Vesicle Shrinking and Enlargement Play Opposing Roles in the Release of Exocytotic Contents

For decades, two fusion modes were thought to control hormone and transmitter release essential to life; one facilitates release via fusion pore dilation and flattening (full collapse), and the other limits release by closing a narrow fusion pore (kiss-and-run). Using super-resolution stimulated emission depletion (STED) microscopy to visualize fusion modes of dense-core vesicles in neuroendocrine cells, we find that facilitation of release is mediated not by full collapse but by shrink fusion, in which the Ω-profile generated by vesicle fusion shrinks but maintains a large non-dilating pore. We discover that the physiological osmotic pressure of a cell squeezes, but does not dilate, the Ω-profile, which explains why shrink fusion prevails over full collapse. Instead of kiss-and-run, enlarge fusion, in which Ω-profiles grow while maintaining a narrow pore, slows down release. Shrink and enlarge fusion may thus account for diverse hormone and transmitter release kinetics observed in secretory cells, previously interpreted within the full-collapse/kiss-and-run framework.

Simultaneous monitoring of monoamines, amino acids, nucleotides and neuropeptides by liquid chromatography-tandem mass spectrometry and its application to neurosecretion in bovine chromaffin cells

The primary functions of adrenal medullary chromaffin cells are the synthesis and storage in their chromaffin vesicles of the catecholamines noradrenaline (NA) and adrenaline (AD), and their subsequent release into the bloodstream by Ca²⁺ -dependent exocytosis under conditions of fear or stress (fight or flight response). Several monoamines, nucleotides and opiates, such as leucine-enkephalin (LENK) and methionine-enkephalin (MENK), are also co-stored and co-released with the catecholamines. However, other neurotransmitters have not been studied in depth. Here, we present a novel high-resolution liquid chromatography-tandem mass spectrometry approach for the simultaneous monitoring of 14 compounds stored and released in bovine chromaffin cells (BCCs). We validated the analytical method according to the recommendations of the EMA and FDA by testing matrix effect, selectivity, sensitivity, precision, accuracy, stability and carry-over. After testing on six batches of BCCs from different cultures, the method enabled simultaneous quantitative determination of monoamines (AD, NA, dopamine, serotonin, 5-hydroxyindoleacetic acid, histamine and metanephrine), amino acids (L-glutamic acid, γ-aminobutyric acid), nucleotides (adenosine 5'-diphosphate, adenosine 5'-monophosphate, cyclic adenosine 5'-monophosphate) and neuropeptides (LENK and MENK) in the intracellular content, basal secretion and acetylcholine induced secretion of BBCs. The high-resolution approach used here enabled us to determine the levels of 14 compounds in the same BCC batch in only 16 min. This novel approach will make it possible to study the regulatory mechanisms of Ca²⁺ signaling, exocytosis and endocytosis using different neurotrophic factors and/or secretagogues as stimuli in primary BCC cultures. Our method is actually being applied to human plasma samples of different therapeutic areas where sympathoadrenal axis is involved in stress situations such as Alzheimer's disease, migraine or cirrhosis, to improve diagnosis and clinical practice. Copyright © 2016 John Wiley & Sons, Ltd.

Meta-analysis of microarray-derived data from PACAP-deficient adrenal gland in vivo and PACAP-treated chromaffin cells identifies distinct classes of PACAP-regulated genes

Initial PACAP-regulated transcriptomes of PACAP-treated cultured chromaffin cells, and the adrenal gland of wild-type versus PACAP-deficient mice, have been assembled using microarray analysis. These were compared to previously acquired PACAP-regulated transcriptome sets from PC12 cells and mouse central nervous system, using the same microarray platform. The Ingenuity Pathways Knowledge Base was then employed to group regulated transcripts into common first and second messenger regulatory clusters. The purpose of our meta-analysis was to identify sets of genes regulated distinctly or in common by the neurotransmitter/neurotrophin PACAP in specific physiological contexts. Results suggest that PACAP participates in both the basal differentiated expression, and the induction upon physiological stimulation, of distinct sets of transcripts in neuronal and endocrine cells. PACAP in both developmental and acute regulatory paradigms acts on target genes also regulated by either TNFalpha or TGFbeta, two first messengers acting on transcription mainly through NFkappaB and Smads, respectively.