Browsing by Subject "Insulinstoffwechsel"

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    Identification and functional studies of two novel serine phosphorylation sites of insulin receptor substrate (IRS)-2: Ser 675 and Ser 907
    (2010) Fritsche, Louise; Schleicher, Erwin D.
    Insulin receptor substrate (IRS) proteins are major transducers of the insulin and IGF-1 signal into the PI-3 kinase/PKB and the MAP kinase pathway. In addition to tyrosine phosphoryla-tion, a large number of serine/threonine phosphorylation sites enable the IRS proteins to inte-grate different extra- and intracellular stimuli resulting in positive and negative modulation of the insulin and IGF-1 signal. Chronic hyperphosphorylation of serine/threonine sites of IRS-1 is involved in the development of insulin resistance. IRS-2 is of great importance for β-cell survival and for the regulation of hepatic metabolism. The study of serine/threonine phos-phorylations is required to understand the physiological and pathophysiological regulation of this important mediator of insulin signaling. In this thesis two novel IRS-2 serine phosphoryla-tion sites have been identified and characterized (mouse amino acid numbering): Ser 675, which is located in the kinase regulatory loop binding (KRLB) domain unique to IRS-2 and Ser 907, which is adjacent to the Grb2 binding site Tyr 911. Using phospho-site specific antibod-ies both sites were demonstrated to be phosphorylated upon insulin, phorbol ester and ani-somycin treatment in Fao rat hepatoma cells. The phosphorylation was also detected in pri-mary human hepatocytes and in liver tissue of insulin treated or refed mice. The insulin-induced phosphorylation of Ser 907 was mediated by the MAP kinase ERK1/2. Simulation of a permanent phosphorylation of this site in BHK cells expressing IRS-2 Glu 907 led to a slight decrease of IRS-2 tyrosine phosphorylation with no apparent effect on insulin downstream signaling. The insulin-induced association of IRS-2 with Grb2 in HEK293 cells was abrogated by mutation of the adjacent Tyr 911 to Phe, but not influenced by mutation of Ser 907 to Ala. Of note, the activation of MAP kinase signaling was not impaired in HEK293 cells expressing IRS-2 Phe 911 and not regulated by the expression level of IRS-2 wildtype, but completely dependent on IR expression, indicating the importance of an alternative, IRS-2-Grb2-independent pathway for the activation of MAP kinase signaling in these cells. The insulin-induced phosphorylation of Ser 675 was dependent on mTOR, but not on the downstream kinase p70 S6K1. Prevention of this phosphorylation in BHK cells or HEK293 cells expressing IRS-2 Ala 675 had no effect on proximal or distal insulin signal transduction. But compared with IRS-2 wildtype, the mutated IRS-2 protein Ala 675 showed increased half life in cycloheximide-treated HEK293 cells. Thus, phosphorylation of Ser 675 could have a similar function as its homologous site Ser 632 in IRS-1 and could be involved in the regula-tion of mTOR-dependent IRS-2 proteasom-mediated protein degradation.
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    Unterstützung eines Gewichtsreduktionsprogramms durch Coenzym Q10 und Alpha-Liponsäure in micellierter wasserlöslicher Formulierung
    (2013) Franz, Karen; Biesalski, Hans-Konrad
    Overweight and obesity affects about half of the adult population in Germany and increase the risk for a series of subsequent diseases. A promising approach to treat obesity is to regulate the food intake ? and thus body weight ? in the hypothalamus. Adenosine monophosphate-activated protein kinase (AMPK) plays a central role in this mechanism. Consequently, suppression of the hypothalamic AMPK is an imaginable mechanism to improve repletion and limit the food intake. Alpha lipoic acid (ALA) inhibits the hypothalamic AMPK and therefore delays the onset of hunger. By increasing the muscular AMPK, ALA promotes the energy expenditure. In the respiratory chain Coenzyme Q10 is directly involved in the electron transport and the transformation of energy. Therefore, the combination of ALA and Coenzyme Q10 is an interesting approach. In the context of the randomized double blind intervention study the effect of daily intake of 90 mg of Coenzyme Q10 und 100 mg alpha lipoic acid in comparison to a placebo was investigated. In total 22 overweight adults per group (BMI 27 to 33 kg/m2) with no severe pre-existing diseases participated in the study. Over the course of 12 weeks the participants received regular nutritional counseling with the goal to reduce weight. Body weight, body composition using Bioelectric Impedance Analysis (BIA), and circumference of waist and hip were measured regularly. Prospective assessment of the food intake using 3-day protocols accompanied the measurements. Concurrently, the level of repletion was documented using a visual analog scale. Participants of both groups reduced their calorie intake during the time of the study. In the first part of the study this resulted an average weight reduction of 2.7±3.7 kg in the verum group and of 1.2±3.3 kg in the placebo group. The weight reduction in the verum group reached statistical significance compared to the placebo group (p<0.05). For the participants of verum group, the ratio of fasting insulin level and fasting blood glucose level (HOMA-index) improved as well. In the verum group, the HOMA-index in the first part improved from 2.4±1.2 (µU*dl)/(mg/ml) to 1.5±1.0 (µU*dl)/(mg/ml) with statistical significance (p=0,012). No significant improvement of the HOMA-index was found in the placebo group (from 3.0±1.3 (µU*dl)/(mg/ml) to 2.5±1.2 (µU*dl)/(mg/ml)). In the second part of the study the participants of the verum group reduced their body weight for 2.1±3.5 kg and for 3.9±3.2 kg in the placebo group. The difference between the two groups didn?t reach statistical significance. The HOMA-Index of the verum group was reduced from 3.0±1.6 (µU*dl)/(mg/ml) to 2.2±1.5 (µU*dl)/(mg/ml) without statistical significance. No changes were found in the placebo group (from 2.1±1.2 (µU*dl)/(mg/ml) to 2.3±1.0 (µU*dl)/(mg/ml). Further studies must deal with the improvement of the hepatic insulin resistance (HOMA Index) and the weight reduction (first part of this study) with the combination of Q10 and ALA.