Browsing by Subject "Insulin signaling"

Now showing 1 - 7 of 7
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    Activin signaling promotes the competence of the prothoracic gland during Drosophila metamorphosis
    (2010-08) Gibbens, Ying Ye
    In insects, the timing of metamorphosis is modulated by a large titer of the steroid hormone ecdysone produced by the prothoracic gland. However, the molecular mechanisms that control production of the ecdysone titer are not completely understood. Here we show that blocking Activin signaling in Drosophila prothoracic gland causes developmental arrest prior to metamorphosis. This defect is due to the absence of the ecdysone titer, a likely consequence of reduced expression of the ecdysone biosynthetic enzymes. We further demonstrate that Activin signaling may regulate the competence of the prothoracic gland to respond to prothoracicotropic hormone and insulin, two hormonal signals that have been shown to trigger ecdysone synthesis. These findings suggest that Activin signaling is required for insect metamorphosis by providing competence that allows tissue- and stage-specific response to metamorphic stimuli.
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    Beyond the allosteric role of Fructose-2,6-bisphosphate: exploring its effects on gene expression and signal transduction.
    (2009-09) Khan, Salmaan Ahmed
    In diabetes, insulin is either not available or not effective in suppressing glucose output by the liver. Enhancing hepatic glucose flux through glycolysis by raising fructose-2,6-bisphosphate (F26BP) levels ameliorates the diabetic phenotype in type 1 and type 2 diabetic mouse models (WU et al. 2001b; WU et al. 2002). This is attributed to the well characterized allosteric effects F26BP has on glucose metabolism enzymes. Recent studies have determined that raising F26BP levels has an additional role in regulating gene expression and signal transduction proteins (WU et al. 2005; WU et al. 2004). In terms of glucose metabolism, raising F26BP levels stimulates glucokinase gene expression and inhibits glucose-6-phosphatase gene expression, thus, also favoring enhanced glycolysis. These effects are not limited to glucose metabolism, as raising F26BP levels in type 2 diabetic mice leads to decreased weight gain and adiposity as well as a decrease in lipogenic enzyme gene expression. To fully characterize this new role of raising F26BP levels on gene expression, a microarray together with iTRAQ proteomic analysis was carried out. Through functional analysis of the microarray biological pathways were identified that changed when F26BP levels were raised in type 2 diabetic mice. In this way a wider array of lipid and cholesterol metabolism genes was shown to be down-regulated. Additionally, several other novel effects of F26BP on gene expression were elucidated. Comparison of the microarray and proteomic datasets elucidated that 87% of the protein expression changes were concomitant with gene expression changes. It is our hypothesis that some of these gene and protein expression changes are mediated through F26BP effect on the insulin signaling pathway component, Akt. Raising F26BP levels in a streptozotocin-treated mouse model (type 1 diabetic) leads to increased Akt levels and phosphorylation at serine-473 (WU et al. 2004). Based on this, experiments were carried out to determine the mechanism by which F26BP activates Akt and interacts with the insulin signaling pathway. Raising F26BP in cultured cells enhances insulin's effect on Akt and this effect requires phosphatidylinositol-3 kinase to be active. However, different from what is observed in vivo, in cell culture F26BP alone is not able to affect Akt phosphorylation.
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    Determining the effect of lipid nanoemulsions on insulin signaling and the inflammatory pathways at the Blood-Brain Barrier
    (2022-01) Nair, Sanjana
    Several studies have shown that metabolic disorders such as type-2 diabetes (T2DM) play a role in propagating neurodegenerative disorders like Alzheimer’s Disease (AD)(1). As the brain is an insulin-sensitive organ and requires insulin for promoting neuronal integrity and function, impairment of insulin signaling in the CNS has huge implications for memory and cognition(2). Hyperinsulinemia observed in AD and T2DM contributes to vascular inflammation, which in turn, leads to endothelial insulin resistance by impairing insulin receptor (IR) and insulin resistance substrate (IRS)-1(1). The insulin resistance leads to a compensatory increase in circulating insulin leading to hyperinsulinemia. In addition to the impairment of insulin signaling, another hallmark of AD is lipid dysfunction(3). The lipid bilayer of the Blood-Brain Barrier (BBB) endothelial cells harbors lipid rafts that play a vital role in transcytosis and maintaining various signaling functions(3). Lipid metabolism at the BBB changes with age and diet and results in a decrease of unsaturated fatty acid content and an increase in lipid peroxidation. In this study, we hypothesize that the delivery of lipid nanoemulsion, which is rich in unsaturated fatty acids, will improve insulin signaling at the BBB, and ameliorate insulin resistance caused by cytokines like TNF-α. This, in turn, is expected to decrease VCAM-1 expression and mitigate BBB dysfunction. This hypothesis has been verified by treating BBB endothelial cells with inflammatory cytokines like TNF-α, which inhibited insulin signaling and increase the expression of vascular cell adhesion molecule-1 (VCAM-1), a marker for endothelial inflammation. Alternatively, exposure to soybean oil nanoemulsion (SNEs) like that of Humulin® triggered insulin signaling and reduced VCAM-1 expression. The results showed that the SNEs have the ability to overcome the resistance induced by TNF-α, and increased the insulin signaling to the level comparable to Humulin® control and the opposite effect was seen when the cells were treated with nanoemulsion rich in saturated fatty acids. Lipid-based nanoemulsion could be used as a strategy to mitigate insulin resistance and the consequent inflammation commonly seen in neurodegenerative disorders like AD.
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    Gut Microbial Metabolite, Sodium Butyrate Regulates The Blood-Brain Barrier Transport And Intra-Endothelial Accumulation Of Alzheimer’S Disease Amyloid-Beta Peptides
    (2024-01) Veerareddy, Vaishnavi
    Alzheimer's disease (AD) is a common type of dementia observed in the elderly with brain amyloid beta (Aꞵ) deposits as one of its pathological hallmarks. Risk factors contributing to AD include age, genetics, inflammation, gut dysbiosis, and co-morbidities like diabetes, hypertension, and insulin resistance1. Recent studies have highlighted the necessity of investigating the combined effect of risk factors on AD onset and progression2. In addition, a majority of AD patients are diagnosed with cerebrovascular dysfunction, which is considered to be a significant contributor to the disease progression3. Moreover, the gut microbiome diversity was shown to be diminished in AD patients4. One of the interactions between the gut and the brain is mediated by gut microbial metabolites through the gut-brain axis5. Gut microbial metabolites include mainly short-chain fatty acids (acetate, propionate, butyrate) and trimethylamine N-oxide (TMAO)6. Particularly, butyrate treatment was shown to improve impaired cognition and reduce Aꞵ deposition in the AD brain, although the underlying mechanisms are yet to be characterized7. Previously, we reported the impact of insulin signaling on Aꞵ trafficking between the brain and the blood via the blood-brain barrier (BBB), which lines the cerebrovascular lumen and regulates Aꞵ levels in the brain8. However, the effect of gut microbiome metabolites on Aꞵ trafficking/accumulation at the BBB and endothelial insulin signaling remains unknown. In this study, we investigated the effect of one of the bacterial metabolites, sodium butyrate (NaBu), on Aꞵ accumulation at the BBB endothelium and the role of endothelial insulin signaling. The NaBu decreased Aꞵ40 with 6 h treatment and Aꞵ42 accumulation upon 2 h and 6 h treatments in BBB cell (hCMEC/D3) monolayers in vitro. Moreover, NaBu increased the phosphorylation of protein kinase B (PKB/AKT) and extracellular signal-regulated kinase (ERK) upon 6 h treatment. Inhibitor studies were conducted to evaluate if NaBu effect on Aꞵ accumulation at the BBB is regulated by insulin signaling. Treatment with AKT inhibitor (MK2206) and NaBu increased Aꞵ42 accumulation compared to the NaBu alone treated group. Similarly, treatment with MEK inhibitor (trametinib) and NaBu increased Aꞵ42 accumulation compared to the NaBu-treated group. These findings suggest the involvement of AKT and ERK pathways in NaBu-mediated changes in Aꞵ42 accumulation at the BBB. Also, NaBu affects the expression of transporters and receptors at the BBB. The NaBu treatment increased permeability glycoprotein (P-gp) and decreased receptors for advanced glycated end products (RAGE) compared to the Aꞵ treated group. Further, studies need to be conducted to elucidate mechanisms underlying NaBu effect on the BBB endothelium in AD. Keywords: Alzheimer’s, Aβ, Blood-brain barrier, dysbiosis, sodium butyrate, Insulin signaling, P-gp, RAGE.
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    Insulin signals through IGF-IR in insulin receptor knockout breast cancer cell line
    (2020-07) Monteiro, Marvis
    Breast cancer is a common malignancy observed more in females than in males. In breast cancer there is an upregulation of the IGF system. Upregulation of insulin and InsR are associated with poor patient prognosis. In order to understand the role of InsR in breast cancer biology, an InsR knockout cell line was created from MCF-7L breast cancer cells. Clone 35 showed loss of InsR expression, despite this loss, clone 35 showed activation of p-Akt and p-MAPK on stimulation with insulin. The hypothesis was developed that in the InsR knockout cell line insulin bound to IGF-IR and activated signaling. This hypothesis was proven by developing a knockout model, then using InsR and IGF-IR specific inhibitors on clone 35 to suggest the involvement of IGF-IR in activation through insulin. The following research substantiate the claims and provide a new understanding in the role of InsR and IGF-IR in breast cancer biology.
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    Rab GTPase mediated regulation of the autophagic pathway and mTOR signaling in the larval fat body of Drosophila melanogaster
    (2016-07) Ayala-Navarro, Carlos I
    Autophagy is a conserved lysosomal dependent pathway employed by cells during stress conditions as an alternative source of nutrients to maintain cellular homeostasis and promote survival. The pathway is negatively regulated by the mechanistic target of rapamycin (mTOR) and induced by depletion of nutrients. Over the last decade input in the form of vesicular traffic from an array of cellular organelles (e.g. Golgi, ER, endocytic pathway and mitochondria) has been shown to be required for the delivery of proteins, enzymes and lipids during progression of the autophagic pathway. However, how these organelles switch from their constitutive roles to supply the autophagic pathway with proteins and lipids upon induction is not fully understood. In addition the extent to which these cellular organelles modulate autophagosomal growth and mTOR-Insulin signaling remains incompletely understood. The main goal of this thesis was to uncover novel traffic regulators of the Rab GTPase family required for starvation-induced autophagy in Drosophila fat body cells and evaluate their role in mTOR signaling regulation. To this end we carried a reverse screen using RNAi to knockdown 30 of the 33 Drosophila Rab GTPases. We show Rab 2, 7 and 14 GTPases are required for the induction and growth of autophagosomes and autolysosomal function. Rab5 is required for autophagic vesicle induction and growth, endocytosis and lysosomal maturation. Lastly, that Rab6 is required for the sorting of lysosomal hydrolases, autolysosome turnover and the regulation of mTOR signaling via regulation of the insulin receptor localization in fat body cells. Altogether we uncovered novel regulators in the vesicular traffic regulator Rab GTPase family required for autophagy and mTOR-Insulin signaling regulation in Drosophila.
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    Regulation of insulin signaling in Drosophila melanogaster
    (2015-08) Kim, Jung
    Secreted ligands of the insulin family promote cell growth and maintain sugar homeostasis. Insulin release is tightly regulated in response to dietary conditions, but how insulin producing cells (IPCs) coordinate their responses to distinct nutrient signals is unclear. Here I show that regulation of insulin secretion in Drosophila larvae has been segregated into distinct branches: circulating sugars selectively promote the release of Drosophila insulin-like peptide 3 (Dilp3), whereas amino acids selectively promote secretion of Dilp2. Dilp3 is uniquely required for sugar-mediated activation of TOR signaling and suppression of autophagy in the larval fat body. Sugar levels are not sensed directly by the IPCs, but rather by the adipokinetic hormone (AKH)-producing cells of the corpora cardiaca, and I demonstrate that AKH signaling is required in the IPCs for sugar-dependent Dilp3 release. Thus, IPCs integrate multiple cues to regulate secretion of distinct insulin subtypes under varying nutrient conditions. The sensitivity of insulin signaling determines the activity of insulin in the presence of insulin, and misregulation of insulin sensitivity leads to metabolic diseases such as type-2 diabetes. Mechanical stress is a known regulator of insulin sensitivity, but the mechanisms by which mechanical stress regulates insulin sensitivity are unclear. Here, I showed that mechanical stress is required for activation of insulin signaling in the Drosophila larval fat body both ex vivo and in vivo. Interestingly, mechanical stress affects most of components in the insulin pathway: localization of insulin receptor (InR), chico, and lnk, and the activities of PI3K, AKT, and TOR. I demonstrated that integrin signaling, previously shown to sense mechanical stress, is necessary for the insulin- and mechanical stress-dependent activation of TOR. Together, my data suggest that mechanical stress sensed by integrin signaling regulates insulin sensitivity by altering upstream components of insulin signaling, such as InR, chico and lnk.