title: Low Level Pro-inflammatory Cytokines Decrease Connexin36 Gap Junction Coupling in Mouse and Human Islets through Nitric Oxide-mediated Protein Kinase Cδ.
abstract: Pro-inflammatory cytokines contribute to the decline in islet function during the development of diabetes. Cytokines can disrupt insulin secretion and calcium dynamics; however, the mechanisms underlying this are poorly understood. Connexin36 gap junctions coordinate glucose-induced calcium oscillations and pulsatile insulin secretion across the islet. Loss of gap junction coupling disrupts these dynamics, similar to that observed during the development of diabetes. This study investigates the mechanisms by which pro-inflammatory cytokines mediate gap junction coupling. Specifically, as cytokine-induced NO can activate PKCδ, we aimed to understand the role of PKCδ in modulating cytokine-induced changes in gap junction coupling. Isolated mouse and human islets were treated with varying levels of a cytokine mixture containing TNF-α, IL-1β, and IFN-γ. Islet dysfunction was measured by insulin secretion, calcium dynamics, and gap junction coupling. Modulators of PKCδ and NO were applied to determine their respective roles in modulating gap junction coupling. High levels of cytokines caused cell death and decreased insulin secretion. Low levels of cytokine treatment disrupted calcium dynamics and decreased gap junction coupling, in the absence of disruptions to insulin secretion. Decreases in gap junction coupling were dependent on NO-regulated PKCδ, and altered membrane organization of connexin36. This study defines several mechanisms underlying the disruption to gap junction coupling under conditions associated with the development of diabetes. These mechanisms will allow for greater understanding of islet dysfunction and suggest ways to ameliorate this dysfunction during the development of diabetes.
authors.affiliation: From the Barbara Davis Center for Childhood Diabetes, Department of Bioengineering, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Nikki L
authors.initials: NL
authors.lastname: Farnsworth
authors.affiliation: Department of Bioengineering, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Rachelle L
authors.initials: RL
authors.lastname: Walter
authors.affiliation: Department of Bioengineering, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Alireza
authors.initials: A
authors.lastname: Hemmati
authors.affiliation: Department of Bioengineering, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Westacott
authors.affiliation: From the Barbara Davis Center for Childhood Diabetes, Department of Bioengineering, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045 richard.benninger@ucdenver.edu.
authors.forename: Richard K P
authors.initials: RK
authors.lastname: Benninger
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D017630:Connexins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017629:Gap Junctions / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007371:Interferon-gamma / Q000235:genetics / Q000378:metabolism; D053583:Interleukin-1beta / Q000235:genetics / Q000378:metabolism; D007515:Islets of Langerhans / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011236:Prediabetic State / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014015:Tissue Banks; D046509:Tissue Culture Techniques; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism; D000097004:Gap Junction delta-2 Protein
chemical_list: D017630:Connexins; D016207:Cytokines; D004791:Enzyme Inhibitors; D007328:Insulin; D007371:Interferon-gamma; D053583:Interleukin-1beta; D009569:Nitric Oxide; D051745:Protein Kinase C-delta; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D000097004:Gap Junction delta-2 Protein; C587672:IL1B protein, mouse; C497259:Prkcd protein, mouse; C497258:PRKCD protein, human
keywords: PKC-δ; connexin36; cytokine; diabetes; gap junction; islet; nitric oxide