Fibroblast growth factor 15/19 (FGF15/19) protects from diet-induced hepatic steatosis: development of an FGF19-based chimeric molecule to promote fatty liver regeneration

TCF7L2 transcriptionally regulates Fgf15 to maintain bile acid and lipid homeostasis through gut-liver crosstalk

FGF19/FGF15 is an endocrine regulator of hepatic bile salt and lipid metabolism, which has shown promising effects in the treatment of NASH in clinical trials. FGF19/15 is transcribed and released from enterocytes of the small intestine into enterohepatic circulation in response to bile-induced FXR activation. Previously, the TSS of FGF19 was identified to bind Wnt-regulated TCF7L2/encoded transcription factor TCF4 in colorectal cancer cells. Impaired Wnt signaling and specifical loss of function of its coreceptor LRP6 have been associated with NASH. We, therefore, examined if TCF7L2/TCF4 upregulates Fgf19 in the small intestine and restrains NASH through gut-liver crosstalk. We examined the mice globally overexpressing, haploinsufficient, and conditional knockout models of TCF7L2 in the intestinal epithelium. The TCF7L2^+/- mice exhibited increased plasma bile salts and lipids and developed diet-induced fatty liver disease while mice globally overexpressing TCF7L2 were protected against these traits. Comprehensive in vivo analysis revealed that TCF7L2 transcriptionally upregulates FGF15 in the gut, leading to reduced bile synthesis and diminished intestinal lipid uptake. Accordingly, Vilin^Creert2 ; Tcf7L2^fl/fl mice showed reduced Fgf19 in the ileum, and increased plasma bile. The global overexpression of TCF7L2 in mice with metabolic syndrome-linked LRP6^R611C substitution rescued the fatty liver and fibrosis in the latter. Strikingly, the hepatic levels of TCF4 were reduced and CYP7a1 was increased in human NASH, indicating the relevance of TCF4-dependent regulation of bile synthesis to human disease. These studies identify the critical role of TCF4 as an upstream regulator of the FGF15-mediated gut-liver crosstalk that maintains bile and liver triglyceride homeostasis.

Nuclear Receptors Linking Metabolism, Inflammation, and Fibrosis in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) and its progressive form nonalcoholic steatohepatitis (NASH) comprise a spectrum of chronic liver diseases in the global population that can lead to end-stage liver disease and hepatocellular carcinoma (HCC). NAFLD is closely linked to the metabolic syndrome, and comorbidities such as type 2 diabetes, obesity and insulin resistance aggravate liver disease, while NAFLD promotes cardiovascular risk in affected patients. The pathomechanisms of NAFLD are multifaceted, combining hepatic factors including lipotoxicity, mechanisms of cell death and liver inflammation with extrahepatic factors including metabolic disturbance and dysbiosis. Nuclear receptors (NRs) are a family of ligand-controlled transcription factors that regulate glucose, fat and cholesterol homeostasis and modulate innate immune cell functions, including liver macrophages. In parallel with metabolic derangement in NAFLD, altered NR signaling is frequently observed and might be involved in the pathogenesis. Therapeutically, clinical data indicate that single drug targets thus far have been insufficient for reaching patient-relevant endpoints. Therefore, combinatorial treatment strategies with multiple drug targets or drugs with multiple mechanisms of actions could possibly bring advantages, by providing a more holistic therapeutic approach. In this context, peroxisome proliferator-activated receptors (PPARs) and other NRs are of great interest as they are involved in wide-ranging and multi-organ activities associated with NASH progression or regression. In this review, we summarize recent advances in understanding the pathogenesis of NAFLD, focusing on mechanisms of cell death, immunometabolism and the role of NRs. We outline novel therapeutic strategies and discuss remaining challenges.

The Role of Gut–Liver Axis in Gut Microbiome Dysbiosis Associated NAFLD and NAFLD-HCC

Nonalcoholic fatty liver disease (NAFLD) is considered as one of the most prevalent chronic liver diseases worldwide due to the rapidly rising prevalence of obesity and metabolic syndrome. As a hepatic manifestation of metabolic disease, NAFLD begins with hepatic fat accumulation and progresses to hepatic inflammation, termed as non-alcoholic steatohepatitis (NASH), hepatic fibrosis/cirrhosis, and finally leading to NAFLD-related hepatocellular carcinoma (NAFLD-HCC). Accumulating evidence showed that the gut microbiome plays a vital role in the initiation and progression of NAFLD through the gut–liver axis. The gut–liver axis is the mutual communication between gut and liver comprising the portal circulation, bile duct, and systematic circulation. The gut microbiome dysbiosis contributes to NAFLD development by dysregulating the gut–liver axis, leading to increased intestinal permeability and unrestrained transfer of microbial metabolites into the liver. In this review, we systematically summarized the up-to-date information of gut microbiome dysbiosis and metabolomic changes along the stages of steatosis, NASH, fibrosis, and NAFLD-HCC. The components and functions of the gut–liver axis and its association with NAFLD were then discussed. In addition, we highlighted current knowledge of gut microbiome-based treatment strategies targeting the gut–liver axis for preventing NAFLD and its associated HCC.

The Role of the Intestinal Microbiota in Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a serious disease threatening public health, and its pathogenesis remains largely unclear. Recent scientific research has shown that intestinal microbiota and its metabolites have an important impact on the development of NASH. A balanced intestinal microbiota contributes to the maintenance of liver homeostasis, but when the intestinal microbiota is disequilibrated, it serves as a source of pathogens and molecules that lead to NASH. In this review, we mainly emphasize the key mechanisms by which the intestinal microbiota and its metabolites affect NASH. In addition, recent clinical trials and animal studies on the treatment of NASH by regulating the intestinal microbiota through prebiotics, probiotics, synbiotics and FMT have also been briefly elaborated. With the increasing understanding of interactions between the intestinal microbiota and liver, accurate and personalized detection and treatment methods for NASH are expected to be established.

The expression of Nanog protein and fibroblast growth factor-inducible molecule 14 in patients with non-small cell lung cancer and their relationship with pathological characteristics and prognosis

Background

This study aimed to explore the expression of Nanog and fibroblast growth factor-inducible molecule 14 (Fn14) in patients with non-small cell lung cancer (NSCLC), and to explore their relationship with pathological characteristics and prognosis.

Methods

The clinical data of 89 patients with NSCLC admitted to this hospital from March 2015 to January 2019 were analyzed. The expression of Nanog and Fn14 in NSCLC tissues and normal tissues (5 cm around the tumor tissue) were analyzed by immunohistochemical staining. The relationship between Nanog and Fn14 expression and the patients’ pathological parameters was analyzed. Receiver operating characteristic curve (ROC) and Kaplan-Meier survival curves were drawn to analyze the influence of Nanog and Fn14 expression on prognosis, and logistic regression analysis was used to examine the related factors affecting the 2-year prognostic mortality of patients.

Results

The positive rates of Nanog and Fn14 in the observation group were significantly higher than those in the control group (P<0.05). The positive expression rates of Nanog and Fn14 were higher in patients with moderate/high differentiation, TNM stage III-IV, and lymph node metastasis (P<0.05). Among 89 patients with NSCLC, 25 patients died within 2 years of follow-up, with a survival rate of 71.91%. The mortality of patients with positive expression of Nanog and Fn14 was significantly higher than that of patients with negative expression (P<0.05). The median survival times of patients with negative and positive Nanog expression were (20.60±2.71) months and (18.03±2.11) months, respectively. The median survival times of patients with negative and positive Fn14 expression were (19.55±2.60) months and (15.65±2.14) months, respectively. The Kaplan-Meier survival curve showed that patients with both negative expression of Nanog and Fn14 had a longer survival time (P<0.05). Poor differentiation, TNM stage III-IV, lymph node metastasis, positive expression of Nanog, and positive expression of Fn14 were identified as risk factors affecting the prognostic mortality of patients with NSCLC (P<0.05).

Conclusions

Nanog and Fnl4 are closely related to the occurrence, development, and prognosis of NSCLC. Detection of their expression levels can provide reliable information for the early diagnosis of patients with NSCLC.

Endocrine Fibroblast Growth Factors in Relation to Stress Signaling

Fibroblast growth factors (FGFs) play important roles in various growth signaling processes, including proliferation, development, and differentiation. Endocrine FGFs, i.e., atypical FGFs, including FGF15/19, FGF21, and FGF23, function as endocrine hormones that regulate energy metabolism. Nutritional status is known to regulate the expression of endocrine FGFs through nuclear hormone receptors. The increased expression of endocrine FGFs regulates energy metabolism processes, such as fatty acid metabolism and glucose metabolism. Recently, a relationship was found between the FGF19 subfamily and stress signaling during stresses such as endoplasmic reticulum stress and oxidative stress. This review focuses on endocrine FGFs and the recent progress in FGF studies in relation to stress signaling. In addition, the relevance of the stress-FGF pathway to disease and human health is discussed.

Association of Cholecystectomy With Liver Fibrosis and Cirrhosis Among Adults in the USA: A Population-Based Propensity Score-Matched Study

Background and Aims: Cholecystectomy is the “gold standard” for treating diseases of the gallbladder. In addition, non-alcoholic fatty liver disease (NAFLD), liver fibrosis or cirrhosis, are major causes of morbidity and mortality across the world. However, the association between cholecystectomy and these diseases is still unclear. We assessed the association among US adults and examined the possible risk factors.

Methods: This cross-sectional study used data from 2017 to 2018 National Health and Nutrition Examination Survey, a population-based nationally representative sample of US. Liver fibrosis and cirrhosis were defined by median stiffness, which was assessed by transient elastography. Furthermore, patients who had undergone cholecystectomy were identified based on the questionnaire. In addition, Propensity Score Matching (PSM, 1:1) was performed based on gender, age, body mass index (BMI) and diabetes.

Results: Of the 4,497 included participants, cholecystectomy was associated with 60.0% higher risk of liver fibrosis (OR:1.600;95% CI:1.278–2.002), and 73.3% higher risk of liver cirrhosis (OR:1.733, 95% CI:1.076–2.792). After PSM based on age, gender, BMI group and history of diabetes, cholecystectomy was associated with 139.3% higher risk of liver fibrosis (OR: 2.393;95% CI: 1.738–3.297), and 228.7% higher risk of liver cirrhosis (OR: 3.287, 95% CI: 1.496–7.218).

Conclusions: The present study showed that cholecystectomy is positively associated with liver fibrosis and cirrhosis in US adults. The discovery of these risk factors therefore provides new insights on the prevention of NAFLD, liver fibrosis, and cirrhosis.

A short report on NGM282/aldafermin for the treatment of nonalcoholic steatohepatitis (NASH)

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is rapidly becoming the major cause of liver disease worldwide. Bile acids play a central part in the pathogenesis of NAFLD with agents that target bile acid synthesis and metabolism in development as potential therapies.

AREAS COVERED

The paper presents an overview of NAFLD and its pathogenesis, with focus on bile acid metabolism and regulation through fibroblast growth factor 19 (FGF-19), and the development of aldafermin as a non-tumorigenic FGF-19 analogue. We explore results from preclinical studies on the efficacy and safety of aldafermin.

EXPERT OPINION

Bile acid regulation is a promising therapeutic target in the management of NAFLD. FGF-19 plays key role in this mechanistic pathway, but also exhibits hepatocarcinogenic effect. Aldafermin is an FGF-19 analogue that has shown promising results in nonalcoholic steatohepatitis animal models, with preclinical data supporting its safety profile, specifically, the lack of a tumorigenic effect. The preclinical data presented in this paper support the clinical development of aldafermin, and indeed early data from several phase II clinical trials report promising results in relation to the ability of aldafermin to improve the histological features of NASH particularly in relation to a reduction in liver fat content.

Mast Cells Regulate Ductular Reaction and Intestinal Inflammation in Cholestasis Through Farnesoid X Receptor Signaling

BACKGROUND AND AIMS

Cholestasis is characterized by increased total bile acid (TBA) levels, which are regulated by farnesoid X receptor (FXR)/FGF15. Patients with primary sclerosing cholangitis (PSC) typically present with inflammatory bowel disease (IBD). Mast cells (MCs) (i) express FXR and (ii) infiltrate the liver during cholestasis promoting liver fibrosis. In bile-duct-ligated (BDL) MC-deficient mice (B6.Cg-Kit^W-sh /HNihrJaeBsmJ [Kit^W-sh ]), ductular reaction (DR) and liver fibrosis decrease compared with BDL wild type, and MC injection exacerbates liver damage in normal mice.

APPROACH AND RESULTS

In this study, we demonstrated that MC-FXR regulates biliary FXR/FGF15, DR, and hepatic fibrosis and alters intestinal FXR/FGF15. We found increased MC number and biliary FXR expression in patients with liver injury compared with control. Histamine and FGF19 serum levels and small heterodimer partner expression increase in patients PSC and PSC-IBD compared with healthy controls. MC injection increased liver damage, DR, inflammation, biliary senescence/senescence-associated secretory phenotype (SASP), fibrosis, and histamine in Kit^W-sh mice. Inhibition of MC-FXR before injection reduced these parameters. BDL and Kit^W-sh mice injected with MCs displayed increased TBA content, biliary FXR/FGF15, and intestinal inflammation, which decreased in BDL Kit^W-sh and Kit^W-sh mice injected with MC-FXR. MCs increased ileal FXR/FGF15 expression in Kit^W-sh mice that was reduced following FXR inhibition. BDL and multidrug resistance 2/ATP-binding cassette family 2 member 4 knockout (Mdr2^-/- ) mice, models of PSC, displayed increased intestinal MC infiltration and FXR/FGF15 expression. These were reduced following MC stabilization with cromolyn sodium in Mdr2^-/- mice. In vitro, MC-FXR inhibition decreased biliary proliferation/SASP/FGF and hepatic stellate cell activation.

CONCLUSIONS

Our studies demonstrate that MC-FXR plays a key role in liver damage and DR, including TBA regulation through alteration of intestinal and biliary FXR/FGF15 signaling.

Emodin palliates high-fat diet-induced nonalcoholic fatty liver disease in mice via activating the farnesoid X receptor pathway

BACKGROUND

Cassia mimosoides Linn (CMD) is a traditional Chinese herb that clears liver heat and dampness. It has been widely administered in clinical practice to treat jaundice associated with damp-heat pathogen and obesity. Emodin (EMO) is a major bioactive constituent of CMD that has apparent therapeutic efficacy against obesity and fatty liver. Here, we investigated the protective effects and underlying mechanisms of EMO against high-fat diet (HFD)-induced nonalcoholic fatty liver disease (NAFLD).

OBJECTIVE

We aimed to investigate whether EMO activates farnesoid X receptor (FXR) signaling to alleviate HFD-induced NAFLD.

MATERIALS AND METHODS

In vivo assays included serum biochemical indices tests, histopathology, western blotting, and qRT-PCR to evaluate the effects of EMO on glucose and lipid metabolism disorders in wild type (WT) and FXR knockout mice maintained on an HFD. In vitro experiments included intracellular triglyceride (TG) level measurement and Oil Red O staining to assess the capacity of EMO to remove lipids induced by oleic acid and palmitic acid in WT and FXR knockout mouse primary hepatocytes (MPHs). We also detected mRNA expression of FXR signaling genes in MPHs.

RESULTS

After HFD administration, body weight and serum lipid and inflammation levels were dramatically increased in the WT mice. The animals also presented with impaired glucose tolerance, insulin resistance, and antioxidant capacity, liver tissue attenuation, and pathological injury. EMO remarkably reversed the foregoing changes in HFD-induced mice. EMO improved HFD-induced lipid accumulation, insulin resistance, inflammation, and oxidative stress in a dose-dependent manner in WT mice by inhibiting FXR expression. EMO also significantly repressed TG hyperaccumulation by upregulating FXR expression in MPHs. However, it did not improve lipid accumulation, insulin sensitivity, or glucose tolerance in HFD-fed FXR knockout mice.

CONCLUSIONS

The present study demonstrated that EMO alleviates HFD-induced NAFLD by activating FXR signaling which improves lipid accumulation, insulin resistance, inflammation, and oxidative stress.

Intestine-liver crosstalk in Type 2 Diabetes and non-alcoholic fatty liver disease

Type 2 diabetes (T2D) and Non-Alcoholic Fatty Liver Disease (NAFLD) are pathologies whose prevalence continues to increase worldwide. Both diseases are precipitated by an excessive caloric intake, which promotes insulin resistance and fatty liver. The role of the intestine and its crosstalk with the liver in the development of these metabolic diseases is receiving increasing attention. Alterations in diet-intestinal microbiota interactions lead to the dysregulation of intestinal functions, resulting in altered metabolite and energy substrate production and increased intestinal permeability. Connected through the portal circulation, these changes in intestinal functions impact the liver and other metabolic organs, such as visceral adipose tissue, hence participating in the development of insulin resistance, and worsening T2D and NAFLD. Thus, targeting the intestine may be an efficient therapeutic approach to cure T2D and NAFLD. In this review, we will first introduce the signaling pathways linking T2D and NAFLD. Next, we will address the role of the gut-liver crosstalk in the development of T2D and NAFLD, with a particular focus on the gut microbiota and the molecular pathways behind the increased intestinal permeability and inflammation. Finally, we will summarize the therapeutic strategies which target the gut and its functions and are currently used or under development to treat T2D and NAFLD.

MERTK+/hi M2c Macrophages Induced by Baicalin Alleviate Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. An accumulation of fat, followed by inflammation, is the major cause of NAFLD progression. During inflammation, macrophages are the most abundant immune cells recruited to the site of injury. Macrophages are classified into "proinflammatory" M1 macrophages, and "anti-inflammatory" M2 macrophages. In NAFLD, M1 macrophages are the most prominent macrophages that lead to an excessive inflammatory response. Previously, we found that baicalin could polarize macrophages into anti-inflammatory M2c subtype macrophages with an increased level of MERTK expression. Several studies have also shown a strong correlation between MERTK expression and cholesterol efflux, efferocytosis, as well as phagocytosis capability. Therefore, in this study, we aim to elucidate the potential and efficacy of mononuclear-cell (MNC)-derived MERTK+/hi M2c macrophages induced by baicalin as a cell-based therapy for NAFLD treatment. In our results, we have demonstrated that a MERTK+/hi M2c macrophage injection to NAFLD mice contributes to an increased level of serum HDL secretion in the liver, a decline in the circulating CD4+CD25- and CD8+CD25- T cells and lowers the total NAFLD pathological score by lessening the inflammation, necrosis, and fibrosis. In the liver, profibrotic COL1A1 and FN, proinflammation TNFα, as well as the regulator of lipid metabolism PPARɣ expression, were also downregulated after injection. In parallel, the transcriptomic profiles of the injected MERTK+/hi M2c macrophages showed that the various genes directly or indirectly involved in NAFLD progression (e.g., SERPINE1, FADS2) were also suppressed. Downregulation of cytokines and inflammation-associated genes, such as CCR5, may promote a pro-resolving milieu in the NAFLD liver. Altogether, cell-based therapy using MERTK+/hi M2c macrophages is promising, as it ameliorates NAFLD in mice.

Beyond classic concepts in thyroid homeostasis: Immune system and microbiota

It has long been known that thyroid hormones have implications for multiple physiological processes and can lead to serious illness when there is an imbalance in its metabolism. The connections between thyroid hormone metabolism and the immune system have been extensively described, as they can participate in inflammation, autoimmunity, or cancer progression. In addition, changes in the normal intestinal microbiota involve the activation of the immune system while triggering different pathophysiological disorders. Recent studies have linked the microbiota and certain bacterial fragments or metabolites to the regulation of thyroid hormones and the general response in the endocrine system. Even if the biology and function of the thyroid gland has attracted more attention due to its pathophysiological importance, there are essential mechanisms and issues related to it that are related to the interplay between the intestinal microbiota and the immune system and must be further investigated. Here we summarize additional information to uncover these relationships, the knowledge of which would help establish new personalized medical strategies.

Bile Salt and FGF19 Signaling in the Early Phase of Human Liver Regeneration

The involvement of bile salt-fibroblast growth factor 19 (FGF19) signaling in human liver regeneration (LR) is not well studied. Therefore, we studied aspects of bile salt-FGF19 signaling shortly after liver resection in patients. We compared plasma bile salt and FGF19 levels in arterial, portal and hepatic venous blood, calculated venous-arterial differences (ΔVA), and determined hepatic transcript levels on two intra-operative time points: before (< 1 hour) and immediately after (> 2-3 hours) liver resection (i.e., following surgery). Postoperative bile salt and FGF19 levels were assessed on days 1, 2, and 3. LR was studied by computed tomography (CT)-liver volumetry. Following surgery, the liver, arterial, and portal bile salt levels were elevated (P < 0.05). Furthermore, an increased amount of bile salts was released in portal blood and extracted by the remnant liver (P < 0.05). Postoperatively, bile salt levels were elevated from day 1 onward (P < 0.001). For FGF19, intra-operative or postoperative changes of ΔVA or plasma levels were not observed. The bile salt-homeostatic regulator farnesoid X receptor (FXR) was markedly up-regulated following surgery (P < 0.001). Cell-cycle re-entry priming factors (interleukin 6 [IL-6], signal transducer and activator of transcription 3 [STAT3], and cJUN) were up-regulated following surgery and were positively correlated with FXR expression (P < 0.05). Postoperative hyperbilirubinemia was preceded by postsurgery low FXR and high Na+/Taurocholate cotransporting polypeptide (NTCP) expression in the remnant liver coupled with higher liver bile salt content (P < 0.05). Finally, bile salt levels on postoperative day 1 were an independent predictor of LR (P < 0.05). Conclusion: Systemic, portal, and liver bile salt levels are rapidly elevated after liver resection. Postoperative bile salts were positively associated with liver volume gain. In the studied time frame, FGF19 levels remained unaltered, suggesting that FGF19 plays a minor role in human LR. These findings indicate a more relevant role of bile salts in human LR.

Cholecystectomy as a risk factor for metabolic dysfunction-associated fatty liver disease: unveiling the metabolic and chronobiologic clues behind the bile acid enterohepatic circulation

Metabolic dysfunction-associated fatty liver disease (MAFLD) is highly prevalent worldwide. Recent clinical and experimental studies have addressed the association between cholecystectomy and MAFLD, confirming that cholecystectomy is an independent risk factor for MAFLD. In this review, we describe the epidemiologic evidence that links cholecystectomy to MAFLD, and discuss the possible mechanisms behind these connections, in order to unveil the metabolic and chronobiologic signals conveyed by the waves of the bile acid enterohepatic circulation.

Aberrant FGFR4 signaling worsens nonalcoholic steatohepatitis in FGF21KO mice

Background: Nonalcoholic steatohepatitis (NASH) is the most severe form of non-alcoholic fatty liver disease (NAFLD) and a potential precursor of hepatocellular carcinoma (HCC). In our previous studies, we found that endocrine fibroblast growth factor 21 (FGF21) played a key role in preventing the development of NASH, however, the FGF15/19 mediated-FGFR4 signaling worsened NASH and even contributed to the NASH-HCC transition. The aim of this study is to determine whether FGF15/FGFR4 signaling could alleviate or aggravate NASH in the FGF21KO mice.

Methods: NASH models were established in FGF21KO mice fed with high fat methionine-choline deficient (HFMCD) diet to investigate FGF15/FGFR4 signaling during early stage NASH and advanced stage NASH. Human hepatocytes, HepG2 and Hep3B cells, were cultured with human enterocytes Caco-2 cells to mimic gut-liver circulation to investigate the potential mechanism of NASH development.

Results: Significant increase of FGF15 production was found in the liver of the NASH-FGF21KO mice, however the increased FGF15 protein was unable to alleviate hepatic lipid accumulation. In contrast, up-regulated FGF15/19/FGFR4 signaling was found in the FGF21KO mice with increased NASH severity, as evident by hepatocyte injury/repair, fibrosis and potential malignant events. In in vitro studies, blockage of FGFR4 by BLU9931 treatment attenuated the lipid accumulation, up-regulated cyclin D1, and epithelial-mesenchymal transition (EMT) in the hepatocytes.

Conclusion: The increased FGF15 in NASH-FGF21KO mice could not substitute for FGF21 to compensate its lipid metabolic benefits thereby to prevent NASH development. Up-regulated FGFR4 signaling in NASH-FGF21KO mice coupled to proliferation and EMT events which were widely accepted to be associated with carcinogenic transformation.

Role of FGF15 in Hepatic Surgery in the Presence of Tumorigenesis: Dr. Jekyll or Mr. Hyde?

The pro-tumorigenic activity of fibroblast growth factor (FGF) 19 (FGF15 in its rodent orthologue) in hepatocellular carcinoma (HCC), as well as the unsolved problem that ischemia-reperfusion (IR) injury supposes in liver surgeries, are well known. However, it has been shown that FGF15 administration protects against liver damage and regenerative failure in liver transplantation (LT) from brain-dead donors without tumor signals, providing a benefit in avoiding IR injury. The protection provided by FGF15/19 is due to its anti-apoptotic and pro-regenerative properties, which make this molecule a potentially beneficial or harmful factor, depending on the disease. In the present review, we describe the preclinical models currently available to understand the signaling pathways responsible for the apparent controversial effects of FGF15/19 in the liver (to repair a damaged liver or to promote tumorigenesis). As well, we study the potential pharmacological use that has the activation or inhibition of FGF15/19 pathways depending on the disease to be treated. We also discuss whether FGF15/19 non-pro-tumorigenic variants, which have been developed for the treatment of liver diseases, might be promising approaches in the surgery of hepatic resections and LT using healthy livers and livers from extended-criteria donors.

Fibroblast Growth Factor 19: Potential modulation of hepatic metabolism for the treatment of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a spectrum of liver disease that is becoming more prevalent in concert with obesity and poor lifestyle habits. Although NAFLD is treatable via lifestyle modification in early stages, more advanced liver pathologies (eg non-alcoholic steatohepatitis [NASH]) are harder to reverse. There is no Food and Drug Administration approved pharmacological treatment for NAFLD, and little research has been done to identify compounds that target key NAFLD mechanisms. Bile acids and bile acid receptors have been implicated in NAFLD pathogenesis and modulating bile acids and bile acid receptors has recently been targeted as a therapeutic treatment option for NAFLD. Fibroblast growth factor 19 (FGF19), a nutritionally regulated post-prandial hormone, is a chief regulator of bile acid metabolism and an important player in lipid and carbohydrate metabolism, including key mechanisms of NAFLD pathogenesis. In this review, we discuss recent findings related to FGF19-regulated processes involved in the pathogenesis of NAFLD. We summarize known and conjectural frameworks and limitations for the clinical application of FGF19-targeted therapies as they relate to NAFLD.

FGF19 protects skeletal muscle against obesity-induced muscle atrophy, metabolic derangement and abnormal irisin levels via the AMPK/SIRT-1/PGC-α pathway

Obesity is associated with biological dysfunction in skeletal muscle. As a condition of obesity accompanied by muscle mass loss and physical dysfunction, sarcopenic obesity (SO) has become a novel public health problem. Human fibroblast growth factor 19 (FGF19) plays a therapeutic role in metabolic diseases. However, the protective effects of FGF19 on skeletal muscle in obesity and SO are still not completely understood. Our results showed that FGF19 administration improved muscle loss and grip strength in young and aged mice fed a high‐fat diet (HFD). Increases in muscle atrophy markers (FOXO‐3, Atrogin‐1, MuRF‐1) were abrogated by FGF19 in palmitic acid (PA)‐treated C2C12 myotubes and in the skeletal muscle of HFD‐fed mice. FGF19 not only reduced HFD‐induced body weight gain, excessive lipid accumulation and hyperlipidaemia but also promoted energy expenditure (PGC‐1α, UCP‐1, PPAR‐γ) in brown adipose tissue (BAT). FGF19 treatment restored PA‐ and HFD‐induced hyperglycaemia, impaired glucose tolerance and insulin resistance (IRS‐1, GLUT‐4) and mitigated the PA‐ and HFD‐induced decrease in FNDC‐5/irisin expression. However, these beneficial effects of FGF19 on skeletal muscle were abolished by inhibiting AMPK, SIRT‐1 and PGC‐1α expression. Taken together, this study suggests that FGF19 protects skeletal muscle against obesity‐induced muscle atrophy, metabolic derangement and abnormal irisin secretion partially through the AMPK/SIRT‐1/PGC‐α signalling pathway, which might be a potential therapeutic target for obesity and SO.

New Drugs on the Block-Emerging Treatments for Nonalcoholic Steatohepatitis

Patients with nonalcoholic steatohepatitis (NASH) are at higher risk of progression to advanced stages of fibrosis, cirrhosis, hepatocellular carcinoma and other end-stage liver disease complications. When addressing treatment of NASH, we have limited approved options, and the mainstay of therapy is lifestyle intervention. Extensive research and revelation in the field of pathogenesis of NASH has offered new possibilities of treatment and emerging new drugs that are being tested currently in numerous preclinical and clinical trials. These drugs target almost all steps in the pathogenesis of NASH to improve insulin sensitivity, glucose and lipid metabolism, to inhibit de novo lipogenesis and delivery of lipids to the liver, and to influence apoptosis, inflammation and fibrogenesis. Although NASH is a multifactorial disease, in the future we could identify the predominating pathological mechanism and, by choosing the most appropriate specific medication, tailor the treatment for every patient individually.

The Liver under the Spotlight: Bile Acids and Oxysterols as Pivotal Actors Controlling Metabolism

Among the myriad of molecules produced by the liver, both bile acids and their precursors, the oxysterols are becoming pivotal bioactive lipids which have been underestimated for a long time. Their actions are ranging from regulation of energy homeostasis (i.e., glucose and lipid metabolism) to inflammation and immunity, thereby opening the avenue to new treatments to tackle metabolic disorders associated with obesity (e.g., type 2 diabetes and hepatic steatosis) and inflammatory diseases. Here, we review the biosynthesis of these endocrine factors including their interconnection with the gut microbiota and their impact on host homeostasis as well as their attractive potential for the development of therapeutic strategies for metabolic disorders.

Transcriptional Regulation of Metabolic Pathways via Lipid-Sensing Nuclear Receptors PPARs, FXR, and LXR in NASH

Nonalcoholic fatty liver disease comprises a wide spectrum of liver injuries from simple steatosis to steatohepatitis and cirrhosis. Nonalcoholic steatohepatitis (NASH) is defined when liver steatosis is associated with inflammation, hepatocyte damage, and fibrosis. A genetic predisposition and environmental insults (ie, dietary habits, obesity) are putatively responsible for NASH progression. Here, we present the impact of the lipid-sensing nuclear receptors in the pathogenesis and treatment of NASH. In detail, we discuss the pros and cons of the putative transcriptional action of the fatty acid sensors (peroxisome proliferator-activated receptors), the bile acid sensor (farnesoid X receptor), and the oxysterol sensor (liver X receptors) in the pathogenesis and bona fide treatment of NASH.

Enterohepatic circulation of bile acids and their emerging roles on glucolipid metabolism

Bile acids (BAs) are amphiphilic molecules with a nonpolar steroid carbon skeleton and a polar carboxylate side chain. Recently, BAs have aroused the attention of scholars due to their potential roles on metabolic diseases. As important endogenous ligands, BAs are wildly active in the enterohepatic circulation, during which microbiota play a significant role in promoting the hydrolysis and dehydroxylation of BAs. Besides, many pathways initiated by BAs including glucolipid metabolism and inflammation signaling pathways have been reported to regulate the host metabolism and maintain immune homeostasis. Herein, the characteristics on the enterohepatic circulation and metabolism of BAs are systematically summarized. Moreover, the regulation mechanism of the glucolipid metabolism by BAs is intensively discussed. Worthily, FXR and TGR5, which are involved in glucolipid metabolism, are the prime candidates for targeted therapies of chronic metabolic diseases such as diabetes and hypercholesterolemia.

Cell Sources and Influencing Factors of Liver Regeneration: A Review

Liver regeneration (LR) is a set of complicated mechanisms between cells and molecules in which the processes of initiation, maintenance, and termination of liver repair are regulated. Although LR has been studied extensively, there are still numerous challenges in gaining its full understanding. Cells for LR have a wide range of sources and the feature of plasticity, and regeneration patterns are not the same under different conditions. Many patients undergoing partial hepatectomy develop cirrhosis or steatosis. The changes of LR in these cases are not clear. Many types of cells participate in LR. Hepatocytes, biliary epithelial cells, hepatic progenitor cells, and human liver stem cells can serve as the cell sources for LR. However, different types and degrees of damage trigger the response from the most suitable cells. Exploring the cell sources of LR is of great significance for accelerating recovery of liver function under different pathological patterns and developing a cell therapy strategy to cope with the shortage of donors for liver transplantation. In clinical practice, the background of the liver influences regeneration. Fibrosis and steatosis create different LR microenvironments and signal molecule interaction patterns. In addition, factors such as partial hepatectomy, aging, platelets, nerves, hormones, bile acids, and gut microbiota are widely involved in this process. Understanding the influencing factors of LR has practical value for individualized treatment of patients with liver diseases. In this review, we have summarized recent studies and proposed our views. We discuss cell sources and the influential factors on LR to help in solving clinical problems.

Selenoprotein V protects against endoplasmic reticulum stress and oxidative injury induced by pro-oxidants

Selenoprotein V (SELENOV) contains a thioredoxin-like fold and a conserved CxxU motif with a potential redox function. This study was to assess its in vivo and in vitro roles and mechanisms in coping with different oxidant insults. In Experiment (Expt.)1, SELENOV knockout (KO) and wild type (WT) mice (male, 8-wk old) were given an ip injection of saline, diquat (DQ, 12.5 mg/kg), or N-acetyl-para-aminophenol (APAP, 300 mg/kg) (n = 10), and killed 5 h after the injection. In Expt. 2, primary hepatocytes of WT and KO were treated with DQ (0-0.75 mM) or APAP (0-6 mM) for 12 h. In Expt. 3, 293 T cells overexpressing Selenov gene (OE) were treated with APAP (0-4 mM) for 24 h or H₂O₂ (0-0.4 mM) for 12 h. Compared with the WT, the DQ- and APAP-injected KO mice had higher (P < 0.05) serum alanine aminotransferase activities and hepatic malondialdehyde (MDA), protein carbonyl, endoplasmic reticulum (ER) stress-related proteins (BIP and CHOP), apoptosis-related proteins (FAK and caspase-9), and 3-nitrotyrosine, along with lower total anti-oxidizing-capability (T-AOC) and severer hepatic necrosis. Likewise, the DQ and APAP-treated KO hepatocytes had elevated (P < 0.05) cell death (10-40%), decreased (P < 0.05) T-AOC (63-83%), glutathione (26-87%), superoxide dismutase (SOD) activity (28-36%), mRNA levels of redox enzymes (Cat, Gcs, Gpx3, and Sod) and (or) sharper declines (P < 0.05) in cellular respiration and ATP production than that of the WT cells. In contrast, the OE cells had greater viability and T-AOC and lower MDA, and carbonyl contents after the APAP and H₂O₂ exposures (all at P < 0.05) than the controls. Moreover, the OE cells had greater (P < 0.05) redox enzyme activities (GPX, TrxR, and SOD), and lower (P < 0.05) expressions of ER stress-related genes (Atf4, Atf6, Bip, Xbp1t, Xbp1s, and Chop) and proteins (BIP, CHOP, FAK, and caspase-9) than the control cells after the treatment of H₂O₂ (0.4 mM). In conclusion, SELENOV conferred protections in vivo and in vitro against the reactive oxygen and nitrogen species-mediated ER stress-related signaling and oxidative injuries.

FGF15/19 is required for adipose tissue plasticity in response to thermogenic adaptations

Objective

To determine the role of enterokine FGF15/19 in adipose tissue thermogenic adaptations.

Methods

Circulating FGF19 and gene expression (qRT-PCR) levels were assessed in subcutaneous adipose tissue from obese human patients. Effects of experimentally increased FGF15 and FGF19 levels in vivo were determined in mice using adenoviral and adeno-associated vectors. Adipose tissues were characterized in FGF15-null mice under distinct cold-related thermogenic challenges. The analyses spanned metabolic profiling, tissue characterization, histology, gene expression, and immunoblot assays.

Results

In humans, FGF19 levels are directly associated with UCP1 gene expression in subcutaneous adipose tissue. Experimental increases in FGF15 or FGF19 induced white fat browning in mice as demonstrated by the appearance of multilocular beige cells and markers indicative of a beige phenotype, including increased UCP1 protein levels. Mice lacking FGF15 showed markedly impaired white adipose tissue browning and a mild reduction in parameters indicative of BAT activity in response to cold-induced environmental thermogenic challenges. This was concomitant with signs of altered systemic metabolism, such as reduced glucose tolerance and impaired cold-induced insulin sensitization.

Conclusions

Enterokine FGF15/19 is a key factor required for adipose tissue plasticity in response to thermogenic adaptations.

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Circulating FGF19 levels correlate positively with signs of fat browning in humans.

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Adaptive adipose tissue browning in response to cold is impaired in mice lacking FGF15.

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Experimentally induced increase in FGF15 or FGF19 promotes fat browning in mice.

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FGF15/19 signaling is required for thermogenic challenge-induced plasticity of adipose tissue.

Curtailing FGF19's mitogenicity by suppressing its receptor dimerization ability

As a physiological regulator of bile acid homeostasis, FGF19 is also a potent insulin sensitizer capable of normalizing plasma glucose concentration, improving lipid profile, ameliorating fatty liver disease, and causing weight loss in both diabetic and diet-induced obesity mice. There is therefore a major interest in developing FGF19 as a therapeutic agent for treating type 2 diabetes and cholestatic liver disease. However, the known tumorigenic risk associated with prolonged FGF19 administration is a major hurdle in realizing its clinical potential. Here, we show that nonmitogenic FGF19 variants that retain the full beneficial glucose-lowering and bile acid regulatory activities of WT FGF19 (FGF19^WT) can be engineered by diminishing FGF19's ability to induce dimerization of its cognate FGF receptors (FGFR). As proof of principle, we generated three such variants, each with a partial defect in binding affinity to FGFR (FGF19^ΔFGFR) and its coreceptors, i.e., βklotho (FGF19^ΔKLB) or heparan sulfate (FGF19^ΔHBS). Pharmacological assays in WT and db/db mice confirmed that these variants incur a dramatic loss in mitogenic activity, yet are indistinguishable from FGF19^WT in eliciting glycemic control and regulating bile acid synthesis. This approach provides a robust framework for the development of safer and more efficacious FGF19 analogs.

FGF15 improves outcomes after brain dead donor liver transplantation with steatotic and non-steatotic grafts in rats

BACKGROUND & AIMS

Donation after brain death (DBD) grafts are associated with reduced graft quality and function post liver transplantation (LT). We aimed to elucidate i) the impact of FGF15 levels on DBD grafts; ii) whether this impact resulted from altered intestinal FXR-FGF15; iii) whether administration of FGF15 to donors after brain death could confer a benefit on graft function post LT; and iv) whether FGF15 affects bile acid (BA) accumulation.

METHODS

Steatotic and non-steatotic grafts from DBD donors and donors without brain death were transplanted in rats. FGF15 was administered alone or combined with either a BA (cholic acid) or a YAP inhibitor.

RESULTS

Brain death induced intestinal damage and downregulation of FXR. The resulting reduced intestinal FGF15 was associated with low hepatic FGF15 levels, liver damage and regenerative failure. Hepatic FGFR4-Klb - the receptor for FGF15 - was downregulated whereas CYP7A1 was overexpressed, resulting in BA accumulation. FGF15 administration to DBD donors increased hepatic FGFR4-Klb, reduced CYP7A1 and normalized BA levels. The benefit of FGF15 on liver damage was reversed by cholic acid, whereas its positive effect on regeneration was maintained. YAP signaling in DBD donors was activated after FGF15 treatment. When a YAP inhibitor was administered, the benefits of FGF15 on regeneration were abolished, whereas its positive effect on hepatic damage remained. Neither the Hippo-YAP-BA nor the BA-IQGAP1-YAP axis was involved in the benefits of FGF15.

CONCLUSION

Alterations in the gut-liver axis contribute to the reduced quality of DBD grafts and the associated pathophysiology of LT. FGF15 pre-treatment in DBD donors protected against damage and promoted cell proliferation.

LAY SUMMARY

After brain death, potential liver donors have reduced intestinal FXR, which is associated with reduced intestinal, circulatory and hepatic levels of FGF15. A similar reduction in the cell-surface receptor complex Fgfr4/Klb is observed, whereas CYP7A1 is overexpressed; together, these molecular events result in the dangerous accumulation of bile acids, leading to damage and regenerative failure in brain dead donor grafts. Herein, we demonstrate that when such donors receive appropriate doses of FGF15, CYP7A1 levels and hepatic bile acid toxicity are reduced, and liver regeneration is promoted.

Metabolic consequences of ileal interruption of the enterohepatic circulation of bile acids

The enterohepatic circulation of bile acids comprises a tightly regulated process of hepatic bile acid secretion, intestinal reabsorption and transport back to the liver. Disruption of this process has significant consequences for gastrointestinal, liver and whole body homeostasis and therefore offers opportunities for therapeutic intervention. In this review we discuss the effects of (pharmacological) interruption of the enterohepatic circulation at different levels. Recently, several studies have been published on ileal interruption of the enterohepatic circulation of bile acids, targeting the apical-sodium dependent bile acid transporter (ASBT, SLC10A2), as therapy for various diseases. However, ambiguous results have been reported and in-depth mechanistic insights are lacking. Here we discuss these novel studies and review the current knowledge on the consequences of ASBT inhibition and its potential effects on physiology and metabolism.

Hepatic Autophagy Deficiency Remodels Gut Microbiota for Adaptive Protection via FGF15-FGFR4 Signaling

BACKGROUND & AIMS

The functions of the liver and the intestine are closely tied in both physiological and pathologic conditions. The gut microbiota (GM) often cause deleterious effects during hepatic pathogenesis. Autophagy is essential for liver homeostasis, but the impact of hepatic autophagy function on liver-gut interaction remains unknown. Here we investigated the effect of hepatic autophagy deficiency (Atg5Δhep) on GM and in turn the effect of GM on the liver pathology.

METHODS

Fecal microbiota were analyzed by 16S sequencing. Antibiotics were used to modulate GM. Cholestyramine was used to reduce the enterohepatic bile acid (BA) level. The functional role of fibroblast growth factor 15 (FGF15) and ileal farnesoid X receptor (FXR) was examined in mice overexpressing FGF15 gene or in mice given a fibroblast growth factor receptor-4 (FGFR4) inhibitor.

RESULTS

Atg5Δhep causes liver injury and alterations of intestinal BA composition, with a lower proportion of tauro-conjugated BAs and a higher proportion of unconjugated BAs. The composition of GM is significantly changed with an increase in BA-metabolizing bacteria, leading to an increased expression of ileal FGF15 driven by FXR that has a higher affinity to unconjugated BAs. Notably, antibiotics or cholestyramine treatment decreased FGF15 expression and exacerbated liver injury. Consistently, inhibition of FGF15 signaling in the liver enhances liver injury.

CONCLUSIONS

Deficiency of autophagy function in the liver can affect intestinal environment, leading to gut dysbiosis. Surprisingly, such changes provide an adaptive protection against the liver injury through the FGF15-FGFR4 signaling. Antibiotics use in the condition of liver injury may thus have unexpected adverse consequences via the gut-liver axis.

A Villin-Driven Fxr Transgene Modulates Enterohepatic Bile Acid Homeostasis and Response to an n-6-Enriched High-Fat Diet

A diet high in n-6 polyunsaturated fatty acids (PUFAs) may contribute to inflammation and tissue damage associated with obesity and pathologies of the colon and liver. One contributing factor may be dysregulation by n-6 fatty acids of enterohepatic bile acid (BA) metabolism. The farnesoid X receptor (FXR) is a nuclear receptor that regulates BA homeostasis in the liver and intestine. This study aims to compare the effects on FXR regulation and BA metabolism of a palm oil-based diet providing 28% energy (28%E) from fat and low n-6 linoleic acid (LA, 2.5%E) (CNTL) with those of a soybean oil-based diet providing 50%E from fat and high (28%E) in LA (n-6HFD). Wild-type (WT) littermates and a transgenic mouse line overexpressing the Fxrα1 isoform under the control of the intestine-specific Villin promoter (Fxrα1^TG) were fed the CNTL or n-6HFD starting at weaning through 16 weeks of age. Compared to the CNTL diet, the n-6HFD supports higher weight gain in both WT and Fxrα^TG littermates; increases the expression of Fxrα1/2, and peroxisome proliferator-activated receptor-γ1 (Pparγ1) in the small intestine, Fxrα1/2 in the colon, and cytochrome P4507A1 (Cyp7a1) and small heterodimer protein (Shp) in the liver; and augments the levels of total BA in the liver, and primary chenodeoxycholic (CDCA), cholic (CA), and β-muricholic (βMCA) acid in the cecum. Intestinal overexpression of the Fxra1^TG augments expression of Shp and ileal bile acid-binding protein (Ibabp) in the small intestine and Ibabp in the proximal colon. Conversely, it antagonizes n-6HFD-dependent accumulation of intestinal and hepatic CDCA and CA; hepatic levels of Cyp7a1; and expression of Pparγ in the small intestine. We conclude that intestinal Fxrα1 overexpression represses hepatic de novo BA synthesis and protects against n-6HFD-induced accumulation of human-specific primary bile acids in the cecum.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

Advances in the Involvement of Gut Microbiota in Pathophysiology of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis and progresses to non-steatohepatitis (NASH) when the liver displays overt inflammatory damage. Increasing evidence has implicated critical roles for dysbiosis and microbiota-host interactions in NAFLD pathophysiology. In particular, microbiota alter intestine absorption of nutrients and intestine permeability, whose dysregulation enhances the delivery of nutrients, endotoxin, and microbiota metabolites to the liver and exacerbates hepatic fat deposition and inflammation. While how altered composition of gut microbiota attributes to NAFLD remains to be elucidated, microbiota metabolites are shown to be involved in the regulation of hepatocyte fat metabolism and liver inflammatory responses. In addition, intestinal microbes and circadian coordinately adjust metabolic regulation in different stages of life. During aging, altered composition of gut microbiota, along with circadian clock dysregulation, appears to contribute to increased incidence and/or severity of NAFLD.

Gut Microbiota Metabolites in NAFLD Pathogenesis and Therapeutic Implications

Gut microbiota dysregulation plays a key role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) through its metabolites. Therefore, the restoration of the gut microbiota and supplementation with commensal bacterial metabolites can be of therapeutic benefit against the disease. In this review, we summarize the roles of various bacterial metabolites in the pathogenesis of NAFLD and their therapeutic implications. The gut microbiota dysregulation is a feature of NAFLD, and the signatures of gut microbiota are associated with the severity of the disease through altered bacterial metabolites. Disturbance of bile acid metabolism leads to underactivation of bile acid receptors FXR and TGR5, causal for decreased energy expenditure, increased lipogenesis, increased bile acid synthesis and increased macrophage activity. Decreased production of butyrate results in increased intestinal inflammation, increased gut permeability, endotoxemia and systemic inflammation. Dysregulation of amino acids and choline also contributes to lipid accumulation and to a chronic inflammatory status. In some NAFLD patients, overproduction of ethanol produced by bacteria is responsible for hepatic inflammation. Many approaches including probiotics, prebiotics, synbiotics, faecal microbiome transplantation and a fasting-mimicking diet have been applied to restore the gut microbiota for the improvement of NAFLD.

Molecular regulators of lipid metabolism in the intestine - Underestimated therapeutic targets for obesity?

The incidence of obesity and type 2 diabetes continues to rise across the globe necessitating the need to identify new therapeutic approaches to manage these diseases. In this review, we explore the potential for therapeutic interventions focussed on the intestinal epithelium, by targeting the role of this tissue in lipid uptake, lipid-mediated cross talk and lipid oxidation. We focus initially on ongoing strategies to manage obesity by targeting the essential role of the intestinal epithelium in lipid uptake, and in mediating tissue cross talk to regulate food intake. Subsequently, we explore a previously underestimated capacity of intestinal epithelial cells to oxidize fatty acids. In this context, we describe recent findings which have unveiled a key role for the peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors and histone deacetylases (HDACs) in the regulation of lipid oxidation genes in enterocytes and how targeted genetic manipulation of these factors in enterocytes reduces weight gain, identifying intestinal PPARs and HDACs as potential therapeutic targets in the management of obesity.

Hallmarks of postoperative liver regeneration: An updated insight on the regulatory mechanisms

Performance and advances in liver surgery makes remarkable progress of the understanding of liver regeneration. Liver regeneration after liver resection has been widely researched, and the underlying mechanism mostly concerns proliferation of hepatocytes and the influence by inflammation through activation of Kupffer cells and the other parenchymal cells, the second regenerative pathway by hepatic progenitor cells (HPCs), inducing angiogenesis, remodeling of a extracellular matrix (ECM), and termination mechanisms. New clinical surgeries and the updated multiomics analysis are exploiting the remarkable progress, especially in immune regulation and metabolic process of two emerging hallmarks. This review briefly represents a systemic outline of eight hallmarks, including hepatocyte proliferation, contribution of hepatic progenitor cells, inducing angiogenesis, reprogramming of the extracellular matrix, apoptosis and termination of proliferation, inflammation, immune and metabolic regulation, which are set as organizing characteristics of postoperative liver regeneration and future directions of refining treatment targets.

Fibroblast growth factor 19 alleviates palmitic acid-induced mitochondrial dysfunction and oxidative stress via the AMPK/PGC-1α pathway in skeletal muscle

Obesity-induced fat ectopic deposition results in mitochondrial dysfunction and oxidative stress in skeletal muscle, which could impair the quality and function of the skeletal muscle. Human fibroblast growth factor 19 (FGF19) acts as a vital metabolic regulator of bile acid synthesis and metabolic homeostasis. Recent studies have shown that FGF19 regulates skeletal muscle mass through the enlargement of muscle fiber size and protects muscles from atrophy. However, the role of FGF19 in regulating mitochondrial function and the antioxidant response in skeletal muscle remains unknown. Therefore, we investigated the effect of FGF19 on palmitic acid (PA)-induced mitochondrial dysfunction and oxidative stress in C2C12 cells. In this study, we found that FGF19 can increase the mRNA and protein expression levels of mitochondrial biogenesis regulators (PGC-1α, Nrf-1, and TFAM) and antioxidant response regulators (Nrf-2 and HO-1), alleviating PA-induced mitochondrial dysfunction and oxidative stress. However, the regulatory effect of FGF19 was blocked by Compound C, an AMP-activated protein kinase (AMPK) inhibitor, and siRNA knockdown of PGC-1a. Taken together, these findings indicate that FGF19 might promote mitochondrial biogenesis and antioxidant response via the AMPK/PGC-1α pathway, attenuating the effect of PA on mitochondrial dysfunction and oxidative stress; therefore, FGF19 might be a potential therapeutic target for the effects of obesity on skeletal muscle.

Targeting of Secretory Proteins as a Therapeutic Strategy for Treatment of Nonalcoholic Steatohepatitis (NASH)

Nonalcoholic steatohepatitis (NASH) is defined as a progressive form of nonalcoholic fatty liver disease (NAFLD) and is a common chronic liver disease that causes significant worldwide morbidity and mortality, and has no approved pharmacotherapy. Nevertheless, growing understanding of the molecular mechanisms underlying the development and progression of NASH has suggested multiple potential therapeutic targets and strategies to treat this disease. Here, we review this progress, with emphasis on the functional role of secretory proteins in the development and progression of NASH, in addition to the change of expression of various secretory proteins in mouse NASH models and human NASH subjects. We also highlight secretory protein-based therapeutic approaches that influence obesity-associated insulin resistance, liver steatosis, inflammation, and fibrosis, as well as the gut–liver and adipose–liver axes in the treatment of NASH.

Markers of liver regeneration-the role of growth factors and cytokines: a systematic review

BACKGROUND

Post-hepatectomy liver failure contributes significantly to postoperative mortality after liver resection. The prediction of the individual risk for liver failure is challenging. This review aimed to provide an overview of cytokine and growth factor triggered signaling pathways involved in liver regeneration after resection.

METHODS

MEDLINE and Cochrane databases were searched without language restrictions for articles from the time of inception of the databases till March 2019. All studies with comparative data on the effect of cytokines and growth factors on liver regeneration in animals and humans were included.

RESULTS

Overall 3.353 articles comprising 40 studies involving 1.498 patients and 101 animal studies were identified and met the inclusion criteria. All included trials on humans were retrospective cohort/observational studies. There was substantial heterogeneity across all included studies with respect to the analyzed cytokines and growth factors and the described endpoints.

CONCLUSION

High-level evidence on serial measurements of growth factors and cytokines in blood samples used to predict liver regeneration after resection is still lacking. To address the heterogeneity of patients and potential markers, high throughput serial analyses may offer a method to predict an individual's regenerative potential in the future.

Fibroblast growth factor signaling in non-alcoholic fatty liver disease and non-alcoholic steatohepatitis: Paving the way to hepatocellular carcinoma

Metabolic disorders are increasingly leading to non-alcoholic fatty liver disease, subsequent steatohepatitis, cirrhosis and hepatocellular carcinoma. Fibroblast growth factors and their receptors play an important role in maintaining metabolic homeostasis also in the liver and disorders in signaling have been identified to contribute to those pathophysiologic conditions leading to hepatic lipid accumulation and chronic inflammation. While specific and well tolerated inhibitors of fibroblast growth factor receptor activity are currently developed for (non-liver) cancer therapy, treatment of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis is still limited. Fibroblast growth factor-mimicking or restoring approaches have recently evolved as a novel therapeutic option and the impact of such interactions with the fibroblast growth factor receptor signaling network during non-alcoholic fatty liver disease/non-alcoholic steatohepatitis development is reviewed here.

Growth Factor Engineering Strategies for Regenerative Medicine Applications

Growth factors are critical molecules for tissue repair and regeneration. Therefore, recombinant growth factors have raised a lot of hope for regenerative medicine applications. While using growth factors to promote tissue healing has widely shown promising results in pre-clinical settings, their success in the clinic is not a forgone conclusion. Indeed, translation of growth factors is often limited by their short half-life, rapid diffusion from the delivery site, and low cost-effectiveness. Trying to circumvent those limitations by the use of supraphysiological doses has led to serious side-effects in many cases and therefore innovative technologies are required to improve growth factor-based regenerative strategies. In this review, we present protein engineering approaches seeking to improve growth factor delivery and efficacy while reducing doses and side effects. We focus on engineering strategies seeking to improve affinity of growth factors for biomaterials or the endogenous extracellular matrix. Then, we discuss some examples of increasing growth factor stability and bioactivity, and propose new lines of research that the field of growth factor engineering for regenerative medicine may adopt in the future.

Pathogenesis of Nonalcoholic Steatohepatitis: An Overview

Nonalcoholic fatty liver disease (NAFLD) is a heterogeneous group of liver diseases characterized by the accumulation of fat in the liver. The heterogeneity of NAFLD is reflected in a clinical and histologic spectrum where some patients develop isolated steatosis of the liver, termed nonalcoholic fatty liver, whereas others develop hepatocyte injury, ballooning, inflammation, and consequent fibrosis, termed nonalcoholic steatohepatitis (NASH). Systemic insulin resistance is a major driver of hepatic steatosis in NAFLD. Lipotoxicity of accumulated lipids along with activation of the innate immune system are major drivers of NASH. Lipid‐induced sublethal and lethal stress culminates in the activation of inflammatory processes, such as the release of proinflammatory extracellular vesicles and cell death. Innate and adaptive immune mechanisms involving macrophages, dendritic cells, and lymphocytes are central drivers of inflammation that recognize damage‐ and pathogen‐associated molecular patterns and contribute to the progression of the inflammatory cascade. While the activation of the innate immune system and the recruitment of proinflammatory monocytes into the liver in NASH are well known, the exact signals that lead to this remain less well defined. Further, the contribution of other immune cell types, such as neutrophils and B cells, is an area of intense research. Many host factors, such as the microbiome and gut–liver axis, modify individual susceptibility to NASH. In this review, we discuss lipotoxicity, inflammation, and the contribution of interorgan crosstalk in NASH pathogenesis.

Therapeutic targets for liver regeneration after acute severe injury: a preclinical overview

Introduction: Liver transplantation is the only viable treatment with a proven survival benefit for acute liver failure (ALF). Donor organ shortage is, however, a major hurdle; hence, alternative approaches that enable liver regeneration and target acute severe hepatocellular damage are necessary.Areas covered: This article sheds light on therapeutic targets for liver regeneration and considers their therapeutic potential. ALF following extensive hepatocyte damage and small-for-size syndrome (SFSS) are illuminated for the reader while the molecular mechanisms of liver regeneration are assessed in accordance with relevant therapeutic strategies. Furthermore, liver background parameters and predictive biomarkers that might associate with liver regeneration are reviewed.Expert opinion: There are established and novel experimental strategies for liver regeneration to prevent ALF resulting from SFSS. Granulocyte-colony stimulating factor (G-CSF) is a promising agent targeting liver regeneration after acute severe injury. Autophagy and hepatocyte senescence represent attractive new targets for liver regeneration in acute severe hepatic injury. Liver support strategies, including tissue engineering, constitute novel regenerative means; the success of this is dependent on stem cell research advances. However, there is no firm clinical evidence that these supportive strategies may alleviate hepatocellular damage until liver transplantation becomes available or successful self-liver regeneration occurs.

FGF19 and FGF21 for the Treatment of NASH-Two Sides of the Same Coin? Differential and Overlapping Effects of FGF19 and FGF21 From Mice to Human

FGF19 and FGF21 analogues are currently in clinical development for the potential treatment of NASH. In Phase 2 clinical trials analogues of FGF19 and FGF21 decrease hepatic steatosis with up to 70% (MRI-PDFF) after 12 weeks and as early as 12-16 weeks of treatment an improvement in NASH resolution and fibrosis has been observed. Therefore, this class of compounds is currently of great interest in the field of NASH. FGF19 and FGF21 belong to the endocrine FGF19 subfamily and both require the co-receptor beta-klotho for binding and signalling through the FGF receptors. FGF19 is expressed in the ileal enterocytes and is released into the enterohepatic circulation in response to bile acids stimuli and in the liver FGF19 inhibits hepatic bile acids synthesis by transcriptional regulation of Cyp7A1, which is the rate limiting enzyme. FGF21 is, on the other hand, highly expressed in the liver and is released in response to high glucose, high free-fatty acids and low amino-acid supply and regulates energy, glucose and lipid homeostasis by actions in the CNS and in the adipose tissue. FGF19 and FGF21 are differentially expressed, have distinct target tissues and separate physiological functions. It is therefore of peculiar interest to understand why treatment with both FGF19 and FGF21 analogues have strong beneficial effects on NASH parameters in mice and human and whether the mode of action is overlapping This review will highlight the physiological and pharmacological effects of FGF19 and FGF21. The potential mode of action behind the anti-steatotic, anti-inflammatory and anti-fibrotic effects of FGF19 and FGF21 will be discussed. Finally, development of drugs is always a risk benefit analysis and the human relevance of adverse effects observed in pre-clinical species as well as findings in humans will be discussed. The aim is to provide a comprehensive overview of the current understanding of this drug class for the potential treatment of NASH.

The Effect of Fibroblast Growth Factor 15 Signaling in Non-Steatotic and Steatotic Liver Transplantation from Cardiocirculatory Death

We elucidate the relevance of fibroblast growth factor 15 (FGF15) in liver transplantation (LT) using rats with both steatotic and non-steatotic organs from donors after cardiocirculatory death (DCD). Compared to LT from non-DCDs, the induction of cardiocirculatory death (CD) increases hepatic damage, proliferation, and intestinal and circulatory FGF15. This is associated with high levels of FGF15, bilirubin and bile acids (BAs), and overexpression of the enzyme involved in the alternative BA synthesis pathway, CYP27A1, in non-steatotic livers. Furthermore, CD activates the proliferative pathway, Hippo/YAP, in these types of liver. Blocking FGF15 action in LT from DCDs does not affect CYP27A1 but causes an overexpression of CYP7A, an enzyme from the classic BA synthesis pathway, and this is related to further accumulation of BAs and exacerbated damage. FGF15 inhibition also impairs proliferation without changing Hippo/YAP. In spite of worse damage, steatosis prevents a proliferative response in livers from DCDs. In steatotic grafts, CD does not modify CYP7A1, CYP27A1, BA, or the Hippo/YAP pathway, and FGF15 is not involved in damage or proliferation. Thus, endogenous FGF15 protects against BA accumulation and damage and promotes regeneration independently of the Hippo/YAP pathway, in non-steatotic LT from DCDs. Herein we show a minor role of FGF15 in steatotic LT from DCDs.

Current and Emerging Approaches for Nonalcoholic Steatohepatitis Treatment

Nonalcoholic steatohepatitis (NASH) is the second leading cause of liver transplantation in the US with a high risk of liver-related morbidities and mortality. Given the global burden of NASH, development of appropriate therapeutic strategies is an important clinical need. Where applicable, lifestyle modification remains the primary recommendation for the treatment of NASH, even though such changes are difficult to sustain and even insufficient to cure NASH. Bariatric surgery resolves NASH in such patients where lifestyle modifications have failed, and is recommended for morbidly obese patients with NASH. Thus, pharmacotherapies are of high value for NASH treatment. Though no drug has been approved by the US Food and Drug Administration for treatment of NASH, substantial progress in pharmacological development has been made in the last few years. Agents such as vitamin E and pioglitazone are recommended in patients with NASH, and yet concerns about their side effects remain. Many agents targeting various vital molecules and pathways, including those impacting metabolic perturbations, inflammatory cascades, and oxidative stress, are in clinical trials for the treatment of NASH. Some agents have shown promising results in phase II or III clinical trials, but more studies are required to assess their long-term effects. Herein, we review the potential strategies and challenges in therapeutic approaches to treating NASH.

Why Bile Acids Are So Important in Non-Alcoholic Fatty Liver Disease (NAFLD) Progression

Non-alcoholic fatty liver disease (NAFLD) is a complex disease, affecting not just the liver, but also all other organs in the body. Despite an increasing amount of people worldwide developing NAFLD and having it progress to non-alcoholic steatohepatitis (NASH) and potentially cirrhosis, there is still no approved therapy. Therefore, huge efforts are being made to find and develop a successful treatment. One of the special interests is understanding the liver-gut axis and especially the role of bile acids in the progression of NAFLD. Farnesoid X receptor (FXR)-agonists have been approved und used in other liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), and have shown signs of being able to decrease inflammation and potentially steatosis. This review will mainly focus on targets/ligands that play an important role in bile acid metabolism and give an overview of ongoing clinical as well as pre-clinical trials. With the complexity of the issue, we did not aim at giving a complete review, rather highlighting important targets and potential treatments that could be approved for NAFLD/NASH treatment within the next few years.

Pharmacologic Modulation of Bile Acid-FXR-FGF15/FGF19 Pathway for the Treatment of Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is within the spectrum of nonalcoholic fatty liver disease (NAFLD) and can progress to fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). The prevalence of NASH is rising and has become a large burden to the medical system worldwide. Unfortunately, despite its high prevalence and severe health consequences, there is currently no therapeutic agent approved to treat NASH. Therefore, the development of efficacious therapies is of utmost urgency and importance. Many molecular targets are currently under investigation for their ability to halt NASH progression. One of the most promising and well-studied targets is the bile acid (BA)-activated nuclear receptor, farnesoid X receptor (FXR). In this chapter, the characteristics, etiology, and prevalence of NASH will be discussed. A brief introduction to FXR regulation of BA homeostasis will be described. However, for more details regarding FXR in BA homeostasis, please refer to previous chapters. In this chapter, the mechanisms by which tissue and cell type-specific FXR regulates NASH development will be discussed in detail. Several FXR agonists have reached later phase clinical trials for treatment of NASH. The progress of these compounds and summary of released data will be provided. Lastly, this chapter will address safety liabilities specific to the development of FXR agonists.