Regulation of hepatocyte nuclear factor 4 alpha-mediated transcription

Deubiquitinase OTUD7B stabilizes HNF4α to alleviate pressure overload-induced cardiac hypertrophy by regulating fatty acid oxidation and inhibiting ferroptosis

BACKGROUND

Cardiac hypertrophy, a leading cause of heart failure, threatens global public health. Deubiquitinating enzymes (DUBs) are critical in cardiac pathophysiology by regulating protein stability, function, and degradation. Here, we investigated the role and regulating mechanism of ovarian tumor domain-containing 7B (OTUD7B) in cardiac hypertrophy by modulating fatty acid metabolism.

METHODS

Mice subjected to transverse aortic constriction (TAC) and cardiomyocytes treated with phenylephrine (PE) were used to explore the role of OTUD7B in myocardial hypertrophy. The potential molecular mechanisms underlying OTUD7B's regulation of cardiac hypertrophy were explored through transcriptome analysis and further validated in cardiomyocytes.

RESULTS

Reduced OTUD7B expression was observed in hypertrophic hearts following TAC surgery. Cardiac-specific OTUD7B deficiency exacerbated, while OTUD7B overexpression mitigated, pressure overload-induced hypertrophy and cardiac dysfunction both in vivo and in vitro. OTUD7B knockdown resulted in ferroptosis, as evidenced by decreased mitochondrial cristae, increased Fe2+ ion content, lipid peroxide accumulation, while OTUD7B overexpression inhibited ferroptosis. Mechanistically, transcriptomic analysis identified OTUD7B plays a role in the regulation of fatty acid metabolism and pathological cardiac hypertrophy. OTUD7B was found to directly bind to HNF4α, a transcription factor regulating fatty acid oxidation-related genes. Further, OTUD7B exerted deubiquitination activity to stabilize the HNF4α protein by removing K48-linked ubiquitin chains, thereby preventing its degradation via the proteasomal pathway and linking the HNF4α degradation and ferroptosis. Finally, ferroptosis inhibitors, ferrostatin-1, alleviated OTUD7B inhibition-induced ferroptosis, fatty acid metabolism suppression, and myocardial hypertrophy.

CONCLUSIONS

We confirmed that OTUD7B is involved in the regulation of ferroptosis in pressure overload-induced cardiac hypertrophy and highlighted that OTUD7B alleviates cardiac hypertrophy by regulating ferroptosis and fatty acid oxidation through deubiquitination and stabilization of HNF4α.

Heterotypic spheroids as a strategy for 3D culture of cryopreserved primary human hepatocytes in stirred-tank systems

Primary human hepatocytes (PHHs) are the preferred cell source to address liver function. Despite originating from the native tissue, one of the bottlenecks when using primary material is the donor-to-donor variability. Cryopreserved PHHs offer a high number of cells from the same donor and standardization of cell isolation and cryopreservation procedures, mitigating some of the inter-donor variability. Still, PHHs from different commercial sources present variability in vitro in several parameters, including viability post-thawing, plating capacity, aggregation potential and culture longevity. Here we combine stirred-tank culture systems, which allow robust aggregation processes, and co-culture approaches with the HepaRG cell line to generate spheroids from cryopreserved PHHs. By employing small-scale stirred-tank culture systems we could cope with the scarce availability and high cost of primary material. In the optimized co-culture conditions we could generate PHH:HepaRG spheroids from 12 donors acquired from 4 different commercial sources. All PHHs showed similar aggregation profiles, forming small compact heterotypic spheroids as early as 3 days in co-culture and were maintained for at least 5 weeks in culture. The heterotypic spheroids maintained the hepatocyte polarization and identity and showed metabolization capacity for 5 main phase I metabolizing enzymes, namely CYP3A4, CYP2C9, CYP1A2, CYP2D6, and CYP2C8. Moreover, the heterotypic spheroids showed the capacity to metabolize a novel compound under clinical development, showing their potential to be employed in drug discovery applications. Overall, we present a robust aggregation strategy for cryopreserved PHHs from different suppliers, applicable for pharmacological and toxicological in vitro research.

Hepatic Nuclear Receptors in Cholestasis-to-Cholangiocarcinoma Pathology

Cholestasis, characterized by impaired bile flow, is associated with an increased risk of cholangiocarcinoma (CCA), a malignancy originating from the biliary epithelium and hepatocytes. Hepatic nuclear receptors (NRs) are pivotal in regulating bile acid and metabolic homeostasis, and their dysregulation is implicated in cholestatic liver diseases and the progression of liver cancer. This review elucidates the role of various hepatic NRs in the pathogenesis of cholestasis-to-CCA progression. It explores their impact on bile acid metabolism as well as their interactions with other signaling pathways implicated in CCA development. Additionally, it introduces available murine models of cholestasis/primary sclerosing cholangitis leading to CCA and discusses the clinical potential of targeting hepatic NRs as a promising approach for the prevention and treatment of cholestatic liver diseases and CCA. Understanding the complex interplay between hepatic NRs and cholestasis-to-CCA pathology holds promise for the development of novel preventive and therapeutic strategies for this devastating disease.

Structure-based identification of HNF4α agonists: Rosmarinic acid as a promising candidate for NAFLD treatment

The prevention and treatment of metabolic disorders, such as non-alcoholic fatty liver disease (NAFLD), have emerged as critical global health challenges. Current lipid-lowering pharmacotherapies are associated with side effects, including hepatotoxicity, rhabdomyolysis, and decreased erythrocyte counts, underscoring the urgent need for safer therapeutic alternatives. Hepatocyte nuclear factor 4α (HNF4α) has been identified as a pivotal regulator of lipid metabolism, making it an attractive target for drug development. In this study, we investigated the structural characteristics and binding interactions of four HNF4α agonists: Alverine, Benfluorex, N-trans caffeoyltyramine (NCT), and N-trans feruloyltyramine (NFT). Our results indicate that the conjugated structure formed by the amide bond and the aromatic ring in NCT and NFT enhances electron density, potentially contributing to their increased specificity for HNF4α relative to Alverine and Benfluorex. Additionally, electrostatic interactions between the aromatic moieties of the compounds and HNF4α residues were found to play a crucial role in ligand binding. Leveraging these insights, we performed a high-throughput virtual screening of 2131 natural compounds, using the binding modes of NCT and NFT as reference templates. Rosmarinic acid emerged as a promising HNF4α agonist, exhibiting a high consensus score and favorable binding affinity. Subsequent biological assays demonstrated that rosmarinic acid significantly inhibited HepG2 cell proliferation which related to the enhancement of autophagy. After the knockdown of P2 isoform of HNF4α, HepG2 was more sensitive to the administration of NCT and rosmarinic acid. Furthermore, the proliferation of DLD-1 cell, which only expresses the P2 isoform of HNF4α, was not significantly inhibited by the administration of NCT and rosmarinic acid. Collectively, these findings suggest that rosmarinic acid is a promising HNF4α agonist which is more effective to activate the P1 isoform of HNF4α and holds potential as an effective treatment for NAFLD, providing a foundation for the development of novel lipid-lowering drugs with enhanced efficacy and reduced side effect.

Data Availability

Data will be made available on request.

Regulation of hepatic xenosensor function by HNF4alpha

Nuclear receptors such as constitutive androstane receptor (CAR), pregnane X receptor (PXR), and peroxisome proliferator-activated receptor-alpha (PPARα), and transcription factors with nuclear receptor type activity such as aryl hydrocarbon receptor (AhR) function as xenobiotic sensors. Hepatocyte nuclear factor 4alpha (HNF4α) is a highly conserved orphan nuclear receptor essential for liver function. We tested the hypothesis that HNF4α is essential for the function of these 4 major xenosensors. Wild-type (WT) and hepatocyte-specific Hnf4a null (HNF4α-KO) mice were treated with the mouse-specific activators of AhR (TCDD, 30 µg/kg), CAR (TCPOBOP, 2.5 µg/g), PXR, (PCN, 100 µg/g), and PPARα (WY-14643, 1 mg/kg). Blood and liver tissue samples were collected to study receptor activation. TCDD (AhR agonist) treatment did not affect the liver-to-body weight ratio (LW/BW) in either WT or HNF4α-KO mice. Further, TCDD activated AhR in both WT and HNF4α-KO mice, confirmed by increase in expression of AhR target genes. TCPOBOP (CAR agonist) significantly increased the LW/BW ratio and CAR target gene expression in WT mice, but not in HNF4α-KO mice. PCN (a mouse PXR agonist) significantly increased LW/BW ratio in both WT and HNF4α-KO mice however, failed to induce PXR target genes in HNF4α-KO mice. The treatment of WY-14643 (PPARα agonist) increased LW/BW ratio and PPARα target gene expression in WT mice but not in HNF4α-KO mice. Together, these data indicate that the function of CAR, PXR, and PPARα but not of AhR was disrupted in HNF4α-KO mice. These results demonstrate that HNF4α function is critical for the activation of hepatic xenosensors, which are critical for toxicological responses.

Role of Hepatocyte Nuclear Factor 4 Alpha in Liver Cancer

Liver cancer is the sixth most common cancer and the fourth leading cause of cancer-related deaths worldwide. Hepatocellular carcinoma (HCC) is the most prevalent primary liver cancer and the incidence of HCC is on the rise. Liver cancers in general and HCC in particular do not respond to chemotherapy. Radiological ablation, surgical resection, and liver transplantation are the only medical therapies currently available. Hepatocyte nuclear factor 4 α (HNF4α) is an orphan nuclear receptor expressed only in hepatocytes in the liver. HNF4α is considered the master regulator of hepatic differentiation because it regulates a significant number of genes involved in various liver-specific functions. In addition to maintaining hepatic differentiation, HNF4α also acts as a tumor suppressor by inhibiting hepatocyte proliferation by suppressing the expression of promitogenic genes and inhibiting epithelial to mesenchymal transition in hepatocytes. Loss of HNF4α expression and function is associated with rapid progression of chronic liver diseases that ultimately lead to liver cirrhosis and HCC, including metabolism-associated steatohepatitis, alcohol-associated liver disease, and hepatitis virus infection. This review summarizes the role of HNF4α in liver cancer pathogenesis and highlights its potential as a potential therapeutic target for HCC.

Role of HNF4alpha-cMyc interaction in liver regeneration after partial hepatectomy

Background

Hepatocyte nuclear factor 4 alpha (HNF4α) is the master regulator of hepatic differentiation. Recent studies have also revealed the role of HNF4α in hepatocyte proliferation via negatively regulating the expression of proto-mitogenic genes, including cMyc. Here, we aimed to study the interaction between HNF4α-cMyc during liver regeneration after partial hepatectomy (PHX).

Methods

Wild-type (WT), hepatocyte-specific knockout of HNF4α (HNF4α-KO), cMyc (cMyc-KO), and HNF4α-cMyc double knockout (DKO) mice were subjected to PHX to induce liver regeneration. Blood and liver tissue samples were collected at 0h, 24h, 48h, 7D, and 14D after PHX for further analysis.

Results

WT, HNF4α-KO, cMyc-KO and DKO mice regained liver weight by 14 days after PHX. The deletion of cMyc did not affect liver regeneration, which was similar to the WT mice. WT and cMyc-KO mice started regaining liver weight as early as 24 hours after PHX, with a peak proliferation response at 48 hours after PHX. HNF4α- KO and DKO showed a delayed response with liver weight increase by day 7 after PHX. The overall hepatocyte proliferation response by DKO mice following PHX was lower than that of other genotypes. Interestingly, the surviving HNF4α-KO and DKO mice showed re-expression of HNF4α at mRNA and protein levels on day 14 after PHX. This was accompanied by a significant increase in the expression of Krt19 and Epcam, hepatic progenitor cell markers, in the DKO mice on day 14 after PHX.

Conclusion

These data indicate that, in the absence of HNF4α, cMyc contributes to hepatocyte-driven proliferation to compensate for the lost tissue mass. Furthermore, in the absence of both HNF4α and cMyc, HPC-driven proliferation occurs to support liver regeneration.

HNF4α is required for Tkfc promoter activation by ChREBP

Triokinase/FMN cyclase (Tkfc) is involved in fructose metabolism and is responsible for the phosphorylation of glyceraldehyde to glyceraldehyde-3-phosphate. In this study, we showed that refeeding induced hepatic expression of Tkfc in mice. Luciferase reporter gene assays using the Tkfc promoter revealed the existence of 2 hepatocyte nuclear factor 4α (HNF4α)-responsive elements (HNF4RE1 and HNF4RE2) and 1 carbohydrate-responsive element-binding protein (ChREBP)-responsive element (ChoRE1). Deletion and mutation of HNF4RE1 and HNF4RE2 or ChoRE1 abolished HNF4α and ChREBP responsiveness, respectively. HNF4α and ChREBP synergistically stimulated Tkfc promoter activity. ChoRE1 mutation attenuated but maintained HNF4α responsiveness, whereas HNF4RE1 and HNF4RE2 mutations abolished ChREBP responsiveness. Moreover, Tkfc promoter activity stimulation by ChREBP was attenuated upon HNF4α knockdown. Furthermore, Tkfc expression was decreased in the livers of ChREBP-/- and liver-specific HNF4-/- (Hnf4αΔHep) mice. Altogether, our data indicate that Tkfc is a target gene of ChREBP and HNF4α, and Tkfc promoter activity stimulation by ChREBP requires HNF4α.

Screening of Chelidonium majus isoquinoline alkaloids reveals berberine and chelidonine as selective ligands for the nuclear receptors RORβ and HNF4α, respectively

The nuclear receptors hepatocyte nuclear factor 4α (HNF4α) and retinoic acid receptor-related orphan receptor-β (RORβ) are ligand-regulated transcription factors and potential drug targets for metabolic disorders. However, there is a lack of small molecular, selective ligands to explore the therapeutic potential in further detail. Here, we report the discovery of greater celandine (Chelidonium majus) isoquinoline alkaloids as nuclear receptor modulators: Berberine is a selective RORβ inverse agonist and modulated target genes involved in the circadian clock, photoreceptor cell development, and neuronal function. The structurally related chelidonine was identified as a ligand for the constitutively active HNF4α receptor, with nanomolar potency in a cellular reporter gene assay. In human liver cancer cells naturally expressing high levels of HNF4α, chelidonine acted as an inverse agonist and downregulated genes associated with gluconeogenesis and drug metabolism. Both berberine and chelidonine are promising tool compounds to further investigate their target nuclear receptors and for drug discovery.

Tripartite Motif-Containing Protein 65 (TRIM65) Inhibits Hepatitis B Virus Transcription

Tripartite motif (TRIM) proteins, comprising a family of over 100 members with conserved motifs, exhibit diverse biological functions. Several TRIM proteins influence viral infections through direct antiviral mechanisms or by regulating host antiviral innate immune responses. To identify TRIM proteins modulating hepatitis B virus (HBV) replication, we assessed 45 human TRIMs in HBV-transfected HepG2 cells. Our study revealed that ectopic expression of 12 TRIM proteins significantly reduced HBV RNA and subsequent capsid-associated DNA levels. Notably, TRIM65 uniquely downregulated viral pregenomic (pg) RNA in an HBV-promoter-specific manner, suggesting a targeted antiviral effect. Mechanistically, TRIM65 inhibited HBV replication primarily at the transcriptional level via its E3 ubiquitin ligase activity and intact B-box domain. Though HNF4α emerged as a potential TRIM65 substrate, disrupting its binding site on the HBV genome did not completely abolish TRIM65's antiviral effect. In addition, neither HBx expression nor cellular MAVS signaling was essential to TRIM65-mediated regulation of HBV transcription. Furthermore, CRISPR-mediated knock-out of TRIM65 in the HepG2-NTCP cells boosted HBV infection, validating its endogenous role. These findings underscore TRIM proteins' capacity to inhibit HBV transcription and highlight TRIM65's pivotal role in this process.

HNF4α ubiquitination mediated by Peli1 impairs FAO and accelerates pressure overload-induced myocardial hypertrophy

Impaired fatty acid oxidation (FAO) is a prominent feature of metabolic remodeling observed in pathological myocardial hypertrophy. Hepatocyte nuclear factor 4alpha (HNF4α) is closely associated with FAO in both cellular processes and disease conditions. Pellino 1 (Peli1), an E3 ligase containing a RING-like domain, plays a crucial role in catalyzing polyubiquitination of various substrates. In this study, we aimed to investigate the involvement of HNF4α and its ubiquitination, facilitated by Peli1, in FAO during pressure overload-induced cardiac hypertrophy. Peli1 systemic knockout mice (Peli1KO) display improved myocardial hypertrophy and cardiac function following transverse aortic constriction (TAC). RNA-seq analysis revealed that changes in gene expression related to lipid metabolism caused by TAC were reversed in Peli1KO mice. Importantly, both HNF4α and its downstream genes involved in FAO showed a significant increase in Peli1KO mice. We further used the antagonist BI6015 to inhibit HNF4α and delivered rAAV9-HNF4α to elevate myocardial HNF4α level, and confirmed that HNF4α inhibits the development of cardiac hypertrophy after TAC and is essential for the enhancement of FAO mediated by Peli1 knockout. In vitro experiments using BODIPY incorporation and FAO stress assay demonstrated that HNF4α enhances FAO in cardiomyocytes stimulated with angiotension II (Ang II), while Peli1 suppresses the effect of HNF4α. Mechanistically, immunoprecipitation and mass spectrometry analyses confirmed that Peli1 binds to HNF4α via its RING-like domain and promotes HNF4α ubiquitination at residues K307 and K309. These findings shed light on the underlying mechanisms contributing to impaired FAO and offer valuable insights into a promising therapeutic strategy for addressing pathological cardiac hypertrophy.

Acanthopanax senticosus ameliorates steatohepatitis through HNF4 alpha pathway activation in mice

Non-alcoholic fatty liver disease is a common liver disease worldwide, and is associated with dysregulation of lipid metabolism, leading to inflammation and fibrosis. Acanthopanax senticosus Harms (ASH) is widely used in traditional medicine as an adaptogen food. We examined the effect of ASH on steatohepatitis using a high-fat diet mouse model. Mice were fed a choline-deficient, L-amino acid-defined, high-fat diet with ASH extract (ASHE). After 6 weeks, liver RNA transcriptome sequencing (RNA-Seq) was performed, followed by Ingenuity Pathway Analysis (IPA). Our findings revealed that mice fed a high-fat diet with 5% ASHE exhibited significantly reduced liver steatosis. These mice also demonstrated alleviated inflammation and reduced fibrosis in the liver. IPA of RNA-Seq indicated that hepatocyte nuclear factor 4 alpha (HNF4 alpha), a transcription factor, was the activated upstream regulator (P-value 0.00155, z score = 2.413) in the liver of ASHE-fed mice. Adenosine triphosphate binding cassette transporter 8 and carboxylesterase 2, downstream targets of HNF4 alpha pathway, were upregulated. Finally, ASHE-treated HepG2 cells exposed to palmitate exhibited significantly decreased lipid droplet contents. Our study provides that ASHE can activate HNF4 alpha pathway and promote fat secretion from hepatocytes, thereby serving as a prophylactic treatment for steatohepatitis in mice.

Revelation of genes associated with energy generating metabolic pathways in the fighter type Aseel chicken of India through skeletal muscle transcriptome sequencing

In this study, comparative analysis of skeletal muscle transcriptome was carried out for four biological replicates of Aseel, a fighter type breed and Punjab Brown, a meat type breed of India. The profusely expressed genes in both breeds were related to muscle contraction and motor activity. Differential expression analysis identified 961 up-regulated and 979 down-regulated genes in Aseel at a threshold of log2 fold change ≥ ±2.0 (padj<0.05). Significantly enriched KEGG pathways in Aseel included metabolic pathways and oxidative phosphorylation, with higher expression of genes associated with fatty acid beta-oxidation, formation of ATP by chemiosmotic coupling, response to oxidative stress, and muscle contraction. The highly connected hub genes identified through gene network analysis in the Aseel gamecocks were HNF4A, APOA2, APOB, APOC3, AMBP, and ACOT13, which are primarily associated with energy generating metabolic pathways. The up-regulated genes in Punjab Brown chicken were found to be related to muscle growth and differentiation. There was enrichment of pathways such as focal adhesion, insulin signaling pathway and ECM receptor interaction in these birds. The results presented in this study help to improve our understanding of the molecular mechanisms associated with fighting ability and muscle growth in Aseel and Punjab Brown chicken, respectively.

Effect of Lauric acid against ethanol-induced hepatotoxicity by modulating oxidative stress/apoptosis signalling and HNF4α in Wistar albino rats

Ethanol (EtOH) is most widely used in alcoholic beverages to prepare alcohol. As EtOH is mainly metabolised in the liver, the excessive consumption of EtOH forms a primary toxic metabolic product called acetaldehyde, as the gradual increase in acetaldehyde leads to liver injury, as reported. Lauric acid (LA) is rich in antioxidant, antifungal, antibacterial, anticancer, and antiviral properties. LA is an edible component highly present in coconut oil. However, no report on LA protective effects against the EtOH-instigated hepatotoxicity exists. Therefore, the experiment is carried out to investigate the potency effects of LA on EtOH-instigated hepatotoxicity in thirty male albino rats. Rats were divided into five groups (n-6): control DMSO alone, EtOH -intoxicated, EtOH + LA 180 mg/kg, EtOH + LA 360 mg/kg, and LA alone were administered orally using oral gavage. The study measured body weight every weekend in all rat groups. The rats were sacrificed and assessed for serum markers (alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase), antioxidant activity (superoxide dismutase, reduced glutathione, glutathione peroxidase), lipid peroxidation (malondialdehyde), histopathological, cytokine levels (TNF-α, IL-1β and IL-6), protein expression (caspase 3 and caspase 8 and Bcl-2 and HNF4α) were evaluated after the 56-days study period. The impact of EtOH intoxication reduces the rat's body weight by 90 g, upregulates the liver enzyme markers, depletes the antioxidant levels, produces malondialdehyde, changes the histoarchitecture (periportal inflammation and hepatocyte damage), downregulates the Bcl-2 expressions and HNF4α, and elevates the expression of cytokines and apoptotic markers. LA alleviated EtOH-induced liver toxicity by significant (p < 0.05) modulation of biochemical levels, caspase-8/3 signalling, reducing pro-inflammatory cytokines, and restoring the normal histoarchitecture, upregulating the Bcl-2 and HNF4α Expressions. In conclusion, LA treatment can protect the liver against EtOH-induced hepatotoxicity, evidenced by alleviating Oxidative stress, lipid peroxidation, inflammation, apoptosis, and upregulation of HNF4α.

Regulation of Hepatic Xenosensor Function by HNF4alpha

Nuclear receptors including Aryl hydrocarbon Receptor (AhR), Constitutive Androstane Receptor (CAR), Pregnane X Receptor (PXR), and Peroxisome Proliferator-Activated Receptor-alpha (PPARα) function as xenobiotic sensors. Hepatocyte nuclear factor 4alpha (HNF4α) is a highly conserved orphan nuclear receptor essential for liver function. We tested the hypothesis that HNF4α is essential for function of these four major xenosensors. Wild-type (WT) and hepatocyte-specific HNF4α knockout (HNF4α-KO) mice were treated with the mouse-specific activators of AhR (TCDD, 30 µg/kg), CAR (TCPOBOP, 2.5 µg/g), PXR, (PCN, 100 µg/g), and PPARα (WY-14643, 1 mg/kg). Blood and liver tissue samples were collected to study nuclear receptor activation. TCDD (AhR agonist) treatment did not affect the liver-to-body weight ratio (LW/BW) in either WT or HNF4α-KO mice. Further, TCDD activated AhR in both WT and HNF4-KO mice, confirmed by increase in expression of its target genes. TCPOBOP (CAR agonist) significantly increased the LW/BW ratio and CAR target gene expression in WT mice, but not in HNF4α-KO mice. PCN (a mouse PXR agonist) significantly increased LW/BW ratio in both WT and HNF4α-KO mice however, it failed to induce PXR target genes in HNF4 KO mice. The treatment of WY-14643 (PPARα agonist) increased LW/BW ratio and PPARα target gene expression in WT mice but not in HNF4α-KO mice. Together, these data indicate that the function of CAR, PXR, and PPARα but not of AhR was disrupted in HNF4α-KO mice. These results demonstrate that HNF4α function is critical for the activation of hepatic xenosensors, which are critical for toxicological responses.

The protein architecture and allosteric landscape of HNF4α

Hepatocyte nuclear factor 4 alpha (HNF4α) is a multi-faceted nuclear receptor responsible for governing the development and proper functioning of liver and pancreatic islet cells. Its transcriptional functions encompass the regulation of vital metabolic processes including cholesterol and fatty acid metabolism, and glucose sensing and control. Various genetic mutations and alterations in HNF4α are associated with diabetes, metabolic disorders, and cancers. From a structural perspective, HNF4α is one of the most comprehensively understood nuclear receptors due to its crystallographically observed architecture revealing interconnected DNA binding domains (DBDs) and ligand binding domains (LBDs). This review discusses key properties of HNF4α, including its mode of homodimerization, its binding to fatty acid ligands, the importance of post-translational modifications, and the mechanistic basis for allosteric functions. The surfaces linking HNF4α's DBDs and LBDs create a convergence zone that allows signals originating from any one domain to influence distant domains. The HNF4α-DNA complex serves as a prime illustration of how nuclear receptors utilize individual domains for specific functions, while also integrating these domains to create cohesive higher-order architectures that allow signal responsive functions.

HNF4α in Hepatocyte Health and Disease

Hepatocyte nuclear factor 4 α (HNF4α) is a highly conserved member of the nuclear receptor superfamily expressed at high levels in the liver, kidney, pancreas, and gut. In the liver, HNF4α is exclusively expressed in hepatocytes, where it is indispensable for embryonic and postnatal liver development and for normal liver function in adults. It is considered a master regulator of hepatic differentiation because it regulates a significant number of genes involved in hepatocyte-specific functions. Loss of HNF4α expression and function is associated with the progression of chronic liver disease. Further, HNF4α is a target of chemical-induced liver injury. In this review, we discuss the role of HNF4α in liver pathophysiology and highlight its potential use as a therapeutic target for liver diseases.

Exposure to serum perfluoroalkyl substances and biomarkers of liver function: The Korean national environmental health survey 2015-2017

BACKGROUND

Exposure to perfluoroalkyl substances (PFAS) may increase the risk of liver disease by disrupting cholesterol and lipid synthesis/metabolism, leading to higher liver-enzyme concentrations. However, most studies assessing association between PFAS and liver enzymes focused on individual PFAS. Moreover, PFAS concentrations differ based on sex and obesity status, and it remains unclear whether these factors affect associations with liver function. Therefore, we examined the association between exposure to both individual and combined PFAS and liver-function biomarkers and assessed sex and obesity as effect modifiers in Korean adults.

METHODS

We measured serum concentrations of the five most abundant PFAS (PFOA, PFOS, PFHxS, PFDA, PFNA) and three liver enzymes (alanine transaminase [ALT], aspartate aminotransferase [AST], γ-glutamyl transferase [GGT]) in 1404 adults from the Korean National Environmental Health Survey Cycle 3, 2015-2017. We used linear regression to evaluate associations between individual PFAS and liver-function biomarkers, assessing sex and obesity as possible effect modifiers, and performed Bayesian kernel machine regression and quantile g-computation to evaluate the overall effect of PFAS mixture on biomarkers of liver function.

RESULTS

Among 1404 Korean adults, all five PFAS were detected. Geometric mean concentration was highest for PFOS (16.11 μg/L), followed by PFOA (5.83 μg/L), PFHxS (2.21 μg/L), PFNA (2.03 μg/L), and PFDA (1.06 μg/L). In multivariable linear regression, all PFAS were positively associated with ALT, AST, and GGT; 2-fold increase in each PFAS was associated with 3.4-8.6% higher ALT, 2.4-4.6% higher AST, and 4.6-11.1% higher GGT (all p < 0.05). Positive associations for PFOA, PFDA, and PFNA with AST were stronger in men, and positive associations for PFOS with ALT and GGT were stronger in women. Compared to obese participants, nonobese participants had higher average percent changes in each enzyme, particularly GGT, when individual PFAS concentration doubled. Additionally, increased exposure to PFAS mixtures was associated with higher ALT, AST, and GGT. In quantile g-computations, simultaneous quartile increase in all PFAS was significantly associated with 6.9% (95%CI: 3.7, 10.2) higher ALT, 4.5% (95%CI: 2.4, 6.6) higher AST, and 8.3% (95%CI: 3.7, 13.1) higher GGT levels, on average.

CONCLUSIONS

Exposure to individual and combined PFAS is associated with higher liver enzymes in Korean adults, providing additional evidence for the association between PFAS exposure and risk of liver disease.

A Hepatocyte Nuclear Factor BtabHNF4 Mediates Desiccation Tolerance and Fecundity in Whitefly (Bemisia tabaci)

Hepatocyte nuclear factor 4 (HNF4) is essential for glucose homeostasis and lipid metabolism in insects. However, little is known about the role of HNF4 in whiteflies. In the present study, we identified a hepatocyte nuclear factor protein from Bemsia tabaci (Diptera: Drosophilidae) and named it BtabHNF4. The full-length of BtabHNF4 was 3,006 bp, encoding a sequence of 434 amino acids that contains a conserved zinc-finger DNA-binding domain (DBD) and a well-conserved ligand-binding domain (LBD). The temporal and spatial expression showed that BtabHNF4 was highly expressed in the female adult stage and abdominal tissues of B. tabaci. A leaf-mediated RNA interference method was used to explore the function of BtabHNF4 in whiteflies. Our results showed that the knockdown of BtabHNF4 influences the desiccation tolerance, egg production, and egg hatching rate of whiteflies. Additionally, BtabHNF4 silencing significantly inhibited the expression level of vitellogenin. These results expand the function of HNF4 and pave the way for understanding the molecular mechanisms of HNF4 in regulating multiple physiological processes.

A transcriptional regulatory network of HNF4α and HNF1α involved in human diseases and drug metabolism

HNF4α and HNF1α are core transcription factors involved in the development and progression of a variety of human diseases and drug metabolism. They play critical roles in maintaining the normal growth and function of multiple organs, mainly the liver, and in the metabolism of endogenous and exogenous substances. The twelve isoforms of HNF4α may exhibit different physiological functions, and HNF4α and HNF1α show varying or even opposing effects in different types of diseases, particularly cancer. Additionally, the regulation of CYP450, phase II drug-metabolizing enzymes, and drug transporters is affected by several factors. This article aims to review the role of HNF4α and HNF1α in human diseases and drug metabolism, including their structures and physiological functions, affected diseases, regulated drug metabolism genes, influencing factors, and related mechanisms. We also propose a transcriptional regulatory network of HNF4α and HNF1α that regulates the expression of target genes related to disease and drug metabolism.

The Role of CYP3A in Health and Disease

CYP3A is an enzyme subfamily in the cytochrome P450 (CYP) superfamily and includes isoforms CYP3A4, CYP3A5, CYP3A7, and CYP3A43. CYP3A enzymes are indiscriminate toward substrates and are unique in that these enzymes metabolize both endogenous compounds and diverse xenobiotics (including drugs); almost the only common characteristic of these compounds is lipophilicity and a relatively large molecular weight. CYP3A enzymes are widely expressed in human organs and tissues, and consequences of these enzymes' activities play a major role both in normal regulation of physiological levels of endogenous compounds and in various pathological conditions. This review addresses these aspects of regulation of CYP3A enzymes under physiological conditions and their involvement in the initiation and progression of diseases.

Hepatic circadian and differentiation factors control liver susceptibility for fatty liver disease and tumorigenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths, and the most common primary liver malignancy to present in the clinic. With the exception of liver transplant, treatment options for advanced HCC are limited, but improved tumor stratification could open the door to new treatment options. Previously, we demonstrated that the circadian regulator Aryl Hydrocarbon-Like Receptor Like 1 (ARNTL, or Bmal1) and the liver-enriched nuclear factor 4 alpha (HNF4α) are robustly co-expressed in healthy liver but incompatible in the context of HCC. Faulty circadian expression of HNF4α- either by isoform switching, or loss of expression- results in an increased risk for HCC, while BMAL1 gain-of-function in HNF4α-positive HCC results in apoptosis and tumor regression. We hypothesize that the transcriptional programs of HNF4α and BMAL1 are antagonistic in liver disease and HCC. Here, we study this antagonism by generating a mouse model with inducible loss of hepatic HNF4α and BMAL1 expression. The results reveal that simultaneous loss of HNF4α and BMAL1 is protective against fatty liver and HCC in carcinogen-induced liver injury and in the "STAM" model of liver disease. Furthermore, our results suggest that targeting Bmal1 expression in the absence of HNF4α inhibits HCC growth and progression. Specifically, pharmacological suppression of Bmal1 in HNF4α-deficient, BMAL1-positive HCC with REV-ERB agonist SR9009 impairs tumor cell proliferation and migration in a REV-ERB-dependent manner, while having no effect on healthy hepatocytes. Collectively, our results suggest that stratification of HCC based on HNF4α and BMAL1 expression may provide a new perspective on HCC properties and potential targeted therapeutics.

Progressive loss of hepatocyte nuclear factor 4 alpha activity in chronic liver diseases in humans

BACKGROUND AND AIMS

Hepatocyte nuclear factor 4 alpha (HNF4α) is indispensable for hepatocyte differentiation and critical for maintaining liver health. Here, we demonstrate that loss of HNF4α activity is a crucial step in the pathogenesis of chronic liver diseases (CLDs) that lead to development of HCC.

APPROACH AND RESULTS

We developed an HNF4α target gene signature, which can accurately determine HNF4α activity, and performed an exhaustive in silico analysis using hierarchical and K-means clustering, survival, and rank-order analysis of 30 independent data sets containing over 3500 individual samples. The association of changes in HNF4α activity to CLD progression of various etiologies, including HCV- and HBV-induced liver cirrhosis (LC), NAFLD/NASH, and HCC, was determined. Results revealed a step-wise reduction in HNF4α activity with each progressive stage of pathogenesis. Cluster analysis of LC gene expression data sets using the HNF4α signature showed that loss of HNF4α activity was associated with progression of Child-Pugh class, faster decompensation, incidence of HCC, and lower survival with and without HCC. A moderate decrease in HNF4α activity was observed in NAFLD from normal liver, but a further significant decline was observed in patients from NAFLD to NASH. In HCC, loss of HNF4α activity was associated with advanced disease, increased inflammatory changes, portal vein thrombosis, and substantially lower survival.

CONCLUSIONS

In conclusion, these data indicate that loss of HNF4α function is a common event in the pathogenesis of CLDs leading to HCC and is important from both diagnostic and therapeutic standpoints.

Clinical Relevance of the Constitutive Androstane Receptor

Constitutive androstane receptor (CAR) (NR1I3), a xenobiotic receptor, has long been considered a master mediator of drug disposition and detoxification. Accumulating evidence indicates that CAR also participates in various physiologic and pathophysiological pathways regulating the homeostasis of glucose, lipid, and bile acids, and contributing to cell proliferation, tissue regeneration and repair, as well as cancer development. The expression and activity of CAR can be regulated by various factors, including small molecular modulators, CAR interaction with other transcription factors, and naturally occurring genetic variants. Given that the influence of CAR has extended beyond the realm of drug metabolism and disposition and has expanded into a potential modulator of human diseases, growing efforts have centered on understanding its clinical relevance and impact on human pathophysiology. This review highlights the current information available regarding the contribution of CAR to various metabolic disorders and cancers and ponders the possible challenges that might arise from pursuing CAR as a potential therapeutic target for these diseases. SIGNIFICANCE STATEMENT: The growing importance of the constitutive androstane receptor (CAR) in glucose and lipid metabolism as well as its potential implication in cell proliferation emphasizes a need to keenly understand the biological function and clinical impact of CAR. This minireview captures the clinical relevance of CAR by highlighting its role in metabolic disorders and cancer development.

Lauric acid impairs insulin-induced Akt phosphorylation by upregulating SELENOP expression via HNF4α induction

Selenoprotein P (SeP; encoded by SELENOP in humans, Selenop in rodents) is a hepatokine that is upregulated in the liver of humans with type 2 diabetes. Excess SeP contributes to the onset of insulin resistance and various type 2 diabetes-related complications. We have previously reported that the long-chain saturated fatty acid, palmitic acid, upregulates Selenop expression, whereas the polyunsaturated fatty acids (PUFAs) downregulate it in hepatocytes. However, the effect of medium-chain fatty acids (MCFAs) on Selenop is unknown. Here we report novel mechanisms that underlie the lauric acid-mediated Selenop gene regulation in hepatocytes. Lauric acid upregulated Selenop expression in Hepa1-6 hepatocytes and mice liver. A luciferase promoter assay and computational analysis of transcription factor-binding sites identified the hepatic nuclear factor 4α (HNF4α) binding site in the SELENOP promoter. A chromatin immunoprecipitation (ChIP) assay showed that lauric acid increased the binding of HNF4α to the SELENOP promoter. The knockdown of Hnf4α using siRNA canceled the upregulation of lauric acid-induced Selenop. Thus, the lauric acid-induced impairment of Akt phosphorylation brought about by insulin was rescued by the knockdown of either Hnf4α or Selenop. These results provide new insights into the regulation of SeP by fatty acids and suggest that SeP may mediate MCFA-induced hepatic insulin signal reduction.

Adenosine-to-Inosine RNA Editing and N 6-Methyladenosine Modification Modulating Expression of Drug Metabolizing Enzymes

Interindividual differences in the expression and activity of drug metabolizing enzymes including cytochrome P450, UDP-glucuronosyltransferase, and esterases cause variable therapeutic efficacy or adverse events of drugs. As the major mechanisms causing the variability in the expression of drug metabolizing enzymes, transcriptional regulation by transcription factors, epigenetic regulation including DNA methylation, and posttranscriptional regulation by microRNA are well known. Recently, adenosine-to-inosine RNA editing and methylation of adenosine at the N 6 position on RNA have emerged as novel regulators of drug metabolism potency. In this review article, the current knowledge of these two prevalent types of posttranscriptional modification mediated modulation of drug metabolism involved genes is introduced. SIGNIFICANCE STATEMENT: Elucidation of the significance of adenosine-to-inosine RNA editing and N 6-methyladenosine in the regulation of drug metabolizing enzymes is expected to lead to a deeper understanding of interindividual variability in the therapeutic efficacy or adverse effects of medicines.

Spatial Environment Affects HNF4A Mutation-Specific Proteome Signatures and Cellular Morphology in hiPSC-Derived β-Like Cells

Studies of monogenic diabetes are particularly useful because we can gain insight into the molecular events of pancreatic β-cell failure. Maturity-onset diabetes of the young 1 (MODY1) is a form of monogenic diabetes caused by a mutation in the HNF4A gene. Human-induced pluripotent stem cells (hiPSCs) provide an excellent tool for disease modeling by subsequently directing differentiation toward desired pancreatic islet cells, but cellular phenotypes in terminally differentiated cells are notoriously difficult to detect. Re-creating a spatial (three-dimensional [3D]) environment may facilitate phenotype detection. We studied MODY1 by using hiPSC-derived pancreatic β-like patient and isogenic control cell lines in two different 3D contexts. Using size-adjusted cell aggregates and alginate capsules, we show that the 3D context is critical to facilitating the detection of mutation-specific phenotypes. In 3D cell aggregates, we identified irregular cell clusters and lower levels of structural proteins by proteome analysis, whereas in 3D alginate capsules, we identified altered levels of glycolytic proteins in the glucose sensing apparatus by proteome analysis. Our study provides novel knowledge on normal and abnormal function of HNF4A, paving the way for translational studies of new drug targets that can be used in precision diabetes medicine in MODY.

Intestine-specific ablation of the Hepatocyte Nuclear Factor 4a (Hnf4a) gene in mice has minimal impact on serum lipids and ileum gene expression profile due to upregulation of its paralog Hnf4g

Ablation of the gene encoding the nuclear receptor Hepatocyte Nuclear Factor 4a (Hnf4a) in the liver strongly affects HDL concentration, structure and functionality but the role of this receptor in the intestine, the second organ contributing to serum HDL levels, has been overlooked. In the present study we show that mice with intestine-specific ablation of Hnf4a (H4IntKO) had undetectable levels of ΗΝF4A in ileum, proximal and distal colon but normal expression in liver. H4IntKO mice presented normal serum lipid levels, HDL-C and particle size (α1-α3). The expression of the major HDL biogenesis genes Apoa1, Abca1, Lcat was not affected but there was significant increase in Apoc3 as well as in Hnf4g, a paralog of Hnf4a. RNA-sequencing identified metabolic pathways significantly affected by Hnf4a ablation such as type II diabetes, glycolysis, gluconeogenesis and p53 signaling. Chromatin immunoprecipitation assays showed that HNF4G bound to various apolipoprotein gene promoters in control mice but its binding affinity was reduced in the ileum of H4IntKO mice suggesting a redundancy but also a cooperation between the two factors. In the distal colon of H4IntKO mice, where both HNF4A and HNF4G are absent and in a mouse model of DSS-induced colitis presenting decreased levels of HNF4A, most lipoprotein genes were strongly downregulated. In conclusion, Hnf4a ablation in mice does not significantly affect serum lipid levels or lipoprotein gene expression in ileum possibly due to compensatory effects by its paralog Hnf4g in this tissue.

Antisense RNAs Influence Promoter Usage of Their Counterpart Sense Genes in Cancer

Multiple noncoding natural antisense transcripts (ncNAT) are known to modulate key biological events such as cell growth or differentiation. However, the actual impact of ncNATs on cancer progression remains largely unknown. In this study, we identified a complete list of differentially expressed ncNATs in hepatocellular carcinoma. Among them, a previously undescribed ncNAT HNF4A-AS1L suppressed cancer cell growth by regulating its sense gene HNF4A, a well-known cancer driver, through a promoter-specific mechanism. HNF4A-AS1L selectively activated the HNF4A P1 promoter via HNF1A, which upregulated expression of tumor suppressor P1-driven isoforms, while having no effect on the oncogenic P2 promoter. RNA-seq data from 23 tissue and cancer types identified approximately 100 ncNATs whose expression correlated specifically with the activity of one promoter of their associated sense gene. Silencing of two of these ncNATs ENSG00000259357 and ENSG00000255031 (antisense to CERS2 and CHKA, respectively) altered the promoter usage of CERS2 and CHKA. Altogether, these results demonstrate that promoter-specific regulation is a mechanism used by ncNATs for context-specific control of alternative isoform expression of their counterpart sense genes. SIGNIFICANCE: This study characterizes a previously unexplored role of ncNATs in regulation of isoform expression of associated sense genes, highlighting a mechanism of alternative promoter usage in cancer.

Functional screen of inflammatory bowel disease genes reveals key epithelial functions

BACKGROUND

Genetic studies have been tremendously successful in identifying genomic regions associated with a wide variety of phenotypes, although the success of these studies in identifying causal genes, their variants, and their functional impacts has been more limited.

METHODS

We identified 145 genes from IBD-associated genomic loci having endogenous expression within the intestinal epithelial cell compartment. We evaluated the impact of lentiviral transfer of the open reading frame (ORF) of these IBD genes into the HT-29 intestinal epithelial cell line via transcriptomic analyses. By comparing the genes in which expression was modulated by each ORF, as well as the functions enriched within these gene lists, we identified ORFs with shared impacts and their putative disease-relevant biological functions.

RESULTS

Analysis of the transcriptomic data for cell lines expressing the ORFs for known causal genes such as HNF4a, IFIH1, and SMAD3 identified functions consistent with what is already known for these genes. These analyses also identified two major clusters of genes: Cluster 1 contained the known IBD causal genes IFIH1, SBNO2, NFKB1, and NOD2, as well as genes from other IBD loci (ZFP36L1, IRF1, GIGYF1, OTUD3, AIRE and PITX1), whereas Cluster 2 contained the known causal gene KSR1 and implicated DUSP16 from another IBD locus. Our analyses highlight how multiple IBD gene candidates can impact on epithelial structure and function, including the protection of the mucosa from intestinal microbiota, and demonstrate that DUSP16 acts a regulator of MAPK activity and contributes to mucosal defense, in part via its regulation of the polymeric immunoglobulin receptor, involved in the protection of the intestinal mucosa from enteric microbiota.

CONCLUSIONS

This functional screen, based on expressing IBD genes within an appropriate cellular context, in this instance intestinal epithelial cells, resulted in changes to the cell's transcriptome that are relevant to their endogenous biological function(s). This not only helped in identifying likely causal genes within genetic loci but also provided insight into their biological functions. Furthermore, this work has highlighted the central role of intestinal epithelial cells in IBD pathophysiology, providing a scientific rationale for a drug development strategy that targets epithelial functions in addition to the current therapies targeting immune functions.

Hepatocyte Nuclear Factor 4 alpha 2 Messenger RNA Reprograms Liver-Enriched Transcription Factors and Functional Proteins in End-Stage Cirrhotic Human Hepatocytes

The only definitive therapy for end-stage liver disease is whole-organ transplantation. The success of this intervention is severely limited by the complexity of the surgery, the cost of patient care, the need for long-term immunosuppression, and the shortage of donor organs. In rodents and humans, end-stage degeneration of hepatocyte function is associated with disruption of the liver-specific transcriptional network and a nearly complete loss of promoter P1-driven hepatocyte nuclear factor 4-alpha (P1-HNF4α) activity. Re-expression of HNF4α2, the predominant P1-HNF4α, reinstates the transcriptional network, normalizes the genes important for hepatocyte function, and reverses liver failure in rodents. In this study, we tested the effectiveness of supplementary expression of human HNF4α2 messenger RNA (mRNA) in primary human hepatocytes isolated from explanted livers of patients who underwent transplant for end-stage irreversibly decompensated liver failure (Child-Pugh B, C) resulting from alcohol-mediated cirrhosis and nonalcoholic steatohepatitis. Re-expression of HNF4α2 in decompensated cirrhotic human hepatocytes corrects the disrupted transcriptional network and normalizes the expression of genes important for hepatocyte function, improving liver-specific protein expression. End-stage liver disease in humans is associated with both loss of P1-HNF4α expression and failure of its localization to the nucleus. We found that while HNF4α2 re-expression increased the amount of P1-HNF4α protein in hepatocytes, it did not alter the ability of hepatocytes to localize P1-HNF4α to their nuclei. Conclusion: Re-expression of HNF4α2 mRNA in livers of patients with end-stage disease may be an effective therapy for terminal liver failure that would circumvent the need for organ transplantation. The efficacy of this strategy may be enhanced by discovering the cause for loss of nuclear P1-HNF4α localization in end-stage cirrhosis, a process not found in rodent studies.

Therapeutic Potential of HNF4α in End-stage Liver Disease

The prevalence of end-stage liver disease (ESLD) in the US is increasing at an alarming rate. It can be caused by several factors; however, one of the most common routes begins with nonalcoholic fatty liver disease (NAFLD). ESLD is diagnosed by the presence of irreversible damage to the liver. Currently, the only definitive treatment for ESLD is orthotopic liver transplantation (OLT). Nevertheless, OLT is limited due to a shortage of donor livers. Several promising alternative treatment options are under investigation. Researchers have focused on the effect of liver-enriched transcription factors (LETFs) on disease progression. Specifically, hepatocyte nuclear factor 4-alpha (HNF4α) has been reported to reset the liver transcription network and possibly play a role in the regression of fibrosis and cirrhosis. In this review, we describe the function of HNF4α, along with its regulation at various levels. In addition, we summarize the role of HNF4α in ESLD and its potential as a therapeutic target in the treatment of ESLD.

A Western diet with alcohol in drinking water recapitulates features of alcohol-associated liver disease in mice

BACKGROUND

Mouse models of alcohol-associated liver disease vary greatly in their ease of implementation and the pathology they produce. Effects range from steatosis and mild inflammation with the Lieber-DeCarli liquid diet to severe inflammation, fibrosis, and pyroptosis seen with the Tsukamoto-French intragastric feeding model. Implementation of all of these models is limited by the labor-intensive nature of the protocols and the specialized skills necessary for successful intragastric feeding. We thus sought to develop a new model to reproduce features of alcohol-induced inflammation and fibrosis with minimal operational requirements.

METHODS

Over a 16-week period, mice were fed ad libitum with a pelleted high-fat Western diet (WD; 40% calories from fat) and alcohol added to the drinking water. We found the optimal alcohol consumption to be that at which the alcohol concentration was 20% for 4 days and 10% for 3 days per week. Control mice received WD pellets with water alone.

RESULTS

Alcohol consumption was 18 to 20 g/kg/day in males and 20 to 22 g/kg/day in females. Mice in the alcohol groups developed elevated serum transaminase levels after 12 weeks in males and 10 weeks in females. At 16 weeks, both males and females developed liver inflammation, steatosis, and pericellular fibrosis. Control mice on WD without alcohol had mild steatosis only. Alcohol-fed mice showed reduced HNF4α mRNA and protein expression. HNF4α is a master regulator of hepatocyte differentiation, down-regulation of which is a known driver of hepatocellular failure in alcoholic hepatitis.

CONCLUSION

A simple-to-administer, 16-week WD alcohol model recapitulates the inflammatory, fibrotic, and gene expression aspects of human alcohol-associated steatohepatitis.

Cellular Organelles Involved in Hepatitis E Virus Infection

Hepatitis E virus (HEV), a major cause of acute hepatitis worldwide, infects approximately 20 million individuals annually. HEV can infect a wide range of mammalian and avian species, and cause frequent zoonotic spillover, increasingly raising public health concerns. To establish a successful infection, HEV needs to usurp host machineries to accomplish its life cycle from initial attachment to egress. However, relatively little is known about the HEV life cycle, especially the functional role(s) of cellular organelles and their associated proteins at different stages of HEV infection. Here, we summarize current knowledge regarding the relation of HEV with the different cell organelles during HEV infection. Furthermore, we discuss the underlying mechanisms by which HEV infection is precisely regulated in infected cells and the modification of host cell organelles and their associated proteins upon HEV infection.

Maturity Onset Diabetes of the Young-New Approaches for Disease Modelling

Maturity-onset diabetes of the young (MODY) is a genetically heterogeneous group of monogenic endocrine disorders that is characterised by autosomal dominant inheritance and pancreatic β-cell dysfunction. These patients are commonly misdiagnosed with type 1 or type 2 diabetes, as the clinical symptoms largely overlap. Even though several biomarkers have been tested none of which could be used as single clinical discriminator. The correct diagnosis for individuals with MODY is of utmost importance, as the applied treatment depends on the gene mutation or is subtype-specific. Moreover, in patients with HNF1A-MODY, additional clinical monitoring can be included due to the high incidence of vascular complications observed in these patients. Finally, stratification of MODY patients will enable better and newer treatment options for MODY patients, once the disease pathology for each patient group is better understood. In the current review the clinical characteristics and the known disease-related abnormalities of the most common MODY subtypes are discussed, together with the up-to-date applied diagnostic criteria and treatment options. Additionally, the usage of pluripotent stem cells together with CRISPR/Cas9 gene editing for disease modelling with the possibility to reveal new pathophysiological mechanisms in MODY is discussed.

Hepatocyte-Specific Hepatocyte Nuclear Factor 4 Alpha (HNF4) Deletion Decreases Resting Energy Expenditure by Disrupting Lipid and Carbohydrate Homeostasis

Hepatocyte nuclear factor 4 alpha (HNF4) is required for hepatocyte differentiation and regulates expression of genes involved in lipid and carbohydrate metabolism including those that control VLDL secretion and gluconeogenesis. Whereas previous studies have focused on specific genes regulated by HNF4 in metabolism, its overall role in whole-body energy utilization has not been studied. In this study, we used indirect calorimetry to determine the effect of hepatocyte-specific HNF4 deletion (HNF4-KO) in mice on whole-body energy expenditure (EE) and substrate utilization in fed, fasted, and high-fat diet (HFD) conditions. HNF4-KO had reduced resting EE during fed conditions and higher rates of carbohydrate oxidation with fasting. HNF4-KO mice exhibited decreased body mass caused by fat mass depletion despite no change in energy intake and evidence of positive energy balance. HNF4-KO mice were able to upregulate lipid oxidation during HFD, suggesting that their metabolic flexibility was intact. However, only hepatocyte-specific HNF4-KO mice exhibited significant reduction in basal metabolic rate and spontaneous activity during HFD. Consistent with previous studies, hepatic gene expression in HNF4-KO supports decreased gluconeogenesis and decreased VLDL export and hepatic -oxidation in HNF4-KO livers across all feeding conditions. Together, our data suggest that deletion of hepatic HNF4 increases dependence on dietary carbohydrates and endogenous lipids for energy during fed and fasted conditions by inhibiting hepatic gluconeogenesis, hepatic lipid export, and intestinal lipid absorption resulting in decreased whole-body energy expenditure. These data clarify the role of hepatic HNF4 on systemic metabolism and energy homeostasis.

Cellular plasticity balances the metabolic and proliferation dynamics of a regenerating liver

The adult liver has an exceptional ability to regenerate, but how it maintains its specialized functions during regeneration is unclear. Here, we used partial hepatectomy (PHx) in tandem with single-cell transcriptomics to track cellular transitions and heterogeneities of ∼22,000 liver cells through the initiation, progression, and termination phases of mouse liver regeneration. Our results uncovered that, following PHx, a subset of hepatocytes transiently reactivates an early-postnatal-like gene expression program to proliferate, while a distinct population of metabolically hyperactive cells appears to compensate for any temporary deficits in liver function. Cumulative EdU labeling and immunostaining of metabolic, portal, and central vein-specific markers revealed that hepatocyte proliferation after PHx initiates in the midlobular region before proceeding toward the periportal and pericentral areas. We further demonstrate that portal and central vein proximal hepatocytes retain their metabolically active state to preserve essential liver functions while midlobular cells proliferate nearby. Through combined analysis of gene regulatory networks and cell-cell interaction maps, we found that regenerating hepatocytes redeploy key developmental regulons, which are guided by extensive ligand-receptor-mediated signaling events between hepatocytes and nonparenchymal cells. Altogether, our study offers a detailed blueprint of the intercellular crosstalk and cellular reprogramming that balances the metabolic and proliferative requirements of a regenerating liver.

Identification of promoter response elements that mediate propionate induction of bovine cytosolic phosphoenolpyruvate carboxykinase (PCK1) gene transcription

Cytosolic phosphoenolpyruvate carboxykinase (PCK1) is a key enzyme for gluconeogenesis that is positively regulated by propionate in bovines at the transcription level. The specific elements that determine propionate responsiveness within the bovine PCK1 promoter are unknown. In silico promoter analysis of the bovine PCK1 gene revealed several clusters of transcription factor binding sites. In the present study, we determined the essentiality of the putative cyclic AMP response element (CRE) at -94 through -87 bp and the 2 putative hepatic nuclear factor 4α (HNF4α) binding elements at +68 through +72 and -1,078 through -1,074, respectively, in mediating bovine PCK1 promoter responses to propionate and other regulators, including butyrate, cyclic AMP (cAMP), and glucocorticoids. The wild-type bovine PCK1 promoter [PCK1_(WT)] was ligated to a luciferase reporter gene and transfected into rat hepatoma (H4IIE) cells. Activities of PCK1_(WT) were induced by approximately 2-, 2-, 4-, 8-, 9-, 18-, and 16-fold respectively when exposed to cAMP (as 1.0 mM 8-Br-cAMP), 5.0 μM dexamethasone, cAMP + dexamethasone, 2.5 mM propionate, cAMP + propionate, cAMP + dexamethasone + propionate, and 2.5 mM butyrate. Seven mutants lacking either one single site, 2 of the 3 sites, or all 3 sites, generated by site-directed mutagenesis, were tested. Responses to propionate and all other treatments were completely abolished when CRE at -94 through -87 bp and HNF4α at +68 through +72 bp were both deleted. Our data indicate that these 2 regulatory elements act synergistically to mediate the bovine PCK1 promoter responses to propionate as well as butyrate, cAMP, and dexamethasone. The activation of PCK1 through these regulatory elements serves to activate the metabolic potential of bovine toward gluconeogenesis when the primary substrate for gluconeogenesis, propionate, is also present.

A review on molecular mechanism of alcoholic liver disease

Excessive alcohol consumption leads to damage to the organs of the body. More importantly, the liver is majorly affected organ upon alcohol consumption for most of the people; it causes inflammation and affects various pathways involved in metabolism. If the person is with high response of inflammatory in conduct with alcohol leads to the liver damage, which involves the creating effects with major cycle leads to homeostasis. In this review, we summarize the molecular mechanisms of alcoholic liver disease, such as the important role of genes, risk factors, pathogenicity, and role of micro RNA, the role of inflammation in the liver, and alcoholic fibrosis in the liver. There is increased oxidative stress, change in the biochemical alterations, and reduction in the antioxidant enzymes. These changes in the mechanism lead to liver injury. Hepatocyte nuclear factor-4 is the major transcriptional factor for the regulation of some genes involved in the lipid metabolism and oxidation process; with the help of the agonist, we can attenuate the level of the gene in the site of hepatic tissues, which will prevent the homeostatic condition. This review shows a clear view of the various pathways involved in alcohol consumption, which helps in the prevention of ALD using an agonist.

PPARα/RXRα downregulates amino acid catabolism in the liver via interaction with HNF4α promoting its proteasomal degradation

The preservation of body proteins is essential to guarantee their functions in organisms. Therefore, the utilization of amino acids as energy substrates is regulated by a precise fine-tuned mechanism. Recent evidence suggests that the transcription factors peroxisome proliferator-activated receptor alpha (PPARα) and hepatocyte nuclear factor 4 alpha (HNF4α) are involved in this regulatory mechanism. Thus, the aim of this study was to determine how these transcription factors interact to regulate the expression of amino acid catabolism genes. In vivo studies using PPARα-knockout mice (Pparα-null) fed different amounts of dietary protein showed that in the absence of PPARα, there was a significant increase in HNF4α abundance in the liver, which corresponded with an increase in amino acid catabolizing enzyme (AACE) expression and the generation of increased amounts of postprandial urea. Moreover, this effect was proportional to the increase in dietary protein consumed. Chromatin immunoprecipitation assays showed that HNF4α can bind to the promoter of AACE serine dehydratase (SDS), an effect that was potentiated by dietary protein in the Pparα-null mice. The mechanistic studies revealed that the presence of retinoid X receptor alpha (RXRα) is essential to repress HNF4α activity in the presence of PPARα, and this interaction accelerates HNF4α degradation via the proteasome pathway. These results showed that PPARα can downregulate liver amino acid catabolism in the presence of RXRα by inhibiting HNF4α activity.

Polysaccharides of vinegar-baked radix bupleuri promote the hepatic targeting effect of oxymatrine by regulating the protein expression of HNF4α, Mrp2, and OCT1

ETHNOPHARMACOLOGICAL RELEVANCE

Vinegar-baked Radix Bupleuri (VBRB) is a processed form of Bupleurum chinense DC. As a well-known meridian-guiding drug, it is traditionally used as a component of traditional Chinese medicine formulations indicated for the treatment of liver diseases. However, the liver targeting component in VBRB remains unclear. Therefore, this study aims to explore the efficacy and mechanism of PSS (polysaccharides in Vinegar-baked Radix Bupleuri) in enhancing liver targeting.

MATERIALS AND METHODS

Drug distribution of OM alone or combined with PSS was investigated in vivo. Relative uptake efficiency (RUE) and relative targeting efficiency (RTE) were calculated to evaluate liver targeting efficiency. The mRNA and protein expression of organic cation transporter 1 (OCT1), multi-drug resistance protein 2 (Mrp2), and hepatocyte nuclear factor 4α (HNF4α) in the liver were determined by q-PCR and Western blot. Then, AZT, the inhibitor of OCT1 and BI6015, the inhibitor of HNF4α were used to investigate regulatory mechanisms involved in the uptake of OM in the cell. At last, the role of PSS in the anti-hepatitis B virus (HBV) was explored on HepG2.2.15.

RESULTS

PSS increased the AUC of OM in the liver and increase the RUE and RTE in the liver which indicated a liver targeting enhancing effect. The mRNA and protein expression of OCT1 was increased while Mrp2 and HNF4α decreased. PSS could increase the uptake of OM in HepG2 by increasing the protein expression of HNF4α and OCT1, while inhibited Mrp2. Moreover, PSS combined with OM could enhance the anti-HBV effect of OM.

CONCLUSION

PSS enhanced the liver targeting efficiency and the underlying mechanism related to up-regulating the expression of OCT1 and HNF4α, while down-regulating of Mrp2. These results suggest that PSS may become a potential excipient and provide a new direction for new targeted research.

Cellular plasticity balances the metabolic and proliferation dynamics of a regenerating liver

The adult liver has an exceptional ability to regenerate, but how it maintains its specialized functions during regeneration is unclear. Here, we used partial hepatectomy (PHx) in tandem with single-cell transcriptomics to track cellular transitions and heterogeneities of ∼22,000 liver cells through the initiation, progression, and termination phases of mouse liver regeneration. Our results uncovered that, following PHx, a subset of hepatocytes transiently reactivates an early-postnatal-like gene expression program to proliferate, while a distinct population of metabolically hyperactive cells appears to compensate for any temporary deficits in liver function. Cumulative EdU labeling and immunostaining of metabolic, portal, and central vein-specific markers revealed that hepatocyte proliferation after PHx initiates in the midlobular region before proceeding toward the periportal and pericentral areas. We further demonstrate that portal and central vein proximal hepatocytes retain their metabolically active state to preserve essential liver functions while midlobular cells proliferate nearby. Through combined analysis of gene regulatory networks and cell-cell interaction maps, we found that regenerating hepatocytes redeploy key developmental regulons, which are guided by extensive ligand-receptor-mediated signaling events between hepatocytes and nonparenchymal cells. Altogether, our study offers a detailed blueprint of the intercellular crosstalk and cellular reprogramming that balances the metabolic and proliferative requirements of a regenerating liver.

The N6-methyladenosine modification posttranscriptionally regulates hepatic UGT2B7 expression

UDP-glucuronosyltransferases (UGTs) are enzymes catalyzing the glucuronidation of various endogenous and exogenous compounds. In this study, we examined the possibility that N⁶-methyladenosine (m⁶A) modification affects hepatic UGT expression. Treatment of HepaRG cells with 3-deazaadenosine, an inhibitor of RNA methylation, significantly increased UGT1A1, UGT1A3, UGT1A4, UGT1A9, UGT2B7, UGT2B10, and UGT2B15 mRNA levels (1.3- to 2.6-fold). Among them, we focused on UGT2B7 because it most highly contributes to glucuronidation of clinically used drugs. Methylated RNA immunoprecipitation assays revealed that UGT2B7 mRNA in HepaRG cells and human livers is subjected to m⁶A modification mainly at the 5' untranslated region (UTR) and secondarily at the 3'UTR. UGT2B7 mRNA and protein levels in Huh-7 cells were significantly increased by double knockdown of methyltransferase-like 3 (METTL3) and METTL14, whereas those were decreased by knockdown of fat mass and obesity-associated protein (FTO) or alkB homolog 5, RNA demethylase (ALKBH5), suggesting that m⁶A modification downregulates UGT2B7 expression. By experiments using actinomycin D, an inhibitor of transcription, it was demonstrated that ALKBH5-mediated demethylation would attenuate UGT2B7 mRNA degradation, whereas METTL3/METTL14 or FTO-mediated m⁶A modification would alter the transactivity of UGT2B7. Luciferase assays revealed that the promoter region at -118 to -106 has a key role in the decrease in transactivity of UGT2B7 by FTO knockdown. We found that hepatocyte nuclear factor 4α (HNF4α) expression was significantly decreased by knockdown of FTO, indicating that this would be the underlying mechanism of the decreased transactivity of UGT2B7 by knockdown of FTO. Interestingly, treatment with entacapone, which is used for the treatment of Parkinson's disease and is an inhibitor of FTO, decreased HNF4α and UGT2B7 expression. In conclusion, this study clarified that RNA methylation posttranscriptionally controls hepatic UGT2B7 expression.

Cytochrome P450 expression and regulation in the brain

The regulation of brain cytochrome P450 enzymes (CYPs) is different compared with respective hepatic enzymes. This may result from anatomical bases and physiological functions of the two organs. The brain is composed of a variety of functional structures built of different interconnected cell types endowed with specific receptors that receive various neuronal signals from other brain regions. Those signals activate transcription factors or alter functioning of enzyme proteins. Moreover, the blood-brain barrier (BBB) does not allow free penetration of all substances from the periphery into the brain. Differences in neurotransmitter signaling, availability to endogenous and exogenous active substances, and levels of transcription factors between neuronal and hepatic cells lead to differentiated expression and susceptibility to the regulation of CYP genes in the brain and liver. Herein, we briefly describe the CYP enzymes of CYP1-3 families, their distribution in the brain, and discuss brain-specific regulation of CYP genes. In parallel, a comparison to liver CYP regulation is presented. CYP enzymes play an essential role in maintaining the levels of bioactive molecules within normal ranges. These enzymes modulate the metabolism of endogenous neurochemicals, such as neurosteroids, dopamine, serotonin, melatonin, anandamide, and exogenous substances, including psychotropics, drugs of abuse, neurotoxins, and carcinogens. The role of these enzymes is not restricted to xenobiotic-induced neurotoxicity, but they are also involved in brain physiology. Therefore, it is crucial to recognize the function and regulation of CYP enzymes in the brain to build a foundation for future medicine and neuroprotection and for personalized treatment of brain diseases.

Responsive polymer-assisted 3D cryogel supports Huh7.5 as in vitro hepatitis C virus model and ectopic human hepatic tissue in athymic mice

The three-dimensional (3D) cell culture models serve as the interface between conventional two-dimensional (2D) monolayer culture and animal models. 3D culture offers the best possible model system to understand the pathophysiology of human pathogens such as hepatitis C virus (HCV), which lacks a small animal model, due to narrow host tropism and non-permissiveness of murine hepatocytes. In this study, functionally robust spheroids of HCV permissive Huh7.5 cells were generated, assisted by the temperature or pH-responsive polymers PNIPAAm and Eudragit respectively, followed by the long-term growth of the multilayered 3D aggregates in poly(ethylene glycol) (PEG)-alginate-gelatin (PAG) cryogel. The human serum albumin (HSA), marker of hepatic viability was detected up to 600 ng/ml on 24th day of culture. The 3D spheroid culture exhibited a distinct morphology and transcript levels with the upregulation of hepato-specific transcripts, nuclear factor 4α (HNF4α), transthyretin (TTr), albumin (Alb), phase I and phase II drug-metabolizing genes. The two most important phase I enzymes CYP3A4 and CYP2D6, together responsible for 90% metabolism of drugs exhibited up to 9- and 12-fold increment, respectively in transcripts. The 3D culture was highly permissive to HCV infection and supported higher multiplicity of infection compared to monolayer Huh7.5 culture. Quantitation of high levels of HSA (500-200 ng/ml) in circulation in mice for 32 days asserted integration with host vasculature and in vivo establishment of 3D culture implants as an ectopic human hepatic tissue in mice. The study demonstrates the 3D spheroid Huh7.5 culture as a model for HCV studies and screening potential for anti-HCV drug candidates.

Selenium-binding protein 1 alters energy metabolism in prostate cancer cells

OBJECTIVE

The broad goal of the research described in this study was to investigate the contributions of selenium-binding protein 1 (SBP1) loss in prostate cancer development and outcome.

METHODS

SBP1 levels were altered in prostate cancer cell lines and the consequences on oxygen consumption, expression of proteins associated with energy metabolism, and cellular transformation and migration were investigated. The effects of exposing cells to the SBP1 reaction products, H₂ O₂ and H₂ S were also assessed. In silico analyses identified potential HNF4α binding sites within the SBP1 promoter region and this was investigated using an inhibitor specific for that transcription factor.

RESULTS

Using in silico analyses, it was determined that the promoter region of SBP1 contains putative binding sites for the HNF4α transcription factor. The potential for HNF4α to regulate SBP1 expression was supported by data indicating that HNF4α inhibition resulted in a dose-response increase in the levels of SBP1 messenger RNA and protein, identifying HNF4α as a novel negative regulator of SBP1 expression in prostate cancer cells. The consequences of altering the levels of SBP1 were investigated by ectopically expressing SBP1 in PC-3 prostate cancer cells, where SBP1 expression attenuated anchorage-independent cellular growth and migration in culture, both properties associated with transformation. SBP1 overexpression reduced oxygen consumption in these cells and increased the activation of AMP-activated protein kinase (AMPK), a major regulator of energy homeostasis. In addition, the reaction products of SBP1, H₂ O₂ , and H₂ S also activated AMPK.

CONCLUSIONS

Based on the obtained data, it is hypothesized that SBP1 negatively regulates oxidative phosphorylation (OXPHOS) in the healthy prostate cells by the production of H₂ O₂ and H₂ S and consequential activation of AMPK. The reduction of SBP1 levels in prostate cancer can occur due to increased binding of HNF4α, acting as a transcriptional inhibitor to the SBP1 promoter. Consequently, there is a reduction in H₂ O₂ and H₂ S-mediated signaling, inhibition of AMPK, and stimulation of OXPHOS and building blocks of biomolecules needed for tumor growth and progression. Other effects of SBP1 loss in tumor cells remain to be discovered.

CTRP12 inhibits triglyceride synthesis and export in hepatocytes by suppressing HNF-4α and DGAT2 expression

C1q/TNF-related protein 12 (CTRP12) is an antidiabetic adipokine whose circulating levels are reduced in obesity and diabetes. Although partial and complete loss-of-function mouse models suggest a role for CTRP12 in modulating lipid metabolism and adiposity, its effect on cellular lipid metabolism remains poorly defined. Here, we demonstrate a direct action of CTRP12 in regulating lipid synthesis and secretion. In hepatoma cells and primary mouse hepatocytes, CTRP12 treatment inhibits triglyceride synthesis by suppressing glycerophosphate acyltransferase (GPAT) and diacylglycerol acyltransferase (DGAT) expression. CTRP12 treatment also downregulates the expression of hepatocyte nuclear factor-4α (HNF-4α) and its target gene microsomal triglyceride transfer protein (MTTP), leading to reduced very-low-density lipoprotein (VLDL)-triglyceride export from hepatocytes. Consistent with the in vitro findings, overexpressing CTRP12 lowers fasting and postprandial serum triglyceride levels in mice. These results underscore the important function of CTRP12 in lipid metabolism in hepatocytes.

Andrographolide modulates HNF4α activity imparting on hepatic metabolism

Hepatic nuclear factor 4 alpha (HNF4α) drives the expression of apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A2 G12B (PLA2G12B), governing hepatic very-low-density lipoprotein (VLDL) production and secretion. Andrographolide (AP) is a major constituent isolated from Andrographis paniculata. We found that AP can disrupt the interaction between HNF4α and its coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α). Virtual docking and mutational analysis indicated that arginine 235 of HNF4α is essential for binding to AP. As a consequence of antagonizing the activity of HNF4α, AP suppresses the expression of ApoB, MTP and PLA2G12B and reduces the rate of hepatic VLDL secretion in vivo. AP additionally reduced gluconeogenesis via down-regulating the expression of HNF4α target genes phosphoenolpyruvate carboxykinase (Pepck) and glucose-6-phosphatase (G6pc). Collectively, our results suggest that AP affects liver function via modulating the transcriptional activity of HNF4α.