Oligodendrocyte progenitor cells: role and function in the healthy and injured brain
Abstract: The idea that NG2-glia and myelin can also influence diseases mainly associated with neurons has emerged in the last years. Here, I am going to introduce NG2-glia and their role in health, injury and disease and show an example of a neuronal disease with a synaptic phenotype where glia and myelination are also affected and can even cause at least part of the pathology. 
Phelan-Mc-Dermid syndrome (PMDS) is a subtype of Autism Spectrum Disorders (ASDs), which is caused by mutations or deletion of the postsynaptic scaffold protein SHANK3, leading to synaptic deficits. PMDS-patients show alterations in the white matter tracts and we could recently identify various myelin defects in SHANK3 deficient mice. As synaptic connections also occur between neurons and NG2-glia, we aimed to study whether these myelin abnormalities could be due to a disruption in this synaptic communication. Indeed, deletion of SHANK3 specifically in NG2-glia affects their proliferation and differentiation and leads to motor and behavioural abnormalities. 
Using this novel mouse model, we reveal new insights into the role of NG2-glia in ASDs as well as into the physiological function of neuron-NG2-glia synapses in the adult CNS. These results show an early and strong involvement of oligodendrocytes and myelin in neurological/-psychiatric diseases that were thought to be fully neuronal and open new avenues for the development of therapeutic strategies this time targeting glia.

The role of microglia in Aβ propagation
Abstract: The aggregation of Aβ is an essential early trigger in Alzheimer’s disease (AD) pathogenesis that leads to neurofibrillary tangles, neuronal dysfunction and dementia. Several cell types have been proposed to be causally involved in amyloid plaque formation, including microglia, owing to their close association with Aβ plaques. As soon as Aβ plaques form in the brain, microglia establish an intimate contact with them and become reactive. Those activated microglia have been linked to plaque growth by Aβ uptake followed by microglial cell death. Our group and others have recently implicated microglia in Aβ seeding and at later stages in compacting amyloid plaques, yet their role in propagating Aβ pathology remains elusive. The fact that microglia are phagocytic cells prompted us to speculate that Aβ can be transported by microglia. By using neural grafting experiments we could show that the formation of Aβ plaques in grafted, unaffected tissue depend on the host microglia functionality. Targeting microglia function might therefore provide an opportunity to interfere with the propagation of Aβ.

Large-scale brain architecture in disease: lessons from acute and chronic damage
Abstract: The wiring of the brain is determined during development but continue to evolve in the adulthood and does respond to disease in peculiar ways. The structure of the brain circuits upon neurodegeneration or neurotrauma constitutes the link between clinical manifestations and personal perspectives one one side and cellular and molecular events on the other side. We employ adeno-associated virus and rabies virus tracing systems to detail mesoscale (area to area) and single-cell resolution circuits in murine models of brain disorders. We have uncovered increases and decreases in connectivity taking place in motoneuron diseases, which changes affecting not only the primary motor cortex but also the connections between cortex and hypothalamus. Furthermore, we have used the cell-resolved connectome of distinct hypothalamic cells to identify new vulnerable subpopularions. Finally, we have traced the recovery of the connectome upon acute injury. These datasets contribute to interpret how the structure of the brain gives raise to the clinical manifestations of disease and to the subjective symptoms experienced by patients.

Huntingtin's Hidden Partner: How HAP40 Rewrites the Story of Huntington's Disease
Abstract: Huntington's disease (HD) is a devastating neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the huntingtin gene (HTT). While much attention has focused on the toxic gain-of-function of mutant huntingtin, the physiological role of the huntingtin protein and its interaction partners remains incompletely understood. In this talk, I will introduce huntingtin-associated protein 40 (HAP40) as an obligate partner of huntingtin and present our journey toward understanding their interplay in health and disease.

Tracing HAP40's evolutionary history reveals that it has co-evolved with huntingtin across hundreds of millions of years, underscoring the functional significance of their partnership. Critically, HAP40 protein levels depend on huntingtin binding and are reduced in HD patient cells and tissues, establishing HAP40 as a potential disease biomarker.

Building on these findings, I will present recent work demonstrating that the huntingtin-HAP40 complex acts as a bidirectional cellular rheostat: the balance between free and complexed forms of both proteins governs opposing cellular programs, including mitochondrial homeostasis and cholesterol biosynthesis. In HD, disruption of this balance triggers a dual failure of bioenergetics and lipid metabolism. Together, these findings challenge the prevailing gain-of-toxic-function paradigm and highlight the critical contribution of loss-of-function mechanisms to HD pathogenesis.

Quantification of Infiltration Mechanisms in a Stem Cell–Based Brain Tumor Organoid Model
Abstract: Glioblastoma is among the most aggressive and lethal brain tumors, with untreated patients surviving only a few months due to its infiltrative growth. Its molecular drivers have been studied for decades. Recent experiments have revealed that (I) the aggressiveness is linked to the interplay between astrocytes, microglia, and macrophages, and (II) all three cell types are mechanosensitive. How mechanical signals steer tumor invasion is still unclear.

In my project, we dissect the roles of mechanical signals that affect glioblastoma infiltration. To obtain a highly physiological in vitro model that features key cell types, we implanted patient-derived glioblastoma cells into cerebral organoids derived from human pluripotent stem cells (iPSCs).

To assess the mechanical properties underlying tumor infiltration, we injected and magnetically deformed ferrofluid droplets within the infiltration zone. Surprisingly, we found that glioblastoma tissue composed of LN229 cells is significantly stiffer, whereas tumor tissue from a primary patient-derived cell line (GBM14NSC) is significantly softer than the surrounding brain tissue. As GBM cells display negative durotaxis, our results might explain the difference in invasiveness.

In the next step, we will explore how mechanical signals modulate tumor progression via the mechanosensitive ion channel PIEZO1. This channel transduces physical forces into biochemical signals and has been associated with tumor aggressiveness and poor prognosis. On a broader scope, our experiments aim to reveal the mechanical cues influencing glioblastoma invasion and how they can be used as therapeutic targets.

Towards Modelling of Leber’s Hereditary Optic Neuropathy in Retinal Organoids
Abstract: Leber’s Hereditary Optic Neuropathy (LHON) is a mitochondrial neurodegenerative disease affecting retinal ganglion cells (RGCs) leading to vision loss. Retina tissue is suited for Adeno-Associated Virus (AAV)-based gene therapy treatments. Retinal organoids (ROs) allow testing and optimizing of AAV serotypes.

We developed a machine-learning pipeline to assess AAV transduction in 3D images, enabling spatial and temporal tracking of viral transduction. Although AAV-based therapies for LHON have been in clinical trials, their validation within human retina tissue remains a bottleneck. Since mice do not recapitulate the human LHON disease phenotype, human in vitro models are needed. Current LHON ROs models lack an isogenic control making it difficult dissecting the effects of mtDNA from nDNA. In this project, RO are differentiated using a characterized iPSC (induced pluripotent stem cell) line with a fluorescent reporter for RGCs.

To isolate effects of mtDNA and nDNA we are fusing the iPSC nucleus with mitochondria from a patient donor cell line. We will assess organoid metabolism, electrophysiology, physiology, and stress to establish an in vitro model for evaluating LHON phenotype and therapy effects. By establishing an in vitro model for LHON with an isogenic control and combining it with our recent quantification pipeline for AAV treatment our research may guide serotype optimization for LHON and other retinal diseases.