Surface electrical impedance myography detects disease in an adult-onset SOD1-G93A zebrafish model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that is characterized by loss of motor neurons and atrophy of skeletal muscle. Current FDA-approved drugs to treat ALS are only modestly effective at slowing the progression of the disease. Rodents have been the standard preclinical animal model for testing candidate ALS drugs; however, alternative animal models, including zebrafish, are being studied to accelerate therapeutic discovery. Here, we sought to advance a model of ALS in zebrafish with associated tools to serve as biomarkers of neuromuscular deterioration. Thus, we applied noninvasive, surface electrical impedance myography (EIM) methodology to SOD1^G93A zebrafish and control animals to evaluate its ability to serve as an electrophysiological biomarker of disease in ALS zebrafish. Measurements were acquired from the caudal musculature of animals at 2 time points by applying an alternating current at 41 frequencies (1 kHz-1 MHz) and measuring the resulting voltages. At the first time point, SOD1^G93A animals still exhibited normal body morphometrics, spinal cord motor neuron numbers, and skeletal muscle mass, while at the second time point, these SOD1^G93A animals exhibited reduced weight, loss of motor neurons, type 1 and 2 myofiber atrophy, and decreased capacity for endurance swimming. We found that non-invasive surface EIM detected the alterations observed in diseased ALS zebrafish at the second time point. Specifically, EIM measurements (phase angle, reactance, and resistance) at 2 and 50 kHz were robust metrics that distinguished between healthy and diseased zebrafish. To assess the reliability of our EIM technique in healthy and ALS zebrafish, we calculated the intraclass correlation coefficient and conducted Bland-Altman analyses. The EIM methodology exhibited excellent reproducibility in both healthy and ALS zebrafish. In sum, these findings demonstrate that EIM is an effective tool to detect neuromuscular disease in symptomatic adult ALS zebrafish, and the approach described here offers a fast, noninvasive, and reliable platform that holds the potential to test candidate drug therapeutic efficacy.