Jeon Ok Moon

Reduced liver fibrosis in hypoxia-inducible factor-1α-deficient mice

Liver fibrosis is characterized by excessive deposition of extracellular matrix in the liver during chronic injury. During early stages of this disease, cells begin to synthesize and secrete profibrotic proteins that stimulate matrix production and inhibit matrix degradation. Although it is clear that these proteins are important for development of fibrosis, what remains unknown is the mechanism by which chronic liver injury stimulates their production. In the present study, the hypothesis was tested that hypoxia-inducible factor-1alpha (HIF-1alpha) is activated in the liver during chronic injury and regulates expression of profibrotic proteins. To investigate this hypothesis, mice were subjected to bile duct ligation (BDL), an animal model of liver fibrosis. HIF-1alpha protein was increased in the livers of mice subjected to BDL by 3 days after surgery. To test the hypothesis that HIF-1alpha is required for the development of fibrosis, control and HIF-1alpha-deficient mice were subjected to BDL. Levels of type I collagen and alpha-smooth muscle actin mRNA and protein were increased in control mice by 14 days after BDL. These levels were significantly reduced in HIF-1alpha-deficient mice. Next, the levels of several profibrotic mediators were measured to elucidate the mechanism by which HIF-1alpha promotes liver fibrosis. Platelet-derived growth factor (PDGF)-A, PDGF-B, and plasminogen activator inhibitor-1 mRNA levels were increased to a greater extent in control mice subjected to BDL compared with HIF-1alpha-deficient mice at 7 and 14 days after BDL. Results from these studies suggest that HIF-1alpha is a critical regulator of profibrotic mediator production during the development of liver fibrosis.

Hypoxia-inducible factor-1α regulates the expression of genes in hypoxic hepatic stellate cells important for collagen deposition and angiogenesis.

Background/Aims: Several studies have shown that regions of hypoxia develop in the liver during chronic injury. Furthermore, it has been demonstrated that hypoxia stimulates the release of mediators from hepatic stellate cells (HSCs) that may affect the progression of fibrosis. The mechanism by which hypoxia modulates gene expression in HSCs is not known. Recent studies demonstrated that the hypoxia‐activated transcription factor, hypoxia‐inducible factor (HIF)‐1α, is critical for the development of fibrosis. Accordingly, the hypothesis was tested that HIF‐1α is activated in HSCs and regulates the expression of genes important for HSC activation and liver fibrosis.

Hypoxia‐inducible factor‐dependent production of profibrotic mediators by hypoxic hepatocytes

Background/Aims: During the development of liver fibrosis, mediators are produced that stimulate cells in the liver to differentiate into myofibroblasts and to produce collagen. Recent studies demonstrated that the transcription factor, hypoxia‐inducible factor‐1α (HIF‐1α), is critical for upregulation of profibrotic mediators, such as platelet‐derived growth factor‐A (PDGF‐A), PDGF‐B and plasminogen activator inhibitor‐1 (PAI‐1) in the liver, during the development of fibrosis. What remains unknown is the cell type‐specific regulation of these genes by HIF‐1α in liver cell types. Accordingly, the hypothesis was tested that HIF‐1α is activated in hypoxic hepatocytes and regulates the production of profibrotic mediators by these cells.

Aspirin induces apoptosis in vitro and inhibits tumor growth of human hepatocellular carcinoma cells in a nude mouse xenograft model

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to induce apoptosis in a variety of cancer cells, including colon, prostate, breast and leukemia. Among them, aspirin, a classical NSAID, shows promise in cancer therapy in certain types of cancers. We hypothesized that aspirin might affect the growth of liver cancer cells since liver is the principal site for aspirin metabolism. Therefore, we investigated the effects of aspirin on the HepG2 human hepatocellular carcinoma cell line in vitro and the HepG2 cell xenograft model in BALB/c nude mice. We found that treatment with aspirin inhibited cell growth and induced apoptosis involving both extrinsic and intrinsic pathways as measured by DNA ladder formation, alteration in the Bax/Bcl-2 ratio, activation of the caspase activities and related protein expressions. In vivo antitumor activity assay also showed that aspirin resulted in significant tumor growth inhibition compared to the control. Oral administration of aspirin (100 mg/kg/day) caused a significant reduction in the growth of HepG2 tumors in nude mice. These findings suggest that aspirin may be used as a promising anticancer agent against liver cancer.

Upregulation of Early Growth Response Factor-1 by Bile Acids Requires Mitogen-activated Protein Kinase Signaling

Cholestasis results when excretion of bile acids from the liver is interrupted. Liver injury occurs during cholestasis, and recent studies showed that inflammation is required for injury. Our previous studies demonstrated that early growth response factor-1 (Egr-1) is required for development of inflammation in liver during cholestasis, and that bile acids upregulate Egr-1 in hepatocytes. What remains unclear is the mechanism by which bile acids upregulate Egr-1. Bile acids modulate gene expression in hepatocytes by activating the farnesoid X receptor (FXR) and through activation of mitogen-activated protein kinase (MAPK) signaling. Accordingly, the hypothesis was tested that bile acids upregulate Egr-1 in hepatocytes by FXR and/or MAPK-dependent mechanisms. Deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA) stimulated upregulation of Egr-1 to the same extent in hepatocytes isolated from wild-type mice and FXR knockout mice. Similarly, upregulation of Egr-1 in the livers of bile duct-ligated (BDL) wild-type and FXR knockout mice was not different. Upregulation of Egr-1 in hepatocytes by DCA and CDCA was prevented by the MEK inhibitors U0126 and SL-327. Furthermore, pretreatment of mice with U0126 prevented upregulation of Egr-1 in the liver after BDL. Results from these studies demonstrate that activation of MAPK signaling is required for upregulation of Egr-1 by bile acids in hepatocytes and for upregulation of Egr-1 in the liver during cholestasis. These studies suggest that inhibition of MAPK signaling may be a novel therapy to prevent upregulation of Egr-1 in liver during cholestasis.

Hypoxia-inducible Factor-dependent Production of Profibrotic Mediators by Hypoxic Kupffer Cells

Aim:  Liver fibrosis develops when chronic liver injury stimulates cells in the liver to produce mediators that activate hepatic stellate cells and stimulate them to secrete collagen. Recent studies suggest that the hypoxia‐regulated transcription factor, hypoxia‐inducible factor‐1α, is essential for upregulation of profibrotic mediators, such as platelet‐derived growth factor, in the liver during the development of liver fibrosis. What remains unknown, however, is the cell type‐specific regulation of profibrotic mediators by hypoxia‐inducible factors. Accordingly, in the present study the hypothesis tested was that hypoxia‐inducible factors regulate production of profibrotic mediators by hypoxic Kupffer cells.

Aspirin enhances doxorubicin-induced apoptosis and reduces tumor growth in human hepatocellular carcinoma cells in vitro and in vivo

Combined therapy with multiple drugs is a common practice in the treatment of cancer, which can achieve better therapeutic effects than a single drug, and can reduce the side effects as well as drug resistance. This study aimed to determine whether aspirin (ASA) shows synergism with doxorubicin (DOX) in HepG2 human hepatocellular carcinoma cells in vitro and in a HepG2 cell xenograft model in BALB/c nude mice. When treated in combination, DOX (0.25 nmol/ml) and ASA (5 µmol/ml) produced strong synergy in growth inhibition, cell cycle arrest and importantly, apoptosis in vitro in comparison to single treatments. Moreover, ASA (100 mg/kg/day orally) and DOX (1.2 mg/kg biweekly ip) induced synergistic antitumor activity in the HepG2 cell xenograft model in nude mice. Therefore, the combination of ASA and DOX could be used as a novel combination regimen which provides a strong anticancer synergy in the treatment of hepatocellular carcinoma.

RANKL stimulates proliferation, adhesion and IL-7 expression of thymic epithelial cells

In many clinical situations which cause thymic involution and thereby result in immune deficiency, T cells are the most often affected, leading to a prolonged deficiency of T cells. Since only the thymic-dependent T cell production pathway secures stable regeneration of fully mature T cells, seeking strategies to enhance thymic regeneration should be a key step in developing therapeutic methods for the treatment of these significant clinical problems. This study clearly shows that receptor activator of NF-κB ligand (RANKL) stimulates mouse thymic epithelial cell activities including cell proliferation, thymocyte adhesion to thymic epithelial cells, and the expression of cell death regulatory genes favoring cell survival, cell adhesion molecules such as ICAM-1 and VCAM-1, and thymopoietic factors including IL-7. Importantly, RANKL exhibited a significant capability to facilitate thymic regeneration in mice. In addition, this study demonstrates that RANKL acts directly on the thymus to activate thymus regeneration regardless of its potential influences on thymic regeneration through an indirect or systemic effect. In light of this, the present study provides a greater insight into the development of novel therapeutic strategies for effective thymus repopulation using RANKL in the design of therapies for many clinical conditions in which immune reconstitution is required.

Abstract 226: Aspirin alone or in combination with doxorubicin induced efficient apoptosis in human hepatocellular carcinoma cells

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Hepatocellular carcinoma (HCC), one of the most common cancers worldwide, is refractory to most anticancer drugs. Doxorubicin offers a survival benefit to patients with intermediate hepatocellular carcinoma. However, the favorable therapeutic response to doxorubicin is often associated with severe toxicity. The present research was aimed at developing a strategy of increasing doxorubicin sensitivity so that lower doses may be used without compromising efficacy. Recently, aspirin (ASA) and some other nonsteroidal anti-inflammatory drugs (NSAIDs) have drawn much attention for their protective effects against colon cancer and cardiovascular disease. Several studies also found that regular ASA use is significantly associated with reduced risk of lung cancer. We investigated the effects of ASA on HepG2 human hepatocellular carcinoma cell line. Growth inhibition effect of aspirin was measured by MTT assay. Flow cytometry analysis revealed that aspirin can induce G2/M phase arrest which we observed by the level of cell cycle regulatory proteins and DNA ladder formation indicates apoptosis dose dependently. We found that ASA treatment followed both extrinsic and intrinsic pathways for apoptosis induction. In addition to this, when administered in combination, doxorubicin (DOX) and ASA produced synergistic effect in growth inhibition in human hepatocellular carcinoma cells and induced apoptosis in caspase-dependent pathway. Therefore, clinically achievable concentrations of DOX and ASA used in combination may produce a strong anticancer synergy that warrants investigation as a therapeutic strategy to enhance the efficacy of doxorubicin for treating HCC. [This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MOST) (R01-2006-000-11117-0)]. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 226.