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Neuroprotective properties of the AAV-Syn-BDNF-EGFP Virus Vector in Hypoxia Model

Elena V. Mitroshina1, 2*, Ekaterina A. Epifanova1, Tatiana A. Mishchenko1, 2, Roman S. Yarkov1, Mark D. Urazov1, Alexey A. Babaev1 and Maria V. Vedunova1
  • 1 N. I. Lobachevsky State University of Nizhny Novgorod, Russia
  • 2 Privolzhsky Research Medical University (PIMU), Russia

Motivation In recent decades, it has been shown that BDNF has a pronounced neuroprotective effect against ischemia damaging factors, including hypoxia [1, 2]. The use of the recombinant BDNF increases the resistance of nervous cells to the ischemia factors both in vitro and in vivo [2,3]. Based on these results, studies on the use of the Brain-derived neurotrophic factor in clinical treatment of ischemic brain injury can be recommended. However, systemic application of recombinant proteins causes a temporary effect, which requires their permanent supply to the organism. Therefore, targeted gene delivery to damaged areas of the nervous system could be more effective in long-term treatment of CNS injuries [4]. We have developed a virus construct containing the sequence of the BDNF gene that allows increasing the BDNF expression in brain neurons. In this regard, the aim of the study was to study the effect of the AAV-Syn-BDNF-EGFP virus vector on nervous cell in normal conditions and under hypoxia in vitro and in vivo. Materials and methods. We used plasmids AAV-Syn-EGFP, pDP5, DJvector, and pHelper to develop the sought virus construct. To obtain the construct, polymerase chain reaction and plasmid cloning were used. A Phusion High-Fidelity PCR Kit containing Phusion High-Fidelity DNA polymerase (Thermo Fisher Scientific, USA) was used for PCR. For plasmid construction we used enzymes from Thermo Fisher Scientific (USA) and «New England BioLabs», competent TopTEN cells, the ISOLATE II Plasmid Mini Kit (Bioline, UK) and NucleoBondXtra Midi / Maxi (MACHEREY-NAGEL, Germany) and the «VectorNTI» software. Long-term cultivation of primary hippocampal cells obtained from C57BL/6 embryos (E18) was performed according to the previously developed protocol [5]. The cells were seeded on multielectrode arrays MEA 60 (Multichannel systems, Germany) and cover slips at approximate initial density — 9000 cells/mm2. Infection of primary cultures with the developed virus construct was carried out on day 7 of cultivation (DIV 7). Hypoxia model was performed on DIV14 by replacing the culture medium with a low oxygen medium for 10 minutes. To study the spontaneous bioelectrical activity, multielectrode arrays MEA 60 (Multichannel Systems, Germany), a set of Conductor ™ software (Alpha Med Scientific, Japan) and “Meaman” original package of algorithms developed in the custom-made software (MATLAB®) were used. Extracellular action potentials recording was carried out on DIV7 before the addition of the virus construct and during 14 days after application. Detection of small network bursts was performed by calculating the total spiking rate (TSR), accounting the total number of spikes from all electrodes within 50 ms time bins. The criterion of small network burst is the rapid appearance of a large number of spikes over 4 electrodes within a small (50 ms) time bin. The main parameters of the spontaneous bioelectrical activity were analyzed: the number of bursts, the number of spikes in a burst, the burst duration [6]. The metabolic activity of the hippocampal cells was evaluated using a calcium imaging. A specific calcium dye Oregon Green 488 BAPTA-1 AM-OGB1 (Invitrogen, USA) was used as a fluorescent probe. Fluorescence was recorded using a laser scanning microscope LSM 510 NLO (Carl Zeiss, Germany). Using an “Astroscanner” original software we analyzed the following parameters: the duration of calcium oscillations (s), the frequency of calcium oscillations (the number of oscillations per minute), and the percentage of cells exhibited calcium activity. Results. To assess the effects of the virus construct on the neuronal network activity in primary hippocampal cultures, the functional metabolic and bioelectrical activity of the infected and virus-free cultures were analyzed on day 1, 7 and 14 after the virus addition. According to our results, the developed construct did not inhibit the spontaneous bioelectrical and calcium activity of the primary hippocampal cultures. In both sham and infected cultures, the spontaneous network burst activity continued throughout the observation period. It was found that upon the AAV-Syn-BDNF-EGFP addition on DIV7, the level of the spontaneous bioelectrical activity did not significantly change by any of the measured parameters during 14 days after infection (Figure 1). Figure 1. Characteristic profile of network burst forming spontaneous bioelectrical activity of primary hippocampal cultures on days 1, 7 and 14 after virus application: A – Sham, B – AAV-Syn-BDNF-EGFP The developed virus construct was tested for its neuroprotective potential under hypoxic conditions in comparison with the exogenous application of recombinant BDNF (1 ng/ml) (Merck, France) to the сulture medium. It was shown that hypoxia caused a significant decrease in the number of living cells, inhibition of calcium and bioelectrical neural network activity in the primary culture on day 7 of the post-hypoxic period (ANOVA, p <0.05). The developed virus construct promoted cell preservation to negative hypoxic effects. The proportion of living cells in the “Hypoxia” group was 62.9 ± 1.8%, in the “Hypoxia + BDNF” group - 81.6 ± 4.1%, and in the “Hypoxia + AAV-Syn-BDNF-EGFP” group – 89.2 ± 5.2%. Also the main parameters of bioelectrical and calcium activity were studied both AAV-Syn-BDNF-EGFP and exogenous BDNF. The maintenance of spontaneous activity was shown. Next we tested the AAV-Syn-BDNF-EGFP virus in vivo. For this purpose, the virus was injected into the cerebral cortex according to stereotaxic coordinates. Visualization of GFP expression was performed on 7, 14 and 21 days after virus injection. Conclusion. The developed virus containing the BDNF gene reduces the nervous cell death and maintains calcium and bioelectrical neural network activity in the hypoxia model.

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Acknowledgements

The reported study was funded by RFBR according to the research projects No.18-015-00391, 17-04-01128, 16-04-00245 and Grant of the President of the Russian Federation MD-2634.2017.4. This publication has been also prepared as a part of the state projects “Provision of scientific research” No.6.6379.2017/8.9, 17.3335.2017/4.6, and 6.6659.2017/6.7.

References

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Keywords: BDNF, AAV vectors, Neuroprotection, Hypoxia, Brain, primary hippocampal cell cultures

Conference: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays, Reutlingen, Germany, 4 Jul - 6 Jul, 2018.

Presentation Type: Poster Presentation

Topic: Neural Networks

Citation: Mitroshina EV, Epifanova EA, Mishchenko TA, Yarkov RS, Urazov MD, Babaev AA and Vedunova MV (2019). Neuroprotective properties of the AAV-Syn-BDNF-EGFP Virus Vector in Hypoxia Model. Conference Abstract: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays. doi: 10.3389/conf.fncel.2018.38.00008

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Received: 18 Mar 2018; Published Online: 17 Jan 2019.

* Correspondence: PhD. Elena V Mitroshina, N. I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia, helenmitroshina@gmail.com