Expression, Localization and Regulation of NADPH Oxidases in Pancreatic Beta Cells

Reactive oxygen species (ROS) are short-lived and redox signaling is likely site-dependent; underscoring the importance of resolving the intracellular localization of their sources. ROS-generating NADPH oxidases (NOX) regulate pancreatic beta cell function and viability, but the subcellular localization and cytokine regulation of isoforms in these cells remain mostly unknown. Thus, we aimed to characterize NOXs in beta cells. Isoform expression, intracellular localization and time-dependent cytokine-induced regulation were investigated in rat pancreatic islets and insulin-secreting cells by RT-qPCR, immunoblotting and immunofluorescence. Islets and beta cells express DUOX1 and DUOX2 proteins and Duoxa2 transcripts; and lack Duoxa1 expression. NOX1 and DUOX1 are expressed in the endoplasmic reticulum (ER); DUOX2 in insulin vesicles; and NOX2 and NOX4 in vesicles, ER and plasma membrane. Cytokine-induced upregulation of Nox1 and Duox1 transcripts peaks at 4-8 h and disappears at 16 h. Nox2 and p47phox transcript upregulation peaks at 8 h, persisting until 24 h. Duox(a)2, p67phox and p40phox transcripts were downregulated and DUOX1 protein upregulated at 16-24 h. Putatively, Duoxa1 disallowance in beta cells causes DUOX1 mismatching; impairing its trafficking and activity. Also, NOX might regulate insulin secretion and cytokine-induced ER stress and apoptosis; probably acting as fine-tuners of beta cell (patho)physiology.