Structure and Functions of Gap Junctions and Their Constituent Connexins in the Mammalian CNS.

Numerous data obtained in the last 20 years indicate that all parts of the mature central nervous system, from the retina and olfactory bulb to the spinal cord and brain, contain cells connected by gap junctions (GJs). The morphological basis of the GJs is a group of joined membrane hemichannels called connexons, the subunit of each connexon is the protein connexin. In the central nervous system, connexins show specificity and certain types of them are expressed either in neurons or in glial cells. Connexins and GJs of neurons, combining certain types of inhibitory hippocampal and neocortical neuronal ensembles, provide synchronization of local impulse and rhythmic activity, thalamocortical conduction, control of excitatory connections, which reflects their important role in the processes of perception, concentration of attention and consolidation of memory, both on the cellular and at the system level. Connexins of glial cells are ubiquitously expressed in the brain, and the GJs formed by them provide molecular signaling and metabolic cooperation and play a certain role in the processes of neuronal migration during brain development, myelination, tissue homeostasis, and apoptosis. At the same time, mutations in the genes of glial connexins, as well as a deficiency of these proteins, are associated with such diseases as congenital neuropathies, hearing loss, skin diseases, and brain tumors. This review summarizes the existing data of numerous molecular, electrophysiological, pharmacological, and morphological studies aimed at progress in the study of the physiological and pathophysiological significance of glial and neuronal connexins and GJs for the central nervous system.

[Connexin 43 expression in human brain glial tumors]. / Ékspressiia konneksina 43 v glial'nykh opukholiakh golovnogo mozga cheloveka.

AIM: Тo conduct an immunohistochemical (IHC) study of the expression of connexin 43 in the samples of glial tumors of various grades: gemistocytic astrocytomas (Grade 2), oligodendrogliomas (Grade 2) and glioblastomas (Grade 4). MATERIAL AND METHODS: The material investigated was fragments of human brain glial tumors (grade 2 gemistocytic astrocytomas (n=2), grade 2 oligodendrogliomas (n=2), and grade 4 glioblastomas (n=14) and those of tumor-surrounding tissue (n=4). The material was fixed in 10% buffered formalin, dehydrated, and embedded in paraffin according to the standard technique. IHC studies of the slices applied primary rabbit polyclonal antibodies against connexin 43 ('Spring Bioscience', USA) and the Dako EnVision + Peroxidase (DAB) visualization system ('Dako', Denmark). After the immunohistochemical reaction, the cell nuclei were stained with Mayer's hematoxylin. RESULTS: Immunohistochemistry showed the changing pattern of connexin 43 expression as compared with intact tissue in the glial tumors. Instead of the fine-granular expression in the thin cellular processes in the neuropil, the tumors mainly displayed a coarse-grained cytoplasmic and even nuclear reaction. The morphology and localization of positive structures depended on the variant of an examined tumor. In addition, the most malignant brain gliomas generally exhibited a reduction in the expression of connexin 43, i.e. its quantity is inversely proportional to the degree of malignancy of the tumor. CONCLUSION: The low connexin 43 expression levels may reflect both a reduction in astroglial functional gap junctions and semicanals and a decrease in the amount of the protein itself that has independently antioncogenic properties. The observed cytoplasmic and nuclear expression of connexin 43 is most likely to be associated with the aberrant activity of a number of kinases, such as proto-oncogene tyrosine-kinase Src or protein kinase C (PKC).

[Ultrastructural characteristics of gap junctions in human glial brain tumors]. / Ul'trastrukturnaya identifikatsiya shchelevykh kontaktov v glial'nykh opukholyakh golovnogo mozga cheloveka.

AIM: to conduct an electron microscopic study of intercellular communication in the samples of gemistocytic astrocytoma, oligodendroglioma, and glioblastoma. MATERIAL AND METHODS: Surgically resected tumor tissue fragments were fixed in 2.5% glutaraldehyde solution, afterfixed in 1% OsO4 solution, dehydrated, and embedded in epoxy resin. Ultrathin sections were examined using a Jem 1011 electron microscope (Jeol, Japan). RESULTS: Solitary and closely spaced gap junctions (GJs) formed by the thin processes that have the ultrastructure of an astroglial processes were identified in the astrocytoma samples. In this case, chemical synapses were noted to be completely absent in gemistocytic astrocytoma and glioblastoma. The identified GJs had a small length and deformed nexuses. The oligodendroglioma samples exhibited intact astroglial processes around the chemical synapses; however, interglial GJs were not found. CONCLUSION: The investigation showed the presence of intercellular GJs with some ultrastructural differences in the samples of low- and high-grade astroglial tumors. According to current data, astrocytomic GJs are able to create a stable self-sustaining network that promotes tumor progression and provides resistance to a therapeutic intervention. At the same time, the noticeable reduction in the number of GJs, which is most pronounced in the oligodendroglioma sample, can accelerate tumor cell migration into the surrounding parenchyma. The investigation of GJs should be, of course, continued using a group of a larger number of glial tumors to confirm the intercellular communication features revealed in this study.

[THE LONG NON-CODING RNA ASSOCIATED WITH CANCEROGENESIS: BIOLOGICAL SIGNIFICANCE AND PERSPECTIVES OF APPLICATION IN DIAGNOSTIC].

The last decade is characterized by development of such technologies as RNA-sequencing and biochips which resulted in discovery of new perspective biomarkersfor personalized diagnostic of cancer. Among them, the long non-coding RNA (IncRNA) are of special interest because according the recent studies they are positioned as important regulators of gene expression on epigenetic, transcription and post-transcription levels. The review considers the role of long non-coding RNA in cancerogenesis. The corresponding of their application in diagnostic is evaluated. A number of examples ofperspective diagnostic and prognostic markers. Their degree of implementation in oncological practice is discussed.

[The expression of connexin 36 and some neuroglial antigens in human brain astrocytic tumors of different grades].

OBJECTIVE: To reveal the expression of neuronal connexin 36 (Cx36) in gliomas and then to analyze the ratio of expression of Cx36 to that of neuroglial antigens (synaptophysin, neurofilaments, and glial fibrillary acidic protein). MATERIAL AND METHODS: Varying grade human glioma samples and tumor-adjacent tissue fragments were used for immunohistochemical examination. RESULTS: A procedure for immunohistochemical detection of Cx36 in brain tissue was tried out. It was shown that the decreased level of the examined neuronal proteins was accompanied by the impaired coexpression of synaptophysin/neurofilaments and Cx36 in the series of astrocytomas--anaplastic astrocytomas--glioblastomas. The immunohistochemical heterogeneity of glioblastomas was found. CONCLUSION: The findings suggest that it is promising to include anti-Cx36 antibodies in immunohistochemical panels when examining brain tumors. Data on the lower levels of the examined neuronal proteins, on the specific features of their distribution and impaired coexpression expand their idea on the pathogenesis of a brain tumor process and determine an area for further investigations.

Role of gap junctions in local rhythmogenesis in cortical columns.

Complex morphofunctional studies of the barrel cortex of the rat identified and analyzed the ultrastructural characteristics of the dendrodendritic electrical synapses--gap junctions (GJ)--of stellate neurons of barrels D2-D3. The local nature of dendrite branching of barrel cells, limited to the volume of the barrel, suggests that these GJ, which account for 7% of all synapses, may be the structural basis of local intrabarrel electrotonic synchronization of pacemaker potentials of barrel neuron hyperpolarization on development of spindle-type activity in the corresponding column.