressing Pax7. MRTF-A and STARS mRNA levels significantly declined with aging in the triceps brachii and quadriceps muscles. The amount of MRTF-A protein was markedly reduced in the nuclear fraction of aged muscle of mice. The amounts of RhoA and RhoGDI in the crude homogenate or the cytosolic and membrane fractions were greater in the aged muscle. Senescent mice possessed significantly higher levels of MyoD protein in the cytosol and nucleus. Decreased SRF and MRTF expression may induce the atrophy of skeletal muscle with aging.

The expression pattern of PKCtheta in satellite cells of normal and regenerating muscle in the rat.

Protein kinase C (PKC) is a key enzyme in regulating a variety of cellular functions. PKCtheta is the most abundant PKC isoform expressed in skeletal muscle. However, the functional role of PKCtheta linked to muscle regeneration has not yet been identified. Using reverse transcription (RT)-PCR and immunofluorescence analysis, we investigated the expression patterns of PKCtheta in normal and regenerating tibialis anterior (TA) muscles in the rat. The amount of PKCtheta mRNA in the muscle increased from the 4th to 6th post-surgical day. Immunofluorescence revealed PKCtheta protein in quiescent satellite cells identified by c-Met. PKCtheta immunoreactivity was not observed in many proliferating satellite cells by labeling with BrdU in the regenerating muscle. At 4, 6 and 10 days postsurgery, PKCtheta immunoreactivity was observed in half the differentiating satellite cells labeling with myogenin. After 4 and 6 days, the localization of PKCtheta coincided with those of Pax7 and TGF-beta. Thus, PKCtheta may play an important role in inhibiting differentiation and maintaining the quiescent satellite cells in muscle regeneration.

Normal distribution of presenilin-1 and nicastrin in skeletal muscle and the differential responses of these proteins after denervation.

Presenilin-1 and nicastrin, two components of gamma-secretase associated with Alzheimer's disease plaques, are present in the synapses of the brain and in various peripheral organs, including skeletal muscle. In the present study, we examined the expression pattern of presenilin-1 and nicastrin in normal and denervated hindlimb muscles of the rat. Using immunohistochemical approaches, we found that presenilin-1 and AChRalpha was co-localized at the neuromuscular junction in the normal skeletal muscles of rats. The immunoreactivities of both presenilin-1 and nicastrin were also observed at the sarcolemma of muscle fibers. We discovered that presenilin-1 mRNA and its protein are upregulated after denervation of the soleus and tibialis anterior muscles. Furthermore, clear co-localization between presenilin-1 and DAPI, but not nicastrin, was noted in several myonuclei in the denervated muscles. We recognized a few fibers possessing both ubiquitin and presenilin-1 protein in the cytosol. The amount of presenilin-1 in the nucleus and membrane fraction was more abundantly expressed in the denervated muscle fibers. In contrast, no significant difference in the nicastrin protein level was observed between normal and denervated muscle fibers. These data suggest that enhanced presenilin-1 protein may play a role in the degeneration and regeneration of skeletal muscle.

p62/SQSTM1 but not LC3 is accumulated in sarcopenic muscle of mice.

AIM: We investigated the pathway of autophagy signaling linked to sarcopenia of mice. METHODS: Young adult (3-month) and aged (24- month) C57BL/6J mice were used. Using real-time PCR, Western blotting, and immunohistochemical microscopy, we evaluated the amounts of p62/SQSTM1, LC3, and Beclin-1 in the quadriceps muscle change with aging in mice. RESULTS: Marked fiber atrophy (30%) and many fibers with central nuclei were observed in the aged mice. Western blotting using homogenate of the cytosolic fraction clearly showed that the amounts of p62/SQSTM1 and Beclin-1 proteins were significantly increased in the aged skeletal muscle. The amounts of these proteins in both nuclear and membrane fractions did not change significantly with age. Immunofluorescence labeling indicated that aged mice more frequently possessed p62/SQSTM1-positive fibers in the cytosol in quadriceps muscle than young ones (aged: 14% vs. young: 1%). In aged muscle, p62/SQSTM1-positive fibers were significantly smaller than the surrounding p62/SQSTM1-negative fibers. Aging did not elicit significant changes in the mRNA levels of p62/SQSTM1 and Beclin-1, but decreased LC3 mRNA level. In aged muscle, the location of p62/SQSTM1 immunoreactivity was similar to that of Beclin-1 protein, but not LC3. CONCLUSION: Sarcopenia in mice appears to include a marked defect of autophagy signaling.

Prolactin receptor knockdown in the rat paraventricular nucleus by a morpholino-antisense oligonucleotide causes hypocalcemia and stress gastric erosion.

Under acute stress conditions in the rat, there is rapid and transient increase in circulating prolactin (PRL). This leads to an elevated expression of the long form of PRLR (PRLR-L) first in the hypothalamus and the choroid plexus. This increase in PRL is involved in the inhibition of stress-induced hypocalcemia and gastric erosion. In this study we used rat PRL and a PRLR morpholino-antisense oligonucleotide to elucidate the mechanism by which hypothalamic PRLR mediates the inhibition of restraint stress in water (RSW)-induced hypocalcemia and gastric erosion. We found that this effect is largely mediated by PRLRs in the paraventricular nucleus (PVN), medial preoptic nucleus, and ventromedial hypothalamus. We also show that when measured after 7 h of RSW, microinjection of the PRLR antisense oligonucleotide into these areas down-regulates RSW-enhanced expression of PRLR-L protein in the PVN and increases the plasma PRL level, but does not affect plasma levels of another hormone, GH. Furthermore, our experiments demonstrated that under nonstress conditions, knockdown of the PRLR in the PVN significantly lowers circulating Ca2+ levels, but does not affect gastric erosion. These results suggest that PRL acting on the PRLR-L in the PVN is one of the critical pathways for regulating circulating Ca2+ levels under both acute stress and nonstress conditions.