Cyprus Institute of Neurology and Genetics

Nicosia, Cyprus

Cyprus Institute of Neurology and Genetics

Nicosia, Cyprus
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Markoullis K.,Cyprus Institute of Neurology and Genetics | Sargiannidou I.,Cyprus Institute of Neurology and Genetics | Gardner C.,Imperial College London | Hadjisavvas A.,Cyprus Institute of Neurology and Genetics | And 2 more authors.
GLIA | Year: 2012

Gap junctions (GJs) are vital for oligodendrocyte survival and myelination. In order to examine how different stages of inflammatory demyelination affect oligodendrocyte GJs, we studied the expression of oligodendrocytic connexin32 (Cx32) and Cx47 and astrocytic Cx43 in the experimental autoimmune encephalomyelitis (EAE) mouse model of multiple sclerosis (MS) induced by recombinant myelin oligodendrocyte glycoprotein. EAE was characterized by remissions and relapses with demyelination and axonal loss. Formation of GJ plaques was quantified in relation to the lesions and in normal appearing white matter (NAWM). During acute EAE at 14 days postimmunization (dpi) both Cx47 and Cx32 GJs were severely reduced within and around lesions but also in the NAWM. Cx47 was localized intracellularly in oligodendrocytes while protein levels remained unchanged, and this redistribution coincided with the loss of Cx43 GJs in astrocytes. Cx47 and Cx32 expression increased during remyelination at 28 dpi but decreased again at 50 dpi in the relapsing phase. Oligodendrocyte GJs remained reduced even in NAWM, despite increased formation of Cx43 GJs toward lesions indicating astrogliosis. EAE induced in Cx32 knockout mice resulted in an exacerbated clinical course with more demyelination and axonal loss compared with wild-type EAE mice of the same backcross, despite similar degree of inflammation, and an overall milder loss of Cx47 and Cx43 GJs. Thus, EAE causes persistent impairment of both intra- and intercellular oligodendrocyte GJs even in the NAWM, which may be an important mechanism of MS progression. Furthermore, GJ deficient myelinated fibers appear more vulnerable to CNS inflammatory demyelination. © 2012 Wiley Periodicals, Inc.

Gooderham N.J.,Imperial College London | Koufaris C.,Cyprus Institute of Neurology and Genetics
Toxicology Letters | Year: 2014

Novel chemical entities have to be assessed for potential adverse effects in exposed human populations, including increased cancer incidence. The liver is an organ of particular interest for such evaluations, due to its central metabolic and detoxifying functions that render it a frequent target of exogenous carcinogens. In recent years a number of studies have investigated the use of microRNA (miRNA) biomarkers to facilitate the identification, characterization, and mechanistic understanding of chemical hepatocarcinogens. In this review we discuss the main findings of these studies, the potential biological significance of observed miRNA perturbations, and avenues of future research. © 2014 Elsevier Ireland Ltd.

Kleopa K.A.,Cyprus Institute of Neurology and Genetics | Orthmann-Murphy J.,University of Pennsylvania | Sargiannidou I.,Cyprus Institute of Neurology and Genetics
Reviews in the Neurosciences | Year: 2010

Gap junctions (GJs) are channels that allow the diffusion of ions and small molecules across apposed cell membranes. In peripheral nerves, Schwann cells express the GJ proteins connexin32 (Cx32) and Cx29, which have distinct localizations. Cx32 forms GJs through non-compact myelin areas, whereas Cx29 forms hemichannels in the innermost layers of myelin apposing axonal Shaker-type K+ channels. In the CNS, rodent oligodendrocytes express Cx47, Cx32 and Cx29. Cx47 is expressed by all types of oligodendrocytes both in the white and grey matter and forms GJs on cell bodies and proximal processes, as well as most of the intercellular channels with astrocytes. Cx32 is expressed mostly by white matter oligodendrocytes and is localized in the myelin sheath of large diameter fibers. Cx29, and its human ortholog Cx31.3, appear to be restricted to oligodendrocytes that myelinate small caliber fibers, likely forming hemichannels. The importance of intercellular and intracellular GJs in myelinating cells are demonstrated by human disorders resulting from mutations affecting GJ proteins. The X-linked Charcot Marie Tooth disease (CMT1X) is caused by hundreds of mutations affecting Cx32. Patients with CMTlX present mainly with a progressive peripheral neuropathy, which may be accompanied by CNS myelin dysfunction. Mutations in Cx47 may cause a devastating leukodystrophy called Pelizaeus-Merzbacher-like disease or a milder spastic paraplegia. In addition, CNS demyelination may be caused by defects in genes expressing astrocytic GJ proteins, which are essential for oligodendrocytes. Findings from in vitro and in vivo models of these disorders developed over the last decade indicate that most mutations cause loss of function and an inability of the mutant connexins to form functional GJs. Here we review the clinical, genetic, and neurobiological aspects of GJ disorders affecting the PNS and CNS myelinating cells. © Freund & Pettman.

Kleopa K.A.,Cyprus Institute of Neurology and Genetics | Abrams C.K.,SUNY Downstate Medical Center | Scherer S.S.,University of Pennsylvania
Brain Research | Year: 2012

The X-linked form of Charcot-Marie-Tooth disease (CMT1X) is the second most common form of hereditary motor and sensory neuropathy. The clinical phenotype is characterized by progressive weakness, atrophy, and sensory abnormalities that are most pronounced in the distal extremities. Some patients have CNS manifestations. Affected males have moderate to severe symptoms, whereas heterozygous females are usually less affected. Neurophysiology shows intermediate slowing of conduction and length-dependent axonal loss. Nerve biopsies show more prominent axonal degeneration than de/remyelination. Mutations in GJB1, the gene that encodes the gap junction (GJ) protein connexin32 (Cx32) cause CMT1X; more than 400 different mutations have been described. Many Cx32 mutants fail to form functional GJs, or form GJs with abnormal biophysical properties. Schwann cells and oligodendrocytes express Cx32, and the GJs formed by Cx32 play an important role in the homeostasis of myelinated axons. Animal models of CMT1X demonstrate that loss of Cx32 in myelinating Schwann cells causes a demyelinating neuropathy. Effective therapies remain to be developed. This article is part of a Special Issue entitled Electrical Synapses. © 2012 Elsevier B.V.

Papageorgiou E.A.,Cyprus Institute of Neurology and Genetics | Karagrigoriou A.,University of Cyprus | Tsaliki E.,Cyprus Institute of Neurology and Genetics | Tsaliki E.,Mitera Hospital | And 4 more authors.
Nature Medicine | Year: 2011

The trials performed worldwide toward noninvasive prenatal diagnosis (NIPD) of Down's syndrome (or trisomy 21) have shown the commercial and medical potential of NIPD compared to the currently used invasive prenatal diagnostic procedures. Extensive investigation of methylation differences between the mother and the fetus has led to the identification of differentially methylated regions (DMRs). In this study, we present a strategy using the methylated DNA immunoprecipitation (MeDiP) methodology in combination with real-time quantitative PCR (qPCR) to achieve fetal chromosome dosage assessment, which can be performed noninvasively through the analysis of fetal-specific DMRs. We achieved noninvasive prenatal detection of trisomy 21 by determining the methylation ratio of normal and trisomy 21 cases for each tested fetal-specific DMR present in maternal peripheral blood, followed by further statistical analysis. The application of this fetal-specific methylation ratio approach provided correct diagnosis of 14 trisomy 21 and 26 normal cases. © 2011 Nature America, Inc. All rights reserved.

Pafiti K.S.,University of Cyprus | Mastroyiannopoulos N.P.,Cyprus Institute of Neurology and Genetics | Phylactou L.A.,Cyprus Institute of Neurology and Genetics | Patrickios C.S.,University of Cyprus
Biomacromolecules | Year: 2011

Four cationic hydrophilic star homopolymers based on the novel hydrophilic, positively ionizable cross-linker bis(methacryloyloxyethyl)methylamine (BMEMA) were synthesized using sequential group transfer polymerization (GTP) and were, subsequently, evaluated for their ability to deliver siRNA to mouse myoblast cells. The nominal degrees of polymerization (DP) of the arms were varied from 10 to 50. For the polymerizations, 2-(dimethylamino)ethyl methacrylate (DMAEMA) was employed as the hydrophilic, positively ionizable monomer. For comparison, four linear DMAEMA homopolymers were also synthesized, whose nominal DPs were the same as those of the arms of the stars. The numbers of arms of the star homopolymers were determined using gel permeation chromatography with static light scattering detection, and found to range from 7 to 19, whereas the hydrodynamic diameters of the star homopolymers in aqueous solution were measured using dynamic light scattering and found to increase with the arm DP from 13 to 26 nm. The presence of the hydrophilic BMEMA cross-linker enabled the solubility of all star homopolymers in pure water. The cloud points of the star homopolymers in aqueous solution increased with the arm DP from 23 to 29°C, while the cloud points of the linear homopolymers were found to decrease with their DP, from 42 to 32°C. The effective pK values of the DMAEMA units were in the range of 6.9 to 7.3 for the star homopolymers, whereas they ranged between 7.3 and 7.4 for the linear homopolymers. Subsequently, all star and linear homopolymers were evaluated for their ability to deliver siRNA to the C2C12 mouse myoblast cell line, expressing the reporter enhanced green fluorescent protein (EGFP). All star homopolymers and the largest linear homopolymer presented significant EGFP suppression, whereas the smaller linear homopolymers were much less efficient. For all star homopolymers and the largest linear homopolymer both the EGFP suppression and the cell toxicity increased with polymer loading. The siRNA-specific EGFP suppression, calculated by subtracting the effect of cell toxicity on EGFP suppression, slightly increased with star polymer loading for the two smaller stars, whereas it presented a shallow maximum and a decrease for the other two stars. Moreover, the siRNA-specific EGFP suppression also increased slightly with the DP of the arms of the DMAEMA star homopolymers. Overall, the EGFP suppression efficiencies with the present star homopolymers were at levels comparable to that of the commercially available transfection reagent Lipofectamine. © 2011 American Chemical Society.

Spanaki C.,University of Crete | Zaganas I.,University of Crete | Kleopa K.A.,Cyprus Institute of Neurology and Genetics | Plaitakis A.,University of Crete
Journal of Biological Chemistry | Year: 2010

Mammalian glutamate dehydrogenase (GDH) is an allosterically regulated enzyme that is expressed widely. Its activity is potently inhibited by GTP and thought to be controlled by the need of the cell for ATP. In addition to this housekeeping human (h) GDH1, humans have acquired (via a duplication event) a highly homologous isoenzyme (hGDH2) that is resistant to GTP. Although transcripts of GLUD2, the gene encoding hGDH2, have been detected in human neural and testicular tissues, data on the endogenous protein are lacking. Here, we developed an antibody specific for hGDH2 and used it to study human tissues. Western blot analyses revealed, to our surprise, that endogenous hGDH2 is more densely expressed in testis than in brain. At the subcellular level, hGDH2 localized to mitochondria. Study of testicular tissue using immunocytochemical and immunofluorescence methods revealed that the Sertoli cells were strongly labeled by our anti-hGDH2 antibody. In human cerebral cortex, a robust labeling of astrocytes was detected, with neurons showing faint hGDH2 immunoreactivity. Astrocytes and Sertoli cells are known to support neurons and germ cells, respectively, providing them with lactate that largely derives from the tricarboxylic acid cycle via conversion of glutamate to α-ketoglutarate (GDH reaction). As hGDH2 is not subject to GTP control, the enzyme is able to metabolize glutamate even when the tricarboxylic acid cycle generates GTP amounts sufficient to inactivate the housekeeping hGDH1 protein. Hence, the selective expression of hGDH2 by astrocytes and Sertoli cells may provide a significant biological advantage by facilitating metabolic recycling processes essential to the supportive role of these cells. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.

The largest proportion of microRNAs in humans (ca. 40-50%) originated in the phylogenetic grouping defined as primates. The dynamic evolution of this family of non-coding RNA is further demonstrated by the presence of microRNA unique to the human species. Investigations into the role of microRNA in cancer have until recently mainly focused on the more ancient members of this RNA family that are widely conserved in the animal kingdom. As I describe in this review the evolutionary young lineage and species-specific microRNA could be important contributors to cancers, especially in particular organs in primates compared to more distantly-related research models. Elucidating the biological significance of primate and human-specific microRNA in cancer could have important implications for cancer research and the use of non-primate animal models. The human miRNAome can be divided into miRNAs that are widely conserved, those that are primate-specific, and those that are human-specific. The latter two categories can also contribute to tumor development and complicate the study of human cancers in non-primate animal models. © 2016 WILEY Periodicals, Inc.

Tanteles G.A.,Cyprus Institute of Neurology and Genetics | Christophidou-Anastasiadou V.,Cyprus Institute of Neurology and Genetics
Clinical Dysmorphology | Year: 2014

Patient 1, the oldest of the three children, was born to healthy nonconsanguineous parents, a 37-year-old father and a 24-year-old mother. Family history was noncontributory and no known exposure to teratogens was reported. Antenatal scans were normal. She was born following a normal vaginal delivery at term with a birth weight of 3 kg (10th-25th centile), a birth length of 49 cm (25th-50th centile) and a birth occipitofrontal circumference of 33 cm (10th centile). Apgar scores were normal and she did not require any resuscitation. Initial concerns were raised because of poor visual contact. Subsequent ophthalmology assessment revealed bilateral iris and chorioretinal colobomata as well as involvement of the optic nerves. Examination at infancy was significant for distinct facial features (high forehead with frontal bossing, hypertelorism, strabismus, deep set eyes, large uplifted earlobes, prominent nasal tip, prominent columella, open mouth with M-shaped upper lip and a prominent chin). Hypotonia, severe global developmental delay, absent speech and mild to moderate constipation were also recorded. She developed seizures at the age of 11 years. Her facial features coarsened with time, her eyebrows became 'heavier', broad and horizontal with an increased medial separation and sparseness. The columella became more prominent leading to a short philtrum appearance, the face was more elongated and the jaw more pronounced (Fig. 1). Her MRI brain scan was unremarkable, as were an abdominal ultrasound scan and echocardiography. Karyotype and array-comparative genomic hybridization analyses as well as a basic metabolic screen were either normal or negative for abnormalities. Patient 2, the younger of the two children, was born to nonconsanguineous parents, a 31-year-old father and a 29-year-old mother. Review of the family history revealed that the father had unspecified renal problems and proteinuria. The mother enjoyed a good general health. The couple had two first trimester miscarriages in addition to their two live-born offspring. This was the mother's fourth pregnancy. No known exposure to teratogens was reported. Antenatal scans raised the possibility of microphthalmia and hypospadias. He was born following a Caesarean section at 36 weeks gestation with a birth weight of 3 kg (10th-25th centile). Soon after birth, he was transferred to the neonatal ICU because of respiratory distress. Multiple congenital anomalies were noted at the time, which included a perimembranous ventricular septal defect with pulmonary hypertension and a persistent ductus arteriosus that was subsequently ligated, bilateral microphthalmia, a right iris coloboma, left partial aniridia, hypospadias and distinct facial features including hypertelorism, round nasal tip, prominent columella and uplifted earlobes (Fig. 2). Mild hypotonia and developmental delay were subsequently recorded. He developed seizures at the age of 16 months. He had mild to moderate constipation that resolved by the age of 18 months. His MRI brain scan did not reveal any brain malformations. Karyotype analysis and a basic metabolic screen were normal. Array-comparative genomic hybridization analysis revealed a 16q23.2q23.3 deletion of ∼0.265Mb in size. As this deletion was maternally inherited and the clinical evaluation of the mother was unremarkable, it was concluded that it was probably of no clinical significance. © 2013 Wolters Kluwer Health | Lippincott Williams & Wilkins.

Oikonomopoulou K.,Mount Sinai Hospital | Kyriacou K.,Cyprus Institute of Neurology and Genetics | Diamandis E.P.,Mount Sinai Hospital
Clinical Cancer Research | Year: 2013

Several studies have shown that persistent infections and inflammation can favor carcinogenesis. At the same time, certain types of pathogens and antitumor immune responses can decrease the risk of tumorigenesis or lead to cancer regression. Infectious agents and their products can orchestrate a wide range of host immune responses, through which they may positively or negatively modulate cancer development and/or progression. The factors that direct this dichotomous influence of infection-mediated immunity on carcinogenesis are not well understood. Even though not universal, several previous reports have investigated the inverse link of pathogen-induced "benign" inflammation to carcinogenesis and various other pathologies, ranging from autoimmune diseases to allergy and cancer. Several models and ideas are discussed in this review, including the impact of decreased exposure to pathogens, as well as the influence of pathogen load, the timing of infection, and the type of instigated immune response on carcinogenesis. These phenomena should guide future investigations into identifying novel targets within the microbial and host proteome, which will assist in the development of cancer therapeutics and vaccine remedies, analogous to earlier efforts based on helminthic components for the prevention and/or treatment of several pathologies. ©2013 AACR.

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