bims-moremu 2023-07-30 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–07–30
29 papers selected by
Anna Vainshtein, Craft Science Inc.

Impact of short-term, pharmacological CARM1 inhibition on skeletal muscle mass, function, and atrophy in mice.
Exercise, mitochondrial dysfunction and inflammasomes in skeletal muscle.
MicroRNA-142a-3p regulates neurogenic skeletal muscle atrophy by targeting Mef2a.
Endurance Exercise-Induced Fgf21 Promotes Skeletal Muscle Fiber Conversion through TGF-β1 and p38 MAPK Signaling Pathway.
Exercise training induces depot-specific remodeling of protein secretion in skeletal muscle and adipose tissue of obese male mice.
Musculoskeletal defects associated with myosin heavy chain-embryonic loss of function are mediated by the YAP signaling pathway.
Mitochondrial dysfunction: roles in skeletal muscle atrophy.
MTM1 overexpression prevents and reverts BIN1-related centronuclear myopathy.
MicroRNA-140 is not involved in sepsis-induced muscle atrophy.
Assessment of Therapeutic Potential of a Dual AAV Approach for Duchenne Muscular Dystrophy.
Intrinsic contractile dysfunction due to impaired sarcoplasmic reticulum Ca2+ release in compensatory hypertrophied muscle fibers following synergist ablation.
Ablation of the carboxy-terminal end of MAMDC2 causes a distinct muscular dystrophy.
Impaired Insulin Signaling Mediated by the Small GTPase Rac1 in Skeletal Muscle of the Leptin-Deficient Obese Mouse.
Disuse-induced muscle fibrosis, cellular senescence, and senescence-associated secretory phenotype in older adults are alleviated during re-ambulation with metformin pre-treatment.
Mitochondrial proteostasis mediated by CRL5 Ozz and Alix maintains skeletal muscle function.
Secretion of Interleukin 6 in Human Skeletal Muscle Cultures Depends on Ca2+ Signalling.
Regulation of the Wnt signaling pathway during myogenesis by the mammalian SWI/SNF ATPase BRG1.
GDF8 Contributes to Liver Fibrogenesis and Concomitant Skeletal Muscle Wasting.
Acidosis attenuates CPT-I supported bioenergetics as a potential mechanism limiting lipid oxidation.
Migration of Myogenic Cells Is Highly Influenced by Cytoskeletal Septin7.
Leveraging genetic diversity to identify small molecules that reverse mouse skeletal muscle insulin resistance.
Old muscle, new tricks: a clinician perspective on sarcopenia and where to next.
Calpain-3 not only proteolyzes calpain-1 and -2 but also is a substrate for calpain-1 and -2.
MicroRNA-668-3p inhibits myoblast proliferation and differentiation by targeting Appl1.
Chemokine/ITGA4 Interaction Directs iPSC-Derived Myogenic Progenitor Migration to Injury Sites in Aging Muscle for Regeneration.
Bioactive nanoglass regulating the myogenic differentiation and skeletal muscle regeneration.
N-acetylcysteine alleviates oxidative stress and apoptosis and prevents skeletal muscle atrophy in type 1 diabetes mellitus through the NRF2/HO-1 pathway.
Loss of Mtm1 causes cholestatic liver disease in a model of X-linked myotubular myopathy.
Alterations in skeletal muscle morphology and mechanics in juvenile male Sprague Dawley rats exposed to a high-fat high-sucrose diet.

Am J Physiol Endocrinol Metab. 2023 Jul 26.

Impact of short-term, pharmacological CARM1 inhibition on skeletal muscle mass, function, and atrophy in mice.

Erin K Webb, Sean Y Ng, Andrew I Mikhail, Derek W Stouth, Tiffany L vanLieshout, Anika L Syroid, Vladimir Ljubicic.

  Coactivator-associated arginine methyltransferase 1 (CARM1) catalyzes the methylation of arginine residues on target proteins critical for health and disease. The purpose of this study was to characterize the effects of short-term, pharmacological CARM1 inhibition on skeletal muscle size, function, and atrophy. Adult mice (n = 10-11/sex) were treated with either a CARM1 inhibitor (150 mg/kg EZM2302; EZM) or vehicle (Veh) via oral gavage for 11-13 days and muscle mass, function, and exercise capacity were assessed. Additionally, we investigated the effect of CARM1 suppression on unilateral hindlimb denervation (DEN)-induced muscle atrophy (n = 8/sex). We report that CARM1 inhibition caused significant reductions in the asymmetric dimethylation of known CARM1 substrates but no change in CARM1 protein or mRNA content in skeletal muscle. Reduced CARM1 activity did not affect body or muscle mass, however, we observed a decrease in exercise capacity and muscular endurance in male mice. CARM1 methyltransferase activity increased in the muscle of Veh-treated mice following 7 days of DEN and this response was blunted in EZM-dosed mice. Skeletal muscle mass and myofibre cross-sectional area were significantly reduced in DEN compared to contralateral, non-DEN limbs to a similar degree in both treatment groups. Furthermore, skeletal muscle atrophy and autophagy gene expression programs were elevated in response to DEN independent of CARM1 suppression. Collectively, these results suggest that short-term, pharmacological CARM1 inhibition in adult animals affects muscle performance in a sex-specific manner but does not impact the maintenance and remodeling of skeletal muscle mass during conditions of neurogenic muscle atrophy.

Keywords:  Arginine methylation; Autophagy; Exercise; Mitochondria; PRMT

DOI:  https://doi.org/10.1152/ajpendo.00047.2023
Biomed J. 2023 Jul 25. pii: S2319-4170(23)00073-2. [Epub ahead of print] 100636

Exercise, mitochondrial dysfunction and inflammasomes in skeletal muscle.

Mikhaela B Slavin, Priyanka Khemraj, David A Hood.

  In the broad field of inflammation, skeletal muscle is a tissue that is understudied. Yet it represents about 40% of body mass in non-obese individuals and is therefore of fundamental importance for whole body metabolism and health. This article provides an overview of the unique features of skeletal muscle tissue, as well as its adaptability to exercise. This ability to adapt, particularly with respect to mitochondrial content and function, confers a level of metabolic "protection" against energy consuming events, and adds a measure of quality control that determines the phenotypic response to stress. Thus, we describe the particular role of mitochondria in promoting inflammasome activation in skeletal muscle, contributing to muscle wasting and dysfunction in aging, disuse and metabolic disease. We will then discuss how exercise training can be anti-inflammatory, mitigating the chronic inflammation that is observed in these conditions, potentially through improvements in mitochondrial quality and function.

Keywords:  aging; exercise; inflammation; mitochondria; muscle disuse; skeletal muscle

DOI:  https://doi.org/10.1016/j.bj.2023.100636
Mol Ther Nucleic Acids. 2023 Sep 12. 33 191-204

MicroRNA-142a-3p regulates neurogenic skeletal muscle atrophy by targeting Mef2a.

Xinyi Gu, Shen Wang, Dongdong Li, Bo Jin, Zhidan Qi, Jin Deng, Chen Huang, Xiaofeng Yin.

  Peripheral nerve injury can lead to progressive muscle atrophy and poor motor function recovery, which is a difficult point of treatment, and the mechanism needs to be further explored. In previous studies, we found that miR-142a-3p was significantly upregulated and persistently highly expressed in denervated mouse skeletal muscle. Here, we show that overexpression of miR-142a-3p inhibited the growth and differentiation of C2C12 myoblast, while knockdown of miR-142a-3p had a promoting effect. In vitro, knockdown of miR-142a-3p in denervated mouse skeletal muscle effectively increased proliferating muscle satellite cells and ameliorated muscle atrophy. Mechanistically, the myoregulator Mef2a was proved to be an important downstream target of miR-142a-3p, and miR-142a-3p regulates skeletal muscle differentiation and regeneration by inhibiting the expression of Mef2a. The co-knockdown of Mef2a and miR-142a-3p effectively alleviated or offset the biological effects of miR-142a-3p knockdown. In conclusion, our data revealed that miR-142a-3p regulates neurogenic skeletal muscle atrophy by targeting Mef2a.

Keywords:  MT: Non-coding RNAs; differentiation; miR-142a-3p; microRNA; muscle atrophy; skeletal muscle

DOI:  https://doi.org/10.1016/j.omtn.2023.05.023
Int J Mol Sci. 2023 Jul 13. pii: 11401. [Epub ahead of print]24(14):

Endurance Exercise-Induced Fgf21 Promotes Skeletal Muscle Fiber Conversion through TGF-β1 and p38 MAPK Signaling Pathway.

Xiaomao Luo, Huiling Zhang, Xiaorui Cao, Ding Yang, Yi Yan, Jiayin Lu, Xiaonan Wang, Haidong Wang.

  Fgf21 has been identified as playing a regulatory role in muscle growth and function. Although the mechanisms through which endurance training regulates skeletal muscle have been widely studied, the contribution of Fgf21 remains poorly understood. Here, muscle size and function were measured, and markers of fiber type were evaluated using immunohistochemistry, immunoblots, or qPCR in endurance-exercise-trained wild-type and Fgf21 KO mice. We also investigated Fgf21-induced fiber conversion in C2C12 cells, which were incubated with lentivirus and/or pathway inhibitors. We found that endurance exercise training enhanced the Fgf21 levels of liver and GAS muscle and exercise capacity and decreased the distribution of skeletal muscle fiber size, and fast-twitch fibers were observed converting to slow-twitch fibers in the GAS muscle of mice. Fgf21 promoted the markers of fiber-type transition and eMyHC-positive myotubes by inhibiting the TGF-β1 signaling axis and activating the p38 MAPK signaling pathway without apparent crosstalk. Our findings suggest that the transformation and function of skeletal muscle fiber types in response to endurance training could be mediated by Fgf21 and its downstream signaling pathways. Our results illuminate the mechanisms of Fgf21 in endurance-exercise-induced fiber-type conversion and suggest a potential use of Fgf21 in improving muscle health and combating fatigue.

Keywords:  Fgf21; TGF-β1; endurance exercise; fiber type; p38 MAPK

DOI:  https://doi.org/10.3390/ijms241411401
Am J Physiol Endocrinol Metab. 2023 Jul 26.

Exercise training induces depot-specific remodeling of protein secretion in skeletal muscle and adipose tissue of obese male mice.

Magdalene K Montgomery, William De Nardo, Matthew J Watt.

  Acute exercise induces changes in circulating proteins which are known to alter metabolism and systemic energy balance. Skeletal muscle is a primary contributor to changes in the plasma proteome with acute exercise. An important consideration when assessing the endocrine function of muscle is the presence of different fibre types, which show distinct functional and metabolic properties and likely secrete different proteins. Similarly, adipokines are important regulators of systemic metabolism and have been shown to differ between depots. Given the health-promoting effects of exercise, we proposed that understanding depot-specific remodelling of protein secretion in muscle and adipose tissue would provide new insights into inter-tissue communication and uncover novel regulators of energy homeostasis. Here, we examined the effect of endurance exercise training on protein secretion from fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscle, and visceral and subcutaneous adipose tissue. High-fat diet-fed mice were exercise trained for six weeks, while a Control group remained sedentary. Secreted proteins from excised EDL and soleus muscle, inguinal and epididymal adipose tissues were detected using mass spectrometry. We detected 575 and 784 secreted proteins from EDL and soleus muscle, and 738 and 920 proteins from inguinal and epididymal adipose tissue, respectively. Of these, 331 proteins were secreted from all tissues, while secretion of many other proteins was tissue and depot specific. Exercise training led to substantial remodelling of protein secretion from EDL, while soleus showed only minor changes. Myokines released exclusively from EDL or soleus were associated with glycogen metabolism and cellular stress response, respectively. Adipokine secretion was completely refractory to exercise regulation in both adipose depots. This study provides an in-depth resource of protein secretion from muscle and adipose tissue, and its regulation following exercise training, and identifies distinct depot-specific secretion patterns that are related to the metabolic properties of the tissue of origin.

Keywords:  adipokine; endocrine; exercise; mitochondrial function; myokine

DOI:  https://doi.org/10.1152/ajpendo.00178.2023
EMBO Mol Med. 2023 Jul 26. e17187

Musculoskeletal defects associated with myosin heavy chain-embryonic loss of function are mediated by the YAP signaling pathway.

Anushree Bharadwaj, Jaydeep Sharma, Jagriti Singh, Mahima Kumari, Tanushri Dargar, Bhargab Kalita, Sam J Mathew.

  Mutations in MYH3, the gene encoding the developmental myosin heavy chain-embryonic (MyHC-embryonic) skeletal muscle-specific contractile protein, cause several congenital contracture syndromes. Among these, recessive loss-of-function MYH3 mutations lead to spondylocarpotarsal synostosis (SCTS), characterized by vertebral fusions and scoliosis. We find that Myh3 germline knockout adult mice display SCTS phenotypes such as scoliosis and vertebral fusion, in addition to reduced body weight, muscle weight, myofiber size, and grip strength. Myh3 knockout mice also exhibit changes in muscle fiber type, altered satellite cell numbers and increased muscle fibrosis. A mass spectrometric analysis of embryonic skeletal muscle from Myh3 knockouts identified integrin signaling and cytoskeletal regulation as the most affected pathways. These pathways are closely connected to the mechanosensing Yes-associated protein (YAP) transcriptional regulator, which we found to be significantly activated in the skeletal muscle of Myh3 knockout mice. To test whether increased YAP signaling might underlie the musculoskeletal defects in Myh3 knockout mice, we treated these mice with CA3, a small molecule inhibitor of YAP signaling. This led to increased muscle fiber size, rescue of most muscle fiber type alterations, normalization of the satellite cell marker Pax7 levels, increased grip strength, reduced fibrosis, and decline in scoliosis in Myh3 knockout mice. Thus, increased YAP activation underlies the musculoskeletal defects seen in Myh3 knockout mice, indicating its significance as a key pathway to target in SCTS and other MYH3-related congenital syndromes.

Keywords:  Homeostasis; Mice; Myosin heavy chain-embryonic; Skeletal muscle; YAP

DOI:  https://doi.org/10.15252/emmm.202217187
J Transl Med. 2023 07 26. 21(1): 503

Mitochondrial dysfunction: roles in skeletal muscle atrophy.

Xin Chen, Yanan Ji, Ruiqi Liu, Xucheng Zhu, Kexin Wang, Xiaoming Yang, Boya Liu, Zihui Gao, Yan Huang, Yuntian Shen, Hua Liu, Hualin Sun.

  Mitochondria play important roles in maintaining cellular homeostasis and skeletal muscle health, and damage to mitochondria can lead to a series of pathophysiological changes. Mitochondrial dysfunction can lead to skeletal muscle atrophy, and its molecular mechanism leading to skeletal muscle atrophy is complex. Understanding the pathogenesis of mitochondrial dysfunction is useful for the prevention and treatment of skeletal muscle atrophy, and finding drugs and methods to target and modulate mitochondrial function are urgent tasks in the prevention and treatment of skeletal muscle atrophy. In this review, we first discussed the roles of normal mitochondria in skeletal muscle. Importantly, we described the effect of mitochondrial dysfunction on skeletal muscle atrophy and the molecular mechanisms involved. Furthermore, the regulatory roles of different signaling pathways (AMPK-SIRT1-PGC-1α, IGF-1-PI3K-Akt-mTOR, FoxOs, JAK-STAT3, TGF-β-Smad2/3 and NF-κB pathways, etc.) and the roles of mitochondrial factors were investigated in mitochondrial dysfunction. Next, we analyzed the manifestations of mitochondrial dysfunction in muscle atrophy caused by different diseases. Finally, we summarized the preventive and therapeutic effects of targeted regulation of mitochondrial function on skeletal muscle atrophy, including drug therapy, exercise and diet, gene therapy, stem cell therapy and physical therapy. This review is of great significance for the holistic understanding of the important role of mitochondria in skeletal muscle, which is helpful for researchers to further understanding the molecular regulatory mechanism of skeletal muscle atrophy, and has an important inspiring role for the development of therapeutic strategies for muscle atrophy targeting mitochondria in the future.

Keywords:  Antioxidants; Mitochondrial dysfunction; Muscle atrophy; Therapy

DOI:  https://doi.org/10.1186/s12967-023-04369-z
Brain. 2023 Jul 25. pii: awad251. [Epub ahead of print]

MTM1 overexpression prevents and reverts BIN1-related centronuclear myopathy.

Quentin Giraud, Coralie Spiegelhalter, Nadia Messaddeq, Jocelyn Laporte.

  Centronuclear and myotubular myopathies (CNM) are rare and severe genetic diseases associated with muscle weakness and atrophy as well as intracellular disorganization of myofibres. The main mutated proteins control lipid and membrane dynamics and are the lipid phosphatase myotubularin (MTM1), and the membrane remodeling proteins amphiphysin 2 (BIN1) and dynamin 2 (DNM2). There is no available therapy. Here, to validate a novel therapeutic strategy for BIN1- and DNM2-CNM, we evaluated adeno-associated virus-mediated MTM1 overexpression in relevant mouse models. Early systemic MTM1 overexpression prevented the development of the CNM pathology in Bin1mck-/- mice, while late intramuscular MTM1 expression partially reverted the established phenotypes after only 4 weeks of treatment. However, AAV-MTM1 injection did not change the DNM2-CNM mouse phenotypes. We investigated the mechanism of the rescue of the myopathy in BIN1-CNM and found that the lipid phosphatase activity of MTM1 was essential for the rescue of muscle atrophy and myofibre hypotrophy but dispensable for the rescue of myofibre disorganization including organelle mis-position and T-tubule defects. Furthermore, the improvement of T-tubule organization correlated with normalization of key regulators of T-tubule morphogenesis, dysferlin and caveolin. Overall, these data support the inclusion of BIN1-CNM patients in an AAV-MTM1 clinical trial.

Keywords:  congenital myopathy; gene therapy; mTOR; neuromuscular disease; skeletal muscle

DOI:  https://doi.org/10.1093/brain/awad251
Am J Physiol Cell Physiol. 2023 Jul 24.

MicroRNA-140 is not involved in sepsis-induced muscle atrophy.

Jaehoon Shin, Shigeru Miyaki, Hiroshi Asahara, Takayuki Akimoto.

  Sepsis is a life-threatening inflammatory response to infection, often accompanied by skeletal muscle atrophy. A previous study demonstrated that the administration of microRNA-140 (miR-140) attenuated lipopolysaccharides (LPS)-induced muscle atrophy, whereas miR-140 knockdown with siRNA promoted atrophy. Therefore, we investigated whether miR-140 is involved in LPS-induced muscle atrophy using a genetic model, miR-140-/- mice. We found that a single injection of LPS induced atrophy both in slow-twitch and fast-twitch muscles. The muscle weights and fiber cross-sectional areas were significantly reduced in both the wild-type (WT) and miR-140-/- mice, with no difference between genotypes. The expression of several proteolysis markers, muscle-specific RING-finger 1 (MuRF1) and MAFbx/atrogin-1, increased in both groups after LPS injection. The ubiquitinated proteins in the miR-140-/- mice were similar to those in the WT mice. Therefore, the deletion of miR-140 did not affect sepsis-induced muscle atrophy.

Keywords:  apoptosis; muscle wasting; noncoding RNA; proteolysis

DOI:  https://doi.org/10.1152/ajpcell.00157.2023
Int J Mol Sci. 2023 Jul 13. pii: 11421. [Epub ahead of print]24(14):

Assessment of Therapeutic Potential of a Dual AAV Approach for Duchenne Muscular Dystrophy.

Sonia Albini, Laura Palmieri, Auriane Dubois, Nathalie Bourg, William Lostal, Isabelle Richard.

  Duchenne muscular dystrophy (DMD) is a yet incurable rare genetic disease that affects the skeletal and cardiac muscles, leading to progressive muscle wasting and premature death. DMD is caused by the lack of dystrophin, a muscle protein essential for the biochemical support and integrity of muscle fibers. Gene replacement strategies for Duchenne muscular dystrophy (DMD) employing the adeno-associated virus (AAV) face the challenge imposed by the limited packaging capacity of AAV, only allowing the accommodation of a short version of dystrophin (µDys) that is still far removed from correcting human disease. The need to develop strategies leading to the expression of a best performing dystrophin variant led to only few studies reporting on the use of dual vectors, but none reported on a method to assess in vivo transgene reconstitution efficiency, the degree of which directly affects the use of safe AAV dosing. We report here on the generation of a dual AAV vector approach for the expression of a larger dystrophin version (quasidystrophin) based on homologous recombination, and the development of a methodology employing a strategic droplet digital PCR design, to determine the recombination efficiency as well as the occurrence of unwanted concatemerization events or aberrant expression from the single vectors. We demonstrated that, upon systemic delivery in the dystrophic D2.B10-Dmdmdx/J (DBA2mdx) mice, our dual AAV approach led to high transgene reconstitution efficiency and negligible Inverted Terminal Repeats (ITR)-dependent concatemerization, with consequent remarkable protein restoration in muscles and improvement of muscle pathology. This evidence supports the suitability of our system for gene therapy application and the potential of this methodology to assess and improve the feasibility for therapeutic translation of multiple vector approaches.

Keywords:  AAV; DMD; concatemerization; dual vector; dystrophin; gene therapy; homologous recombination

DOI:  https://doi.org/10.3390/ijms241411421
Am J Physiol Cell Physiol. 2023 Jul 24.

Intrinsic contractile dysfunction due to impaired sarcoplasmic reticulum Ca2+ release in compensatory hypertrophied muscle fibers following synergist ablation.

Nao Tokuda, Daiki Watanabe, Azuma Naito, Nao Yamauchi, Yuki Ashida, Arthur J Cheng, Takashi Yamada.

  Synergist ablation (SA) is an experimental procedure for the induction of hypertrophy. However, SA causes a decrease in specific force (i.e., force per cross-sectional area), likely due to excessive muscle use. Here, we investigated the mechanisms behind the SA-induced intrinsic contractile dysfunction, especially focusing on the excitation-contraction (EC) coupling. Male Wistar rats had unilateral surgical ablation of gastrocnemius and soleus muscles to induce the compensatory hypertrophy in the plantaris muscles. Two weeks after SA, plantaris muscle was dissected from each animal and used for later analyses. SA significantly increased the mean fiber cross-sectional area (+18%). On the other hand, the ratio of depolarization-induced force to the maximum Ca2+-activated specific force, an indicator of sarcoplasmic reticulum (SR) Ca2+ release, were markedly reduced in mechanically skinned fibers from the SA group (-51%). These functional defects were accompanied by an extensive fragmentation of the SR Ca2+ release channel, the ryanodine receptor 1 (RyR1), and a decrease in the amount of other triad proteins (i.e., DHPR, STAC3, and junctophilin1). SA treatment also caused an activation of calpain-1 and increased the amount of NADPH oxidase 2, ER stress proteins (i.e., Grp78, Grp94, PDI and Ero1), and lipid peroxidation (i.e., 4-HNE) in SA-treated muscles. Our findings show that SA causes skeletal muscle weakness due to impaired EC coupling. This is likely to be induced by Ca2+-dependent degradation of triad proteins, which may result from Ca2+ leak from fragmented RyR1 triggered by increased oxidative stress.

Keywords:  excitation-contraction coupling; overload; overuse; specific force; synergist ablation

DOI:  https://doi.org/10.1152/ajpcell.00127.2023
Brain. 2023 Jul 28. pii: awad256. [Epub ahead of print]

Ablation of the carboxy-terminal end of MAMDC2 causes a distinct muscular dystrophy.

Fabiola Mavillard, Emilia Servian-Morilla, Lein Dofash, Iñigo Rojas-Marcos, Chiara Folland, Gavin Monahan, Gerardo Gutierrez-Gutierrez, Eloy Rivas, Aurelio Hernández-Lain, Amador Valladares, Gloria Cantero, Jose M Morales, Nigel G Laing, Carmen Paradas, Gianina Ravenscroft, Macarena Cabrera-Serrano.

  The extracellular matrix (ECM) has an important role in the development and maintenance of skeletal muscle, and several muscle diseases are associated with the dysfunction of ECM elements. MAMDC2 is a putative ECM protein and its role in cell proliferation has been investigated in certain cancer types. However, its participation in skeletal muscle physiology has not been previously studied. We describe 17 individuals with an autosomal dominant muscular dystrophy belonging to two unrelated families in which different heterozygous truncating variants in the last exon of MAMDC2 co-segregate correctly with the disease. The radiological aspect of muscle involvement resembles that of COL6 myopathies with fat replacement at the peripheral rim of vastii muscles. In this cohort, a subfascial and peri-tendinous pattern is observed in upper and lower limb muscles. Here we show that MAMDC2 is expressed in adult skeletal muscle and differentiating muscle cells where it appears to localise to the sarcoplasm and myonuclei. In addition, we show it is secreted by myoblasts and differentiating myotubes into to the extracellular compartment. The last exon encodes a disordered region with a polar residue compositional bias loss of which likely induces a toxic effect of the mutant protein. The precise mechanisms by which the altered MAMDC2 proteins cause disease remains to be determined. MAMDC2 is a skeletal muscle disease-associated protein. Its role in muscle development and ECM-muscle communication remains to be fully elucidated. Screening of the last exon of MAMDC2 should be considered in patients presenting with autosomal dominant muscular dystrophy, particularly in those with a subfascial radiological pattern of muscle involvement.

Keywords:  COL6 disorders; MAMDC2; extracellular matrix; muscular dystrophy; subfascial muscle degeneration

DOI:  https://doi.org/10.1093/brain/awad256
Int J Mol Sci. 2023 Jul 16. pii: 11531. [Epub ahead of print]24(14):

Impaired Insulin Signaling Mediated by the Small GTPase Rac1 in Skeletal Muscle of the Leptin-Deficient Obese Mouse.

Man Piu Chan, Nobuyuki Takenaka, Takaya Satoh.

  Insulin-stimulated glucose uptake in skeletal muscle is mediated by the glucose transporter GLUT4. The small GTPase Rac1 acts as a switch of signal transduction that regulates GLUT4 translocation to the plasma membrane following insulin stimulation. However, it remains obscure whether signaling cascades upstream and downstream of Rac1 in skeletal muscle are impaired by obesity that causes insulin resistance and type 2 diabetes. In an attempt to clarify this point, we investigated Rac1 signaling in the leptin-deficient (Lepob/ob) mouse model. Here, we show that insulin-stimulated GLUT4 translocation and Rac1 activation are almost completely abolished in Lepob/ob mouse skeletal muscle. Phosphorylation of the protein kinase Akt2 and plasma membrane translocation of the guanine nucleotide exchange factor FLJ00068 following insulin stimulation were also diminished in Lepob/ob mice. On the other hand, the activation of another small GTPase RalA, which acts downstream of Rac1, by the constitutively activated form of Akt2, FLJ00068, or Rac1, was partially abrogated in Lepob/ob mice. Taken together, we conclude that insulin-stimulated glucose uptake is impaired by two mechanisms in Lepob/ob mouse skeletal muscle: one is the complete inhibition of Akt2-mediated activation of Rac1, and the other is the partial inhibition of RalA activation downstream of Rac1.

Keywords:  Akt2; GLUT4; GTPase; Rac1; RalA; glucose uptake; insulin; obesity; skeletal muscle

DOI:  https://doi.org/10.3390/ijms241411531
Aging Cell. 2023 Jul 24. e13936

Disuse-induced muscle fibrosis, cellular senescence, and senescence-associated secretory phenotype in older adults are alleviated during re-ambulation with metformin pre-treatment.

Jonathan J Petrocelli, Alec I McKenzie, Naomi M M P de Hart, Paul T Reidy, Ziad S Mahmassani, Alexander R Keeble, Katie L Kaput, Matthew P Wahl, Matthew T Rondina, Robin L Marcus, Corrine K Welt, William L Holland, Katsuhiko Funai, Christopher S Fry, Micah J Drummond.

  Muscle inflammation and fibrosis underlie disuse-related complications and may contribute to impaired muscle recovery in aging. Cellular senescence is an emerging link between inflammation, extracellular matrix (ECM) remodeling and poor muscle recovery after disuse. In rodents, metformin has been shown to prevent cellular senescence/senescent associated secretory phenotype (SASP), inflammation, and fibrosis making it a potentially practical therapeutic solution. Thus, the purpose of this study was to determine in older adults if metformin monotherapy during bed rest could reduce muscle fibrosis and cellular senescence/SASP during the re-ambulation period. A two-arm controlled trial was utilized in healthy male and female older adults (n = 20; BMI: <30, age: 60 years+) randomized into either placebo or metformin treatment during a two-week run-in and 5 days of bedrest followed by metformin withdrawal during 7 days of recovery. We found that metformin-treated individuals had less type-I myofiber atrophy during disuse, reduced pro-inflammatory transcriptional profiles, and lower muscle collagen deposition during recovery. Collagen content and myofiber size corresponded to reduced whole muscle cellular senescence and SASP markers. Moreover, metformin treatment reduced primary muscle resident fibro-adipogenic progenitors (FAPs) senescent markers and promoted a shift in fibroblast fate to be less myofibroblast-like. Together, these results suggest that metformin pre-treatment improved ECM remodeling after disuse in older adults by possibly altering cellular senescence and SASP in skeletal muscle and in FAPs.

Keywords:  SASP; aging; atrophy; collagen; fibrosis; inflammation; metformin; senescence

DOI:  https://doi.org/10.1111/acel.13936
bioRxiv. 2023 Jul 11. pii: 2023.07.11.548601. [Epub ahead of print]

Mitochondrial proteostasis mediated by CRL5 Ozz and Alix maintains skeletal muscle function.

Yvan Campos, Ricardo Rodriguez-Enriquez, Gustavo Palacios, Diantha Van de Vlekkert, Xiaohui Qiu, Jayce Weesner, Elida Gomero, Jeroen Demmers, Tulio Bertorini, Joseph T Opferman, Gerard C Grosveld, Alessandra d'Azzo.

High energy-demanding tissues, such as skeletal muscle, require mitochondrial proteostasis to function properly. Two quality-control mechanisms, the ubiquitin proteasome system (UPS) and the release of mitochondria-derived vesicles, safeguard mitochondrial proteostasis. However, whether these processes interact is unknown. Here we show that the E3 ligase CRL5 Ozz , a member of the UPS, and its substrate Alix control the mitochondrial concentration of Slc25A4, a solute carrier that is essential for ATP production. The mitochondria in Ozz -/- or Alix -/- skeletal muscle share overt morphologic alterations (they are supernumerary, swollen, and dysmorphic) and have abnormal metabolomic profiles. We found that CRL5 Ozz ubiquitinates Slc25A4 and promotes its proteasomal degradation, while Alix facilitates SLC25A4 loading into exosomes destined for lysosomal destruction. The loss of Ozz or Alix offsets steady-state levels of Slc25A4, which disturbs mitochondrial metabolism and alters muscle fiber composition. These findings reveal hitherto unknown regulatory functions of Ozz and Alix in mitochondrial proteostasis.

DOI: https://doi.org/10.1101/2023.07.11.548601
Biology (Basel). 2023 Jul 07. pii: 968. [Epub ahead of print]12(7):

Secretion of Interleukin 6 in Human Skeletal Muscle Cultures Depends on Ca2+ Signalling.

Blanca Calle-Ciborro, Teresa Espin-Jaime, Francisco J Santos, Ana Gomez-Martin, Isaac Jardin, Maria J Pozo, Juan A Rosado, Pedro J Camello, Cristina Camello-Almaraz.

  The systemic effects of physical activity are mediated by the release of IL-6 and other myokines from contracting muscle. Although the release of IL-6 from muscle has been extensively studied, the information on the cellular mechanisms is fragmentary and scarce, especially regarding the role of Ca2+ signals. The aim of this study was to characterize the role of the main components of Ca2+ signals in human skeletal muscle cells during IL-6 secretion stimulated by the Ca2+ mobilizing agonist ATP. Primary cultures were prepared from surgical samples, fluorescence microscopy was used to evaluate the Ca2+ signals and the stimulated release of IL-6 into the medium was determined using ELISA. Intracellular calcium chelator Bapta, low extracellular calcium and the Ca2+ channels blocker La3+ reduced the ATP-stimulated, but not the basal secretion. Secretion was inhibited by blockers of L-type (nifedipine, verapamil), T-type (NNC55-0396) and Orai1 (Synta66) Ca2+ channels and by silencing Orai1 expression. The same effect was achieved with inhibitors of ryanodine receptors (ryanodine, dantrolene) and IP3 receptors (xestospongin C, 2-APB, caffeine). Inhibitors of calmodulin (calmidazolium) and calcineurin (FK506) also decreased secretion. IL-6 transcription in response to ATP was not affected by Bapta or by the T channel blocker. Our results prove that ATP-stimulated IL-6 secretion is mediated at the post-transcriptional level by Ca2+ signals, including the mobilization of calcium stores, the activation of store-operated Ca2+ entry, and the subsequent activation of voltage-operated Ca2+ channels and calmodulin/calcineurin pathways.

Keywords:  Ca2+ signals; IL-6; intracellular calcium stores; skeletal muscle; store operated calcium channels; voltage operated calcium channels

DOI:  https://doi.org/10.3390/biology12070968
Front Cell Dev Biol. 2023 ;11 1160227

Regulation of the Wnt signaling pathway during myogenesis by the mammalian SWI/SNF ATPase BRG1.

Tapan Sharma, Monserrat Olea-Flores, Anthony N Imbalzano.

  Skeletal muscle differentiation is a tightly regulated process, and the importance of the mammalian SWI/SNF (mSWI/SNF) chromatin remodeling family for regulation of genes involved in skeletal myogenesis is well-established. Our prior work showed that bromodomains of mSWI/SNF ATPases BRG1 and BRM contribute to myogenesis by facilitating the binding of mSWI/SNF enzymes to regulatory regions of myogenic and other target genes. Here, we report that pathway analyses of differentially expressed genes from that study identified an additional role for mSWI/SNF enzymes via the regulation of the Wnt signaling pathway. The Wnt pathway has been previously shown to be important for skeletal muscle development. To investigate the importance of mSWI/SNF enzymes for the regulation of the Wnt pathway, individual and dual knockdowns were performed for BRG1 and BRM followed by RNA-sequencing. The results show that BRG1, but not BRM, is a regulator of Wnt pathway components and downstream genes. Reactivation of Wnt pathway by stabilization of β-catenin could rescue the defect in myogenic gene expression and differentiation due to BRG1 knockdown or bromodomain inhibition using a specific small molecule inhibitor, PFI-3. These results demonstrate that BRG1 is required upstream of β-catenin function. Chromatin immunoprecipitation of BRG1, BRM and β-catenin at promoters of Wnt pathway component genes showed binding of BRG1 and β-catenin, which provides further mechanistic insight to the transcriptional regulation of these genes.

Keywords:  BRG1; BRM; SWI/SNF; Wnt signaling; bromodomain; chromatin remodeling enzymes; myogenesis; β-catenin

DOI:  https://doi.org/10.3389/fcell.2023.1160227
Biomedicines. 2023 Jul 06. pii: 1909. [Epub ahead of print]11(7):

GDF8 Contributes to Liver Fibrogenesis and Concomitant Skeletal Muscle Wasting.

Alexander Culver, Matthew Hamang, Yan Wang, Huaizhou Jiang, Jennifer Yanum, Emily White, Samer Gawrieh, Raj K Vuppalanchi, Naga P Chalasani, Guoli Dai, Benjamin C Yaden.

  Patients with end-stage liver disease exhibit progressive skeletal muscle atrophy, highlighting a negative crosstalk between the injured liver and muscle. Our study was to determine whether TGFβ ligands function as the mediators. Acute or chronic liver injury was induced by a single or repeated administration of carbon tetrachloride. Skeletal muscle injury and repair was induced by intramuscular injection of cardiotoxin. Activin type IIB receptor (ActRIIB) ligands and growth differentiation factor 8 (Gdf8) were neutralized with ActRIIB-Fc fusion protein and a Gdf8-specific antibody, respectively. We found that acute hepatic injury induced rapid and adverse responses in muscle, which was blunted by neutralizing ActRIIB ligands. Chronic liver injury caused muscle atrophy and repair defects, which were prevented or reversed by inactivating ActRIIB ligands. Furthermore, we found that pericentral hepatocytes produce excessive Gdf8 in injured mouse liver and cirrhotic human liver. Specific inactivation of Gdf8 prevented liver injury-induced muscle atrophy, similar to neutralization of ActRIIB ligands. Inhibition of Gdf8 also reversed muscle atrophy in a treatment paradigm following chronic liver injury. Direct injection of exogenous Gdf8 protein into muscle along with acute focal muscle injury recapitulated similar dysregulated muscle regeneration as that observed with liver injury. The results indicate that injured liver negatively communicate with the muscle largely via Gdf8. Unexpectedly, inactivation of Gdf8 simultaneously ameliorated liver fibrosis in mice following chronic liver injury. In vitro, Gdf8 induced human hepatic stellate (LX-2) cells to form a septa-like structure and stimulated expression of profibrotic factors. Our findings identified Gdf8 as a novel hepatomyokine contributing to injured liver-muscle negative crosstalk along with liver injury progression.

Keywords:  Gdf8; TGFβ family; liver injury; liver–muscle crosstalk; muscle atrophy

DOI:  https://doi.org/10.3390/biomedicines11071909
J Biol Chem. 2023 Jul 21. pii: S0021-9258(23)02107-5. [Epub ahead of print] 105079

Acidosis attenuates CPT-I supported bioenergetics as a potential mechanism limiting lipid oxidation.

Sara M Frangos, Geneviève J DesOrmeaux, Graham P Holloway.

  Fuel interactions in contracting muscle represent a complex interplay between enzymes regulating carbohydrate and fatty acid catabolism, converging in the mitochondrial matrix. While increasing exercise intensity promotes carbohydrate use at the expense of fatty acid oxidation, the mechanisms underlying this effect remain poorly elucidated. As a potential explanation, we investigated whether exercise-induced reductions in intramuscular pH (acidosis) attenuate carnitine palmitoyltransferase-I (CPT-I) supported bioenergetics, the rate-limiting step for fatty acid oxidation within mitochondria. Specifically, we assessed the effect of a physiologically relevant reduction in pH (pH 7.2 vs 6.8) on single and mixed substrate respiratory responses in murine skeletal muscle isolated mitochondria and permeabilized fibers. While pH did not influence OXPHOS stoichiometry (ADP/O ratios), coupling efficiency, oxygen affinity or ADP respiratory responses, acidosis impaired lipid bioenergetics by attenuating respiration with L-carnitine and palmitoyl-CoA, while enhancing the inhibitory effect of malonyl-CoA on CPT-I. These acidotic effects were largely retained following a single bout of intense exercise. At rest, pyruvate and succinate supported respiration were also impaired by acidosis. However, providing more pyruvate and ADP at pH 6.8 to model increases in glycolytic flux and ATP turnover with intense exercise, overcame the acidotic attenuation of carbohydrate-linked OXPHOS. Importantly, this situation is fundamentally different from lipids where CPT-I substrate sensitivity and availability is impaired at higher power outputs suggesting lipid metabolism may be more susceptible to the effects of acidosis, possibly contributing to fuel shifts with increasing exercise intensity.

Keywords:  CPT-I; Mitochondrial bioenergetics; exercise; fuel metabolism; lipid metabolism; pH; skeletal muscle

DOI:  https://doi.org/10.1016/j.jbc.2023.105079
Cells. 2023 Jul 11. pii: 1825. [Epub ahead of print]12(14):

Migration of Myogenic Cells Is Highly Influenced by Cytoskeletal Septin7.

Zsolt Ráduly, László Szabó, Beatrix Dienes, Péter Szentesi, Ágnes Viktória Bana, Tibor Hajdú, Endre Kókai, Csaba Hegedűs, László Csernoch, Mónika Gönczi.

  Septin7 as a unique member of the GTP binding protein family, is widely expressed in the eukaryotic cells and considered to be essential in the formation of hetero-oligomeric septin complexes. As a cytoskeletal component, Septin7 is involved in many important cellular processes. However, its contribution in striated muscle physiology is poorly described. In skeletal muscle, a highly orchestrated process of migration is crucial in the development of functional fibers and in regeneration. Here, we describe the pronounced appearance of Septin7 filaments and a continuous change of Septin7 protein architecture during the migration of myogenic cells. In Septin7 knockdown C2C12 cultures, the basic parameters of migration are significantly different, and the intracellular calcium concentration change in migrating cells are lower compared to that of scrambled cultures. Using a plant cytokinin, forchlorfenuron, to dampen septin dynamics, the altered behavior of the migrating cells is described, where Septin7-depleted cells are more resistant to the treatment. These results indicate the functional relevance of Septin7 in the migration of myoblasts, implying its contribution to muscle myogenesis and regeneration.

Keywords:  Septin7; cytoskeleton; forchlorfenuron; intracellular calcium; migration; myogenesis; regeneration

DOI:  https://doi.org/10.3390/cells12141825
Elife. 2023 Jul 26. pii: RP86961. [Epub ahead of print]12

Leveraging genetic diversity to identify small molecules that reverse mouse skeletal muscle insulin resistance.

Stewart W C Masson, Søren Madsen, Kristen C Cooke, Meg Potter, Alexis Diaz Vegas, Luke Carroll, Senthil Thillainadesan, Harry B Cutler, Ken R Walder, Gregory J Cooney, Grant Morahan, Jacqueline Stöckli, David E James.

  Systems genetics has begun to tackle the complexity of insulin resistance by capitalising on computational advances to study high-diversity populations. 'Diversity Outbred in Australia (DOz)' is a population of genetically unique mice with profound metabolic heterogeneity. We leveraged this variance to explore skeletal muscle's contribution to whole-body insulin action through metabolic phenotyping and skeletal muscle proteomics of 215 DOz mice. Linear modelling identified 553 proteins that associated with whole-body insulin sensitivity (Matsuda Index) including regulators of endocytosis and muscle proteostasis. To enrich for causality, we refined this network by focusing on negatively associated, genetically regulated proteins, resulting in a 76-protein fingerprint of insulin resistance. We sought to perturb this network and restore insulin action with small molecules by integrating the Broad Institute Connectivity Map platform and in vitro assays of insulin action using the Prestwick chemical library. These complementary approaches identified the antibiotic thiostrepton as an insulin resistance reversal agent. Subsequent validation in ex vivo insulin-resistant mouse muscle and palmitate-induced insulin-resistant myotubes demonstrated potent insulin action restoration, potentially via upregulation of glycolysis. This work demonstrates the value of a drug-centric framework to validate systems-level analysis by identifying potential therapeutics for insulin resistance.

Keywords:  Diversity Outbred; computational biology; drug repurposing; insulin resistance; mouse; skeletal muscle; systems biology; thiostrepton

DOI:  https://doi.org/10.7554/eLife.86961
Curr Opin Neurol. 2023 Jul 25.

Old muscle, new tricks: a clinician perspective on sarcopenia and where to next.

Katie Schütze, Madeline Schopp, Timothy J Fairchild, Merrilee Needham.

PURPOSE OF REVIEW: This review offers a contemporary clinical approach to the recognition, prevention and management of sarcopenia, and discusses recent clinically relevant advances in the aetiopathogenesis of muscle ageing that may lead to future therapeutic targets.
RECENT FINDINGS: The key recent directions for sarcopenia are in the diagnosis, understanding molecular mechanisms and management. Regarding the recognition of the condition, it has become increasingly clear that different definitions hamper progress in understanding. Therefore, the Global Leadership in Sarcopenia has been established in 2022 to develop a universally accepted definition. Moreover, substantial work is occurring to understand the various roles and contribution of inflammation, oxidative stress, mitochondrial dysfunction and metabolic dysregulation on skeletal muscle function and ageing. Finally, the role of resistance-based exercise regimes has been continually emphasised. However, the role of protein supplementation and hormone replacement therapy (HRT) are still under debate, and current clinical trials are underway.
SUMMARY: With the global ageing of our population, there is increasing emphasis on maintaining good health. Maintenance of skeletal muscle strength and function are key to preventing frailty, morbidity and death.

DOI: https://doi.org/10.1097/WCO.0000000000001185
J Biochem. 2023 Jul 26. pii: mvad057. [Epub ahead of print]

Calpain-3 not only proteolyzes calpain-1 and -2 but also is a substrate for calpain-1 and -2.

Koichi Ojima, Shoji Hata, Fumiko Shinkai-Ouchi, Yasuko Ono, Susumu Muroya.

  Calpain is an intracellular cysteine protease that cleaves its specific substrates in a limited region to modulate cellular function. Calpain-1 (C1) and calpain-2 (C2) are ubiquitously expressed in mammalian cells, but calpain-3 (C3) is a skeletal muscle-specific type. In the course of calpain activation, the N-terminal regions of all three isoforms are clipped off in an intramolecular or intermolecular fashion. C1 proteolyzes C2 to promote further proteolysis, but C2 proteolyzes C1 to suspend C1 proteolysis, indicating the presence of C1-C2 reciprocal proteolysis. However, whether C3 is involved in the calpain proteolysis network is unclear. To address this, we examined whether GFP-tagged C3:C129S (GFP-C3:CS), an inactive protease form of C3, was a substrate for C1 or C2 in HEK cells. Intriguingly, the N-terminal region of C3:CS was cleaved by C1 and C2 at the site identical to that of the C3 autoproteolysis site. Furthermore, the N-terminal clipping of C3:CS by C1 and C2 was observed in mouse skeletal muscle lysates. Meanwhile, C3 preferentially cleaved the N-terminus of C1 over that of C2, and the sizes of these cleaved proteins were identical to their autoproteolysis forms. Our findings suggest an elaborate inter-calpain network to prime and suppress proteolysis of other calpains.

Keywords:  Calpain; LGMD2A/R1; autolysis; calpain-3; skeletal muscle

DOI:  https://doi.org/10.1093/jb/mvad057
BMC Genomics. 2023 Jul 24. 24(1): 415

MicroRNA-668-3p inhibits myoblast proliferation and differentiation by targeting Appl1.

Haigang Cao, Tianning Du, Chenchen Li, Lingling Wu, Jieming Liu, Yuan Guo, Xiao Li, Gongshe Yang, Jianjun Jin, Xin'e Shi.

   BACKGROUND: Skeletal muscle is the largest tissue in the body, and it affects motion, metabolism and homeostasis. Skeletal muscle development comprises myoblast proliferation, fusion and differentiation to form myotubes, which subsequently form mature muscle fibres. This process is strictly regulated by a series of molecular networks. Increasing evidence has shown that noncoding RNAs, especially microRNAs (miRNAs), play vital roles in regulating skeletal muscle growth. Here, we showed that miR-668-3p is highly expressed in skeletal muscle.
METHODS: Proliferating and differentiated C2C12 cells were transfected with miR-668-3p mimics and/or inhibitor, and the mRNA and protein levels of its target gene were evaluated by RT‒qPCR and Western blotting analysis. The targeting of Appl1 by miR-668-3p was confirmed by dual luciferase assay. The interdependence of miR-668-3p and Appl1 was verified by cotransfection of C2C12 cells.
RESULTS: Our data reveal that miR-668-3p can inhibit myoblast proliferation and myogenic differentiation. Phosphotyrosine interacting with PH domain and leucine zipper 1 (Appl1) is a target gene of miR-668-3p, and it can promote myoblast proliferation and differentiation by activating the p38 MAPK pathway. Furthermore, the inhibitory effect of miR-668-3p on myoblast cell proliferation and myogenic differentiation could be rescued by Appl1.
CONCLUSION: Our results indicate a new mechanism by which the miR-668-3p/Appl1/p38 MAPK pathway regulates skeletal muscle development.

Keywords:  Appl1; Cell differentiation; Cell proliferation; Myogenesis; miR-668-3p

DOI:  https://doi.org/10.1186/s12864-023-09431-0
Cells. 2023 Jul 12. pii: 1837. [Epub ahead of print]12(14):

Chemokine/ITGA4 Interaction Directs iPSC-Derived Myogenic Progenitor Migration to Injury Sites in Aging Muscle for Regeneration.

Muhammad Ashraf, Srinivas M Tipparaju, Joung Woul Kim, Wanling Xuan.

  The failure of muscle to repair after injury during aging may be a major contributor to muscle mass loss. We recently generated muscle progenitor cells (MPCs) from human-induced pluripotent stem-cell (iPSC) cell lines using small molecules, CHIR99021 and Givinostat (Givi-MPCs) sequentially. Here, we test whether the chemokines overexpressed in injured endothelial cells direct MPC migration to the site by binding to their receptor, ITGA4. ITGA4 was heavily expressed in Givi-MPCs. To study the effects on the mobilization of Givi-MPCs, ITGA4 was knocked down by an ITGA4 shRNA lentiviral vector. With and without ITGA4 knocked down, cell migration in vitro and cell mobilization in vivo using aged NOD scid gamma (NSG) mice and mdx/scid mice were analyzed. The migration of shITGA4-Givi-MPCs was significantly impaired, as shown in a wound-healing assay. The knockdown of ITGA4 impaired the migration of Givi-MPCs towards human aortic endothelial cells (HAECs), in which CX3CL1 and VCAM-1 were up-regulated by the treatment of TNF-α compared with scramble ones using a transwell system. MPCs expressing ITGA4 sensed chemokines secreted by endothelial cells at the injury site as a chemoattracting signal to migrate to the injured muscle. The mobilization of Givi-MPCs was mediated by the ligand-receptor interaction, which facilitated their engraftment for repairing the sarcopenic muscle with injury.

Keywords:  ITGA4; aging; chemokines; migration; muscle injury; muscle progenitor cell; sarcopenia

DOI:  https://doi.org/10.3390/cells12141837
Regen Biomater. 2023 ;10 rbad059

Bioactive nanoglass regulating the myogenic differentiation and skeletal muscle regeneration.

Dagogo Dorothy Winston, Ting Li, Bo Lei.

  Bioactive glass nanoparticles (BGNs) are widely used in the field of biomedicine, including drug delivery, gene therapy, tumor therapy, bioimaging, molecular markers and tissue engineering. Researchers are interested in using BGNs in bone, heart and skin regeneration. However, there is inadequate information on skeletal muscle tissue engineering, limited information on the biological effects of BGNs on myoblasts, and the role of bioactive glass composite materials on myogenic differentiation is unknown. Herein, we report the effects of BGNs with different compositions (60Si-BGN, 80Si-BGN, 100Si-BGN) on the myogenic differentiation in C2C12 cells and in vivo skeletal tissue regeneration. The results showed that 80Si-BGN could efficiently promote the myogenic differentiation of C1C12 cells, including the myotube formation and myogenic gene expression. The in vivo experiment in a rat skeletal muscle defect model also confirmed that 80Si-BGN could significantly improve the complete regeneration of skeletal muscle tissue during 4 weeks implantation. This work firstly demonstrated evidence that BGN could be the bioactive material in enhancing skeletal muscle regeneration.

Keywords:  bioactive ceramic; bioactive glass nanoparticles; bioactive materials; skeletal tissue engineering

DOI:  https://doi.org/10.1093/rb/rbad059
Life Sci. 2023 Jul 24. pii: S0024-3205(23)00610-0. [Epub ahead of print]329 121975

N-acetylcysteine alleviates oxidative stress and apoptosis and prevents skeletal muscle atrophy in type 1 diabetes mellitus through the NRF2/HO-1 pathway.

Qingyu Ding, Bingxia Sun, Mengran Wang, Tingyu Li, Huayu Li, Qingyue Han, Jianzhao Liao, Zhaoxin Tang.

   AIMS: Type 1 diabetes mellitus (T1DM) has been linked to the occurrence of skeletal muscle atrophy. Insulin monotherapy may lead to excessive blood glucose fluctuations. N-acetylcysteine (NAC), a clinically employed antioxidant, possesses cytoprotective, anti-inflammatory, and antioxidant properties. The objective of our study was to evaluate the viability of NAC as a supplementary treatment for T1DM, specifically regarding its therapeutic and preventative impacts on skeletal muscle.
MAIN METHODS: Here, we used beagles as T1DM model for 120d to explore the mechanism of NRF2/HO-1-mediated skeletal muscle oxidative stress and apoptosis and the therapeutic effects of NAC. Oxidative stress and apoptosis related factors were analyzed by immunohistochemistry, immunofluorescence, western blotting, and RT-qPCR assay.
KEY FINDINGS: The findings indicated that the co-administration of NAC and insulin led to a reduction in creatine kinase levels, preventing weight loss and skeletal muscle atrophy. Improvement in the reduction of muscle fiber cross-sectional area. The expression of Atrogin-1, MuRF-1 and MyoD1 was downregulated, while Myh2 and MyoG were upregulated. In addition, CAT and GSH-Px levels were increased, MDA levels were decreased, and redox was maintained at a steady state. The decreased of key factors in the NRF2/HO-1 pathway, including NRF2, HO-1, NQO1, and SOD1, while KEAP1 increased. In addition, the apoptosis key factors Caspase-3, Bax, and Bak1 were found to be downregulated, while Bcl-2, Bcl-2/Bax, and CytC were upregulated.
SIGNIFICANCE: Our findings demonstrated that NAC and insulin mitigate oxidative stress and apoptosis in T1DM skeletal muscle and prevent skeletal muscle atrophy by activating the NRF2/HO-1 pathway.

Keywords:  Apoptosis; N-Acetylcysteine; NRF2/HO-1 pathway; Oxidative stress; Skeletal muscle atrophy; Type 1 diabetes mellitus

DOI:  https://doi.org/10.1016/j.lfs.2023.121975
J Clin Invest. 2023 Jul 25. pii: e166275. [Epub ahead of print]

Loss of Mtm1 causes cholestatic liver disease in a model of X-linked myotubular myopathy.

Sophie Karolczak, Ashish R Deshwar, Evangelina Aristegui, Binita M Kamath, Michael W Lawlor, Gaia Andreoletti, Jonathan R Volpatti, Jillian L Ellis, Chunyue Yin, James J Dowling.

  X-linked myotubular myopathy (XLMTM) is a fatal congenital disorder caused by mutations in the MTM1 gene. Currently, there are no approved treatments, though AAV8-mediated gene transfer therapy has shown promise in animal models and preliminarily in patients. However, four patients with XLMTM treated with gene therapy have died from progressive liver failure, and hepatobiliary disease has now been recognized more broadly in association with XLMTM. In an attempt to understand whether loss of MTM1 itself is associated with liver pathology, we have characterized a novel liver phenotype in a zebrafish model of this disease. Specifically, we have found that loss-of-function mutations in mtm1 lead to severe liver abnormalities including impaired bile flux, structural abnormalities of the bile canaliculus, and improper endosomal-mediated trafficking of canalicular transporters. Using a reporter tagged Mtm1 zebrafish line, we have established localization of Mtm1 in the liver in association with Rab11 and canalicular transport proteins, and demonstrated that hepatocyte specific re-expression of Mtm1 can rescue the cholestatic phenotype. Lastly, we completed a targeted chemical screen, and found that Dynasore, a dynamin II inhibitor, is able to partially restore bile flow and transporter localization to the canalicular membrane. In summary, we demonstrate for the first time liver abnormalities that are directly caused by MTM1 mutation in a pre-clinical model, thus establishing the critical framework for better understanding and comprehensive treatment of the human disease.

Keywords:  Hepatology; Monogenic diseases; Muscle Biology

DOI:  https://doi.org/10.1172/JCI166275
Sci Rep. 2023 07 25. 13(1): 12013

Alterations in skeletal muscle morphology and mechanics in juvenile male Sprague Dawley rats exposed to a high-fat high-sucrose diet.

Mauricio Delgado-Bravo, David A Hart, Raylene A Reimer, Walter Herzog.

Although once a health concern largely considered in adults, the obesity epidemic is now prevalent in pediatric populations. While detrimental effects on skeletal muscle function have been seen in adulthood, the effects of obesity on skeletal muscle function in childhood is not clearly understood. The purpose of this study was to determine if the consumption of a high-fat high-sucrose (HFS) diet, starting in the post-weaning period, leads to changes in skeletal muscle morphology and mechanics after 14 weeks on the HFS diet. Eighteen 3-week-old male CD-Sprague Dawley rats were randomly assigned to a HFS (C-HFS, n = 10) or standard chow diet (C-CHOW, n = 8). Outcome measures included: weekly energy intake, activity levels, oxygen consumption, body mass, body composition, metabolic profile, serum protein levels, and medial gastrocnemius gene expression, morphology, and mechanics. The main findings from this study were that C-HFS rats: (1) had a greater body mass and percent body fat than control rats; (2) showed early signs of metabolic syndrome; (3) demonstrated potential impairment in muscle remodeling; (4) produced lower relative muscle force; and (5) had a shift in the force-length relationship, indicating that the medial gastrocnemius had shorter muscle fiber lengths compared to those of C-CHOW rats. Based on the results of this study, we conclude that exposure to a HFS diet led to increased body mass, body fat percentage, and early signs of metabolic syndrome, resulting in functional deficits in MG of childhood rats.

DOI: https://doi.org/10.1038/s41598-023-38487-x