Purified IgG from aquaporin-4 neuromyelitis optica spectrum disorder patients alters blood-brain barrier permeability

Abstract Background: Blood-brain barrier (BBB) breakdown is considered one of the key steps for the development and lesion formation of neuromyelitis optica spectrum disorder (NMOSD). However, little is known about the molecular mechanisms involved. The aim of the study was to evaluate the effect of human immunoglobulins from NMOSD patients (NMO-IgG) on BBB properties.Methods: Freshly isolated brain microvessels (IBM) from rat brains that mirror the blood-CNS barrier were used as a study model. At first, analysis of the secretome profile (cytokine protein array) from IBM exposed to purified NMO-IgG, to healthy donor IgG (Control-IgG), or non-treated, was performed. Second, structural BBB properties were analysed by Western blotting (Wb) to measure the expression of tight junction (TJ) proteins (Claudin-5, occludin, and ZO-1) in fresh IBM and primary cultures of brain microvascular endothelial cells (BMEC) after exposition to NMO-IgG and Control-IgG. Finally, functional BBB properties were investigated using two approaches; 1) in the NMO-rat model, the presence of rat-IgG in tissue lysate from brain periventricular regions was analysed using Wb, and 2) in a bicameral model simulating the blood and brain compartments of the BBB, the passage of NMO-IgG and sucrose was assessed by using ELISA.Results: We found that NMO-IgG induces several functional and morphological changes of the BBB in our different study models, including: 1) increase of pro-inflammatory cytokines production (CXCL-10 [IP-10], IL-6, IL1-ra, IL1-β and CXCL-3) by at least three-fold in IBM when exposed to NMO-IgG in comparison to Control-IgG or non-treated IBM; 2) decrease of Claudin-5 levels by 25.6% after treatment of fresh IBM by NMO-IgG compared to Control-IgG (p=0.002), and similarly, decrease of Claudin-5 by at least 20% when BMEC were cultured with NMO-IgG from five different patients; 3) a higher level of rat-IgG accumulated in periventricular regions of NMO-rats compared to Control-rats and an increase the permeability of BBB after NMO-IgG treatment in the bicameral model.Conclusion: Human NMO-IgG induces both structural and functional alterations of BBB properties, suggesting a direct role of NMO-IgG on modulation of BBB permeability in NMOSD.