Yutaka Uehara

Akt2 phosphorylates Synip to regulate docking and fusion of GLUT4-containing vesicles

We have identified an unusual potential dual Akt/protein kinase B consensus phosphorylation motif in the protein Synip (RxKxRS97xS99). Surprisingly, serine 97 is not appreciably phosphorylated, whereas serine 99 is only a specific substrate for Akt2 but not Akt1 or Akt3. Although wild-type Synip (WT-Synip) undergoes an insulin-stimulated dissociation from Syntaxin4, the Synip serine 99 to phenylalanine mutant (S99F-Synip) is resistant to Akt2 phosphorylation and fails to display insulin-stimulated Syntaxin4 dissociation. Furthermore, overexpression of WT-Synip in 3T3L1 adipocytes had no effect on insulin-stimulated recruitment of glucose transporter 4 (GLUT4) to the plasma membrane, whereas overexpression of S99F-Synip functioned in a dominant-interfering manner by preventing insulin-stimulated GLUT4 recruitment and plasma membrane fusion. These data demonstrate that insulin activation of Akt2 specifically regulates the docking/fusion step of GLUT4-containing vesicles at the plasma membrane through the regulation of Synip phosphorylation and Synip–Syntaxin4 interaction.

The significance of decreased ambulatory activity during the generation by long-term observation of obesity in ovariectomized rats.

We attempted to determine the significance of ambulatory activity as a cause of overweight in ovariectomized rats. Drinking and ambulation were measured continuously and directly for periods up to 12 months in special apparatus developed at Gunma University. In older rats, ambulatory activity decreased much more in the ovariectomy group than in the control group. There was no difference in food intake between the ovariectomized and the control group. After 2 months, the ovariectomy group increased body weight more than the control group despite no difference in food intake. The decrease in ambulatory activity was consistent in the ovariectomy group, regardless of any differences in age and body weight. These results indicate that decrease of energy expenditure by gradual decrease in ambulatory activity may be an important factor as a cause of overweight in ovariectomized, obese rats.

CDK5-dependent Phosphorylation of the Rho Family GTPase TC10α Regulates Insulin-stimulated GLUT4 Translocation

Insulin stimulation results in the activation of cyclin-dependent kinase-5 (CDK5) in lipid raft domains via a Fyn-dependent phosphorylation on tyrosine residue 15. In turn, activated CDK5 phosphorylates the Rho family GTP-binding protein TC10α on threonine 197 that is sensitive to the CDK5 inhibitor olomoucine and blocked by small interfering RNA-mediated knockdown of CDK5. The phosphorylation deficient mutant T197A-TC10α was not phosphorylated and excluded from the lipid raft domain, whereas the phosphorylation mimetic mutant (T197D-TC10α) was lipid raft localized. Insulin resulted in the GTP loading of T197D-TC10α but not T197A-TC10α and in parallel, T197D-TC10α but not T197A-TC10α depolymerized cortical actin and inhibited insulin-stimulated GLUT4 translocation. These data demonstrate that CDK5-dependent phosphorylation maintains TC10α in lipid raft compartments thereby disrupting cortical actin, whereas subsequent dephosphorylation of TC10α through inactivation of CDK5 allows for the re-assembly of F-actin. Because cortical actin reorganization is required for insulin-stimulated GLUT4 translocation, these data are consistent with a CDK5-dependent TC10α cycling between lipid raft and non-lipid raft compartments.

LEPTIN STIMULATES INSULIN SECRETION AND SYNTHESIS IN HIT-T 15 CELLS

Leptin, an ob gene product, corrects hyperinsulinemia in ob/ob mice. The leptin receptor may exist in pancreatic islets. The present studies were undertaken to determine the direct effect of 1-100 ng/ml recombinant leptin on insulin secretion and synthesis in HIT-T 15 cells by using static culture system. The addition of recombinant leptin significantly increased insulin secretion for 20 min at the highest concentration (100 ng/ml). The addition of recombinant leptin dose-dependently increased insulin secretion for 24 h in the 7 mM glucose-containing F-12 K medium. The incubation with recombinant leptin for 24 h increased preproinsulin mRNA expression, assessed with reverse transcription-polymerase chain reaction (RT-PCR) method. It was furthermore demonstrated that HIT-T 15 cells possessed the specific binding site for [125I]-labeled leptin. The present study demonstrated the existence of the leptin-specific binding sites that mediate its stimulatory effect on insulin secretion and synthesis in HIT-T 15 cells.

Both cyclooxygenase and lipoxygenase inhibitor partially restore the anorexia by interleukin-1β

Since the peripheral prostaglandin synthetizing system may at least partly involved in the anorexia that follows central interleukin-1 beta (IL-1) administration, this study was undertaken to investigate the effect of ibuprofen (ip), selective cyclooxygenase blocker and AA 861, selective lipoxygenase inhibitor, on changes of food and water intake by a single injection of IL-1 (2 micrograms/rat, ip). We demonstrated that food and water intake were suppressed by peripheral administration of IL-1. Throughout the entire observation periods, suppressed food intake was partially restored to control levels by ibuprofen, while water intake completely restored. In addition, no significant differences about water/food intake were observed in the IL-1 + ibuprofen-treated groups, respectively. In the next experiment, IL-1 induced anorexia was also partially restored to the control level following pretreatment with AA 861. These results may suggest that other mechanism including lipoxygenase blocker besides prostaglandin production may be involved in IL-1 induced anorexia.

Circulating concentrations of soluble leptin receptor: influence of menstrual cycle and diet therapy.

Concentrations of the soluble leptin receptor (sOB-R) may be related to leptin resistance in obesity. We measured sOB-R concentrations in serum in 103 non-diabetic Japanese men and women. All subjects were grouped according to body mass index (BMI; in kg/m(2)). Serum sOB-R concentrations did not differ significantly between normal-weight (18.5 < or = BMI < 25.0) men and women, but were significantly higher in underweight subjects (BMI < 18.5) than in normal-weight subjects. In contrast, overweight (25 < or = BMI < 30) and obese (30 < or = BMI < 35.0, 35.0 < or = BMI < 40, and BMI > or = 40) subjects had significantly lower sOB-R concentrations than did normal-weight subjects. Serum sOB-R concentrations were inversely correlated with BMI and serum immunoreactive leptin concentrations. Very low-energy diet therapy for 4 wk significantly lowered serum immunoreactive leptin concentrations but did not significantly affect serum sOB-R concentrations. Serum sOB-R concentrations did not change significantly during the menstrual cycle. Our results showed that serum sOB-R concentrations decrease with increasing BMI and that sex hormones likely do not affect serum sOB-R concentrations in non-pregnant women. The reduction in serum sOB-R concentrations in overweight and obese persons may reflect downregulation of hypothalamic leptin receptor production as a result of an increase in circulating leptin and might be an important factor in leptin resistance.

Hypertonic glucose inhibits the production of oxygen-derived free radicals by rat neutrophils

We studied the influence of graded degrees of hypertonic glucose or sucrose on the generation of oxygen-derived free radicals by rat neutrophils. Hypertonic glucose and sucrose exerted dose- and time-dependent inhibition of chemiluminescence amplified by luciferin analog (CLA-DCL) and luminol (L-DCL) in response to fMLP. Hypertonic glucose was more effective to this chemiluminescence inhibition than hypertonic sucrose was. This inhibition of hypertonicity was more effective in CLA-DCL than in L-DCL. Although the production of superoxide anion measured by the reduction of ferricytochrome c was more inhibited by hypertonic glucose than by hypertonic sucrose, the myeloperoxidase activity was not affected by either glucose or sucrose hyperosmolarity. These data suggest that hyperosmotic state by itself and an additional direct glucose-toxicity may contribute to the impaired neutrophil function in the diabetic state.

Effects of peripheral administration of recombinant human Interleukin-1 beta on feeding behavior of the rat

This study was undertaken to investigate the changes in feeding behavior, including ambulatory activity, induced by a single injection of Interleukin-1 beta (IL-1) (2 micrograms/rat) at 18:00, just before the dark phase. For this purpose, we used the Gunma University-type automatic apparatus for continuous and direct measurement of ambulation and drinking. A significant decrease in food intake was observed for 12 hours after treatment with IL-1. Peripheral administration of IL-1 also produced a marked decrease in ambulatory activity within 3 hours which continued for 6 hours. In addition, IL-1 produced a marked decrease in drinking behavior during the first 6 hours. We reported here the changes in consummatory and ambulatory behavior of rats after acute administration of IL-1. The sickness which IL-1 produced may, at least in part, contribute to these phenomena, although precise mechanisms are still unknown.

Orchiectomy and response to testosterone in the development of obesity in young Otsuka-Long-Evans-Tokushima Fatty (OLETF) rats.

OBJECTIVE: Withdrawal of testosterone prevents the development of hyperglycaemia in male Otsuka-Long-Evans-Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus (NIDDM), but the exact mechanism has not been established. The present studies were undertaken to examine a possible role of testosterone in the development of obesity in young OLETF rats who have not shown marked hyperphagia.METHODS: Body weight, food intake and circulating concentrations of metabolic factors including immunoreactive leptin (IRL) were measured at five weeks of age in young male OLETF rats and their lean controls, Long-Evans-Tokushima-Otsuka (LETO) rats. At six weeks of age, both LETO and OLETF rats were bilaterally orchiectomized (Orchx) and half of each group implanted with a silastic tube containing testosterone. After a three week observation period, all animals were killed and circulating concentrations of metabolic factors and the ob gene expression in retroperitoneal white adipose tissues were measured.RESULTS: Body weight and 24 h food intake were already increased in OLETF rats at five weeks of age. Serum testosterone concentrations were significantly lower in OLETF rats than in LETO rats. Expression of the ob gene was significantly decreased in the retroperitoneal white adipose tissue of OLETF rats, and their serum IRL concentrations were lower. Food intake and body weight gain for three weeks after the operation were significantly lower in the Orchx group of OLETF rats than in the sham-operated group. Hyperglycaemia, accompanied by hyperinsulinaemia, was attenuated by orchiectomy in OLETF rats. Circulating IRL concentrations were significantly higher in OLETF rats than in LETO rats and decreased by orchiectomy. Testosterone supplement reversed all of the changes caused by orchiectomy in OLETF rats. In contrast, the changes, which were observed after orchiectomy in OLETF rats, were not obvious in LETO rats.CONCLUSION: The present data indicate that testosterone plays a role in the development of obesity and NIDDM in young OLETF rats, but that changes of leptin production in white adipose tissue may not be important in the development of obesity in young OLETF rats.

Epalrestat, an Aldose Reductase Inhibitor, Improves an Impaired Generation of Oxygen-Derived Free Radicals by Neutrophils From Poorly Controlled NIDDM Patients

OBJECTIVE To study the in vivo effect of epalrestat (Epa), an aldose reductase inhibitor, on the generation of oxygen-derived free radicals by neutrophils from poorly controlled NIDDM patients (HbA1c > 10%). RESEARCH DESIGN AND METHODS A total of 31 diabetic patients were randomly divided into two groups: an Epa(+) group of 16 patients treated with 150 mg/day epalrestat and an Epa(−) group of 15 patients treated without epalrestat. A control group of 20 age- and sex-matched normal healthy subjects also participated. HbA1c, postprandial plasma glucose (PPG), and neutrophil bactericidal function were measured before and at the end of the drug treatment period (4 weeks). Neutrophil bactericidal function was measured as chemilu-minescence amplified by a Cypridina luciferin analog (CLA), which is dependent on O2− generation, and by luminol (L), which is highly dependent on OCl− generation, in response to formyl-methonyl-leucyl-phenylalanine (fMLP). RESULTS At the start of the experiment, both CLA-dependent chemiluminescence (CLA-DCL) and L-dependent chemiluminescence (L-DCL) were clearly decreased in diabetic subjects (64 and 54%, respectively; P < 0.05) compared with control subjects (2,182 ± 144 and 3,221 ± 173 kc · min−1 · 10−6 cells, respectively). At the end of the experiment, CLA-DCL and L-DCL in the Epa(+) group were significantly improved by 44 and 46%, respectively; however, these values were still lower than the corresponding results in the control group. HbA1c and PPG in both the Epa(+) and Epa (−) groups were significantly higher than in the control group, and treatment had no effect on either HbA1c or PPG. CONCLUSIONS These data suggest that epalrestat may be a useful drug to prevent infection by improving the impaired O2− and OCl− generation by neutrophils from poorly controlled NIDDM patients.