Don-Kyu Kim

Metformin Inhibits Hepatic Gluconeogenesis Through AMP-Activated Protein Kinase–Dependent Regulation of the Orphan Nuclear Receptor SHP

OBJECTIVE—Metformin is an antidiabetic drug commonly used to treat type 2 diabetes. The aim of the study was to determine whether metformin regulates hepatic gluconeogenesis through the orphan nuclear receptor small heterodimer partner (SHP; NR0B2). RESEARCH DESIGN AND METHODS—We assessed the regulation of hepatic SHP gene expression by Northern blot analysis with metformin and adenovirus containing a constitutive active form of AMP-activated protein kinase (AMPK) (Ad-AMPK) and evaluated SHP, PEPCK, and G6Pase promoter activities via transient transfection assays in hepatocytes. Knockdown of SHP using siRNA SHP was conducted to characterize the metformin-induced inhibition of hepatic gluconeogenic gene expression in hepatocytes, and metformin–and adenovirus SHP (Ad-SHP)–mediated hepatic glucose production was measured in B6-Lepob/ob mice. RESULTS—Hepatic SHP gene expression was induced by metformin, 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), and Ad-AMPK. Metformin-induced SHP gene expression was abolished by adenovirus containing the dominant negative form of AMPK (Ad-DN-AMPK), as well as by compound C. Metformin inhibited hepatocyte nuclear factor-4α–or FoxA2-mediated promoter activity of PEPCK and G6Pase, and the inhibition was blocked with siRNA SHP. Additionally, SHP knockdown by adenovirus containing siRNA SHP inhibited metformin-mediated repression of cAMP/dexamethasone-induced hepatic gluconeogenic gene expression. Furthermore, oral administration of metformin increased SHP mRNA levels in B6-Lepob/ob mice. Overexpression of SHP by Ad-SHP decreased blood glucose levels and hepatic gluconeogenic gene expression in B6-Lepob/ob mice. CONCLUSIONS—We have concluded that metformin inhibits hepatic gluconeogenesis through AMPK-dependent regulation of SHP.

The orphan nuclear receptor SHP acts as a negative regulator in inflammatory signaling triggered by Toll-like receptors

The orphan nuclear receptor SHP (small heterodimer partner) is a transcriptional corepressor that regulates hepatic metabolic pathways. Here we identified a role for SHP as an intrinsic negative regulator of Toll-like receptor (TLR)-triggered inflammatory responses. SHP-deficient mice were more susceptible to endotoxin-induced sepsis. SHP had dual regulatory functions in a canonical transcription factor NF-κB signaling pathway, acting as both a repressor of transactivation of the NF-κB subunit p65 and an inhibitor of polyubiquitination of the adaptor TRAF6. SHP-mediated inhibition of signaling via the TLR was mimicked by macrophage-stimulating protein (MSP), a strong inducer of SHP expression, via an AMP-activated protein kinase–dependent signaling pathway. Our data identify a previously unrecognized role for SHP in the regulation of TLR signaling.

BMP2 Protein Regulates Osteocalcin Expression via Runx2-mediated Atf6 Gene Transcription

Background: BMP2 activates UPR transducers during osteoblast differentiation. Results: BMP2 signaling increased ATF6 expression and cleavage, and activated ATF6 increased OC expression. Conclusion: BMP2 induced osteoblast differentiation through Runx2-dependent ATF6 expression, which directly regulates OC transcription. Significance: BMP2-induced mild ER stress positively regulates osteoblast differentiation via activation of UPR transducers, including ATF6. Bone morphogenetic protein 2 (BMP2) activates unfolded protein response (UPR) transducers, such as PERK and OASIS, in osteoblast cells. ATF6, a bZIP transcription factor, is also a UPR transducer. However, the involvement of ATF6 in BMP2-induced osteoblast differentiation has not yet been elucidated. In the present study, BMP2 treatment was shown to markedly induce the expression and activation of ATF6 with an increase in alkaline phosphatase (ALP) and OC expression in MC3T3E1 cells. In contrast, ATF6 activation by BMP2 was not observed in the Runx2−/− primary calvarial osteoblasts, and Runx2 overexpression recovered BMP2 action. BMP2 stimulated ATF6 transcription by enhancing the direct binding of Runx2 to the osteoblast-specific cis-acting element 2 (OSE2, ACCACA, −205 to −200 bp) motif of the Atf6 promoter region. In addition, the overexpression of ATF6 increased the Oc promoter activity by enhancing the direct binding to a putative ATF6 binding motif (TGACGT, −1126 to −1121 bp). The inhibition of ATF6 function with the dominant negative form of ATF6 (DN-ATF6) blocked BMP2- or Runx2-induced OC expression. Interestingly, OASIS, which is structurally similar to ATF6, did not induce Oc expression. ALP and Alizarin red staining results confirmed that BMP2-induced matrix mineralization was also dependent on ATF6 in vitro. Overall, these results suggest that BMP2 induces osteoblast differentiation through Runx2-dependent ATF6 expression, which directly regulates Oc transcription.

Inverse agonist of estrogen-related receptor γ controls Salmonella typhimurium infection by modulating host iron homeostasis

In response to microbial infection, expression of the defensin-like peptide hepcidin (encoded by Hamp) is induced in hepatocytes to decrease iron release from macrophages. To elucidate the mechanism by which Salmonella enterica var. Typhimurium (S. typhimurium), an intramacrophage bacterium, alters host iron metabolism for its own survival, we examined the role of nuclear receptor family members belonging to the NR3B subfamily in mouse hepatocytes. Here, we report that estrogen-related receptor γ (ERRγ, encoded by Esrrg) modulates the intramacrophage proliferation of S. typhimurium by altering host iron homeostasis, and we demonstrate an antimicrobial effect of an ERRγ inverse agonist. Hepatic ERRγ expression was induced by S. typhimurium–stimulated interleukin-6 signaling, resulting in an induction of hepcidin and eventual hypoferremia in mice. Conversely, ablation of ERRγ mRNA expression in liver attenuated the S. typhimurium–mediated induction of hepcidin and normalized the hypoferremia caused by S. typhimurium infection. An inverse agonist of ERRγ ameliorated S. typhimurium–mediated hypoferremia through reduction of ERRγ–mediated hepcidin mRNA expression and exerted a potent antimicrobial effect on the S. typhimurium infection, thereby improving host survival. Taken together, these findings suggest an alternative approach to control multidrug-resistant intracellular bacteria by modulating host iron homeostasis.

Fenofibrate Differentially Regulates Plasminogen Activator Inhibitor-1 Gene Expression via Adenosine Monophosphate-Activated Protein Kinase-Dependent Induction of Orphan Nuclear Receptor Small Heterodimer Partner

Plasminogen activator inhibitor type I (PAI‐1) is a marker of the fibrinolytic system and serves as a possible predictor for hepatic metabolic syndromes. Fenofibrate, a peroxisome proliferator‐activated receptor α (PPARα) agonist, is a drug used for treatment of hyperlipidemia. Orphan nuclear receptor small heterodimer partner (SHP) plays a key role in transcriptional repression of crucial genes involved in various metabolic pathways. In this study, we show that fenofibrate increased SHP gene expression in cultured liver cells and in the normal and diabetic mouse liver by activating the adenosine monophosphate–activated protein kinase (AMPK) signaling pathway in a PPARα‐independent manner. Administration of transforming growth factor beta (TGF‐β) or a methionine‐deficient and choline‐deficient (MCD) diet to induce the progressive fibrosing steatohepatitis model in C57BL/6 mice was significantly reversed by fenofibrate via AMPK‐mediated induction of SHP gene expression with a dramatic decrease in PAI‐1 messenger RNA (mRNA) and protein expression along with other fibrotic marker genes. No reversal was observed in SHP null mice treated with fenofibrate. Treatment with another PPARα agonist, WY14643, showed contrasting effects on these marker gene expressions in wild‐type and SHP null mice, demonstrating the specificity of fenofibrate in activating AMPK signaling. Fenofibrate exhibited a differential inhibitory pattern on PAI‐1 gene expression depending on the transcription factors inhibited by SHP. Conclusion: By demonstrating that a PPARα‐independent fenofibrate‐AMPK‐SHP regulatory cascade can play a key role in PAI‐1 gene down‐regulation and reversal of fibrosis, our study suggests that various AMPK activators regulating SHP might provide a novel pharmacologic option in ameliorating hepatic metabolic syndromes. (HEPATOLOGY 2009.)

Clinicopathological characteristics of gastric carcinoma in young patients.

Background and aimsGastric carcinoma is a common disease that usually affects older patients, rarely younger patients. Although the relationship between prognosis and the age of patients with gastric carcinoma is controversial, most investigators have suggested that young patients have a poorer prognosis. This study examined the clinicopathological features of young patients with gastric carcinoma.Patients and methodsWe retrospectively reviewed the hospital records of 1,833 patients with gastric carcinoma to compare the clinicopathological findings in young (aged <36 years) and older (aged ≥ 36 years) patients during the period 1988 to 1998 in a tertiary referral center in Gwangju City. Overall survival was the main outcome measure.ResultsOf the 1,833 patients, 137 (7.5%) were in the young age group. There were no significant differences in depth of invasion, lymph node invasion, hepatic metastasis, peritoneal dissemination, tumor stage or rate of curative resection. A significantly higher percentage of young patients had poorly differentiated histology (P=0.0001). The young patients with curatively resected gastric carcinoma had a better survival rate than young patients with non-resected gastric carcinoma (P<0.001). The 5-year survival rates of young and older patients did not differ statistically (39.6% vs 42.4%; P=0.254).ConclusionYoung patients with gastric carcinoma do not have a worse prognosis than older patients. The important prognostic factor was whether the patients underwent curative resection.

Estrogen-related Receptor γ (ERRγ) Is a Novel Transcriptional Regulator of Phosphatidic Acid Phosphatase, LIPIN1, and Inhibits Hepatic Insulin Signaling

Background: The PAP function of LIPINs is involved in the regulation of intracellular lipid levels and hepatic insulin receptor signaling. Results: ERRγ-mediated induction of LIPIN1 results in the perturbation of hepatic insulin signaling through DAG-mediated activation of PKCϵ. Conclusion: ERRγ is a novel transcriptional regulator of LIPIN1. Significance: An ERRγ inverse agonist could ameliorate LIPIN1-mediated perturbation of hepatic insulin signaling. LIPINs have been reported to perform important roles in the regulation of intracellular lipid levels. Their mutations induce lipodystrophy, myoglobinuria, and inflammatory disorders. Recently, the phosphatidic acid phosphatase function of LIPINs has been associated with the perturbation of hepatic insulin receptor signaling via the diacylglycerol-mediated stimulation of PKCϵ activity. Here, we report that nuclear estrogen-related receptor (ERR) γ is a novel transcriptional regulator of LIPIN1. Overexpression of ERRγ significantly increased LIPIN1 expression in primary hepatocytes, whereas the abolition of ERRγ gene expression attenuated the expression of LIPIN1. Deletion and mutation analyses of the LIPIN1 promoter showed that ERRγ exerts its effect on the transcriptional regulation of LIPIN1 via ERRE1 of the LIPIN1 promoter, as confirmed by ChIP assay. We also determined that the gene transcription of LIPIN1 by ERRγ is controlled by the competition between PGC-1α and small heterodimer partner. Additionally, ERRγ leads to the induction of hepatic LIPIN1 expression and diacylglycerol production in vivo. Finally, an inverse agonist of ERRγ, GSK5182, restores the impaired insulin signaling induced by LIPIN1-mediated PKCϵ activation. Our findings indicate that the selective control of ERRγ transcriptional activity by its specific inverse agonist could provide a novel therapeutic approach to the amelioration of impaired hepatic insulin signaling induced by LIPIN1-mediated PKCϵ activation.

Metformin ameliorates acetaminophen hepatotoxicity via Gadd45β-dependent regulation of JNK signaling in mice

BACKGROUND & AIMS Acetaminophen (APAP) overdose is a leading cause of drug-induced acute liver failure. Prolonged c-Jun N-terminal kinase (JNK) activation plays a central role in APAP-induced liver injury and growth arrest, and DNA damage-inducible 45 beta (Gadd45β) is known to inhibit JNK phosphorylation. Metformin has recently been shown to have hepatoprotective effects. The aim of the present study is to investigate whether metformin mitigates APAP-induced hepatotoxicity and to ascertain the molecular basis of this effect. METHODS We used APAP- and/or metformin-treated Gadd45β knockout (KO) mice and wild type (WT) C57BL/6J control mice. Primary mouse hepatocytes were isolated from WT and Gadd45β KO mice were used for in vitro study. RESULTS Metformin pretreatment protected against APAP toxicity with decreased liver damage, and inhibited APAP-induced prolonged hepatic JNK phosphorylation in WT mice. Gadd45β expression was increased after APAP treatment, and the expression of Gadd45β was further enhanced by metformin. The effects of metformin on APAP-induced liver injury and JNK phosphorylation were abolished in Gadd45β KO mice. Notably, subtoxic doses of APAP caused cell death and sustained JNK phosphorylation in Gadd45β-deficient primary hepatocytes. In parallel, APAP increased mortality, severe liver injury, and JNK activation in Gadd45β KO mice. Interestingly, metformin administered after APAP treatment protected against APAP-evoked hepatotoxicity in WT mice, but not in Gadd45β KO mice. CONCLUSIONS This study is the first to demonstrate that metformin shows protective and therapeutic effects against APAP overdose-evoked hepatotoxicity via Gadd45β-dependent JNK regulation. Metformin would be a promising therapeutic strategy for treatment of APAP overdose.

Clinicopathologic Features of Mucinous Gastric Carcinoma

Background/Aims: Mucinous gastric carcinoma (MGC) is a histopathologic subtype of gastric carcinoma with a poor prognosis. The purpose of this study was to compare the disease course of MGC with non-mucinous gastric carcinoma (NMGC) and study the clinicopathologic features that influence the prognosis of MGC patients. Methods: We reviewed the records of 2,383 patients with a confirmed histologic diagnosis of gastric carcinoma. There were 157 patients with MGC compared to 2,226 with NMGC. Results: A depth of invasion greater than T3 was more frequently found in MGC than in NMGC. The mean number of lymph nodes with metastases was 2.78 in MGC and 2.28 in NMGC (p < 0.001). There were more MGC patients with TNM stages II through IV (UICC classification). The overall survival rate was lower for the MGC group (46.5%) than for the NMGC group (64.0%; p < 0.05). Depth of invasion, lymph node metastases, and stage at diagnosis were significant factors affecting the outcome. Conclusion: The factors influencing the poorer prognosis (lower 5-year survival rate) of MGC are the advanced stage at the time of diagnosis, lymph node metastases, and a higher TNM status. Mucinous histologic type itself was not an independent predictive factor in survival.

Efficient Discovery of Selective Small Molecule Agonists of Estrogen-Related Receptor γ using Combinatorial Approach

With the goal of discovering a selective agonist of estrogen-related receptor gamma (ERRgamma) with enhanced potency, we designed a series of small-molecule ligands derived from a known ERRgamma agonist, GSK4716, that can substantially potentiate the transcriptional activity of ERRgamma. Individual compounds among a 30-member library of acyl hydrazones were pre-evaluated through in silico docking studies on the receptor cavities of ERRgamma LBDs using X-ray crystal structures cocrystallized with GSK4716 and 4-OHT. This rational approach to achieve the enhanced potency in ERRgamma transcriptional activity with selectivity over ERRalpha/beta enables us to complete the construction of a focused library by carrying out microwave-assisted parallel synthesis with excellent yields and purities. Finally, we identified a more potent ERRgamma agonist, E6, with excellent selectivity over ERRalpha/beta.