Published online Jul 21, 2020. doi: 10.3748/wjg.v26.i27.3917
Peer-review started: December 15, 2019
First decision: April 1, 2020
Revised: May 15, 2020
Accepted: July 1, 2020
Article in press: July 1, 2020
Published online: July 21, 2020
Chronic hepatitis B virus (HBV) infection is a leading cause of liver morbidity and mortality worldwide. Liver fibrosis resulting from viral infection-associated inflammation and direct liver damage plays an important role in disease management and prognostication. The mechanisms underlying the contribution of the liver microenvironment to fibrosis in HBV patients are not fully understood. There is an absence of effective clinical treatments for liver fibrosis progression; thus, establishing a suitable in vitro microenvironment in order to design novel therapeutics and identify molecular biomarkers to stratify patients is urgently required.
To examine a subset of pre-selected microenvironment factors of chronic HBV patients that may underlie fibrosis, with a focus on fibroblast activation.
We examined the gene expression of key microenvironment factors in liver samples from patients with more advanced fibrosis compared with those with less severe fibrosis. We also used the human stellate cell line LX-2 in the in vitro study. Using different recombinant cytokines and growth factors or their combination, we studied how these factors interacted with LX-2 cells and pinpointed the cross-talk between the aforementioned factors and screened the most important factors.
Of the secreted factors examined, transforming growth factor (TGF)-β1, interleukin (IL)-1β and tumor necrosis factor (TNF)-α were increased in patients with advanced fibrosis. We found that besides TGF-β1, IL-1β can also induce a profibrotic cascade by stimulating the expression of connective tissue growth factor and platelet-derived growth factor (PDGF) in LX-2 cells. Furthermore, the proinflammatory response can be elicited in LX-2 cells following treatment with IL-1β and TNF-α, suggesting that stellate cells can respond to proinflammatory stimuli. By combining IL-1β and TGF-β1, we observed not only fibroblast activation as shown by αlpha-smooth muscle actin and PDGF induction, but also the inflammatory response as shown by increased expression of IL-1β.
Collectively, our data from HBV patients and in vitro studies demonstrate that the hepatic microenvironment plays an important role in mediating the crosstalk between profibrotic and proinflammatory responses and modulating fibrosis in chronic HBV patients. For the establishment of a suitable in vitro microenvironment for HBV-induced liver fibrosis, not only TGF-β1 but also IL-1β should be considered as a necessary environmental factor.
Core tip: We partially profiled the microenvironment factors in hepatitis B virus (HBV) infected patients. In vitro, we stimulated the hepatic stellate cell line LX-2 with different growth factors, cytokines or their combination. This study demonstrated that the hepatic microenvironment, which involves the crosstalk between profibrotic and proinflammatory factors, underlies fibrosis in hepatitis patients. The treatment of stellate cells with interleukin-1β combined with transforming growth factor-β1 may serve as an in vitro model for fibrotic HBV infected patients, which better represents the liver microenvironment.