Abstract
Substantial evidence suggests that the ability to sense and respond to nutrients in the intestinal lumen can
determine predisposition to metabolic disorders such as obesity and diabetes. The enteroendocrine cell (EEC)
is responsible for this function despite being the least abundant cell type in the intestine. In response to
intestinal stimulants, EECs synthesize and secrete enteroendocrine peptides (EEPs) that control important
physiological processes including satiety, intestinal contractions, and systemic metabolism. Although EEP
function has been extensively studied, the connection between EEP synthesis and secretion pathways is
poorly understood. Our lab uses Drosophila melanogaster, a genetically tractable model organism, to study
conserved intestinal processes. Preliminary studies in Drosophila established a link between the previously
uncharacterized, EEC-specific G protein-coupled receptor GPRx and lipid homeostasis in the intestine.
Specifically, GPRx mutant flies exhibit lipid droplet accumulation in their intestines despite no changes in the
number of EECs expressing tachykinin (Tk), an EEP that represses lipid synthesis in Drosophila. Published
studies suggest a possible connection between GPRx and calcium (Ca2+)-mediated exocytosis and further
unpublished work in our lab pointed to a downstream role of the calcium response factor CaMKII. CaMKII is
known to promote production and release of neurotransmitters and in related insect species, it was shown to
act in response to the Drosophila steroid hormone 20-hydroxyecdysone (20E). The aim of this work is to
elucidate the function of GPRx in the maintenance intestinal lipid homeostasis and assess co-regulation of Tk
transcription and release. First I will test the hypothesis that GPRx modulates Tk release from EECs via Ca2+-
mediated exocytosis. To do this, I will employ live imaging techniques to determine whether GPRx has an
impact on calcium transients in EECs. I will also assess the ability of an exocytosis inducer to bypass GPRx
and rescue the lipid accumulation phenotype observed in GPRx mutant and knockdown flies using
fluorescence microscopy. Additionally, I plan to identify the factor(s) that triggers GPRx stimulation. Of
particular interest are acetate and 20E because in addition to regulating Tk transcription and activation of
CaMKII, respectively, both can rescue the lipid accumulation phenotype observed in antibiotic-treated flies
when added to the fly diet. Thus, I will first determine whether acetate and 20E regulate GPRx expression and
then, through genetic manipulation, assess the impact of acetate availability on the ability of GPRx to maintain
intestinal lipid homeostasis. Lastly, I will test the role of GPRx in acetate- and 20E-mediated rescue of
intestinal lipid homeostasis in antibiotic-treated flies. Collectively, experimental outcomes will 1) elucidate the
role of GPRx in the maintenance of intestinal lipid homeostasis and 2) provide new insights into the regulatory
connection between EEP expression and secretion. Therefore, findings could potentially inform innovative
therapeutic strategies for the treatment of metabolic disease.
