Akt-mediated phosphorylation controls the activity of the Y-box protein MSY3 in skeletal muscle

CaMKIIβ deregulation contributes to neuromuscular junction destabilization in Myotonic Dystrophy type I

BACKGROUND

Myotonic Dystrophy type I (DM1) is the most common muscular dystrophy in adults. Previous reports have highlighted that neuromuscular junctions (NMJs) deteriorate in skeletal muscle from DM1 patients and mouse models thereof. However, the underlying pathomechanisms and their contribution to muscle dysfunction remain unknown.

METHODS

We compared changes in NMJs and activity-dependent signalling pathways in HSALR and Mbnl1ΔE3/ΔE3 mice, two established mouse models of DM1.

RESULTS

Muscle from DM1 mouse models showed major deregulation of calcium/calmodulin-dependent protein kinases II (CaMKIIs), which are key activity sensors regulating synaptic gene expression and acetylcholine receptor (AChR) recycling at the NMJ. Both mouse models exhibited increased fragmentation of the endplate, which preceded muscle degeneration. Endplate fragmentation was not accompanied by changes in AChR turnover at the NMJ. However, the expression of synaptic genes was up-regulated in mutant innervated muscle, together with an abnormal accumulation of histone deacetylase 4 (HDAC4), a known target of CaMKII. Interestingly, denervation-induced increase in synaptic gene expression and AChR turnover was hampered in DM1 muscle. Importantly, CaMKIIβ/βM overexpression normalized endplate fragmentation and synaptic gene expression in innervated Mbnl1ΔE3/ΔE3 muscle, but it did not restore denervation-induced synaptic gene up-regulation.

CONCLUSIONS

Our results indicate that CaMKIIβ-dependent and -independent mechanisms perturb synaptic gene regulation and muscle response to denervation in DM1 mouse models. Changes in these signalling pathways may contribute to NMJ destabilization and muscle dysfunction in DM1 patients.

Comprehensive metabolomic analysis of Mangifera indica leaves using UPLC-ESI-Q-TOF-MSE for cell differentiation: An in vitro and in vivo study

The comprehensive metabolic profiling was performed in the leaf extracts of Mangifera indica and assessed for their significant therapeutic application in tissue engineering and regenerative medicine in both in vitro and in vivo studies. About 147 compounds were identified in the ethyl acetate and methanol extracts of M. indica using MS/MS fragmentation analysis and the selected compounds were quantified using LC-QqQ-MS analysis. The in vitro cytotoxic activity showed that the M. indica extracts enhance the proliferation of mouse myoblast cells in concentration-dependent manner. As well, the extracts of M. indica induce the myotube formation by generating oxidative stress in the C2C12 cells was confirmed. The western blot analysis clearly showed that the M. indica induce myogenic differentiation by upregulating the myogenic marker proteins such as PI3K, Akt, mTOR, MyoG, and MyoD. The in vivo studies showed that the extracts expedites the acute wound repair by formation of crust, wound closure and improves the blood perfusion towards the wound area. Together, the leaves of M. indica can be used as excellent therapeutic agent for tissue repair and wound healing applications.

Low carbohydrate availability impairs hypertrophy and anaerobic performance

PURPOSE OF REVIEW

Highlight contemporary evidence examining the effects of carbohydrate restriction on the intracellular regulation of muscle mass and anaerobic performance.

RECENT FINDINGS

Low carbohydrate diets increase fat oxidation and decrease fat mass. Emerging evidence suggests that dietary carbohydrate restriction increases protein oxidation, thereby limiting essential amino acid availability necessary to stimulate optimal muscle protein synthesis and promote muscle recovery. Low carbohydrate feeding for 24 h increases branched-chain amino acid (BCAA) oxidation and reduces myogenic regulator factor transcription compared to mixed-macronutrient feeding. When carbohydrate restriction is maintained for 8 to 12 weeks, the alterations in anabolic signaling, protein synthesis, and myogenesis likely contribute to limited hypertrophic responses to resistance training. The blunted hypertrophic response to resistance training when carbohydrate availability is low does not affect muscle strength, whereas persistently low muscle glycogen does impair anaerobic output during high-intensity sprint and time to exhaustion tests.

SUMMARY

Dietary carbohydrate restriction increases BCAA oxidation and impairs muscle hypertrophy and anaerobic performance, suggesting athletes who need to perform high-intensity exercise should consider avoiding dietary strategies that restrict carbohydrate.

Novel Compound Heterozygous Splice-Site Variants in TPM3 Revealed by RNA Sequencing in a Patient with an Unusual Form of Nemaline Myopathy: A Case Report

BACKGROUND

Pathogenic variants in the TPM3 gene, encoding slow skeletal muscle α-tropomyosin account for less than 5% of nemaline myopathy cases. Dominantly inherited or de novo missense variants in TPM3 are more common than recessive loss-of-function variants. The recessive variants reported to date seem to affect either the 5' or the 3' end of the skeletal muscle-specific TPM3 transcript.

OBJECTIVES

The aim of the study was to identify the disease-causing gene and variants in a Finnish patient with an unusual form of nemaline myopathy.

METHODS

The genetic analyses included Sanger sequencing, whole-exome sequencing, targeted array-CGH, and linked-read whole genome sequencing. RNA sequencing was done on total RNA extracted from cultured myoblasts and myotubes of the patient and controls. TPM3 protein expression was assessed by Western blot analysis. The diagnostic muscle biopsy was analyzed by routine histopathological methods.

RESULTS

The patient had poor head control and failure to thrive, but no hypomimia, and his upper limbs were clearly weaker than his lower limbs, features which in combination with the histopathology suggested TPM3-caused nemaline myopathy. Muscle histopathology showed increased fiber size variation and numerous nemaline bodies predominantly in small type 1 fibers. The patient was found to be compound heterozygous for two splice-site variants in intron 1a of TPM3: NM_152263.4:c.117+2_5delTAGG, deleting the donor splice site of intron 1a, and NM_152263.4:c.117 + 164 C>T, which activates an acceptor splice site preceding a non-coding exon in intron 1a. RNA sequencing revealed inclusion of intron 1a and the non-coding exon in the transcripts, resulting in early premature stop codons. Western blot using patient myoblasts revealed markedly reduced levels of the TPM3 protein.

CONCLUSIONS

Novel biallelic splice-site variants were shown to markedly reduce TPM3 protein expression. The effects of the variants on splicing were readily revealed by RNA sequencing, demonstrating the power of the method.

Identification of crucial circRNAs in skeletal muscle during chicken embryonic development

Background

Chicken provides humans with a large amount of animal protein every year, in which skeletal muscle plays a leading role. The embryonic skeletal muscle development determines the number of muscle fibers and will affect the muscle production of chickens. CircRNAs are involved in a variety of important biological processes, including muscle development. However, studies on circRNAs in the chicken embryo muscle development are still lacking.

Results

In the study, we collected chicken leg muscles at 14 and 20-day embryo ages both in the fast- and slow-growing groups for RNA-seq. We identified 245 and 440 differentially expressed (DE) circRNAs in the comparison group F14vsF20 and S14vsS20 respectively. GO enrichment analysis for the host genes of DE circRNAs showed that biological process (BP) terms in the top 20 related to growth in F14vsF20 were found such as positive regulation of transcription involved in G1/S phase of mitotic cell cycle, multicellular organismal macromolecule metabolic process, and multicellular organismal metabolic process. In group S14vsS20, we also found some BP terms associated with growth in the top 20 including actomyosin structure organization, actin cytoskeleton organization and myofibril assembly. A total of 7 significantly enriched pathways were obtained, containing Adherens junction and Tight junction. Further analysis of those pathways found three crucial host genes MYH9, YBX3, IGF1R in both fast- and slow-growing groups, three important host genes CTNNA3, AFDN and CREBBP only in the fast-growing group, and six host genes FGFR2, ACTN2, COL1A2, CDC42, DOCK1 and MYL3 only in the slow-growing group. In addition, circRNA-miRNA network also revealed some key regulation pairs such as novel_circ_0007646-miR-1625-5p, novel_circ_0007646-miR-1680-5p, novel_circ_0008913-miR-148b-5p, novel_circ_0008906-miR-148b-5p and novel_circ_0001640-miR-1759-3p.

Conclusions

Comprehensive analysis of circRNAs and their targets would contribute to a better understanding of the molecular mechanisms in poultry skeletal muscle and it also plays an important guiding role in the next research.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08588-4.

Development of ovarian tumour causes significant loss of muscle and adipose tissue: a novel mouse model for cancer cachexia study

BACKGROUND

Cancer-associated cachexia (CAC) is a complex syndrome of progressive muscle wasting and adipose loss with metabolic dysfunction, severely increasing the morbidity and mortality risk in cancer patients. However, there are limited studies focused on the underlying mechanisms of the progression of CAC due to the complexity of this syndrome and the lack of preclinical models that mimics its stagewise progression.

METHODS

We characterized the initiation and progression of CAC in transgenic female mice with ovarian tumours. We measured proposed CAC biomarkers (activin A, GDF15, IL-6, IL-1β, and TNF-α) in sera (n = 6) of this mouse model. The changes of activin A and GDF15 (n = 6) were correlated with the decline of bodyweight over time. Morphometry and signalling markers of muscle atrophy (n ≥ 6) and adipose tissue wasting (n ≥ 7) were assessed during CAC progression.

RESULTS

Cancer-associated cachexia symptoms of the transgenic mice model used in this study mimic the progression of CAC seen in humans, including drastic body weight loss, skeletal muscle atrophy, and adipose tissue wasting. Serum levels of two cachexia biomarkers, activin A and GDF15, increased significantly during cachexia progression (76-folds and 10-folds, respectively). Overactivation of proteolytic activity was detected in skeletal muscle through up-regulating muscle-specific E3 ligases Atrogin-1 and Murf-1 (16-folds and 14-folds, respectively) with decreasing cross-sectional area of muscle fibres (P < 0.001). Muscle wasting mechanisms related with p-p38 MAPK, FOXO3, and p-AMPKα were highly activated in concurrence with an elevation in serum activin A. Dramatic fat loss was also observed in this mouse model with decreased fat mass (n ≥ 6) and white adipocytes sizes (n = 6) (P < 0.0001). The adipose tissue wasting was based on thermogenesis, supported by the up-regulation of uncoupling protein 1 (UCP1). Fibrosis in adipose tissue was also observed in concurrence with adipose tissue loss (n ≥ 13) (p < 0.0001).

CONCLUSIONS

Our novel preclinical CAC mouse model mimics human CAC phenotypes and serum biomarkers. The mouse model in this study showed proteolysis in muscle atrophy, browning in adipose tissue wasting, elevation of serum activin A and GDF15, and atrophy of pancreas and liver. This mouse line would be the best preclinical model to aid in clarifying molecular mediators of CAC and dissecting metabolic dysfunction and tissue atrophy during the progression of CAC.

Diverse Regulation of YB-1 and YB-3 Abundance in Mammals

YB proteins are DNA/RNA binding proteins, members of the family of proteins with cold shock domain. Role of YB proteins in the life of cells, tissues, and whole organisms is extremely important. They are involved in transcription regulation, pre-mRNA splicing, mRNA translation and stability, mRNA packaging into mRNPs, including stress granules, DNA repair, and many other cellular events. Many processes, from embryonic development to aging, depend on when and how much of these proteins have been synthesized. Here we discuss regulation of the levels of YB-1 and, in part, of its homologs in the cell. Because the amount of YB-1 is immediately associated with its functioning, understanding the mechanisms of regulation of the protein amount invariably reveals the events where YB-1 is involved. Control over the YB-1 abundance may allow using this gene/protein as a therapeutic target in cancers, where an increased expression of the YBX1 gene often correlates with the disease severity and poor prognosis.

The genome variation and developmental transcriptome maps reveal genetic differentiation of skeletal muscle in pigs

Natural and artificial directional selections have resulted in significantly genetic and phenotypic differences across breeds in domestic animals. However, the molecular regulation of skeletal muscle diversity remains largely unknown. Here, we conducted transcriptome profiling of skeletal muscle across 27 time points, and performed whole-genome re-sequencing in Landrace (lean-type) and Tongcheng (obese-type) pigs. The transcription activity decreased with development, and the high-resolution transcriptome precisely captured the characterizations of skeletal muscle with distinct biological events in four developmental phases: Embryonic, Fetal, Neonatal, and Adult. A divergence in the developmental timing and asynchronous development between the two breeds was observed; Landrace showed a developmental lag and stronger abilities of myoblast proliferation and cell migration, whereas Tongcheng had higher ATP synthase activity in postnatal periods. The miR-24-3p driven network targeting insulin signaling pathway regulated glucose metabolism. Notably, integrated analysis suggested SATB2 and XLOC_036765 contributed to skeletal muscle diversity via regulating the myoblast migration and proliferation, respectively. Overall, our results provide insights into the molecular regulation of skeletal muscle development and diversity in mammals.

Initiating aerobic exercise with low glycogen content reduces markers of myogenesis but not mTORC1 signaling

Background

The effects of low muscle glycogen on molecular markers of protein synthesis and myogenesis before and during aerobic exercise with carbohydrate ingestion is unclear. The purpose of this study was to determine the effects of initiating aerobic exercise with low muscle glycogen on mTORC1 signaling and markers of myogenesis.

Methods

Eleven men completed two cycle ergometry glycogen depletion trials separated by 7-d, followed by randomized isocaloric refeeding for 24-h to elicit low (LOW; 1.5 g/kg carbohydrate, 3.0 g/kg fat) or adequate (AD; 6.0 g/kg carbohydrate, 1.0 g/kg fat) glycogen. Participants then performed 80-min of cycle ergometry (64 ± 3% VO_2peak) while ingesting 146 g carbohydrate. mTORC1 signaling (Western blotting) and gene transcription (RT-qPCR) were determined from vastus lateralis biopsies before glycogen depletion (baseline, BASE), and before (PRE) and after (POST) exercise.

Results

Regardless of treatment, p-mTORC1^Ser2448, p-p70S6K^Ser424/421, and p-rpS6^Ser235/236 were higher (P < 0.05) POST compared to PRE and BASE. PAX7 and MYOGENIN were lower (P < 0.05) in LOW compared to AD, regardless of time, while MYOD was lower (P < 0.05) in LOW compared to AD at PRE, but not different at POST.

Conclusion

Initiating aerobic exercise with low muscle glycogen does not affect mTORC1 signaling, yet reductions in gene expression of myogenic regulatory factors suggest that muscle recovery from exercise may be reduced.

Structural basis of DNA binding to human YB-1 cold shock domain regulated by phosphorylation

Human Y-box binding protein 1 (YB-1) is a multifunctional protein and overexpressed in many types of cancer. It specifically recognizes DNA/RNA through a cold shock domain (CSD) and regulates nucleic acid metabolism. The C-terminal extension of CSD and the phosphorylation of S102 are indispensable for YB-1 function. Until now, the roles of the C-terminal extension and phosphorylation in gene transcription and translation are still largely unknown. Here, we solved the structure of human YB-1 CSD with a C-terminal extension sequence (CSDex). The structure reveals that the extension interacts with several residues in the conventional CSD and adopts a rigid structure instead of being disordered. Either deletion of this extension or phosphorylation of S102 destabilizes the protein and results in partial unfolding. Structural characterization of CSDex in complex with a ssDNA heptamer shows that all the seven nucleotides are involved in DNA-protein interactions and the C-terminal extension provides a unique DNA binding site. Our DNA-binding study indicates that CSDex can recognize more DNA sequences than previously thought and the phosphorylation reduces its binding to ssDNA dramatically. Our results suggest that gene transcription and translation can be regulated by changing the affinity of CSDex binding to DNA and RNA through phosphorylation, respectively.

mTORC1 and PKB/Akt control the muscle response to denervation by regulating autophagy and HDAC4

Loss of innervation of skeletal muscle is a determinant event in several muscle diseases. Although several effectors have been identified, the pathways controlling the integrated muscle response to denervation remain largely unknown. Here, we demonstrate that PKB/Akt and mTORC1 play important roles in regulating muscle homeostasis and maintaining neuromuscular endplates after nerve injury. To allow dynamic changes in autophagy, mTORC1 activation must be tightly balanced following denervation. Acutely activating or inhibiting mTORC1 impairs autophagy regulation and alters homeostasis in denervated muscle. Importantly, PKB/Akt inhibition, conferred by sustained mTORC1 activation, abrogates denervation-induced synaptic remodeling and causes neuromuscular endplate degeneration. We establish that PKB/Akt activation promotes the nuclear import of HDAC4 and is thereby required for epigenetic changes and synaptic gene up-regulation upon denervation. Hence, our study unveils yet-unknown functions of PKB/Akt-mTORC1 signaling in the muscle response to nerve injury, with important implications for neuromuscular integrity in various pathological conditions.

Denervation leads to muscle atrophy and neuromuscular endplate remodeling. Here, the authors show that a balanced activation of mTORC1 contributes to the dynamic regulation of autophagic flux in denervated muscle and that activation of PKB/Akt promotes the nuclear import of HDAC4, which is essential for endplate maintenance upon nerve injury