Lentivirus-mediated Bcl-2 expression in betaTC-tet cells improves resistance to hypoxia and cytokine-induced apoptosis while preserving in vitro and in vivo control of insulin secretion

Adiponectin gene therapy prevents islet loss after transplantation

Significant pancreatic islet dysfunction and loss shortly after transplantation to the liver limit the widespread implementation of this procedure in the clinic. Nonimmune factors such as reactive oxygen species and inflammation have been considered as the primary driving force for graft failure. The adipokine adiponectin plays potent roles against inflammation and oxidative stress. Previous studies have demonstrated that systemic administration of adiponectin significantly prevented islet loss and enhanced islet function at post‐transplantation period. In vitro studies indicate that adiponectin protects islets from hypoxia/reoxygenation injury, oxidative stress as well as TNF‐α‐induced injury. By applying adenovirus mediated transfection, we now engineered islet cells to express exogenous adiponectin gene prior to islet transplantation. Adenovirus‐mediated adiponectin transfer to a syngeneic suboptimal islet graft transplanted under kidney capsule markedly prevented inflammation, preserved islet graft mass and improved islet transplant outcomes. These results suggest that adenovirus‐mediated adiponectin gene therapy would be a beneficial clinical engineering approach for islet preservation in islet transplantation.

An engineered cell sheet composed of human islets and human fibroblast, bone marrow-derived mesenchymal stem cells, or adipose-derived mesenchymal stem cells: An in vitro comparison study

BACKGROUND

We previously reported the utility of engineered cell sheets composed of human islets and supporting cells in vitro and in vivo. It is unclear which type of supporting cell is most suitable for constructing cell sheets with human islets. The present study aimed to compare human fibroblasts, bone marrow-derived mesenchymal stem cells (BM-MSCs), and adipose-derived mesenchymal stem cells (ADSCs) as a supporting source for cell sheets.

METHODS

Engineered cell sheets were fabricated with human islets using human fibroblasts, BM-MSCs, or ADSCs as supporting cells. The islet viability, recovery rate, glucose-stimulated insulin release (determined by the stimulation index), and cytokine secretion (TGF-β1, IL-6, and VEGF) of groups-including an islet-alone group as a control-were compared.

RESULTS

All three sheet groups consistently exhibited higher viability, recovery rate, and stimulation index values than the islet-alone group. The ADSC group showed the highest viability and recovery rate among the three sheet groups. There were no discernible differences in the stimulation index values of the groups. The fibroblast group exhibited significantly higher TGF-β1 values in comparison to the other groups. The IL-6 level of the ADSC group was more than five times higher than that of the other groups. The ADSC group showed the VEGF level; however, it did not differ from that of the BM-MSC group to a statistically significant extent.

CONCLUSION

Engineered cell sheets composed of islets and supporting cells had a cytoprotective effect on islets. These results suggest that individual cell types could be a more attractive source for crafting engineered cell sheets in comparison to islets alone.

Retrovirally Transferred Genes Inhibit Apoptosis in an Insulin-Secreting Cell Line: Implications for Islet Transplantation

The transplantation of pancreatic islets for the treatment of type I diabetes is hindered by the enormous loss of cells due to early apoptotic events. Genetic engineering of islets with cytoprotective genes is an important strategy aimed to enhance the survival of these cells in the transplant setting. The present study was designed to evaluate and compare the effects of five genes on a cell line derived from insulin-producing β-cells, NIT-1. Cells were transduced using a Maloney murine leukemia virus (MLV) vector coding for yellow fluorescent protein (YFP) and for one of the following antiapoptotic genes: cFLIP, FADD-DN, BcL-2, PI-9, and ICAM-2. These genes were able to protect NIT-1 cells from cytokine-induced apoptosis to varying degrees ranging from no protection to significant protection equivalent to an optimal dose of a chemical caspase inhibitor. The data demonstrate that cFLIP, FADD-DN, and PI-9 are significantly more effective in protecting NIT-1 cells than BcL-2 and ICAM-2. Additionally, the data show that despite its weak in vitro inhibition of caspase-3, PI-9 affords significant protection against TNF-α-induced apoptosis in these cells. These genes may be ideal candidates to augment islet survival following transplantation.

Cytokines and Pancreatic β-Cell Apoptosis

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

Clic4, a novel protein that sensitizes β-cells to apoptosis

Objectives

Chloride intracellular channel protein 4 (Clic4) is a ubiquitously expressed protein involved in multiple cellular processes including cell-cycle control, cell differentiation, and apoptosis. Here, we investigated the role of Clic4 in pancreatic β-cell apoptosis.

Methods

We used βTC-tet cells and islets from β-cell specific Clic4 knockout mice (βClic4KO) and assessed cytokine-induced apoptosis, Bcl2 family protein expression and stability, and identified Clic4-interacting proteins by co-immunoprecipitation and mass spectrometry analysis.

Results

We show that cytokines increased Clic4 expression in βTC-tet cells and in mouse islets and siRNA-mediated silencing of Clic4 expression in βTC-tet cells or its genetic inactivation in islets β-cells, reduced cytokine-induced apoptosis. This was associated with increased expression of Bcl-2 and increased expression and phosphorylation of Bad. Measurement of Bcl-2 and Bad half-lives in βTC-tet cells showed that Clic4 silencing increased the stability of these proteins. In primary islets β-cells, absence of Clic4 expression increased Bcl-2 and Bcl-xL expression as well as expression and phosphorylation of Bad. Mass-spectrometry analysis of proteins co-immunoprecipitated with Clic4 from βTC-tet cells showed no association of Clic4 with Bcl-2 family proteins. However, Clic4 co-purified with proteins from the proteasome suggesting a possible role for Clic4 in regulating protein degradation.

Conclusions

Collectively, our data show that Clic4 is a cytokine-induced gene that sensitizes β-cells to apoptosis by reducing the steady state levels of Bcl-2, Bad and phosphorylated Bad.

Aβ1-42 monomers or oligomers have different effects on autophagy and apoptosis

The role of autophagy and its relationship with apoptosis in Alzheimer disease (AD) pathogenesis is poorly understood. Disruption of autophagy leads to buildup of incompletely digested substrates, amyloid-β (Aβ) peptide accumulation in vacuoles and cell death. Aβ, in turn, has been found to affect autophagy. Thus, Aβ might be part of a loop in which it is both the substrate of altered autophagy and its cause. Given the relevance of different soluble forms of Aβ1-42 in AD, we have investigated whether monomers and oligomers of the peptide have a differential role in causing altered autophagy and cell death. Using differentiated SK-N-BE neuroblastoma cells, we found that monomers hamper the formation of the autophagic BCL2-BECN1/Beclin 1 complex and activate the MAPK8/JNK1-MAPK9/JNK2 pathway phosphorylating BCL2. Monomers also inhibit apoptosis and allow autophagy with intracellular accumulation of autophagosomes and elevation of levels of BECN1 and LC3-II, resulting in an inhibition of substrate degradation due to an inhibitory action on lysosomal activity. Oligomers, in turn, favor the formation of the BCL2-BECN1 complex favoring apoptosis. In addition, they cause a less profound increase in BECN1 and LC3-II levels than monomers without affecting the autophagic flux. Thus, data presented in this work show a link for autophagy and apoptosis with monomers and oligomers, respectively. These studies are likely to help the design of novel disease modifying therapies.

Gluco-incretins regulate beta-cell glucose competence by epigenetic silencing of Fxyd3 expression

BACKGROUND/AIMS

Gluco-incretin hormones increase the glucose competence of pancreatic beta-cells by incompletely characterized mechanisms.

METHODS

We searched for genes that were differentially expressed in islets from control and Glp1r-/-; Gipr-/- (dKO) mice, which show reduced glucose competence. Overexpression and knockdown studies; insulin secretion analysis; analysis of gene expression in islets from control and diabetic mice and humans as well as gene methylation and transcriptional analysis were performed.

RESULTS

Fxyd3 was the most up-regulated gene in glucose incompetent islets from dKO mice. When overexpressed in beta-cells Fxyd3 reduced glucose-induced insulin secretion by acting downstream of plasma membrane depolarization and Ca++ influx. Fxyd3 expression was not acutely regulated by cAMP raising agents in either control or dKO adult islets. Instead, expression of Fxyd3 was controlled by methylation of CpGs present in its proximal promoter region. Increased promoter methylation reduced Fxyd3 transcription as assessed by lower abundance of H3K4me3 at the transcriptional start site and in transcription reporter assays. This epigenetic imprinting was initiated perinatally and fully established in adult islets. Glucose incompetent islets from diabetic mice and humans showed increased expression of Fxyd3 and reduced promoter methylation.

CONCLUSIONS/INTERPRETATION

Because gluco-incretin secretion depends on feeding the epigenetic regulation of Fxyd3 expression may link nutrition in early life to establishment of adult beta-cell glucose competence; this epigenetic control is, however, lost in diabetes possibly as a result of gluco-incretin resistance and/or de-differentiation of beta-cells that are associated with the development of type 2 diabetes.

MRI-detectable pH nanosensors incorporated into hydrogels for in vivo sensing of transplanted-cell viability

Biocompatible nanomaterials and hydrogels have become an important tool for improving cell-based therapies by promoting cell survival and protecting cell transplants from immune rejection. Although their potential benefit has been widely evaluated, at present it is not possible to determine, in vivo, if and how long cells remain viable following their administration without the use of a reporter gene. Here, we report a pH-nanosensor-based magnetic resonance imaging (MRI) technique that can monitor cell death in vivo non-invasively. We demonstrate that specific MRI parameters that change on cell death of microencapsulated hepatocytes are associated with the measured bioluminescence imaging radiance. Moreover, the readout from this pH-sensitive nanosensor can be directly co-registered with high-resolution anatomical images. All of the components of these nanosensors are clinical grade and hence this approach should be a translatable and universal modification of hydrogels.

Bcl-2 and Bcl-xL suppress glucose signaling in pancreatic β-cells

B-cell lymphoma 2 (Bcl-2) family proteins are established regulators of cell survival, but their involvement in the normal function of primary cells has only recently begun to receive attention. In this study, we demonstrate that chemical and genetic loss-of-function of antiapoptotic Bcl-2 and Bcl-x(L) significantly augments glucose-dependent metabolic and Ca(2+) signals in primary pancreatic β-cells. Antagonism of Bcl-2/Bcl-x(L) by two distinct small-molecule compounds rapidly hyperpolarized β-cell mitochondria, increased cytosolic Ca(2+), and stimulated insulin release via the ATP-dependent pathway in β-cell under substimulatory glucose conditions. Experiments with single and double Bax-Bak knockout β-cells established that this occurred independently of these proapoptotic binding partners. Pancreatic β-cells from Bcl-2(-/-) mice responded to glucose with significantly increased NAD(P)H levels and cytosolic Ca(2+) signals, as well as significantly augmented insulin secretion. Inducible deletion of Bcl-x(L) in adult mouse β-cells also increased glucose-stimulated NAD(P)H and Ca(2+) responses and resulted in an improvement of in vivo glucose tolerance in the conditional Bcl-x(L) knockout animals. Our work suggests that prosurvival Bcl proteins normally dampen the β-cell response to glucose and thus reveals these core apoptosis proteins as integrators of cell death and physiology in pancreatic β-cells.

Induction of beta-cell resistance to hypoxia and technologies for oxygen delivery to transplanted pancreatic islets

Hypoxia is believed to be a crucial factor involved in cell adaptation to environmental stress. Islet transplantation, especially with immunoisolated islets, interrupts vascular connections, resulting in the substantially decreased delivery of oxygen and nutrients to islet cells. Insulin-producing pancreatic beta cells are known to be highly susceptible to oxygen deficiency. Such susceptibility to hypoxia is believed to be one of the main causes of beta-cell death in the post-transplantation period. Different strategies have been developed for the protection of beta cells against hypoxic injury and for oxygen delivery to transplanted islets. The enhancement of beta-cell defense properties against hypoxia has been achieved using various techniques such as gene transfection, drug supplementation, co-culturing with stem cells and cell selection. Technologies for oxygen delivery to transplanted islets include local neovascularization of subcutaneous sites, electrochemical and photosynthetic oxygen generation, oxygen refuelling of bio-artificial pancreas and whole body oxygenation by using hyperbaric therapy. Progress in the field of oxygen technologies for islet transplantation requires a multidisciplinary approach to explore and optimize the interaction between components of the biological system and different technological processes. This review article focuses mainly on the recently developed strategies for oxygenation and protection from hypoxic injury - to achieve stable and long-term normoglycaemia in diabetic patients with transplanted pancreatic islets.

Beneficial effects of desferrioxamine on encapsulated human islets--in vitro and in vivo study

As many as 2000 IEQs (islet equivalent) of encapsulated human islets are required to normalize glucose levels in diabetic mice. To reduce this number, encapsulated islets were exposed to 100 μM desferrioxamine (DFO) prior to transplantation. Cell viability, glucose-induced insulin secretion, VEGF (Vascular endothelial growth factor), HIF-1α (Hypoxia inducible factor-1 alpha), caspase-3 and caspase-8 levels were assessed after exposure to DFO for 12, 24 or 72 h. Subsequently, 1000, 750 or 500 encapsulated IEQs were infused into peritoneal cavity of diabetic mice after 24 h exposure to DFO. Neither viability nor function in vitro was affected by DFO, and levels of caspase-3 and caspase-8 were unchanged. DFO significantly enhanced VEGF secretion by 1.6- and 2.5-fold at 24 and 72 h, respectively, with a concomitant increase in HIF-1α levels. Euglycemia was achieved in 100% mice receiving 1000 preconditioned IEQs, as compared to only 36% receiving unconditioned IEQs (p < 0.001). Similarly, with 750 IEQ, euglycemia was achieved in 50% mice receiving preconditioned islets as compared to 10% receiving unconditioned islets (p = 0.049). Mice receiving preconditioned islets had lower glucose levels than those receiving unconditioned islets. In summary, DFO treatment enhances HIF-1α and VEGF expression in encapsulated human islets and improves their ability to function when transplanted.

Beta cell apoptosis in diabetes

Apoptosis of beta cells is a feature of both type 1 and type 2 diabetes as well as loss of islets after transplantation. In type 1 diabetes, beta cells are destroyed by immunological mechanisms. In type 2 diabetes abnormal levels of metabolic factors contribute to beta cell failure and subsequent apoptosis. Loss of beta cells after islet transplantation is due to many factors including the stress associated with islet isolation, primary graft non-function and allogeneic graft rejection. Irrespective of the exact mediators, highly conserved intracellular pathways of apoptosis are triggered. This review will outline the molecular mediators of beta cell apoptosis and the intracellular pathways activated.

Proinflammatory cytokines activate the intrinsic apoptotic pathway in beta-cells

OBJECTIVE

Proinflammatory cytokines are cytotoxic to beta-cells and have been implicated in the pathogenesis of type 1 diabetes and islet graft failure. The importance of the intrinsic mitochondrial apoptotic pathway in cytokine-induced beta-cell death is unclear. Here, cytokine activation of the intrinsic apoptotic pathway and the role of the two proapoptotic Bcl-2 proteins, Bad and Bax, were examined in beta-cells.

RESEARCH DESIGN AND METHODS

Human and rat islets and INS-1 cells were exposed to a combination of proinflammatory cytokines (interleukin-1beta, interferon-gamma, and/or tumor necrosis factor-alpha). Activation of Bad was determined by Ser136 dephosphorylation, mitochondrial stress by changes in mitochondrial metabolic activity and cytochrome c release, downstream apoptotic signaling by activation of caspase-9 and -3, and DNA fragmentation. The inhibitors FK506 and V5 were used to investigate the role of Bad and Bax activation, respectively.

RESULTS

We found that proinflammatory cytokines induced calcineurin-dependent dephosphorylation of Bad Ser136, mitochondrial stress, cytochrome c release, activation of caspase-9 and -3, and DNA fragmentation. Inhibition of Bad Ser136 dephosphorylation or Bax was found to inhibit cytokine-induced intrinsic proapoptotic signaling.

CONCLUSIONS

Our findings demonstrate that the intrinsic mitochondrial apoptotic pathway contributes significantly to cytokine-induced beta-cell death and suggest a functional role of calcineurin-mediated Bad Ser136 dephosphorylation and Bax activity in cytokine-induced apoptosis.

Lentivectors encoding immunosuppressive proteins genetically engineer pancreatic beta-cells to correct diabetes in allogeneic mice

The effectiveness of genetic engineering with lentivectors to protect transplanted cells from allogeneic rejection was examined using, as a model, type 1 diabetes treatment with beta-cell transplantation, whose widespread use has been limited by the requirement for sustained immunosuppressive treatment to prevent graft rejection. We examined whether lentivectors expressing select immunosuppressive proteins encoded by the adenoviral genome early region 3 (AdE3) would protect transplanted beta-cells from an alloimmune attack. The insulin-producing beta-cell line beta TC-tet (C3HeB/FeJ-derived) was transduced with lentiviruses encoding the AdE3 proteins gp19K and RID alpha/beta. The efficiency of lentiviral transduction of beta TC-tet cells exceeded 85%. Lentivector expression of gp19K decreased surface class I major histocompatibility complex expression by over 90%, whereas RID alpha/beta expression inhibited cytokine-induced Fas upregulation by over 75%. beta TC-tet cells transduced with gp19K and RID alpha/beta lentivectors, but not with a control lentivector, provided prolonged correction of hyperglycemia after transplantation into diabetic BALB/c severe combined immunodeficient mice reconstituted with allogeneic immune effector cells or into diabetic allogeneic BALB/c mice. Thus, genetic engineering of beta-cells using gp19K- and RID alpha/beta-expressing lentiviral vectors may provide an alternative that has the potential to eliminate or reduce treatment with the potent immunosuppressive agents necessary at present for prolonged engraftment with transplanted islets.

Treatment of diabetic rats with encapsulated islets

Immunoprotection of islets using bioisolator systems permits introduction of allogeneic cells to diabetic patients without the need for immunosuppression. Using TheraCyte™ immunoisolation devices, we investigated two rat models of type 1 diabetes mellitus (T1DM), BB rats and rats made diabetic by streptozotocin (STZ) treatment. We chose to implant islets after the onset of diabetes to mimic the probable treatment of children with T1DM as they are usually diagnosed after disease onset. We encapsulated 1000 rat islets and implanted them subcutaneously (SQ) into diabetic biobreeding (BB) rats and STZ-induced diabetic rats, defined as two or more consecutive days of blood glucose >350 mg/dl. Rats were monitored for weight and blood glucose. Untreated BB rats rapidly lost weight and were euthanized at >20% weight loss that occurred between 4 and 10 days from implantation. For period of 30–40 days following islet implantation weights of treated rats remained steady or increased. Rapid weight loss occurred after surgical removal of devices that contained insulin positive islets. STZ-treated rats that received encapsulated islets showed steady weight gain for up to 130 days, whereas untreated control rats showed steady weight loss that achieved >20% at around 55 days. Although islet implants did not normalize blood glucose, treated rats were apparently healthy and groomed normally. Autologous or allogeneic islets were equally effective in providing treatment. TheraCyte™ devices can sustain islets, protect allogeneic cells from immune attack and provide treatment for diabetic-mediated weight loss in both BB rats and STZ-induced diabetic rats.

Beta-cell replacement for insulin-dependent diabetes mellitus

Beta-cell replacement is considered the optimal treatment for type 1 diabetes, however, it is hindered by a shortage of human organ donors. Given the difficulty of expanding adult beta cells in vitro, stem/progenitor cells, which can be expanded in tissue culture and induced to differentiate into multiple cell types, represent an attractive source for generation of cells with beta-cell properties. In the absence of well-characterized human pancreas progenitor cells, investigators are exploring the use of embryonic stem cells and stem/progenitor cells from other tissues. Once abundant surrogate beta cells are available, the challenge will be to protect them from recurring autoimmunity.

Tetracycline-regulated expression of VEGF-A in beta cells induces angiogenesis: improvement of engraftment following transplantation

Early revascularization of pancreatic islet cells after transplantation is crucial for engraftment, and it has been suggested that vascular endothelial growth factor-A (VEGF-A) plays a significant role in this process. Although VEGF gene therapy can improve angiogenesis, uncontrolled VEGF secretion can lead to vascular tumor formation. Here we have explored the role of temporal VEGF expression, controlled by a tetracycline (TC)-regulated promoter, on revascularization and engraftment of genetically modified beta cells following transplantation. To this end, we modified the CDM3D beta cell line using a lentiviral vector to promote secretion of VEGF-A either in a TC-regulated (TET cells) or a constitutive (PGK cells) manner. VEGF secretion, angiogenesis, cell proliferation, and stimulated insulin secretion were assessed in vitro. VEGF secretion was increased in TET and PGK cells, and VEGF delivery resulted in angiogenesis, whereas addition of TC inhibited these processes. Insulin secretion by the three cell types was similar. We used a syngeneic mouse model of transplantation to assess the effects of this controlled VEGF expression in vivo. Time to normoglycemia, intraperitoneal glucose tolerance test, graft vascular density, and cellular mass were evaluated. Increased expression of VEGF resulted in significantly better revascularization and engraftment after transplantation when compared to control cells. In vivo, there was a significant increase in vascular density in grafted TET and PGK cells versus control cells. Moreover, the time for diabetic mice to return to normoglycemia and the stimulated plasma glucose clearance were also significantly accelerated in mice transplanted with TET and PGK cells when compared to control cells. VEGF was only needed during the first 2-3 weeks after transplantation; when removed, normoglycemia and graft vascularization were maintained. TC-treated mice grafted with TC-treated cells failed to restore normoglycemia. This approach allowed us to switch off VEGF secretion when the desired effects had been achieved. TC-regulated temporal expression of VEGF using a gene therapy approach presents a novel way to improve early revascularization and engraftment after islet cell transplantation.

Distal tubular epithelial cells of the kidney: Potential support for proximal tubular cell survival after renal injury

The tubular epithelium of the kidney is susceptible to injury from many causes, such as ischemia-reperfusion and the associated oxidative stress, nephrotoxins, inflammatory and immune disorders and many others. The outcome is often acute kidney injury, which may progress to chronic kidney disease and fibrosis. Acute kidney injury involves not only direct injury to the distal tubular (DT) and proximal tubular (PT) epithelium during and immediately following the injurious event, but the closely-associated and sometimes dysfunctional renal vascular endothelium also plays an important part in modulating the tubular epithelial injury. In comparison with the PT, the DT epithelium is less sensitive to cell death, especially after ischemic injury. It is more prone to apoptosis than necrosis when it dies, and has key paracrine and autocrine functions in secreting an array of inflammatory, reparative, and survival cytokines that include chemotactic cytokines, polypeptide growth factors, and vasoactive peptides. In a neighborly way, the cytokines and growth factors secreted by the DT epithelium may then act positively on the ischemia-sensitive PT that has receptors to many of these proteins, but may not be able to synthesize them. A more complete understanding of these cellular events will allow protection against nephron destruction, regeneration leading to re-epithelialization of the injured tubules, or prevention of progression to chronic kidney disease. This review looks at these functions in the DT epithelial cells, specifically the cells in the medullary thick ascending limb of the loop of Henle, in contrast with those of the straight segment of the PT.

Interventional strategies to prevent beta-cell apoptosis in islet transplantation

A substantial proportion of the transplanted islet mass fails to engraft due to death by apoptosis, and a number of strategies have been explored to inhibit beta-cell loss. Inhibition of extrinsic signals of apoptosis (i.e., cFLIP or A20) have been explored in experimental islet transplantation but have only shown limited impact. Similarly, strategies targeted at intrinsic signal inhibition (i.e., BCL-2) have not yet provided substantial improvement in islet engraftment. Recently, investigation of downstream apoptosis inhibitors that block the final common pathway (i.e., X-linked inhibitor of apoptosis protein [XIAP]) have demonstrated promise in both human and rodent models of engraftment. In addition, XIAP has enhanced long-term murine islet allograft survival. The complexities of both intrinsic and extrinsic apoptotic pathway inhibition are discussed in depth.

Gene therapy for type 1 diabetes

The most intensively studied autoimmune disorder, type 1 diabetes mellitus (DM1), has attracted perhaps the greatest interest for gene-based therapeutic and prophylactic interventions. The final clinical manifestation of this immunologically and genetically complex disease, the absence of insulin, is the major starting point for almost all the gene therapy modalities attempted to date. Insulin replacement by transplantation of islets of Langerhans or surrogate beta cells is the obvious choice, but the allogeneic nature of the transplants activates potent antidonor immunoreactivity necessitating gene and cell-based immunosuppressive strategies as an alternative to the toxic pharmacologic immunosuppressives indicated for classic solid organ transplants. Accumulating knowledge of the cellular mechanisms involved in onset, however, have yielded promising tolerance induction prophylactic approaches using genes and cells. Despite the early successes in a number of animal models, the true test of efficacy in humans remains to be demonstrated.

XIAP overexpression in human islets prevents early posttransplant apoptosis and reduces the islet mass needed to treat diabetes

The Edmonton Protocol for treatment of type 1 diabetes requires islets from two or more donors to achieve euglycemia in a single recipient, primarily because soon after portal infusion, the majority of the transplanted cells undergo apoptosis due to hypoxia and hypoxia reperfusion injury. X-linked inhibitor of apoptosis protein (XIAP) is a potent endogenous inhibitor of apoptosis that is capable of blocking the activation of multiple downstream caspases, and XIAP overexpression has previously been shown to enhance engraftment of a murine beta-cell line. In this study, human islets transduced with a XIAP-expressing recombinant adenovirus were resistant to apoptosis and functionally recovered following in vitro stresses of hypoxia and hypoxia with reoxygenation (models reperfusion injury). Furthermore Ad-XIAP transduction dramatically reduced the number of human islets required to reverse hyperglycemia in chemically diabetic immunodeficient mice. These results suggest that by transiently overexpressing XIAP in the immediate posttransplant period, human islets from a single donor might be used to effectively treat two diabetic recipients.

Expression of an uncleavable N-terminal RasGAP fragment in insulin-secreting cells increases their resistance toward apoptotic stimuli without affecting their glucose-induced insulin secretion

Apoptosis of pancreatic beta cells is implicated in the onset of type 1 and type 2 diabetes. Consequently, strategies aimed at increasing the resistance of beta cells toward apoptosis could be beneficial in the treatment of diabetes. RasGAP, a regulator of Ras and Rho GTPases, is an atypical caspase substrate, since it inhibits, rather than favors, apoptosis when it is partially cleaved by caspase-3 at position 455. The antiapoptotic signal generated by the partial processing of RasGAP is mediated by the N-terminal fragment (fragment N) in a Ras-phosphatidylinositol 3-kinase-Akt-dependent, but NF-kappaB-independent, manner. Further cleavage of fragment N at position 157 abrogates its antiapoptotic properties. Here we demonstrate that an uncleavable form of fragment N activates Akt, represses NF-kappaB activity, and protects the conditionally immortalized pancreatic insulinoma betaTC-tet cell line against various insults, including exposure to genotoxins, trophic support withdrawal, and incubation with inflammatory cytokines. Fragment N also induced Akt activity and protection against cytokine-induced apoptosis in primary pancreatic islet cells. Fragment N did not alter insulin cell content and insulin secretion in response to glucose. These data indicate that fragment N protects beta cells without affecting their function. The pathways regulated by fragment N are therefore promising targets for antidiabetogenic therapy.

Nonhuman primate models in type 1 diabetes research

The recent success of "steroid-free" immunosuppressive protocols and improvements in islet preparation techniques have proven that pancreatic islet transplantation (PIT) is a valid therapeutic approach for patients with type 1 diabetes. However, there are major obstacles to overcome before PIT can become a routine therapeutic procedure, such as the need for chronic immunosuppression, the loss of functional islet mass after transplantation requiring multiple islet infusion to achieve euglycemia without exogenous administration of insulin, and the shortage of human tissue for transplantation. With reference to the first obstacle, stable islet allograft function without immunosuppressive therapy has been achieved after tolerance was induced in diabetic primates. With reference to the second obstacle, different strategies, including gene transfer of antiapoptotic genes, have been used to protect isolated islets before and after transplantation. With reference to the third obstacle, pigs are an attractive islet source because they breed rapidly, there is a long history of porcine insulin use in humans, and there is the potential for genetic engineering. To accomplish islet transplantation, experimental opportunities must be balanced by complementary characteristics of basic mouse and rat models and preclinical large animal models. Well-designed preclinical studies in primates can provide the quality of information required to translate islet transplant research safely into clinical transplantation.

XIAP overexpression in islet beta-cells enhances engraftment and minimizes hypoxia-reperfusion injury

Recent advances in clinical islet transplantation have allowed patients with type 1 diabetes to become insulin independent, but the procedure is limited since islets from two donors per recipient are typically required. This limitation arises because within a few days of the islets being embolized into the portal circulation, at least half of the transplanted beta-cells have undergone apoptotic cell death triggered by hypoxic and chemokine/cytokine-mediated stress. We hypothesized that the survival of beta-cells in the early post-transplant period would be enhanced if naturally occurring inhibitor of apoptosis proteins (IAPs) were transiently overexpressed in the grafts. In the present study, we used a growth-regulatable beta-cell line (betaTC-Tet) as a model for beta-cells within islets, and examined whether adenovirally delivered XIAP (X-linked IAP-a highly potent IAP) could enhance beta-cell survival. In vitro, XIAP-expressing betaTC-Tet cells were markedly resistant to apoptosis in an ischemia-reperfusion injury model system and following exposure to cytokines. When Ad-XIAP transduced betaTC-Tet cells were transplanted subcutaneously into immunodeficient mice, the grafts were able to reverse diabetes in 3 days, vs. 21 days for Ad-betaGal transduced cells. This approach may allow more efficient use of the limited existing supply of human islets.

Toxin-based selection of insulin-producing cells with improved defense properties for islet cell transplantation

Insulin-producing pancreatic beta-cells are known to be extremely susceptible to destruction, primarily by autoimmune mechanisms, infectious agents, and by chemical toxins that cause overt type I diabetes. As development of highly protected insulin-producing cells would be important for successful cell therapy of diabetic patients, gene transfection technique was utilized by several investigators in order to improve the defense properties of transplanted cells. In this article, we summarize other approaches based on a selection strategy that has been developed in our laboratory and by other research groups that engineer pancreatic beta-cells to provide protection against diabetogenic toxins (streptozotocin and alloxan), oxidative stress and cytokines. Selection strategies based on acute repeated or long-term continuous treatment of cell lines with cytotoxic agents have resulted in the selection of highly resistant cell subpopulations. We discuss possible involvement of different expression of cytoprotective genes in the selection of cell subpopulations, which demonstrate a broad spectrum of resistance. Importantly, toxin-based selection did not impair functional activity of the cells as it was shown in vitro. In addition, selected cells preserved their improved metabolic characteristics following encapsulation in alginate and subsequent implantation in diabetic animals. Identifying the mechanisms through which cell defense properties act will help clarify the process responsible for beta-cell regeneration in type I diabetes patients. Such knowledge might be useful in developing strategies focusing on the regeneration of beta-cell resistant populations.

Lentivirus-mediated gene transfer of viral interleukin-10 delays but does not prevent cardiac allograft rejection

Human immunodeficiency virus (HIV)-based lentiviral vectors expressing viral interleukin-10 (vIL-10) were used to transduce rat cardiac allografts with the aim of extending graft survival. vIL-10 expression was first shown, by RT-PCR, to persist in transduced heart isografts for at least 28 days after transduction. Cardiac transplants were performed in a fully allogeneic rat strain combination (Lewis to DA); allografts transduced by vectors expressing vIL-10 showed significantly prolonged survival (14.5 vs 7.5 days median survival time). Mixed lymphocyte reactions (MLRs) were used to determine the influence, in vitro, of vIL-10 on alloantigen-induced T-cell proliferation. Bioactive vIL-10, produced by DA rat aortic endothelial cells transduced with HIV-PGK-vIL-10, was added to MLRs at different time points and lymphocyte proliferation was assessed by uptake of [3H]thymidine. T-cell proliferation was inhibited by >80% when vIL-10 was added to the MLR at day 1, 2 or 3 of coculture. The inhibitory effect was significantly decreased when addition of vIL-10 was delayed until day 4 or 5 (47 and 35% inhibition, respectively). The extended graft survival time is comparable to that using adenoviral vectors delivering vIL-10 in a similar rat strain combination. The limited improvement in survival may be due to lack of inhibition of the early phase of the alloimmune response as suggested by in vitro studies confirming that maximum suppression of the MLR by vIL-10 can only be achieved if the cytokine is present at the initiation of alloimmune recognition. The delay in expression of vIL-10 from the lentiviral vector means that protocols must be developed to suppress the early stages of alloimmune stimulation before vIL-10 is produced.

IL-6 protects pancreatic islet beta cells from pro-inflammatory cytokines-induced cell death and functional impairment in vitro and in vivo

Protection of pancreatic islet beta cells from pro-inflammatory cytokines-induced cell death and functional impairment is a key issue in developing therapeutic interventions of type 1 diabetes mellitus including islet transplantation. The effects of IL-6 on the protection of beta cells in vitro and in vivo were examined. Freshly isolated islets or MIN6 beta cells, when pre-incubated with IL-6, showed significantly higher viabilities measured by MTT assay and FACS analysis of PI stained cells against pro-apoptotic signaling delivered by IL-1beta, TNF-alpha and IFN-gamma. Insulin secretory function was also significantly protected in static culture with glucose and KCl stimulation. In vivo assessment using marginal mass syngeneic islet transplantation in mouse model revealed IL-6 conferred significantly better blood glucose control and graft survival rate over 50 days. Conclusively, IL-6 protects pancreatic islets or beta-cells from inflammatory cytokines-induced cell death and functional impairment both in vitro and in vivo. This strategy could be exploited in the clinical setting to maintain functional islet mass.

Partial cleavage of RasGAP by caspases is required for cell survival in mild stress conditions

Tight control of apoptosis is required for proper development and maintenance of homeostasis in multicellular organisms. Cells can protect themselves from potentially lethal stimuli by expressing antiapoptotic factors, such as inhibitors of apoptosis, FLICE (caspase 8)-inhibitory proteins, and members of the Bcl2 family. Here, we describe a mechanism that allows cells to survive once executioner caspases have been activated. This mechanism relies on the partial cleavage of RasGAP by caspase 3 into an amino-terminal fragment called fragment N. Generation of this fragment leads to the activation of the antiapoptotic Akt kinase, preventing further amplification of caspase activity. Partial cleavage of RasGAP is required for cell survival under stress conditions because cells expressing an uncleavable RasGAP mutant cannot activate Akt, cannot prevent amplification of caspase 3 activity, and eventually undergo apoptosis. Executioner caspases therefore control the extent of their own activation by a feedback regulatory mechanism initiated by the partial cleavage of RasGAP that is crucial for cell survival under adverse conditions.

Can we make surrogate beta-cells better than the original?

Insufficient pancreatic beta-cell mass is fundamental to the pathogenesis of both types 1 and 2 diabetes and constitutes the basis for the goal of beta-cell replacement therapy. Current methods for isolating islets from organ donor pancreases do not come close to supplying all in need, thus providing a compelling need to find new sources of insulin-producing cells. Possible sources include generation of cells from embryonic stem cells (ESC), adult stem/precursor cells, transdifferentiation of other cell types and xenodonors. Bioengineering can be used to improve secretory performance and strengthen cells to better withstand the challenges of transplantation. Strategies include protection against hypoxia, inflammation, and immune attack.

Delivery of Bcl-XL or its BH4 domain by protein transduction inhibits apoptosis in human islets

Viability of isolated islets is one of the main obstacles limiting islet transplantation success. It has been reported that overexpression of Bcl-2/Bcl-XL proteins enhances islet viability. To avoid potential complications associated with long-term expression of anti-apoptotic proteins, we investigated the possibility of delivering Bcl-XL or its anti-apoptotic domain BH4 to islets by protein transduction. Bcl-XL and BH4 molecules were fused to TAT/PTD, the 11-aa cell penetrating peptide from HIV-1 transactivating protein, generating TAT-Bcl-XL and TAT-BH4, respectively. Transduction efficiency was assessed by laser scanning confocal microscopy of live islets. Biological activity was tested as the ability to protect NIT-1 insulinoma cell line from death induced by staurosporine or serum deprivation. Spontaneous caspase activation in human islets and cytotoxicity caused by IL-1beta were significantly reduced in the presence of TAT-Bcl-XL and TAT-BH4. We conclude that both TAT proteins are biologically active after transduction and could be an asset in the improvement of islet viability.

Identification of iduronate-2-sulfatase in mouse pancreatic islets

The lysosomal enzyme iduronate-2-sulfatase (IDS) is expressed in pancreatic islets and is responsible for degradation of proteoglycans, such as perlecan and dermatan sulfate. To determine the role of IDS in islets, expression and regulation of the gene and localization of the enzyme were investigated in mouse pancreatic islets and clonal cells. The Ids gene was expressed in mouse islets and beta- and alpha-clonal cells, in which it was localized intracellularly in lysosomes. The transcriptional expression of Ids in mouse islets increased with glucose in a dose-dependent manner (11.5, 40.2, 88, and 179% at 5.5, 11.1, 16.7, and 24.4 mM, respectively, P < 0.01 for 16.7 and 24.4 mM glucose vs. 3 mM glucose). This increase was not produced by glyceraldehyde (1 mM) or 6-deoxyglucose (21.4 mM) and was blocked by the addition of mannoheptulose (21.4 mM). Neither insulin content nor secretory response to glucose (16.7 mM) was altered in mouse islets infected with lentiviral constructs carrying the IDS gene in sense orientation. Furthermore, no decrease in islet cell viability was observed in mouse islets carrying lentiviral contracts compared with controls. However, insulin content was reduced (35% vs. controls, P < 0.001) in islets infected with IDS antisense construct, while the secretory response of those islets to glucose was maintained. Inhibition of IDS by antisense infection led to an increase in lysosomal size and a high rate of insulin granule degradation via the crinophagic route in pancreatic beta-cells. We conclude that IDS is localized in lysosomes in pancreatic islet cells and expression is regulated by glucose. IDS has a potential role in the normal pathway of lysosomal degradation of secretory peptides and is likely to be essential to maintain pancreatic beta-cell function.

The JNK binding domain of islet-brain 1 inhibits IL-1 induced JNK activity and apoptosis but not the transcription of key proapoptotic or protective genes in insulin-secreting cell lines

The stress-activated protein kinase c-Jun NH2-terminal kinase (JNK) is a central signal for interleukin-1beta (IL-1beta)-induced apoptosis in insulin-producing beta-cells. The cell-permeable peptide inhibitor of JNK (JNKI1), that introduces the JNK binding domain (JBD) of the scaffold protein islet-brain 1 (IB1) inside cells, effectively prevents beta-cell death caused by this cytokine. To define the molecular targets of JNK involved in cytokine-induced beta-cell apoptosis we investigated whether JNKI1 or stable expression of JBD affected the expression of selected pro- and anti-apoptotic genes induced in rat (RIN-5AH-T2B) and mouse (betaTC3) insulinoma cells exposed to IL-1beta. Inhibition of JNK significantly reduced phosphorylation of the specific JNK substrate c-Jun (p<0.05), IL-1beta-induced apoptosis (p<0.001), and IL-1beta-mediated c-fos gene expression. However, neither JNKI1 nor JBD did influence IL-1beta-induced NO synthesis or iNOS expression or the transcription of the genes encoding mitochondrial manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase rho (GSTrho), heat shock protein (HSP) 70, IL-1beta-converting enzyme (ICE), caspase-3, apoptosis-inducing factor (AIF), Bcl-2 or Bcl-xL. We suggest that the anti-apoptotic effect of JNK inhibition by JBD is independent of the transcription of major pro- and anti-apoptotic genes, but may be exerted at the translational or posttranslational level.

Bcl-2 PROTECTION OF ISLET ALLOGRAFTS IS UNMASKED BY COSTIMULATION BLOCKADE

One major limitation in pancreatic islet transplantation is availability of donor tissue. Donor shortage is exacerbated by islet apoptosis from the stresses of islet isolation and transplantation. Furthermore, the side effects of immunosuppressive drugs preclude transplants into patients whose diabetes is controlled by parenteral insulin. We hypothesised that over-expressing anti-apoptotic Bcl-2 or secretion of immunomodulatory CTLA4Ig molecules in islet beta cells would enhance survival of transplanted islets while minimizing systemic side effects. Over-expression of Bcl-2 neither significantly increased preservation of islet cell mass after transplantation into immunocompromised recipients nor decreased cytokine-mediated apoptosis in vitro. Although Bcl-2 over-expression alone was insufficient in protecting islet allografts from rejection, its beneficence was shown by the enhancement of protection when the adaptive immune response was inhibited by locally produced CTLA4Ig. Thus, the combination of anti-apoptotic and immunosuppressive intervention has additive or synergistic efficacy and may reduce the level of systemic immunosuppression or quantity of donor tissue required.

Understanding of basic mechanisms of beta-cell function and survival: prelude to new diabetes therapies

Type 1 and type 2 diabetes are both diseases of insulin insufficiency, although they develop by distinct pathways. The recent surge in the incidence of type 2 diabetes and the chronic ailments confronted by patients with either form of the disease highlight the need for better understanding of beta-cell biology. In this review, we present recent work focused on this goal. Our hope is that basic research being conducted in this and other laboratories will ultimately contribute to the development of methods for enhancing beta-cell function and survival in the context of both major forms of diabetes. Our strategy for understanding the beta-cell involves a multidisciplinary approach in which tools from the traditional fields of biochemistry, enzymology, and physiology are teamed with newer technologies from the fields of molecular biology, gene discovery, cell and developmental biology, and biophysical chemistry. We have focused on two important aspects of beta-cell biology in our studies: beta-cell function, specifically the metabolic regulatory mechanisms involved in glucose-stimulated insulin secretion, and beta-cell resistance to immune attack, with emphasis on resistance to inflammatory cytokines and reactive oxygen species.

Discrete and complementary mechanisms of protection of beta-cells against cytokine-induced and oxidative damage achieved by bcl-2 overexpression and a cytokine selection strategy

We have been investigating the potential utility of engineered cell lines as surrogates for primary islet cells in treatment of type 1 diabetes. To this end, two strategies that have emerged for procuring cell lines with resistance to immune-mediated damage are 1) selection of cytokine-resistant cell lines by growth of INS-1 insulinoma cells in iteratively increasing concentrations of interleukin (IL)-1beta + gamma-interferon (IFN-gamma), and 2) stable overexpression of the anti-apoptotic gene bcl-2 in INS-1 cells. Herein, we show that bcl-2-overexpressing cells are resistant to the cytotoxic effects of reactive oxygen and nitrogen species (ROS/RNS), but are only modestly protected against high concentrations of IL-1beta + INF-gamma, whereas the converse is true in cytokine selected cells. We also found that the combination of bcl-2 expression and cytokine selection confers a broader spectrum of resistance than either procedure alone, such that the resultant cells are highly resistant to cytokines and ROS/RNS, with no impairment in glucose-stimulated insulin secretion. INS-1-derived cells with combined bcl-2 expression and cytokine selection are also more resistant to damage induced by coculture with mitogen-activated peripheral blood mononuclear cells. Surprisingly, application of the cytokine selection procedure to bcl-2-overexpressing cells does not result in impairment of nuclear factor-kappaB translocation, iNOS expression, and NO production, as clearly occurs upon application of the selection procedure to cells without bcl-2 overexpression. Further investigation of the diverse pathways involved in the development of cytokine and ROS/RNS resistance may define simplified and specific strategies for preservation of beta-cell mass.

Molecular pathways involved in the antineoplastic effects of calcitriol on insulinoma cells

We have previously reported that in tumorigenic pancreatic beta-cells, calcitriol exerts a potent antitumorigenic effect by inducing apoptosis, cell growth inhibition, and reduction of solid beta-cell tumors. Here we have studied the molecular pathways involved in the antineoplastic activity of calcitriol on mouse insulinoma beta TC(3) cells, mouse insulinoma beta TC expressing or not expressing the oncogene p53, and beta TC-tet cells overexpressing or not the antiapoptotic gene Bcl2. Our results indicate that calcitriol-induced apoptosis was dependent on the function of p53 and was associated with a biphasic increase in protein levels of transcription factor nuclear factor-kappa B. Calcitriol decreased cell viability by about 40% in p53-retaining beta TC and in beta TC(3) cells; in contrast, beta TC p53(-/-) cells were only minimally affected. Calcitriol-induced cell death was regulated by members of the Bcl-2 family of apoptosis regulatory proteins, as shown by calcitriol-induced up-regulation of proapoptotic Bax and Bak and the lack of calcitriol-induced cytotoxicity in Bcl-2-overexpressing insulinoma cells. Moreover, calcitriol-mediated arrest of beta TC(3) cells in the G(1) phase of the cell cycle was associated with the abnormal expression of p21 and G(2)/M-specific cyclin B2 genes and involved the DNA damage-inducible factor GADD45. Finally, in beta TC(3) cells, calcitriol modulated the expression of IGF-I and IGF-II genes. In conclusion, these findings contribute to the understanding of the antitumorigenic effects of calcitriol on tumorigenic pancreatic beta-cells and further support the rationale of its utilization in the treatment of patients with malignant insulinomas.

Gene- and cell-based therapeutics for type I diabetes mellitus

Type 1 diabetes mellitus, an autoimmune disorder is an attractive candidate for gene and cell-based therapy. From the use of gene-engineered immune cells to induce hyporesponsiveness to autoantigens to islet and beta cell surrogate transplants expressing immunoregulatory genes to provide a local pocket of immune privilege, these strategies have demonstrated proof of concept to the point where translational studies can be initiated. Nonetheless, along with the proof of concept, a number of important issues have been raised by the choice of vector and expression system as well as the point of intervention; prophylactic or therapeutic. An assessment of the current state of the science and potential leads to the conclusion that some strategies are ready for safety trials while others require varying degrees of technical and conceptual refinement.

Destruction of conditional insulinoma cell lines in NOD mice: a role for autoimmunity

AIMS/HYPOTHESIS

betaTC-tet (H2(k)) is a conditional insulinoma cell line derived from transgenic mice expressing a tetracycline-regulated oncogene. Transgenic expression of several proteins implicated in the apoptotic pathways increase the resistance of betaTC-tet cells in vitro. We tested in vivo the sensitivity of the cells to rejection and the protective effect of genetic alterations in NOD mice.

METHODS

betaTC-tet cells and genetically engineered lines expressing Bcl-2 (CDM3D), a dominant negative mutant of MyD88 or SOCS-1 were transplanted in diabetic female NOD mice or in male NOD mice with diabetes induced by high-dose streptozotocin. Survival of functional cell grafts in NOD-scid mice was also analyzed after transfer of splenocytes from diabetic NOD mice. Autoreactive T-cell hybridomas and splenocytes from diabetic NOD mice were stimulated by betaTC-tet cells.

RESULTS

betaTC-tet cells and genetically engineered cell lines were all similarly rejected in diabetic NOD mice and in NOD-scid mice after splenocyte transfer. In 3- to 6-week-old male NOD mice treated with high-dose streptozotocin, the cells temporarily survived, in contrast with C57BL/6 mice treated with high-dose streptozotocin (indefinite survival) and untreated 3- to 6-week-old male NOD mice (rejection). The protective effect of high-dose streptozotocin was lost in older male NOD mice. betaTC-tet cells did not stimulate autoreactive T-cell hybridomas, but induced IL-2 secretion by splenocytes from diabetic NOD mice.

CONCLUSION/INTERPRETATION

The autoimmune process seems to play an important role in the destruction of betaTC-tet cells in NOD mice. Genetic manipulations intended at increasing the resistance of beta cells were inefficient. Similar approaches should be tested in vivo as well as in vitro. High dose streptozotocin influences immune rejection and should be used with caution.

Preventing type 1 diabetes mellitus: the promise of gene therapy

Type 1 (insulin-dependent) diabetes mellitus is an autoimmune disease that has no cure. Closed-loop insulin administration strategies and approaches for replacement of the insulin-producing beta cells may offer improved treatments, which could delay or prevent diabetes complications. In the long run, however, prevention of type 1 diabetes in susceptible individuals represents the best chance for reducing the toll of the disease. Prevention of type 1 diabetes will require reliable methods for early diagnosis of predisposition to the disease, using improved genetic and serological screening on a wide scale. Identification of the primary antigenic target(s) for autoimmunity will allow intervention in prediabetes stages aimed at the induction of antigen-specific tolerance. In addition to manipulation of the immune system, the susceptibility of beta cells to autoimmunity could be reduced. A number of genes have been shown to increase beta-cell resistance to immune effector molecules in animal models and cultured beta-cell lines. These genes could be used for preventive gene therapy of type 1 diabetes mellitus if expressed in beta cells prior to the onset of autoimmune destruction. This prospect depends on the development of safe and efficient vectors, and approaches for cell-specific targeting of these vectors to beta cells in vivo.

Delivery of erythropoietin by encapsulated myoblasts in a genetic model of severe anemia

BACKGROUND

Existing animal models of anemia inadequately reflect the hematocrit usually present in chronic renal failure (CRF) patients and do not permit long-term treatment studies. The transgenic mouse strain 134.3LC (Epo-TAg(H)) displays a severe chronic anemia resembling that observed clinically during CRF, while displaying an active, normal life span. This phenotype makes it a particularly interesting mouse model for testing erythropoietin (Epo)-based gene transfer strategies.

METHODS

Ex vivo gene therapy was employed to administer mouse Epo to homozygous anemic Epo-TAg(H) mice. Encapsulated C(2)C(12) myoblasts genetically engineered to secrete 163 IU mouse Epo/10(6) cells/day were subcutaneously transplanted on the dorsal flank of the mice. Efficacy of delivered Epo was monitored by weekly measurements of animal hematocrit.

RESULTS

Most treated homozygous Epo-TAg(H) mice displayed only a transient rise in hematocrit before eventually decreasing to levels as low as 3%. Administering the immunosuppressor anti-CD4+ monoclonal antibody (mAb) to homozygous Epo-TAg(H) mice, beginning at the time of implantation, permitted a rise in hematocrit that remained stable at elevated levels in cases of continued immunosuppression.

CONCLUSIONS

Mice having the T antigen insertion in both Epo alleles appeared to develop an immune response to the natural mouse Epo delivered by encapsulated cells. By preventing this reaction using immunosuppression, we demonstrate that encapsulated myoblasts can deliver therapeutic doses of mouse Epo systemically and restore hemopoiesis in a genetic model of severe anemia.

Cell replacement therapy for type 1 diabetes

Replacement of the insulin-producing pancreatic islet beta cells represents the ultimate treatment for type 1 diabetes. Recent advances in islet transplantation underscore the urgent need for developing alternatives to human tissue donors, which are scarce. Two possible approaches are the expansion of differentiated beta cells by reversible immortalization and the generation of insulin-producing cells from embryonic or adult stem cells. It is possible that new insights into endocrine pancreas development will ultimately lead to manipulation of progenitor-cell fate towards the beta-cell phenotype of insulin production, storage and regulated secretion. Both allogeneic and autologous surrogate beta cells are likely to require protection from recurring autoimmunity. This protection might take the form of tolerization, cell encapsulation, or cell engineering with immunoprotective genes. If successful, these approaches could lead to widespread cell replacement therapy for type 1 diabetes.

cFLIP protein prevents tumor necrosis factor-alpha-mediated induction of caspase-8-dependent apoptosis in insulin-secreting betaTc-Tet cells

Type 1 diabetes is characterized by the infiltration of activated leukocytes within the pancreatic islets, leading to beta-cell dysfunction and destruction. The exact role played by interferon-gamma, tumor necrosis factor (TNF)-alpha, and interleukin-1beta in this pathogenic process is still only partially understood. To study cytokine action at the cellular level, we are working with the highly differentiated insulin-secreting cell line, betaTc-Tet. We previously reported that it was susceptible to apoptosis induced by TNF-alpha, in combination with interleukin-1beta and interferon-gamma. Here, we report that cytokine-induced apoptosis was correlated with the activation of caspase-8. We show that in betaTc-Tet cells, overexpression of cFLIP, the cellular FLICE (FADD-like IL-1beta-converting enzyme)-inhibitory protein, completely abolished cytokine-dependent activation of caspase-8 and protected the cells against apoptosis. Furthermore, cFLIP overexpression increased the basal and interleukin-1beta-mediated transcriptional activity of nuclear factor (NF)-kappaB, whereas it did not change cytokine-induced inducible nitric oxide synthase gene transcription and nitric oxide secretion. The presence of cFLIP prevented the weak TNF-alpha-induced reduction in cellular insulin content and secretion; however, it did not prevent the decrease in glucose-stimulated insulin secretion induced by the combined cytokines, in agreement with our previous data demonstrating that interferon-gamma alone could induce these beta-cell dysfunctions. Together, our data demonstrate that overexpression of cFLIP protects mouse beta-cells against TNF-alpha-induced caspase-8 activation and apoptosis and is correlated with enhanced NF-kappaB transcriptional activity, suggesting that cFLIP may have an impact on the outcome of death receptor-triggered responses by directing the intracellular signals from beta-cell death to beta-cell survival.