Andrea Forero, Veronica M. Pravatà, Fabrizia Pipicelli, Elisa Frenna, Alessandro Soloperto, Marta Ianni, Natalia Abate, Francesco Di Matteo, Zagorka Bekjarova, Laura Canafoglia, Francesca Ragona, Giuseppina Maccarrone, Mariano Gonzalez Pisfil, Christian Whal-Schott, Filippo M. Cernilogar, Matthias Eder, Rossella Di Giaimo, Silvia Cappello
The extracellular milieu, including extracellular vesicles (EVs), plays a pivotal role in brain development. In this study, we sought to elucidate the pathogenesis of progressive myoclonus epilepsy type 1 (EPM1), a disease caused by mutations in the CSTB gene, using cerebral organoids (COs) derived from patient cells. The results demonstrate that EPM1 COs display increased electrophysiological activity and disrupted excitatory/inhibitory (E/I) balance. Single-cell RNA sequencing analysis of ventral EPM1-COs revealed an abnormal specification of progenitor fate, with a shift toward dorsal neuron identities. We demonstrated that this misspecification is driven by a functional alteration of the ventral signaling niche, resulting from impaired EV dynamics and altered protein cargo. Mechanistically, we identified Sonic Hedgehog (SHH) as a direct physical interactor of CSTB and demonstrated that CSTB deficiency leads to reduced SHH content and secretion. Our findings establish CSTB as a safeguard of ventral patterning and identify the CSTB-SHH-EV axis as a potential therapeutic target for mitigating the E/I imbalance associated with EPM1.