Lipopolysaccharide‐Induced Activation of Bone Marrow‐Derived Macrophages Disrupts Brain Microvascular Endothelial Cell Function in a Mouse Model of Psychological Resilience

Abstract

Psychological resilience, as measured by the ability of an individual to overcome the development of psychological disorders following exposure to stressful or traumatic events, varies significantly from individual to individual. Inflammation, and the breakdown of the blood‐brain barrier (BBB) are thought to be key factors in the development and progression of psychological disorders such as depression, schizophrenia, and post‐traumatic stress disorder. The activation of macrophages is associated with the disruption of barrier function of the BBB, and thus may play an important role in determining resilience to stress. It is unknown whether the macrophage phenotype and/or BBB phenotype of resilient individuals is significantly different from that of non‐resilient individuals, or whether these phenotypic differences and their interaction contribute to the degree of resilience in individuals. In this study, we tested the hypothesis that resilient individuals possess macrophage and blood brain barrier phenotypes that are more resistant to the activating effects of lipopolysaccharide (LPS), than non‐resilient individuals. We used Electric Cell‐substrate Impedance Signaling (ECIS) technology (Applied BioPhysics, Troy, NY) to measure transendothelial electrical resistance (TEER) of cultured brain microvascular endothelial cells of the resilient C57BL6 mouse (BMECC57BL6), and the non‐resilient BalbC mouse (BMECBalbC). BMECs were plated at a density of 4.8 × 104 cells/cm2, and allowed to establish a monolayer for 48 hours. BMECs were then treated with LPS derived from E. coli (0, 10, or 100 ng/ml). After 24 hours, bone marrow‐derived macrophages of C57BL6 mice (BMM C57BL6) or BalbC mice (BMM BalbC) (4.0 × 104 cells/cm2) were added to the BMEC monolayer. TEER was continuously recorded for an additional 72 hours. Barrier function (Rb), membrane capacitance (Cm), and constraint on current flow beneath the cells (α) were derived via ECIS mathematical modeling. At baseline, BMECC57BL6 had significantly lower Rb (1.90±0.26 versus 2.81±0.26 Ωcm2, p = 0.03, n = 7) and α (7.01±0.14 versus 8.01±0.16 Ω0.5cm, p = 0.0006, n =7), and significantly higher Cm (1.42±0.03 versus 1.22±0.02 μF/cm2, p = 0.0003, n = 7) when compared to BMECBalbC. LPS treatment alone or BMM alone did not have significantly differential effects on any of these parameters between BMECC57BL6 and BMECBalbC; however, in the presence of 100 ng/ml LPS, only α value of BMECBalbC significantly declined over the 6 hours after addition of BMM C57BL6 (from 7.50±0.211 to 6.71±0.221 Ω0.5cm; one‐way ANOVA, p = 0.02, n = 4), or BMM BalbC (from 7.54±0.17 to 6.16±0.17 Ω0.5cm; one‐way ANOVA, p > 0.0001, n = 4). These findings indicate that variability in psychological resilience among individuals may be associated with functional differences in blood brain barrier and macrophages.Support or Funding InformationThe views expressed in this presentation are those of the authors and do not reflect the official policy or position of the Department of the Army, the Department of Defense, or the U.S. government.