Date of Award:

5-1-2014

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Advisor/Chair:

Timothy A. Gilbertson

Abstract

The multifunctional fatty acid (FA) binding protein, Cluster of Differentiation 36 (CD36), has been found to be expressed in a variety of tissues where it is involved in multiple fat-related biological processes, such as lipid metabolism in mammals and the detection of lipid-like pheromones in insects. As identified in the apical membranes of taste cells, along with functional evidence in behavioral and cellular level, its involvement in the gustatory FAs detection is suggested. Nonetheless, whether CD36 acts as a direct lipid sensor or as a chaperone protein that facilitates the function of FA-activated G protein coupled receptors (GPCRs), such as taste cell expressing GPR120, remains to be determined. To characterize the role of CD36 in FA signaling, either as a primary receptor or in concert with GPCRs, I utilized human embryonic kidney 293 (HEK293) cell lines that express the different combination of the LCFA receptor GPR120 and CD36. By using intracellular calcium imaging, the presence of CD36

increased the cell sensitivity to LA slightly in GPR120+ cells. Treating the CD36+GPR120+ cells with CD36 inhibitor, sulfo-N-succinimidyl oleate (SSO), resulted in a large reduction, but not abolishment of the LA activated response, which was absent in CD36+GPR120- cells. To investigate the role of CD36 in FA transduction specifically in taste, a mouse taste bud-derived (TBD) cell line, TBD-a1, was used. Knockdown of CD36 by RNA interference in these cells reduced but did not eliminate their intracellular calcium responses to LA. In vivo, isolated taste cells from CD36-KO mice and WT mice were compared for their FA sensitivity. CD36-KO cells were capable of responding to LA with the concentration-response curve not shifted significantly compared to WT cells. However, SSO significantly reduced the LA response in WT mice. At the behavioral level, responsiveness to LA in CD36-KO mice was not eliminated comparing to WT mice after formation of a conditioned taste aversion to LA. These data suggest that CD36 is a protein that facilitates the activation of GPR120 by FAs instead of a primary receptor for FAs itself. In the taste system, CD36 is not required but may facilitate activity in FAs responsive pathways.

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