Characterisation of Ppy-lineage cells clarifies the functional heterogeneity of pancreatic beta cells in mice

The Beneficial Impact of a Novel Pancreatic Polypeptide Analogue on Islet Cell Lineage

(Proline3)PP, or (P3)PP, is an enzymatically stable, neuropeptide Y4 receptor (NPY4R)-selective, pancreatic polypeptide (PP) analogue with established weight-lowering and pancreatic islet morphology benefits in obesity-diabetes. In the current study, we now investigate the impact of twice-daily (P3)PP administration (25 nmol/kg) for 11 days on islet cell lineage, using streptozotocin (STZ) diabetic Ins1Cre/+;Rosa26-eYFP and GluCreERT2;Rosa26-eYFP transgenic mice with enhanced yellow fluorescent protein (eYFP) labelling of beta-cell and alpha-cells, respectively. (P3)PP had no obvious impact on body weight or blood glucose levels in STZ-diabetic mice at the dose tested, but did return food intake towards control levels in Ins1Cre/+;Rosa26-eYFP mice. Notably, pancreatic insulin content was augmented by (P3)PP treatment in both Ins1Cre/+;Rosa26-eYFP and GluCreERT2;Rosa26-eYFP mice, alongside enhanced beta-cell area and reduced alpha-cell area. Beneficial (P3)PP-induced changes on islet morphology were consistently associated with decreased beta-cell apoptosis, while (P3)PP also augmented beta-cell proliferation in Ins1Cre/+;Rosa26-eYFP mice. Alpha-cell turnover rates were returned towards healthy control levels by (P3)PP intervention in both mouse models. In terms of islet cell lineage, increased transition of alpha- to beta-cells as well as decreased beta- to alpha-cell differentiation were shown to contribute towards the enhancement of beta-cell area in (P3)PP-treated mice. Together these data reveal, for the first time, sustained NPY4R activation positively modulates beta-cell turnover, as well as islet cell plasticity, to help preserve pancreatic islet architecture following STZ-induced metabolic stress.

Novel enzyme-resistant pancreatic polypeptide analogs evoke pancreatic beta-cell rest, enhance islet cell turnover, and inhibit food intake in mice

Pancreatic polypeptide (PP) is a postprandial hormone secreted from pancreatic islets that activates neuropeptide Y4 receptors (NPY4Rs). PP is known to induce satiety but effects at the level of the endocrine pancreas are less well characterized. In addition, rapid metabolism of PP by dipeptidyl peptidase-4 (DPP-4) limits the investigation of the effects of the native peptide. Therefore, in the present study, five novel amino acid substituted and/or fatty acid derivatized PP analogs were synthesized, namely [P3]PP, [K13Pal]PP, [P3,K13Pal]PP, [N-Pal]PP, and [N-Pal,P3]PP, and their impact on pancreatic beta-cell function, as well as appetite regulation and glucose homeostasis investigated. All PP analogs displayed increased resistance to DPP-4 degradation. In addition, all peptides inhibited alanine-induced insulin secretion from BRIN-BD11 beta cells. Native PP and related analogs (10-8 and 10-6 M), and especially [P3]PP and [K13Pal]PP, significantly protected against cytokine-induced beta-cell apoptosis and promoted cellular proliferation, with effects dependent on the NPY4R for all peptides barring [N-Pal,P3]PP. In mice, all peptides, except [N-Pal]PP and [N-Pal,P3]PP, evoked a dose-dependent (25, 75, and 200 nmol/kg) suppression of appetite, with native PP and [P3]PP further augmenting glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK) induced reductions of food intake. The PP peptides had no obvious detrimental effect on glucose tolerance and they did not noticeably impair the glucose-regulatory actions of GLP-1 or CCK. In conclusion, Pro3 amino acid substitution of PP, either alone or together with mid-chain acylation, creates PP analogs with benefits on beta-cell rest, islet cell turnover, and energy regulation that may be applicable to the treatment of diabetes and obesity.

Metabolic Stress Levels Influence the Ability of Myelin Transcription Factors to Regulate β-Cell Identity and Survival

A hallmark of type 2 diabetes (T2D) is endocrine islet β-cell failure, which can occur via cell dysfunction, loss of identity, and/or death. How each is induced remains largely unknown. We used mouse β-cells deficient for myelin transcription factors (Myt TFs; including Myt1, -2, and -3) to address this question. We previously reported that inactivating all three Myt genes in pancreatic progenitor cells (MytPancΔ) caused β-cell failure and late-onset diabetes in mice. Their lower expression in human β-cells is correlated with β-cell dysfunction, and single nucleotide polymorphisms in MYT2 and MYT3 are associated with a higher risk of T2D. We now show that these Myt TF-deficient postnatal β-cells also dedifferentiate by reactivating several progenitor markers. Intriguingly, mosaic Myt TF inactivation in only a portion of islet β-cells did not result in overt diabetes, but this created a condition where Myt TF-deficient β-cells remained alive while activating several markers of Ppy-expressing islet cells. By transplanting MytPancΔ islets into the anterior eye chambers of immune-compromised mice, we directly show that glycemic and obesity-related conditions influence cell fate, with euglycemia inducing several Ppy+ cell markers and hyperglycemia and insulin resistance inducing additional cell death. These findings suggest that the observed β-cell defects in T2D depend not only on their inherent genetic/epigenetic defects but also on the metabolic load.

ARTICLE HIGHLIGHTS

Identification of Ppy-lineage cells as a novel origin of pancreatic ductal adenocarcinoma

The Ppy gene encodes pancreatic polypeptide (PP) secreted by PP- or γ-cells, which are a subtype of endocrine cells localised mainly in the islet periphery. For a detailed characterisation of PP cells, we aimed to establish PP cell lines. To this end, we generated a mouse model harbouring the SV40 large T antigen (TAg) in the Rosa26 locus, which is expressed upon Ppy-promoter-mediated Cre-loxP recombination. Whereas Insulin1-CreERT-mediated TAg expression in beta cells resulted in insulinoma, surprisingly, Ppy-Cre-mediated TAg expression resulted in the malignant transformation of Ppy-lineage cells. These mice showed distorted islet structural integrity at 5 days of age compared with normal islets. CK19+ duct-like lesions contiguous with the islets were observed at 2 weeks of age, and mice developed aggressive pancreatic ductal adenocarcinoma (PDAC) at 4 weeks of age, suggesting that PDAC can originate from the islet/endocrine pancreas. This was unexpected as PDAC is believed to originate from the exocrine pancreas. RNA-sequencing analysis of Ppy-lineage islet cells from 7-day-old TAg+ mice showed a downregulation and an upregulation of endocrine and exocrine genes, respectively, in addition to the upregulation of genes and pathways associated with PDAC. These results suggest that the expression of an oncogene in Ppy-lineage cells induces a switch from endocrine cell fate to PDAC. Our findings demonstrate that Ppy-lineage cells may be an origin of PDAC and may provide novel insights into the pathogenesis of pancreatic cancer, as well as possible therapeutic strategies. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Acinar to β-like cell conversion through inhibition of focal adhesion kinase

Insufficient functional β-cell mass causes diabetes; however, an effective cell replacement therapy for curing diabetes is currently not available. Reprogramming of acinar cells toward functional insulin-producing cells would offer an abundant and autologous source of insulin-producing cells. Our lineage tracing studies along with transcriptomic characterization demonstrate that treatment of adult mice with a small molecule that specifically inhibits kinase activity of focal adhesion kinase results in trans-differentiation of a subset of peri-islet acinar cells into insulin producing β-like cells. The acinar-derived insulin-producing cells infiltrate the pre-existing endocrine islets, partially restore β-cell mass, and significantly improve glucose homeostasis in diabetic mice. These findings provide evidence that inhibition of the kinase activity of focal adhesion kinase can convert acinar cells into insulin-producing cells and could offer a promising strategy for treating diabetes.

Mechanism exploration and biomarker identification of glycemic deterioration in patients with diseases of the exocrine pancreas

The damage to the endocrine pancreas among patients with diseases of the exocrine pancreas (DP) leads to reduced glycemic deterioration, ultimately resulting in diabetes of the exocrine pancreas (DEP). The present research aims to investigate the mechanism responsible for glycemic deterioration in DP patients, and to identify useful biomarkers, with the ultimate goal of enhancing clinical practice awareness. Gene expression profiles of patients with DP in this study were acquired from the Gene Expression Omnibus database. The original study defines DP patients to belong in one of three categories: non-diabetic (ND), impaired glucose tolerance (IGT) and DEP, which correspond to normoglycemia, early and late glycemic deterioration, respectively. After ensuring quality control, the discovery cohort included 8 ND, 20 IGT, and 12 DEP, while the validation cohort included 27 ND, 15 IGT, and 20 DEP. Gene set enrichment analysis (GSEA) employed differentially expressed genes (DEGs), while immunocyte infiltration was determined using single sample gene set enrichment analysis (ssGSEA). Additionally, correlation analysis was conducted to establish the link between clinical characteristics and immunocyte infiltration. The least absolute shrinkage and selection operator regression and random forest combined to identify biomarkers indicating glycemic deterioration in DP patients. These biomarkers were further validated through independent cohorts and animal experiments. With glycemic deterioration, biological processes in the pancreatic islets such as nutrient metabolism and complex immune responses are disrupted in DP patients. The expression of ACOT4, B2M, and ACKR2 was upregulated, whereas the expression of CACNA1F was downregulated. Immunocyte infiltration in the islet microenvironment showed a significant positive correlation with the age, body mass index (BMI), HbA1c and glycemia at the 2-h of patients. It was a crucial factor in glycemic deterioration. Additionally, B2M demonstrated a significant positive correlation with immunocyte infiltration and clinical features. Quantitative real-time PCR (qRT-PCR) and western blotting confirmed the upregulation in B2M. Immunofluorescent staining suggested the alteration of B2M was mainly in the alpha cells and beta cells. Overall, the study showed that gradually increased immunocyte infiltration was a significant contributor to glycemic deterioration in patients with DP, and it also highlighted B2M as a biomarker.

Single-Cell Transcriptome Profiling of Pancreatic Islets From Early Diabetic Mice Identifies Anxa10 for Ca2+ Allostasis Toward β-Cell Failure

Type 2 diabetes is a progressive disorder denoted by hyperglycemia and impaired insulin secretion. Although a decrease in β-cell function and mass is a well-known trigger for diabetes, the comprehensive mechanism is still unidentified. Here, we performed single-cell RNA sequencing of pancreatic islets from prediabetic and diabetic db/db mice, an animal model of type 2 diabetes. We discovered a diabetes-specific transcriptome landscape of endocrine and nonendocrine cell types with subpopulations of β- and α-cells. We recognized a new prediabetic gene, Anxa10, that was induced by and regulated Ca2+ influx from metabolic stresses. Anxa10-overexpressed β-cells displayed suppression of glucose-stimulated intracellular Ca2+ elevation and potassium-induced insulin secretion. Pseudotime analysis of β-cells predicted that this Ca2+-surge responder cluster would proceed to mitochondria dysfunction and endoplasmic reticulum stress. Other trajectories comprised dedifferentiation and transdifferentiation, emphasizing acinar-like cells in diabetic islets. Altogether, our data provide a new insight into Ca2+ allostasis and β-cell failure processes.

ARTICLE HIGHLIGHTS

The transcriptome of single-islet cells from healthy, prediabetic, and diabetic mice was studied. Distinct β-cell heterogeneity and islet cell-cell network in prediabetes and diabetes were found. A new prediabetic β-cell marker, Anxa10, regulates intracellular Ca2+ and insulin secretion. Diabetes triggers β-cell to acinar cell transdifferentiation.

The beta cell-immune cell interface in type 1 diabetes (T1D)

BACKGROUND

T1D is an autoimmune disease in which pancreatic islets of Langerhans are infiltrated by immune cells resulting in the specific destruction of insulin-producing islet beta cells. Our understanding of the factors leading to islet infiltration and the interplay of the immune cells with target beta cells is incomplete, especially in human disease. While murine models of T1D have provided crucial information for both beta cell and autoimmune cell function, the translation of successful therapies in the murine model to human disease has been a challenge.

SCOPE OF REVIEW

Here, we discuss current state of the art and consider knowledge gaps concerning the interface of the islet beta cell with immune infiltrates, with a focus on T cells. We discuss pancreatic and immune cell phenotypes and their impact on cell function in health and disease, which we deem important to investigate further to attain a more comprehensive understanding of human T1D disease etiology.

MAJOR CONCLUSIONS

The last years have seen accelerated development of approaches that allow comprehensive study of human T1D. Critically, recent studies have contributed to our revised understanding that the pancreatic beta cell assumes an active role, rather than a passive position, during autoimmune disease progression. The T cell-beta cell interface is a critical axis that dictates beta cell fate and shapes autoimmune responses. This includes the state of the beta cell after processing internal and external cues (e.g., stress, inflammation, genetic risk) that that contributes to the breaking of tolerance by hyperexpression of human leukocyte antigen (HLA) class I with presentation of native and neoepitopes and secretion of chemotactic factors to attract immune cells. We anticipate that emerging insights about the molecular and cellular aspects of disease initiation and progression processes will catalyze the development of novel and innovative intervention points to provide additional therapies to individuals affected by T1D.

New discoveries in the field of metabolism by applying single-cell and spatial omics

Single-cell multi-Omics (SCM-Omics) and spatial multi-Omics (SM-Omics) technologies provide state-of-the-art methods for exploring the composition and function of cell types in tissues/organs. Since its emergence in 2009, single-cell RNA sequencing (scRNA-seq) has yielded many groundbreaking new discoveries. The combination of this method with the emergence and development of SM-Omics techniques has been a pioneering strategy in neuroscience, developmental biology, and cancer research, especially for assessing tumor heterogeneity and T-cell infiltration. In recent years, the application of these methods in the study of metabolic diseases has also increased. The emerging SCM-Omics and SM-Omics approaches allow the molecular and spatial analysis of cells to explore regulatory states and determine cell fate, and thus provide promising tools for unraveling heterogeneous metabolic processes and making them amenable to intervention. Here, we review the evolution of SCM-Omics and SM-Omics technologies, and describe the progress in the application of SCM-Omics and SM-Omics in metabolism-related diseases, including obesity, diabetes, nonalcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD). We also conclude that the application of SCM-Omics and SM-Omics approaches can help resolve the molecular mechanisms underlying the pathogenesis of metabolic diseases in the body and facilitate therapeutic measures for metabolism-related diseases. This review concludes with an overview of the current status of this emerging field and the outlook for its future.

Heterogeneity of Islet Cells during Embryogenesis and Differentiation

Diabetes is caused by insufficient insulin secretion due to β-cell dysfunction and/or β-cell loss. Therefore, the restoration of functional β-cells by the induction of β-cell differentiation from embryonic stem (ES) and induced-pluripotent stem (iPS) cells, or from somatic non-β-cells, may be a promising curative therapy. To establish an efficient and feasible method for generating functional insulin-producing cells, comprehensive knowledge of pancreas development and β-cell differentiation, including the mechanisms driving cell fate decisions and endocrine cell maturation is crucial. Recent advances in single-cell RNA sequencing (scRNA-seq) technologies have opened a new era in pancreas development and diabetes research, leading to clarification of the detailed transcriptomes of individual insulin-producing cells. Such extensive high-resolution data enables the inference of developmental trajectories during cell transitions and gene regulatory networks. Additionally, advancements in stem cell research have not only enabled their immediate clinical application, but also has made it possible to observe the genetic dynamics of human cell development and maturation in a dish. In this review, we provide an overview of the heterogeneity of islet cells during embryogenesis and differentiation as demonstrated by scRNA-seq studies on the developing and adult pancreata, with implications for the future application of regenerative medicine for diabetes.

Pancreatic polypeptide revisited: Potential therapeutic effects in obesity-diabetes

Pancreatic polypeptide (PP), a member of the neuropeptide Y (NPY) family of peptides, is a hormone secreted from the endocrine pancreas with established actions on appetite regulation. Thus, through activation of hypothalamic neuropeptide Y4 (NPY4R or Y4) receptors PP induces satiety in animals and humans, suggesting potential anti-obesity actions. In addition, despite being actively secreted from pancreatic islets and evidence of local Y4 receptor expression, PP mediated effects on the endocrine pancreas have not been fully elucidated. To date, it appears that PP possesses an acute insulinostatic effect, similar to the impact of other peptides from the NPY family. However, it is interesting that prolonged activation of pancreatic Y1 receptors leads to established benefits on beta-cell turnover, preservation of beta-cell identity and improved insulin secretory responsiveness. This may hint towards possible similar anti-diabetic actions of sustained Y4 receptor modulation, since the Y1 and Y4 receptors trigger comparable cell signalling pathways. In terms of exploiting the prospective therapeutic promise of PP, this is severely restricted by a short circulating half-life as is the case for many regulatory peptide hormones. It follows that long-acting, enzyme resistant, forms of PP will be required to determine viability of the Y4 receptor as an anti-obesity and -diabetes drug target. The current review aims to refocus interest on the biology of PP and highlight opportunities for therapeutic development.

Therapeutic effects of acylated ghrelin-specific receptor GHS-R1a antagonist in islet transplantation

Islet transplantation is a type of cellular replacement therapy for severe diabetes that is limited by compromising effect on engrafted islets. Trials aiming to improve the function of transplanted islets have also been challenging. This study attempted to elucidate whether regulation of growth hormone secretagogue receptor-1a (GHS-R1a), one of the ghrelin receptors, improve the therapeutic effects of islet transplantation using [D-Lys3]-GHRP-6 (DLS), a specific GHS-R1a antagonist. The therapeutic effects of DLS were assessed in terms of the expression/production of endocrine genes/proteins, insulin-releasing function under glucose stimulation of mouse islets, and outcomes of syngeneic murine islet transplantation with systemic DLS administration. DLS treatment promoted insulin production and suppressed somatostatin production, suggesting that cancelation of the binding between ghrelin and GHS-R1a on β or δ cells improved insulin expression. DLS also promoted the glucose-dependent insulin-releasing function of β cells. However, the therapeutic effect of DLS in islet transplantation was fractional. In conclusion, the GHS-R1a antagonist showed preferable effects in improving the therapeutic outcomes of islet transplantation, including the promotion of insulin-releasing function.