Liver-specific Gene Inactivation of the Transcription Factor ATF4 Alleviates Alcoholic Liver Steatosis in Mice.

Although numerous biological functions of the activating transcription factor 4 (ATF4) have been identified, a direct effect of ATF4 on alcoholic liver steatosis has not been described previously. The aim of our current study is to investigate the role of ATF4 in alcoholic liver steatosis and elucidate the underlying mechanisms. Here, we showed that the expression of ATF4 is induced by ethanol in hepatocytes in vitro and in vivo, and liver-specific ATF4 knock-out mice are resistant to ethanol-induced liver steatosis, associated with stimulated hepatic AMP-activated protein kinase (AMPK) activity. Furthermore, adenovirus-mediated AMPK knockdown significantly reversed the suppressive effects of ATF4 deficiency on ethanol-induced liver steatosis in mice. In addition, ethanol-fed ATF4 knock-out mice exhibit AMPK-dependent inhibition of fatty acid synthase and stimulation of carnitine palmitoyltransferase 1 (CPT1) in the liver. Moreover, hepatic Tribbles homolog 3 (TRB3) expression was stimulated by ethanol in an ATF4-dependent manner, and adenovirus-mediated TRB3 knockdown blocked ATF4-dependent ethanol-induced AMPK inhibition and triglyceride accumulation in AML-12 cells. Finally, TRB3 directly interacted with AMPK to suppress its phosphorylation. Taken together, these results identify the ATF4-TRB3-AMPK axis as a novel pathway responsible for ethanol-induced liver steatosis.

Hepatic serum- and glucocorticoid-regulated protein kinase 1 (SGK1) regulates insulin sensitivity in mice via extracellular-signal-regulated kinase 1/2 (ERK1/2).

Insulin resistance is a major hallmark of metabolic syndromes, including Type 2 diabetes. Although numerous functions of SGK1 (serum- and glucocorticoid-regulated kinase 1) have been identified, a direct effect of SGK1 on insulin sensitivity has not been previously reported. In the present study, we generated liver-specific SGK1-knockout mice and found that these mice developed glucose intolerance and insulin resistance. We also found that insulin signalling is enhanced or impaired in Hep1-6 cells infected with adenoviruses expressing SGK1 (Ad-SGK1) or shRNA directed against the coding region of SGK1 (Ad-shSGK1) respectively. In addition, we determined that SGK1 inhibits ERK1/2 (extracellular-signal-regulated kinase 1/2) activity in liver and Ad-shERK1/2-mediated inhibition of ERK1/2 reverses the attenuated insulin sensitivity in Ad-shSGK1 mice. Finally, we found that SGK1 functions are compromised under insulin-resistant conditions and overexpression of SGK1 by Ad-SGK1 significantly ameliorates insulin resistance in both glucosamine-treated HepG2 cells and livers of db/db mice, a genetic model of insulin resistance.

Central prolactin receptors (PRLRs) regulate hepatic insulin sensitivity in mice via signal transducer and activator of transcription 5 (STAT5) and the vagus nerve.

AIMS/HYPOTHESIS: Recent studies have revealed the crucial role of the central nervous system (CNS), especially the hypothalamus, in the regulation of insulin sensitivity in peripheral tissues. The aim of our current study was to investigate the possible involvement of hypothalamic prolactin receptors (PRLRs) in the regulation of hepatic insulin sensitivity. METHODS: We employed overexpression of PRLRs in mouse hypothalamus via intracerebroventricular injection of adenovirus expressing PRLR and inhibition of PRLRs via adenovirus expressing short-hairpin RNA (shRNA) specific for PRLRs in vivo. Selective hepatic vagotomy was employed to verify the important role of the vagus nerve in mediating signals from the brain to peripheral organs. In addition, a genetic insulin-resistant animal model, the db/db mouse, was used in our study to investigate the role of hypothalamic PRLRs in regulating whole-body insulin sensitivity. RESULTS: Overexpression of PRLRs in the hypothalamus improved hepatic insulin sensitivity in mice and inhibition of hypothalamic PRLRs had the opposite effect. In addition, we demonstrated that hypothalamic PRLR-improved insulin sensitivity was significantly attenuated by inhibiting the activity of signal transducer and activator of transcription 5 (STAT5) in the CNS and by selective hepatic vagotomy. Finally, overexpression of PRLRs significantly ameliorated insulin resistance in db/db mice. CONCLUSIONS/INTERPRETATION: Our study identifies a novel central pathway involved in the regulation of hepatic insulin sensitivity, mediated by hypothalamic PRLR/STAT5 signalling and the vagus nerve, thus demonstrating an important role for hypothalamic PRLRs under conditions of insulin resistance.

Reducing Hypothalamic Stem Cell Senescence Protects against Aging-Associated Physiological Decline.

Age-dependent loss of hypothalamic neural stem cells (htNSCs) is important for the pathological consequences of aging; however, it is unclear what drives the senescence of htNSCs. Here, we report that a long non-coding RNA, Hnscr, is abundantly expressed in the htNSCs of young mice but decreases markedly in middle-aged mice. We show that depletion of Hnscr is sufficient to drive the senescence of htNSCs and aging-like phenotypes in mice. Mechanistically, Hnscr binds to Y-box protein 1 (YB-1) to prevent its degradation and thus the attenuation of transcription of the senescence marker gene p16INK4A. Through molecular docking, we discovered that a naturally occurring small compound, theaflavin 3-gallate, can mimic the activity of Hnscr. Treatment of middle-aged mice with theaflavin 3-gallate reduced the senescence of htNSCs while improving aging-associated pathology. These results point to a mediator of the aging process and one that can be pharmacologically targeted to improve aging-related outcomes.

MicroRNA-188 regulates aging-associated metabolic phenotype.

With the increasing aging population, aging-associated diseases are becoming epidemic worldwide, including aging-associated metabolic dysfunction. However, the underlying mechanisms are poorly understood. In the present study, we aimed to investigate the role of microRNA miR-188 in the aging-associated metabolic phenotype. The results showed that the expression of miR-188 increased gradually in brown adipose tissue (BAT) and inguinal white adipose tissue (iWAT) of mice during aging. MiR-188 knockout mice were resistant to the aging-associated metabolic phenotype and had higher energy expenditure. Meanwhile, adipose tissue-specific miR-188 transgenic mice displayed the opposite phenotype. Mechanistically, we identified the thermogenic-related gene Prdm16 (encoding PR domain containing 16) as the direct target of miR-188. Notably, inhibition of miR-188 expression in BAT and iWAT of aged mice by tail vein injection of antagomiR-188 ameliorated aging-associated metabolic dysfunction significantly. Taken together, our findings suggested that miR-188 plays an important role in the regulation of the aging-associated metabolic phenotype, and targeting miR-188 could be an effective strategy to prevent aging-associated metabolic dysfunction.

The miR-26a/AP-2α/Nanog signaling axis mediates stem cell self-renewal and temozolomide resistance in glioma.

Aberrant expression of transcription factor AP-2α has been functionally associated with various cancers, but its clinical significance and molecular mechanisms in human glioma are largely elusive. Methods: AP-2α expression was analyzed in human glioma tissues by immunohistochemistry (IHC) and in glioma cell lines by Western blot. The effects of AP-2α on glioma cell proliferation, migration, invasion and tumor formation were evaluated by the 3-(4,5-dimethyNCthiazol-2-yl)-25-diphenyltetrazolium bromide (MTT) and transwell assays in vitro and in nude mouse models in vivo. The influence of AP-2α on glioma cell stemness was analyzed by sphere-formation, self-renewal and limiting dilution assays in vitro and in intracranial mouse models in vivo. The effects of AP-2α on temozolomide (TMZ) resistance were detected by the MTT assay, cell apoptosis, real-time PCR analysis, western blotting and mouse experiments. The correlation between AP-2α expression and the expression of miR-26a, Nanog was determined by luciferase reporter assays, electrophoretic mobility shift assay (EMSA) and expression analysis. Results: AP-2α expression was downregulated in 58.5% of glioma tissues and in 4 glioma cell lines. AP-2α overexpression not only reduced the proliferation, migration and invasion of glioma cell lines but also suppressed the sphere-formation and self-renewal abilities of glioma stem cells in vitro. Moreover, AP-2α overexpression inhibited subcutaneous and intracranial xenograft tumor growth in vivo. Furthermore, AP-2α enhanced the sensitivity of glioma cells to TMZ. Finally, AP-2α directly bound to the regulatory region of the Nanog gene, reduced Nanog, Sox2 and CD133 expression. Meanwhile, AP-2α indirectly downregulated Nanog expression by inhibiting the interleukin 6/janus kinase 2/signal transducer and activator of transcription 3 (IL6/JAK2/STAT3) signaling pathway, consequently decreasing O6-methylguanine methyltransferase (MGMT) and programmed death-ligand 1 (PD-L1) expression. In addition, miR-26a decreased AP-2α expression by binding to the 3' untranslated region (UTR) of AP-2α and reversed the tumor suppressive role of AP-2α in glioma, which was rescued by a miR-26a inhibitor. TMZ and the miR-26a inhibitor synergistically suppressed intracranial GSC growth. Conclusion: These results suggest that AP-2α reduces the stemness and TMZ resistance of glioma by inhibiting the Nanog/Sox2/CD133 axis and IL6/STAT3 signaling pathways. Therefore, AP-2α and miR-26a inhibition might represent a new target for developing new therapeutic strategies in TMZ resistance and recurrent glioma patients.

Bone Marrow Mesenchymal Stem Cells-Derived Exosomal MiR-29b-3p Regulates Aging-Associated Insulin Resistance.

Insulin resistance is the major pathological characteristic of type 2 diabetes, and the elderly often develop insulin resistance. However, the deep-seated mechanisms for aging-related insulin resistance remain unclear. Here, we showed that nanosized exosomes released by bone marrow mesenchymal stem cells (BM-MSCs) of aged mice could be taken up by adipocytes, myocytes, and hepatocytes, resulting in insulin resistance both in vivo and in vitro. Using microRNA (miRNA) array assays, we found that the amount of miR-29b-3p was dramatically increased in exosomes released by BM-MSCs of aged mice. Mechanistically, SIRT1 (sirtuin 1) was identified to function as the downstream target of exosomal miR-29b-3p in regulating insulin resistance. Notably, utilizing an aptamer-mediated nanocomplex delivery system that down-regulated the level of miR-29b-3p in BM-MSCs-derived exosomes significantly ameliorated the insulin resistance of aged mice. Meanwhile, BM-MSCs-specific overexpression of miR-29b-3p induced insulin resistance in young mice. Taken together, these findings suggested that BM-MSCs-derived exosomal miR-29b-3p could modulate aging-related insulin resistance, which may serve as a potential therapeutic target for aging-associated insulin resistance.

Hepatic c-Jun regulates glucose metabolism via FGF21 and modulates body temperature through the neural signals.

OBJECTIVE: c-Jun, a prominent member of the activator protein 1 (AP-1) family, is involved in various physiology processes such as cell death and survival. However, a role of hepatic c-Jun in the whole-body metabolism is poorly understood. METHODS: We generated liver-specific c-Jun knock-out (c-jun△li) mice to investigate the effect of hepatic c-Jun on the whole-body physiology, particularly in blood glucose and body temperature. Primary hepatocytes were also used to explore a direct regulation of c-Jun in gluconeogenesis. RESULTS: c-jun△li mice showed higher hepatic gluconeogenic capacity compared with control mice, and similar results were obtained in vitro. In addition, fibroblast growth factor 21 (FGF21) expression was directly inhibited by c-Jun knockdown and adenovirus-mediated hepatic FGF21 over-expression blocked the effect of c-Jun on gluconeogenesis in c-jun△li mice. Interestingly, c-jun△li mice also exhibited higher body temperature, with induced thermogenesis and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). Furthermore, the body temperature became comparable between c-jun△li and control mice at thermoneutral temperature (30 °C). Moreover, the activity of sympathetic nervous system (SNS) was increased in c-jun△li mice and the higher body temperature was inhibited by beta-adrenergic receptor blocker injection. Finally, the activated SNS and increased body temperature in c-jun△li mice was most likely caused by the signals from the brain and hepatic vagus nerve, as the expression of c-Fos (the molecular marker of neuronal activation) was changed in several brain areas controlling body temperature and body temperature was decreased by selective hepatic vagotomy. CONCLUSIONS: These data demonstrate a novel function of hepatic c-Jun in the regulation of gluconeogenesis and body temperature via FGF21 and neural signals. Our results also provide novel insights into the organ crosstalk in the regulation of the whole-body physiology.

Krüppel-like factor 3 inhibition by mutated lncRNA Reg1cp results in human high bone mass syndrome.

High bone mass (HBM) is usually caused by gene mutations, and its mechanism remains unclear. In the present study, we identified a novel mutation in the long noncoding RNA Reg1cp that is associated with HBM. Subsequent analysis in 1,465 Chinese subjects revealed that heterozygous Reg1cp individuals had higher bone density compared with subjects with WT Reg1cp Mutant Reg1cp increased the formation of the CD31hiEmcnhi endothelium in the bone marrow, which stimulated angiogenesis during osteogenesis. Mechanistically, mutant Reg1cp directly binds to Krüppel-like factor 3 (KLF3) to inhibit its activity. Mice depleted of Klf3 in endothelial cells showed a high abundance of CD31hiEmcnhi vessels and increased bone mass. Notably, we identified a natural compound, Ophiopogonin D, which functions as a KLF3 inhibitor. Administration of Ophiopogonin D increased the abundance of CD31hiEmcnhi vessels and bone formation. Our findings revealed a specific mutation in lncRNA Reg1cp that is involved in the pathogenesis of HBM and provides a new target to treat osteoporosis.

AP-2ß inhibits hepatocellular carcinoma invasion and metastasis through Slug and Snail to suppress epithelial-mesenchymal transition.

Transcription factor AP-2ß plays an important role in human cancer, but its clinical significance in hepatocellular carcinogenesis is largely unknown. Methods: AP-2ß expression was detected in human hepatocellular cancer (HCC) tissues and cell lines. The effects of AP-2ß on HCC proliferation, migration, invasion, tumor formation and metastasis were evaluated by MTT, colony formation and transwell assays in vitro and mouse experiments in vivo. The association between AP-2ß and miR-27a/EMT markers in HCC cell lines and tissues was analyzed. Results: AP-2ß expression was decreased in HCC tissues and cell lines. Reduced expression of AP-2ß was significantly associated with more advanced tumor stages and larger tumor sizes. The overexpression of AP-2ß reduced HCC proliferation, migration, invasion, tumor formation and metastasis in vitro and in vivo. Additionally, AP-2ß overexpression increased the sensitivity of HCC cells to cisplatin. Moreover, AP-2ß modulates the levels of EMT markers through Slug and Snail in HCC cell lines and tissues. Furthermore, oncogenic miR-27a inhibits AP-2ß expression by binding to the AP-2ß 3' untranslated region (UTR) and reverses the tumor suppressive role of AP-2ß. Conclusion: These results suggested that AP-2ß is lowly expressed in HCC by inhibiting EMT signaling to regulate HCC cell growth and migration. Therefore, AP-2ß in the novel miR-27a/AP-2ß/Slug/EMT regulatory axis enhances the chemotherapeutic drug sensitivity of HCC and might represent a potential target for evaluating the treatment and prognosis of human HCC.

SGK1/FOXO3 Signaling in Hypothalamic POMC Neurons Mediates Glucocorticoid-Increased Adiposity.

Although the central nervous system has been implicated in glucocorticoid-induced gain of fat mass, the underlying mechanisms are poorly understood. The aim of this study was to investigate the possible involvement of hypothalamic serum- and glucocorticoid-regulated kinase 1 (SGK1) in glucocorticoid-increased adiposity. It is well known that SGK1 expression is induced by acute glucocorticoid treatment, but it is interesting that we found its expression to be decreased in the arcuate nucleus of the hypothalamus, including proopiomelanocortin (POMC) neurons, following chronic dexamethasone (Dex) treatment. To study the role of SGK1 in POMC neurons, we produced mice that developed or experienced adult-onset SGK1 deletion in POMC neurons (PSKO). As observed in Dex-treated mice, PSKO mice exhibited increased adiposity and decreased energy expenditure. Mice overexpressing constitutively active SGK1 in POMC neurons consistently had the opposite phenotype and did not experience Dex-increased adiposity. Finally, Dex decreased hypothalamic α-melanocyte-stimulating hormone (α-MSH) content and its precursor Pomc expression via SGK1/FOXO3 signaling, and intracerebroventricular injection of α-MSH or adenovirus-mediated FOXO3 knockdown in the arcuate nucleus largely reversed the metabolic alterations in PSKO mice. These results demonstrate that POMC SGK1/FOXO3 signaling mediates glucocorticoid-increased adiposity, providing new insights into the mechanistic link between glucocorticoids and fat accumulation and important hints for possible treatment targets for obesity.

MAEL contributes to gastric cancer progression by promoting ILKAP degradation.

The cancer-testis gene MAEL is involved in the development and progression of bladder, liver and colorectal cancers. However, its role in other cancers is unclear. By systematically analyzing transcriptomics and genomics data from various cancer databases, we identified that the MAEL gene is aberrantly elevated in gastric cancer (GC) tissues and that its expression is strongly negatively correlated with DNA methylation (Pearson's correlation coefficient = -0.675). Survival analysis revealed that MAEL expression may serve as a prognostic marker for GC patients (overall survival: hazard ratio [HR] = 1.54, p = 1.2E-4; first progression: HR = 1.51, p = 8.7E-4). In vitro and in vivo experiments demonstrated that silencing MAEL expression in the GC cell lines HGC-27 and AGS inhibits proliferation, colony formation, migration, invasion and growth of xenograft tumors, whereas MAEL overexpression exerts the opposite effects in the normal gastric cell line GES-1. Mechanistically, MAEL promotes the lysosome-dependent degradation of the protein phosphatase ILKAP, leading to increased phosphorylation of its substrates (p38, CHK1 and RSK2). Moreover, adenovirus-mediated ILKAP overexpression reversed the oncogenic effects of MAEL in vitro and in vivo. Taken together, these results indicate that MAEL exerts its oncogenic function by promoting ILKAP degradation in the GC.

ATF4/ATG5 Signaling in Hypothalamic Proopiomelanocortin Neurons Regulates Fat Mass via Affecting Energy Expenditure.

Although many biological functions of activating transcription factor 4 (ATF4) have been identified, a role of hypothalamic ATF4 in the regulation of energy homeostasis is poorly understood. In this study, we showed that hypothalamic proopiomelanocortin (POMC) neuron-specific ATF4 knockout (PAKO) mice are lean and have higher energy expenditure. Furthermore, PAKO mice were resistant to high-fat diet-induced obesity, glucose intolerance, and leptin resistance. Moreover, the expression of autophagy protein 5 (ATG5) was increased or decreased by ATF4 knockdown or overexpression, respectively, and ATF4 inhibited the transcription of ATG5 by binding to the basic zipper-containing protein sites on its promoter. Importantly, mice with double knockout of ATF4 and ATG5 in POMC neurons gained more fat mass and reduced energy expenditure compared with PAKO mice under a high-fat diet. Finally, the effect of ATF4 deletion in POMC neurons was possibly mediated via enhanced ATG5-dependent autophagy and α-melanocyte-stimulating hormone production in the hypothalamus. Taken together, these results identify the beneficial role of hypothalamic ATF4/ATG5 axis in the regulation of energy expenditure, obesity, and obesity-related metabolic disorders, which suggests that ATF4/ATG5 axis in the hypothalamus may be a new potential therapeutic target for treating obesity and obesity-related metabolic diseases.

An ATF4-ATG5 signaling in hypothalamic POMC neurons regulates obesity.

ATF4 (activating transcription factor 4) is an important transcription factor that has many biological functions, while its role in hypothalamic POMC (pro-opiomelanocortin-α) neurons in the regulation of energy homeostasis has not been explored. We recently discovered that mice with an Atf4 deletion specific to POMC neurons (PAKO mice) are lean and have higher energy expenditure. Furthermore, these mice are resistant to high-fat diet (HFD)-induced obesity and obesity-related metabolic disorders. Mechanistically, we found the expression of ATG5 (autophagy-related 5) is upregulated in POMC neurons of PAKO mice, and ATF4 regulates ATG5 expression by binding directly to its promoter. Mice with Atf4 and Atg5 double knockout in POMC neurons have reduced energy expenditure and gain more fat mass compared with PAKO mice under a HFD. Finally, the effect of Atf4 knockout in POMC neurons is possibly mediated by enhanced ATG5-dependent macroautophagy/autophagy and α-melanocyte-stimulating hormone (α-MSH) production in the hypothalamus. Together, this work not only identifies a beneficial role for ATF4 in hypothalamic POMC neurons in the regulation of obesity, but also provides a new potential therapeutic target for obesity and obesity-related metabolic diseases.

Deletion of ATF4 in AgRP Neurons Promotes Fat Loss Mainly via Increasing Energy Expenditure.

Although many functions of activating transcription factor 4 (ATF4) are identified, a role of ATF4 in the hypothalamus in regulating energy homeostasis is unknown. Here, we generated adult-onset agouti-related peptide neuron-specific ATF4 knockout (AgRP-ATF4 KO) mice and found that these mice were lean, with improved insulin and leptin sensitivity and decreased hepatic lipid accumulation. Furthermore, AgRP-ATF4 KO mice showed reduced food intake and increased energy expenditure, mainly because of enhanced thermogenesis in brown adipose tissue. Moreover, AgRP-ATF4 KO mice were resistant to high-fat diet-induced obesity, insulin resistance, and liver steatosis and maintained at a higher body temperature under cold stress. Interestingly, the expression of FOXO1 was directly regulated by ATF4 via binding to the cAMP-responsive element site on its promoter in hypothalamic GT1-7 cells. Finally, Foxo1 expression was reduced in the arcuate nucleus (ARC) of the hypothalamus of AgRP-ATF4 KO mice, and adenovirus-mediated overexpression of FOXO1 in ARC increased the fat mass in AgRP-ATF4 KO mice. Collectively, our data demonstrate a novel function of ATF4 in AgRP neurons of the hypothalamus in energy balance and lipid metabolism and suggest hypothalamic ATF4 as a potential drug target for treating obesity and its related metabolic disorders.

Knockout of inositol-requiring enzyme 1α in pro-opiomelanocortin neurons decreases fat mass via increasing energy expenditure.

Although numerous functions of inositol-requiring enzyme 1α (IRE1α) have been identified, a role of IRE1α in pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus is largely unknown. Here, we showed that mice lacking IRE1α specifically in POMC neurons (PIKO) are lean and resistant to high-fat diet-induced obesity and obesity-related insulin resistance, liver steatosis and leptin resistance. Furthermore, PIKO mice had higher energy expenditure, probably due to increased thermogenesis in brown adipose tissue. Additionally, α-melanocyte-stimulating hormone production was increased in the hypothalamus of PIKO mice. These results demonstrate that IRE1α in POMC neurons plays a critical role in the regulation of obesity and obesity-related metabolic disorders. Our results also suggest that IRE1α is not only an endoplasmic reticulum stress sensor, but also a new potential therapeutic target for obesity and obesity-related metabolic diseases.

Activation of ERK1/2 Ameliorates Liver Steatosis in Leptin Receptor-Deficient (db/db) Mice via Stimulating ATG7-Dependent Autophagy.

Although numerous functions of extracellular signal-regulated kinase 1/2 (ERK1/2) are identified, a direct effect of ERK1/2 on liver steatosis has not been reported. Here, we show that ERK1/2 activity is compromised in livers of leptin receptor-deficient (db/db) mice. Adenovirus-mediated activation of mitogen-activated protein kinase kinase 1 (MEK1), the upstream regulator of ERK1/2, significantly ameliorated liver steatosis in db/db mice, increased expression of genes related to fatty acid ß-oxidation and triglyceride (TG) export and increased serum ß-hydroxybutyrate (3-HB) levels. Opposite effects were observed in adenovirus-mediated ERK1/2 knockdown C57/B6J wild-type mice. Furthermore, autophagy and autophagy-related protein 7 (ATG7) expression were decreased or increased by ERK1/2 knockdown or activation, respectively, in primary hepatocytes and liver. Blockade of autophagy by the autophagy inhibitor chloroquine or adenovirus-mediated ATG7 knockdown reversed the ameliorated liver steatosis in recombinant adenoviruses construct expressing rat constitutively active MEK1 Ad-CA MEK1 db/db mice, decreased expression of genes related to fatty acid ß-oxidation and TG export, and decreased serum 3-HB levels. Finally, ERK1/2 regulated ATG7 expression in a p38-dependent pathway. Taken together, these results identify a novel beneficial role for ERK1/2 in liver steatosis via promoting ATG7-dependent autophagy, which provides new insights into the mechanisms underlying liver steatosis and important hints for targeting ERK1/2 in treating liver steatosis.

A Novel Function of Hepatic FOG2 in Insulin Sensitivity and Lipid Metabolism Through PPARα.

Friend of GATA 2 (FOG2) is a transcriptional cofactor involved mostly in cardiac function. The aim of this study was to investigate the role of hepatic FOG2 in insulin sensitivity and lipid accumulation. FOG2 overexpression by adenovirus-expressing FOG2 (Ad-FOG2) significantly attenuates insulin signaling in hepatocytes in vitro. Opposite effects were observed when FOG2 was knocked down through adenovirus-expressing small hairpin RNA for FOG2 (Ad-shFOG2). Furthermore, FOG2 knockdown by Ad-shFOG2 ameliorated insulin resistance in leptin receptor-mutated (db/db) mice, and FOG2 overexpression by Ad-FOG2 attenuated insulin sensitivity in C57BL/6J wild-type (WT) mice. In addition, Ad-FOG2 reduced, whereas Ad-shFOG2 promoted, hepatic triglyceride (TG) accumulation in WT mice under fed or fasted conditions, which was associated with increased or decreased hepatic peroxisome proliferator-activated receptor α (PPARα) expression, respectively. Moreover, the improved insulin sensitivity and increased hepatic TG accumulation by Ad-shFOG2 were largely reversed by adenovirus-expressing PPARα (Ad-PPARα) in WT mice. Finally, we generated FOG2 liver-specific knockout mice and found that they exhibit enhanced insulin sensitivity and elevated hepatic TG accumulation, which were also reversed by Ad-PPARα. Taken together, the results demonstrate a novel function of hepatic FOG2 in insulin sensitivity and lipid metabolism through PPARα.

MAPK1/3 regulate hepatic lipid metabolism via ATG7-dependent autophagy.

Although many biological functions of MAPK1/ERK2-MAPK3/ERK1 (mitogen-activated protein kinase 1/3) have been reported, a direct effect of MAPK1/3 on hepatic lipid metabolism remains largely unknown. We recently showed that activation of MAPK1/3 ameliorates liver steatosis in LEPR (leptin receptor)-deficient (db/db) mice, a classic animal model for liver steatosis. Consistent with these results, knockdown of MAPK1/3 promotes liver steatosis in C57/B6J wild-type (WT) mice. Autophagic flux and ATG7 (autophagy related 7) levels are increased by MAPK1/3 activation or decreased by MAPK1/3 knockdown in livers and primary hepatocytes. Blockade of autophagic flux by chloroquine (CQ) or ATG7 knockdown reverses the ameliorated liver steatosis in MAPK1/3-activated db/db mice. Together, these findings identify a beneficial role for MAPK1/3 in liver steatosis that is mediated by ATG7-dependent autophagy, which provides novel insights into the mechanisms underlying liver steatosis and create a rationale for targeting MAPK1/3 in the treatment of liver steatosis.

Proteomic analysis reveals that MAEL, a component of nuage, interacts with stress granule proteins in cancer cells.

The Maelstrom (MAEL) gene is a cancer-testis (or cancer-germline) gene, which is predominantly expressed in germline cells under normal conditions, but is aberrantly expressed in a range of human cancer cells. In germline cells, MAEL is found predominantly in the nuage, where it plays an essential role in piRNA biogenesis and piRNA-mediated silencing of transposons. However, the role of MAEL in cancer has not been elucidated. We performed immunoprecipitation and Nano-LC-MS/MS analysis to investigate the interactome of MAEL, and identified 14 components of stress granules (SGs) as potential binding partners of MAEL in MDA-MB-231 human breast cancer and SW480 colorectal cancer cells. The interactions between MAEL and 8 of these SG components (PABPC1, YBX1, KHSRP, SYNCRIP, DDX39, ELAV1, EIF4A1 and EIF3F) were confirmed by anti-tag immunoprecipitation. Immunofluorescence analysis showed that MAEL co-localizes with the SG marker PABPC1 in SGs during oxidative stress. Nuages and SGs are the cytoplasmic RNA granules of germline cells and stressed somatic cells, respectively, and both serve as a platform for small RNA-mediated gene silencing. It is, therefore, suggested that MAEL may be involved in miRNA-mediated gene silencing in SGs, as it does in the nuage. This finding should be valuable toward understanding the function of MAEL in carcinogenesis.