Abstracts

Rationale: There is a growing body of evidence that mitochondrial dysfunction plays a considerable role in the process of epileptogenesis and seizure generation in temporal lobe epilepsy with hippocampal sclerosis. In this work we analysed mutations of mitochondrial DNA to address the molecular cause for the mitochondrial dysfunction in hippocampal subfields of patients with hippocampal sclerosis, one of the most common forms of therapy-resistant temporal lobe epilepsy. Methods: We evaluated the presence of multiple deletions of the mitochondrial DNA in hippocampal tissue of patients with temporal lobe epilepsy using long range PCR by amplifying overlapping PCR products of 9.5-12.7 kb size. Applying single molecule PCR we quantified the amount of deletions and mapped the individual breakpoints of the identified deletions. Results: In hippocampal subfield CA3 and dentate gyrus of 7 patients with hippocampal sclerosis we identified abundant multiple deletions of mitochondrial DNA, which were almost absent in corresponding brain tissue samples from the adjacent parahippocampal gyrus. Applying single molecule PCR we quantified and mapped the deletions. Their amount approached in the CA3 subfield and the dentate gyrus 2-8 % of total mtDNA content. A major fraction of the detected deletions had the 3' breakpoint at a deletion hot spot around np 16070 in the HVR1 region. This implies ROS-caused double strand breaks of mitochondrial DNA as potential mechanism of deletion formation. Hippocampal samples from 8 age-matched patients with epilepsy due to lesions in the temporal lobe did not contain elevated levels of deleted mitochondrial DNA. Conclusions: We directly show that the dysfunction of mitochondrial oxidative phosphorylation in hippocampal subfields of patients with Ammon’s horn sclerosis is related to clonal expansion of a specific type of deletions of mitochondrial DNA. We propose that this might be relevant for seizure generation.