Beta-cell apoptosis is responsible for the development of IDDM in the multiple low-dose streptozotocin model

In situ electrophysiological examination of pancreatic α cells in the streptozotocin-induced diabetes model, revealing the cellular basis of glucagon hypersecretion

Early-stage type 1 diabetes (T1D) exhibits hyperglucagonemia by undefined cellular mechanisms. Here we characterized α-cell voltage-gated ion channels in a streptozotocin (STZ)-induced diabetes model that lead to increased glucagon secretion mimicking T1D. GYY mice expressing enhanced yellow fluorescence protein in α cells were used to identify α cells within pancreas slices. Mice treated with low-dose STZ exhibited hyperglucagonemia, hyperglycemia, and glucose intolerance, with 71% reduction of β-cell mass. Although α-cell mass of STZ-treated mice remained unchanged, total pancreatic glucagon content was elevated, coinciding with increase in size of glucagon granules. Pancreas tissue slices enabled in situ examination of α-cell electrophysiology. α cells of STZ-treated mice exhibited the following: 1) increased exocytosis (serial depolarization-induced capacitance), 2) enhanced voltage-gated Na(+) current density, 3) reduced voltage-gated K(+) current density, and 4) increased action potential (AP) amplitude and firing frequency. Hyperglucagonemia in STZ-induced diabetes is thus likely due to increased glucagon content arising from enlarged glucagon granules and increased AP firing frequency and amplitude coinciding with enhanced Na(+) and reduced K(+) currents. These alterations may prime α cells in STZ-treated mice for more glucagon release per cell in response to low glucose stimulation. Thus, our study provides the first insight that STZ treatment sensitizes release mechanisms of α cells.

Quantitative determination of apoptosis of pancreatic β-cells in a murine model of type 1 diabetes mellitus

Type 1 diabetes mellitus is characterized by a significant deficit in pancreatic β-cell mass, presumably caused by β-cell apoptosis. We investigated the incidence of β-cell apoptosis in streptozotocin-treated mice and nonobese diabetic (NOD) mice with (99m)Tc-annexin A5.

METHODS

Vehicle-treated mice, streptozotocin-treated mice, and NOD mice at the ages of 5, 9, 16, and 20 wk (5-8 mice per group) were injected with (99m)Tc-annexin A5 and sacrificed 6 h later for autoradiography, and the regional (99m)Tc-annexin A5 level in the pancreas was evaluated. Pancreatic islets were identified by insulin immunohistochemical staining, and apoptotic cells were determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining. The (99m)Tc-annexin A5 level in pancreatic islets was expressed as the percentage injected dose per area of pancreatic islets and normalized by animal body weight (%ID × 10(6)/mm(2)/kg). The level of apoptotic cells in pancreatic islets was expressed as the number of TUNEL-positive cells per area of pancreatic islets (cells/mm(2)).

RESULTS

The (99m)Tc-annexin A5 accumulation level was significantly higher (2.5 ± 0.7 vs. 0.7 ± 0.1 %ID × 10(6)/mm(2)/kg, P < 0.05) and the number of TUNEL-positive cells was significantly higher (1,170 ± 535 vs. 5 ± 6 cells/mm(2), P < 0.05) in the pancreatic islets of the streptozotocin-treated mice than in those of the vehicle-treated mice. The (99m)Tc-annexin A5 accumulation level was significantly higher (1.1 ± 0.4 vs. 0.5 ± 0.1 %ID × 10(6)/mm(2)/kg, P < 0.05) and the number of TUNEL-positive cells was significantly higher (152 ± 82 vs. 4 ± 9 cells/mm(2), P < 0.05) in the pancreatic islets of 16-wk-old NOD mice than in those of 5-wk-old NOD mice. In addition, the level of (99m)Tc-annexin A5 correlated with the number of TUNEL-positive cells in the pancreatic islets of the streptozotocin-treated mice (r = 0.821, P < 0.001) and NOD mice (r = 0.721, P < 0.001).

CONCLUSION

There is significant islet cell apoptosis with (99m)Tc-annexin A5 accumulation in the pancreas of both streptozotocin and NOD mice.

Endoplasmic reticulum stress induces the expression of fetuin-A to develop insulin resistance

Fetuin-A is a biomarker reported to be important in many metabolic disorders, including obesity, diabetes, and hepatic steatosis. Although it is well known that fetuin-A is increased in diabetes and nonalcoholic fatty liver disease (NAFLD), the levels of fetuin-A in diabetic patients with NAFLD are unknown. Furthermore, the regulation of fetuin-A expression is still obscure. In this study, a total of 180 age- and sex-matched subjects with normal glucose tolerance, NAFLD, newly diagnosed diabetes (NDD), and NDD with NAFLD were recruited. We found that the levels of fetuin-A were significantly increased in NDD with NAFLD as compared with NDD or NAFLD subjects. We further used HepG2 cells to investigate the regulation of fetuin-A. Treatment with endoplasmic reticulum (ER) stress activator, thapsigargin, increased the expression of fetuin-A mRNA and protein in a time- and dose-dependent manner. Pretreatment with ER stress inhibitor, 4-phenylbutyrate, reversed high glucose or palmitate-induced fetuin-A expression. Moreover, treatment with 4-phenylbutyrate in both streptozotocin-induced and high-fat diet-induced diabetic mice not only decreased hepatic fetuin-A levels but also improved hyperglycemia. Taken together, we found that fetuin-A levels were increased in diabetes patients with NAFLD. Moreover, ER stress induced by high glucose and palmitate increased the expression of fetuin-A and further contributed to the development of insulin resistance.

Acetylcholinesterase is associated with apoptosis in β cells and contributes to insulin-dependent diabetes mellitus pathogenesis

Acetylcholinesterase (AChE) expression is pivotal during apoptosis. Indeed, AChE inhibitors partially protect cells from apoptosis. Insulin-dependent diabetes mellitus (IDDM) is characterized in part by pancreatic β-cell apoptosis. Here, we investigated the role of AChE in the development of IDDM and analyzed protective effects of AChE inhibitors. Multiple low-dose streptozotocin (MLD-STZ) administration resulted in IDDM in a mouse model. Western blot analysis, cytochemical staining, and immunofluorescence staining were used to detect AChE expression in MIN6 cells, primary β cells, and apoptotic pancreatic β cells of MLD-STZ-treated mice. AChE inhibitors were administered intraperitoneally to the MLD-STZ mice for 30 days. Blood glucose, plasma insulin, and creatine levels were measured, and glucose tolerance tests were performed. The effects of AChE inhibitors on MIN6 cells were also evaluated. AChE expression was induced in the apoptotic MIN6 cells and primary β cells in vitro and pancreatic islets in vivo when treated with STZ. Induction and progressive accumulation of AChE in the pancreatic islets were associated with apoptotic β cells during IDDM development. The administration of AChE inhibitors effectively decreased hyperglycemia and incidence of diabetes, and restored plasma insulin levels and plasma creatine clearance in the MLD-STZ mice. AChE inhibitors partially protected MIN6 cells from the damage caused by STZ treatment. Induction and accumulation of AChE in pancreatic islets and the protective effects of AChE inhibitors on the onset and development of IDDM indicate a close relationship between AChE and IDDM.

Towards PET imaging of intact pancreatic beta cell mass: a transgenic strategy

PURPOSE

We have generated transgenic mouse lines expressing the positron emission tomography (PET) reporter gene, sr39tk, under the control of the mouse insulin I promoter (MIP-sr39tk) to image endogenous islets using PET.

PROCEDURES

The MIP-sr39tk transgene was constructed using the 8.3 kb fragment of the mouse insulin I promoter and the sr39tk coding sequence from the mrfp-hrl-ttk trifusion construct. Expression of sr39TK in beta cells was confirmed by fluorescence immunohistochemistry of pancreatic sections. Histological sections were used to determine beta cell mass, islet area and islet number. Beta cell function was determined using intraperitoneal glucose tolerance tests. For ex vivo biodistrubution, mice were injected i.v. with 9.25 MBq [(18)F]fluorohydroxymethyl-butyl-guanine (FHBG), euthanized 1 h later and pancreata and other organs were collected and counted. For PET scans, mice were injected i.v. with 9.25 MBq [(18)F]FHBG, and dynamic scans were conducted for 1 h, followed by a 30 min static acquisition. To induce type 1 diabetes-like symptoms, MIP-sr39tk mice were injected i.p. with 40 mg/kg streptozotocin (STZ) once per day for five consecutive days, and biodistribution and PET scans were conducted thereafter.

RESULTS

Ex vivo quantification of [(18)F]FHBG uptake in the pancreas showed a 4.5-fold difference in transgenic vs. non-transgenics, confirming that expression of sr39TK results in the retention of the PET tracer. In STZ-treated MIP-sr39tk mice, impairments in glucose tolerance and decreases in beta cell mass correlated significantly with a diminishment in [(18)F]FHBG uptake before fasting hyperglycemia became apparent.

CONCLUSIONS

The MIP-sr39tk mouse demonstrates that PET imaging can detect changes in beta cell mass that precede the onset of diabetes.

IL-27 inhibits hyperglycemia and pancreatic islet inflammation induced by streptozotocin in mice

Inflammation driven by immune cells and pro-inflammatory cytokines is implicated in pancreatic β-cell injury, leading to the development of diabetes mellitus. IL-27, a cytokine consisting of IL-27p28 and Epstein-Barr virus-induced gene 3 (EBI3), binds a membrane-bound heterodimeric receptor consisting of the IL-27 receptor α chain (WSX-1) and gp130. IL-27 has anti-inflammatory properties that regulate T-cell polarization and cytokine production. We evaluated blood glucose and islet proinsulin concentrations, inflammatory cell infiltration in islets, and expression of IL-1β mRNA in pancreas in wild-type (WT), EBI3(-/-), and WSX-1(-/-) mice treated with streptozotocin (STZ). Hyperglycemia was augmented in EBI3(-/-) and WSX-1(-/-) mice compared with WT mice. Islet proinsulin levels after STZ treatment were lower in EBI3(-/-) and WSX-1(-/-) mice than in WT mice. The infiltration of islets by F4/80(+)CD11c(-)7/4(-) macrophages, CD4(+) T cells, and CD8(+) T cells was increased in EBI3(-/-) and WSX-1(-/-) mice compared with WT mice. The administration of recombinant IL-27, compared with control, decreased the blood glucose level, immune cell infiltration into islets, and IL-1β mRNA expression in the pancreas and increased islet proinsulin levels in WT and EBI3(-/-) mice. Thus, IL-27 inhibits STZ-induced hyperglycemia and pancreatic islet inflammation in mice and represents a potential novel therapeutic approach for β-cell protection in diabetes.

Single dose streptozotocin-induced diabetes: considerations for study design in islet transplantation models

Streptozotocin (STZ)-induced diabetes mellitus (DM) offers a very cost-effective and expeditious technique that can be used in most strains of rodents, opening the field of DM research to an array of genotypic and phenotypic options that would otherwise be inaccessible. Despite widespread use of STZ in small animal models, the data available concerning drug preparation, dosing and administration, time to onset and severity of DM, and any resulting moribundity and mortality are often limited and inconsistent. Because of this, investigators inexperienced with STZ-induced diabetes may find it difficult to precisely design new studies with this potentially toxic chemical and account for the severity of DM it is capable of inducing. Until a better option becomes available, attempts need to be made to address shortcomings with current STZ-induced DM models. In this paper we review the literature and provide data from our pancreatic islet transplantation experiments using single high-dose STZ-induced DM in NCr athymic nude mice with hopes of providing clarification for study design, suggesting refinements to the process, and developing a more humane process of chemical diabetes induction.

The pathogenic role of cystathionine γ-lyase/hydrogen sulfide in streptozotocin-induced diabetes in mice

Reduced β-cell mass and increased activities of ATP-sensitive K(+) channels in pancreatic β cells are associated with the pathogenesis of diabetes. Cystathionine γ-lyase (CSE) is a major hydrogen sulfide (H(2)S)-producing enzyme in pancreatic β cells. Herein, we examine the effects of genetic and pharmacologic ablation of CSE on β-cell functions and their correlation with streptozotocin (STZ)-induced diabetes. Compared with wild-type mice, CSE knockout (CSE KO) mice that received STZ injections exhibited a delayed onset of diabetic status. The application of dl-propargylglycine (PPG) to inhibit CSE activity protected wild-type mice from STZ-induced hyperglycemia and hypoinsulinemia. STZ significantly increased pancreatic H(2)S production in wild-type mice but not in CSE KO mice. STZ induced more apoptotic β-cell death in wild-type mice than in CSE KO mice. STZ exposure decreased the viability of cultured INS-1E cells, which was partly reversed by PPG co-treatment. STZ also significantly stimulated H(2)S production in cultured INS-1E cells. In addition, STZ stimulated ATP-sensitive K(+) currents in pancreatic β cells from wild-type mice but not in the presence of PPG or in β cells from CSE KO mice. Sodium hydrosulfide injection instantly increased blood glucose, decreased plasma insulin, and deteriorated glucose tolerance in mice. Take together, these results provide evidence that the CSE/H(2)S system plays a critical role in regulating β-cell functions.

Multimodality imaging of β-cells in mouse models of type 1 and 2 diabetes

OBJECTIVE

β-Cells that express an imaging reporter have provided powerful tools for studying β-cell development, islet transplantation, and β-cell autoimmunity. To further expedite diabetes research, we generated transgenic C57BL/6 "MIP-TF" mice that have a mouse insulin promoter (MIP) driving the expression of a trifusion (TF) protein of three imaging reporters (luciferase/enhanced green fluorescent protein/HSV1-sr39 thymidine kinase) in their β-cells. This should enable the noninvasive imaging of β-cells by charge-coupled device (CCD) and micro-positron emission tomography (PET), as well as the identification of β-cells at the cellular level by fluorescent microscopy.

RESEARCH DESIGN AND METHODS

MIP-TF mouse β-cells were multimodality imaged in models of type 1 and type 2 diabetes.

RESULTS

MIP-TF mouse β-cells were readily identified in pancreatic tissue sections using fluorescent microscopy. We show that MIP-TF β-cells can be noninvasively imaged using microPET. There was a correlation between CCD and microPET signals from the pancreas region of individual mice. After low-dose streptozotocin administration to induce type 1 diabetes, we observed a progressive reduction in bioluminescence from the pancreas region before the appearance of hyperglycemia. Although there have been reports of hyperglycemia inducing proinsulin expression in extrapancreatic tissues, we did not observe bioluminescent signals from extrapancreatic tissues of diabetic MIP-TF mice. Because MIP-TF mouse β-cells express a viral thymidine kinase, ganciclovir treatment induced hyperglycemia, providing a new experimental model of type 1 diabetes. Mice fed a high-fat diet to model early type 2 diabetes displayed a progressive increase in their pancreatic bioluminescent signals, which were positively correlated with area under the curve-intraperitoneal glucose tolerance test (AUC-IPGTT).

CONCLUSIONS

MIP-TF mice provide a new tool for monitoring β-cells from the single cell level to noninvasive assessments of β-cells in models of type 1 diabetes and type 2 diabetes.

Pancreatic islet-specific overexpression of Reg3β protein induced the expression of pro-islet genes and protected the mice against streptozotocin-induced diabetes mellitus

Reg family proteins have been implicated in islet β-cell proliferation, survival, and regeneration. The expression of Reg3β (pancreatitis-associated protein) is highly induced in experimental diabetes and acute pancreatitis, but its precise role has not been established. Through knockout studies, this protein was shown to be mitogenic, antiapoptotic, and anti-inflammatory in the liver and pancreatic acinars. To test whether it can promote islet cell growth or survival against experimental damage, we developed β-cell-specific overexpression using rat insulin I promoter, evaluated the changes in normal islet function, gene expression profile, and the response to streptozotocin-induced diabetes. Significant and specific overexpression of Reg3β was achieved in the pancreatic islets of RIP-I/Reg3β mice, which exhibited normal islet histology, β-cell mass, and in vivo and in vitro insulin secretion in response to high glucose yet were slightly hyperglycemic and low in islet GLUT2 level. Upon streptozotocin treatment, in contrast to wild-type littermates that became hyperglycemic in 3 days and lost 15% of their weight, RIP-I/Reg3β mice were significantly protected from hyperglycemia and weight loss. To identify specific targets affected by Reg3β overexpression, a whole genome DNA microarray on islet RNA isolated from the transgenic mice revealed more than 45 genes significantly either up- or downregulated. Among them, islet-protective osteopontin/SPP1 and acute responsive nuclear protein p8/NUPR1 were significantly induced, a result further confirmed by real-time PCR, Western blots, and immunohistochemistry. Our results suggest that Reg3β is unlikely an islet growth factor but a putative protector that prevents streptozotocin-induced damage by inducing the expression of specific genes.

Chemical arsenal for the study of O-GlcNAc

The concepts of both protein glycosylation and cellular signaling have been influenced by O-linked-β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) on the hydroxyl group of serine or threonine residues. Unlike conventional protein glycosylation, O-GlcNAcylation is localized in the nucleocytoplasm and its cycling is a dynamic process that operates in a highly regulated manner in response to various cellular stimuli. These characteristics render O-GlcNAcylation similar to phosphorylation, which has long been considered a major regulatory mechanism in cellular processes. Various efficient chemical approaches and novel mass spectrometric (MS) techniques have uncovered numerous O-GlcNAcylated proteins that are involved in the regulation of many important cellular events. These discoveries imply that O-GlcNAcylation is another major regulator of cellular signaling. However, in contrast to phosphorylation, which is regulated by hundreds of kinases and phosphatases, dynamic O-GlcNAc cycling is catalyzed by only two enzymes: uridine diphospho-N-acetyl-glucosamine:polypeptide β-N-acetylglucosaminyl transferase (OGT) and β-D-N-acetylglucosaminidase (OGA). Many useful chemical tools have recently been used to greatly expand our understanding of the extensive crosstalk between O-GlcNAcylation and phosphorylation and hence of cellular signaling. This review article describes the various useful chemical tools that have been developed and discusses the considerable advances made in the O-GlcNAc field.

No non-redundant function of suppressor of cytokine signaling 2 in insulin producing β-cells

The members of the Suppressor of Cytokine Signaling (SOCS) protein family mainly modulate the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway. SOCS-1 and SOCS-3 have already been shown to influence growth and apoptosis of pancreatic beta cells. We hypothesized that SOCS-2, which is expressed in pancreatic islets, also contributes to β-cell physiology. We tested this hypothesis in vivo in SOCS-2-/- knockout mice and in vitro in Ins-1E rat insulinoma cells. We found that SOCS-2-/- mice have normal islet insulin secretion and unchanged glucose and insulin tolerance compared to wildtype controls. SOCS-2-/- are bigger than wildtype mice but body weight-corrected β-cell mass and islet morphology were normal. Growth hormone-induced proliferation of Ins-1E cells was not affected by either siRNA-mediated SOCS-2 knockdown or stable SOCS-2 overexpression. Interleukin-1β mediated cell death in vitro was unchanged after SOCS-2 knockdown. Similarly, autoimmune destruction of beta cells in vivo after multiple low-dose injections of streptozotocin (STZ) was not altered in SOCS-2-/- mice. In summary, SOCS-2-/- knockout mice have a normal function of insulin-producing pancreatic β-cells, a fully adapted beta cell mass and a normal morphology of the endocrine islets. Based on in vitro evidence, the increased β-cell mass in the mutants is likely due to indirect adaptive mechanisms and not the result of altered growth hormone signaling within the β-cells. Immune mediated β-cell destruction is also not affected by SOCS-2 ablation in vitro and in vivo.

The protective effect of testosterone on streptozotocin-induced apoptosis in beta cells is sex specific

OBJECTIVES

To investigate the protective role of steroid hormones on streptozotocin (STZ)-induced apoptosis in rat pancreatic beta cells.

METHODS

Two sets of experiments were performed. In the first, male rats were orchidectomized and substituted 72 hours later with testosterone, estradiol, or progesterone, and 24 hours later, administered with STZ. Subjects were killed 6 hours later, and apoptosis was determined in sections of the pancreas. In the second experiment, male or female rats were gonadectomized, were further substituted with testosterone, and then administered STZ. Six hours later, the animals were killed, and apoptosis, as well as immunoreactive expression of insulin, catalase, or Cu/Zn superoxide dismutase, was determined in sections of the pancreas. In addition, gonadectomized male or female subjects were substituted with testosterone and administered STZ, and 24 hours later, serum glucose and insulin were measured.

RESULTS

It was found that the cytoprotective effect was only shown in testosterone-treated male rats but not progesterone- or estradiol-treated male rats. In addition, the effect was seen in male rats but not in female rats, and there was an inverse correlation between apoptotic index and antioxidant enzyme immunoreactivity.

CONCLUSIONS

The cytoprotective effect of testosterone is sex specific and is related to the induction of antioxidant enzyme activities in pancreatic beta cells.

The activating receptor NKp46 is essential for the development of type 1 diabetes

The mechanism of action of natural killer (NK) cells in type 1 diabetes is still unknown. Here we show that the activating receptor NKp46 recognizes mouse and human ligands on pancreatic beta cells. NK cells appeared in the pancreas when insulitis progressed to type 1 diabetes, and NKp46 engagement by beta cells led to degranulation of NK cells. NKp46-deficient mice had less development of type 1 diabetes induced by injection of a low dose of streptozotocin. Injection of soluble NKp46 proteins into nonobese diabetic mice during the early phase of insulitis and the prediabetic stage prevented the development of type 1 diabetes. Our findings demonstrate that NKp46 is essential for the development of type 1 diabetes and highlight potential new therapeutic modalities for this disease.

Islet beta-cells deficient in Bcl-xL develop but are abnormally sensitive to apoptotic stimuli

OBJECTIVE

Bcl-xL is an antiapoptotic member of the Bcl-2 family of proteins and a potent regulator of cell death. We investigated the importance of Bcl-xL for beta-cells by deleting the Bcl-x gene specifically in beta-cells and analyzing their survival in vivo and in culture.

RESEARCH DESIGN AND METHODS

Islets with beta-cells lacking the Bcl-x gene were assessed in vivo by histology and by treatment of mice with low-dose streptozotocin (STZ). Islets were isolated by collagenase digestion and treated in culture with the apoptosis inducers staurosporine, thapsigargin, gamma-irradiation, proinflammatory cytokines, or Fas ligand. Cell death was assessed by flow cytometric analysis of subgenomic DNA.

RESULTS

Bcl-xL-deficient beta-cells developed but were abnormally sensitive to apoptosis induced in vivo by low-dose STZ. Although a small proportion of beta-cells still expressed Bcl-xL, these did not have a survival advantage over their Bcl-xL-deficient neighbors. Islets appeared normal after collagenase isolation and whole-islet culture. They were, however, abnormally sensitive in culture to a number of different apoptotic stimuli including cytotoxic drugs, proinflammatory cytokines, and Fas ligand.

CONCLUSIONS

Bcl-xL expression in beta-cells is dispensible during islet development in the mouse. Bcl-xL is, however, an important regulator of beta-cell death under conditions of synchronous stress. Bcl-xL expression at physiological levels may partially protect beta-cells from apoptotic stimuli, including apoptosis because of mediators implicated in type 1 diabetes and death or degeneration of transplanted islets.

Heat shock protein 27 overexpression mitigates cytokine-induced islet apoptosis and streptozotocin-induced diabetes

Beta-cell apoptosis occurs in diabetes mellitus (DM). Heat shock protein (HSP) 27 (human homolog of rodent HSP25) mitigates stress-induced apoptosis but has not been studied in beta-cells. We tested whether HSP27 overexpression attenuates streptozotocin (SZ)-induced DM in vivo and cytokine-induced islet apoptosis in vitro. DM was ascertained by ip glucose tolerance testing, and fasting serum insulin/glucose was measured. Pancreas was stained for insulin, HSP27, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling, and insulin content was measured. HSP25/27 was measured by immunoblotting, isoelectric focusing, and RT-PCR. Islet HSP25/27 oligomerization and inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator) binding were assessed by coimmunoprecipitation. HSP27 transgene (TG) in pancreas localized predominantly in beta-cells. Baseline pancreatic insulin levels in wild-type (WT) and HSP27TG mice were similar, but lower in WT than HSP27TG after SZ (P < 0.01). Intraperitoneal glucose tolerance testing confirmed protection from SZ-DM in HSP27TG. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and inducible nitric oxide synthase staining were increased in WT vs. HSP27TG islets (P < 0.05) after SZ. Caspase-3 activity was lower in islets from HSP27TG vs. WT mice after cytokine stress in vitro (P < 0.05). There was more HSP25 plus 27 protein from HSP27TG islets than HSP25 from WT (P < 0.01). HSP25 protein but not mRNA was increased in HSP27TG mice. Isoelectric focusing showed similar relative HSP phosphorylation in HSP27TG and WT (P > 0.05). HSP27 bound native HSP25 in TG islets; both bound to inhibitory kappaB protein kinase gamma (nuclear factor kappaB essential modulator). These data show islet protection by HSP27 by mitigation of apoptosis, possibly through nuclear factor kappaB regulation.

High beta-cell mass prevents streptozotocin-induced diabetes in thioredoxin-interacting protein-deficient mice

Thioredoxin-interacting protein (TxNIP) is an endogenous inhibitor of thioredoxin, a ubiquitous thiol oxidoreductase, that regulates cellular redox status. Diabetic mice exhibit increased expression of TxNIP in pancreatic islets, and recent studies suggest that TxNIP is a proapoptotic factor in beta-cells that may contribute to the development of diabetes. Here, we examined the role of TxNIP deficiency in vivo in the development of insulin-deficient diabetes and whether it impacted on pancreatic beta-cell mass and/or insulin secretion. TxNIP-deficient (Hcb-19/TxNIP(-/-)) mice had lower baseline glycemia, higher circulating insulin concentrations, and higher total pancreatic insulin content and beta-cell mass than control mice (C3H). Hcb-19/TxNIP(-/-) did not develop hyperglycemia when injected with standard multiple low doses of streptozotocin (STZ), in contrast to C3H controls. Surprisingly, although beta-cell mass remained higher in Hcb-19/TxNIP(-/-) mice compared with C3H after STZ exposure, the relative decrease induced by STZ was as great or even greater in the TxNIP-deficient animals. Consistently, cultured pancreatic INS-1 cells transfected with small-interfering RNA against TxNIP were more sensitive to cell death induced by direct exposure to STZ or to the combination of inflammatory cytokines interleukin-1beta, interferon-gamma, and tumor necrosis factor-alpha. Furthermore, when corrected for insulin content, isolated pancreatic islets from TxNIP(-/-) mice exhibited reduced glucose-induced insulin secretion. These data indicate that TxNIP functions as a regulator of beta-cell mass and influences insulin secretion. In conclusion, the relative resistance of TxNIP-deficient mice to STZ-induced diabetes appears to be because of an increase in beta-cell mass. However, TxNIP deficiency is associated with sensitization to STZ- and cytokine-induced beta-cell death, indicating complex regulatory roles of TxNIP under different physiological and pathological conditions.

The toll-like receptor signaling molecule Myd88 contributes to pancreatic beta-cell homeostasis in response to injury

Commensal flora and pathogenic microbes influence the incidence of diabetes in animal models yet little is known about the mechanistic basis of these interactions. We hypothesized that Myd88, an adaptor molecule in the Toll-like-receptor (TLR) pathway, regulates pancreatic beta-cell function and homeostasis. We first examined beta-cells histologically and found that Myd88-/- mice have smaller islets in comparison to C57Bl/6 controls. Myd88-/- mice were nonetheless normoglycemic both at rest and after an intra-peritoneal glucose tolerance test (IPGTT). In contrast, after low-dose streptozotocin (STZ) challenge, Myd88-/-mice had an abnormal IPGTT relative to WT controls. Furthermore, Myd88-/- mice suffer enhanced beta-cell apoptosis and have enhanced hepatic damage with delayed recovery upon low-dose STZ treatment. Finally, we treated WT mice with broad-spectrum oral antibiotics to deplete their commensal flora. In WT mice, low dose oral lipopolysaccharide, but not lipotichoic acid or antibiotics alone, strongly promoted enhanced glycemic control. These data suggest that Myd88 signaling and certain TLR ligands mediate a homeostatic effect on beta-cells primarily in the setting of injury.

A novel steroid from Elephantopus scaber L. an ethnomedicinal plant with antidiabetic activity

Acetone extract of Elephantopus scaber, an ethnomedicnal plant, reduced the blood glucose levels in streptozotocin-induced diabetic rats significantly. Acute toxicity studies revealed the non-toxic nature of the crude extract. Fractionation of the acetone extract yielded a new steroid, 28Nor-22(R)Witha 2,6,23-trienolide. Biological testing of the compound demonstrated a significant antidiabetic activity by reducing the elevated blood glucose levels and restoring the insulin levels in streptozotocin-induced diabetic rats. This compound can be a useful candidate to treat diabetes.

Impact of whole body irradiation and vascular endothelial growth factor-A on increased beta cell mass after bone marrow transplantation in a mouse model of diabetes induced by streptozotocin

AIMS/HYPOTHESIS

Recent studies have shown that bone marrow transplantation reduces hyperglycaemia in a mouse model of diabetes induced by streptozotocin. However, the essential factors for the improvement of hyperglycaemia by bone marrow transplantation have not been fully elucidated. The aim of this study was to search for such factors.

METHODS

We investigated the effect of irradiation to whole body, to abdomen alone or to whole body excluding abdomen, followed by infusion or no infusion of bone marrow cells. We also investigated the effect of bone marrow transplantation on beta cell-specific vascular endothelial growth factor-A gene (Vegfa) knockout mice.

RESULTS

Bone marrow transplantation improved streptozotocin-induced hyperglycaemia and partially restored islet mass. This change was associated with increased islet vascularisation. Among the other methods investigated, low-dose irradiation of the whole body without infusion of bone marrow cells also improved blood glucose level. In streptozotocin-treated beta cell-specific Vegfa knockout mice, which exhibit impaired islet vascularisation, bone marrow transplantation neither improved hyperglycaemia, relative beta cell mass nor islet vascularisation.

CONCLUSION/INTERPRETATION

Our results indicate that whole body irradiation is essential and sufficient for restoration of beta cell mass after streptozotocin treatment independent of infusion of bone marrow cells. Vascular endothelial growth factor-A produced in beta cells is also essential for this phenomenon.

Nitroreductase-mediated cell ablation in transgenic zebrafish embryos

Prodrug dependent cell ablation is a method that allows inducible and spatially restricted cell destruction. We describe transgenic methods to express the Escherichia coli nfsB in a tissue restricted manner in the zebrafish. This bacterial gene encodes a nitroreductase (NTR) enzyme that can render prodrugs such as metronidazole (Met) cytotoxic. Using the expression of NTR fused to a fluorescent protein, one can simultaneously make cells susceptible to prodrug treatment and visualize cell ablation as it occurs.

Methadone ameliorates multiple-low-dose streptozotocin-induced type 1 diabetes in mice

Type 1 diabetes is an autoimmune disease characterized by inflammation of pancreatic islets and destruction of beta cells by the immune system. Opioids have been shown to modulate a number of immune functions, including T helper 1 (Th1) and T helper 2 (Th2) cytokines. The immunosuppressive effect of long-term administration of opioids has been demonstrated both in animal models and humans. The aim of this study was to determine the effect of methadone, a mu-opioid receptor agonist, on type 1 diabetes. Administration of multiple low doses of streptozotocin (STZ) (MLDS) (40 mg/kg intraperitoneally for 5 consecutive days) to mice resulted in autoimmune diabetes. Mice were treated with methadone (10 mg/kg/day subcutaneously) for 24 days. Blood glucose, insulin and pancreatic cytokine levels were measured. Chronic methadone treatment significantly reduced hyperglycemia and incidence of diabetes, and restored pancreatic insulin secretion in the MLDS model. The protective effect of methadone can be overcome by pretreatment with naltrexone, an opioid receptor antagonist. Also, methadone treatment decreased the proinflammatory Th1 cytokines [interleukin (IL)-1beta, tumor necrosis factor-alpha and interferon-gamma] and increased anti-inflammatory Th2 cytokines (IL-4 and IL-10). Histopathological observations indicated that STZ-mediated destruction of beta cells was attenuated by methadone treatment. It seems that methadone as an opioid agonist may have a protective effect against destruction of beta cells and insulitis in the MLDS model of type 1 diabetes.

Newly weaned nonobese diabetic mice show heightened early diabetes sensitivity to multiple low doses of streptozotocin than nondiabetes-prone CD-1 mice: initial beta-cell damage a key trigger for type 1 diabetes?

OBJECTIVES

We determined if newly weaned female nonobese diabetic (NOD) mice show greater diabetes sensitivity to dose-adjusted regimens of multiple low doses of streptozotocin (Stz) than nondiabetes-prone CD-1 mice.

METHODS

Female NOD mice received 5 daily doses of Stz from day 21 (0, 5, 10, 15, 20, 30, and 40 mg/kg body weight) and CD-1 mice 20, 30, and 40 mg.

RESULTS

: Streptozotocin, at the 15-, 20-, 30-, and 40-mg dose, induced rapid diabetes in NOD mice. By day 100, 90% to 95% of NOD mice became diabetic after the 40- and 30-mg dose and 33% to 40% with the 15- and 20-mg dose. In comparison, only about 50% and 33% of CD-1 mice developed diabetes with the 40- and 30-mg dose, respectively, and 5.5% with the 20-mg dose. In NOD mice, the 20-mg dose also partially suppressed spontaneous diabetes. All diabetic mice displayed insulitis, variable immunostaining for insulin, and redistribution of glucagon and somatostatin cells. Glucose transporter-2 was markedly attenuated in selective beta cells.

CONCLUSIONS

Newly weaned female NOD mice show heightened early sensitivity to low doses of Stz than CD-1 mice. At diabetes, several beta cells remain and show variable immunostaining for insulin and an attenuated expression for glucose transporter-2. Specific low doses of Stz may also suppress spontaneous diabetes.

A general and islet cell-enriched overexpression of IGF-I results in normal islet cell growth, hypoglycemia, and significant resistance to experimental diabetes

Insulin-like growth factor I (IGF-I) is normally produced from hepatocytes and various other cells and tissues, including the pancreas, and is known to stimulate islet cell replication in vitro, prevent Fas-mediated beta-cell destruction and delay the onset of diabetes in nonobese diabetic mice. Recently, however, the notion that IGF-I stimulates islet cell growth has been challenged by the results of IGF-I and receptor gene targeting. To test the effects of a general, more profound increase in circulating IGF-I on islet cell growth and glucose homeostasis, we have characterized MT-IGF mice, which overexpress the IGF-I gene under the metallothionein I promoter. In early reports, a 1.5-fold-elevated serum IGF-I level caused accelerated somatic growth and pancreatic enlargement. We demonstrated that the transgene expression, although widespread, was highly concentrated in the beta-cells of the pancreatic islets. Yet, islet cell percent and pancreatic morphology were unaffected. IGF-I overexpression resulted in significant hypoglycemia, hypoinsulinemia, and improved glucose tolerance but normal insulin secretion and sensitivity. Pyruvate tolerance test indicated significantly suppressed hepatic gluconeogenesis, which might explain the severe hypoglycemia after fasting. Finally, due to a partial prevention of beta-cell death against onset of diabetes and/or the insulin-like effects of IGF-I overexpression, MT-IGF mice (which overexpress the IGF-I gene under the metallothionein I promoter) were significantly resistant to streptozotocin-induced diabetes, with diminished hyperglycemia and prevention of weight loss and death. Although IGF-I might not promote islet cell growth, its overexpression is clearly antidiabetic by improving islet cell survival and/or providing insulin-like effects.

Macrophage migration inhibitory factor (MIF) is necessary for progression of autoimmune diabetes mellitus

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine of the innate immune system that plays a major role in the induction of immunoinflammatory responses. To examine the role of endogenous MIF in the pathogenesis of type 1 diabetes (TID) we evaluated the effects of administration of neutralizing anti-MIF antibodies to NOD mice with accelerated forms of diabetes induced by injection of cyclophosphamide or by transfer of diabetogenic spleen cells. Both accelerated forms of diabetes were markedly reduced by anti-MIF antibody. Furthermore, MIF-deficient (MIF(-/-)) mice were less susceptible to the induction of immunoinflammatory diabetes, insulitis and apoptosis within the endocrine pancreas by multiple low doses of streptozotocin (MLD-STZ) than genetically matched wild type (WT) mice. MIF deficiency resulted in lower proliferation and lymphocyte adhesion, as well as reduced production from the spleens and peritoneal cells of a variety of inflammatory mediators typically associated with development of the disease including IL-12, IL-23, TNF-alpha, and IL-1beta. Furthermore, MIF deletion affected the production of IL-18, TNF-alpha, IL-1beta, and iNOS in the islets of Langerhans. These data, along with the higher expression of IL-4 and TGF-beta observed in the periphery and in the pancreas of MLD-STZ-challenged MIF(-/-) mice as compared to WT controls suggest that MIF deficiency has induced an immune deviation towards protective type 2/3 response. These results suggest that MIF participates in T1D by controlling the functional activity of monocytes/macrophages and T cells and modulating their secretory capacity of pro- and anti-inflammatory molecules.

Systemic administration of multipotent mesenchymal stromal cells reverts hyperglycemia and prevents nephropathy in type 1 diabetic mice

Multipotent mesenchymal stromal cells (MSCs), often labeled mesenchymal stem cells, contribute to tissue regeneration in injured bone and cartilage, as well as in the infarcted heart, brain, and kidney. We hypothesize that MSCs might also contribute to pancreas and kidney regeneration in diabetic individuals. Therefore, in streptozotocin (STZ)-induced type 1 diabetes C57BL/6 mice, we tested whether a single intravenous dose of MSCs led to recovery of pancreatic and renal function and structure. When hyperglycemia, glycosuria, massive beta-pancreatic islets destruction, and mild albuminuria were evident (but still without renal histopathologic changes), mice were randomly separated in 2 groups: 1 received 0.5 x 10(6) MSCs that have been ex vivo expanded (and characterized according to their mesenchymal differentiation potential), and the other group received the vehicle. Within a week, only MSC-treated diabetic mice exhibited significant reduction in their blood glucose levels, reaching nearly euglycemic values a month later. Reversion of hyperglycemia and glycosuria remained for 2 months at least. An increase in morphologically normal beta-pancreatic islets was observed only in MSC-treated diabetic mice. Furthermore, in those animals albuminuria was reduced and glomeruli were histologically normal. On the other side, untreated diabetic mice presented glomerular hyalinosis and mesangial expansion. Thus, MSC administration resulted in beta-pancreatic islets regeneration and prevented renal damage in diabetic animals. Our preclinical results suggest bone marrow-derived MSC transplantation as a cell therapy strategy to treat type 1 diabetes and prevent diabetic nephropathy, its main complication.

MKK3 signalling plays an essential role in leukocyte-mediated pancreatic injury in the multiple low-dose streptozotocin model

In vitro studies have implicated activation of the p38 mitogen-activated protein kinase (MAPK) signalling pathway in cytokine-mediated pancreatic beta-cell injury. Activation of the p38 MAPK occurs through two different upstream kinases, mitogen-activated protein kinase kinase 3 (MKK3) and MKK6. This study examined the role of MKK3 signalling in an in vivo model of cytokine-dependent pancreatic injury induced by multiple low doses of streptozotocin (MLD-STZ). Groups of wild-type (WT) or Mkk3-/- C57BL/6J mice received 5 daily injections of STZ (40 mg/kg) and were killed on day 5, week 2 or week 4. MLD-STZ in WT mice exhibited two distinct phases of pancreatic damage: islet cell apoptosis (immunostaining for cleaved caspase-3) on day 5 in the absence of leukocyte infiltration, and this was followed by islet inflammation (leukocyte infiltration and cytokine production) and further islet cell apoptosis on day 14 resulting in a loss of insulin-producing beta-cells and an 80% incidence of hyperglycaemia. Mkk3-/- mice were not protected from the initial phase of STZ-induced islet cell apoptosis day 5. However, Mkk3-/- mice were completely protected from the induction of hyperglycaemia. This was attributed to inhibition of leukocyte infiltration, production of pro-inflammatory cytokines and islet cell apoptosis at day 14 of MLD-STZ. In vitro studies showed that cultured islets from Mkk3-/- and WT mice are equally susceptible to STZ and cytokine-induced apoptosis. In conclusion, MKK3 signalling plays an essential role in the development of islet inflammation leading to destruction of beta-cells and hyperglycaemia in MLD-STZ-induced pancreatic injury.

Glial cell line-derived neurotrophic factor increases beta-cell mass and improves glucose tolerance

BACKGROUND & AIMS

Pancreatic beta-cell mass increases in response to increased demand for insulin, but the factors involved are largely unknown. Glial cell line-derived neurotrophic factor (GDNF) is a growth factor that plays a role in the development and survival of the enteric nervous system. We investigated the role of GDNF in regulating beta-cell survival.

METHODS

Studies were performed using the beta-TC-6 pancreatic beta-cell line, isolated mouse pancreatic beta cells, and in vivo in transgenic mice that overexpress GDNF in pancreatic glia. GDNF receptor family alpha1 and c-Ret receptor expression were assessed by reverse-transcription polymerase chain reaction and immunofluorescence microscopy. Apoptosis was evaluated by assessing caspase-3 cleavage. Phosphoinositol-3-kinase signaling pathway was analyzed by Akt phosphorylation. Glucose homeostasis was assessed by performing intraperitoneal glucose tolerance tests. Insulin sensitivity was assessed using intraperitoneal injection of insulin.

RESULTS

We demonstrate the presence of receptors for GDNF, GFRalpha1, and c-Ret on beta cells. GDNF promoted beta-cell survival and proliferation and protected them from thapsigargin-induced apoptosis (P<.0001) in vitro. Exposure of beta-cells to GDNF also resulted in phosphorylation of Akt and GSK3beta. Transgenic mice that overexpress GDNF in glia exhibit increased beta-cell mass, proliferation, and insulin content. No differences in insulin sensitivity and c-peptide levels were noted. Compared with wild-type mice, GDNF-transgenic mice have significantly lower blood glucose levels and improved glucose tolerance (P<.01). GDNF-transgenic mice are resistant to streptozotocin-induced beta-cell loss (P<.001) and subsequent hyperglycemia.

CONCLUSIONS

We demonstrate that over expression of GDNF in pancreatic glia improves glucose tolerance and that GDNF may be a therapeutic target for improving beta-cell mass.

c-Jun amino terminal kinase 1 deficient mice are protected from streptozotocin-induced islet injury

In vitro studies have implicated the c-Jun amino terminal kinase (JNK) in cytokine-induced pancreatic injury leading to a loss of insulin production and hyperglycemia. We examined the role of JNK1 in the multiple low dose streptozotocin (MLD-STZ) model in which islet injury and hyperglycemia are dependent upon T cell immunity and pro-inflammatory cytokines. MLD-STZ in wild type mice induced islet leukocyte infiltration, cytokine production, beta-cell apoptosis, and hyperglycemia. In contrast, Jnk1-/- mice were substantially protected from a loss of insulin producing cells and hyperglycemia in the MLD-STZ model despite a marked islet T cell and macrophage infiltrate. Based upon several lines of evidence, this protection was attributed to a reduction in TNF-alpha production by infiltrating Jnk1-/- macrophages leading to reduced beta-cell apoptosis. In conclusion, JNK1 signaling plays an essential role in macrophage induced beta-cell apoptosis and the development of hyperglycemia in MLD-STZ induced pancreatic injury.

Reactive Nitrogen Species Induced by Hyperglycemia Suppresses Akt Signaling and Triggers Apoptosis by Upregulating Phosphatase PTEN (Phosphatase and Tensin Homologue Deleted on Chromosome 10) in an LKB1-Dependent Manner

Background— Oxidative stress plays a causal role in vascular injury in diabetes mellitus, but the mechanisms and targets remain poorly understood.

Methods and Results— Exposure of cultured human umbilical vein endothelial cells to either peroxynitrite (ONOO − ) or high glucose significantly inhibited both basal and insulin-stimulated Akt phosphorylation at Ser473 and Akt activity in parallel with increased apoptosis, phosphorylation, and activity of phosphatase and tensin homologue deleted on chromosome 10 (PTEN). Furthermore, protein kinase B/Akt inhibition induced by ONOO − or high glucose and apoptosis triggered by high glucose could be abolished by transfection of PTEN-specific small interfering RNA, suggesting that PTEN mediated the Akt inhibition by ONOO − . In addition, exposure of human umbilical vein endothelial cells to ONOO − or high glucose remarkably increased Ser428 phosphorylation of LKB1, a tumor suppressor. Interestingly, the ONOO − -enhanced PTEN phosphorylation and Akt inhibition can be blocked by LKB1-specific small interfering RNA. Consistently, LKB1 phosphorylated PTEN at Ser380/Thr382/383 in vitro, suggesting that LKB1 might act as an upstream kinase for PTEN. Compared with nondiabetic mice, the levels of PTEN, LKB1-Ser428 phosphorylation, and 3-nitrotyrosine (a biomarker of ONOO − ) were significantly increased in the aortas of streptozotocin-induced diabetic mice, which was in parallel with a reduction in Akt-Ser473 phosphorylation and an increase in apoptosis. Furthermore, administration of PTEN-specific small interfering RNA suppressed diabetes-enhanced apoptosis and Akt inhibition. Finally, treatment with Tempol, a superoxide dismutase mimetic, and insulin, both of which reduced the ONOO − formation, markedly reduced diabetes-enhanced LKB1-Ser428 phosphorylation, PTEN, and apoptosis in the endothelium of mouse aortas.

Conclusion— We conclude that hyperglycemia triggers apoptosis by inhibiting Akt signaling via ONOO − -mediated LKB1-dependent PTEN activation.

Suppression of SOCS3 expression in the pancreatic beta-cell leads to resistance to type 1 diabetes

Type 1 diabetes results from the selective destruction of insulin-producing pancreatic beta-cells during islet inflammation, which involves inflammatory cytokines and free radicals. However, mechanisms for protecting beta-cells from destruction have not been clarified. In this study, we define the role of SOCS3 on beta-cell destruction using beta-cell-specific SOCS3-conditional knockout (cKO) mice. The beta-cell-specific SOCS3-deficient mice were resistant to the development of diabetes caused by streptozotocin (STZ), a genotoxic methylating agent, which has been used to trigger beta-cell destruction. The islets from cKO mice demonstrated hyperactivation of STAT3 and higher induction of Bcl-xL than did islets from WT mice, and SOCS3-deficient beta-cells were more resistant to apoptosis induced by STZ in vitro than were WT beta-cells. These results suggest that enhanced STAT3 signaling protects beta-cells from destruction induced by a genotoxic stress and that STAT3/SOCS3 can be a potential therapeutic target for the treatment of type 1 diabetes.

Targeted ablation of beta cells in the embryonic zebrafish pancreas using E. coli nitroreductase

In order to generate a zebrafish model of beta cell regeneration, we have expressed an Escherichia coli gene called nfsB in the beta cells of embryonic zebrafish. This bacterial gene encodes a nitroreductase (NTR) enzyme, which can convert prodrugs such as metronidazole (Met) to cytotoxins. By fusing nfsB to mCherry, we can simultaneously render beta cells susceptible to prodrug and visualize Met dependent cell ablation. We show that the neighboring alpha and delta cells are unaffected by prodrug treatment and that ablation is beta cell specific. Following drug removal and 36h of recovery, beta cells regenerate. Using ptf1a morphants, it is clear that this beta cell recovery occurs independently of the presence of the exocrine pancreas. Also, by using photoconvertible Kaede to cell lineage trace and BrdU incorporation to label proliferation, we investigate mechanisms for beta regeneration. Therefore, we have developed a unique resource for the study of beta cell regeneration in a living vertebrate organism, which will provide the opportunity to conduct large-scale screens for pharmacological and genetic modifiers of beta cell regeneration.

STAT5 activity in pancreatic beta-cells influences the severity of diabetes in animal models of type 1 and 2 diabetes

Pancreatic beta-cell growth and survival and insulin production are stimulated by growth hormone and prolactin through activation of the transcription factor signal transducer and activator of transcription (STAT)5. To assess the role of STAT5 activity in beta-cells in vivo, we generated transgenic mice that expressed a dominant-negative mutant of STAT5a (DNSTAT5) or constitutive active mutant of STAT5b (CASTAT5) under control of the rat insulin 1 promoter (RIP). When subjected to a high-fat diet, RIP-DNSTAT5 mice showed higher body weight, increased plasma glucose levels, and impairment of glucose tolerance, whereas RIP-CASTAT5 mice were more glucose tolerant and less hyperleptinemic than wild-type mice. Although the pancreatic insulin content and relative beta-cell area were increased in high-fat diet-fed RIP-DNSTAT5 mice compared with wild-type or RIP-CASTAT5 mice, RIP-DNSTAT5 mice showed reduced beta-cell proliferation at 6 months of age. The inhibitory effect of high-fat diet or leptin on insulin secretion was diminished in isolated islets from RIP-DNSTAT5 mice compared with wild-type islets. Upon multiple low-dose streptozotocin treatment, RIP-DNSTAT5 mice exhibited higher plasma glucose levels, lower plasma insulin levels, and lower pancreatic insulin content than wild-type mice, whereas RIP-CASTAT5 mice maintained higher levels of plasma insulin. In conclusion, our results indicate that STAT5 activity in beta-cells influences the susceptibility to experimentally induced type 1 and type 2 diabetes.

Antioxidative enzyme and glutathione S-transferase activities in diabetic rats exposed to long-term ASA treatment

Low-dose acetylsalicylic acid (ASA) treatment is a standard therapeutic approach in diabetes mellitus for prevention of long-term vascular complications. The aim of the present work was to investigate the effect of long-term ASA administration in experimental diabetes on activities of some liver enzymes: glutathione peroxidase (GSHPx), catalase, glucose-6-phosphate dehydrogenase (G6PDH) and glutathione S-transferase (GST). Blood glucose, glycated hemoglobin, as well as plasma ALT and AST activities increased in rats with streptozotocin-induced experimental diabetes. The long-term hyperglycemia resulted in decreased activities of GSHPx (by 26%), catalase (by 34%), GST (by 38%) and G6PDH (by 27%) in diabetic animals. We did not observe increased accumulation of membrane lipid peroxidation products or altered levels of reduced glutathione in livers. The linear correlation between blood glucose and glycated hemoglobin in diabetic animals was distorted upon ASA treatment, which was likely due to a chemical competition between nonenzymatic protein glycosylation and protein acetylation. The long-term ASA administration partially reversed the decrease in GSHPx activity, but did not influence the activities of catalase and GST in diabetic rats. Otherwise, some decrease in these parameters was noted in ASA-treated nondiabetic animals. Increased ASA-induced G6PDH activity was recorded in both diabetic and nondiabetic rats. While both glycation due to diabetic hyperglycemia and ASA-mediated acetylation had very similar effects on the activities of all studied enzymes but G6PDH, we conclude that non-enzymatic modification by either glucose or ASA may be a common mechanism of the observed convergence.

Selective deletion of Pten in pancreatic beta cells leads to increased islet mass and resistance to STZ-induced diabetes

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a lipid phosphatase. PTEN inhibits the action of phosphatidylinositol-3-kinase and reduces the levels of phosphatidylinositol triphosphate, a crucial second messenger for cell proliferation and survival, as well as insulin signaling. In this study, we deleted Pten specifically in the insulin producing beta cells during murine pancreatic development. Pten deletion leads to increased cell proliferation and decreased cell death, without significant alteration of beta-cell differentiation. Consequently, the mutant pancreas generates more and larger islets, with a significant increase in total beta-cell mass. PTEN loss also protects animals from developing streptozotocin-induced diabetes. Our data demonstrate that PTEN loss in beta cells is not tumorigenic but beneficial. This suggests that modulating the PTEN-controlled signaling pathway is a potential approach for beta-cell protection and regeneration therapies.

Conditional and specific NF-kappaB blockade protects pancreatic beta cells from diabetogenic agents

Type 1 diabetes is characterized by the infiltration of inflammatory cells into pancreatic islets of Langerhans, followed by the selective and progressive destruction of insulin-secreting beta cells. Islet-infiltrating leukocytes secrete cytokines such as IL-1beta and IFN-gamma, which contribute to beta cell death. In vitro evidence suggests that cytokine-induced activation of the transcription factor NF-kappaB is an important component of the signal triggering beta cell apoptosis. To study the in vivo role of NF-kappaB in beta cell death, we generated a transgenic mouse line expressing a degradation-resistant NF-kappaB protein inhibitor (DeltaNIkappaBalpha), acting specifically in beta cells, in an inducible and reversible manner, by using the tet-on regulation system. In vitro, islets expressing the DeltaNIkappaBalpha protein were resistant to the deleterious effects of IL-1beta and IFN-gamma, as assessed by reduced NO production and beta-cell apoptosis. This effect was even more striking in vivo, where nearly complete protection against multiple low-dose streptozocin-induced diabetes was observed, with reduced intraislet lymphocytic infiltration. Our results show in vivo that beta cell-specific activation of NF-kappaB is a key event in the progressive loss of beta cells in diabetes. Inhibition of this process could be a potential effective strategy for beta-cell protection.

Novel actions of IGFBP-3 on intracellular signaling pathways of insulin-secreting cells

Understanding mechanisms underlying apoptotic destruction of insulin-secreting cells is critical to validate therapeutic targets for type 1 diabetes mellitus. We recently reported insulin-like growth factor binding protein-3 (IGFBP-3) as a novel mediator of apoptosis in insulin-secreting cells. In light of emerging IGF-independent roles for IGFBP-3, we investigated the mechanisms underlying actions of the novel, recombinant human mutant G(56)G(80)G(81)-IGFBP-3, which lacks intrinsic IGF binding affinity. Using the rat insulinoma RINm5F cell line, we report the first studies in insulin-secreting cells that IGFBP-3 selectively suppresses multiple, key intracellular phosphorelays. By immunoblot, we demonstrate that G(56)G(80)G(81)-IGFBP-3 suppresses phosphorylation of c-raf-MEK-ERK pathway and p38 kinase in time-dependent and dose-dependent manners. SAPK/JNK signaling was unaffected. These data delineate several novel intracellular sites of action for IGFBP-3 in insulin-secreting cells.

Roles of poly(ADP-ribose) polymerase activation in the pathogenesis of diabetes mellitus and its complications

Activation of poly(ADP-ribose) polymerase (PARP) plays a role in the pathogenesis of beta-cell necrosis that occurs in response to autoimmune disease associated with Type I diabetes. In addition, PARP activation also plays a role in the pathogenesis of endothelial injury that underlies the ethiology of various diabetic complications (vasculopathy, cardiomyopathy, retinopathy, neuropathy), which develop on the basis of chronically elevated circulating glucose levels in diabetes. Both during the pathogenesis of diabetes and during the pathogenesis of diabetic complications, free radical and oxidant production leads to DNA strand-breakage which activates the nuclear enzyme PARP and initiates an energy consuming, inefficient cellular metabolic cycle with transfer of the ADP-ribosyl moiety of NAD+ to protein acceptors. These processes lead to the functional impairment of the affected cells (beta-cells or vascular endothelial cells, respectively). PARP also promotes the activation of various pro-inflammatory signal transduction pathways. During the last two decades, a growing number of experimental studies demonstrated the beneficial effects PARP inhibition in various models of diabetes and diabetic complications. The current review provides an overview of the experimental evidence implicating PARP as a causative factor in the pathogenesis of diabetes and diabetic complications in vitro and in vivo.

Imaging beta-cell death with a near-infrared probe

Evidence exists for an essential role of beta-cell apoptosis in the pathology of type 1 and type 2 diabetes. Current methods for diabetes-associated apoptosis detection, however, suffer the drawbacks of relying on in situ-based strategies. In this study, we attempted to measure, both in vitro and ex vivo, levels of beta-cell apoptosis in diabetic mice using Cy5.5-labeled annexin V. We used streptozotocin-treated BALB/c mice and NOD mice of different ages as models of type 1 diabetes and db/db mice as a model of type 2 diabetes. With annexin V Cy5.5, we established differences in levels of apoptosis between diabetic and control animals. Intravenously administered annexin V Cy5.5 accumulated in pancreata of diabetic mice but not in nondiabetic controls. Furthermore, its localization was specific to apoptotic events within diabetic islets; its selectivity was supported by transferase-mediated dUTP nick-end labeling staining. Because annexin V defines an early marker of apoptosis and the developed probe is suitable for in vivo administration, it may provide a promising tool for real-time identification in intact animals of the earliest stages of diabetes-associated beta-cell death and for tracing the events that characterize the pathology of the disease.

Early manifestations in multiple-low-dose streptozotocin-induced diabetes in mice

OBJECTIVE

Administration of multiple low doses of streptozotocin (mld-SZ) to mice results in the development of autoimmune diabetes. Hyperglycemia does not develop until a few days after the last injection. In this study, we explored immune-related alterations found in the very early stages of this diabetic syndrome and the capacity of mononuclear spleen cells (MSs) from mld-SZ mice to impair insulin secretion.

METHODS

Mice injected with mld-SZ were used as an animal model of type 1 diabetes. MSs were isolated from control and mld-SZ mice at days 4, 6, 9, 12, and 16 after the first injection of the diabetogenic drug. MSs were transferred to normal syngeneic recipients or were cocultured with dispersed rat islet cells as an in vitro insulin secretion study.

RESULTS

MSs from mld-SZ mice were able to diminish insulin secretion when transferred to normal syngeneic recipients and presented anti-beta-cell immune aggression when cocultured with dispersed rat islet cells as early as day 4 after mld-SZ administration. This capacity persisted throughout the experimental period. As early as 6 days after mld-SZ, islets showed insulitis followed by cell death with progressive severity. Hyperglycemia and diminished insulin secretion from perifused pancreatic islets only appeared at day 9 after mld-SZ.

CONCLUSIONS

This study suggests that transferred or cocultured MSs from mld-SZ mice exert a functional immune aggression against beta cells at a very early stage, before donor mice develop impaired insulin secretion and hyperglycemia.

Insulin hypersensitivity and resistance to streptozotocin-induced diabetes in mice lacking PTEN in adipose tissue

In adipose tissue, insulin controls glucose and lipid metabolism through the intracellular mediators phosphatidylinositol 3-kinase and serine-threonine kinase AKT. Phosphatase and a tensin homolog deleted from chromosome 10 (PTEN), a negative regulator of the phosphatidylinositol 3-kinase/AKT pathway, is hypothesized to inhibit the metabolic effects of insulin. Here we report the generation of mice lacking PTEN in adipose tissue. Loss of Pten results in improved systemic glucose tolerance and insulin sensitivity, associated with decreased fasting insulin levels, increased recruitment of the glucose transporter isoform 4 to the cell surface in adipose tissue, and decreased serum resistin levels. Mutant animals also exhibit increased insulin signaling and AMP kinase activity in the liver. Pten mutant mice are resistant to developing streptozotocin-induced diabetes. Adipose-specific Pten deletion, however, does not alter adiposity or plasma fatty acids. Our results demonstrate that in vivo PTEN is a potent negative regulator of insulin signaling and insulin sensitivity in adipose tissue. Furthermore, PTEN may be a promising target for nutritional and/or pharmacological interventions aimed at reversing insulin resistance.

Overexpression of cyclin D1 in pancreatic beta-cells in vivo results in islet hyperplasia without hypoglycemia

Cyclin D1 can stimulate proliferation by driving cells from the G1 into the S-phase of the mammalian cell cycle. Previous animal studies have implicated the G1-S transition as a key regulatory checkpoint governing the proliferation of pancreatic islet cells. We expressed cyclin D1 in the beta-cells of mice and islet hyperplasia developed in a time-dependent manner. The hyperplastic beta-cells exhibited higher rates of proliferation. However, blood glucose levels in fasting as well as nonfasting conditions remained normal. Furthermore, glucose tolerance tests demonstrated nearly normal responses, and diabetes did not develop in any of the animals. No islet cell tumors were observed, even among animals >2 years of age. Under our experimental conditions, the proliferative stimulus provided by cyclin D1 is not tumorigenic, does not result in diabetes, and does not result in hypoglycemia. Cyclin D1 may thus be considered a potential candidate to augment the beta-cell population ex vivo as a prelude to islet transplantation for diabetes.

Role of lipids in the early developmental stages of experimental immune diabetes induced by multiple low-dose streptozotocin

The present work examines the role of lipids in the development of the Type 1 diabetes induced by the administration of multiple low doses of streptozotocin (STZ) in C57BL/6J mice. The study was performed before and after the onset of clear hyperglycemia, and the results were as follows. First, 6 days after the first dose of STZ, while plasma glucose and insulin levels remained similar to those observed in the control mice, plasma free fatty acid (FFA) levels were significantly increased ( P < 0.05). At that time, a marked increase of triglyceride content in gastronemius muscle was accompanied by a diminished activity of pyruvate dehydrogenase complex, suggesting an impaired glucose oxidation. Furthermore, a decrease of both triglyceride content and lipoprotein lipase activity was observed in the epididymal fat tissue. Second, 12 days after the first injection of STZ, hyperglycemia was accompanied by hypertriglyceridemia, a more pronounced increase of plasma FFA, and a significant ( P < 0.05) reduction of insulinemia. At this time, both the adipose tissue and the gastrocnemius muscle showed a further deterioration of all parameters mentioned after 6 days. Moreover, in the gastrocnemius muscle, an impaired nonoxidative pathway of glucose metabolism was observed [significant reduction ( P < 0.05) of glycogen mass, glucose-6-phosphate content, and glycogen synthase activities] at this time point. Finally, the data suggest for the first time that, in mice, Type 1 diabetes induced by multiple low doses of STZ and enhanced lipolysis of fat pads leads to an increase in the availability of plasma FFA, which seems to play a role in the early steps of diabetes evolution.

Blood Treatment Influences the Yield of Apoptotic Lymphocytes after Maximal Exercise

PURPOSE

No systematic investigation has been reported assessing the effect of cell isolation processes on postexercise apoptosis. Therefore, the effect of cell isolation procedures on apoptosis was evaluated in this study.

METHODS

Untrained healthy individuals participated (N=13). Blood samples obtained at rest and immediately after an incremental exercise test to exhaustion were partitioned into three treatments: 1) whole blood smears made immediately after the sample was obtained (WB), 2) cells subjected to density-gradient isolation before smears were made (ISO), and 3) samples allowed to sit at room temperature (i.e., time-treated) before centrifugation and smearing (TT). Blood smears were stained using the May-Grünwald Giemsa procedure and lymphocytes were evaluated under a light microscope for characteristic features of apoptosis. Data were analyzed using a 2x3 ANOVA.

RESULTS

A significant interaction effect existed (P<0.0001) such that at rest, no difference was detected in the amount of lymphocyte apoptosis among WB, ISO, or TT samples. However, after exhaustive exercise, the amount of apoptotic lymphocytes was significantly greater in WB compared with ISO and TT samples (P<0.0001).

CONCLUSION

Lymphocyte isolation results in a significant decrease in the percent of apoptotic lymphocytes after exhaustive exercise. This reduction is likely due to the time needed to isolate cells, rather than the isolation process itself. Because apoptosis is a time-sensitive process that occurs within minutes rather than hours, the length of time from initial sampling to the preparation of cells for assessment of apoptosis is critical and should be considered in future exercise studies.

Pancreatic-specific inactivation of IGF-I gene causes enlarged pancreatic islets and significant resistance to diabetes

The dogma that IGF-I stimulates pancreatic islet growth has been challenged by combinational targeting of IGF or IGF-IR (IGF receptor) genes as well as beta-cell-specific IGF-IR gene deficiency, which caused no defect in islet cell growth. To assess the physiological role of locally produced IGF-I, we have developed pancreatic-specific IGF-I gene deficiency (PID) by crossing Pdx1-Cre and IGF-I/loxP mice. PID mice are normal except for decreased blood glucose level and a 2.3-fold enlarged islet cell mass. When challenged with low doses of streptozotocin, control mice developed hyperglycemia after 6 days that was maintained at high levels for at least 2 months. In contrast, PID mice only exhibited marginal hyperglycemia after 12 days, maintained throughout the experiment. Fifteen days after streptozotocin, PID mice demonstrated significantly higher levels of insulin production. Furthermore, streptozotocin-induced beta-cell apoptosis (transferase-mediated dUTP nick-end labeling [TUNEL] assay) was significantly prevented in PID mice. Finally, PID mice exhibited a delayed onset of type 2 diabetes induced by a high-fat diet, accompanied by super enlarged pancreatic islets, increased insulin mRNA levels, and preserved sensitivity to insulin. Our results suggest that locally produced IGF-I within the pancreas inhibits islet cell growth; its deficiency provides a protective environment to the beta-cells and potential in combating diabetes.

The effect of insulin-dependent diabetes mellitus on basal and distention-induced acid and pepsin secretion in rat

BACKGROUND

Diabetes mellitus is one of the most common endocrine diseases and affects most body organs. It affects gastric acid secretion, but this effect has not been fully understood. As the effects of diabetes on gastric pepsin secretion has not been proved yet, in this experimental study basal and distension-stimulated acid and pepsin secretions of diabetic and non-diabetic rats have been compared.

MATERIAL AND METHODS

Female N-Mari rats weighing 200-250 g were used. Diabetic state was induced by intraperitoneal injection of 75 mg/kg streptozotocin. Animals were anaesthetized by the interaperitoneal injection of 60 mg/kg thiopental sodium. Then tracheostomy and laparotomy were done and gastric secretions were collected by a cannula entered via duodenum. Gastric distention induce by 1.5 ml normal saline per each 100g of body weight in stomach. Acid and pepsin were measured by titration and Anson's method, respectively.

RESULTS

Basal gastric secretions were similar in diabetic and non-diabetic animals. Distention-stimulated acid secretions in diabetic and non-diabetic rats were 3.24 +/- 0.16 and 8.05 +/- 0.21 micromol/15 min, respectively, which were significantly different (P = 0.00001). Distention-induced pepsin secretion in diabetic and non diabetic rats were 3.16 +/- 0.13 and 5.24 +/- 0.16 microg/15min, respectively, which were significantly different (P = 0.00001).

CONCLUSION

In this study the stomach of diabetic animals showed less reaction to distention, which may be due to the reduction of acid and pepsin secretary cells, reduction of the function of the cells, gastric atrophy or gastric vagus neuropathy. These probabilities need to be examined.