Histone Demethylase KDM7A Contributes to the Development of Hepatic Steatosis by Targeting Diacylglycerol Acyltransferase 2.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. While the development of NAFLD is correlated with aberrant histone methylation, modifiers of histone methylation involved in this event remain poorly understood. Here, we studied the functional role of the histone demethylase KDM7A in the development of hepatic steatosis. KDM7A overexpression in AML12 cells upregulated diacylglycerol acyltransferase 2 (DGAT2) expression and resulted in increased intracellular triglyceride (TG) accumulation. Conversely, KDM7A knockdown reduced DGAT2 expression and TG accumulation, and significantly reversed free fatty acids-induced TG accumulation. Additionally, adenovirus-mediated overexpression of KDM7A in mice resulted in hepatic steatosis, which was accompanied by increased expression of hepatic DGAT2. Furthermore, KDM7A overexpression decreased the enrichment of di-methylation of histone H3 lysine 9 (H3K9me2) and H3 lysine 27 (H3K27me2) on the promoter of DGAT2. Taken together, these results indicate that KDM7A overexpression induces hepatic steatosis through upregulation of DGAT2 by erasing H3K9me2 and H3K27me2 on the promoter.

Histone H3K9 Demethylase JMJD2B Plays a Role in LXRα-Dependent Lipogenesis.

Ligand-activated liver X receptor α (LXRα) upregulates the expression of hepatic lipogenic genes, which leads to triglyceride (TG) accumulation, resulting in nonalcoholic fatty liver disease (NAFLD). Thus, LXRα regulation may provide a novel therapeutic target against NAFLD. However, histone methylation-mediated epigenetic regulation involved in LXRα-dependent lipogenesis is poorly understood. In this study, we investigated the functional role of the histone demethylase Jumonji domain-containing protein 2B (JMJD2B) in LXRα-dependent lipogenesis. JMJD2B expression level was upregulated in HepG2 cells treated with LXRα agonist T0901317 or palmitate and the liver of mice administered with T0901317 or fed a high-fat diet. Knockdown of JMJD2B using siRNA abrogated T0901317-induced LXRα-dependent lipogenic gene expression and lowered intracellular TG accumulation. Conversely, overexpression of JMJD2B in HepG2 cells upregulated the expression of LXRα-dependent lipogenic genes, in line with increased intracellular TG levels. JMJD2B overexpression or T0901317 treatment induced the recruitment of JMJD2B and LXRα to LXR response elements (LXRE) in the promoter region of LXRα-target gene and reduced the enrichment of H3K9me2 and H3K9me3 in the vicinity of the LXRE. Furthermore, JMJD2B enhanced T0901317 or LXRα-induced transcriptional activities of reporters containing LXRE. A co-immunoprecipitation assay revealed that JMJD2B interacted with activated LXRα. Moreover, overexpression of JMJD2B in mice resulted in upregulation of hepatic LXRα-dependent lipogenic genes, consistent with development of hepatic steatosis. Taken together, these results indicate that JMJD2B plays a role in LXRα-mediated lipogenesis via removing the repressive histone marks, H3K9me2 and H3K9me3, at LXRE, which might contribute to hepatic steatosis.

Role of Cannabinoid Receptor Type 1 in Insulin Resistance and Its Biological Implications.

Endogenous cannabinoids (ECs) are lipid-signaling molecules that specifically bind to cannabinoid receptor types 1 and 2 (CB1R and CB2R) and are highly expressed in central and many peripheral tissues under pathological conditions. Activation of hepatic CB1R is associated with obesity, insulin resistance, and impaired metabolic function, owing to increased energy intake and storage, impaired glucose and lipid metabolism, and enhanced oxidative stress and inflammatory responses. Additionally, blocking peripheral CB1R improves insulin sensitivity and glucose metabolism and also reduces hepatic steatosis and body weight in obese mice. Thus, targeting EC receptors, especially CB1R, may provide a potential therapeutic strategy against obesity and insulin resistance. There are many CB1R antagonists, including inverse agonists and natural compounds that target CB1R and can reduce body weight, adiposity, and hepatic steatosis, and those that improve insulin sensitivity and reverse leptin resistance. Recently, the use of CB1R antagonists was suspended due to adverse central effects, and this caused a major setback in the development of CB1R antagonists. Recent studies, however, have focused on development of antagonists lacking adverse effects. In this review, we detail the important role of CB1R in hepatic insulin resistance and the possible underlying mechanisms, and the therapeutic potential of CB1R targeting is also discussed.

Cryptotanshinone from the Salvia miltiorrhiza Bunge Attenuates Ethanol-Induced Liver Injury by Activation of AMPK/SIRT1 and Nrf2 Signaling Pathways.

Cryptotanshinone (CT), a diterpene that is isolated from Salvia miltiorrhiza Bunge, exhibits anti-cancer, anti-oxidative, anti-fibrosis, and anti-inflammatory properties. Here, we examined whether CT administration possess a hepatoprotective effect on chronic ethanol-induced liver injury. We established a chronic alcohol feeding mouse model while using C57BL/6 mice, and examined the liver sections with hematoxylin-eosin (H&E) and Oil Red O (ORO) staining. Further, we analyzed the lipogenesis, fatty acid oxidation, oxidative stress, and inflammation genes by using quantitative polymerase chain reaction (qPCR) and immunoblotting in in vivo, and in vitro while using HepG2 and AML-12 cells. CT treatment significantly ameliorated ethanol-promoted hepatic steatosis, which was consistent with the decreased hepatic triglyceride levels. Interestingly, CT activated the phosphorylation of AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), and nuclear factor E2-related factor 2 (Nrf2) proteins. Importantly, compound C (AMPK inhibitor) significantly blocked the CT-mediated reduction in TG accumulation, but not Ex52735 (SIRT1 inhibitor), which suggested that CT countering ethanol-promoted hepatic steatosis is mediated by AMPK activation. Furthermore, CT significantly inhibited cytochrome P450 2E1 (CYP2E1) and enhanced both the expression of antioxidant genes and hepatic glutathione levels. Finally, CT inhibited the ethanol-induced inflammation in ethanol-fed mice and HepG2 cells. Overall, CT exhibits a hepatoprotective effect against ethanol-induced liver injury by the inhibition of lipogenesis, oxidative stress, and inflammation through the activation of AMPK/SIRT1 and Nrf2 and the inhibition of CYP2E1. Therefore, CT could be an effective therapeutic agent for treating ethanol-induced liver injury.

Poria cocus Wolf Extract Ameliorates Hepatic Steatosis through Regulation of Lipid Metabolism, Inhibition of ER Stress, and Activation of Autophagy via AMPK Activation.

Poria cocos Wolf (PCW) is an edible, pharmaceutical mushroom with remarkable biological properties including anti-tumor, anti-inflammation, anti-oxidation, anti-ageing, and anti-diabetic effects. In the current study, we investigated the effects of PCW extract on hepatic steatosis under in vitro and in vivo conditions, and elucidated the underlying mechanisms. In this study, a mixture of HepG2 cells treated with free fatty acid (FFA)-palmitic and oleic acid-and high-fat diet (HFD)-fed obese mice were used; in this background, the triglyceride (TG) levels in HepG2 cells and mice liver were measured, and the expression levels of genes associated with lipogenesis, fatty acid oxidation, endoplasmic reticulum (ER) stress, and autophagy were determined. Treatment of HepG2 cells with FFA enhanced intracellular TG levels in HepG2 cells, but co-treatment with PCW significantly attenuated the TG levels. Notably, PCW significantly enhanced the phosphorylation of AMP-activated protein kinase (AMPK), acetyl-CoA carboxylase (ACC), and sterol regulatory element-binding protein-1c (SREBP-1c) in FFA-treated HepG2 cells. PCW downregulated the expression of lipogenesis-related genes, but upregulated the expression of genes associated with fatty acid oxidation. Further, PCW inhibited FFA-induced expression of ER stress markers and induced autophagy proteins. However, inhibition of AMPK significantly attenuated the beneficial effects of PCW in HepG2 cells. Moreover, PCW efficiently decreased HFD-induced hepatic TG accumulation in vivo and increased the phosphorylation of hepatic AMPK. Three compounds present in PCW including poricoic acid, pachymic acid, and ergosterol, significantly decreased FFA-induced increase in intracellular TG levels, consistent with increased AMPK phosphorylation, suggesting that poricoic acid, pachymic acid, and ergosterol are responsible for PCW-mediated amelioration of hepatic steatosis. Taken together, these results demonstrated that PCW ameliorates hepatic steatosis through the regulation of lipid metabolism, inhibition of ER stress, and activation of autophagy in an AMPK-dependent manner. This suggested that PCW can be potentially used for the treatment of hepatic steatosis.

Protective Effects of Gomisin N against Hepatic Cannabinoid Type 1 Receptor-Induced Insulin Resistance and Gluconeogenesis.

Activation of the hepatic cannabinoid type 1 receptor (CB1R) induces insulin resistance and gluconeogenesis via endoplasmic reticulum (ER) stress, thereby contributing to hyperglycemia. Gomisin N (GN) is a phytochemical derived from Schisandra chinensis. In the current study, we investigated the inhibitory effects of GN on hepatic CB1R-mediated insulin resistance and gluconeogenesis in 2-arachidonoylglycerol (AG; an agonist of CB1R)-treated HepG2 cells and in high-fat diet (HFD)-induced obese mice. Treatment with 2-AG induced the expression of ER stress markers, serine/threonine phosphatase PHLPP1, Lipin1, and ceramide synthesis genes, but reduced the expression of ceramide degradation genes in HepG2 cells. However, GN reversed 2-AG-mediated effects and improved the 2-AG-mediated impairment of insulin signaling. Furthermore, GN inhibited 2-AG-induced intracellular triglyceride accumulation and glucose production in HepG2 cells by downregulation of lipogenesis and gluconeogenesis genes, respectively. In vivo, GN administration to HFD obese mice reduced the HFD-induced increase in fasting blood glucose and insulin levels, which was accompanied with downregulation of HFD-induced expression of CB1R, ER stress markers, ceramide synthesis gene, and gluconeogenesis genes in the livers of HFD obese mice. These findings demonstrate that GN protects against hepatic CB1-mediated impairment of insulin signaling and gluconeogenesis, thereby contributing to the amelioration of hyperglycemia.

Gomisin N Alleviates Ethanol-Induced Liver Injury through Ameliorating Lipid Metabolism and Oxidative Stress.

Gomisin N (GN), a lignan derived from Schisandra chinensis, has been shown to possess antioxidant, anti-inflammatory, and anticancer properties. In the present study, we investigated the protective effect of GN against ethanol-induced liver injury using in vivo and in vitro experiments. Histopathological examination revealed that GN administration to chronic-binge ethanol exposure mice significantly reduced ethanol-induced hepatic steatosis through reducing lipogenesis gene expression and increasing fatty acid oxidation gene expression, and prevented liver injury by lowering the serum levels of aspartate transaminase and alanine transaminase. Further, it significantly inhibited cytochrome P450 2E1 (CYP2E1) gene expression and enzyme activity, and enhanced antioxidant genes and glutathione level in hepatic tissues, which led to decreased hepatic malondialdehyde levels. It also lowered inflammation gene expression. Finally, GN administration promoted hepatic sirtuin1 (SIRT1)-AMP-activated protein kinase (AMPK) signaling in ethanol-fed mice. Consistent with in vivo data, treatment with GN decreased lipogenesis gene expression and increased fatty acid oxidation gene expression in ethanol-treated HepG2 cells, thereby preventing ethanol-induced triglyceride accumulation. Furthermore, it inhibited reactive oxygen species generation by downregulating CYP2E1 and upregulating antioxidant gene expression, and suppressed inflammatory gene expression. Moreover, GN prevented ethanol-mediated reduction in SIRT1 and phosphorylated AMPK. These findings indicate that GN has therapeutic potential against alcoholic liver disease through inhibiting hepatic steatosis, oxidative stress and inflammation.

Antidiabetic effect of gomisin N via activation of AMP-activated protein kinase.

Gomisin N (GN) is a lignan derived from Schisandra chinensis. AMP-activated kinase (AMPK) has gained attention as a therapeutic target for the treatment of metabolic syndrome. Previously, we reported that GN activated the AMPK pathway and ameliorated high-fat diet (HFD)-induced hepatic steatosis. In this study, we investigated the anti-diabetic effects of GN in C2C12 myotubes and HFD obese mice. GN enhanced the phosphorylation of AMPK/acetyl-CoA carboxylase (ACC) and Akt. In addition, GN promoted glucose uptake in C2C12 myotubes, which was accompanied by the translocation of glucose transporter 4 (GLUT4) to the plasma membrane. Treatment with compound C, an AMPK inhibitor, suppressed GN-mediated stimulation of glucose uptake. Furthermore, GN increased the expression of mitochondria biogenesis and fatty acid oxidation genes in C2C12 myotubes. In the in vivo study, administration of GN to HFD mice decreased the levels of fasting blood glucose and insulin, and improved glucose tolerance in HFD obese mice. GN administration rescued the decreased phosphorylation of AMPK and Akt and stimulated the expression of mitochondria biogenesis genes in the skeletal muscle of HFD mice. These findings suggested that GN exerted anti-hyperglycemic effects through AMPK activation.

Protective effects of gomisin N against hepatic steatosis through AMPK activation.

Gomisin N (GN) is a phytochemical derived from Schisandra chinensis. It has been reported to exert a protective effect against hepatic steatosis by attenuating endoplasmic reticulum (ER) stress. However, the detailed mechanism by which GN inhibits hepatic steatosis remains to be elucidated. In this study, we examined whether GN activates AMP-activated protein kinase (AMPK) and exerts therapeutic effects on liver X receptor (LXR)- or palmitic acid (PA)-induced triglyceride (TG) accumulation in HepG2 cells. Furthermore, in vivo protective effects of GN against hepatic steatosis were assessed in high-fat diet (HFD)-induced obese mice. GN stimulated the phosphorylation of AMPK, acetyl-CoA carboxylase (ACC), and sterol regulatory element-binding protein 1c (SREBP1c) in HepG2 cells. It decreased the expression of lipogenesis genes, but increased the expression of fatty acid oxidation genes. Additionally, GN decreased the expression of lipogenesis genes induced by the LXR agonist T0901317 or PA in HepG2 cells, resulting in reduced intracellular TG content. However, preincubation with compound C, an AMPK inhibitor, prevented GN-mediated effects. Administration of GN to HFD-induced obese mice decreased HFD-induced liver weight, hepatic TG accumulation, and cytoplasmic lipid droplet. These findings demonstrate that GN activates the AMPK pathway and ameliorates HFD-induced hepatic steatosis.

Menthol Modulates Pacemaker Potentials through TRPA1 Channels in Cultured Interstitial Cells of Cajal from Murine Small Intestine.

BACKGROUND/AIMS: ICCs are the pacemaker cells responsible for slow waves in gastrointestinal (GI) smooth muscle, and generate periodic pacemaker potentials in current-clamp mode. METHODS: The effects of menthol on the pacemaker potentials of cultured interstitial cells of Cajal (ICCs) from mouse small intestine were studied using the whole cell patch clamp technique. RESULTS: Menthol (1 - 10 µM) was found to induce membrane potential depolarization in a concentration-dependent manner. The effects of various TRP channel antagonists were examined to investigate the receptors involved. The addition of the TRPM8 antagonist, AMTB, did not block menthol-induced membrane potential depolarizations, but TRPA1 antagonists (A967079 or HC-030031) blocked the effects of menthol, as did intracellular GDPßS. Furthermore, external and internal Ca2+ levels were found to depolarize menthol-induced membrane potentials, whereas external Na+ was not. Y-27632 (a Rho kinase inhibitor), SC-560 (a selective COX 1 inhibitor), NS-398 (a selective COX 2 inhibitor), ozagrel (a thromboxane A2 synthase inhibitor) and SQ-29548 (highly selective thromboxane receptor antagonist) were used to investigate the involvements of Rho-kinase, cyclooxygenase (COX), and the thromboxane pathway in menthol-induced membrane potential depolarizations, and all inhibitors were found to block the effect of menthol. CONCLUSIONS: These results suggest that menthol-induced membrane potential depolarizations occur in a G-protein-, Ca2+-, Rho-kinase-, COX-, and thromboxane A2-dependent manner via TRPA1 receptor in cultured ICCs in murine small intestine. The study shows ICCs are targeted by menthol and that this interaction can affect intestinal motility.

Protective Effect of Gomisin N against Endoplasmic Reticulum Stress-Induced Hepatic Steatosis.

Gomisin N is a physiological substance derived from Schisandra chinensis. In the present study, the in vitro and in vivo effects of gomisin N on endoplasmic reticulum (ER) stress and hepatic steatosis were investigated. We quantified the expression of markers of ER stress, including glucose regulated protein 78 (GRP78), CCAAT/enhancer binding protein (C/EBP) homolog protein (CHOP), and X-box-binding protein-1 (XBP-1), and triglyceride (TG) accumulation, in HepG2 cells treated with tunicamycin or palmitate. Tunicamycin treatment in HepG2 cells induced expression of markers of ER stress and increased TG levels; Gomisin N reversed these effects, reducing the expression of markers of ER stress and TG levels. Similar effects were seen following palmitate pretreatment of HepG2 cells. The inhibitory effects of gomisin N were further confirmed in mice injected with tunicamycin. Gomisin N reduced expression of markers of ER stress and decreased TG levels in mouse liver after tunicamycin injection. Furthermore, gomisin N decreased expression of inflammatory and lipogenic genes in palmitate-incubated HepG2 cells. These results suggest that gomisin N inhibits ER stress and ameliorates hepatic steatosis induced by ER stress.

Hominis Placenta facilitates hair re-growth by upregulating cellular proliferation and expression of fibroblast growth factor-7.

BACKGROUND: Hominis Placenta (HP) known as a restorative medicine in Traditional Chinese Medicine (TCM), has been widely applied in the clinics of Korea and China as an anti-aging agent to enhance the regeneration of tissue. This study was conducted to investigate whether topical treatment of HP promotes hair regrowth in the animal model. METHODS: The dorsal hairs of 8-week-old C57BL/6 mice were depilated to synchronize hair follicles to the anagen phase. HP was applied topically once a day for 15 days. Hair growth was evaluated visually and microscopically. The incorporation of bromodeoxyuridine (BrdU) and expression of proliferating cell nuclear antigen (PCNA), fibroblast growth factor-7 (FGF-7) in dorsal skin tissue was examined by immunohistochemical analysis. Reverse transcription polymerase chain reaction (RT-PCR) was used to measure the mRNA expression of FGF-7. RESULTS: HP exhibited potent hair growth-promoting activity in C57BL/6 mice. Gross examination indicated that HP markedly increased hair regrowth as well as hair density and diameter. Histologic analysis showed that HP treatment enhanced the anagen induction of hair follicles. Immunohistochemical analysis revealed that BrdU incorporation and the expressions of PCNA were increased by treatment of HP. HP treatment significantly increased the expression of FGF-7, which plays pivotal roles to maintain anagen phase both protein and mRNA levels. CONCLUSIONS: Taken together, our results indicate that HP has a potent hair growth-promoting activity; therefore, it may be a good candidate for the treatment of alopecia.

ATF3 inhibits PPARγ-stimulated transactivation in adipocyte cells.

Previously, we reported that activating transcription factor 3 (ATF3) downregulates peroxisome proliferator activated receptor (PPARγ) gene expression and inhibits adipocyte differentiation in 3T3-L1 cells. Here, we investigated another role of ATF3 on the regulation of PPARγ activity. ATF3 inhibited PPARγ-stimulated transactivation of PPARγ responsive element (PPRE)-containing reporter or GAL4/PPARγ chimeric reporter. Thus, ATF3 effectively repressed rosiglitazone-stimulated expression of adipocyte fatty acid binding protein (aP2), PPARγ target gene, in 3T3-L1 cells. Coimmunoprecipitation and GST pulldown assay demonstrated that ATF3 interacted with PPARγ. Accordingly, ATF3 prevented PPARγ from binding to PPRE on the aP2 promoter. Furthermore, ATF3 suppressed p300-mediated transcriptional coactivation of PPRE-containing reporter. Chromatin immunoprecipitation assay showed that overexpression of ATF3 blocked both binding of PPARγ and recruitment of p300 to PPRE on aP2 promoter induced by rosiglitazone treatment in 3T3-L1 cells. Taken together, these results suggest that ATF3 interacts with PPARγ and represses PPARγ-mediated transactivation through suppression of p300-stimulated coactivation in 3T3-L1 cells, which may play a role in inhibition of adipocyte differentiation.

Protective Effects of Alisma orientale Extract against Hepatic Steatosis via Inhibition of Endoplasmic Reticulum Stress.

Endoplasmic reticulum (ER) stress is associated with the pathogenesis of hepatic steatosis. Alisma orientale Juzepzuk is a traditional medicinal herb for diuretics, diabetes, hepatitis, and inflammation. In this study, we investigated the protective effects of methanol extract of the tuber of Alisma orientale (MEAO) against ER stress-induced hepatic steatosis in vitro and in vivo. MEAO inhibited the tunicamycin-induced increase in luciferase activity of ER stress-reporter constructs containing ER stress response element and ATF6 response element. MEAO significantly inhibited tunicamycin-induced ER stress marker expression including GRP78, CHOP, and XBP-1 in tunicamycin-treated Human hepatocellular carcinoma (HepG2) cells and the livers of tunicamycin-injected mice. It also inhibited tunicamycin-induced accumulation of cellular triglyceride. Similar observations were made under physiological ER stress conditions such as in palmitate (PA)-treated HepG2 cells and the livers of high-fat diet (HFD)-induced obese mice. MEAO repressed hepatic lipogenic gene expression in PA-treated HepG2 cells and the livers of HFD obese mice. Furthermore, MEAO repressed very low-density lipoprotein receptor (VLDLR) expression and improved ApoB secretion in the livers of tunicamycin-injected mice or HFD obese mice as well as in tunicamycin or PA-treated HepG2 cells. Alismol, a guaiane-type sesquiterpenes in Alisma orientale, inhibited GRP78 expression in tunicamycin-treated HepG2 cells. In conclusion, MEAO attenuates ER stress and prevents hepatic steatosis pathogenesis via inhibition of expression of the hepatic lipogenic genes and VLDLR, and enhancement of ApoB secretion.

ATF3 represses PPARγ expression and inhibits adipocyte differentiation.

Activating transcription factor 3 (ATF3) is a stress-adaptive transcription factor that mediates cellular stress response signaling. We previously reported that ATF3 represses CCAAT/enhancer binding protein α (C/EBPα) expression and inhibits 3T3-L1 adipocyte differentiation. In this study, we explored potential role of ATF3 in negatively regulating peroxisome proliferator activated receptor-γ (PPARγ). ATF3 decreased the expression of PPARγ and its target gene in 3T3-L1 adipocytes. ATF3 also repressed the activity of -2.6Kb promoter of mouse PPARγ2. Overexpression of PPARγ significantly prevented the ATF3-mediated inhibition of 3T3-L1 differentiation. Transfection studies with 5' deleted-reporters showed that ATF3 repressed the activity of -2037bp promoter, whereas it did not affect the activity of -1458bp promoter, suggesting that ATF3 responsive element is located between the -2037 and -1458. An electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that ATF3 binds to ATF/CRE site (5'-TGACGTTT-3') between -1537 and -1530. Mutation of the ATF/CRE site abrogated ATF3-mediated transrepression of the PPARγ2 promoter. Treatment with thapsigargin, endoplasmic reticulum (ER) stress inducer, increased ATF3 expression, whereas it decreased PPARγ expression. ATF3 knockdown significantly blocked the thapsigargin-mediated downregulation of PPARγ expression. Furthermore, overexpression of PPARγ prevented inhibition of 3T3-L1 differentiation by thapsigargin. Collectively, these results suggest that ATF3-mediated inhibition of PPARγ expression may contribute to inhibition of adipocyte differentiation during cellular stress including ER stress.

ATF3 plays a role in adipocyte hypoxia-mediated mitochondria dysfunction in obesity.

Obesity-associated adipose tissue hypoxia plays a pivotal role in insulin resistance via impaired adipocyte dysfunction including mitochondria dysfunction. In this study, we investigated the involvement of hypoxia-inducible ATF3 in adipocyte hypoxia-mediated mitochondrial dysfunction. While HIF-1α and ATF3 were increased in white adipose tissue of high fat diet (HFD) obese mice compared with control lean mice, mitochondria-related genes were significantly reduced. Treatment with hypoxia mimetics CoCl(2) or incubation with 2% O(2) impaired mitochondria function as demonstrated by decreases in ATP production, NADH dehydrogenase activity, mitochondrial membrane potential, and reduced expression of mitochondria-related genes including NRF-1, PGC-1α, COX1 and SOD in 3T3-L1 adipocyte cells. Furthermore, overexpression of ATF3 in 3T3-L1 cells also decreased mitochondria function as well as expression of mitochondria-related genes. ATF3 knockdown in 3T3-L1 cells partly prevented the hypoxia-mediated decrease in mitochondria function and expression of mitochondria-related genes. The mitochondria-related genes were decreased in white adipose tissue of ATF3-overexpressing mice compared with wild-type mice. These results suggest that ATF3 may play a role in adipocyte hypoxia-mediated mitochondrial dysfunction in obesity.

Antiobesity activity of Vigna nakashimae extract in high-fat diet-induced obesity.

In this study, we evaluated the antiobesity effects of Vigna nakashimae (VN) extract and elucidated the underlying mechanisms. VN extract suppressed adipocyte differentiation and significantly attenuated the expression of adipogenic genes in 3T3-L1 cells. It decreased the expression of peroxisome proliferator-activated receptor γ (PPARγ) and its target genes in fully differentiated 3T3-L1 cells. Moreover, it enhanced the phosphorylation of AMP-activated protein kinase (AMPK) and acetyl CoA carboxylase (ACC), and increased the expression of fatty acid oxidation genes. In high-fat diet (HFD) fed mice, VN extract suppressed HFD-induced increases in body weight, epididymal fat tissue weight, and hepatic lipid levels, and decreased the plasma levels of triacylglycerols, fatty acid, total cholesterol, and inflammatory cytokines. Consistently with in vitro study results, VN extract prevented HFD-induced increases in the expression of PPARγ and its target genes, and restored the decrease in the phosphorylation of AMPK and ACC in epididymal fat and liver tissues. These findings suggest that Vigna nakashimae prevents obesity through suppression of PPARγ expression and activation of AMPK, and that it might be a useful dietary supplement for the prevention of obesity.

ATF3 inhibits adipocyte differentiation of 3T3-L1 cells.

ATF3 is a stress-adaptive gene that regulates proliferation or apoptosis under stress conditions. However, the role of ATF3 is unknown in adipocyte cells. Therefore, in this study, we investigated the functional role of ATF3 in adipocytes. Both lentivirus-mediated overexpression of ATF3 and stably-overexpressed ATF3 inhibited adipocyte differentiation in 3T3-L1 cells, as revealed by decreased lipid staining with oil red staining and reduction in adipogenic genes. Thapsigargin treatment and overexpression of ATF3 decreased C/EBPα transcript and repressed the activity of the 3.6-kb mouse C/EBPα promoter, demonstrating that ATF3 downregulates C/EBPα expression. Transfection studies using mutant constructs containing 5'-deletions in the C/EBPα promoter revealed that a putative ATF/CRE element, GGATGTCA, is located between -1921 and -1914. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that ATF3 directly binds to mouse C/EBPα promoter spanning from -1928 to -1907. Both chemical hypoxia-mimetics or physical hypoxia led to reduce the C/EBPα mRNA and repress the promoter activity of the C/EBPα gene, whereas increase ATF3 mRNA, suggesting that ATF3 may contribute to the inhibition of adipocyte differentiation in hypoxia through downregulation of C/EBPα expression. Collectively, these results demonstrate that ATF3 represses the C/EBPα gene, resulting in inhibition of adipocyte differentiation, and thus plays a role in hypoxia-mediated inhibition of adipocyte differentiation.

Tanshinone 1 prevents high fat diet-induced obesity through activation of brown adipocytes and induction of browning in white adipocytes.

AIM: Increasing brown adipocytes activity and inducting browning of white adipocytes are potential therapeutic targets for the treatment of obesity. In the present study, we investigated the effects of Tanshinone 1 (Tan 1), a major compound from Salvia miltiorrhiza Bunge, on the activation of brown adipocytes and browning of white adipocytes in vivo and in vitro. MATERIALS AND METHODS: Expression of genes associated with brown adipocyte function including thermogenesis, mitochondria biogenesis and fatty acid oxidation was examined in brown adipose tissue (BAT) and white adipose tissue (WAT) of high fat diet (HFD)-fed obese mice administrated with Tan 1 or in immortalized brown adipocytes (iBAs) and 3T3-L1 adipocytes treated with Tan 1. Mitochondria DNA (mtDNA) content, lipolysis and phosphorylated AMP-activated protein kinase (AMPK) were further assessed in Tan 1 treated-iBAs and 3T3-L1 adipocytes. KEY FINDINGS: The administration of Tan 1 protected against HFD-induced obesity in mice, which was associated with enhanced expression of brown adipocyte function-related genes in BAT and WAT. Tan 1 treatment also upregulated brown adipocyte function-related genes in iBA and induced beige adipocytes genes in 3T3-L1 adipocytes, resulting in increased mtDNA content and lipolysis. Tan 1 activated AMPK in BAT and WAT of HFD-fed obese mice as well as in iBAs and 3T3-L1 adipocytes. Inhibition of AMPK by compound C prevented Tan 1-induced expression of beige adipocytes genes. SIGNIFICANCE: These results indicate that Tan 1 activates brown adipocytes and induces browning of white adipocytes, which may contribute to anti-obesity activity of Tan 1.

ATF3 represses PDX-1 expression in pancreatic ß-cells.

The downregulation of PDX-1 expression plays an important role in development of type 2 diabetes. However, the negative regulator of PDX-1 expression is not well known. In this study, we analyzed the mouse PDX-1 promoter to characterize the effects of ATF3 on PDX-1 expression in pancreatic ß-cells. Both thapsigargin treatment, an inducer of ER stress, and ATF3 expression decreased PDX-1 expression in pancreatic ß-cells, MIN6N8. Furthermore, they also repressed the activity of -4.5 Kb promoter of mouse PDX-1 gene. Transfection studies with 5' deleted-reporters showed that ATF3 repressed the activity of 0.9Kb PDX-1 promoter, whereas it did not affect the activity of 0.7 Kb PDX-1 promoter, suggesting that ATF3 responsive element is located between the -903 and -702. An electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that ATF3 binds directly to the promoter region spanning from -759 to -738. Moreover, mutation of the putative ATF/CRE site between -752 and -745 abrogated ATF3-mediated transrepression of the PDX-1 promoter. PDX-1 was decreased in MIN6N8 cells treated with high glucose or high palmitate, whereas ATF3 was increased, indicating that ATF3 plays a role in hyperglycemia or hyperlipidemia-mediated downregulation of PDX-1 expression. Collectively, these results demonstrate that ATF3 represses PDX-1 expression via binding to an ATF3-responsive element in its promoter, which plays an important role in suppression of pancreatic ß-cells function.