bims-moremu 2024-06-23 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024–06–23
thirty papers selected by
Anna Vainshtein, Craft Science Inc.

Skeletal muscle immobilisation-induced atrophy: mechanistic insights from human studies.
A multimodal exercise countermeasure prevents the negative impact of head-down tilt bed rest on muscle volume and mitochondrial health in older adults.
Exploring the Role of Extracellular Vesicles in Skeletal Muscle Regeneration.
Ulk1 Phosphorylation at S555 is Not Required in Exercise Training-mediated Improvements in Endurance and Metabolic Capacity in Healthy Mice.
Unlocking the Nexus of Sirtuins: A Comprehensive Review of Their Role in Skeletal Muscle Metabolism, Development, and Disorders.
Dual inhibition of P38 MAPK and JNK pathways preserves stemness markers and alleviates premature activation of muscle stem cells during isolation.
Suppressed basal mitophagy drives cellular aging phenotypes that can be reversed by a p62-targeting small molecule.
Spatial proteomics of skeletal muscle using thin cryosections reveals metabolic adaptation at the muscle-tendon transition zone.
Direct and acute effects of advanced glycation end products on proteostasis in isolated mouse skeletal muscle.
Zebrafish as a Human Muscle Model for Studying Age-Dependent Sarcopenia and Frailty.
Lost in translation: challenges of current pharmacotherapy for sarcopenia.
Muscle cofilin alters neuromuscular junction postsynaptic development to strengthen functional neurotransmission.
Muscle-specific lack of GFPT1 in knock-in mice triggers ER stress to alleviate misfolded proteins.
Free essential amino acid feeding improves endurance during resistance training via DRP1-dependent mitochondrial remodelling.
Activation of the ROS/TXNIP/NLRP3 pathway disrupts insulin-dependent glucose uptake in skeletal muscle of insulin-resistant obese mice.
Spatial transcriptomics in embryonic mouse diaphragm muscle reveals regional gradients and subdomains of developmental gene expression.
An Amino Acid Mixture to Counteract Skeletal Muscle Atrophy: Impact on Mitochondrial Bioenergetics.
Characterization of Undiscovered miRNA Involved in Tumor Necrosis Factor Alpha-Induced Atrophy in Mouse Skeletal Muscle Cell Line.
Unilateral hindlimb ischaemia-induced systemic inflammation is associated with non-ischaemic skeletal muscle inflammation.
Biocomputational screening of natural compounds targeting 15-hydroxyprostaglandin dehydrogenase to improve skeletal muscle during aging.
Effects of HMGCR deficiency on skeletal muscle development.
The Development of Robust Antibodies to Sarcospan, a Dystrophin- and Integrin-Associated Protein, for Basic and Translational Research.
A Novel CRISPR-Cas9 Strategy to Target DYSTROPHIN Mutations Downstream of Exon 44 in Patient-Specific DMD iPSCs.
Knockout of Hsp70 genes significantly affects locomotion speed and gene expression in leg skeletal muscles of Drosophila melanogaster.
Bioengineered Model of Human LGMD2B Skeletal Muscle Reveals Roles of Intracellular Calcium Overload in Contractile and Metabolic Dysfunction in Dysferlinopathy.
Mitochondria Transplantation: Rescuing Innate Muscle Bioenergetic Impairment in a Model of Aging and Exercise Intolerance.
Genome-wide Association Study of Exercise-induced Skeletal Muscle Hypertrophy and the Construction of Predictive Model.
Arginine Regulates Skeletal Muscle Fiber Type Formation via mTOR Signaling Pathway.
Adipose Kiss1 controls aerobic exercise-related adaptive responses in adipose tissue energy homeostasis.
Adaptive gene expression of alternative splicing variants of PGC-1α regulates whole-body energy metabolism.

Clin Sci (Lond). 2024 Jun 19. 138(12): 741-756

Skeletal muscle immobilisation-induced atrophy: mechanistic insights from human studies.

Colleen S Deane, Matthew Piasecki, Philip J Atherton.

  Periods of skeletal muscle disuse lead to rapid declines in muscle mass (atrophy), which is fundamentally underpinned by an imbalance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). The complex interplay of molecular mechanisms contributing to the altered regulation of muscle protein balance during disuse have been investigated but rarely synthesised in the context of humans. This narrative review discusses human models of muscle disuse and the ensuing inversely exponential rate of muscle atrophy. The molecular processes contributing to altered protein balance are explored, with a particular focus on growth and breakdown signalling pathways, mitochondrial adaptations and neuromuscular dysfunction. Finally, key research gaps within the disuse atrophy literature are highlighted providing future avenues to enhance our mechanistic understanding of human disuse atrophy.

Keywords:  atrophy; disuse; skeletal muscle

DOI:  https://doi.org/10.1042/CS20231198
J Physiol. 2024 Jun 15.

A multimodal exercise countermeasure prevents the negative impact of head-down tilt bed rest on muscle volume and mitochondrial health in older adults.

Maude Dulac, Guy Hajj-Boutros, Vita Sonjak, Andréa Faust, Sabah N A Hussain, Stéphanie Chevalier, Isabelle J Dionne, José A Morais, Gilles Gouspillou.

  Mitochondrial dysfunctions are thought to contribute to muscle atrophy and weakness that develop during ageing and mechanical unloading caused by immobilization, bed rest and microgravity. Older adults are at greater risk of developing muscle and mitochondrial dysfunctions in response to unloading. Although exercise is well known to promote muscle and mitochondrial health, its protective effect during mechanical unloading in older adults remains largely unexplored. Here, we investigated the impact of 14 days of head-down tilt bed rest (HDBR) with and without a multimodal exercise countermeasure in older men and women (55-65 years). Leg muscle volume was assessed using magnetic resonance imaging. Biopsies of the vastus lateralis were performed to assess markers of mitochondrial content, respiration, reactive oxygen species (ROS) production and calcium retention capacity (mCRC). Indices of mitochondrial quality control (MQC), including markers of fusion (MFN1 and 2), fission (Drp1), mitophagy (Parkin) and autophagy (p62 and LC3I and II) were measured using immunoblots. Muscle cross-sections were stained for neural cell adhesion molecule (NCAM, a marker of denervation). HDBR triggered muscle atrophy, decreased mitochondrial content and respiration and increased mitochondrial ROS production. HDBR had no impact on mCRC or MQC markers but increased markers of autophagy and denervation. Exercise prevented the deleterious effects of HDBR on leg muscle volume, mitochondrial ROS production and markers of autophagy and denervation. Exercise also increased mitochondrial content and respiration without altering mCRC and MQC markers. Collectively, our results indicate that an exercise countermeasure that can be performed in bed is effective in protecting muscle and mitochondrial health during HDBR in older adults. KEY POINTS: Conditions associated with muscle unloading, such as immobilization, bed rest or microgravity, result in muscle atrophy and weakness, particularly in older adults. Mitochondrial dysfunctions are thought to contribute to muscle atrophy caused by unloading and ageing. However, whether exercise can counteract the deleterious effects of unloading in older adults remains largely unexplored. Here, we report that older adults exposed to 14 days of head-down tilt bed rest (HDBR) displayed upper leg muscle atrophy, a decrease in mitochondrial content and respiration, an increase in H2O2 emission, and an increase in autophagy and denervation markers. No impact of HDBR on mitochondrial quality control was observed. A multimodal exercise countermeasure prevented the deleterious effects of HDBR on upper leg muscle volume, mitochondrial reactive oxygen species emission, and markers of autophagy and denervation and increased mitochondrial content and respiration. These findings highlight the effectiveness of exercise in promoting muscle and mitochondrial health in older adults undergoing bed rest.

Keywords:  ageing; atrophy; autophagy; disuse; inactivity; mitochondria; mitochondrial dynamics; neuromuscular junction; skeletal muscle; space flight; weakness

DOI:  https://doi.org/10.1113/JP285897
Int J Mol Sci. 2024 May 27. pii: 5811. [Epub ahead of print]25(11):

Exploring the Role of Extracellular Vesicles in Skeletal Muscle Regeneration.

Cristiana Porcu, Gabriella Dobrowolny, Bianca Maria Scicchitano.

  Skeletal muscle regeneration entails a multifaceted process marked by distinct phases, encompassing inflammation, regeneration, and remodeling. The coordination of these phases hinges upon precise intercellular communication orchestrated by diverse cell types and signaling molecules. Recent focus has turned towards extracellular vesicles (EVs), particularly small EVs, as pivotal mediators facilitating intercellular communication throughout muscle regeneration. Notably, injured muscle provokes the release of EVs originating from myofibers and various cell types, including mesenchymal stem cells, satellite cells, and immune cells such as M2 macrophages, which exhibit anti-inflammatory and promyogenic properties. EVs harbor a specific cargo comprising functional proteins, lipids, and nucleic acids, including microRNAs (miRNAs), which intricately regulate gene expression in target cells and activate downstream pathways crucial for skeletal muscle homeostasis and repair. Furthermore, EVs foster angiogenesis, muscle reinnervation, and extracellular matrix remodeling, thereby modulating the tissue microenvironment and promoting effective tissue regeneration. This review consolidates the current understanding on EVs released by cells and damaged tissues throughout various phases of muscle regeneration with a focus on EV cargo, providing new insights on potential therapeutic interventions to mitigate muscle-related pathologies.

Keywords:  extracellular vesicles; miRNAs; muscle regeneration; skeletal muscle damage

DOI:  https://doi.org/10.3390/ijms25115811
J Appl Physiol (1985). 2024 Jun 20.

Ulk1 Phosphorylation at S555 is Not Required in Exercise Training-mediated Improvements in Endurance and Metabolic Capacity in Healthy Mice.

Yuntian Guan, Hannah Spaulding, Yu Qing, Mei Zhang, Orion Willoughby, Joshua C Drake, Zhen Yan.

  Endurance exercise training improves exercise capacity as well as skeletal muscle and whole-body metabolism, which are hallmarks of high quality-of-life and healthy aging. However, its mechanisms are not yet fully understood. Exercise-induced mitophagy has merged as an important step in mitochondrial remodeling. ULK1, specifically its activation by phosphorylation at serine 555, was discovered as an autophagy driver and to be important for energetic stress-induced mitophagy in skeletal muscle, making it a potential mediator the benefit of exercise on mitochondrial remodeling. Here, we employed CRISPR/Cas9-mediated gene editing and generated knock-in mice with a serine-to-alanine mutation of Ulk1. We now report that these mice displayed normal endurance capacity and cardiac function at baseline with a mild impairment of energy metabolism as indicated by accelerated increase of respiratory exchange ratio (RER) during acute exercise stress; however, this was completely corrected by 8 weeks of voluntary running. Ulk1-S555A mice also completely retained the exercise-mediated improvements of endurance capacity. We conclude that Ulk1 phosphorylation at S555 is not required for exercise-mediated improvements of endurance and metabolic capacity in healthy mice.

Keywords:  Autophagy; Endurance Capacity; Exercise; Metabolism; Mitophagy

DOI:  https://doi.org/10.1152/japplphysiol.00742.2023
Int J Biol Sci. 2024 ;20(8): 3219-3235

Unlocking the Nexus of Sirtuins: A Comprehensive Review of Their Role in Skeletal Muscle Metabolism, Development, and Disorders.

Bahareldin Ali Abdalla Gibril, Xinwei Xiong, Xuewen Chai, Qiao Xu, Jishang Gong, Jiguo Xu.

  The sirtuins constitute a group of histone deacetylases reliant on NAD+ for their activity that have gained recognition for their critical roles as regulators of numerous biological processes. These enzymes have various functions in skeletal muscle biology, including development, metabolism, and the body's response to disease. This comprehensive review seeks to clarify sirtuins' complex role in skeletal muscle metabolism, including glucose uptake, fatty acid oxidation, mitochondrial dynamics, autophagy regulation, and exercise adaptations. It also examines their critical roles in developing skeletal muscle, including myogenesis, the determination of muscle fiber type, regeneration, and hypertrophic responses. Moreover, it sheds light on the therapeutic potential of sirtuins by examining their impact on a range of skeletal muscle disorders. By integrating findings from various studies, this review outlines the context of sirtuin-mediated regulation in skeletal muscle, highlighting their importance and possible consequences for health and disease.

Keywords:  development; disorders; sirtuins; skeletal muscle metabolism

DOI:  https://doi.org/10.7150/ijbs.96885
Stem Cell Res Ther. 2024 Jun 21. 15(1): 179

Dual inhibition of P38 MAPK and JNK pathways preserves stemness markers and alleviates premature activation of muscle stem cells during isolation.

Teoman Ozturk, Julien Mignot, Francesca Gattazzo, Marianne Gervais, Frédéric Relaix, Hélène Rouard, Nathalie Didier.

   BACKGROUND: Adult skeletal muscle contains resident muscle stem cells (MuSC) with high myogenic and engraftment potentials, making them suitable for cell therapy and regenerative medicine approaches. However, purification process of MuSC remains a major hurdle to their use in the clinic. Indeed, muscle tissue enzymatic dissociation triggers a massive activation of stress signaling pathways, among which P38 and JNK MAPK, associated with a premature loss of MuSC quiescence. While the role of these pathways in the myogenic progression of MuSC is well established, the extent to which their dissociation-induced activation affects the functionality of these cells remains unexplored.
METHODS: We assessed the effect of P38 and JNK MAPK induction on stemness marker expression and MuSC activation state during isolation by pharmacological approaches. MuSC functionality was evaluated by in vitro assays and in vivo transplantation experiments. We performed a comparative analysis of the transcriptome of human MuSC purified with pharmacological inhibitors of P38 and JNK MAPK (SB202190 and SP600125, respectively) versus available RNAseq resources.
RESULTS: We monitored PAX7 protein levels in murine MuSC during muscle dissociation and demonstrated a two-step decline partly dependent on P38 and JNK MAPK activities. We showed that simultaneous inhibition of these pathways throughout the MuSC isolation process preserves the expression of stemness markers and limits their premature activation, leading to improved survival and amplification in vitro as well as increased engraftment in vivo. Through a comparative RNAseq analysis of freshly isolated human MuSC, we provide evidence that our findings in murine MuSC could be relevant to human MuSC. Based on these findings, we implemented a purification strategy, significantly improving the recovery yields of human MuSC.
CONCLUSION: Our study highlights the pharmacological limitation of P38 and JNK MAPK activities as a suitable strategy to qualitatively and quantitatively ameliorate human MuSC purification process, which could be of great interest for cell-based therapies.

Keywords:  Cell therapy; Enzymatic dissociation; MAPK signaling pathways; Muscle stem cells; PAX7

DOI:  https://doi.org/10.1186/s13287-024-03795-0
Dev Cell. 2024 May 20. pii: S1534-5807(24)00295-8. [Epub ahead of print]

Suppressed basal mitophagy drives cellular aging phenotypes that can be reversed by a p62-targeting small molecule.

George Kelly, Tetsushi Kataura, Johan Panek, Gailing Ma, Hanna Salmonowicz, Ashley Davis, Hannah Kendall, Charlotte Brookes, Daniel Moscoh Ayine-Tora, Peter Banks, Glyn Nelson, Laura Dobby, Patricia R Pitrez, Laura Booth, Lydia Costello, Gavin D Richardson, Penny Lovat, Stefan Przyborski, Lino Ferreira, Laura Greaves, Karolina Szczepanowska, Thomas von Zglinicki, Satomi Miwa, Max Brown, Michael Flagler, John E Oblong, Charles C Bascom, Bernadette Carroll, Jóhannes Reynisson, Viktor I Korolchuk.

  Selective degradation of damaged mitochondria by autophagy (mitophagy) is proposed to play an important role in cellular homeostasis. However, the molecular mechanisms and the requirement of mitochondrial quality control by mitophagy for cellular physiology are poorly understood. Here, we demonstrated that primary human cells maintain highly active basal mitophagy initiated by mitochondrial superoxide signaling. Mitophagy was found to be mediated by PINK1/Parkin-dependent pathway involving p62 as a selective autophagy receptor (SAR). Importantly, this pathway was suppressed upon the induction of cellular senescence and in naturally aged cells, leading to a robust shutdown of mitophagy. Inhibition of mitophagy in proliferating cells was sufficient to trigger the senescence program, while reactivation of mitophagy was necessary for the anti-senescence effects of NAD precursors or rapamycin. Furthermore, reactivation of mitophagy by a p62-targeting small molecule rescued markers of cellular aging, which establishes mitochondrial quality control as a promising target for anti-aging interventions.

Keywords:  PINK1; Parkin; aging; autophagy; mitophagy; nicotinamide; nicotinamide riboside; p62; rapamycin; redox; senescence

DOI:  https://doi.org/10.1016/j.devcel.2024.04.020
Cell Rep. 2024 Jun 19. pii: S2211-1247(24)00702-2. [Epub ahead of print]43(7): 114374

Spatial proteomics of skeletal muscle using thin cryosections reveals metabolic adaptation at the muscle-tendon transition zone.

Luisa Schmidt, Michael Saynisch, Christian Hoegsbjerg, Andreas Schmidt, Abigail Mackey, Jan-Wilm Lackmann, Stefan Müller, Manuel Koch, Bent Brachvogel, Michael Kjaer, Philipp Antczak, Marcus Krüger.

  Morphological studies of skeletal muscle tissue provide insights into the architecture of muscle fibers, the surrounding cells, and the extracellular matrix (ECM). However, a spatial proteomics analysis of the skeletal muscle including the muscle-tendon transition zone is lacking. Here, we prepare cryotome muscle sections of the mouse soleus muscle and measure each slice using short liquid chromatography-mass spectrometry (LC-MS) gradients. We generate 3,000 high-resolution protein profiles that serve as the basis for a network analysis to reveal the complex architecture of the muscle-tendon junction. Among the protein profiles that increase from muscle to tendon, we find proteins related to neuronal activity, fatty acid biosynthesis, and the renin-angiotensin system (RAS). Blocking the RAS in cultured mouse tenocytes using losartan reduces the ECM synthesis. Overall, our analysis of thin cryotome sections provides a spatial proteome of skeletal muscle and reveals that the RAS acts as an additional regulator of the matrix within muscle-tendon junctions.

Keywords:  CP: Metabolism; distance-based network; myotendinous junction; skeletal muscle; spatial proteomics

DOI:  https://doi.org/10.1016/j.celrep.2024.114374
Physiol Rep. 2024 Jun;12(12): e16121

Direct and acute effects of advanced glycation end products on proteostasis in isolated mouse skeletal muscle.

Haiyu Zhao, Ryota Iyama, Eriko Kurogi, Tatsuya Hayashi, Tatsuro Egawa.

  Advanced glycation end products (AGEs) have been implicated in several skeletal muscle dysfunctions. However, whether the adverse effects of AGEs on skeletal muscle are because of their direct action on the skeletal muscle tissue is unclear. Therefore, this study aimed to investigate the direct and acute effects of AGEs on skeletal muscle using an isolated mouse skeletal muscle to eliminate several confounders derived from other organs. The results showed that the incubation of isolated mouse skeletal muscle with AGEs (1 mg/mL) for 2-6 h suppressed protein synthesis and the mechanistic target of rapamycin signaling pathway. Furthermore, AGEs showed potential inhibitory effects on protein degradation pathways, including autophagy and the ubiquitin-proteasome system. Additionally, AGEs stimulated endoplasmic reticulum (ER) stress by modulating the activating transcription factor 6, PKR-like ER kinase, C/EBP homologous protein, and altered inflammatory cytokine expression. AGEs also stimulated receptor for AGEs (RAGE)-associated signaling molecules, including mitogen-activated protein kinases. These findings suggest that AGEs have direct and acute effect on skeletal muscle and disturb proteostasis by modulating intracellular pathways such as RAGE signaling, protein synthesis, proteolysis, ER stress, and inflammatory cytokines.

Keywords:  AGEs; ER stress; protein synthesis; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.16121
Int J Mol Sci. 2024 Jun 03. pii: 6166. [Epub ahead of print]25(11):

Zebrafish as a Human Muscle Model for Studying Age-Dependent Sarcopenia and Frailty.

Paula Aranda-Martínez, Ramy K A Sayed, José Fernández-Martínez, Yolanda Ramírez-Casas, Yang Yang, Germaine Escames, Darío Acuña-Castroviejo.

  Currently, there is an increase in the aging of the population, which represents a risk factor for many diseases, including sarcopenia. Sarcopenia involves progressive loss of mass, strength, and function of the skeletal muscle. Some mechanisms include alterations in muscle structure, reduced regenerative capacity, oxidative stress, mitochondrial dysfunction, and inflammation. The zebrafish has emerged as a new model for studying skeletal muscle aging because of its numerous advantages, including histological and molecular similarity to human skeletal muscle. In this study, we used fish of 2, 10, 30, and 60 months of age. The older fish showed a higher frailty index with a value of 0.250 ± 0.000 because of reduced locomotor activity and alterations in biometric measurements. We observed changes in muscle structure with a decreased number of myocytes (0.031 myocytes/μm2 ± 0.004 at 60 months) and an increase in collagen with aging up to 15% ± 1.639 in the 60-month group, corresponding to alterations in the synthesis, degradation, and differentiation pathways. These changes were accompanied by mitochondrial alterations, such as a nearly 50% reduction in the number of intermyofibrillar mitochondria, 100% mitochondrial damage, and reduced mitochondrial dynamics. Overall, we demonstrated a similarity in the aging processes of muscle aging between zebrafish and mammals.

Keywords:  aging; mitochondria; sarcopenia; skeletal muscle; zebrafish

DOI:  https://doi.org/10.3390/ijms25116166
Trends Mol Med. 2024 Jun 15. pii: S1471-4914(24)00138-2. [Epub ahead of print]

Lost in translation: challenges of current pharmacotherapy for sarcopenia.

Shih-Yin Tsai.

  A healthy lifespan relies on independent living, in which active skeletal muscle is a critical element. The cost of not recognizing and acting earlier on unhealthy or aging muscle could be detrimental, since muscular weakness is inversely associated with all-cause mortality. Sarcopenia is characterized by a decline in skeletal muscle mass and strength and is associated with aging. Exercise is the only effective therapy to delay sarcopenia development and improve muscle health in older adults. Although numerous interventions have been proposed to reduce sarcopenia, none has yet succeeded in clinical trials. This review evaluates the biological gap between recent clinical trials targeting sarcopenia and the preclinical studies on which they are based, and suggests an alternative approach to bridge the discrepancy.

Keywords:  hormone therapy; mTOR; muscle hypertrophy; myostatin-based therapy; sarcopenia

DOI:  https://doi.org/10.1016/j.molmed.2024.05.016
Development. 2024 Jun 13. pii: dev.202558. [Epub ahead of print]

Muscle cofilin alters neuromuscular junction postsynaptic development to strengthen functional neurotransmission.

Briana Christophers, Shannon N Leahy, David B Soffar, Victoria E von Saucken, Kendal Broadie, Mary K Baylies.

  Cofilin, an actin severing protein, plays key roles in muscle sarcomere addition and maintenance. Our previous work found that Drosophila cofilin (DmCFL) muscle knockdown causes progressive deterioration of muscle structure and function and produces features seen in nemaline myopathy (NM) caused by cofilin mutations. We hypothesized that disruption of actin cytoskeleton dynamics by DmCFL knockdown would impact other aspects of muscle development, and, thus, conducted an RNA sequencing analysis that unexpectedly revealed upregulated expression of numerous neuromuscular junction (NMJ) genes. We found that DmCFL is enriched in the muscle postsynaptic compartment and that DmCFL muscle knockdown causes F-actin disorganization in this subcellular domain prior to the sarcomere defects observed later in development. Despite NMJ gene expression changes, we found no significant changes in gross presynaptic Bruchpilot active zones or total postsynaptic glutamate receptor levels. However, DmCFL knockdown results in mislocalization of GluRIIA class glutamate receptors in more deteriorated muscles and strongly impaired NMJ transmission strength. These findings expand our understanding of cofilin's roles in muscle to include NMJ structural development and suggest that NMJ defects may contribute to NM pathophysiology.

Keywords:  Actin; Cofilin (CFL); Glutamate receptor; Muscle; Nemaline myopathy; Neuromuscular junction; Postsynapse

DOI:  https://doi.org/10.1242/dev.202558
Dis Model Mech. 2024 Jun 21. pii: dmm.050768. [Epub ahead of print]

Muscle-specific lack of GFPT1 in knock-in mice triggers ER stress to alleviate misfolded proteins.

Ruchen Zhang, Paniz Farshadyeganeh, Bisei Ohkawara, Kazuki Nakajima, Jun-Ichi Takeda, Mikako Ito, Shaochuan Zhang, Yuki Miyasaka, Tamio Ohno, Madoka Mori-Yoshimura, Akio Masuda, Kinji Ohno.

  Pathogenic variants in GFPT1, encoding a key enzyme to synthesize UDP-N-acetylglucosamine (UDP-GlcNAc), cause congenital myasthenic syndrome (CMS). We made a knock-in (KI) mouse model carrying a frameshift variant in Gfpt1 exon 9 simulating a CMS patient. As Gfpt1 exon 9 is exclusively included in striated muscles, Gfpt1-KI mice were deficient for Gfpt1 only in skeletal muscles. In Gfpt1-KI mice, (i) UDP-HexNAc, CMP-NeuAc, and protein O-GlcNAcylations were reduced in skeletal muscles; (ii) aged Gfpt1-KI mice showed poor exercise performance and abnormal neuromuscular junction structures; and (iii) markers for unfolded protein response (UPR) were elevated in skeletal muscles. Denervation-mediated enhancement of ER stress in Gfpt1-KI mice facilitated protein folding, ubiquitin-proteasome degradation, and apoptosis, whereas autophagy was not induced and protein aggregates were markedly increased. Lack of autophagy was accounted for by enhanced degradation of FoxO1 by increased Xbp1-s/u proteins. Similarly, in Gfpt1-silenced C2C12 myotubes, ER stress exacerbated protein aggregates and activated apoptosis, but autophagy was attenuated. In both skeletal muscles in Gfpt1-KI mice and Gfpt1-silenced C2C12 myotubes, maladaptive UPR failed to eliminate protein aggregates and provoked apoptosis.

Keywords:  And unfolded protein response (UPR); Congenital myasthenic syndrome (CMS); Endoplasmic reticulum (ER) stress; Glutamine fructose-6-phosphate transaminase 1 (GFPT1); Hexosamine biosynthesis pathway (HBP); Neuromuscular junction (NMJ)

DOI:  https://doi.org/10.1242/dmm.050768
J Cachexia Sarcopenia Muscle. 2024 Jun 16.

Free essential amino acid feeding improves endurance during resistance training via DRP1-dependent mitochondrial remodelling.

Jiwoong Jang, Yeongmin Kim, Taejeong Song, Sanghee Park, Hee-Joo Kim, Jin-Ho Koh, Yoonil Cho, Shi-Young Park, Sakthivel Sadayappan, Hyo-Bum Kwak, Robert R Wolfe, Il-Young Kim, Cheol Soo Choi.

   BACKGROUND: Loss of muscle strength and endurance with aging or in various conditions negatively affects quality of life. Resistance exercise training (RET) is the most powerful means to improve muscle mass and strength, but it does not generally lead to improvements in endurance capacity. Free essential amino acids (EAAs) act as precursors and stimuli for synthesis of both mitochondrial and myofibrillar proteins that could potentially confer endurance and strength gains. Thus, we hypothesized that daily consumption of a dietary supplement of nine free EAAs with RET improves endurance in addition to the strength gains by RET.
METHODS: Male C57BL6J mice (9 weeks old) were assigned to control (CON), EAA, RET (ladder climbing, 3 times a week), or combined treatment of EAA and RET (EAA + RET) groups. Physical functions focusing on strength or endurance were assessed before and after the interventions. Several analyses were performed to gain better insight into the mechanisms by which muscle function was improved. We determined cumulative rates of myofibrillar and mitochondrial protein synthesis using 2H2O labelling and mass spectrometry; assessed ex vivo contractile properties and in vitro mitochondrial function, evaluated neuromuscular junction (NMJ) stability, and assessed implicated molecular singling pathways. Furthermore, whole-body and muscle insulin sensitivity along with glucose metabolism, were evaluated using a hyperinsulinaemic-euglycaemic clamp.
RESULTS: EAA + RET increased muscle mass (10%, P < 0.05) and strength (6%, P < 0.05) more than RET alone, due to an enhanced rate of integrated muscle protein synthesis (19%, P < 0.05) with concomitant activation of Akt1/mTORC1 signalling. Muscle quality (muscle strength normalized to mass) was improved by RET (i.e., RET and EAA + RET) compared with sedentary groups (10%, P < 0.05), which was associated with increased AchR cluster size and MuSK activation (P < 0.05). EAA + RET also increased endurance capacity more than RET alone (26%, P < 0.05) by increasing both mitochondrial protein synthesis (53%, P < 0.05) and DRP1 activation (P < 0.05). Maximal respiratory capacity increased (P < 0.05) through activation of the mTORC1-DRP1 signalling axis. These favourable effects were accompanied by an improvement in basal glucose metabolism (i.e., blood glucose concentrations and endogenous glucose production vs. CON, P < 0.05).
CONCLUSIONS: Combined treatment with balanced free EAAs and RET may effectively promote endurance capacity as well as muscle strength through increased muscle protein synthesis, improved NMJ stability, and enhanced mitochondrial dynamics via mTORC1-DRP1 axis activation, ultimately leading to improved basal glucose metabolism.

Keywords:  Metabolic flux; Mitochondrial dynamics; Muscle mass; Neuromuscular junction stability; Physical performance; Protein synthesis rate

DOI:  https://doi.org/10.1002/jcsm.13519
Free Radic Biol Med. 2024 Jun 17. pii: S0891-5849(24)00528-8. [Epub ahead of print]222 187-198

Activation of the ROS/TXNIP/NLRP3 pathway disrupts insulin-dependent glucose uptake in skeletal muscle of insulin-resistant obese mice.

Javier Russell-Guzmán, Luan Américo-Da Silva, Cynthia Cadagan, Martín Maturana, Jesús Palomero, Manuel Estrada, Genaro Barrientos, Sonja Buvinic, Cecilia Hidalgo, Paola Llanos.

  Oxidative stress and the activation of the nucleotide-binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome have been linked to insulin resistance in skeletal muscle. In immune cells, the exacerbated generation of reactive oxygen species (ROS) activates the NLRP3 inflammasome, by facilitating the interaction between thioredoxin interacting protein (TXNIP) and NLRP3. However, the precise role of ROS/TXNIP-dependent NLRP3 inflammasome activation in skeletal muscle during obesity-induced insulin resistance remains undefined. Here, we induced insulin resistance in C57BL/6J mice by feeding them for 8 weeks with a high-fat diet (HFD) and explored whether the ROS/TXNIP/NLRP3 pathway was involved in the induction of insulin resistance in skeletal muscle. Skeletal muscle fibers from insulin-resistant mice exhibited increased oxidative stress, as evidenced by elevated malondialdehyde levels, and altered peroxiredoxin 2 dimerization. Additionally, these fibers displayed augmented activation of the NLRP3 inflammasome, accompanied by heightened ROS-dependent proximity between TXNIP and NLRP3, which was abolished by the antioxidant N-acetylcysteine (NAC). Inhibition of the NLRP3 inflammasome with MCC950 or suppressing the ROS/TXNIP/NLRP3 pathway with NAC restored insulin-dependent glucose uptake in muscle fibers from insulin-resistant mice. These findings provide insights into the mechanistic link between oxidative stress, NLRP3 inflammasome activation, and obesity-induced insulin resistance in skeletal muscle.

Keywords:  High-fat diet; Low-grade inflammation; NLRP3 inflammasome; Non-communicable diseases; Oxidative stress

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.06.011
iScience. 2024 Jun 21. 27(6): 110018

Spatial transcriptomics in embryonic mouse diaphragm muscle reveals regional gradients and subdomains of developmental gene expression.

Mehmet Mahsum Kaplan, Maximilian Zeidler, Annabella Knapp, Martina Hölzl, Michaela Kress, Helga Fritsch, Anne Krogsdam, Bernhard E Flucher.

  The murine embryonic diaphragm is a primary model for studying myogenesis and neuro-muscular synaptogenesis, both representing processes regulated by spatially organized genetic programs of myonuclei located in distinct myodomains. However, a spatial gene expression pattern of embryonic mouse diaphragm has not been reported. Here, we provide spatially resolved gene expression data for horizontally sectioned embryonic mouse diaphragms at embryonic days E14.5 and E18.5. These data reveal gene signatures for specific muscle regions with distinct maturity and fiber type composition, as well as for a central neuromuscular junction (NMJ) and a peripheral myotendinous junction (MTJ) compartment. Comparing spatial expression patterns of wild-type mice with those of transgenic mice lacking either the skeletal muscle calcium channel CaV1.1 or β-catenin, reveals curtailed muscle development and dysregulated expression of genes potentially involved in NMJ formation. Altogether, these datasets provide a powerful resource for further studies of muscle development and NMJ formation in the mouse.

Keywords:  Developmental biology; Model organism; Molecular physiology; Transcriptomics

DOI:  https://doi.org/10.1016/j.isci.2024.110018
Int J Mol Sci. 2024 May 31. pii: 6056. [Epub ahead of print]25(11):

An Amino Acid Mixture to Counteract Skeletal Muscle Atrophy: Impact on Mitochondrial Bioenergetics.

Francesco Bellanti, Aurelio Lo Buglio, Giuseppe Pannone, Maria Carmela Pedicillo, Ilenia Sara De Stefano, Angela Pignataro, Cristiano Capurso, Gianluigi Vendemiale.

  Skeletal muscle atrophy (SMA) is caused by a rise in muscle breakdown and a decline in protein synthesis, with a consequent loss of mass and function. This study characterized the effect of an amino acid mixture (AA) in models of SMA, focusing on mitochondria. C57/Bl6 mice underwent immobilization of one hindlimb (I) or cardiotoxin-induced muscle injury (C) and were compared with controls (CTRL). Mice were then administered AA in drinking water for 10 days and compared to a placebo group. With respect to CTRL, I and C reduced running time and distance, along with grip strength; however, the reduction was prevented by AA. Tibialis anterior (TA) muscles were used for histology and mitochondria isolation. I and C resulted in TA atrophy, characterized by a reduction in both wet weight and TA/body weight ratio and smaller myofibers than those of CTRL. Interestingly, these alterations were lightly observed in mice treated with AA. The mitochondrial yield from the TA of I and C mice was lower than that of CTRL but not in AA-treated mice. AA also preserved mitochondrial bioenergetics in TA muscle from I and C mice. To conclude, this study demonstrates that AA prevents loss of muscle mass and function in SMA by protecting mitochondria.

Keywords:  amino acids; cardiotoxin; immobilization; sarcopenia

DOI:  https://doi.org/10.3390/ijms25116056
Int J Mol Sci. 2024 May 31. pii: 6064. [Epub ahead of print]25(11):

Characterization of Undiscovered miRNA Involved in Tumor Necrosis Factor Alpha-Induced Atrophy in Mouse Skeletal Muscle Cell Line.

Dominika Pigoń-Zając, Marcin Mazurek, Mirosław Maziarz, Michael Ochieng' Otieno, Javier Martinez-Useros, Teresa Małecka-Massalska, Tomasz Powrózek.

  Muscular atrophy is a complex catabolic condition that develops due to several inflammatory-related disorders, resulting in muscle loss. Tumor necrosis factor alpha (TNF-α) is believed to be one of the leading factors that drive inflammatory response and its progression. Until now, the link between inflammation and muscle wasting has been thoroughly investigated, and the non-coding RNA machinery is a potential connection between the candidates. This study aimed to identify specific miRNAs for muscular atrophy induced by TNF-α in the C2C12 murine myotube model. The difference in expression of fourteen known miRNAs and two newly identified miRNAs was recorded by next-generation sequencing between normal muscle cells and treated myotubes. After validation, we confirmed the difference in the expression of one novel murine miRNA (nov-mmu-miRNA-1) under different TNF-α-inducing conditions. Functional bioinformatic analyses of nov-mmu-miRNA-1 revealed the potential association with inflammation and muscle atrophy. Our results suggest that nov-mmu-miRNA-1 may trigger inflammation and muscle wasting by the downregulation of LIN28A/B, an anti-inflammatory factor in the let-7 family. Therefore, TNF-α is involved in muscle atrophy through the modulation of the miRNA cellular machinery. Here, we describe for the first time and propose a mechanism for the newly discovered miRNA, nov-mmu-miRNA-1, which may regulate inflammation and promote muscle atrophy.

Keywords:  TNF-α; inflammation; miRNA; muscle atrophy; myotubes

DOI:  https://doi.org/10.3390/ijms25116064
Exp Physiol. 2024 Jun 18.

Unilateral hindlimb ischaemia-induced systemic inflammation is associated with non-ischaemic skeletal muscle inflammation.

William S Evans, Gabriel S Pena, Beata Gelman, Sarah Kuzmiak-Glancy, Steven J Prior.

  Skeletal muscle atrophy and dysfunction commonly accompany cardiovascular diseases such as peripheral arterial disease and may be partially attributable to systemic inflammation. We sought to determine whether acute systemic inflammation in a model of hindlimb ischaemia (HLI) could affect skeletal muscle macrophage infiltration, fibre size, or capillarization, independent of the ischaemia. Eight-week-old C57BL/6 male mice underwent either Sham or HLI surgery, and were killed 1, 3, or 7 days post-surgery. Circulating inflammatory cytokine concentrations were measured, as well as immune cell infiltration and morphology of skeletal muscle from both limbs of HLI and Sham mice. In HLI compared with Sham mice at day 1, plasma interleukin-1β levels were 216% higher (0.48 ± 0.10 vs. 0.15 ± 0.01 pg/μL, P = 0.005) and decreased by day 3. This was followed by increased macrophage presence in muscle from both ischaemic and non-ischaemic limbs of HLI mice by day 7 (7.3- and 2.3-fold greater than Sham, respectively, P < 0.0001). In HLI mice, muscle from the ischaemic limb had 21% lower fibre cross-sectional area than the non-ischaemic limb (724 ± 28 vs. 916 ± 46 μm2, P = 0.01), but the non-ischaemic limb of HLI mice was no different from Sham. This shows that HLI induces acute systemic inflammation accompanied by immune infiltration in both ischaemic and remote skeletal muscle; however, this did not induce skeletal muscle atrophy in remote muscle within the 7-day time course of this study. This effect of local skeletal muscle ischaemia on the inflammatory status of remote skeletal muscle may signal a priming of muscle for subsequent atrophy over a longer time course. HIGHLIGHTS: What is the central question of this study? Does hindlimb ischaemia-induced inflammation cause acute immune, inflammatory and morphological alterations in remote non-ischaemic skeletal muscle? What is the main finding and its importance? Hindlimb ischaemia induced systemic inflammation with subsequent neutrophil and macrophage infiltration in both ischaemic and non-ischaemic skeletal muscle; however, morphological changes did not occur in non-ischaemic muscle within 7 days. These immune alterations may have functional implications that take longer than 7 days to manifest, and subsequent or prolonged systemic inflammation and immune infiltration of muscle could lead to morphological changes and functional decline.

Keywords:  angiogenesis; macrophage; muscle atrophy; neutrophil

DOI:  https://doi.org/10.1113/EP091901
Mol Divers. 2024 Jun 21.

Biocomputational screening of natural compounds targeting 15-hydroxyprostaglandin dehydrogenase to improve skeletal muscle during aging.

Syed Sayeed Ahmad, Jeong Ho Lim, Inho Choi, Eun Ju Lee.

  Skeletal muscle (SM) contains a diverse population of muscle stem (or satellite) cells, which are essential for the maintenance of muscle tissue and positively regulated by prostaglandin E2 (PGE2). However, in aged SM, PGE2 levels are reduced due to increased prostaglandin catabolism by 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a negative regulator of SM tissue repair and regeneration. Screening of a library of 80,617 natural compounds in the ZINC database against 15-PGDH was conducted from PyRx. Further, drug-likeness rules, including those of Lipinski, Ghose, Veber, Egan, and Muegge were performed. The selected complex was forwarded for MD simulations up to 100ns. Based on free energy of binding obtained from docking revealed that ZINC14557836 and ZINC14638400 more potently inhibiting to 15-PGDH than SW033291 (the control and high-affinity inhibitor of 15-PGDH). The free energies of binding obtained from PyRx for 15-PGDH-ZINC14557836, 15-PGDH-ZINC14638400, and 15-PGDH-SW033291 complexes were - 10.30, -9.80, and - 8.0 kcal/mol, respectively. Root mean square deviations (RMSDs), root mean square fluctuations (RMSFs), radii of gyration (Rg), solvent-accessible surface areas (SASAs), and H-bond parameters obtained by 100 ns MD simulations predicted ZINC14557836 and ZINC14638400 more stably complexed with 15-PGDH than SW033291. The several parameters, including physicochemical properties and drug-likenesses, were within acceptable limits, and ZINC14557836 and ZINC14638400 also satisfied other drug-likeness rules, including those of Lipinski, Ghose, Veber, Egan, and Muegge. These findings suggest that ZINC14557836 and ZINC14638400 provide starting points for the development of medications that increase SM regeneration and muscle stem (or satellite) cell numbers by inhibiting 15-PGDH.

Keywords:  15-PGDH; Muscle stem (or satellite) cells; Natural compounds; Screening; Skeletal muscle

DOI:  https://doi.org/10.1007/s11030-024-10825-9
bioRxiv. 2024 May 08. pii: 2024.05.06.591934. [Epub ahead of print]

Effects of HMGCR deficiency on skeletal muscle development.

Mekala Gunasekaran, Hannah R Littel, Natalya M Wells, Johnnie Turner, Gloriana Campos, Sree Venigalla, Elicia A Estrella, Partha S Ghosh, Audrey L Daugherty, Seth A Stafki, Louis M Kunkel, A Reghan Foley, Sandra Donkervoort, Carsten G Bönnemann, Laura Toledo-Bravo de Laguna, Andres Nascimento, Daniel Natera-de Benito, Isabelle Draper, Christine C Bruels, Christina A Pacak, Peter B Kang.

Pathogenic variants in HMGCR were recently linked to a limb-girdle muscular dystrophy (LGMD) phenotype. The protein product HMG CoA reductase (HMGCR) catalyzes a key component of the cholesterol synthesis pathway. The two other muscle diseases associated with HMGCR, statin-associated myopathy (SAM) and autoimmune anti-HMGCR myopathy, are not inherited in a Mendelian pattern. The mechanism linking pathogenic variants in HMGCR with skeletal muscle dysfunction is unclear. We knocked down Hmgcr in mouse skeletal myoblasts, knocked down hmgcr in Drosophila, and expressed three pathogenic HMGCR variants (c.1327C>T, p.Arg443Trp; c.1522_1524delTCT, p.Ser508del; and c.1621G>A, p.Ala541Thr) in Hmgcr knockdown mouse myoblasts. Hmgcr deficiency was associated with decreased proliferation, increased apoptosis, and impaired myotube fusion. Transcriptome sequencing of Hmgcr knockdown versus control myoblasts revealed differential expression involving mitochondrial function, with corresponding differences in cellular oxygen consumption rates. Both ubiquitous and muscle-specific knockdown of hmgcr in Drosophila led to lethality. Overexpression of reference HMGCR cDNA rescued myotube fusion in knockdown cells, whereas overexpression of the pathogenic variants of HMGCR cDNA did not. These results suggest that the three HMGCR-related muscle diseases share disease mechanisms related to skeletal muscle development.

DOI: https://doi.org/10.1101/2024.05.06.591934
Int J Mol Sci. 2024 Jun 01. pii: 6121. [Epub ahead of print]25(11):

The Development of Robust Antibodies to Sarcospan, a Dystrophin- and Integrin-Associated Protein, for Basic and Translational Research.

Ekaterina I Mokhonova, Ravinder Malik, Hafsa Mamsa, Jackson Walker, Elizabeth M Gibbs, Rachelle H Crosbie.

  Sarcospan (SSPN) is a 25-kDa transmembrane protein that is broadly expressed at the cell surface of many tissues, including, but not limited to, the myofibers from skeletal and smooth muscles, cardiomyocytes, adipocytes, kidney epithelial cells, and neurons. SSPN is a core component of the dystrophin-glycoprotein complex (DGC) that links the intracellular actin cytoskeleton with the extracellular matrix. It is also associated with integrin α7β1, the predominant integrin expressed in skeletal muscle. As a tetraspanin-like protein with four transmembrane spanning domains, SSPN functions as a scaffold to facilitate protein-protein interactions at the cell membrane. Duchenne muscular dystrophy, Becker muscular dystrophy, and X-linked dilated cardiomyopathy are caused by the loss of dystrophin at the muscle cell surface and a concomitant loss of the entire DGC, including SSPN. SSPN overexpression ameliorates Duchenne muscular dystrophy in the mdx murine model, which supports SSPN being a viable therapeutic target. Other rescue studies support SSPN as a biomarker for the proper assembly and membrane expression of the DGC. Highly specific and robust antibodies to SSPN are needed for basic research on the molecular mechanisms of SSPN rescue, pre-clinical studies, and biomarker evaluations in human samples. The development of SSPN antibodies is challenged by the presence of its four transmembrane domains and limited antigenic epitopes. To address the significant barrier presented by limited commercially available antibodies, we aimed to generate a panel of robust SSPN-specific antibodies that can serve as a resource for the research community. We created antibodies to three SSPN protein epitopes, including the intracellular N- and C-termini as well as the large extracellular loop (LEL) between transmembrane domains 3 and 4. We developed a panel of rabbit antibodies (poly- and monoclonal) against an N-terminal peptide fragment of SSPN. We used several assays to show that the rabbit antibodies recognize mouse SSPN with a high functional affinity and specificity. We developed mouse monoclonal antibodies against the C-terminal peptide and the large extracellular loop of human SSPN. These antibodies are superior to commercially available antibodies and outperform them in various applications, including immunoblotting, indirect immunofluorescence analysis, immunoprecipitation, and an ELISA. These newly developed antibodies will significantly improve the quality and ease of SSPN detection for basic and translational research.

Keywords:  antibody; dystrophin; monoclonal; muscular dystrophy; polyclonal; sarcoglycan; sarcospan; skeletal muscle

DOI:  https://doi.org/10.3390/ijms25116121
Cells. 2024 Jun 04. pii: 972. [Epub ahead of print]13(11):

A Novel CRISPR-Cas9 Strategy to Target DYSTROPHIN Mutations Downstream of Exon 44 in Patient-Specific DMD iPSCs.

Neha R Dhoke, Hyunkee Kim, Karim Azzag, Sarah B Crist, James Kiley, Rita C R Perlingeiro.

  Mutations in the DMD gene cause fatal Duchenne Muscular Dystrophy (DMD). An attractive therapeutic approach is autologous cell transplantation utilizing myogenic progenitors derived from induced pluripotent stem cells (iPSCs). Given that a significant number of DMD mutations occur between exons 45 and 55, we developed a gene knock-in approach to correct any mutations downstream of exon 44. We applied this approach to two DMD patient-specific iPSC lines carrying mutations in exons 45 and 51 and confirmed mini-DYSTROPHIN (mini-DYS) protein expression in corrected myotubes by western blot and immunofluorescence staining. Transplantation of gene-edited DMD iPSC-derived myogenic progenitors into NSG/mdx4Cv mice produced donor-derived myofibers, as shown by the dual expression of human DYSTROPHIN and LAMIN A/C. These findings further provide proof-of-concept for the use of programmable nucleases for the development of autologous iPSC-based therapy for muscular dystrophies.

Keywords:  CRISPR-Cas9; DMD; dystrophin; gene editing; patient-specific iPS cells; transplantation

DOI:  https://doi.org/10.3390/cells13110972
Physiol Genomics. 2024 Jun 17.

Knockout of Hsp70 genes significantly affects locomotion speed and gene expression in leg skeletal muscles of Drosophila melanogaster.

Pavel A Makhnovskii, Inna V Kukushkina, Nadia S Kurochkina, Daniil V Popov.

  The functions of the Hsp70 genes were studied using a line of D. melanogaster with knockout of six these genes out of thirteen. Namely, effect of knockout of Hsp70 genes on negative geotaxis climbing (locomotor) speed and the ability to adapt to climbing training (0.5-1.5 h/day, 7 days/week, 19 days) were examined. Seven- and 23-day-old Hsp70- flies demonstrated a comparable reduction (2-fold) in locomotor speed and widespread changes in leg skeletal muscle transcriptome (RNA-seq), compared to w1118 flies. To identify the functions of genes related to decreased locomotor speed the overlapped differentially expressed genes at both time points were analyzed: the up-regulated genes encoded extracellular proteins, regulators of drug metabolism and antioxidant response, while down-regulated genes encoded regulators of carbohydrate metabolism and transmembrane proteins. Additionally, in Hsp70- flies, activation of transcription factors related to disruption of the fibril structure and heat shock response (Hsf) were predicted, using the position weight matrix approach. In the control flies, adaptation to chronic exercise training was associated mainly with gene response to a single exercise bout, while the predicted transcription factors were related to stress/immune (Hsf, NF-kB, etc.) and early gene response. In contrast, Hsp70- flies demonstrated no adaptation to training, as well as significantly impaired gene response to a single exercise bout. In conclusion, the knockout of Hsp70 genes not only reduced physical performance, but also disrupted adaptation to chronic physical training, which is associated with changes in leg skeletal muscle transcriptome and impaired gene response to a single exercise bout.

Keywords:  exercise; heat shock proteins; skeletal muscle; training; transcriptome

DOI:  https://doi.org/10.1152/physiolgenomics.00143.2023
Adv Sci (Weinh). 2024 Jun 17. e2400188

Bioengineered Model of Human LGMD2B Skeletal Muscle Reveals Roles of Intracellular Calcium Overload in Contractile and Metabolic Dysfunction in Dysferlinopathy.

Alastair Khodabukus, Neel K Prabhu, Taylor Roberts, Meghan Buldo, Amber Detwiler, Zachary D Fralish, Megan E Kondash, George A Truskey, Timothy R Koves, Nenad Bursac.

  Dysferlin is a multi-functional protein that regulates membrane resealing, calcium homeostasis, and lipid metabolism in skeletal muscle. Genetic loss of dysferlin results in limb girdle muscular dystrophy 2B/2R (LGMD2B/2R) and other dysferlinopathies - rare untreatable muscle diseases that lead to permanent loss of ambulation in humans. The mild disease severity in dysferlin-deficient mice and diverse genotype-phenotype relationships in LGMD2B patients have prompted the development of new in vitro models for personalized studies of dysferlinopathy. Here the first 3-D tissue-engineered hiPSC-derived skeletal muscle ("myobundle") model of LGMD2B is described that exhibits compromised contractile function, calcium-handling, and membrane repair, and transcriptomic changes indicative of impaired oxidative metabolism and mitochondrial dysfunction. In response to the fatty acid (FA) challenge, LGMD2B myobundles display mitochondrial deficits and intracellular lipid droplet (LD) accumulation. Treatment with the ryanodine receptor (RyR) inhibitor dantrolene or the dissociative glucocorticoid vamorolone restores LGMD2B contractility, improves membrane repair, and reduces LD accumulation. Lastly, it is demonstrated that chemically induced chronic RyR leak in healthy myobundles phenocopies LGMD2B contractile and metabolic deficit, but not the loss of membrane repair capacity. Together, these results implicate intramyocellular Ca2+ leak as a critical driver of dysferlinopathic phenotype and validate the myobundle system as a platform to study LGMD2B pathogenesis.

Keywords:  calcium; dysferlin; limb girdle muscular dystrophy 2B/2R; lipid droplet; mitochondria; skeletal muscle; tissue engineering

DOI:  https://doi.org/10.1002/advs.202400188
J Strength Cond Res. 2024 Jul 01. 38(7): 1189-1199

Mitochondria Transplantation: Rescuing Innate Muscle Bioenergetic Impairment in a Model of Aging and Exercise Intolerance.

Tasnim Arroum, Gerald A Hish, Kyle J Burghardt, Mohamed Ghamloush, Belal Bazzi, Abdallah Mrech, Paul T Morse, Steven L Britton, Lauren G Koch, James D McCully, Maik Hüttemann, Moh H Malek.

ABSTRACT: Arroum, T, Hish, GA, Burghardt, KJ, Ghamloush, M, Bazzi, B, Mrech, A, Morse, PT, Britton, SL, Koch, LG, McCully, JD, Hüttemann, M, and Malek, MH. Mitochondria transplantation: Rescuing innate muscle bioenergetic impairment in a model of aging and exercise intolerance. J Strength Cond Res 38(7): 1189-1199, 2024-Mitochondria, through oxidative phosphorylation, are crucial for energy production. Disease, genetic impairment, or deconditioning can harm muscle mitochondria, affecting energy production. Endurance training enhances mitochondrial function but assumes mobility. Individuals with limited mobility lack effective treatments for mitochondrial dysfunction because of disease or aging. Mitochondrial transplantation replaces native mitochondria that have been damaged with viable, respiration-competent mitochondria. Here, we used a rodent model selectively bred for low-capacity running (LCR), which exhibits innate mitochondrial dysfunction in the hind limb muscles. Hence, the purpose of this study was to use a distinct breed of rats (i.e., LCR) that display hereditary skeletal muscle mitochondrial dysfunction to evaluate the consequences of mitochondrial transplantation. We hypothesized that the transplantation of mitochondria would effectively alleviate mitochondrial dysfunction in the hind limb muscles of rats when compared with placebo injections. In addition, we hypothesized that rats receiving the mitochondrial transplantation would experience an improvement in their functional capacity, as evaluated through incremental treadmill testing. Twelve aged LCR male rats (18 months old) were randomized into 2 groups (placebo or mitochondrial transplantation). One LCR rat of the same age and sex was used as the donor to isolate mitochondria from the hindlimb muscles. Isolated mitochondria were injected into both hindlimb muscles (quadriceps femoris, tibialis anterior (TA), and gastrocnemius complex) of a subset LCR (n = 6; LCR-M) rats. The remaining LCR (n = 5; LCR-P) subset received a placebo injection containing only the vehicle without the isolated mitochondria. Four weeks after mitochondrial transplantation, rodents were euthanized and hindlimb muscles harvested. The results indicated a significant (p < 0.05) increase in mitochondrial markers for glycolytic (plantaris and TA) and mixed (quadricep femoris) muscles, but not oxidative muscle (soleus). Moreover, we found significant (p < 0.05) epigenetic changes (i.e., hypomethylation) at the global and site-specific levels for a key mitochondrial regulator (transcription factor A mitochondrial) between the placebo and mitochondrial transplantation groups. To our knowledge, this is the first study to examine the efficacy of mitochondrial transplantation in a rodent model of aging with congenital skeletal muscle dysfunction.

DOI: https://doi.org/10.1519/JSC.0000000000004793
Physiol Genomics. 2024 Jun 17.

Genome-wide Association Study of Exercise-induced Skeletal Muscle Hypertrophy and the Construction of Predictive Model.

Xiaolin Yang, Yanchun Li, Tao Mei, Jiayan Duan, Xu Yan, Lars McNaughton, Zihong He.

  To investigate inter-individual differences in muscle thickness of Rectus Femoris (MTRF) following 12 weeks of Resistance Training (RT) or High-Intensity Interval Training (HIIT) to explore the genetic architecture underlying skeletal muscle hypertrophy and to construct predictive models. We conducted musculoskeletal ultrasound assessments of the MTRF response in 440 physically inactive adults after the 12-week exercise period. A Genome-wide Association study (GWAS) was employed to identify variants associated with MTRF response, separately for RT and HIIT. Utilizing polygenic predictor score (PPS), we estimated the genetic contribution to exercise-induced hypertrophy. Predictive models for MTRF response were constructed using Random Forest (RF), Support Vector Mac (SVM), and Generalized Linear Model (GLM) in 10 cross-validated approach. MTRF increased significantly after both RT (8.8%, P<0.05) and HIIT (5.3%, P<0.05), but with considerable inter-individual differences (RT: -13.5~38.4%, HIIT: -14.2%~30.7%). Eleven lead SNPs in RT and eight lead SNPs in HIIT were identified at a significance level of P<1×10-5. The PPS was associated with MTRF response, explaining 47.2% of the variation in response to RT and 38.3% of the variation in response to HIIT. Notably, the GLM and SVM predictive models exhibited superior performance in comparison to RF models (p<0.05), and the GLM demonstrated optimal performance with an AUC of 0.809 (95%CI:0.669-0.949). Factors such as PPS, baseline MTRF, and exercise protocol exerted influence on the MTRF response to exercise, with PPS being the primary contributor. The GLM and SVM predictive model, incorporating both genetic and phenotypic factors, emerged as promising tools for predicting exercise-induced skeletal muscle hypertrophy.

Keywords:  Genome-wide association; Inter-individual differences; Predictive model; Response to exercise training; Skeletal muscle hypertrophy

DOI:  https://doi.org/10.1152/physiolgenomics.00019.2024
Int J Mol Sci. 2024 Jun 04. pii: 6184. [Epub ahead of print]25(11):

Arginine Regulates Skeletal Muscle Fiber Type Formation via mTOR Signaling Pathway.

Min Zhou, Yihan Wei, Yue Feng, Shumin Zhang, Ning Ma, Kaige Wang, Peng Tan, Ying Zhao, Jinbiao Zhao, Xi Ma.

  The composition of skeletal muscle fiber types affects the quality of livestock meat and human athletic performance and health. L-arginine (Arg), a semi-essential amino acid, has been observed to promote the formation of slow-twitch muscle fibers in animal models. However, the precise molecular mechanisms are still unclear. This study investigates the role of Arg in skeletal muscle fiber composition and mitochondrial function through the mTOR signaling pathway. In vivo, 4-week C56BL/6J male mice were divided into three treatment groups and fed a basal diet supplemented with different concentrations of Arg in their drinking water. The trial lasted 7 weeks. The results show that Arg supplementation significantly improved endurance exercise performance, along with increased SDH enzyme activity and upregulated expression of the MyHC I, MyHC IIA, PGC-1α, and NRF1 genes in the gastrocnemius (GAS) and quadriceps (QUA) muscles compared to the control group. In addition, Arg activated the mTOR signaling pathway in the skeletal muscle of mice. In vitro experiments using cultured C2C12 myotubes demonstrated that Arg elevated the expression of slow-fiber genes (MyHC I and Tnnt1) as well as mitochondrial genes (PGC-1α, TFAM, MEF2C, and NRF1), whereas the effects of Arg were inhibited by the mTOR inhibitor rapamycin. In conclusion, these findings suggest that Arg modulates skeletal muscle fiber type towards slow-twitch fibers and enhances mitochondrial functions by upregulating gene expression through the mTOR signaling pathway.

Keywords:  arginine; fiber type; mTOR signaling pathway; mitochondrial biogenesis; skeletal muscle

DOI:  https://doi.org/10.3390/ijms25116184
FASEB J. 2024 Jul 15. 38(13): e23743

Adipose Kiss1 controls aerobic exercise-related adaptive responses in adipose tissue energy homeostasis.

Chunyu Liang, Xuehan Li, Ge Song, Søren Fisker Schmidt, Lingyu Sun, Jianhao Chen, Xinliang Pan, Haotian Zhao, Yi Yan.

  Kisspeptin signaling regulates energy homeostasis. Adiposity is the principal source and receiver of peripheral Kisspeptin, and adipose Kiss1 metastasis suppressor (Kiss1) gene expression is stimulated by exercise. However, whether the adipose Kiss1 gene regulates energy homeostasis and plays a role in adaptive alterations during prolonged exercise remains unknown. Here, we investigated the role of Kiss1 role in mice and adipose tissues and the adaptive changes it induces after exercise, using adipose-specific Kiss1 knockout (Kiss1adipoq-/-) and adeno-associated virus-induced adipose tissue Kiss1-overexpressing (Kiss1adipoq over) mice. We found that adipose-derived kisspeptin signal regulates lipid and glucose homeostasis to maintain systemic energy homeostasis, but in a sex-dependent manner, with more pronounced metabolic changes in female mice. Kiss1 regulated adaptive alterations of genes and proteins in tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OxPhos) pathways in female gWAT following prolonged aerobic exercise. We could further show that adipose Kiss1 deficiency leads to reduced peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1α) protein content of soleus muscle and maximum oxygen uptake (VO2 max) of female mice after prolonged exercise. Therefore, adipose Kisspeptin may be a novel adipokine that increases organ sensitivity to glucose, lipids, and oxygen following exercise.

Keywords:  Adipose tissue; Aerobic oxidation; Energy metabolism; Exercise; Kiss1; Kisspeptin

DOI:  https://doi.org/10.1096/fj.202302598RR
Mol Metab. 2024 Jun 15. pii: S2212-8778(24)00099-1. [Epub ahead of print] 101968

Adaptive gene expression of alternative splicing variants of PGC-1α regulates whole-body energy metabolism.

Kazuhiro Nomura, Shinichi Kinoshita, Nao Mizusaki, Yoko Senga, Tsutomu Sasaki, Tadahiro Kitamura, Hiroshi Sakaue, Aki Emi, Tetsuya Hosooka, Masahiro Matsuo, Hitoshi Okamura, Taku Amo, Alexander M Wolf, Naomi Kamimura, Shigeo Ohta, Tomoo Itoh, Yoshitake Hayashi, Hiroshi Kiyonari, Anna Krook, Juleen R Zierath, Masato Kasuga, Wataru Ogawa.

  The transcriptional coactivator PGC-1α has been implicated in the regulation of multiple metabolic processes. However, the previously reported metabolic phenotypes of mice deficient in PGC-1α have been inconsistent. PGC-1α exists as multiple isoforms, including variants transcribed from an alternative first exon. We show here that alternative PGC-1α variants are the main entity that increases PGC-1α during exercise. These variants, unlike the canonical isoform of PGC-1α, are robustly upregulated in human skeletal muscle after exercise. Furthermore, the extent of this upregulation correlates with oxygen consumption. Mice lacking these variants manifest impaired energy expenditure during exercise, leading to the development of obesity and hyperinsulinemia. The alternative variants are also upregulated in brown adipose tissue in response to cold exposure, and mice lacking these variants are intolerant of a cold environment. Our findings thus indicate that an increase in PGC-1α expression, attributable mostly to upregulation of alternative variants, is pivotal for adaptive enhancement of energy expenditure and heat production and thereby essential for the regulation of whole-body energy metabolism.

Keywords:  PGC-1α; diabetes; energy expenditure; exercise; obesity; skeletal muscle

DOI:  https://doi.org/10.1016/j.molmet.2024.101968