C/EBP Homologous Protein (CHOP) Activates Macrophages and Promotes Liver Fibrosis in Schistosoma japonicum-Infected Mice

EgCF mediates macrophage polarisation by influencing the glycolytic pathway

Human cystic echinococcosis (CE) is a zoonotic disorder triggered by the larval stage of Echinococcus granulosus (E. granulosus) and predominantly occurred in the liver and lungs. The M2 macrophage level is considerably elevated among the liver of patients with hepatic CE and performs an integral function in liver fibrosis. However, the mechanism of CE inducing polarisation of macrophage to an M2 phenotype is unknown. In this study, macrophage was treated with E. granulosus cyst fluid (EgCF) to explore the mechanism of macrophage polarisation. Consequently, the expression of the M2 macrophage and production of anti-inflammatory cytokines increased after 48 h treatment by EgCF. In addition, EgCF promoted polarisation of macrophage to an M2 phenotype by inhibiting the expression of transcriptional factor hypoxia-inducible factor 1-alpha (HIF-1α), which increased the expression of glycolysis-associated genes, including hexokinase 2 (HK2) and pyruvate kinase 2 (PKM2). The HIF-1α agonist ML228 also inhibited the induction of macrophage to an M2 phenotype by EgCF in vitro. Our findings indicate that E. granulosus inhibits glycolysis by suppressing the expression of HIF-1α.

Schisandrin B Promotes Hepatic Stellate Cell Ferroptosis via Wnt Pathway-Mediated Ly6Clo Macrophages

A key event in liver fibrosis is the activation of the hepatic stellate cell (HSC). Schisandrin B (Sch B), a major component extracted from Schisandra chinensis, has been shown to inhibit HSC activation. Recently, ferroptosis (FPT) has been reported to be involved in HSC activation. However, whether Sch B has an effect on the HSC FPT remains unclear. Herein, we explored the effects of Sch B on liver fibrosis in vivo and in vitro and the roles of Wnt agonist 1 and ferrostatin-1 in the antifibrotic effects of Sch B. Sch B effectively alleviated CCl4-induced liver fibrosis, with decreased collagen deposition and α-SMA level. Additionally, Sch B resulted in an increase in lymphocyte antigen 6 complex locus C low (Ly6Clo) macrophages, contributing to a reduced level of TIMP1 and increased MMP2. Notably, the Wnt pathway was involved in Sch B-mediated Ly6C macrophage phenotypic transformation. Further studies demonstrated that Sch B-treated macrophages had an inhibitory effect on HSC activation, which was associated with HSC FPT. GPX4, a negative regulator of FPT, was induced by Sch B and found to be involved in the crosstalk between macrophage and HSC FPT. Furthermore, HSC inactivation as well as FPT induced by Sch B-treated macrophages was blocked down by Wnt pathway agonist 1. Collectively, we demonstrate that Sch B inhibits liver fibrosis, at least partially, through mediating Ly6Clo macrophages and HSC FPT. Sch B enhances Wnt pathway inactivation, leading to the increase in Ly6Clo macrophages, which contributes to HSC FPT. Sch B may be a promising drug for liver fibrosis treatment.

An update on animal models of liver fibrosis

The development of liver fibrosis primarily determines quality of life as well as prognosis. Animal models are often used to model and understand the underlying mechanisms of human disease. Although organoids can be used to simulate organ development and disease, the technology still faces significant challenges. Therefore animal models are still irreplaceable at this stage. Currently, in vivo models of liver fibrosis can be classified into five categories based on etiology: chemical, dietary, surgical, transgenic, and immune. There is a wide variety of animal models of liver fibrosis with varying efficacy, which have different implications for proper understanding of the disease and effective screening of therapeutic agents. There is no high-quality literature recommending the most appropriate animal models. In this paper, we will describe the progress of commonly used animal models of liver fibrosis in terms of their development mechanisms, applications, advantages and disadvantages, and recommend appropriate animal models for different research purposes.

Pathology and molecular mechanisms of Schistosoma japonicum-associated liver fibrosis

Schistosomiasis has been widely disseminated around the world, and poses a significant threat to human health. Schistosoma eggs and soluble egg antigen (SEA) mediated inflammatory responses promote the formation of egg granulomas and liver fibrosis. With continuous liver injuries and inflammatory stimulation, liver fibrosis can develop into liver cirrhosis and liver cancer. Therefore, anti-fibrotic therapy is crucial to increase the survival rate of patients. However, current research on antifibrotic treatments for schistosomiasis requires further exploration. In the complicated microenvironment of schistosome infections, it is important to understand the mechanism and pathology of schistosomiasis-associated liver fibrosis(SSLF). In this review, we discuss the role of SEA in inhibiting liver fibrosis, describe its mechanism, and comprehensively explore the role of host-derived and schistosome-derived microRNAs (miRNAs) in SSLF. Inflammasomes and cytokines are significant factors in promoting SSLF, and we discuss the mechanisms of some critical inflammatory signals and pro-fibrotic cytokines. Natural killer(NK) cells and Natural killer T(NKT) cells can inhibit SSLF but are rarely described, therefore, we highlight their significance. This summarizes and provides insights into the mechanisms of key molecules involved in SSLF development.

Pattern recognition receptor signaling and innate immune responses to schistosome infection

Schistosomiasis remains to be a significant public health problem in tropical and subtropical regions. Despite remarkable progress that has been made in the control of the disease over the past decades, its elimination remains a daunting challenge in many countries. This disease is an inflammatory response-driven, and the positive outcome after infection depends on the regulation of immune responses that efficiently clear worms and allow protective immunity to develop. The innate immune responses play a critical role in host defense against schistosome infection and pathogenesis. Initial pro-inflammatory responses are essential for clearing invading parasites by promoting appropriate cell-mediated and humoral immunity. However, elevated and prolonged inflammatory responses against the eggs trapped in the host tissues contribute to disease progression. A better understanding of the molecular mechanisms of innate immune responses is important for developing effective therapies and vaccines. Here, we update the recent advances in the definitive host innate immune response to schistosome infection, especially highlighting the critical roles of pattern recognition receptors and cytokines. The considerations for further research are also provided.

CCAAT/Enhancer-Binding Proteins in Fibrosis: Complex Roles Beyond Conventional Understanding

CCAAT/enhancer-binding proteins (C/EBPs) are a family of at least six identified transcription factors that contain a highly conserved basic leucine zipper domain and interact selectively with duplex DNA to regulate target gene expression. C/EBPs play important roles in various physiological processes, and their abnormal function can lead to various diseases. Recently, accumulating evidence has demonstrated that aberrant C/EBP expression or activity is closely associated with the onset and progression of fibrosis in several organs and tissues. During fibrosis, various C/EBPs can exert distinct functions in the same organ, while the same C/EBP can exert distinct functions in different organs. Modulating C/EBP expression or activity could regulate various molecular processes to alleviate fibrosis in multiple organs; therefore, novel C/EBPs-based therapeutic methods for treating fibrosis have attracted considerable attention. In this review, we will explore the features of C/EBPs and their critical functions in fibrosis in order to highlight new avenues for the development of novel therapies targeting C/EBPs.

The role of C/EBP homologous protein (CHOP) in regulating macrophage polarization in RAW264.7 cells

Schistosomiasis is a zoonotic parasitic disease that is endemic in Asia. Macrophages are mainly involved in the inflammatory response of late schistosoma infection. Our previous study found that C/EBP homologous protein (CHOP) expression is significantly increased, and M2 macrophages are activated in schistosome-induced liver fibrosis mice. However, the role of CHOP in the regulation of macrophage polarization remains to be further studied. Western blotting or quantitative PCR revealed that IL-4 increased the expression of arginase-1, macrophage mannose receptor 1, phosphorylation signal transducer and activator of transcription 6 (p-STAT6), Krüppel-like factor 4 (KLF4), CHOP, and IL-13 receptor alpha (IL-13Rα) and induced M2 polarization in RAW264.7 as measured by flow cytometry. Inhibiting STAT6 phosphorylation (AS1517499) reduced the IL-4-induced expression of KLF4, CHOP, and IL-13Rα and also the number of M2 macrophages. The overexpression of CHOP stimulated M2 polarization, but AS1517499 inhibited this effect. CHOP increased the protein expression of KLF4 but did not change the expression of p-STAT6. Soluble egg antigen (SEA) could promote the IL-4-induced protein expression of p-STAT6, CHOP, and KLF4. Overall, the findings show that SEA can promote the activation of M2 macrophages by causing increased CHOP-induced KLF4 levels and activation of STAT6 phosphorylation.

Endoplasmic Reticulum Stress, a Target for Drug Design and Drug Resistance in Parasitosis

Endoplasmic reticulum stress (ER stress) can be induced when cellular protein homeostasis is damaged, and cells can activate the unfolded protein response (UPR) to restore protein homeostasis or induce cell death to facilitate the survival of the whole system. Globally, parasites are a constant threat to human health and are therefore considered a serious public health problem. Parasitic infection can cause ER stress in host cells, and parasites also possess part or all of the UPR under ER stress conditions. In this review, we aim to clarify the role of ER stress pathways and related molecules in parasites for their survival and development, the pathogenesis of parasitosis in hosts, and the artemisinin resistance of Plasmodium, which provides some potential drug design targets to inhibit survival of parasites, relieves pathological damage of parasitosis, and solves the problem of artemisinin resistance.

Exogenous Therapeutics of Microrna-29a Attenuates Development of Hepatic Fibrosis in Cholestatic Animal Model through Regulation of Phosphoinositide 3-Kinase p85 Alpha

Recent studies have found that microRNA-29a (miR-29a) levels are significantly lower in fibrotic livers, as shown with human liver cirrhosis. Such downregulation influences the activation of hepatic stellate cells (HSC). Phosphoinositide 3-kinase p85 alpha (PI3KP85α) is implicated in the regulation of proteostasis mitochondrial integrity and unfolded protein response (UPR) and apoptosis in hepatocytes. This study aimed to investigate the potential therapeutic role of miR-29a in a murine bile duct ligation (BDL)-cholestatic injury and liver fibrosis model. Mice were assigned to four groups: sham, BDL, BDL + scramble miRs, and BDL + miR-29a-mimic. Liver fibrosis and inflammation were assessed by histological staining and mRNA/protein expression of representative markers. Exogenous therapeutics of miR-29a in BDL-stressed mice significantly attenuated glutamic oxaloacetic transaminase (GOT)/glutamic-pyruvic transaminase (GPT) and liver fibrosis, and caused a significant downregulation in markers related to inflammation (IL-1β), fibrogenesis (TGF-β1, α-SMA, and COL1α1), autophagy (p62 and LC3B II), mitochondrial unfolded protein response (UPR^mt; C/EBP homologous protein (CHOP), heat shock protein 60 (HSP60), and Lon protease-1 (LONP1, a mitochondrial protease), and PI3KP85α within the liver tissue. An in vitro luciferase reporter assay further confirmed that miR-29a mimic directly targets mRNA 3′ untranslated region (UTR) of PI3KP85α to suppress its expression in HepG2 cell line. Our data provide new insights that therapeutic miR-29a improves cholestasis-induced hepatic inflammation and fibrosis and proteotstasis via blocking PI3KP85α, highlighting the potential of miR-29a targeted therapy for liver injury.