|The objectives of our team is to better understand the mechanisms regulating the biogenesis and functions of multivesicular late endosomes in different specialized cell types, in vitro and in vivo. Depending on their environment and the stimuli they received, the different cell types of the organism can adapt their endosomal system to degrade the content of their multivesicular endosomes in lysosomes or to secrete their intraluminal vesicles as exosomes in the extracellular space. Our studies aim at identifying different molecular mechanisms that regulate these functional adaptations and at developing different tools to monitor the endosomal dynamics in vitro and in vivo. These studies will allow us to better understand the role of the endosomal dynamic in different neuropathies and in particular the metabolism of amyloids in Alzheimer's disease.|
FJ Verweij, C Revenu, G Arras, F Dingli, D Loew, MD Pegtel, G Follain, G Allio, JG Goetz, P Zimmermann, Ph Herbomel, F Del Bene, G Raposo, G van Niel.Live Tracking of Inter-organ Communication by Endogenous Exosomes In Vivo. Published: February 7, 2019 DOI:https://doi.org/10.1016/j.devcel.2019.01.004
Bissig C, Croisé P, Heiligenstein X, Hurbain I, Lenk GM, Kaufman E, Sannerud R, Annaert W, Meisler MH, Weisman LS, Raposo G, van Niel G. PIKfyve complex regulates early melanosome homeostasis required for physiological amyloid formation. J Cell Sci. 2019 Feb 1. pii: jcs.229500. doi: 10.1242/jcs.229500. PubMed PMID: 30709920.
FJ Verweij, MP Bebelman, CR Jimenez, JJ. Garcia‑Vallejo,H Janssen, J Neefjes,JC. Knol, R Goeij‑de Haas, SR Piersma, S Rubina Baglio,M Verhage, JM Middeldorp, AZomer, J van Rheenen, MG Coppolino, I Hurbain, G Raposo, MJ. Smit, RFG Toonen, Gvan Niel, and DM Pegtel : Quantifying exosome secretion from single cells reveals a modulatory role for GPCR signaling. J. Cell Biol. https://doi.org/10.1083/jcb.201703206
Within the Center for Psychiatry and Neuroscience, our project is divided into three objectives, which will be developed in parallel.
The first objective aims to deepen and generalize our fundamental knowledge about the mechanisms regulating the functions of multivesicular endosomes and in particular the balance between exosome secretion and lysosomal degradation. To do this, we develop new tools to better understand this balance. In particular, we focus on the role of membrane contact sites in the regulation of this balance.
The second objective is to evaluate, in parallel, the relevance of these mechanisms in the cells of the nervous system and in an in vivo model, the zebrafish. This multi-scale approach, based on advanced imaging methods such as correlative microscopy or subcellular videomicroscopy, allows us to analyze the endosomal dynamics and the secretion of exosomes on living and in vivo neuronal cells.
All the physiological functions of multivesicular endosomes are involved in various pathological processes affecting the nervous system. The third objective is to combine the knowledge and tools developed in the first two parts in order to evaluate their relevance in different neuropathies, particularly in the development of Alzheimer's disease and the metabolism of pathological amyloids. In this perspective, we will evaluate the relevance of the regulatory mechanisms of the endosomal balance in the generation of pathological amyloid fibers.
Our multi-scale approach, based on the complementarity of cellular models and in vivo, will allow us to unveil new mechanisms regulating the multiple functions of multivesicular endosomes. By exploring the role of these mechanisms in the homeostasis of pathological amyloid fibers during Alzheimer's disease, our research will open new avenues of research to improve therapeutic approaches targeting this still incurable disease. In addition, the development of an in vivo model to study intracellular trafficking and inter-cellular communication in vivo by exosomes will provide the basis for new collaborations.
Figure : Schematic model of the role of endosomal dynamics
Schematic model of the role of endosomal dynamic regulated by membrane contact site (MCS) in the metabolism of the amyloid peptide Abeta. Abeta accumulating in MVB after APP endocytosis is either degraded by fusion of MVB with lysosome or secreted by fusion of MVB with the plasma membrane. Membrane contact sites are emerging regulators of endosomal dynamic. Our unpublished data show that MCS regulate the balance between endosomal secretion and degradation.
Guillaume Van Niel
Since 1998, Guillaume van Niel has investigated exosomes and their compartment of origin, multivesicular bodies. During his Ph.D at the Necker institute (Paris, France), he reported and investigated the secretion and the function of exosomes secreted by intestinal epithelial cells. In 2003 at the Utrecht medial center (Utrecht, the Netherlands) he demonstrated ubiquitination of MHC II molecules, a key post-translational modification for sorting to multivesicular bodies in dendritic cells. In 2005 he joined the Curie Institute (Paris, France) and obtained a CNRS permanent position in this team in 2008 to investigate the biogenesis of multivesicular bodies in pigment cells. He notably reported the role of intraluminal vesicles in the generation of physiological amyloid fibrils. Since 2017 he is team leader at the Center of Psychiatry and Neurosciences (Paris, France) developing new tools to visualize exosomes, notably in vivo, and to understand the role of endosomal dynamic between degradation and secretion in amyloid associated pathologies. He has a strong expertise in the cell biology of exosomes and uses extensively different techniques of imaging among which electron microscopy.
During her Ph.D. at the "Cellular and Integrative Neurosciences Institute" (Strasbourg, France), Pauline Croisé has investigated the mechanisms involved in the regulation of membrane trafficking (endocytosis/exocytosis). Her research has especially focused on the role of the Rho GTPases in neuroendocrine tumors, in which secretion is perturbed. She has demonstrated that the activity of two Rho‐GTPases is decreased in human adrenal medulla tumors and correlates with two Rho‐GEFs expression (Croisé et al., 2016, Endocr Relat Cancer). She also has participated in the understanding of the role of the Rho‐GAP Oligophrenin-1 in the coupling between exocytosis and endocytosis in chromaffin cells (Houy et al., 2015, J Neurosci.).
Frederik Verweij started his PhD in 2009, studying the sorting of a viral oncoprotein in exosomes at the Free University Medical Center (VUmc) in Amsterdam (The Netherlands) under supervision of Drs Michiel D. Pegtel and Jaap Middeldorp. This protein, LMP1, is encoded by Epstein Barr virus (EBV), a virus that hijacks human B-cell development to establish a latent infection in approximately 90% of the world population. LMP1 is a viral mimic of CD40 and one of the viral key-proteins that drives EBV infected B-cells through the B-cell germinal center reaction to become a memory B-cell, He demonstrated that mechanistically, the sorting of LMP1 depends on its association with CD63, one of the tetraspanins enriched on late-endosomal intraluminal vesicles (ILVs), the intracellular precursors of exosomes. Functionally, the sorting of this protein restrains the constitutively active NF-kB signaling of this protein, that would otherwise lead to uncontrolled NF-kB signaling, which is associated with lymphomagenesis in in vivo mouse models. During his PhD, he also pioneered the use of CD63-pHluorin to visualize exosome secretion from living cells in vitro. This novel approach circumventes cumbersome isolation procedures that had prevented dynamic insight into the exosome secretion process till then. This work also laid the basis for his current work, where he is studying exosome secretion and trafficking in vivo during development and cancer, using zebrafish embryos as a model organism.