Investigations into the Signaling Pathways Involving Glucose-Stimulated Zinc Secretion (GSZS) from Prostate Epithelial Cells In Vitro and In Vivo

Purpose: Recently, we reported that exposure of prostate cells in vitro or the in vivo prostate to high glucose results in release of Zn2+ ions, a process now referred to as glucose-stimulated zinc secretion (GSZS). To our knowledge, the metabolic event(s) that trigger GSZS remain largely unknown. Here, we explore several signaling pathways both in vitro using a prostate epithelial cell line and in vivo from the rat prostate.

Methods: PNT1A cells grown to confluence were washed and tagged with ZIMIR to monitor zinc secretion by optical methods. The expression levels of GLUT1, GLUT4, and Akt in cells cultured in either zinc-rich or zinc-poor media and after exposure to high versus low glucose were determined. Zinc secretion from the rat prostate in vivo as detected by MRI was compared in control animals after injection of glucose, deoxyglucose, or pyruvate to initiate zinc secretion and in animals pre-treated with WZB-117 (a GLUT1 inhibitor) or S961 (a peripheral insulin receptor inhibitor).

Results: PNT1A cells exposed to high levels of glucose secrete zinc whereas cells exposed to an equivalent amount of deoxyglucose or pyruvate do not. Expression of Akt was dramatically altered by zinc supplementation of the culture media but not after exposure to glucose while GLUT1 and GLUT4 levels were less affected. Rats pre-treated with WZB-117 prior to imaging showed a reduction in GSZS from the prostate compared to controls whereas rats pre-treated with S961 showed no difference. Interestingly, in comparison to PNT1A cells, pyruvate and deoxyglucose also stimulate zinc secretion in vivo likely through indirect mechanisms.

Conclusions: GSZS requires metabolism of glucose both in vitro (PNT1A cells) and in vivo (rat prostate). Pyruvate also stimulates zinc secretion in vivo but likely via an indirect pathway involving rapid production of glucose via gluconeogenesis. These combined results support the conclusion that glycolytic flux is required to trigger GSZS in vivo.

 

Comments:

Summary of the study: The purpose of this study was to investigate the metabolic events that trigger glucose-stimulated zinc secretion (GSZS) in prostate cells. The researchers used both in vitro and in vivo models to explore various signaling pathways involved in GSZS.

In the in vitro experiments, a prostate epithelial cell line (PNT1A cells) was cultured and exposed to high glucose levels. Zinc secretion was monitored using a zinc-specific fluorescent probe called ZIMIR. The expression levels of GLUT1 (glucose transporter 1), GLUT4 (glucose transporter 4), and Akt (protein kinase B) were measured in the cells cultured in zinc-rich or zinc-poor media, as well as after exposure to high or low glucose levels. The results showed that high glucose levels induced zinc secretion, whereas equivalent amounts of deoxyglucose or pyruvate did not have the same effect. Additionally, zinc supplementation of the culture media affected Akt expression, but exposure to glucose had a lesser impact on GLUT1 and GLUT4 levels.

For the in vivo experiments, rats were used to study zinc secretion from the prostate. Magnetic resonance imaging (MRI) was employed to detect zinc secretion. Glucose, deoxyglucose, or pyruvate was injected into the rats to initiate zinc secretion. Some rats were pre-treated with WZB-117 (a GLUT1 inhibitor) or S961 (a peripheral insulin receptor inhibitor) before imaging to assess their effects on GSZS. The results showed that rats pre-treated with WZB-117 exhibited reduced GSZS compared to control animals, while rats pre-treated with S961 showed no significant difference. Interestingly, in vivo experiments revealed that pyruvate and deoxyglucose also stimulated zinc secretion, but through indirect mechanisms.

Based on the combined findings, the researchers concluded that GSZS is triggered by glucose metabolism both in vitro (using PNT1A cells) and in vivo (in the rat prostate). Pyruvate, as well as deoxyglucose, also stimulated zinc secretion in vivo, likely through an indirect pathway involving the rapid production of glucose via gluconeogenesis. The study supports the notion that glycolytic flux is necessary to initiate GSZS in vivo.

It is important to note that this summary is based on the provided information, and the study's complete findings and implications may be more nuanced and detailed.