Laube

AG Neurophysiology and Neurosensory Systems

Prof. Dr. Bodo Laube

The research of the department “Neurophysiology and Neurosensory Systems” focuses on the structure and function of biological sensors involved in synaptic transmission, neuronal development and cancer progression by combining biochemical, morphological, mouse genetic, behavioral, molecular modeling and electrophysiological methods.

Synaptic neurotransmission between nerve cells in the central nervous system is mediated by phylogenetically and structurally distinct families of ligand-gated ion channels (Fig. 1).

Fig. 1: Crystal structure of different integral membran receptors
Fig. 1: Crystal structure of different integral membran receptors

These channels are composed of different subunits which are differentially expressed in the developing and adult brain and, remarkably, also in cells constituting tissues of diverse cancers. Thus, these channels are crucially involved in both, i) brain function and malfunction, such as memory formation and neurodegeneration, and ii) in the stress response and in survival strategies of tumor cells, i.e. malignant progression or radio resistance. As these channels constitute specific sites for the allosteric action of clinically relevant drugs, we intend to find new perspectives for the development of novel therapeutically useful compounds and for the treatment of diverse neurological diseases, of chronic pain and malignant brain tumors. In addition, based on the knowledge about the structural constraints determining the function and pharmacology of receptors, we use coupling of modified binding domains to biological and artificial nanopores for the rational design of synthetic BioSensors employed for identifying and analyzing substances of biological interest.

Major Research Goals

Role of synaptic proteins in neurological diseases and developmental disorders

Fig. 2: Schematic drawing of a synapse in an in vitro co-culture system
Fig. 2: Schematic drawing of a synapse in an in vitro co-culture system

Proper functioning of the nervous system depends on the balance of excitatory and inhibitory synaptic information processing and is mediated by distinct families of neurotransmitter receptors. In addition, synapses comprise a variety of specific proteins, such as cell adhesion proteins and scaffold proteins (Fig. 2).

Neurotransmitter receptors represent key players in the physiology and pathophysiology of central neurons during development and the maintenance of cognitive functions in the brain. Inappropriate activation induces developmental malformations, neuronal loss in acute trauma as well as certain neurodegenerative diseases. Mutations in these proteins are associated with a variety of different neurodevelopmental phenotypes, including intellectual disability (ID), epilepsy, hyperekplexia and autism spectrum disorders (ASD), and different psychiatric diseases. By analyzing structural and functional consequences upon heterologous expression of missense mutations in receptors associated with neurological diseases, Hannah Schütz and Alex Winschel hope to get insights into the underlying pathological mechanisms. As submembraneous scaffolding proteins and cell adhesion molecules organise postsynaptic membrane spezialisations and link these receptors to different intracellular signalling cascades, Lisa Conzen and Jan Baltzer use heterologous expression systems, that allow the analyses of postsynaptic maturation of disease-associated receptor mutants and synaptic proteins in co-culture with neuronal primary cells.

Structural and functional analysis of neurotransmitter receptors (funded by MRC DPFS “PAMS”)

Fig. 3: Homology-model of a glycine receptor with putative binding-sites for the anaesthetic propofol
Fig. 3: Homology-model of a glycine receptor with putative binding-sites for the anaesthetic propofol

Neurotransmitter receptors in postsynaptic membranes are important targets for drug development and pharmacological studies. Thus, selective compounds acting on specific receptor combinations have considerable promises. By comparing representatives of different receptor families, i.e. members of the tetrameric ionotropic glutamate receptor (iGluR), the pentameric Cys-loop receptor and the transient receptor potential family, Vito Grasso and Michael Kilb hope to obtain insights into the molecular determinants of ligand selectivity and efficacy that regulate the specific activation and allosteric modulation of these receptors. For example, in a MRC funded collaboration with the University of Liverpool, we are currently developing and synthesizing selective positive allosteric modulators (PAMS) of glycine receptors on the basis of the anaesthetic propofol (Fig. 3) to prevent and treat chronic pain as well as glycine receptor mediated hereditary diseases.

Role of cellular stress responses and ionizing radiation in neuronal development (funded by BMBF “NeuroRad”)

In the developing and adult brain the exact cellular proliferation, migration, and differentiation mechanisms of neural stem cells (NSCs) are of prime importance. NSCs are characterized by the ability of self-renewal and the ability to differentiate to neurons, astrocytes and oligodendrocytes (Fig. 4). A large body of in vitro evidences indicates that neurotransmitters influence these early developmental stages, thus playing an important role in promoting neuronal differentiation, death or survival. In addition, it is becoming apparent that oxidative and nitrosative stress mediated by both hyper- and hypoactivity of receptors and ionizing radiation (IR) affects adult neurogenesis in the dentate gyrus of the hippocampus, a brain region involved in learning and memory processes.

Fig. 4: Oligodendrocytes, astrocytes and neurons differentiated from neural stem cells
Fig. 4: Oligodendrocytes, astrocytes and neurons differentiated from neural stem cells

In our group, NSCs can be successfully differentiated by a 2D differentiation protocol into functional neural networks with differential developmental patterns. Upon IR induced DNA-damage, Kerstin Rau, Katja Häupl and Bastian Roth are studying individual differentiation events like channel expression, synaptogenesis, migration, neuronal functionality and network formation in NSC derived cultures by combining immunohistochemical, morphological and different electrophysiological methods (patch clamp recording; multi-electrode array; Fig. 5). Analyses of individual differentiation stages of irradiated NSCs reveal that even low dose IR leads to significant variations in the electrophysiological homeostasis and the biophysical properties.

Fig. 5: Functional analyses of differentiated NSCs by patch-clamp recording and multi-electrode arrays
Fig. 5: Functional analyses of differentiated NSCs by patch-clamp recording and multi-electrode arrays
Fig. 6: (a) Behavioral tests for mice of different learning paradigms. (b) Immunohistochemical analyses of immature granule cells in the hippocampus
Fig. 6: (a) Behavioral tests for mice of different learning paradigms. (b) Immunohistochemical analyses of immature granule cells in the hippocampus

In addition, Axel Klink uses mouse models to analyze the consequences of low dose irradiation on learning behavior and brain histomorphology. Besides testing the locomotion and the exploratory behavior of mice, we use different learning paradigms (Morris Water Maze; Barnes Maze; Fig. 6a) to characterize spatial learning abilities. Subsequent immunohistochemical evaluation of irradiated brains by Axel Klink and Gabi Wenz (Fig. 6b) serves as a link between the systemic behavioral approach and molecular biological DNA damage analyses.

Role of membrane receptors in cellular stress response and tumour progression (funded by GRK 1657)

Fig. 7: Ionizing radiation induced DNA-damage (foci) in glioblastoma stem cells
Fig. 7: Ionizing radiation induced DNA-damage (foci) in glioblastoma stem cells

This research projects attempt to understand the function of membrane receptors as part of the cellular stress response in cancer cells and how extracellular signaling interferes with brain tumor proliferation and metastasis upon IR.

Glioblastoma multiforme (GBM) is one of the most common and aggressive malignant primary brain tumors in humans characterized by a high radio-resistance and a high degree of invasive growth. The median survival of patients who suffer of GBM is in the range of 15 months due to recurrence of the cancer in almost all patients. These relapses are probably promoted by a highly tumorigenic subpopulation of cancer cells, so called cancer stem cells. Several lines of evidences indicate that GBMs secrete the excitatory neurotransmitter glutamate at concentrations sufficiently to stimulate proliferation, infiltration, and cell survival of tumor cells. Furthermore, the increased glutamate concentrations in the vicinity of the tumor are assumed to cause excitotoxic neuronal cell death in the surrounding tissue. As glutamate receptors are expressed in tumor cells, it is assumed that glutamatergic signaling in GBM is involved in promoting tumor survival, metastasis, and endowing tumors with an enhanced resistance to radiation- and chemotherapy. Thus, the aim of the work of Henrik Lutz is to examine the impact of glutamate and IR on cell survival, migration, intracellular signaling pathways regulating gene expression and DNA damage response (DDR) in glioblastoma cells, especially in the highly tumorigenic subpopulation of glioblastoma stem cells (Fig. 7), which are in focus of new therapeutic approaches.

Design and Use of BioSensors (funded by LOEWE “iNAPO”)

Fig. 8: BioSensor modules stable integrated into solid-state pores
Fig. 8: BioSensor modules stable integrated into solid-state pores

The Project Group “Design and Use of Biosensors” uses electrophysiological, biochemical, and molecular modeling approaches for the rational design of sensors employed for identifying substances of biological interest. As ligand-gated ion channels in cell membranes represent biological nanopores converting physical, biological and chemical signals into robust current signals, Max Bernhard and Michael Schönrock try to engineer new BioSensors on the basis of modified neurotransmitter receptors and binding proteins. The aim of this project is to produce specific BioSensor modules for stable integration into solid-state pores (Fig. 8) and subsequent incorporation in a lab on a chip system for medical and environmental analysis.

Perspectives

By combining the knowledge about both structural constraints determining the pharmacology of receptors and their differential physiological roles, new therapeutically useful perspectives for the treatment of diverse neurological diseases should be found. In addition our research focus will have impact on the construction and modification of synthetic ion channels, biomimetic nanopores or gated nano-channels for the rational design of BioSensors.