Stabilization of BBB Junction Protein Attenuates Epileptic Brain Activity

Vignesh Subramanian ’24

Figure 1: A simplified view of the blood-brain barrier (BBB), a semipermeable network of close-packed border cells and capillaries protecting the brain from non-selective substance influx.

Epilepsy is a chronic central nervous system disorder characterized by abnormal neuronal activity in the brain that triggers repeated, spontaneous seizures. Treatment-resistant epilepsy has previously been linked to disruption of the blood-brain barrier (BBB), a semipermeable network of close-packed endothelial (border) cells and capillaries that controls the influx of solutes circulating in the bloodstream into the extracellular fluid of the brain. The BBB’s compound structure contains many tight-junction (TJ) proteins, which are situated between the BBB’s border cells and ordinarily seal the paracellular space (space between cells), blocking the non-selective flow of ions and other substances across the barrier. Dysfunction of the most concentrated TJ protein, claudin-5, has already been identified as responsible for breakdowns in influx control at the BBB, threatening the integrity of the microvasculature. Researchers led by Dr. Chris Greene of Trinity College Dublin sought to determine whether changes to claudin-5 levels at the BBB were linked to incidence of human epilepsy.

The researchers first collected sclerotic brain tissue from 16 patients with treatment-resistant temporal lobe epilepsy via resection surgeries and submitted these samples to magnetic resonance imaging (MRI) to screen for signs of neuroinflammation. Intra-hippocampal injections of kainic acid were then administered to mouse subjects to evoke seizures and thus determine whether aberrant neuronal activity directly induced changes to claudin-5 levels and vascular patterning. Finally, selected knockdown mice were supplemented with a doxycycline-inducible virus vector followed by reinfusion of a growth factor (TGF-beta) that downregulated and upregulated claudin-5 protein expression, respectively, to examine the extent of neurological deficits and either recurrence or attenuation (reduction) of seizures.

The researchers found that modulation of TJ protein claudin-5 levels induced inflammatory responses, blood-derived protein passage, and immune cell infiltration into the brain parenchyma, or functional tissue, establishing that BBB breakdown is enough to trigger subsequent seizure rhythm-associated brain activity. Both downregulation and knockout of claudin-5 expression had the same effect, suggesting that already vulnerable BBB elements may fail to regain the selectiveness of their permeability once influx control has broken down. Finally, the study correlated seizure attenuation with claudin-5 upregulation via promotion of both the protein’s regulator and the TGF-beta signaling pathway. This showed for the first time that it was both possible and effective to restore claudin-5 levels and stabilize BBB integrity. Together, these findings identify a potential therapeutic route to controlling epileptic manifestations via stabilization of microvascular tight junction proteins.

Works Cited:

[1] C. Greene, et al., Microvascular stabilization via blood-brain barrier regulation prevents seizure activity. Nature Communications 13, 1-13 (2022). doi: 10.1016/j.neuron.2015.10.046

[2] Image retrieved from:
https://commons.wikimedia.org/wiki/File:Blood_Brain_Barrier.jpg

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