Omega-3 fatty acid EPA improves regenerative capacity of mouse skeletal muscle cells exposed to saturated fat and inflammation

© 2016 The Author(s) Sarcopenic obesity is characterised by high fat mass, low muscle mass and an elevated inflammatory environmental milieu. We therefore investigated the effects of elevated inflammatory cytokine TNF-α (aging/obesity) and saturated fatty acid, palmitate (obesity) on skeletal muscle cells in the presence/absence of EPA, a-3 polyunsaturated fatty acid with proposed anti-inflammatory, anti-obesity activities. In the present study we show that palmitate was lipotoxic, inducing high levels of cell death and blocking myotube formation. Cell death under these conditions was associated with increased caspase activity, suppression of differentiation, reductions in both creatine kinase activity and gene expression of myogenic factors; IGF-II, IGFBP-5, MyoD and myogenin. However, inhibition of caspase activity via administration of Z-VDVAD-FMK (caspase-2), Z-DEVD-FMK (caspase-3) and ZIETD-KMK (caspase 8) was without effect on cell death. By contrast, lipotoxicity associated with elevated palmitate was reduced with the MEK inhibitor PD98059, indicating palmitate induced cell death was MAPK mediated. These lipotoxic conditions were further exacerbated in the presence of inflammation via TNF-α co-administration. Addition of EPA under cytotoxic stress (TNF-α) was shown to partially rescue differentiation with enhanced myotube formation being associated with increased MyoD, myogenin, IGF-II and IGFBP-5 expression. EPA had little impact on the cell death phenotype observed in lipotoxic conditions but did show benefit in restoring differentiation under lipotoxic plus cytotoxic conditions. Under these conditions Id3 (inhibitor of differentiation) gene expression was inversely linked with survival rates, potentially indicating a novel role of EPA and Id3 in the regulation of apoptosis in lipotoxic/cytotoxic conditions. Additionally, signalling studies indicated the combination of lipo- and cyto-toxic effects on the muscle cells acted through ceramide, JNK and MAPK pathways and blocking these pathways using PD98059 (MEK inhibitor) and Fumonisin B1 (ceramide inhibitor) significantly reduced levels of cell death. These findings highlight novel pathways associated with in vitro models of lipotoxicity (palmitate-mediated) and cytotoxicity (inflammatory cytokine mediated) in the potential targeting of molecular modulators of sarcopenic obesity

The molecular and cellular aspects of muscle degeneration and regeneration

The concept of skeletal muscle homeostasis - often viewed as the net balance between two separate processes, namely protein degradation and protein synthesis - are not occurring independently of each other, but are finely co-ordinated by a web of intricate signalling networks (Nader, 2005). Such signalling networks are in charge of executing environmental and cellular cues that ultimately determine whether muscle proteins are synthesised or degraded. Prolonged elevations of proinflammatory cytokines are closely associated with muscle wasting that occurs during the sarcopenia of ageing and in cachectic AIDS and cancer patients (Strle et a/. 2007). These clinical disorders occur along with a decline in IGF-I anabolic activity, which is consistent with in vitro findings in muscle progenitor cells (Strle et a/. 2007). Very low concentrations ofTNF-a (0.01-1 ng.ml") inhibit IGF-I-induced protein synthesis (Broussard et a/. 2003; Strle et al. 2004) and expression of the critical muscle differentiation factors, MyoD (Strle et a/., 2004) and myogenin (Broussard et al. 2003; Strle et a/. 2004). Potential treatments that might overcome TNF-a-induced hormone resistance in myoblasts are unknown. Increased activation of the IGF/insulin pathway is an attractive target for combating many of the cachectic conditions associated with muscle wasting. Using rodent skeletal muscle cell lines we have investigated TNF-a/IGF-I interactions, in an attempt to mimic and understand mechanisms underlying the wasting process. We hypothesised that treatment of mouse myoblasts with TNF-a at specific doses ranging from high (20 ng.ml') to low (1.25 ng.ml") would result in dose-dependent block of differentiation and induction of apoptosis and that subsequent IGF-I co-incubations would stimulate myoblast survival and myotube formation. Objectives were to ascertain signalling pathways underpinning these outcomes. In contrast to our hypothesis, a novel role of IGF-I has been identified whereby eo-incubation of skeletal muscle C2 cells with IGF-I (1.5 ng.ml') and a non- apoptotic dose of TNF-a (1.25 ng.ml"; sufficient to block differentiation) unexpectedly were shown to facilitate a significant four-fold increase in myoblast death (P < 0.05). Specificity of the apoptotic potential of this growth factor was confirmed when neither bFGF-2 nor PDGF-BB (10 or 30 ng.ml' and 1.25 or 5 ng.rnl", respectively) were able to reveal the apoptotic potential of low dose TNF-a. By contrast, but in line with our II hypothesis, dosing with 10 ng.ml" TNF-a resulted in a block of differentiation and initiation of apoptosis, which was rescued by IGF-1. Preliminary signalling studies suggest that MAPK activation rather than the caspases are involved in the induction of death associated with low dose TNF-a (1.25 ng.mrl)/IGF-I incubation and therefore blocking the caspases would be without effect in this circumstance. The PI(3)K pathway is involved in the survival effects of high TNF-a (10 ng.mrl)/IGF co-incubations. Importantly, the rescue of death (regardless of the means required) did not facilitate differentiation and did not rescue the block of expression of IGF-ll or IGFBP-5 (produced by skeletal myoblasts as early events in their terminal differentiation and associated with preventing cell death) in our models. Using array technology we further established potential insulin survival and apoptotic genes that were upregulated in the above conditions and confirmed their expression with qRT-PCR. Of these genes three were selected to conduct gene silencing experiments. The gene silencing studies were effective in reducing expression of Adrald, Birc2 and Sirtl. Our findings suggest that inhibition of Adrald leads to an increase in myoblast death in conditions that are associated with myoblast survival and include basal conditions. This novel finding indicates Adrald expression to be essential for the general maintenance of myoblasts. This may be due to the multiple signalling pathways which the al-ARs regulate which include the PI(3)K-Akt pathway that is associated with growth and anti-apoptosis. Birc2 expression, which is upregulated in our cell model under conditions of myotoxic stress showed no significant effect on myoblast survival when suppressed. Associated with inhibition of apoptosis, it was hypothesised that inhibition of Birc2 would result in an increase in myoblast death however levels of damage were comparable to control myoblasts. Recent articles have stated that Birc, only when overexpressed above physiological levels, is associated with anti-apoptosis and consequently have proposed an alternative nomenclature that names the family after its distinctive structural feature, the BIR, rather than by inhibitor of apoptosis proteins lAPs (Silke & Vaux, 200 l; for review Srinivasula & Ashwell, 2008). Finally Sirtl, similar to Birc2 was highly expressed in conditions that induced the greatest incidence of myoblast death. Subsequent inhibition resulted in further increase in death which was not observed under basal conditions where myoblasts received DM alone. Unlike Adrald, this implicates Sirtl expression as a III survival mechanism which is specific for conditions associated with myotoxic stress. The mammalian Sirtl deacetylase was originally shown to modulate life-span in various species. However, the molecular mechanisms by which Sirtl increases longevity and with regard to the present study, survival, are largely unknown. In mammalian cells, Sirtl appears to control the cellular response to stress by regulating the FOXO family of Forkhead transcription factors. The FOXO family members are negatively regulated by the PI(3)K-Akt signalling pathway. Mammalian FOXOs control various biological functions, including cell cycle arrest, differentiation, repair of damaged DNA and apoptosis. Because the ability to regulate apoptosis and repair damage is correlated with increased organismal longevity and survival in many species these particular functions of FOXO transcription factors may be relevant to Sirtl ability to control longevity These experiments in myoblasts show that IGF-I (Lcng.ml') can facilitate apoptosis in the presence of non-a pop to tic doses ofTNF-a (1.25ng.mr\ which appears to depend not only on the upregulation of specific apoptosis genes (potentially downstream of MAPK) but also on the suppression of survival factors IGF-ll and IGFBP-5 which may also lie downstream of MAPK. These studies highlight the complex regulation of cell survival and cell death at the signalling level, as a consequence of interactions of one cytokine, TNF-a, and one growth factor, IGF-I. More information regarding the pathways involved in regulating their expression and activity will be necessary to fully understand the action of these molecules.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

In-vivo radiation diode dosimetry for therapeutic photon beams

In-vivo dosimetry with diode detectors is used in radiation therapy as a quality assurance tool. The diode sensitivity under radiation depends upon temperature, dose rate and SDD (source-to-detector distance), field size, beam angle, and energy. This dissertation presents the first systematic and quantitative study of dosimetric characteristics for most of the commercial radiation diodes (n-type and p-type) under different radiation beams.In the temperature dependence study, the systematic study on the dose rate dependence of svwt (sensitivity variation with temperature) was performed. It was concluded that sufficient preirradiation can eliminate dose rate dependence of svwt. However, preirradiation cannot eliminate dose rate dependence of the diode sensitivity, S, itself. In the dose rate and SDD dependence study, it was shown that the p-type diodes do not always show less dose rate dependence than the n-type diodes. Preirradiation does not always reduce diode dose rate dependence. SDD dependence of diode sensitivity can be explained by the instantaneous dose rate dependence if sufficient buildup is provided to eliminate electron contamination. An empirical formula was proposed to fit the dose rate dependence of diode sensitivity. In the energy dependence study, the energy dependence diode detectors are quantified. The empirical theory to quantify this effect was developed. Monte Carlo simulation and the cavity theory are used to predict the energy dependence. It was concluded that the energy dependence does not depend on whether the diode is n- or p- type but rather depends mainly on the material around the die (buildup and its geometry). A systematic study of the correction factors for accurate diode dosimetry is presented in this dissertation.This dissertation has established a theoretical foundation for the modeling of the transient electric and radiation properties of the diode detectors, separately. We believe that the Monte Carlo simulations code for radiation transport should be coupled with the continuity equations to describe the charge transport in the diode detector, and thus provides a complete quantitative description of dosimetric characteristics of the diode detectors. The ultimate goal is to use the diode detector as an absolute dosimeter, rather than as a relative dosimeter

In-vivo radiation diode dosimetry for therapeutic photon beams

In-vivo dosimetry with diode detectors is used in radiation therapy as a quality assurance tool. The diode sensitivity under radiation depends upon temperature, dose rate and SDD (source-to-detector distance), field size, beam angle, and energy. This dissertation presents the first systematic and quantitative study of dosimetric characteristics for most of the commercial radiation diodes (n-type and p-type) under different radiation beams.In the temperature dependence study, the systematic study on the dose rate dependence of svwt (sensitivity variation with temperature) was performed. It was concluded that sufficient preirradiation can eliminate dose rate dependence of svwt. However, preirradiation cannot eliminate dose rate dependence of the diode sensitivity, S, itself. In the dose rate and SDD dependence study, it was shown that the p-type diodes do not always show less dose rate dependence than the n-type diodes. Preirradiation does not always reduce diode dose rate dependence. SDD dependence of diode sensitivity can be explained by the instantaneous dose rate dependence if sufficient buildup is provided to eliminate electron contamination. An empirical formula was proposed to fit the dose rate dependence of diode sensitivity. In the energy dependence study, the energy dependence diode detectors are quantified. The empirical theory to quantify this effect was developed. Monte Carlo simulation and the cavity theory are used to predict the energy dependence. It was concluded that the energy dependence does not depend on whether the diode is n- or p- type but rather depends mainly on the material around the die (buildup and its geometry). A systematic study of the correction factors for accurate diode dosimetry is presented in this dissertation.This dissertation has established a theoretical foundation for the modeling of the transient electric and radiation properties of the diode detectors, separately. We believe that the Monte Carlo simulations code for radiation transport should be coupled with the continuity equations to describe the charge transport in the diode detector, and thus provides a complete quantitative description of dosimetric characteristics of the diode detectors. The ultimate goal is to use the diode detector as an absolute dosimeter, rather than as a relative dosimeter

Adult stem cells: the therapeutic potential of skeletal muscle

Embryonic stem cells have revolutionised our understanding of normal and deregulated growth and development. The potential to produce cells and tissues as needed offers enormous therapeutic potential. The use of these cells, however, is accompanied by ongoing ethical, religious and biomedical issues. The expansion potential and plasticity of adult stem cells have therefore received much interest. Adult skeletal muscle is highly adaptable, responding to both the hypertrophic and degenerative stresses placed upon it. This extreme plasticity is in part regulated by resident stem cells. In addition to regenerating muscle, if exposed to osteogenic or adipogenic inducers, these cells spontaneously form osteoblasts or adipocytes. The potential for and heterogeneity of muscle stem cells is underscored by the observation that CD45+ muscle side population cells are capable of reconstituting bone marrow in lethally irradiated mice and of contributing to neo-vascularisation of regenerating muscle. Finally, first attempts to replace infarcted myocardium relied on injection of skeletal myoblasts into the heart. Cells successfully engrafted and cardiac function was improved. Harnessing their differentiation/trans-differentiation capacity provides enormous potential for adult stem cells. In this review, current understanding of the different stem cells within muscle will be discussed as will their potential utility for regenerative medicine

Waste management—cytokines, growth factors and cachexia

Muscle damage with a lack of regeneration, manifests itself in several life-threatening diseases, including cancer cachexia, congestive heart failure, AIDS and sepsis. Often misdiagnosed as a condition simply of weight loss, cachexia is actually a highly complex metabolic disorder involving features of anorexia, anaemia, lipolysis and insulin resistance. A significant loss of lean body mass arises from such conditions, resulting in wasting of skeletal muscle. Unlike starvation, the weight loss seen in chronic illnesses arises equally from loss of muscle and of fat. The cachectic state is particularly problematic in cancer, typifying poor prognosis and often lowering responses to chemotherapy and radiation treatment. More than half of cancer patients suffer from cachexia, and strikingly, nearly one-third of cancer deaths are related to cachexia rather than the tumour burden. In considering this disorder, we are faced with a conundrum; how is it possible for uncontrolled growth to prevail in the tumour, in the face of unrestrained tissue loss in our muscles? Consistently, the catabolic state has been associated with a shift in the homeostatic balance between muscle synthesis and degradation mediated by the actions of growth factors and cytokines. Indeed, tumour necrosis factor-alpha (TNF-α) levels are raised in several animal models of cachectic muscle wasting, whereas the insulin-like growth factor (IGF) system acts potently to regulate muscle development, hypertrophy and maintenance. This concept of skeletal muscle homeostasis, often viewed as the net balance between two separate processes of protein synthesis and degradation has however changed. More recently, the view is that these two biochemical processes are not occurring independently of each other but in fact are finely co-ordinated by a web of intricate signalling networks. This review, therefore, aims to discuss data currently available regarding the mechanisms of degeneration and regeneration with specific emphasis on the potential and controversial cross-talk which may exist between anabolic growth factors (e.g. IGF-I) and catabolic cytokines (e.g. TNF-α). Also importantly, the potential impact at a cellular level of exercise, diet and age will be addressed. Finally, the ability to ‘hi-jack’ signalling pathways traditionally believed to be for growth and survival or death will be reviewed. It is anticipated that such a review will highlight significant gaps in our knowledge of the cachectic state as well as provide caution with regards to therapeutics suggesting total block on inflammatory processes such as that associated with TNF-α action

‘From Death, Lead Me to Immortality’ – Mantra of Ageing Skeletal Muscle

Skeletal muscle is a post-mitotic tissue maintained by repair and regeneration through a population of stem cell-like satellite cells. Following muscle injury, satellite cell proliferation is mediated by local signals ensuring sufficient progeny for tissue repair. Age–related changes in satellite cells as well as to the local and systemic environment potentially impact on the capacity of satellite cells to generate sufficient progeny in an ageing organism resulting in diminished regeneration. ‘Rejuvenation’ of satellite cell progeny and regenerative capacity by environmental stimuli effectors suggest that a subset of age-dependent satellite cell changes may be reversible. Epigenetic regulation of satellite stem cells that include DNA methylation and histone modifications which regulate gene expression are potential mechanisms for such reversible changes and have been shown to control organismal longevity. The area of health and ageing that is likely to benefit soonest from advances in the biology of adult stem cells is the emerging field of regenerative medicine. Further studies are needed to elucidate the mechanisms by which epigenetic modifications regulate satellite stem cell function and will require an increased understanding of stem-cell biology, the environment of the aged tissue and the interaction between the two

C2 skeletal myoblast survival, death, proliferation and differentiation: regulation by Adra1d

IGF-I positively impacts on muscle anabolism/regeneration. Using C2 skeletal myoblasts, we previously reported high dose TNF-α -induced (10 ng.ml-1) cell death is rescued by IGF-I. However, non-myotoxic low dose TNF-α (1.25 ng.ml-1) elicits a MAPK-mediated apoptotic response when co-incubated with IGF-I (1.5 ng.ml-1). Our aim was to investigate these conflicting roles of IGF-I in our model. Insulin array and qRT-PCR identified Adra1d as a potential regulatory gene that was up-regulated in survival and down-regulated under apoptotic conditions. TNF-α administration (1.25 or 10 ng.ml-1) induced significant decreases (∼50% both incubations) in Adra1d expression relative to DM. IGF-I addition to high dose TNF-α (10 ng.ml-1) induced myoblast survival and matched a significant (P < 0.05) increase in Adra1d expression. By contrast, IGF-I addition to low dose TNF-α (1.25 ng.ml-1) induced elevated death resulting in a significant (P < 0.05) decline (∼55%) in Adra1d expression. Pre-administration of PD98059 (20 uM), which rescues death induced by co-incubation of low dose TNF-α with IGF-I, Adra1d levels were again comparable to DM control. Since Adra1d was elevated following incubations that induced myoblast survival, we investigated effects of Adra1d siRNA gene silencing under these conditions. Adra1d knockdown resulted in significantly higher levels of cell death under all incubations suggesting Adra1d expression is essential for skeletal muscle cell survival

Powerful signals for weak muscles

The aim of the present review is to summarise, evaluate and critique the different mechanisms involved in anabolic growth of skeletal muscle and the catabolic processes involved in cancer cachexia and sarcopenia of ageing. This is highly relevant, since they represent targets for future promising clinical investigations. Sarcopenia is an inevitable process associated with a gradual reduction in muscle mass and strength, associated with a reduction in motor unit number and atrophy of muscle fibres, especially the fast type IIa fibres. The loss of muscle mass with ageing is clinically important because it leads to diminished functional ability and associated complications. Cachexia is widely recognised as severe and rapid wasting accompanying disease states such as cancer or immunodeficiency disease. One of the main characteristics of cancer cachexia is asthenia or lack of strength, which is directly related to the muscle loss. Indeed, apart from the speed of loss, muscle wasting during cancer and ageing share many common metabolic pathways and mediators. In healthy young individuals, muscles maintain their mass and function because of a balance between protein synthesis and protein degradation associated with rates of anabolic and catabolic processes, respectively. Muscles grow (hypertrophy) when protein synthesis exceeds protein degradation. Conversely, muscles shrink (atrophy) when protein degradation dominates. These processes are not occurring independently of each other, but are finely coordinated by a web of intricate signalling networks. Such signalling networks are in charge of executing environmental and cellular cues that ultimately determine whether muscle proteins are synthesised or degraded. Increasing our understanding for the pathways involved in hypertrophy and atrophy and particularly the interaction of these pathways is essential in designing therapeutic strategies for both prevention and treatment of muscle wasting conditions with age and with disease