In inclusion-body myositis muscle fibers Parkinson-associated DJ-1 is increased and oxidized

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.

Sporadic Inclusion Body Myositis at the Crossroads between Muscle Degeneration, Inflammation, and Aging

Sporadic inclusion body myositis (sIBM) is the most common muscle disease of older people and is clinically characterized by slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors. At present, there are no enduring treatments for this relentless disease that eventually leads to severe disability and wheelchair dependency. Although sIBM is considered a rare muscle disorder, its prevalence is certainly higher as the disease is often undiagnosed or misdiagnosed. The histopathological phenotype of sIBM muscle biopsy includes muscle fiber degeneration and endomysial lymphocytic infiltrates that mainly consist of cytotoxic CD8+ T cells surrounding nonnecrotic muscle fibers expressing MHCI. Muscle fiber degeneration is characterized by vacuolization and the accumulation of congophilic misfolded multi-protein aggregates, mainly in their non-vacuolated cytoplasm. Many players have been identified in sIBM pathogenesis, including environmental factors, autoimmunity, abnormalities of protein transcription and processing, the accumulation of several toxic proteins, the impairment of autophagy and the ubiquitin-proteasome system, oxidative and nitrative stress, endoplasmic reticulum stress, myonuclear degeneration, and mitochondrial dysfunction. Aging has also been proposed as a contributor to the disease. However, the interplay between these processes and the primary event that leads to the coexistence of autoimmune and degenerative changes is still under debate. Here, we outline our current understanding of disease pathogenesis, focusing on degenerative mechanisms, and discuss the possible involvement of aging.

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.

Inhibition of phosphodiesterase 4 by FCPR16 protects SH-SY5Y cells against MPP+-induced decline of mitochondrial membrane potential and oxidative stress

Phosphodiesterase 4 (PDE4) is a promising target for the treatment of Parkinson's disease (PD). However, the underlying mechanism has not yet been well elucidated. Additionally, most of current PDE4 inhibitors produce severe nausea and vomiting response in patients, which limit their clinical application. FCPR16 is a novel PDE4 inhibitor with little emetic potential. In the present study, the neuroprotective effect and underlying mechanism of FCPR16 against cellular apoptosis induced by 1-methyl-4-phenylpyridinium (MPP⁺) were examined in SH-SY5Y cells. FCPR16 (12.5–50 μM) dose-dependently reduced MPP⁺-induced loss of cell viability, accompanied by reductions in nuclear condensation and lactate dehydrogenase release. The level of cleaved caspase 3 and the ratio of Bax/Bcl-2 were also decreased after treatment with FCPR16 in MPP⁺-treated cells. Furthermore, FCPR16 (25 μM) significantly suppressed the accumulation of reactive oxygen species (ROS), prevented the decline of mitochondrial membrane potential (Δψm) and attenuated the expression of malonaldehyde level. Further studies disclosed that FCPR16 enhanced the levels of cAMP and the exchange protein directly activated by cAMP (Epac) in SH-SY5Y cells. Western blotting analysis revealed that FCPR16 increased the phosphorylation of cAMP response element-binding protein (CREB) and protein kinase B (Akt) down-regulated by MPP⁺ in SH-SY5Y cells. Moreover, the inhibitory effects of FCPR16 on the production of ROS and Δψm loss could be blocked by PKA inhibitor H-89 and Akt inhibitor KRX-0401. Collectively, these results suggest that FCPR16 attenuates MPP⁺-induced dopaminergic degeneration via lowering ROS and preventing the loss of Δψm in SH-SY5Y cells. Mechanistically, cAMP/PKA/CREB and Epac/Akt signaling pathways are involved in these processes. Our findings indicate that FCPR16 is a promising pre-clinical candidate for the treatment of PD and possibly other oxidative stress-related neuronal diseases.

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FCPR16 protected SH-SY5Y cells against MPP⁺-induced apoptosis.

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FCPR16 attenuated Δψm loss and ROS generation in SH-SY5Y cells treated with MPP⁺.

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FCPR16 activated cAMP/PKA/CREB and Epac/Akt signaling pathways in SH-SY5Y cells.

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Blocking cAMP/PKA/CREB or Epac/Akt pathways canceled the protective role of FCPR16.

Chaperone-mediated autophagy components are upregulated in sporadic inclusion-body myositis muscle fibres

AIMS

Sporadic inclusion-body myositis (s-IBM) is an age-associated degenerative muscle disease. Characteristic features are muscle-fibre vacuolization and intramuscle-fibre accumulations of multiprotein aggregates, which may result from the demonstrated impairments of the 26S proteasome and autophagy. Chaperone-mediated autophagy (CMA) is a selective form of lysosomal degradation targeting proteins carrying the KFERQ motif. Lysosome-associated membrane protein type 2A (LAMP2A) and the heat-shock cognate protein 70 (Hsc70) constitute specific CMA components. Neither CMA components nor CMA activity has been studied in normal or disease human muscle, to our knowledge.

METHODS

We studied CMA components by immunocytochemistry, immunoblots, real-time PCR and immunoprecipitation in: (a) 16 s-IBM, nine aged-matched normal and nine disease control muscle biopsies; and (b) cultured human muscle fibres (CHMFs) with experimentally inhibited activities of either the 26S proteasome or autophagy.

RESULTS

Compared with age-matched controls, in s-IBM muscle, LAMP2A and Hsc70 were on a given transverse section accumulated as aggregates in approximately 5% of muscle fibres, where they (a) colocalized with each other and α-synuclein (α-syn), a CMA-targeted protein; and (b) were bound to each other and to α-syn by immunoprecipitation. By immunoblots, LAMP2A was increased sevenfold P < 0.001 and Hsc70 2.6-fold P < 0.05. LAMP2A mRNA was increased 4.4-fold P < 0.001 and Hsc70 mRNA 1.9-fold P < 0.05. In CHMFs inhibition of either the 26S proteasome or autophagy induced CMA, evidenced by a significant increase of both LAMP2A and Hsc70.

CONCLUSIONS

Our study demonstrates, for the first time, up-regulation of CMA components in s-IBM muscle, and it provides further evidence that altered protein degradation is likely an important pathogenic aspect in s-IBM.

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.

Pathogenic considerations in sporadic inclusion-body myositis, a degenerative muscle disease associated with aging and abnormalities of myoproteostasis

The pathogenesis of sporadic inclusion-body myositis (s-IBM) is complex; it involves multidimensional pathways and the most critical issues are still unresolved. The onset of muscle fiber damage is age related and the disease is slowly, but inexorably, progressive. Muscle fiber degeneration and mononuclear cell inflammation are major components of s-IBM pathology, but which is precedent and how they interrelate is not known. There is growing evidence that aging of the muscle fiber associated with intramyofiber accumulation of conformationally modified proteins plays a primary pathogenic role leading to muscle fiber destruction. Here, we review the presumably most important known molecular abnormalities that occur in s-IBM myofibers and that likely contribute to s-IBM pathogenesis. Abnormal accumulation within the fibers of multiprotein aggregates (several of which are congophilic and, therefore, generically called "amyloid") may result from increased transcription of several proteins, their abnormal posttranslational modifications and misfolding, and inadequate protein disposal, that is, abnormal "myoproteostasis," which is combined with and may be provoked or abetted by an aging intracellular milieu. The potential cytotoxicity of accumulated amyloid β protein (Aβ42) and its oligomers, phosphorylated tau in the form of paired helical filaments and α-synuclein, and the putative pathogenic role and cause of the mitochondrial abnormalities and oxidative stress are reviewed. On the basis of our experimental evidence, potential interventions in the complex, interwoven pathogenic cascade of s-IBM are suggested.

Activation of the γ-secretase complex and presence of γ-secretase-activating protein may contribute to Aβ42 production in sporadic inclusion-body myositis muscle fibers

The muscle-fiber phenotype of sporadic inclusion-body myositis (s-IBM), the most common muscle disease associated with aging, shares several pathological abnormalities with Alzheimer disease (AD) brain, including accumulation of amyloid-β 42 (Aβ42) and its cytotoxic oligomers. The exact mechanisms leading to Aβ42 production within s-IBM muscle fibers are not known. Aβ42 and Aβ40 are generated after the amyloid-precursor protein (AβPP) is cleaved by β-secretase and the γ-secretase complex. Aβ42 is considered more cytotoxic than Aβ40, and it has a higher propensity to oligomerize, form amyloid fibrils, and aggregate. Recently, we have demonstrated in cultured human muscle fibers that experimental inhibition of lysosomal enzyme activities leads to Aβ42 oligomerization. In s-IBM muscle, we here demonstrate prominent abnormalities of the γ-secretase complex, as evidenced by: a) increase of γ-secretase components, namely active presenilin 1, presenilin enhancer 2, nicastrin, and presence of its mature, glycosylated form; b) increase of mRNAs of these γ-secretase components; c) increase of γ-secretase activity; d) presence of an active form of a newly-discovered γ-secretase activating protein (GSAP); and e) increase of GSAP mRNA. Furthermore, we demonstrate that experimental inhibition of lysosomal autophagic enzymes in cultured human muscle fibers a) activates γ-secretase, and b) leads to posttranslational modifications of AβPP and increase of Aβ42. Since autophagy is impaired in biopsied s-IBM muscle, the same mechanism might be responsible for its having increased γ-secretase activity and Aβ42 production. Accordingly, improving lysosomal function might be a therapeutic strategy for s-IBM patients.

AICAR prevents heat-induced sudden death in RyR1 mutant mice independent of AMPK activation

Mice with a knock-in mutation (Y524S) in the type I ryanodine receptor (RyR1) die when exposed to short periods of temperature elevation (≥ 37 °C). We demonstrate that treatment with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) prevents heat-induced sudden death in Y524S mice. The AICAR protection is independent of AMPK activation and results from a newly identified action on the mutant RyR1 to reduce Ca²⁺ leak, preventing Ca²⁺ dependent increases in both reactive oxygen and reactive nitrogen species that act to further increase resting Ca²⁺ concentrations. If unchecked, the temperature driven increases in resting Ca²⁺ and ROS/RNS create an amplifying cycle that ultimately triggers sustained muscle contractions, rhabdomyolysis and death. Although antioxidants are effective in reducing this cycle in vitro, only AICAR prevents the heat induced death in vivo. Our findings suggest that AICAR is likely to be effective in prophylactic treatment of humans with enhanced susceptibility to exercise/heat-induced sudden death associated with RyR1 mutations.

Oxidative stress-induced proteome alterations target different cellular pathways in human myoblasts

Although increased oxidative stress has been associated with the impairment of proliferation and function of adult human muscle stem cells, proteins either involved in the stress response or damaged by oxidation have not been identified. A parallel proteomics approach was performed for analyzing the protein expression profile as well as proteins preferentially oxidized upon hydrogen peroxide-induced oxidative stress. Fifteen proteins involved in the oxidative stress response were identified. Among them, protein spots identified as peroxiredoxins 1 and 6, glyceraldehyde-3-phosphate dehydrogenase, and α-enolase were shifted to a more acidic isoelectric point upon oxidative stress, indicating posttranslational modifications. Oxidized proteins were evidenced by immunodetection of derivatized carbonyl groups followed by identification by mass spectrometry. The carbonylated proteins identified are mainly cytosolic and involved in carbohydrate metabolism, cellular assembly, cellular homeostasis, and protein synthesis and degradation. Pathway analysis revealed skeletal and muscular disorders, cell death, and cancer-related as the main molecular networks altered. Interestingly, these pathways were focused on two distinct proteins: p53 for altered protein expression and huntingtin for increased protein carbonylation. This study emphasizes the importance of performing analysis addressing different aspects of the cellular proteome to have a more accurate view of their changes upon stress.

Sporadic inclusion-body myositis: conformational multifactorial ageing-related degenerative muscle disease associated with proteasomal and lysosomal inhibition, endoplasmic reticulum stress, and accumulation of amyloid-β42 oligomers and phosphorylated tau

The pathogenesis of sporadic inclusion-body myositis (s-IBM), the most common muscle disease of older persons, is complex and multifactorial. Both the muscle fiber degeneration and the mononuclear-cell inflammation are components of the s-IBM pathology, but how each relates to the pathogenesis remains unsettled. We consider that the intramuscle fiber degenerative component plays the primary and the major pathogenic role leading to muscle fiber destruction and clinical weakness. In this article we review the newest research advances that provide a better understanding of the s-IBM pathogenesis. Cellular abnormalities occurring in s-IBM muscle fibers are discussed, including: several proteins that are accumulated in the form of aggregates within muscle fibers, including amyloid-β42 and its oligomers, and phosphorylated tau in the form of paired helical filaments, and we consider their putative detrimental influence; cellular mechanisms leading to protein misfolding and aggregation, including evidence of their inadequate disposal; pathogenic importance of endoplasmic reticulum stress and the unfolded protein response demonstrated in s-IBM muscle fibers; and decreased deacetylase activity of SIRT1. All these factors are combined with, and perhaps provoked by, an ageing intracellular milieu. Also discussed are 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 ageing. Muscle biopsy diagnostic criteria are also described and illustrated.

Impaired autophagy in sporadic inclusion-body myositis and in endoplasmic reticulum stress-provoked cultured human muscle fibers

The hallmark pathologies of sporadic inclusion-body myositis (s-IBM) muscle fibers are autophagic vacuoles and accumulation of ubiquitin-positive multiprotein aggregates that contain amyloid-beta or phosphorylated tau in a beta-pleated sheet amyloid configuration. Endoplasmic reticulum stress (ERS) and 26S proteasome inhibition, also associated with s-IBM, putatively aggrandize the accumulation of misfolded proteins. However, autophagosomal-lysosomal pathway formation and function, indicated by autophagosome maturation, have not been previously analyzed in this system. Here we studied the autophagosomal-lysosomal pathway using 14 s-IBM and 30 disease control and normal control muscle biopsy samples and our cultured human muscle fibers in a microenvironment modified to resemble aspects of s-IBM pathology. We report for the first time that in s-IBM, lysosomal enzyme activities of cathepsin D and B were decreased 60% (P < 0.01) and 40% (P < 0.05), respectively. We also detected two indicators of increased autophagosome maturation, the presence of LC3-II and decreased mammalian target of rapamycin-mediated phosphorylation of p70S6 kinase. Moreover, in cultured human muscle fibers, ERS induction significantly decreased activities of cathepsins D and B, increased levels of LC3-II, decreased phosphorylation of p70S6 kinase, and decreased expression of VMA21, a chaperone for assembly of lysosomal V-ATPase. We conclude that in s-IBM muscle, decreased lysosomal proteolytic activity might enhance accumulation of misfolded proteins, despite increased maturation of autophagosomes, and that ERS is a possible cause of s-IBM-impaired lysosomal function. Thus, unblocking protein degradation in s-IBM muscle fibers may be a desirable therapeutic strategy.

Increased BACE1 mRNA and noncoding BACE1-antisense transcript in sporadic inclusion-body myositis muscle fibers--possibly caused by endoplasmic reticulum stress

Sporadic inclusion-body myositis (s-IBM) is the most common muscle disease of older persons. Its muscle-fiber phenotype shares several molecular similarities with Alzheimer-disease (AD) brain, including increased AbetaPP, accumulation of amyloid-beta (Abeta), and increased BACE1 protein. Abeta42 is prominently increased in AD brain and within s-IBM fibers, and its oligomers are putatively toxic to both tissues--accordingly, minimizing Abeta42 production can be a therapeutic objective in both tissues. The pathogenic development of s-IBM is unknown, including the mechanisms of BACE1 protein increase. BACE1 is an enzyme essential for production from AbetaPP of Abeta42 and Abeta40, which are proposed to be detrimental within s-IBM muscle fibers. Novel noncoding BACE1-antisense (BACE1-AS) was recently shown (a) to be increased in AD brain, and (b) to increase BACE1 mRNA and BACE1 protein. We studied BACE1-AS and BACE1 transcripts by real-time PCR (a) in 10 s-IBM and 10 age-matched normal muscle biopsies; and (b) in our established ER-Stress-Human-Muscle-Culture-IBM Model, in which we previously demonstrated increased BACE1 protein. Our study demonstrated for the first time that (a) in s-IBM biopsies BACE1-AS and BACE1 transcripts were significantly increased, suggesting that their increased expression can be responsible for the increase of BACE1 protein; and (b) experimental induction of ER stress significantly increased both BACE1-AS and BACE1 transcripts, suggesting that ER stress can participate in their induction in s-IBM muscle. Accordingly, decreasing BACE1 through a targeted downregulation of its regulatory BACE1-AS, or reducing ER stress, might be therapeutic strategies in s-IBM, assuming that it would not impair any normal cellular functions of BACE1.

DJ-1 and prevention of oxidative stress in Parkinson's disease and other age-related disorders

Mutations in the PARK7/DJ-1 gene are rare causes of autosomal-recessive hereditary Parkinson's disease. Loss-of-function mutations lead to the characteristic selective neurodegeneration of nigrostriatal dopaminergic neurons, which accounts for parkinsonian symptoms. Originally identified as an oncogene, DJ-1 is a ubiquitous redox-responsive cytoprotective protein with diverse functions. In addition to cell-autonomous neuroprotective roles, DJ-1 may act in a transcellular manner, being up-regulated in reactive astrocytes in chronic neurodegenerative diseases as well as in stroke. Thus, DJ-1, particularly in its oxidized form, has been recognized as a biomarker for cancer and neurodegenerative diseases. The crystal structure of DJ-1 has been solved, allowing detailed investigations of the redox-reactive center of DJ-1. Structure-function studies revealed that DJ-1 may become activated in the presence of reactive oxygen species, under conditions of oxidative stress, but also as part of physiological receptor-mediated signal transduction. DJ-1 regulates redox signaling kinase pathways and acts as a transcriptional regulator of antioxidative gene batteries. Therefore, DJ-1 is an important redox-reactive signaling intermediate controlling oxidative stress after ischemia, upon neuroinflammation, and during age-related neurodegenerative processes. Augmenting DJ-1 activity might provide novel approaches to treating chronic neurodegenerative illnesses such as Parkinson's disease and acute damage such as stroke.

In AbetaPP-overexpressing cultured human muscle fibers proteasome inhibition enhances phosphorylation of AbetaPP751 and GSK3beta activation: effects mitigated by lithium and apparently relevant to sporadic inclusion-body myositis

Muscle fiber degeneration in sporadic inclusion-body myositis (s-IBM) is characterized by accumulation of multiprotein aggregates, including aggregated amyloid-beta (Abeta)-precursor protein 751 (AbetaPP751), Abeta, phosphorylated tau, and other 'Alzheimer-characteristic' proteins. Proteasome inhibition is an important component of the s-IBM pathogenesis. In brains of Alzheimer's disease (AD) patients and AD transgenic-mouse models, phosphorylation of neuronal AbetaPP695 (p-AbetaPP) on Thr668 (equivalent to T724 of AbetaPP751) is considered detrimental because it increases generation of cytotoxic Abeta and induces tau phosphorylation. Activated glycogen synthase kinase3beta (GSK3beta) is involved in phosphorylation of both AbetaPP and tau. Lithium, an inhibitor of GSK3beta, was reported to reduce levels of both the total AbetaPP and p-AbetaPP in AD animal models. In relation to s-IBM, we now show for the first time that (1) In AbetaPP-overexpressing cultured human muscle fibers (human muscle culture IBM model: (a) proteasome inhibition significantly increases GSK3beta activity and AbetaPP phosphorylation, (b) treatment with lithium decreases (i) phosphorylated-AbetaPP, (ii) total amount of AbetaPP, (iii) Abeta oligomers, and (iv) GSK3beta activity; and (c) lithium improves proteasome function. (2) In biopsied s-IBM muscle fibers, GSK3beta is significantly activated and AbetaPP is phosphorylated on Thr724. Accordingly, treatment with lithium, or other GSK3beta inhibitors, might benefit s-IBM patients.

p62/SQSTM1 is overexpressed and prominently accumulated in inclusions of sporadic inclusion-body myositis muscle fibers, and can help differentiating it from polymyositis and dermatomyositis

p62, also known as sequestosome1, is a shuttle protein transporting polyubiquitinated proteins for both the proteasomal and lysosomal degradation. p62 is an integral component of inclusions in brains of various neurodegenerative disorders, including Alzheimer disease (AD) neurofibrillary tangles (NFTs) and Lewy bodies in Parkinson disease. In AD brain, the p62 localized in NFTs is associated with phosphorylated tau (p-tau). Sporadic inclusion-body myositis (s-IBM) is the most common progressive muscle disease associated with aging, and its muscle tissue has several phenotypic similarities to AD brain. Abnormal accumulation of intracellular multiprotein inclusions, containing p-tau in the form of paired helical filaments, amyloid-beta, and several other "Alzheimer-characteristic proteins", is a characteristic feature of the s-IBM muscle fiber phenotype. Diminished proteasomal and lysosomal protein degradation appear to play an important role in the formation of intra-muscle-fiber inclusions. We now report that: (1) in s-IBM muscle fibers, p62 protein is increased on both the protein and the mRNA levels, and it is strongly accumulated within, and as a dense peripheral shell surrounding, p-tau containing inclusions, by both the light- and electron-microscopy. Accordingly, our studies provide a new, reliable, and simple molecular marker of p-tau inclusions in s-IBM muscle fibers. The prominent p62 immunohistochemical positivity and pattern diagnostically distinguish s-IBM from polymyositis and dermatomyositis. (2) In normal cultured human muscle fibers, experimental inhibition of either proteasomal or lysosomal protein degradation caused substantial increase of p62, suggesting that similar in vivo mechanisms might contribute to the p62 increase in s-IBM muscle fibers.

Altered Ca2+ homeostasis in the skeletal muscle of DJ-1 null mice

Loss-of-function mutations in DJ-1 are associated with early-onset of Parkinson's disease. Although DJ-1 is ubiquitously expressed, the functional pathways affected by it remain unresolved. Here we demonstrate an involvement of DJ-1 in the regulation of Ca(2+) homeostasis in mouse skeletal muscle. Using enzymatically dissociated flexor digitorum brevis muscle fibers from wild-type (wt) and DJ-1 null mice, we examined the effects of DJ-1 protein on resting, cytoplasmic [Ca(2+)] ([Ca(2+)](i)) and depolarization-evoked Ca(2+) release in the mouse skeletal muscle. The loss of DJ-1 resulted in a more than two-fold increase in resting [Ca(2+)](i). While there was no alteration in the resting membrane potential, there was a significant decrease in depolarization-evoked Ca(2+) release from the sarcoplasmic reticulum in the DJ-1 null muscle cells. Consistent with the role of DJ-1 in oxidative stress regulation and mitochondrial functional maintenance, treatments of DJ-1 null muscle cells with resveratrol, a mitochondrial activator, or glutathione, a potent antioxidant, reversed the effects of the loss of DJ-1 on Ca(2+) homeostasis. These results provide evidence of DJ-1's association with Ca(2+) regulatory pathways in mouse skeletal muscle, and suggest the potential benefit of resveratrol to functionally compensate for the loss of DJ-1.

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

Sporadic inclusion-body myositis (s-IBM), the most common muscle disease of older persons, is of unknown cause and lacks successful treatment. Here we summarize diagnostic criteria and discuss our current understanding of the steps in the pathogenic cascade. While it is agreed that both degeneration and mononuclear-cell inflammation are components of the s-IBM pathology, how each relates to the pathogenesis remains unsettled. We suggest that the intra-muscle-fiber degenerative component plays the primary role, leading to muscle-fiber destruction and clinical weakness, since anti-inflammatory treatments are not of sustained benefit. We discuss possible treatment strategies aimed toward ameliorating a degenerative component, for example, lithium and resveratrol. Also discussed are the intriguing phenotypic similarities between s-IBM muscle fibers and the brains of Alzheimer and Parkinson's diseases, the most common neurodegenerative diseases associated with aging. Similarities include, in the respective tissues, cellular aging, mitochondrial abnormalities, oxidative and endoplasmic-reticulum stresses, proteasome inhibition and multiprotein aggregates.