Cholesterol crystals activate NLRP3 inflammasomes and promote gallstone formation by increasing mucin secretion.

Cholesterol crystals participate in cholesterol nucleation; however, the role of cholesterol crystals in gallstone development is unknown. Mucin secretion contributes to increased size of gallstones. Cholesterol crystals activate inflammasomes and participate in many sterile inflammation related human diseases. We investigated the role of cholesterol crystals and mucins in sterile inflammation and gallstone enlargement. We found that expression of mucin 5AC (MUC5AC), NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) and interleukin-1b (IL-1b) was increased significantly in tissues adjacent to gallstones. Experiments in vitro showed that cholesterol crystals promote MUC5AC secretion; they also increase expression of NLRP3, NLR family CARD domain-containing 4 (NLRC4), apoptosis-associated speck-like protein containing caspase recruitment domain (ASC), and cleaved caspase-1 in biliary epithelial cells. Inhibition of Inflammasomes by NLRP3, ASC or caspase-1 small interfering RNAs reduced MUC5AC secretion. Also, the IL-1 receptor antagonist, IL1RA, and caspase-1 inhibitor, Ac-YVAD, both inhibited MUC5AC secretion induced by cholesterol crystals. We found that inflammasome activation participates in cholesterol crystal induced mucin secretion and gallstone development.