Muscle Of Wild-type Mice Research Articles

Boosting BDNF in muscle rescues impaired axonal transport in a mouse model of DI-CMTC peripheral neuropathy

Charcot-Marie-Tooth disease (CMT) is a genetic peripheral neuropathy caused by mutations in many functionally diverse genes. The aminoacyl-tRNA synthetase (ARS) enzymes, which transfer amino acids to partner tRNAs for protein synthesis, represent the largest protein family genetically linked to CMT aetiology, suggesting pathomechanistic commonalities. Dominant intermediate CMT type C (DI-CMTC) is caused by YARS1 mutations driving a toxic gain-of-function in the encoded tyrosyl-tRNA synthetase (TyrRS), which is mediated by exposure of consensus neomorphic surfaces through conformational changes of the mutant protein. In this study, we first showed that human DI-CMTC-causing TyrRSE196K mis-interacts with the extracellular domain of the BDNF receptor TrkB, an aberrant association we have previously characterised for several mutant glycyl-tRNA synthetases linked to CMT type 2D (CMT2D). We then performed temporal neuromuscular assessments of YarsE196K mice modelling DI-CMT. We determined that YarsE196K homozygotes display a selective, age-dependent impairment in in vivo axonal transport of neurotrophin-containing signalling endosomes, phenocopying CMT2D mice. This impairment is replicated by injection of recombinant TyrRSE196K, but not TyrRSWT, into muscles of wild-type mice. Augmenting BDNF in DI-CMTC muscles, through injection of recombinant protein or muscle-specific gene therapy, resulted in complete axonal transport correction. Therefore, this work identifies a non-cell autonomous pathomechanism common to ARS-related neuropathies, and highlights the potential of boosting BDNF levels in muscles as a therapeutic strategy.

Stanniocalcin-2 inhibits skeletal muscle growth and is upregulated in functional overload-induced hypertrophy.

Stanniocalcin-2 (STC2) has recently been implicated in human muscle mass variability by genetic analysis. Biochemically, STC2 inhibits the proteolytic activity of the metalloproteinase PAPP-A, which promotes muscle growth by upregulating the insulin-like growth factor (IGF) axis. The aim was to examine if STC2 affects skeletal muscle mass and to assess how the IGF axis mediates muscle hypertrophy induced by functional overload. We compared muscle mass and muscle fiber morphology between Stc2-/- (n = 21) and wild-type (n = 15) mice. We then quantified IGF1, IGF2, IGF binding proteins -4 and -5 (IGFBP-4, IGFBP-5), PAPP-A and STC2 in plantaris muscles of wild-type mice subjected to 4-week unilateral overload (n = 14). Stc2-/- mice showed up to 10% larger muscle mass compared with wild-type mice. This increase was mediated by greater cross-sectional area of muscle fibers. Overload increased plantaris mass and components of the IGF axis, including quantities of IGF1 (by 2.41-fold, p = 0.0117), IGF2 (1.70-fold, p = 0.0461), IGFBP-4 (1.48-fold, p = 0.0268), PAPP-A (1.30-fold, p = 0.0154) and STC2 (1.28-fold, p = 0.019). Here we provide evidence that STC2 is an inhibitor of muscle growth upregulated, along with other components of the IGF axis, during overload-induced muscle hypertrophy.

A positive feedback loop between AMPK and GDF15 promotes metformin antidiabetic effects

Background and aimsMetformin, the most prescribed drug for the treatment of type 2 diabetes mellitus, has been recently reported to promote weight loss by upregulating the anorectic cytokine growth differentiation factor 15 (GDF15). Since the antidiabetic effects of metformin are mostly mediated by the activation of AMPK, a key metabolic sensor in energy homeostasis, we examined whether the activation of this kinase by metformin was dependent on GDF15. MethodsCultured hepatocytes and myotubes, and wild-type and Gdf15-/- mice were utilized in a series of studies to investigate the involvement of GDF15 in the activation of AMPK by metformin. ResultsA low dose of metformin increased GDF15 levels without significantly reducing body weight or food intake, but it ameliorated glucose intolerance and activated AMPK in the liver and skeletal muscle of wild-type mice but not Gdf15-/- mice fed a high-fat diet. Cultured hepatocytes and myotubes treated with metformin showed AMPK-mediated increases in GDF15 levels independently of its central receptor GFRAL, while Gdf15 knockdown blunted the effect of metformin on AMPK activation, suggesting that AMPK is required for the metformin-mediated increase in GDF15, which in turn is needed to sustain the full activation of this kinase independently of the CNS. ConclusionOverall, these findings uncover a novel mechanism through which GDF15 upregulation by metformin is involved in achieving and sustaining full AMPK activation by this drug independently of the CNS.

The fibrotic niche impairs satellite cell function and muscle regeneration in mouse models of Marfan syndrome.

It has been suggested that the proliferation and early differentiation of myoblasts are impaired in Marfan syndrome (MFS) mice during muscle regeneration. However, the underlying cellular and molecular mechanisms remain poorly understood. Here, we investigated muscle regeneration in MFS mouse models by analyzing the influence of the fibrotic niche on satellite cell function. In vivo, ex vivo, and in vitro experiments were performed. In addition, we evaluated the effect of the pharmacological inhibition of fibrosis using Ang-(1-7) on regenerating skeletal muscles of MFS mice. The skeletal muscle of MFS mice shows an increased accumulation of collagen fibers (81.2%), number of fibroblasts (157.1%), and Smad2/3 signaling (110.5%), as well as an aberrant number of fibro-adipogenic progenitor cells in response to injury compared with wild-type mice. There was an increased number of proinflammatory and anti-inflammatory macrophages (3.6- and 3.1-fold, respectively) in regenerating muscles of wild-type mice, but not in the regenerating muscles of MFS mice. Our data show that proliferation and differentiation of satellite cells are altered (p ≤ 0.05) in MFS mice. Myoblast transplantation assay revealed that the regenerating muscles from MFS mice have reduced satellite cell self-renewal capacity (74.7%). In addition, we found that treatment with Ang-(1-7) reduces fibrosis (71.6%) and ameliorates satellite cell dysfunction (p ≤ 0.05) and muscle contractile function (p ≤ 0.05) in MFS mice. The fibrotic niche, caused by Fbn1 mutations, reduces the myogenic potential of satellite cells, affecting structural and functional muscle regeneration. In addition, the fibrosis inhibitor Ang-(1-7) partially counteracts satellite cell abnormalities and restores myofiber size and contractile force in regenerating muscles.

Neoadjuvant Radiation Therapy and Surgery Improves Metastasis-Free Survival over Surgery Alone in a Primary Mouse Model of Soft Tissue Sarcoma.

This study aims to investigate whether adding neoadjuvant radiotherapy (RT), anti-programmed cell death protein-1 (PD-1) antibody (anti-PD-1), or RT + anti-PD-1 to surgical resection improves disease-free survival for mice with soft tissue sarcomas (STS). We generated a high mutational load primary mouse model of STS by intramuscular injection of adenovirus expressing Cas9 and guide RNA targeting Trp53 and intramuscular injection of 3-methylcholanthrene (MCA) into the gastrocnemius muscle of wild-type mice (p53/MCA model). We randomized tumor-bearing mice to receive isotype control or anti-PD-1 antibody with or without radiotherapy (20 Gy), followed by hind limb amputation. We used micro-CT to detect lung metastases with high spatial resolution, which was confirmed by histology. We investigated whether sarcoma metastasis was regulated by immunosurveillance by lymphocytes or tumor cell-intrinsic mechanisms. Compared with surgery with isotype control antibody, the combination of anti-PD-1, radiotherapy, and surgery improved local recurrence-free survival (P = 0.035) and disease-free survival (P = 0.005), but not metastasis-free survival. Mice treated with radiotherapy, but not anti-PD-1, showed significantly improved local recurrence-free survival and metastasis-free survival over surgery alone (P = 0.043 and P = 0.007, respectively). The overall metastasis rate was low (∼12%) in the p53/MCA sarcoma model, which limited the power to detect further improvement in metastasis-free survival with addition of anti-PD-1 therapy. Tail vein injections of sarcoma cells into immunocompetent mice suggested that impaired metastasis was due to inability of sarcoma cells to grow in the lungs rather than a consequence of immunosurveillance. In conclusion, neoadjuvant radiotherapy improves metastasis-free survival after surgery in a primary model of STS.

Globular adiponectin ameliorates insulin resistance in skeletal muscle by enhancing the LKB1-mediated AMPK activation via SESN2

Adiponectin has been demonstrated to be a mediator of insulin sensitivity; however, the underlined mechanisms remain unclear. SESN2 is a stress-inducible protein that phosphorylates AMPK in different tissues. In this study, we aimed to validate the amelioration of insulin resistance by globular adiponectin (gAd) and to reveal the role of SESN2 in the improvement of glucose metabolism by gAd. We used a high-fat diet-induced wild-type and SESN2−/− C57BL/6J insulin resistance mice model to study the effects of six-week aerobic exercise or gAd administration on insulin resistance. In vitro study, C2C12 myotubes were used to determine the potential mechanism by overexpressing or inhibiting SESN2. Similar to exercise, six-week gAd administration decreased fasting glucose, triglyceride and insulin levels, reduced lipid deposition in skeletal muscle and reversed whole-body insulin resistance in mice fed on a high-fat diet. Moreover, gAd enhanced skeletal muscle glucose uptake by activating insulin signaling. However, these effects were diminished in SESN2−/− mice. We found that gAd administration increased the expression of SESN2 and Liver kinase B1 (LKB1) and increased AMPK-T172 phosphorylation in skeletal muscle of wild-type mice, while in SESN2−/− mice, LKB1 expression was also increased but the pAMPK-T172 was unchanged. At the cellular level, gAd increased cellular SESN2 and pAMPK-T172 expression. Immunoprecipitation experiment suggested that SESN2 promoted the formation of complexes of AMPK and LKB1 and hence phosphorylated AMPK. In conclusion, our results revealed that SESN2 played a critical role in gAd-induced AMPK phosphorylation, activation of insulin signaling and skeletal muscle insulin sensitization in mice with insulin resistance.

Lectin Biomarker Development in a Mouse Model of GNE Myopathy

GNE Myopathy (GNEM) is a rare autosomal recessive disease that causes progressive muscle wasting. GNEM occurs due to mutations in the GNE gene that encodes a key enzyme of the biosynthetic pathway of sialic acid, a terminal glycan on extracellular chains of muscle cells. Mutations in the GNE gene cause a significant reduction in the production of sialic acid, which is associated with muscle weakness and wasting. In order to assess the cellular effects of sialic acid‐producing therapies in clinical studies, a robust biomarker is needed to quantify the levels of sialic acid in muscle. Several lectins have shown robust and replicable changes after sialic acid perturbations in human cells. However, the ideal lectin biomarker for GNEM would also need to reflect relevant sialic acid changes in mouse models of GNEM, which are used to test the efficacy of gene therapies during pre‐clinical studies. Here, we compare lectin staining in skeletal muscle of wild type mice and the GNED207VTgGne‐/‐ mouse model of GNEM. Validation of a biomarker in this mouse model can facilitate pre‐clinical studies of GNEM gene therapy in mice.

Compromised membrane repair in muscle cells from GNE myopathy patients

GNE myopathy (GNEM) is an adult onset autosomal recessive neuromuscular disease that initially presents as distal muscle weakness and slowly progresses to atrophy of skeletal muscles throughout the body. GNEM results from mutations in the GNE gene that is located on chromosome 9 and encodes for the N‐acetylglucosamine 2‐epimerase/N‐acetylmannosamine kinase (GNE) which is the rate‐limiting enzyme for the biosynthesis of sialic acid. Sialic acid plays an important role in cellular interactions through modification of the terminal carbohydrate chains on glycoproteins in the plasma membrane. While minimal GNE activity is required for viability, hyposialylation has been observed in GNEM patients. Even though the mechanism of the disease requires further investigations beyond the impaired sialic acid pathway, hyposialylation is still thought to be responsible, at least partially, for the disease pathology. This study aims to elucidate the molecular mechanism of GNEM that links hyposialylation to muscle atrophy and weakness. The association of sialic acid with membrane proteins suggests possible implications for the plasma membrane integrity and repair capacity. We hypothesized that GNEM involves reduced membrane repair capacity in skeletal muscle. To test this hypothesis, we performed laser injury assays on myoblasts transdifferentiated from human skin fibroblasts of GNE patients. Isolated fibroblasts were transdifferentiated into myoblasts using overexpression of MyoD. A multiphoton laser was used to injure the myoblasts in the presence of FM4‐64 lipophilic dye. The resealing capacity is measured by observing the change in fluorescent dye uptake following injury. Our results indicate reduced sarcolemmal membrane repair in GNE myoblasts when compared to healthy controls. To test if sialic acid is required for effective membrane repair, we assessed the level of plasma membrane damage using a glass bead wounding assay on C2C12 myoblasts treated with neuraminidase to remove sialic acid from these cells. The results indicate that sialic acid depleted myoblasts have a more fragile plasma membrane. To further elucidate the mechanism of GNEM we measured the expression levels of key membrane repair proteins in myoblasts and myotubes derived from GNE patients and healthy volunteers. Overall, our results indicate that hyposialylation is correlated with reduced sarcolemmal membrane integrity and repair capacity. To confirm this as a mechanism of GNE myopathy, future studies will use shRNA to knock down GNE in electroporated wild‐type mouse muscle. Muscles from the electroporated mice will be tested using laser injury and western blots to confirm the results we observed in vitro. Future studies also include analyzing expression levels of sarcolemma repair proteins in GNEM patients. Preliminary data from our studies show that sialic acid deficiency is associated with impaired sarcolemma repair leading to muscle atrophy in GNEM.

Corticosteroid suppresses urea-cycle-related gene expressions in ornithine transcarbamylase deficiency

BackgroundOrnithine transcarbamylase deficiency (OTCD) is most common among urea cycle disorders (UCDs), defined by defects in enzymes associated with ureagenesis. Corticosteroid administration to UCD patients, including OTCD patients, is suggested to be avoided, as it may induce life-threatening hyperammonemia. The mechanism has been considered nitrogen overload due to the catabolic effect of corticosteroids; however, the pathophysiological process is unclear.MethodsTo elucidate the mechanism of hyperammonemia induced by corticosteroid administration in OTCD patients, we analyzed a mouse model by administering corticosteroids to OTCspf−ash mice deficient in the OTC gene. Dexamethasone (DEX; 20 mg/kg) was administered to the OTCspf−ash and wild-type (WT) mice at 0 and 24 h, and the serum ammonia concentrations, the levels of the hepatic metabolites, and the gene expressions related with ammonia metabolism in the livers and muscles were analyzed.ResultsThe ammonia levels in Otcspf−ash mice that were administered DEX tended to increase at 24 h and increased significantly at 48 h. The metabolomic analysis showed that the levels of citrulline, arginine, and ornithine did not differ significantly between Otcspf−ash mice that were administered DEX and normal saline; however, the level of aspartate was increased drastically in Otcspf−ash mice owing to DEX administration (P < 0.01). Among the enzymes associated with the urea cycle, mRNA expressions of carbamoyl-phosphate synthase 1, ornithine transcarbamylase, arginosuccinate synthase 1, and arginosuccinate lyase in the livers were significantly downregulated by DEX administration in both the Otcspf−ash and WT mice (P < 0.01). Among the enzymes associated with catabolism, mRNA expression of Muscle RING-finger protein-1 in the muscles was significantly upregulated in the muscles of WT mice by DEX administration (P < 0.05).ConclusionsWe elucidated that corticosteroid administration induced hyperammonemia in Otcspf−ash mice by not only muscle catabolism but also suppressing urea-cycle-related gene expressions. Since the urea cycle intermediate amino acids, such as arginine, might not be effective because of the suppressed expression of urea-cycle-related genes by corticosteroid administration, we should consider an early intervention by renal replacement therapy in cases of UCD patients induced by corticosteroids to avoid brain injuries or fatal outcomes.

The effect of hypoxia on myogenic differentiation and multipotency of the skeletal muscle-derived stem cells in mice

BackgroundSkeletal muscle-derived stem cells (SC) have become a promising approach for investigating myogenic differentiation and optimizing tissue regeneration. Muscle regeneration is performed by SC, a self-renewal cell population underlying the basal lamina of muscle fibers. Here, we examined the impact of hypoxia condition on the regenerative capacity of SC either in their native microenvironment or via isolation in a monolayer culture using ectopic differentiation inductions. Furthermore, the effect of low oxygen tension on myogenic differentiation protocols of the myoblasts cell line C2C12 was examined.MethodsHind limb muscles of wild type mice were processed for both SC/fiber isolation and myoblast extraction using magnetic beads. SC were induced for myogenic, adipogenic and osteogenic commitments under normoxic (21% O2) and hypoxic (3% O2) conditions. SC proliferation and differentiation were evaluated using histological staining, immunohistochemistry, morphometric analysis and RT-qPCR. The data were statistically analyzed using ANOVA.ResultsThe data revealed enhanced SC proliferation and motility following differentiation induction after 48 h under hypoxia. Following myogenic induction, the number of undifferentiated cells positive for Pax7 were increased at 72 h under hypoxia. Hypoxia upregulated MyoD and downregulated Myogenin expression at day-7 post-myogenic induction. Hypoxia promoted both SC adipogenesis and osteogenesis under respective induction as shown by using Oil Red O and Alizarin Red S staining. The expression of adipogenic markers; peroxisome proliferator activated receptor gamma (PPARγ) and fatty acid-binding protein 4 (FABP4) were upregulated under hypoxia up to day 14 compared to normoxic condition. Enhanced osteogenic differentiation was detected under hypoxic condition via upregulation of osteocalcin and osteopontin expression up to day 14 as well as, increased calcium deposition at day 21. Hypoxia exposure increases the number of adipocytes and the size of fat vacuoles per adipocyte compared to normoxic culture. Combining the differentiation medium with dexamethasone under hypoxia improves the efficiency of the myogenic differentiation protocol of C2C12 by increasing the length of the myotubes.ConclusionsHypoxia exposure increases cell resources for clinical applications and promotes SC multipotency and thus beneficial for tissue regeneration.

Enrichment of the exocytosis protein STX4 in skeletal muscle remediates peripheral insulin resistance and alters mitochondrial dynamics via Drp1

Mitochondrial dysfunction is implicated in skeletal muscle insulin resistance. Syntaxin 4 (STX4) levels are reduced in human diabetic skeletal muscle, and global transgenic enrichment of STX4 expression improves insulin sensitivity in mice. Here, we show that transgenic skeletal muscle-specific STX4 enrichment (skmSTX4tg) in mice reverses established insulin resistance and improves mitochondrial function in the context of diabetogenic stress. Specifically, skmSTX4tg reversed insulin resistance caused by high-fat diet (HFD) without altering body weight or food consumption. Electron microscopy of wild-type mouse muscle revealed STX4 localisation at or proximal to the mitochondrial membrane. STX4 enrichment prevented HFD-induced mitochondrial fragmentation and dysfunction through a mechanism involving STX4-Drp1 interaction and elevated AMPK-mediated phosphorylation at Drp1 S637, which favors fusion. Our findings challenge the dogma that STX4 acts solely at the plasma membrane, revealing that STX4 localises at/proximal to and regulates the function of mitochondria in muscle. These results establish skeletal muscle STX4 enrichment as a candidate therapeutic strategy to reverse peripheral insulin resistance.

Acetylcholine receptor subunit expression in Huntington's disease mouse muscle

Huntington's disease (HD) causes neurological impairments, as well as muscle dysfunction, including smaller neuromuscular junctions (NMJs). This study assessed the expression levels of the subunits of the nicotinic acetylcholine receptor (nAChR) in muscles of the R6/2 mouse model of HD. Based on our previous findings of reduced NMJ size in R6/2 mice, it was hypothesized that muscles from R6/2 mice would also show an altered expression pattern of nAChR subunits compared to wild-type (WT) mice. Therefore, the mRNA levels of nAChR subunits were quantified in R6/2 and WT mouse muscles using qRT-PCR. Denervated muscles from WT mice served as positive controls for alterations in nAChR expression. Although some changes in nAChR subunit expression occurred in R6/2 muscles, the expression levels closely resembled WT. However, the expression of nAChR subunit-ε (Chrne) was significantly decreased in R6/2 muscles relative to WT. This study demonstrates that only minor changes in nAChR subunit expression occurs in R6/2 mouse muscles and that reduction in Chrne expression may be related to a reduction in NMJ size in R6/mice.

Methionine sulfoxide reductase B3 deficiency inhibits the development of diet-induced insulin resistance in mice

Oxidative and endoplasmic reticulum (ER) stress are involved in mediating high-fat diet (HFD)-induced insulin resistance. As the ER-localized methionine sulfoxide reductase B3 (MsrB3) protects cells against oxidative and ER stress, we hypothesized that MsrB3 might be associated with HFD-induced insulin resistance. To test this hypothesis, we examined the effect of MsrB3 deficiency on HFD-induced insulin resistance using MsrB3 knockout (KO) mice. Mice were fed a control diet or HFD for 12 weeks and insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp. HFD consumption increased the body weight of both wild-type and MsrB3 KO mice, and no significant difference was observed between the genotypes. The HFD increased oxidative stress and induced insulin resistance in the skeletal muscle of wild-type mice, but did not affect either in MsrB3 KO mice. The unfolded protein response (UPR) was increased in MsrB3 KO mice upon consumption of HFD, but not in wild-type mice. Mitochondrial oxidative phosphorylation proteins and the levels of superoxide dismutase 2 and glutathione peroxidase 1 were increased in MsrB3 KO mice upon HFD consumption. The respiratory control ratio was reduced in wild-type mice consuming HFD but not in MsrB3 KO mice. The levels of calcium/calmodulin-dependent protein kinase kinase β, phosphorylated AMP-activated protein kinase, and peroxisome proliferator-activated receptor gamma coactivator 1α were increased in MsrB3 KO mice following HFD consumption. These results suggest that MsrB3 deficiency inhibits HFD-induced insulin resistance, and the increased mitochondrial biogenesis and antioxidant induction might be the mechanisms underlying this phenomenon.

Myogenic Cell Expression of Intercellular Adhesion Molecule-1 Contributes to Muscle Regeneration after Injury

This study investigated intercellular adhesion molecule-1 (ICAM-1), a membrane protein that mediates cell-to-cell adhesion and communication, as a mechanism through which the inflammatory response facilitates muscle regeneration after injury. Toxin-induced muscle injury to tibialis anterior muscles of wild-type mice caused ICAM-1 to be expressed by a population of satellite cells/myoblasts and myofibers. Myogenic cell expression of ICAM-1 contributed to the restoration of muscle structure after injury, as regenerating myofibers were more abundant and myofiber size was larger for wild-type compared with Icam1-/- mice during 28 days of recovery. Contrastingly, restoration of muscle function after injury was similar between the genotypes. ICAM-1 facilitated the restoration of muscle structure after injury through mechanisms involving the regulation of myofiber branching, protein synthesis, and the organization of nuclei within myofibers after myogenic cell fusion. These findings provide support for a paradigm in which ICAM-1 expressed by myogenic cells after muscle injury augments their adhesive and fusogenic properties, which, in turn, facilitates regenerative and hypertrophic processes that restore structure to injured muscle.

Transglutaminase 2 Has Metabolic and Vascular Regulatory Functions Revealed by In Vivo Activation of Alpha1-Adrenergic Receptor.

The multifunctional tissue transglutaminase has been demonstrated to act as α1-adrenergic receptor-coupled G protein with GTPase activity in several cell types. To explore further the pathophysiological significance of this function we investigated the in vivo effects of the α1-adrenergic receptor agonist phenylephrine comparing responses in wild type and TG2-/- mice. Injection of phenylephrine, but not a beta3-adrenergic agonist (CL-316,243), resulted in the long-term decline of the respiratory exchange ratio and lower lactate concentration in TG2-/- mice indicating they preferred to utilize fatty acids instead of glucose as fuels. Measurement of tail blood pressure revealed that the vasoconstrictive effect of phenylephrine was milder in TG2-/- mice leading to lower levels of lactate dehydrogenase (LDH) isoenzymes in blood. LDH isoenzyme patterns indicated more damage in lung, liver, kidney, skeletal, and cardiac muscle of wild type mice; the latter was confirmed by a higher level of heart-specific CK-MB. Our data suggest that TG2 as an α1-adrenergic receptor-coupled G protein has important regulatory functions in alpha1-adrenergic receptor-mediated metabolic processes and vascular functions.

PAI-1 is involved in delayed bone repair induced by glucocorticoids in mice.

Glucocorticoid (GC) treatments induce osteoporosis and chronic GC treatments have been suggested to induce delayed bone repair; however, the mechanisms by which GC induces delayed bone repair remain unclear. We herein investigated the roles of plasminogen activator inhibitor-1 (PAI-1) in GC-induced effects on bone repair after femoral bone injury using female mice with a PAI-1 deficiency and their wild-type counterparts. Dexamethasone (Dex) increased plasma PAI-1 levels as well as PAI-1 mRNA levels in the adipose tissues and muscles of wild-type mice. PAI-1 deficiency significantly blunted Dex-induced delayed bone repair in mice. Moreover, PAI-1 deficiency significantly blunted Runx2 mRNA levels suppressed by Dex as well as Dex-induced osteoblast apoptosis at the damaged site 7days after bone injury in mice. On the other hand, PAI-1 deficiency did not affect adipogenic gene expression enhanced by Dex at the damaged site 7days after bone injury in mice. In conclusion, we herein showed for the first time that PAI-1 is involved in delayed bone repair after bone injury induced by GC in mice. PAI-1 may influence early stage osteoblast differentiation and apoptosis during the osteoblastic restoration phase of the bone repair process.

It's well and truly time to stop stating that AMPK regulates glucose uptake and fat oxidation during exercise.

None for Perspective.

Follistatin-based ligand trap ACE-083 induces localized hypertrophy of skeletal muscle with functional improvement in models of neuromuscular disease

Skeletal muscle is under inhibitory homeostatic regulation by multiple ligands of the transforming growth factor-β (TGFβ) superfamily. Follistatin is a secreted protein that promotes muscle growth and function by sequestering these ligands extracellularly. In the present study, we evaluated the potential of ACE-083 – a locally acting, follistatin-based fusion protein – as a novel therapeutic agent for focal or asymmetric myopathies. Characterization of ACE-083 in vitro revealed its high affinity for heparin and extracellular matrix while surface plasmon resonance and cell-based assays confirmed that ACE-083 binds and potently neutralizes myostatin, activin A, activin B and growth differentiation factor 11 (GDF11). Intramuscular administration of ACE-083 caused localized, dose-dependent hypertrophy of the injected muscle in wild-type mice and mouse models of Charcot-Marie-Tooth disease (CMT) and Duchenne muscular dystrophy, with no evidence of systemic muscle effects or endocrine perturbation. Importantly, ACE-083 also increased the force of isometric contraction in situ by the injected tibialis anterior muscle in wild-type mice and disease models and increased ankle dorsiflexion torque in CMT mice. Our results demonstrate the potential of ACE-083 as a therapeutic agent for patients with CMT, muscular dystrophy and other disorders with focal or asymmetric muscle atrophy or weakness.

Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) Mutations: a Potential Common Cause of Alzheimer's Disease and Musculoskeletal Disorders

Alzheimer's disease (AD), a worldwide growing health issue, is a purely neurodegenerative form of age‐induced dementia. Interestingly, weight loss is frequently associated with disease severity and clinical progression and has been shown to begin at least ten years before the diagnosis of the disease. Bone frailty and sarcopenia have each also been linked to the onset of this disease, although very little is known about the pathogenesis of these conditions in subjects with AD. Indeed, although a common link between dementia and osteoporosis has been suggested, it has never been conclusively demonstrated. The prevalence of both conditions increase with aging, and some genetic conditions can lead to both AD and osteoporosis. Examples for the potential common cause of the 2 conditions are mutations of the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) gene, primarily expressed in myeloid cells or microglia in brain and in osteoclasts in bone, which result in AD and dementia, as well as in bone fragility. In a recent Genome Wide Association Study, a single nucleotide polymorphism (SNP) encoding the R47H variant in TREM2 was linked with strong single allele genetic risk factors for AD, as well as with increased risk for Parkinson's disease, amyotrophic lateral sclerosis and frontotemporal dementia. In addition, recent studies showed that mice expressing the R47H TREM2 variant exhibit loss of TREM2 function and neuritic dystrophy. In a similar manner, another TREM2 mutation, the Y38C variant, was previously described in the pathogenesis of Nasu‐Hakola disease (also known as PLOSL) which is characterized by extensive white matter loss and frontotemporal‐like dementia and polycystic lipomembranous osteodysplasia. To investigate whether mutations in the TREM2 gene, previously associated with AD and frontotemporal dementia, also affect the skeleton, we analyzed the musculoskeletal phenotype of mice in which the Y38C and R47H variants of the TREM2 gene are ubiquitously expressed, generated by Drs. Lamb and Landreth at the Stark Neuroscience Research Institute, Indiana University School of Medicine. Our studies showed decreased bone mass in mice expressing the TREM2 mutants at 6–8 months of age. Interestingly, even though TREM2 expression was absent in skeletal muscle of wild type mice, mice expressing the R47H TREM2 variant exhibit decrease muscle mass. In summary, our results suggest a common cause of cognitive disorders and bone loss, and support an indirect role of TREM2 mutations on the loss of muscle mass, secondary to the altered bone remodeling.Support or Funding InformationNIH/NIAMS R01AR067210ICMH Collaborative Pilot Project AwardThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

PGC-1β modulates statin-associated myotoxicity in mice

Statins inhibit cholesterol biosynthesis and lower serum LDL-cholesterol levels. Statins are generally well tolerated, but can be associated with potentially life-threatening myopathy of unknown mechanism. We have shown previously that statins impair PGC-1β expression in human and rat skeletal muscle, suggesting that PGC-1β may play a role in statin-induced myopathy. PGC-1β is a transcriptional co-regulator controlling the expression of important genes in mitochondrial biogenesis, antioxidative capacity and energy metabolism. The principle aim of the current study was to investigate the interaction between atorvastatin and PGC-1β in more detail. We therefore treated wild-type mice and mice with selective skeletal muscle knockout of PGC-1β (PGC-1β(i)skm-/- mice) with oral atorvastatin (5mg/kg/day) for 2weeks. At the end of treatment, we determined body parameters, muscle function, structure, and composition as well as the function of muscle mitochondria, mitochondrial biogenesis and activation of apoptotic pathways. In wild-type mice, atorvastatin selectively impaired mitochondrial function in glycolytic muscle and caused a conversion of oxidative type IIA to glycolytic type IIB myofibers. Conversely, in oxidative muscle of wild-type mice, atorvastatin enhanced mitochondrial function via activation of mitochondrial biogenesis pathways and decreased apoptosis. In PGC-1β(i)skm-/- mice, atorvastatin induced a switch towards glycolytic fibers, caused mitochondrial dysfunction, increased mitochondrial ROS production, impaired mitochondrial proliferation and induced apoptosis in both glycolytic and oxidative skeletal muscle. Our work reveals that atorvastatin mainly affects glycolytic muscle in wild-type mice and demonstrates the importance of PGC-1β for oxidative muscle integrity during long-term exposure to a myotoxic agent.