CC BY
23
Section CELLULAR NEUROSCIENCE
A New Pathway for Presynapse to Nucleus Communication: Potential Implications for Information Storage in the Brain
E.D. Gundelfinger*, D. Ivanova, A. Dirks, C. Montenegro-Venegas and A. Fejtova
Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany. * Presenting e-mail: [email protected]
Formation of long-term memories requires synapto-nudear communication that in turn regulates expression of relevant genes in neurons. While various signaling pathways and protein mediators for communication between the postsynaptic and dendritic compartments with the nucleus have been identified our knowledge about presynapse to nucleus signaling is rather limited (1). Recent studies in our laboratory have revealed that the multifunctional protein CtBPl (C-terminal binding protein-1) may fulfill such a task. CtBPl has been discovered originally as a transcriptional co-repressor. CtBPs including CtBP1 and CtBP2 are widely expressed proteins involved in developmental gene regulation and chromatin modification. In addition CtBPl (also named BARS-50) has been implicated in regulating intracellular membrane trafficking processes and, in neurons, it has been localized to presynaptic boutons.
Synaptic localization of CtBP1 depends on its interaction with the presynaptic cytomatrix proteins Bassoon and Piccolo - giant proteins involved in the organization of the apparatus for neurotransmitter release at the active zone (2). Presynaptic and nuclear pools of CtBP1 can communicate in an activity-dependent manner and the absence of the two large presynaptic anchor proteins causes increased levels of nuclear CtBPl, what in turn affects the expression of activity-regulated genes (3). The interaction of CtBP1 with Bassoon and Piccolo is regulated by cellular NAD/NADH levels and thus may act as a sensing system for presynaptic activity and metabolic state. Accordingly, CtBP1 is a prime candidate for a protein mediator that couples activity-driven changes in presynaptic performance with plasticity-related alterations of neuronal gene expression.
Potential implications for the interaction of the CtBP signaling pathway with postsynapse to nucleus communication pathways and for setting of the gene expression pattern in a given neuron will be discussed.
Acknowledgements
Supported by the DFG (SFB779/B9 and GRK1167 to EDG; FE1335/1 to AF), ERANET-Neuron (FKZ 01EW1101) to EDG, the Leibniz Association (SAW 2013-15) to AF and EDG, and by the Federal State of Saxony-Anhalt (CBBS, NeuroNetwork #5) to AF.
References
1. Panayotis, N., Karpova, A., Kreute, M.R., and Fainzilber, M. (2015). Trends Neurosci. 38, 108-116,
Synaptic and Extrasynaptic Neuron-Glia Interactions
Alexey Semyanov*
Lobachevsky University of Nizhny Novgorod, Russia. * Presenting e-mail: [email protected]
Brain is often viewed as large neuronal connectome where the information is encoded in the patterns of action potentials and stored in the changes of synaptic strength or appearance of new wiring routes. However, recent studies have demonstrated that astrocytes also possess complex patterns of calcium signals influenced by neuronal activity. Astrocytic calcium signals regulate various functions of these cells including release of gliotransmitters and morphological changes in the astrocytic processes (Tanaka et al., 2013). It has been tempting to suggest that information in astrocytes is encoded in the frequency of calcium events, similar to patters of neuronal action potentials. Synaptically released neurotransmitters thought to trigger new calcium events in perisynaptic astrocytic processes (PAPs) though activation of metabotropic glutamate receptors (mGluRs). In contrast, our recent findings suggest that PAPs are devoid of calcium stores that are required for mGluR-mediated calcium signaling (Patrushev et al., 2013). This makes unlikely any significant role of mGluRs in triggering calcium events in PAPs. Instead, we show that activation of 'extrasynaptic7 astrocytic mGluRs increases proportion of spatially extended calcium events in the power-law based distribution of calcium event sizes (Wu et al., 2014). This effect takes place without any significant increase in the frequency of calcium events. These findings suggest that astrocytic response to surrounding neuronal activity is rather encoded in spatial
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10 Opera Med Physiol 2016 Vol. 2 (S1)
Section CELLULAR NEUROSCIENCE
characteristics of their calcium events and fundamentally different from temporal information coding in neurons (e.g. coincidence detection, action potentials sequences etc). Nevertheless, we cannot exclude local ionic changes in PAPs in response to synaptic activity. For example, potassium ions accumulate in the synaptic cleft of glutamatergic synapses during repetitive activity. We have demonstrated that the bulk of these ions is contributed by potassium efflux through postsynaptic NMDA receptors (Shih et al., 2013). Potassium mediated depolarization of presynaptic terminal increases glutamate release probability. Now we have found that accumulation of intracleft potassium during repetitive synaptic activity could also inhibit astrocytic glutamate uptake by depolarizing PAPs. This extends glutamate dwell-time in the synaptic cleft and boosts glutamate spillover effects.
Acknowledgements
This work was supported by the grant Russian Science Foundation (16-14-00201).
Cell Protective and Trophic Properties of GDNF and its Derivatives
G. Pavlova1,2, Dz. Shamadykova u, N. Kust1,2, D. Panteleev1, V. Kovalzon3, A.Revishchin1,2
1 Institute of Gene Biology, Russian Academy of Sciences, Moscow, Russian Federation;
2 Apto-Pharm Ltd , Moscow, Russian Federation;
3 Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russian Federation. * Presenting e-mail: [email protected]
GDNF is a major factor for a survival of the dopamine neurons of the midbrain. It supports the axon growth as well as survival of the neurons. For different models of the Parkinson disease GDNF could prevent the neurotoxically provoked death of the dopamine neurons, and supports recuperation of its functional activity. Though some by-side effects are also known, like loosing weight and chance of neoplastic transformation. We prepared a genetic construct caring human GDNF gene, introduced it into HEK293 cells, and then transplanted the cells into parenchyma of the mouse brain. Transgenic cells, which express GDNF, essentially reduce the glial scar formation. Therefore GDNF could be applied during transplantation into the brain to improve the transplant survival. In humans GDNF gene supplies two versions of mRNA for: pre-(a)pro-GDNF and truncated pre-(p) pro-GDNF (1). Pre-(a)pro-GDNF is secreted through Golgi apparatus and pre-(p) pro-GDNF is located in the secretory vesicles and moves by fast secretion pathway. Probably, pre-(a)pro-GDNF is needed for conventional neuron survival, and pre-(p) pro-GDNF serves as SOS system during traumatic injury of neurons or neurodegenerative diseases. To study 'pro' region function during fast transport and factor induction properties several derivatives of GDNF were made. A secretion of the factor into medium has been shown by western blot analysis. All modified GDNF were introduced into HEK293 cells, and transgenic cell lines were maintained (2). After culturing the cells with modified GDNF, the condition media was added into culture medium of rat embrional spinal ganglion explant, and growth of neural sprouts were analyzed. Deletion of 'pro' region essentially increases GDNF effects as neural inductor. A study of culture of dissociated spinal ganglion and calculation of neural sprouts yielded the same results. HEK293 cells were transfected with a vector encoding an isoform of the human. GDNF gene with deleted pre- and pro-regions (mGDNF) in the medium conditioned by the transfected cells was shown to induce axonal growth in PC12 cells. Then the early Parkinson's disease model was established by injection of the dopaminergic proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into C57Bl/6 mice. Transgenic HEK293/mGDNF/GFP cells were transplanted into the striatum (caudateputamen) of experimental mice. The motor activity was monitored 1 and 2 weeks after MPTP injection. After the experiment, the motor coordination of experimental animals was evaluated in the rotarod test, and dopaminergic neurons in the substantia nigra pars compacta were counted in cross-sections of the midbrain. MPTP administration lowered the number of tyrosine hydroxylase immunopositive cells in the substantia nigra pars compacta, decreased motor coordination. The transplantation of HEK293/mGDNF cells into the caudate-putamen smoothed the effects after MPTP, while the control transplantation of HEK293 cells showed no notable impact.
Conclusions
Transplantation of transgenic cells with GDNF gene lacking the pre- and pro-sequences can protect dopaminergic neurons in the mouse midbrain from the subsequent administration of the pro-neurotoxin MPTP, which is confirmed by polysomnographic, behavioral and histochemical data. Hence, GDNF is released from transfected cells, and provides the differentiation activity and neuroprotective properties.
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Opera Med Physiol 2016 Vol. 2 (S1) 11
