Abstracts

Rationale: Focal cortical dysplasia (FCD) represents a group of diverse localized cortical lesions that are highly epileptogenic and occur due to abnormal brain development caused by genetic mutations, involving the mammalian target of rapamycin (mTOR). These somatic mutations lead to mosaicism in the affected brain, posing challenges to unravel the direct and indirect functional consequences of these mutations. A deeper understanding of the underlying molecular changes across the different brain cell types in FCD is needed to design novel treatments with disease modifying properties. To comprehensively characterize the impact of mTOR mutations on the brain cell types we employed here a multimodal approach to define the proteomic and lipidomic changes in a preclinical mouse model of FCD type II and transcriptomic changes in human brain tissue samples.


Methods: We established a preclinical mouse model of epilepsy-associated FCD type II using in utero electroporation of mutations into the embryonic brain (Rheb CA mutation). Pharmacological characterization with mTOR inhibitors was evaluated. Mouse samples from a control group, injected with an empty plasmid, and a FCD group, injected with the mutated plasmid were generated for subsequent imaging analysis. Spatial Mass Spectrometry Imaging (MSI) combined with fluorescence imaging and label free proteomics was used to gain insights into the brain’s lipidome and proteome within the FCD type II affected region in the mouse model. Surgical resections of FCD type IIb and postmortem human cortex were analyzed by bulk transcriptomics.


Results: We confirmed that post-symptomatic treatment of FCD type II mice at 2 months-old with everolimus (10 mg/kg-2 weeks) leads to a significant reduction in seizure frequency. MSI analysis identified disrupted neuronal migration and differential lipid distribution including a reduction in sulfatides in the FCD type II-affected region, which play a role in brain myelination. MSI-guided laser capture microdissection was conducted on FCD type II and control regions, followed by label free proteomics, revealing changes in myelination pathways by oligodendrocytes. Transcriptomics of human FCD type II tissues indicated changes in relevant gene expression profiles similar to the ones identified in the animal model.

Conclusions: Our comparative analysis of protein pathways and enriched Gene Ontology pathways related to myelination in the FCD type II-affected mouse model and human FCD type IIb transcriptomics highlights the translational value of the disease pathways. This dual approach, including mouse model proteomics and human transcriptomics strengthens our understanding of the functional consequences arising from somatic mutations in FCD type II, as well as the identification of pathways that may be used as therapeutic strategies in the future.

Funding: UCB Pharma and Maastricht Multimodal Molecular Imaging Institute (M4i), Maastricht University