Myosin Heavy Chain IIx Research Articles

Effects of age on human skeletal muscle: A systematic review and meta-analysis of myosin heavy chain isoform protein expression, fiber size and distribution.

Human studies examining the cellular mechanisms behind sarcopenia, or age-related loss of skeletal muscle mass and function, have produced inconsistent results. A systematic review and meta-analysis were performed to determine the aging effects on protein expression, size and distribution of fibers with various myosin heavy chain (MyHC) isoforms. Study eligibility included MyHC comparisons between young (18-49 years) and older (≥ 60 years) adults, with 27 studies identified. Relative protein expression was higher with age for the slow-contracting MyHC I fibers, with correspondingly lower fast-contracting MyHC II and IIA values. Fiber sizes were similar with age for MyHC I, while smaller for MyHC II and IIA. Fiber distributions were similar with age. When separated by sex, the few studies that examined females showed atrophy of MyHC II and IIA fibers with age, but no change in MyHC protein expression. Additional analyses by measurement technique, physical activity, and muscle biopsied provided important insights. In summary, age-related atrophy in fast-contracting fibers lead to more of the slow-contracting, lower force-producing isoform in older male muscles, which helps explain their age-related loss in whole muscle force, velocity, and power. Exercise or pharmacological interventions that shift MyHC expression towards faster isoforms and/or increase fast-contracting fiber size should decrease the prevalence of sarcopenia. Our findings also indicate that future studies need to include or focus solely on females, measure MyHC IIA and IIX isoforms separately, examine fiber type distribution, sample additional muscles to the vastus lateralis, and incorporate an objective measurement of physical activity.

Abnormal expression of myosin heavy chains in early postnatal stages of spinal muscular atrophy type I at single fibre level.

We investigated myosin heavy chain (MyHC) isoform expression at early postnatal stages of clinically and genetically confirmed spinal muscular atrophy type 1 (SMA1) patients, in order to study the muscle fibre differentiation compared to age-matched controls at single fibre level. Open skeletal muscle biopsies were performed from the quadriceps muscle in four SMA1 patients and three age-matched controls. Standard techniques were used for immunohistochemistry of embryonic and foetal MyHCs. Type I, IIa and IIx MyHCs were assessed by applying quadruple immunofluorescence. Western blot was performed to analyse the amount of survival motor neuron (SMN) protein in the muscle samples. There were profound and early alterations in MyHC expression from 7 days of life compared to age-matched controls. The expression of type IIx MyHC was completely lost in SMA1 and instead developmental isoforms remained highly expressed. Foetal MyHC was still, at 3.5 months of age, expressed in the majority of muscle fibres in SMA1 patients, whereas it was completely downregulated in age-matched controls. The level of SMN protein was reduced in all SMN1 patients. The abnormal pattern of MyHC expression in postnatal stages of SMA1 was observed early in the newborn period, which may have implications for the effects of gene therapy, since there are clear clinical benefits from early treatment. Whether such aberrant and delayed expression of MyHCs can be completely restored by postnatal gene therapy remains to be studied and may also have implications for new phenotypes that will evolve with new therapies.

N-Acetylcysteine assists muscle development in offspring of mice subjected to maternal heat stress during pregnancy.

Heat stress (HS) has been shown to affect reproductive performance and muscle development negatively in animals. N-Acetylcysteine (NAC) plays a pivotal role in enhancing the antioxidant performance in animals as a recognized antioxidant. The present study assesses the potential of NAC to modulate the reproductive performance and antioxidant function in pregnant mice exposed to HS. The role of NAC in muscle development of offspring mice was also explored. The results showed that NAC supplementation from day 12 to day 18 of gestation increased the number of litters and enhanced the antioxidant function in pregnant mice under HS exposure. It improved the weight and body condition significantly in the offspring mice (P < 0.05). The alleviation of HS-induced muscle impairment with NAC was consistent with the alleviation of apoptosis, the enrichment of the proliferation and differentiation in the offspring mice muscle. N-Acetylcysteine also reversed HS-induced reduction in the cross-sectional area of the leg muscle and increased the proportion of myosin heavy chain IIx (MYHCIIx) in the muscle fiber. The results of the present study support the use of NAC at a dose of 100 mg kg-1 body weight as supplement for protecting the offspring derived from pregnant mice exposed to HS from muscle impairment by accelerating proliferation and differentiation. © 2024 Society of Chemical Industry.

Transcriptomics reveals transient and dynamic muscle fibrosis and atrophy differences following spinal cord injury in rats.

The rate and magnitude of skeletal muscle wasting after severe spinal cord injury (SCI) exceeds most other disuse conditions. Assessing the time course of molecular changes can provide insight into the progression of muscle wasting post-SCI. The goals of this study were (1) to identify potential targets that may prevent the pathologic features of SCI in soleus muscles and (2) to establish therapeutic windows for treating these pathologic changes. Four-month-old Sprague-Dawley male rats received T9 laminectomy (SHAM surgery) or severe contusion SCI. Hindlimb locomotor function was assessed weekly, with soleus muscles obtained 1week, 2weeks, 1month and 3months post-surgery (n=6-7 per group per timepoint). RNA was extracted from muscles for bulk RNA-sequencing analysis (n=3-5 per group per timepoint). Differentially expressed genes (DEGs) were evaluated between age-matched SHAM and SCI animals. Myofiber size, muscle fibre type and fibrosis were assessed on contralateral muscles. SCI produced immediate and persistent hindlimb paralysis, with Basso-Beattie-Bresnahan locomotor scores remaining below 7 throughout the study, contributing to a progressive 25-50% lower soleus mass and myofiber atrophy versus SHAM (P<0.05 at all timepoints). Transcriptional comparisons of SCI versus SHAM resulted in 184 DEGs (1week), 436 DEGs (2weeks), 133 DEGs (1month) and 1200 DEGs (3months). Upregulated atrophy-related genes included those associated with cell senescence, nuclear factor kappa B, ubiquitin proteasome and unfolded protein response pathways, along with upregulated genes that negatively influence muscle growth through the transforming growth factor beta pathway and inhibition of insulin-like growth factor-I/Akt/mechanistic target of rapamycin and p38/mitogen-activated protein kinase signalling. Genes associated with extracellular matrix (ECM), including collagens, collagen crosslinkers, proteoglycans and those regulating ECM integrity, were enriched within upregulated DEGs at 1week but subsequently downregulated at 2weeks and 3months and were accompanied by >50% higher ECM areas and hydroxyproline levels in SCI muscles (P<0.05). Myofiber remodelling genes were enriched in upregulated DEGs at 2weeks and 1month and were downregulated at 3months. Genes that regulate neuromuscular junction remodelling were evident in muscles post-SCI, along with slow-to-fast fibre-type shifts: 1 week and 2 weeks SCI muscles were composed of 90% myosin heavy chain (MHC) type I fibres, which decreased to only 16% at 3months and were accompanied by 50% fibres containing MHC IIX (P<0.05). Metabolism genes were enriched in upregulated DEGs at 1month and were further enriched at 3months. Our results substantiate many known pathologic features of SCI-induced wasting in rat skeletal muscle and identify a progressive and dynamic transcriptional landscape within the post-SCI soleus. Future studies are warranted to consider these therapeutic treatment windows when countering SCI muscle pathology.

Meat Characteristics, Expression of Myosin Heavy Chain and Metabolism-Related Genes in Thai Native Pigs.

This study investigated the meat quality, expression of myosin heavy chain (MyHC) and metabolism-related genes, ribonucleotides and fatty acids in Longissimus thoracis of Thai native pigs (TNPs) from different geographical regions (GR). Forty-one 9-10-month-old castrated TNPs (BW 60 kg), consisting of 18, 11 and 12 pigs from Northern (NT), Southern (ST) and Northeastern (NE) regions, respectively, were slaughtered. GR did not affect (p > 0.05) the expression of MyHC, phosphoglycerate mutase 1, cytosolic glycerol-3-phosphate dehydrogenase, triosephosphate isomerase 1 and adipocyte fatty acid binding protein genes. The trend of MyHC was MyHC IIx > MyHC IIb > MyHC IIa > MyHC I. The NT loin had higher (p < 0.05) glycogen, C18:2n6, C20:4n6 and cooking loss, lower inosine, inosine monophosphate and hypoxanthine and a shorter sarcomere length than the ST and NE loins. The ST loin had a lower (p < 0.05) a* compared to other loins. Principal component analysis established significant relationships between the TNP and specific meat quality traits. This finding suggests that GR affected the meat quality, ribonucleotides and selected fatty acids in TNPs. These results provide relevant information that can be used to optimize the use of Thai native pork.

The influence of skeletal muscle mitochondria and sex on critical torque and performance fatiguability in humans.

Critical torque (CT) represents the highest oxidative steady state for intermittent knee extensor exercise, but the extent to which it is influenced by skeletal muscle mitochondria and sex is unclear. Vastus lateralis muscle biopsy samples were collected from 12 females and 12males -matched for relative maximal oxygen uptake normalized to fat-free mass (FFM) (F: 57.3 (7.5) ml(kg FFM)-1 min-1 ; M: 56.8 (7.6) ml(kg FFM)-1 min-1 ; P=0.856) - prior to CT determination and performance fatiguability trials. Males had a lower proportion of myosin heavy chain (MHC) I isoform (40.6 (18.4)%) compared to females (59.5 (18.9)%; P=0.021), but MHC IIa and IIx isoform distributions and protein markers of mitochondrial content were not different between sexes (P > 0.05). When normalized to maximum voluntary contraction (MVC), the relative CT (F: 42.9 (8.3)%; M: 37.9 (9.0)%; P=0.172) and curvature constant, W' (F: 26.6 (11.0) Nms(Nm)-1 ; M: 26.4 (6.5) Nms(Nm)-1 ; P=0.962) were not significantly different between sexes. All protein biomarkers of skeletal muscle mitochondrial content, as well as the proportion of MHC I isoform, positively correlated with relative CT (0.48<r<0.70; P<0.05), and the proportion of MHC IIx isoform correlated positively with relative W' (r=0.57; P=0.007). Indices of performance fatiguability were not different between males and females for MVC- and CT-controlled trials (P > 0.05). Greater mitochondrial protein abundance was associated with attenuated declines in potentiated twitch torque for exercise at 60% MVC (P<0.05); however, the influence of mitochondrial protein abundance on performance fatiguability was reduced when exercise was prescribed relative to CT. Whether these findings translate to whole-body exercise requires additional research. KEY POINTS: The quadriceps critical torque represents the highest intensity of intermittent knee extensor exercise for which an oxidative steady state is attainable, but its relationship with skeletal muscle mitochondrial protein abundance is unknown. Matching males and females for maximal oxygen uptake relative to fat-free mass facilitates investigations of sex differences in exercise physiology, but studies that have compared critical torque and performance fatiguability during intermittent knee extensor exercise have not ensured equal aerobic fitness between sexes. Skeletal muscle mitochondrial protein abundance was correlated with critical torque and fatigue resistance for exercise prescribed relative to maximum voluntary contraction but not for exercise performed relative to the critical torque. Differences between sexes in critical torque, skeletal muscle mitochondrial protein abundance and performance fatiguability were not statistically significant. Our results suggest that skeletal muscle mitochondrial protein abundance may contribute to fatigue resistance by influencing the critical intensity of exercise.

Exercise-induced changes to the fiber type-specific redox state in human skeletal muscle are associated with aerobic capacity.

The benefits of exercise involve skeletal muscle redox state alterations of nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). We determined the fiber-specific effects of acute exercise on the skeletal muscle redox state in healthy adults. Muscle biopsies were obtained from 19 participants (11 M, 8 F; 26 ± 4 yr) at baseline (fasted) and 30 min and 3 h after treadmill exercise at 80% maximal oxygen consumption (V̇o2max). Muscle samples were probed for autofluorescence of NADH (excitation at 340-360 nm) and oxidized flavoproteins (Fp; excitation at 440-470 nm) and subsequently, fiber typed to quantify the redox signatures of individual muscle fibers. Redox state was calculated as the oxidation-to-reduction redox ratio: Fp/(Fp + NADH). At baseline, pair-wise comparisons revealed that the redox ratio of myosin heavy chain (MHC) I fibers was 7.2% higher than MHC IIa (P = 0.023, 95% CI: 5.2, 9.2%) and the redox ratio of MHC IIa was 8.0% higher than MHC IIx (P = 0.035, 95% CI: 6.8, 9.2%). MHC I fibers also displayed greater NADH intensity than MHC IIx (P = 0.007) and greater Fp intensity than both MHC IIa (P = 0.019) and MHC IIx (P < 0.0001). Fp intensities increased in all fiber types (main effect, P = 0.039) but redox ratios did not change (main effect, P = 0.483) 30 min after exercise. The change in redox ratio was positively correlated with capillary density in MHC I (rho = 0.762, P = 0.037), MHC IIa fibers (rho = 0.881, P = 0.007), and modestly in MHC IIx fibers (rho = 0. 771, P = 0.103). These findings support the use of redox autofluorescence to interrogate skeletal muscle metabolism.NEW & NOTEWORTHY This study is the first to use autofluorescent imaging to describe differential redox states within human skeletal muscle fiber types with exercise. Our findings highlight an easy and efficacious technique for assessing skeletal muscle redox in humans.

Exploring the impact of temporal heat stress on skeletal muscle hypertrophy in bovine myocytes

The primary aim of this investigation was to explore the impact of different temporal stress conditions on the regulators associated with skeletal muscle hypertrophy in bovine myocytes. Bovine satellite cells (BSCs) were extracted from three-month-old Holstein bull calves and subjected to myogenic differentiation under three thermal treatments: 38 °C (control; CON), 39.5 °C (moderate heat stress; MHS), and 41 °C (extreme heat stress; EHS) for a duration of 3 or 48 h. Exposure to EHS resulted in elevated (P < 0.01) expression levels of heat shock protein (HSP)20, HSP27, HSP70, and HSP90, along with increased (P < 0.01) protein levels. Moreover, cells exposed to MHS and EHS exhibited enhanced (P < 0.01) gene expression of myoblast determination protein 1 (MyoD), while myogenin (MyoG) was overexpressed (P < 0.01) in cells exposed to EHS. These findings suggest that heat exposure can potentially induce myogenic differentiation through the modulation of myogenic regulatory factors. Furthermore, our investigations revealed that exposure to EHS upregulated (P < 0.01) myosin heavy chain (MHC) I expression, whereas MHC IIA (P < 0.01) and IIX (P < 0.01) expression were increased; P < 0.01) under MHS conditions. These observations suggest that the temperature of the muscle may alter the proportion of muscle fiber types. Additionally, our data indicated that EHS activated (P < 0.01) the expression of insulin-like growth factor 1 (IGF-1) and triggered the activation of the Akt/mTOR/S6KB1 pathway, a known anabolic pathway associated with cellular protein synthesis. Consequently, these altered signaling pathways contributed to enhanced protein synthesis and increased myotube size. Overall, the results obtained from our current study revealed that extreme heat exposure (41 °C) may promote skeletal muscle hypertrophy by regulating myogenic regulatory factors and IGF-1-mediated mTOR pathway in bovine myocytes.

Sex differences in skeletal muscle size, function, and myosin heavy chain isoform expression during post-injury regeneration in mice.

Skeletal muscle regeneration is an essential process to restore muscle function after injury and is influenced by various factors. Despite the known importance of sex hormones in muscle regeneration, whether and what sex difference exists in this process is still unclear. In this study, we provide evidence for a clear sex difference in muscle regeneration in mice. At 7 and 14 days after barium chloride-induced muscle injury, female mice showed a faster recovery of muscle fiber size than males. Consistently, muscle force in female mice was restored faster than in males after injury, and this functional difference was maintained at 14 months of age when regenerative capacity declined. Myosin heavy chain isoform profiling and fatigability test revealed dynamic remodeling of myosin heavy chain isoform expression including a type IIB to IIA/X MHC transition and reduced fatigability in regenerated muscles compared to uninjured muscles. A significant sex difference was detected in myosin heavy chain IIX content, although this did not lead to different fatigability. Together, our results suggest that sex is an important determinant of the recovery of regenerating skeletal muscle and is partially involved in the remodeling of myosin heavy chain isoforms during muscle regeneration.

Effects of Creatine Supplementation on the Myostatin Pathway and Myosin Heavy Chain Isoforms in Different Skeletal Muscles of Resistance-Trained Rats

Creatine has been used to maximize resistance training effects on skeletal muscles, including muscle hypertrophy and fiber type changes. This study aimed to evaluate the impact of creatine supplementation on the myostatin pathway and myosin heavy chain (MyHC) isoforms in the slow- and fast-twitch muscles of resistance-trained rats. Twenty-eight male Wistar rats were divided into four groups: a sedentary control (Cc), sedentary creatine supplementation (Cr), resistance training (Tc), and resistance training combined with creatine supplementation (Tcr). Cc and Tc received standard commercial chow; Cr and Tcr received a 2% creatine-supplemented diet. Tc and Tcr performed a resistance training protocol on a ladder for 12 weeks. Morphology, MyHC isoforms, myostatin, follistatin, and ActRIIB protein expressions were analyzed in soleus and white gastrocnemius portion samples. The results were analyzed using two-way ANOVA and Tukey’s test. Tc and Tcr exhibited higher performance than their control counterparts. Resistance training increased the ratio between muscle and body weight, the cross-sectional area, as well as the interstitial collagen fraction. Resistance training alone increased MyHC IIx and follistatin while reducing myostatin (p &lt; 0.001) and ActRIIB (p = 0.040) expressions in the gastrocnemius. Resistance training induced skeletal muscle hypertrophy and interstitial remodeling, which are more evident in the gastrocnemius muscle. The effects were not impacted by creatine supplementation.

A chronic high-fat diet does not exacerbate muscle atrophy in fast-twitch skeletal muscle of aged mice.

What is the central question of this study? Ageing leads to a loss of mass in skeletal muscle, but the effect of obesity on ageing-related muscle wasting is unclear. In this study, we aimed to demonstrate the specific effect of obesity on fast-twitch skeletal muscle in ageing. What is the main finding and its importance? Our findings show that the obesity induced by long-term ingestion of a high-fat diet does not aggravate muscle wasting in fast-twitch skeletal muscle of aged mice, indicating that the present study provides morphological characteristics for skeletal muscle of sarcopenic obesity. Obesity and ageing reduce muscle mass and lead to deficits in muscle maintenance, but it is not known whether obesity accelerates muscle wasting additively in the setting of ageing. We investigated morphological characteristics in fast-twitch extensor digitorum longus (EDL) muscle of mice fed a low-fat diet (LFD) or a high-fat diet (HFD) for 4 or 20 months. The fast-twitch EDL muscle was harvested, and the muscle fibre-type composition, individual muscle cross-sectional area and myotube diameter were measured. We found an increase in the percentage of type IIa and IIx myosin heavy chain fibres in the whole EDL muscle, but a decrease in type IIB myosin heavy chain in both HFD protocols. The cross-sectional area and myofibre diameter were lower in both groups of aged mice (after 20 months of LFD or HFD) compared with young mice (after 4 months of the diets), but there were no differences between mice fed LFD or HFD for 20 months. These data suggest that long-term feeding of HFD does not aggravate muscle wasting in fast-twitch EDL muscle of male mice.

Palmitic Acid Inhibits Myogenic Activity and Expression of Myosin Heavy Chain MHC IIb in Muscle Cells through Phosphorylation-Dependent MyoD Inactivation.

Sarcopenia associated with aging and obesity is characterized by the atrophy of fast-twitch muscle fibers and an increase in intramuscular fat deposits. However, the mechanism of fast-twitch fiber-specific atrophy remains unclear. In this study, we aimed to assess the effect of palmitic acid (PA), the most common fatty acid component of human fat, on muscle fiber type, focusing on the expression of fiber-type-specific myosin heavy chain (MHC). Myotubes differentiated from C2C12 myoblasts were treated with PA. The PA treatment inhibited myotube formation and hypertrophy while reducing the gene expression of MHC IIb and IIx, specific isoforms of fast-twitch fibers. Consistent with this, a significant suppression of MHC IIb protein expression in PA-treated cells was observed. A reporter assay using plasmids containing the MHC IIb gene promoter revealed that the PA-induced reduction in MHC IIb gene expression was caused by the suppression of MyoD transcriptional activity through its phosphorylation. Treatment with a specific protein kinase C (PKC) inhibitor recovered the reduction in MHC IIb gene expression levels in PA-treated cells, suggesting the involvement of the PA-induced activation of PKC. Thus, PA selectively suppresses the mRNA and protein expression of fast-twitch MHC by modulating MyoD activity. This finding provides a potential pathogenic mechanism for age-related sarcopenia.

Stretch activated force production increases during fatigue in fast-contracting skeletal muscle fibers.

Stretch activation (FSA) is the delayed increase in fiber tension (force per cross-sectional area) following a rapid stretch and can improve muscle performance during repetitive cyclical contractions. Historically considered minimal in skeletal muscle, our recent work showed the ratio of stretch activation to calcium-activated tension (FSA/F0) increased from 10 to 40% with greater inorganic phosphate (Pi) levels in soleus muscle fibers (Straight et al., 2019). Given Pi increases with muscle fatigue, we hypothesize that FSA helps maintain force generation during fatigue. To test this, FSA, induced by a stretch of 0.5% fiber length, was examined during control (pCa 4.5, pH 7.0, Pi 5 mM), high calcium fatigue (pCa 4.5, pH 6.2, Pi 30 mM) and low calcium fatigue (pCa 5.1, pH 6.2, Pi 30 mM) in fibers expressing myosin heavy chain (MHC) I, IIA, IIX and IIB isoforms from soleus and extensor digitorum longus muscles of C57BL/6NJ mice. F0 of all MHC isoforms decreased from control to high calcium fatigue to low calcium fatigue, as expected. In MHC IIX and IIB fibers, FSA occurred under all conditions and FSA/F0 increased from control (17-20%) to high calcium fatigue (32-35%) to low calcium fatigue (42-44%). In MHC IIA fibers, FSA/F0 was similar to MHC IIX and IIB fibers in control and high calcium fatigue, however MHC I fiber values were much less (5% and 18%). For MHC I and IIA fibers, no discernable FSA was apparent in low calcium fatigue. These results show that FSA is a significant modulator of force production under fatiguing conditions in fast-contracting muscle fibers. This mechanism could play an important physiological role during cyclical contractions, when the antagonistic muscle rapidly stretches the agonist muscle, by reducing the effect of fatigue on force production.

Effects of the F94L myostatin gene mutation in beef × dairy crossed cattle on muscle fiber type, live performance, carcass characteristics, and boxed beef and retail cut yields.

Producer live performance data and carcasses from steers (n = 116) resulting from the mating of four Limousin/Angus sires heterozygous for the F94L myostatin mutation to Jersey/Holstein dams were utilized to evaluate the effects of one copy of the F94L allele on live performance, carcass traits and USDA grades, and boxed beef and retail yields. Slaughter data were collected at time of harvest and carcass data were collected 48 hours postmortem. One side from each of the 58 carcasses was fabricated into boxed beef and retail cuts by experienced lab personnel 5-8 d postmortem. One copy of the F94L allele did not affect gestation length, birth weight, percentage of unassisted births, feedlot average daily gain, live weight at harvest, hot carcass weight, or dressing percentage (P > 0.05). Muscle fiber analysis indicated that the increase in muscularity by the F94L allele in the semitendinosus and longissimus was likely due to hyperplasia as there was a 19% increase in the quantity of myosin heavy chain type IIA and IIX fibers in the semitendinosus (P < 0.05) with no effect on muscle fiber size (P > 0.05). Carcasses from steers with one F94L allele had larger ribeye areas (99.2 vs. 92.3 sq.cm.), greater ribeye width:length ratios (0.498 vs. 0.479), lower USDA yield grades (2.21 vs. 2.66), and lower marbling scores (438 vs. 480) (P < 0.05). Additionally, for boxed beef yields, one F94L allele, vs. zero F94L alleles, increased (P < 0.05) 85/15 trimmings (+0.59%), top round (+0.28%), strip loin (+0.12%), eye round (+0.11%), tenderloin (+0.07%), boneless foreshank (+0.07%), cap/wedge (+0.06%), and tri-tip (+0.04%). Overall, carcasses from steers with one F94L allele had a greater boxed beef yield (+1.06%), boxed beef plus 85/15 trimmings yield (+1.65%), and total retail cuts plus ground beef 85/15 yield (+1.78%) than carcasses from steers with zero F94L alleles (P < 0.05). One copy of the F94L allele utilized in beef-on-dairy breeding system had no significant impact on live performance traits but resulted in lower marbling scores and increased muscularity as evidenced through larger, more beef-shaped ribeyes, lower USDA yield grades, and greater carcass cutout yields (both boxed beef and retail yields).

UBR2 targets myosin heavy chain IIb and IIx for degradation: Molecular mechanism essential for cancer-induced muscle wasting

Cancer cachexia is a lethal metabolic syndrome featuring muscle wasting with preferential loss of fast-twitching muscle mass through an undefined mechanism. Here, we show that cancer induces muscle wasting by selectively degrading myosin heavy chain (MHC) subtypes IIb and IIx through E3 ligase UBR2-mediated ubiquitylation. Induction of MHC loss and atrophy in C2C12 myotubes and mouse tibialis anterior (TA) by murine cancer cells required UBR2 up-regulation by cancer. Genetic gain or loss of UBR2 function inversely altered MHC level and muscle mass in TA of tumor-free mice. UBR2 selectively interacted with and ubiquitylated MHC-IIb and MHC-IIx through its substrate recognition and catalytic domain, respectively, in C2C12 myotubes. Elevation of UBR2 in muscle of tumor-bearing or free mice caused loss of MHC-IIb and MHC-IIx but not MHC-I and MHC-IIa or other myofibrillar proteins, including α-actin, troponin, tropomyosin, and tropomodulin. Muscle-specific knockout of UBR2 spared KPC tumor-bearing mice from losing MHC-IIb and MHC-IIx, fast-twitching muscle mass, cross-sectional area, and contractile force. The rectus abdominis (RA) muscle of patients with cachexia-prone cancers displayed a selective reduction of MHC-IIx in correlation with higher UBR2 levels. These data suggest that UBR2 is a regulator of MHC-IIb/IIx essential for cancer-induced muscle wasting, and that therapeutic interventions can be designed by blocking UBR2 up-regulation by cancer.

Low Protein Diet Improves Meat Quality and Modulates the Composition of Gut Microbiota in Finishing Pigs.

This study investigated the effect of a low protein (LP) diet on growth performance, nitrogen emission, carcass traits, meat quality, and gut microbiota in finishing pigs. Fifty-four barrows (Duroc × Landrace × Yorkshire) were randomly assigned to three treatments with six replicates (pens) of three pigs each. The pigs were fed with either high protein (HP, 16% CP), medium protein (MP, 12% CP), and LP diets (10% CP), respectively. The LP diets did not influence the growth performance, but significantly decreased the plasma urea nitrogen contents and fecal nitrogen emission (P < 0.05). The LP diet significantly decreased the plasma contents of malondialdehyde (MDA) and increased the plasma glutathione (GSH) contents (P < 0.05). The LP diets significantly increased the backfat thickness at the first and last ribs, L* (lightness) value of meat color, and muscle fiber density in the longissimus dorsi (P < 0.05). The messenger RNA (mRNA) expression of fatty acid synthetase (FAS), peroxisome proliferator-activated receptor-gamma (PPARγ), leptin, and acetyl-CoA carboxylase (ACC) was significantly downregulated, while that of carnitine palmitoyltransferase 1 (CPT1) and myosin heavy chain (MYHC) IIx in the longissimus Dorsi muscle was significantly upregulated by LP diets (P < 0.05). The 16S sequencing analysis showed that the abundance of unidentified Bacteria at the phylum level, and Halanaerobium and Butyricicoccusat at the genus level in the colonic digesta were significantly decreased by LP diet (P < 0.05). The LP diet significantly decreased the observed species of α-diversity in both ileal and colonic microbiota (P < 0.05). Spearman correlation analysis identified a significant positive correlation between the abundance of the ileal genera Streptococcus and L* value at 24 and 48 h, and a significant negative correlation between unidentified_Ruminococcasceae in both ileum and colon with L* value at 24 h (P < 0.05). Collectively, the LP diet supplemented with lysine, methionine, threonine, and tryptophan could reduce the fecal nitrogen emission without affecting growth performance and improve meat quality by regulating the antioxidant capacity and gene expression involved in fat metabolism as well as modulating the gut microbiota composition in finishing pigs.

Effects of feeding high-energy diet on growth performance, blood parameters, and carcass traits in Hanwoo steers

ObjectiveOur study aimed to investigate the effects of a 2% increase in dietary total digestible nutrients (TDN) value during the growing (7 to 12 mo of age) and fattening (13 to 30 mo of age) period of Hanwoo steers.MethodsTwo hundred and twenty Hanwoo steers were assigned to one of two treatments: i) a control group (basal TDN, BTDN, n = 111 steers, growing = 70.5%, early fattening = 71.0%, late fattening = 74.0%) or high TDN (HTDN, n = 109 steers, growing = 72.6%, early = 73.1%, late = 76.2%). Growth performance, carcass traits, blood parameters, and gene expression of longissimus dorsi (LD) (7, 18, and 30 mo) were quantified.ResultsSteers on the BTDN diets had increased (p≤0.02) DMI throughout the feeding trial compared to HTDN, but gain did not differ appreciably. A greater proportion of cattle in HTDN received Korean quality grade 1 (82%) or greater compared to BTDN (77%), while HTDN had a greater yield grade (29%) than BTDN (20%). Redness (a*) of LD muscle was improved (p = 0.021) in steers fed HTDN. Feeding the HTDN diet did not alter blood parameters. Steers fed HTDN diet increased (p = 0.015) the proportion of stearic acid and tended to alter linoleic acid. Overall, saturated, unsaturated, monounsaturated, and polyunsaturated fatty acids of LD muscle were not impacted by the HTDN treatment. A treatment by age interaction was noted for mRNA expression of myosin heavy chain (MHC) IIA, IIX, and stearoyl CoA desaturase (SCD) (p≤0.026). No treatment effect was detected on gene expression from LD muscle biopsies at 7, 18, and 30 mo of age; however, an age effect was detected for all variables measured (p≤0.001).ConclusionOur results indicated that feeding HTDN diet could improve overall quality grade while minimum effects were noted in gene expression, blood parameters, and growing performance. Cattle performance prediction in the feedlot is a critical decision-making tool for optimal planning of cattle fattening and these data provide both benchmark physiological parameters and growth performance measures for Hanwoo cattle feeding enterprises.

A Reduction in Tafazzin Decreases Mitochondrial Function in C2C12 Myotubes

Mitochondria, which are often regarded as the “powerhouse of the cell”, are labile organelles that regulate cellular metabolism, determine cell fate, and act as important signaling hubs. A phospholipid that is exclusively found within mitochondria that serves numerous roles is cardiolipin (CL). In healthy mitochondria, CL is predominately localized in the inner mitochondrial membrane (IMM) and binds to several membrane proteins including those in the electron transport chain (ETC) and in the protein import machinery (PIM). Similarly, CL has also been shown to regulate cell death and mitophagy in dysfunctional mitochondria. Following the biosynthesis of nascent CL in the inner membrane, it is remodeled into its mature form by a transacylase, tafazzin (Taz). The absence of this enzyme is associated with Barth Syndrome, a disease characterized by cardiomyopathy and skeletal myopathy. Interestingly, little is known about the role of mature CL in skeletal muscle. Therefore, the objective of this study was to identify whether Taz deficiency diminishes mitochondrial function in the presence or absence of changes in organelle volume and function. We hypothesized that a reduction in Taz will attenuate mitochondrial function, while lysosomal and mitochondrial content will be elevated. To test this hypothesis, C2C12 myotubes were transfected on day 3 of differentiation with either a scrambled or Taz siRNA vector. Cells were harvested for analysis on day 7 of differentiation. Organelle volume was assessed using immunohistochemistry and Western blot techniques, whereas Seahorse technology was used to measure mitochondrial respiration. In comparison to C2C12 myotubes that were treated with a scrambled vector, Taz protein content was reduced by 85% (P&lt;0.05) in siRNA‐treated cells. Maximal oxygen consumption and ATP production were attenuated in Taz‐deficient cells by 18% and 14%, respectively, while basal respiration remained unaffected. Lysosome and mitochondrial content were increased 20% and 24%, respectively, in Taz‐deficient cells. Similarly, myotubes lacking Taz exhibited a 7% increase (P=0.056) in Complex IV protein content, but lysosomal‐associated membrane protein 1 (LAMP1) decreased 33% (P&lt;0.05). Myosin heavy chain (MHC) IIX was also elevated by 32% in mature CL depleted myotubes. CL‐deficient myotubes were 32% smaller in diameter and 10% longer when compared to scrambled treated myotubes. These data suggest that a reduction in mature CL impairs skeletal muscle mitochondrial function. Moreover, although lysosomal content was elevated, lysosomes appear to have a reduced capacity to fuse with autophagosomes, which may in part explain why there is an increase in dysfunctional mitochondria. Future research should evaluate mitophagy flux and mitochondrial membrane potential in the presence of reduced mature CL in C2C12 myotubes, and whether exercise has the ability to rescue mitochondrial function.

Fish Protein Promotes Skeletal Muscle Hypertrophy via the Akt/mTOR Signaling Pathways.

Skeletal muscle is the largest organ in the body and has a broad range of plasticity, undergoing atrophy in response to aging or disease and hypertrophy in response to nutritional supplements or exercise. Loss of skeletal muscle mass and force increases the risk of falls, impairs mobility, and leads to reduced quality of life. In a previous study, we demonstrated that taking in Alaska pollock protein (APP) for only 7 d increased the gastrocnemius muscle mass in rats. This study was conducted to identify hypertrophic myofibers and analyze how hypertrophy occurs within them. Twenty male rats were randomly divided into two groups and administered a diet of casein or APP for 7 d. The expression of each myosin heavy chain (MyHC) isoform in a cross-sectional area was then measured. MyHC IIb and IIx isoforms exhibited hypertrophic features in the gastrocnemius muscles of the APP-fed rats. Furthermore, comprehensive proteomic analyses were conducted to identify changes in protein expression due to muscle hypertrophy. Our results, evaluated by pathway analyses, indicated that the activity of the growth factor signaling pathway was significantly impacted by APP consumption. Moreover, APP could promote protein synthesis by activating the protein kinase B/mechanistic target of the rapamycin signaling pathway, which is also promoted by exercise.

Effects of sheep slaughter age on myogenic characteristics in skeletal muscle satellite cells.

ObjectiveThe objective of this study was to investigate the effects of sheep slaughter age on myogenic characteristics in skeletal muscle satellite cells (SMSCs).MethodsPrimary SMSCs were isolated from hind leg biceps femoris muscles of Wurank lambs (slaughtered at three months, Mth-3) and adults (slaughtered at fifteen months, Mth-15). SMSCs were selected by morphological observation and fluorescence staining. Myogenic regulatory factors (MRF) and myosin heavy chain (MyHC) expressions of SMSCs were analyzed on days 1, 3, 4, and 5.ResultsThe expressions of myogenic factor 5 (Myf5), myogenic differentiation (MyoD), Myf6, and myogenin (MyoG) in Mth-15 were significantly higher in Mth-15 than in Mth-3 on days 1, 3, and 4 (p<0.05). However, MyoG expression in Mth-15 was significantly lower than in Mth-3 on day 5 (p<0.05). The expressions of MyHC I, MyHC IIa, and MyHC IIx in Mth-15 were significantly higher than in Mth-3 on days 1 and 3 (p<0.05), and MyHC IIb were significantly lower than in Mth-3 on days 3 and 4 (p<0.05). In contrast, the expression of MyHC IIx in Mth-15 was significantly lower and MyHC IIb was significantly higher than in Mth-3 on days 5 (p<0.05).ConclusionThe slaughter age altered the expression of MRFs and MyHCs in SMSCs while differentiation, which caused the variation of myogenic characteristics, and thus may affect the meat quality of Wurank sheep.