Blood Brain Barrier Permeability and Brain Capillary Endothelial Cell Tight Junctions in the Dahl S Model of Spontaneous Superimposed Preeclampsia

Abstract

Previous studies in our lab have shown increases in brain water content and Evan’s Blue extravasation in the brains of pregnant Dahl salt‐sensitive (Dahl S) rats compared to Sprague Dawley (SD) rats. The goal of this study was to test the hypothesis that pregnant Dahl S rats display increased blood brain barrier (BBB) permeability and disruption of brain capillary endothelial cell tight junctions.Female (20 week old) Dahl S and SD virgin and pregnant rats were used. Female rats were mated with males of the same strain, and gestational day 1 (G1) of pregnancy was defined by the detection of sperm histologically from a vaginal swab. On G20, rats were perfused with a 1.0% paraformaldehyde/2.0% glutaraldehyde solution and brains were collected for electron microscopy. Transmission electron microscopic images were used to assess the following parameters of brain capillaries: basement membrane status (% dissolved), basement membrane thickness, vesicle formation, tight junction status (% open), luminal membrane protrusions, and vessel diameter. In a separate group, rats were perfused with 5mg/kg of 3kDa Texas Red dextran (1 hour circulation) followed by 5mg/kg injection of 500kDa FITC (3 minute circulation) on G20, brains were collected, and 5μm sections from the posterior cortex were used for confocal microscopy. A ratio of extra‐:intra‐vascular Texas Red mean intensity values was determined to portray a percentage of Texas Red extravasation. All image analyses were conducted blindly.Dahl S pregnant rats showed significant differences in basement membrane status (23% increase of dissolution) and vesicle formation (11±1 vs. 4±1) compared to SD pregnant rats (p < 0.01, 2way ANOVA for multiple comparisons – Tukey post‐hoc). Significant differences were observed in tight junction status among the groups (% open: SD Virgin = 3.03, SD Pregnant = 11.77, Dahl S Virgin = 11.77, Dahl S Pregnant = 26.47, p = 0.04, Fisher’s Exact Test of Independence). No statistical differences were found for measurements of basement membrane thickness, luminal membrane protrusions, or vessel diameter. Dahl S pregnant rats displayed a 17% increase in Texas Red extravasation compared to Dahl S virgin rats (p = 0.01, unpaired t‐test with Welch’s correction).Our results indicate that pregnant Dahl S rats display increases in BBB permeability to low molecular weight fluorescent dextran and increased disruption of brain capillary endothelial cell tight junctions as well as decreased basement membrane integrity. In addition, the increase in vesicle formation may suggest increases in BBB permeability as it relates to transcellular transport across the BBB.Support or Funding InformationKJM was supported by 5T32HL105324‐10 and 20PRE352000021. Work was supported by 1R01HL137673 to MRG and R01HL134711 to JMS.