The hedgehog pathway in nonalcoholic fatty liver disease

Comprehensive profiling of serum microRNAs in normal and non-alcoholic fatty liver disease (NAFLD) patients

Pediatric non-alcoholic fatty liver disease (NAFLD) is emerging as a worldwide health concern with the potential to advance to cirrhosis and liver cancer. NAFLD can also directly contribute to heart problems through inflammation and insulin resistance, even in individuals without other risk factors. The pathological mechanisms of NAFLD are linked to functional differences of miRNAs in different biological environments. The miRNA in serum exosomes may reflect the pathological state of the liver and changes in systemic metabolism, while the miRNA in serum may be associated with physiological processes other than the liver. Pediatric non-alcoholic fatty liver disease (NAFLD) is emerging as a worldwide health concern with the potential to advance to cirrhosis and liver cancer. NAFLD can also directly contribute to heart problems through inflammation and insulin resistance, even in individuals without other risk factors. The pathological mechanisms of NAFLD are linked to functional differences of miRNAs in different biological environments. The miRNA in serum exosomes may reflect the pathological state of the liver and changes in systemic metabolism, while the miRNA in serum may be associated with physiological processes other than the liver. Pediatric non-alcoholic fatty liver disease (NAFLD) is emerging as a worldwide health concern with the potential to advance to cirrhosis and liver cancer. NAFLD can also directly contribute to heart problems through inflammation and insulin resistance, even in individuals without other risk factors. The pathological mechanisms of NAFLD are linked to functional differences of miRNAs in different biological environments. The miRNA in serum exosomes may reflect the pathological state of the liver and changes in systemic metabolism, while the miRNA in serum may be associated with physiological processes other than the liver. Our study identified 36 miRNAs with differential expression in the serum of NAFLD patients compared to the control group, including 21 miRNAs with significantly increased expression and 15 with decreased expression. Consistent with our previously reported data on serum-derived exosomal miRNA profiling, this study also observed a notable upregulation of serum miR-122-5p levels in NAFLD patients. PCR validation confirmed the differential expression of miR-122-5p identified through RNA sequencing. Functional analysis using GO and KEGG pathways revealed a diverse range of biological roles associated with these differentially expressed miRNAs. Notably, NAFLD significantly impacts heart health, with miR-122-5p playing a key role in regulating cardiovascular function. Furthermore, activation of the miR-122/Sirt-6/ACE2 axis may contribute to myocardial necrosis, highlighting its potential role in NAFLD-associated cardiovascular risks. Our study suggests that miR-122 plays a key role in the progression of NAFLD and its associated metabolic disturbances, which can increase the risk of cardiovascular disease. Targeting miR-122 may offer potential therapeutic benefits for improving both liver and heart health in individuals with NAFLD.

Hedgehog Signaling Pathway in Fibrosis and Targeted Therapies

Hedgehog (Hh) signaling is a well-established developmental pathway; it is crucial for early embryogenesis, cell differentiation, and damage-driven regeneration. It is being increasingly recognized that dysregulated Hh signaling is also involved in fibrotic diseases, which are characterized by excessive extracellular matrix deposition that compromises tissue architecture and function. As in-depth insights into the mechanisms of Hh signaling are obtained, its complex involvement in fibrosis is gradually being illuminated. Notably, some Hh-targeted inhibitors are currently under exploration in preclinical and clinical trials as a means to prevent fibrosis progression. In this review, we provide a concise overview of the biological mechanisms involved in Hh signaling. We summarize the latest advances in our understanding of the roles of Hh signaling in fibrogenesis across the liver, kidneys, airways, and lungs, as well as other tissues and organs, with an emphasis on both the shared features and, more critically, the distinct functional variations observed across these tissues and organs. We thus highlight the context dependence of Hh signaling, as well as discuss the current status and the challenges of Hh-targeted therapies for fibrosis.

MAFLD-related hepatocellular carcinoma: Exploring the potent combination of immunotherapy and molecular targeted therapy

Hepatocellular carcinoma (HCC) is a common cause of cancer-related mortality and morbidity globally, and with the prevalence of metabolic-related diseases, the incidence of metabolic dysfunction-associated fatty liver disease (MAFLD) related hepatocellular carcinoma (MAFLD-HCC) continues to rise with the limited efficacy of conventional treatments, which has created a major challenge for HCC surveillance. Immune checkpoint inhibitors (ICIs) and molecularly targeted drugs offer new hope for advanced MAFLD-HCC, but the evidence for the use of both types of therapy in this type of tumour is still insufficient. Theoretically, the combination of immunotherapy, which awakens the body's anti-tumour immunity, and targeted therapies, which directly block key molecular events driving malignant progression in HCC, is expected to produce synergistic effects. In this review, we will discuss the progress of immunotherapy and molecular targeted therapy in MAFLD-HCC and look forward to the opportunities and challenges of the combination therapy.

Unveiling the role of the Hedgehog signaling pathway in chronic liver disease: Therapeutic insights and strategies

The Hedgehog (Hh) signaling plays a crucial role in adult liver repair by promoting the expansion and differentiation of hepatic progenitor cells into mature hepatocytes and cholangiocytes. Elevated Hh signaling is associated with severe chronic liver diseases, making Hh inhibitors a promising therapeutic option. Sonidegib and vismodegib, both FDA-approved Smoothened (Smo) inhibitors for basal cell carcinoma (BCC), have shown potential for application in chronic liver disorders based on clinical evidence. We highlight the vital role of the Hh pathway in metabolic dysfunction-associated steatotic liver disease (MASLD)/metabolic dysfunction-associated steatohepatitis (MASH), liver fibrosis, and hepatocellular carcinoma (HCC). Moreover, therapeutic strategies targeting the Hh pathway in chronic liver diseases have been discussed, providing a basis for improving disease management and outcomes.

A novel combination therapy targets sonic hedgehog signaling by the dual inhibition of HMG-CoA reductase and HSP90 in rats with non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is characterized by liver inflammation, fat accumulation, and collagen deposition. Due to the limited availability of effective treatments, there is a pressing need to develop innovative strategies. Given the complex nature of the disease, employing combination approaches is essential. Hedgehog signaling has been recognized as potentially promoting NASH, and cholesterol can influence this signaling by modifying the conformation of PTCH1 and SMO activity. HSP90 plays a role in the stability of SMO and GLI proteins. We revealed significant positive correlations between Hedgehog signaling proteins (Shh, SMO, GLI1, and GLI2) and both cholesterol and HSP90 levels. Herein, we investigated the novel combination of the cholesterol-lowering agent lovastatin and the HSP90 inhibitor PU-H71 in vitro and in vivo. The combination demonstrated a synergy score of 15.09 and an MSA score of 22.85, as estimated by the ZIP synergy model based on growth inhibition rates in HepG2 cells. In a NASH rat model induced by thioacetamide and a high-fat diet, this combination therapy extended survival, improved liver function and histology, and enhanced antioxidant defense. Additionally, the combination exhibited anti-inflammatory and anti-fibrotic potential by influencing the levels of TNF-α, TGF-β, TIMP-1, and PDGF-BB. This effect was evident in the suppression of the Col1a1 gene expression and the levels of hydroxyproline and α-SMA. These favorable outcomes may be attributed to the combination's potential to inhibit key Hedgehog signaling molecules. In conclusion, exploring the applicability of this combination contributes to a more comprehensive understanding and improved management of NASH and other fibrotic disorders.

Liver-specific Mettl14 deletion induces nuclear heterotypia and dysregulates RNA export machinery

Modification of RNA with N6-methyladenosine (m6A) has gained attention in recent years as a general mechanism of gene regulation. In the liver, m6A, along with its associated machinery, has been studied as a potential biomarker of disease and cancer, with impacts on metabolism, cell cycle regulation, and pro-cancer state signaling. However these observational data have yet to be causally examined in vivo. For example, neither perturbation of the key m6A writers Mettl3 and Mettl14, nor the m6A readers Ythdf1 and Ythdf2 have been thoroughly mechanistically characterized in vivo as they have been in vitro. To understand the functions of these machineries, we developed mouse models and found that deleting Mettl14 led to progressive liver injury characterized by nuclear heterotypia, with changes in mRNA splicing, processing and export leading to increases in mRNA surveillance and recycling.

Phytochemicals as Potential Lead Molecules against Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most prevalent form of liver cancer, accounting for 85-90% of liver cancer cases and is a leading cause of cancer-related mortality worldwide. The major risk factors for HCC include hepatitis C and B viral infections, along with chronic liver diseases, such as cirrhosis, fibrosis, and non-alcoholic steatohepatitis associated with metabolic syndrome. Despite the advancements in modern medicine, there is a continuous rise in the annual global incidence rate of HCC, and it is estimated to reach >1 million cases by 2025. Emerging research in phytomedicine and chemotherapy has established the anti-cancer potential of phytochemicals, owing to their diverse biological activities. In this review, we report the major phytochemicals that have been explored in combating hepatocellular carcinoma and possess great potential to be used as an alternative or in conjunction with the existing HCC treatment modalities. An overview of the pre-clinical observations, mechanism of action and molecular targets of some of these phytochemicals is also incorporated.

Time course of western diet (WD) induced nonalcoholic steatohepatitis (NASH) in female and male Ldlr-/- mice

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is a global health problem. Identification of factors contributing to the onset and progression of NAFLD have the potential to direct novel strategies to combat NAFLD.

METHODS

We examined the time course of western diet (WD)-induced NAFLD and its progression to nonalcoholic steatohepatitis (NASH) in age-matched female and male Ldlr-/- mice, with time-points at 1, 4, 8, 20 and 40 weeks on the WD. Controls included Ldlr-/- mice maintained on a purified low-fat diet (LFD) for 1 and 40 weeks. The approach included quantitation of anthropometric, plasma and liver markers of disease, plus hepatic histology, lipids, oxylipins, gene expression and selected metabolites.

RESULTS

One week of feeding the WD caused a significant reduction in hepatic essential fatty acids (EFAs: 18:2, ω6, 18:3, ω3) which preceded the decline in many C20-22 ω3 and ω6 polyunsaturated fatty acids (PUFA) and PUFA-derived oxylipins after 4 weeks on the WD. In addition, expression of hepatic inflammation markers (CD40, CD44, Mcp1, Nlrp3, TLR2, TLR4, Trem2) increased significantly in both female & male mice after one week on the WD. These markers continued to increase over the 40-week WD feeding study. WD effects on hepatic EFA and inflammation preceded all significant WD-induced changes in body weight, insulin resistance (HOMA-IR), oxidative stress status (GSH/GSSG ratio) and histological and gene expression markers of macrosteatosis, extracellular matrix remodeling and fibrosis.

CONCLUSIONS

Our findings establish that feeding Ldlr-/- mice the WD rapidly lowered hepatic EFAs and induced key inflammatory markers linked to NASH. Since EFAs have an established role in inflammation and hepatic inflammation plays a major role in NASH, we suggest that early clinical assessment of EFA status and correcting EFA deficiencies may be useful in reducing NASH severity.

The impact and role of identified long noncoding RNAs in nonalcoholic fatty liver disease: A narrative review

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide, but its mechanism and pathophysiology remain unclear. Long noncoding RNAs (lncRNAs) may exert a vital influence on regulating various biological functions in NAFLD.

METHODS

The databases such as Google Scholar, PubMed, and Medline were searched using the following keywords: nonalcoholic fatty liver disease, nonalcoholic fatty liver disease, NAFLD, nonalcoholic steatohepatitis, nonalcoholic steatohepatitis, NASH, long noncoding RNAs, and lncRNAs. Considering the titles and abstracts, unrelated studies were excluded. The authors evaluated the full texts of the remaining studies.

RESULTS

We summarized the current knowledge of lncRNAs and the main signaling pathways of lncRNAs involved in NAFLD explored in recent years. As a heterogeneous group of noncoding RNAs (ncRNAs), lncRNAs play crucial roles in biological processes underlying the pathophysiology of NAFLD. The mechanisms, particularly those associated with the regulation of the expression and activities of lncRNAs, play important roles in NAFLD.

CONCLUSION

A better comprehension of the mechanism controlled by lncRNAs in NAFLD is necessary for the identification of novel therapeutic targets for drug development and improved, noninvasive methods for diagnosis.

Osteocalcin and Its Potential Functions for Preventing Fatty Liver Hemorrhagic Syndrome in Poultry

Osteocalcin (OCN) is synthesized and secreted by differentiating osteoblasts. In addition to its role in bone, OCN acts as a hormone in the pancreas, liver, muscle, fat, and other organs to regulate multiple pathophysiological processes including glucose homeostasis and adipic acid metabolism. Fat metabolic disorder, such as excessive fat buildup, is related to non-alcoholic fatty liver disease (NAFLD) in humans. Similarly, fatty liver hemorrhage syndrome (FLHS) is a metabolic disease in laying hens, resulting from lipid accumulation in hepatocytes. FLHS affects hen health with significant impact on poultry egg production. Many studies have proposed that OCN has protective function in mammalian NAFLD, but its function in chicken FLHS and related mechanism have not been completely clarified. Recently, we have revealed that OCN prevents laying hens from FLHS through regulating the JNK pathway, and some pathways related to the disease progression have been identified through both in vivo and vitro investigations. In this view, we discussed the current findings for predicting the strategy for using OCN to prevent or reduce FLHS impact on poultry production.

Non-alcoholic fatty liver disease: the pathologist's perspective

Non-alcoholic fatty liver disease (NAFLD) is a spectrum of diseases characterized by fatty accumulation in hepatocytes, ranging from steatosis, non-alcoholic steatohepatitis, to cirrhosis. While histopathological evaluation of liver biopsies plays a central role in the diagnosis of NAFLD, limitations such as the problem of interobserver variability still exist and active research is underway to improve the diagnostic utility of liver biopsies. In this article, we provide a comprehensive overview of the histopathological features of NAFLD, the current grading and staging systems, and discuss the present and future roles of liver biopsies in the diagnosis and prognostication of NAFLD.

Cerebrolysin Use in Patients with Liver Damage-A Translational Study

The treatment of acute life-threatening events in patients suffering from chronic pathologies is problematic, as physicians need to consider multisystemic drug effects. Regarding Cerebrolysin, a Sonic Hedgehog signaling pathway amplifier and one of the few approved neurotrophic treatments for stroke patients, concerns of excessive Hedgehog pathway activation that could accelerate NAFLD progression to cirrhosis seem valid. We investigated stroke patients treated with Cerebrolysin that presented elevated levels of aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT). We also investigated the efficiency of Cerebrolysin in reversing the neurogenesis inhibition within the hippocampus in a mouse model of NAFLD by evaluating behavior and histological outcomes. NeuN, BrdU and Iba1 positive signals in the cortex and hippocampus of the animals were also observed. Clinically, Cerebrolysin improved AST levels in a majority of stroke patients with hepatic damage. The same treatment in an experimental setup was able to reverse anxiety-like behavior in MCD mice, reducing their freezing time from 333.61 ± 21.81 s in MCD animals to 229.17 ± 26.28 in treated ones. The use of Cerebrolysin did not improve short-term memory nor rescued cell multiplication in the hippocampus after MCD food intake. Understanding the neuroprotective and neurotrophic effects that drugs have on NAFLD patients can significantly contribute to a suitable therapeutic approach.

Hepatogenesis and hepatocarcinogenesis: Alignment of the main signaling pathways

Development is a symphony of cells differentiation in which different signaling pathways are orchestrated at specific times and periods to form mature and functional cells from undifferentiated cells. The similarity of the gene expression profile in malignant and undifferentiated cells is an interesting topic that has been proposed for many years and gave rise to the differentiation-therapy concept, which appears a rational insight and should be reconsidered. Hepatocellular carcinoma (HCC), as the sixth common cancer and the third leading cause of cancer death worldwide, is one of the health-threatening complications in communities where hepatotropic viruses are endemic. Sedentary lifestyle and high intake of calories are other risk factors. HCC is a complex condition in which various dimensions must be addressed, including heterogeneity of cells in the tumor mass, high invasiveness, and underlying diseases that limit the treatment options. Under these restrictions, recognizing, and targeting common signaling pathways during liver development and HCC could expedite to a rational therapeutic approach, reprograming malignant cells to well-differentiated ones in a functional state. Accordingly, in this review, we highlighted the commonalities of signaling pathways in hepatogenesis and hepatocarcinogenesis, and comprised an update on the current status of targeting these pathways in laboratory studies and clinical trials.

Hesperetin derivative decreases CCl4 -induced hepatic fibrosis by Ptch1-dependent mechanisms

Hepatic fibrosis (HF), a continuous wound-healing response of the liver to repeated injuries, is characterized by abnormal extracellular matrix (ECM) accumulation. Hepatic stellate cells (HSCs) are considered a major cell type for ECM production. However, recent evidence indicates the lack of effective treatments for HF. Hesperetin, a Traditional Chinese Medicine monomer, has been isolated from the fruit peel of Citrusaurantium L. (Rutaceae). Growing evidence suggests the partial function of hesperetin in HF treatment. A hesperetin derivative (HD) was synthesized in our laboratory to increase the bioavailability and the water solubility of hesperetin. In this study, we detected the functions of HD in a mouse model of CCl₄ -induced HF and transforming growth factor-β1-stimulated HSC-T6 cells, in vivo and in vitro. HD reduced histological damage and CCl₄ -induced HF. Moreover, HD interference was associated with the activation of indicators in HSC-T6 cells, showing that HD is involved in HSCs activation in HF. Mechanistically, the Hedgehog pathway is involved in the HD treatment of HF, and HD may attenuate the aberrant expression of patched1. In conclusion, the studies indicate that HD may function as a potential antifibrotic Traditional Chinese Medicine monomer in HF therapy.

Overexpression of NAG-1/GDF15 prevents hepatic steatosis through inhibiting oxidative stress-mediated dsDNA release and AIM2 inflammasome activation

Mitochondrial dysfunction and oxidative stress-mediated inflammasome activation play critical roles in the pathogenesis of the non-alcoholic fatty liver disease (NAFLD). Non-steroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1), or growth differentiation factor-15 (GDF15), is associated with many biological processes and diseases, including NAFLD. However, the role of NAG-1/GDF15 in regulating oxidative stress and whether this process is associated with absent in melanoma 2 (AIM2) inflammasome activation in NAFLD are unknown. In this study, we revealed that NAG-1/GDF15 is significantly downregulated in liver tissues of patients with steatosis compared to normal livers using the Gene Expression Omnibus (GEO) database, and in free fatty acids (FFA, oleic acid/palmitic acid, 2:1)-induced HepG2 and Huh-7 cellular steatosis models. Overexpression of NAG-1/GDF15 in transgenic (Tg) mice significantly alleviated HFD-induced obesity and hepatic steatosis, improved lipid homeostasis, enhanced fatty acid β-oxidation and lipolysis, inhibited fatty acid synthesis and uptake, and inhibited AIM2 inflammasome activation and the secretion of IL-18 and IL-1β, as compared to their wild-type (WT) littermates without reducing food intake. Furthermore, NAG-1/GDF15 overexpression attenuated FFA-induced triglyceride (TG) accumulation, lipid metabolism deregulation, and AIM2 inflammasome activation in hepatic steatotic cells, while knockdown of NAG-1/GDF15 demonstrated opposite effects. Moreover, NAG-1/GDF15 overexpression inhibited HFD- and FFA-induced oxidative stress and mitochondrial damage which in turn reduced double-strand DNA (dsDNA) release into the cytosol, while NAG-1/GDF15 siRNA showed opposite effects. The reduced ROS production and dsDNA release may be responsible for attenuated AIM2 activation by NAG-1/GDF15 upon fatty acid overload. In conclusion, our results provide evidence that other than regulating lipid homeostasis, NAG-1/GDF15 protects against hepatic steatosis through a novel mechanism via suppressing oxidative stress, mitochondrial damage, dsDNA release, and AIM2 inflammasome activation.

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NAG-1/GDF15 is downregulated in human steatotic liver and FFA-induced liver cells.

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NAG-1/GDF15 inhibits hepatic steatosis and improves lipid homeostasis.

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AIM2 inflammasome is activated in steatosis models and is inhibited by NAG-1/GDF15.

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NAG-1/GDF15 reduces oxidative stress and mitochondrial damage in steatosis models.

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NAG-1/GDF15 inhibits mitochondrial dsDNA release and thus inhibits AIM2 activation.

Functional Roles of Chemokine Receptor CCR2 and Its Ligands in Liver Disease

Chemokines are a family of cytokines that orchestrate the migration and positioning of immune cells within tissues and are critical for the function of the immune system. CCR2 participates in liver pathology, including acute liver injury, chronic hepatitis, fibrosis/cirrhosis, and tumor progression, by mediating the recruitment of immune cells to inflammation and tumor sites. Although a variety of chemokines have been well studied in various diseases, there is no comprehensive review presenting the roles of all known chemokine ligands of CCR2 (CCL2, CCL7, CCL8, CCL12, CCL13, CCL16, and PSMP) in liver disease, and this review aims to fill this gap. The introduction of each chemokine includes its discovery, its corresponding chemotactic receptors, physiological functions and roles in inflammation and tumors, and its impact on different immune cell subgroups.

Aging reduces liver resiliency by dysregulating Hedgehog signaling

Older age is a major risk factor for damage to many tissues, including liver. Aging undermines resiliency and impairs liver regeneration. The mechanisms whereby aging reduces resiliency are poorly understood. Hedgehog is a signaling pathway with critical mitogenic and morphogenic functions during development. Recent studies indicate that Hedgehog regulates metabolic homeostasis in adult liver. The present study evaluates the hypothesis that Hedgehog signaling becomes dysregulated in hepatocytes during aging, resulting in decreased resiliency and therefore, impaired regeneration and enhanced vulnerability to damage. Partial hepatectomy (PH) was performed on young and old wild‐type mice and Smoothened (Smo)‐floxed mice treated with viral vectors to conditionally delete Smo and disrupt Hedgehog signaling specifically in hepatocytes. Changes in signaling were correlated with changes in regenerative responses and compared among groups. Old livers had fewer hepatocytes proliferating after PH. RNA sequencing identified Hedgehog as a top downregulated pathway in old hepatocytes before and after the regenerative challenge. Deleting Smo in young hepatocytes before PH prevented Hedgehog pathway activation after PH and inhibited regeneration. Gene Ontogeny analysis demonstrated that both old and Smo‐deleted young hepatocytes had activation of pathways involved in innate immune responses and suppression of several signaling pathways that control liver growth and metabolism. Hedgehog inhibition promoted telomere shortening and mitochondrial dysfunction in hepatocytes, consequences of aging that promote inflammation and impair tissue growth and metabolic homeostasis. Hedgehog signaling is dysregulated in old hepatocytes. This accelerates aging, resulting in decreased resiliency and therefore, impaired liver regeneration and enhanced vulnerability to damage.

Inhibition of Hedgehog Delays Liver Regeneration through Disrupting the Cell Cycle

Liver regeneration is a complicated biological process orchestrated by various liver resident cells. Hepatic cell proliferation and reconstruction of the hepatic architecture involve multiple signaling pathways. It has been reported that the Hh signal is involved in liver regeneration. However, the signal transduction pathways and cell types involved are ill studied. This study aimed to investigate hedgehog signal response cell types and the specific molecular mechanism involved in the process of liver regeneration. Partial hepatectomy (PH) of 70% was performed on ICR (Institute of Cancer Research) mice to study the process of liver regeneration. We found that the hedgehog signal was activated significantly after PH, including hedgehog ligands, receptors and intracellular signaling molecules. Ligand signals were mainly expressed in bile duct cells and non-parenchymal hepatic cells, while receptors were expressed in hepatocytes and some non-parenchymal cells. Inhibition of the hedgehog signal treated with vismodegib reduced the liver regeneration rate after partial hepatectomy, including inhibition of hepatic cell proliferation by decreasing Cyclin D expression and disturbing the cell cycle through the accumulation of Cyclin B. The current study reveals the important role of the hedgehog signal and its participation in the regulation of hepatic cell proliferation and the cell cycle during liver regeneration. It provides new insight into the recovery of the liver after liver resection.

Zonation in NASH - A key paradigm for understanding pathophysiology and clinical outcomes

Non-alcoholic fatty liver disease (NAFLD) exists as a spectrum ranging from simple steatosis to histologically defined hepatocyte injury and inflammatory changes that define steatohepatitis (NASH), and increase risk for fibrosis. Although zonal differences in NASH have not been systematically studied, periportal involvement has been associated with worse metabolic outcomes and more hepatic fibrosis as compared to pericentral disease. These data suggest that hepatic zonation of disease may influence the diversity of clinical presentations. Similarly, several randomized clinical trials suggest a differential response based on zonation of disease, with preferential effects on periportal (cysteamine) or pericentral disease (obeticholic acid, pioglitazone). Intriguingly, morphogenic pathways known to affect zonal development and maintenance - WNT/β-Catenin, Hedgehog, HIPPO/Yap/TAZ and Notch - have been implicated in NASH pathogenesis, and nuclear hormone receptors downstream of potential NASH therapeutics show zonal preferences. In this review, we summarize these data and propose that patient-specific activation of these pathways may explain the variability in clinical presentation, and the zone-specific response observed in clinical trials.

Hepatocyte and immune cell crosstalk in non-alcoholic fatty liver disease

Introduction: Nonalcoholic fatty liver disease (NAFLD) is the most widespread chronic liver disease in the world. It can evolve into nonalcoholic steatohepatitis (NASH) where inflammation and hepatocyte ballooning are key participants in the determination of this steatotic state.Areas covered: To provide a systematic overview and current understanding of the role of inflammation in NAFLD and its progression to NASH, the function of the cells involved, and the activation pathways of the innate immunity and cell death; resulting in inflammation and chronic liver disease. A PubMed search was made with relevant articles together with relevant references were included for the writing of this review.Expert opinion: Innate and adaptive immunity are the key players in the NAFLD progression; some of the markers presented during NAFLD are also known to be immunity biomarkers. All cells involved in NAFLD and NASH are known to have immunoregulatory properties and their imbalance will completely change the cytokine profile and form a pro-inflammatory microenvironment. It is necessary to fully answer the question of what initiators and metabolic imbalances are particularly important, considering sterile inflammation as the architect of the disease. Due to the shortage of elucidation of NASH progression, we discuss in this review, how inflammation is a key part of this development and we presume the targets should lead to inflammation and oxidative stress treatment.

Interaction of tacrolimus through hedgehog signaling pathway: An in vitro evaluation using rat hepatocytes

Tacrolimus (TAC) is the drug of choice in immunosuppressive therapy for organ transplantation; however, adverse effects are still a major concern. The current study aims to decipher the short-term exposure of TAC on rat hepatocytes in relation to activation of hedgehog (HH) signaling pathway. Time dependent study was conducted using primary rat hepatocytes treated with TAC (36 µM) for 6, 12, 24 and 48 h. Western blot analysis was performed using cell lysate in order to analyze the regulation of HH pathway proteins including HHIP, SMO, PTCH, IHH, SHH, and GLI transcription factors. The study revealed change in protein expression of HH signaling molecules with activation of HH pathway, due to downregulation of HHIP, and enrichment of HH ligands with activation of SMO and GLI transcription factors. It is therefore, concluded that short term TAC exposure leads to upregulation of HH pathway in liver, which may initially act to repair the liver damage but can worsen the condition in case of prolonged immunosuppressive therapy. This insight could lead to understand association of off target effects of immunosuppressive drugs and occurrence of other liver diseases in transplant patients when it comes to long term immunosuppressive therapy. These findings also illuminate a novel direction that use of HH inhibitor might provide a therapeutic strategy for immune suppression related liver disorders.

Relationship between lipid metabolism and Hedgehog signaling pathway

The Hedgehog (Hh) signaling pathway is highly conserved signaling pathway in cells. Steroids was found to play a vital role in Hh signaling pathway and aberrant Hh signaling was found to lead a series of disease correlate with abnormal lipid metabolism. This paper aimed to elucidate the relationship between lipid metabolism and Hedgehog signaling pathway.

Molecular Mechanisms Linking Nonalcoholic Steatohepatitis to Cancer

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Transcriptomic and Proteomic Analysis of Steatohepatitic Hepatocellular Carcinoma Reveals Novel Distinct Biologic Features

OBJECTIVES

Steatohepatitic hepatocellular carcinoma is a distinct variant of hepatocellular carcinoma strongly associated with underlying nonalcoholic steatohepatitis. The molecular biology of steatohepatitic hepatocellular carcinoma is not fully elucidated, and thus we aimed to investigate the molecular underpinnings of this entity.

METHODS

Transcriptomic analysis using RNAseq was performed on eight tumor-nonneoplastic pairs of steatohepatitic hepatocellular carcinoma with comparison to conventional hepatocellular carcinoma transcriptomes curated in The Cancer Genome Atlas. Immunohistochemistry was used to validate key RNA-level findings.

RESULTS

Steatohepatitic hepatocellular carcinoma demonstrated a distinctive differential gene expression profile compared with The Cancer Genome Atlas curated conventional hepatocellular carcinomas (n = 360 cases), indicating the distinctive steatohepatitic hepatocellular carcinoma morphology is associated with a unique gene expression profile. Pathway analysis comparing tumor-nonneoplastic pairs revealed significant upregulation of the hedgehog pathway based on GLI1 overexpression and significant downregulation of carnitine palmitoyltransferase 2 transcript. Glutamine synthetase transcript was significantly upregulated, and fatty acid binding protein 1 transcript was significantly downregulated and immunohistochemically confirmed, indicating steatohepatitic hepatocellular carcinoma tumor cells display a zone 3 phenotype.

CONCLUSIONS

Steatohepatitic hepatocellular carcinoma demonstrates a distinctive morphology and gene expression profile, phenotype of zone 3 hepatocytes, and activation of the hedgehog pathway and repression of carnitine palmitoyltransferase 2, which may be important in tumorigenesis.

Current and Potential Therapies Targeting Inflammation in NASH

Nonalcoholic steatohepatitis (NASH) is the advanced form of nonalcoholic fatty liver disease (NAFLD). It is characterized by hepatic steatosis, inflammation, hepatocellular injury, and fibrosis. Inflammation plays a key role in the progression of NASH and can be provoked by intrahepatic (e.g., lipotoxicity, immune responses, oxidative stress and cell death) and extrahepatic sources (adipose tissue or gut). The identification of triggers of inflammation is central to understanding the mechanisms in NASH development and progression and in designing targeted therapies that can halt or reverse the disease. In this review, we summarize the current and potential therapies targeting inflammation in NASH.

Recent advances targeting C-C chemokine receptor type 2 for liver diseases in monocyte/macrophage

Liver plays a critical role in metabolism, nutrient storage and detoxification. Emergency signals or appropriate immune response leads to pathological inflammation and breaks the steady state when liver dysfunction appears, which makes body more susceptible to chronic liver infection, autoimmune diseases and tumour. Compelling proof has illustrated the non-redundant importance of C-C chemokine receptor type 2 (CCR2), one of G-protein-coupled receptors, in different diseases. Selectively expressed on the surface of cells, CCR2 is involved in various signalling pathways and regulates the migration of cells. Especially, a peculiar role of CCR2 has been identified within decades in the onset and progression of hepatic diseases, which led to particular focusing on CCR2 as a new therapeutic and diagnostic target for non-alcoholic fatty liver disease and hepatocellular carcinoma. In this review, we discuss the effect of CCR2 in monocytes/macrophages on liver diseases. The application and translation of the decades of discoveries into therapies promise novel approaches in the treatment of liver disease.

Mutual Zonated Interactions of Wnt and Hh Signaling Are Orchestrating the Metabolism of the Adult Liver in Mice and Human

The Hedgehog (Hh) and Wnt/β-Catenin (Wnt) cascades are morphogen pathways whose pronounced influence on adult liver metabolism has been identified in recent years. How both pathways communicate and control liver metabolic functions are largely unknown. Detecting core components of Wnt and Hh signaling and mathematical modeling showed that both pathways in healthy liver act largely complementary to each other in the pericentral (Wnt) and the periportal zone (Hh) and communicate mainly by mutual repression. The Wnt/Hh module inversely controls the spatiotemporal operation of various liver metabolic pathways, as revealed by transcriptome, proteome, and metabolome analyses. Shifting the balance to Wnt (activation) or Hh (inhibition) causes pericentralization and periportalization of liver functions, respectively. Thus, homeostasis of the Wnt/Hh module is essential for maintaining proper liver metabolism and to avoid the development of certain metabolic diseases. With caution due to minor species-specific differences, these conclusions may hold for human liver as well.

Cyclopamine and Rapamycin Synergistically Inhibit mTOR Signalling in Mouse Hepatocytes, Revealing an Interaction of Hedgehog and mTor Signalling in the Liver

In the liver, energy homeostasis is mainly regulated by mechanistic target of rapamycin (mTOR) signalling, which influences relevant metabolic pathways, including lipid metabolism. However, the Hedgehog (Hh) pathway is one of the newly identified drivers of hepatic lipid metabolism. Although the link between mTOR and Hh signalling was previously demonstrated in cancer development and progression, knowledge of their molecular crosstalk in healthy liver is lacking. To close this information gap, we used a transgenic mouse model, which allows hepatocyte-specific deletion of the Hh pathway, and in vitro studies to reveal interactions between Hh and mTOR signalling. The study was conducted in male and female mice to investigate sexual differences in the crosstalk of these signalling pathways. Our results reveal that the conditional Hh knockout reduces mitochondrial adenosine triphosphate (ATP) production in primary hepatocytes from female mice and inhibits autophagy in hepatocytes from both sexes. Furthermore, in vitro studies show a synergistic effect of cyclopamine and rapamycin on the inhibition of mTor signalling and oxidative respiration in primary hepatocytes from male and female C57BL/6N mice. Overall, our results demonstrate that the impairment of Hh signalling influences mTOR signalling and therefore represses oxidative phosphorylation and autophagy.

Pyrvinium pamoate attenuates non-alcoholic steatohepatitis: Insight on hedgehog/Gli and Wnt/β-catenin signaling crosstalk

Non-alcoholic steatohepatitis (NASH) is a devastating form of non-alcoholic fatty liver disease (NAFLD). Pyrvinium pamoate (PP) has been recently introduced as anti-adipogenic compound. We aimed to investigate the effects of PP on high fat diet (HFD)-induced NASH in rats and examine the underlying mechanisms. NASH was induced by exposing rats to HFD for 16 weeks and a single dose of streptozotocin (STZ) 35 mg/kg at the fifth week. At the tenth week, PP was given orally at a dose of 60 µg/kg, day after day for 6 weeks. HFD/STZ induced significant steatohepatitis and insulin resistance as was evident by the elevated transaminases activity, NAFLD activity score and HOMA-IR level. Also, HFD induced serum hyperlipidemia and hepatic lipid accumulation. In addition, HFD induced an imbalance in the oxidative status of the liver via upregulating lipid peroxides and mitochondrial oxidative stress markers (MnSOD, UCP-2), together with marked decrease in anti-oxidant glutathione level, glutathione peroxidase activity and expression of mitophagy related markers (PINK1, Parkin, ULK1) and increase in SQSTM1/p62 and LC3II/LC3I. Upregulation of inflammatory mediators (TNF-α, IL-6, IL-1β) and apoptotic marker (caspase 3) were observed. Those events all together precipitated in initiation of liver fibrosis as confirmed by elevation of transforming growth factor-β1 (TGF-β1), alpha-smooth muscle actin (α-SMA) and liver collagen content. Co-treatment with PP protected against HFD-induced NASH and liver fibrosis via downregulating the expression of key factors in Hedgehog and Wnt/ β-catenin signaling pathway. These findings imply that PP can attenuate the progression of NASH and its associated sequela of liver fibrosis.

6-Amino[1,2,5]oxadiazolo[3,4-b]pyrazin-5-ol Derivatives as Efficacious Mitochondrial Uncouplers in STAM Mouse Model of Nonalcoholic Steatohepatitis

Small molecule mitochondrial uncouplers have recently garnered great interest for their potential in treating nonalcoholic steatohepatitis (NASH). In this study, we report the structure-activity relationship profiling of a 6-amino[1,2,5]oxadiazolo[3,4-b]pyrazin-5-ol core, which utilizes the hydroxy moiety as the proton transporter across the mitochondrial inner membrane. We demonstrate that a wide array of substituents is tolerated with this novel scaffold that increased cellular metabolic rates in vitro using changes in oxygen consumption rate as a readout. In particular, compound SHS4121705 (12i) displayed an EC50 of 4.3 μM in L6 myoblast cells and excellent oral bioavailability and liver exposure in mice. In the STAM mouse model of NASH, administration of 12i at 25 mg kg-1 day-1 lowered liver triglyceride levels and improved liver markers such as alanine aminotransferase, NAFLD activity score, and fibrosis. Importantly, no changes in body temperature or food intake were observed. As potential treatment of NASH, mitochondrial uncouplers show promise for future development.

The Association between SOCS1-1656G>A Polymorphism, Insulin Resistance and Obesity in Nonalcoholic Fatty Liver Disease (NAFLD) Patients

Suppressor of cytokine signaling (SOCS) proteins prevent uncontrolled cytokine signaling and appear to play a role in the pathological processes behind obesity and insulin resistance. The polymorphism of the SOCS1 gene (rs243330, −1656G>A) is associated with obesity and glucose sensitivity. To estimate the effect of this SOCS1 gene polymorphism on nonalcoholic fatty liver disease (NAFLD) susceptibility, we performed a study on 138 patients with ultrasound-confirmed NAFLD and 1000 healthy blood donors. The relationship between the SOCS1−1656G>A polymorphism and serum biochemical parameters in NAFLD was additionally investigated. The SOCS1 variant was genotyped using a dedicated TaqMan assay. The frequency of rs243330 polymorphism did not differ between patients and controls. However, in a cohort of obese individuals (BMI ≥ 30 kg/m²) the occurrence of the G allele of the SOCS1−1656G>A polymorphism was strongly associated with NAFLD (odds ratio (OR) 1.6; 95% CI,1.1–2.5; p = 0.009), and carriers of the AA genotype have lower risk of developing NAFLD (OR 0.4; 95% CI, 0.2–0.7; p = 0.004). Overweight NAFLD patients who were carriers of GG genotypes had significantly lower levels of homeostasis model assessment of insulin resistance (HOMA-IR) values (p = 0.03 vs. AA), and the obese GG homozygotes had lower serum concertation of triglyceride (GG vs. AA; p = 0.02). Serum liver enzyme activities were not modified by the presence of SOCS1 risk variants. In conclusion, the observed phenotype of overweight NAFLD patients with non-elevated levels of TG and HOMA-IR, which is associated with genetic variants of SOCS1, provides a rationale for further research on the pathophysiology of fatty liver disease.

Laparoscopic sleeve gastrectomy reverses non-alcoholic fatty liver disease modulating oxidative stress and inflammation

BACKGROUND & AIMS

Hepatic alterations, such as in non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are frequently associated with obesity. To investigate the molecular mechanisms of these alterations and to identify molecules that could be used as potential therapeutic targets, we investigated the modulation of hepatic indices of oxidative stress and inflammation in obese patients undergoing laparoscopic sleeve gastrectomy (LSG).

METHODS

Patients (n = 436) attending our obesity clinic underwent LSG for weight loss. We obtained a diagnostic intraoperative liver biopsy, and a sub-cohort (n = 120) agreed to a 1-year follow-up that included donation of blood samples and additional liver biopsies. Selected key molecules in blood and liver tissue were used to investigate the hepatic alterations in obesity, and their response to LSG.

RESULTS

One year post-surgery, the prevalence of diabetes, dyslipidemia and hypertension decreased significantly. LSG improved liver histology features in all patients. Improvement was greater in severe cases of NAFLD including those with steatohepatitis, bridging fibrosis or cirrhosis. Significant pre-surgery differences in plasma, and liver markers of oxidative stress and inflammation (including chemokine C-C motif ligand 2, paraoxonase-1, galectin-3, and sonic hedgehog) were observed between patients with, and those without, NASH; post-surgery indicated consistent improvements in these parameters.

CONCLUSION

Our study shows that the histology and liver function of patients with morbid obesity are significantly improved after LSG via mechanisms that involve the reduction of oxidative stress and inflammatory processes. These data encourage the use of LSG as a therapeutic option to improve, or resolve, NAFLD.

Hesperetin derivative attenuates CCl4-induced hepatic fibrosis and inflammation by Gli-1-dependent mechanisms

Hepatic fibrosis, a common pathological feature and leading cause of various chronic liver diseases, still lacks effective therapy. Hesperetin derivative (HD) is a derivative of Traditional Chinese Medicine monomer isolated from the fruit peel of Citrusaurantium L. (Rutaceae). In the present study, we revealed the anti-fibrotic effects of HD in CCl₄-induced mouse hepatic fibrosis model and in TGF-β1-activated LX-2 cells, in vivo and in vitro. Results showed that HD prevented CCl₄-induced liver injury and histological damage. Consistently, HD inhibited the up-regulation of liver fibrogenesis markers α-SMA, Col1α1, Col3α1 and TIMP-1 in primary hepatic stellate cells (HSCs) and suppressed inflammatory responses in primary liver macrophages from hepatic fibrosis mice. Furthermore, HD promoted the apoptosis of activated HSCs, a key step in the onset of fibrosis regression. Mechanistically, the Hedgehog pathway was involved in HD-treated hepatic fibrosis, and HD specifically contributed to attenuate the aberrant expression of Glioma associated oncogene-1 (Gli-1). Interestingly, blockade of Gli-1 removed the inhibitory effect of HD on activated HSCs, indicating that Gli-1 may play a pivotal role in mediating the anti-fibrotic effect of HD in hepatic fibrosis. Collectively, our results suggest that HD may be a potential anti-fibrotic Traditional Chinese Medicine monomer for the treatment of hepatic fibrosis.

Downregulation of hedgehog ligands in human simple steatosis may protect against nonalcoholic steatohepatitis: Is TAZ a crucial regulator?

The conversion of simple steatosis into nonalcoholic steatohepatitis (NASH) in patients with nonalcoholic fatty liver disease (NAFLD) has attracted many attentions in recent years. The role of the hedgehog (HH) pathway in the regulation of lipogenesis has been addressed in the literature. This study aimed to investigate the levels of the sonic hedgehog (SHH) and Indian hedgehog (IHH) ligands and the correlation of these ligands with levels of proteins involved in the transforming growth factor-β1 (TGF-β1) pathway, as well as the evaluation of the transcriptional coactivator with PDZ binding motif (TAZ) expression in human simple steatosis, NASH cirrhosis, and controls. Patients were divided into two groups: the first group consisted of patients diagnosed with simple steatosis (n = 16) and the second group included those diagnosed with NASH cirrhosis (n = 15). As a control group, 18 histologically normal liver tissues were collected in this study. The expression of the TGF-β1pathway components and SHH and IHH ligands were analyzed by means of the quantitative real-time polymerase chain reaction and western blot analyses. A significant decrease was found in the hepatic expression of the SHH, IHH, and TGF-β1 pathways along with the expression of TAZ in tissue specimens with simple steatosis in comparison with patients affected by NASH cirrhosis and controls. Also, the levels of SHH and IHH proteins were significantly correlated with the expression of proteins involved in the TGF-β1 pathway. Moreover, the expression of the HH pathway ligands was positively associated with the expression of TAZ, supporting the notion that TAZ may play a role in the activation of the HH pathway thereby regulating the expression of its ligands. It seems that in patients with NAFLD, the downregulation of the HH pathway ligands may stem from steatosis; however, at the same time, it may prevent the conversion of simple steatosis into NASH in patients with liver diseases. © 2019 IUBMB Life, 71(9):1382-1390, 2019.

Insulin-like growth factor binding protein related protein 1 knockdown attenuates hepatic fibrosis via the regulation of MMPs/TIMPs in mice

BACKGROUND

Previous research suggested that insulin-like growth factor binding protein related protein 1 (IGFBPrP1), as a novel mediator, contributes to hepatic fibrogenesis. Matrix metalloproteinases (MMP) and tissue inhibitors of metalloproteinases (TIMP) play an essential role in hepatic fibrogenesis by regulating homeostasis and remodeling of the extracellular matrix (ECM). However, the interaction between IGFBPrP1 and MMP/TIMP is not clear. The present study was to knockdown IGFBPrP1 to investigate the correlation between IGFBPrP1 and MMP/TIMP in hepatic fibrosis.

METHODS

Hepatic fibrosis was induced by thioacetamide (TAA) in mice. Knockdown of IGFBPrP1 expression by ultrasound-targeted microbubble destruction-mediated CMB-shRNA-IGFBPrP1 delivery, or inhibition of the Hedgehog (Hh) pathway by cyclopamine treatment, was performed in TAA-induced liver fibrosis mice. Hepatic fibrosis was determined by hematoxylin and eosin and Sirius red staining. Hepatic expression of IGFBPrP1, α-smooth muscle actin (α-SMA), transforming growth factor β 1 (TGFβ1), collagen I, MMPs/TIMPs, Sonic Hedgehog (Shh), and glioblastoma family transcription factors (Gli1) were investigated by immunohistochemical staining and Western blotting analysis.

RESULTS

We found that hepatic expression of IGFBPrP1, TGFβ1, α-SMA, and collagen I were increased longitudinally in mice with TAA-induced hepatic fibrosis, concomitant with MMP2/TIMP2 and MMP9/TIMP1 imbalance and Hh pathway activation. Knockdown of IGFBPrP1 expression, or inhibition of the Hh pathway, reduced the hepatic expression of IGFBPrP1, TGFβ1, α-SMA, and collagen I and re-established MMP2/TIMP2 and MMP9/TIMP1 balance.

CONCLUSIONS

Our findings suggest that IGFBPrP1 knockdown attenuates liver fibrosis by re-establishing MMP2/TIMP2 and MMP9/TIMP1 balance, concomitant with the inhibition of hepatic stellate cell activation, down-regulation of TGFβ1 expression, and degradation of the ECM. Furthermore, the Hh pathway mediates IGFBPrP1 knockdown-induced attenuation of hepatic fibrosis through the regulation of MMPs/TIMPs balance.

Molecular pathways of nonalcoholic fatty liver disease development and progression

Nonalcoholic fatty liver disease (NAFLD) is a main hepatic manifestation of metabolic syndrome. It represents a wide spectrum of histopathological abnormalities ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with or without fibrosis and, eventually, cirrhosis and hepatocellular carcinoma. While hepatic simple steatosis seems to be a rather benign manifestation of hepatic triglyceride accumulation, the buildup of highly toxic free fatty acids associated with insulin resistance-induced massive free fatty acid mobilization from adipose tissue and the increased de novo hepatic fatty acid synthesis from glucose acts as the "first hit" for NAFLD development. NAFLD progression seems to involve the occurrence of "parallel, multiple-hit" injuries, such as oxidative stress-induced mitochondrial dysfunction, endoplasmic reticulum stress, endotoxin-induced, TLR4-dependent release of inflammatory cytokines, and iron overload, among many others. These deleterious factors are responsible for the triggering of a number of signaling cascades leading to inflammation, cell death, and fibrosis, the hallmarks of NASH. This review is aimed at integrating the overwhelming progress made in the characterization of the physiopathological mechanisms of NAFLD at a molecular level, to better understand the factor influencing the initiation and progression of the disease.

CXC Motif Ligand 16 Promotes Nonalcoholic Fatty Liver Disease Progression via Hepatocyte-Stellate Cell Crosstalk

CONTEXT

Nonalcoholic fatty liver disease (NAFLD) is a focus of attention because of its prevalence. CXC motif ligand 16 (CXCL16) has been studied in inflammatory and metabolic diseases.

OBJECTIVE

To investigate the role of CXCL16 in steatosis and fibrosis in patients with NAFLD.

DESIGN

Liver specimens and sera of patients with NAFLD were collected from 2012 to 2017.

SETTING

Beijing 302 Hospital.

PARTICIPANTS

117 patients with NAFLD and 15 healthy controls.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The main outcome measures were CXCL16 levels in sera and biopsy specimens of patients with NAFLD.

RESULTS

CXCL16 serum level was markedly elevated in patients with NAFLD, especially in those at the S3 steatosis level according to the steatosis, activity, and fibrosis (SAF) scoring system. The different serum levels of CXCL16 between groups were due to data in patients with A or F scores ≥2, according to the SAF scoring system. CXCL16 accumulated around steatotic hepatocytes in biopsy specimens. In vitro, CXCL16 treatment led to severe steatosis of hepatocytes in the hepatocyte-stellate cell coculture system and suppressed the respiration rate of hepatocytes. Lipogenic gene expression and hepatic stellate cell activation indexes were increased in a CXCL16 overexpression system. In addition, ligands in the Hedgehog pathway cascade were downregulated in hepatocytes.

CONCLUSIONS

CXCL16 was highly expressed in patients with NAFLD, suggesting that it may contribute to steatotic and fibrotic progression. CXCL16 may be a potential noninvasive marker of NAFLD and a future potential therapeutic target to treat NAFLD.

Pathogenesis of NASH: The Impact of Multiple Pathways

Purpose of review

Advancing our understanding of the mechanisms that underlie NASH pathogenesis.

Recent findings

Recent findings on NASH pathogenesis have expanded our understanding of its complexity including: (1) there are multiple parallel hits that lead to NASH; (2) the microbiota play an important role in pathogenesis, with bacterial species recently shown to accurately differentiate between NAFL and NASH patients; (3) the main drivers of liver cell injury are lipotoxicity caused by free fatty acids (FFAs) and their derivatives combined with mitochondrial dysfunction; (4) decreased endoplasmic reticulum (ER) efficiency with increased demand for protein synthesis/folding/repair results in ER stress, protracted unfolded protein response, and apoptosis; (5) upregulated proteins involved in multiple pathways including JNK, CHOP, PERK, BH3-only proteins, and caspases result in mitochondrial dysfunction and apoptosis; and (6) subtypes of NASH in which these pathophysiological pathways vary may require patient subtype identification to choose effective therapy.

Summary

Recent pathogenesis studies may lead to important therapeutic advances, already seen in patients treated with ACC, ASK1 and SCD1 inhibitors and FXR agonists. Further advancing our understanding of mechanisms underlying NASH pathogenesis and the complex interplay between them will be crucial for developing effective therapies.

Upregulation of non-canonical Wnt ligands and oxidative glucose metabolism in NASH induced by methionine-choline deficient diet

Wnt ligands regulate metabolic pathways, and dysregulation of Wnt signaling contributes to chronic inflammatory disease. A knowledge gap exists concerning the role of aberrant Wnt signaling in non-alcoholic steatohepatitis (NASH), which exhibits metabolic syndrome and inflammation. Using a mouse model of methionine-choline deficient diet (MCDD)-induced NASH, we investigated the Wnt signaling pathways in relation to hepatic glucose oxidation. Mice fed the MCD diet for 6 weeks developed prominent NASH marked by macrovesicular steatosis, inflammation and lipid peroxidation. qPCR analysis reveals differential hepatic expression of canonical and non-canonical Wnt ligands. While expression of Wnt3a was decreased in NASH vs chow diet control, expression of Wnt5a and Wnt11 were increased 3 fold and 15 fold, respectively. Consistent with activation of non-canonical Wnt signaling, expression of the alternative Wnt receptor ROR2 was increased 5 fold with no change in LRP6 expression. Activities of the metabolic enzymes glucokinase, phosphoglucoisomerase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate kinase, and pyruvate dehydrogenase were all elevated by MCDD. NASH-driven glucose oxidation was accompanied by a 6-fold increase in lactate dehydrogenase (LDH)-B with no change in LDH-A. In addition, glucose-6-phosphate dehydrogenase, the regulatory and NADPH-producing enzyme of the pentose phosphate pathway, was elevated in NASH. These data support a role of accelerated glucose oxidation in the development of NASH, which may be driven by non-canonical Wnt signaling.