Suppression of NADPH oxidase 2 substantially restores glucose‐induced dysfunction of pancreatic NIT‐1 cells

Abstract

Defects in insulin secretion by pancreatic cells and/or decreased sensitivity of target tissues to insulin action are the key features of type 2 diabetes. It has been shown that excessive generation of reactive oxygen species (ROS) is linked to glucose‐induced β‐cell dysfunction. However, cellular mechanisms involved in ROS generation in β‐cells and the link between ROS and glucose‐induced β‐cell dysfunction are poorly understood. Here, we demonstrate a key role of NADPH oxidase 2 (NOX2)‐derived ROS in the deterioration of β‐cell function induced by a high concentration of glucose. Sprague–Dawley rats were fed a high‐fat diet for 24 weeks to induce diabetes. Diabetic rats showed increased glucose levels and elevated ROS generation in blood, but decreased insulin content in pancreatic β‐cells. In vitro, increased ROS levels in pancreatic NIT‐1 cells exposed to high concentrations of glucose (33.3 mmol·L−1) were associated with elevated expression of NOX2. Importantly, decreased glucose‐induced insulin expression and secretion in NIT‐1 cells could be rescued via siRNA‐mediated NOX2 reduction. Furthermore, high glucose concentrations led to apoptosis of β‐cells by activation of p38MAPK and p53, and dysfunction of β‐cells through phosphatase and tensih homolog (PTEN)‐dependent Jun N‐terminal kinase (JNK) activation and protein kinase B (AKT/PKB) inhibition, which induced the translocation of forkhead box O1 and pancreatic duodenal homeobox‐1, followed by reduced insulin expression and secretion. In conclusion, NOX2‐derived ROS could play a critical role in high glucose‐induced β‐cell dysfunction through PTEN‐dependent JNK activation and AKT inhibition.

The regulatory roles of NADPH oxidase, intra- and extra-cellular HSP70 in pancreatic islet function, dysfunction and diabetes

“…In pancreatic β-cells, chronic high glucose concentrations are associated with reduced insulin expression, elevated cell stress and apoptosis via oxidative damage delivered from NOX2 activation [67]. However, metabolic overload in vivo is not necessarily associated with NOX2-derived oxidative stress and decreased function of pancreatic β-cells since it was demonstrated that pancreatic islets isolated from rats fed a high-fat diet for 13 weeks had increased pancreatic islet functionality, associated with high levels of glucose metabolism and GSIS, but also low levels of NOX2 expression and ROS production [68].…”

Reactive oxygen and nitrogen species generation, antioxidant defenses, and β-cell function: a critical role for amino acids

“…Islets isolated from Wistar rats fed a high-fat diet for 13 weeks resulted in increased pancreatic islet functionality, associated with high levels of glucose metabolism and GSIS but also low levels of NOX2 expression and ROS production (Valle et al 2011). On the other hand, when Sprague Dawley rats (which are prone to develop insulin resistance and obesity (Reaven & Reaven 1981)) were submitted to a high-fat diet for a longer period (24 weeks), diabetes ensued that was associated with increased islet ROS and reduced insulin expression (Yuan et al 2010). Moreover, human islets isolated from type 2 diabetic patients demonstrated increased mRNA levels of the p22 subunit of NAD(P)H oxidase (Marchetti et al 1998).…”

Expression of NADPH oxidase in human pancreatic islets

“…NOX2, and of other NOX isoforms (NOX1 and NOX4) has been reported in rat pancreatic islets (Oliveira et al, 2003;Uchizono et al, 2006). In β-cells NOX2 appeared to be involved in oxidative stress induced by high chronic glucose levels in glucotoxicity (Yuan et al, 2010). Interestingly, although NOX2 deficiency protected against streptozotocin-induced β-cell destruction (Xiang et al, 2010), the suppression of its activity also impaired the mechanisms of glucose-stimulated insulin secretion (GSIS) in rodent islets (Imoto et al, 2008;Morgan et al, 2009).…”