Hedgehog signaling inhibitor GANT61 induces endoplasmic reticulum stress-mediated protective autophagy in hepatic stellate cells

Abstract

Hedgehog (Hh) signaling plays an important role in the viability maintenance of hepatic stellate cells (HSC). HSCs have been identified as the major profibrogenic cells in the liver. The present study revealed that a novel Hh signaling antagonist GANT61 induced apoptosis in the activated human hepatic stellate cell line LX-2 cells, as it dose-dependently caused mitochondrial inner transmembrane potential (ΔΨm) loss and caspase-3 cleavage. Autophagic flux was markedly increased after GANT61 treatment. Moreover, we found that autophagy was a pro-survival factor in GANT61-treated LX-2 cells because autophagic inhibitors 3-Methyladenine (3-MA) or Chloroquine (CQ) significantly aggravated GANT61-induced cytotoxicity. Furthermore, the endoplasmic reticulum (ER)-resident molecular chaperone BiP, a marker of ER stress, was markedly increased after incubation with GANT61. Meanwhile, the PERK-eIF2α-ATF4-CHOP pathway was observed to be activated by GANT61. Salubrinal, a selective inhibitor of ER stress, suppressed GANT61-induced LC3BII expression and enhanced poly (ADP-ribose) polymerase (PARP) cleavage, indicating that ER stress is a trigger of autophagy and suppresses apoptosis in GANT61-treated LX-2 cells. Overall, these results demonstrate that simultaneous inhibition of Hh signaling and autophagy or ER stress could be a better way to reduce activated HSCs.