MMP9 and COVID-19: In conclusion, our data indicated that SARS-CoV-2 could infect brain vascular endothelial cells and cross the BBB via transcellular pathway by MMP9-mediated BM with intact TJs, consequently leading to neuronal damage, which further promoting the understanding of the mechanisms underlying CNS invasion by SARS-CoV-2 and neurologic manifestations in COVID-19 patients.