Blood-spinal cord barrier leakage is independent of motor neuron pathology in ALS

Sarah Waters,Molly E V Swanson,Robert Bowser,Jiyan An,Birger V Dieriks,Helen C Murray,Henry J Waldvogel,Emma Scotter,Yibin B Zhang,Mike Dragunow,Clinton Turner,Maurice A Curtis,Natasha L Grimsey,Richard L M Faull

doi:10.1186/s40478-021-01244-0

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving progressive degeneration of upper and lower motor neurons. The pattern of lower motor neuron loss along the spinal cord follows the pattern of deposition of phosphorylated TDP-43 aggregates. The blood-spinal cord barrier (BSCB) restricts entry into the spinal cord parenchyma of blood components that can promote motor neuron degeneration, but in ALS there is evidence for barrier breakdown. Here we sought to quantify BSCB breakdown along the spinal cord axis, to determine whether BSCB breakdown displays the same patterning as motor neuron loss and TDP-43 proteinopathy. Cerebrospinal fluid hemoglobin was measured in living ALS patients (n = 87 control, n = 236 ALS) as a potential biomarker of BSCB and blood–brain barrier leakage. Cervical, thoracic, and lumbar post-mortem spinal cord tissue (n = 5 control, n = 13 ALS) were then immunolabelled and semi-automated imaging and analysis performed to quantify hemoglobin leakage, lower motor neuron loss, and phosphorylated TDP-43 inclusion load. Hemoglobin leakage was observed along the whole ALS spinal cord axis and was most severe in the dorsal gray and white matter in the thoracic spinal cord. In contrast, motor neuron loss and TDP-43 proteinopathy were seen at all three levels of the ALS spinal cord, with most abundant TDP-43 deposition in the anterior gray matter of the cervical and lumbar cord. Our data show that leakage of the BSCB occurs during life, but at end-stage disease the regions with most severe BSCB damage are not those where TDP-43 accumulation is most abundant. This suggests BSCB leakage and TDP-43 pathology are independent pathologies in ALS.

Highlights

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive and eventually fatal degeneration of upper and lower motor neurons [1,2,3]
Hemoglobin levels in the Cerebrospinal fluid (CSF) of living ALS patients For studies of ALS biomarkers, cerebrospinal fluid (CSF) was banked from individuals living with ALS and healthy controls (n = 87) using standard operating procedures established by the Northeast ALS Consortium (NEALS)
Scale bars = 10 μm Discussion Finding high levels of hemoglobin in the CSF of subjects living with ALS, we examined the relationship between blood-spinal cord barrier (BSCB) integrity, endothelial barrier protein expression, motor neuron degeneration and Transactive response DNA-binding protein of 43 kDa (TDP-43) proteinopathy

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive and eventually fatal degeneration of upper and lower motor neurons [1,2,3]. The blood–brain barrier (BBB), blood-spinal cord barrier (BSCB), and blood-cerebrospinal fluid (blood-CSF) barrier are specialized interfaces that regulate the influx of nutrients and ions into the central nervous system, and the removal of waste and other solutes [12, 13] These barriers separate the brain, spinal cord parenchyma, and CSF respectively from potentially neurotoxic blood-borne components in the circulation, such as peripheral leukocytes, erythrocytes and plasma proteins [14,15,16]. Many of the blood components that leak across the BBB, BSCB, or blood-CSF barrier act as neurotoxins [23,24,25,26,27] which, when allowed into contact with motor neurons, are likely to enhance motor neuron vulnerability to autonomous TDP-43-mediated damage It remains unclear whether brain barrier leakage in ALS causes, is caused by, or is independent from motor neuron damage

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