Cholestasis is one of the most important causes of liver fibrosis. Due to the lack of effective treatment so far, it can eventually develop into end-stage liver disease with the need for liver transplantation. Therefore, the study of reliable biomarkers for predicting cholestatic hepatic fibrosis has great clinical significance. There is increasing evidence that alterations in transcriptome are associated with human disease, ranging from cancer to autoimmune diseases to cardiovascular pathology16–18. Herein we performed RNA high-throughput sequencing to explore the variations of transcriptome of hepatic fibrosis induced by BDL.
In this study, the hepatic fibrosis model we used was induced by BDL. Consistent with our previous study14, the appearance of many pathological features including the enlarged gallbladder, bile duct dilatation and collagen fiber formation indicated that BDL-induced hepatic fibrosis model was established successfully, which makes preparations for the next step of sequencing. Through researching differential gene expression, we look forward to discovering probable gene targets of BDL-induced hepatic fibrosis, and further described underlying signaling pathways, which may provide a new idea for the clinical treatment of cholestatic liver fibrosis.
Through transcriptome information analysis, a total of 239,727,428 clean reads were obtained. After data accusation and comparative analysis, we obtained the FPKM values of 22299 genes for subsequent analysis, and finally got 3224 DEGs. These results showed that loads of genes were significantly altered in hepatic fibrosis treated with BDL, suggesting an important role in BDL-induced hepatic fibrosis. According to the results of differential genes, we verified three significantly up-regulated and three significantly down-regulated genes, which including Gpx3, Serpinb6b, Cd63, Slco1a1, Ugt2b1, Serpina1e.
Glutathione peroxidase 3 (Gpx3) is an antioxidant enzyme, the only exocrine form of glutathione peroxidase family, which acts in detoxification of hydrogen peroxide to shields cells and enzymes from oxidative damage and regulates redox19. Besides, as a tumor suppressor gene, Gpx3 is involved in the occurrence of a variety of cancer diseases20, including ovarian cancer, breast cancer21, thyroid cancer22and lung cancer23. Furthermore, Gpx3 is also a tumor suppressor gene in HCC. Qi et al reported that GPx3 overexpression obviously suppressed proliferation and invasiveness of HCC cells, possessing a potential value in the prognosis and treatment of liver cancer patients 24,25. Similarly, the increased expression of Gpx3 in cholestatic liver fibrosis may inhibit the development of liver fibrosis to liver cancer. Granzymes (Gzms) is an exogenous serine protease, derived from cytoplasmic granules released by cytotoxic lymphocyte (CLTs) and natural killer cells (NK). Together with perforin, Gzms enters into the target cells, thus causing DNA degradation in cells. When lymphocytes combine with the damaged cells, perforin and Gzms are released. Perforating protein enters the target cells and forms pores in the plasma membrane to allow the Gzms into the cytosol of target cells where they carry out their effector functions 26. Serpinb6b is a specific Granzyme A (GzmA) inhibitor. Garzon et al informed that serpinb6b increased the survival rate of abdominal sepsis model mice by reducing the inflammatory reaction of serum and peritoneal lavage fluid 27. In our study, serpinb6b is significantly up-regulated, which may play a role in inhibiting biliary inflammation. Another significantly upregulated gene we found was CD63. CD63, also known as lysosomal associated membrane protein 3 (LAMP3), is the first identified member of the tetraspanin family. CD63 is a cell surface protein, which is related to cell activation, adhesion, variation and tumor invasion, metastasis and other life processes28. CD63 is considered to be a tumor suppressor, and is expressed in endosomes and lysosomes. In addition, CD63 plays a significant role in immunological processes. Studies showed that CD63 enhanced the activation of CD4 + T cells in MHC-II molecule mediated antigen presentation29. At the same time, CD63 plays an important role in mast cell degranulation and allergic reaction mediated by specific IgE. Knockout of CD63 results in a significant decrease in mast cell degranulation, thereby reducing the acute allergic reaction in the body30. CD63 is a surface marker of extracellular vesicles (EVs), and a report found that heparinase-1 resulted in the imbalance of extracellular matrix (ECM) by increasing CD63 synthesis and exosome secretion, thus favoring HCV infection31. High-fat diet induced upregulation of EVs phosphatidylcholine through inhibiting the expression of genes essential for activation of the insulin signaling pathway such as PI3K and Akt, contributing to insulin resistance 32. The increase of CD63 in BDL-induced hepatic fibrosis indicates that CD63 may be involved in the regulation in the form of EVs.
Slco1a1, also known as solute carrier organic anion transporter family member 1a1, is responsible for transporting bile acids into hepatocytes. In this study, we identified Slco1a1 is the most down-regulated mRNA, and negatively correlated with serum cholic acid level, which is consistent with the report that in alcohol-associated liver diseases 33. UDP-Glucuronosyltransferase (Ugt) is a membrane protein that binds to the endoplasmic reticulum, which plays a catalytic role in transferring glucuronic acid from UDP-glucuronic acid to other hydrophobic molecules. In this catalytic process, the water solubility of receptor molecules is greatly improved, thus promoting the elimination of these molecules, including steroid, thyroid hormones, bile acids, retinoids and fatty acids 34. Ugt2b1 is a phase II drug metabolizing enzyme, which plays a major role in the metabolism of xenobiotic and endogenous compounds. It is reported that the expression of ugt2b1 gene is significantly increased in the liver, and different nonsteroidal anti-inflammatory drugs (NSAIDs) downregulated its expression 35, which is consistent with the article that downregulation of ugt2b1 by metallic nanoparticles (NPs) is associated with inflammation and IL-6 gene induction in the liver 36. In this study, we found the decrease of ugt2b1 in the mouse model of cholestatic liver fibrosis, indicating that the inflammatory reaction caused by toxic bile leads to the downregulation of ugt2b1, ultimately affecting the metabolism of bile acids. Serpins is the most widely distributed and largest superfamily of protease inhibitors, which is highly expressed in the liver 37. There is a report shows that serpina1e has inhibitory effects on hepatic gluconeogenesis 38. Here, we found that BDL treatment decreased serpina1e expression, which suggested that serpina1e may be involved in glucose metabolism in cholestatic hepatic fibrosis.
In summary, this report showed that bile duct ligation successfully induced cholestatic hepatic fibrosis. A total of 3224 DEGs were identified with 2852 genes were upregulated and 372 genes were downregulated. Most upregulated DEGs were enriched in peroxisome, Granzymes and immune molecules, indicating there is a series complex immune response in cholestatic hepatic fibrosis. Besides, genes related to metabolism were mostly downregulated, implying cholestatic hepatic fibrosis may exhibit a severe metabolic disorder. In conclusion, this work provides some possible mRNA changes in liver fibrosis. However, further investigation in vitro and in vivo will be needed to confirm these mechanisms, aiming to provide a new perspective for the pathogenesis and drug treatment of clinical cholestatic hepatic fibrosis.