Related Experiment Video
Updated: Jul 16, 2025
In Vivo Fiber-Coupled Pre-Clinical Confocal Laser-scanning Endomicroscopy pCLE of Hippocampal Capillaries in Awake Mice
Published on: April 21, 2023
Hippocampal and neocortical BRAF mutant non-expansive lesions in focal epilepsies
Julie Lerond1, Bertrand Mathon2, Mélina Scopin3
1Institut du Cerveau-Paris Brain Institute-ICM, Inserm, CNRS, Sorbonne Université, Paris, France.
Objective:
Mesial Temporal Lobe Epilepsy-associated Hippocampal Sclerosis (MTLE-HS) is a syndrome associated with various aetiologies. We previously identified CD34-positive extravascular stellate cells (CD34+ cells) possibly related to BRAFV600E oncogenic variant in a subset of MTLE-HS. We aimed to identify the BRAFV600E oncogenic variants and characterise the CD34+ cells.
Methods:
We analysed BRAFV600E oncogenic variant by digital droplet Polymerase Chain Reaction in 53 MTLE-HS samples (25 with CD34+ cells) and nine non-expansive neocortical lesions resected during epilepsy surgery (five with CD34+ cells). Ex vivo multi-electrode array recording, immunolabelling, methylation microarray and single nuclei RNAseq were performed on BRAFwildtype MTLE-HS and BRAFV600E mutant non-expansive lesion of hippocampus and/or neocortex.
Results:
We identified a BRAFV600E oncogenic variant in five MTLE-HS samples with CD34+ cells (19%) and in five neocortical samples with CD34+ cells (100%). Single nuclei RNAseq of resected samples revealed two unique clusters of abnormal cells (including CD34+ cells) associated with senescence and oligodendrocyte development in both hippocampal and neocortical BRAFV600E mutant samples. The co-expression of the oncogene-induced senescence marker p16INK4A and the outer subventricular zone radial glia progenitor marker HOPX in CD34+ cells was confirmed by multiplex immunostaining. Pseudotime analysis showed that abnormal cells share a common lineage from progenitors to myelinating oligodendrocytes. Epilepsy surgery led to seizure freedom in eight of the 10 patients with BRAF mutant lesions.
Interpretation:
BRAFV600E underlies a subset of MTLE-HS and epileptogenic non-expansive neocortical focal lesions. Detection of the oncogenic variant may help diagnosis and open perspectives for targeted therapies.
Insights
The BRAFV600E oncogenic variant was identified in a subset of Mesial Temporal Lobe Epilepsy-associated Hippocampal Sclerosis (MTLE-HS) and neocortical lesions. This discovery may aid in diagnosing MTLE-HS and developing targeted therapies for epilepsy.
Area of Science:
- Neuroscience
- Oncology
- Genetics
Background:
- Mesial Temporal Lobe Epilepsy-associated Hippocampal Sclerosis (MTLE-HS) is a complex neurological syndrome with diverse underlying causes.
- Previous research suggested a potential link between CD34-positive extravascular stellate cells (CD34+ cells) and the BRAFV600E oncogenic variant in a subset of MTLE-HS cases.
Purpose of the Study:
- To identify the presence and prevalence of the BRAFV600E oncogenic variant in MTLE-HS and related lesions.
- To characterize the nature and cellular origins of CD34+ cells in these conditions.
Main Methods:
- BRAFV600E variant analysis using digital droplet Polymerase Chain Reaction in MTLE-HS and neocortical lesion samples.
- Ex vivo multi-electrode array recording, immunolabelling, methylation microarray, and single nuclei RNA sequencing were employed.
Main Results:
- The BRAFV600E variant was detected in 19% of MTLE-HS samples with CD34+ cells and 100% of neocortical samples with CD34+ cells.
- Single nuclei RNA sequencing revealed unique cell clusters associated with senescence and oligodendrocyte development in BRAFV600E mutant samples.
- CD34+ cells expressed p16INK4A and HOPX, indicating a progenitor-to-myelinating oligodendrocyte lineage.
Conclusions:
- The BRAFV600E oncogenic variant is implicated in a subset of MTLE-HS and epileptogenic neocortical focal lesions.
- Identifying this variant could improve diagnostic accuracy for these conditions.
- The findings open avenues for developing targeted therapeutic strategies for BRAFV600E-driven epilepsy.
Related Concept Videos
01:19Role of Hippocampus in Memory
01:24Arteries of the Lower Limbs
Various factors can trigger epilepsy, including genetic factors, brain damage, metabolic causes, and unknown etiology. Diagnosis of epilepsy involves electroencephalography (EEG), which...