Baicalein Ameliorates Experimental Ulcerative Colitis Recurrency by Downregulating Neonatal Fc Receptor via the NF-κB Signaling Pathway

Ulcerative colitis (UC) is a chronic autoimmune disease (AID) that causes mild to moderate unpredictable symptoms, including diarrhea and abdominal pain. Against neonatal Fc receptor (FcRn) has been proven to be a unique AID treatment strategy by decreasing the effects of pathogenic autoantibody. Our previous study revealed that FcRn inhibition is beneficial in UC treatment through reducing colonic neutrophil extracellular trap (NET) formation via accelerating serum antineutrophil cytoplasm antibodies (ANCA) clearance. In this study, we initially confirmed the specific impact of downregulating FcRn in preventing UC relapse by injecting rAAV, which is carrying Fcgrt-shRNA, in mice. Next, we investigated the inhibition effects and regulation mechanisms of baicalein (BCL) on FcRn and assessed its capacity to withstand UC recurrence using NCM460 cells and dextran sodium sulfate-induced mice models by determining the expression of FcRn and its related transcription factors. We also measured colonic NET-associated protein (NAP) expression and serum concentrations of IgG, ANCA, TNF-α, IL-1β, and c-reactive protein (CRP). UC inflammation severity was determined by using the disease activity index (DAI) and histopathological score (HS). BCL treatment remarkably decreased the mRNA and protein contents of FcRn, p50, and p65 but did not impact STAT1 expression or the phosphorylation of IκB and STAT1. Long-term BCL administration inhibited colonic FcRn expression and reduced serum ANCA levels, colonic NAP expression, serum inflammation-related indexes (including TNF-α, IL-1β, and CRP), and DAI and HS scores in UC mice during inflammation relapse better than salazosulfapyridine. Our study indicates that BCL ameliorates UC recurrency by inhibiting FcRn expression via p50/p65 heterodimer-mediated NF-κB signaling.