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Pancreatic islet transplantation has therapeutic potential in type 1 diabetes and is also an established therapy in chronic pancreatitis. However, the long-term transplant outcomes are modest. Identifying indicators of graft function will aid the preservation of transplanted islets and glycemic control. We analyzed beta cell prohormone peptide levels in a retrospective cohort of total pancreatectomy autologous islet transplant patients (n = 28). Proinsulin-to-C-peptide (PI/C) and proIAPP-to-total IAPP (proIAPP/IAPP) ratios measured at 3 months post-transplant were significantly higher in patients who remained insulin dependent at 1 year follow-up. In an immuno-deficient mouse model of human islet transplantation, recipient mice that later became hyperglycemic displayed significantly higher PI/C ratios than mice that remained normoglycemic. Histological analysis of islet grafts showed reduced proportional insulin- and proinsulin-positive area, but elevated glucagon-positive area in grafts that experienced greater secretory demand. Increased prohormone convertase 1/3 was detected in glucagon-positive cells, and glucagon-like peptide 1 (GLP-1) area was elevated in grafts from mice that displayed hyperglycemia or elevated plasma PI/C ratios, demonstrating intra-islet incretin production in metabolically challenged human islet grafts. These data indicate that in failing grafts, alpha cell prohormone processing is likely altered, and incomplete beta cell prohormone processing may be an early indicator of insulin dependency.

SUMMARYCancer immunotherapy using antigen-specific CD8+T cells depends on long-lasting anti-tumor function of thein vitroexpanded T cells. T cell function is intricately linked to the activity of many metabolic pathways directly impacting the ability of CD8+T cells to kill tumor cells. Metabolic conditioningin vitrobetter prepares CD8+T cells forin vivosurvival, tumor infiltration and tumor clearance. The mechanism underlyingin vitrometabolic conditioning-induced augmentedin vivoT cell function remains poorly understood. Here we show that metabolic conditioning of CD8+effector T cells induces an oxidized cellular redox balance at least in part mediated by increased mitochondrial reactive oxygen species (ROS). This redox shift contributes to enhancedin vivopersistence and tumor clearance. In human tumour-infiltrating T cells, altering the redox balanceex-vivoreinvigorated pro-inflammatory cytokine production. Therefore, we believe that redox alterations present a targetable pathway to increase T cell-based anti-tumor immunotherapy efficacy.

Adoptive immunotherapy with Tregs is a promising approach for prevention or treatment of type 1 diabetes. Islet antigen-specific Tregs have more potent therapeutic effects than polyclonal cells, but their low frequency is a barrier for clinical application. To generate Tregs that recognize islet antigens, we engineered a chimeric antigen receptor (CAR) derived from a monoclonal antibody with specificity for the insulin B-chain 10-23 peptide presented in the context of the IAg7MHC class II allele present in NOD mice. Peptide specificity of the resulting InsB-g7 CAR was confirmed by tetramer staining and T cell proliferation in response to recombinant or islet-derived peptide. The InsB-g7 CAR re-directed NOD Treg specificity such that insulin B 10-23-peptide stimulation enhanced suppressive function, measured via reduction of proliferation and IL-2 production by BDC2.5 T cells and CD80 and CD86 expression on dendritic cells. Co-transfer of InsB-g7 CAR Tregs prevented adoptive transfer diabetes by BDC2.5 T cells in immunodeficient NOD mice. In wild type NOD mice, InsB-g7 CAR Tregs stably expressed Foxp3 and prevented spontaneous diabetes. These results show that engineering Treg specificity for islet antigens using a T cell receptor-like CAR is a promising new therapeutic approach for the prevention of autoimmune diabetes.Brief SummaryChimeric antigen receptor Tregs specific for an insulin B-chain peptide presented by MHC class II prevent autoimmune diabetes.

Type 1 diabetes results from defects in immune self-tolerance that lead to inflammatory infiltrate in pancreatic islets, beta cell dysfunction and T cell-mediated killing of beta cells. Although therapies that broadly inhibit immunity show promise to mitigate autoinflammatory damage caused by effector T cells, these are unlikely to permanently reset tolerance or promote regeneration of the already diminished pool of beta cells. An emerging concept is that certain populations of immune cells may have the capacity to both promote tolerance and support the restoration of beta cells by supporting proliferation, differentiation and/or regeneration. Here we will highlight three immune cell types-macrophages, regulatory T cells and innate lymphoid cells-for which there is evidence of dual roles of immune regulation and tissue regeneration. We explore how findings in this area from other fields might be extrapolated to type 1 diabetes and highlight recent discoveries in the context of type 1 diabetes. We also discuss technological advances that are supporting this area of research and contextualise new therapeutic avenues to consider for type 1 diabetes.

Carboxypeptidase E (CPE) facilitates the conversion of prohormones into mature hormones and is highly expressed in multiple neuroendocrine tissues. Carriers ofCPEmutations have elevated plasma proinsulin and develop severe obesity and hyperglycemia. We aimed to determine whether loss ofCpein pancreatic beta cells disrupts proinsulin processing and accelerates development of diabetes and obesity in mice. Pancreatic beta cell-specific Cpe knockout mice (βCpeKO;Cpefl/flxIns1Cre/+) lack mature insulin granules and have elevated proinsulin in plasma; however, glucose-and KCl-stimulated insulin secretion in βCpeKO islets remained intact. High fat diet-fed βCpeKO mice showed comparable weight gain and glucose tolerance compared toWtlittermates. Notably, beta-cell area was increased in chow-fed βCpeKO mice and beta-cell replication was elevated in βCpeKO islets. Transcriptomic analysis of βCpeKO beta cells revealed elevated glycolysis andHif1α-target gene expression. Upon high glucose challenge, beta cells from βCpeKO mice showed reduced mitochondrial membrane potential, increased reactive oxygen species, reducedMafA, and elevatedAldh1a3transcript levels. Following multiple low-dose streptozotocin treatment, βCpeKO mice had accelerated hyperglycemia with reduced beta-cell insulin and Glut2 expression. These findings suggest thatCpeand proper proinsulin processing are critical in maintaining beta cell function during the development of diabetes.

Pancreatic cancer risk is elevated approximately two-fold in type 1 and type 2 diabetes. Islet amyloid polypeptide (IAPP) is an abundant beta-cell peptide hormone that declines with diabetes progression. IAPP has been reported to act as a tumour-suppressor in p53-deficient cancers capable of regressing tumour volumes. Given the decline of IAPP during diabetes development, we investigated the actions of IAPP in pancreatic ductal adenocarcinoma (PDAC; the most common form of pancreatic cancer) to determine if IAPP loss in diabetes may increase the risk of pancreatic cancer.PANC-1, MIA PaCa-2, and H1299 cells were treated with rodent IAPP, and the IAPP analogs pramlintide and davalintide, and assayed for changes in proliferation, death, and glycolysis. An IAPP-deficient mouse model of PDAC (IappIAPP did not impact glycolysis in MIA PaCa-2 cells, and did not impact cell death, proliferation, or glycolysis in PANC-1 cells or in H1299 cells, which were previously reported as IAPP-sensitive. Iapp deletion in KrasIn contrast to previous reports, we find that IAPP does not function as a tumour suppressor. This suggests that loss of IAPP signalling likely does not increase the risk of pancreatic cancer in individuals with diabetes.

One hundred years have passed since the discovery of insulin—an achievement that transformed diabetes from a fatal illness into a manageable chronic condition. The decades since that momentous achievement have brought ever more rapid innovation and advancement in diabetes research and clinical care. To celebrate the important work of the past century and help to chart a course for its continuation into the next, the Canadian Institutes of Health Research’s Institute of Nutrition, Metabolism and Diabetes and the U.S. National Institutes of Health’s National Institute of Diabetes and Digestive and Kidney Diseases recently held a joint international symposium, bringing together a cohort of researchers with diverse interests and backgrounds from both countries and beyond to discuss their collective quest to better understand the heterogeneity of diabetes and thus gain insights to inform new directions in diabetes treatment and prevention. This article summarizes the proceedings of that symposium, which spanned cutting-edge research into various aspects of islet biology, the heterogeneity of diabetic phenotypes, and the current state of and future prospects for precision medicine in diabetes.

Up to 6% of diabetes has a monogenic cause including mutations in the insulin gene, and patients are candidates for a gene therapy. Using a mouse model of permanent neonatal diabetes, we assessed the efficacy of an adeno-associated virus (AAV)-mediated gene therapy. We used AAVs with a rat insulin 1 promoter (Ins1) regulating a human insulin gene (INS; AAV Ins1-INS) or native mouse insulin 1 (Ins1; AAV Ins-Ins1) to deliver an insulin gene to β-cells of constitutive insulin null mice (Ins1−/−Ins2−/−) and adult inducible insulin-deficient mice [Ins1−/−Ins2f/f PdxCreER and Ins1−/−Ins2f/f mice administered AAV Ins1-Cre)]. Although AAV Ins1-INS could successfully infect and confer insulin expression to β-cells, insulin null β-cells had a prohormone processing defect. Secretion of abundant proinsulin transiently reversed diabetes. We reattempted therapy with AAV Ins1-Ins1, but Ins1−/−Ins2−/− β-cells still had a processing defect of both replaced Ins1 and pro-islet amyloid polypeptide (proIAPP). In adult inducible models, β-cells that lost insulin expression developed a processing defect that resulted in impaired proIAPP processing and elevated circulating proIAPP, and cells infected with AAV Ins1-Ins1 to rescue insulin expression secreted proinsulin. We assessed the subcellular localization of prohormone convertase 1/3 (PC1/3) and detected defective sorting of PC1/3 to glycogen-containing vacuoles and retention in the endoplasmic reticulum as a potential mechanism underlying defective processing. We provide evidence that persistent production of endogenous proinsulin within β-cells is necessary for β-cells to be able to properly store and process proinsulin.

ObjectiveHyperglycemia and type 2 diabetes (T2D) are caused by failure of pancreatic beta cells. The role of the gut microbiota in T2D has been studied but causal links remain enigmatic.DesignObese individuals with or without T2D were included from two independent Dutch cohorts. Human data was translated in vitro and in vivo by using pancreatic islets from C57BL6/J mice and by injecting flagellin into obese mice.ResultsFlagellin is part of the bacterial locomotor appendage flagellum, present on gut bacteria including Enterobacteriaceae, which we show to be more abundant in the gut of individuals with T2D. Subsequently, flagellin induces a pro-inflammatory response in pancreatic islets mediated by the Toll-like receptor (TLR)-5 expressed on resident islet macrophages. This inflammatory response associated with beta-cell dysfunction, characterized by reduced insulin gene expression, impaired proinsulin processing and stress-induced insulin hypersecretion in vitro and in vivo in mice.ConclusionWe postulate that increased systemically disseminated flagellin in T2D is a contributing factor to beta cell failure in time and represents a novel therapeutic target.Graphical abstract

The pathogenesis of hyperglycemia observed in most forms of diabetes is intimately tied to the islet β cell. Impairments in propeptide processing and secretory function, along with the loss of these vital cells, is demonstrable not only in those in whom the diagnosis is established but typically also in individuals who are at increased risk of developing the disease. Biomarkers are used to inform on the state of a biological process, pathological condition, or response to an intervention and are increasingly being used for predicting, diagnosing, and prognosticating disease. They are also proving to be of use in the different forms of diabetes in both research and clinical settings. This review focuses on the β cell, addressing the potential utility of genetic markers, circulating molecules, immune cell phenotyping, and imaging approaches as biomarkers of cellular function and loss of this critical cell. Further, we consider how these biomarkers complement the more long-established, dynamic, and often complex measurements of β-cell secretory function that themselves could be considered biomarkers.

Amyloid formation contributes to the development of progressive metabolic and neurodegenerative diseases, while also serving functional roles in host defense. Emerging evidence suggests that as amyloidogenic peptides populate distinct aggregation states, they interact with different combinations of pattern recognition receptors (PRRs) to direct the phenotype and function of tissue-resident and infiltrating innate immune cells. We review recent evidence of innate immunomodulation by distinct forms of amyloidogenic peptides produced by mammals (humans, non-human primates), bacteria, and fungi, as well as the corresponding cell-surface and intracellular PRRs in these interactions, in human and mouse models. Our emerging understanding of peptide aggregate-innate immune cell interactions, and the factors regulating the balance between amyloid function and pathogenicity, might aid the development of anti-amyloid and immunomodulating therapies.

Autophagy can help protect stressed β-cells. We investigated if disruption of Transcription Factor EB (Tfeb), a transcriptional master-regulator of lysosomes and autophagy, contributes to β-cell failure and death under various ER stress-inducing conditions. Short-term β-cell autophagy-deficiency (inducible Atg5 knockout) reduced β-cell survival under hypoxic stress in vitro and impaired the ability of syngeneic marginal mass islet grafts to maintain glucose homeostasis in streptozotocin (STZ)-induced diabetic mice, with >80% of recipients of Atg5-deficient islets returning to diabetes within 10 days post-transplant (vs. 30% of controls, p=0.05). Hypoxic culture activated pro-apoptotic ER stress pathways, and confocal analysis of islet cells from LC3-RFP-EGFP autophagy reporter mice demonstrated that autophagic flux was interrupted. Hypoxia-induced impairment of autophagy was associated with reduced lysosomal cathepsin B activity and a significant loss of Tfeb, both of which could be partially rescued by Torin-1. Lipotoxicity and thapsigargin-induced ER-stress similarly reduced Tfeb protein and cell viability, suggesting ER stress-specific mechanisms may drive dysregulation of Tfeb and lysosomes. Conversely, overexpression of Tfeb:GFP reduced thapsigargin-induced death in MIN6 cells. To directly study the consequences of Tfeb loss we generated mice with Ins1Cre-driven, β-cell-specific, Tfeb deletion (TfebβKO). Notably, both male and female TfebβKO mice had normal glucose tolerance, but cultured Tfeb KO β-cells showed impaired lysosomal cathepsin B activity and TfebβKO mice had worsened glucose tolerance compared to Tfeb flox littermates following injection with multiple low-doses STZ. In summary, autophagy protects β-cells under hypoxia but is impaired under prolonged hypoxic stress, possibly through Tfeb dysregulation. Our data further suggest loss of Tfeb is a common feature of ER stress and that this loss exacerbates stress-induced β-cell failure and death. Disclosure Y. Zou: None. D. Pasula: None. B. Verchere: Advisory Panel; Self; Integrated Nanotherapeutics Inc., Sirona Biochem, Stock/Shareholder; Self; Integrated Nanotherapeutics Inc. D. S. Luciani: None. Funding JDRF (2-2013-50)

Proinsulin (PI) is processed to mature insulin by prohormone convertases 1/3 (Pcsk1) and 2 (Pcsk2). In individuals with T1D and T2D, there is an increase in the circulating PI:insulin ratio. We hypothesized that β-cell Pcsk1 and Pcsk2 deletion would result in β-cell dysfunction, loss of insulin production, and marked hyperglycemia. Single Pcsk1flox/flox Ins1cre/+ (Pcsk1βKO), Pcsk2flox/flox Ins1cre/+ (Pcsk2βKO), and double Pcsk1flox/flox Pcsk2flox/flox Ins1cre/+ (DPCβKO) β-cell prohormone convertase knockout mice were generated (with respective Pcsk1+/+ Pcsk2+/+ Ins1cre/+ controls) and monitored until 30 weeks old. Pcsk2βKO mice displayed no glycemic phenotype, while Pcsk1βKO mice displayed mild hyperglycemia and impaired glucose tolerance by 26 weeks of age. DPCβKO mice displayed mild hyperglycemia (10.1±1.6 vs. 12.3±2.1 mM; p=0.006) and marked glucose intolerance by 10 weeks of age (AUC: 418±135 vs. 1485±360; p Our results suggest that complete loss of β-cell prohormone processing, including PI processing, can drive β-cell dysfunction and expansion, but only mild diabetes and glucose intolerance. Although Pcsk2 deletion in β cells does not impact glycemia or PI processing, it is required for normal proIAPP processing. In total, our data support the idea that altered β-cell prohormone processing does not impact obesity but can contribute to the pathogenesis of diabetes via β-cell dysfunction. Disclosure A. Taylor: None. Y. Chen: None. D. Pasula: None. D. S. Luciani: None. B. Verchere: Advisory Panel; Self; Integrated Nanotherapeutics Inc., Sirona Biochem, Stock/Shareholder; Self; Integrated Nanotherapeutics Inc. Funding Canadian Institutes of Health Research

Type 1 diabetes (T1D) is an auto-immune disease that destructs insulin-producing pancreatic beta-cells within the islets of Langerhans. The incidence of T1D has tripled over the last decades, while the pathophysiology of the disease is still largely unknown. Currently, there is no cure for T1D. The only treatment option consists of blood-glucose regulation with insulin injections and intensive monitoring of blood glucose levels. In recent years, perturbations in the ecosystem of the gut microbiome also referred to as dysbiosis, have gained interest as a possible contributing factor in the development of T1D. Changes in the microbiome seem to occur before the onset of T1D associated auto-antibodies. Furthermore, rodent studies demonstrate that administering antibiotics at a young age may accelerate the onset of T1D. This review provides an overview of the research performed on the epidemiology, pathophysiology, interventions, and possible treatment options in the field of the gut microbiome and T1D.

Type 1 diabetes results from defects in immune self-tolerance that lead to inflammatory infiltrate in pancreatic islets, beta cell dysfunction and T cell-mediated killing of beta cells. Although therapies that broadly inhibit immunity show promise to mitigate autoinflammatory damage caused by effector T cells, these are unlikely to permanently reset tolerance or promote regeneration of the already diminished pool of beta cells. An emerging concept is that certain populations of immune cells may have the capacity to both promote tolerance and support the restoration of beta cells by supporting proliferation, differentiation and/or regeneration. Here we will highlight three immune cell types-macrophages, regulatory T cells and innate lymphoid cells-for which there is evidence of dual roles of immune regulation and tissue regeneration. We explore how findings in this area from other fields might be extrapolated to type 1 diabetes and highlight recent discoveries in the context of type 1 diabetes. We also discuss technological advances that are supporting this area of research and contextualise new therapeutic avenues to consider for type 1 diabetes.

Pro-opiomelanocortin (POMC) neurons form an integral part of the central melanocortin system regulating food intake and energy expenditure. Genetic and pharmacological studies have revealed that defects in POMC synthesis, processing, and receptor signaling lead to obesity. It is well established that POMC is extensively processed by a series of enzymes, including prohormone convertases PC1/3 and PC2, and that genetic insufficiency of both PC1/3 and POMC is strongly associated with obesity risk. However, whether PC1/3-mediated POMC processing is absolutely tied to body weight regulation is not known. To investigate this question, we generated a Pomc-CreER T2; Pcsk1 lox/lox mouse model in which Pcsk1 is specifically and temporally knocked out in POMC-expressing cells of adult mice by injecting tamoxifen at eight weeks of age. We then measured the impact of Pcsk1 deletion on POMC cleavage to ACTH and α-MSH, and on body weight. In whole pituitary, POMC cleavage was significantly impacted by the loss of Pcsk1, while hypothalamic POMC-derived peptide levels remained similar in all genotypes. However, intact POMC levels were greatly elevated in Pomc-CreER T2; Pcsk1 lox/lox mice. Males expressed two-fold greater levels of pituitary PC1/3 protein than females, consistent with their increased POMC cleavage. Past studies show that mice with germline removal of PC1/3 do not develop obesity, while mice expressing mutant PC1/3 forms do develop obesity. We conclude that obesity pathways are not disrupted by PC1/3 loss solely in POMC-expressing cells, further disfavoring the idea that alterations in POMC processing underlie obesity in PCSK1 deficiency.

Additional file 1.

Analysis of data from clinical cohorts, and more recently from human pancreatic tissue, indicates that reduced prohormone processing is an early and persistent finding in type 1 diabetes. In this article, we review the current state of knowledge regarding alterations in islet prohormone expression and processing in type 1 diabetes and consider the clinical impact of these findings. Lingering questions, including pathologic etiologies and consequences of altered prohormone expression and secretion in type 1 diabetes, and the natural history of circulating prohormone production in health and disease, are considered. Finally, key next steps required to move forward in this area are outlined, including longitudinal testing of relevant clinical populations, studies that probe the genetics of altered prohormone processing, the need for combined functional and histologic testing of human pancreatic tissues, continued interrogation of the intersection between prohormone processing and autoimmunity, and optimal approaches for analysis. Successful resolution of these questions may offer the potential to use altered prohormone processing as a biomarker to inform therapeutic strategies aimed at personalized intervention during the natural history of type 1 diabetes and as a pathogenic anchor for identification of potential disease-specific endotypes.

BackgroundThe resident immune population of pancreatic islets has roles in islet development, beta cell physiology, and the pathology of diabetes. These roles have largely been attributed to islet macrophages, comprising 90% of islet immune cells (in the absence of islet autoimmunity), and, in the case of type 1 diabetes, to infiltrating autoreactive T cells. In adipose, tissue-resident and recruited T and B cells have been implicated in the development of insulin resistance during diet-induced obesity and aging, but whether this is paralleled in the pancreatic islets is not known. Here, we investigated the non-macrophage component of resident islet immune cells in islets isolated from C57BL/6J male mice during aging (3 to 24 months of age) and following diet-induced obesity (12 weeks 60% high fat diet). Immune cells were also examined by flow cytometry in cadaveric non-diabetic human islets.ResultsImmune cells comprised 2.7 ± 1.3% of total islet cells in non-diabetic mouse islets, and 2.3 ± 1.7% of total islet cells in non-diabetic human islets. In 3-month old mice on standard diet, B and T cells each comprised approximately 2-4% of the total islet immune cell compartment, and approximately 0.1% of total islet cells. A similar amount of T cells were present in non-diabetic human islets. Islet T cells were comprised of CD8-positive, CD4-positive, and regulatory T cells. Interestingly, while islet B cells and macrophage numbers were unaltered by age, the number of islet T cells increased linearly (R2=0.9902) with age from 0.10 ± 0.05% (3 months) to 0.38 ±0.11% (24 months) of islet cells. This increase was uncoupled from body weight, and was not phenocopied by a degree similar weight gain induced by high fat diet in mice.ConclusionsThis study reveals that T cells are a part of the normal islet immune population in mouse and human islets, and that they accumulate in islets during aging in a body weight-independent manner. Though comprising only a small subset of the immune cells within islets, islet T cells may play a role in the physiology of islet aging.

Proinsulin (PI) is processed to mature insulin by prohormone convertases 1/3 (Pcsk1) and 2 (Pcsk2). In individuals with T1D and T2D, there is an increase in the circulating PI:insulin ratio. We hypothesized that beta-cell Pcsk1 deletion would result in beta-cell dysfunction and hyperglycemia. Male and female Pcsk1flox/flox Ins1cre/+ (Pcsk1beta-KO) and Pcsk1+/+ Ins1cre/+ (Pcsk1beta-WT) mice were fed either a chow or a high fat diet (HFD; 45% fat) and monitored until 30 weeks of age. Despite an approximately 150-fold increase in fasting plasma PI (p < 0.001) and only immature insulin granules detectable by electron microscopy, chow-fed Pcsk1beta-KO male mice had normal glucose tolerance early in life and only developed glucose intolerance by 26 weeks of age (AUC: 934±294 vs. 597±223; p = 0.008). Histological analysis showed that male Pcsk1beta-KO mice displayed a trend toward increased beta-cell area (1.3±0.6 vs. 0.8±0.4%; p = 0.08). The unexpectedly mild hyperglycemia in Pcsk1beta-KO mice is likely due to incomplete disruption of proinsulin processing, as mass spectrometry and western blot analysis of Pcsk1beta-KO islets confirmed markedly elevated proinsulin, but detectable mature insulin. In HFD-fed cohorts, 3/10 Pcsk1beta-KO male mice developed sustained fasting hyperglycemia (>16 mM) after 19 weeks of diet. Chow and HFD-fed female Pcsk1beta-KO mice displayed no differences in glycemia or body weight from Pcsk1beta-WT controls. Deletion of both Pcsk1 and Pcsk2 in beta cells (Pcsk1flox/flox Pcsk2flox/flox Ins1cre/+) resulted in undetectable mature insulin in islets (western blot), and impaired glucose tolerance at 10 weeks of age in both chow-fed male and female mice. Our results suggest that beta-cell Pcsk1 deficiency is not sufficient to drive diabetes development, but increases diabetes susceptibility in conditions of increased insulin secretory demand. Our data in mice support the idea that beta-cell prohormone processing errors likely contribute to pathogenesis of diabetes but not obesity. Disclosure A. Taylor: None. Y. Chen: None. B. Verchere: Advisory Panel; Self; Integrated Nanotherapeutics Inc., Sirona Biochem. Stock/Shareholder; Self; Integrated Nanotherapeutics Inc. Funding Canadian Institutes of Health Research (PJT153156)

Overexpression of the X-linked inhibitor of apoptosis (XIAP) prevents islet allograft rejection. We constructed an adeno-associated virus expressing XIAP driven by the rat insulin promoter (dsAAV8-RIP-XIAP) for long-term beta-cell gene expression in vivo. Pancreatic delivery of dsAAV8-RIP-XIAP prevented autoimmune diabetes in 70% of non-obese diabetic (NOD) mice, associated with decreased insulitis. Islets from Balb/c mice transduced with dsAAV8-RIP-XIAP were protected following transplantation into streptozotocin (STZ)-diabetic Bl/6 recipients, associated with decreased graft infiltration. Interestingly, dsAAV8-RIP-XIAP transduction induced expression of lactate dehydrogenase (LDHA) and monocarboxylate transporter 1 (MCT1), two genes normally suppressed in beta cells and involved in production and release of lactate, a metabolite known to suppress local immune responses. Transduction of Balb/c islets with AAV8-RIP-LDHA-MCT1 tended to prolong allograft survival following transplant into STZ-diabetic Bl/6 recipients. These findings suggest that XIAP has therapeutic potential in autoimmune diabetes and raise the possibility that local lactate production may play a role in XIAP-mediated immunomodulation.

Biosynthesis of peptide hormones by pancreatic islet endocrine cells is a tightly orchestrated process that is critical for metabolic homeostasis. Like neuroendocrine peptides, insulin and other islet hormones are first synthesized as larger precursor molecules that are processed to their mature secreted products through a series of proteolytic cleavages, mediated by the prohormone convertases Pc1/3 and Pc2, and carboxypeptidase E. Additional posttranslational modifications including C-terminal amidation of the β-cell peptide islet amyloid polypeptide (IAPP) by peptidyl-glycine α-amidating monooxygenase (Pam) may also occur. Genome-wide association studies (GWAS) have showed genetic linkage of these processing enzymes to obesity, β-cell dysfunction, and type 2 diabetes (T2D), pointing to their important roles in metabolism and blood glucose regulation. In both type 1 diabetes (T1D) and T2D, and in the face of metabolic or inflammatory stresses, islet prohormone processing may become impaired; indeed elevated proinsulin:insulin (PI:I) ratios are a hallmark of the β-cell dysfunction in T2D. Recent studies suggest that genetic or acquired defects in proIAPP processing may lead to the production and secretion of incompletely processed forms of proIAPP that could contribute to T2D pathogenesis, and additionally that impaired processing of both PI and proIAPP may be characteristic of β-cell dysfunction in T1D. In islet α-cells, the prohormone proglucagon is normally processed to bioactive glucagon by Pc2 but may express Pc1/3 under certain conditions leading to production of GLP-1(7-36NH2 ). A better understanding of how β-cell processing of PI and proIAPP, as well as α-cell processing of proglucagon, are impacted by genetic susceptibility and in the face of diabetogenic stresses, may lead to new therapeutic approaches for improving islet function in diabetes.

Epidemiologic studies have reported relationships between maternal high folate and/or low B12 status during pregnancy and greater adiposity and insulin resistance in children. The goal of this study was to determine the effects of maternal folic acid supplementation (10 mg/kg diet), with (50 μg/kg diet) and without B12, on adult female offspring adiposity and glucose homeostasis. Female C57BL/6J mice were fed 1 of 3 diets from weaning and throughout breeding, pregnancy, and lactation: control (2 mg/kg diet folic acid, 50 μg/kg diet B12), supplemental folic acid with no B12 (SFA-B12), or supplemental folic acid with adequate B12 (SFA+B12). Female offspring were weaned onto the control diet or a Western diet (45% energy fat, 2 mg/kg diet folic acid, 50 μg/kg diet B12) for 35 wk. After weaning, control diet-fed offspring with SFA-B12 dams had fasting hyperglycemia, glucose intolerance, lower β cell mass, and greater islet hepatocyte nuclear factor 1 homeobox α and nuclear receptor subfamily 1 group H member 3 mRNA than did offspring from control dams. In Western diet-fed offspring, those with SFA-B12 dams had lower fasting blood glucose and plasma insulin concentrations, and were smaller than control offspring. Our findings suggest that maternal folic acid supplementation with B12 deficiency during pregnancy/lactation programs the metabolic health of adult female offspring but is dependent on offspring diet.-Henderson, A. M., Tai, D. C., Aleliunas, R. E., Aljaadi, A. M., Glier, M. B., Xu, E. E., Miller, J. W., Verchere, C. B., Green, T. J., Devlin, A. M. Maternal folic acid supplementation with vitamin B12 deficiency during pregnancy and lactation affects the metabolic health of adult female offspring but is dependent on offspring diet.