Abstracts

Rationale: Disruption to the blood-brain barrier (BBB) is commonly observed in experimental models of epilepsy and in resected brain tissue from patients with treatment resistant temporal lobe epilepsy. While previous studies have shown associations between BBB dysfunction and seizure activity in epilepsy, there is a paucity of investigations exploring the underlying molecular mechanisms that drive microvascular dysfunction in the condition.

Methods: Patients with treatment resistant temporal lobe epilepsy were recruited for pre- and post-surgical dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Hippocampal and cortical brain tissue samples were used for histological and transcriptomic analysis of BBB integrity. Seizures were induced in mice via systemic or unilateral intrahippocampal injection of kainic acid and blood-brain barrier integrity was assessed by perfusion of different molecular weight tracer molecules.

Results: DCE-MRI revealed widespread BBB disruption in pre-surgical patients with temporal lobe epilepsy which was subsequently ameliorated following surgical resection of affected regions. Molecular analysis of resected tissue uncovered breakdown of the endothelial cell tight junction proteins, leakage of plasma proteins into the brain parenchyma, and extensive neuroinflammation characterised by microglial activation and astrogliosis. Correlation analysis revealed strong associations between markers of inflammation and disease severity and the incidence of psychiatric comorbidities. In rodents, intrahippocampal injection of kainic acid disrupted the tight junction proteins claudin-5, occludin and ZO-1. In mice heterozygous for claudin-5 there was increased vulnerability to evoked seizures and more extensive BBB disruption and neuroinflammation compared to wild-type mice. Finally, in an inducible claudin-5 knockdown mouse model, loss of claudin-5 resulted in spontaneous recurrent seizures, astrogliosis, and increased mortality.

Conclusions: Overall, our findings suggest that epilepsy can alter BBB integrity by modulating the tight junction protein claudin-5. Surgical resection of affected brain regions attenuated BBB disruption which suggests that microvascular stabilisation is important for seizure freedom. In mice, kainic acid induced seizures resulted in loss of the tight junction protein claudin-5. While loss of claudin-5 is lethal with severe neuroinflammation and recurrent seizures occurring, haploinsufficiency is sufficient to reduce the threshold for the induction of convulsive seizures. This data complements decades of research showing that BBB breakdown is sufficient to induce epileptiform activity.

Funding: Please list any funding that was received in support of this abstract.: This work was supported by grants from Science Foundation Ireland (SFI), (12/YI/B2614 and 11/PI/1080), The Irish Research Council (IRC) and by a research grant from SFI under grant number 16/RC/3948 and co‐funded under the European Regional Development fund by FutureNeuro industry partners. The Campbell lab is also supported by a European Research Council (ERC) grant, “Retina‐Rhythm” (864522).