Apolipoprotein E and apolipoprotein E messenger RNA in muscle of inclusion body myositis and myopathies

Sporadic inclusion body myositis-derived myotube culture revealed muscle cell-autonomous expression profiles

Sporadic inclusion body myositis (sIBM) is a muscle disease in older people and is characterized by inflammatory cell invasion into intact muscle fibers and rimmed vacuoles. The pathomechanism of sIBM is not fully elucidated yet, and controversy exists as to whether sIBM is a primary autoimmune disease or a degenerative muscle disease with secondary inflammation. Previously, we established a method of collecting CD56-positive myoblasts from human skeletal muscle biopsy samples. We hypothesized that the myoblasts derived from these patients are useful to see the cell-autonomous pathomechanism of sIBM. With these resources, myoblasts were differentiated into myotubes, and the expression profiles of cell-autonomous pathology of sIBM were analyzed. Myoblasts from three sIBM cases and six controls were differentiated into myotubes. In the RNA-sequencing analysis of these "myotube" samples, 104 differentially expressed genes (DEGs) were found to be significantly upregulated by more than twofold in sIBM, and 13 DEGs were downregulated by less than twofold. For muscle biopsy samples, a comparative analysis was conducted to determine the extent to which "biopsy" and "myotube" samples differed. Fifty-three DEGs were extracted of which 32 (60%) had opposite directions of expression change (e.g., increased in biopsy vs decreased in myotube). Apolipoprotein E (apoE) and transmembrane protein 8C (TMEM8C or MYMK) were commonly upregulated in muscle biopsies and myotubes from sIBM. ApoE and myogenin protein levels were upregulated in sIBM. Given that enrichment analysis also captured changes in muscle contraction and development, the triggering of muscle atrophy signaling and abnormal muscle differentiation via MYMK or myogenin may be involved in the pathogenesis of sIBM. The presence of DEGs in sIBM suggests that the myotubes formed from sIBM-derived myoblasts revealed the existence of muscle cell-autonomous degeneration in sIBM. The catalog of DEGs will be an important resource for future studies on the pathogenesis of sIBM focusing on primary muscle degeneration.

SIL1, the endoplasmic-reticulum-localized BiP co-chaperone, plays a crucial role in maintaining skeletal muscle proteostasis and physiology

Mutations in SIL1, a cofactor for the endoplasmic reticulum (ER)-localized Hsp70 chaperone, BiP, cause Marinesco-Sjögren syndrome (MSS), an autosomal recessive disorder. Using a mouse model, we characterized molecular aspects of the progressive myopathy associated with MSS. Proteomic profiling of quadriceps at the onset of myopathy revealed that SIL1 deficiency affected multiple pathways critical to muscle physiology. We observed an increase in ER chaperones prior to the onset of muscle weakness, which was complemented by upregulation of multiple components of cellular protein degradation pathways. These responses were inadequate to maintain normal expression of secretory pathway proteins, including insulin and IGF-1 receptors. There was a paradoxical enhancement of downstream PI3K-AKT-mTOR signaling and glucose uptake in SIL1-disrupted skeletal muscles, all of which were insufficient to maintain skeletal muscle mass. Together, these data reveal a disruption in ER homeostasis upon SIL1 loss, which is countered by multiple compensatory responses that are ultimately unsuccessful, leading to trans-organellar proteostasis collapse and myopathy.

Editor's choice: This study provides molecular insights into the progressive myopathy and cellular compensatory responses attempted upon loss of SIL1, a component of the endoplasmic-reticulum-resident Hsp70 protein-folding machinery.

Immune and myodegenerative pathomechanisms in inclusion body myositis

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

Sporadic inclusion body myositis: the genetic contributions to the pathogenesis

Sporadic inclusion body myositis (sIBM) is the commonest idiopathic inflammatory muscle disease in people over 50 years old. It is characterized by slowly progressive muscle weakness and atrophy, with typical pathological changes of inflammation, degeneration and mitochondrial abnormality in affected muscle fibres. The cause(s) of sIBM are still unknown, but are considered complex, with the contribution of multiple factors such as environmental triggers, ageing and genetic susceptibility. This review summarizes the current understanding of the genetic contributions to sIBM and provides some insights for future research in this mysterious disease with the advantage of the rapid development of advanced genetic technology. An international sIBM genetic study is ongoing and whole-exome sequencing will be applied in a large cohort of sIBM patients with the aim of unravelling important genetic risk factors for sIBM.

Apolipoprotein E in Alzheimer's disease and other neurological disorders

Apolipoprotein E (APOE) is a 299-aminoacid protein encoded by the APOE gene. Three common polymorphisms in the APOE gene, ɛ2, ɛ3, and ɛ4, result in a single aminoacid change in the APOE protein. APOE ɛ2, ɛ3, and ɛ4 alleles strongly alter, in a dose-dependent manner, the likelihood of developing Alzheimer's disease and cerebral amyloid angiopathy. In particular, APOE ɛ4 is associated with increased risk for Alzheimer's disease whereas APOE ɛ2 is associated with decreased risk. The effects of APOE genotype on risk of these diseases are likely to be mediated by differential effects of APOE on amyloid-β accumulation in the brain and its vasculature. Response to treatment for Alzheimer's disease might differ according to APOE genotype. Because convincing evidence ties the APOE genotype to risk of Alzheimer's disease and cerebral amyloid angiopathy, APOE has been studied in other neurological diseases. APOE ɛ4 is associated with poor outcome after traumatic brain injury and brain haemorrhage, although the mechanisms underlying these associations are unclear. The possibility that APOE has a role in these and other neurological diseases has been of great interest, but convincing associations have not yet emerged.

Essential muscle pathology for the rheumatologist

This review introduces/refreshes some basic histopathologic methods and findings of skeletal muscle biopsies with emphasis on those diseases commonly encountered in a rheumatologist's practice. The 3 general areas of myopathology discussed are metabolic myopathies, toxic myopathies, and inflammatory myopathies. The authors, neuropathologists, hope to provide in this article what they think are some commonalities and disease-specific methods in their pathologic workup as well as a practical approach to the collaboration that pathologists undertake with their rheumatology colleagues to come to a working diagnosis.

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.

Apolipoprotein epsilon alleles in sporadic inclusion body myositis: a reappraisal

Previous studies have differed as to whether APOE epsilon4 is a susceptibility factor for developing sporadic inclusion body myositis (sIBM), with a positive association being found only in an Australian cohort of cases. We have now re-examined this in a larger cohort of 57 sIBM cases and have also carried out a meta-analysis of all the published studies looking for evidence of a risk association or effect of APOE alleles on disease expression. Our findings argue against a specific role for any APOE alleles in conferring susceptibility to sIBM but have demonstrated a non-significant trend towards an earlier age-of-onset in patients with the epsilon2 allele.

Genetics of inclusion-body myositis

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

Neprilysin participates in skeletal muscle regeneration and is accumulated in abnormal muscle fibres of inclusion body myositis

Neprilysin (NEP, EP24.11), a metallopeptidase originally shown to modulate signalling events by degrading small regulatory peptides, is also an amyloid-beta- (Abeta) degrading enzyme. We investigated a possible role of NEP in inclusion body myositis (IBM) and other acquired and hereditary muscle disorders and found that in all myopathies NEP expression was directly associated with the degree of muscle fibre regeneration. In IBM muscle, NEP protein was also strongly accumulated in Abeta-bearing abnormal fibres. In vitro, during the experimental differentiation of myoblasts, NEP protein expression was regulated at the post-transcriptional level with a rapid increase in the early stage of myoblast differentiation followed by a gradual reduction thereafter, coincident with the progression of the myogenic programme. Treatment of differentiating muscle cells with the NEP inhibitor dl-3-mercapto-2-benzylpropanoylglycine resulted in impaired differentiation that was mainly associated with an abnormal regulation of Akt activation. Therefore, NEP may play an important role during muscle cell differentiation, possibly through the regulation, either directly or indirectly, of the insulin-like growth factor I-driven myogenic programme. In IBM muscle increased NEP may be instrumental in (i) reducing the Abeta accumulation in vulnerable fibres and (ii) promoting a repair/regenerative attempt of muscle fibres possibly through the modulation of insulin-like growth factor I-dependent pathways.

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.

Insulin-like growth factor I in inclusion-body myositis and human muscle cultures

Possible pathogenic mechanisms of sporadic inclusion-body myositis (sIBM) include abnormal production and accumulation of amyloid beta (A beta), muscle aging, and increased oxidative stress. Insulin-like growth factor I (IGF-I), an endocrine and autocrine/paracrine trophic factor, provides resistance against A beta toxicity and oxidative stress in vitro and promotes cell survival. In this study we analyzed the IGF-I signaling pathway in sIBM muscle and found that 16.2% +/- 2.5% of nonregenerating fibers showed increased expression of IGF-I, phosphatidylinositide 3'OH-kinase, and Akt. In the majority of sIBM abnormal muscle fibers, increased IGF-I mRNA and protein correlated with the presence of A beta cytoplasmic inclusions. To investigate a possible relationship between A beta toxicity and IGF-I upregulation, normal primary muscle cultures were stimulated for 24 hours with the A beta(25-35) peptide corresponding to the biologically active domain of A beta. This induced an increase of IGF-I mRNA and protein in myotubes at 6 hours, followed by a gradual reduction thereafter. The level of phosphorylated Akt showed similar changes. We suggest that in sIBM. IGF-I overexpression represents a reactive response to A beta toxicity, possibly providing trophic support to vulnerable fibers. Understanding the signaling pathways activated by IGF-I in sIBM may lead to novel therapeutic strategies for the disease.

Unfolding story of inclusion-body myositis and myopathies: role of misfolded proteins, amyloid-beta, cholesterol, and aging

Sporadic inclusion-body myositis and hereditary inclusion-body myopathies are progressive muscle diseases leading to severe disability. We briefly summarize their clinical pictures and pathologic diagnostic criteria and discuss the latest advances in illuminating their pathogenic mechanism(s). We emphasize how different etiologies might lead to the strikingly similar pathology and possibly similar pathogenic cascade. On the basis of our research, several processes seem to be important in relation to the still speculative pathogenesis, including (a) increased transcription and accumulation of amyloid-beta precursor protein and accumulation of its proteolytic fragment amyloid-beta; (b) abnormal accumulation of components related to lipid metabolism, for example, cholesterol, accumulation of which is possibly owing to its abnormal trafficking; (c) oxidative stress; (d) accumulations of other Alzheimer's disease-related proteins; and (e) a milieu of muscle cellular aging in which these changes occur. We discuss a potentially very important role of unfolded and/or misfolded proteins as a possible mechanism in the formations of the inclusion bodies and other abnormalities.

BACE1 and BACE2 in pathologic and normal human muscle

BACE1 and BACE2 are recently discovered enzymes participating in processing of amyloid beta precursor protein (AbetaPP). Their discovery is contributing importantly to understanding the mechanism of amyloid-beta generation, and hence the pathogenesis of Alzheimer's disease (AD). Sporadic inclusion-body myositis (s-IBM) and hereditary inclusion-body myopathy (h-IBM) are progressive muscle diseases in which overproduction of AbetaPP and accumulation of its presumably toxic proteolytic product amyloid-beta (Abeta) in abnormal muscle fibers appear to play an important upstream role in the pathogenic cascade. In normal human muscle AbetaPP was also shown to be present and presumably playing a role (a) at neuromuscular junctions and (b) during muscle development. To investigate whether BACE1 and BACE2 play a role in normal and diseased human muscle, we have now studied them by immunocytochemistry and immunoblotting in 35 human muscle biopsies, including: 5 s-IBM; 5 chromosome-9p1-linked quadriceps-sparing h-IBM; and 25 control muscle biopsies. In addition, expression of BACE1 and BACE2 was studied in normal cultured human muscle. Our studies demonstrate that BACE1 and BACE2 (a) are expressed in normal adult muscle at the postsynaptic domain of neuromuscular junctions, and in cultured human muscle; (b) are accumulated in the form of plaque-like inclusions in both s-IBM and h-IBM vacuolated muscle fibers; and (c) are immunoreactive in necrotizing muscle fibers. Accordingly, BACE1 and BACE2 participate in normal and abnormal processes of human muscle, suggesting that their functions are broader than previously thought.

Genetic and environmental risk factors for idiopathic inflammatory myopathies

Although the studies discussed are beginning to reveal a number of genetic and possible environmental risk factors for myositis, further investigations are needed to fully understand and classify these syndromes. The difficulties in this process include small numbers of subjects with varying disease phenotypes available for study, polygenic risk factors for which it remains unclear which are primary and which are secondary or linked genes, and the lack of validated environmental exposure assessment tools. New technologies and international collaborative approaches, however, may overcome some of these difficulties and allow us to identify genetic and environmental risk factors, as well as the critical gene-environment interactions in the IIM and its subgroups. Nonetheless, our understanding of these diseases is still in the early stages. Although we have learned a great deal about these disorders through detailed investigations over the last several decades, we have even further to go to understand the environmental triggers and genetic susceptibilities for the myositis syndromes.

Inclusion-body myositis and myopathies: different etiologies, possibly similar pathogenic mechanisms

PURPOSE OF REVIEW

Sporadic inclusion-body myositis (s-IBM) and hereditary inclusion body myopathies are progressive muscle diseases that lead to severe disability. We discuss recent advances in illuminating their pathogenic mechanism(s).

RECENT FINDINGS

We emphasize how different etiologies might lead to the strikingly similar pathology and possibly similar pathogenic cascade. Our basic hypothesis is that over-expression of amyloid-beta precursor protein within aging muscle fibers is an early upstream event causing the subsequent pathogenic cascade. On the basis of our research, several processes seem to be important in relation to the still speculative pathogenesis: (a) increased transcription and accumulation of amyloid-beta precursor protein, and accumulation of its proteolytic fragment Abeta; (b) accumulations of phosphorylated tau and other Alzheimer-related proteins; (c) accumulation of cholesterol and low-density lipoprotein receptors, the cholesterol accumulation possibly due to its abnormal trafficking; (d) oxidative stress; and (e) a milieu of muscle cellular aging in which these changes occur. We discuss unfolded and/or misfolded proteins as a possible mechanism in formation of the inclusion bodies and their consequences. The remarkable pathologic similarities between s-IBM muscle and Alzheimer disease brain are discussed.

SUMMARY

Unfolding knowledge of the various pathogenetic aspects of the s-IBMs and hereditary inclusion body myopathies may lead to new therapeutic avenues.

Sporadic inclusion body myositis and hereditary inclusion body myopathy

Sporadic inclusion body myositis (s-IBM) is a common but under-recognized myopathy in individuals over 50 years of age. An awareness of the clinical phenotype and of the electrodiagnostic and histopathologic features should lead to improved recognition, and should minimize confusion with polymyositis, motor neuron disease, and other neuromuscular disorders. Treatment efficacy has been difficult to judge because of the insidious progression of the disease over many years, but immunomodulating therapy is generally less effective than in polymyositis and dermatomyositis, and may not be effective at all in many patients. The hereditary inclusion body myopathies (h-IBM) are a heterogeneous group of recessively and dominantly inherited vacuolar myopathies that share some histologic features with s-IBM. Oxidative stress may play a role in the pathogenesis of both s-IBM and h-IBM.

Inclusion-body myositis: newest concepts of pathogenesis and relation to aging and Alzheimer disease

We review the newest advances related to seeking the pathogenic mechanism(s) of sporadic inclusion-body myositis (s-IBM) and present the pathologic diagnostic criteria of s-IBM. We discuss the possible pathogenic role of several themes, such as 1) increased amyloid-beta precursor protein (AbetaPP) and of its fragment Abeta; 2) phosphorylation of tau protein; 3) oxidative stress; 4) abnormal a) signal-transduction, b) transcription, and c) RNA accumulation; 5) "junctionalization" and myogenous" denervation; and 6) lymphocytic inflammation. Evidence is provided supporting our hypothesis that overexpression of AbetaPP within the aging muscle fibers is an early upstream event causing the subsequent pathogenic cascade. The remarkable pathologic similarities between s-IBM muscle and Alzheimer disease (AD) brain are discussed, and the possible cause and significance are addressed.

Mechanisms of resistance to pathogenesis in muscular dystrophies

A mechanistic definition of the dystrophic process is proposed, and the effects of growth factors vs. down-regulation of growth are critically analyzed. A conceptual scheme is presented to illustrate the steps leading to pathology, and various compensatory systems which ameliorate the pathology are examined, particularly in regards to the mdv mouse which is resistant to the deficiency of dystrophin, the main protein product of the Duchenne and Becker muscular dystrophy (DMD/BMD) gene. These compensatory systems are analyzed in terms of the differential resistance of fiber types to pathogenesis. The generation of a stable population of maturationally arrested centronucleated fibers which express the mature adult myosin isoforms is proposed to be the main strategy of mdx muscle to minimize apoptosis. Physiological properties of these fibers, such as utrophin expression, and high mitochondrial and endoplasmic reticulum content, together with probable increased glycerophosphorylcholine concentrations and facile access to the vascular system, are hypothesized to be instrumental in their resistance to pathogenesis. It is proposed that the major element that determines the susceptibility of most human muscles to the dystrophic process is their inability to arrest the maturation of regenerated fibers at the centronucleated stage with a concomitant expression of the adult myosins.

Transgenic mice over-expressing the C-99 fragment of betaPP with an alpha-secretase site mutation develop a myopathy similar to human inclusion body myositis

Inclusion body myositis (IBM) is the most common muscle disease in the elderly. Amyloid-beta protein (A beta) has been shown to accumulate abnormally in the vacuolated fibers and to localize to amyloid-like fibrils in muscles from IBM patients. We studied the skeletal muscles from a line of transgenic mice over-expressing the carboxyl-terminal 99 amino acids (C99) of the beta-amyloid precursor protein (betaPP) with a substitution of lysine-612 to valine (K612V), intended to abolish alpha-secretase recognition and to preserve the A beta domain of C99. The majority (87%) of the 24-month-old transgenic mice showed myopathic changes, and approximately one-third of them had degenerating fibers with sarcoplasmic vacuoles and thioflavin-S-positive deposits. Ultrastructurally, the inclusions were aggregates of short thin amyloid-like fibrils, 6 to 8 nm in diameter. These features are similar to those of human IBM. Immunocytochemistry using an antibody against A beta showed membranous staining in most muscle fibers of transgenic mice, as well as granular or vacuolar cytoplasmic staining in the atrophic fibers. Western blots showed a high level of accumulation of carboxyl-terminal fragments of betaPP in the muscles of the transgenic mice with the most severe IBM-like lesions. The expression of IBM-like lesions was age dependent. These transgenic mice provide a model for the study of IBM and for the peripheral expression of a key element in the pathogenesis of Alzheimer disease.

[Immunocytochemical analysis of the inflammatory infiltrate in inclusion body myositis and other neuromuscular disorders with rimmed vacuoles]

Among 1400 muscle biopsies, we found 16 cases with rimmed vacuoles whose diagnosis were sporadic inclusion body myositis (IBM) (4 cases), juvenile spinal muscular atrophy (6 cases), distal myopathies (3 cases), limb-girdle muscular dystrophy (2 cases), and peripheral neuropathy (1 case). Monoclonal antibodies reactive for T lymphocytes and subsets, B lymphocytes, macrophages, natural killer cells, immunoglobulins, and complement were used to analyze the inflammatory infiltrate. The analysis was quantitative and according to the site of accumulation (interstitial, endomysial, and perivascular). The immunocytochemical analysis showed CD8+ lymphocytes in the interstitial in most cases, occasionally inside of muscle fibers, and rarely in the perivascular region. The IBM cases had an increased number of CD8+ lymphocytes comparing with the other diseases. CD8+/CD4+ ratio was increased in IBM compared with the other diseases. Macrophages were frequent in IBM, distal myopathy, and one case of limb-girdle muscular dystrophy. Natural killer cells were frequent at interstitial.

Immunolocalization of nitric oxide synthases at the postsynaptic domain of human and rat neuromuscular junctions--light and electron microscopic studies

Neuronal (n) and inducible (i) nitric oxide synthase (NOS) were immunolocalized at the postsynaptic domain of human and rat neuromuscular junctions (NMJs) by light and electron microscopy. We applied polyclonal and monoclonal antibodies for colocalization with three other synaptic proteins, utilizing double and triple fluorescence labeling, and gold and peroxidase for immunoelectron microscopy. By light microscopy, nNOS and iNOS colocalized with desmin and dystrophin, known postsynaptic components, but not with neurofilament protein, a presynaptic component. By electronmicroscopy, nNOS, but not iNOS, colocalized postsynaptically on the same structures as desmin; iNOS was also postsynaptic, but did not colocalize with desmin immunoreactivity. At the NMJs of Duchenne muscular dystrophy patients, both nNOS and iNOS were strongly immunoreactive. At the NMJs of a patient with myasthenia gravis, nNOS was weaker than in controls. Total denervation of rat sciatic nerve did not cause any decrease of nNOS or iNOS immunoreactivity 7 days thereafter. At 15 days after denervation, there was a gradual decrease of immunoreactivity, and immunoreactivity disappeared 30 days after denervation, corresponding to the ultrastructurally detectable disorganization of the postsynaptic region. This seems to be the first combined light and electron microscopic description of the postsynaptic localization of nNOS and iNOS at human and rat NMJs.