CE17 - Recherche translationnelle en santé

Gene therapies approaches for Charcot-Marie-Tooth diseases: targeting the right cell type and compartment – GENERATE

Submission summary

Charcot-Marie-Tooth disease (CMT) is a rare and incurable disease of the peripheral nervous system. CMTs are defined according to the cell type affected: either the Schwann Cell (SC) in demyelinating CMT, or motor (MNs) and sensory neurons (SNs) in axonal CMT. More than 100 causative CMT-related genes have been identified. This genetic and cell-type diversity limits the prospect of a broadly applicable therapeutic approach. Given that most CMT subtypes are monogenic and caused by the dysfunction of a well-defined population of cells (SC or MNs and SNs), we believe that gene therapy strategies aimed at restoring the altered function of the mutated protein in the appropriate cell type or even compartment could be a promising approach for CMT.
We will focus on two different CMT forms which mechanisms are currently studied by the GENERATE project members: the axonal form CMT2A and the demyelinating type CMT4H.
CMT2A is linked to heterozygous mutations in the MFN2 gene. MFN2 protein is localized at the mitochondrial membrane, where it regulates mitochondria fusion with its homolog, MFN1. In contrast to this latter, MFN2 has been also observed at the surface of the endoplasmic reticulum (ER) where it controls ER-mitochondria contacts, called MAM. Previous work suggest that MAM dysregulation contributes to CMT2A pathology via a loss-of-function mechanism, which argues for an approach aimed at rescuing MAM function. On this premise, we aim at counteracting the effects of CMT2A mutation by overexpressing wild-type MFN2 in MNs and SNs. As an alternative approach, we will engineer a construct enabling the ectopic expression of the MFN2 protein-homolog MFN1 in the ER. Those constructs will be selectively expressed in MNs and SNs using the appropriate AAVs vectors and neuronal-specific promoter (human Synapsin).
CMT4H is linked to homozygous mutations in the FGD4 gene encoding FRABIN. FRABIN is a guanine exchange factor that regulates the activity of the small RhoGTPase cdc42. Nerves from CMT4H patients display myelin abnormalities. Similar alterations were observed in the sciatic nerves from mice in which Fgd4 or cdc42 is specifically deleted in SCs. That suggests that the pathological effect molecular basis of CMT4H relies on the loss of function of FGD4/FRABIN and cdc42 in SCs. Therefore, we aim at developing a gene-replacement therapy for CMT4H based on the selective expression of either the wildtype full-length FRABIN or a shorten version of FRABIN comprising only the functional domains required for the activity of cdc42 in SCs. Those constructs will be selectively expressed in SCs using the appropriate AAVs and Lvs vectors and SC-specific promoter (Mpz/P0).
We will test the effect of the aforementioned therapeutical strategies on the molecular, cellular and functional alterations associated with CMT2A or CMT4H (MAM and axonal degeneration in CMT2A, myelination abnormalities in CMT4H, motor and sensory functions for both CMT forms). To that end we will use a combination of molecular biology and imaging strategies as well as behavioral testing, in vitro preparations (cellular models originating from rodents and patients with CMT) and in vivo transgenic mouse models.
We believe the GENERATE project is achievable in three years since: 1) most of the tools and models are available 2) most of the tasks described above rely on solid preliminary data 3) members of the project display all the necessary conceptual and technical expertise to perform each proposed experiment. This project will benefit from the close collaboration of our team with clinicians and patients, an important asset given the anticipated translation of the project towards clinical application. Therefore, the GENERATE project fully complies with the ANR’s and the French State’s 2021 strategic priority regarding translational research on rare diseases.

Project coordination

Nathalie Marissal (Centre de Génétique Médicale de Marseille (Marseille Medical Genetics))

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

MMG Centre de Génétique Médicale de Marseille (Marseille Medical Genetics)
EPFL / Bertarelli Foundation gene therapy platform

Help of the ANR 171,478 euros
Beginning and duration of the scientific project: March 2022 - 42 Months

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