New therapeutic targets to develop molecules active in drug‐resistant epilepsies

• Published in: Epilepsia (Copenhagen) 2010-07, Vol.51 (s3), p.43-47
• Main Authors: SidAhmed‐Mezi, Mounia, Pumain, René, Louvel, Jacques, Sokoloff, Pierre, Laschet, Jacques
• Format: Article
• Language: English
• Subjects: Animals; Anticonvulsants - pharmacology; Anticonvulsants - therapeutic use; Anticonvulsants. Antiepileptics. Antiparkinson agents; Biological and medical sciences; Cerebral Cortex - drug effects; Cerebral Cortex - enzymology; Cerebral Cortex - physiopathology; Drug‐resistant epilepsy; Epilepsy - drug therapy; Epilepsy - etiology; GABAA receptor; GAPDH; Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating) - drug effects; Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating) - physiology; Headache. Facial pains. Syncopes. Epilepsia. Intracranial hypertension. Brain oedema. Cerebral palsy; Humans; Mass spectrometry; Medical sciences; Nervous system (semeiology, syndromes); Neurology; Neuropharmacology; Pharmacology. Drug treatments; Phosphatase; Phosphorylation - drug effects; Polyamine; Receptors, GABA-A - drug effects; Receptors, GABA-A - physiology; Spermine - physiology
• ISSN: 0013-9580; 1528-1167
• DOI: 10.1111/j.1528-1167.2010.02608.x

Summary We have shown that the glycolytic enzyme glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) is the kinase involved in the endogenous phosphorylation of the α1 subunit of the γ‐aminobutyric acid (GABA)A receptor (GABAAR), maintaining GABAA‐R function. GABAAR endogenous phosphorylation is opposed by one or several atypical phosphatases. We have shown in addition, using cerebral tissue obtained during epilepsy surgery and control tissue from patients undergoing brain tumor surgery, that both endogenous phosphorylation and GABAAR function are significantly reduced in the “epileptogenic” cerebral cortex when compared to control. This dysfunction likely contributes to seizure generation and/or transition from the interictal to the ictal state. The therapeutic challenge is to alleviate the endogenous phosphorylation deficiency of GABAAR in the epileptogenic cortical tissue, either through activating the endogenous kinase activity, or inhibiting dephosphorylation of the α1 subunit. Following the first trail, we have shown that spermine (the most effective polyamine) increases the GAPDH kinase activity on GABAAR and that subsequently such modulation potentiates its function as assessed by rundown studies on isolated neurons. Following the second trail, we have developed methods to identify these atypical membrane‐bound phosphatases. Their activities were detected using two synthetic phosphopeptides corresponding to the α1 regions of phosphorylation by GAPDH. After purification, the active fractions are submitted to proteomic analysis by nanoLC‐Maldi‐TOF/TOF for protein identification. Two candidate proteins have been identified, which will be used as targets for high‐throughput screening in order to develop original antiepileptic molecules.