Endoplasmic reticulum stress mediates the neurotoxic effect of misfolded proteins in neurodegenerative diseases

Endoplasmic reticulum (ER) stress can be caused by disturbances in the function of the ER with the accumulation of misfolded proteins. The ER response is characterized by unfolded protein response (UPR) causing translational attenuation, induction of ER chaperones and degradation of misfolded proteins. In case of prolonged or aggravated ER stress, cellular signals leading to apoptosis are activated. ER stress has been suggested to be involved in human neurodegenerative diseases, such as Alzheimers disease, Parkinsons disease, and amyotrophic lateral sclerosis, as well as other disorders. Here we will discuss the neurotoxic effect of ER stress in these three major neurodegenerative diseases, and highlight current knowledge in this field that may reveal novel insight into disease mechanisms and help to design better therapies for these disorders.     

Impaired function of pancreatic β cells in the R6/2 transgenic mouse model of Huntington's disease

AIM: To study the function of pancreatic β cells in the R6/2 transgenic mouse of Huntingtons disease(HD), and to elucidate the pathogenetic mechanisms underlying diabetes mellitus in transgenic mice of HD. METHODS: By using the R6/2 transgenic mouse model of HD, fasting blood glucose and fasting insulin concentration in plasma of normal and HD mice were detected. Further, HE staining and immunofluorescence technique were used for morphometric analysis of islets in normal and HD mice. RESULTS: In contrast to normal mouse, R6/2 HD mouse showed hyperglycemia and hypoinsulinemia in fasting state. Pancreatic islets morphology showed that islets atrophied and cell number decreased in HD mouse. Poor functional index was observed in these mice, but insulin resistance index was normal. CONCLUSION: Impaired function of pancreatic cells may be the key factor contributing to the pathogenesis of diabetes in the R6/2 transgenic mouse model of HD.     

Correlation of serum omentin-1 level and insulin resistance in rats

AIM：To establish the insulin resistance rat model for evaluating the correlation of omentin-1 level and insulin resistance. METHODS：SPF male Wistar rats (n=30) were randomly divided into normal control group (NC, n=15) and high-fat diet group (HF, n=15). The rats in NC group were fed with basic diet. The insulin resistant model was established by feeding the rats with high-fat diet in HF group. After 10 weeks, 5 rats in each group were assessed by the technique of hyperinsulinaemic-euglycaemic clamp. After the insulin resistant model was successfully established, the body weight and fasting blood glucose were detected. The concentration of fasting serum omentin-1 was analyzed by ELISA. Fasting serum insulin was measured by radioimmunoassay. RESULTS：No difference of fasting blood glucose between the 2 groups was observed. The level of fasting serum insulin in HF group was significantly higher than that in NC group (P<0.05). The level of serum omentin-1 in HF group were significantly decreased compared with NC group (P<0.01). Pearson’s correlation analysis showed that negative correlations between serum omentin-1 and fasting serum insulin (r=-0.654,P<0.01), serum omentin-1 and free fatty acid (r=-0.446, P<0.05) was found. CONCLUSION：In rats, serum omentin-1 level began to decrease at insulin resistance stage. As serum omentin-1 level decreased, the basal insulin level increased, indicating that decreased serum omentin-1 level may be an early factor of IR, diabetes and cardiovascular diseases.     

A pilot study on mechanisms of hyperadiponectinemia in two rat models with different in vivo insulin sensitivity

AIM:To explore the possible mechanisms of hyperadiponectinemia in the insulin-resistant Zucker fatty rats (ZF) and insulin-sensitive nephrotic syndrome rats induced by puromycin aminonucleoside (PA).METHODS:8-week old Zucker rats were fed with standard rat chow for 4 weeks and Wistar rats were intraperitoneally injected single dose of PA 10 d before experiments.Blood samples and 24 h urines were collected for detecting the lipid profiles, adiponectin (ADPN), albumin and urine albumin excretion rate (UAER).A frequently sample intravenous glucose tolerance test (FSIVGTT) was conducted.The insulin sensitivity index (SI) and glucose effectiveness index (SG) were calculated according to Bergmans minimal model.Epididymal white adipose tissues were then extracted for weighting.Correlations between ADPN and other parameters were analyzed by Pearsons correlation.RESULTS:Both ZF rats and PA-injected rats showed significantly higher plasma ADPN levels compared with their own controls ［(7.44±1.23)mg/L vs (2.44±0.33)mg/L and (8.64±0.88)mg/L vs (2.95±0.46)mg/L, respectively, P<0.01］.SI and SG were markedly decreased and negatively correlated to ADPN in Zucker rats, but not changed and correlated to ADPN in Wistar rats.Hyperlipidemia was observed in either ZF rats or PA-injected rats and was positively correlated to ADPN levels.Two hyperadiponectinemic rats showed markedly higher UAER ［(64.8±14.2)mg/24 h vs (14.9±14.6)mg/24 h and (275.1±64.5)mg/24 h vs (15.4± 4.5)mg/24 h, respectively, P<0.01］ and positively correlated with ADPN.The ratio of white adipose tissue to body weight was higher in ZF rats than that in their control rats despite its disproportion with ADPN, while it was comparable between PA-injected and normal rats.The renal creatinine clearance rate was not altered in both strains of rats.CONCLUSION:Hyperadiponectinemia is a common property in ZF rats and PA-induced nephrotic syndrome rats, and it cant be interpreted by changes of in vivo insulin sensitivity.Markedly increased UAER in both rats is the key mechanism of hyperadiponectinemia.     

Effect of insulin resistance on biological function of HepG2 cells and sensitivity to cisplatin

AIM: To investigate the effect of insulin resistance (IR) on the biological function of hepatocellular carcinoma (HCC) and sensitivity to cisplatin. METHODS: IR was induced in HepG2 cells via incubation with a high concentration of insulin. Afterwards, the effects of IR on adhesion, migration, invasion and sensitivity to cisplatin of the cells were detected.RESULTS: The results indicated that glucose consumption was reduced in the IR cells. The expression of the insulin receptor and glucose transporter 2 was down-regulated. Furthermore, HepG2/IR cells displayed markedly enhanced adhesion, migration, and invasion. These cells exhibited a lower sensitivity to cisplatin. On the contrary, HepG2/IR cells exhibited decreased adhesion and invasion after treatment with the insulin sensitizer pioglitazone hydrochloride.CONCLUSION: IR is closely related to drug resistance, adhesion, migration and invasion in HepG2 cells. These findings may help explain the clinical observation of the limited efficacy of chemotherapy on a background of IR.     

Effect of glucocorticoid on PI-3K and p38 MAPK signaling pathways in 3T3-L1 adipocytes

AIM: To study the effects of dexamethasone (DEX) on the glucose transport system and the PI-3K/Akt and p38 MAPK insulin signaling pathways in 3T3-L1 adipocytes,and to investigate the possible mechanism in glucocorticoid induced insulin resistance. METHODS: The 3T3-L1 adipocytes were exposed to DEX for 48 h and incubated with 100 nmol/L insulin for additional 30 min. The glucose uptake was measured by detecting the glucose content in cell culture supernatants. Then expression and distribution of Glut4 was measured. The insulin signaling proteins Akt,phospho-Akt,p38MAPK and phospho-p38MAPK were also measured with Western blotting. RESULTS: DEX inhibited insulin stimulated glucose transport capacity in 3T3-L1 adipocytes. DEX did not alter the amount of Glut4 protein in total cell lysates but attenuated the insulin-stimulated Glut4 translocation to the plasma membrane. DEX significantly inhibited insulin stimulated phosphorylation of Akt and p38 MAPK. CONCLUSION: These results suggest that DEX alters insulin stimulated glucose transport capacity in 3T3-L1 adipocytes,which is mediated by attenuating insulin stimulated activation of PI3K-Akt and p38 MAPK pathways,and reducing insulin stimulated Glut4 translocation and transport activity. These may lead to insulin resistance in 3T3-L1 adipocytes.     

Tetramethylpyrazine combined with aminoguanidine improves renal functions in n0-STZ Wistar rats

AIM: To investigate the effects of tetramethylpyrazine combined with aminoguanidine on the renal functions of neonatal-0 streptozotocin-induced (n0-STZ) rats. METHODS: Neonatal Wistar rats were intraperitoneally injected with a single dose of streptozotocin (STZ) to establish the n0-STZ rat model. The n0-STZ rats were divided into 4 groups: normal control group, insulin resistance group, metformin treatment group and tetramethylpyrazine+aminoguanidine treatment group. Fasting plasm glucose, fasting insulin, insulin resistance index, blood urea nitrogen, serum creatinine, urine albumin and glomerular filtration rate were measured at the 32nd week. The mRNA content of inducible nitric oxide synthase (iNOS) in peripheral blood leukocytes was detected by the technique of in situ hybridization. Nitric oxide (NO) concentration, iNOS activity, the protein expression of iNOS and 3-nitrotyrosine(3-NT) were also assessed in the renal tissues. RESULTS: At the 8th week after the administration of STZ, 82.5% of Wistar rats showed that the fasting plasm glucose level was ≥7.0 mmol/L and the renal functions were seriously damaged. Although both metformin and the combined treatment reduced fasting plasm glucose, fasting insulin and insulin resistance index, the combined treatment was superior in improving the insulin resistance. The damaged renal functions were improved by the combined treatment as reducing blood urea nitrogen and creatinine, increasing glomerular filtration rate were observed. Furthermore, the combined treatment reduced NO concentration, decreased iNOS activity and diminished mRNA content of iNOS, resulting in depressing the generation of 3-NT and iNOS, which surpassed the treatment of metformin. CONCLUSION: Tetramethylpyrazine combined with aminoguanidine improves the renal functions of n0-STZ rats by depressing nitrative stress and enhancing the effect of metformin.     

Mechanism of interleukin-6 induced insulin resistance in 3T3-L1 adipocytes

AIM: To investigate the molecular mechanism of interleukin-6 induced insulin resistance in 3T3-L1 adipocytes.METHODS: 3T3-L1 adipocytes were treated with IL-6 at concentration of 20 μg/L within 48 hours. Insulin stimulated glucose uptake was measured by 2-deoxy ［3H］ glucose. Western blotting was used to measure insulin receptor substrate-1(IRS-1), protein kinase B(PKB) expression, tyrosine phosphorylation on IRS-1, and PKB phosphorylation. RESULTS: On basal status, glucose uptake in 3T3-L1 cells, PKB phosphorylation and tyrosine phosphorylation of IRS-1 were all at low level. Insulin stimulation induced a rapid increase in glucose uptake, PKB phosphorylation and IRS-1 tyrosine phosphorylation. IL-6 inhibited insulin-induced glucose uptake and PKB phosphorylation level about 50%. After IL-6 treatment, IRS-1 protein expression and tyrosine phosphorylation of IRS-1 were decreased 35% and 40%, respectively. The inhibitor of mammalian target of rapamycin(mTOR), rapamycin, reversed above effects of IL-6. CONCLUSION: IL-6 induced insulin resistance in 3T3-L1 adipocytes is related to decrease IRS-1 expression and impairs IRS-1 tyrosine phosphorylation. IL-6 induced insulin resistance in adipocytes may be related to the activity of mTOR.     

Role of intestinal microbiota-farnesoid X receptor axis in metabolic diseases

Intestinal microbiota is associated with metabolic diseases such as obesity, nonalcoholic fatty liver disease and insulin resistance. Farnesoid X receptor (FXR), also known as bile acid receptor, is a typical nuclear receptor, which is involved in the regulation of bile acid and glycolipid metabolism. Intestinal microbiota regulates FXR activity by affecting bile acid composition, where bile acid hydrolase plays an important role. Recent studies have found that intestinal microbiota affects the development of metabolic diseases through regulating the FXR, and the intestinal microbiota-FXR axis may be an ideal drug target for metabolic diseases.     

Effects of recombinant adenovirus-mediated chronic hyperresistinemia on glucose metabolism in mice

AIM: To establish the animal model of hyperresistinemia and to observe the effects of resistin on glucose metabolism and insulin sensitivity in vivo. METHODS: We established a mouse model of hyperresistinemia in C57BL/6 mice by intravenous administration of the recombinant adenovirus encoding mouse resistin. Then we observed the fasting blood glucose and insulin levels. We also investigated glucose tolerance by IPGTT, and insulin sensitivity by IPITT. RESULTS: On 5 d after the injection, the concentration of plasma resistin was more than 15-fold higher in Adv-resistin-EGFP-treated mice than that in saline- or Adv-EGFP-treated mice. In the fasting state, no difference in glucose levels was observed among three groups. However, mice injected with Adv-resistin showed higher insulin levels, impaired glucose tolerance and insulin sensitivity. CONCLUSION: Hyperresistinemia affects glucose metabolism in mice and it may play an important role in the pathogenesis of insulin resistance and type 2 diabetes.     

“2006中国蔬菜产业可持续发展研讨会”在武汉召开

由中国园艺学会主办，湖北省园艺学会、国家蔬菜改良中心华中分中心、华中农业大学园艺林学学院共同承办的“2006中国蔬菜产业可持续发展研讨会”于2006年4月13-15日在湖北武汉华中农业大学举行，来自全国17个省（市）和自治区47个单位的近120名代表出席这次全国性会议。会议开幕式由中国园艺学会蔬菜专业委员会主任、中国农业科学院蔬菜花卉研究所副所长孙日飞研究员主持。华中农业大学副校长李名家教授、武汉市张学忙副市长、科技部农村司魏勤芳处长、农业部科技司刘艳处长、武汉市科协黄和平主席和中国园艺学会理事长方智远院士先后致辞。     

Osteopontin-induced ER stress results in insulin resistance in C2C12 myocytes

AIM: To investigate the potential role of osteopontin (OPN) in insulin resistance in C2C12 myocytes and its underlying mechanism. METHODS: C2C12 myoblasts were induced by low concentration of serum and insulin treatment to differentiate into myocytes. Western blot was performed to detect the protein abundance and phosphorylation using specific antibodies. Plasma membrane was isolated by centrifugation. Glucose uptake was measured by glucose uptake assay. RESULTS: OPN treatment suppressed insulin-stimulated protein kinase B (Akt) phosphorylation in a dose-and time-dependent manner, accompanied with decreased membrane translocation of glucose transporter type 4 (Glut4) and reduced glucose uptake. Neutralization of OPN specific receptor in skeletal muscle with CD44 antibody mitigated OPN-induced inhibitory impact on insulin action. Furthermore, OPN treatment resulted in endoplasmic reticulum (ER) stress and phosphorylation of c-Jun N-terminal kinase (JNK). Administration of ER stress inhibitor 4-phenylbutyrate (4-PBA) diminished the detrimental effects of OPN on JNK phosphorylation, Glut4 membrane translocation and glucose uptake. CONCLUSION: ER stress mediated OPN-induced insulin resistance in C2C12 myocytes.     

Correlation among plasma leptin,resistin an type 2 diabetes mellitus

AIM：To assess the association of resistin,obesity,serum lipid levels and insulin resistance with plasma leptin.METHODS：The concentrations of fasting serum glucose,insulin,lipid profiles,plasma resistin and leptin were assayed in 80 cases (including 37 controls with normal glucose tolerance and 43 patients with type 2 diabetes mellitus).RESULTS：Fasting plasma leptin level was positively correlated with sex,body mass index (BMI),waist circumference (WC),waist-hip ratio and fasting serum insulin (F Ins) （P<0.01）.Fasting plasma leptin level was negatively correlated with insulin sensitivity index (r=-0.373,P<0.01).There was no correlation between the concentrations of plasma leptin and FPG,TG,TC and resistin （P>0.05）.CONCLUSION：Fasting plasma leptin level is positively correlated with obesity and insulin resistance,not resistin.Leptin may play a role in the pathogenesis of type 2 diabetes mellitus.     

Establishment and verification of insulin resistance model in mouse skeletal muscle cells

AIM:To establish a stable and repeatable insulin resistance model of skeletal muscle cells in vitro, so as to promote the exploration of the pathological mechanism of insulin resistance and the development and screening of related drugs. METHODS:C2C12 mouse myoblasts were used to induce differentiation in normal differentiation medium and differentiation medium containing glucose at 40 and 60 mmol/L, respectively. The effects of glucose at different concentrations on cell convergence, fusion and formation of multinucleated myotubes were observed under phase contrast microscope every day. After 1, 3, 5 and 7 d of differentiation, 2-NBDG assay was used to detect the effects of different interventions on C2C12 basal glucose uptake and insulin-stimulated glucose uptake. The effects of different interventions on the protein expression of glucose transporter 4 (GLUT4) after 5 d and 7 d of differentiation were determined by Western blot. The effects of different interventions on the distribution of GLUT4 protein after 5 d of differentiation were detected by immunofluorescence staining. RESULTS:After treated with glucose at 60 mmol/L, the morphological observation showed that high glucose treatment significantly inhibited the growth and differentiation of C2C12 cells after 3 d. High glucose treatment significantly inhibited basal glucose uptake and insulin-stimulated glucose uptake of the C2C12 cells after 5 d and 7 d (P<0.01). No difference between insulin-stimulated GLUT4 expression and basal GLUT4 expression after 5 d and 7 d of high glucose treatment was observed (P>0.05), but there was significant difference between control group and 60 mmol/L group (P<0.05) determined by Western blot. Immunofluorescence staining observation showed that the distribution of GLUT4 protein in the C2C12 cell membrane was significantly decreased after 5 d of high glucose treatment (P<0.01). Glucose treatment (40 mmol/L) also played a role to some extent, but the effect was not as obvious and stable as 60 mmol/L glucose. CONCLUSION:A stable insulin resistance model of mouse skeletal muscle cells in vitro was successfully established by high glucose stimulation. The treatment of glucose at 60 mmol/L for 5 d was the best. Morphological observation and detection of basic and insulin-stimulated glucose uptake and GLUT4 protein expression and distribution evaluates the insulin resistance level of skeletal muscle cells in vitro.     

Functional change of globus pallidus and Parkinson's disease

As an important nucleus of basal ganglia, globus pallidus was concerned to involve in the neural mechanism of Parkinss disease (PD). Previous studies of PD patients and animal model indicate that neurotransmitters and receptors are changed in globus pallidus neurons, the balance between inhibition and excitation is broken in the output nuclei of basal ganglia, and globus pallidus neurons display bursting and oscillatory discharge, the synchronous tendency of neighboring neurons enhances. These neurophysiological changes are associated with PD symptoms, such as bradykinesia, rigidity and tremor, which reflects that globus pallidus plays an important role in the process of PD. In the present paper, the recent advances in pathophysiology in globus pallidus, its clinical application in treatment of Parkinsons disease, and the study direction in the future are reviewed.     

JNK mediates TNF-α or H2O2-induced insulin resistance in 3T3-L1 adipocytes

AIM: To study the role of c-Jun NH2-terminal kinase (JNK) in the development of insulin resistance induced by tumor necrosis factor-α (TNF-α) or H2O2 in 3T3-L1 adipocytes. METHODS: Differentiated 3T3-L1 adipocytes were pretreated with JNK1 small interfering RNA (siRNA) or JNK inhibitor SP600125, then exposed to 1 nmol/L of TNF-α or micromolar H2O2 generated by adding glucose oxidase (50 U/L) to the medium for 12 h. The cellular glucose uptake was determined by radioactive method. RESULTS: Compared to control adipocytes, 12 h incubation with TNF-α or H2O2 led to 50%-55% reduction (P<0.01) of the insulin-dependent glucose uptake. JNK1 siRNA transfection significantly inhibited JNK1 expression and blocked the TNF-α or H2O2-induced impairments of cellular glucose uptake. Pretreatment with SP600125 (20 μmol/L) resulted in significant increases in insulin-stimulated glucose uptakes in both TNF-α (66%) and H2O2 (62%) treated adipocytes (P<0.01). CONCLUSION: JNK plays a key role in TNF-α or H2O2 induced insulin resistance in 3T3-L1 adipocytes, and inhibition of JNK over-activation may be a new therapeutic target for insulin resistance.     

Oxymatrine ameliorates high fat-induced insulin resistance in ApoE-/- mice

ATM: To investigate the effect of oxymatrine (OXY) on high fat-induced insulin resistance in mice, and to investigate the mechanism. METHODS: ApoE^-/-mice with high-fat diet for 16 weeks were divided into insulin resistance group, and OXY groups at concentrations of 25, 50 and 100 mg/kg. C57BL/6J mice served as normal control group. The mice in OXY groups were gavaged with OXY for 8 weeks. Glucose tolerance test in the mice was performed. Fasting blood glucose (FBG), total cholesterol (TC), triglyceride (TG), fatty acid (FFA) and fasting insulin (FINS) in the plasma were measured. The mRNA expression of insulin receptor (INSR), insulin receptor substrate-2 (IRS-2), glucose transporter 2 (GLUT2) in the liver tissues was examined by RT-qPCR. The protein levels of GLUT2, INSR, IRS-2, p-INSR, p-IRS-2, PI3K, p-PI3K, serine/threonine protein kinase (AKT) and p-AKT were examined by Western blot.RESULTS: OXY reduced the levels of FBG, TC, TG, FFA and FINS, and attenuated insulin resistance. Compared with insulin resistance group, the mRNA expression of INSR, IRS-2 and GLUT2 significantly increased in OXY groups (P<0.05). The protein levels of p-INSR/INSR, p-IRS-2/IRS-2, p-PI3K/PI3K, p-AKT/AKT and GLUT2 also increased in OXY groups (P<0.05).CONCLUSION: OXY ameliorates high fat-induced insulin resistance in mice via PI3K/AKT pathway.     

The alteration of expression of iNOS mRNA and ecNOS mRNA in peripheral leukocytes from insulin resistance rats fed with fructose

AIM: To study the alteration of expression of iNOS mRNA and ecNOS mRNA in peripheral leukocytes of Wistar rats fed with fructose. METHODS: Wistar rats were randomly divided into the control group (n=10) and the fructose feeding group(n=10). The fructose feeding group drank12% fructose water for 6 months. The blood glucose, blood insulin, and the expression of iNOS mRNA and ecNOS mRNA in peripheral leukocytes of rats were determined. RESULTS: The levels of blood insulin (P<0.01) and the expression of ecNOS mRNA were higher in fructose feeding group than that in control group after1month. The level of blood insulin(P<0.01), the level of blood glucose (P<0.05), the expression of ecNOS mRNA and the iNOS mRNA were also higher in fructose feeding group than that in control group after 2 months. The levels of blood insulin and glucose, the expression of ecNOS mRNA and the iNOS mRNA were increased persistently during 3 to 6 months. CONCLUSIONS: These results indicate that fructose can increase the level, but reduce the sensitivity of insulin. It can also induce the expression of ecNOS mRNA firstly and the expression of iNOS mRNA secondly, the former can delay the formation of insulin resistance and the later can accelerate the formation of insulin resistance.