SARS-CoV-2 infection of substantia nigra pars compacta induces expression of miR-330-5p at 10 days post-infection.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been linked to several neurological symptoms in coronavirus disease 2019 (COVID-19) patients; however, the molecular mechanisms underlying virus-induced neuroinflammation are not well identified. For example, the effect of SARS-CoV-2 infection of the substantia nigra pars compacta (SNpc) of the midbrain has not been addressed, in spite of its importance in dopaminergic signalling and neurodegenerative abnormalities. The purpose of this study was to understand the SARS-CoV-2-induced inflammatory response in the SNpc region of the brain. We inoculated (intranasally) transgenic mice expressing human ACE2 under control of the human keratin 18 promoter (K18-hACE-2 mice) with a 4×10³ TCID₅₀ (mild) dose of SARS-CoV-2. Ten days post-inoculation, SARS-CoV-2 was detected in the SNpc of mice, along with increased levels of IL-1β, B1R and ADAM17, and reduced microglial/macrophage occurrence. miR-330-5p expression was significantly reduced in virus-positive SNpc tissue. Luciferase reporter assays supported ADAM17 as a direct target of miR-330-5p. There was no significant difference in miR-330-5p expression levels in the experimental autoimmune encephalomyelitis mice compared to control mice, demonstrating a crucial role for SARS-CoV-2-induced miR-330-5p in brain pathology. Our study uncovers for the first time that SARS-CoV-2 can invade the SNpc and downregulate miR-330-5p expression levels, causing an enhanced ADAM17 expression and possible neuroinflammatory signalling. The results implicate miR-330-5p as a prospective therapeutic target for alleviating midbrain inflammation associated with SARS-CoV-2 infection.