Increased blood-brain barrier permeability and alterations in perivascular astrocytes and pericytes induced by intracisternal glutaric acid.

Eugenia Isasi,Luis Barbeito,Silvia Olivera-Bravo

doi:10.1186/2045-8118-11-15

Abstract

BackgroundGlutaric acid (GA) is a dicarboxylic acid that accumulates in millimolar concentrations in glutaric acidemia I (GA-I), an inherited neurometabolic childhood disease characterized by extensive neurodegeneration. Vascular dysfunction is a common and early pathological feature in GA-I, although the underlying mechanisms remain unknown. In the present study, we have used a previously-validated rat model of GA-I to determine the effect of GA on the blood- brain barrier (BBB) and the neurovascular unit.MethodsNewborn rat pups received a single injection of GA (1 μmol/g) or vehicle into the cisterna magna. BBB permeability was analyzed at 14 and 30 days post injection (DPI) by assessing Evans blue (EB) and immunoglobulin G (IgG) extravasation. Blood vessels and microglia were labeled with tomato lectin. Characterization of EB positive cells was made by double labeling with antibodies to astrocyte and neuronal markers. Immunohistochemistry against aquaporin 4 (AQP4), β receptor of the platelet derived growth factor (PDGFRβ) and laminin was used to recognize astrocyte endfeet, pericytes and basal lamina. Zonula occludens 1 (ZO-1) and occludin striatal expression was assessed by Western blotting.ResultsPerinatal intracisternal GA administration caused an increased extravasation of free EB, but not of IgG, into the striatal parenchyma at 14 and 30 DPI. EB extravasated through the BBB was internalized exclusively into neurons. GA-injected animals did not show significant changes in the area of small blood vessels in the striatum, but at 30 DPI there was a significant decrease in AQP4, PDGFRβ and laminin positive areas associated with small blood vessels. Occludin and ZO-1 expression in the striatal tissue was unchanged in all conditions analyzed.ConclusionsThe present study shows a previously-unknown effect of a perinatal administration of a single intracisternal GA injection on BBB permeability and on key components of the neurovascular unit. The results suggest BBB leakage is a pathogenic mechanism and a potential therapeutic target for patients with GA-I.

Highlights

Glutaric acid (GA) is a dicarboxylic acid that accumulates in millimolar concentrations in glutaric acidemia I (GA-I), an inherited neurometabolic childhood disease characterized by extensive neurodegeneration
Evans blue (EB) staining was located in blood vessel lumen or wall, in the lateral ventricles and in the parenchyma of areas lacking a blood- brain barrier (BBB) such as the circumventricular organs, in all experimental conditions (Figure 1)
At 30 days post injection (DPI), control animals showed EB extravasation restricted to the brain areas that lack BBB with an almost undetectable blue and red staining in cortical and striatal parenchyma

Summary

Introduction

Glutaric acid (GA) is a dicarboxylic acid that accumulates in millimolar concentrations in glutaric acidemia I (GA-I), an inherited neurometabolic childhood disease characterized by extensive neurodegeneration. Between 6 and 18 months of life, up to 90% of untreated GA-I children suffer an encephalopathic crisis, usually precipitated by infectious or viral illness This initiates a process leading to permanent neurological deficits including dystonic-dyskinetic movement disorders, growth and cognitive impairments [2,4,5,6]. Vascular pathology described in GA-I patients, include blood–brain barrier (BBB) breakdown, intradural or retinal hemorrhages, subdural effusions and chronic extravasation from trans-arachnoid vessels [3,7,8,9,10]. These pathological events may occur independently of the encephalopathic crisis [10]. The significance and impact of BBB dysfunction in GA-I as causative of neuronal death is still poorly understood

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