Early responses of insulin signaling to high-carbohydrate and high-fat overfeeding

<p>Abstract</p> <p>Background</p> <p>Early molecular changes of nutritionally-induced insulin resistance are still enigmatic. It is also unclear if acute overnutrition alone can alter insulin signaling in humans or if the macronutrient composition of the diet can modulate such effects.</p> <p>Methods</p> <p>To investigate the molecular correlates of metabolic adaptation to either high-carbohydrate (HC) or high-fat (HF) overfeeding, we conducted overfeeding studies in 21 healthy lean (BMI < 25) individuals (10 women, 11 men), age 20-45, with normal glucose metabolism and no family history of diabetes. Subjects were studied first following a 5-day eucaloric (EC) diet (30% fat, 50% CHO, 20% protein) and then in a counter balanced manner after 5 days of 40% overfeeding of both a HC (20% fat, 60% CHO) diet and a HF (50% fat, 30% CHO) diet. At the end of each diet phase, <it>in vivo </it>insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp technique. <it>Ex vivo </it>insulin action was measured from skeletal muscle tissue samples obtained 15 minutes after insulin infusion was initiated.</p> <p>Results</p> <p>Overall there was no change in whole-body insulin sensitivity as measured by glucose disposal rate (GDR, EC: 12.1 ± 4.7; HC: 10.9 ± 2.7; HF: 10.8 ± 3.4). Assessment of skeletal muscle insulin signaling demonstrated increased tyrosine phosphorylation of IRS-1 (p < 0.001) and increased IRS-1-associated phosphatidylinositol 3 (PI 3)-kinase activity (p < 0.001) following HC overfeeding. In contrast, HF overfeeding increased skeletal muscle serine phosophorylation of IRS-1 (p < 0.001) and increased total expression of p85α (P < 0.001).</p> <p>Conclusion</p> <p>We conclude that acute bouts of overnutrition lead to changes at the cellular level before whole-body insulin sensitivity is altered. On a signaling level, HC overfeeding resulted in changes compatible with increased insulin sensitivity. In contrast, molecular changes in HF overfeeding were compatible with a reduced insulin sensitivity.</p

Disruption of Growth Hormone Receptor Prevents Calorie Restriction from Improving Insulin Action and Longevity

Most mutations that delay aging and prolong lifespan in the mouse are related to somatotropic and/or insulin signaling. Calorie restriction (CR) is the only intervention that reliably increases mouse longevity. There is considerable phenotypic overlap between long-lived mutant mice and normal mice on chronic CR. Therefore, we investigated the interactive effects of CR and targeted disruption or knock out of the growth hormone receptor (GHRKO) in mice on longevity and the insulin signaling cascade. Every other day feeding corresponds to a mild (i.e. 15%) CR which increased median lifespan in normal mice but not in GHRKO mice corroborating our previous findings on the effects of moderate (30%) CR on the longevity of these animals. To determine why insulin sensitivity improves in normal but not GHRKO mice in response to 30% CR, we conducted insulin stimulation experiments after one year of CR. In normal mice, CR increased the insulin stimulated activation of the insulin signaling cascade (IR/IRS/PI3K/AKT) in liver and muscle. Livers of GHRKO mice responded to insulin by increased activation of the early steps of insulin signaling, which was dissipated by altered PI3K subunit abundance which putatively inhibited AKT activation. In the muscle of GHRKO mice, there was elevated downstream activation of the insulin signaling cascade (IRS/PI3K/AKT) in the absence of elevated IR activation. Further, we found a major reduction of inhibitory Ser phosphorylation of IRS-1 seen exclusively in GHRKO muscle which may underpin their elevated insulin sensitivity. Chronic CR failed to further modify the alterations in insulin signaling in GHRKO mice as compared to normal mice, likely explaining or contributing to the absence of CR effects on insulin sensitivity and longevity in these long-lived mice

Abstract 3129: miR-340 is a modulator of oncogenic signaling in melanoma

Abstract Melanoma is responsible for only 4% of skin cancer diagnoses; nonetheless 80% of skin cancer deaths are attributed to this aggressive skin cancer each year. Growing evidence points to an important role miRNAs may play in the aberrant cellular signaling of cancers, including melanoma. microRNAs (miRNAs) are highly conserved 22-25nt non-coding RNAs involved in regulating RNA stability and translation and are predicted to regulate ∼60% of the human transcriptome. We are investigating the tumor suppressor role miR-340 plays in the development and progression of melanoma. A limited number of miR-340 targets were previously characterized, however, it is unlikely the effects of miR-340 on the melanoma phenotype are the result of directly targeting a few mRNAs, as miRNAs are likely to target upwards of 100 mRNAs each. Using an in silico target identification and pathway mapping system, we identified a multitude of potential miR-340 mRNA targets that encode proteins distributed amongst a variety of cellular signaling pathways. In silico analysis revealed a high proportion of miR-340 predicted mRNA targets that encode for members of the MAPK signaling pathway. Our results show that miR-340 modulated most of the assayed mRNAs that encode MAPK components. We also demonstrate that miR-340 inhibits the tumorigenic phenotype of melanoma cells. We recently developed a novel method to identify direct targets of miRNAs. Using this method, we demonstrate miR-340 directly targets mRNAs that encode protein kinases of the MAPK pathway. Further direct target identification is crucial toward understanding the role miR-340-directed regulation plays in triggering pleiotropic effects during melanoma development and progression. Elucidating the roles aberrant gene regulatory networks play in melanoma is critical for understanding the disease and developing treatment options to improve the melanoma prognosis. Supported by NIH grants ES007015 (to A.M.P.S.), AR063361 (to V.S.S.) and CA191550 (to V.S.S.). Citation Format: Ashley M. Poenitzsch Strong, Emily G. Adochio, Vijayasaradhi Setaluri, Vladimir S. Spiegelman. miR-340 is a modulator of oncogenic signaling in melanoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3129. doi:10.1158/1538-7445.AM2015-3129</jats:p

Effects of a hypercaloric diet on beta-cell responsivity in lean healthy men

Insulin resistance and hyperinsulinaemia precede the onset of obesity-induced DM2. The early adaptation of the β-cell during the initial phase of overfeeding and weight gain has only been partly elucidated. We studied the early changes in insulin clearance and β-cell responsivity during a positive and negative energy balance in lean healthy men. We studied in nine healthy lean men [age, 37 (27-43) years; BMI, 23·6 (20·6-25·6) kg/m(2) ] insulin sensitivity, insulin clearance, insulin secretion and static and dynamic β-cell responsivity at baseline and after the hypercaloric and subsequent hypocaloric diet. Participants gained 7 [5·1-7·6]% of their initial body weight on the hypercaloric diet. Compared to baseline, insulin sensitivity and insulin clearance decreased, while glucose-stimulated insulin secretion was higher. The GLP-1 response to oral glucose did not change. The dynamic β-cell responsivity index increased but the basal and static responsivity indexes did not change. Total and static disposition indexes (DIs) in the hypercaloric state showed a trend towards a decrease. During the hypocaloric diet, insulin sensitivity, glucose-stimulated insulin secretion and insulin clearance returned to baseline. The responsivity and the DIs were not different in the hypocaloric phase compared to baseline. A positive energy balance resulting in weight gain in lean men induces hyperinsulinaemia, which is explained by a combined effect on insulin clearance and insulin secretion. Increased insulin secretion was related to insulin resistance-induced higher glucose concentrations but also to increased dynamic β-cell responsivity. Glucose sensitivity of the β-cell did not change. These early adaptations are completely reversible during a negative energy balance after loss of the gained weigh