Why does trehalose not improve autophagy in the SOD1G93A transgenic mouse model of familial ALS?

Sammanfattning: Amyotrophic lateral sclerosis is one of the major neurodegenerative diseases, causing an ascending paralysis that usually kills the patient within a few years from disease onset. The motor neurons show aggregates of proteins which in approximately 20 % of cases of the familial form contain mutated SOD1 protein. Trehalose is a disaccharide which has been shown to reduce protein aggregation and increase viability in cell models and alleviate symptoms in animal models of several neurodegenerative diseases associated with protein aggregation. When given orally to the SOD1G93A mouse model of ALS, trehalose failed to slow down the disease progression, which has led to questions about the uptake and distribution of the molecule in this mouse strain. The aim of this study was to investigate whether significant levels of trehalose reach the central nervous system of the SOD1G93A mouse after oral administration. This was performed by a trehalose assay of the brain of trehalose treated animals. A glucose assay was optimised for use in small samples of brain lysate after the digestion of trehalose into glucose by trehalase, and the difference in glucose concentration before and after digestion represented the trehalose level. No significant differences were detected between digested and undigested samples in trehalose treated mice (46.58±10.39 μg/g wet tissue and 41.86±7.93 μg/g, respectively) or in control mice (60.94±11.39 μg/g wet tissue and 71.58±10.25 μg/g, respectively). Additionally, the possible effects of trehalose were assessed by histological evaluation of spinal cord sections stained with an antibody directed towards misfolded SOD1 protein. A semi-quantitative method was used to evaluate the number of neurons in different categories of staining and significant differences were only found in the extracellular staining of female mouse spinal cord, where trehalose treated animals showed more intense extracellular staining (p=0.031). Since the study used small groups of animals (n = 4-5 mice), it is possible that the significant result is a false positive, which would support the overall conclusion that trehalose does not reach the central nervous system of the SOD1G93A mouse in significant amounts.