title: EX4 stabilizes and activates Nrf2 via PKCδ, contributing to the prevention of oxidative stress-induced pancreatic beta cell damage.
abstract: Oxidative stress in pancreatic beta cells can inhibit insulin secretion and promote apoptotic cell death. Exendin-4 (EX4), a glucagon-like peptide-1 receptor agonist, can suppress beta cell apoptosis, improve beta cell function and protect against oxidative damage. In this study, we investigated the molecular mechanisms for antioxidative effects of EX4 in pancreatic beta cells. INS-1 cells, a rat insulinoma cell line, were pretreated with EX4 and exposed to palmitate or H2O2. Reactive oxygen species (ROS) production, and glutathione and insulin secretion were measured. The mRNA and protein expression levels of antioxidant genes were examined. The level of nuclear factor erythroid 2-related factor 2 (Nrf2), its binding to antioxidant response element (ARE), and its ubiquination in the presence of EX4 were determined. The Nrf2 signaling pathway was determined using rottlerin (protein kinase [PK]Cδ inhibitor), H89 (PKA inhibitor) and LY294002 (phosphatidylinositide 3-kinase [PI3K] inhibitor). EX4 treatment decreased ROS production, recovered cellular glutathione levels and insulin secretion in the presence of oxidative stress in INS-1 cells. The expression levels of glutamate-cysteine ligase catalytic subunit and heme oxygenase-1 were increased by EX4 treatment. EX4 promoted Nrf2 translocation, ARE binding activity and enhanced stabilization of Nrf2 by inhibition of ubiquitination. Knockdown of Nrf2 abolished the effect of EX4 on increased insulin secretion. Inhibition of PKCδ attenuated Nrf2 translocation and antioxidative gene expression by EX4 treatment. We suggest that EX4 activates and stabilizes Nrf2 through PKCδ activation, contributing to the increase of antioxidant gene expression and consequently improving beta cell function in the presence of oxidative stress.
authors.affiliation: College of Pharmacy, Gachon Institute of Pharmaceutical Science, Gachon University, Yeonsu-ku, Incheon, South Korea; Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Yeonsu-ku, Incheon, South Korea.
authors.forename: Mi-Hwi
authors.initials: MH
authors.lastname: Kim
authors.affiliation: College of Pharmacy, Gachon Institute of Pharmaceutical Science, Gachon University, Yeonsu-ku, Incheon, South Korea; Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Yeonsu-ku, Incheon, South Korea.
authors.forename: Eung-Hwi
authors.initials: EH
authors.lastname: Kim
authors.affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul, South Korea.
authors.forename: Hye Seung
authors.initials: HS
authors.lastname: Jung
authors.affiliation: Department of Physiology, Gachon University College of Medicine, Incheon, South Korea.
authors.forename: Dongki
authors.initials: D
authors.lastname: Yang
authors.affiliation: College of Pharmacy, Natural Medicine Research Institute, Mokpo National University, Muan-gun, Jeonnam, South Korea. Electronic address: parkey@mokpo.ac.kr.
authors.forename: Eun-Young
authors.initials: EY
authors.lastname: Park
authors.affiliation: College of Pharmacy, Gachon Institute of Pharmaceutical Science, Gachon University, Yeonsu-ku, Incheon, South Korea; Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Yeonsu-ku, Incheon, South Korea; Gachon Medical Research Institute, Gil Hospital, Incheon, South Korea. Electronic address: hsjun@gachon.ac.kr.
authors.forename: Hee-Sook
authors.initials: HS
authors.lastname: Jun
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D000077270:Exenatide; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D018384:Oxidative Stress; D010455:Peptides / Q000494:pharmacology*; D051745:Protein Kinase C-delta / Q000378:metabolism*; D051381:Rats; D014688:Venoms / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D051267:NF-E2-Related Factor 2; C495637:Nfe2l2 protein, rat; D010455:Peptides; D014688:Venoms; D000077270:Exenatide; D051745:Protein Kinase C-delta
keywords: Beta cell; Exendin-4; INS-1 cell; Nrf2; Oxidative stress; Type 2 diabetes