Sterol Regulatory Element-binding Protein-1c Expression Research Articles

N-3 Polyunsaturated Fatty Acids Protect against Alcoholic Liver Steatosis by Activating FFA4 in Kupffer Cells.

Supplementation with fish oil rich in omega-3 polyunsaturated fatty acids (n-3 PUFAs) effectively reduces acute and chronic alcohol-induced hepatic steatosis. We aimed to find molecular mechanisms underlying the effects of n-3 PUFAs in alcohol-induced hepatic steatosis. Because free fatty acid receptor 4 (FFA4, also known as GPR120) has been found as a receptor for n-3 PUFAs in an ethanol-induced liver steatosis model, we investigated whether n-3 PUFAs protect against liver steatosis via FFA4 using AH7614, an FFA4 antagonist, and Ffa4 knockout (KO) mice. N-3 PUFAs and compound A (CpdA), a selective FFA4 agonist, reduced the ethanol-induced increase in lipid accumulation in hepatocytes, triglyceride content, and serum ALT levels, which were not observed in Ffa4 KO mice. N-3 PUFAs and CpdA also reduced the ethanol-induced increase in lipogenic sterol regulatory element-binding protein-1c expression in an FFA4-dependent manner. In Kupffer cells, treatment with n-3 PUFA and CpdA reversed the ethanol-induced increase in tumor necrosis factor-α, cyclooxygenase-2, and NLR family pyrin domain-containing 3 expression levels in an FFA4-dependent manner. In summary, n-3 PUFAs protect against ethanol-induced hepatic steatosis via the anti-inflammatory actions of FFA4 on Kupffer cells. Our findings suggest FFA4 as a therapeutic target for alcoholic hepatic steatosis.

Dimethyloxalylglycine Suppresses SREBP1c and Lipogenic Gene Expressions in Hepatocytes Independently of HIF1A.

Dimethyloxalylglycine (DMOG) is a representative inhibitor of the prolyl hydroxylase domain (PHD), which mediates the degradation of hypoxia-inducible factor-1-alpha (HIF1A). DMOG exerts its pharmacological effects via the canonical pathway that involves PHD inhibition; however, it remains unclear whether DMOG affects lipogenic gene expression in hepatocytes. We aimed to elucidate the effects of DMOG on sterol regulatory element-binding protein-1c (SREBP1c), a master regulator of fatty acid synthesis in hepatocytes. DMOG treatment inhibited SREBP1c mRNA and protein expression in HepG2 and AML12 hepatocytes and reduced the transcript levels of SREBP1c-regulated lipogenic genes. A luciferase reporter assay revealed that DMOG inhibited the transcriptional activity of SREBP1c. Moreover, DMOG suppressed SREBP1c expression in mice liver. Mechanistically, treatment with DMOG enhanced the expression of HIF1A and insulin-induced gene 2 (INSIG2), which inhibits the activation of SREBP1c. However, HIF1A or INSIG2 knockdown failed to reverse the inhibitory effect of DMOG on SREBP1c expression, suggesting a redundant role of HIF1A and INSIG2 in terms of repressing SREBP1c. DMOG did not function through the canonical pathway involving inhibition of SREBP1c by PHD, highlighting the presence of non-canonical pathways that mediate its anti-lipogenic effect.

GPAT1 Activity and Abundant Palmitic Acid Impair Insulin Suppression of Hepatic Glucose Production in Primary Mouse Hepatocytes

BackgroundGlycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance. ObjectiveWe asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur. MethodsMouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined. ResultsOverexpressing GPAT1 in mouse hepatocytes impaired insulin’s suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects. ConclusionThese data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin’s ability to suppress hepatic glucose production in primary mouse hepatocytes.

Studies on the Effect of Piperine on Hepatocyte Nuclear Factor 1 Alpha (HNF-1α) and Sterol Regulatory Element-Binding Protein 1c (SREBP-1c) Levels in High-Fat-Diet and Sucrose-Induced Type 2 Diabetes Mellitus Rats.

Piperine, a naturally occurring compound in black pepper (Piper nigrum), is known for its potential health benefits, including its reported enhancement of insulin sensitivity. However, the precise impact of piperine on hepatocyte nuclear factor 1 alpha (HNF-1α) and sterol regulatory element-binding protein 1c (SREBP-1c), transcription factors for insulin signaling and glucose metabolism in hepatocytes, remains unclear. This study aims to investigate the effect of piperine, compared to metformin, on blood glucose and insulin levels by modifying the expression of hepatic HNF-1α and SREBP-1c in high-fat-diet (HFD) and sucrose-induced type 2 diabetes mellitus (T2DM) rats and in human Chang liver cells. Adult male albino rats were categorized into four groups: group 1 as the control, group 2 as T2DM, group 3 as T2DM rats treated with piperine (40 mg), and group 4 as T2DM rats treated with metformin (50 mg). Fasting blood glucose (FBG) and serum insulin levels were measured using enzyme-linked immunosorbent assay (ELISA), while real-time polymerase chain reaction (RT-PCR) analysis was conducted to assess the mRNA expression of HNF-1α and SREBP-1c. Further, piperine was treated with normal and high glucose-induced Chang liver cells, and gene expression was analysed.Data analysis was performed using one-way analysis of variance (ANOVA), with a significance set at p<0.05. Treatment with piperine led to a notable decrease in blood glucose levels and circulating insulin when compared with T2DM rats (group 2). Additionally, piperine administration resulted in the upregulation of HNF-1α mRNA expression and downregulation of SREBP-1c mRNA levels whose effects were found to be near that of the control and standard drug metformin's effects. In vitro study also confirmed that piperine improved the HNF-1αexpression and reduced the expression of SREBP-1c in Chang liver cells. Our findings suggest that piperine treatment effectively regulates hyperglycemic and hyperinsulinemic insulin resistance in the liver by modulating the expression of HNF-1α and SREBP-1c. Consequently, piperine emerges as a promising candidate for therapeutic intervention in managing T2DM.

The Influence of Hyperglycemia on Liver Triglyceride Deposition in Partially Pancreatectomized Rats.

Nonalcoholic fatty liver disease and diabetes always coexist. The relationship of fatty liver and hyperglycemia is not clear. We studied the influence of hyperglycemia on triglyceride (TG) accumulation in the liver and explored its possible mechanisms. SD rats were divided into three groups: Group A (sham operation control), Group B (partially pancreatectomized rats), and Group C (partially pancreatectomized rats treated with insulin). At 4 weeks after surgery, pancreatic weights and liver TG contents were measured. Serum biochemical parameters were determined, and oral glucose tolerance tests (OGTT) were performed. The gene expression of sterol regulatory element-binding protein1c (SREBP-1c), carbohydrate regulatory element-binding protein (ChREBP), fatty acid synthase(FAS), carnitine palmitoyltransferase 1 (CPT-1), and fibroblast growth factor 21 (FGF21) was determined by real-time PCR. Compared with Group A, postprandial glucose increased significantly; the concentrations of insulin and C-peptides, pancreatic weights and serum FGF21 levels were decreased, liver TG was increased significantly in Group B, and insulin treatment improved these changes. Compared with Group A, the gene expressions of FGF21, CPT-1 and FAS in the liver were decreased in Group B (all p<0.05). Compared with Group B, the gene expressions of FGF21, FAS, ChREBP, SREBP-1c and CPT-1 in the liver in Group C were all increased significantly (p<0.05, respectively). Hyperglycemia induced by partial pancreatectomy could lead to increased liver TG. Insulin treatment could decrease glucose levels and improve fatty liver, and genes related to lipid metabolism may play a role in this process.

Diosgenin alleviates NAFLD induced by a high-fat diet in rats via mTOR/SREBP-1c/HSP60/MCAD/SCAD signaling pathway

This study aims to observe the effects of diosgenin on the expression of mammalian target of rapamycin(mTOR), sterol regulatory element-binding protein-1c(SREBP-1c), heat shock protein 60(HSP60), medium-chain acyl-CoA dehydrogenase(MCAD), and short-chain acyl-CoA dehydrogenase(SCAD) in the liver tissue of the rat model of non-alcoholic fatty liver disease(NAFLD) and explore the mechanism of diosgenin in alleviating NAFLD. Forty male SD rats were randomized into five groups: a control group, a model group, low-(150 mg·kg~(-1)·d~(-1)) and high-dose(300 mg·kg~(-1)·d~(-1)) diosgenin groups, and a simvastatin(4 mg·kg~(-1)·d~(-1)) group. The rats in the control group were fed with a normal diet, while those in the other four groups were fed with a high-fat diet. After feeding for 8 weeks, the body weight of rats in the high-fat diet groups increased significantly. After that, the rats were administrated with the corresponding dose of diosgenin or simvastatin by gavage every day for 8 weeks. The levels of triglyceride(TG), total cholesterol(TC), alanine transaminase(ALT), and aspartate transaminase(AST) in the serum were determined by the biochemical method. The levels of TG and TC in the liver were measured by the enzyme method. Oil-red O staining was employed to detect the lipid accumulation, and hematoxylin-eosin(HE) staining to detect the pathological changes in the liver tissue. The mRNA and protein levels of mTOR, SREBP-1c, HSP60, MCAD, and SCAD in the liver tissue of rats were determined by real-time fluorescence quantitative polymerase chain reaction(RT-qPCR) and Western blot, respectively. Compared with the control group, the model group showed increased body weight, food uptake, liver index, TG, TC, ALT, and AST levels in the serum, TG and TC levels in the liver, lipid deposition in the liver, obvious hepatic steatosis, up-regulated mRNA and protein expression levels of mTOR and SREBP-1c, and down-regulated mRNA and protein expression levels of HSP60, MCAD, and SCAD. Compared with the model group, the rats in each treatment group showed obviously decreased body weight, food uptake, liver index, TG, TC, ALT, and AST levels in the serum, TG and TC levels in the liver, lessened lipid deposition in the liver, ameliorated hepatic steatosis, down-regulated mRNA and protein le-vels of mTOR and SREBP-1c, and up-regulated mRNA and protein levels of HSP60, MCAD, and SCAD. The high-dose diosgenin outperformed the low-dose diosgenin and simvastatin. Diosgenin may prevent and treat NAFLD by inhibiting the expression of mTOR and SREBP-1c and promoting the expression of HSP60, MCAD, and SCAD to reduce lipid synthesis, improving mitochondrial function, and promoting fatty acid β oxidation in the liver.

Modulation of PPAR-γ, SREBP-1c and inflammatory mediators by luteolin ameliorates β-cell dysfunction and renal damage in a rat model of type-2 diabetes mellitus.

Natural products have been recommended as a complementary therapy for type 2 diabetes mellitus (T2DM) due to constraints of safety and tolerability of existing anti-diabetic agents. Luteolin exhibits anti-diabetic and anti-inflammatory effects. Hence, the impact of luteolin on glucose homoeostasis and organ damage was investigated in high-fat diet (HFD) and streptozotocin (STZ) induced T2DM in rats. Male Wistar rats were maintained on HFD (provided 55% energy as fat) for 10days. Subsequently, a single dose of 40mg/kg STZ was injected intraperitoneally on the 11th day. Seventy-two hours after STZ administration, diabetic rats with established hyperglycemia (fasting serum glucose > 200mg/dL) were randomized into different groups having six rats each and orally administered either 0.5% hydroxy propyl cellulose or pioglitazone (10mg/kg) or luteolin (50mg/kg or 100mg/kg) once daily for 28days, while continuing HFD for respective groups. Luteolin significantly reduced hyperglycaemia, homoeostasis model assessment (HOMA) of insulin resistance (HOMA-IR) levels, and improved hypoinsulinemia and HOMA of b-cell function (HOMA-B) in a dose-dependent manner. Increased TNF-α, IL-6 and NFκB levels in diabetic rats were significantly regulated. Additionally, luteolin significantly augmented PPAR-γ expression while attenuating sterol regulatory element binding protein-1c (SREBP-1c) expression. Histopathological scrutiny validated that luteolin effectively attenuated HFD-STZ-induced injury in pancreatic β-cells and kidneys to near normalcy. Our study showed that luteolin ameliorated hyperglycemia and improved hypoinsulinemia, β-cell dysfunction, and renal impairment in HFD-STZ-induced diabetic rats by attenuating inflammation and dysregulated cytokine secretion through modulation of PPAR-γ, TNF-α, IL-6 and NF-kB expression and down-regulation of SREBP-1c.

The PKA-SREBP1c Pathway Plays a Key Role in the Protective Effects of Lactobacillus johnsonii JNU3402 Against Diet-Induced Fatty Liver in Mice.

The present study aims to assess the protective effect of Lactobacillus johnsonii JNU3402 (LJ3402) against diet-induced non-alcoholic fatty liver disease (NAFLD) and determine the mechanism underlying its beneficial effect on the liver in mice. Seven-week-old male mice are fed a high-fat diet (HFD) with or without oral supplementation of LJ3402 for 14 weeks. In mice fed an HFD, LJ3402 administration alleviates liver steatosis, diet-induced obesity, and insulin resistance with a decreased hepatic expression of sterol-regulatory element-binding protein-1c (SREBP-1c), fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC), and an increased phosphorylation of SREBP-1c. The mechanistic study shows that LJ3402 inhibits SREBP-1c transcriptional activity by enhancing protein kinase A (PKA)-mediated phosphorylation and reduces the expression of its lipogenic target genes in AML12 and HepG2 cells, thereby attenuating hepatic lipid accumulation. Moreover, silencing the PKA α catalytic subunit or the inhibition of PKA activity by H89 abolishes LJ3402 suppression of free fatty acid (FFA)-induced SREBP-1c activity in hepatocytes. In addition, LJ3402 administration elevates the plasma lactate levels in mice fed an HFD; this lactate increases PKA-mediated SREBP-1c phosphorylation in AML12 cells with a decreased expression of its target genes, reducing hepatic lipid accumulation. LJ3402 attenuates HFD-induced fatty liver in mice through the lactate-PKA-SREBP-1c pathway.

Sesamin ameliorates lipotoxicity and lipid accumulation through the activation of the estrogen receptor alpha signaling pathway

Nonalcoholic fatty liver disease (NAFLD) has been linked to fat accumulation in the liver and lipid metabolism imbalance. Sesamin, a lignan commonly found in sesame seed oil, possesses antioxidant, anti-inflammatory, and anticancer properties. However, the precise mechanisms by which sesamin prevents hepatic steatosis are not well understood. This study aimed to explore the molecular mechanisms by which sesamin may improve lipid metabolism dysregulation. A in vitro hepatic steatosis model was established by exposing HepG2 cells to palmitate sodium. The results showed that sesamin effectively mitigated lipotoxicity and reduced reactive oxygen species production. Additionally, sesamin suppressed lipid accumulation by regulating key factors involved in lipogenesis and lipolysis, such as fatty acid synthase (FASN), sterol regulatory element–binding protein 1c (SREBP-1c), forkhead box protein O-1, and adipose triglyceride lipase. Molecular docking results indicated that sesamin could bind to estrogen receptor α (ERα) and reduce FASN and SREBP-1c expression via the Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ)/AMP-activated protein kinase (AMPK) signaling pathway. Sesamin attenuated palmitate-induced lipotoxicity and regulated hepatic lipid metabolism in HepG2 cells by activating the ERα/CaMKKβ/AMPK signaling pathway. These findings suggest that sesamin can improve lipid metabolism disorders and is a promising candidate for treating hepatic steatosis.

Antihyperlipidemic effect of bread fortified with potato peel powder against Triton X-100-induced hyperlipidemia in male albino rats

The present investigation aimed to improve the nutritional and healthy values and evaluate the influence of bread fortified with dried potato peels (BPP) on Triton X-100-induced hyperlipidemia in male albino rats. The findings demonstrated that BPP lowered hepatic triglycerides and total cholesterol while increasing high-density lipoprotein (HDL-C). BPP exhibited potential lipid-lowering and hepatoprotective actions that were generated by the reduction of oxidative damage and preservation of the non-enzymatic and enzymatic antioxidant systems compromised by hyperlipidemic condition. Furthermore, BPP considerably enhanced the mRNA expression of AMPKα (AMP-activated protein kinase-alpha), suppressed the expression of fatty acid synthase (FAS) and acetyl-CoA carboxylase alpha (ACCα), and decreased the mRNA expression of the adipogenic transcription factor SREBP-1c (sterol regulatory element-binding protein-1c), which are essential regulators of hepatocyte lipid metabolism. A histopathological assessment of the liver confirmed the results. In conclusion, this investigation revealed a positive impact of bread fortified with BPP therapy in preventing hyperlipidemia.

Bisphenol A induced hepatic steatosis by disturbing bile acid metabolism and FXR/TGR5 signaling pathways via remodeling the gut microbiota in CD-1 mice

Dysregulation of gut microbiota-mediated bile acid (BA) metabolism plays an important role in the pathogenesis of hepatic steatosis and nonalcoholic fatty liver disease (NAFLD). Our previous studies found that bisphenol A (BPA) exposure induced hepatic steatosis and gut microbiota dysbiosis. However, whether the gut microbiota-dependent BA metabolism alterations were involved in BPA-induced hepatic steatosis remains unclear. Therefore, we explored the gut microbiota-related metabolic mechanisms of hepatic steatosis induced by BPA. Male CD-1 mice were exposed to low-dose BPA (50 μg/kg/day) for 6 months. Fecal microbiota transplantation (FMT) and broad-spectrum antibiotic cocktail (ABX) treatment were further adopted to test the role of gut microbiota in the adverse effects of BPA. We found that BPA induced hepatic steatosis in mice. Additionally, 16S rRNA gene sequencing showed that BPA reduced the relative abundance of Bacteroides, Parabacteroides and Akkermansia, which are associated with BA metabolism. Metabolomic analyses demonstrated that BPA significantly altered the ratio of conjugated to unconjugated BAs and increased the total level of taurine-α/β-muricholic acid while decreasing the level of chenodeoxycholic acid, thus inhibiting the activation of special receptors, including farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5), in the ileum and liver. The inhibition of FXR reduced short heterodimer partner and subsequently induced cholesterol 7α-hydroxylase and sterol regulatory element-binding protein-1c expression, which is related to hepatic BA synthesis and lipogenesis, eventually leading to liver cholestasis and steatosis. Furthermore, we found that mice that received FMT from BPA-exposed mice developed hepatic steatosis, and the influences of BPA on hepatic steatosis and FXR/TGR5 signaling pathways could be eliminated by ABX treatment, confirming the role of gut microbiota in BPA effects. Collectively, our study illustrates that suppressed microbiota-BA-FXR/TGR signaling pathways may be a potential mechanism for hepatic steatosis induced by BPA, providing a new target for the prevention of BPA-induced NAFLD.

GPRC6A is a key mediator of palmitic acid regulation of lipid synthesis in bovine mammary epithelial cells.

Fatty acids (FAs) can promote lipid synthesis in the mammary gland via stimulating lipogenic gene expression, but the underlying molecular mechanism is still not fully understood. Here, we showed the dose-dependent effects of palmitic acid (PA) on lipid synthesis in primary bovine mammary epithelial cells (BMECs) and explored the corresponding molecular mechanism. BMECs were treated with PA (0, 50, 100, 150, and 200 μM), and the 100 μM treatment had the best stimulatory effect on lipid synthesis and expression and maturation of sterol regulatory element-binding protein 1c (SREBP-1c) in cells. Inhibition of phosphatidylinositol 3-kinase (PI3K) almost totally blocked the stimulation of PA on SREBP-1c expression, whereas protein kinase Cα (PKCα) knockdown only partially decreased the stimulation of PA on SREBP-1c expression but abolished the stimulation of PA on its maturation. Knockdown of GPR120 did not change the stimulation of PA on the SREBP-1c signaling. G protein-coupled receptor family C group 6 member A (GPRC6A) knockdown almost totally blocked the stimulation of FA on PI3K and PKCα phosphorylation as well as SREBP-1c expression and maturation. Furthermore, PA dose-dependently promoted GPRC6A expression and plasma membrane localization. Together, these above results reveal that GPRC6A is a key mediator of PA signaling to lipid synthesis in BMECs via the PI3K/PKCα-SREBP-1c pathways.

Isoleucine stimulates mTOR and SREBP-1c gene expression for milk synthesis in mammary epithelial cells through BRG1-mediated chromatin remodelling.

Several amino acids can stimulate milk synthesis in mammary epithelial cells (MEC); however, the regulatory role of isoleucine (Ile) and underlying molecular mechanism remain poorly understood. In this study, we aimed to evaluate the regulatory effects of Ile on milk protein and fat synthesis in MEC and reveal the mediation mechanism of Brahma-related gene 1 (BRG1) on this regulation. Ile dose dependently affected milk protein and fat synthesis, mechanistic target of rapamycin (mTOR) phosphorylation, sterol regulatory element binding protein 1c (SREBP-1c) expression and maturation, and BRG1 protein expression in bovine MEC. Phosphatidylinositol 3 kinase (PI3K) inhibition by LY294002 treatment blocked the stimulation of Ile on BRG1 expression. BRG1 knockdown and gene activation experiments showed that it mediated the stimulation of Ile on milk protein and fat synthesis, mTOR phosphorylation, and SREBP-1c expression and maturation in MEC. ChIP-PCR analysis detected that BRG1 bound to the promoters of mTOR and SREBP-1c, and ChIP-qPCR further detected that these bindings were increased by Ile stimulation. In addition, BRG1 positively regulated the binding of H3K27ac to these two promoters, while it negatively affected the binding of H3K27me3 to these promoters. BRG1 knockdown blocked the stimulation of Ile on these two gene expressions. The expression of BRG1 was higher in mouse mammary gland in the lactating period, compared with that in the puberty or dry period. Taken together, these experimental data reveal that Ile stimulates milk protein and fat synthesis in MEC via the PI3K-BRG1-mTOR/SREBP-1c pathway.

CTRP9 overexpression attenuates palmitic acid-induced inflammation, apoptosis and impaired migration in HTR8/SVneo cells through AMPK/SREBP1c signaling.

Obesity in pregnant mothers often leads to a range of obstetric complications, including miscarriage, pre-eclampsia, gestational hypertension and diabetes. C1q/TNF-related protein 9 (CTRP9) is an adipokine with an anti-inflammatory effect. The aim of the present study was to identify the role of CTRP9 in the pathogenesis of maternal obesity during pregnancy. Following treatment with palmitic acid (PA), HTR8/SVneo cell viability and CTRP9 expression were analyzed using Cell Counting Kit-8 (CCK-8), reverse transcription-quantitative PCR (RT-qPCR) and western blot analyses. The effects of CTRP9 overexpression on cell viability, apoptosis, pro-inflammatory cytokine levels and migration were assessed using CCK-8, TUNEL, RT-qPCR and Transwell assays, respectively. Subsequently, sterol-regulatory element binding protein 1c (SREBP1c) overexpression efficiency was verified using RT-qPCR, and its effects on cell viability, apoptosis, pro-inflammatory cytokines and migration damage were then examined in HTR8/SVneo cells. The results showed that CTRP9 overexpression attenuated the inhibition of cell viability and apoptosis caused by PA in HTR8/SVneo cells, reduced pro-inflammatory cytokine release, improved cell migration and regulated the protein expression level of AMP-activated protein kinase (AMPK)/SREBP1c signaling. In addition, CTRP9 inhibited SREBP1c expression through AMPK signaling, thereby attenuating the inflammation, apoptosis and inhibited migration caused by PA in HTR8/SVneo cells. In brief, CTRP9 protected against inflammation, apoptosis and migration defects in HTR8/SVneo cells exposed to PA treatment through AMPK/SREBP1c signaling, which suggested the potential role of CTRP9 in alleviating the toxicity of PA.

Qingluotongbi formula regulates the LXRα-ERS-SREBP-1c pathway in hepatocytes to alleviate the liver injury caused by Tripterygium wilfordii Hook. f.

Ethnopharmacological relevanceTripterygium wilfordii Hook. f. (TW) is widely used to treat autoimmune and inflammatory diseases; however, its development and application is limited by its significant association with liver injury. The compound formula Qingluotongbi (QLT) employs TW as its main component and is used to treat rheumatoid arthritis with no adverse reactions, suggesting that QLT may reduce the liver toxicity of TW. Aim of the studyWe examined whether TW interferes with lipid metabolism to induce liver injury, and evaluated the protective effect of QLT in in vivo and in vitro experiments. Materials and methodsAfter administration of QLT and its ingredients, HepaRG cells and SD rats were tested for biochemical indicators, hepatocytes lipid changes, and rat liver pathological changes, and then we analyzed for the gene expression of liver X receptor α (LXRα), endoplasmic reticulum stress (ERS) key proteins, sterol regulatory element binding protein-1c (SREBP-1c), and lipid-synthesizing enzymes. In HepaRG cells, the protein expression of glucose-regulated protein 78 kDa (GRP78) and LXRα was detected after addition of an LXRα inhibitor, LXRα agonist, and ERS inhibitor. ResultsTW caused significant elevation of biochemical indicators and lipid droplet deposition in hepatocytes, as well as upregulated the gene expression of LXRα, ERS key proteins, SREBP-1c, and lipid-synthesizing enzymes in both in vitro and in vivo settings, and caused liver injury in rats. QLT can alleviate the lipotoxic liver injury caused by TW. LXRα agonist further activated ERS induced by TW, whereas LXRα inhibitor significantly reduced ERS and lipotoxic injury induced by TW in HepaRG cells. ConclusionsTW upregulated LXRα to activate ERS and increased the gene expression of SREBP-1c and lipid-synthesizing enzymes, leading to increased lipid synthesis in hepatocytes to result in liver injury. QLT inhibited the LXRα-ERS-SREBP-1c pathway and reduced abnormal lipid synthesis in hepatocytes and the hepatotoxicity of TW.

Hepatic retinaldehyde dehydrogenases are modulated by tocopherol supplementation in mice with hepatic steatosis

ObjectivesAn altered retinol metabolism might play a role in the development of nonalcoholic fatty liver disease (NAFLD). Tocopherols (TF) modulate metabolic pathways and have been proposed as a complementary treatment of obesity-induced metabolic alterations. Moreover, there is evidence suggesting that TF may modulate retinol metabolism. The aim of this study was to evaluate whether the dietary supplementation of α- and γ-TF modulates the expression of hepatic retinaldehyde dehydrogenases, RALDH1, RALDH2, and RALDH3 (involved in retinol metabolism) and, lipogenic factors sterol regulatory element binding protein-1c (SREBP-1c) and cluster differentiation 36 (CD36) in an animal model of diet-induced NAFLD. MethodsMale C57BL/6J mice were divided into four groups: a control diet (CD) group (10% fat, 20% protein, 70% carbohydrates); a CD + TF group (α-tocopherol: 0.7 mg·kg·d–1, γ-tocopherol: 3.5 mg·kg·d–1); a high-fat diet (HFD) group (60% fat, 20% protein, 20% carbohydrates); and a HFD + TF group (0.01 mL·g body weight·d–1), for 12 wk. General parameters (body-adipose tissue weight, glucose-triacylglyceride serum levels), liver steatosis (histology, liver triacylglycerides content), and hepatic RALDH1, RALDH2, RALDH3, SREBP-1c and CD36 (qPCR, quantitative polymerase chain reaction; IHQ, immunohistochemistry) were measured. ResultsTF supplementation in HFD-fed mice decreased the presence of lipid vesicles (90%) and total lipid content (75%) and downregulated the expression of RALDH1, RALDH3, SREBP-1c, and CD36. ConclusionsThe present study demonstrated that α- and γ-TF (1:5 ratio) might play a role in modulating retinol metabolism in the prevention of NAFLD induced by a HFD.

Renal lipid accumulation induced by high-fat diet regulates glucose homeostasis via sodium-glucose cotransporter 2

AimsVisceral lipid accumulation is involved in a variety of physiological aberrations. In the current study, we aimed to investigate whether lipid accumulation had an impact on glucose reabsorption in the kidney. MethodsWe examined renal lipid content and renal threshold for glucose (RTG) of each subject. We compared sodium-glucose cotransporter 2 (SGLT2) and sterol regulatory element-binding protein 1c (SREBP1c) levels in kidneys between rats fed with high fat diet (HFD) and normal chow diet. In vitro, HK2 cells were treated with palmitic acid (PA). Intracellular lipid droplet deposition, glucose uptake, SGLT2 and SREBP1c expression were examined. ResultsRenal fat fraction was positively associated with RTG among the recruited subjects. Moreover, renal lipid content was significantly increased in HFD rats, as well as SGLT2 expression. Accompanied with lipid droplet deposition in HK2 cells, PA stimulated SGLT2 expression and glucose uptake. In addition, after PA treatment, SREBP1c expression was significantly enhanced. However, transfection with siRNA-SREBP1c resulted in significant amelioration of lipid accumulation induced by PA in HK2 cells. Further examination indicated that accompanied with improvement of lipid deposition, SGLT2 expression and glucose uptake were attenuated. ConclusionsThe results of our study demonstrate the involvement of renal lipid accumulation in glucose homeostasis.

All-trans retinoic acid impairs glucose-stimulated insulin secretion by activating the RXR/SREBP-1c/UCP2 pathway.

Diabetes is often associated with vitamin A disorders. All-trans retinoic acid (ATRA) is the main active constituent of vitamin A. We aimed to investigate whether ATRA influences diabetic progression and its mechanisms using both Goto-Kazizazi (GK) rats and INS-1 cells. Rat experiments demonstrated that ATRA treatment worsened diabetes symptoms, as evidenced by an increase in fasting blood glucose (FBG) levels and impairment of glucose homeostasis. Importantly, ATRA impaired glucose-stimulated insulin secretion (GSIS) and increased the expression of sterol regulatory element-binding protein 1c (SREBP-1c) and uncoupling protein 2 (UCP2) in the rat pancreas. Data from INS-1 cells also showed that ATRA upregulated SREBP-1c and UCP2 expression and impaired GSIS at 23 mM glucose. Srebp-1c or Ucp2 silencing attenuated GSIS impairment by reversing the ATRA-induced increase in UCP2 expression and decrease in ATP content. ATRA and the retinoid X receptor (RXR) agonists 9-cis RA and LG100268 induced the gene expression of Srebp-1c, which was almost completely abolished by the RXR antagonist HX531. RXRα-LBD luciferase reporter plasmid experiments also demonstrated that ATRA concentration-dependently activated RXRα, the EC50 of which was 1.37 μM, which was lower than the ATRA concentration in the pancreas of GK rats treated with a high dose of ATRA (approximately 3 μM), inferring that ATRA can upregulate Srebp-1c expression in the pancreas by activating RXR. In conclusion, ATRA impaired GSIS partly by activating the RXR/SREBP-1c/UCP2 pathway, thus worsening diabetic symptoms. The results highlight the roles of ATRA in diabetic progression and establish new strategies for diabetes treatment.

Exposure to Plasma From Non-alcoholic Fatty Liver Disease Patients Affects Hepatocyte Viability, Generates Mitochondrial Dysfunction, and Modulates Pathways Involved in Fat Accumulation and Inflammation.

Changes of lipidic storage, oxidative stress and mitochondrial dysfunction may be involved in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Although the knowledge of intracellular pathways has vastly expanded in recent years, the role and mechanisms of circulating triggering factor(s) are debated. Thus, we tested the hypothesis that factors circulating in the blood of NAFLD patients may influence processes underlying the disease. Huh7.5 cells/primary human hepatocytes were exposed to plasma from 12 NAFLD patients and 12 healthy subjects and specific assays were performed to examine viability, H2O2 and mitochondrial reactive oxygen species (ROS) release, mitochondrial membrane potential and triglycerides content. The involvement of NLRP3 inflammasome and of signaling related to peroxisome-proliferator-activating-ligand-receptor-γ (PPARγ), sterol-regulatory-element-binding-protein-1c (SREBP-1c), nuclear-factor-kappa-light-chain-enhancer of activated B cells (NF-kB), and NADPH oxidase 2 (NOX2) was evaluated by repeating the experiments in the presence of NLRP3 inflammasome blocker, MCC950, and through Western blot. The results obtained shown that plasma of NAFLD patients was able to reduce cell viability and mitochondrial membrane potential by about 48 and 24% (p < 0.05), and to increase H2O2, mitochondrial ROS, and triglycerides content by about 42, 19, and 16% (p < 0.05), respectively. An increased expression of SREBP-1c, PPARγ, NF-kB and NOX2 of about 51, 121, 63, and 46%, respectively, was observed (p < 0.05), as well. Those effects were reduced by the use of MCC950. Thus, in hepatocytes, exposure to plasma from NAFLD patients induces a NAFLD-like phenotype by interference with NLRP3-inflammasome pathways and the activation of intracellular signaling related to SREBP-1c, PPARγ, NF-kB and NOX2.

Elucidation of the mechanism of NEFA-induced PERK-eIF2α signaling pathway regulation of lipid metabolism in bovine hepatocytes

During the periparturient transition period, negative energy balance (NEB) characterized by high concentrations of non-esterified fatty acids (NEFA) may cause fatty liver and ketosis in dairy cows. Previous studies have shown that the protein kinase R-like endoplasmic reticulum kinase (PERK) branch of the endoplasmic reticulum stress (ERS) response plays an important role in lipid metabolism in hepatocytes. This study, therefore, investigated the role of the PERK-branch in NEFA-induced fatty liver. Different concentrations of NEFA or GSK2656157 (a novel catalytic inhibitor of PERK) were used to treat hepatocytes isolated from calves. The NEFA treatment significantly increased the triacylglycerol (TG) content, the phosphorylation level of PERK and eukaryotic initiation factor 2α (eIF2α), and the abundance of glucose-regulated protein 78 (Grp78), C/EBP homologous protein (CHOP), sterol regulatory element-binding protein 1c (SREBP-1c), fatty acid synthase (FASN), peroxisome proliferator-activated receptor-α (PPARα), carnitine palmitoyltransferase 1A (CPT1A), apolipoprotein B (APOB), and the low-density lipoprotein receptor (LDLR). Compared with the 1.2 mM NEFA group, inhibition of PERK activity further increased the TG content in hepatocytes, the very-low-density lipoprotein (VLDL) content in the supernatant and the protein abundance of APOB while reducing the expression and nuclear levels of SREBP-1c and PPARα, as well as the expression of CPT1A and CPT2. In conclusion, the results showed that the NEFA-induced PERK-eIF2α signaling pathway promotes lipid synthesis, lipid oxidation, but inhibits the assembly and secretion of VLDL. Therefore, during the transition period, the activation of the PERK-eIF2α signaling pathway in the liver of dairy cows could defeat the acid-induced lipotoxicity and provide energy to alleviate NEB.