Subcellular Feature-Based Classification of α and ß Cells Using Soft X-ray Tomography.

The dysfunction of α and ß 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 ß 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.

DNA Methylation-Dependent Restriction of Tyrosine Hydroxylase Contributes to Pancreatic ß-Cell Heterogeneity.

The molecular and functional heterogeneity of pancreatic ß-cells is well recognized, but the underlying mechanisms remain unclear. Pancreatic islets harbor a subset of ß-cells that co-express tyrosine hydroxylase (TH), an enzyme involved in synthesis of catecholamines that repress insulin secretion. Restriction of the TH+ ß-cells within islets is essential for appropriate function in mice, such that a higher proportion of these cells corresponds to reduced insulin secretion. Here, we use these cells as a model to dissect the developmental control of ß-cell heterogeneity. We define the specific molecular and metabolic characteristics of TH+ ß-cells and show differences in their developmental restriction in mice and humans. We show that TH expression in ß-cells is restricted by DNA methylation during ß-cell differentiation. Ablation of de novo DNA methyltransferase Dnmt3a in the embryonic progenitors results in a dramatic increase in the proportion of TH+ ß-cells, whereas ß-cell-specific ablation of Dnmt3a does not. We demonstrate that maintenance of Th promoter methylation is essential for its continued restriction in postnatal ß-cells. Loss of Th promoter methylation in response to chronic overnutrition increases the number of TH+ ß-cells, corresponding to impaired ß-cell function. These results reveal a regulatory role of DNA methylation in determining ß-cell heterogeneity.

A Novel De Novo Frameshift Pathogenic Variant in the FAM111B Resulting in Progressive Osseous Heteroplasia Phenotype.

INTRODUCTION: Progressive osseous heteroplasia (POH) is a rare, debilitating disorder characterized by heterotopic ossification in the skin and muscles, resulting in contractures of the joints and progressive loss of function. While 60-70% of the POH patients have paternally inherited, inactivating pathogenic variants in GNAS, the remaining 30-40% have no known etiology. FAM111B pathogenic variants, located on chromosome 11q12.1, cause POIKTMP (hereditary fibrosing poikiloderma with tendon contractures, myopathy, and pulmonary fibrosis), a very rare, autosomal-dominant disorder with high frequency of de novo missense pathogenic variants, which affects multiple tissues and organs, causing extensive fibrosis and muscle adiposis, though the exact mechanism is unknown. To our knowledge, there are no reports of FAM111B associated with POH. We describe the first case of POH phenotype associated with a novel de novo frameshift pathogenic variant in the FAM111B and present an analysis of the protein structure and function caused by this genomic disruption. CASE: A 15-year-old African-American male presented with generalized calcific nodules, progressive contractures, and muscle weakness leading to immobility, beginning at 6 years of age. Cutaneous examination showed generalized hard nodules varying from small to plaque-like ulcerated erupted skin lesions. Biochemical evaluation revealed 25(OH) vitamin D insufficiency (20 ng/mL), and normal levels of parathyroid hormone, FGF-23, alkaline phosphatase, calcium, and phosphorus. Skeletal survey radiographs and computed tomography (CT) of the chest, abdomen, and pelvis showed extensive soft tissue and muscle heterotopic ossifications involving shoulders, axillae, trunk, abdomen, pelvis, upper and lower extremities, in a clumped, conglomerate distribution within muscle, subcutaneous fat, and in some areas extending to the skin. There was no pulmonary fibrosis on the chest CT. The clinical and radiographic findings were most consistent with POH. A trio-clinical exome sequencing revealed a de novo heterozygous likely pathogenic variant in the FAM111B (OMIM # 615584) (c.1462delT [p.Cys488Valfs*21]). The resulted frameshift change in exon 4 replaced C-terminal region with 21 alternative amino acids. Multiple, previously reported disease-associated variants appear to localize within the trypsin-like cysteine/serine peptidase domain in which this variant occurs, supporting the functional significance of this region, though none have been previously reported to be associated with POH phenotype. Our 3D protein modeling showed obliteration of predicted protein folding and structure, and elimination of the zinc-binding domain, likely severely affecting protein function. CONCLUSION: This is the first case of POH phenotype associated with a novel de novo pathogenic frameshift variant in FAM111B. Whether the frameshift change in FAM111B predicts POH remains unclear. Further evaluations are necessary to fully elucidate this finding and the potential role and mechanism by which the FAM111B variants contributes to POH phenotype.

Systematic Bayesian posterior analysis guided by Kullback-Leibler divergence facilitates hypothesis formation.

Bayesian inference produces a posterior distribution for the parameters of a mathematical model that can be used to guide the formation of hypotheses; specifically, the posterior may be searched for evidence of alternative model hypotheses, which serves as a starting point for hypothesis formation and model refinement. Previous approaches to search for this evidence are largely qualitative and unsystematic; further, demonstrations of these approaches typically stop at hypothesis formation, leaving the questions they raise unanswered. Here, we introduce a Kullback-Leibler (KL) divergence-based ranking to expedite Bayesian hypothesis formation and investigate the hypotheses it generates, ultimately generating novel, biologically significant insights. Our approach uses KL divergence to rank parameters by how much information they gain from experimental data. Subsequently, rather than searching all model parameters at random, we use this ranking to prioritize examining the posteriors of the parameters that gained the most information from the data for evidence of alternative model hypotheses. We test our approach with two examples, which showcase the ability of our approach to systematically uncover different types of alternative hypothesis evidence. First, we test our KL divergence ranking on an established example of Bayesian hypothesis formation. Our top-ranked parameter matches the one previously identified to produce alternative hypotheses. In the second example, we apply our ranking in a novel study of a computational model of prolactin-induced JAK2-STAT5 signaling, a pathway that mediates beta cell proliferation. Within the top 3 ranked parameters (out of 33), we find a bimodal posterior revealing two possible ranges for the prolactin receptor degradation rate. We go on to refine the model, incorporating new data and determining which degradation rate is most plausible. Overall, while the effectiveness of our approach depends on having a properly formulated prior and on the form of the posterior distribution, we demonstrate that our approach offers a novel and generalizable quantitative framework for Bayesian hypothesis formation and use it to produce a novel, biologically-significant insight into beta cell signaling.

Phosphatases are predicted to govern prolactin-mediated JAK-STAT signaling in pancreatic beta cells.

Patients with diabetes are unable to produce a sufficient amount of insulin to properly regulate their blood glucose levels. One potential method of treating diabetes is to increase the number of insulin-secreting beta cells in the pancreas to enhance insulin secretion. It is known that during pregnancy, pancreatic beta cells proliferate in response to the pregnancy hormone, prolactin (PRL). Leveraging this proliferative response to PRL may be a strategy to restore endogenous insulin production for patients with diabetes. To investigate this potential treatment, we previously developed a computational model to represent the PRL-mediated JAK-STAT signaling pathway in pancreatic beta cells. Here, we applied the model to identify the importance of particular signaling proteins in shaping the response of a population of beta cells. We simulated a population of 10 000 heterogeneous cells with varying initial protein concentrations responding to PRL stimulation. We used partial least squares regression to analyze the significance and role of each of the varied protein concentrations in producing the response of the cell. Our regression models predict that the concentrations of the cytosolic and nuclear phosphatases strongly influence the response of the cell. The model also predicts that increasing PRL receptor strengthens negative feedback mediated by the inhibitor suppressor of cytokine signaling. These findings reveal biological targets that can potentially be used to modulate the proliferation of pancreatic beta cells to enhance insulin secretion and beta cell regeneration in the context of diabetes.

Exogenous Lactogenic Signaling Stimulates Beta Cell Replication In Vivo and In Vitro.

As patients recently diagnosed with T1D and patients with T2D have residual beta cell mass, there is considerable effort in beta cell biology to understand the mechanisms that drive beta cell regeneration as a potential cellular therapy for expanding patients' residual beta cell population. Both mouse and human studies have established that beta cell mass expansion occurs rapidly during pregnancy. To investigate the mechanisms of beta cell mass expansion during pregnancy, we developed a novel in vivo and in vitro models of pseudopregnancy. Our models demonstrate that pseudopregnancy promotes beta cell mass expansion in parous mice, and this expansion is driven by beta cell proliferation rather than hypertrophy. Importantly, estrogen, progesterone, and placental lactogen induce STAT5A signaling in the pseudopregnancy model, demonstrating that this model successfully recapitulates pregnancy-induced beta cell replication. We then created an in vitro model of pseudopregnancy and found that the combination of estrogen and placental lactogen induced beta cell replication in human islets and rat insulinoma cells. Therefore, beta cells both in vitro and in vivo increase proliferation when subjected to the pseudopregnancy cocktail compared to groups treated with estradiol or placental lactogen alone. The pseudopregnancy models described here may help inform novel methods of inducing beta cell replication in patients with diabetes.

SARS-CoV2 infects pancreatic beta cells in vivo and induces cellular and subcellular disruptions that reflect beta cell dysfunction.

Increasing evidence of new-onset diabetes during the COVID19 pandemic indicates that the SARS-CoV2 virus may drive beta-cell dysfunction leading to diabetes, but it is unclear if it is a primary or secondary effect. Here, we present evidence of SARS-CoV-2 infection of pancreatic beta cells in vivo using a robust and reproducible non-human primates model of mild to moderate COVID19 pathogenesis. Pancreas from SARS-CoV-2 infected subjects were positive for the SARS-CoV2 spike protein by immunohistochemistry and structures indicative of viral replication were evident by electron microscopy. Total beta cell area was decreased in SARS-CoV-2-infected pancreas, attributable to beta cell atrophy. Beta cell granularity was decreased. These histologic phenotypes persisted beyond the duration of the clinical disease course. Detailed electron microscopy of SARS-CoV-2 infected beta-cells revealed ultrastructural hallmarks of beta cell stress that are seen in islets of patients with Type 2 diabetes, including disrupted mitochondria and dilated endoplasmic reticulum. To assess the metabolic status of beta cells from SARS-CoV-2-infected subjects, we used fluorescence life-time imaging to measure the ratio of free and bound NADH as a surrogate of glycolytic and oxidative metabolism. We report an increase in free NADH levels, suggesting that beta cells from SARS-CoV-2-infected subjects adopt a more glycolytic metabolic profile. Taken together, we conclude that SARS-CoV-2 infection induces beta cell stress that may compromise beta-cell function beyond the duration of the disease course. This raises the possibility that the beta cell stress and injury may have clinical implications of the long-term future health of patients that have recovered from COVID19.

The Effects of Non-Nutritive Sweetener Consumption in the Pediatric Populations: What We Know, What We Don't, and What We Need to Learn.

Childhood obesity is increasing at an alarming rate in the United States. This trend carries serious risk of children developing obesity-related diseases including Type 2 diabetes and cardiovascular disease. Non-nutritive sweeteners (NNS) are used as substitution for table sugar as a way to prevent weight gain. Their consumption is ubiquitous in adults and children; however the long-term health outcomes of chronic NNS consumption in children are unclear. Conflicting observational studies suggest that children consuming NNS are at risk of obesity and development of type 2 diabetes, while others concluded some benefits in weight reduction. Here, we review the physiological mechanisms that can contribute to the negative metabolic effects of NNS. We will focus on how NNS alters the sweet perception leading to increase caloric consumption, how NNs alters the gut microbiota, and how NNS may disrupt glucose homeostasis and initiate a vicious cycle of pancreatic endocrine dysfunction. Studies focused on the pediatric population are limited but necessary to determine whether the potential weight loss benefits outweigh the potential negative metabolic outcomes during this critical development period.

Spike in Diabetic Ketoacidosis Rates in Pediatric Type 2 Diabetes During the COVID-19 Pandemic.

OBJECTIVE: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) on the incidence of new-onset type 2 diabetes and diabetic ketoacidosis (DKA) is unclear. It is unknown whether the coincidence of DKA noted in adult patients with type 2 diabetes is an issue for youth during the coronavirus disease 2019 pandemic. RESEARCH DESIGN AND METHODS: A retrospective single-center medical record review was conducted in a large, urban children's hospital of pediatric subjects presenting with new-onset type 2 diabetes between March and August of 2018 to 2020. RESULTS: The proportion of subjects presenting with new-onset type 2 diabetes in DKA dramatically increased in 2020 (9% in 2018, 3% in 2019, and 20% in 2020, P = 0.029). CONCLUSIONS: In 2020, youth with new-onset type 2 diabetes had a greater incidence of DKA at presentation than previously observed. Future studies should examine the impact of SARS-CoV2 exposure on the presentation of type 2 diabetes in all age-groups to inform better patient care.

Dynamic Regulation of JAK-STAT Signaling Through the Prolactin Receptor Predicted by Computational Modeling.

INTRODUCTION: The expansion of insulin-producing beta cells during pregnancy is critical to maintain glucose homeostasis in the face of increasing insulin resistance. Prolactin receptor (PRLR) signaling is one of the primary mediators of beta cell expansion during pregnancy, and loss of PRLR signaling results in reduced beta cell mass and gestational diabetes. Harnessing the proliferative potential of prolactin signaling to expand beta cell mass outside of the context of pregnancy requires quantitative understanding of the signaling at the molecular level. METHODS: A mechanistic computational model was constructed to describe prolactin-mediated JAK-STAT signaling in pancreatic beta cells. The effect of different regulatory modules was explored through ensemble modeling. A Bayesian approach for likelihood estimation was used to fit the model to experimental data from the literature. RESULTS: Including receptor upregulation, with either inhibition by SOCS proteins, receptor internalization, or both, allowed the model to match experimental results for INS-1 cells treated with prolactin. The model predicts that faster dimerization and nuclear import rates of STAT5B compared to STAT5A can explain the higher STAT5B nuclear translocation. The model was used to predict the dose response of STAT5B translocation in rat primary beta cells treated with prolactin and reveal possible strategies to modulate STAT5 signaling. CONCLUSIONS: JAK-STAT signaling must be tightly controlled to obtain the biphasic response in STAT5 activation seen experimentally. Receptor up-regulation, combined with SOCS inhibition, receptor internalization, or both is required to match experimental data. Modulating reactions upstream in the signaling can enhance STAT5 activation to increase beta cell survival.

Null mutations of NEUROG3 are associated with delayed-onset diabetes mellitus.

Biallelic mutations of the gene encoding the transcription factor NEUROG3 are associated with a rare disorder that presents in neonates as generalized malabsorption - due to a complete absence of enteroendocrine cells - followed, in early childhood or beyond, by insulin-dependent diabetes mellitus (IDDM). The commonly delayed onset of IDDM suggests a differential requirement for NEUROG3 in endocrine cell generation in the human pancreas versus the intestine. However, previously identified human mutations were hypomorphic and, hence, may have had residual function in pancreas. We report 2 patients with biallelic functionally null variants of the NEUROG3 gene who nonetheless did not present with IDDM during infancy but instead developed permanent IDDM during middle childhood ages. The variants showed no evidence of function in traditional promoter-based assays of NEUROG3 function and also failed to exhibit function in a variety of potentially novel in vitro and in vivo molecular assays designed to discern residual NEUROG3 function. These findings imply that, unlike in mice, pancreatic endocrine cell generation in humans is not entirely dependent on NEUROG3 expression and, hence, suggest the presence of unidentified redundant in vivo pathways in human pancreas capable of yielding ß cell mass sufficient to maintain euglycemia until early childhood.

The cellular regulators PTEN and BMI1 help mediate NEUROGENIN-3-induced cell cycle arrest.

Neurogenin-3 (NEUROG3) is a helix-loop-helix (HLH) transcription factor involved in the production of endocrine cells in the intestine and pancreas of humans and mice. However, the human NEUROG3 loss-of-function phenotype differs subtly from that in mice, but the reason for this difference remains poorly understood. Because NEUROG3 expression precedes exit of the cell cycle and the expression of endocrine cell markers during differentiation, we investigated the effect of lentivirus-mediated overexpression of the human NEUROG3 gene on the cell cycle of BON4 cells and various human nonendocrine cell lines. NEUROG3 overexpression induced a reversible cell cycle exit, whereas expression of a neuronal lineage homolog, NEUROG1, had no such effect. In endocrine lineage cells, the cellular quiescence induced by short-term NEUROG3 expression required cyclin-dependent kinase inhibitor 1A (CDKN1A)/p21CIP1 expression. Expression of endocrine differentiation markers required sustained NEUROG3 expression in the quiescent, but not in the senescent, state. Inhibition of the phosphatase and tensin homolog (PTEN) pathway reversed quiescence by inducing cyclin-dependent kinase 2 (CDK2) and reducing p21CIP1 and NEUROG3 protein levels in BON4 cells and human enteroids. We discovered that NEUROG3 expression stimulates expression of CDKN2a/p16INK4a and BMI1 proto-oncogene polycomb ring finger (BMI1), with the latter limiting expression of the former, delaying the onset of CDKN2a/p16INK4a -driven cellular senescence. Furthermore, NEUROG3 bound to the promoters of both CDKN1a/p21CIP1 and BMI1 genes, and BMI1 attenuated NEUROG3 binding to the CDKN1a/p21CIP1 promoter. Our findings reveal how human NEUROG3 integrates inputs from multiple signaling pathways and thereby mediates cell cycle exit at the onset of differentiation.

Quantifying RANKL and OPG levels in healthy children: A large cross-sectional analysis.

BACKGROUND: There have been new advances in understanding bone remodeling on a molecular level including the RANKL-OPG pathway, leading to advancements in targeted therapeutic intervention. There is however limited data in pediatrics with little known on normative values in healthy children. This is the largest cohort to quantify RANKL, OPG, and RANKL: OPG levels in healthy children as well as study the influence of age, gender, Tanner stage, and BMI in this population. METHODS: Healthy subjects, 1-21 years of age, were recruited from general pediatric clinics affiliated with CHLA and in collaboration with samples stored from a previously completed study. Healthy children were defined as those with no chronic disease, daily medication, or fractures in the past six months. Free soluble RANKL and OPG levels were quantified using a sandwich ELISA. RESULTS: Three hundred samples were collected with overall serum concentrations of RANKL, OPG and RANKL: OPG of 0.28 pmol/L, 3.56 pmol/L and 0.08 pmol/L, respectively. Serum RANKL and RANKL: OPG concentrations were significantly different by age (p = 0.0001 and 0.0027, respectively). There was an overall downward trend by age except in the 11-15-year age group where a slight increase was noted. RANKL concentrations were also significantly different between Tanner stages, with highest concentrations seen at Tanner 3 (p = 0.0481), and zBMI (p = 0.001). OPG was inversely correlated with zBMI, but not influenced by gender, age, or Tanner stage. CONCLUSION: We showed significant difference in RANKL levels by age, Tanner stage, and zBMI. OPG was inversely correlated with zBMI. Insight into circulating levels of RANKL, OPG and RANKL: OPG in healthy children may be a potential tool to better understand disease states in pediatrics. Future studies are needed to evaluate the clinical significance of RANKL and OPG levels for diagnostic and therapeutic purposes in this population.

Estrogen receptor α protects pancreatic ß-cells from apoptosis by preserving mitochondrial function and suppressing endoplasmic reticulum stress.

Estrogen receptor α (ERα) action plays an important role in pancreatic ß-cell function and survival; thus, it is considered a potential therapeutic target for the treatment of type 2 diabetes in women. However, the mechanisms underlying the protective effects of ERα remain unclear. Because ERα regulates mitochondrial metabolism in other cell types, we hypothesized that ERα may act to preserve insulin secretion and promote ß-cell survival by regulating mitochondrial-endoplasmic reticulum (EndoRetic) function. We tested this hypothesis using pancreatic islet-specific ERα knockout (PERαKO) mice and Min6 ß-cells in culture with Esr1 knockdown (KD). We found that Esr1-KD promoted reactive oxygen species production that associated with reduced fission/fusion dynamics and impaired mitophagy. Electron microscopy showed mitochondrial enlargement and a pro-fusion phenotype. Mitochondrial cristae and endoplasmic reticulum were dilated in Esr1-KD compared with ERα replete Min6 ß-cells. Increased expression of Oma1 and Chop was paralleled by increased oxygen consumption and apoptosis susceptibility in ERα-KD cells. In contrast, ERα overexpression and ligand activation reduced both Chop and Oma1 expression, likely by ERα binding to consensus estrogen-response element sites in the Oma1 and Chop promoters. Together, our findings suggest that ERα promotes ß-cell survival and insulin secretion through maintenance of mitochondrial fission/fusion-mitophagy dynamics and EndoRetic function, in part by Oma1 and Chop repression.

Gene Editing and Human Pluripotent Stem Cells: Tools for Advancing Diabetes Disease Modeling and Beta-Cell Development.

PURPOSE OF REVIEW: This review will focus on the multiple approaches to gene editing and address the potential use of genetically modified human pluripotent stem cell-derived beta cells (SC-ß) as a tool to study human beta-cell development and model their function in diabetes. We will explore how new variations of CRISPR/Cas9 gene editing may accelerate our understanding of beta-cell developmental biology, elucidate novel mechanisms that establish and regulate beta-cell function, and assist in pioneering new therapeutic modalities for treating diabetes. RECENT FINDINGS: Improvements in CRISPR/Cas9 target specificity and homology-directed recombination continue to advance its use in engineering stem cells to model and potentially treat disease. We will review how CRISPR/Cas9 gene editing is informing our understanding of beta-cell development and expanding the therapeutic possibilities for treating diabetes and other diseases. Here we focus on the emerging use of gene editing technology, specifically CRISPR/Cas9, as a means of manipulating human gene expression to gain novel insights into the roles of key factors in beta-cell development and function. Taken together, the combined use of SC-ß cells and CRISPR/Cas9 gene editing will shed new light on human beta-cell development and function and accelerate our progress towards developing new therapies for patients with diabetes.

Cyclin D2 is sufficient to drive ß cell self-renewal and regeneration.

Diabetes results from an inadequate mass of functional ß cells, due to either ß cell loss caused by autoimmune destruction (type I diabetes) or ß cell failure in response to insulin resistance (type II diabetes). Elucidating the mechanisms that regulate ß cell mass may be key to developing new techniques that foster ß cell regeneration as a cellular therapy to treat diabetes. While previous studies concluded that cyclin D2 is required for postnatal ß cell self-renewal in mice, it is not clear if cyclin D2 is sufficient to drive ß cell self-renewal. Using transgenic mice that overexpress cyclin D2 specifically in ß cells, we show that cyclin D2 overexpression increases ß cell self-renewal post-weaning and results in increased ß cell mass. ß cells that overexpress cyclin D2 are responsive to glucose stimulation, suggesting they are functionally mature. ß cells that overexpress cyclin D2 demonstrate an enhanced regenerative capacity after injury induced by streptozotocin toxicity. To understand if cyclin D2 overexpression is sufficient to drive ß cell self-renewal, we generated a novel mouse model where cyclin D2 is only expressed in ß cells of cyclin D2-/- mice. Transgenic overexpression of cyclin D2 in cyclin D2-/- ß cells was sufficient to restore ß cell mass, maintain normoglycaemia, and improve regenerative capacity when compared with cyclin D2-/- littermates. Taken together, our results indicate that cyclin D2 is sufficient to regulate ß cell self-renewal and that manipulation of its expression could be used to enhance ß cell regeneration.

Neuropeptide Y expression marks partially differentiated ß cells in mice and humans.

ß Cells are formed in embryonic life by differentiation of endocrine progenitors and expand by replication during neonatal life, followed by transition into functional maturity. In this study, we addressed the potential contribution of neuropeptide Y (NPY) in pancreatic ß cell development and maturation. We show that NPY expression is restricted from the progenitor populations during pancreatic development and marks functionally immature ß cells in fetal and neonatal mice and humans. NPY expression is epigenetically downregulated in ß cells upon maturation. Neonatal ß cells that express NPY are more replicative, and knockdown of NPY expression in neonatal mouse islets reduces replication and enhances insulin secretion in response to high glucose. These data show that NPY expression likely promotes replication and contributes to impaired glucose responsiveness in neonatal ß cells. We show that NPY expression reemerges in ß cells in mice fed with high-fat diet as well as in diabetes in mice and humans, establishing a potential new mechanism to explain impaired ß cell maturity in diabetes. Together, these studies highlight the contribution of NPY in the regulation of ß cell differentiation and have potential applications for ß cell supplementation for diabetes therapy.