Host Muscle Research Articles

Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta—a literature review

Salmon farming increases the abundance of salmon lice, which are ectoparasites of salmonids in the sea. Here we review the current knowledge on the effects of salmon lice on wild sea trout. Salmon lice feed on host mucus, skin and muscle, and infestation may induce osmoreg- ulatory dysfunction, physiological stress, anaemia, reduced feeding and growth, increased sus- ceptibility to secondary infections, reduced disease resistance and ultimately mortality of individ- ual sea trout. Wild sea trout in farm-free areas generally show low lice levels. In farm-intensive areas, lice levels on wild sea trout are typically higher, and more variable than in farm-free areas. Lice on wild sea trout are found at elevated levels particularly within 30 km of the nearest farms but can also extend to further ranges. Salmon lice in intensively farmed areas have negatively impacted wild sea trout populations by reducing growth and increasing marine mortality. Quan- tification of these impacts remains a challenge, although population-level effects have been quan- tified in Atlantic salmon by comparing the survival of chemically protected fish with control groups, which are relevant also for sea trout. Mortality attributable to salmon lice can lead to an average of 12�29% fewer salmon spawners. Reduced growth and increased mortality will reduce the benefits of marine migration for sea trout, and may also result in selection against anadromy in areas with high lice levels. Salmon lice-induced effects on sea trout populations may also extend to altered genetic composition and reduced diversity, and possibly to the local loss of sea trout, and establishment of exclusively freshwater resident populations.

The effect of the muscle environment on the regenerative capacity of human skeletal muscle stem cells.

BackgroundMuscle stem cell transplantation is a possible treatment for muscular dystrophy. In addition to the intrinsic properties of the stem cells, the local and systemic environment plays an important role in determining the fate of the grafted cells. We therefore investigated the effect of modulating the host muscle environment in different ways (irradiation or cryoinjury or a combination of irradiation and cryoinjury) in two immunodeficient mouse strains (mdx nude and recombinase-activating gene (Rag)2-/γ chain-/C5-) on the regenerative capacity of two types of human skeletal muscle-derived stem cell (pericytes and CD133+ cells).MethodsHuman skeletal muscle-derived pericytes or CD133+ cells were transplanted into muscles of either mdx nude or recombinase-activating gene (Rag)2-/γ chain-/C5- host mice. Host muscles were modulated prior to donor cell transplantation by either irradiation, or cryoinjury, or a combination of irradiation and cryoinjury. Muscles were analysed four weeks after transplantation, by staining transverse cryostat sections of grafted muscles with antibodies to human lamin A/C, human spectrin, laminin and Pax 7. The number of nuclei and muscle fibres of donor origin and the number of satellite cells of both host and donor origin were quantified.ResultsWithin both host strains transplanted intra-muscularly with both donor cell types, there were significantly more nuclei and muscle fibres of donor origin in host muscles that had been modulated by cryoinjury, or irradiation+cryoinjury, than by irradiation alone. Irradiation has no additive effects in further enhancing the transplantation efficiency than cryodamage. Donor pericytes did not give rise to satellite cells. However, using CD133+ cells as donor cells, there were significantly more nuclei, muscle fibres, as well as satellite cells of donor origin in Rag2-/γ chain-/C5- mice than mdx nude mice, when the muscles were injured by either cryodamage or irradiation+cryodamage.ConclusionsRag2-/γ chain-/C5- mice are a better recipient mouse strain than mdx nude mice for human muscle stem cell transplantation. Cryodamage of host muscle is the most effective method to enhance the transplantation efficiency of human skeletal muscle stem cells. This study highlights the importance of modulating the muscle environment in preclinical studies to optimise the efficacy of transplanted stem cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s13395-015-0036-8) contains supplementary material, which is available to authorized users.

Trichinella pseudospiralis in the Iberian peninsula

Nematode worms of the genus Trichinella are zoonotic parasites circulating in most continents, including Europe. In Spain, Trichinella spiralis and Trichinella britovi are highly prevalent in wildlife but seldom in domestic pigs. In Portugal, only T. britovi was documented in wild carnivores. In the period 2006–2013 in Spain, 384 (0.0001%) pigs and 1399 (0.20%) wild boars (Sus scrofa) were positive for Trichinella spp. larvae, which were identified as T. spiralis or T. britovi. In 2014, Trichinella pseudospiralis larvae were isolated from a wild boar hunted in the Gerona province, Cataluña region, North-East of Spain, near the border to France. This is the first report of T. pseudospiralis in the Iberian peninsula, which suggests a broad distribution area of this zoonotic nematode in Europe. Since larvae of this Trichinella species do not encapsulate in the host muscles, they can be detected only by artificial digestion of muscle samples. T. pseudospiralis is the only Trichinella species infecting both mammals and birds. Birds can spread this pathogen over great distances including islands triggering new foci of infections in areas previously considered at low risk for this pathogen.

Trophic relationships between the larvae of two freshwater mussels and their fish hosts

AbstractFreshwater mussels of the order Unionoida have life cycles that include larval attachment to and later metamorphosis on suitable host fishes. Information on the trophic relationship between unionoid larvae and their host fishes is scarce. We investigated the trophic interaction between fish hosts and encysted larvae of two species of freshwater mussels, Margaritifera margaritifera and Unio crassus, using stable isotope analyses of larvae and juvenile mussels as well as of host fish gill and muscle tissues before and after infestation. Due to different life histories and durations of host‐encystment, mass and size increase in M. margaritifera during the host‐dependent phase were greater than those of U. crassus. δ13C and δ15N signatures of juvenile mussels approached isotopic signatures of fish tissues, indicating a parasitic relationship between mussels and their hosts. Shifts were more pronounced for M. margaritifera, which had a five‐fold longer host‐dependent phase than U. crassus. The results of this study suggest that stable isotope analyses are a valuable tool for characterizing trophic relationships and life history strategies in host–parasite systems. In the case of unionoid mussels, stable isotopic shifts of the larvae are indicative of the nutritional versus phoretic importance of the host.

In vivo generation of a mature and functional artificial skeletal muscle.

Extensive loss of skeletal muscle tissue results in mutilations and severe loss of function. In vitro-generated artificial muscles undergo necrosis when transplanted in vivo before host angiogenesis may provide oxygen for fibre survival. Here, we report a novel strategy based upon the use of mouse or human mesoangioblasts encapsulated inside PEG-fibrinogen hydrogel. Once engineered to express placental-derived growth factor, mesoangioblasts attract host vessels and nerves, contributing to in vivo survival and maturation of newly formed myofibres. When the graft was implanted underneath the skin on the surface of the tibialis anterior, mature and aligned myofibres formed within several weeks as a complete and functional extra muscle. Moreover, replacing the ablated tibialis anterior with PEG-fibrinogen-embedded mesoangioblasts also resulted in an artificial muscle very similar to a normal tibialis anterior. This strategy opens the possibility for patient-specific muscle creation for a large number of pathological conditions involving muscle tissue wasting.

Microbiomes, plausible players or not in alteration of host behavior.

Many parasites can affect the physiology and behavior of their hosts in ways that seem to improve the parasites' chances of completing their life cycle (Biron and Loxdale, 2013; Lafferty and Shaw, 2013; Webster et al., 2013). These parasite species are so-called “manipulative parasites.” Common habitats of manipulative parasites are the host's body cavity, muscles and brain (Lafferty and Shaw, 2013). Typically the host's neural, endocrine, neuromodulatory, and immunomodulatory systems are targeted (Adamo, 2013; Lafferty and Shaw, 2013). In evolutionary biology, manipulation of host behavior by parasites is considered to be an example of the “extended phenotype” concept (Dawkins, 1982; Libersat et al., 2009). There are numerous fascinating cases of alteration of host behavior induced by a parasite; for instance, the suicidal behavior of crickets induced by hairworms (Thomas et al., 2002; Biron and Loxdale, 2013). Many studies on strategies used by manipulative parasites assume that only two organisms are involved in crosstalk based on Dawkins' assumption: the host and a manipulative parasite. However, hosts are frequently invaded by more than one species of parasite (Ferrari and Vavre, 2011; Cezilly et al., 2014). The interests of different parasitic species may conflict; for example, two parasites may share an intermediate host but require a different definitive host. Parasite-parasite interactions in the intermediate host can result in perturbation of the parasite infection process for each parasite species (Lafferty and Shaw, 2013; Cezilly et al., 2014). As far as we know, microbiomes are not considered to be taking part in crosstalk between an aquatic host and a manipulative parasite. Therefore, we first briefly present the background for microbiomes as plausible and underestimated players in the crosstalk in host-manipulative parasite associations in aquatic ecosystems, and secondly we discuss concepts and -omics methods to determine whether or not host microbiomes can influence host behavior in aquatic models. Finally, we discuss the importance of considering context-dependent changes in the analysis of -omics data to decode and understand the role of a host microbiome in the alteration of host behavior in aquatic ecosystems.

Trypanorhynch Cestodes Infecting Mediterranean Sea Fishes, Egypt: Callitetrarhynchus gracilis Larvae (Pintner, 1931) as a Bio-indicator of Heavy Metals Pollution

A total of 150 fish samples belonging to three families were collected from Mediterranean sea, Egypt and examined for Trypanorhynch Cestode larvae infection from September 2011 till February 2012. Sixty three (42%) of the investigated fish were parasitized with different larval species belonging to Lacistorhynchidae and Tentaculariidae. All Trypanorhynch species larvae were isolated from muscles and abdominal cavities. Results revealed that, 46%; 44% and 36% of the examined fish species Epinephelus gigas; Sciaena umbra and Scomber spp. were infected respectively and were considered as new hosts for the detected parasites. Callitetrarhynchus gracilis larvae (Pintner, 1931) showed the highest prevalence (30%) and maximum intensity (37). The collected C. gracilis larvae and its host muscles (Epinephelus gigas) were analyzed for some heavy metals ( Cu, Pb, and Cd) using atomic absorption spectrophotometer, the results indicated a significance higher concentration of the heavy metals in the parasite tissues compared with its fish host muscles. The present study has concluded for the 1st time that; the Trypanorhynch C. gracilis larvae could be used as bio-indicator of heavy metals pollution and add further evidence to the usefulness of parasites in monitoring environmental impacts.

Muscle extracellular matrix scaffold is a multipotent environment.

The multipotency of scaffolds is a new concept. Skeletal muscle acellular scaffolds (MAS) implanted at the interface of Tibialis Anterior/tibial bone and masseter muscle/mandible bone in a murine model were colonized by muscle cells near the host muscle and by bone-cartilaginous tissues near the host bone, thus highlighting the importance of the environment in directing cell homing and differentiation. These results unveil the multipotency of MAS and point to the potential of this new technique as a valuable tool in musculo-skeletal tissue regeneration.

Trichinella spiralis: genome database searches for the presence and immunolocalization of protein disulphide isomerase family members.

The formation of nurse cells in host muscle cells during Trichinella spiralis infection is a key step in the infective mechanism. Collagen trimerization is set up via disulphide bond formation, catalysed by protein disulphide isomerase (PDI). In T. spiralis, some PDI family members have been identified but no localization is described and no antibodies specific for T. spiralis PDIs are available. In this work, computational approaches were used to search for non-described PDIs in the T. spiralis genome database and to check the cross-reactivity of commercial anti-human antibodies with T. spiralis orthologues. In addition to a previously described PDI (PDIA2), endoplasmic reticulum protein (ERp57/PDIA3), ERp72/PDIA4, and the molecular chaperones calreticulin (CRT), calnexin (CNX) and immunoglobulin-binding protein/glucose-regulated protein (BIP/GRP78), we identified orthologues of the human thioredoxin-related-transmembrane proteins (TMX1, TMX2 and TMX3) in the genome protein database, as well as ERp44 (PDIA10) and endoplasmic reticulum disulphide reductase (ERdj5/PDIA19). Immunocytochemical staining of paraffin sections of muscle infected by T. spiralis enabled us to localize some orthologues of the human PDIs (PDIA3 and TMX1) and the chaperone GRP78. A theoretical three-dimensional model for T. spiralis PDIA3 was constructed. The localization and characteristics of the predicted linear B-cell epitopes and amino acid sequence of the immunogens used for commercial production of anti-human PDIA3 antibodies validated the use of these antibodies for the immunolocalization of T. spiralis PDIA3 orthologues. These results suggest that further study of the role of the PDIs and chaperones during nurse cell formation is desirable.

Abstract 3380: Cancer usurps skeletal muscle as an energy repository

Abstract Cancer cells produce energy through aerobic glycolysis, but contributions of host tissues to cancer energy metabolism is unclear. In this study, we aimed to elucidate the cancer-host energy production relationship, in particular, between cancer energy production and host muscle. During the development and progression of colorectal cancer (CRC), expression of the secreted autophagy-inducing stress protein HMGB1 increased in the muscle of tumor-bearing animals. This effect was associated with decreased expression of pyruvate kinase PKM1 and pyruvate kinase activity in muscle via the HMGB1 receptor RAGE. However, muscle mitochondrial energy production was maintained. In contrast, HMGB1 addition to CRC cells increased lactate fermentation. In the muscle, HMGB1 addition induced autophagy by decreasing levels of active mTOR and increasing autophagy-associated proteins, plasma glutamate and 13C-glutamine incorporation into acetyl-CoA. In a mouse model of colon carcinogenesis, a temporal increase in HMGB1 occurred in serum and colonic mucosa with an increase in autophagy associated with altered plasma free amino acids levels, increased glutamine and decreased PKM1 levels. These differences were abolished by administration of an HMGB1 neutralizing antibody. Similar results were obtained in a mouse xenograft model of human CRC. Taken together, our findings suggest that HMGB1 released during tumorigenesis recruits muscle to supply glutamine to cancer cells as an energy source. Citation Format: Yi Luo, Junya Yoneda, Hitoshi Ohmori, Takamitsu Sasaki, Hiroki Kuniyasu. Cancer usurps skeletal muscle as an energy repository. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3380. doi:10.1158/1538-7445.AM2014-3380

In situ regeneration of skeletal muscle tissue through host cell recruitment

Standard reconstructive procedures for restoring normal function after skeletal muscle defects involve the use of existing host tissues such as muscular flaps. In many instances, this approach is not feasible and delays the rehabilitation process and restoration of tissue function. Currently, cell-based tissue engineering strategies have been used for reconstruction; however, donor tissue biopsy and ex vivo cell manipulation are required prior to implantation. The present study aimed to overcome these limitations by demonstrating mobilization of muscle cells into a target-specific site for in situ muscle regeneration. First, we investigated whether host muscle cells could be mobilized into an implanted scaffold. Poly(l-lactic acid) (PLLA) scaffolds were implanted in the tibialis anterior (TA) muscle of rats, and the retrieved scaffolds were characterized by examining host cell infiltration in the scaffolds. The host cell infiltrates, including Pax7+ cells, gradually increased with time. Second, we demonstrated that host muscle cells could be enriched by a myogenic factor released from the scaffolds. Gelatin-based scaffolds containing a myogenic factor were implanted in the TA muscle of rats, and the Pax7+ cell infiltration and newly formed muscle fibers were examined. By the second week after implantation, the Pax7+ cell infiltrates and muscle formation were significantly accelerated within the scaffolds containing insulin-like growth factor 1 (IGF-1). Our data suggest an ability of host stem cells to be recruited into the scaffolds with the capability of differentiating to muscle cells. In addition, the myogenic factor effectively promoted host cell recruitment, which resulted in accelerating muscle regeneration in situ.

Human Skeletal Muscle–derived CD133+ Cells Form Functional Satellite Cells After Intramuscular Transplantation in Immunodeficient Host Mice

Stem cell therapy is a promising strategy for treatment of muscular dystrophies. In addition to muscle fiber formation, reconstitution of functional stem cell pool by donor cells is vital for long-term treatment. We show here that some CD133(+) cells within human muscle are located underneath the basal lamina of muscle fibers, in the position of the muscle satellite cell. Cultured hCD133(+) cells are heterogeneous and multipotent, capable of forming myotubes and reserve satellite cells in vitro. They contribute to extensive muscle regeneration and satellite cell formation following intramuscular transplantation into irradiated and cryodamaged tibialis anterior muscles of immunodeficient Rag2-/γ chain-/C5-mice. Some donor-derived satellite cells expressed the myogenic regulatory factor MyoD, indicating that they were activated. In addition, when transplanted host muscles were reinjured, there was significantly more newly-regenerated muscle fibers of donor origin in treated than in control, nonreinjured muscles, indicating that hCD133(+) cells had given rise to functional muscle stem cells, which were able to activate in response to injury and contribute to a further round of muscle regeneration. Our findings provide new evidence for the location and characterization of hCD133(+) cells, and highlight that these cells are highly suitable for future clinical application.

Acetylcholinesterase secreted by Anisakis simplex larvae (Nematoda: Anisakidae) parasitizing herring, Clupea harengus: an inverse relationship of enzyme activity in the host–parasite system

Acetylcholinesterase (AChE) is a key enzyme involved in nerve impulse transmission in both vertebrates and invertebrates. In addition to neuromuscular AChE, many parasitic nematodes synthesize AChE in secretory glands and release the enzyme into their external environment. In this study, we evaluate the activities of both somatic and secreted AChE from larvae (L3) of the parasitic nematode Anisakis simplex, and compare these to the AChE activity in its host, herring, Clupea harengus. A. simplex larvae were obtained from a herring sampled in three areas of the southern Baltic. Enzyme kinetics were determined for excretory/secretory (E/S) products and somatic extracts of larvae as well as for herring muscle tissue. The results reveal that mean AChE activity is approximately fourfold higher in E/S products and eightfold higher in somatic extracts of post-secretory A. simplex larvae than in host muscle tissue. The level of AChE activity in nematodes is inversely related to the enzyme activity in their hosts, i.e. reduced AChE activity in herring was accompanied by increased enzyme activity in its parasites. The physiological function of AChE secreted by parasitic nematodes has been widely discussed in the literature, and numerous roles for this form of enzyme have been suggested. The results of our investigation indicate that AChE secretion by A. simplex larvae may constitute an adaptive mechanism that promotes survival under adverse environmental conditions. Larvae probably increase secretion of AChE in response to a direct and/or indirect effect of neurotoxic compounds. This is the first report of such a phenomenon in A. simplex.

Cancer Usurps Skeletal Muscle as an Energy Repository

Cancer cells produce energy through aerobic glycolysis, but contributions of host tissues to cancer energy metabolism are unclear. In this study, we aimed to elucidate the cancer-host energy production relationship, in particular, between cancer energy production and host muscle. During the development and progression of colorectal cancer, expression of the secreted autophagy-inducing stress protein HMGB1 increased in the muscle of tumor-bearing animals. This effect was associated with decreased expression of pyruvate kinase PKM1 and pyruvate kinase activity in muscle via the HMGB1 receptor for advanced glycation endproducts (RAGE). However, muscle mitochondrial energy production was maintained. In contrast, HMGB1 addition to colorectal cancer cells increased lactate fermentation. In the muscle, HMGB1 addition induced autophagy by decreasing levels of active mTOR and increasing autophagy-associated proteins, plasma glutamate, and (13)C-glutamine incorporation into acetyl-CoA. In a mouse model of colon carcinogenesis, a temporal increase in HMGB1 occurred in serum and colonic mucosa with an increase in autophagy associated with altered plasma free amino acid levels, increased glutamine, and decreased PKM1 levels. These differences were abolished by administration of an HMGB1 neutralizing antibody. Similar results were obtained in a mouse xenograft model of human colorectal cancer. Taken together, our findings suggest that HMGB1 released during tumorigenesis recruits muscle to supply glutamine to cancer cells as an energy source.

Clinical-Grade Human Neural Stem Cells Promote Reparative Neovascularization in Mouse Models of Hindlimb Ischemia

CTX0E03 (CTX) is a clinical-grade human neural stem cell (hNSC) line that promotes angiogenesis and neurogenesis in a preclinical model of stroke and is now under clinical development for stroke disability. We evaluated the therapeutic activity of intramuscular CTX hNSC implantation in murine models of hindlimb ischemia for potential translation to clinical studies in critical limb ischemia. Immunodeficient (CD-1 Fox(nu/nu)) mice acutely treated with hNSCs had overall significantly increased rates and magnitude of recovery of surface blood flow (laser Doppler), limb muscle perfusion (fluorescent microspheres, P<0.001), and capillary and small arteriole densities in the ischemic limb (fluorescence immunohistochemistry, both P<0.001) when compared with the vehicle-treated group. Hemodynamic and anatomic improvements were dose related and optimal at a minimum dose of 3×10(5) cells. Dose-dependent improvements in blood flow and increased vessel densities by hNSC administration early after ischemia were confirmed in immunocompetent CD-1 and streptozotocin-induced diabetic mice, together with marked reductions in the incidence of necrotic toes (P<0.05). Delayed administration of hNSCs, 7 days after occlusion, produced restorative effects when comparable with acute treatment of 35 days after hindlimb ischemia. Histological studies in hindlimb ischemia immunocompetent mice for the first 7 days after treatment revealed short-term hNSC survival, transient elevation of early host muscle inflammatory, and angiogenic responses and acceleration of myogenesis. hNSC therapy represents a promising treatment option for critical limb ischemia.

P.20.10 Human adipose mesenchymal stem-cells injections in golden retriever muscular dystrophy (GRMD) dogs: a four-year follow-up

The possibility to treat Duchenne dystrophy (DMD) through cell therapy has been widely investigated but before starting clinical trials in humans many questions still need to be addressed in pre-clinical studies. In addition to clarifying the role of the exogenous cells in dystrophic muscle, one important concern is whether there is an increased risk of tumors or any other long-term side effects following stem-cells injections. Since murine models have a short life span, the best animal model to address these questions is the Golden Retriever Muscular Dystrophy (GRMD) dog, which reproduces the full spectrum of human DMD. They present clinical signs within the first weeks of life and most of them do not survive beyond age two. However, due to their phenotype variability each dog must be compared separately before and after any experiment. We have injected human adipose-derived mesenchymal stromal cells (hAMSCs), from two different donors, in three GRMD dogs, without immunosuppression. They were injected in the cephalic vein with 5 × 107 cells/kg within their first year of life: weekly in the first month of injections and then monthly. Dolar and Yuan were born in September of 2008 and Rum in July of 2011. In Dolar and Yuan, who received cells from donor 1, we observed that hAMSCs injected systemically were able to reach and express human dystrophin in the host GRMD dystrophic muscle up to 6 months after transplantation. When cells from donor 2 were injected in Rum, no human dystrophin was found in the host muscle. However, the three dogs showed clinical improvement following hAMSCS injections with an apparent stabilization afterwards, suggesting a beneficial effect from factors released by the injected cells. Most importantly, after almost four years of follow-up for Dolar and Yuan there was no tumor or other side effect suggesting that hAMSCS transplantation is a safe procedure, which may have important applications for future therapy in muscular dystrophy patients. The possibility to treat Duchenne dystrophy (DMD) through cell therapy has been widely investigated but before starting clinical trials in humans many questions still need to be addressed in pre-clinical studies. In addition to clarifying the role of the exogenous cells in dystrophic muscle, one important concern is whether there is an increased risk of tumors or any other long-term side effects following stem-cells injections. Since murine models have a short life span, the best animal model to address these questions is the Golden Retriever Muscular Dystrophy (GRMD) dog, which reproduces the full spectrum of human DMD. They present clinical signs within the first weeks of life and most of them do not survive beyond age two. However, due to their phenotype variability each dog must be compared separately before and after any experiment. We have injected human adipose-derived mesenchymal stromal cells (hAMSCs), from two different donors, in three GRMD dogs, without immunosuppression. They were injected in the cephalic vein with 5 × 107 cells/kg within their first year of life: weekly in the first month of injections and then monthly. Dolar and Yuan were born in September of 2008 and Rum in July of 2011. In Dolar and Yuan, who received cells from donor 1, we observed that hAMSCs injected systemically were able to reach and express human dystrophin in the host GRMD dystrophic muscle up to 6 months after transplantation. When cells from donor 2 were injected in Rum, no human dystrophin was found in the host muscle. However, the three dogs showed clinical improvement following hAMSCS injections with an apparent stabilization afterwards, suggesting a beneficial effect from factors released by the injected cells. Most importantly, after almost four years of follow-up for Dolar and Yuan there was no tumor or other side effect suggesting that hAMSCS transplantation is a safe procedure, which may have important applications for future therapy in muscular dystrophy patients.

Grafting of a Single Donor Myofibre Promotes Hypertrophy in Dystrophic Mouse Muscle

Skeletal muscle has a remarkable capability of regeneration following injury. Satellite cells, the principal muscle stem cells, are responsible for this process. However, this regenerative capacity is reduced in muscular dystrophies or in old age: in both these situations, there is a net loss of muscle fibres. Promoting skeletal muscle muscle hypertrophy could therefore have potential applications for treating muscular dystrophies or sarcopenia. Here, we observed that muscles of dystrophic mdx nude host mice that had been acutely injured by myotoxin and grafted with a single myofibre derived from a normal donor mouse exhibited increased muscle area. Transplantation experiments revealed that the hypertrophic effect is mediated by the grafted fibre and does not require either an imposed injury to the host muscle, or the contribution of donor cells to the host muscle. These results suggest the presence of a crucial cross-talk between the donor fibre and the host muscle environment.

Adult and juvenile dermatomyositis: are the distinct clinical features explained by our current understanding of serological subgroups and pathogenic mechanisms?

Adult and juvenile dermatomyositis share the hallmark features of pathognomic skin rash and muscle inflammation, but are heterogeneous disorders with a range of additional disease features and complications. The frequency of important clinical features such as calcinosis, interstitial lung disease and malignancy varies markedly between adult and juvenile disease. These differences may reflect different disease triggers between children and adults, but whilst various viral and other environmental triggers have been implicated, results are so far conflicting. Myositis-specific autoantibodies can be detected in both adults and children with idiopathic inflammatory myopathies. They are associated with specific disease phenotypes and complications, and divide patients into clinically homogenous subgroups. Interestingly, whilst the same autoantibodies are found in both adults and children, the disease features remain different within autoantibody subgroups, particularly with regard to life-threatening disease associations, such as malignancy and rapidly progressive interstitial lung disease. Our understanding of the mechanisms that underlie these differences is limited by a lack of studies directly comparing adults and children. Dermatomyositis is an autoimmune disease, which is believed to develop as a result of an environmental trigger in a genetically predisposed individual. Age-specific host immune responses and muscle physiology may be additional complicating factors that have significant impact on disease presentation. Further study into this area may produce new insights into disease pathogenesis.

Plastic parasites: Extreme dimorphism creates a taxonomic conundrum in the phylum Microsporidia

In this paper, we combine field observations of highly statistically significant co-occurrence with histopathological, ultrastructural and molecular phylogenetic analyses, to provide evidence for extreme morphological plasticity in a microsporidium parasite infecting the musculature of marine crabs. The parasite appears to alternate between lineages that culminate in production of either bizarre needle-like spores in the peripheral sarcoplasm of heart and skeletal muscle fibres (reminiscent of Nadelspora canceri infecting Cancer magister) or alternatively, Ameson-like spores with pronounced surface projections, in the skeletal muscles (as for Ameson pulvis, previously described infecting Carcinus maenas). Both lineages occur in direct contact with the cytoplasm of host muscle cells and can exist simultaneously within the same cell. Pathological data appears to reveal a remarkable shift in morphology during pathogenic remodelling of host tissues. Sequence analysis of multiple clones derived from amplification of the ssrRNA gene from infected regions of the heart and skeletal muscles appear to confirm the genetic identity of the two lineages. Furthermore, derived ssrRNA gene sequences are more similar (>99%) to N. canceri than to the coparasite Ameson michaelis infecting Callinectes sapidus (93%). Although molecular phylogenetic data support transfer of A. pulvis into the genus Nadelspora, the expansion in the generic description required to include such widely divergent characteristics is so significant as to be unfeasible within the current taxonomic framework of the phylum Microsporidia. At present, it is preferable to propose that the parasite infecting C. maenas forms a clade with other morphologically diverse but phylogenetically and ecologically similar muscle-infecting microsporidians from marine crustacean hosts. Given the strong evidence for significant plasticity in morphology amongst members of the phylum Microsporidia, novel approaches to phylogeny, based predominantly upon the informed use of molecular sequence data, are now deemed a necessity.

Expression of the Skeletal Calsequestrin Isoform in Normal and Regenerated Skeletal Muscles and in the Hearts of Rats With Altered Thyroid Status

We have investigated expression of skeletal calsequestrin (CSQ1) and fiber type composition in normal and regenerated fast and slow skeletal muscles and in the left heart ventricles of euthyroid (EU), hypothyroid (HY) and hyperthyroid (TH) adult inbred Lewis strain rats. The CSQ1 level was determined by SDS-PAGE followed by Western blot analysis. CSQ1 gene expression was assessed using reverse transcription and subsequent real time polymerase chain reaction. Muscle regeneration was achieved by intramuscular grafting of either soleus or extensor digitorum longus (EDL) from 3- to 4-week-old rats to either EDL or soleus muscle of 2-month-old rats. The fiber type composition was assessed by a stereological method applied to stained muscle cross sections. We found that the protein and mRNA levels for CSQ1 were highest in the EDL muscle, the relative CSQ1 protein levels in the soleus muscle were two times lower and the transcript levels more than 5 times lower compared to the EDL. In the left heart ventricle, protein isoform and CSQ1 transcript were also present, although at protein level, CSQ1 was hardly detectable. TH status increased and HY status decreased the expression of CSQ1 in the EDL, but its relative levels in the soleus and in the heart did not change. The regenerated soleus transplanted into EDL, as well as EDL transplanted into soleus exhibited protein and mRNA levels of CSQ1 corresponding to the host muscle and not to the graft source. TH status increased the percentages of the fastest 2X/D and 2B fibers at the expense of slow type 1 and fast 2A fibers in the EDL and that of fast 2A fibers in the soleus at the expense of slow type 1 fibers. HY status led to converse fiber type changes. We suggest that the observed changes in CSQ1 levels in TH and HY compared to EU rats can be related to fiber type changes caused by alteration of the thyroid status rather than to the direct effect of thyroid hormones on CSQ1 gene expression.