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Glucose plays a key role in shaping pancreatic [beta] cell function. Thus, deciphering the mechanisms by which this nutrient stimulates [beta] cells holds therapeutic promise for combating [beta] cell failure in type 2 diabetes (T2D). [beta] cells respond to hyperglycemia in part by rewiring their mRNA metabolism, yet the mechanisms governing these changes remain poorly understood. Here, we identify a requirement for the RNA-binding protein PCBP2 in maintaining [beta] cell function basally and during sustained hyperglycemic challenge. PCBP2 was induced in primary mouse islets incubated with elevated glucose and was required to adapt insulin secretion. Transcriptomic analysis of primary Pcbp2-deficient [beta] cells revealed impacts on basal and glucose-regulated mRNAs encoding core components of the insulin secretory pathway. Accordingly, Pcbp2-deficient [beta] cells exhibited defects in calcium flux, insulin granule ultrastructure and exocytosis, and the amplification pathway of insulin secretion. Further, PCBP2 was induced by glucose in primary human islets, was downregulated in islets from T2D donors, and impacted genes commonly altered in islets from donors with T2D and linked to single-nucleotide polymorphisms associated with T2D. Thus, these findings establish a paradigm for PCBP2 in governing basal and glucose-adaptive gene programs critical for shaping the functional state of [beta] cells., Introduction Glucose uptake and metabolism are the most physiologically important driver of insulin release from pancreatic islet [beta] cells, a highly specialized class of endocrine cells that secrete this hormone [...]

The recognition of β cell dedifferentiation in type 2 diabetes raises the translational relevance of mechanisms that direct and maintain β cell identity. LIM domain-binding protein 1 (LDB1) nucleates multimeric transcriptional complexes and establishes promoter-enhancer looping, thereby directing fate assignment and maturation of progenitor populations. Many terminally differentiated endocrine cell types, however, remain enriched for LDB1, but its role is unknown. Here, we have demonstrated a requirement for LDB1 in maintaining the terminally differentiated status of pancreatic β cells. Inducible ablation of LDB1 in mature β cells impaired insulin secretion and glucose homeostasis. Transcriptomic analysis of LDB1-depleted β cells revealed the collapse of the terminally differentiated gene program, indicated by a loss of β cell identity genes and induction of the endocrine progenitor factor neurogenin 3 (NEUROG3). Lineage tracing confirmed that LDB1-depleted, insulin-negative β cells express NEUROG3 but do not adopt alternate endocrine cell fates. In primary mouse islets, LDB1 and its LIM homeodomain-binding partner islet 1 (ISL1) were coenriched at chromatin sites occupied by pancreatic and duodenal homeobox 1 (PDX1), NK6 homeobox 1 (NKX6.1), forkhead box A2 (FOXA2), and NK2 homeobox 2 (NKX2.2) - factors that co-occupy active enhancers in 3D chromatin domains in human islets. Indeed, LDB1 was enriched at active enhancers in human islets. Thus, LDB1 maintains the terminally differentiated state of β cells and is a component of active enhancers in both murine and human islets.

Protein tyrosine phosphatase N2 (PTPN2) is a type 1 diabetes (T1D) candidate gene identified from human genome-wide association studies. PTPN2 is highly expressed in human and murine islets and becomes elevated upon inflammation and models of T1D, suggesting that PTPN2 may be important for β-cell survival in the context of T1D. To test whether PTPN2 contributed to β-cell dysfunction in an inflammatory environment, we generated a β-cell–specific deletion of Ptpn2 in mice (PTPN2-β knockout [βKO]). Whereas unstressed animals exhibited normal metabolic profiles, low- and high-dose streptozotocin-treated PTPN2-βKO mice displayed hyperglycemia and accelerated death, respectively. Furthermore, cytokine-treated Ptpn2 -KO islets resulted in impaired glucose-stimulated insulin secretion, mitochondrial defects, and reduced glucose-induced metabolic flux, suggesting β-cells lacking Ptpn2 are more susceptible to inflammatory stress associated with T1D due to maladaptive metabolic fitness. Consistent with the phenotype, proteomic analysis identified an important metabolic enzyme, ATP-citrate lyase, as a novel PTPN2 substrate. Article Highlights: Although the type 1 diabetes (T1D) susceptibility factor protein tyrosine phosphatase N2 (PTPN2) has been shown to function in β-cells in vitro, an unbiased assessment of its in vivo function in the context of T1D was lacking. β-Cells deleted for Ptpn2 have reduced mitochondrial function with age and are more susceptible to inflammatory stress associated with T1D due to maladaptive metabolic fitness. Consistent with the phenotype, the metabolic enzyme ATP-citrate lyase was identified as a novel PTPN2 substrate. In the absence of PTPN2, β-cells are not able to metabolically compensate for an inflammatory environment. [ABSTRACT FROM AUTHOR]

In a society where physical activity is limited and food supply is abundant, metabolic diseases are becoming a serious epidemic. Metabolic syndrome (MetS) represents a cluster of metabolically related symptoms such as obesity, hypertension, dyslipidemia, and carbohydrate intolerance, and significantly increases type 2 diabetes mellitus risk. Insulin resistance and hyperinsulinemia are consistent characteristics of MetS, but which of these features is the initiating insult is still widely debated. Regardless, both of these conditions trigger adverse responses from the pancreatic [beta] cell, which is responsible for producing, storing, and releasing insulin to maintain glucose homeostasis. The observation that the degree of [beta] cell dysfunction correlates with the severity of MetS highlights the need to better understand [beta] cell dysfunction in the development of MetS. This Review focuses on the current understanding from rodent and human studies of the progression of [beta] cell responses during the development of MetS, as well as recent findings addressing the complexity of [beta] cell identity and heterogeneity within the islet during disease progression. The differential responses observed in [beta] cells together with the heterogeneity in disease phenotypes within the patient population emphasize the need to better understand the mechanisms behind [beta] cell adaptation, identity, and dysfunction in MetS., Introduction Nutrient excess and sedentary behaviors of our modern society are forerunners of metabolic syndrome (MetS), a condition that represents a cluster of metabolically related symptoms that can have life-threatening [...]

Notch signaling regulates differentiation of the pancreatic endocrine lineage during embryogenesis, but the role of Notch in mature [beta] cells is unclear. We found that islets derived from lean mice show modest [beta] cell Notch activity, which increases in obesity and in response to high glucose. This response appeared maladaptive, as mice with [beta] cell-specific-deficient Notch transcriptional activity showed improved glucose tolerance when subjected to high-fat diet feeding. Conversely, mice with [beta] cell-specific Notch gain of function ([beta]-NICD) had a progressive loss of [beta] cell maturity, due to proteasomal degradation of MafA, leading to impaired glucose-stimulated insulin secretion and glucose intolerance with aging or obesity. Surprisingly, Notch-active [beta] cells had increased proliferative capacity, leading to increased but dysfunctional [beta] cell mass. These studies demonstrate a dynamic role for Notch in developed [beta] cells for simultaneously regulating [beta] cell function and proliferation., Introduction[beta] Cell mass and function adapt to the insulin requirements of the organism to maintain euglycemia across a wide range of pathophysiology, such as insulin resistance, pregnancy, or aging (1). [...]

Loss of β cell identity, the presence of polyhormonal cells, and reprogramming are emerging as important features of β cell dysfunction in patients with type 1 and type 2 diabetes. In this study, we have demonstrated that the transcription factor NKX2.2 is essential for the active maintenance of adult β cell identity as well as function. Deletion of Nkx2.2 in β cells caused rapid onset of a diabetic phenotype in mice that was attributed to loss of insulin and downregulation of many β cell functional genes. Concomitantly, NKX2.2-deficient murine β cells acquired non-β cell endocrine features, resulting in populations of completely reprogrammed cells and bihormonal cells that displayed hybrid endocrine cell morphological characteristics. Molecular analysis in mouse and human islets revealed that NKX2.2 is a conserved master regulatory protein that controls the acquisition and maintenance of a functional, monohormonal β cell identity by directly activating critical β cell genes and actively repressing genes that specify the alternative islet endocrine cell lineages. This study demonstrates the highly volatile nature of the β cell, indicating that acquiring and sustaining β cell identity and function requires not only active maintaining of the expression of genes involved in β cell function, but also continual repression of closely related endocrine gene programs., Introduction Type 1 and type 2 diabetes mellitus (T1D and T2D) are chronic conditions in which glycemic control becomes severely dysregulated. Although there are many causes of diabetes, one of [...]

Pancreatic agenesis is a human disorder caused by defects in pancreas development. To date, only a few genes have been linked to pancreatic agenesis in humans, with mutations in pancreatic and duodenal homeobox 1 (PDX1) and pancreas-specific transcription factor la (PTF1A) reported in only 5 families with described cases. Recently, mutations in GATA6 have been identified in a large percentage of human cases, and a GATA4 mutant allele has been implicated in a single case. In the mouse, Gata4 and Gata6 are expressed in several endoderm-d erived tissues, including the pancreas. To analyze the functions of GATA4 and/or GATA6 during mouse pan-creatic development, we generated pancreas-specific deletions of Gata4 and Gata6. Surprisingly, loss of either Gata4 or Gata6 in the pancreas resulted in only mild pancreatic defects, which resolved postnatally. However, simultaneous deletion ofboth Gata4 and Gata6 in the pancreas caused severe pancreatic agenesis due to disrup-tion ofpancreatic progenitor cell proliferation, defects in branching morphogenesis, and a subsequent failure to induce the differentiation of progenitor cells expressing carboxypeptidase Al (CPA1) and neurogenin 3 (NEUROG3). These studies address the conserved and nonconserved mechanisms underlying GATA4 and GATA6 function during pancreas development and provide a new mouse model to characterize the underlying developmental defects associated with pancreatic agenesis., Introduction In vertebrates, the mature pancreas comprises primarily 3 morphologically and functionally distinct tissues that are denved from cells within the embryonic foregut endoderm. Nearly 90% of the pancreas is [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2007.09.057 Byline: Christina S. Chao (a)(b), Zoe L. Loomis (a), Jacqueline E. Lee (c), Lori Sussel (a) Keywords: Nkx2.2; NeuroD1; Islet development; [alpha] Cells; Cell differentiation; Glucagon; Ghrelin; Genetic analysis Abstract: Nkx2.2 and NeuroD1 are vital for proper differentiation of pancreatic islet cell types. Nkx2.2-null mice fail to form [beta] cells, have reduced numbers of [alpha] and PP cells and display an increase in ghrelin-producing I[micro] cells. NeuroD1-null mice display a reduction of [alpha] and [beta] cells after embryonic day (e) 17.5. To begin to determine the relative contributions of Nkx2.2 and NeuroD1 in islet development, we generated Nkx2.2-/-;NeuroD1-/- double knockout (DKO) mice. As expected, the DKO mice fail to form [beta] cells, similar to the Nkx2.2-null mice, suggesting that the Nkx2.2 phenotype may be dominant over the NeuroD1 phenotype in the [beta] cells. Surprisingly, however, the [alpha], PP and I[micro] phenotypes of the Nkx2.2-null mice are partially rescued by the simultaneous elimination of NeuroD1, even at early developmental time points when NeuroD1 null mice alone do not display a phenotype. Our results indicate that Nkx2.2 and NeuroD1 interact to regulate pancreatic islet cell fates, and this epistatic relationship is cell-type dependent. Furthermore, this study reveals a previously unappreciated early function of NeuroD1 in regulating the specification of [alpha], PP and I[micro] cells. Author Affiliation: (a) University of Colorado at Denver and Health Science Center, Biochemistry and Molecular Genetics Department, Aurora, CO 80045, USA (b) Medical Scientist Training Program and Cell and Developmental Biology Program, UCHSC, Aurora, CO 80045, USA (c) University of Colorado at Boulder, Department of Molecular, Cellular, and Developmental Biology, Boulder, CO 80309, USA Article History: Received 17 April 2007; Revised 27 September 2007; Accepted 27 September 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.ydbio.2006.06.046 Byline: Kimberly Decker (a), Devorah C. Goldman (b), Catherine L. Grasch (b), Lori Sussel (a) Keywords: Gata4; Gata6; Pancreas development; Islet Abstract: Gata4, Gata5, and Gata6 represent a subfamily of zinc-finger transcriptional regulators that are important in the development and differentiation of numerous tissues, including many endodermally-derived organs. We demonstrate that Gata4 and Gata6 have overlapping expression patterns in the early pancreatic epithelium. Later, Gata4 becomes restricted to exocrine tissue and Gata6 becomes restricted to a subset of endocrine cells. In addition, we show Gata6, but not Gata4, physically interacts with Nkx2.2, an essential islet transcription factor. To begin determining the roles that Gata4 and Gata6 play during pancreatic development, we expressed Gata4-Engrailed and Gata6-Engrailed dominant repressor fusion proteins in the pancreatic epithelium and in the islet. At e17.5, transgenic Gata6-Engrailed embryos exhibit two distinct phenotypes: a complete absence of pancreas or a reduction in pancreatic tissue. In the embryos that do form pancreas, there is a significant reduction of all pancreatic cell types, with the few differentiated endocrine cells clustered within, or in close proximity to, enlarged ductal structures. Conversely, the majority of transgenic Gata4-Engrailed embryos do not have a pancreatic phenotype. This study suggests that Gata6 is an important regulator of pancreas specification. Author Affiliation: (a) Program in Molecular Biology, Department of Biochemistry and Molecular Genetics, University of Colorado at Denver Health Sciences Center, Aurora, CO 80045, USA (b) Department of Biochemistry and Molecular Genetics, University of Colorado at Denver Health Sciences Center, Aurora, CO 80045, USA Article History: Received 13 February 2006; Revised 2 June 2006; Accepted 27 June 2006

The pancreatic islet is necessary for maintaining glucose homeostasis. Within the pancreatic islet, the homeodomain protein Nkx2.2 is essential for the differentiation of all insulin-producing [beta] cells and a subset of glucagon-producing [alpha] cells (1). Mice lacking Nkx2.2 have relatively normal sized islets, but a large number of cells within the mutant islet fail to produce any of the four major isle hormones. In this study we demonstrate that Nkx2.2 mutant endocrine cells have been replaced by cells that produce ghrelin, an appetite-promoting peptide predominantly found in the stomach. Intriguingly, normal mouse pancreas also contains a small population of ghrelin-producing cells, defining a new islet '[epsilon]' cell population. The expansion of ghrelin-producing cells at the expense of [beta] cells may be a general phenomenon, because we demonstrate that Pax4 mutant mice display a similar phenotype. We propose that insulin and ghrelin cells share a common progenitor and that Nkx2.2 and Pax4 are required to specify or maintain differentiation of the [beta] cell fate. This finding also suggests that there is a genetic component underlying the balance between insulin and ghrelin in regulating glucose metabolism. islet | Nkx2.2 | Pax4 | cell-type specification

Pancreatic [beta] cells play a central role in maintaining glucose homeostasis because they secrete insulin in response to increased level of blood glucose; failure of this capacity constitutes a major component of the pathogenesis of diabetes. The identification of key regulators of pancreatic [beta]-cell differentiation is relevant for the overall understanding of this process and for future experiments aimed at regenerating insulin-producing [beta] cells from pancreatic or embryonic stem cells. Several studies using transgenic or knockout mice have established that the development and function of pancreatic [beta] cells are controlled by several genes encoding specific transcription factors. By inactivating the homeobox gene Pax4, we previously demonstrated that its function is required for the formation of mature insulin-producing cells. Here, we show that during pancreas ontogeny, Pax4 is expressed in differentiating endocrine cells, including cells. Pax4 activity appears essential for appropriate initiation of [beta]-cell differentiation because loss of Pax4 prevents the expression of Pdx1, HB9 and insulin in [beta]-cell precursors. This role of Pax4 appears to be accomplished via its genetic interaction with another homeobox gene, Nkx2.2. Keywords: Pax4; Nkx2.2; Pax6; Mouse; Pancreas; [beta]-cell differentiation