Transcriptomic profile of semitendinosus muscle of bulls of different breed and performance

The aim of the study was to compare the transcriptomic profiles of fully differentiated skeletal muscle derived from bulls belonging to different breeds of varying performance. Microarray analyses were performed to determine the differences in the expression profiles of genes between semitendinosus muscles of 15-month-old beef-breed bulls (Limousin—LIM and Hereford—HER) and dairy-breed bulls (Holstein Friesian—HF). These analyses allowed for the identification of those genes the expression of which is similar and characteristic of fully differentiated muscle in beef breeds, but differs in skeletal muscle of a typical dairy breed. The analysis revealed 463 transcripts showing similar expression in the semitendinosus muscle of beef breeds (LIM/HER), in comparison with the dairy breed (HF). Among the identified genes, 227 were upregulated and 236 were downregulated in beef breeds. The ontological analyses revealed that the largest group of genes similarly expressed in LIM and HER was involved in the processes of protein metabolism and development of muscle organ. In beef breeds, some genes involved in protein synthesis and proteolysis showed an upregulation, including ctsd, ctsf, fhl2, fhl3, fst, sirt1, and trim63, whereas some were downregulated, including bmpr1a, bmpr2, mstn, smad2, hspa8, gsk3β, and tgfβ2. The expression of the chosen genes was confirmed by RT-qPCR technique. Thus, it can be assumed that the identified genes involved in the regulation of growth and development of muscle tissue and the processes of protein metabolism in the examined cattle breeds may be responsible for the greater gain of muscle mass in beef-breed bulls.

Impaired regeneration: A role for the muscle microenvironment in cancer cachexia

While changes in muscle protein synthesis and degradation have long been known to contribute to muscle wasting, a body of literature has arisen which suggests that regulation of the satellite cell and its ensuing regenerative program are impaired in atrophied muscle. Lessons learned from cancer cachexia suggest that this regulation is simply not a consequence, but a contributing factor to the wasting process. In addition to satellite cells, evidence from mouse models of cancer cachexia also suggests that non-satellite progenitor cells from the muscle microenvironment are also involved. This chapter in the series reviews the evidence of dysfunctional muscle repair in multiple wasting conditions. Potential mechanisms for this dysfunctional regeneration are discussed, particularly in the context of cancer cachexia.

Growth and Development Symposium: Impacts of inflammation on cattle growth and carcass merit

Inflammation caused by bovine respiratory disease (BRD) continues to be one of the greatest challenges facing beef cattle producers and feedlot managers. Inflammation decreases DMI, ADG, and G:F in feedlot calves, decreasing growth rate and increasing days on feed, which results in economic losses during the feeding period. During the past decade, marketing of feedlot animals has changed from selling cattle on a live basis to a grid-based marketing system. When cattle are marketed on a live basis, the economic effects of BRD stop at increased health cost and decreased feedlot performance, carcass weight, and death loss. However, when cattle are marketed in a grid-based system, inflammation has the potential to also affect carcass cutability and quality. The effects of inflammation on feedlot cattle in regards to performance are well understood; however, specific effects on cattle growth and ultimately carcass merit are not as well described. Recent studies in feedlot cattle have indicated that the incidence of BRD decreases both HCW and marbling; however, mechanisms are not understood. Research in other species has demonstrated that during the acute phase response, pro-inflammatory cytokines promote skeletal muscle catabolism to supply AA and energy substrates for immune tissues. Further, during this early immune response, the liver changes its metabolic priorities to the production of acute phase proteins for use in host defense. Together these dramatic shifts in systemic metabolism may explain the detrimental effects on performance and carcass traits commonly associated with BRD in feedlot calves. Moreover, recent studies relative to human health have revealed complex multilevel interactions between the metabolic and immune systems, and highlighted inflammation as being a significant contributor to major metabolic diseases. The objective of this paper is to review data to help explain the economical and physiological effects of inflammation on cattle growth and carcass merit.

The central role of myostatin in skeletal muscle and whole body homeostasis

Myostatin is a powerful negative regulator of skeletal muscle mass in mammalian species. It plays a key role in skeletal muscle homeostasis and has now been well described since its discovery. Myostatin is capable of inducing muscle atrophy via its inhibition of myoblast proliferation, increasing ubiquitin-proteasomal activity and downregulating activity of the IGF-Akt pathway. These well-recognized effects are seen in multiple atrophy causing situations, including injury, diseases such as cachexia, disuse and space flight, demonstrating the importance of the myostatin signalling mechanism. Based on this central role, significant work has been pursued to inhibit myostatin's actions in vivo. Importantly, several new studies have uncovered roles for myostatin distinct from skeletal muscle size. Myostatin has been suggested to play a role in cardiomyocyte homeostasis, glucose metabolism and adipocyte proliferation, all of which are examined in detail below. Based on these effects, myostatin inhibition has potential to be widely utilized in many Western diseases such as chronic obstructive pulmonary disease, type II diabetes and obesity. However, if myostatin inhibitors are to successfully translate from bench-top to bedside in the near future, awareness must be raised on these non-traditional effects of myostatin away from skeletal muscle. Indeed, further research into these novel areas is required.

The role of myostatin in muscle wasting: an overview

Myostatin is an extracellular cytokine mostly expressed in skeletal muscles and known to play a crucial role in the negative regulation of muscle mass. Upon the binding to activin type IIB receptor, myostatin can initiate several different signalling cascades resulting in the upregulation of the atrogenes and downregulation of the important for myogenesis genes. Muscle size is regulated via a complex interplay of myostatin signalling with the insulin-like growth factor 1/phosphatidylinositol 3-kinase/Akt pathway responsible for increase in protein synthesis in muscle. Therefore, the regulation of muscle weight is a process in which myostatin plays a central role but the mechanism of its action and signalling cascades are not fully understood. Myostatin upregulation was observed in the pathogenesis of muscle wasting during cachexia associated with different diseases (i.e. cancer, heart failure, HIV). Characterisation of myostatin signalling is therefore a perspective direction in the treatment development for cachexia. The current review covers the present knowledge about myostatin signalling pathways leading to muscle wasting and the state of therapy approaches via the regulation of myostatin and/or its downstream targets in cachexia.

NF-kappaB signaling: a tale of two pathways in skeletal myogenesis

NF-kappaB is a ubiquitiously expressed transcription factor that plays vital roles in innate immunity and other processes involving cellular survival, proliferation, and differentiation. Activation of NF-kappaB is controlled by an IkappaB kinase (IKK) complex that can direct either canonical (classical) NF-kappaB signaling by degrading the IkappaB inhibitor and releasing p65/p50 dimers to the nucleus, or causes p100 processing and nuclear translocation of RelB/p52 via a noncanonical (alternative) pathway. Under physiological conditions, NF-kappaB activity is transiently regulated, whereas constitutive activation of this transcription factor typically in the classical pathway is associated with a multitude of disease conditions, including those related to skeletal muscle. How NF-kappaB functions in muscle diseases is currently under intense investigation. Insight into this role of NF-kappaB may be gained by understanding at a more basic level how this transcription factor contributes to skeletal muscle cell differentiation. Recent data from knockout mice support that the classical NF-kappaB pathway functions as an inhibitor of skeletal myogenesis and muscle regeneration acting through multiple mechanisms. In contrast, alternative NF-kappaB signaling does not appear to be required for myofiber conversion, but instead functions in myotube homeostasis by regulating mitochondrial biogenesis. Additional knowledge of these signaling pathways in skeletal myogenesis should aid in the development of specific inhibitors that may be useful in treatments of muscle disorders.

Impact of exercise training on myostatin expression in the myocardium and skeletal muscle in a chronic heart failure model

AIMS

In late-stage chronic heart failure (CHF), elevated cytokines and cachexia are often observed. Several studies have shown that exercise training exerts beneficial effects on skeletal muscle in this setting. Furthermore, it has been shown that the expression of myostatin, a key regulator of skeletal muscle mass, is increased in a variety of cachectic states. This study aimed to investigate the expression of myostatin in CHF, the influence of exercise training on myostatin levels, and regulation of myostatin by tumour necrosis factor-alpha (TNF-alpha).

METHODS AND RESULTS

In an animal model of CHF (LAD-ligation model), protein expression of myostatin was elevated 2.4-fold in the skeletal muscle and more than four-times in the myocardium, compared with control (Co). Exercise training on a treadmill over 4 weeks led to a significant reduction in myostatin protein expression in the skeletal muscle and the myocardium of CHF animals, with values returning to baseline levels. In differentiated C2C12 cells, TNF-alpha induced the expression of myostatin through a p38MAPK-dependent pathway involving nuclear factor kappa-B (NF-kappaB). The increased TNF-alpha mRNA levels in the skeletal muscle of CHF animals correlated significantly with myostatin expression.

CONCLUSION

These alterations in myostatin expression in the skeletal and heart muscle following exercise training could help to explain the beneficial anti-catabolic effects of exercise training in CHF.

Skeletal muscle diseases, inflammation, and NF-kappaB signaling: insights and opportunities for therapeutic intervention

Signaling through nuclear factor-kappa B (NF-kappaB) is emerging as an important regulator of muscle development, maintenance, and regeneration. Classic signaling modulates early muscle development by enhancing proliferation and inhibiting differentiation, and alternative signaling promotes myofiber maintenance and metabolism. Likewise, NF-kappaB signaling is critical for the development of immunity. Although these processes occur normally, dysregulation of NF-kappaB signaling has prohibitive effects on muscle growth and regeneration and can perpetuate inflammation in muscle diseases. Aberrant NF-kappaB signaling from immune and muscle cells has been detected and implicated in the pathologic progression of numerous dystrophies and myopathies, indicating that targeted NF-kappaB inhibitors may prove clinically beneficial.

Myostatin is a procachectic growth factor during postnatal myogenesis

PURPOSE OF REVIEW

To describe the most relevant recent observations concerning the molecular mechanisms behind myostatin-induced muscle wasting.

RECENT FINDINGS

The main theme of this review is to summarize the biology and function of myostatin. Myostatin is a secreted growth factor that negatively regulates muscle growth. While inactivation of myostatin leads to muscle growth in vivo, excess levels of myostatin induces cachectic-like muscle wasting. Molecular analyses reveal that excess levels of myostatin induce Atrogin-1 expression by reducing Akt phosphorylation and thereby increasing FoxO1 activity. Recent findings have further speculated that myostatin may also play a role in cardiac cachexia.

SUMMARY

As myostatin is a potent inducer of muscle wasting, antagonists to myostatin have been speculated to have great therapeutic value in alleviating muscle wasting. Indeed, myostatin peptide antagonists and antibodies have shown great promise in containing muscle loss in animal models of muscle wasting. Given the beneficial effects of myostatin antagonists in animal models, clinical trials are underway with myostatin antibodies, peptibodies and soluble receptor. Therefore, this review article on the role of myostatin in muscle wasting is highly relevant to current themes in muscle biology.

NF-kappaB regulation of YY1 inhibits skeletal myogenesis through transcriptional silencing of myofibrillar genes

NF-kappaB signaling is implicated as an important regulator of skeletal muscle homeostasis, but the mechanisms by which this transcription factor contributes to muscle maturation and turnover remain unclear. To gain insight into these mechanisms, gene expression profiling was examined in C2C12 myoblasts devoid of NF-kappaB activity. Interestingly, even in proliferating myoblasts, the absence of NF-kappaB caused the pronounced induction of several myofibrillar genes, suggesting that NF-kappaB functions as a negative regulator of late-stage muscle differentiation. Although several myofibrillar promoters contain predicted NF-kappaB binding sites, functional analysis using the troponin-I2 gene as a model revealed that NF-kappaB-mediated repression does not occur through direct DNA binding. In the search for an indirect mediator, the transcriptional repressor YinYang1 (YY1) was identified. While inducers of NF-kappaB stimulated YY1 expression in multiple cell types, genetic ablation of the RelA/p65 subunit of NF-kappaB in both cultured cells and adult skeletal muscle correlated with reduced YY1 transcripts and protein. NF-kappaB regulation of YY1 occurred at the transcriptional level, mediated by direct binding of the p50/p65 heterodimer complex to the YY1 promoter. Furthermore, YY1 was found associated with multiple myofibrillar promoters in C2C12 myoblasts containing NF-kappaB activity. Based on these results, we propose that NF-kappaB regulation of YY1 and transcriptional silencing of myofibrillar genes represent a new mechanism by which NF-kappaB functions in myoblasts to modulate skeletal muscle differentiation.

Cancer Cachexia Signaling Pathways Continue to Emerge Yet Much Still Points to the Proteasome: Fig. 1

Cachexia is a life-threatening consequence of cancer that diminishes both quality of life and survival. It is a syndrome that is characterized by extreme weight loss resulting mainly from the depletion of skeletal muscle. Research from the past decades investigating the mechanisms of tumor-induced muscle wasting has identified several key cachectic factors that act through the ubiquitin-dependent proteasome system. Signaling pathways that mediate the effects of these cachectic factors have also subsequently emerged. Here, we review some of these pathways specific to myostatin, nuclear factor kappaB, and the newly elucidated dystrophin glycoprotein complex. Although these molecules are likely to employ distinct modes of action, results suggest that they nevertheless maintain a link to the proteasome pathway. Therefore, although the proteasome remains a preferred choice for therapy, the continually emerging upstream signaling molecules serve as additional promising therapeutic targets for the treatment of tumor-induced muscle wasting.

Endoplasmic reticulum stress induces myostatin precursor protein and NF-kappaB in cultured human muscle fibers: relevance to inclusion body myositis

Sporadic-inclusion body myositis (s-IBM) is the most common progressive muscle disease of older persons. It leads to pronounced muscle fiber atrophy and weakness, and there is no successful treatment. We have previously shown that myostatin precursor protein (MstnPP) and myostatin (Mstn) dimer are increased in biopsied s-IBM muscle fibers, and proposed that MstnPP/Mstn increase may contribute to muscle fiber atrophy and weakness in s-IBM patients. Mstn is known to be a negative regulator of muscle fiber mass. It is synthesized as MstnPP, which undergoes posttranslational processing in the muscle fiber to produce mature, active Mstn. To explore possible mechanisms involved in Mstn abnormalities in s-IBM, in the present study we utilized primary cultures of normal human muscle fibers and experimentally modified the intracellular micro-environment to induce endoplasmic-reticulum (ER)-stress, thereby mimicking an important aspect of the s-IBM muscle fiber milieu. ER stress was induced by treating well-differentiated cultured muscle fibers with either tunicamycin or thapsigargin, both well-established ER stress inducers. Our results indicate for the first time that the ER stress significantly increased MstnPP mRNA and protein. The results also suggest that in our system ER stress activates NF-kappaB, and we suggest that MstnPP increase occurred through the ER-stress-activated NF-kappaB. We therefore propose a novel mechanism leading to the Mstn increase in s-IBM. Accordingly, interfering with pathways inducing ER stress, NF-kappaB activation or its action on the MstnPP gene promoter might prevent Mstn increase and provide a new therapeutic approach for s-IBM and, possibly, for muscle atrophy in other neuromuscular diseases.

Myostatin induces cachexia by activating the ubiquitin proteolytic system through an NF-κB-independent, FoxO1-dependent mechanism

Myostatin, a transforming growth factor-beta (TGF-beta) super-family member, has been well characterized as a negative regulator of muscle growth and development. Myostatin has been implicated in several forms of muscle wasting including the severe cachexia observed as a result of conditions such as AIDS and liver cirrhosis. Here we show that Myostatin induces cachexia by a mechanism independent of NF-kappaB. Myostatin treatment resulted in a reduction in both myotube number and size in vitro, as well as a loss in body mass in vivo. Furthermore, the expression of the myogenic genes myoD and pax3 was reduced, while NF-kappaB (the p65 subunit) localization and expression remained unchanged. In addition, promoter analysis has confirmed Myostatin inhibition of myoD and pax3. An increase in the expression of genes involved in ubiquitin-mediated proteolysis is observed during many forms of muscle wasting. Hence we analyzed the effect of Myostatin treatment on proteolytic gene expression. The ubiquitin associated genes atrogin-1, MuRF-1, and E214k were upregulated following Myostatin treatment. We analyzed how Myostatin may be signaling to induce cachexia. Myostatin signaling reversed the IGF-1/PI3K/AKT hypertrophy pathway by inhibiting AKT phosphorylation thereby increasing the levels of active FoxO1, allowing for increased expression of atrophy-related genes. Therefore, our results suggest that Myostatin induces cachexia through an NF-kappaB-independent mechanism. Furthermore, increased Myostatin levels appear to antagonize hypertrophy signaling through regulation of the AKT-FoxO1 pathway.