bims-moremu 2023-01-22 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–01–22
thirty papers selected by
Anna Vainshtein, Craft Science Inc.

Loss of skeletal muscle estrogen related receptors leads to severe exercise intolerance.
Age-Related Dysfunction in Proteostasis and Cellular Quality Control in the Development of Sarcopenia.
Carboxyl-terminal modulator protein (CTMP) deficiency mitigates denervation-induced skeletal muscle atrophy.
Decrease in the expression of muscle-specific miRNAs, miR-133a and miR-1, in myoblasts with replicative senescence.
Bioengineered 3D Skeletal Muscle Model Reveals Complement 4b as a Cell-Autonomous Mechanism of Impaired Regeneration with Aging.
Sarcopenia phenotype and impaired muscle function in male mice with fast-twitch muscle-specific knockout of the androgen receptor.
Quantitative Proteomics Identifies Novel Nrf2-Mediated Adaptative Signaling Pathways in Skeletal Muscle Following Exercise Training.
Challenging Dogma about Myonuclei Behavior in Skeletal Muscle Cells.
Potential Therapeutic Strategies for Skeletal Muscle Atrophy.
Exercise Training and Skeletal Muscle Antioxidant Enzymes: An Update.
Eccentric contraction-induced strength loss in dystrophin-deficient muscle: Preparations, protocols, and mechanisms.
The Mef2c/AdipoR1 axis is responsible for myogenic differentiation and is regulated by resistin in skeletal muscles.
Skeletal Muscle DNA Methylation and mRNA Responses to a Bout of Higher versus Lower Load Resistance Exercise in Previously Trained Men.
NRAP reduction rescues sarcomere defects in nebulin-related nemaline myopathy.
Evolutionary isolation of ryanodine receptor isoform 1 for muscle-based thermogenesis in mammals.
The "normal" adjustment of oxygen delivery to small muscle mass exercise is not optimized for muscle contractile function.
Physiologically-obtainable polyphenol exposures modulate reactive oxygen and nitrogen species signaling in the C2C12 model of skeletal muscle ageing.
Intramuscular lipid utilisation during exercise: A systematic review, meta-analysis and meta-regression.
Triterpenoid CDDO-EA inhibits lipopolysaccharide-induced inflammatory responses in skeletal muscle cells through suppression of NF-κB.
Inhibiting myostatin signaling partially mitigates structural and functional adaptations to hindlimb suspension in mice.
Early Stage Alzheimer's Disease: Are Skeletal Muscle and Exercise the Key?
PGC-1α senses the CBC of pre-mRNA to dictate the fate of promoter-proximally paused RNAPII.
High-Intensity Exercise Training Alters the Effect of N-Acetylcysteine on Exercise-Related Muscle Ionic Shifts in Men.
Targeting ryanodine receptors to treat human diseases.
The Contribution of Tumor Derived Exosomes to Cancer Cachexia.
Tangeretin alleviates Tunicamycin-induced endoplasmic reticulum stress and associated complications in skeletal muscle cells.
Mitochondrial stress and mitokines in aging.
FOXO1 represses PPARα-Mediated induction of FGF21 gene expression.
Genome-wide RNA polymerase stalling shapes the transcriptome during aging.
Endurance training changes the expression of miR-1 and miR-133 and predicted genes in slow and fast twitch muscles.

Mol Metab. 2023 Jan 13. pii: S2212-8778(23)00004-2. [Epub ahead of print] 101670

Loss of skeletal muscle estrogen related receptors leads to severe exercise intolerance.

Jean-Sébastien Wattez, Elodie Eury, Bethany C Hazen, Alexa Wade, Sarah Chau, Shu-Ching Ou, Aaron P Russell, Yoshitake Cho, Anastasia Kralli.

   OBJECTIVE: Skeletal muscle oxidative capacity is central to physical activity, exercise capacity and whole-body metabolism. The three estrogen related receptors (ERRs) are regulators of oxidative metabolism in many cell types, yet their roles in skeletal muscle remain unclear. The main aim of this study was to compare the relative contributions of ERRs to oxidative capacity in glycolytic and oxidative muscle, and to determine defects associated with loss of skeletal muscle ERR function.
METHODS: We assessed ERR expression, generated mice lacking one or two ERRs specifically in skeletal muscle and compared the effects of ERR loss on the transcriptomes of EDL (predominantly glycolytic) and soleus (oxidative) muscles. We also determined the consequences of the loss of ERRs for exercise capacity and energy metabolism in mice with the most severe loss of ERR activity.
RESULTS: ERRs are induced in skeletal muscle in response to an exercise bout. Mice lacking both ERRα and ERRγ (ERRα/γ dmKO) had the broadest and most dramatic disruption in skeletal muscle gene expression. The most affected pathway was "mitochondrial function", in particular Oxphos and TCA cycle genes, and transcriptional defects were more pronounced in the glycolytic EDL than the oxidative soleus. Mice lacking ERRβ and ERRγ, the two isoforms expressed highly in oxidative muscles, also exhibited defects in lipid and branch chain amino acid metabolism genes, specifically in the soleus. The pronounced disruption of oxidative metabolism in ERRα/γ dmKO mice led to pale muscles, decreased oxidative capacity, histochemical patterns reminiscent of minicore myopathies, and severe exercise intolerance, with the dmKO mice unable to switch to lipid utilization upon running. ERRα/γ dmKO mice showed no defects in whole-body glucose and energy homeostasis.
CONCLUSIONS: Our findings define gene expression programs in skeletal muscle that depend on different combinations of ERRs, and establish a central role for ERRs in skeletal muscle oxidative metabolism and exercise capacity. Our data reveal a high degree of functional redundancy among muscle ERR isoforms for the protection of oxidative capacity, and show that ERR isoform-specific phenotypes are driven in part, but not exclusively, by their relative levels in different muscles.

Keywords:  Estrogen related receptor (ERR); Exercise capacity; Exercise intolerance; Mitochondrial oxidative metabolism; Multi-minicore myopathy; Skeletal muscle

DOI:  https://doi.org/10.1016/j.molmet.2023.101670
Cells. 2023 Jan 07. pii: 249. [Epub ahead of print]12(2):

Age-Related Dysfunction in Proteostasis and Cellular Quality Control in the Development of Sarcopenia.

Hector G Paez, Christopher R Pitzer, Stephen E Alway.

  Sarcopenia is a debilitating skeletal muscle disease that accelerates in the last decades of life and is characterized by marked deficits in muscle strength, mass, quality, and metabolic health. The multifactorial causes of sarcopenia have proven difficult to treat and involve a complex interplay between environmental factors and intrinsic age-associated changes. It is generally accepted that sarcopenia results in a progressive loss of skeletal muscle function that exceeds the loss of mass, indicating that while loss of muscle mass is important, loss of muscle quality is the primary defect with advanced age. Furthermore, preclinical models have suggested that aged skeletal muscle exhibits defects in cellular quality control such as the degradation of damaged mitochondria. Recent evidence suggests that a dysregulation of proteostasis, an important regulator of cellular quality control, is a significant contributor to the aging-associated declines in muscle quality, function, and mass. Although skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) plays a critical role in cellular control, including skeletal muscle hypertrophy, paradoxically, sustained activation of mTORC1 recapitulates several characteristics of sarcopenia. Pharmaceutical inhibition of mTORC1 as well as caloric restriction significantly improves muscle quality in aged animals, however, the mechanisms controlling cellular proteostasis are not fully known. This information is important for developing effective therapeutic strategies that mitigate or prevent sarcopenia and associated disability. This review identifies recent and historical understanding of the molecular mechanisms of proteostasis driving age-associated muscle loss and suggests potential therapeutic interventions to slow or prevent sarcopenia.

Keywords:  aging; anabolic resistance; atrophy; autophagy; caloric restriction; dynapenia; mTORC1; mitochondria; mitophagy; muscle protein synthesis; rapamycin; sarcopenia; skeletal muscle; ubiquitin proteasome

DOI:  https://doi.org/10.3390/cells12020249
Biochem Biophys Res Commun. 2023 Jan 11. pii: S0006-291X(23)00046-3. [Epub ahead of print]644 155-161

Carboxyl-terminal modulator protein (CTMP) deficiency mitigates denervation-induced skeletal muscle atrophy.

Junmei Wang, Lydia Tierney, Christopher Wilson, Victoria Phillips, Lillian Goldman, Christen Mumaw, En Muang, Chandler L Walker.

  Denervated skeletal muscles show decreased Akt activity and phosphorylation, resulting in atrophy. Akt inhibits downstream transcription of atrophy-associated ubiquitin ligases like muscle ring-finger protein 1 (MuRF-1). In addition, reduced Akt signaling contributes to aberrant protein synthesis in muscles. In ALS mice, we recently found that carboxyl-terminator modulator protein (CTMP) expression is increased and correlated with reduced Akt signaling in atrophic skeletal muscle. CTMP has also been implicated in promoting muscle degeneration and catabolism in an in vitro muscle atrophy model. The present study examined whether sciatic nerve injury (SNI) stimulated CTMP expression in denervated skeletal muscle during muscle atrophy. We hypothesized that CTMP deficiency would reduce neurogenic atrophy and reverse Akt signaling downregulation. Compared to the unaffected contralateral muscle, wild-type (WT) gastrocnemius muscle had a significant increase in CTMP (p < 0.05). Furthermore, denervated CTMP knockout (CTMP-KO) gastrocnemius weighed more than WT muscle (p < 0.05). Denervated CTMP-KO gastrocnemius also showed higher Akt and downstream glycogen synthase kinase 3β (GSK3β) phosphorylation compared to WT muscle (p < 0.05) as well as ribosomal proteins S6 and 4E-BP1 phosphorylation (p < 0.001 and p < 0.05, respectively). Moreover, CTMP-KO mice showed significantly lower levels of E3 ubiquitin ligase MuRF-1 and myostatin than WT muscle (p < 0.05). Our findings suggest that CTMP is essential to muscle atrophy after denervation and it may act by reducing Akt signaling, protein synthesis, and increasing myocellular catabolism.

Keywords:  Akt signaling; CTMP; Denervation; Muscle atrophy; Nerve injury

DOI:  https://doi.org/10.1016/j.bbrc.2023.01.023
PLoS One. 2023 ;18(1): e0280527

Decrease in the expression of muscle-specific miRNAs, miR-133a and miR-1, in myoblasts with replicative senescence.

Kaori Shintani-Ishida, Riko Tsurumi, Hiroshi Ikegaya.

Muscles that are injured or atrophied by aging undergo myogenic regeneration. Although myoblasts play a pivotal role in myogenic regeneration, their function is impaired with aging. MicroRNAs (miRNAs) are also involved in myogenic regeneration. MiRNA (miR)-1 and miR-133a are muscle-specific miRNAs that control the proliferation and differentiation of myoblasts. In this study, we determined whether miR-1 and miR-133a expression in myoblasts is altered with cellular senescence and involved in senescence-impaired myogenic differentiation. C2C12 murine skeletal myoblasts were converted to a replicative senescent state by culturing to a high passage number. Although miR-1 and miR-133a expression was largely induced during myogenic differentiation, expression was suppressed in cells at high passage numbers (passage 10 and/or passage 20). Although the senescent myoblasts exhibited a deterioration of myogenic differentiation, transfection of miR-1 or miR-133a into myoblasts ameliorated cell fusion. Treatment with the glutaminase 1 inhibitor, BPTES, removed senescent cells from C2C12 myoblasts with a high passage number, whereas myotube formation and miR-133a expression was increased. In addition, primary cultured myoblasts prepared from aged C57BL/6J male mice (20 months old) exhibited a decrease in miR-1 and miR-133a levels compared with younger mice (3 months old). The results suggest that replicative senescence suppresses muscle-specific miRNA expression in myoblasts, which contributes to the senescence-related dysfunction of myogenic regeneration.

DOI: https://doi.org/10.1371/journal.pone.0280527
Adv Mater. 2023 Jan 17. e2207443

Bioengineered 3D Skeletal Muscle Model Reveals Complement 4b as a Cell-Autonomous Mechanism of Impaired Regeneration with Aging.

Kai Wang, Stephen H Smith, Hirotaka Iijima, Zachary R Hettinger, Adarsh Mallepally, Sanjeev G Shroff, Fabrisia Ambrosio.

  A mechanistic understanding of cell-autonomous skeletal muscle changes after injuries can lead to novel interventions to improve functional recovery in an aged population. However, major gaps in our understanding persist owing to limitations of commonly used biological aging models. Two-dimensional cell culture represents an artificial environment, while aging mammalian models are contaminated by influences from non-muscle cells and other organs. We created a three-dimensional muscle aging system to overcome the limitations of these traditional platforms. Here, we first show that old muscle constructs (OMC) manifest a sarcopenic phenotype, as evidenced by hypotrophic myotubes, reduced contractile function, and decreased regenerative capacity compared to young muscle constructs (YMC). OMC also phenocopy the regenerative responses of aged muscle to two interventions, pharmacological and biological. Next, interrogation of muscle cell-specific mechanisms that contribute to impaired regeneration over time reveals that an aging-induced increase of complement component 4b (C4b) delays muscle progenitor cell amplification and impairs functional recovery. However, administration of complement factor I, a C4b inactivator, improves muscle regeneration in vitro and in vivo, indicating C4b inhibition may be a novel approach to enhance aged muscle repair. Collectively, our model exhibits capabilities to study cell-autonomous changes in skeletal muscle during aging, regeneration, and intervention. This article is protected by copyright. All rights reserved.

Keywords:  Biomimetic muscle models; drug testing; inflammation; muscle stem cells; skeletal muscle aging

DOI:  https://doi.org/10.1002/adma.202207443
Proc Natl Acad Sci U S A. 2023 Jan 24. 120(4): e2218032120

Sarcopenia phenotype and impaired muscle function in male mice with fast-twitch muscle-specific knockout of the androgen receptor.

Tatsuya Hosoi, Mitsutaka Yakabe, Hiroko Sasakawa, Takayoshi Sasako, Kohjiro Ueki, Shigeaki Kato, Suzumi M Tokuoka, Yoshiya Oda, Masahiro Abe, Toshio Matsumoto, Masahiro Akishita, Sumito Ogawa.

  Sarcopenia is distinct from normal muscle atrophy in that it is closely related to a shift in the muscle fiber type. Deficiency of the anabolic action of androgen on skeletal muscles is associated with sarcopenia; however, the function of the androgen receptor (AR) pathway in sarcopenia remains poorly understood. We generated a mouse model (fast-twitch muscle-specific AR knockout [fmARKO] mice) in which the AR was selectively deleted in the fast-twitch muscle fibers. In young male mice, the deletion caused no change in muscle mass, but it reduced muscle strength and fatigue resistance and induced a shift in the soleus muscles from fast-twitch fibers to slow-twitch fibers (14% increase, P = 0.02). After middle age, with the control mice, the male fmARKO mice showed much less muscle function, accompanied by lower hindlimb muscle mass; this phenotype was similar to the progression of sarcopenia. The bone mineral density of the femur was significantly reduced in the fmARKO mice, indicating possible osteosarcopenia. Microarray and gene ontology analyses revealed that in male fmARKO mice, there was downregulation of polyamine biosynthesis-related geneswhich was confirmed by liquid chromatography-tandem mass spectrometry assay and the primary cultured myofibers. None of the AR deletion-related phenotypes were observed in female fmARKO mice. Our findings showed that the AR pathway had essential muscle type- and sex-specific roles in the differentiation toward fast-twitch fibers and in the maintenance of muscle composition and function. The AR in fast-twitch muscles was the dominant regulator of muscle fiber-type composition and muscle function, including the muscle-bone relationship.

Keywords:  androgen; androgen receptor; fast-twitch muscle; polyamine; sarcopenia

DOI:  https://doi.org/10.1073/pnas.2218032120
Antioxidants (Basel). 2023 Jan 09. pii: 151. [Epub ahead of print]12(1):

Quantitative Proteomics Identifies Novel Nrf2-Mediated Adaptative Signaling Pathways in Skeletal Muscle Following Exercise Training.

Anjali Bhat, Rafay Abu, Sankarasubramanian Jagadesan, Neetha Nanoth Vellichirammal, Ved Vasishtha Pendyala, Li Yu, Tara L Rudebush, Chittibabu Guda, Irving H Zucker, Vikas Kumar, Lie Gao.

  Exercise training (ExT) improves skeletal muscle health via multiple adaptative pathways. Nrf2 is a principal antioxidant transcription factor responsible for maintaining intracellular redox homeostasis. In this study, we hypothesized that Nrf2 is essential for adaptative responses to ExT and thus beneficial for muscle. Experiments were carried out on male wild type (WT) and iMS-Nrf2flox/flox inducible muscle-specific Nrf2 (KO) mice, which were randomly assigned to serve as sedentary controls (Sed) or underwent 3 weeks of treadmill ExT thus generating four groups: WT-Sed, WT-ExT, KO-Sed, and KO-ExT groups. Mice were examined for exercise performance and in situ tibialis anterior (TA) contractility, followed by mass spectrometry-based proteomics and bioinformatics to identify differentially expressed proteins and signaling pathways. We found that maximal running distance was significantly longer in the WT-ExT group compared to the WT-Sed group, whereas this capacity was impaired in KO-ExT mice. Force generation and fatigue tolerance of the TA were enhanced in WT-ExT, but reduced in KO-ExT, compared to Sed controls. Proteomic analysis further revealed that ExT upregulated 576 proteins in WT but downregulated 207 proteins in KO mice. These proteins represent pathways in redox homeostasis, mitochondrial respiration, and proteomic adaptation of muscle to ExT. In summary, our data suggest a critical role of Nrf2 in the beneficial effects of SkM and adaptation to ExT.

Keywords:  Nrf2; exercise; proteomics; skeletal muscle

DOI:  https://doi.org/10.3390/antiox12010151
Function (Oxf). 2023 ;4(1): zqac068

Challenging Dogma about Myonuclei Behavior in Skeletal Muscle Cells.

Espen E Spangenburg.

DOI: https://doi.org/10.1093/function/zqac068
Antioxidants (Basel). 2022 Dec 26. pii: 44. [Epub ahead of print]12(1):

Potential Therapeutic Strategies for Skeletal Muscle Atrophy.

Li Huang, Ming Li, Chunyan Deng, Jiayi Qiu, Kexin Wang, Mengyuan Chang, Songlin Zhou, Yun Gu, Yuntian Shen, Wei Wang, Ziwei Huang, Hualin Sun.

  The maintenance of muscle homeostasis is vital for life and health. Skeletal muscle atrophy not only seriously reduces people's quality of life and increases morbidity and mortality, but also causes a huge socioeconomic burden. To date, no effective treatment has been developed for skeletal muscle atrophy owing to an incomplete understanding of its molecular mechanisms. Exercise therapy is the most effective treatment for skeletal muscle atrophy. Unfortunately, it is not suitable for all patients, such as fractured patients and bedridden patients with nerve damage. Therefore, understanding the molecular mechanism of skeletal muscle atrophy is crucial for developing new therapies for skeletal muscle atrophy. In this review, PubMed was systematically screened for articles that appeared in the past 5 years about potential therapeutic strategies for skeletal muscle atrophy. Herein, we summarize the roles of inflammation, oxidative stress, ubiquitin-proteasome system, autophagic-lysosomal pathway, caspases, and calpains in skeletal muscle atrophy and systematically expound the potential drug targets and therapeutic progress against skeletal muscle atrophy. This review focuses on current treatments and strategies for skeletal muscle atrophy, including drug treatment (active substances of traditional Chinese medicine, chemical drugs, antioxidants, enzyme and enzyme inhibitors, hormone drugs, etc.), gene therapy, stem cell and exosome therapy (muscle-derived stem cells, non-myogenic stem cells, and exosomes), cytokine therapy, physical therapy (electroacupuncture, electrical stimulation, optogenetic technology, heat therapy, and low-level laser therapy), nutrition support (protein, essential amino acids, creatine, β-hydroxy-β-methylbutyrate, and vitamin D), and other therapies (biomaterial adjuvant therapy, intestinal microbial regulation, and oxygen supplementation). Considering many treatments have been developed for skeletal muscle atrophy, we propose a combination of proper treatments for individual needs, which may yield better treatment outcomes.

Keywords:  cytokine therapy; drug treatment; gene therapy; skeletal muscle atrophy; stem cell therapy

DOI:  https://doi.org/10.3390/antiox12010044
Antioxidants (Basel). 2022 Dec 25. pii: 39. [Epub ahead of print]12(1):

Exercise Training and Skeletal Muscle Antioxidant Enzymes: An Update.

Scott K Powers, Erica Goldstein, Matthew Schrager, Li Li Ji.

  The pivotal observation that muscular exercise is associated with oxidative stress in humans was first reported over 45 years ago. Soon after this landmark finding, it was discovered that contracting skeletal muscles produce oxygen radicals and other reactive species capable of oxidizing cellular biomolecules. Importantly, the failure to eliminate these oxidant molecules during exercise results in oxidation of cellular proteins and lipids. Fortuitously, muscle fibers and other cells contain endogenous antioxidant enzymes capable of eliminating oxidants. Moreover, it is now established that several modes of exercise training (e.g., resistance exercise and endurance exercise) increase the expression of numerous antioxidant enzymes that protect myocytes against exercise-induced oxidative damage. This review concisely summarizes the impact of endurance, high-intensity interval, and resistance exercise training on the activities of enzymatic antioxidants within skeletal muscles in humans and other mammals. We also discuss the evidence that exercise-induced up-regulation of cellular antioxidants reduces contraction-induced oxidative damage in skeletal muscles and has the potential to delay muscle fatigue and improve exercise performance. Finally, in hopes of stimulating further research, we also discuss gaps in our knowledge of exercise-induced changes in muscle antioxidant capacity.

Keywords:  endurance exercise; high-intensity interval training; oxidative stress; resistance exercise

DOI:  https://doi.org/10.3390/antiox12010039
J Gen Physiol. 2023 Feb 06. pii: e202213208. [Epub ahead of print]155(2):

Eccentric contraction-induced strength loss in dystrophin-deficient muscle: Preparations, protocols, and mechanisms.

Leonit Kiriaev, Cory W Baumann, Angus Lindsay.

The absence of dystrophin hypersensitizes skeletal muscle of lower and higher vertebrates to eccentric contraction (ECC)-induced strength loss. Loss of strength can be accompanied by transient and reversible alterations to sarcolemmal excitability and disruption, triad dysfunction, and aberrations in calcium kinetics and reactive oxygen species production. The degree of ECC-induced strength loss, however, appears dependent on several extrinsic and intrinsic factors such as vertebrate model, skeletal muscle preparation (in vivo, in situ, or ex vivo), skeletal muscle hierarchy (single fiber versus whole muscle and permeabilized versus intact), strength production, fiber branching, age, and genetic background, among others. Consistent findings across research groups show that dystrophin-deficient fast(er)-twitch muscle is hypersensitive to ECCs relative to wildtype muscle, but because preparations are highly variable and sensitivity to ECCs are used repeatedly to determine efficacy of many preclinical treatments, it is critical to evaluate the impact of skeletal muscle preparations on sensitivity to ECC-induced strength loss in dystrophin-deficient skeletal muscle. Here, we review and discuss variations in skeletal muscle preparations to evaluate the factors responsible for variations and discrepancies between research groups. We further highlight that dystrophin-deficiency, or loss of the dystrophin-glycoprotein complex in skeletal muscle, is not a prerequisite for accelerated strength loss-induced by ECCs.

DOI: https://doi.org/10.1085/jgp.202213208
Gene. 2023 Jan 11. pii: S0378-1119(23)00034-3. [Epub ahead of print]857 147193

The Mef2c/AdipoR1 axis is responsible for myogenic differentiation and is regulated by resistin in skeletal muscles.

Fengyun Wen, Junjie Hou, Xiang Ji, Xiaoran Chu, Xiaoping Liu, Zhuoyan Shi, Zhen Song.

  Previous studies have shown that accumulated lipid and insulin resistance emerges in skeletal muscle after the onset of obesity and diabetes. We have previously shown that resistin significantly increases lipid contents in C2C12 cells. However, studies evaluating the effects of resistin on skeletal muscle cells and tissues are limited; despite that, an understanding of resistin action and function on lipid alteration in skeletal muscle tissues is critical for understanding obesity-related diseases. In this study, we document that resistin increases lipid deposition both in vitro and in vivo. Further, resistin promotes fiber type transformation, decreases enzyme activities, inhibits myogenic differentiation, and decreases muscle grip and excise endurance. In addition, adiponectin signaling is activated during myocyte differentiation, but it is inhibited at elevated resistin concentrations. Mechanistic investigation revealed that mef2c is responsible for adiponectin signaling pathway inhibition by inhibiting adipoR1 expression at the transcriptional level. In conclusion, this is the first study to document that resistin increases ectopic lipid deposition in skeletal muscles via a mef2c-adipoR1 signaling pathway, which reveals for the first time the presence of crosstalk between resistin and adiponectin in skeletal muscles.

Keywords:  Adiponectin receptor; Mef2; Myogenic differentiation; Resisitin

DOI:  https://doi.org/10.1016/j.gene.2023.147193
Cells. 2023 Jan 09. pii: 263. [Epub ahead of print]12(2):

Skeletal Muscle DNA Methylation and mRNA Responses to a Bout of Higher versus Lower Load Resistance Exercise in Previously Trained Men.

Casey L Sexton, Joshua S Godwin, Mason C McIntosh, Bradley A Ruple, Shelby C Osburn, Blake R Hollingsworth, Nicholas J Kontos, Philip J Agostinelli, Andreas N Kavazis, Tim N Ziegenfuss, Hector L Lopez, Ryan Smith, Kaelin C Young, Varun B Dwaraka, Andrew D Frugé, Christopher B Mobley, Adam P Sharples, Michael D Roberts.

  We sought to determine the skeletal muscle genome-wide DNA methylation and mRNA responses to one bout of lower load (LL) versus higher load (HL) resistance exercise. Trained college-aged males (n = 11, 23 ± 4 years old, 4 ± 3 years self-reported training) performed LL or HL bouts to failure separated by one week. The HL bout (i.e., 80 Fail) consisted of four sets of back squats and four sets of leg extensions to failure using 80% of participants estimated one-repetition maximum (i.e., est. 1-RM). The LL bout (i.e., 30 Fail) implemented the same paradigm with 30% of est. 1-RM. Vastus lateralis muscle biopsies were collected before, 3 h, and 6 h after each bout. Muscle DNA and RNA were batch-isolated and analyzed using the 850k Illumina MethylationEPIC array and Clariom S mRNA microarray, respectively. Performed repetitions were significantly greater during the 30 Fail versus 80 Fail (p < 0.001), although total training volume (sets × reps × load) was not significantly different between bouts (p = 0.571). Regardless of bout, more CpG site methylation changes were observed at 3 h versus 6 h post exercise (239,951 versus 12,419, respectively; p < 0.01), and nuclear global ten-eleven translocation (TET) activity, but not global DNA methyltransferase activity, increased 3 h and 6 h following exercise regardless of bout. The percentage of genes significantly altered at the mRNA level that demonstrated opposite DNA methylation patterns was greater 3 h versus 6 h following exercise (~75% versus ~15%, respectively). Moreover, high percentages of genes that were up- or downregulated 6 h following exercise also demonstrated significantly inversed DNA methylation patterns across one or more CpG sites 3 h following exercise (65% and 82%, respectively). While 30 Fail decreased DNA methylation across various promoter regions versus 80 Fail, transcriptome-wide mRNA and bioinformatics indicated that gene expression signatures were largely similar between bouts. Bioinformatics overlay of DNA methylation and mRNA expression data indicated that genes related to "Focal adhesion," "MAPK signaling," and "PI3K-Akt signaling" were significantly affected at the 3 h and 6 h time points, and again this was regardless of bout. In conclusion, extensive molecular profiling suggests that post-exercise alterations in the skeletal muscle DNA methylome and mRNA transcriptome elicited by LL and HL training bouts to failure are largely similar, and this could be related to equal volumes performed between bouts.

Keywords:  DNA methylation; resistance exercise; training volume; transcriptomics

DOI:  https://doi.org/10.3390/cells12020263
Hum Mol Genet. 2023 Jan 20. pii: ddad011. [Epub ahead of print]

NRAP reduction rescues sarcomere defects in nebulin-related nemaline myopathy.

Jennifer G Casey, Euri S Kim, Remi Joseph, Frank Li, Henk Granzier, Vandana A Gupta.

Nemaline myopathy is a rare neuromuscular disorder associated with congenital or childhood-onset of skeletal muscle weakness and hypotonia that results in limited motor function. Nemaline myopathy is a genetic disorder and mutations in 12 genes are known to contribute to autosomal dominant or recessive forms of the disease. Recessive mutations in nebulin (NEB) are the most common cause of nemaline myopathy affecting about 50% of patients. Due to the large size of the NEB gene and lack of mutational hot spots, developing therapies that can benefit a wide group of patients is challenging. Although there are several promising therapies under investigation, there is no cure for nemaline myopathy. Therefore, targeting disease modifiers that can stabilize or improve skeletal muscle function may represent alternative therapeutic strategies. Our studies have identified Nrap upregulation in nebulin deficiency that contributes to structural and functional deficits in nemaline myopathy. We show that genetic ablation of nrap in nebulin deficiency restored sarcomeric disorganization, reduced protein aggregates and improved skeletal muscle function in zebrafish. Our findings suggest that Nrap is a disease modifier that affects skeletal muscle structure and function in nemaline myopathy, thus therapeutic targeting of Nrap in nebulin related nemaline myopathy and related diseases may be beneficial for patients.

DOI: https://doi.org/10.1093/hmg/ddad011
Proc Natl Acad Sci U S A. 2023 Jan 24. 120(4): e2117503120

Evolutionary isolation of ryanodine receptor isoform 1 for muscle-based thermogenesis in mammals.

Daniel P Singh, Luke Pearce, Rocky H Choi, Aldo Meizoso-Huesca, Stefan G Wette, John W Scott, Cedric R Lamboley, Robyn M Murphy, Bradley S Launikonis.

  Resting skeletal muscle generates heat for endothermy in mammals but not amphibians, while both use the same Ca2+-handling proteins and membrane structures to conduct excitation-contraction coupling apart from having different ryanodine receptor (RyR) isoforms for Ca2+ release. The sarcoplasmic reticulum (SR) generates heat following Adenosine triphosphate (ATP) hydrolysis at the Ca2+ pump, which is amplified by increasing RyR1 Ca2+ leak in mammals, subsequently increasing cytoplasmic [Ca2+] ([Ca2+]cyto). For thermogenesis to be functional, rising [Ca2+]cyto must not interfere with cytoplasmic effectors of the sympathetic nervous system (SNS) that likely increase RyR1 Ca2+ leak; nor should it compromise the muscle remaining relaxed. To achieve this, Ca2+ activated, regenerative Ca2+ release that is robust in lower vertebrates needs to be suppressed in mammals. However, it has not been clear whether: i) the RyR1 can be opened by local increases in [Ca2+]cyto; and ii) downstream effectors of the SNS increase RyR Ca2+ leak and subsequently, heat generation. By positioning amphibian and malignant hyperthermia-susceptible human-skinned muscle fibers perpendicularly, we induced abrupt rises in [Ca2+]cyto under identical conditions optimized for activating regenerative Ca2+ release as Ca2+ waves passed through the junction of fibers. Only mammalian fibers showed resistance to rising [Ca2+]cyto, resulting in increased SR Ca2+ load and leak. Fiber heat output was increased by cyclic adenosine monophosphate (cAMP)-induced RyR1 phosphorylation at Ser2844 and Ca2+ leak, indicating likely SNS regulation of thermogenesis. Thermogenesis occurred despite the absence of SR Ca2+ pump regulator sarcolipin. Thus, evolutionary isolation of RyR1 provided increased dynamic range for thermogenesis with sensitivity to cAMP, supporting endothermy.

Keywords:  calcium; mammals; ryanodine receptor; skeletal muscle; thermogenesis

DOI:  https://doi.org/10.1073/pnas.2117503120
J Physiol. 2023 Jan 16.

The "normal" adjustment of oxygen delivery to small muscle mass exercise is not optimized for muscle contractile function.

P J Drouin, T Liu, L A Lew, E McGarity-Shipley, M E Tschakovsky.

   KEY POINTS: Oxygen delivery is viewed as tightly coupled to demand in exercise below critical power because increasing oxygen delivery does not increase the rate of oxygen uptake. Whether the "normal" adjustment of oxygen delivery in small muscle mass exercise below critical power is optimal for excitation-contraction coupling is not known. Here we show in humans that increasing oxygen delivery above "normal" improves excitation-contraction coupling. These results suggest that, in the heavy exercise intensity domain, the "normal" matching of oxygen delivery to metabolic demand is not optimal for muscle excitation-contraction coupling. Therefore, the nature of vasoregulation in exercising muscle is such that it does not support optimal perfusion for excitation-contraction coupling.
ABSTRACT: Oxygen delivery is viewed as tightly coupled to demand in exercise below critical power because increasing oxygen delivery does not increase VO2 . However, whether the "normal" adjustment of oxygen delivery to small muscle mass exercise in the heavy intensity domain is optimal for excitation-contraction coupling is currently unknown. In 20 participants (10 female), a remote skeletal muscle (i.e., tibialis anterior) metaboreflex was (Hyperperfusion condition) or was not (control condition) activated for 4-min during both force of contraction (experimental model 1) and muscle activation targeted (experimental model 2) rhythmic forearm handgrip exercise. Analysis was completed on the combined data from both experimental models. After 30-sec of remote skeletal muscle metaboreflex activation, mean arterial blood pressure, forearm blood flow, and muscle oxygenation were increased and remained increased until metaboreflex discontinuation. While oxygen delivery was elevated, the muscle activation to force of contraction ratio was improved. Upon metaboreflex discontinuation, forearm oxygen delivery and the muscle activation and force of contraction ratio was rapidly (within 30-sec) returned to control levels. These findings demonstrate that (a) the metaboreflex was effective at increasing forearm muscle oxygen delivery and oxygenation, (b) the muscle activation to force of contraction ratio was improved with increased oxygen delivery, and (c) in the heavy exercise intensity domain, the normal matching of oxygen delivery to metabolic demand is not optimal for muscle excitation-contraction coupling. These results suggest that the nature of vasoregulation in exercising muscle is such that it does not support optimal perfusion for excitation-contraction coupling. Abstract figure legend Purpose: To test the hypothesis that the "normal" adjustment of oxygen delivery is optimized for muscle contractile function.
METHODOLOGY: In 20 participants (10 female), a remote skeletal muscle (i.e., tibialis anterior) metaboreflex was (Hyperperfusion condition) or was not (Control condition) activated for 4-min during both force of contraction and muscle activation targeted rhythmic forearm handgrip exercise.
RESULTS: Under hyperperfusion conditions, the force of contraction to muscle activation ratio was rapidly improved with increased blood flow above "normal" and then the ratio was rapidly restored to control levels upon restoration of normal blood flow conditions.
CONCLUSION: The nature of vasoregulation in exercising muscle is such that it does not support optimal perfusion for excitation-contraction coupling. This article is protected by copyright. All rights reserved.

Keywords:  blood flow; contraction force; excitation-contraction coupling; hyperperfusion; metaboreflex; muscle activation; oxygen delivery demand matching; vasoregulation

DOI:  https://doi.org/10.1113/JP283933
Eur J Pharmacol. 2023 Jan 14. pii: S0014-2999(23)00022-5. [Epub ahead of print]941 175511

Physiologically-obtainable polyphenol exposures modulate reactive oxygen and nitrogen species signaling in the C2C12 model of skeletal muscle ageing.

Nathan Hayes, Mark Fogarty, Laura Sadofsky, Huw Simon Jones.

  Age-related frailty is a significant health and social care burden, with limited treatment options. There is a lack of suitable cell culture model for screening large numbers of test compounds to identify those which promote healthy skeletal muscle function. This paper describes the characterization of reactive oxygen and nitrogen species (RONS) signalling changes in young and aged myoblasts and myotubes using C2C12 cells, and the application of aged cultures to assess the effect of dietary polyphenols on RONS signalling. Aged myoblasts and myotubes showed significantly increased reactive oxygen species (p < 0.01 and p < 0.001 respectively), nitric oxide (p < 0.05 for myoblasts and myotubes), and lipid peroxidation (p < 0.05 for myoblasts and myotubes). Nine polyphenols were assessed in aged myoblasts and myotubes using concentrations and incubation times consistent with known pharmacokinetic parameters for these compounds. Although several polyphenols were seen to reduce single markers of RONS signalling, only kaempferol and resveratrol significantly reduced multiple markers in both cell models. Modulation of enzymatic antioxidant activities was assessed as a possible mechanism of action, although superoxide dismutase and catalase activities were significantly reduced in aged (versus young) myotubes (p < 0.01 and p < 0.05 respectively), no effect of polyphenol treatment on these enzyme activities were observed. Overall, this research has shown the utility of the C2C12 model (myoblasts and myotubes) for screening compounds in aged muscle, and that resveratrol and kaempferol (using pharmacokinetically-informed exposures) can modulate RONS signalling in skeletal muscle cells after an acute exposure.

Keywords:  Dietary polyphenols; Oxidative stress; RONS; Skeletal muscle ageing

DOI:  https://doi.org/10.1016/j.ejphar.2023.175511
J Appl Physiol (1985). 2023 Jan 19.

Intramuscular lipid utilisation during exercise: A systematic review, meta-analysis and meta-regression.

Jayden R Stokie, Gavin Abbott, Kirsten F Howlett, David L Hamilton, Christopher S Shaw.

  Intramuscular lipid (IMCL) utilisation during exercise was controversial as numerous studies did not observe a decline in IMCL content post-exercise was assessed in muscle biopsies using biochemical techniques. Contemporary techniques including immunofluorescence microscopy and 1H-magnetic resonance spectroscopy (1H-MRS) offer advantages over biochemical techniques. The primary aim of this systematic review, meta-analysis and meta-regression was to examine the net degradation of IMCL in response to an acute bout of cycling exercise in humans, as assessed with different analytical approaches. A secondary aim was to explore the factors influencing IMCL degradation including feeding status, exercise variables and participant characteristics. A total of 44 studies met the inclusion criteria using biochemical, immunofluorescence and 1H-MRS techniques. A meta-analysis was completed using a random effects model and percentage change in IMCL content calculated from the standardized mean difference. Cycling exercise resulted in a net degradation of IMCL regardless of technique (total effect -23.7%, 95% CI = -28.7 to -18.7%) and there was no difference when comparing fasted versus fed-state exercise (P > 0.05). IMCL degradation using immunofluorescence techniques detected larger effects in type I fibres compared to whole muscle using biochemical techniques (P = 0.003) and in type I fibres compared to type II fibres (P < 0.001). While IMTG degradation was associated with exercise duration, VO2 max, and BMI, none of these factors independently related to IMTG degradation. These findings provide strong evidence that the analytical approach can influence the assessment of IMCL degradation in human skeletal muscle in response to exercise.

Keywords:  Exercise; Intramuscular Triglyceride; Lipid; Metabolism; Skeletal Muscle

DOI:  https://doi.org/10.1152/japplphysiol.00637.2021
Exp Biol Med (Maywood). 2023 Jan 20. 15353702221139188

Triterpenoid CDDO-EA inhibits lipopolysaccharide-induced inflammatory responses in skeletal muscle cells through suppression of NF-κB.

Phoebe Fang-Mei Chang, Daniel Acevedo, Lawrence J Mandarino, Sara M Reyna.

  Chronic inflammation is a major contributor to the development of obesity-induced insulin resistance, which then can lead to the development of type 2 diabetes (T2D). Skeletal muscle plays a pivotal role in insulin-stimulated whole-body glucose disposal. Therefore, dysregulation of glucose metabolism by inflammation in skeletal muscle can adversely affect skeletal muscle insulin sensitivity and contribute to the pathogenesis of T2D. The mechanism underlying insulin resistance is not well known; however, macrophages are important initiators in the development of the chronic inflammatory state leading to insulin resistance. Skeletal muscle consists of resident macrophages which can be activated by lipopolysaccharide (LPS). These activated macrophages affect myocytes via a paracrine action of pro-inflammatory mediators resulting in secretion of myokines that contribute to inflammation and ultimately skeletal muscle insulin resistance. Therefore, knowing that synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acids (CDDOs) can attenuate macrophage pro-inflammatory responses in chronic disorders, such as cancer and obesity, and that macrophage pro-inflammatory responses can modulate skeletal muscle inflammation, we first examined whether CDDO-ethyl amide (CDDO-EA) inhibited chemokine and cytokine production in macrophages since this had not been reported for CDDO-EA. CDDO-EA blocked LPS-induced tumor necrosis factor-alpha (TNF-α), monocyte chemotactic protein-1 (MCP-1), interleukine-1beta (IL-1β), and interleukine-6 (IL-6) production in RAW 264.7 mouse and THP-1 human macrophages. Although many studies show that CDDOs have anti-inflammatory properties in several tissues and cells, little is known about the anti-inflammatory effects of CDDOs on skeletal muscle. We hypothesized that CDDO-EA protects skeletal muscle from LPS-induced inflammation by blocking nuclear factor kappa B (NF-κB) signaling. Our studies demonstrate that CDDO-EA prevented LPS-induced TNF-α and MCP-1 gene expression by inhibiting the NF-κB signaling pathway in L6-GLUT4myc rat myotubes. Our findings suggest that CDDO-EA suppresses LPS-induced inflammation in macrophages and myocytes and that CDDO-EA is a promising compound as a therapeutic agent for protecting skeletal muscle from inflammation.

Keywords:  Inflammation; insulin resistance; macrophage; nuclear factor kappa B; skeletal muscle cells; triterpenoid

DOI:  https://doi.org/10.1177/15353702221139188
NPJ Microgravity. 2023 Jan 16. 9(1): 2

Inhibiting myostatin signaling partially mitigates structural and functional adaptations to hindlimb suspension in mice.

Andrea M Hanson, Mary H Young, Brooke C Harrison, Xiaolan Zhou, H Q Han, Louis S Stodieck, Virginia L Ferguson.

Novel treatments for muscle wasting are of significant value to patients with disease states that result in muscle weakness, injury recovery after immobilization and bed rest, and for astronauts participating in long-duration spaceflight. We utilized an anti-myostatin peptibody to evaluate how myostatin signaling contributes to muscle loss in hindlimb suspension. Male C57BL/6 mice were left non-suspended (NS) or were hindlimb suspended (HS) for 14 days and treated with a placebo vehicle (P) or anti-myostatin peptibody (D). Hindlimb suspension (HS-P) resulted in rapid and significantly decreased body mass (-5.6% by day 13) with hindlimb skeletal muscle mass losses between -11.2% and -22.5% and treatment with myostatin inhibitor (HS-D) partially attenuated these losses. Myostatin inhibition increased hindlimb strength with no effect on soleus tetanic strength. Soleus mass and fiber CSA were reduced with suspension and did not increase with myostatin inhibition. In contrast, the gastrocnemius showed histological evidence of wasting with suspension that was partially mitigated with myostatin inhibition. While expression of genes related to protein degradation (Atrogin-1 and Murf-1) in the tibialis anterior increased with suspension, these atrogenes were not significantly reduced by myostatin inhibition despite a modest activation of the Akt/mTOR pathway. Taken together, these findings suggest that myostatin is important in hindlimb suspension but also motivates the study of other factors that contribute to disuse muscle wasting. Myostatin inhibition benefitted skeletal muscle size and function, which suggests therapeutic potential for both spaceflight and terrestrial applications.

DOI: https://doi.org/10.1038/s41526-022-00233-4
J Appl Physiol (1985). 2023 Jan 19.

Early Stage Alzheimer's Disease: Are Skeletal Muscle and Exercise the Key?

Matthew H Brisendine, Joshua C Drake.

  Alzheimer's disease (AD) is the most common form of dementia affecting approximately 6.5 million people in the United States alone. The development of AD progresses over a span of years to possible decades before resulting in cognitive impairment and clinically diagnosed AD. The time leading up to a clinical diagnosis is known as the preclinical phase, a time in which recent literature has noted a more severe loss of body mass and more specifically lean muscle mass and strength prior to diagnosis. Mitochondria dysfunction in neurons is also closely associated with AD, and mitochondrial dysfunction has been seen to occur in skeletal muscle with mild cognitive impairment prior to AD manifestation. Evidence from animal models of AD suggest a close link between skeletal muscle mass, mitochondria function, and cognition. Exercise is a powerful stimulus for improving mitochondria function, muscle health, and offers benefits to cognition has been suggested as a possible therapeutic strategy for AD. However, evidence for beneficial effects of exercise in AD afflicted populations and animal models have produced conflicting results. In this mini-review, we discuss these findings and highlight potential avenues for further investigation that may lead to the implementation of exercise as a therapeutic intervention to delay or prevent the development of AD.

Keywords:  alzheimer's disease; exercise; mitochondria; mitophagy; skeletal muscle

DOI:  https://doi.org/10.1152/japplphysiol.00659.2022
Mol Cell. 2023 Jan 19. pii: S1097-2765(22)01179-0. [Epub ahead of print]83(2): 186-202.e11

PGC-1α senses the CBC of pre-mRNA to dictate the fate of promoter-proximally paused RNAPII.

Xavier Rambout, Hana Cho, Roméo Blanc, Qing Lyu, Joseph M Miano, Joe V Chakkalakal, Geoffrey M Nelson, Hari K Yalamanchili, Karen Adelman, Lynne E Maquat.

  PGC-1α is well established as a metazoan transcriptional coactivator of cellular adaptation in response to stress. However, the mechanisms by which PGC-1α activates gene transcription are incompletely understood. Here, we report that PGC-1α serves as a scaffold protein that physically and functionally connects the DNA-binding protein estrogen-related receptor α (ERRα), cap-binding protein 80 (CBP80), and Mediator to overcome promoter-proximal pausing of RNAPII and transcriptionally activate stress-response genes. We show that PGC-1α promotes pausing release in a two-arm mechanism (1) by recruiting the positive transcription elongation factor b (P-TEFb) and (2) by outcompeting the premature transcription termination complex Integrator. Using mice homozygous for five amino acid changes in the CBP80-binding motif (CBM) of PGC-1α that destroy CBM function, we show that efficient differentiation of primary myoblasts to myofibers and timely skeletal muscle regeneration after injury require PGC-1α binding to CBP80. Our findings reveal how PGC-1α activates stress-response gene transcription in a previously unanticipated pre-mRNA quality-control pathway.

Keywords:  CBP80; ERRα; Integrator; Mediator; P-TEFb; PGC-1α; cap-binding complex; gene transcription; interferon signaling; myogenesis; pre-mRNP quality control; promoter-proximal pausing; skeletal muscle regeneration

DOI:  https://doi.org/10.1016/j.molcel.2022.12.022
Antioxidants (Basel). 2022 Dec 27. pii: 53. [Epub ahead of print]12(1):

High-Intensity Exercise Training Alters the Effect of N-Acetylcysteine on Exercise-Related Muscle Ionic Shifts in Men.

Anders K Lemminger, Matteo Fiorenza, Kasper Eibye, Jens Bangsbo, Morten Hostrup.

  This study investigated whether high-intensity exercise training alters the effect of N-acetylcysteine (a precursor of antioxidant glutathione) on exercise-related muscle ionic shifts. We assigned 20 recreationally-active men to 6 weeks of high-intensity exercise training, comprising three weekly sessions of 4-10 × 20-s all-out bouts interspersed by 2 min recovery (SET, n = 10), or habitual lifestyle maintenance (n = 10). Before and after SET, we measured ionic shifts across the working muscle, using leg arteriovenous balance technique, during one-legged knee-extensor exercise to exhaustion with and without N-acetylcysteine infusion. Furthermore, we sampled vastus lateralis muscle biopsies for analyses of metabolites, mitochondrial respiratory function, and proteins regulating ion transport and antioxidant defense. SET lowered exercise-related H+, K+, lactate-, and Na+ shifts and enhanced exercise performance by ≈45%. While N-acetylcysteine did not affect exercise-related ionic shifts before SET, it lowered H+, HCO3-, and Na+ shifts after SET. SET enhanced muscle mitochondrial respiratory capacity and augmented the abundance of Na+/K+-ATPase subunits (α1 and β1), ATP-sensitive K+ channel subunit (Kir6.2), and monocarboxylate transporter-1, as well as superoxide dismutase-2 and glutathione peroxidase-1. Collectively, these findings demonstrate that high-intensity exercise training not only induces multiple adaptations that enhance the ability to counter exercise-related ionic shifts but also potentiates the effect of N-acetylcysteine on ionic shifts during exercise.

Keywords:  NAC; ROS; antioxidant; high-intensity training; lactate; oxygen species; pH; performance; potassium; scavengers

DOI:  https://doi.org/10.3390/antiox12010053
J Clin Invest. 2023 Jan 17. pii: e162891. [Epub ahead of print]133(2):

Targeting ryanodine receptors to treat human diseases.

Andrew R Marks.

This Review provides an update on ryanodine receptors (RyRs) and their role in human diseases of heart, muscle, and brain. Calcium (Ca2+) is a requisite second messenger in all living organisms. From C. elegans to mammals, Ca2+ is necessary for locomotion, bodily functions, and neural activity. However, too much of a good thing can be bad. Intracellular Ca2+ overload can result in loss of function and death. Intracellular Ca2+ release channels evolved to safely provide large, rapid Ca2+ signals without exposure to toxic extracellular Ca2+. RyRs are intracellular Ca2+ release channels present throughout the zoosphere. Over the past 35 years, our knowledge of RyRs has advanced to the level of atomic-resolution structures revealing their role in the mechanisms underlying the pathogenesis of human disorders of heart, muscle, and brain. Stress-induced RyR-mediated intracellular Ca2+ leak in the heart can promote heart failure and cardiac arrhythmias. In skeletal muscle, RyR1 leak contributes to muscle weakness in inherited myopathies, to age-related loss of muscle function and cancer-associated muscle weakness, and to impaired muscle function in muscular dystrophies, including Duchenne. In the brain, leaky RyR channels contribute to cognitive dysfunction in Alzheimer's disease, posttraumatic stress disorder, and Huntington's disease. Novel therapeutics targeting dysfunctional RyRs are showing promise.

DOI: https://doi.org/10.1172/JCI162891
Cells. 2023 Jan 12. pii: 292. [Epub ahead of print]12(2):

The Contribution of Tumor Derived Exosomes to Cancer Cachexia.

Christopher R Pitzer, Hector G Paez, Stephen E Alway.

  Cancer cachexia is defined as unintentional weight loss secondary to neoplasia and is associated with poor prognosis and outcomes. Cancer cachexia associated weight loss affects both lean tissue (i.e., skeletal muscle) and adipose tissue. Exosomes are extracellular vesicles that originate from multivesicular bodies that contain intentionally loaded biomolecular cargo. Exosome cargo includes proteins, lipids, mitochondrial components, and nucleic acids. The cargo carried in exosomes is thought to alter cell signaling when it enters into recipient cells. Virtually every cell type secretes exosomes and exosomes are known to be present in nearly every biofluid. Exosomes alter muscle and adipose tissue metabolism and biological processes, including macrophage polarization and apoptosis which contribute to the development of the cachexia phenotype. This has led to an interest in the role of tumor cell derived exosomes and their potential role as biomarkers of cancer cell development as well as their contribution to cachexia and disease progression. In this review, we highlight published findings that have studied the effects of tumor derived exosomes (and extracellular vesicles) and their cargo on the progression of cancer cachexia. We will focus on the direct effects of tumor derived exosomes and their cellular cross talk on skeletal muscle and adipose tissue, the primary sites of weight loss due to cancer cachexia.

Keywords:  adipocytes; adipose; cachexia; exosomes; extracellular vesicles; inflammation; metabolism; muscle

DOI:  https://doi.org/10.3390/cells12020292
Cell Stress Chaperones. 2023 Jan 19.

Tangeretin alleviates Tunicamycin-induced endoplasmic reticulum stress and associated complications in skeletal muscle cells.

Eveline M Anto, C R Sruthi, Lekshmy Krishnan, K G Raghu, Jayamurthy Purushothaman.

  Endoplasmic reticulum (ER) stress and associated oxidative stress are involved in the genesis and progression of skeletal muscle diseases such as myositis and atrophy or muscle wasting. Targeting the ER stress and associated downstream pathways can aid in the development of better treatment strategies for these diseases with limited therapeutic approaches. There is a growing interest in identifying natural products against ER stress due to the lower toxicity and cost effectiveness. In the present study, we investigated the protective effect of Tangeretin, a citrus methoxyflavone found in citrus peels against Tunicamycin (pharmacological ER stress inducer)-induced ER stress and associated complications in rat skeletal muscle L6 cell lines. Treatment with Tunicamycin for a period of 24 h resulted in the upregulation of ER stress marker proteins, ER resident oxidoreductases and cellular reactive oxygen species (ROS). Co-treatment with Tangeretin was effective in alleviating Tunicamycin-induced ER stress and associated redox-related complications by significantly downregulating the unfolded protein response (UPR), ER resident oxidoreductase proteins, cellular ROS and improving the antioxidant enzyme activity. Tunicamycin also induced upregulation of phosphorylated p38 MAP Kinase and loss of mitochondrial membrane potential. Tangeretin significantly reduced the levels of phosphorylated p38 MAP Kinase and improved the mitochondrial membrane potential. From the results, it is evident that Tangeretin can be explored further as a potential candidate for skeletal muscle diseases involving protein misfolding and ER stress.

Keywords:  ER stress; L6 cell lines; Oxidative stress; Tangeretin; Tunicamycin

DOI:  https://doi.org/10.1007/s12192-023-01322-3
Aging Cell. 2023 Jan 15. e13770

Mitochondrial stress and mitokines in aging.

Johannes Burtscher, Afsaneh Soltany, Nishant P Visavadiya, Martin Burtscher, Grégoire P Millet, Kayvan Khoramipour, Andy V Khamoui.

  Mitokines are signaling molecules that enable communication of local mitochondrial stress to other mitochondria in distant cells and tissues. Among those molecules are FGF21, GDF15 (both expressed in the nucleus) and several mitochondrial-derived peptides, including humanin. Their responsiveness to mitochondrial stress induces mitokine-signaling in response for example to exercise, following mitochondrial challenges in skeletal muscle. Such signaling is emerging as an important mediator of exercise-derived and dietary strategy-related molecular and systemic health benefits, including healthy aging. A compensatory increase in mitokine synthesis and secretion could preserve mitochondrial function and overall cellular vitality. Conversely, resistance against mitokine actions may also develop. Alterations of mitokine-levels, and therefore of mitokine-related inter-tissue cross talk, are associated with general aging processes and could influence the development of age-related chronic metabolic, cardiovascular and neurological diseases; whether these changes contribute to aging or represent "rescue factors" remains to be conclusively shown. The aim of the present review is to summarize the expanding knowledge on mitokines, the potential to modulate them by lifestyle and their involvement in aging and age-related diseases. We highlight the importance of well-balanced mitokine-levels, the preventive and therapeutic properties of maintaining mitokine homeostasis and sensitivity of mitokine signaling but also the risks arising from the dysregulation of mitokines. While reduced mitokine levels may impair inter-organ crosstalk, also excessive mitokine concentrations can have deleterious consequences and are associated with conditions such as cancer and heart failure. Preservation of healthy mitokine signaling levels can be achieved by regular exercise and is associated with an increased lifespan.

Keywords:  FGF21; GDF15; humanin; mitochondria-derived peptides; mitochondrial stress response; mitohormesis; mitokines

DOI:  https://doi.org/10.1111/acel.13770
Biochem Biophys Res Commun. 2023 Jan 06. pii: S0006-291X(23)00024-4. [Epub ahead of print]644 122-129

FOXO1 represses PPARα-Mediated induction of FGF21 gene expression.

Ana Luísa De Sousa-Coelho, Mar Gacias, Brian T O'Neill, Joana Relat, Wolfgang Link, Diego Haro, Pedro F Marrero.

  Fibroblast growth factor 21 (FGF21) has emerged as a metabolic regulator that exerts potent anti-diabetic and lipid-lowering effects in animal models of obesity and type 2 diabetes, showing a protective role in fatty liver disease and hepatocellular carcinoma progression. Hepatic expression of FGF21 is regulated by PPARα and is induced by fasting. Ablation of FoxO1 in liver has been shown to increase FGF21 expression in hyperglycemia. To better understand the role of FOXO1 in the regulation of FGF21 expression we have modified HepG2 human hepatoma cells to overexpress FoxO1 and PPARα. Here we show that FoxO1 represses PPARα-mediated FGF21 induction, and that the repression acts on the FGF21 gene promoter without affecting other PPARα target genes. Additionally, we demonstrate that FoxO1 physically interacts with PPARα and that FoxO1/3/4 depletion in skeletal muscle contributes to increased Fgf21 tissue levels. Taken together, these data indicate that FOXO1 is a PPARα-interacting protein that antagonizes PPARα activity on the FGF21 promoter. Because other PPARα target genes remained unaffected, these results suggest a highly specific mechanism implicated in FGF21 regulation. We conclude that FGF21 can be specifically modulated by FOXO1 in a PPARα-dependent manner.

Keywords:  FGF21; FOXO1; Metabolic diseases; PPARα

DOI:  https://doi.org/10.1016/j.bbrc.2023.01.012
Nat Genet. 2023 Jan 19.

Genome-wide RNA polymerase stalling shapes the transcriptome during aging.

Akos Gyenis, Jiang Chang, Joris J P G Demmers, Serena T Bruens, Sander Barnhoorn, Renata M C Brandt, Marjolein P Baar, Marko Raseta, Kasper W J Derks, Jan H J Hoeijmakers, Joris Pothof.

Gene expression profiling has identified numerous processes altered in aging, but how these changes arise is largely unknown. Here we combined nascent RNA sequencing and RNA polymerase II chromatin immunoprecipitation followed by sequencing to elucidate the underlying mechanisms triggering gene expression changes in wild-type aged mice. We found that in 2-year-old liver, 40% of elongating RNA polymerases are stalled, lowering productive transcription and skewing transcriptional output in a gene-length-dependent fashion. We demonstrate that this transcriptional stress is caused by endogenous DNA damage and explains the majority of gene expression changes in aging in most mainly postmitotic organs, specifically affecting aging hallmark pathways such as nutrient sensing, autophagy, proteostasis, energy metabolism, immune function and cellular stress resilience. Age-related transcriptional stress is evolutionary conserved from nematodes to humans. Thus, accumulation of stochastic endogenous DNA damage during aging deteriorates basal transcription, which establishes the age-related transcriptome and causes dysfunction of key aging hallmark pathways, disclosing how DNA damage functionally underlies major aspects of normal aging.

DOI: https://doi.org/10.1038/s41588-022-01279-6
Arch Gerontol Geriatr. 2023 Jan 11. pii: S0167-4943(23)00009-2. [Epub ahead of print]108 104929

Endurance training changes the expression of miR-1 and miR-133 and predicted genes in slow and fast twitch muscles.

Farid Bahrami, Mohammad Fathi, Hassan Ahmadvand, Naser Pajohi.

   PURPOSE OF THE RESEARCH: Endurance training can modify signaling and gene expression pathways that play a pivotal role in determining the phenotype of the fibers. The present study aimed to investigate the effects of endurance training on the expression of some myomiRs and related genes in slow and fast twitch muscles.
METHODS: Twenty healthy male adult Wistar rats (281 ± 14 g) were randomized to either control (n = 10) or treated (n = 10). The treated group performed an endurance program for eight weeks (running on a treadmill for eight weeks, 50 min, 23 m/min). After the end of the training protocol, the slow (soleus) and fast (EDL) twitch muscles were removed to assess the miR-1, miR-133 expression, and hdac4, mef2c genes, and protein by real-time PCR and western blot, respectively.
RESULTS: The soleus muscle miR-1 expression and mef2c gene in the treated group were significantly lower compared control (p = 0.0001). In contrast, miR-133 and hdac4 gene expression of the soleus muscle of the treated group increased significantly (p = 0001), and the EDL miR-133 and mef2c expression of the treated group increased in the compared control group (p = 0.0001). The EDL MEF2c protein expression in the treated group significantly decreased compared to the control group, although the expression of EDL HDAC4 protein significantly increased (p = 0.0001).
CONCLUSIONS: Endurance training changes the expression of the miR-1, miR-133, and their predicted genes in slow and fast twitch muscles. Also, the rate of HDAC4 and MEF2c protein synthesis, which are upstream and downstream of these myomiRs, was affected by endurance training.

Keywords:  Endurance training; HDAC4; MEF2c; microRNA

DOI:  https://doi.org/10.1016/j.archger.2023.104929