Calcium has a permissive role in interleukin-1beta-induced c-jun N-terminal kinase activation in insulin-secreting cells

The Membrane Phospholipidomics Research of Oxidatively Damaged INS-1 Pancreatic Beta Cells Intervened by the Effective Constituents of Anemarrhenae Asphodeloides Rhizoma

The rhizoma of Anemarrhenae asphodeloides has a long history of hypoglycemic use in Chinese traditional medicine. In this article, 400 μmol/L H2 O2 induced normal INS-1 pancreatic beta cells to establish experimental model of oxidative damage. Quercetin was used as a positive drug, and mangiferin and its ethanolic extract were selected as therapeutic agents in an oxidative damage model to evaluate the ameliorative effect of the active ingredients of Anemarrhenae asphodeloides rhizoma on oxidative damage in INS-1 pancreatic β-cells. Building a qualitative analysis method of membrane phospholipids of INS-1 pancreatic beta cells and identified 82 phospholipids based on the UPLC/Q-TOF MS technology, which could provide a database for further statistics analysis. OPLS-DA was used to screen the phospholipid biomarkers from the raw data. Exploring the biological significances of these biomarkers, and discussing the toxic effect of the effective components of Anemarrhena asphodeloides rhizoma, on oxidatively damaged INS-1 pancreatic beta cell.

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

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.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Nicotinic acetylcholine receptors regulate type 1 inositol 1,4,5-trisphosphate receptor expression via calmodulin kinase IV activation

Type 1 inositol 1,4,5-trisphosphate receptors (IP3 R-1) are among the important calcium channels regulating intracellular Ca(2+) concentration in the central nervous system. In a previous study, we showed that drugs of abuse, such as cocaine, methamphetamine, and ethanol, induced IP3 R-1 upregulation via the calcium signal transduction pathway in psychological dependence. Although nicotine, a major component in tobacco smoke, participates in psychological and/or physical dependence, it has not yet been clarified how nicotine alters IP3 R-1 expression. The present study, therefore, seeks to clarify the mechanism bgy which nicotine modifies IP3 R-1 expression by using mouse cerebral cortical neurons in primary culture. Nicotine induced dose- and time-dependent upregulation of IP3 R-1 protein following its mRNA increase, and the latter was significantly suppressed by a nonselective nicotinic acetylcholine receptors (nAChR) antagonist, mecamylamine. Both cFos and phosphorylated-cJun (p-cJun) were immediately increased in the nucleus, together with an increase of calmodulin kinase (CaMK) IV but not CaMKII expression after nicotine exposure. A nonselective inhibitor of CaMKs, KN-93, and a calcium chelating regent, BAPTA-AM, completely suppressed the expression of cFos and p-cJun in the nucleus as well as the nicotine-induced IP3 R-1 upregulation. These results indicate that nAChR activation by nicotine upregulates IP3 R-1 via increase of activator protein-1, which is a cFos and cJun dimmer, in the nucleus, with activation of Ca(2+) signaling transduction processes.

18beta-glycyrrhetinic acid induces apoptosis in pituitary adenoma cells via ROS/MAPKs-mediated pathway

The purpose of the present study was to evaluate the anti-tumor effects of 18beta-glycyrrhetinic acid (GA), a natural compound extracted from liquorice, against pituitary adenoma and its underlying mechanisms in cultured cells and mouse model of xenografted tumor. GA induced cellular damage in rat pituitary adenoma-derived MMQ and GH3 cells, manifested as reduced cell viability, increased lactate dehydrogenase release, elevated intracellular reactive oxygen species (ROS) and Ca(2+) concentration. GA also caused G0/G1 phase arrest, increased apoptosis rate and increased mitochondrial membrane permeabilization by suppressing the mitochondrial membrane potential and down-regulating a ratio of B cell lymphoma 2 (Bcl-2) and Bax. GA activated calcium/calmodulin-dependent protein kinase II (CaMKII), c-Jun N-terminal kinase (JNK) and P38; but these activating effects were attenuated by pretreatment with N-acetyl-L-cysteine, a ROS inhibitor. Pretreatment with KN93, a CaMKII inhibitor, also abolished the GA activation of JNK and P38. GA remarkably inhibited growth of pituitary adenoma grafted on nude mice. These results suggest that the anti-pituitary adenoma effect of GA is associated with its apoptotic actions by activating mitochondria-mediated ROS/mitogen-activated protein kinase pathways in particular CaMKII that may serve a linkage between ROS accumulation and the activation of JNK and P38. This study provides experimental evidence in the support of further developing GA as a chemotherapeutic agent for pituitary adenoma.

JNK1/2 regulates ER-mitochondrial Ca2+ cross-talk during IL-1β-mediated cell death in RINm5F and human primary β-cells

Elevated interleukin-1β (IL-1β) induces apoptosis in pancreatic β-cells through endoplasmic reticulum (ER) stress induction and subsequent c-jun-N-terminal kinase 1/2 (JNK1/2) activation. In earlier work we showed that JNK1/2 activation is initiated before ER stress and apoptotic induction in response to IL-1β. However, the detailed regulatory mechanisms are not completely understood. Because the ER is the organelle responsible for Ca(2+) handling and storage, here we examine the effects of IL-1β on cellular Ca(2+) movement and mitochondrial dysfunction and evaluate the role of JNK1/2. Our results show that in RINm5F cells and human primary β-cells, IL-1β alters mitochondrial membrane potential, mitochondrial permeability transition pore opening, ATP content, and reactive oxygen species production and these alterations are preceded by ER Ca(2+) release via IP3R channels and mitochondrial Ca(2+) uptake. All these events are prevented by JNK1/2 small interfering RNA (siRNA), indicating the mediating role of JNK1/2 in IL-1β-induced cellular alteration. This is accompanied by IL-1β-induced apoptosis, which is prevented by JNK1/2 siRNA and the IP3R inhibitor xestospongin C. This suggests a regulatory role of JNK1/2 in modulating the ER-mitochondrial-Ca(2+) axis by IL-1β in apoptotic cell death.

Brain-derived neurotrophic factor-dependent synaptic plasticity is suppressed by interleukin-1β via p38 mitogen-activated protein kinase

Evolving evidence suggests that brain inflammation and the buildup of proinflammatory cytokine increases the risk for cognitive decline and cognitive dysfunction. Interleukin-1β (IL-1β), acting via poorly understood mechanisms, appears to be a key cytokine in causing these deleterious effects along with a presumably related loss of long-term potentiation (LTP)-type synaptic plasticity. We hypothesized that IL-1β disrupts brain-derived neurotrophic factor (BDNF) signaling cascades and thereby impairs the formation of filamentous actin (F-actin) in dendritic spines, an event that is essential for the stabilization of LTP. Actin polymerization in spines requires phosphorylation of the filament severing protein cofilin and is modulated by expression of the immediate early gene product Arc. Using rat organotypic hippocampal cultures, we found that IL-1β suppressed BDNF-dependent regulation of Arc and phosphorylation of cofilin and cAMP response element-binding protein (CREB), a transcription factor regulating Arc expression. IL-1β appears to act on BDNF signal transduction by impairing the phosphorylation of insulin receptor substrate 1, a protein that couples activation of the BDNF receptor TrkB to downstream signaling pathways regulating CREB, Arc, and cofilin. IL-1β upregulated p38 mitogen-activated protein kinase (MAPK), and inhibiting p38 MAPK prevented IL-1β from disrupting BDNF signaling. IL-1β also prevented the formation of F-actin in spines and impaired the consolidation, but not the induction, of BDNF-dependent LTP in acute hippocampal slices. The suppressive effect of IL-1β on F-actin and LTP was prevented by inhibiting p38 MAPK. These findings define a new mechanism for the action of IL-1β on LTP and point to a potential therapeutic target to restore synaptic plasticity.

Traumatic noise activates Rho-family GTPases through transient cellular energy depletion

Small GTPases mediate transmembrane signaling and regulate the actin cytoskeleton in eukaryotic cells. Here, we characterize the auditory pathology of adult male CBA/J mice exposed to traumatic noise (2-20 kHz; 106 dB; 2 h). Loss of outer hair cells was evident 1 h after noise exposure in the basal region of the cochlea and spread apically with time, leading to permanent threshold shifts of 35, 60, and 65 dB at 8, 16, and 32 kHz. Several biochemical and molecular changes correlated temporally with the loss of cells. Immediately after exposure, the concentration of ATP decreased in cochlear tissue and reached a minimum after 1 h while the immunofluorescent signal for p-AMPKα significantly increased in sensory hair cells at that time. Levels of active Rac1 increased, whereas those of active RhoA decreased significantly 1 h after noise attaining a plateau at 1-3 h; the formation of a RhoA-p140mDia complex was consistent with an activation of Rho GTPase pathways. Also at 1-3 h after exposure, the caspase-independent cell death marker, Endo G, translocated to the nuclei of outer hair cells. Finally, experiments with the inner ear HEI-OC1 cell line demonstrated that the energy-depleting agent oligomycin enhanced both Rac1 activity and cell death. The sum of the results suggests that traumatic noise induces transient cellular ATP depletion and activates Rho GTPase pathways, leading to death of outer hair cells in the cochlea.

Augmented generation of protein fragments during wakefulness as the molecular cause of sleep: a hypothesis

Despite extensive understanding of sleep regulation, the molecular-level cause and function of sleep are unknown. I suggest that they originate in individual neurons and stem from increased production of protein fragments during wakefulness. These fragments are transient parts of protein complexes in which the fragments were generated. Neuronal Ca²⁺ fluxes are higher during wakefulness than during sleep. Subunits of transmembrane channels and other proteins are cleaved by Ca²⁺-activated calpains and by other nonprocessive proteases, including caspases and secretases. In the proposed concept, termed the fragment generation (FG) hypothesis, sleep is a state during which the production of fragments is decreased (owing to lower Ca²⁺ transients) while fragment-destroying pathways are upregulated. These changes facilitate the elimination of fragments and the remodeling of protein complexes in which the fragments resided. The FG hypothesis posits that a proteolytic cleavage, which produces two fragments, can have both deleterious effects and fitness-increasing functions. This (previously not considered) dichotomy can explain both the conservation of cleavage sites in proteins and the evolutionary persistence of sleep, because sleep would counteract deleterious aspects of protein fragments. The FG hypothesis leads to new explanations of sleep phenomena, including a longer sleep after sleep deprivation. Studies in the 1970s showed that ethanol-induced sleep in mice can be strikingly prolonged by intracerebroventricular injections of either Ca²⁺ alone or Ca²⁺ and its ionophore (Erickson et al., Science 1978;199:1219-1221; Harris, Pharmacol Biochem Behav 1979;10:527-534; Erickson et al., Pharmacol Biochem Behav 1980;12:651-656). These results, which were never interpreted in connection to protein fragments or the function of sleep, may be accounted for by the FG hypothesis about molecular causation of sleep.

Dopamine D1 receptors regulate type 1 inositol 1,4,5-trisphosphate receptor expression via both AP-1- and NFATc4-mediated transcriptional processes

Although our recent report demonstrates the essential involvement of up-regulation of a regulator of intracellular Ca(2+) concentration, type 1 inositol 1,4,5-trisphosphate receptors (IP(3) Rs-1), mediated via dopamine D1-like receptor (D1DR) stimulation in the cocaine-induced psychological dependence, the exact mechanisms of regulation of IP(3) R-1 expression by D1DRs have not yet been clarified. This study attempted to clarify these mechanisms using mouse cerebral cortical neurons. An agonist for phosphatidylinositide-linked D1DRs, SKF83959, induced dose- and time-dependently IP(3) R-1 protein up-regulation following its mRNA increase without cAMP production. U73122 (a phospholipase C inhibitor), BAPTA-AM (an intracellular calcium chelating reagent), W7 (a calmodulin inhibitor), KN-93 (a calmodulin-dependent protein kinases inhibitor), and FK506 (a calcineurin inhibitor), significantly inhibited the SKF83959-induced IP(3) R-1 up-regulation. Furthermore, immunohistochemical examinations showed that SKF83959 increased expression of both cFos and cJun in nucleus as well as enhanced translocation of both calcineurin and NFATc4 complex to nucleus from cytoplasm. In addition, SKF83959 directly recruited binding of both AP-1 and NFATc4 to IP(3) R-1 promoter region. These results indicate that D1DR activation induces IP(3) R-1 up-regulation via increased translocation of AP-1 as well as NFATc4 in Gαq protein-coupled calcium signaling transduction pathway.

Prunella vulgaris aqueous extract attenuates IL-1β-induced apoptosis and NF-κB activation in INS-1 cells

We previously reported that Prunella vulgaris aqueous extract (PVAE) promotes hepatic glycogen synthesis and decreases postprandial hyperglycemia in ICR mice. Inflammatory cytokines play a critical role in the pathogenesis of diabetes. This study was designed to examine whether PVAE has a protective effect on IL-1β-induced apoptosis in INS-1 cells. INS-1 pancreatic β cells were plated at 2×10(6)/ml and treated with PVAE (100 µg/ml) 30 min before the cells were challenged with IL-1β (10 ng/ml). Untreated INS-1 cells served as control. INS-1 cell cytotoxicity was examined by MTT and lactate dehydrogenase (LDH) activity assays. Caspase-3 activity and activation of the apoptotic signaling pathway were analyzed by western blotting. NF-κB binding activity was examined by EMSA. The levels of inflammatory cytokines in the supernatant were measured by ELISA. IL-1β treatment significantly induced INS-1 cell death by 49.2%, increased LDH activity by 1.5-fold and caspase-3 activity by 7.6-fold, respectively, compared with control cells. However, PVAE administration significantly prevented IL-1β-increased INS-1 cell death and LDH activity and attenuated IL-1β-increased caspase-3 activity. Western blot data showed that PVAE also significantly attenuated IL-1β-increased Fas, FasL and phospho-JNK levels in the INS-1 cells. In addition, PVAE treatment significantly attenuated IL-1β-increased NF-κB binding activity and prevented IL-1β-increased TNF-α and IL-6 expression in INS-1 cells. Our data suggest that PVAE has a protective effect on IL-1β-induced INS-1 cell apoptosis. PVAE also attenuates IL-1β-increased NF-κB binding activity and inflammatory cytokine expression in INS-1 cells. PVAE may have a benefit for type I diabetic patients.

The central role of calcium in the effects of cytokines on beta-cell function: implications for type 1 and type 2 diabetes

The appropriate regulation of intracellular calcium is a requirement for proper cell function and survival. This review focuses on the effects of proinflammatory cytokines on calcium regulation in the insulin-producing pancreatic beta-cell and how normal stimulus-secretion coupling, organelle function, and overall beta-cell viability are impacted. Proinflammatory cytokines are increasingly thought to contribute to beta-cell dysfunction not only in type 1 diabetes (T1D), but also in the progression of type 2 diabetes (T2D). Cytokine-induced disruptions in calcium handling result in reduced insulin release in response to glucose stimulation. Cytokines can alter intracellular calcium levels by depleting calcium from the endoplasmic reticulum (ER) and by increasing calcium influx from the extracellular space. Depleting ER calcium leads to protein misfolding and activation of the ER stress response. Disrupting intracellular calcium may also affect organelles, including the mitochondria and the nucleus. As a chronic condition, cytokine-induced calcium disruptions may lead to beta-cell death in T1D and T2D, although possible protective effects are also discussed. Calcium is thus central to both normal and pathological cell processes. Because the tight regulation of intracellular calcium is crucial to homeostasis, measuring the dynamics of calcium may serve as a good indicator of overall beta-cell function.

Apolipoprotein CIII reduces proinflammatory cytokine-induced apoptosis in rat pancreatic islets via the Akt prosurvival pathway

Apolipoprotein CIII (ApoCIII) is mainly synthesized in the liver and is important for triglyceride metabolism. The plasma concentration of ApoCIII is elevated in patients with type 1 diabetes (T1D), and in vitro ApoCIII causes apoptosis in pancreatic β-cells in the absence of inflammatory stress. Here, we investigated the effects of ApoCIII on function, signaling, and viability in intact rat pancreatic islets exposed to proinflammatory cytokines to model the intraislet inflammatory milieu in T1D. In contrast to earlier observations in mouse β-cells, exposure of rat islets to ApoCIII alone (50 μg/ml) did not cause apoptosis. In the presence of the islet-cytotoxic cytokines IL-1β + interferon-γ, ApoCIII reduced cytokine-mediated islet cell death and impairment of β-cell function. ApoCIII had no effects on mitogen-activated protein kinases (c-Jun N-terminal kinase, p38, and ERK) and had no impact on IL-1β-induced c-Jun N-terminal kinase activation. However, ApoCIII augmented cytokine-mediated nitric oxide (NO) production and inducible NO synthase expression. Further, ApoCIII caused degradation of the nuclear factor κB-inhibitor inhibitor of κB and stimulated Ser473-phosphorylation of the survival serine-threonine kinase Akt. Inhibition of the Akt signaling pathway by the phosphatidylinositol 3 kinase inhibitor LY294002 counteracted the antiapoptotic effect of ApoCIII on cytokine-induced apoptosis. We conclude that ApoCIII in the presence of T1D-relevant proinflammatory cytokines reduces rat pancreatic islet cell apoptosis via Akt.

Neutralizing interleukin-1beta (IL-1beta) induces beta-cell survival by maintaining PDX1 protein nuclear localization

The transcription factor PDX1 plays a critical role during β-cell development and in glucose-induced insulin gene transcription in adult β-cells. Acute glucose exposure leads to translocalization of PDX1 to the nucleoplasm, whereas under conditions of oxidative stress, PDX1 shuttles from the nucleus to the cytosol. Here we show that cytosolic PDX1 expression correlated with β-cell failure in diabetes. In isolated islets from patients with type 2 diabetes and from diabetic mice, we found opposite regulation of insulin and PDX1 mRNA; insulin was decreased in diabetes, but PDX1 was increased. This suggests that elevated PDX1 mRNA levels may be insufficient to regulate insulin. In diabetic islets, PDX1 protein was localized in the cytosol, whereas in non-diabetic controls, PDX1 was in the nucleus. In contrast, overexpression of either IL-1 receptor antagonist or shuttling-deficient PDX1 restored β-cell survival and function and PDX1 nuclear localization. Our results show that nuclear localization of PDX1 is essential for a functional β-cell and provides a novel mechanism of the protective effect of IL-1 receptor antagonist on β-cell survival and function.

Blockade of interleukin 1 in type 1 diabetes mellitus

Interleukin 1 (IL-1) is a 17 kDa protein highly conserved through evolution and is a key mediator of inflammation, fever and the acute-phase response. IL-1 has important functions in the innate immune defense against microbes, trauma and stress, and is also an effector molecule involved in tissue destruction and fibrosis. The inhibition of IL-1 action has clinical efficacy in many inflammatory diseases, such as hereditary autoinflammatory disorders, familial hereditary fever, gout, rheumatoid arthritis and type 2 diabetes mellitus (T2DM). The latter is a common metabolic condition caused by insulin resistance and pancreatic beta-cell failure, the causes of both of which have inflammatory components. IL-1 signaling has roles in beta-cell dysfunction and destruction via the NFkappaB and mitogen-activated-protein-kinase pathways, leading to endoplasmic reticulum and mitochondrial stress and eventually activating the apoptotic machinery. In addition, IL-1 acts on T-lymphocyte regulation. The modulating effect of IL-1 on the interaction between the innate and adaptive immune systems and the effects of IL-1 on the beta-cell point to this molecule being a potential interventional target in autoimmune diabetes mellitus. Genetic or pharmacological abrogation of IL-1 action reduces disease incidence in animal models of type 1 diabetes mellitus (T1DM) and clinical trials have been started to study the feasibility, safety and efficacy of IL-1 therapy in patients with T1DM. Here, we review the rationale for blocking IL-1 in patients with T1DM.

Calcium/calmodulin-dependent protein kinase II links ER stress with Fas and mitochondrial apoptosis pathways

ER stress-induced apoptosis is implicated in various pathological conditions, but the mechanisms linking ER stress-mediated signaling to downstream apoptotic pathways remain unclear. Using human and mouse cell culture and in vivo mouse models of ER stress-induced apoptosis, we have shown that cytosolic calcium resulting from ER stress induces expression of the Fas death receptor through a pathway involving calcium/calmodulin-dependent protein kinase IIgamma (CaMKIIgamma) and JNK. Remarkably, CaMKIIgamma was also responsible for processes involved in mitochondrial-dependent apoptosis, including release of mitochondrial cytochrome c and loss of mitochondrial membrane potential. CaMKII-dependent apoptosis was also observed in a number of cultured human and mouse cells relevant to ER stress-induced pathology, including cultured macrophages, endothelial cells, and neuronal cells subjected to proapoptotic ER stress. Moreover, WT mice subjected to systemic ER stress showed evidence of macrophage mitochondrial dysfunction and apoptosis, renal epithelial cell apoptosis, and renal dysfunction, and these effects were markedly reduced in CaMKIIgamma-deficient mice. These data support an integrated model in which CaMKII serves as a unifying link between ER stress and the Fas and mitochondrial apoptotic pathways. Our study also revealed what we believe to be a novel proapoptotic function for CaMKII, namely, promotion of mitochondrial calcium uptake. These findings raise the possibility that CaMKII inhibitors could be useful in preventing apoptosis in pathological settings involving ER stress-induced apoptosis.

Inhibition of nuclear factor-kappaB or Bax prevents endoplasmic reticulum stress- but not nitric oxide-mediated apoptosis in INS-1E cells

Accumulating evidence suggests that endoplasmic reticulum (ER) stress by mechanisms that include ER Ca(2+) depletion via NO-dependent down-regulation of sarcoendoplasmic reticulum Ca(2+) ATPase 2b (SERCA2b) contributes to beta-cell death in type 1 diabetes. To clarify whether the molecular pathways elicited by NO and ER Ca(2+) depletion differ, we here compare the direct effects of NO, in the form of the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP), with the effects of SERCA2 inhibitor thapsigargin (TG) on MAPK, nuclear factor kappaB (NFkappaB), Bcl-2 proteins, ER stress, and apoptosis. Exposure of INS-1E cells to TG or SNAP caused caspase-3 cleavage and apoptosis. Both TG and SNAP induced activation of the proapoptotic transcription factor CCAAT/enhancer-binding protein homologous protein (CHOP). However, other classical ER stress-induced markers such as up-regulation of ER chaperone Bip and alternative splicing of the transcription factor Xbp-1 were exclusively activated by TG. TG exposure caused NFkappaB activation, as assessed by IkappaB degradation and NFkappaB DNA binding. Inhibition of NFkappaB or the Bcl-2 family member Bax pathways protected beta-cells against TG- but not SNAP-induced beta-cell death. These data suggest that NO generation and direct SERCA2 inhibition cause two quantitative and qualitative different forms of ER stress. In contrast to NO, direct ER stress induced by SERCA inhibition causes activation of ER stress signaling pathways and elicit proapoptotic signaling via NFkappaB and Bax.

Cytokines and beta-cell biology: from concept to clinical translation

The tale of cytokines and the beta-cell is a long story, starting with in vitro discovery in 1984, evolving via descriptive and phenomenological studies to detailed mapping of the signalling pathways, gene- and protein expression patterns, molecular and biochemical effector mechanisms to in vivo studies in spontaneously diabetic and transgenic animal models. Only very recently have steps been taken to translate the accumulating compelling preclinical data into clinical trials. The aim of this chapter is to present an overview of early and recent key observations from our own groups as well as other laboratories that serve to illuminate the road from concept to clinical translation.

Glucose and leptin induce apoptosis in human beta-cells and impair glucose-stimulated insulin secretion through activation of c-Jun N-terminal kinases

c-Jun N-terminal kinases (SAPK/JNKs) are activated by inflammatory cytokines, and JNK signaling is involved in insulin resistance and beta-cell secretory function and survival. Chronic high glucose concentrations and leptin induce interleukin-1beta (IL-1beta) secretion from pancreatic islets, an event that is possibly causal in promoting beta-cell dysfunction and death. The present study provides evidence that chronically elevated concentrations of leptin and glucose induce beta-cell apoptosis through activation of the JNK pathway in human islets and in insulinoma (INS 832/13) cells. JNK inhibition by the dominant inhibitor JNK-binding domain of IB1/JIP-1 (JNKi) reduced JNK activity and apoptosis induced by leptin and glucose. Exposure of human islets to leptin and high glucose concentrations leads to a decrease of glucose-induced insulin secretion, which was partly restored by JNKi. We detected an interplay between the JNK cascade and the caspase 1/IL-1beta-converting enzyme in human islets. The caspase 1 gene, which contains a potential activating protein-1 binding site, was up-regulated in pancreatic sections and in isolated islets from type 2 diabetic patients. Similarly, cultured human islets exposed to high glucose- and leptin-induced caspase 1 and JNK inhibition prevented this up-regulation. Therefore, JNK inhibition may protect beta-cells from the deleterious effects of high glucose and leptin in diabetes.

Animal models to test drugs with potential antidiabetic activity

Although medicinal plants have been historically used for diabetes treatment throughout the world, few of them have been validated by scientific criteria. Recently, a large diversity of animal models has been developed to better understand the pathogenesis of diabetes mellitus and new drugs have been introduced in the market to treat this disease. The aim of this work was to review the available animal models of diabetes and some in vitro models which have been used as tools to investigate the mechanism of action of drugs with potential antidiabetic properties. In addition, a MEDLINE/PUBMED search for articles on natural products, pancreatectomy and diabetes mellitus treatment published between 1996 and 2006 was done. In the majority of the studies, natural products mainly derived from plants have been tested in diabetes models induced by chemical agents. This review contributes to the researcher in the ethnopharmacology field to designs new strategies for the development of novel drugs to treat this serious condition that constitutes a global public health.

Mitochondrial dysfunction induces aberrant insulin signalling and glucose utilisation in murine C2C12 myotube cells

AIMS/HYPOTHESIS

Mitochondrial dysfunction is considered a critical component in the development of diabetes. The aim of this study was to elucidate the molecular mechanisms involved in the development of insulin resistance and diabetes through investigation of mitochondrial retrograde signalling.

MATERIALS AND METHODS

Mitochondrial function of C2C12 myotube cells was impaired by genetic (ethidium bromide) and metabolic (oligomycin) stress, and changes in target molecules related to insulin signalling were analysed.

RESULTS

Concomitant with reductions in mitochondrial membrane potential (DeltaPsim) and ATP synthesis, production of IRS1 and solute carrier family 2 (facilitated glucose transporter), member 4 (SLC2A4, formerly known as GLUT4) were reduced. Moreover, serine phosphorylation of IRS1 increased, resulting in decreased tyrosine phosphorylation. This indicates that mitochondrial dysfunction decreases insulin-stimulated SLC2A4 translocation and glucose uptake. Mitochondrial stress activated c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) signalling in a Ca(2+)-dependent manner, and removal of free Ca(2+) by BAPTA-AM, as well as inhibition of JNK and p38 MAPK, abrogated mitochondrial stress-induced reductions in IRS1 and SLC2A4 production. Mitochondrial dysfunction after oligomycin treatment significantly increased levels of activating transcription factor 3 (ATF3), which represses Irs1 promoter activity. Removal of the 5' flanking region of Irs1 demonstrated that the promoter region within 191 bases from the transcription site may be involved in the transcriptional repression of Irs1 by mitochondrial stress.

CONCLUSIONS/INTERPRETATION

We show distinct mitochondrial retrograde signalling, where Irs1 is downregulated through ATF3 in a Ca(2+)-, JNK- and p38 MAPK-dependent manner, and IRS1 is inactivated. Therefore, mitochondrial dysfunction causes aberrant insulin signalling and abnormal utilisation of glucose, as observed in many insulin resistance states.

IL-1beta-induced pro-apoptotic signalling is facilitated by NCAM/FGF receptor signalling and inhibited by the C3d ligand in the INS-1E rat beta cell line

AIMS/HYPOTHESIS

IL-1beta released from immune cells induces beta cell pro-apoptotic signalling via mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB). In neurons, the neural cell adhesion molecule (NCAM) signals to several elements involved in IL-1beta-induced pro-apoptotic signalling in beta cells. Pancreatic beta cells express NCAM, but its biological effects in these cells are unclear. The aim of this study was to investigate whether there is cross-talk between NCAM signalling and cytokine-induced pro-apoptotic signalling.

MATERIALS AND METHODS

Western blotting was used to investigate levels of NCAM and inducible nitric oxide synthase, phosphorylation of Src and MAPKs, and cleavage of caspase-3. MAPK activity was investigated with an in vitro kinase assay. Apoptosis was detected by cleaved caspase-3 and a Cell Death Detection ELISA(plus) assay. NCAM-induced fibroblast growth factor receptor (FGFR) activation was investigated in NCAM(-/-) Trex293 cells where FGFR phosphorylation was measured by Western blotting after NCAM transfection.

RESULTS

Pre-exposure of INS-1E cells to the FGFR-inhibitor SU5402, but not to the Src-inhibitor PP2, dose-dependently inhibited IL-1beta-mediated MAPK activity. A synthetic peptide, C3d, reported to bind NCAM, did not activate MAPK or Akt as reported in neurons but inhibited IL-1beta-induced MAPK activity, thereby mimicking the effect of SU5402. Furthermore, C3d inhibited NCAM-induced FGFR phosphorylation and apoptosis induced by IL-1beta plus IFN-gamma, but did not affect IL-1beta-induced NF-kappaB signalling.

CONCLUSIONS/INTERPRETATION

We suggest that NCAM signalling through FGFR is required for efficient IL-1beta pro-apoptotic signalling by facilitating IL-1beta-induced MAPK activation downstream of the NF-kappaB-MAPK branching point. Further, these data identify a novel function of C3d as an inhibitor of NCAM-induced FGFR activity and of IL-1beta-induced MAPK activation in beta cells.

RX871024 reduces NO production but does not protect against pancreatic beta-cell death induced by proinflammatory cytokines

The imidazoline compound RX871024 reduces IL-1beta-induced NO production thereby protecting against IL-1beta-induced beta-cell apoptosis. The aim of this study was to evaluate whether imidazolines RX871024 and efaroxan protect beta-cells against death in the presence of a combination of the cytokines IL-1beta, IFNgamma, and TNFalpha. To address this issue, experiments involving different methods for detection of cell death, different concentrations of the cytokines, and a variety of conditions of preparation and culturing of ob/ob mouse islets and beta-cells have been carried out. Thoroughly performed experiments have not been able to demonstrate a protective effect of RX871024 and efaroxan on beta-cell death induced by the combination of cytokines. However, the inhibitory effect of RX871024 on NO production in ob/ob mouse islets and beta-cells was still observed in the presence of all three cytokines and correlated with the decrease in p38 MAPK phosphorylation. Conversely, efaroxan did not affect cytokine-induced NO production. Our data indicate that a combination of pro-inflammatory cytokines IL-1beta, IFNgamma, and TNFalpha, conditions modelling those that take place in type 1 diabetes, induces pancreatic beta-cell death that does not directly correlate with NO production and cannot be counteracted with imidazoline compounds.

Involvement of calcium-mediated apoptotic signals in H2O2-induced MIN6N8a cell death

Reactive oxygen species are believed to be the central mediators of beta-cell destruction that leads to type 1 and 2 diabetes, and calcium has been reported to be an important mediator of beta cell death. In the present study, the authors investigated whether Ca(2+) plays a role in hydrogen peroxide (H(2)O(2))-induced MIN6N8a mouse beta cell death. Treatment with low concentration H(2)O(2) (50 microM) was found to be sufficient to reduce MIN6N8a cell viability by 55%, largely via apoptosis. However, this H(2)O(2)-induced cell death was near completely blocked by pretreatment with BAPTA/AM (5 microM), a chelator of intracellular Ca(2+). Moreover, the intracellular calcium store channel blockers, such as, xestospongin c and ryanodine, significant protected cells from 50 microM H(2)O(2)-induced cell death and under extracellular Ca(2+)-free conditions, 50 microM H(2)O(2) elicited transient [Ca(2+)](i) increases. In addition, pharmacologic inhibitors of calpain, calcineurin, and calcium/calmodulin-dependent protein kinase II were found to have a protective effect on H(2)O(2)-induced death. Moreover, H(2)O(2)-induced apoptotic signals, such as c-JUN N-terminal kinase activation, cytochrome c release, caspase 3 activation, and poly (ADP-ribose) polymerase cleavage were all down-regulated by the intracellular Ca(2+) chelation. These findings show that [Ca(2+)](i) elevation, possibly due to release from intracellular calcium stores and the subsequent activation of Ca(2+)-mediated apoptotic signals, critically mediates low concentration H(2)O(2)-induced MIN6N8a cell death. These findings suggest that a breakdown of calcium homeostasis by low level of reactive oxygen species may be involved in beta cell destruction during diabetes development.

The -822G/A polymorphism in the promoter region of the MAP4K5 gene is associated with reduced risk of type 2 diabetes in Chinese Hans from Shanghai

MAP4K5 (mitogen-activated protein kinase kinase kinase kinase 5), an early component of MAP kinase signal cascades was shown to activate Jun kinase in mammalian cells. The association between SNPs of MAP4K5 and type 2 diabetes (T2DM) was investigated due to the known relationship of the JNK pathway with T2DM. A total of 1,399 cases were included in the study. Oral glucose tolerance test (OGTT) and insulin release test (IRT) were performed, and blood DNA samples were extracted and genotyped on the MAP4K5 -822G/A site. These cases were subdivided into central-obesity and nonobesity groups, based upon their individual waist circumference. Allele-specific real-time PCR was employed for genotyping. No difference was found between the two groups in the distribution of three genotypes on MAP4K5 -822G/A. In the central-obesity group, fewer diabetic patients (38.9%) were present in the AA genotype group than the GG/GA group (58.5%, P=0.024). Glucose levels after 30 and 60 min of 75 g glucose tolerance, area under the curve for glucose, and insulin secretion indexes were lower (P<0.05) in AA than those in GG/GA genotype group in the central-obesity cases. Other variables did not show significant differences between the two groups. In the Han population from Shanghai, the AA genotype of MAP4K5 -822G/A in central-obesity cases appears less likely to develop diabetes compared with the other genotypes. Therefore, the G allele may be a factor that does not protect central-obesity cases from developing into diabetes.

Growth arrest- and DNA-damage-inducible 45beta gene inhibits c-Jun N-terminal kinase and extracellular signal-regulated kinase and decreases IL-1beta-induced apoptosis in insulin-producing INS-1E cells

AIMS/HYPOTHESIS

IL-1beta is a candidate mediator of apoptotic beta cell destruction, a process that leads to type 1 diabetes and progression of type 2 diabetes. IL-1beta activates beta cell c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK) and p38, all of which are members of the mitogen-activated protein kinase (MAPK) family. Inhibition of JNK prevents IL-1beta-mediated beta cell destruction. In mouse embryo fibroblasts and 3DO T cells, overexpression of the gene encoding growth arrest and DNA-damage-inducible 45beta (Gadd45b) downregulates pro-apoptotic JNK signalling. The aim of this study was to investigate if Gadd45b prevents IL-1beta-induced beta cell MAPK signalling and apoptosis.

MATERIALS

Rat insulinoma INS-1E cells and mouse beta-TC3 cells stably expressing Gadd45b were generated. The effects of Gadd45b expression on signalling by JNK, ERK and p38 were assessed by Western blotting and kinase assays. Apoptosis rate was measured by terminal deoxynucleotidyl-mediated dUTP-biotin nick end-labelling (TUNEL) and an ELISA designed to detect apoptotic nucleosomes. Expression of endogenous Gadd45b mRNA was measured by RT-PCR.

RESULTS

In INS-1E and beta-TC3 cells, expression of Gadd45b inhibited IL-1beta-induced activation of JNK and ERK, but augmented IL-1beta-mediated p38 activity. IL-1beta-induced nitric oxide production and decreases in insulin content and secretion were reduced by GADD45beta. IL-1beta-induced apoptosis was reduced by GADD45beta by up to 77%. Although IL-1beta stimulated the time-dependent induction of endogenous Gadd45b in INS-1E cells and rat islets, expression levels were lower in these cells than in IL-1beta-exposed NIH-3T3 and 3DO T cells.

CONCLUSIONS/INTERPRETATION

Inadequate induction of Gadd45b, which encodes a novel beta cell JNK and ERK inhibitor, may in part explain the pro-apoptotic response of beta cells to IL-1beta.