O2‐04‐01: Beta‐amyloid peptides undergo activity‐dependent secretion with neurotransmitters

Abstract

Secretion and extracellular accumulation of neurotoxic beta-amyloid peptides (Abeta) represent a major factor in the development of Alzheimer's disease that results in memory deficit. Knowledge of the secretory pathway(s) utilized by Abeta peptides can enhance understanding of the neurobiology of Abeta. Because neurons undergo activity-dependent secretion of Abeta and neurotransmitters, this study sought to investigate the hypothesis of that Abeta undergoes co-secretion with neurotransmitters via the regulated secretory pathway that provides activity-dependent secretion of neurotansmitters. Neuronal-like chromaffin cells in primary culture were subjected to activity-dependent secretion, induced by KCl depolarization (50 mM, 30 min), and stimulated secretion of Abeta was measured by ELISA. Selected neuropeptides and catecholamines (dopamine, norepinephrie, and epinephrine) were measured in the secretion media. In addition, dense core secretory vesicles were purified from chromaffin cells and their content of Abeta peptides with neurotransmitters was measured. APP processing components (beta- and gamma-secretases) were assessed by western blots. Neuronal immunofluorescence confocal microscopy assessed localization of Abeta peptides with neurotransmitters. The data show that Abeta peptides undergo activity-dependent secretion from neuronal chromaffin cells (induced by KCl depolarization). Furthermore, Abeta undergos cosecretion with the peptide neurotransmitters (neuropeptides) and catecholamines. Investigation of the secretory vesicles that provide regulated secretion of signaling molecules from these cells showed that isolated dense core secretory vesicles (DCSV) of neuronal-like chromaffin cells contain Abeta peptides with multiple peptide neurotransmitters of enkephalin, NPY, galanin, VIP, and somatostatin. Furthermore, these secretory vesicles contain the catecholamine neurotransmitters dopamine, norepipnephrine, and epinephrine that are co-secreted with Abeta and neuropeptides. This organelle contains full-length APP, Abeta peptides, and components for beta- and gamma-secretases that produce Abeta. These APP processing components co-reside with processing proteases for neuropeptide biosynthesis, as well as with catecholamine biosynthetic enzymes. The colocalization of Abeta with neuropeptides in secretory vesicles was further illustrated by cellular immunofluorescence confocal microscopy. These findings indicate the biosynthesis and secretion of Abeta peptides in dense core secretory vesicles with neuropeptide and catecholamine neurotransmitters, suggesting that Abeta peptide forms function with multiple neurotransmitter systems.