Abstracts

Rationale: MALDI imaging mass spectrometry has a great potential for the discovery of disease markers. Unfortunately this approach is unable to point out the most significant markers among a list a markers which can be long. Here we used an innovative statistical method to identify the most relevant protein markers in a mouse model for absence epilepsy. Methods: Our study is based on the use of two inbred mouse lines, BS/Orl and BR/Orl, issued from a bidirectional genetic selection and representing a dual genetic model for Childhood Absence Epilepsy (CAE). The BS/Orl strain displays spontaneous and recurrent spike-and-wave discharges (SWD) in both the cortex and the ventrolateral thalamus. These SWD are suppressed by the anti-absence seizure drugs ethosuximide and sodium valproate. In contrast, seizures are exacerbated by the carbamazepine, known to aggravate CAE. By contrast, the BR/Orl strain does not display any SWD either spontaneously or after injection of pentylenetetrazol known to induce SWD. Protein mass spectra were acquired on whole brain sections using MALDI-TOF mass spectrometer. Identification of potential protein markers (m/z values) was performed by top-down analysis. A new cross-classification method specifically adapted to large MALDI imaging datasets was thus developed for the identification of the most significant markers and applied on our mouse model of absence-epilepsy. Finally, a top-down approach based on the analysis of intact proteins was used to identify which proteins are responsible for the significant markers that we observed. Results: Seven proteins were differentially identified between BS/Orl and BR/Orl. One of them, Synapsin-1 was chosen to validate our method. The localization and differential expression of Synapsin-1 observed by MALDI imaging were confirmed by both Western blot and immunohistochemistry experiments. Functional assays are being performed to explore the involvement of Synapsin-1 in the mechanisms underlying absence epilepsy. Conclusions: The Western blot and immunohistochemistry experiments have confirmed the validity of our approach to identify the most relevant protein markers. Applied to an experimental model for absence epilepsy, it has permitted to suggest the Synapsin-1 as a protein of great interest in absence epilepsy.