Research Interests

Working on the border of chemistry and biology, the main research interests of the group are to

  • explore the role of astrocytes in modulating neuronal function in the healthy and diseased brain
  • identify potentially druggable (primarily astrocytic) target proteins or mechanisms in pathophysiological conditions
  • develop and apply toxicological test platforms for drug development projects

The applied multidisciplinary approaches include in vitro and in vivo simultaneous fluorescent imaging and electrophysiology, toxicology, synthetic chemistry.

Current Research Projects

Contribution of astrocytes to neuronal synchronization in health and disease

Astrocytes have long been considered to have only supporting role in the central nervous system. Substantial advances in the past two decades, however, identified them as important players in the modulation of physiological neuronal function and various pathophysiological conditions and diseases (Héja, 2014). Recently, we investigated whether astrocytic Ca2+ transients, an established readout of astroglial activity follows the activation pattern of neurons monitored by electrophysiological or optical methods. We demonstrated (Kékesi et al., 2015) that astrocytes show highly synchronized activity after the onset of recurrent neuronal epileptiform discharges which evolves into astrocytic seizure-like events. Therefore, we showed that astrocytes do have the capability to induce neuronal synchronization in epilepsy.

To extend the above studies we are also exploring whether astrocytes contribute to the emergence of physiological synchronous activity in the neuronal network, like the sleep-associated slow wave activity that plays a major role in memory consolidation. To this end we use Ca2+ sensor expressing rat lines developed in cooperation with the Biomembrane Research Group (Institute of Enzimology). These rat lines have been successfully used for simultaneous in vivo monitoring of neuronal and astrocytic activity during sleep. We demonstrate that synchronization of the astrocytic network precedes the build-up of neuronal synchronization, suggesting a causal role of the astrocytic syncytium in the generation of slow wave activity.

Both astrocytes and neurons are active during in vivo slow wave activity. A: In vivo imaging of GCaMP2 expressing stable transgenic rat line. B: Expression of GCaMP2 (green), labeling of astrocytes with intravenously applied SR101 (red). Both neurons (arrows) and astrocytes (arrowheads) express GCaMP2. C: Simultaneous recording of local field potential (LFP) and corresponding Ca2+ transients in a neuron (black) and an astrocyte (red) during slow wave activity.

Astroglial neurotransmitter transporters and gap junctions as potential anti-epileptic drugs

We have previously shown that astrocytes are able to significantly contribute to the tonic inhibition of neurons by releasing GABA. The glial Glu/GABA exchange (Héja et al., 2009, 2012) mechanism has been shown to be triggered by glial uptake of synaptically released Glu. The negative feedback provided by the astrocytes is proportional to the network activity, making this mechanism an attractive target for antiepileptic drug (AED) development that holds considerable promise for finding way to a market niche. Important players in the mechanism, the putrescine-GABA synthetic pathway and the expression of GAT-3 are upregulated under epileptic conditions, further supporting the role of the Glu/GABA exchange in epilepsy. From a pharmacological point of view, it is also important to note that the widely used AEDs levetiracetam and clobazam have been demonstrated to increase GAT-3 expression in the hippocampus.

Schematic representation of the Glu/GABA exchange

In addition to the GABA and Glu transporters, we also showed that blockade of intercellular gap junctional communication between astrocytes decreased the astrocytic synchronization and consequently inhibited or completely prevented the generation of recurrent SLEs. Therefore, the potential glial targets in AED development also includes another glial protein, the gap junction forming connexin43.

Hepatocyte-Kupffer cell cultures as advanced toxicity platforms

Our group is interested in the evaluation of the role of hepatic uptake and efflux transporters in drug induced liver injury, in the pharmacokinetic behavior of drugs and drug candidates and studying drug-transporter interactions. We also investigate drug induced induction and inhibition of phase I, phase II metabolic enzymes and biliary transport proteins. We succeeded in the elaboration of an in vitro hepatic model based on a primary hepatocyte and Kupffer cell co-culture system for studying the role of nonparenchimal cells in drug induced hepatotoxicity. Cytotoxicity assays, Ca2+ homeostasis measurements, assays for the expression, localization and function of phase I, phase II metabolic enzymes, uptake and efflux transporters are applied using sandwich culture of hepatocytes originated from different species (human, rodents, and dog).

We develop and characterize a novel hepatocyte–Kupffer cell co-culture based in vitro model for toxicological screening of drugs and nanoparticles. Toxicity investigation are provided regularly to other groups within the center.

To support hepatotoxicity studies we also synthesize fluorescent bile acids due to their role in fat digestion and absorption. By the use of fluorescent bile acids the mechanism of numerous transporters such as OATPs (organic anion transport proteins) and BSEP (bile salt export pump) proteins can be studied. Multistep synthesis of NBD (4-nitrobenzo-2-oxa-1,3-diazole)-labeled bile acids provides valuables conjugates for bioassays.

Equipment and facilities

  • FEMTONICS 2D two-photon microscope with simultaneous electrophysiological detection, Ti-Sapphire laser
  • OLYMPUS FV300 confocal laser scanning microscope with lasers 458 nm, 488 nm, 514 nm, 543 nm, 633 nm, infrared camera (CCDIR XC-EI50) and simultaneous electrophysiological detection
  • Setup for electrophysiology with simultaneous optical detection comprising OLYMPUS BX51WI microscope, Axopatch 200B and Multiclamp 700A amplifiers, Digidata 1320 and Digidata 1322A converters & 5 MHz Micromax CCD camera, NeuroPDA-III, WuTech H-469IV photodiode matrix array
  • Laboratories for receptor and transporter pharmacological studies, micro-centrifuges, filtration equipments
  • Multi-mode microplate readers for radioactivity or fluorescence detection
  • Cell and tissue culture laboratories, cold rooms
  • HPLC, fluorimeter, ultracentrifuge, Western blot equipment, deep-freezers
  • Access to the Radioisotope laboratory of the Centre, liquid scintillation counters
  • Access to the Animal House core facility of the Centre
  • Access to the Human Brain Tissue Sample Bank, Semmelweis University, Budapest

Collaborations

  • Semmelweis University
  • Eötvös University
  • Biological Research Centre, HAS
  • Szent István University
  • Catholic University of Louvain,
  • Charité, Berlin
  • University of Copenhagen
  • Biopredic International, France
  • University of Rennes
  • Richter Gedeon Pharmaceuticals
  • Solvo Biotechnology
  • Toxi Coop

Educational Activities

  • PhD programs of Eötvös University, Technical University of Budapest and Semmelweis University, Budapest
  • Master Program of the University of Technology and Economics, Budapest and Szent István University, Gödöllő

Selected Publications

Kardos J, Szabó Z, Héja L. J Med Chem, 2016, 59:777-787
Kékesi O, Ioja E, Szabó Zs, Kardos J, Héja L. Front Cell Neurosci 2015, 9: 215
Héja L, Nyitrai G, Kékesi O, Dobolyi A, Szabó P, Fiáth R, Ulbert I, Pál-Szenthe B, Palkovits M, Kardos J. BMC Biol. 2012, 10:26
Carta M, Lanore F, Rebola N, Szabo Z, Da Silva SV, Lourenço J, Verraes A, Nadler A, Schultz C, Blanchet C, Mulle C. Neuron 2014, 81:787.
Okiyoneda T, Veit G, Dekkers JF, Bagdany M, Soya N, Xu H, Roldan A, Verkman AS, Kurth M, Simon A, Hegedus T, Beekman JM, Lukacs GL. Nature Chem Biol. 2013, 9:444.
Jemnitz K, Szabo M, Batai-Konczos A, Szabo P, Magda B, Veres Z. Drug Metab Lett. 2015, 9:17-27.
Szabo M, Veres Z, Baranyai Z, Jakab F, Jemnitz K. PLoS One 2013, 8:e59432.

Leader

László Héja

Members