Interleukin‑10 promotes primary rat hepatic stellate cell senescence by upregulating the expression levels of p53 and p21

A molecular index for biological age identified from the metabolome and senescence-associated secretome in humans

Unlike chronological age, biological age is a strong indicator of health of an individual. However, the molecular fingerprint associated with biological age is ill-defined. To define a high-resolution signature of biological age, we analyzed metabolome, circulating senescence-associated secretome (SASP)/inflammation markers and the interaction between them, from a cohort of healthy and rapid agers. The balance between two fatty acid oxidation mechanisms, β-oxidation and ω-oxidation, associated with the extent of functional aging. Furthermore, a panel of 25 metabolites, Healthy Aging Metabolic (HAM) index, predicted healthy agers regardless of gender and race. HAM index was also validated in an independent cohort. Causal inference with machine learning implied three metabolites, β-cryptoxanthin, prolylhydroxyproline, and eicosenoylcarnitine as putative drivers of biological aging. Multiple SASP markers were also elevated in rapid agers. Together, our findings reveal that a network of metabolic pathways underlie biological aging, and the HAM index could serve as a predictor of phenotypic aging in humans.

Inhibition of endogenous hydrogen sulfide production reduces activation of hepatic stellate cells via the induction of cellular senescence

In chronic liver injury, quiescent hepatic stellate cells (HSCs) transdifferentiate into activated myofibroblast-like cells and produce large amounts of extracellular matrix components, e.g. collagen type 1. Cellular senescence is characterized by irreversible cell-cycle arrest, arrested cell proliferation and the acquisition of the senescence-associated secretory phenotype (SASP) and reversal of HSCs activation. Previous studies reported that H2S prevents induction of senescence via its antioxidant activity. We hypothesized that inhibition of endogenous H2S production induces cellular senescence and reduces activation of HSCs. Rat HSCs were isolated and culture-activated for 7 days. After activation, HSCs treated with H2S slow-releasing donor GYY4137 and/or DL-propargylglycine (DL-PAG), an inhibitor of the H2S-producing enzyme cystathionine γ-lyase (CTH), as well as the PI3K inhibitor LY294002. In our result, CTH expression was significantly increased in fully activated HSCs compared to quiescent HSCs and was also observed in activated stellate cells in a in vivo model of cirrhosis. Inhibition of CTH reduced proliferation and expression of fibrotic markers Col1a1 and Acta2 in HSCs. Concomitantly, DL-PAG increased the cell-cycle arrest markers Cdkn1a (p21), p53 and the SASP marker Il6. Additionally, the number of β-galactosidase positive senescent HSCs was increased. GYY4137 partially restored the proliferation of senescent HSCs and attenuated the DL-PAG-induced senescent phenotype. Inhibition of PI3K partially reversed the senescence phenotype of HSCs induced by DL-PAG. Inhibition of endogenous H2S production reduces HSCs activation via induction of cellular senescence in a PI3K-Akt dependent manner. Our results show that cell-specific inhibition of H2S could be a novel target for anti-fibrotic therapy via induced cell senescence.

Inflammatory response in mouse lungs to haze episodes under different backgrounds of particulate matter exposure

Particulate matter (PM) toxicity has mostly been investigated through in vitro exposure or tracheal infusion in animal models. However, given the complexity of ambient conditions, most animal studies do not mimic real-life PM exposure. In this work, we established a novel integrated exposure model to study the dynamic inflammatory response and defense strategies in ambient PM-exposed mice. Three groups of male C57BL/6 mice were kept in three chambers with pre-exposure to filtered air (FA), unfiltered air (UFA), or the air with a low PM concentration (PM2.5 ≤ 75 μg/m3) (LPM), respectively, for 37 days. Then all three groups of mice were exposed to haze challenge for 3 days, followed by exposure in filtered air for 7 days to allow recovery. Our results suggest that following a haze challenge, the defense strategies of mice of filtered air (FA) and low PM (LPM) groups comprised a form of "counterattack", whereas the response of the unfiltered air (UFA) group could be viewed as a "silence". While the latter strategy protected the lung tissues of mice from acute inflammatory damage, it also foreshadowed the development of chronic inflammatory diseases. These findings contribute to explaining previously documented PM-associated pathogenic mechanisms.

Upregulation of GLT25D1 in Hepatic Stellate Cells Promotes Liver Fibrosis via the TGF-β1/SMAD3 Pathway In Vivo and In vitro

BACKGROUND AND AIMS

Collagen β(1-O) galactosyltransferase 25 domain 1 (GLT25D1) is associated with collagen production and glycosylation, and its knockout in mice results in embryonic death. However, its role in liver fibrosis remains elusive, particularly in hepatic stellate cells (HSCs), the primary collagen-producing cells associated with liver fibrogenesis. Herein, we aimed to elucidate the role of GLT25D1 in HSCs.

METHODS

Bile duct ligation (BDL)-induced mouse liver fibrosis models, primary mouse HSCs (mHSCs), and transforming growth factor beta 1 (TGF-β1)-stimulated LX-2 human hepatic stellate cells were used in in vivo and in vitro studies. Stable LX-2 cell lines with either GLT25D1 overexpression or knockdown were established using lentiviral transfection. RNA-seq was performed to investigate the genomic differences. HPLC-MS/MS were used to identify glycosylation sites. Scanning electronic microscopy (SEM) and second-harmonic generation/two-photon excited fluorescence (SHG/TPEF) were used to image collagen fibril morphology.

RESULTS

GLT25D1 expression was upregulated in nonparenchymal cells in human cirrhotic liver tissues. Meanwhile, its knockdown attenuated collagen deposition in BDL-induced mouse liver fibrosis and inhibited mHSC activation. GLT25D1 was overexpressed in activated versus quiescence LX-2 cells and regulated in vitro LX-2 cell activation, including proliferation, contraction, and migration. GLT25D1 also significantly increased liver fibrogenic gene and protein expression. GLT25D1 upregulation promoted HSC activation and enhanced collagen expression through the TGF-β1/SMAD signaling pathway. Mass spectrometry showed that GLT25D1 regulated the glycosylation of collagen in HSCs, affecting the diameter of collagen fibers.

CONCLUSIONS

Collectively, the upregulation of GLT25D1 in HSCs promoted the progression of liver fibrosis by affecting HSCs activation and collagen stability.

Decursin ameliorates carbon tetrachloride-induced liver fibrosis by facilitating ferroptosis of hepatic stellate cells

Decursin possesses the potential to alleviate transforming growth factor (TGF)-β-induced hepatic stellate cells (HSCs) activation. However, the mechanisms by which decursin alleviates hepatic fibrosis remain not fully understood. Our aim is to explore the function of decursin on regulating HSCs activation and hepatic fibrosis. The anti-fibrotic effect of decursin was evaluated by Masson and Sirius red staining, and immunohistochemical (IHC) and quantitative real-time PCR (qRT-PCR) analysis for alpha-smooth muscle actin (α-SMA) and collagen types I (Col1a1) expression. Ferroptosis was assessed by measuring iron concentration, glutathione peroxidase 4 (Gpx4) and Prostaglandin endoperoxide synthase 2 (Ptgs2) expression, glutathione (GSH) level, lipid peroxidation, and reactive oxygen species (ROS) level. We found that decursin treatment decreased CCl4-induced liver fibrosis. The primary HSCs isolated from decursin-treated group showed an increased Fe2+, lipid ROS level, and decreased Gpx4 and GSH levels compared with HSCs from model group. Moreover, decursin promoted ferroptosis in activated HSCs in vitro, as evidenced by declined Gpx4 and GSH levels, increased Fe2+, ROS, and Ptgs2 levels compared with control. More important, ferroptosis inhibitor destroyed the anti-fibrosis effect of decursin on HSCs. In summary, these data suggest that decursin has potential to treat hepatic fibrosis.

Cellular and Molecular Mechanisms Underlying Liver Fibrosis Regression

Chronic liver injury of different etiologies may result in hepatic fibrosis, a scar formation process consisting in altered deposition of extracellular matrix. Progression of fibrosis can lead to impaired liver architecture and function, resulting in cirrhosis and organ failure. Although fibrosis was previous thought to be an irreversible process, recent evidence convincingly demonstrated resolution of fibrosis in different organs when the cause of injury is removed. In the liver, due to its high regenerative ability, the extent of fibrosis regression and reversion to normal architecture is higher than in other tissues, even in advanced disease. The mechanisms of liver fibrosis resolution can be recapitulated in the following main points: removal of injurious factors causing chronic hepatic damage, elimination, or inactivation of myofibroblasts (through various cell fates, including apoptosis, senescence, and reprogramming), inactivation of inflammatory response and induction of anti-inflammatory/restorative pathways, and degradation of extracellular matrix. In this review, we will discuss the major cellular and molecular mechanisms underlying the regression of fibrosis/cirrhosis and the potential therapeutic approaches aimed at reversing the fibrogenic process.

TLR3 Mediates Senescence and Immunosurveillance of Hepatic Stellate Cells

Background: Activation of hepatic stellate cells (HSCs) is an important driver of liver fibrosis, which is a health problem of global concern, and there is no effective solution for it at the present. Senescent activated HSCs are preferentially killed by natural killer cells (NK cells) to promote the regression of hepatic fibrosis. Objectives: The purpose of this study was to investigate the effect of polyinosinic-polycytidylic acid (poly I:C) on HSCs’ senescence, a trigger for NK cell-induced cytotoxicity. Methods: The senescence of HSCs was assessed by western blot, qRT-PCR, and flow cytometry, and NK cell cytotoxicity was assessed in a co-culture of NK cells with poly I:C-treated HSCs by measuring CD107a expression. Results: The expression of p16, p21, SA-β-gal, MICA/MICB, and ULBP2 increased in poly I:C-treated HSCs, rendering them significantly susceptible to NK cell cytotoxicity. Conclusions: Poly I:C induces cellular senescence in HSCs and triggers NK cell immunosurveillance, suggesting that the role of poly I:C in HSC senescence may promote fibrosis regression.

Efficient Preparation of Black Tea Extract (BTE) with the High Content of Theaflavin Mono- and Digallates and the Protective Effects of BTE on CCl4-Induced Rat Liver and Renal Injury

Theaflavins (TFs), formed by the dimerization of green tea catechins during "fermentation" to prepare black tea, possess antioxidant and anti-inflammatory effects. Reported efficacious effects of black tea (∼2% of TFs) or related products come from catechins unless TFs are assayed. The present study aimed to target the preparation of black tea extract (BTE) enriched with theaflavin mono- and digallates majorly from dry tea leaves in aqueous media versus traditional fermentation of fresh leaves. We further investigated the protective function of the produced BTE on rat liver and kidney injury induced by CCl₄ and its underlying molecular mechanisms. The results showed that BTE suppressed the activation level of hepatic stellate cells (HSCs), and the secretion of collagen was induced by CCl₄. The relative expression levels of TGF-β, p-ERK1/ERK1, p-ERK2/ERK2, p-Smad1/Smad1, and p-Smad2/Smad2 were reduced to 56, 68, 56, 44, and 32%, respectively, compared with those of CCl₄-treated rats. Therefore, BTE enriched with TFs prevented rat hepatic fibrosis through the TGF-β/Smad/ERK signaling pathway and kidney injury by inhibiting the expression of TGF-β and proinflammatory cytokines in rats. We predict the broad application of TFs and related products because of their strong antioxidant and inhibitory effects on chronic inflammation.

Silencing p53 inhibits interleukin 10-induced activated hepatic stellate cell senescence and fibrotic degradation in vivo

Activated hepatic stellate cells are reported to play a significant role in liver fibrogenesis. Beside the phenotype reversion and apoptosis of activated hepatic stellate cells, the senescence of activated hepatic stellate cells limits liver fibrosis. Our previous researches have demonstrated that interleukin-10 could promote hepatic stellate cells senescence via p53 signaling pathway in vitro. However, the relationship between expression of p53 and senescence of activated hepatic stellate cells induced by interleukin-10 in fibrotic liver is unclear. The purpose of present study was to explore whether p53 plays a crucial role in the senescence of activated hepatic stellate cells and degradation of collagen mediated by interleukin-10. Hepatic fibrosis animal model was induced by carbon tetrachloride through intraperitoneal injection and transfection of interleukin-10 gene to liver was performed by hydrodynamic-based transfer system. Depletions of p53 in vivo and in vitro were carried out by adenovirus-based short hairpin RNA against p53. Regression of fibrosis was assessed by liver biopsy and collagen staining. Cellular senescence in the liver was observed by senescence-associated beta-galactosidase (SA-β-Gal) staining. Immunohistochemistry, immunofluorescence double staining, and Western blot analysis were used to evaluate the senescent cell and senescence-related protein expression. Our data showed that interleukin-10 gene treatment could lighten hepatic fibrosis induced by carbon tetrachloride and induce the aging of activated hepatic stellate cells accompanied by up-regulating the expression of aging-related proteins. We further demonstrated that depletion of p53 could abrogate up-regulation of interleukin-10 on the expression of senescence-related protein in vivo and vitro. Moreover, p53 knockout in fibrotic mice could block not only the senescence of activated hepatic stellate cells, but also the degradation of fibrosis induced by interleukin-10 gene intervention. Taken together, our results suggested that interleukin-10 gene treatment could attenuate carbon tetrachloride-induced hepatic fibrosis by inducing senescence of activated hepatic stellate cells in vivo, and this induction was closely related to p53 signaling pathway.

Strategies Targeting the Innate Immune Response for the Treatment of Hepatitis C Virus-Associated Liver Fibrosis

Direct-acting antivirals eliminate hepatitis C virus (HCV) in more than 95% of treated individuals and may abolish liver injury, arrest fibrogenesis, and reverse fibrosis and cirrhosis. However, liver regeneration is usually a slow process that is less effective in the late stages of fibrosis. What is more, fibrogenesis may prevail in patients with advanced cirrhosis, where it can progress to liver failure and hepatocellular carcinoma. Therefore, the development of antifibrotic drugs that halt and reverse fibrosis progression is urgently needed. Fibrosis occurs due to the repair process of damaged hepatic tissue, which eventually leads to scarring. The innate immune response against HCV is essential in the initiation and progression of liver fibrosis. HCV-infected hepatocytes and liver macrophages secrete proinflammatory cytokines and chemokines that promote the activation and differentiation of hepatic stellate cells (HSCs) to myofibroblasts that produce extracellular matrix (ECM) components. Prolonged ECM production by myofibroblasts due to chronic inflammation is essential to the development of fibrosis. While no antifibrotic therapy is approved to date, several drugs are being tested in phase 2 and phase 3 trials with promising results. This review discusses current state-of-the-art knowledge on treatments targeting the innate immune system to revert chronic hepatitis C-associated liver fibrosis. Agents that cause liver damage may vary (alcohol, virus infection, etc.), but fibrosis progression shows common patterns among them, including chronic inflammation and immune dysregulation, hepatocyte injury, HSC activation, and excessive ECM deposition. Therefore, mechanisms underlying these processes are promising targets for general antifibrotic therapies.

miR-16 integrates signal pathways in myofibroblasts: determinant of cell fate necessary for fibrosis resolution

Liver fibrosis is characterized by the transdifferentiation of hepatic stellate cells (HSCs) to myofibroblasts and poor response to treatment. This can be attributed to the myofibroblast-specific resistance to phenotype reversal. In this study, we complemented miR-16 into miR-16-deficient myofibroblasts and analyzed the global role of miR-16 using transcriptome profiling and generating a pathway-based action model underlying transcriptomic regulation. Phenotypic analysis of myofibroblasts and fibrogenic characterization were used to understand the effect of miR-16 on phenotypic remodeling of myofibroblasts. miR-16 expression altered the transcriptome of myofibroblasts to resemble that of HSCs. Simultaneous targeting of Smad2 and Wnt3a, etc. by miR-16 integrated signaling pathways of TGF-β and Wnt, etc., which underlay the comprehensive regulation of transcriptome. The synergistic effect of miR-16 on the signaling pathways abolished the phenotypic characteristics of myofibroblasts, including collagen production and inhibition of adipogenesis. In vivo, myofibroblast-specific expression of miR-16 not only eliminated mesenchymal cells with myofibroblast characteristics but also restored the phenotype of HSCs in perisinusoidal space. This phenotypic remodeling resolved liver fibrosis induced by chronic wound healing. Therefore, miR-16 may integrate signaling pathways crucial for the fate determination of myofibroblasts. Its global effect induces the reversal of HSC-to-myofibroblast transdifferentiation and, subsequently, the resolution of fibrogenesis. Taken together, these findings highlight the potential of miR-16 as a promising therapeutic target for liver fibrosis.

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.

Cellular Interplay as a Consequence of Inflammatory Signals Leading to Liver Fibrosis Development

Inflammation has been known to be an important driver of fibrogenesis in the liver and onset of hepatic fibrosis. It starts off as a process meant to protect the liver from further damage, but it can become the main promoter of liver fibrosis. There are many inflammation-related pathways activated during liver fibrosis that lead to hepatic stellate cells (HSCs) activation and collagen-deposition in the liver. Such events are mostly modulated upstream of HSCs and involve signals from hepatocytes and innate immune cells. One particular event is represented by cell death during liver injury that generates multiple inflammatory signals that further trigger sterile inflammation and enhancement of inflammatory response. The assembly of inflammasome that responds to danger-associated molecular patterns (DAMPs) stimulates the release of pro-inflammatory cytokines and at the same time, initiates programmed cell death called pyroptosis. This review focuses on cellular and molecular mechanisms responsible for initiation and progress of inflammation in the liver.