Le cœur est le tout premier organe fonctionnel chez les vertébrés pendant le développement embryonnaire.  Des défauts du développement cardiaque entraînent un grand nombre de malformations appelées cardiopathies congénitales (CHDs – Congenital Heart Diseases), qui représentent l’anomalie congénitale la plus fréquente, touchant près de 1% des nouveaux-nés.  L’étude des mécanismes cellulaires qui conduisent à la formation du coeur est nécessaire pour comprendre l’origine des CHDs.

La morphogénèse du sytème cardiovasculaire dépend de processus cellulaires et génétiques très complexes. Le département DevCard comprend trois équipes (Michel Pucéat, Francesca Rochais et Stéphane Zaffran) qui s’intéressent aux mécanismes moléculaires et cellulaires impliqués dans la fonction et dans le développement cardiaque normal et pathologique. A l’aide de modèles animaux et cellulaires, le département cherche à identifier les réseaux de régulation importants pour le développement du cœur, des vaisseaux sanguins, des valves cardiaques, mais aussi au cours de régénération et la réparation cardiaques.

Des profils lipidiques anormaux sont souvent associés à un métabolisme altéré dans les cellules tumorales, caractéristique du cancer. Notre objectif est d’élucider la façon dont le métabolisme des sphingolipides (SLs) affecte les processus biologiques clés qui sous-­‐tendent le développement du cancer, comme la mort, la prolifération et la migration cellulaires, le remodelage du stroma tumoral et la réponse immunitaire. Nous étudions en particulier la contribution des SLs dans le développement du mélanome cutané et du cancer du sein. Non seulement ces formes de cancer sont fréquentes et/ou résistantes aux thérapies actuelles, mais elles présentent également des dérégulations du métabolisme des SLs. Notre objectif ultime est de cibler le métabolisme des SLs afin d’améliorer les thérapies antitumorales, donc prévenir la progression de la tumeur et surmonter la résistance aux médicaments anticancéreux, aux cytokines et aux cellules immunitaires.

Our team investigates how Toxoplasma gondii is able to co-opt specific host cell signaling pathways upon invasion. Along the way, we uncovered novel effector proteins that are singularly exported beyond the vacuole-containing parasites and reach the host cell nucleus to rewire the host genome expression. A second avenue of investigation of our team is to study the epigenetic mechanisms involved in the regulation of the developmental transition between acute and chronic stages of infection. Along the way, we discovered a family of benzoxaborole compounds that efficiently prevent parasite growth.

The team’s previous projects were mainly focused to decipher the closely intertwined relationship between cannabinoid receptor activation and sub-neuronal targeting, by using quantitative in vitro imaging approaches of neurons. In the last years, we became increasingly interested in the understanding of cannabinoid-mediated regulation of neuronal structure. Established techniques range from molecular constructions through imaging-based measurements of GPCR activation in cultured hippocampal neurons to the use of animal models of cerebral plasticity.

Current projects of the team are targeted to develop and use new tools to better understand, at multiple spatio-temporal scales, the role of the highly dynamic actomyosin cytoskeleton in neuronal function and neuropsychiatric pathogenesis.

Cannabinoids contract neurons

We have recently identified the contraction of the neuronal actomyosin cytoskeleton as a mechanism conveying a wide-ranging inhibitory role for cannabinoids in neuronal expansion and growth (Roland et al., eLife, 2014). This mechanism acts downstream of cannabinoid receptor CB1R, the major brain target of endocannabinoids and marijuana, atypically coupled to G12/G13 proteins and the Rho-associated kinase ROCK. Such modulation of the neural actomyosin cytoskeleton has not yet been reported downstream of neurotransmitter GPCRs. Therefore our results open previously unexpected perspectives in the study and comprehension of brain function.

Functional consequences of actomyosin remodelling in the brain

Ultrafast functional Ultrasound (fUS) imaging revealed is adapted to access nervous system function through imaging the neurovascular coupling (Osmanski et al., Nat Commun, 2014; Errico et al., Nature, 2015). An important part of our current efforts is focused to further develop this powerful tool either in collaborative projects or in-house, the latter focused on imaging the functional consequences of actomyosin remodeling on brain structure and connectivity.

5 MAIN PUBLICATIONS

  1. Várkuti BH, Képiró M, Horváth IÁ, Végner L, Ráti S, Zsigmond Á, Hegyi G, Lenkei Z, Varga M, Málnási-Csizmadia A. A highly soluble, non-phototoxic, non-fluorescent blebbistatin derivative. Sci Rep. 2016 May 31;6:26141. doi: 10.1038/srep26141.
  2. Errico C, Pierre J, Pezet S, Desailly Y, Lenkei Z, Couture O, Tanter M. Ultrafast ultrasound localization microscopy for deep super-resolution vascular imaging. Nature. 2015 Nov 26;527(7579):499-502. doi: 10.1038/nature16066.
  3. Osmanski BF, Pezet S, Ricobaraza A, Lenkei Z, Tanter M. Functional ultrasound imaging of intrinsic connectivity in the living rat brain with high spatiotemporal resolution. Nat Commun. 2014 Oct 3;5:5023. doi: 10.1038/ncomms6023.
  4. Roland AB, Ricobaraza A, Carrel D, Jordan BM, Rico F, Simon A, Humbert-Claude M, Ferrier J, McFadden MH, Scheuring S, Lenkei Z. Cannabinoid-induced actomyosin contractility shapes neuronal morphology and growth. Elife. 2014 Sep 15;3:e03159. doi: 10.7554/eLife.03159.
  5. Thibault K, Carrel D, Bonnard D, Gallatz K, Simon A, Biard M, Pezet S, Palkovits M, Lenkei Z. Activation-dependent subcellular distribution patterns of CB1 cannabinoid receptors in the rat forebrain. Cereb Cortex. 2013 Nov;23(11):2581-91. doi: 10.1093/cercor/bhs240.

Metastasis can be considered as the end product of a multistep bio-mechano-chemical process where cancer cells disseminate to distant organs and home in a new tissue microenvironment (Fig.1). Metastases are resistantto multiple therapies and are responsible for the large majority of cancer-related deaths. It is now clear that the invasion-angiogenesis-metastasis cascade is not only dependent on genetic and epigenetic alterations within cancer cells, but also involves non-neoplastic stromal cells that contribute to cancer progression. However, the molecular and cellular mechanisms driving metastasis formation remain to be elucidated and better described in a realistic in vivo context. In this context, tumor cells interact with their surrounding microenvironment and corrupt it to their own benefit. For example, exosomes are small extracellular vesicles, which recently emerged as potent mediators involved in this communication. These vesicles are from an endosomal origin, contain proteins, mRNAs, non-coding RNAs and DNA; they circulate in all our body fluids and can be internalized by specific distant cells and ultimately deliver a functional message. Tumor cells release large amounts of exosomes bearing tumoral markers, which can subsequently disseminate at distance. In addition, tumor exosomes contain pro-metastatic factors that shape pre-metastatic niches (PMN), before the actual arrival of tumor cells, while determining tumor metastatic organo-tropism. These properties have promoted exosomes as new targets for anti-tumoral therapies and major candidates for non-invasive diagnosis in cancer using liquid biopsies (blood and urine), and intense research is currently conducted to identify exosome-carried biomarkers.

Development of the cerebral cortex and adult hippocampal neurogenesis are complex processes where huntingtin, the protein mutated in Huntington disease, plays a central role. Understanding these mechanisms will open new avenues potentially leading to treatment of Huntington disease and other neuropathologies.

Our overall goal is to understand the mechanisms coordinating division, cell fate choices and differentiation of neuronal stem/progenitor cells during development and adulthood. We are tackling these issues through the study of one protein, huntingtin. Huntingtin is the perfect model protein, being a scaffold for complexes involved in spindle orientation, cell-cell junctions and cell polarization. Furthermore, huntingtin is mutated in Huntington disease, an inherited neurodegenerative disorder with adult onset. Studying huntingtin thus allows integration of cellular mechanisms and physiological and pathophysiological conditions.

More specifically, we are studying the contribution of huntingtin to different steps of cortical development and adult hippocampal neurogenesis. We aim to define the molecular complexes involved. We also address the questions of how these mechanisms participate in the proper establishment and maintenance of neuronal networks and whether these pathways are altered in Huntington disease. Our working hypothesis is that abnormal development could be a predisposing factor contributing to the symptoms observed in Huntington disease. In the adult, we propose that the depressive behaviour observed in patients is not just an epiphenomenon to a severe disorder with a fatal outcome, but the result of a modification in the biological function of huntingtin in adult neurogenesis.

GIN – Inserm U1216 – University Grenoble Alpes

Lab members: Fabienne Agasse; Monia Barnat; Barbara Braz; Caroline Benstaali; Mariacristina Capizzi; Rémi Carpentier; Julien Le Friec; Elodie Martin; Doris Wennagel.

 

Our group studies the dynamics of intracellular membranes in developing and mature neurons, in healthy and pathogenic contexts. Dysfunction of intracellular endosomal and mitochondrial dynamics has been linked to a variety of psychiatric including depression and schizophrenia and neurodegenerative disorders, including Charcot-Marie-Tooth (CMT), Alzheimer, Parkinson and Huntington diseases. This certainly suggests a crucial role of membrane dynamics in the formation and maintenance of neuronal elaborated shapes and contacts. Despite a large amount of literature, the molecular and cellular principles that govern the establishment and maintenance of neuronal shapes and contacts (synapses) still remain to be elucidated.

Massive membrane expansion during development and maintenance of large cell surface area during life require continuous addition of new membrane. Our recent work has shown that close contacts between the ER, where most lipids are synthesized, and the PM also play a role in neurite growth through non-vesicular lipid transfer. Which types of secretory vesicles are involved and how non-vesicular mechanisms participate to membrane expansion is not clear at all. How the neuronal membranes are maintained during life and aging and how the underlying mechanisms may be impaired in neurodegeneration are still open questions.

The aim of the team is to understand the basic mechanisms and the regulation of membrane trafficking in the context of brain development, psychiatric diseases, brain tumors and neurodegeneration (Parkinson, Alzheimer). We use techniques of cellular and molecular biology with special emphasis on live cell imaging and proteomics, as well as biophysical approaches to study membrane dynamics, adhesion and fusion in vitro.

5 MAIN PUBLICATIONS

Maja Petkovic, Aymen Jemaiel, Frédéric Daste, Christian G. Specht, Ignacio Izeddin, Daniela Vorkel, Jean-Marc Verbavatz, Xavier Darzacq, Antoine Triller, Karl H. Pfenninger, David Tareste, Catherine L. Jackson & Thierry Galli (2014)
The SNARE Sec22b has a non-fusogenic function in plasma membrane expansion 
Nature Cell Biology 16, 434–444 (2014)

Paola Larghi, David J Williamson, Jean-Marie Carpier, Stéphanie Dogniaux, Karine Chemin, Armelle Bohineust, Lydia Danglot, Katharina Gaus, Thierry Galli & Claire Hivroz (2013)
VAMP7 controls T cell activation by regulating the recruitment and phosphorylation of vesicular Lat at TCR-activation sites
Nature Immunology 14, 723–731

Burgo A., Proux-Gillardeaux, V., Sotirakis, E., Bun, P., Casano,A., Verraes, A., Liem, R., Formstecher, E.,  Coppey-Moisan, M. Galli, T. (2012). 
A molecular network for the transport of the TI-VAMP/VAMP7 vesicles from cell center to periphery. 
Dev Cell 23:166-180

Danglot L, Zylbersztejn K, Petkovic M, Meziane H, Combe R, Champy Mf, Birling Mc, Pavlovic G, Bizot Jc, Trovero F, Della Ragione F, Proux-Gillardeaux V, Sorg T, D’esposito M, Galli T. (2012). 
Absence of TI-VAMP/Vamp7 leads to increased anxiety in mice. 
J Neurosci 32:1962-1968. (Comment in Faculty of 1000: 6)

Zylbersztejn K, Petkovic M, Burgo A, Deck M, Garel S, Marcos S, Bloch-Gallego E, Nothias F, Serini G, Bagnard D, Binz T, Galli T. (2012). 
The vesicular SNARE Synaptobrevin is required for Semaphorin 3A axonal repulsion.  
J Cell Biol 196:37-46. (Comment in Faculty of 1000: 8)