Preferential lipolysis of DGAT1 over DGAT2 generated triacylglycerol in Huh7 hepatocytes

Two distinct diacylglycerol acyltransferases (DGAT1 and DGAT2) catalyze the final committed step of triacylglycerol (TG) synthesis in hepatocytes. After its synthesis in the endoplasmic reticulum (ER) TG is either stored in cytosolic lipid droplets (LDs) or is assembled into very low-density lipoproteins in the ER lumen. TG stored in cytosolic LDs is hydrolyzed by adipose triglyceride lipase (ATGL) and the released fatty acids are converted to energy by oxidation in mitochondria. We hypothesized that targeting/association of ATGL to LDs would differ depending on whether the TG stores were generated through DGAT1 or DGAT2 activities. Individual inhibition of DGAT1 or DGAT2 in Huh7 hepatocytes incubated with oleic acid did not yield differences in TG accretion while combined inhibition of both DGATs completely prevented TG synthesis suggesting that either DGAT can efficiently esterify exogenously supplied fatty acid. DGAT2-made TG was stored in larger LDs, whereas TG formed by DGAT1 accumulated in smaller LDs. Inactivation of DGAT1 or DGAT2 did not alter expression (mRNA or protein) of ATGL, the ATGL activator ABHD5/CGI-58, or LD coat proteins PLIN2 or PLIN5, but inactivation of both DGATs increased PLIN2 abundance despite a dramatic reduction in the number of LDs. ATGL was found to preferentially target to LDs generated by DGAT1 and fatty acids released from TG in these LDs were also preferentially used for fatty acid oxidation. Combined inhibition of DGAT2 and ATGL resulted in larger LDs, suggesting that the smaller size of DGAT1-generated LDs is the result of increased lipolysis of TG in these LDs.     

Nonadditive expression of lipid metabolism pathway-related genes in intestine of hybrids of Nile tilapia females (Oreochromis niloticus) and blue tilapia males (Oreochromis aureus)

Nonadditive expression contributes to heterosis in hybrids. In this study, the expression profiles of twelve lipid metabolism pathway-related genes were investigated in the intestine of Nile tilapia (Oreochromis niloticus) ♀?×?blue tilapia (Oreochromis aureus) ♂ hybrid. The expression of genes from the hybrid were assigned to nonadditive and additive expression pattern groups and compared with expression patterns from Nile tilapia and blue tilapia. In the intestine of the hybrid, apoA4B was expressed at intermediate levels, but apoB and MTP were assigned to ELD-B and ELD-N categories, respectively. The LPL and LRP1 showed transgressive up-regulation in the hybrid, but LDLR was assigned to the ELD-B category. For fatty acid uptake related genes, only FABP11a was categorized as nonadditive expression with transgressive up-regulation, while CD36 and FABP3 were categorized as additive expression in the intestine of the hybrid. Two genes in triacylglycerol metabolism, namely, FAS and DGAT2, showed transgressive up-regulation in the hybrid. Most of the genes analyzed in the present study showed nonadditive expression (8 in 12), and five genes showed transgressive up-regulation. These results indicated that the stimulation of lipid metabolism in the hybrid compared to that of its parents. The hyperactive expression of these genes in the hybrid may be associated with the growth and lipid usage vigor.

     

The use of stable isotope-labeled glycerol and oleic acid to differentiate the hepatic functions of DGAT1 and -2

Diacylglycerol acyltransferase (DGAT) catalyzes the final step in triglyceride (TG) synthesis. There are two isoforms, DGAT1 and DGAT2, with distinct protein sequences and potentially different physiological functions. To date, the ability to determine clear functional differences between DGAT1 and DGAT2, especially with respect to hepatic TG synthesis, has been elusive. To dissect the roles of these two key enzymes, we pretreated HepG2 hepatoma cells with (13)C(3)-D(5)-glycerol or (13)C(18)-oleic acid, and profiled the major isotope-labeled TG species by liquid chromatography tandem mass spectrometry. Selective DGAT1 and DGAT2 inhibitors demonstrated that (13)C(3)-D(5)-glycerol-incorporated TG synthesis was mediated by DGAT2, not DGAT1. Conversely, (13)C(18)-oleoyl-incorporated TG synthesis was predominantly mediated by DGAT1. To trace hepatic TG synthesis and VLDL triglyceride (VLDL-TG) secretion in vivo, we administered D(5)-glycerol to mice and measured plasma levels of D(5)-glycerol-incorporated TG. Treatment with an antisense oligonucleotide (ASO) to DGAT2 led to a significant reduction in D(5)-glycerol incorporation into VLDL-TG. In contrast, the DGAT2 ASO had no effect on the incorporation of exogenously administered (13)C(18)-oleic acid into VLDL-TG. Thus, our results indicate that DGAT1 and DGAT2 mediate distinct hepatic functions: DGAT2 is primarily responsible for incorporating endogenously synthesized FAs into TG, whereas DGAT1 plays a greater role in esterifying exogenous FAs to glycerol.     

过表达微小RNA-130a-3P对LPS诱导心肌细胞损伤的干预作用及其机制*

目的: 探讨miRNA-130a-3p对脂多糖(LPS)诱导的心肌细胞自噬与凋亡的影响及分子机制。方法: H9C2心肌细胞随机分为5组,即正常对照组,LPS模型组,miRNA阴性对照组(miRNA-negative control组),miRNA-130a-3p mimics组(过表达miRNA-130a-3p),miRNA-130a-3p mimics+LY294002组(过表达miRNA-130a-3p + PI3K抑制)。LPS模型组即终浓度为10 μg/ml的LPS诱导24 h,miRNA阴性对照组与miRNA-130a-3p mimics组是利用lipo3000将阴性对照miRNA及miRNA-130a-3p mimics转染至H9C2细胞,培养24 h后,再将LPS加入培养基中培养24 h。miRNA-130a-3p mimics + LY294002组是利用lipo3000将miRNA-130a-3p mimics转染至H9C2细胞,同时在培养基中加入10 μmol/L(终浓度)的LY294002,培养24 h后,再将浓度为10 μg/ml的LPS加入培养基中培养24 h。所有实验均重复5次以上。利用RT-qPCR检测细胞中miRNA-130a-3p mRNA的表达水平,利用CCK-8实验检测细胞活性,利用ELISA实验检测细胞培养液中肿瘤坏死因子-α(TNF-α),白细胞介素-6(IL-6),白细胞介素-1β (IL-1β)的含量,利用比色法检测细胞培养液中超氧化物歧化酶(SOD)、乳酸脱氢酶(LDH)的含量;利用Western blot检测细胞中p-PI3K蛋白,p-AKT蛋白,Bax蛋白,Bcl-2蛋白,cleaved-caspase-3蛋白,LC3蛋白,p62蛋白的表达水平。结果: 结果显示,与正常组相比较,LPS模型细胞中miRNA-130a-3p mRNA水平,p-PI3K蛋白与p-AKT蛋白的水平显著低于正常对照组(P<0.01);与LPS组相比较,miRNA-130a-3p mimics组细胞中p-PI3K,p-AKT蛋白的表达显著升高(P<0.01,P<0.05);与正常对照组相比较,LPS组细胞活性显著降低,细胞培养液中TNF-α,IL-6,IL-1β及 LDH的含量显著升高(P<0.01), SOD的含量显著降低(P<0.01),细胞中Bax蛋白,cleaved caspase-3蛋白,p62蛋白的表达显著升高(P<0.01),Bcl-2蛋白的表达和LC3II/I的比率显著降低(P<0.01);与LPS组相比较,miRNA-130a-3p mimics可提高细胞活性,降低细胞培养液中TNF-α,IL-6,IL-1β及LDH的含量(P<0.01,P<0.05),提高SOD的含量(P<0.05),降低细胞中Bax蛋白,cleaved caspase-3蛋白,p62蛋白的表达(P<0.01),促进Bcl-2蛋白的表达(P<0.01),提高LC3II/I的比率(P<0.05);与miRNA-130a-3p mimics组相比较,miRNA-130a-3p mimics+LY294002组,可部分逆转miRNA-130a-3p mimics对细胞的作用。结论: 过表达miRNA-130a-3p可部分通过激活PI3K/AKT信号通路促进细胞的自噬与抑制细胞凋亡,减轻LPS诱导的心肌细胞损伤。     

尼罗罗非鱼生长激素及其受体的cDNA克隆与mRNA表达的雌雄差异

尼罗罗非鱼(Oreochromis niloticus)雌雄鱼生长差异明显,为了探讨其原因,本文采用RT-PCR方法克隆了尼罗罗非鱼生长激素(Growthhormone,GH)及其受体(Growth hormone receptor,GHR)的cDNA序列,并应用半定量RT-PCR方法比较了雌、雄尼罗罗非鱼垂体GHmRNA、肝脏GHRmRNA、肌肉GHRmRNA的表达差异。序列分析表明:GH开放阅读框为615bp,共编码204个氨基酸;GHR开放阅读框为1908bp,共编码635个氨基酸。以RT-PCR方法研究了GH、GHR在各组织的分布情况,结果表明:GH仅在垂体中检测到有表达,而GHR在所检测的18种组织中均有表达,其中以肝脏、肌肉、性腺、下丘脑、胸腺表达量较高。以半定量RT-PCR方法进一步比较了雌、雄尼罗罗非鱼垂体GHmRNA、肝脏GHRmRNA、肌肉GHRmRNA的表达量,结果表明:雄鱼垂体GHmRNA和肝脏GHRmRNA的表达量均显著高于雌鱼,肌肉GHRmRNA的表达量则无显著差异,推测垂体GHmRNA和肝脏GHRmRNA表达的雌雄差异是尼罗罗非鱼雌雄生长差异的主要原因之一。     

Construction of a recombinant human FGF1 expression vector for mammary gland-specific expression in human breast cancer cells

Studies have shown that not only does palmitic acid promote triglyceride (TG) accumulation, but it also affects cell viability in in vitro steatosis models. However, to what degree these effects are mediated by steatosis in goose primary hepatocytes is unknown. In this study, the effects of palmitic acid on the lipid metabolism homeostasis pathway and on apoptosis were determined. The authors measured the mRNA levels of genes involved in TG synthesis, lipid deposition, fatty acid oxidation and the assembly and secretion of VLDL-TG in goose primary hepatocytes. The results indicated that palmitic acid can significantly reduce the activity of goose hepatocytes, and that palmitic acid had a significant effect on TG accumulation; however, with increasing palmitic acid concentrations, the extracellular TG and extracellular VLDL concentration gradually decreased. With increasing palmitic acid concentrations, the gene expression levels of DGAT1, DGAT2, PPARα, CPT-1, FoxO1 and MTTP (which regulate hepatic TG synthesis, fatty acid oxidation and the assembly and secretion of VLDL-TGs) first increased and then decreased; the change in PLIN gene expression was palmitic acid dose-dependent, similar to the regulatory mode of intracellular TG accumulation. In conclusion, this study clearly shows that palmitic acid can promote TG accumulation and induce apoptosis in goose primary hepatocytes, and this effect may be related to the lipid metabolism pathway.     

Increased very low density lipoprotein secretion and gonadal fat mass in mice overexpressing liver DGAT1

Acyl-CoA:diacylglycerol acyltransferases (DGATs) catalyze the last step in triglyceride (TG) synthesis. The genes for two DGAT enzymes, DGAT1 and DGAT2, have been identified. To examine the roles of liver DGAT1 and DGAT2 in TG synthesis and very low density lipoprotein (VLDL) secretion, liver DGAT1- and DGAT2-overexpressing mice were created by adenovirus-mediated gene transfection. DGAT1-overexpressing mice had markedly increased DGAT activity in the presence of the permeabilizing agent alamethicin. This suggests that DGAT1 possesses latent DGAT activity on the lumen of the endoplasmic reticulum. DGAT1-overexpressing mice showed increased VLDL secretion, resulting in increased gonadal (epididymal or parametrial) fat mass but not subcutaneous fat mass. The VLDL-mediated increase in gonadal fat mass might be due to the 4-fold greater expression of the VLDL receptor protein in gonadal fat than in subcutaneous fat. DGAT2-overexpressing mice had increased liver TG content, but VLDL secretion was not affected. These results indicate that DGAT1 but not DGAT2 has a role in VLDL synthesis and that increased plasma VLDL concentrations may promote obesity, whereas increased DGAT2 activity has a role in steatosis.     

MicroRNA-29a-3p regulates abdominal aortic aneurysm development and progression via direct interaction with PTEN

Various research studies have been conducted in deducing the role of microRNAs (miRNAs) in the pathogenesis and physiological processes of various systematic diseases. This study aims at demonstration of the important role played by miR-29a-3p, through association with phosphatase and tensin homolog (PTEN), in the regulation of abdominal aortic aneurysm development and progression. Quantitative real-time polymerase chain reaction (RT-qPCR) examined miRNA-19a-3p and PMEPA1 expression in multiplied vascular smooth muscle cells (VSMCs). Cell transfection upregulated or downregulated the genes and cell counting kit-8 assay determined cellular viability. RT-qPCR detected cellular proliferation and cell death using the cell proliferation and apoptosis biomarkers Ki87 and proliferating cell nuclear antigen, caspase-8 and caspase-3, respectively. Furthermore, luciferase assay analyzed the luciferase activity and western blot analysis determined miRNA-19a-3p and PMEPA1 protein expression in proliferation and apoptosis biomarkers. TargetScan 4.2 online software ( www.targetscan.org ) was used to perform the bioinformatics analysis so as to forecast the putative targets of miR-29a-3p and PTEN. The results inferred that there was an increased expression of miRNA-29a-3p found in AAA-mimic cells with increased cellular viability and significant pathological apoptosis. Further, when the expression of miRNA-29a-3p was downregulated, it reduced the cell viability of AAA cells. On the basis of the gene interplays, it can be understood that the PTEN was directly targeted by miRNA-29a-3p so as to regulate the AAA progression. Thus, PTEN was found to strengthen the proliferation effect of miRNA-29a-3p in AAA cells. The current study thus shed more insights about the molecular mechanistic roles of miRNA-29a-3p and PTEN, opening doors for novel therapeutic approach to AAA.     

Aberrant expression of microRNA induced by high-fructose diet: implications in the pathogenesis of hyperlipidemia and hepatic insulin resistance

Fructose is a highly lipogenic sugar that can alter energy metabolism and trigger metabolic disorders. In the current study, microRNAs (miRNAs) altered by a high-fructose diet were comprehensively explored to elucidate their significance in the pathogenesis of chronic metabolic disorders. miRNA expression profiling using small noncoding RNA sequencing revealed that 19 miRNAs were significantly upregulated and 26 were downregulated in the livers of high-fructose-fed mice compared to chow-fed mice. Computational prediction and functional analysis identified 10 miRNAs, miR-19b-3p, miR-101a-3p, miR-30a-5p, miR-223-3p, miR-378a-3p, miR-33-5p, miR-145a-3p, miR-128-3p, miR-125b-5p and miR-582-3p, assembled as a regulatory network to potentially target key genes in lipid and lipoprotein metabolism and insulin signaling at multiple levels. qRT-PCR analysis of their potential target genes [IRS-1, FOXO1, SREBP-1c/2, ChREBP, insulin-induced gene-2 (Insig-2), microsomal triglyceride transfer protein (MTTP) and apolipoprotein B (apoB)] demonstrated that fructose-induced alterations of miRNAs were also reflected in mRNA expression profiles of their target genes. Moreover, the miRNA profile induced by high-fructose diet differed from that induced by high-fat diet, indicating that miRNAs mediate distinct pathogenic mechanisms in dietary-induced metabolic disorders. This study presents a comprehensive analysis of a new set of hepatic miRNAs, which were altered by high-fructose diet and provides novel insights into the interaction between miRNAs and their target genes in the development of metabolic syndrome.     

Knockdown of acyl-CoA:diacylglycerol acyltransferase 2 with antisense oligonucleotide reduces VLDL TG and ApoB secretion in mice

Acyl-CoA:diacylglycerol acyltransferases (DGATs) are enzymes that catalyze the formation of triglyceride (TG) from acyl-CoA and diacylglycerol. Two DGATs have been identified which belong to two distinct gene families and both are ubiquitously expressed. DGAT2 knockout mice are lipopenic and die shortly after birth. In the current study, wild type mice were treated with increasing doses (25-60 mg/kg twice weekly) of a DGAT2 gene-specific antisense oligonucleotide (ASO). Treatment resulted in a dose dependent decrease in hepatic DGAT2 gene expression (up to 80%) which was associated with a 40% decrease in hepatic DGAT2 activity and a 45% decrease in hepatic TG. Decreased levels of DGAT2 resulted in a significant dose dependent decrease in VLDL TG secretion (up to 52%) and reduced plasma TG, total cholesterol, and ApoB. Similar results were obtained when DGAT1 KO mice were treated with the DGAT2 ASO. Treatment of ob/ob mice with the DGAT2 ASO resulted in significant decreases in weight gain (10%), adipose weight (25%) and hepatic TG content (80%). Our findings indicate that the majority of TG destined for secretion by liver is synthesized by DGAT2 and suggests that DGAT2 may be a therapeutic target for treatment of hypertriglyceridemia, hepatic steatosis and obesity.     

Effects of linoleate on cell viability and lipid metabolic homeostasis in goose primary hepatocytes

Studies have shown linoleate could not only promote cell viability but also affect lipid metabolism in mammals. However, to what degree these effects are mediated by steatosis in goose primary hepatocytes is unknown. In this study, the effect of linoleate on the lipid metabolic homeostasis pathway was determined. We measured the mRNA levels of genes involved in triglyceride synthesis, lipid deposition, β-oxidation, and assembly and secretion of VLDL-TGs in goose (Anser cygnoides) primary hepatocytes. Linoleate significantly increased goose hepatocyte viability, and linoleate at 0.125 mM, 0.25 mM, 0.5 mM and 1.0 mM all showed a significant effect on TG accumulation. However, with increasing linoleate concentrations, the extracellular TG concentration and extracellular VLDL gradually decreased. DGAT1, DGAT2, PPARα, PPARγ, FoxO1, MTP, PLIN and CPT-1 mRNA was detected by real-time PCR. With increasing linoleate concentrations, the changes in DGAT1, DGAT2, PPARα and CPT-1 gene expression, which regulates hepatic TG synthesis and fatty acid oxidation, first increased and then decreased. Additionally, FoxO1 and MTP gene expression was reduced with increasing linoleate concentrations, and the change in PLIN gene expression was increased at all concentrations, similar to the regulation of intracellular TG accumulation. In conclusion, linoleate regulated TG accumulation and increased hepatocyte viability. The data suggest that linoleate does promote goose hepatocyte viability and steatosis, which may up-regulate TG synthesis-relevant gene expression, suppress assembly and secretion of VLDL-TGs, and increase fatty acid oxidation properly to function of goose primary hepatocytes.     

MicroRNA-411a-3p过表达抑制Ca2+信号转导与羊驼黑色素细胞的增殖和迁移

黑色素细胞中产生的黑色素转移及黑色素细胞的增殖和迁移均与色素沉积有关。黑色素细胞的增殖需要有丝分裂原协同进行。黑色素细胞的增殖和分化受组织环境以及多种毛色基因的调控。miRNA-411a-3p在不同毛色羊驼皮肤中呈差异表达,且通过靶向IGF1R调控黑色素生成。但miRNA-411a-3p是否与黑色素颗粒迁移、黑色素细胞的增殖和迁移相关未见报道。本研究通过miRNA-411a-3p转染羊驼黑色素细胞后发现,与对照组相比,钙离子信号转导水平下降了（91.73±1.53）% (P<0.01),与黑色素转移有关的Rab27a和肌球蛋白Va在蛋白质水平的表达均被下调,同时与细胞增殖有关的整联蛋白β1和β5相关基因在转录水平分别下降了（44.67 ± 13.67）%（P<0.01）和（30.72 ± 6.23）% (P<0.01),在蛋白质水平表达下降了（45.18 ± 1.96）% (P<0.001)和（11.52 ± 1.09）% (P<0.001)。综上所述,miRNA-411a-3p过表达后会抑制钙离子信号转导,以及羊驼黑色素细胞的增殖和迁移。