Lipid Metabolism Regulate the Inflammatory Microenvironment in the Hepatic Fibrosis Induced by Schistosoma Japonicum Infection in China: A Genotype-Phenotype Association Study

Background: Schistosomiasis (japonica) is a neglected infectious disease, influencing millions of people at risk of infection worldwide. The patients are at high risk of gradually developing hepatic fibrosis. Immune regulation is recognized to contribute to schistosomal liver fibrosis. However, we still lack appropriate preventive and therapeutic modalities. Previous evidence points out that there is an interaction between lipid regulation and inflammation which moderates the homeostasis after parasitic infection. Moreover, while immune response to Schistosoma infection is considered affected by genetic diversity; yet so far little is known regarding the mechanism of action. To explore the association between lipid metabolism-related genes and the hepatic fibrosis induced by Schistosoma japonicum infection, we conducted the following study. Methods: This study combines epidemiological investigation, in-vitro studies, and animal experiment. First, we conducted a whole-genome sequencing in the epidemic area of China and established a S. japonicum-infected mice model and liver tissue morphology and mRNA analysis of PLA2G2D and PPARG were conducted. Then we expanded the sample size and collected biological information under epidemiological investigation. This was followed with genotyping of the candidate genes, the serum protein expression, as well as the level of three inflammation-related lipid mediators, which were measured and compared in different groups. Finally, we evaluated whether the allelic changes alter PLA2G2D enzymatic activity in vitro and compared the Pro and Ala PPARγ forms concerning the ability to activate transcription via dimerizing with the retinoid X receptor α (RXRα) and response element (PPRE). Findings: A group of lipid metabolism-related genes in schistosomiasis patients were identified. We found schistosome immunoregulation accompanied by the development of lipid metabolism in the murine model. We confirmed the genetic variation of arachidonic acid metabolic pathway related genes (PLA2G2D rs584367 and PPARG rs1801282) associated with a reduced risk of high grades of schistosomiasis induced hepatic fibrosis in a large sample size. Moreover, the levels of serum PLA2G2D and the 15d-PGJ2、PGE2 and TXB2 showed significant differences due to grades of fibrosis. Besides, the level of TXB2 significantly correlated with PLA2G2D. The enzyme activity of the PLA2G2D was increased approximately four-fold in the variant relative to the wild-type. The PPARγ 12Ala allele showed 18.7%-fold reduction in the ability to transactivate responsive promoters. Interpretation: This study raises a novel perspective conclusion from whole-genome sequencing that lipid metabolism particularly arachidonic acid metabolic pathway may play a regulatory role in the balance of inflammatory microenvironment which is essential for the development of Schistosoma liver fibrosis. Patients with risk polymorphism have more probability to develop uncontrollable inflammation, which eventually progress to hepatic fibrosis. The significant markers we found in this investigation may be used to facilitate diagnosis. Funding Statement: This study was supported by National Natural Science Foundation of China (Grant Number: 81601781) and the China Postdoctoral Science Foundation (Grant Number: 2016M591605), Science and Technology Program of Guangzhou (Grant Number: 201803010116). Declaration of Interests: The authors have no conflicts of interest to disclose. Ethics Approval Statement: Epidemiological studies were approved by the Ethics Committees of Fudan University (IRB#2016-TYSQ-03-17), and all participants gave informed written consent. Animals were cared for by the guidelines developed by the China Council on Animal care, and all animal experiments were performed according to the procedures approved by the Human Research Ethics Committee of the Sun Yat-sen University (No·2016-104).