Gene expression profiles for the human pancreas and purified islets in type 1 diabetes: new findings at clinical onset and in long-standing diabetes

Multiple microRNAs within the 14q32 cluster target the mRNAs of major type 1 diabetes autoantigens IA-2, IA-2β, and GAD65

Islet antigen (IA)-2, IA-2β, and glutamate decarboxylase (GAD65) are major autoantigens in type 1 diabetes (T1D). Autoantibodies to these autoantigens appear years before disease onset and are widely used as predictive markers. Little is known, however, about what regulates the expression of these autoantigens. The present experiments were initiated to test the hypothesis that microRNAs (miRNAs) can target and affect the levels of these autoantigens. Bioinformatics was used to identify miRNAs predicted to target the mRNAs coding IA-2, IA-2β, and GAD65. RNA interference for the miRNA processing enzyme Dicer1 and individual miRNA mimics and inhibitors were used to confirm the effect in mouse islets and MIN6 cells. We show that the imprinted 14q32 miRNA cluster contains 56 miRNAs, 32 of which are predicted to target the mRNAs of T1D autoantigens and 12 of which are glucose-sensitive. Using miRNA mimics and inhibitors, we confirmed that at least 7 of these miRNAs modulate the mRNA levels of the T1D autoantigens. Dicer1 knockdown significantly reduced the mRNA levels of all 3 autoantigens, further confirming the importance of miRNAs in this regulation. We conclude that miRNAs are involved in regulating the expression of the major T1D autoantigens.

Function of Isolated Pancreatic Islets From Patients at Onset of Type 1 Diabetes: Insulin Secretion Can Be Restored After Some Days in a Nondiabetogenic Environment In Vitro: Results From the DiViD Study

The understanding of the etiology of type 1 diabetes (T1D) remains limited. One objective of the Diabetes Virus Detection (DiViD) study was to collect pancreatic tissue from living subjects shortly after the diagnosis of T1D. Here we report the insulin secretion ability by in vitro glucose perifusion and explore the expression of insulin pathway genes in isolated islets of Langerhans from these patients. Whole-genome RNA sequencing was performed on islets from six DiViD study patients and two organ donors who died at the onset of T1D, and the findings were compared with those from three nondiabetic organ donors. All human transcripts involved in the insulin pathway were present in the islets at the onset of T1D. Glucose-induced insulin secretion was present in some patients at the onset of T1D, and a perfectly normalized biphasic insulin release was obtained after some days in a nondiabetogenic environment in vitro. This indicates that the potential for endogenous insulin production is good, which could be taken advantage of if the disease process was reversed at diagnosis.

In search of a surrogate: engineering human beta cell lines for therapy

Replacement of insulin-producing cells is a promising therapy for the restoration of the beta cell mass that is destroyed in patients with type 1 diabetes (T1D). However, the use of large amounts of islets per transplant, coupled with the scarcity of donor tissue, diminishes its feasibility. Here we briefly discuss current progress in developing ideal functional beta cells as well as the rationale for developing renewable sources of insulin-producing cells that can be transplanted.

Insulitis in human type 1 diabetes: a comparison between patients and animal models

Human type 1 diabetes (T1D) is considered to be an autoimmune disease, with CD8+ T-cell-mediated cytotoxicity being directed against the insulin-producing beta cells, leading to a gradual decrease in beta cell mass and the development of chronic hyperglycemia. The histopathologically defining lesion in recent-onset T1D patients is insulitis, a relatively subtle leucocytic infiltration present in approximately 10 % of the islets of Langerhans from children with recent-onset (<1 year) disease. Due to the transient nature of the infiltrate, its heterogeneous distribution in the pancreas and the nature of the patient population, material for research is extremely rare and limited to a cumulative total of approximately 150 cases collected over the past century. Most studies on the etiopathogenesis of T1D have therefore focused on the non-obese diabetic (NOD) mouse model, which shares many genetic and immunological disease characteristics with human T1D, although its islet histopathology is remarkably different. In view of these differences and in view of the limited success of clinical immune interventions based on observations in the NOD mouse, there is a renewed focus on studying the pathogenetic process in patient material.

In silico Analysis of TCR Vβ7 of Two Patients with Type 1 Diabetes Mellitus

OBJECTIVE

To compare the sequences and crystal structures of variable region of beta chain 7 (Vβ7) of T cell receptor (TCR) of two patients with type 1 diabetes mellitus (T1DM).

PATIENTS AND METHODS

The skewness of TCR Vβ7 of two T1DM patients were detected with real-time florescence quantitative polymerase chain reaction (FQ-PCR) and deoxyribonucleic acid (DNA) melting curve analysis technique followed by being sequenced, the crystal structures of them were simulated according to CPH models 2.0 Server, IMGT database, and RasMol 2 software.

RESULTS

The whole sequences of TCR Vβ7 of T1DM patient-1 were "CASRTAGQYEQYFGPGTR", that of patient-2 were "CASRTAGQYEQFFGPGTR"; the only difference between them lied on the 12(th) amino acid. The crystal structures of Vβ7 of the two patients simulated with backbone model were rather similar, while that with sphere model were obviously different.

CONCLUSION

Although the TCR Vβ7 of the T1DM patients share the similar gene sequences, their crystal structures simulated with sphere model are different, and the mechanism needs further study.

Long-term IKK2/NF-κB signaling in pancreatic β-cells induces immune-mediated diabetes

Type 1 diabetes is a multifactorial inflammatory disease in genetically susceptible individuals characterized by progressive autoimmune destruction of pancreatic β-cells initiated by yet unknown factors. Although animal models of type 1 diabetes have substantially increased our understanding of disease pathogenesis, heterogeneity seen in human patients cannot be reflected by a single model and calls for additional models covering different aspects of human pathophysiology. Inhibitor of κB kinase (IKK)/nuclear factor-κB (NF-κB) signaling is a master regulator of inflammation; however, its role in diabetes pathogenesis is controversially discussed by studies using different inhibition approaches. To investigate the potential diabetogenic effects of NF-κB in β-cells, we generated a gain-of-function model allowing conditional IKK2/NF-κB activation in β-cells. A transgenic mouse model that expresses a constitutively active mutant of human IKK2 dependent on Pdx-1 promoter activity (IKK2-CA(Pdx-1)) spontaneously develops full-blown immune-mediated diabetes with insulitis, hyperglycemia, and hypoinsulinemia. Disease development involves a gene expression program mimicking virus-induced diabetes and allergic inflammatory responses as well as increased major histocompatibility complex class I/II expression by β-cells that could collectively promote diabetes development. Potential novel diabetes candidate genes were also identified. Interestingly, animals successfully recovered from diabetes upon transgene inactivation. Our data give the first direct evidence that β-cell-specific IKK2/NF-κB activation is a potential trigger of immune-mediated diabetes. Moreover, IKK2-CA(Pdx-1) mice provide a novel tool for studying critical checkpoints in diabetes pathogenesis and mechanisms governing β-cell degeneration/regeneration.

Maternal microchimerism: friend or foe in type 1 diabetes?

Increased levels of non-inherited maternal HLA alleles have been detected in the periphery of children with type 1 diabetes and an increased frequency of maternal cells have been identified in type 1 diabetes pancreas. It is now clear that the phenotype of these cells is pancreatic, supporting the hypothesis that maternal cells in human pancreas are derived from multipotent maternal progenitors. Here we hypothesize how increased levels of maternal cells could play a role in islet autoimmunity.

PAP/HIP protein is an obesogenic factor

In this article we report the obesogenic role of the acute phase protein PAP/HIP. We found that the transgenic TgPAP/HIP mice develop spontaneous obesity under standard nutritional conditions, with high levels of glucose, leptin, and LDL and low levels of triglycerides and HDL in blood. Accordingly, PAP/HIP-deficient mice are skinny under standard nutritional conditions. We also found that expression of PAP/HIP is induced in intestinal epithelial cells in response to gavage with olive oil and this induction is AG490 sensitive. We demonstrated that incubation of 3T3-L1 preadipocytes with a low concentration as 1 ng/ml of recombinant PAP/HIP results in accelerated BrdU incorporation in vitro. PAP/HIP-dependent adipocytes growth is sensitive to the MEK inhibitor U0126. Finally, patients with severe obesity present higher blood levels of PAP/HIP than non-obese control individuals. Altogether our data suggest that PAP/HIP could be a mediator of fat tissue development, released by the intestine and induced by the presence of food into the gut.

The role of the complement system in metabolic organs and metabolic diseases

Emerging evidence points to a close crosstalk between metabolic organs and innate immunity in the course of metabolic disorders. In particular, cellular and humoral factors of innate immunity are thought to contribute to metabolic dysregulation of the adipose tissue or the liver, as well as to dysfunction of the pancreas; all these conditions are linked to the development of insulin resistance and diabetes mellitus. A central component of innate immunity is the complement system. Interestingly, the classical view of complement as a major system of host defense that copes with infections is changing to that of a multi-functional player in tissue homeostasis, degeneration, and regeneration. In the present review, we will discuss the link between complement and metabolic organs, focusing on the pancreas, adipose tissue, and liver and the diverse effects of complement system on metabolic disorders.

Biomarkers for diagnosis and monitoring of celiac disease

Celiac disease (CD) is an autoimmune disorder, which damages the small intestine and is caused by ingestion of gluten in genetically susceptible individuals. The only known effective treatment is a lifelong gluten-free diet. Genetic risk factors have been identified and nearly all patients are HLA-DQ2 and/or HLA-DQ8 positive. Specific autoantibodies, IgA antitissue transglutaminase-2, antiendomysium, and antideaminated forms of gliadin peptide antibodies, are widely used as diagnostic aids in celiac patients. However, the discovery of new biomarkers may help in the diagnosis and follow-up of the disease. Recently, the molecule REG Iα, involved in tissue regeneration, has been proposed as a new biomarker of CD. REG Iα expression is increased in the target tissue and in the sera of celiac patients during damage and inflammation, decreasing after gluten-free diet. In this article we review the main biomarkers for diagnosis and monitoring of CD, focusing on the immune response-related mechanisms.

Antibody cross-reactivity and the viral aetiology of type 1 diabetes

Type 1 diabetes (T1D) is caused by the destruction of insulin-producing pancreatic β cells by the patient's immune system. While the underlying genetics and immunopathology are fairly well characterized, the environmental trigger remains unidentified. Numerous studies have centred on the role of enteroviruses as aetiological factors that could initiate or accelerate T1D development. The most convincing evidence to date consists of an array of reports documenting the presence of enteroviral nucleic acids in peripheral blood at diagnosis. A prominent hypothesis is that enteroviruses may infect the pancreatic islets and thus be responsible for the islet-specific up-regulation of MHC class I that is commonly observed, possibly enabling T cell recognition and cytotoxicity. Past immunohistochemical studies have indeed shown that antibodies binding the enteroviral capsid protein VP1 preferentially stain the pancreatic β cells from diabetic individuals. New data now indicate that the VP1 antibody used in these studies cross-reacts with mitochondrial proteins.

Immunological pathways to β-cell damage in Type 1 diabetes

Following almost 30 years of intensive research, initiated by the observation that Type 1 diabetes development is associated with a characteristic pancreatic immune cell infiltrate, a picture is emerging of which of the diverse effector arms of the immune system are involved in β-cell destruction. Like any chronic pathology, there is considerable complexity, and our ability to model the disease is hampered by a lack of ready access to the target organ and limited longitudinal analyses. However, it seems that putative pathways can start to be ruled in and out, in part as a result of focused mechanistic studies that make use of new technologies, and in part through analysis of the outcomes of clinical trials of new agents aimed at halting the disease process. The picture that emerges suggests a pathway to prevention that may require combinations of therapeutic agents that target different aspects of the immune system and will need to be used with due attention to their risk-benefit profiles.

Novel biomarkers in type 1 diabetes

Biomarkers are useful tools for research into type 1 diabetes (T1D) for a number of purposes, including elucidation of disease pathogenesis, risk prediction, and therapeutic monitoring. Susceptibility genes and islet autoantibodies are currently the most useful biomarkers for T1D risk prediction. However, these markers do not fully meet the needs of scientists and physicians for several reasons. First, improvement of the specificity and sensitivity is still desirable to achieve better positive predictive values. Second, autoantibodies appear relatively late in the disease process, thus limiting their value in early disease prediction. Third, the currently available biomarkers are not useful for assessing therapeutic outcomes because some are not involved in the disease process (autoantibodies) and others do not change during disease progression (susceptibility genes). Therefore, considerable effort has been devoted to the discovery of novel T1D biomarkers in the last three decades. The advent of high-throughput technologies for genetic, transcriptomic, and proteomic studies has allowed genome-wide examinations of genetic polymorphisms, global gene changes, and protein expression changes in T1D patients and prediabetic subjects. These large-scale studies resulted in the discovery of a large number of susceptibility genes and changes in gene and protein expression. While these studies have provided a number of novel biomarker candidates, their clinical benefits remain to be evaluated in prospective studies, and no new "star biomarker" has been identified until now. Previous studies suggest that significant improvements in study design and analytical methodologies have to be made to identify clinically relevant biomarkers. In this review, we discuss progress, opportunities, challenges, and future directions in the development of T1D biomarkers, mainly by focusing on the genetic, transcriptomic, and proteomic aspects.

Co-clustering phenome-genome for phenotype classification and disease gene discovery

Understanding the categorization of human diseases is critical for reliably identifying disease causal genes. Recently, genome-wide studies of abnormal chromosomal locations related to diseases have mapped >2000 phenotype–gene relations, which provide valuable information for classifying diseases and identifying candidate genes as drug targets. In this article, a regularized non-negative matrix tri-factorization (R-NMTF) algorithm is introduced to co-cluster phenotypes and genes, and simultaneously detect associations between the detected phenotype clusters and gene clusters. The R-NMTF algorithm factorizes the phenotype–gene association matrix under the prior knowledge from phenotype similarity network and protein–protein interaction network, supervised by the label information from known disease classes and biological pathways. In the experiments on disease phenotype–gene associations in OMIM and KEGG disease pathways, R-NMTF significantly improved the classification of disease phenotypes and disease pathway genes compared with support vector machines and Label Propagation in cross-validation on the annotated phenotypes and genes. The newly predicted phenotypes in each disease class are highly consistent with human phenotype ontology annotations. The roles of the new member genes in the disease pathways are examined and validated in the protein–protein interaction subnetworks. Extensive literature review also confirmed many new members of the disease classes and pathways as well as the predicted associations between disease phenotype classes and pathways.

Diabetogenic T lymphocytes in human Type 1 diabetes

The field of Type 1 diabetes research has been quick to embrace the era of translational medicine in the recent epoch. Building upon some 30 years of intense immunological research, the past decade has been marked by a series of clinical trials designed to evaluate the potential beneficial effects of a range of immune intervention and prevention strategies [1(••),2-5]. At the heart of Type 1 diabetes is an autoimmune process, the consequence of which is immune-mediated destruction of islet β-cells. Although understanding the pathogenesis of islet autoimmunity is critical, there are also good reasons to focus research onto the β-cell destructive process itself. Measuring preservation of function of insulin-producing cells is currently the best means available to evaluate potential beneficial effects of immunotherapy, but there is an urgent need to discover and monitor immunological correlates of this β-cell destructive process. Whilst the best approach to intervention and prevention has yet to emerge, it is logical that future attempts to intelligently design therapeutics for Type 1 diabetes will need to be predicated on a clear understanding of the process of β-cell destruction and the immune components involved. For these reasons, this review will focus on the role of diabetogenic T lymphocytes in this disease-defining event.

Discovery and validation of serum protein changes in type 1 diabetes patients using high throughput two dimensional liquid chromatography-mass spectrometry and immunoassays

Type 1 diabetes (T1D) is expected to cause significant changes in the serum proteome; however, few studies have systematically assessed the proteomic profile change associated with the disease. In this study, a semiquantitative spectral counting-based two dimensional liquid chromatography mass spectrometry platform was used to analyze serum samples from T1D patients and controls. In this discovery phase, significant differences were found for 21 serum proteins implicated in inflammation, oxidation, metabolic regulation, and autoimmunity. To assess the validity of these findings, six candidate proteins including adiponectin, insulin-like growth factor binding protein 2, serum amyloid protein A, C-reactive protein, myeloperoxidase, and transforming growth factor beta induced were selected for subsequent immune assays for 1139 T1D patients and 848 controls. A series of statistical analyses using cases and controls matched for age, sex, and genetic risk confirmed that T1D patients have significantly higher serum levels for four of the six proteins: adiponectin (odds ratio (OR) = 1.95, p = 10(-27)), insulin-like growth factor binding protein 2 (OR = 2.02, p < 10(-20)), C-reactive protein (OR = 1.13, p = 0.007), serum amyloid protein A (OR = 1.51, p < 10(-16)); whereas the serum levels were significantly lower in patients than controls for the two other proteins: transforming growth factor beta induced (OR = 0.74, p < 10(-5)) and myeloperoxidase (OR = 0.51, p < 10(-41)). Compared with subjects in the bottom quartile, subjects in the top quartile for adiponectin (OR = 6.29, p < 10(-37)), insulin-like growth factor binding protein 2 (OR = 7.95, p < 10(-46)), C-reactive protein (OR = 1.38, p = 0.025), serum amyloid protein A (OR = 3.36, p < 10(-16)) had the highest risk of T1D, whereas subjects in the top quartile of transforming growth factor beta induced (OR = 0.41, p < 10(-11)) and myeloperoxidase (OR = 0.10, p < 10(-43)) had the lowest risk of T1D. These findings provided valuable information on the proteomic changes in the sera of T1D patients.

Peripheral and islet interleukin-17 pathway activation characterizes human autoimmune diabetes and promotes cytokine-mediated β-cell death

OBJECTIVE

CD4 T-cells secreting interleukin (IL)-17 are implicated in several human autoimmune diseases, but their role in type 1 diabetes has not been defined. To address the relevance of such cells, we examined IL-17 secretion in response to β-cell autoantigens, IL-17A gene expression in islets, and the potential functional consequences of IL-17 release for β-cells.

RESEARCH DESIGN AND METHODS

Peripheral blood CD4 T-cell responses to β-cell autoantigens (proinsulin, insulinoma-associated protein, and GAD65 peptides) were measured by IL-17 enzyme-linked immunospot assay in patients with new-onset type 1 diabetes (n = 50). mRNA expression of IL-17A and IFNG pathway genes was studied by qRT-PCR using islets obtained from subjects who died 5 days and 10 years after diagnosis of disease, respectively, and from matched control subjects. IL-17 effects on the function of human islets, rat β-cells, and the rat insulinoma cell line INS-1E were examined.

RESULTS

A total of 27 patients (54%) showed IL-17 reactivity to one or more β-cell peptides versus 3 of 30 (10%) control subjects (P = 0.0001). In a single case examined close to diagnosis, islet expression of IL17A, RORC, and IL22 was detected. It is noteworthy that we show that IL-17 mediates significant and reproducible enhancement of IL-1β/interferon (IFN)-γ-induced and tumor necrosis factor (TNF)-α/IFN-γ-induced apoptosis in human islets, rat β-cells, and INS-1E cells, in association with significant upregulation of β-cell IL17RA expression via activation of the transcription factors STAT1 and nuclear factor (NF)-κB.

CONCLUSIONS

Circulating IL-17(+) β-cell-specific autoreactive CD4 T-cells are a feature of type 1 diabetes diagnosis. We disclose a novel pathway to β-cell death involving IL-17 and STAT1 and NF-κB, rendering this cytokine a novel disease biomarker and potential therapeutic target.

Insulitis in human type 1 diabetes: The quest for an elusive lesion

The histopathology of type 1 diabetes is defined by a decreased β-cell mass in association with insulitis, a characteristic lymphocytic infiltration limited to the islets of Langerhans and prominent in early stage disease in children. A cytotoxic T-cell mediated destruction of insulin-producing β-cells is thought to be initiated by an unknown (auto)antigen, leading to the destruction > 75% of β-cell mass at clinical diagnosis. Although considered to be pathognomonic for recent onset disease, insulitis has only been described in approximately 150 cases over the past century. This review describes the quest for this elusive lesion and gives its incidence in various patient subpopulations stratified for age of onset and duration of the disease. It discusses recent new insights into the regenerative capacity of the β-cell mass in the pre-clinical stages of the disease and relates these findings to the inflammatory processes within the islet tissue.

TCR bias of in vivo expanded T cells in pancreatic islets and spleen at the onset in human type 1 diabetes

Autoreactive T cells, responsible for the destruction of pancreatic β cells in type 1 diabetes, are known to have a skewed TCR repertoire in the NOD mouse. To define the autoreactive T cell repertoire in human diabetes, we searched for intraislet monoclonal expansions from a recent onset in human pancreas to then trace them down to the patient's peripheral blood and spleen. Islet infiltration was diverse, but five monoclonal TCR β-chain variable expansions were detected for Vβ1, Vβ7, Vβ11, Vβ17, and Vβ22 families. To identify any sequence bias in the TCRs from intrapancreatic T cells, we analyzed 139 different CDR3 sequences. We observed amino acid preferences in the NDN region that suggested a skewed TCR repertoire within infiltrating T cells. The monoclonal expanded TCR sequences contained amino acid combinations that fit the observed bias. Using these CDR3 sequences as a marker, we traced some of these expansions in the spleen. There, we identified a Vβ22 monoclonal expansion with identical CDR3 sequence to that found in the islets within a polyclonal TCR β-chain variable repertoire. The same Vβ22 TCR was detected in the patient's PBMCs, making a cross talk between the pancreas and spleen that was reflected in peripheral blood evident. No other pancreatic monoclonal expansions were found in peripheral blood or the spleen, suggesting that the Vβ22 clone may have expanded or accumulated in situ by an autoantigen present in both the spleen and pancreas. Thus, the patient's spleen might be contributing to disease perpetuation by expanding or retaining some autoreactive T cells.

Why are levels of maternal microchimerism higher in type 1 diabetes pancreas?

Maternal microchimerism (MMc) results from transfer of maternal cells to the fetus in pregnancy. These cells have been shown to persist into adulthood in healthy individuals and an increased frequency of MMc has been associated with autoimmune disease. Female (presumed maternal) islet beta cells have recently been identified at higher levels in pancreas from a child with T1D compared to three controls. There was, however, no evidence that these cells were the targets of autoimmune attack. The aim of this study was to analyze well-characterized T1D pancreases encompassing a spectrum in age at diagnosis, and duration of diabetes, for the presence of maternal microchimerism compared to control pancreases.Pancreas samples were available from six males with T1D and four male controls. Fluorescent-labeled probes were used to detect X and Y chromosomes. At least 1,000 cells, usually 4,000-8,000 cells underwent confocal imaging for each pancreas. The frequency of MMc was higher in T1D pancreases (range 0.31-0.80%, mean 0.58%) than in controls (0.24-0.50%, mean 0.38%) (p = 0.05). Intriguingly, clusters of 2-3 MMc were occasionally found in the pancreases, particularly T1D pancreases, suggesting replication of these cells. Concomitant FISH and immunofluorescence staining for insulin or CD45 was performed to phenotype cells of maternal origin. Insulin positive and insulin negative MMc were identified indicating that MMc contribute to the exocrine and endocrine compartments. No CD45 positive MMc were observed. These data confirm the presence of maternal cells in human pancreas and support previous observations that levels of MMc are higher in T1D pancreas compared to controls. MMc do not appear to be immune effector cells and those that stain positive for insulin within intact islets in T1D tissue appear healthy with no evidence that they are the focus of immune attack. This study adds support to the hypothesis that maternal stem cells have the capacity to cross the placental barrier and differentiate into both endocrine and exocrine cells but more detailed characterization of MMc in the pancreas is required.

Global gene expression changes in type 1 diabetes: insights into autoimmune response in the target organ and in the periphery

Type 1 diabetes (T1D) is an autoimmune disease caused by the selective destruction of the insulin-producing β cells. Research into the pathogenesis of T1D has been hindered by the lack of detection of the autoimmune process during the asymptomatic period and by the inaccessibility to the target tissue. Therefore current understanding of the immunological phenomena that take place in the pancreas of the patients is very limited and much of the current knowledge on T1D has been obtained using animal models. Microarray technology and bioinformatics allow the comparison of the gene expression profile - transcriptome - in normal and pathological conditions, creating a global picture of altered processes. Microarray experiments have defined new transcriptional alterations associated with several autoimmune diseases, and are focused on the identification of specific biomarkers. In this review we summarize current data on gene expression profiles in T1D from an immunological point of view. Reported transcriptome studies have been performed in T1D patients and Non-Obese Diabetic mouse models analyzing peripheral blood, lymphoid organs and pancreas/islets. In the periphery, the distinctive profiles are inflammatory pathways inducible by IL-1β and IFNs that can help in the identification of new biomarkers. In the target organ, a remarkable finding is the overexpression of inflammatory and innate immune response genes and the active autoimmune response at longstanding stages, contrary to the pre-existing concept of acute autoimmune process in T1D.

The role of transmembrane protein 27 (TMEM27) in islet physiology and its potential use as a beta cell mass biomarker

AIMS/HYPOTHESIS

Transmembrane protein 27 (TMEM27) is a membrane protein cleaved and shed by pancreatic beta cells that has been proposed as a beta cell mass biomarker. Despite reports of its possible role in insulin exocytosis and cell proliferation, its function in beta cells remains controversial. We aimed to characterise the function of TMEM27 in islets and its potential use as a beta cell mass biomarker.

METHODS

To determine TMEM27 function, we studied TMEM27 gene expression and localisation in human healthy and diabetic islets, the correlation of its expression with cell cycle and insulin secretion genes in human islets, its expression in tungstate-treated rats, and the effects of its overproduction on insulin secretion and proliferation in a beta cell line and islets. To elucidate its utility as a beta cell mass biomarker, we studied TMEM27 cleavage in a beta cell line, islets and primary proximal tubular cells.

RESULTS

TMEM27 mRNA levels in islets are lower in diabetic donors than in controls. Its gene expression correlates with that of insulin and SNAPIN in human islets. TMEM27 expression is downregulated in islets of tungstate-treated rats, which exhibit decreased insulin secretion and increased proliferation. TMEM27 overproduction in a beta cell line and islets significantly enhanced glucose-induced insulin secretion, with modest or no effects on proliferation. Finally, TMEM27 is cleaved and shed by renal proximal tubular cells and pancreatic islets.

CONCLUSIONS/INTERPRETATION

Our data support a role for TMEM27 in glucose-induced insulin secretion but not in cell proliferation. The finding that its cleavage is not specific to beta cells challenges the current support for its use as a potential beta cell mass biomarker.

Islet inflammation and CXCL10 in recent-onset type 1 diabetes

Type 1 diabetes results from a T cell-mediated destruction of insulin-producing pancreatic beta cells. Little is known on local factors contributing to migration of T cells to pancreatic tissue. We recently demonstrated evidence of viral infection in beta cells in several recent-onset type 1 diabetes patients. Islet inflammation was analysed in a series of new- or recent-onset type 1 diabetic patients and non-diabetic control subjects. Autoimmune T cell reactivity was studied in lymphocytes derived from pancreas-draining lymph nodes of one recent-onset type 1 diabetes patient in partial clinical remission. Insulitic lesions were characterized by presence of beta cells, elevated levels of the chemokine CXCL10 and infiltration of lymphocytes expressing the corresponding chemokine receptor CXCR3 in all pancreatic lesions of type 1 diabetes patients, regardless of enterovirus infection of beta cells. CXCR3 and CXCL10 were undetectable in pancreata of non-diabetic control subjects. T cells isolated from draining lymph nodes of a recent-onset patient with virally infected beta cells and in clinical remission reacted with multiple islet autoantigens and displayed a mixed interferon (IFN)-gamma/interleukin (IL)-10 cytokine pattern. Our data point to CXCL10 as an important cytokine in distressed islets that may contribute to inflammation leading to insulitis and beta cell destruction, regardless of local viral infection. We demonstrate further pro- and anti-inflammatory islet autoreactivity, indicating that different adaptive and innate immune responses may contribute to insulitis and beta cell destruction.