Lipopolysaccharide Reverses Hepatic Stellate Cell Activation Through Modulation of cMyb, Small Mothers Against Decapentaplegic, and CCAAT/Enhancer-Binding Protein C/EBP Transcription Factors

CD14 is not required for carbon tetrachloride-induced hepatic inflammation and fibrosis with or without lipopolysaccharide challenge

Binding of lipopolysaccharide (LPS) to CD14 is required for its cellular effects via TLR4. A role of LPS/TLR4-mediated signaling in activated hepatic stellate cells (aHSCs), the major fibrogenic cells, in liver fibrosis has been reported. We investigated effects of LPS on carbon tetrachloride (CCl4)-induced fibrosis in CD14-knockout (KO) mice in vivo, and culture-activated HSCs in vitro. CCl4 (biweekly; 4 weeks)-treated wild type (WT) and CD14-KO mice were challenged with single LPS administration for 24 h. Liver injury, inflammation and fibrosis were determined. Culture-activated HSCs from WT or CD14-KO mice were stimulated with LPS. Parameters of fibrogenic activity (expression of collagen1a1 [Col1a1], α-smooth muscle actin [αSMA] and TGFβ1) and inflammatory cytokines/chemokines were measured. CCl4 treatment caused similar liver injury and fibrosis in WT and CD14-KO mice. LPS increased liver injury and inflammation similarly in CCl4-treated WT and CD14-KO mice, but downregulated Timp1 and upregulated Mmp13. LPS elicited similar NFκB activation and inflammatory response in WT and CD14-KO aHSCs. LPS similarly downregulated Acta2 (encodes αSMA), Pdgfrb, Col1a1 and Mmp13 expression but did not affect Timp1 expression in WT and CD14-KO aHSCs. LPS did not alter Tgfb1 but increased expression of decorin (Dcn) (inhibitor of TGFβ1) expression in WT and CD14-KO aHSCs. The results indicate that the effects of LPS on HSCs are CD14-independent, and CD14 is not required for hepatic fibrosis. LPS-induced down-modulation of fibrogenic markers in aHSCs is also CD14-independent.

Stellate cell in hepatic inflammation and acute injury

The perisinusoidal hepatic stellate cells (HSCs) have been investigated extensively for their role as the major fibrogenic cells during chronic liver injury. HSCs also produce numerous cytokines, chemokines, and growth mediators, and express cell adhesion molecules constitutively and in response to stimulants such as endotoxin (lipopolysaccharide). With this property and by interacting with resident and recruited immune and inflammatory cells, HSCs regulate hepatic immune homeostasis, inflammation, and acute injury. Indeed, experiments with HSC-depleted animal models and cocultures have provided evidence for the prominent role of HSCs in the initiation and progression of inflammation and acute liver damage due to various toxic agents. Thus HSCs and/or mediators derived thereof during acute liver damage may be considered as potential therapeutic targets.

c-Myb Dominates TBK1-Mediated Endotoxin Tolerance in Kupffer Cells by Negatively Regulating DTX4

As a protective mechanism regulating excessive inflammation, endotoxin tolerance plays a vital role in regulating endotoxin shock. Kupffer cells are players in mediating endotoxin tolerance. Nonetheless, the regulatory mechanism regulating endotoxin tolerance is barely known. A nonclassical IKK kinase called TRAF-associated NF-κB activator (TANK)-binding kinase 1 (TBK1) can regulate inflammation. Here, we found that TBK1 is required for endotoxin tolerance in Kupffer cells. TBK1 plays a dominant role in regulating endotoxin tolerance by negatively regulating the induction of p100 processing. Deltex E3 ubiquitin ligase 4 (DTX4), a negative regulator of TBK1, can promote TBK1 K48-mediated ubiquitination and indirectly regulate endotoxin tolerance in Kupffer cells. We demonstrate that the c-Myb transcription factor could negatively regulate DTX4. Overexpression of c-Myb can be used to reduce the ubiquitination of TBK1 by reducing DTX4 transcription and to boost the anti-inflammatory effect of endotoxin tolerance. Thus, this study reveals a novel theory of TBK1-mediated endotoxin tolerance in Kupffer cells.

Protective effect of hepatocyte-enriched lncRNA-Mir122hg by promoting hepatocyte proliferation in acute liver injury

Some long noncoding RNAs (lncRNAs), which harbor microRNAs in their gene sequence and are also known as microRNA host gene derived lncRNAs (lnc-MIRHGs), play a dominant role alongside miRNAs, or both perform biological functions synergistically or independently. However, only a small number of lnc-MIRHGs have been identified. Here, multiple liver injury datasets were analyzed to screen and identify the target lncRNA Mir122hg. Mir122hg was mainly enriched in liver tissues with human-mouse homology. In both CCl₄-induced acute liver injury and Dgal/LPS-induced fulminant liver failure in mice, Mir122hg was sharply downregulated at the early stage, while a subsequent significant increase was only found in the CCl₄ group with liver recovery. Overexpression and silencing assays confirmed that Mir122hg played a protective role in acute injury by promoting hepatocyte proliferation in vivo and in vitro. Consistent with the results of gene enrichment analysis, Mir122hg binding to C/EBPα affected its transcriptional repression, promoted gene transcription of downstream chemokines, Cxcl2, Cxcl3, and Cxcl5, and exerted pro-proliferative effects on hepatocytes through activation of the AKT/GSK-3β/p27 signaling pathway by CXC/CXCR2 complexes. This study identifies a novel lncRNA with protective effects in acute liver injury and demonstrates that the binding of Mir122hg-C/EBPα promotes hepatocyte proliferation via upregulation of CXC chemokine and activation of AKT signaling.

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.

Traditional Chinese medicine: An important source for discovering candidate agents against hepatic fibrosis

Hepatic fibrosis (HF) refers to the pathophysiological process of connective tissue dysplasia in the liver caused by various pathogenic factors. Nowadays, HF is becoming a severe threat to the health of human being. However, the drugs available for treating HF are limited. Currently, increasing natural agents derived from traditional Chinese medicines (TCMs) have been found to be beneficial for HF. A systemic literature search was conducted from PubMed, GeenMedical, Sci-Hub, CNKI, Google Scholar and Baidu Scholar, with the keywords of “traditional Chinese medicine,” “herbal medicine,” “natural agents,” “liver diseases,” and “hepatic fibrosis.” So far, more than 76 natural monomers have been isolated and identified from the TCMs with inhibitory effect on HF, including alkaloids, flavones, quinones, terpenoids, saponins, phenylpropanoids, and polysaccharides, etc. The anti-hepatic fibrosis effects of these compounds include hepatoprotection, inhibition of hepatic stellate cells (HSC) activation, regulation of extracellular matrix (ECM) synthesis & secretion, regulation of autophagy, and antioxidant & anti-inflammation, etc. Natural compounds and extracts from TCMs are promising agents for the prevention and treatment of HF, and this review would be of great significance to development of novel drugs for treating HF.

Luteolin attenuates hepatic injury in septic mice by regulating P2X7R-based HMGB1 release

P2X7 receptor (P2X7R) and NLRP3 cooperatively participate in inflammation and hepatocyte damage during hepatic injury induced by lipopolysaccharides (LPS). High-mobility group box 1 (HMGB1) released from immune cells in response to such stimuli plays a vital role in mediating inflammation via TLR4 and the receptor for advanced glycation end products (RAGE), a receptor for HMGB1. However, the correlation among P2X7R, RAGE and TLR4 in regulating the release of HMGB1 has not been elucidated. Increasing the number of daily foods is found to be beneficial for hepatocyte damage in septic hepatic injury. Hence, we investigated the effects of luteolin, a natural flavonoid mainly existing in vegetables and fruits, on liver injury, focusing on how luteolin participates in hepatitis based on the P2X7R-RAGE-TLR4 axis by regulating the release of HMGB1. The results demonstrated that the indicators of hepatic injury such as increased ALT, AST in the serum and infiltration of immune cells were attenuated after luteolin treatment in LPS-induced mice. Luteolin could also suppress the production and release of HMGB1 and the activation of caspase 1 both in LPS-induced mice and LPS/ATP-stimulated HepG2 cells. Collectively, luteolin reversed LPS-induced hepatic injury, especially inflammation, likely by regulating the release of HMGB1 through the P2X7R-RAGE-TLR4 axis.

Crosstalk between hepatic stellate cells and surrounding cells in hepatic fibrosis

Hepatic fibrosis represents as a dynamic pathological process characterized by the net accumulation of extracellular matrix in the progression of various chronic liver diseases, including viral hepatitis, alcoholic liver disease, and metabolic associated fatty liver disease (MAFLD). Activation of hepatic stellate cells (HSCs) is well-defined to play a central role in the initiation and progression of hepatic fibrosis. However, the activation of HSCs is affected by the complicated microenvironments in liver, which largely attributes to the communication between hepatocytes and multiple tissue-resident cells, including sinusoidal endothelial cells, bile duct epithelial cells, platelets, T cells, B cells, macrophages, natural killer cells, neutrophils, dendritic cells, in the direct or indirect mechanisms. Cellular crosstalk between HSCs and surrounding cells contributes to the activation of HSCs and the progression of hepatic fibrosis. Currently, accumulating evidence have proven the complexity and plasticity of HSCs activation, and further clarification of cellular communication between HSCs and surrounding cells will provide sufficient clue to the development of novel diagnostic methods and therapeutic strategies for hepatic fibrosis.

MRI Measures of Murine Liver Fibrosis

BACKGROUND

An imaging method that allows quantitative fibrosis estimates is needed to facilitate the diagnosis of chronic liver disease. Amide proton transfer (APT) and tissue sodium concentration (TSC) estimates could meet this need.

HYPOTHESIS

APT and TSC estimates correlate with fibrosis in a mouse model of chronic liver disease.

STUDY TYPE

Prospective.

PHANTOMS/ANIMAL MODEL

Male C57Bl/6 mice given CCl₄ or vehicle (N = 8 each) twice weekly for 16 weeks.

FIELD STRENGTH/SEQUENCE

Liver T₁ (Look-Locker gradient recalled echo [GRE] sequence), T₂ (multiecho spin echo sequence), T_1rho (fast spin echo sequence with 500 Hz spin locking pulse), and APT (GRE sequence with off-resonance pulses) data were acquired at 7 T at 12 and 16 weeks. Liver sodium data (multiple echo GRE sequence) were acquired at 12 weeks at 9.4 T.

ASSESSMENT

Liver proton T₁ , T₂ , T_1rho , APT, sodium T₂ *, and TSC were calculated. Histological measures included Sirius Red, hematoxylin and eosin, liver hydroxyproline content, and serum alanine transaminase (ALT).

STATISTICAL TESTS

Welch's two-sided t-test was used to test for differences between control and CCl₄ -treated groups for serum ALT, hydroxyproline, Sirius Red staining, T₁ , T₂ , T_1rho , APT, TSC, and sodium T₂ *. Pearson's correlations between liver T₁ , APT, TSC, or sodium T₂ * with Sirius Red staining and hydroxyproline levels were calculated.

RESULTS

APT was significantly different (P < 0.05) between groups in the left liver lobe at 16 weeks (CCl₄ : 8.0% ± 1.2%, controls: 6.2% ± 1.0%), as were average liver TSC at 12 weeks (CCl₄ : 38 mM ± 5 mM, controls: 27 mM ± 2 mM), and average sodium liver T₂ * at 12 weeks (CCl₄ : 10 msec ± 1.0 msec, controls: 12 msec ± 1.9 msec). APT, TSC, and sodium T₂ * correlated significantly (P < 0.05) with Sirius Red staining and hydroxyproline levels.

DATA CONCLUSION

Liver TSC and APT significantly correlated with histopathologic markers of fibrosis in this mouse model.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 3.

Phosphate Groups in the Lipid A Moiety Determine the Effects of LPS on Hepatic Stellate Cells: A Role for LPS-Dephosphorylating Activity in Liver Fibrosis

Alkaline phosphatase (AP) activity is highly upregulated in plasma during liver diseases. Previously, we demonstrated that AP is able to detoxify lipopolysaccharide (LPS) by dephosphorylating its lipid A moiety. Because a role of gut-derived LPS in liver fibrogenesis has become evident, we now examined the relevance of phosphate groups in the lipid A moiety in this process. The effects of mono-phosphoryl and di-phosphoryl lipid A (MPLA and DPLA, respectively) were studied in vitro and LPS-dephosphorylating activity was studied in normal and fibrotic mouse and human livers. The effects of intestinal AP were studied in mice with CCL4-induced liver fibrosis. DPLA strongly stimulated fibrogenic and inflammatory activities in primary rat hepatic stellate cells (rHSCs) and RAW264.7 macrophages with similar potency as full length LPS. However, MPLA did not affect any of the parameters. LPS-dephosphorylating activity was found in mouse and human livers and was strongly increased during fibrogenesis. Treatment of fibrotic mice with intravenous intestinal-AP significantly attenuated intrahepatic desmin+- and αSMA+ -HSC and CD68+- macrophage accumulation. In conclusion, the lack of biological activity of MPLA, contrasting with the profound activities of DPLA, shows the relevance of LPS-dephosphorylating activity. The upregulation of LPS-dephosphorylating activity in fibrotic livers and the protective effects of exogenous AP during fibrogenesis indicate an important physiological role of intestinal-derived AP during liver fibrosis.

Endothelin-1 in portal hypertension: The intricate role of hepatic stellate cells

IMPACT STATEMENT

Portal hypertension is pathologically defined as increase of portal venous pressure, mainly due to chronic liver diseases such as fibrosis and cirrhosis. In fibrotic liver, activated hepatic stellate cells increase their contraction in response to endothelin-1 (ET-1) via autocrine and paracrine stimulation from liver sinusoidal endothelial cells and injured hepatocytes. Clinical studies are limited with ET receptor antagonists in cirrhotic patients with portal hypertension. Hence, studies are needed to find molecules that block ET-1 synthesis. Accumulation of extracellular matrix proteins in the perisinusoidal space, tissue contraction, and alteration in blood flow are prominent during portal hypertension. Therefore, novel matrix modulators should be tested experimentally as well as in clinical studies. Specifically, tumor necrosis factor-α, transforming growth factor-β1, Wnt, Notch, rho-associated protein kinase 1 signaling antagonists, and peroxisome proliferator-activated receptor α and γ, interferon-γ and sirtuin 1 agonists should be tested elaborately against cirrhosis patients with portal hypertension.

Chrysophanol attenuates hepatitis B virus X protein-induced hepatic stellate cell fibrosis by regulating endoplasmic reticulum stress and ferroptosis

Hepatitis B virus X protein (HBx) and hepatic stellate cells (HSCs) are critical for liver fibrosis development. Anti-fibrosis occurs via reversion to quiescent-type HSCs or clearance of HSCs via apoptosis or ferroptosis. We aimed to elucidate the role of chrysophanol in rat HSC-T6 cells expressing HBx and investigate whether chrysophanol (isolated from Rheum palmatum rhizomes) influences cell death via ferroptosis in vitro. Analysis of lipid reactive oxygen species (ROS), Bip, CHOP, p-IRE1α, GPX4, SLC7A11, α-SMA, and CTGF showed that chrysophanol attenuated HBx-repressed cell death. Chrysophanol can impair HBx-induced activation of HSCs via endoplasmic reticulum stress (ER stress) and ferroptosis-dependent and GPX4-independent pathways.

Bile Acid Sequestrant, Sevelamer Ameliorates Hepatic Fibrosis with Reduced Overload of Endogenous Lipopolysaccharide in Experimental Nonalcoholic Steatohepatitis

Despite the use of various pharmacotherapeutic strategies, fibrosis due to nonalcoholic steatohepatitis (NASH) remains an unsatisfied clinical issue. We investigated the effect of sevelamer, a hydrophilic bile acid sequestrant, on hepatic fibrosis in a murine NASH model. Male C57BL/6J mice were fed a choline-deficient, L-amino acid-defined, high-fat (CDHF) diet for 12 weeks with or without orally administered sevelamer hydrochloride (2% per diet weight). Histological and biochemical analyses revealed that sevelamer prevented hepatic steatosis, macrophage infiltration, and pericellular fibrosis in CDHF-fed mice. Sevelamer reduced the portal levels of total bile acid and inhibited both hepatic and intestinal farnesoid X receptor activation. Gut microbiome analysis demonstrated that sevelamer improved a lower α-diversity and prevented decreases in Lactobacillaceae and Clostridiaceae as well as increases in Desulfovibrionaceae and Enterobacteriaceae in the CDHF-fed mice. Additionally, sevelamer bound to lipopolysaccharide (LPS) in the intestinal lumen and promoted its fecal excretion. Consequently, the sevelamer treatment restored the tight intestinal junction proteins and reduced the portal LPS levels, leading to the suppression of hepatic toll-like receptor 4 signaling pathway. Furthermore, sevelamer inhibited the LPS-mediated induction of fibrogenic activity in human hepatic stellate cells in vitro. Collectively, sevelamer inhibited the development of murine steatohepatitis by reducing hepatic LPS overload.

Pro- and Anti-fibrogenic Functions of Gram-Negative Bacterial Lipopolysaccharide in the Liver

Extensive research performed over several decades has identified cells participating in the initiation and progression of fibrosis, and the numerous underlying inter- and intra-cellular signaling pathways. However, liver fibrosis continues to be a major clinical challenge as the precise targets of treatment are still elusive. Activation of physiologically quiescent perisinusoidal hepatic stellate cells (HSCs) to a myofibroblastic proliferating, contractile and fibrogenic phenotype is a critical event in the pathogenesis of chronic liver disease. Thus, elucidation of the mechanisms of the reversal to quiescence or inhibition of activated HSCs, and/or their elimination via apoptosis has been the focus of intense investigation. Lipopolysaccharide (LPS), a gut-resident Gram-negative bacterial endotoxin, is a powerful pro-inflammatory molecule implicated in hepatic injury, inflammation and fibrosis. In both acute and chronic liver injury, portal venous levels of LPS are elevated due to increased intestinal permeability. LPS, via CD14 and Toll-like receptor 4 (TLR4) and its adapter molecules, stimulates macrophages, neutrophils and several other cell types to produce inflammatory mediators as well as factors that can activate HSCs and stimulate their fibrogenic activity. LPS also stimulates synthesis of pro- and anti-inflammatory cytokines/chemokines, growth mediators and molecules of immune regulation by HSCs. However, LPS was found to arrest proliferation of activated HSCs and to convert them into non-fibrogenic phenotype. Interestingly, LPS can elicit responses in HSCs independent of CD14 and TLR4. Identifying and/or developing non-inflammatory but anti-fibrogenic mimetics of LPS could be relevant for treating liver fibrosis.