Curcumin Inhibits Hedgehog Pathway In Hepatic Stellate Cells For Anti-Liver Fibrosis

BackgroundHepatic fibrosis is the common pathological process of various chronic liver diseases. Currently there still have been no effective drugs for prevention and treatment of liver fibrosis. Activation of hepatic stellate cells (HSCs) and secretion of large amounts of extracellular matrix components are key events in the pathogenesis of hepatic fibrosis. Therefore, inhibition of HSC activation by drugs may be promising approaches for halting and reversing liver fibrogenesis. Accumulating evidence indicates that activation of hepatic hedgehog (Hh) pathway is tightly associated with the pathogenesis of liver fibrosis. Hh pathway may be a novel target for drug intervention of liver fibrosis. Nowadays bioactive compounds isolated from Chinese medicinal herbs have been an important source of antifibrotic candidates. Our group has long-termly studied the therapeutic role of the natural compound curcumin in combating liver fibrosis. We have established the potent antifibrotic activity of curcumin in vivo and in vitro, and uncovered that disruption of profibrogenic signaling transduction in HSCs could be the primary mechanisms underlying curcumin inhibition of HSC activation. Based on these discoveries, we herein hypothesized that modulating Hh signaling could contribute to curcumin suppression of HSC activation for antifibrotic purposes. We performed experiments to testify this hypothesis.Methods and ResultsWe first established the model of CCl4-indcued liver fibrosis in rats, which were spontaneously received curcumin administration. We found that curcumin reduced the levels of the Hh ligand Shh and downregulated the expression of Patched and Smo, two key receptors in Hh pathway but upregulated the expression of Hhip, an inhibitory factor of Hh pathway in rat fibrotic liver. In parallel, our in vitro experiments showed that curcumin not only modulated the above molecules in the same way, but also suppressed the nuclear translocation of Gli, inhibited Gli binding to DNA and reduced Gli target gene expression in HSCs. We further used Hh pathway specific inhibitor cyclopamine and agonist SAG to evaluate the association of blockade of Hh signaling with suppression of HSC activation. The obtained results demonstrated that cyclopamine, similarly to curcumin, inhibited HSC proliferation, arrested cell cycle at G0/G1 phase, induced apoptosis, restored lipid droplet accumulation and increased lipid gene expression, reduced fibrogenic marker expression, and weakened cell invasion and migration in HSCs; however, SAG abrogated curcumin effects in these aspects. Taken together, these results indicated that curcumin inhibited the biological properties of HSC activation by interrupting Hh pathway.When activated HSCs are transformed to myofibroblast-like cells, the energy mechanism could be shifted to glycolytic pathway within cells, which could be linked to HSC activation process. Our data showed that the glycolysis inhibitor 2-deoxy-D-glucose and the lactate dehydrogenase inhibitor Galloflavin, two compounds independently block the glycolytic pathway at different levels, significantly reduced profibrotic marker expression, and restored lipid droplet accumulation and increased lipid gene expression in HSCs, suggesting that activation of glycolytic pathway could be essential for maintaining HSC activation. Then, our in vivo and in vitro data showed that curcumin inhibited the expression of a series of key molecules in glycolytic pathway in HSCs, and that cyclopamine exerted similar effects but SAG abolished curcumin inhibition of glycolysis. These data collectively revealed that curcumin-inhibited the glycolytic pathway by blocking Hh pathway contributing to curcumin inhibition of HSC activation.ConclusionsIn summary, the current data validated the target role for Hh pathway in curcumin reduction of HSC activation for combating liver fibrosis, and preliminarily uncovered the underlying molecular mechanisms. Our studies provided experimental evidence for drug targeting Hh signaling for the management of hepatic fibrosis.