Cystatin C colocalizes with amyloid-beta and coimmunoprecipitates with amyloid-beta precursor protein in sporadic inclusion-body myositis muscles

The Positive Side of the Alzheimer's Disease Amyloid Cross-Interactions: The Case of the Aβ 1-42 Peptide with Tau, TTR, CysC, and ApoA1

Alzheimer's disease (AD) represents a progressive amyloidogenic disorder whose advancement is widely recognized to be connected to amyloid-β peptides and Tau aggregation. However, several other processes likely contribute to the development of AD and some of them might be related to protein-protein interactions. Amyloid aggregates usually contain not only single type of amyloid protein, but also other type of proteins and this phenomenon can be rationally explained by the process of protein cross-seeding and co-assembly. Amyloid cross-interaction is ubiquitous in amyloid fibril formation and so a better knowledge of the amyloid interactome could help to further understand the mechanisms of amyloid related diseases. In this review, we discuss about the cross-interactions of amyloid-β peptides, and in particular Aβ1-42, with other amyloids, which have been presented either as integrated part of Aβ neurotoxicity process (such as Tau) or conversely with a preventive role in AD pathogenesis by directly binding to Aβ (such as transthyretin, cystatin C and apolipoprotein A1). Particularly, we will focus on all the possible therapeutic strategies aiming to rescue the Aβ toxicity by taking inspiration from these protein-protein interactions.

Journey of cystatins from being mere thiol protease inhibitors to at heart of many pathological conditions

Cystatins are thiol proteinase inhibitors (TPI), present ubiquitously in animals, plants and micro-organisms. These are not merely inhibitors rather they are at heart of many pathological conditions ranging from diabetes to renal failure. These are essential for maintenance of protein balance of the cell; once this balance gets disturbed, it may lead to cell death. Thus, cystatins cannot be merely regarded as TPI's as these have been found to play a pivotal role in tumorigenesis and neurodegenerative diseases. Many studies have reported the variation in cystatin level in incidences of different types of cancer; highlighting an important role played by these inhibitors in cancer development and progression. Cystatin C is increasingly replacing creatinine as a biomarker of glomerular filtration rate (GFR) thereby highlighting the importance of this important inhibitor. Some recent studies have also reported the interaction pattern of various anti-cancer drugs with cystatins in a bid to find how these drugs affect this important inhibitors and whether these drugs have any side effect on cystatins. Thus, in this growing disease era it can be said that cystatins are no more just inhibitors blocking the activity of thiol proteases rather they play a pivotal role in variety of pathological conditions.

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.

Intracellular β-amyloid accumulation leads to age-dependent progression of Ca2+ dysregulation in skeletal muscle

Intramyofiber accumulation of β-amyloid fragments (Aβ) is a pathologic hallmark of inclusion-body myositis (IBM), a progressive skeletal muscle disorder. We investigated the temporal pattern of alterations in the resting cytoplasmic [Ca(2+)] ([Ca(2+)](i)) as well as the depolarization-evoked Ca(2+) release from the sarcoplasmic reticulum in skeletal muscle from transgenic mice expressing human βAPP (MCK-βAPP). MCK-βAPP mice show an age-dependent increase in [Ca(2+)](i) along with a reduction in depolarization-evoked Ca(2+) release, which appear well before the other reported aspects of IBM, such as inclusion formation, inflammation, centralized nuclei, atrophy, and skeletal muscle weakness. In the young MCK-βAPP animals the increase in resting [Ca(2+)](i) can be attributed largely to Ca(2+) influx through nifedipine-sensitive Ca(2+) channels. In the adult MCK-βAPP mice, in addition to the nifedipine-sensitive pathway, there is also a substantial contribution by the intracellular compartments to the increase in [Ca(2+)](i). These results suggest that β-amyloid-induced disuption of Ca(2+) handling may represent an early event in the pathogenesis of IBM.

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.

Cystatin superfamily

Cystatins, the classical inhibitors of C1 cysteine proteinases, have been extensively studied and reviewed in the literature. Over the last 20 years, however, proteins containing cystatin domains but lacking protease inhibitory activities have been identified, and most likely more will be described in the near future. These proteins together with family 1, 2, and 3 cystatins constitute the cystatin superfamily. Mounting evidence points to the new roles that some members of the superfamily have acquired over the course of their evolution. This review is focused on the roles of cystatins in: 1) tumorigenesis, 2) stabilization of matrix metalloproteinases, 3) glomerular filtration rate, 4) immunomodulation, and 5) neurodegenerative diseases. It is the goal of this review to get as many investigators as possible to take a second look at the cystatin superfamily regarding their potential involvement in serious human ailments.

How citation distortions create unfounded authority: analysis of a citation network

OBJECTIVE

To understand belief in a specific scientific claim by studying the pattern of citations among papers stating it.

DESIGN

A complete citation network was constructed from all PubMed indexed English literature papers addressing the belief that beta amyloid, a protein accumulated in the brain in Alzheimer's disease, is produced by and injures skeletal muscle of patients with inclusion body myositis. Social network theory and graph theory were used to analyse this network.

MAIN OUTCOME MEASURES

Citation bias, amplification, and invention, and their effects on determining authority.

RESULTS

The network contained 242 papers and 675 citations addressing the belief, with 220,553 citation paths supporting it. Unfounded authority was established by citation bias against papers that refuted or weakened the belief; amplification, the marked expansion of the belief system by papers presenting no data addressing it; and forms of invention such as the conversion of hypothesis into fact through citation alone. Extension of this network into text within grants funded by the National Institutes of Health and obtained through the Freedom of Information Act showed the same phenomena present and sometimes used to justify requests for funding.

CONCLUSION

Citation is both an impartial scholarly method and a powerful form of social communication. Through distortions in its social use that include bias, amplification, and invention, citation can be used to generate information cascades resulting in unfounded authority of claims. Construction and analysis of a claim specific citation network may clarify the nature of a published belief system and expose distorted methods of social citation.

Inclusion body myositis: a degenerative muscle disease associated with intra-muscle fiber multi-protein aggregates, proteasome inhibition, endoplasmic reticulum stress and decreased lysosomal degradation

Sporadic inclusion body myositis (s-IBM), the most common muscle disease of older persons, is of unknown cause, and there is no enduring treatment. Abnormal accumulation of intracellular multi-protein inclusions is a characteristic feature of the s-IBM phenotype, and as such s-IBM can be considered a "conformational disorder," caused by protein unfolding/misfolding combined with the formation of inclusion bodies. Abnormal intracellular accumulation of unfolded proteins may lead to their aggregation and inclusion body formation. The present article is focusing on the multiple proteins that are accumulated in the form of aggregates within s-IBM muscle fibers, and it explores the most recent research advances directed toward a better understanding of mechanisms causing their impaired degradation and abnormal aggregation. We illustrate that, among other factors, abnormal misfolding, accumulation and aggregation of proteins are associated with their inadequate disposal-and these factors are combined with, and perhaps provoked by, an aging intracellular milieu. Other concurrent and possibly provocative phenomena known within s-IBM muscle fibers are: endoplasmic reticulum stress and unfolded protein response, mitochondrial abnormalities, proteasome inhibition, lysosome abnormality and endodissolution. Together, these appear to lead to the s-IBM-specific vacuolar degeneration, and muscle fiber atrophy, concluding with muscle fiber death.

Immunization with amyloid-beta attenuates inclusion body myositis-like myopathology and motor impairment in a transgenic mouse model

Inclusion body myositis (IBM), the most common muscle disease to afflict the elderly, causes slow but progressive degeneration of skeletal muscle and ultimately paralysis. Hallmark pathological features include T-cell mediated inflammatory infiltrates and aberrant accumulations of proteins, including amyloid-beta (Abeta), tau, ubiquitinated-proteins, apolipoprotein E, and alpha-synuclein in skeletal muscle. A large body of work indicates that aberrant Abeta accumulation contributes to the myodegeneration. Here, we investigated whether active immunization to promote clearance of Abeta from affected skeletal muscle fibers mitigates the IBM-like myopathological features as well as motor impairment in a transgenic mouse model. We report that active immunization markedly reduces intracellular Abeta deposits and attenuates the motor impairment compared with untreated mice. Results from our current study indicate that Abeta oligomers contribute to the myopathy process as they were significantly reduced in the affected skeletal muscle from immunized mice. In addition, the anti-Abeta antibodies produced in the immunized mice blocked the toxicity of the Abeta oligomers in vitro, providing a possible key mechanism for the functional recovery. These findings provide support for the hypothesis that Abeta is one of the key pathogenic components in IBM pathology and subsequent skeletal muscle degeneration.

Binding epitopes and interaction structure of the neuroprotective protease inhibitor cystatin C with beta-amyloid revealed by proteolytic excision mass spectrometry and molecular docking simulation

Human cystatin C (HCC) is a protease inhibitor with a propensity to form beta-amyloid (Abeta)-like fibrils and to coassociate with amyloidogenic proteins. Recently, a specific interaction between HCC and Abeta has been found. Here, we report the identification of the Abeta and HCC binding epitopes in the Abeta-HCC complex, using a combination of selective proteolytic excision and high resolution mass spectrometry. Proteolytic excision of Abeta(1-40) on sepharose-immobilized HCC and MALDI-MS identified the epitope Abeta(17-28). On immobilized Abeta(1-40), affinity MS of HCC fragments identified a specific C-terminal epitope, HCC(101-117). Binding specificities of both epitopes were ascertained by ELISA and surface plasmon resonance and by direct electrospray MS of the HCC-Abeta epitope peptide complexes. A structure model of the HCC-Abeta complex by molecular docking simulation showed full agreement with the identified Abeta and HCC epitopes. Inhibition studies in vitro revealed Abeta-fibril inhibiting activity of the HCC(101-117)-epitope. The Abeta-HCC interacting epitopes provide lead structures of neuroprotective inhibitors for AD and HCC amyloidosis therapy.

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.

Biochemistry and Clinical Role of Human Cystatin C

Low molecular-mass plasma proteins play a key role in health and disease. Cystatin C is an endogenous cysteine proteinase inhibitor belonging to the type 2 cystatin superfamily. The mature, active form of human cystatin C is a single non-glycosylated polypeptide chain consisting of 120 amino acid residues, with a molecular mass of 13,343-13,359 Da, and containing four characteristic disulfide-paired cysteine residues. Human cystatin C is encoded by the CST3 gene, ubiquitously expressed at moderate levels. Cystatin C monomer is present in all human body fluids; it is preferentially abundant in cerebrospinal fluid, seminal plasma, and milk. Cystatin C L68Q variant is an amyloid fibril-forming protein with a high tendency to dimerize. It forms self-aggregates with massive amyloid deposits in the brain arteries of young adults, leading to lethal cerebral hemorrhage. The main catabolic site of cystatin C is the kidney: more than 99% of the protein is cleared from the circulation by glomerular ultrafiltration and tubular reabsorption. The diagnostic value of cystatin C as a marker of kidney dysfunction has been extensively investigated in multiple clinical studies on adults, children, and in the elderly. In almost all the clinical studies, cystatin C demonstrated a better diagnostic accuracy than serum creatinine in discriminating normal from impaired kidney function, but controversial results have been obtained by comparing this protein with other indices of kidney disease, especially serum creatinine-based equations. In this review, we present and discuss most of the available data from the literature, critically reviewing conclusions and suggestions for the use of cystatin C in clinical practice. Despite the multitude of clinical data in the literature, cystatin C has not been widely used, perhaps because of a combination of factors, such as a general diffidence among clinicians, the absence of definitive cut-off values, conflicting results in clinical studies, no clear evidence on when and how to request the test, the poor commutability of results, and no accurate examination of costs and of its routine use in a stat laboratory.

Cystatin C reduces the in vitro formation of soluble Abeta1-42 oligomers and protofibrils

There are an increasing number of genetic and neuropathological observations to suggest that cystatin C, an extracellular protein produced by all nucleated cells, might play a role in the pathophysiology of sporadic Alzheimer's disease (AD). Recent observations indicate that small and large soluble oligomers of the beta-amyloid protein (Abeta) impair synaptic plasticity and induce neurotoxicity in AD. The objective of the present study was to investigate the influence of cystatin C on the production of such oligomers in vitro. Co-incubation of cystatin C with monomeric Abeta1-42 significantly attenuated the in vitro formation of Abeta oligomers and protofibrils, as determined using electron microscopy (EM), dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting, thioflavin T (ThT) spectrofluorimetry and gel chromatography. However, cystatin C did not dissolve preformed Abeta oligomers. Direct binding of cystatin C to Abeta was demonstrated with the formation of an initial 1:1 molar high-affinity complex. These observations suggest that cystatin C might be a regulating element in the transformation of monomeric Abeta to larger and perhaps more toxic molecular species in vivo.

AbetaPP-overexpression and proteasome inhibition increase alphaB-crystallin in cultured human muscle: relevance to inclusion-body myositis

Amyloid-beta precursor protein (AbetaPP) and its fragment amyloid-beta (Abeta) are increased in s-IBM muscle fibers and appear to play an important role in the pathogenic cascade. alphaB-Crystallin (alphaBC) was shown immunohistochemically to be accumulated in s-IBM muscle fibers, but the stressor(s) influencing alphaBC accumulation was not identified. We now demonstrate, using our experimental IBM model based on genetic overexpression of AbetaPP into cultured normal human muscle fibers, that: (1) AbetaPP overexpression increased alphaBC 3.7-fold (p=0.025); (2) additional inhibition of proteasome with epoxomicin increased alphaBC 7-fold (p=0.002); and (3) alphaBC physically associated with AbetaPP and Abeta oligomers. We also show that in biopsied s-IBM muscle fibers, alphaBC was similarly increased 3-fold (p=0.025) and physically associated with AbetaPP and Abeta oligomers. We propose that increased AbetaPP is a stressor increasing alphaBC expression in s-IBM muscle fibers. Determining the consequences of alphaBC association with Abeta oligomers could have clinical therapeutic relevance.

The role of cystatin C in cerebral amyloid angiopathy and stroke: cell biology and animal models

A variant of the cysteine protease inhibitor, cystatin C, forms amyloid deposited in the cerebral vasculature of patients with hereditary cerebral hemorrhage with amyloidosis, Icelandic type (HCHWA-I), leading to cerebral hemorrhages early in life. However, cystatin C is also implicated in neuronal degenerative diseases in which it does not form the amyloid protein, such as Alzheimer disease (AD). Accumulating data suggest involvement of cystatin C in the pathogenic processes leading to amyloid deposition in cerebral vasculature and most significantly to cerebral hemorrhage in patients with cerebral amyloid angiopathy (CAA). This review focuses on cell culture and animal models used to study the role of cystatin C in these processes.

Homocysteine-induced endoplasmic reticulum protein (Herp) is up-regulated in sporadic inclusion-body myositis and in endoplasmic reticulum stress-induced cultured human muscle fibers

Herp is a stress-response protein localized in the endoplasmic reticulum (ER) membrane. Herp was proposed to improve ER-folding, decrease ER protein load, and participate in ER-associated degradation (ERAD). Intra-muscle-fiber ubiquitinated multiprotein-aggregates containing, among other proteins, either amyloid-beta (Abeta) or phosphorylated tau are characteristic of sporadic inclusion-body myositis (s-IBM). ER stress and proteasome inhibition appear to play a role in s-IBM pathogenesis. We have now studied Herp in s-IBM muscle fibers and in ER-stress-induced or proteasome-inhibited cultured human muscle fibers. In s-IBM muscle fibers: (i) Herp was strongly immunoreactive in the form of aggregates, which co-localized with Abeta, GRP78, and beta2 proteasome subunit; (ii) Herp mRNA and protein were increased. In ER-stress-induced cultured human muscle fibers: (i) Herp immunoreactivity was diffusely increased; (ii) Herp mRNA and protein were increased. In proteasome-inhibited cultured human muscle fibers: (i) Herp immunoreactivity was in the form of aggregates; (ii) Herp protein was increased, but its mRNA was not. Accordingly, in s-IBM muscle fibers: (i) increase of Herp might be due to both ER-stress and proteasome inhibition; (ii) co-localization of Herp with Abeta, proteasome, and ER-chaperone GRP78 could reflect its possible role in processing and degradation of cytotoxic proteins in ER.

Expression of cystatin C prevents oxidative stress-induced death in PC12 cells

Cystatin C, an inhibitor of cysteine proteinases, is suggested to be involved in oxidative stress-induced apoptosis of cultured CNS neurons and various neuronal diseases in vivo; however, little is known about its mechanism of action. To address the role cystatin C plays in oxidative stress-induced neuronal cell death, we established PC12 cell lines that stably expressed rat cystatin C. These cystatin C-expressing PC12 cells showed remarkable resistance to high (50%) oxygen atmosphere. This resistance correlate with expression levels of cystatin C, demonstrating that cystatin C has a protective effect on high oxygen-induced cell death. In contrast, in a normal (20%) oxygen atmosphere neither control nor cystatin C-expressing PC12 cells showed a significant change in the number of living cells, indicating that cystatin C does not play an important role in the regulation of cellular proliferation. Furthermore, the cystatin C-expressing cell line also resisted other oxidative stresses, including glutamate- and 13-L-hydroperoxylinoleic acid (LOOH)-induced cell death. These results demonstrate that cystatin C has protective effects against various oxidative stresses that induce cell death.

Proteasome inhibition and aggresome formation in sporadic inclusion-body myositis and in amyloid-beta precursor protein-overexpressing cultured human muscle fibers

The 26S proteasome system is involved in eliminating various proteins, including ubiquitinated misfolded/unfolded proteins, and its inhibition results in cellular accumulation of protein aggregates. Intramuscle-fiber ubiquitinated multiprotein-aggregates are characteristic of sporadic inclusion-body myositis (s-IBM) muscle fibers. Two major types of aggregates exist, containing either amyloid-beta (Abeta) or phosphorylated tau (p-tau). We have now asked whether abnormalities of the 26S proteasome contribute to s-IBM pathogenesis and whether the multiprotein aggregates have features of aggresomes. Using cultured human muscle fibers we also studied the effect of amyloid-beta precursor protein (AbetaPP) overexpression on proteasome function and the influence of proteasome inhibition on aggresome formation. We report that in s-IBM muscle biopsies 26S proteasome subunits were immunodetected in the gamma-tubulin-associated aggresomes, which also contained Abeta, p-tau, ubiquitin, and HSP70. In addition, a) expression of proteasome subunits was greatly increased, b) the 20Salpha proteasome subunit co-immunoprecipitated with AbetaPP/Abeta, and c) the three major proteasomal proteolytic activities were reduced. In cultured muscle fibers, AbetaPP-overexpressing fibers displayed diminished proteasomal proteolytic activities, and addition of proteasome inhibitor strikingly increased aggresome formation. Accordingly, proteasome dysfunction in s-IBM muscle fibers may play a role in accumulation of misfolded, potentially cytotoxic proteins and may be induced by increased intracellular AbetaPP/Abeta.

Myostatin is increased and complexes with amyloid-beta within sporadic inclusion-body myositis muscle fibers

Myostatin is a negative regulator of muscle mass and strength. Sporadic inclusion-body myositis (s-IBM) is the most common degenerative muscle disease of older persons and is characterized by pronounced muscle wasting. s-IBM is of unknown etiology and pathogenesis, and it lacks definitive treatment. We have now demonstrated in samples from 12 s-IBM biopsies that: (1) by light and electron microscopic immunocytochemistry, myostatin/myostatin precursor is accumulated within muscle fibers and co-localized with amyloid-beta (Abeta); (2) by immunoblots, both myostatin and myostatin precursor are increased; and (3) by immunoprecipitation, myostatin precursor complexes with Abeta. Our study suggests that myostatin/myostatin precursor, either alone, or bound to Abeta, may play a novel role in the pathogenesis of s-IBM.

Inflammatory disorders of muscle: progress in polymyositis, dermatomyositis and inclusion body myositis

PURPOSE OF REVIEW

To provide an update on the major advances in inflammatory myopathies.

RECENT FINDINGS

Polymyositis is an uncommon disorder that can be misdiagnosed when the old, and never validated, criteria of Bohan and Peter are used. New diagnostic criteria were recently introduced, in which the MHC/CD8 complex is considered a specific immunopathological marker because it distinguishes the antigen-driven inflammatory cells that characterize polymyositis and sporadic inclusion-body myositis from the non-specific, secondary inflammation seen in other disorders, such as dystrophies. In sporadic inclusion-body myositis the inflammatory cells invade non-vacuolated fibers, whereas the vacuolated fibers are not invaded by T cells, implying two independent processes, a primary immune process with antigen-driven T cells identical to polymyositis, and a degenerative process in which beta-amyloid and amyloid-related proteins participate in vacuolar degeneration. In polymyositis and sporadic inclusion-body myositis, antigen-specific and clonally expanded autoinvasive T cells persist for years, even in different muscles, as reconfirmed by proof-of-principle techniques involving CDR3 spectratyping combined with laser microdissected single-cell polymerase chain reaction of the T-cell receptor genes. The formation of immunological synapse between autoinvasive T cells and muscle fibers was recently strengthened by the upregulation of co-stimulatory molecules ICOS/ICOS-L and PD-L1. A new, distinct myopathy characterized by T-cell-triggered macrophage hyperactivation has now been recognized in patients with dermatomyositis-like disease.

SUMMARY

Despite recent progress, the antigen(s) responsible for T-cell activation in polymyositis and sporadic inclusion-body myositis and the cause of vacuolar degeneration in sporadic inclusion-body myositis remain unclear. Newer, more aggressive immunotherapies may be encouraging, but control trials are needed to prove efficacy.

Oxidative imbalance and cathepsin D changes as peripheral blood biomarkers of Alzheimer disease: A pilot study

Markers of oxidative stress in peripheral blood from patients with Alzheimer disease (AD) were analyzed. Thirty-three AD patients were recruited. Plasma antioxidant power (AOP), plasma Cystatin C as well as Cathepsin D in PBL were evaluated. We found that the AOP levels were significantly decreased in AD patients if compared to healthy donors, while the plasma level of Cystatin C was significantly higher. Importantly, a significantly decreased expression of Cathepsin D in PBL was also observed. These results suggest that oxidative imbalance in the peripheral blood of AD patients could mirror oxidative changes previously described in the central nervous system.

The contribution of microscopy to the study of Alzheimer's disease, amyloid plaques and Abeta fibrillogenesis

A broad survey is presented in this chapter, dealing with the impact that microscopy has made to the study of Alzheimer's disease, amyloid plaques and amyloid-beta fibrillogenesis. This includes classical light microscopy and the modem immunolabelling and confocal microscopies, together with the contribution of transmission electron microscopy and atomic force microscopy. Whilst usefully standing alone, the individual microscopies often contribute most effectively when they are integrated with cellular, biophysical and molecular approaches.

Molecular pathology and pathogenesis of inclusion-body myositis

We summarize the molecular phenotype, diagnostic criteria, and the newest advances related to seeking the pathogenic mechanism(s) of sporadic inclusion-body myositis (s-IBM), a muscle disease usually of persons over age 50. On the basis of our research, several processes seem to be important in relation to the still-speculative pathogenesis: 1) increased transcription and accumulation of amyloid-beta precursor protein (AbetaPP), and accumulation of its proteolytic fragment Abeta; 2) abnormal accumulation of cholesterol, caveolin-1, and apolipoprotein E; 3) oxidative stress; 4) accumulations of intramuscle fiber multiprotein aggregates; and 5) evidence that unfolded/misfolded proteins participate in s-IBM pathogenesis. Our basic hypothesis is that overexpression of AbetaPP within the aging muscle fibers is an early upstream event causing a subsequent pathogenic cascade.

Autophagic vacuoles are enriched in amyloid precursor protein-secretase activities: implications for β-amyloid peptide over-production and localization in Alzheimer’s disease

In Alzheimer's disease (AD), the neuropathologic hallmarks of beta-amyloid deposition and neurofibrillary degeneration are associated with early and progressive pathology of the endosomal-lysosomal system. Abnormalities of autophagy, a major pathway to lysosomes for protein and organelle turnover, include marked accumulations of autophagy-related vesicular compartments (autophagic vacuoles or AVs) in affected neurons. Here, we investigated the possibility that AVs contain the proteases and substrates necessary to cleave the amyloid precursor protein (APP) to A beta peptide that forms beta-amyloid, a key pathogenic factor in AD. AVs were highly purified using a well-established metrizamide gradient procedure from livers of transgenic YAC mice overexpressing wild-type human APP. By Western blot analysis, AVs contained APP, beta CTF - the beta-cleaved carboxyl-terminal domain of APP, and BACE, the protease-mediating beta-cleavage of APP. beta-Secretase activity measured against a fluorogenic peptide was significantly enriched in the AV fraction relative to whole-liver lysate. Compared to other recovered subcellular fractions, AVs exhibited the highest specific activity of gamma-secretase based on a fluorogenic assay and inhibition by a specific inhibitor of gamma-secretase, DAPT. AVs were also the most enriched subcellular fraction in levels of the gamma-secretase components presenilin and nicastrin. Immunoelectron microscopy demonstrated selective immunogold labeling of AVs with antibodies specific for the carboxyl termini of human A beta 40 and A beta 42. These data indicate that AVs are a previously unrecognized and potentially highly active compartment for A beta generation and suggest that the abnormal accumulation of AVs in affected neurons of the AD brain contributes to beta-amyloid deposition.

Binding of cystatin C to Alzheimer’s amyloid β inhibits in vitro amyloid fibril formation

The colocalization of cystatin C, an inhibitor of cysteine proteases, with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients may reflect cystatin C involvement in amyloidogenesis. We therefore sought to determine the association of cystatin C with Abeta. Immunofluorescence analysis of transfected cultured cells demonstrated colocalization of cystatin C and beta amyloid precursor protein (betaAPP) intracellularly and on the cell surface. Western blot analysis of immunoprecipitated cell lysate or medium proteins revealed binding of cystatin C to full-length betaAPP and to secreted betaAPP (sbetaAPP). Deletion mutants of betaAPP localized the cystatin C binding site within betaAPP to the Abeta region. Cystatin C association with betaAPP resulted in increased sbetaAPP but did not affect levels of secreted Abeta. Analysis of the association of cystatin C and Abeta demonstrated a specific, saturable and high affinity binding between cystatin C and both Abeta(1-42) and Abeta(1-40). Notably, cystatin C association with Abeta results in a concentration-dependent inhibition of Abeta fibril formation.

Overexpression of human cystatin C in transgenic mice does not affect levels of endogenous brain amyloid Beta Peptide

Cystatin C, an inhibitor of cysteine proteases, colocalizes with amyloid beta (Abeta) in parenchymal and vascular amyloid deposits in brains of Alzheimer's disease (AD) patients, suggesting that cystatin C has a role in AD. Cystatin C also colocalizes with beta amyloid precursor protein (betaAPP) in transfected cultured cells. In vitro analysis of the association between the two proteins revealed that binding of cystatin C to full-length betaAPP does not affect the level of Abeta secretion. Here we studied the effect of in vivo overexpression of cystatin C on the levels of endogenous brain Abeta. We have generated lines of transgenic mice expressing either wild-type human cystatin C or the Leu68Gln variant that forms amyloid deposits in the cerebral vessels of Icelandic patients with hereditary cerebral hemorrhage, under control sequences of the human cystatin C gene. Western blot analysis of brain homogenates was used to select lines of mice expressing various levels of the transgene. Analysis of Abeta40 and Abeta42 concentrations in the brain showed no difference between transgenic mice and their nontransgenic littermates. Thus, in vivo overexpression of human cystatin C does not affect Abeta levels in mice that do not deposit Abeta.

Association of Human Neuroglobin with Cystatin C, a Cysteine Proteinase Inhibitor

Neuroglobin (Ngb) is a newly discovered globin that is expressed in vertebrate brain. It has been reported that Ngb levels increase in neurons in response to oxygen deprivation, and that Ngb protects neurons from hypoxia. However, the mechanism of this neuroprotection remains unclear. In the present study, we identified human cystatin C, a cysteine proteinase inhibitor, as an Ngb-binding protein by using a yeast two-hybrid system. Surface plasmon resonance experiments verified that Ngb binds to cystatin C dimers, not to the monomers. Because both intracellular cystatin C and the amyloidogenic variant of cystatin C form dimers, Ngb may modulate the intracellular transport (or secretion) of cystatin C to protect against neuronal death under conditions of oxidative stress and/or it may have a role in the development of neurodegenerative diseases.

Endoplasmic reticulum stress and unfolded protein response in inclusion body myositis muscle

Proteins in the endoplasmic reticulum (ER) require an efficient system of molecular chaperones whose role is to assure their proper folding and to prevent accumulation of unfolded proteins. The response of cells to accumulation of unfolded proteins in the ER is termed "unfolded protein response" (UPR). UPR is a functional mechanism by which cells attempt to protect themselves against ER stress, resulting from the accumulation of the unfolded/misfolded proteins. Because intracellular inclusions, containing either amyloid-beta (Abeta) or phosphorylated tau, are the characteristic feature of sporadic inclusion body myositis (s-IBM) muscle biopsies, we studied expression and immunolocalization of five ER chaperones, calnexin, calreticulin, GRP94, BiP/GRP78, and ERp72, in s-IBM and control muscle biopsies. Physical interaction of the ER chaperones with amyloid-beta precursor protein (AbetaPP) was studied by a combined immunoprecipitation/immunoblotting technique in s-IBM and control muscle biopsies, and in AbetaPP-overexpressing cultured human muscle fibers. In all s-IBM muscle biopsies, all five of the ER chaperones were immunodetected in the form of inclusions that co-localized with amyloid-beta. By immunoblotting, expression of ER chaperones was greatly increased as compared to the controls. By immunoprecipitation/immunoblotting experiments, ER chaperones co-immunoprecipitated with AbetaPP. Our studies provide evidence of the UPR in s-IBM muscle and demonstrate for the first time that the ER chaperones calnexin, calreticulin, GRP94, BiP/GRP78, and ERp72 physically associate with AbetaPP in s-IBM muscle, suggesting their playing a role in AbetaPP folding and processing.

Proposed pathogenetic cascade of inclusion-body myositis: importance of amyloid-beta, misfolded proteins, predisposing genes, and aging

PURPOSE OF REVIEW

Sporadic inclusion-body myositis, the most common muscle disease of older persons, is of unknown cause, and there is no successful treatment. Interest in sporadic inclusion-body myositis has been enhanced by the recent identification within the sporadic inclusion-body myositis muscle fibers of several abnormally accumulated proteins, which provides novel and important clues to the pathogenesis of sporadic inclusion-body myositis.

RECENT FINDINGS

This article summarizes the most recent findings leading to better understanding of the players in the pathogenetic cascade. It is suggested that lymphocytic inflammatory component is probably secondary, and it may contribute only slightly to muscle fiber damage in sporadic inclusion-body myositis. However, it is proposed that the identified abnormal accumulation, aggregation, and misfolding of proteins, combined with and perhaps provoked by an aging intracellular milieu, more essentially lead to the vacuolar degeneration and atrophy of the muscle fibers that are specific to sporadic inclusion-body myositis. Abnormal accumulations of the amyloid-beta precursor protein and of its proteolytic fragment, amyloid-beta, associated with the aging cellular muscle fiber environment, appear to be key pathogenic events.

SUMMARY

In conceptualizing a treatment for sporadic inclusion-body myositis, the accumulations of amyloid-beta42 and other unfolded proteins are now phenomena to be reckoned with. One would like to stop intracellular increase of the unfolded/misfolded proteins by reducing their formation and/or increasing their disposal. In addition, the identification of factors that would decrease intra-muscle fiber expressions of beta- and gamma-secretases might lead to decreased production of putatively myotoxic oligomeric amyloid-beta42. Better understanding of the mechanisms and consequences of genes that predispose to sporadic inclusion-body myositis, and of human muscle fiber aging, could also provide new avenues toward the therapy of sporadic inclusion-body myositis. How to therapeutically capitalize on the new findings is now the challenge.