Venue: Centre Broca
Xuesi Zhou 
Team Giannone – IINS
Thesis directors: Grégory Giannone (IINS) & Brahim Louinis (LP2N)
Title
Deciphering the mechano-properties of the membrane periodic skeleton in neurons using super-resolution microscopy
(Déchiffre les propriétés mécaniques du squelette périodique de la membrane dans les neurones à l’aide de la microscopie à super-résolution)
Abstract
Mechanotransduction is the detection of mechanical forces by cells and their conversion into biochemical signals. Mechanotransduction events is key for regulating neuronal functions during physiological processes, such as development and synaptic transmission, and pathophysiological events, including traumatic brain injury and neurodegeneration, or during aging. Axons experience forces during limb flexion, but also during interactions with post-synapses and neuroglia in brain. The membrane periodic actin-spectrin skeleton (MPS) of axons, revealed by super-resolution with a period of approximately 190 nm, could play a crucial role in neuron mechanosensing. ab-spectrin tetramers within MPS can theoretically extend under force. The MPS is also composed of adhesion, actin-binding and signaling proteins (such as Src, CB1), some identified as mechanosensors of non-neuronal cells.
My PhD aims to uncover whether the MPS in axons is a mechano-sensitive structure by studying the mechanical response and reorganizations of its components at molecular level. We recently developed the only cell stretching device compatible with super-resolution microscopy, allowing to capture the acute mechanical response of individual proteins inside mechanosensitive structures. We first adapted the stretching device to neurons to image the MPS by super-resolution and quantified its molecular deformations and reorganizations after stretch. We then applied a 30% stretch to axons at different rates (0.1s, 1s, 100s). Fast stretch (0.1s, 1s) induced increased period of spectrin and MPS irreversible plastic deformation (0.1s) or MPS reversible elastic deformation (1s), while slow stretch (100s) did not alter spectrin period. Thus, the MPS is a resilient mechanosensitive structure, but extreme fast deformations disrupt its molecular organization. We also revealed the mechano-dependent dissociation of adducin (actin capping protein), demonstrating an active molecular reorganization of the MPS. We are confident that, we will be able to obtain all the results to demonstrate for the first time that the MPS is a mechanosensitive structure responding to force through reorganization of spectrin and actin-binding proteins.
In collaboration with the group of Christophe Lamaze at Institut Curie (Paris, France), we adapted our strategy to assessed the impact of mechanical stretching in caveolin nanoscale reorganization in endothelial cells, using super-resolution.
Keywords: mechanosensing, axon, membrane periodic skeleton, spectrin, cell stretching, super resolution microscopy
Jury
- Christophe Leterrier, INP (Rapporteur)
- Marina Mikhaylova, HU Berlin (Rapporteur)
- Pierre Nassoy, LP2N (Examiner)
- Nils Gauthier, IFOM (Examiner)
- Francesca Pennacchietti, KTH (Examiner)
- Brahim Louis, Université de Bordeaux (Director)
- Grégory Giannone, IINS (Co-director)
- Anna Brachet, IINS (Guest)