Effects of Acute and Chronic Resistance Exercise on the Skeletal Muscle Metabolome

Skeletal muscle hypertrophy rewires glucose metabolism: An experimental investigation and systematic review

BACKGROUND

Proliferating cancer cells shift their metabolism towards glycolysis, even in the presence of oxygen, to especially generate glycolytic intermediates as substrates for anabolic reactions. We hypothesize that a similar metabolic remodelling occurs during skeletal muscle hypertrophy.

METHODS

We used mass spectrometry in hypertrophying C2C12 myotubes in vitro and plantaris mouse muscle in vivo and assessed metabolomic changes and the incorporation of the [U-13C6]glucose tracer. We performed enzyme inhibition of the key serine synthesis pathway enzyme phosphoglycerate dehydrogenase (Phgdh) for further mechanistic analysis and conducted a systematic review to align any changes in metabolomics during muscle growth with published findings. Finally, the UK Biobank was used to link the findings to population level.

RESULTS

The metabolomics analysis in myotubes revealed insulin-like growth factor-1 (IGF-1)-induced altered metabolite concentrations in anabolic pathways such as pentose phosphate (ribose-5-phosphate/ribulose-5-phosphate: +40%; P = 0.01) and serine synthesis pathway (serine: -36.8%; P = 0.009). Like the hypertrophy stimulation with IGF-1 in myotubes in vitro, the concentration of the dipeptide l-carnosine was decreased by 26.6% (P = 0.001) during skeletal muscle growth in vivo. However, phosphorylated sugar (glucose-6-phosphate, fructose-6-phosphate or glucose-1-phosphate) decreased by 32.2% (P = 0.004) in the overloaded muscle in vivo while increasing in the IGF-1-stimulated myotubes in vitro. The systematic review revealed that 10 metabolites linked to muscle hypertrophy were directly associated with glycolysis and its interconnected anabolic pathways. We demonstrated that labelled carbon from [U-13C6]glucose is increasingly incorporated by ~13% (P = 0.001) into the non-essential amino acids in hypertrophying myotubes, which is accompanied by an increased depletion of media serine (P = 0.006). The inhibition of Phgdh suppressed muscle protein synthesis in growing myotubes by 58.1% (P < 0.001), highlighting the importance of the serine synthesis pathway for maintaining muscle size. Utilizing data from the UK Biobank (n = 450 243), we then discerned genetic variations linked to the serine synthesis pathway (PHGDH and PSPH) and to its downstream enzyme (SHMT1), revealing their association with appendicular lean mass in humans (P < 5.0e-8).

CONCLUSIONS

Understanding the mechanisms that regulate skeletal muscle mass will help in developing effective treatments for muscle weakness. Our results provide evidence for the metabolic rewiring of glycolytic intermediates into anabolic pathways during muscle growth, such as in serine synthesis.

Harmful Free Radicals in Aging: A Narrative Review of Their Detrimental Effects on Health

The production of harmful free radicals (H-FRs), especially those with oxygen or nitrogen atoms, depends on both internal and environmental causes. The negative effects of H-FRs are greatly alleviated by antioxidant protection. The harmful impact of oxidative stress, or OS, is brought on by a disparity between the defense mechanisms of the body and the creation of H-FRs. Aging is characterized by a slow decline in tissue and organ competence. Age-mediated pathologies start as an aberrant accumulation of H-FRs, which inhibit cells' capacity to divide, repair, and operate, based on the OS theorem of aging. The natural outcome of this situation is apoptosis. These conditions may include skeletal muscle dysfunction, cancer, cardiovascular, chronic hepatitis, chronic renal, and chronic pulmonary disorders. Given the substantial role that OS plays in the progression of many of these illnesses, antioxidant-based therapy may have a favorable impact on how these diseases progress. To ascertain the true efficacy of this therapy strategy, more research is necessary. The aim of this study is to provide an overview of the literature on this challenging issue that is attracting interest.

Effect of Veau Class on Levator Veli Palatini Muscle Composition

OBJECTIVE

To examine levator veli palatini muscle composition in patients with nonsyndromic cleft palate and investigate the impact of Veau class.

DESIGN

Prospective cohort study.

SETTING

Tertiary care academic hospital.

PATIENTS/PARTICIPANTS

Thirteen patients with nonsyndromic cleft palate were recruited.

INTERVENTIONS

During primary palatoplasty, a sample of levator veli palatini muscle was excised and prepared for histological analysis.

MAIN OUTCOME MEASURES

Fat and collagen content were determined utilizing Oil Red and Sirius red stains, respectively, while muscle fiber cross-sectional areas were calculated from H&E-stained samples, with analysis using histomorphometric methods. Immunofluorescent staining of myosin heavy chain isoforms was performed.

RESULTS

Patients underwent repair at 10.8 months of age (interquartile range [IQR] 10.2-12.9). Fat content of the levator veli palatini muscle was low in both groups, ranging from 0% to 5.2%. Collagen content ranged from 8.5% to 39.8%; neither fat nor collagen content showed an association with Veau classes. Mean muscle fiber cross-sectional area decreased with increasing Veau class, from 808 µm2 (range 692-995 µm2) in Veau II to 651 µm2 (range 232-750 µm2) in Veau III (P = .02). There was also a nonsignificant decrease in proportion of type I muscle fibers with increasing Veau class (44.3% [range 31.4%-84.4%] in Veau II vs 35.3% [range 17.4%-61.3%] in Veau III).

CONCLUSIONS

Muscle fiber area in levator veli palatini muscles decreases in Veau III clefts in comparison to Veau II. The impact of these differences in velopharyngeal dysfunction requires further analysis of a larger cohort.

Research advances in the application of metabolomics in exercise science

Exercise training can lead to changes in the metabolic composition of an athlete's blood, the magnitude of which depends largely on the intensity and duration of exercise. A variety of behavioral, biochemical, hormonal, and immunological biomarkers are commonly used to assess an athlete's physical condition during exercise training. However, traditional invasive muscle biopsy testing methods are unable to comprehensively detect physiological differences and metabolic changes in the body. Metabolomics technology is a high-throughput, highly sensitive technique that provides a comprehensive assessment of changes in small molecule metabolites (molecular weight <1,500 Da) in the body. By measuring the overall metabolic characteristics of biological samples, we can study the changes of endogenous metabolites in an organism or cell at a certain moment in time, and investigate the interconnection and dynamic patterns between metabolites and physiological changes, thus further understanding the interactions between genes and the environment, and providing possibilities for biomarker discovery, precise training and nutritional programming of athletes. This paper summaries the progress of research on the application of exercise metabolomics in sports science, and looks forward to the future development of exercise metabolomics, with a view to providing new approaches and perspectives for improving human performance, promoting exercise against chronic diseases, and advancing sports science research.

Physical exercise plays a role in rebalancing the bile acids of enterohepatic axis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered as one of the most common diseases of lipid metabolism disorders, which is closely related to bile acids disorders and gut microbiota disorders. Bile acids are synthesized from cholesterol in the liver, and processed by gut microbiota in intestinal tract, and participate in metabolic regulation through the enterohepatic circulation. Bile acids not only promote the consumption and absorption of intestinal fat but also play an important role in biological metabolic signaling network, affecting fat metabolism and glucose metabolism. Studies have demonstrated that exercise plays an important role in regulating the composition and function of bile acid pool in enterohepatic axis, which maintains the homeostasis of the enterohepatic circulation and the health of the host gut microbiota. Exercise has been recommended by several health guidelines as the first-line intervention for patients with NAFLD. Can exercise alter bile acids through the microbiota in the enterohepatic axis? If so, regulating bile acids through exercise may be a promising treatment strategy for NAFLD. However, the specific mechanisms underlying this potential connection are largely unknown. Therefore, in this review, we tried to review the relationship among NAFLD, physical exercise, bile acids, and gut microbiota through the existing data and literature, highlighting the role of physical exercise in rebalancing bile acid and microbial dysbiosis.

Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.

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.

Exercise Metabolome: Insights for Health and Performance

Exercise has many benefits for physical and mental well-being. Metabolomics research has allowed scientists to study the impact of exercise on the body by analyzing metabolites released by tissues such as skeletal muscle, bone, and the liver. Endurance training increases mitochondrial content and oxidative enzymes, while resistance training increases muscle fiber and glycolytic enzymes. Acute endurance exercise affects amino acid metabolism, fat metabolism, cellular energy metabolism, and cofactor and vitamin metabolism. Subacute endurance exercise alters amino acid metabolism, lipid metabolism, and nucleotide metabolism. Chronic endurance exercise improves lipid metabolism and changes amino acid metabolism. Acute resistance exercise changes several metabolic pathways, including anaerobic processes and muscular strength. Chronic resistance exercise affects metabolic pathways, resulting in skeletal muscle adaptations. Combined endurance-resistance exercise alters lipid metabolism, carbohydrate metabolism, and amino acid metabolism, increasing anaerobic metabolic capacity and fatigue resistance. Studying exercise-induced metabolites is a growing field, and further research can uncover the underlying metabolic mechanisms and help tailor exercise programs for optimal health and performance.

Mass Sportrometry: An annual look back at applications of mass spectrometry in sport and exercise science

Research in sport and exercise science (SES) is reliant on robust analyses of biomarker measurements to assist with the interpretation of physiological outcomes. Mass spectrometry (MS) is an analytical approach capable of highly sensitive, specific, precise, and accurate analyses of a range of biomolecules, many of which are of interest in SES including, but not limited to, endogenous metabolites, exogenously administered compounds (e.g. supplements), mineral ions, and circulating/tissue proteins. This annual review provides a summary of the applications of MS across studies investigating aspects related to sport or exercise in manuscripts published, or currently in press, in 2022. In total, 93 publications are included and categorized according to their methodologies including targeted analyses, metabolomics, lipidomics, proteomics, and isotope ratio/elemental MS. The advantageous analytical opportunities afforded by MS technologies are discussed across a selection of relevant articles. In addition, considerations for the future of MS in SES, including the need to improve the reporting of assay characteristics and validation data, are discussed, alongside the recommendation for selected current methods to be superseded by MS-based approaches where appropriate. The review identifies that a targeted, mostly quantitative, approach is the most commonly applied MS approach within SES, although there has also been a keen interest in the use of 'omics' to perform hypothesis-generating research studies. Nonetheless, MS is not commonplace in SES at this time, but its use to expand, and possibly improve, the analytical options should be continually considered to exploit the benefits of analytical chemistry in exercise/sports-based research. Overall, it is exciting to see the gradually increasing adoption of MS in SES and it is expected that the number, and quality, of MS-based assays in SES will increase over time, with the potential for 2023 to further establish this technique within the field.

Serum Metabolites Associated with Muscle Hypertrophy after 8 Weeks of High- and Low-Load Resistance Training

The mechanisms responsible for the similar muscle growth attained with high- and low-load resistance training (RT) have not yet been fully elucidated. One mechanism is related to the mechanical stimulus and the level of motor unit recruitment; another mechanism is related to the metabolic response. We investigated the electromyographic signal amplitude (sEMG) and the general metabolic response to high-load RT (HL) and low-load resistance training (LL). We measured muscle thickness by ultrasound, sEMG amplitude by electromyography, and analysis of metabolites expressed through metabolomics. No differences were observed between the HL and LL groups for metabolic response and muscle thickness. A greater amplitude of sEMG was observed in the HL group. In addition, a correlation was observed between changes in muscle thickness of the vastus lateralis muscle in the HL group and levels of the metabolites carnitine, creatine, 3-hydroxyisovalerate, phenylalanine, asparagine, creatine phosphate, and methionine. In the LL group, a correlation was observed between changes in muscle thickness of the vastus lateralis muscle and levels of the metabolites acetoacetate, creatine phosphate, and oxypurinol. These correlations seem to be related to the characteristics of activated muscle fibers, the metabolic demand of the training protocols used, and the process of protein synthesis.