Deficiency of liver adipose triglyceride lipase in mice causes progressive hepatic steatosis

Accumulation of cytoplasmic triacylglycerol (TG) underlies hepatic steatosis, a major cause of cirrhosis. The pathways of cytoplasmic TG metabolism are not well known in hepatocytes, but evidence suggests an important role in lipolysis for adipose triglyceride lipase (ATGL). We created mice with liver-specific inactivation of Pnpla2, the ATGL gene. These ATGLLKO mice had severe progressive periportal macrovesicular and pericentral microvesicular hepatic steatosis (73, 150, and 226 μmol TG/g liver at 4, 8, and 12 months, respectively). However, plasma levels of glucose, TG, and cholesterol were similar to those of controls. Fasting 3-hydroxybutyrate level was normal, but in thin sections of liver, beta oxidation of palmitate was decreased by one-third in ATGLLKO mice compared with controls. Tests of very low-density lipoprotein production, glucose, and insulin tolerance and gluconeogenesis from pyruvate were normal. Plasma alanine aminotransferase levels were elevated in ATGLLKO mice, but histological estimates of inflammation and fibrosis and messenger RNA (mRNA) levels of tumor necrosis factor-α and interleukin-6 were similar to or lower than those in controls. ATGLLKO cholangiocytes also showed cytoplasmic lipid droplets, demonstrating that ATGL is also a major lipase in cholangiocytes. There was a 50-fold reduction of hepatic diacylglycerol acyltransferase 2 mRNA level and a 2.7-fold increase of lipolysosomes in hepatocytes (P < 0.001), suggesting reduced TG synthesis and increased lysosomal degradation of TG as potential compensatory mechanisms. CONCLUSION: Compared with the hepatic steatosis of obesity and diabetes, steatosis in ATGL deficiency is well tolerated metabolically. ATGLLKO mice will be useful for studying the pathophysiology of hepatic steatosis.     

内质网应激相关基因在肥胖患者内脏脂肪组织中表达水平观察

肥胖患者网膜脂肪组织中内质网应激相关基因重链结合蛋白(Bip)、肌醇需求激酶1(IRE1)、类PKR的内质网激酶(PERK)及氧调节蛋白150(ORP150)的mRNA表达量明显高于正常体重者[1.4(1.4)对0.9(0.6)、2.0±0.8对1.3±0.8、2.4(2.9)对1.5(1.2)、1.6(2.6)对0.6(0.5),均P<0.05],PERK和ORP150的表达量与体重指数相关,Bip、ORP150、X盒结合蛋白1(XBP1)及IRE1表达量与肿瘤坏死因子α、白细胞介素6表达量相关,提示肥胖患者内脏脂肪组织中内质网应激被激活,内质网应激相关基因表达和局部炎症相关.     

Fasting energy homeostasis in mice with adipose deficiency of desnutrin/adipose triglyceride lipase

Adipose triglyceride lipase (ATGL) catalyzes the first step of lipolysis of cytoplasmic triacylglycerols in white adipose tissue (WAT) and several other organs. We created adipose-specific ATGL-deficient (ATGLAKO) mice. In these mice, in vivo lipolysis, measured as the increase of plasma nonesterified fatty acid and glycerol levels after injection of a β3-adrenergic agonist, was undetectable. In isolated ATGLAKO adipocytes, β3-adrenergic-stimulated glycerol release was 10-fold less than in controls. Under fed conditions, ATGLAKO mice had normal viability, mild obesity, low plasma nonesterified fatty acid levels, increased insulin sensitivity, and increased daytime food intake. After 5 h of fasting, ATGLAKO WAT showed phosphorylation of the major protein kinase A-mediated targets hormone-sensitive lipase and perilipin A and ATGLAKO liver showed low glycogen and triacylglycerol contents. During a 48-h fast, ATGLAKO mice developed striking and complex differences from controls: progressive reduction of oxygen consumption, high respiratory exchange ratio, consistent with reduced fatty acid availability for energy production, lethargy, hypothermia, and undiminished fat mass, but greater loss of lean mass than controls. Plasma of 48 h-fasted ATGLAKO mice had a unique pattern: low 3-hydroxybutyrate, insulin, adiponectin, and fibroblast growth factor 21 with elevated leptin and corticosterone. ATGLAKO WAT, liver, skeletal muscle, and heart showed increased levels of mRNA related to autophagy and proteolysis. In murine ATGL deficiency, adipose lipolysis is critical for fasting energy homeostasis, and fasting imposes proteolytic stress on many organs, including heart and skeletal muscle.     

脂肪组织甘油三酯脂肪酶的研究进展

脂肪组织甘油三酯脂肪酶(ATGL)是新近发现的启动脂肪动员的另一关键酶,其主要催化脂肪组织中甘油三酯生成甘油二酯,与长期认为的经典限速酶激素敏感性脂肪酶(HSL)在脂肪分解途径中共同承担着重要作用.鉴于ATGL与脂肪分解密切相关,并在脂肪代谢紊乱性疾病中发挥着重要的作用,本文就ATGL的研究进展及与脂肪分解、肥胖和2型糖尿病等脂代谢紊乱性疾病的关系作一综述.     

Inactivation of hepatic microsomal triglyceride transfer protein protects mice from diet-induced gallstones

BACKGROUND & AIMS: Microsomal triglyceride transfer protein (MTTP) is critical for the production of very-low-density lipoproteins (VLDL). The current studies were undertaken to examine the in vivo role of MTTP in hepatic cholesterol and fatty acid metabolism, as well as in biliary lipid secretion. We also tested whether MTTP plays a role in diet-induced cholelithiasis in mice. METHODS: We used mice in which Mttp had been inactivated in the liver (Mttp(Delta/Delta) mice). We measured several parameters of cholesterol metabolism, fatty acid synthesis, and biliary lipid levels in mice fed a normal or a lithogenic diet. We also assessed the incidence of diet-associated gallstones. RESULTS: Hepatic Mttp inactivation markedly decreased plasma triglyceride and cholesterol levels and increased biliary cholesterol and bile acid output. Hepatic cholesterogenesis and fatty acid synthesis were significantly decreased in Mttp(Delta/Delta) mice compared with control mice. The incidence of gallstones decreased from 90% in control mice to 33% in Mttp(Delta/Delta) mice after 8 weeks of a lithogenic diet (P < .0001). The mechanism of the protective effect appears to be increased biliary phospholipid output in Mttp(Delta/Delta) mice, leading to significant unsaturation of gallbladder bile. CONCLUSIONS: These results indicate that modulation of Mttp expression in the liver affects hepatic lipid synthesis and storage as well as biliary lipid secretion. Our findings further indicate that inhibition of hepatic MTTP activity decreases the risk of experimental cholelithiasis by favoring phospholipid output into the bile.     

7,8-dihydroxyflavone protects human renal proximal tubular cells from hypoxia injury via inhibiting endoplasmic reticulum stress

正Objective To observe the effects of 7,8-dihydroxyflavone(7,8-DHF)on hypoxia induced endoplasmic reticulum stress(ERS)in human proximal tubular epithelial cells(HK-2).Methods The mRNA level of ERS associated biomarkers was evaluated by RT-PCR assay in     

Neuronal nitric oxide synthase protects the pancreatic beta cell from glucolipotoxicity-induced endoplasmic reticulum stress and apoptosis

Aims/hypothesis  

Cytokines stimulate nitric oxide production in pancreatic beta cells, leading to endoplasmic reticulum (ER) stress and apoptosis. Treatment of beta cells with glucose and NEFA induces nitric oxide synthase (NOS) as well as ER stress. However, the role of NO in glucolipotoxicity-induced ER stress in beta cells is not clear.     

脂肪细胞的内质网应激

肥胖常伴有炎性反应、胰岛素抵抗和全身代谢紊乱,脂肪细胞内质网应激在其中发挥莺要作用,内质网有合成、折叠和运输蛋白质的作用.脂肪细胞内质网还可以合成脂肪和感受营养物质的变化.在肥胖状态下,脂肪细胞受到营养过剩、细胞内胰岛素抵抗及氧化应激等因素的刺激后,内质网的生理功能发生紊乱.导致内质网应激,内质网应激的表现主要是未折叠蛋白质反应被激活以后,可以通过炎性反应和氧化应激等通路加重胰岛素抵抗.导致全身代谢紊乱.维持和增强内质网功能可能是改善胰岛素抵抗有效的方法之一,一些可以缓解内质网应激的化学分子伴侣是有前景的治疗药物.     

Missense PNLIP mutations impeding pancreatic lipase secretion cause protein misfolding and endoplasmic reticulum stress

Background/ObjectiveMutation-induced misfolding of digestive enzymes has been shown to cause chronic pancreatitis. Recently, heterozygous pancreatic lipase (PNLIP) mutations leading to reduced secretion were identified. The aim of the present study was to investigate whether PNLIP mutants with a secretion defect result in endoplasmic reticulum (ER) stress in cell culture models.MethodsWe introduced the coding DNA for wild-type and A174P, G233E, C254R and V454F mutant PNLIP into two mammalian cell lines and carried out functional assays to assess PNLIP expression, secretion and ER stress.ResultsWe found that wild-type PNLIP was readily secreted from the investigated cell lines. In contrast, none of the lipase mutants were detectable in the conditioned media. PNLIP variants accumulated in the cells as intracellular protein aggregates probably due to misfolding in the ER. Consistent with this notion, PNLIP mutants induced ER stress, as indicated by increased mRNA levels of spliced X-box Binding Protein 1 (XBP1) and the ER chaperone Immunoglobulin Binding Protein (BiP).ConclusionThe results indicate that PNLIP mutations associated with a lipase secretion defect cause ER stress and thereby may increase the risk for chronic pancreatitis.     

脂联素抑制内质网应激干预慢性间歇性缺氧所致肾损伤

目的探讨脂联素(Ad)对慢性间歇性缺氧(CIH)所致肾损伤的干预作用及相关机制。方法 60只成年Wistar大鼠随机分成4组:正常对照(NC)组、NC+Ad组、CIH组和CIH+Ad组。其中CIH组和CIH+Ad组大鼠接受CIH处理4个月。其余2组接受正常空气处理,同时NC+Ad组和CIH+Ad组大鼠接受Ad(10l人開)治疗,每周2次,持续4个月。荧光显微镜下观察活性氧(ROS)的水平。TUNEL染色检测肾脏细胞凋亡情况。Western blotting检测各组大鼠肾脏组织中GRP78、CHOP、IRE1、PERK、pro-ATF6蛋白的表达,以反映各组大鼠内质网应激情况。采用SPSS 17.0软件进行统计学分析。计量资料用均数±标准差(±s)表示,组间比较用t检验。结果实验满4个月时,组间比较示各参数在NC与NC+Ad组间差异均无统计学意义(P均0.05)。与NC组和NC+Ad组比较:(1)ROS水平在CIH组显著增高,而CIH+Ad组低于CIH组,但仍高于NC组和NC+Ad组(尸均0.05);(2)肾细胞凋亡率和反映凋亡的caspase-12和caspase-3蛋白水平在CIH组明显增加,CIH+Ad组较CIH组明显减少,但仍然高于NC组和NC+Ad组(P均0.05);(3)CIH组肾脏组织的GRP78、CHOP、IRE1、PERK蛋白水平明显增加,在CIH+Ad组明显减少,但仍高于NC组和NC+Ad组(P均0.05);pro-ATF6蛋白水平在CIH组明显降低,在CIH+Ad组有所增加,但仍然低于NC组和NC+Ad组(P均0.05)。结论 CIH可以通过激活ROS和ERS相关的细胞凋亡途径导致肾脏损伤,而补充外源性Ad后,可能通过抑制ROS,进而抑制ERS,保护肾脏细胞。     

Adiponectin protects the kidney against chronic intermittent hypoxia-induced injury through inhibiting endoplasmic reticulum stress

Purpose

The current study was carried out to assess the effects of chronic intermittent hypoxia (CIH) on the kidney, the intervention roles of adiponectin (Ad), and the associated mechanisms.

Methods

Sixty Wistar rats were randomly divided into four groups: the normal control (NC), normal control plus Ad supplement (NC + Ad), CIH, and CIH plus Ad supplement (CIH + Ad) groups. The rats in both CIH and CIH + Ad groups were submitted to a CIH environment for 4 months, while the rats in NC and NC + Ad groups were housed with the normal air for 4 months. In addition, the rats in NC + Ad and CIH + Ad groups were treated with an intravenous injection of Ad at a dosage of 10 μg per injection, twice a week, for four successive months.

Results

The production level of reactive oxygen species (ROS) and the protein levels of endoplasmic reticulum (ER) stress, as well as the cell apoptosis level in kidney, were all higher in the CIH group than in the NC and NC + Ad groups (all p < 0.05). However, the ROS production, the protein of ER stress, and cell apoptosis levels in kidney were all lower in the CIH + Ad group than those in the CIH group (all p < 0.05).

Conclusion

Ad could protect against CIH-induced renal cell apoptosis through inhibiting ROS-related ER stress.

     

内质网应激对2型糖尿病小鼠脂肪肝发生的影响

目的:探讨内质网应激(ERS)在2型糖尿病(T2DM)小鼠脂肪肝发生中的作用机制.方法:应用实时定量RT-PCR技术检测T2DM与非糖尿病小鼠肝脏ERS和脂代谢相关基因表达差异, 并进行血生化指标及肝脏形态学检测.结果:与同龄非T2DM小鼠相比T2DM小鼠表现为:(1)胰岛素抵抗、空腹血糖升高(30.76±4.52 vs 12.80±2.13, 14.73±2.74v s 4.61±1.12). (2)肝脏TG和F FA水平明显升高( P<0.01); 脂肪肝病变明显. (3)肝脏GRP78、XBP1、CHOP、EDEM1、GSK3β、apoB100、SREBP1c、ACCα及FAS的mRNA水平均显著上调( P<0.05). (4)血清TG、TC、LDL-C、FFA、ALT及AST显著升高( P<0.01).血清apoB100水平先升高, 后下降( P<0.05).结论:ERS参与调节肝脏脂质及apoB100的合成与代谢过程, 在T2DM小鼠脂肪肝发生过程中起着重要作用.