Single pancreatic beta cells co-express multiple islet hormone genes in mice

Stem/progenitor cells in normal physiology and disease of the pancreas

Though embryonic pancreas progenitors are well characterised, the existence of stem/progenitor cells in the postnatal mammalian pancreas has been long debated, mainly due to contradicting results on regeneration after injury or disease in mice. Despite these controversies, sequencing advancements combined with lineage tracing and organoid technologies indicate that homeostatic and trigger-induced regenerative responses in mice could occur. The presence of putative progenitor cells in the adult pancreas has been proposed during homeostasis and upon different stress challenges such as inflammation, tissue damage and oncogenic stress. More recently, single cell transcriptomics has revealed a remarkable heterogeneity in all pancreas cell types, with some cells showing the signature of potential progenitors. In this review we provide an overview on embryonic and putative adult pancreas progenitors in homeostasis and disease, with special emphasis on in vitro culture systems and scRNA-seq technology as tools to address the progenitor nature of different pancreatic cells.

High Coexpression of the Ghrelin and LEAP2 Receptor GHSR With Pancreatic Polypeptide in Mouse and Human Islets

Islets represent an important site of direct action of the hormone ghrelin, with expression of the ghrelin receptor (growth hormone secretagogue receptor; GHSR) having been localized variably to alpha cells, beta cells, and/or somatostatin (SST)-secreting delta cells. To our knowledge, GHSR expression by pancreatic polypeptide (PP)-expressing gamma cells has not been specifically investigated. Here, histochemical analyses of Ghsr-IRES-Cre × Cre-dependent ROSA26-yellow fluorescent protein (YFP) reporter mice showed 85% of GHSR-expressing islet cells coexpress PP, 50% coexpress SST, and 47% coexpress PP + SST. Analysis of single-cell transcriptomic data from mouse pancreas revealed 95% of Ghsr-expressing cells coexpress Ppy, 100% coexpress Sst, and 95% coexpress Ppy + Sst. This expression was restricted to gamma-cell and delta-cell clusters. Analysis of several single-cell human pancreatic transcriptome data sets revealed 59% of GHSR-expressing cells coexpress PPY, 95% coexpress SST, and 57% coexpress PPY + SST. This expression was prominent in delta-cell and beta-cell clusters, also occurring in other clusters including gamma cells and alpha cells. GHSR expression levels were upregulated by type 2 diabetes mellitus in beta cells. In mice, plasma PP positively correlated with fat mass and with plasma levels of the endogenous GHSR antagonist/inverse agonist LEAP2. Plasma PP also elevated on LEAP2 and synthetic GHSR antagonist administration. These data suggest that in addition to delta cells, beta cells, and alpha cells, PP-expressing pancreatic cells likely represent important direct targets for LEAP2 and/or ghrelin both in mice and humans.

Harnessing the Endogenous Plasticity of Pancreatic Islets: A Feasible Regenerative Medicine Therapy for Diabetes?

Diabetes is a chronic metabolic disease caused by an absolute or relative deficiency in functional pancreatic β-cells that leads to defective control of blood glucose. Current treatments for diabetes, despite their great beneficial effects on clinical symptoms, are not curative treatments, leading to a chronic dependence on insulin throughout life that does not prevent the secondary complications associated with diabetes. The overwhelming increase in DM incidence has led to a search for novel antidiabetic therapies aiming at the regeneration of the lost functional β-cells to allow the re-establishment of the endogenous glucose homeostasis. Here we review several aspects that must be considered for the development of novel and successful regenerative therapies for diabetes: first, the need to maintain the heterogeneity of islet β-cells with several subpopulations of β-cells characterized by different transcriptomic profiles correlating with differences in functionality and in resistance/behavior under stress conditions; second, the existence of an intrinsic islet plasticity that allows stimulus-mediated transcriptome alterations that trigger the transdifferentiation of islet non-β-cells into β-cells; and finally, the possibility of using agents that promote a fully functional/mature β-cell phenotype to reduce and reverse the process of dedifferentiation of β-cells during diabetes.

Establishment of a long-term stable β-cell line and its application to analyze the effect of Gcg expression on insulin secretion

A pancreatic β-cell line MIN6 was previously established in our lab from an insulinoma developed in an IT6 transgenic mouse expressing the SV40 T antigen in β-cells. This cell line has been widely used for in vitro analysis of β-cell function, but tends to lose the mature β-cell features, including glucose-stimulated insulin secretion (GSIS), in long-term culture. The aim of this study was to develop a stable β-cell line that retains the characteristics of mature β-cells. Considering that mice derived from a cross between C3H and C57BL/6 strains are known to exhibit higher insulin secretory capacity than C57BL/6 mice, an IT6 male mouse of this hybrid background was used to isolate insulinomas, which were independently cultured. After 7 months of continuous culturing, we obtained the MIN6-CB4 β-cell line, which stably maintains its GSIS. It has been noted that β-cell lines express the glucagon (Gcg) gene at certain levels. MIN6-CB4 cells were utilized to assess the effects of differential Gcg expression on β-cell function. Our data show the functional importance of Gcg expression and resulting basal activation of the GLP-1 receptor in β-cells. MIN6-CB4 cells can serve as an invaluable tool for studying the regulatory mechanisms of insulin secretion, such as the GLP-1/cAMP signaling, in β-cells.

Selection for CD26- and CD49A+ Cells From Pluripotent Stem Cells-Derived Islet-Like Clusters Improves Therapeutic Activity in Diabetic Mice

BACKGROUND

Cell therapy of diabetes aims at restoring the physiological control of blood glucose by transplantation of functional pancreatic islet cells. A potentially unlimited source of cells for such transplantations would be islet cells derived from an in vitro differentiation of human pluripotent stem cells (hESC/hiPSC). The islet-like clusters (ILC) produced by the known differentiation protocols contain various cell populations. Among these, the β-cells that express both insulin and the transcription factor Nkx6.1 seem to be the most efficient to restore normoglycemia in diabetes animal models. Our aim was to find markers allowing selection of these efficient cells.

METHODS

Functional Cell-Capture Screening (FCCS) was used to identify markers that preferentially capture the cells expressing both insulin and Nkx6.1, from hESC-derived ILC cells. In order to test whether selection for such markers could improve cell therapy in diabetic mouse models, we used ILC produced from a clinical-grade line of hESC by a refined differentiation protocol adapted to up-scalable bioreactors. Re-aggregated MACS sorted cells were encapsulated in microspheres made of alginate modified to reduce foreign body reaction. Implantation was done intraperitoneally in STZ-treated C57BL/6 immuno-competent mice.

RESULTS

CD49A (integrin alpha1) was identified by FCCS as a marker for cells that express insulin (or C-peptide) as well as Nkx6.1 in ILC derived by hESC differentiation. The ILC fraction enriched in CD49A ⁺ cells rapidly reduced glycemia when implanted in diabetic mice, whereas mice receiving the CD49A depleted population remained highly diabetic. CD49A-enriched ILC cells also produced higher levels of human C-peptide in the blood of transplanted mice. However, the difference between CD49A-enriched and total ILC cells remained small. Another marker, CD26 (DPP4), was identified by FCCS as binding insulin-expressing cells which are Nkx6.1 negative. Depletion of CD26 ⁺ cells followed by enrichment for CD49A ⁺ cells increased insulin⁺/Nkx6.1⁺ cells fraction to ~70%. The CD26 ^- /CD49A ⁺ enriched ILC exhibited improved function over non-sorted ILC or CD49A ⁺ cells in diabetic mice and maintain prolonged blood C-peptide levels.

CONCLUSIONS

Refining the composition of ILC differentiated from hPSC by negative selection to remove cells expressing CD26 and positive selection for CD49A expressing cells could enable more effective cell therapy of diabetes.

Peptidylglycine α-amidating monooxygenase is required for atrial secretory granule formation

The discovery of atrial secretory granules and the natriuretic peptides stored in them identified the atrium as an endocrine organ. Although neither atrial nor brain natriuretic peptide (ANP, BNP) is amidated, the major membrane protein in atrial granules is peptidylglycine α-amidating monooxygenase (PAM), an enzyme essential for amidated peptide biosynthesis. Mice lacking cardiomyocyte PAM (Pam ^Myh6-cKO/cKO) are viable, but a gene dosage-dependent drop in atrial ANP and BNP content occurred. Ultrastructural analysis of adult Pam ^Myh6-cKO/cKO atria revealed a 13-fold drop in the number of secretory granules. When primary cultures of Pam ^{0-Cre-cKO/cKO} atrial myocytes (no Cre recombinase, PAM floxed) were transduced with Cre-GFP lentivirus, PAM protein levels dropped, followed by a decline in ANP precursor (proANP) levels. Expression of exogenous PAM in Pam ^Myh6-cKO/cKO atrial myocytes produced a dose-dependent rescue of proANP content; strikingly, this response did not require the monooxygenase activity of PAM. Unlike many prohormones, atrial proANP is stored intact. A threefold increase in the basal rate of proANP secretion by Pam ^Myh6-cKO/cKO myocytes was a major contributor to its reduced levels. While proANP secretion was increased following treatment of control cultures with drugs that block the activation of Golgi-localized Arf proteins and COPI vesicle formation, proANP secretion by Pam ^Myh6-cKO/cKO myocytes was unaffected. In cells lacking secretory granules, expression of exogenous PAM led to the accumulation of fluorescently tagged proANP in the cis-Golgi region. Our data indicate that COPI vesicle-mediated recycling of PAM from the cis-Golgi to the endoplasmic reticulum plays an essential role in the biogenesis of proANP containing atrial granules.

Single-cell RNA-seq with spike-in cells enables accurate quantification of cell-specific drug effects in pancreatic islets

BACKGROUND

Single-cell RNA-seq (scRNA-seq) is emerging as a powerful tool to dissect cell-specific effects of drug treatment in complex tissues. This application requires high levels of precision, robustness, and quantitative accuracy-beyond those achievable with existing methods for mainly qualitative single-cell analysis. Here, we establish the use of standardized reference cells as spike-in controls for accurate and robust dissection of single-cell drug responses.

RESULTS

We find that contamination by cell-free RNA can constitute up to 20% of reads in human primary tissue samples, and we show that the ensuing biases can be removed effectively using a novel bioinformatics algorithm. Applying our method to both human and mouse pancreatic islets treated ex vivo, we obtain an accurate and quantitative assessment of cell-specific drug effects on the transcriptome. We observe that FOXO inhibition induces dedifferentiation of both alpha and beta cells, while artemether treatment upregulates insulin and other beta cell marker genes in a subset of alpha cells. In beta cells, dedifferentiation and insulin repression upon artemether treatment occurs predominantly in mouse but not in human samples.

CONCLUSIONS

This new method for quantitative, error-correcting, scRNA-seq data normalization using spike-in reference cells helps clarify complex cell-specific effects of pharmacological perturbations with single-cell resolution and high quantitative accuracy.

Multifaceted secretion of htNSC-derived hypothalamic islets induces survival and antidiabetic effect via peripheral implantation in mice

We report that mouse hypothalamic stem/progenitor cells produce multiple pancreatic, gastrointestinal and hypothalamic peptides in addition to exosomes. Through cell sorting and selection according to insulin promoter activity, we generated a subpopulation(s) of these cells which formed 3D spherical structure with combined features of hypothalamic neurospheres and pancreatic islets. Through testing streptozotocin-induced pancreatic islet disruption and fatal diabetes, we found that peripheral implantation of these spheres in mice led to remarkable improvements in general health and survival in addition to a moderate antidiabetic effect, and notably these pro-survival versus metabolic effects were dissociable to a significant extent. Mechanistically, secretion of exosomes by these spheres was essential for enhancing survival while production of insulin was important for the antidiabetic effect. In summary, hypothalamic neural stem/progenitor cells comprise subpopulations with multifaceted secretion, and their derived hypothalamic islets can be implanted peripherally to enhance general health and survival together with an antidiabetic benefit.

Targeted pharmacological therapy restores β-cell function for diabetes remission

Dedifferentiation of insulin-secreting β cells in the islets of Langerhans has been proposed to be a major mechanism of β-cell dysfunction. Whether dedifferentiated β cells can be targeted by pharmacological intervention for diabetes remission, and ways in which this could be accomplished, are unknown as yet. Here we report the use of streptozotocin-induced diabetes to study β-cell dedifferentiation in mice. Single-cell RNA sequencing (scRNA-seq) of islets identified markers and pathways associated with β-cell dedifferentiation and dysfunction. Single and combinatorial pharmacology further show that insulin treatment triggers insulin receptor pathway activation in β cells and restores maturation and function for diabetes remission. Additional β-cell selective delivery of oestrogen by Glucagon-like peptide-1 (GLP-1-oestrogen conjugate) decreases daily insulin requirements by 60%, triggers oestrogen-specific activation of the endoplasmic-reticulum-associated protein degradation system, and further increases β-cell survival and regeneration. GLP-1-oestrogen also protects human β cells against cytokine-induced dysfunction. This study not only describes mechanisms of β-cell dedifferentiation and regeneration, but also reveals pharmacological entry points to target dedifferentiated β cells for diabetes remission.

Single-cell transcriptomics from human pancreatic islets: sample preparation matters

Single-cell RNA sequencing (scRNA-seq) of human primary tissues is a rapidly emerging tool for investigating human health and disease at the molecular level. However, optimal processing of solid tissues presents a number of technical and logistical challenges, especially for tissues that are only available at autopsy, which includes pancreatic islets, a tissue that is highly relevant to diabetes. To assess the possible effects of different sample preparation protocols on fresh islet samples, we performed a detailed comparison of scRNA-seq data generated with islets isolated from a human donor but processed according to four treatment strategies, including fixation and cryopreservation. We found significant and reproducible differences in the proportion of cell types identified, and more minor effects on cell-specific patterns of gene expression. Fresh islets from a second donor confirmed gene expression signatures of alpha and beta subclusters. These findings may well apply to other tissues, emphasizing the need for careful consideration when choosing processing methods, comparing results between different studies, and/or interpreting data in the context of multiple cell types from preserved tissue.

Long-Term Liraglutide Administration Induces Pancreas Neogenesis in Adult T2DM Mice

In vivo beta-cell neogenesis may be one way to treat diabetes. We aimed to investigate the effect of glucagon-like peptide-1 (GLP-1) on beta-cell neogenesis in type 2 diabetes mellitus (T2DM). Male C57BL/6J mice, 6 wk old, were randomly divided into three groups: Control, T2DM, and T2DM + Lira. T2DM was induced using high-fat diet and intraperitoneal injection of streptozotocin (40 mg/kg/d for 3 d). At 8 wk after streptozotocin injection, T2DM + Lira group was injected intraperitoneally with GLP-1 analog liraglutide (0.8 mg/kg/d) for 4 wk. Apparently for the first time, we report the appearance of a primitive bud connected to pancreas in all adult mice from each group. The primitive bud was characterized by scattered single monohormonal cells expressing insulin, GLP-1, somatostatin, or pancreatic polypeptide, and four-hormonal cells, but no acinar cells and ductal epithelial cells. Monohormonal cells in it were small, newborn, immature cells that rapidly proliferated and expressed cell markers indicative of immaturity. In parallel, Ngn3+ endocrine progenitors and Nestin+ cells existed in the primitive bud. Liraglutide facilitated neogenesis and rapid growth of acinar cells, pancreatic ducts, and blood vessels in the primitive bud. Meanwhile, scattered hormonal cells aggregated into cell clusters and grew into larger islets; polyhormonal cells differentiated into monohormonal cells. Extensive growth of exocrine and endocrine glands resulted in the neogenesis of immature pancreatic lobes in adult mice of T2DM + Lira group. Contrary to predominant acinar cells in mature pancreatic lobes, there were still a substantial number of mesenchymal cells around acinar cells in immature pancreatic lobes, which resulted in the loose appearance. Our results suggest that adult mice preserve the capacity of pancreatic neogenesis from the primitive bud, which liraglutide facilitates in adult T2DM mice. To our knowledge, this is the first time such a phenomenon has been reported.

Contribution of Oxidative Stress and Impaired Biogenesis of Pancreatic β-Cells to Type 2 Diabetes

Significance: Type 2 diabetes development involves multiple changes in β-cells, related to the oxidative stress and impaired redox signaling, beginning frequently by sustained overfeeding due to the resulting lipotoxicity and glucotoxicity. Uncovering relationships among the dysregulated metabolism, impaired β-cell "well-being," biogenesis, or cross talk with peripheral insulin resistance is required for elucidation of type 2 diabetes etiology. Recent Advances: It has been recognized that the oxidative stress, lipotoxicity, and glucotoxicity cannot be separated from numerous other cell pathology events, such as the attempted compensation of β-cell for the increased insulin demand and dynamics of β-cell biogenesis and its "reversal" at dedifferentiation, that is, from the concomitantly decreasing islet β-cell mass (also due to transdifferentiation) and low-grade islet or systemic inflammation. Critical Issues: At prediabetes, the compensation responses of β-cells, attempting to delay the pathology progression-when exaggerated-set a new state, in which a self-checking redox signaling related to the expression of Ins gene expression is impaired. The resulting altered redox signaling, diminished insulin secretion responses to various secretagogues including glucose, may lead to excretion of cytokines or chemokines by β-cells or excretion of endosomes. They could substantiate putative stress signals to the periphery. Subsequent changes and lasting glucolipotoxicity promote islet inflammatory responses and further pathology spiral. Future Directions: Should bring an understanding of the β-cell self-checking and related redox signaling, including the putative stress signal to periphery. Strategies to cure or prevent type 2 diabetes could be based on the substitution of the "wrong" signal by the "correct" self-checking signal.

Metabolic and Functional Heterogeneity in Pancreatic β Cells

Metabolic and secretory heterogeneity are fundamental properties of pancreatic islet β cells. Emerging data suggest that stable differences in the transcriptome and proteome of individual cells may create cellular hierarchies, which, in turn, establish coordinated functional networks. These networks appear to govern the secretory activity of the whole islet and be affected in some forms of diabetes mellitus. Functional imaging, for example, of intracellular calcium dynamics, has led to the demonstration of "small worlds" behavior, and the identification of highly connected "hub" (or "leader") cells and of follower populations subservient to them. Subsequent inactivation of members of either population, for example, using optogenetic approaches or photoablation, has confirmed the importance of hub cells as possible pacemakers. Hub cells appear to be enriched for the glucose phosphorylating enzyme glucokinase and for genes encoding other enzymes involved in glucose metabolism compared to follower cells. Recent findings have shown the relevance of cellular hierarchy in islets from multiple species including human, mouse and fish, and shown that it is preserved in vivo in the context of the fully vascularized and innervated islet. Importantly, connectivity is impaired by insults, which mimic the diabetic milieu, including high glucose and/or fatty levels, and by the ablation of genes associated with type 2 diabetes risk in genome-wide association studies. We discuss here the evidence for the existence of these networks and their failure in disease settings. We also briefly survey the challenges in understanding their properties.

Navigating the Depths and Avoiding the Shallows of Pancreatic Islet Cell Transcriptomes

Islet gene expression has been widely studied to better understand the transcriptional features that define a healthy β-cell. Transcriptomes of FACS-purified α-, β-, and δ-cells using bulk RNA-sequencing have facilitated our understanding of the complex network of cross talk between islet cells and its effects on β-cell function. However, these approaches were by design not intended to resolve heterogeneity between individual cells. Several recent studies used single-cell RNA sequencing (scRNA-Seq) to report considerable heterogeneity within mouse and human β-cells. In this Perspective, we assess how this newfound ability to assess gene expression at single-cell resolution has enhanced our understanding of β-cell heterogeneity. We conduct a comprehensive assessment of several single human β-cell transcriptome data sets and ask if the heterogeneity reported by these studies showed overlap and concurred with previously known examples of β-cell heterogeneity. We also illustrate the impact of the inevitable limitations of working at or below the limit of detection of gene expression at single cell resolution and their consequences for the quality of single-islet cell transcriptome data. Finally, we offer some guidance on when to opt for scRNA-Seq and when bulk sequencing approaches may be better suited.

Endogenous Pancreatic β Cell Regeneration: A Potential Strategy for the Recovery of β Cell Deficiency in Diabetes

Endogenous pancreatic β cell regeneration is a potential strategy for β cell expansion or neogenesis to treat diabetes. Regeneration can occur through stimulation of existing β cell replication or conversion of other pancreatic cells into β cells. Recently, various strategies and approaches for stimulation of endogenous β cell regeneration have been evaluated, but they were not suitable for clinical application. In this paper, we comprehensively review these strategies, and further discuss various factors involved in regulation of β cell regeneration under physiological or pathological conditions, such as mediators, transcription factors, signaling pathways, and potential pharmaceutical drugs. Furthermore, we discuss possible reasons for the failure of regenerative medicines in clinical trials, and possible strategies for improving β cell regeneration. As β cell heterogeneity and plasticity determines their function and environmental adaptability, we focus on β cell subtype markers and discuss the importance of research evaluating the characteristics of new β cells. In addition, based on the autoimmunologic features of type 1 diabetes, NOD/Lt-SCID-IL2rg ^null (NSG) mice grafted with human immune cells and β cells are recommended for use in evaluation of antidiabetic regenerative medicines. This review will further understand current advances in endogenous β cell regeneration, and provide potential new strategies for the treatment of diabetes focused on cell therapy.

Single-cell analyses of human islet cells reveal de-differentiation signatures

Human pancreatic islets containing insulin-secreting β-cells are notoriously heterogeneous in cell composition. Since β-cell failure is the root cause of diabetes, understanding this heterogeneity is of paramount importance. Recent reports have cataloged human islet transcriptome but not compared single β-cells in detail. Here, we scrutinized ex vivo human islet cells from healthy donors and show that they exhibit de-differentiation signatures. Using single-cell gene expression and immunostaining analyses, we found healthy islet cells to contain polyhormonal transcripts, and INS+ cells to express decreased levels of β-cell genes but high levels of progenitor markers. Rare cells that are doubly positive for progenitor markers/exocrine signatures, and endocrine/exocrine hormones were also present. We conclude that ex vivo human islet cells are plastic and can possibly de-/trans-differentiate across pancreatic cell fates, partly accounting for β-cell functional decline once isolated. Therefore, stabilizing β-cell identity upon isolation may improve its functionality.

Porcine Neonatal Pancreatic Cell Clusters Maintain Their Multipotency in Culture and After Transplantation

Ductal epithelium is primarily detected in porcine neonatal pancreatic cell clusters (NPCCs) bearing grafts, suggesting that transplants might exhibit progenitor-like phenotypes. Here we found that soon after NPCC isolation, PDX1⁺/insulin⁻ and SOX9⁺ pancreatic progenitor-like cells dramatically increased while dual-hormonal progenitor-like cells were routinely observed in NPCC culture. After transplantation (Tx), insulin⁺ cells increased and PDX1⁺ and SOX9⁺ cells gradually decreased in both non-diabetic (NDM) and streptozotocin-induced diabetic (DM) grafts over 2 months. Strikingly, a significantly higher percentage of insulin⁺ cells were detected in 9-day and 16-day, but not in 23-day, 30-day and 60-day grafts implying that hyperglycemia could only facilitate NPCC-derived β cells early post-Tx. A higher percentage of NPCC-derived β cells in early DM grafts was determined via an enhanced neogenic differentiation based on the detection of insulin⁺ cells budding out from PDX1⁺/SOX9⁺ epithelium. Interestingly, a drop in SOX9⁺ progenitor-like cells was detected 16 days post-Tx in DM grafts whilst PDX1⁺ cells do not show a significant difference until 60 days post-Tx between DM and NDM grafts, demonstrating that distinct progenitor-like populations fuel new β cells post-Tx. In conclusion, PDX1⁺/SOX9⁺ cells could be quickly activated after NPCC isolation, maintain their multipotency in culture and differentiate into new β cell post-Tx.

Gcg CreERT2 knockin mice as a tool for genetic manipulation in pancreatic alpha cells

AIMS/HYPOTHESIS

The Cre/loxP system, which enables tissue-specific manipulation of genes, is widely used in mice for diabetes research. Our aim was to develop a new Cre-driver mouse line for the specific and efficient manipulation of genes in pancreatic alpha cells.

METHODS

A Gcg ^CreERT2 knockin mouse, which expresses a tamoxifen-inducible form of Cre from the endogenous preproglucagon (Gcg) gene locus, was generated by homologous recombination. The new Gcg ^CreERT2 mouse line was crossed to the Rosa26 ^tdTomato (R26 ^tdTomato ) Cre reporter mouse line in order to evaluate the tissue specificity, efficiency and tamoxifen dependency of Gcg ^CreERT2 -mediated recombination. Cell types of pancreatic islets were identified using immunohistochemistry. Biochemical and physiological data, including blood glucose levels, plasma glucagon and glucagon-like peptide (GLP)-1 levels, and pancreatic glucagon content, were collected and used to assess the overall effect of Gcg gene targeting on Gcg ^CreERT2/w heterozygous mice.

RESULTS

Tamoxifen-treated Gcg ^CreERT2/w ;R26 ^tdTomato/w mice displayed Cre reporter activity, i.e. expression of tdTomato red fluorescent protein (RFP) in all known cells that produce proglucagon-derived peptides. In the adult pancreas, RFP was detected in 94-97% of alpha cells, whereas it was detected in a negligible (~ 0.2%) proportion of beta cells. While more than 98% of cells labelled with tamoxifen-induced RFP were glucagon-positive cells, 14-25% of pancreatic polypeptide (PP)-positive cells were also positive for RFP, indicating the presence of glucagon/PP bihormonal cell population. Tamoxifen-independent expression of RFP occurred in approximately 6% of alpha cells. In contrast to alpha cells and GLP-1-producing neurons, in which RFP expression persisted for at least 5 months after tamoxifen administration (presumably due to rare neogenesis in these cell types in adulthood), nearly half of RFP-positive intestinal L cells were replaced with RFP-negative L cells over the first 2 weeks after tamoxifen administration. Heterozygous Gcg ^CreERT2/w mice showed reduced Gcg mRNA levels in islets, but maintained normal levels of pancreatic and plasma glucagon. The mice did not exhibit any detectable baseline physiological abnormalities, at least in young adulthood.

CONCLUSIONS/INTERPRETATION

The newly developed Gcg ^CreERT2 knockin mouse shows faithful expression of CreER^T2 in pancreatic alpha cells, intestinal L cells and GLP-1-producing neurons. This mouse line will be particularly useful for manipulating genes in alpha cells, due to highly specific and efficient CreER^T2-mediated recombination in this cell type in the pancreas.

Single-Cell Analysis of Human Pancreas Reveals Transcriptional Signatures of Aging and Somatic Mutation Patterns

As organisms age, cells accumulate genetic and epigenetic errors that eventually lead to impaired organ function or catastrophic transformation such as cancer. Because aging reflects a stochastic process of increasing disorder, cells in an organ will be individually affected in different ways, thus rendering bulk analyses of postmitotic adult cells difficult to interpret. Here, we directly measure the effects of aging in human tissue by performing single-cell transcriptome analysis of 2,544 human pancreas cells from eight donors spanning six decades of life. We find that islet endocrine cells from older donors display increased levels of transcriptional noise and potential fate drift. By determining the mutational history of individual cells, we uncover a novel mutational signature in healthy aging endocrine cells. Our results demonstrate the feasibility of using single-cell RNA sequencing (RNA-seq) data from primary cells to derive insights into genetic and transcriptional processes that operate on aging human tissue.

Systematic single-cell analysis provides new insights into heterogeneity and plasticity of the pancreas

BACKGROUND

Diabetes mellitus is characterized by loss or dysfunction of insulin-producing β-cells in the pancreas, resulting in failure of blood glucose regulation and devastating secondary complications. Thus, β-cells are currently the prime target for cell-replacement and regenerative therapy. Triggering endogenous repair is a promising strategy to restore β-cell mass and normoglycemia in diabetic patients. Potential strategies include targeting specific β-cell subpopulations to increase proliferation or maturation. Alternatively, transdifferentiation of pancreatic islet cells (e.g. α- or δ-cells), extra-islet cells (acinar and ductal cells), hepatocytes, or intestinal cells into insulin-producing cells might improve glycemic control. To this end, it is crucial to systematically characterize and unravel the transcriptional program of all pancreatic cell types at the molecular level in homeostasis and disease. Furthermore, it is necessary to better determine the underlying mechanisms of β-cell maturation, maintenance, and dysfunction in diabetes, to identify and molecularly profile endocrine subpopulations with regenerative potential, and to translate the findings from mice to man. Recent approaches in single-cell biology started to illuminate heterogeneity and plasticity in the pancreas that might be targeted for β-cell regeneration in diabetic patients.

SCOPE OF REVIEW

This review discusses recent literature on single-cell analysis including single-cell RNA sequencing, single-cell mass cytometry, and flow cytometry of pancreatic cell types in the context of mechanisms of endogenous β-cell regeneration. We discuss new findings on the regulation of postnatal β-cell proliferation and maturation. We highlight how single-cell analysis recapitulates described principles of functional β-cell heterogeneity in animal models and adds new knowledge on the extent of β-cell heterogeneity in humans as well as its role in homeostasis and disease. Furthermore, we summarize the findings on cell subpopulations with regenerative potential that might enable the formation of new β-cells in diseased state. Finally, we review new data on the transcriptional program and function of rare pancreatic cell types and their implication in diabetes.

MAJOR CONCLUSION

Novel, single-cell technologies offer high molecular resolution of cellular heterogeneity within the pancreas and provide information on processes and factors that govern β-cell homeostasis, proliferation, and maturation. Eventually, these technologies might lead to the characterization of cells with regenerative potential and unravel disease-associated changes in gene expression to identify cellular and molecular targets for therapy.

Impact of islet architecture on β-cell heterogeneity, plasticity and function

Although β-cell heterogeneity was discovered more than 50 years ago, the underlying principles have been explored only during the past decade. Islet-cell heterogeneity arises during pancreatic development and might reflect the existence of distinct populations of progenitor cells and the developmental pathways of endocrine cells. Heterogeneity can also be acquired in the postnatal period owing to β-cell plasticity or changes in islet architecture. Furthermore, β-cell neogenesis, replication and dedifferentiation represent alternative sources of β-cell heterogeneity. In addition to a physiological role, β-cell heterogeneity influences the development of diabetes mellitus and its response to treatment. Identifying phenotypic and functional markers to discriminate distinct β-cell subpopulations and the mechanisms underpinning their regulation is warranted to advance current knowledge of β-cell function and to design novel regenerative strategies that target subpopulations of β cells. In this context, the Wnt/planar cell polarity (PCP) effector molecule Flattop can distinguish two unique β-cell subpopulations with specific transcriptional signatures, functional properties and differential responses to environmental stimuli. In vivo targeting of these β-cell subpopulations might, therefore, represent an alternative strategy for the future treatment of diabetes mellitus.

RNA Sequencing of Single Human Islet Cells Reveals Type 2 Diabetes Genes

Pancreatic islet cells are critical for maintaining normal blood glucose levels, and their malfunction underlies diabetes development and progression. We used single-cell RNA sequencing to determine the transcriptomes of 1,492 human pancreatic α, β, δ, and PP cells from non-diabetic and type 2 diabetes organ donors. We identified cell-type-specific genes and pathways as well as 245 genes with disturbed expression in type 2 diabetes. Importantly, 92% of the genes have not previously been associated with islet cell function or growth. Comparison of gene profiles in mouse and human α and β cells revealed species-specific expression. All data are available for online browsing and download and will hopefully serve as a resource for the islet research community.

Targeting insulin-producing beta cells for regenerative therapy

Pancreatic beta cells differ in terms of glucose responsiveness, insulin secretion and proliferative capacity; however, the molecular pathways that regulate this cellular heterogeneity are unknown. We have identified the Wnt-planar cell polarity (PCP) effector Flattop (FLTP) as a biomarker that identifies mature beta cells in the islets of Langerhans. Interestingly, three-dimensional architecture and Wnt-PCP ligands are sufficient to trigger mouse and human beta cell maturation. These results highlight the fact that novel biomarkers shed light on the long-standing mystery of beta cell heterogeneity and identify the Wnt-PCP pathway as triggering beta cell maturation. Understanding heterogeneity in the islets of Langerhans might allow targeting of beta cell subpopulations for regenerative therapy and provide building principles for stem cell-derived islets. This review summarises a presentation given at the 'Can we make a better beta cell?' symposium at the 2015 annual meeting of the EASD. It is accompanied by two other reviews on topics from this symposium (by Amin Ardestani and Kathrin Maedler, DOI: 10.1007/s00125-016-3892-9 , and by Harry Heimberg and colleagues, DOI: 10.1007/s00125-016-3879-6 ) and a commentary by the Session Chair, Shanta Persaud (DOI: 10.1007/s00125-016-3870-2 ).

Identification of proliferative and mature β-cells in the islets of Langerhans

Insulin-dependent diabetes is a complex multifactorial disorder characterized by loss or dysfunction of β-cells. Pancreatic β-cells differ in size, glucose responsiveness, insulin secretion and precursor cell potential; understanding the mechanisms that underlie this functional heterogeneity might make it possible to develop new regenerative approaches. Here we show that Fltp (also known as Flattop and Cfap126), a Wnt/planar cell polarity (PCP) effector and reporter gene acts as a marker gene that subdivides endocrine cells into two subpopulations and distinguishes proliferation-competent from mature β-cells with distinct molecular, physiological and ultrastructural features. Genetic lineage tracing revealed that endocrine subpopulations from Fltp-negative and -positive lineages react differently to physiological and pathological changes. The expression of Fltp increases when endocrine cells cluster together to form polarized and mature 3D islet mini-organs. We show that 3D architecture and Wnt/PCP ligands are sufficient to trigger β-cell maturation. By contrast, the Wnt/PCP effector Fltp is not necessary for β-cell development, proliferation or maturation. We conclude that 3D architecture and Wnt/PCP signalling underlie functional β-cell heterogeneity and induce β-cell maturation. The identification of Fltp as a marker for endocrine subpopulations sheds light on the molecular underpinnings of islet cell heterogeneity and plasticity and might enable targeting of endocrine subpopulations for the regeneration of functional β-cell mass in diabetic patients.

Use of the Fluidigm C1 platform for RNA sequencing of single mouse pancreatic islet cells

This study provides an assessment of the Fluidigm C1 platform for RNA sequencing of single mouse pancreatic islet cells. The system combines microfluidic technology and nanoliter-scale reactions. We sequenced 622 cells, allowing identification of 341 islet cells with high-quality gene expression profiles. The cells clustered into populations of α-cells (5%), β-cells (92%), δ-cells (1%), and pancreatic polypeptide cells (2%). We identified cell-type-specific transcription factors and pathways primarily involved in nutrient sensing and oxidation and cell signaling. Unexpectedly, 281 cells had to be removed from the analysis due to low viability, low sequencing quality, or contamination resulting in the detection of more than one islet hormone. Collectively, we provide a resource for identification of high-quality gene expression datasets to help expand insights into genes and pathways characterizing islet cell types. We reveal limitations in the C1 Fluidigm cell capture process resulting in contaminated cells with altered gene expression patterns. This calls for caution when interpreting single-cell transcriptomics data using the C1 Fluidigm system.

Research Resource: Genetic Labeling of Human Islet Alpha Cells

The 2 most abundant human pancreatic islet cell types are insulin-producing β-cells and glucagon-producing α-cells. Defined cis-regulatory elements from rodent Insulin genes have permitted genetic labeling of human islet β-cells, enabling lineage tracing and generation of human β-cell lines, but analogous elements for genetically labeling human α-cells with high specificity do not yet exist. To identify genetic elements that specifically direct reporter expression to human α-cells, we investigated noncoding sequences adjacent to the human GLUCAGON and ARX genes, which are expressed in islet α-cells. Elements with high evolutionary conservation were cloned into lentiviral vectors to direct fluorescent reporter expression in primary human islets. Based on the specificity of reporter expression for α- and β-cells, we found that rat glucagon promoter was not specific for human α-cells but that addition of human GLUCAGON untranslated region sequences substantially enhanced specificity of labeling in both cultured and transplanted islets to a degree not previously reported, to our knowledge. Specific transgene expression from these cis-regulatory sequences in human α-cells should enable targeted genetic modification and lineage tracing.

Characterization of Antibodies to Products of Proinsulin Processing Using Immunofluorescence Staining of Pancreas in Multiple Species

The efficient processing of proinsulin into mature insulin and C-peptide is often compromised under conditions of beta cell stress, including diabetes. Impaired proinsulin processing has been challenging to examine by immunofluorescence staining in pancreas tissue because the characterization of antibodies specific for proinsulin, proinsulin intermediates, processed insulin and C-peptide has been limited. This study aimed to identify and characterize antibodies that can be used to detect products of proinsulin processing by immunofluorescence staining in pancreata from different species (mice, rats, dog, pig and human). We took advantage of several knockout mouse lines that lack either an enzyme involved in proinsulin processing or an insulin gene. Briefly, we report antibodies that are specific for several proinsulin processing products, including: a) insulin or proinsulin that has been appropriately processed at the B-C junction; b) proinsulin with a non-processed B-C junction; c) proinsulin with a non-processed A-C junction; d) rodent-specific C-peptide 1; e) rodent-specific C-peptide 2; and f) human-specific C-peptide or proinsulin. In addition, we also describe two 'pan-insulin' antibodies that react with all forms of insulin and proinsulin intermediates, regardless of the species. These antibodies are valuable tools for studying proinsulin processing by immunofluorescence staining and distinguishing between proinsulin products in different species.

Rapid, high efficiency isolation of pancreatic ß-cells

The ability to isolate pure pancreatic ß-cells would greatly aid multiple areas of diabetes research. We developed a fluorescent exendin-4-like neopeptide conjugate for the rapid purification and isolation of functional mouse pancreatic β-cells. By targeting the glucagon-like peptide-1 receptor with the fluorescent conjugate, β-cells could be quickly isolated by flow cytometry and were >99% insulin positive. These studies were confirmed by immunostaining, microscopy and gene expression profiling on isolated cells. Gene expression profiling studies of cytofluorometrically sorted β-cells from 4 and 12 week old NOD mice provided new insights into the genetic programs at play of different stages of type-1 diabetes development. The described isolation method should have broad applicability to the β-cell field.

Novel Observations From Next-Generation RNA Sequencing of Highly Purified Human Adult and Fetal Islet Cell Subsets

Understanding distinct gene expression patterns of normal adult and developing fetal human pancreatic α- and β-cells is crucial for developing stem cell therapies, islet regeneration strategies, and therapies designed to increase β-cell function in patients with diabetes (type 1 or 2). Toward that end, we have developed methods to highly purify α-, β-, and δ-cells from human fetal and adult pancreata by intracellular staining for the cell-specific hormone content, sorting the subpopulations by flow cytometry, and, using next-generation RNA sequencing, we report the detailed transcriptomes of fetal and adult α- and β-cells. We observed that human islet composition was not influenced by age, sex, or BMI, and transcripts for inflammatory gene products were noted in fetal β-cells. In addition, within highly purified adult glucagon-expressing α-cells, we observed surprisingly high insulin mRNA expression, but not insulin protein expression. This transcriptome analysis from highly purified islet α- and β-cell subsets from fetal and adult pancreata offers clear implications for strategies that seek to increase insulin expression in type 1 and type 2 diabetes.

Glucagon-reactive islet-infiltrating CD8 T cells in NOD mice

Type 1 diabetes is characterized by T-cell-mediated destruction of the insulin-producing β cells in pancreatic islets. A number of islet antigens recognized by CD8 T cells that contribute to disease pathogenesis in non-obese diabetic (NOD) mice have been identified; however, the antigenic specificities of the majority of the islet-infiltrating cells have yet to be determined. The primary goal of the current study was to identify candidate antigens based on the level and specificity of expression of their genes in mouse islets and in the mouse β cell line MIN6. Peptides derived from the candidates were selected based on their predicted ability to bind H-2K(d) and were examined for recognition by islet-infiltrating T cells from NOD mice. Several proteins, including those encoded by Abcc8, Atp2a2, Pcsk2, Peg3 and Scg2, were validated as antigens in this way. Interestingly, islet-infiltrating T cells were also found to recognize peptides derived from proglucagon, whose expression in pancreatic islets is associated with α cells, which are not usually implicated in type 1 diabetes pathogenesis. However, type 1 diabetes patients have been reported to have serum autoantibodies to glucagon, and NOD mouse studies have shown a decrease in α cell mass during disease pathogenesis. Our finding of islet-infiltrating glucagon-specific T cells is consistent with these reports and suggests the possibility of α cell involvement in development and progression of disease.

Reduced Tyk2 gene expression in β-cells due to natural mutation determines susceptibility to virus-induced diabetes

Accumulating evidence suggests that viruses play an important role in the development of diabetes. Although the diabetogenic encephalomyocarditis strain D virus induces diabetes in restricted lines of inbred mice, the susceptibility genes to virus-induced diabetes have not been identified. We report here that novel Tyrosine kinase 2 (Tyk2) gene mutations are present in virus-induced diabetes-sensitive SJL and SWR mice. Mice carrying the mutant Tyk2 gene on the virus-resistant C57BL/6 background are highly sensitive to virus-induced diabetes. Tyk2 gene expression is strongly reduced in Tyk2-mutant mice, associated with low Tyk2 promoter activity, and leads to decreased expression of interferon-inducible genes, resulting in significantly compromised antiviral response. Tyk2-mutant pancreatic β-cells are unresponsive even to high dose of Type I interferon. Reversal of virus-induced diabetes could be achieved by β-cell-specific Tyk2 gene expression. Thus, reduced Tyk2 gene expression in pancreatic β-cells due to natural mutation is responsible for susceptibility to virus-induced diabetes.

Diabetes can be caused by viral infections in humans and some inbred mice, suggesting genetic predisposition. Here the authors show that mutations in Tyk2 gene underlie susceptibility to virus-induced diabetes in mice, due to Tyk2 requirement for antiviral response in insulin-producing cells.

In vitro reprogramming of pancreatic alpha cells towards a beta cell phenotype following ectopic HNF4α expression

There is currently a shortage of organ donors available for pancreatic beta cell transplantation into diabetic patients. An alternative source of beta cells is pre-existing pancreatic cells. While we know that beta cells can arise directly from alpha cells during pancreatic regeneration we do not understand the molecular basis for the switch in phenotype. The aim of the present study was to investigate if hepatocyte nuclear factor 4 alpha (HNF4α), a transcription factor essential for a normal beta cell phenotype, could induce the reprogramming of alpha cells towards potential beta cells. We utilised an in vitro model of pancreatic alpha cells, the murine αTC1-9 cell line. We initially characterised the αTC1-9 cell line before and following adenovirus-mediated ectopic expression of HNF4α. We analysed the phenotype at transcript and protein level and assessed its glucose-responsiveness. Ectopic HNF4α expression in the αTC1-9 cell line induced a change in morphology (1.7-fold increase in size), suppressed glucagon expression, induced key beta cell-specific markers (insulin, C-peptide, glucokinase, GLUT2 and Pax4) and pancreatic polypeptide (PP) and enabled the cells to secrete insulin in a glucose-regulated manner. In conclusion, HNF4α reprograms alpha cells to beta-like cells.

Chronological analysis with fluorescent timer reveals unique features of newly generated β-cells

Although numerous studies have uncovered the molecular mechanisms regulating pancreas development, it remains to be clarified how β-cells arise from progenitors and how recently specified β-cells are different from preexisting β-cells. To address these questions, we developed a mouse model in which the insulin 1 promoter drives DsRed-E5 Timer fluorescence that shifts its spectrum over time. In transgenic embryos, green fluorescent β-cells were readily detected by FACS and could be distinguished from mature β-cells only until postnatal day 0, suggesting that β-cell neogenesis occurs exclusively during embryogenesis. Transcriptome analysis with green fluorescent cells sorted by FACS demonstrated that newly differentiated β-cells highly expressed progenitor markers, such as Sox9, Neurog3, and Pax4, showing the progenitor-like features of newborn β-cells. Flow cytometric analysis of cell cycle dynamics showed that green fluorescent cells were mostly quiescent, and differentiated β-cells were mitotically active. Thus, the precise temporal resolution of this model enables us to dissect the unique features of newly specified insulin-producing cells, which could enhance our understanding of β-cell neogenesis for future cell therapy.

Generation and characterization of MafA-Kusabira Orange mice

MafA and MafB are basic leucine zipper transcription factors expressed in mature pancreatic β- and α-cells, respectively. MafA is not only an insulin gene transcription factor but is also critical for the maturation and maintenance of β-cell function, whereas MafB is expressed in immature β-cells during development and in compromised β-cells in diabetes. In this study, we developed a mouse model to easily trace the promoter activity of MafA in β-cells as a tool for studying β-cell differentiation, maturation, regeneration and function using the expression of the fluorescent protein Kusabira Orange (KOr) driven by the BAC-mafA promoter. The expression of KOr was highly restricted to β-cells in the transgenic pancreas. By crossing MafA-KOr mice with MafB(GFP/+) reporter mice, simultaneous monitoring of MafA and MafB expressions in the isolated islets was successfully performed. This system can be a useful tool for examining dynamic changes in the differentiation and function of pancreatic islets by visualizing the expressions of MafA and MafB.

Immunohistochemical study of α- and β-cell distribution in human pancreatic Langerhans islets of various types

Various types of insulin- and glucagon-containing endocrine cell distribution were found by double staining with antibodies to insulin and glucagon in the pancreatic autopsy material from subjects without carbohydrate metabolism disorders. The cell composition of the islets and their morphogenetic maturity depended on the vascularization degree. Insulin-containing cells predominated in small clusters of endocrine cells and in islets with few capillaries, while glucagon predominated in large islets with rich vascularization. A scheme of development and differentiation of Langerhans islets in the adult human pancreas was presented.

IL-6-dependent proliferation of alpha cells in mice with partial pancreatic-duct ligation

AIMS/HYPOTHESIS

IL-6 was recently shown to control alpha cell expansion. As beta cells expand following partial pancreatic-duct ligation (PDL) in adult mice, we investigated whether PDL also causes alpha cells to expand and whether IL-6 signalling is involved. As alpha cells can reprogramme to beta cells in a number of beta cell (re)generation models, we examined whether this phenomenon also exists in PDL pancreas.

METHODS

Total alpha cell volume, alpha cell size and total glucagon content were evaluated in equivalent portions of PDL- and sham-operated mouse pancreases. Proliferation of glucagon(+) cells was assessed by expression of the proliferation marker Ki67. Inter-conversions between alpha and beta cells were monitored in transgenic mice with conditional cell-type-specific labelling. The role of IL-6 in regulating alpha cell proliferation was evaluated by in situ delivery of an IL-6-inactivating antibody.

RESULTS

In response to PDL surgery, alpha cell volume in the ligated tissue was increased threefold, glucagon content fivefold and alpha cell size by 10%. Activation of alpha cell proliferation in PDL pancreas required IL-6 signalling. A minor fraction of alpha cells derived from beta cells, whereas no evidence for alpha to beta cell conversion was obtained.

CONCLUSIONS/INTERPRETATION

In PDL-injured adult mouse pancreas, new alpha cells are generated mainly by IL-6-dependent self-duplication and seldom by reprogramming of beta cells.

Grg3/TLE3 and Grg1/TLE1 induce monohormonal pancreatic β-cells while repressing α-cell functions

In the pancreas, α- and β-cells possess a degree of plasticity. In vitro differentiation of pluripotent cells yields mostly α- and polyhormonal β-like cells, indicating a gap in understanding of how functional monohormonal β-cells are formed and of the endogenous repressive mechanisms used to maintain β-cell identity. We show that the corepressor Grg3 is expressed in almost all β-cells throughout embryogenesis to adulthood. However, Grg3 is expressed in fewer nascent α-cells and is progressively lost from α-cells as endocrine cells mature into adulthood. We show that mouse Grg3(+/-) β-cells have increased α-specific gene expression, and Grg3(+/-) pancreata have more α-cells and more polyhormonal cells, indicating that Grg3 is required for the physiologic maintenance of monohormonal β-cell identity. Ectopic expression of Grg3 in α-cells represses glucagon and Arx, and the addition of Pdx1 induces Glut2 expression and glucose-responsive insulin secretion. Furthermore, we found that Grg1 is the predominant Groucho expressed in human β-cells but acts functionally similarly to Grg3. Overall, we find that Grg3 and Grg1 establish a monohormonal β-cell identity, and Groucho family members may be useful tools or markers for making functional β-cells.

The pancreatic β-cell transcriptome and integrated-omics

PURPOSE OF REVIEW

β Cells represent one of many cell types in heterogeneous pancreatic islets and play the central role in maintaining glucose homeostasis, such that disrupting β-cell function leads to diabetes. This review summarizes the methods for isolating and characterizing β cells, and describes integrated 'omics' approaches used to define the β cell by its transcriptome and proteome.

RECENT FINDINGS

RNA sequencing and mass spectrometry-based protein identification have now identified RNA and protein profiles for mouse and human pancreatic islets and β cells, and for β-cell lines. Recent publications have outlined these profiles and, more importantly, have begun to assign the presence or absence of specific genes and regulatory molecules to β-cell function and dysfunction. Overall, researchers have focused on understanding the pathophysiology of diabetes by connecting genome, transcriptome, proteome, and regulatory RNA profiles with findings from genome-wide association studies.

SUMMARY

Studies employing these relatively new techniques promise to identify specific genes or regulatory RNAs with altered expression as β-cell function begins to deteriorate in the spiral toward the development of diabetes. The ultimate goal is to identify the potential therapeutic targets to prevent β-cell dysfunction and thereby better treat the individual with diabetes.

VIDEO ABSTRACT

http://links.lww.com/COE/A5.

Quality of Air-Transported Human Islets for Single Islet Cell Preparations

In new generation medical therapies for type 1 diabetes mellitus (DM), cell-based approaches using pancreatic islets have attracted significant attention worldwide. In particular, dispersed islet cells obtained from isolated pancreatic islets have been a valuable source in the cell biology and tissue engineering fields. Our experimental approach to the development of new islet-based DM therapies consisted of creating a monolithic islet cell sheet format using dispersed islet cells. In this experiment, we explored the potential of internationally transporting human islets from Alberta, Canada to Tokyo, Japan and obtaining viable dispersed islet cells. A total of 34 batches of isolated and purified human islets were transported using a commercial air courier service. Prior to shipping, the human islets had been in culture for 0-108 h at the University of Alberta. The transportation period from Alberta to Tokyo was 2-5 days. The transported human islet cells were enzymatically dispersed as single cells in Tokyo. The number of single islet cells decreased as the number of transportation days increased. In contrast, cell viability was maintained regardless of the number of transportation days. The preshipment culture time had no effect on the number or viability of single cells dispersed in Tokyo. When dispersed single islet cells were plated on laminin-5-coated temperature-responsive polymer-grafted culture dishes, the cells showed favorable attachment followed by extension as a monolithic format. The present study demonstrated that long-distance transported human islets are a viable cell source for experiments utilizing dispersed human islet cells.

α-Cells are dispensable in postnatal morphogenesis and maturation of mouse pancreatic islets

Glucagon-producing α-cells are the second-most abundant cell type in the islet. Whereas α-cells make up less than 20% of the cells in a mature mouse islet, they occupy a much larger proportion of the pancreatic endocrine cell population during the early postnatal period, the time when morphological and functional maturation occurs to form adult islets. To determine whether α-cells have a role in postnatal islet development, a diphtheria toxin-mediated α-cell ablation mouse model was established. Rapid and persistent depletion of α-cells was achieved by daily injection of the toxin for 2 wk starting at postnatal day 1 (P1). Total pancreatic glucagon content in the α-cell-ablated mice was undetectable at P14 and still less than 0.3% of that of the control mice at 4 mo of age. Histological analyses revealed that formation of spherical islets occurred normally, and the islet size distribution was not changed despite the near-total lack of α-cells. Furthermore, there were no differences in expression of β-cell maturation marker proteins, including urocortin 3 and glucose transporter 2, in the α-cell-ablated islets at P14. Mice lacking α-cells grew normally and appeared healthy. Both glucose and insulin tolerance tests demonstrated that the α-cell-ablated mice had normal glucose homeostasis. These results indicate that α-cells do not play a critical role in postnatal islet morphogenesis or functional maturation of β-cells.

Interaction between cytokines and inflammatory cells in islet dysfunction, insulin resistance and vascular disease

Inflammation is an established pathogenic player in insulin resistance, islet demise and atherosclerosis. The complex interactions between cytokines, immune cells and affected tissues result in sustained inflammation in diabetes and atherosclerosis. 12- and 15-lipoxygenase (LO), such as 12/15-LO, produces a variety of metabolites through peroxidation of fatty acids and potentially contributes to the complex molecular crosstalk at the site of inflammation. 12- and 15-LO pathways are frequently activated in tissues affected by diabetes and atherosclerosis including adipose tissue (AT), islets and the vasculature. Moreover, mice with whole body and tissue-specific knockout of 12/15-LO are protected against insulin resistance, hyperglycaemia and atherosclerosis supporting functional contribution of 12- and 15-LO pathways in diabetes and atherosclerosis. Recently, it has emerged that there is a temporal regulation of the particular isoforms of 12- and 15-LO in human AT and islets during the development of type 1 and type 2 diabetes and obesity. Analyses of tissues affected by diabetes and atherosclerosis also implied the roles of interleukin (IL)-12 and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-1 (NOX-1) in islets and IL-17A in atherosclerosis. Future studies should aim to test the efficacy of inhibitions of these mediators for treatment of diabetes and atherosclerosis.

β-cell dedifferentiation in diabetes is important, but what is it?

This commentary discusses the concept of β-cell dedifferentiation in diabetes, which is important but not well defined. A broad interpretation is that a state of differentiation has been lost, which means changes in gene expression as well as in structural and functional elements. Thus, a fully mature healthy β cell will have its unique differentiation characteristics, but maturing cells and old β cells will have different patterns of gene expression and might therefore be considered as dedifferentiated. The meaning of dedifferentiation is now being debated because β cells in the diabetic state lose components of their differentiated state, which results in severe dysfunction of insulin secretion. The major cause of this change is thought to be glucose toxicity (glucotoxicity) and that lowering glucose levels with treatment results in some restoration of function. An issue to be discussed is whether dedifferentiated β cells return to a multipotent precursor cell phenotype or whether they follow a different pathway of dedifferentiation.

Incorporation of bone marrow cells in pancreatic pseudoislets improves posttransplant vascularization and endocrine function

Failure of revascularization is known to be the major reason for the poor outcome of pancreatic islet transplantation. In this study, we analyzed whether pseudoislets composed of islet cells and bone marrow cells can improve vascularization and function of islet transplants. Pancreatic islets isolated from Syrian golden hamsters were dispersed into single cells for the generation of pseudoislets containing 4×10³ cells. To create bone marrow cell-enriched pseudoislets 2×10³ islet cells were co-cultured with 2×10³ bone marrow cells. Pseudoislets and bone marrow cell-enriched pseudoislets were transplanted syngeneically into skinfold chambers to study graft vascularization by intravital fluorescence microscopy. Native islet transplants served as controls. Bone marrow cell-enriched pseudoislets showed a significantly improved vascularization compared to native islets and pseudoislets. Moreover, bone marrow cell-enriched pseudoislets but not pseudoislets normalized blood glucose levels after transplantation of 1000 islet equivalents under the kidney capsule of streptozotocin-induced diabetic animals, although the bone marrow cell-enriched pseudoislets contained only 50% of islet cells compared to pseudoislets and native islets. Fluorescence microscopy of bone marrow cell-enriched pseudoislets composed of bone marrow cells from GFP-expressing mice showed a distinct fraction of cells expressing both GFP and insulin, indicating a differentiation of bone marrow-derived cells to an insulin-producing cell-type. Thus, enrichment of pseudoislets by bone marrow cells enhances vascularization after transplantation and increases the amount of insulin-producing tissue. Accordingly, bone marrow cell-enriched pseudoislets may represent a novel approach to increase the success rate of islet transplantation.

Glucose-stimulated calcium dynamics in islets of Langerhans in acute mouse pancreas tissue slices

In endocrine cells within islets of Langerhans calcium ions couple cell stimulation to hormone secretion. Since the advent of modern fluorimetry, numerous in vitro studies employing primarily isolated mouse islets have investigated the effects of various secretagogues on cytoplasmic calcium, predominantly in insulin-secreting beta cells. Due to technical limitations, insights of these studies are inherently limited to a rather small subpopulation of outermost cells. The results also seem to depend on various factors, like culture conditions and duration, and are not always easily reconcilable with findings in vivo. The main controversies regard the types of calcium oscillations, presence of calcium waves, and the level of synchronized activity. Here, we set out to combine the in situ acute mouse pancreas tissue slice preparation with noninvasive fluorescent calcium labeling and subsequent confocal laser scanning microscopy to shed new light on the existing controversies utilizing an innovative approach enabling the characterization of responses in many cells from all layers of islets. Our experiments reproducibly showed stable fast calcium oscillations on a sustained plateau rather than slow oscillations as the predominant type of response in acute tissue slices, and that calcium waves are the mechanistic substrate for synchronization of oscillations. We also found indirect evidence that even a large amplitude calcium signal was not sufficient and that metabolic activation was necessary to ensure cell synchronization upon stimulation with glucose. Our novel method helped resolve existing controversies and showed the potential to help answer important physiological questions, making it one of the methods of choice for the foreseeable future.

Subpopulations of GFP-marked mouse pancreatic β-cells differ in size, granularity, and insulin secretion

There is growing information about the heterogeneity of pancreatic β-cells and how it relates to insulin secretion. This study used the approach of flow cytometry to sort and analyze β-cells from transgenic mice expressing green fluorescent protein (GFP) under the control of the mouse insulin I gene promoter. Three populations of β-cells with differing GFP brightness could be identified, which were classified as GFP-low, GFP-medium, and GFP-bright. The GFP-medium population comprised about 70% of the total. The GFP-low population had less insulin secretion as determined by the reverse hemolytic plaque assay and reduced insulin gene expression. Additionally, all three subpopulations of β-cells were found in mice of varying ages (embryonic d 15.5 and postnatal wk 1-9). The three populations from the youngest had larger cells (forward scatter) and less granularity (side scatter) than those from the adults. This approach opens up new ways to advance knowledge about β-cell heterogeneity.

Research resource: RNA-Seq reveals unique features of the pancreatic β-cell transcriptome

The pancreatic β-cell is critical for the maintenance of glycemic control. Knowing the compendium of genes expressed in β-cells will further our understanding of this critical cell type and may allow the identification of future antidiabetes drug targets. Here, we report the use of next-generation sequencing to obtain nearly 1 billion reads from the polyadenylated RNA of islets and purified β-cells from mice. These data reveal novel examples of β-cell-specific splicing events, promoter usage, and over 1000 long intergenic noncoding RNA expressed in mouse β-cells. Many of these long intergenic noncoding RNA are β-cell specific, and we hypothesize that this large set of novel RNA may play important roles in β-cell function. Our data demonstrate unique features of the β-cell transcriptome.

Ectopic transgenic expression of NKX2.2 induces differentiation of adult pancreatic progenitors and mediates islet regeneration

To pursue islet regeneration in situ in adult pancreas with a diabetic animal model, we used ultrasound targeted microbubble destruction (UTMD) to deliver islet transcription factor genes to the pancreas of STZ-treated rats, specifically using a piggyBac transposon gene delivery system for long-term transgene expression of Nkx2.2 in STZ rat pancreas. Our results show that Nkx2.2 gene induced robust proliferation and differentiation of adult pancreatic progenitors. Our high-resolution confocal images precisely displayed how one single pancreatic progenitor cell differentiated into islets-like clusters and, further, into mature islets with normal morphology in situ in postnatal pancreas. Nkx2.2 targeted to the pancreas by UTMD induces pancreatic progenitor cell proliferation and differentiation with subsequent islet regeneration and cure of STZ-induced diabetes for three months.

Block of Kv1.7 potassium currents increases glucose-stimulated insulin secretion

Glucose-stimulated insulin secretion (GSIS) relies on repetitive, electrical spiking activity of the beta cell membrane. Cyclic activation of voltage-gated potassium channels (K_v) generates an outward, ‘delayed rectifier’ potassium current, which drives the repolarizing phase of each spike and modulates insulin release. Although several K_v channels are expressed in pancreatic islets, their individual contributions to GSIS remain incompletely understood. We take advantage of a naturally occurring cone-snail peptide toxin, Conkunitzin-S1 (Conk-S1), which selectively blocks K_v1.7 channels to provide an intrinsically limited, finely graded control of total beta cell delayed rectifier current and hence of GSIS. Conk-S1 increases GSIS in isolated rat islets, likely by reducing K_v1.7-mediated delayed rectifier currents in beta cells, which yields increases in action potential firing and cytoplasmic free calcium. In rats, Conk-S1 increases glucose-dependent insulin secretion without decreasing basal glucose. Thus, we conclude that K_v1.7 contributes to the membrane-repolarizing current of beta cells during GSIS and that block of this specific component of beta cell K_v current offers a potential strategy for enhancing GSIS with minimal risk of hypoglycaemia during metabolic disorders such as Type 2 diabetes.

Musashi expression in β-cells coordinates insulin expression, apoptosis and proliferation in response to endoplasmic reticulum stress in diabetes

Diabetes is associated with the death and dysfunction of insulin-producing pancreatic β-cells. In other systems, Musashi genes regulate cell fate via Notch signaling, which we recently showed regulates β-cell survival. Here we show for the first time that human and mouse adult islet cells express mRNA and protein of both Musashi isoforms, as well Numb/Notch/Hes/neurogenin-3 pathway components. Musashi expression was observed in insulin/glucagon double-positive cells during human fetal development and increased during directed differentiation of human embryonic stem cells (hESCs) to the pancreatic lineage. De-differentiation of β-cells with activin A increased Msi1 expression. Endoplasmic reticulum (ER) stress increased Msi2 and Hes1, while it decreased Ins1 and Ins2 expression, revealing a molecular link between ER stress and β-cell dedifferentiation in type 2 diabetes. These effects were independent of changes in Numb protein levels and Notch activation. Overexpression of MSI1 was sufficient to increase Hes1, stimulate proliferation, inhibit apoptosis and reduce insulin expression, whereas Msi1 knockdown had the converse effects on proliferation and insulin expression. Overexpression of MSI2 resulted in a decrease in MSI1 expression. Taken together, these results demonstrate overlapping, but distinct roles for Musashi-1 and Musashi-2 in the control of insulin expression and β-cell proliferation. Our data also suggest that Musashi is a novel link between ER stress and the compensatory β-cell proliferation and the loss of β-cell gene expression seen in specific phases of the progression to type 2 diabetes.