Intravenous SARS-CoV-2 Spike protein induces neuroinflammation and alpha-Synuclein accumulation in brain regions relevant to Parkinson's disease

Abstract

Background: Coronavirus disease 2019 (COVID-19) frequently presents with neurological symptoms in human patients and leads to long-lasting brain pathology in a hamster model. There is no overt SARS-CoV-2 virus replication in central neurons. Whether viral proteins are sufficient to cause this pathology requires further investigations. The SARS-CoV-2 Spike-protein S1-subunit (S1-protein) has recently gained interest for causing neuroinflammation and accelerating aggregation of alpha-Synuclein (aSyn) in vitro. Here, we show the impact of S1-protein in a broad spectrum of brain regions after injection via three different application routes in C57/BL6 mice.

Methods: S1-protein was administered either intranasally, intravenously or intracerebrally. We quantified aSyn immunoreactivity and phosphorylated aSyn (pS129), microglia and astrocyte reactivity, ACE2/Neuropilin-1 receptor expression, and parvalbumin-positive interneurons in limbic system, basal ganglia, and cortical regions 14 days post-application. Plasma cytokine profiles were assessed 6 days post-injection.

Results: While intracerebral injection resulted in decreased aSyn immunoreactivity with increased pS129 in males, intravenous injection led to increased levels of aSyn immunoreactivity and microglia cell density, predominantly in brain regions associated with Parkinson's disease pathology. Intranasal application of S1-protein induced microgliosis in some brain regions but resulted in sex-dependent alterations of aSyn levels, with increases in females and decreases in males. All routes showed sex-dependent alterations in astrocytic reactivity, receptor expression, and parvalbumin-positive interneurons.

Conclusion: Our results demonstrate that S1-protein itself leads to neuroinflammation, altered aSyn homeostasis, and disruption of inhibitory circuits in a route- and sex-dependent manner. These findings indicate the possibility of S1-protein being a crucial agent for both neuroinflammatory processes and altered protein regulation mechanisms. S1-protein trapped in tissue reservoirs could therefore explain symptoms occurring or persisting beyond viral clearance (Post COVID-19 condition).

Keywords: Long-COVID; Neurodegenerative disease; Neuroinflammation; Neurological symptoms; S1-protein.