Mechanism of activation of guanine nucleotide exchange factor by insulin

Insulin increases activity of the guanine nucleotide exchange factor (GEF) in Rat-1 fibroblasts transfected with human insulin receptors (HIRc cells), thereby promoting formation of the active form of p21Ras (p21Ras•GTP). In order to identify the upstream molecules mediating this aspect of insulin action, we selectively removed some of these molecules by immunoprecipitation and examined GEF activity in the post-immunoprecipitation lysated of the insulin-treated HIRc cells. The removal of Shc or Grb-2 depleted GEF activity from the cell lysates, whereas immuno-precipitation of the insulin receptors, IRS-1, PLCγ and GAP, were without effect. In summary, the current data demonstrate that a majority of cellular Ras GEF activity after insulin stimulation is associated with Shc and involves interactions among Shc, Grb-2 and Sos.     

Synergistic role of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase cascade in the regulation of insulin receptor trafficking.

To examine the molecular mechanism of insulin receptor trafficking, we investigated the intracellular signaling molecules that regulate this process in Rat1 fibroblasts overexpressing insulin receptors. Cellular localization of insulin receptors was assessed by confocal laser microscopy with indirect immunofluorescence staining. Insulin receptors were visualized diffusely in the basal state. Insulin treatment induced the change of insulin receptor localization to perinuclear compartment. This insulin-induced insulin receptor trafficking was not affected by treatment of the cells with PI3-kinase inhibitor (wortmannin), whereas treatment with MEK [mitogen-activated protein (MAP) kinase-Erk kinase] inhibitor (PD98059) partly inhibited the process in a dose-dependent manner. Interestingly, treatment with both wortmannin and PD98059 almost completely inhibited insulin receptor trafficking. The functional importance of PI3-kinase and MAP kinase in the trafficking process was directly assessed by using single cell microinjection analysis. Microinjection of p85-SH2 and/or catalytically inactive MAP kinase ([K71A]Erk1) GST fusion protein gave the same results as treatment with wortmannin and PD98059. Furthermore, to determine the crucial step for the requirement of PI3-kinase and MAP kinase pathways, the effect of wortmannin and PD98059 on insulin receptor endocytosis was studied. Insulin internalization from the plasma membrane and subsequent insulin degradation were not affected by treatment with wortmannin and PD98059. In contrast, insulin receptor down-regulation from the cell surface and insulin receptor degradation, after prolonged incubation with insulin, were markedly impaired by the treatment. These results suggest that PI3-kinase and MAP kinase pathways synergistically regulate insulin receptor trafficking at a step subsequent to the receptor internalization.     

Sib-size, birth order and risk of overweight in junior high school students in Japan: results of the Toyama Birth Cohort Study

OBJECTIVE: To investigate whether there is a relationship between sib-size, birth order and the risk of overweight in junior high school students. METHOD: Sib-size, birth order, height and weight of subjects and their parents, and other lifestyle factors were obtained through a questionnaire survey conducted between June and July 2002 from 7,959 junior high students in Toyama prefecture, Japan. Logistic regression analysis was performed to examine the associations. Boys and girls were analyzed separately. RESULTS: Boys from three-child families showed a significantly lower risk of overweight than only boys (odds ratio (OR)=0.66, p=0.010), and girls from larger families have a significantly lower risk than only girls (p for trend=0.001). Compared to middle-born girls, only girls have a significantly higher risk of overweight (OR=2.22, p<0.001). The risk of overweight in boys was significantly lower with increasing number of elder sibling or sister. However, increasing of any one sibling almost had the same risk reduction effect on the risk of overweight in girls (OR ranged from 0.74 to 0.76, p<=0.001). CONCLUSION: Children without siblings are the ones most at risk for overweight, especially in girls. Birth order and sib-size are possible risk factors for the development of overweight and obesity.     

Comparison of four blood pressure indexes for the prediction of 10-year stroke risk in middle-aged and older Asians

Information has been sparse on the comparison of 4 blood pressure (BP) indexes (systolic BP [SBP], diastolic BP [DBP], pulse pressure [PP], and mean BP [MBP]) in relation to long-term stroke incidence, especially in middle-aged and older Asian people. A prospective cohort study was performed in 4989 Japanese (1523 men and 3466 women) aged 35 to 79 at baseline with 10 years of follow-up. End points included stroke incidence (total, ischemic, and hemorrhagic). Multivariate-adjusted hazard ratios with a 1-SD higher value for each BP index were determined by Cox proportional hazard analyses; Wald chi2 tests were used to compare the strength of relationships. Analyses were also done for each of 4 age-gender groups consisting of men and women aged 35 to 64 and 65 to 79 years. During follow-up, 132 participants developed stroke. Adjusted hazard ratios for all strokes were 1.68 for SBP, 1.72 for DBP, and 1.80 for MBP, which were higher than that for PP (1.34). SBP and DBP were related positively to stroke risk after adjustment of each other. PP was not the strongest predictor in any age-gender groups among 4 BP indexes. In men aged 65 to 79 years, SBP showed the strongest relationship to all stoke risk (hazard ratio 1.62) among 4 BP indexes. In women aged 65 to 79 years, hazard ratios for all strokes were 2.48 for MBP, 2.46 for DBP, 2.25 for SBP, and 1.57 for PP. The long-term incident stroke risk of high BP in Asians should be assessed by SBP and DBP together, or by MBP, not by PP.     

Smoking among premenopausal women is associated with increased risk of low bone status: the JPOS Study

The impact of smoking on peak bone density has not been conclusively established. We examined how smoking exposure influences bone mineral density (BMD) or the risk of low bone status in premenopausal women. We conducted a baseline survey with a representative sample of Japanese women in 1996. The effect of current and former smokers (ever-smoker) was investigated with 789 premenopausal women aged 20–40 years. The multiple regression with stepwise method was used to identify significant determinants for BMD or the risk of low bone status (T-score < −1) with age, height, weight, calcium intake, coffee consumption, exercise habits, level of daily activity, parity ≥ 1, and smoking as explanatory variables. The smoking effect was determined after adjusting for age, height, weight, and significant variables in the multiple regression with stepwise method. Ever-smoker was significantly associated with decreased lumbar BMD adjusted for age, height, and weight. The odds ratio of an ever-smoker for low bone status at the lumbar spine was 2.03 (95% CI 1.12, 5.82) adjusted for age, height, weight, and parity. The odds ratio for low bone status at the lumbar spine was 1.59 (95% CI 0.65, 3.91) and 2.55 (95% CI 1.12, 5.82) in those with less than 3 pack-years of tobacco use and in those with 3 or more pack-years of tobacco use, respectively. These values were adjusted for age, height, weight, and parity using a never-smoker as a reference. Cumulative smoking exposure may be associated with increased risk of low bone status among premenopausal women.     

Work and family characteristics as determinants of socioeconomic and sex inequalities in sleep: The Japanese Civil Servants Study

STUDY OBJECTIVE: To clarify whether socioeconomic and sex inequalities in poor sleep quality are explained by socioeconomic and sex differences in work and family characteristics. DESIGN: A cross-sectional study. PARTICIPANTS: Three thousand five hundred fifty-six employees (2397 men and 1159 women) aged 20 to 65 years in local government in Japan. MEASUREMENTS: Respondents completed a self-administered questionnaire that asked about sleep quality, as measured by the Pittsburgh Sleep Quality Index; work characteristics, as measured by the job-demand-control-support model, work hours, and shift work; and family characteristics, such as family structure and family-work conflicts. RESULTS: Lower control at work, higher work demands, lower social support, shorter and longer working hours, shift work, being single, higher family-to-work conflict, and higher work-to-family conflict were independently associated with poorer sleep quality in both men and women. In men, the age-adjusted odds ratio (OR) of low-grade employees for poor sleep quality was 1.64 (95% confidence interval: 1.14-2.36) in comparison with high-grade employees. The difference in sleep was attenuated when work and family characteristics were adjusted for (OR=1.25 [0.84-1.86]). Among women, there was no significant grade difference in sleep. Women tended to have poorer sleep quality than men (the age-adjusted OR=1.75 [1.49-2.06]). The sex difference was attenuated and no longer significant when adjustments were made for work and family characteristics (OR=1.04 [0.85-1.27]). CONCLUSIONS: The results of this study suggest that work and family characteristics may be important for reducing socioeconomic and sex inequalities in sleep. Sex differences in the pattern of socioeconomic inequalities in sleep deserve further research.     

Reinfusion of unwashed salvaged blood after total knee arthroplasty in patients with rheumatoid arthritis

Autotransfusion with unwashed salvaged blood (USB) is effective for avoiding allogeneic blood transfusion (ABT) in patients undergoing total knee arthroplasty (TKA). We performed a retrospective study to determine the percentage of patients receiving ABT and the volume of postoperative blood drainage after introduction of autotransfusion with USB for patients with rheumatoid arthritis (RA) undergoing TKA. In 100 patients without autotransfusion (group 1) and 100 patients receiving autotransfusion of USB (group 2), we compared the number of patients who required ABT, as well as the postoperative drainage volume, ABT volume, and autotransfusion volume. In group 1, 83% of the patients received ABT, while only 47% received ABT in group 2, and there was a significant decrease (p < 0.001). However, the postoperative drainage volume was significantly increased in group 2 (p < 0.001).