Abstract 466: Myopathy Causing Bag3 P209L Protein Leads to Restrictive Cardiomyopathy Caused by Aggregate Formation and Sarcomere Disruption in Cardiomyocytes

The co-chaperone BAG3 (Bcl-2 associated athanogene 3) is strongly expressed in cross-striated muscles and plays a key role in the turnover of muscle-proteins as a member of the CASA (chaperone-assisted selected autophagy) complex. An amino acid exchange (P209L) in the human BAG3 gene, caused by a single base mutation, gives rise to a severe dominant childhood muscular dystrophy, restrictive cardiomyopathy, and respiratory insufficiency. To get deeper insights into the pathophysiological mechanisms of the disease, we generated a transgenic mouse model of the human mutation BAG3 P209L , in which a fusion protein consisting of the human BAG3 P209L and the green fluorescent protein eGFP can be conditionally overexpressed. Ubiquitous overexpression of BAG3 P209L -eGFP leads to a severe phenotype between the second and fourth week of life, including decreased body weight, skeletal muscle weakness, and heart failure. Echocardiography revealed that the BAG3 P209L -mice suffer from restrictive cardiomyopathy and Sirius-red-staining of heart tissue showed extensive fibrosis. In cardiomyocytes, isolated from hearts of transgenic mice overexpressing BAG3 wt -eGFP or BAG3 P209L -eGFP, BAG3 wt -eGFP stringently localizes to sarcomeres and intercalated discs, whereas cardiomyocytes from BAG3 P209L -eGFP mice displayed formation of BAG3 containing aggregates and disruption of sarcomeres in vivo . While BAG3 P209L -eGFP binding to á-Hsp70, Filamin C and á-HspB8 was unchanged it was less soluble than BAG3 and had a tendency to aggregate, thereby sequestering BAG3 and its clients. Depletion of the BAG3 pool leads to an impairment of CASA and accumulation of damaged proteins, causing sarcomere disintegration leading to restrictive cardiomyopathy.

HLA typing by next-generation sequencing - getting closer to reality

Next generation sequencing (NGS) denotes novel sequencing technologies that enable the generation of a large number of clonal sequences in a single sequencing run. NGS was initially introduced for whole genome sequencing and for quantitation of viral variants or genetic mutations in tumor tissues; more recently, the potential for high resolution HLA typing and high throughput analyses has been explored. It became clear that the complexity of the HLA system implicates new challenges, especially for bioinformatics. From an economical point of view, NGS is becoming increasingly attractive for HLA typing laboratories currently relying on Sanger based sequencing. Realizing the full potential of NGS will require the development of specifically adapted typing strategies and software algorithms. In the present review, three laboratories that were among the first to perform HLA-typing using different NGS platforms, the Roche 454, the Illumina Miseq and the Ion Torrent system, respectively, give an overview of these applications and point out advantages and limitations.

Severe protein aggregate myopathy in a knockout mouse model points to an essential role of cofilin2 in sarcomeric actin exchange and muscle maintenance

Mutations in the human actin depolymerizing factor cofilin2 result in an autosomal dominant form of nemaline myopathy. Here, we report on the targeted ablation of murine cofilin2, which leads to a severe skeletal muscle specific phenotype within the first two weeks after birth. Apart from skeletal muscle, cofilin2 is also expressed in heart and CNS, however the pathology was restricted to skeletal muscle. The two close family members of cofilin2 - ADF and cofilin1 - were co-expressed in muscle, but unable to compensate for the loss of cofilin2. While primary myofibril assembly and muscle development were unaffected in cofilin2 mutant mice, progressive muscle degeneration was observed between postnatal days 3 and 7. Muscle pathology was characterized by sarcoplasmic protein aggregates, fiber size disproportion, mitochondrial abnormalities and internal nuclei. The observed muscle pathology differed from nemaline myopathy, but showed combined features of actin-associated myopathy and myofibrillar myopathy. In cofilin2 mutant mice, the postnatal expression pattern and turnover of sarcomeric α-actin isoforms were altered. Levels of smooth muscle α-actin were increased and remained high in developing muscles, suggesting that cofilin2 plays a crucial role during the exchange of α-actin isoforms during the early postnatal remodeling of the sarcomere.

TNFA promoter alleles--frequencies and linkage with classical HLA genes in a South German Caucasian population

The tumor necrosis factor alpha (TNFA) promoter region exhibits several polymorphisms, which have been hypothesized to influence gene expression, thereby associating positively or negatively with inflammatory conditions. Many studies have focused on single nucleotide polymorphisms (SNPs) taking not into account additive or inverse effects between different SNPs. We typed 1,021 healthy Caucasian volunteer stem cell donors for their TNFA promoter as well as their HLA-A,-C,-B,-DRB1 loci. Using statistical methods, we reconstructed TNFA promoter alleles and analyzed their frequency and linkage with HLA genes. We show that the number of TNFA promoter alleles frequent enough to be analyzed in clinical studies is limited and that a strong linkage with classical HLA genes is present, especially for the extended HLA-haplotype HLA-A*01:01/HLA-C*07:01/HLA-B*08:01/TNFA promoter allele 3/HLA*DRB1*03:01. Taking into account SNP frequency information, it is possible to quite accurately deduce TNFA promoter alleles by generic Sanger sequencing, obviating the need for elaborating allele-specific sequencing. This information may enable investigators to consider the complete TNFA regulatory region in a phase-separated manner in contrast to previous approaches examining only one or few isolated SNPs.

HLA-E polymorphisms in hematopoietic stem cell transplantation

Human leukocyte antigen (HLA)-E is an inhibitory ligand of natural killer cells and γ/δ T-cells. Differential expression of HLA-E alleles on the cell surface has been reported to influence outcome of hematopoietic stem cell transplantation (HSCT). We performed HLA-E genotyping in 116 HSCT patients and their HLA-matched unrelated donors. The impact of HLA-E genotypes on patient's overall survival (OS), disease free survival (DFS), cumulative incidences for relapse, transplant-related mortality (TRM) and acute graft vs host disease (aGvHD) was assessed. Neither univariate nor multivariate analysis showed any influence of HLA-E polymorphisms on the investigated endpoints of HSCT in our cohort. We could not confirm any of the previous observations in our cohort and consider it unlikely that HLA-E polymorphisms affect outcome of HSCT.

One amino acid change located in the conserved region of the alpha 1 domain specifies the novel HLA-C*07:147 allele

The novel HLA-C allele HLA-C*07:147 contains one nucleotide substitution in exon 2 leading to an amino acid change in the alpha 1 domain from phenylalanine to leucine.

Nuclear localization of the zebrafish tight junction protein nagie oko

The tight junctions-associated MAGUK protein nagie oko is closely related to Drosophila Stardust, mouse protein associated with lin-seven 1 (Pals1), and human MAGUK p55 subfamily member 5 (Mpp5). As a component of the evolutionarily conserved Crumbs protein complex, nagie oko is essential for the maintenance of epithelial cell polarity. Here, we show that nagie oko contains a predicted nuclear export and two conserved nuclear localization signals. We find that loss of the predicted nuclear export signal results in nuclear protein accumulation. We show that nagie oko nuclear import is redundantly controlled by the two nuclear localization signals and the evolutionarily conserved region 1 (ECR1), which links nagie oko with Par6-aPKC. Finally, deletion forms of nagie oko that lack nuclear import and export signals complement several nagie oko mutant defects in cell polarity and epithelial integrity. This finding provides an entry point to potentially novel and unknown roles of this important cell polarity regulator.

Radiosynthesis and evaluation of [11C]BTA-1 and [11C]3'-Me-BTA-1 as potential radiotracers for in vivo imaging of beta-amyloid plaques

AIM

To evaluate the in vitro and in vivo characteristics of [N-methyl-(11)C]2-(4'-(methylaminophenyl)-benzothiazole ([(11)C]BTA-1) as well as [N-methyl-(11)C]2-(3'-methyl-4'-(methylamino)phenyl)-benzothiazole ([(11)C]3'-Me-BTA-1) as diagnostic markers of amyloid-beta (Abeta) in Alzheimer's disease (AD).

MATERIAL, METHODS

Brain uptake and clearance was determined in wild-type mice. Binding affinities (K(i)) of [(11)C]BTA-1 and [(11)C]3'-Me-BTA-1 for aggregated Abeta(1-40) fibrils were assessed. Autoradiography was performed on brain sections of AD patients. To demonstrate binding specificity in vivo BTA-1 was injected i.p. in transgenic mice (Tg2576). Brain sections were analysed consecutively. Additionally, a [(11)C]BTA-1 PET study of an AD patient and a healthy control was performed.

RESULTS

In mice brain uptake and clearance of [(11)C]BTA-1 is compatible with the half life of (11)C (2 min: 12.7 % ID/g; 30 min: 4.6% ID/g). In contrast clearance rate of [(11)C]3'-Me-BTA-1 is too slow (2 min 4% ID/g; 30 min 12% ID/g) to achieve sufficient clearance of free and non specifically bound radioactivity. K(i) of [(11)C]BTA-1 is 11 nmol/l and that of [(11)C]3'-Me-BTA-1 27 nmol/l. Both radioligands label Abeta selectively and specifically in AD patients and transgenic mice in vitro. The in vivo stained brain sections show a labelling of Abeta plaques. The AD patient has a higher prefrontal, parietal and striatal [(11)C]BTA-1 accumulation than the healthy control. Metabolite analysis revealed approximately 75% intact [(11)C]BTA-1 after 30min in plasma.[(11)C]BTA-1 is favourable for in vivo imaging of Abeta due to its rapid brain entry, sufficient clearance and good binding affinity for Abeta.

CONCLUSION

The ability to label Abeta plaques in vivo in human subjects supports the suitability of [(11)C]BTA-1 as a plaque imaging agent.

Uncoordinated Expression of Myosin Heavy Chains and Myosin-Binding Protein C Isoforms in Human Extraocular Muscles

PURPOSE

To examine the distribution of myosin-binding protein C (MyBP-C) in human extraocular muscles (EOMs) and to correlate the myosin heavy chain (MyHC) and the MyBP-C composition of the fibers.

METHODS

Samples from 17 EOMs, 3 levator palpebrae (LP), and 6 limb muscles were analyzed with SDS-PAGE and immunoblot or processed for immunocytochemistry with monoclonal antibodies (mAbs) against MyBP-C-fast, MyBP-C-slow, MyHCIIa, MyHCI, MyHCsto, MyHCalpha-cardiac, and MyHCemb.

RESULTS

In the limb muscle samples, fast fibers were labeled with anti-MyBP-C-fast and anti-MyBP-C-slow, whereas the slow fibers were immunostained with anti-MyBP-C-slow only, in accordance with previous studies. In 11 EOM samples MyBP-C-fast was not detected, and weak staining with anti-MyBP-C-fast was seen only in a few fibers in the proximal part of 2 muscles. The mAb against MyBP-C-slow labeled all fibers, but fibers containing MyHCI were generally more strongly stained. In the levator palpebrae, immunostaining with anti-MyBP-C-fast was present in some fibers labeled with anti-MyHCIIa and/or anti-MyHCeom. MyBP-C-fast and -intermediate were not detected biochemically in the EOMs.

CONCLUSIONS

The lack of MyBP-C-fast and intermediate is an additional feature of the human EOM allotype. The true EOMs have a unique myofibrillar protein isoform composition reflecting their special structural and functional properties. The levator palpebrae muscle phenotype is intermediate between that of the EOMs and the limb muscles.

Calpain 1-gamma filamin interaction in muscle cells: a possible in situ regulation by PKC-alpha

Calpains are a family of calcium-dependent cysteine-proteases involved in cytoskeleton remodelling and muscle differentiation. In a recent study, we observed the presence of calpain 1 in the muscle contractile apparatus and specifically in the N1- and N2-lines. This calpain isoform was found to be involved in the degradation of muscle fibres via proteolysis of key proteins in Z-disk and costameric junctions. The goal of this study was to determine whether gamma-filamin--a specific muscle isoform of the filamin family--is a calpain 1 substrate and to characterise this interaction. Gamma-filamin is a major muscle architectural protein located in the Z-line and under the sarcolemmal membrane. This protein is a component of the chain binding the sarcolemma to the sarcomeric structure. In this study, we found that gamma-filamin formed a stable complex in vitro and in cells with calpain 1 in the absence of calcium stimulation. We also located the binding domains in the C-terminus of gamma-filamin with a cleavage site between serine 2626 and serine 2627 in the hinge 2 region. The catalytic (80 kDa) and regulatory (28 kDa) subunits of calpain 1 are both involved in high affinity binding at gamma-filamin. Moreover, we showed that phosphorylation of the filamin C-terminus domain by PKC alpha protected gamma-filamin against proteolysis by calpain 1 in COS cells. Stimulation of PKC activity in myotubes, prevented gamma-filamin proteolysis by calpain and resulted in an increase in myotube adhesion.

The spectrum of pathology in central core disease

Central core disease is a congenital myopathy with muscle weakness defined pathologically by the presence of extensive areas in muscle fibres that are devoid of oxidative enzyme activity. The gene responsible has been shown to be the ryanodine receptor 1 on chromosome 19q13 and mutations have now been identified in several patients. Some cases with the morphological defect remain molecularly undefined, particularly those studied before molecular studies were available. We have studied three families with congenital onset, each with a dominantly inherited mutation in a C-terminal exon of the ryanodine receptor 1. They illustrate the spectrum of pathology that can be observed in patients with the myopathic features of central core disease. We show that extensive fibrosis and fat may be present, type 1 fibre uniformity may occur in the absence of cores; cores may be central or peripheral, single or multiple; and that an appearance of multiple focal minicores might cause a diagnostic pathological dilemma. In addition, we show the value of immunocytochemistry in identifying cores, in particular the use of antibodies to desmin and gamma-filamin.

Loss of beta1 integrin function results in a retardation of myogenic, but an acceleration of neuronal, differentiation of embryonic stem cells in vitro

Integrin cell surface receptors play an important role for cell adhesion, migration, and differentiation during embryonic development by mediating cell-cell and cell-matrix interactions. Less is known about the function of integrins during commitment and lineage determination of early embryogenesis. Homozygous inactivation of the beta1 integrin gene results in embryonal death in mice around the time of implantation. In vitro, differentiation of embryonic stem (ES) cells which lack beta1 integrin (beta1-/-) into the cardiogenic lineage is delayed and results in a disordered cellular specification (Fässler et al., J. Cell Sci. 109, 2989-2999, 1996). To analyze beta1 integrin function during myogenesis and neurogenesis we studied differentiation of beta1-/- ES cells via embryoid bodies into skeletal muscle and neuronal cells in vitro. beta1-/- cells showed delayed and reduced myogenic differentiation compared to wildtype and heterozygous (beta1+/-) ES cells. RT-PCR analysis demonstrated delayed expression of skeletal muscle-specific genes in the absence of beta1 integrin. Immunofluorescence studies with antibodies against the sarcomeric proteins myosin heavy chain, titin, nebulin, and slow C-protein showed that myotubes formed, but their number was reduced and the assembly of sarcomeric structures was retarded. In contrast, neuronal cells differentiating from beta1-/- ES cells appeared earlier than wildtype and heterozygous (beta1+/-) ES cells. This was shown by the accelerated expression of neuron-specific genes and an increased number of neuronal cells in beta1-/- embryoid bodies. However, neuronal outgrowth was retarded in the absence of beta1 integrin. No functional difference between wildtype and beta1-/- cells was found with respect to secretion of gamma-aminobutyric acid, the main neurotransmitter of ES cell-derived neuronal cells. The lineage-specific effects of loss of beta1 integrin function, that is the inhibition of mesodermal and acceleration of neuroectodermal differentiation, were supported by differential expression of genes encoding lineage-specific transcription factors (Brachyury, Pax-6, Mash1) and signaling molecules (BMP-4 and Wnt-1). Because of the reduced and delayed expression of the BMP-4 encoding gene in beta1-/- cells, we analyzed in wildtype and beta1-/- cells the regulatory role of exogenously added BMP-4 on the expression of the mesodermal and neuronal marker genes, Brachyury and wnt-1, respectively. The data suggest that BMP-4 plays a regulatory role during differentiation of wildtype and beta1-/- cells by modifying mesodermal and neuronal pathways. The reduced expression of BMP-4 in beta1-/- cells may account for the accelerated neuronal differentiation in beta1-/- ES cells.

C-terminally deleted fragments of 40-kDa earthworm actin modulator still show gelsolin activities

C- and N-terminally truncated fragments of earthworm gelsolin were constructed, cloned and expressed in Escherichia coli. G-actin-binding properties of these fragments and their influences on the polymeric state of actin were investigated. A construct lacking a large part of the third segment [E(1-295)] supports actin nucleation similar to the complete protein and shows reduced actin fragmentation property, but is no longer Ca2+-sensitive in its activity. The first and the second segments (E1 and E2) each contain one actin-binding site. In contrast to human gelsolin, E1 in combination with a short N-terminal region of E2 is not sufficient for the F-actin-severing activity of the protein.

Molecular changes of titin in left ventricular dysfunction as a result of chronic hibernation

Cardiomyocytes of chronic hibernating myocardium are affected by partial to complete loss of sarcomeres, accumulation of glycogen, adaptations in size and shape of mitochondria, reorganisation of nuclear chromatin and depletion of sarcoplasmic reticulum. The nature of these changes, which from a purely morphologic viewpoint are akin to dedifferentiation, needed further clarification at the molecular level. For this purpose we have studied the expression and reorganization of titin, one of the earliest markers of cardiomyocytes differentiation. By use of monoclonal antibodies, recognizing different epitopes distributed over the whole length of the titin molecule, we were able to detect changes in its molecular organization as a result of chronic hibernation. The epitopes of the titin molecule attached to the Z-disc and those present close to the M-line remained detectable at all stages of hibernation, while epitopes at the A-I junction and parts of the myosin anchoring region of the molecule became masked or were lost. A fragmented or punctuated appearance of the titin staining pattern with antibodies to A-I junction related epitopes is found in cells which we consider to represent a more advanced stage of dedifferentiation. Changes in the distribution of the titin molecule or its molecular environment in hibernating myocardium resemble at least in part changes occurring during muscle cell differentiation, although in reversed order.

Purification and physical properties of nematode mini-titins and their relation to twitchin

We have isolated mini-titin from the nematodes Ascaris lumbricoides and Caenorhabditis elegans under native conditions using a modification in the procedure to prepare this protein from insect muscle. The proteins have an apparent molecular weight of 600,000 and appear in oriented specimens as flexible thin rods with a length around 240–250 nm. The circular dichroism spectrum of the Ascaris protein is dominated by beta-structure. The proteins react with antibodies to insect mini-titin and also with antibodies raised against peptides contained in the sequence predicted for twitchin, the product of the Caenorhabditis elegans unc-22 gene. Antibodies to insect mini-titin decorate the body musculature as well as the pharynx of wild-type C. elegans in immunofluorescence microscopy. In the twitchin mutant E66 only the pharynx is decorated. We conclude that the mini-titins of invertebrate muscles defined earlier by ultrastructural criteria are very likely to be twitchins, i.e. molecules necessary for normal muscle contraction. We discuss the molecular properties of the proteins in the light of the sequence established for twitchin.

Nebulin and titin expression in Duchenne muscular dystrophy appears normal

Monoclonal antibodies which recognize different epitopes on either titin or nebulin show normal staining patterns on frozen sections of three muscle biopsies of Duchenne muscular dystrophy (DMD). Gel electrophoresis and immunoblotting performed on two of these muscle biopsies show the normal pattern of titin and nebulin polypeptides. Since the donor of one of these biopsies has a large deletion of the 5'-region of the DMD gene, our results argue against the recent proposal that nebulin is the gene mutated in DMD.

Structural and biochemical analysis of skinned smooth muscle preparations

This paper describes a biochemical and immunocytochemical analysis of smooth muscle strips that were chemically skinned and subjected to contraction and relaxation cycles according to procedures commonly employed in current skinned smooth muscle work. The fate of four major proteins, myosin, filamin, caldesmon and actin, was followed with respect to the proportionate loss of these proteins to the bathing medium as well as to their structural redistribution within the cells in the muscle strips. Large losses (of the order of 50%) of both myosin and filamin occurred at the skinning step, using either Triton X-100 or Saponin as the detergent; losses of actin were up to 30% with Triton X-100 and around 15% with Saponin. Losses of caldesmon were difficult to assess due to the rapid degradation of this protein in the bathing medium. Subsequent cycles of contraction and relaxation resulted in accumulated loss, notably of myosin and filamin, so that after the third contraction as little as 20% and 40% respectively of the original complement of these proteins remained in the muscle strips. These changes in protein composition were accompanied by a drastic redistribution of the proteins in the muscle cells. Most marked were the changes seen with myosin, significant amounts of this protein being already found in the connective tissue space after the first relaxation. These findings point to the need for a careful reappraisal of the conditions currently used in skinned smooth muscle research.