Lung-targeted lipid nanoparticle-delivered siUSP33 attenuates SARS-CoV-2 replication and virulence by promoting envelope degradation

As a structural protein of SARS-CoV-2, the E protein not only plays a key role in the formation of viral particles but also forms ion channels and has pathogenic functions, including triggering cell death and inflammatory responses. The stability of E proteins is controlled by the host ubiquitin-proteasome system. By screening human deubiquitinases, we found that ubiquitin-specific protease 33 (USP33) could enhance the stability of E proteins depending on its deubiquitinase activity, thereby promoting viral replication. In the absence of USP33, E proteins are rapidly degraded, leading to a reduced viral load and inflammation. Using lipid nanoparticle (LNP) encapsulation of siUSP33 by adjusting the lipid components (ionizable cationic lipids), siUSP33 was successfully delivered to mouse lung tissues, rapidly reducing USP33 expression in the lungs and maintaining knockdown for at least 14 d, effectively suppressing viral replication and virulence. This method of delivery allows efficient targeting of the lungs and a response to acute infections without long-term USP33 deficiency. Our research, based on the deubiquitination mechanism of USP33 on the E protein, demonstrates that LNP-mediated siRNA delivery targeting USP33 plays a role in antiviral and anti-inflammatory responses, offering a novel strategy for the prevention and treatment of SARS-CoV-2.