Chromogranin A mediates glucocorticoid-induced enhancement of vesicular dopamine storage and secretion in PC12 cells

Biogenic amines, including catecholamines, are concentrated within large dense-core vesicles through interactions with intravesicular matrix proteins and ATP. Efficient accumulation also depends on additional accessory components that regulate vesicular storage and release. Glucocorticoids are known to enhance catecholamine secretion and quantal size in PC12 cells, although the molecular mechanisms linking these effects to vesicular dopamine storage remain incompletely understood. Glucocorticoid treatment upregulated key enzymes involved in catecholamine biosynthesis, most notably tyrosine hydroxylase, while also enhancing the expression of chromogranin A. These molecular adaptations were postulated to increase vesicular dopamine content and improve secretion efficiency. To determine how the observed molecular alterations translated into functional changes, we quantified transcriptional and protein level regulation of key targets using qRT-PCR and western blotting. We then linked these molecular effects to cellular function by measuring intracellular dopamine content via high-performance liquid chromatography, monitoring stimulus-evoked secretion with online secretion assays and characterizing quantal exocytosis at single-cell resolution using carbon-fiber amperometry. Corticosteroids enhance dopamine storage within secretory vesicles in a time dependent manner, likely by promoting matrix formation. Our results indicate that dopamine accumulation is limited by vesicular storage capacity rather than synthesis alone in PC12 cells. Furthermore, combining glucocorticoid treatment with L-DOPA to increase amine availability produces a marked increase in vesicular dopamine content and a robust augmentation of stimulus-evoked secretion. Collectively, these findings identify chromogranin A-dependent secretory vesicle matrix formation, temporally coupled to dopamine loading, as a previously underappreciated mechanism by which glucocorticoids regulate vesicular dopamine storage and secretory efficiency.