Intramuscular Lipid Deposition Research Articles

Profiling of m6A methylation in porcine intramuscular adipocytes and unravelling PHKG1 represses porcine intramuscular lipid deposition in an m6A-dependent manner

Intramuscular fat (IMF) content is mainly determined by intramuscular preadipocyte adipogenesis. Epigenetic modifications are known to have a regulatory effect on IMF. As N6-methyladenosine (m6A) is the most abundant epigenetic modification in eukaryotic RNAs. In the present study, we used m6A methylation and RNA sequencing (seq) to identify the m6A-modified RNAs associated with the adipogenic differentiation of intramuscular preadipocytes. Among them, the expression and m6A level of phosphorylase kinase subunit G1 (PHKG1) were found to be significantly changed during adipogenesis. Further studies revealed that knockdown of the methylase METTL3 decreased the m6A methylation of PHKG1 and led to a reduction in PHKG1. Moreover, knockdown of PHKG1 promoted adipogenic differentiation by upregulating the expression of adipogenic genes. In addition, we found that the IMF content in the longissimus thoracis (LT) of Bamei (BM) pigs was greater than that in Large White (LW) pigs, whereas the m6A and PHKG1 expression levels were lower in BM pigs. These findings indicate that the m6A level and expression of PHKG1 were significantly correlated with IMF content and meat quality. In conclusion, this study sheds light on the mechanism by which m6A modification regulates IMF deposition.

Identification and functional prediction of lncRNAs associated with intramuscular lipid deposition in Guangling donkeys.

Many studies have shown that long non-coding RNAs (lncRNAs) play key regulatory roles in various biological processes. However, the importance and molecular regulatory mechanisms of lncRNAs in donkey intramuscular fat deposition remain to be further investigated. In this study, we used published transcriptomic data from the longissimus dorsi muscle of Guangling donkeys to identify lncRNAs and obtained 196 novel lncRNAs. Compared with the coding genes, the novel lncRNAs and the known lncRNAs exhibited some typical features, such as shorter transcript length and smaller exons. A total of 272 coding genes and 52 lncRNAs were differentially expressed between the longissimus dorsi muscles of the low-fat and high-fat groups. The differentially expressed genes were found to be involved in various biological processes related to lipid metabolism. The potential target genes of differentially expressed lncRNAs were predicted by cis and trans. Functional analysis of lncRNA targets showed that some lncRNAs may act on potential target genes involved in lipid metabolism processes and regulate lipid deposition in the longissimus dorsi muscle. This study provides valuable information for further investigation of the molecular mechanisms of lipid deposition traits in donkeys, which may improve meat traits and facilitate the selection process of donkeys in future breeding.

MiR-130b duplex (miR-130b-3p/miR-130b-5p) negatively regulates goat intramuscular preadipocyte lipid droplets accumulation by inhibiting Krüppel-like factor 3 expression.

Intramuscular lipid deposition is important for meat quality improvement. microRNAs and their target mRNAs provide a new approach for studying the mechanism of fat deposition. The present study aimed to investigate the effect of miR-130b duplex (miR-130b-5p, miR-130b-3p) and its target gene KLF3 in regulating goat intramuscular adipocyte differentiation. Goat intramuscular preadipocytes were isolated from 7-d-old male Jianzhou big-ear goats and identified by Oil red O staining after differentiation induction. miR-130b-5p and miR-130b-3p mimics or inhibitors and their corresponding controls were transfected into goat intramuscular preadipocytes, respectively, and differentiation was induced by 50μM oleic acid for 48 h. Oil red O and Bodipy staining indicated that both miR-130b-5p and miR-130b-3p can reduce lipid droplets accumulation and triglyceride (TG) content (P < 0.01). Differentiation markers C/EBPα, C/EBPβ, PPARγ, pref1, fatty acids synthesis markers ACC, FASN, DGAT1, DGAT2, AGPAT6, TIP47, GPAM, ADRP, AP2, SREBP1, and TG markers LPL, ATGL, HSL were assessed by qPCR. All the markers measured were downregulated by miR-130b-5p and miR-130b-3p analog (P < 0.01), suggesting that miR-130b inhibits goat intramuscular adipocyte adipogenic differentiation, fatty acids synthesis, and lipid lipolysis. To examine the mechanism of miR-130b duplex inhibition of lipid deposition, TargetScan, miRDB, and starBase were used to predict the potential targets, KLF3 was found to be the only one intersection. Furthermore, the 3'UTR of KLF3 was cloned, qPCR analysis and dual luciferase activity assay showed that both miR-130b-5p and miR-130b-3p could directly regulate KLF3 expression (P < 0.01). In addition, overexpression and interference of KLF3 were conducted, it was found that KLF3 positively regulated lipid droplets accumulation by Oil red O, Bodipy staining, and TG content detection (P < 0.01). Quantitative PCR result indicated that KLF3 overexpression promoted lipid droplets accumulation relative genes C/EBPβ, PPARγ, pref1, ACC, FASN, DGAT1, DGAT2, AGPAT6, TIP47, GPAM, ADRP, SREBP1, LPL, and ATGL expression (P < 0.01). Downregulation of KLF3 inhibited the expression of genes such as C/EBPα, C/EBPβ, PPARγ, pref1, TIP47, GPAM, ADRP, AP2, LPL, and ATGL expression (P < 0.01). Taken together, these results indicate that miR-130b duplex could directly inhibit KLF3 expression, then attenuated adipogenic and TG synthesis genes expression, thus leading to its anti-adipogenic effect.

The aqueous fraction of Castanea crenata inner shell extract reduces obesity and intramuscular lipid accumulation via induction of mitochondrial respiration and fatty acid oxidation in muscle

BackgroundSkeletal muscle is responsible for free fatty acid (FFA) disposal via mitochondrial respiration and fatty acid oxidation (FAO). Obesity triggers high levels of circulating FFAs, which can cause intramuscular lipid (IMCL) deposition. Diverse phytochemicals, including crude Castanea crenata inner shell extract (CCE), have been shown to possess an anti-obesity effect. PurposeWe aimed to demonstrate whether the aqueous fraction of CCE (ACCE) provides an anti-obesity effect with a decrease in plasma FFAs and reduces IMCL. MethodsHigh-fat-fed C57BL/6 mice received ACCE via water intake. A204 cells incubated with fatty acids were treated with ACCE. Lipid accumulation and mitochondrial metabolism were assessed using histological and molecular techniques. ResultsACCE possessed a notably higher gallic acid content than CCE among the constituents. ACCE-administered mice exhibited reduced plasma FFA levels, adiposity, and IMCL. Muscle lipotoxicity was suppressed, including apoptosis, ER stress, and inflammation. The anti-lipid effect of ACCE was observed with the induction of mitochondrial respiration and fatty acid oxidation in muscle. ConclusionsACCE increases mitochondrial respiration and FAO in skeletal muscle and protects muscle from IMCL and lipotoxicity, reducing plasma FFA and adiposity.

MicroRNA-100 Reduced Fetal Bovine Muscle Satellite Cell Myogenesis and Augmented Intramuscular Lipid Deposition by Modulating IGF1R.

Previously, microRNA-100 (miR-100) and its putative mRNA target, insulin-like growth factor receptor-1 (IGF1R) were identified as differentially and inversely expressed in bovine longissimus dorsi (LD) muscles with divergent intramuscular fat (IMF) content by our group. While IGF1R signaling is implicated in myogenesis and muscle lipid metabolism, the underlying regulatory mechanisms are poorly understood. In the present study, we aimed to investigate the regulation of IGF1R by miR-100 during bovine muscle satellite cell (BMSC) myogenesis and lipid deposition. MiR-100 was confirmed to target the IGF1R 3′-untranslated region (3′-UTR) by luciferase reporter assay. Furthermore, expression of miR-100 and IGF1R was reciprocal during BMSC differentiation, suggesting a crosstalk between the two. Correspondingly, miR-100 mimic (agomiR) suppressed the levels of IGF1R, PI3K/AKT pathway signaling, myogenic gene MYOG, muscle structural components MYH7 and MYH8, whereas the inhibitor (antagomiR) had no clear stimulating effects. The IGF1R inhibitor (BMS-754807) curtailed receptor levels and triggered atrophy in muscle myotubes but did not influence miR-100 expression. AgomiR increased oleic acid-induced lipid deposition in BMSC myotubes supporting its involvement in intramuscular fat deposition, while antagomiR had no effect. Moreover, mitochondrial beta-oxidation and long-chain fatty acid synthesis-related genes were modulated by agomiR addition. Our results demonstrate modulatory roles of miR-100 in BMSC development, lipid deposition, and metabolism and suggest a role of miR-100 in marbling characteristics of meat animals and fat oxidation in muscle.

Comprehensive functional core microbiome comparison in genetically obese and lean hosts under the same environment

Our study provides an exhaustive comparison of the microbiome core functionalities (captured by 3,936 microbial gene abundances) between hosts with divergent genotypes for intramuscular lipid deposition. After 10 generations of divergent selection for intramuscular fat in rabbits and 4.14 phenotypic standard deviations (SD) of selection response, we applied a combination of compositional and multivariate statistical techniques to identify 122 cecum microbial genes with differential abundances between the lines (ranging from −0.75 to +0.73 SD). This work elucidates that microbial biosynthesis lipopolysaccharides, peptidoglycans, lipoproteins, mucin components, and NADH reductases, amongst others, are influenced by the host genetic determination for lipid accretion in muscle. We also differentiated between host-genetically influenced microbial mechanisms regulating lipid deposition in body or intramuscular reservoirs, with only 28 out of 122 MGs commonly contributing to both. Importantly, the results of this study are of relevant interest for the efficient development of strategies fighting obesity.

Distinct Roles of Perilipins in the Intramuscular Deposition of Lipids in Glutamine-Supplemented, Low-, and Normal-Birth-Weight Piglets.

Piglets with low birth weight (LBW) usually have reduced muscle mass and increased lipid deposition compared with their normal-birth-weight (NBW) littermates. Supplementation of piglets with amino acids during the first days of life may improve muscle growth and simultaneously alter the intramuscular lipid deposition. The aim of the current study was to investigate the influence of glutamine (Gln) supplementation during the early suckling period on lipid deposition in the longissimus muscle (MLD) and the role of different perilipin (PLIN) family members in this process. Four groups were generated consisting of 72 male LBW piglets and 72 NBW littermates. Piglets were supplemented with either 1 g Gln/kg body weight or an isonitrogenous amount of alanine (Ala) between days post natum (dpn) 1 and 12. Twelve piglets per group were slaughtered at 5, 12, and 26 dpn, and muscle tissue was collected. Perilipins were localized by immunohistochemistry in muscle sections. The mRNA and protein abundances of PLIN family members and related lipases were quantified by quantitative RT-PCR (qPCR) and western blots, respectively. While PLIN1 was localized around lipid droplets in mature and developing adipocytes, PLIN2 was localized at intramyocellular lipid droplets, PLIN3 and 4 at cell membranes of muscle fibers and adipocytes, and PLIN5 in the cytoplasm of undefined cells. The western blot results indicated higher protein abundances of PLIN2, 3, 4, and 5 in LBW piglets (p < 0.05) at 5 dpn compared with their NBW littermates independent of supplementation, while not directly reflecting the mRNA expression levels. The mRNA abundance of PLIN2 was lower while PLIN4 was higher in piglets at 26 dpn in comparison with piglets at 5 dpn (p < 0.01). Relative mRNA expression of LPL and CGI-58 was lowest in piglets at 5 dpn (p < 0.001). However, ATGL mRNA was not influenced by birth weight or supplementation, but the Spearman correlation coefficient analysis revealed close correlations with PLIN2, 4, and 5 mRNA at 5 and 26 dpn (r > 0.5, p < 0.001). The results indicated the importance of birth weight and age for intramuscular lipid deposition and different roles of PLIN family members in this process, but no clear modulating effect of Gln supplementation.

Identification of miRNA in Sheep Intramuscular Fat and the Role of miR-193a-5p in Proliferation and Differentiation of 3T3-L1.

Intramuscular fat (IMF) is one of the most critical parameters affecting meat quality and mainly affected by genetic factors. MicroRNA as an important regulatory factor, which is still a lack of research in the development of sheep IMF deposition. We used RNA sequencing (RNA-seq) and cell-level validation to explore the role of miRNA in IMF deposition. As for this purpose, longissimus thoracis et lumborum (LTL) samples of 2 month-old (Mth-2) and 12 months-old (Mth-12) Aohan fine-wool sheep (AFWS) were used to identified miRNAs expression. We found 59 differentially expressed miRNAs (DE-miRNA) between these age groups and predicted their 1,796 target genes. KEGG functional enrichment analysis revealed eight pathways involved in lipid metabolism-related processes, including fatty acid elongation and the AMPK signaling pathway. A highly expressed DE-miRNA, miR-193a-5p, was found to serve a function in 3T3-L1 preadipocyte differentiation. Luciferase assay demonstrated that miR-193a-5p directly binds to the 3′-UTR region of ACAA2. By constructing mimics and inhibitor vector transfecting into 3T3-L1 cells to explore the effect of miR-193a-5p on cell proliferation and differentiation, we demonstrated that overexpression of miR-193a-5p inhibited 3T3-L1 preadipocyte proliferation, as evidenced by decreased mRNA and protein expression of CDK4 and CyclinB. CCK-8 assay showed that miR-193a-5p significantly inhibited cell proliferation. Similarly, the overexpression of miR-193a-5p inhibited 3T3-L1 preadipocyte differentiation and adipocyte-specific molecular markers’ expression, leading to a decrease in PPARγ and C/EBPα and ACAA2. Inhibition of miR-193a-5p had the opposite effects. Our study lists the miRNAs associated with intramuscular lipid deposition in sheep and their potential targets, striving to improve sheep meat quality.

Identification and co-expression analysis of long noncoding RNAs and mRNAs involved in the deposition of intramuscular fat in Aohan fine-wool sheep

BackgroundIntramuscular fat (IMF) content has become one of the most important indicators for measuring meat quality, and levels of IMF are affected by various genes. Long non-coding RNAs (lncRNAs) are widely expressed non-coding RNAs that play an important regulatory role in a variety of biological processes; however, research on the lncRNAs involved in sheep IMF deposition is still in its infancy. Aohan fine-wool sheep (AFWS), one of China’s most important meat-hair, dual-purpose sheep breed, provides a great model for studying the role of lncRNAs in the regulation of IMF deposition. We identified lncRNAs by RNA sequencing in Longissimus thoracis et lumborum (LTL) samples of sheep at two ages: 2 months (Mth-2) and 12 months (Mth-12).ResultsWe identified a total of 26,247 genes and 6935 novel lncRNAs in LTL samples of sheep. Among these, 199 mRNAs and 61 lncRNAs were differentially expressed. We then compared the structural characteristics of lncRNAs and mRNAs. We obtained target genes of differentially expressed lncRNAs (DELs) and performed enrichment analyses using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). We found that target mRNAs were enriched in metabolic processes and developmental pathways. One pathway was significantly enriched, namely tight junction. Based on the analysis of critical target genes, we obtained seven candidate lncRNAs that potentially regulated lipid deposition and constructed a lncRNA-mRNA co-expression network that included MSTRG.4051.3-FZD4, MSTRG.16157.3-ULK1, MSTRG.21053.3-PAQR3, MSTRG.19941.2-TPI1, MSTRG.12864.1-FHL1, MSTRG.2469.2-EXOC6 and MSTRG.21381.1-NCOA1. We speculated that these candidate lncRNAs might play a role by regulating the expression of target genes. We randomly selected five mRNAs and five lncRNAs to verify the accuracy of the sequencing data by qRT-PCR.ConclusionsOur study identified the differentially expressed mRNAs and lncRNAs during intramuscular lipid deposition in Aohan fine-wool sheep. The work may widen the knowledge about the annotation of the sheep genome and provide a working basis for investigating intramuscular fat deposition in sheep.

Metformin ameliorates skeletal muscle atrophy in Grx1 KO mice by regulating intramuscular lipid accumulation and glucose utilization

Skeletal muscle is the largest tissue in the body, and plays a remarkable role in energy and metabolic homeostasis. Disorder in lipid metabolism and glucose utilization could impair the quality and function of skeletal muscle. Glutaredoxin-1 (Grx1) acts as a vital metabolic regulator of redox homeostasis. Recent studies have shown that Grx1 regulates hepatic lipid metabolism. The skeletal muscle also contains abundant Grx1, but the role of Grx1 in skeletal muscle remains unknown. Therefore, we investigated the effect of Grx1 on skeletal muscle. In this study, we found that Grx1-deficient mice (Grx1−/−) spontaneously developed muscle atrophy by 3 months of age. And the p-AMPK activity and Sirt1 activity were inhibited in Grx1−/− mice, which led to intramuscular lipid deposition and glucose utilization disorder in skeletal muscle. However, intraperitoneal injection of metformin for 15 consecutive days ameliorated skeletal muscle atrophy caused by Grx1 deficiency to a certain extent. Taken together, these findings indicate that Grx1 deficiency might induce skeletal muscle atrophy by regulating the intramuscular lipid deposition and glucose utilization, which could be attenuated by metformin. Therefore, the expression or activity of Grx1 may be a pharmacological approach to ameliorate muscle atrophy diseases, such as sarcopenia.

MiR-324-5p Inhibits C2C12 cell Differentiation and Promotes Intramuscular Lipid Deposition through lncDUM and PM20D1

Skeletal muscle is an important metabolic organ of the body, and impaired skeletal muscle differentiation can result in a wide range of metabolic diseases. It has been shown that microRNAs (miRNAs) play an important role in skeletal muscle differentiation. The aim of this study was to investigate the role of mmu-miR-324-5p in the differentiation of C2C12 myoblasts and lipid droplet deposition in myotubes for future targeted therapies. We found that mmu-miR-324-5p was highly expressed in mouse skeletal muscle. Overexpression of miR-324-5p significantly inhibited C2C12 myoblast differentiation while promoting oleate-induced lipid accumulation and β-oxidation in C2C12 myoblasts. Conversely, inhibition of mmu-miR-324-5p promoted C2C12 myoblast differentiation and inhibited lipid deposition in myotubes. Mechanistically, mmu-miR-324-5p negatively regulated the expression of long non-coding Dum (lncDum) and peptidase M20 domain containing 1 (Pm20d1) in C2C12 myoblasts. Reduced lncDum expression was associated with a significant decrease in the expression of myogenesis-related genes. Knockdown of mmu-miR-324-5p increased the levels of lncDum and myogenesis-related gene expression. Following oleate-induced lipid deposition in C2C12 myoblasts, overexpression of mmu-miR-324-5p decreased the expression of Pm20d1 while increasing the expression of mitochondrial β-oxidation and long-chain fatty acid synthesis-related genes. In conclusion, we provide evidence that miR-324-5p inhibits C2C12 myoblast differentiation and promotes intramuscular lipid deposition by targeting lncDum and Pm20d1, respectively.

Loss of CD36 protects against diet-induced obesity but results in impaired muscle stem cell function, delayed muscle regeneration and hepatic steatosis.

The prevalence of obesity is a major risk factor for cardiovascular and metabolic diseases including impaired skeletal muscle regeneration. Since skeletal muscle regenerative capacity is regulated by satellite cells, we aimed to investigate whether a high-fat diet impairs satellite cell function and whether this is linked to fatty acid uptake via CD36. We also aimed to determine whether loss of CD36 impacts on muscle redox homeostasis and skeletal muscle regenerative capacity. We studied the impact of a high-fat diet and CD36 deficiency on murine skeletal muscle morphology, redox homeostasis, satellite cell function, bioenergetics and lipid accumulation in the liver. We also determined the effect of CD36 deficiency on skeletal muscle regeneration. High-fat diet increased body weight, intramuscular lipid accumulation and oxidative stress in wild-type mice that were significantly mitigated in CD36-deficient mice. High-fat diet and CD36 deficiency independently attenuated satellite cell function on single fibres and myogenic capacity on primary satellite cells. CD36deficiency resulted in delayed skeletal muscle regeneration following acute injury with cardiotoxin. CD36-deficient and wild-type primary satellite cells had distinct bioenergetic profiles in response to palmitate. High-fat diet induced hepatic steatosis in both genotypes that was more pronounced in the CD36-deficient mice. This study demonstrates that CD36 deficiency protects against diet-induced obesity, intramuscular lipid deposition and oxidative stress but results in impaired muscle satellite cell function, delayed muscle regeneration and hepatic steatosis. CD36 is a key mediator of fatty acid uptake in skeletal muscle, linking obesity with satellite cell function and muscle regeneration.

Ectopic Lipid Deposition Is Associated With Insulin Resistance in Postmenopausal Women.

Menopause is associated with an increased incidence of insulin resistance and diabetes. The aim of this study was to explore the lipid deposition in liver and skeletal muscle and investigate the association with insulin sensitivity in postmenopausal and premenopausal women. Single-center cross-sectional study of 55 healthy women between 45 and 60 years of age. We measured lipid deposition in the liver with magnetic resonance spectroscopy, intramuscular and intra-abdominal lipid deposition with MRI, body composition with a dual-energy X-ray absorptiometry scan, and insulin sensitivity with the composite Matsuda Index. We studied the association between fat distribution, ectopic lipid deposition, and insulin sensitivity in pre- and postmenopausal women. Postmenopausal women had an increased lipid deposition in the liver [0.68% (0.44 to 0.99) vs 0.49% (0.38 to 0.64), P = 0.01] and skeletal muscle [3% (2 to 4) vs 2% (1 to 3), P = 0.001] and had a 28% lower Matsuda insulin sensitivity index during an oral glucose tolerance test (6.31 ± 3.48 vs 8.78 ± 4.67, P = 0.05) compared with premenopausal women. Total fat mass and leg fat mass were stronger predictors of ectopic lipid deposition, and visceral fat mass was a stronger predictor of both ectopic lipid deposition and insulin resistance in postmenopausal women compared with premenopausal women. For a given subcutaneous and visceral fat depot size, postmenopausal women show increased ectopic lipid deposition and insulin resistance compared with premenopausal women. It is suggested that lipid deposition in liver and skeletal muscle may represent important mechanistic links between the changes in fat depots and the increased incidence of insulin resistance seen after menopause.

Modeling of intramuscular lipids in different muscles in bulls, steers, and cows.

Intramuscular fat depot is of major interest for consumers, producers, and the industry. To predict intramuscular (i.m.) lipid deposition in cattle of continental breeds, different models were constructed for different muscles in bulls, steers, and cows. Two independent databases (DB1 and DB2) were developed with homogeneous individual data collected in the same slaughterhouse and total lipids, phospholipids, and triglycerides were analyzed in the same lab with the same procedures. Database DB1 was used with the meta-analysis methodology to fit the predictive models of i.m. lipids, phospholipids, and triglycerides with carcass fatness. Database DB2 was used to evaluate the accuracy of the models predicted. Total lipid and triglyceride contents varied linearly with carcass fatness in bulls, steers, and cows, but phospholipids were more independent of carcass fatness, regardless of the type of cattle studied. In bulls, LM had a lower minimal value (intercept in the model) and greater slope than semitendinosus (ST) and triceps brachii (TB) muscles. In cows, LM showed a greater intercept than ST and TB muscles but a similar slope. In steers, lipid content increased similarly in LM, rectus abdominis (RA) muscle, and ST muscle with carcass fatness. Bulls had a lower intercept than steers but showed a similar trend with carcass fatness. According to the external evaluation using DB2, the models obtained to predict total lipids in LM were more accurate than those obtained in the ST muscle in bulls and cows and in the RA muscle in steers. The models proposed for cows should be used only in the range of carcass fatness used to fit the equations, and further data are needed to fully validate them.

Short-term muscle disuse atrophy is not associated with increased intramuscular lipid deposition or a decline in the maximal activity of key mitochondrial enzymes in young and older males

Aging is generally accompanied by a progressive loss of skeletal muscle mass and impairments in metabolic function. Even a few days of muscle disuse (such as that occurring during injury or illness) leads to considerable loss of muscle mass and strength. It has been speculated that short, successive periods of muscle disuse throughout the lifespan may be largely responsible for the age-related loss of muscle mass. However, it remains unknown whether such short periods of disuse also induce impairments in metabolic function within skeletal muscle. Here, we investigated the effects of a five day period of muscle disuse on intramyocellular triacylglycerol (IMTG) content, muscle oxidative capacity, and the expression of key genes that regulate oxidative metabolism in healthy young and elderly men. Muscle biopsies were collected from healthy, young (n=12; 23±1y) and elderly (n=12; 70±1y) men prior to and immediately after a five day period of one-legged knee immobilization by way of a full leg cast. At baseline, elderly men had a greater IMTG content when compared with the young (56.2±5.1 and 34.8±7.3μmol·g−1, respectively; P<0.05) with no changes in either group following immobilization (53.4±5.0 and 35.7±5.0μmol·g−1, respectively; P>0.05). In line, five days of disuse did not lower citrate synthase, β-HAD or cytochrome C oxidase activity in skeletal muscle tissue. Pyruvate dehydrogenase activity increased following immobilization in the older subjects only, from 0.39±0.06 to 0.55 0.05μmol·g−1·min−1 (71±33%; P<0.01). The skeletal muscle mRNA expression of PGC1α and citrate synthase both declined following immobilization in both the young and elderly subjects. We conclude that five days of muscle disuse does not increase intramuscular lipid deposition or reduce the maximal activity of key mitochondrial enzymes within the skeletal muscle of young or older men.

Metformin limits ceramide-induced senescence in C2C12 myoblasts

High lipid and ceramide concentrations are hallmarks of obese and/or insulin resistant skeletal muscle, yet little is known about its role on cell cycle and senescence. The purpose of this study was to examine the role of ceramide on muscle senescence, and whether metformin limited this response. MethodsLow passage, proliferating C2C12 myoblasts were treated with a control, 50μM C2-ceramide (8h), and/or 2mM metformin, then examined for insulin sensitivity, cell senescence, cell proliferation, cell cycle, protein expression of cell cycle regulators. ResultsCeramide treatment caused a dephosphorylation (p<0.05) of Akt and 4E-BP1, regardless of the presence of insulin. The ceramide treated myoblasts displayed higher β-galactosidase staining (p<0.05), reduced BrDu incorporation and total number of cells (p<0.05), and an increased proportion of cells in G2-phase (p<0.05) versus control cultures. Ceramide treatment also upregulated (p<0.05) p53 and p21 protein expression, that was reversed by either pifithrin-α or shRNA for p53. Metformin limited (p<0.05) ceramide's effects on insulin signaling, senescence, and cell cycle regulation. ConclusionsHigh ceramide concentrations reduced myoblast proliferation that was associated with aberrant cell cycle regulation and a senescent phenotype, which could provide an understanding of skeletal muscle cell adaptation during conditions of high intramuscular lipid deposition and/or obesity.

Effect of long‐term betaine supplementation on chemical and physical characteristics of three muscles from the Alentejano pig

The use of betaine as a dietary supplement to reduce fat deposition and increase lean muscle mass in pigs is increasing. However, there is no available information on its effect on the physical and chemical (i.e. fatty acid (FA) profile) characteristics of pork. The effects of long-term betaine intake (1 g betaine kg(-1) diet for 20 weeks) on the chemical and physical characteristics of Musculus longissimus dorsi, M. biceps femoris and M. semimembranosus from the Alentejano pig were investigated. The contents of total protein, intramuscular lipids (neutral and polar), myoglobin and total collagen as well as the water-holding capacity, physical colour characteristics and FA profile of the three muscles were determined. With the exception of a significant increase in the intramuscular lipid content of M. longissimus dorsi and M. biceps femoris, betaine supplementation did not influence muscle chemical and colour characteristics or body fat deposition. These data suggest that long-term betaine supplementation selectively increases intramuscular lipid deposition (a trait related to meat quality) while not affecting other chemical (including the atheroprotective FA profile) and physical characteristics of the Alentejano pig muscles studied.

The curious case of anabolic resistance: old wives' tales or new fables?

the progressive loss of muscle mass, commonly termed sarcopenia, accompanies the process of healthy aging ([27][1]). The underlying basis of this condition, in a very simplistic view, would be at a more advanced age skeletal muscle proteins are being lost because of an imbalance between muscle

Effect of trans-fatty acid intake on insulin sensitivity and intramuscular lipids—a randomized trial in overweight postmenopausal women

Intake of industrially produced trans-fatty acids (TFA) has been linked to increased risk of type 2 diabetes mellitus in observational studies. We investigated the causality of this association by examining if a high intake of TFA impairs measures of glucose homeostasis and induces intramuscular lipid deposition in abdominally obese women. In a double-blind, parallel dietary intervention study, 52 healthy but overweight postmenopausal women were randomized to receive either partially hydrogenated soybean oil (15 g/d TFA) or a control oil (mainly oleic and palmitic acid) for 16 weeks. Three markers of glucose homeostasis and 4 markers of lipolysis were derived from glucose, insulin, C-peptide, nonesterified fatty acid, and glycerol concentrations during a 3-hour frequent sampling oral glucose tolerance test. Intramuscular lipids were assessed by magnetic resonance spectroscopy. Forty-nine women completed the study. Insulin sensitivity (assessed by ISI composite), β-cell function (the disposition index), and the metabolic clearance rate of insulin were not significantly affected by the dietary intervention. Neither was the ability of insulin to suppress plasma nonesterified fatty acid and glycerol during oral glucose ingestion nor the intramuscular lipid deposition. In conclusion, high TFA intake did not affect glucose metabolism over 16 weeks in postmenopausal overweight women. A study population with a stronger predisposition to insulin resistance and/or a longer duration of exposure may be required for insulin sensitivity to be affected by intake of industrial TFA.

The effect of anabolic implants on intramuscular lipid deposition in finished beef cattle

Two experiments were conducted to determine the effects of anabolic implants on performance, changes in ultrasound measurements, carcass quality, cellularity of i.m. and s.c. adipose depots, and mRNA expression of acetyl CoA carboxylase (ACC), stearoyl CoA desaturase (SCD), and lipoprotein lipase (LPL) in i.m. adipose tissue of finished beef cattle. Angus heifers (experiment 1: n = 10; 411 kg of BW) and steers (experiment 2: n = 18; 279 kg of BW) were randomly allotted as control (C) or implanted with Synovex-Plus (SP) at d 0 and midway through the finishing period. The cattle were fed a high-concentrate diet and were weighed at approximately 28-d intervals. Heifers and steers were finished for 108 and 133 d, respectively. At slaughter, a section of the LM (sixth to ninth rib) was removed, and i.m. adipose tissue was dissected for mRNA analysis. Subcutaneous and i.m. adipose tissues also were collected for determination of cellularity. At 48 h postmortem, carcass data were collected, and a steak (12th rib) was removed for analysis of lipid and fatty acid composition. Body weight did not differ (P > 0.10) between treatments until after reimplanting of the heifers (d 55) or steers (d 73). Average daily gain was 36 and 16% faster (P < or = 0.01) for implanted heifers and steers, respectively, compared with their control counterparts. Implanting resulted in larger (P < or = 0.10) HCW and LM area for heifers and steers. However, implanting did not affect (P > 0.10) dressing percent, fat thickness, percentage of KPH, yield grade, or marbling score. Intramuscular lipid content and concentrations of major fatty acids did not differ (P > 0.10) between treatments. Percentage of SC adipocytes was greater at larger diameters ( > 150 microm), whereas the majority of i.m. adipocytes were at small to middle diameters (50 to 150 microm). The number of i.m. adipocytes per gram of tissue was greater (P < 0.05) for SP than C and also were greater (P < 0.05) than the number of s.c. adipocytes in SP heifers. In experiment 2, adipocytes per gram of tissue tended to be greater (P = 0.07) for SP than C and were greater (P < 0.01) for i.m. than s.c. In experiment 1, average cell diameter and volume did not differ (P > 0.10) between treatments and tissues, but in experiment 2 both cellularity traits were greater (P < 0.01) for s.c. than for i.m.. Implanting did not alter mRNA expression of ACC, SCD, or LPL in i.m. adipose tissue. This study shows that anabolic implants do not appear to have direct effects on i.m. lipid deposition.