Glial activation precedes alpha-synuclein pathology in a mouse model of Parkinson's disease

Neuroinflammation is increasingly recognized as an important feature in the pathogenesis of Parkinson's disease (PD). However, it remains unclear whether neuroinflammation contributes to nigral degeneration in PD or is merely a secondary marker of neurodegeneration. We aimed to investigate the temporal relationship between synucleopathy, neuroinflammation and nigrostriatal degeneration in a mouse model of PD. Mice received unilateral intrastriatal injection of alpha-synuclein pre-formed fibrils, alpha-synuclein monomer or vehicle and were sacrificed at 15, 30 and 90 days post-injection. Intrastriatal inoculation of alpha-synuclein fibrils led to significant alpha-synuclein aggregation in the substantia nigra peaking at 30 days after injection while the significant increase in Iba-1 cells, GFAP cells and IL-1β expression peaked earlier at 15 days. At 90 days, the striatal dopaminergic denervation was associated with astroglial activation. Alpha-synuclein monomer did not result in long-term glia activation or increase in inflammatory markers. The spread of alpha-synuclein aggregates into the cortex was not associated with any changes to neuroinflammatory markers. Our results demonstrate that in the substantia nigra glial activation is an early event that precedes alpha-synuclein inclusion formation, suggesting neuroinflammation could play an important early role in the pathogenesis of PD

Systemic Exosomal Delivery of shRNA Minicircles Prevents Parkinsonian Pathology

The development of new therapies to slow-down or halt Parkinson’s disease progression is a healthcare priority. A key pathological feature is the presence of alpha-synuclein aggregates and there is increasing evidence that alpha-synuclein propagation plays a central role in disease progression. Consequently the down-regulation of alpha-synuclein is a potential therapeutic target. As a chronic disease, the ideal treatment will be minimally invasive and effective in the long-term. Knockdown of gene expression has clear potential and siRNAs specific to alpha-synuclein have been designed, however the efficacy of siRNA treatment is limited by its short-term efficacy. To combat this we designed shRNA minicircles (shRNA-MC), with the potential for prolonged effectiveness, and used RVG-exosomes as vehicle for specific delivery into the brain. We optimized this system using transgenic mice expressing green fluorescent protein (GFP) and demonstrated its ability to down-regulate GFP protein expression in the brain for up to 6 weeks. RVG exosomes were used to deliver anti alpha-synuclein shRNA-MC therapy to the alpha-synuclein preformed fibrils induced model of parkinsonism. This therapy decreased alpha-synuclein aggregation, reduced the loss of dopaminergic neurones and improved the clinical symptoms. Our results confirm the therapeutic potential of shRNA-MC delivered by RVG-exosomes for long-term treatment of neurodegenerative diseases