Chondroitinase ABC reduces dopaminergic nigral cell death and striatal terminal loss in a 6-hydroxydopamine partial lesion mouse model of Parkinson's disease

Abstract

Background: Parkinson's disease (PD) is characterised by dopaminergic cell loss within the substantia nigra pars compacta (SNc) that leads to reduced striatal dopamine content and resulting motor deficits. Identifying new strategies to protect these cells from degeneration and retain striatal dopaminergic innervation is therefore of great importance. Chondroitin sulphate proteoglycans (CSPGs) are recognised contributors to the inhibitory extracellular milieu known to hinder tissue recovery following CNS damage. Digestion of these molecules by the bacterial lyase chondroitinase ABC (ChABC) has been shown to promote functional recovery in animal models of neurological injury. Although ChABC has been shown to promote sprouting of dopaminergic axons following transection of the nigrostriatal pathway, its ability to protect against nigrostriatal degeneration in a toxin-based module with better construct validity for PD has yet to be explored. Here we examined the neuroprotective efficacy of ChABC treatment in the full and partial 6-hydroxydopamine (6-OHDA) lesion mouse models of PD.

Results: In mice bearing a full 6-OHDA lesion, ChABC treatment failed to protect against the loss of either nigral cells or striatal terminals. In contrast, in mice bearing a partial 6-OHDA lesion, ChABC treatment significantly protected cells of the rostral SNc, which remained at more than double the numbers seen in vehicle-treated animals. In the partial lesion model, ChABC treatment also significantly preserved dopaminergic fibres of the rostral dorsal striatum which increased from 15.3 ± 3.5% of the intact hemisphere in saline-treated animals to 36.3 ± 6.5% in the ChABC-treated group. These protective effects of ChABC treatment were not accompanied by improvements in either the cylinder or amphetamine-induced rotations tests of motor function.

Conclusions: ChABC treatment provided significant protection against a partial 6-OHDA lesion of the nigrostriatal tract although the degree of protection was not sufficient to improve motor outcomes. These results support further investigations into the benefits of ChABC treatment for providing neuroprotection in PD.

Keywords: 6-Hydroxydopamine; Chondroitin sulphate proteoglycans; Chondroitinase ABC; Neuroprotection; Parkinson’s disease.

Fig. 1

ChABC fails to improve cellular or motor outcomes in the full 6-OHDA lesion mouse model. Representative TH-stained coronal sections of a rostral SNc and b striatum from animals that received saline (top panel) or ChABC (bottom panel) into the 6-OHDA lesioned hemisphere (left hand side). Regions analysed for SNc cell counts and TH-fibre mean grey value (MGV) are outlined. c The number of SNc cells remaining and d TH-positive fibre MGV within the dorsal (D) and ventral (V) striatum are quantified in the lesioned hemisphere as a percentage of the intact hemisphere. Data are averaged across all three rostrocaudal levels. No significance was detected between saline- and ChABC-treated animals. Similarly, no difference was observed between saline- or ChABC-treated animals in either e asymmetry score or f net amphetamine induced ipsiversive rotations. Saline (Sal): n = 14 and ChABC: n = 13. Data are mean ± SEM. Scale bars: a = 200 µm; b = 1000 µm. g ChABC-mediated digestion was confirmed by C4S immunoreactivity. Digestion of the CSPGs, evidenced by C4S stain, was detected along the entire nigrostriatal tract from the SNc level (bottom section) to the striatal level (top section). Black arrows indicate ChABC injection sites

Fig. 2

ChABC improves cellular but not behavioural outcomes in the partial 6-OHDA lesion mouse model. Representative TH-stained coronal sections of a, b rostral SNc and c striatum from animals that received saline (top panel) or ChABC (bottom panel) into the 6-OHDA lesioned hemisphere (left hand side). Animals treated with ChABC show enhanced preservation of SNc cells and TH-positive fibres. Regions analysed for cell counts and TH-fibre mean grey value (MGV) are outlined. d Quantification of the number of SNc cells remaining in the lesioned hemisphere as a percentage of the intact hemisphere. ChABC treatment significantly protected cells in the rostral SNc when compared to control (*p = 0.02; unpaired t-test) but showed no protection at medial or caudal levels. e Quantification of the TH-positive fibre MGV within the lesioned striatum as a percentage of the intact striatum. While no differences were noted within either the medial or caudal striatum, the rostral striatum of ChABC-treated animals showed a group-wise increase in TH-positive fibre MGV (^##p = 0.002). Post-hoc analysis revealed TH-positive fibre density was significantly preserved in the dorsal (D) rather than ventral (V) aspect of the ChABC-treated rostral striatum when compared to controls (*p = 0.049; Bonferroni post-hoc). No change was detected between saline- or ChABC-treated animals in either f asymmetry score or g net amphetamine-induced ipsiversive rotations. Saline (Sal): n = 17 and ChABC: n = 17. Data are mean ± SEM. Scale bars: a = 200 µm; b = 50 µm; c = 1000 µm. h ChABC-mediated digestion was confirmed by C4S immunoreactivity. Digestion of the CSPGs, evidenced by C4S stain was detected along the entire nigrostriatal tract from the SNc level (bottom section) to the striatal level (top section). Black arrows indicate ChABC injection sites