Elsevier

Brain Research

Volume 1157, 9 July 2007, Pages 126-137
Brain Research

Research Report
Ultrastructure of blood–brain barrier and blood–spinal cord barrier in SOD1 mice modeling ALS

https://doi.org/10.1016/j.brainres.2007.04.044Get rights and content

Abstract

The purpose of this study was to determine the ultrastructure of the blood–brain barrier (BBB) and blood–spinal cord barrier (BSCB) in G93A SOD1 mice modeling ALS at different stages of disease. Electron microscope examination of brainstem, cervical and lumbar spinal cords was performed in ALS mice at early and late stages of disease. Our results show disorganized mitochondrial cristae and degenerating mitochondria in endothelial cells and neuropil, swollen astrocyte foot processes, swollen and degenerating capillary endothelial cells, astrocytes and motor neurons and extensive extracellular edema. In spite of progressive extracellular edema in neural tissue, capillary endothelial cell tight junctions appeared to remain intact in early and late symptomatic animals. Results show that disruption of BBB and BSCB was evident in areas of motor neuron degeneration in G93A mice at both early and late stages of disease. Capillary rupture was observed in brainstem in early symptomatic G93A mice. Capillary ultrastructure revealed that endothelial cell membrane and/or basement membrane damage occurred, followed by vascular leakage.

Introduction

The blood–brain barrier (BBB), blood–spinal cord barrier (BSCB) and blood–cerebrospinal fluid barrier (BCSFB) control the exchange of substances between the blood and brain/spinal cord. BBB and BSCB components such as the capillary endothelium, endothelial cell tight junctions, capillary basement membrane and astrocyte play essential roles in maintaining cerebral homeostasis (reviewed in Pardridge, 1999, Nag, 2003, Ballabh et al., 2004). Impairment of this cellular machinery may cause BBB or BSCB breakdown leading to edema in many brain and spinal cord diseases or injuries.

In amyotrophic lateral sclerosis (ALS), which is characterized by multifactor motor neuron degeneration in the brain and spinal cord, there is some evidence that BCSFB permeability may be affected. Increased levels of albumin, IgG and C3c have been found in the cerebrospinal fluid (CSF) in ALS patients (Leonardi et al., 1984, Annunziata and Volpi, 1985, Apostolski et al., 1991, Meucci et al., 1993). Moreover, IgG was detected in spinal cord motor neurons of ALS patients, localizing in the rough endoplasmic reticulum and microtubules (Engelhardt et al., 2005). Ultrastructural examination of post-mortem spinal cord samples also showed that IgG was taken up in endothelial cells in the ventral horn of ALS patients. The high molecular weight (150,000 Da) of IgG makes it unlikely that this molecule could cross an intact brain capillary endothelium. However, some studies showed that insulin-like growth factor (IGF)-1, IGF binding protein-2 or nitric oxide (Pirttila et al., 2004) as well as levels of the growth hormone and insulin (Bilic et al., 2006) were not elevated in CSF of ALS patients in comparison with those of controls. Pirttila et al. (2004) suggested that since “a large portion of these proteins in CSF may originate from blood, and BBB regulates concentrations of these molecules in CSF”, there is not a major disruption in the BCSFB. But it is possible that disruption or dysfunction of the BBB or BSCB occurs in ALS.

We demonstrated (Garbuzova-Davis et al., submitted for publication) that the BSCB is compromised in the cervical and lumbar spinal cords, areas of motor neuron degeneration, of G93A mice at the appearance of initial disease symptoms and, more severely, at the late stage of disease. Leakage of Evans Blue dye from spinal cord microvessels was seen in ALS mice at early (13 weeks of age) and late (17–18 weeks of age) stages of disease. More leakage was found in the lumbar spinal cords of mice in the terminal stage of disease. Additionally, the integrity of the basement membrane was altered at both early and late stages of disease, as evidenced by the lack of laminin staining in the G93A mice. Downregulation of Glut-1 expression in the endothelial cells of the BSCB was detected that may be related to altered endothelial lining. A disruption of the vascular endothelium or other components of the BSCB occurs in G93A mice, resulting in the observed vascular leakage. However, it was not possible to determine the nature of this breakdown of the BSCB in G93A SOD1 mice at the level of a light microscope. The aim of this study was to examine the ultrastructure of BBB and BSCB in G93A SOD1 mice modeling ALS at different stages of disease to document the damage to the microvasculature in areas of motor neuron degeneration.

Section snippets

Results

The endothelial cells and the surrounding parenchyma in the brainstem, cervical and lumbar spinal cords of G93A mice at early (13 weeks of age) and late (17–18 weeks of age) stages of disease and control C57BL/6J mice (19–20 weeks of age) were analyzed using an electron microscope. Examination of the immersion-fixed tissues from all animals revealed well-preserved and well-processed tissues.

Discussion

The normal blood–brain barrier and blood–spinal cord barrier functions depend on the integrity of their cellular components to prevent many blood-borne substances from infiltrating the brain and spinal cord. However, disease or brain and spinal cord injury can alter the integrity of the BBB or BSCB resulting in the development of severe edema and consequent migration of leukocytes into the CNS (reviewed in Avata and Ropper, 2002, Ballabh et al., 2004). Disruption of the BBB or BSCB could be an

Animals

All described procedures were approved by the Institutional Animal Care and Use Committee at USF and conducted in compliance with the Guide for the Care and Use of Laboratory Animals. Transgenic male mice B6SJL-TgN (SOD1-G93A) 1GUR (G93A; Jackson Laboratories), over-expressing human SOD1, carrying the Gly93  Ala mutation, were used. Eight mice at 8 weeks of age, 1 week after acclimatization, were assessed on extension reflex of the hindlimbs, an indicator of disease state. Extension reflex was

Acknowledgments

This work was supported by the USF Internal Awards Program.

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