SREBP-1 Protein Research Articles

P53 Regulates Progression of Injury and Liver Regeneration After Acetaminophen Overdose

Liver regeneration in response to acetaminophen (APAP) overdose is a critical determinant of final patient outcome. Intricate cellular signaling during liver regeneration triggers liver cell proliferation, wound healing (if required) and restoration of liver mass and function. The p53 tumor suppressor protein is a critical regulator of cell cycle and apoptosis. However its role in liver regeneration after APAP overdose induced Acute Liver Failure (ALF) is not known. The pathogenesis of acute liver failure induced by APAP overdose can be divided into three phases including initiation of injury (formation of a reactive metabolite NAPQI and protein adducts) progression of injury (oxidative stress, mitochondrial and DNA damage resulting in necrosis) and regeneration/recovery phase (cell proliferation, angiogenesis and tissue repair). Here we show that p53 plays a critical role in inhibiting progression of injury and liver regeneration following APAP overdose mediated Acute Liver Injury (ALI). Eight‐week‐old male WT and p53KO mice (C57BL/6J background) were studied over time course of 0 to 96 hr following treatment with APAP300 (300mg/kg). Histology and serum ALT analysis showed similar liver injury in WT and p53KO mice at 1 and 12 hr however p53KO mice had significantly higher injury at 24 hr after APAP treatment. Interestingly, despite higher liver injury p53KO mice recovered equally to WT mice at 48 and 96 hr after APAP administration. Transcriptome analysis using liver RNA at 12, 24, 48hr from both groups revealed that p53KO mice had disrupted metabolic homeostasis, induced pro‐inflammatory and proliferative signaling. Further, molecular analysis of these pathways was done to confirm the findings. p53KO mice showed prolonged steatosis, lower mitochondrial DNA content, reduced expression of TFAM and mitochondrial complexes up to 24hr correlating with prolonged higher liver injury. p53 targets involved in fatty acid homeostasis, SREBP2 protein and GAMT mRNA expression correlated with prolonged steatosis in p53KO group. Liver regeneration determined by PCNA staining and cell cycle protein expression demonstrated that p53KO mice had rapid liver regeneration. Western blot analysis of EGFR, ERK and AKT showed sustained growth factor signaling in p53KO mice than WT mice after APAP treatment. These data illustrate that p53 has stage specific role during APAP‐induced ALF. p53 prevents progression of liver injury by maintaining mitochondrial and metabolic homeostasis after APAP overdose induced ALI. Further, p53 regulates initiation of liver regeneration through inflammatory and proliferative signaling after APAP overdose. These studies have revealed a novel role of p53 in acute liver injury pathogenesis.Support or Funding InformationNational Center for Research Resources (5P20RR021940‐07) Liver Scholar Award by AASLD/American Liver Foundation R01 DK098414

Dietary flavones counteract phorbol 12-myristate 13-acetate-induced SREBP-2 processing in hepatic cells

Consumption of fruits and vegetables is generally regarded as beneficial to plasma lipid profile. The mechanism by which the plant foods induce desirable lipid changes remains unclear. SREBP-2 is crucial in cholesterol metabolism, and it is a major regulator of the cholesterol biosynthesis enzyme HMGCR. Our lab has previously illustrated that apigenin and luteolin could attenuate the nuclear translocation of SREBP-2 through an AMPK-dependent pathway. In the present study, these two flavones were studied for their ability to deter the same in an AMPK-independent signaling route. The processing of SREBP-2 protein was promoted by phorbol 12-myristate 13-acetate (PMA) in the hepatic cells WRL and HepG2, and the increased processing was reversed by apigenin or luteolin co-administration. EMSA results demonstrated that the PMA-induced DNA-binding activity was weakened by the flavones. The increased amount of nuclear SREBP-2 in cells was attenuated by the flavonoid as shown by immunocytochemical imaging. Quantitative reverse transcriptase-polymerase chain reaction assay demonstrated that the transcription of HMGCR under both flavone treatments was reduced. However, apigenin appeared to be stronger than luteolin in restraining PMA-induced HMGCR mRNA expression. Since PMA is a diacylglycerol analog, these findings might have some physiological implications.

Effects of SIRT1 gene knock-out via activation of SREBP2 protein-mediated PI3K/AKT signaling on osteoarthritis in mice.

This study investigated the effects of SIRT1 gene knock-out on osteoarthritis in mice, and the possible roles of SREBP2 protein and the PI3K/AKT signaling pathway in the effects. Mice were randomly divided into a normal group and a SIRT1 gene knock-out group (6 mice in each group). In these groups, one side of the knee anterior cruciate ligament was traversed, and the ipsilateral medial meniscus was cut to establish an osteoarthritis model of knee joint. The countralateral synovial bursa was cut out, serving as controls. The knee joint specimens were then divided into four groups: SIRT1+/+ control group (group A, n=6); SIRT1+/+ osteoarthritis group (group B, n=6); SIRT1-/- control group (group C, n=6); SIRT1-/- osteoarthritis group (group D, n=6). HE staining, Masson staining, Safranin O-Fast Green staining and Van Gieson staining were used to observe the morphological changes in the articular cartilage of the knee. Immunohistochemical staining was employed to detect the expression of SIRT1, SREBP2, VEGF, AKT, HMGCR and type II collagen proteins. SA-β-gal staining was utilized to evaluate chondrocyte aging. The results showed clear knee joint cartilage destruction and degeneration in the SIRT1-/- osteoarthritis group. The tidal line was twisted and displaced anteriorly. Type II collagen was destroyed and distributed unevenly. Compared with the SIRT1+/+ osteoarthritis group and SIRT1-/- control group, SIRT1 protein expression was not obviously changed in the SIRT1-/- osteoarthritis group (P>0.05), while the expression levels of the SREBP2, VEGF and HMGCR proteins were significantly increased (P<0.05) and the levels of AKT and type II collagen proteins were significantly decreased (P<0.05). SIRT1 gene knock-out may aggravate cartilage degeneration in osteoarthritis by activating the SREBP2 protein-mediated PI3K/AKT signalling pathway, suggesting that SIRT1 gene may play a protective role against osteoarthritis.

Luteolin Inhibits Proliferation and Induces Apoptosis of Human Placental Choriocarcinoma Cells by Blocking the PI3K/AKT Pathway and Regulating Sterol Regulatory Element Binding Protein Activity.

Luteolin is a natural compound known for its anticancer effects on various human cancers by regulating signal transduction cascades. However, the effects of luteolin on human placental choriocarcinoma are not known. Results of the present study revealed that luteolin decreased viability of JAR and JEG-3 cells, which are valuable placental models, in a dose-dependent manner, and it induced apoptosis and loss of mitochondrial membrane potential in JAR and JEG-3 cells. The results also suggested that the PI3K/AKT pathway was inhibited by luteolin treatment of JAR and JEG-3 cells in a dose- and time-dependent manner. Next, we established effects of luteolin in the presence of pharmacological inhibitors of PI3K/AKT, ERK1/2 MAPK, and mTOR on proliferation of JAR and JEG-3 cells. In addition, these inhibitors were used to verify phosphorylation of AKT, GSK3beta, and ERK1/2 and to confirm mechanisms regulated by luteolin in JAR and JEG-3 cells. We also determined levels of SREBP1 and SREBP2 expression to investigate regulatory functions of luteolin in lipid metabolism in JAR and JEG-3 cells. Expression levels of both SREBP1 and SREBP2 mRNAs were significantly reduced, but only SREBP1 protein was influenced by luteolin. We compared viability of JAR and JEG-3 cells in response to luteolin alone or in combination with other chemotherapeutic drugs (etoposide, cisplatin, and paclitaxel) and found that luteolin has synergistic effects with the conventional chemotherapeutic drugs as an anticancer agent. Collectively, these results showed that luteolin plays an important role in the treatment of human choriocarcinoma cells by inhibiting the PI3K/AKT/mTOR/SREBP cascade and expression of lipogenic genes.

Reduced miR-200b and miR-200c expression contributes to abnormal hepatic lipid accumulation by stimulating JUN expression and activating the transcription of srebp1.

Previous studies indicated that miR-200s participated in IL-6-induced hepatic insulin resistance. However, the role of miR-200s in hepatic lipid accumulation has not been elucidated. Here we found that miR-200b and miR-200c were reduced in the steatotic livers of mice fed a high-fat diet (HFD) and patients with nonalcoholic fatty liver disease. This down-regulation was accompanied by an increase in the expression of lipogenic proteins such as sterol regulatory element-binding protein 1 (SREBP1) and fatty acid synthase (FAS). The suppression of miR-200b and miR-200c in Hep1-6 and NCTC1469 hepatocytes enhanced intracellular triglyceride levels, which were associated with increased SREBP-1 and FAS protein levels. In contrast, the over-expression of miR-200b and miR-200c suppressed lipid accumulation and reduced the expression of SREBP1 and FAS in Hep1-6 and NCTC1469 cells transfected with miR-200b or miR-200c mimics. Importantly, the up-regulation of miR-200b and miR-200c could reverse oleic acid/palmitic acid-induced lipid accumulation in hepatocytes. A luciferase reporter assay identified that miR-200b and miR-200c could directly bind the 3′UTR of jun. JUN activated the transcription of srebp1 to increase lipid accumulation. The data also demonstrated that increased miR-200b and miR-200c expression might be associated with sitagliptin-reduced hepatic lipid accumulation in mice fed a HFD. These findings suggest, for the first time, that reduced miR-200b and miR-200c expression contributes to abnormal hepatic lipid accumulation by stimulating JUN expression and activating the transcription of srebp1.

TCDD-inducible poly-ADP-ribose polymerase (TIPARP/PARP7) mono-ADP-ribosylates and co-activates liver X receptors.

Members of the poly-ADP-ribose polymerase (PARP) family catalyse the ADP-ribosylation of target proteins and are known to play important roles in many cellular processes, including DNA repair, differentiation and transcription. The majority of PARPs exhibit mono-ADP-ribosyltransferase activity rather than PARP activity; however, little is known about their biological activity. In the present study, we report that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP), mono-ADP-ribosylates and positively regulates liver X receptor α (LXRα) and LXRβ activity. Overexpression of TIPARP enhanced LXR-reporter gene activity. TIPARP knockdown or deletion reduced LXR regulated target gene expression levels in HepG2 cells and in Tiparp(-/-)mouse embryonic fibroblasts (MEFs) respectively. Deletion and mutagenesis studies showed that TIPARP's zinc-finger and catalytic domains were required to enhance LXR activity. Protein interaction studies using TIPARP and LXRα/β peptide arrays revealed that LXRs interacted with an N-terminal sequence (a.a. 209-236) of TIPARP, which also overlapped with a putative co-activator domain of TIPARP (a.a. 200-225). Immunofluorescence studies showed that TIPARP and LXRα or LXRβ co-localized in the nucleus.In vitroribosylation assays provided evidence that TIPARP mono-ADP-ribosylated both LXRα and LXRβ. Co-immunoprecipitation (co-IP) studies revealed that ADP-ribosylase macrodomain 1 (MACROD1), but not MACROD2, interacted with LXRs in a TIPARP-dependent manner. This was complemented by reporter gene studies showing that MACROD1, but not MACROD2, prevented the TIPARP-dependent increase in LXR activity. GW3965-dependent increases in hepatic Srebp1 mRNA and protein expression levels were reduced in Tiparp(-/-)mice compared with Tiparp(+/+)mice. Taken together, these data identify a new mechanism of LXR regulation that involves TIPARP, ADP-ribosylation and MACROD1.

Fucoidan improves serum lipid levels and atherosclerosis through hepatic SREBP-2-mediated regulation

Hyperlipidemia is associated with increased risk of the development of cardiovascular diseases. Although a great deal of attention has been paid to the hypolipidemic activity of fucoidan, complex polysaccharides from brown seaweeds, the underlying mechanism is still unclear. This study was performed to investigate whether and how fucoidan has lipid-lowering potential in poloxamer-407 (P407)-induced hyperlipidemic mice. Fucoidan treatment 2 h after acute administration of P407 in these mice significantly reduced serum total cholesterol, triglycerides, and LDL cholesterol levels, but increased the levels of HDL cholesterol. In HepG2 hepatocytes and the liver, fucoidan decreased the expression of FAS and ACC mRNA with no or only a moderate inhibitory effect on SREBP-1c mRNA expression. Furthermore, fucoidan attenuated the hepatic expression of mature SREBP-2 protein with a subsequent decrease in hepatic HMG-CoA reductase mRNA expression and an increase in hepatic LDL receptor mRNA expression. In addition, atherosclerotic lesions in the aorta of chronically P407-treated mice were also reduced by fucoidan. These findings indicate that fucoidan improves serum lipid levels by regulating the expression of key enzymes of cholesterol and triglyceride syntheses in the liver through modulation of SREBP-2.

SREBP2 Activation Induces Hepatic Long-chain Acyl-CoA Synthetase 1 (ACSL1) Expression in Vivo and in Vitro through a Sterol Regulatory Element (SRE) Motif of the ACSL1 C-promoter

Long-chain acyl-CoA synthetase 1 (ACSL1) plays a key role in fatty acid metabolism. To identify novel transcriptional modulators of ACSL1, we examined ACSL1 expression in liver tissues of hamsters fed a normal diet, a high fat diet, or a high cholesterol and high fat diet (HCHFD). Feeding hamsters HCHFD markedly reduced hepatic Acsl1 mRNA and protein levels as well as acyl-CoA synthetase activity. Decreases in Acsl1 expression strongly correlated with reductions in hepatic Srebp2 mRNA level and mature Srebp2 protein abundance. Conversely, administration of rosuvastatin (RSV) to hamsters increased hepatic Acsl1 expression. These new findings were reproduced in mice treated with RSV or fed the HCHFD. Furthermore, the RSV induction of acyl-CoA activity in mouse liver resulted in increases in plasma and hepatic cholesterol ester concentrations and reductions in free cholesterol amounts. Investigations on different ACSL1 transcript variants in HepG2 cells revealed that the mRNA expression of C-ACSL1 was specifically regulated by the sterol regulatory element (SRE)-binding protein (SREBP) pathway, and RSV treatment increased the C-ACSL1 abundance from a minor mRNA species to an abundant transcript. We analyzed 5'-flanking sequence of exon 1C of the human ACSL1 gene and identified one putative SRE site. By performing a promoter activity assay and DNA binding assays, we firmly demonstrated the key role of this SRE motif in SREBP2-mediated activation of C-ACSL1 gene transcription. Finally, we demonstrated that knockdown of endogenous SREBP2 in HepG2 cells lowered ACSL1 mRNA and protein levels. Altogether, this work discovered an unprecedented link between ACSL1 and SREBP2 via the specific regulation of the C-ACSL1 transcript.

Pre-germinated brown rice prevented high fat diet induced hyperlipidemia through ameliorating lipid synthesis and metabolism in C57BL/6J mice.

Pre-germinated brown rice (PGBR) can ameliorate hyperlipidemia, but the action mechanism is not clear. We focus the mechanisms of PGBR prevented hyperlipidemia. Six-week-old mice were divided into: standard-regular diet (SRD), high-fat diet (HFD) and HFD with PGBR (HFD + PGBR) groups for 16 weeks. The HFD group has higher concentrations of TG, TC, HDL and Non-HDL in the blood, and a higher atherosclerosis index (AI). The TG levels in the liver, and TG, bile acid levels in the feces were enhanced; and the total adipocytokines level in adipose tissue was reduced. The HFD group had higher protein expressions of SREBP-1, SCD-1, FAS, LDLR, and CYP7α1 in the liver. Moreover, the greater expressions of SREBP-1, SCD-1, FAS and the less expressions of PPAR-α and adiponectin were in adipose tissue. In the HFD + PGBR group, the PGBR regulated the levels of TG, TC, HDL, Non-HDL, AI and adipocytokines. PGBR increased more cholesterol and bile acid exhaust in feces. The SREBP-1, SCD-1, FAS, HMGCR, LDLR, CYP7α1 and PPAR-α proteins in the liver; and the SREBP-1, SCD-1, FAS, PPAR-α and adiponectin proteins in adipose tissue were reversed by PGBR. Taken together, PGBR can improve lipid synthesis and metabolism, and we suggest PGBR is a recommendable food for controlling hyperlipidemia.

Decreased MiR-155 Level in the Peripheral Blood of Non-Alcoholic Fatty Liver Disease Patients may Serve as a Biomarker and may Influence LXR Activity

Background: Obesity is now a common risk factor for non-alcoholic fatty liver disease (NAFLD). Thus, it is important to explore its underlying mechanisms. Methods: Total RNA was extracted from peripheral whole blood samples from 50 NAFLD patients and 50 healthy controls. In addition, human liver specimens were obtained through liver biopsies from NAFLD patients and healthy controls. The level of miRNA was studied using real-time PCR. The expression of lipogenic genes was analyzed using western blot, and a dual luciferase reporter assay was conducted to identify the possible target gene. Adenovirus vectors were injected into the tail vein of the high fat diet (HFD)-fed mice to study the role of miR-155 on lipid accumulation in vivo. Results: The level of miR-155 was markedly reduced in the livers and peripheral blood of NAFLD patients compared with healthy controls. Upregulation of miR-155 decreased intracellular lipid content and the SREBP1 and FAS protein levels, while inhibition of miR-155 enhanced the intracellular lipid content. The dual luciferase reporter assay showed that Liver X receptor (LXR)α was the target gene of miR-155, and silencing miR-155 reduced the expression of SREBP1 and FAS. An in vivo study showed that upregulation of miR-155 decreased the hepatic lipid accumulation mainly by suppressing the LXRα-dependent lipogenic signaling pathway. Conclusions: In summary, decreased expression of miR-155 in the peripheral blood may be utilized as a potential novel biomarker for NAFLD screening mainly by targeting LXRα.

Sodium sulfite promotes the assembly and secretion of very low-density lipoprotein in HL-7702 hepatocytes.

Na2SO3 treatment (10mM, 24h/48h) significantly increased the intra TG level in the hepatocytes. Different concentrations of Na2SO3 increased the extra-hepatocellular TG content. After 24h exposure, the extracellular VLDL levels and secretions of apoB100 in 0.1-10mM Na2SO3 groups were significantly higher than that of the negative control (P<0.05). Meanwhile, the expression of CPT1 and SREBP1 protein were significantly reduced by Na2SO3. MTP and TGH protein expressions were significantly elevated in each Na2SO3 treatment group. The expression level of LDLR in hepatocytes was reduced by Na2SO3. Na2SO3 exposure may promote the hepatocellular VLDL assembly and secretion, through increasing of MTP and TGH expressions and inhibiting the uptake of extracelluar VLDL.

Abstract 17627: Is the Post-menopausal Rise in PCSK9 Levels Due to Loss of the Estrogen Responsive Anti-atherogenic Protein, Heat Shock Protein 27? Insights Into a Potential New PCSK9 Lowering Therapy

Introduction: Previously we reported that elevated serum levels of Heat Shock Protein 27 represent a predictive biomarker of reduced cardiovascular clinical events. Moreover, attenuation of experimental atherogenesis, characterized by reduced cholesterol levels in both the artery wall and serum, can be achieved by augmenting serum HSP27 levels (e.g., with recombinant HSP27). PCSK9 plays a central role in regulating the abundance of hepatic LDL-receptors, and hence serum and plaque cholesterol levels. Interestingly, PCSK9 levels rise with menopause (Dallas Heart Study) and we previously published that HSP27 levels are markedly attenuated post-ovariectomy. Hence, we hypothesize that HSP27 augments hepatic cholesterol uptake via reductions in PCSK9 levels. Methods / Results: 1. In vitro studies: HepG2 (liver) cells were maintained in culture for 24 hours with or without rHSP27. The hepatic levels of apoB100 did not change with rHSP27 treatment. ApoB100 containing lipoproteins were reduced in the cell culture media with rHSP27 treatment (Western Blot: p=0.008; ELISA: p=0.0025). rHSP27 treatment reduced hepatic PCSK9 protein levels (Western Blot: p=0.019), increased LDL receptor protein levels (Western Blot: p=0.001) and increased (fluorescent) LDL uptake (p=0.022). Levels of hepatic SREBP2 and HMG-CoA reductase proteins were unaltered with rHSP27 treatment. 2. In vivo studies: Female ApoE-/- mice fed high fat diet and injected weekly with rHSP27 or PBS for 8 weeks. Serum total cholesterol and plasma PCSK9 levels were ~20-40% lower in the rHSP27 treated vs. control mice. Mice treated with rHSP27 showed reductions in aortic lesion area of ~40% for en face and ~35% for cross-sectional sinus tissue sections. Conclusions: These findings suggest that HSP27, an endogenous estrogen responsive protein, can lower extracellular cholesterol levels by reducing PCSK9 expression. Hence there is promise for the development of HSP27 “replacement” therapy for the prevention and modification of atherosclerosis via reductions in PCSK9 expression. Current clinical studies examining the relationship between HSP27 and PCSK9 levels in women undergoing prophylactic ovariectomy for BRAC1/2 (i.e., the “Angelina Effect”) are ongoing.

An Ester of β‐Hydroxybutyrate Regulates Cholesterol Biosynthesis in Rats and a Cholesterol Biomarker in Humans

In response to carbohydrate deprivation or prolonged fasting the ketone bodies, β-hydroxybutyrate (βHB) and acetoacetate (AcAc), are produced from the incomplete β-oxidation of fatty acids in the liver. Neither βHB nor AcAc are well utilized for synthesis of sterols or fatty acids in human or rat liver. To study the effects of ketones on cholesterol homeostasis a novel βHB ester (KE) ((R)-3-hydroxybutyl (R)-3-hydroxybutyrate) was synthesized and given orally to rats and humans as a partial dietary carbohydrate replacement. Rats maintained on a diet containing 30-energy % as KE with a concomitant reduction in carbohydrate had lower plasma cholesterol and mevalonate (-40 and -27 %, respectively) and in the liver had lower levels of the mevalonate precursors acetoacetyl-CoA and HMG-CoA (-33 and -54 %) compared to controls. Whole liver and membrane LDL-R as well as SREBP-2 protein levels were higher (+24, +67, and +91 %, respectively). When formulated into a beverage for human consumption subjects consuming a KE drink (30-energy %) had elevated plasma βHB which correlated with decreased mevalonate, a liver cholesterol synthesis biomarker. Partial replacement of dietary carbohydrate with KE induced ketosis and altered cholesterol homeostasis in rats. In healthy individuals an elevated plasma βHB correlated with lower plasma mevalonate.

Exogenous administration of chronic corticosterone affects hepatic cholesterol metabolism in broiler chickens showing long or short tonic immobility

Tonic immobility (TI) is an innate characteristic of animals related to fear or stress response. Animals can be classified into long TI (LTI) and short TI (STI) phenotypes based on TI test duration. In this study, effect of TI phenotype, chronic corticosterone administration (CORT), and their interaction on cholesterol metabolism in liver was evaluated in broilers. LTI broilers showed higher level of cholesterol in liver compared to STI chickens (p<0.05), and CORT significantly increased hepatic cholesterol content (p<0.01). Real-time PCR results showed that both TI and CORT potentially altered ABCA1 and CYP7A1 gene expressions (0.05<p<0.1), while there was no significant interaction of CORT and TI on both gene expressions. CORT treatment significantly increased the level of SREBP2 (p=0.00), LDLR (p<0.05), GR (p<0.05) and 11β-HSD2 (p<0.05) protein abundance in liver. However, TI phenotype only affected hepatic HMGCR protein expression, and LTI broilers showed higher level of HMGCR protein expression in liver than STI (p<0.05). These results indicate that chronic CORT administration causes hepatic cholesterol accumulation in broiler chickens mainly by enhancing cholesterol synthesis and uptake into liver. LTI chickens had higher amount of total cholesterol in liver, which might be associated with an increase of hepatic HMGCR protein expression. However, there is no interaction between TI and CORT on cholesterol metabolism in liver of broilers.

Combination of curcumin and piperine prevents formation of gallstones in C57BL6 mice fed on lithogenic diet: whether NPC1L1/SREBP2 participates in this process?

BackgroundA disruption of cholesterol homeostasis characterized by the physical-chemical imbalance of cholesterol solubility in bile often results in formation of cholesterol gallstones. Our earlier studies revealed that curcumin (1000 mg/kg) could prevent formation of gallstones. It has been proved that curcumin is poorly absorbed while piperine is a bioavailability-enhancer. Nevertheless, whether curcumin combined with piperine could enhance the effect of curcumin in preventing gallstones is still awaited.MethodC57BL6 mice were fed on a lithogenic diet concomitant with curcumin at 500 or 1000 mg/kg and/or piperine at 20 mg/kg for 4 weeks. The ratio of gallbladder stone formation was recorded and samples of blood, bile, gallbladder, liver and small intestine were also collected. The volume of gallbladder and weight of liver were calculated, and blood and bile samples were analyzed through biochemical methods. Intestinal NPC1L1 and SREBP2 mRNA and protein expression were detected by real-time PCR and Western blot.ResultCombining with piperine can significantly enhance the effect of curcumin, thus preventing the development of gallbladder stones, lowering the saturation of blood lipids and cholesterol in bile, as well as decreasing the expression of NPC1L1 and SREBP2 in both mRNA and protein levels.ConclusionCurcumin can prevent the formation of cholesterol gallstones induced by high fat diet in mice and SREBP2 and NPC1L1 may participate in this process. Piperine can increase curcumin’s bioavailability, thereby enhancing the effect of curcumin.

The Flavone Luteolin Suppresses SREBP-2 Expression and Post-Translational Activation in Hepatic Cells.

High blood cholesterol has been associated with cardiovascular diseases. The enzyme HMG CoA reductase (HMGCR) is responsible for cholesterol synthesis, and inhibitors of this enzyme (statins) have been used clinically to control blood cholesterol. Sterol regulatory element binding protein (SREBP) -2 is a key transcription factor in cholesterol metabolism, and HMGCR is a target gene of SREBP-2. Attenuating SREBP-2 activity could potentially minimize the expression of HMGCR. Luteolin is a flavone that is commonly detected in plant foods. In the present study, Luteolin suppressed the expression of SREBP-2 at concentrations as low as 1 μM in the hepatic cell lines WRL and HepG2. This flavone also prevented the nuclear translocation of SREBP-2. Post-translational processing of SREBP-2 protein was required for nuclear translocation. Luteolin partially blocked this activation route through increased AMP kinase (AMPK) activation. At the transcriptional level, the mRNA and protein expression of SREBP-2 were reduced through luteolin. A reporter gene assay also verified that the transcription of SREBF2 was weakened in response to this flavone. The reduced expression and protein processing of SREBP-2 resulted in decreased nuclear translocation. Thus, the transcription of HMGCR was also decreased after luteolin treatment. In summary, the results of the present study showed that luteolin modulates HMGCR transcription by decreasing the expression and nuclear translocation of SREBP-2.

Abstract 1194: O-GlcNAcylation regulates breast cancer lipid metabolism via sterol regulatory element binding protein 1

Abstract The Warburg hypothesis states that cancer cells display altered metabolic features to support their rapid growth and biosynthetic demands including increased glycolytic flux to synthesize necessary building blocks required by growing cells. Increased glucose uptake feeds not only glycolysis but other glucose dependent pathways as well, such as the Hexosamine Biosynthetic Pathway (HBP). HBP diverts fructose-6-phosphate from glycolysis to produce UDP-GlcNAc, the amino sugar donor to O-GlcNAc Transferase (OGT). Analagous to phosphorylation, O-GlcNAcylation can alter protein function and stability and itself is altered in several disease states. Our lab has demonstrated that OGT and O-GlcNAcylation are elevated in breast cancer and that expression of this enzyme is critical for various cancer phenotypes such as avoidance of ER stress and apoptosis, supporting invasion and metastasis and more recently promotion of Warburg effect. Here we demonstrate that OGT and O-GlcNAc are important for lipid metabolism in cancer cells through regulation of transcription factor SREBP-1 and its targets. Metabolic profiling revealed that OGT depletion in MDA-MB-231 cells decreased various lipids metabolites measured, including long-chain fatty acids, lysolipids and essential fatty acids. OGT suppression results in a decrease in SREBP-1 protein and mRNA and reduction of its transcriptional targets, enzymes involved in lipid synthesis, in both breast cancer cells and highly lipogenic normal tissue, the mammary fat pad. Over-expression of SREBP-1 blocks apoptosis induced by OGT suppression in 2D and 3D culture. Overall, we show that OGT and O-GlcNAc play a role in yet another process critical to cancer cell survival, lipid metabolism. Citation Format: Valerie L. Sodi, Zachary Bacigalupa, Christina Ferrer, Mauricio Reginato. O-GlcNAcylation regulates breast cancer lipid metabolism via sterol regulatory element binding protein 1. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1194. doi:10.1158/1538-7445.AM2015-1194

Regulation of SREBPs by Sphingomyelin in Adipocytes via a Caveolin and Ras-ERK-MAPK-CREB Signaling Pathway.

Sterol response element binding protein (SREBP) is a key transcription factor in insulin and glucose metabolism. We previously demonstrated that elevated levels of membrane sphingomyelin (SM) were related to peroxisome proliferator–activated receptor-γ (PPARγ), which is a known target gene of SREBP-1 in adipocytes. However, the role of SM in SREBP expression in adipocytes remains unknown. In human abdominal adipose tissue from obese women with various concentrations of fasting plasma insulin, SREBP-1 proteins decreased in parallel with increases in membrane SM levels. An inverse correlation was found between the membrane SM content and the levels of SREBP-1c/ERK/Ras/PPARγ/CREB proteins. For the first time, we demonstrate the effects of SM and its signaling pathway in 3T3-F442A adipocytes. These cells were enriched or unenriched with SM in a range of concentrations similar to those observed in obese subjects by adding exogenous natural SMs (having different acyl chain lengths) or by inhibiting neutral sphingomyelinase. SM accumulated in caveolae of the plasma membrane within 24 h and then in the intracellular space. SM enrichment decreased SREBP-1 through the inhibition of extracellular signal-regulated protein kinase (ERK) but not JNK or p38 mitogen-activated protein kinase (MAPK). Ras/Raf-1/MEK1/2 and KSR proteins, which are upstream mediators of ERK, were down-regulated, whereas SREBP-2/caveolin and cholesterol were up-regulated. In SM-unmodulated adipocytes treated with DL-1-Phenyl-2-Palmitoylamino-3-morpholino-1-propanol (PPMP), where the ceramide level increased, the expression levels of SREBPs and ERK were modulated in an opposite direction relative to the SM-enriched cells. SM inhibited the insulin-induced expression of SREBP-1. Rosiglitazone, which is an anti-diabetic agent and potent activator of PPARγ, reversed the effects of SM on SREBP-1, PPARγ and CREB. Taken together, these findings provide novel insights indicating that excess membrane SM might be critical for regulating SREBPs in adipocytes via a MAPK-dependent pathway.

Co-regulation of SREBP-1 and mTOR ameliorates lipid accumulation in kidney of diabetic mice

SREBP-1 and mTOR have been proved to involve in renal lipid metabolism of diabetes mellitus. In the present study, we investigated the effect of co-regulation of SREBP-1 and mTOR on renal lipid metabolism using diabetic mice and cultured renal tubular cells. The results showed that compared with those in high glucose-stimulated HKC cells single transfected with shRNA-SREBP-1 vector, the level of SREBP-1 protein were significantly reduced by 64.1% followed by decreased FASN mRNA, ACC mRNA, ADRP protein and lipid droplets in HKC cells co-transfected with shRNA-SREBP-1 vector and kinase-dead mTOR vector. Furthermore, diabetic mice co-injected with shRNA-SREBP-1 vector and kinase-dead mTOR vector showed that renal SREBP-1 protein, FASN mRNA and ACC mRNA were respectively decreased by 34.6%, 45.9%, 22.0% in comparison with those in diabetic mice single injected with shRNA-SREBP-1 vector accompanied by reduced ADRP protein and triglyceride content. In the end our study suggests that co-regulation of SREBP-1 and mTOR in kidney of diabetic mice is more effective in lowering renal lipogenesis than only regulation of SREBP-1.

Abstract 692: Therapeutic Inhibition of miR-33 Does Not Promote Obesity, Insulin Resistance or Hepatic Lipid Accumulation

Inhibition of miR-33, a critical post-transcriptional regulator of cholesterol homeostasis, prevents atherosclerosis progression both dependently and independently of its effects on circulating HDL levels. However, recent studies suggest that genetic deletion or inhibition of miR-33 may adversely affect metrics of insulin resistance, lipid metabolism and hepatic steatosis. Given the therapeutic interest in miR-33 inhibitors for treating atherosclerosis, we sought to determine the effects of long-term pharmacological inhibition of miR33 in a mouse model of diet-induced obesity (DIO). Results: C57BL6/J mice were fed a high-fat diet in conjunction with anti-miR therapy (10mg/kg of control anti-miR or anti-miR33) for 20 weeks. There was significant but equivalent weight gain in all 3 groups. While anti-miR33 therapy increased total plasma cholesterol compared to control anti-miR treated mice (p≤0.01), there was no differences relative to PBS treated mice. Anti-miR33 treatment also resulted in a marked decrease in serum triglycerides relative to control anti-miR (29% decrease, p≤0.05) but once again not compared to PBS treated mice. Metrics of insulin resistance (GTT, ITT) were not altered in anti-miR33 treated mice relative to controls. Interestingly, indirect calorimetric measurements demonstrated that anti-miR33 treated mice had reduced respiratory exchange ratios (RER) compared to both control anti-miR and PBS treated mice (18% decrease, p≤0.05), suggesting an increase in fatty acid versus carbohydrate utilization in anti-miR33 treated mice. In addition, hepatic protein expression of known miR-33 target gene ABCA1 was de-repressed upon miR-33 inhibition, indicating that miR-33 was efficiently inhibited in this model. In contrast, putative miR-33 target gene SREBP-1 protein expression was not altered, nor were SREBP-1 downstream target genes FASN and ACC. Finally, anti-miR33 treated mice did not accumulate more lipids in their livers relative to control. In conclusion, we show in a DIO model that therapeutic silencing of miR-33 does not promote hepatic steatosis nor does it increase metrics of insulin resistance, suggesting that pharmacological inhibition of miR-33 may be a safe therapeutic for the treatment of atherosclerosis.