Reduced MUNC18-1 Levels, Synaptic Proteome Changes, and Altered Network Activity in STXBP1-Related Disorder Patient Neurons

• Published in: Biological psychiatry global open science 2024-01, Vol.4 (1), p.284-298
• Main Authors: Van Berkel, Annemiek Arienne, Lammertse, Hanna Charlotte Andrea, Öttl, Miriam, Koopmans, Frank, Misra-Isrie, Mala, Meijer, Marieke, Dilena, Robertino, Van Hasselt, Peter Marin, Van Engelen, Marc, Van Haelst, Mieke, Smit, August Bernard, Van der Sluis, Sophie, Toonen, Ruud Ferdinand, Verhage, Matthijs
• Format: Article
• Language: English
• Subjects: Archival Report; iPSC; MUNC18-1; Neurodevelopmental disorder; SNAREopathy; STXBP1-related disorder; Synaptic transmission
• ISSN: 2667-1743; 2667-1743
• DOI: 10.1016/j.bpsgos.2023.05.004

STXBP1-related disorder (STXBP1-RD) is a neurodevelopmental disorder caused by pathogenic variants in the STXBP1 gene. Its gene product MUNC18-1 organizes synaptic vesicle exocytosis and is essential for synaptic transmission. Patients present with developmental delay, intellectual disability, and/or epileptic seizures, with high clinical heterogeneity. To date, the cellular deficits of neurons of patients with STXBP1-RD are unknown. We combined live-cell imaging, electrophysiology, confocal microscopy, and mass spectrometry proteomics to characterize cellular phenotypes of induced pluripotent stem cell–derived neurons from 6 patients with STXBP1-RD, capturing shared features as well as phenotypic diversity among patients. Neurons from all patients showed normal in vitro development, morphology, and synapse formation, but reduced MUNC18-1 RNA and protein levels. In addition, a proteome-wide screen identified dysregulation of proteins related to synapse function and RNA processes. Neuronal networks showed shared as well as patient-specific phenotypes in activity frequency, network irregularity and synchronicity, especially when networks were challenged by increasing excitability. No shared effects were observed in synapse physiology of single neurons except for a few patient-specific phenotypes. Similarities between functional and proteome phenotypes suggested 2 patient clusters, not explained by gene variant type. Together, these data show that decreased MUNC18-1 levels, dysregulation of synaptic proteins, and altered network activity are shared cellular phenotypes of STXBP1-RD. The 2 patient clusters suggest distinctive pathobiology among subgroups of patients, providing a plausible explanation for the clinical heterogeneity. This phenotypic spectrum provides a framework for future validation studies and therapy design for STXBP1-RD.