Beyond LGMD1A: myotilin is a component of central core lesions and nemaline rods

Myotilin is a Z-disc protein that binds alpha-actinin, gamma-filamin and F-actin. The essential role of myotilin in skeletal muscle is highlighted by the recent observation that autosomal dominant limb girdle muscular dystrophy type 1A is caused by mutations in the human myotilin gene. We studied the expression and subcellular distribution of myotilin in nemaline myopathy, central core disease, centronuclear myopathy, and myopathies with tubular aggregates. A prominent myotilin immunostaining of nemaline rods and core lesions was detected in all ten cases of nemaline myopathy and five cases of central core disease. This renders myotilin a sensitive, though non-specific marker for these structural lesions. Western blot analysis did not indicate an increased myotilin expression in nemaline myopathy muscle. However, the analysis indicated upregulation of a 75 kDa immunoreactive band, very weak in control muscle but previously detected in limb girdle muscular dystrophy 1A samples. Our findings indicate that myotilin is a core structural molecule in nemaline rods and central core lesions and suggest modification of myotilin in nemaline myopathy, and further support the notion that myotilin may have a key role in the dynamic molecular events mediating myofibril assembly in normal and diseased human skeletal muscle.

On noxious desmin: functional effects of a novel heterozygous desmin insertion mutation on the extrasarcomeric desmin cytoskeleton and mitochondria

Recent studies in desmin (-/-) mice have shown that the targeted ablation of desmin leads to pathological changes of the extrasarcomeric intermediate filament cytoskeleton, as well as structural and functional abnormalities of mitochondria in striated muscle. Here, we report on a novel heterozygous single adenine insertion mutation (c.5141_5143insA) in a 40-year-old patient with a distal myopathy. The insertion mutation leads to a frameshift and a truncated desmin (K239fs242). Using transfection studies in SW13 and BHK21 cells, we show that the K239fsX242 desmin mutant is incapable of forming a desmin intermediate filament network. Furthermore, it induces the collapse of a pre-existing desmin cytoskeleton, alters the subcellular distribution of mitochondria and leads to abnormal cytoplasmic protein aggregates reminiscent of desmin-immunoreactive granulofilamentous material seen in the ultrastructural analysis of the patient's muscle. Analysis of mitochondrial function in isolated saponin-permeablized skeletal muscle fibres from our patient showed decreased maximal rates of respiration with the NAD-dependent substrate combination glutamate and malate, as well as a higher amytal sensitivity of respiration, indicating an in vivo inhibition of complex I activity. Our findings suggest that the heterozygous K239fsX242 desmin insertion mutation has a dominant negative effect on the polymerization process of desmin intermediate filaments and affects not only the subcellular distribution, but also biochemical properties of mitochondria in diseased human skeletal muscle. As a consequence, the intermediate filament pathology-induced mitochondrial dysfunction may contribute to the degeneration/regeneration process leading to progressive muscle dysfunction in human desminopathies.

Mitochondrial dysfunction in myofibrillar myopathy

'Myofibrillar myopathy' defines a myopathic condition with focal myofibrillar destruction and accumulation of degraded myofibrillar elements. Despite the fact that a number of mutations in different genes as well as cytotoxic agents lead to the disease, abnormal accumulation of desmin is a typical, common feature. Pathological changes of mitochondrial morphology and function have been observed in animal models with intermediate filament pathology. Therefore, in the present study we tested for mitochondrial pathology in skeletal muscle of five patients with the pathohistological diagnosis of myofibrillar myopathy. Screening for large-scale mtDNA deletions and the frequent MERRF (myoclonic epilepsy; ragged red fibres) and MELAS (mitochondrial encephalomyopathy; lactic acidosis; stroke) point mutations was negative in all patients. Histologically, all muscle biopsies showed nonspecific abnormalities of the oxidative/mitochondrial enzyme stainings (histochemistry for reduced nicotinamide adenine dinucleotide, succinic dehydrogenase, cytochrome c oxidase), only one of them had ragged red fibres and a significant number of cytochrome c oxidase-negative fibres. Upon biochemical investigation, four of our patients showed pathologically low respiratory chain complex I activities. Only one of our patients had a pathologically low complex IV activity, while the measurements of the others were within low normal range. The single patient with pathological values for both complex I and IV was the one with the clear histological hallmarks (ragged red and cytochrome c oxidase-negative fibres) of mitochondrial pathology. She also was the only patient with clinical signs hinting at a mitochondrial disorder. Together with data from observations in desmin- and plectin-deficient mice, our results support the view that desmin intermediate filament pathology in these cases is closely linked to mitochondrial dysfunction in skeletal muscle.

Filamin C accumulation is a strong but nonspecific immunohistochemical marker of core formation in muscle

Filamin C is the muscle isoform of a group of large actin-crosslinking proteins. On the one hand, filamin C is associated with the Z-disk of the myofibrillar apparatus and binds to myotilin; on the other hand, it interacts with the sarcoglycan complex at the sarcolemma. Filamin C may be involved in reorganizing the cytoskeleton in response to signalling events and in muscle it may, in addition, fulfill structural functions at the Z-disk. An examination of biopsies from patients with multi-minicore myopathy, central core myopathy and neurogenic target fibers with core-like target formations (TF) revealed strong reactivity of all the cores and target formations with two different anti-filamin C antibodies. In all three conditions, the immunoreactivity in the cores for filamin C was considerably stronger than that for desmin. Only for alphaB-crystallin were comparable levels of immunoreactivity detected. There was no difference in intensity for filamin C between the three pathological conditions. Thus, filamin C along with alphaB-crystallin is a strong and robust, but nonspecific marker of core formation. The reason why filamin C accumulates in cores is unclear at present, but we postulate that it may be critically involved in the chain of events eventually leading to myofibrillar degeneration.

[Multifocal motor neuropathy: diagnosis and differential diagnosis]

Multifocal motor neuropathy (MMN) is an acquired immune mediated motor neuropathy with characteristic clinical and neurographic features.Clinically, MMN is characterized by progressive, predominantly distal and asymmetrical limb weakness. Neurographic recordings demonstrate features of multifocal demyelination with or without conduction block. Sensory nerves are not affected. Due to strict diagnostic criteria,MMN may be underdiagnosed in patients with motor neuropathies. Since intravenous immunglobulins are an efficient therapy for MMN,clinical and electrophysiological differentiation from other neuromuscular disorders is mandatory to prevent progressive impairment of motor function. We present a patient with MMN and review the clinical, electrophysiological, and histological features. In addition,pathogenesis, differential diagnosis and treatment of MMN are discussed.

Primary longitudinal adhesion structures: plectin-containing precursors of costameres in differentiating human skeletal muscle cells

Plectin is a high molecular mass protein (ca 530 kDa) that binds actin, intermediate filaments, and microtubules. Mutations of the human plectin gene cause epidermolysis bullosa simplex with muscular dystrophy. In mature human skeletal muscle, plectin is localized between neighboring myofibrils and between myofibrils and the sarcolemma, both at the level of Z-discs. In the present study we have analyzed plectin expression patterns with emphasis on its sarcolemmal localization during human skeletal muscle differentiation in vitro. In myoblasts plectin showed a cytoplasmic intermediate filament-like distribution, whereas in myotubes plectin is also found at the level of the sarcolemma. In particular, in early myotubes a specific plectin isoform colocalizes with the costameric proteins vinculin and beta1D integrin in longitudinally orientated structures which increased in number and longitudinal extension upon further maturation. In mature myotubes processes perpendicular to the parallel system of longitudinal structures became apparent. Subsequent to the occurrence of spontaneous myofibrillar contractions, the number of longitudinal streaks decreased, and plectin and other costameric proteins were found in an orderly cross-striated sarcolemmal lattice overlying myofibrillar Z-discs. Our study demonstrates that plectin is preassembled together with vinculin and beta1D integrin into primary longitudinal adhesion structures. After the occurrence of spontaneous contractions, these structures reorient and mature costameres are assembled.

Expression, localization and functional divergence of alphaB-crystallin and heat shock protein 27 in core myopathies and neurogenic atrophy

AlphaB-crystallin (alphaBC) and heat shock protein 27 (hsp 27) are members of the family of small heat shock proteins (shsps), which exert a role as molecular chaperones by binding unfolded or denatured proteins, thereby suppressing irreversible protein aggregation and consecutive cell damage. The essential role of shsps in human neuromuscular disorders is highlighted by the observation that a mutation of the human alphaBC gene causes an autosomal dominant "myofibrillar myopathy" characterized by alphaBC and desmin accumulation. Furthermore, an aberrant immunostaining of alphaBC was recently reported in sporadic inclusion body myositis. In the present study we analyzed the expression and localization of alphaB-crystallin and hsp 27 in various congenital myopathies by means of indirect immunofluorescence, immunogold electron microscopy and Western blotting. We demonstrate an increased immunoreactivity of alphaBC and hsp 27 in central and minicore lesions as well as in target fibers, which renders both shsps as reliable, but nonspecific, markers for core and target structures. In contrast, Western blotting demonstrated a normal expression level of alphaBC and hsp 27, which indicates that the increased immunostaining is not the result of an enhanced protein expression. Furthermore, thiocyanate-induced degradation of actin filaments led to a dramatic decrease of hsp 27 immunostaining in core and target lesions, whereas the increased alphaBC and desmin immunostaining was found to be even more enhanced. The latter findings imply a functional diversity of both shsps with a preferential association of hsp 27 with the actin microfilament system and alphaBC with the intermyofibrillar desmin cytoskeleton in human skeletal muscle.

Disorganization of the desmin cytoskeleton and mitochondrial dysfunction in plectin-related epidermolysis bullosa simplex with muscular dystrophy

Mutations of the human plectin gene (Plec1) cause autosomal recessive epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). Here, we report on molecular mechanisms leading to severe dystrophic muscle alterations in EBS-MD. Analysis of a 25-yr-old EBS-MD patient carrying a novel homozygous 16-bp insertion mutation (13803ins16/13803ins16) close to the intermediate filament (IF) binding site of plectin showed severe disorganization of the myogenic IF cytoskeleton. Intermyofibrillar and subsarcolemmal accumulations of assembled but highly unordered desmin filaments may be attributed to impaired desmin binding capability of the mutant plectin. This IF pathology was also associated with severe mitochondrial dysfunction, suggesting that the muscle pathology of EBS-MD caused by IF disorganization leads not only to defects in mechanical force transduction but also to metabolic dysfunction. Beyond EBS-MD, our data may contribute to the understanding of other myopathies characterized by sarcoplasmic IF accumulations such as desminopathies or alpha-B-crystallinopathies.

Modulation of gene-gun-mediated Th2 immunity to hepatitis B surface antigen by bacterial CpG motifs or IL-12

Using different DNA vaccination techniques, we studied the IgG1/IgG2a antibody and MHC-I-restricted cytotoxic T lymphocyte (CTL) responses to the hepatitis B surface antigen (HBsAg) in mice. A single intramuscular injection of 100 microg HBsAg-encoding pCI/S plasmid DNA efficiently primed IgG2a antibody (IgG1/IgG2a ratio <0.3) and CTL responses to HBsAg (Th1 immunity). In contrast, a single intradermal injection of 1 microg of particle-coated pCI/S DNA with the gene-gun-primed IgG1 antibody responses to HBsAg (IgG1/IgG2a ratio >80) but there was no CTL response (Th2 immunity). Injection of immune-stimulating CpG-containing oligodeoxy-nucleotides (ODN) into the skin area used for gene-gun-mediated pCI/S DNA delivery shifted the polarization of the response towards Th1 immunity. A similar shift from Th2 to Th1 immunity was observed when the skin area used for gene-gun-mediated DNA transfer was conditioned by injection of recombinant IL-12. DNA vaccination can thus prime polarized immunity to HBsAg. The polarization of immunity is determined by the technique of plasmid DNA delivery as well as by conditions of the tissue into which DNA is inoculated. Th1 immunity to HBsAg (primed by injection of naked pCI/S DNA) dominated Th2 immunity (primed by gene-gun-mediated pCI/S DNA). In contrast, an established HBsAg-specific Th2 immunity was readily shifted towards Th1 immunity (including specific CTL priming) by an intramuscular boost injection of pCI/S DNA. These data contribute to the rational design of DNA vaccination strategies to efficiently prime anti-viral Th1 immune effector specificities using the gene gun.

Early and selective disappearance of telethonin protein from the sarcomere in neurogenic atrophy

Mutations of the human telethonin gene have recently been shown to cause limb girdle muscular dystrophy type 2G in three Brazilian families. The mRNA has been shown to be dynamically regulated in animals, however, the fate of the protein in human muscle is unknown. In order to assess the expression of telethonin in more frequently encountered myopathological conditions we generated and characterized a rabbit antiserum raised against the C-terminal end of telethonin by immunoblotting and immunogold EM. Indirect immunofluorescence analysis of a wide variety of neuromuscular disorders including dystrophinopathies, metabolic myopathies, denervation disorders, congenital and inflammatory myopathies revealed that the characteristic Z-band staining of telethonin was preserved in all disease entities included in our study. However, a reduced telethonin immunoreactivity was observed in up to 10% of type II fibers in 10 cases of neurogenic atrophy. A decreased telethonin staining was more frequently observed in early stages of fiber atrophy than in type II fibers displaying normal or highly atrophic fiber diameters. Hence, not only the telethonin transcript is rapidly downregulated in denervated muscle but the protein itself undergoes dynamic changes while its known sarcomeric binding partner titin remains unaltered. Beyond its role as a static component of Z-bands, these findings indicate that telethonin protein levels seems to be at least in part regulated by neuronal activity and is thus linked to the dynamic control of myofibrillogenesis and muscle turnover in human skeletal muscle.

Further survey of the occurrence of Fusarium toxins in wheat grown in southwest Germany

A total of 53, 54, 57, 52 and 60 wheat samples for feed use were collected randomly after the 1989, 1990, 1991, 1992 and 1993 crops, respectively, from farms in an area of southwest Germany. Deoxynivalenol (DON), 3- and 15-acetyldeoxynivalenol (3-, 15-ADON), nivalenol (NIV), HT-2 toxin (HT-2), T-2 toxin (T-2), diacetoxyscirpenol (DAS), and fusarenon-X (FUS-X) were determined by gas chromatography, combined with mass selective detection (GC-MS), zearalenone (ZEA), alpha- and beta-zearalenol (alpha-beta-ZOL) were determined by HPLC. DON was the major toxin, with incidences at 77 to 93% and mean contents at 167 to 735 micrograms/kg. In contrast, incidences of ZEA, 3-ADON, NIV, HT-2, and T-2 were at 13 to 37%, 10 to 44%, 15 to 67%, 0 to 11%, and 0 to 12%, respectively, with mean contents in positive samples between 2 and 73 micrograms/kg, except for 948 micrograms/kg 3-ADON in samples from 1993. 15-ADON and FUS-X were assayed in samples from 1991, 1992 and 1993. 15-ADON was found in 0 to 11% of samples at mean levels < or = 17 mu/kg, DAS, alpha- and beta-ZOL, and FUS-X were not detected in any sample. Over the years, incidences and levels of toxins remained constant, decreased or increased, with most differences between years being slight and insignificant. The risk for livestock due to DON, HT-2 and ZEA was estimated based on maximum tolerated levels recommended for these toxins in some countries.

Modulating specific priming of immune effector functions by DNA-based vaccination strategies

We have used the hepatitis B virus system in mice to investigate under which conditions the different DNA delivery techniques used in DNA vaccination introduce a T2 or T1 bias into the responses they elicit. Priming mice by an intramuscular injection of 100 microg plasmid DNA stimulated long-lasting T1 immune responses that included specific activation of potent MHC-1-restricted CTL responses. In contrast, priming mice with an intradermal injection of a low dose of plasmid DNA (0.1-1 microg/mouse) stimulated long-lasting T2 immune responses but no CTL responses. This polarization (spectrum of immune effector specificities) of immune responses elicited by plasmid DNA vaccines is determined by different factors, e.g. (i) the vaccination technique used; (ii) the age of the immunized animal; (iii) the condition of the local tissue environment to which DNA is delivered; (iv) the co delivery of immune-modulating factors; and (v) the type of antigen encoded by the plasmid DNA vaccine. DNA vaccination offers the possibility of constructing endogenous, chimaeric antigens with enhanced, hsp-facilitated expression, enhanced immunogenicity for B cells, and alternative, TAP-independent processing for MHC-1 restricted peptide presentation.

PsaA (pneumococcal surface adhesin A) and PspA (pneumococcal surface protein A) DNA vaccines induce humoral and cellular immune responses against Streptococcus pneumoniae

Streptococcus pneumoniae is one of the most important human pathogens and improvement of the currently used polysaccharide vaccines is being pursued. We constructed DNA vaccine vectors containing either the full-length psaA (pneumococcal surface adhesin A) or a truncated pspA (pneumococcal surface protein A--pspA') gene. Both constructs showed transient expression of the antigens in vertebrate cells and induced significant antibody response to the pneumococcal antigens in BALB/c mice injected intramuscularly (i.m.). Fusion with an N-terminal cytoplasmatic SV40 T-antigen (CT-Ag), which was previously shown to stabilize poorly expressed antigens through association with Hsp73, also induced anti-PspA antibody response. The induction of antibodies with a low IgG1:IgG2a ratio and elevated gamma interferon (IFN-gamma) production by spleen cells elicited by DNA vaccination indicate preferential priming of Th1 immunity. Since induction of antibodies against both PsaA and PspA was previously shown to correlate with protection against fatal infection with S. pneumoniae and cell-mediated immune responses could contribute to protection, further evaluation of PsaA and PspA as antigens for a DNA vaccine against S. pneumoniae could be promising.

Clustering of colonic lamina propria CD4(+) T cells to subepithelial dendritic cell aggregates precedes the development of colitis in a murine adoptive transfer model

Initial lesions in inflammatory bowel disease induced during the repopulation of immunodeficient RAG1(-/-) mice with immunocompetent CD4(+) T cells have not been previously described. In this transfer colitis model, we followed CD4(+) T cell repopulation in the host by injecting autofluorescent CD4(+) T cells from congenic, enhanced green fluorescent protein (eGFP)-transgenic mice. This allowed the direct, sensitive, and unambiguous histological detection of the repopulation of the intestinal tract, mesenteric lymph nodes, and spleen of the host with donor eGFP(+) CD4(+) T cells. We identified in RAG1(-/-) mice intestinal dendritic cell (DC) aggregates under the basal crypt epithelium at the mucosa/submucosa junction from which F4/80(+) macrophages were excluded. At Days 8 to 11 posttransfer (before colitis was manifest), CD4(+) T cells clustered and proliferated in CD11c(+) DC aggregates. T cell clustering was most pronounced in the cecum where histologically overt colitis became manifest 5 to 10 days later. Junctional DC aggregates were thus prevalent in the triggering phase of the disease. The data suggest that pathogenic T cell responses inducing inflammatory bowel disease are primed or restimulated in situ in junctional CD4(+) T cell/DC aggregates.