Protection of NIT-1 pancreatic beta-cells from immune attack by inhibition of NF-kappaB

Untangling the genetics of beta cell dysfunction and death in type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is a complex multi-system disease which arises from both environmental and genetic factors, resulting in the destruction of insulin-producing pancreatic beta cells. Over the past two decades, human genetic studies have provided new insight into the etiology of T1D, including an appreciation for the role of beta cells in their own demise.

SCOPE OF REVIEW

Here, we outline models supported by human genetic data for the role of beta cell dysfunction and death in T1D. We highlight the importance of strong evidence linking T1D genetic associations to bona fide candidate genes for mechanistic and therapeutic consideration. To guide rigorous interpretation of genetic associations, we describe molecular profiling approaches, genomic resources, and disease models that may be used to construct variant-to-gene links and to investigate candidate genes and their role in T1D.

MAJOR CONCLUSIONS

We profile advances in understanding the genetic causes of beta cell dysfunction and death at individual T1D risk loci. We discuss how genetic risk prediction models can be used to address disease heterogeneity. Further, we present areas where investment will be critical for the future use of genetics to address open questions in the development of new treatment and prevention strategies for T1D.

Immunopeptidome mining reveals a novel ERS-induced target in T1D

Autoreactive CD8+ T cells play a key role in type 1 diabetes (T1D), but the antigen spectrum that activates autoreactive CD8+ T cells remains unclear. Endoplasmic reticulum stress (ERS) has been implicated in β-cell autoantigen generation. Here, we analyzed the major histocompatibility complex class I (MHC-I)-associated immunopeptidome (MIP) of islet β-cells under steady and ERS conditions and found that ERS reshaped the MIP of β-cells and promoted the MHC-I presentation of a panel of conventional self-peptides. Among them, OTUB258-66 showed immunodominance, and the corresponding autoreactive CD8+ T cells were diabetogenic in nonobese diabetic (NOD) mice. High glucose intake upregulated pancreatic OTUB2 expression and amplified the OTUB258-66-specific CD8+ T-cell response in NOD mice. Repeated OTUB258-66 administration significantly reduced the incidence of T1D in NOD mice. Interestingly, peripheral blood mononuclear cells (PBMCs) from patients with T1D, but not from healthy controls, showed a positive IFN-γ response to human OTUB2 peptides. This study provides not only a new explanation for the role of ERS in promoting β-cell-targeted autoimmunity but also a potential target for the prevention and treatment of T1D. The data are available via ProteomeXchange with the identifier PXD041227.

Inherent ER stress in pancreatic islet β cells causes self-recognition by autoreactive T cells in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease characterized by pancreatic β cell destruction induced by islet reactive T cells that have escaped central tolerance. Many physiological and environmental triggers associated with T1D result in β cell endoplasmic reticulum (ER) stress and dysfunction, increasing the potential for abnormal post-translational modification (PTM) of proteins. We hypothesized that β cell ER stress induced by environmental and physiological conditions generates abnormally-modified proteins for the T1D autoimmune response. To test this hypothesis we exposed the murine CD4(+) diabetogenic BDC2.5 T cell clone to murine islets in which ER stress had been induced chemically (Thapsigargin). The BDC2.5 T cell IFNγ response to these cells was significantly increased compared to non-treated islets. This β cell ER stress increased activity of the calcium (Ca(2+))-dependent PTM enzyme tissue transglutaminase 2 (Tgase2), which was necessary for full stress-dependent immunogenicity. Indeed, BDC2.5 T cells responded more strongly to their antigen after its modification by Tgase2. Finally, exposure of non-antigenic murine insulinomas to chemical ER stress in vitro or physiological ER stress in vivo caused increased ER stress and Tgase2 activity, culminating in higher BDC2.5 responses. Thus, β cell ER stress induced by chemical and physiological triggers leads to β cell immunogenicity through Ca(2+)-dependent PTM. These findings elucidate a mechanism of how β cell proteins are modified and become immunogenic, and reveal a novel opportunity for preventing β cell recognition by autoreactive T cells.

Distinct differences in the responses of the human pancreatic β-cell line EndoC-βH1 and human islets to proinflammatory cytokines

While insulinoma cells have been developed and proven to be extremely useful in studies focused on mechanisms controlling β-cell function and viability, translating findings to human β-cells has proven difficult because of the limited access to human islets and the absence of suitable insulinoma cell lines of human origin. Recently, a human β-cell line, EndoC-βH1, has been derived from human fetal pancreatic buds. The purpose of this study was to determine whether human EndoC-βH1 cells respond to cytokines in a fashion comparable to human islets. Unlike most rodent-derived insulinoma cell lines that respond to cytokines in a manner consistent with rodent islets, EndoC-βH1 cells fail to respond to a combination of cytokines (IL-1, IFN-γ, and TNF) in a manner consistent with human islets. Nitric oxide, produced following inducible nitric oxide synthase (iNOS) expression, is a major mediator of cytokine-induced human islet cell damage. We show that EndoC-βH1 cells fail to express iNOS or produce nitric oxide in response to this combination of cytokines. Inhibitors of iNOS prevent cytokine-induced loss of human islet cell viability; however, they do not prevent cytokine-induced EndoC-βH1 cell death. Stressed human islets or human islets expressing heat shock protein 70 (HSP70) are resistant to cytokines, and, much like stressed human islets, EndoC-βH1 cells express HSP70 under basal conditions. Elevated basal expression of HSP70 in EndoC-βH1 cells is consistent with the lack of iNOS expression in response to cytokine treatment. While expressing HSP70, EndoC-βH1 cells fail to respond to endoplasmic reticulum stress activators, such as thapsigargin. These findings indicate that EndoC-βH1 cells do not faithfully recapitulate the response of human islets to cytokines. Therefore, caution should be exercised when making conclusions regarding the actions of cytokines on human islets when using this human-derived insulinoma cell line.

Role of the mitochondria in immune-mediated apoptotic death of the human pancreatic β cell line βLox5

Mitochondria are indispensable in the life and death of many types of eukaryotic cells. In pancreatic beta cells, mitochondria play an essential role in the secretion of insulin, a hormone that regulates blood glucose levels. Unregulated blood glucose is a hallmark symptom of diabetes. The onset of Type 1 diabetes is preceded by autoimmune-mediated destruction of beta cells. However, the exact role of mitochondria has not been assessed in beta cell death. In this study, we examine the role of mitochondria in both Fas- and proinflammatory cytokine-mediated destruction of the human beta cell line, βLox5. IFNγ primed βLox5 cells for apoptosis by elevating cell surface Fas. Consequently, βLox5 cells were killed by caspase-dependent apoptosis by agonistic activation of Fas, but only after priming with IFNγ. This beta cell line undergoes both apoptotic and necrotic cell death after incubation with the combination of the proinflammatory cytokines IFNγ and TNFα. Additionally, both caspase-dependent and -independent mechanisms that require proper mitochondrial function are involved. Mitochondrial contributions to βLox5 cell death were analyzed using mitochondrial DNA (mtDNA) depleted βLox5 cells, or βLox5 ρ⁰ cells. βLox5 ρ⁰ cells are not sensitive to IFNγ and TNFα killing, indicating a direct role for the mitochondria in cytokine-induced cell death of the parental cell line. However, βLox5 ρ⁰ cells are susceptible to Fas killing, implicating caspase-dependent extrinsic apoptotic death is the mechanism by which these human beta cells die after Fas ligation. These data support the hypothesis that immune mediators kill βLox5 cells by both mitochondrial-dependent intrinsic and caspase-dependent extrinsic pathways.

Impaired synthesis of erythropoietin, glutamine synthetase and metallothionein in the skin of NOD/SCID/gamma(c)(null) and Foxn1 nu/nu mice with misbalanced production of MHC class II complex

Most skin pathologies are characterized by unbalanced synthesis of major histocompatability complex II (MHC-II) proteins. Healthy skin keratinocytes simultaneously produce large amounts of MHC-II and regeneration-supporting proteins, e.g. erythropoietin (EPO), EPO receptor (EPOR), glutamine synthetase (GS) and metallothionein (MT). To investigate the level of regeneration-supporting proteins in the skin during misbalanced production of MHC-II, skin sections from nonobese diabetic/severe combined immunodeficient (NOD/SCID)/gamma (c) (null) and or Foxn1 nu/nu mice which are a priory known to under- and over-express MHC II, respectively, were used. Double immunofluorescence analysis of NOD/SCID/gamma (c) (null) skin sections showed striking decrease in expression of MHC-II, EPO, GS and MT. In Foxn1 nu/nu mouse skin, GS was strongly expressed in epidermis and in hair follicles (HF), which lacked EPO. In nude mouse skin EPO and MHC-II were over-expressed in dermal fibroblasts and they were completely absent from cortex, channel, medulla and keratinocytes surrounding the HF, suggest a role for EPO in health and pathology of hair follicle. The level of expression of EPO and GS in both mutant mice was confirmed by results of Western blot analyses. Strong immunoresponsiveness of EPOR in the hair channels of NOD/SCID/gamma (c) (null) mouse skin suggests increased requirements of skin cells for EPO and possible benefits of exogenous EPO application during disorders of immune system accompanied by loss MHC-II in skin cells.

Activation of CDCA1-KNTC2, members of centromere protein complex, involved in pulmonary carcinogenesis

We found cotransactivation of cell division associated 1 (CDCA1) and kinetochore associated 2 (KNTC2), members of the evolutionarily conserved centromere protein complex, in non-small cell lung carcinomas (NSCLC). Immunohistochemical analysis using lung cancer tissue microarray confirmed high levels of CDCA1 and KNTC2 proteins in the great majority of lung cancers of various histologic types. Their elevated expressions were associated with poorer prognosis of NSCLC patients. Knockdown of either CDCA1 or KNTC2 expression with small interfering RNA significantly suppressed growth of NSCLC cells. Furthermore, inhibition of their binding by a cell-permeable peptide carrying the CDCA1-derived 19-amino-acid peptide (11R-CDCA1(398-416)) that correspond to the binding domain to KNTC2 effectively suppressed growth of NSCLC cells. As our data imply that human CDCA1 and KNTC2 seem to fall in the category of cancer-testis antigens, and that their simultaneous up-regulation is a frequent and important feature of cell growth/survival of lung cancer, selective suppression of CDCA1 or KNTC2 activity and/or inhibition of the CDCA1-KNTC2 complex formation could be a promising therapeutic target for treatment of lung cancers.

Enhanced expression of glutathione peroxidase protects islet beta cells from hypoxia-reoxygenation

The survival of pancreatic islet beta-cell xenografts and allografts may be affected by damaging reactive oxygen and nitrogen species generated during hypoxia-reoxygenation. Peroxynitrite, which is formed from superoxide and nitric oxide, appears to be an important mediator of beta-cell destruction. The intracellular antioxidant enzymes glutathione peroxidase-1 (Gpx-1) and copper-zinc superoxide dismutase (CuZn SOD) detoxify peroxynitrite and superoxide, respectively. The aim of this study was to examine whether enhanced expression of Gpx-1 and/or CuZn SOD protected NIT-1 mouse insulinoma cells from hypoxia-reoxygenation injury. Stable transfectants expressing human Gpx-1 or CuZn SOD were isolated and tested for their resistance to hydrogen peroxide (H(2)O(2)) and menadione, which generates superoxide intracellularly. Clones expressing one or both enzymes were subjected to hypoxia in glucose-free medium for 18 h, followed by reoxygenation in complete medium for 1.5 h. Cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) reduction assay. Increases of up to two fold in Gpx or total SOD activity protected NIT-1 cells from H(2)O(2) and menadione. Expression of Gpx-1 significantly increased NIT-1 survival following hypoxia-reoxygenation (viability 65 +/- 9% vs. control 15 +/- 3%, P < 0.001) but CuZn SOD expression had no effect (15 +/- 1%). Expression of both enzymes was no more protective (60 +/- 6%) than expression of Gpx-1 alone. Genetic manipulation of islet beta cells to increase expression of Gpx-1 may protect them from oxidative injury associated with the transplantation procedure.

Expression of nuclear factor-kappa B in hepatocellular carcinoma and its relation with the X protein of hepatitis B virus

AIM

In this study we investigated the relationship of the X protein of HBV and nuclear factor-kappa B (NF-kappa B) and the expression of NF-kappa B in human hepatocellular carcinoma tissues.

METHODS

Immunohistochemistry SP method was used to detect the expression of NF-kappa B and the X protein of HBV in human hepatocellular carcinoma tissues of 52 cases. Gene transfection mediated by lipofectamine was used to transfect the eukaryotic expression vector pCDNA3.1-HBX of HBV x gene into human hepatocellular carcinoma cell line HCC-9204 and NF-kappa B was detected.

RESULTS

NF kappa B was widely expressed in human hepatocellular carcinoma tissues in a total of 52 cases and its expression was related to the X protein of HBV. NF-kappa B was localized both in the cytoplasm and the nuclei of hepatocellular carcinoma cells in 11 cases which were positive for the X protein of HBV while in 41 cases negative for the X protein of HBV, NF-kappa B was only localized in the cytoplasm of hepatocellular carcinoma cells but translocated to the nuclei of hepatocellular carcinoma cells after the eukaryotic expression vector pCDNA3.1-HBX was transfected into HCC-9204 cells.

CONCLUSION

This study strongly suggests that the nuclear factor NF-kappa B is widely expressed in hepatocellular carcinoma tissues in different styles according to the expression of the X protein of HBV. NF-kappa B is abnormally activated in hepatocellular carcinoma, which is probably related to the X protein of HBV. The X protein of HBV can activate NF-kappa B to translocate into nuclei of hepatocellular carcinoma cells.

Insulinoma-induced hypoglycemic death in mice is prevented with beta cell-specific gene therapy

OBJECTIVE AND SUMMARY BACKGROUND DATA

Tumor-specific gene therapy can be achieved if a tumor-specific promoter can be identified. In this study the authors investigated the use of the rat insulin promoter (RIP) for insulinoma-specific expression of a reporter gene. Insulinoma-specific cytotoxicity using the suicide gene thymidine kinase (tk) was studied both in vitro and in vivo. RIPtk gene therapy, delivered by a nontoxic, noninflammatory liposomal delivery system, was used in an insulinoma ICR/SCID mouse model to prevent hypoglycemic death.

METHODS

Rat insulin promoter (0.502 kb) was ligated to the reporter gene lacZ and ligated to the tk gene. These two genes were transfected into a mouse insulinoma (NIT) cell line to ascertain insulinoma-specific expression and insulinoma-specific cytotoxicity in vitro. Reverse transcriptase-polymerase chain reaction and electrophoretic mobility-shift assays were performed on NIT-1 cell RNA and nuclear extract, respectively, to determine the transcription factors present and responsible for RIP activation in NIT-1 cells. A mouse insulinoma model was created with NIT-1 cells. These mice were treated with the RIPtk gene, and both blood sugars and animal viability were monitored.

RESULTS

Only NIT-1 cells stained blue after X-gal staining or had detectable levels of beta-galactosidase protein. A significant decrease in cell survival was observed in NIT-1 cells transfected with RIPtk in vitro. Messenger RNA for both BETA2 and PDX-1 was found in NIT-1 cells, and a supershift was observed for both BETA2 and PDX-1. Experimental mice treated with the RIPtk gene, delivered by a liposomal gene delivery system, maintained their blood glucose levels, and the animals did not die of hypoglycemia.

CONCLUSIONS

The data suggest that the RIP is an insulinoma-specific promoter. An ICR/SCID mouse insulinoma model was used to show that insulinoma-specific cytotoxicity can be accomplished by RIP coupled to a suicide gene in vivo, preventing hypoglycemic death.

Cell-permeable peptide inhibitors of JNK: novel blockers of beta-cell death

Stress conditions and proinflammatory cytokines activate the c-Jun NH2-terminal kinase (JNK), a member of the stress-activated group of mitogen-activated protein kinases (MAPKs). We recently demonstrated that inhibition of JNK signaling with the use of the islet-brain (IB) 1 and 2 proteins prevented interleukin (IL)-1beta-induced pancreatic beta-cell death. Bioactive cell-permeable peptide inhibitors of JNK were engineered by linking the minimal 20-amino acid inhibitory domains of the IB proteins to the 10-amino acid HIV-TAT sequence that rapidly translocates inside cells. Kinase assays indicate that the inhibitors block activation of the transcription factor c-Jun by JNK. Addition of the peptides to the insulin-secreting betaTC-3 cell line results in a marked inhibition of IL-1beta-induced c-jun and c-fos expression. The peptides protect betaTC-3 cells against apoptosis induced by IL-1beta. All-D retro-inverso peptides penetrate cells as efficiently as the L-enantiomers, decrease c-Jun activation by JNK, and remain highly stable inside cells. These latter peptides confer full protection against IL-1beta-induced apoptosis for up to 2 weeks of continual treatment with IL-1beta. These data establish these bioactive cell-permeable peptides as potent pharmacological compounds that decrease intracellular JNK signaling and confer long-term protection to pancreatic beta-cells from IL-1beta-induced apoptosis.

The role of the proteasome in autoimmunity

Type 1 diabetes is believed to be caused by T cell-mediated autoimmunity, with a prediabetic state characterized by the production of autoantibodies specific for proteins expressed by pancreatic beta cells. The non-obese diabetic (NOD) mouse is a spontaneous model of Type 1 diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) region of the genome. A specific proteasome defect has now been identified in NOD mouse lymphocytes that results from down-regulation of expression of the proteasome subunit LMP2, which is encoded by a gene in the MHC genomic region. This defect both prevents the proteolytic processing required for the production and activation of the transcription factor nuclear factor-kappaB (NF-kappaB), which plays an important role in immune and inflammatory responses, in addition to increasing the susceptibility of the affected cells to apoptosis induced by tumor necrosis factor-alpha (TNF-alpha). The proteasome dysfunction is both tissue- and developmental stage-specific and likely contributes to disease pathogenesis and tissue targeting.

Cell-ELISA using beta-galactosidase conjugated antibodies

Cell-enzyme-linked immunosorbent assay (cell-ELISA) is a technique for the rapid, convenient, and quantitative detection of molecules expressed on the cell surface. Here we present an evaluation of beta-galactosidase as an antibody-tag for cell-ELISA. In contrast to substrates for horseradish peroxidase (HRP) and alkaline phosphatase, murine splenocytes do not hydrolyze the beta-galactosidase substrate chlorophenolred-beta-D-galactopyranoside (CPRG). beta-Galactosidase-antibody conjugates show much lower background binding to murine T cells than conjugates with HRP or alkaline phosphatase. We describe step-by-step procedures for direct and indirect beta-galactosidase based cell-ELISA to quantitate the expression of molecules on the surface of unfixed, live cells. Variations of the basic protocol are suitable for adherent and non-adherent cells, large scale screening for expression of cell surface molecules, and the screening of hybridomas for production of antibodies to cell surface epitopes. Since relatively few beta-galactosidase conjugated antibodies are commercially available, we describe an efficient method to couple beta-galactosidase to antibodies using a novel water soluble heterobifunctional crosslinker, sulfosuccinimidyl 4-[N-maleimidomethyl]-cyclohexane-1-carboxylate (sulfo-SMCC). We demonstrate the utility of this method by conjugating F(ab')(2) fragments of an anti-B7-2 antibody, and using this conjugate to assay B7-2 on Fc-receptor bearing cells.

Defective function of the proteasome in autoimmunity: involvement of impaired NF-kappaB activation

Type 1 diabetes (also known as insulin-dependent diabetes mellitus or juvenile-onset diabetes) is usually caused by T cell-mediated autoimmunity, with a prediabetic state characterized by the production of autoantibodies specific for proteins expressed by pancreatic beta cells. The nonobese patient with diabetes (NOD) mouse is a spontaneous model of type 1 diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) region of the genome. A specific proteasome defect has been identified in NOD mouse in select lymphocytic and monocytic lineages that results from down-regulation of expression of the proteasome subunit LMP2, which is encoded by a gene in the MHC genomic region. This defect prevents the proteolytic processing required for the production and activation of the transcription factor nuclear factor-kappaB (NF-kappaB), which plays important roles in immune and inflammatory responses, as well as increases the susceptibility of the affected cells to apoptosis induced by tumor necrosis factor-alpha (TNF-alpha). The novel role of the proteasome in dysfunction in autoimmunity is presented and documented to be both tissue and developmental stage specific. We propose a role of the proteasome as a step in disease pathogenesis and tissue targeting.

NOD mice are defective in proteasome production and activation of NF-kappaB

The nonobese diabetic (NOD) mouse is an animal model of human type I diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) of the genome. We have identified in NOD lymphocytes a specific proteasome defect that results from the lack of the LMP2 subunit. The pronounced proteasome defect results in defective production and activation of the transcription factor NF-kappaB, which plays an important role in immune and inflammatory responses as well as in preventing apoptosis induced by tumor necrosis factor alpha. The defect in proteasome function in NOD mouse splenocytes was evident from impaired NF-kappaB subunit p50 and p52 generation by proteolytic processing and impaired degradation of the NF-kappaB-inhibitory protein IkappaBalpha. An obligatory role of MHC-linked proteasome subunits in transcription factor processing and activation has been established in a spontaneous-disease model and mutant cells similarly lacking the MHC-encoded subunit. These data suggest that NOD proteasome dysfunction is due to a tissue- and developmental-stage-specific defect in expression of the MHC-linked Lmp2 gene, resulting in altered transcription factor NF-kappaB activity, and that this defect contributes to pathogenesis in NOD mice. These observations are consistent with the diverse symptomatology of type I diabetes and demonstrate clear sex-, tissue-, and age-specific differences in the expression of this error which parallel the initiation and disease course of insulin-dependent (type I) diabetes mellitus.