Date of Award:

5-2009

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

Timothy A Gilbertson

Committee

Timothy A Gilbertson

Committee

David A. York

Committee

Kytai T. Nguyen

Committee

Marie K. Walsh

Committee

Jon Y. Takemoto

Abstract

The current epidemic of obesity has been linked to an increase in fat intake associated with the Western diet. Nutrient-induced stimulation of enteroendocrine cells in the small intestine leads to the release of hormones that contribute to satiety and the control of food intake. In particular, ingested fat, specifically in the form of free fatty acids, is potent activator of enteroendocrine cells in the proximal small intestine. However, the underlying signaling cascade that free fatty acids initiate in these enteroendocrine cells, which leads to secretion of satiety hormones, is not known. In general, my research is focused on identifying nutrient-responsive pathways in enteroendocrine cells involved with the release of satiety signals and using this information to begin to develop novel drug delivery strategies to reduce food intake. In general, my results revealed that activation of the fatty acid receptor GPR120 was ecessary for the linoleic acid-induced intracellular calcium rise, a necessary precursor for hormone release. Using patch clamp recording, I discovered that linoleic acid activated enteroendocrine cells by inducing membrane depolarization, a process requiring the calcium-activated, monovalent cation permeable channel TRPM5, which is activated downstream of GPR120. To validate the unexpected finding that TRPM5 was involved in fattyacid signaling, I performed experiments using bitter compounds, whose transduction pathway is known to involve TRPM5. Enteroendocrine cells express the bitter taste receptors and release cholecystokinin in response to bitter stimuli, suggesting the probable role of gut in initiation of protective behavior against ingestion of potentially harmful substances. Armed with the data on the specifics of the fatty acid transduction, I performed experiments using nanoparticles to determine their utility for delivering pharmaceuticals specifically to the enteroendocrine cells. I fabricated and characterized PLGA nanoparticles and performed intracellular uptake studies in order to optimally delivery payloads inside cells. Finally, I validated their use by using cell-based assays to determine the effects of internalized PLGA nanoparticles on ion channels and signaling pathways involved in CCK release. Taken together, this dissertation research has identified the signaling pathways (pharmacological targets) involved in fatty acid-mediated satiety hormone release and validated the potential therapeutic use of nanoparticle-mediated drug delivery for the eventual control of food intake.

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