Metabolic and Stress Response Changes Precede Disease Onset in the Spinal Cord of Mutant SOD1 ALS Mice.

Gavin Pharaoh,Jake Gregston,Kaitlyn Street,Shauna Hill,Kavithalakshmi Sataranatarajan,Michael Kinter,Bumsoo Ahn,Caroline Kinter,Holly Van Remmen

doi:10.3389/fnins.2019.00487

Abstract

Many Amyotrophic Lateral Sclerosis (ALS) patients experience hypermetabolism, or an increase in measured vs. calculated metabolic rate. The cause of hypermetabolism and the effects on neuronal metabolism in ALS are currently unknown, but the efficacy of dietary interventions shows promise for metabolism as an ALS therapeutic target. The goal of this study is to measure changes in metabolic pathways as a function of disease progression in spinal cords of the SOD1G93A mouse model of ALS. We conducted a comprehensive assessment of protein expression for metabolic pathways, antioxidants, chaperones, and proteases in lumbar spinal cord from male SOD1G93A mice at pre-onset, onset, and end-stages of the disease using targeted proteomic analysis. These results reveal that protein content of metabolic proteins including proteins involved in glycolysis, β-oxidation, and mitochondrial metabolism is altered in SOD1G93A mouse spinal cord well before disease onset. The changes in mitochondrial metabolism proteins are associated with decreased maximal respiration and glycolytic flux in SOD1G93A dermal fibroblasts and increased hydrogen peroxide and lipid hydroperoxide production in mitochondria from sciatic nerve and gastrocnemius muscle fibers at end stage of disease. Consistent with redox dysregulation, expression of the glutathione antioxidant system is decreased, and peroxiredoxins and catalase expression are increased. In addition, stress response proteases and chaperones, including those involved in the mitochondrial unfolded protein response (UPRmt), are induced before disease onset. In summary, we report that metabolic and stress response changes occur in SOD1G93A lumbar spinal cord before motor symptom onset, and are primarily caused by SOD1G93A expression and do not vary greatly as a function of disease course.

Highlights

Amyotrophic Lateral Sclerosis (ALS) is a cell non-autonomous disease affecting motor neurons as well as surrounding support cells including astrocytes, oligodendrocytes, and microglia (Ilieva et al, 2009; Rizzo et al, 2014) and skeletal muscle (Dobrowolny et al, 2008)
Principal component analysis (PCA) demonstrates that protein expression in lumbar spinal cord from SOD1G93A mice clusters distinctly from spinal cord from control mice beginning before onset of symptoms, but no separation occurs in clustering between disease stages (Figure 1B). 49% of assayed proteins exhibit a significant difference due to genotype effect, while only 10% exhibited a significant difference based on disease stage using two-way ANOVA corrected for false discovery rate with the Benjamini-Hochberg procedure
These results show that metabolism and stress response protein content is already dramatically altered in spinal cords from SOD1G93A mice before onset of motor symptoms

Summary

Introduction

Amyotrophic Lateral Sclerosis (ALS) is a cell non-autonomous disease affecting motor neurons as well as surrounding support cells including astrocytes, oligodendrocytes, and microglia (Ilieva et al, 2009; Rizzo et al, 2014) and skeletal muscle (Dobrowolny et al, 2008). Several transgenic mouse lines expressing mutant Sod, including SOD1G93A, have been generated that recapitulate fALS symptoms and have allowed exploration of biochemical mechanisms underlying fALS pathogenesis (Ilieva et al, 2009). One phenotype of SOD1 mutant mice that recapitulates the human disease is a hypermetabolic phenotype that occurs before the onset of motor symptoms (Dupuis et al, 2004). Hypermetabolic patients display a trend toward decreased survival length from symptom onset (Bouteloup et al, 2009), and a phase II clinical trial suggested that high calorie diets had beneficial survival effects in ALS patients (Wills et al, 2014). The hypermetabolism phenotype is a potential disease modifier that can be targeted to affect patient disease progression

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