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Cachexia does not induce loss of myonuclei or muscle fibers during xenografted prostate cancer in mice
Abstract
Aim
Cachexia is a severe wasting disorder involving loss of body‐ and muscle mass reducing survival and quality of life in cancer patients. We aim at determining if cachexia is a mere perturbation of the protein balance or if the condition also involves a degenerative loss myonuclei within the fiber syncytia or loss of whole muscle fibers.
Methods
We induced cachexia by xenografting PC3 prostate cancer cells in nu/nu mice. Six weeks later, we counted myonuclei by in vivo microscopic imaging of single live fibers in the extensor digitorum longus muscle (EDL), and the EDL, soleus and tibialis anterior muscles were also harvested for ex vivo histology.
Results
The mice lost on average 15% of the whole‐body weight. The muscle wet weight of the glycolytic, fast EDL was reduced by 14%, the tibialis anterior by 17%, and the slow, oxidative soleus by 6%. The fiber cross sectional area in the EDL was reduced by 21% with no loss of myonuclei or any significant reduction in the number of muscle fibers. TUNEL‐positive nuclei or fibers with embryonic myosin were rare both in cachectic and control muscles, and hematoxylin‐eosin staining revealed no clear signs of muscle pathology.
Conclusion
The data suggest that the cachexia induced by xenografted prostate tumors induces a pronounced atrophy not accompanied by a loss of myonuclei or a loss of muscle fibers. Thus, stem‐cell related treatment might not be beneficial, and the quest for treatment options should rather focus on intervening with intracellular pathways regulating muscle fiber‐size.
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... Staining against laminin or dystrophin protein is currently most frequently used to visualize muscle fibre cell borders. Some have suggested that staining of dystrophin may be more accurate in the assessment of myonuclear content than laminin, 36,37 however, this remains to be more firmly established in both rodent as well as human skeletal muscle cross-sections. Besides delineation of the muscle fibre border, it is critical to exclude muscle satellite cells from the myonuclear count as these cells are also located inside (between sarcolemma and basal lamina) the muscle fibre. ...
... 35 However, when nuclear labelling by for example DAPI or Hoechst is used, co-staining should be performed to delineate the cell border (eg laminin, dystrophin) and satellite cells (eg NCAM or Pax7) to make a reliable and valid estimation of myonuclear number. In the past, some 30,39-41 but certainly not all, [15][16]21,[23][24]26,[28][29][32][33][34]36,[42][43][44] studies have used this approach to evaluate myonuclear content in response to different animal muscle atrophy models. Caution should also be taken when myonuclear number per fibre length is inferred from muscle cross-sectional data, as myonuclear shape and size have been observed to change in various experimental models. ...
... Caution should also be taken when myonuclear number per fibre length is inferred from muscle cross-sectional data, as myonuclear shape and size have been observed to change in various experimental models. 22 Alternatively, myonuclear number can also be determined in mechanically isolated muscle fibres, which has the advantage that non-muscle nuclei are removed 15,[19][20][25][26][27][28]31,34,36,[40][41][44][45][46][47][48] ( Table 1). Although fibre isolation allows inclusion of a relatively high number of myonuclei per fibre, the total number of evaluated fibres is often low, which may limit accurate representation of muscle tissue. ...
Within the current paradigm of the myonuclear domain theory, it is postulated that a linear relationship exists between muscle fiber size and myonuclear content. The myonuclear domain is kept (relatively) constant by adding additional nuclei (supplied by muscle satellite cells) during muscle fiber hypertrophy and nuclear loss (by apoptosis) during muscle fiber atrophy. However, data from recent animal studies suggest that myonuclei that are added to support muscle fiber hypertrophy are not lost within various muscle atrophy models. Such myonuclear permanence has been suggested to constitute a mechanism allowing the muscle fiber to (re)grow more efficiently during retraining, a phenomenon referred to as ‘muscle memory’. The concept of ‘muscle memory by myonuclear permanence’ has mainly been based on data attained from rodent experimental models. Whether the postulated mechanism also holds true in humans remains largely ambiguous. Nevertheless, there are several studies in humans that provide evidence to potentially support or contradict (parts of) the muscle memory hypothesis. The goal of the present review is to discuss the evidence for the existence of ‘muscle memory’ in both animal and human models of muscle fiber hypertrophy as well as atrophy. Furthermore, to provide additional insight in the potential presence of muscle memory by myonuclear permanence in humans, we present new data on previously performed exercise training studies. Finally, suggestions for future research are provided to establish whether muscle memory really exists in humans.
... 8 Winje et al used microscopic imaging to address the question if cachexia-a severe wasting disorder including muscle atrophy-is a mere perturbation of the protein balance or if the condition also involves a degenerative loss of myonuclei within the fibre syncytia or loss of whole muscle fibres. 9 Single live fibres in the extensor digitorum longus muscle of mice were injected a solution containing oligonucleotides that serves as an intravital nuclear dye for counting myonuclei. 9 Utilizing in vivo microscopy of single muscle fibres, as well as conventional immunohistochemical ex vivo analysis, the authors detected no significant fibre loss and no reduction in myonuclear number in spite of a 21% reduction in fibre size. ...
... 9 Single live fibres in the extensor digitorum longus muscle of mice were injected a solution containing oligonucleotides that serves as an intravital nuclear dye for counting myonuclei. 9 Utilizing in vivo microscopy of single muscle fibres, as well as conventional immunohistochemical ex vivo analysis, the authors detected no significant fibre loss and no reduction in myonuclear number in spite of a 21% reduction in fibre size. 9 It was concluded that with no loss of cells or myonuclei, targets for therapeutic interventions could be narrowed down to intracellular signalling pathways of the atrophying muscle fibres. ...
... 9 Utilizing in vivo microscopy of single muscle fibres, as well as conventional immunohistochemical ex vivo analysis, the authors detected no significant fibre loss and no reduction in myonuclear number in spite of a 21% reduction in fibre size. 9 It was concluded that with no loss of cells or myonuclei, targets for therapeutic interventions could be narrowed down to intracellular signalling pathways of the atrophying muscle fibres. 9 In vivo Ca 2+ imaging is a powerful tool in physiology, which provides temporal resolution at the millisecond range and spatial resolution at micrometer range. ...
One of the most exciting areas of innovation in biomedical research concerns the visualization on multiple scales in space and time: imaging biological objects in size ranging from Ångströms and nanometers to the scale of whole body imaging, and from picoseconds to decades in large population imaging studies. In the Century of Biology, enabled by the tools of information technology and artificial intelligence, one can imagine a concept like ‘Google Maps’ for each fundamental biological research question, in which views at the macroscopic, mesoscopic, microscopic and the nanoscopic scales are stitched together for seamless zooming, depending on the needs and interests of the scientists and users, the research fields and the patients.
... Loss of muscle fibers and nuclei in disuse induced muscle wasting has been recently doubted (Bruusgard and Gunderson) and brings into question whether cancer-induced muscle wasting involves the process of hyperplasia (Winje et al.). 1,2 Cancer cachexia leads to muscle wasting, a multifactorial syndrome observed in more than 50% of oncological patients. The loss of muscle mass and function influences survival and quality of life. ...
... In principle, the underlying cell biological alterations in the muscle tissue could be derived on one side from degeneration of muscle fibers or loss of myonuclei, or on the other side from a change of the balance between protein degradation and synthesis in otherwise intact muscle fibers, or from both principal cell biological mechanisms. 2 For a longtime it has been predicted that muscle loss is parallelized or determined by loss of muscle fibers or at least loss of muscle fiber myonuclei. Meanwhile, there is new knowledge which casts doubt on the role of muscle fibers and myonuclei loss as the major reason for muscle wasting. 1 The focus was shifted to the disturbed balance of muscle protein degradation and synthesis induced by a complex interplay of factors including muscle disuse, systemic inflammation and malnutrition. ...
... 4,5 The study of Winje et al. promotes the comprehension of the cell biological mechanisms leading to this muscle wasting through the analysis of the muscle degeneration in cancer cachexia. 2 A xenograft prostate cancer mouse model is used to analyze in vivo and in vitro changes of muscle fiber size and loss of muscle fibers and myonuclei after 6 weeks of cancer induction. A significant fiber loss and reduction in myonuclear number cannot be found in spite of a 25% reduction in fiber size. 2 The maintenance of myonuclei despite the muscle volume decrease leads to a reduction of myonuclei domain size which could be a requirement for the regeneration of muscle fiber volume by the increase of protein synthesis. ...
Loss of muscle fibers and nuclei in disuse induced muscle wasting has been recently doubted (Bruusgard and Gunderson) and brings into question whether cancer‐induced muscle wasting involves the process of hyperplasia (Winje et al.). Cancer cachexia leads to muscle wasting, a multifactorial syndrome observed in more than 50% of oncological patients. The loss of muscle mass and function influences survival and quality of life. Therefore, the search of a countermeasure for the prevention of muscle wasting in cancer patients remains a major goal in cancer research.
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... Until recently it was assumed that myonuclei content would autoregulate with myofiber atrophy by means of myonuclear apoptosis (18). However, seminal studies from the Gundersen Laboratory using novel in vivo time-lapse analysis in mice have demonstrated that the myonuclei pool remains stable (invariant) during a broad range of muscle atrophy conditions in vivo, including disuse, denervation, and cancer cachexia, hence resulting in increased myonuclei density (19)(20)(21)(22). Moreover, myofiber cross-sectional area (mCSA) and myonuclei numbers have been reported to increase by more than 60% after 14 days of exogenous testosterone supplementation in female mice (23). ...
Background and objective:
No information exists on the long-lasting effects of supraphysiological anabolic androgenic steroids (AAS) usage on the myocellular properties of human skeletal muscle in previous AAS users. We hypothesized former AAS users would demonstrate smaller myonuclei domains (i.e., higher myonuclei density) compared to matched controls.
Methods:
A community-based cross-sectional study in men aged 18-50 years engaged in recreational strength training. Muscle biopsies were obtained from the m. vastus lateralis. Immunofluorescence analyses were performed to quantify myonuclei density and myofiber size.
Results:
Twenty-five males were included: 8 current and 7 previous AAS users and 10 controls. Median (25th-75th percentiles) accumulated duration of AAS use was 174 (101-206) and 140 (24-260) weeks in current and former AAS users, respectively (P = 0.482). Geometric mean (95%CI) elapsed duration since AAS cessation was 4.0 (1.2; 12.7) years among former AAS users. Type II muscle fibers in former AAS users displayed higher myonuclei density and DNA-to-cytoplasm ratio than controls, corresponding to smaller myonuclei domains (P = 0.013). Longer accumulated AAS use (weeks, log2) was associated with smaller myonuclei domains in previous AAS users, beta-coefficient (95%CI), -94 (-169; -18), P = 0.024. Type I fibers in current AAS users exhibited a higher amount of satellite cells per myofiber (P = 0.031) compared to controls.
Conclusion:
Muscle fibers in former AAS users demonstrated persistently higher myonuclei density and DNA-to-cytoplasm ratio four years after AAS cessation suggestive of enhanced retraining capacity.
... The recent demonstration that protein pericentriolar J Physiol 600.9 material 1 (PCM1) selectively labels myonuclei should aid in these analyses (Winje et al., 2018). To help resolve this conundrum, the Gundersen lab performed a series of experiments in rodents in which they injected muscle fibres in vivo with fluorescent dyes that label DNA and then followed the fate of individual myonuclei over time following interventions that induced atrophy or hypertrophy (Bruusgaard & Gundersen, 2008;Bruusgaard et al., 2010Bruusgaard et al., , 2012Winje et al., 2019). When muscles were induced to undergo atrophy by any of several different means, the myonuclei persisted despite dramatic reductions in muscle volume (Bruusgaard & Gundersen, 2008;Bruusgaard et al., 2010Bruusgaard et al., , 2012 (Fig. 1A). ...
... After suffering ER stress, prostate cancer cells PC3, an inductor of cachexia [74], cause an increase in GRP78, XBP1s and CHOP mRNA in other tumor cells [23] (Figure 3). This TERS between tumor cells increases cellular resistance to stress [23]. ...
Cancer cachexia is associated with deficient response to chemotherapy. On the other hand, the tumors of cachectic patients remarkably express more chemokines and have higher immune infiltration. For immunogenicity, a strong induction of the unfolded protein response (UPR) is necessary. UPR followed by cell surface exposure of calreticulin on the dying tumor cell is essential for its engulfment by macrophages and dendritic cells. However, some tumor cells upon endoplasmic reticulum (ER) stress can release factors that induce ER stress to other cells, in the so-called transmissible ER stress (TERS). The cells that received TERS produce more interleukin 6 (IL-6) and chemokines and acquire resistance to subsequent ER stress, nutrient deprivation, and genotoxic stress. Since ER stress enhances the release of extracellular vesicles (EVs), we suggest they can mediate TERS. It was found that ER stressed cachexia-inducing tumor cells transmit factors that trigger ER stress in other cells. Therefore, considering the role of EVs in cancer cachexia, the release of exosomes can possibly play a role in the process of blunting the immunogenicity of the cachexia-associated tumors. We propose that TERS can cause an inflammatory and immunosuppressive phenotype in cachexia-inducing tumors.
... After suffering ER stress, prostate cancer cells PC3, an inductor of cachexia [74], cause an increase in GRP78, XBP1s and CHOP mRNA in other tumor cells [23] (Figure 3). This TERS between tumor cells increases cellular resistance to stress [23]. ...
Cancer cachexia is associated with deficient response to chemotherapy. On the other hand, the tumors of cachectic patients remarkably express more chemokines and have higher immune infiltration. For immunogenicity, a strong induction of the unfolded protein response (UPR) is necessary. UPR followed by cell surface exposure of calreticulin on the dying tumor cell is essential for its engulfment by macrophages and dendritic cells. However, some tumor cells upon endoplasmic reticulum (ER) stress can release factors that induce ER stress to other cells, in the so-called transmissible ER stress (TERS). The cells that received TERS produce more interleukin 6 (IL-6) and chemokines and acquire resistance to subsequent ER stress, nutrient deprivation, and genotoxic stress. Since ER stress enhances the release of extracellular vesicles (EVs), we suggest they can mediate TERS. It was found that ER stressed cachexia-inducing tumor cells transmit factors that trigger ER stress in other cells. Therefore, considering the role of EVs in cancer cachexia, the release of exosomes can possibly play a role in the process of blunting the immunogenicity of the cachexia-associated tumors. We propose that TERS can cause an inflammatory and immunosuppressive phenotype in cachexia-inducing tumors.
... These results indicate that the molecular mechanisms observed in vitro persist under in vivo conditions. Finally, the beneficial effects of I 2 evidenced by reduced weight loss in mice with the SK-N-AS xenograft could be associated with lower tumor growth or with the prevention of cachexia installation accompanying the cancer progression (Winje et al. 2019). We described the attenuation of these conditions in previous protocols (Mendieta et al. 2019), which was explained in part by the antioxidant effect of this chemical form of iodine whose reducing capacity is ten times greater than ascorbic acid and 60 times more than potassium iodide (Alfaro et al. 2013). ...
Neuroblastoma (NB) is the most common solid childhood tumor, and all-trans retinoic acid (ATRA) is used as a treatment to decrease minimal residual disease. Molecular iodine (I 2 ) induces differentiation and/or apoptosis in several neoplastic cells through activation of PPARγ nuclear receptors. Here, we analyzed whether the co-administration of I 2 and ATRA increases the efficacy of NB treatment. ATRA-sensitive (SH-SY5Y), partially-sensitive (SK-N-BE(2)), and non-sensitive (SK-N-AS) NB cells were used to analyze the effect of I 2 and ATRA in vitro and in xenografts (Foxn1 nu/nu mice), exploring actions on cellular viability, differentiation, and molecular responses. In the SH-SY5Y cells, 200 μM I 2 caused a 100-fold (0.01 µM) reduction in the antiproliferative dose of ATRA and promoted neurite extension and neural marker expression (tyrosine hydroxylase (TH) and tyrosine kinase receptor alpha (Trk-A)). In SK-N-AS, the I 2 supplement sensitized these cells to 0.1 μM ATRA, increasing the ATRA-receptor (RARα) and PPARγ expression, and decreasing the Survivin expression. The I 2 supplement increased the mitochondrial membrane potential in SK-N-AS suggesting the participation of mitochondrial-mediated mechanisms involved in the sensibilization to ATRA. In vivo, oral I2 supplementation (0.025%) synergized the anti-tumor effect of ATRA (1.5 mg/Kg BW) and prevented side effects (body weight loss and diarrhea episodes). The immunohistochemical analysis showed that I 2 supplementation decreased the intratumoral vasculature (CD34). We suggest that the I 2 + ATRA combination should be studied in preclinical and clinical trials to evaluate its potential adjuvant effect in addition to conventional treatments.
... Therefore, we presented trends in individual data as well. Altogether, this indicates that myonuclear loss may occur at a slower pace than fibre atrophy, since myonuclear loss has mostly been reported during slow models of atrophy in humans (interruption of training while still maintaining daily life physical activities Murach et al., 2019;Psilander et al., 2019;Snijders et al., 2019)), and not during fast or invasive ones in humans (Brooks et al., 2010;Dirks et al., 2014;Ohira et al., 1999;Snijders et al., 2014) and rodents (Aravamudan et al., 2006;Bruusgaard et al., 2012;Bruusgaard and Gundersen, 2008;Duddy et al., 2011;Wada et al., 2002;Winje et al., 2019). ...
Introduction:
Aging is associated with an attenuated hypertrophic response to resistance training and periods of training interruptions. Hence, elderly would benefit from the 'muscle memory' effects of resistance training on muscle strength and mass during detraining and retraining. As the underlying mechanisms are not yet clear, this study investigated the role of myonuclei during training, detraining and retraining by using PCM1 labelling in muscle cross-sections of six older men.
Methods:
Knee extension strength and power were measured in thirty older men and ten controls before and after twelve weeks resistance training and after detraining and retraining of similar length. In a subset, muscle biopsies from the vastus lateralis were taken for analysis of fibre size, fibre type distribution, Pax7+ satellite cell number and myonuclear domain size.
Results:
Resistance training increased knee extension strength parameters (+10 to +36%, p < .001) and decreased the frequency of type IIax fibres by half (from 20 to 10%, p = .034). Detraining resulted in a modest loss of strength (-5 to -15%, p ≤ .004) and a trend towards a fibre-type specific decrease in type II fibre cross-sectional area (-17%, p = .087), type II satellite cell number (-30%, p = .054) and type II myonuclear number (-12%, p = .084). Less than eight weeks of retraining were needed to reach the post-training level of one-repetition maximum strength. Twelve weeks of retraining were associated with type II fibre hypertrophy (+29%, p = .050), which also promoted an increase in the number of satellite cells (+72%, p = .036) and myonuclei (+13%, p = .048) in type II fibres. Changes in the type II fibre cross-sectional area were positively correlated with changes in the myonuclear number (Pearson's r between 0.40 and 0.73), resulting in a stable myonuclear domain.
Conclusion:
Gained strength and power and fibre type changes were partially preserved following twelve weeks of detraining, allowing for a fast recovery of the 1RM performance following retraining. Myonuclear number tended to follow individual changes in type II fibre size, which is in support of the myonuclear domain theory.
... Interestingly, I 2 supplementation prevented an 18-20% body weight loss observed in control implanted mice. This weight loss has been described as part of cachexia installation, which is associated with cancer progression, in preclinical [30] and clinical studies [31]. Cachexia is defined as a multifactorial syndrome with alterations in skeletal muscle mass and/or metabolic equilibrium related to an increase in pro-inflammatory cytokines such as TNF-α, interleukin 6 (IL-6), IL-8, and interferon gamma (IFN-γ) [31]. ...
Background
The immune system is a crucial component in cancer progression or regression. Molecular iodine (I2) exerts significant antineoplastic effects, acting as a differentiation inductor and immune modulator, but its effects in antitumor immune response are not elucidated.
Methods
The present work analyzed the effect of I2 in human breast cancer cell lines with low (MCF-7) and high (MDA-MB231) metastatic potential under both in vitro (cell proliferation and invasion assay) and in vivo (xenografts of athymic nude mice) conditions.
Results
In vitro analysis showed that the 200 μM I2 supplement decreases the proliferation rate in both cell lines and diminishes the epithelial-mesenchymal transition (EMT) profile and the invasive capacity in MDA-MB231. In immunosuppressed mice, the I2 supplement impairs implantation (incidence), tumoral growth, and proliferation of both types of cells. Xenografts of the animals treated with I2 decrease the expression of invasion markers like CD44, vimentin, urokinase plasminogen activator and its receptor, and vascular endothelial growth factor; and increase peroxisome proliferator-activated receptor gamma. Moreover, in mice with xenografts, the I2 supplement increases the circulating level of leukocytes and the number of intratumoral infiltrating lymphocytes, some of them activated as CD8+, suggesting the activation of antitumor immune responses.
Conclusions
I2 decreases the invasive potential of a triple negative basal cancer cell line, and under in vivo conditions the oral supplement of this halogen activates the antitumor immune response, preventing progression of xenografts from laminal and basal mammary cancer cells. These effects allow us to propose iodine supplementation as a possible adjuvant in breast cancer therapy.
Electronic supplementary material
The online version of this article (10.1186/s12885-019-5437-3) contains supplementary material, which is available to authorized users.
... Denervation led to an approximately 50% reduction in muscle fiber volume, but no loss of myonuclei (Figure 1; Bruusgaard et al., 2010). The failure to observe nuclear loss was not due to the atrophic stimulus employed since they obtained the same results when the muscles were induced to atrophy in response to tetrodotoxin-induced nerve blockade, hindlimb suspension, cancer cachexia, or detraining Bruusgaard et al., 2010;Winje et al., 2018a). In fact, during the course of their studies, they examined more than 200,000 individual myonuclei in atrophic muscles and observed only 4 TUNEL-positive (apoptotic) nuclei, which represents a loss of only ~0.002% of the nuclei (Bruusgaard et al., 2012). ...
Skeletal muscles are the largest cells in the body and are one of the few syncytial ones. There is a longstanding belief that a given nucleus controls a defined volume of cytoplasm, so when a muscle grows (hypertrophy) or shrinks (atrophy), the number of myonuclei change accordingly. This phenomenon is known as the “myonuclear domain hypothesis.” There is a general agreement that hypertrophy is accompanied by the addition of new nuclei from stem cells to help the muscles meet the enhanced synthetic demands of a larger cell. However, there is a considerable controversy regarding the fate of pre-existing nuclei during atrophy. Many researchers have reported that atrophy is accompanied by the dramatic loss of myonuclei via apoptosis. However, since there are many different non-muscle cell populations that reside within the tissue, these experiments cannot easily distinguish true myonuclei from those of neighboring mononuclear cells. Recently, two independent models, one from rodents and the other from insects, have demonstrated that nuclei are not lost from skeletal muscle fibers when they undergo either atrophy or programmed cell death. These and other data argue against the current interpretation of the myonuclear domain hypothesis and suggest that once a nucleus has been acquired by a muscle fiber it persists.
Muscle disuse has rapid and debilitating effects on muscle mass and overall health, making it an important issue from both scientific and clinical perspectives. However, the myocellular adaptations to muscle disuse are not yet fully understood, particularly those related to the myonuclear permanence hypothesis. Therefore, in this study, we assessed fiber size, number of myonuclei, satellite cells, and capillaries in human gastrocnemius muscle after a period of immobilization following an Achilles tendon rupture. Six physically active patients (5M/1F, 43 {plus minus} 15 years) were recruited to participate after sustaining an acute unilateral Achilles tendon rupture. Muscle biopsies were obtained from the lateral part of the gastrocnemius before and after six weeks of immobilization using a plaster cast and orthosis. Muscle fiber characteristics were analyzed in tissue cross-sections and isolated single fibers using immunofluorescence and high-resolution microscopy.
Immobilization did not change muscle fiber type composition nor cross-sectional area of type I or type II fibers, but muscle fiber volume tended to decline by 13% (p=0.077). After immobilization, the volume per myonucleus was significantly reduced by 20% (p=0.008). Myonuclei were not lost in response to immobilization but tended to increase in single fibers and type II fibers. No significant changes were observed for satellite cells or capillaries.
Myonuclei were not lost in the gastrocnemius muscle after a prolonged period of immobilization, which may provide support to the myonuclear permanence hypothesis in human muscle. Capillaries remained stable throughout the immobilization period, whereas the response was variable for satellite cells, particularly in type II fibers.
Correspondence: Emer Dight BMC Proceedings 2021, 15(Suppl 4):A01: Background In recent decades overcrowding of hospitals has become a major issue in Ireland. The emergency department, by nature of its walk-in attendees, has been put under increasing pressure. Frequent at-tenders (FA) have been shown to have increased mortality rates compared to non-frequent attenders (NFA) [1]. The primary aim of this audit was to profile Cork University Hospital's (CUH) emergency department (ED) FAs and to describe their prevalence. FA were also then compared to NFA where possible. An FA is defined as any patient that attends five or more times per annum. Materials and Methods A retrospective audit of CUH's 358 FAs from 1 st January to 31 st De-cember 2019 was completed. NFA were also analysed for comparative purposes. All data was recorded on Microsoft Excel. The data collected included: arrival date, age, time spent in department, discharge destination and preliminary diagnosis. Results Approximately 01.1% of patients accounted for 5.7% of attendances in 2019. 358 patients presented a total of 2,565 times to the emergency department. The number of visits per patients ranged from 5 to 68. The average number of visits per patient was seven. The mean age was 56 years. 47% of FA were female and 53% were male. 40% of FA visits were by ambulance compared with 30% by NFAs. FAs were discharged to a ward to receive further care in 43% of cases where NFA went to a ward 29%. FA's top presenting complaint was 'unwell adult' and 4.7% of FA attendances were due to mental illness compared to 0.75% of NFA. Conclusion This audit was the first of its kind to be done analysing CUH's FA. Further studies are required to examine measures to reduce FA
Muscle cells have different phenotypes adapted to different usage, and can be grossly divided into fast/glycolytic and slow/oxidative types. While most muscles contain a mixture of such fiber types, we aimed at providing a genome-wide analysis of the epigenetic landscape by ChIP-Seq in two muscle extremes, the fast/glycolytic extensor digitorum longus (EDL) and slow/oxidative soleus muscles. Muscle is a heterogeneous tissue where up to 60% of the nuclei can be of a different origin. Since cellular homogeneity is critical in epigenome-wide association studies we developed a new method for purifying skeletal muscle nuclei from whole tissue, based on the nuclear envelope protein Pericentriolar material 1 (PCM1) being a specific marker for myonuclei. Using antibody labelling and a magnetic-assisted sorting approach, we were able to sort out myonuclei with 95% purity in muscles from mice, rats and humans. The sorting eliminated influence from the other cell types in the tissue and improved the myo-specific signal. A genome-wide comparison of the epigenetic landscape in EDL and soleus reflected the differences in the functional properties of the two muscles, and revealed distinct regulatory programs involving distal enhancers, including a glycolytic super-enhancer in the EDL. The two muscles were also regulated by different sets of transcription factors; e.g. in soleus, binding sites for MEF2C, NFATC2 and PPARA were enriched, while in EDL MYOD1 and SIX1 binding sites were found to be overrepresented. In addition, more novel transcription factors for muscle regulation such as members of the MAF family, ZFX and ZBTB14 were identified.
Background
The COVID-19 Pandemic has been shown to have a large negative impact on the mental health of healthcare workers. Evidence-based interventions that could be used to mitigate this are lacking in the literature. This systematic review aims to evaluate psychological interventions used for employees following disasters and assess the transferability of these interventions to a healthcare setting during the COVID-19 pandemic.
Materials & Methods
Electronic Database Embase was searched from 2015 to 2020. Studies identified alongside studies received from a previous review [1] were assessed for transferability using a checklist based on the PIET-T process model [2].
Results
An additional three studies were identified in the updated literature search. Eighteen studies were included for assessment of transferability. Interventions evaluated included psychological debriefing, meditation courses, cognitive behavioural therapy, mental health training courses/psychoeducation courses and Trauma Risk Management (TRiM).
Conclusions
TRiM could improve help seeking behaviour in healthcare workers. Meditation courses could alleviate stress in healthcare workers. Mental health training courses could build resilience in healthcare workers. Psychological debriefing has potential negative effects and is not recommended for transfer. More research needs to be undertaken in this area to assess the transferability of these interventions.
Muscle cells have different phenotypes adapted to different usage and can be grossly divided into fast/glycolytic and slow/oxidative types. While most muscles contain a mixture of such fiber types, we aimed at providing a genome-wide analysis of chromatin environment by ChIP-Seq in two muscle extremes, the almost completely fast/glycolytic extensor digitorum longus (EDL) and slow/oxidative soleus muscles. Muscle is a heterogeneous tissue where less than 60% of the nuclei are inside muscle fibers. Since cellular homogeneity is critical in epigenome-wide association studies we devised a new method for purifying skeletal muscle nuclei from whole tissue based on the nuclear envelope protein Pericentriolar material 1 (PCM1) being a specific marker for myonuclei. Using antibody labeling and a magnetic-assisted sorting approach we were able to sort out myonuclei with 95% purity. The sorting eliminated influence from other cell types in the tissue and improved the myo-specific signal. A genome-wide comparison of the epigenetic landscape in EDL and soleus reflected the functional properties of the two muscles each with a distinct regulatory program involving distal enhancers, including a glycolytic super-enhancer in the EDL. The two muscles are also regulated by different sets of transcription factors; e.g. in soleus binding sites for MEF2C, NFATC2 and PPARA were enriched, while in EDL MYOD1 and SOX1 binding sites were found to be overrepresented. In addition, novel factors for muscle regulation such as MAF, ZFX and ZBTB14 were identified.
Purpose of the study. Analyzing the dynamics of VEGF-А, TGF-β and their receptors in the lung tissues in rats with antitumor effect of 1,3-diethylbenzimidazolium triiodide (Stellanin).
Material and methods. The study included white outbred rats weighing 180–220 g. The main group included males (n=27) and females (n=27) with sarcoma 45 (s45) inoculated into the subclavian vein but not developed in the lungs (2×106 cells in 0.5 ml of saline) due to the subsequent intragastric administration of Stellanin (0.4 mg/kg once a day) according to an intermittent scheme: administration for 5 days and a break for 2 days. The control group included males (n=14) and females (n=14) without treatment with growing s45 in the lungs. Intact groups included 5 males and 5 females. After 4, 5 and 8 weeks of the experiment animals were decapitated, and levels of VEGF-A, sVEGF-R1, sVEGF-R2, TGF-β and sTGFβR2 were measured in 10% lung homogenates by ELISA (CUSABIO BIOTECH Co., Ltd., China).
Results. Lung tissues of intact females showed 1.4 times (p<0.05) lower VEGF-А and 3.3 times higher sVEGF-R1, compared to males. The development of tumors in all control rats was accompanied by the VEGF-А increase (by 1.6–3.0 times) and the TGF-β reduction (by 3 times). The dynamics of both VEGF receptors differed in males and females. The levels of sVEGF-R1 in males increased by 1.5 times (p<0.05), while in females it decreased by 1.8 times (p<0.05), and as a result, the levels became similar in all animals. The levels of sVEGF-R2 in males decreased by 2 times, and in females it increased by 1.4 times (p<0.05), so the sVEGF-R2 content in females became 2.4 times higher than in males. In two-thirds of rats, Stellanin prevented s45 development in the lungs due to inhibition of VEGF-A growth by more than 2.0 times and an increase in concentrations of sVEGF-R1 by 10.0 times and TGF-β by 6.0 times, together with normalization of sVEGF-R2 and sTGFβR2.
Conclusions . Stellanin prevents the development of malignant process in the lungs by inhibiting neoangiogenesis (deficiency of VEGF-A and excess of sVEGF-R1) and suppressing the proliferation of malignant cells (TGF-β growth).
Background
Cancer cachexia is largely irreversible, at least via nutritional means, and responsible for 20–40% of cancer‐related deaths. Therefore, preventive measures are of primary importance; however, little is known about muscle perturbations prior to onset of cachexia. Cancer cachexia is associated with mitochondrial degeneration; yet, it remains to be determined if mitochondrial degeneration precedes muscle wasting in cancer cachexia. Therefore, our purpose was to determine if mitochondrial degeneration precedes cancer‐induced muscle wasting in tumour‐bearing mice.
Methods
First, weight‐stable (MinStable) and cachectic (MinCC) ApcMin/+ mice were compared with C57Bl6/J controls for mRNA contents of mitochondrial quality regulators in quadriceps muscle. Next, Lewis lung carcinoma (LLC) cells or PBS (control) were injected into the hind flank of C57Bl6/J mice at 8 week age, and tumour allowed to develop for 1, 2, 3, or 4 weeks to examine time course of cachectic development. Succinate dehydrogenase stain was used to measure oxidative phenotype in tibialis anterior muscle. Mitochondrial quality and function were assessed using the reporter MitoTimer by transfection to flexor digitorum brevis and mitochondrial function/ROS emission in permeabilized adult myofibres from plantaris. RT‐qPCR and immunoblot measured the expression of mitochondrial quality control and antioxidant proteins. Data were analysed by one‐way ANOVA with Student–Newman–Kuels post hoc test.
Results
MinStable mice displayed ~50% lower Pgc‐1α, Pparα, and Mfn2 compared with C57Bl6/J controls, whereas MinCC exhibited 10‐fold greater Bnip3 content compared with C57Bl6/J controls. In LLC, cachectic muscle loss was evident only at 4 weeks post‐tumour implantation. Oxidative capacity and mitochondrial content decreased by ~40% 4 weeks post‐tumour implantation. Mitochondrial function decreased by ~25% by 3 weeks after tumour implantation. Mitochondrial degeneration was evident by 2 week LLC compared with PBS control, indicated by MitoTimer red/green ratio and number of pure red puncta. Mitochondrial ROS production was elevated by ~50 to ~100% when compared with PBS at 1–3 weeks post‐tumour implantation. Mitochondrial quality control was dysregulated throughout the progression of cancer cachexia in tumour‐bearing mice. In contrast, antioxidant proteins were not altered in cachectic muscle wasting.
Conclusions
Functional mitochondrial degeneration is evident in LLC tumour‐bearing mice prior to muscle atrophy. Contents of mitochondrial quality regulators across ApcMin/+ and LLC mice suggest impaired mitochondrial quality control as a commonality among pre‐clinical models of cancer cachexia. Our data provide novel evidence for impaired mitochondrial health prior to cachectic muscle loss and provide a potential therapeutic target to prevent cancer cachexia.
It is often assumed that mechanical factors are important for effects of exercise on muscle, but during voluntary training and most experimental conditions the effects could solely be attributed to differences in electrical activity, and direct evidence for a mechano-sensory pathway has been scarce. We here show that in rat muscles stimulated in vivo under deep anesthesia with identical electrical activity patterns isometric contractions induced two-fold more hypertrophy than contractions with 50-60 % of the isometric force. The number of myonuclei and the RNA levels of myogenin and MRF4 were increased with high load, suggesting that activation of satellite cells are mechano-dependent. On the other hand, training induced a major shift in fiber type distribution from type 2b to 2x that was load-independent, indicating that the electrical signaling rather than mechano-signaling controls fiber type. Akt and S6K1 were not significantly differentially activated by load, suggesting that the difference in mechanical factors were not important for activating the Akt/mTOR/S6K1-pathway. The transmembrane molecule syndecan-4 implied in overload hypertrophy in cardiac muscle was not load dependent suggesting that mechano-signaling in skeletal muscle is different.
Quantitative assessment of myocardial development and disease requires accurate measurement of cardiomyocyte volume, nuclearity (nuclei per cell), and ploidy (genome copies per cell). Current methods require enzymatically isolating cells, which excludes the use of archived tissue, or serial sectioning. We describe a method of analysis that permits the direct simultaneous measurement of cardiomyocyte volume, nuclearity, and ploidy in thick histological sections. To demonstrate the utility of our technique, heart tissue was obtained from four species (rat, mouse, rabbit, sheep) at up to three life stages: prenatal, weaning and adulthood. Thick (40 μm) paraffin sections were stained with Wheat Germ Agglutinin-Alexa Fluor 488 to visualise cell membranes, and DAPI (4′,6-diamidino-2-phenylindole) to visualise nuclei and measure ploidy. Previous methods have been restricted to thin sections (2–10 μm) and offer an incomplete picture of cardiomyocytes. Using confocal microscopy and three-dimensional image analysis software (Imaris Version 8.2, Bitplane AG, Switzerland), cardiomyocyte volume, nuclearity, and ploidy were measured. This method of staining and analysis of cardiomyocytes enables accurate morphometric measurements in thick histological sections, thus unlocking the potential of archived tissue. Our novel time-efficient method permits the entire cardiomyocyte to be visualised directly in 3D, eliminating the need for precise alignment of serial sections.
Background:
A longstanding goal in regenerative medicine is to reconstitute functional tissus or organs after injury or disease. Attention has focused on the identification and relative contribution of tissue specific stem cells to the regeneration process. Relatively little is known about how the physiological process is regulated by other tissue constituents. Numerous injury models are used to investigate tissue regeneration, however, these models are often poorly understood. Specifically, for skeletal muscle regeneration several models are reported in the literature, yet the relative impact on muscle physiology and the distinct cells types have not been extensively characterised.
Methods:
We have used transgenic Tg:Pax7nGFP and Flk1GFP/+ mouse models to respectively count the number of muscle stem (satellite) cells (SC) and number/shape of vessels by confocal microscopy. We performed histological and immunostainings to assess the differences in the key regeneration steps. Infiltration of immune cells, chemokines and cytokines production was assessed in vivo by Luminex®.
Results:
We compared the 4 most commonly used injury models i.e. freeze injury (FI), barium chloride (BaCl2), notexin (NTX) and cardiotoxin (CTX). The FI was the most damaging. In this model, up to 96% of the SCs are destroyed with their surrounding environment (basal lamina and vasculature) leaving a "dead zone" devoid of viable cells. The regeneration process itself is fulfilled in all 4 models with virtually no fibrosis 28 days post-injury, except in the FI model. Inflammatory cells return to basal levels in the CTX, BaCl2 but still significantly high 1-month post-injury in the FI and NTX models. Interestingly the number of SC returned to normal only in the FI, 1-month post-injury, with SCs that are still cycling up to 3-months after the induction of the injury in the other models.
Conclusions:
Our studies show that the nature of the injury model should be chosen carefully depending on the experimental design and desired outcome. Although in all models the muscle regenerates completely, the trajectories of the regenerative process vary considerably. Furthermore, we show that histological parameters are not wholly sufficient to declare that regeneration is complete as molecular alterations (e.g. cycling SCs, cytokines) could have a major persistent impact.
Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P?<?0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.
Background:
Muscle wasting during cancer cachexia contributes to patient morbidity. Cachexia-induced muscle damage may be understood by comparing its symptoms with those of other skeletal muscle diseases, but currently available data are limited.
Methods:
We modelled cancer cachexia in mice bearing Lewis lung carcinoma/colon adenocarcinoma and compared the associated muscle damage with that in a murine muscular dystrophy model (mdx mice). We measured biochemical and immunochemical parameters: amounts/localization of cytoskeletal proteins and/or Ca(2+) signalling proteins related to muscle function and abnormality. We analysed intracellular Ca(2+) mobilization and compared results between the two models. Involvement of Ca(2+)-permeable channel transient receptor potential vanilloid 2 (TRPV2) was examined by inoculating Lewis lung carcinoma cells into transgenic mice expressing dominant-negative TRPV2.
Results:
Tumourigenesis caused loss of body and skeletal muscle weight and reduced muscle force and locomotor activity. Similar to mdx mice, cachexia muscles exhibited myolysis, reduced sarcolemmal sialic acid content, and enhanced lysosomal exocytosis and sarcolemmal localization of phosphorylated Ca(2+)/CaMKII. Abnormal autophagy and degradation of dystrophin also occurred. Unlike mdx muscles, cachexia muscles did not exhibit regeneration markers (centrally nucleated fibres), and levels of autophagic proteolytic pathway markers increased. While a slight accumulation of TRPV2 was observed in cachexia muscles, Ca(2+) influx via TRPV2 was not elevated in cachexia-associated myotubes, and the course of cachexia pathology was not ameliorated by dominant-negative inhibition of TRPV2.
Conclusions:
Thus, cancer cachexia may induce muscle damage through TRPV2-independent mechanisms distinct from those in muscular dystrophy; this may help treat patients with tumour-induced muscle wasting.
Background:
Cancer associated cachexia affects the majority of cancer patients during the course of the disease and thought to be directly responsible for about a quarter of all cancer deaths. Current evidence suggests that a pro-inflammatory state may be associated with this syndrome although the molecular mechanisms responsible for the development of cachexia are poorly understood. The purpose of this work was the identification of key drivers of cancer cachexia that could provide a potential point of intervention for the treatment and/or prevention of this syndrome.
Methods:
Genetically engineered and xenograft tumour models were used to dissect the molecular mechanisms driving cancer cachexia. Cytokine profiling from the plasma of cachectic and non-cachectic cancer patients and mouse models was utilized to correlate circulating cytokine levels with the cachexia phenotype.
Results:
Utilizing engineered tumour models we identified MAP3K11/GDF15 pathway activation as a potent inducer of cancer cachexia. Increased expression and high circulating levels of GDF15 acted as a key mediator of this process. In animal models, tumour-produced GDF15 was sufficient to trigger the cachexia phenotype. Elevated GDF15 circulating levels correlated with the onset and progression of cachexia in animal models and in patients with cancer. Inhibition of GDF15 biological activity with a specific antibody reversed body weight loss and restored muscle and fat tissue mass in several cachectic animal models regardless of their complex secreted cytokine profile.
Conclusions:
The combination of correlative observations, gain of function, and loss of function experiments validated GDF15 as a key driver of cancer cachexia and as a potential therapeutic target for the treatment and/or prevention of this syndrome.
The unfolded protein response (UPR) is a homeostatic mechanism to maintain endoplasmic reticulum (ER) function. The UPR is activated by various physiological conditions as well as in disease states, such as cancer. As androgens regulate secretion and development of the normal prostate and drive prostate cancer (PCa) growth, they may affect UPR pathways. Here, we show that the canonical UPR pathways are directly and divergently regulated by androgens in PCa cells, through the androgen receptor (AR), which is critical for PCa survival. AR bound to gene regulatory sites and activated the IRE1α branch, but simultaneously inhibited PERK signaling. Inhibition of the IRE1α arm profoundly reduced PCa cell growth in vitro as well as tumor formation in preclinical models of PCa in vivo. Consistently, AR and UPR gene expression were correlated in human PCa, and spliced XBP-1 expression was significantly upregulated in cancer compared with normal prostate. These data establish a genetic switch orchestrated by AR that divergently regulates the UPR pathways and suggest that targeting IRE1α signaling may have therapeutic utility in PCa.
© 2015 The Authors. Published under the terms of the CC BY 4.0 license.
Background:
Cachexia in both mice and humans is associated with tumour production of a sulphated glycoprotein called proteolysis-inducing factor (PIF). In mice PIF binds with high affinity to a surface receptor in skeletal muscle, but little is known about the human receptor. This study compares the human PIF receptor with the murine.
Methods:
Human PIF was isolated from the G361 melanoma and murine PIF from the MAC16 colon adenocarcinoma. The human PIF receptor was isolated from human skeletal muscle myotubes. Protein synthesis and degradation induced by human and murine PIF was studied in human and murine skeletal muscle myotubes.
Results:
Both the human and murine PIF receptors showed the same immunoreactivity and Mr 40 000. Both murine and human PIF inhibited total protein synthesis and stimulated protein degradation in human and murine myotubes to about the same extent, and this was attenuated by a rabbit polyclonal antibody to the murine PIF receptor, but not by a non-specific rabbit antibody. Both murine and human PIF increased the activity of the ubiquitin-proteasome pathway in both human and murine myotubes, as evidenced by an increased 'chymotrypsin-like' enzyme activity, protein expression of the 20S and 19S proteasome subunits, and increased expression of the ubiquitin ligases MuRF1 and MAFbx, and this was also attenuated by the anti-mouse PIF receptor antibody.
Conclusions:
These results suggest that the murine and human PIF receptors are identical.
Cancer cachexia is a metabolic syndrome featuring many alterations typical of type 2 diabetes (T2D). While muscle wasting is a hallmark of cachexia, epidemiological evidence also supports an accelerated age-related muscle loss in T2D. Insulin resistance manifests in both conditions and impairs glucose disposal and protein anabolism by tissues. A greater contribution of gluconeogenesis to glucose production may limit amino acid availability for muscle protein synthesis, further aggravating muscle loss. In the context of inter-dependence between glucose and protein metabolism, the present review summarizes the current state of knowledge on alterations that may lead to muscle wasting in human cancer. By highlighting the similarities with T2D, a disease that has been more extensively studied, the objective of this review is to provide a better understanding of the pathophysiology of cancer cachexia and to consider potential treatments usually targeted for T2D. Nutritional approaches aimed at stimulating protein anabolism might include specially formulated food with optimal protein and amino acid composition. Because the gradual muscle loss in T2D may be attenuated by diabetes treatment, anti-diabetic drugs might be considered in cachexia treatment. Metformin emerges as a choice candidate as it acts both on reducing gluconeogenesis and improving insulin sensitivity, and has demonstrated tumour suppressor properties in multiple cancer types. Such a multimodal approach to slow or reverse muscle wasting in cachexia warrants further investigation.
Existing data suggest that NF-kappaB signaling is a key regulator of cancer-induced skeletal muscle wasting. However, identification of the components of this signaling pathway and of the NF-κB transcription factors that regulate wasting is far from complete. In muscles of C26 tumor bearing mice, overexpression of dominant negative (d.n.) IKKβ blocked muscle wasting by 69% and the IκBα-super repressor blocked wasting by 41%. In contrast, overexpression of d.n. IKKα or d.n. NIK did not block C26-induced wasting. Surprisingly, overexpression of d.n. p65 or d.n. c-Rel did not significantly affect muscle wasting. Genome-wide mRNA expression arrays showed upregulation of many genes previously implicated in muscle atrophy. To test if these upregulated genes were direct targets of NF-κB transcription factors, we compared genome-wide p65 binding to DNA in control and cachectic muscle using ChIP-sequencing. Bioinformatic analysis of ChIP-sequencing data from control and C26 muscles showed very little p65 binding to genes in cachexia and little to suggest that upregulated p65 binding influences the gene expression associated with muscle based cachexia. The p65 ChIP-seq data are consistent with our finding of no significant change in protein binding to an NF-κB oligonucleotide in a gel shift assay, no activation of a NF-κB-dependent reporter, and no effect of d.n.p65 overexpression in muscles of tumor bearing mice. Taken together, these data support the idea that although inhibition of IκBα, and particularly IKKβ, blocks cancer-induced wasting, the alternative NF-κB signaling pathway is not required. In addition, the downstream NF-κB transcription factors, p65 and c-Rel do not appear to regulate the transcriptional changes induced by the C26 tumor. These data are consistent with the growing body of literature showing that there are NF-κB-independent substrates of IKKβ and IκBα that regulate physiological processes.
Abstract The molecular mechanisms underlying skeletal muscle maintenance involve interplay between multiple signaling pathways. Under normal physiological conditions, a network of interconnected signals serves to control and coordinate hypertrophic and atrophic messages, culminating in a delicate balance between muscle protein synthesis and proteolysis. Loss of skeletal muscle mass, termed "atrophy", is a diagnostic feature of cachexia seen in settings of cancer, heart disease, chronic obstructive pulmonary disease, kidney disease, and burns. Cachexia increases the likelihood of death from these already serious diseases. Recent studies have further defined the pathways leading to gain and loss of skeletal muscle as well as the signaling events that induce differentiation and post-injury regeneration, which are also essential for the maintenance of skeletal muscle mass. In this review, we summarize and discuss the relevant recent literature demonstrating these previously undiscovered mediators governing anabolism and catabolism of skeletal muscle.
Cachexia is a debilitating condition characterized by extreme skeletal muscle wasting that contributes significantly to morbidity and mortality. Efforts to elucidate the underlying mechanisms of muscle loss have predominantly focused on events intrinsic to the myofiber. In contrast, less regard has been given to potential contributory factors outside the fiber within the muscle microenvironment. In tumor-bearing mice and patients with pancreatic cancer, we found that cachexia was associated with a type of muscle damage resulting in activation of both satellite and nonsatellite muscle progenitor cells. These muscle progenitors committed to a myogenic program, but were inhibited from completing differentiation by an event linked with persistent expression of the self-renewing factor Pax7. Overexpression of Pax7 was sufficient to induce atrophy in normal muscle, while under tumor conditions, the reduction of Pax7 or exogenous addition of its downstream target, MyoD, reversed wasting by restoring cell differentiation and fusion with injured fibers. Furthermore, Pax7 was induced by serum factors from cachectic mice and patients, in an NF-κB-dependent manner, both in vitro and in vivo. Together, these results suggest that Pax7 responds to NF-κB by impairing the regenerative capacity of myogenic cells in the muscle microenvironment to drive muscle wasting in cancer.
Muscle fibers are the cells in the body with the largest volume, and they have multiple nuclei serving different domains of cytoplasm. A large body of previous literature has suggested that atrophy induced by hindlimb suspension leads to a loss of "excessive" myonuclei by apoptosis. We demonstrate here that atrophy induced by hindlimb suspension does not lead to loss of myonuclei despite a strong increase in apoptotic activity of other types of nuclei within the muscle tissue. Thus hindlimb suspension turns out to be similar to other atrophy models such as denervation, nerve impulse block, and antagonist ablation. We discuss how the different outcome of various studies can be attributed to difficulties in separating myonuclei from other nuclei, and to systematic differences in passive properties between normal and unloaded muscles. During reload, after hindlimb suspension, a radial regrowth is observed, which has been believed to be accompanied by recruitment of new myonuclei from satellite cells. The lack of nuclear loss during unloading, however, puts these findings into question. We observed that reload led to an increase in cross sectional area of 59%, and fiber size was completely restored to the presuspension levels. Despite this notable growth there was no increase in the number of myonuclei. Thus radial regrowth seems to differ from de novo hypertrophy in that nuclei are only added during the latter. We speculate that the number of myonuclei might reflect the largest size the muscle fibers have had in its previous history.
Skeletal muscle is the most abundant tissue in the human body, and the maintenance of its mass is essential to ensure basic function as locomotion, strength and respiration. The decision to synthesize or to break down skeletal muscle proteins is regulated by a network of signaling pathways that transmit external stimuli to intracellular factors regulating gene transcription. The tightly regulated balance of muscle protein breakdown and synthesis is disturbed in several distinct myopathies, but also in two pathologies: sarcopenia and cachexia. In recent years, it became evident that in these two muscle wasting disorders specific regulating molecules are increased in expression (e.g. members of the ubiquitin-proteasome system, myostatin, apoptosis inducing factors), whereas other factors (e.g. insulin-like growth factor 1) are down-regulated. So far, not many treatment options to fight the muscle loss are available. One of the most promising approaches is exercise training that, due to its multifactorial effects, can act on several signaling pathways. Therefore, this review will concentrate on specific alterations discussed in the current literature that are present in the skeletal muscle of both muscle wasting disorders. In addition, we will focus on exercise training as an intervention strategy.
Muscle fibres have different properties with respect to force, contraction speed, endurance, oxidative/glycolytic capacity etc. Although adult muscle fibres are normally post-mitotic with little turnover of cells, the physiological properties of the pre-existing fibres can be changed in the adult animal upon changes in usage such as after exercise. The signal to change is mainly conveyed by alterations in the patterns of nerve-evoked electrical activity, and is to a large extent due to switches in the expression of genes. Thus, an excitation-transcription coupling must exist. It is suggested that changes in nerve-evoked muscle activity lead to a variety of activity correlates such as increases in free intracellular Ca(2+) levels caused by influx across the cell membrane and/or release from the sarcoplasmatic reticulum, concentrations of metabolites such as lipids and ADP, hypoxia and mechanical stress. Such correlates are detected by sensors such as protein kinase C (PKC), calmodulin, AMP-activated kinase (AMPK), peroxisome proliferator-activated receptor δ (PPARδ), and oxygen dependent prolyl hydroxylases that trigger intracellular signaling cascades. These complex cascades involve several transcription factors such as nuclear factor of activated T-cells (NFAT), myocyte enhancer factor 2 (MEF2), myogenic differentiation factor (myoD), myogenin, PPARδ, and sine oculis homeobox 1/eyes absent 1 (Six1/Eya1). These factors might act indirectly by inducing gene products that act back on the cascade, or as ultimate transcription factors binding to and transactivating/repressing genes for the fast and slow isoforms of various contractile proteins and of metabolic enzymes. The determination of size and force is even more complex as this involves not only intracellular signaling within the muscle fibres, but also muscle stem cells called satellite cells. Intercellular signaling substances such as myostatin and insulin-like growth factor 1 (IGF-1) seem to act in a paracrine fashion. Induction of hypertrophy is accompanied by the satellite cells fusing to myofibres and thereby increasing the capacity for protein synthesis. These extra nuclei seem to remain part of the fibre even during subsequent atrophy as a form of muscle memory facilitating retraining. In addition to changes in myonuclear number during hypertrophy, changes in muscle fibre size seem to be caused by alterations in transcription, translation (per nucleus) and protein degradation.
Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P < 0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.
Effects of previous strength training can be long-lived, even after prolonged subsequent inactivity, and retraining is facilitated by a previous training episode. Traditionally, such "muscle memory" has been attributed to neural factors in the absence of any identified local memory mechanism in the muscle tissue. We have used in vivo imaging techniques to study live myonuclei belonging to distinct muscle fibers and observe that new myonuclei are added before any major increase in size during overload. The old and newly acquired nuclei are retained during severe atrophy caused by subsequent denervation lasting for a considerable period of the animal's lifespan. The myonuclei seem to be protected from the high apoptotic activity found in inactive muscle tissue. A hypertrophy episode leading to a lasting elevated number of myonuclei retarded disuse atrophy, and the nuclei could serve as a cell biological substrate for such memory. Because the ability to create myonuclei is impaired in the elderly, individuals may benefit from strength training at an early age, and because anabolic steroids facilitate more myonuclei, nuclear permanency may also have implications for exclusion periods after a doping offense.
Microtubule organization has been studied in serially sectioned myogenic cells in the tail muscle regeneration blastema of Rana pipiens tadpoles. In mesenchymal cells and in some premyoblasts, microtubules radiate from centriolar satellites in a cell center, while in more mature myoblasts and myotubes the centrioles no longer appear to serve as organizing centers for microtubules. In all elongate, fusiform myogenic cells, the microtubules are predominately oriented in the longitudinal axis of the cell. Counts of microtubules in transverse sections spaced at regular intervals along the cells show that the absolute number of microtubules is greatest in the thickened midregions of the cells and decreases relatively smoothly toward the tapered ends of the cells. Close paraxial association of microtubules (within 40 nm surface-to-surface) occurs along the entire lengths of cells but appears with greatest frequency in their tapered ends. In two myoblasts, serial sections were used to trace all microtubules in 8-microm long segments of the cells located about midway between the nucleus and one end of the cell. Since tracings show that as many as 50% of the microtubules terminate within the 8-microm long segment, it seems unlikely that any microtubules extend the entire length of the cell. It is proposed that lateral interactions between paraxial microtubules stabilize the overall microtubular apparatus and contribute to maintenance of the bipolar form of the cells. A three-dimensional model of the complete microtubular array in one of the 8-microm long segments of a myoblast has been constructed. The model reveals that a few microtubules within the segment are bent into smooth curves and loops that could be generated by sliding interaction between paraxial microtubules.
This report describes qualitative and quantitative studies performed on ten muscle biopsies from chronic uremic patients on renal dialysis at light and electron microscopic (EM) levels. The muscle biopsies showed myopathic changes (variation in fiber size, central nuclei, and fiber splitting). Histochemical studies showed type II fiber atrophy and lipid deposits. The ultrastructural study showed disruption of myofibrillary architecture and subsarcolemmal deposits of glycogen, mitochondria, and lipids. Quantitative estimations of the subcellular organelles revealed a statistically significant increase in lipid and glycogen contents of the muscle. The myopathic changes, type II atrophy, and lipid and glycogen deposits in chronic uremic patients raise the question of the effects of uremia and/or chronic dialysis on muscle metabolism.
A prominent feature of several type of cancer is cachexia. This syndrome causes a marked loss of lean body mass and muscle wasting, and appears to be mediated by cytokines and tumour products. There are several proteases and proteolytic pathways that could be responsible for the protein breakdown. In the present study, we investigated whether caspases are involved in the proteolytic process of skeletal muscle catabolism observed in a murine model of cancer cachexia (MAC16), in comparison with a related tumour (MAC13), which does not induce cachexia. Using specific peptide substrates, there was an increase of 54% in the proteolytic activity of caspase-1, 84% of caspase-8, 98% of caspase-3 151% to caspase-6 and 177% of caspase-9, in the gastrocnemius muscle of animals bearing the MAC16 tumour (up to 25% weight loss), in relation to muscle from animals bearing the MAC13 tumour (1-5% weight loss). The dual pattern of 89 kDa and 25 kDa fragmentation of poly (ADP-ribose) polymerase (PARP) occurred in the muscle samples from animals bearing the MAC16 tumour and with a high amount of caspase-like activity. Cytochrome c was present in the cytosolic fractions of gastrocnemius muscles from both groups of animals, suggesting that cytochrome c release from mitochondria may be involved in caspase activation. There was no evidence for DNA fragmentation into a nucleosomal ladder typical of apoptosis in the muscles of either group of mice. This data supports a role for caspases in the catabolic events in muscle involved in the cancer cachexia syndrome.
Age-related but not artificially induced muscle fiber atrophy has been shown to occur without any decrease in myonuclear number, although these results remain controversial. The present study was carried out to clarify whether age difference affects the degree of decrease in myonuclear number occurring with denervation-induced fiber atrophy. After denervation of 3-wk-old (young) and 4-mo-old (mature) mice, single myofibers were isolated from the plantaris muscles by alkali maceration, and their fiber cross-sectional area (CSA), myonuclear number, and cytoplasm-to-myonucleus (C/N) ratios were analyzed. Fiber CSA in both young and mature mice decreased with denervation. Myonuclear number decreased in young mice 5 and 10 days after denervation but was unchanged in mature mice 10 and 120 days after denervation. C/N ratio decreased in mature mice but was unchanged in denervated young mice. These results suggest that age differences affect the degree of decrease of myonuclear number with denervation and that fiber cytoplasmic atrophy may occur without decrease in myonuclear number.
We present here a new technique with which to visualize nuclei in living muscle fibres in the intact animal, involving injection of labelled DNA into single cells. This approach allowed us to determine the position of all of nuclei within a sarcolemma without labelling satellite cells. In contrast to what has been reported in tissue culture, we found that the nuclei were immobile, even when observed over several days. Nucleic density was uniform along the fibre except for the endplate and some myotendinous junctions, where the density was higher. The perijunctional region had the same number of nuclei as the rest of the fibre. In the extensor digitorum longus (EDL) muscle, the extrajunctional nuclei were elongated and precisely aligned to the long axis of the fibre. In the soleus, the nuclei were rounder and not well aligned. When comparing small and large fibres in the soleus, the number of nuclei varied approximately in proportion to cytoplasmic volume, while in the EDL the number was proportional to surface area. Statistical analysis revealed that the nuclei were not randomly distributed in either the EDL or the soleus. For each fibre, actual distributions were compared with computer simulations in which nuclei were assumed to repel each other, which optimizes the distribution of nuclei with respect to minimizing transport distances. The simulated patterns were regular, with clear row-like structures when the density of nuclei was low. The non-random and often row-like distribution of nuclei observed in muscle fibres may thus reflect regulatory mechanisms whereby nuclei repel each other in order to minimize transport distances.
In cancer cachexia both cardiac and skeletal muscle suffer an important protein mobilization as a result of increased proteolysis. Administration of the beta2-agonist formoterol to both rats and mice bearing highly cachectic tumors resulted in an important reversal of the muscle-wasting process. The anti-wasting effects of the drug were based on both an activation of the rate of protein synthesis and an inhibition of the rate of muscle proteolysis. Northern blot analysis revealed that formoterol treatment resulted in a decrease in the mRNA content of ubiquitin and proteasome subunits in gastrocnemius muscles; this, together with the decreased proteasome activity observed, suggest that the main anti-proteolytic action of the drug may be based on an inhibition of the ATP-ubiquitin-dependent proteolytic system. Interestingly, the beta2-agonist was also able to diminish the increased rate of muscle apoptosis (measured as DNA laddering as well as caspase-3 activity) present in tumor-bearing animals. The present results indicate that formoterol exerted a selective, powerful protective action on heart and skeletal muscle by antagonizing the enhanced protein degradation that characterizes cancer cachexia, and it could be revealed as a potential therapeutic tool in pathologic states wherein muscle protein hypercatabolism is a critical feature such as cancer cachexia or other wasting diseases.
The aim of the study was to assess the total energy expenditure (TEE), resting energy expenditure (REE) and physical activity level (PAL) in home-living cachectic patients with advanced pancreatic cancer. The influence of an energy and protein dense oral supplement either enriched with or without the n-3 fatty acid eicosapentaenoic acid (EPA) and administered over an 8-week period was also determined. In total, 24 patients were studied at baseline. The total energy expenditure was measured using doubly labelled water and REE determined by indirect calorimetry. Patients were studied at baseline and then randomised to either oral nutritional supplement. Measurements were repeated at 8 weeks. At baseline, REE was increased compared with predicted values for healthy individuals (1387(42) vs 1268(32) kcal day(-1), P=0.001), but TEE (1732(82) vs 1903(48) kcal day(-1), P=0.023) and PAL (1.24(0.04) vs 1.50) were reduced. After 8 weeks, the REE, TEE and PAL of patients who received the control supplement did not change significantly. In contrast, although REE did not change, TEE and PAL increased significantly in those who received the n-3 (EPA) enriched supplement. In summary, patients with advanced pancreatic cancer were hypermetabolic. However, TEE was reduced and this was secondary to a reduction in physical activity. The control energy and protein dense oral supplement did not influence the physical activity component of TEE. In contrast, administration of the supplement enriched with EPA was associated with an increase in physical activity, which may reflect improved quality of life.
Numerous studies have suggested that muscle atrophy is accompanied by apoptotic loss of myonuclei and therefore recovery would require replenishment by muscle stem cells. We used in vivo time-lapse microscopy to observe the loss and replenishment of myonuclei in murine muscle fibers following induced muscle atrophy. To our surprise, imaging of single fibers for up to 28 days did not support the concept of nuclear loss during atrophy. Muscles were inactivated by denervation, nerve impulse block, or mechanical unloading. Nuclei were stained in vivo either acutely by intracellular injection of fluorescent oligonucleotides or in time-lapse studies after transfection with a plasmid encoding GFP with a nuclear localization signal. We observed no loss of myonuclei in fast- or slow-twitch muscle fibers despite a greater than 50% reduction in fiber cross-sectional area. TUNEL labeling of fragmented DNA on histological sections revealed high levels of apoptotic nuclei in inactive muscles. However, when costained for laminin and dystrophin, virtually none of the TUNEL-positive nuclei could be classified as myonuclei; apoptosis was confined to stromal and satellite cells. We conclude that disuse atrophy is not a degenerative process, but is rather a change in the balance between protein synthesis and proteolysis in a permanent cell syncytium.
Cachexia, a debilitating syndrome characterized by skeletal muscle wasting, is associated to many chronic diseases and diminishes the quality of life and survival of patients. Tumor-derived factors and proinflammatory cytokines, including TNF-alpha, IL-6 and IL-1 beta, mediate cachexia. In response to elevated cytokine levels, increased proteasome-mediated proteolysis and auto-phagocytosis result in muscle wasting. The histologic features of muscle cachexia are not fully elucidated. Therefore, we analysed alterations of different cell populations in cachectic muscle.
By immunohistochemical and cytological approaches, we characterized changes in the abundance of cellular populations in the musculature of a murine model of cancer cachexia (C26-bearing mice).
Cachectic muscle displayed a decreased DNA content proportional to muscle mass wastage. A decrease in the number of nuclei occurred in the muscular but not in the stromal compartment. Cachectic muscle showed: mild modulation of myeloperoxidase activity, a neutrophil marker; reduction of macrophages in the endomysium; decrease in CD3(+) lymphocyte number. Conversely, a statistically significant enrichment in Sca-1(+) CD45(+) hematopoietic stem cells (HSCs) occurred in cachectic muscle.
The elevated levels of cytokines which characterize cachexia may represent a trigger for inflammatory cell activation. However, we find that in cachexia, inflammatory cells in muscle are not increased while muscle tissue nuclei decline. Our data suggest that the inflammatory cell-mediated stress is not an etiologic component of muscle wasting in cachexia. The relative increase in HSCs in cachectic skeletal muscle suggests an attempt to maintain muscle homeostasis by recruitment and/or activation of stem cells.
According to the current paradigm, muscle nuclei serve a certain cytoplasmic domain. To preserve the domain size, it is believed that nuclei are injected from satellite cells fusing to fibres undergoing hypertrophy, and lost by apoptosis during atrophy. Based on single fibre observations in and ex vivo we suggest that nuclear domains are not as constant as is often indicated. Moreover, recent time lapse in vivo imaging of single fibres suggests that at least for the first few weeks, atrophy is not accompanied by any loss of nuclei. Apoptosis is abundant in muscle tissue during atrophy conditions, but in our opinion it has not been unequivocally demonstrated that such nuclei are myonuclei. As we see it, the preponderance of current evidence suggests that disuse atrophy is not accompanied by loss of nuclei, at least not for the first 2 months. Moreover, it has not been proven that myonuclear apoptosis does occur in permanent fibres undergoing atrophy; it seems more likely that it is confined to stromal cells and satellite cells. If muscle atrophy is not related to loss of nuclei, design of intervention therapies should focus on protein metabolism rather than regeneration from stem cells.
Cachexia is a wasting syndrome observed in many patients suffering from several chronic diseases including cancer. In addition to the progressive loss of skeletal muscle mass, cancer cachexia results in cardiac function impairment. During the severe stage of the disease, patients as well as animals bearing cancer cells display cardiac atrophy. Cardiac energy metabolism is also impeded with disruption of mitochondrial homeostasis and reduced oxidative capacity, although the available data remain equivocal. The release of inflammatory cytokines by tumor is a key mechanism in the initiation of heart failure. Oxidative stress, which results from the combination of chemotherapy, inadequate antioxidant consumption and chronic inflammation, will further foster heart failure. Protein catabolism is due to the concomitant activation of proteolytic systems and inhibition of protein synthesis, both processes being triggered by the deactivation of the Akt/mammalian target of rapamycin pathway. The reduction in oxidative capacity involves AMP-activated protein kinase and peroxisome proliferator-activated receptor gamma coactivator 1α dysregulation. The nuclear factor-κB transcription factor plays a prominent role in the coordination of these alterations. Physical exercise appears as an interesting non-pharmaceutical way to counteract cancer cachexia-induced-heart failure. Indeed, aerobic training has anti-inflammatory effects, increases anti-oxidant defenses, prevents atrophy and promotes oxidative metabolism. The present review points out the importance of better understanding the concurrent structural and metabolic changes within the myocardium during cancer and the protective effects of exercise against cardiac cachexia.
Memory is a process in which information is encoded, stored, and retrieved. For vertebrates, the modern view has been that it occurs only in the brain. This review describes a cellular memory in skeletal muscle in which hypertrophy is 'remembered' such that a fibre that has previously been large, but subsequently lost its mass, can regain mass faster than naive fibres. A new cell biological model based on the literature, with the most reliable methods for identifying myonuclei, can explain this phenomenon. According to this model, previously untrained fibres recruit myonuclei from activated satellite cells before hypertrophic growth. Even if subsequently subjected to grave atrophy, the higher number of myonuclei is retained, and the myonuclei seem to be protected against the elevated apoptotic activity observed in atrophying muscle tissue. Fibres that have acquired a higher number of myonuclei grow faster when subjected to overload exercise, thus the nuclei represent a functionally important 'memory' of previous strength. This memory might be very long lasting in humans, as myonuclei are stable for at least 15 years and might even be permanent. However, myonuclei are harder to recruit in the elderly, and if the long-lasting muscle memory also exists in humans, one should consider early strength training as a public health advice. In addition, myonuclei are recruited during steroid use and encode a muscle memory, at least in rodents. Thus, extending the exclusion time for doping offenders should be considered.
Cancer cachexia is a complex syndrome of progressive weight loss especially devastating to skeletal muscle and adipose tissue. In about 30% of cancer patients, cachexia is the most common cause of death. Often cachexia is accompanied with loss of appetite, inflammation and insulin resistance. Several inflammatory cytokines including Tumor Necrosis Factor-α (TNF-α) and Interleukin-6 (IL-6) are known to be involved in cachexia. Besides the humoral factors, the tumoral factors such as Proteolysis Inducing Factor (PIF) play a role in inducing cachexia. Recently, our laboratory discovered that Myostatin, a Transforming Growth Factor-β (TGF-β) superfamily member, is abundantly secreted by C26 tumor cells. Previously others and our laboratory have established Myostatin as a pro-cachectic factor inducing muscle wasting through up-regulation of muscle-specific E3 ligases, Atrogin-1 and MuRF1, and enhanced activity of the ubiquitin-proteasome pathway. Myostatin has also been shown to induce Reactive Oxygen Species (ROS), TNF-α and IL-6. Collectively, these results indicate that Myostatin is a potential target of cancer cachexia and antagonism of Myostatin would be beneficial during cancer cachexia. On the nutrition front, nutrients like Omega-3 fatty acids, Leucine and l-Carnitine have been shown to be beneficial during cancer cachexia. Based on the above findings, we propose that a combination of Myostatin antagonist and Omega-3 fatty acids or Leucine or l-Carnitine may have potential to improve muscle mass during cancer cachexia.
Skeletal muscle mass increases during postnatal development through a process of hypertrophy, namely enlargement of individual muscle fibers, and a similar process can be induced in adult skeletal muscle in response to contractile activity, such as strength exercise, and specific hormones, such as androgens and β-adrenergic agonists. Muscle hypertrophy occurs when the overall rates of protein synthesis exceed rates of protein degradation. Two major signaling pathways control protein synthesis, the IGF1-Akt-mTOR pathway, acting as a positive regulator, and the myostatin-Smad2/3 pathway, acting as a negative regulator, and additional pathways have been recently identified. Proliferation and fusion of satellite cells, leading to an increase in the number of myonuclei, may also contribute to muscle growth during early but not late stages of postnatal development and in some forms of muscle hypertrophy in the adult. Muscle atrophy occurs when protein degradation rates exceed protein synthesis, and can be induced in adult skeletal muscle in a variety of conditions, including starvation, denervation, cancer cachexia, heart failure, and aging. Two major protein degradation pathways, the proteasomal and the autophagic-lysosomal pathways, are activated during muscle atrophy and variably contribute to the loss of muscle mass. These pathways involve a variety of atrophy-related genes or atrogenes, which are controlled by specific transcription factors, such as FoxO3, which is negatively regulated by Akt, and NF-κB, which is activated by inflammatory cytokines. © 2013 The Authors Journal compilation © 2013 FEBS.
We investigated the temporal effects of sepsis on muscle wasting and function in order to study the contribution of wasting to the decline in muscle function; we also studied the fiber-type specificity of this muscle wasting. Sepsis was induced by injecting rats intraperitoneally with a zymosan suspension. At 2 h and at 2, 6, and 11 days after injection, muscle function was measured using in situ electrical stimulation. Zymosan injection induced severe muscle wasting compared to pair-fed and ad libitum fed controls. At 6 days, isometric force-generating capacity was drastically reduced in zymosan-treated rats. We conclude that this was fully accounted for by the reduction of muscle mass. At day 6, we also observed increased activity of the 20S proteasome in gastrocnemius but not soleus muscle from septic rats. In tibialis anterior but not in soleus, muscle wasting occurred in a fiber-type specific fashion, i.e., the reduction in cross-sectional area was significantly smaller in type 1 than type 2A and 2B/X fibers. These findings suggest that both the inherent function of a muscle and the muscle fiber-type distribution affect the responsiveness to catabolic signals. Muscle Nerve, 2005
It is well established that long durations of bed rest, limb immobilization, or reduced activity in respiratory muscles during mechanical ventilation results in skeletal muscle atrophy in humans and other animals. The idea that mitochondrial damage/dysfunction contributes to disuse muscle atrophy originated over 40 years ago. These early studies were largely descriptive and did not provide unequivocal evidence that mitochondria play a primary role in disuse muscle atrophy. However, recent experiments have provided direct evidence connecting mitochondrial dysfunction to muscle atrophy. Numerous studies have described changes in mitochondria shape, number, and function in skeletal muscles exposed to prolonged periods of inactivity. Furthermore, recent evidence indicates that increased mitochondrial ROS production plays a key signaling role in both immobilization-induced limb muscle atrophy and diaphragmatic atrophy occurring during prolonged mechanical ventilation. Moreover, new evidence reveals that, during denervation-induced muscle atrophy, increased mitochondrial fragmentation due to fission is a required signaling event that activates the AMPK-FoxO3 signaling axis, which induces the expression of atrophy genes, protein breakdown, and ultimately muscle atrophy. Collectively, these findings highlight the importance of future research to better understand the mitochondrial signaling mechanisms that contribute to disuse muscle atrophy and to develop novel therapeutic interventions for prevention of inactivity-induced skeletal muscle atrophy.
To develop a framework for the definition and classification of cancer cachexia a panel of experts participated in a formal consensus process, including focus groups and two Delphi rounds. Cancer cachexia was defined as a multifactorial syndrome defined by an ongoing loss of skeletal muscle mass (with or without loss of fat mass) that cannot be fully reversed by conventional nutritional support and leads to progressive functional impairment. Its pathophysiology is characterised by a negative protein and energy balance driven by a variable combination of reduced food intake and abnormal metabolism. The agreed diagnostic criterion for cachexia was weight loss greater than 5%, or weight loss greater than 2% in individuals already showing depletion according to current bodyweight and height (body-mass index [BMI] <20 kg/m(2)) or skeletal muscle mass (sarcopenia). An agreement was made that the cachexia syndrome can develop progressively through various stages--precachexia to cachexia to refractory cachexia. Severity can be classified according to degree of depletion of energy stores and body protein (BMI) in combination with degree of ongoing weight loss. Assessment for classification and clinical management should include the following domains: anorexia or reduced food intake, catabolic drive, muscle mass and strength, functional and psychosocial impairment. Consensus exists on a framework for the definition and classification of cancer cachexia. After validation, this should aid clinical trial design, development of practice guidelines, and, eventually, routine clinical management.
On December 13th and 14th a group of scientists and clinicians met in Washington, DC, for the cachexia consensus conference. At the present time, there is no widely agreed upon operational definition of cachexia. The lack of a definition accepted by clinician and researchers has limited identification and treatment of cachectic patient as well as the development and approval of potential therapeutic agents. The definition that emerged is: "cachexia, is a complex metabolic syndrome associated with underlying illness and characterized by loss of muscle with or without loss of fat mass. The prominent clinical feature of cachexia is weight loss in adults (corrected for fluid retention) or growth failure in children (excluding endocrine disorders). Anorexia, inflammation, insulin resistance and increased muscle protein breakdown are frequently associated with cachexia. Cachexia is distinct from starvation, age-related loss of muscle mass, primary depression, malabsorption and hyperthyroidism and is associated with increased morbidity. While this definition has not been tested in epidemiological or intervention studies, a consensus operational definition provides an opportunity for increased research.
Causes of death in the year 1970 were analyzed retrospectively on the basis of clinical and pathologic reports of 506 cases in the Roswell Park Memorial Institute and Hospital. The single major cause of death was infection (36%), which was also a contributory factor in an additional 68% of the cases. Other important causes of death were hemorrhagic and thromboembolic phenomena (18%), which also were contributory factors in an additional 43%. Organ invasion by neoplastic cells including hepatic failure was the major cause of death in 10% and was a contributory factor in 5%. Cachexia was reported as major cause of death in 1% and as contributory factor in 0.4%. Respiratory failure due to various causes (including aspiration) was the main mechanism of death in 19% and a contributory factor in 3%. Cardiovascular insufficiency was the major cause of death in 7% and a contributory factor in 3%.
Cancer cachexia is a syndrome of progressive wasting which has been suggested to be mediated by tumour-necrosis factor-alpha, interleukins 1 and 6, interferon-gamma and leukaemia-inhibitory factor. It has proved difficult to correlate levels of tumour-necrosis factor-alpha and interleukin-6 with cancer cachexia, and the weight loss induced by leukaemia-inhibitory factor may be due to toxicity. In the murine adenocarcinoma MAC16, cachexia is mediated by circulatory catabolic factors, which we have now isolated using an antibody cloned from splenocytes of mice transplanted with the MAC16 tumour, with a delayed cachexia. The material is a proteoglycan of relative molecular mass 24K which produces cachexia in vivo by inducing catabolism of skeletal muscle. The 24K material was also present in urine of cachectic cancer patients, but was absent from normal subjects, patients with weight loss due to trauma, and cancer patients with little or no weight loss. This suggests that cachexia in mice and humans may be produced by the same material.
We report 17 patients seropositive for the human immunodeficiency virus, with muscle tissue involvement in different stages of the disease. Some patients are treated with azidothymidine (AZT). Others have no opportunistic infections. In all cases, there are some muscular symptoms such as progressive symetric and proximal muscular weakness with myalgias, elevated serum muscle enzymes, abnormal electromyogramma and very often a peripheral neuropathy. The muscle biopsy reveals the following features: rarely a focal muscular opportunistic infection in advanced stage of the disease is observed; a polymyositis is quite often the first clinical manifestation of the disease; a myopathy with mitochondrial involvement is observed in some of the AZT treated patients; some cachectic, under nourrished, bedridden patients present a type II muscle fiber atrophy. We conclude that a muscle biopsy could help us in our therapeutic planning directing us to a corticotherapy in the polymyositis, mitochondriopathies and wasting syndrome. Interruption alone of AZT or associated with a treatment by carnitine could allow remission of the muscular pathology.
We describe a technique wherein single muscle fibers of intact mice are made transgenic by intracellular injection of DNA expression vectors for the reporter genes lacZ and green fluorescent protein (GFP). Application of in vivo imaging techniques allowed identification of single cells during the injections, and of the same single cells when the muscle was reexposed days or weeks later. DNA concentration by itself had little effect on fiber survival or expression efficacy, but it seemed crucial to exceed a threshold of about 10(6) injected plasmid molecules in order to obtain expression. On the other hand, experiments with coinjection of two different plasmids suggested that relatively few individual molecules were eventually transcribed in expressing cells. Plasmid DNA remained localized to the injection site, and expression was confined to nuclei in the vicinity. Expression was stable, as reporter was detected 2-61 days after injection.
The mechanism of body weight loss in the tumor-bearing state is still unclear. In this study, we investigated expressions of apoptosis regulatory proteins in the skeletal muscle of tumor-bearing and diet-restricted rabbits, and tried to evaluate the differences between the two groups. The apoptotic index (AI) in the tumor-bearing group was 28.1+/-2.84 on day 10. By day 20, many more apoptotic cells were found (AI: 40.5+/-3.20), but then after day 20 their numbers gradually decreased (AI: 9.67+/-2.22 on day 30 and 0.93+/-0.96 on day 40). By contrast, no apoptotic cells were detected in the diet-restricted group at any of the times examined. Bcl-2 immunoreactivity was either not detected at all or only weakly observed in both groups. By contrast, Bax expression increased gradually after implantation in the tumor-bearing group. Bax expression in skeletal muscle cell was graded (moderate) 10 days after tumor implantation, and (high) by day 20, in 2 of the 5 tumor-bearing rabbits. After day 20, however, Bax immunoreactivity decreased continuously in the tumor-bearing group. By contrast, hardly any Bax-immuno-positive cells were detected in the diet-restricted group. These results suggest that loss of body weight in the tumor-bearing group is different from that in the diet-restricted group, and is related to apoptosis of skeletal muscles.
The time-course of degeneration/regeneration was investigated in leg muscles throughout the life of the mdx mutant mouse, which is a biochemical homologue of Duchenne muscular dystrophy (DMD). In young and adult mice (up to 52 weeks old), muscle fibre necrosis was compensated by a vigorous regeneration, but in old mdx mice (65-104 weeks) this regeneration slightly declined, while the necrotic process persisted. Body and muscles weights declined strikingly after 52 weeks. Life span of mdx mutants was reduced in comparison with the control C57BL/10 animals. Immunostaining of old mdx muscles showed clusters of dystrophin-positive fibres. Muscle fibres in old mdx mice showed great variation in size, many being atrophied or split. Endomysial fibrosis became increasingly conspicuous, and there was some accumulation of adipose tissue. These progressive degenerative changes of old mdx mice resemble those found in DMD and imply that basic pathological similarities between the murine and human diseases previously observed in diaphragm of mdx mice may be extended to other skeletal muscles.
Administration of interleukin-15 (IL-15) to rats bearing the Yoshida AH-130 ascites hepatoma (a tumour that induces an important cachectic response) resulted in a significant reduction of muscle wasting, both measured as muscle weight and as protein content of different types of skeletal muscle. In addition, the administration of the cytokine completely reversed the increased DNA fragmentation observed in skeletal muscle of tumour-bearing animals. Concerning the mechanism(s) involved in the anti-apoptotic effects of IL-15 on skeletal muscle, the administration of the cytokine resulted in a considerable decrease in both R1 (43%) and R2 (64%) TNF-alpha receptors (TNFRs), and therefore it may be suggested that IL-15 decreases apoptosis by affecting TNF-alpha signalling. Formation of NO could be the signalling event associated with the activation of apoptosis in muscle of tumour-bearing rats; indeed, administration of IL-15 decreased the inducible nitric oxide synthase protein levels by 73%, suggesting that NO formation and muscle apoptosis during tumour growth are related. In conclusion, IL-15 seems to be able to reduce/suppress protein loss and apoptosis related to muscle wasting during cancer cachexia in experimental animals.
Cachexia contributes to nearly a third of all cancer deaths, yet the mechanisms underlying skeletal muscle wasting in this syndrome remain poorly defined. We report that tumor-induced alterations in the muscular dystrophy-associated dystrophin glycoprotein complex (DGC) represent a key early event in cachexia. Muscles from tumor-bearing mice exhibited membrane abnormalities accompanied by reduced levels of dystrophin and increased glycosylation on DGC proteins. Wasting was accentuated in tumor mdx mice lacking a DGC but spared in dystrophin transgenic mice that blocked induction of muscle E3 ubiquitin ligases. Furthermore, DGC deregulation correlated positively with cachexia in patients with gastrointestinal cancers. Based on these results, we propose that, similar to muscular dystrophy, DGC dysfunction plays a critical role in cancer-induced wasting.
Reports from this laboratory suggested that expression of skeletal muscle-derived, inducible nitric oxide synthase (iNOS), is associated with resistance of a particular rat strain to the autoimmune model of myasthenia gravis (MG). The study reported below demonstrates a similar association between iNOS induction in skeletal muscle and disease-resistance when comparing different skeletal muscles originating from the same rat strain. Thus, soleus muscles, shown previously to be relatively resistant to disease even when obtained from disease-susceptible Lewis rats, were observed to express high levels of iNOS following exposure to antibody reactive with the nicotinic acetylcholine receptor (AChR). Increased iNOS expression appears to be associated with slow-twitch, type 1 fibers and would explain the relatively high iNOS expression in soleus muscles since they are dominated by this fiber type, compared to disease-susceptible EDL muscles which are dominated by fast-twitch, type 2 fibers.
The fiber specificity of skeletal muscle abnormalities in chronic heart failure (CHF) has not been defined. We show here that transgenic mice (8 weeks old) with cardiac-specific overexpression of calsequestrin developed CHF (50.9% decrease in fractional shortening and 56.4% increase in lung weight, P<0.001), cachexia (37.8% decrease in body weight, P<0.001), and exercise intolerance (69.3% decrease in running distance to exhaustion, P<0.001) without a significant change in muscle fiber-type composition. Slow oxidative soleus muscle maintained muscle mass, whereas fast glycolytic tibialis anterior and plantaris muscles underwent atrophy (11.6 and 13.3%, respectively; P<0.05). In plantaris muscle, glycolytic type IId/x and IIb, but not oxidative type I and IIa, fibers displayed significant decreases in cross-sectional area (20.3%, P<0.05). Fast glycolytic white vastus lateralis muscle showed sarcomere degeneration and decreased cytochrome c oxidase IV (39.5%, P<0.01) and peroxisome proliferator-activated receptor gamma co-activator 1alpha protein expression (30.3%, P<0.01) along with a dramatic induction of the MAFbx/Atrogin-1 mRNA. These findings suggest that exercise intolerance can occur in CHF without fiber type switching in skeletal muscle and that oxidative phenotype renders myofibers resistant to pathological insults induced by CHF.
Cancer cachexia is a syndrome of progressive nutritional depletion which causes significant morbidity and mortality in cancer patients. One of the main pathogenetic mechanisms underlying cancer cachexia is a complex interaction between the host and the tumour. Tumour cells interact with host cells within the tumour mass resulting in the production of catabolic mediators which degrade host tissue. In addition, the host may mount an aberrant metabolic response to the tumour. However, in recent years, it has also been understood that patient factors, including age and levels of physical activity, and the specific mechanics of protein metabolism in cancer patients may also have a significant impact. In this review article, we not only summarise previous knowledge surrounding host-tumour interaction, but we also discuss these broader concepts in the pathogenesis of cancer cachexia. Clinicians should consider such concepts in the design of an effective multimodal therapy for cachexia.
Cancer cachexia is a multi-factorial syndrome that encompasses a spectrum from early weight loss (pre-cachexia) to a state of severe incapacity incompatible with life. The molecular basis of the syndrome in animal models (based on host-tumour cell interaction, the neuro-hormonal control of appetite and the hypertrophy/atrophy pathways that govern muscle-wasting) has provided a new raft of biomarkers and therapeutic targets. Key defining features of cachexia in humans (weight loss, reduced food intake and systemic inflammation) now provide not only a framework for classification but also a rationale for targets for therapeutic intervention. The role of age and immobility in muscle-wasting also provides a rationale for the nature of nutritional support in cachexia. There is now a substantive evidence that multimodal approaches that address these key issues can stabilise and even improve the nutritional status, function and quality of life of at least a proportion of advanced cancer patients. Novel biomarkers for patient stratification and more specific techniques for the estimation of muscle mass and physical activity level herald a new era in trial design. The current evidence-base justifies new enthusiasm for the design of complex intervention studies in the management of cancer cachexia.
Dupre-Aucouturier S, Desplanches D, Gundersen K. No change in myonuclear number during muscle unloading and reloading
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