Jan R. Detrez

Sustained synchronized neuronal network activity in a human astrocyte co-culture system

Impaired neuronal network function is a hallmark of neurodevelopmental and neurodegenerative disorders such as autism, schizophrenia, and Alzheimer’s disease and is typically studied using genetically modified cellular and animal models. Weak predictive capacity and poor translational value of these models urge for better human derived in vitro models. The implementation of human induced pluripotent stem cells (hiPSCs) allows studying pathologies in differentiated disease-relevant and patient-derived neuronal cells. However, the differentiation process and growth conditions of hiPSC-derived neurons are non-trivial. In order to study neuronal network formation and (mal)function in a fully humanized system, we have established an in vitro co-culture model of hiPSC-derived cortical neurons and human primary astrocytes that recapitulates neuronal network synchronization and connectivity within three to four weeks after final plating. Live cell calcium imaging, electrophysiology and high content image analyses revealed an increased maturation of network functionality and synchronicity over time for co-cultures compared to neuronal monocultures. The cells express GABAergic and glutamatergic markers and respond to inhibitors of both neurotransmitter pathways in a functional assay. The combination of this co-culture model with quantitative imaging of network morphofunction is amenable to high throughput screening for lead discovery and drug optimization for neurological diseases.

Early pathologic amyloid induces hypersynchrony of BOLD resting-state networks in transgenic mice and provides an early therapeutic window before amyloid plaque deposition.

In Alzheimers disease (AD), pathologic amyloid‐beta (Aβ) is synaptotoxic and impairs neuronal function at the microscale, influencing brain networks at the macroscale before Aβ deposition. The latter can be detected noninvasively, in vivo, using resting‐state functional MRI (rsfMRI), a technique used to assess brain functional connectivity (FC).

Immune remodelling of stromal cell grafts in the central nervous system: therapeutic inflammation or (harmless) side-effect?

Over the past two decades, several cell types with fibroblast‐like morphology, including mesenchymal stem/stromal cells, but also other adult, embryonic and extra‐embryonic fibroblast‐like cells, have been brought forward in the search for cellular therapies to treat severe brain injuries and/or diseases. Although current views in regenerative medicine are highly focused on the immune modulating and regenerative properties of stromal cell transplantation in vivo, many open questions remain regarding their true mode of action. In this perspective, this study integrates insights gathered over the past 10 years to formulate a unifying model of the cellular events that accompany fibroblast‐like cell grafting in the rodent brain. Cellular interactions are discussed step‐by‐step, starting from the day of implantation up to 10 days after transplantation. During the short period that precedes stable settlement of autologous/syngeneic stromal cell grafts, there is a complex interplay between hypoxia‐mediated cell death of grafted cells, neutrophil invasion, microglia and macrophage recruitment, astrocyte activation and neo‐angiogenesis within the stromal cell graft site. Consequently, it is speculated that regenerative processes following cell therapeutic intervention in the CNS are not only modulated by soluble factors secreted by grafted stromal cells (bystander hypothesis), but also by in vivo inflammatory processes following stromal cell grafting. Copyright

Dysregulation of Microtubule Stability Impairs Morphofunctional Connectivity in Primary Neuronal Networks

Functionally related neurons assemble into connected networks that process and transmit electrochemical information. To do this in a coordinated manner, the number and strength of synaptic connections is tightly regulated. Synapse function relies on the microtubule (MT) cytoskeleton, the dynamics of which are in turn controlled by a plethora of MT-associated proteins, including the MT-stabilizing protein Tau. Although mutations in the Tau-encoding MAPT gene underlie a set of neurodegenerative disorders, termed tauopathies, the exact contribution of MT dynamics and the perturbation thereof to neuronal network connectivity has not yet been scrutinized. Therefore, we investigated the impact of targeted perturbations of MT stability on morphological (e.g., neurite- and synapse density) and functional (e.g., synchronous calcium bursting) correlates of connectivity in networks of primary hippocampal neurons. We found that treatment with MT-stabilizing or -destabilizing compounds impaired morphofunctional connectivity in a reversible manner. We also discovered that overexpression of MAPT induced significant connectivity defects, which were accompanied by alterations in MT dynamics and increased resistance to pharmacological MT depolymerization. Overexpression of a MAPT variant harboring the P301L point mutation in the MT-binding domain did far less, directly linking neuronal connectivity with Taus MT binding affinity. Our results show that MT stability is a vulnerable node in tauopathies and that its precise pharmacological tuning may positively affect neuronal network connectivity. However, a critical balance in MT turnover causes it to be a difficult therapeutic target with a narrow operating window.

Image Informatics Strategies for Deciphering Neuronal Network Connectivity

Brain function relies on an intricate network of highly dynamic neuronal connections that rewires dramatically under the impulse of various external cues and pathological conditions. Amongst the neuronal structures that show morphological plasticity are neurites, synapses, dendritic spines and even nuclei. This structural remodelling is directly connected with functional changes such as intercellular communication and the associated calcium bursting behaviour. In vitro cultured neuronal networks are valuable models for studying these morpho-functional changes. Owing to the automation and standardization of both image acquisition and image analysis, it has become possible to extract statistically relevant readouts from such networks. Here, we focus on the current state-of-the-art in image informatics that enables quantitative microscopic interrogation of neuronal networks. We describe the major correlates of neuronal connectivity and present workflows for analysing them. Finally, we provide an outlook on the challenges that remain to be addressed, and discuss how imaging algorithms can be extended beyond in vitro imaging studies.

BiDiFuse: a FIJI plugin for fusing bi-directionally recorded microscopic image volumes.

Deep tissue imaging is increasingly used for non-destructive interrogation of intact organs and small model organisms. An intuitive approach to increase the imaging depth by almost a factor of 2 is to record a sample from two sides and fuse both image stacks. However, imperfect three-dimensional alignment of both stacks presents a computational challenge. We have developed a FIJI plugin, called BiDiFuse, which merges bi-directionally recorded image stacks via 3D rigid transformations. The method is broadly applicable, considering it is compatible with all optical sectioning microscopes and it does not rely on fiducial markers for image registration. AVAILABILITY AND IMPLEMENTATION The method is freely available as a plugin for FIJI from https://github.com/JanDetrez/BiDiFuse/ CONTACT: winnok.devos@uantwerpen.be.

A multilevel framework to reconstruct anatomical 3D models of the hepatic vasculature in rat livers (vol 230, pg 471, 2017) (corrigendum)

Geert Peeters, Charlotte Debbaut, Wim Laleman, Adrian Friebel, Diethard Monbaliu, Ingrid Vander Elst, Jan R. Detrez, Tim Vandecasteele, Tim Johann, Thomas De Schryver, Luc Van Hoorebeke, Kasper Favere, Jonas Verbeke, Dirk Drasdo, Stefan Hoehme, Patrick Segers, Pieter Cornillie, Winnok H. De Vos IBiTech – bioMMeda, Department of Electronics and Information Systems, Ghent University, Ghent, Belgium Gastroenterology & Hepatology, University Hospitals Leuven, Leuven, Belgium Department of Clinical and Experimental Medicine, KU Leuven, Leuven, Belgium Interdisciplinary Centre for Bioinformatics (IZBI), University of Leipzig, Leipzig, Germany Institute of Computer Science, University of Leipzig, Leipzig, Germany (Present address) Abdominal Transplant Surgery, University Hospitals Leuven, Leuven, Belgium Department of Microbiology and Immunology, KU Leuven, Leuven, Belgium Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, Antwerp, Belgium Department of Morphology, Faculty of Veterinary Medicine, Ghent University, Ghent, Belgium INRIA Paris & Sorbonne Universit es UPMC Univ Paris 6, LJLL, France (Permanent address) Centre for X-Ray Tomography, Department of Physics and Astronomy, Ghent University, Ghent, Belgium Leibniz Research Centre for Working Environment and Human Factors at the Technical University Dortmund, Dortmund, Germany Cell Systems and Imaging, Department of Molecular Biotechnology, Ghent University, Ghent, Belgium *Shared senior co-authorship