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Published on: March 25, 2022
Mosaic human cortical organoids model mTOR-related focal cortical dysplasia through DEPDC5 deletion
Marina Maletic1, Sara Bizzotto1,2, Théo Ribierre1,3,4
1Sorbonne Université, Paris Brain Institute (ICM), Team MOSAIC "Genetic Mosaicism in Epilepsy and Neurodevelopmental Disorders" Inserm, CNRS, AP-HP, Pitié-Salpêtrière Hospital, 75013 Paris, France.
Abstract:
Focal cortical dysplasia type II (FCDII), a major cause of paediatric drug-resistant focal epilepsy, results from brain somatic variants in mTOR pathway genes, including germline and somatic second-hit loss-of-function variants in the mTOR repressor DEPDC5. Here, we present a proof-of-concept model of DEPDC5 two-hit inactivation mosaicism using patient-derived human cortical organoids (hCOs). Mosaic hCOs displayed increased mTOR activity that was rescued by the mTOR inhibitor rapamycin. Mosaic hCOs also exhibited dysmorphic-like neurons and enhanced neuronal excitability, recapitulating key FCDII pathology hallmarks. Single-cell transcriptomics across three developmental stages revealed aberrant differentiation trajectories leading to premature upper-layer neuron generation, upregulated Notch and Wnt signalling pathways in neural progenitors, and altered expression of synaptic- and epilepsy-associated genes in excitatory neurons. In addition, we identified cell-autonomous alterations in metabolism and translation in mosaic DEPDC5 two-hit hCOs. This study provides novel insights into how DEPDC5 deficiency perturbs human corticogenesis, highlighting that mosaic biallelic inactivation of the gene is necessary for FCDII pathogenesis.
Insights
Focal cortical dysplasia type II (FCDII) arises from DEPDC5 gene inactivation. Patient-derived organoids modeled this, showing mTOR pathway overactivation and epilepsy hallmarks, confirming DEPDC5
Area of Science:
- Neuroscience
- Genetics
- Developmental Biology
Background:
- Focal cortical dysplasia type II (FCDII) is a leading cause of pediatric drug-resistant epilepsy.
- It stems from somatic mutations in mTOR pathway genes, particularly DEPDC5, which represses mTOR signaling.
- Understanding the pathogenic mechanisms of DEPDC5 mutations is crucial for developing targeted therapies.
Purpose of the Study:
- To establish a proof-of-concept model for DEPDC5 two-hit inactivation mosaicism using human cortical organoids (hCOs).
- To investigate the cellular and molecular consequences of DEPDC5 deficiency in human corticogenesis.
- To explore potential therapeutic interventions targeting the mTOR pathway.
Main Methods:
- Generation of mosaic human cortical organoids (hCOs) modeling DEPDC5 two-hit inactivation.
- Assessment of mTOR pathway activity and rescue with rapamycin.
- Characterization of neuronal morphology and excitability.
- Single-cell transcriptomics analysis across developmental stages.
- Investigation of cell-autonomous metabolic and translational alterations.
Main Results:
- Mosaic hCOs exhibited increased mTOR activity, which was reversed by rapamycin treatment.
- These organoids displayed dysmorphic neurons and heightened neuronal excitability, mirroring FCDII pathology.
- Single-cell transcriptomics revealed aberrant neural progenitor differentiation, upregulated Notch and Wnt signaling, and altered gene expression in excitatory neurons.
- Cell-autonomous defects in metabolism and translation were identified in DEPDC5-deficient hCOs.
Conclusions:
- Mosaic biallelic inactivation of DEPDC5 is essential for FCDII pathogenesis.
- DEPDC5 deficiency disrupts human corticogenesis through cell-autonomous mechanisms.
- This hCO model provides valuable insights into FCDII and offers a platform for therapeutic screening.
