Transcription factors, pancreatic development, and β-cell maintenance

Islet transplantation into brown adipose tissue can delay immune rejection

Type 1 diabetes is an autoimmune disease characterized by insulin-producing β cell destruction. Although islet transplantation restores euglycemia and improves patient outcomes, an ideal transplant site remains elusive. Brown adipose tissue (BAT) has a highly vascularized and antiinflammatory microenvironment. Because these tissue features can promote islet graft survival, we hypothesized that islets transplanted into BAT will maintain islet graft and BAT function while delaying immune-mediated rejection. We transplanted syngeneic and allogeneic islets into BAT or under the kidney capsule of streptozotocin-induced diabetic NOD.Rag and NOD mice to investigate islet graft function, BAT function, metabolism, and immune-mediated rejection. Islet grafts within BAT restored euglycemia similarly to kidney capsule controls. Islets transplanted in BAT maintained expression of islet hormones and transcription factors and were vascularized. Compared with those in kidney capsule and euglycemic mock-surgery controls, no differences in glucose or insulin tolerance, thermogenic regulation, or energy expenditure were observed with islet grafts in BAT. Immune profiling of BAT revealed enriched antiinflammatory macrophages and T cells. Compared with the kidney capsule control, there were significant delays in autoimmune and allograft rejection of islets transplanted in BAT, possibly due to increased antiinflammatory immune populations. Our data support BAT as an alternative islet transplant site that may improve graft survival.

S6K1 controls epigenetic plasticity for the expression of pancreatic α/β cell marker genes

The failure of insulin production by pancreatic β cells is a common hallmark of type 1 diabetes mellitus (T1DM). Because administration of exogenous insulin is associated with diabetes-derived complications, endogenous α to β cell transition can be an attractive alternative. Although decreased β cell size and hypoinsulinaemia have been observed in S6K1-deficient mice, the molecular mechanism underlying the involvement of S6K1 in the transcriptional regulation of insulin remains elusive. Here, we show that the hypoinsulinaemic phenotype of S6K1-deficient mice stems from the dysregulated transcription of a set of genes required for insulin and glucagon production. First, we observed that increased expression of α cell marker genes and decreased expression of β cell marker genes in pancreas tissues from S6K1-deficient mice. Furthermore, S6K1 was highly activated in murine β cell line, βTC6, compared to murine α cell line αTC1. In both α and β cells, active S6K1 promoted the transcription of β cell marker genes, including insulin, whereas S6K1 inhibition increased the transcription of α cell marker genes. Moreover, S6K1 mediated pancreatic gene regulation by modifying two histone marks (activating H3K4me3 and repressing H3K27me3) on gene promoters. These results suggest that S6K1 drives the α to β transition through the epigenetic regulation of cell-specific genes, including insulin and glucagon. This novel role of S6K1 in islet cells provides basic clues to establish therapeutic strategies against T1DM.

Investigating the role of transcription factors of pancreas development in pancreatic cancer

Pancreatic cancer (PC) is the seventh most common cause of cancer-related deaths worldwide that kills more than 300,000 people every year. Prognosis of PC is very poor with a five-year survival rate about 5%. The most common and highly observed type of PC is pancreatic ductal adenocarcinoma (PDAC). It is preceded by the progression of precursor lesions such as Pancreatic Intraepithelial Neoplasia (PanIN), Intraductal Papillary Neoplasm (IPMN) and Mucinous Cystic Neoplasm (MCN). PanIN is the most common among these premalignant lesions. Genes orchestrating the origin and differentiation of cells during organogenesis have the tendency to produce tumor cells in response to activating or inactivating mutations. Based on the following premise, we discuss the role of transcription factors (TFs) of pancreas development and cell fate differentiation in PC. Pancreas/duodenum homeobox protein 1 (PDX1), Pancreas transcription factor 1 subunit alpha (PTF1A), Nuclear receptor subfamily 5 group A member 2 (NR5A2), Hepatocyte nuclear factor 1-alpha (HNF1A) and Hepatocyte nuclear factor 1-beta (HNF1B) play vital role in the development and differentiation of pancreatic precursor cells. Mutated KRAS induces abnormalities in the regular function of these TFs which in turn cause abnormal cell growth and proliferation that leads to cancer. Thus, these TFs are highly susceptible for the origin of PC. Therefore, we propose that these TFs can be treated as therapeutic targets for the development of anticancer drugs.

Expression of the ZIP/SLC39A transporters in β-cells: a systematic review and integration of multiple datasets

BACKGROUND

Pancreatic β-cells require a constant supply of zinc to maintain normal insulin secretory function. Following co-exocytosis with insulin, zinc is replenished via the Zrt- and Irt-like (ZIP; SLC39A) family of transporters. However the ZIP paralogues of particular importance for zinc uptake, and associations with β-cell function and Type 2 Diabetes remain largely unexplored. We retrieved and statistically analysed publically available microarray and RNA-seq datasets to perform a systematic review on the expression of β-cell SLC39A paralogues. We complemented results with experimental data on expression profiling of human islets and mouse β-cell derived MIN6 cells, and compared transcriptomic and proteomic sequence conservation between human, mouse and rat.

RESULTS

The 14 ZIP paralogues have 73-98% amino sequence conservation between human and rodents. We identified 18 datasets for β-cell SLC39A analysis, which compared relative expression to non-β-cells, and expression in response to PDX-1 activity, cytokines, glucose and type 2 diabetic status. Published expression data demonstrate enrichment of transcripts for ZIP7 and ZIP9 transporters within rodent β-cells and of ZIP6, ZIP7 and ZIP14 within human β-cells, with ZIP1 most differentially expressed in response to cytokines and PDX-1 within rodent, and ZIP6 in response to diabetic status in human and glucose in rat. Our qPCR expression profiling data indicate that SLC39A6, -9, -13, and - 14 are the highest expressed paralogues in human β-cells and Slc39a6 and -7 in MIN6 cells.

CONCLUSIONS

Our systematic review, expression profiling and sequence alignment reveal similarities and potentially important differences in ZIP complements between human and rodent β-cells. We identify ZIP6, ZIP7, ZIP9, ZIP13 and ZIP14 in human and rodent and ZIP1 in rodent as potentially biologically important for β-cell zinc trafficking. We propose ZIP6 and ZIP7 are key functional orthologues in human and rodent β-cells and highlight these zinc importers as important targets for exploring associations between zinc status and normal physiology of β-cells and their decline in Type 2 Diabetes.

Cellular reprogramming for pancreatic β-cell regeneration: clinical potential of small molecule control

Recent scientific breakthroughs in stem cell biology suggest that a sustainable treatment approach to cure diabetes mellitus (DM) can be achieved in the near future. However, the transplantation complexities and the difficulty in obtaining the stem cells from adult cells of pancreas, liver, bone morrow and other cells is a major concern. The epoch-making strategy of transcription-factor based cellular reprogramming suggest that these barriers could be overcome, and it is possible to reprogram any cells into functional β cells. Contemporary biological and analytical techniques help us to predict the key transcription factors needed for β-cell regeneration. These β cell-specific transcription factors could be modulated with diverse reprogramming protocols. Among cellular reprogramming strategies, small molecule approach gets proclaimed to have better clinical prospects because it does not involve genetic manipulation. Several small molecules targeting certain epigenetic enzymes and/or signaling pathways have been successful in helping to induce pancreatic β-cell specification. Recently, a synthetic DNA-based small molecule triggered targeted transcriptional activation of pancreas-related genes to suggest the possibility of achieving desired cellular phenotype in a precise mode. Here, we give a brief overview of treating DM by regenerating pancreatic β-cells from various cell sources. Through a comprehensive overview of the available transcription factors, small molecules and reprogramming strategies available for pancreatic β-cell regeneration, this review compiles the current progress made towards the generation of clinically relevant insulin-producing β-cells.

Forgotten and novel aspects in pancreas development

Diseases related to the pancreas are of highest importance in public health. It is anticipated that a detailed understanding of the molecular events that govern the embryonic development of this organ will have an immediate impact on clinical research relating to this issue. One major aim is the reconstruction of embryonic development in vitro with appropriate precursor cells, a second strategy is aimed at understanding the transdifferentiation of non-pancreatic into pancreatic tissue, and a third avenue is defined by the stimulation of the intrinsic ability of the pancreas to regenerate. Recent progress in developmental biology with respect to these different topics is reviewed in the present article. In addition, we also address evolutionary aspects of pancreas development, emphasizing the role of the South African clawed frog, Xenopus laevis, as an additional useful model system to study the molecular control of pancreas development.

Genetic identification of a novel NeuroD1 function in the early differentiation of islet alpha, PP and epsilon cells

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 epsilon 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 epsilon 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 epsilon cells.

Hyperglycaemia and reduced glucokinase expression in weanling offspring from dams maintained on a high-fat diet

High-fat feeding reduces the expression of GLUT-2 and the glycolytic enzyme glucokinase (GK). The transcription factor, pancreatic duodenal homeobox-1 (Pdx-1), is important for β-cell maintenance. The aim of the present study was to determine, in weanling Wistar rats, the effect of a maternal high-fat diet (HFD) during defined periods of gestation and lactation, on body weight, circulating glucose and insulin concentrations, and the expression of GLUT-2, GK and Pdx-1. At postnatal day 21, weights were recorded and glucose and insulin concentrations were measured. The expression levels for mRNA were quantified by LightCycler PCR. Pancreatic sections, immunostained for GLUT-2, GK or Pdx-1, were assessed by image analysis. Weanlings from dams fed an HFD throughout gestation were lighter, with heavier weanlings produced from dams fed an HFD throughout gestation and lactation. Both these groups of weanlings were normoglycaemic, all the others being hyperglycaemic. Hypoinsulinaemia was evident in weanlings from dams fed an HFD throughout gestation only and also for either the first week of lactation or throughout lactation. GLUT-2 mRNA expression was reduced and GLUT-2 immunoreactivity was increased in most of the weanlings. GK mRNA expression and immunoreactivity was reduced in most of the offspring. Pdx-1 mRNA expression was increased in weanlings from dams fed an HFD throughout both gestation and lactation and reduced in those from dams only fed a lactational HFD. Normal Pdx-1 immunoreactivity was found in all of the weanlings. A maternal HFD induces hyperglycaemia in weanlings concomitant with reduced GK expression which may compromise β-cell function.

Members of the Plag gene family are expressed in complementary and overlapping regions in the developing murine nervous system

In the developing nervous system, cell fate specification and proliferation are tightly coupled events, ensuring the coordinated generation of the appropriate numbers and correct types of neuronal and glial cells. While it has become clear that tumor suppressor genes and oncogenes are key regulators of cell division in tumor cells, their role in normal cellular and developmental processes is less well understood. Here we present a comparative analysis of the expression profiles of the three members of the pleiomorphic adenoma gene (Plag) family, which encode zinc finger transcription factors previously characterized as tumor suppressors (Zac1) or oncogenes (Plag1, Plag-l2). We focused our analysis on the developing nervous system of mouse where we found that the Plag genes were expressed in both unique and overlapping patterns in the central and peripheral nervous systems, and in olfactory and neuroendocrine lineages. Based on their patterns of expression, we suggest that members of the Plag gene family might control cell fate and proliferation decisions in the developing nervous system and propose that deciphering these functions will help to explain why their inappropriate inactivation/activation leads to tumor formation.

Insulin-producing cells

Embryonic stem (ES) cells offer great potential for cell replacement and tissue engineering therapies because of their almost unlimited proliferation capacity and the potential to differentiate into cellular derivatives of all three primary germ layers. This chapter describes a strategy for the in vitro differentiation of mouse ES cells into insulin-producing cells. The three-step protocol does not select for nestin-expressing cells as performed in previous differentiation systems. It includes (1) the spontaneous differentiation of ES cells via embryoid bodies and (2) the formation of progenitor cells of all three primary germ layers (multilineage progenitors) followed by (3) directed differentiation into the pancreatic lineage. The application of growth and extracellular matrix factors, including laminin, nicotinamide, and insulin, leads to the development of committed pancreatic progenitors, which subsequently differentiate into islet-like clusters that release insulin in response to glucose. During differentiation, transcript levels of pancreas-specific transcription factors (i.e., Pdx1, Pax4) and of genes specific for early and mature beta cells, including insulin, islet amyloid pancreatic peptide, somatostatin, and glucagon, are upregulated. C-peptide/insulin-positive islet-like clusters are formed, which release insulin in response to high glucose concentrations at terminal stages. The differentiated cells reveal functional properties with respect to voltage-activated Na+ and ATP-modulated K+ channels and normalize blood glucose levels in streptozotocin-treated diabetic mice. In conclusion, we demonstrate the efficient differentiation of murine ES cells into insulin-producing cells, which may help in the future to establish ES cell-based therapies in diabetes mellitus.