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The dysfunction of α and β cells in pancreatic islets can lead to diabetes. Many questions remain on the subcellular organization of islet cells during the progression of disease. Existing three-dimensional cellular mapping approaches face challenges such as time-intensive sample sectioning and subjective cellular identification. To address these challenges, we have developed a subcellular feature-based classification approach, which allows us to identify α and β cells and quantify their subcellular structural characteristics using soft X-ray tomography (SXT). We observed significant differences in whole-cell morphological and organelle statistics between the two cell types. Additionally, we characterize subtle biophysical differences between individual insulin and glucagon vesicles by analyzing vesicle size and molecular density distributions, which were not previously possible using other methods. These sub-vesicular parameters enable us to predict cell types systematically using supervised machine learning. We also visualize distinct vesicle and cell subtypes using Uniform Manifold Approximation and Projection (UMAP) embeddings, which provides us with an innovative approach to explore structural heterogeneity in islet cells. This methodology presents an innovative approach for tracking biologically meaningful heterogeneity in cells that can be applied to any cellular system.

Type 2 diabetes is characterised by hyperglucagonaemia and perturbed function of pancreatic glucagon-secreting alpha cells but the molecular mechanisms contributing to these phenotypes are poorly understood. Insulin-degrading enzyme (IDE) is present within all islet cells, mostly in alpha cells, in both mice and humans. Furthermore, IDE can degrade glucagon as well as insulin, suggesting that IDE may play an important role in alpha cell function in vivo. We have generated and characterised a novel mouse model with alpha cell-specific deletion of Ide, the A-IDE-KO mouse line. Glucose metabolism and glucagon secretion in vivo was characterised; isolated islets were tested for glucagon and insulin secretion; alpha cell mass, alpha cell proliferation and α-synuclein levels were determined in pancreas sections by immunostaining. Targeted deletion of Ide exclusively in alpha cells triggers hyperglucagonaemia and alpha cell hyperplasia, resulting in elevated constitutive glucagon secretion. The hyperglucagonaemia is attributable in part to dysregulation of glucagon secretion, specifically an impaired ability of IDE-deficient alpha cells to suppress glucagon release in the presence of high glucose or insulin. IDE deficiency also leads to α-synuclein aggregation in alpha cells, which may contribute to impaired glucagon secretion via cytoskeletal dysfunction. We showed further that IDE deficiency triggers impairments in cilia formation, inducing alpha cell hyperplasia and possibly also contributing to dysregulated glucagon secretion and hyperglucagonaemia. We propose that loss of IDE function in alpha cells contributes to hyperglucagonaemia in type 2 diabetes.

As in type 1 diabetes, the loss of pancreatic ß-cells leads to insulin deficiency and the subsequent development of hyperglycemia. Exercise has been proposed as a viable remedy for hyperglycemia. Lithium, which has been used as a treatment for bipolar disorder, has also been shown to improve glucose homeostasis under the conditions of obesity and type 2 diabetes by enhancing the effects of exercise on the skeletal muscles. In this study, we demonstrated that unlike in obesity and type 2 diabetic conditions, under the condition of insulin-deficient type 1 diabetes, lithium administration attenuated pancreatic a-cell mass without altering insulin-secreting ß-cell mass, implying a selective impact on glucagon production. Additionally, we also documented that lithium downregulated the hepatic gluconeogenic program by decreasing G6Pase protein levels and upregulating AMPK activity. These findings suggest that lithium's effect on glucose metabolism in type 1 diabetes is mediated through a different mechanism than those associated with exerciseinduced metabolic changes in the muscle. Therefore, our research presents the novel therapeutic potential of lithium in the treatment of type 1 diabetes, which can be utilized along with insulin and independently of exercise. [ABSTRACT FROM AUTHOR]

Pancreatic α-cells are important in maintaining metabolic homeostasis, but their role in regulating maternal metabolic adaptations to pregnancy has not been studied. The objective of this study was to determine whether pancreatic α-cells respond to pregnancy and their contribution to maternal metabolic adaptation. With use of C57BL/6 mice, the findings of our study showed that pregnancy induced a significant increase of α-cell mass by promoting α-cell proliferation that was associated with a transitory increase of maternal serum glucagon concentration in early pregnancy. Maternal pancreatic GLP-1 content also was significantly increased during pregnancy. Using the inducible Cre/loxp technique, we ablated the α-cells (α-null) before and during pregnancy while maintaining enteroendocrine L-cells and serum GLP-1 in the normal range. In contrast to an improved glucose tolerance test (GTT) before pregnancy, significantly impaired GTT and remarkably higher serum glucose concentrations in the fed state were observed in α-null dams. Glucagon receptor antagonism treatment, however, did not affect measures of maternal glucose metabolism, indicating a dispensable role of glucagon receptor signaling in maternal glucose homeostasis. However, the GLP-1 receptor agonist improved insulin production and glucose metabolism of α-null dams. Furthermore, GLP-1 receptor antagonist Exendin (9-39) attenuated pregnancy-enhanced insulin secretion and GLP-1 restored glucose-induced insulin secretion of cultured islets from α-null dams. Together, these results demonstrate that α-cells play an essential role in controlling maternal metabolic adaptation to pregnancy by enhancing insulin secretion.

Single-nucleus assay for transposase-accessible chromatin using sequencing (snATAC-seq) creates new opportunities to dissect cell type-specific mechanisms of complex diseases. Since pancreatic islets are central to type 2 diabetes (T2D), we profiled 15,298 islet cells by using combinatorial barcoding snATAC-seq and identified 12 clusters, including multiple alpha, beta and delta cell states. We cataloged 228,873 accessible chromatin sites and identified transcription factors underlying lineage- and state-specific regulation. We observed state-specific enrichment of fasting glucose and T2D genome-wide association studies for beta cells and enrichment for other endocrine cell types. At T2D signals localized to islet-accessible chromatin, we prioritized variants with predicted regulatory function and co-accessibility with target genes. A causal T2D variant rs231361 at the KCNQ1 locus had predicted effects on a beta cell enhancer co-accessible with INS and genome editing in embryonic stem cell-derived beta cells affected INS levels. Together our findings demonstrate the power of single-cell epigenomics for interpreting complex disease genetics.

ObjectiveMaintenance of glucose homeostasis requires the precise regulation of hormone secretion from the endocrine pancreas. Free fatty acid receptor 4 (FFAR4/GPR120) is a G protein-coupled receptor whose activation in islets of Langerhans promotes insulin and glucagon secretion and inhibits somatostatin secretion. However, the contribution of individual islet cell types (α, β, and δ cells) to the insulinotropic and glucagonotropic effects of GPR120 remains unclear. As gpr120 mRNA is enriched in somatostatin-secreting δ cells, we hypothesized that GPR120 activation stimulates insulin and glucagon secretion via inhibition of somatostatin release.MethodsGlucose tolerance tests were performed in mice after administration of selective GPR120 agonist Compound A. Insulin, glucagon, and somatostatin secretion were measured in static incubations of isolated mouse islets in response to endogenous (ω-3 polyunsaturated fatty acids) and/or pharmacological (Compound A and AZ-13581837) GPR120 agonists. The effect of Compound A on hormone secretion was tested further in islets isolated from mice with global or somatostatin cell-specific knock-out of gpr120. Gpr120 expression was assessed in pancreatic sections by RNA in situ hybridization. Cyclic AMP (cAMP) and calcium dynamics in response to pharmacological GPR120 agonists were measured specifically in α, β, and δ cells in intact islets using cAMPER and GCaMP6 reporter mice, respectively.ResultsAcute exposure to Compound A increased glucose tolerance, circulating insulin, and glucagon levels in vivo. Endogenous and/or pharmacological GPR120 agonists reduced somatostatin secretion in isolated islets and concomitantly demonstrated dose-dependent potentiation of glucose-stimulated insulin secretion and arginine-stimulated glucagon secretion. Gpr120 was enriched in δ cells. Pharmacological GPR120 agonists reduced cAMP and calcium levels in δ cells but increased these signals in α and β cells. Compound A-mediated inhibition of somatostatin secretion was insensitive to pertussis toxin. The effect of Compound A on hormone secretion was completely absent in islets from mice with either global or somatostatin cell-specific deletion of gpr120 and partially reduced upon blockade of somatostatin receptor signaling by cyclosomatostatin.ConclusionsInhibitory GPR120 signaling in δ cells contributes to both insulin and glucagon secretion in part by mitigating somatostatin release.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone that potentiates glucose-stimulated insulin secretion. GLP-1 is classically produced by gut L cells; however, under certain circumstances α cells can express the prohormone convertase required for proglucagon processing to GLP-1, prohormone convertase 1/3 (PC1/3), and can produce GLP-1. However, the mechanisms through which this occurs are poorly defined. Understanding the mechanisms by which α cell PC1/3 expression can be activated may reveal new targets for diabetes treatment. Here, we demonstrate that the GLP-1 receptor (GLP-1R) agonist, liraglutide, increased α cell GLP-1 expression in a β cell GLP-1R-dependent manner. We demonstrate that this effect of liraglutide was translationally relevant in human islets through application of a new scRNA-seq technology, DART-Seq. We found that the effect of liraglutide to increase α cell PC1/3 mRNA expression occurred in a subcluster of α cells and was associated with increased expression of other β cell-like genes, which we confirmed by IHC. Finally, we found that the effect of liraglutide to increase bihormonal insulin+ glucagon+ cells was mediated by the β cell GLP-1R in mice. Together, our data validate a high-sensitivity method for scRNA-seq in human islets and identify a potentially novel GLP-1-mediated pathway regulating human α cell function.

Type 2 diabetes is characterized by β and α cell dysfunction. We used phasor-FLIM (Fluorescence Lifetime Imaging Microscopy) to monitor oxidative phosphorylation and glycolysis in living islet cells before and after glucose stimulation. In healthy cells, glucose enhanced oxidative phosphorylation in β cells and suppressed oxidative phosphorylation in α cells. In Type 2 diabetes, glucose increased glycolysis in β cells, and only partially suppressed oxidative phosphorylation in α cells. FLIM uncovers key perturbations in glucose induced metabolism in living islet cells and provides a sensitive tool for drug discovery in diabetes.

This study aimed to investigate the contributions of two factors potentially impairing glucagon response to insulin-induced hypoglycemia (IIH) in insulin-deficient diabetes: 1) loss of paracrine disinhibition by intra-islet insulin and 2) defects in the activation of the autonomic inputs to the islet. Plasma glucagon responses during hyperinsulinemic-hypoglycemic clamps ([Formula: see text]40 mg/dL) were assessed in dogs with spontaneous diabetes (n = 13) and in healthy nondiabetic dogs (n = 6). Plasma C-peptide responses to intravenous glucagon were measured to assess endogenous insulin secretion. Plasma pancreatic polypeptide, epinephrine, and norepinephrine were measured as indices of parasympathetic and sympathoadrenal autonomic responses to IIH. In 8 of the 13 diabetic dogs, glucagon did not increase during IIH (diabetic nonresponder [DMN]; ∆ = -6 ± 12 pg/mL). In five other diabetic dogs (diabetic responder [DMR]), glucagon responses (∆ = +26 ± 12) were within the range of nondiabetic control dogs (∆ = +27 ± 16 pg/mL). C-peptide responses to intravenous glucagon were absent in diabetic dogs. Activation of all three autonomic responses were impaired in DMN dogs but remained intact in DMR dogs. Each of the three autonomic responses to IIH was positively correlated with glucagon responses across the three groups. The study conclusions are as follows: 1) Impairment of glucagon responses in DMN dogs is not due to generalized impairment of α-cell function. 2) Loss of tonic inhibition of glucagon secretion by insulin is not sufficient to produce loss of the glucagon response; impairment of autonomic activation is also required. 3) In dogs with major β-cell function loss, activation of the autonomic inputs is sufficient to mediate an intact glucagon response to IIH.NEW & NOTEWORTHY In dogs with naturally occurring, insulin-dependent (C-peptide negative) diabetes mellitus, impairment of glucagon responses is not due to generalized impairment of α-cell function. Loss of tonic inhibition of glucagon secretion by insulin is not sufficient, by itself, to produce loss of the glucagon response. Rather, impaired activation of the parasympathetic and sympathoadrenal autonomic inputs to the pancreas is also required. Activation of the autonomic inputs to the pancreas is sufficient to mediate an intact glucagon response to insulin-induced hypoglycemia in dogs with naturally occurring diabetes mellitus. These results have important implications that include leading to a greater understanding and insight into the pathophysiology, prevention, and treatment of hypoglycemia during insulin treatment of diabetes in companion dogs and in human patients.

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.

Human but not mouse islets transplanted into immunodeficient NSG mice effectively accumulate lipid droplets (LDs). Because chronic lipid exposure is associated with islet β-cell dysfunction, we investigated LD accumulation in the intact human and mouse pancreas over a range of ages and states of diabetes. Very few LDs were found in normal human juvenile pancreatic acinar and islet cells, with numbers subsequently increasing throughout adulthood. While accumulation appeared evenly distributed in postjuvenile acinar and islet cells in donors without diabetes, LDs were enriched in islet α- and β-cells from donors with type 2 diabetes (T2D). LDs were also found in the islet β-like cells produced from human embryonic cell-derived β-cell clusters. In contrast, LD accumulation was nearly undetectable in the adult rodent pancreas, even in hyperglycemic and hyperlipidemic models or 1.5-year-old mice. Taken together, there appear to be significant differences in pancreas islet cell lipid handling between species, and the human juvenile and adult cell populations. Moreover, our results suggest that LD enrichment could be impactful to T2D islet cell function.

Diabetic β cell failure is associated with β cell dedifferentiation. To identify effector genes of dedifferentiation, we integrated analyses of histone methylation as a surrogate of gene activation status and RNA expression in β cells sorted from mice with multiparity-induced diabetes. Interestingly, only a narrow subset of genes demonstrated concordant changes to histone methylation and RNA levels in dedifferentiating β cells. Notable among them was the α cell signature gene Gc, encoding a vitamin D-binding protein. While diabetes was associated with Gc induction, Gc-deficient islets did not induce β cell dedifferentiation markers and maintained normal ex vivo insulin secretion in the face of metabolic challenge. Moreover, Gc-deficient mice exhibited a more robust insulin secretory response than normal controls during hyperglycemic clamps. The data are consistent with a functional role of Gc activation in β cell dysfunction, and indicate that multiparity-induced diabetes is associated with altered β cell fate.

The mechanisms that restrict regeneration and maintain cell identity following injury are poorly characterized in higher vertebrates. Following β-cell loss, 1-2% of the glucagon-producing α-cells spontaneously engage in insulin production in mice. Here we explore the mechanisms inhibiting α-cell plasticity. We show that adaptive α-cell identity changes are constrained by intra-islet insulin- and Smoothened-mediated signalling, among others. The combination of β-cell loss or insulin-signalling inhibition, with Smoothened inactivation in α- or δ-cells, stimulates insulin production in more α-cells. These findings suggest that the removal of constitutive 'brake signals' is crucial to neutralize the refractoriness to adaptive cell-fate changes. It appears that the maintenance of cell identity is an active process mediated by repressive signals, which are released by neighbouring cells and curb an intrinsic trend of differentiated cells to change.

We recently discovered a novel subset of beta cells that resemble immature beta cells during pancreas development. We named these "virgin" beta cells as they do not stem from existing mature beta cells. Virgin beta cells are found exclusively at the islet periphery in areas that we therefore designated as the "neogenic niche." As beta cells are our only source of insulin, their loss leads to diabetes. Islets also contain glucagon-producing alpha cells and somatostatin-producing delta cells, that are important for glucose homeostasis and form a mantle surrounding the beta cell core. This 3D architecture is important and determines access to blood flow and innervation. We propose that the distinctive islet architecture may also play an important, but hitherto unappreciated role in generation of new endocrine cells, including beta cells. We discuss several predictions to further test the contribution of the neogenic niche to beta cell regeneration.

Bariatric surgery, such as vertical sleeve gastrectomy (VSG), causes high rates of type 2 diabetes remission and remarkable increases in postprandial glucagon-like peptide-1 (GLP-1) secretion. GLP-1 plays a critical role in islet function by potentiating glucose-stimulated insulin secretion; however, the mechanisms remain incompletely defined. Therefore, we applied a murine VSG model to an inducible β cell-specific GLP-1 receptor (GLP-1R) knockout mouse model to investigate the role of the β cell GLP-1R in islet function. Our data show that loss of β cell GLP-1R signaling decreases α cell GLP-1 expression after VSG. Furthermore, we find a β cell GLP-1R-dependent increase in α cell expression of the prohormone convertase required for the production of GLP-1 after VSG. Together, the findings herein reveal two concepts. First, our data support a paracrine role for α cell-derived GLP-1 in the metabolic benefits observed after VSG. Second, we have identified a role for the β cell GLP-1R as a regulator of α cell proglucagon processing.

Pancreatic α cells retain considerable plasticity and can, under the right circumstances, transdifferentiate into functionally mature β cells. In search of a targetable mechanistic basis, a recent paper suggested that the widely used anti-malaria drug artemether suppresses the α cell transcription factor Arx to promote transdifferentiation into β cells. However, key initial experiments in this paper were carried out in islet cell lines, and most subsequent validation experiments implied transdifferentiation without direct demonstration of α to β cell conversion. Indeed, we find no evidence that artemether promotes transdifferentiation of primary α cells into β cells. Moreover, artemether reduces Ins2 expression in primary β cells >100-fold, suppresses glucose uptake, and abrogates β cell calcium responses and insulin secretion in response to glucose. Our observations suggest that artemether induces general islet endocrine cell dedifferentiation and call into question the utility of artemisinins to promote α to β cell transdifferentiation in treating diabetes.

BackgroundType 1 and Type 2 diabetes mellitus (T1DM and T2DM) are caused by beta(β)-cell loss and functional impairment. Identification of mechanisms of β-cell death and therapeutic interventions to enhance β-cell survival are essential for prevention and treatment of diabetes. Oxidative stress is a common feature of both T1DM and T2DM; elevated biomarkers of oxidative stress are detected in blood, urine and tissues including pancreas of patients with DM. Islet transplantation is a promising treatment for diabetes. However, exposure to stress (chemical and mechanical) and ischemia-reperfusion during isolation and transplantation causes islet loss by generation of reactive oxygen species (ROS). Human intracellular antioxidant enzymes and related molecules are essential defenses against ROS. Antioxidant enzyme levels including superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPX) have been shown to be low in islet cells. However, little is known about the expression and function of antioxidant enzymes within islet cell subsets. We evaluated the expression of the key antioxidant enzymes in β- and alpha(α)-cell and accessed effects of oxidative stress, islet isolation and transplantation on β/α-cell ratio and viability in human islets.MethodsHuman pancreata from T1DM, T2DM and non-diabetic deceased donors were obtained and analyzed by confocal microscopy. Isolated islets were (I) transplanted in the renal sub-capsular space of streptozotocin-induced diabetic nude mice (in vivo bioassay), or (II) exposed to oxidative (H2O2) and nitrosative (NO donor) stress for 24 hrs in vitro. The ratio, % viability and death of β- and α-cells, and DNA damage (8OHdG) were measured.Results and conclusionsCatalase and GPX expression was much lower in β- than α-cells. The β/α-cell ratio fells significantly following islet isolation and transplantation. Exposure to oxidative stress caused a significantly lower survival and viability, with higher DNA damage in β- than α-cells. These findings identified the weakness of β-cell antioxidant capacity as a main cause of vulnerability to oxidative stress. Potential strategies to enhance β-cell antioxidant capacity might be effective in prevention/treatment of diabetes.

Postnatal maintenance or regeneration of pancreatic beta cells is considered to occur exclusively via the replication of existing beta cells, but clinically meaningful restoration of human beta cell mass by proliferation has never been achieved. We discovered a population of immature beta cells that is present throughout life and forms from non-beta precursors at a specialized micro-environment or "neogenic niche" at the islet periphery. These cells express insulin, but lack other key beta cell markers, and are transcriptionally immature, incapable of sensing glucose, and unable to support calcium influx. They constitute an intermediate stage in the transdifferentiation of alpha cells to cells that are functionally indistinguishable from conventional beta cells. We thus identified a lifelong source of new beta cells at a specialized site within healthy islets. By comparing co-existing immature and mature beta cells within healthy islets, we stand to learn how to mature insulin-expressing cells into functional beta cells.

Type 1 diabetes (T1D) is caused by autoreactive T cells that recognize pancreatic islet antigens and destroy insulin-producing β-cells. This attack results from a breakdown in tolerance for self-antigens, which is controlled by ectopic antigen expression in the thymus and pancreatic lymph nodes (PLNs). The autoantigens known to be involved include a set of islet proteins, such as insulin, GAD65, IA-2, and ZnT8. In an attempt to identify additional antigenic proteins, we performed an expression-based genome-wide association study using microarray data from 118 arrays of the thymus and PLNs of T1D mice. We ranked all 16,089 protein-coding genes by the likelihood of finding repeated differential expression and the degree of tissue specificity for pancreatic islets. The top autoantigen candidate was vitamin D-binding protein (VDBP). T-cell proliferation assays showed stronger T-cell reactivity to VDBP compared with control stimulations. Higher levels and frequencies of serum anti-VDBP autoantibodies (VDBP-Abs) were identified in patients with T1D (n = 331) than in healthy control subjects (n = 77). Serum vitamin D levels were negatively correlated with VDBP-Ab levels in patients in whom T1D developed during the winter. Immunohistochemical localization revealed that VDBP was specifically expressed in α-cells of pancreatic islets. We propose that VDBP could be an autoantigen in T1D.

Background: This study explored the correlation between pancreatic islet α cell function, as reflected by the plasma glucagon levels, and Diabetic Peripheral Neuropathy (DPN) in patients with Type 2 Diabetes Mellitus (T2DM)., Methods: A total of 358 patients with T2DM were retrospectively enrolled in this study and divided into the Non-DPN (NDPN) group (n = 220) and the DPN group (n = 138). All patients underwent an oral glucose tolerance test to detect levels of blood glucose, insulin and glucagon, and the Area Under the Curve (AUC) for Glucagon (AUCglu) was used to estimate the overall glucagon level. The Peripheral Nerve Conduction Velocity (PNCV), Amplitude (PNCA) and Latency (PNCL) were obtained with electromyography, and their Z scores were calculated., Results: There were significant differences regarding the age, disease duration, serum levels of alanine aminotransferase, aspartate aminotransferase, urea nitrogen, high-density lipoprotein, and 2h-C peptide between these two groups (p < 0.05). The NDPN group had higher glucagon levels at 30, 60 and 120 min and AUCglu (p < 0.05). The Z-scores of PNCV and PNCA showed an increasing trend (p < 0.05), while the Z-score of PNCL showed a decreasing trend (p < 0.05). The glucagon levels were positively correlated with PNCV and PNCA, but negatively correlated with PNCL, with Gluca30min having the strongest correlation (p < 0.05). Gluca30min was independently related to PNCV, PNCL, PNCA and DPN, respectively (p < 0.05). The function of pancreatic α islet cells, as reflected by the plasma glucagon level, is closely related to the occurrence of DPN in T2DM patients., Conclusion: Gluca30min may be a potentially valuable independent predictor for the occurrence of DPN., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2024. Published by Elsevier España, S.L.U.)

The α and β cells act in concert to maintain blood glucose. The α cells release glucagon in response to low levels of glucose to stimulate glycogenolysis in the liver. In contrast, β cells release insulin in response to elevated levels of glucose to stimulate peripheral glucose disposal. Despite these opposing roles in glucose homeostasis, α and β cells are derived from a common progenitor and share many proteins important for glucose sensing and hormone secretion. Results from recent work have underlined these similarities between the two cell types by revealing that β-to-α as well as α-to-β transdifferentiation can take place under certain experimental circumstances. These exciting findings highlight unexpected plasticity of adult islets and offer hope of novel therapeutic paths to replenish β cells in diabetes. In this review, we focus on the transcription factor networks that establish and maintain pancreatic endocrine cell identity and how they may be perturbed to facilitate transdifferentiation.

BackgroundInsulin producing beta cell and glucagon producing alpha cells are colocalized in pancreatic islets in an arrangement that facilitates the coordinated release of the two principal hormones that regulate glucose homeostasis and prevent both hypoglycemia and diabetes. However, this intricate organization has also complicated the determination of the cellular source(s) of the expression of genes that are detected in the islet. This reflects a significant gap in our understanding of mouse islet physiology, which reduces the effectiveness by which mice model human islet disease.ResultsTo overcome this challenge, we generated a bitransgenic reporter mouse that faithfully labels all beta and alpha cells in mouse islets to enable FACS-based purification and the generation of comprehensive transcriptomes of both populations. This facilitates systematic comparison across thousands of genes between the two major endocrine cell types of the islets of Langerhans whose principal hormones are of cardinal importance for glucose homeostasis. Our data leveraged against similar data for human beta cells reveal a core common beta cell transcriptome of 9900+ genes. Against the backdrop of overall similar beta cell transcriptomes, we describe marked differences in the repertoire of receptors and long non-coding RNAs between mouse and human beta cells.ConclusionsThe comprehensive mouse alpha and beta cell transcriptomes complemented by the comparison of the global (dis)similarities between mouse and human beta cells represent invaluable resources to boost the accuracy by which rodent models offer guidance in finding cures for human diabetes.

Mutations in the human homolog of the Vhlh gene [encoding the von-Hippel Lindau (VHL) protein] lead to tumor development. In mice, depletion of Vhlh in pancreatic ß-cells causes perturbed glucose homeostasis, but the role of this gene in other pancreatic cells is poorly understood. To investigate the function of VHL/HIF pathway in pancreatic cells, we inactivated Vhlh in the pancreatic epithelium as well as in the endocrine and exocrine lineages. Our results show that embryonic depletion of Vhlh within the pancreatic epithelium causes postnatal lethality due to severe hypoglycemia. The hypoglycemia is recapitulated in mice with endocrine-specific removal of Vhlh, while animals with loss of Vhlh predominantly in the exocrine compartment survive to adulthood with no overt defects in glucose metabolism. Mice with hypoglycemia display diminished insulin release in response to elevated glucose. Significantly, the glucagon response is impaired both in vivo (circulating glucagon levels) as well as in an in vitro secretion assay in isolated islets. Hypoxia also impairs glucagon secretion in a glucagon-expressing cell line in culture. Our results reveal a novel role for the hypoxia/HIF pathway in islet hormone secretion and maintenance of the fine balance that allows for the establishment of normoglycemia.

The peptide hormone Urocortin 3 (Ucn 3) is abundantly and exclusively expressed in mouse pancreatic beta cells where it regulates insulin secretion. Here we demonstrate that Ucn 3 first appears at embryonic day (E) 17.5 and, from approximately postnatal day (p) 7 and onwards throughout adult life, becomes a unifying and exclusive feature of mouse beta cells. These observations identify Ucn 3 as a potential beta cell maturation marker. To determine whether Ucn 3 is similarly restricted to beta cells in humans, we conducted comprehensive immunohistochemistry and gene expression experiments on macaque and human pancreas and sorted primary human islet cells. This revealed that Ucn 3 is not restricted to the beta cell lineage in primates, but is also expressed in alpha cells. To substantiate these findings, we analyzed human embryonic stem cell (hESC)-derived pancreatic endoderm that differentiates into mature endocrine cells upon engraftment in mice. Ucn 3 expression in hESC-derived grafts increased robustly upon differentiation into mature endocrine cells and localized to both alpha and beta cells. Collectively, these observations confirm that Ucn 3 is expressed in adult beta cells in both mouse and human and appears late in beta cell differentiation. Expression of Pdx1, Nkx6.1 and PC1/3 in hESC-derived Ucn 3(+) beta cells supports this. However, the expression of Ucn 3 in primary and hESC-derived alpha cells demonstrates that human Ucn 3 is not exclusive to the beta cell lineage but is a general marker for both the alpha and beta cell lineages. Ucn 3(+) hESC-derived alpha cells do not express Nkx6.1, Pdx1 or PC1/3 in agreement with the presence of a separate population of Ucn 3(+) alpha cells. Our study highlights important species differences in Ucn 3 expression, which have implications for its utility as a marker to identify mature beta cells in (re)programming strategies.

Insulin dysregulation in horses is characterised by hyperinsulinaemia and/or tissue insulin resistance and is associated with increased risk of laminitis. There is growing evidence in other species that dopamine attenuates insulin release from the pancreas; however, this has yet to be examined in horses. The present study aimed to identify whether there are cells capable of producing or responding to dopamine within the equine gastrointestinal mucosa and pancreas. Tissue samples were collected from the stomach, small and large intestines, and pancreas of six mature horses following euthanasia. Samples of stomach contents and faeces were also collected. Immunohistochemistry was performed to identify tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine production, and dopamine D2 receptors in tissue sections. Additional immunostaining for glucagon, insulin and chromogranin A was performed to identify α cells, β cells and enteroendocrine cells, respectively. Gastric parietal cells expressed both TH and D2 receptors, indicating that they are capable of both producing and responding to dopamine. Dopamine was quantified in stomach contents and faeces by high-performance liquid chromatography with electrochemical detection, with similar concentrations found at both sites. Dopamine D2 receptors were expressed in duodenal epithelial cells but not more distally. A subset of enteroendocrine cells, located sporadically along the gastrointestinal tract, were found to be immunopositive for the D2 receptor. In pancreatic islets, TH was present in α cells, while D2 receptors were strongly expressed in β cells and variably expressed in α cells. These findings are consistent with studies of other species; however, dynamic studies are required to further elucidate the role of dopamine in the modulation of insulin and glucagon secretion in horses. This descriptive study provides preliminary evidence for a potential role of dopamine to act as a paracrine messenger in the gastrointestinal mucosa and endocrine pancreas of horses., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Galinelli et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

As in type 1 diabetes, the loss of pancreatic β-cells leads to insulin deficiency and the subsequent development of hyperglycemia. Exercise has been proposed as a viable remedy for hyperglycemia. Lithium, which has been used as a treatment for bipolar disorder, has also been shown to improve glucose homeostasis under the conditions of obesity and type 2 diabetes by enhancing the effects of exercise on the skeletal muscles. In this study, we demonstrated that unlike in obesity and type 2 diabetic conditions, under the condition of insulin-deficient type 1 diabetes, lithium administration attenuated pancreatic a-cell mass without altering insulin-secreting β-cell mass, implying a selective impact on glucagon production. Additionally, we also documented that lithium downregulated the hepatic gluconeogenic program by decreasing G6Pase protein levels and upregulating AMPK activity. These findings suggest that lithium's effect on glucose metabolism in type 1 diabetes is mediated through a different mechanism than those associated with exerciseinduced metabolic changes in the muscle. Therefore, our research presents the novel therapeutic potential of lithium in the treatment of type 1 diabetes, which can be utilized along with insulin and independently of exercise.

Previous studies indicated that ductal cells can contribute to endocrine neogenesis in adult rodents after alpha cells convert into beta cells. This can occur through Pax4 mis-expression in alpha cells or through long-term administration of gamma-aminobutyric acid (GABA) to healthy mice. GABA has also been reported to increase the number of beta cells through direct effects on their proliferation, but only in specific genetic mouse backgrounds. To test whether GABA induces neogenesis of beta cells from ductal cells or affects pancreatic cell proliferation, we administered GABA or saline over 2 or 6 months to Sox9CreER;R26R YFP mice in which 60-80% of large or small ducts were efficiently lineage labeled. We did not observe any increases in islet neogenesis from ductal cells between 1 and 2 months of age in saline treated mice, nor between 2 and 6 months of saline treatment, supporting previous studies indicating that adult ductal cells do not give rise to new endocrine cells during homeostasis. Unlike previous reports, we did not observe an increase in beta cell neogenesis after 2 or 6 months of GABA administration. Nor did we observe a significant increase in the pancreatic islet area, the number of insulin and glucagon double positive cells, or cell proliferation in the pancreas. This indicates that the effect of long term GABA administration on the pancreas is minimal or highly context dependent.

Type 2 diabetes (T2D) has been known as 'bi-hormonal disorder' since decades ago, the role of glucagon from α-cell has languished whereas β-cell taking center stage. Recently, numerous findings indicate that the defects of glucagon secretion get involve with development and exacerbation of hyperglycemia in T2D. Aberrant α-cell responses exhibit both fasting and postprandial states: hyperglucagonemia contributes to fasting hyperglycemia caused by inappropriate hepatic glucose production, and to postprandial hyperglycemia owing to blunted α-cell suppression. During hypoglycemia, insufficient counter-regulation response is also observed in advanced T2D. Though many debates still remained for exact mechanisms behind the dysregulation of α-cell in T2D, it is clear that the blockade of glucagon receptor or suppression of glucagon secretion from α-cell would be novel therapeutic targets for control of hyperglycemia. Whereas there have not been remarkable advances in developing new class of drugs, currently available glucagon-like peptide-1 and dipeptidyl peptidase-IV inhibitors could be options for treatment of hyperglucagonemia. In this review, we focus on α-cell dysfunction and therapeutic potentials of targeting α-cell in T2D.

Introduction: Blood sugar homeostasis relies largely on the action of pancreatic islet hormones, particularly insulin and glucagon. In a prototypical fashion, glucagon is released upon hypoglycemia to elevate glucose by acting on the liver while elevated glucose induces the secretion of insulin which leads to sugar uptake by peripheral tissues. This simplified view of glucagon and insulin does not consider the paracrine roles of the two hormones modulating the response to glucose of α- and β-cells. In particular, glucose-stimulated glucagon secretion by isolated α-cells exhibits a Hill-function pattern, while experiments with intact pancreatic islets suggest a 'U'-shaped response., Methods: To this end, a framework was developed based on first principles and coupled to experimental studies capturing the glucose-induced response of pancreatic α- and β-cells influenced by the two hormones. The model predicts both the transient and steady-state profiles of secreted insulin and glucagon, including the typical biphasic response of normal β-cells to hyperglycemia., Results and Discussion: The results underscore insulin activity as a differentiating factor of the glucagon secretion from whole islets vs . isolated α-cells, and highlight the importance of experimental conditions in interpreting the behavior of islet cells in vitro . The model also reproduces the hyperglucagonemia, which is experienced by diabetes patients, and it is linked to a failure of insulin to inhibit α-cell activity. The framework described here is amenable to the inclusion of additional islet cell types and extrapancreatic tissue cells simulating multi-organ systems. The study expands our understanding of the interplay of insulin and glucagon for pancreas function in normal and pathological conditions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Brown and Tzanakakis.)