Muscle Fiber Type Research Articles

Sex differences in skeletal muscle fiber types: A meta-analysis.

Biopsies have been acquired from living men and women to determine proportions of Type I (slow-twitch) and II (fast-twitch) skeletal muscle fibers since the 1970s. Sex differences have been assumed but the literature has not been submitted to meta-analysis. Here, the aim was to generate effect sizes of sex differences in muscle fiber cross-sectional areas, distribution percentages, and area percentages. Data from 2875 men and 2452 women, who participated in 110 studies, were analyzed. Myofibrillar adenosine triphosphatase histochemistry was used in 71.8% of studies to classify fibers as Type I, II, IIA, and/or IIX; immunohistochemistry, immunofluorescence, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used in 35.4% of studies to similarly classify myosin heavy chain (MHC) isoform content. Most studies involved biopsies from vastus lateralis (79.1%) in healthy individuals (92.7%) between 18 and 59 years old (80.9%). Men exhibited greater cross-sectional areas for all fiber types (g = 0.40-1.68); greater distribution percentages for Type II, MHC II, IIA, IIX fibers (g = 0.26-0.34); greater area percentages for Type II, IIA, MHC IIA, IIX fibers (g = 0.39-0.93); greater Type II/I and Type IIA/I fiber area ratios (g = 0.63, 0.94). Women exhibited greater Type I and MHC I distribution percentages (g = -0.13, -0.44); greater Type I and MHC I area percentages (g = -0.53, -0.69); greater Type I/II fiber area ratios (g = -1.24). These data, which represent the largest repository of comparative muscle fiber type data from living men and women, can inform discussions about biological sex and its impact on pathologies and sports performance (e.g., explaining sex differences in muscle strength and muscle endurance).

Integrated analysis of circRNA, lncRNA, miRNA and mRNA to reveal the ceRNA regulatory network of postnatal skeletal muscle development in Ningxiang pig.

Introduction: The development of skeletal muscle is regulated by regulatory factors of genes and non-coding RNAs (ncRNAs). Methods: The objective of this study was to understand the transformation of muscle fiber type in the longissimus dorsi muscle of male Ningxiang pigs at four different growth stages (30, 90, 150, and 210 days after birth, n = 3) by histological analysis and whole transcriptome sequencing. Additionally, the study investigated the expression patterns of various RNAs involved in muscle fiber transformation and constructed a regulatory network for competing endogenous RNA (ceRNA) that includes circular RNA (circRNA)/long non-coding RNA (lncRNA)-microRNA (miRNA)-messenger RNA (mRNA). Results: Histomorphology analysis showed that the diameter of muscle fiber reached its maximum at 150 days after birth. The slow muscle fiber transformation showed a pattern of initial decrease followed by an increase. 29,963 circRNAs, 2,683 lncRNAs, 986 miRNAs and 22,411 mRNAs with expression level ≥0 were identified by whole transcriptome sequencing. Furthermore, 642 differentially expressed circRNAs (DEc), 505 differentially expressed lncRNAs (DEl), 316 differentially expressed miRNAs (DEmi) and 6,090 differentially expressed mRNAs (DEm) were identified by differential expression analysis. Functions of differentially expressed mRNA were identified by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). GO enrichment analysis indicates that 40 known genes and 6 new genes are associated with skeletal muscle development. Additionally, KEGG analysis shows that these genes regulate skeletal muscle development via MAPK, FoxO, Hedgehog, PI3K-Akt, Notch, VEGF and other signaling pathways. Through protein-protein interaction (PPI) and transcription factor prediction (TFP), the action mode of skeletal muscle-related genes was explored. PPI analysis showed that there were stable interactions among 19 proteins, meanwhile, TFP analysis predicted 22 transcription factors such as HMG20B, MYF6, MYOD1 and MYOG, and 12 of the 19 interacting proteins were transcription factors. The regulatory network of ceRNA related to skeletal muscle development was constructed based on the correlation of various RNA expression levels and the targeted binding characteristics with miRNA. The regulatory network included 31 DEms, 59 miRNAs, 667 circRNAs and 224 lncRNAs. conclusion: Overall, the study revealed the role of ceRNA regulatory network in the transformation of skeletal muscle fiber types in Ningxiang pigs, which contributes to the understanding of ceRNA regulatory network in Ningxiang pigs during the skeletal muscle development period.

Deletion of Nmnat1 in Skeletal Muscle Leads to the Reduction of NAD+ Levels but Has No Impact on Skeletal Muscle Morphology and Fiber Types.

Nicotinamide adenine dinucleotide (NAD+) is a coenzyme that mediates many redox reactions in energy metabolism. NAD+ is also a substrate for ADP-ribosylation and deacetylation by poly (ADP-ribose) polymerase and sirtuin, respectively. Nicotinamide mononucleotide adenylyltransferase 1 (Nmnat1) is a NAD+ biosynthesizing enzyme found in the nucleus. Recent research has shown that the maintaining NAD+ levels is critical for sustaining muscle functions both in physiological and pathological conditions. However, the role of Nmnat1 in skeletal muscle remains unexplored. In this study, we generated skeletal muscle-specific Nmnat1 knockout (M-Nmnat1 KO) mice and investigated its role in skeletal muscle. We found that NAD+ levels were significantly lower in the skeletal muscle of M-Nmnat1 KO mice than in control mice. M-Nmnat1 KO mice, in contrast, had similar body weight and normal muscle histology. Furthermore, the distribution of muscle fiber size and gene expressions of muscle fiber type gene expression were comparable in M-Nmnat1 KO and control mice. Finally, we investigated the role of Nmnat1 in muscle regeneration using cardiotoxin-induced muscle injury model, but muscle regeneration appeared almost normal in M-Nmnat1 KO mice. These findings imply that Nmnat1 has a redundancy in the pathophysiology of skeletal muscle.

(008) Chronic High Fat Diet Decreases Vaginal Smooth Muscle Tone but does not Affect Pelvic Floor Skeletal Muscle in Mice

Abstract Introduction Pelvic organ prolapse (POP) is a disease that affects the physical and mental health of women, as well as their quality of life. POP, regardless of severity, can be a direct cause of female sexual dysfunction (FSD) by producing pain during intercourse or a general reluctance to engage in sexual activity. The largest risk factors for POP include parity, obesity, and advanced age. Obesity, a modifiable risk factor, is believed to increase intra-abdominal pressure and weaken the pelvic floor muscles and fascia. Studies have shown that obesity and a high fat diet (HFD) can weaken skeletal muscle by increasing collagen deposition and inducing muscle apoptosis. Objectives There is paucity in the literature of animal studies that have specifically investigated the effect of obesity on the support structures of the pelvic floor and how it contributes to POP. The objective of this study is to examine the structure and function of the vagina and pelvic floor in female mice fed a chronic HFD. Methods Adult female C57/Blk6N mice (10 weeks, n=32) were fed a control (10% kcal fat) or HFD (45% kcal fat) for 24 weeks. Ex vivo external vaginal sphincter contraction to increasing concentrations of adrenergic agonist norepinephrine and relaxation to nitric oxide donor DEA NONOate and electric field stimulation (EFS) was measured. Iliococcygeus (IC) muscles of the pelvic floor were isolated and set to optimal length and tetanic contractions were performed at increasing frequencies to asses absolute and specific force. Fatigue was measured following repetitive stimulations over 5 minutes. IC muscle fiber types were characterized with anti-myosin antibodies and cross-sectional area (CSA) of each fiber type was measured. Results Vaginal sphincter adrenergic-mediated contraction was a significantly decreased in HFD-fed mice (Fig 1A; p<0.05). The vaginal sphincter smooth muscle relaxation in response to a nitric oxide donor was greater in the HFD mice (Fig 1B; p<0.05). Neurogenic-mediated EFS vaginal relaxations were also enhanced in the HFD mice (p<0.05). Surprisingly, chronic HFD did not impact iliococcygeus muscle specific force, absolute force, or muscle fatigue (Fig 1C). Furthermore, HFD did not affect the CSA or population of type I, IIa, IIX, or IIb iliococcygeus muscle fibers. Conclusions HFD-induced obesity in mice leads to pelvic floor weakness by enhancing relaxation and decreasing tone of the vaginal smooth muscle. Interestingly, the function and composition of pelvic skeletal muscle was unaffected by HFD. As the vagina serves as a primary support structure to the pelvic organs, lack in muscle contractility and increase in relaxation following HFD suggests that obesity-induced POP may play a direct role in FSD. Disclosure

Early stages of the formation of axial musculature of the juvenile Russian sturgeon (Acipenser gueldenstaedtii Brandt, 1833)

The purpose of the research was to study the peculiarities of the development of the Russian sturgeon in a specialized fish farm to assess the compliance of the technological conditions of cultivation with the biological needs and physiological characteristics of this type of sturgeon, as well as to ensure the further receipt of highquality fish products. The article considers histogenesis and morphological features of axial musculature of juvenile Russian sturgeon (Acipenser gueldenstaedtii) at the early stages of its formation, aspects of histological structure of musculature in the process of its differentiation into deep (musculus lateralis profundus) and superficial (musculus lateralis superficialis) lateral muscles. The formation and variability in diameter of muscle fibers of various types (oxidative and glycolytic) are discussed. It was found that the main part of the axial musculature is represented by a deep lateral muscle (musculus lateralis profundus). This muscle is formed by typical white (glycolytic) fibers. A smaller part of the axial musculature is represented by red (oxidative) type fibers. The results of the studies indicate the heterogeneity of the studied structures and the uneven period of fiber growth in different parts of the body, a large variability in the diameter of glycolytic fibers in the fingerlings of the Russian sturgeon. Together with the data on the beginning of differentiation of deep and lateral fibers at the age of one month, this allows us to estimate the approximate time of laying the main muscles and pay special attention to nutrition and conditions of fish keeping. The absence of pathologies in the structure and development of muscle fibers suggests that the cultivation of sturgeon fish in a cooling pond on running water is more favorable for the health of fish, unlike farms with closed water supply.

Effects of pregnancy and lactation on muscle-tendon morphology.

Pregnancy and lactation hormones have been shown to mediate anatomical changes to the musculoskeletal system that generates animal movement. In this study, we characterize changes in the medial gastrocnemius muscle, its tendon and aponeuroses that are likely to have an effect on whole animal movement and energy expenditure, using the rat model system, Rattus norvegicus. We quantified muscle architecture (mass, cross-sectional area, and pennation angle), muscle fiber type and diameter, and Young's modulus of stiffness for the medial gastrocnemius aponeuroses as well as its contribution to Achilles tendon in three groups of three-month-old female rats: virgin, primiparous pregnant, and primiparous lactating animals. We found that muscle mass drops by 23% during lactation but does not change during pregnancy. We also found that during pregnancy muscle fibers switch from Type I to IIa and during lactation from Type IIb to Type I. The stiffness of connective tissues that has a demonstrated role in locomotion, the aponeurosis and tendon, also changed. Pregnant animals had a significantly less stiff aponeurosis. However, tendon stiffness was most affected during lactation, with a significant drop in stiffness and interindividual variation. We propose that the energetic demands of locomotion may have driven the evolution of these anatomical changes in muscle-tendon units during pregnancy and lactation to ensure more energy can be allocated to fetal development and lactation.

"Biqi" Bayberry Extract Promotes Skeletal Muscle Fiber Type Remodeling by Increasing Fast Myofiber Formation via the Akt/FoxO1 Pathway in Mice.

Bayberry is known to be a rich source of natural flavonoids and has been reported to have various health-promoting abilities. However, its function on regulating skeletal muscle fiber type remains unclear. This study examined whether bayberry extract affects skeletal muscle fiber type by promoting fast myofiber formation, as well as the potential molecular mechanism. After eight weeks, the "Biqi" bayberry extract (BBE) groups mice displayed markedly enhanced grip strength and improved metabolic rate compared to the control group mice. BBE also significantly increased myofibers size, LDH activity, MyHC-IIb (fast-twitch mRNA) expression, and the percentage of fast-twitch myofibers, while decreasing SDH activity, MyHC-I (slow-twitch mRNA) expression, and slow-twitch myofibers percentage in the skeletal muscle of the mice. The effect of BBE on regulating skeletal muscle fiber type remodeling is likely attributed to its activation of the Akt-FoxO1 pathway. Our findings indicated that BBE can effectively regulate the expression and proportion of fast-twitch fibers, making it a potential therapy for improving glucose homeostasis of skeletal muscle.

Muscle fibre transition and transcriptional changes of horse skeletal muscles during traditional Mongolian endurance training.

Traditional Mongolian endurance training is an effective way to improve the athletic ability of the horse for endurance events and is widely used. This incorporates aerobic exercise and intermittent fasting and these altered physiologic conditions are associated with switches between muscle fibre types. To better understand the adaption of horse skeletal muscle to traditional Mongolian endurance training from muscle fibre characteristics and transcriptional levels and to explore possible molecular mechanisms associated with the endurance performance of horses. Before-after study. Muscle fibre type switches and muscle transcriptome changes in six Mongolian horses were assessed during 4 weeks of training. Transcriptomic and histochemical analyses were performed. The activities of oxidative and glycolytic metabolic enzymes were analysed and we generated deep RNA-sequencing data relating to skeletal muscles. A fast-to-slow muscle fibre transition occurred in horse skeletal muscles, with a concomitant increase of oxidative enzyme activity and decreased glycolytic enzyme activity. Numerous differentially expressed genes were involved in the control of muscle protein balance and degradation. Differential alternative splicing events were also found during training which included exon-skipping events in Ttn that were associated with muscle atrophy. Differentially expressed noncoding RNAs showed connections with muscle protein balance-related pathways and fibre type specification via the post-transcriptional regulation of miRNA. The study focuses on horse athletic ability only from the aspect of muscular adaptation. Traditional Mongolian endurance training-induced muscle fibre transition and metabolic and transcriptional changes. Muscle-specific non-coding RNAs could contribute to these transcriptomic changes during training.

Can lizards become alligators? Muscle fibre type and other factors that may influence (or not) hypertrophy responsiveness after resistance training.

Can lizards become alligators? Muscle fibre type and other factors that may influence (or not) hypertrophy responsiveness after resistance training.

1630-P: Reduced Fatty Acid Oxidation Does Not Prevent Intralipid-Induced Peripheral Insulin Resistance in Humans

Mitochondrial handling of excess lipid substrate is thought to be an important determinant of insulin resistance. Evidence from animal models support insulin signaling defects resulting from either intra-cellular lipid accumulation or by mitochondrial dysfunction and altered fatty acid oxidation (FAO) flux. To explore the relationship between FAO and insulin sensitivity, we measured the change in peripheral glucose disposal (Rd) during a 5-hour hyperinsulinemic euglycemic clamp with co-infusion of a control glycerol solution versus a 20% intralipid solution in 18 subjects with an inherited defect in FAO (FAOD; including Carnitine Palmitoyltransferase 2, Very long-chain, medium-chain or long-chain 3-hydroxy AcylcoA Dehydrogenase Deficiencies) and 18 age, sex, and weight-matched normal healthy controls. Rd was similar between groups during the glycerol control clamp. Intramyocellular lipid (IMCL) content as measured by MRS increased after the 5 hour intralipid infusion in controls but not in participants with FAOD. Plasma free fatty acids during intralipid infusion were higher in FAOD compared to controls suggesting infused lipid remained in circulation. Muscle fiber type and expression of lipid transporters CD36 and FATP1 were similar in biopsy samples between groups and cannot explain decreased lipid uptake into muscle among FAOD subjects. However, intralipid suppressed Rd equally in subjects with FAOD and controls inducing peripheral insulin resistance in both groups. Impaired FAO decreased lipid accumulation in the muscle during intralipid infusion, but despite lower IMCL, subjects with FAOD developed peripheral insulin resistance similar to controls. Increased IMCL is not essential for, nor is reduced FAO flux protective against, the development of peripheral insulin resistance during intralipid infusion. Disclosure M.B.Gillingham: None. J.Q.Purnell: Advisory Panel; Boehringer Ingelheim International GmbH, Novo Nordisk. A.N.Gregor: None. O.Varlamov: None. J.J.Robino: None. C.E.Mccurdy: None. K.T.Greyslak: None. D.Choi: None. E.Baetscher: Consultant; Biogen. W.Rooney: Consultant; Ultragenix, Research Support; Revalesio. Funding National Institutes of Health (DK102813)

1494-P: ILV-001, a Highly Promising Therapeutic Agent for Islet Transplantation

Introduction: Our team has shown a bimodal effect on β-cells of muscle-secreted myokines from normal or insulin-resistant human skeletal muscle. We identified ILV-001, a component of the muscle secretome regulated by muscle fiber type and physical exercise, moreover naturally present in the extracellular matrix of the islet niche. Thus, we aimed at investigating the therapeutic potential of ILV-001 in protecting β-cell function and survival during islet transplantation. Methods: In vitro: Rat islets were incubated 24h ± ILV-001 (1µg/mL). Islet survival was assessed by TUNEL assay ± cytomix. Islet function was evaluated using GSIS test. In vivo: 10000 IEQ/kg ± ILV-001 were injected intraportaly in diabetic syngeneic rats. For 3 months body weight gain, glycaemia, c-peptidemia and graft function (IPGTT) were followed. Inflammation was evaluated titrating plasmatic α2-macroglobulin. Histology was performed on grafted islets. Results: In vitro: ILV-001 improves islet function and survival and potentiates insulin secretion after GSIS test. In vivo: ILV-001 improves graft function in terms of glycaemia (p<0.001) and c-peptidaemia (p<0.01) and decreases exogenous insulin intake requirements. ILV-001 reduced inflammation 24h post graft with a lower plasmatic α2-macroglobulin versus control with respectively 459±70 versus 903±191 µg/mL (p<0.05). Finally, histology showed a preservation of insulin positive cells with ILV-001 versus control at the end of study (69±3% versus 39±3% of β-cells/islet, p< 0.001). Conclusion: ILV-001 is a highly promising candidate for the achievement of a functional cure in T1D thanks to potent β-cell preservation and obtaining long term graft maintenance following islet transplant. Disclosure A.Langlois: None. A.Grabarz: Stock/Shareholder; Ilonov. M.Pinget: Consultant; Novo Nordisk, Stock/Shareholder; ILONOV. K.Bouzakri: Consultant; Adocia, Stock/Shareholder; ILONOV.

1640-P: Meroterpenoid-Rich Ethanolic Extract of Sargassum serratifolium (MES) Alters Macrophage Transcriptome and Secretion Profile toward Improving Muscle Atrophy and Glucose Intolerance

Skeletal muscle plays an essential role in glucose homeostasis. Of many cell types in the skeletal muscle, recent studies indicate that secretion factors derived from macrophages are important for glucose metabolism in the skeletal muscle. Here, RNA Sequencing analysis showed that Lipopolysaccharide (LPS) treatment broadly altered the transcriptome of macrophages, of which signaling related to secretion factors was markedly altered toward elevating unfavorable cytokines to maintain skeletal muscle metabolism. On the other hand, the treatment of the Meroterpenoid-Rich Extract of Sargassum Serratifolium (MES), a strong anti-inflammatory and antioxidant extract found in our previous studies, reversed the LPS-induced signaling pathways. We further tested whether the treatment of conditioned media (CM) derived from LPS-macrophage (LPS-CM) or CM derived from LPS-macrophage treated with MES (MES-CM) affects glucose homeostasis in differentiated C2C12 myotube cells. LPS-CM treatment notably increased mRNA levels of muscle atrophy-associated genes including MuRF1, MAFbx, and Myostatin, and decreased glucose uptake, and MES-CM treatment reversed these characteristics, indicating that secretion factors induced by LPS or MES either impair or improve muscle glucose homeostasis, respectively. We further analyzed secretion factors inside by proteome array and data showed that LPS-CM includes GDF-15, IL-1 α/β, RAGE, etc related to muscle atrophy and glucose intolerance, which were significantly reduced in MES-CM. These data indicate that LPS- or MES-induced changes in the transcriptome in macrophages are closely related to the alteration in secretion factors toward either impairing or improving glucose metabolism in the skeletal muscle respectively. Of many, the decrease in macrophage-derived cytokine mentioned above may be important for glucose homeostasis in the skeletal muscle. Disclosure H.Ryu: None. B.Lee: None.

Neuromuscular defects after infection with a beta coronavirus in mice

COVID-19 affects primarily the lung. However, several other systemic alterations, including muscle weakness, fatigue and myalgia have been reported and may contribute to the disease outcome. We hypothesize that changes in the neuromuscular system may contribute to the latter symptoms observed in COVID-19 patients. Here, we showed that C57BL/6J mice inoculated intranasally with the murine betacoronavirus hepatitis coronavirus 3 (MHV-3), a model for studying COVID-19 in BSL-2 conditions that emulates severe COVID-19, developed robust motor alterations in muscle strength and locomotor activity. The latter changes were accompanied by degeneration and loss of motoneurons that were associated with the presence of virus-like particles inside the motoneuron. At the neuromuscular junction level, there were signs of atrophy and fragmentation in synaptic elements of MHV-3-infected mice. Furthermore, there was muscle atrophy and fiber type switch with alteration in myokines levels in muscles of MHV-3-infected mice. Collectively, our results show that acute infection with a betacoronavirus leads to robust motor impairment accompanied by neuromuscular system alteration.

1643-P: Unique Signature of Circular RNA in Skeletal Muscle of Different Insulin Sensitivity

Diabetes pathologies are complex, affecting numerous organs such as liver, pancreas, and skeletal muscle. Circular RNAs (circRNA) are a class of non-coding RNAs that are characterized by a covalently closed loop structure. Functionally, they can act on cell physiology by sponging microRNAs and thus regulating gene and protein expression. The emerging function of these circRNA is not fully understood, but initial studies have recently shown that circRNA are involved in insulin secretion regulation. Therefore, deregulation of this class of RNAs may lead to metabolic disorders in pancreatic β-cells and thus be involved in the pathogenesis of type 1 (T1DM) and type 2 diabetes (T2DM). Our research is focused on the unique signature by circular RNA and the impact on skeletal muscle metabolism. We demonstrated that human skeletal muscle cells in culture maintain their gene expression phenotype. A different gene signature of the cells according to their different muscular fiber type sources (oxidative versus glycolytic versus mixt) was confirmed. Moreover, an independent microRNA composition has also been highlighted. As CircRNA can regulate microRNAs and then gene expression and proteins, we wondered whether these observed signatures could be explained by circRNA. We therefore focused on key circRNAs involved in myogenesis (such as circZNF609, circHIPK3) and we were able to see that there is a difference in expression of circRNA according to the muscle type. Moreover, we analyzed correlations between circRNA levels and insulin sensitivity (measured by PKB phosphorylation). Finally, we are currently completing our analysis with in-depth sequencing techniques to identify all expressed circRNA in muscle fiber types to potentially identify new targets in insulin metabolic pathways. Disclosure M.Yepmo: None. E.Meugnier: None. M.Pinget: Consultant; Novo Nordisk, Stock/Shareholder; ILONOV. K.Bouzakri: Consultant; Adocia, Stock/Shareholder; ILONOV.

1625-P: Osteoprotection by FNIP1 Signaling in Skeletal Muscle

Obesity is increasingly recognized to exert negative impact on bone mass. Skeletal muscle and bone are closely related throughout life, and muscle dysfunction can cause osteoporosis. Understanding of the crosstalk between muscle and bone could have implications for maintaining bone fitness in various disease states such as obesity. FNIP1 is emerging as key regulator of muscle metabolism acting via AMPK. However, the role of muscle FNIP1 in bone mass control is unknown. Using both gain- and loss-of function muscle-specific genetic models, we show that in addition to the known role in the regulation of mitochondrial function muscle fiber type, FNIP1 participates in muscle programs that govern bone homeostasis. FNIP1 KO mice showed a decrease in trabecular bone volume and bone mineral density, whereas muscle specific restoration of FNIP1 expression in KO mice (FNIP1Tg/KO) reversed the bone loss phenotypes. Femoral bending tests revealed a marked decrease in elastic modulus and maximum force in FNIP1 KO mice but increase in FNIP1 TgKO mice. Consistent with these findings, muscle cell-specific deletion of FNIP1 resulted in a pronounced bone structural and mechanical dysfunction. Using AMPKα1/α2 KO lines, we show that muscle FNIP1 exerts control actions upon bone homeostasis independently of AMPK. Through comprehensive RNA-seq and genomic analyses, we reveal that muscle FNIP1 deficiency induces IGF2 secretion, thereby driving an IGF2-depenent osteoclast program. Importantly, we also found that the muscle FNIP1-IGF2 regulatory circuit is associated with osteoporosis in humans. Thus, muscle FNIP1 is a critical safeguard of bone mass. These findings provide new therapeutic opportunities for enhancing muscle fitness to combat a variety of metabolic and musculoskeletal diseases. Disclosure M.Yan: None. Z.Xu: None. Y.Yin: None. T.Fu: None. Z.Zhou: None. L.Yang: None. Z.Gan: None.

Evaluation of recurrent laryngeal neuropathy in domestic and feral horse populations in Australia using histologic and immunohistochemical analysis: A pilot study.

Little is known about potential differences in the left recurrent laryngeal nerve (Lrln) and left cricoarytenoideus dorsalis (LCAD) muscle between domestic and feral horse populations. If a difference exists, feral horses may provide a useful control population for research related to recurrent laryngeal neuropathy (RLN) and increase our understanding of potential population pressures influencing the incidence RLN. The objective of this study was to compare the Lrln and LCAD of domestic and feral horses using histological and immunohistochemical techniques (IHC). Sixteen horses, domestic (n = 8) and feral (n = 8), without clinical or ancillary examinations that were processed at an abattoir had the Lrln and LCAD muscle harvested immediately following death. Carcass weights were recorded. Subjective and morphometric histologic assessment were performed on Lrln sections. The LCAD was assessed for myosin heavy chain (fibre type proportion, diameter and grouping using IHC. Fibre-type grouping consistent with RLN was seen in both groups. Regenerating fibre clusters were more common in domestic compared to feral horses (p = 0.04). No other histologic differences occurred between groups. Muscle fibre typing demonstrated a lower mean percentage of type IIX fibres in the feral group compared to the domestic group (p = 0.03). There was no difference in type I or IIA proportions or mean diameter of any fibre type between the groups. The domestic population showed evidence of nerve regeneration suggesting RLN in this group, yet this was not supported by the higher proportion of type IIX muscle fibres compared to the feral population. Further evaluation to clarify the significance and wider occurrence of the differences is indicated.

Cyclin D3 deficiency promotes a slower, more oxidative skeletal muscle phenotype and ameliorates pathophysiology in the mdx mouse model of Duchenne muscular dystrophy.

We previously reported that cyclin D3-null mice display a shift toward the slow, oxidative phenotype in skeletal muscle, improved exercise endurance, and increased energy expenditure. Here, we explored the role of cyclin D3 in the physiologic response of skeletal muscle to external stimuli and in a model of muscle degenerative disease. We show that cyclin D3-null mice exhibit a further transition from glycolytic to oxidative muscle fiber type in response to voluntary exercise and an improved response to fasting. Since fast glycolytic fibers are known to be more susceptible to degeneration in Duchenne muscular dystrophy (DMD), we examined the effects of cyclin D3 inactivation on skeletal muscle phenotype in the mdx mouse model of DMD. Compared with control mdx mice, cyclin D3-deficient mdx mice display a higher proportion of slower and more oxidative myofibers, reduced muscle degenerative/regenerative processes, and reduced myofiber size variability, indicating an attenuation of dystrophic histopathology. Furthermore, mdx muscles lacking cyclin D3 exhibit reduced fatigability during repeated electrical stimulations. Notably, cyclin D3-null mdx mice show enhanced performance during recurrent trials of endurance treadmill exercise, and post-exercise muscle damage results decreased while the regenerative capacity is boosted. In addition, muscles from exercised cyclin D3-deficient mdx mice display increased oxidative capacity and increased mRNA expression of genes involved in the regulation of oxidative metabolism and the response to oxidative stress. Altogether, our findings indicate that depletion of cyclin D3 confers benefits to dystrophic muscle, suggesting that cyclin D3 inhibition may represent a promising therapeutic strategy against DMD.

Hepatic protein kinase Cbeta deficiency mitigates late-onset obesity

Although aging is associated with progressive adiposity and a decline in liver function, the underlying molecular mechanisms and metabolic interplay are incompletely understood. Here, we demonstrate that aging induces hepatic protein kinase Cbeta (PKCβ) expression, while hepatocyte PKCβ deficiency (PKCβHep-/-) in mice significantly attenuates obesity in aged mice fed a high-fat diet. Compared with control PKCβfl/fl mice, PKCβHep-/- mice showed elevated energy expenditure with augmentation of oxygen consumption and carbon dioxide production which was dependent on β3-adrenergic receptor signaling, thereby favoring negative energy balance. This effect was accompanied by induction of thermogenic genes in brown adipose tissue (BAT) and increased BAT respiratory capacity, as well as a shift to oxidative muscle fiber type with an improved mitochondrial function, thereby enhancing oxidative capacity of thermogenic tissues. Furthermore, in PKCβHep-/- mice, we determined that PKCβ overexpression in the liver mitigated elevated expression of thermogenic genes in BAT. In conclusion, our study thus establishes hepatocyte PKCβ induction as a critical component of pathophysiological energy metabolism by promoting progressive hepatic and extrahepatic metabolic derangements in energy homeostasis, contributing to late-onset obesity. These findings have potential implications for augmenting thermogenesis as a means of combating aging-induced obesity.

Myosin Heavy-Chain Messenger Ribonucleic Acid (mRNA) Expression and Fibre Cross-Sectional Area in Masseter, Digastric, Gastrocnemius and Soleus Muscles of Young and Adult Rats.

Different demands on the muscles of mastication may influence their functional profile (size and distribution of muscle fibre types), which may change during growth and maturation, potentially influencing craniofacial growth. The aim of this study was to evaluate mRNA expression and cross-sectional area of masticatory muscle fibres compared with limb muscles in young and adult rats. Twenty-four rats were sacrificed at two different ages, namely 12 at 4 weeks (young) and 12 at 26 weeks (adult). The masseter, digastric, gastrocnemius and soleus muscles were dissected. Gene expression of myosin heavy-chain isoforms Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx) in the muscles was measured using qRT-PCR RNA analysis, and immunofluorescence staining was performed to measure the cross-sectional area of different muscle fibre types. Different muscle types and ages were compared. Significant differences were found in the functional profile between masticatory and limb muscles. For the masticatory muscles, there was an increase in Myh4 expression with age, and this change was more intense for the masseter muscles, which also presented an increase in Myh1 expression, similarly to limb muscles. The fibre cross-sectional area of the masticatory muscles was generally smaller in young rats; however, this difference was less pronounced than in limb muscles.

Skeletal muscle fibre type and enzymatic activity in adult offspring following placental and peripheral malaria exposure in foetal life.

Maternal malaria may restrict foetal growth. Impaired utero-placental blood flow due to malaria infection may cause hypoxia-induced altered skeletal muscle fibre type distribution in the offspring, which may contribute to insulin resistance and impaired glucose metabolism. This study assessed muscle fibre distribution 20 years after placental and/or peripheral in-utero malaria exposure compared to no exposure, i.e., PPM+, PM+, and M-, respectively. We traced 101 men and women offspring of mothers who participated in a malaria chemosuppression study in Muheza, Tanzania. Of 76 eligible participants, 50 individuals (29 men and 21 women) had skeletal muscle biopsy taken from m. vastus lateralis in the right leg. As previously reported, fasting and 30 min post-oral glucose challenge plasma glucose values were higher, and insulin secretion disposition index was lower, in the PPM+ group. Aerobic capacity (fitness) was estimated by an indirect VO2max test on a stationary bicycle. Muscle fibre sub-type (myosin heavy chain, MHC) distribution was analysed, as were muscle enzyme activities (citrate synthase (CS), 3-hydroxyacyl-CoA dehydrogenase, myophosphorylase, phosphofructokinase, lactate dehydrogenase, and creatine kinase activities. Between-group analyses were adjusted for MHC-I %. No differences in aerobic capacity were found between groups. Despite subtle elevations of plasma glucose levels in the PPM+ group, there was no difference in MHC sub-types or muscle enzymatic activities between the malaria-exposed and non-exposed groups. The current study did not show differences in MHC towards glycolytic sub-types or enzymatic activity across the sub-groups. The results support the notion of the mild elevations of plasma glucose levels in people exposed to placental malaria in pregnancy being due to compromised pancreatic insulin secretion rather than insulin resistance.