Impaired β-cell-β-cell coupling mediated by Cx36 gap junctions in prediabetic mice

Abstract

Gap junctional intercellular communication between ␤-cells is crucial for proper insulin biosynthesis and secretion. The aim of this work was to investigate the expression of connexin (Cx)36 at the protein level as well as the function and structure of gap junctions (GJ) made by this protein in the endocrine pancreas of prediabetic mice. C57BL/6 mice were fed a high-fat (HF) or regular chow diet for 60 days. HF-fed mice became obese and prediabetic, as shown by peripheral insulin resistance, moderate hyperglycemia, hyperinsulinemia, and compensatory increase in endocrine pancreas mass. Compared with control mice, prediabetic animals showed a significant decrease in insulin-secretory response to glucose and displayed a significant reduction in islet Cx36 protein.Ultrastructural analysis further showed that prediabetic mice had GJ plaques about one-half the size of those of the control group. Microinjection of isolated pancreatic islets with ethidium bromide revealed that prediabetic mice featured a ␤-cell-␤-cell coupling 30% lower than that of control animals. We conclude that ␤-cell-␤-cell coupling mediated by Cx36 made-channels is impaired in prediabetic mice, suggesting a role of Cx36-dependent cell-to-cell communication in the pathogenesis of the early ␤-cell dysfunctions that lead to type 2-diabetes.high-fat-fed mice; type 2 diabetes mellitus; connexin 36; connexins; cell-cell communication; insulin secretion; insulin resistance; ␤-cell dysfunction GAP JUNCTION (GJ) CHANNELS provide a pathway for direct exchanges of ions, metabolites, and signaling molecules between adjacent cells. Intercellular communication mediated by these channels, also referred to as cell coupling, plays a crucial role in several cellular and physiological processes, in both developing and adult tissues (7). Thus, GJ coupling has been implicated in the control of cell growth, differentiation and secretion, embryonic development, the propagation and synchronization of neural and cardiac electrical impulses, and many other functions (9,17,24,32). The central role of GJs is further strengthened by increasing evidence linking the etiology of several genetic diseases to mutations or single nucleotide polymorphisms of connexin-coding genes and/or to the dysfunction of connexin-made channels (16,22).Cell-to-cell contacts mediated by GJs are also crucial for proper and fully mature secretory response of the pancreatic ␤-cells (7,10,11,23). Recent data further indicate that GJs may also play a role in controlling the mass of these cells by modulating their growth and their resistance to proapoptotic conditions (20, 21). However, whether GJs participate in the ␤-cell dysfunction, which plays a central role in the pathogenesis of diabetes, is presently supported by only indirect data (7). Thus, the ␤-cells of connexin 36 (Cx36)-null mice are uncoupled and show impaired intercellular synchronization of [Ca 2ϩ ] i transients, increased basal release of insulin, lack of glucose-stimulated insulin release in a normal pulsatile fashion, and a mar...

Beta-cell hubs maintain Ca2+ oscillations in human and mouse islet simulations

“…6,86 The strength of this coupling decreases with age 87,88 and in animal models of diabetes. 89,90 Therefore, our simulations predict that a reduction in GJ coupling would reduce the ability of hubs to generate whole-islet Ca 2+ oscillations, greatly impairing insulin output. Whether such dysfunctions in hub cells occur in T2DM and contribute to the impaired insulin secretion observed in this disease, remains to be seen.…”

Butyrate reduces high-fat diet-induced metabolic alterations, hepatic steatosis and pancreatic beta cell and intestinal barrier dysfunctions in prediabetic mice

“…These procedures were performed as previously described 19,40,41 and at the same period during the day (9 a.m.-11 a.m.). The blood glucose concentration was measured using an Accu-Chek Advantage II glucometer (Roche Diagnostic, Switzerland).…”

“…20,41 Briefly, homogenate aliquots (containing 50 mg of total protein) were applied on 12% polyacrylamide gels and proteins were fractionated by electrophoresis and electrophoretically transferred to nitrocellulose membranes (Bio-Rad). After staining with Ponceau solution (Sigma) to check the efficiency of sample loading and transfer, membranes were blocked for 4 h at RT with a buffer solution (0.01 M Trisma Base, 0.15 M NaCl, 0.05% Tween 20; pH 7.4) containing 5% skimmed milk powder and then incubated overnight at 4 C with primary antibody anti-claudin-1 (Abcam; cat number ab15098; dilution 1:150 in basal solution containing 3% skimmed milk powder).…”

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

“…Implications for Altered Gap Junction Coupling in DiabetesRecent studies have indicated that Cx36 gap junction coupling is decreased in islets from high-fat diet fed mouse models of pre-diabetes (24). [Ca 2ϩ ] i dynamics are also disrupted in an ob/ob mouse model of obesity (63) consistent with a decrease in gap junction coupling (18).…”

“…This suggests that disruptions to gap junction coupling occur under these pre-diabetic and diabetic conditions. Recent studies have shown that Cx36 gap junction coupling is decreased in high-fat diet fed mice (24), which suggests a role for altered coupling in the development of disease. Furthermore, in vitro studies have shown that hyperglycemia (25) and hyperlipidemia (26,27), conditions that stimulate high levels of cytokine production from ␤-cells (28,29), reduce Cx36 gap junction coupling.…”