Regulation of insulin biosynthesis in pancreatic beta cells by an endoplasmic reticulum-resident protein kinase IRE1.

In pancreatic beta cells, the endoplasmic reticulum (ER) is an important site for insulin biosynthesis and the folding of newly synthesized proinsulin. Here, we show that IRE1alpha, an ER-resident protein kinase, has a crucial function in insulin biosynthesis. IRE1alpha phosphorylation is coupled to insulin biosynthesis in response to transient exposure to high glucose; inactivation of IRE1alpha signaling by siRNA or inhibition of IRE1alpha phosphorylation hinders insulin biosynthesis. IRE1 activation by high glucose does not accompany XBP-1 splicing and BiP dissociation but upregulates its target genes such as WFS1. Thus, IRE1 signaling activated by transient exposure to high glucose uses a unique subset of downstream components and has a beneficial effect on pancreatic beta cells. In contrast, chronic exposure of beta cells to high glucose causes ER stress and hyperactivation of IRE1, leading to the suppression of insulin gene expression. IRE1 signaling is therefore a potential target for therapeutic regulation of insulin biosynthesis.

TLR agonists prevent the establishment of allogeneic hematopoietic chimerism in mice treated with costimulation blockade.

Activation of TLR4 by administration of LPS shortens the survival of skin allografts in mice treated with costimulation blockade through a CD8 T cell-dependent, MyD88-dependent, and type I IFN receptor-dependent pathway. The effect of TLR activation on the establishment of allogeneic hematopoietic chimerism in mice treated with costimulation blockade is not known. Using a costimulation blockade protocol based on a donor-specific transfusion (DST) and a short course of anti-CD154 mAb, we show that LPS administration at the time of DST matures host alloantigen-presenting dendritic cells, prevents the establishment of mixed allogeneic hematopoietic chimerism, and shortens survival of donor-specific skin allografts. LPS mediates its effects via a mechanism that involves both CD4(+) and CD8(+) T cells and results from signaling through either the MyD88 or the type I IFN receptor pathways. We also document that timing of LPS administration is critical, as injection of LPS 24 h before treatment with DST and anti-CD154 mAb does not prevent hematopoietic engraftment but administration the day after bone marrow transplantation does. We conclude that TLR4 activation prevents the induction of mixed allogeneic hematopoietic chimerism through type I IFN receptor and MyD88-dependent signaling, which leads to the up-regulation of costimulatory molecules on host APCs and the generation of alloreactive T cells. These data suggest that distinct but overlapping cellular and molecular mechanisms control the ability of TLR agonists to block tolerance induction to hematopoietic and skin allografts in mice treated with costimulation blockade.

Dynamic glucoregulation and mammalian-like responses to metabolic and developmental disruption in zebrafish.

Zebrafish embryos are emerging as models of glucose metabolism. However, patterns of endogenous glucose levels, and the role of the islet in glucoregulation, are unknown. We measured absolute glucose levels in zebrafish and mouse embryos, and demonstrate similar, dynamic glucose fluctuations in both species. Further, we show that chemical and genetic perturbations elicit mammalian-like glycemic responses in zebrafish embryos. We show that glucose is undetectable in early zebrafish and mouse embryos, but increases in parallel with pancreatic islet formation in both species. In zebrafish, increasing glucose is associated with activation of gluconeogenic phosphoenolpyruvate carboxykinase1 (pck1) transcription. Non-hepatic Pck1 protein is expressed in mouse embryos. We show using RNA in situ hybridization, that zebrafish pck1 mRNA is similarly expressed in multiple cell types prior to hepatogenesis. Further, we demonstrate that the Pck1 inhibitor 3-mercaptopicolinic acid suppresses normal glucose accumulation in early zebrafish embryos. This shows that pre- and extra-hepatic pck1 is functional, and provides glucose locally to rapidly developing tissues. To determine if the primary islet is glucoregulatory in early fish embryos, we injected pdx1-specific morpholinos into transgenic embryos expressing GFP in beta cells. Most morphant islets were hypomorphic, not a genetic, but embryos still exhibited persistent hyperglycemia. We conclude from these data that the early zebrafish islet is functional, and regulates endogenous glucose. In summary, we identify mechanisms of glucoregulation in zebrafish embryos that are conserved with embryonic and adult mammals. These observations justify use of this model in mechanistic studies of human metabolic disease.

Parameters for establishing humanized mouse models to study human immunity: analysis of human hematopoietic stem cell engraftment in three immunodeficient strains of mice bearing the IL2rgamma(null) mutation.

"Humanized" mouse models created by engraftment of immunodeficient mice with human hematolymphoid cells or tissues are an emerging technology with broad appeal across multiple biomedical disciplines. However, investigators wishing to utilize humanized mice with engrafted functional human immune systems are faced with a myriad of variables to consider. In this study, we analyze HSC engraftment methodologies using three immunodeficient mouse strains harboring the IL2rgamma(null) mutation; NOD-scid IL2rgamma(null), NOD-Rag1(null) IL2rgamma(null), and BALB/c-Rag1(null) IL2rgamma(null) mice. Strategies compared engraftment of human HSC derived from umbilical cord blood following intravenous injection into adult mice and intracardiac and intrahepatic injection into newborn mice. We observed that newborn recipients exhibited enhanced engraftment as compared to adult recipients. Irrespective of the protocol or age of recipient, both immunodeficient NOD strains support enhanced hematopoietic cell engraftment as compared to the BALB/c strain. Our data define key parameters for establishing humanized mouse models to study human immunity.

Passing the baton--to whom?

Scientific discovery occasionally occurs as a sudden and dramatic leap ahead but more often proceeds at a subtler and steadier pace. Each small step forward may escape public notice but is ultimately vital to the journey's success. Indeed, such gradual advancement represents the collective contributions of many workers in the field, some new to the journey. While the notion of combined effort and multiple contributors is honorable, it poses an inherent danger. In our society, unproven, unorthodox, or unnoticed researchers may not receive the funding or support needed to make their contributions. Furthermore, even if they have the potential to make a leap, a hostile environment may preclude their doing so. This article concentrates on the looming crisis in diabetes research, but the principles pertain to all fields of clinical and biomedical science.

Depletion of the programmed death-1 receptor completely reverses established clonal anergy in CD4(+) T lymphocytes via an interleukin-2-dependent mechanism.

Recent studies have implicated the cell surface receptor Programmed Death-1 (PD-1) in numerous models of T cell anergy, though the specific mechanisms by which the PD-1 signal maintains tolerance is not clear. We demonstrate that the depletion of PD-1 with siRNA results in a complete reversal of clonal anergy in the A.E7 T cell model, suggesting that the mechanism by which PD-1 maintains the anergic phenotype is a T-cell-intrinsic phenomenon, and not one dependent on other cell populations in vivo. We have also shown that the neutralization of IL-2 during restimulation abrogates the effect of PD-1 depletion, suggesting that tolerance mediated by PD-1 is wholly IL-2 dependent, and likewise intrinsic to the tolerized cells.

Role of innate immunity in transplantation tolerance.

Allogeneic organ transplantation has proven to be an effective therapeutic strategy for patients with end-stage organ disease. However, the chronic immunosuppression that is required for the survival of the allograft increases the risk for infection and malignancy. The establishment of transplantation tolerance, defined functionally as the survival of a donor allograft in the absence of immunosuppression, is the ultimate goal in the field of transplantation. Transplantation tolerance can be achieved using approaches that induce peripheral and/or central tolerance to the allograft. Protocols based on costimulation blockade (CB) have emerged as some of the most promising protocols for inducing long-term allograft survival in the absence of chronic immunosuppression. Despite its potential, recent evidence suggests that the efficacy of costimulation blockade can be reduced by environmental perturbations such as infection or inflammation, which activate Toll-like receptors (TLR). In this review, we discuss how the activation of TLRs can affect the induction and maintenance of transplantation tolerance.

Failure of alpha-galactosylceramide to prevent diabetes in virus-inducible models of type 1 diabetes in the rat.

BACKGROUND: Alpha-galactosylceramide (alpha-GalCer) is an invariant natural killer T (iNKT) cell ligand that prevents type 1 diabetes in NOD mice. However, alpha-GalCer can activate or suppress immune responses, raising concern about its potential use in human diabetes. MATERIALS AND METHODS: To evaluate this therapeutic issue further, BBDR and LEW.1WR1 rats were treated with Kilham rat virus (KRV) plus polyinosinic-polycytidylic acid, with or without alpha-GalCer, and followed for onset of diabetes. RESULTS: alpha-GalCer did not prevent diabetes in inducible rat models. To investigate this discrepancy, we analyzed iNKT cell function. Splenocytes stimulated with alpha-GalCer produced similar levels of IFNgamma in all rat strains, but less than mouse splenocytes. Rat splenocytes stimulated with alpha-GalCer preferentially produced IL-12, whereas mouse splenocytes preferentially produced IL-4. CONCLUSION: alpha-GalCer elicits species-specific cytokine responses in iNKT cells. In humans with type 1 diabetes, differences in iNKT cell responses to stimulation with alpha-GalCer due to age, genetic variability and other factors may influence its therapeutic potential.

Protein kinase C signaling during T cell activation induces the endoplasmic reticulum stress response.

T cell receptor (TCR) ligation (signal one) in the presence of co-stimulation (signal two) results in downstream signals that increase protein production enabling naïve T cells to fully activate and gain effector function. Enhanced production of proteins by a cell requires an increase in endoplasmic reticulum (ER) chaperone expression, which is accomplished through activation of a cellular mechanism known as the ER stress response. The ER stress response is initiated during the cascade of events that occur for the activation of many cells; however, this process has not been comprehensively studied for T cell function. In this study, we used primary T cells and mice circulating TCR transgenic CD8(+) T cells to investigate ER chaperone expression in which TCR signaling was initiated in the presence or absence of co-stimulation. In the presence of both signals, in vitro and in vivo analyses demonstrated induction of the ER stress response, as evidenced by elevated expression of GRP78 and other ER chaperones. Unexpectedly, ER chaperones were also increased in T cells exposed only to signal one, a treatment known to cause T cells to enter the 'nonresponsive' states of anergy and tolerance. Treatment of T cells with an inhibitor to protein kinase C (PKC), a serine/threonine protein kinase found downstream of TCR signaling, indicated PKC is involved in the induction of the ER stress response during the T cell activation process, thus revealing a previously unknown role for this signaling protein in T cells. Collectively, these data suggest that induction of the ER stress response through PKC signaling is an important component for the preparation of a T cell response to antigen.

Expanded CD34+ human umbilical cord blood cells generate multiple lymphohematopoietic lineages in NOD-scid IL2rgamma(null) mice.

Umbilical cord blood (UCB) is increasingly being used for human hematopoietic stem cell (HSC) transplantation in children but often requires pooling multiple cords to obtain sufficient numbers for transplantation in adults. To overcome this limitation, we have used an ex vivo two-week culture system to expand the number of hematopoietic CD34(+) cells in cord blood. To assess the in vivo function of these expanded CD34(+) cells, cultured human UCB containing 1 x 10(6) CD34(+) cells were transplanted into conditioned NOD-scid IL2rgamma(null) mice. The expanded CD34(+) cells displayed short- and long-term repopulating cell activity. The cultured human cells differentiated into myeloid, B-lymphoid, and erythroid lineages, but not T lymphocytes. Administration of human recombinant TNFalpha to recipient mice immediately prior to transplantation promoted human thymocyte and T-cell development. These T cells proliferated vigorously in response to TCR cross-linking by anti-CD3 antibody. Engrafted TNFalpha-treated mice generated antibodies in response to T-dependent and T-independent immunization, which was enhanced when mice were co-treated with the B cell cytokine BLyS. Ex vivo expanded CD34(+) human UCB cells have the capacity to generate multiple hematopoietic lineages and a functional human immune system upon transplantation into TNFalpha-treated NOD-scid IL2rgamma(null) mice.

Viral infection: a potent barrier to transplantation tolerance.

Transplantation of allogeneic organs has proven to be an effective therapeutic for a large variety of disease states, but the chronic immunosuppression that is required for organ allograft survival increases the risk for infection and neoplasia and has direct organ toxicity. The establishment of transplantation tolerance, which obviates the need for chronic immunosuppression, is the ultimate goal in the field of transplantation. Many experimental approaches have been developed in animal models that permit long-term allograft survival in the absence of chronic immunosuppression. These approaches function by inducing peripheral or central tolerance to the allograft. Emerging as some of the most promising approaches for the induction of tolerance are protocols based on costimulation blockade. However, as these protocols move into the clinic, there is recognition that little is known as to their safety and efficacy when confronted with environmental perturbants such as virus infection. In animal models, it has been reported that virus infection can prevent the induction of tolerance by costimulation blockade and, in at least one experimental protocol, can lead to significant morbidity and mortality. In this review, we discuss how viruses modulate the induction and maintenance of transplantation tolerance.

Hematopoietic chimerism and central tolerance created by peripheral-tolerance induction without myeloablative conditioning.

Allogeneic hematopoietic chimerism leading to central tolerance has significant therapeutic potential. Realization of that potential has been impeded by the need for myeloablative conditioning of the host and development of graft-versus-host disease (GVHD). To surmount these impediments, we have adapted a costimulation blockade-based protocol developed for solid organ transplantation for use in stem cell transplantation. The protocol combines donor-specific transfusion (DST) with anti-CD154 mAb. When applied to stem cell transplantation, administration of DST, anti-CD154 mAb, and allogeneic bone marrow leads to hematopoietic chimerism and central tolerance with no myeloablation and no GVHD. Tolerance in this system results from deletion of both peripheral host alloreactive CD8+ T cells and nascent intrathymic alloreactive CD8+ T cells. In the absence of large numbers of host alloreactive CD8+ T cells, the transfusion that precedes transplantation need not be of donor origin, suggesting that both allospecific and non-allospecific mechanisms regulate engraftment. Agents that interfere with peripheral transplantation tolerance impair establishment of chimerism. We conclude that robust allogeneic hematopoietic chimerism and central tolerance can be established in the absence of host myeloablative conditioning using a peripheral transplantation tolerance protocol.

Diabetes research in jeopardy: the extinction of clinical diabetes researchers.

Finding a cure for an autoimmune disease, such as diabetes, must be viewed as a marathon. Although there are occasional quick sprints forward on the road to discovery, the bulk of research is carried out steadily over time. Over the years, researchers have made progressive strides toward a cure, but our field is now facing a crisis. We need youthful researchers with fresh new perspectives to carry on the work started by forerunners in the field. In fact, many young people never get the opportunity to work in a scientific field. Of those who do choose to study science, after receiving a bachelor's degree in that field, only 4% eventually receive their doctorate. There are many reasons for the abrupt end of the academic path for these students. Perhaps they are stymied in their education, frustrated by the lack of grant support and mentorship provided to young scientists. On average, a scientist receives his or her first NIH R01 award at the age of 43 years. Moreover, many young researchers lack the mentorship they seek from more established scientists. This hurdle can be overcome by providing young scientists the ability to work unreservedly with other mature scientists. Ideally, a Diabetes Research Center needs to be geared toward facilitating collaboration and free exchange of ideas to promote the maturation of young scientists. Additionally, this environment, can offer young scientists the resources that would otherwise be unavailable to them. This concept is fundamental to creating more experienced and prolific scientists in the field of diabetes.

Development of new-generation HU-PBMC-NOD/SCID mice to study human islet alloreactivity.

The use of "humanized" mice represents an appealing translational model for studies of the pathogenesis of immune-mediated diseases and for the evaluation of potential therapeutics. The utility of humanized mice depends on their ability to model the human immune system with high fidelity, and, in this respect, previous models have fallen short. The recently developed NOD-scid Il2rgamma(null) mouse, however, exhibits greatly enhanced ability to support the engraftment of human peripheral blood mononuclear cells. Herein, we describe the challenges of recapitulating human immunity in humanized mice and features of NOD-scid Il2rgamma(null) mice that help overcome them.

Humanized NOD/LtSz-scid IL2 receptor common gamma chain knockout mice in diabetes research.

There are many rodent models of autoimmune diabetes that have been used to study the pathogenesis of human type 1 diabetes (T1D), including the non-obese diabetic (NOD) mouse, the biobreeding (BB) rat, and the transgenic mouse models. However, mice and rats are not humans, and these rodent models do not completely recapitulate the autoimmune pathogenesis of the human disease. In addition, many of the reagents, tools, and therapeutics proposed for use in humans may be species specific and cannot be investigated in rodents. Researchers have used nonhuman primates to more closely mimic the human immune system and, to study species-specific therapeutics, but these studies are associated with additional ethical and economic constraints and, to date, no model of autoimmune diabetes in this species has been described. New animal models are needed that will permit the in vivo investigation of human immune systems and analyses of the pathogenesis of human T1D without putting individuals at risk. To fill this need, we are developing humanized mouse models for the in vivo study of T1D. These models are based on our newly generated stock of NOD-scid IL2rgamma(null) mice, which engraft at higher levels with human hematolymphoid cells and exhibit enhanced function of the engrafted human immune systems compared with previous humanized mouse models. Overall, development of these new generations of humanized mice should facilitate in vivo studies of the human immune system as well as permit the investigation of the pathogenesis and effector phases of human T1D.

Autoimmune diabetes and resistance to xenograft transplantation tolerance in NOD mice.

Costimulation blockade induces prolonged rat islet and skin xenograft survival in C57BL/6 mice. Nonobese diabetic (NOD) mice, which are used to model human autoimmune diabetes, are resistant to costimulation blockade-induced allograft tolerance. We tested the hypothesis that NOD mice would also be resistant to costimulation blockade-induced rat xenograft tolerance. We report that rat islet xenograft survival is short in spontaneously diabetic NOD mice treated with a tolerizing regimen of donor-specific transfusion and anti-CD154 antibody. Rat islet xenograft survival is only marginally longer in chemically diabetic NOD mice treated with costimulation blockade but is prolonged further in NOD Idd congenic mice bearing C57-derived chromosome 3 loci. Reciprocally, the presence of NOD-derived chromosome 3 loci shortens islet xenograft survival in tolerized C57BL/6 mice. Islet xenograft survival is longer in tolerized NOD.CD4a(-/-) and (NOD x C57BL/6)F1 mice than in NOD mice but still much shorter than in C57BL/6 mice. Skin xenograft survival in (NOD x C57BL/6)F1 mice treated with costimulation blockade is short, suggesting a strong genetic resistance to skin xenograft tolerance induction. We conclude that the resistance of NOD mice to xenograft tolerance induction involves some mechanisms that also participate in the expression of autoimmunity and other mechanisms that are distinct.

Costimulatory blockade induces hyporesponsiveness in T cells that recognize alloantigen via indirect antigen presentation.

BACKGROUND: Blockade of T cell costimulation by treatment with donor-specific transfusion (DST) and anti-CD154 monoclonal antibody (mAb) induces prolonged allograft survival in mice. This effect is due in part to deletion of host CD8 and CD4 T cells that recognize alloantigen by direct presentation. The fate of host CD4 T cells that recognize alloantigen by indirect presentation, however, is unclear. METHODS: We studied Tg361 TCR transgenic CD4 T cells that recognize alloantigen by indirect presentation. Carboxyfluorescein diacetate, succinimidyl ester-labeled Tg361 cells were adoptively transferred into syngeneic nontransgenic recipients and their fate in the peripheral blood, spleen, and lymph nodes following treatment with DST and anti-CD154 was analyzed. RESULTS: Treatment of mice with DST plus anti-CD154 mAb does not delete Tg361 CD4 T cells, but instead renders them hyporesponsive to rechallenge with alloantigen. Mice circulating hyporesponsive CD4 T cells also fail to reject skin allografts. The hyporesponsive state of the T cells is not reversed by the addition of interleukin-2, anti-CD28 mAb, or an agonistic anti-CD134 mAb in the presence of antigen. These T cells are capable of activation, however, as evidenced by in vitro proliferation in response to anti-CD3 mAb. CONCLUSIONS: These results demonstrate that costimulation blockade can induce hyporesponsiveness of host CD4 T cells recognizing alloantigens by indirect presentation, thus prolonging graft survival by a mechanism that does not involve deletion of alloreactive T cells.

Autoimmune diabetes and the circle of tolerance.

The concept of immunological tolerance is central to our understanding of type 1 diabetes and the development of strategies for its prediction, prevention, and cure. Tolerance simply refers to the absence of an immune response. Most of us are born with an immune system that develops tolerance to all the other systems of our bodies as well as to the things that we eat. It is the loss of immunological tolerance that leads to autoimmunity. And when that autoimmune response directly or indirectly targets the beta-cell, type 1 diabetes is the result. In the U.S., 1 in 600 of us loses tolerance to pancreatic beta-cells. Interference with T-cell function after the loss of tolerance, as can be achieved with immunosuppressive drugs like cyclosporin, arrests the disease, but the cost in side effects is high. Clearly, stopping the loss of tolerance would be preferable. If we can stop the loss of tolerance, we can prevent the disease. We and many others have investigated both approaches. But what of the people who already have diabetes? For them a separate but related strategy, tolerance induction, is required. Specifically, islet transplantation tolerance induction holds out the promise of being able to cure the disease. This has been the ultimate goal of our laboratory's work for the past two decades.

NOD congenic mice genetically protected from autoimmune diabetes remain resistant to transplantation tolerance induction.

The loss of self-tolerance leading to autoimmune type 1 diabetes in the NOD mouse model involves at least 19 genetic loci. In addition to their genetic defects in self-tolerance, NOD mice resist peripheral transplantation tolerance induced by costimulation blockade using donor-specific transfusion and anti-CD154 antibody. Hypothesizing that these two abnormalities might be related, we investigated whether they could be uncoupled through a genetic approach. Diabetes-resistant NOD and C57BL/6 stocks congenic for various reciprocally introduced Idd loci were assessed for their ability to be tolerized. Surprisingly, in NOD congenic mice that are almost completely protected from diabetes, costimulation blockade failed to prolong skin allograft survival. In reciprocal C57BL/6 congenic mice with NOD-derived Idd loci, skin allograft survival was readily prolonged by costimulation blockade. These data indicate that single or multiple combinations of evaluated Idd loci that dramatically reduce diabetes frequency do not correct resistance to peripheral transplantation tolerance induced by costimulation blockade. We suggest that mechanisms controlling autoimmunity and transplantation tolerance in NOD mice are not completely overlapping and are potentially distinct, or that the genetic threshold for normalizing the transplantation tolerance defect is higher than that for preventing autoimmune diabetes.

Islet allograft survival induced by costimulation blockade in NOD mice is controlled by allelic variants of Idd3.

NOD mice develop type 1 autoimmune diabetes and exhibit genetically dominant resistance to transplantation tolerance induction. These two phenotypes are genetically separable. Costimulation blockade fails to prolong skin allograft survival in (NOD x C57BL/6)F1 mice and in NOD-related strains made diabetes-resistant by congenic introduction of protective major histocompatibility complex (MHC) or non-MHC Idd region genes. Here, we tested the hypothesis that the genetic basis for the resistance of NOD mice to skin allograft tolerance also applies to islet allografts. Surprisingly, costimulation blockade induced permanent islet allograft survival in (NOD x C57BL/6)F1 mice but not in NOD mice. After costimulation blockade, islet allograft survival was prolonged in diabetes-resistant NOD.B6 Idd3 mice and shortened in diabetes-free C57BL/6 mice congenic for the NOD Idd3 variant. Islet allograft tolerance could not be induced in diabetes-resistant NOD.B10 Idd5 and NOD.B10 Idd9 mice. The data demonstrate that 1) NOD mice resist islet allograft tolerance induction; 2) unlike skin allografts, resistance to islet allograft tolerance is a genetically recessive trait; 3) an Idd3 region gene(s) is an important determinant of islet allograft tolerance induction; and 4) there may be overlap in the mechanism by which the Idd3 resistance locus improves self-tolerance and the induction of allotolerance.