Enhanced Wnt Signalling in Hepatocytes is Associated with Schistosoma japonicum Infection and Contributes to Liver Fibrosis
Liver fibrosis is the most serious pathology caused by Schistosoma japonicum infection, which arises when schistosome eggs are deposited in the liver. Eosinophils, macrophages and hepatic stellate cells (HSCs) have been identified as major cellular contributors to the development of granulomas and fibrosis, but little is known about the effects of hepatocytes on granuloma formation. Here, we found that the levels of Wnt signalling-related molecules, transforming growth factor β (TGF-β) and connective tissue growth factor (CTGF) in hepatocytes were markedly elevated after S. japonicum infection. Liver fibrosis was exacerbated when exogenous Wnt3a was introduced, but was alleviated when Wnt signalling was suppressed by DKK1, accompanied by the reduced expression of TGF-β and CTGF in hepatocytes. These results indicate that the hepatocytic expression of TGF-β and CTGF is mediated by Wnt signalling. Additionally, the hepatocytes isolated from infected mice promoted the activation of primary HSCs in vitro, however, this effect was not observed when hepatocytes from DKK1 treated S. japonicum-infected mice was employed in the co-culture system. Our findings identify a novel pro-fibrogenic role of hepatocytes in schistosomiasis-induced liver fibrosis that is dependent on Wnt signalling, which may serve as a potential target for ameliorating hepatic fibrosis caused by helminths.BALB/c mice were infected with 25 cercariae of S. japonicum through percutaneous exposure of the abdominal skin, and the hepatocytes were successfully isolated from the liver (Supplementary Fig. 1A,B) at the indicated time. The infected mice exhibited increased mRNA levels of canonical (Wnt1, Wnt2, Wnt3, and Wnt3a) and noncanonical (Wnt5a) Wnt molecules, receptors (Fz1 and Fz5) and the Wnt signalling target gene Sox9 in hepatocytes at 6 and 12 weeks post-infection (Fig. 1A). No significant differences in β-catenin were observed at the mRNA level (Fig. 1A). In addition, there was an increase in the protein levels of Wnt3/3a, β-catenin and Sox9 in the hepatocytes after S. japonicum infection (Fig. 2B,C and Supplementary Fig. 9). These results suggest that both canonical and non-canonical Wnt signalling in hepatocytes was obviously induced after egg deposition, and this signalling was involved in the development of schistosomiasis.The animal experiments were performed in accordance with the guidelines of the Chinese Council on Animal Care, and the study was approved by the Tongji Medical College Committee (Wuhan, China).We thank Professor Jilong Shen from Anhui Medical University for his helpful discussion about this research and constructive suggestion regarding the manuscript. This work was financially supported by the grants from National Nature Science Foundation of China (No. 81471979 and No. 81672047) to Wenqi Liu.The authors declare that they have no competing interests.Electronic supplementary materialSupplementary information accompanies this paper at doi:10.1038/s41598-017-00377-4Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.