Yin Yang 1 promotes hepatic steatosis through repression of farnesoid X receptor in obese mice

Expression of hepatic genes involved in bile acid metabolism in dairy cows with fatty liver

Bile acids are cholesterol-derived molecules that are primarily produced in the liver. In nonruminants with fatty liver, overproduction of bile acids is associated with liver injury. During the transition period, fatty liver is a metabolic disorder that can affect up to 50% of high-producing dairy cows. The purpose of this study was to provide a comprehensive evaluation on hepatic bile acid metabolism in dairy cows with fatty liver by assessing expression changes of genes involved in bile acid synthesis, export and uptake. The serum activities of aspartate aminotransferase, alanine aminotransferase and glutamate dehydrogenase and concentration of total bile acids were all greater, whereas serum concentration of total cholesterol was lower in cows with fatty liver than in healthy cows. Content of total bile acids was higher but total cholesterol was slightly lower in liver tissues from fatty liver cows than from healthy cows. The hepatic mRNA abundance of cholesterol 7a-hydroxylase (CYP7A1), hydroxy-delta-5-steroid dehydrogenase, 3 β- and steroid delta-isomerase 7 (HSD3B7) and sterol 12α-hydroxylase (CYP8B1), enzymes involved in the classic pathway of bile acid synthesis, was higher in fatty liver cows than in healthy cows. Compared with healthy cows, the hepatic mRNA abundance of alternative bile acid synthesis pathway-related genes sterol 27-hydroxylase (CYP27A1) and oxysterol 7α-hydroxylase (CYP7B1) did not differ in cows with fatty liver. The protein and mRNA abundance of bile acid transporter bile salt efflux pump (BSEP) were lower in the liver of dairy cow with fatty liver. Compared with healthy cows, the hepatic mRNA abundance of bile acid transporters solute carrier family 51 subunit α (SLC51A), ATP binding cassette subfamily C member 1 (ABCC1) and 3 (ABCC3) was greater in cows with fatty liver, whereas the solute carrier family 51 subunit β (SLC51B) did not differ. The expression of genes involved in bile acid uptake, including solute carrier family 10 member 1 (NTCP), solute carrier organic anion transporter family member 1A2 (SLCO1A2) and 2B1 (SLCO2B1) was upregulated in dairy cows with fatty liver. Furthermore, the hepatic protein and mRNA abundance of bile acid metabolism regulators farnesoid X receptor (FXR) and small heterodimer partner (SHP) were lower in cows with fatty liver than in healthy cows. Overall, these data suggest that inhibition of FXR signaling pathway may lead to the increased bile acid synthesis and uptake and decreased secretion of bile acids from hepatocytes to the bile, which elevates hepatic bile acids content in dairy cows with fatty liver. As the hepatotoxicity of bile acids has been demonstrated on nonruminant hepatocytes, it is likely that the liver injury is induced by increased hepatic bile acids content in dairy cows with fatty liver.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Endoplasmic reticulum stress PERK-ATF4-CHOP pathway is involved in non-alcoholic fatty liver disease in type 1 diabetic rats: The rescue effect of treatment exercise and insulin-like growth factor I

Endoplasmic Reticulum Stress (ERS) is a key factor in the development of Non-Alcoholic Fatty Liver Disease (NAFLD) in diabetes. The current study aimed to examine the effects of exercise and IGF-I on ERS markers in liver tissue. Rats were divided into five groups (n = 8 per group), including control (CON), diabetes (DIA), diabetes + exercise (DIA + EX), diabetes + IGF-I (DIA + IGF-I), and diabetes + exercise + IGF-I (DIA + EX + IGF-I). Type 1 diabetes was induced by an I.P. injection of streptozotocin (60 mg/kg). After 30 days of treatment with exercise or IGF-I alone or in combination, liver tissue was assessed for caspase 12, 8, and CHOP protein levels, and expression of ERS markers (ATF-6, PERK, IRE-1A) and lipid metabolism-involved genes (FAS, FXR, SREBP-1c) by western immunoblotting. In addition, for the evaluation of histopathological changes in the liver, Hematoxylin - Eosin and Masson's Trichrome staining were done. Compared to the control group, diabetes significantly caused liver fibrosis, induced ERS, increased caspase 12 and 8 levels in the liver, and changed expression levels of genes associated with lipid metabolism, including FAS, FXR, and SREBP-1c. Treatment with either exercise or IGF-I reduced fibrosis levels suppressed ER stress markers and apoptosis, and improved expression of genes associated with lipid metabolism. In addition, simultaneous treatment with exercise and IGF-I showed a synergistic effect compared to DIA + E and DIA + IGF-I. The results suggest that IGF-1 and exercise reduced liver fibrosis possibly by reducing ERS, creating adaptive ER stress status, and improving protein folding.

MiR-192-5p Ameliorates Hepatic Lipid Metabolism in Non-Alcoholic Fatty Liver Disease by Targeting Yy1

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive lipid accumulation in the liver. Clarifying the molecular mechanism of lipid metabolism is crucial for the treatment of NAFLD. We examined miR-192-5p levels in the livers of mice in which NAFLD was induced via a high-fat diet (HFD), as well as in mouse primary hepatocytes and human HepG2 cells treated with free fatty acids (FFAs). MiR-192-5p inhibitor was administered to NAFLD mice and hepatocytes to verify the specific function of miR-192-5p in NAFLD. We validated the target gene of miR-192-5p and further illustrated the effects of this miRNA on the regulation of triglyceride (TG) metabolism. We found that miR-192-5p was significantly increased in the livers of NAFLD mice and FFA-treated hepatocytes. Inhibition of miR-192-5p increased the accumulation of hepatic TGs and aggravated hepatic steatosis in NAFLD mice. In FFA-treated hepatocytes, miR-192-5p inhibitors markedly increased TG content, whereas overexpression of miR-192-5p reduced TG levels. Yin Yang 1 (Yy1) was identified as the target gene of miR-192-5p, which regulates TG synthesis via the YY1/fatty-acid synthase (FASN) pathway. Our results demonstrated that miR-192-5p should be considered a protective regulator in NAFLD that can inhibit hepatic TG synthesis by targeting Yy1.

Correction to: YY1 inactivated transcription co-regulator PGC-1α to promote mitochondrial dysfunction of early diabetic nephropathy-associated tubulointerstitial fibrosis

The development of diabetic nephropathy (DN) could be promoted by the occurrence of tubulointerstitial fibrosis (TIF), which has a close relationship with mitochondrial dysfunction of renal tubular epithelial cells (RTECs). As a key regulator of metabolic homeostasis, Yin Yang 1 (YY1) plays an important role not only in regulating the fibrosis process but also in maintaining the mitochondrial function of pancreatic β-cells. However, it was not clear whether YY1 participated in maintaining mitochondrial function of RTECs in early DN-associated TIF. In this study, we dynamically detected mitochondrial functions and protein expression of YY1 in db/db mice and high glucose (HG)-cultured HK-2 cells. Our results showed that comparing with the occurrence of TIF, the emergence of mitochondrial dysfunction of RTECs was an earlier even, besides the up-regulated and nuclear translocated YY1. Correlation analysis showed YY1 expressions were negatively associated with PGC-1α in vitro and in vivo. Further mechanism research demonstrated the formation of mTOR-YY1 heterodimer induced by HG up-regulated YY1, the nuclear translocation of which inactivated PGC-1α by binding to the PGC-1α promoter. Overexpression of YY1 induced mitochondrial dysfunctions in normal glucose-cultured HK-2 cells and 8-weeks-old db/m mice. While, dysfunctional mitochondria induced by HG could be improved by knockdown of YY1. Finally, downregulation of YY1 could retard the progression of TIF by preventing mitochondrial functions, resulting in the improvement of epithelial-mesenchymal transition (EMT) in early DN. These findings suggested that YY1 was a novel regulator of mitochondrial function of RTECs and contributed to the occurrence of early DN-associated TIF.

Bioinformatics and system biology approach to identify the influences of SARS-CoV-2 on metabolic unhealthy obese patients

Introduction: The severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) has posed a significant challenge to individuals' health. Increasing evidence shows that patients with metabolic unhealthy obesity (MUO) and COVID-19 have severer complications and higher mortality rate. However, the molecular mechanisms underlying the association between MUO and COVID-19 are poorly understood. Methods: We sought to reveal the relationship between MUO and COVID-19 using bioinformatics and systems biology analysis approaches. Here, two datasets (GSE196822 and GSE152991) were employed to extract differentially expressed genes (DEGs) to identify common hub genes, shared pathways, transcriptional regulatory networks, gene-disease relationship and candidate drugs. Results: Based on the identified 65 common DEGs, the complement-related pathways and neutrophil degranulation-related functions are found to be mainly affected. The hub genes, which included SPI1, CD163, C1QB, SIGLEC1, C1QA, ITGAM, CD14, FCGR1A, VSIG4 and C1QC, were identified. From the interaction network analysis, 65 transcription factors (TFs) were found to be the regulatory signals. Some infections, inflammation and liver diseases were found to be most coordinated with the hub genes. Importantly, Paricalcitol, 3,3',4,4',5-Pentachlorobiphenyl, PD 98059, Medroxyprogesterone acetate, Dexamethasone and Tretinoin HL60 UP have shown possibility as therapeutic agents against COVID-19 and MUO. Conclusion: This study provides new clues and references to treat both COVID-19 and MUO.

Uncovering Novel Roles of miR-122 in the Pathophysiology of the Liver: Potential Interaction with NRF1 and E2F4 Signaling

MicroRNA miR-122 plays a pivotal role in liver function. Despite numerous studies investigating this miRNA, the global network of genes regulated by miR-122 and its contribution to the underlying pathophysiological mechanisms remain largely unknown. To gain a deeper understanding of miR-122 activity, we employed two complementary approaches. Firstly, through transcriptome analysis of polyribosome-bound RNAs, we discovered that miR-122 exhibits potential antagonistic effects on specific transcription factors known to be dysregulated in liver disease, including nuclear respiratory factor-1 (NRF1) and the E2F transcription factor 4 (E2F4). Secondly, through proteome analysis of hepatoma cells transfected with either miR-122 mimic or antagomir, we discovered changes in several proteins associated with increased malignancy. Interestingly, many of these proteins were reported to be transcriptionally regulated by NRF1 and E2F4, six of which we validated as miR-122 targets. Among these, a negative correlation was observed between miR-122 and glucose-6-phosphate dehydrogenase levels in the livers of patients with hepatitis B virus-associated hepatocellular carcinoma. This study provides novel insights into potential alterations of molecular pathway occurring at the early stages of liver disease, driven by the dysregulation of miR-122 and its associated genes.

Baohuoside I inhibits FXR signaling pathway to interfere with bile acid homeostasis via targeting ER α degradation

Epimedii folium (EF) is an effective herbal medicine in osteoporosis treatment, but the clinical utilization of EF has been limited due to potential hepatotoxicity. The previous studies identified that baohuoside I (BI), the main active component of EF, was relevant to EF-induced liver injury. However, the mechanisms of BI causing direct injury to hepatocytes remain unclear. Here, we reveal that BI inhibits FXR-mediated signaling pathway via targeting estrogen receptor α (ER α), leading to the accumulation of bile acids (BAs). Targeted bile acid analyses show BI alters the BA composition and distribution, resulting in impaired BA homeostasis. Mechanistically, BI induces FXR-dependent hepatotoxicity at transcriptional level. Additionally, ER α is predicted to bind to the FXR promoter region based on transcription factor binding sites databases and we further demonstrate that ER α positively regulates FXR promoter activity and affects the expression of target genes involved in BA metabolism. Importantly, we discover that ER α and its mediated FXR transcription regulation might be involved in BI-induced liver injury via ligand-dependent ER α degradation. Collectively, our findings indicate that FXR is a newly discovered target gene of ER α mediated BI-induced liver injury, and suggest BI may be responsible for EF-induced liver injury.

Hepatocyte NLRP3 interacts with PKCε to drive hepatic insulin resistance and steatosis

Hepatic insulin resistance (IR), as a downstream sequela of nonalcoholic fatty liver disease (NAFLD), is strongly associated with liver steatosis. Despite numerous mechanism advancements, the molecular underpinnings and pathogenesis of hepatic IR, especially regarding the pattern recognition receptors in hepatocytes, remain elusive. Here, we identified hepatocyte NLRP3 as a direct and previously-unresolved driver of hepatic IR to promote steatosis response. Under the model of NAFLD, we identified hepatocyte NLRP3 as a crucial inducer of hepatic IR by undertaking multilayer transcriptomic searches and further confirmed that its expression was increased in the liver tissues from NAFLD patients and mouse models (high-fat diet (HFD), leptin-receptor-deficient (db/db) mice), and in palmitic acid (PA)-induced hepatocytes. Loss- or gain-of-function of hepatocyte-specific NLRP3 in HFD-induced mice ameliorated or exacerbated hepatic IR and steatosis, respectively. Mechanistically, NLRP3 directly bound to and promoted protein kinase C epsilon (PKCε) activation to impair insulin signaling and increase liver steatosis, while inhibition of PKCε activation dampened the beneficial effects seen in HFD-induced NLRP3-deficient mice. Moreover, we performed screening and discovered that the transcription factor Yin Yang 1 (YY1) positively controlled NLRP3 expression. In translational potential, adeno-associated virus serotype 8 (AAV8)-mediated NLRP3 knockdown in the liver alleviated hepatic IR and steatosis in db/db mice, and pharmacological inhibition of NLRP3 markedly alleviated diet-induced metabolic disorders. This finding reveals a previously-unexpected regulatory axis from YY1 to PKCε via NLRP3 induction for metabolic diseases and establishes the YY1-NLRP3-PKCε axis as a potential therapeutic target for NAFLD.

Dissecting the roles and clinical potential of YY1 in the tumor microenvironment

Yin-Yang 1 (YY1) is a member of the GLI-Kruppel family of zinc finger proteins and plays a vital dual biological role in cancer as an oncogene or a tumor suppressor during tumorigenesis and tumor progression. The tumor microenvironment (TME) is identified as the “soil” of tumor that has a critical role in both tumor growth and metastasis. Many studies have found that YY1 is closely related to the remodeling and regulation of the TME. Herein, we reviewed the expression pattern of YY1 in tumors and summarized the function and mechanism of YY1 in regulating tumor angiogenesis, immune and metabolism. In addition, we discussed the potential value of YY1 in tumor diagnosis and treatment and provided a novel molecular strategy for the clinical diagnosis and treatment of tumors.

Epiberberine regulates lipid synthesis through SHP (NR0B2) to improve non-alcoholic steatohepatitis

Epiberberine (EPI), extracted from Rhizome Coptidis, has been shown to attenuate hyperlipidemia in vivo. Herein we have studied the mechanism by which EPI is active against non-alcoholic steatohepatitis (NASH) using, mice fed on a methionine- and choline-deficient (MCD) diet and HepG2 cells exposed to free fatty acids (FFA). We show that small heterodimer partner (SHP) protein is key in the regulation of lipid synthesis. In HepG2 cells and in the livers of MCD-fed mice, EPI elevated SHP levels, and this was accompanied by a reduction in sterol regulatory element-binding protein-1c (SREBP-1c) and FASN. Therefore, EPI reduced triglyceride (TG) accumulation in steatotic hepatocytes, even in HepG2 cells treated with siRNA-SHP, and also improved microbiota. Thus, EPI suppresses hepatic TG synthesis and ameliorates liver steatosis by upregulating SHP and inhibiting the SREBP1/FASN pathway, and improves gut microbiome.

Unveiling IL-33/ST2 Pathway Unbalance in Cardiac Remodeling Due to Obesity in Zucker Fatty Rats

Obesity is an epidemic condition linked to cardiovascular disease severity and mortality. Fat localization and type represent cardiovascular risk estimators. Importantly, visceral fat secretes adipokines known to promote low-grade inflammation that, in turn, modulate its secretome and cardiac metabolism. In this regard, IL-33 regulates the functions of various immune cells through ST2 binding and-following its role as an immune sensor to infection and stress-is involved in the pro-fibrotic remodeling of the myocardium. Here we further investigated the IL-33/ST2 effects on cardiac remodeling in obesity, focusing on molecular pathways linking adipose-derived IL-33 to the development of fibrosis or hypertrophy. We analyzed the Zucker Fatty rat model, and we developed in vitro models to mimic the adipose and myocardial relationship. We demonstrated a dysregulation of IL-33/ST2 signaling in both adipose and cardiac tissue, where they affected Epac proteins and myocardial gene expression, linked to pro-fibrotic signatures. In Zucker rats, pro-fibrotic effects were counteracted by ghrelin-induced IL-33 secretion, whose release influenced transcription factor expression and ST2 isoforms balance regulation. Finally, the effect of IL-33 signaling is dependent on several factors, such as cell types' origin and the balancing of ST2 isoforms. Noteworthy, it is reasonable to state that considering IL-33 to have a unique protective role should be considered over-simplistic.

YY1 inactivated transcription co-regulator PGC-1α to promote mitochondrial dysfunction of early diabetic nephropathy-associated tubulointerstitial fibrosis

The development of diabetic nephropathy (DN) could be promoted by the occurrence of tubulointerstitial fibrosis (TIF), which had a closely relationship with mitochondrial dysfunction of renal tubular epithelial cells (RTECs). As a key regulator of metabolic homeostasis, Yin Yang 1 (YY1) played an important role not only in regulating fibrosis process, but also in maintaining mitochondrial function of pancreatic β cells. However, it was not clear whether YY1 participated in maintaining mitochondrial function of RTECs in early DN-associated TIF. In this study, we dynamically detected mitochondrial functions and protein expression of YY1 in db/db mice and high glucose (HG)-cultured HK-2 cells. Our results showed that comparing with the occurrence of TIF, the emergence of mitochondrial dysfunction of RTECs was an earlier even, besides the up-regulated and nuclear translocated YY1. Correlation analysis showed YY1 expressions were negatively associated with PGC-1α in vitro and in vivo. Further mechanism research demonstrated the formation of mTOR-YY1 heterodimer induced by HG upregulated YY1, the nuclear translocation of which inactivated PGC-1α by binding to the PGC-1α promoter. Overexpression of YY1 induced mitochondrial dysfunctions in normal glucose cultured HK-2 cells and 8-week-old db/m mice. While, dysfunctional mitochondria induced by HG could be improved by knockdown of YY1. Finally, downregulation of YY1 could retard the progression of TIF by preventing mitochondrial functions, resulting in the improvement of epithelial-mesenchymal transition (EMT) in early DN. These findings suggested that YY1 was a novel regulator of mitochondrial function of RTECs and contributed to the occurrence of early DN-associated TIF .

Obesity I: Overview and molecular and biochemical mechanisms

Obesity is a chronic, relapsing condition characterized by excess body fat. Its prevalence has increased globally since the 1970s, and the number of obese and overweight people is now greater than those underweight. Obesity is a multifactorial condition, and as such, many components contribute to its development and pathogenesis. This is the first of three companion reviews that consider obesity. This review focuses on the genetics, viruses, insulin resistance, inflammation, gut microbiome, and circadian rhythms that promote obesity, along with hormones, growth factors, and organs and tissues that control its development. It shows that the regulation of energy balance (intake vs. expenditure) relies on the interplay of a variety of hormones from adipose tissue, gastrointestinal tract, pancreas, liver, and brain. It details how integrating central neurotransmitters and peripheral metabolic signals (e.g., leptin, insulin, ghrelin, peptide YY_3-36) is essential for controlling energy homeostasis and feeding behavior. It describes the distinct types of adipocytes and how fat cell development is controlled by hormones and growth factors acting via a variety of receptors, including peroxisome proliferator-activated receptor-gamma, retinoid X, insulin, estrogen, androgen, glucocorticoid, thyroid hormone, liver X, constitutive androstane, pregnane X, farnesoid, and aryl hydrocarbon receptors. Finally, it demonstrates that obesity likely has origins in utero. Understanding these biochemical drivers of adiposity and metabolic dysfunction throughout the life cycle lends plausibility and credence to the "obesogen hypothesis" (i.e., the importance of environmental chemicals that disrupt these receptors to promote adiposity or alter metabolism), elucidated more fully in the two companion reviews.

MiR-320-3p Regulates the Proliferation and Differentiation of Myogenic Progenitor Cells by Modulating Actin Remodeling

Skeletal myogenesis is essential for the maintenance of muscle quality and quantity, and impaired myogenesis is intimately associated with muscle wasting diseases. Although microRNA (miRNA) plays a crucial role in myogenesis and relates to muscle wasting in obesity, the molecular targets and roles of miRNAs modulated by saturated fatty acids (SFA) are largely unknown. In the present study, we investigated the role of miR-320-3p on the differentiation of myogenic progenitor cells. Palmitic acid (PA), the most abundant dietary SFA, suppressed myogenic factors expression and impaired differentiation in C2C12 myoblasts, and these effects were accompanied by CFL2 downregulation and miR-320-3p upregulation. In particular, miR-320-3p appeared to target CFL2 mRNA directly and suppress the expression of CFL2, an essential factor for filamentous actin (F-actin) depolymerization. Transfection of myoblasts with miR-320-3p mimic increased F-actin formation and nuclear translocation of Yes-associated protein 1 (YAP1), a key component of mechanotransduction. Furthermore, miR-320-3p mimic increased myoblast proliferation and markedly impeded the expression of MyoD and MyoG, consequently inhibiting myoblast differentiation. In conclusion, our current study highlights the role of miR-320-3p on CFL2 expression, YAP1 activation, and myoblast differentiation and suggests that PA-inducible miR-320-3p is a significant mediator of muscle wasting in obesity.

A network-based approach reveals the dysregulated transcriptional regulation in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver disease worldwide. We performed network analysis to investigate the dysregulated biological processes in the disease progression and revealed the molecular mechanism underlying NAFLD. Based on network analysis, we identified a highly conserved disease-associated gene module across three different NAFLD cohorts and highlighted the predominant role of key transcriptional regulators associated with lipid and cholesterol metabolism. In addition, we revealed the detailed metabolic differences between heterogeneous NAFLD patients through integrative systems analysis of transcriptomic data and liver-specific genome-scale metabolic model. Furthermore, we identified transcription factors (TFs), including SREBF2, HNF4A, SREBF1, YY1, and KLF13, showing regulation of hepatic expression of genes in the NAFLD-associated modules and validated the TFs using data generated from a mouse NAFLD model. In conclusion, our integrative analysis facilitates the understanding of the regulatory mechanism of these perturbed TFs and their associated biological processes.

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Disease-associated gene modules are conserved across multiple NAFLD cohorts

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The central genes in disease-associated modules are key enzymes in cholesterol synthesis

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YY1 and KLF13 are potential key transcriptional regulators of NAFLD development

The Role and Mechanism of Oxidative Stress and Nuclear Receptors in the Development of NAFLD

The overproduction of reactive oxygen species (ROS) and consequent oxidative stress contribute to the pathogenesis of acute and chronic liver diseases. It is now acknowledged that nonalcoholic fatty liver disease (NAFLD) is characterized as a redox-centered disease due to the role of ROS in hepatic metabolism. However, the underlying mechanisms accounting for these alternations are not completely understood. Several nuclear receptors (NRs) are dysregulated in NAFLD, and have a direct influence on the expression of a set of genes relating to the progress of hepatic lipid homeostasis and ROS generation. Meanwhile, the NRs act as redox sensors in response to metabolic stress. Therefore, targeting NRs may represent a promising strategy for improving oxidation damage and treating NAFLD. This review summarizes the link between impaired lipid metabolism and oxidative stress and highlights some NRs involved in regulating oxidant/antioxidant turnover in the context of NAFLD, shedding light on potential therapies based on NR-mediated modulation of ROS generation and lipid accumulation.

Hypoglycemic mechanism of intestinal bypass surgery in type 2 diabetic rats

To investigate the effect of duodenal-jejunal bypass (DJB) surgery on postoperative blood glucose in type 2 diabetic rats, and further explore possible mechanisms for the effect of surgical treatment of type 2 diabetes. Forty rats with type 2 diabetes were randomly assigned to 4 groups (n = 10 rats per group), which subsequently underwent DJB, new biliopancreatic diversion (NBPD) or duodenal-jejunal exclusion (DJE) surgery or a sham operation (SHAM). Fasting glucose, 2-h postprandial glucose and blood lipids were measured, and the mRNA in liver and intestinal tissue for bile acid receptor (FXR), as well as the FXR protein expression in the liver tissues were determined. Postprandial blood glucose and fasting TG and FFA in the DJB and NBPD groups were significantly lower than those in the SHAM group and preoperative (p < 0.05) at 8 weeks postoperation. Liver FXR protein was expressed at significantly higher in the DJB and NBPD groups than in the other two (p < 0.05), and the intestinal FXR mRNA in the DJE group were highest. DJB up-regulates the expression of bile acid receptors in the liver and down-regulates those receptors in the intestinal tract via biliopancreatic diversion. This process reduces TG levels, and subsequently any lipotoxicity to islet cells to produce a hypoglycemic effect.

Sparcl1 promotes nonalcoholic steatohepatitis progression in mice through upregulation of CCL2

Nonalcoholic fatty liver disease (NAFLD) represents a spectrum of chronic liver disease ranging from simple steatosis (NAFL) to nonalcoholic steatohepatitis (NASH). However, the molecular mechanisms of NASH progression remain incompletely understood. White adipose tissue (WAT) has emerged as an important endocrine organ and contributes not only to the initial stage of NAFLD, but also to its severity. In the current study, through transcriptomic analysis we identified increased expression of Sparcl1, a secreted glycoprotein, in the WAT from NASH mice. Plasma Sparcl1 levels were similarly elevated and positively correlated with hepatic pathological features in NASH patients. Functional studies showed that both chronic injection of recombinant Sparcl1 protein and overexpression of Sparcl1 exaggerated hepatic inflammation and liver injury in mice. In contrast, genetic ablation of Sparcl1, knockdown of Sparcl1 in WAT, and treatment with a Sparcl1-neutralizing antibody dramatically alleviated diet-induced NASH pathogenesis. Mechanistically, Sparcl1 promoted the expression of C-C motif chemokine ligand 2 (CCL2) in hepatocytes through binding to Toll-like receptor 4 (TLR4) and activation of the NF-κB/p65 signaling pathway. Genetically or pharmacologically blocking the CCL2/CCR2 pathway attenuated the hepatic inflammatory response evoked by Sparcl1. Thus, our results demonstrated an important role for Sparcl1 in NASH progression, suggesting a potential target for therapeutic intervention.

Multifaceted regulation of hepatic lipid metabolism by YY1

This study shows that YY1 regulates hepatic lipid metabolism by directly or indirectly regulating the expression of several key upstream transcription factors and their coactivators.

Recent studies suggested that dysregulated YY1 plays a pivotal role in many liver diseases. To obtain a detailed view of genes and pathways regulated by YY1 in the liver, we carried out RNA sequencing in HepG2 cells after YY1 knockdown. A rigid set of 2,081 differentially expressed genes was identified by comparing the YY1-knockdown samples (n = 8) with the control samples (n = 14). YY1 knockdown significantly decreased the expression of several key transcription factors and their coactivators in lipid metabolism. This is illustrated by YY1 regulating PPARA expression through binding to its promoter and enhancer regions. Our study further suggest that down-regulation of the key transcription factors together with YY1 knockdown significantly decreased the cooperation between YY1 and these transcription factors at various regulatory regions, which are important in regulating the expression of genes in hepatic lipid metabolism. This was supported by the finding that the expression of SCD and ELOVL6, encoding key enzymes in lipogenesis, were regulated by the cooperation between YY1 and PPARA/RXRA complex over their promoters.

Prenatal dexamethasone exposure induces nonalcoholic fatty liver disease in male rat offspring via the miR-122/YY1/ACE2-MAS1 pathway

Epidemiological studies have shown that nonalcoholic fatty liver disease (NAFLD) has an intrauterine developmental origin. We aimed to demonstrate that NAFLD is caused by prenatal dexamethasone exposure (PDE) in adult male rat offspring and to investigate the intrauterine programming mechanism. Liver samples were obtained on gestational day (GD) 21 and postnatal week (PW) 28. The effects and epigenetic mechanism of dexamethasone were studied with bone marrow mesenchymal stem cells (BMSCs) hepatoid differentiated cells and other cell models. In the PDE group, lipid accumulation increased, triglyceride synthesis-related gene expression increased, and oxidation-related gene expression decreased in livers of adult male rat offspring. In utero, hepatic triglyceride synthesis increased and oxidative function decreased in PDE fetal male rats. Moreover, low hepatic miR-122 expression, high Yin Yang-1 (YY1) expression and angiotensin-converting enzyme 2 (ACE2)-Mas receptor (MAS1) signaling pathway inhibition were observed before and after birth. At the cellular level, dexamethasone (100-2500 nM) elevated the intracellular triglyceride content, increased triglyceride synthesis-related gene expression and decreased oxidation-related gene expression. Dexamethasone treatment also decreased miR-122 expression, increased YY1 expression and inhibited the ACE2-MAS1 signaling pathway. Interference or overexpression of glucocorticoid receptor (GR), miR-122, YY1 and ACE2 could reverse the changes in downstream gene expression. In summary, PDE could induce NAFLD in adult male rat offspring. The programming mechanism included inhibition of miR-122 expression after GR activation, and dexamethasone increased hepatocyte YY1 expression; these effects resulted in ACE2-MAS1 signaling pathway inhibition, which led to increased hepatic triglyceride synthesis and decreased oxidative function. The increased triglyceride synthesis and decreased oxidative function of hepatocytes caused by low miR-122 expression due to dexamethasone could continue postnatally, eventually leading to NAFLD in adult rat offspring.

N6 -Methyladenosine Reader Protein YT521-B Homology Domain-Containing 2 Suppresses Liver Steatosis by Regulation of mRNA Stability of Lipogenic Genes

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease (NAFLD) is characterized by accumulation of excessive triglycerides (TGs) in hepatocytes. Obesity is a major risk factor for developing fatty liver, although the intracellular molecular basis remains largely unclear. N⁶ -methyladenosine (m⁶ A) RNA methylation is the most common internal modification in eukaryotic mRNA.

APPROACH AND RESULTS

In the present study, by m⁶ A sequencing and RNA sequencing, we found that both m⁶ A enrichment and mRNA expression of lipogenic genes were significantly increased in leptin-receptor-deficient db/db mice. Importantly, our results showed that YT521-B homology domain-containing 2 (Ythdc2), an m⁶ A reader, was markedly down-regulated in livers of obese mice and NAFLD patients. Suppression of Ythdc2 in livers of lean mice led to TG accumulation, whereas ectopic overexpression of Ythdc2 in livers of obese mice improved liver steatosis and insulin resistance. Mechanistically, we found that Ythdc2 could bind to mRNA of lipogenic genes, including sterol regulatory element-binding protein 1c, fatty acid synthase, stearoyl-CoA desaturase 1, and acetyl-CoA carboxylase 1, to decrease their mRNA stability and inhibit gene expression.

CONCLUSIONS

Our findings describe an important role of the m⁶ A reader, Ythdc2, for regulation of hepatic lipogenesis and TG homeostasis, which might provide a potential target for treating obesity-related NAFLD.

Overexpression of p53 accelerates puberty in high-fat diet-fed mice through Lin28/let-7 system

IMPACT STATEMENT

High-fat intake and subsequent obesity are associated with premature onset of puberty, but the exact neuroendocrine mechanisms are still unclear. The transcriptional factor p53 has been predicted to be a central hub of the gene networks controlling the pubertal onset. Besides, p53 also plays crucial roles in metabolism. Here, we explored p53 in the hypothalami of mice fed a high-fat diet (HFD), which showed an up-regulated expression. Besides, we also revealed that overexpressed p53 may accelerate hypothalamo-pituitary-gonadal (HPG) axis activation partially through the c-Myc/Lin28/let-7 system. These results can deepen our understanding of the interaction between metabolic regulation and puberty onset control, and may shed light on the neuroendocrine mechanisms of obesity-related central precocious puberty.

Farnesol induces mitochondrial/peroxisomal biogenesis and thermogenesis by enhancing the AMPK signaling pathway in vivo and in vitro

Thermogenic activation of brown adipose tissue has been considered as an obesity treatment strategy that consumes energy. In this study, we investigated whether farnesol in vivoandin vitro models induces thermogenesis and affect the activation of the mitochondria and peroxisomes, which are key organelles in activated brown adipocytes. Farnesol induced the expression of thermogenic factors such as uncoupling protein 1 (UCP1), peroxisome proliferator-activated receptor γ coactivator 1 alpha (PGC1α), and PR domain zinc-finger protein 16 (PRDM16) together with the phosphorylation of AMP-activated protein kinase alpha (AMPKα) in brown adipose tissue and primary cultured brown adipocytes. Farnesol promoted lipolytic enzymes: hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL). We confirmed that these inductions of lipolysis by farnesol were the underlying causes of β-oxidation activation. Farnesol also increased the expression of oxidative phosphorylation (OXPHOS) complexes and the oxygen consumption rate (OCR) and the expansion of peroxisomes. Moreover, we proved that the thermogenic activity of farnesol was dependent on AMPKα activation using Compound C inhibitor or siRNA-AMPKα knockdown. These results suggest that farnesol may be a potential agent for the treatment of obesity by inducing energy consumption through heat generation.

Dietary betaine prevents obesity through gut microbiota-drived microRNA-378a family

Betaine is a natural compound present in commonly consumed foods and may have a potential role in the regulation of glucose and lipids metabolism. However, the underlying molecular mechanism of its action remains largely unknown. Here, we show that supplementation with betaine contributes to improved high-fat diet (HFD)-induced gut microbiota dysbiosis and increases anti-obesity strains such as Akkermansia muciniphila, Lactobacillus, and Bifidobacterium. In mice lacking gut microbiota, the functional role of betaine in preventing HFD-induced obesity, metabolic syndrome, and inactivation of brown adipose tissues are significantly reduced. Akkermansia muciniphila is an important regulator of betaine in improving microbiome ecology and increasing strains that produce short-chain fatty acids (SCFAs). Increasing two main members of SCFAs including acetate and butyrate can significantly regulate the levels of DNA methylation at host miR-378a promoter, thus preventing the development of obesity and glucose intolerance. However, these beneficial effects are partially abolished by Yin yang (YY1), a common target gene of the miR-378a family. Taken together, our findings demonstrate that betaine can improve obesity and associated MS via the gut microbiota-derived miR-378a/YY1 regulatory axis, and reveal a novel mechanism by which gut microbiota improve host health.

The Nuclear Orphan Receptor NR2F6 Promotes Hepatic Steatosis through Upregulation of Fatty Acid Transporter CD36

Nuclear receptors (NRs) are a superfamily of transcription factors which sense hormonal signals or nutrients to regulate various biological events, including development, reproduction, and metabolism. Here, this study identifies nuclear receptor subfamily 2, group F, member 6 (NR2F6), as an important regulator of hepatic triglyceride (TG) homeostasis and causal factor in the development of non-alcoholic fatty liver disease (NAFLD). Adeno-associated virus (AAV)-mediated overexpression of NR2F6 in the liver promotes TG accumulation in lean mice, while hepatic-specific suppression of NR2F6 improves obesity-associated hepatosteatosis, insulin resistance, and methionine and choline-deficient (MCD) diet-induced non-alcoholic steatohepatitis (NASH). Mechanistically, the fatty acid translocase CD36 is identified as a transcriptional target of NR2F6 to mediate its steatotic role. NR2F6 is able to bind directly onto the CD36 promoter region in hepatocytes and increases the enrichment of nuclear receptor coactivator 1 (SRC-1) and histone acetylation at its promoter. Of pathophysiological significance, NR2F6 is significantly upregulated in the livers of obese mice and NAFLD patients. Moreover, treatment with metformin decreases NR2F6 expression in obese mice, resulting in suppression of CD36 and reduced hepatic TG contents. Therefore, these results provide evidence for an unpredicted role of NR2F6 that contributes to liver steatosis and suggest that NR2F6 antagonists may present a therapeutic strategy for reversing or treating NAFLD/NASH pathogenesis.

Molecular Physiology of Bile Acid Signaling in Health, Disease, and Aging

Over the past two decades, bile acids (BAs) have become established as important signaling molecules that enable fine-tuned inter-tissue communication from the liver, their site of production, over the intestine, where they are modified by the gut microbiota, to virtually any organ, where they exert their pleiotropic physiological effects. The chemical variety of BAs, to a large extent determined by the gut microbiome, also allows for a complex fine-tuning of adaptive responses in our body. This review provides an overview of the mechanisms by which BA receptors coordinate several aspects of physiology and highlights new therapeutic strategies for diseases underlying pathological BA signaling.

Betulinic acid improves nonalcoholic fatty liver disease through YY1/FAS signaling pathway

The increasing prevalence of nonalcoholic fatty liver disease (NAFLD) worldwide indicates the urgent need to develop novel and effective treatment strategies. Betulinic acid (BA), a naturally occurring plant-derived pentacyclic triterpenoid, has an outstanding effect in improving metabolism. However, the pharmacological action and mechanism of BA in NAFLD remain unclear. Here, we show that BA-treated high-fat diet mice and methionine-choline deficient diet-fed mice are resistant to hepatic steatosis when compared with vehicle-treated mice. BA alleviates fatty acid synthesis, fibrosis, and inflammation and promotes fatty acid oxidation. Meanwhile, fatty acid synthase (FAS) expression and activity are markedly inhibited with BA treatment both in vitro and in vivo. Moreover, BA inhibits FAS expression through transcriptional suppression of Yin Yang 1 (YY1), leading to retard hepatocytes triglyceride accumulation. Collectively, BA protects hepatocytes from abnormal lipid deposition in NAFLD through YY1/FAS pathway. Our findings establish a novel role of BA in representing a possible therapeutic strategy to reverse NAFLD.

Maternal glucose homeostasis is impaired in mouse models of gestational cholestasis

Women with intrahepatic cholestasis of pregnancy (ICP), a disorder characterised by raised serum bile acids, are at increased risk of developing gestational diabetes mellitus and have impaired glucose tolerance whilst cholestatic. FXR and TGR5 are modulators of glucose metabolism, and FXR activity is reduced in normal pregnancy, and further in ICP. We aimed to investigate the role of raised serum bile acids, FXR and TGR5 in gestational glucose metabolism using mouse models. Cholic acid feeding resulted in reduced pancreatic β-cell proliferation and increased apoptosis in pregnancy, without altering insulin sensitivity, suggesting that raised bile acids affect β-cell mass but are insufficient to impair glucose tolerance. Conversely, pregnant Fxr-/- and Tgr5-/- mice are glucose intolerant and have reduced insulin secretion in response to glucose challenge, and Fxr-/- mice are also insulin resistant. Furthermore, fecal bile acids are reduced in pregnant Fxr-/- mice. Lithocholic acid and deoxycholic acid, the principal ligands for TGR5, are decreased in particular. Therefore, we propose that raised serum bile acids and reduced FXR and TGR5 activity contribute to the altered glucose metabolism observed in ICP.

Molecular Mechanisms Regulating Obesity-Associated Hepatocellular Carcinoma

Obesity is a global, intractable issue, altering inflammatory and stress response pathways, and promoting tissue adiposity and tumorigenesis. Visceral fat accumulation is correlated with primary tumor recurrence, poor prognosis and chemotherapeutic resistance. Accumulating evidence highlights a close association between obesity and an increased incidence of hepatocellular carcinoma (HCC). Obesity drives HCC, and obesity-associated tumorigenesis develops via nonalcoholic fatty liver (NAFL), progressing to nonalcoholic steatohepatitis (NASH) and ultimately to HCC. The better molecular elucidation and proteogenomic characterization of obesity-associated HCC might eventually open up potential therapeutic avenues. The mechanisms relating obesity and HCC are correlated with adipose tissue remodeling, alteration in the gut microbiome, genetic factors, ER stress, oxidative stress and epigenetic changes. During obesity-related hepatocarcinogenesis, adipokine secretion is dysregulated and the nuclear factor erythroid 2 related factor 1 (Nrf-1), nuclear factor kappa B (NF-κB), mammalian target of rapamycin (mTOR), phosphatidylinositol-3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/Akt, and Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathways are activated. This review captures the present trends allied with the molecular mechanisms involved in obesity-associated hepatic tumorigenesis, showcasing next generation molecular therapeutic strategies and their mechanisms for the successful treatment of HCC.

Repositioning an Immunomodulatory Drug Vidofludimus as a Farnesoid X Receptor Modulator With Therapeutic Effects on NAFLD

Non-alcoholic fatty liver disease (NAFLD) has become the most common chronic liver disorder, and yet with no pharmacological treatment approved worldwide. The repositioning of old drugs provides a safe approach for drug development. Vidofludimus, an inhibitor for dihydroorotate dehydrogenase (DHODH) for the treatment of autoimmune disorders, is herein uncovered as a novel modulator for farnesoid X receptor (FXR) by biochemical and crystallographic analysis. We further revealed that vidofludimus exerts in vivo therapeutic effects on dextran sodium sulfate (DSS)-induced colitis in an FXR-dependent manner. Notably, vidofludimus also possesses remarkable beneficial effects in reducing NAFLD by targeting FXR, which may represent a unique approach in developing the treatment for NAFLD. Our findings not only reveal a promising template for the design of novel FXR ligands in treating autoimmune disorders, but also uncover a novel therapeutic effect for vidofludimus on NAFLD based on the newly established relationships among drugs, targets, and diseases.

Induction of SIRT1 by melatonin improves alcohol-mediated oxidative liver injury by disrupting the CRBN-YY1-CYP2E1 signaling pathway

Alcoholic liver disease is the most prevalent chronic liver disease. Melatonin is known to control many vital processes. Here, we explored a novel molecular mechanism by which melatonin-induced SIRT1 signaling protects against alcohol-mediated oxidative stress and liver injury. Gene expression profiles and metabolic changes were measured in liver specimens of mice and human subjects. Expression levels of Cb1r, Crbn, Btg2, Yy1, pro-inflammatory cytokines, and Cyp2e1 were significantly enhanced in chronic alcohol-challenged mice and human subjects. Levels of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), hepatic CYP2E1 protein, and reactive oxygen species (ROS) were elevated in alcohol-fed WT mice but not in Cb1r antagonist-treated, Crbn null, or Yy1-silenced mice. Importantly, alcohol-induced Yy1 and Cyp2e1 expression, ROS amount, and liver injury were markedly diminished by melatonin treatment and the transduction of Sirt1 in mice, whereas this phenomenon was prominently ablated by silencing of Sirt1. Notably, SIRT1 physically interacted with YY1 and attenuated YY1 occupancy on the Cyp2e1 gene promoter. Melatonin-SIRT1 signaling ameliorates alcohol-induced oxidative liver injury by disrupting the CRBN-YY1-CYP2E1 signaling pathway. The manipulation of CRBN-YY1-CYP2E1 signaling network by the melatonin-SIRT1 pathway highlights a novel entry point for treating alcoholic liver disease.

Intestinal microbiome and NAFLD: molecular insights and therapeutic perspectives

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of dysregulated lipid and glucose metabolism, which is often associated with obesity, dyslipidemia and insulin resistance. In view of the high morbidity and health risks of NAFLD, the lack of effective cure has drawn great attention. In recent years, a line of evidence has suggested a close linkage between the intestine and liver diseases such as NAFLD. We summarized the composition and characteristics of intestinal microbes and reviewed molecular insights into the intestinal microbiome in development and progression of NAFLD. Intestinal microbes mainly include bacteria, archaea, viruses and fungi, and the crosstalk between non-bacterial intestinal microbes and human liver diseases should be paid more attention. Intestinal microbiota imbalance may not only increase the intestinal permeability to gut microbes but also lead to liver exposure to harmful substances that promote hepatic lipogenesis and fibrosis. Furthermore, we focused on reviewing the latest "gut-liver axis"-targeting treatment, including the application of antibiotics, probiotics, prebiotics, synbiotics, farnesoid X receptor agonists, bile acid sequestrants, gut-derived hormones, adsorbents and fecal microbiota transplantation for NAFLD. In this review, we also discussed the potential mechanisms of "gut-liver axis" manipulation and efficacy of these therapeutic strategies for NAFLD treatment.

p53 Mediates GnRH Secretion via Lin28/let-7 System in GT1-7 Cells

STUDY OBJECTIVE

The well-known tumor suppressor transcriptional factor p53 has been proposed to be one of the central hubs of a functionally related and hierarchically arranged gene network coordinating pubertal timing. Our previous studies revealed that p53 is involved in the metabolic control of puberty. The current study aimed to investigate the underlying signaling pathway, through which p53 mediated the metabolic control of puberty.

DESIGN SETTING PARTICIPANTS INTERVENTIONS AND MAIN OUTCOME MEASURES

We engineered the expression of p53 and/or Lin28a in GT1-7 cells to investigate the interaction between p53 and Lin28/let-7 system, and their impact on GnRH secretion.

RESULTS

Overexpression of p53 stimulated, while inhibition of p53 by pifithrin-α significantly suppressed the GnRH secretion and GPR54 expression levels in response to kisspeptin stimulation in GT1-7 cells. Furthermore, overexpressed p53 suppressed Lin28a and c-Myc expression levels and increased let-7 expression levels in GT1-7 cell lines. On the other hand, inhibition of p53 by pifithrin-α upregulated Lin28a and c-Myc levels and downregulated let-7 expression levels. Moreover, Lin28a overexpression counteracted the effect of p53 overexpression in p53 and Lin28a co-overexpression cells, whose GnRH secretion and GPR54 expression levels were not different from controls. Meanwhile, Lin28a suppression counteracted the effect of pifithrin-α, and the GnRH secretion and GPR54 expression levels are not different from controls in p53 and Lin28a co-suppression cells.

CONCLUSION

These data suggest that p53 is a central mediator of GnRH secretion in hypothalamus, and this effect is at least partly through the Lin28/let-7 pathway.

Yin Yang 1 facilitates hepatocellular carcinoma cell lipid metabolism and tumor progression by inhibiting PGC-1β-induced fatty acid oxidation

Lipid accumulation is a driving force in tumor development, as it provides tumor cells with both energy and the building blocks of phospholipids for construction of cell membranes. Aberrant homeostasis of lipid metabolism has been observed in various tumors; however, the molecular mechanism has not been fully elucidated.

Methods: Yin yang 1 (YY1) expression in hepatocellular carcinoma (HCC) was analyzed using clinical specimens, and its roles in HCC in lipid metabolism were examined using gain- and loss-of function experiments. The mechanism of YY1 regulation on peroxisome proliferator-activated receptor gamma coactivator-1β (PGC-1β) and its downstream genes medium-chain acyl-CoA dehydrogenase (MCAD) and long-chain acyl-CoA dehydrogenase (LCAD) were investigated using molecular biology and biochemical methods. The role of YY1/ PGC-1β axis in hepatocarcinogenesis was studied using xenograft experiment.

Results: This study showed that YY1 suppresses fatty acid β-oxidation, leading to increase of cellular triglyceride level and lipid accumulation in HCC cells, and subsequently induction of the tumorigenesis potential of HCC cells. Molecular mechanistic study revealed that YY1 blocks the expression of PGC-1β, an activator of fatty acid β-oxidation, by directly binding to its promoter; and thus downregulates PGC-1β/MCAD and PGC1-β/LCAD axis. Importantly, we revealed that YY1 inhibition on PGC-1β occurs irrespective of the expression of hypoxia-inducible factor-1α (HIF1-α), enabling it to promote lipid accumulation under both normoxic and hypoxic conditions.

Conclusion: Our study reveals the critical role of YY1/PGC-1β axis in HCC cell lipid metabolism, providing novel insight into the molecular mechanisms associated with tumor cell lipid metabolism, and a new perspective regarding the function of YY1 in tumor progression. Thus, our study provides evidences regarding the potential of YY1 as a target for lipid metabolism-based anti-tumor therapy.

Osteoprotegerin Promotes Liver Steatosis by Targeting the ERK-PPAR-γ-CD36 Pathway

Previous cross-sectional studies have established that circulating osteoprotegerin (OPG) levels are associated with nonalcoholic fatty liver disease (NAFLD). However, the role of OPG in metabolic diseases, such as diabetes and NAFLD, is still unclear. In the current study, we demonstrated that hepatic OPG expression was downregulated in NAFLD individuals and in obese mice. OPG deficiency decreased lipid accumulation and expression of CD36 and peroxisome proliferator-activated receptor-γ (PPAR-γ) in the livers of OPG^-/- mice and cultured cells, respectively, whereas OPG overexpression elicited the opposite effects. The stimulatory role of OPG in lipid accumulation was blocked by CD36 inactivation in hepatocytes isolated from CD36^-/- mice. The overexpression of OPG led to a decrease in extracellular signal-regulated kinase (ERK) phosphorylation in the livers of OPG^-/- mice and in cultured cells, while OPG deficiency resulted in the opposite effect. The inhibition of PPAR-γ or the activation of ERK blocked the induction of CD36 expression by OPG in cultured cells. Mechanistically, OPG facilitated CD36 expression by acting on PPAR response element (PPRE) present on the CD36 promoter. Taken together, our study revealed that OPG signaling promotes liver steatosis through the ERK-PPAR-γ-CD36 pathway. The downregulation of OPG in NAFLD might be a compensatory response of the body to dampen excess hepatic fat accumulation in obesity.

Yin Yang 1 protein ameliorates diabetic nephropathy pathology through transcriptional repression of TGFβ1

Transforming growth factor–β1 (TGFβ1) has been identified as a major pathogenic factor underlying the development of diabetic nephropathy (DN). However, the current strategy of antagonizing TGFβ1 has failed to demonstrate favorable outcomes in clinical trials. To identify a different therapeutic approach, we designed a mass spectrometry–based DNA-protein interaction screen to find transcriptional repressors that bind to the TGFB1 promoter and identified Yin Yang 1 (YY1) as a potent repressor of TGFB1. YY1 bound directly to TGFB1 promoter regions and repressed TGFB1 transcription in human renal mesangial cells. In mouse models, YY1 was elevated in mesangial cells during early diabetic renal lesions and decreased in later stages, and knockdown of renal YY1 aggravated, whereas overexpression of YY1 attenuated glomerulosclerosis. In addition, although their duration of diabetic course was comparable, patients with higher YY1 expression developed diabetic nephropathy more slowly compared to those who presented with lower YY1 expression. We found that a small molecule, eudesmin, suppressed TGFβ1 and other profibrotic factors by increasing YY1 expression in human renal mesangial cells and attenuated diabetic renal lesions in DN mouse models by increasing YY1 expression. These results suggest that YY1 is a potent transcriptional repressor of TGFB1 during the development of DN in diabetic mice and that small molecules targeting YY1 may serve as promising therapies for treating DN.

YY1: A novel therapeutic target for diabetic nephropathy orchestrated renal fibrosis

BACKGROUND

Renal fibrosis promotes the development of diabetic nephropathy (DN). A growing number of studies have reported that Yin Yang 1 (YY1), which is involved in cellular proliferation and differentiation, plays a crucial role in the pathogenesis of many diseases, such as pulmonary fibrosis, hepatic steatosis and cancer.

METHODS

We detected the expression of YY1 under various glucose concentration and time gradient conditions. Rapamycin was used to verify the mTORC1/p70S6K/YY1 signaling pathway in HK-2 cells. We used db/db mice to examine the connection between renal fibrosis and YY1. A luciferase assay and chromatin immunoprecipitation (ChIP) assay were used to identify whether YY1 directly regulated α-SMA by binding to the α-SMA promoter. RNA silencing and overexpression were performed by using a YY1 expression/knockdown plasmid to investigate the function of YY1 in renal fibrosis of DN.

RESULTS

YY1 expression and subsequent nuclear translocation were upregulated in a glucose- and time-dependent manner via the mTORC1/p70S6K signaling pathway in HK-2 cells. YY1 expression and nuclear translocation was significantly upregulated in db/db mice. Furthermore, YY1 upregulated α-SMA expression and activity in high-glucose-cultured HK-2 cells. Overexpression of YY1 promoted renal fibrosis in db/m mice mainly by upregulating α-SMA expression and inducing epithelial-mesenchymal transition (EMT) in vitro and in vivo. Finally, downregulation of YY1 reversed renal fibrosis by improving EMT in vivo and in vitro.

CONCLUSIONS

These results reveal that upregulation of YY1 plays a critical role in HG-induced deregulation of EMT-associated protein expression, which finally results in renal fibrosis of DN. Therefore, decreasing YY1 expression might represent a new therapeutic target for diabetic nephropathy-induced renal fibrosis.

Myofibroblast-specific YY1 promotes liver fibrosis

Liver fibrosis is a common consequence of various chronic hepatitis and liver injuries. The myofibroblasts, through the accumulation of extracellular matrix (ECM) proteins, are closely associated with the progression of liver fibrosis. However, the molecular mechanisms underlying transcriptional regulation of fibrogenic genes and ECM proteins in myofibroblasts remain largely unknown. Using tamoxifen inducible myofibroblast-specific Cre-expressing mouse lines with selective deletion of the transcription factor Yin Yang 1 (YY1), here we show that YY1 deletion in myofibroblasts mitigates carbon tetrachloride-induced liver fibrosis. This protective effect of YY1 ablation on liver fibrosis was accompanied with reduced expression of profibrogenic genes and ECM proteins, including TNF-α, TGF-β, PDGF, IL-6, α-SMA and Col1α1 in liver tissues from YY1 mutant mice. Moreover, using the human hepatic stellate cell (HSC) line LX-2, we found that knockdown of YY1 in myofibroblasts by siRNA treatment diminished myofibroblast proliferation, α-SMA expression, and collagen deposition. Collectively, our findings reveal a specific role of YY1 in hepatic myofibroblasts and suggest a new therapeutic strategy for hepatic fibrosis-associated liver diseases.

Endocrine-Mediated Mechanisms of Metabolic Disruption and New Approaches to Examine the Public Health Threat

Obesity and metabolic disorders are of great societal concern and generate substantial human health care costs globally. Interventions have resulted in only minimal impacts on disrupting this worsening health trend, increasing attention on putative environmental contributors. Exposure to numerous environmental contaminants have, over decades, been demonstrated to result in increased metabolic dysfunction and/or weight gain in cell and animal models, and in some cases, even in humans. There are numerous mechanisms through which environmental contaminants may contribute to metabolic dysfunction, though certain mechanisms, such as activation of the peroxisome proliferator activated receptor gamma or the retinoid x receptor, have received considerably more attention than less-studied mechanisms such as antagonism of the thyroid receptor, androgen receptor, or mitochondrial toxicity. As such, research on putative metabolic disruptors is growing rapidly, as is our understanding of molecular mechanisms underlying these effects. Concurrent with these advances, new research has evaluated current models of adipogenesis, and new models have been proposed. Only in the last several years have studies really begun to address complex mixtures of contaminants and how these mixtures may disrupt metabolic health in environmentally relevant exposure scenarios. Several studies have begun to assess environmental mixtures from various environments and study the mechanisms underlying their putative metabolic dysfunction; these studies hold real promise in highlighting crucial mechanisms driving observed organismal effects. In addition, high-throughput toxicity databases (ToxCast, etc.) may provide future benefits in prioritizing chemicals for in vivo testing, particularly once the causative molecular mechanisms promoting dysfunction are better understood and expert critiques are used to hone the databases. In this review, we will review the available literature linking metabolic disruption to endocrine-mediated molecular mechanisms, discuss the novel application of environmental mixtures and implications for in vivo metabolic health, and discuss the putative utility of applying high-throughput toxicity databases to answering complex organismal health outcome questions.

Single-nucleotide polymorphism rs731384 is associated with plasma lipid levels and the risk of coronary artery disease in Chinese populations

AIMS

To investigate the relationship between the miR-130a polymorphism rs731384 and coronary artery disease (CAD) and to further explore the molecular mechanism of the pathogenesis of CAD, an observational single-center study was conducted.

METHOD

A total of 876 subjects were recruited in the present study. Four milliliters of venous blood was drawn after 12 h of fasting to perform biochemical assays. CAD patients and controls were distinguished by coronary angiography. Rs731384 was genotyped on the Agena MassARRAY system according to the manufacturer's user guide. Statistical analysis was conducted using SPSS 16.0 software.

RESULTS

The study found that the plasma levels of total cholesterol (TC) (P=0.006), low-density lipoprotein cholesterol (LDL-C) (P=0.030), apolipoprotein A (ApoA) (P=0.038), and apolipoprotein B (ApoB) (P=0.022) distributed differently in patients with various alleles. Additionally, the AA genotype of rs731384 was found to be a protective factor against CAD in a recessive model (AA:AG+GG, odds ratio (OR) = 0.408, 95% confidence interval (95% CI) = 0.171-0.973, P=0.043). A significant association was found between the gene-environment interaction and CAD risk. The AA genotype along with high-density lipoprotein cholesterol (HDL-C) level ≥ 1.325 mmol/l significantly decreased the CAD risk (AA:AG+GG, OR = 0.117, 95% CI = 0.023-0.588, P=0.009).

CONCLUSION

The mutant AA genotype of rs731384 seems to be a protective factor against CAD, and rs731384 plays an important role in the human metabolism of plasma lipids.

Proteome-wide analysis of USP14 substrates revealed its role in hepatosteatosis via stabilization of FASN

Ubiquitin-specific protease 14 (USP14) is one of the major proteasome-associated deubiquitinating enzymes critical for proteome homeostasis. However, substrates of USP14 remain largely unknown, hindering the understanding of its functional roles. Here we conduct a comprehensive proteome, ubiquitinome and interactome analysis for USP14 substrate screening. Bioinformatics analysis reveals broad new potential roles of USP14, especially in lipid and carbohydrate metabolism. Among the potential substrates identified, we show that fatty acid synthase (FASN), a key enzyme involved in hepatic lipogenesis, is a bona fide substrate of USP14. USP14 directly interacts with and increases FASN stability. As a result, overexpression of USP14 promotes liver triglyceride accumulation in C57BL/6 mice, whereas genetic ablation or pharmacological inhibition of USP14 ameliorates hepatosteatosis, hyperglycemia and insulin resistance in obese mice. In conclusion, our findings reveal for the first time an indispensable role of USP14 in hepatosteatosis through FASN stabilization.

Ubiquitin-specific protease 14 (USP14) is a proteasome-associated deubiquitinating enzyme with known roles in physiology and disease. Here the authors show that fatty acid synthase (FASN) is a substrate of USP14, and that by stabilizing FASN, it plays a role in hepatosteatosis.

SRY-Box Containing Gene 4 Promotes Liver Steatosis by Upregulation of SREBP-1c

Obesity is usually associated with an increased risk of nonalcoholic fatty liver disease that is characterized by accumulation of excessive triglyceride (TG) in hepatocytes. However, the factors involved in the obesity-induced hepatosteatosis are poorly defined. Here, we report that SRY-box containing gene 4 (Sox4), a transcription factor that regulates cell proliferation and differentiation, plays an important role in hepatic TG metabolism. Sox4 expression levels are markedly upregulated in livers of obese rodents and humans. Adenovirus-medicated overexpression of Sox4 in the livers of lean mice promotes liver steatosis, whereas liver-specific knockdown of Sox4 ameliorates TG accumulation and improves insulin resistance in obese mice. At the molecular level, we show that Sox4 could directly control the transcription of SREBP-1c gene through binding to its proximal promoter region. Thus, we have identified Sox4 as an important component of hepatic TG metabolism.

Hepatic expression of Yin Yang 1 (YY1) is associated with the non-alcoholic fatty liver disease (NAFLD) progression in patients undergoing bariatric surgery

BACKGROUND

This study is to investigate the association between the hepatic expression of Yin Yang 1 (YY1) and the progression of non-alcoholic fatty liver disease (NAFLD) in patients undergoing bariatric surgery.

METHODS

Obese patients undergoing bariatric surgery were included. Liver tissues were subjected to the quantitative real-time PCR, Western blot analysis, and immunohistochemical assay, to determine the expression levels of YY1.

RESULTS

Totally 88 patients were included. According to the NAFLD activity score (NAS), these patients were divided into the control (n = 12), steatosis (n = 20), non-defining NASH (n = 38), and NASH (n = 18) groups. Significant differences in the serum glucose, insulin, ALT, AST, and HOMA-IR levels were observed among these different NAFLD groups. Hepatic YY1 expression had correlation with serum glucose, insulin, HOMA-IR, ALT, AST, triglycerides, HDL, and GGT. Immunohistochemical analysis showed that, compared with the control group, the expression levels of YY1 were significantly higher in the non-defining NASH and NASH groups. In addition, multivariate regression model showed that the serum ALT and YY1 levels were strongly associated with the NAFLD activity.

CONCLUSIONS

Several factors are associated with NAFLD progression, including the expression of YY1. Our findings contribute to understanding of the pathogenesis of NAFLD.

TRIAL REGISTRATION

NCT03296605 , registered on September 28, 2017.

Pharmacological induction of hypoxia-inducible transcription factor ARNT attenuates chronic kidney failure

Progression of chronic kidney disease associated with progressive fibrosis and impaired tubular epithelial regeneration is still an unmet biomedical challenge because, once chronic lesions have manifested, no effective therapies are available as of yet for clinical use. Prompted by various studies across multiple organs demonstrating that preconditioning regimens to induce endogenous regenerative mechanisms protect various organs from later incurring acute injuries, we here aimed to gain insights into the molecular mechanisms underlying successful protection and to explore whether such pathways could be utilized to inhibit progression of chronic organ injury. We identified a protective mechanism controlled by the transcription factor ARNT that effectively inhibits progression of chronic kidney injury by transcriptional induction of ALK3, the principal mediator of antifibrotic and proregenerative bone morphogenetic protein-signaling (BMP-signaling) responses. We further report that ARNT expression itself is controlled by the FKBP12/YY1 transcriptional repressor complex and that disruption of such FKBP12/YY1 complexes by picomolar FK506 at subimmunosuppressive doses increases ARNT expression, subsequently leading to homodimeric ARNT-induced ALK3 transcription. Direct targeting of FKBP12/YY1 with in vivo morpholino approaches or small molecule inhibitors, including GPI-1046, was equally effective for inducing ARNT expression, with subsequent activation of ALK3-dependent canonical BMP-signaling responses and attenuated chronic organ failure in models of chronic kidney disease, and also cardiac and liver injuries. In summary, we report an organ-protective mechanism that can be pharmacologically modulated by immunophilin ligands FK506 and GPI-1046 or therapeutically targeted by in vivo morpholino approaches.

Liver-directed microRNA-7a depletion induces nonalcoholic fatty liver disease by stabilizing YY1-mediated lipogenic pathways in zebrafish

Nonalcoholic fatty liver disease (NAFLD) has been associated with the function and changes in expression levels of microRNAs (miRs). MiR-7 has been proven to play an important role in many cellular processes; however, its functions in the context of liver lipogenesis remain unknown. We applied the microRNA-sponge (miR-SP) technology and generated transgenic miR-7a-SP models (hC7aSP and bC7aSP), which disrupted the activities of hepatic miR-7a and induced the early onset of NAFLD and nonalcoholic steatohepatitis (NASH) in zebrafish. We identified a novel miR-7a target, YY1, and demonstrated novel miR-7a functions to regulate zebrafish hepatic lipid metabolism by controlling YY1 stabilization through the regulation of the expression of lipogenic signaling pathways. Correspondingly, liver specific miR-7a depletion functionally promoted lipid accumulation in hC7ASP livers. NASH hC7aSP increased the expression of inflammatory genes (il-1b, il-6, tnf-α, ifn-γ, nfkb2, and NF-kB) and endoplasmic reticulum stress markers (atf6, ern2, ire1, perk, hspa5 and ddit3). Molecular analysis revealed that miR-7a-SP can stabilize YY1 expression and contribute to the accumulation of hepatic triglycerides by reducing the CHOP-10 expression in the hC7aSP and then inducing the transactivation of C/EBP-α and PPAR-γ expression. PPAR-γ antagonists and miR-7a mimic treatment ameliorate hC7aSP NASH phenotypes.

CONCLUSION

Our results suggest that miR-7a-SP acts as a lipid enhancer by directly increasing YY1 stability to disrupt CHOP-10-dependent suppression of lipogenic pathways, resulting in increased lipid accumulation. MiR-7a expression improves liver steatosis and steatohepatitis in hC7aSPs, which suggests a novel strategy for the prevention and early treatment of NASH in humans.

miR199a-5p inhibits hepatic insulin sensitivity via suppression of ATG14-mediated autophagy

MicroRNAs (miRNAs) are known to contribute to many metabolic diseases, including diabetes. In this study, we investigated the role of miR199a-5p in the regulation of hepatic insulin sensitivity. Ad-anti-miR199a-5p adenoviruses were injected into male C57BL/6J WT mice fed a high-fat diet to inhibit miR199a-5p expression before the glucose levels and insulin resistance were assessed. Similarly, Ad-miR199a-5p adenoviruses were injected into male C57BL/6J WT mice to cause the overexpression of miR199a-5p. To investigate the roles of autophagy-related protein 14 (ATG14) and miR199a-5p in the regulation of insulin sensitivity, we injected Ad-miR199a-5p with or without Ad-ATG14 viruses into WT C57BL/6J mice before performing functional assays. Moreover, we infected HepG2 cells or primary hepatocytes with Ad-anti-miR199a-5p or Ad-miR199a-5p viruses to determine the effect of miR199a-5p on insulin resistance in vitro. Finally, we explored the clinical relevance of miR199a-5p by examining the expression level of miR199a-5p in liver samples derived from diabetes patients. We first demonstrated that knocking down miR199a-5p led to decreased glucose tolerance and clearance in vivo, whereas the overexpression of miR199a-5p had the opposite effect. We further identified ATG14 as the target of miR199a-5p, and ATG14 partially rescued miR199a-5p-potentiated glucose and insulin tolerance. In addition, transmission electron microscopy data and western blot data regarding ATG14, LC3 and BECLIN1 illustrated that miR199a-5p regulates autophagy via ATG14. Knocking down miR199a-5p in primary hepatocytes and HepG2 cells suppressed the insulin-stimulated phosphorylation of insulin receptor β, glycogen synthase kinase 3β and protein kinase B, whereas the overexpression of miR199a-5p further potentiated their phosphorylation. Finally, we detected upregulated miR199a-5p levels, which were correlated with reduced ATG14 mRNA levels and downregulated autophagy in liver samples obtained from diabetes patients. Our study uncovered a novel biological role of miR199a-5p in the regulation of hepatic insulin sensitivity via ATG14-mediated autophagy.

Nuclear receptor FXR, bile acids and liver damage: Introducing the progressive familial intrahepatic cholestasis with FXR mutations

The nuclear receptor farnesoid X receptor (FXR) is the master regulator of bile acids (BAs) homeostasis since it transcriptionally drives modulation of BA synthesis, influx, efflux, and detoxification along the enterohepatic axis. Due to its crucial role, FXR alterations are involved in the progression of a plethora of BAs associated inflammatory disorders in the liver and in the gut. The involvement of the FXR pathway in cholestasis development and management has been elucidated so far with a direct role of FXR activating therapy in this condition. However, the recent identification of a new type of genetic progressive familial intrahepatic cholestasis (PFIC) linked to FXR mutations has strengthen also the bona fide beneficial effects of target therapies that by-pass FXR activation, directly promoting the action of its target, namely the enterokine FGF19, in the repression of hepatic BAs synthesis with reduction of total BA levels in the liver and serum, accomplishing one of the major goals in cholestasis. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni and Peter Jansen.