Background
The Niemann Pick C1 (NPC1) protein is an intracellular cholesterol transporter located in the late endosome/lysosome (LE/Ly) that is involved in the mobilization of endocytosed cholesterol. Loss-of-function mutations in the NPC1 gene lead to the accumulation of cholesterol and sphingolipids in LE/Ly, resulting in severe fatal NPC1 disease. Cellular alterations associated with NPC1 inactivation affect both the integrity of lipid rafts and the endocytic pathway. Because the angiotensin-converting enzyme 2 (ACE2) and type 2 serine transmembrane protease (TMPRSS2), interactors of the SARS-CoV-2 Spike protein also localize to lipid rafts, we sought to investigate the hypothesis that NPC1 inactivation would generate an intrinsically unfavorable barrier to SARS-CoV-2 entry.
Conclusion
Overall, this study provides compelling evidence that the inhibition of NPC1 cholesterol transporter activity generates a cellular environment that hinders SARS-CoV-2 entry. ACE2 depletion from the plasma membrane appears to play a major role as limiting factor for viral entry.
Results
In this study, we show that inhibition of the cholesterol transporter activity of NPC1 in cells that express both ACE2 and TMPRSS2, considerably reduces SARS-CoV-2 infectivity, evaluated as early as 4 h post-infection. Mechanistically, treatment with NPC1 specific inhibitor U18666A relocalizes ACE2 from the plasma membrane to the autophagosomal/lysosomal compartment, thereby reducing SARS-CoV-2 entry into treated cells. Reduction of viral entry was observed for both fully infectious SARS-CoV-2 virus and with a pseudotyped VSV-Spike-GFP virus. For instance, U18666A-treated Caco-2 cells infected with the pseudotyped VSV-Spike-GFP showed a > threefold and > 40-fold reduction in virus titer when infectivity was measured at 4 h or 24 h post-infection, respectively. A similar effect was observed in CRISP/R-Cas9-edited Caco-2 cells, which were even more resistant to SARS-CoV-2 infection as indicated by a 97% reduction of viral titers.