Adrenal chromaffin cells of the sympathetic nervous system have been used for over 40 years as the model neuronal and neuroendocrine cell. Chromaffin cells secrete small molecule neurotransmitters (catecholamines and dopamine) and neuropeptides (enkephalins and endorphins) that regulate critical biological processes including energy homeostasis, blood pressure, pain, and stress response. Secretion from neuroendocrine cells occurs primarily through dense-core secretory vesicles (DCSVs), which package neurotransmitters and neuropeptides and secrete upon stimulation. Despite the critical importance of this secretory system, almost all previous studies have used DCSVs isolated from bovine or rodent species. Our knowledge of the human secretory organelle is limited.

In this study, we have combined biochemical isolation and mass spectrometry to define the protein machinery used by the human adrenal DCSV in unprecedented detail. We were exceptionally fortunate to obtain a human tissue sample (clinical diagnosis: benign pheochromocytoma) shortly after resection. The peptide and protein components comprising the human DSCV organelle are more complex than we anticipated and include proteins regulating neurotransmitter and neuropeptide processing, internal environment, secretion, and a plethora of signaling proteins. These data suggest multiple different proteolytic processes contribute to neuropeptide production, a direct role for diverse signaling proteins in vesicle function, and differential effects from stimulation through different kinases. In light of this research, we will also elaborate on the capabilities of mass spectrometry to provide a unique perspective on systems of proteins comprising biological organelles.