Paracrine signaling in islet function and survival

Network representation of multicellular activity in pancreatic islets: Technical considerations for functional connectivity analysis

Within the islets of Langerhans, beta cells orchestrate synchronized insulin secretion, a pivotal aspect of metabolic homeostasis. Despite the inherent heterogeneity and multimodal activity of individual cells, intercellular coupling acts as a homogenizing force, enabling coordinated responses through the propagation of intercellular waves. Disruptions in this coordination are implicated in irregular insulin secretion, a hallmark of diabetes. Recently, innovative approaches, such as integrating multicellular calcium imaging with network analysis, have emerged for a quantitative assessment of the cellular activity in islets. However, different groups use distinct experimental preparations, microscopic techniques, apply different methods to process the measured signals and use various methods to derive functional connectivity patterns. This makes comparisons between findings and their integration into a bigger picture difficult and has led to disputes in functional connectivity interpretations. To address these issues, we present here a systematic analysis of how different approaches influence the network representation of islet activity. Our findings show that the choice of methods used to construct networks is not crucial, although care is needed when combining data from different islets. Conversely, the conclusions drawn from network analysis can be heavily affected by the pre-processing of the time series, the type of the oscillatory component in the signals, and by the experimental preparation. Our tutorial-like investigation aims to resolve interpretational issues, reconcile conflicting views, advance functional implications, and encourage researchers to adopt connectivity analysis. As we conclude, we outline challenges for future research, emphasizing the broader applicability of our conclusions to other tissues exhibiting complex multicellular dynamics.

A practical and robust method to evaluate metabolic fluxes in primary pancreatic islets

OBJECTIVE

Evaluation of mitochondrial oxygen consumption and ATP production is important to investigate pancreatic islet pathophysiology. Most studies use cell lines due to difficulties in measuring primary islet respiration, which requires specific equipment and consumables, is expensive and poorly reproducible. Our aim was to establish a practical method to assess primary islet metabolic fluxes using standard commercial consumables.

METHODS

Pancreatic islets were isolated from mice/rats, dispersed with trypsin, and adhered to pre-coated standard Seahorse or Resipher microplates. Oxygen consumption was evaluated using a Seahorse Extracellular Flux Analyzer or a Resipher Real-time Cell Analyzer.

RESULTS

We provide a detailed protocol with all steps to optimize islet isolation with high yield and functionality. Our method requires a few islets per replicate; both rat and mouse islets present robust basal respiration and proper response to mitochondrial modulators and glucose. The technique was validated by other functional assays, which show these cells present conserved calcium influx and insulin secretion in response to glucose. We also show that our dispersed islets maintain robust basal respiration levels, in addition to maintaining up to 89% viability after five days in dispersed cultures. Furthermore, OCRs can be measured in Seahorse analyzers and in other plate respirometry systems, using standard materials.

CONCLUSIONS

Overall, we established a practical and robust method to assess islet metabolic fluxes and oxidative phosphorylation, a valuable tool to uncover basic β-cell metabolic mechanisms as well as for translational investigations, such as pharmacological candidate discovery and islet transplantation protocols.

Illuminating the complete ß-cell mass of the human pancreas- signifying a new view on the islets of Langerhans

Pancreatic islets of Langerhans play a pivotal role in regulating blood glucose homeostasis, but critical information regarding their mass, distribution and composition is lacking within a whole organ context. Here, we apply a 3D imaging pipeline to generate a complete account of the insulin-producing islets throughout the human pancreas at a microscopic resolution and within a maintained spatial 3D context. These data show that human islets are far more heterogenous than previously accounted for with regards to their size distribution and cellular make up. By deep tissue 3D imaging, this in-depth study demonstrates that 50% of the human insulin-expressing islets are virtually devoid of glucagon-producing α-cells, an observation with significant implications for both experimental and clinical research.

An organism-wide atlas of hormonal signaling based on the mouse lemur single-cell transcriptome

Hormones mediate long-range cell communication and play vital roles in physiology, metabolism, and health. Traditionally, endocrinologists have focused on one hormone or organ system at a time. Yet, hormone signaling by its very nature connects cells of different organs and involves crosstalk of different hormones. Here, we leverage the organism-wide single cell transcriptional atlas of a non-human primate, the mouse lemur (Microcebus murinus), to systematically map source and target cells for 84 classes of hormones. This work uncovers previously-uncharacterized sites of hormone regulation, and shows that the hormonal signaling network is densely connected, decentralized, and rich in feedback loops. Evolutionary comparisons of hormonal genes and their expression patterns show that mouse lemur better models human hormonal signaling than mouse, at both the genomic and transcriptomic levels, and reveal primate-specific rewiring of hormone-producing/target cells. This work complements the scale and resolution of classical endocrine studies and sheds light on primate hormone regulation.

MDIC3: Matrix decomposition to infer cell-cell communication

Crosstalk among cells is vital for maintaining the biological function and intactness of systems. Most existing methods for investigating cell-cell communications are based on ligand-receptor (L-R) expression, and they focus on the study between two cells. Thus, the final communication inference results are particularly sensitive to the completeness and accuracy of the prior biological knowledge. Because existing L-R research focuses mainly on humans, most existing methods can only examine cell-cell communication for humans. As far as we know, there is currently no effective method to overcome this species limitation. Here, we propose MDIC3 (matrix decomposition to infer cell-cell communication), an unsupervised tool to investigate cell-cell communication in any species, and the results are not limited by specific L-R pairs or signaling pathways. By comparing it with existing methods for the inference of cell-cell communication, MDIC3 obtained better performance in both humans and mice.

Pharmacologic inhibition of somatostatin receptor 2 to restore glucagon counterregulation in diabetes

Glucose homeostasis is primarily maintained by pancreatic hormones, insulin and glucagon, with an emerging role for a third islet hormone, somatostatin, in regulating insulin and glucagon responses. Under healthy conditions, somatostatin secreted from pancreatic islet δ-cells inhibits both insulin and glucagon release through somatostatin receptor- induced cAMP-mediated downregulation and paracrine inhibition of β- and α-cells, respectively. Since glucagon is the body's most important anti-hypoglycemic hormone, and because glucagon counterregulation to hypoglycemia is lost in diabetes, the study of somatostatin biology has led to new investigational medications now in development that may help to restore glucagon counterregulation in type 1 diabetes. This review highlights the normal regulatory role of pancreatic somatostatin signaling in healthy islet function and how the inhibition of somatostatin receptor signaling in pancreatic α-cells may restore normal glucagon counterregulation in diabetes mellitus.

Exendin-4 affects calcium signalling predominantly during activation and activity of beta cell networks in acute mouse pancreas tissue slices

Tight control of beta cell stimulus-secretion coupling is crucial for maintaining homeostasis of energy-rich nutrients. While glucose serves as a primary regulator of this process, incretins augment beta cell function, partly by enhancing cytosolic [Ca2+] dynamics. However, the details of how precisely they affect beta cell recruitment during activation, their active time, and functional connectivity during plateau activity, and how they influence beta cell deactivation remain to be described. Performing functional multicellular Ca2+ imaging in acute mouse pancreas tissue slices enabled us to systematically assess the effects of the GLP-1 receptor agonist exendin-4 (Ex-4) simultaneously in many coupled beta cells with high resolution. In otherwise substimulatory glucose, Ex-4 was able to recruit approximately a quarter of beta cells into an active state. Costimulation with Ex-4 and stimulatory glucose shortened the activation delays and accelerated beta cell activation dynamics. More specifically, active time increased faster, and the time required to reach half-maximal activation was effectively halved in the presence of Ex-4. Moreover, the active time and regularity of [Ca2+]IC oscillations increased, especially during the first part of beta cell response. In contrast, subsequent addition of Ex-4 to already active cells did not significantly enhance beta cell activity. Network analyses further confirmed increased connectivity during activation and activity in the presence of Ex-4, with hub cell roles remaining rather stable in both control experiments and experiments with Ex-4. Interestingly, Ex-4 demonstrated a biphasic effect on deactivation, slightly prolonging beta cell activity at physiological concentrations and shortening deactivation delays at supraphysiological concentrations. In sum, costimulation by Ex-4 and glucose increases [Ca2+]IC during beta cell activation and activity, indicating that the effect of incretins may, to an important extent, be explained by enhanced [Ca2+]IC signals. During deactivation, previous incretin stimulation does not critically prolong cellular activity, which corroborates their low risk of hypoglycemia.

Understanding the Structural Arrangement of Islets in Chronic Pancreatitis

Islet transplantation has become an established method for the treatment of insulin-deficient diabetes such as type 1 and type 3C (pancreatogenic). An effective transplantation necessitates a thorough understanding of the islet architecture and related functions to improve engraftment outcomes. However, in chronic pancreatitis (CP), the structural and related functional information is inadequate. Hence, the present study is aimed to understand the cytoarchitecture of endocrine cells and their functional implications in CP with and without diabetes. Herein, a set of human pancreatic tissue specimens (normal, n=5 and CP, n=20) was collected and processed for islet isolation. Furthermore, immunohistochemistry was used to assess the vascular densities, cell mass, organization, and cell-cell interactions. The glucose-stimulated insulin release results revealed that in chronic pancreatitis without diabetes mellitus altered (CPNDA), at basal glucose concentration the insulin secretion was increased by 24.2%, whereas at high glucose concentration the insulin levels were reduced by 77.4%. The impaired insulin secretion may be caused by alterations in the cellular architecture of islets during CP progression, particularly in chronic pancreatitis with diabetes mellitus and CPNDA conditions. Based on the results, a deeper comprehension of islet architecture would be needed to enhance successful transplantation in CP patients: (J Histochem Cytochem XX.XXX-XXX, XXXX).

Gut feelings in the islets: The role of the gut microbiome and the FFA2 and FFA3 receptors for short chain fatty acids on β-cell function and metabolic regulation

Short-chain fatty acids (SCFAs) are biosynthesized via fermentation of polysaccharides by gastrointestinal microbiota and have been shown to have wide-reaching effects on almost all tissues, including the pancreatic islets. Historically, the effects of SCFAs have been attributed to their intracellular metabolism and function as energy sources, but the discovery of free fatty acid G protein-coupled receptors (GPCRs) in the 2000s suggested that many functional outcomes of SCFAs are receptor-mediated. The SCFA receptors FFA2/GPR43 and FFA3/GPR41 are expressed on β-cells, where they regulate glucose-dependent insulin secretion, making them attractive targets for treatment of diabetes and other metabolic disorders. Here, we provide an update on the current evidence regarding regulation of FFA2/FFA3 receptors by specific probiotic bacterial species within the gut microbiome that synthesize SCFAs. We also review the body of research regarding the FFA2- and FFA3 receptor-specific function of SCFAs on β-cells and discuss the somewhat controversial and opposing findings within these studies.

Trace Amine-Associated Receptors and Monoamine-Mediated Regulation of Insulin Secretion in Pancreatic Islets

Currently, metabolic syndrome treatment includes predominantly pharmacological symptom relief and complex lifestyle changes. Trace amines and their receptor systems modulate signaling pathways of dopamine, norepinephrine, and serotonin, which are involved in the pathogenesis of this disorder. Trace amine-associated receptor 1 (TAAR1) is expressed in endocrine organs, and it was revealed that TAAR1 may regulate insulin secretion in pancreatic islet β-cells. For instance, accumulating data demonstrate the positive effect of TAAR1 agonists on the dynamics of metabolic syndrome progression and MetS-associated disease development. The role of other TAARs (TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) in the islet's function is much less studied. In this review, we summarize the evidence of TAARs' contribution to the metabolic syndrome pathogenesis and regulation of insulin secretion in pancreatic islets. Additionally, by the analysis of public transcriptomic data, we demonstrate that TAAR1 and other TAAR receptors are expressed in the pancreatic islets. We also explore associations between the expression of TAARs mRNA and other genes in studied samples and demonstrate the deregulation of TAARs' functional associations in patients with metabolic diseases compared to healthy donors.

Defining the ferroptotic phenotype of beta cells in type 1 diabetes and its inhibition as a potential antidiabetic strategy

Introduction

Recently, the involvement of ferroptotic cell death in the reduction of β-cell mass in diabetes has been demonstrated. To elucidate the mechanisms of β-cell ferroptosis and potential antidiabetic effects of the ferroptosis inhibitor ferrostatin-1 (Fer-1) in vivo, a mouse model of type 1 diabetes (T1D) was used.

Methods

Animals were divided into three groups: control (vehicle-treated), diabetic (streptozotocin-treated, 40 mg/kg, from days 1-5), and diabetic treated with Fer-1 (1 mg/kg, from days 1-21). On day 22, glycemia and insulinemia were measured and pancreases were isolated for microscopic analyses.

Results

Diabetes disturbed general parameters of β-cell mass (islet size, β-cell abundance and distribution) and health (insulin and PDX-1 expression), increased lipid peroxidation in islet cells, and phagocytic removal of iron-containing material. It also downregulated the main players of the antiferroptotic pathway - Nrf2, GPX4, and xCT. In contrast, Fer-1 ameliorated the signs of deterioration of β-cell/islets, decreased lipid peroxidation, and reduced phagocytic activity, while upregulated expression of Nrf2 (and its nuclear translocation), GPX4, and xCT in β-cell/islets.

Discussion

Overall, our study confirms ferroptosis as an important mode of β-cell death in T1D and suggests antiferroptotic agents as a promising strategy for the prevention and treatment of diabetes.

The human α cell in health and disease

In commemoration of 100 years since the discovery of glucagon, we review current knowledge about the human α cell. Alpha cells make up 30-40% of human islet endocrine cells and play a major role in regulating whole-body glucose homeostasis, largely through the direct actions of their main secretory product - glucagon - on peripheral organs. Additionally, glucagon and other secretory products of α cells, namely acetylcholine, glutamate, and glucagon-like peptide-1, have been shown to play an indirect role in the modulation of glucose homeostasis through autocrine and paracrine interactions within the islet. Studies of glucagon's role as a counterregulatory hormone have revealed additional important functions of the α cell, including the regulation of multiple aspects of energy metabolism outside that of glucose. At the molecular level, human α cells are defined by the expression of conserved islet-enriched transcription factors and various enriched signature genes, many of which have currently unknown cellular functions. Despite these common threads, notable heterogeneity exists amongst human α cell gene expression and function. Even greater differences are noted at the inter-species level, underscoring the importance of further study of α cell physiology in the human context. Finally, studies on α cell morphology and function in type 1 and type 2 diabetes, as well as other forms of metabolic stress, reveal a key contribution of α cell dysfunction to dysregulated glucose homeostasis in disease pathogenesis, making targeting the α cell an important focus for improving treatment.

Evaluation of pancreatic δ- cells as a potential target site of graphene oxide toxicity in Japanese medaka (Oryzias latipes) fish

In continuation to our previous investigations on graphene oxide (GO) as an endocrine disrupting chemical (EDC), in the present experiment, we have investigated endocrine pancreas of Japanese medaka adults focusing on δ-cells in the islet organs as an endpoint. Breeding pairs of adult male and female fish were exposed to 0 mg/L (control) or 20 mg/L GO by continuous immersion (IMR) for 96 h, or to 0 µg/g or 100 µg/g GO by a single intraperitoneal (IP) administration and depurated 21 days in a GO-free environment. Histological investigations indicated that the endocrine cells are concentrated in one large principal islet, and several small secondary islets scattered within the mesentery near the liver and intestine. The cells of the islet organ are in various shapes with basophilic nuclei and eosinophilic cytoplasm. Immunohistochemical evaluation using rabbit polyclonal antisomatostatin antibody indicated that immunoreactivity is localized either at the periphery or at the central region in principal islets, and throughout the secondary islets, and found to be enhanced in fish exposed to GO than controls. The soma of δ-cells exhibits neuron-like morphology and have filopodia like processes. Cell sorting as non-communicating δ-cells (NCDC), communicating cells (CC), and non- δ-cells (NDC) indicated that within an islet organ, the population of NDCC is found to be the least and NDC is the highest. Our data further indicated that GO-induced impairments in the islet organs of medaka pancreas are inconsistent and could be affected by the exposure roots as well as the sex of the fish.

Responses of INS-1 cells to glucose stimulation patterns

Diabetes has become a major public health problem in the world for many years, and it is driving us to probe into its complex mechanism of insulin secretion in pancreatic β cells. The nanoscale resolution characterization of pancreatic β cells in response to glucose led to insights into diverse mechanical and functional processes at the single cell level. Recent advances allowed the direct observations of cytoskeleton dynamics which were quantitatively determined. Here, we firstly performed the glucose stimulation with multiple physiologically relevant glucose patterns. Atomic force microscopy (AFM) produced high spatial resolution mechanical images together with the insulin secretions linking the physical interactions to the biochemical process of INS-1 cells. Altered material properties of the INS-1 cells revealed the regulation of multiple glucose stimulation patterns. Rapidly responded to high glucose (HG), INS-1 cells presented the unique meshing networks of elasticities. The decreases of Young's modulus (YM) and insulin secretion suggested that mechanical changes affected the insulin release. Furthermore, the frequency and gradient of glucose patterns induced nanomechanical and secreting changes of the INS-1 cells and gained the knowledge on the potential controllability of glucose. The relationships between the cellular mechanics and insulin secretion of INS-1 cells could contribute to establish a mechanical cell model for the study of β cells in diabetes. The results also indicated the cell mechanics as promising mechanical biomarkers for β cells, and promoted the understanding of specific mechanical mechanism of glucose regulation, which lighted on the further application of functional glucose regulation in therapy.

Importance of multiple endocrine cell types in islet organoids for type 1 diabetes treatment

Almost 50 years ago, scientists developed the bi-hormonal abnormality hypothesis, stating that diabetes is not caused merely by the impaired insulin signaling. Instead, the presence of inappropriate level of glucagon is a prerequisite for the development of type 1 diabetes (T1D). It is widely understood that the hormones insulin and glucagon, secreted by healthy β and α cells respectively, operate in a negative feedback loop to maintain the body's blood sugar levels. Despite this fact, traditional T1D treatments rely solely on exogenous insulin injections. Furthermore, research on cell-based therapies and stem-cell derived tissues tends to focus on the replacement of β cells alone. In vivo, the pancreas is made up of 4 major endocrine cell types, that is, insulin-producing β cells, glucagon-producing α cells, somatostatin-producing δ cells, and pancreatic polypeptide-producing γ cells. These distinct cell types are involved synergistically in regulating islet functions. Therefore, it is necessary to produce a pancreatic islet organoid in vitro consisting of all these cell types that adequately replaces the function of the native islets. In this review, we describe the unique function of each pancreatic endocrine cell type and their interactions contributing to the maintenance of normoglycemia. Furthermore, we detail current sources of whole islets and techniques for their long-term expansion and culture. In addition, we highlight a vast potential of the pancreatic islet organoids for transplantation and diabetes research along with updated new approaches for successful transplantation using stem cell-derived islet organoids.

Differential effects of RYGB surgery and best medical treatment for obesity-diabetes on intestinal and islet adaptations in obese-diabetic ZDSD rats

Modification of gut-islet secretions after Roux-En-Y gastric bypass (RYBG) surgery contributes to its metabolic and anti-diabetic benefits. However, there is limited knowledge on tissue-specific hormone distribution post-RYGB surgery and how this compares with best medical treatment (BMT). In the present study, pancreatic and ileal tissues were excised from male Zucker-Diabetic Sprague Dawley (ZDSD) rats 8-weeks after RYGB, BMT (daily oral dosing with metformin 300mg/kg, fenofibrate 100mg/kg, ramipril 1mg/kg, rosuvastatin 10mg/kg and subcutaneous liraglutide 0.2mg/kg) or sham operation (laparotomy). Insulin, glucagon, somatostatin, PYY, GLP-1 and GIP expression patterns were assessed using immunocytochemistry and analyzed using ImageJ. After RYGB and BMT, body weight and plasma glucose were decreased. Intestinal morphometry was unaltered by RYGB, but crypt depth was decreased by BMT. Intestinal PYY cells were increased by both interventions. GLP-1- and GIP-cell counts were unchanged by RYGB but BMT increased ileal GLP-1-cells and decreased those expressing GIP. The intestinal contents of PYY and GLP-1 were significantly enhanced by RYGB, whereas BMT decreased ileal GLP-1. No changes of islet and beta-cell area or proliferation were observed, but the extent of beta-cell apoptosis and islet integrity calculated using circularity index were improved by both treatments. Significantly decreased islet alpha-cell areas were observed in both groups, while beta- and PYY-cell areas were unchanged. RYGB also induced a decrease in islet delta-cell area. PYY and GLP-1 colocalization with glucagon in islets was significantly decreased in both groups, while co-staining of PYY with glucagon was decreased and that with somatostatin increased. These data characterize significant cellular islet and intestinal adaptations following RYGB and BMT associated with amelioration of obesity-diabetes in ZDSD rats. The differential responses observed and particularly those within islets, may provide important clues to the unique ability of RYGB to cause diabetes remission.

New Developments in Glucagon Treatment for Hypoglycemia

Glucagon is essential for endogenous glucose regulation along with the paired hormone, insulin. Unlike insulin, pharmaceutical use of glucagon has been limited due to the unstable nature of the peptide. Glucagon has the potential to address hypoglycemia as a major limiting factor in the treatment of diabetes, which remains very common in the type 1 and type 2 diabetes. Recent developments are poised to change this paradigm and expand the use of glucagon for people with diabetes. Glucagon emergency kits have major limitations for their use in treating severe hypoglycemia. A complicated reconstitution and injection process often results in incomplete or aborted administration. New preparations include intranasal glucagon with an easy-to-use and needle-free nasal applicator as well as two stable liquid formulations in pre-filled injection devices. These may ease the burden of severe hypoglycemia treatment. The liquid preparations may also have a role in the treatment of non-severe hypoglycemia. Despite potential benefits of expanded use of glucagon, undesirable side effects (nausea, vomiting), cost, and complexity of adding another medication may limit real-world use. Additionally, more long-term safety and outcome data are needed before widespread, frequent use of glucagon is recommended by providers.

Urocortin3: Local inducer of somatostatin release and bellwether of beta cell maturity

Urocortin 3 (UCN3) is a peptide hormone expressed in pancreatic islets of Langerhans of both human alpha and human beta cells and solely in murine beta cells. UCN3 signaling acts locally within the islet to activate its cognate receptor, corticotropin releasing hormone receptor 2 (CRHR2), which is expressed by delta cells, to potentiate somatostatin (SST) negative feedback to reduce islet cell hormone output. The functional importance of UCN3 signaling in the islet is to modulate the amount of SST tone allowing for finely tuned regulation of insulin and glucagon secretion. UCN3 signaling is a hallmark of functional beta cell maturation, increasing the beta cell glucose threshold for insulin secretion. In doing so, UCN3 plays a relevant functional role in accurately maintaining blood glucose homeostasis. Additionally, UCN3 acts as an indicator of beta cell maturation and health, as UCN3 is not expressed in immature beta cells and is downregulated in dedifferentiated and dysfunctional beta cell states. Here, we review the mechanistic underpinnings of UCN3 signaling, its net effect on islet cell hormone output, as well as its value as a marker for beta cell maturation and functional status.

Expression of Transient Receptor Potential Channel Genes and Their Isoforms in Alpha-Cells and Beta-Cells of Human Islets of Langerhans

Expression of the transient receptor potential (TRP) channel genes and their isoforms in the alpha-cells and the beta-cells of the human islets of Langerhans has not been studied in detail. In this study, we have analyzed the RNA sequencing data obtained from purified human alpha-cells and beta-cells to identify the genes and their isoforms that are expressed differentially in these two cell types. We found that TRPC1, TRPC4, TRPC7, TRPM3, and TRPML1 were differentially expressed in these two cell types. TRPC1, TRPM3, and TRPML1 were expressed at a higher level in the beta-cells than in the alpha-cells. TRPC4 and TRPC7 were expressed at a higher level in the alpha-cells than in the beta-cells. The TRPC4-206 isoform was expressed at a 45-fold higher level in the alpha-cells compared to the beta-cells. Expression of TRPM3-202 was 200-fold and TRPM3-209 was 25-fold higher in the beta-cells than in the alpha-cells. Our study has demonstrated the relative abundance of expression of the TRP channel genes and their isoforms in the human alpha-cells and the beta-cells.

The endocrine pancreas during exercise in people with and without type 1 diabetes: Beyond the beta-cell

Although important for digestion and metabolism in repose, the healthy endocrine pancreas also plays a key role in facilitating energy transduction around physical exercise. During exercise, decrements in pancreatic β-cell mediated insulin release opposed by increments in α-cell glucagon secretion stand chief among the hierarchy of glucose-counterregulatory responses to decreasing plasma glucose levels. As a control hub for several major glucose regulatory hormones, the endogenous pancreas is therefore essential in ensuring glucose homeostasis. Type 1 diabetes (T1D) is pathophysiological condition characterised by a destruction of pancreatic β-cells resulting in pronounced aberrations in glucose control. Yet beyond the beta-cell perhaps less considered is the impact of T1D on all other pancreatic endocrine cell responses during exercise and whether they differ to those observed in healthy man. For physicians, understanding how the endocrine pancreas responds to exercise in people with and without T1D may serve as a useful model from which to identify whether there are clinically relevant adaptations that need consideration for glycaemic management. From a physiological perspective, delineating differences or indeed similarities in such responses may help inform appropriate exercise test interpretation and subsequent program prescription. With more complex advances in automated insulin delivery (AID) systems and emerging data on exercise algorithms, a timely update is warranted in our understanding of the endogenous endocrine pancreatic responses to physical exercise in people with and without T1D. By placing our focus here, we may be able to offer a nexus of better understanding between the clinical and engineering importance of AIDs requirements during physical exercise.

Restoring normal islet mass and function in type 1 diabetes through regenerative medicine and tissue engineering

Type 1 diabetes is characterised by autoimmune-mediated destruction of pancreatic β-cell mass. With the advent of insulin therapy a century ago, type 1 diabetes changed from a progressive, fatal disease to one that requires lifelong complex self-management. Replacing the lost β-cell mass through transplantation has proven successful, but limited donor supply and need for lifelong immunosuppression restricts widespread use. In this Review, we highlight incremental advances over the past 20 years and remaining challenges in regenerative medicine approaches to restoring β-cell mass and function in type 1 diabetes. We begin by summarising the role of endocrine islets in glucose homoeostasis and how this is altered in disease. We then discuss the potential regenerative capacity of the remaining islet cells and the utility of stem cell-derived β-like cells to restore β-cell function. We conclude with tissue engineering approaches that might improve the engraftment, function, and survival of β-cell replacement therapies.

The Feasibility and Applicability of Stem Cell Therapy for the Cure of Type 1 Diabetes

Stem cell therapy using islet-like insulin-producing cells derived from human pluripotent stem cells has the potential to allow patients with type 1 diabetes to withdraw from insulin therapy. However, several issues exist regarding the use of stem cell therapy to treat type 1 diabetes. In this review, we will focus on the following topics: (1) autoimmune responses during the autologous transplantation of stem cell-derived islet cells, (2) a comparison of stem cell therapy with insulin injection therapy, (3) the impact of the islet microenvironment on stem cell-derived islet cells, and (4) the cost-effectiveness of stem cell-derived islet cell transplantation. Based on these various viewpoints, we will discuss what is required to perform stem cell therapy for patients with type 1 diabetes.

Loss of growth hormone signaling in the mouse germline or in adulthood reduces islet mass and alters islet function with notable sex differences

In the endocrine pancreas, growth hormone (GH) is known to promote pancreatic islet growth and insulin secretion. In this study, we show that GH receptor (GHR) loss in the germline and in adulthood impacts islet mass in general but more profoundly in male mice. GHR knockout (GHRKO) mice have enhanced insulin sensitivity and low circulating insulin. We show that the total cross-sectional area of isolated islets (estimated islet mass) was reduced by 72% in male but by only 29% in female GHRKO mice compared with wild-type controls. Also, islets from GHRKO mice secreted ∼50% less glucose-stimulated insulin compared with size-matched islets from wild-type mice. We next used mice with a floxed Ghr gene to knock down the GHR in adult mice at 6 mo of age (6mGHRKO) and examined the impact on glucose and islet metabolism. By 12 mo of age, female 6mGHRKO mice had increased body fat and reduced islet mass but had no change in glucose tolerance or insulin sensitivity. However, male 6mGHRKO mice had nearly twice as much body fat, substantially reduced islet mass, and enhanced insulin sensitivity, but no change in glucose tolerance. Despite large losses in islet mass, glucose-stimulated insulin secretion from isolated islets was not significantly different between male 6mGHRKO and controls, whereas isolated islets from female 6mGHRKO mice showed increased glucose-stimulated insulin release. Our findings demonstrate the importance of GH to islet mass throughout life and that unique sex-specific adaptations to the loss of GH signaling allow mice to maintain normal glucose metabolism.NEW & NOTEWORTHY Growth hormone (GH) is important for more than just growth. GH helps to maintain pancreatic islet mass and insulin secretion throughout life. Sex-specific adaptations to the loss of GH signaling allow mice to maintain normal glucose regulation despite losing islet mass.

Developmental programming: Prenatal testosterone excess disrupts pancreatic islet developmental trajectory in female sheep

Prenatal testosterone (T)- treated female sheep manifest juvenile insulin resistance, post-pubertal increase in insulin sensitivity and return to insulin resistance during adulthood. Since compensatory hyperinsulinemia is associated with insulin resistance, altered pancreatic islet ontogeny may contribute towards metabolic defects. To test this, pregnant sheep were treated with or without T propionate from days 30-90 of gestation and pancreas collected from female fetuses at gestational day 90 and female offspring at 21 months-of-age. Uterine (maternal) and umbilical (fetal) arterial blood insulin/glucose ratios were determined at gestational day 90. The morphological and functional changes in pancreatic islet were assessed through detection of 1) islet hormones (insulin, glucagon) and apoptotic beta cells at fetal day 90 and 2) islet hormones (insulin, glucagon and somatostatin), and pancreatic lipid and collagen accumulation in adults. At gestational day 90, T-treatment led to maternal but not fetal hyperinsulinemia, decrease in pancreatic/fetal weight ratio and alpha cells, and a trend for increase in beta cell apoptosis in fetal pancreas. Adult prenatal T-treated female sheep manifested 1) significant increase in beta cell size and a tendency for increase in insulin and somatostatin stained area and proportion of beta cells in the islet; and 2) significant increase in pancreatic islet collagen and a tendency towards increased lipid accumulation. Gestational T-treatment induced changes in pancreatic islet endocrine cells during both fetal and adult ages track the trajectory of hyperinsulinemic status with the increase in adult pancreatic collagen accumulation indicative of impending beta cell failure with chronic insulin resistance.

Paracrine regulation of insulin secretion

Pancreatic beta cells are the only cell type in our body capable of producing and secreting insulin to instruct the insulin-sensitive cells and tissues of our bodies to absorb nutrients after a meal. Accurate control of insulin release is of critical importance; too little insulin leads to diabetes, while an excess of insulin can cause potentially fatal hypoglycaemia. Yet, the pancreas of most people will control insulin secretion safely and effectively over decades and in response to glucose excursions driven by tens of thousands of meals. Because we only become aware of the important contributions of the pancreas when it fails to maintain glucose homeostasis, it is easy to forget just how well insulin release from a healthy pancreas is matched to insulin need to ensure stable blood glucose levels. Beta cells achieve this feat by extensive crosstalk with the rest of the endocrine cell types in the islet, notably the glucagon-producing alpha cells and somatostatin-producing delta cells. Here I will review the important paracrine contributions that each of these cells makes to the stimulation and subsequent inhibition of insulin release in response to a transient nutrient stimulation, and make the case that a breakdown of this local crosstalk contributes to the pathophysiology of diabetes. Graphical abstract.