Absence Of Mitochondria Research Articles

Anti-Cryptosporidial Drug-Discovery Challenges and Existing Therapeutic Avenues: A "One-Health" Concern.

Cryptosporidiosis is the leading cause of life-threatening diarrheal infection, especially in infants. Oocysts contaminate the environment, and also, being a zoonotic disease, cryptosporidiosis is a threat to One Health. Nitazoxanide is the only FDA-approved drug, effective only in immunocompetent adults, and is not safe for infants. The absence of mitochondria and apicoplast, the presence of an electron-dense band (ED band), hindrances in its genetic and phenotypic manipulations, and its unique position inside the host cell are some challenges to the anti-cryptosporidial drug-discovery process. However, many compounds, including herbal products, have shown efficacy against Cryptosporidium during in vitro and in vivo trials. Still, the "drug of choice" against this protozoan parasite, especially in immunocompromised individuals and infants, has not yet been explored. The One-Health approach addresses this issue, focusing on the intersection of animal, human, and environmental health. The objective of this review is to provide knowledge about novel anti-cryptosporidial drug targets, available treatment options with associated limitations, and possible future shifts toward natural products to treat cryptosporidiosis. The current review is organized to address the treatment and prevention of cryptosporidiosis. An anti-cryptosporidial drug that is effective in immunocompromised individuals and infants is a necessity of our time.

Application of fluorescence lifetime imaging microscopy to monitor glucose metabolism in pancreatic islets in vivo.

Glucose stimulated insulin secretion is mediated by glucose metabolism via oxidative phosphorylation generating ATP that triggers membrane depolarization and exocytosis of insulin. In stressed beta cells, glucose metabolism is remodeled, with enhanced glycolysis uncoupled from oxidative phosphorylation, resulting in the impaired glucose-mediated insulin secretion characteristic of diabetes. Relative changes in glycolysis and oxidative phosphorylation can be monitored in living cells using the 3-component fitting approach of fluorescence lifetime imaging microscopy (FLIM). We engrafted pancreatic islets onto the iris to permit in vivo FLIM monitoring of the trajectory of glucose metabolism. The results show increased oxidative phosphorylation of islet cells (∼90% beta cells) in response to hyperglycemia; in contrast red blood cells traversing the islets maintained exclusive glycolysis as expected in the absence of mitochondria.

Yeast Mitochondria Import Aqueous FeII and, When Activated for Iron-Sulfur Cluster Assembly, Export or Release Low-Molecular-Mass Iron and Also Export Iron That Incorporates into Cytosolic Proteins.

Iron-sulfur cluster (ISC) assembly occurs in both mitochondria and cytosol. Mitochondria are thought to export a low-molecular-mass (LMM) iron and/or sulfur species which is used as a substrate for cytosolic ISC assembly. This species, called X-S or (Fe-S)int, has not been directly detected. Here, an assay was developed in which mitochondria were isolated from 57Fe-enriched cells and incubated in various buffers. Thereafter, mitochondria were separated from the supernatant, and both fractions were investigated by ICP-MS-detected size exclusion liquid chromatography. Aqueous 54FeII in the buffer declined upon exposure to intact 57Fe-enriched mitochondria. Some 54Fe was probably surface-absorbed but some was incorporated into mitochondrial iron-containing proteins when mitochondria were activated for ISC biosynthesis. When activated, mitochondria exported/released two LMM nonproteinaceous iron complexes. One species, which comigrated with an Fe-ATP complex, developed faster than the other Fe species, which also comigrated with phosphorus. Both were enriched in 54Fe and 57Fe, suggesting that the added 54Fe entered a pre-existing pool of 57Fe, which was also the source of the exported species. When 54Fe-loaded 57Fe-enriched mitochondria were mixed with isolated cytosol and activated, multiple cytosolic proteins became enriched with Fe. No incorporation was observed when 54Fe was added directly to the cytosol in the absence of mitochondria. This suggests that a different Fe source in mitochondria, the one enriched mainly with 57Fe, was used to export a species that was ultimately incorporated into cytosolic proteins. Iron from buffer was imported into mitochondria fastest, followed by mitochondrial ISC assembly, LMM iron export, and cytosolic ISC assembly.

Lophomonas blattarum-like organism in bronchoalveolar lavage from a pneumonia patient: current diagnostic scheme and polymerase chain reaction can lead to false-positive results.

Lophomonas blattarum is an anaerobic protozoan living in the intestine of cockroaches and house dust mites, with ultramicroscopic characteristics such as the presence of a parabasal body, axial filament, and absence of mitochondria. More than 200 cases of Lophomonas infection of the respiratory tract have been reported worldwide. However, the current diagnosis of such infection depends only on light microscopic morphological findings from respiratory secretions. In this study, we attempted to provide more robust evidence of protozoal infection in an immunocompromised patient with atypical pneumonia, positive for Lophomonas-like protozoal cell forms. A direct search of bronchoalveolar lavage fluid via polymerase chain reaction (PCR), transmission electron microscopy (TEM), and metagenomic next-generation sequencing did not prove the presence of protozoal infection. PCR results were not validated with sufficient rigor, while de novo assembly and taxonomic classification results did not confirm the presence of an unidentified pathogen. The TEM results implied that such protozoal forms in light microscopy are actually non-detached ciliated epithelial cells. After ruling out infectious causes, the patient's final diagnosis was drug-induced pneumonitis. These findings underscore the lack of validation in the previously utilized diagnostic methods, and more evidence in the presence of L. blattarum is required to further prove its pathogenicity.

Myricetin-induced suicidal erythrocyte death.

Myricetin, a type of flavonol commonly found in fruits and herbs, has demonstrated anticancer properties by triggering the process of apoptosis or programmed cell death in tumor cells. Despite the absence of mitochondria and nuclei, erythrocytes can undergo programmed cell death, also known as eryptosis.This process is characterized by cell shrinkage, externalization of phosphatidylserine (PS) on the cell membrane, and the formation of membrane blebs. The signaling of eryptosis involves Ca2+ influx, the formation of reactive oxygen species (ROS), and the accumulation of cell surface ceramide. The present study explored the effects of myricetin on eryptosis. Human erythrocytes were exposed to various concentrations of myricetin (2-8 µM) for 24h. Flow cytometry was used to assess the markers of eryptosis, including PS exposure, cellular volume, cytosolic Ca2+ concentration, and ceramide accumulation. In addition, the levels of intracellular ROS were measured using the 2',7'-dichlorofluorescin diacetate (DCFDA) assay. The myricetin-treated (8 µM) erythrocytes significantly increased Annexin-positive cells, Fluo-3 fluorescence intensity, DCF fluorescence intensity, and the accumulation of ceramide. The impact of myricetin on the binding of annexin-V was significantly reduced, but not completely eliminated, by the nominal removal of extracellular Ca2+. Myricetin triggers eryptosis, which is accompanied and, at least in part, caused by Ca2+ influx, oxidative stress and increase of ceramide abundance.

High quality genome assembly of the amitochondriate eukaryote Monocercomonoides exilis.

Monocercomonoides exilis is considered the first known eukaryote to completely lack mitochondria. This conclusion is based primarily on a genomic and transcriptomic study which failed to identify any mitochondrial hallmark proteins. However, the available genome assembly has limited contiguity and around 1.5 % of the genome sequence is represented by unknown bases. To improve the contiguity, we re-sequenced the genome and transcriptome of M. exilis using Oxford Nanopore Technology (ONT). The resulting draft genome is assembled in 101 contigs with an N50 value of 1.38 Mbp, almost 20 times higher than the previously published assembly. Using a newly generated ONT transcriptome, we further improve the gene prediction and add high quality untranslated region (UTR) annotations, in which we identify two putative polyadenylation signals present in the 3′UTR regions and characterise the Kozak sequence in the 5′UTR regions. All these improvements are reflected by higher BUSCO genome completeness values. Regardless of an overall more complete genome assembly without missing bases and a better gene prediction, we still failed to identify any mitochondrial hallmark genes, thus further supporting the hypothesis on the absence of mitochondrion.

Создание цибридных клеточных культур, содержащих однонуклеотидную замену в гене MT-TL2, ассоциированную с атеросклерозом

Введение. Цибридные клеточные модели наиболее перспективны для изучения патогенеза различных заболеваний. Авторами статьи впервые были созданы такие модели для изучения митохондриальной дисфункции и патологических процессов, развивающихся при атеросклерозе. Цель работы - создание цибридных культур с высоким уровнем гетероплазмии по мутации митохондриального генома m.12315G>A. В предварительных исследованиях авторами статьи было установлено, что пороговый уровень гетероплазмии мутации m.12315G>A ассоциирован с атеросклерозом. Методика. Цибридные культуры создавали путем слияния безмитохондриальных клеток (rho0) и митохондрий из тромбоцитов участников исследования с высоким уровнем гетероплазмии исследуемых мутаций. Для создания rho0-клеток была взята культура моноцитарного происхождения THP-1. Безмитохондриальные клетки были получены с помощью метода M. Kинга и Г. Аттарди. Тромбоциты выделяли из цельной крови участников исследования. Для этого был применен метод центрифугирования в градиенте плотности фиколла-урографина. Для получения цибридных культур клеток была использована методика «ПЭГ-слияния». В созданных безмитохондриальных и цибридных клеточных культурах был проведен количественный анализ копий митохондриального генома. Согласно результатам данного анализа было подтверждено либо отсутствие митохондрий (rho0-клетки), либо их наличие (цибриды). Количество копий мтДНК детектировалось с помощью реал-тайм ПЦР в присутствии красителя SYBR Green I. Результаты. Получены 4 цибридные клеточные линии, содержащие мутацию m.12315G>A с уровнем гетероплазмии выше порогового значения. Заключение. Созданы 4 цибридные культуры с высоким уровнем гетероплазмии по мутации митохондриального генома m.12315G>A. Полученные цибридные клеточные линии могут служить моделями для изучения молекулярно-клеточных механизмов митохондриальной дисфункции при атеросклерозе и других сердечно-сосудистых заболеваниях. Цибридные культуры можно использовать для моделирования атерогенеза, а также для подбора патогенетически обоснованной лекарственной терапии при атеросклерозе. Introduction. Cybrid cell models are most promising for studying pathological mechanisms in different diseases. The authors for the first time created such models for studying mitochondrial dysfunction and pathological processes underlying atherosclerosis. Aim. Creation of cybrid cultures with a high heteroplasmy level for mitochondrial genome mutation m.12315G>A. A preliminary study by the authors showed that the heteroplasmy level of mutation m.12315G>A was associated with atherosclerosis. Methods. Cybrid cultures were created by fusing non-mitochondrial cells (rho0) and mitochondria from platelets of study participants with a high heteroplasmy level of the mutations under study. A THP-1 culture of monocytic origin was used to create rho0 cells. Non-mitochondrial cells were obtained using the M. King and G. Attardi method. Platelets were extracted from whole blood of study participants with Ficoll-Urografin density gradient centrifugation. Cybrid cell cultures were obtained by the PEG-mediated fusion method. In the created non-mitochondrial and cybrid cell cultures, quantitative analysis of mitochondrial genome copies was performed. This analysis confirmed either the absence of mitochondria (rho0-cells) or their presence (cybrids). The mtDNA copies were quantified using real-time PCR in the presence of the SYBR Green I stain. Results. Four cybrid cell lines were obtained, which contained the m.12315G>A mutation with heteroplasmy levels higher than the threshold level. Conclusion. Four cybrid cultures were created with a high heteroplasmy level for the mitochondrial genome mutation m.12315G>A. The obtained cell lines can be used as models for studying molecular cellular mechanisms of mitochondrial dysfunction in atherosclerosis and cardiovascular diseases. In addition, they may be useful for modeling atherogenesis in cells and for selecting therapy for patients with atherosclerosis.

Mikrocytos mytilicoli n.sp. (Cercozoa, Mikrocytida, Mikrocytiidae) infecting the copepod Mytilicola intestinalis (Arthropoda, Cyclopoida, Mytilicolidae), a symbiont of Mytilus galloprovincialis in Galicia (NW Spain)

During a histopathological survey of Mytilus galloprovincialis in Galicia (NW Spain), microcells were observed infecting several organs of the symbiont copepod Mytilicola intestinalis. Positive results of PCR assay with specific primers for genus Mikrocytos and a clear signal of in situ hybridization with MACKINI-1 digoxigenin- labelled DNA probe (DIG-ISH) indicated a protozoan parasite of Mikrocytos genus. The ultrastructural study revealed intra and extracellular locations, polymorphic nuclei, intracellular round vesicles in the cytoplasm and absence of mitochondria. The present paper reports the characterization of the Mikrocytos sp. infecting M. intestinalis and proposes a novel species in the genus: Mikrocytos mytilicoli n. sp. A sequence of 18S-28S rDNA was obtained with 95.6% maximum identity (query cover 100%) with Mikrocytos mackini. Phylogenetic analysis showed that M. mytilicoli n. sp. and M. mackini share a common ancestor. However, comparison of the ITS1 rDNA region showed low similarity (75.8%) with M. mackini, which, combined with differences in ultrastructural details, host and geographic location, support the designation of a new species. This is the first description of a microcytid parasite of the genus Mikrocytos from a non-bivalve host.

The Oxymonad Genome Displays Canonical Eukaryotic Complexity in the Absence of a Mitochondrion.

The discovery that the protist Monocercomonoides exilis completely lacks mitochondria demonstrates that these organelles are not absolutely essential to eukaryotic cells. However, the degree to which the metabolism and cellular systems of this organism have adapted to the loss of mitochondria is unknown. Here, we report an extensive analysis of the M. exilis genome to address this question. Unexpectedly, we find that M. exilis genome structure and content is similar in complexity to other eukaryotes and less “reduced” than genomes of some other protists from the Metamonada group to which it belongs. Furthermore, the predicted cytoskeletal systems, the organization of endomembrane systems, and biosynthetic pathways also display canonical eukaryotic complexity. The only apparent preadaptation that permitted the loss of mitochondria was the acquisition of the SUF system for Fe–S cluster assembly and the loss of glycine cleavage system. Changes in other systems, including in amino acid metabolism and oxidative stress response, were coincident with the loss of mitochondria but are likely adaptations to the microaerophilic and endobiotic niche rather than the mitochondrial loss per se. Apart from the lack of mitochondria and peroxisomes, we show that M. exilis is a fully elaborated eukaryotic cell that is a promising model system in which eukaryotic cell biology can be investigated in the absence of mitochondria.

Calcium Stimulation of Mitochondrial Respiration is Substrate Dependent and Tissue Specific

Mitochondrial enzymes, such as pyruvate dehydrogenase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase, have been shown to be stimulated by calcium ion in isolated enzyme experimental systems. However, the extent of Ca2+ stimulation of these enzymes and the resulting integrated stimulatory effect on mitochondrial energy metabolism in in-situ and in-vivo states in the heart and kidney remains to be clarified. In this study, we hypothesized that Ca2+ stimulation of mitochondrial respiration and ATP synthesis is substrate dependent and tissue-specific. To test this hypothesis, we isolated mitochondria from heart and kidney outer medulla from Sprague-Dawley rats. Oxygen consumption rates were determined under different respiratory states: leak state (energized mitochondria in absence of ADP) and the ADP-stimulated state (energized mitochondria in presence of saturating concentration of ADP) with/without bolus injection of different concentrations of CaCl2 using an Oroboros Oxygraph-2k Instrument with various respiratory substrates, including pyruvate+malate (PM), glutamate+malate (GM), alpha-ketoglutarate+malate (AM), palmitoyl-L-carnitine+malate (PCM), and succinate (SUC). The results demonstrated that the various respiratory substrates yielded differences in ADP consumption rates and hence, led to dramatically different respiratory rates in isolated mitochondria from the heart and kidney. Importantly, it was found that Ca2+ significantly increased mitochondrial state III respiration with GM and AM substrates compared to the other substrates in both organs. Moreover, Ca2+ effects on mitochondrial respiration were found to be biphasic, i.e. a small increases in [Ca2+] had a stimulatory effect while large increases had inhibitory effect. These results suggest that energized isolated mitochondria in presence of Ca2+ do not respond the same extent when different substrates are used. We conclude that isolated mitochondria require a suitable substrate combination, optimal [Ca2+], and specific tissue source of mitochondria to achieve a level of energy metabolism and ATP production comparable to in-vivo conditions.

Correction: LKB1 Regulates Mitochondria-Dependent Presynaptic Calcium Clearance and Neurotransmitter Release Properties at Excitatory Synapses along Cortical Axons.

[This corrects the article DOI: 10.1371/journal.pbio.1002516.].

Molecular and Morphological Diversity of the Oxymonad Genera Monocercomonoides and Blattamonas gen. nov.

Oxymonads are a group of flagellates living as gut symbionts of insects or vertebrates. They have several unique features, one of them being the absence of mitochondria. Diversity of this group is seriously understudied, which is particularly true for small species from the family Polymastigidae. We isolated 34 strains of oxymonads with Polymastigidae-like morphology from 24 host species and unused cesspits and sequenced the SSU rRNA gene. Our strains formed two clades in the phylogenetic tree with Streblomastix strix branching between them. This topology was also supported by a three-gene phylogenetic analysis. Despite considerable genetic differences between the clades, light and electron microscopy revealed only subtle differences. The larger clade is considered genus Monocercomonoides and the isolates belonging here were classified into three new species (including the first potentially free-living species), two previously described species, and three unclassified lineages. The smaller clade, here described as Blattamonas gen. nov., consists of three newly described species. Concomitantly with the description of Blattamonas, we elevate the Monocercomonoides subgenus Brachymonas to the genus level. Our study shows that, despite their conserved morphology, the molecular diversity of Polymastigidae-like oxymonads is broad and represents a substantial part of the diversity of oxymonads.

P.295 - C-terminal binding protein 1 (CtBP1) deficiency, mimicking congenital myopathy during infancy

The CtBP1 gene was identified as transcriptional co-repressor that modulates gene expression in multiple cellular pathways. CtBP1 plays a critical role during human embryogenic period. CtBP1 gene presents an active role in myogenesis and post synaptic membrane receptor formation. Its has been associated recently with human disease. Hypotony and muscle weakness are two of the most relevant clinical features, however its effects in muscle pathology has not been described enough . Herein, we describe the fifth reported patient, who showed a similar phenotype of former described patients, sharing the same mutation. Currently is 8 year- old girl born from a non-consanguineous parent. Because her early hypotonia, motor development delay and myogenic EMGs patterns, congenital myopathy was suspected. Muscle biopsy performed at 3 years old showed, atrophic and hypertrophic fibers with abnormal intermyofibrillar network in several fibers. Electron microscope revealed disruption of sarcomeres with Z-line streaming, Intermyofibrillar neatwork disruption and absence of mitochondria. These features extended from 1 to 4–5 sarcomeres. At that time, truncal ataxia was noticed evolving to a progressive cerebellar syndrome, losing their motor and cognitive acquired abilities and developing a severe scoliosis. Tooth enamel defects were also observed. Exome sequencing studies confirmed a heterozygous p.R331W mutation in CtBP1 gene, previously reported and affecting all the former described patients. Segregation analysis did not show this variant in neither of the parents in her brother. Mutation in CtBP1 may be considered as a congenital regressive and severe condition affecting several organs. Because hypotonia is one of the main and first clinical symptoms, CTBP1 deficiency must be added to causes of floppy infant syndrome.

Microparticle and mitochondrial release during extended storage of different types of platelet concentrates

On activation, platelets release vesicles called microparticles (MPs). MPs are heterogeneous with regard to the presence or absence of mitochondria. We quantified MPs in platelet concentrates (PCs) taking their mitochondrial content into account. Platelet-rich plasma (PRP), buffy coat (BC) and apheresis (AP) PCs were tested through 7 days of storage. A combination of flow cytometry and spanning-tree progression analysis of density-normalized events (SPADE) was used to determine MP and mitochondrial release during storage. All the PC biochemical parameters complied with transfusion standards at all times. Platelet activation markers increased during storage and were higher for PRP than other types of PCs. Concentrations of MPs and extracellular mitochondria interpreted by SPADE algorithm were significantly higher in PRP than other in PCs and were stable throughout storage. The mode of preparation, rather than storage duration, impacts the release of MPs and mitochondria in PCs.

LKB1 Regulates Mitochondria-Dependent Presynaptic Calcium Clearance and Neurotransmitter Release Properties at Excitatory Synapses along Cortical Axons.

Individual synapses vary significantly in their neurotransmitter release properties, which underlie complex information processing in neural circuits. Presynaptic Ca2+ homeostasis plays a critical role in specifying neurotransmitter release properties, but the mechanisms regulating synapse-specific Ca2+ homeostasis in the mammalian brain are still poorly understood. Using electrophysiology and genetically encoded Ca2+ sensors targeted to the mitochondrial matrix or to presynaptic boutons of cortical pyramidal neurons, we demonstrate that the presence or absence of mitochondria at presynaptic boutons dictates neurotransmitter release properties through Mitochondrial Calcium Uniporter (MCU)-dependent Ca2+ clearance. We demonstrate that the serine/threonine kinase LKB1 regulates MCU expression, mitochondria-dependent Ca2+ clearance, and thereby, presynaptic release properties. Re-establishment of MCU-dependent mitochondrial Ca2+ uptake at glutamatergic synapses rescues the altered neurotransmitter release properties characterizing LKB1-null cortical axons. Our results provide novel insights into the cellular and molecular mechanisms whereby mitochondria control neurotransmitter release properties in a bouton-specific way through presynaptic Ca2+ clearance.

Zearalenone impairs the male reproductive system functions via inducing structural and functional alterations of sertoli cells.

The aim of this study was to investigate the effects of ZEA on the cytoskeletal structure, and factors specifically expressed by Sertoli cells. Primary Sertoli cells from rats aged 18-21 days were exposed to increasing ZEA concentrations (0, 5, 10, 20 μg mL(-1)) for 24 h. The results of immunofluorescence showed disruption of α-tubulin filaments and F-actin bundles, and damage to the nucleus of Sertoli cells on exposure to ZEA. In the control group, the protein level expression of androgen-binding protein (ABP), transferrin, vimentin, N-cadherin, and follicle-stimulating hormone receptor (FSHR) were decreased significantly (p<0.05, p<0.01). The mRNA levels of ABP, transferrin, vimentin, N-cadherin, and FSHR varied significantly in the experimental group (p<0.05). The results of enzyme-linked immunosorbent assay indicated a significant decrease in the levels of inhibin-β and transferrin in the cultural supernatants (p<0.05). Additionally, the ultrastructural analysis indicated the absence of mitochondria and Golgi apparatus, and presence of vacuoles in the cytoplasm. These findings showed that ZEA treatment can damage the cytoskeletal structure and affect specific secretory functions of Sertoli cells, which may be an underlying cause of ZEA-induced reproductive toxicity.

Spermatozoon ultrastructure and semen parameters of Brycon vermelha (Characiformes, Characidae)

This study analyzed semen parameters and the ultrastructure of spermatozoa of Brycon vermelha. The semen was white and viscous, with a mean volume of 5.0±2.6mL/kg body weight and mean spermatozoon concentration of 4.3±0.8×1010 spermatozoa/mL. The estimated motility rate was 90%, with 50% of spermatozoa motile at 35.0±0.1s and 100% immotile by 46.5±0.1s. The spermatozoon of B. vermelha had a distinct head, midpiece, and flagellum. The ovoid head measured 1.9±0.2μm by 1.3±0.1μm, with its volume almost completely occupied by the nucleus, and was enveloped by an irregular nuclear membrane, with no acrosome vesicle. The nuclear fossa held the centriole complex and the initial segment of flagellum. The midpiece was symmetrical and measured 1.3±0.3μm. Mitochondria were scarce and restricted to the anterior region, while vesicles were absent. The posterior region of the midpiece was characterized by the absence of mitochondria and the presence of the cytoplasmic sheath. The flagellum, enclosed by the flagellar membrane, measured 29.6±3.4μm, and possessed an axial filament containing a 9+2 microtubule pattern. The spermatozoa of B. vermelha appeared similar in structure to those of fish that breed through external fertilization, thus classifying them as uniflagellate anacrosomal aquasperm, or Type 1 aquasperm.

Structural and Functional Arrangements of Atrial Myocytes that Facilitate Excitation-Contraction Coupling

Rabbit atrial myocytes lack transverse tubules and only the peripheral sarcoplasmic reticulum (SR) is in contact with the surface membrane (junctional SR; j-SR) and exposed to Ca influx through voltage-gated sarcolemmal Ca channels that initiates Ca release which propagates centripetally by Ca-induced Ca release from non-junctional SR (nj-SR). In this study we examined the structural and functional characteristics of excitation-contraction coupling (ECC) unique to atrial myocytes. Subsarcolemmal (SS) Ca release from j-SR preceded release at central (CT) nj-SR regions, and SS release was of higher amplitude compared to CT release. Using simultaneous measurements of cytosolic ([Ca]i) and intra-SR ([Ca]SR) Ca, we show that depletions of SS [Ca]SR were smaller compared to CT [Ca]SR depletions during electrical stimulation. Atrial myocytes revealed an approximately 1-2 µm wide gap devoid of mitochondria and SR structures between the j-SR and the nj-SR that the Ca signal must traverse to activate release from nj-SR. The spread of Ca from the j-SR to the nj-SR occurred very rapidly and was aided by the absence of mitochondria which might buffer the diffusion of Ca. In contrast to SS release, the continuation of Ca release through the nj-SR to the cell center occurred much slower in a Ca wave-like fashion, and the rise of [Ca]i detected at individual release sites of the nj-SR preceded the depletion of [Ca]SR. During this latency period a transient elevation of [Ca]SR was observed that acted as an intra-SR Ca sensitization wave that may facilitate the spread of excitation through the nj-SR via the luminal Ca-sensitivity of the ryanodine receptor Ca release channel. In summary, we have identified key structural and functional characteristics of atrial myocytes that allow for efficient ECC in the intact heart.

O.22 Autosomal dominant Core Congenital Myopathy caused by a mutation in the MYH7 gene

Autosomal dominant (AD) Central core disease (CCD) named currently congenital myopathy with core is an inherited disorder characterised by the presence of cores which are well-limited rounded areas devoid of any oxidative staining. The cores extend almost along the full length of the fibres; these areas correspond to sarcomeric disorganisation, Z line streaming and absence of mitochondria. Genetic studies of AD-CCD families demonstrated the presence of heterozygous mutations in the RYR1 gene in the large majority of families. However, this gene was excluded in some families, suggesting a genetic heterogeneity of AD-Core myopathies (Romero et al., 2005). To enlarge the genetic spectrum of autosomal dominant congenital myopathies with cores demonstrating mutations in a second gene. AD-CCD family with three affected members: the mother and two of three siblings. The symptoms began during the early childhood with delayed motor development. Later they develop proximal weakness, hypertrophy of calves, scapular winging and significant weakness (amyotrophic) of quadriceps and tibialis anterior. No cardiac or ocular involvement was noted. The muscle biopsies sections showed a particular pattern: relatively large and eccentric cores (placed near the subsarcolemmal regions) associated with type 1 predominance and fibre type disproportion in a patient. The large majority of the cores have abrupt borders. Electron microscopy confirmed the presence of multiple large disorganised sarcomeric areas as characteristic unstructured and structured cores. Moreover, some fibres contain focal disorganised areas. Exome sequencing analysis identified a heterozygous missense mutation L1723P in MYH7 segregating with the disease and affecting a conserved residue in the tail domain. With this study we describe MYH7 as a second causative gene for AD-CCD in addition to RYR1 . Our study enlarges the genetic spectrum of AD-CCD myopathies.

Distinct mechanisms of axonal globule formation in mice expressing human wild type α-synuclein or dementia with Lewy bodies-linked P123H ß-synuclein

BackgroundAxonopathy is critical in the early pathogenesis of neurodegenerative diseases, including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). Axonal swellings such as globules and spheroids are a distinct feature of axonopathy and our recent study showed that transgenic (tg) mice expressing DLB-linked P123H β-synuclein (P123H βS) were characterized by P123H βS-immunoreactive axonal swellings (P123H βS-globules). Therefore, the objectives of this study were to evaluate α-synuclein (αS)-immunoreactive axonal swellings (αS-globules) in the brains of tg mice expressing human wild-type αS and to compare them with the globules in P123H βS tg mice.ResultsIn αS tg mice, αS-globules were formed in an age-dependent manner in various brain regions, including the thalamus and basal ganglia. These globules were composed of autophagosome-like membranous structures and were reminiscent of P123H βS-globules in P123H βS tg mice. In the αS-globules, frequent clustering and deformation of mitochondria were observed. These changes were associated with oxidative stress, based on staining of nitrated αS and 4-hydroxy-2-nonenal (4-HNE). In accord with the absence of mitochondria in the P123H βS-globules, staining of nitrated αS and 4-HNE in these globules was weaker than that for αS-globules. Leucine-rich repeat kinase 2 (LRRK2), the PARK8 of familial PD, was detected exclusively in αS-globules, suggesting a specific role of this molecule in these globules.ConclusionsLysosomal pathology was similarly observed for both αS- and P123H βS-globules, while oxidative stress was associated with the αS-globules, and to a lesser extent with the P123H βS-globules. Other pathologies, such as mitochondrial alteration and LRRK2 accumulation, were exclusively detected for αS-globules. Collectively, both αS- and P123H βS-globules were formed through similar but distinct pathogenic mechanisms. Our findings suggest that synuclein family members might contribute to diverse axonal pathologies.