An improved method for isolation of mouse pancreatic islets

Engineered tools to study endocrine dysfunction of pancreas

Pancreas, a vital organ with intricate endocrine and exocrine functions, is central to the regulation of the body's glucose levels and digestive processes. Disruptions in its endocrine functions, primarily regulated by islets of Langerhans, can lead to debilitating diseases such as diabetes mellitus. Murine models of pancreatic dysfunction have contributed significantly to the understanding of insulitis, islet-relevant immunological responses, and the optimization of cell therapies. However, genetic differences between mice and humans have severely limited their clinical translational relevance. Recent advancements in tissue engineering and microfabrication have ushered in a new era of in vitro models that offer a promising solution. This paper reviews the state-of-the-art engineered tools designed to study endocrine dysfunction of the pancreas. Islet on a chip devices that allow precise control of various culture conditions and noninvasive readouts of functional outcomes have led to the generation of physiomimetic niches for primary and stem cell derived islets. Live pancreatic slices are a new experimental tool that could more comprehensively recapitulate the complex cellular interplay between the endocrine and exocrine parts of the pancreas. Although a powerful tool, live pancreatic slices require more complex control over their culture parameters such as local oxygenation and continuous removal of digestive enzymes and cellular waste products for maintaining experimental functionality over long term. The combination of islet-immune and slice on chip strategies can guide the path toward the next generation of pancreatic tissue modeling for better understanding and treatment of endocrine pancreatic dysfunctions.

Structure, interaction and nervous connectivity of beta cell primary cilia

Primary cilia are sensory organelles present in many cell types, partaking in various signaling processes. Primary cilia of pancreatic beta cells play pivotal roles in paracrine signaling and their dysfunction is linked to diabetes. Yet, the structural basis for their functions is unclear. We present three-dimensional reconstructions of beta cell primary cilia by electron and expansion microscopy. These cilia are spatially confined within deep ciliary pockets or narrow spaces between cells, lack motility components and display an unstructured axoneme organization. Furthermore, we observe a plethora of beta cell cilia-cilia and cilia-cell interactions with other islet and non-islet cells. Most remarkably, we have identified and characterized axo-ciliary synapses between beta cell cilia and the cholinergic islet innervation. These findings highlight the beta cell cilia's role in islet connectivity, pointing at their function in integrating islet intrinsic and extrinsic signals and contribute to understanding their significance in health and diabetes.

Acute inhibition of iron-sulfur cluster biosynthesis disrupts metabolic flexibility in mice

Iron-sulfur clusters (ISCs) are cell-essential cofactors present in ∼60 proteins including subunits of OXPHOS complexes I-III, DNA polymerases, and iron-sensing proteins. Dysfunctions in ISC biosynthesis are associated with anemias, neurodegenerative disorders, and metabolic diseases. To assess consequences of acute ISC inhibition in a whole body setting, we developed a mouse model in which key ISC biosynthetic enzyme NFS1 can be acutely and reversibly suppressed. Contrary to in vitro ISC inhibition and pharmacological OXPHOS suppression, global NFS1 inhibition rapidly enhances lipid utilization and decreases adiposity without affecting caloric intake and physical activity. ISC proteins decrease, including key proteins involved in OXPHOS (SDHB), lipoic acid synthesis (LIAS), and insulin mRNA processing (CDKAL1), causing acute metabolic inflexibility. Age-related metabolic changes decelerate loss of adiposity substantially prolonged survival of mice with NFS1 inhibition. Thus, the observation that ISC metabolism impacts organismal fuel choice will aid in understanding the mechanisms underlying ISC diseases with increased risk for diabetes.

Graphical abstract

Highlights

Acute ISC inhibition leads to rapid loss of adiposity in miceMulti-metabolic pathway disruption upon ISC deficiency blocks energy storageNfs1 inhibition induces glucose dyshomeostasis due to ISC deficiency in β-cellsEnergy distress caused by inhibition of ISC synthesis is attenuated in aged mice.

Purification of time-resolved insulin granules reveals proteomic and lipidomic changes during granule aging

Endocrine cells employ regulated exocytosis of secretory granules to secrete hormones and neurotransmitters. Secretory granule exocytosis depends on spatiotemporal variables such as proximity to the plasma membrane and age, with newly generated granules being preferentially released. Despite recent advances, we lack a comprehensive view of the molecular composition of insulin granules and associated changes over their lifetime. Here, we report a strategy for the purification of insulin secretory granules of distinct age from insulinoma INS-1 cells. Tagging the granule-resident protein phogrin with a cleavable CLIP tag, we obtain intact fractions of age-distinct granules for proteomic and lipidomic analyses. We find that the lipid composition changes over time, along with the physical properties of the membrane, and that kinesin-1 heavy chain (KIF5b) as well as Ras-related protein 3a (RAB3a) associate preferentially with younger granules. Further, we identify the Rho GTPase-activating protein (ARHGAP1) as a cytosolic factor associated with insulin granules.

Tau suppresses microtubule-regulated pancreatic insulin secretion

Tau protein is implicated in the pathogenesis of Alzheimer's disease (AD) and other tauopathies, but its physiological function is in debate. Mostly explored in the brain, tau is also expressed in the pancreas. We further explored the mechanism of tau's involvement in the regulation of glucose-stimulated insulin secretion (GSIS) in islet β-cells, and established a potential relationship between type 2 diabetes mellitus (T2DM) and AD. We demonstrate that pancreatic tau is crucial for insulin secretion regulation and glucose homeostasis. Tau levels were found to be elevated in β-islet cells of patients with T2DM, and loss of tau enhanced insulin secretion in cell lines, drosophila, and mice. Pharmacological or genetic suppression of tau in the db/db diabetic mouse model normalized glucose levels by promoting insulin secretion and was recapitulated by pharmacological inhibition of microtubule assembly. Clinical studies further showed that serum tau protein was positively correlated with blood glucose levels in healthy controls, which was lost in AD. These findings present tau as a common therapeutic target between AD and T2DM.

Possibility of adiponectin use to improve islet transplantation outcomes

Although islet transplantation (ITx) is a promising therapy for severe diabetes mellitus, further advancements are necessary. Adiponectin, an adipokine that regulates lipid and glucose metabolism, exerts favorable effects on islets, such as reinforcement of the insulin-releasing function. This study evaluated the possibility of adiponectin use to improve ITx outcomes. We treated mouse islets with 10 µg/mL recombinant mouse adiponectin by overnight culture and then assessed the insulin-releasing, angiogenic, and adhesion functions of the islets. Furthermore, 80 syngeneic islet equivalents with or without adiponectin treatment were transplanted into the renal subcapsular space of diabetic mice. In in vitro assessment, released insulin at high glucose stimulation, insulin content, and expressions of vascular endothelial growth factor and integrin β1 were improved in adiponectin-treated islets. Furthermore, adiponectin treatment improved the therapeutic effect of ITx on blood glucose levels and promoted angiogenesis of the transplanted islets. However, the therapeutic effect was not pronounced in glucose tolerance test results. In conclusion, adiponectin treatment had preferable effects in the insulin-releasing, angiogenic, and adhesion functions of islets and contributed to the improvement of ITx. The future use of adiponectin treatment in clinical settings to improve ITx outcomes should be investigated.

Vitamin D supplementation induces CatG-mediated CD4+ T cell inactivation and restores pancreatic β-cell function in mice with type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease accompanied by the immune-mediated destruction of pancreatic β-cells. In this study, we aimed to explore the regulatory effects of vitamin D (VD) supplementation on pancreatic β-cell function by altering the expression of bioinformatically identified cathepsin G (CatG) in T1D mice. A T1D mouse model was established in nonobese diabetic (NOD) mice, and their islets were isolated and purified. Pancreatic mononuclear cells (MNCs) were collected, from which CD4⁺ T cells were isolated. The levels of interleukin (IL)-2, IL-10, tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ) in the supernatant of mouse pancreatic tissue homogenate were assessed using ELISA. Immunohistochemistry and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labelin (TUNEL) staining were conducted to evaluate the effects of VD supplementation on pancreatic tissues of T1D mice. The pancreatic β-cell line MIN6 was used for in vitro substantiation of findings in vivo. VD supplementation reduced glucose levels and improved glucose tolerance in T1D mice. Furthermore, VD supplementation improved pancreatic β-cell function and suppressed immunological and inflammatory reactions in the T1D mice. We documented overexpression of CatG in diabetes tissue samples, and then showed that VD supplementation normalized the islet immune microenvironment through downregulating CatG expression in T1D mice. Experiments in vitro subsequently demonstrated that VD supplementation impeded CD4⁺ T activation by downregulating CatG expression and thereby enhanced pancreatic β-cell function. Results of the present study elucidated that VD supplementation can downregulate the expression of CatG and inhibit CD4⁺ T cell activation, thereby improving β-cell function in T1D.NEW & NOTEWORTHY We report that vitamin D (VD) supplementation downregulates CatG expression and inhibits CD4⁺ T cell activation, thereby improving β-cell function in type 1 diabetes (T1D). This study deepens our understanding of the pathogenesis of T1D and clarifies molecular events underlying the alleviatory effect of VD for immunotherapy against T1D.

A high-fat diet catalyzes progression to hyperglycemia in mice with selective impairment of insulin action in Glut4-expressing tissues

Insulin resistance impairs postprandial glucose uptake through glucose transporter type 4 (GLUT4) and is the primary defect preceding type 2 diabetes. We previously generated an insulin-resistant mouse model with human GLUT4 promoter-driven insulin receptor knockout (GIRKO) in the muscle, adipose, and neuronal subpopulations. However, the rate of diabetes in GIRKO mice remained low prior to 6 months of age on normal chow diet (NCD), suggesting that additional factors/mechanisms are responsible for adverse metabolic effects driving the ultimate progression of overt diabetes. In this study, we characterized the metabolic phenotypes of the adult GIRKO mice acutely switched to high-fat diet (HFD) feeding in order to identify additional metabolic challenges required for disease progression. Distinct from other diet-induced obesity (DIO) and genetic models (e.g., db/db mice), GIRKO mice remained leaner on HFD feeding, but developed other cardinal features of insulin resistance syndrome. GIRKO mice rapidly developed hyperglycemia despite compensatory increases in β-cell mass and hyperinsulinemia. Furthermore, GIRKO mice also had impaired oral glucose tolerance and a limited glucose-lowering benefit from exendin-4, suggesting that the blunted incretin effect contributed to hyperglycemia. Secondly, GIRKO mice manifested severe dyslipidemia while on HFD due to elevated hepatic lipid secretion, serum triglyceride concentration, and lipid droplet accumulation in hepatocytes. Thirdly, GIRKO mice on HFD had increased inflammatory cues in the gut, which were associated with the HFD-induced microbiome alterations and increased serum lipopolysaccharide (LPS). In conclusion, our studies identified important gene/diet interactions contributing to diabetes progression, which might be leveraged to develop more efficacious therapies.

Induction of Immune Tolerance in Islet Transplantation Using Apoptotic Donor Leukocytes

Allogeneic islet transplantation has become an effective treatment option for severe Type 1 diabetes with intractable impaired awareness due to hypoglycemic events. Although current immunosuppressive protocols effectively prevent the acute rejection associated with initial T cell activation in recipients, chronic rejection has remained an obstacle for achieving long-term allogeneic islet engraftment. The development of donor-specific immune tolerance to the allograft is the ultimate goal given its potential ability to overcome chronic rejection and disregard the need for maintenance immunosuppression, which may be toxic to islet grafts. Recently, a breakthrough in tolerance induction during allogeneic islet transplantation using apoptotic donor lymphocytes (ADLs) in a non-human primate model had been reported. Several studies have suggested that the clonal depletion, anergy, and expansion of the antigen-specific regulatory immune network are the mechanisms for donor-specific tolerance with ADLs, which act synergistically to induce robust transplant tolerance. This achievement represents a huge step forward toward the clinical application of immune tolerance induction. We herein summarize the reported operational induction therapies in islet transplantation using the ADLs. Moreover, a few obstacles for the engraftment of transplanted islets, such as islet immunogenicity and instant blood-mediated response, which need to be resolved in the future, are also discussed.

An open-access volume electron microscopy atlas of whole cells and tissues

Understanding cellular architecture is essential for understanding biology. Electron microscopy (EM) uniquely visualizes cellular structures with nanometre resolution. However, traditional methods, such as thin-section EM or EM tomography, have limitations in that they visualize only a single slice or a relatively small volume of the cell, respectively. Focused ion beam-scanning electron microscopy (FIB-SEM) has demonstrated the ability to image small volumes of cellular samples with 4-nm isotropic voxels1. Owing to advances in the precision and stability of FIB milling, together with enhanced signal detection and faster SEM scanning, we have increased the volume that can be imaged with 4-nm voxels by two orders of magnitude. Here we present a volume EM atlas at such resolution comprising ten three-dimensional datasets for whole cells and tissues, including cancer cells, immune cells, mouse pancreatic islets and Drosophila neural tissues. These open access data (via OpenOrganelle2) represent the foundation of a field of high-resolution whole-cell volume EM and subsequent analyses, and we invite researchers to explore this atlas and pose questions.

Identification of four novel QTL linked to the metabolic syndrome in the Berlin Fat Mouse

Background

The Berlin Fat Mouse Inbred line (BFMI) is a model for obesity and the metabolic syndrome. This study aimed to identify genetic variants associated with impaired glucose metabolism using the obese lines BFMI861-S1 and BFMI861-S2, which are genetically closely related, but differ in several traits. BFMI861-S1 is insulin resistant and stores ectopic fat in the liver, whereas BFMI861-S2 is insulin sensitive.

Methods

In generation 10, 397 males of an advanced intercross line (AIL) BFMI861-S1 × BFMI861-S2 were challenged with a high-fat, high-carbohydrate diet and phenotyped over 25 weeks. QTL-analysis was performed after selective genotyping of 200 mice using the GigaMUGA Genotyping Array. Additional 197 males were genotyped for 7 top SNPs in QTL regions. For the prioritization of positional candidate genes whole genome sequencing and gene expression data of the parental lines were used.

Results

Overlapping QTL for gonadal adipose tissue weight and blood glucose concentration were detected on chromosome (Chr) 3 (95.8–100.1 Mb), and for gonadal adipose tissue weight, liver weight, and blood glucose concentration on Chr 17 (9.5–26.1 Mb). Causal modeling suggested for Chr 3-QTL direct effects on adipose tissue weight, but indirect effects on blood glucose concentration. Direct effects on adipose tissue weight, liver weight, and blood glucose concentration were suggested for Chr 17-QTL. Prioritized positional candidate genes for the identified QTL were Notch2 and Fmo5 (Chr 3) and Plg and Acat2 (Chr 17). Two additional QTL were detected for gonadal adipose tissue weight on Chr 15 (67.9–74.6 Mb) and for body weight on Chr 16 (3.9–21.4 Mb).

Conclusions

QTL mapping together with a detailed prioritization approach allowed us to identify candidate genes associated with traits of the metabolic syndrome. In addition, we provided evidence for direct and indirect genetic effects on blood glucose concentration in the insulin-resistant mouse line BFMI861-S1.

Autoantibody against angiotensin II type I receptor induces pancreatic β-cell apoptosis via enhancing autophagy

Autoantibody against the angiotensin II type I receptor (AT1-AA) has been found in the serum of patients with diabetes mellitus (DM). However, it remains unclear whether AT1-AA induces β-cell apoptosis and participates in the development of DM. In this study, an AT1-AA-positive rat model was set up by active immunization, and AT1-AA IgG was purified. INS-1 cells were treated with AT1-AA, and cell viability, apoptosis, and autophagy-related proteins were detected by Cell Counting Kit-8 assay, flow cytometry, and western blot analysis, respectively. Results showed that existence of AT1-AA impaired the islet function and increased the apoptosis of pancreatic islet cells in rats, and the autophagy level in rat pancreatic islet tissues tended to increase gradually with the prolongation of immunization time. AT1-AA markedly reduced INS-1 cell viability, promoted cell apoptosis, and decreased insulin secretion in vitro. In addition, the autophagy level was gradually increased along with the prolongation of AT1-AA treatment time. Meanwhile, it was determined that treatment with autophagy inhibitor 3-methyladenine and angiotensin II type 1 receptor (AT1R) blocker telmisartan could improve insulin secretion and apoptosis in vitro and in vivo. In conclusion, it is deduced that upregulation of autophagy contributed to the AT1-AA-induced β-cell apoptosis and islet dysfunction, and AT1R mediated the signal transduction.

Protocol for determining zinc-dependent β cell-selective small-molecule delivery in mouse pancreas

Targeted drug delivery to pancreatic islet β cells is an unmet clinical need. β cells possess a uniquely high Zn2+ concentration, and integrating Zn2+-binding activity into a small molecule can bias drug accumulation and activity toward β cells. This protocol can be used to evaluate a molecule's capacity to chelate islet Zn2+, accumulate in islets, and stimulate β cell-selective replication in mouse pancreas. One obstacle is establishing an LC-MS/MS-based method for compound measurement. Limitations include target compound ionizability and the time-sensitive nature of some experimental assay steps. For complete details on the use and execution of this protocol, please refer to Horton et al. (2019).

A Practical Guide to Rodent Islet Isolation and Assessment Revisited

Insufficient insulin secretion is a key component of both type 1 and type 2 diabetes. Since insulin is released by the islets of Langerhans, obtaining viable and functional islets is critical for research and transplantation. The effective and efficient isolation of these small islands of endocrine cells from the sea of exocrine tissue that is the rest of the pancreas is not necessarily simple or quick. Choosing and administering the digestive enzyme, separation of the islets from acinar tissue, and culture of islets are all things that must be considered. The purpose of this review is to provide a history of the development of islet isolation procedures and to serve as a practical guide to rodent islet research for newcomers to islet biology. We discuss key elements of mouse islet isolation including choosing collagenase, the digestion process, purification of islets using a density gradient, and islet culture conditions. In addition, this paper reviews techniques for assessing islet viability and function such as visual assessment, glucose-stimulated insulin secretion and intracellular calcium measurements. A detailed protocol is provided that describes a common method our laboratory uses to obtain viable and functional mouse islets for in vitro study. This review thus provides a strong foundation for successful procurement and purification of high-quality mouse islets for research purposes.

Comprehensive analysis of gene expression of isolated pancreatic islets during pretransplant culture

Background:

The aim of this study was to investigate the effect of pretransplant culture on the survival of pancreatic islet grafts, and to determine the biological characteristics of isolated islets during pretransplant culture.

Methods:

The survival of islets from Wistar rats, transplanted to diabetic C57BL/B6 mice, was compared between fresh islets and cultured islets. A comprehensive gene expression analysis was employed to investigate biological processes during pretransplant culture, and in vitro validation studies were performed.

Results:

Survival of cultured xenografts was significantly prolonged as compared to that of fresh islets (fresh: 12.5 ± 1.9 days, 1-day cultured: 16.0 ± 1.3 days (p= 0.017), 3-day cultured: 17.0 ± 2.6 days (p= 0.014)). Comprehensive gene expression analysis identified significant upregulation of annotated functions associated with inflammation in cultured groups. Six proinflammatory genes, including heme oxygenase 1 (HO-1) and IL-6, were significantly upregulated during culture. Validation studies revealed significantly higher levels of IL-6 in the supernatant of cultured islets and HO-1 in the cultured islets when compared with fresh islets.

Conclusion:

Transplantation of cultured islets induced significant but minimal prolongation of graft survival in xenogeneic combinations. Comprehensive analysis of gene expression in cultured islets showed biological processes associated with proinflammation during culture.

Beneficial actions of the [A14K] analog of the frog skin peptide PGLa-AM1 in mice with obesity and degenerative diabetes: A mechanistic study

The antidiabetic actions of [A14K]PGLa-AM1, an analog of peptide glycine-leucine-amide-AM1 isolated from skin secretions of the octoploid frog Xenopus amieti, were investigated in genetically diabetic-obese db/db mice. Twice daily administration of [A14K]PGLa-AM1 (75 nmol/kg body weight) for 28 days significantly (P < 0.05) decreased circulating blood glucose and HbA1c and increased plasma insulin concentrations leading to improvements in glucose tolerance. The elevated levels of triglycerides, LDL and cholesterol associated with the db/db phenotype were significantly reduced by peptide administration. Elevated plasma alanine transaminase, aspartic acid transaminase, and alkaline phosphatase activities and creatinine concentrations were also significantly decreased. Peptide treatment increased pancreatic insulin content and improved the responses of isolated islets to established insulin secretagogues. No significant changes in islet β-cell and α-cell areas were observed in [A14K]PGLa-AM1 treated mice but the loss of large and medium-size islets was prevented. Peptide administration resulted in a significant (P < 0.01) increase in islet expression of the gene encoding Pdx-1, a major transcription factor in islet cells determining β-cell survival and function, resulting in increased expression of genes involved with insulin secretion (Abcc8, Kcnj11, Slc2a2, Cacn1c) together with the genes encoding the incretin receptors Glp1r and Gipr. In addition, the elevated expression of insulin signalling genes (Slc2a4, Insr, Irs1, Akt1, Pik3ca, Ppm1b) in skeletal muscle associated with the db/db phenotype was downregulated by peptide treatment These data suggest that the anti-diabetic properties of [A14K]PGLa-AM1 are mediated by molecular changes that enhance both the secretion and action of insulin.

3D FIB-SEM reconstruction of microtubule-organelle interaction in whole primary mouse β cells

Microtubules play a major role in intracellular trafficking of vesicles in endocrine cells. Detailed knowledge of microtubule organization and their relation to other cell constituents is crucial for understanding cell function. However, their role in insulin transport and secretion is under debate. Here, we use FIB-SEM to image islet β cells in their entirety with unprecedented resolution. We reconstruct mitochondria, Golgi apparati, centrioles, insulin secretory granules, and microtubules of seven β cells, and generate a comprehensive spatial map of microtubule-organelle interactions. We find that microtubules form nonradial networks that are predominantly not connected to either centrioles or endomembranes. Microtubule number and length, but not microtubule polymer density, vary with glucose stimulation. Furthermore, insulin secretory granules are enriched near the plasma membrane, where they associate with microtubules. In summary, we provide the first 3D reconstructions of complete microtubule networks in primary mammalian cells together with evidence regarding their importance for insulin secretory granule positioning and thus their supportive role in insulin secretion.

Mechanism of Transplanted Islet Engraftment in Visceral White Adipose Tissue

BACKGROUND

White adipose tissue (WAT) is a candidate transplantation site for islets. However, the mechanism of islet engraftment in WAT has not been fully investigated. In this study, we attempted to clarify the therapeutic effect and mechanism of islet transplantation into visceral WAT.

METHODS

Two hundred mouse islets were transplanted into epididymal WAT of syngeneic diabetic mice by wrapping islets with the tissue (fat-covered group). Mice that received intraperitoneal and renal subcapsular islet transplantations were used as negative and positive control groups, respectively.

RESULTS

The transplant efficacy, including improvements in blood glucose and plasma insulin levels and in glucose tolerance tests, of the fat-covered group was superior to the negative control group and almost equal to the positive control group. Vessel density of engrafted islets in the fat-covered group was higher than that in the positive control group. It was speculated that the mechanism of islet engraftment in WAT might consist of trapping islets in WAT, adhesion of islets via a combination of adhesion factors (fibronectin and integrin β1), and promotion of angiogenesis in islets by expression of angiogenic factors induced by adiponectin.

CONCLUSIONS

Visceral WAT is an important candidate for islet transplantation. Adhesion factors and adiponectin might contribute to islet engraftment into WAT. Further studies to elucidate the detailed mechanism are necessary.

Allograft inflammatory factor-1 in myeloid cells drives autoimmunity in type 1 diabetes

Allograft inflammatory factor-1 (AIF1) is a calcium-responsive cytoplasmic scaffold protein that directs hematopoiesis and immune responses within dendritic cells (DC) and macrophages. Although the role of AIF1 in transplant rejection and rheumatoid arthritis has been explored, little is known about its role in type 1 diabetes. Here, we show that in vivo silencing of AIF1 in NOD mice restrained infiltration of immune cells into the pancreas and inhibited diabetes incidence. Analyses of FACS-sorted CD45neg nonleukocyte populations from resected pancreatic islets showed markedly higher expression of insulin in the AIF1-silenced groups. Evaluation of CD45+ leukocytes revealed diminished infiltration of effector T cells and DC in the absence of AIF1. Transcriptional profiling further revealed a marked decrease in cDC1 DC-associated genes CD103, BATF3, and IRF8, which are required for orchestrating polarized type 1 immunity. Reduced T cell numbers within the islets were observed, with concomitant lower levels of IFN-γ and T-bet in AIF1-silenced cohorts. In turn, there was a reciprocal increase in functionally suppressive pancreas-resident CD25+Foxp3+CD4+ Tregs. Taken together, results show that AIF1 expression in myeloid cells plays a pivotal role in promoting type 1 diabetes and that its suppression restrains insulitis by shifting the immune microenvironment toward tolerance.

Antibody-induced NKG2D blockade in a rat model of intraportal islet transplantation leads to a deleterious reaction

Intraportal islet transplantation is plagued by an acute destruction of transplanted islets. Amongst the first responders, NK cells and macrophages harbour an activating receptor, NKG2D, recognizing ligands expressed by stressed cells. We aimed to determine whether islet NKG2D ligand expression increases with culture time, and to analyse the impact of antibody-induced NKG2D blockade in islet transplantation. NKG2D-ligand expression was analysed in rat and human islets. Syngeneic marginal mass intraportal islet transplantations were performed in rats: control group, recipients transplanted with NKG2D-recombinant-treated islets (recombinant group), and recipients treated with a mouse anti-rat anti-NKG2D antibody and transplanted with recombinant-treated islets (antibody-recombinant group). Islets demonstrated increased gene expression of NKG2D ligands with culture time. Blockade of NKG2D on NK cells decreased in vitro cytotoxicity against islets. Recipients from the control and recombinant groups showed similar metabolic results; conversely, treatment with the antibody resulted in lower diabetes reversal. The antibody depleted circulating and liver NK cells in recipients, who displayed increased macrophage infiltration of recipient origin around the transplanted islets. In vitro blockade of NKG2D ligands had no impact on early graft function. Systemic treatment of recipients with an anti-NKG2D antibody was deleterious to the islet graft, possibly through an antibody-dependent cell-mediated cytotoxicity reaction.

An anti-CD103 antibody-drug conjugate prolongs the survival of pancreatic islet allografts in mice

CD103 mediates T-cell infiltration and organ allograft rejection, and depletion of CD103-expressing cells is a promising therapeutic strategy for allograft intolerance. Recently, we verified that M290-MC-MMAF, an anti-CD103 antibody-drug conjugate, potently eliminates CD103-positive cells in vivo, with high specificity and minimal toxicity. However, the contribution of M290-MC-MMAF to blocking the CD103/E-cadherin pathway involved in transplant rejection remains unclear. Herein, we examined the impact of systemic administration of M290-MC-MMAF on allografts in an islet transplantation model. M290-MC-MMAF treatment maintained the long-term survival of islet allografts (>60 days) compared to mock injection or unconjugated M290 antibody treatment (<18 days). The change was associated with a decrease in CD103⁺CD8⁺ effector T cells and an increase in CD4⁺CD25⁺ regulatory T cells. CD103⁺CD8⁺ effector T-cell transfer or CD4⁺CD25⁺ regulatory T-cell depletion resulted in a rapid loss of allografts in long-surviving islet hosts. Moreover, M290-MC-MMAF treatment reduced IL-4, IL-6, and TNF-α expression levels and increased IL-10 expression in the grafts, which presented an immunosuppressive cytokine profile. In conclusion, targeting CD103 with M290-MC-MMAF induced immunosuppression and prolonged the survival of pancreatic islet allografts in mice, indicating the potential clinical value of M290-MC-MMAF in therapeutic interventions for allograft rejection.

A Simple High Efficiency Protocol for Pancreatic Islet Isolation from Mice

Pancreatic islets, also called the Islets of Langerhans, are a cluster of endocrine cells which produces hormones for glucose regulation and other important biological functions. The islets primarily consist of five types of hormone-secreting cells: α cells secrete glucagon, β cells secrete insulin, δ cells secrete somatostatin, ε cells secrete ghrelin, and PP cells secrete pancreatic polypeptide. Sixty to 80% of the cells in the islets are β cells, which are the most important cell population to study insulin secretion. Pancreatic islets are a crucial model system to study ex vivo insulin secretion. Acquiring high quality islets is of great importance for diabetes research. Most islet isolation procedures require technically difficult to access site of collagenase injection, harsh and complex digestion procedures, and multiple density gradient purification steps. This paper features a simple high yield mouse islet isolation method with detailed descriptions and realistic demonstrations, showing the following specific steps: 1) injection of collagenase P at the ampulla of Vater, a small area joining the pancreatic duct and the common bile duct, 2) enzymatic digestion and mechanical separation of the exocrine pancreas, and 3) a single gradient purification step. The advantages of this method are the injection of digestive enzyme using the more accessible ampulla of Vater, more complete digestion using combination of enzymatic and mechanical approaches, and a simpler single gradient purification step. This protocol produces approximately 250-350 islets per mouse; and islets are suitable for various ex vivo studies. Possible caveats of this procedure are potentially damaged islets due to enzymatic digestion and/or prolonged gradient incubation, all of which can be largely avoided by careful ad justification of incubation time.

A Trimodal Imaging Platform for Tracking Viable Transplanted Pancreatic Islets In Vivo: F-19 MR, Fluorescence, and Bioluminescence Imaging

PURPOSE

Combining specific and quantitative F-19 magnetic resonance imaging (MRI) with sensitive and convenient optical imaging provides complementary information about the distribution and viability of transplanted pancreatic islet grafts. In this study, pancreatic islets (PIs) were labeled with positively charged multimodal nanoparticles based on poly(lactic-co-glycolic acid) (PLGA-NPs) with encapsulated perfluoro-15-crown-5-ether and the near-infrared fluorescent dye indocyanine green.

PROCEDURES

One thousand and three thousand bioluminescent PIs were transplanted into subcutaneous artificial scaffolds, which served as an alternative transplant site. The grafts were monitored using in vivo F-19 MR, fluorescence, and bioluminescence imaging in healthy rats for 2 weeks.

RESULTS

Transplanted PIs were unambiguously localized in the scaffolds by F-19 MRI throughout the whole experiment. Fluorescence was detected in the first 4 days after transplantation only. Importantly, in vivo bioluminescence correlated with the F-19 MRI signal.

CONCLUSIONS

We developed a trimodal imaging platform for in vivo examination of transplanted PIs. Fluorescence imaging revealed instability of the fluorescent dye and its limited applicability for longitudinal in vivo studies. A correlation between the bioluminescence signal and the F-19 MRI signal indicated the fast clearance of PLGA-NPs from the transplantation site after cell death, which addresses a major issue with intracellular imaging labels. Therefore, the proposed PLGA-NP platform is reliable for reflecting the status of transplanted PIs in vivo.

Glucagon-related peptides from phylogenetically ancient fish reveal new approaches to the development of dual GCGR and GLP1R agonists for type 2 diabetes therapy

The insulinotropic and antihyperglycaemic properties of glucagons from the sea lamprey (Petromyzontiformes), paddlefish (Acipenseriformes) and trout (Teleostei) and oxyntomodulin from dogfish (Elasmobranchii) and ratfish (Holocephali) were compared with those of human glucagon and GLP-1 in mammalian test systems. All fish peptides produced concentration-dependent stimulation of insulin release from BRIN-BD11 rat and 1.1 B4 human clonal β-cells and isolated mouse islets. Paddlefish glucagon was the most potent and effective peptide. The insulinotropic activity of paddlefish glucagon was significantly (P < 0.01) decreased after incubating BRIN-BD11 cells with the GLP1R antagonist, exendin-4(9-39) and the GCGR antagonist [des-His¹,Pro⁴, Glu⁹] glucagon amide but GIPR antagonist, GIP(6-30)Cex-K⁴⁰[palmitate] was without effect. Paddlefish and lamprey glucagons and dogfish oxyntomodulin (10 nmol L^-1) produced significant (P < 0.01) increases in cAMP concentration in Chinese hamster lung (CHL) cells transfected with GLP1R and human embryonic kidney (HEK293) cells transfected with GCGR. The insulinotropic activity of paddlefish glucagon was attenuated in CRISPR/Cas9-engineered GLP1R knock-out INS-1 cells but not in GIPR knock-out cells. Intraperitoneal administration of all fish peptides, except ratfish oxyntomodulin, to mice together with a glucose load produced significant (P < 0.05) decreases in plasma glucose concentrations and paddlefish glucagon produced a greater release of insulin compared with GLP-1. Paddlefish glucagon shares the sequences Glu¹⁵-Glu¹⁶ and Glu²⁴-Trp²⁵-Leu²⁶-Lys²⁷-Asn²⁸-Gly²⁹ with the potent GLP1R agonist, exendin-4 so may be regarded as a naturally occurring, dual-agonist hybrid peptide that may serve as a template design of new drugs for type 2 diabetes therapy.

Effects of remote ischaemic preconditioning on intraportal islet transplantation in a rat model

Remote ischaemic preconditioning (RIPC), which is the intermittent interruption of blood flow to a site distant from the target organ, is known to improve solid organ resistance to ischaemia-reperfusion injury. This procedure could be of interest in islet transplantation to mitigate hypoxia-related loss of islet mass after isolation and transplantation. Islets isolated from control or RIPC donors were analyzed for yield, metabolic activity, gene expression and high mobility group box-1 (HMGB1) content. Syngeneic marginal mass transplantation was performed in four streptozotocin-induced diabetic groups: control, RIPC in donor only, RIPC in recipient only, and RIPC in donor and recipient. Islets isolated from RIPC donors had an increased yield of 20% after 24 h of culture compared to control donors (P = 0.007), linked to less cell death (P = 0.08), decreased expression of hypoxia-related genes (Hif1a P = 0.04; IRP94 P = 0.008), and increased intra-cellular (P = 0.04) and nuclear HMGB1. The use of RIPC in recipients only did not allow for reversal of diabetes, with increased serum HMGB1 at day 1; the three other groups demonstrated significantly better outcomes. Performing RIPC in the donors increases islet yield and resistance to hypoxia. Validation is needed, but this strategy could help to decrease the number of donors per islet recipient.

The zinc transporter Slc39a5 controls glucose sensing and insulin secretion in pancreatic β-cells via Sirt1- and Pgc-1α-mediated regulation of Glut2

Zinc levels are high in pancreatic β-cells, and zinc is involved in the synthesis, processing and secretion of insulin in these cells. However, precisely how cellular zinc homeostasis is regulated in pancreatic β-cells is poorly understood. By screening the expression of 14 Slc39a metal importer family member genes, we found that the zinc transporter Slc39a5 is significantly down-regulated in pancreatic β-cells in diabetic db/db mice, obese ob/ob mice and high-fat diet-fed mice. Moreover, β-cell-specific Slc39a5 knockout mice have impaired insulin secretion. In addition, Slc39a5-deficient pancreatic islets have reduced glucose tolerance accompanied by reduced expression of Pgc-1α and its downstream target gene Glut2. The down-regulation of Glut2 in Slc39a5-deficient islets was rescued using agonists of Sirt1, Pgc-1α and Ppar-γ. At the mechanistic level, we found that Slc39a5-mediated zinc influx induces Glut2 expression via Sirt1-mediated Pgc-1α activation. These findings suggest that Slc39a5 may serve as a possible therapeutic target for diabetes-related conditions.

Insulinotropic activity of the host-defense peptide frenatin 2D: Conformational, structure-function and mechanistic studies

Of four naturally occurring frenatin peptides tested, frenatin 2D (DLLGTLGNLPLPFI.NH₂) from Discoglossus sardus was the most potent and effective in producing concentration-dependent stimulation of insulin release from BRIN-BD11 rat clonal β-cells without displaying cytotoxicity. The peptide also stimulated insulin release from 1.1B4 human-derived clonal β-cells and isolated mouse islets and improved glucose tolerance concomitant with increased circulating insulin concentrations in mice following intraperitoneal administration. The insulinotropic activity of frenatin 2D was not associated with membrane depolarization or an increase in intracellular [Ca²⁺] but incubation of the peptide (1 μM) with BRIN-BD11 cells produced a modest, but significant (P < 0.05), increase in cAMP production. Stimulation of insulin release was abolished in protein kinase A-downregulated cells but maintained in protein kinase C-downregulated cells. Circular dichroism studies showed that, in the presence of dodecylphosphocholine micelles, frenatin 2D exhibited a helical content of 35% and a turn content of 28%. Substitution of the Thr⁵, Asn⁸, Pro¹⁰, and Ile¹⁴ residues in frenatin-2D by Trp and interchange of Pro¹² and Phe¹³ led to loss of insulinotropic activity but the [D1W] and [G7W] analogues were as potent and effective as the native peptide. Frenatin 2D (1 μM) also stimulated proliferation of BRIN-BD11 cells and provided significant protection of the cells against cytokine-induced apoptosis. It is concluded that the insulinotropic activity of frenatin 2D is mediated predominantly, if not exclusively, by the K_ATP channel-independent pathway.

Estradiol Prevents High Glucose-Induced β-cell Apoptosis by Decreased BTG2 Expression

Hyperglycemia stimulates several pathways to induce pancreatic β-cell apoptosis. In our previous study by mRNA analysis, we demonstrated that B-cell translocation gene 2 (BTG₂) expression was up-regulated in INS-1 cells cultured under high glucose conditions, but this effect was reversed by estrogen. In the present study, we demonstrated that BTG₂ mRNA and protein expressions in both INS-1 cells and mouse pancreatic islets increased under high glucose conditions compared to those cultured under basal glucose conditions, while in the presence of estrogen, the BTG₂ mRNA and protein expressions decreased. SiRNA-BTG₂ significantly reduced cell apoptosis, cleaved-caspase 3, and Bax, compared to the siRNA-control in INS-1 cultured under high glucose conditions. We further demonstrated that BTG₂ promoter activity was activated under high glucose conditions whereas estrogen significantly reduced it. The effects of estrogen on BTG₂ expression were inhibited by estrogen receptor inhibitors. Also, under high glucose conditions, p53 and Bax mRNA and protein expressions increased, but they decreased in the presence of estrogen. Again, the effect of estrogen on p53 and Bax expression was inhibited by estrogen receptor inhibitors. Taken together, this study demonstrates that estrogen reduces pancreatic β-cell apoptosis under high glucose conditions via suppression of BTG2, p53, and Bax expressions.

Treatment of T1D via optimized expansion of antigen-specific Tregs induced by IL-2/anti-IL-2 monoclonal antibody complexes and peptide/MHC tetramers

Type 1 diabetes can be overcome by regulatory T cells (Treg) in NOD mice yet an efficient method to generate and maintain antigen-specific Treg is difficult to come by. Here, we devised a combination therapy of peptide/MHC tetramers and IL-2/anti-IL-2 monoclonal antibody complexes to generate antigen-specific Treg and maintain them over extended time periods. We first optimized treatment protocols conceived to obtain an improved islet-specific Treg/effector T cell ratio that led to the in vivo expansion and activation of these Treg as well as to an improved suppressor function. Optimized protocols were applied to treatment for testing diabetes prevention in NOD mice as well as in an accelerated T cell transfer model of T1D. The combined treatment led to robust protection against diabetes, and in the NOD model, to a close to complete prevention of insulitis. Treatment was accompanied with increased secretion of IL-10, detectable in total splenocytes and in Foxp3⁻ CD4 T cells. Our data suggest that a dual protection mechanism takes place by the collaboration of Foxp3⁺ and Foxp3⁻ regulatory cells. We conclude that antigen-specific Treg are an important target to improve current clinical interventions against this disease.

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

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.

Heterogeneity of SOX9 and HNF1β in Pancreatic Ducts Is Dynamic

Pancreatic duct epithelial cells have been suggested as a source of progenitors for pancreatic growth and regeneration. However, genetic lineage-tracing experiments with pancreatic duct-specific Cre expression have given conflicting results. Using immunofluorescence and flow cytometry, we show heterogeneous expression of both HNF1β and SOX9 in adult human and murine ductal epithelium. Their expression was dynamic and diminished significantly after induced replication. Purified pancreatic duct cells formed organoid structures in 3D culture, and heterogeneity of expression of Hnf1β and Sox9 was maintained even after passaging. Using antibodies against a second cell surface molecule CD51 (human) or CD24 (mouse), we could isolate living subpopulations of duct cells enriched for high or low expression of HNF1β and SOX9. Only the CD24^high (Hnfβ^high/Sox9^high) subpopulation was able to form organoids.

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HNF1β and SOX9 are differentially expressed across the pancreatic ductal tree

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Their expression was dynamic and diminished significantly after replication

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Live subpopulations can be isolated using CD51 (human) and CD24 (mouse).

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Only the CD24^high (Hnfβ^high/Sox9^high) subpopulation was able to form organoids

Evaluation of the insulinotropic and glucose-lowering actions of zebrafish GIP in mammalian systems: Evidence for involvement of the GLP-1 receptor

The insulinotropic properties of zebrafish GIP (zfGIP) were assessed in vitro using clonal pancreatic β-cell lines and isolated mouse islets and acute effects on glucose tolerance and insulin release in vivo were evaluated in mice. The peptide produced a dose-dependent increase in the rate of insulin release from BRIN-BD11 rat clonal β-cells at concentrations ≥30nM. Insulin release from 1.1 B4 human clonal β-cells and mouse islets was significantly increased by zfGIP (10nM and 1μM). The in vitro insulinotropic activity of zfGIP was decreased after incubating BRIN-BD11 cells with the GLP-1 receptor antagonist, exendin-4(9-39) (p<0.001) and the GIP receptor antagonist, GIP (6-30) Cex-K⁴⁰[Pal] (p<0.05) but the glucagon receptor antagonist [des-His¹,Pro⁴,Glu⁹]glucagon amide was without effect. zfGIP (10nM and 1μM) produced significant increases in cAMP concentration in CHL cells transfected with the human GLP-1 receptor but was without effect on HEK293 cells transfected with the human glucagon receptor. Conversely, zfGIP, but not human GIP, significantly stimulated insulin release from CRISPR/Cas9-engineered INS-1 clonal β-cells from which the GIP receptor had been deleted. Intraperitoneal administration of zfGIP (25 and 75nmol/kg body weight) to mice together with an intraperitoneal glucose load (18mmol/kg body weight) produced a significant decrease in plasma glucose concentrations concomitant with an increase in insulin concentrations. The study provides evidence that the insulinotropic action of zfGIP in mammalian systems involves activation of both the GLP-1 and the GIP receptors but not the glucagon receptor.

Apelin-13 analogues show potent in vitro and in vivo insulinotropic and glucose lowering actions

Nine structurally modified apelin-13 analogues were assessed for their in vitro and acute in vivo antidiabetic potential. Stability was assessed in mouse plasma and insulinotropic efficacy tested in cultured pancreatic BRIN-BD11 cells and isolated mouse pancreatic islets. Intracellular Ca²⁺ and cAMP production in BRIN-BD11 cells was determined, as was glucose uptake in 3T3-L1 adipocytes. Acute antihyperglycemic effects of apelin analogues were assessed following i.p. glucose tolerance tests (ipGGT, 18 mmol/kg) in normal and diet-induced-obese (DIO) mice and on food intake in normal mice. Apelin analogues all showed enhanced in vitro stability (up to 5.8-fold, t½ = 12.8 h) in mouse plasma compared to native apelin-13 (t½ = 2.1 h). Compared to glucose controls, stable analogues exhibited enhanced insulinotropic responses from BRIN-BD11 cells (up to 4.7-fold, p < 0.001) and isolated mouse islets (up to 5.3-fold) for 10^-7 M apelin-13 amide (versus 7.6-fold for 10^-7 M GLP-1). Activation of APJ receptors on BRIN-BD11 cells increased intracellular Ca²⁺ (up to 3.0-fold, p < 0.001) and cAMP (up to 1.7-fold, p < 0.01). Acute ipGTT showed improved insulinotropic and glucose disposal responses in normal and DIO mice (p < 0.05 and p < 0.01, respectively). Apelin-13 amide and (pGlu)apelin-13 amide were the most effective analogues exhibiting acute, dose-dependent and persistent biological actions. Both analogues stimulated insulin-independent glucose uptake by differentiated adipocytes (2.9-3.3-fold, p < 0.05) and inhibited food intake (26-33%, p < 0.001), up to 180 min in mice, versus saline. In contrast, (Ala¹³)apelin-13 and (Val¹³)apelin-13 inhibited insulin secretion, suppressed beta-cell signal transduction and stimulated food intake in mice. Thus, stable analogues of apelin-13 have potential for diabetes/obesity therapy.

Olfactory receptors are expressed in pancreatic β-cells and promote glucose-stimulated insulin secretion

Olfactory receptors (ORs) mediate olfactory chemo-sensation in OR neurons. Herein, we have demonstrated that the OR chemo-sensing machinery functions in pancreatic β-cells and modulates insulin secretion. First, we found several OR isoforms, including OLFR15 and OLFR821, to be expressed in pancreatic islets and a β-cell line, MIN6. Immunostaining revealed OLFR15 and OLFR821 to be uniformly expressed in pancreatic β-cells. In addition, mRNAs of Olfr15 and Olfr821 were detected in single MIN6 cells. These results indicate that multiple ORs are simultaneously expressed in individual β-cells. Octanoic acid, which is a medium-chain fatty acid contained in food and reportedly interacts with OLFR15, potentiated glucose-stimulated insulin secretion (GSIS), thereby improving glucose tolerance in vivo. GSIS potentiation by octanoic acid was confirmed in isolated pancreatic islets and MIN6 cells and was blocked by OLFR15 knockdown. While Gα_olf expression was not detectable in β-cells, experiments using inhibitors and siRNA revealed that the pathway dependent on phospholipase C-inositol triphosphate, rather than cAMP-protein kinase A, mediates GSIS potentiation via OLFR15. These findings suggest that the OR system in pancreatic β-cells has a chemo-sensor function allowing recognition of environmental substances obtained from food, and potentiates insulin secretion in a cell-autonomous manner, thereby modulating systemic glucose metabolism.

3-Iodothyronamine reduces insulin secretion in vitro via a mitochondrial mechanism

PURPOSE

3-iodothyronamine (3-T₁AM), a decarboxylated and deiodinated thyroid hormone metabolite, leads at pharmacological doses to hypoinsulinemia, hyperglucagonemia and hyperglycemia in vivo. As the pancreatic Langerhans islets express thyroid hormone transmembrane transporters (THTT), we tested the hypothesis that not only plasma membrane-mediated 3-T₁AM binding to and activation of G-protein coupled receptors, but also 3-T₁AM metabolite(s) generated by 3-T₁AM uptake and metabolism might decrease glucose-stimulated insulin secretion (GSIS).

METHODS

Murine pancreatic β-cells MIN6 were characterized for gene expression of THTT, deiodinases and monoamine oxidases. 3-T₁AM uptake and intracellular metabolism to the corresponding 3-iodothyroacetic acid were analysed by liquid-chromatography tandem mass spectrometry (LC-MS/MS) at different time points in cells as well as the conditioned medium. Mitochondrial activity, especially ATP-production, was monitored real-time after 3-T₁AM application using Seahorse Bioanalyzer technique. Effect of 3-T₁AM on GSIS into the culture medium was assayed by ELISA.

RESULTS

MIN6 cells express classical THTT, proposed to transport 3-T₁AM, as well as 3-T₁AM metabolizing enzymes comparable to murine primary pancreatic islets. 3-T₁AM accumulates in MIN6 cells and is metabolized by intracellular MaoB to 3-iodothyroacetic, which in turn is rapidly exported. 3-T₁AM decreases mitochondrial ATP-production concentration dependently. GSIS is diminished by 3-T₁AM treatment. Using LC-MS/MS, no further 3-T₁AM metabolites except 3-iodothyroacetic were detectable.

CONCLUSIONS

This data provides a first link between cellular 3-T₁AM uptake and regulation of mitochondrial energy metabolism in ß-cells, resulting in reduced insulin secretion. We conclude that MIN6 is an appropriate cell model to study 3-T₁AM-dependent (intra-)cellular biochemical mechanisms affecting insulin production in vitro.

Effect of resveratrol treatment on graft revascularization after islet transplantation in streptozotocin-induced diabetic mice

We evaluated the effect of resveratrol (RSV) on graft survival after islet transplantation (ITx) in diabetic mice. Isolated islets from Balb/c mice (200 IEQ) were transplanted under the kidney capsule of diabetic Balb/c mice. Vehicle or RSV (200 mg/kg/day, orally) was given for 14 days after ITx. Two more control groups [STZ-treated (No-ITx-Control) and STZ+RSV-treated (No-ITx-RSV) mice without ITx] were added. Glucose tolerance tests (GTT) was performed at 14 days after ITx. In vitro, isolated islets pretreated with vehicle or RSV (1 μM) were incubated in a hypoxic chamber (O2 1%, 1hr). Some of the ITx was performed in mouse insulin 1 gene promoter-green fluorescent protein (MIP-GFP) transgenic mice and analyzed using an in vivo imaging system. After 14 days of ITx, 2-hr glucose levels on GTT in the RSV-treated group were significantly lower than those of other control groups. But the glucose status was not improved in No-ITx mice with RSV. At day 3, the percentage of Ki-67/insulin co-stained cells in islet graft was significantly increased in the RSV-ITx group. Immunostaining with anti-insulin and anti-BS-1 antibodies revealed significantly higher insulin-stained area and vascular density in RSV-treated islet grafts. The mean vessel volume per islet graft measured by in vivo imaging was significantly higher in the RSV-treated group at day 3. In isolated islets cultured in hypoxic conditions, the cell death rate and oxidative stress were significantly attenuated with RSV pretreatment. Hypoxic treatment for isolated islets decreased the expression of SIRT-1 mRNA, and this attenuation was recovered by RSV pretreatment. Our data suggest that RSV treatment improved glycemic control, beta-cell proliferation, reduced oxidative stress, and enhanced islet revascularization and the outcome of ITx in diabetic mice.

The Optimal Timing for Pancreatic Islet Transplantation into Subcutaneous Scaffolds Assessed by Multimodal Imaging

Subcutaneously implanted polymeric scaffolds represent an alternative transplantation site for pancreatic islets (PIs) with the option of vascularisation enhancement by mesenchymal stem cells (MSC). Nevertheless, a proper timing of the transplantation steps is crucial. In this study, scaffolds supplemented with plastic rods were implanted into diabetic rats and two timing schemes for subsequent transplantation of bioluminescent PIs (4 or 7 days after rod removal) were examined by multimodal imaging. The cavities were left to heal spontaneously or with 10 million injected MSCs. Morphological and vascularisation changes were examined by MRI, while the localisation and viability of transplanted islets were monitored by bioluminescence imaging. The results show that PIs transplanted 4 days after rod removal showed the higher optical signal and vascularisation compared to transplantation after 7 days. MSCs slightly improved vascularisation of the graft but hindered therapeutic efficiency of PIs. Long-term glycaemia normalisation (4 months) was attained in 80% of animals. In summary, multimodal imaging confirmed the long-term survival and function of transplanted PIs in the devices. The best outcome was reached with PIs transplanted on day 4 after rod removal and therefore the suggested protocol holds a potential for further applications.

Estrogen attenuates AGTR1 expression to reduce pancreatic β-cell death from high glucose

Chronic exposure of pancreatic β-cells to high glucose levels results in β-cell dysfunction and death. These effects can be protected by estrogen. The local pancreatic renin-angiotensin system (RAS) has been shown as a novel pathological pathway of high-glucose-induced cell death. The effect of estrogen on pancreatic RAS is still unknown. This study examines whether estrogen protects against pancreatic β-cell death caused by glucotoxicity via a decrease in the pancreatic β-cell RAS pathway. When INS-1 cells were cultured in a high glucose medium, cell death was significantly higher than when the cells were cultured in a basal glucose medium; similarly, there were also higher levels of AGTR1 and p47^ph°^x mRNA, and protein expression. Moreover, the addition of 10⁻⁸ M 17β-estradiol to INS-1 cells cultured in a high glucose medium markedly reduced cell death, AGTR1 and p47^ph°^x mRNA levels, and protein expression. Similar results were demonstrated in the pancreatic islets. The presence of 10⁻⁸ M 17β-estradiol, losartan, or a combination of both, in a high glucose medium had similar levels of reduction of p47^ph°^x mRNA and protein expression, compared with those cultured in high glucose. Taken together, estrogen protected pancreatic β-cells from high-glucose-induced cell death by reducing the AGTR1 pathway.

Pleckstrin homology-like domain family A, member 3 (PHLDA3) deficiency improves islets engraftment through the suppression of hypoxic damage

Islet transplantation is a useful cell replacement therapy that can restore the glycometabolic function of severe diabetic patients. It is known that many transplanted islets failed to engraft, and thus, new approaches for overcoming graft loss that may improve the outcome of future clinical islet transplantations are necessary. Pleckstrin homology-like domain family A, member 3 (PHLDA3) is a known suppressor of neuroendocrine tumorigenicity, yet deficiency of this gene increases islet proliferation, prevents islet apoptosis, and improves their insulin-releasing function without causing tumors. In this study, we examined the potential use of PHLDA3-deficient islets in transplantation. We observed that: 1) transplanting PHLDA3-deficient islets into diabetic mice significantly improved their glycometabolic condition, 2) the improved engraftment of PHLDA3-deficient islets resulted from increased cell survival during early transplantation, and 3) Akt activity was elevated in PHLDA3-deficient islets, especially under hypoxic conditions. Thus, we determined that PHLDA3-deficient islets are more resistant against stresses induced by islet isolation and transplantation. We conclude that use of islets with suppressed PHLDA3 expression could be a novel and promising treatment for improving engraftment and consequent glycemic control in islet transplantation.

Mesenchymal cells are required for epithelial duct cell-to-beta cell maturation and function in an injured adult pancreas in the rat

The islet, the endocrine portion of the pancreas - develops from an invagination of the pancreatic duct epithelial cells (PDECs) into the surrounding tissue. The contact of the PDECs with mesenchymal cells (MSCs) may be an essential drive for endocrine cell fate. During pancreatic development, cells that express Neurogenin-3 (Ngn3) biomarker are precursors of insulin- producing beta cells. These precursors have been reported in the neogenesis of islets from adult tissues following the surgical ligation of the main pancreatic duct (PDL). But the capacity of these precursors to induce the appropriate signals to complete the entire neogenesis program has been questioned. We studied the fate of co-culture of PDECs and MSCs from the ligated adult pancreas and established the exact location of adult stem- or progenitor-like cells that give rise to beta cells. PDECs were cultured in direct contact with or without MSCs in serum-containing culture media. The cytomorphology of the cells in co-cultures was determined and the immunocytochemical study of the cells was carried out using anti-Ngn3, anti-insulin and anti-cytokeratin-7 (CK7) antibodies. Both the PDEC/MSC- and PDEC/MSC+ cultures showed out- pocketing from duct epithelium by the end of the second week, which are distinct as cell clusters only in PDEC/MSC+ cells later in week four, exhibiting numerous branching ducts. Co-expression of Ngn3 with insulin was observed in both cultures from the second week. However, characterizations of these Ngn3+ cells in the PDEC/MSC+ culture revealed that these cells also co-expressed a CK7 biomarker. This study provides new evidence of the ductal epithelial nature of beta cells in injured adult pancreata; and that the mesenchymal stromal cells are required to sustain Ngn3 expression for beta cell maturation and function.

Pre-Microporation Improves Outcome of Pancreatic Islet Labelling for Optical and 19F MR Imaging

Background

In vitro labelling of cells and small cell structures is a necessary step before in vivo monitoring of grafts. We modified and optimised a procedure for pancreatic islet labelling using bimodal positively charged poly(lactic-co-glycolic acid) nanoparticles with encapsulated perfluoro crown ethers and indocyanine green dye via microporation and compared the method with passive endocytosis.

Results

Pancreatic islets were microporated using two pulses at various voltages. We tested a standard procedure (poration in the presence of nanoparticles) and a modified protocol (pre-microporation in a buffer only, and subsequent islet incubation with nanoparticles on ice for 10 min).

We compared islet labelling by microporation with labelling by endocytosis, i.e. pancreatic islets were incubated for 24 h in a medium with suspended nanoparticles.

In order to verify the efficiency of the labelling procedures, we used ¹⁹F magnetic resonance imaging, optical fluorescence imaging and confocal microscopy.

The experiment confirmed that microporation, albeit fast and effective, is invasive and may cause substantial harm to islets. To achieve sufficient poration and to minimise the reduction of viability, the electric field should be set at 20 kV/m (two pulses, 20 ms each).

Poration in the presence of nanoparticles was found to be unsuitable for the nanoparticles used. The water suspension of nanoparticles (which served as a surfactant) was slightly foamy and microbubbles in the suspension were responsible for sparks causing the destruction of islets during poration. However, pre-microporation (poration of islets in a buffer only) followed by 10-min incubation with nanoparticles was safer.

Conclusions

For labelling of pancreatic islets using poly(lactic-co-glycolic acid) nanoparticles, the modified microporation procedure with low voltage was found to be safer than the standard microporation procedure. The modified procedure was fast, however, efficiency was lower compared to endocytosis.

Entrapment of Cultured Pancreas Islets in Three-Dimensional Collagen Matrices

In vitro culture of islets of Langerhans decreases their immunogenecity, presumably by eliminating passenger leukocytes and other Ia+ presenting cells within the islets. Islets cultivated in petri dishes either at 37°C or at 25°C gradually disintegrate during culture in a time-dependent manner which is related to the free-floating condition of the islets. Also, a fraction of the islets disperse as single cells and beta-cell aggregates or adhere to the bottom of the culture dishes. Thus, the retrieval rate of transplantable islets is dampened due to their disintegration and spontaneous dispersion in conventional petri dish cultures.

Entrapment of freshly harvested islets of Langerhans in a three-dimensional collagen matrix was studied as an alternative method for islet cultivation. The contraction of collagen fibrils during in vitro culture counteracts the dispersion of islets and helps in maintaining their integrity while in culture. It was observed that the entrapped islets maintain satisfactory morphology, viability, and capability of glucose-dependent insulin secretion for over 2 wk. The oxygen consumption rate and glucose metabolism of these islets was not deranged when entrapped in collagen. Also, the retrieval of islets is easier and more efficient than that observed in conventional culture systems.

Our results indicate that culture of islets in three-dimensional collagen gels can potentially develop into an ideal system applicable to clinical transplantation of cultured islets or beta-cell aggregates.

High Yield of Rodent Islets with Intraductal Collagenase and Stationary Digestion—A Comparison with Standard Technique

Intraductal distention of the pancreas with collagenase followed by stationary warm incubation improves the recovery of islets of Langerhans in the rat, but controlled studies are needed for valid comparison with standard isolation methods. We have modified Gotoh's technique of stationary digestion for high-yield isolation in the rat (Stationary). The method is subjected herein to rigorous blinded comparison with the standard chopped tissue (Chopped) technique, based on Lacy et al., as performed in our laboratory for over 10 yr. Islet recovery was determined by a single observer ‘blinded’ to the method of isolation used, and only intact islets of diameter ≥ 100 μm were included. Stationary gave 719 ± 114 islets per pancreas (mean ± SD, n = 21 isolations) vs. 487.5 ± 69 for Chopped (n = 36 isolations), a 47.5% increment in yield (p < 0.0001). In vitro islet perifusion showed no statistical difference in stimulation index (SI) or stimulated area under the curve (SAUC) between the two methods, but Stationary showed a trend towards improved phase II insulin release. In vivo function was assessed by isogeneic transplantation of 2,000 islets beneath the renal capsule of streptozotocin diabetic recipients (65 mg/kg Sigma); Stationary recipients (n = 7) became normoglycemic (≤ 8 mmol/L) by 3.3 ± 4.8 days vs. 1.6 ± 1.5 days for Chopped recipients (p = 0.4 ns, mean ± SEM). IVGTT performed at 1 mo posttransplant gave K-values for Stationary of 2.64 ± 0.8 vs. 2.62 ± 0.8 for Chopped (mean ± SD, p = 0.9 ns, n = 6, unpaired t-test), which were not distinguishable from normal control rats (2.59 ± 0.8) (p = 0.9 ns, n = 10). Graft function remained stable until graft bearing nephrectomy induced hyperglycemia uniformly within 1 day. Graft histology showed a healthy well-preserved structure on light microscopy, with well-granulated beta cells on EM. Economic costs of rat, collagenase, and Ficoll were 26% ($50.82) lower per recipient for Stationary. We conclude that modified stationary digestion significantly improves islet recovery with excellent in vitro and in vivo function, and is cost effective.

Successful Reversal of Diabetes by Single Donor Isologous Islet Transplantation in a Mouse Model

A method for isolating mouse islets which consistently gives a high yield with good purity is described. Using a bovine serum albumin gradient, the mean yield of islets per pancreas is 425 (SEM ± 15) with a consistent purity of over 90%. Single donor to single recipient of islets transplanted under the renal capsule restores normoglycemia in the diabetic recipients within 2 to 5 days of transplantation.