Altered Mitochondrial Superoxide Production in Skeletal Muscle of an ALS Mouse Model during the Disease Progression

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal neuromuscular disease that involves severe skeletal muscle atrophy. Mitochondria are critically affected in ALS muscle. To better understand the role of mitochondria in ALS onset and progression, we generated a double transgenic (dTG) mouse model overexpressing an ALS mutant (SOD1G93A) and a mitochondrial superoxide biosensor (mt-cpYFP) that reports dynamic production of superoxide inside mitochondria termed as (Wang 2008; Fang 2011). We found that flash signal in muscle changed significantly during the disease progression. Before disease onset, 2-month old dTG mice (ALS) showed an increase in mitochondrial superoxide production, which was manifested by a marked increase in the ratio of flashing area to cell area (ALS: 2.3±0.29, n=80, 5 mice; WT: 1.2±0.18, n=74, 4 mice; P=0.008), while there was no significant change in the kinetic parameters of the flash signal at this stage. At end stage (ESALS, 4.5-month old, n=36, 4 mice), there was a drastic decrease in mitochondrial superoxide production characterized by a decrease in the ratio of flashing area to cell area compared to WT (0.69±0.11, P<0.05). Remarkably, the kinetic parameters of the flash signal were significantly slower in ESALS dGT mice. Compared to WT and early stage ALS, there is an increase in the rising time (RT) (WT:15.82±1.38, ALS:14.63±1.2 vs ESALS:23.62±2.97, P=0.008 and 0.001), the half decay time (T50) (WT:9.81±1.13, ALS:11.93±1.43 vs ESALS:20.56±3.65, P<0.001 and 0.013), and the full duration at half maximum (FDHM) (WT:16.76±1.72, ALS:18.28±2.07 vs ESALS:33.37±5.33, P<0.001 and 0.003). Our data demonstrate drastic changes in muscle mitochondrial metabolic function in the course of ALS. Ongoing studies aim to explore the cause and the role of this abnormal mitochondrial function at different ALS stages. Supported by MDA and NIAMS/NIH.