Potential Role of Omega-3 Fatty Acids on the Myogenic Program of Satellite Cells

Eicosapentaenoic acid (EPA) improves grass carp (Ctenopharyngodon idellus) muscle development and nutritive value by activating the mTOR signaling pathway

Skeletal muscle is the mainly edible part of fish. Eicosapentaenoic acid (EPA) is a crucial nutrient for fish. This study investigated the effect of EPA on the muscle development of grass carp along with the potential molecular mechanisms in vivo and in vitro. Muscle cells treated with 50 μM EPA in vitro showed the elevated proliferation, and the expression of mammalian target of rapamycin (mTOR) signaling pathway-related genes was upregulated (P < 0.05). In vivo experiments, 270 grass carp (27.92 g) were fed with one of the three experimental diets for 56 days: control diet (CN), 0.3% EPA-supplement diet (EPA), and the diet supplemented with 0.3% EPA and 30 mg/kg rapamycin (EPA + Rap). Fish weight gain rate (WGR) was improved in EPA group (P < 0.05). There was no difference in the viscerosomatic index (VSI) and body height (BH) among all groups (P > 0.05), whereas the carcass ratio (CR) and body length in the EPA group were obviously higher than those of other groups (P < 0.05), indicating that the increase of WGR was due to muscle growth. In addition, both muscle fiber density and muscle crude protein also increased in EPA group (P < 0.05). The principal component analysis showed that total weight of muscle amino acid in EPA group ranked first. Dietary EPA also increased protein levels of the total mTOR, S6k1, Myhc, Myog, and Myod in muscle (P < 0.05). In conclusion, EPA promoted the muscle development and nutritive value via activating the mTOR signaling pathway.

Combined Plasma DHA-Containing Phosphatidylcholine PCaa C38:6 and Tetradecanoyl-Carnitine as an Early Biomarker for Assessing the Mortality Risk among Sarcopenic Patients

The coming of the hyper-aged society in Taiwan prompts us to investigate the relationship between the metabolic status of sarcopenic patients and their most adverse outcome-death. We studied the association between any plasma metabolites and the risk for mortality among older Taiwanese sarcopenic patients. We applied a targeted metabolomic approach to study the plasma metabolites of adults aged ≥65 years, and identified the metabolic signature predictive of the mortality of sarcopenic patients who died within a 5.5-year follow-up period. Thirty-five sarcopenic patients who died within the follow-up period (Dead cohort) had shown a specific plasma metabolic signature, as compared with 54 patients who were alive (Alive cohort). Only 10 of 116 non-sarcopenic individuals died during the same period. After multivariable adjustment, we found that sex, hypertension, tetradecanoyl-carnitine (C14-carnitine), and docosahexaenoic acid (DHA)-containing phosphatidylcholine diacyl (PCaa) C38:6 and C40:6 were important risk factors for the mortality of sarcopenic patients. Low PCaa C38:6 levels and high C14-carnitine levels correlated with an increased mortality risk; this was even the same for those patients with hypertension (HTN). Our findings suggest that plasma PCaa C38:6 and acylcarnitine C14-carnitine, when combined, can be a better early biomarker for evaluating the mortality risk of sarcopenia patients.

A Brief Narrative Review of the Underlying Mechanisms Whereby Omega-3 Fatty Acids May Influence Skeletal Muscle: From Cell Culture to Human Interventions

Skeletal muscle is essential for human locomotion as well as maintaining metabolic homeostasis. Age-related reduction in skeletal muscle mass, strength, and function (i.e., sarcopenia) is a result of pathophysiological processes that include inflammation, alteration of molecular signaling for muscle protein synthesis and degradation, changes in insulin sensitivity, as well as altered skeletal muscle satellite cell activity. Finding strategies to mitigate skeletal muscle loss with age is deemed paramount as the percentage of the population continues to shift towards having more older adults with sarcopenia. Recent research indicates omega-3 fatty acid supplementation can influence anabolic or catabolic pathways in skeletal muscle. Our brief review will provide a synopsis of some underlying mechanisms that may be attributed to omega-3 fatty acid supplementation's effects on skeletal muscle. We will approach this review by focusing on cell culture, animal (pre-clinical models), and human studies evaluating omega-3 fatty acid supplementation, with suggestions for future research. In older adults, omega-3 fatty acids may possess some potential to modify pathophysiological pathways associated with sarcopenia; however, it is highly likely that omega-3 fatty acids need to be combined with other anabolic interventions to effectively ameliorate sarcopenia.

Improving flesh quality of grass carp (Ctenopharyngodon idellus) by completely replacing dietary soybean meal with yellow mealworm (Tenebrio molitor)

In order to find viable alternative protein sources for aquaculture, we evaluated the effect of partial or complete replacement of dietary soybean meal with yellow mealworm (TM) on the flesh quality of grass carp. In this study, 180 grass carp (511.85 ± 0.25 g) were fed 3 experimental diets in which 0% (CN), 30% (YM30) and 100% (YM100) dietary soybean meal was replaced by TM for 90 d. The results showed that growth performance, biological parameters and serum antioxidant capacity of grass carp were not affected by dietary TM (P > 0.05). Both muscle and whole body crude protein were obviously promoted with the increase of dietary TM (P < 0.05), and the concentration of heavy metal in muscle was not influenced (P > 0.05), indicating that food safety was not influenced by TM. Dietary TM improved muscle textural characteristics by elevating adhesiveness, springiness and chewiness in YM100 (P < 0.05). In addition, the muscle tenderness was significantly increased by declining the shear force (P < 0.05). The muscle fiber density in YM30 &YM100 and length of dark bands and sarcomeres in YM100 were obviously increased (P < 0.05). The expression of myf5, myog and myhc exhibited a significant upward trend with the increase of dietary TM (P < 0.05), which promoted fiber density, length of sarcomere and texture of grass carp muscle. According to the results of metabolomics, the arachidonate (ARA) and eicosapentaenoic acid (EPA) were notably elevated in YM30 and YM100, which indicated that the improvement of flesh quality of grass carp may contribute to the dietary TM influence on muscle lipid metabolism, especially the polyunsaturated fatty acids. In conclusion, TM can completely replace dietary soybean meal and improve the nutritional value of grass carp.

Regulation of Skeletal Muscle Satellite Cell Differentiation by Omega-3 Polyunsaturated Fatty Acids: A Critical Review

Skeletal muscle is composed of multinuclear cells called myofibres, which are formed by the fusion of myoblasts during development. The size of the muscle fiber and mass of skeletal muscle are altered in response to several pathological and physiological conditions. Skeletal muscle regeneration is primarily mediated by muscle stem cells called satellite cells (SCs). In response to injury, these SCs replenish myogenic progenitor cells to form new myofibers to repair damaged muscle. During myogenesis, activated SCs proliferate and differentiate to myoblast and then fuse with one another to form muscle fibers. A reduced number of SCs and an inability to undergo myogenesis may contribute to skeletal muscle disorders such as atrophy, cachexia, and sarcopenia. Myogenic regulatory factors (MRF) are transcription factors that regulate myogenesis and determines whether SCs will be in the quiescent, activated, committed, or differentiated state. Mitochondria oxidative phosphorylation and oxidative stress play a role in the determination of the fate of SCs. The potential activation and function of SCs are also affected by inflammation during skeletal muscle regeneration. Omega-3 polyunsaturated fatty acids (PUFAs) show promise to reduce inflammation, maintain muscle mass during aging, and increase the functional capacity of the muscle. The aim of this critical review is to highlight the role of omega-3 PUFAs on the myogenic differentiation of SCs and pathways affected during the differentiation process, including mitochondrial function and inflammation from the current body of literature.

PUFA Treatment Affects C2C12 Myocyte Differentiation, Myogenesis Related Genes and Energy Metabolism

Polyunsaturated fatty acids (PUFAs) are the main components of cell membrane affecting its fluidity, signaling processes and play a vital role in muscle cell development. The effects of docosahexaenoic acid (DHA) on myogenesis are well known, while the effects of arachidonic acid (AA) are largely unclear. The purpose of this study is to evaluate the effect of two PUFAs (DHA and AA) on cell fate during myogenic processes, Wnt signaling and energy metabolism by using the C2C12 cells. The cells were treated with different concentrations of AA or DHA for 48 h during the differentiation period. PUFA treatment increased mRNA level of myogenic factor 5 (Myf5), which is involved in early stage of myoblast proliferation. Additionally, PUFA treatment prevented myoblast differentiation, indicated by decreased myotube fusion index and differentiation index in parallel with reduced mRNA levels of myogenin (MyoG). After PUFA withdrawal, some changes in cell morphology and myosin heavy chain mRNA levels were still observed. Expression of genes associated with Wnt signaling pathway, and energy metabolism changed in PUFA treatment in a dose and time dependent manner. Our data suggests that PUFAs affect the transition of C2C12 cells from proliferation to differentiation phase by prolonging proliferation and preventing differentiation.

Marine Phytoplankton Improves Exercise Recovery in Humans and Activates Repair Mechanisms in Rats

This study investigated the effects of marine phytoplankton supplementation on 1) perceived recovery and ground reaction forces in humans following a non-functional overreaching resistance-training program and 2) myogenic molecular markers associated with muscle cell recovery in a rat model. In the human trial, a 5-week resistance-training program with intentional overreaching on weeks 2 and 5 was implemented. Results indicate that marine phytoplankton prompted positive changes in perceived recovery at post-testing and, while both marine phytoplankton and placebo conditions demonstrated decreased peak and mean rate of force development following the overreaching weeks, placebo remained decreased at post-testing while marine phytoplankton returned to baseline levels. In the rat model, rats were divided into four conditions: (i) control, (ii) exercise, (iii) exercise + marine phytoplankton 2.55 mg·d^-1, or (iv) exercise+marine phytoplankton 5.1 mg·d^-1. Rats in exercising conditions performed treadmill exercise 5 d·wk^-1 for 6 weeks. Marine phytoplankton in exercising rats increased positive and decrease negative myogenic factors regulating satellite cell proliferation. Taken together, marine phytoplankton improved perceptual and functional indices of exercise recovery in an overreaching human model and, mechanistically, this could be driven through cell cycle regulation and a potential to improve protein turnover.

The regulatory role of dietary factors in skeletal muscle development, regeneration and function

Skeletal muscle plays a crucial role in motor function, respiration, and whole-body energy homeostasis. How to regulate the development and function of skeletal muscle has become a hot research topic for improving lifestyle and extending life span. Numerous transcription factors and nutritional factors have been clarified are closely associated with the regulation of skeletal muscle development, regeneration and function. In this article, the roles of different dietary factors including green tea, quercetin, curcumin (CUR), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and resveratrol (RES) in regulating skeletal muscle development, muscle mass, muscle function, and muscle recovery have been summarized and discussed. We also reviewed the potential regulatory molecular mechanism of these factors. Based on the current findings, dietary factors may be used as a potential therapeutic agent to treat skeletal muscle dysfunction as well as its related diseases.

Lower Serum n-3 Fatty Acid Level in Older Adults with Sarcopenia

The n-3 fatty acid (FA) has evoked considerable interest as a modifiable factor for maintenance of muscle health owing to its anti-inflammatory properties. To clarify this possibility, we investigated circulating n-3 FA level, a reliable biomarker of FA status in the body, in relation to sarcopenia in a cohort of Asian older adults. Blood samples were collected from 125 participants who underwent comprehensive assessment of muscle mass and function. Serum FA level was measured by gas chromatography/mass spectrometry. Sarcopenia was diagnosed using the cut-off points specified for the Asian population. After adjusting for sex, age, and body mass index, subjects with sarcopenia and those with low muscle strength had 36.5% and 32.4% lower serum n-3 levels (P = 0.040 and 0.030), respectively, than controls. The odds ratios per standard deviation increment in serum n-3 level for sarcopenia and low muscle strength were 0.29 and 0.40 (P = 0.015 and 0.028), respectively. A higher serum n-3 level was significantly associated with greater muscle strength (P = 0.038). These findings suggest a possible protective effect of n-3 FA on human muscle homeostasis. Further well-designed large-scale longitudinal studies are necessary to understand the definite role of circulating n-3 FA level in sarcopenia risk assessment.

Potential Roles of n-3 PUFAs during Skeletal Muscle Growth and Regeneration

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), which are commonly found in fish oil supplements, are known to possess anti-inflammatory properties and more recently alter skeletal muscle function. In this review, we discuss novel findings related to how n-3 PUFAs modulate molecular signaling responsible for growth and hypertrophy as well as the activity of muscle stem cells. Muscle stem cells commonly known as satellite cells, are primarily responsible for driving the skeletal muscle repair process to potentially damaging stimuli, such as mechanical stress elicited by exercise contraction. To date, there is a paucity of human investigations related to the effects of n-3 PUFAs on satellite cell content and activity. Based on current in vitro investigations, this review focuses on novel mechanisms linking n-3 PUFA’s to satellite cell activity and how they may improve muscle repair. Understanding the role of n-3 PUFAs during muscle growth and regeneration in association with exercise could lead to the development of novel supplementation strategies that increase muscle mass and strength, therefore possibly reducing the burden of muscle wasting with age.

Total substitution of dietary fish oil by vegetable oils stimulates muscle hypertrophic growth in Senegalese sole and the upregulation of fgf6

The long term effects of fish oil (FO) substitution by increasing the levels of vegetable oils (VO), 0% (CTR), 50% (VO50) and 100% (VO100), in diets for Senegalese sole were evaluated in terms of skeletal muscle cellularity and expression of related genes. After 140 days of feeding, all fish had similar body weight and length. The inclusion of 50% VO did not result in differences in muscle cellularity, but dorsal muscle cross-sectional area and fast-twitch fibre diameter increased in fish fed total FO substitution, whilst fibre density was reduced (P < 0.05) in relation to CTR. The total number of fibres was similar in all treatments. FO substitution did not affect the transcript levels of myogenic genes (myf5, mrf4, myog, myod1, myod2), but resulted in a two-fold increase of fgf6 transcript levels compared to CTR (P < 0.05). The relative expression of igf-I was higher in VO100 than in VO50, but was similar to CTR. FO substitution resulted in cellularity changes related to the stimulation of muscle hypertrophic growth, but not hyperplastic growth, and associated with a nutritional modulation of fgf6 by dietary VO. This study indicates that 50% VO does not affect the muscle phenotype, but total FO substitution stimulates muscle hypertrophy.