Transient NADPH oxidase 2-dependent H₂O₂ production drives early palmitate-induced lipotoxicity in pancreatic islets

Modern lifestyles, including lack of physical activity and poor nutritional habits, are driving the rapidly increasing prevalence of obesity and type 2 diabetes. Increased levels of free fatty acids (FFAs), particularly saturated FFAs, in obese individuals have been linked to pancreatic β-cell failure. This process, termed lipotoxicity, involves activation of several stress responses, including ER stress and oxidative stress. However, the molecular underpinnings and causal relationships between the disparate stress responses remain unclear. Here we employed transgenic mice, expressing a genetically-encoded cytosolic H₂O₂ sensor, roGFP2-Orp1, to monitor dynamic changes in H₂O₂ levels in pancreatic islets in response to chronic palmitate exposure. We identified a transient increase in H₂O₂ levels from 4 to 8 h after palmitate addition, which was mirrored by a concomitant decrease in cellular NAD(P)H levels. Intriguingly, islets isolated from NOX2 knock-out mice displayed no H₂O₂ transient upon chronic palmitate treatment. Furthermore, NOX2 knockout rescued palmitate-dependent impairment of insulin secretion, calcium homeostasis and viability. Chemical inhibition of NOX activity protected islets from palmitate-induced impairment in insulin secretion, however had no detectable impact upon the induction of ER stress. In summary, our results reveal that transient NOX2-dependent H₂O₂ production is a likely cause of early palmitate-dependent lipotoxic effects.