Bile acid stimulation of early growth response gene and mitogen-activated protein kinase is protein kinase C-dependent

Loss of SLC27A5 Activates Hepatic Stellate Cells and Promotes Liver Fibrosis via Unconjugated Cholic Acid

Although the dysregulation of bile acid (BA) composition has been associated with fibrosis progression, its precise roles in liver fibrosis is poorly understood. This study demonstrates that solute carrier family 27 member 5 (SLC27A5), an enzyme involved in BAs metabolism, is substantially downregulated in the liver tissues of patients with cirrhosis and fibrosis mouse models. The downregulation of SLC27A5 depends on RUNX family transcription factor 2 (RUNX2), which serves as a transcriptional repressor. The findings reveal that experimental SLC27A5 knockout (Slc27a5-/- ) mice display spontaneous liver fibrosis after 24 months. The loss of SLC27A5 aggravates liver fibrosis induced by carbon tetrachloride (CCI4 ) and thioacetamide (TAA). Mechanistically, SLC27A5 deficiency results in the accumulation of unconjugated BA, particularly cholic acid (CA), in the liver. This accumulation leads to the activation of hepatic stellate cells (HSCs) by upregulated expression of early growth response protein 3 (EGR3). The re-expression of hepatic SLC27A5 by an adeno-associated virus or the reduction of CA levels in the liver using A4250, an apical sodium-dependent bile acid transporter (ASBT) inhibitor, ameliorates liver fibrosis in Slc27a5-/- mice. In conclusion, SLC27A5 deficiency in mice drives hepatic fibrosis through CA-induced activation of HSCs, highlighting its significant implications for liver fibrosis treatment.

Mechanism of Bile Acid-Induced Programmed Cell Death and Drug Discovery against Cancer: A Review

Bile acids are major signaling molecules that play a significant role as emulsifiers in the digestion and absorption of dietary lipids. Bile acids are amphiphilic molecules produced by the reaction of enzymes with cholesterol as a substrate, and they are the primary metabolites of cholesterol in the body. Bile acids were initially considered as tumor promoters, but many studies have deemed them to be tumor suppressors. The tumor-suppressive effect of bile acids is associated with programmed cell death. Moreover, based on this fact, several synthetic bile acid derivatives have also been used to induce programmed cell death in several types of human cancers. This review comprehensively summarizes the literature related to bile acid-induced programmed cell death, such as apoptosis, autophagy, and necroptosis, and the status of drug development using synthetic bile acid derivatives against human cancers. We hope that this review will provide a reference for the future research and development of drugs against cancer.

The Nuclear Farnesoid X Receptor Reduces p53 Ubiquitination and Inhibits Cervical Cancer Cell Proliferation

The role of farnesoid X receptor (FXR) in cervical cancer and the underlying molecular mechanism remain largely unknown. Therefore, this study aimed to assess the mechanism of FXR in cervical cancer. Western blot, qRT-PCR, and immunohistochemistry demonstrated that FXR was significantly reduced in squamous cell carcinoma tissues, although there were no associations of metastasis and TNM stage with FXR. In Lenti-FXR cells obtained by lentiviral transfection, the overexpression of FXR reduced cell viability and colony formation. Compared with the Lenti-Vector groups, the overexpression of FXR induced early and late apoptosis and promoted G1 arrest. With time, early apoptosis decreased, and late apoptosis increased. In tumor xenograft experiments, overexpression of FXR upregulated small heterodimer partner (SHP), murine double minute-2 (MDM2), and p53 in the nucleus. Co-immunoprecipitation (Co-IP) showed that SHP directly interacted with MDM2, which is important to protect p53 from ubiquitination. Nutlin3a increased MDM2 and p53 amounts in the Lenti-Vector groups, without effects in the Lenti-FXR groups. Silencing SHP reduced MDM2 and p53 levels in the Lenti-FXR groups, and Nutlin3a counteracted these effects. Taken together, these findings suggest that FXR inhibits cervical cancer via upregulation of SHP, MDM2, and p53.

Conjugated secondary 12α-hydroxylated bile acids promote liver fibrogenesis

BACKGROUND

Significantly elevated serum and hepatic bile acid (BA) concentrations have been known to occur in patients with liver fibrosis. However, the roles of different BA species in liver fibrogenesis are not fully understood.

METHODS

We quantitatively measured blood BA concentrations in nonalcoholic steatohepatitis (NASH) patients with liver fibrosis and healthy controls. We characterized BA composition in three mouse models induced by carbon tetrachloride (CCl4), streptozotocin-high fat diet (STZ-HFD), and long term HFD, respectively. The molecular mechanisms underlying the fibrosis-promoting effects of BAs were investigated in cell line models, a 3D co-culture system, and a Tgr5 (HSC-specific) KO mouse model.

FINDINGS

We found that a group of conjugated 12α-hydroxylated (12α-OH) BAs, such as taurodeoxycholate (TDCA) and glycodeoxycholate (GDCA), significantly increased in NASH patients and liver fibrosis mouse models. 12α-OH BAs significantly increased HSC proliferation and protein expression of fibrosis-related markers. Administration of TDCA and GDCA directly activated HSCs and promoted liver fibrogenesis in mouse models. Blockade of BA binding to TGR5 or inhibition of ERK1/2 and p38 MAPK signaling both significantly attenuated the BA-induced fibrogenesis. Liver fibrosis was attenuated in mice with Tgr5 depletion.

INTERPRETATION

Increased hepatic concentrations of conjugated 12α-OH BAs significantly contributed to liver fibrosis via TGR5 mediated p38MAPK and ERK1/2 signaling. Strategies to antagonize TGR5 or inhibit ERK1/2 and p38 MAPK signaling may effectively prevent or reverse liver fibrosis.

FUNDINGS

This study was supported by the National Institutes of Health/National Cancer Institute Grant 1U01CA188387-01A1, the National Key Research and Development Program of China (2017YFC0906800); the State Key Program of National Natural Science Foundation (81430062); the National Natural Science Foundation of China (81974073, 81774196), China Postdoctoral Science Foundation funded project, China (2016T90381), and E-institutes of Shanghai Municipal Education Commission, China (E03008).

Bile acids and stellate cells

Hepatic stellate cells are mainly known for their contribution to fibrogenesis in chronic liver diseases, but their identity and function in normal liver remain unclear. They were recently identified as liver-resident mesenchymal stem cells (MSCs), which can differentiate not only into adipocytes and osteocytes, but also into liver epithelial cells such as hepatocytes and bile duct cells as investigated in vitro and in vivo. During hepatic differentiation, stellate cells and other MSCs transiently develop into liver progenitor cells with epithelial characteristics before hepatocytes are established. Transplanted stellate cells from the liver and pancreas are able to contribute to liver regeneration in stem cell-based liver injury models and can also home into the bone marrow, which is in line with their classification as MSCs. There is experimental evidence that bile acids support liver regeneration and are able to activate signaling pathways in hepatic stellate cells. For this reason, it is important to analyze the influence of bile acids on developmental fate decisions of hepatic stellate cells and other MSC populations.

Diurnal regulation of the early growth response 1 (Egr-1) protein expression by hepatocyte nuclear factor 4alpha (HNF4alpha) and small heterodimer partner (SHP) cross-talk in liver fibrosis

Early growth response 1 (Egr-1) protein is a critical regulator of genes contributing to liver fibrosis; however, little is known about the upstream transcriptional factors that control its expression. Here we show that Egr-1 expression is tightly regulated by nuclear receptor signaling. Hepatocyte nuclear factor 4α (HNF4α) activated the Egr-1 promoter through three DR1 response elements as identified by trans-activation assays. Deletion of these response elements or knockdown of HNF4α using siRNA largely abrogated Egr-1 promoter activation. HNF4α activity, as well as its enrichment on the Egr-1 promoter, were markedly repressed by small heterodimer partner (SHP) co-expression. Egr-1 mRNA and protein were transiently induced by HNF4α. On the contrary, HNF4α siRNA reduced Egr-1 expression at both the mRNA and protein levels, and overexpression of SHP reversed these effects. Conversely, knockdown of SHP by siRNA elevated Egr-1 protein. Interestingly, Egr-1 mRNA exhibited diurnal fluctuation, which was synchronized to the cyclic expression of SHP and HNF4α after cells were released from serum shock. Unexpectedly, the levels of Egr-1 mRNA and protein were highly up-regulated in Hnf4α(-/-) mice. Both HNF4α and Egr-1 expression were dramatically increased in SHP(-/-) mice with bile duct ligation and in human cirrhotic livers, which was inversely correlated with diminished SHP expression. In conclusion, our study revealed control network for Egr-1 expression through a feedback loop between SHP and HNF4α.

Inflammatory pseudo-tumor of the liver: a rare pathological entity

Inflammatory pseudo-tumor (IPT) of the liver is a rare benign neoplasm and is often mistaken as a malignant entity. Few cases have been reported in the literature and the precise etiology of inflammatory pseudotumor remains unknown. Patients usually present with fever, abdominal pain and jaundice. The proliferation of spindled myofibroblast cells mixed with variable amounts of reactive inflammatory cells is characteristics of IPT. We reviewed the literature regarding possible etiology for IPT with a possible suggested etiology.

Biliary acute pancreatitis in mice is mediated by the G-protein-coupled cell surface bile acid receptor Gpbar1

BACKGROUND & AIMS

The mechanisms by which reflux of bile acids into the pancreas induces pancreatitis are unknown. We reasoned that key events responsible for this phenomenon might be mediated by Gpbar1, a recently identified and widely expressed G-protein-coupled, cell surface bile acid receptor.

METHODS

Acute pancreatitis was induced in wild-type and Gpbar1(-/-) mice by either retrograde ductal infusion of taurolithocholic acid-3-sulfate (TLCS) or supramaximal secretagogue stimulation with caerulein. In vitro experiments were performed in which acini obtained from wild-type and Gpbar1(-/-) mice were exposed to either submicellar concentrations of TLCS (200-500 microM) or a supramaximally stimulating concentration of caerulein (10 nM).

RESULTS

Gpbar1 is expressed at the apical pole of acinar cells and its genetic deletion is associated with reduced hyperamylasemia, edema, inflammation, and acinar cell injury in TLCS-induced, but not caerulein-induced, pancreatitis. In vitro, genetic deletion of Gpbar1 is associated with markedly reduced generation of pathological calcium transients, intracellular activation of digestive zymogens, and cell injury when these responses are induced by exposure to TLCS, but not when they are induced by exposure to caerulein.

CONCLUSIONS

Gpbar1 may play a critical role in the evolution of bile-acid-induced pancreatitis by coupling exposure to bile acids with generation of pathological intracellular calcium transients, intra-acinar cell zymogen activation, and acinar cell injury. Acute biliary pancreatitis may be a "receptor-mediated" disease and interventions that interfere with Gpbar1 function might prove beneficial in the treatment and/or prevention of biliary acute pancreatitis.

Bile acids inhibit NAD+-dependent 15-hydroxyprostaglandin dehydrogenase transcription in colonocytes

Multiple lines of evidence have suggested a role for both bile acids and prostaglandins (PG) in gastrointestinal carcinogenesis. Levels of PGE(2) are determined by both synthesis and catabolism. Previously, bile acid-mediated induction of cyclooxygenase-2 (COX-2) was found to stimulate PGE(2) synthesis. NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH), the key enzyme responsible for the catabolism of PGE(2), has been linked to colorectal carcinogenesis. In this study, we determined whether bile acids altered the expression of 15-PGDH in human colon cancer cell lines. Treatment with unconjugated bile acids (chenodeoxycholate and deoxycholate) suppressed the transcription of 15-PGDH, resulting in reduced amounts of 15-PGDH mRNA, protein, and enzyme activity. Conjugated bile acids were less potent suppressors of 15-PGDH expression than unconjugated bile acids. Treatment with chenodeoxycholate activated protein kinase C (PKC), leading in turn to increased extracellular signal-regulated kinase (ERK) 1/2 activity. Small molecules that inhibited bile acid-mediated activation of PKC and ERK1/2 also blocked the downregulation of 15-PGDH. Bile acids induced early growth response factor-1 (Egr-1) and Snail, a repressive transcription factor that bound to the 15-PGDH promoter. Silencing Egr-1 or Snail blocked chenodeoxycholate-mediated downregulation of 15-PGDH. Together, these data indicate that bile acids activate the signal transduction pathway PKC --> ERK1/2 --> Egr-1 --> Snail and thereby suppress 15-PGDH transcription. Bile acids appear to increase the release of PGs from cells by downregulating catabolism in addition to stimulating synthesis. These results provide new mechanistic insights into the link between bile acids and gastrointestinal carcinogenesis.

Divergent transforming growth factor-beta signaling in hepatic stellate cells after liver injury: functional effects on ECE-1 regulation

In liver wound healing, transforming growth factor-beta (TGF-beta) plays a critical role in stellate cell activation as well as signaling cascades in the fibrogenic response to injury. We postulate that the TGF-beta-dependent downstream signaling pathway may vary according to the mechanism of stellate cell activation; this study was undertaken to ascertain whether the downstream signaling pathways mediated by TGF-beta vary in different liver injury models. We measured Smad3 and MAP kinase activation after isolating stellate cells from rat livers injured by either bile duct ligation (BDL) or repeated carbon tetrachloride (CCl(4)) administration. Phospho-Smad3 was dramatically up-regulated in stellate cells after CCl(4) injury, but not after BDL-induced injury. TGF-beta signaling in stellate cells activated after BDL was mediated prominently through ERK activation, whereas activation induced by CCl(4) injury or culture led to a cross-signaling mechanism involving both Smad3 and p38. The divergent Smad signaling pathways observed appeared to be attributable to the differential regulation of the early growth response gene-1 (Egr-1), an apparent negative transcriptional factor for Smad3 in our system. In addition, inhibition of ERK activation in stellate cells from BDL-injured liver led to a decrease in expression of endothelin-converting enzyme-1, a critical regulator of endothelin-1. We speculate that TGF-beta signaling proceeds through differential signaling pathways depending on the mechanism of liver injury that leads to stellate cell activation.

NIM811 (N-methyl-4-isoleucine cyclosporine), a mitochondrial permeability transition inhibitor, attenuates cholestatic liver injury but not fibrosis in mice

Cholestasis causes hepatocyte death, possibly because of mitochondrial injury. This study investigated whether NIM811 (N-methyl-4-isoleucine cyclosporine), an inhibitor of the mitochondrial permeability transition (MPT), attenuates cholestatic liver injury in vivo. Cholestasis was induced in mice by bile duct ligation (BDL). NIM811 was gavaged (20 mg/kg) before BDL and daily (10 mg/kg) afterward. Mitochondrial depolarization, cell death, and MPT onset were assessed by intravital confocal/multiphoton microscopy of rhodamine 123, propidium iodide, and calcein. After BDL, serum alanine aminotransferase (ALT), hepatic necrosis, and apoptosis all increased. NIM811 decreased ALT, necrosis, and apoptosis by 60 to 86%. In vehicle-treated mice at 6 h after BDL, viable hepatocytes with depolarized mitochondria were 18/high-power field (hpf), and nonviable cells were approximately 1/hpf, showing that depolarization preceded necrosis. Calcein entered mitochondria after BDL, indicating MPT onset in vivo. NIM811 decreased depolarization by 72%, prevented calcein entry into mitochondria, and blocked release of cytochrome c. Hepatic tumor necrosis factor alpha, transforming growth factor-beta1, procollagen alpha1(I) mRNA, alpha-smooth muscle actin, and Sirius red staining for collagen increased after BDL but were not different in vehicle- and NIM811-treated mice. Taken together, NIM811 decreased cholestatic necrosis and apoptosis but did not block fibrosis, indicating that the MPT plays an important role in cholestatic cell death in vivo.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Activation of MUC1 mucin expression by bile acids in human esophageal adenocarcinomatous cells and tissues is mediated by the phosphatidylinositol 3-kinase

BACKGROUND

In esophageal adenocarcinoma, MUC1 mucin expression increases in early stages of the carcinogenetic sequence, during which bile reflux has been identified as a major carcinogen. However, no link between MUC1 overexpression and the presence of bile acids in the reflux has been established so far, and molecular mechanisms regulating MUC1 expression during esophageal carcinogenetic sequence are unknown. Our aim was to identify (1) the bile acids able to upregulate MUC1 expression in esophageal cancer cells and mucosal samples, (2) the regulatory regions in MUC1 promoter responsive to bile acids, and (3) the signaling pathway(s) involved in this regulation.

METHODS

MUC1 mRNA and mucin expression were studied by the means of real-time reverse transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry, both in the human esophageal OE33 adenocarcinoma cell line and in an ex vivo explant model. MUC1 promoter was cloned and transcription regulation was studied by transient cell transfection to identify the bile acid-responsive regions. Signaling pathways involved were identified using specific pharmacologic inhibitors and siRNA approach.

RESULTS

Taurocholic, taurodeoxycholic, taurochenodeoxycholic, glycocholic, sodium glycocholate, and deoxycholic bile acids upregulated MUC1 mRNA and protein expression. The highest induction was obtained with deoxycholic and taurocholic acids in both cellular and explant models. The bile acid-mediated upregulation of MUC1 transcription occurs at the promoter level, with responsive elements located in the -1472/-234 region of the promoter, and involves the phosphatidylinositol 3-kinase signaling pathway.

CONCLUSIONS

Bile acids induce MUC1 mucin overexpression in human esophageal adenocarcinoma cells and tissues by activating its transcription through a process involving phosphatidylinositol 3-kinase.

Effect of phorbol ester and platelet-derived growth factor on protein kinase C in rat hepatic stellate cells

BACKGROUND/AIMS

Hepatic stellate cells (HSC) play a key role in hepatic fibrogenesis and thus, it is important to understand the intracellular signalling pathways that influence their behaviour. This study investigated the expression and regulation of protein kinase C (PKC) in HSC.

RESULTS

Western blot analysis indicates that rat HSC express at least four PKC isoforms, PKC-alpha, PKC-delta, PKC-epsilon and PKC-zeta. PKC-alpha and PKC-zeta were located predominantly in the cytosol and were redistributed to the membrane by the PKC agonist, phorbol 12-myristate 13-acetate (PMA), while PKC-delta and PKC-epsilon were highly membrane-bound and did not undergo translocation by PMA. PKC-alpha, PKC-delta and PKC-zeta were rapidly downregulated by PMA. However, PKC-epsilon was resistant to downregulation. We also examined phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS), a specific substrate of PKC, as another approach to assess activation of PKC. Platelet-derived growth factor (PDGF) and PMA increased the phosphorylation of MARCKS, suggesting that PDGF can induce PKC activation. PDGF-induced stimulation of extracellular signal-regulated kinase, phosphatidylinositol 3-kinase and p70-S6 kinase was not abrogated by downregulation of PKC-alpha, PKC-delta and PKC-zeta. Prolonged PKC inhibition did not inhibit the fibrogenic phenotype.

CONCLUSION

Multiple PKC isoforms are expressed in rat HSC and are differentially regulated by PMA. PDGF activates certain mitogenic signalling pathways independent of PKC-alpha, PKC-delta and PKC-zeta. Specific PKC isoforms may modulate different cell functions in HSC.

Succinate is a paracrine signal for liver damage

BACKGROUND/AIMS

A G-protein-coupled succinate receptor has recently been identified in several tissues, including the liver. The objectives of this work were to determine the hepatic cell types that express this receptor and to determine its physiological role.

METHODS

Expression and distribution of the succinate receptor was determined by RT-PCR and confocal immunofluorescence. Biochemical assays were used to measure succinate and cAMP. Cytosolic Ca2+ was monitored in single cells by time-lapse imaging. Western blot was used to study the effect of succinate on activation of hepatic stellate cells.

RESULTS

The succinate receptor was expressed in quiescent hepatic stellate cells, and expression decreased with activation. Ischemia induced release of succinate in isolated perfused livers. In contrast to what is observed in cell expression systems, succinate did not inhibit cAMP production or increase cytosolic Ca2+ in primary hepatic stellate cells. However, succinate accelerated stellate cell activation.

CONCLUSIONS

Hepatic stellate cells express the succinate receptor. Succinate may behave as a paracrine signal by which ischemic hepatocytes trigger stellate cell activation.

Bile acid interactions with cholangiocytes

Cholangiocytes are exposed to high concentrations of bile acids at their apical membrane. A selective transporter for bile acids, the Apical Sodium Bile Acid Cotransporter (ASBT) (also referred to as Ibat; gene name Slc10a2) is localized on the cholangiocyte apical membrane. On the basolateral membrane, four transport systems have been identified (t-ASBT, multidrug resistance (MDR)3, an unidentified anion exchanger system and organic solute transporter (Ost) heteromeric transporter, Ostα-Ostβ. Together, these transporters unidirectionally move bile acids from ductal bile to the circulation. Bile acids absorbed by cholangiocytes recycle via the peribiliary plexus back to hepatocytes for re-secretion into bile. This recycling of bile acids between hepatocytes and cholangiocytes is referred to as the cholehepatic shunt pathway. Recent studies suggest that the cholehepatic shunt pathway may contribute in overall hepatobiliary transport of bile acids and to the adaptation to chronic cholestasis due to extrahepatic obstruction. ASBT is acutely regulated by an adenosine 3', 5’-monophosphate (cAMP)-dependent translocation to the apical membrane and by phosphorylation-dependent ubiquitination and proteasome degradation. ASBT is chronically regulated by changes in gene expression in response to biliary bile acid concentration and inflammatory cytokines. Another potential function of cholangiocyte ASBT is to allow cholangiocytes to sample biliary bile acids in order to activate intracellular signaling pathways. Bile acids trigger changes in intracellular calcium, protein kinase C (PKC), phosphoinositide 3-kinase (PI3K), mitogen-activated protein (MAP) kinase and extracellular signal-regulated protein kinase (ERK) intracellular signals. Bile acids significantly alter cholangiocyte secretion, proliferation and survival. Different bile acids have differential effects on cholangiocyte intracellular signals, and in some instances trigger opposing effects on cholangiocyte secretion, proliferation and survival. Based upon these concepts and observations, the cholangiocyte has been proposed to be the principle target cell for bile acids in the liver.

Bile acid induces hydrophobicity-dependent membrane alterations

Elevated concentrations of fecal bile acids are a known risk factor for colon cancer, owing to alterations in cellular signaling. In colonic cells, where bile acid uptake is minimal, the hydrophobicity-induced membrane perturbation and alterations have been proposed, but these membrane alterations are largely uncharacterized. In this study, we examined the determinants and characteristics of bile acid-induced membrane alterations, utilizing PKCalpha activation and cholesterol up-regulation as model indicators. We found that bile acid-induced PKCalpha activation is a function of hydrophobicity and correlated with alteration in membrane lipid composition, as evident by the significant up-regulation in membrane cholesterol and phospholipid. We found that bile acid do not cause cell membrane disruption at a concentration sufficient to activate PKCalpha, but do induce drastic alterations in membrane composition. Bile acid also induced the modification and up-regulation of caveolin-1 in a hydrophobicity-dependent manner, implying widespread receptor dysregulation. Similarly, ERK1/2 activation was observed only in response to hydrophobic bile acids, suggesting hydrophobicity-induced caveolar or membrane stress. Experiments with sodium lauryl sarcosine and cholesteryl hemisuccinate showed that bile acid-induced membrane alterations can be mimicked by hydrophobic molecules unrelated to bile acids, strongly implicating hydrophobicity as an important determinant of bile acid signaling.

Bile acids induce hepatic stellate cell proliferation via activation of the epidermal growth factor receptor

BACKGROUND & AIMS

Hepatic stellate cell (HSC) proliferation is a key event in the development of liver fibrosis. In many liver diseases, HSCs are exposed to inflammatory cytokines, reactive oxygen species, and bile acids. Although inflammatory cytokines and reactive oxygen species are known to promote proliferation of HSCs, nothing is known about the effects of bile acids on HSC proliferation or apoptosis. The aim of this study was to investigate the effects of bile acids on HSC proliferation.

METHODS

HSCs were exposed to bile acids with different hydrophobicity (5-200 micromol/L). HSC proliferation and cell cycle-related events were assessed by bromodeoxyuridine incorporation, cell counting and proliferating cell nuclear antigen and cyclin E expression, apoptosis by caspase-3 activity assay, immunocytochemistry for active caspase-3 and acridine orange staining, and activation of signal transduction pathways by Western blot using phospho-specific antibodies. Uptake of bile acids was investigated using fluorescent bile acids.

RESULTS

All bile acids, at concentrations >25 micromol/L, induce a 2.5- to 3-fold increase in HSC proliferation via activation of the epidermal growth factor receptor. Bile acid-induced proliferation is mediated by activation of a protein kinase C/extracellular signal-regulated kinase/p70S6K-dependent pathway. Bile acids did not induce apoptosis in HSCs. HSCs do not take up fluorescent bile acids and do not express the bile acid importer ntcp.

CONCLUSIONS

Bile acids at levels reached in cholestatic conditions are an independent profibrogenic factor. Bile acids induce HSC proliferation via the activation of the epidermal growth factor receptor, whereas HSCs are protected against bile acid-induced apoptosis by excluding bile acids.

Synthetic bile acid derivatives induce apoptosis through a c-Jun N-terminal kinase and NF-kappaB-dependent process in human cervical carcinoma cells

Recently, we have reported that a synthetic derivative of ursodeoxycholic acid (UDCA), HS-1183, and those of chenodeoxycholic acid (CDCA), HS-1199 and HS-1200, induced apoptosis in human breast carcinoma cells through a p53-independent pathway. Here, we present that the synthetic bile acid derivatives induce apoptosis in SiHa human cervical carcinoma cells as well. The parental compounds, UDCA and CDCA, exhibited no significant effect on the cell viability at the concentration ranges tested. However, their synthetic bile acid derivatives significantly decreased cell viability in a concentration dependent manner. Characteristic manifestations of apoptosis including DNA fragmentation, an increased level of proapoptotic protein Bax, and cleavage of poly(ADP-ribose) polymerase were shown when the cells were treated with these synthetic compounds. Nuclear translocation of nuclear transcription factor NF-kappaB was increased and this suggests that the synthetic compounds induce apoptosis in a NF-kappaB dependent pathway. Phosphorylations of p38 and extracellular signal-regulated kinase were not affected, whereas c-Jun N-terminal kinase (JNK) was activated along with an increased level of transcription factor c-Jun. Our studies demonstrate that the newly synthesized bile acids are capable of inhibiting cell proliferation and inducing apoptosis in SiHa cells through activation of JNK and NF-kappaB.

Nephroblastoma overexpressed gene (NOV) expression in rat hepatic stellate cells

Using the expression-profiling method, we identified nephroblastoma overexpressed gene (NOV) mRNA as one member of the mRNA population that was upregulated in cultured activated hepatic stellate cell (HSC). Northern analysis showed that NOV mRNA was increasingly expressed during progressive activation of cultured rat HSCs, and a significant increase was observed in both the carbon tetrachloride-induced and bile duct ligation/scission rat models of liver fibrosis. RT-PCR showed human NOV mRNA was increased in most fibrotic livers compared with normal livers. The expression of NOV protein in fibrotic rat and human livers was predominantly located in areas of ductular proliferation and HSC of the fibrous septa. HSCs stimulated with transforming growth factor beta1 showed increased expression of NOV protein without changing its mRNA levels. Dexamethasone stimulated the expression of NOV mRNA and protein. Furthermore, we demonstrated that bile acids have a modulating effect on the induction of NOV mRNA expression. In conclusion, this study suggests that NOV is expressed during liver fibrogenesis and HSCs may be an important source of hepatic NOV.

Synthetic CDCA derivatives-induced apoptosis of stomach cancer cell line SNU-1 cells

PURPOSE

This study was conducted to explore whether CDCA derivatives induce apoptosis in a stomach cancer cell line, and to dissect the detailed mechanism underlying apoptosis.

MATERIALS AND METHODS

The human stomach cancer cell line, SNU-1, cells were treated with the synthetic CDCA derivatives, HS-1199 and HS-1200. DNA and mitochondrial stains were used to detect apoptotic cells by fluorescence imaging or flow cytometry. The caspase-3 activity was measured by Western blotting.

RESULTS

Both the HS-1199 and HS-1200 induced decreased viabilities of the SNU-1 cells, in time-dependent manners. The CDCA derivatives demonstrated various apoptosis hallmarks, such as mitochondrial changes (reduction of MMP, cytochrome c release, and Smac/ DIABLO translocation), activation of caspase-3 (resulting in the degradation of PARP and DFF45), DNA fragmentation and nuclear condensation.

CONCLUSION

The CDCA derivatives, HS-1199 and HS-1200, both induced apoptosis of the SNU-1 gastric cancer cells in caspase- and mitochondria-dependent fashions. Many important issues relating to their therapeutic applications remain to be elucidated.

Transcriptional regulation of human mucin MUC4 by bile acids in oesophageal cancer cells is promoter-dependent and involves activation of the phosphatidylinositol 3-kinase signalling pathway

Abnormal gastro-oesophageal reflux and bile acids have been linked to the presence of Barrett's oesophageal premalignant lesion associated with an increase in mucin-producing goblet cells and MUC4 mucin gene overexpression. However, the molecular mechanisms underlying the regulation of MUC4 by bile acids are unknown. Since total bile is a complex mixture, we undertook to identify which bile acids are responsible for MUC4 up-regulation by using a wide panel of bile acids and their conjugates. MUC4 apomucin expression was studied by immunohistochemistry both in patient biopsies and OE33 oesophageal cancer cell line. MUC4 mRNA levels and promoter regulation were studied by reverse transcriptase-PCR and transient transfection assays respectively. We show that among the bile acids tested, taurocholic, taurodeoxycholic, taurochenodeoxycholic and glycocholic acids and sodium glycocholate are strong activators of MUC4 expression and that this regulation occurs at the transcriptional level. By using specific pharmacological inhibitors of mitogen-activated protein kinase, phosphatidylinositol 3-kinase, protein kinase A and protein kinase C, we demonstrate that bile acid-mediated up-regulation of MUC4 is promoter-specific and mainly involves activation of phosphatidylinositol 3-kinase. This new mechanism of regulation of MUC4 mucin gene points out an important role for bile acids as key molecules in targeting MUC4 overexpression in early stages of oesophageal carcinogenesis.

Cholesterol and cholate components of an atherogenic diet induce distinct stages of hepatic inflammatory gene expression

Atherosclerosis in inbred mouse strains has been widely studied by using an atherogenic (Ath) diet containing cholesterol, cholic acid, and fat, but the effect of these components on gene expression has not been systematically examined. We employed DNA microarrays to interrogate gene expression levels in liver of C57BL/6J mice fed the following five diets: mouse chow, the Ath diet, or modified versions of the Ath diet in which either cholesterol, cholate, or fat were omitted. Dietary cholesterol and cholate produced discrete gene expression patterns. Cholesterol was required for induction of genes involved in acute inflammation, including three genes of the serum amyloid A family, three major histocompatibility class II antigen genes, and various cytokine-related genes. In contrast, cholate induced expression of genes involved in extracellular matrix deposition in hepatic fibrosis, including five collagen family members, collagen-interacting proteins, and connective tissue growth factor. The gene expression findings were confirmed by biochemical measurements showing that cholesterol was required for elevation of circulating serum amyloid A, and cholate was required for accumulation of collagen in the liver. The possibility that these gene expression changes are relevant to atherogenesis in C57BL/6J mice was supported by the observation that the closely related, yet atherosclerosis-resistant, C57BL/6ByJ strain was largely resistant to dietary induction of the inflammatory and fibrotic response genes. These results establish that cholesterol and cholate components of the Ath diet have distinct proatherogenic effects on gene expression and suggest a strategy to study the contribution of acute inflammatory response and fibrogenesis independently through dietary manipulation.

Bile acids enhance low density lipoprotein receptor gene expression via a MAPK cascade-mediated stabilization of mRNA

Recent studies have indicated that bile acids regulate the expression of several genes involved in bile acid and lipid metabolism as ligands for the farnesoid X receptor (FXR). We report here that bile acids are directly able to govern cholesterol metabolism by a novel mechanism. We show that chenodeoxycholic acid (CDCA) enhances low density lipoprotein (LDL) receptor gene expression in human cultured cell lines (HeLa, Hep G2, and Caco-2). The proteolytic activation of sterol regulatory element-binding protein-2 (SREBP-2), a major regulator for LDL receptor gene expression, is not affected by CDCA. Both deoxycholic acid and lithocholic acid as well as CDCA, but not ursodeoxycholic acid, increase the mRNA level for the LDL receptor, even when Hep G2 cells are cultured with 25-hydroxycholesterol, a potent suppressor of gene expression for the LDL receptor. Although it seems possible that FXR might be involved in genetic regulation, both reporter assays with a reporter gene containing the LDL receptor promoter as well as Northern blot analysis reveal that FXR is not involved in the process. On the other hand, inhibition of mitogen-activated protein (MAP) kinase activities, which are found to be induced by CDCA, abolishes the CDCA-mediated up-regulation of LDL receptor gene expression. We further demonstrate that CDCA stabilizes LDL receptor mRNA and that the MAP kinase inhibitors accelerate its turnover. Taken together, these results indicate that bile acids increase LDL uptake and the intracellular cholesterol levels through the activation of MAP kinase cascades in conjunction with a down-regulation of bile acid biosynthesis by FXR. This work opens up a new avenue for developing pharmaceutical interventions that lower plasma LDL by stabilizing LDL receptor mRNA.

Bile acids mimic oxidative stress induced upregulation of thioredoxin reductase in colon cancer cell lines

Bile acids have been suggested to play an important role in the etiology of colon and gastric cancer after gastrectomy, but the molecular biology of these effects is poorly understood. We evaluated the effect of different bile acids on human gastric and colon carcinoma cells and identified genes by RNA arbitrarily primed PCR for differential display that are modulated following treatment with hydrophobic bile acids. Thioredoxin reductase (TR) mRNA was upregulated after treatment with taurochenodeoxycholic acid (TCDCA) in St 23132 cells. This raised the question whether deoxycholic acid (DCA) would have regulative effects on TR in HT-29 cells. After an incubation time of 6 h with DCA, TR mRNA expression was increased up to threefold. Ursodeoxycholic acid had no influence on TR mRNA expression. The upregulation of TR after DCA incubation was almost identical to incubation with 12-O-tetradecanoylphorbol-13-acetate. This implies that hydrophobic bile acids mediate oxidative stress in gastrointestinal cancer cells, which was confirmed by measurement of oxidative burst after treatment with DCA. The results suggest that hydrophobic bile acids induce oxidative stress in gastrointestinal cancer resulting in a compensatory upregulation of TR mRNA, one of the key components in the complex anti-oxidant defense system within eukaryotic cells. The activation of at least parts of the redox signaling system is potentially related to the cytotoxicity and the stimulation of the cell death machinery induced by toxic bile acids.

An electron microscopic and morphometric study of ursodeoxycholic effect in primary biliary cirrhosis

BACKGROUND/AIMS

Primary biliary cirrhosis (PBC) is a chronic liver disease that results in cholestasis and bile duct loss. Ursodeoxycholic acid (UDCA) has been shown to reduce hepatocellular damage in PBC. The study attempted to quantify perisinusoidal collagenization and the number of apoptotic bodies in PBC liver biopsies from patients in a randomized control trial treated with UDCA compared to those who received placebo.

METHODS

Twenty-eight patients with PBC (10 cirrhotic, 18 non-cirrhotic; 13 treated with UDCA, 15 treated with placebo) were compared with 32 controls with normal hepatic histology on light microscopy. Liver biopsies were examined for degree of perisinusoidal fibrosis and apoptotic activity using electron microscopy.

RESULTS

The degree of perisinusoidal fibrosis and apoptotic activity was similar in pretreatment biopsies of UDCA and placebo-treated patients. After two years of placebo, patients showed a significant increase in fibrosis (P < 0.001). In contrast, there were no changes in non-cirrhotic and a decrease in fibrosis in cirrhotic patients given UDCA. At baseline, PBC patients had higher numbers (apoptotic cells/100 hepatocytes +/- SE) of apoptotic cells (7 +/- 3), than controls (2 +/- 0.5) (P < 0.05), with no difference between cirrhotic and non-cirrhotic patients in the two groups of patients. After two years, the numbers of apoptotic cells in UDCA-treated patients decreased significantly compared to baseline (3 +/- 2) (P < 0.05); with placebo patients the number of apoptotic cells increased (12 +/- 5) (P < 0.05).

CONCLUSION

Treatment with UDCA prevents the deposition of perisinusoidal collagen and reduces the apoptotic activity in PBC patients after 2 years of therapy.

Down-regulation of cholesterol 7alpha-hydroxylase (CYP7A1) gene expression by bile acids in primary rat hepatocytes is mediated by the c-Jun N-terminal kinase pathway

Cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis, is feedback-inhibited at the transcriptional level by hydrophobic bile acids. Recent studies show that bile acids are physiological ligands for farnesoid X receptor (FXR). Activated FXR indirectly represses CYP7A1 transcription through induction of small heterodimer protein (SHP-1). In this study, we provide evidence that bile acids rapidly down-regulate CYP7A1 transcription via activation of the JNK/c-Jun pathway. Furthermore, we demonstrate that SHP-1 is also a direct target of activated c-Jun. In primary rat hepatocyte cultures, taurocholate (TCA) strongly activated JNK in a time- and concentration-dependent manner. Tumor necrosis factor-alpha, a potent activator of JNK, also rapidly activated JNK and down-regulated CYP7A1 mRNA levels. Overexpression of dominant-negative JNK1 or a transactivating domain mutant of c-Jun significantly blocked the ability of TCA to down-regulate CYP7A1 mRNA. In contrast, overexpression of wild-type c-Jun (c-Jun(wt)) enhanced the repression of CYP7A1 by TCA. Moreover, overexpression of c-Jun(wt) resulted in increased SHP-1 promoter activity. Mutation of a putative AP-1 (c-Jun) element suppressed c-Jun-mediated activation of the SHP-1 promoter construct. These results indicate that the bile acid-activated JNK pathway plays a pivotal role in regulating CYP7A1 levels in primary rat hepatocytes.

Effects of specific bile acids on c-fos messenger RNA levels in human colon carcinoma Caco-2 cells

Bile acids may play a role in the pathogenesis of intestinal inflammation by activating the signalling pathways that control cell proliferation, among other cell systems. We investigated the action of different bile acids, particularly chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA), on steady-state and transcriptional regulation of the protooncogene c-fos, involved in the regulation of cell proliferation and differentiation, in colon carcinoma Caco-2 cells. Specific bile acids had a stimulatory effect of on the expression of c-fos mRNA. This proved to be concentration- and time-dependent and may be partly due to an increase in the rate of transcription of the corresponding gene rather than to any change in the stability of mRNA. In Caco-2 cells exposed to 250 microM CDCA for 1 h a maximal increase of c-fos mRNA ( approximately 2.5-fold induction over the control) was observed; deoxycholic acid (DCA; 250 microM) and lithocholic acid (LCA; 250 microM) were less effective (approximately 2-fold induction over the control). UDCA and cholic acid (CA) did not modify c-fos gene expression in this cell line. Finally, we investigated the role of protein kinase C (PKC) in transcriptional regulation of the c-fos gene by bile acids. Although induction of c-fos by 12-O-tetradecanoyl 13-acetate (10 nM), a potent PKC activator, was completely antagonised by bis-indolyl-maleimide I (1 microM); only about 40% of the bile acid-mediated rise in c-fos mRNA was blocked. Thus it appears that PKC, as well as other signalling pathways, is involved in CDCA-, DCA- and LCA-induced c-fos gene expression.

Platelet-derived growth factor is a principal inductive factormodulating mannose 6-phosphate/insulin-like growth factor-II receptorgene expression via a distal E-box in activated hepatic stellate cells

Hepatic stellate cells (HSCs) become activated during the earlystages of hepatic injury associated with fibrogenesis. The mannose 6-phosphate/insulin-like growth factor-II receptor (M6P/IGFIIR) plays animportant role in early fibrogenesis by participating in the activationof latent transforming growth factor-beta, a potent inducer of thematrix proteins in activated stellate cells that produce the hepaticnodule. Platelet-derived growth factor (PDGF), a potent HSC mitogen, isreleased early in hepatic injury and activates several signallingpathways in HSCs. In this study we examined the role of PDGF-BB in HSCregulation of M6P/IGFIIR gene expression. Several promoter elementswere found and characterized that modulate M6P/IGFIIR expression inactivated stellate cells. The presence of a distal CACGTG E-box at-2695 was required for M6P/IGFIIR expression in transfectedstellate cells. When the distal E-box was removed there was no significant M6P/IGFIIR promoter activity. The distal E-box-binding protein responded specifically to PDGF-BB with increased binding. This coincided with PDGF-BB up-regulation of M6P/IGFIIR mRNA transcript levels. Downstream elements include two proximal (-2 to-48) CACGTG E-boxes that bind a different protein to the distal(-2695) E-box. The proximal E-boxes respond moderately to PDGF-BB. The promoter segment encompassing -144 to +109 is able to respond dramatically to serum but is refractory to PDGF-BB. However, a constitutively bound protein binding to the -611/-716 fragment appears to be a repressor that suppresses inductive changes in protein binding occurring downstream of -611. These results indicate that the M6P/IGFIIR promoter responds primarily and specifically to PDGF-BB through a distal E-box element and possibly through two proximal E-box elements.

Catabolites of cholesterol synthesis pathways and forskolin as activators of the farnesoid X-activated nuclear receptor

The nuclear receptors are a family of transcriptional mediators that, upon activation, bind DNA and regulate gene transcription. Among these receptors, the farnesoid X-activated receptor (FXR) has recently been identified as one activated by bile acids and farnesol. To investigate the potential of other sterols to activate FXR, as well as to examine relevant relationships among identified activators of FXR, the current study used a mammalian cell transcription assay to quantify and compare activation potential. In addition to the classical bile acids deoxycholate (DCA) and chenodeoxycholate (CDCA), FXR was shown to be transcriptionally active in the presence of the androgen catabolites 5alpha-androstan-3alpha-ol-17-one (androsterone) and 5beta-androstan-3alpha-ol-17-one (etiocholanolone), as well as the sterol bronchodilatory drug forskolin. Conversely, cholesterol and several other key precursors to the androgens and bile acids were either not active or only slightly active. Furthermore, it was observed that the bile acid ursodeoxycholate (UDCA) could inhibit DCA and CDCA activation of FXR in a manner parallel to its ability to antagonize DCA and CDCA induction of apoptosis. By far, the most efficacious activator of FXR was forskolin. Interestingly, although it is classically viewed as an initiator of the adenylate cyclase/protein kinase A (PKA) pathway, PKA inhibition did not inhibit forskolin's activation of FXR nor was cyclic AMP (cAMP) able to stimulate FXR-mediated transcription. These data would suggest that forskolin acts as a ligand for FXR rather than as a secondary activator of FXR and could have important implications with respect to its potential toxicity and pharmacological use.

Platelet-derived growth factor is a principal inductive factormodulating mannose 6-phosphate/insulin-like growth factor-II receptorgene expression via a distal E-box in activated hepatic stellate cells

Hepatic stellate cells (HSCs) become activated during the earlystages of hepatic injury associated with fibrogenesis. The mannose 6-phosphate/insulin-like growth factor-II receptor (M6P/IGFIIR) plays animportant role in early fibrogenesis by participating in the activationof latent transforming growth factor-beta, a potent inducer of thematrix proteins in activated stellate cells that produce the hepaticnodule. Platelet-derived growth factor (PDGF), a potent HSC mitogen, isreleased early in hepatic injury and activates several signallingpathways in HSCs. In this study we examined the role of PDGF-BB in HSCregulation of M6P/IGFIIR gene expression. Several promoter elementswere found and characterized that modulate M6P/IGFIIR expression inactivated stellate cells. The presence of a distal CACGTG E-box at-2695 was required for M6P/IGFIIR expression in transfectedstellate cells. When the distal E-box was removed there was no significant M6P/IGFIIR promoter activity. The distal E-box-binding protein responded specifically to PDGF-BB with increased binding. This coincided with PDGF-BB up-regulation of M6P/IGFIIR mRNA transcript levels. Downstream elements include two proximal (-2 to-48) CACGTG E-boxes that bind a different protein to the distal(-2695) E-box. The proximal E-boxes respond moderately to PDGF-BB. The promoter segment encompassing -144 to +109 is able to respond dramatically to serum but is refractory to PDGF-BB. However, a constitutively bound protein binding to the -611/-716 fragment appears to be a repressor that suppresses inductive changes in protein binding occurring downstream of -611. These results indicate that the M6P/IGFIIR promoter responds primarily and specifically to PDGF-BB through a distal E-box element and possibly through two proximal E-box elements.

Epithelial injury induces egr-1 and fos expression by a pathway involving protein kinase C and ERK

The signaling pathways activated in response to gastrointestinal injury remain poorly understood. Previous work has implicated the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase as a mediator of wound-signal transduction and a possible regulator of epithelial restitution. Monolayer injury resulted in rapid activation of p42 and p44 ERK. Injury-induced ERK activation was blocked by protein kinase C inhibition or by disruption of the cell cytoskeleton. Significant increases in Fos and early growth response (Egr)-1 mRNA levels were stimulated by injury, peaking by 20 min. ERK activation and the induction of Egr-1 mRNA were inhibited in a dose-dependent fashion with PD-98059. Fos mRNA expression was partially blocked by PD-98059. Western blot analysis demonstrated strong expression and nuclear localization of Fos and Egr after wounding. Electrophoretic mobility shift assays demonstrated that nuclear extracts contained a protein that specifically bound double-stranded oligonucleotides containing the Egr consensus binding element. Gel supershift assays demonstrated that the protein-DNA complexes were recognized by anti-Egr antibody. Inhibition of injury-induced ERK activation by PD-98059 or direct interference with Egr by expression of a dominant negative mutant led to significantly reduced in vitro monolayer restitution.

Polyenylphosphatidylcholine inhibits PDGF-induced proliferation in rat hepatic stellate cells

Polyenylphosphatidylcholine (PPC), a polyunsaturated phospholipid extract from soy beans, prevents the development of liver cirrhosis in animal models. Its mechanism of action is unknown. Based on the hypothesis that PPC might act by decreasing hepatic stellate cell proliferation, we studied the effect of PPC and its main components, dilinoleoylphosphatidylcholine (DLPC) and palmitoyl-linoleoylphosphatidylcholine (PLPC), on PDGF-induced stellate cell proliferation and intracellular signal transduction. Normal rat hepatic stellate cells in tissue culture were serumstarved, and incubated with 10ng/ml PDGF in the absence or presence of phospholipids. Cell proliferation was measured by 3H-thymidine incorporation. P44MAPK activation was determined by kinase assay, and AP-1 binding by electrophoretic mobility shift assay. PPC (200 ng/ml) significantly inhibited PDGF-induced proliferation (p < 0.05; ANOVA, n = 3) and antagonized PDGF-induced P44MAPK activation and AP-1 binding. This effect was mimicked by DLPC but not by PLPC. Neither DLPC nor PLPC prevented PDGF receptor activation. We conclude that PPC exerts a previously unrecognized effect on mitogen-induced stellate cell proliferation which may be mediated by DLPC. Inhibition of this cascade represents a potential mechanism for the inhibitory effect of PPC on hepatic fibrogenesis.