Hedgehog controls hepatic stellate cell fate by regulating metabolism

Inhibition of carnitine palmitoyltransferase 1A in hepatic stellate cells protects against fibrosis

BACKGROUND & AIMS

The pathogenesis of liver fibrosis requires activation of hepatic stellate cells (HSCs); once activated, HSCs lose intracellular fatty acids but the role of fatty acid oxidation and carnitine palmitoyltransferase 1A (CPT1A) in this process remains largely unexplored.

METHODS

CPT1A was found in HSCs of patients with fibrosis. Pharmacological and genetic manipulation of CPT1A were performed in human HSC cell lines and primary HCSs. Finally, we induced fibrosis in mice lacking CPT1A specifically in HSCs.

RESULTS

Herein, we show that CPT1A expression is elevated in HSCs of patients with non-alcoholic steatohepatitis, showing a positive correlation with the fibrosis score. This was corroborated in rodents with fibrosis, as well as in primary human HSCs and LX-2 cells activated by transforming growth factor β1 (TGFβ1) and fetal bovine serum (FBS). Furthermore, both pharmacological and genetic silencing of CPT1A prevent TGFβ1- and FBS-induced HSC activation by reducing mitochondrial activity. The overexpression of CPT1A, induced by saturated fatty acids and reactive oxygen species, triggers mitochondrial activity and the expression of fibrogenic markers. Finally, mice lacking CPT1A specifically in HSCs are protected against fibrosis induced by a choline-deficient high-fat diet, a methionine- and choline-deficient diet, or treatment with carbon tetrachloride.

CONCLUSIONS

These results indicate that CPT1A plays a critical role in the activation of HSCs and is implicated in the development of liver fibrosis, making it a potentially actionable target for fibrosis treatment.

LAY SUMMARY

We show that the enzyme carnitine palmitoyltransferase 1A (CPT1A) is elevated in hepatic stellate cells (HSCs) in patients with fibrosis and mouse models of fibrosis, and that CPT1A induces the activation of these cells. Inhibition of CPT1A ameliorates fibrosis by preventing the activation of HSCs.

The mitochondrial pyruvate carrier at the crossroads of intermediary metabolism

Pyruvate metabolism, a central nexus of carbon homeostasis, is an evolutionarily conserved process and aberrant pyruvate metabolism is associated with and contributes to numerous human metabolic disorders including diabetes, cancer, and heart disease. As a product of glycolysis, pyruvate is primarily generated in the cytosol before being transported into the mitochondrion for further metabolism. Pyruvate entry into the mitochondrial matrix is a critical step for efficient generation of reducing equivalents and ATP and for the biosynthesis of glucose, fatty acids, and amino acids from pyruvate. However, for many years, the identity of the carrier protein(s) that transported pyruvate into the mitochondrial matrix remained a mystery. In 2012, the molecular-genetic identification of the mitochondrial pyruvate carrier (MPC), a heterodimeric complex composed of protein subunits MPC1 and MPC2, enabled studies that shed light on the many metabolic and physiological processes regulated by pyruvate metabolism. A better understanding of the mechanisms regulating pyruvate transport and the processes affected by pyruvate metabolism may enable novel therapeutics to modulate mitochondrial pyruvate flux to treat a variety of disorders. Herein, we review our current knowledge of the MPC, discuss recent advances in the understanding of mitochondrial pyruvate metabolism in various tissue and cell types, and address some of the outstanding questions relevant to this field.

Fibrogenic Pathways in Metabolic Dysfunction Associated Fatty Liver Disease (MAFLD)

The prevalence of nonalcoholic fatty liver disease (NAFLD), recently also re-defined as metabolic dysfunction associated fatty liver disease (MAFLD), is rapidly increasing, affecting ~25% of the world population. MALFD/NAFLD represents a spectrum of liver pathologies including the more benign hepatic steatosis and the more advanced non-alcoholic steatohepatitis (NASH). NASH is associated with enhanced risk for liver fibrosis and progression to cirrhosis and hepatocellular carcinoma. Hepatic stellate cells (HSC) activation underlies NASH-related fibrosis. Here, we discuss the profibrogenic pathways, which lead to HSC activation and fibrogenesis, with a particular focus on the intercellular hepatocyte–HSC and macrophage–HSC crosstalk.

Hepatic stellate cells in physiology and pathology

Hepatic stellate cells (HSCs) comprise a minor cell population in the liver but serve numerous critical functions in the normal liver and in response to injury. HSCs are primarily known for their activation upon liver injury and for producing the collagen-rich extracellular matrix in liver fibrosis. In the absence of liver injury, HSCs reside in a quiescent state, in which their main function appears to be the storage of retinoids or vitamin A-containing metabolites. Less appreciated functions of HSCs include amplifying the hepatic inflammatory response and expressing growth factors that are critical for liver development and both the initiation and termination of liver regeneration. Recent single-cell RNA sequencing studies have corroborated earlier studies indictaing that HSC activation involves a diverse array of phenotypic alterations and identified unique HSC populations. This review serves to highlight these many functions of HSCs, and to briefly describe the recent genetic tools that will help to thoroughly investigate the role of HSCs in hepatic physiology and pathology.

Bmal1 inhibits phenotypic transformation of hepatic stellate cells in liver fibrosis via IDH1/α-KG-mediated glycolysis

Hepatic stellate cells (HSCs) play an important role in the initiation and development of liver fibrogenesis, and abnormal glucose metabolism is increasingly being considered a crucial factor controlling phenotypic transformation in HSCs. However, the role of the factors affecting glycolysis in HSCs in the experimental models of liver fibrosis has not been completely elucidated. In this study, we showed that glycolysis was significantly enhanced, while the expression of brain and muscle arnt-like protein-1 (Bmal1) was downregulated in fibrotic liver tissues of mice, primary HSCs, and transforming growth factor-β1 (TGF-β1)-induced LX2 cells. Overexpression of Bmal1 in TGF-β1-induced LX2 cells blocked glycolysis and inhibited the proliferation and phenotypic transformation of activated HSCs. We further confirmed the protective effect of Bmal1 in liver fibrosis by overexpressing Bmal1 from hepatic adeno-associated virus 8 in mice. In addition, we also showed that the regulation of glycolysis by Bmal1 is mediated by the isocitrate dehydrogenase 1/α-ketoglutarate (IDH1/α-KG) pathway. Collectively, our results indicated that a novel Bmal1-IDH1/α-KG axis may be involved in regulating glycolysis of activated HSCs and might hence be used as a therapeutic target for alleviating liver fibrosis.

Focal adhesion kinase-related non-kinase ameliorates liver fibrosis by inhibiting aerobic glycolysis via the FAK/Ras/c-myc/ENO1 pathway

BACKGROUND

Hepatic stellate cell (HSC) hyperactivation is a central link in liver fibrosis development. HSCs perform aerobic glycolysis to provide energy for their activation. Focal adhesion kinase (FAK) promotes aerobic glycolysis in cancer cells or fibroblasts, while FAK-related non-kinase (FRNK) inhibits FAK phosphorylation and biological functions.

AIM

To elucidate the effect of FRNK on liver fibrosis at the level of aerobic glycolytic metabolism in HSCs.

METHODS

Mouse liver fibrosis models were established by administering CCl₄, and the effect of FRNK on the degree of liver fibrosis in the model was evaluated. Transforming growth factor-β1 was used to activate LX-2 cells. Tyrosine phosphorylation at position 397 (pY397-FAK) was detected to identify activated FAK, and the expression of the glycolysis-related proteins monocarboxylate transporter 1 (MCT-1) and enolase1 (ENO1) was assessed. Bioinformatics analysis was performed to predict putative binding sites for c-myc in the ENO1 promoter region, which were validated with chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays.

RESULTS

The pY397-FAK level was increased in human fibrotic liver tissue. FRNK knockout promoted liver fibrosis in mouse models. It also increased the activation, migration, proliferation and aerobic glycolysis of primary hepatic stellate cells (pHSCs) but inhibited pHSC apoptosis. Nevertheless, opposite trends for these phenomena were observed after exogenous FRNK treatment in LX-2 cells. Mechanistically, the FAK/Ras/c-myc/ENO1 pathway promoted aerobic glycolysis, which was inhibited by exogenous FRNK.

CONCLUSION

FRNK inhibits aerobic glycolysis in HSCs by inhibiting the FAK/Ras/c-myc/ ENO1 pathway, thereby improving liver fibrosis. FRNK might be a potential target for liver fibrosis treatment.

Skin aging: Dermal adipocytes metabolically reprogram dermal fibroblasts

Emerging data connects the aging process in dermal fibroblasts with metabolic reprogramming, provided by enhanced fatty acid oxidation and reduced glycolysis. This switch may be caused by a significant expansion of the dermal white adipose tissue (dWAT) layer in aged, hair-covered skin. Dermal adipocytes cycle through de-differentiation and re-differentiation. As a result, there is a strongly enhanced release of free fatty acids into the extracellular space during the de-differentiation of dermal adipocytes in the catagen phase of the hair follicle cycle. Both caveolin-1 and adiponectin are critical factors influencing these processes. Controlling the expression levels of these two factors also offers the ability to manipulate the metabolic preferences of the different cell types within the microenvironment of the skin, including dermal fibroblasts. Differential expression of adiponectin and caveolin-1 in the various cell types may also be responsible for the cellular metabolic heterogeneity within the cells of the skin.

Metabolic Reprogramming of Liver Fibrosis

Liver fibrosis is an excessive and imbalanced deposition of fibrous extracellular matrix (ECM) that is associated with the hepatic wound-healing response. It is also the common mechanism that contributes to the impairment of the liver function that is observed in many chronic liver diseases (CLD). Despite the efforts, no effective therapy against fibrosis exists yet. Worryingly, due to the growing obesity pandemic, fibrosis incidence is on the rise. Here, we aim to summarize the main components and mechanisms involved in the progression of liver fibrosis, with special focus on the metabolic regulation of key effectors of fibrogenesis, hepatic stellate cells (HSCs), and their role in the disease progression. Hepatic cells that undergo metabolic reprogramming require a tightly controlled, fine-tuned cellular response, allowing them to meet their energetic demands without affecting cellular integrity. Here, we aim to discuss the role of ribonucleic acid (RNA)-binding proteins (RBPs), whose dynamic nature being context- and stimuli-dependent make them very suitable for the fibrotic situation. Thus, we will not only summarize the up-to-date literature on the metabolic regulation of HSCs in liver fibrosis, but also on the RBP-dependent post-transcriptional regulation of this metabolic switch that results in such important consequences for the progression of fibrosis and CLD.

Mitochondrial Dysfunction in Advanced Liver Disease: Emerging Concepts

Mitochondria are entrusted with the challenging task of providing energy through the generation of ATP, the universal cellular currency, thereby being highly flexible to different acute and chronic nutrient demands of the cell. The fact that mitochondrial diseases (genetic disorders caused by mutations in the nuclear or mitochondrial genome) manifest through a remarkable clinical variation of symptoms in affected individuals underlines the far-reaching implications of mitochondrial dysfunction. The study of mitochondrial function in genetic or non-genetic diseases therefore requires a multi-angled approach. Taking into account that the liver is among the organs richest in mitochondria, it stands to reason that in the process of unravelling the pathogenesis of liver-related diseases, researchers give special focus to characterizing mitochondrial function. However, mitochondrial dysfunction is not a uniformly defined term. It can refer to a decline in energy production, increase in reactive oxygen species and so forth. Therefore, any study on mitochondrial dysfunction first needs to define the dysfunction to be investigated. Here, we review the alterations of mitochondrial function in liver cirrhosis with emphasis on acutely decompensated liver cirrhosis and acute-on-chronic liver failure (ACLF), the latter being a form of acute decompensation characterized by a generalized state of systemic hyperinflammation/immunosuppression and high mortality rate. The studies that we discuss were either carried out in liver tissue itself of these patients, or in circulating leukocytes, whose mitochondrial alterations might reflect tissue and organ mitochondrial dysfunction. In addition, we present different methodological approaches that can be of utility to address the diverse aspects of hepatocyte and leukocyte mitochondrial function in liver disease. They include assays to measure metabolic fluxes using the comparatively novel Biolog’s MitoPlates in a 96-well format as well as assessment of mitochondrial respiration by high-resolution respirometry using Oroboros’ O2k-technology and Agilent Seahorse XF technology.

Proteomic Changes of Activated Hepatic Stellate Cells

Hepatic stellate cells (HSC) are the major cellular drivers of liver fibrosis. Upon liver inflammation caused by a broad range of insults including non-alcoholic fatty liver, HSC transform from a quiescent into a proliferating, fibrotic phenotype. Although much is known about the pathophysiology of this process, exact cellular processes which occur in HSC and enable this transformation remain yet to be elucidated. In order to investigate this HSC transformation, we employed a simple, yet reliable model of HSC activation via an increase in growth medium serum concentration (serum activation). For that purpose, immortalized human LX-2 HSC were exposed to either 1% or 10% fetal bovine serum (FBS). Resulting quiescent (1% FBS) and activated (10% FBS) LX-2 cells were then subjected to in-depth mass spectrometry-based proteomics analysis as well as comprehensive phenotyping. Protein network analysis of activated LX-2 cells revealed an increase in the production of ribosomal proteins and proteins related to cell cycle control and migration, resulting in higher proliferation and faster migration phenotypes. Interestingly, we also observed a decrease in the expression of cholesterol and fatty acid biosynthesis proteins in accordance with a concomitant loss of cytosolic lipid droplets during activation. Overall, this work provides an update on HSC activation characteristics using contemporary proteomic and bioinformatic analyses and presents an accessible model for HSC activation. Data are available via ProteomeXchange with identifier PXD029121.

Novel Therapeutic Targets in Liver Fibrosis

Liver fibrosis is end-stage liver disease that can be rescued. If irritation continues due to viral infection, schistosomiasis and alcoholism, liver fibrosis can progress to liver cirrhosis and even cancer. The US Food and Drug Administration has not approved any drugs that act directly against liver fibrosis. The only treatments currently available are drugs that eliminate pathogenic factors, which show poor efficacy; and liver transplantation, which is expensive. This highlights the importance of clarifying the mechanism of liver fibrosis and searching for new treatments against it. This review summarizes how parenchymal, nonparenchymal cells, inflammatory cells and various processes (liver fibrosis, hepatic stellate cell activation, cell death and proliferation, deposition of extracellular matrix, cell metabolism, inflammation and epigenetics) contribute to liver fibrosis. We highlight discoveries of novel therapeutic targets, which may provide new insights into potential treatments for liver fibrosis.

Transforming growth factor beta-1 upregulates glucose transporter 1 and glycolysis through canonical and noncanonical pathways in hepatic stellate cells

BACKGROUND

Hepatic stellate cells (HSCs) are the key effector cells mediating the occurrence and development of liver fibrosis, while aerobic glycolysis is an important metabolic characteristic of HSC activation. Transforming growth factor-β1 (TGF-β1) induces aerobic glycolysis and is a driving factor for metabolic reprogramming. The occurrence of glycolysis depends on a high glucose uptake level. Glucose transporter 1 (GLUT1) is the most widely distributed glucose transporter in the body and mainly participates in the regulation of carbohydrate metabolism, thus affecting cell proliferation and growth. However, little is known about the relationship between TGF-β1 and GLUT1 in the process of liver fibrosis and the molecular mechanism underlying the promotion of aerobic glycolysis in HSCs.

AIM

To investigate the mechanisms of action of GLUT1, TGF-β1 and aerobic glycolysis in the process of HSC activation during liver fibrosis.

METHODS

Immunohistochemical staining and immunofluorescence assays were used to examine GLUT1 expression in fibrotic liver tissue. A Seahorse extracellular flux (XF) analyzer was used to examine changes in aerobic glycolytic flux, lactate production levels and glucose consumption levels in HSCs upon TGF-β1 stimulation. The mechanism by which TGF-β1 induces GLUT1 protein expression in HSCs was further explored by inhibiting/promoting the TGF-β1/mothers-against-decapentaplegic-homolog 2/3 (Smad2/3) signaling pathway and inhibiting the p38 and phosphoinositide 3-kinase (PI3K)/AKT signaling pathways. In addition, GLUT1 expression was silenced to observe changes in the growth and proliferation of HSCs. Finally, a GLUT1 inhibitor was used to verify the in vivo effects of GLUT1 on a mouse model of liver fibrosis.

RESULTS

GLUT1 protein expression was increased in both mouse and human fibrotic liver tissues. In addition, immunofluorescence staining revealed colocalization of GLUT1 and alpha-smooth muscle actin proteins, indicating that GLUT1 expression was related to the development of liver fibrosis. TGF-β1 caused an increase in aerobic glycolysis in HSCs and induced GLUT1 expression in HSCs by activating the Smad, p38 MAPK and P13K/AKT signaling pathways. The p38 MAPK and Smad pathways synergistically affected the induction of GLUT1 expression. GLUT1 inhibition eliminated the effect of TGF-β1 on HSC proliferation and migration. A GLUT1 inhibitor was administered in a mouse model of liver fibrosis, and GLUT1 inhibition reduced the degree of liver inflammation and liver fibrosis.

CONCLUSION

TGF-β1 induces GLUT1 expression in HSCs, a process related to liver fibrosis progression. In vitro experiments revealed that TGF-β1-induced GLUT1 expression might be one of the mechanisms mediating the metabolic reprogramming of HSCs. In addition, in vivo experiments also indicated that the GLUT1 protein promotes the occurrence and development of liver fibrosis.

Extra- and Intra-Cellular Mechanisms of Hepatic Stellate Cell Activation

Hepatic fibrosis is characterized by the pathological accumulation of extracellular matrix (ECM) in the liver resulting from the persistent liver injury and wound-healing reaction induced by various insults. Although hepatic fibrosis is considered reversible after eliminating the cause of injury, chronic injury left unchecked can progress to cirrhosis and liver cancer. A better understanding of the cellular and molecular mechanisms controlling the fibrotic response is needed to develop novel clinical strategies. It is well documented that activated hepatic stellate cells (HSCs) is the most principal cellular players promoting synthesis and deposition of ECM components. In the current review, we discuss pathways of HSC activation, emphasizing emerging extra- and intra-cellular signals that drive this important cellular response to hepatic fibrosis. A number of cell types and external stimuli converge upon HSCs to promote their activation, including hepatocytes, liver sinusoidal endothelial cells, macrophages, cytokines, altered ECM, hepatitis viral infection, enteric dysbiosis, lipid metabolism disorder, exosomes, microRNAs, alcohol, drugs and parasites. We also discuss the emerging signaling pathways and intracellular events that individually or synergistically drive HSC activation, including TGFβ/Smad, Notch, Wnt/β-catenin, Hedgehog and Hippo signaling pathways. These findings will provide novel potential therapeutic targets to arrest or reverse fibrosis and cirrhosis.

Mitochondria: A critical hub for hepatic stellate cells activation during chronic liver diseases

BACKGROUND

Upon liver injury, quiescent hepatic stellate cells (qHSCs), reside in the perisinusoidal space, phenotypically transdifferentiate into myofibroblast-like cells (MFBs). The qHSCs in the normal liver are less fibrogenic, migratory, and also have less proliferative potential. However, activated HSCs (aHSCs) are more fibrogenic and have a high migratory and proliferative MFBs phenotype. HSCs activation is a highly energetic process that needs abundant intracellular energy in the form of adenosine triphosphate (ATP) for the synthesis of extracellular matrix (ECM) in the injured liver to substantiate the injury.

DATA SOURCES

The articles were collected through PubMed and EMBASE using search terms "mitochondria and hepatic stellate cells", "mitochondria and HSCs", "mitochondria and hepatic fibrosis", "mitochondria and liver diseases", and "mitochondria and chronic liver disease", and relevant publications published before September 31, 2020 were included in this review.

RESULTS

Mitochondria homeostasis is affected during HSCs activation. Mitochondria in aHSCs are highly energetic and are in a high metabolically active state exhibiting increased activity such as glycolysis and respiration. aHSCs have high glycolytic enzymes expression and glycolytic activity induced by Hedgehog (Hh) signaling from injured hepatocytes. Increased glycolysis and aerobic glycolysis (Warburg effect) end-products in aHSCs consequently activate the ECM-related gene expressions. Increased Hh signaling from injured hepatocytes downregulates peroxisome proliferator-activated receptor-γ expression and decreases lipogenesis in aHSCs. Glutaminolysis and tricarboxylic acid cycle liberate ATPs that fuel HSCs to proliferate and produce ECM during their activation.

CONCLUSIONS

Available studies suggest that mitochondria functions can increase in parallel with HSCs activation. Therefore, mitochondrial modulators should be tested in an elaborate manner to control or prevent the HSCs activation during liver injury to subsequently regress hepatic fibrosis.

Roles of nuclear receptors in hepatic stellate cells

Introduction: Hepatic stellate cells (HSCs) are essential for physiological homeostasis of the liver extracellular matrix (ECM). Excessive transdifferentiation of HSC from a quiescent to an activated phenotype contributes to disrupt this balance and can lead to liver fibrosis. Accumulating evidence has suggested that nuclear receptors (NRs) are involved in the regulation of HSC activation, proliferation, and function. Therefore, these NRs may be therapeutic targets to balance ECM homeostasis and inhibit HSC activation in liver fibrosis.Areas covered: In this review, the authors summarized the recent progress in the understanding of the regulatory role of NRs in HSCs and their potential as drug targets in liver fibrosis.Expert opinion: NRs are still potential therapy targets for inhibiting HSCs activation and liver fibrosis. However, the development of NRs agonists or antagonists to inhibit HSCs requires fully consideration of systemic effects.

The emerging role of metabolism in fibrosis

The metabolic shift that cancer cells undergo towards aerobic glycolysis was identified as a defining feature in tumours almost 100 years ago; however, it has only recently become apparent that similar metabolic reprogramming is a key feature in other diseases - with fibrosis now entering the fray. In this perspective, an overview of the recent evidence implicating increased glycolysis and glutaminolysis as mediators of fibrosis is presented, with a particular emphasis on the novel therapeutic possibilities this introduces. Furthermore, the impact that metabolic reprogramming has on redox homeostasis is discussed, providing an insight into how this often-overlooked mechanism may drive the pathogenesis.

PFKFB3 Promotes Liver Fibrosis by Regulating Aerobic Glycolysis of Hepatic Stellate Cells

Background: Hepatic stellate cells (HSCs) are the key effector cells in the occurrence and development of liver fibrosis, while aerobic glycolysis is one of the important metabolic characteristics of HSC activation. 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3) is a homodimeric bifunctional enzyme, which is a rate-limiting enzyme in glycolysis. This metabolite is important for the dynamic regulation of glycolytic flux. However, little is known about the role of PFKFB3 in liver fibrosis. Objectives: In this study, we aimed to explore the effects of PFKFB3 on aerobic glycolysis in the process of HSC trans-differentiation and liver fibrosis. Methods: Immunohistochemical (IHC) staining and immunofluorescence assays were used to examine PFKFB3 expression in mice fibrotic liver tissue. The determination of extracellular acidification rate was used to examine changes in aerobic glycolytic flux, lactate production levels, and glucose consumption levels in HSCs upon TGF-β1 stimulation. Western blot analysis of the expression of PFKFB3, α-SMA protein, and type I collagen was done. Liver histopathology was also examined. Besides, glycolytic inhibition by pharmacologic approaches was used to demonstrate the critical role of glycolysis in liver fibrosis. Results: The PFKFB3 protein expression was increased in mouse fibrotic liver tissue. In addition, immunofluorescence revealed the colocalization of PFKFB3 and alpha-smooth muscle actin (α-SMA) protein. In vitro experiments showed that PFKFB3 could promote glycolysis flux, lactic acid production, and glucose consumption of hepatic stellate cells. The PFKFB3 inhibitor was used in a mouse model of liver fibrosis, and the inhibition of PFKFB3 reduced the degree of liver inflammation and liver fibrosis. Conclusions: PFKFB3 can promote HSC aerobic glycolysis, which, in turn, promotes HSC activation and liver fibrosis.

A review of cutting-edge therapies for hepatocellular carcinoma (HCC): Perspectives from patents

Rationale: Hepatocellular carcinoma (HCC) is a challenging disease due to its heterogenous etiology. Several breakthroughs have occurred in treatment of HCC, associated with an enormous number of patent publications for a variety of HCC treatment modalities. As patents can provide valuable information for academic research and commercial development, this study aims to unravel the cutting-edge therapies for HCC by using patents as an indicator. The outcome from this analysis may offer meaningful insights for respective policymaking, strategic plan and research and development (R&D) prioritization. Methods: Derwent Innovation platform was employed to collect the sample data of patents related to HCC treatment technologies worldwide as of December 31, 2019. Data inclusion, screening and exclusion were according to the rules of preferred reporting items for systematic reviews and meta-analyses (PRISMA). Technologies were classified based on Barcelona Clinic Liver Cancer (BCLC) staging system and recent clinical publications. Patent citation network analysis was carried out to identify and understand HCC therapeutic technology flow. Results: A dataset of 2543 patent documents and 528 patent families was generated. 11 technological categories were classified. Numerous researches were focalized on refinements in technologies and innovations within the field of HCC therapy, and the major achievements are technology advancement on molecular target therapy, chemotherapy, locoregional therapy, combination therapy and immunotherapy with demonstrated clinical benefits. In patent citation network, Notch pathway investigation, antibody drug conjugate (ADC) technology development and drug eluting beads trans artery chemoembolization (DEB-TACE) advancement are the major technological communities involving patents with the greatest future exploratory potential. Conclusion: Numerous emerging technologies have been identified in this study, in which exploring novel therapeutic targets in molecular target therapy, more localized and visible locoregional therapy and combination of immunotherapy with target therapy or other traditional therapies are highlighted as the future trends in treating HCC.

The Sonic Hedgehog signaling pathway regulates autophagy and migration in ovarian cancer

Background

The Sonic Hedgehog (SHH) signaling pathway plays an important role in various types of human cancers including ovarian cancer; however, its function and underlying mechanism in ovarian cancer are still not entirely understood.

Methods

We detected the expressions of SHH and SQSTM1 in borderline ovarian tumor tissues, epithelial ovarian cancer (EOC) tissues and benign ovarian tumor tissues. Cyclopamine (Cyp, a well‐known inhibitor of SHH signaling pathway) and chloroquine (CQ, the pharmaceutical inhibitor of autophagy) were used in vivo and in vitro (autophagic flux, CCK‐8 assay, wound healing assay, transwell assay, tumor xenograft model). The mechanism of action was explored through Quantitative RT‐PCR and Western Blot.

Results

We found up‐regulation of SHH and accumulation of SQSTM1/P62 in epithelial ovarian cancer. Cyp induced autophagy through the PI3K/AKT signaling pathway. Moreover, low‐dose Cyp and chloroquine (CQ) significantly promoted the migratory ability of SKOV3 cells.

Conclusions

Our findings suggest that inhibition of the SHH pathway and autophagy may be a potential and effective therapy for the treatment of ovarian cancer.

Targeting cell-intrinsic metabolism for antifibrotic therapy

In recent years, there have been major advances in our understanding of the mechanisms underlying fibrosis progression and regression, and how coordinated interactions between parenchymal and non-parenchymal cells impact on the fibrogenic process. Recent studies have highlighted that metabolic reprogramming of parenchymal cells, immune cells (immunometabolism) and hepatic stellate cells is required to support the energetic and anabolic demands of phenotypic changes and effector functions. In this review, we summarise how targeting cell-intrinsic metabolic modifications of the main fibrogenic cell actors may impact on fibrosis progression and we discuss the antifibrogenic potential of metabolically targeted interventions.

Hepatic Stellate Cell Activation and Inactivation in NASH-Fibrosis-Roles as Putative Treatment Targets?

Hepatic fibrosis is the primary predictor of mortality in patients with non-alcoholic steatohepatitis (NASH). In this process, the activated hepatic stellate cells (HSCs) constitute the principal cells responsible for the deposition of a fibrous extracellular matrix, thereby driving the hepatic scarring. HSC activation, migration, and proliferation are controlled by a complex signaling network involving growth factors, lipotoxicity, inflammation, and cellular stress. Conversely, the clearance of activated HSCs is a prerequisite for the resolution of the extracellular fibrosis. Hence, pathways regulating the fate of the HSCs may represent attractive therapeutic targets for the treatment and prevention of NASH-associated hepatic fibrosis. However, the development of anti-fibrotic drugs for NASH patients has not yet resulted in clinically approved therapeutics, underscoring the complex biology and challenges involved when targeting the intricate cellular signaling mechanisms. This narrative review investigated the mechanisms of activation and inactivation of HSCs with a focus on NASH-associated hepatic fibrosis. Presenting an updated overview, this review highlights key cellular pathways with potential value for the development of future treatment modalities.

The mechanism and role of intracellular α-ketoglutarate reduction in hepatic stellate cell activation

Background: The activation of hepatic stellate cells (HSCs) plays a central role in liver fibrosis. α-ketoglutarate is a natural metabolite and previous studies have shown that increase in intracellular α-ketoglutarate can inhibit HSC activation. Aim: The aim of the present study is to determine the changes and role of intracellular α-ketoglutarate in HSC activation and clarify its mechanism of action. Methods: A human HSC cell line (LX-2) and the primary mouse HSC were used in the present study. We detected the changes of intracellular α-ketoglutarate levels and the expression of enzymes involved in the metabolic processes during HSC activation. We used siRNA to determine the role of intracellular α-ketoglutarate in HSC activation and elucidate the mechanism of the metabolic changes. Results: Our results demonstrated that intracellular α-ketoglutarate levels decreased with an HSC cell line and primary mouse HSC activation, as well as the expression of isocitrate dehydrogenase 2 (IDH2), an enzyme that catalyzes the production of α-ketoglutarate. In addition, knockdown of IDH2 efficiently promoted the activation of HSCs, which was able to be reversed by introduction of an α-ketoglutarate analogue. Furthermore, we demonstrated that α-ketoglutarate regulated HSC activation is independent of transforming growth factor-β1 (TGF-β1). Conclusions: Our findings demonstrated that decrease in IDH2 expression limits the production of α-ketoglutarate during HSC activation and in turn promotes the activation of HSCs through a TGF-β1 independent pathway. The present study suggests that IDH2 and α-ketoglutarate may be potential new targets for the prevention and treatment of liver fibrosis.

A Metabolic Reprogramming of Glycolysis and Glutamine Metabolism Is a Requisite for Renal Fibrogenesis-Why and How?

Chronic Kidney Disease (CKD) is characterized by organ remodeling and fibrosis due to failed wound repair after on-going or severe injury. Key to this process is the continued activation and presence of matrix-producing renal fibroblasts. In cancer, metabolic alterations help cells to acquire and maintain a malignant phenotype. More recent evidence suggests that something similar occurs in the fibroblast during activation. To support these functions, pro-fibrotic signals released in response to injury induce metabolic reprograming to meet the high bioenergetic and biosynthetic demands of the (myo)fibroblastic phenotype. Fibrogenic signals such as TGF-β1 trigger a rewiring of cellular metabolism with a shift toward glycolysis, uncoupling from mitochondrial oxidative phosphorylation, and enhanced glutamine metabolism. These adaptations may also have more widespread implications with redirection of acetyl-CoA directly linking changes in cellular metabolism and regulatory protein acetylation. Evidence also suggests that injury primes cells to these metabolic responses. In this review we discuss the key metabolic events that have led to a reappraisal of the regulation of fibroblast differentiation and function in CKD.

Silencing of CD147 inhibits hepatic stellate cells activation related to suppressing aerobic glycolysis via hedgehog signaling

Hepatic stellate cells (HSCs) activation is a key step that promotes hepatic fibrosis. Emerging evidence suggests that aerobic glycolysis is one of its important metabolic characteristics. Our previous study has reported that CD147, a glycosylated transmembrane protein, contributes significantly to the activation of HSCs. However, whether and how it is involved in the aerobic glycolysis of HSCs activation is unknown. The objective of the present study was to validate the effect of CD147 in HSCs activation and the underlying molecular mechanism. Our results showed that the silencing of CD147 decreased the expression of α-smooth muscle-actin (α-SMA) and collagen I at both mRNA and protein levels. Furthermore, CD147 silencing decreased the glucose uptake, lactate production in HSCs, and repressed the lactate dehydrogenase (LDH) activity, the expression of hexokinase 2 (HK2), glucose transporter 1 (Glut1). The effect of galloflavin, a well-defined glycolysis inhibitor, was similar to CD147 siRNA. Mechanistically, CD147 silencing suppressed glycolysis-associated HSCs activation through inhibiting the hedgehog signaling. Moreover, the hedgehog signaling agonist SAG could rescue the above effect of CD147 silencing. In conclusion, CD147 silencing blockade of aerobic glycolysis via suppression of hedgehog signaling inhibited HSCs activation, suggesting CD147 as a novel therapeutic target for hepatic fibrosis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-021-00460-9.

Regulatory long non-coding RNAs of hepatic stellate cells in liver fibrosis (Review)

Liver fibrosis (LF) is a continuous wound healing process caused by numerous chronic hepatic diseases and poses a major threat to human health. Activation of hepatic stellate cells (HSCs) is a critical event in the development of hepatic fibrosis. Long non-coding RNAs (lncRNAs) that are involved in HSC activation, participate in the development of LF and are likely to be therapeutic targets for LF. In the present review, the cellular signaling pathways of LF with respect to HSCs were discussed. In particular, this present review highlighted the current knowledge on the role of lncRNAs in activating or inhibiting LF, revealing lncRNAs that are likely to be biomarkers or therapeutic targets for LF. Additional studies should be performed to elucidate the potential of lncRNAs in the diagnosis and prognosis of LF and to provide novel therapeutic approaches for the reversion of LF.

3-Bromopyruvate decreased kidney fibrosis and fibroblast activation by suppressing aerobic glycolysis in unilateral ureteral obstruction mice model

AIMS

Enhanced aerobic glycolysis is a motivation of fibroblast-myofibroblast transdifferentiation (FMT), leading to kidney fibrosis. 3-Bromopyruvate (3-BrPA) is a glycolysis inhibitor and has fibrosis-protected effect in liver. This study aims to explore the effects of 3-BrPA on aerobic glycolysis and kidney fibrosis in a unilateral ureteral obstruction (UUO) mice model and transforming growth factor-β1(TGF-β1)-stimulated normal rat kidney fibroblast (NRK49F) cell model in vitro.

MAIN METHODS

In vivo UUO mouse model and in vitro TGF-β1 stimulated cell model were built. Immunohistochemical staining, Western blots, Real-time PCR and fluorescence microscopy were employed to detect extra cellular matrix (ECM) synthesis, fibroblast activation, aerobic glycolysis switch and related signaling pathways.

KEY FINDINGS

HE and Masson's Trichrome staining showed that 3-BrPA substantially suppressed kidney injury and interstitial collagen production. 3-BrPA also attenuated ECM accumulation in a dose-dependent manner, as shown by immunohistochemistry staining, RT-PCR and western blot. Furthermore, 3-BrPA inhibited FMT, as indicated by α-SMA and PCNA immunofluorescence double staining. Additionally, the results of MTT assay indicated 3-BrPA prevented TGF-β1 induced fibroblasts proliferation in a time- and dose-dependent manner. Mechanistically, molecular docking results showed that 3-BrPA effectively decreased the aerobic glycolysis related enzymes Hexokinase-2 (HK-2), Lactate dehydrogenase A (LDHA) and Pyruvate kinase isozymes M2 (PKM-2), as well as inhibited IL-1 receptor-associated kinase 4 (IRAK4)/MYC protein levels.

SIGNIFICANCE

Our study highlighted that 3-BrPA is a potential reno-protective agent in kidney fibrosis through the inhibition of fibroblasts aerobic glycolysis might via IRAK4/MYC signal pathways.

The Power of Plasticity-Metabolic Regulation of Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are resident non-parenchymal liver pericytes whose plasticity enables them to regulate a remarkable range of physiologic and pathologic responses. To support their functions in health and disease, HSCs engage pathways regulating carbohydrate, mitochondrial, lipid, and retinoid homeostasis. In chronic liver injury, HSCs drive hepatic fibrosis and are implicated in inflammation and cancer. To do so, the cells activate, or transdifferentiate, from a quiescent state into proliferative, motile myofibroblasts that secrete extracellular matrix, which demands rapid adaptation to meet a heightened energy need. Adaptations include reprogramming of central carbon metabolism, enhanced mitochondrial number and activity, endoplasmic reticulum stress, and liberation of free fatty acids through autophagy-dependent hydrolysis of retinyl esters that are stored in cytoplasmic droplets. As an archetype for pericytes in other tissues, recognition of the HSC's metabolic drivers and vulnerabilities offer the potential to target these pathways therapeutically to enhance parenchymal growth and modulate repair.

Glycolysis-derived acidic microenvironment as a driver of endothelial dysfunction in systemic sclerosis

OBJECTIVES

Systemic sclerosis (SSc) is an autoimmune disease characterized by peripheral vasculopathy and skin and internal organ fibrosis. Accumulating evidence underlines a close association between a metabolic reprogramming of activated fibroblasts and fibrosis. This prompted us to determine the metabolism of SSc dermal fibroblasts and the effect on the vasculopathy characterizing the disease.

METHODS

Seahorse XF96 Extracellular Flux Analyzer was exploited to evaluate SSc fibroblast metabolism. In vitro invasion and capillary morphogenesis assays were used to determine the angiogenic ability of endothelial cells (EC). Immunofluorescence, flow cytometer and real time PCR techniques provided evidence of the molecular mechanism behind the impaired vascularization that characterizes SSc patients.

RESULTS

SSc fibroblasts, compared with control, showed a boosted glycolytic metabolism with increased lactic acid release and subsequent extracellular acidification, that in turn was found to impair EC invasion and organization in capillary-like networks without altering cell viability. A molecular link between extracellular acidosis and endothelial dysfunction was identified as acidic EC up-regulated MMP-12 which cleaves and inactivates uPAR, impairing angiogenesis in SSc. Moreover, the acidic environment was found to induce the loss of endothelial markers and the acquisition of mesenchymal-like features in EC, thus promoting the endothelial-to-mesenchymal transition (EndoMT) process that contributes to both capillary rarefaction and tissue fibrosis in SSc.

CONCLUSION

This study disclosed a liaison among the metabolic reprogramming of SSc dermal fibroblasts, extracellular acidosis and endothelial dysfunction that may contribute to the impairment and loss of peripheral capillary networks in SSc disease.

Hedgehog Signaling, a Critical Pathway Governing the Development and Progression of Hepatocellular Carcinoma

Hedgehog (Hh) signaling is a classic morphogen in controlling embryonic development and tissue repairing. Aberrant activation of Hh signaling has been well documented in liver cancer, including hepatoblastoma, hepatocellular carcinoma (HCC) and cholangiocarcinoma. The present review aims to update the current understanding on how abnormal Hh signaling molecules modulate initiation, progression, drug resistance and metastasis of HCC. The latest relevant literature was reviewed with our recent findings to provide an overview regarding the molecular interplay and clinical relevance of the Hh signaling in HCC management. Hh signaling molecules are involved in the transformation of pre-carcinogenic lesions to malignant features in chronic liver injury, such as nonalcoholic steatohepatitis. Activation of GLI target genes, such as ABCC1 and TAP1, is responsible for drug resistance in hepatoma cells, with a CD133⁻/EpCAM⁻ surface molecular profile, and GLI1 and truncated GLI1 account for the metastatic feature of the hepatoma cells, with upregulation of matrix metalloproteinases. A novel bioassay for the Sonic Hh ligand in tissue specimens may assist HCC diagnosis with negative α-fetoprotein and predict early microvascular invasion. In-depth exploration of the Hh signaling deepens our understanding of its molecular modulation in HCC initiation, drug sensitivity and metastasis, and guides precise management of HCC on an individual basis.

Biological insights in the pathogenesis of hypermobile Ehlers-Danlos syndrome from proteome profiling of patients' dermal myofibroblasts

Hypermobile Ehlers-Danlos syndrome (hEDS), mainly characterized by generalized joint hypermobility and its complications, minor skin changes, and apparently segregating with an autosomal dominant pattern, is still without a known molecular basis. Hence, its diagnosis is only clinical based on a strict set of criteria defined in the revised EDS nosology. Moreover, the hEDS phenotypic spectrum is wide-ranging and comprises multiple associated signs and symptoms shared with other heritable or acquired connective tissue disorders and chronic inflammatory diseases. In this complex scenario, we previously demonstrated that hEDS patients' skin fibroblasts show phenotypic features of myofibroblasts, widespread extracellular matrix (ECM) disarray, perturbation of ECM-cell contacts, and dysregulated expression of genes involved in connective tissue architecture and related to inflammatory and pain responses. Herein, the cellular proteome of 6 hEDS dermal myofibroblasts was compared to that of 12 control fibroblasts to deepen the knowledge on mechanisms involved in the disease pathogenesis. Qualitative and quantitative differences were assessed based on top-down and bottom-up approaches and some differentially expressed proteins were proofed by biochemical analyses. Proteomics disclosed the differential expression of proteins principally implicated in cytoskeleton organization, energy metabolism and redox balance, proteostasis, and intracellular trafficking. Our findings offer a comprehensive view of dysregulated protein networks and related pathways likely associated with the hEDS pathophysiology. The present results can be regarded as a starting point for future in-depth investigations aimed to decipher the functional impact of potential bioactive molecules for the development of targeted management and therapies.

Curcumin- and Cyclopamine-Loaded Liposomes to Enhance Therapeutic Efficacy Against Hepatic Fibrosis

BACKGROUND AND PURPOSE

Hepatic fibrosis is a public health problem characterized by activation of hepatic stellate cells (HSCs), which triggers excessive production of extracellular matrix (ECM). Inhibition of HSC activation may be an effective treatment. Since various pathways control HSC activation, a combination of drugs with different mechanisms may be more effective than monotherapy.

METHODS

Here, we prepared liposomes loaded with curcumin and cyclopamine to inhibit HSC activation. We systematically analyzed the physicochemical characteristics of liposomes loaded with the two drugs, as well as their effects on HSC proliferation, activation and collagen production on gene, protein and cellular levels.

RESULTS

The prepared liposomes helped solubilize both drugs, contributing to their uptake by cells. Liposomes loaded with both drugs inhibited cell proliferation, migration and invasion, as well as induced more apoptosis and perturbed the cell cycle more than the free combination of both drugs in solution or liposomes loaded with either drug alone. Liposomes loaded with both drugs strongly suppressed HSC activation and collagen secretion.

CONCLUSION

Our results suggest that liposome encapsulation can increase the uptake of curcumin and cyclopamine as well as the synergism between them in anti-fibrosis. This approach shows potential for treating hepatic fibrosis.

Novel Interplay Between Sonic Hedgehog and Transforming Growth Factor-β1 in Human Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) has the potential to progress to fibrosis, cirrhosis, and hepatocellular carcinoma. Upregulation of sonic hedgehog (Shh) has been documented in development of NASH through sustained cell stress. At the same time, transforming growth factor-β1 (TGF-β1), which is a central element in fibrogenic reactions in various diseases and sites, has been reported to be associated with hepatic inflammation and fibrotic reaction. To explore crosstalk between Shh and TGF-β1 in the development and progression of NASH, we investigated the expression of both these proteins in 135 human specimens of NASH, 35 fatty liver specimens, 35 specimens of alcoholic steatohepatitis with immunohistochemistry. Shh protein was expressed in the cytoplasm of ballooned hepatocytes with an ubiquitin-like pattern. In addition, a few scattered apoptotic hepatocytes in the inflammatory foci showed homogeneous cytoplasmic Shh expression. TGF-β1 protein was observed mainly in the activated hepatic stellate cells (HSCs) which were located in the inflammatory foci surrounding ballooned hepatocytes. Moreover, the mRNA levels of both Shh and TGF-β1 in the liver biopsy specimens from NASH patients was significantly increased compared with those in fatty liver patients. Statistically, there was a significant association of the expressions of Shh and TGF-β1 proteins in NASH (r=0.6, P<0.05). In addition, increased expression of Shh protein significantly parallels the severity of hepatocellular ballooning, lobular, and portal inflammatory responses and progression of fibrosis in NASH patients. Moreover, we found that much HSCs transformed into myofibroblast-like phenotype and migrated downward to HepG2 hepatocellular carcinoma cells with overexpression of Shh by transwell assay. We also observed overexpression of proteins of Shh and TGF-β1 in cultured activated HSCs with confocal microscopy. These findings strongly suggest there is interplay between Shh and TGF-β1 in hepatic inflammatory reactions. Shh secreted through damaged hepatocytes may result in activation of TGF-β1 and subsequent transformation of HSCs, which together modulate the progression of human NASH.

PNPLA3 I148M Up-Regulates Hedgehog and Yap Signaling in Human Hepatic Stellate Cells

Liver fibrosis represents the wound healing response to sustained hepatic injury with activation of hepatic stellate cells (HSCs). The I148M variant of the PNPLA3 gene represents a risk factor for development of severe liver fibrosis. Activated HSCs carrying the I148M variant display exacerbated pro-inflammatory and pro-fibrogenic features. We aimed to examine whether the I148M variant may impair Hedgehog and Yap signaling, as key pathways implicated in the control of energy expenditure and maintenance of myofibroblastic traits. First, we show that TGF-β rapidly up-regulated the PNPLA3 transcript and protein and Yap/Hedgehog target gene expression. In addition, HSCs overexpressing PNPLA3 I148M boosted anaerobic glycolysis, as supported by higher lactate release and decreased phosphorylation of the energy sensor AMPK. These cells displayed higher Yap and Hedgehog signaling, due to accumulation of total Yap protein, Yap promoter activity and increased downstream targets expression, compared to WT cells. HSCs exposed to TGF-β and leptin rapidly increased total Yap, together with a reduction in its inhibited form, phosphorylated Yap. In line, Yap-specific inhibitor Verteporfin strongly abolished Yap-mediated genes expression, at baseline as well as after TGF-β and leptin treatments in HSCs with I148M PNPLA3. Finally, Yap transcriptional activity was strongly reduced by a combination of Verteporfin and Rosiglitazone, a PPARγ synthetic agonist. In conclusion, HSCs carrying the PNPLA3 variant show activated Yap/Hedgehog pathways, resulting in altered anaerobic glycolysis and enhanced synthesis of Hedgehog markers and sustained Yap signaling. TGF-β and leptin exacerbate Yap/Hedgehog-related fibrogenic genes expression, while Yap inhibitors and PPARγ agonists abrogate these effects in PNPLA3 I148M carrying HSCs.

Simultaneous Induction of Glycolysis and Oxidative Phosphorylation during Activation of Hepatic Stellate Cells Reveals Novel Mitochondrial Targets to Treat Liver Fibrosis

Upon liver injury, hepatic stellate cells (HSCs) transdifferentiate to migratory, proliferative and extracellular matrix-producing myofibroblasts (e.g., activated HSCs; aHSCs) causing liver fibrosis. HSC activation is associated with increased glycolysis and glutaminolysis. Here, we compared the contribution of glycolysis, glutaminolysis and mitochondrial oxidative phosphorylation (OXPHOS) in rat and human HSC activation. Basal levels of glycolysis (extracellular acidification rate ~3-fold higher) and particularly mitochondrial respiration (oxygen consumption rate ~5-fold higher) were significantly increased in rat aHSCs, when compared to quiescent rat HSC. This was accompanied by extensive mitochondrial fusion in rat and human aHSCs, which occurred without increasing mitochondrial DNA content and electron transport chain (ETC) components. Inhibition of glycolysis (by 2-deoxy-D-glucose) and glutaminolysis (by CB-839) did not inhibit rat aHSC proliferation, but did reduce Acta2 (encoding α-SMA) expression slightly. In contrast, inhibiting mitochondrial OXPHOS (by rotenone) significantly suppressed rat aHSC proliferation, as well as Col1a1 and Acta2 expression. Other than that observed for rat aHSCs, human aHSC proliferation and expression of fibrosis markers were significantly suppressed by inhibiting either glycolysis, glutaminolysis or mitochondrial OXPHOS (by metformin). Activation of HSCs is marked by simultaneous induction of glycolysis and mitochondrial metabolism, extending the possibilities to suppress hepatic fibrogenesis by interfering with HSC metabolism.

Pathophysiological mechanisms underlying MAFLD

BACKGROUND AND AIMS

The pathophysiology underlying metabolic associated fatty liver disease (MAFLD) involves a multitude of interlinked processes, including insulin resistance (IR) underlying the metabolic syndrome, lipotoxicity attributable to the accumulation of toxic lipid species, infiltration of proinflammatory cells causing hepatic injury and ultimately leading to hepatic stellate cell (HSC) activation and fibrogenesis. The proximal processes, such as IR, lipid overload and lipotoxicity are relatively well established, but the downstream molecular mechanisms, such as inflammatory processes, hepatocyte lipoapoptosis, and fibrogenesis are incompletely understood.

METHODS

A literature search was performed with Medline (PubMed), Scopus and Google Scholar electronic databases till June 2020, using relevant keywords (nonalcoholic fatty liver disease; metabolic associated fatty liver disease; nonalcoholic steatohepatitis; NASH pathogenesis) to extract relevant studies describing pathogenesis of MAFLD/MASH.

RESULTS

Several studies have reported new concepts underlying pathophysiology of MAFLD. Activation of HSCs is the common final pathway for diverse signals from damaged hepatocytes and proinflammatory cells. Activated HSCs then secrete excess extracellular matrix (ECM) which accumulates and impairs structure and function of the liver. TAZ (a transcriptional regulator), hedgehog (HH) ligands, transforming growth factor-β (TGF-β), bone morphogenetic protein 8B (BMP8B) and osteopontin play important roles in activating these HSCs. Dysfunctional gut microbiome, dysregulated bile acid metabolism, endogenous alcohol production, and intestinal fructose handling, modify individual susceptibility to MASH.

CONCLUSIONS

Newer concepts of pathophysiology underlying MASH, such as TAZ/Ihh pathway, extracellular vesicles, microRNA, dysfunctional gut microbiome and intestinal fructose handling present promising targets for the development of therapeutic agents.

Pyruvate Kinase M2 Tetramerization Protects against Hepatic Stellate Cell Activation and Liver Fibrosis

Liver fibrosis is an increasing health problem worldwide, for which no effective antifibrosis drugs are available. Although the involvement of aerobic glycolysis in hepatic stellate cell (HSC) activation has been reported, the role of pyruvate kinase M2 (PKM2) in liver fibrogenesis still remains unknown. We examined PKM2 expression and location in liver tissues and primary hepatic cells. The in vitro and in vivo effects of a PKM2 antagonist (shikonin) and its allosteric agent (TEPP-46) on liver fibrosis were investigated in HSCs and liver fibrosis mouse model. Chromatin immunoprecipitation sequencing and immunoprecipitation were performed to identify the relevant molecular mechanisms. PKM2 expression was significantly up-regulated in both mouse and human fibrotic livers compared with normal livers, and mainly detected in activated, rather than quiescent, HSCs. PKM2 knockdown markedly inhibited the activation and proliferation of HSCs in vitro. Interestingly, the PKM2 dimer, rather than the tetramer, induced HSC activation. PKM2 tetramerization induced by TEPP-46 effectively inhibited HSC activation, reduced aerobic glycolysis, and decreased MYC and CCND1 expression via regulating histone H3K9 acetylation in activated HSCs. TEPP-46 and shikonin dramatically attenuated liver fibrosis in vivo. Our findings demonstrate a nonmetabolic role of PKM2 in liver fibrosis. PKM2 tetramerization or suppression could prevent HSC activation and protects against liver fibrosis.

Acetyl-CoA carboxylase inhibition disrupts metabolic reprogramming during hepatic stellate cell activation

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease characterized by hepatic lipid accumulation, inflammation, and progressive fibrosis. Acetyl-CoA carboxylase (ACC) catalyzes the rate-limiting step of de novo lipogenesis and regulates fatty acid β-oxidation in hepatocytes. ACC inhibition reduces hepatic fat content and markers of liver injury in patients with NASH; however, the effect of ACC inhibition on liver fibrosis has not been reported.

METHODS

A direct role for ACC in fibrosis was evaluated by measuring de novo lipogenesis, procollagen production, gene expression, glycolysis, and mitochondrial respiration in hepatic stellate cells (HSCs) in the absence or presence of small molecule inhibitors of ACC. ACC inhibitors were evaluated in rodent models of liver fibrosis induced by diet or the hepatotoxin, diethylnitrosamine. Fibrosis and hepatic steatosis were evaluated by histological and biochemical assessments.

RESULTS

Inhibition of ACC reduced the activation of TGF-β-stimulated HSCs, as measured by both α-SMA expression and collagen production. ACC inhibition prevented a metabolic switch necessary for induction of glycolysis and oxidative phosphorylation during HSC activation. While the molecular mechanism by which inhibition of de novo lipogenesis blocks glycolysis and oxidative phosphorylation is unknown, we definitively show that HSCs require de novo lipogenesis for activation. Consistent with this direct antifibrotic mechanism in HSCs, ACC inhibition reduced liver fibrosis in a rat choline-deficient, high-fat diet model and in response to chronic diethylnitrosamine-induced liver injury (in the absence of hepatic lipid accumulation).

CONCLUSIONS

In addition to reducing lipid accumulation in hepatocytes, ACC inhibition also directly impairs the profibrogenic activity of HSCs. Thus, small molecule inhibitors of ACC may lessen fibrosis by reducing lipotoxicity in hepatocytes and by preventing HSC activation, providing a mechanistic rationale for the treatment of patients with advanced liver fibrosis due to NASH.

LAY SUMMARY

Hepatic fibrosis is the most important predictor of liver-related outcomes in patients with non-alcoholic steatohepatitis (NASH). Small molecule inhibitors of acetyl-CoA carboxylase (ACC) reduce hepatic fat content and markers of liver injury in patients with NASH. Herein, we report that inhibition of ACC and de novo lipogenesis also directly suppress the activation of hepatic stellate cells - the primary cell responsible for generating fibrotic scar in the liver - and thus fibrosis. These data provide further evidence for the use of ACC inhibitors to treat patients with NASH and advanced fibrosis.

Microcystin-leucine-arginine induces liver fibrosis by activating the Hedgehog pathway in hepatic stellate cells

Microcystin-leucine-arginine (MC-LR), produced by cyanobacteria, accumulates in the liver through blood circulation. We investigated the impact of MC-LR on liver fibrosis. Mice received a daily injection of MC-LR at various concentrations for 14 consecutive days aa and then mouse liver was obtained for histopathological and immunoblot analysis. Next, a human hepatic stellate cell line (LX-2) was treated with MC-LR at various concentrations followed by measurement of cell viability, cell cycle and relevant protein expression levels. Our data confirmed the induction of mouse liver fibrosis after exposure to MC-LR at 15 μg/kg and 30 μg/kg. Furthermore, we demonstrated that LX-2 cells could uptake MC-LR, resulting in cell proliferation and differentiation through impacting the Hedgehog signaling after the treatment of MC-LR at 50 nM. Our data supported that MC-LR could induce liver fibrosis by modulating the expression of the transcription factor Gli2 in the Hedgehog signaling in hepatic stellate cells.

MicroRNA interplay between hepatic stellate cell quiescence and activation

Hepatic stellate cells (HSCs) activation play a significant role in the progression of hepatic fibrosis. During chronic liver diseases, hepatocytes are damaged severely and secrete several pro-inflammatory markers and profibrogenic cytokines via modulation of a variety of signaling pathways that are responsible for the activation of HSCs. The microRNAs (miRNA or miR) have the potential to modulate fibrogenic signaling pathways in HSCs. A variety of miRNAs are identified as profibrogenic and are capable of activating HSCs by modulating fibrosis-associated signaling pathways such as transforming growth factor-β/Smad, Wnt/β-catenin, Hedgehog, Snail and Notch in the injured liver. On the other hand, HSCs also have certain antifibrotic miRNAs and these include miR-16, miR-19b, miR-29, miR-30, miR-101, miR-122, miR-133a, miR-144, miR-146a, miR-150-5p, miR-155, miR-195, miR-200a, miR-214, miR-335, miR-370, miR-454, miR-483, etc. are responsible for maintenance of the quiescent phenotype of normal HSCs, apoptosis induction and phenotypic reversion of activated HSCs, inhibition of HSCs proliferation, suppression of the extracellular matrix-associated gene expressions, etc. Thus, understanding of HSCs specific miRNAs regulation may provide new ideas for the targeted therapy of hepatic fibrosis at molecular level in the near future. Therefore, this review focusses on the modulation of miRNAs profile during the HSCs activation in the fibrotic liver.

Myofibroblasts and Fibrosis: Mitochondrial and Metabolic Control of Cellular Differentiation

Cardiac fibrosis is mediated by the activation of resident cardiac fibroblasts, which differentiate into myofibroblasts in response to injury or stress. Although myofibroblast formation is a physiological response to acute injury, such as myocardial infarction, myofibroblast persistence, as occurs in heart failure, contributes to maladaptive remodeling and progressive functional decline. Although traditional pathways of activation, such as TGFβ (transforming growth factor β) and AngII (angiotensin II), have been well characterized, less understood are the alterations in mitochondrial function and cellular metabolism that are necessary to initiate and sustain myofibroblast formation and function. In this review, we highlight recent reports detailing the mitochondrial and metabolic mechanisms that contribute to myofibroblast differentiation, persistence, and function with the hope of identifying novel therapeutic targets to treat, and potentially reverse, tissue organ fibrosis.

Fibroblast Reprogramming in Gastrointestinal Cancer

Gastrointestinal cancers are a significant cause of cancer mortality worldwide and have been strongly linked with chronic inflammation. Current therapies focus on epithelial/cancer cells; however, the importance of the tumor microenvironment in the development and treatment of the disease is also now well established. Cancer-associated fibroblasts (CAFs) are a major component of the tumor microenvironment, and are actively participating in tumor initiation, promotion and metastasis. They structurally and functionally affect cancer cell proliferation, tumor immunity, angiogenesis, extracellular matrix remodeling and metastasis through a variety of signaling pathways. CAFs originate predominantly from resident mesenchymal cells, which are activated and reprogrammed in response to cues from cancer cells. In recent years, chronic inflammation of the gastrointestinal tract has also proven an important driver of mesenchymal cell activation and subsequent CAF development, which in turn are capable of regulating the transition from acute to chronic inflammation and cancer. In this review, we will provide a concise overview of the mechanisms that drive fibroblast reprogramming in cancer and the recent advances on the downstream signaling pathways that regulate the functional properties of the activated mesenchyme. This new mechanistic insight could pave the way for new therapeutic strategies and better prognosis for cancer patients.

Long non-coding RNA Linc00092 inhibits cardiac fibroblast activation by altering glycolysis in an ERK-dependent manner

AIMS

Cardiac fibroblast (CF) activation is the key event for cardiac fibrosis. The role of glycolysis and the glycolysis-related lncRNAs in CF activation are unknown. Thus, we aimed to investigate the role of glycolysis in CF activation and to identify the glycolysis-related lncRNAs involved.

MAIN METHODS

Glycolysis-related lncRNAs were searched and their expression profiles were validated in activated human CF (HCF) and human failing heart tissues. Expression of the target lncRNA was manipulated to determine its effects on HCF activation and glycolysis. The underlying mechanisms of lncRNA-dependent glycolysis regulation were also addressed.

KEY FINDINGS

HCF activation induced by transforming growth factor-β1 was accompanied by an enhanced glycolysis, and 2-Deoxy-d-glucose, a specific glycolysis inhibitor, dramatically attenuated HCF activation. Twenty-eight glycolysis-related lncRNAs were identified and Linc00092 expression was changed mostly upon HCF activation. In human heart tissue, Linc00092 is primarily expressed in cardiac fibroblasts. Linc00092 knockdown activated HCFs with enhanced glycolysis, while its overexpression rescued the activated phenotype of HCFs and down-regulated glycolysis. Restoration of glycolysis abolished the anti-fibrotic effects conferred by Linc00092. Linc00092 inhibited ERK activation in activated HCFs, and ERK inhibition counteracted the fibrotic phenotype in Linc00092 knockdown HCFs.

SIGNIFICANCE

These results revealed that Linc00092 could attenuate HCF activation by suppressing glycolysis. The inhibition of ERK by Linc00092 may play an important role in this process. Together, this provides a better understanding of the mechanism of CF activation and may serve as a novel target for cardiac fibrosis treatment.

CPEB4 Increases Expression of PFKFB3 to Induce Glycolysis and Activate Mouse and Human Hepatic Stellate Cells, Promoting Liver Fibrosis

BACKGROUND & AIMS

We investigated mechanisms of hepatic stellate cell (HSC) activation, which contributes to liver fibrogenesis. We aimed to determine whether activated HSCs increase glycolysis, which is regulated by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3 (PFKFB3), and whether this pathway might serve as a therapeutic target.

METHODS

We performed studies with primary mouse HSCs, human LX2 HSCs, human cirrhotic liver tissues, rats and mice with liver fibrosis (due to bile duct ligation [BDL] or administration of carbon tetrachloride), and CPEB4-knockout mice. Glycolysis was inhibited in cells and mice by administration of a small molecule antagonist of PFKFB3 (3-[3-pyridinyl]-1-[4-pyridinyl]-2-propen-1-one [3PO]). Cells were transfected with small interfering RNAs that knock down PFKFB3 or CPEB4.

RESULTS

Up-regulation of PFKFB3 protein and increased glycolysis were early and sustained events during HSC activation and accompanied by increased expression of markers of fibrogenesis; incubation of HSCs with 3PO or knockdown of PFKFB3 reduced their activation and proliferation. Mice with liver fibrosis after BDL had increased hepatic PFKFB3; injection of 3PO immediately after the surgery prevented HSC activation and reduced the severity of liver fibrosis compared with mice given vehicle. Levels of PFKFB3 protein were increased in fibrotic liver tissues from patients compared with non-fibrotic liver. Up-regulation of PFKFB3 in activated HSCs did not occur via increased transcription, but instead via binding of CPEB4 to cytoplasmic polyadenylation elements within the 3'-untranslated regions of PFKFB3 messenger RNA. Knockdown of CPEB4 in LX2 HSCs prevented PFKFB3 overexpression and cell activation. Livers from CPEB4-knockout had decreased PFKFB3 and fibrosis after BDL or administration of carbon tetrachloride compared with wild-type mice.

CONCLUSIONS

Fibrotic liver tissues from patients and rodents (mice and rats) have increased levels of PFKFB3 and glycolysis, which are essential for activation of HSCs. Increased expression of PFKFB3 is mediated by binding of CPEB4 to its untranslated messenger RNA. Inhibition or knockdown of CPEB4 or PFKFB3 prevents HSC activation and fibrogenesis in livers of mice.

Astaxanthin inhibits the reduction of glycolysis during the activation of hepatic stellate cells

AIMS

Hepatic stellate cells (HSCs) play an essential role in the development of liver fibrosis by producing extracellular matrix proteins, growth factors, and pro-inflammatory and pro-fibrogenic cytokines once activated. We previously demonstrated that astaxanthin (ASTX), a xanthophyll carotenoid, attenuates HSC activation. The objective of this study was to investigate whether there is a difference in glycolysis between quiescent and activated HSCs and the effect of ASTX on glycolysis during HSC activation.

MATERIALS AND METHODS

Mouse primary HSCs were activated for 7 days in the presence or absence of 25 μM of ASTX. Quiescent HSCs (qHSCs), 1 day after isolation, and activated HSCs (aHSCs) treated with/without ASTX were plated in a Seahorse XF24 cell culture microplate for Glycolysis Stress tests.

KEY FINDINGS

aHSCs had significantly lower glycolysis, but higher glycolytic capacity, maximum capacity of glycolysis, and non-glycolytic acidification than qHSCs. Importantly, ASTX markedly increased glycolysis during HSC activation with a concomitant increase in lactate formation and secretion. Compared with qHSCs, aHSCs had significantly lower expression of glucose transporter 1, the major glucose transporter in HSCs, and its transcription factor hypoxia-inducible factor 1α, which was markedly increased by ASTX in aHSCs.

SIGNIFICANCE

Our data suggest that ASTX may prevent the activation of HSCs by altering glycolysis and the expression of genes involved in the pathways.

PAX6 contributes to the activation and proliferation of hepatic stellate cells via activating Hedgehog/GLI1 pathway

Aberrant activation of Hedgehog signaling is considered as the key player in hepatic stellate cell (HSC) activation involved in liver fibrosis (LF). The glioma-associated protein gene (GLI) has a predicted paired box 6 (PAX6)-binding site within its transcribed region. Therefore, this study aimed to investigate the relationship between PAX6 and GLI and their contribution to HSC activation and proliferation. PAX6 expression was upregulated in platelet-derived growth factor-BB (PDGF-BB)-induced LX-2 cells. The activation and proliferation of HSC were inhibited by interference of PAX6 with short hairpin RNA (shPAX6) via curbing Hedgehog signaling. Notably, PAX6 directly bound to the promoter sequence of GLI1 independent of the PTCH/SMO axis. Therefore, we propose that PAX6 upregulation induces HSC activation and proliferation through crosstalk with GLI1 signaling. Thus, these novel mechanistic insights involving the PAX6-mediated regulation of the activation and proliferation of HSC may provide a new therapeutic target for LF.

Mechanisms of liver fibrosis and its role in liver cancer

Hepatic fibrogenesis is a pathophysiological outcome of chronic liver injury hallmarked by excessive accumulation of extracellular matrix proteins. Fibrosis is a dynamic process that involves cross-talk between parenchymal cells (hepatocytes), hepatic stellate cells, sinusoidal endothelial cells and both resident and infiltrating immune cells. In this review, we focus on key cell-types that contribute to liver fibrosis, cytokines, and chemokines influencing this process and what it takes for fibrosis to regress. We discuss how mitochondria and metabolic changes in hepatic stellate cells modulate the fibrogenic process. We also briefly review how the presence of fibrosis affects development of hepatocellular carcinoma.

Increased Glutaminolysis Marks Active Scarring in Nonalcoholic Steatohepatitis Progression

BACKGROUND & AIMS

Nonalcoholic steatohepatitis (NASH) occurs in the context of aberrant metabolism. Glutaminolysis is required for metabolic reprograming of hepatic stellate cells (HSCs) and liver fibrogenesis in mice. However, it is unclear how changes in HSC glutamine metabolism contribute to net changes in hepatic glutaminolytic activity during fibrosis progression, or whether this could be used to track fibrogenic activity in NASH. We postulated that increased HSC glutaminolysis marks active scarring in NASH.

METHODS

Glutaminolysis was assessed in mouse NASH fibrosis models and in NASH patients. Serum and liver levels of glutamine and glutamate and hepatic expression of glutamine transporter/metabolic enzymes were correlated with each other and with fibrosis severity. Glutaminolysis was disrupted in HSCs to examine if this directly influenced fibrogenesis. ¹⁸F-fluoroglutamine positron emission tomography was used to determine how liver glutamine assimilation tracked with hepatic fibrogenic activity in situ.

RESULTS

The serum glutamate/glutamine ratio increased and correlated with its hepatic ratio, myofibroblast content, and fibrosis severity. Healthy livers almost exclusively expressed liver-type glutaminase (Gls2); Gls2 protein localized in zone 1 hepatocytes, whereas glutamine synthase was restricted to zone 3 hepatocytes. In fibrotic livers, Gls2 levels reduced and glutamine synthase zonality was lost, but both Slc1a5 (glutamine transporter) and kidney-type Gls1 were up-regulated; Gls1 protein was restricted to stromal cells and accumulated in fibrotic septa. Hepatocytes did not compensate for decreased Gls2 by inducing Gls1. Limiting glutamine or directly inhibiting GLS1 inhibited growth and fibrogenic activity in cultured human HSCs. Compared with healthy livers, fibrotic livers were ¹⁸F-fluoroglutamine-avid by positron emission tomography, suggesting that glutamine-addicted myofibroblasts drive increased hepatic utilization of glutamine as fibrosis progresses.

CONCLUSIONS

Glutaminolysis is a potential diagnostic marker and therapeutic target during NASH fibrosis progression.