Slow Myosin Research Articles

Impaired Extraocular Muscle Innervation Is Present Before Eye Opening in a Mouse Model of Infantile Nystagmus Syndrome.

PurposeTo determine if extraocular muscles (EOMs) from mice with nystagmus show abnormalities in myofiber composition and innervation, as seen in EOMs from human nystagmus patients, and to determine when in development those changes occur.MethodsBalb/c albino mice were crossed to pigmented mice to generate heterozygous mice, which were mated to create experimental litters containing albinos and wild-type controls. Orbits were harvested from adult animals (12 weeks old); on postnatal day (P)0, P10, P14, and P21; and from 6-week-old animals. EOM sections were collected from the intraorbital portion of the muscles. Sections were immunostained for slow and fast myosin and for neuromuscular junctions (NMJs). The proportion of each myofiber subtype and the density and size of NMJs were quantified. Initial innervation patterns were assessed using whole-mount immunostaining of embryonic day (E)13.5 embryos expressing IslMN:GFP.ResultsAdult albino EOMs display an increased proportion of slow myofibers, larger slow myofibers, and a decreased density of NMJs—similar to human nystagmus patients. The percentage of NMJs on slow myofibers is also lower in albino animals. The initial innervation pattern of the incoming ocular motor neurons is normal in E13.5 albino embryos. Differences in the proportion of slow and fast myofiber subtypes are present as early as P14, and a lower percentage of NMJs on slow myofibers is present by P21. There is a lower density of NMJs on albino EOMs as early as P10, prior to eye opening.ConclusionsChanges in NMJ development observed before eye opening indicate that nystagmus is not solely secondary to poor vision.

Young bone marrow transplantation prevents aging-related muscle atrophy in a senescence-accelerated mouse prone 10 model.

Young bone marrow transplantation (YBMT) has been shown to stimulate vascular regeneration in pathological conditions, including ageing. Here, we investigated the benefits and mechanisms of the preventive effects of YBMT on loss of muscle mass and function in a senescence-associated mouse prone 10 (SAMP10) model, with a special focus on the role of growth differentiation factor 11 (GDF-11). Nine-week-old male SAMP10 mice were randomly assigned to a non-YBMT group (n=6) and a YBMT group (n=7) that received the bone marrow of 8-week-old C57BL/6 mice. Compared to the non-YBMT mice, the YBMT mice showed the following significant increases (all P < 0.05 in 6-7 mice): endurance capacity (>61.3%); grip strength (>37.9%), percentage of slow myosin heavy chain fibres (>14.9-15.9%). The YBMT also increased the amounts of proteins or mRNAs for insulin receptor substrate 1, p-Akt, p-extracellular signal-regulated protein kinase1/2, p-mammalian target of rapamycin, Bcl-2, peroxisom proliferator-activated receptor-γ coactivator (PGC-1α), plus cytochrome c oxidase IV and the numbers of proliferating cells (n = 5-7, P < 0.05) and CD34+/integrin-α7+ muscle stem cells (n = 5-6, P < 0.05). The YMBT significantly decreased the levels of gp91phox, caspase-9 proteins and apoptotic cells (n = 5-7, P < 0.05) in both muscles; these beneficial changes were diminished by the blocking of GDF-11 (n = 5-6, P < 0.05). An administration of mouse recombinant GDF-11 improved the YBMT-mediated muscle benefits (n = 5-6, P < 0.05). Cell therapy with young bone marrow from green fluorescent protein (GFP) transgenic mice exhibited GFP+ myofibres in aged muscle tissues. These findings suggest that YBMT can prevent muscle wasting and dysfunction by mitigating apoptosis and proliferation via a modulation of GDF-11 signalling and mitochondrial dysfunction in SAMP10 mice.

White Paper: An Integrated Perspective on the Causes of Hypometric Metabolic Scaling in Animals.

Larger animals studied during ontogeny, across populations, or across species, usually have lower mass-specific metabolic rates than smaller animals (hypometric scaling). This pattern is usually observed regardless of physiological state (e.g. basal, resting, field, maximally-active). The scaling of metabolism is usually highly correlated with the scaling of many life history traits, behaviors, physiological variables, and cellular/molecular properties, making determination of the causation of this pattern challenging. For across-species comparisons of resting and locomoting animals (but less so for across populations or during ontogeny), the mechanisms at the physiological and cellular level are becoming clear. Lower mass-specific metabolic rates of larger species at rest are due to a) lower contents of expensive tissues (brains, liver, kidneys), and b) slower ion leak across membranes at least partially due to membrane composition, with lower ion pump ATPase activities. Lower mass-specific costs of larger species during locomotion are due to lower costs for lower-frequency muscle activity, with slower myosin and Ca++ ATPase activities, and likely more elastic energy storage. The evolutionary explanation(s) for hypometric scaling remain(s) highly controversial. One subset of evolutionary hypotheses relies on constraints on larger animals due to changes in geometry with size; for example, lower surface-to-volume ratios of exchange surfaces may constrain nutrient or heat exchange, or lower cross-sectional areas of muscles and tendons relative to body mass ratios would make larger animals more fragile without compensation. Another subset of hypotheses suggests that hypometric scaling arises from biotic interactions and correlated selection, with larger animals experiencing less selection for mass-specific growth or neurolocomotor performance. A additional third type of explanation comes from population genetics. Larger animals with their lower effective population sizes and subsequent less effective selection relative to drift may have more deleterious mutations, reducing maximal performance and metabolic rates. Resolving the evolutionary explanation for the hypometric scaling of metabolism and associated variables is a major challenge for organismal and evolutionary biology. To aid progress, we identify some variation in terminology use that has impeded cross-field conversations on scaling. We also suggest that promising directions for the field to move forward include: 1) studies examining the linkages between ontogenetic, population-level, and cross-species allometries, 2) studies linking scaling to ecological or phylogenetic context, 3) studies that consider multiple, possibly interacting hypotheses, and 4) obtaining better field data for metabolic rates and the life history correlates of metabolic rate such as lifespan, growth rate and reproduction.

Ellagic Acid Alters Muscle Fiber-Type Composition and Promotes Mitochondrial Biogenesis through the AMPK Signaling Pathway in Healthy Pigs.

Ellagic acid (EA), because of its remarkable health-promoting ability, has aroused widespread interest in the fields of nutrition and medicine. However, no reports showed that EA regulates mitochondrial biogenesis as well as muscle fiber-type composition in pigs. Our study found that dietary 75 and 150 mg/kg EA obviously augmented the slow myosin heavy chain (MyHC) protein level, the number of slow-twitch muscle fibers, and the activity of malate dehydrogenase (MDH) in the longissimus thoracis (LT) muscle of growing-finishing pigs. In contrast, dietary 75 and 150 mg/kg EA decreased the fast MyHC level, the number of fast-twitch muscle fibers, and the activity of lactate dehydrogenase (LDH) in the LT muscle. In addition, our further study found that dietary 75 and 150 mg/kg EA promoted the mitochondrial DNA (mtDNA) content, the mRNA expressions of ATP synthase (ATP5G), mtDNA transcription factor A (TFAM), AMP-activated protein kinase α1 (AMPKα1), peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and sirtuin 1 (Sirt1), and the level of phospho-LKB1 (P-LKB1), phospho-AMPK (P-AMPK), Sirt1, and PGC-1α in the LT muscle. In vitro, 5, 10, and 20 μmol/L EA treatment upregulated the level of slow MyHC, but only 10 μmol/L EA treatment decreased fast MyHC protein expression in porcine skeletal muscle satellite cells (PSCs). In addition, our data again found that 10 μmol/L EA treatment promoted the mtDNA content, the mRNA levels of ATP5G, mitochondrial transcription factor b1 (TFB1M), citrate synthase (Cs), AMPKα1, PGC-1α, and Sirt1, and the protein expressions of P-AMPK, P-LKB1, PGC-1α, and Sirt1 in PSCs. What is more, inhibition of the AMPK signaling pathway by AMPKα1 siRNA significantly eliminated the improvement of EA on muscle fiber-type composition as well as the mtDNA content in PSCs. In conclusion, EA altered muscle fiber-type composition and promoted mitochondrial biogenesis through the AMPK signaling pathway.

Using the articularis genu to test peri-articular muscle health during knee osteoarthritis

Knee osteoarthritis (OA) involves peri-articular sarcopenia. The infrapatellar articularis genu (AG) links to the quadriceps femoris (QF) and can be sampled from discarded tissue during arthroplasty. We predict disuse-mediated changes in AG myofiber type ratio and atrophy similar to reports on the QF during OA. OA AGs (n = 40) were preserved and grouped by poor (≤ 85°; n = 11), fair (90°–110°; n = 19), and good (≥ 115°; n = 10) range of motion (ROM). Immunolabeling of slow and fast myosin heavy chains in AG sections allowed comparing distribution and cross-sectional area (CSA) of type-I (T1) and type-II (T2) myofibers between groups and associating to ROM. T1/T2 ratios in fair and poor ROM groups was consistent with those published in OA QF. Increasing mean ± SD T2 percentages from good (43.31 ± 11.76), to fair (50.96 ± 5.85), and poor (60.02 ± 8.29) ROM groups was significant between poor versus fair (p = 0.018) and good (p < 0.0001) in association with ROM deficits (r = − 0.729; p < 0.0001). T1 and T2 CSA decreased with worsening ROM, which associates with lower symptom scores (r = 0.3198; p = 0.0472). In-depth evaluation of the OA AG as a surrogate for the OA QF relative to serum and/or synovial fluid biomarkers of sarcopenia could refine diagnostics of peri-articular muscle health to guide individualized strength rehabilitation after surgery.

Endogenous slow and fast myosin dynamics in myofibers isolated from mice expressing GFP-Myh7 and Kusabira Orange-Myh1.

Skeletal muscle consists of slow and fast myofibers in which different myosin isoforms are expressed. Approximately 300 myosins form a single-thick filament in the myofibrils, where myosin is continuously exchanged. However, endogenous slow and fast myosin dynamics have not been fully understood. To elucidate those dynamics, here we generated mice expressing green fluorescence protein-tagged slow myosin heavy chain (GFP-Myh7) and Kusabira Orange fluorescence protein-tagged fast myosin heavy chain (KuO-Myh1). First, these mice enabled us to distinguish between GFP- and KuO-myofibers under fluorescence microscopy: GFP-Myh7 and KuO-Myh1 were exclusively expressed in slow myofibers and fast myofibers, respectively. Next, to monitor endogenous myosin dynamics, fluorescence recovery after photobleaching (FRAP) was conducted. The mobile fraction (Mf) of GFP-Myh7 and that of KuO-Myh1 were almost constant values independent of the regions of the myofibers and the muscle portions where the myofibers were isolated. Intriguingly, proteasome inhibitor treatment significantly decreased the Mf in GFP-Myh7 but not in KuO-Myh1 myofibers, indicating that the response to a disturbance in protein turnover depended on muscle fiber type. Taken together, the present results indicated that the mice we generated are promising tools not only for distinguishing between GFP- and KuO-myofibers but also for studying the dynamics of endogenous myosin isoforms by live-cell fluorescence imaging.

Cardiac ventricular myosin and slow skeletal myosin exhibit dissimilar chemomechanical properties despite bearing the same myosin heavy chain isoform

The myosin II motors are ATP-powered force-generating machines driving cardiac and muscle contraction. Myosin II heavy chain isoform-beta (β-MyHC) is primarily expressed in the ventricular myocardium and in slow-twitch muscle fibers, such as M. soleus. M. soleus–derived myosin II (SolM-II) is often used as an alternative to the ventricular β-cardiac myosin (βM-II); however, the direct assessment of biochemical and mechanical features of the native myosins is limited. By employing optical trapping, we examined the mechanochemical properties of native myosins isolated from the rabbit heart ventricle and soleus muscles at the single-molecule level. We found purified motors from the two tissue sources, despite expressing the same MyHC isoform, displayed distinct motile and ATPase kinetic properties. We demonstrate βM-II was approximately threefold faster in the actin filament–gliding assay than SolM-II. The maximum actomyosin (AM) detachment rate derived in single-molecule assays was also approximately threefold higher in βM-II, while the power stroke size and stiffness of the “AM rigor” crossbridge for both myosins were comparable. Our analysis revealed a higher AM detachment rate for βM-II, corresponding to the enhanced ADP release rates from the crossbridge, likely responsible for the observed differences in the motility driven by these myosins. Finally, we observed a distinct myosin light chain 1 isoform (MLC1sa) that associates with SolM-II, which might contribute to the observed kinetics differences between βM-II and SolM-II. These results have important implications for the choice of tissue sources and justify prerequisites for the correct myosin heavy and light chains to study cardiomyopathies.

Role of creatine supplementation on the myofiber characteristics and muscle protein synthesis of grass carp (Ctenopharyngodon idellus).

To assess the role of dietary creatine on myofiber characteristics and protein synthesis in muscle, we fed grass carp (Ctenopharyngodon idellus, initial body weight: 88.47 ± 1.44 g) creatine-supplemented diets (1.84, 5.91, 8.48, and 15.44 g/kg diet) for 8 weeks. Creatine supplementation did not affect growth performance, but significantly increased creatine contents in muscle and liver. At 8.48 g/kg, creatine decreased the activities of alanine transaminase and aspartate aminotransferase in serum, and improved hardness and chewiness of muscle due to shorter myofiber mean diameter, higher myofiber density and the frequencies of the diameters of class I and III and collagen content, longer sarcomere length, and upregulated mRNA levels of slow myosin heavy chains. Creatine supplementation upregulated the mRNA expressions of myogenic regulatory factors. The 8.48 g/kg creatine-supplemented diet significantly increased the contents of protein, total amino acids (AAs), essential AAs, and free flavor AAs in muscle, the protein levels of insulin-like growth factor I, myogenic differentiation antigen, and peroxisome proliferator-activated receptor-γ coactlvator-1α in muscle, and stimulated the phosphorylation of target of rapamycin (TOR) pathway in muscle. In summary, 8.48 mg/kg creatine improved fish health and skeletal muscle growth, and increased hardness and protein synthesis in muscle of grass carp by affecting myofiber characteristics and the TOR signaling pathway. A second-order regression model revealed that the optimal dietary creatine supplementation of grass carp ranges between 8.48 and 12.04 g/kg.

The Optimized Quantum Dots Mediated Thermometry Reveals the Efficiency of Myosin Extracted from Muscle Mini Bundles

The biophysical function of myosin in vitro has been extensively investigated in different motility assays. However, the study of myosin ATPase properties at the fiber level is still limited. In this study we aimed to optimize quantum dots (QD) mediated thermometry to measure the efficiency of myosin extracted from muscle mini bundles. A reduction in fluorescent intensity of QD reflects an increase in temperature caused by the heat release during ATP hydrolysis, denoting the efficiency of the motor protein myosin. The procedure for extracting myosin was modified from the single fiber in vitro motility assay, and the concentration of myosin was represented by the extracted total protein since the ratio of extracted myosin to total protein was constant. Moreover, the efficiency of myosin extracted from preparations containing different isoform compositions revealed that slow myosin has a lower efficiency than fast myosin, i.e., a higher amount of heat was released resulting in faster decay of QD fluorescence intensity. Thus, the optimized QD mediated thermometry provides a new sensitive approach to evaluate myosin function from a thermometrical perspective based on minimal muscle tissue.

The optimized quantum dot mediated thermometry reveals isoform specific differences in efficiency of myosin extracted from muscle mini bundles

The biophysical function of myosin in vitro has been extensively investigated in different motility assays, but the study of myosin ATPase properties at the fiber level is insufficiently investigated. In this study, quantum dot (QD) mediated thermometry measurements were optimized to measure the efficiency of myosin extracted from muscle mini bundles. A reduction in fluorescent intensity of QD reflects an increase in temperature caused by the heat released during ATP hydrolysis and denotes the efficiency of the motor protein myosin. The procedure for extracting myosin was similar to the single fiber in vitro motility assay with some small modifications, and the concentration of myosin was represented by the extracted total protein since the ratio of extracted myosin to total protein was constant. Moreover, the efficiencies of myosin extracted from preparations containing different myosin heavy chain isoforms reveal lower efficiency of slow compared to fast myosin isoforms. Specifically, more heat was released in slow myosin enzymatic reaction, resulting in faster decay of QD fluorescence intensity. Hence, the optimized QD mediated thermometry provides a novel and sensitive approach to evaluate efficiency of myosin ATPase obtained from small muscle samples, representing a significant advantage in the clinical evaluation of neuromuscular disorders.

Resveratrol regulates muscle fiber type gene expression through AMPK signaling pathway and miR-22-3p in porcine myotubes

This study aimed to investigate the effect and underlying mechanisms of resveratrol on porcine muscle fiber type gene expression in porcine myotubes. Here, results showed that resveratrol treatment significantly promoted slow myosin heavy chain (MyHC) and inhibited fast MyHC in porcine myotubes. The phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and the downstream factors of AMPK signaling, such as Sirtuin1 (Sirt1) and peroxlsome proliferator-activated receptor-γ coactlvator-1α (PGC-1α), were also increased by resveratrol, suggesting that resveratrol could activate the AMPK signaling pathway. Interestingly, resveratrol inhibited the expression of miR-22-3p in porcine myotubes. Furthermore, AMPK inhibitor compound C and miR-22-3p mimic effectively eliminated the effects of resveratrol on slow MyHC and fast MyHC expressions in porcine myotubes. Taken together, our findings indicate that resveratrol regulates muscle fiber type gene expression through the AMPK signaling pathway and miR-22-3p in porcine myotubes.

Reinnervation of Vastus lateralis is increased significantly in seniors (70-years old) with a lifelong history of high-level exercise (2013, revisited here in 2022).

In 2013 we presented results showing that at the histological level lifelong increased physical activity promotes reinnervation of muscle fibers in aging muscles. Indeed, in muscle biopsies from 70-year old men with a lifelong history of high-level physical activity, we observed a considerable increase in fiber-type groupings (F-TG), almost exclusively of the slow type. Slow-type transformation by denervation-reinnervation in senior sportsmen seems to fluctuate from those with scarce fiber-type transformation and groupings to almost fully transformed muscle, going through a process in which isolated fibers co-expressing fast and slow Myosin Heavy Chains (MHCs) seems to fill the gaps. Taken together, our results suggest that, beyond the direct effects of aging on the muscle fibers, changes occurring in skeletal muscle tissue appear to be largely, although not solely, a result of sparse denervation-reinnervation. The lifelong exercise allows the body to adapt to the consequences of the age-related denervation and to preserve muscle structure and function by saving otherwise lost muscle fibers through recruitment to different, mainly slow, motor units. These beneficial effects of high-level life-long exercise on motoneurons, specifically on the slow type motoneurones that are those with higher daily activity, and on muscle fibers, serve to maintain size, structure and function of muscles, delaying the functional decline and loss of independence that are commonly seen in late aging. Several studies of independent reserchers with independent analyses confirmed and cited our 2013 results. Thus, the results we presented in our paper in 2013 seem to have held up rather well. Trial Registration: ClinicalTrials.gov: NCT01679977

Resveratrol Blunts Mitochondrial Loss in Slow and Mixed Skeletal Muscle Phenotypes of Non-Human Primates following a Long-Term High Fat/Sugar Diet

Mitochondrial biogenesis and destruction in skeletal muscle are coordinated by distinct signaling pathways that are influenced by internal and exogenous variables including, but not limited to, muscle phenotype, physical activity, dietary composition, or drug administration. Previously we found that long-term resveratrol administration (up to 480 mg/day) ameliorates the slow-to-fast phenotypic shift in soleus muscles and promotes the expression in slow myosin heavy chain in the mixed plantaris muscle of non-human primates consuming a high fat/sugar (HFS) diet. Here, we expand on these earlier findings by examining whether mitochondrial content and the markers that dictate their biogenesis and mitophagy/autophagy are similarly affected by HFS and/or influenced by resveratrol while consuming this diet (HFSR). Compared to controls (n = 9), there was a ∼20–25% decrease in mitochondrial content in HFS (n = 8) muscles as reflected in the COX2- and CYTB-to-GAPDH ratios using PCR analysis, which was blunted by resveratrol in HFSR (n = 7) soleus and, to a lesser degree, in plantaris muscles. A ∼1.5 and 3-fold increase in Rev-erb-α protein was detected in HFSR soleus and plantaris muscles compared to controls, respectively. Unlike in HFSR animals, HFS soleus and plantaris muscles exhibited a ∼2-fold elevation in phosphor-AMPKα (Thr172). HFS soleus muscles had elevated phosphorylated-to-total TANK binding protein-1 (TBK1) ratio suggesting an enhancement in mito/autophagic events. Taken together, resveratrol appears to blunt mitochondrial losses with a high fat/sugar diet by tempering mito/autophagy rather than promoting mitochondrial biogenesis, suggesting that the quantity of daily resveratrol supplement ingested and/or its long-term consumption are important considerations. Supplemental data for this article is available online at http://dx.doi.org/ .

Plantar stimulation prevents the decrease in fatigue resistance in rat soleus muscle under one week of hindlimb suspension

Support afferentation in recent years was shown to be a key physiological stimulus controlling postural muscle function, structure and phenotype. Lack of support afferentation under various types of muscle disuse leads to a decline of size and percentage of slow-type fatigue-resistant muscle fibers, which can negatively affect muscle performance and life quality. In this study we simulated support afferentation during rat hindlimb unloading and investigated its effect on postural soleus muscle functional properties and signaling. Plantar mechanical stimulation prevented the unloading-induced muscle fatigue increase, maintained the level of mitochondrial DNA copy number and the percent of slow-type muscle fibers and partially prevented the increase of CpG methylation in pgc 1α promoter region and decline in myonuclear content of several transcriptional activators of slow myosin and PGC1 α expression. So, support afferentation under hindlimb suspension leads to maintaining of a slow-twitch oxidative and fatigue-resistant soleus muscle fibers phenotype.

In situ replacement of slow skeletal myosin binding protein-c

Myosin binding protein (MyBP-C) is a modular protein that interacts with both thin and thick filaments and regulates striated muscle contraction. The functional characteristics of MyBP-C have yet to be fully uncovered in all 3 isoforms (cardiac, fast skeletal, and slow skeletal). To manipulate cardiac (c) MyBP-C at its precise position in the sarcomere in situ, we created gene-edited ‘SpyC’ mice that allow us to use a novel ‘cut and paste’ method for cMyBP-C recombination in cardio-myocytes. This ‘cut and paste’ method allows for the in situ removal of endogenous N’-terminal domains from MyBP-C via TEV proteolysis, followed by its replacement with any desired recombinant N’-terminal MyBP-C.

Investigating the effects of mutations within the coiled-coil tail of cardiac and skeletal myosin

Myosin is an essential driver of cardiac and skeletal muscle function. Multiple mutations identified in β-cardiac/skeletal slow myosin heavy chain (MYH7) and skeletal fast myosin heavy chain 2A (MYH2), cause a group of human skeletal muscle diseases termed myosinopathies. Over 90% of these mutations are found in the filament-forming region of the coiled-coil tail, also known as light meromyosin (LMM). Mutation to a proline residue or deletion of a single residue are common. Both are predicted to strongly affect the secondary structure of the coiled coil, and by extension their incorporation into the thick filament.

Nampt activator P7C3 ameliorates diabetes and improves skeletal muscle function modulating cell metabolism and lipid mediators.

BackgroundNicotinamide phosphoribosyltransferase (Nampt), a key enzyme in NAD salvage pathway is decreased in metabolic diseases, and its precise role in skeletal muscle function is not known. We tested the hypothesis, Nampt activation by P7C3 (3,6‐dibromo‐α‐[(phenylamino)methyl]‐9H‐carbazol‐9‐ethanol) ameliorates diabetes and muscle function.MethodsWe assessed the functional, morphometric, biochemical, and molecular effects of P7C3 treatment in skeletal muscle of type 2 diabetic (db/db) mice. Nampt+/− mice were utilized to test the specificity of P7C3.ResultsInsulin resistance increased 1.6‐fold in diabetic mice compared with wild‐type mice and after 4 weeks treatment with P7C3 rescued diabetes (P < 0.05). In the db‐P7C3 mice fasting blood glucose levels decreased to 0.96‐fold compared with C57Bl/6J wild‐type naïve control mice. The insulin and glucose tolerance tests blood glucose levels were decreased to 0.6‐fold and 0.54‐folds, respectively, at 120 min along with an increase in insulin secretion (1.76‐fold) and pancreatic β‐cells (3.92‐fold) in db‐P7C3 mice. The fore‐limb and hind‐limb grip strengths were increased to 1.13‐fold and 1.17‐fold, respectively, together with a 14.2‐fold increase in voluntary running wheel distance in db‐P7C3 mice. P7C3 treatment resulted in a 1.4‐fold and 7.1‐fold increase in medium‐sized and larger‐sized myofibres cross‐sectional area, with a concomitant 0.5‐fold decrease in smaller‐sized myofibres of tibialis anterior (TA) muscle. The transmission electron microscopy images also displayed a 1.67‐fold increase in myofibre diameter of extensor digitorum longus muscle along with 2.9‐fold decrease in mitochondrial area in db‐P7C3 mice compared with db‐Veh mice. The number of SDH positive myofibres were increased to 1.74‐fold in db‐P7C3 TA muscles. The gastrocnemius and TA muscles displayed a decrease in slow oxidative myosin heavy chain type1 (MyHC1) myofibres expression (0.46‐fold) and immunostaining (6.4‐fold), respectively. qPCR analysis displayed a 2.9‐fold and 1.3‐fold increase in Pdk4 and Cpt1, and 0.55‐fold and 0.59‐fold decrease in Fgf21 and 16S in db‐P7C3 mice. There was also a 3.3‐fold and 1.9‐fold increase in Fabp1 and CD36 in db‐Veh mice. RNA‐seq differential gene expression volcano plot displayed 1415 genes to be up‐regulated and 1726 genes down‐regulated (P < 0.05) in db‐P7C3 mice. There was 1.02‐fold increase in serum HDL, and 0.9‐fold decrease in low‐density lipoprotein/very low‐density lipoprotein ratio in db‐P7C3 mice. Lipid profiling of gastrocnemius muscle displayed a decrease in inflammatory lipid mediators n‐6; AA (0.83‐fold), and n‐3; DHA (0.69‐fold) and EPA (0.81‐fold), and a 0.66‐fold decrease in endocannabinoid 2‐AG and 2.0‐fold increase in AEA in db‐P7C3 mice.ConclusionsOverall, we demonstrate that P7C3 activates Nampt, improves type 2 diabetes and skeletal muscle function in db/db mice.

HDAC4 Is Indispensable for Reduced Slow Myosin Expression at the Early Stage of Hindlimb Unloading in Rat Soleus Muscle.

It is well known that reduced contractile activity of the main postural soleus muscle during long-term bedrest, immobilization, hindlimb unloading, and space flight leads to increased expression of fast isoforms and decreased expression of the slow isoform of myosin heavy chain (MyHC). The signaling cascade such as HDAC4/MEF2-D pathway is well-known to take part in regulating MyHC I gene expression. Earlier, we found a significant increase of HDAC4 in myonuclei due to AMPK dephosphorylation during 24 h of hindlimb unloading via hindlimb suspension (HU) and it had a significant impact on the expression of MyHC isoforms in rat soleus causing a decrease in MyHC I(β) pre-mRNA and mRNA expression as well as MyHC IIa mRNA expression. We hypothesized that dephosphorylated HDAC4 translocates into the nuclei and can lead to a reduced expression of slow MyHC. To test this hypothesis, Wistar rats were treated with HDAC4 inhibitor (Tasquinimod) for 7 days before HU as well as during 24 h of HU. We discovered that Tasquinimod treatment prevented a decrease in pre-mRNA expression of MyHC I. Furthermore, 24 h of hindlimb suspension resulted in HDAC4 nuclear accumulation of rat soleus but Tasquinimod pretreatment prevented this accumulation. The results of the study indicate that HDAC4 after 24 h of HU had a significant impact on the precursor MyHC I mRNA expression in rat soleus.

A case report of deglutition triggered atrial fibrillation in a patient with Laing distal myopathy

BackgroundDeglutition-induced atrial fibrillation is a rare clinical entity with a reported prevalence of 0.6%. Laing distal myopathy is a rare autosomal dominant muscular dystrophy that is the result of mutations within the slow skeletal muscle fibre myosin heavy chain gene (MYH7). Atrial fibrillation has not been previously reported in patients with Laing distal myopathy. We describe the first reported case of deglutition triggered atrial fibrillation in a female with a history of Laing distal myopathy.Case summaryA 44-year-old female with a history of Laing distal myopathy diagnosed at age 32, began experiencing intermittent episodes of pre-syncope and palpitations which occurred after deglutition with food. An ambulatory 30-day patient triggered event monitor recorded episodes of atrial fibrillation with rapid ventricular response. Family history was significant for Laing distal myopathy, atrial fibrillation, as well as sudden cardiac death. Laboratory data, transthoracic echocardiogram, cardiac magnetic resonance imaging, and an exercise treadmill SPECT Imaging stress test were normal. An oesophagram revealed a mild oesophageal dysmotility with no other abnormalities. She was started on flecainide 50 mg p.o. every 8 h and verapamil 40 mg p.o. every 8 h with no further episodes of atrial fibrillation.DiscussionGiven the strong genetic component of this myopathy, one could postulate as to a possible genetic component in the development of atrial fibrillation in our patient. Although we cannot make definite correlation between deglutition-induced atrial fibrillation and Laing myopathy, it is important to report this unusual association which has not been described before.

Dietary lycopene supplementation improves meat quality, antioxidant capacity and skeletal muscle fiber type transformation in finishing pigs.

This study aimed to investigate effects of dietary lycopene supplementation on meat quality, antioxidant ability and muscle fiber type transformation in finishing pigs. In a 70-day experiment, 18 Duroc × Landrace × Yorkshire barrows were randomly allocated to 3 dietary treatments including a basal diet supplemented with 0, 100 and 200 mg/kg lycopene, respectively. Each dietary treatment had 6 replicates with one pig each. Results showed that dietary 200 mg/kg lycopene supplementation increased muscle redness a∗ value, intramuscular fat and crude protein contents, and decreased muscle lightness L∗ and yellowness b∗ values (P < 0.05), suggesting that addition of 200 mg/kg lycopene to the diet of finishing pigs improved color, nutritional value and juiciness of pork after slaughter. Results also showed that dietary lycopene supplementation enhanced antioxidant capacity of finishing pigs (P < 0.05). Moreover, dietary supplementation of 200 mg/kg lycopene significantly increased slow myosin heavy chain (MyHC) protein level and slow-twitch fiber percentage, and decreased fast MyHC protein level and fast-twitch fiber percentage (P < 0.05), suggesting that the addition of 200 mg/kg lycopene to the diet of finishing pigs promoted muscle fiber type conversion from fast-twitch to slow-twitch. Together, we provide the first evidence that dietary 200 mg/kg lycopene supplementation improves meat quality, enhances antioxidant capacity and promotes muscle fiber type transformation from fast-twitch to slow-twitch in finishing pigs.