Background: Charcot-Marie-Tooth (CMT) neuropathy is one of the most common neurodegenerative diseases of the PNS. CMT involves both axonal (CMT2) and demyelinating (CMT1) forms but ultimate progression of neuropathy reflects axonal degeneration in either type. CMT1B, the second most common CMT1, is caused by mutations in the Myelin Protein Zero (MPZ) gene. Most patients with CMT1B present with one of two distinct phenotypes: one with extremely slow nerve conduction velocities and onset in the period of motor development. Surprisingly, since MPZ is only expressed by Schwann cells, the second major group presents as an axonal neuropathy, with onset of symptoms as adults, and therefore is classified as CMT2J/I. The glial mechanisms contributing to axon protection are considered the key to understand and cure neuropathies but remain largely uncharacterized. In CMT2J/I axonal degeneration is uncoupled from demyelination, providing a unique opportunity to understand how to protect axons. Specific Aims: To dissect the glial mechanisms contributing to axon protection or degeneration in this project we pursue the following aims: Aim1: Explore the molecular mechanisms of axonal degeneration in CMT2J/I models Aim2: Genetically and pharmacologically modulate the axon degeneration-promoting SARM1 pathway in CMT2J mice. Aim3: Characterize phenotype and disease course in CMT2J/I patients Results: We generated two authentic models of CMT2J (Mpz-T124M) and CMT2I (Mpz-P70S). Both mice recapitulate the axonopathy observed in humans. In particular, T124M mice show axonal loss with only minor defects in compact myelin, metabolic changes that could lead to axonal degeneration, and prominent alterations in non-compact myelin domains. One of the most promising "druggable" target to counteract axonal degeneration is the NADase SARM1. To explore the contribution of SARM1 to CMT2J, we generated Mpz-T124M/SARM1 null mice. Unfortunately, SARM1 deletion did not fully rescue the neuropathy of 12-month-old T124M mice. Nerve conduction velocity and compound motor action potential are lowered in T124M mice but remain unaltered in the double mutants. At earlier time points we could not observe a delayed disease onset or slowed progression either. However, we detected a reduction in the concentration of NF-L and, through crossbreeding these mice with a Thy-YFP reporter line, reduced signs of degenerating axons. Overall, our data suggest that SARM1 is only marginally protective in CMT2J and that further disease mechanism must be involved. Finally, we are clinically characterizing 30 P70S-CMT2I and eight T124M-CMT2J patients; for some of them, we are conducting every year follow-up visits according to a specific protocol. We collected skin samples for immunohistochemistry studies from a total of 13 patients. Interestingly, at least in T124M samples, preliminary results suggest an involvement of non-compact myelin. Plasma samples' collection and analysis for NF-L are also ongoing.

MECCANISMI DI DEGENERAZIONE ASSONALE NELLE MALATTIE DI CHARCOT-MARIE-TOOTH DI TIPO 1B AD INSORGENZA TARDIVA: PATHWAYS MOLECOLARI E APPROCCI TERAPEUTICI Le neuropatie di Charcot-Marie-Tooth (CMT) sono un gruppo di patologie rare del sistema nervoso periferico che colpiscono lo sviluppo e l'integrità della mielina, la guaina isolante che avvolge i nervi. Sebbene siano stati identificati diversi geni coinvolti nelle neuropatie, come essi causino la malattia è ancora poco chiaro, e al momento non esistono terapie efficaci. Per esempio, ancora non si conoscono quali siano i meccanismi che causano la degenerazione assonale (che è alla base della disabilità in tutti i pazienti) nelle CMT. Alcune forme di CMT sono causate da mutazioni nel gene che codifica per la proteina zero della mielina (MPZ). Studi recenti suggeriscono che mutazioni in MPZ che portano a degenerazione assonale possano agire alterando le connessioni tra la mielina e l'assone. Per capire meglio queste connessioni, e per poter disegnare delle terapie efficaci, studiamo dei topi che contengono il gene MPZ mutato. Abbiamo infatti mostrato che questi topi rappresentano un eccellente modello della malattia. In questi animali abbiamo identificato un meccanismo potenzialmente tossico, e in questo progetto ci proponiamo di caratterizzarlo ulteriormente e di verificare se la sua modulazione genetica e farmacologica sia in grado di migliorare la malattia, con il fine ultimo di identificare un trattamento per le neuropatie ereditarie. In parallelo, analizzeremo una vasta coorte di pazienti con neuropatia assonale dovuta alle stesse mutazioni dei modelli murini da un punto di clinico, seguendo specifici protocolli per essere pronti ia futuri trial clinici.

Charcot-Marie-Tooth neuropathy

malattia di Charcot-Marie-Tooth