The Connexin 43 Regulator Rotigaptide Reduces Cytokine-Induced Cell Death in Human Islets.

Seyed Mojtaba Ghiasi,Dan Ploug Christensen,Thomas Mandrup-Poulsen,Björn Tyrberg,Jakob Bondo Hansen

doi:10.3390/ijms21124311

Abstract

Background: Intercellular communication mediated by cationic fluxes through the Connexin family of gap junctions regulates glucose-stimulated insulin secretion and beta cell defense against inflammatory stress. Rotigaptide (RG, ZP123) is a peptide analog that increases intercellular conductance in cardiac muscle cells by the prevention of dephosphorylation and thereby uncoupling of Connexin-43 (Cx43), possibly via action on unidentified protein phosphatases. For this reason, it is being studied in human arrhythmias. It is unknown if RG protects islet cell function and viability against inflammatory or metabolic stress, a question of considerable translational interest for the treatment of diabetes. Methods: Apoptosis was measured in human islets shown to express Cx43, treated with RG or the control peptide ZP119 and exposed to glucolipotoxicity or IL-1β + IFNɣ. INS-1 cells shown to lack Cx43 were used to examine if RG protected human islet cells via Cx43 coupling. To study the mechanisms of action of Cx43-independent effects of RG, NO, IkBα degradation, mitochondrial activity, ROS, and insulin mRNA levels were determined. Results: RG reduced cytokine-induced apoptosis ~40% in human islets. In Cx43-deficient INS-1 cells, this protective effect was markedly blunted as expected, but unexpectedly, RG still modestly reduced apoptosis, and improved mitochondrial function, insulin-2 gene levels, and accumulated insulin release. RG reduced NO production in Cx43-deficient INS-1 cells associated with reduced iNOS expression, suggesting that RG blunts cytokine-induced NF-κB signaling in insulin-producing cells in a Cx43-independent manner. Conclusion: RG reduces cytokine-induced cell death in human islets. The protective action in Cx43-deficient INS-1 cells suggests a novel inhibitory mechanism of action of RG on NF-κB signaling.

Highlights

By inducing beta cell endoplasmic reticulum stress and apoptosis via the intrinsic mitochondrial pathway, proinflammatory cytokines have been implicated as mediators of beta cell failure and destruction causing type 1 diabetes (T1D) and type 2 diabetes (T2D) [1]
Since IL-1-induced beta cell apoptosis is potentiated by other proinflammatory cytokines, such as TNFα, IFNγ, and IL-6, and since anti-TNF therapy improved beta cell function in a small placebo-controlled trial [7], it is likely that a combination of treatments targeting various aspects of signaling caused by the cytokine network is needed to improve the efficacy of anti-cytokine strategies in T1D, as has been demonstrated in animal models [8]
RG reduced Nitric Oxide (NO) production in Cx43-deficient INS-1 cells associated with reduced iNOS expression and IkBα degradation, suggesting that RG blunts cytokine-induced NF-κB signaling in insulin-producing cells in a Cx43-independent manner

Summary

Introduction

By inducing beta cell endoplasmic reticulum stress and apoptosis via the intrinsic mitochondrial pathway, proinflammatory cytokines have been implicated as mediators of beta cell failure and destruction causing type 1 diabetes (T1D) and type 2 diabetes (T2D) [1]. Rotigaptide (RG, ZP123) is a peptide analog that increases intercellular conductance in cardiac muscle cells by the prevention of dephosphorylation and thereby uncoupling of Connexin-43 (Cx43), possibly via action on unidentified protein phosphatases. For this reason, it is being studied in human arrhythmias. In Cx43-deficient INS-1 cells, this protective effect was markedly blunted as expected, but unexpectedly, RG still modestly reduced apoptosis, and improved mitochondrial function, insulin-2 gene levels, and accumulated insulin release. RG reduced NO production in Cx43-deficient INS-1 cells associated with reduced iNOS expression, suggesting that RG blunts cytokine-induced NF-κB signaling in insulin-producing cells in a Cx43-independent manner. The protective action in Cx43-deficient INS-1 cells suggests a novel inhibitory mechanism of action of RG on NF-κB signaling

Methods

Results

Conclusion