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

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.