Evolution of the neurochemical profiles in the G93A-SOD1 mouse model of amyotrophic lateral sclerosis

In vivo 1H magnetic resonance spectroscopy (1H-MRS) investigations of amyotrophic lateral sclerosis (ALS) mouse brain may provide neurochemical profiles and alterations in association with ALS disease progression. We aimed to longitudinally follow neurochemical evolutions of striatum, brainstem and motor cortex of mice transgenic for G93A mutant human superoxide dismutase type-1 (G93A-SOD1), an ALS model. Region-specific neurochemical alterations were detected in asymptomatic G93A-SOD1 mice, particularly in lactate (−19%) and glutamate (+8%) of brainstem, along with γ-amino-butyric acid (−30%), N-acetyl-aspartate (−5%) and ascorbate (+51%) of motor cortex. With disease progression towards the end-stage, increased numbers of metabolic changes of G93A-SOD1 mice were observed (e.g. glutamine levels increased in the brainstem (>+66%) and motor cortex (>+54%)). Through ALS disease progression, an overall increase of glutamine/glutamate in G93A-SOD1 mice was observed in the striatum ( p < 0.01) and even more so in two motor neuron enriched regions, the brainstem and motor cortex ( p < 0.0001). These 1H-MRS data underscore a pattern of neurochemical alterations that are specific to brain regions and to disease stages of the G93A-SOD1 mouse model. These neurochemical changes may contribute to early diagnosis and disease monitoring in ALS patients.

Perturbations in intracellular Ca2+ handling in skeletal muscle in the G93A*SOD1 mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by skeletal muscle atrophy and weakness, ultimately leading to respiratory failure. The purpose of this study was to assess changes in skeletal muscle excitation-contraction (E-C) coupling and intracellular Ca2+ handling during disease progression in the G93A*SOD1 ALS transgenic (ALS Tg) mouse model. To assess E-C coupling, single muscle fibers were electrically stimulated (10–150 Hz), and intracellular free Ca2+ concentration was assessed using fura-2. There were no differences in peak fura-2 ratio at any stimulation frequency at 70 days (early presymptomatic). However, at 90 days (late presymptomatic) and 120–140 days (symptomatic), fura-2 ratio was increased at 10 Hz in ALS Tg compared with wild-type (WT) fibers (0.670 ± 0.02 vs. 0.585 ± 0.02 for 120–140 days; P < 0.05). There was also a significant increase in resting fura-2 ratio at 90 days (0.351 ± 0.008 vs. 0.390 ± 0.009 in WT vs. ALS Tg; P < 0.05) and 120–140 days (0.374 ± 0.001 vs. 0.415 ± 0.003 in WT vs. ALS Tg; P < 0.05). These increases in intracellular Ca2+ in ALS Tg muscle were associated with reductions in the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase proteins SERCA1 (to 54% and 19% of WT) and SERCA2 (to 56% and 11% of WT) and parvalbumin (to 80 and 62% of WT) in gastrocnemius muscle at 90 and 120–140 days, respectively. There was no change in dihydropyridine receptor/l-type Ca2+ channel at any age. Overall, these data demonstrate minimal changes in electrically evoked Ca2+ transients but elevations in intracellular Ca2+ attributable to decreased Ca2+-clearance proteins. These data suggest that elevations in cellular Ca2+ could contribute to muscle weakness during disease progression in ALS mice.