Abstracts

Rationale: Disruption of the blood-brain barrier (BBB) and leakage of serum proteins into the brain parenchyma have recently emerged as important mechanisms involved in the pathogenesis of chronic epilepsy. BBB dysfunction may trigger neuroinflammation and oxidative stress, and finally impact normal neuronal function. Yet, the role of BBB in the pathogenesis of Tuberous Sclerosis Complex (TSC)-related epilepsy is still unknown, despite its significant potential as a novel therapeutic target. The purpose of this study was to evaluate the BBB integrity in human TSC cortical tubers by examining the abundance of brain microvessels, the degree of vascular permeability, and the expression of endothelial cell tight junction (TJ) and adherens junction (AJ) proteins. Methods: Cortical tissue samples from TSC patients with therapy-resistant epilepsy (n=14, mean age 8.6 years) and control subjects (n=8, mean age 11.2 years) were used for quantitative double label immunohistochemistry. TSC samples were obtained from post-mortem cases (n=3) and patients who underwent epilepsy surgery at NYULMC (n=11). Post-mortem TSC and control tissue was obtained from the NIH NeuroBioBank's Brain and Tissue repository at the University of Maryland, Baltimore. Sections (20µm) were immunolabeled for the serum protein fibrinogen and the AJ and TJ proteins V-cadherin and occludin, respectively. Lectin was used to visualize blood vessels. Quantification was performed using ImageJ software version 1.48 (NIH, Bethesda, MD). The average blood vessel length was assessed using the segmented line tool. Blood vessel branching was quantified by manually counting the branch nodes. The fraction of membrane-associated V-cadherin and occludin, relative to the blood vessel surface area represented by lectin, was analyzed using the particle analysis tool on the thresholded images. All analyses were performed blindly. Statistical significance (p<0.05) was assessed by Mann-Whitney t-tests. Results: The average blood vessel length was significantly greater in TSC samples compared to controls (157% of control; p=0.015). Furthermore, the average number of nodes in TSC tissues was trending greater than that of the control group, although results did not reach significance (145% of control; p=0.15). The average surface area fraction of V-cadherin was 19.7% in TSC, which was significantly reduced relative to the control group (26.0%; p=0.003). Similarly, the average surface area fraction of occludin was 19.4% in TSC, which was also significantly smaller than the control group’s average of 25.0% (p=0.008). These changes were accompanied by extensive fibrinogen staining outside of the blood vessels, indicative of a dysfunctional BBB. Conclusions: Our results show increased vascular proliferation in TSC accompanied by increased BBB permeability, likely due to decreased expression of both TJs and AJs. Preventing or repairing BBB disruption with clinically available antiangiogenic therapies could provide a new approach of attenuating epileptogenesis in TSC. Funding: Finding A Cure for Epilepsy and Seizures, University Research Foundation, and NIH/NINDS R01NS101156