Dimebon slows progression of proteinopathy in γ-synuclein transgenic mice

Abstract

Intermediates and final products of protein aggregation play crucial role in the development of degenerative changes in a number of neurological diseases. Pathological protein aggregation is currently regarded as one of the most promising therapeutic targets for treatment of these diseases. Transgenic mouse models of proteinopathies are an effective tool for screening and validation of compounds, which can selectively affect metabolism of aggregate-prone proteins. In this study, we assessed effects of dimebon, a compound with known neuroprotective properties, on a recently established transgenic mouse model recapitulating key pathological features of amyotrophic lateral sclerosis (ALS) as the consequence of neuron-specific overexpression of γ-synuclein. Cohorts of experimental transgenic mice received dimebon in drinking water with this chronic treatment starting either before or after the onset of clinical signs of pathology. We detected statistically significant improvement of motor performance in a rotarod test in both dimebon-treated animal groups, with more pronounced effect in a group that received dimebon from an earlier age. We also revealed substantially reduced number of amyloid inclusions, decreased amount of insoluble γ-synuclein species and a notable amelioration of astrogliosis in the spinal cord of dimebon-treated compared with control transgenic animals. However, dimebon did not prevent the loss of spinal motor neurons in this model. Our results demonstrated that chronic dimebon administration is able to slow down but not halt progression of γ-synucleinopathy and resulting signs of pathology in transgenic animals, suggesting potential therapeutic use of this drug for treatment of this currently incurable disease.

Fig. 1

Lifespan and motor performance of control and dimebon-treated γ-synuclein transgenic mice. Thy1mγSN transgenic mice (TG) were tested on accelerating rotarod after 3 and 6 months of drug administration in both dimebon-treated groups, and additionally after 9 months in the group with an early start of treatment. Line graphs show means ± SEM of latency to fall from the rotarod (a). Statistically significant differences between the control group of transgenic animals and each of the treated groups (*P < 0.05, **P < 0.01) as well as between dimebon-treated groups (^# P < 0.05) were detected at all time points. b Kaplan–Meier survival analysis of dimebon-treated and control Thy1mγSN transgenic mice demonstrates increased survival in the group that received dimebon from the age of 3 months. In both panels, results for wild-type animals (WT) animals are given for reference

Fig. 2

Dimebon treatment reduces the number of amyloid inclusions in the spinal cord of γ-synuclein transgenic mice. Representative images of histological sections through the spinal cord of 12-month-old control Thy1mγSN mice (a) and Thy1mγSN mice treated with dimebon from the age of 3 months (b) stained for amyloid deposits using Congo Red. Scale bar = 100 μm. The bar chart (c) shows means ± SEM of the number of inclusions in the anterior horn of the spinal cord. Statistically significant difference between the control and each experimental group (*P < 0.05, Mann–Whitney U-test) as well as total number of sections analysed per three animals for each group are shown

Fig. 3

Dimebon decreases amount of detergent-insoluble γ-synuclein species in the spinal cord of γ-synuclein transgenic mice. Representative western blot of fractions obtained by sequential extraction of proteins from the spinal cord of 12-month-old control Thy1mγSN mice (−) and Thy1mγSN mice treated with dimebon from the age of 3 months (+) probed with an antibody against mouse γ-synuclein is shown. Proteins were extracted from pooled thoracic spinal cords of five animals for each group. To detect low-abundant high molecular weight γ-synuclein species (upper panel), the membrane was exposed for longer period than for detection of predominant monomeric form of the protein (lower panel). HS high salt-soluble fraction, TX Triton-X soluble fraction, and SDS detergent-insoluble fraction

Fig. 4

Dimebon treatment ameliorates astrocytosis in the spinal cord of γ-synuclein transgenic mice. Representative images of histological sections through the spinal cord of 12-month-old control Thy1mγSN mice (left panel) and Thy1mγSN mice treated with dimebon from the age of 3 months (right panel) immunostained for reactive astroglia marker GFAP. Scale bar = 50 μm

Fig. 5

The loss of spinal motor neurons in γ-synuclein transgenic mice is not affected by dimebon treatment. a Representative images of Nissle-stained histological sections through the spinal cord of 12-month-old control wild-type (WT), Thy1mγSN mice (TG) and Thy1mγSN mice treated with dimebon from the age of 3 months (TG + DIM). Scale bar = 30 μm. b The bar chart shows means ± SEM of the number of motor neurons in the anterior horn of the spinal cord of 12-month-old control wild-type (WT), Thy1mγSN transgenic mice (TG) and Thy1mγSN mice treated with dimebon from the age of 3 months (three to four animals per group). Thy1mγSN mice have significantly less motor neurons than wild-type mice (**P < 0.01, Mann–Whitney U-test) but no significant difference between two groups of transgenic mice was found