Muscle 4EBP1 activation modifies the structure and function of the neuromuscular junction in mice

We need to talk-how muscle stem cells communicate

Skeletal muscle is one of the tissues with the highest ability to regenerate, a finely controlled process which is critically depending on muscle stem cells. Muscle stem cell functionality depends on intrinsic signaling pathways and interaction with their immediate niche. Upon injury quiescent muscle stem cells get activated, proliferate and fuse to form new myofibers, a process involving the interaction of multiple cell types in regenerating skeletal muscle. Receptors in muscle stem cells receive the respective signals through direct cell-cell interaction, signaling via secreted factors or cell-matrix interactions thereby regulating responses of muscle stem cells to external stimuli. Here, we discuss how muscle stem cells interact with their immediate niche focusing on how this controls their quiescence, activation and self-renewal and how these processes are altered in age and disease.

Lost in translation: challenges of current pharmacotherapy for sarcopenia

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.

Large-scale transcriptomic and genomic analyses reveal a novel functional gene SERPINB6 for chicken carcass traits

BACKGROUND

Carcass traits are crucial indicators of meat production efficiency. However, the molecular regulatory mechanisms associated with these traits remain unclear.

RESULTS

In this study, we conducted comprehensive transcriptomic and genomic analyses on 399 Tiannong partridge chickens to identify key genes and variants associated with carcass traits and to elucidate the underlying regulatory mechanisms. Based on association analyses with the elastic net (EN) model, we identified 12 candidate genes (AMY1A, AP3B2, CEBPG, EEF2, EIF4EBP1, FGFR1, FOXD3, GOLM1, LOC107052698, PABPC1, SERPINB6 and TBC1D16) for 4 carcass-related traits, namely live weight, dressed weight, eviscerated weight, and breast muscle weight. SERPINB6 was identified as the only overlapping gene by 3 analyses, EN model analysis, weighted gene co-expression network analysis and differential expression analysis. Cell-level experiments confirmed that SERPINB6 promotes the proliferation of chicken DF1 cells and primary myoblasts. Further expression genome-wide association study and association analysis indicated that rs317934171 is the critical site that enhances SERPINB6 expression. Furthermore, a dual-luciferase reporter assay proved that gga-miR-1615 targets the 3'UTR of SERPINB6.

CONCLUSIONS

Collectively, our findings reveal that SERPINB6 serves as a novel gene for chicken carcass traits by promoting fibroblast and myoblast proliferation. Additionally, the downstream variant rs317934171 regulates SERPINB6 expression. These results identify a new target gene and molecular marker for the molecular mechanisms of chicken carcass traits.

Postsynaptic BMP signaling regulates myonuclear properties in Drosophila larval muscles

The syncytial mammalian muscle fiber contains a heterogeneous population of (myo)nuclei. At the neuromuscular junction (NMJ), myonuclei have specialized positioning and gene expression. However, it remains unclear how myonuclei are recruited and what regulates myonuclear output at the NMJ. Here, we identify specific properties of myonuclei located near the Drosophila larval NMJ. These synaptic myonuclei have increased size in relation to their surrounding cytoplasmic domain (scaling), increased DNA content (ploidy), and increased levels of transcription factor pMad, a readout for BMP signaling activity. Our genetic manipulations show local BMP signaling affects muscle size, nuclear size, ploidy, and NMJ size and function. In support, RNA sequencing analysis reveals that pMad regulates genes involved in muscle growth, ploidy (i.e., E2f1), and neurotransmission. Our data suggest that muscle BMP signaling instructs synaptic myonuclear output that then positively shapes the NMJ synapse. This study deepens our understanding of how myonuclear heterogeneity supports local signaling demands to fine tune cellular function and NMJ activity.

Muscle stem cell niche dynamics during muscle homeostasis and regeneration

The process of skeletal muscle regeneration involves a coordinated interplay of specific cellular and molecular interactions within the injury site. This review provides an overview of the cellular and molecular components in regenerating skeletal muscle, focusing on how these cells or molecules in the niche regulate muscle stem cell functions. Dysfunctions of muscle stem cell-to-niche cell communications during aging and disease will also be discussed. A better understanding of how niche cells coordinate with muscle stem cells for muscle repair will greatly aid the development of therapeutic strategies for treating muscle-related disorders.

Unraveling the causes of sarcopenia: Roles of neuromuscular junction impairment and mitochondrial dysfunction

Sarcopenia is a systemic skeletal muscle disease characterized by a decline in skeletal muscle mass and function. Originally defined as an age-associated condition, sarcopenia presently also encompasses muscular atrophy due to various pathological factors, such as intensive care unit-acquired weakness, inactivity, and malnutrition. The exact pathogenesis of sarcopenia is still unknown; herein, we review the pathological roles of the neuromuscular junction and mitochondria in this condition. Sarcopenia is caused by complex and interdependent pathophysiological mechanisms, including aging, neuromuscular junction impairment, mitochondrial dysfunction, insulin resistance, lipotoxicity, endocrine factors, oxidative stress, and inflammation. Among these, neuromuscular junction instability and mitochondrial dysfunction are particularly significant. Dysfunction in neuromuscular junction can lead to muscle weakness or paralysis. Mitochondria, which are plentiful in neurons and muscle fibers, play an important role in neuromuscular junction transmission. Therefore, impairments in both mitochondria and neuromuscular junction may be one of the key pathophysiological mechanisms leading to sarcopenia. Moreover, this article explores the structural and functional alterations in the neuromuscular junction and mitochondria in sarcopenia, suggesting that a deeper understanding of these changes could provide valuable insights for the prevention or treatment of sarcopenia.

Age Is Just a Number: Progress and Obstacles in the Discovery of New Candidate Drugs for Sarcopenia

Sarcopenia is a disease characterized by the progressive loss of skeletal muscle mass and function that occurs with aging. The progression of sarcopenia is correlated with the onset of physical disability, the inability to live independently, and increased mortality. Due to global increases in lifespan and demographic aging in developed countries, sarcopenia has become a major socioeconomic burden. Clinical therapies for sarcopenia are based on physical therapy and nutritional support, although these may suffer from low adherence and variable outcomes. There are currently no clinically approved drugs for sarcopenia. Consequently, there is a large amount of pre-clinical research focusing on discovering new candidate drugs and novel targets. In this review, recent progress in this research will be discussed, along with the challenges that may preclude successful translational research in the clinic. The types of drugs examined include mitochondria-targeting compounds, anti-diabetes agents, small molecules that target non-coding RNAs, protein therapeutics, natural products, and repositioning candidates. In light of the large number of drugs and targets being reported, it can be envisioned that clinically approved pharmaceuticals to prevent the progression or even mitigate sarcopenia may be within reach.

Maintenance of subsynaptic myonuclei number is not driven by neural input

The development and maintenance of neuromuscular junctions (NMJ) are supported by a specialized population of myonuclei that are referred to as the subsynaptic myonuclei (SSM). The relationship between the number of SSM and the integrity of the NMJ as well as the impact of a loss of innervation on SSM remain unclear. This study aimed to clarify these associations by simultaneously analyzing SSM counts and NMJ innervation status in three distinct mouse models of acute and chronic NMJ disruption. SSM were identified using fluorescent immunohistochemistry for Nesprin1 expression, which is highly enriched in SSM, along with anatomical location beneath the muscle fiber motor endplate. Acute denervation, induced by surgical nerve transection, did not affect SSM number after 7 days. Additionally, no significant changes in SSM number were observed during normal aging or in mice with chronic oxidative stress (Sod1 -/-). Both aging WT mice and Sod1 -/- mice accumulated degenerating and denervated NMJ in skeletal muscle, but there was no correlation between innervation status of a given NMJ and SSM number in aged or Sod1 -/- mice. These findings challenge the notion that a loss of SSM is a primary driver of NMJ degradation and leave open questions of the mechanisms that regulate SSM number as well as the physiological significance of the precise SSM number. Further investigations are required to define other properties of the SSM, such as transcriptional profiles and structural integrity, to better understand their role in NMJ maintenance.

Vemurafenib improves muscle histopathology in a mouse model of LAMA2-related congenital muscular dystrophy

Laminin-α2-related congenital muscular dystrophy (LAMA2-CMD) is a neuromuscular disease affecting around 1-9 in 1,000,000 children. LAMA2-CMD is caused by mutations in the LAMA2 gene resulting in the loss of laminin-211/221 heterotrimers in skeletal muscle. LAMA2-CMD patients exhibit severe hypotonia and progressive muscle weakness. Currently, there is no effective treatment for LAMA2-CMD and patients die prematurely. The loss of laminin-α2 results in muscle degeneration, defective muscle repair and dysregulation of multiple signaling pathways. Signaling pathways that regulate muscle metabolism, survival and fibrosis have been shown to be dysregulated in LAMA2-CMD. As vemurafenib is a US Food and Drug Administration (FDA)-approved serine/threonine kinase inhibitor, we investigated whether vemurafenib could restore some of the serine/threonine kinase-related signaling pathways and prevent disease progression in the dyW-/- mouse model of LAMA2-CMD. Our results show that vemurafenib reduced muscle fibrosis, increased myofiber size and reduced the percentage of fibers with centrally located nuclei in dyW-/- mouse hindlimbs. These studies show that treatment with vemurafenib restored the TGF-β/SMAD3 and mTORC1/p70S6K signaling pathways in skeletal muscle. Together, our results indicate that vemurafenib partially improves histopathology but does not improve muscle function in a mouse model of LAMA2-CMD.