ω-3 PUFAs ameliorate liver fibrosis and inhibit hepatic stellate cells proliferation and activation by promoting YAP/TAZ degradation

AMPK stimulation inhibits YAP/TAZ signaling to ameliorate hepatic fibrosis

Hepatic fibrosis is driven by the activation of hepatic stellate cells (HSCs). The Hippo pathway and its effectors, YAP and TAZ, are key regulators of HSC activation and fibrosis. However, there is a lack of mechanistic understanding of YAP/TAZ regulation in HSCs. Here we show that AMPK activation leads to YAP/TAZ inhibition and HSC inactivation in vitro, while the expression of a kinase-inactive mutant reversed these effects compared to wild type AMPKɑ1. Notably, the depletion of LATS1/2, an upstream kinase of YAP/TAZ signaling, rescues YAP/TAZ activation, suggesting that AMPK may be mediating YAP/TAZ inhibition via LATS1/2. In the carbon tetrachloride mouse model of fibrosis, pharmacologic activation of AMPK in HSCs inhibits YAP/TAZ signaling and reduces fibrosis. The findings implicate AMPK as a critical regulator of YAP/TAZ signaling and HSC inactivation and highlight AMPK activation as a therapeutic target for the treatment of hepatic fibrosis.

Abnormal metabolism in hepatic stellate cells: Pandora's box of MAFLD related hepatocellular carcinoma

Metabolic associated fatty liver disease (MAFLD) is a significant risk factor for the development of hepatocellular carcinoma (HCC). Hepatic stellate cells (HSCs), as key mediators in liver injury response, are believed to play a crucial role in the repair process of liver injury. However, in MAFLD patients, the normal metabolic and immunoregulatory mechanisms of HSCs become disrupted, leading to disturbances in the local microenvironment. Abnormally activated HSCs are heavily involved in the initiation and progression of HCC. The metabolic disorders and abnormal activation of HSCs not only initiate liver fibrosis but also contribute to carcinogenesis. In this review, we provide an overview of recent research progress on the relationship between the abnormal metabolism of HSCs and the local immune system in the liver, elucidating the mechanisms of immune imbalance caused by abnormally activated HSCs in MAFLD patients. Based on this understanding, we discuss the potential and challenges of metabolic-based and immunology-based mechanisms in the treatment of MAFLD-related HCC, with a specific focus on the role of HSCs in HCC progression and their potential as targets for anti-cancer therapy. This review aims to enhance researchers' understanding of the importance of HSCs in maintaining normal liver function and highlights the significance of HSCs in the progression of MAFLD-related HCC.

Role of Hippo pathway dysregulation from gastrointestinal premalignant lesions to cancer

BACKGROUND

First identified in Drosophila melanogaster, the Hippo pathway is considered a major regulatory cascade controlling tissue homeostasis and organ development. Hippo signaling components include kinases whose activity regulates YAP and TAZ final effectors. In response to upstream stimuli, YAP and TAZ control transcriptional programs involved in cell proliferation, cytoskeletal reorganization and stemness.

MAIN TEXT

While fine tuning of Hippo cascade components is essential for maintaining the balance between proliferative and non-proliferative signals, pathway signaling is frequently dysregulated in gastrointestinal cancers. Also, YAP/TAZ aberrant activation has been described in conditions characterized by chronic inflammation that precede cancer development, suggesting a role of Hippo effectors in triggering carcinogenesis. In this review, we summarize the architecture of the Hippo pathway and discuss the involvement of signaling cascade unbalances in premalignant lesions of the gastrointestinal tract, providing a focus on the underlying molecular mechanisms.

CONCLUSIONS

The biology of premalignant Hippo signaling dysregulation needs further investigation in order to elucidate the evolutionary trajectories triggering cancer inititation and develop effective early therapeutic strategies targeting the Hippo/YAP pathway.

Nobiletin Alleviated Epithelial-Mesenchymal Transition of Hepatocytes in Liver Fibrosis Based on Autophagy-Hippo/YAP Pathway

SCOPE

The current researches indicated that the epithelial-mesenchymal transition (EMT) of hepatocytes plays a crucial role in the development of liver fibrosis. To date, there is a paucity of literature regarding the impact of nobiletin (NOB) on liver fibrosis. This study investigates the inhibitory effect of NOB on EMT in hepatocytes during the progression of liver fibrosis and its underlying mechanism.

METHODS AND RESULTS

The findings demonstrated that NOB significantly suppresses liver fibrosis in carbon tetrachloride (CCl4 )-induced mice by reducing inflammation and fiber deposition in the liver. Moreover, NOB mitigates EMT in hepatocytes, concurrently alleviating inflammatory status and reducing the production of reactive oxygen species (ROS) generation. The comprehensive investigation reveals that the hepatoprotective effect of NOB in liver fibrosis is attributed to autophagy activation, as evidenced by a significant increase in LC3 II expression and p62 degradation upon NOB treatment. Additionally, NOB activates the Hippo/YAP pathway by downregulating YAP and its downstream targets in liver fibrosis, which is regulated by autophagy based on experiments with chloroquine (CQ), 3-methyladenine (3-MA), and siYAP intervention.

CONCLUSION

Therefore, this study provides evidences that NOB can protect hepatocytes from undergoing EMT during liver fibrosis by inducing autophagy and subsequently modulating the Hippo/YAP pathway.

Ginsenoside Rg3 promotes hepatic stellate cell ferroptosis by epigenetically regulating ACSL4 to suppress liver fibrosis progression

BACKGROUND

Ginsenoside Rg3 (G-Rg3), extracted from Panax notoginseng, possesses hepatoprotective properties. Hepatic stellate cells (HSCs) activation is responsible for liver fibrosis. Recent studies have reported the suppressive effects of G-Rg3 on HSC activation and proliferation. Ferroptosis is a novel iron regulated cell death. ACSL4, a key indicator of ferroptosis, is commonly methylated in various diseases.

PURPOSE

However, the role of ACSL4 methylation-mediated HSC ferroptosis in G-Rg3 inhibition of hepatic fibrosis needs to be explored.

METHODS

Effects of G-Rg3 on inhibiting fibrosis were evaluated in vivo and in vitro. The impact of G-Rg3 on HSC ferroptosis was assessed in vitro. Furthermore, the expression of ACSL4, ACSL4 methylation and microRNA-6945-3p (miR-6945-3p) levels were determined.

RESULTS

G-Rg3 significantly alleviated CCl4-induced liver fibrosis, accompanied by collagen downregulation. In vitro, G-Rg3 contributed to HSC inactivation, leading to decreased collagen production. G-Rg3 induced HSC ferroptosis, characterized by increased iron accumulation, depletion of glutathione, malondialdehyde levels, and generation of lipid reactive oxygen species. Moreover, G-Rg3 promoted ACSL4 demethylation and restored its expression. Notably, DNMT3B counteracted the effect of G-Rg3-mediated inhibition of ACSL4 methylation and was targeted by miR-6945-3p. Further investigations revealed that G-Rg3 suppressed ACSL4 methylation through miR-6945-3p-mediated DNMT3B inhibition. Consistent with this, miR-6945-3p inhibition reversed G-Rg3-induced ACSL4 expression and HSC ferroptosis.

CONCLUSION

G-Rg3 inhibits ACSL4 methylation by miR-6945-3p-mediated DNMT3B inhibition, thereby promoting HSC ferroptosis and mitigating liver fibrosis.

SLIT3 knockdown inhibited TGF-β-induced hepatic stellate cells activation by down-regulating YAP signal

Objective

Liver fibrosis is a chronic liver disease caused by a variety of pathophysiological. However, there are no effective treatments to combat it. HSCs are a major source of fibrotic cells and exploring the mechanisms of HSC activation may provide new strategies for the treatment of liver fibrosis.

Objectives

To explore the role and underlying mechanism of SLIT3 in HSCs fibrosis.

Results

GSE163211 dataset analysis identified aberrant expression of SLIT3 in NASH F1-F4 tissues and SLIT3 expression level was positively correlated with fibrosis-related proteins. In vitro experiments showed that TGF-β induced upregulation of SLIT3 in LX-2 cells. Knockdown of SLIT3 significantly inhibited TGF-β-induced α-SMA, COL1A2, and COL1A1 expression, inhibited excessive cell proliferation and migration, and suppressed YAP activity.

Conclusion

Collectively, our findings suggest that SLIT3 deficiency alleviates TGF-β-induced HSCs activation by inhibiting YAP activity.

Regulators, functions, and mechanotransduction pathways of matrix stiffness in hepatic disease

The extracellular matrix (ECM) provides physical support and imparts significant biochemical and mechanical cues to cells. Matrix stiffening is a hallmark of liver fibrosis and is associated with many hepatic diseases, especially liver cirrhosis and carcinoma. Increased matrix stiffness is not only a consequence of liver fibrosis but is also recognized as an active driver in the progression of fibrotic hepatic disease. In this article, we provide a comprehensive view of the role of matrix stiffness in the pathological progression of hepatic disease. The regulators that modulate matrix stiffness including ECM components, MMPs, and crosslinking modifications are discussed. The latest advances of the research on the matrix mechanics in regulating intercellular signaling and cell phenotype are classified, especially for hepatic stellate cells, hepatocytes, and immunocytes. The molecular mechanism that sensing and transducing mechanical signaling is highlighted. The current progress of ECM stiffness's role in hepatic cirrhosis and liver cancer is introduced and summarized. Finally, the recent trials targeting ECM stiffness for the treatment of liver disease are detailed.

Role of the Hippo pathway in liver regeneration and repair: recent advances

Although the signaling pathways involved in normal liver regeneration have been well characterized, less has been done for livers affected by chronic tissue damage. These "abnormal livers" have an impaired regenerative response that leads to liver repair and fibrosis. The tumor suppressor Hippo pathway plays a key role in liver regeneration and repair. On this basis, this review discusses recent studies focusing on the involvement of the Hippo signaling pathway during "normal healthy liver regeneration" (i.e., in a normal liver after 2/3 partial hepatectomy) and "abnormal liver regeneration" (i.e., in a liver damaged by chronic disease). This could be an important question to address with respect to new therapies aimed at improving impaired liver regenerative responses. The studies reported here have shown that activation of the Hippo coactivators YAP/TAZ during normal liver regeneration promotes the formation of a new bile duct network through direct BEC proliferation or/and hepatocyte dedifferentiation to HPCs which can trans-differentiate to BECs. Moreover, YAP/TAZ signaling interaction with other signaling pathways mediates the recruitment and activation of Kupffer cells, which release mitogenic cytokines for parenchymal and/or non-parenchymal cells and engage in phagocytosis of cellular debris. In addition, YAP-mediated activation of stellate cells (HSCs) promotes liver regeneration through the synthesis of extracellular matrix. However, in chronically diseased livers, where the predetermined threshold for proper liver regeneration is exceeded, YAP/TAZ activation results in a reparative process characterized by liver fibrosis. In this condition, YAP/TAZ activation in parenchymal and non-parenchymal cells results in (i) differentiation of quiescent HSCs into myofibroblastic HSCs; (ii) recruitment of macrophages releasing inflammatory cytokines; (iii) polarization of macrophages toward the M2 phenotype. Since accumulation of damaged hepatocytes in chronic liver injury represent a significant risk factor for the development of hepatocarcinoma, this review also discussed the involvement of the Hippo pathway in the clearance of damaged cells.

TKF, a mexicanolide-type limonoid derivative, suppressed hepatic stellate cells activation and liver fibrosis through inhibition of the YAP/Notch3 pathway

BACKGROUND

Liver fibrosis is a common scarring response and may ultimately lead to liver cancer, unfortunately, there is currently no effective antifibrotic drug approved for human use. Limonoids exhibit a broad spectrum of biological activities; however, the potential role of limonoids against fibrosis is largely unknown.

PURPOSE

This study investigates the antifibrotic activities and potential mechanisms of TKF (3-tigloyl-khasenegasin F), a natural mexicanolide-type limonoid derivative.

STUDY DESIGN/METHODS

Two well-established mouse models (CCl₄ challenge and bile duct ligation) were used to assess anti-fibrotic effects of TKF in vivo. Human hepatic stellate cell (HSC) line LX-2 and mouse primary hepatic stellate cells (pHSCs) also served as in vitro liver fibrosis models.

RESULT

TKF administration significantly attenuated hepatic histopathological injury and collagen accumulation and suppressed fibrogenesis-associated gene expression including Col1a1, Acta2, and Timp1. In LX-2 cells and mouse pHSCs, TKF dose-dependently suppressed HSC activation and the expression levels of fibrogenic markers. Mechanistic studies showed that TKF inhibited Notch3-Hes1 and YAP signalings in vivo and in vitro. Furthermore, YAP inhibition or knockdown downregulated the Notch3 expression; however, Notch3 inhibition or knockdown did not affect the level of YAP in activated HSC. We revealed that TKF inhibited Notch3-Hes1 activation and downregulated hepatic fibrogenic gene expression via inhibiting YAP.

CONCLUSION

The therapeutic benefit of TKF against liver fibrosis results from inhibition of YAP and Notch3-Hes1 pathways, indicating that TKF may be a novel therapeutic candidate for liver fibrosis.

Sirtuin 6 protects against hepatic fibrogenesis by suppressing the YAP and TAZ function

Hepatic fibrosis occurs in response to prolonged tissue injury in the liver, which results in abnormal accumulation of extracellular matrix. Hepatic stellate cells (HSCs) have been suggested to play a major role in liver fibrosis. However, the molecular mechanisms remain incompletely understood. Sirtuin 6 (SIRT6), an NAD⁺ -dependent deacetylase, has been previously implicated in the regulation of the transforming growth factor β (TGFβ)-SMAD3 pathway that plays a significant role in liver fibrosis. In this work, we aimed to identify other important players during hepatic fibrogenesis, which are modulated by SIRT6. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ or WWTR1), key players in the Hippo pathway, have been implicated in the promotion of hepatic fibrosis. Our data show that HSC-specific Sirt6 knockout mice are more susceptible to high-fat-cholesterol-cholate diet-induced hepatic fibrosis than their wildtype counterparts. Our signaling analyses suggest that in addition to the TGFβ-SMAD3 pathway, YAP and TAZ are also highly activated in the SIRT6-deficient HSCs. As it is not clear how SIRT6 might regulate YAP and TAZ, we have decided to elucidate the mechanism underlying the regulation of YAP and TAZ by SIRT6 in HSCs. Overexpression or knockdown of SIRT6 corroborates the role of SIRT6 in the negative regulation of YAP and TAZ. Further biochemical analyses reveal that SIRT6 deacetylates YAP and TAZ and reprograms the composition of the TEA domain transcription factor complex to suppress their downstream target genes, particularly those involved in hepatic fibrosis. In conclusion, our data suggest that SIRT6 plays a critical role in the regulation of the Hippo pathway to protect against hepatic fibrosis.

BMP4 and Gremlin 1 regulate hepatic cell senescence during clinical progression of NAFLD/NASH

The role of hepatic cell senescence in human non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) is not well understood. To examine this, we performed liver biopsies and extensive characterization of 58 individuals with or without NAFLD/NASH. Here, we show that hepatic cell senescence is strongly related to NAFLD/NASH severity, and machine learning analysis identified senescence markers, the BMP4 inhibitor Gremlin 1 in liver and visceral fat, and the amount of visceral adipose tissue as strong predictors. Studies in liver cell spheroids made from human stellate and hepatocyte cells show BMP4 to be anti-senescent, anti-steatotic, anti-inflammatory and anti-fibrotic, whereas Gremlin 1, which is particularly highly expressed in visceral fat in humans, is pro-senescent and antagonistic to BMP4. Both senescence and anti-senescence factors target the YAP/TAZ pathway, making this a likely regulator of senescence and its effects. We conclude that senescence is an important driver of human NAFLD/NASH and that BMP4 and Gremlin 1 are novel therapeutic targets.

Dysregulation of Subcutaneous White Adipose Tissue Inflammatory Environment Modelling in Non-Insulin Resistant Obesity and Responses to Omega-3 Fatty Acids – A Double Blind, Randomised Clinical Trial

Background

Obesity is associated with enhanced lipid accumulation and the expansion of adipose tissue accompanied by hypoxia and inflammatory signalling. Investigation in human subcutaneous white adipose tissue (scWAT) in people living with obesity in which metabolic complications such as insulin resistance are yet to manifest is limited, and the mechanisms by which these processes are dysregulated are not well elucidated. Long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFAs) have been shown to modulate the expression of genes associated with lipid accumulation and collagen deposition and reduce the number of inflammatory macrophages in adipose tissue from individuals with insulin resistance. Therefore, these lipids may have positive actions on obesity associated scWAT hypertrophy and inflammation.

Methods

To evaluate obesity-associated tissue remodelling and responses to LC n-3 PUFAs, abdominal scWAT biopsies were collected from normal weight individuals and those living with obesity prior to and following 12-week intervention with marine LC n-3 PUFAs (1.1 g EPA + 0.8 g DHA daily). RNA sequencing, qRT-PCR, and histochemical staining were used to assess remodelling- and inflammatory-associated gene expression, tissue morphology and macrophage infiltration.

Results

Obesity was associated with scWAT hypertrophy (P < 0.001), hypoxia, remodelling, and inflammatory macrophage infiltration (P = 0.023). Furthermore, we highlight the novel dysregulation of Wnt signalling in scWAT in non-insulin resistant obesity. LC n-3 PUFAs beneficially modulated the scWAT environment through downregulating the expression of genes associated with inflammatory and remodelling pathways (P <0.001), but there were altered outcomes in individuals living with obesity in comparison to normal weight individuals.

Conclusion

Our data identify dysregulation of Wnt signalling, hypoxia, and hypertrophy, and enhanced macrophage infiltration in scWAT in non-insulin resistant obesity. LC n-3 PUFAs modulate some of these processes, especially in normal weight individuals which may be preventative and limit the development of restrictive and inflammatory scWAT in the development of obesity. We conclude that a higher dose or longer duration of LC n-3 PUFA intervention may be needed to reduce obesity-associated scWAT inflammation and promote tissue homeostasis.

Clinical Trial Registration

www.isrctn.com, identifier ISRCTN96712688.

Roles of Yes-associated protein and transcriptional coactivator with PDZ-binding motif in non-neoplastic liver diseases

The prevalence of liver disease has been increasing worldwide. Moreover, the burden of end-stage liver disease, including cirrhosis and liver cancer, is high because of high mortality and suboptimal treatment. The pathological process of liver disease includes steatosis, hepatocyte death, and fibrosis, which ultimately lead to cirrhosis and liver cancer. Clinical and preclinical evidence indicates that non-neoplastic liver diseases, particularly cirrhosis, are major risk factors for liver cancer, although the mechanism underlying this association remains unclear. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are transcriptional activators that regulate organ size and cancer development. YAP and TAZ play important roles in liver development, regeneration, and homeostasis. Abnormal YAP and TAZ levels have also been implicated in non-neoplastic liver diseases (e.g., non-alcoholic fatty liver disease, alcoholic liver disease, liver injury, and liver fibrosis). Here, we review recent findings on the roles of YAP and TAZ in non-neoplastic liver diseases and discuss directions for future research. This review provides a basis for the study of non-neoplastic liver diseases.

New Insights into Hippo/YAP Signaling in Fibrotic Diseases

Fibrosis results from defective wound healing processes often seen after chronic injury and/or inflammation in a range of organs. Progressive fibrotic events may lead to permanent organ damage/failure. The hallmark of fibrosis is the excessive accumulation of extracellular matrix (ECM), mostly produced by pathological myofibroblasts and myofibroblast-like cells. The Hippo signaling pathway is an evolutionarily conserved kinase cascade, which has been described well for its crucial role in cell proliferation, apoptosis, cell fate decisions, and stem cell self-renewal during development, homeostasis, and tissue regeneration. Recent investigations in clinical and pre-clinical models has shown that the Hippo signaling pathway is linked to the pathophysiology of fibrotic diseases in many organs including the lung, heart, liver, kidney, and skin. In this review, we have summarized recent evidences related to the contribution of the Hippo signaling pathway in the development of organ fibrosis. A better understanding of this pathway will guide us to dissect the pathophysiology of fibrotic disorders and develop effective tissue repair therapies.

Empagliflozin Reduces the Progression of Hepatic Fibrosis in a Mouse Model and Inhibits the Activation of Hepatic Stellate Cells via the Hippo Signalling Pathway

Hepatic fibrosis is the excessive production and deposition of the extracellular matrix, resulting in the activation of the fibrogenic phenotype of hepatic stellate cells (HSCs). The Hippo/Yes-associated protein (YAP) signalling pathway is a highly conserved kinase cascade that is critical in regulating cell proliferation, differentiation, and survival, and controls stellate cell activation. Empagliflozin, a sodium-glucose cotransporter type-2 inhibitor, is an antidiabetic drug that may prevent fibrotic progression by reducing hepatic steatosis and inflammation. However, little is known about its mechanism of action in liver fibrosis. In this study, we used male C57 BL/6 J mice fed a choline-deficient, l-amino acid-defined, high-fat diet (CDAHFD) as a model for hepatic fibrosis. For 5 weeks, the mice received either a vehicle or empagliflozin based on their assigned group. Empagliflozin attenuated CDAHFD-induced liver fibrosis. Thereafter, we identified the Hippo pathway, along with its effector, YAP, as a key pathway in the mouse liver. Hippo signalling is inactivated in the fibrotic liver, but empagliflozin treatment activated Hippo signalling and decreased YAP activity. In addition, empagliflozin downregulated the expression of pro-fibrogenic genes and activated Hippo signalling in HSCs. We identified a mechanism by which empagliflozin ameliorates liver fibrosis.

Influence of Varying Dietary ω6 to ω3 Fatty Acid Ratios on the Hepatic Transcriptome, and Association with Phenotypic Traits (Growth, Somatic Indices, and Tissue Lipid Composition), in Atlantic Salmon (Salmo salar)

Simple Summary

Plant oils are routinely used in fish feeds as a fish oil replacement. However, these terrestrial alternatives typically contain high levels of ω6 fatty acids (FA) and, thus, high ω6 to ω3 (ω6:ω3) FA ratios, which influence farmed fish and their consumers. The ω6:ω3 ratio is known to affect many biological processes (e.g., inflammation, FA metabolism) and human diseases; however, its impacts on fish physiology and the underlying molecular mechanisms are less well understood. In this study, we used 44 K microarrays to examine which genes and molecular pathways are altered by variation in dietary ω6:ω3 in Atlantic salmon. Our microarray study showed that several genes related to immune response, lipid metabolism, cell proliferation, and translation were differentially expressed between the two extreme ω6:ω3 dietary treatments. We also revealed that the PPARα activation-related transcript helz2 is a potential novel molecular biomarker of tissue variation in ω6:ω3. Further, correlation analyses illustrated the relationships between liver transcript expression and tissue (liver, muscle) lipid composition, and other phenotypic traits in salmon fed low levels of fish oil. This nutrigenomic study enhanced the current understanding of Atlantic salmon gene expression response to varying dietary ω6:ω3.

Abstract

The importance of dietary omega-6 to omega-3 (ω6:ω3) fatty acid (FA) ratios for human health has been extensively examined. However, its impact on fish physiology, and the underlying molecular mechanisms, are less well understood. This study investigated the influence of plant-based diets (12-week exposure) with varying ω6:ω3 (0.4–2.7) on the hepatic transcriptome of Atlantic salmon. Using 44 K microarray analysis, genes involved in immune and inflammatory response (lect2a, itgb5, helz2a, p43), lipid metabolism (helz2a), cell proliferation (htra1b), control of muscle and neuronal development (mef2d) and translation (eif2a, eif4b1, p43) were identified; these were differentially expressed between the two extreme ω6:ω3 dietary treatments (high ω6 vs. high ω3) at week 12. Eight out of 10 microarray-identified transcripts showed an agreement in the direction of expression fold-change between the microarray and qPCR studies. The PPARα activation-related transcript helz2a was confirmed by qPCR to be down-regulated by high ω6 diet compared with high ω3 diet. The transcript expression of two helz2 paralogues was positively correlated with ω3, and negatively with ω6 FA in both liver and muscle, thus indicating their potential as biomarkers of tissue ω6:ω3 variation. Mef2d expression in liver was suppressed in the high ω6 compared to the balanced diet (ω6:ω3 of 2.7 and 0.9, respectively) fed fish, and showed negative correlations with ω6:ω3 in both tissues. The hepatic expression of two lect2 paralogues was negatively correlated with viscerosomatic index, while htra1b correlated negatively with salmon weight gain and condition factor. Finally, p43 and eif2a were positively correlated with liver Σω3, while these transcripts and eif4b2 showed negative correlations with 18:2ω6 in the liver. This suggested that some aspects of protein synthesis were influenced by dietary ω6:ω3. In summary, this nutrigenomic study identified hepatic transcripts responsive to dietary variation in ω6:ω3, and relationships of transcript expression with tissue (liver, muscle) lipid composition and other phenotypic traits.

Targeting acid ceramidase inhibits YAP/TAZ signaling to reduce fibrosis in mice

Hepatic stellate cells (HSCs) drive hepatic fibrosis. Therapies that inactivate HSCs have clinical potential as antifibrotic agents. We previously identified acid ceramidase (aCDase) as an antifibrotic target. We showed that tricyclic antidepressants (TCAs) reduce hepatic fibrosis by inhibiting aCDase and increasing the bioactive sphingolipid ceramide. We now demonstrate that targeting aCDase inhibits YAP/TAZ activity by potentiating its phosphorylation-mediated proteasomal degradation via the ubiquitin ligase adaptor protein β-TrCP. In mouse models of fibrosis, pharmacologic inhibition of aCDase or genetic knockout of aCDase in HSCs reduces fibrosis, stromal stiffness, and YAP/TAZ activity. In patients with advanced fibrosis, aCDase expression in HSCs is increased. Consistently, a signature of the genes most down-regulated by ceramide identifies patients with advanced fibrosis who could benefit from aCDase targeting. The findings implicate ceramide as a critical regulator of YAP/TAZ signaling and HSC activation and highlight aCDase as a therapeutic target for the treatment of fibrosis.

Hippo signaling pathway in companion animal diseases, an under investigated signaling cascade

The Hippo pathway is a highly conserved kinase cascade in mammals with the proteins YAP and TAZ as its most important downstream effectors that shuttle between cytoplasma and nucleus. It has a crucial role in processes such as embryogenesis, organ size control, homeostasis and tissue regeneration, where mechanosensing and/or cell-cell interactions are involved. As the pathway is associated with many essential functions in the body, its dysregulation is related to many diseases. In contrast to human pathology, a PubMed-search on Hippo, YAP/TAZ and companion animals (horse, equine, dog, canine, cat, feline) retrieved few publications. Because of its high level of functional conservation, it is anticipated that also in veterinary sciences aberrant Hippo YAP/TAZ signaling would be implicated in animal pathologies. Publications on Hippo YAP/TAZ in companion animals are mainly in cats and dogs and related to oncology. Here, we emphasize the important role of YAP/TAZ in liver diseases. First the liver has a remarkable regeneration capacity and a strict size control and the liver has a moderate liver cell renewal (homeostasis). The last years numerous papers show the importance of YAP/TAZ in hepatocellular carcinoma (HCC), hepatocyte differentiation and bile duct epithelial (BEC) cell survival. YAP/TAZ signaling is involved in activation of hepatic stellate cells crucial in fibrogenesis. The availability of drugs (e.g. verteporfin) targeting the YAP/TAZ pathway are described as is their potential usage in veterinary medicine. The aim of this overview is to stimulate researchers' and clinicians' interest in the potential role of Hippo YAP/TAZ signaling in veterinary medicine.

Exploratory Data Analysis of Cell and Mitochondrial High-Fat, High-Sugar Toxicity on Human HepG2 Cells

Non-alcoholic steatohepatitis (NASH), one of the deleterious stages of non-alcoholic fatty liver disease, remains a significant cause of liver-related morbidity and mortality worldwide. In the current work, we used an exploratory data analysis to investigate time-dependent cellular and mitochondrial effects of different supra-physiological fatty acids (FA) overload strategies, in the presence or absence of fructose (F), on human hepatoma-derived HepG2 cells. We measured intracellular neutral lipid content and reactive oxygen species (ROS) levels, mitochondrial respiration and morphology, and caspases activity and cell death. FA-treatments induced a time-dependent increase in neutral lipid content, which was paralleled by an increase in ROS. Fructose, by itself, did not increase intracellular lipid content nor aggravated the effects of palmitic acid (PA) or free fatty acids mixture (FFA), although it led to an up-expression of hepatic fructokinase. Instead, F decreased mitochondrial phospholipid content, as well as OXPHOS subunits levels. Increased lipid accumulation and ROS in FA-treatments preceded mitochondrial dysfunction, comprising altered mitochondrial membrane potential (ΔΨm) and morphology, and decreased oxygen consumption rates, especially with PA. Consequently, supra-physiological PA alone or combined with F prompted the activation of caspase pathways leading to a time-dependent decrease in cell viability. Exploratory data analysis methods support this conclusion by clearly identifying the effects of FA treatments. In fact, unsupervised learning algorithms created homogeneous and cohesive clusters, with a clear separation between PA and FFA treated samples to identify a minimal subset of critical mitochondrial markers in order to attain a feasible model to predict cell death in NAFLD or for high throughput screening of possible therapeutic agents, with particular focus in measuring mitochondrial function.

Mechanisms and disease consequences of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide. Its more advanced subtype, nonalcoholic steatohepatitis (NASH), connotes progressive liver injury that can lead to cirrhosis and hepatocellular carcinoma. Here we provide an in-depth discussion of the underlying pathogenetic mechanisms that lead to progressive liver injury, including the metabolic origins of NAFLD, the effect of NAFLD on hepatic glucose and lipid metabolism, bile acid toxicity, macrophage dysfunction, and hepatic stellate cell activation, and consider the role of genetic, epigenetic, and environmental factors that promote fibrosis progression and risk of hepatocellular carcinoma in NASH.

Endogenous production of n-3 polyunsaturated fatty acids protects mice from carbon tetrachloride-induced liver fibrosis by regulating mTOR and Bcl-2/Bax signalling pathways

NEW FINDINGS

What is the central question of this study? What is the protective benefit of n-3 polyunsaturated fatty acids (PUFAs) on liver fibrosis and what are the relevant signalling pathways in a transgenic mouse model overexpressing the mfat-1 enzyme? What is the main finding and its importance? n-3 PUFA elevation strongly prevented carbon tetrachloride (CCl₄ )-induced hepatic damage and inhibited the activation of hepatic stellate cells. n-3 PUFAs suppressed CCl₄ -induced activation of mTOR, elevated Bcl-2 expression, and reduced Bax level, suggesting that n-3 PUFAs can render strong protective effects against liver fibrosis and point to the potential of mfat-1 gene therapy as a treatment modality.

ABSTRACT

Liver fibrosis is a reversible wound healing response with excessive accumulation of extracellular matrix proteins. It is a globally prevalent disease with ultimately severe pathological consequences. However, very few current clinical therapeutic options are available. Nutritional addition of n-3 polyunsaturated fatty acids (PUFAs) can delay and lessen the development of liver fibrosis. Herein, this study examined the protective benefit of n-3 PUFAs on liver fibrosis and the relevant signalling pathways using a transgenic mouse model overexpressing the mfat-1 enzyme that converts n-6 to n-3 PUFAs. Male C57BL/6 wild-type and mfat-1 transgenic mice were administered carbon tetrachloride (CCl₄ ) or control corn oil by intraperitoneal injection. Blood alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were subsequently measured. CCl₄ -induced hepatic damage and fibrosis were assessed using haematoxylin-eosin and Masson's trichrome staining. Western blot assays were used to detect and quantify fibrosis-related proteins and mechanistic target of rapamycin (mTOR) and B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein (Bax) signalling components. The direct effect of docosahexaenoic acid (DHA) on primary hepatic stellate cells (HSCs) was also investigated in a co-culture experiment. n-3 PUFAs, as a result of mfat-1 activity, had a strong protective effect on liver fibrosis. The elevation of ALT and AST induced by CCl₄ was significantly lessened in the mfat-1 mice. Histological determination revealed the protective effects of n-3 PUFAs on liver inflammation and collagen deposition. Co-incubation with DHA reduced the expression of profibrogenic factors in the primary HSCs. Moreover, mfat-1 transgenic mice showed significant reduction of proteins that are involved in mTOR and Bcl-2/Bax signalling pathways. Collectively, these results suggest that n-3 PUFA elevation strongly prevents CCl₄ -induced hepatic damage by directly inhibiting the activation of HSCs and regulating the basal activity of the mTOR and Bcl-2/Bax signalling pathways. Gene therapy applying mfat-1 and elevating n-3 PUFAs represents a promising treatment strategy to prevent liver fibrosis.

Ileum Gene Expression in Response to Acute Systemic Inflammation in Mice Chronically Fed Ethanol: Beneficial Effects of Elevated Tissue n-3 PUFAs

Chronic alcohol consumption leads to disturbances in intestinal function which can be exacerbated by inflammation and modulated by different factors, e.g., polyunsaturated fatty acids (PUFAs). The mechanisms underlying these alterations are not well understood. In this study, RNA-seq analysis was performed on ileum tissue from WT and fat-1 transgenic mice (which have elevated endogenous n-3 PUFAs). Mice were chronically fed ethanol (EtOH) and challenged with a single lipopolysaccharide (LPS) dose to induce acute systemic inflammation. Both WT and fat-1 mice exhibited significant ileum transcriptome changes following EtOH + LPS treatment. Compared to WT, fat-1 mice had upregulated expression of genes associated with cell cycle and xenobiotic metabolism, while the expression of pro-inflammatory cytokines and pro-fibrotic genes was decreased. In response to EtOH + LPS, fat-1 mice had an increased expression of genes related to antibacterial B cells (APRIL and IgA), as well as an elevation in markers of pro-restorative macrophages and γδ T cells that was not observed in WT mice. Our study significantly expands the knowledge of regulatory mechanisms underlying intestinal alterations due to EtOH consumption and inflammation and identifies the beneficial transcriptional effects of n-3 PUFAs, which may serve as a viable nutritional intervention for intestinal damage resulting from excessive alcohol consumption.

Therapeutic effects of Chlorella vulgaris on carbon tetrachloride induced liver fibrosis by targeting Hippo signaling pathway and AMPK/FOXO1 axis

This study was conducted to present the mechanism of the therapeutic effects of Chlorella vulgaris extract (CV) on the carbon tetrachloride (CCl₄) induced liver fibrosis model. Primarily, the mechanism of antioxidant effects of CV were investigated via measuring the expression of forkhead box protein O1 (FOXO1) and phosphorylated 5' adenosine monophosphate-activated protein kinase (p-AMPK) as upstream regulators of superoxide dismutase (SOD) and catalase (CAT). Subsequently, we investigated the regulatory effect of CV treatment on the yes-associated protein (YAP) and transcriptional coactivators with a PDZ-binding motif (TAZ) as fibrogenic factors. Male Wistar rats received CCl₄ and olive oil solution 1 ml/kg intraperitoneally for 12 weeks, twice weekly. CV 50 and 100 mg/kg were administered on a daily basis by gavage in the last 4 weeks. Ultimately, liver marker enzymes and hepatic hydroxyproline content were measured. The activity of SOD and CAT and the expression of YAP, TAZ, FOXO1, SOD, and CAT were analyzed. Finally, the protein levels of YAP, TAZ, and p-AMPK were detected. CV administration decreased liver marker enzymes and hydroxyproline content significantly. The expression and protein levels of YAP and TAZ reduced by CV treatment. Furthermore, the augmentation of expression and function of CAT and SOD by CV treatment was followed by an increase in the expression of FOXO1 and protein level of p-AMPK. Our data revealed that the stimulation of expression and function of SOD and CAT by CV treatment could be mediated by FOXO1/p-AMPK axis. Moreover, anti-fibrotic effect of CV might be associated with its inhibitory effect on the hepatic expression of YAP and TAZ. Chlorella vulgaris treatment ameliorates liver fibrosis via two cellular mechanisms. A) Likely, Chlorella vulgaris treatment increases gene expression of enzymatic antioxidants superoxide dismutase (SOD) and catalase (CAT) via upregulating its upstream regulatory elements i.e. phosphorylated 5' adenosine monophosphate-activated protein kinase (p-AMPK) and forkhead box protein O1 (FOXO1). These possible regulatory effects maybe lead to reduce reactive oxygen species level (ROS). B) Chlorella vulgaris treatment decreases hepatic protein level and gene expression of key elements of Hippo signaling pathway i.e. Yes-associated protein (YAP) and Transcriptional coactivators with a PDZ-binding motif (TAZ). Figure created with BioRender ( https://biorender.com ). ROS: Reactive oxygen species, YAP: Yes-associated protein, TAZ: Transcriptional coactivators with a PDZ-binding motif, FOXO1: Fork head Box O1, AMPK: 5' adenosine monophosphate activated protein kinase, SOD: Superoxide dismutase, CAT: Catalase, P: Phosphate group.

Exosomal miR-107 antagonizes profibrotic phenotypes of pericytes by targeting a pathway involving HIF-1/Notch1/PDGFR/YAP1/Twist1 axis in vitro

Microvascular pericytes have been demonstrated as an origin for myofibroblasts that produce excessive extracellular matrix (ECM) proteins such as α-smooth muscle actin (α-SMA) and type I collagen (ColIA1) and contribute to pulmonary fibrosis (PF). However, the signaling mechanism responsible for ECM production within pericytes is poorly understood. In this study, we examined exosomal miR-107 in the fibrotic phenotypes of pericytes and the pathogenesis of PF. Using RT-qPCR, MiR-107 level was compared between clinical or bleomycin-induced PF and normal pulmonary tissues. Exosomes were isolated from cultured microvascular endothelial cells (ECs) derived from either normal or PF tissues, characterized using dynamic light scattering, transmission electron microscopy, flow cytometry, Western blot, and immunofluorescence, and then applied to pericytes. The effects of exosomes or different fibrosis-related signaling molecules were examined by Western blot, and the potential regulations between the signaling molecules were identified using bioinformatic analysis and assessed by electrophoretic mobility shift assay, chromatin immunoprecipitation, luciferase assay, and RNA binding protein immunoprecipitation. MiR-107 was downregulated in clinical or experimental PF tissues and also in exosomes from PF-derived ECs. EC-derived exosomal miR-107 essentially controlled the miR-107 level and inhibited α-SMA and ColIA1 expression in pericytes. The antifibrosis effect of miR-107 was mediated through the suppression of a pathway involving HIF-1α/Notch1/PDGFRβ/YAP1/Twist1, where miR-107 directly targeted HIF-1α mRNA, whereas the latter directly activated the transcriptions of both Notch1 and PDGFRβ. Functionally, targeting miR-107 promoted and targeting HIF-1α abolished the fibrotic phenotypes of pericytes. Exosomal miR-107 produced by pulmonary vascular ECs may alleviate pericyte-induced fibrosis by inhibiting a signaling pathway involving HIF-1α/Notch1/PDGFRβ/YAP1/Twist1.NEW & NOTEWORTHY This work reveals a novel mechanism by which pulmonary vascular endothelial cells, via regulating the transdifferentiation of microvascular pericytes into myofibroblasts, contribute to the pathogenesis of pulmonary fibrosis. Since targeting the formation of myofibroblasts may prevent the development and benefit the treatment of pulmonary fibrosis, this study provides not only mechanistic understanding but also promising therapeutic targets for pulmonary fibrosis.

Limited potential of resolvin D1 in treatment of cholestatic liver fibrosis

Background

Several studies suggest a role for EPA- and DHA-derived pro-resolving mediators like resolvins in reversing metabolic and inflammatory disturbances seen in various chronic diseases. Here, we investigated the effects of resolvin D1 (RvD1) on bile duct ligation (BDL)-induced cholestatic liver injury.

Methods

Mice were treated daily with RvD1 or 0.1% ethanol (control) from the day of BDL until the final observation time points. Blood and liver tissue were collected 2, 5 and 14 days after BDL for different analyses.

Results

RvD1 treatment of mice had no impact on the extent of cholestatic liver injury upon BDL, neither in the acute phase nor in the progressive state of liver fibrosis. Although RvD1 treatment resulted in a significantly reduced activity of hepatic stellate cells as well as reduced deposition of extracellular matrix 2 days after BDL, mice were not protected from inflammation and further fibrosis progression.

Conclusions

These data indicate that RvD1 has a limited therapeutic potential to treat cholestatic liver diseases, as it has no significant impact on regression of hepatic necroinflammation and fibrotic changes in bile duct-ligated mice.

Targeting n-3 Polyunsaturated Fatty Acids in Non-Alcoholic Fatty Liver Disease

BACKGROUND

Non-Alcoholic Fatty Liver Disease (NAFLD) is characterized by abnormal hepatic accumulation of triacylglycerides in the absence of alcohol consumption, in association with Oxidative Stress (OS), a pro-inflammatory state and Insulin Resistance (IR), which are attenuated by n-3 long-chain polyunsaturated Fatty Acids (FAs) C20-C22 (LCPUFAs) supplementation. Main causes of NAFLD comprise high caloric intake and a sedentary lifestyle, with high intakes of saturated FAs.

METHODS

The review includes several searches considering the effects of n-3 LCPUFAs in NAFLD in vivo and in vitro models, using the PubMed database from the National Library of Medicine- National Institutes of Health.

RESULT

The LCPUFAs eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n- 3, DHA) have a positive effect in diminishing liver steatosis, OS, and the levels of aspartate aminotransferase, alanine aminotransferase and pro-inflammatory cytokines, with improvement of insulin sensitivity and adiponectin levels. The molecular pathways described for n-3 LCPUFAs in cellular and animal models and humans include peroxisome proliferator-activated receptor-α activation favouring FA oxidation, diminution of lipogenesis due to sterol responsive element binding protein-1c downregulation and inflammation resolution. Besides, nuclear factor erythroid-2-related factor-2 activation is elicited by n-3 LCPUFA-derived oxidation products producing direct and indirect antioxidant responses, with concomitant anti-fibrogenic action.

CONCLUSION

The discussed effects of n-3 LCPUFA supplementation support its use in NAFLD, although having a limited value in NASH, a contention that may involve n-3 LCPUFA oxygenated derivatives. Clinical trials establishing optimal dosages, intervention times, type of patients and possible synergies with other natural products are needed in future studies.

Role of YAP/TAZ in Cell Lineage Fate Determination and Related Signaling Pathways

The penultimate effectors of the Hippo signaling pathways YAP and TAZ, are transcriptional co-activator proteins that play key roles in many diverse biological processes, ranging from cell proliferation, tumorigenesis, mechanosensing and cell lineage fate determination, to wound healing and regeneration. In this review, we discuss the regulatory mechanisms by which YAP/TAZ control stem/progenitor cell differentiation into the various major lineages that are of interest to tissue engineering and regenerative medicine applications. Of particular interest is the key role of YAP/TAZ in maintaining the delicate balance between quiescence, self-renewal, proliferation and differentiation of endogenous adult stem cells within various tissues/organs during early development, normal homeostasis and regeneration/healing. Finally, we will consider how increasing knowledge of YAP/TAZ signaling might influence the trajectory of future progress in regenerative medicine.

Relation Between Immunohistochemical Expression of Hippo Pathway Effectors and Chronic Hepatitis Induced Fibrosis in Egyptian Patients

OBJECTIVE

Chronic hepatitis is a global health problem especially in Egypt. Hepatic fibrosis is a common end clinical manifestation of many chronic liver diseases. Although it is a wound-healing process, excessive accumulation of fibrillary collagen leads to architectural damage, cirrhosis and liver failure. Recently, a few studies have linked Hippo pathway effectors of yes-associated protein (YAP) and its paralog transcriptional coactivator with PDZ-binding motif (TAZ) to extracellular matrix deposition and ongoing fibrosis.

MATERIAL AND METHOD

Immunohistochemical expression of YAP and TAZ were analyzed in 121 liver needle core biopsies (91 core biopsies of chronic viral hepatitis, 20 biopsies of autoimmune hepatitis and 10 normal liver cores).

RESULTS

YAP and TAZ nuclear localization was absent in all normal liver cores. Autoimmune hepatitis cases showed higher nuclear expression of both YAP and TAZ in comparison to chronic viral cases. YAP and TAZ expression were correlated with severity of hepatocyte injury together with fibrosis in chronic viral cases but these correlations were absent in AIH cases despite the pronounced increase of YAP and TAZ nuclear localization.

CONCLUSION

The correlation between Hippo effectors activation and fibrosis in chronic viral hepatitis patients emphasize their role in the development and advancement of hepatic scarring and highlight the use of both YAP and TAZ as novel targets to ameliorate liver fibrosis.

Liver stiffness correlates with serum osteopontin and TAZ expression in human liver cirrhosis

The pivotal role of the extracellular matrix (ECM) as both a cause and consequence of liver fibrosis is striking. However, mechanotransducer molecules and profibrogenic factors induced by liver stiffness are still unclear. The current study aimed to investigate liver stiffness and its correlation with the expression of the transcriptional coactivator with PDZ-binding motif (TAZ) and serum osteopontin (OPN) in human cirrhosis. In this case-control study, liver tissue stiffness was determined using atomic force microscopy in cirrhotic livers (n = 38) of different etiologies and in controls (n = 10). Immunohistochemical and qRT-PCR analyses were performed to analyze TAZ expression. Besides, western blotting and ELISA were performed to assess liver Indian hedgehog and serum OPN levels, respectively. Liver stiffness, TAZ expression, and hepatic gene expression and serum protein levels of OPN were significantly increased in patients with cirrhosis compared with the control groups (all P < 0.001), specifically in autoimmune- and alcohol-related cirrhosis. In cirrhotic patients, liver stiffness was significantly associated with the expression of nuclear TAZ and OPN. The correlation between matrix stiffness as a mechanical property, TAZ as a potential mechanotransducer, and OPN as a matricellular factor suggests possible effects of mechanical features of the ECM on the expression of the aforementioned profibrogenic markers, which is predominant in autoimmune- and alcohol-related cirrhosis.

The hepatocyte-specifically expressed lnc-HSER alleviates hepatic fibrosis by inhibiting hepatocyte apoptosis and epithelial-mesenchymal transition

Liver fibrosis leading to cirrhosis is one of the major health burdens worldwide with currently limited therapeutic options available. Long noncoding RNAs (lncRNAs) play important roles in various biological and pathological processes in a cell- or tissue-specific manner. However, there is still an important gap in the understanding of the role of hepatocyte-specific lncRNAs in liver fibrosis. Methods: The expressions of lnc-Hser in human and mice fibrotic livers as well as primary hepatocytes (HCs) of mice developing liver fibrosis were determined by real-time RT-PCR. The roles and mechanisms of lnc-Hser in HCs and liver fibrosis were determined in vitro and in vivo. Results: In this study, we have identified a hepatocyte-specifically expressed lnc-Hser, which was reduced in human and mice fibrotic livers as well as primary HCs of mice developing liver fibrosis. We have shown that silencing lnc-Hser aggravated liver fibrosis both in vitro and in vivo through inducing the epithelial-mesenchymal transition (EMT) and the apoptosis of HCs. In addition, knockdown of lnc-Hser promoted hepatic stellate cells (HSCs) activation through the signals derived from injured HCs. Mechanistically, we have revealed that lnc-Hser inhibited HCs apoptosis via the C5AR1-Hippo-YAP pathway and suppressed HCs EMT via the Notch signaling. Conclusions: Our work has identified a hepatocyte-specific lnc-HSER that regulates liver fibrosis, providing a proof that this molecule is a novel biomarker for damaged HCs and a potential target for anti-fibrotic therapy.

Matrix Mechanics as Regulatory Factors and Therapeutic Targets in Hepatic Fibrosis

The hallmark of liver fibrosis is excessive extracellular matrix (ECM) synthesis and deposition that improve liver matrix remodeling and stiffening. Increased matrix stiffness is not only a pathological consequence of liver fibrosis in traditional view, but also recognized as a key driver in pathological progression of hepatic fibrosis. Cells can perceive changes in the mechanical characteristics of hepatic matrix and respond by means of mechanical signal transduction pathways to regulate cell behavior. In this review, the authors first classify causes of liver matrix stiffening during fibrotic progression, such as higher degree of collagen cross-linking. The latest advances of the research on the matrix mechanics in regulating activation of HSCs or fibroblasts under two-dimensional (2D) and three-dimensional (3D) microenvironment is also classified and summarized. The mechanical signaling pathways involved in the process of hepatic matrix stiffening, such as YAP-TAZ signaling pathway, are further summarized. Finally, some potential therapeutic concepts and strategies based on matrix mechanics will be detailed. Collectively, these findings reinforce the importance of matrix mechanics in hepatic fibrosis, and underscore the value of clarifying its modulation in hopes of advancing the development of novel therapeutic targets and strategies for hepatic fibrosis.

Docosahexaenoic acid inhibits hepatic stellate cell activation to attenuate liver fibrosis in a PPARγ-dependent manner

Docosahexaenoic acid (DHA) has been found to have a hepatoprotective effect. In this study, we investigated the role of peroxisome proliferator-activated receptor γ (PPARγ) in DHA regulation of liver fibrosis. DHA was found to inhibit hepatic stellate cell (HSC)-LX2 cell viability and downregulate marker proteins of HSC activation. Furthermore, DHA induced cell cycle arrest at G1 phase in HSCs. Antagonism of PPARγ by GW9662 abrogated the effects of DHA on HSCs. Computer-aided molecular docking predicted that DHA bound to PPARγ via hydrogen bonding with residues Ser289, His323, Tyr473, and His499. We overexpressed Ser289 mutant PPARγ in HSC-LX2 cells and investigated fibrotic marker modulation, and found that DHA effects on HSCs were diminished. Thus, bonding with the Ser289 residue might be indispensable for DHA to activate PPARγ to exert its inhibiting effect on activated HSCs. Last, data from a CCl₄-treated mouse model confirmed that PPARγ activation was required for DHA to attenuate liver fibrosis.

Role of the Hippo Pathway in Fibrosis and Cancer

The Hippo pathway is the key player in various signaling processes, including organ development and maintenance of tissue homeostasis. This pathway comprises a core kinases module and transcriptional activation module, representing a highly conserved mechanism from Drosophila to vertebrates. The central MST1/2-LATS1/2 kinase cascade in this pathway negatively regulates YAP/TAZ transcription co-activators in a phosphorylation-dependent manner. Nuclear YAP/TAZ bind to transcription factors to stimulate gene expression, contributing to the regenerative potential and regulation of cell growth and death. Recent studies have also highlighted the potential role of Hippo pathway dysfunctions in the pathology of several diseases. Here, we review the functional characteristics of the Hippo pathway in organ fibrosis and tumorigenesis, and discuss its potential as new therapeutic targets.

Omega-3 and -6 fatty acid plasma levels are not associated with liver cirrhosis-associated systemic inflammation

BACKGROUND

Liver cirrhosis is associated with profound immunodysfunction, i.e. a parallel presence of chronic systemic inflammation and immunosuppression, which can result in acute-on-chronic liver failure (ACLF). Omega-3 fatty acids are precursors of pro-resolving mediators and support the resolution of inflammation.

OBJECTIVE

The aim of this study was to determine plasma levels of omega-3 fatty acids in patients with liver cirrhosis and ACLF.

METHODS

Patients with liver cirrhosis with and without ACLF were enrolled in a prospective cohort study and analyzed post-hoc for the present sub-study. Clinical data and biomaterials were collected at baseline and at day 7, 28 and after 3 months of follow-up. Plasma concentrations of arachidonic acid (ARA) and docosahexaenoic acid (DHA), which represent key omega-6 and -3 fatty acids, respectively, were quantified and associated with markers of systemic inflammation and severity of liver cirrhosis.

RESULTS

A total of 117 patients were included in the present analyses. Of those, 26 (22.2%), 51 (43.6%) and 40 (34.2%) patients had compensated or decompensated liver cirrhosis, and ACLF. Plasma levels of ARA and DHA were similar in patients with compensated cirrhosis, decompensated cirrhosis, and ACLF. Furthermore, no significant association between plasma ARA or DHA and C-reactive protein or peripheral blood leukocytes were observed (P>0.05).

CONCLUSION

In our study plasma levels of key omega-3 and omega-6 fatty acid are neither associated with the severity of liver cirrhosis nor with liver-cirrhosis-associated systemic inflammation.

High Risk of Hepatocellular Carcinoma Development in Fibrotic Liver: Role of the Hippo-YAP/TAZ Signaling Pathway. Int J Mol Sci. 2019;20. [PMID: 30700007 PMCID: PMC6387126 DOI: 10.3390/ijms20030581]

Liver cancer is the fourth leading cause of cancer-related death globally, accounting for approximately 800,000 deaths annually. Hepatocellular carcinoma (HCC) is the most common type of liver cancer, making up about 80% of cases. Liver fibrosis and its end-stage disease, cirrhosis, are major risk factors for HCC. A fibrotic liver typically shows persistent hepatocyte death and compensatory regeneration, chronic inflammation, and an increase in reactive oxygen species, which collaboratively create a tumor-promoting microenvironment via inducing genetic alterations and chromosomal instability, and activating various oncogenic molecular signaling pathways. In this article, we review recent advances in fields of liver fibrosis and carcinogenesis, and consider several molecular signaling pathways that promote hepato-carcinogenesis under the microenvironment of liver fibrosis. In particular, we pay attention to emerging roles of the Hippo-YAP/TAZ signaling pathway in stromal activation, hepatic fibrosis, and liver cancer.

Are Long-Chain Polyunsaturated Fatty Acids the Link between the Immune System and the Microbiome towards Modulating Cancer?

Three recent studies revealed synergy between immune-checkpoint inhibitors and the microbiome as a new approach in the treatment of cancer. Incidentally, there has been significant progress in understanding the role of polyunsaturated fatty acids (PUFAs) in modulating cancer and the immune system, as well as in regulating the microbiome. Inflammation seems to be the common denominator among these seemingly unrelated biological entities-immune system, the microbiome, and long-chain polyunsaturated fatty acids (LC-PUFAs). This commentary presents a hypothesis proposing the existence of an optimal level of LC-PUFAs that nurtures the suitable gut microbiota preventing dysbiosis. This synergy between optimal LC-PUFAs and gut microbiota helps the immune system overcome the immunosuppressive tumour microenvironment including enhancing the efficacy of immune checkpoint inhibitors. A model on how LC-PUFAs (such as omega(n)-3 and n-6 fatty acids) forms a synergistic triad with the immune system and the microbiome in regulating inflammation to maintain homeostasis is presented. The principles underlying the hypothesis provide a basis in managing and even preventing cancer and other chronic diseases associated with inflammation.

The Hippo pathway in organ development, homeostasis, and regeneration

The Hippo pathway is a universal governor of organ size, tissue homeostasis, and regeneration. A growing body of work has advanced our understanding of Hippo pathway regulation of cell proliferation, differentiation, and spatial patterning not only in organ development but also upon injury-induced regeneration. The pathway's central role in stem cell biology thus implicates its potential for therapeutic manipulation in mammalian organ regeneration. In this review, we survey recent literature linking the Hippo pathway to the development, homeostasis, and regeneration of various organs, including Hippo-independent roles for YAP, defined here as YAP functions that are not regulated by the Hippo pathway kinases LATS1/2.

Thymosin β4 attenuates liver fibrosis via suppressing Notch signaling

Thymosin β4 (Tβ4) has been shown to have beneficial effects in a number of pathological processes. Although there was research reporting the endogenous expression of Tβ4 influences hepatic stellate cells (HSCs) activation, the effect of exogenous administration of Tβ4 in hepatic fibrosis remains unclear. In the current study, we used CCl₄-induced liver fibrosis model mice to investigate the effect of Tβ4 administration on fibrosis in vivo and the underlying mechanism. Our study indicates that Tβ4 attenuates hepatic fibrosis and down-regulates the expression of fibrogenic genes in hepatic liver. In addition, Tβ4 inhibits the expression of pro fibrogenic and proliferation genes in activated HSCs. Further study revealed that Tβ4 attenuates liver fibrosis through inhibition of the Notch signaling, as Tβ4 significantly reduces the expression of Notch2 and Notch 3 that were increased in hepatic liver. Our data indicate that Tβ4 might be an effective anti-fibrotic drug for the treatment of liver fibrosis.

Hippo Signaling in the Liver Regulates Organ Size, Cell Fate, and Carcinogenesis

The Hippo signaling pathway, also known as the Salvador-Warts-Hippo pathway, is a regulator of organ size. The pathway takes its name from the Drosophila protein kinase, Hippo (STK4/MST1 and STK3/MST2 in mammals), which, when inactivated, leads to considerable tissue overgrowth. In mammals, MST1 and MST2 negatively regulate the transcriptional co-activators yes-associated protein 1 and WW domain containing transcription regulator 1 (WWTR1/TAZ), which together regulate expression of genes that control proliferation, survival, and differentiation. Yes-associated protein 1 and TAZ activation have been associated with liver development, regeneration, and tumorigenesis. How their activity is dynamically regulated in these contexts is just beginning to be elucidated. We review the mechanisms of Hippo signaling in the liver and explore outstanding questions for future research.