title: Phagocyte-like NADPH oxidase (Nox2) promotes activation of p38MAPK in pancreatic β-cells under glucotoxic conditions: Evidence for a requisite role of Ras-related C3 botulinum toxin substrate 1 (Rac1).
abstract: It is well established that glucotoxicity (caused by high glucose concentrations; HG) underlies pathogenesis of islet dysfunction in diabetes. We have recently demonstrated that Nox2 plays a requisite role in the generation of reactive oxygen species (ROS) under HG conditions, resulting in mitochondrial dysregulation and loss of islet β-cell function. Herein, we investigated roles of Nox2 in the regulation of downstream stress kinase (p38MAPK) activation under HG conditions (20mM; 24h) in normal rodent islets and INS-1 832/13 cells. We observed that gp91-ds-tat, a specific inhibitor of Nox2, but not its inactive analog, significantly attenuated HG-induced Nox2 activation, ROS generation and p38MAPK activation, thus suggesting that Nox2 activation couples with p38MAPK activation. Since Rac1, is an integral member of the Nox2 holoenzyme, we also assessed the effects of Rac1 inhibitors (EHT 1864, NSC23766 and Ehop-016) on HG-induced p38MAPK activation in isolated β-cells. We report a significant inhibition of p38MAPK phosphorylation by Rac1 inhibitors, implying a regulatory role for Rac1 in promoting the Nox2-p38MAPK signaling axis in the β-cell under the duress of HG. 2-Bromopalmitate, a known inhibitor of protein (Rac1) palmitoylation, significantly reduced HG-induced p38MAPK phosphorylation. However, GGTI-2147, a specific inhibitor of geranylgeranylation of Rac1, failed to exert any significant effects on HG-induced p38MAPK activation. In conclusion, we present the first evidence that the Rac1-Nox2 signaling module plays novel regulatory roles in HG-induced p38MAPK activation and loss in glucose-stimulated insulin secretion (GSIS) culminating in metabolic dysfunction and the onset of diabetes.
authors.affiliation: Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA.
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Sidarala
authors.affiliation: Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA.
authors.forename: Rajakrishnan
authors.initials: R
authors.lastname: Veluthakal
authors.affiliation: Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA.
authors.forename: Khadija
authors.initials: K
authors.lastname: Syeda
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Puerto Rico Medical School Campus, Post Office Box 365067, San Juan, PR 00936-5067, USA.
authors.forename: Cornelis
authors.initials: C
authors.lastname: Vlaar
authors.affiliation: School of Biomedical Sciences, Curtin Health Sciences Innovation Research Institute, Curtin University, Perth, WA 6845, Australia.
authors.forename: Philip
authors.initials: P
authors.lastname: Newsholme
authors.affiliation: Beta-Cell Biochemistry Laboratory, John D. Dingell VA Medical Center, and Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI 48201, USA. Electronic address: akowluru@med.wayne.edu.
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Kowluru
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017368:Protein Prenylation; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D017382:Reactive Oxygen Species; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C500593:Cybb protein, rat; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D048051:p38 Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein; D005947:Glucose
keywords: Diabetes; Glucotoxicity; Pancreatic islet β-cell; Rac1; p38MAPK