Comparing therapeutic modulators of the SOD1 G93A Amyotrophic Lateral Sclerosis mouse pathophysiology

Introduction

Amyotrophic Lateral Sclerosis (ALS) is a paralyzing, multifactorial neurodegenerative disease with limited therapeutics and no known cure. The study goal was to determine which pathophysiological treatment targets appear most beneficial.

Methods

A big data approach was used to analyze high copy SOD1 G93A experimental data. The secondary data set comprised 227 published studies and 4,296 data points. Treatments were classified by pathophysiological target: apoptosis, axonal transport, cellular chemistry, energetics, neuron excitability, inflammation, oxidative stress, proteomics, or systemic function. Outcome assessment modalities included onset delay, health status (rotarod performance, body weight, grip strength), and survival duration. Pairwise statistical analysis (two-tailed t-test with Bonferroni correction) of normalized fold change (treatment/control) assessed significant differences in treatment efficacy. Cohen's d quantified pathophysiological treatment category effect size compared to "all" (e.g., all pathophysiological treatment categories combined).

Results

Inflammation treatments were best at delaying onset (d = 0.42, p > 0.05). Oxidative stress treatments were significantly better for prolonging survival duration (d = 0.18, p < 0.05). Excitability treatments were significantly better for prolonging overall health status (d = 0.22, p < 0.05). However, the absolute best pathophysiological treatment category for prolonging health status varied with disease progression: oxidative stress was best for pre-onset health (d = 0.18, p > 0.05); excitability was best for prolonging function near onset (d = 0.34, p < 0.05); inflammation was best for prolonging post-onset function (d = 0.24, p > 0.05); and apoptosis was best for prolonging end-stage function (d = 0.49, p > 0.05). Finally, combination treatments simultaneously targeting multiple pathophysiological categories (e.g., polytherapy) performed significantly (p < 0.05) better than monotherapies at end-stage.

Discussion

In summary, the most effective pathophysiological treatments change as function of assessment modality and disease progression. Shifting pathophysiological treatment category efficacy with disease progression supports the homeostatic instability theory of ALS disease progression.

Characterization of the Mitochondrial Aerobic Metabolism in the Pre- and Perisynaptic Districts of the SOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset fatal neurodegenerative disease characterized by muscle wasting, weakness, and spasticity due to a progressive degeneration of cortical, brainstem, and spinal motor neurons. The etiopathological causes are still largely obscure, although astrocytes definitely play a role in neuronal damage. Several mechanisms have been proposed to concur to neurodegeneration in ALS, including mitochondrial dysfunction. We have previously shown profound modifications of glutamate release and presynaptic plasticity in the spinal cord of the SOD1^G93A mouse model of ALS. In this work, we characterized, for the first time, the aerobic metabolism in two specific compartments actively involved in neurotransmission (i.e. the presynaptic district, using purified synaptosomes, and the perisynaptic astrocyte processes, using purified gliosomes) in SOD1^G93A mice at different stages of the disease. ATP/AMP ratio was lower in synaptosomes isolated from the spinal cord, but not from other brain areas, of SOD1^G93A vs. control mice. The energy impairment was linked to altered oxidative phosphorylation (OxPhos) and increment of lipid peroxidation. These metabolic dysfunctions were present during disease progression, starting at the very pre-symptomatic stages, and did not depend on a different number of mitochondria or a different expression of OxPhos proteins. Conversely, gliosomes showed a reduction of the ATP/AMP ratio only at the late stages of the disease and an increment of oxidative stress also in the absence of a significant decrement in OxPhos activity. Data suggest that the presynaptic neuronal moiety plays a pivotal role for synaptic energy metabolism dysfunctions in ALS. Changes in the perisynaptic compartment seem subordinated to neuronal damage.

Upregulation of Vesicular Glutamate Transporter 2 and STAT3 Activation in the Spinal Cord of Mice Receiving 3,3'-Iminodipropionitrile

Chronic administration of 3,3'-iminodipropionitrile (IDPN) causes axonal impairment. Although controversy still remains, it has been suggested that IDPN intoxication mimics the axonopathy of amyotrophic lateral sclerosis (ALS). Interestingly, recent studies including our own showed that signal transducer and activator of transcription 3 (STAT3) in spinal α-motoneurons was activated in both IDPN-treated mice and SOD1 ^G93A mice, a genetic model of familial ALS. Because activation of STAT3 occurs in response to various stimuli, such as axonal injury, ischemia, and excessive glutamate, here we focused on a potential link between phosphorylated STAT3 (pSTAT3, an active form) and vesicular glutamate transporter 2 (VGluT2, a regulator of glutamate storage and release) in IDPN-treated mice and SOD1 ^G93A mice. Impairment of axonal transport was confirmed by western blot analysis: the expression levels of phosphorylated neurofilament H were elevated in both models. As shown in SOD1 ^G93A mice, the expression frequencies of VGluT2 in synaptophysin-positive (SYP)⁺ presynaptic terminals around spinal α-motoneurons were significantly higher in IDPN-treated mice than in vehicle controls. The coverages of spinal α-motoneurons by VGluT2⁺ presynaptic terminals were more elevated around pSTAT3⁺ cells than around pSTAT3^- cells in IDPN-treated mice and SOD1 ^G93A mice. Considering that excessive glutamate is shown to be involved in axonal impairment and STAT3 activation, the present results suggest that IDPN-induced upregulation of VGluT2 may result in an increase in glutamate, which might cause axonopathy and induction of pSTAT3. The link between upregulation of VGluT2 and activation of STAT3 via glutamate may represent a common pathological feature of IDPN-treated mice and SOD1 ^G93A mice.