N-Acylethanolamine Signaling in Neurons

Duncan, Raymond S., N-acylethanolamine signaling in neurons. Doctor of Philosophy (Biomedical Sciences), December 2008, 356 pp., 1 table, 70 illustrations, bibliography, 576 titles. Neurodegenerative diseases including Alzheimer’s disease are and will continue to be significant health problems as the aging population increases. The maintenance of neuronal calcium homeostasis has been a focus in degenerative disease research for many years. Within the last several years, lipids that activate cannabinoid receptors, and thus called cannabinoids, have gained recognition as neuroprotectants in models of neurodegenerative diseases. A subset of these cannabinoids, the N-acylethanolamines (NAEs), includes the well characterized neuroprotective lipid, arachidonylethanolamine. Other NAEs, such as palmitoylethanolamine (PEA), are more abundant in neurons and do not activate cannabinoid receptors, suggesting other targets for these lipids exist. Since non-cannabinoid NAEs rapidly accumulate after neuronal injury, it is likely they play a role in cellular responses to injury. Interestingly, some NAEs can alter intracellular Ca2+ signaling, but the underlying mechanism of action remains unclear. I hypothesized that the non-cannabinoid NAEs, such as PEA, protect the hippocampal cell line, HT22, from oxidative stress in part by reducing intracellular calcium release. I determined that HT22 cells and cultured mouse cortical neurons express proteins involved in NAE signaling, thus warranting the use of pharmacological inhibitors of these proteins in subsequent neuroprotection studies. Using HT22 cells, I determined that PEA exhibitis antiproliferative effects and neuroprotects against oxidative stress. In addition, I determined that PEA facilitates the nuclear translocation of putative protective proteins that can be regulated by Ca2+ through a mechanism not involving cannabinoid receptor activation. These findings led me to hypothesize that PEA alters release of Ca2+ from intracellular stores. To test this hypothesis, I determined that our cell models express inositol 1,4,5-trisphosphate receptors (IP3Rs) and ryanodine receptors (RyRs) both of which are intracellular Ca2+ channels elevated in response to oxidative stress. I determined that treatment of HT22 cells with PEA reduced intracellular Ca2+ release elicited by chemical depolarization with KCI. My results suggest that non-cannabinoid NAEs, such as PEA, protect the hippocampal cell line, HT22, from oxidative stress in part by activating putative neuroprotective signaling proteins and by reducing intracellular calcium release.