NRP1 promotes hepatic fibrosis by regulating Src/Rab7-mediated lysosomal degradation of TβRI.

BACKGROUND AND AIMS: Activation of hepatic stellate cells (HSCs) and subsequent dysregulation of the TGF-β1 signaling pathway are central to the progression of hepatic fibrosis. Neuropilin-1 (NRP1) has been identified as a co-receptor involved in multiple signaling pathways, yet its role in modulating TGF-β receptor stability in HSCs remains to be fully elucidated. This study investigated the regulatory role of the NRP1/Src/Rab7 axis in TβRI lysosomal degradation during HSC activation.

METHODS

Hepatic fibrosis was induced in male C57BL/6 mice via intraperitoneal CCl4 injection for four weeks. HSC-specific knockdown of Nrp1 was achieved using an AAV8-pLrat-shNrp1 vector. TβRI stability and lysosomal degradation were evaluated through cycloheximide (CHX) chase assays and chloroquine treatment. The impact on the TGF-β1/Smad signaling pathway was assessed both in vitro and in vivo.

RESULTS

Nrp1 silencing in primary HSCs reduced TβRI protein levels and attenuated p-Smad2/3 signaling without affecting mRNA levels. Consistently, NRP1 deficiency accelerated lysosomal degradation of TβRI, accompanied by increased TβRI-LAMP1 colocalization and enhanced trafficking of TβRI into Rab7-positive late endosomes. Mechanistically, NRP1 loss diminished Src kinase activity and consequently reduced Src-dependent tyrosine phosphorylation of Rab7, leading to elevated Rab7-GTP levels and enhanced late endosomal sorting of TβRI. Rab7 knockdown or Src reactivation partially rescued TβRI stability and restored downstream signaling. In vivo, HSC-specific Nrp1 knockdown attenuated CCl4-induced fibrosis and reduced TβRI levels, while Rab7 inhibition partially reversed these effects.

CONCLUSIONS

These data suggest that the NRP1/Src/Rab7 axis contributes to TβRI stability by modulating its lysosomal degradation pathway. Targeting this axis may provide a potential approach for intervening in the progression of hepatic fibrosis.