Identification of alverine and benfluorex as HNF4α activators

The effects of free fatty acid-free bovine serum albumin and palmitate on pancreatic β-cell function

Pancreatic β-cells release insulin in response to fluctuations in plasma glucose, amino acids, and free fatty acids (FFA). Clonal cell lines and isolated islets serve as essential early models for studying the impact of nutrients and evaluating potential therapies to address β-cell dysfunction. Acute and chronic changes in FFA levels have been shown to have positive and negative effects on β-cell function both in vivo and in vitro. A key problem in comparing islet lipid studies from different laboratories is that a wide variety of methods are used to isolate, culture, and assess islet function. The current study compares bovine serum albumin (BSA) types and lipid preparation methods in clonal 832/13 cells and human islets. Changing the percentage and culture conditions when using FFA-free BSA can negatively affect β-cell function compared to regular BSA. Preparing palmitate with FFA-free BSA can rescue insulin secretion compared to treating cells alone with FFA-free BSA. Different methods of preparing palmitate can have unique effects on insulin secretion. Overall, interpreting the effects of lipids on β-cell function is complicated by a number of variables that need to be controlled for in islet experiments.

Comparative Evaluation and Profiling of Chemical Tools for the Nuclear Hormone Receptor Family 2

Nuclear receptors regulate transcription in response to ligand signals and enable the pharmacological control of gene expression. However, many nuclear receptors are still poorly explored and are not accessible to ligand-based target identification studies. In particular, most members of the NR2 family are among the least studied proteins of the class, and apart from the retinoid X receptors (RXR), validated NR2 ligands are very rare. Here, we gathered the NR2 modulators reported in literature for comparative profiling in uniform test systems. Most candidate compounds displayed insufficient on-target activity or selectivity to be used as chemical tools for NR2 receptors underscoring the urgent need for further NR2 ligand development. Nevertheless, a small NR2 modulator set could be assembled for application in a chemogenomic fashion. There are 48 ligand-activated transcription factors in humans forming the superfamily of nuclear receptors (NRs, Figure 1a),1,2 which translate (endogenous) ligand signals into changes in gene expression patterns.3 The multifaceted roles of NRs span pivotal physiological processes, encompassing metabolism, inflammation, and cellular differentiation.4 Over decades, the NR1 and NR3 receptor families, including (steroid) hormone receptors and lipid sensors, have emerged as well-explored therapeutic targets of essential drugs like, for example, glucocorticoids as anti-inflammatory drugs, estrogen receptor modulators as contraceptives and anticancer agents, and PPAR agonists as oral antidiabetics.5-7 Despite this progress, a significant portion of the NR superfamily remains understudied, particularly within the NR2 family which comprises the hepatocyte nuclear factor-4 receptors (HNF4α/γ; NR2A1/2), the retinoid X receptors (RXRα/β/γ; NR2B1-3), the testicular receptors (TR2/4; NR2C1/2), the tailless-like receptors (TLX and PNR; NR2E1/3), and the COUP-TF-like receptors (COUP-TF1/2, V-erBA-related gene; NR2F1/2/6).8,9 Apart from RXR, all NR2 receptors are considered as orphan, and their ligands remain widely elusive. Therefore, chemical tools for most NR2 receptors are rare and poorly annotated posing an obstacle to target identification and validation studies. To enable chemogenomics on NR2 receptors and improve annotation, of the few available ligands, we gathered a scarce collection of NR2 modulators (agonists, antagonists, inverse agonists) for comparative evaluation and profiling. While the NR2B family (RXR) is well covered with high-quality ligands and a few early tools are available for NR2E1, we found the available ligands of the NR2A and NR2C families of insufficient quality to be used as chemical tools.

Hypoxia reduces SLC27A5 to promote hepatocellular carcinoma proliferation by repressing HNF4A

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related mortality globally, with hypoxia recognized as a key factor in its progression. Solute carrier family 27 member 5 (SLC27A5/FATP5), a pivotal enzyme in hepatic fatty acid transport and bile acid metabolism, is frequently downregulated in hepatocellular carcinoma, resulting in poor prognosis. However, the link between hypoxia and the suppression of SLC27A5 in HCC remains to be elucidated. Here, we investigated the hypoxia-induced downregulation of SLC27A5 and its impact on HCC proliferation via the repression of hepatocyte nuclear factor 4 alpha (HNF4A). Utilizing in vitro and in vivo hepatocellular carcinoma models, we have demonstrated that hypoxic conditions significantly reduce SLC27A5 transcription, which is mediated by the suppression of HNF4A. This reduction leads to the activation of the AKT pathway and an increase in cyclin-dependent kinase 2 (CDK2) and Cyclin E1 (CCNE1) expression, promoting the transition from the G1 to S phase of the cell cycle and driving HCC proliferation. Furthermore, we show that the pharmacological activation of HNF4A using Benfluorex, in combination with the AKT inhibitor MK2206, significantly inhibits tumor growth in a subcutaneous MHCC-97H xenograft model, suggesting a synergistic therapeutic potential. Together, our study provides novel insights into the hypoxia-mediated regulatory mechanisms in HCC and highlights the HNF4A/SLC27A5/AKT axis as a promising target for combination therapy.

The potential for improving the efficacy of treatment for irritable bowel syndrome with a multi-target drug alverine citrate plus simethicone: The Expert Panel Statement

The irritable bowel syndrome (IBS) is one of the most prevalent functional gastrointestinal disorders. However, at most, one-third of IBS patients are satisfied with the results of their treatment. A combination of pharmaceuticals or multi-target drugs should be used for the treatment to be effective due to the complexity of IBS pathophysiology. The Russian Expert Panel in gastroenterology, including functional gastrointestinal disorders, currently considered to be disorders of gut-brain interaction, at its open session has discussed the possibilities to increase the efficacy of treatment of patients with IBS with a multitargeted agent alverine citrate combined with simethicone registered under the trade name of Meteospasmyl® (Mayoly Pharma, France) and adopted the respective resolution. Based on the results of multiple experimental and clinical studies, the experts declared that the combination of alverine citrate with simethicone relieves pain through the alleviation of its main mechanisms (spasms, flatulence, visceral hypersensitivity, and inflammation), and normalizes bowel movements demonstrating the normokinetic (eukinetic) properties. All clinical effects of the combination of alverine citrate and simethicone are prolonged. Alverine citrate combined with simethicone improves patients’ quality of life, including their psychological well-being. Due to the efficacy and good safety profile, it is possible to use the combination of alverine citrate and simethicone as on-demand and ex juvantibus treatment. The combination of alverine citrate and simethicone is a single selective antispasmodic that allows for a simultaneous solution of two clinical challenges: to rid the patient of abdominal pains and to properly prepare the patient for instrumental examinations (colonoscopy, abdominal ultrasound, and radiological examination), due to a high simethicone dose and spasmolytic properties of alverine citrate. In addition, Meteospasmyl® is a single antispasmodic, which has demonstrated high efficacy and safety in a clinical study of its combination with a probiotic (Probiolog® IBS), containing the strains (Lactobacillus plantarum CECT 7484, Lactobacillus plantarum CECT 7485, and Pediococcus acidilactici CECT 7483) acting on all IBS pathogenesis steps. This is extremely important, considering the proven role of gut dysbiosis in IBS pathophysiology.

A critical role for HNF4α in polymicrobial sepsis-associated metabolic reprogramming and death

In sepsis, limited food intake and increased energy expenditure induce a starvation response, which is compromised by a quick decline in the expression of hepatic PPARα, a transcription factor essential in intracellular catabolism of free fatty acids. The mechanism upstream of this PPARα downregulation is unknown. We found that sepsis causes a progressive hepatic loss-of-function of HNF4α, which has a strong impact on the expression of several important nuclear receptors, including PPARα. HNF4α depletion in hepatocytes dramatically increases sepsis lethality, steatosis, and organ damage and prevents an adequate response to IL6, which is critical for liver regeneration and survival. An HNF4α agonist protects against sepsis at all levels, irrespectively of bacterial loads, suggesting HNF4α is crucial in tolerance to sepsis. In conclusion, hepatic HNF4α activity is decreased during sepsis, causing PPARα downregulation, metabolic problems, and a disturbed IL6-mediated acute phase response. The findings provide new insights and therapeutic options in sepsis.

Drosophila HNF4 acts in distinct tissues to direct a switch between lipid storage and export in the gut

Nutrient digestion, absorption, and export must be coordinated in the gut to meet the nutritional needs of the organism. We used the Drosophila intestine to characterize the mechanisms that coordinate the fate of dietary lipids. We identified enterocytes specialized in absorbing and exporting lipids to peripheral organs. Distinct hepatocyte-like cells, called oenocytes, communicate with these enterocytes to adjust intestinal lipid storage and export. A single transcription factor, Drosophila hepatocyte nuclear factor 4 (dHNF4), supports this gut-liver axis. In enterocytes, dHNF4 maximizes dietary lipid export by preventing their sequestration in cytoplasmic lipid droplets. In oenocytes, dHNF4 promotes the expression of the insulin antagonist ImpL2 to activate Foxo and suppress lipid retention in enterocytes. Disruption of this switch between lipid storage and export is associated with intestinal inflammation, suggesting a lipidic origin for inflammatory bowel diseases. These studies establish dHNF4 as a central regulator of intestinal metabolism and inter-organ lipid trafficking.

HNF4A as a potential target of PFOA and PFOS leading to hepatic steatosis: Integrated molecular docking, molecular dynamic and transcriptomic analyses

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are indeed among the most well known and extensively studied Per- and polyfluoroalkyl substances (PFASs), and increasing evidence confirm their effects on human health, especially liver steatosis. Nonetheless, the molecular mechanisms of their initiation of hepatic steatosis is still elusive. Therefore, potential targets of PFOA/PFOS must be explored to ameliorate its adverse consequences. This research aims to investigate the molecular mechanisms of PFOA and PFOS-induced liver steatosis, with emphasis on identifying a potential target that links these PFASs to liver steatosis. The potential target that causes PFOA and PFOS-induced liver steatosis have been explored and determined based on molecular docking, molecular dynamics (MD) simulation, and transcriptomics analysis. In silico results show that PFOA/PFOS can form a stable binding conformation with HNF4A, and PFOA/PFOS may interact with HNF4A to affect the downstream conduction mechanism. Transcriptome data from PFOA/PFOS-induced human stem cell spheres showed that HNF4A was inhibited, suggesting that PFOA/PFOS may constrain its function. PFOS mainly down-regulated genes related to cholesterol synthesis while PFOA mainly up-regulated genes related to fatty acid β-oxidation. This study explored the toxicological mechanism of liver steatosis caused by PFOA/PFOS. These compounds might inhibit and down-regulate HNF4A, which is the molecular initiation events (MIE) that induces liver steatosis.

Health-Promoting Opportunities of Hemp Hull: The Potential of Bioactive Compounds

Hemp hull is the outer coat of the hemp seed, derived from the plant Cannabis sativa L., Cannabaceae. While much attention has been paid to hemp seed for its oil, protein and micronutrient content, far less attention has been given to hemp hull, a side stream of hemp processing. Hemp hull is a source of bioactive compounds, dietary fiber, minerals as well as protein, lipids and carbohydrates. Of note, two bioactive compounds, n-trans-caffeoyltyramine and n-trans-feruloyltyramine have been identified in hemp hull as key bioactive compounds that support gut health, liver function and other physiological processes. Both of these compounds were identified as agonists of the transcription factor, hepatic nuclear factor-4 alpha which has been implicated in gene expression that governs gut permeability, factors associated with inflammatory bowel diseases, and hepatic lipid homeostasis. Additionally, the dietary fibers in hemp hull have been demonstrated to be novel prebiotics, which may further amplify hemp hull's effect on gut health and metabolic health. This review article summarizes the nutritional content of hemp hull, explores the physiological effects of bioactive compounds found in hemp hull, and identifies opportunities for further research on hemp hull for human health benefit.

The Application of High-Throughput Approaches in Identifying Novel Therapeutic Targets and Agents to Treat Diabetes

During the past decades, unprecedented progress in technologies has revolutionized traditional research methodologies. Among these, advances in high-throughput drug screening approaches have permitted the rapid identification of potential therapeutic agents from drug libraries that contain thousands or millions of molecules. Moreover, high-throughput-based therapeutic target discovery strategies can comprehensively interrogate relationships between biomolecules (e.g., gene, RNA, and protein) and diseases and significantly increase the authors' knowledge of disease mechanisms. Diabetes is a chronic disease primarily characterized by the incapacity of the body to maintain normoglycemia. The prevalence of diabetes in modern society has become a severe public health issue that threatens the well-being of millions of patients. Although a number of pharmacological treatments are available, there is no permanent cure for diabetes, and discovering novel therapeutic targets and agents continues to be an urgent need. The present review discusses the technical details of high-throughput screening approaches in drug discovery, followed by introducing the applications of such approaches to diabetes research. This review aims to provide an example of the applicability of high-throughput technologies in facilitating different aspects of disease research.

Significance of UGT1A6, UGT1A9, and UGT2B7 genetic variants and their mRNA expression in the clinical outcome of renal cell carcinoma

UDP-glucuronosyltransferase (UGT) metabolizes a number of endogenous and exogenous substrates. Renal cells express high amounts of UGT; however, the significance of UGT in patients with renal cell carcinoma (RCC) remains unknown. In this study, we profile the mRNA expression of UGT subtypes (UGT1A6, UGT1A9, and UGT2B7) and their genetic variants in the kidney tissue of 125 Japanese patients with RCC (Okayama University Hospital, Japan). In addition, we elucidate the association between the UGT variants and UGT mRNA expression levels and clinical outcomes in these patients. The three representative genetic variants, namely, UGT1A6 541A > G, UGT1A9 i399C > T, and UGT2B7-161C > T, were genotyped, and their mRNA expression levels in each tissue were determined. We found that the mRNA expression of the three UGTs (UGT1A6, UGT1A9, and UGT2B7) are significantly downregulated in RCC tissues. Moreover, in patients with RCC, the UGT2B7-161C > T variant and high UGT2B7 mRNA expression are significantly correlated with preferable cancer-specific survival (CSS) and overall survival (OS), respectively. As such, the UGT2B7-161C > T variant and UGT2B7 mRNA expression level were identified as significant independent prognostic factors of CSS and CSS/OS, respectively. Taken together, these findings indicate that UGT2B7 has a role in RCC progression and may, therefore, represent a potential prognostic biomarker for patients with RCC.

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.

Aldehyde dehydrogenase 6 family member A1 negatively regulates cell growth and to cisplatin sensitivity in bladder cancer

Aldehyde dehydrogenase 6 family member A1 (ALDH6A1) is a highly conserved member of aldehyde dehydrogenase (ALDHs) family. Recent studies reveal that it broadly involved in tumorigenesis and drug metabolism in kinds of cancer. However, the critical role of ALDH6A1 in bladder cancer progression and cisplatin resistance of cancer cells are still poorly understood. In this study, we researched the significant function of ALDH6A1 in bladder cancer. Our results showed that ALDH6A1 exhibited a decreased expression in clinical bladder cancer tissues and bladder cancer cell lines. Stable ALDH6A1 knockdown not only could promote cell growth and colony formation in bladder cancer cells, but also enhance drug resistance to cisplatin treatment. On the contrary, we found the active transcript factor hepatocyte nuclear factor 4α (HNF4α, NR2A1) by alveriene could upregulate ALDH6A1 expression, significantly inhibit the cell growth and colony formation of bladder cancer cells, and improve cisplatin sensitivity of bladder cancer cells. Together, our results show that ALDH6A1 plays as a tumor suppressor in bladder cancer, which regulated by HNF4a. ALDH6A1 could be a promising diagnostic marker and treatment target in bladder cancer.

A potent HNF4α agonist reveals that HNF4α controls genes important in inflammatory bowel disease and Paneth cells

HNF4α has been implicated in IBD through a number of genome-wide association studies. Recently, we developed potent HNF4α agonists, including N-trans caffeoyltyramine (NCT). NCT was identified by structural similarity to previously the previously identified but weak HNF4α agonists alverine and benfluorex. Here, we administered NCT to mice fed a high fat diet, with the goal of studying the role of HNF4α in obesity-related diseases. Intestines from NCT-treated mice were examined by RNA-seq to determine the role of HNF4α in that organ. Surprisingly, the major classes of genes altered by HNF4α were involved in IBD and Paneth cell biology. Multiple genes downregulated in IBD were induced by NCT. Paneth cells identified by lysozyme expression were reduced in high fat fed mice. NCT reversed the effect of high fat diet on Paneth cells, with multiple markers being induced, including a number of defensins, which are critical for Paneth cell function and intestinal barrier integrity. NCT upregulated genes that play important role in IBD and that are downregulated in that disease. It reversed the loss of Paneth cell markers that occurred in high fat diet fed mice. These data suggest that HNF4α could be a therapeutic target for IBD and that the agonists that we have identified could be candidate therapeutics.

Alverine citrate promotes myogenic differentiation and ameliorates muscle atrophy

Sarcopenia is the age-related loss of muscle mass and function and no pharmacological medication has been approved for its treatment. We established an atrogin-1/MAFbx promoter assay to find drug candidates that inhibit myotube atrophy. Alverine citrate (AC) was identified using high-throughput screening of an existing drug library. AC is an established medicine for stomach and intestinal spasms. AC treatment increased myotube diameter and inhibited atrophy signals induced by either C26-conditioned medium or dexamethasone in cultured C2C12 myoblasts. AC also enhanced myoblast fusion through the upregulation of fusion-related genes during C2C12 myoblast differentiation. Oral administration of AC improves muscle mass and physical performance in aged mice, as well as hindlimb-disused mice. Taken together, our data suggest that AC may be a novel therapeutic candidate for improving muscle weakness, including sarcopenia.

Long-term oral administration of an HNF4α agonist prevents weight gain and hepatic steatosis by promoting increased mitochondrial mass and function

We report here that the potent HNF4α agonist N-trans-caffeoyltyramine (NCT) promotes weight loss by inducing an increase in mitochondrial mass and function, including fatty acid oxidation. Previously, we found in a short term trial in obese mice that NCT promoted reversal of hepatic steatosis through a mechanism involving the stimulation of lipophagy by dihydroceramides. NCT led to increased dihydroceramide levels by inhibiting dihydroceramide conversion to ceramides. Here, we were able to administer NCT orally, permitting longer term administration. Mice fed NCT mixed with high fat diet exhibited decreased weight. Examination of RNA-seq data revealed an increase in PPARGC1A, a central regulator of mitochondrial biogenesis. In addition to the decreased hepatic steatosis that we found previously, mice fed a high fat diet containing NCT mice weighed substantially less than control mice fed high fat diet alone. They had increased mitochondrial mass, exhibited increased fatty acid oxidation, and had an increased level of NAD. Markers of liver inflammation such as interleukin-6 (IL-6) and tumor necrosis factor alpha (TNFα), which are important in the progression of non-alcoholic fatty liver disease to non-alcoholic steatohepatitis were decreased by NCT. There was no evidence of any toxicity from NCT consumption. These results indicate that HNF4α is an important regulator of mitochondrial mass and function and support that use of HNF4α to treat disorders of fatty acid excess, potentially including obesity, NAFLD, and NASH.

Functional gastrointestinal disorders. Overlap syndrome Clinical guidelines of the Russian Scientific Medical Society of Internal Medicine and Gastroenterological Scientific Society of Russia

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GATA binding protein 4 promotes the expression and transcription of hepatitis B virus by facilitating hepatocyte nuclear factor 4 alpha in vitro

Background

GATA binding protein 4 (GATA4) has been reported as a potential target of gene therapy for hepatocellular carcinoma (HCC). It is well known that the main cause of HCC is the chronic infection of hepatitis B virus (HBV). However, whether the effect of GATA4 on HBV has not yet been reported.

Methods

In this study, the regulation of GATA4 on HBV was analyzed in vitro. In turn, the effect of HBV on GATA4 was also observed in vitro, in vivo, and clinical HCC patients. Subsequently, we analyzed whether the effect of GATA4 on HBV was related to hepatocyte nuclear factor 4 alpha (HNF4α) in vitro.

Results

The results showed that GATA4 significantly promoted the secretion of HBV surface antigen (HBsAg) and HBV e antigen in the cell culture medium, improved the replication of HBV genomic DNA, and increased the level of HBV 3.5 kb pre-genomic RNA and HBV total RNA (P < 0.05). Moreover, it was showed that HBV had no significant effect on GATA4 in vitro and in vivo (P > 0.05). At the same time, GATA4 expression was decreased in 78.9% (15/19) of HCC patients regardless of the HBV and HBsAg status. Among them, there were 76.9% (10/13) in HBV-associated patients with HCC (HBV-HCC), and 83.3% (5/6) in non-HBV-HCC patients. In addition, the expression of HNF4α was also up-regulated or down-regulated accordingly when stimulating or interfering with the expression of GATA4. Furthermore, stimulating the expression of HNF4α could only alleviate the HBsAg level and HBV transcription levels, but had no significant effect on GATA4.

Conclusions

In summary, this study found that GATA4 has a positive effect on HBV, and the potential pathway may be related to another transcription factor HNF4α that regulates HBV.

Liver fat storage is controlled by HNF4α through induction of lipophagy and is reversed by a potent HNF4α agonist

We report the discovery of strong HNF4α agonists and their use to uncover a previously unknown pathway by which HNF4α controls the level of fat storage in the liver. This involves the induction of lipophagy by dihydroceramides, the synthesis and secretion of which is controlled by genes induced by HNF4α. The HNF4α activators are N-trans caffeoyltyramine (NCT) and N-trans feruloyltyramine (NFT), which are structurally related to the known drugs alverine and benfluorex, which we previously showed to be weak HNF4α activators. In vitro, NCT and NFT induced fat clearance from palmitate-loaded cells. In DIO mice, NCT led to recovery of hepatic HNF4α expression and reduction of steatosis. Mechanistically, increased dihydroceramide production and action downstream of HNF4α occurred through increased expression of HNF4α downstream genes, including SPNS2 and CYP26A1. NCT was completely nontoxic at the highest dose administered and so is a strong candidate for an NAFLD therapeutic.

A Novel Pharmacological Approach to Enhance the Integrity and Accelerate Restitution of the Intestinal Epithelial Barrier

BACKGROUND

Disruption of the gut barrier is an essential mechanism of inflammatory bowel diseases (IBDs) contributing to the development of mucosal inflammation. A hallmark of barrier disruption is the disassembly of epithelial adherens junctions (AJs) driven by decreased expression of a major AJ protein, E-cadherin. A group of isoxazole compounds, such as E-cadherin-upregulator (ECU) and ML327, were previously shown to stimulate E-cadherin expression in poorly differentiated human cancer cells. This study was designed to examine whether these isoxazole compounds can enhance and protect model intestinal epithelial barriers in vitro.

METHODS

The study was conducted using T84, SK-CO15, and HT-29 human colonic epithelial cell monolayers. Disruption of the epithelial barrier was induced by pro-inflammatory cytokines, tumor necrosis factor-α, and interferon-γ. Barrier integrity and epithelial junction assembly was examined using different permeability assays, immunofluorescence labeling, and confocal microscopy. Epithelial restitution was analyzed using a scratch wound healing assay.

RESULTS

E-cadherin-upregulator and ML327 treatment of intestinal epithelial cell monolayers resulted in several barrier-protective effects, including reduced steady-state epithelial permeability, inhibition of cytokine-induced barrier disruption and junction disassembly, and acceleration of epithelial wound healing. Surprisingly, these effects were not due to upregulation of E-cadherin expression but were mediated by multiple mechanisms including inhibition of junction protein endocytosis, attenuation of cytokine-induced apoptosis, and activation of promigratory Src and AKT signaling.

CONCLUSIONS

Our data highlight ECU and ML327 as promising compounds for developing new therapeutic strategies to protect the integrity and accelerate the restitution of the intestinal epithelial barrier in IBD and other inflammatory disorders.

HNF4a transcription is a target of trichloroethylene toxicity in the embryonic mouse heart

In exploration of congenital heart defects produced by TCE, Hepatocyte Nuclear Factor 4 alpha (HNF4a) transcriptional activity was identified as a central component. TCE exposure altered gene transcription in the chick heart in a non-monotonic pattern where only low dose exposure inhibited transcription by HNF4a. As the chick embryo is non-placental, we examine here HNF4a as a target of TCE in developing mouse embryos. Benfluorex and Bi6015, published agonist and antagonist, respectively, of HNF4a were compared to low dose TCE exposure. Pregnant mice were exposed to 10 ppb (76 nM) TCE, 5 μM Benfluorex, 5 μM Bi6015, or a combination of Bi6015 and TCE in drinking water. Litters (E12) were collected during a sensitive window in heart development. Embryonic hearts were collected, pooled for extraction of RNA and marker expression was examined by quantitative PCR. Multiple markers, previously identified as sensitive to TCE exposure in chicks or as published targets of HNF4a transcription were significantly affected by Benfluorex, Bi6015 and TCE. Activity of TCE and both HNF4a-specific reagents on transcription argues that HNF4a is a component of TCE cardiotoxicity and likely a proximal target of low dose exposure during development. The effectiveness of these reagents after delivery in maternal drinking water suggests that neither maternal metabolism, nor placental transport is protective of exposure.

Dimerization defective MODY mutations of hepatocyte nuclear factor 4α

HNF4α is a culprit gene product for a monogenic and dominantly-inherited form of diabetes, referred to as MODY1 (Maturity Onset Diabetes of the Young type 1). Reduced HNF4α activities have been linked to impaired insulin secretion and β-cell function. Numerous mutations have been identified from the patients and they have been instructive as to the individual residue's role in protein structure-function and dysfunction. As a member of the nuclear receptor (NR) superfamily, HNF4α is made of characteristic modular domains and it functions exclusively as a homodimer despite its sequence homology to RXR, a common heterodimer partner of non-steroidal NRs. Transcription factors commonly dimerize to enhance their molecular functions mainly by facilitating the recognition of double helix target DNAs that display an intrinsic pseudo-2-fold symmetry and the recruitment of the remainder of the main transcriptional machinery. HNF4α is no exception and its dimerization is maintained by the ligand binding domain (LBD) mainly through the leucine-zipper-like interactions at the stalk of two interacting helices. Although many MODY1 mutations have been previously characterized, including DNA binding disruptors, ligand binding disruptors, coactivator binding disruptors, and protein stability disruptors, protein dimerization disruptors have not been formally reported. In this report, we present a set of data for the two MODY1 mutations found right at the dimerization interface (L332 P and L328del mutations) which clearly exhibit the disruptive effects of directly affecting dimerization, protein stability, and transcriptional activities. These data reinforced the fact that MODY mutations are loss-of-function mutations and HNF4α dimerization is essential for its optimal function and normal physiology.

Hnf4α Is Involved in LC-PUFA Biosynthesis by Up-Regulating Gene Transcription of Elongase in Marine Teleost Siganus canaliculatus

The rabbitfish Siganus canaliculatus is the first marine teleost shown to be able to biosynthesize long-chain polyunsaturated fatty acids (LC-PUFA) from C18 PUFA precursors catalyzed by two fatty acyl desaturases (fad) including Δ4 Fad and Δ6/Δ5 Fad as well as two elongases (Elovl4 and Elovl5). Previously, hepatocyte nuclear factor 4α (Hnf4α) was demonstrated to be predominant in the transcriptional regulation of two fads. To clarify the regulatory mechanisms involved in rabbitfish lipogenesis, the present study focused on the regulatory role of Hnf4α to elovl5 expression and LC-PUFA biosynthesis. Bioinformatics analysis predicted two potential Hnf4α elements in elovl5 promoter, one binding site was confirmed to interact with Hnf4α by gel shift assays. Moreover, overexpression of hnf4α caused a remarkable increase both in elovl5 promoter activity and mRNA contents, while knock-down of hnf4α in S. canaliculatus hepatocyte line (SCHL) resulted in a significant decrease of elovl5 gene expression. Meanwhile, hnf4α overexpression enhanced LC-PUFA biosynthesis in SCHL cell, and intraperitoneal injection to rabbitfish juveniles with Hnf4α agonists (Alverine and Benfluorex) increased the expression of hnf4α, elvol5 and Δ4 fad, coupled with an increased proportion of total LC-PUFA in liver. The results demonstrated that Hnf4α is involved in LC-PUFA biosynthesis by up-regulating the transcription of the elovl5 gene in rabbitfish, which is the first report of Hnf4α as a transcription factor of the elovl5 gene in vertebrates.

Hnf4α is involved in the regulation of vertebrate LC-PUFA biosynthesis: insights into the regulatory role of Hnf4α on expression of liver fatty acyl desaturases in the marine teleost Siganus canaliculatus

Long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis is an important metabolic pathway in vertebrates, especially fish, considering they are the major source of n-3 LC-PUFA in the human diet. However, most fish have only limited capability for biosynthesis of LC-PUFA. The rabbitfish (Siganus canaliculatus) is able to synthesize LC-PUFA as it has all the key enzyme activities required including Δ6Δ5 Fads2, Δ4 Fads2, Elovl5, and Elovl4. We previously reported a direct interaction between the transcription factor Hnf4α and the promoter regions of Δ4 and Δ6Δ5 Fads2, which suggested that Hnf4α was involved in the transcriptional regulation of fads2 in rabbitfish. For functionally investigating it further, a full-length cDNA of 1736-bp-encoding rabbitfish Hnf4α with 454 amino acids was cloned, which was highly expressed in intestine, followed by liver and eyes. Similar to the expression characteristics of its target genes Δ4 and Δ6Δ5 fads2, levels of hnf4α mRNA in liver and eyes were higher in fish reared at low salinity than those reared in high salinity. After the rabbitfish primary hepatocytes were, respectively, incubated with alverine, benfluorex or BI6015, which were anticipated agonists or antagonist for Hnf4α, the mRNA level of Δ6Δ5 and Δ4 fads2 displayed a similar change tendency with that of hnf4α mRNA. Furthermore, when the mRNA level of hhf4α was knocked down using siRNA, the expression of Δ6Δ5 and Δ4 fads2 also decreased. Together, these data suggest that Hnf4α is involved in the transcriptional regulation of LC-PUFA biosynthesis, specifically, by targeting Δ4 and Δ6Δ5 fads2 in rabbitfish.

Insulin acts as a repressive factor to inhibit the ability of PAR2 to induce islet cell transdifferentiation

Recently, we showed that pancreatitis in the context of profound β-cell deficiency was sufficient to induce islet cell transdifferentiation. In some circumstances, this effect was sufficient to result in recovery from severe diabetes. More recently, we showed that the molecular mechanism by which pancreatitis induced β-cell neogenesis by transdifferentiation was activation of an atypical GPCR called Protease-Activated Receptor 2 (PAR2). However, the ability of PAR2 to induce transdifferentiation occurred only in the setting of profound β-cell deficiency, implying the existence of a repressive factor from those cells. Here we show that the repressor from β-cells is insulin. Treatment of primary islets with a PAR2 agonist (2fLI) in combination with inhibitors of insulin secretion and signaling was sufficient to induce insulin and PAX4 gene expression. Moreover, in primary human islets, this treatment also led to the induction of bihormonal islet cells coexpressing glucagon and insulin, a hallmark of islet cell transdifferentiation. Mechanistically, insulin inhibited the positive effect of a PAR2 agonist on insulin gene expression and also led to an increase in PAX4, which plays an important role in islet cell transdifferentiation. The studies presented here demonstrate that insulin represses transdifferentiation of α- to β-cells induced by activation of PAR2. This provides a mechanistic explanation for the observation that α- to β-cell transdifferentiation occurs only in the setting of severe β-cell ablation. The mechanistic understanding of islet cell transdifferentiation and the ability to modulate that process using available pharmacological reagents represents an important step along the path towards harnessing this novel mechanism of β-cell neogenesis as a therapy for diabetes.

Trichloroethylene perturbs HNF4a expression and activity in the developing chick heart

Exposure to trichloroethylene (TCE) is linked to formation of congenital heart defects in humans and animals. Prior interactome analysis identified the transcription factor, Hepatocyte Nuclear Factor 4 alpha (HNF4a), as a potential target of TCE exposure. As a role for HNF4a is unknown in the heart, we examined developing avian hearts for HNF4a expression and for sensitivity to TCE and the HNF4a agonist, Benfluorex. In vitro analysis using a HNF4a reporter construct showed both TCE and HFN4a to be antagonists of HNF4a-mediated transcription at the concentrations tested. HNF4a mRNA is expressed transiently in the embryonic heart during valve formation and cardiac development. Embryos were examined for altered gene expression in the presence of TCE or Benfluorex. TCE altered expression of selected mRNAs including HNF4a, TRAF6 and CYP2C45. There was a transition between inhibition and induction of marker gene expression in embryos as TCE concentration increased. Benfluorex was largely inhibitory to selected markers. Echocardiography of exposed embryos showed reduced cardiac function with both TCE and Benfluorex. Cardiac contraction was reduced by 29% and 23%, respectively at 10 ppb. The effects of TCE and Benfluorex on autocrine regulation of HNF4a, selected markers and cardiac function argue for a functional interaction of TCE and HNF4a. Further, the dose-sensitive shift between inhibition and induction of marker expression may explain the nonmonotonic-like dose response observed with TCE exposure in the heart.