Nuclear localization of Toll/interleukin-1 receptor domain-containing adaptor protein reveals a previously unrecognized role in hepatic stellate cell activation

Abstract

Background The Toll/interleukin-1 receptor domain-containing adaptor protein (TIRAP) is a key adaptor in Toll-like receptor signaling, classically functioning as a cytoplasmic bridging adaptor for Myeloid differentiation primary response 88 (MyD88) recruitment. While its role in inflammatory signaling is well established, its contribution to alcohol-induced liver fibrosis remains unclear. Methods We used lipopolysaccharide (LPS) and ethanol-stimulated hepatic stellate cells (LX-2) for in vitro analysis. Immunofluorescence and immunoblotting were performed to check TIRAP’s expression. siRNA was used for TIRAP silencing to monitor its significant activity. mRNA expression for pro-fibrotic markers was checked via qRT-PCR. Results We demonstrated for the first time, nuclear translocation of TIRAP under alcoholic conditions. Confocal microscopy and nuclear–cytoplasmic fractionation confirmed TIRAP enrichment in the nucleus. Importantly, silencing of TIRAP in LX-2 significantly reduced the nuclear translocation and expression of fibrotic markers (such as α-SMA and collagen) in HSCs, suggesting a key role of nuclear TIRAP in driving fibrogenesis. Conclusion Overall, these findings reveal a novel role for TIRAP beyond cytoplasmic signaling, suggesting potential nuclear functions that may regulate transcriptional programs driving inflammation and fibrosis.