Gap Junction Coupling and Calcium Waves in the Pancreatic Islet

Benninger, Richard K.P.; Zhang, Min; Head, W. Steven; Satin, Leslie S.; Piston, David W.

doi:10.1529/biophysj.108.140863

Cited by 212 publications

(349 citation statements)

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“…This follows the well established role gap junctions play in synchronizing the oscillatory regulation of [Ca 2ϩ ] i (18,20). In mouse islets, the decrease in average gap junction coupling (average recovery rate) was substantially greater than the decrease in the number of cells showing measurable gap junction coupling (% of cells showing recovery).…”

Section: Low Levels Of Pro-inflammatory Cytokines Disrupt [Ca 2ϩ ] Isupporting

confidence: 76%

“…Connexin36 (Cx36) gap junctions strongly regulate [Ca 2ϩ ] i dynamics within the islet (18) by coordinating glucose-induced membrane depolarization. Under stimulatory conditions, gap junction coupling coordinates [Ca 2ϩ ] i oscillations across the islet, first phase insulin release, and second phase insulin pulses (19).…”

mentioning

confidence: 99%

“…Under stimulatory conditions, gap junction coupling coordinates [Ca 2ϩ ] i oscillations across the islet, first phase insulin release, and second phase insulin pulses (19). Altered Cx36 gap junction coupling in pancreatic islets can cause disruptions to [Ca 2ϩ ] i signaling and insulin secretion dynamics (18,20). These dynamics, specifically first phase insulin release and pulsatile insulin release, are similarly disrupted in states of pre-diabetes in animal models and humans (21)(22)(23).…”

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confidence: 99%

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

Farnsworth

Walter

Hemmati

et al. 2016

Journal of Biological Chemistry

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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 PKC␦, we aimed to understand the role of PKC␦ 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-␣, IL-1␤, and IFN-␥. Islet dysfunction was measured by insulin secretion, calcium dynamics, and gap junction coupling. Modulators of PKC␦ 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 PKC␦, 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.Diabetes is characterized by a progressive decrease in function and mass of ␤-cells, which comprise the majority of cells in the islets of Langerhans (1). Pro-inflammatory cytokines have been implicated as mediators of ␤-cell death in both type 1 diabetes (T1D) 2 and type 2 diabetes (T2D) (2-4). However, pro-inflammatory cytokines also play a role in causing ␤-cell dysfunction early in disease progression (3, 5). In T1D, high levels of pro-inflammatory cytokines, including tumor necrosis factor-␣ (TNF-␣), interleukin-1␤ (IL-1␤), and interferon ␥ (IFN-␥), are released by immune cells, such as CD4 ϩ and CD8 ϩ T-cells and macrophages, which infiltrate the pancreas (3, 6). In T2D, adipocyte stress resulting from obesity can lead to secretion of low levels of circulating TNF-␣ from activated macrophages in adipose tissue; whereas elevated free fatty acids and/or hyperglycemia can also lead to local release of IL-1␤ in the islets (4, 7). Although the mechanisms of cytokine-induced cell death in diabetes are well characterized, cytokine-induced islet dysfunction is poorly understood.In vitro, the pro-inflammatory cytokines TNF-␣, IL-1␤, and IFN-␥ work synergistically (8) to induce islet dysfunction and disrupt insulin secretion (9, 10). The effect of pro-inflammatory cytokines on the ␤-cell is thought to be mediated in part by...

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Section: Low Levels Of Pro-inflammatory Cytokines Disrupt [Ca 2ϩ ] Isupporting

confidence: 76%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

Farnsworth

Walter

Hemmati

et al. 2016

Journal of Biological Chemistry

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“…This is consistent with previous studies showing a critical role of the cation in the activation of ER stress, the generation of ROS, the control of mitochondrial function 40 and the activation of AMPK. 41 Cx36 overexpression increases the basal Ca 2 þ stores of ER and prevents their depletion after exposure to cytokines (present data), whereas loss of Cx36 impairs the intercellular synchronization of Ca 2 þ transients, [42][43][44][45] whose generation requires proper ER Ca 2 þ stores. 46 The homeostasis of ER Ca 2 þ is controlled by many factors, including inositol 1,4,5-trisphosphate (IP3), which can permeate gap junctions and contribute to mitochondrial apoptosis.…”

Section: Discussionsupporting

confidence: 56%

Connexin36 contributes to INS-1E cells survival through modulation of cytokine-induced oxidative stress, ER stress and AMPK activity

et al. 2013

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Cell-to-cell communication mediated by gap junctions made of Connexin36 (Cx36) contributes to pancreatic b-cell function. We have recently demonstrated that Cx36 also supports b-cell survival by a still unclear mechanism. Using specific Cx36 siRNAs or adenoviral vectors, we now show that Cx36 downregulation promotes apoptosis in INS-1E cells exposed to the pro-inflammatory cytokines (IL-1b, TNF-a and IFN-c) involved at the onset of type 1 diabetes, whereas Cx36 overexpression protects against this effect. Cx36 overexpression also protects INS-1E cells against endoplasmic reticulum (ER) stress-mediated apoptosis, and alleviates the cytokine-induced production of reactive oxygen species, the depletion of the ER Ca 2 þ stores, the CHOP overexpression and the degradation of the anti-apoptotic protein Bcl-2 and Mcl-1. We further show that cytokines activate the AMP-dependent protein kinase (AMPK) in a NO-dependent and ER-stress-dependent manner and that AMPK inhibits Cx36 expression. Altogether, the data suggest that Cx36 is involved in Ca 2 þ homeostasis within the ER and that Cx36 expression is downregulated following ER stress and subsequent AMPK activation. As a result, cytokine-induced Cx36 downregulation elicits a positive feedback loop that amplifies ER stress and AMPK activation, leading to further Cx36 downregulation. The data reveal that Cx36 plays a central role in the oxidative stress and ER stress induced by cytokines and the subsequent regulation of AMPK activity, which in turn controls Cx36 expression and mitochondria-dependent apoptosis of insulin-producing cells.

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“…This separation is possible in juvenile MLIs, which have a well-characterized cellular biophysical compartmentalization with time constants below ∼5 ms (18). The present method may likewise be of use in estimating the electrical connectivity of coupled networks formed by relatively compact cells with a small number of neighbors like pancreatic β-cells (35). It remains to be seen whether a similar separation can be obtained in other interneuron networks.…”

Section: (Yellow Cellsmentioning

confidence: 66%

Estimating functional connectivity in an electrically coupled interneuron network

Alcamí

Marty

2013

Proc. Natl. Acad. Sci. U.S.A.

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Even though it has been known for some time that in many mammalian brain areas interneurons are electrically coupled, a quantitative description of the network electrical connectivity and its impact on cellular passive properties is still lacking. Approaches used so far to solve this problem are limited because they do not readily distinguish junctions among direct neighbors from indirect junctions involving intermediary, multiply connected cells. In the cerebellar cortex, anatomical and functional evidence indicates electrical coupling between molecular layer interneurons (basket and stellate cells). An analysis of the capacitive currents obtained under voltage clamp in molecular layer interneurons of juvenile rats or mice reveals an exponential component with a time constant of ∼20 ms, which represents capacitive loading of neighboring cells through gap junctions. These results, taken together with dual cell recording of electrical synapses, have led us to estimate the number of direct neighbors to be ∼4 for rat basket cells and ∼1 for rat stellate cells. The weighted number of neighbors (number of neighbors, both direct and indirect, weighted with the percentage of voltage deflection at steady state) was 1.69 in basket cells and 0.23 in stellate cells. The last numbers indicate the spread of potential changes in the network and serve to estimate the contribution of gap junctions to cellular input conductance. In conclusion the present work offers effective tools to analyze the connectivity of electrically connected interneuron networks, and it indicates that in juvenile rodents, electrical communication is stronger among basket cells than among stellate cells. To model the functional role of gap junctions (GJs) in the IN network and in cellular computation, it is necessary to determine the number of cells that are connected to a given cell, as well as the geometry of the network. Methods that have been developed to extract this information include dye coupling analysis (e.g., ref. 6), paired recordings coupled with anatomical descriptions (7), and frequency-dependent impedance measurements (8). The first two methods do not readily distinguish direct connections from indirect connections involving an intermediate IN (7,9,10), and all three methods are labor intensive and difficult to implement in a fully quantitative manner. In addition, they do not provide information on the spatial arrangement of the GJs. Therefore, the data that have been exploited for modeling GJ connectivity in IN networks are missing critical elements.In the cerebellum, Golgi cells and molecular layer interneurons (MLIs) have been shown to form anatomical and functional networks involving GJs that are specific to a given cell type (6,(11)(12)(13)(14). In both cases GJs may be involved in the generation of concerted oscillations under some pharmacological conditions (12, 15), and spikelets (spikes of coupled cells filtered through GJs) have been shown to encode sensory information in MLIs (16). MLIs are particularly interesting because th...

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Gap Junction Coupling and Calcium Waves in the Pancreatic Islet

Cited by 212 publications

References 47 publications

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

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

Connexin36 contributes to INS-1E cells survival through modulation of cytokine-induced oxidative stress, ER stress and AMPK activity

Estimating functional connectivity in an electrically coupled interneuron network

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