Impaired Skeletal Muscle Research Articles

CRISPR/Cas9-Mediated Constitutive Loss of VCP (Valosin-Containing Protein) Impairs Proteostasis and Leads to Defective Striated Muscle Structure and Function In Vivo.

Valosin-containing protein (VCP) acts as a key regulator of cellular protein homeostasis by coordinating protein turnover and quality control. Mutations in VCP lead to (cardio-)myopathy and neurodegenerative diseases such as inclusion body myopathy with Paget’s disease of the bone and frontotemporal dementia (IBMPFD) or amyotrophic lateral sclerosis (ALS). To date, due to embryonic lethality, no constitutive VCP knockout animal model exists. Here, we generated a constitutive CRISPR/Cas9-induced vcp knockout zebrafish model. Similar to the phenotype of vcp morphant knockdown zebrafish embryos, we found that vcp-null embryos displayed significantly impaired cardiac and skeletal muscle function. By ultrastructural analysis of skeletal muscle cells and cardiomyocytes, we observed severely disrupted myofibrillar organization and accumulation of inclusion bodies as well as mitochondrial degeneration. vcp knockout was associated with a significant accumulation of ubiquitinated proteins, suggesting impaired proteasomal function. Additionally, markers of unfolded protein response (UPR)/ER-stress and autophagy-related mTOR signaling were elevated in vcp-deficient embryos, demonstrating impaired proteostasis in VCP-null zebrafish. In conclusion, our findings demonstrate the successful generation of a stable constitutive vcp knockout zebrafish line that will enable characterization of the detailed mechanistic underpinnings of vcp loss, particularly the impact of disturbed protein homeostasis on organ development and function in vivo.

Extracellular stiffness as a determinant of cardiac dysfunction in duchenne muscular distrophy: a study on human iPSC derived cardiomyocytes

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Fondazione Intesa San Paolo Introduction Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive degeneration of striated muscles; in addition to skeletal muscle impairment, DMD is also characterized by progressive myocardial disfunction. The low translational value of animal models and the low availability of human samples make DMD hard to investigate; induced pluripotent stem cells (iPSCs) represent a novel tool to model this disease, preserving the genetic heritage of the patient, including the pathogenic mutation causing dystrophy. Aim Our aim is to characterize cardiomyocytes differentiated from iPSCs (iPSC-CMs) derived from healthy donors (CTRL) and DMD patients, to identify the pathophysiological mechanisms of DMD-related cardiomyopathy. Materials and Methods Cardiomyocytes are differentiated from IPSCs obtained by reprogramming isolated mononucleated blood cells from healthy donors and DMD patients. IPSC-CMs are cultured until day 60, 75 or 90 post-differentiation after plating on nanostructured substrates with two different stiffness levels: PEG-substrates, with lower rigidity, mimicking healthy extracellular tissue, and DEG-substrates, with greater rigidity, that mimic the presence of myocardial fibrosis. Through imaging techniques, we evaluated calcium handling and action potentials (AP) on DMD and CTRL iPSC-CMs by using specific fluorescent dyes for Ca2+ (CAL630) and membrane voltage (Fluovolt). Cells were stimulated at different pacing rates. Results The calcium transient amplitude of CTRL-iPSC-CMs became larger during maturation. This adaptation did not occur in DMD lines, showing a deficit calcium release due to poor maturation of the sarcoplasmic reticulum (SR). AP duration was shorter in the DMD line at d75 but at d90 we observed no differences when compared with the CTRL line. CTRL iPSC-CMs showed a marked ability to adapt to different substrate stiffnesses. Indeed, the calcium transient amplitude was larger and its kinetics faster when cells were grown on the rigid DEG substrates rather than on PEG plates. In the DMD line, however, no differences were observed between the substrates. Conclusions Our results highlight a scarce ability of DMD iPSC-CM to adapt to different substrate stiffness, resulting in mechanical and electrical impairment, especially in the presence of stiffer substrates. This might explain why cardiac impairment is usually absent in the early stages of DMD, when cardiac structural changes are still absent. However, the electrophysiological and mechanical impairment of DMD hearts may precipitate rapidly when extracellular stiffness starts to increase due to development of cardiac fibrosis.

Is vascular insulin resistance an early step in diet-induced whole-body insulin resistance?

There is increasing evidence that skeletal muscle microvascular (capillary) blood flow plays an important role in glucose metabolism by increasing the delivery of glucose and insulin to the myocytes. This process is impaired in insulin-resistant individuals. Studies suggest that in diet-induced insulin-resistant rodents, insulin-mediated skeletal muscle microvascular blood flow is impaired post-short-term high fat feeding, and this occurs before the development of myocyte or whole-body insulin resistance. These data suggest that impaired skeletal muscle microvascular blood flow is an early vascular step before the onset of insulin resistance. However, evidence of this is still lacking in humans. In this review, we summarise what is known about short-term high-calorie and/or high-fat feeding in humans. We also explore selected animal studies to identify potential mechanisms. We discuss future directions aimed at better understanding the ‘early’ vascular mechanisms that lead to insulin resistance as this will provide the opportunity for much earlier screening and timing of intervention to assist in preventing type 2 diabetes.

Hospital based study on demographic profile and clinical spectrum on hereditary muscle disorder

Background: Myopathies are disorders in which a primary functional or structural impairment of skeletal muscle. In general, Muscle disorders are classified into hereditary and acquired disorders. The approach to a patient with a suspected muscle disease is to determine the correct site of the lesion from history and physical examination. This will help to decide on management and prognostication issues. We undertook this study of hereditary muscle disorders to identify the demographic profile and clinical spectrum of hereditary muscle disorders. Aims and Objectives: To study the demographic profile of patients with hereditary muscle disorders and to study the clinical spectrum of hereditary muscle disorders. Methods and Materials: A cross sectional study was conducted on Institute of Neurology, Madras Medical College, Chennai during the period of July 2018 to February 2019 (8 months), among 44 patients (Males-32, Females-12), with clinical features suggestive of hereditary muscle disorders, with certain exclusion criteria’s. Clinical evaluation was done by detailed history taking followed by general and CNS examination, along with motor system examination. All the data were tabulated in Microsoft XL sheet, followed by analysis using SPSS software (version 20.0).

225-LB: Impaired Microvascular Responses May Explain Health Disparities and Impaired Metabolic Flexibility in Hispanic Residents of the Rio Grande Valley

Purpose: Impaired skeletal muscle microvascular blood flow (MBF) is one of the earliest pathophysiologies of type 2 diabetes (T2D) . People with a family history of T2D (FH+ are at greater risk for developing T2D than those with no family history (FH-) . Further, we have shown that normoglycemic Caucasian FH+ individuals have impaired skeletal muscle microvascular responses and metabolic flexibility (MF - ability to switch substrate oxidation upon stimulation) to a mixed meal challenge (MMC) when compared with matched FH- (p<0.01) , suggesting early vascular insulin resistance. Mexican Hispanic individuals have the highest prevalence of T2D in the US and make up ∼95% of Hispanic residents of the Rio Grande Valley (HRGV) where T2D diagnosis rates are ∼3x the national average. Therefore, we sought to determine if impaired MBF responses are present in healthy HRGV. Methods: 15 FH- and 13 FH+ HRGV were recruited to assess MF and MBF responses to a MMC. MF was measured via indirect calorimetry and MBF via contrast-enhanced ultrasound while fasting and again 60-min post MMC. Results: No changes in skeletal MBF were noted in FH- (1.21 ± 0.53 SEM and 0.86 ± 0.23 SEM fasting and postprandial MBF respectively) or FH+ (2.17 ± 0.98 SEM and 1.49 ± 0.66 SEM fasting and postprandial MBF respectively) groups. Abdominal adipose MBF responses increased in FH+ (-2.3 ± 0.71 SEM, p=0.004) , but not in FH- (-0.49 ± 0.39 SEM p=0.39) . FH+ display impaired postprandial metabolic flexibility (MF) responses during 60-min of testing post-MMC. Neither blood glucose responses (99.3 ± 1.3 SEM and 102.27 ± 2.1 SEM fasting and post-prandial respectively, p=0.2) nor body composition differed between FH groups. Conclusions: HRGV display impaired skeletal muscle MBF responses, indicating early vascular insulin resistance. Further, the impairment in MF in FH+ may be partially explained by increased adipose MBF responses, as adipose is less metabolically active than skeletal muscle. Disclosure R. D. Russell: None. Y. Tai: None. S. Marupudi: None.

Impaired Mitochondrial Folate Metabolism Reduces Mitochondrial Respiration in Mouse Muscle Progenitor Cells

ObjectivesMitochondrial dysfunction is a central contributor to aging. Mitochondrial DNA mutations increase with aging and are associated with low serum folate. Furthermore, both increased age and low serum folate are suggested to increase skeletal muscle fiber loss and impair muscle function. However, no research has focused on the metabolic pathway linking the causal relationship. Data from our lab indicate that folate-mediated one-carbon metabolism may play a role, as loss of the mitochondrial specific isozyme (serine hydroxymethyltransferase 2, SHMT2) and folate depletion both result in mitochondrial DNA instability and impaired mitochondrial function. Furthermore, serum folate and SHMT2 gene expression levels decrease with aging, potentially providing a causal mechanism for age-associated mitochondrial DNA mutations and skeletal muscle impairments. To date, little is known about the relationship between loss of SHMT2 enzyme expression and folate status in skeletal muscles.MethodsTibialis anterior muscles were harvested from 10-week-old wild-type (Shmt2+/+) and heterozygous (Shmt2+/−) mice that were weaned onto either a folate-sufficient diet or a modified diet lacking folic acid. Skeletal muscles used to isolate primary muscle progenitor cells (MPCs) were isolated from 20-week-old Shmt2+/+ and Shmt2+/− mouse hindlimbs. MPCs were cultured to 80–90% confluency and then differentiated in low-serum medium for 7–10 days. Skeletal muscles were examined for mitochondrial DNA content and MPCs were examined for mitochondrial function.ResultsHeterozygous loss of Shmt2 resulted in an 80% reduction in SHMT2 protein levels in mouse tibialis anterior muscle. Mice fed a folate-depleted diet for 7 weeks exhibited a 25% reduction in mitochondrial DNA content compared to the folate-sufficient group. In MPCs, reduced Shmt2 expression impaired basal and maximal respiration. Furthermore, protein levels of mitochondrial NADH dehydrogenase 3 were reduced and protein levels of PGC1α and mitofusin 2 were elevated with Shmt2 heterozygosity in MPCs.ConclusionsOur results demonstrate that folate depletion reduced mitochondrial DNA content in tibialis anterior skeletal muscle and loss of SHMT2 impairs MPCs mitochondrial respiration and may influence mitochondrial biogenesis and dynamics.Funding SourcesPresident's Council of Cornell Women Award.

148-OR: Partial Knockout of Skeletal Muscle Dynamin-Related Protein 1 Improves Insulin Sensitivity in Diet-Induced Insulin Resistant Mice, but Not in Normal Control Mice

Dynamin-related protein 1 (Drp1) is the key regulator of mitochondrial fission. We and others have reported excessive Drp1 activity in skeletal muscle from both animals and humans with insulin resistance, which is strongly correlated to impaired skeletal muscle insulin sensitivity. To examine whether Drp1 directly regulates skeletal muscle insulin sensitivity and whole-body glucose homeostasis, we generated tamoxifen-inducible skeletal muscle-specific heterozygous Drp1 partial knockout mice (mDrp1+/-) . Male mDrp1+/- and wildtype (WT) mice were fed with either a high-fat diet (HFD) or low-fat diet (LFD) for four weeks, received tamoxifen injections for five consecutive days, and remained on their respective diet for another four weeks. Improvements in whole-body glucose tolerance and insulin sensitivity were observed in HFD-fed mDrp1+/- mice (P<0.05) , but not in LFD-fed mDrp1+/- mice, when compared to their respective WT controls. Further, HFD-induced impairment in skeletal muscle insulin-stimulated Akt Ser473 phosphorylation (P<0.05) was mitigated in HFD-fed mDrp1+/- mice. In contrast, insulin-stimulated Akt Ser473 phosphorylation was reduced in LFD-fed mDrp1+/- mice compared to LFD-fed WT mice (P<0.05) . mDrp1+/- mice exhibited more fused and interconnected mitochondrial networks in skeletal muscle than WT mice. The examination of mitochondrial function revealed no change in mitochondrial respiration but reductions in mitochondrial Complex I and II and pyruvate dehydrogenase derived H2O2 production in HFD-fed mDrp1+/- mice compared to HFD-fed WT mice (P<0.05) . In conclusion, our data suggest that partial knockout of skeletal muscle Drp1 improves skeletal muscle insulin sensitivity and whole-body glucose homeostasis in diet-induced insulin-resistant mice but not in normal control mice. These improvements are, at least in part, due to reduced mitochondrial-derived H2O2 production. Disclosure B.A.Kugler: None. N.Lin: None. P.D.Nguyen: None. A.Ali: None. A.Sesay: None. B.Kalemba: None. H.Sesaki: None. K.Zou: None. Funding National Institutes of Health (R15DK131512) Diabetes Action Research and Education Foundation Grant (#505)

Using exercise training to improve glycaemic control and uncover mechanisms of impaired skeletal muscle in type 1 diabetics.

Using exercise training to improve glycaemic control and uncover mechanisms of impaired skeletal muscle in type 1 diabetics.

Exercise Responsiveness in Obese Adults

Obesity is associated with several skeletal muscle impairments which can be improved through an aerobic exercise prescription. The possibility that exercise responsiveness is diminished in people with obesity has been suggested but not well‐studied.PURPOSEThe purpose of this study was to investigate how obesity influences acute exercise responsiveness within skeletal muscle.METHODSNon‐obese (NO; n=19; 10F/9M; BMI=25.1 ± 2.8 kg/m2) and Obese (O; n=21; 14F/7M; BMI=37.3 ± 4.6 kg/m2) adults performed 30 minutes of single‐leg cycling at 70% of VO2peak. Serial muscle biopsies (vastus lateralis) were collected before exercise and 3 and 6 hours post‐exercise to measure protein synthesis and gene expression.RESULTSThe exercise‐induced fold change in mixed muscle protein synthesis trended (p=0.058) higher in NO (1.28 ± 0.54‐fold) compared to O (0.95 ± 0.42‐fold) and was inversely related to BMI (r=‐.374, p=0.027). RNA sequencing revealed 331 and 280 genes that were up or downregulated after exercise in NO and O, respectively. Gene set enrichment analysis showed O had blunted post‐exercise pathways related to MAPK signaling, chemokine‐mediated signaling, FC receptor mediated stimulation signaling, cell proliferation, apoptosis, and RNA polymerase II promotion. Quantitative polymerase chain reaction of select metabolic (PGC1a, PGC1b, TFAM, PDK4, IRS, MAPK, and PRKAA1) and muscle growth (SLC, TBC, MSTN, MyoD, TRIM32, FOX03, and FBXO3) genes were similar between groups 3 and 6 hours after exercise.ConclusionThese data highlight several unique pathways in individuals with obesity that result in a blunted exercise response.

Key Facilitator Proteins that Mediate Sarcolemma Membrane Repair have Potential as Therapeutics for Muscle Disease and Injury

A common aspect of many diseases and traumatic injuries affecting skeletal muscle is the necrotic death of muscle fibers. Necrotic death of muscle fibers involves the breakdown of the sarcolemmal membrane that can be exacerbated by increased fragility of the membrane or by compromised endogenous sarcolemmal membrane repair processes. Increasing the efficacy of these repair mechanisms could act as a therapeutic approach for several muscular diseases and injuries. Limb‐girdle muscular dystrophy 2B (LGMD2B), a subtype of LGMD, is an autosomal recessive neuromuscular disorder caused by mutations in the DYSF gene that encodes dysferlin, a protein that is vital in membrane repair. The dysferlin protein has been previously shown to facilitate membrane repair in skeletal muscle and knockout mice for dysferlin develop progressive muscular dystrophy. When dysferlin is absent or inactivated through mutation, membrane damage that cannot be repaired accumulates until muscle fibers undergo necrosis that eventually overwhelms the regenerative capacity of the muscle. This causes skeletal muscle deterioration in LGMD2B patients, particularly in the pelvic and shoulder girdle muscles. There is currently no cure for LGMD2B and treatments that stimulate the membrane repair process in muscle fibers have been greatly overlooked and underutilized as a potential therapeutic approach. This project investigates a novel membrane repair signaling cascade in skeletal cells by utilizing SC79, an Akt activator, to increase membrane repair capacity in skeletal muscle. We hypothesize that activation of the phosphoinositide‐3 kinase (PI3K)/Akt1 signaling axis regulates membrane repair in cultured muscle cells and mouse tissue. Based on our data, we find that SC79 injection leads to decreased sarcolemmal membrane injury during treadmill exercises where injection of SC79 decreases the entry of Evans blue dye into muscle fibers. We determined that various doses of SC79 can increase membrane repair in cultured muscle cells and Bla/J dysferlin deficient mice. In these studies, multi‐photon infrared laser microscopy was used to damage the cell membrane of myoblasts, transdifferentiated from skin fibroblasts isolated from LGMD2B patients, in the presence of FM4‐64 dye, a lipophilic dye that fluoresces when it enters the cells and binds to the phospholipids of the cell membrane and intracellular organelles. The extent of localized FM4‐64 dye fluorescence provides a measurement of how well the membrane is repaired. We found SC79 could increase membrane repair in these human patient myoblasts in a dose dependent fashion. This assay was also used on isolated complete muscles from the Bla/J dysferlin deficient mice, where SC79 also increased membrane repair responses. We conclude that activation of the PI3K/Akt1 signaling axis increases membrane repair in dysferlin deficient skeletal muscle. This project explores a novel signaling cascade controlling membrane repair that could be leveraged to develop new therapies for muscle disease and injury.

Extracellular Vesicles from iPSC derived Muscle Progenitor Cells Rejuvenate the Dysfunctional Muscle Stem Cells during Aging

Background and ObjectiveSarcopenia is defined as the loss of skeletal muscle mass and function due to age, which is a major concern for life long health and wellbeing in elderly population. Age‐associated decline in the performance of muscle stem cells (MuSC) contributes to the deterioration of skeletal muscle during aging. Using small molecule Givinostat and CHIR99021 we previously demonstrated the generation of muscle progenitor cells (Givi‐MPC) of human Induced pluripotent stem cells (iPSC) from multiple cell lines. We found that extracellular vesicles (EVs) from these MPC have a specific cargo compared with human myoblasts. Here, we investigated whether these EVs can rejuvenate the aging dysfunctional muscle stem cells.Methods and ResultsUsing size exclusion chromatography EVs were isolated and purified from iPSC derived Givi‐MPC and primary human myoblasts. The EVs were visualized by transmission electron microscopy. Next, we isolated primary MuSC from 25 months old aged C57/B6 mice, which were confirmed by the expression of myogenic transcription factor, Pax7. We found the aged MuSC pretreated with EVs from MPC promoted clonal expansion and restored myogenic potential in vitro with more myotubes formed after 72h differentiation in medium with 2% horse serum compared with PBS pretreated MuSC (MuSC (Fusion index: 40.3±5.2% vs.15.0± 2.1%, n=3).). To test the regenerative potential of the EVs on aged MuSC, 8 weeks old mdx/scid mice (dystrophin deficient mice) were irradiated to destroy the host MuSC and then injured their tibialis anterior (TA) muscle with cardiotoxin (CTX). 24 hours after injury, we transplanted the aging MuSC (5000 cells) either with EV or PBS pretreatment into TA muscles, respectively. 5 days after transplantation, the EVs pretreated MuSC increased muscle regeneration with muscle fibers positive for embryonic myosin heavy chain compared to PBS pretreated MuSC. One month later, we found transplantation of EVs pretreated MuSC restored dystrophin expression in these mdx mice. We further tested the effects of EVs pretreatment on MuSC in 25 months old mice following CTX injury. Consistent with the results in mdx mice, pretreatment of mice with EVs from Givi‐MPC showed enhanced regeneration (6‐fold increase in number of new muscle cells with central nuclei) in CTX injured aged muscle accompanied by an increase of Pax7 positive MuSC compared with PBS treated mice or treatment with EVs from human myoblasts (number of Pax7 positive MuSC: EVs‐Givi‐MPC 10±5/mm2; PBS 2±1/mm2; EVs‐human myoblast 6±2/mm2, n=3).ConclusionThe regenerative potential of aging MuSC is restored with the treatment of EVs from Givi‐MPC allowing stem cell renewal and differentiation upon activation.

Overexpression of human OGG1 improves skeletal muscle endurance in mice

8‐oxoguanine glycosylase 1 (OGG1) is a DNA glycosylase that catalyzes the excision of oxidized guanines as part of the base excision repair (BER) DNA repair pathway. While OGG1 has been studied extensively for its role in tumor prevention and neurodegeneration, recent studies have indicated a novel role for this enzyme in maintaining metabolic health. In particular, deletion of OGG1 increased propensity to diet‐ and age‐induced obesity, as well as impaired skeletal muscle dysfunction. In contrast, overexpression of human OGG1 (hOGG1) significantly protected mice from diet‐induced obesity and related metabolic sequelae. Unbiased transcriptomics studies using mice constitutively overexpression OGG1 (Ogg1‐transgenic ‐Ogg1Tg) revealed significant transcriptional changes in skeletal muscle of these mice. Among the most highly induced genes, expression of the myokine fibroblast growth factor‐21(FGF21) was elevated by 9.9 fold in RNA‐Seq analyses. qPCR analysis further confirmed these changes in skeletal muscle without any alterations in the hepatic or cardiac expression of Fgf21. Commensurate with gene expression changes, plasma FGF21 was elevated by 11.2 fold in Ogg1Tg mice relative to WT controls. Conversely, Fgf21 gene expression in skeletal muscle and plasma FGF21 levels were decreased by 25 and 29% respectively in Ogg1‐/‐ mice. Consistent with increased FGF21 activity, phosphorylation of AMPK and its target acetyl CoA carboxylase (ACC), and Ser/Thr phosphorylation of Akt were significantly increased in Ogg1Tg muscle. FGF21 is known to increase expression of PGC‐1α protein. Consistently, Ogg1Tg mice had a 1.6 fold increase in PGC‐1α protein. Given these alterations, we asked if markers of muscle health such as endurance would be altered in Ogg1Tg mice. Interestingly, Ogg1Tg mice displayed a 3.4 fold increase in running capacity, consistent with improved skeletal muscle health in these animals. This improvement in exercise capacity was evident in both young and aged mice and have important implications to the management of age‐related declines in muscle health and DNA repair capacity.

Exploring the Combined Effect of High‐Fat High‐Sugar Diets and Volumetric Muscle Injury on Skeletal Muscle Metabolic and Contractile Function in Mice

INTRODUCTIONVolumetric muscle loss (VML) injuries due to trauma or surgery cannot fully recover muscle mass and function, resulting in long‐term disability. Western diets, i.e., high‐fat, high‐sugar (HFHS) diets, promote metabolic stress and are associated with impaired skeletal muscle contractile function. The objective of this study was to investigate the extent to which a HFHS diet affected the pathophysiology following a VML injury as diet and disability may influence the effectiveness of rehabilitation. To determine the combined effects of HFHS diet and VML injury on skeletal muscle, metabolic and muscle contractile function was assessed. We hypothesized that a HFHS diet would worsen skeletal muscle metabolic and contractile function after VML injury.METHODSMale C57BL/6 mice (N=23) were randomly divided into four groups: Normal Chow (NC), High‐Fat High‐Sugar (HFHS), Volumetric Muscle Loss (VML), Volumetric Muscle Loss plus High‐Fat High‐Sugar (VML+HFHS). At age 12 weeks, VML animals underwent unilateral VML surgery to the ankle plantarflexors (gastrocnemius, plantaris, soleus muscles). HFHS groups received 60% high‐fat diet and 11% high‐fructose corn syrup for 8 weeks ad libitum. Oxygen respiration and electron conductance of mitochondria within permeabilized gastrocnemius muscle fibers and peak‐isometric torque of the ankle plantarflexors were measured to assess skeletal muscle metabolic and contractile function, respectively. Data were analyzed using a two‐way ANOVA to detect significant interactions between diet and injury, or in the absence of a significant interaction, the main effects of diet or injury.RESULTSIndependent of injury, mice on HFHS diet had 51% greater body mass compared to mice on NC (p<0.001). Additionally, mice on HFHS diet had less endurance capacity on a treadmill test compared to NC, independent of injury (77% less distance covered, p<0.001). Peak‐isometric torque was 6% less in HFHS mice, independent of injury (p=0.011) and peak‐isometric torque was 20% less in VML‐injured mice, independent of diet (p<0.01). There was a significant interaction between diet and injury for permeabilized muscle fiber oxygen respiration (p=0.016) where NC mice had greater oxygen respiration compared to HFHS, VML, and VML+HFMS mice. Electron conductance was 32% less in mice on HFHS diet, independent of injury (p<0.001) and 20% less in VML‐injured mice, independent of diet (p<0.001).CONCLUSIONThe current study indicates that both HFHS diet and VML injury have detrimental consequences on skeletal muscle contractile and metabolic function. Ongoing and future research is needed to determine the extent to which HFHS diets influence skeletal muscle plasticity and if diet impacts the effectiveness of rehabilitation strategies for VML‐injured skeletal muscle.

Dexamethasone-Induced Sarcopenia and Physical Frailty in Children With Acute Lymphoblastic Leukemia: Protocol for a Prospective Cohort Study.

BackgroundDuring treatment for pediatric acute lymphoblastic leukemia (ALL), children receive high doses of dexamethasone for its apoptotic effect on leukemia cells; however, muscle atrophy is a well-known serious side effect. Muscle atrophy (loss of muscle mass) accompanied by a decreased muscle strength may lead to a generalized impaired skeletal muscle state called sarcopenia. Loss of muscle mass is also an indicator of physical frailty, which is defined as a state of increased vulnerability that is characterized by co-occurrence of low muscle mass, muscle weakness, fatigue, slow walking speed, and low physical activity. Both sarcopenia and physical frailty are related to an increased risk of infections, hospitalizations, and decreased survival in children with chronic diseases.ObjectiveThis study aims to (1) estimate the occurrence of sarcopenia and physical frailty in children during ALL maintenance therapy, (2) evaluate the effect of administering dexamethasone, and (3) explore determinants associated with these outcomes.MethodsThis prospective study is being pursued within the framework of the DexaDays-2 study: a randomized controlled trial on neurobehavioral side effects in pediatric patients with ALL. A total of 105 children (3-18 years) undergoing ALL maintenance treatment at the Princess Máxima Center for Pediatric Oncology are included in this study. Sarcopenia/frailty assessments are performed before and just after a 5-day dexamethasone course. A subset of 50 children participating in the DexaDays-2 trial because of severe dexamethasone-induced neurobehavioral problems were assessed at 3 additional timepoints. The sarcopenia/frailty assessment consists of bioimpedance analysis (skeletal muscle mass [SMM]), handheld dynamometry (handgrip strength), Pediatric Quality of Life Inventory Multidimensional Fatigue Scale (fatigue), Timed Up and Go Test (TUG; walking speed), and physical activity questionnaires. To evaluate potential change in sarcopenia/frailty components after a 5-day dexamethasone administration, a paired Student t test or Mann-Whitney U test will be used. Because of the presence of repeated measurements, generalized linear mixed models will be used to estimate the effect of dexamethasone on sarcopenia and frailty outcomes. Multivariable regression models will be estimated to investigate associations between the assessment scores and patient and treatment-related factors.ResultsPatient accrual started in 2018 and was finalized in spring 2021. From autumn 2021 onward final data analyses will be performed.ConclusionsThis first study combining parameters of sarcopenia and physical frailty is of importance because these conditions can seriously complicate continuation of ALL therapy, independence in physical functioning, reaching motor milestones, and participating in daily life activities. The results will provide knowledge about these complications, the association between dexamethasone treatment and muscle loss and other components of frailty, and therefore insights into the severity of this side effect. By exploring potential determinants that may be associated with sarcopenia and physical frailty, we may be able to identify children at risk at an earlier stage and provide timely interventions.International Registered Report Identifier (IRRID)DERR1-10.2196/33517

Morphological and functional changes in skeletal muscle in type 2 diabetes mellitus: A systematic review and meta-analysis

ABSTRACT Introduction Changes in the skeletal muscle are common in patients with type 2 diabetes mellitus (T2DM). These changes impair your motor skills. Objective This systematic review aimed to investigate changes in skeletal muscle in patients with T2DM. Methods The search was carried out in the PubMed, Scopus, and Web of Science databases until December 1, 2021. Observational studies that evaluated musculoskeletal changes in people with T2DM were included. The review was based on PRISMA recommendations. The primary parameters analyzed were muscle strength, muscle mass, muscle power, and muscle endurance. Results Forty-eight studies were included, with a total of 26,042 participants. The results revealed that T2DM is associated with a reduction in handgrip [−2.64 (CI 95% = −3.33 to −1.95, Z = −7.50, p < .0001], and knee extension muscle strength [−0.56 (CI 95% = −0.76 to −0.36, Z = −5.64, p < .0001)], a higher percentage of type II fibers [11.74 (CI 95% = 6.24 to 17.25, Z = 4.18, p < .0001)], and a lower percentage of type I fibers [−15.69 (CI 95% = −18.22 to −13.16, Z = −12.16, p < .0001], in addition to a greater thickness of the calcaneus tendon (p < .0001). Conclusion Individuals with T2DM present skeletal muscle impairments, mainly reduced muscle strength, mass, and endurance; increase in the thickness of the calcaneus tendon, and alteration in the proportion of type I and II fibers, even in the initial stage of the disease.

Mini-Review on SARS-CoV-2 Infection and Neurological Manifestations: A Perspective

The coronavirus, also known as SARS-CoV-2 (Severe Acute Respiratory Syndrome Corona Virus-19), with its rapid rate of transmission, has progressed with a great impact on respiratory function and mortality worldwide. The nasal cavity is the promising gateway of SARS-CoV-2 to reach the brain via systemic circulatory distribution. Recent reports have revealed that the loss of involuntary process of breathing control into the brainstem that results in death is a signal of neurological involvement. Early neurological symptoms, like loss of smell, convulsions, and ataxia, are the clues of the involvement of the central nervous system that makes the entry of SARS-CoV-2 further fatal and life-threatening, requiring artificial respiration and emergency admission in hospitals. Studies performed on patients infected with SARS-CoV-2 has revealed three-stage involvement of the Central Nervous System (CNS) in the progression of SARS-CoV-2 infection: Direct involvement of CNS with headache, ataxia, dizziness, altered or impaired consciousness, acute stroke or seizures as major symptoms, peripheral involvement with impaired taste, smell, vision, and altered nociception, and skeletal muscle impairment that includes skeletal muscle disorders leading to acute paralysis in a particular area of the body. In the previous era, most studied and researched viruses were beta coronavirus and mouse hepatitis virus, which were studied for acute and chronic encephalitis and Multiple Sclerosis (MS). Although the early symptoms of SARS-CoV are respiratory pathogenesis, the differential diagnosis should always be considered for neurological perspective to stop the mortalities.

Role of exercise in estrogen deficiency-induced sarcopenia.

A decline in estrogen levels during menopause is associated with the loss of muscle mass and function, and it can accelerate sarcopenia. However, with the growing number of postmenopausal women due to the increase in life expectancy, the effects of estrogen on skeletal muscle are not completely understood. This article reviews the relationship between estrogen deficiency and skeletal muscle, its potential mechanisms, including those involving mitochondria, and the effects of exercise on estrogen deficiency-induced skeletal muscle impairment. In particular, mitochondrial dysfunction induced by estrogen deficiency accelerates sarcopenia via mitochondrial dynamics, mitophagy, and mitochondrial-mediated apoptosis. It is well known that exercise training is essential for health, including for the improvement of sarcopenia. This review highlights the importance of exercise training (aerobic and resistance exercise) as a therapeutic intervention against estrogen deficiency-induced sarcopenia.

Comprehensive Research on Past and Future Therapeutic Strategies Devoted to Treatment of Amyotrophic Lateral Sclerosis.

Amyotrophic lateral sclerosis (ALS) is a rapidly debilitating fatal neurodegenerative disorder, causing muscle atrophy and weakness, which leads to paralysis and eventual death. ALS has a multifaceted nature affected by many pathological mechanisms, including oxidative stress (also via protein aggregation), mitochondrial dysfunction, glutamate-induced excitotoxicity, apoptosis, neuroinflammation, axonal degeneration, skeletal muscle deterioration and viruses. This complexity is a major obstacle in defeating ALS. At present, riluzole and edaravone are the only drugs that have passed clinical trials for the treatment of ALS, notwithstanding that they showed modest benefits in a limited population of ALS. A dextromethorphan hydrobromide and quinidine sulfate combination was also approved to treat pseudobulbar affect (PBA) in the course of ALS. Globally, there is a struggle to prevent or alleviate the symptoms of this neurodegenerative disease, including implementation of antisense oligonucleotides (ASOs), induced pluripotent stem cells (iPSCs), CRISPR-9/Cas technique, non-invasive brain stimulation (NIBS) or ALS-on-a-chip technology. Additionally, researchers have synthesized and screened new compounds to be effective in ALS beyond the drug repurposing strategy. Despite all these efforts, ALS treatment is largely limited to palliative care, and there is a strong need for new therapeutics to be developed. This review focuses on and discusses which therapeutic strategies have been followed so far and what can be done in the future for the treatment of ALS.

Mitochondrial Function and Reactive Oxygen/Nitrogen Species in Skeletal Muscle

Skeletal muscle fibers contain a large number of mitochondria, which produce ATP through oxidative phosphorylation (OXPHOS) and provide energy for muscle contraction. In this process, mitochondria also produce several types of “reactive species” as side product, such as reactive oxygen species and reactive nitrogen species which have attracted interest. Mitochondria have been proven to have an essential role in the production of skeletal muscle reactive oxygen/nitrogen species (RONS). Traditionally, the elevation in RONS production is related to oxidative stress, leading to impaired skeletal muscle contractility and muscle atrophy. However, recent studies have shown that the optimal RONS level under the action of antioxidants is a critical physiological signal in skeletal muscle. Here, we will review the origin and physiological functions of RONS, mitochondrial structure and function, mitochondrial dynamics, and the coupling between RONS and mitochondrial oxidative stress. The crosstalk mechanism between mitochondrial function and RONS in skeletal muscle and its regulation of muscle stem cell fate and myogenesis will also be discussed. In all, this review aims to describe a comprehensive and systematic network for the interaction between skeletal muscle mitochondrial function and RONS.

Glycine receptor subunit-β-deficiency in a mouse model of spasticity results in attenuated physical performance, growth, and muscle strength.

Spasticity is the most common neurological disorder associated with increased muscle contraction causing impaired movement and gait. The aim of this study was to characterize the physical performance, skeletal muscle function, and phenotype of mice with a hereditary spastic mutation (B6.Cg-Glrbspa/J). Motor function, gait, and physical activity of juvenile and adult spastic mice and the morphological, histological, and mechanical characteristics of their soleus and gastrocnemius medialis muscles were compared with those of their wild-type (WT) littermates. Spastic mice showed attenuated growth, impaired motor function, and low physical activity. Gait of spastic mice was characterized by a typical hopping pattern. Spastic mice showed lower muscle forces, which were related to the smaller physiological cross-sectional area of spastic muscles. The muscle-tendon complex length-force relationship of adult gastrocnemius medialis was shifted toward shorter lengths, which was explained by attenuated longitudinal tibia growth. Spastic gastrocnemius medialis was more fatigue resistant than WT gastrocnemius medialis. This was largely explained by a higher mitochondrial content in muscle fibers and relatively higher percentage of slow-type muscle fibers. Muscles of juvenile spastic mice showed similar differences compared with WT juvenile mice, but these were less pronounced than between adult mice. This study shows that in spastic mice, disturbed motor function and gait is likely to be the result of hyperactivity of skeletal muscle and impaired skeletal muscle growth, which progress with age.