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; therefore, establishing a suitable in vitro microenvironment is urgently required in order to design novel therapeutics and identify molecular biomarkers to stratify patients.
Due to the lack of HBV receptors in mice, the in vivo study of HBV-induced liver fibrosis is time consuming and costly. For in vitro study, neither cell lines nor 3D liver organoids can correctly simulate the patient's viral hepatitis internal environment. Therefore, determining the roles the hepatic environment play in the patient will greatly facilitate the establishment of a suitable in vitro environment to reflect more hepatitis patient-specific pathogenic factors. Such factors are important for developing in vitro fibrosis assays which can be used to identify novel drug targets and drug screening.
In this study, we set out to screen a subset of preselected microenvironment factors, including growth and inflammatory factors, in chronic HBV patients with different degrees of fibrosis. In addition, hepatic stellate cells (HSCs) were used to study how these factors interact to modulate fibrogenesis and progression of fibrosis in chronic hepatitis B patients.
We examined the gene expression of key microenvironment factors using liver samples from patients with more advanced fibrosis compared to those with less severe fibrosis. We also carried out an in vitro study using the human stellate cell line LX-2. Different recombinant cytokines and growth factors or their combination were used to study how these factors interacted with LX-2 cells and to pinpoint the cross-talk between the aforementioned factors and screen the most important factors.
Of the secreted factors examined, transforming growth factor (TGF)-β1, interleukin-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 during treatment with IL-1β and TNF-α, suggesting that stellate cells can respond to proinflammatory stimuli. When IL-1β and TGF-β1 were combined, we observed not only fibroblast activation as shown by α-SMA 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. Our findings indicate that the inflammatory factor IL-1β is a central player in fibrogenesis and progression of fibrosis in chronic hepatitis B patients. IL-1β may activate HSCs via PDGF, and synergize with TGF-β1 in fibrosis progression. To establish 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.
Our study demonstrated that the hepatic microenvironment involves crosstalk between profibrotic and proinflammatory factors in hepatitis patients and underlies fibrosis. The treatment of stellate cells with IL-1β combined with TGF-β1 may serve as an in vitro model for fibrotic HBV infected patients and can reflect the liver microenvironment.