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Advisory Committee Chair

Maria De Luca

Advisory Committee Members

Doulgas Moellering

Barbara Gower

Document Type

Thesis

Date of Award

2014

Degree Name by School

Master of Science (MS) School of Health Professions

Abstract

Drosophila melanogaster is a powerful model organism for studying human metabolic disease due to the conservation of various signaling processes and pathways. The insulin producing cells (IPCs) in the brain of adult flies sense circulating nutrients and respond by producing three insulin-like peptides (dILP2, dILP3, and dILP5). Several studies have shown that dILPs play a major role in Drosophila reproduction, metabolism, growth, and longevity. Previous data showed that flies homozygous for a hypomorphic mutation in the Drosophila syndecan (dSdc) gene had defects in energy metabolism and lower expression of brain dilp2-3 and dilp5 genes. Syndecan is a transmembrane proteoglycan that serves as a co-receptor in the binding of a variety of ligands, such as growth factors and cytokines. The objective of this study was to investigate the role of dSdc in the IPCs and dILP regulation. An experimental fly model with reduced expression of dSdc specifically in the IPCs was generated. IPCs-specific dilp2-GAL4 driver flies were crossed over UAS-dSdc RNAi flies or w1118 control flies. Gene expression was measured by quantitative PCR and protein quantity by Western blot in the offspring of each cross. Total glycogen and triacylglycerol storage were measured using standard assay kits. Total protein content was assessed by Lowry assay. Food intake was tested by capillary feeding method and metabolic rate by flow-through respirometry. An oral glucose tolerance test was performed by subjecting flies to an overnight fast, re- feeding in a glucose medium, and measuring whole-body glucose over the subsequent four hours. Adult lifespan and starvation resistance were also assessed. Flies with reduced dSdc in the IPCs showed increased dilp2 and dilp3 expression, but decreased circulating dILP2 peptide compared with controls. They had lower glucose tolerance, higher glycogen and triacylglycerol storage, and lower protein levels. Furthermore, the IPC- specific dSdc knockdown flies displayed increased life span and starvation resistance. Taken together, these findings suggest that dSdc plays a cell autonomous role in mediating the proper functioning of the IPCs and the release of dILP2 in D. melanogaster and provide a framework for approaching the study of the role of mammalian syndecan in the function of the pancreatic beta-cell.

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