BRP39 Regulates Neutrophil Recruitment in NLRP3 Inflammasome-Induced Liver Inflammation

Abstract

Background and AimsBRP-39 (Chi3L1) and its human homolog YKL-40, is an established biomarker of liver fibrosis in nonalcoholic steatohepatitis (NASH) patients, but its role in NASH pathogenesis remains unclear. We have recently identified Chi3L1 as one of the top upregulated genes in mice with inducible gain-of-function NOD-like receptor protein 3 (NLRP3) activation that mimics several liver features of NASH. This study aimed to investigate the effects of BRP39 deficiency on NLRP3-induced liver inflammation using Tamoxifen-inducible Nlrp3 knock-in mice sufficient (Nlrp3A350V CRT) and deficient for BRP39 (Nlrp3A350V /BRP-/- CRT). MethodsUsing Tamoxifen-inducible Nlrp3A350V knock-in mice (Nlrp3A350V CRT) mice and Tamoxifen-inducible Nlrp3A350V knock-in BRP39 deficient mice (Nlrp3A350V BRP-/- CRT), we investigated the consequence of BRP39 deficiency influencing NLRP3 induced liver inflammation. ResultsOur results showed that BRP39 deficiency in NLRP3 induced inflammation improved body weight and liver weight. Moreover, liver inflammation, fibrosis and HSC activation were significantly reduced, corresponding to significantly decreased Ly6C+ infiltrating macrophages, CD68+ OPN+ hepatic LAMs (lipid associated macrophages), and activated Ly6G+ and H3Cit+ neutrophils accumulation in the liver. Further investigation revealed that circulatory neutrophils from NLRP3 induced BRP39 deficient mice have impaired chemotaxis and migration ability, and this was confirmed by RNA-bulk sequencing showing reduced immune activation, migration and signaling responses in neutrophils. ConclusionThese data showcase the importance of BRP39 in regulating the NLRP3 inflammasome during liver inflammation and fibrotic NASH by altering cellular activation, recruitment and infiltration during disease progression, and revealing BRP39 to be a potential therapeutic target for future treatment of inflammatory NASH and its associated diseases.