Low Level Pro-inflammatory Cytokines Decrease Connexin36 Gap Junction Coupling in Mouse and Human Islets through Nitric Oxide-mediated Protein Kinase Cδ

J Biol Chem. 2016 Feb 12;291(7):3184-96. doi: 10.1074/jbc.M115.679506. Epub 2015 Dec 14.

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.

Keywords: PKC-δ; connexin36; cytokine; diabetes; gap junction; islet; nitric oxide.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium Signaling / drug effects
  • Cell Survival / drug effects
  • Connexins / antagonists & inhibitors*
  • Connexins / metabolism
  • Cytokines / genetics
  • Cytokines / metabolism*
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Gap Junctions / drug effects
  • Gap Junctions / immunology
  • Gap Junctions / metabolism*
  • Humans
  • Insulin / metabolism
  • Insulin Secretion
  • Interferon-gamma / genetics
  • Interferon-gamma / metabolism
  • Interleukin-1beta / genetics
  • Interleukin-1beta / metabolism
  • Islets of Langerhans / drug effects
  • Islets of Langerhans / immunology
  • Islets of Langerhans / metabolism*
  • Mice, Inbred C57BL
  • Nitric Oxide / agonists
  • Nitric Oxide / antagonists & inhibitors
  • Nitric Oxide / metabolism*
  • Prediabetic State / immunology
  • Prediabetic State / metabolism
  • Prediabetic State / pathology
  • Protein Kinase C-delta / antagonists & inhibitors
  • Protein Kinase C-delta / chemistry
  • Protein Kinase C-delta / metabolism*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Tissue Banks
  • Tissue Culture Techniques
  • Tumor Necrosis Factor-alpha / genetics
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Connexins
  • Cytokines
  • Enzyme Inhibitors
  • IL1B protein, mouse
  • Insulin
  • Interleukin-1beta
  • Recombinant Proteins
  • Tumor Necrosis Factor-alpha
  • connexin 36
  • Nitric Oxide
  • Interferon-gamma
  • Prkcd protein, mouse
  • PRKCD protein, human
  • Protein Kinase C-delta