Bringing the human pancreas into focus: new paradigms for the understanding of Type 1 diabetes

Clinical, glycometric features and treatment in a family with monogenic diabetes due to a new mutation in the insulin gene

Monogenic diabetes caused by changes in the gene that encodes insulin (INS) is a very rare form of monogenic diabetes (<1%). The aim of this work is to describe the clinical and glycaemic control characteristics over time from four members of a family diagnosed with monogenic diabetes with the novel mutation: c.206del,p.(Gly69Aalfs*62) located in exon 3 of the gene INS. 75% are females, with debut in adolescence and negative autoimmunity. In all cases, C-peptide is detectable decades after diagnosis (>0.6ng/ml). Currently, patients are being treated either with insulin in a bolus-basal regimen, oral antidiabetics or hybrid closed loop system. Monogenic diabetes due to mutation in the INS is an entity with heterogeneous presentation, whose diagnosis requires high suspicion and presents an important clinical impact. Given the lack of standards in this regard, therapy must be individualized, although insulin therapy could help preserve beta cell functionality in these subjects.

Type 1 diabetes in the pancreas: A histological perspective

AIMS

This review aims to introduce research in the pancreas to a broader audience. The pancreas is a heterocrine gland residing deep within our abdominal cavity. It is the home to our islets, which play a pivotal role in regulating metabolic homeostasis. Due to its structure and location, it is an impossible organ to study, in molecular detail, in living humans, and yet, understanding the pancreas is critical if we aim to characterise the immunopathology of type 1 diabetes (T1D) and one day prevent the triggering of the autoimmune attack associated with ß-cell demise.

METHODS

Over a 100 years ago, we began studying pancreatic histology using cadaveric samples and clever adaptations to microscopes. As histologists, some may say nothing much has changed. Nevertheless, our microscopes can now interrogate multiple proteins at molecular resolution. Images of pancreas sections are no longer constrained to a single field of view and can capture a thousands and thousands of cells. AI-image-analysis packages can analyse these massive data sets offering breakthrough findings.

CONCLUSION

This narrative review will provide an overview of pancreatic anatomy, and the importance of research focused on the pancreas in T1D. It will range from histological breakthroughs to briefly discussing the challenges associated with characterising the organ. I shall briefly introduce a selection of the available global biobanks and touch on the distinct pancreatic endotypes that differ immunologically and in ß-cell behaviour. Finally, I will introduce the idea of developing a collaborative tool aimed at developing a cohesive framework for characterising heterogeneity and stratifying endotypes in T1D more readily.

The extent and magnitude of islet T cell infiltration as powerful tools to define the progression to type 1 diabetes

AIMS/HYPOTHESIS

Insulitis is not present in all islets, and it is elusive in humans. Although earlier studies focused on islets that fulfilled certain criteria (e.g. ≥15 CD45+ cells or ≥6 CD3+ cells), there is a fundamental lack of understanding of the infiltration dynamics in terms of its magnitude (i.e. how much) and extent (i.e. where). Here, we aimed to perform an in-depth characterisation of T cell infiltration by investigating islets with moderate (1-5 CD3+ cells) and high (≥6 CD3+ cells) infiltration in individuals with and without type 1 diabetes.

METHODS

Pancreatic tissue sections from 15 non-diabetic, eight double autoantibody-positive and ten type 1 diabetic (0-2 years of disease duration) organ donors were obtained from the Network for Pancreatic Organ Donors with Diabetes, and stained for insulin, glucagon, CD3 and CD8 by immunofluorescence. T cell infiltration was quantified in a total of 8661 islets using the software QuPath. The percentage of infiltrated islets and islet T cell density were calculated. To help standardise the analysis of T cell infiltration, we used cell density data to develop a new T cell density threshold capable of differentiating non-diabetic and type 1 diabetic donors.

RESULTS

Our analysis revealed that 17.1% of islets in non-diabetic donors, 33% of islets in autoantibody-positive and 32.5% of islets in type 1 diabetic donors were infiltrated by 1 to 5 CD3+ cells. Islets infiltrated by ≥6 CD3+ cells were rare in non-diabetic donors (0.4%) but could be found in autoantibody-positive (4.5%) and type 1 diabetic donors (8.2%). CD8+ and CD8- populations followed similar patterns. Likewise, T cell density was significantly higher in the islets of autoantibody-positive donors (55.4 CD3+ cells/mm2) and type 1 diabetic donors (74.8 CD3+ cells/mm2) compared with non-diabetic individuals (17.3 CD3+ cells/mm2), which was accompanied by higher exocrine T cell density in type 1 diabetic individuals. Furthermore, we showed that the analysis of a minimum of 30 islets and the use of a reference mean value for T cell density of 30 CD3+ cells/mm2 (the 30-30 rule) can differentiate between non-diabetic and type 1 diabetic donors with high specificity and sensitivity. In addition, it can classify autoantibody-positive individuals as non-diabetic or type 1 diabetic-like.

CONCLUSIONS/INTERPRETATION

Our data indicates that the proportion of infiltrated islets and T cell density change dramatically during the course of type 1 diabetes, and these changes can be already observed in double autoantibody-positive individuals. This suggests that, as disease progresses, T cell infiltration extends throughout the pancreas, reaching the islets and exocrine compartment. While it predominantly targets insulin-containing islets, large accumulations of cells are rare. Our study fulfils the need to further understand T cell infiltration, not only after diagnosis but also in individuals with diabetes-related autoantibodies. Furthermore, the development and application of new analytical tools based on T cell infiltration, like the 30-30 rule, will allow us to correlate islet infiltration with demographic and clinical variables with the aim of identifying individuals at the very early stages of the disease.

Advanced Delivery Strategies for Immunotherapy in Type I Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) has been defined as an autoimmune disease characterised by immune-mediated destruction of the pancreatic β cells, leading to absolute insulin deficiency and hyperglycaemia. Current research has increasingly focused on immunotherapy based on immunosuppression and regulation to rescue T-cell-mediated β-cell destruction. Although T1DM immunotherapeutic drugs are constantly under clinical and preclinical development, several key challenges remain, including low response rates and difficulty in maintaining therapeutic effects. Advanced drug delivery strategies can effectively harness immunotherapies and improve their potency while reducing their adverse effects. In this review, we briefly introduce the mechanisms of T1DM immunotherapy and focus on the current research status of the integration of the delivery techniques in T1DM immunotherapy. Furthermore, we critically analyse the challenges and future directions of T1DM immunotherapy.

A century later, still fighting back: antigen-specific immunotherapies for type 1 diabetes

Type 1 diabetes (T1D) is a chronic metabolic disease caused by the autoimmune destruction of insulin-producing β-cells. Ever since the 1920s, the fate of patients suffering from T1D was dramatically improved owing to the isolation and production of insulin, and the scientific field has largely progressed as a result of the evidence gathered about its underpinnings and mechanisms. The last years have seen this knowledge transformed into actual antigen-specific immunotherapies with potential to restore selectively the breach of tolerance to β-cell autoantigens and halt the autoimmune aggression. However, so far, the results of both prevention and reversion trials in T1D have been rather discouraging, so there is still an urgent need to optimize those immunotherapies and their associated factors, for example, posology and administration patterns, route and timing. In this review, we look back on what has been achieved in the last century and identify the main autoantigens driving the autoimmune attack in T1D. Then, we take a deep dive into the numerous antigen-specific immunotherapies trialed and the ones still at a preclinical phase, ranging from peptides, proteins and agent combinations to gene transfer, nanoparticles, cell-based strategies and novel approaches exploiting naturally occurring tolerogenic processes. Finally, we provide insight into the several features to be considered in a T1D clinical trial, the ideal time point for intervention and the biomarkers needed for monitoring the successful regulatory effect of the antigen-specific immunotherapy. Although further research and optimization remain imperative, the development of a therapeutic armamentarium against T1D autoimmunity is certainly advancing with a confident step.

Effects of low-level fluoride exposure on glucose homeostasis in female NOD mice

Water fluoridation is an important public health measure for the control of dental caries. Recent animal studies have shown that low doses of fluoride (F) in the drinking water, similar to those found in public water supplies, increase insulin sensitivity and reduce blood glucose. In the present study we evaluated the effects of low-level F exposure through the drinking water on glucose homeostasis in female NOD mice. Seventy-two 6-week mice were randomly divided into 2 groups according to the concentration of F in the drinking water (0-control, or 10 mg/L) they received for 14 weeks. After the experimental period the blood was collected for analyses of plasma F, glucose and insulin. Liver and gastrocnemius muscle were collected for proteomic analysis. Plasma F concentrations were significantly higher in the F-treated than in the control group. Despite treatment with fluoridated water reduced plasma levels glucose by 20% compared to control, no significant differences were found between the groups for plasma glucose and insulin. In the muscle, treatment with fluoridated water increased the expression of proteins related to muscle contraction, while in the liver, there was an increase in expression of antioxidant proteins and in proteins related to carboxylic acid metabolic process. Remarkably, phosphoenolpyruvate carboxykinase (PEPCK) was found exclusively in the liver of control mice. The reduction in PEPCK, a positive regulator of gluconeogenesis, thus increasing glucose uptake, might be a probable mechanism to explain the anti-diabetic effects of low doses of F, which should be evaluated in further studies.

Pancreatic autoantibodies and CD14+CD16+ monocytes subset are associated with the impairment of ß-cell function after simultaneous pancreas-kidney transplantation

Pancreatic autoantibodies (AAb) has been associated with a worse pancreas graft survival after simultaneous pancreas-kidney transplantation (SPK). However, due to the variable time for AAb to become positive and the lack of early biomarkers suggesting such autoimmune activation, the mechanisms leading ß-cell destruction remain uncertain. The present study aimed to evaluate the association between post-transplant AAb and the functional impairment of the pancreatic ß-cell and also the association of such AAb with inflammation after SPK. In a longitudinal study, we analyzed the impact of post-transplant glutamic acid decarboxylase (GAD-65) and the insulinoma-associated autoantigen 2 (IA-2) AAb on pancreas graft function. Serum Hb1Ac and C-peptide (C-pep) were longitudinally compared between a group with positive posttransplant AAb (AAb+; n = 40) and another matched group with negative AAb (AAb-; n = 40) until the fifth year following seroconversion. In the cross-sectional analysis, we further evaluated the systemic signatures of inflammation by measuring pro-inflammatory CD14⁺CD16⁺ monocytes by flow-cytometry and interleukin 17-A serum levels in 38 SPK recipients and ten healthy controls. In the longitudinal study, patients with AAb+ showed higher levels of Hb1Ac (p<0.001) and lower C-pep levels (p<0.001) compared to those who remained AAb- throughout the follow-up. In the cross-sectional study, AAb+ patients showed a higher percentage of CD14⁺CD16⁺ monocytes compared with those with AAb- and the healthy controls (6.70±4.19% versus 4.0±1.84% and 3.44±0.93%; p = 0.026 and 0.009 respectively). Also, CD14⁺CD16⁺ monocytes correlated with Hb1Ac and C-pep serum levels. Multivariate logistic regression showed that posttransplant AAb+ was independently associated with a higher percentage of pro-inflammatory monocytes (adjusted-OR 1.59, 95%CI 1.05–2.40, p = 0.027). The group of patients with positive AAb also showed higher levels of IL17A as compared with the other groups (either healthy control or the negative AAb subjects). In conclusion, pancreatic AAb+ after SPK were not only associated with higher Hb1Ac and lower c-peptide serum levels but also with an increased percentage of CD14⁺CD16⁺ monocytes and higher levels of circulating IL17-A.

Low-level fluoride exposure reduces glycemia in NOD mice

Water fluoridation is the most widespread measure to prevent dental caries but its relationship with the development of type-1 diabetes (T1D), which has been increasing by 2-5% worldwide, is not quite well understood.

AIM

This study evaluated if fluoride (F) administered in the drinking water can prevent or reduce the development of T1D in non-obese diabetic (NOD) mice, as well as to explore the underlying mechanisms.

MATERIALS AND METHODS

Twenty-four weaning NOD mice received water containing 0, 10 or 50 ppm F for 21 days. Plasma glucose and insulin were analyzed. Quantitative proteomic analysis was conducted in the liver and gastrocnemius muscle.

RESULTS

Animals treated with 10 ppm F had significantly lower glucose levels than the control group, but there was no significant difference among the groups in relation to insulin. The % of β-cell function was significantly higher in the 10 ppm F group. Changes in the proteomic profile of muscle and liver were seen among the groups. In the muscle, the 10 ppm F group presented, when compared with control, increased expression of proteins involved in energy metabolism. The 50 ppm F group, compared with control, presented increased expression of proteins related to muscle contraction, differentiation of brown adipose tissue and apoptosis. For the liver, the 10 ppm F group had increase in proteins involved in energy metabolism and protein synthesis, in respect to control. There was also an increase in isoforms of Glutathione S transferase, which was confirmed by Western blotting. In the group treated with 50 ppm F, proteins related to ROS metabolism and energetic metabolism were altered.

CONCLUSION

Increased expression of antioxidant proteins by treatment with low F concentration may possibly help to explain protection against the development of T1D, which should be better explored in future mechanistic studies.

The eye as a novel imaging site in diabetes research

Diabetes develops due to deficient functional β cell mass, insulin resistance, or both. Yet, various challenges in understanding the mechanisms underlying diabetes development in vivo remain to be overcome owing to the lack of appropriate intravital imaging technologies. To meet these challenges, we have exploited the anterior chamber of the eye (ACE) as a novel imaging site to understand diabetes basics and clinics in vivo. We have developed a technology platform transplanting pancreatic islets into the ACE where they later on can be imaged non-invasively for long time. It turns out that the ACE serves as an optimal imaging site and provides implanted islets with an oxygen-rich milieu and an immune-privileged niche where they undergo optimal engraftment, rich vascularization and dense innervation, preserve organotypic features and live with satisfactory viability and functionality. The ACE technology has led to a series of significant observations. It enables in vivo microscopy of islet cytoarchitecture, function and viability in the physiological context and intravital imaging of a variety of pathological events such as autoimmune insulitis, defects in β cell function and mass and insulin resistance during diabetes development in a real-time manner. Furthermore, application of the ACE technology in humanized mice and non-human primates verifies translational and clinical values of the technology. In this article, we describe the ACE technology in detail, review accumulated knowledge gained by means of the ACE technology and delineate prospective avenues for the ACE technology.

Fifty years of pancreatic islet pathology in human type 1 diabetes: insights gained and progress made

Type 1 diabetes is increasing in incidence in many parts of the world and it might be imagined that the pathological processes that underlie disease progression are firmly understood. However, this is not the case; rather, our collective understanding is still surprisingly rudimentary. There are various reasons for this but one of the most important is that the target organ (the pancreas) has been examined at, or soon after, diagnosis in only a small number of cases worldwide over the past half a century. This review provides a summary of some of the insights gained from these studies and highlights areas of ongoing uncertainty. In particular, it considers the process of insulitis (a form of islet inflammation that occurs characteristically in type 1 diabetes) and discusses the factors that may influence the access of immune cells to the beta cells. Attention is also drawn to recent evidence implying that two distinct profiles of insulitis exist, which occur differentially in people who develop type 1 diabetes at increasing ages. Emphasis is also placed on the emerging (and somewhat surprising) consensus that the extent of beta cell loss is variable among people with type 1 diabetes and that many (especially those who are older at onset) retain significant numbers of insulin-producing cells long after diagnosis. We conclude by emphasising the importance of renewed efforts to study the human pancreas at disease onset and consider how the current insights may inform the design of future strategies to slow or halt the rate of beta cell loss.

Pancreas Pathology During the Natural History of Type 1 Diabetes

PURPOSE OF REVIEW

We provide an overview of pancreas pathology in type 1 diabetes (T1D) in the context of its clinical stages.

RECENT FINDINGS

Recent studies of pancreata from organ donors with T1D and non-diabetic donors expressing T1D-associated autoantibodies reveal pathological changes/disease mechanisms beyond the well-known loss of β cells and lymphocytic infiltrates of the islets (insulitis), including β-cell stress, dysfunction, and viral infections. Pancreas pathology evolves through disease stages, is asynchronous, and demonstrates a chronic disease that remains active years after diagnosis. Critically, β-cell loss is not complete at onset, although young age is associated with increased severity. The recognition of multiple pathogenic alterations and the chronic nature of disease mechanisms during and after the development of T1D inform improved clinical trial design and reveal additional targets for therapeutic manipulation, in the context of an expanded time window for intervention.

The chromosome 6q22.33 region is associated with age at diagnosis of type 1 diabetes and disease risk in those diagnosed under 5 years of age

AIMS/HYPOTHESIS

The genetic risk of type 1 diabetes has been extensively studied. However, the genetic determinants of age at diagnosis (AAD) of type 1 diabetes remain relatively unexplained. Identification of AAD genes and pathways could provide insight into the earliest events in the disease process.

METHODS

Using ImmunoChip data from 15,696 cases, we aimed to identify regions in the genome associated with AAD.

RESULTS

Two regions were convincingly associated with AAD (p < 5 × 10-8): the MHC on 6p21, and 6q22.33. Fine-mapping of 6q22.33 identified two AAD-associated haplotypes in the region nearest to the genes encoding protein tyrosine phosphatase receptor kappa (PTPRK) and thymocyte-expressed molecule involved in selection (THEMIS). We examined the susceptibility to type 1 diabetes at these SNPs by performing a meta-analysis including 19,510 control participants. Although these SNPs were not associated with type 1 diabetes overall (p > 0.001), the SNP most associated with AAD, rs72975913, was associated with susceptibility to type 1 diabetes in those individuals diagnosed at less than 5 years old (p = 2.3 × 10-9).

CONCLUSION/INTERPRETATION

PTPRK and its neighbour THEMIS are required for early development of the thymus, which we can assume influences the initiation of autoimmunity. Non-HLA genes may only be detectable as risk factors for the disease in individuals diagnosed under the age 5 years because, after that period of immune development, their role in disease susceptibility has become redundant.