Role of HNF4α-cMyc Interaction in CDE Diet-Induced Liver Injury and Regeneration.

Hepatocyte nuclear factor 4 alpha (HNF4α) is a nuclear factor essential for liver function that regulates the expression of cMyc and plays an important role during liver regeneration. This study investigated the role of the HNF4α-cMyc interaction in regulating liver injury and regeneration using the choline-deficient and ethionine-supplemented (CDE) diet model. Wild-type (WT), hepatocyte-specific HNF4α-knockout (KO), cMyc-KO, and HNF4α-cMyc double KO (DKO) mice were fed a CDE diet for 1 week to induce subacute liver injury. To study regeneration, normal chow diet was fed for 1 week after CDE diet. WT mice exhibited significant liver injury and decreased HNF4α mRNA and protein expression after CDE diet. HNF4α deletion resulted in significantly higher injury with increased inflammation, fibrosis, proliferation, and hepatic progenitor cell activation compared with WT mice after CDE diet but indicated similar recovery. Deletion of cMyc lowered liver injury with activation of inflammatory genes compared with WT and HNF4α-KO mice after CDE diet. DKO mice had a phenotype comparable to that of the HNF4α-KO mice after CDE diet and a complete recovery. DKO mice exhibited a significant increase in hepatic progenitor cell markers both after injury and recovery phase. Taken together, these data show that HNF4α protects against inflammatory and fibrotic changes after CDE diet-induced injury, which is driven by cMyc.

S-Adenosyl-l-ethionine is a Catalytically Competent Analog of S-Adenosyl-l-methione (SAM) in the Radical SAM Enzyme HydG.

Radical S-adenosyl-l-methionine (SAM) enzymes initiate biological radical reactions with the 5'-deoxyadenosyl radical (5'-dAdo•). A [4Fe-4S]+ cluster reductively cleaves SAM to form the Ω organometallic intermediate in which the 5'-deoxyadenosyl moiety is directly bound to the unique iron of the [4Fe-4S] cluster, with subsequent liberation of 5'-dAdo•. Here we present synthesis of the SAM analog S-adenosyl-l-ethionine (SAE) and show SAE is a mechanistically-equivalent SAM-alternative for HydG, both supporting enzymatic turnover of substrate tyrosine and forming the organometallic intermediate Ω. Photolysis of SAE bound to HydG forms an ethyl radical trapped in the active site. The ethyl radical withstands prolonged storage at 77 K and its EPR signal is only partially lost upon annealing at 100 K, making it significantly less reactive than the methyl radical formed by SAM photolysis. Upon annealing above 77K, the ethyl radical adds to the [4Fe-4S]2+ cluster, generating an ethyl-[4Fe-4S]3+ organometallic species termed ΩE.

Two-carbon folate cycle of commensal Lactobacillus reuteri 6475 gives rise to immunomodulatory ethionine, a source for histone ethylation.

Colonization of the gut by certain probiotic Lactobacillus reuteri strains has been associated with reduced risk of inflammatory diseases and colorectal cancer. Previous studies pointed to a functional link between immunomodulation, histamine production, and folate metabolism, the central 1-carbon pathway for the transfer of methyl groups. Using mass spectrometry and NMR spectroscopy, we analyzed folate metabolites of L. reuteri strain 6475 and discovered that the bacterium produces a 2-carbon-transporting folate in the form of 5,10-ethenyl-tetrahydrofolyl polyglutamate. Isotopic labeling permitted us to trace the source of the 2-carbon unit back to acetate of the culture medium. We show that the 2C folate cycle of L. reuteri is capable of transferring 2 carbon atoms to homocysteine to generate the unconventional amino acid ethionine, a known immunomodulator. When we treated monocytic THP-1 cells with ethionine, their transcription of TNF-α was inhibited and cell proliferation reduced. Mass spectrometry of THP-1 histones revealed incorporation of ethionine instead of methionine into proteins, a reduction of histone-methylation, and ethylation of histone lysine residues. Our findings suggest that the microbiome can expose the host to ethionine through a novel 2-carbon transporting variant of the folate cycle and modify human chromatin via ethylation.-Röth, D., Chiang, A. J., Hu, W., Gugiu, G. B., Morra, C. N., Versalovic, J., Kalkum, M. The two-carbon folate cycle of commensal Lactobacillus reuteri 6475 gives rise to immunomodulatory ethionine, a source for histone ethylation.

A Cholecystokinin Receptor Antagonist Halts Nonalcoholic Steatohepatitis and Prevents Hepatocellular Carcinoma.

BACKGROUND AND AIMS: Nonalcoholic steatohepatitis (NASH) is a common inflammatory liver condition that may lead to cirrhosis and hepatocellular carcinoma (HCC). Risk factors for NASH include a saturated fat diet, altered lipid metabolism, and genetic and epigenetic factors, including microRNAs. Serum levels of cholecystokinin (CCK) are elevated in mice and humans that consume a high-saturated fat diet. CCK receptors (CCK-Rs) have been reported on fibroblasts which when activated can induce fibrosis; however, their role in hepatic fibrosis remains unknown. We hypothesized that elevated levels of CCK acting on the CCK-Rs play a role in the development of NASH and in NASH-associated HCC. METHODS: We performed a NASH Prevention study and Reversal study in mice fed a saturated fat 75% choline-deficient-ethionine-supplemented (CDE) diet for 12 or 18 weeks. In each study, half of the mice received untreated drinking water, while the other half received water supplemented with the CCK-R antagonist proglumide. CCK-R expression was evaluated in mouse liver and murine HCC cells. RESULTS: CCK receptor antagonist treatment not only prevented NASH but also reversed hepatic inflammation, fibrosis, and steatosis and normalized hepatic transaminases after NASH was established. Thirty-five percent of the mice on the CDE diet developed HCC compared with none in the proglumide-treated group. We found that CCK-BR expression was markedly upregulated in mouse CDE liver and HCC cells compared with normal hepatic parenchymal cells, and this expression was epigenetically regulated by microRNA-148a. CONCLUSION: These results support the novel role of CCK receptors in the pathogenesis of NASH and HCC.

Excessive apoptosis and ROS induced by ethionine affect neural cell viability and differentiation.

The central nervous system (CNS) diseases are still a major cause of morbidity and mortality throughout the world, which imposes heavy burden on the development of society. Ethionine is a non-proteinogenic amino acid having similar chemical structure and activity to that of methionine, with which it competes. Previous studies have confirmed that ethionine affects various cellular functions by inhibiting the biosynthesis of proteins, RNA, DNA, and phospholipids, or all of them. The relationship of ethionine with some CNS diseases, including neural tube defects, has been investigated recently. However, the detailed effects of ethionine on the nerve cell bioactivities and the underlying mechanisms have not been fully explored. Herein, we systematically investigated the influences of ethionine on the proliferation, differentiation, and apoptosis of neural stem cells (NSCs) and post-mitotic nerve cells. We demonstrated that ethionine inhibited cell viability by disrupting the balance between proliferation and apoptosis, prevented NSCs from differentiating into neurons and astrocytes, and blocked cell progression from G1 to S phase via reducing cyclin D1 function in nerve cells including NSCs, a mouse hippocampal neuron cell line (HT-22), and a mouse brain neuroma cell line (Neuro-2a). We speculated that the inhibitory effect of ethionine on cell viability and differentiation are associated with increased reactive oxygen species production. Our results also supported the concept that ethionine may be an underlying cause of abnormal folate metabolism-induced CNS diseases. Our findings may provide important direction for the application of abnormal folate metabolism-induced CNS diseases in future NSC-based therapies.

Dysregulated Bile Transporters and Impaired Tight Junctions During Chronic Liver Injury in Mice.

BACKGROUND & AIMS: Liver fibrosis, hepatocellular necrosis, inflammation, and proliferation of liver progenitor cells are features of chronic liver injury. Mouse models have been used to study the end-stage pathophysiology of chronic liver injury. However, little is known about differences in the mechanisms of liver injury among different mouse models because of our inability to visualize the progression of liver injury in vivo in mice. We developed a method to visualize bile transport and blood-bile barrier (BBlB) integrity in live mice. METHODS: C57BL/6 mice were fed a choline-deficient, ethionine-supplemented (CDE) diet or a diet containing 0.1% 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) for up to 4 weeks to induce chronic liver injury. We used quantitative liver intravital microscopy (qLIM) for real-time assessment of bile transport and BBlB integrity in the intact livers of the live mice fed the CDE, DDC, or chow (control) diets. Liver tissues were collected from mice and analyzed by histology, immunohistochemistry, real-time polymerase chain reaction, and immunoblots. RESULTS: Mice with liver injury induced by a CDE or a DDC diet had breaches in the BBlB and impaired bile secretion, observed by qLIM compared with control mice. Impaired bile secretion was associated with reduced expression of several tight-junction proteins (claudins 3, 5, and 7) and bile transporters (NTCP, OATP1, BSEP, ABCG5, and ABCG8). A prolonged (2-week) CDE, but not DDC, diet led to re-expression of tight junction proteins and bile transporters, concomitant with the reestablishment of BBlB integrity and bile secretion. CONCLUSIONS: We used qLIM to study chronic liver injury, induced by a choline-deficient or DDC diet, in mice. Progression of chronic liver injury was accompanied by loss of bile transporters and tight junction proteins.

Mitochondrial Dysfunction, Through Impaired Autophagy, Leads to Endoplasmic Reticulum Stress, Deregulated Lipid Metabolism, and Pancreatitis in Animal Models.

BACKGROUND & AIMS: Little is known about the signaling pathways that initiate and promote acute pancreatitis (AP). The pathogenesis of AP has been associated with abnormal increases in cytosolic Ca2+, mitochondrial dysfunction, impaired autophagy, and endoplasmic reticulum (ER) stress. We analyzed the mechanisms of these dysfunctions and their relationships, and how these contribute to development of AP in mice and rats. METHODS: Pancreatitis was induced in C57BL/6J mice (control) and mice deficient in peptidylprolyl isomerase D (cyclophilin D, encoded by Ppid) by administration of L-arginine (also in rats), caerulein, bile acid, or an AP-inducing diet. Parameters of pancreatitis, mitochondrial function, autophagy, ER stress, and lipid metabolism were measured in pancreatic tissue, acinar cells, and isolated mitochondria. Some mice with AP were given trehalose to enhance autophagic efficiency. Human pancreatitis tissues were analyzed by immunofluorescence. RESULTS: Mitochondrial dysfunction in pancreas of mice with AP was induced by either mitochondrial Ca2+ overload or through a Ca2+ overload-independent pathway that involved reduced activity of ATP synthase (80% inhibition in pancreatic mitochondria isolated from rats or mice given L-arginine). Both pathways were mediated by cyclophilin D and led to mitochondrial depolarization and fragmentation. Mitochondrial dysfunction caused pancreatic ER stress, impaired autophagy, and deregulation of lipid metabolism. These pathologic responses were abrogated in cyclophilin D-knockout mice. Administration of trehalose largely prevented trypsinogen activation, necrosis, and other parameters of pancreatic injury in mice with L-arginine AP. Tissues from patients with pancreatitis had markers of mitochondrial damage and impaired autophagy, compared with normal pancreas. CONCLUSIONS: In different animal models, we find a central role for mitochondrial dysfunction, and for impaired autophagy as its principal downstream effector, in development of AP. In particular, the pathway involving enhanced interaction of cyclophilin D with ATP synthase mediates L-arginine-induced pancreatitis, a model of severe AP the pathogenesis of which has remained unknown. Strategies to restore mitochondrial and/or autophagic function might be developed for treatment of AP.

ß-Arrestin1 alleviates acute pancreatitis via repression of NF-κBp65 activation.

BACKGROUND AND AIM: ß-Arrestins (ß-arrs) are regulators and mediators of G protein-coupled receptor signaling that are functionally involved in inflammation. Nuclear factor-κB p65 (NF-κBp65) activation has been observed early in the onset of pancreatitis. However, the effect of ß-arrs in acute pancreatitis (AP) is unclear. The aim of this study is to investigate whether ß-arrs are involved in AP through activation of NF-κBp65. METHODS: Acute pancreatitis was induced by either caerulein injection or choline-deficient supplemented with ethionine diet (CDE). ß-arr1 wild-type and ß-arr1 knockout mice were used in the experiment. The survival rate was calculated in the CDE model mice. Histological and western blot analyses were performed in the caerulein model. Inflammatory mediators were detected by real-time polymerase chain reaction in the caerulein-induced AP mice. Furthermore, AR42J and PANC-1 cell lines were used to further study the effects of ß-arr1 in caerulein-induced pancreatic cells. RESULTS: ß-Arr1 but not ß-arr2 is significantly downregulated in caerulein-induced AP in mice. Targeted deletion of ß-arr1 notably upregulated expression of the pancreatic inflammatory mediators including tumor necrosis factor α and interleukin 1ß as well as interleukin 6 and aggravated AP in caerulein-induced mice. ß-Arr1 deficiency increased mortality in mice with CDE-induced AP. Further, ß-arr1 deficiency enhanced caerulein-induced phosphorylation of NF-κBp65 both in vivo and in vitro. CONCLUSION: ß-Arr1 alleviates AP via repression of NF-κBp65 activation, and it is a potentially therapeutic target for AP.

Loss of trefoil factor 1 inhibits biliary regeneration but accelerates the hepatic differentiation of progenitor cells in mice.

Although the regeneration of the adult liver depends on hepatic progenitor cells (HPCs), many uncertainties regarding hepatic regeneration in the injured liver remain. Trefoil factor family 1 (TFF1), a secretory protein predominantly expressed in the gastrointestinal tract, is responsible for mucosal restitution. Here, we investigated the role of TFF1 in liver regeneration using a mouse model of hepatic injury (choline-deficient ethionine-supplemented diet and carbon tetrachloride administration) and genetically engineered mice (TFF1 knockout (TFF1-/-)). Immunohistochemistry analysis of human liver samples revealed TFF1 expression in the hepatocytes close to ductular reaction and the regenerating biliary epithelium in injured liver. The number of cytokeratin 19 (CK19)-positive bile ducts was significantly decreased in the TFF1-/- mice after liver injury. Notch pathway in the TFF1-/- mice was also downregulated. HPCs in the control mice differentiated into biliary cells (CK19+/SRY HMG box 9 (SOX9)+) more frequently. In contrast, HPCs in the TFF1-/- mice more frequently differentiated into a hepatic lineage (alpha fetoprotein+/SOX9+) after acute liver damage. Hepatocyte proliferation was upregulated, and the liver weight was increased in TFF1-/- mice in response to chronic liver damage. Thus, TFF1 is responsible for liver regeneration after liver injury by promoting HPC differentiation into a biliary lineage and inhibiting HPC differentiation into a hepatic lineage.

Clusterin and Pycr1 alterations associate with strain and model differences in susceptibility to experimental pancreatitis.

Acute pancreatitis has several underlying etiologies, and results in consequences ranging from mild to complex multi-organ failure. The wide range of pathology suggests a genetic predisposition for progression. We compared the susceptibility to acute pancreatitis in BALB/c and FVB/N mice, coupled with proteomic analysis, in order to identify potential protein associations with pancreatitis progression. METHODS: Pancreatitis was induced in BALB/c and FVB/N mice by administration of cerulein or feeding a choline-deficient, ethionine-supplemented (CDE) diet. Histology and changes in serum amylase were examined. Proteome profiling in cerulein-treated mice was performed using 2-dimensional differential in gel electrophoresis (2D-DIGE) followed by mass spectrometry analysis and biochemical validation. RESULTS: Male and female FVB/N mice manifested more severe cerulein-induced pancreatitis as compared with BALB/c mice, but both strains were similarly susceptible to CDE-induced pancreatitis. Few of the 2D-DIGE alterations were validated by immunoblotting. Clusterin was markedly up-regulated after cerulein-induced pancreatitis in FVB/N but less-so in BALB/c mice. Pyrroline-5-carboxylate reductase (Pycr1), an enzyme involved in proline biosynthesis, had higher basal levels in FVB/N male and female mouse pancreata compared with BALB/c pancreata, and was relatively more resistant to degradation in FVB/N pancreata. However, serum and pancreas tissue proline levels were similar in the two strains. CONCLUSION: FVB/N is more susceptible than BALB/c mice to cerulein-induced but not CDE-induced pancreatitis. Most of the 2D-DIGE alterations in the two strains likely relate to posttranslational modifications rather than protein level differences. Clusterin levels increase dramatically in association with pancreatitis severity, while Pycr1 is higher in FVB/N versus BALB/c pancreata basally and after induction of pancreatitis. Changes in proline metabolism may represent a novel potential genetic modifier in the context of pancreatitis.

Capturing Unknown Substrates via in Situ Formation of Tightly Bound Bisubstrate Adducts: S-Adenosyl-vinthionine as a Functional Probe for AdoMet-Dependent Methyltransferases.

Identifying an enzyme's substrates is essential to understand its function, yet it remains challenging. A fundamental impediment is the transient interactions between an enzyme and its substrates. In contrast, tight binding is often observed for multisubstrate-adduct inhibitors due to synergistic interactions. Extending this venerable concept to enzyme-catalyzed in situ adduct formation, unknown substrates were affinity-captured by an S-adenosyl-methionine (AdoMet, SAM)-dependent methyltransferase (MTase). Specifically, the electrophilic methyl sulfonium (alkyl donor) in AdoMet is replaced with a vinyl sulfonium (Michael acceptor) in S-adenosyl-vinthionine (AdoVin). Via an addition reaction, AdoVin and the nucleophilic substrate form a covalent bisubstrate-adduct tightly complexed with thiopurine MTase (2.1.1.67). As such, an unknown substrate was readily identified from crude cell lysates. Moreover, this approach is applicable to other systems, even if the enzyme is unknown.

Ablation of Foxl1-Cre-labeled hepatic progenitor cells and their descendants impairs recovery of mice from liver injury.

BACKGROUND & AIMS: Foxl1(+) hepatic progenitor cells (HPCs) differentiate into cholangiocytes and hepatocytes after liver injury. We investigated the requirement for Foxl1(+) HPCs in recovery from liver injury in mice. METHODS: We developed mice in which we could trace and delete Foxl1-expressing HPCs and their descendants (Foxl1-Cre;Rosa(YFP/iDTR)-inducible diphtheria toxin receptor [iDTR] mice). Foxl1-Cre-negative mice were used as controls. Liver damage was induced in male mice by placing them on choline-deficient, ethionine-supplemented (CDE) diets for 15 days; mice then were placed on normal diets and allowed to recover. Liver damage was induced in female mice by placing them on 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-containing diets, followed by a recovery period. Some mice were given injections of diphtheria toxin during the recovery phase to delete Foxl1-Cre-marked HPCs and their descendants. Livers were collected from all mice and analyzed by immunofluorescence, quantitative reverse-transcription polymerase chain reaction, flow cytometry, and histologic analyses. RESULTS: Foxl1-Cre-marked HPCs were required for the development of cholangiocytes and hepatocytes in livers after CDE diet-induced injury. A smaller percentage of yellow fluorescent protein-positive (YFP(+)) hepatocytes contained markers of oxidative stress, DNA damage, or cell death than YFP-negative hepatocytes, indicating that YFP(+) hepatocytes are newly formed cells. Injection of diphtheria toxin deleted YFP(+) cells from Foxl1-Cre;Rosa(YFP/iDTR) mice and prevented the resolution of hepatic steatosis. In mice recovering from DDC diet-induced injury, most cholangiocytes arose from Foxl1-Cre-marked HPCs. Deletion of YFP(+) cells did not alter levels of markers of liver injury or liver function. CONCLUSIONS: Based on studies of Foxl1-Cre;Rosa(YFP/iDTR) mice, Foxl1(+) HPCs and/or their descendants are required for the development of cholangiocytes and hepatocytes in liver after CDE diet-induced injury.

Imatinib accelerates progenitor cell-mediated liver regeneration in choline-deficient ethionine-supplemented diet-fed mice.

Severe chronic hepatic injury can induce complex reparative processes. Ductular reaction and the appearance of small hepatocytes are standard components of this response, which is thought to have both adverse (e.g. fibrosis, carcinogenesis) and beneficial (regeneration) consequences. This complex tissue reaction is regulated by orchestrated cytokine action. We have investigated the influence of the tyrosine kinase inhibitor imatinib on a regenerative process. Ductular reaction was induced in mice by the widely used choline-deficient ethionine-supplemented diet (CDE). Test animals were treated daily with imatinib. After 6 weeks of treatment, imatinib successfully reduced the extent of ductular reaction and fibrosis in the CDE model. Furthermore, the number of small hepatocytes increased, and these cells had high proliferative activity, were positive for hepatocyte nuclear factor 4 and expressed high levels of albumin and peroxisome proliferator-activated receptor alpha. The overall functional zonality of the hepatic parenchyma (cytochrome P450 2E1 and glucose 6 phosphatase activity; endogenous biotin content) was maintained. The expression of platelet-derived growth factor receptor beta, which is the major target of imatinib, was downregulated. The anti-fibrotic activity of imatinib has already been reported in several experimental models. Additionally, in the CDE model imatinib was able to enhance regeneration and preserve the functional arrangement of hepatic lobules. These results suggest that imatinib might promote the recovery of the liver following parenchymal injury through the inhibition of platelet-derived growth factor receptor beta.

Intriguing cellular processing of a fluorinated amino acid during protein biosynthesis in Escherichia coli.

Bioincorporation of the methionine analogue S-(2-fluoroethyl)-l-homocysteine (l-MFE) into bacteriophage lysozyme overproduced in Escherichia coli results not only in the expected l-MFE incorporation but surprisingly substantial l-vinthionine incorporation into the labeled lysozymes. Synthetic l-vinthionine itself however is not activated by purified Escherichia coli methionyl-tRNA synthetase. The indirect preparation of vinthionine-containing proteins has the potential to be an alternate strategy to prepare vinyl thioether moieties for click chemistry applications on proteins.

Loss of keratin 19 favours the development of cholestatic liver disease through decreased ductular reaction.

Keratins (K) are cytoprotective proteins and keratin mutations predispose to the development of multiple human diseases. K19 represents the most widely used marker of biliary and hepatic progenitor cells as well as a marker of ductular reaction that constitutes the basic regenerative response to chronic liver injury. In the present study, we investigated the role of K19 in biliary and hepatic progenitor cells and its importance for ductular reaction. K19 wild-type (WT) and knockout (KO) mice were fed: (a) 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC); (b) cholic acid (CA); (c) a choline-deficient, ethionine-supplemented (CDE) diet; or (d) were subjected to common bile duct ligation (CBDL). The bile composition, liver damage, bile duct proliferation, oval cell content and biliary fibrosis were analysed. In untreated animals, loss of K19 led to redistribution of the K network in biliary epithelial cells (BECs) but to no obvious biliary phenotype. After DDC feeding, K19 KO mice exhibited (compared to WTs): (a) increased cholestasis; (b) less pronounced ductular reaction with reduced ductular proliferation and fewer oval cells; (c) impaired Notch 2 signalling in BECs; (d) lower biliary fibrosis score and biliary bicarbonate concentration. An attenuated oval cell proliferation in K19 KOs was also found after feeding with the CDE diet. K19 KOs subjected to CBDL displayed lower BEC proliferation, oval cell content and less prominent Notch 2 signal. K19 deficiency did not change the extent of CA- or CBDL-induced liver injury and fibrosis. Our results demonstrate that K19 plays an important role in the ductular reaction and might be of importance in multiple chronic liver disorders that frequently display a ductular reaction.

Programmed Effects in Neurobehavior and Antioxidative Physiology in Zebrafish Embryonically Exposed to Cadmium: Observations and Hypothesized Adverse Outcome Pathway Framework.

Non-communicable diseases (NCDs) are a major cause of premature mortality. Recent studies show that predispositions for NCDs may arise from early-life exposure to low concentrations of environmental contaminants. This developmental origins of health and disease (DOHaD) paradigm suggests that programming of an embryo can be disrupted, changing the homeostatic set point of biological functions. Epigenetic alterations are a possible underlying mechanism. Here, we investigated the DOHaD paradigm by exposing zebrafish to subtoxic concentrations of the ubiquitous contaminant cadmium during embryogenesis, followed by growth under normal conditions. Prolonged behavioral responses to physical stress and altered antioxidative physiology were observed approximately ten weeks after termination of embryonal exposure, at concentrations that were 50-3200-fold below the direct embryotoxic concentration, and interpreted as altered developmental programming. Literature was explored for possible mechanistic pathways that link embryonic subtoxic cadmium to the observed apical phenotypes, more specifically, the probability of molecular mechanisms induced by cadmium exposure leading to altered DNA methylation and subsequently to the observed apical phenotypes. This was done using the adverse outcome pathway model framework, and assessing key event relationship plausibility by tailored Bradford-Hill analysis. Thus, cadmium interaction with thiols appeared to be the major contributor to late-life effects. Cadmium-thiol interactions may lead to depletion of the methyl donor S-adenosyl-methionine, resulting in methylome alterations, and may, additionally, result in oxidative stress, which may lead to DNA oxidation, and subsequently altered DNA methyltransferase activity. In this way, DNA methylation may be affected at a critical developmental stage, causing the observed apical phenotypes.

The role of surface electrostatics on the stability, function and regulation of human cystathionine ß-synthase, a complex multidomain and oligomeric protein.

Human cystathionine ß-synthase (hCBS) is a key enzyme of sulfur amino acid metabolism, controlling the commitment of homocysteine to the transsulfuration pathway and antioxidant defense. Mutations in hCBS cause inherited homocystinuria (HCU), a rare inborn error of metabolism characterized by accumulation of toxic homocysteine in blood and urine. hCBS is a complex multidomain and oligomeric protein whose activity and stability are independently regulated by the binding of S-adenosyl-methionine (SAM) to two different types of sites at its C-terminal regulatory domain. Here we study the role of surface electrostatics on the complex regulation and stability of hCBS using biophysical and biochemical procedures. We show that the kinetic stability of the catalytic and regulatory domains is significantly affected by the modulation of surface electrostatics through noticeable structural and energetic changes along their denaturation pathways. We also show that surface electrostatics strongly affect SAM binding properties to those sites responsible for either enzyme activation or kinetic stabilization. Our results provide new insight into the regulation of hCBS activity and stability in vivo with implications for understanding HCU as a conformational disease. We also lend experimental support to the role of electrostatic interactions in the recently proposed binding modes of SAM leading to hCBS activation and kinetic stabilization.

Opposite effects of GPR120 and GPR40 on cell motile activity induced by ethionine in liver epithelial cells.

Free fatty acids (FFAs) are dietary nutrients which act as ligands for FFAs receptors. G-protein-coupled receptor 120 (GPR120) and GPR40 are activated by long and medium chain FFAs. In the present study, we investigated the role of the GPR120 and GPR40 in cell motile activity stimulated by ethionine in rat liver epithelial WB-F344 cells. Cells were treated with ethionine at a concentration of 10µM every 24h for 2days. The expression levels of the Gpr120 and Gpr40 genes in WB-F344 cells treated ethionine were significantly higher than those in untreated cells. In cell motility assay, the cell motile activity of WB-F344 cells was markedly elevated by ethionine, compared with untreated cells. To evaluate the effects of GPR120 on the cell motile activity by ethionine, we established GPR120 knockdown cells from WB-F344 cells. The cell motile activity stimulated by ethionine was significantly suppressed by GPR120 knockdown. In addition, a potent GPR40 antagonist GW1100 enhanced the cell motile activity by ethionine. These results suggest that opposite effects of GPR120 and GPR40 may be involved in the cell motile activity stimulated by ethionine in WB-F344 cells.

Bmi1 is required for regeneration of the exocrine pancreas in mice.

BACKGROUND & AIMS: Bmi1 is a member of the Polycomb protein family and represses transcription by modifying chromatin organization at specific promoters. Bmi1 is implicated in the control of stem cell self-renewal and has been shown to regulate cell proliferation, tissue homeostasis, and differentiation. Bmi1 is present in a subpopulation of self-renewing pancreatic acinar cells and is expressed in response to pancreatic damage. We investigated the role of Bmi1 in regeneration of exocrine pancreas. METHODS: Acute pancreatitis was induced in Bmi1(-/-) mice with cerulein; pancreatic cell regeneration, differentiation, and apoptosis were assessed. Cultured Bmi1(-/-) and wild-type primary acini were analyzed in vitro to determine acinar-specific consequences of Bmi1 deletion. To investigate cell autonomous versus non-cell autonomous roles for Bmi1 in vivo, pancreatitis was induced in Bmi1(-/-) mice reconstituted with a wild-type hematopoietic system. RESULTS: Bmi1 expression was up-regulated in the exocrine pancreas during regeneration after cerulein-induced pancreatitis. Exocrine regeneration was impaired following administration of cerulein to Bmi1(-/-) mice. Pancreata of Bmi1(-/-) mice were hypoplastic, and the exocrine pancreas was replaced with ductal metaplasia that had increased apoptosis and decreased cell proliferation compared with that of wild-type mice. Expression of Cdkn2a and p53-dependent apoptotic genes was markedly up-regulated in Bmi1(-/-) pancreas compared with wild-type mice after injury. Furthermore, after transplantation of bone marrow from wild-type to Bmi1(-/-) mice, the chimeric mice had intermediate levels of pancreatic hypoplasia and significant but incomplete rescue of impaired exocrine regeneration after cerulein injury. CONCLUSIONS: Bmi1 contributes to regeneration of the exocrine pancreas after cerulein-induced injury through cell autonomous mechanisms, in part by regulating Cdkn2a expression, and non-cell autonomous mechanisms.

Propranolol, a ß-adrenoceptor antagonist, worsens liver injury in a model of non-alcoholic steatohepatitis.

Prazosin an α1-adrenoceptor (AR) antagonist has been shown to reduce liver injury in a mouse model of non-alcoholic steatohepatitis (NASH) and is suggested as a potential treatment of NASH especially given its concomitant anti-fibrotic properties. The effect however, of ß-AR blockade in non-cirrhotic NASH is unknown and is as such investigated here. In the presence of the ß-blocker propranolol (PRL), mice fed normal chow or a half methionine and choline deficient diet, supplemented with ethionine (HMCDE), to induce NASH, showed significantly enhanced liver injury, as evidenced by higher hepatic necrosis scores and elevated serum aminotransferases (ALT). Mechanistically, we showed that murine hepatocytes express α and ß adrenoceptors; that PRL directly induces hepatocyte injury and death as evidenced by increased release of lactate dehydrogenase, FASL and TNF-α from hepatocytes in the presence of PRL; and that PRL activated the apoptotic pathway in primary hepatocyte cultures, as indicated by upregulation of Fas receptor and caspase-8 proteins. The ß-AR antagonist PRL therefore appears to enhance liver injury through induction of hepatocyte death via the death pathway. Further studies are now required to extrapolate these findings to humans but meanwhile, ß-AR antagonists should be avoided or used with caution in patients with non-cirrhotic NASH as they may worsen liver injury.