Ursolic acid alleviates liver fibrosis by regulating Hepatic stellate cell activation via the Notch3/NOX4 pathway.

Background: Mutual regulation exists between the Notch and Nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4) signaling pathways, both of which are significant drivers of liver fibrosis. It remains uncertain whether there is a reciprocal regulatory relationship between them in hepatic fibrosis. Ursolic acid (UA), a herbal monomer, has demonstrated unique potential in preventing fibrosis, yet its specific mechanism remains unclear.

Methods: The study uses in vitro and in vivo fibrosis models in LX2 cells and C57BL/6J mice to assess UA's impact on LX2 cell activation and liver fibrosis. It also examines the relationship between Notch3 and NOX4 at both the upstream and downstream levels in vitro and in vivo, and confirms whether UA alleviates HSCs activation and liver fibrosis through this pathway.

Results: We conducted a wide range of assays in HSCs and mice. We found that UA inhibited HSCs activation and hepatic fibrosis in mice. UA suppressed the expression of NOX4, Notch3, and Hes1. Silencing or inhibiting Notch3 downregulated NOX4 expression, whereas silencing or inhibiting NOX4 had no impact on the expression of Notch3. When Notch3 was silenced in the presence of UA, HSCs activation was not significantly suppressed compared with silencing Notch3 alone. Consistent with in vitro findings, inhibiting Notch3 in the presence of UA didn't significantly attenuate mice liver fibrosis when compared with inhibiting Notch3 alone. Moreover, Silencing or inhibiting NOX4 yielded similar outcomes as the knock-down of Notch3 in vitro and in vivo.

Conclusion: UA reversed liver fibrosis through suppression of Notch3/NOX4 signaling.