Activation of Phosphotyrosine-Mediated Signaling Pathways in the Cortex and Spinal Cord of SOD1G93A, a Mouse Model of Familial Amyotrophic Lateral Sclerosis.

Cinzia Mallozzi,Maria Rosaria Domenici,Patrizia Longone,Alida Spalloni

doi:10.1155/2018/2430193

Abstract

Degeneration of cortical and spinal motor neurons is the typical feature of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease for which a pathogenetic role for the Cu/Zn superoxide dismutase (SOD1) has been demonstrated. Mice overexpressing a mutated form of the SOD1 gene (SOD1G93A) develop a syndrome that closely resembles the human disease. The SOD1 mutations confer to this enzyme a “gain-of-function,” leading to increased production of reactive oxygen species. Several oxidants induce tyrosine phosphorylation through direct stimulation of kinases and/or phosphatases. In this study, we analyzed the activities of src and fyn tyrosine kinases and of protein tyrosine phosphatases in synaptosomal fractions prepared from the motor cortex and spinal cord of transgenic mice expressing SOD1G93A. We found that (i) protein phosphotyrosine level is increased, (ii) src and fyn activities are upregulated, and (iii) the activity of tyrosine phosphatases, including the striatal-enriched tyrosine phosphatase (STEP), is significantly decreased. Moreover, the NMDA receptor (NMDAR) subunit GluN2B tyrosine phosphorylation was upregulated in SOD1G93A. Tyrosine phosphorylation of GluN2B subunits regulates the NMDAR function and the recruitment of downstream signaling molecules. Indeed, we found that proline-rich tyrosine kinase 2 (Pyk2) and ERK1/2 kinase are upregulated in SOD1G93A mice. These results point out an involvement of tyrosine kinases and phosphatases in the pathogenesis of ALS.

Highlights

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a progressive loss of motor neurons in the cortex, brain stem, and spinal cord [1]
We found that proline-rich tyrosine kinase 2 (Pyk2) and ERK1/2 kinase are upregulated in SOD1G93A mice
The pattern of phosphotyrosine distribution was assayed by Western blot analysis using an anti-phosphotyrosine antibody in synaptosomes prepared from the motor cortex and spinal cord of control, SOD1WT, and SOD1G93A mice

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a progressive loss of motor neurons in the cortex, brain stem, and spinal cord [1]. The degeneration of motor neurons leads to skeletal muscle weakness, paralysis, and eventually death, with a mean survival between three and five years after disease onset [2,3,4,5]. As familial and sporadic ALS (fALS and sALS, resp.) are symptomatically indistinguishable, it is likely that they share common pathogenetic mechanisms. Such mechanisms include protein misfolding, inflammation, oxidative stress, and mitochondrial dysfunction (reviewed in [7, 8]). Excitotoxicity is defined as an excessive activation of glutamate receptors by excitatory amino acids, such as glutamate, that initiates a series of cytoplasmic and nuclear processes promoting neuronal cell death [11, 12]. Overstimulation of the ionotropic glutamate receptors in neurons causes massive influx of calcium into the cytosol, and numerous enzymes are activated in response to the increase in intracellular calcium [13,14,15]

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