MicroRNAs in Skeletal Muscle and Hints on Their Potential Role in Muscle Wasting During Cancer Cachexia

The Neuromuscular Disorder Mediated by Extracellular Vesicles in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) represents a neurodegenerative disorder characterized by the progressive loss of both upper and lower motor neurons, resulting in muscular atrophy and eventual paralysis. While much research has concentrated on investigating the impact of major mutations associated with ALS on motor neurons and central nervous system (CNS) cells, recent studies have unveiled that ALS pathogenesis extends beyond CNS imbalances, encompassing dysregulation in other tissues such as skeletal muscle. Evidence from animal models and patients supports this broader perspective. Skeletal muscle, once considered solely as an effector organ, is now recognized as possessing significant secretory activity capable of influencing motor neuron survival. However, the precise cellular and molecular mechanisms underlying the detrimental effects observed in muscle and its associated structures in ALS remain poorly understood. Additionally, emerging data suggest that extracellular vesicles (EVs) may play a role in the establishment and function of the neuromuscular junction (NMJ) under both physiological and pathological conditions and in wasting and regeneration of skeletal muscles, particularly in neurodegenerative diseases like ALS. This review aims to explore the key findings about skeletal muscle involvement in ALS, shedding light on the potential underlying mechanisms and contributions of EVs and their possible application for the design of biosensors.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Exploring the Integrated Role of miRNAs and lncRNAs in Regulating the Transcriptional Response to Amino Acids and Insulin-like Growth Factor 1 in Gilthead Sea Bream (Sparus aurata) Myoblasts

In this study, gilthead sea bream (Sparus aurata) fast muscle myoblasts were stimulated with two pro-growth treatments, amino acids (AA) and insulin-like growth factor 1 (Igf-1), to analyze the transcriptional response of mRNAs, microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) and to explore their possible regulatory network using bioinformatic approaches. AA had a higher impact on transcription (1795 mRNAs changed) compared to Igf-1 (385 mRNAs changed). Both treatments stimulated the transcription of mRNAs related to muscle differentiation (GO:0042692) and sarcomere (GO:0030017), while AA strongly stimulated DNA replication and cell division (GO:0007049). Both pro-growth treatments altered the transcription of over 100 miRNAs, including muscle-specific miRNAs (myomiRs), such as miR-133a/b, miR-206, miR-499, miR-1, and miR-27a. Among 111 detected lncRNAs (>1 FPKM), only 30 were significantly changed by AA and 11 by Igf-1. Eight lncRNAs exhibited strong negative correlations with several mRNAs, suggesting a possible regulation, while 30 lncRNAs showed strong correlations and interactions with several miRNAs, suggesting a role as sponges. This work is the first step in the identification of the ncRNAs network controlling muscle development and growth in gilthead sea bream, pointing out potential regulatory mechanisms in response to pro-growth signals.

The role of extracellular vesicles in skeletal muscle wasting

Skeletal muscle wasting is a complicated metabolic syndrome accompanied by multiple diseases ranging from cancer to metabolic disorders and infectious conditions. The loss of muscle mass significantly impairs muscle function, resulting in poor quality of life and high mortality of associated diseases. The fundamental cellular and molecular mechanisms inducing muscle wasting have been well established, and those related pathways can be activated by a variety of extracellular signals, including inflammatory cytokines and catabolic stimuli. As an emerging messenger of cell-to-cell communications, extracellular vesicles (EVs) also get involved in the progression of muscle wasting by transferring bioactive cargoes including various proteins and non-coding RNAs to skeletal muscle. Like a double-edged sword, EVs play either a pro-wasting or anti-wasting role in the progression of muscle wasting, highly dependent on their parental cells as well as the specific type of cargo they encapsulate. This review aims to illustrate the current knowledge about the biological function of EVs cargoes in skeletal muscle wasting. Additionally, the potential therapeutic implications of EVs in the diagnosis and treatment of skeletal muscle wasting are also discussed. Simultaneously, several outstanding questions are included to shed light on future research.

Modelling three-dimensional cancer-associated cachexia and therapy: The molecular basis and therapeutic potential of interleukin-6 transignalling blockade

BACKGROUND

Causes and mechanisms underlying cancer cachexia are not fully understood, and currently, no therapeutic approaches are available to completely reverse the cachectic phenotype. Interleukin-6 (IL-6) has been extensively described as a key factor in skeletal muscle physiopathology, exerting opposite roles through different signalling pathways.

METHODS

We employed a three-dimensional ex vivo muscle engineered tissue (X-MET) to model cancer-associated cachexia and to study the effectiveness of selective inhibition of IL-6 transignalling in counteracting the cachectic phenotype. Conditioned medium (CM) derived from C26 adenocarcinoma cells was used as a source of soluble factors contributing to the establishment of cancer cachexia in the X-MET model. A dose of 1.2 ng/mL of glycoprotein-130 fused chimaera (gp130Fc) was added to cachectic culture medium to neutralize IL-6 transignalling.

RESULTS

C26-conditioned medium induced a cachectic-like phenotype in the X-MET, leading to a decline of muscle mass (-60%; P < 0.001), a reduction in myosin expression (-92.4%; P < 0.005) and a reduction of the contraction frequency spectrum (-94%). C26-conditioned medium contains elevated amounts of IL-6 (8.61 ± 4.09 pg/mL) and IL6R (56.85 ± 10.96 pg/mL). These released factors activated the signal transducer and activator of transcription 3 (STAT3) signalling in the C26_CM X-MET system (phosphorylated STAT3/TOTAL +54.6%; P < 0.005), which in turn promote an enhancement of Il-6 (+69.2%; P < 0.05) and Il6r (+43%; P < 0.05) gene expression, suggesting the induction of a feed-forward loop. The selective neutralization of IL-6 transignalling, by gp130Fc, in C26_CM X-MET prevented the hyperactivation of STAT3 (-55.8%; P < 0.005), countered the reduction of cross-sectional area (+28.2%; P < 0.05) and reduced the expression of proteolytic factors including muscle ring finger-1 (-88%; P < 0.005) and ATROGIN1 (-92%; P < 0.05), thus preserving the robustness and increasing the contractile force (+20%) of the three-dimensional muscle system. Interestingly, the selective inhibition of IL-6 transignalling modulated gene regulatory networks involved in myogenesis and apoptosis, normalizing the expression of pro-apoptotic miRNAs, including miR-31 (-53.2%; P < 0.05) and miR-34c (-65%; P < 0.005), and resulting in the reduction of apoptotic pathways highlighted by the sensible reduction of cleaved caspase 3 (-92.5%; P < 0.005) in gp130Fc-treated C26_CM X-MET.

CONCLUSIONS

IL-6 transignalling appeared as a promising target to counter cancer cachexia-related alterations. The X-MET model has proven to be a reliable drug-screening tool to identify novel therapeutic approaches and to test them in preclinical studies, significantly reducing the use of animal models.

Targeting Epigenetic Regulators with HDAC and BET Inhibitors to Modulate Muscle Wasting

Epigenetic changes contribute to the profound alteration in the transcriptional program associated with the onset and progression of muscle wasting in several pathological conditions. Although HDACs and their inhibitors have been extensively studied in the field of muscular dystrophies, the potential of epigenetic inhibitors has only been marginally explored in other disorders associated with muscle atrophy, such as in cancer cachexia and sarcopenia. BET inhibitors represent a novel class of recently developed epigenetic drugs that display beneficial effects in a variety of diseases beyond malignancies. Based on the preliminary in vitro and preclinical data, HDACs and BET proteins contribute to the pathogenesis of cancer cachexia and sarcopenia, modulating processes related to skeletal muscle mass maintenance and/or metabolism. Thus, epigenetic drugs targeting HDACs and BET proteins may emerge as promising strategies to reverse the catabolic phenotype associated with cachexia and sarcopenia. Further preclinical studies are warranted to delve deeper into the molecular mechanisms associated with the functions of HDACs and BET proteins in muscle atrophy and to establish whether their epigenetic inhibitors represent a prospective therapeutic avenue to alleviate muscle wasting.

Mitochondrial Dysfunction in Intensive Care Unit-Acquired Weakness and Critical Illness Myopathy: A Narrative Review

Mitochondria are key structures providing most of the energy needed to maintain homeostasis. They are the main source of adenosine triphosphate (ATP), participate in glucose, lipid and amino acid metabolism, store calcium and are integral components in various intracellular signaling cascades. However, due to their crucial role in cellular integrity, mitochondrial damage and dysregulation in the context of critical illness can severely impair organ function, leading to energetic crisis and organ failure. Skeletal muscle tissue is rich in mitochondria and, therefore, particularly vulnerable to mitochondrial dysfunction. Intensive care unit-acquired weakness (ICUAW) and critical illness myopathy (CIM) are phenomena of generalized weakness and atrophying skeletal muscle wasting, including preferential myosin breakdown in critical illness, which has also been linked to mitochondrial failure. Hence, imbalanced mitochondrial dynamics, dysregulation of the respiratory chain complexes, alterations in gene expression, disturbed signal transduction as well as impaired nutrient utilization have been proposed as underlying mechanisms. This narrative review aims to highlight the current known molecular mechanisms immanent in mitochondrial dysfunction of patients suffering from ICUAW and CIM, as well as to discuss possible implications for muscle phenotype, function and therapeutic approaches.

The Cellular and Molecular Signature of ALS in Muscle

Amyotrophic lateral sclerosis is a disease affecting upper and lower motor neurons. Although motor neuron death is the core event of ALS pathology, it is increasingly recognized that other tissues and cell types are affected in the disease, making potentially major contributions to the occurrence and progression of pathology. We review here the known cellular and molecular characteristics of muscle tissue affected by ALS. Evidence of toxicity in skeletal muscle tissue is considered, including metabolic dysfunctions, impaired proteostasis, and deficits in muscle regeneration and RNA metabolism. The role of muscle as a secretory organ, and effects on the skeletal muscle secretome are also covered, including the increase in secretion of toxic factors or decrease in essential factors that have consequences for neuronal function and survival.

Coding and Noncoding Genes Involved in Atrophy and Compensatory Muscle Growth in Nile Tilapia

Improvements in growth-related traits reduce fish time and production costs to reach market size. Feed deprivation and refeeding cycles have been introduced to maximize aquaculture profits through compensatory growth. However, the molecular compensatory growth signature is still uncertain in Nile tilapia. In this study, fish were subjected to two weeks of fasting followed by two weeks of refeeding. The growth curve in refed tilapia was suggestive of a partial compensatory response. Transcriptome profiling of starved and refed fish was conducted to identify genes regulating muscle atrophy and compensatory growth. Pairwise comparisons revealed 5009 and 478 differentially expressed (differential) transcripts during muscle atrophy and recovery, respectively. Muscle atrophy appears to be mediated by the ubiquitin-proteasome and autophagy/lysosome systems. Autophagy-related 2A, F-box and WD repeat domain containing 7, F-box only protein 32, miR-137, and miR-153 showed exceptional high expression suggesting them as master regulators of muscle atrophy. On the other hand, the muscle compensatory growth response appears to be mediated by the continuous stimulation of muscle hypertrophy which exceeded normal levels found in control fish. For instance, genes promoting ribosome biogenesis or enhancing the efficiency of translational machinery were upregulated in compensatory muscle growth. Additionally, myogenic microRNAs (e.g., miR-1 and miR-206), and hypertrophy-associated microRNAs (e.g., miR-27a-3p, miR-29c, and miR-29c) were reciprocally expressed to favor hypertrophy during muscle recovery. Overall, the present study provided insights into the molecular mechanisms regulating muscle mass in fish. The study pinpoints extensive growth-related gene networks that could be used to inform breeding programs and also serve as valuable genomic resources for future mechanistic studies.

MicroRNAs: Novel players in the diagnosis and treatment of cancer cachexia (Review)

Cachexia denotes a complex metabolic syndrome featuring severe loss of weight, fatigue and anorexia. In total, 50-80% of patients suffering from advanced cancer are diagnosed with cancer cachexia, which contributes to 40% of cancer-associated mortalities. MicroRNAs (miRNAs) are non-coding RNAs capable of regulating gene expression. Dysregulated miRNA expression has been observed in muscle tissue, adipose tissue and blood samples from patients with cancer cachexia compared with that of samples from patients with cancer without cachexia or healthy controls. In addition, miRNAs promote and maintain the malignant state of systemic inflammation, while inflammation contributes to cancer cachexia. The present review discusses the role of miRNAs in the progression of cancer cachexia, and assess their diagnostic value and potential therapeutic value.

Cardiac Remodeling After Myocardial Infarction: Functional Contribution of microRNAs to Inflammation and Fibrosis

After an ischemic injury, the heart undergoes a complex process of structural and functional remodeling that involves several steps, including inflammatory and fibrotic responses. In this review, we are focusing on the contribution of microRNAs in the regulation of inflammation and fibrosis after myocardial infarction. We summarize the most updated studies exploring the interactions between microRNAs and key regulators of inflammation and fibroblast activation and we discuss the recent discoveries, including clinical applications, in these rapidly advancing fields.

Non-coding RNA basis of muscle atrophy

Muscle atrophy is a common complication of many chronic diseases including heart failure, cancer cachexia, aging, etc. Unhealthy habits and usage of hormones such as dexamethasone can also lead to muscle atrophy. However, the underlying mechanisms of muscle atrophy are not completely understood. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long ncRNAs (lncRNAs), and circular RNAs (circRNAs), play vital roles in muscle atrophy. This review mainly discusses the regulation of ncRNAs in muscle atrophy induced by various factors such as heart failure, cancer cachexia, aging, chronic obstructive pulmonary disease (COPD), peripheral nerve injury (PNI), chronic kidney disease (CKD), unhealthy habits, and usage of hormones; highlights the findings of ncRNAs as common regulators in multiple types of muscle atrophy; and summarizes current therapies and underlying mechanisms for muscle atrophy. This review will deepen the understanding of skeletal muscle biology and provide new strategies and insights into gene therapy for muscle atrophy.

Therapeutic Implications of miRNAs for Muscle-Wasting Conditions

MicroRNAs (miRNAs) are small, non-coding RNA molecules that are mainly involved in translational repression by binding to specific messenger RNAs. Recently, miRNAs have emerged as biomarkers, relevant for a multitude of pathophysiological conditions, and cells can selectively sort miRNAs into extracellular vesicles for paracrine and endocrine effects. In the overall context of muscle-wasting conditions, a multitude of miRNAs has been implied as being responsible for the typical dysregulation of anabolic and catabolic pathways. In general, chronic muscle disorders are associated with the main characteristic of a substantial loss in muscle mass. Muscular dystrophies (MDs) are a group of genetic diseases that cause muscle weakness and degeneration. Typically, MDs are caused by mutations in those genes responsible for upholding the integrity of muscle structure and function. Recently, the dysregulation of miRNA levels in such pathological conditions has been reported. This revelation is imperative for both MDs and other muscle-wasting conditions, such as sarcopenia and cancer cachexia. The expression levels of miRNAs have immense potential for use as potential diagnostic, prognostic and therapeutic biomarkers. Understanding the role of miRNAs in muscle-wasting conditions may lead to the development of novel strategies for the improvement of patient management.

Dynamic changes of miRNAs in skeletal muscle development at New Zealand rabbits

BACKGROUND

miRNA is one of the crucial roles in the complex and dynamic network that regulates the development of skeletal muscle. The landscape of skeletal muscle miRNAs from fetus to adult in New Zealand rabbits has not been revealed yet.

RESULTS

In this study, nine RNA-seq libraries of fetus, child and adult rabbits' leg muscles were constructed. A total of 278 differentially expressed miRNAs (DEmiRNAs) were identified. In the fetus vs. child group, the main functional enrichments were involved in membrane and transport. Pathway enriched terms of up-regulated DEmiRNAs were connected with the differentiation and hypertrophy of skeletal muscle, and down-regulated ones were related to muscle structure and metabolic capacity. In the child vs. adult group, functions were associated to positioning and transportation, and pathways were relevant to ECM, muscle structure and hypertrophy. Finally, ocu-miR-185-3p and ocu-miR-370-3p, which had the most target genes, were identified as hub-miRNAs in these two groups.

CONCLUSIONS

In short, we summarized the highly expressed and uniquely expressed DEmiRNAs of fetus, child and adult rabbits' leg muscles. Besides, the potential functional changes of miRNAs in two consecutive stages have been explored. Among them, the ocu-miR-185-3p and ocu-miR-370-3p with the most target genes were selected as hub-miRNAs. These data improved the understanding of the regulatory molecules of meat rabbit development, and provided a novel perspective for molecular breeding of meat rabbits.

Mechanisms of exercise as a preventative measure to muscle wasting

Skeletal muscle is the most abundant tissue in healthy individuals and it has important roles in health beyond voluntary movement. The overall mass and energy requirements of skeletal muscle require it to be metabolically active and flexible to multiple energy substrates. The tissue has evolved to be largely load dependent and it readily adapts in a number of positive ways to repetitive overload, such as various forms of exercise training. However, unloading from extended bed rest and/or metabolic derangements in response to trauma, acute illness, or severe pathology, commonly results in rapid muscle wasting. Decline in muscle mass contributes to multimorbidity, reduces function, and exerts a substantial, negative impact on the quality of life. The principal mechanisms controlling muscle mass have been well described and these cellular processes are intricately regulated by exercise. Accordingly, exercise has shown great promise and efficacy in preventing or slowing muscle wasting through changes in molecular physiology, organelle function, cell signaling pathways, and epigenetic regulation. In this review, we focus on the role of exercise in altering the molecular landscape of skeletal muscle in a manner that improves or maintains its health and function in the presence of unloading or disease.epigenetics; exercise; muscle wasting; resistance training; skeletal muscle.