Skeletal Muscle Metabolism Research Articles

Tissue regeneration and gut microbiota-skeletal muscle axis via microRNAs and nutrition: a systematic review

Introduction: In the scenario of muscle regeneration in athletes, maintenance of skeletal muscle function is the prerequisite for tissue homeostasis and increased performance. MicroRNAs play a positive role in expanding our understanding of the controlling factors for skeletal muscle function. Recent progress has been made regarding gut microbiota, regenerative nutrition, and skeletal muscle metabolism. Objective: It was to carry out a systematic review of the main relations of regeneration of skeletal muscle-gut microbiota through nutrological functions, cells, and microRNAs. Methods: The systematic review rules of the PRISMA Platform were followed. The research was carried out from February to April 2023 in Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases. The quality of the studies was based on the GRADE instrument and the risk of bias was analyzed according to the Cochrane instrument. Results and Conclusion: A total of 217 articles were found. A total of 97 articles were fully evaluated and 49 were included and developed in the present systematic review study. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 54 studies at high risk of bias and 34 studies that did not meet the GRADE. It was concluded that miRNAs are widely present in skeletal muscle and play an irreplaceable tuning role in the proliferation, differentiation, apoptosis, development, and other physiological processes of skeletal muscle cells. The proposal that miRNAs are primarily involved in the cell's stress response makes miRNAs ideal for mediating the skeletal muscle response to changes in contractile activity. Research has accumulated evidence that confirms that miRNAs have played an important regulatory role in cell proliferation and differentiation, thus regulating skeletal muscle growth as highlighted in the small intestine by intestinal stem cells (LGR5+). The ketogenic or high-glucose diet regulates the self-renewal balance of LGR5+. Self-renewal and HSC differentiation can be regulated by manipulating vitamin C, A, or D levels and valine restriction. The composition of each athlete's microbiome influences sports performance.

Chronic UCN2 treatment desensitizes CRHR2 and improves insulin sensitivity

Urocortin 2 (UCN2) acts as a ligand for the G protein-coupled receptor corticotropin-releasing hormone receptor 2 (CRHR2). UCN2 has been reported to improve or worsen insulin sensitivity and glucose tolerance in vivo. Here we show that acute dosing of UCN2 induces systemic insulin resistance in male mice and skeletal muscle. Inversely, chronic elevation of UCN2 by injection with adenovirus encoding UCN2 resolves metabolic complications, improving glucose tolerance. CRHR2 recruits Gs in response to low concentrations of UCN2, as well as Gi and β-Arrestin at high concentrations of UCN2. Pre-treating cells and skeletal muscle ex vivo with UCN2 leads to internalization of CRHR2, dampened ligand-dependent increases in cAMP, and blunted reductions in insulin signaling. These results provide mechanistic insights into how UCN2 regulates insulin sensitivity and glucose metabolism in skeletal muscle and in vivo. Importantly, a working model was derived from these results that unifies the contradictory metabolic effects of UCN2.

Recovery from FOLFOX chemotherapy-induced systemic and skeletal muscle metabolic dysfunction in mice.

FOLFOX (5-fluorouracil, leucovorin, oxaliplatin) chemotherapy is used to treat colorectal cancer and can acutely induce metabolic dysfunction. However, the lasting effects on systemic and skeletal muscle metabolism after treatment cessation are poorly understood. Therefore, we investigated the acute and lasting effects of FOLFOX chemotherapy on systemic and skeletal muscle metabolism in mice. Direct effects of FOLFOX in cultured myotubes were also investigated. Male C57BL/6J mice completed four cycles (acute) of FOLFOX or PBS. Subsets were allowed to recover for 4 wk or 10 wk. Comprehensive Laboratory Animal Monitoring System (CLAMS) metabolic measurements were performed for 5 days before study endpoint. C2C12 myotubes were treated with FOLFOX for 24 hr. Acute FOLFOX attenuated body mass and body fat accretion independent of food intake or cage activity. Acute FOLFOX decreased blood glucose, oxygen consumption (V̇o2), carbon dioxide production (V̇co2), energy expenditure, and carbohydrate (CHO) oxidation. Deficits in V̇o2 and energy expenditure remained at 10 wk. CHO oxidation remained disrupted at 4 wk but returned to control levels after 10 wk. Acute FOLFOX reduced muscle COXIV enzyme activity, AMPK(T172), ULK1(S555), and LC3BII protein expression. Muscle LC3BII/I ratio was associated with altered CHO oxidation (r = 0.75, P = 0.03). In vitro, FOLFOX suppressed myotube AMPK(T172), ULK1(S555), and autophagy flux. Recovery for 4 wk normalized skeletal muscle AMPK and ULK1 phosphorylation. Our results provide evidence that FOLFOX disrupts systemic metabolism, which is not readily recoverable after treatment cessation. FOLFOX effects on skeletal muscle metabolic signaling did recover. Further investigations are warranted to prevent and treat FOLFOX-induced metabolic toxicities that negatively impact survival and life quality of patients with cancer.NEW & NOTEWORTHY The present study demonstrates that FOLFOX chemotherapy induces long-lasting deficits in systemic metabolism. Interestingly, FOLFOX modestly suppressed skeletal muscle AMPK and autophagy signaling in vivo and in vitro. The FOLFOX-induced suppression of muscle metabolic signaling recovered after treatment cessation, independent of systemic metabolic dysfunction. Future research should investigate if activating AMPK during treatment can prevent long-term toxicities to improve health and quality of life of patients with cancer and survivors.

LC–MS/MS based characterisation and differential expression of proteins in Himalayan snow trout, Schizothorax labiatus using LFQ technique

Molecular characterization of fish muscle proteins are nowadays considered as a key component to understand the role of specific proteins involved in various physiological and metabolic processes including their up and down regulation in the organisms. Coldwater fish specimens including snow trouts hold different types of proteins which help them to survive in highly diversified temperatures fluctuating from 0 to 20 °C. So, in current study, the liquid chromatography mass spectrometry using label free quantification technique has been used to investigate the muscle proteome profile of Schizothorax labiatus. For proteomic study, two weight groups of S. labiatus were taken from river Sindh. The proteomic analysis of group 1 revealed that a total of 235 proteins in male and 238 in female fish were recorded. However, when male and female S. labiatus were compared with each other on the basis of spectral count and abundance of peptides by ProteinLynx Global Server software, a total of 14 down-regulated and 22 up-regulated proteins were noted in this group. The highly down-regulated ones included homeodomain protein HoxA2b, retinol-binding protein 4, MHC class II beta chain and proopiomelanocortin while as the highly expressed up-regulated proteins comprised of gonadotropin I beta subunit, NADH dehydrogenase subunit 4, manganese superoxide dismutase, recombinase-activating protein 2, glycosyltransferase, chymotrypsin and cytochrome b. On the other hand, the proteomic characterisation of group 2 of S. labiatus revealed that a total of 227 proteins in male and 194 in female fish were recorded. When male and female S. labiatus were compared with each other by label free quantification, a total of 20 down-regulated and 18 up-regulated proteins were recorded. The down-regulated protein expression of group 2 comprised hepatic lipase, allograft inflammatory factor-1, NADH dehydrogenase subunit 4 and myostatin 1 while the highly expressed up-regulated proteins included glycogen synthase kinase-3 beta variant 2, glycogen synthase kinase-3 beta variant 5, cholecystokinin, glycogen synthase kinase-3 beta variant 3 and cytochrome b. Significant (P < 0.05) difference in the expression of down-regulated and up-regulated proteins was also noted between the two sexes of S. labiatus in each group. According to MS analysis, the proteins primarily concerned with the growth, skeletal muscle development and metabolism were down-regulated in river Sindh, which indicates that growth of fish during the season of collection i.e., winter was slow owing to less food availability, gonad development and low metabolic activity. While, the proteins related to immune response of fish were also noted to be down-regulated thereby signifying that the ecosystem has less pollution loads, microbial, pathogenic and anthropogenic activities. It was also found that the proteins involved in glycogen metabolism, reproductive and metabolic processes, particularly lipid metabolism were up-regulated in S. labiatus. The significant expression of these proteins may be connected to pre-spawning, gonad development and use of stored food as source of energy. The information generated in this study can be applied to future research aimed at enhancing food traceability, food safety, risk management and authenticity analysis.

1644-P: Exercise and Caloric Restriction Exert Different Benefits on Metabolism and Mechanical Function of Skeletal Muscle in Aging Condition

Exercise and caloric restriction improve skeletal muscle metabolism. However, the benefits of exercise and caloric restriction on metabolism and mechanical function of skeletal muscle in aging condition have never been compared. Seven-week-old male Wistar rats (n = 24) were divided into 4 groups (n = 6 per group) to receive subcutaneous injection with either 1) normal saline solution as a vehicle for 28 weeks, 2) 150 mg/kg/day of D-galactose [D-gal] for 28 weeks to induce premature aging, 3) D-gal for 28 weeks and exercise for 16 weeks (week 13-28), and 4) D-gal for 28 weeks and 30% caloric restriction for 16 weeks (week 13-28). The 17-month-old male Wistar rats (n = 6) were subcutaneously injected with the vehicle for 28 weeks as the naturally aged control. At the end of week 28, whole-body substrate oxidation during vigorous physical activity, total walking distance, and fitness level were determined. Then, all rats were sacrificed to collect the tibialis anterior muscle for protein expression analyses and mass spectrometry-based metabolomics study. We found that skeletal muscle of D-gal successfully mimicked that of natural aging. Exercise and caloric restriction equally improved whole-body carbohydrate oxidation during vigorous physical activity, myogenesis, and amino acid metabolism in skeletal muscle. However, exercise was superior to caloric restriction in terms of improving fatty acid oxidation, oxidative phosphorylation, and mechanical function of skeletal muscle. Interestingly, caloric restriction decreased oxidative stress, whereas exercise increased oxidative stress in skeletal muscle. These findings suggested that the benefits of exercise and caloric restriction on metabolism and mechanical function of skeletal muscle in aging were different. Hence, either combined exercise and caloric restriction, exercise with antioxidant supplement, or caloric restriction with fatty acid oxidation enhancement is highly recommended. Disclosure C.Thonusin: None. P.Pantiya: None. W.Nawara: None. B.Arunsak: None. S.Sriwichaiin: None. N.Chattipakorn: None. S.C.Chattipakorn: None.

581-P: The Effects of Resistance Training on Insulin Resistance Development in Female Rodents with Type 1 Diabetes

The etiology of insulin resistance (IR) development in type 1 diabetes (T1D) remains unclear; however, impaired glucose metabolism in skeletal muscle may play a role. While IR development has been established in male rodents with T1D, female rodents have yet to be examined in this context. Resistance exercise training (RT) has been shown to improve IR and is associated with a lower risk of hypoglycemia onset in T1D compared to aerobic exercise. The purpose of this study was to investigate the effects of RT on IR development in female rodents with T1D. Forty Sprague-Dawley 8-week-old female rats were divided into four groups: control sedentary (CS; n=10), control trained (CT; n=10), T1D sedentary (DS; n=10), T1D trained (DT; n=10). Multiple low-dose Streptozotocin injections (20 mg/kg each day for 7 consecutive days) were used to induce T1D. Blood glucose levels were maintained in normal range (4-9mmol/L) with one implanted insulin pellet (2IU/day). CT and DT underwent weighted ladder climbing 5 days/week for 6 weeks. Intravenous glucose tolerance tests (IVGTT) were conducted on all animals during weeks 4 and 7. Results demonstrate that DS animals exhibited significantly increased weekly blood glucose measures compared to all groups including DT (p&amp;lt;0.05), despite similar insulin dosage levels. This was concomitant with a significant increase in area under the curve following IVGTT from week 4 to week 7 in DS (p&amp;lt;0.05), indicative of a reduction in insulin sensitivity. DS animals also exhibited significantly greater glycogen content in white gastrocnemius muscle compared to all groups (p&amp;lt;0.05). These results indicate that female rodents with T1D develop poor glycemic control and IR which can be attenuated with RT, possibly related to differences in glycogen content within muscle. This data supports the negative role of elevated muscle glycogen on insulin sensitivity in T1D and the potential role of RT in ameliorating these metabolic changes. Disclosure M.Sammut: None. D.Mcbey: None. C.Melling: None.

1643-P: Unique Signature of Circular RNA in Skeletal Muscle of Different Insulin Sensitivity

Diabetes pathologies are complex, affecting numerous organs such as liver, pancreas, and skeletal muscle. Circular RNAs (circRNA) are a class of non-coding RNAs that are characterized by a covalently closed loop structure. Functionally, they can act on cell physiology by sponging microRNAs and thus regulating gene and protein expression. The emerging function of these circRNA is not fully understood, but initial studies have recently shown that circRNA are involved in insulin secretion regulation. Therefore, deregulation of this class of RNAs may lead to metabolic disorders in pancreatic β-cells and thus be involved in the pathogenesis of type 1 (T1DM) and type 2 diabetes (T2DM). Our research is focused on the unique signature by circular RNA and the impact on skeletal muscle metabolism. We demonstrated that human skeletal muscle cells in culture maintain their gene expression phenotype. A different gene signature of the cells according to their different muscular fiber type sources (oxidative versus glycolytic versus mixt) was confirmed. Moreover, an independent microRNA composition has also been highlighted. As CircRNA can regulate microRNAs and then gene expression and proteins, we wondered whether these observed signatures could be explained by circRNA. We therefore focused on key circRNAs involved in myogenesis (such as circZNF609, circHIPK3) and we were able to see that there is a difference in expression of circRNA according to the muscle type. Moreover, we analyzed correlations between circRNA levels and insulin sensitivity (measured by PKB phosphorylation). Finally, we are currently completing our analysis with in-depth sequencing techniques to identify all expressed circRNA in muscle fiber types to potentially identify new targets in insulin metabolic pathways. Disclosure M.Yepmo: None. E.Meugnier: None. M.Pinget: Consultant; Novo Nordisk, Stock/Shareholder; ILONOV. K.Bouzakri: Consultant; Adocia, Stock/Shareholder; ILONOV.

266-LB: SGLT2 Inhibition Improved Endurance Performance of db/db Mice Accompanied by an Increased Endogenous AMPK Activator in Skeletal Muscles

Background: Diabetes is associated with loss of skeletal muscle mass and function. Specifically, diabetes may affect the function of oxidative muscle fibers with lower fatigability and higher oxidative capacity in skeletal muscle. The effects of SGLT2 inhibition on skeletal muscle metabolism and function in patients with type 2 diabetes remain unclear. Methods: Male db/db (diabetic) and db/+ (non-diabetic) mice at 8 weeks of age were fed a normal chow diet or a diet containing canagliflozin (CANA) for 4 weeks. Grip strength and running distance were assessed during CANA treatment. At the end of CANA treatment, we measured muscle weight and analyzed metabolites in skeletal muscle. Results: The weights of the oxidative soleus and glycolytic extensor digitorum longus muscles were reduced by approximately 50% in the diabetic group compared to the non-diabetic group, but neither was altered by CANA treatment. Grip strength did not differ between the CANA-treated diabetic, diabetic, and non-diabetic groups. However, the running distance decreased in the diabetic group compared to the non-diabetic group (89 ± 60 m vs. 1980 ± 276 m). This was partially restored by CANA treatment (89 ± 60 m vs. 415 ± 140 m). Metabolomic analysis revealed that long-chain acyl-CoA increased and medium-chain and short-chain acyl-CoA decreased in diabetic soleus muscle. In contrast, CANA treatment increased medium-chain and short-chain acyl-CoA. Furthermore, CANA increased 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranosyl 5’-monophosphate (AICARP), an endogenous AMPK activator, by approximately 3-fold in diabetic soleus muscle with increased levels of AMPK phosphorylation (Thr172). Conclusion: These results suggest that SGLT2 inhibitors may activate the AICARP/AMPK pathway and improve impaired oxidative muscle function in patients with type 2 diabetes. Disclosure S. Nakamura: None. Y. Miyachi: None. H. Yokomizo: None. H. Otsuka: None. R. Sakamoto: None. M. Takahashi: None. Y. Izumi: None. T. Miyazawa: None. T. Bamba: None. Y. Ogawa: None.

1640-P: Meroterpenoid-Rich Ethanolic Extract of Sargassum serratifolium (MES) Alters Macrophage Transcriptome and Secretion Profile toward Improving Muscle Atrophy and Glucose Intolerance

Skeletal muscle plays an essential role in glucose homeostasis. Of many cell types in the skeletal muscle, recent studies indicate that secretion factors derived from macrophages are important for glucose metabolism in the skeletal muscle. Here, RNA Sequencing analysis showed that Lipopolysaccharide (LPS) treatment broadly altered the transcriptome of macrophages, of which signaling related to secretion factors was markedly altered toward elevating unfavorable cytokines to maintain skeletal muscle metabolism. On the other hand, the treatment of the Meroterpenoid-Rich Extract of Sargassum Serratifolium (MES), a strong anti-inflammatory and antioxidant extract found in our previous studies, reversed the LPS-induced signaling pathways. We further tested whether the treatment of conditioned media (CM) derived from LPS-macrophage (LPS-CM) or CM derived from LPS-macrophage treated with MES (MES-CM) affects glucose homeostasis in differentiated C2C12 myotube cells. LPS-CM treatment notably increased mRNA levels of muscle atrophy-associated genes including MuRF1, MAFbx, and Myostatin, and decreased glucose uptake, and MES-CM treatment reversed these characteristics, indicating that secretion factors induced by LPS or MES either impair or improve muscle glucose homeostasis, respectively. We further analyzed secretion factors inside by proteome array and data showed that LPS-CM includes GDF-15, IL-1 α/β, RAGE, etc related to muscle atrophy and glucose intolerance, which were significantly reduced in MES-CM. These data indicate that LPS- or MES-induced changes in the transcriptome in macrophages are closely related to the alteration in secretion factors toward either impairing or improving glucose metabolism in the skeletal muscle respectively. Of many, the decrease in macrophage-derived cytokine mentioned above may be important for glucose homeostasis in the skeletal muscle. Disclosure H.Ryu: None. B.Lee: None.

Association of carnitine insufficiency with sarcopenia and dynapenia in patients with heart failure.

L-carnitine transports fatty acids into mitochondria and contributes to energy metabolism in skeletal muscles. However, the association between carnitine insufficiency and skeletal muscle weakness, namely sarcopenia and dynapenia, in patients with heart failure (HF) remains unclear. In total, 124 patients with HF were enrolled in this study. Carnitine insufficiency was indicated by a decrease in serum free carnitine (FC) levels of less than 36 μmol/L or an elevated serum acylcarnitine (AC) to free carnitine (FC) ratio (AC/FC ratio) of 0.27 or higher. Skeletal muscle weakness was defined as reduced handgrip strength and classified into two phenotypes: sarcopenia (low muscle strength with low skeletal muscle mass) and dynapenia (low muscle strength with normal skeletal muscle mass). Patients with carnitine insufficiency had a significantly higher prevalence of muscle weakness and a lower 6-min walk distance than those without carnitine insufficiency (P < 0.05). A machine learning model showed that older age (≥77 years) and, in patients aged 64-76 years, a higher AC/FC ratio (≥0.31) were associated with sarcopenia. However, there was only a week association between carnitine levels and dynapenia. The effect of carnitine insufficiency on skeletal muscle weakness was greater in patients with low skeletal muscle mass than in those with normal skeletal muscle mass (P < 0.05 for interaction). Carnitine insufficiency is more closely associated with sarcopenia than with dynapenia in patients with HF, suggesting carnitine insufficiency as a potential therapeutic target for sarcopenia in these patients. Geriatr Gerontol Int 2023; 23: 524-530.

Skeletal Muscle-Specific Bis Depletion Leads to Muscle Dysfunction and Early Death Accompanied by Impairment in Protein Quality Control.

Bcl-2-interacting cell death suppressor (BIS), also called BAG3, plays a role in physiological functions such as anti-apoptosis, cell proliferation, autophagy, and senescence. Whole-body Bis-knockout (KO) mice exhibit early lethality accompanied by abnormalities in cardiac and skeletal muscles, suggesting the critical role of BIS in these muscles. In this study, we generated skeletal muscle-specific Bis-knockout (Bis-SMKO) mice for the first time. Bis-SMKO mice exhibit growth retardation, kyphosis, a lack of peripheral fat, and respiratory failure, ultimately leading to early death. Regenerating fibers and increased intensity in cleaved PARP1 immunostaining were observed in the diaphragm of Bis-SMKO mice, indicating considerable muscle degeneration. Through electron microscopy analysis, we observed myofibrillar disruption, degenerated mitochondria, and autophagic vacuoles in the Bis-SMKO diaphragm. Specifically, autophagy was impaired, and heat shock proteins (HSPs), such as HSPB5 and HSP70, and z-disk proteins, including filamin C and desmin, accumulated in Bis-SMKO skeletal muscles. We also found metabolic impairments, including decreased ATP levels and lactate dehydrogenase (LDH) and creatine kinase (CK) activities in the diaphragm of Bis-SMKO mice. Our findings highlight that BIS is critical for protein homeostasis and energy metabolism in skeletal muscles, suggesting that Bis-SMKO mice could be used as a therapeutic strategy for myopathies and to elucidate the molecular function of BIS in skeletal muscle physiology.

The Effect of the Microbiota Metabolite – Butyric Acid on Motor Coordination, Muscle Strength and the Level of Oxidative Stress in Skeletal Muscles in Mice with Dysbiosis

According to modern concepts, the composition and diversity of the intestinal microbiota play an essential role in maintaining immunity, homeostasis, and, in general, the physiological functions of the host organism. Recently the positive role of the microbiota and its metabolites especially short-chain fatty acids, in the metabolism and functional activity of skeletal muscles was reported. The aim of our work was to analyze muscle strength and motor coordination in mice after injection of broad–spectrum antibiotics with simultaneous administration of a microbiota metabolite – one of the representatives of short-chain fatty acids – butyric acid. In addition, we determined the level of malondialdehyde, the concentration of total glutathione and the activity of glutathione peroxidases in the muscles of the hind limbs in mice with administration of antibiotics and butyric acid. The administration of antibiotics to adolescent mice for two weeks induced higher mortality and decrease of weight, and also caused significant changes in motor behavior, including an increase in horizontal motor activity, decrease in vertical motor activity, muscle strength, and motor coordination. A higher level of oxidative stress was found in the muscle tissues of the hind limbs of mice treated with antibiotics. At the same time, oral administration of butyric acid prevented the observed changes and improved not only behavioral disorders, but also partially reduced the level of oxidative stress. In conclusion, metabolite of normal microbiota has a positive effect on the functional and biochemical parameters of skeletal muscles in dysbiosis, which can be used to prevent loss of muscle function in various pathological conditions.

Determination of Vitamin K1, MK-4, MK-7, and D Levels in Human Serum of Postmenopausal Osteoporosis Women Based on High Stability LC-MS/MS: MK-7 May Be a New Marker of Bone Metabolism

Introduction: Vitamin K (VK) as well as vitamin D (VD) plays an important role in osteoporosis. Vitamin K1 (VK1), vitamin K2 (VK2, menaquinone-4 (MK-4), and menaquinone-7 (MK-7)) are significant for the metabolism of skeletal muscle. 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 (25(OH)D2 and 25(OH)D3) reflect circulating VD levels. More sensitive measurements remain to be developed. In the present study, a new high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of VK1, VK2 (MK-4 and MK-7), as well as 25(OH)D2 and 25(OH)D3 levels in human serum. Methods: We developed a simple LC-MS/MS method for the determination of VK1, MK-4, MK-7, 25(OH)D2, and 25(OH)D3 levels in human serum and validated the method in a study cohort of 200 patients divided into the premenopausal women group and postmenopausal osteoporosis patient group. Results: The overall precision (coefficient of variation) ranged from 2.66 to 10.11% in the specified working range (0.05–5 ng/mL) for VK1, MK-4, and MK-7. Serum VK1, MK-4, and MK-7 levels in postmenopausal women with osteoporosis were 1.187 ± 0.094 ng/mL, 0.058 ± 0.009 ng/mL, and 0.885 ± 0.064 ng/mL, respectively (mean ± standard deviation). Serum VK1, MK-4, and MK-7 levels in premenopausal women were 1.143 ± 0.103 ng/mL, 0.028 ± 0.003 ng/mL, and 1.553 ± 0.226 ng/mL, respectively. Serum 25(OH)D2 and 25(OH)D3 levels in postmenopausal women with osteoporosis were 0.757 ± 0.056 ng/mL and 11.72 ± 0.632 ng/mL, respectively. Serum 25(OH)D2 and 25(OH)D3 levels in premenopausal were 1.793 ± 0.575 ng/mL and 12.42 ± 1.069 ng/mL, respectively. Conclusion: A new LC-MS/MS method for determination of serum VK and VD levels was evaluated and validated. MK-7 in plasma decreased earlier than VD in postmenopausal osteoporosis patients. MK-7 status is significantly associated with osteoporosis and could be considered a predictable biomarker in the diagnosis of osteoporosis in postmenopausal women.

Association of Gene Variants with Seasonal Variation in Muscle Strength and Aerobic Capacity in Elite Skiers.

Background: The training of elite skiers follows a systematic seasonal periodization with a preparation period, when anaerobic muscle strength, aerobic capacity, and cardio-metabolic recovery are specifically conditioned to provide extra capacity for developing ski-specific physical fitness in the subsequent competition period. We hypothesized that periodization-induced alterations in muscle and metabolic performance demonstrate important variability, which in part is explained by gene-associated factors in association with sex and age. Methods: A total of 34 elite skiers (20.4 ± 3.1 years, 19 women, 15 men) underwent exhaustive cardiopulmonary exercise and isokinetic strength testing before and after the preparation and subsequent competition periods of the World Cup skiing seasons 2015-2018. Biometric data were recorded, and frequent polymorphisms in five fitness genes, ACE-I/D (rs1799752), TNC (rs2104772), ACTN3 (rs1815739), and PTK2 (rs7460, rs7843014), were determined with specific PCR reactions on collected DNA. Relative percentage changes of cardio-pulmonary and skeletal muscle metabolism and performance over the two seasonal periods were calculated for 160 data points and subjected to analysis of variance (ANOVA) to identify hypothesized and novel associations between performance alterations and the five respective genotypes and determine the influence of age × sex. A threshold of 0.1 for the effect size (h2) was deemed appropriate to identify relevant associations and motivate a post hoc test to localize effects. Results: The preparation and competition periods produced antidromic functional changes, the extent of which varied with increasing importance for anaerobic strength, aerobic performance, cardio-metabolic efficiency, and cardio-metabolic/muscle recovery. Only peak RER (-14%), but not anaerobic strength and peak aerobic performance, and parameters characterizing cardio-metabolic efficiency, differed between the first and last studied skiing seasons because improvements over the preparation period were mostly lost over the competition period. A number of functional parameters demonstrated associations of variability in periodic changes with a given genotype, and this was considerably influenced by athlete "age", but not "sex". This concerned age-dependent associations between periodic changes in muscle-related parameters, such as anaerobic strength for low and high angular velocities of extension and flexion and blood lactate concentration, with rs1799752 and rs2104772, whose gene products relate to sarcopenia. By contrast, the variance in period-dependent changes in body mass and peak VO2 with rs1799752 and rs2104772, respectively, was independent of age. Likely, the variance in periodic changes in the reliance of aerobic performance on lactate, oxygen uptake, and heart rate was associated with rs1815739 independent of age. These associations manifested at the post hoc level in genotype-associated differences in critical performance parameters. ACTN3 T-allele carriers demonstrated, compared to non-carriers, largely different periodic changes in the muscle-associated parameters of aerobic metabolism during exhaustive exercise, including blood lactate and respiration exchange ratio. The homozygous T-allele carriers of rs2104772 demonstrated the largest changes in extension strength at low angular velocity during the preparation period. Conclusions: Physiological characteristics of performance in skiing athletes undergo training period-dependent seasonal alterations the extent of which is largest for muscle metabolism-related parameters. Genotype associations for the variability in changes of aerobic metabolism-associated power output during exhaustive exercise and anaerobic peak power over the preparation and competition period motivate personalized training regimes. This may help to predict and maximize the benefit of physical conditioning of elite skiers based on chronological characteristics and the polymorphisms of the ACTN3, ACE, and TNC genes investigated here.

Physical activity impacts resting skeletal muscle myosin conformation and lowers its ATP consumption.

It has recently been established that myosin, the molecular motor protein, is able to exist in two conformations in relaxed skeletal muscle. These conformations are known as the super-relaxed (SRX) and disordered-relaxed (DRX) states and are finely balanced to optimize ATP consumption and skeletal muscle metabolism. Indeed, SRX myosins are thought to have a 5- to 10-fold reduction in ATP turnover compared with DRX myosins. Here, we investigated whether chronic physical activity in humans would be associated with changes in the proportions of SRX and DRX skeletal myosins. For that, we isolated muscle fibers from young men of various physical activity levels (sedentary, moderately physically active, endurance-trained, and strength-trained athletes) and ran a loaded Mant-ATP chase protocol. We observed that in moderately physically active individuals, the amount of myosin molecules in the SRX state in type II muscle fibers was significantly greater than in age-matched sedentary individuals. In parallel, we did not find any difference in the proportions of SRX and DRX myosins in myofibers between highly endurance- and strength-trained athletes. We did however observe changes in their ATP turnover time. Altogether, these results indicate that physical activity level and training type can influence the resting skeletal muscle myosin dynamics. Our findings also emphasize that environmental stimuli such as exercise have the potential to rewire the molecular metabolism of human skeletal muscle through myosin.

Exercise metabolism and adaptation in skeletal muscle.

Viewing metabolism through the lens of exercise biology has proven an accessible and practical strategy to gain new insights into local and systemic metabolic regulation. Recent methodological developments have advanced understanding of the central role of skeletal muscle in many exercise-associated health benefits and have uncovered the molecular underpinnings driving adaptive responses to training regimens. In this Review, we provide a contemporary view of the metabolic flexibility and functional plasticity of skeletal muscle in response to exercise. First, we provide background on the macrostructure and ultrastructure of skeletal muscle fibres, highlighting the current understanding of sarcomeric networks and mitochondrial subpopulations. Next, we discuss acute exercise skeletal muscle metabolism and the signalling, transcriptional and epigenetic regulation of adaptations to exercise training. We address knowledge gaps throughout and propose future directions for the field. This Review contextualizes recent research of skeletal muscle exercise metabolism, framing further advances and translation into practice.

Magnetic Resonance Imaging Techniques in Peripheral Arterial Disease.

Significance: Peripheral arterial disease (PAD) leads to a significant burden of morbidity and impaired quality of life globally. Diabetes is a significant risk factor accelerating the development of PAD with an associated increase in the risk of chronic wounds, tissue, and limb loss. Various magnetic resonance imaging (MRI) techniques are being increasingly acknowledged as useful methods of accurately assessing PAD. Recent Advances: Conventionally utilized MRI techniques for assessing macrovascular disease have included contrast enhanced magnetic resonance angiography (MRA), noncontrast time of flight MRA, and phase contrast MRI, but have significant limitations. In recent years, novel noncontrast MRI methods assessing skeletal muscle perfusion and metabolism such as arterial spin labeling (ASL), blood-oxygen-level dependent (BOLD) imaging, and chemical exchange saturation transfer (CEST) have emerged. Critical Issues: Conventional non-MRI (such as ankle-brachial index, arterial duplex ultrasonography, and computed tomographic angiography) and MRI based modalities image the macrovasculature. The underlying mechanisms of PAD that result in clinical manifestations are, however, complex, and imaging modalities that can assess the interaction between impaired blood flow, microvascular tissue perfusion, and muscular metabolism are necessary. Future Directions: Further development and clinical validation of noncontrast MRI methods assessing skeletal muscle perfusion and metabolism, such as ASL, BOLD, CEST, intravoxel incoherent motion microperfusion, and techniques that assess plaque composition, are advancing this field. These modalities can provide useful prognostic data and help in reliable surveillance of outcomes after interventions.

Alterations in skeletal muscle abundance of protein turnover, stress, and antioxidant proteins during the periparturient period in dairy cows fed ethyl-cellulose rumen-protected methionine

Skeletal muscle turnover helps support the physiological needs of dairy cows during the transition into lactation. We evaluated effects of feeding ethyl-cellulose rumen-protected methionine (RPM) during the periparturient period on abundance of proteins associated with transport AA and glucose, protein turnover, metabolism, and antioxidant pathways in skeletal muscle. Sixty multiparous Holstein cows were used in a block design and assigned to a control or RPM diet from -28 to 60 d in milk. The RPM was fed at a rate of 0.09% or 0.10% of dry matter intake (DMI) during the prepartal and postpartal periods to achieve a target Lys:Met ratio in the metabolizable protein of ∼2.8:1. Muscle biopsies from the hind leg of 10 clinically healthy cows per diet collected at -21, 1, and 21 d relative to calving were used for western blotting of 38 target proteins. Statistical analysis was performed using the PROC MIXED statement of SAS version 9.4 (SAS Institute Inc.) with cow as random effect, whereas diet, time, and diet × time were the fixed effects. Diet × time tended to affect prepartum DMI, with RPM cows consuming 15.2 kg/d and controls 14.6 kg/d. However, diet had no effect on postpartum DMI (17.2 and 17.1 ± 0.4 kg/d for control and RPM, respectively). Milk yield during the first 30 d in milk was also not affected by diet (38.1 and 37.5 ± 1.9 kg/d for control and RPM, respectively). Diet or time did not affect the abundance of several AA transporters or the insulin-induced glucose transporter (SLC2A4). Among evaluated proteins, feeding RPM led to lower overall abundance of proteins associated with protein synthesis (phosphorylated EEF2, phosphorylated RPS6KB1), mTOR activation (RRAGA), proteasome degradation (UBA1), cellular stress responses (HSP70, phosphorylated MAPK3, phosphorylated EIF2A, ERK1/2), antioxidant response (GPX3), and de novo synthesis of phospholipids (PEMT). Regardless of diet, there was an increase in the abundance of the active form of the master regulator of protein synthesis phosphorylated MTOR and the growth-factor-induced serine/threonine kinase phosphorylated AKT1 and PIK3C3, whereas the abundance of a negative regulator of translation (phosphorylated EEF2K) decreased over time. Compared with d 1 after calving and regardless of diet, the abundance of proteins associated with endoplasmic reticulum stress (XBP1 spliced), cell growth and survival (phosphorylated MAPK3), inflammation (transcription factor p65), antioxidant responses (KEAP1), and circadian regulation (CLOCK, PER2) of oxidative metabolism was upregulated at d 21 relative to parturition. These responses coupled with the upregulation of transporters for Lys, Arg, and His (SLC7A1) and glutamate/aspartate (SLC1A3) over time were suggestive of dynamic adaptations in cellular functions. Overall, management approaches that could take advantage of this physiological plasticity may help cows make a smoother transition into lactation.

Mitochondrial transplantation as a possible therapeutic option for sarcopenia.

With advancing age, the skeletal muscle phenotype is characterized by a progressive loss of mass, strength, and quality. This phenomenon, known as sarcopenia, has a negative impact on quality of life and increases the risk of morbidity and mortality in older adults. Accumulating evidence suggests that damaged and dysfunctional mitochondria play a critical role in the pathogenesis of sarcopenia. Lifestyle modifications, such as physical activity, exercise, and nutrition, as well as medical interventions with therapeutic agents, are effective in the management of sarcopenia and offer solutions to maintain and improve skeletal muscle health. Although a great deal of effort has been devoted to the identification of the best treatment option, these strategies are not sufficient to overcome sarcopenia. Recently, it has been reported that mitochondrial transplantation may be a possible therapeutic approach for the treatment of mitochondria-related pathological conditions such as ischemia, liver toxicity, kidney injury, cancer, and non-alcoholic fatty liver disease. Given the role of mitochondria in the function and metabolism of skeletal muscle, mitochondrial transplantation may be a possible option for the treatment of sarcopenia. In this review, we summarize the definition and characteristics of sarcopenia and molecular mechanisms associated with mitochondria that are known to contribute to sarcopenia. We also discuss mitochondrial transplantation as a possible option. Despite the progress made in the field of mitochondrial transplantation, further studies are needed to elucidate the role of mitochondrial transplantation in sarcopenia. KEY MESSAGES: Sarcopenia is the progressive loss of skeletal muscle mass, strength, and quality. Although the specific mechanisms that lead to sarcopenia are not fully understood, mitochondria have been identified as a key factor in the development of sarcopenia. Damaged and dysfunctional mitochondria initiate various cellular mediators and signaling pathways, which largely contribute to the age-related loss of skeletal muscle mass and strength. Mitochondrial transplantation has been reported to be a possible option for the treatment/prevention of several diseases. Mitochondrial transplantation may be a possible therapeutic option for improving skeletal muscle health and treating sarcopenia. Mitochondrial transplantation as a possible treatment option for sarcopenia.

Clofazimine-Mediated, Age-Related Changes in Skeletal Muscle Mitochondrial Metabolites.

Mitochondrial health declines with age, and older patients can demonstrate dysfunction in mitochondrial-rich tissues, such as cardiac and skeletal muscle. Aged mitochondria may make older adults more susceptible to adverse drug reactions (ADRs). We assessed mitochondrial metabolic function by measuring two metabolites, l-carnitine and acetylcarnitine, to determine their effectiveness as candidate clinical biomarkers for age-related, drug-induced alterations in mitochondrial metabolism. To study age- and medication-related changes in mitochondrial metabolism, we administered the FDA-approved mitochondriotropic drug, clofazimine (CFZ), or vehicle for 8 weeks to young (4-week-old) and old (61-week-old) male C57BL/6J mice. At the end of treatment, whole blood and cardiac and skeletal muscle were analyzed for l-carnitine, acetylcarnitine, and CFZ levels; muscle function was measured via a treadmill test. No differences were found in blood or cardiac carnitine levels of CFZ-treated mice, but CFZ-treated mice displayed lost body mass and alterations in endurance and levels of skeletal muscle mitochondrial metabolites. These findings demonstrate the age-related susceptibility of the skeletal muscle to mitochondria drug toxicity. Since drug-induced alterations in mitochondrial metabolism in skeletal muscle were not reflected in the blood by l-carnitine or acetylcarnitine levels, drug-induced catabolism and changes in muscle function appear more relevant to stratifying individuals at increased risk for ADRs.