Vitamin D3 attenuates SARS‐CoV‐2 nucleocapsid protein‐caused hyperinflammation by inactivating the NLRP3 inflammasome through the VDR‐BRCC3 signaling pathway in vitro and in vivo

Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection‐caused coronavirus disease 2019 (COVID‐19) is a global crisis with no satisfactory therapies. Vitamin D3 (VD3) is considered a potential candidate for COVID‐19 treatment; however, little information is available regarding the exact effects of VD3 on SARS‐CoV‐2 infection and the underlying mechanism. Herein, we confirmed that VD3 reduced SARS‐CoV‐2 nucleocapsid (N) protein‐caused hyperinflammation in human bronchial epithelial (HBE) cells. Meanwhile, VD3 inhibited the NOD‐like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation in N protein‐overexpressed HBE (HBE‐N) cells. Notably, the inhibitors of caspase‐1, NLRP3, and NLRP3 or caspase‐1 small interference RNA (siRNA) enhanced VD3‐induced NLRP3 inflammasome inactivation, with subsequent suppression of interleukin‐6 (IL6) and IL1β release in HBE‐N cells, which were abolished by the NLRP3 agonist. Moreover, VD3 increased NLRP3 ubiquitination (Ub‐NLRP3) expression and the binding of the VDR with NLRP3, with decreased BRCA1/BRCA2‐containing complex subunit 3 (BRCC3) expression and NLRP3‐BRCC3 association. VD3‐induced Ub‐NLRP3 expression, NLRP3 inflammasome inactivation, and hyperinflammation inhibition were improved by the BRCC3 inhibitor or BRCC3 siRNA, which were attenuated by the vitamin D receptor (VDR) antagonist or VDR siRNA in HBE‐N cells. Finally, the results of the in vivo study in AAV‐Lung‐enhanced green fluorescent protein‐N‐infected lungs were consistent with the findings of the in vitro experiment. In conclusion, VD3 attenuated N protein‐caused hyperinflammation by inactivating the NLRP3 inflammasome partially through the VDR‐BRCC3 signaling pathway.