ß-Cell Insulin Secretion Requires the Ubiquitin Ligase COP1.

A variety of signals finely tune insulin secretion by pancreatic ß cells to prevent both hyper-and hypoglycemic states. Here, we show that post-translational regulation of the transcription factors ETV1, ETV4, and ETV5 by the ubiquitin ligase COP1 (also called RFWD2) in ß cells is critical for insulin secretion. Mice lacking COP1 in ß cells developed diabetes due to insulin granule docking defects that were fully rescued by genetic deletion of Etv1, Etv4, and Etv5. Genes regulated by ETV1, ETV4, or ETV5 in the absence of mouse COP1 were enriched in human diabetes-associated genes, suggesting that they also influence human ß-cell pathophysiology. In normal ß cells, ETV4 was stabilized upon membrane depolarization and limited insulin secretion under hyperglycemic conditions. Collectively, our data reveal that ETVs negatively regulate insulin secretion for the maintenance of normoglycemia.

Diabetic ß Cells: To Be or Not To Be?

ß cell dysfunction with subsequent apoptosis is considered a significant contributor to the development of type 2 diabetes. Emerging data from Talchai et al. suggest ß cell dedifferentiation as an alternative mechanism of insulin insufficiency that might be more amenable to intervention in at least a subset of patients.

All mixed up: defining roles for ß-cell subtypes in mature islets.

Following differentiation during fetal development, ß cells further adapt to their postnatal role through functional maturation. While adult islets are thought to contain functionally mature ß cells, recent analyses of transgenic rodent and human pancreata reveal a number of novel heterogeneity markers in mammalian ß cells. The marked heterogeneity long after maturation raises the prospect that diverse populations harbor distinct roles aside from glucose-stimulated insulin secretion. In this review, we outline our current understanding of the ß-cell maturation process, emphasize recent literature on novel heterogeneity markers, and offer perspectives on reconciling the findings from these two areas.

PDX1 dynamically regulates pancreatic ductal adenocarcinoma initiation and maintenance.

Aberrant activation of embryonic signaling pathways is frequent in pancreatic ductal adenocarcinoma (PDA), making developmental regulators therapeutically attractive. Here we demonstrate diverse functions for pancreatic and duodenal homeobox 1 (PDX1), a transcription factor indispensable for pancreas development, in the progression from normal exocrine cells to metastatic PDA. We identify a critical role for PDX1 in maintaining acinar cell identity, thus resisting the formation of pancreatic intraepithelial neoplasia (PanIN)-derived PDA. Upon neoplastic transformation, the role of PDX1 changes from tumor-suppressive to oncogenic. Interestingly, subsets of malignant cells lose PDX1 expression while undergoing epithelial-to-mesenchymal transition (EMT), and PDX1 loss is associated with poor outcome. This stage-specific functionality arises from profound shifts in PDX1 chromatin occupancy from acinar cells to PDA. In summary, we report distinct roles of PDX1 at different stages of PDA, suggesting that therapeutic approaches against this potential target need to account for its changing functions at different stages of carcinogenesis. These findings provide insight into the complexity of PDA pathogenesis and advocate a rigorous investigation of therapeutically tractable targets at distinct phases of PDA development and progression.

Brg1 promotes both tumor-suppressive and oncogenic activities at distinct stages of pancreatic cancer formation.

Pancreatic ductal adenocarcinoma (PDA) develops predominantly through pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) precursor lesions. Pancreatic acinar cells are reprogrammed to a "ductal-like" state during PanIN-PDA formation. Here, we demonstrate a parallel mechanism operative in mature duct cells during which functional cells undergo "ductal retrogression" to form IPMN-PDA. We further identify critical antagonistic roles for Brahma-related gene 1 (Brg1), a catalytic subunit of the SWI/SNF complexes, during IPMN-PDA development. In mature duct cells, Brg1 inhibits the dedifferentiation that precedes neoplastic transformation, thus attenuating tumor initiation. In contrast, Brg1 promotes tumorigenesis in full-blown PDA by supporting a mesenchymal-like transcriptional landscape. We further show that JQ1, a drug that is currently being tested in clinical trials for hematological malignancies, impairs PDA tumorigenesis by both mimicking some and inhibiting other Brg1-mediated functions. In summary, our study demonstrates the context-dependent roles of Brg1 and points to potential therapeutic treatment options based on epigenetic regulation in PDA.

Non-xenogeneic expansion and definitive endoderm differentiation of human pluripotent stem cells in an automated bioreactor.

Scalable processes are requisite for the robust biomanufacturing of human pluripotent stem cell (hPSC)-derived therapeutics. Toward this end, we demonstrate the xeno-free expansion and directed differentiation of human embryonic and induced pluripotent stem cells to definitive endoderm (DE) in a controlled stirred suspension bioreactor (SSB). Based on previous work on converting hPSCs to insulin-producing progeny, differentiation of two hPSC lines was optimized in planar cultures yielding up to 87% FOXA2+ /SOX17+ cells. Next, hPSCs were propagated in an SSB with controlled pH and dissolved oxygen. Cultures displayed a 10- to 12-fold increase in cell number over 5-6 days with the maintenance of pluripotency (>85% OCT4+ ) and viability (>85%). For differentiation, SSB cultures yielded up to 89% FOXA2+ /SOX17+ cells or ~ 8 DE cells per seeded hPSC. Specification to DE cell fate was consistently more efficient in the bioreactor compared to planar cultures. Hence, a tunable strategy is established that is suitable for the xeno-free manufacturing of DE cells from different hPSC lines in scalable SSBs. This study advances bioprocess development for producing a wide gamut of human DE cell-derived therapeutics.

VHL-mediated disruption of Sox9 activity compromises ß-cell identity and results in diabetes mellitus.

Precise functioning of the pancreatic ß cell is paramount to whole-body glucose homeostasis, and ß-cell dysfunction contributes significantly to diabetes mellitus. Using transgenic mouse models, we demonstrate that deletion of the von Hippel-Lindau (Vhlh) gene (encoding an E3 ubiquitin ligase implicated in, among other functions, oxygen sensing in pancreatic ß cells) is deleterious to canonical ß-cell gene expression. This triggers erroneous expression of factors normally active in progenitor cells, including effectors of the Notch, Wnt, and Hedgehog signaling cascades. Significantly, an up-regulation of the transcription factor Sox9, normally excluded from functional ß cells, occurs upon deletion of Vhlh. Sox9 plays important roles during pancreas development but does not have a described role in the adult ß cell. ß-Cell-specific ectopic expression of Sox9 results in diabetes mellitus from similar perturbations in ß-cell identity. These findings reveal that assaults on the ß cell that impact the differentiation state of the cell have clear implications toward our understanding of diabetes mellitus.

Pancreatic pericytes originate from the embryonic pancreatic mesenchyme.

The embryonic origin of pericytes is heterogeneous, both between and within organs. While pericytes of coelomic organs were proposed to differentiate from the mesothelium, a single-layer squamous epithelium, the embryonic origin of pancreatic pericytes has yet to be reported. Here, we show that adult pancreatic pericytes originate from the embryonic pancreatic mesenchyme. Our analysis indicates that pericytes of the adult mouse pancreas originate from cells expressing the transcription factor Nkx3.2. In the embryonic pancreas, Nkx3.2-expressing cells constitute the multilayered mesenchyme, which surrounds the pancreatic epithelium and supports multiple events in its development. Thus, we traced the fate of the pancreatic mesenchyme. Our analysis reveals that pancreatic mesenchymal cells acquire various pericyte characteristics, including gene expression, typical morphology, and periendothelial location, during embryogenesis. Importantly, we show that the vast majority of pancreatic mesenchymal cells differentiate into pericytes already at embryonic day 13.5 and progressively acquires a more mature pericyte phenotype during later stages of pancreas organogenesis. Thus, our study indicates the embryonic pancreatic mesenchyme as the primary origin to adult pancreatic pericytes. As pericytes of other coelomic organs were suggested to differentiate from the mesothelium, our findings point to a distinct origin of these cells in the pancreas. Thus, our study proposes a complex ontogeny of pericytes of coelomic organs.

Controlled induction of human pancreatic progenitors produces functional beta-like cells in vitro.

Directed differentiation of human pluripotent stem cells into functional insulin-producing beta-like cells holds great promise for cell replacement therapy for patients suffering from diabetes. This approach also offers the unique opportunity to study otherwise inaccessible aspects of human beta cell development and function in vitro. Here, we show that current pancreatic progenitor differentiation protocols promote precocious endocrine commitment, ultimately resulting in the generation of non-functional polyhormonal cells. Omission of commonly used BMP inhibitors during pancreatic specification prevents precocious endocrine formation while treatment with retinoic acid followed by combined EGF/KGF efficiently generates both PDX1(+) and subsequent PDX1(+)/NKX6.1(+) pancreatic progenitor populations, respectively. Precise temporal activation of endocrine differentiation in PDX1(+)/NKX6.1(+) progenitors produces glucose-responsive beta-like cells in vitro that exhibit key features of bona fide human beta cells, remain functional after short-term transplantation, and reduce blood glucose levels in diabetic mice. Thus, our simplified and scalable system accurately recapitulates key steps of human pancreas development and provides a fast and reproducible supply of functional human beta-like cells.

Antithetical NFATc1-Sox2 and p53-miR200 signaling networks govern pancreatic cancer cell plasticity.

In adaptation to oncogenic signals, pancreatic ductal adenocarcinoma (PDAC) cells undergo epithelial-mesenchymal transition (EMT), a process combining tumor cell dedifferentiation with acquisition of stemness features. However, the mechanisms linking oncogene-induced signaling pathways with EMT and stemness remain largely elusive. Here, we uncover the inflammation-induced transcription factor NFATc1 as a central regulator of pancreatic cancer cell plasticity. In particular, we show that NFATc1 drives EMT reprogramming and maintains pancreatic cancer cells in a stem cell-like state through Sox2-dependent transcription of EMT and stemness factors. Intriguingly, NFATc1-Sox2 complex-mediated PDAC dedifferentiation and progression is opposed by antithetical p53-miR200c signaling, and inactivation of the tumor suppressor pathway is essential for tumor dedifferentiation and dissemination both in genetically engineered mouse models (GEMM) and human PDAC. Based on these findings, we propose the existence of a hierarchical signaling network regulating PDAC cell plasticity and suggest that the molecular decision between epithelial cell preservation and conversion into a dedifferentiated cancer stem cell-like phenotype depends on opposing levels of p53 and NFATc1 signaling activities.

Taming the young and restless--epigenetic gene regulation in pancreas and beta-cell precursors.

The in vivo assessment of epigenetic changes during mouse pancreatic beta­cell differentiation reveals surprising differences to directed, in vitro differentiation of human embryonic stem cells. New findings reported in this issue of The EMBO Journal further identify Ezh2 as a critical determinant of endocrine progenitor number and could instruct improved protocols for stem cell-based therapies.

Human stem cells from single blastomeres reveal pathways of embryonic or trophoblast fate specification.

Mechanisms of initial cell fate decisions differ among species. To gain insights into lineage allocation in humans, we derived ten human embryonic stem cell lines (designated UCSFB1-10) from single blastomeres of four 8-cell embryos and one 12-cell embryo from a single couple. Compared with numerous conventional lines from blastocysts, they had unique gene expression and DNA methylation patterns that were, in part, indicative of trophoblast competence. At a transcriptional level, UCSFB lines from different embryos were often more closely related than those from the same embryo. As predicted by the transcriptomic data, immunolocalization of EOMES, T brachyury, GDF15 and active ß-catenin revealed differential expression among blastomeres of 8- to 10-cell human embryos. The UCSFB lines formed derivatives of the three germ layers and CDX2-positive progeny, from which we derived the first human trophoblast stem cell line. Our data suggest heterogeneity among early-stage blastomeres and that the UCSFB lines have unique properties, indicative of a more immature state than conventional lines.

Rebranding asymptomatic type 1 diabetes: the case for autoimmune beta cell disorder as a pathological and diagnostic entity.

The asymptomatic phase of type 1 diabetes is recognised by the presence of beta cell autoantibodies in the absence of hyperglycaemia. We propose that an accurate description of this stage is provided by the name 'Autoimmune Beta Cell Disorder' (ABCD). Specifically, we suggest that this nomenclature and diagnosis will, in a proactive manner, shift the paradigm towards type 1 diabetes being first and foremost an immune-mediated disease and only later a metabolic disease, presaging more active therapeutic intervention in the asymptomatic stage of disease, before end-stage beta cell failure. Furthermore, we argue that accepting ABCD as a diagnosis will be critical in order to accelerate pharmaceutical, academic and public activities leading to clinical trials that could reverse beta cell autoimmunity and halt progression to symptomatic insulin-requiring type 1 diabetes. We recognize that there are both opportunities and challenges in the implementation of the ABCD concept but hope that the notion of 'asymptomatic autoimmune disease' as a disorder will be widely discussed and eventually accepted.

Atypical flat lesions derive from pancreatic acinar cells.

OBJECTIVES: Pancreatic ductal adenocarcinoma (PDAC) is thought to derive from different precursor lesions including the recently identified atypical flat lesions (AFL). While all precursor lesions and PDAC share ductal characteristics, there is an ongoing debate about the cellular origin of the different PDAC precursor lesions. In particular, pancreatic acinar cells have previously been shown to display a remarkable plasticity being able to undergo ductal dedifferentiation in the context of oncogenic stimuli. METHODS: Histological analyses were performed in a murine PDAC model that specifically expresses oncogenic Kras in adult pancreatic acinar cells. Occurrence, characterization, and lineage tracing of AFLs were investigated. RESULTS: Upon expression of oncogenic Kras in adult pancreatic acinar cells, AFLs with typical morphology and expression profile arise. Lineage tracing confirmed that the AFLs were of acinar origin. CONCLUSIONS: Using a murine PDAC model, this study identifies pancreatic acinar cells as a cellular source for AFLs.

GLI1 is regulated through Smoothened-independent mechanisms in neoplastic pancreatic ducts and mediates PDAC cell survival and transformation.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by the deregulation of the hedgehog signaling pathway. The Sonic Hedgehog ligand (Shh), absent in the normal pancreas, is highly expressed in pancreatic tumors and is sufficient to induce neoplastic precursor lesions in mouse models. We investigated the mechanism of Shh signaling in PDAC carcinogenesis by genetically ablating the canonical bottleneck of hedgehog signaling, the transmembrane protein Smoothened (Smo), in the pancreatic epithelium of PDAC-susceptible mice. We report that multistage development of PDAC tumors is not affected by the deletion of Smo in the pancreas, demonstrating that autocrine Shh-Ptch-Smo signaling is not required in pancreatic ductal cells for PDAC progression. However, the expression of Gli target genes is maintained in Smo-negative ducts, implicating alternative means of regulating Gli transcription in the neoplastic ductal epithelium. In PDAC tumor cells, we find that Gli transcription is decoupled from upstream Shh-Ptch-Smo signaling and is regulated by TGF-beta and KRAS, and we show that Gli1 is required both for survival and for the KRAS-mediated transformed phenotype of cultured PDAC cancer cells.

NFATc1 Links EGFR Signaling to Induction of Sox9 Transcription and Acinar-Ductal Transdifferentiation in the Pancreas.

BACKGROUND & AIMS: Oncogenic mutations in KRAS contribute to the development of pancreatic ductal adenocarcinoma, but are not sufficient to initiate carcinogenesis. Secondary events, such as inflammation-induced signaling via the epidermal growth factor receptor (EGFR) and expression of the SOX9 gene, are required for tumor formation. Herein we sought to identify the mechanisms that link EGFR signaling with activation of SOX9 during acinar-ductal metaplasia, a transdifferentiation process that precedes pancreatic carcinogenesis. METHODS: We analyzed pancreatic tissues from Kras(G12D);pdx1-Cre and Kras(G12D);NFATc1(Δ/Δ);pdx1-Cre mice after intraperitoneal administration of caerulein, vs cyclosporin A or dimethyl sulfoxide (controls). Induction of EGFR signaling and its effects on the expression of Nuclear factor of activated T cells c1 (NFATc1) or SOX9 were investigated by quantitative reverse-transcription polymerase chain reaction, immunoblot, and immunohistochemical analyses of mouse and human tissues and acinar cell explants. Interactions between NFATc1 and partner proteins and effects on DNA binding or chromatin modifications were studied using co-immunoprecipitation and chromatin immunoprecipitation assays in acinar cell explants and mouse tissue. RESULTS: EGFR activation induced expression of NFATc1 in metaplastic areas from patients with chronic pancreatitis and in pancreatic tissue from Kras(G12D) mice. EGFR signaling also promoted formation of a complex between NFATc1 and C-JUN in dedifferentiating mouse acinar cells, leading to activation of Sox9 transcription and induction of acinar-ductal metaplasia. Pharmacologic inhibition of NFATc1 or disruption of the Nfatc1 gene inhibited EGFR-mediated induction of Sox9 transcription and blocked acinar-ductal transdifferentiation and pancreatic cancer initiation in mice. CONCLUSIONS: EGFR signaling induces expression of NFATc1 and Sox9, leading to acinar cell transdifferentiation and initiation of pancreatic cancer. Strategies designed to disrupt this pathway might be developed to prevent pancreatic cancer initiation in high-risk patients with chronic pancreatitis.

Life and death of ß cells in Type 1 diabetes: A comprehensive review.

Type 1 diabetes (T1D) is an autoimmune disorder characterized by the destruction of insulin-producing pancreatic ß cells. Immune modulators have achieved some success in modifying the course of disease progression in T1D. However, there are parallel declines in C-peptide levels in treated and control groups after initial responses. In this review, we discuss mechanisms of ß cell death in T1D that involve necrosis and apoptosis. New technologies are being developed to enable visualization of insulitis and ß cell mass involving positron emission transmission that identifies ß cell ligands and magnetic resonance imaging that can identify vascular leakage. Molecular signatures that identify ß cell derived insulin DNA that is released from dying cells have been described and applied to clinical settings. We also consider changes in ß cells that occur during disease progression including the induction of DNA methyltransferases that may affect the function and differentiation of ß cells. Our findings from newer data suggest that the model of chronic long standing ß cell killing should be reconsidered. These studies indicate that the pathophysiology is accelerated in the peridiagnosis period and manifest by increased rates of ß cell killing and insulin secretory impairments over a shorter period than previously thought. Finally, we consider cellular explanations to account for the ongoing loss of insulin production despite continued immune therapy that may identify potential targets for treatment. The progressive decline in ß cell function raises the question as to whether ß cell failure that is independent of immune attack may be involved.

Nr5a2 maintains acinar cell differentiation and constrains oncogenic Kras-mediated pancreatic neoplastic initiation.

OBJECTIVES: Emerging evidence from mouse models suggests that mutant Kras can drive the development of pancreatic ductal adenocarcinoma (PDA) precursors from acinar cells by enforcing ductal de-differentiation at the expense of acinar identity. Recently, human genome-wide association studies have identified NR5A2, a key regulator of acinar function, as a susceptibility locus for human PDA. We investigated the role of Nr5a2 in exocrine maintenance, regeneration and Kras driven neoplasia. DESIGN: To investigate the function of Nr5a2 in the pancreas, we generated mice with conditional pancreatic Nr5a2 deletion (PdxCre(late); Nr5a2(c/c)). Using this model, we evaluated acinar differentiation, regeneration after caerulein pancreatitis and Kras driven pancreatic neoplasia in the setting of Nr5a2 deletion. RESULTS: We show that Nr5a2 is not required for the development of the pancreatic acinar lineage but is important for maintenance of acinar identity. Nr5a2 deletion leads to destabilisation of the mature acinar differentiation state, acinar to ductal metaplasia and loss of regenerative capacity following acute caerulein pancreatitis. Loss of Nr5a2 also dramatically accelerates the development of oncogenic Kras driven acinar to ductal metaplasia and PDA precursor lesions. CONCLUSIONS: Nr5a2 is a key regulator of acinar plasticity. It is required for maintenance of acinar identity and re-establishing acinar fate during regeneration. Nr5a2 also constrains pancreatic neoplasia driven by oncogenic Kras, providing functional evidence supporting a potential role as a susceptibility gene for human PDA.

Transcriptional analysis of pluripotency reveals the Hippo pathway as a barrier to reprogramming.

Pluripotent stem cells are derived from culture of early embryos or the germline and can be induced by reprogramming of somatic cells. Barriers to reprogramming that stabilize the differentiated state and have tumor suppression functions are expected to exist. However, we have a limited understanding of what such barriers might be. To find novel barriers to reprogramming to pluripotency, we compared the transcriptional profiles of the mouse germline with pluripotent and somatic cells, in vivo and in vitro. There is a remarkable global expression of the transcriptional program for pluripotency in primordial germ cells (PGCs). We identify parallels between PGC reprogramming to pluripotency and human germ cell tumorigenesis, including the loss of LATS2, a tumor suppressor kinase of the Hippo pathway. We show that knockdown of LATS2 increases the efficiency of induction of pluripotency in human cells. LATS2 RNAi, unlike p53 RNAi, specifically enhances the generation of fully reprogrammed iPS cells without accelerating cell proliferation. We further show that LATS2 represses reprogramming in human cells by post-transcriptionally antagonizing TAZ but not YAP, two downstream effectors of the Hippo pathway. These results reveal transcriptional parallels between germ cell transformation and the generation of iPS cells and indicate that the Hippo pathway constitutes a barrier to cellular reprogramming.

Control of cell identity in pancreas development and regeneration.

The endocrine and exocrine cells in the adult pancreas are not static, but can change their differentiation state in response to injury or stress. This concept of cells in flux means that there may be ways to generate certain types of cells (such as insulin-producing ß-cells) and prevent formation of others (such as transformed neoplastic cells). We review different aspects of cell identity in the pancreas, discussing how cells achieve their identity during embryonic development and maturation, and how this identity remains plastic, even in the adult pancreas.