These 22 articles are from a conference held on inclusion body myositis (s-IBM) - Inclusion-body myositis: Clinical and pathologic aspects, and basic research potentially relevant to treatment. January 26-28, 2005 in Santa Monica. The TMA funded the Conference and the Muscular Dystrophy Association assisted by funding the printing and distribution of the Conference report. The 22 articles were published in electronic format as an Expedited E-Pub at www.neurology.org on December 16, 2005. They appear in print in Neurology Volume 66(2) Supplement 1 January 24, 2006. Abstracts and some very selective excerpts are offered here.
Table of Contents
1). December 2005
Neurology. 2005 Dec 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1): Si
Inclusion-body myositis. Clinical and pathologic aspects, and basic research potentially relevant to treatment.
Askanas V, Dalakas MC, Engel WK. Introductory Paper
From the Department of Neurology (Drs. Askanas and Engel), University of Southern California, Keck School of Medicine, Los Angeles; and National Institutes of Health (Dr. Dalakas), Neuromuscular Diseases Section, NINDS, Bethesda.
Two hypotheses predominate regarding the key pathogenic mechanisms involved in s-IBM: an amyloid-b-related degenerative process and an immune dysregulation. Ultimately, both may be considered important, and their possible interrelationship may be clarified. An intriguing feature is the accumulation within s-IBM muscle fibers of amyloid-b (Ab), phosphorylated tau, and at least 20 other proteins that are also accumulated in Alzheimer brain. In the s-IBM muscle fibers, there is evidence of misfolding of proteins, pathologic proteinaceous inclusions including aggresomes, abnormalities of the two protein-disposal systems involving the ubiquitin proteasome pathway and the lysosomes, mitochondrial dysfunctions, and oxidative stress. The pronounced T-cell inflammation can be striking, and it is characterized by activated, antigen-driven, cytotoxic CD8+ T-cells.
This supplement is based on a small 'think-tank' conference that was organized to promote ideas regarding new treatments for s-IBM. We have obtained the participation of outstanding basic scientists from various fields not directly involving s-IBM but ones related to Alzheimer disease, the ubiquitin-proteasome system, virology, autoimmune cytotoxicity, RNA interference, protein misfolding, and intracellular cholesterol metabolism. They have enthusiastically contributed their knowledge and experience to the conference, and have also generously contributed their state-of-the-art chapters to facilitate the formulation of ideas concerning possibilities relevant to new treatments for s-IBM.
2). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1): S1-S6
A perspective on sporadic inclusion-body myositis. The role of aging and inflammatory processes.
From the Andrus Gerontology Center, Department of Biological Sciences, University of Southern California, Los Angeles, CA
Abstract--Sporadic inclusion-body myositis (sIBM) is an age-related condition manifested after midlife. This review points out salient features of sIBM that are shared with normal aging in muscle and with inflammatory changes in vascular atheromas and senile plaques of Alzheimer disease (AD). The amyloid precursor protein (APP) and derived Ab peptides are found in both AD and sIBM. Because transgenic expression of human APP induces sIBM like changes, it is of potential interest that an inducer of APP, IL-1, increases during aging in mouse muscle. Because various subsets of the usual aging changes in aging brain, muscle, and vessels can be attenuated in rodents by caloric intake and possibly in humans by drugs with anti-inflammatory and anticoagulant activities, this study suggests that diet and inflammation may be useful experimental variations in exploring the pathogenesis of sIBM.
The evolutionary depth of the toxic Abeta sequence is remarkable, extending at least 300 million years back into the paleozoic vertebrate stem lines: fish and the great apes and humans have functionally equivalent Abeta sequences. Although aging rodent brains do show some accumulation of their endogenous Abeta sequence during aging, the increases are modest and no amyloid fibrils are formed. On this basis, the author suggests that sIBM will be less common in wild type aging rodents than humans, whereas aging primates should also show sIBM because of their similar APP sequence to humans.
Several muscle changes of normal aging are pertinent to sIBM. The most obvious is the progressive increase of mtDNA deletions in aging skeletal muscle and cardiac muscle, which are localized to COX negative fibers. Thus, aging skeletal muscle becomes a mosaic of fibers with a spectrum of mtDNA deletions. Because similar COX-negative fibers with mtDNA deletions are also a hallmark of sIBM, the author suggests the hypothesis that sIBM arises in such COX-negative fibers.
. . . the author suggests that mtDNA deletions could be the initiating event, with subsequent cell stress that induces IL-1 and APP in a feedforward cascade. Although average muscle APP did not increase with aging, it would still be worth a look at APP expression at a cell level by immunohistochemistry or in situ hybridization, because larger increases might be found in damaged fibers, especially those with mtDNA deletions.
The 'inflammatory burden' is being recognized as a general indicator of function and future risk of morbidity.
A remarkable and unexpected generalization may be at hand: anti-inflammatory drugs and statins give general protection against chronic diseases of aging. It is now widely accepted that vascular disease, either first event or recurrence, is lowered 30% to 50% by aspirin and statins. Moreover, several cancers are similarly decreased by NSAIDs (colorectal and esophageal), and there may be a benefit of aspirin and statins to risk of breast cancer. The possibility of benefits to AD from NSAIDs, aspirin, and statins is under intense study. The impact of these widely used drugs may be influenced by the apoE genotype, because apoE4 allele is proinflammatory as noted above.
Caloric restriction is another anti-inflammatory paradigm that may be useful experimental manipulations in the transgenic sIBM models. Caloric restriction attenuates mtDNA deletions and muscle fiber loss in rodent models. The mechanism may be to lower blood glucose, because mtDNA deletions in skeletal muscle are accelerated by chronic hyperglycemia in humans in proportion to the duration of diabetes and in rodent smooth muscle. Caloric restriction also increases expression of genes for free radical scavenging in muscle mitochondria. Because these same variations also influence the amount of 8-hydroxyguanosine (8-OHG) in mtDNA, it is hypothesized that blood glucose influences the rate of mtDNA oxidation. Besides COX-negative fibrils and 8-OHG, caloric restriction also attenuates markers of oxidative stress in aging muscle and other tissues.
The author concludes with several suggestions for future studies on sIBM based on this brief review:
1. Close examination of the overlap between normal aging changes in muscle and the characteristics of sIBM, particularly mtDNA deletions and COX negative fibrils and the expression of IL-1 and APP. Herein may be found the 'age milieu' for sIBM. It might be predicted that earliest stages of sIBM arise in COX-negative muscle fibers and that APP inductions are subsequent, because of evidence that elevated IL-1b induces APP.
2. In sIBM, transgenics define the role of soluble toxic Ab forms and hybrid human-rodent Ab structures.
3. The influence of blood glucose levels on the onset and progression of sIBM in transgenic APP models, in vivo and in vitro.
4. Relationship of sIBM to other inflammatory processes and diseases of aging.
5. The influence of salicylate, NSAIDs and statins on models of sIBM and in human populations.
6. The influence of apoE4 alleles on the inflammatory aspects of sIBM in human patients and in apoE allele targeted replacement mice.
7. Comparative studies on sIBM with aging, which should be rare in rodents because of their divergent APP sequence, but like humans in primates because of their similar APP sequence.
3). December 2005
NEUROLOGY 2006;66(Suppl 1):S7-S19
The ubiquitin proteolytic system From a vague idea, through basic mechanisms, and onto human diseases and drug targeting
Aaron Ciechanover, MD, DSc
Translation of the genetic code to proteins was a main focus of biological research before the 1980s. How proteins are removed had remained a neglected area of research. With the discovery of the lysosome, it was suggested that cellular proteins are degraded within this organelle. Yet, a growing body of experimental evidence had strongly suggested that intracellular proteolysis is largely nonlysosomal; however, the mechanism(s) involved had remained obscure. The discovery of modification of protein substrates by ubiquitin and their subsequent degradation by the downstream 26S proteasome has resolved the enigma. Later developments have broadened the scope of the ubiquitin system beyond proteolysis, and we now know that modification by ubiquitin and ubiquitin-like proteins serve many nonproteolytic functions as well.
4). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S20-S29
Inclusion-body myositis. Clinical, diagnostic, and pathologic aspects.
Engel WK, Askanas V.
From the Neuromuscular Center, Department of Neurology, University of Southern California Keck School of Medicine, Good Samaritan Hospital, Los Angeles, CA.
Abstract--The diagnostic aspects of sporadic inclusion-body myositis (s-IBM), and a few comments on our own approach to its treatment, are presented to foster the goals of this symposium, which was organized to provoke new ideas concerning the cause and treatment of this currently unsolvable disease. s-IBM is the most common, progressive, debilitating muscle disease beginning in persons over age 50 years, and it is more common in men. Diagnostic parameters reviewed are clinical, muscle-biopsy histochemistry, electrophysiologic and CSF evaluations. Overall, the degenerative phenomena in s-IBM muscle fibers seem to be the major cause of the progressive, unstoppable weakness, rather than the lymphocytic inflammation. Available treatments are of only slight, temporary benefit for only some s-IBM patients, indicating a desperate need for definitive therapies.
The progressive course of s-IBM leads slowly to severe disability. Finger functions can become very impaired, such as for manipulating pens, keys, buttons, and zippers, pulling handles, and firmly grasping handshakes. Arising from a chair becomes difficult. Walking becomes more precarious. Sudden falls, sometimes resulting in major injury to the skull or other bones, can occur, even from walking on minimally-irregular ground or from other minor imbalances outside or in the home, due to weakness of quadriceps and gluteus muscles depriving the patient of automatic posture maintenance. A foot-drop can increase the likelihood of tripping. Dysphagia can occur, usually caused by upper esophageal constriction that often can be symptomatically improved, for several months to years, by bougie dilation per a GI or ENT physician. Respiratorymuscle weakness can sometimes eventuate.
Neuropathy. In s-IBM, a neuropathy component have been recognized by ourselves, and by others. Our own studies indicate that it often is of dysschwannian type.
Monoclonal SMI-31 antibody, originally made to react with phosphorylated neurofilament heavy-chain, recognizes p-tau of PHFs within s-IBM muscle fibers and AD brain. This antibody, which can be used in a very high dilution (1:1000), is highly specific and economic. If SMI-31 antibody is not available, antiubiquitin antibody can be used to react with both p-tau and Ab deposits within s-IBM muscle fibers. These stains together differentiate s-IBM from polymyositis and dermatomyositis, which do not have intrafiber congophilic or ubiquitin-positive deposits.
Nerve conduction velocities (NCVs) in some s-IBM patients we have found to be abnormally slow and reflect a dysschwannian ('demyelinative') polyneuropathy. When present in an s-IBM patient, this pattern strongly suggests a component of dysimmune neuropathy, viz. a CIDP (chronic immune dysschwannian polyneuropathy, our preferred term to emphasize the cell that is the dysimmune victim and which must be therapeutically protected). This likelihood is enhanced in a patient if the CSF protein is elevated above the normal of 45 mg/dL, and if there are serum markers of dysimmunity, such as a monoclonal antibody, free light-chains, circulating immune complexes, or tissue-, cell-, or protein specific antibodies.
A good treatment of s-IBM should produce increased strength, because muscle fibers (cells) can repair and regenerate. The overall difficulty is that in sIBM the regenerative fibers seem to not get a chance for sustained, effective rematuration, probably because they become afflicted by the basic degenerative process. (This raises an unanswered question of possible cell-to-cell extracellular transfer of myotoxic molecules.)
'Cocktail Royal.' As speculative cytoprotection since 1997, one 73-year-old man has been taking for 8 years our empiric combination. It consists of daily high-doses: L-carnitine 900 mg 5X, Co-Q10 100 mg 4X, B-1 100 mg, B-2 100 mg, B-6 100 mg, E 1000 mg 3X, and s.q. B-12 1 mg.
Better treatment is certainly needed. To know the unknown at the very top of the pathogenic cascade would sharpen the therapeutic focus. Drugs must, of course, be safe, target the muscle fibers, and not damage other organs. Drugs for s-IBM should be easier to develop than ones for AD, because they would not have to cross the blood-brain barrier. For both, they would need to effect benefit intracellularly.
5). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S30-S32
The current status of treatment for inclusion-body myositis.
From the Departments of Neurology, Medicine, Pathology and Laboratory Medicine, and Pediatrics, University of Rochester School of Medicine and Dentistry, Rochester, NY.
Abstract--There is no established treatment that improves, arrests, or slows the progression of inclusion-body myositis (IBM). Many anti-inflammatory, immunosuppressant, or immunomodulating agents have been administered to patients with IBM but the design of clinical trials was such that it can only be concluded that none produced rapid improvement. The natural history of the disease is for stabilization or improvement in a third of patients for 6 months or more. Thus some agents that did not produce dramatic benefit may have been prematurely abandoned. However, because high-dose prednisone worsens strength while decreasing inflammation but increases amyloid accumulation, alternative targets for intervention and novel treatment strategies are needed.
One open but prospective prednisone treatment trial in IBM deserves specific comment.
. . .This study suggests that prednisone worsened IBM (because the natural history stabilizes or improves in one-third of patients). It also suggests that a fall in CK is not a useful marker for a favorable response to treatment. Most importantly it suggests that anti-inflammatory treatment, even when successful at reducing inflammation, may not be effective.
Pain, in particular, is not usual in IBM and its response to treatment can not be considered a response of the myopathy of IBM.
A study of the natural history of IBM noted that one-third of cases appear stable or show improvement for periods of 6 months or more. Clearly if such cases were given an agent, patient and physician would be tempted to conclude that there was a benefit from treatment.
The failure of corticosteroids and many other immune active agents in IBM has not dampened enthusiasm for trying new classes of agents that have immune modulating effects. TNF-alpha receptor blockers, calcineurin inhibitors, and anti-integrins are each under active discussion as possible treatments. There has been progress in understanding the importance of amyloid-B, misfolded proteins and genetic predisposition, 20 all in the context of aging. These will form the basis for considering new strategies for treatment.
6). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S33-S38
Inflammatory, immune, and viral aspects of inclusion-body myositis.
From the Neuromuscular Diseases Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD.
Abstract--Muscle biopsies from patients with sporadic inclusion-body myositis (sIBM) consistently demonstrate that the inflammatory T cells almost invariably invade intact (not vacuolated) fibers, whereas the vacuolated fibers are rarely invaded by T cells. This indicates two concurrently ongoing processes, an autoimmune mediated by cytotoxic T cells and a degenerative manifested by the vacuolated muscle fibers and deposits of amyloid-related proteins. The autoimmune features of IBM are highlighted by the strong association of the disease with: a) HLA I, II antigens, in frequency identical to classic autoimmune diseases; b) other autoimmune disorders in up to 32% of the patients, autoantibodies, paraproteinemias, or immunodeficiency; c) HIV and HTLV-I infection with increasingly recognized frequency (up to 13 known cases); and d) antigen-specific, cytotoxic, and clonally expanded CD8+ autoinvasive T cells with rearranged T-cell receptor genes that persist over time, even in different muscles, and invade muscle fibers expressing MHC-I antigen and costimulatory molecules. In contrast to IBM, in various dystrophies the inflammatory cells are clonally diverse and the muscle fibers do not express MHC-I or costimulatory molecules in the pattern seen in IBM. Like other chronic autoimmune conditions with coexisting inflammatory and degenerative features (i.e., primary progressive MS), IBM is resistant to conventional immunotherapies. Recent data suggest that strong anti-T cell therapies can be promising and they are the focus of ongoing research.
Table: Factors supporting the immunopathogenesis of sIBM
1. Immunogenetic association with DRb10301, DQb10201 alleles and B8-DR3-DR52-DQ2 haplotype; the HLA-A-haplotype is associated with earlier disease onset
2. Sporadic IBM can occur in family members of the same generation (familial inflammatory IBM), as seen with other autoimmune disorders.
3. Association with other autoimmune disorders and autoantibodies in frequency analogous to the one seen in other autoimmune disorders (i.e., MG, LEMS).
4. Increased association with paraproteinemia (22.8%) in frequency significantly higher than age-matched controls (2%).
5. Association with common variable immunodeficiency and natural killer cells.
6. Association with HIV and HTLV-1 infection, with increasingly recognized frequency (up to 13 cases reported).
7. The CD8+ autoinvasive T cells: a) Surround MHC-I expressing fibers (MHC-I/CD8+ lesion) b) Express perforin and activation markers of cytotoxicity; c) Are clonally expanded with restricted ammino acid sequences in the CDR3 region of the T cell receptors (TCR); and d) TCR families persist over time even in different muscles.
8. There is ubiquitous upregulation of MHC-I antigen and the costimulatory molecules BB1, ICOS-L and CD40 on muscle fibers, even on those not invaded by T cells, while the counterreceptors CD28, CTLA-4, ICOS and CD40L are overexpressed on the autoinvasive T cells.
9. There is strong upregulation of cytokines, chemokines and their receptors at the protein, mRNA, and gene levels.
Figure 2. Molecules, receptors and their ligands involved in the transgression of T cells through the endothelial cell wall and recognition of antigens on muscle fibers of patients with sIBM. LFA I/ICAM-I binding and TCR scanning for antigen initiates the formation of an immunologic synapse between MHC-I and TCR. Stimulation is supported and enhanced by the engagement of costimulatory molecules BB1, ICOS and CD40 on the muscle fibers and their ligands CD28, CTLA-4, ICOS-L and CD40L on the autoinvasive T cells. Metalloproteinases facilitate the migration of T cells and their attachment to the muscle surface. Muscle fiber necrosis occurs via the perforin granules released by the autoaggressive T cells. A direct myocytotoxic effect exerted by the released IFN-g, IL1, or TNFa may also play a role. Death of the muscle fiber is mediated by a form of necrosis rather than apoptosis, presumably because of the counterbalancing effect or protection by the antiapoptotic molecules such as Bcl-2, hILP, and FLIP, which are upregulated in PM and IBM muscles. Fas is also expressed, but it does not mediate apoptosis in the muscle.
Despite the above described primary immune factors, sIBM remains resistant to most immunotherapies, justifying the contention by some that it could be more of a degenerative disease rather than autoimmune. However IBM is not the only immune disease unresponsive to such therapies. Primary progressive MS is a classic example where immune and degenerative features coexist and the disease is resistant to therapies.
. . . an aggressive anti-T cell agent may be beneficial, offering further justification for using other similar therapies. A relevant study using alemtuzumab (Campath), a T-cell depleting monoclonal antibody against CD52, is now in progress at the National Institutes of Health (M.C. Dalakas, Principal Investigator). Campath is even a stronger agent than ATG because it causes T cell depletion for at least 6 months. It is anticipated that depletion of the T cells from the periphery will also result in T-cell depletion from the muscle. At the time of this writing, eight patients have completed the study. Other promising agents along these lines could be rapamycin, which acts via a calcineurin-independent pathway to prevent the translation of mRNA for key cytokines, and drugs such as natalizumab that block the transmigration of T cells across the endothelial cell wall.
7). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S39-S48
Inclusion-body myositis. A myodegenerative conformational disorder associated with A|gb, protein misfolding, and proteasome inhibition.
Askanas V, Engel WK.
From the USC Neuromuscular Center, Department of Neurology, University of Southern California Keck School of Medicine, Good Samaritan Hospital, Los Angeles, CA.
Abstract--Sporadic inclusion-body myositis (s-IBM), the most common muscle disease of older persons, is of unknown cause and there is no successful treatment. We summarize our most recent findings, which provide a better understanding of the steps in the pathogenetic cascade. We suggest that s-IBM is primarily a myodegenerative disease. Intriguing are the phenotypic similarities between s-IBM muscle fibers and the brains of Alzheimer disease, the most common neurodegenerative disease of older persons. In s-IBM, abnormal accumulation of the amyloid-b (Ab) precursor protein and its proteolytic fragment, Ab, associated with the aging intracellular milieu of the muscle fiber, appear to be key upstream pathogenic events. We propose that the identified abnormal accumulation, misfolding, and aggregation of proteins, perhaps provoked by the aging milieu and aggravated by the oxidative stress, lead to the s-IBM-specific vacuolar degeneration and atrophy of muscle fibers.
IBM patients do not develop dementia and AD patients do not have the muscle weakness characteristic of IBM, indicating that the mechanism of organ targeting is different in IBM and AD. The tissue affected, muscle vs brain, may be influenced by: 1) etiologic agent (a virus), 2) previous exposure to environmental factor(s), and 3) the patient's genetic background (the cellular microclimate).
A bPP overexpression induces several aspects of the IBM phenotype in those cultured human muscle fibers providing a very suitable 'IBM culture model,' which we have been using during the last several years.
Figure 1. Proposed pathogenetic cascade of s-IBM.
In this schema, we consider s-IBM to be a multifactorial muscle disease associated with aging. We propose that various factors, including predisposing genes and possibly infectious agents and other environmental extracorporeal factors in association of aging, lead to key presently-unknown intracellular mechanisms, which cause increased AbPP-transcription and result in AbPP overexpression. That overexpression, with participation of factors causing abnormal AbPP processing, leads to Ab42 greater than Ab40 accumulation and oligomerization. Subsequently, the increased Ab, both partially aggregated (oligomerized), and fully aggregated (fibrillar, congophilic), leads to oxidative stress and several other intracellular pathogenic abnormalities, resulting in muscle-fiber degeneration, atrophy, and death. Those abnormalities may be induced either by Ab acting independently or in conjunction with oxidative stress and other known and unknown cellular disturbances.
We propose that the aging cellular environment of s-IBM muscle fibers, combined with factors such as oxidative stress and perhaps other detrimental molecular events, leads to abnormal production and accumulation of UBB+1. We propose that in s-IBM muscle UBB+1 contributes to proteasome inhibition.
Conclusions regarding pathogenesis, and possible treatment avenues. Based on
our studies utilizing s-IBM muscle biopsies and our cultured IBM-mode, we propose
the following regarding the s-IBM pathogenesis (also see figure 1).
1. Accumulation of AbPP/Ab plays a key pathogenetic role leading to other abnormalities.
2. Misfolding and aggregation of proteins, and inhibition of proteasome caused by increased Ab, (and possibly by other factors) play a major pathogenic role.
3. Proteasome inhibition leads to even further accumulation of Ab, and of several other proteins.
4. Cholesterol binds to Ab, and is accumulated together with Ab and caveolin-1, in the form of large aggregates, resulting in abnormal cholesterol trafficking.
5. Cholesterol binding to Ab enhances Ab oligomerization. This increases Ab toxicity, which in turn leads to further proteasome inhibition, increased accumulation of misfolded proteins, greater accumulation of cholesterol, and additional cellular toxicity-a vicious cycle.
Based on our studies, we hypothesize that the following approaches are of potential therapeutic value in s-IBM: 1. Stimulate Ab degradation, or decrease Ab production. 2. Diminish oligomerization and fibrillization of Ab, and other proteins, perhaps utilizing novel small molecules that are being developed in vitro. 3. Diminish protein aggregation through protecting and stimulating 26S proteasome activity, and other aspects of the ubiquitin proteasome system. 4. Reduce myostatin, possibly through growth hormone, which decreases myostatin mRNA in human muscle, or through another mechanism. 5. Protect mitochondria possibly with other molecules to be developed. 6. Diminish adverse effects of intra-muscle fibers cholesterol by improving proteasome function (the therapeutic value of high-dose statins is currently uncertain).
8). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S49-S55
Mitochondrial abnormalities in inclusion-body myositis.
Oldfors A, Moslemi AR, Jonasson L, Ohlsson M, Kollberg G, Lindberg C.
From the Departments of Pathology (A.O., A.-R.M., L.J., M.O., G.K.) and Neurology (C.L.), Sahlgrenska University Hospital, Goteborg, Sweden.
Abstract--Mitochondrial changes are frequently encountered in sporadic inclusion-body myositis (s-IBM). Cytochrome c oxidase (COX)-deficient muscle fibers and large-scale mitochondrial DNA (mtDNA) deletions are more frequent in s-IBM than in age-matched controls. COX deficient muscle fibers are due to clonal expansion of mtDNA deletions and point mutations in segments of muscle fibers. Such segments range from 75 microm to more than 1,000 microm in length. Clonal expansion of the 4977 bp "common deletion" is a frequent cause of COX deficient muscle fiber segments, but many other deletions also occur. The deletion breakpoints cluster in a few regions that are similar to what is found in human mtDNA deletions in general. Analysis in s-IBM patients of three nuclear genes associated with multiple mtDNA deletions, POLG1, ANT1 and C10orf2, failed to demonstrate any mutations. In s-IBM patients with high number of COX-deficient fibers, the impaired mitochondrial function probably contribute to muscle weakness and wasting. Treatment that has positive effects in mitochondrial myopathies may be tried also in s-IBM.
In disorders due to primary mtDNA mutations, there is at present no curative treatment. CoQ10 is frequently used because it is a component of the respiratory chain that may be reduced in mitochondrial diseases and acts as an oxygen radical scavenger. Although the positive effects have not been unequivocally proven, CoQ10 treatment could possibly be beneficial also in s-IBM. Vitamin C is another free-radical scavenger that has been considered in treatment of s-IBM. Other compounds that have been tried in mitochondrial diseases include vitamin K, riboflavin, thiamine, folic acid, L-carnitine, and creatine, but with limited and uncertain effects.
9). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S56-S58
Controlling autoimmunity in sporadic inclusion-body myositis.
From the Department of Neurology and Neurological Sciences, Beckman Center for Molecular Medicine, Stanford University, Stanford, CA.
Sporadic inclusion-body myositis (s-IBM) spans two areas of interest in my research lab, the role of protein aggregation in neurodegenerative disease and the role of secondary autoimmunity in degenerative conditions in the nervous system and in muscle. After some comments on the potential pathologic role of inclusion bodies themselves, I shall focus attention on two approaches to controlling the autoimmune response in muscle tissue: inhibition of lymphocyte homing with antibodies to a 4 b 1 integrin, and nonspecific downregulation of autoimmunity with statins.
Benefits and risks of statin therapy for s-IBM
Mechanism of action
Reduction in expression of inducible MHC class II in muscle
Reduction in lymphocyte homing to muscle
Reduction in inflammatory cytokine and NO production in muscle
Reduction of inflammation at multiple levels
Reduction in cholesterol, reduction in A beta misfolding and aggregation
Potential side effects
Statins, devised as HMG-CoA reductase inhibitors to lower cholesterol, have remarkable anti-inflammatory properties. Oral administration of 80 mg/kg simvastatin (Zocor) reduced the expected number of new gadolinium enhancing lesions in relapsing-remitting MS patients by 44% in a small 6-month open-label trial. Atorvastatin (Lipitor) has also shown promising results in lowering disease scores and vascular risk factors in patients with rheumatoid arthritis and is currently being tested in MS in a multicenter, placebo-controlled trial.
[Therefore], a treatment that not only has multiple virtues as an anti-inflammatory, but also lowers cholesterol would seem to have optimal specifications for use in S-IBM. The benefits and risks of statins for treatment of s-IBM are outlined in the table.
10). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S59-S64
Immunotherapeutic relief from persistent infections and amyloid disorders.
From the Division of Virology, Department of Neuropharmacology, The Scripps Research Institute, La Jolla, CA.
Abstract--Persistent infections and amyloid disorders afflict a significant number of people worldwide. It would appear at first glance that the treatment of these afflictions should be entirely unrelated; however, in both cases components of the adaptive immune system have been harnessed in an attempt to provide some therapeutic relief. Given that the ability of a pathogen to establish persistence often depends in part on a shortcoming of the adaptive immune response, it seems logical to devise immunotherapies with the intention of supplementing (or replacing) the insufficient immunologic element. A case in point is an intervention referred as immunocytotherapy, which relies upon the adoptive transfer of pathogen-specific T lymphocytes into a persistently infected host. Remarkably, the adoptively transferred T lymphocytes not only have the capacity to clear the persistent infection, but can also provide the recipient with protection against subsequent rechallenge (i.e., immunologic memory). Treatment of amyloid disorders (e.g., Alzheimer disease, sporadic inclusion-body myositis) with a similar therapeutic approach is complicated by the fact that the aberrant protein accumulations are self-derived. Focusing the adaptive response on these aberrant self-proteins has the potential to result in autoimmune pathology. This review critically evaluates the importance of immunotherapeutic approaches for the treatment of persistent infections and amyloid disorders, and attempts to delineate the interventions that are most likely to succeed in an exceedingly complex disorder such as sporadic inclusion-body myositis.
The key to treatment [of sIBM] may rest in defining the specificity of CTL clones isolated from s-IBM patients. Through the use of peptide libraries and protein databases, it should be possible to determine whether the CTL found in s-IBM patients are specific to a pathogen or a selfprotein. Because treatment of persistent infection and autoimmune disease lie at the opposite ends of the spectrum, determination of CTL specificity could provide a much needed clue to unlock the etiology of the disease and direct clinicians toward the most appropriate therapeutic interventions.
11). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S65-S68
Inclusion-body myositis and Alzheimer disease. Two sides of the same coin, or different currencies altogether?
Murphy MP, Golde TE.
From the Department of Molecular and Cellular Biochemistry (M.P.M.), Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY; and the Department of Neuroscience (T.E.G.), Mayo Clinic College of Medicine, Jacksonville, FL.
Inclusion-body myositis (IBM) is an age-related, slowly progressive degenerative disorder of the skeletal musculature with no effective treatment. Clinically, the disease is characterized by the atrophy of both proximal and distal muscle groups, leading to a gradually advancing weakness. The muscle fibers from IBM patients display characteristic vacuolizations and contain heterogeneous, filamentous inclusions. Although initially characterized as a form of polymyositis, the disease is only weakly responsive to corticosteroid treatment or other forms of immunomodulation and is now recognized as a distinct disease entity.
Though it might appear that a definitive evaluation of Ab's role in IBM is lagging far behind that of AD, this is not so: the experience gained from the study of AD has marked a trail for IBM investigators. It may not exactly be a pristine thoroughfare, but it is at least a reasonably clear path to take. In our view, there are two main, interconnected routes to follow: observations based on what is already known of AD molecular genetics and cell biology, and pharmacologic experiments in IBM transgenic mouse models. Following these leads it may be possible to rule in or out a role for Ab and amyloid in IBM.
Our knowledge of AD genetics and APP biology can be extended to the creation of transgenic mice modeling IBM. Because the overexpression of FAD linked mutant APPs or the coexpression of mutant APP and FAD-linked PSs in the brains of transgenic mice leads to Ab deposition and other AD-like pathologies, it would be a simple matter to generate and cross the appropriate mutants and evaluate the resulting IBM-like pathology. For instance, a knock in mutant PS1 mouse could be crossed with an appropriate model of human APP expression in muscle. If IBM is truly similar to AD, then the development of muscle pathology will be accelerated.
There is no doubt that the over expression of mutant forms of APP in muscle causes pathology in mice. What has not been resolved is what 'piece' of APP is responsible.
Chronic use of nonaspirin NSAIDs is widely acknowledged to reduce the risk of AD. A subset of NSAIDs can act to selectively modulate Ab42 production, both in cell culture and in APP transgenic mice. For example, ibuprofen is effective at lowering Ab42 production and reversing AD-like pathology in the brains of Tg2576 mice, whereas naproxen is ineffective. This effect is independent of antiinflammatory activity mediated through the inhibition of the cyclooxygenase enzymes (COX) and many other known targets of these compounds. Although these compounds likely target the g-secretase enzyme, they appear to act to allosterically modulate activity by shifting cleavage sites to generate shorter secreted peptides. Similarly, other compounds can act in the opposite manner, increasing the proportion of longer fragments at the expense of the shorter ones. If IBM pathology is driven by the production of Ab42, then treatment with Ab42- lowering compounds will either prevent or reverse the development of pathology, whereas raising compounds will cause it to accelerate. If these compounds are ineffective, this would point to a mechanism other than Ab42 production.
Ultimately, if the two pathologies prove to be related, it may be that therapies developed to treat AD might be useful in IBM, or that therapies developed in preclinical studies in mice that mimic IBM pathology might be tested in humans with AD.
12). December 2005
NEUROLOGY 2006;66(Suppl 1):S69-S73
Amyloidogenic processing of b-amyloid precursor protein in intracellular compartments
Kulandaivelu S. Vetrivel, PhD; and Gopal Thinakaran, PhD
Abstract-Trafficking and proteolytic processing of amyloid precursor protein (APP) have been the focus of numerous investigations in the past two decades, since the identification of Ab as the principal component of brain senile plaques and the cloning of APP cDNA. Tremendous progress has been made in the recent past toward the characterization of b- and g-secretases. Here, we review the salient features of Alzheimer disease amyloidogenesis, and discuss the current knowledge on APP trafficking and amyloidogenic processing of APP in intracellular membrane compartments and microdomains.
Perspectives on amyloidogenesis in sporadic inclusion-body myositis. Accumulation of APPand its proteolytic derivatives including Ab peptides in vacuolated muscle fibers is a prominent pathologic feature of sporadic inclusion-body myositis (s-IBM). Unusually high levels of BACE and components of the g-secretase have been observed in s-IBM muscle fibers, providing one potential mechanism for increased amyloidogenic processing of APP in the muscle fibers of affected individuals. Other cellular abnormalities such as elevated levels and sustained association of ER chaperones with APP, accumulationof several abnormal proteins, and the presence of aggresomes indicate potential defects in the folding of nascent APP and proteolytic processing of cellular proteins in affected muscle fibers. Furthermore,abnormalities in free cholesterol and caveolin-1 observed in s-IBM muscle fibers are likely to influence amyloidogenic processing of APP by affecting the localization of APP and/or secretases within cholesterol and caveolin-rich lipid raft microdomains of membrane organelles. The development of an appropriate cell culture or transgenic animal model for s-IBM will greatly facilitate further investigation of amyloidogenic processing of APP.
13). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S74-S78
Common structure and toxic function of amyloid oligomers implies a common mechanism of pathogenesis.
Glabe CG, Kayed R.
From the Department of Molecular Biology and Biochemistry, University of California, Irvine, CA.
Abstract--Recent findings indicate that soluble amyloid oligomers may represent the primary pathologic species in degenerative diseases. These amyloid oligomers share common structural features and the ability to permeabilize membranes, suggesting that they also share a common primary mechanism of pathogenesis. Membrane permeabilization by amyloid oligomers may initiate a common group of downstream pathologic processes, including intracellular calcium dyshomeostasis, production of reactive oxygen species, altered signaling pathways, and mitochondrial dysfunction that represent key effectors of cellular dysfunction and cell death in amyloid-associated degenerative disease, such as sporadic inclusion-body myositis.
The accumulation of insoluble, misfolded proteins is increasingly recognized as a key pathogenic feature of degenerative diseases, including Alzheimer disease (AD), Parkinson disease (PD), Huntington disease (HD), type II diabetes, and sporadic inclusion-body myositis. In most of these diseases, the end-stage products that accumulate are amyloid fibers. Amyloids have been defined in a number of different ways: operationally in terms of their ability to bind dyes, like Congo red and thioflavin dyes, morphologically as 6- to 10-nm filaments, and structurally as 'cross b' fibrils by x-ray diffraction. Regardless of their protein sequences, many amyloids fit these definitions.
. . . Accumulating evidence indicates that [these] soluble oligomeric intermediates may represent the primary pathologic species in disease. Recent evidence suggests that amyloid oligomers have a common structure, suggesting that they all may share a common primary mechanism of pathogenesis.
14). December 2005
NEUROLOGY 2006;66(Suppl 1):S79-S85
Apolipoprotein E and Alzheimer disease
Yadong Huang, MD, PhD
Abstract-Apolipoprotein (apo) E, a multifunctional protein with central roles in lipid metabolism and neurobiology, has three common isoforms (apoE2, apoE3, and apoE4) with different effects on lipid homeostasis and neurobiology. Unlike apoE3, the most common isoform, apoE4, is associated with increased risk of developing Alzheimer disease (AD) and other neurodegenerative disorders. Although the mechanisms underlying apoE4's action in AD pathogenesis are still poorly understood, emerging data strongly suggest that apoE4 contributes to this disease by interacting with different factors through various pathways. Thus, multiple molecular and cellular mechanisms should be considered when anti-AD drugs are developed based on apoE studies.
Recently, apoE4 has also been suggested to be associated with other types of neurodegenerative disorders. ApoE4 allele may affect the progression of MS and ALS. ApoE is found in the vacuolated muscle fibers in human sporadic inclusion-body myositis (s-IBM) and apoE4 may be a risk factor for the development of s-IBM.
15). December 2005
NEUROLOGY 2006;66(Suppl 1):S86-S92
Frameshift proteins in autosomal dominant forms of Alzheimer disease and other tauopathies
F.W. van Leeuwen, PhD; P. van Tijn, MSc; M.A.F. Sonnemans, BSc; B. Hobo, BSc; D.M.A. Mann, PhD; C. Van Broeckhoven, PhD; S. Kumar-Singh, MD, PhD; P. Cras, MD, PhD; G. Leuba, PhD; A. Savioz, PhD; M.L.C. Maat-Schieman, MD, PhD; H. Yamaguchi, MD, PhD; J.M. Kros, MD, PhD; W. Kamphorst, MD, PhD; E.M. Hol; PhD; R.A.I. de Vos, MD; and D.F. Fischer, PhD
Abstract-Frameshift (+1) proteins such as APP+1 and UBB+1 accumulate in sporadic cases of Alzheimer disease (AD) and in older subjects with Down syndrome (DS). We investigated whether these proteins also accumulate at an early stage of neuropathogenesis in young DS individuals without neuropathology and in early-onset familial forms of AD (FAD), as well as in other tauopathies, such as Pick disease (PiD) or progressive supranuclear palsy (PSP). APP+1 is present in many neurons and beaded neurites in very young cases of DS, which suggests that it is axonally transported. In older DS patients (greater than 37 years), a mixed pattern of APP+1 immunoreactivity was observed in healthy looking neurons and neurites, dystrophic neurites, in association with neuritic plaques, as well as neurofibrillary tangles. UBB+1 immunoreactivity was exclusively present in AD type of neuropathology. A similar pattern of APP+1 and UBB+1 immunoreactivity was also observed for FAD and much less explicit in nondemented controls after the age of 51 years. Furthermore, we observed accumulation of +1 proteins in other types of tauopathies, such as PiD, frontotemporal dementia, PSP and argyrophylic grain disease. These data suggest that accumulation of +1 proteins contributes to the early stages of dementia and plays a pathogenic role in a number of diseases that involve the accumulation of tau.
Conformational diseases are now acknowledged as a group of disorders that share a common feature: the accumulation of insoluble protein deposits in the affected cells. Many age-related neurodegenerative disorders belong to this group, such as tauopathies (e.g., Alzheimer disease [AD] and Pick disease [PiD], synucleinopathies (e.g., Lewy body disease) and polyglutamine diseases (Huntington's disease). Aberrations in the ubiquitin-proteasome system, necessary for protein turnover, have been implicated, either as a primary or secondary consequence, in the pathogenesis of conformational diseases.
. . . In non-neuronal cells, molecular misreading of the ubiquitin B gene was also shown in a model system and subsequently in inclusions present in hepatocytes of steatohepatitis and in muscles of sporadic inclusion-body myositis (IBM). Consequently, proteasome inhibition occurs in these diseases. Thus again, IBM and AD share common pathologic characteristics. Generating cellular and transgenic models is a logical next step to dissect essential processes in IBM.
16). December 2005
NEUROLOGY 2006;66(Suppl 1):S93-S96
Preferential degradation of oxidized proteins by the 20S proteasome may be inhibited in aging and in inflammatory neuromuscular diseases
Kelvin J.A. Davies, PhD, DS; and Reshma Shringarpure, PhD
Abstract-Free radicals produced by chronic inflammation cause cumulative damage to cellular macromolecules and appear to contribute to senescence/aging, age-related disorders, and neuromuscular degenerative diseases such as inclusion-body myositis. Proteins are major targets for oxidative damage (in addition to DNA and lipids) and the accumulation of oxidized proteins has been reported in many aging and disease models. In young and healthy individuals, moderately oxidized soluble cell proteins are selectively and rapidly degraded by the 20S proteasome. The mechanism of selective proteolysis appears to depend upon oxidation-induced protein unfolding, with increasing surface hydrophobicity as (previously shielded) hydrophobic residues are exposed from the interior. The 20S proteasome can preferentially bind to and degrade such mildly oxidized, hydrophobic proteins without a need for ubiquitin targeting or ATP activation. Severely oxidized, aggregated, and crosslinked proteins, however, are poor substrates for degradation and actually inhibit the proteasome. During aging, and in many age-related diseases/disorders, the proteasome is progressively inhibited by binding to increasing levels of oxidized and cross-linked protein aggregates. Cellular aging and inflammatory neuromuscular degenerative diseases probably include both an increase in the generation of reactive oxygen species as well as a decline in proteasome activity, resulting in the progressive accumulation of oxidatively damaged protein aggregates that eventually contribute to cellular dysfunction and senescence.
We believe that cellular aging, and many age-related diseases, involve both an increase in the mitochondrial generation of free radicals, and a progressive decline in proteasome activity. Eventually so much proteasome is inactivated that oxidized proteins begin to accumulate rapidly and may contribute to cellular senescence.
. . .We propose a mechanism in which protein aggregates are first formed, due to excessive oxidation, and subsequently undergo progressive ubiquitinylation. This is because even poor sites for ubiquitin ligation will eventually react with polyubiquitin chains if the aggregated/crosslinked protein 'host' has a long enough cellular existence. Thus, the progressive ubiquitinylation of (nondegradable) heavily oxidized proteins in degenerative, inflammatory neuromuscular diseases probably actually contributes to further aggregation and damage accumulation.
17). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print]NEUROLOGY 2006;66(Suppl 1):S97-S101
Brain and brawn. Parallels in oxidative strength.
Moreira PI, Honda K, Zhu X, Nunomura A, Casadesus G, Smith MA, Perry G.
From the Institute of Pathology (P.I.M., K.H., X.Z., G.C., M.A.S., G.P.), Case Western Reserve University, Cleveland, OH; the Center for Neuroscience and Cell Biology of Coimbra (P.I.M.), University of Coimbra, Coimbra, Portugal; and the Department of Psychiatry and Neurology (A.N.), Asahikawa Medical College, Asahikawa, Japan.
Abstract--Neuronal oxidative stress occurs early in the progression of Alzheimer disease (AD), significantly before the development of the pathologic hallmarks, neurofibrillary tangles, and senile plaques. Study of Down syndrome, cases with autosomal dominant mutation, and sporadic AD all suggest amyloid-b deposition and hyperphosphorylated tau function as compensatory responses and downstream adaptations to ensure that neuronal cells do not succumb to oxidative damage. Amyloid-b and tau hyperphosphorylation also define vulnerable muscle cells in sporadic inclusion-body myositis (s-IBM). The role of the structural changes of s-IBM, as in AD, remains to be determined but may mark a critical response yielding a novel balance in oxidant homeostasis.
[Discussed findings that suggest that increased oxidative damage is not the terminal sequelae of the disease but instead plays an initial role.]
Figure 2. Similar pathologic changes define vulnerable neurons in AD and muscle cells in s-IBM. They share almost every feature.
Oxidative stress is not the breach of antioxidant defenses for chronic conditions, pathologic and physiologic, and that a better understanding occurs by viewing each circumstance as a different homeostatic balance in which reactive oxygen and nitrogen species play a key regulatory role. In the initial stages of AD development, neuronal cells despite showing increased oxidative damage may actually be in homeostatic balance. If cells survive and function in the presence of high levels of oxidative stress, it is because critical systems of cells are not damaged. In this way, detection of increased oxidative damage, in cells that survive, must be associated with a commensurate increase in compensatory mechanisms such as Ab deposition and hyperphosphorylated t (tau). However, with the progression of AD and the consequent increase of reactive species levels, the efficient removal of Ab-metal complexes and, probably, hyperphosphorylated t would be overtaken by their disproportionately high generation, resulting in an uncontrollable growth of senile plaques and NFT and consequently, an increase in reactive species generation. This would result in a feedback mechanism that could exacerbate plaque and NFT growth and reactive species generation, leading to a functional demise of neurons (figure 1).
Muscle cells in s-IBM show many of the same changes documented in AD (figure 2) and it would seem likely that similar mechanisms are involved. Neurons and muscle share high metabolic activity and are postmitotic. A highly developed cytoskeleton is essential to both, for movement in muscle and transport in neurons. Understanding and dissecting these commonalities that lead to similar pathophysiology will result in a better mechanistic appreciation of s-IBM and AD.
18). December 2005
NEUROLOGY 2006;66(Suppl 1):S102-S109
The unfolded protein response A stress signaling pathway critical for health and disease
Kezhong Zhang, PhD; and Randal J. Kaufman, PhD
Abstract-The endoplasmic reticulum (ER) is an intracellular organelle consisting of a membranous labyrinth network that extends throughout the cytoplasm of the cell and is contiguous with the nuclear envelope. In all eukaryotic cells, the ER is the site where folding and assembly occurs for proteins destined to the extracellular space, plasma membrane, and the exo/endocytic compartments. The ER is exquisitely sensitive to alterations in homeostasis, and provides stringent quality control systems to ensure that only correctly folded proteins transit to the Golgi and unfolded or misfolded proteins are retained and ultimately degraded. A number of biochemical and physiologic stimuli, such as perturbation in calcium homeostasis or redox status, elevated secretory protein synthesis, expression of misfolded proteins, sugar/glucose deprivation, altered glycosylation, and overloading of cholesterol can disrupt ER homeostasis, impose stress to the ER, and subsequently lead to accumulation of unfolded or misfolded proteins in the ER lumen. The ER has evolved highly specific signaling pathways called the unfolded protein response (UPR) to cope with the accumulation of unfolded or misfolded proteins. Recent discoveries of the mechanisms of ER stress signaling have led to major new insights into the diverse cellular and physiologic processes that are regulated by the UPR. This review summarizes the complex regulation of UPR signaling and its relevance to human physiology and disease.
19). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S110-S113
Treatment and prevention of the amyloidoses. Can the lessons learned be applied to sporadic inclusion-body myositis?
From the Department of Molecular and Experimental Medicine, The Keck Autoimmune Disease Center, Division of Rheumatology Research, The Scripps Research Institute, La Jolla, CA.
Abstract--The amyloid fibril represents a final common pathologic pathway for a variety of human proteins, all of which have a propensity to misfold. Each seems to require a predisposing event to realize its fibrillogenic potential. It may be mutation, inappropriate or incomplete cleavage, overproduction, or the availability of a template for misfolding. Therapies have been based on decreasing the stimulus (inflammation in the case of AA) reducing the number of producing cells (AL) and a variety of approaches to removing the extracellular aggregates. Sporadic inclusion-body myositis (sIBM), while physically resembling the extracellular amyloidoses, is an intracellular disease, hence imposes the additional requirement of developing a therapy that can access and function inside the affected or potentially affected, cell. Current approaches to the treatment of other forms of amyloidosis are discussed in the context of their applicability, or lack thereof, to sIBM.
Clearly the human amyloid that is most relevant for sIBM is Ab, because sIBM represents an organismally less devastating form of deposition of this protein.
The greatest excitement in the Ab field was generated when transgenic animals bearing a human mutant Ab were immunized with an Ab peptide and showed resolution of their deposits. A human trial was subsequently instituted but aborted when 10% of the participants showed evidence of inflammatory encephalitis.
Hence it remains to be seen whether removal of fibrils will restore a degree of neuronal function sufficient to arrest the progressive dementia or allow recovery. Although the specificity of the anti-Ab approach is attractive in the case of sIBM, it must be noted that the plaques in the transgenic mice are extracellular and the aggregates of sIBM are intracellular, imposing a requirement for the active principle to enter the myocyte. It is not clear that this will be the case. Nonetheless the antibody approach has received a great deal of attention. It is also possible that myocyte targeted DNA vaccination might be a better method of antibody-mediated clearance for the intracellular aggregates.
20). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S114-S117
RNA interference as potential therapy for neurodegenerative disease. Applications to inclusion-body myositis?
From the Department of Neurology, Carver College of Medicine, University of Iowa, Iowa City, IA.
Abstract--The discovery of RNA interference (RNAi) has led to powerful new approaches to silence targeted genes in a sequence-specific manner. The potential therapeutic application of RNAi to neurologic disease is highlighted by the recent success of several laboratories in suppressing the expression of neurodegenerative disease genes in transgenic mouse models. Here I discuss potential applications of RNAi to inclusion-body myositis (IBM) after first reviewing its application more generally to neurologic disease. The clearest application of RNAi to IBM is as a research tool to identify critical target genes that contribute to pathogenesis. Provided that proximal pathogenic targets are identified, RNAi could surface as a potential therapeutic strategy to modulate their expression.
RNAi is a remarkable intracellular process by which the expression of a gene can be suppressed at the RNA level.
. . . The complementary siRNA causes either cleavage of the targeted mRNA, which destroys the transcript, or translational arrest of the mRNA, which prevents production of the encoded protein without destroying the mRNA.
Applying RNAi to IBM will require that we better understand the molecular pathogenesis of this disease. As a first step, the sporadic form of IBM may have to be distinguished from hereditary forms of inclusion-body myopathy. Though they may share molecular mechanisms, that is not guaranteed. The sporadic form of disease occurs later and appears to have, at its core, a dysregulation of gene/protein expression in the muscle fiber. This results in the accumulation of various abnormal proteins, including amyloid and amyloid-associated proteins. The hallmark inclusions of s-IBM suggest that perturbations in protein quality control may be central to disease. It is important to recognize, however, that s-IBM also has a significant inflammatory component that may contribute to, or possibly even trigger, pathogenesis. It is possible that either the proteinaceous accumulation or the inflammatory component is a secondary phenomenon, not central to pathogenesis. Further study of inherited forms of inclusion-body myopathy, including disease caused by mutations in a glycosyltranferase, GNE, and in valosin containing protein, VCP, may yield further insights to disease mechanisms that apply to s-IBM as well. In the meantime, it seems likely that dysregulation of muscle gene expression contributes to the abnormal accumulation of various proteins comprising the inclusions seen in disease. As is the case with the large array of neurodegenerative diseases characterized by polyglutamine inclusions or Lewy bodies, the direct role of IBM inclusions in disease pathogenesis cannot be assumed. It is possible that they constitute a byproduct of a disease process whose primary pathogenesis lies elsewhere.
With these qualifiers in mind, candidate targets for RNAi in s-IBM will vary depending upon which elements of disease prove to be primary rather than secondary.. . . .It should not be long before we know better the perils and promise of RNAi for chronic diseases like s-IBM.
21). December 2005
NEUROLOGY 2006;66(Suppl 1):S118-S122
Developing therapeutics for the diseases of protein misfolding
Barnaby C.H. May, PhD; Cedric Govaerts, PhD; and Fred E. Cohen, MD, PhD
Abstract-Our current structural and biologic understanding of the misfolding diseases has restricted the development of therapies that target these diseases at a molecular level. The prion diseases are illustrative of this group of misfolding disorders and provide a model system for therapeutic intervention. Strategies to inhibit the replication and accumulation of the prion protein are being developed and have entered animal and clinical studies. Due to the underlying molecular basis of this disease class, many of the therapeutic approaches used to target prion misfolding have parallels in other misfolding diseases.
Approximately 20 human diseases are known to result from or be associated with the misfolding of a cellular protein from its native conformation to a disease-associated isoform.
. . . In AD, PD, and the prion diseases, sporadic disease is more common than
inherited disease. This suggests that a spontaneous misfolding event can initiate
aggregation and argues for the existence of a cellular clearance mechanism that
normally operates to rid healthy cells of misfolded products, thus protecting
cells from these toxic species. However, if this clearance mechanism is compromised
as we age, misfolded products will accumulate. As the population ages, a dramatic
increase in the clinical cases of misfolding diseases is expected unless effective
therapies can be developed to halt or reverse misfolding and disease progression.
Perspective. The challenges of developing mechanistic therapies for the misfolding diseases primarily stem from a lack of structural information about the disease target(s). Although various strategies are proving effective in laboratory models of misfolding and disease, the clinical relevance of these approaches has yet to be established. In the absence of a clearly defined route to therapeutic intervention, all approaches have a place and although some of these strategies may prove clinically ineffective, they may provide much needed insight into protein misfolding and the associated disease.
22/22). December 2005
Neurology. 2005 DEC 16; [Epub ahead of print] Print: NEUROLOGY 2006;66(Suppl 1):S123-S124
Pilot trial of etanercept in the treatment of inclusion-body myositis.
Barohn RJ, Herbelin L, Kissel JT, King W, McVey AL, Saperstein DS, Mendell JR.
From the Department of Neurology (R.J.B., L.H., D.S.S.), University of Kansas Medical Center, Kansas City, KS; and the Department of Neurology (J.K., W.K., A.L.M., J.R.M.), Ohio State University, Columbus, OH.
Abstract--Inclusion-body myositis (IBM) is an inflammatory muscle disease that has proven resistant to treatment. Tumor necrosis factor molecules have been detected in muscle biopsies from patients with IBM. Etanercept is a TNFalpha receptor fusion protein that binds and inactivates tumor necrosis factor. Nine patients were treated with etanercept at a dose of 25 mg, two times a week for an average of 17 +/- 6.1 months. Each patient was evaluated using quantitative strength testing. Their data were compared to two different control groups. The first control group consisted of patients who participated in trials of b-interferon-1A and had received placebo. There was no significant difference. The second control group was a natural history cohort of IBM patients. There was no statistically significant difference between the treated group and the natural history group at 6 and 12 months when looking at elbow flexors, or 6 months when looking at hand grip. In the treated patients there was a small but significant improvement (p = 0.002) in handgrip at 12 months.
. . . an annual incidence estimated at 2-5:100,000. It is a painless, slowly progressive condition that causes both proximal and distal weakness. IBM seldom affects patients under 30 years, and is much more common over the age of 50 years. Despite a considerable body of evidence suggesting that IBM may be an immune-mediated disease, studies of a number of immunosuppressive agents have been negative.
TNFa can be identified in macrophages and connective
tissue of muscle from IBM patients but not normal controls. TNFa
may play an important role in the genesis of IBM by activating T cells, B cells,
and macrophages as well as by including MHC-1 and ICAM-1 gene products, mediating
transendothelial transport of lymphocytes, and producing muscle atrophy. Therefore,
inhibition of TNFa could be a useful treatment option
for IBM. Etanercept is a TNFa receptor fusion protein
that binds and inactivates tumor necrosis factor. Etanercept has been demonstrated
to be safe and effective in the treatment of rheumatoid arthritis. We hypothesize
that etanercept may be able to slow progression in patients with IBM.
Discussion. Etanercept did not improve composite MVIC strength scores at 6 months. There may have been a slight improvement in grip strength at 12 months in etanercept-treated IBM patients when compared to a small natural history control group. This was not seen until after 12 months of treatment. Interestingly, a recent study of high-dose beta interferon-1A in IBM found a small but significant improvement in hand-grip strength (an increase of 1.68 kg, p = 0.01). As in the current study, no significant change in composite MVIC scores was found. In the beta-interferon-1A IBM study, subjects were followed for only 6 months.
There are several potential explanations for the observed improvement in grip strength. This may be an artifact of small patient numbers or due to the unblinded, retrospective study design. In the current study, improved hand-grip strength was not seen until 12 months. It may be that more than 6 months of treatment are required to bring about improvement in IBM patients. Future IBM treatment trials may need to be longer than 6 months. A larger, prospective, placebo-controlled trial of etanercept in IBM is indicated.