Essential role of caspase-3 in apoptosis of mouse beta-cells transfected with human Fas

Urolithin A, a pomegranate metabolite, protects pancreatic β cells from apoptosis by activating autophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Urolithin A is an active metabolite of plant polyphenol ellagic acid generated by intestinal flora, which is derived from strawberry or traditional anti-diabetic Chinese medicine such as Punica granatum L. and Phyllanthus emblica. The present study aimed to whether urolithin A can protect against glycolipid-toxicity-induced apoptosis of pancreatic β-cells and the underlying mechanisms.

MATERIALS AND METHODS

Apoptosis was induced in the pancreas of mice with type 2 diabetes and MIN6 pancreatic β-cells. CC-8 assay was conducted to determine cell viability. Flow cytometry, JC-1 fluorescent probe, and western blot assays were performed to assess apoptosis. Immunofluorescence and western blot assays were used to detect changes in autophagy. The mechanism of apoptosis was elucidated using autophagy inhibitor chloroquine.

RESULTS

Urolithin A intervention significantly reduced pancreatic cell apoptosis in diabetic mice and MIN6 β cells. This was achieved by the downregulation of cleaved-caspase 3, cleaved-caspase 1, and restoration of cell viability, cell morphology and mitochondrial membrane potential, accompanied with the downregulation of autophagic protein SQSTM1/p62 and upregulation of LC3II. Chloroquine, an autophagy inhibitor, reversed the anti-glucolipotoxic and anti-apoptotic effects of urolithin A.

CONCLUSION

These findings suggest that urolithin A protects against glucolipotoxicity-induced apoptosis in pancreatic β-cells by inducing activation of autophagy.

Evidence for Polyamine, Biogenic Amine, and Amino Acid Adduction Resulting from Metabolic Activation of Diosbulbin B

Dioscorea bulbifera L. (DBL), a traditional Chinese medicine, is a well-known herb with hepatotoxicity, and the biochemical mechanisms of the toxic action remain unknown. Diosbulbin B (DSB), a major component of DBL, can induce severer liver injury which requires cytochrome P450-catalyzed oxidation of the furan ring. It is reported that a cis-enedial reactive intermediate resulting from metabolic activation of DSB can react with thiols and amines to form pyrrole or pyrroline derivatives. In this study, we investigated the interaction of the reactive intermediate with polyamines, biogenic amines, and amino acids involved in the polyamine metabolic pathway, including putrescine, spermidine, spermine, histamine, arginine, ornithine, lysine, glutamine, and asparagine. Seven DSB-derived amine adducts were detected in microsomal incubations supplemented with DSB and individual amines. Six adducts were observed in cultured rat primary hepatocytes after exposure to DSB. DSB was found to induce apoptosis and cell death in time- and concentration-dependent manners. Apparently, the observed apoptosis was associated with the detected amine adduction. The findings facilitate the understanding of the mechanisms of toxic action of DSB.

Biphasic changes in β-cell mass around parturition are accompanied by increased serotonin production

Pancreatic β-cell mass is known to be considerably altered during pregnancy and after parturition in rodents and humans. While β-cell mass increases during pregnancy and starts to return toward its original level after parturition, the cellular mechanisms by which β-cell mass during this period is regulated remains unclear. To address this issue in mice, we quantified β-cell mass and investigated the mechanisms underlying its regulation throughout the perinatal and postpartum period. The increased β-cell size and proliferation during pregnancy were significantly reduced shortly after parturition, whereas there was no evidence of β-cell reprogramming or increased apoptosis. Direct RNA sequencing of islets from pregnant and postpartum mice demonstrated dynamic changes in gene expression patterns, showing robust downregulation of cell cycle-related genes 1 day after parturition, and the reupregulation of serotonin metabolism-related genes at postpartum day 7. Serotonin synthesis was activated only in lactating females, accompanied by increased β-cell mass. Taken together, these findings demonstrate that β-cell mass is decreased shortly after parturition owing to reduced β-cell size and proliferation, and is subsequently increased, in association with lactation and serotonin biosynthesis.

Hyperthermic Preconditioning Protects Pig Islet Grafts from Early Inflammation but Enhances Rejection in Immunocompetent Mice

The induction of heat shock proteins (HSP) protects isolated islet cells against the cytotoxicity of inflammatory mediators in vitro. Very little information is available about the effect of HSP overexpression on function of preconditioned islet grafts. The present study investigated the function of heat-exposed pig islets after transplantation into immunocompetent mice in comparison with in vitro resistance against inflammatory mediators. Pig islets were preconditioned at 43°C or sham treated prior to subcapsular transplantation into diabetic C57/Bl6j mice. Nondiabetic mice simultaneously receiving preconditioned and control islets were subjected to bilateral nephrectomy for determination of pig insulin. Resistance against H2O2, NO, human Il-1β, IFN-γ, or TNF-α was assessed by trypan blue exclusion and insulin determination. Heat-induced protein expression was confirmed by Western blot analysis. Graft preconditioning increased resistance against H2O2, NO, or cytokines (p < 0.05) but decreased survival in nondiabetic mice (p < 0.05) and function in diabetic mice (p < 0.01). Upregulation of caspase-3 activity as well as Bax, Fas, FasL, and DFF expression (p < 0.05) indicated simultaneous induction of apoptosis. The coexpression of HSP and proapoptotic proteins reveals the dual character of the stress response simultaneously starting mechanisms for protection and apoptosis. In vitro assays seem to reflect only insufficiently the situation of islets after transplantation.

Short-Term Culture with the Caspase Inhibitor z-VAD.fmk Reduces Beta Cell Apoptosis in Transplanted Islets and Improves the Metabolic Outcome of the Graft

In the initial days after transplantation islets are particularly vulnerable and show increased apoptosis and necrosis. We have studied the effects of caspase inhibition on this early beta cell death in syngeneically transplanted islets. Streptozotocin-diabetic C57BL/6 mice were transplanted with 150 syngeneic islets, an insufficient mass to restore normoglycemia, preincubated with or without the pan-caspase inhibitor z-VAD. fmk 2 h before transplantation. Beta cell apoptosis was increased in control islets on day 3 after transplantation (0.28 ± 0.02%) compared with freshly isolated islets (0.08 ± 0.02%, p< 0.001), and was partially reduced in transplanted islets preincubated with z-VAD.fmk 200 μM (0.14 ± 0.02%, p = 0.003) or with z-VAD.fmk 500 μM (0.17 ± 0.01%, p = 0.012), but not with a lower z-VAD.fmk (100 μM) concentration. Diabetic mice transplanted with islets preincubated with z-VAD.fmk 500 μM showed an improved metabolic evolution compared with control and z-VAD.fmk 200 μM groups. The z-VAD.fmk 500 μM group showed an overall lower blood glucose after transplantation (p = 0.02), and at the end of the study blood glucose values were reduced compared with transplantation day (15.7 ± 3.6 vs. 32.5 ± 0.5 mmol/L, p = 0.001). In contrast, blood glucose was not significantly changed in control and z-VAD.fmk 200 μM groups. Four weeks after transplantation beta cell mass was higher in z-VAD.fmk 500 μM group (0.15 ± 0.02 mg) than in the control group (0.10 ± 0.02 mg) (p = 0.043). In summary, the treatment of freshly isolated islets with the caspase inhibitor z-VAD.fmk reduced the subsequent apoptosis of the islets once they were transplanted and improved the outcome of the graft.

An optimized protocol for purification of functional islets of Langerhans

Islets of Langerhans and β-cell isolation constitute routinely used cell models for diabetic research, and refining islet isolation protocols and cell quality assessment is a high priority. Numerous protocols have been published describing isolate of islets, but often rigorous and systematic assessment of their integrity is lacking. Herein, we propose a new protocol for optimal generation of islets. Pancreases from mice and rats were excised and digested using a low-activity collagenase solution and islets were then purified by a series of sedimentations and a Percoll gradient. Islets were maintained in culture for 5 days, during which viability, pro/antiapoptotic, and islet-specific genes, glucose-stimulated calcium entry, glucose uptake, and insulin secretion were assessed. The commonly used islet isolation technique by collagenase injection through the common bile duct (CBD) was also performed and compared with the present approach. This new protocol produced islets that retained a healthy status as demonstrated by the yield of stable living cells. Furthermore, calcium oscillation, glucose uptake, and insulin secretion remained intact in the islet cultures. This was reproducible when many rodent species were used, and neither sex nor age affected the cells behavior. When compared with the CBD technique, islet physiology was similar. Finally, this approach was used to uncover new ion channel candidates implicated in insulin secretion. In conclusion, this study outlines an efficient protocol for islet preparation that may support research into new therapeutic targets in diabetes research.

Glucotoxic and diabetic conditions induce caspase 6-mediated degradation of nuclear lamin A in human islets, rodent islets and INS-1 832/13 cells

Nuclear lamins form the lamina on the interior surface of the nuclear envelope, and regulate nuclear metabolic events, including DNA replication and organization of chromatin. The current study is aimed at understanding the role of executioner caspase 6 on lamin A integrity in islet β-cells under duress of glucotoxic (20 mM glucose; 24 h) and diabetic conditions. Under glucotoxic conditions, glucose-stimulated insulin secretion and metabolic cell viability were significantly attenuated in INS-1 832/13 cells. Further, exposure of normal human islets, rat islets and INS-1 832/13 cells to glucotoxic conditions leads to caspase 6 activation and lamin A degradation, which is also observed in islets from the Zucker diabetic fatty rat, a model for type 2 diabetes (T2D), and in islets from a human donor with T2D. Z-Val-Glu-Ile-Asp-fluoromethylketone, a specific inhibitor of caspase 6, markedly attenuated high glucose-induced caspase 6 activation and lamin A degradation, confirming that caspase 6 mediates lamin A degradation under high glucose exposure conditions. Moreover, Z-Asp-Glu-Val-Asp-fluoromethylketone, a known caspase 3 inhibitor, significantly inhibited high glucose-induced caspase 6 activation and lamin A degradation, suggesting that activation of caspase 3 might be upstream to caspase 6 activation in the islet β-cell under glucotoxic conditions. Lastly, we report expression of ZMPSTE24, a zinc metallopeptidase involved in the processing of prelamin A to mature lamin A, in INS-1 832/13 cells and human islets; was unaffected by high glucose. We conclude that caspases 3 and 6 could contribute to alterations in the integrity of nuclear lamins leading to metabolic dysregulation and failure of the islet β-cell.

The protective effects and genetic pathways of thorn grape seeds oil against high glucose-induced apoptosis in pancreatic β-cells

Background

Excessive apoptosis of β-cell is closely related to diabetes mellitus. Chronic exposure to high glucose causes β-cell dysfunction and apoptosis in diabetes. Thorn grape (Vitis davidii Foex.) has been used to treat diabetes in Traditional Chinese medicine for many years. In our previous research, thorn grape seeds oil (TGSO) showed promising anti-diabetic effects in animal models. However, it is unknown whether TGSO played an anti-apoptotic role in the anti-diabetic effects and the mechanism regarding signal transduction pathway is unclear either.

Methods

The rattus pancreatic β-cell line RIN-m5F was treated with/without TGSO which was extracted by supercritical carbon dioxide (CO₂) fluid extraction and analyzed by Gas Chromatography/Mass Spectrometry (GC/MS). Cell apoptosis was detected by fluorescence activated cell sorting (FACS), insulin secretion was assayed by Enzyme-Linked Immunosorbent Assay (ELISA), and the apoptosis-related genes expressions were evaluated by quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR).

Results

TGSO, containing 87.02% unsaturated fatty acids (UFAs), significantly reduced pancreatic β-cell apoptosis and protected the insulin secretion impaired by high glucose. The expressions of pro-apoptotic genes such as iNOS, Caspase-3, ATF-3, JNK, p38 and Fas were down-regulated while the anti-apoptotic genes Akt and Bcl-2/Bax were up-regulated.

Conclusions

The results indicated that TGSO protected β-cells from high glucose-induced apoptosis and its protective activity may be linked to mitochondrial pathway, endoplasmic reticulum (ER) stress pathway and Fas signal pathway, which implied that TGSO might be an effective complementary or alternative medicine to reduce β-cell apoptosis and dysfunction.

Thiazolidinediones protect mouse pancreatic β-cells directly from cytokine-induced cytotoxicity through PPARγ-dependent mechanisms

Since most of the current studies of thiazolidinediones (TZDs) are only focused on improving glycemic control, increasing insulin sensitivity, and regulating inflammatory states in Type 2 Diabetes, it is still controversial whether TZDs have direct, protective effects on pancreatic β-cells in autoimmune diabetes. Here, we show the protective effects of TZDs on mouse pancreatic β-cell line cells (NIT-1) impaired by exposure to inflammatory cytokines (IL-1β and IFN-γ) and explore the potential mechanisms for this. The apoptosis rate and caspase-3 activity were remarkably increased, and insulin secretion response to glucose was impaired severely by exposure to IL-1β/IFN-γ for 48 h compared to control cells, whereas apoptosis rate and caspase-3 activity were significantly decreased in cells with treatment of rosiglitazone (RGZ) or pioglitazone (PIG), and the capacity for insulin secretion response to glucose was recovered. TZDs protect pancreatic β-cells from cytokine-induced cytotoxicity through PPARγ activation. The protective effects of the TZDs on NIT-1 cells disappeared when PPARγ was blocked with PPARγ-siRNA interference or treatment with GW9662, the PPARγ antagonist. Additionally, the enhancement of PPARγ expression by treatment with TZDs inhibited the expression of caspase 3 in IL-1β/IFN-γ-induced NIT-cells. Also, the inhibition of caspase 3 expression by TZDs was blocked by co-treatment with GW9662 or infection with PPARγ-siRNA. Taken together, our data suggest that TZDs might serve to protect pancreatic β-cells directly from cytokine-induced cytotoxicity through a PPARγ-dependent pathway, and caspase-3 may play an important role in the mechanisms involved.

Thioredoxin-mimetic peptides (TXM) reverse auranofin induced apoptosis and restore insulin secretion in insulinoma cells

The thioredoxin reductase/thioredoxin system (TrxR/Trx1) plays a major role in protecting cells from oxidative stress. Disruption of the TrxR-Trx1 system keeps Trx1 in the oxidized state leading to cell death through activation of the ASK1-Trx1 apoptotic pathway. The potential mechanism and ability of tri- and tetra-oligopeptides derived from the canonical -CxxC- motif of the Trx1-active site to mimic and enhance Trx1 cellular activity was examined. The Trx mimetics peptides (TXM) protected insulinoma INS 832/13 cells from oxidative stress induced by selectively inhibiting TrxR with auranofin (AuF). TXM reversed the AuF-effects preventing apoptosis, and increasing cell-viability. The TXM peptides were effective in inhibiting AuF-induced MAPK, JNK and p38(MAPK) phosphorylation, in correlation with preventing caspase-3 cleavage and thereby PARP-1 dissociation. The ability to form a disulfide-bridge-like conformation was estimated from molecular dynamics simulations. The TXM peptides restored insulin secretion and displayed Trx1 denitrosylase activity. Their potency was 10-100-fold higher than redox reagents like NAC, AD4, or ascorbic acid. Unable to reverse ERK1/2 phosphorylation, TXM-CB3 (NAc-Cys-Pro-Cys amide) appeared to function in part, through inhibiting ASK1-Trx dissociation. These highly effective anti-apoptotic effects of Trx1 mimetic peptides exhibited in INS 832/13 cells could become valuable in treating adverse oxidative-stress related disorders such as diabetes.

Effects of glucagon-like peptide 1 on glycemia control and its metabolic consequence after severe thermal injury--studies in an animal model

BACKGROUND

Hyperglycemia with insulin resistance is commonly seen in severely burned patients and tight glycemia control with insulin may be beneficial in this condition. The most potent insulinotropic hormone, glucagon-like peptide 1 (GLP-1), stimulates insulin secretion in a glucose-dependent manner. Because infusion of GLP-1 never reduces glucose levels to below ∼70 mg/dL, the risk of hypoglycemia by using insulin is reduced. In this study we investigated the metabolic effects of GLP-1 infusion after burn injury in an animal model.

METHODS

Male CD rats were divided in 3 groups: burn injury with saline, burn injury with GLP-1 treatment, and sham burn (SB). Burn injury was full thickness 40% total body surface area. The burn injury with GLP-1 treatment group received GLP-1 infusion via osmotic pump. Fasting blood glucose, plasma insulin, and plasma GLP-1 levels were measured during intraperitoneal glucose tolerance tests. Expressions of caspase 3 and bcl-2 were evaluated in pancreatic islets. In a subset of animals, protein metabolism and total energy expenditure were measured.

RESULTS

Fasting GLP-1 was reduced in burn injury with saline compared to SB or burn injury with GLP-1 treatment. Burn injury with GLP-1 treatment showed reduced fasting blood glucose, improved intraperitoneal glucose tolerance test results, with increased plasma insulin and GLP-1 responses to glucose. GLP-1 reduced protein breakdown and total energy expenditure in burn injury with GLP-1 treatment versus burn injury with saline, with improved protein balance. Increased expression of caspase 3 and decreased expression of bcl-2 in islet cells by burn injury were ameliorated by GLP-1.

CONCLUSION

Burn injury reduced plasma GLP-1 in association with insulin resistance. GLP-1 infusion improved glucose tolerance and showed anabolic effects on protein metabolism and reduced total energy expenditure after burn injury, possibly via insulinotropic and non insulinotropic mechanisms.

UPR induces transient burst of apoptosis in islets of early lactating rats through reduced AKT phosphorylation via ATF4/CHOP stimulation of TRB3 expression

Endocrine pancreas from pregnant rats undergoes several adaptations that comprise increase in β-cell number, mass and insulin secretion, and reduction of apoptosis. Lactogens are the main hormones that account for these changes. Maternal pancreas, however, returns to a nonpregnant state just after the delivery. The precise mechanism by which this reversal occurs is not settled but, in spite of high lactogen levels, a transient increase in apoptosis was already reported as early as the 3rd day of lactation (L3). Our results revealed that maternal islets displayed a transient increase in DNA fragmentation at L3, in parallel with decreased RAC-alpha serine/threonine-protein kinase (AKT) phosphorylation (pAKT), a known prosurvival kinase. Wortmannin completely abolished the prosurvival action of prolactin (PRL) in cultured islets. Decreased pAKT in L3-islets correlated with increased Tribble 3 (TRB3) expression, a pseudokinase inhibitor of AKT. PERK and eIF2α phosphorylation transiently increased in islets from rats at the first day after delivery, followed by an increase in immunoglobulin heavy chain-binding protein (BiP), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP) in islets from L3 rats. Chromatin immunoprecipitation (ChIP) and Re-ChIP experiments further confirmed increased binding of the heterodimer ATF4/CHOP to the TRB3 promoter in L3 islets. Treatment with PBA, a chemical chaperone that inhibits UPR, restored pAKT levels and inhibited the increase in apoptosis found in L3. Moreover, PBA reduced CHOP and TRB3 levels in β-cell from L3 rats. Altogether, our study collects compelling evidence that UPR underlies the physiological and transient increase in β-cell apoptosis after delivery. The UPR is likely to counteract prosurvival actions of PRL by reducing pAKT through ATF4/CHOP-induced TRB3 expression.

Immunocytochemical localisation of caspase-3 in pancreatic islets from type 2 diabetic subjects

AIMS

Caspase-3 has been recognised as a main effector caspase of the apoptotic cascade. Involvement of caspase-3 has been implicated in a beta-cell cloned cell line from type 1 diabetic subjects and in isolated islets from type 2 diabetic subjects. This study aimed to immunocytochemically identify cleaved caspase-3 positive islet cells in type 2 diabetic subjects compared with control subjects.

METHODS

Using commercially available rabbit anti-cleaved caspase-3 antibody, immunocytochemical staining was performed on 16 cases of pancreatic tissues from type 2 diabetic subjects compared with age-matched controls.

RESULTS

Control islets revealed cleaved caspase-3 positive cells in about 4.7% in total islet cells with large and small islets positive at 4.1% and 7.0%, respectively. Islets from type 2 diabetic subjects showed higher immunostaining percentage at 8.7% in total islets with large and small islets positive for cleaved caspase-3 at 7.7% and 12%, respectively, at about twice that of the control values. Islets from type 2 diabetics were generally insulin cell-less and glucagon cell-rich, but insulin cells still remained. Type 2 diabetic islets showed various stromal amyloid deposits, displacing the residual islet cells. Cleaved caspase-3 positive cells were more in the less amyloid deposited islets than in the islet cell deficient islets containing more amyloid deposits; the latter correspond to the end-stage of type 2 diabetic islets.

CONCLUSIONS

The more cleaved caspase-3 immunostained islets from type 2 diabetics may implicate an accelerated apoptotic cascade in the islets, accompanied by increasing amyloid deposits, before proceeding to ultimate cell death.

Executioners of apoptosis in pancreatic {beta}-cells: not just for cell death

Pancreatic beta-cell mass is dynamic and is regulated by beta-cell proliferation, neogenesis, and apoptosis. Under physiological conditions, apoptosis is tightly regulated with a slow, net rise in beta-cell mass over time. Excessive beta-cell apoptosis is an important contributor to both type 1 and type 2 diabetes development. Therefore, much effort has been given recently to better understand the mechanisms of apoptosis that occur both during physiological homeostasis and during the course of both types of diabetes. Caspases are the executioners of apoptosis that ultimately result in cell suicide. In mammals, there are 14 caspases, of which many participate in the apoptotic pathways. Genetic mouse models have been important tools for elucidation of the specific apoptotic pathways that play an essential role in beta-cell apoptosis under physiological and pathological conditions. This review focuses on the diverse roles of each of the specific caspases and their regulators, unveiling both the classical apoptotic roles as well as emerging nonapoptotic roles.

Mechanisms of pancreatic beta-cell apoptosis in diabetes and its therapies

Diabetes occurs when beta-cells no longer function properly or have been destroyed. Pancreatic beta-cell death by apoptosis contributes significantly in both autoimmune type 1 diabetes and type 2 diabetes. Pancreatic beta-cell death can be induced by multiple stresses in both major types of diabetes. There are also several rare forms of diabetes, including Wolcott-Rallison syndrome, Wolfram syndrome, as well as some forms of maturity onset diabetes of the young that are caused by mutations in genes that may play important roles in beta-cell survival. The use of islet transplantation as a treatment for diabetes is also limited by excessive beta-cell apoptosis. Mechanistic insights into the control of pancreatic beta-cell apoptosis are therefore important for the prevention and treatment of diabetes. Indeed, a substantial quantity of research has been dedicated to this area over the past decade. In this chapter, we review the factors that influence the propensity of beta-cells to undergo apoptosis and the mechanisms of this programmed cell death in the initiation and progression of diabetes.

Absence of caspase-3 protects pancreatic {beta}-cells from c-Myc-induced apoptosis without leading to tumor formation

c-Myc is a powerful trigger of beta-cell apoptosis, proliferation, and dedifferentiation in rodent islets in vivo. In a transgenic mouse model, c-Myc induction causes rapid beta-cell apoptosis and overt diabetes. When suppression of apoptosis is achieved by overexpression of Bcl-x(L) in an inducible model of c-Myc activation, a full spectrum of tumor development, including distant metastasis, occurs. Caspase-3 is a key pro-apoptotic protein involved in the execution phase of multiple apoptotic pathways. To test whether caspase-3 is an essential mediator of apoptosis in this model of tumorigenesis, we generated caspase-3 knock-out mice containing the inducible c-myc transgene (c-Myc(+)Casp3(-/-)). In contrast to Bcl-x(L)-overexpressing c-Myc(+) mice, c-Myc(+)Casp3(-/-) mice remained euglycemic for up to 30 days of c-Myc activation, and there was no evidence of tumor formation. Interestingly, caspase-3 deletion also led to the suppression of proliferation, perhaps through regulation of the cell cycle inhibitory protein p27, suggesting a possible mechanism for maintaining a balance between suppression of apoptosis and excessive proliferation in the context of c-Myc activation. Additionally, c-Myc-activated Casp3(-/-) mice were protected from streptozotocin-induced diabetes. Our studies demonstrate that caspase-3 deletion confers protection from c-Myc-induced apoptosis and diabetes development without unwanted tumorigenic effects. These results may lead to further elucidation of the mechanisms of c-Myc biology relevant to beta-cells, which may result in novel therapeutic strategies for diabetes.

Sequential activation of caspases and synergistic beta-cell cytotoxicity by palmitate and anti-Fas antibodies

To assess the mechanism of beta-cell lipotoxicity in comparison with Fas-mediated cell death, we used a mouse beta-cell clone stably transfected with human Fas. Palmitate induced beta-cell death in correlation with medium glucose levels between 5 and 20 mmol/l, while Fas-mediated cytotoxicity was observed irrespective of glucose concentration. At the glucose level of 10 mmol/l, palmitate induced caspase-6 activity within 3 h, and caspase-3 activity after a lag period of 6 h. The activities of caspases were correlated with glucose concentration. A caspase-6 inhibitor attenuated caspase-3 activation and cell death induced by palmitate. Oxfenicine, an inhibitor of carnitine palmitoyltransferase-1, attenuated both palmitate-induced cytotoxicity and activation of caspases. Finally, beta-cell cytotoxicity caused by the combination of anti-Fas and palmitate at 25 mmol/l of glucose was greater than the sum of those induced by each. These observations suggest that palmitate induces sequential activation of caspase-6 and caspase-3 through a mitochondrial signal(s), and caspase-6 plays a primary role in the mechanism. Fas-mediated beta-cell death and lipotoxicity may share common mechanisms involving caspase activation, and thereby synergistically inducing beta-cell death, although upstream signaling pathways are distinct.

Cytokines activate caspase-3 in insulinoma cells of diabetes-prone NOD mice directly and via upregulation of Fas

In type 1 diabetes, autoimmune inflammation of pancreatic islets of Langerhans ('insulitis') results in destruction of insulin-producing beta cells. Cytokines released from islet-infiltrating mononuclear cells are known to be cytotoxic both directly and by upregulating Fas for FasL-induced apoptosis. To investigate the role of caspase-3, a major effector of apoptosis in beta-cell death, we asked whether cytokine- and/or FasL-induced apoptosis was associated with increased activity of caspase-3 in NIT-1 insulinoma cells and islets of autoimmune diabetes-prone NOD mice. Measurement of caspase-3 activity using a fluorogenic cleavage assay was validated in NOD mouse thymocytes undergoing dexamethasone (Dex)-induced apoptosis. For cytokine-induced apoptosis, NIT-1 cells or islets were exposed to IL-1 beta and IFN-gamma for 24 h. Caspase-3-like activity was increased 2.1+/-0.7 and 2.4+/-0.9-fold in lysates of cytokine-treated NIT-1 cells and NOD mouse islets, respectively. However, NIT-1 cells exhibited 2.1% (4.7 pg active caspase-3/microg protein) and islets 0.8% (1.9 pg active caspase-3/microg protein) of the active caspase-3 content observed in Dex-treated thymocytes (225.1 pg active caspase-3/microg protein). After 24 h cytokine-exposure, the percentage of Fas-positive NIT-1 cells increased from 1.4+/-1.1 to 29.7+/-11.6%. Addition of FasL for a further 3 h increased caspase-3-like activity an additional 1.8-fold in cytokine-treated NIT-1 cells. In summary, exposure of NOD mouse insulinoma cells or islets to IL-1 beta and IFN-gamma for 24 h induced caspase-3-like activity that, in the case of insulinoma cells at least, can be further enhanced by interaction of cytokine-induced Fas receptor with FasL. Compared to thymocytes, insulinoma cells and islets from NOD mice were characterised by low basal and cytokine-induced caspase-3 activity.

Role of caspases in the regulation of apoptotic pancreatic islet beta-cells death

The homeostatic control of beta-cell mass in normal and pathological conditions is based on the balance of proliferation, differentiation, and death of the insulin-secreting cells. A considerable body of evidence, accumulated during the last decade, has emphasized the significance of the disregulation of the mechanisms regulating the apoptosis of beta-cells in the sequence of events that lead to the development of diabetes. The identification of agents capable of interfering with this process needs to be based on a better understanding of the beta-cell specific pathways that are activated during apoptosis. The aim of this article is fivefold: (1) a review of the evidence for beta-cell apoptosis in Type I diabetes, Type II diabetes, and islet transplantation, (2) to review the common stimuli and their mechanisms in pancreatic beta-cell apoptosis, (3) to review the role of caspases and their activation pathway in beta-cell apoptosis, (4) to review the caspase cascade and morphological cellular changes in apoptotic beta-cells, and (5) to highlight the putative strategies for preventing pancreatic beta-cells from apoptosis.

Caspase-3 inhibitor prevents apoptosis of human islets immediately after isolation and improves islet graft function

OBJECTIVES

Apoptosis appears in islets after isolation, and it has a detrimental effect on the islet function. To improve the outcome of clinical islet transplantation, it is crucial to protect islets from apoptosis. The aim of this study was to determine whether a caspase-3 inhibitor (Z-DEVD-FMK) added to culture media protects islets from apoptosis and to compare the effects of fetal bovine serum (FBS) with human serum albumin (HSA) as a protein supplement in culture.

METHODS

Isolated human islets were cultured under 4 different conditions: 0.5% HSA (control), 0.5% HSA + 25 micromol/L Z-DEVD-FMK, 0.5% HSA + 100 micromol/L Z-DEVD-FMK and 10% FBS for 2 days. Next, 1000 IEQ islets precultured with 0.5% HSA and with or without 100 micromol/L Z-DEVD-FMK were transplanted to diabetic nude mice.

RESULTS

The islet yields were higher in Z-DEVD-FMK-treated groups, and the inhibitor prevented apoptosis dose dependently. The yield and insulin release were higher in FBS-treated group than in the control group, but FBS did not affect apoptosis. All 6 mice transplanted with islets pretreated with Z-DEVD-FMK, and 3 of 8 mice with control islets became normoglycemic posttransplantation.

CONCLUSION

Z-DEVD-FMK prevented apoptosis of isolated human islets and improved its function. FBS (10%) improved the islet yield and insulin secretion more than 0.5% HSA.

Metallothionein as an adaptive protein prevents diabetes and its toxicity

Metallothioneins (MTs) are a group of intracellular metal-binding and cysteine-enriched proteins and are highly inducible in many tissues in response to various types of stress. Although it mainly acts as a regulator of metal homeostasis such as zinc and copper in tissues, MT also acts as a potent antioxidant and adaptive (or stress) protein to protect cells and tissues from oxidative stress. Diabetes affects many Americans and other populations, and its development and toxic effect on various organs have been attributed to increased oxidative stress. Studies showed that zinc-induced or genetically enhanced pancreatic MT synthesis prevented diabetes induced by chemicals such as streptozotocin and alloxan, and zinc pretreatment also prevented spontaneously developed diabetes. Since diabetic complications are the consequences of organ damage caused by diabetic hyperglycemia and hyperlipidemia through oxidative stress, whether MT in nonpancreatic organs also provides a preventive effect on diabetic toxicity has been recently investigated. We demonstrated that overexpression of cardiac MT significantly prevented diabetes-induced cardiomyopathy. Likewise, overexpression of renal MT also prevented diabetes-induced renal toxicity. In addition, we also found that MT as an adaptive protein is overexpressed in several organs in response to diabetes. Therefore, the biological importance of diabetes-induced MT in diabetic complications and subsequent other pathogenesis was further explored. We found that diabetes-induced hepatic and renal MT synthesis was accompanied by a significant prevention of endotoxin-induced hepatic toxicity and cisplatin-induced renal toxicity. These studies suggest that MT as an adaptive protein can prevent both diabetes development and its complications or subsequent suffered other pathogenic injury.

Fibrillogenic amylin evokes islet beta-cell apoptosis through linked activation of a caspase cascade and JNK1

Fibrillogenic human amylin elicits pancreatic beta-cell apoptosis that may contribute to development of type-2 diabetes. Here, we demonstrated that activation of a caspase cascade is necessary for induction of apoptosis by fibrillogenic amylin variants in two pancreatic beta-cell lines. Human amylin, as well as truncated 8-37human amylin, evoked sequential activation of caspases-8 and -3, and apoptosis, whereas non-beta-sheet forming and non-fibrillogenic homologs, such as [25,28,29triprolyl]human amylin, did not, implying that the beta-sheet conformer is required for human amylin-induced caspase activation. Significant inhibition of apoptosis was evoked by a selective caspase-1 inhibitor, indicating that caspase-1 is also essential for activation of the caspase cascade. Furthermore, we showed that specific jnk1 antisense oligonucleotides, which suppress phospho-JNK1 expression, effectively decreased human amylin-induced activation of c-Jun. Studies of the interplay between the caspase cascade and the JNK pathway showed that both apoptosis and caspase-3 activation were suppressed by treatment with a JNK inhibitor and by transfection of antisense jnk1 oligonucleotides or antisense-c-jun, whereas a selective inhibitor of caspases-1 and -3 prevented apoptosis but not c-Jun activation. Thus, the JNK1 activation preceded activation of caspases-1 and -3. However, selective JNK inhibition had no effect on caspase-8 activation, and selective caspase-8 inhibition only partially suppressed apoptosis and c-Jun activation, indicating that caspase-8 may partially act upstream of the JNK pathway. Our studies demonstrate a functional interaction of a caspase cascade and JNK1. Fibrillogenic amylin can evoke a JNK1-mediated apoptotic pathway, which is partially dependent and partially independent of caspase-8, and in which caspase-3 acts as a common downstream effector.

Pancreatic-derived factor (FAM3B), a novel islet cytokine, induces apoptosis of insulin-secreting beta-cells

PANDER (PANcreatic DERived factor, FAM3B), a newly discovered secreted cytokine, is specifically expressed at high levels in the islets of Langerhans of the endocrine pancreas. To evaluate the role of PANDER in beta-cell function, we investigated the effects of PANDER on rat, mouse, and human pancreatic islets; the beta-TC3 cell line; and the alpha-TC cell line. PANDER protein was present in alpha- and beta-cells of pancreatic islets, insulin-secreting beta-TC3 cells, and glucagon-secreting alpha-TC cells. PANDER induced islet cell death in rat and human islets. Culture of beta-TC3 cells with recombinant PANDER had a dose-dependent inhibitory effect on cell viability. This effect was also time-dependent. PANDER caused apoptosis of beta-cells as assessed by electron microscopy, annexin V fluorescent staining, and flow-cytometric terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. PANDER did not affect cytosolic Ca(2+) levels or nitric oxide levels. However, PANDER activated caspase-3. Hence, PANDER may have a role in the process of pancreatic beta-cell apoptosis.

Gene and cell therapies for diabetes mellitus: strategies and clinical potential

The last 5 years have witnessed an explosion in the use of genes and cells as biomedicines. While primarily aimed at cancer, gene engineering and cell therapy strategies have additionally been used for Mendelian, neurodegenerative and metabolic disorders. The main focus of gene and cell therapy strategies in metabolism has been diabetes mellitus. This disease is a disorder of glucose homeostasis, either due to the immune-mediated eradication of pancreatic beta cells in the islets of Langerhans (type 1 diabetes) or resulting from insulin resistance and obesity syndromes where the insulin-producing capability of the beta cell is ultimately exhausted in the face of insensitivity to the effects of insulin in the peripheral glucose-utilising tissues (type 2 diabetes). A significant number of animal studies have demonstrated the potential in restoring normoglycaemia by islet transplantation in the context of immunoregulation achieved by gene transfer of immunoregulatory genes to allo- and xenogeneic islets ex vivo. Additionally, gene and cell therapy has also been used to induce tolerance to auto- and alloantigens and to generate the tolerant state in autoimmune rodent animal models of type 1 diabetes or rodent recipients of allogeneic/xenogeneic islet transplants. The achievements of gene and cell therapy in type 2 diabetes are less evident, but seminal studies promise that this modality can be relevant to treat and perhaps prevent the underlying causes of the disease. Here we present an overview of the current status of gene and cell therapy for type 1 and 2 diabetes and we propose potential therapeutic options that could be clinically useful. For type 1 diabetes, transplantation of islets engineered to evade or suppress the recipient immune response is the most readily-available technology today. A number of gene delivery vectors encoding proteins that impair a variety of immune cells have already been examined and proven versatile. More challenging but, nonetheless, just over the horizon are attempts to promote tolerance to islet allografts. Type 2 diabetes will likely require a better understanding of the processes that determine insulin sensitivity in the periphery. Targeting tissues such as muscle and fat with vectors encoding genes whose products promote insulin sensitivity and glucose uptake is an approach that does not carry with it the side-effects often associated with pharmacologic agents currently in use. In the end, progress in vector design, elucidation of antigen-specific immunity and insulin sensitivity will provide the framework for gene drug use in the treatment of type 1 and type 2 diabetes.

Double-stranded RNA cooperates with interferon-gamma and IL-1 beta to induce both chemokine expression and nuclear factor-kappa B-dependent apoptosis in pancreatic beta-cells: potential mechanisms for viral-induced insulitis and beta-cell death in type 1 diabetes mellitus

Viral infections may trigger the autoimmune assault leading to type 1 diabetes mellitus. Double-stranded RNA (dsRNA) is produced by many viruses during their replicative cycle. The dsRNA, tested as synthetic poly(IC) (PIC), in synergism with the proinflammatory cytokines interferon-gamma (IFN-gamma) and/or IL-1 beta, results in nitric oxide production, Fas expression, beta-cell dysfunction, and death. Activation of the transcription nuclear factor-kappa B (NF-kappa B) is required for PIC-induced inducible nitric oxide synthase expression in beta-cells, and we hypothesized that this transcription factor may also participate in PIC-induced Fas expression and beta-cell apoptosis. This hypothesis, and the possibility that PIC induces expression of additional chemokines and cytokines (previously reported as NF-kappa B dependent) in pancreatic beta-cells, was investigated in the present study. We observed that the PIC-responsive region in the Fas promoter is located between nucleotides -223 and -54. Site-directed mutations at the NF-kappa B and CCAAT/enhancer binding protein-binding sites prevented PIC-induced Fas promoter activity. Increased Fas promoter activity was paralleled by enhanced susceptibility of PIC + cytokine-treated beta-cells to apoptosis induced by Fas ligand. beta-Cell infection with the NF-kappa B inhibitor AdI kappa B((SA)2) prevented both necrosis and apoptosis induced by PIC + IL-1 beta or PIC + IFN-gamma. Messenger RNAs for several chemokines and one cytokine were induced by PIC, alone or in combination with IFN-gamma, in pancreatic beta-cells. These included IP-10, interferon-gamma-inducible protein-10, IL-15, macrophage chemoattractant protein-1, fractalkine, and macrophage inflammatory protein-3 alpha. There was not, however, induction of IL-1 beta expression. We propose that dsRNA, generated during a viral infection, may contribute for beta-cell demise by both inducing expression of chemokines and IL-15, putative contributors for the build-up of insulitis, and by synergizing with locally produced cytokines to induce beta-cell apoptosis. Activation of the transcription factor NF-kappa B plays a central role in at least part of the deleterious effects of dsRNA in pancreatic beta-cells.

Specific expression of Bax-omega in pancreatic beta-cells is down-regulated by cytokines before the onset of apoptosis

Cytokines have been implicated in the process of pancreatic beta-cell destruction that leads to type 1 diabetes. This study investigates the beta-cell expression of pro- and antiapoptotic proteins from the Bcl-2 family and their variation during cytokine-mediated apoptosis. Exposure of rat beta-cells to the combination of IL-1beta plus interferon-gamma causes a time-dependent increase in apoptotic cells starting after 3 d (<10% on d 3 and 28 +/- 2% on d 7). This effect was preceded by a marked down-regulation of two antiapoptotic proteins, Bcl-2 and Bax-omega (respectively reduced by 60% and 80% after 3 d), whereas no changes occurred in the expression of Bcl-x(L) and the proapoptotic protein Bax-alpha. No apoptosis or down-regulation of Bcl-2 and Bax-omega proteins was observed with individual cytokines or in the presence of N-methyl-L-arginine, an inhibitor of nitric oxide synthase. The lowered Bcl-2 protein content was associated with a decrease in Bcl-2 mRNA, which was initiated after 24 h of exposure. In MIN6 cells, the cytokine-induced suppression of Bcl-2- and Bax-omega, and apoptosis, occurred within 24 h. Primary rat beta-cells exhibited a higher expression of Bax-omega than MIN6 cells or than other rat cell types. These data suggest that suppression of the antiapoptotic proteins Bcl-2 and Bax-omega mediates cytokine-induced apoptosis of beta-cells. The beta-cell-specific expression of Bax-omega makes this protein a possible effector in the protection of this cell type against apoptosis.

TRAIL (APO-2L) induces apoptosis in human prostate cancer cells that is inhibitable by Bcl-2

To determine if TRAIL-induced apoptosis in human prostate tumor cells was suppressed by bcl-2, we compared the levels of apoptosis induced by recombinant human TRAIL in pairs of isogenic cell lines that do or do not express bcl-2. Three human prostate tumor cell lines (PC3, DU145 and LNCaP) and their bcl-2-expressing counterparts were tested for their susceptibility to TRAIL. Cells were exposed to TRAIL in the presence of cycloheximide which acted as a sensitizer. Apoptosis was induced rapidly in PC3 and DU145 neo-control transfected cells, whereas induction in LNCaP required 24 h. All three cell line variants expressing bcl-2 were resistant to the apoptotic effects of TRAIL. Caspase 3 and 8 activation was also detected in the neo control cells after treatment with TRAIL, demonstrating the rapid activation of the caspase cascade similar to that seen with other death receptors. Bcl-2 overexpression in these cells blocked activation of these caspases, suggesting that bcl-2 expression of human cancer cells may be a critical factor in the therapeutic efficacy of TRAIL.

EARLY ASSESSMENT OF APOPTOSIS IN ISOLATED ISLETS OF LANGERHANS1

BACKGROUND

There is substantial evidence to link early graft loss after islet transplantation to isolation-induced islet cell apoptosis. Measurement of caspase 3 activity and detection of the lost cell membrane asymmetry, revealed by annexin V binding, are newly available assays that allow the analysis of early events of apoptosis.

METHODS

In this study, we compared these tests with the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay and analysis of DNA fragmentation after gel electrophoresis in freshly isolated islets obtained from rats, before and after treatment with interleukin-1 beta, interferon gamma, and tumor necrosis factor a, cytokines known to induce islet cell damage.

RESULTS

A measurable level of apoptosis was observed the day after isolation when caspase 3 activity and annexin V binding were used as assays, although no substantial DNA fragmentation was detected with TUNEL assay and DNA gel electrophoresis. Baseline caspase 3 activity was 0.8+/-0.3 U/100 islet equivalents and it increased to 1.4+/-0.45 U/100 islet equivalents 3 hr after cytokine stimulation (P<0.05 vs. unstimulated islets). The baseline level of apoptosis, as detected by annexin V binding, was 21.1%+/-5.8%, and it increased to 27.5%+/-8.1% 6 hr after addition of the cytokine cocktail (P<0.01 vs. unstimulated islets). An increase in the number of TUNEL-positive nuclei was detected 24 hr after stimulation and peaked at 48 hr. DNA laddering was also evident 24 hr after cytokine treatment.

CONCLUSION

These data suggest that measurement of caspase 3 activity and annexin V binding analysis might represent reliable markers of early events of islet cell apoptosis.

Dissociation between Fas expression and induction of apoptosis in human islets of Langerhans

There is increasing evidence that inappropriate induction of apoptosis in pancreatic beta-cells may precede the development of type 1 diabetes in animal models and in man. One mechanism by which this has been proposed to occur involves up-regulation of the death receptor Fas on beta-cells, resulting in apoptosis of the Fas-bearing beta-cells upon ligation of the receptor. We have examined this hypothesis in isolated human islets of Langerhans and show that--in contrast to data obtained with rodent beta-cells--expression of Fas per se is not sufficient to allow induction of apoptosis upon addition of agonistic anti-Fas serum.

In Vivo Evidence That Caspase-3 Is Required for Fas-Mediated Apoptosis of Hepatocytes

Caspase-3 is essential for Fas-mediated apoptosis in vitro. We investigated the role of caspase-3 in Fas-mediated cell death in vivo by injecting caspase-3-deficient mice with agonistic anti-Fas Ab. Wild-type controls died rapidly of fulminant hepatitis, whereas the survival of caspase-3−/− mice was increased due to a delay in hepatocyte cell death. Bcl-2 expression in the liver was dramatically decreased in wild-type mice following anti-Fas injection, but was unchanged in caspase-3−/− mice. Hepatocytes from anti-Fas-injected wild-type, but not caspase-3−/−, mice released cytochrome c into the cytoplasm. Western blotting confirmed the lack of caspase-3-mediated cleavage of Bcl-2. Presumably the presence of intact Bcl-2 in caspase-3−/− hepatocytes prevents the release of cytochrome c from the mitochondria, a required step for the mitochondrial death pathway. We also show by Western blot that Bcl-xL, caspase-9, caspase-8, and Bid are processed by caspase-3 in injected wild-type mice but that this processing does not occur in caspase-3−/− mice. This study thus provides novel in vivo evidence that caspase-3, conventionally known for its downstream effector function in apoptosis, also modifies Bcl-2 and other upstream proteins involved in the regulation of Fas-mediated apoptosis.