Cutting Edge: Augmenting Muscle MHC Expression Enhances Systemic Pathogen Control at the Expense of T Cell Exhaustion.

Myocytes express low levels of MHC class I (MHC I), perhaps influencing the ability of CD8+ T cells to efficiently detect and destroy pathogens that invade muscle. Trypanosoma cruzi infects many cell types but preferentially persists in muscle, and we asked if this tissue-dependent persistence was linked to MHC expression. Inducible enhancement of skeletal muscle MHC I in mice during the first 20 d of T. cruzi infection resulted in enhanced CD8-dependent reduction of parasite load. However, continued overexpression of MHC I beyond 30 d ultimately led to a collapse of systemic parasite control associated with immune exhaustion, which was reversible in part by blocking PD-1:PD-L1 interactions. These studies demonstrate a surprisingly strong and systemically dominant effect of skeletal muscle MHC expression on maintaining T cell function and pathogen control and argue that the normally low MHC I expression in skeletal muscle is host protective by allowing for pathogen control while preventing immune exhaustion.

Pathogenesis of inclusion body myositis.

PURPOSE OF REVIEW: To review the pathogenesis of inclusion body myositis (IBM). RECENT FINDINGS: IBM is an autoimmune disease. Multiple arms of the immune system are activated, but a direct attack on muscle fibers by highly differentiated T cells drives muscle destruction. SUMMARY: Further understanding of the pathogenesis of IBM guides rational approaches to developing therapeutic strategies.

A new in vitro model of polymyositis reveals CD8+ T cell invasion into muscle cells and its cytotoxic role.

OBJECTIVES: The hallmark histopathology of PM is the presence of CD8+ T cells in the non-necrotic muscle cells. The aim of this study was to clarify the pathological significance of CD8+ T cells in muscle cells. METHODS: C2C12 cells were transduced retrovirally with the genes encoding MHC class I (H2Kb) and SIINFEKL peptide derived from ovalbumin (OVA), and then differentiated to myotubes (H2KbOVA-myotubes). H2KbOVA-myotubes were co-cultured with OT-I CD8+ T cells derived from OVA-specific class I restricted T cell receptor transgenic mice as an in vitro model of PM to examine whether the CD8+ T cells invade into the myotubes and if the myotubes with the invasion are more prone to die than those without. Muscle biopsy samples from patients with PM were examined for the presence of CD8+ T cells in muscle cells. The clinical profiles were compared between the patients with and without CD8+ T cells in muscle cells. RESULTS: Analysis of the in vitro model of PM with confocal microscopy demonstrated the invasion of OT-I CD8+ T cells into H2KbOVA-myotubes. Transmission electron microscopic analysis revealed an electron-lucent area between the invaded CD8+ T cell and the cytoplasm of H2KbOVA-myotubes. The myotubes invaded with OT-I CD8+ T cells died earlier than the uninvaded myotubes. The level of serum creatinine kinase was higher in patients with CD8+ T cells in muscle cells than those without these cells. CONCLUSION: CD8+ T cells invade into muscle cells and contribute to muscle injury in PM. Our in vitro model of PM is useful to examine the mechanisms underlying muscle injury induced by CD8+ T cells.

Pathogenic role of anti-signal recognition protein and anti-3-Hydroxy-3-methylglutaryl-CoA reductase antibodies in necrotizing myopathies: Myofiber atrophy and impairment of muscle regeneration in necrotizing autoimmune myopathies.

OBJECTIVE: Immune-mediated necrotizing myopathies (IMNM) may be associated with either anti-signal recognition protein (SRP) or anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibodies (Abs), and the titer of these Abs is correlated with disease activity. We investigated whether anti-SRP and anti-HMGCR Abs could be involved in muscle damage. METHODS: Muscle biopsies of patients were analyzed for atrophy and regeneration by measuring fiber size and by performing immunostaining of neonatal myosin heavy chain. To further understand the role of the Abs in the pathology, we performed muscle cell coculture with the Abs. Atrophy and regeneration were evaluated based on the myotube surface area as well as gene and cytokine profiles. RESULTS: In muscle biopsies of patients with anti-SRP+ and anti-HMGCR+ Abs, a large number of small fibers corresponding to both atrophic and regenerating fibers were observed. In vitro, anti-SRP and anti-HMGCR Abs induced muscle fiber atrophy and increased the transcription of MAFbx and TRIM63. In addition, the muscle fiber atrophy was associated with high levels of inflammatory cytokines: tumor necrosis factor, interleukin (IL)-6, and reactive oxygen species. In the presence of anti-SRP or anti-HMGCR Abs, mechanisms involved in muscle regeneration were also impaired due to a defect of myoblast fusion. This defect was associated with a decreased production of IL-4 and IL-13. The addition of IL-4 and/or IL-13 totally rescued fusion capacity. INTERPRETATION: These data show that molecular mechanisms of atrophy and regeneration are affected and contribute to loss of muscle function occurring in IMNM. This emphasizes the potential interest of targeted therapies addressing these mechanisms. Ann Neurol 2017;81:538-548.

Genetics in inclusion body myositis.

PURPOSE OF REVIEW: To review the advances in our understanding of the genetics of inclusion body myositis (IBM) in the past year. RECENT FINDINGS: One large genetic association study focusing on immune-related genes in IBM has refined the association within the human leukocyte antigen (HLA) region to HLA-DRB1 alleles, and identified certain amino acid positions in HLA-DRB1 that may explain this risk. A suggestive association with CCR5 may indicate genetic overlap with other autoimmune diseases. Sequencing studies of candidate genes involved in related neuromuscular or neurodegenerative diseases have identified rare variants in VCP and SQSTM1. Proteomic studies of rimmed vacuoles in IBM and subsequent genetic analyses of candidate genes identified rare missense variants in FYCO1. Complex, large-scale mitochondrial deletions in cytochrome c oxidase-deficient muscle fibres expand our understanding of mitochondrial abnormalities in IBM. SUMMARY: The pathogenesis of IBM is likely multifactorial, including inflammatory and degenerative changes, and mitochondrial abnormalities. There has been considerable progress in our understanding of the genetic architecture of IBM, using complementary genetic approaches to investigate these different pathways.

Skeletal muscle cells possess a 'memory' of acute early life TNF-α exposure: role of epigenetic adaptation.

Sufficient quantity and quality of skeletal muscle is required to maintain lifespan and healthspan into older age. The concept of skeletal muscle programming/memory has been suggested to contribute to accelerated muscle decline in the elderly in association with early life stress such as fetal malnutrition. Further, muscle cells in vitro appear to remember the in vivo environments from which they are derived (e.g. cancer, obesity, type II diabetes, physical inactivity and nutrient restriction). Tumour-necrosis factor alpha (TNF-α) is a pleiotropic cytokine that is chronically elevated in sarcopenia and cancer cachexia. Higher TNF-α levels are strongly correlated with muscle loss, reduced strength and therefore morbidity and earlier mortality. We have extensively shown that TNF-α impairs regenerative capacity in mouse and human muscle derived stem cells [Meadows et al. (J Cell Physiol 183(3):330-337, 2000); Foulstone et al. (J Cell Physiol 189(2):207-215, 2001); Foulstone et al. (Exp Cell Res 294(1):223-235, 2004); Stewart et al. (J Cell Physiol 198(2):237-247, 2004); Al-Shanti et al. (Growth factors (Chur, Switzerland) 26(2):61-73, 2008); Saini et al. (Growth factors (Chur, Switzerland) 26(5):239-253, 2008); Sharples et al. (J Cell Physiol 225(1):240-250, 2010)]. We have also recently established an epigenetically mediated mechanism (SIRT1-histone deacetylase) regulating survival of myoblasts in the presence of TNF-α [Saini et al. (Exp Physiol 97(3):400-418, 2012)]. We therefore wished to extend this work in relation to muscle memory of catabolic stimuli and the potential underlying epigenetic modulation of muscle loss. To enable this aim; C2C12 myoblasts were cultured in the absence or presence of early TNF-α (early proliferative lifespan) followed by 30 population doublings in the absence of TNF-α, prior to the induction of differentiation in low serum media (LSM) in the absence or presence of late TNF-α (late proliferative lifespan). The cells that received an early plus late lifespan dose of TNF-α exhibited reduced morphological (myotube number) and biochemical (creatine kinase activity) differentiation vs. control cells that underwent the same number of proliferative divisions but only a later life encounter with TNF-α. This suggested that muscle cells had a morphological memory of the acute early lifespan TNF-α encounter. Importantly, methylation of myoD CpG islands were increased in the early TNF-α cells, 30 population doublings later, suggesting that even after an acute encounter with TNF-α, the cells have the capability of retaining elevated methylation for at least 30 cellular divisions. Despite these fascinating findings, there were no further increases in myoD methylation or changes in its gene expression when these cells were exposed to a later TNF-α dose suggesting that this was not directly responsible for the decline in differentiation observed. In conclusion, data suggest that elevated myoD methylation is retained throughout muscle cells proliferative lifespan as result of early life TNF-α treatment and has implications for the epigenetic control of muscle loss.

CD8 T-cell priming upon mRNA vaccination is restricted to bone-marrow-derived antigen-presenting cells and may involve antigen transfer from myocytes.

Self-amplifying mRNAs (SAM(®) ) are a novel class of nucleic acid vaccines, delivered by a non-viral delivery system. They are effective at eliciting potent and protective immune responses and are being developed as a platform technology with potential to be used for a broad range of targets. However, their mechanism of action has not been fully elucidated. To date, no evidence of in vivo transduction of professional antigen-presenting cells (APCs) by SAM vector has been reported, while the antigen expression has been shown to occur mostly in the muscle fibres. Here we show that bone-marrow-derived APCs rather than muscle cells are responsible for induction of MHC class-I restricted CD8 T cells in vivo, but direct transfection of APCs by SAM vectors is not required. Based on all our in vivo and in vitro data we propose that upon SAM vaccination the antigen is expressed within muscle cells and then transferred to APCs, suggesting cross-priming as the prevalent mechanism for priming the CD8 T-cell response by SAM vaccines.

TNF alpha inhibits myogenic differentiation of C2C12 cells through NF-κB activation and impairment of IGF-1 signaling pathway.

Cachexia or muscle wasting is a common condition that occurs in many chronic diseases. The wasting conditions are characterized by increased levels of TNF-α which was also known as cachectin in the past. But how TNF-α exerts its cachetic effects remains controversial. To clarify this issue, we investigated the impact of TNF-α on C2C12 cell myogenic differentiation. Our results demonstrate that myotube formation was completely inhibited by TNF-α when added to differentiating C2C12 myoblasts. The inhibitory effect of TNF-α on differentiation was accompanied by activation of NF-κB and down regulation of myogenin and Akt. Importantly, TNF-α's effect on differentiation was abolished when IGF-1 was added to the culture. IGF-1 treatment also inhibited NF-κB reporter activity and restored Akt levels. Our data suggest that TNF-α inhibits myogenic differentiation through NF-κB activation and impairment of IGF-1 signaling pathway. The reversal of TNF-α induced inhibition of myogenesis by IGF-1 may have significant therapeutic potential.

Altered RIG-I/DDX58-mediated innate immunity in dermatomyositis.

We investigated the molecular mechanisms involved in the pathogenesis of three inflammatory myopathies, dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). We performed microarray experiments(†) using microdissected pathological muscle fibres from 15 patients with these disorders and five controls. Differentially expressed candidate genes were validated by immunohistochemistry on muscle biopsies, and the altered pathways were analysed in human myotube cultures. Up-regulation of genes involved in viral and nucleic acid recognition were found in the three myopathies but not in controls. In DM, retinoic acid-inducible gene 1 (RIG-I, DDX58) and the novel antiviral factor DDX60, which promotes RIG-I-mediated signalling, were significantly up-regulated, followed by IFIH1 (MDA5) and TLR3. Immunohistochemistry confirmed over-expression of RIG-I in pathological muscle fibres in 5/5 DM, 0/5 PM and 0/5 IBM patients, and in 0/5 controls. Stimulation of human myotubes with a ligand of RIG-I produced a significant secretion of interferon-ß (IFNß; p < 0.05) and up-regulation of class I MHC, RIG-I and TLR3 (p < 0.05) by IFNß-dependent and TLR3-independent mechanisms. RIG-I-mediated innate immunity, triggered by a viral or damage signal, plays a significant role in the pathogenesis of DM, but not in that of PM or IBM.

Chitinase-3-like protein 1 protects skeletal muscle from TNFα-induced inflammation and insulin resistance.

CHI3L1 (chitinase-3-like protein 1) is a glycoprotein consisting of 383 amino acids with a molecular mass of 40 kDa, and its serum level is elevated in inflammatory diseases. Although CHI3L1 is described as a biomarker of inflammation, the function of this protein is not completely understood. In the present study, we examined the regulation of CHI3L1 in primary human skeletal muscle cells. Moreover, we analysed potential autocrine effects of CHI3L1. We show that myotubes express CHI3L1 in a differentiation-dependent manner. Furthermore, pro-inflammatory cytokines up-regulate CHI3L1 expression (6-fold) and release (3-fold). Importantly, CHI3L1 treatment blocked TNFα (tumour necrosis factor α)-induced inflammation by inhibiting NF-κB (nuclear factor κB) activation in skeletal muscle cells. We show that this effect is mediated via PAR2 (protease-activated receptor 2). In addition, CHI3L1 treatment diminished the TNFα-induced expression and secretion of IL (interleukin)-8, MCP1 (monocyte chemoattractant protein 1) and IL-6. In addition, impaired insulin action at the level of Akt and GSK3α/ß (glycogen synthase kinase 3α/ß) phosphoryl-ation and insulin-stimulated glucose uptake was normalized by CHI3L1. In conclusion, the novel myokine CHI3L1, which is induced by pro-inflammatory cytokines, can counteract TNFα-mediated inflammation and insulin resistance in human skeletal muscle cells, potentially involving an auto- and/or para-crine mechanism.

Artemisia dracunculus L. extract ameliorates insulin sensitivity by attenuating inflammatory signalling in human skeletal muscle culture.

AIMS: Bioactives of Artemisia dracunculus L. (termed PMI 5011) have been shown to improve insulin action by increasing insulin signalling in skeletal muscle. However, it was not known if PMI 5011's effects are retained during an inflammatory condition. We examined the attenuation of insulin action and whether PMI 5011 enhances insulin signalling in the inflammatory environment with elevated cytokines. METHODS: Muscle cell cultures derived from lean, overweight and diabetic-obese subjects were used. Expression of pro-inflammatory genes and inflammatory response of human myotubes were evaluated by real-time polymerase chain reaction (RT-PCR). Insulin signalling and activation of inflammatory pathways in human myotubes were evaluated by multiplex protein assays. RESULTS: We found increased gene expression of monocyte chemoattractant protein 1 (MCP1) and TNFα (tumour necrosis factor alpha), and basal activity of the NFkB (nuclear factor kappa-light-chain-enhancer of activated B cells) pathway in myotubes derived from diabetic-obese subjects as compared with myotubes derived from normal-lean subjects. In line with this, basal Akt phosphorylation (Ser473) was significantly higher, while insulin-stimulated phosphorylation of Akt (Ser473) was lower in myotubes from normal-overweight and diabetic-obese subjects compared with normal-lean subjects. PMI 5011 treatment reduced basal phosphorylation of Akt and enhanced insulin-stimulated phosphorylation of Akt in the presence of cytokines in human myotubes. PMI 5011 treatment led to an inhibition of cytokine-induced activation of inflammatory signalling pathways such as Erk1/2 and IkBα (nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha)-NFkB and moreover, NFkB target gene expression, possibly by preventing further propagation of the inflammatory response within muscle tissue. CONCLUSIONS: PMI 5011 improved insulin sensitivity in diabetic-obese myotubes to the level of normal-lean myotubes despite the presence of pro-inflammatory cytokines.

In utero LPS exposure impairs preterm diaphragm contractility.

Preterm birth is associated with inflammation of the fetal membranes (chorioamnionitis). We aimed to establish how chorioamnionitis affects the contractile function and phenotype of the preterm diaphragm. Pregnant ewes received intra-amniotic injections of saline or 10 mg LPS, 2 days or 7 days before delivery at 121 days of gestation (term = 150 d). Diaphragm strips were dissected for the assessment of contractile function after terminal anesthesia. The inflammatory cytokine response, myosin heavy chain (MHC) fibers, proteolytic pathways, and intracellular molecular signaling were analyzed using quantitative PCR, ELISA, immunofluorescence staining, biochemical assays, and Western blotting. Diaphragm peak twitch force and maximal tetanic force were approximately 30% lower than control values in the 2-day and 7-day LPS groups. Activation of the NF-κB pathway, an inflammatory response, and increased proteasome activity were observed in the 2-day LPS group relative to the control or 7-day LPS group. No inflammatory response was evident after a 7-day LPS exposure. Seven-day LPS exposure markedly decreased p70S6K phosphorylation, but no effect on other signaling pathways was evident. The proportion of MHC IIa fibers was lower than that for control samples in the 7-day LPS group. MHC I fiber proportions did not differ between groups. These results demonstrate that intrauterine LPS impairs preterm diaphragmatic contractility after 2-day and 7-day exposures. Diaphragm dysfunction, resulting from 2-day LPS exposure, was associated with a transient activation of proinflammatory signaling, with subsequent increased atrophic gene expression and enhanced proteasome activity. Persistently impaired contractility for the 7-day LPS exposure was associated with the down-regulation of a key component of the protein synthetic signaling pathway and a reduction in the proportions of MHC IIa fibers.

Quality not quantity for transglutaminase antibody 2: the performance of an endomysial and tissue transglutaminase test in screening coeliac disease remains stable over time.

National Institute of Clinical Excellence (NICE) and European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) guidance for the diagnosis of coeliac disease has been published. However, there is some controversy regarding the advice on the use of stratifying levels of immunoglobulin (IgA) tissue transglutaminase antibody (TG2) test positivity in the absence of test standardization and the vagueness of the indication to test equivocal samples. Using repeat service audit, we demonstrate that a combination of TG2 followed by IgA endomysial antibodies (EMA) is the best strategy for all degrees of mucosal abnormality using our test combination. Reliance upon immunoassay titre is not as effective, and cannot be applied consistently across populations in the absence of assay standardization. Guidelines advocating the use of tests should involve experts in laboratory diagnostics and external quality assurance to ensure that errors of generalization do not occur and that test performance is achievable in routine diagnostic use.

Simultaneous visualization of myosin heavy chain isoforms in single muscle sections.

We developed a staining protocol that enables simultaneous visualization of myosin heavy chain (MHC) pure and hybrid muscle fiber types in rat skeletal muscle. Up to eight different muscle fiber types can be visualized in a single section of the rat extensor digitorum longus muscle, which contains all four adult MHC isoforms and shows plasticity during the denervation-reinnervation process. Triple immunofluorescent staining of MHC-1, MHC-2a and MHC-2b with primary antibodies BA-D5 (isotype IgG2b), SC-71 (isotype IgG1) and BF-F3 (isotype IgM) and with three fluorophore-labeled isotype-specific secondary antibodies displays different muscle fiber types in a merged image of red, green and blue channels, each in its own color. Immunoperoxidase staining with primary antibody 6H1 directed against MHC-2x can be additionally applied on the same tissue section to facilitate the identification of muscle fibers containing MHC-2x. Triple staining can also be used in combination with other staining procedures to derive more information about the number of capillaries or the oxidative potential of muscle fiber types. Simultaneous visualization of multiple fiber types in a single merged image enables economical use of muscle samples and provides simple and rapid identification of all fiber types that are present in rat limb muscles.

Autoantibodies in polymyositis and dermatomyositis.

Inflammatory myopathies are a group of acquired diseases, characterized by immunoflogistic processes primarily involving the skeletal muscle. According to recent classification criteria, four major diseases have been identified: polymyositis (PM), dermatomyositis (DM), sporadic inclusion body myositis (IBM), and necrotizing autoimmune myositis (NAM). Autoantibodies can be found in the sera of most patients with myositis. Myositis-specific autoantibodies (MSAs) are markers of very specific disease entities within the spectrum of myositis, and target proteins involved in key processes of protein synthesis. Myositis autoantigens comprise the well-defined aminoacyl-tRNA synthetases, the Mi-2 helicase/histone deacetylase protein complex, and the signal recognition particle (SRP) ribonucleoprotein, together with novel targets such as TIF1-γ, MDA5, NXP2, SAE, and HMGCR. Recent studies suggest that autoantigens drive a B cell antigen-specific immune response in muscles. Interestingly, an increased expression of Jo-1 and Mi-2 in regenerating fibers in muscle biopsies from PM and DM patients compared to normal was demonstrated. Myositis autoantigen up-regulation was observed in neoplastic tissues, thus representing a potential link between cancer and autoimmunity in myositis. Non-immunological mechanisms seem to participate to the pathogenesis of inflammatory myopathies; induction of endoplasmic reticulum stress response in response to abnormal muscle regeneration and inflammation has recently been reported in patients with myositis. This review article provides an update of new emerging insights about the clinical and pathophysiologic role of principal autoantibodies in myositis.

Celiac disease: the new proposed ESPGHAN diagnostic criteria do work well in a selected population.

BACKGROUND: The need for an early and accurate diagnosis in celiac disease (CD) has focused attention on new diagnostic approaches, based on the efficiency of serological markers and the high negative predictive value of human leukocyte antigen (HLA) non-DQ2/8. METHODS: We performed a retrospective review of all of the patients suspected of having CD who had undergone a small bowel biopsy in our gastroenterology unit. All symptomatic children with serological marker at time of biopsy (immunoglobulin A-tissue transglutaminase antibody, endomysial antibody, and HLA genotype) were included. The triple test (TT) was positive if immunoglobulin A-tissue transglutaminase antibody was 10 times the upper limit of normal, plus positive endomysial antibody plus human leukocyte antigen-DQ2/DQ8. RESULTS: A total of 150 patients met the inclusion criteria and were enrolled in the study. One hundred sixteen were positive for the TT; 113 of 116 (97.4%) had a Marsh 2/3 histological lesion and had been considered to have CD. Thus, positive predictive value of the TT was 97.4%. The other 3 cases (2.6%) had Marsh 0/1 lesion, so we consider them to be false-positives for the TT; however, on follow-up, all 3 children developed histological damage after a gluten challenge. Finally, the positive predictive value of the TT was 100%. Thirty-four patients were negative for the TT: 22 patients are celiac, 3 are celiac but challenge gluten diet is pending, and the 9 patients left have other gastrointestinal disorder. CONCLUSIONS: Our study supports the view that in selected children who are symptomatic and positive for the TT, CD diagnosis could be established independent of histological findings.

Characterization of contraction-induced IL-6 up-regulation using contractile C2C12 myotubes.

Muscle contractile activity functions as a potent stimulus for acute interleukin (IL)-6 expression in working skeletal muscles. Recently, we established an "in vitro contraction model" using highly-developed contractile C2C12 myotubes by applying electric pulse stimulation (EPS). Herein, we characterize the effects of EPS-evoked contraction on IL-6 expression in contractile C2C12 myotubes. Both secretion and mRNA expression of IL-6 were significantly up-regulated by EPS in a frequency-dependent manner in contracting myotubes during a 24-h period, and the response was blunted by cyclosporine A, a calcineurin inhibitor. Longer time (~12h) was required for the induction of IL-6 after the initiation of EPS as compared to that of other contraction-inducible CXC chemokines such as CXCL1/KC, which were induced in less than 3 hours. Furthermore, these acute inducible CXC chemokines exhibited no autocrine effect on IL-6 expression. Importantly, contraction-dependent IL-6 up-regulation was markedly suppressed in the presence of high levels of glucose along with increased glycogen accumulations. Experimental manipulation of intracellular glycogen contents by modulating available glucose or pyruvate during a certain EPS period further established the suppressive effect of glycogen accumulations on contraction-induced IL-6 up-regulation, which appeared to be independent of calcineurin activity. We also document that EPS-evoked contractile activity improved insulin-responsiveness in terms of intracellular glycogen accumulations. Taken together, these data provide important insights into the regulation of IL-6 expression in response to contractile activity of muscle cells, which is difficult to examine using in vivo experimental techniques. Our present results thus expand the usefulness of our "in vitro contraction model".

Effects of immunosuppressive treatment on interleukin-15 and interleukin-15 receptor α expression in muscle tissue of patients with polymyositis or dermatomyositis.

OBJECTIVES: To investigate the expression of interleukin (IL)-15 and IL-15 receptor α (IL-15Rα) in muscle tissue from patients with polymyositis or dermatomyositis before and after conventional immunosuppressive (IS) treatment. METHODS: Muscle biopsies from 17 patients before and after conventional IS treatment and seven healthy individuals were investigated by immunohistochemistry using antibodies against IL-15 and IL-15Rα. Quantification was performed by computerised image analysis. Cellular localisation of IL-15 was determined by double immunofluorescence. Clinical outcome was measured by the functional index and serum creatine kinase. Human myotubes were cultured and IL-15 staining was performed by immunocytochemistry. RESULTS: IL-15 was observed in mononuclear inflammatory cells of muscle tissue while IL-15Rα was localised to mononuclear inflammatory cells, capillaries and large vessels. Double staining showed localisation of IL-15 to CD163+ macrophages. A significantly larger number of IL-15 and IL-15Rα-positive cells were seen in muscle tissue of patients compared with healthy individuals. Baseline IL-15 expression correlated negatively with improvement in muscle function. After conventional IS treatment, a significantly lower number of IL-15 and IL-15Rα-positive cells was found. However, compared with controls, eight of 17 patients still had more IL-15-positive cells and less muscle function improvement was shown in this group of patients, both in short-term and long-term observations. Human differentiated myotubes were negative for IL-15 staining. CONCLUSIONS: IL-15 and its receptor are expressed in the muscle tissue of patients with myositis and IL-15 expression is correlated with improvement in muscle function. IL-15 may play a role in the pathogenesis of myositis and could be a biological treatment target, at least in a subgroup of patients with polymyositis or dermatomyositis.

High mobility group box 1 promotes endothelial cell angiogenic behavior in vitro and improves muscle perfusion in vivo in response to ischemic injury.

OBJECTIVES: The angiogenic drive in skeletal muscle ischemia remains poorly understood. Innate inflammatory pathways are activated during tissue injury and repair, suggesting that this highly conserved pathway may be involved in ischemia-induced angiogenesis. We hypothesize that one of the endogenous ligands for innate immune signaling, high mobility group box 1 (HMGB1), in combination with autophagic responses to hypoxia or nutrient deprivation, plays an important role in angiogenesis. METHODS: Human dermal microvascular endothelial cells (ECs) were cultured in normoxia or hypoxia (1% oxygen). Immunocytochemical analysis of HMGB1 subcellular localization, evaluation of tube formation, and Western blot analysis of myotubule light-chain 3I (LC3I) conversion to LC3II, as a marker of autophagy, were conducted. 3-Methyladenine (3MA), chloroquine, or rapamycin were administered to inhibit or promote autophagy, respectively. In vivo, a murine hind limb ischemia model was performed. Muscle samples were collected at 4 hours to evaluate for nuclear HMGB1 and at 14 days to examine endothelial density. Perfusion recovery in the hind limbs was calculated by laser Doppler perfusion imaging (LDPI). RESULTS: Hypoxic ECs exhibited reduced nuclear HMGB1 staining compared with normoxic cells (mean fluorescence intensity, 186.9 ± 17.1 vs 236.0 ± 1.6, P = .01) with a concomitant increase in cytosolic staining. HMGB1 treatment of ECs enhanced tube formation, an angiogenic phenotype of ECs. Neutralization of endogenous HMGB1 markedly impaired tube formation and inhibited LC3II formation. Inhibition of autophagy with 3MA or chloroquine abrogated tube formation, whereas its induction with rapamycin enhanced tubing and promoted HMGB1 translocation. In vivo, ischemic skeletal muscle showed reduced numbers of HMGB1-positive myocyte nuclei compared with nonischemic muscle (34.9% ± 1.9% vs 51.7% ± 2.0%, P < .001). Injection of HMGB1 into ischemic hind limbs increased perfusion recovery by 21% and increased EC density (49.2 ± 4.1 vs 34.2 ± 3.4 ECs/high-powered field, respectively; P = .02) at 14 days compared with control hind limbs. CONCLUSIONS: Nuclear release of HMGB1 and autophagy occur in ECs in response to hypoxia or serum depletion. HMGB1 and autophagy are necessary and likely play an interdependent role in promoting the angiogenic behavior of ECs. In vivo, HMGB1 promotes perfusion recovery and increased EC density after ischemic injury. These findings suggest a possible mechanistic link between autophagy and HMGB1 in EC angiogenic behavior and support the importance of innate immune pathways in angiogenesis.

Dopaminergic neuronal conversion from adult rat skeletal muscle-derived stem cells in vitro.

Muscle-derived stem cells reside in the skeletal muscle tissues and are known for their multipotency to differentiate toward the mesodermal lineage. Recent studies have demonstrated their capacity of neuroectodermal differentiation, including neurons and astrocytes. In this study, we investigated the possibility of dopaminergic neuronal conversion from adult rat skeletal muscle-derived stem cells. Using a neurosphere protocol, muscle-derived stem cells form neurosphere-like cell clusters after cultivation as a suspension, displaying an obvious expression of nestin and a remarkable down-regulation of myogenic associated factors desmin, MyoD, Myf5 and myogenin. Subsequently, these neurosphere-like cell clusters were further directed to dopaminergic differentiation through two major induction steps, patterning to midbrain progenitors with sonic hedgehog and fibroblast growth factor 8, followed by the differentiation to dopaminergic neurons with neurotrophic factors (glial cell line-derived neurotrophic factor) and chemicals (ascorbic acid, forskolin). After the differentiation, these cells expressed tyrosine hydroxylase, dopamine transporter, dopamine D1 receptor and synapse-associated protein synapsin I. Several genes, Nurr1, Lmx1b, and En1, which are critically related with the development of dopaminergic neurons, were also significantly up-regulated. The present results indicate that adult skeletal muscle-derived stem cells could provide a promising cell source for autologous transplantation for neurodegenerative diseases in the future, especially the Parkinson's disease.