Reduction of ephrin-A5 aggravates disease progression in amyotrophic lateral sclerosis

Laura Rué,Ludo Van Den Bosch,Annette Lenaerts,Jasmijn Van Der Vos,Markus Otto,Robin Lemmens,Mieke Timmers,Wim Robberecht,Antina De Boer,Silke Smolders,Patrick Oeckl,Albert C Ludolph,Philip Van Damme,Lindsay Poppe,Jochen H Weishaupt

doi:10.1186/s40478-019-0759-6

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that affects motor neurons in the brainstem, spinal cord and motor cortex. ALS is characterized by genetic and clinical heterogeneity, suggesting the existence of genetic factors that modify the phenotypic expression of the disease. We previously identified the axonal guidance EphA4 receptor, member of the Eph-ephrin system, as an ALS disease-modifying factor. EphA4 genetic inhibition rescued the motor neuron phenotype in zebrafish and a rodent model of ALS. Preventing ligands from binding to the EphA4 receptor also successfully improved disease, suggesting a role for EphA4 ligands in ALS. One particular ligand, ephrin-A5, is upregulated in reactive astrocytes after acute neuronal injury and inhibits axonal regeneration. Moreover, it plays a role during development in the correct pathfinding of motor axons towards their target limb muscles. We hypothesized that a constitutive reduction of ephrin-A5 signalling would benefit disease progression in a rodent model for ALS. We discovered that in the spinal cord of control and symptomatic ALS mice ephrin-A5 was predominantly expressed in neurons. Surprisingly, reduction of ephrin-A5 levels in SOD1G93A mice accelerated disease progression and reduced survival without affecting disease onset, motor neuron numbers or innervated neuromuscular junctions in symptomatic mice. These findings suggest ephrin-A5 as a modifier of disease progression that might play a role in the later stages of the disease. Similarly, we identified a more aggressive disease progression in patients with lower ephrin-A5 protein levels in the cerebrospinal fluid without modifying disease onset. In summary, we identified reduced expression of ephrin-A5 to accelerate disease progression in a mouse model of ALS as well as in humans. Combined with our previous findings on the role of EphA4 in ALS our current data suggests different contribution for various members of the Eph-ephrin system in the pathophysiology of a motor neuron disease.

Highlights

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease in which upper motor neurons in the motor cortex and lower motor neurons in the brainstem and spinal cord degenerate
Ephrin-A5 is mainly expressed in neurons of the ventral horn We first determined EfnA5 gene expression in whole lysates of adult mice lumbar spinal cord in agematched SOD1WT and mutant SOD1G93A mice, at different disease stages
In the SOD1G93A spinal cord the percentage of EfnA5 positive large and small neurons and astrocytes was similar to SOD1WT, but we observed a reduction of 2% of total glial cells expressing EfnA5 (Fig. 2b-d)

Summary

Introduction

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease in which upper motor neurons in the motor cortex and lower motor neurons in the brainstem and spinal cord degenerate. One particular EphA4 ligand, ephrin-A5 (efnA5), is of specific interest since its expression is increased in reactive astrocytes after stroke, resulting in reduced growth of cortical axonal projections during recovery [6, 23, 33]. Blocking efnA5 signalling improved the recovery of mice after stroke injury [33]. This upregulation of efnA5 in reactive astrocytes was induced after experimental stroke, and by physical stress as shown in vitro [33], suggesting that efnA5 might be upregulated in astrocytes under stressful conditions. Microglia and oligodendrocytes contribute to the selective vulnerability of motor neurons in ALS, the study of the role of efnA5 in astrocytes in this disease is of interest [1, 19, 45]

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