ROLE OF GLUCOCORTICOIDS IN VNUT REGULATION AND ITS IMPACT ON ATP AND CATECHOLAMINE STORAGE AND SECRETION

Glucocorticoids modulate several cellular mechanisms including neurotransmitter synthesis, release and vesicular transport. The vesicular nucleotide transporter (VNUT), responsible for ATP uptake into secretory vesicles, is expressed in PC12 cells, a model of neuroendocrine catecholaminergic secretion. This study aimed to investigate how glucocorticoids influence VNUT expression and function, and consequently, vesicular ATP storage and release in PC12 cells.
PC12 cells were treated with dexamethasone, a synthetic glucocorticoid, at different concentrations and times. VNUT mRNA and protein levels were analysed by qPCR and Western blot, respectively. Functional assays involved measuring ATP release using luciferase-based luminescence and vesicle exocytosis monitored by HPLC. Pharmacological inhibitors of glucocorticoid receptors were used to confirm specificity.
The VNUT promoter was sequenced to confirm the presence of glucocorticoid responsive elements, supporting the possibility of glucocorticoid-mediated regulation. Consistent with this, dexamethasone treatment significantly upregulated VNUT expression in PC12 cells at both mRNA and protein levels in a time-dependent manner. Enhanced VNUT expression correlated with increased vesicular ATP uptake and elevated ATP release upon stimulation.
In conclusion, glucocorticoids modulate vesicular catecholamine storage in PC12 cells by upregulating proteins involved in its synthesis and storage, leading to an increase in vesicular content. In parallel, VNUT overexpression elevates intravesicular ATP levels, which may further enhance catecholamine retention within secretory vesicles.