The RAGE pathway in inflammatory myopathies and limb girdle muscular dystrophy

Oxidative stress, mitochondrial dysfunction, and respiratory chain enzyme defects in inflammatory myopathies

We investigated the relationship between oxidative stress and inflammatory myopathies. We searched in the current literature the role of mitochondria and respiratory chain defects as sources of oxidative stress and reactive oxygen species production that led to muscle weakness and fatigue. Different molecules and pathways contribute to redox milieu, reactive oxygen species generation, accumulation of misfolded and carbonylated proteins that lose their ability to fulfil cellular activities. Small peptides and physical techniques proved, in mice models, to reduce oxidative stress. We focused on inclusion body myositis, as a major expression of myopathy related to oxidative stress, where mitochondrial abnormalities are causative agents as well. We described the effect of physical exercise in inclusion body myositis that showed to increase strength and to reduce beta amyloid accumulation with subsequent improvement of the mitochondrial functions. We illustrated the influence of epigenetic control on the immune system by non-coding genetic material in the interaction between oxidative stress and inflammatory myopathies.

Association Between the Accumulation of Pentosidine at the Sciatic Nerve and Cutaneous Hindpaw Hypersensitivity in a Rat Ovariectomy Model

Introduction

Advanced glycation end-products (AGEs) have the potential to serve as biomarkers of aging and metabolic diseases; however, how their expression relates to clinical symptoms is not well defined. In this study, we sought to determine whether the accumulation of pentosidine, one type of AGE, at the peripheral nerve is associated with cutaneous pain or hypersensitivity caused by ovariectomy (OVX).

Methods

We assigned 12-week-old female Sprague Dawley rats into either the OVX group (n = 6) or the sham group (n = 6). Cutaneous hindpaw sensitivity to mechanical stimuli was measured with von Frey filaments, using Chaplan’s adapted method, and the 50% withdrawal threshold was calculated. Then, the accumulation of pentosidine, which represents AGEs, was measured in sciatic nerve fibers after staining with an anti-pentosidine antibody.

Results

OVX rats showed significantly increased plantar hypersensitivity to mechanical stimuli compared to sham rats 8 weeks after OVX (P = 0.017). Pentosidine-positive sciatic nerves were detected at a higher rate in OVX rats than in sham rats (P = 0.035). The pentosidine positivity rate in sciatic nerve fibers showed a negative correlation with withdrawal threshold (P < 0.001).

Conclusions

This study showed that higher levels of pentosidine in sciatic nerve fibers are associated with higher plantar hypersensitivity. Accumulation of pentosidine at the sciatic nerve, caused by OVX, may result in cutaneous hindpaw hypersensitivity.

Elevated level of the soluble receptor for advanced glycation end-products involved in sarcopenia: an observational study

BACKGROUND

The soluble receptor for advanced glycation end products (sRAGE) has been proposed to serve as a marker for disease severity, but its role in sarcopenia, an age-related progressive loss of muscle mass and function, remains elusive. This study examines the association between sRAGE and sarcopenia.

METHODS

A total of 314 community-dwelling elderly adults who had their health examination at Tri-Service General Hospital from 2017 to 2019 underwent protein analysis with enzyme-linked immunosorbent assay. The relationship with sarcopenia and its detailed information, including components and diagnosis status, were examined using linear and logistic regressions.

RESULTS

As for sarcopenia components, low muscle mass (β = 162.8, p = 0.012) and strength (β = 181.31, p = 0.011) were significantly correlated with sRAGE, but not low gait speed (p = 0.066). With regard to disease status, confirmed sarcopenia (β = 436.93, p < 0.001), but not probable (p = 0.448) or severe sarcopenia (p = 0.488), was significantly correlated with sRAGE. In addition, females revealed a stronger association with sRAGE level by showing significant correlations with low muscle mass (β = 221.72, p = 0.014) and low muscle strength (β = 208.68, p = 0.043).

CONCLUSIONS

sRAGE level showed a positive association with sarcopenia, illustrating its involvement in the evolution of sarcopenia. This association is more evident in female groups, which may be attributed to the loss of protection from estrogen in postmenopausal women. Utilizing sRAGE level as a prospective marker for sarcopenia deserves further investigation in future studies.

Role of Immunoglobulins in Muscular Dystrophies and Inflammatory Myopathies

Muscular dystrophies and inflammatory myopathies are heterogeneous muscular disorders characterized by progressive muscle weakness and mass loss. Despite the high variability of etiology, inflammation and involvement of both innate and adaptive immune response are shared features. The best understood immune mechanisms involved in these pathologies include complement cascade activation, auto-antibodies directed against muscular proteins or de-novo expressed antigens in myofibers, MHC-I overexpression in myofibers, and lymphocytes-mediated cytotoxicity. Intravenous immunoglobulins (IVIGs) administration could represent a suitable immunomodulator with this respect. Here we focus on mechanisms of action of immunoglobulins in muscular dystrophies and inflammatory myopathies highlighting results of IVIGs from pre-clinical and case reports evidences.

RAGE in the pathophysiology of skeletal muscle

Emerging evidence suggests that the signalling of the Receptor for Advanced Glycation End products (RAGE) is critical for skeletal muscle physiology controlling both the activity of muscle precursors during skeletal muscle development and the correct time of muscle regeneration after acute injury. On the other hand, the aberrant re-expression/activity of RAGE in adult skeletal muscle is a hallmark of muscle wasting that occurs in response to ageing, genetic disorders, inflammatory conditions, cancer, and metabolic alterations. In this review, we discuss the mechanisms of action and the ligands of RAGE involved in myoblast differentiation, muscle regeneration, and muscle pathological conditions. We highlight potential therapeutic strategies for targeting RAGE to improve skeletal muscle function.

Control of DNA integrity in skeletal muscle under physiological and pathological conditions

Skeletal muscle is a highly oxygen-consuming tissue that ensures body support and movement, as well as nutrient and temperature regulation. DNA damage induced by reactive oxygen species is present in muscles and tends to accumulate with age. Here, we present a summary of data obtained on DNA damage and its implication in muscle homeostasis, myogenic differentiation and neuromuscular disorders. Controlled and transient DNA damage appears to be essential for muscular homeostasis and differentiation while uncontrolled and chronic DNA damage negatively affects muscle health.

Immune and myodegenerative pathomechanisms in inclusion body myositis

Inclusion Body Myositis (IBM) is a relatively common acquired inflammatory myopathy in patients above 50 years of age. Pathological hallmarks of IBM are intramyofiber protein inclusions and endomysial inflammation, indicating that both myodegenerative and inflammatory mechanisms contribute to its pathogenesis. Impaired protein degradation by the autophagic machinery, which regulates innate and adaptive immune responses, in skeletal muscle fibers has recently been identified as a potential key pathomechanism in IBM. Immunotherapies, which are successfully used for treating other inflammatory myopathies lack efficacy in IBM and so far no effective treatment is available. Thus, a better understanding of the mechanistic pathways underlying progressive muscle weakness and atrophy in IBM is crucial in identifying novel promising targets for therapeutic intervention. Here, we discuss recent insights into the pathomechanistic network of mutually dependent inflammatory and degenerative events during IBM.

Plasma carnosine, but not muscle carnosine, attenuates high-fat diet-induced metabolic stress

There is growing in vivo evidence that the dipeptide carnosine has protective effects in metabolic diseases. A critical unanswered question is whether its site of action is tissues or plasma. This was investigated using oral carnosine versus β-alanine supplementation in a high-fat diet rat model. Thirty-six male Sprague-Dawley rats received a control diet (CON), a high-fat diet (HF; 60% of energy from fat), the HF diet with 1.8% carnosine (HFcar), or the HF diet with 1% β-alanine (HFba), as β-alanine can increase muscle carnosine without increasing plasma carnosine. Insulin sensitivity, inflammatory signaling, and lipoxidative stress were determined in skeletal muscle and blood. In a pilot study, urine was collected. The 3 HF groups were significantly heavier than the CON group. Muscle carnosine concentrations increased equally in the HFcar and HFba groups, while elevated plasma carnosine levels and carnosine-4-hydroxy-2-nonenal adducts were detected only in the HFcar group. Elevated plasma and urine N(ε)-(carboxymethyl)lysine in HF rats was reduced by ∼50% in the HFcar group but not in the HFba group. Likewise, inducible nitric oxide synthase mRNA was decreased by 47% (p < 0.05) in the HFcar group, but not in the HFba group, compared with HF rats. We conclude that plasma carnosine, but not muscle carnosine, is involved in preventing early-stage lipoxidation in the circulation and inflammatory signaling in the muscle of rats.

S100B protein in skeletal muscle regeneration: regulation of myoblast and macrophage functions

Not available.

A monoclonal antibody against the receptor for advanced glycation end products attenuates inflammatory and neuropathic pain in the mouse

BACKGROUND

The receptor for advanced glycation end products (RAGE) is a multi-ligand receptor in the immunoglobulin superfamily. RAGE is localized throughout ascending sensory pathways (skin, peripheral nerve, dorsal root ganglion, spinal cord), and in cell types interacting with sensory neurons (endothelial cells, smooth muscle cells, monocytes and macrophages). Neuronal RAGE expression increases in pathological pain states in humans and rodents, and soluble RAGE attenuates thermal hypoalgesia in diabetic mice. The objective of the present study was to investigate whether pharmacological modulation of RAGE could attenuate mechanical allodynia in rodent pain models.

METHODS

We developed an anti-RAGE monoclonal antibody (11E6) that binds to the C2 immunoglobulin domain of human RAGE, binds to mouse RAGE, and presumably to the same domain in mouse RAGE. The antinociceptive activity of 11E6 was investigated in mouse models of inflammatory (complete Freund's adjuvant) and neuropathic (chronic constriction injury of the sciatic nerve) pain. Mice were dosed intraperitoneally with 11E6 or IgG (negative control).

RESULTS

Increased mechanical thresholds were observed following a single dose of 11E6 in both inflammatory and neuropathic pain models. Similar treatment with IgG did not alter nociceptive sensitivity. Repeated dosing with 11E6 significantly attenuated established mechanical hypersensitivity in a neuropathic pain model in a dose-related fashion.

CONCLUSIONS

These data demonstrate that specific modulation of RAGE effectively attenuates nociceptive sensitivity associated with chronic inflammatory and neuropathic pain states.

HMGB1 and RAGE in skeletal muscle inflammation: Implications for protein accumulation in inclusion body myositis

Inflammation is associated with protein accumulation in IBM, but precise mechanisms are elusive. The "alarmin" HMGB1 is upregulated in muscle inflammation. Its receptor RAGE is crucial for β-amyloid-associated neurodegeneration. Relevant signaling via HMGB1/RAGE is expected in IBM pathology. By real-time-PCR, mRNA-expression levels of HMGB1 and RAGE were upregulated in muscle biopsies of patients with IBM and PM, but not in muscular dystrophy or non-myopathic controls. By immunohistochemistry, both molecules displayed the highest signal in IBM, where they distinctly co-localized to intra-fiber accumulations of β-amyloid and neurofilament/tau. In these fibers, identification of phosphorylated Erk suggested that relevant downstream activation is present upon HMGB1 signaling via RAGE. Protein expressions of HMGB1, RAGE, Erk and phosphorylated Erk were confirmed by Western blot. In a well established cell-culture model for pro-inflammatory cell-stress, exposure of human muscle-cells to IL-1β+IFN-γ induced cytoplasmic translocation of HMGB1 and subsequent release as evidenced by ELISA. Upregulation of RAGE on the cell surface was demonstrated by immunocytochemistry and flow-cytometry. Recombinant HMGB1 was equally potent as IL-1β+IFN-γ in causing amyloid-accumulation and cell-death, and both were abrogated by the HMGB1-blocker BoxA. The findings strengthen the concept of unique interactions between degenerative and inflammatory mechanisms and suggest that HMGB1/RAGE signaling is a critical pathway in IBM pathology.

Advanced glycated end-products affect HIF-transcriptional activity in renal cells

Advanced glycated end-products (AGEs) are ligands of the receptor for AGEs and increase in diabetic disease. MAPK organizer 1 (Morg1) via its binding partner prolyl-hydroxylase domain (PHD)-3 presumably plays a role in the regulation of hypoxia-inducible factor (HIF)-1α and HIF-2α transcriptional activation. The purpose of this study was to analyze the influence of AGEs on Morg1 expression and its correlation to PHD3 activity and HIF-transcriptional activity in various renal cell types. The addition of glycated BSA (AGE-BSA) significantly up-regulated Morg1 mRNA levels in murine mesangial cells and down-regulated it in murine proximal tubular cells and differentiated podocytes. These effects were reversible when the cells were preincubated with a receptor for α-AGE antibody. AGE-BSA treatment induced a relocalization of the Morg1 cellular distribution compared with nonglycated control-BSA. Analysis of PHD3 activity demonstrated an elevated PHD3 enzymatic activity in murine mesangial cells but an inhibition in murine proximal tubular cells and podocytes after the addition of AGE-BSA. HIF-transcriptional activity was also affected by AGE-BSA treatment. Reporter gene assays and EMSAs showed that AGEs regulate HIF- transcriptional activity under nonhypoxic conditions in a cell type-specific manner. In proximal tubular cells, AGE-BSA stimulation elevated mainly HIF-1α transcriptional activity and to a lesser extent HIF-2α. We also detected an increased expression of the HIF-1α and the HIF-2α proteins in kidneys from Morg1 heterozygous (HZ) placebo mice compared with the Morg1 wild-type (WT) placebo-treated mice, and the HIF-1α protein expression in the Morg1 HZ streptozotocin-treated mice was significantly higher than the WT streptozotocin-treated mice. Analysis of isolated mesangial cells from Morg1 HZ (±) and WT mice showed an inhibited PHD3 activity and an increased HIF-transcriptional activity in cells with only one Morg1 allele. These findings are important for a better understanding of the molecular mechanisms of diabetic nephropathy.

Wasting mechanisms in muscular dystrophy

Muscular dystrophy is a group of more than 30 different clinical genetic disorders that are characterized by progressive skeletal muscle wasting and degeneration. Primary deficiency of specific extracellular matrix, sarcoplasmic, cytoskeletal, or nuclear membrane protein results in several secondary changes such as sarcolemmal instability, calcium influx, fiber necrosis, oxidative stress, inflammatory response, breakdown of extracellular matrix, and eventually fibrosis which leads to loss of ambulance and cardiac and respiratory failure. A number of molecular processes have now been identified which hasten disease progression in human patients and animal models of muscular dystrophy. Accumulating evidence further suggests that aberrant activation of several signaling pathways aggravate pathological cascades in dystrophic muscle. Although replacement of defective gene with wild-type is paramount to cure, management of secondary pathological changes has enormous potential to improving the quality of life and extending lifespan of muscular dystrophy patients. In this article, we have reviewed major cellular and molecular mechanisms leading to muscle wasting in muscular dystrophy. This article is part of a Directed Issue entitled: Molecular basis of muscle wasting.

Oxidative damage in muscular dystrophy correlates with the severity of the pathology: role of glutathione metabolism

Muscular dystrophies (MDs) such as Duchenne muscular dystrophy (DMD), sarcoglycanopathy (Sgpy) and dysferlinopathy (Dysfy) are recessive genetic neuromuscular diseases that display muscle degeneration. Although these MDs have comparable endpoints of muscle pathology, the onset, severity and the course of these diseases are diverse. Different mechanisms downstream of genetic mutations might underlie the disparity in these pathologies. We surmised that oxidative damage and altered antioxidant function might contribute to these differences. The oxidant and antioxidant markers in the muscle biopsies from patients with DMD (n = 15), Sgpy (n = 15) and Dysfy (n = 15) were compared to controls (n = 10). Protein oxidation and lipid peroxidation was evident in all MDs and correlated with the severity of pathology, with DMD, the most severe dystrophic condition showing maximum damage, followed by Sgpy and Dysfy. Oxidative damage in DMD and Sgpy was attributed to the depletion of glutathione (GSH) and lowered antioxidant activities while loss of GSH peroxidase and GSH-S-transferase activities was observed in Dysfy. Lower GSH level in DMD was due to lowered activity of gamma-glutamyl cysteine ligase, the rate limiting enzyme in GSH synthesis. Similar analysis in cardiotoxin (CTX) mouse model of MD showed that the dystrophic muscle pathology correlated with GSH depletion and lipid peroxidation. Depletion of GSH prior to CTX exposure in C2C12 myoblasts exacerbated oxidative damage and myotoxicity. We deduce that the pro and anti-oxidant mechanisms could be correlated to the severity of MD and might influence the dystrophic pathology to a different extent in various MDs. On a therapeutic note, this could help in evolving novel therapies that offer myoprotection in MD.

Calpeptin attenuated apoptosis and intracellular inflammatory changes in muscle cells

In idiopathic inflammatory myopathies (IIMs), extracellular inflammatory stimulation is considered to induce secondary intracellular inflammatory changes including expression of major histocompatibility complex class-I (MHC-I) and to produce a self-sustaining loop of inflammation. We hypothesize that activation of calpain, a Ca(2+) -sensitive protease, bridges between these extracellular inflammatory stress and intracellular secondary inflammatory changes in muscle cells. In this study, we demonstrated that treatment of rat L6 myoblast cells with interferon-γ (IFN-γ) caused expression of MHC-I and inflammation-related transcription factors (phosphorylated-extracellular signal-regulated kinase 1/2 and nuclear factor-κB). We also demonstrated that treatment with tumor necrosis factor-α (TNF-α) induced apoptotic changes and activation of calpain and cyclooxygenase-2. Furthermore, we found that posttreatment with calpeptin attenuated the intracellular changes induced by IFN-γ or TNF-α. Our results indicate that calpain inhibition attenuates apoptosis and secondary inflammatory changes induced by extracellular inflammatory stimulation in the muscle cells. These results suggest calpain as a potential therapeutic target for treatment of IIMs.

Therapeutic targeting of signaling pathways in muscular dystrophy

Muscular dystrophy refers to a group of genetic diseases that cause severe muscle weakness and loss of skeletal muscle mass. Although research has helped understanding the molecular basis of muscular dystrophy, there is still no cure for this devastating disorder. Numerous lines of investigation suggest that the primary deficiency of specific proteins causes aberrant activation of several cell signaling pathways in skeletal and cardiac muscle leading to the pathogenesis of muscular dystrophy. Studies using genetic mouse models and pharmacological approaches have provided strong evidence that the modulation of the activity of specific cell signaling pathways has enormous potential to improving the quality of life and extending the life expectancy in muscular dystrophy patients. In this article, we have outlined the current understanding regarding the role of different cell signaling pathways in disease progression with particular reference to different models of muscular dystrophy and the development of therapy.

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

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

Molecular pathology of myofibrillar myopathies

Myofibrillar myopathies (MFMs) are clinically and genetically heterogeneous muscle disorders that are defined morphologically by the presence of foci of myofibril dissolution, accumulation of myofibrillar degradation products, and ectopic expression of multiple proteins. MFMs are the paradigm of conformational protein diseases of the skeletal (and cardiac) muscles characterised by intracellular protein accumulation in muscle cells. Understanding of this group of disorders has advanced in recent years through the identification of causative mutations in various genes, most of which encode proteins of the sarcomeric Z-disc, including desmin, alphaB-crystallin, myotilin, ZASP and filamin C. This review focuses on the MFMs arising from defects in these proteins, summarising genetic and clinical features of the disorders and then discussing emerging understanding of the molecular pathogenic mechanisms leading to muscle fibre degeneration. Defective extralysosomal degradation of proteins is now recognised as an important element in this process. Several factors--including mutant proteins, a defective ubiquitin-proteasome system, aggresome formation, mutant ubiquitin, p62, oxidative stress and abnormal regulation of some transcription factors--are thought to participate in the cascade of events occurring in muscle fibres in MFMs.

The RAGE pathway: activation and perpetuation in the pathogenesis of diabetic neuropathy

The molecular mechanisms underlying loss of pain perception in diabetic neuropathy are poorly understood. Experimental diabetic neuropathy models recently provided evidence that engagement of the receptor for advanced glycation end products (RAGE) and RAGE-dependent sustained activation of the proinflammatory transcription factor nuclear factor kappa B might significantly contribute to reduced nociception. Most importantly, diabetes-induced loss of pain perception is largely prevented in RAGE-deficient mice compared to RAGE-bearing wild-type mice. Identifying RAGE-dependent inflammation as one pathomechanism underlying neuronal dysfunction might provide the basis for new therapeutic approaches.

Clinical, molecular, and protein correlations in a large sample of genetically diagnosed Italian limb girdle muscular dystrophy patients

Limb girdle muscular dystrophies (LGMD) are characterized by genetic and clinical heterogeneity: seven autosomal dominant and 12 autosomal recessive loci have so far been identified. Aims of this study were to evaluate the relative proportion of the different types of LGMD in 181 predominantly Italian LGMD patients (representing 155 independent families), to describe the clinical pattern of the different forms, and to identify possible correlations between genotype, phenotype, and protein expression levels, as prognostic factors. Based on protein data, the majority of probands (n=72) presented calpain-3 deficiency; other defects were as follows: dysferlin (n=31), sarcoglycans (n=32), alpha-dystroglycan (n=4), and caveolin-3 (n=2). Genetic analysis identified 111 different mutations, including 47 novel ones. LGMD relative frequency was as follows: LGMD1C (caveolin-3) 1.3%; LGMD2A (calpain-3) 28.4%; LGMD2B (dysferlin) 18.7%; LGMD2C (gamma-sarcoglycan) 4.5%; LGMD2D (alpha-sarcoglycan) 8.4%; LGMD2E (beta-sarcoglycan) 4.5%; LGMD2F (delta-sarcoglycan) 0.7%; LGMD2I (Fukutin-related protein) 6.4%; and undetermined 27.1%. Compared to Northern European populations, Italian patients are less likely to be affected with LGMD2I. The order of decreasing clinical severity was: sarcoglycanopathy, calpainopathy, dysferlinopathy, and caveolinopathy. LGMD2I patients showed both infantile noncongenital and mild late-onset presentations. Age at disease onset correlated with variability of genotype and protein levels in LGMD2B. Truncating mutations determined earlier onset than missense substitutions (20+/-5.1 years vs. 36.7+/-11.1 years; P=0.0037). Similarly, dysferlin absence was associated with an earlier onset when compared to partial deficiency (20.2+/-standard deviation [SD] 5.2 years vs. 28.4+/-SD 11.2 years; P=0.014).

Desmin is oxidized and nitrated in affected muscles in myotilinopathies and desminopathies

Degenerative diseases with abnormal protein aggregates are characterized by the accumulation of proteins with variable posttranslational modifications including phosphorylation, glycoxidation, oxidation, and nitration. Myofibrillar myopathies, including myotilinopathies and desminopathies, are characterized by the intracytoplasmic focal accumulation of proteins in insoluble aggregates in muscle cells. By using single immunohistochemistry, monodimensional gel electrophoresis and Western blotting, and bidimensional gel electrophoresis, in-gel digestion, and mass spectometry, desmin was demonstrated to be a major target of oxidation and nitration in both desminopathies and myotilinopathies. Because oxidized and nitrated proteins may have toxic effects and may impair ubiquitin-proteasomal function, modified desmin can be considered to be an additional element in the pathogenesis of myofibrillar myopathies. In addition to desmin, pyruvate kinase muscle splice form M1 is oxidized, thus supporting complemental mitochondrial damage, at least in some cases of myotilinopathy.

Oxidative stress in desminopathies and myotilinopathies: a link between oxidative damage and abnormal protein aggregation

Myotilinopathies and desminopathies are subgroups of myofibrillar myopathies (MFM) caused by mutations in myotilin and desmin genes, respectively. They are characterized by the presence of protein aggregates in muscle cells. As oxidation of proteins facilitates their aggregation and makes them more resistant to proteolysis, the present study was geared to analyze oxidative stress in MFM. For this purpose, markers of glycoxidation, lipoxidation and nitration were examined with gel electrophoresis and Western blotting, single immunohistochemistry, and double- and triple-labeling immunofluorescence and confocal microscopy in muscle biopsies from patients suffering from myotilinopathy and desminopathy. Increased levels of glycation-end products (AGEs), N-carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL), malondialdehyde-lysine (MDAL), 4-hydroxynonenal (HNE) and nitrotyrosine (N-tyr) were found in MFM. Furthermore, aberrant expression of AGE, CML, CEL, MDAL and HNE, as well as of neuronal, inducible and endothelial nitric oxide synthases (nNOS, iNOS, eNOS), and superoxide dismutase 2 (SOD2), was found in muscle fibers containing protein aggregates in myotilinopathies and desminopathies. AGE, ubiquitin and p62 co-localized in several muscle fibers in MFM. As oxidized proteins are vulnerable to misfolding and are resistant to degradation by the UPS, the present observations support a link between oxidative stress, protein aggregation and abnormal protein deposition in MFMs.

Genetics of inclusion-body myositis

Sporadic inclusion-body myositis (sIBM) is the most common acquired muscle disease in Caucasians over the age of 50 years. Pathologically it is marked by inflammatory, degenerative, and mitochondrial changes that interact in a yet-unknown way to cause progressive muscle degeneration and weakness. The cause of the disease is unknown, but it is thought to involve a complex interplay between environmental factors, genetic susceptibility, and aging. The strongest evidence for genetic susceptibility comes from studies of the major histocompatibility complex (MHC), where different combinations of alleles have been associated with sIBM in different ethnic groups. The rare occurrence of familial cases of inclusion-body myositis (fIBM) adds additional evidence for genetic susceptibility. Other candidate genes such as those encoding some of the proteins accumulating in muscle fibers have been investigated, with negative results. The increased understanding of related disorders, the hereditary inclusion-body myopathies (hIBM), may also provide clues to the underlying pathogenesis of sIBM, but to date there is no indication that the genes responsible for these conditions are involved in sIBM. This review summarizes current understanding of the contribution of genetic susceptibility factors to the development of sIBM.

RAGE-NF-kappaB pathway activation in response to oxidative stress in facioscapulohumeral muscular dystrophy

OBJECTIVES

An increased expression of adenine nucleotide translocator (ANT1), found in facioscapulohumeral muscular dystrophy (FSHD), is known to lead to a decrease in nuclear factor-kappaB (NF-kappaB) DNA binding and to sensitize muscle cells to oxidative stress and apoptosis. Receptor for advanced glycation end products (RAGE) mediated by NF-kappaB activation is involved in proinflammatory pathomechanism and in muscle fiber regeneration in inflammatory myopathies and in limb girdle muscular dystrophy. Oxidative stress can stimulate RAGE- NF-kappaB pathway. Our purpose was to verify if oxidative stress may induce RAGE- NF-kappaB pathway activation in FSHD, contributing to the pathogenesis of such a disease.

MATERIALS AND METHODS

On muscle samples of eight patients with FSHD, eight patients with Duchenne muscular dystrophy and eight normal controls the following studies were carried out: immunocytochemistry for activated NF-kappaB; electrophoretic mobility shift assay of NF-kappaB DNA binding activity; Western blot studies of RAGE and ANT1; hydrogen peroxide (HP), peroxidase and glutathione peroxidase (GPx) assays.

RESULTS

An increased RAGE and ANT1 expression in FSHD with moderate increase of NF-kappaB DNA binding activity was found together with an increased production of HP and a reduced activity of peroxidase and GPx.

CONCLUSIONS

Our data confirm that response to oxidative stress and ANT1 increased activity are early events in FSHD muscle. The study also reveals that the RAGE- NF-kappaB pathway, induced by oxidative stress, is activated independently of the presence of a clear histochemical evidence of muscle damage in FSHD.

Posttranslationally modified proteins as mediators of sustained intestinal inflammation

Oxidative and carbonyl stress leads to generation of N(epsilon)-carboxymethyllysine-modified proteins (CML-mps), which are known to bind the receptor for advanced glycation end products (RAGE) and induce nuclear factor (NF)-kappaB-dependent proinflammatory gene expression. To determine the impact of CML-mps in vivo, RAGE-dependent sustained NF-kappaB activation was studied in resection gut specimens from patients with inflammatory bowel disease. Inflamed gut biopsy tissue demonstrated a significant up-regulation of RAGE and increased NF-kappaB activation. Protein extracts from the inflamed zones, but not from noninflamed resection borders, caused perpetuated NF-kappaB activation in cultured endothelial cells, which was mediated by CML-mps including CML-modified S100 proteins. The resulting NF-kappaB activation, lasting 5 days, was primarily inhibited by either depletion of CML-mps or by the addition of sRAGE, p44/42 and p38 MAPKinase-specific inhibitors. Consistently, CML-mps isolated from inflamed gut areas and rectally applied into mice caused NF-kappaB activation, increased proinflammatory gene expression, and histologically detectable inflammation in wild-type mice, but not in RAGE-/- mice. A comparable up-regulation of NF-kappaB and inflammation on rectal application of CML-mps was observed in IL-10-/- mice. Thus, CML-mps generated in inflammatory lesions have the capacity to elicit a RAGE-dependent intestinal inflammatory response.

Reduced necrosis of dystrophic muscle by depletion of host neutrophils, or blocking TNFalpha function with Etanercept in mdx mice

Necrosis of skeletal muscle fibres in the lethal childhood myopathy Duchenne Muscular Dystrophy results from deficiency of the cell membrane associated protein, dystrophin. We test the hypothesis in dystrophin-deficient mice, that the initial sarcolemmal breakdown resulting from dystrophin deficiency is exacerbated by inflammatory cells, specifically neutrophils, and that cytokines, specifically Tumour Necrosis Factor alpha (TNFalpha), contribute to myofibre necrosis. Antibody depletion of host neutrophils resulted in a delayed and significantly reduced amount of skeletal muscle breakdown in young dystrophic mdx mice. A more striking and prolonged protective effect was seen after pharmacological blockade of TNFalpha bioactivity using Etanercept. The extent of exercise induced myofibre necrosis in adult mdx mice after voluntarily wheel exercise was also reduced after Etanercept administration. These data show a clear role for neutrophils and TNFalpha in necrosis of dystrophic mdx muscle in vivo. Etanercept is a highly specific anti-inflammatory drug, widely used clinically, and potential application to muscular dystrophies is suggested by this reduced breakdown of mdx skeletal muscle.