Inclusion-body myositis: muscle-fiber molecular pathology and possible pathogenic significance of its similarity to Alzheimer's and Parkinson's disease brains

Effects of sporadic inclusion body myositis on skeletal muscle fibre type specific morphology and markers of regeneration and inflammation

Sporadic inclusion body myositis (sIBM) is a subgroup of idiopathic inflammatory myopathies characterised by progressive muscle weakness and skeletal muscle inflammation. Quantitative data on the myofibre morphology in sIBM remains scarce. Further, no previous study has examined fibre type association of satellite cells (SC), myonuclei number, macrophages, capillaries, and myonuclear domain (MD) in sIBM patients. Muscle biopsies from sIBM patients (n = 18) obtained previously (NCT02317094) were included in the analysis for fibre type-specific myofibre cross-sectional area (mCSA), SCs, myonuclei and macrophages, myonuclear domain, and capillarisation. mCSA (p < 0.001), peripheral myonuclei (p < 0.001) and MD (p = 0.005) were higher in association with type 1 (slow-twitch) than type 2 (fast-twitch) fibres. Conversely, quiescent SCs (p < 0.001), centrally placed myonuclei (p = 0.03), M1 macrophages (p < 0.002), M2 macrophages (p = 0.013) and capillaries (p < 0.001) were higher at type 2 fibres compared to type 1 fibres. In contrast, proliferating (Pax7+/Ki67+) SCs (p = 0.68) were similarly associated with each fibre type. Type 2 myofibres of late-phase sIBM patients showed marked signs of muscle atrophy (i.e. reduced mCSA) accompanied by higher numbers of associated quiescent SCs, centrally placed myonuclei, macrophages and capillaries compared to type 1 fibres. In contrast, type 1 fibres were suffering from pathological enlargement with larger MDs as well as fewer nuclei and capillaries per area when compared with type 2 fibres. More research is needed to examine to which extent different therapeutic interventions including targeted exercise might alleviate these fibre type-specific characteristics and countermeasure their consequences in impaired functional performance.

Mitochondrial defects in sporadic inclusion body myositis-causes and consequences

Sporadic inclusion body myositis (sIBM) is a distinct subcategory of Idiopathic Inflammatory Myopathies (IIM), characterized by unique pathological features such as muscle inflammation, rimmed vacuoles, and protein aggregation within the myofibers. Although hyperactivation of the immune system is widely believed as the primary cause of IIM, it is debated whether non-immune tissue dysfunction might contribute to the disease's onset as patients with sIBM are refractory to conventional immunosuppressant treatment. Moreover, the findings that mitochondrial dysfunction can elicit non-apoptotic programmed cell death and the subsequent immune response further support this hypothesis. Notably, abnormal mitochondrial structure and activities are more prominent in the muscle of sIBM than in other types of IIM, suggesting the presence of defective mitochondria might represent an overlooked contributor to the disease onset. The large-scale mitochondrial DNA deletion, aberrant protein aggregation, and slowed organelle turnover have provided mechanistic insights into the genesis of impaired mitochondria in sIBM. This article reviews the disease hallmarks of sIBM, the plausible contributors of mitochondrial damage in the sIBM muscle, and the immunological responses associated with mitochondrial perturbations. Additionally, the potential application of mitochondrial-targeted chemicals as a new treatment strategy to sIBM is explored and discussed.

Generation and characterization of a tractable C. elegans model of tauopathy

Alzheimer's disease(AD) is an age-associated neurodegenerative disease that results in deterioration of memory and cognitive function. As a currently untreatable disorder, AD has emerged as one of the defining biomedical challenges of our time. Thus, new approaches that can examine the cellular and molecular mechanisms underlying age-related AD pathology are sorely needed. One of the hallmarks of Alzheimer's disease is the hyperphosphorylation of the tau protein. Caenorhabditis elegans have been previously used to study the genetic pathways impacted by tau proteotoxic stress; however, currently, available C. elegans tau models express the human protein solely in neurons, which are unresponsive to global RNA interference (RNAi). This limits powerful RNAi screening methods from being utilized effectively in these disease models. Our goal was to develop a C. elegans tau model that has pronounced tau-induced disease phenotypes in cells that can be modified by feeding RNAi methods. Towards this end, we generated a novel C. elegans transgenic line with codon-optimized human 0N4R V337M tau expressed in the body wall muscle under the myo-3 promoter. Immunoblotting experiments revealed that the expressed tau is phosphorylated on epitopes canonically associated with human AD pathology. The tau line has significantly reduced health metrics, including egg laying, growth rate, paralysis, thrashing frequency, crawling speed, and lifespan. These defects are suppressed by RNAi directed against the tau mRNA. Taken together, our results suggest that this alternative tau genetic model could be a useful tool for uncovering the mechanisms that influence the hyperphosphorylation and toxicity of human tau via RNAi screening and other approaches.

Influence of Age on Skeletal Muscle Hypertrophy and Atrophy Signaling: Established Paradigms and Unexpected Links

Skeletal muscle atrophy in an inevitable occurrence with advancing age, and a consequence of disease including cancer. Muscle atrophy in the elderly is managed by a regimen of resistance exercise and increased protein intake. Understanding the signaling that regulates muscle mass may identify potential therapeutic targets for the prevention and reversal of muscle atrophy in metabolic and neuromuscular diseases. This review covers the major anabolic and catabolic pathways that regulate skeletal muscle mass, with a focus on recent progress and potential new players.

A symptomatic male carrier of Duchenne muscular dystrophy with Klinefelter's syndrome mimicking Becker muscular dystrophy

Duchenne and Becker muscular dystrophy (DMD/BMD) are commonly inherited muscle disorders. We report a 31-year-old male who had muscle symptoms with left-right differences and intellectual disability. He was diagnosed with BMD at age 15 primarily based on muscle biopsy findings. A few years later, DMD gene analysis revealed that he was a heterozygous carrier of a normal copy of the gene and a mutated copy with an exon 45-54 deletion, which is expected to result in an out-of-frame mutation. A karyotype analysis was compatible with XXY Klinefelter's syndrome. The analysis of X-chromosome inactivation (XCI) using his skeletal muscle sample revealed a skewed XCI pattern. This is the first reported case of a symptomatic male carrier of DMD caused by skewed XCI in Klinefelter's syndrome with a genetically proven heterozygous mutation of the DMD gene. The skewed XCI pattern could also explain the left-right differences in skeletal muscle symptoms observed in this patient.

Emerging Evidences for an Implication of the Neurodegeneration-Associated Protein TAU in Cancer

Neurodegenerative disorders and cancer may appear unrelated illnesses. Yet, epidemiologic studies indicate an inverse correlation between their respective incidences for specific cancers. Possibly explaining these findings, increasing evidence indicates that common molecular pathways are involved, often in opposite manner, in the pathogenesis of both disease families. Genetic mutations in the MAPT gene encoding for TAU protein cause an inherited form of frontotemporal dementia, a neurodegenerative disorder, but also increase the risk of developing cancer. Assigning TAU at the interface between cancer and neurodegenerative disorders, two major aging-linked disease families, offers a possible clue for the epidemiological observation inversely correlating these human illnesses. In addition, the expression level of TAU is recognized as a prognostic marker for cancer, as well as a modifier of cancer resistance to chemotherapy. Because of its microtubule-binding properties, TAU may interfere with the mechanism of action of taxanes, a class of chemotherapeutic drugs designed to stabilize the microtubule network and impair cell division. Indeed, a low TAU expression is associated to a better response to taxanes. Although TAU main binding partners are microtubules, TAU is able to relocate to subcellular sites devoid of microtubules and is also able to bind to cancer-linked proteins, suggesting a role of TAU in modulating microtubule-independent cellular pathways associated to oncogenesis. This concept is strengthened by experimental evidence linking TAU to P53 signaling, DNA stability and protection, processes that protect against cancer. This review aims at collecting literature data supporting the association between TAU and cancer. We will first summarize the evidence linking neurodegenerative disorders and cancer, then published data supporting a role of TAU as a modifier of the efficacy of chemotherapies and of the oncogenic process. We will finish by addressing from a mechanistic point of view the role of TAU in de-regulating critical cancer pathways, including the interaction of TAU with cancer-associated proteins.

The immune system in sporadic inclusion body myositis patients is not compromised by blood-flow restricted exercise training

BACKGROUND

Sporadic inclusion body myositis (sIBM) is clinically characterised by progressive proximal and distal muscle weakness and impaired physical function while skeletal muscle tissue displays abnormal cellular infiltration of T cells, macrophages, and dendritic cells. Only limited knowledge exists about the effects of low-load blood flow restriction exercise in sIBM patients, and its effect on the immunological responses at the myocellular level remains unknown. The present study is the first to investigate the longitudinal effects of low-load blood flow restriction exercise on innate and adaptive immune markers in skeletal muscle from sIBM patients.

METHODS

Twenty-two biopsy-validated sIBM patients were randomised into either 12 weeks of low-load blood flow restriction exercise (BFRE) or no exercise (CON). Five patients from the control group completed 12 weeks of BFRE immediately following participation in the 12-week control period leading to an intervention group of 16 patients. Muscle biopsies were obtained from either the m. tibialis anterior or the m. vastus lateralis for evaluation of CD3-, CD8-, CD68-, CD206-, CD244- and FOXP3-positive cells by three-colour immunofluorescence microscopy and Visiopharm-based image analysis quantification. A linear mixed model was used for the statistical analysis.

RESULTS

Myocellular infiltration of CD3^-/CD8⁺ expressing natural killer cells increased following BFRE (P < 0.05) with no changes in CON. No changes were observed for CD3⁺/CD8^- or CD3⁺/CD8⁺ T cells in BFRE or CON. CD3⁺/CD244⁺ T cells decreased in CON, while no changes were observed in BFRE. Pronounced infiltration of M1 pro-inflammatory (CD68⁺/CD206^-) and M2 anti-inflammatory (CD68⁺/CD206⁺) macrophages were observed at baseline; however, no longitudinal changes in macrophage content were observed for both groups.

CONCLUSIONS

Low-load blood flow restriction exercise elicited an upregulation in CD3^-/CD8⁺ expressing natural killer cell content, which suggests that 12 weeks of BFRE training evokes an amplified immune response in sIBM muscle. However, the observation of no changes in macrophage or T cell infiltration in the BFRE-trained patients indicates that patients with sIBM may engage in this type of exercise with no risk of intensified inflammatory activity.

The Expanding Clinical Universe of Polyglutamine Disease

Polyglutamine (polyQ) diseases are a group of hereditary neurodegenerative disorders caused by expansion of unstable polyQ repeats in their associated disease proteins. To date, the pathogenesis of each disease remains poorly understood, and there are no effective treatments. Growing evidence has indicated that, in addition to neurodegeneration, polyQ-expanded proteins can cause a wide array of abnormalities in peripheral tissues. Indeed, polyQ-expanded proteins are ubiquitously expressed throughout the body and can affect the function of both the central nervous system (CNS) and peripheral tissues. The peripheral effects of polyQ disease proteins include muscle wasting and reduced muscle strength in patients or animal models of spinal and bulbar muscular atrophy (SBMA), Huntington's disease (HD), dentatorubral-pallidoluysian atrophy (DRPLA), and spinocerebellar ataxia type 17 (SCA17). Since skeletal muscle pathology can reflect disease progression and is more accessible for treatment than neurodegeneration in the CNS, understanding how polyQ disease proteins affect skeletal muscle will help elucidate disease mechanisms and the development of new therapeutics. In this review, we focus on important findings in terms of skeletal muscle pathology in polyQ diseases and also discuss the potential mechanisms underlying the major peripheral effects of polyQ disease proteins, as well as their therapeutic implications.

High Fat With High Sucrose Diet Leads to Obesity and Induces Myodegeneration

Skeletal muscle utilizes both free fatty acids (FFAs) and glucose that circulate in the blood stream. When blood glucose levels acutely increase, insulin stimulates muscle glucose uptake, oxidation, and glycogen synthesis. Under these conditions, skeletal muscle preferentially oxidizes glucose while the oxidation of fatty acids (FAs) oxidation is reciprocally decreased. In metabolic disorders associated with insulin resistance, such as diabetes and obesity, both glucose uptake, and utilization muscle are significantly reduced causing FA oxidation to provide the majority of ATP for metabolic processes and contraction. Although the causes of this metabolic inflexibility or disrupted "glucose-fatty acid cycle" are largely unknown, a diet high in fat and sugar (HFS) may be a contributing factor. This metabolic inflexibility observed in models of obesity or with HFS feeding is detrimental because high rates of FA oxidation in skeletal muscle can lead to the buildup of toxic metabolites of fat metabolism and the accumulation of pro-inflammatory cytokines, which further exacerbate the insulin resistance. Further, HFS leads to skeletal muscle atrophy with a decrease in myofibrillar proteins and phenotypically characterized by loss of muscle mass and strength. Overactivation of ubiquitin proteasome pathway, oxidative stress, myonuclear apoptosis, and mitochondrial dysfunction are some of the mechanisms involved in muscle atrophy induced by obesity or in mice fed with HFS. In this review, we will discuss how HFS diet negatively impacts the various physiological and metabolic mechanisms in skeletal muscle.

Dropped Head Syndrome and the Presence of Rimmed Vacuoles in a Muscle Biopsy in Scleroderma-polymyositis Overlap Syndrome Associated with Anti-Ku Antibody

A 66-year-old woman with a history of interstitial lung disease presented with a 3-month history of dropped head syndrome (DHS), followed by camptocormia and extremity weakness. A clinical examination revealed Raynaud phenomenon, arthralgia, distal skin sclerosis, and microbleeds in the nailfold capillaries. An anti-Ku antibody test was positive. A muscle biopsy revealed inflammatory myopathy with rimmed vacuoles (RVs). The diagnosis of scleroderma-polymyositis (SSc-PM) overlap syndrome was made. RVs on a muscle biopsy in a patient with inflammatory myositis involving axial muscles may be seen either in inclusion body myositis or SSc-PM overlap syndrome. The examination of the skin and autoantibody testing help determine the diagnosis and treatment strategy.

Co-expression Network Approach Reveals Functional Similarities among Diseases Affecting Human Skeletal Muscle

Diseases affecting skeletal muscle exhibit considerable heterogeneity in intensity, etiology, phenotypic manifestation and gene expression. Systems biology approaches using network theory, allows for a holistic understanding of functional similarities amongst diseases. Here we propose a co-expression based, network theoretic approach to extract functional similarities from 20 heterogeneous diseases comprising of dystrophinopathies, inflammatory myopathies, neuromuscular, and muscle metabolic diseases. Utilizing this framework we identified seven closely associated disease clusters with 20 disease pairs exhibiting significant correlation (p < 0.05). Mapping the diseases onto a human protein-protein interaction network enabled the inference of a common program of regulation underlying more than half the muscle diseases considered here and referred to as the “protein signature.” Enrichment analysis of 17 protein modules identified as part of this signature revealed a statistically non-random dysregulation of muscle bioenergetic pathways and calcium homeostasis. Further, analysis of mechanistic similarities of less explored significant disease associations [such as between amyotrophic lateral sclerosis (ALS) and cerebral palsy (CP)] using a proposed “functional module” framework revealed adaptation of the calcium signaling machinery. Integrating drug-gene information into the quantitative framework highlighted the presence of therapeutic opportunities through drug repurposing for diseases affecting the skeletal muscle.

Effects of Huperzin-A on the Beta-amyloid accumulation in the brain and skeletal muscle cells of a rat model for Alzheimer's disease

AIMS

Alzheimer's Disease (AD) is characterized by a loss of cognitive function and also the accumulation of β-amyloid peptide (βAP) in the brain parenchyma, which plays an important role in this disease. However, it is often also associated with the non-cognitive symptoms such as loss of muscle function (Inclusion-Body Myositis-IBM).

MAIN METHODS

Sprague-Dawley rats (13 weeks-n=68) were randomly assigned into five groups: Group C: Control; Group D: d-galactose; Group O+D: Bilateral oophorectomy+d-galactose; Group O: Bilateral oophorectomy; Group O+D+H: Bilateral oophorectomy+d-galactose+Hup-A. Tissue fixation was performed with the perfusion method. The Compound Muscle Action Potential (CMAP) and mechanical muscle activity were recorded using the standard electro-biophysical techniques. Immune staining was performed with specific antibodies, and the pathological changes were examined. RNA was obtained from brain tissue samples with the Trizol Method. Then, the expression data of mature-miRNAs (rno-miR-9-5p, rno-miR-29a-3p, rno-miR-106a-5p, rno-miR-107 and rno-miR-125a-3p), which may be effective in AD, were taken with Real-Time PCR.

KEY FINDINGS

Impairments occurred in behavioral tests of the rats in the O+D group. βAP accumulation and AChE activity increased significantly in the forebrain in the O+D group compared to the C group. It was seen that Huperzine-A (Hup-A) reduced AChE activity and destructed βAP accumulation. There was a significant decrease in the maximum contractile force at different frequencies in the O+D group and in the O group compared to the C group.

SIGNIFICANCE

It was found that Hup-A contributed to the healing process in rats for damage occurring both in the brain and in the neuro-muscular system.

Transforming growth factor-β signaling is upregulated in sporadic inclusion body myositis

INTRODUCTION

In this study we aimed to determine whether transforming growth factor-β (TGF-β) signaling is dysregulated in sporadic inclusion body myositis (sIBM) muscle samples.

METHODS

We examined TGF-β signaling markers in muscle samples from 24 sIBM patients and compared them with those from 10 dermatomyositis (DM) patients using immunohistochemistry and Western blot analyses.

RESULTS

Compared with the DM muscle fibers, the sIBM muscle fibers exhibited greater TGF-β, TGF-β receptor type I (TβRI), and TGF-β receptor type II (TβRII) immunoreactivity in the cytoplasm, as well as greater phosphorylated Smad2 (pSmad2) immunoreactivity in the myonuclei. The signal intensities of TGF-β, TβRI, and TβRII immunoreactivity correlated significantly with muscle fiber cross-sectional areas. Western blot analyses indicated higher expression levels of TGF-β, TβRI, TβRII, and pSmad2 in the sIBM muscle samples than in the DM muscle samples.

CONCLUSIONS

These data indicate that upregulation of TGF-β signaling may be an important molecular event in sIBM. Muscle Nerve 55: 741-747, 2017.

The Presence of Select Tau Species in Human Peripheral Tissues and Their Relation to Alzheimer's Disease

Tau becomes excessively phosphorylated in Alzheimer's disease (AD) and is widely studied within the brain. Further examination of the extent and types of tau present in peripheral tissues and their relation to AD is warranted given recent publications on pathologic spreading. Cases were selected based on the presence of pathological tau spinal cord deposits (n = 18). Tissue samples from sigmoid colon, scalp, abdominal skin, liver, and submandibular gland were analyzed by western blot and enzyme-linked immunosorbent assays (ELISAs) for certain tau species; frontal cortex gray matter was used for comparison. ELISAs revealed brain to have the highest total tau levels, followed by submandibular gland, sigmoid colon, liver, scalp, and abdominal skin. Western blots with antibodies recognizing tau phosphorylated at threonine 231(pT231), serine 396 and 404 (PHF-1), and an unmodified total human tau between residues 159 and 163 (HT7) revealed multiple banding patterns, some of which predominated in peripheral tissues. As submandibular gland had the highest levels of peripheral tau, a second set of submandibular gland samples were analyzed (n = 36; 19 AD, 17 non-demented controls). ELISAs revealed significantly lower levels of pS396 (p = 0.009) and pT231 (p = 0.005) in AD cases but not total tau (p = 0.18). Furthermore, pT231 levels in submandibular gland inversely correlated with Braak neurofibrillary tangle stage (p = 0.04), after adjusting for age at death, gender, and postmortem interval. These results provide evidence that certain tau species are present in peripheral tissues. Of potential importance, submandibular gland pT231 is progressively less abundant with increasing Braak neurofibrillary tangle stage.

Molecular events linking cholesterol to Alzheimer's disease and inclusion body myositis in a rabbit model

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized by cognitive impairment and dementia, resulting from progressive synaptic dysfunction, loss and neuronal cell death. Inclusion body myositis (IBM) is a skeletal muscle degenerative disease, displaying progressive proximal and distal muscle weakness, in association with muscle fiber atrophy, degeneration and death. Studies have shown that the late onset version of AD (LOAD) and sporadic IBM (sIBM) in muscle share many pathological features, including the presence of extracellular plaques of β-amyloid peptides and intracellular tangles of hyperphosphorylated tau proteins. High blood cholesterol is suggested to be a risk factor for LOAD. Many neuropathological changes of LOAD can be reproduced by feeding rabbits a 2% enriched cholesterol diet for 12 weeks. The cholesterol fed rabbit model also simultaneously develops sIBM like pathology, which makes it an ideal model to study the molecular mechanisms common to the development of both diseases. In the present study, we determined the changes of gene expression in rabbit brain and muscle during the progression of LOAD and sIBM pathology using a custom rabbit nucleotide microarray, followed by qRT-PCR analyses. Out of 869 unique transcripts screened, 47 genes showed differential expression between the control and the cholesterol-treated group during the 12 week period and 19 changed transcripts appeared to be common to LOAD and sIBM. The most notable changes are the upregulation of the hemoglobin gene family and the downregulation of the genes required for mitochondrial oxidative phosphorylation in both brain and muscle tissues throughout the time course. The significant overlap on the changes of gene expression in the brain and muscle of rabbits fed with cholesterol-enriched diet supports the notion that LOAD and sIBM may share a common etiology.

ER stress: Autophagy induction, inhibition and selection

An accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) leads to stress conditions. To mitigate such circumstances, stressed cells activate a homeostatic intracellular signaling network cumulatively called the unfolded protein response (UPR), which orchestrates the recuperation of ER function. Macroautophagy (hereafter autophagy), an intracellular lysosome-mediated bulk degradation pathway for recycling and eliminating wornout proteins, protein aggregates, and damaged organelles, has also emerged as an essential protective mechanism during ER stress. These 2 systems are dynamically interconnected, and recent investigations have revealed that ER stress can either stimulate or inhibit autophagy. However, the stress-associated molecular cues that control the changeover switch between induction and inhibition of autophagy are largely obscure. This review summarizes the crosstalk between ER stress and autophagy and their signaling networks mainly in mammalian-based systems. Additionally, we highlight current knowledge on selective autophagy and its connection to ER stress.

Compartment-dependent mitochondrial alterations in experimental ALS, the effects of mitophagy and mitochondriogenesis

Amyotrophic lateral sclerosis (ALS) is characterized by massive loss of motor neurons. Data from ALS patients and experimental models indicate that mitochondria are severely damaged within dying or spared motor neurons. Nonetheless, recent data indicate that mitochondrial preservation, although preventing motor neuron loss, fails to prolong lifespan. On the other hand, the damage to motor axons plays a pivotal role in determining both lethality and disease course. Thus, in the present article each motor neuron compartment (cell body, central, and peripheral axons) of G93A SOD-1 mice was studied concerning mitochondrial alterations as well as other intracellular structures. We could confirm the occurrence of ALS-related mitochondrial damage encompassing total swelling, matrix dilution and cristae derangement along with non-pathological variations of mitochondrial size and number. However, these alterations occur to a different extent depending on motor neuron compartment. Lithium, a well-known autophagy inducer, prevents most pathological changes. However, the efficacy of lithium varies depending on which motor neuron compartment is considered. Remarkably, some effects of lithium are also evident in wild type mice. Lithium is effective also in vitro, both in cell lines and primary cell cultures from the ventral spinal cord. In these latter cells autophagy inhibition within motor neurons in vitro reproduced ALS pathology which was reversed by lithium. Muscle and glial cells were analyzed as well. Cell pathology was mostly severe within peripheral axons and muscles of ALS mice. Remarkably, when analyzing motor axons of ALS mice a subtotal clogging of axoplasm was described for the first time, which was modified under the effects of lithium. The effects induced by lithium depend on several mechanisms such as direct mitochondrial protection, induction of mitophagy and mitochondriogenesis. In this study, mitochondriogenesis induced by lithium was confirmed in situ by a novel approach using [2-³H]-adenosine.

BACE-1, PS-1 and sAPPβ Levels Are Increased in Plasma from Sporadic Inclusion Body Myositis Patients: Surrogate Biomarkers among Inflammatory Myopathies

Sporadic inclusion body myositis (sIBM) is a rare disease that is difficult to diagnose. Muscle biopsy provides three prominent pathological findings: inflammation, mitochondrial abnormalities and fibber degeneration, represented by the accumulation of protein depots constituted by β-amyloid peptide, among others. We aim to perform a screening in plasma of circulating molecules related to the putative etiopathogenesis of sIBM to determine potential surrogate biomarkers for diagnosis. Plasma from 21 sIBM patients and 20 age- and gender-paired healthy controls were collected and stored at -80°C. An additional population of patients with non-sIBM inflammatory myopathies was also included (nine patients with dermatomyositis and five with polymyositis). Circulating levels of inflammatory cytokines (interleukin [IL]-6 and tumor necrosis factor [TNF]-α), mitochondrial-related molecules (free plasmatic mitochondrial DNA [mtDNA], fibroblast growth factor-21 [FGF-21] and coenzyme-Q10 [CoQ]) and amyloidogenic-related molecules (beta-secretase-1 [BACE-1], presenilin-1 [PS-1], and soluble Aβ precursor protein [sAPPβ]) were assessed with magnetic bead-based assays, real-time polymerase chain reaction, enzyme-linked immunosorbent assay (ELISA) and high-pressure liquid chromatography (HPLC). Despite remarkable trends toward altered plasmatic expression of inflammatory and mitochondrial molecules (increased IL-6, TNF-α, circulating mtDNA and FGF-21 levels and decreased content in CoQ), only amyloidogenic degenerative markers including BACE-1, PS-1 and sAPPβ levels were significantly increased in plasma from sIBM patients compared with controls and other patients with non-sIBM inflammatory myopathies (p < 0.05). Inflammatory, mitochondrial and amyloidogenic degeneration markers are altered in plasma of sIBM patients confirming their etiopathological implication in the disease. Sensitivity and specificity analysis show that BACE-1, PS-1 and sAPPβ represent a good predictive noninvasive tool for the diagnosis of sIBM, especially in distinguishing this disease from polymyositis.

Functional protein aggregates: just the tip of the iceberg

An increasing number of both prokaryotic and eukaryotic cell types are being adapted as platforms for recombinant protein production. The overproduction of proteins in such expression systems leads to the formation of insoluble protein-based aggregates. Although these protein clusters have been poorly studied in most of the eukaryotic systems, aggregates formed in E. coli, named inclusion bodies (IBs), have been deeply characterized in the last decades. Contrary to the general belief, an important fraction of the protein embedded in IB is functional, showing promise in biocatalysis, regenerative medicine and cell therapy. Thus, the exploration of all these functional protein clusters would largely expand their potential in both pharma and biotech industry.

Effects of blood-flow-restricted resistance training on muscle function in a 74-year-old male with sporadic inclusion body myositis: a case report

Sporadic inclusion body myositis (sIBM) is a systemic disease that is characterized by substantial skeletal muscle weakness and muscle inflammation, leading to impaired physical function. The objective was to investigate the effect of low-load resistance exercise with concurrent partial blood flow restriction to the working muscles (blood-flow-restricted (BFR) training) in a patient with sIBM. The training consisted of 12 weeks of lower extremity BFR training with low training loads (~25-RM). The patient was tested for mechanical muscle function and functional capacity before and after 6 and 12 weeks of training. Maximal horizontal gait speed increased by 19%, which was accompanied by 38-92% improvements in mechanical muscle function (maximal isometric strength, rate of force development and muscle power). In conclusion, BFR training was well tolerated by the patient with sIBM and led to substantial improvements in mechanical muscle function and gait speed.

The protein oxidation repair enzyme methionine sulfoxide reductase a modulates Aβ aggregation and toxicity in vivo

AIMS

To examine the role of the enzyme methionine sulfoxide reductase A-1 (MSRA-1) in amyloid-β peptide (Aβ)-peptide aggregation and toxicity in vivo, using a Caenorhabditis elegans model of the human amyloidogenic disease inclusion body myositis.

RESULTS

MSRA-1 specifically reduces oxidized methionines in proteins. Therefore, a deletion of the msra-1 gene was introduced into transgenic C. elegans worms that express the Aβ-peptide in muscle cells to prevent the reduction of oxidized methionines in proteins. In a constitutive transgenic Aβ strain that lacks MSRA-1, the number of amyloid aggregates decreases while the number of oligomeric Aβ species increases. These results correlate with enhanced synaptic dysfunction and mislocalization of the nicotinic acetylcholine receptor ACR-16 at the neuromuscular junction (NMJ).

INNOVATION

This approach aims at modulating the oxidation of Aβ in vivo indirectly by dismantling the methionine sulfoxide repair system. The evidence presented here shows that the absence of MSRA-1 influences Aβ aggregation and aggravates locomotor behavior and NMJ dysfunction. The results suggest that therapies which boost the activity of the Msr system could have a beneficial effect in managing amyloidogenic pathologies.

CONCLUSION

The absence of MSRA-1 modulates Aβ-peptide aggregation and increments its deleterious effects in vivo.

Diagnostic histochemistry and clinical-pathological testings as molecular pathways to pathogenesis and treatment of the ageing neuromuscular system: a personal view

Ageing of the neuromuscular system in elderhood ingravescently contributes to slowness, weakness, falling and death, often accompanied by numbness and pain. This article is to put in perspective examples from a half-century of personal and team neuromuscular histochemical-pathological and clinical-pathological research, including a number of lucky and instructive accomplishments identifying new treatments and new diseases. A major focus currently is on some important, still enigmatic, aspects of the ageing neuromuscular system. It is also includes some of the newest references of others on various closely-related aspects of this ageing system. The article may help guide others in their molecular-based endeavors to identify paths leading to discovering new treatments and new pathogenic aspects. These are certainly needed - our ageing and unsteady constituents are steadily increasing. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.

Overexpression of autophagic proteins in the skeletal muscle of sporadic inclusion body myositis

AIMS

Sporadic inclusion body myositis (s-IBM) is characterized by rimmed vacuole formation and misfolded protein accumulation. Intracellular protein aggregates are cleared by autophagy. When autophagy is blocked aggregates accumulate, resulting in abnormal rimmed vacuole formation. This study investigated the autophagy-lysosome pathway contribution to rimmed vacuole accumulation.

METHODS

Autophagy was studied in muscle biopsy specimens obtained from eleven s-IBM patients, one suspected hereditary IBM patient, nine patients with other inflammatory myopathies and nine non-myopathic patients as controls. The analysis employed morphometric methods applied to immunohistochemistry using the endosome marker Clathrin, essential proteins of the autophagic cascade such as AuTophaGy-related protein ATG5, splicing variants of microtubule-associated protein light chain 3a (LC3a) and LC3b, compared with Beclin 1, the major autophagy regulator of both the initiation phase and late endosome/lysosome fusion of the autophagy-lysosome pathway.

RESULTS

In muscle biopsies of s-IBM patients, an increased expression of Clathrin, ATG5, LC3a, LC3b and Beclin 1 was shown. Moreover, the inflammatory components of the disease, essentially lymphocytes, were preferentially distributed around the Beclin 1(+) myofibres. These affected myofibres also showed a moderate sarcoplasmic accumulation of SMI-31(+) phospho-tau paired helical filaments.

CONCLUSION

The overexpression of autophagy markers linked to the decreased clearance of misfolded proteins, including SMI-31, and rimmed vacuoles accumulation may exhaust cellular resources and lead to cell death.

Sporadic inclusion-body myositis: A degenerative muscle disease associated with aging, impaired muscle protein homeostasis and abnormal mitophagy

Sporadic inclusion-body myositis (s-IBM) is the most common degenerative muscle disease in which aging appears to be a key risk factor. In this review we focus on several cellular molecular mechanisms responsible for multiprotein aggregation and accumulations within s-IBM muscle fibers, and their possible consequences. Those include mechanisms leading to: a) accumulation in the form of aggregates within the muscle fibers, of several proteins, including amyloid-β42 and its oligomers, and phosphorylated tau in the form of paired helical filaments, and we consider their putative detrimental influence; and b) protein misfolding and aggregation, including evidence of abnormal myoproteostasis, such as increased protein transcription, inadequate protein disposal, and abnormal posttranslational modifications of proteins. Pathogenic importance of our recently demonstrated abnormal mitophagy is also discussed. The intriguing phenotypic similarities between s-IBM muscle fibers and the brains of Alzheimer and Parkinson's disease patients, the two most common neurodegenerative diseases associated with aging, are also discussed. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.

Muscle biopsy features of idiopathic inflammatory myopathies and differential diagnosis

The gold standard to characterize idiopathic inflammatory myopathies is the morphological, immunohistochemical and immunopathological analysis of muscle biopsy. Mononuclear cell infiltrates and muscle fiber necrosis are commonly shared histopathological features. Inflammatory cells that surround, invade and destroy healthy muscle fibers expressing MHC class I antigen are the typical pathological finding of polymyositis. Perifascicular atrophy and microangiopathy strongly support a diagnosis of dermatomyositis. Randomly distributed necrotic muscle fibers without mononuclear cell infiltrates represent the histopathological hallmark of immune-mediated necrotizing myopathy; meanwhile, endomysial inflammation and muscle fiber degeneration are the two main pathological features in sporadic inclusion body myositis. A correct differential diagnosis requires immunopathological analysis of the muscle biopsy and has important clinical implications for therapeutic approach. In particular, unnecessary, potentially harmful, immune-suppressive therapy should be avoided alike in dystrophic myopathies with secondary inflammation.

Gene expression profiling in tibial muscular dystrophy reveals unfolded protein response and altered autophagy

Tibial muscular dystrophy (TMD) is a late onset, autosomal dominant distal myopathy that results from mutations in the two last domains of titin. The cascade of molecular events leading from the causative Titin mutations to the preterm death of muscle cells in TMD is largely unknown. In this study we examined the mRNA and protein changes associated with the myopathology of TMD. To identify these components we performed gene expression profiling using muscle biopsies from TMD patients and healthy controls. The profiling results were confirmed through quantitative real-time PCR and protein level analysis. One of the pathways identified was activation of endoplasmic reticulum (ER) stress response. ER stress activates the unfolded protein response (UPR) pathway. UPR activation was supported by elevation of the marker genes HSPA5, ERN1 and the UPR specific XBP1 splice form. However, UPR activation appears to be insufficient to correct the protein abnormalities causing its activation because degenerative TMD muscle fibres show an increase in ubiquitinated protein inclusions. Abnormalities of VCP-associated degradation pathways are also suggested by the presence of proteolytic VCP fragments in western blotting, and VCP's accumulation within rimmed vacuoles in TMD muscle fibres together with p62 and LC3B positive autophagosomes. Thus, pathways controlling turnover and degradation, including autophagy, are distorted and lead to degeneration and loss of muscle fibres.

Th1 response and systemic treg deficiency in inclusion body myositis

OBJECTIVE

Sporadic inclusion body myositis (sIBM), the most frequent myositis in elderly patients, is characterized by the presence muscle inflammation and degeneration. We aimed at characterizing immune responses and regulatory T cells, considered key players in the maintenance of peripheral immune tolerance, in sIBM.

METHODS

Serum and muscle tissue levels of 25 cytokines and phenotype of circulating immune cells were measured in 22 sIBM patients and compared with 22 healthy subjects. Cytokine data were analysed by unsupervised hierarchical clustering and principal components analysis.

RESULTS

Compared to healthy controls, sIBM patients had increased levels of Th-1 cytokines and chemokines such as IL-12 (261±138 pg/mL vs. 88±19 pg/mL; p<0.0001), CXCL-9 (186±12 pg/mL vs. 13±7 pg/mL; p<0.0001), and CXCL-10 (187±62 pg/mL vs. 13±6 pg/mL; p<0.0001). This was associated with an increased frequency of CD8+CD28- T cells (45.6±18.5% vs. 13.5±9.9%; p<0.0001), which were more prone to produce IFN-γ (45.6±18.5% vs. 13.5±9.9%; p<0.0001). sIBM patients also had a decreased frequency of circulating regulatory T cells (CD4+CD25+CD127lowFOXP3+, 6.9±1.7%; vs. 5.2±1.1%, p = 0.01), which displayed normal suppressor function and were also present in affected muscle.

CONCLUSION

sIBM patients present systemic immune activation with Th1 polarization involving the IFN-γ pathway and CD8+CD28- T cells associated with peripheral regulatory T cell deficiency.

Mitochondrial oxygen consumption deficits in skeletal muscle isolated from an Alzheimer's disease-relevant murine model

Background

Age is considered a primary risk factor for neurodegenerative diseases including Alzheimer’s disease (AD). It is also now well understood that mitochondrial function declines with age. Mitochondrial deficits have been previously assessed in brain from both human autopsy tissue and disease-relevant transgenic mice. Recently it has been recognized that abnormalities of muscle may be an intrinsic aspect of AD and might contribute to the pathophysiology. However, deficits in mitochondrial function have yet to be clearly assessed in tissues outside the central nervous system (CNS). In the present study, we utilized a well-characterized AD-relevant transgenic mouse strain to assess mitochondrial respiratory deficits in both brain and muscle. In addition to mitochondrial function, we assessed levels of transgene-derived amyloid precursor protein (APP) in homogenates isolated from brain and muscle of these AD-relevant animals.

Results

We now demonstrate that skeletal muscles isolated from these animals have differential levels of mutant full-length APP depending on muscle type. Additionally, isolated muscle fibers from young transgenic mice (3 months) have significantly decreased maximal mitochondrial oxygen consumption capacity compared to non-transgenic, age-matched mice, with similar deficits to those previously described in brain.

Conclusions

This is the first study to directly examine mitochondrial function in skeletal muscle from an AD-relevant transgenic murine model. As with brain, these deficits in muscle are an early event, occurring prior to appearance of amyloid plaques.

Diagnosis and classification of sporadic inclusion body myositis (sIBM)

Sporadic inclusion body myositis (sIBM) is the most common acquired muscle disease in elderly individuals, particularly men. Its prevalence varies among ethnic groups but is estimated at 35 per one million people over 50. Genetic as well as environmental factors and autoimmune processes might both have a role in its pathogenesis. Unlike other inflammatory myopathies, sIBM causes very slowly progressive muscular weakness and atrophy, having a distinctive pattern of muscle involvement and different forms of clinical presentation. In some cases a primary autoimmune disease coexists. Diagnosis is suspected on clinical grounds and is established by typical muscle pathology. As a rule sIBM is refractory to conventional forms of immunotherapy.

De novo prion aggregates trigger autophagy in skeletal muscle

In certain sporadic, familial, and infectious prion diseases, the prion protein misfolds and aggregates in skeletal muscle in addition to the brain and spinal cord. In myocytes, prion aggregates accumulate intracellularly, yet little is known about clearance pathways. Here we investigated the clearance of prion aggregates in muscle of transgenic mice that develop prion disease de novo. In addition to neurodegeneration, aged mice developed a degenerative myopathy, with scattered myocytes containing ubiquitinated, intracellular prion inclusions that were adjacent to myocytes lacking inclusions. Myocytes also showed elevated levels of the endoplasmic reticulum chaperone Grp78/BiP, suggestive of impaired protein degradation and endoplasmic reticulum stress. Additionally, autophagy was induced, as indicated by increased levels of beclin-1 and LC3-II. In C2C12 myoblasts, inhibition of autophagosome maturation or lysosomal degradation led to enhanced prion aggregation, consistent with a role for autophagy in prion aggregate clearance. Taken together, these findings suggest that the induction of autophagy may be a central strategy for prion aggregate clearance in myocytes. IMPORTANCE In prion diseases, the prion protein misfolds and aggregates in the central nervous system and sometimes in other organs, including muscle, yet the cellular pathways of prion aggregate clearance are unclear. Here we investigated the clearance of prion aggregates in the muscle of a transgenic mouse model that develops profound muscle degeneration. We found that endoplasmic reticulum stress pathways were activated and that autophagy was induced. Blocking of autophagic degradation in cell culture models led to an accumulation of aggregated prion protein. Collectively, these findings suggest that autophagy has an instrumental role in prion protein clearance.

Molecular markers for granulovacuolar degeneration are present in rimmed vacuoles

BACKGROUND

Rimmed vacuoles (RVs) are round-oval cytoplasmic inclusions, detected in muscle cells of patients with myopathies, such as inclusion body myositis (IBM) and distal myopathy with RVs (DMRV). Granulovacuolar degeneration (GVD) bodies are spherical vacuoles containing argentophilic and hematoxyphilic granules, and are one of the pathological hallmarks commonly found in hippocampal pyramidal neurons of patients with aging-related neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. These diseases are common in the elderly and share some pathological features. Therefore, we hypothesized that mechanisms of vacuolar formation in RVs and GVD bodies are common despite their role in two differing pathologies. We explored the components of RVs by immunohistochemistry, using antibodies for GVD markers.

METHODS

Subjects included one AD case, eight cases of sporadic IBM, and three cases of DMRV. We compared immunoreactivity and staining patterns for GVD markers. These markers included: (1) tau-modifying proteins (caspase 3, cyclin-dependent kinase 5 [CDK5], casein kinase 1δ [CK1δ], and c-jun N-terminal kinase [JNK]), (2) lipid raft-associated materials (annexin 2, leucine-rich repeat kinase 2 [LRRK2], and flotillin-1), and (3) other markers (charged multi-vesicular body protein 2B [CHMP2B] and phosphorylated transactive response DNA binding protein-43 [pTDP43]) in both GVD bodies and RVs. Furthermore, we performed double staining of each GVD marker with pTDP43 to verify the co-localization.

RESULTS

GVD markers, including lipid raft-associated proteins and tau kinases, were detected in RVs. CHMP2B, pTDP43, caspase 3, LRRK2, annexin 2 and flotillin-1 were detected on the rim and were diffusely distributed in the cytoplasm of RV-positive fibers. CDK5, CK1δ and JNK were detected only on the rim. In double staining experiments, all GVD markers colocalized with pTDP43 in RVs.

CONCLUSIONS

These results suggest that RVs of muscle cells and GVD bodies of neurons share a number of molecules, such as raft-related proteins and tau-modifying proteins.

In vivo interaction proteomics reveal a novel p38 mitogen-activated protein kinase/Rack1 pathway regulating proteostasis in Drosophila muscle

Several recent studies suggest that systemic aging in metazoans is differentially affected by functional decline in specific tissues, such as skeletal muscle. In Drosophila, longevity appears to be tightly linked to myoproteostasis, and the formation of misfolded protein aggregates is a hallmark of senescence in aging muscle. Similarly, defective myoproteostasis is described as an important contributor to the pathology of several age-related degenerative muscle diseases in humans, e.g., inclusion body myositis. p38 mitogen-activated protein kinase (MAPK) plays a central role in a conserved signaling pathway activated by a variety of stressful stimuli. Aging p38 MAPK mutant flies display accelerated motor function decline, concomitant with an enhanced accumulation of detergent-insoluble protein aggregates in thoracic muscles. Chemical genetic experiments suggest that p38-mediated regulation of myoproteostasis is not limited to the control of reactive oxygen species production or the protein degradation pathways but also involves upstream turnover pathways, e.g., translation. Using affinity purification and mass spectrometry, we identified Rack1 as a novel substrate of p38 MAPK in aging muscle and showed that the genetic interaction between p38b and Rack1 controls muscle aggregate formation, locomotor function, and longevity. Biochemical analyses of Rack1 in aging and stressed muscle suggest a model whereby p38 MAPK signaling causes a redistribution of Rack1 between a ribosome-bound pool and a putative translational repressor complex.

Biochemistry and cell biology of tau protein in neurofibrillary degeneration

Tau represents the subunit protein of one of the major hallmarks of Alzheimer disease (AD), the neurofibrillary tangles, and is therefore of major interest as an indicator of disease mechanisms. Many of the unusual properties of Tau can be explained by its nature as a natively unfolded protein. Examples are the large number of structural conformations and biochemical modifications (phosphorylation, proteolysis, glycosylation, and others), the multitude of interaction partners (mainly microtubules, but also other cytoskeletal proteins, kinases, and phosphatases, motor proteins, chaperones, and membrane proteins). The pathological aggregation of Tau is counterintuitive, given its high solubility, but can be rationalized by short hydrophobic motifs forming β structures. The aggregation of Tau is toxic in cell and animal models, but can be reversed by suppressing expression or by aggregation inhibitors. This review summarizes some of the structural, biochemical, and cell biological properties of Tau and Tau fibers. Further aspects of Tau as a diagnostic marker and therapeutic target, its involvement in other Tau-based diseases, and its histopathology are covered by other chapters in this volume.

Oleuropein aglycone protects transgenic C. elegans strains expressing Aβ42 by reducing plaque load and motor deficit

The presence of amyloid aggregates of the 42 amino acid peptide of amyloid beta (Aβ42) in the brain is the characteristic feature of Alzheimer’s disease (AD). Amyloid beta (Aβ deposition is also found in muscle fibers of individuals affected by inclusion body myositis (sIBM), a rare muscular degenerative disease affecting people over 50. Both conditions are presently lacking an effective therapeutic treatment. There is increasing evidence to suggest that natural polyphenols may prevent the formation of toxic amyloid aggregates; this applies also to oleuropein aglycone (OLE), the most abundant polyphenol in extra virgin olive oil, previously shown to hinder amylin and Aβ aggregation. Here we evaluated the ability of OLE to interfere with Aβ proteotoxicity in vivo by using the transgenic CL2006 and CL4176 strains of Caenorhabditis elegans, simplified models of AD and of sIBM, which express human Aβ in the cytoplasm of body wall muscle cells. OLE-fed CL2006 worms displayed reduced Aβ plaque deposition, less abundant toxic Aβ oligomers, remarkably decreased paralysis and increased lifespan with respect to untreated animals. A protective effect was also observed in CL4176 worms but only when OLE was administered before the induction of the Aβ transgene expression. These effects were specific, dose-related, and not mediated by the known polyphenolic anti-oxidant activity, suggesting that, in this model organism, OLE interferes with the Aβ aggregation skipping the appearance of toxic species, as already shown in vitro for Aβ42.

Luminescent conjugated oligothiophenes for sensitive fluorescent assignment of protein inclusion bodies

Small hydrophobic ligands identifying intracellular protein deposits are of great interest, as protein inclusion bodies are the pathological hallmark of several degenerative diseases. Here we report that fluorescent amyloid ligands, termed luminescent conjugated oligothiophenes (LCOs), rapidly and with high sensitivity detect protein inclusion bodies in skeletal muscle tissue from patients with sporadic inclusion body myositis (s-IBM). LCOs having a conjugated backbone of at least five thiophene units emitted strong fluorescence upon binding, and showed co-localization with proteins reported to accumulate in s-IBM protein inclusion bodies. Compared with conventional amyloid ligands, LCOs identified a larger fraction of immunopositive inclusion bodies. When the conjugated thiophene backbone was extended with terminal carboxyl groups, the LCO revealed striking spectral differences between distinct protein inclusion bodies. We conclude that 1) LCOs are sensitive, rapid and powerful tools for identifying protein inclusion bodies and 2) LCOs identify a wider range of protein inclusion bodies than conventional amyloid ligands.

Foxo/atrogin induction in human and experimental myositis

Skeletal muscle atrophy can occur rapidly in various fasting, cancerous, systemic inflammatory, deranged metabolic or neurogenic states. The ubiquitin ligase Atrogin-1 (MAFbx) is induced in animal models of these conditions, causing excessive myoprotein degradation. It is unknown if Atrogin upregulation also occurs in acquired human myositis. Intracellular β-amyloid (Aβi), phosphorylated neurofilaments, scattered infiltrates and atrophy involving selective muscle groups characterize human sporadic Inclusion Body Myositis (sIBM). In Polymyositis (PM), inflammation is more pronounced and atrophy is symmetric and proximal. IBM and PM share various inflammatory markers. We found that forkhead family transcription factor Foxo3A is directed to the nucleus and Atrogin-1 transcript is increased in both conditions. Expression of Aβ in transgenic mice and differentiated C2C12 myotubes was sufficient to upregulate Atrogin-1 mRNA and cause atrophy. Aβi reduces levels of p-Akt and downstream p-Foxo3A, resulting in Foxo3A translocation and Atrogin-1 induction. In a mouse model of autoimmune myositis, cellular inflammation alone was associated with similar Foxo3A and Atrogin changes. Thus, either Aβi accumulation or cellular immune stimulation may independently drive muscle atrophy in sIBM and PM, respectively, through pathways converging on Foxo and Atrogin-1. In sIBM it is additionally possible that both mechanisms synergize.