Sandhya N. Adiyodi Veetil

Doctoral Dissertation Announcement

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Candidate: Sandhya N. Adiyodi Veetil

Degree of: Doctor of Philosophy

Department: Chemistry

Title: Glucosamine Induced Insulin Resistance in Primary Rat Hepatocytes and Role of Selenium as Insulin Mimetic

Committee:
Dr. Susan R. Stapleton, Chair
Dr. David S. Reinhold
Dr. Pamela Hoppe
Dr. Michael J. Barcelona

Date: Tuesday, December 14, 2010 12:30 p.m. to 2:30 p.m.
1220 Chemistry Building

Abstract:
Type 2 diabetes is mediated by insulin resistance, the inability of insulin to elicit a normal biological response in insulin responsive tissues. Several cellular models have been utilized to determine the mechanism of induction of insulin resistance but questions remain unanswered. One model implicates the products of the Hexosamine Biosynthetic Pathway (HBP) in the induction of insulin resistance under hyperglycemia. The major end product of HBP, UDP-GlcNAc, is the substrate for O-GlcNAc transferase, an enzyme that catalyzes the O-GlcNAcylation of numerous proteins. This modification may play a role in induction of insulin resistance and thus needs to be evaluated in different cell types. Therefore, we set out to test whether or not insulin resistance could be established in primary rat hepatocytes. To accomplish this we used a HBP precursor, glucosamine, and first assessed whether or not insulin resistance was established by evaluating insulin’s effect on a key signaling protein, Akt.
Results indicate that the insulin induced phosphorylation of Akt was decreased in the presence of glucosamine when compared to the control, suggesting an insulin resistant state. Signal protein activation is very important for the insulin regulation of gene expression. If the activation of signal proteins is altered, then the effect on gene expression should also be altered. Results show that, under glucosamine treatment, insulin was no longer able to control the gene expression of a number of key enzymes in major metabolic pathways. Additionally, an increase in O-GlcNAc modified proteins under glucosamine compared to control was observed and a number of these proteins were identified through LC-MS.
Lastly, the effect of selenium, an insulin mimetic agent in this model system, was examined. The effects of selenium on the phosphorylation of the insulin signaling protein, Akt, and on the expression of the key enzymes of the major metabolic pathways both under normal and insulin resistant conditions were examined. Results show that selenium is a potent insulin mimetic not only under the normal/control condition but also under the insulin resistant condition as well.