SARS-CoV-2 nucleocapsid protein promotes TMAO-induced NLRP3 inflammasome activation by SCAP–SREBP signaling pathway

The sterol regulatory element-binding protein (SREBP) activation and cytokine level were significantly increased in coronavirus disease-19. The NLRP3 inflammasome is an amplifier for cellular inflammation. This study aimed to elucidate the modulatory effect of SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 NP) on trimethylamine N-oxide (TMAO)-induced lipogenesis and NLRP3 inflammasome activation and the underlying mechanisms in vascular smooth muscle cells (VSMCs). Our data indicated that SARS-CoV-2 NP activates the dissociation of the SREBP cleavage activating protein (SCAP) from the endoplasmic reticulum, resulting in SREBP activation, increased lipogenic gene expression, and NLRP3 inflammasome activation. TMAO was applied to VSMC-induced NLRP3 inflammasome by promoting the SCAP-SREBP complex endoplasmic reticulum-to-Golgi translocation, which facilitates directly binding of SARS-CoV-2 NP to the NLRP3 protein for NLRP3 inflammasome assembly. SARS-CoV-2 NP amplified the TMAO-induced lipogenic gene expression and NLRP3 inflammasome. Knockdown of SCAP-SREBP2 can effectively reduce lipogenic gene expression and alleviate NLRP3 inflammasome-mediated systemic inflammation in VSMCs stimulated with TMAO and SARS-CoV-2 NP. These results reveal that SARS-CoV-2 NP amplified TMAO-induced lipogenesis and NLRP3 inflammasome activation via priming the SCAP-SREBP signaling pathway.