β-Cell Uncoupling Protein 2 Regulates Reactive Oxygen Species Production, Which Influences Both Insulin and Glucagon Secretion

Abstract

OBJECTIVEThe role of uncoupling protein 2 (UCP2) in pancreatic β-cells is highly debated, partly because of the broad tissue distribution of UCP2 and thus limitations of whole-body UCP2 knockout mouse models. To investigate the function of UCP2 in the β-cell, β-cell–specific UCP2 knockout mice (UCP2BKO) were generated and characterized.RESEARCH DESIGN AND METHODSUCP2BKO mice were generated by crossing loxUCP2 mice with mice expressing rat insulin promoter-driven Cre recombinase. Several in vitro and in vivo parameters were measured, including respiration rate, mitochondrial membrane potential, islet ATP content, reactive oxygen species (ROS) levels, glucose-stimulated insulin secretion (GSIS), glucagon secretion, glucose and insulin tolerance, and plasma hormone levels.RESULTSUCP2BKO β-cells displayed mildly increased glucose-induced mitochondrial membrane hyperpolarization but unchanged rates of uncoupled respiration and islet ATP content. UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS. Surprisingly, UCP2BKO mice were glucose-intolerant, showing greater α-cell area, higher islet glucagon content, and aberrant ROS-dependent glucagon secretion under high glucose conditions.CONCLUSIONSUsing a novel β-cell–specific UCP2KO mouse model, we have shed light on UCP2 function in primary β-cells. UCP2 does not behave as a classical metabolic uncoupler in the β-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification. In addition, β-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.

Glutathionylation State of Uncoupling Protein-2 and the Control of Glucose-stimulated Insulin Secretion

“…UCP2 activity and expression are associated with negative regulation of insulin secretion. Knock-out of UCP2 expression or inhibition of UCP2 function with genipin increases GSIS from pancreatic islets, observations that have been replicated in INS-1E cells (7)(8)(9). The putative signaling function of UCP2 is thought to stem from its capacity to control mitochondrial ROS emission (reviewed in Ref.…”

“…10). For instance, using a cell-specific UCP2 deletion mouse model, Robson-Doucette et al (9) demonstrated that ␤ cell UCP2 has little effect on mitochondrial ATP production, but it significantly contributes to the control of mitochondrial ROS production, which in turn regulates GSIS. In support of this, various reports have shown that exposing ␤ cells (either insulinoma cells or in pancreatic islets) to low amounts of superoxide (O 2 .…”

“…, generated artificially with menadione) or H 2 O 2 stimulates insulin release (reviewed in Refs. 9,[11][12][13][14]. Furthermore, Leloup et al.…”

“…(15) showed that the induction of ROS emission from the electron transport chain stimulates insulin release to the same degree as glucose-mediated ATP production. Glucose metabolism has also been shown to increase intracellular ROS levels in rat islets, Min6 (mouse ␤ cell line), and INS-1 832/13 cells (rat ␤ cell line), conditions associated with GSIS (9,12). In addition to the regulation of GSIS-amplifying ROS signals, ROS are also important regulators of UCP2 function itself (1).…”

Uncoupling protein‐2 mediates the protective action of berberine against oxidative stress in rat insulinoma INS‐1E cells and in diabetic mouse islets

“…The mitochondrion is one major source of intracellular ROS and the uncoupling proteins (UCPs), a superfamily of mitochondrial anion transporters, are important natural antioxidants in controlling cellular ROS homeostasis (Chan et al, 2010). Among them, UCP2 contributes to the control of mitochondrial ROS production, thus preventing oxidative stress (Robson-Doucette et al, 2011). Enhanced GSIS and increased intracellular ROS have been found in both islet cells of UCP2-deficient mice (Zhang et al, 2001;Lee et al, 2009) and INS-1E cells (Affourtit et al, 2011) and lean mouse islets (Saleh et al, 2006) with UCP2 knockdown.…”