Rapamycin Upregulates Connective Tissue Growth Factor Expression in Hepatic Progenitor Cells Through TGF-β-Smad2 Dependent Signaling.

Yu Wu,Yi He,Wei Wang,Xiang-Mei Peng,Xiao-Ping Chen,Liang Chu,Hui-Fang Liang,Yi-Xiao Xiong,Bi-Xiang Zhang,Ze-Yang Ding

doi:10.3389/fphar.2018.00877

Abstract

Rapamycin (sirolimus) is a mTOR kinase inhibitor and is widely used as an immunosuppressive drug to prevent graft rejection in organ transplantation currently. However, some recent investigations have reported that it had profibrotic effect in the progression of organ fibrosis, and its precise role in the liver fibrosis is still poorly understood. Here we showed that rapamycin upregulated connective tissue growth factor (CTGF) expression at the transcriptional level in hepatic progenitor cells (HPCs). Using lentivirus-mediated small hairpin RNA (shRNA) we demonstrated that knockdown of mTOR, Raptor, or Rictor mimicked the effect of rapamycin treatment. Mechanistically, inhibition of mTOR activity with rapamycin resulted in a hyperactive PI3K-Akt pathway, whereas this activation inhibited the expression of CTGF in HPCs. Besides, rapamycin activated the TGF-β-Smad signaling, and TGF-β receptor type I (TGFβRI) serine/threonine kinase inhibitors completely blocked the effects of rapamycin on HPCs. Moreover, Smad2 was involved in the induction of CTGF through rapamycin-activated TGF-β-Smad signaling as knockdown completely blocked CTGF induction, while knockdown of Smad4 expression partially inhibited induction, whereas Smad3 knockdown had no effect. Rapamycin also induced ROS generation and latent TGF-β activation which contributed to TGF-β-Smad signaling. In conclusion, this study demonstrates that rapamycin upregulates CTGF in HPCs and suggests that rapamycin has potential fibrotic effect in liver.

Highlights

Liver fibrosis is regarded as an imbalanced tissue repair response with excessive accumulation of extracellular matrix proteins in response to chronic liver injury (Bataller and Brenner, 2005; Pellicoro et al, 2014; Weiskirchen et al, 2018)
Considering that diverse types of cells participate in the progression of liver fibrosis, and hepatic progenitor cells (HPCs) may play a important role, we investigated whether rapamycin modulates connective tissue growth factor (CTGF) expression in two HPCs LE/6 and WB-F344 cells which were widely used as in vitro models for studying functions of HPCs (Nguyen et al, 2007; Ding et al, 2013, 2016; Wu et al, 2018)
These results suggest that rapamycin induces de novo synthesis of CTGF in HPCs

Summary

Introduction

Liver fibrosis is regarded as an imbalanced tissue repair response with excessive accumulation of extracellular matrix proteins in response to chronic liver injury (Bataller and Brenner, 2005; Pellicoro et al, 2014; Weiskirchen et al, 2018). Hepatocyte-mediated regeneration is usually impaired and subsequently triggers activation of the progenitor (oval) cell compartment, which in turn provokes a severe fibrogenic response (Tirnitz-Parker et al, 2014). CTGF is a matricellular protein strongly upregulated in fibrotic liver tissue, and it plays a pivotal role in fibrogenesis of liver (Gressner and Gressner, 2008; Weiskirchen, 2016). Previous investigations have demonstrated that hepatocytes, cholangiocytes, and HSCs, as well as HPCs express and secrete CTGF in the fibrotic liver (Gressner et al, 2007; Ding et al, 2013, 2016; Williams et al, 2014)

Results

Discussion

Conclusion