Palmitate induces reactive oxygen species production and β‐cell dysfunction by activating nicotinamide adenine dinucleotide phosphate oxidase through Src signaling

Abstract

Aims/Introduction: Chronic hyperlipidemia impairs pancreatic b-cell function, referred to as lipotoxicity. We have reported an important role of endogenous reactive oxygen species (ROS) overproduction by activation of Src, a non-receptor tyrosine kinase, in impaired glucose-induced insulin secretion (GIIS) from diabetic rat islets. In the present study, we investigated the role of ROS production by Src signaling in palmitate-induced dysfunction of b-cells. Materials and Methods: After rat insulinoma INS-1D cells were exposed to 0.6 mmol/L palmitate for 24 h (palmitate exposure); GIIS, ROS production and nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity were examined with or without exposure to10 lmol/L 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a Src inhibitior, for 30 or 60 min. Results: Exposure to PP2 recovered impaired GIIS and decreased ROS overproduction as a result of palmitate exposure. Palmitate exposure increased activity of NOX and protein levels of NOX2, a pathological ROS source in b-cells. Palmitate exposure increased the protein level of p47 phox , a regulatory protein of NOX2, in membrane fraction compared with control, which was reduced by PP2. Transfection of small interfering ribonucleic acid of p47 phox suppressed the augmented p47 phox protein level in membrane fraction, decreased augmented ROS production and increased impaired GΙIS by palmitate exposure. In addition, exposure to PP2 ameliorated impaired GIIS and decreased ROS production in isolated islets of KK-A y mice, an obese diabetic model with hyperlipidemia. Conclusions: Activation of NOX through Src signaling plays an important role in ROS overproduction and impaired GΙIS caused by chronic exposure to palmitate, suggesting a lipotoxic mechanism of b-cell dysfunction of obese mice.

Src regulates insulin secretion and glucose metabolism by influencing subcellular localization of glucokinase in pancreatic β‐cells

“…Insulin content was not affected by Src downregulation (Figure b). In addition, exposure of PP2 for 48 h reduced GIIS in INS‐1 cells (Figure c), whereas transient PP2 treatment for 30 min did not change GIIS in INS‐1 cells, as previously reported.…”

“…In the present study, the suppressive effects of Src downregulation on glucose metabolism and insulin secretion were as a result of reduction of glucokinase activity, an underlying mechanism that differs from our previous reports that Src hyperactivation‐related oxidative stress decreased glucose metabolism. These differences illustrate the diversity of Src function, which is especially dependent on cellular environments or conditions.…”

“…We previously reported that Src inhibition by short exposure to PP2 for 30–60 min reduced overproduction of ROS, and restored impaired glucose metabolism and GIIS in pathophysiological conditions, such as that in diabetic Goto‐Kakizaki rat islets and INS‐1 cells exposed to palmitate, but showed little effect on these parameters in physiological conditions. However, the more prolonged effects of Src inhibition on pancreatic β‐cells in physiological conditions are unknown.…”

Inhibition of SH2-domain-containing inositol 5-phosphatase (SHIP2) ameliorates palmitate induced-apoptosis through regulating Akt/FOXO1 pathway and ROS production in HepG2 cells

“…We also observed an increased FOXO-1 phosphorylation in parallel with Another mechanism linking SHIP2 to apoptosis is oxidative stress. A growing body of evidence suggests that the oxidative stress due to excessive production of ROS is the main contributor to the pathophysiology of diabetic complications [21,30]. Increasing ROS production has been demonstrated to account for apoptosis in response to palmitate in numerous cell lines [31,32].…”

Emerging Role of Pancreatic β-Cells during Insulin Resistance

“…GLP-1 effectively inhibits oxidative stress and cell death of β-cells induced by the pro-oxidant tert-butyl hydroperoxide (tert-BOOH) [134]. NOX activation through Src signaling plays an important role in ROS overproduction and impaired GSIS caused by lipotoxicity [135].…”