Research Projects

This section introduces current projects of the Developmental and Cellular Biology group.

On the way to personalized clinical trials in a dish

We use human patient specific midbrain organoids as in vitro disease model for Parkinson’s Disease (PD). The primary cells used in our studies are provided by PD patients that donate their skin cells (e.g. Luxembourg Parkinson Study cohort in NCER-PD). These skin cells harbor the genetic identity of the individual including the mutations that have been shown to cause or increase the risk of developing PD. These skin cells are then reprogrammed into induced pluripotent stem cells (iPSCs), a cell type comparable to embryonic stem cells and able to give rise to every cell within the human body. Currently, we use cells that harbor mutations in the PD associated genes LRRK2, GBA, SNCA, VPS35, PINK1, PARKIN, and MIRO1. Additionally, samples from idiopathic (no known causative mutation) PD patients are used.

Using the iPSCs, we mimic the neurodevelopmental process in a dish and generate complex 3D cellular structures, so-called midbrain organoids - regionalized mini brains. The region we choose to produce is the midbrain, because loss of dopaminergic neurons within the midbrain is the main clinical hallmark of PD and leads to typical PD-associated motor symptoms such as tremor. Using these midbrain organoids, we do in vitro disease modelling by comparing the organoids from patients to those coming from healthy individuals. In addition to these healthy controls, we also genetically engineer isogenic midbrain organoids from iPSCs where we have introduced gene corrected mutations using the CRISPR/Cas9 technology. As PD is a multifactorial disease and each individual has a different genetic background, this methodology helps us to differ between mechanisms and phenotypes that are disease or mutation dependent. The subsequent comparative analyses rely on deep cellular and molecular phenotyping and multi-omics approaches. Once the patient specific phenotypes are established and an underlying mechanism has been discovered, different approaches can be envisioned in order to stratify the patients and find common as well as personalized differences. Ultimately, observed PD phenotypes can be rescued by drug/compound treatment or genetic modifications. Lastly, environmental contributions can be evaluated by the individual patient susceptibility towards external stimulants or toxins. These system manipulations allow us to discover novel potential disease modifiers as well as treatment strategies and to study their impact, leading the way to precision medicine.

Model development

The human brain is an immensely complex structure, with different anatomical and functional regions. In many aspects, iPSC-derived three-dimensional human brain organoids, collectively called minibrains, resemble the developing human brain. They contain the most relevant cell types (neurons, astrocytes and oligodendrocytes), have functional synapses as well as axon myelination. Most importantly, they show a spatial organization and asymmetry that resembles the developing human brain. However, they are lacking components of the immune system, such as microglia cells, as well as components of the circulatory system, such as vasculature, which both are shown to be relevant in neurodegenerative disease pathology, including PD. Therefore, we are constantly developing our models to make them even more physiologically relevant and study new roles of these cell types in healthy and disease context. On the other hand, PD is a complex disease, not only affecting single brain regions (like the midbrain), but the complete brain or even the entire body. By generating assembloids via merging organoids representing different brain regions (e.g. the midbrain and the striatum or the hindbrain), or different parts of the body (e.g. the brain and the intestine), we develop more complex and representative in vitro disease models that allow us to study the disease from a systemic point of view. In order to connect and culture these assembloids, we make use of both in-house and project partner-obtained microfluidic devices, inserts or chips. Interestingly, the different organoids can be derived from a single stem cell culture from any individual rendering our system truly personalised.

Next steps towards an advanced in vitro modelling of disease – Microglia & Vascularization

PD etiology is complex with the implication of many different cells of the brain. Current evidence indicates that the immune system, especially the aspect of neuroinflammation, also plays a critical role in PD. Microglia, the main immune cells in the brain are thus a relevant focus in PD pathology. Study on human microglia is relatively complicated and it is mainly accomplished via in vivo or postmortem brain biopsies. Therefore, by combining iPSC and organoid technology, we aim to study the role of microglia in PD pathogenesis using patient-derived iPSC. By integrating iPSC-derived microglia into midbrain organoids, we aim to resemble the more physiological interaction between microglia and the brain. Hopefully this will give us clues on the mechanistic role of microglia in neurodegeneration.

Furthermore, our recent efforts have focused on combining midbrain and vascular assembloids. The vasculature contain an endothelial network that could be the focus of studies related to the observed vasculature instability in PD and its consequences on brain physiology. By integrating microglia into midbrain-vascular assembloids, we further advance the model into an assembloid that contains all cell types in the brain. Ultimately, this model may better recapitulate the brain microenvironment in an in vitro 3D system, where it can be used to obtain more information about the disease, its molecular mechanism and possibly therapeutic targets in the future.