Objective: To investigate the effects of viral innate immune activation on neurodegeneration and synaptic protein expression in dopaminergic (DA)-like neurons following treatment with Parkinson’s disease (PD) relevant neurotoxins.

Background: Previous clinical studies identified certain viral infections as risk factors for developing PD (Vlajinac et al., 2012). During an innate immune response, a class of pattern recognition receptors called Toll-like receptors (TLRs) recognize infectious agents. TLR3 recognizes viral dsRNA and mediates gene expression via IRF3 and NF-κB, including cytokine/chemokine release. Viral priming alters synaptic/axonal transport (Syn/Ax) proteins related to PD pathology in animal models (Deleidi et al., 2010). Investigation into these alterations may elucidate the link between previous viral infections and PD.

Methods: DA-like neuroblastoma (SH-SY5Y) cells were pre-treated with a synthetic mimetic of viral dsRNA (poly I:C) for 24 hours (see figure1) before neurotoxin treatment (6-OHDA, rotenone, or MPP+). Cell death dose/time response curves were collected for poly I:C (0-100 µg/ml), 6-OHDA (0-100 µM), rotenone (0-500 nM), and MPP+ (0-1 mM) [MTT]. Mode of neurodegeneration (apoptosis vs necrosis) was evaluated [TUNEL, Western Blot (WB)]. Synaptic dysfunction was assessed by protein changes [WB, ELISA, immunocytochemistry].

Results: Neurotoxins and poly I:C induced neurodegeneration. Poly I:C pre-treatment altered the extent of neurodegeneration depending on conditions. Poly I:C (20 µg/ml), 6-OHDA (20 µM), rotenone (250 nM), and MPP+ (1 mM) treatments led to alterations in synaptophysin (Synap), PSD-95, and TH protein levels. Poly I:C pre-treatment resulted in aggregation/co-localization of Synap and α-synuclein proteins. Retaining old culture medium (vs fresh medium) before neurotoxin treatment caused different effects in PSD-95 and cPARP protein levels, likely due to release of IL-6 after poly I:C treatment.

Conclusions: PD model neurotoxins induced neurodegeneration, but was modulated by the innate immune system via TLR3. Viral priming altered Syn/Ax and cell death protein levels not seen with neurotoxin treatment alone. Interestingly, viral priming effects appear to be dependent upon downstream events of TLR3. Neuroprotective processes may instead lead to exacerbation of neurodegeneration in PD due to neuroinflammation.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-effects-of-viral-priming-on-neurotoxin-induced-neurodegeneration-and-synapse-dysfunction-in-cell-culture-models-relevant-to-parkinsons-disease/