Pancreas development and diabetes

Autoimmune CD8+ T cells in type 1 diabetes: from single-cell RNA sequencing to T-cell receptor redirection

Type 1 diabetes (T1D) is an organ-specific autoimmune disease caused by pancreatic β cell destruction and mediated primarily by autoreactive CD8+ T cells. It has been shown that only a small number of stem cell-like β cell-specific CD8+ T cells are needed to convert normal mice into T1D mice; thus, it is likely that T1D can be cured or significantly improved by modulating or altering self-reactive CD8+ T cells. However, stem cell-type, effector and exhausted CD8+ T cells play intricate and important roles in T1D. The highly diverse T-cell receptors (TCRs) also make precise and stable targeted therapy more difficult. Therefore, this review will investigate the mechanisms of autoimmune CD8+ T cells and TCRs in T1D, as well as the related single-cell RNA sequencing (ScRNA-Seq), CRISPR/Cas9, chimeric antigen receptor T-cell (CAR-T) and T-cell receptor-gene engineered T cells (TCR-T), for a detailed and clear overview. This review highlights that targeting CD8+ T cells and their TCRs may be a potential strategy for predicting or treating T1D.

Encapsulation and immune protection for type 1 diabetes cell therapy

Type 1 Diabetes (T1D) involves the autoimmune destruction of insulin-producing β-cells in the pancreas. Exogenous insulin injections are the current therapy but are user-dependent and cannot fully recapitulate physiological insulin secretion dynamics. Since the emergence of allogeneic cell therapy for T1D, the Edmonton Protocol has been the most promising immunosuppression protocol for cadaveric islet transplantation, but the lack of donor islets, poor cell engraftment, and required chronic immunosuppression have limited its application as a therapy for T1D. Encapsulation in biomaterials on the nano-, micro-, and macro-scale offers the potential to integrate islets with the host and protect them from immune responses. This method can be applied to different cell types, including cadaveric, porcine, and stem cell-derived islets, mitigating the issue of a lack of donor cells. This review covers progress in the efforts to integrate insulin-producing cells from multiple sources to T1D patients as a form of cell therapy.

Islet-on-a-chip: Biomimetic micropillar-based microfluidic system for three-dimensional pancreatic islet cell culture

Type 2 diabetes is currently one of the most common metabolic diseases, affecting all ages worldwide. As the incidence of type 2 diabetes increases, a growing number of studies focus on islets of Langerhans. A three-dimensional research model that maps islet morphology and maintains hormonal balance in vivo is still needed. In this work, we present an Islet-on-a-chip system, specifically a micropillar-based microfluidic platform for three-dimensional pancreatic islet cell culture and analysis. The microfluidic system consisted of two culture chambers that were equipped with 15 circular microtraps each, which were built with seven round micropillars each. Micropillars in the structure of microtraps supported cell aggregation by limiting the growth surface and minimizing wall shear stress, thereby ensuring proper medium diffusion and optimal culture conditions for cell aggregates. Our system is compatible with microwell plate readers and confocal laser scanning microscopes. Because of optimization of the immunostaining method, the appropriate cell distribution and high viability and proliferation up to 72 h of culture were confirmed. Enzyme-linked immunosorbent assays were performed to measure insulin and glucagon secretion after stimulation with different glucose concentrations. To our knowledge, this is the first Lab-on-a-chip system which enables the formation and three-dimensional culture of cell aggregates composed of commercially available α and β pancreatic islet cells. The specific composition and arrangement of cells in the obtained model corresponds to the arrangement of the cells in rodent pancreatic islets in vivo. This Islet-on-a-chip system may be utilized to test pathogenic effectors and future therapeutic agents.

Transcriptional regulation of metabolism in disease: From transcription factors to epigenetics

Every cell in an individual has largely the same genomic sequence and yet cells in different tissues can present widely different phenotypes. This variation arises because each cell expresses a specific subset of genomic instructions. Control over which instructions, or genes, are expressed is largely controlled by transcriptional regulatory pathways. Each cell must assimilate a huge amount of environmental input, and thus it is of no surprise that transcription is regulated by many intertwining mechanisms. This large regulatory landscape means there are ample possibilities for problems to arise, which in a medical context means the development of disease states. Metabolism within the cell, and more broadly, affects and is affected by transcriptional regulation. Metabolism can therefore contribute to improper transcriptional programming, or pathogenic metabolism can be the result of transcriptional dysregulation. Here, we discuss the established and emerging mechanisms for controling transcription and how they affect metabolism in the context of pathogenesis. Cis- and trans-regulatory elements, microRNA and epigenetic mechanisms such as DNA and histone methylation, all have input into what genes are transcribed. Each has also been implicated in diseases such as metabolic syndrome, various forms of diabetes, and cancer. In this review, we discuss the current understanding of these areas and highlight some natural models that may inspire future therapeutics.

Type 1 Diabetes: A Chronic Anti-Self-Inflammatory Response

Inflammation is typically induced in response to a microbial infection. The release of proinflammatory cytokines enhances the stimulatory capacity of antigen-presenting cells, as well as recruits adaptive and innate immune effectors to the site of infection. Once the microbe is cleared, inflammation is resolved by various mechanisms to avoid unnecessary tissue damage. Autoimmunity arises when aberrant immune responses target self-tissues causing inflammation. In type 1 diabetes (T1D), T cells attack the insulin producing β cells in the pancreatic islets. Genetic and environmental factors increase T1D risk by in part altering central and peripheral tolerance inducing events. This results in the development and expansion of β cell-specific effector T cells (Teff) which mediate islet inflammation. Unlike protective immunity where inflammation is terminated, autoimmunity is sustained by chronic inflammation. In this review, we will highlight the key events which initiate and sustain T cell-driven pancreatic islet inflammation in nonobese diabetic mice and in human T1D. Specifically, we will discuss: (i) dysregulation of thymic selection events, (ii) the role of intrinsic and extrinsic factors that enhance the expansion and pathogenicity of Teff, (iii) defects which impair homeostasis and suppressor activity of FoxP3-expressing regulatory T cells, and (iv) properties of β cells which contribute to islet inflammation.

DNase I aggravates islet β-cell apoptosis in type 2 diabetes

Deoxyribonuclease I (DNase I) is an endonuclease responsible for the destruction of chromatin during apoptosis. However, its role in diabetes remains unclear. The aim of the current study was to investigate the role of DNase I combined with high glucose levels in β-cell apoptosis. Human samples were collected and the DNase I activity was examined. High glucose-cultured INS-1 cells were transfected with DNase I small interfering RNA (siRNA) and the cell apoptosis was examined by western blotting and flow cytometry. Cell viability was analyzed by the Cell Counting Kit-8 assay. Cell apoptosis resulting from 50 mU/μl DNase I was also observed by flow cytometry, terminal deoxynucleotidyl transferase dUTP nick-end labeling stain and western blotting. Compared with healthy controls, the serum DNase I activity of patients with diabetes was significantly increased (P<0.05). In addition, DNase I expression was observed to be significantly increased in human pancreatic tissues. The addition of high glucose upregulated the cell apoptotic rate, whereas DNase I knockdown significantly reduced apoptosis in cells treated with high glucose. In addition, the western blotting results indicated that caspase-3 was increased subsequent to treatment of cells with 30 mM high glucose, however, this increase can be reversed by transfection with DNase I siRNA (P<0.05). Compared with cells cultured in normal conditions and high glucose, 50 mU/μl DNase I was able to significantly increase the cell apoptotic rate and level of caspase-3. DNase I activity was observed to be increased in type 2 diabetes, and high glucose combined with increased DNase I is suggested to aggravate β-cell apoptosis.

From gut changes to type 2 diabetes remission after gastric bypass surgeries

Increasing evidence suggests that the gut may influence the host's metabolism and ultimately change the outcomes of type 2 diabetes mellitus (T2DM). We review the evidence on the relationship between the gut and T2DM remission after gastric bypass surgery, and discuss the potential mechanisms underlying the above relationship: gut anatomical rearrangement, microbial composition changes, altered gut cells, and gut hormone modulation. However, the exact changes and their relative importance in the metabolic improvements after gastric bypass surgery remain to be further clarified. Elucidating the precise metabolic mechanisms of T2DM resolution after bypass surgery will help to reveal the molecular mechanisms of pathogenesis, and facilitate the development of novel diagnoses and preventative interventions for this common disease.

Conversion of non-endocrine human pancreatic cells to insulin-producing cells for treatment of diabetes

Type I diabetes results from the autoimmune destruction of the insulin-secreting pancreatic β-cells, affecting many millions of people worldwide. The optimal treatment is to restore the endogenous supply of insulin either through the transplantation of pancreas or the transplantation of islets of langerhans or simply the β-cells. However, the donated pancreas organs are limited and the available organs are only able to treat a small portion of the diabetes patients. Thus, glucose-responsive, insulin-producing cells from human origin are urgently needed. The aim of this chapter is to give some insight views to how to turn the potential human pancreatic non-endocrine cells into cells that are capable of secreting insulin in response to glucose and ameliorating insulin-deficient diabetes conditions after transplantation.

Review on monogenic diabetes

PURPOSE OF REVIEW

The goal of this review is to provide an update on the different forms of monogenic diabetes, including maturity-onset diabetes of the young (MODY) and neonatal diabetes (permanent and transient neonatal diabetes).

RECENT FINDINGS

Monogenic diabetes accounts for approximately 1-2% of diabetes cases and results from mutations that primarily reduce β-cell function. Individuals with islet autoantibody negative youth-onset forms of diabetes should be evaluated for either glucokinase-MODY or transcription factors MODY. The mild-fasting hyperglycemia found in glucokinase-MODY typically does not necessitate pharmacological treatment, whereas patients with MODY caused by transcription factor mutations can often be successfully treated with low-dose sulfonylurea. Neonatal diabetes is defined as diabetes onset within the first 6 months of life and most individuals with permanent neonatal diabetes can be treated with high-dose sulfonylurea.

SUMMARY

The discovery of the genetic cause of monogenic diabetes has greatly advanced our understanding and management of these uncommon forms of diabetes.

Nestin in gastrointestinal and other cancers: Effects on cells and tumor angiogenesis

Nestin is a class VI intermediate filament protein that was originally described as a neuronal stem cell marker during central nervous system (CNS) development, and is currently widely used in that capacity. Nestin is also expressed in non-neuronal immature or progenitor cells in normal tissues. Under pathological conditions, nestin is expressed in repair processes in the CNS, muscle, liver, and infarcted myocardium. Furthermore, increased nestin expression has been reported in various tumor cells, including CNS tumors, gastrointestinal stromal tumors, pancreatic cancer, prostate cancer, breast cancer, malignant melanoma, dermatofibrosarcoma protuberances, and thyroid tumors. Nestin is reported to correlate with aggressive growth, metastasis, and poor prognosis in some tumors; however, the roles of nestin in cancer cells have not been well characterized. Furthermore, nestin is more specifically expressed in proliferating small-sized tumor vessels in glioblastoma and gastric, colorectal, and prostate cancers than are other tumor vessel markers. These findings indicate that nestin may be a marker for newly synthesized tumor vessels and a therapeutic target for tumor angiogenesis. It has received a lot of attention recently as a cancer stem cell marker in various cancer cells including brain tumors, malignant rhabdoid tumors, and uterine, cervical, prostate, bladder, head and neck, ovarian, testicular, and pancreatic cancers. The purpose of this review is to clarify the roles of nestin in cancer cells and in tumor angiogenesis, and to examine the association between nestin and cancer stem cells. Nestin has the potential to serve as a molecular target for cancers with nestin-positive cancer cells and nestin-positive tumor vasculature.

Evidence of a generalized defect of acinar cell function in Shwachman-Diamond syndrome

BACKGROUND

: Because the acinar cells of the exocrine pancreas in patients with Shwachman-Diamond syndrome (SDS) are severely depleted, we hypothesized that a similar deficiency may be present in acinar cells of the parotid gland.

PATIENTS AND METHODS

: We determined serum pancreatic isoamylase and parotid amylase activities in 16 patients with SDS, 13 healthy controls, and 13 disease controls (cystic fibrosis or fibrosing pancreatitis). Parotid amylase and electrolyte concentrations were measured in stimulated parotid gland secretions. Starch digestion was assessed by breath hydrogen testing in patients with SDS (with and without enzyme supplements) and healthy controls.

RESULTS

: Serum pancreatic and parotid isoamylase values were lower in the patients with SDS than in the healthy controls (P < 0.0001 and P = 0.0002, respectively). Serum pancreatic isoamylase, but not parotid isoamylase, was significantly lower in the disease controls than in the healthy controls (P < 0.0001 and P = 0.17, respectively). Secreted parotid gland amylase concentration (units per milligram of protein) in patients with SDS was lower than that in the healthy controls (P = 0.04), whereas the disease controls were comparable to the healthy subjects (P = 0.09). Secreted parotid chloride concentration was inversely correlated with amylase concentration in the patients with SDS (P = 0.01), but no correlation was seen in the healthy controls or disease controls. When patients with SDS ingested starch without enzyme supplementation, their breath hydrogen excretion was significantly higher than that in the healthy controls (P = 0.009). Following starch ingestion with enzymes, breath hydrogen in the patients with SDS was lower (P < 0.05) than with no enzyme treatment, and no different from controls (P = 0.37).

CONCLUSIONS

: Mutations in the SBDS gene cause a generalized functional abnormality of exocrine acinar cells.

Mutations of maturity-onset diabetes of the young (MODY) genes in Thais with early-onset type 2 diabetes mellitus

OBJECTIVE

Six known genes responsible for maturity-onset diabetes of the young (MODY) were analysed to evaluate the prevalence of their mutations in Thai patients with MODY and early-onset type 2 diabetes.

PATIENTS AND METHODS

Fifty-one unrelated probands with early-onset type 2 diabetes, 21 of them fitted into classic MODY criteria, were analysed for nucleotide variations in promoters, exons, and exon-intron boundaries of six known MODY genes, including HNF-4alpha, GCK, HNF-1alpha, IPF-1, HNF-1beta, and NeuroD1/beta2, by the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method followed by direct DNA sequencing. Missense mutations or mutations located in regulatory region, which were absent in 130 chromosomes of non-diabetic controls, were classified as potentially pathogenic mutations.

RESULTS

We found that mutations of the six known MODY genes account for a small proportion of classic MODY (19%) and early-onset type 2 diabetes (10%) in Thais. Five of these mutations are novel including GCK R327H, HNF-1alpha P475L, HNF-1alphaG554fsX556, NeuroD1-1972 G > A and NeuroD1 A322N. Mutations of IPF-1 and HNF-1beta were not identified in the studied probands.

CONCLUSIONS

Mutations of the six known MODY genes may not be a major cause of MODY and early-onset type 2 diabetes in Thais. Therefore, unidentified genes await discovery in a majority of Thai patients with MODY and early-onset type 2 diabetes.

Genetic variants of FOXA2: risk of type 2 diabetes and effect on metabolic traits in North Indians

Here, we examined the association of genetic variants of FOXA2, an upstream activator of the beta-cell transcription factor network, with type 2 diabetes and related phenotypes in North India. We genotyped three SNPs (rs1212275, rs1055080, rs6048205) and the (TCC)( n ) repeat polymorphism in 1,656 participants comprising 1,031 patients with type 2 diabetes and 625 controls. SNPs rs1212275 and rs6048205 were uncommon (MAF < 5%) with similar distribution among patients and controls. We found a strong association of (TCC)( n ) common allele A5 with type 2 diabetes [OR = 1.66 (95% CI 1.36-2.04, p = 5.9 x 10(-7)) for A5 homozygotes]. Obese individuals with A5A5 genotype had enhanced risk when segregated from normal-weight subjects [OR = 1.92 (95% CI 1.47-2.51), p = 1.6 x 10(-6)]. A5 was also nominally associated with higher fasting glucose (p = 0.02) and lower fasting insulin (p = 0.0028) and C-peptide (p = 0.036) levels among controls. At the rs1055080 locus, GG was found to provide reduced risk among normal-weight subjects [OR = 0.59 (95% CI 0.40-0.88), p = 0.011]. Combination of protective GG and non-risk genotypes of (TCC)( n ) showed reduced risk of type 2 diabetes both among normal-weight [OR = 0.43 (95% CI 0.29-0.65), p = 1.2 x 10(-6)] and obese individuals [0.47 (95% CI 0.34-0.64), p = 4.3 x 10(-5)]. For the first time we demonstrated that FOXA2 variants may affect risk of type 2 diabetes and metabolic traits in North India, however replication analyses in other cohorts are required to confirm the findings.

Loss of Myt1 function partially compromises endocrine islet cell differentiation and pancreatic physiological function in the mouse

Myelin transcription factor 1 (Myt1) is one of the three vertebrate C2HC-type zinc finger transcription factors that include Myt1 (Nzf1), Myt1L (Png1), and Myt3 (Nzf3, St18). All three paralogs are widely expressed in developing neuronal cells. Yet their function for mammalian development has not been investigated directly. Here we report that only Myt1 is expressed in the embryonic pancreas, in both endocrine progenitors and differentiated islet cells. Myt1(-/-) animals die postnatally, likely due to confounding effects in multiple tissues. The endocrine tissues in the embryonic Myt1(-/-) pancreas contained abnormal islet cells that expressed multiple hormones; although hormone levels were normal. We also created pancreas-specific Myt1 knockout mice. These mutant animals had no obvious physical defects from their wild-type littermates. Male mutant animals had reduced glucose-clearing abilities and abnormal multi-hormone-expressing cells present in their endocrine islets. In addition, they also had reduced Glut2 expression, and attenuated glucose-induced insulin secretion in the adult islets. Surprisingly, the expression of the Myt1 paralogs, Myt1l and Myt3, was induced in the embryonic Myt1(-/-) pancreas. The consequences of Myt1 inactivation in the developing pancreas could be masked by activation of its paralogs, Myt1l and Myt3. These findings suggest Myt1 is involved in proper endocrine differentiation and function.

Early expression of adenosine 5'-triphosphate-gated P2X7 receptors in the developing rat pancreas

OBJECTIVES

Extracellular adenosine 5'-triphosphate modulates the functions of the adult pancreas via 2 nucleotide receptor families, the P2X and P2Y receptors. Expression of the P2X7 receptor has been demonstrated in islet cells of the pancreas, particularly the mature alpha cells that secrete glucagon. In the streptozotocin-induced diabetic model, a loss of insulin-secreting cells was accompanied by an increase in alpha cells that expressed the P2X7 receptor.

METHODS

In the present study, we have examined the expression of P2X7 receptors in the developing pancreas from embryonic days 10 (E10) to E18.

RESULTS

We detected P2X7 receptor-immunoreactive cells in pancreatic islet cells as early as E11' before glucagon expression. Subsequently, P2X7 receptors were expressed in glucagon-secreting cells at E12, and complete colocalization was observed at E14. Occasional colocalization of P2X7 receptors and insulin was observed in scattered cells at E12 and E14, but not at E18, when the glucagon- and insulin-secreting cells were almost completely segregated.

CONCLUSIONS

It was found that P2X7 receptors were expressed early in a subpopulation of glucagon- and insulin-immunopositive cells in developing islets and subsequently became restricted to glucagon-expressing cells as development proceeded. The possible functional significance of these changes is discussed.

Beta cells occur naturally in extrahepatic bile ducts of mice

Insulin-secreting beta cells were thought to reside only in the pancreas. Here, we show that beta cells are also present in the extra-hepatic bile ducts of mice. They are characterised by insulin and C-peptide content, the presence of secretory granules that are immunoreactive for insulin, and the ducts exhibit glucose-stimulated insulin secretion. Genetic lineage labelling shows that these beta cells arise from the liver domain rather than the pancreas and, by histological study, they appear to be formed directly from the bile duct epithelium in late embryogenesis. Other endocrine cell types (producing somatostatin and pancreatic polypeptide) are also found in close association with the bile-duct-derived beta cells, but exocrine pancreatic tissue is not present. This discovery of beta cells outside the mammalian pancreas has implications for regenerative medicine, indicating that biliary epithelium might offer a new source of beta cells for the treatment of diabetes. The finding also has evolutionary significance, because it is known that certain basal vertebrates usually form all of their beta cells from the bile ducts. The mammalian bile-duct-derived beta cells might therefore represent an extant trace of the evolutionary origin of the vertebrate beta cell.

The fringe molecules induce endocrine differentiation in embryonic endoderm by activating cMyt1/cMyt3

Endocrine differentiation in the early embryonic pancreas is regulated by Notch signaling. Activated Notch signaling maintains pancreatic progenitor cells in an undifferentiated state, whereas suppression of Notch leads to endocrine cell differentiation. Yet it is not known what mechanism is employed to inactivate Notch in a correct number of precursor cells to balance progenitor proliferation and differentiation. We report that an established Notch modifier, Manic Fringe (Mfng), is expressed in the putative endocrine progenitors, but not in exocrine pancreatic tissues, during early islet differentiation. Using chicken embryonic endoderm as an assaying system, we found that ectopic Mfng expression is sufficient to induce endodermal cells to differentiate towards an endocrine fate. This endocrine-inducing activity depends on inactivation of Notch. Furthermore, ectopic Mfng expression induces the expression of basic helix-loop-helix gene, Ngn3, and two zinc finger genes, cMyt1 and cMyt3. These results suggest that Mfng-mediated repression of Notch signaling could serve as a trigger for endocrine islet differentiation.

Defined localization of nestin-expressing cells in L-arginine-induced acute pancreatitis

OBJECTIVE

Nestin is a stem cell marker originally described as an intermediate filament protein expressed in neuroepithelial stem cells. In the pancreas, a small number of nestin-expressing cells, which are believed to represent either stem cells or progenitor cells, are known to be present in islets, as well as in some stellate cells, pericytes, and endothelial cells. We monitored pancreatic nestin expression to delineate the location of stem cells/progenitor cells in the pancreas after L-arginine-induced pancreatitis.

METHODS

Male Wistar rats received 2 intraperitoneal injections of L-arginine, each consisting of 250 mg/100 g of body weight, and were killed 3, 6, and 12 hours and 1, 4, 7, and 14 days later.

RESULTS

Serum amylase and lipase levels increased after L-arginine injection, maximal levels occurring at 3 and 12 hours postinjection, respectively. Six hours after L-arginine injection, interstitial edema was observed in the pancreas, whereas on day 4 postinjection, there was severe pancreatic necrosis. Neovascularization and ductal-ductular proliferation were also present in the pancreas. Immunohistochemical analysis revealed increased Ki-67 labeling in acinar cells and capillary endothelial cells. Immunoblotting using antinestin antibody revealed increased nestin expression after L-arginine injection. In the control rat pancreas, nestin immunoreactivity was detected in a few capillary endothelial cells in some islets. After L-arginine injection, nestin was expressed in proliferating capillary endothelial cells, in stellate cells surrounding ductular structures and in submesothelial cells.

CONCLUSIONS

Transient nestin expression occurs in specific cell types during the proliferative stage after recovery from L-arginine-induced pancreatitis and may represent the contribution of stem cells and/or progenitor cells to the regenerative capacity of the pancreas.

Wnt/β-catenin signaling pathway is active in pancreatic development of rat embryo

AIM: To elucidate the role of Wnt/β-catenin signaling pathway in pancreatic development of rat embryo.

METHODS: The mRNAs of β-catenin, APC, cyclin D1 genes were amplified by means of semiquantitative reverse transcription polymerase chain reaction (RT-PCR) from embryonic pancreas in different periods and normal pancreas of rat, respectively. Protein expression of these genes in embryonic pancreas of E14.5-E18.5 was examined by immunohistochemical method.

RESULTS: In embryonic pancreas of E14.5, the transcript amplification of β-catenin and cyclinD1 genes was detected. In embryonic pancreas of E18.5, the transcription levels of β-catenin and cyclinD1 genes became much higher than in other periods. But in adult rat pancreas the transcription of cyclinD1 gene could not be observed. Only until E18.5, the transcript amplification of mRNA of APC gene could be detected. Surprisingly, the transcription level of APC gene became much higher in adult rat pancreas than in embryonic pancreas. By means of immunohistochemical staining, identical results were obtained to the above by RP-PCR, except for β-catenin protein in adult rat pancreas.

CONCLUSION: Active Wnt/β-catenin signaling occurs in rat embryonic pancreas and is probably important for pancreatic development and organ formation.

The molecular basis of transdifferentiation

There is now excellent experimental evidence demonstrating the remarkable ability of some differentiated cells to convert to a completely different phenotype. The conversion of one cellular phenotype to another is referred to as 'transdifferentiation' and belongs to a wider class of cell-type switches termed 'metaplasias'. Defining the molecular steps in transdifferentiation will help us to understand the developmental biology of the cells that interconvert, as well as help identify key regulatory transcription factors that may be important for the reprogramming of stem cells. Ultimately, being able to produce cells at will offers a compelling new approach to therapeutic transplantation and therefore the treatment and cure of diseases such as diabetes.

Insulin-producing cells derived from human pancreatic non-endocrine cell cultures reverse streptozotocin-induced hyperglycaemia in mice

AIMS/HYPOTHESIS

The aim of the study was to investigate the potential of human pancreatic non-endocrine cells to transdifferentiate into endocrine cells that would be capable of secreting insulin in response to glucose and ameliorating insulin-deficient diabetes after transplantation.

MATERIALS AND METHODS

Cell fractions enriched with exocrine cells after human islet isolation were treated with streptozotocin to remove residual beta cells, grown in monolayer culture to allow de-differentiation, transferred to cluster culture for redifferentiation in the presence of activin A, betacellulin, nicotinamide and glucose, supplemented with 10% FCS, and administered to streptozotocin-induced diabetic SCID mice. A subset of cells was transfected with the IPF1 gene (also known as PDX1) before transdifferentiation.

RESULTS

No insulin was detectable in cell preparations after 5 days of treatment with streptozotocin. In monolayer culture, 90% of the streptozotocin-treated pancreatic cells co-expressed cytokeratin-19 and vimentin at 2 weeks and 60% expressed nestin at 4 weeks. Cell cultures with a high proportion of nestin-expressing cells had greater plasticity for transdifferentiation into cells with phenotypic and functional markers of beta cells, this property being significantly enhanced by transfection with IPF1 gene and leading to 15+/-6.7% insulin-positive cells after transplantation vs. 0.01% of cells transplanted after streptozotocin treatment alone. These cells improved glucose control in all of 42 diabetic mice after transplantation, restoring normoglycaemia in 40%.

CONCLUSIONS/INTERPRETATION

Human pancreatic cells are a potential source of new glucose-responsive insulin-producing cells that may be developed further for clinical use.

Large dense-core vesicle exocytosis in pancreatic beta-cells monitored by capacitance measurements

This article discusses the currently used methodologies for monitoring exocytosis as changes in cell capacitance. Details are given on composition of solutions, experimental protocols, and how the observed responses can be interpreted physiologically. The concepts are illustrated by examples from our own work on insulin-releasing pancreatic beta-cells. Finally, we consider the feasibility of applying capacitance measurements to endocrine cells in intact pancreatic islets, where the cells are electrically coupled to each other.

Minireview: transcriptional regulation in pancreatic development

Considerable progress has been made in the understanding of the sequential activation of signal transduction pathways and the expression of transcription factors during pancreas development. Much of this understanding has been obtained by analyses of the phenotypes of mice in which the expression of key genes has been disrupted (knockout mice). Knockout of the genes for Pdx1, Hlxb9, Isl1, or Hex results in an arrest of pancreas development at a very early stage (embryonic d 8-9). Disruption of genes encoding components of the Notch signaling pathway, e.g. Hes1 or neurogenin-3, abrogates development of the endocrine pancreas (islets of Langerhans). Disruption of transcription factor genes expressed more downstream in the developmental cascade (Beta2/NeuroD, Pax4, NKx2.2, and Nkx6.1) curtails the formation of insulin-producing beta-cells. An understanding of the importance of transcription factor genes during pancreas development has provided insights into the pathogenesis of diabetes, in which the mass of insulin-producing beta-cells is reduced.

In vitro-generation of surrogate islets from adult stem cells

Type 1 diabetes is one of the more costly chronic diseases of children and adolescents throughout North America and Europe, exhibiting an average estimated prevalence rate of nearly 0.2%. It occurs in genetically predisposed individuals when the immune system attacks and destroys specifically the insulin-producing beta cells of the pancreatic islets of Langerhans. While routine insulin therapy can provide diabetic patients with their daily insulin requirements, non-compliance and undetected hyperglycemic excursions often lead to subsequent long-term microvascular and macrovascular complications. The only real cure for type 1 diabetes is replacement of the beta cell mass, currently being accomplished through ecto-pancreatic transplantation and islet implantation. Both of these procedures suffer from a chronic shortage of available donor tissue in comparison to the number of potential recipients. To circumvent this need, three alternative approaches are being intensively investigated: (1) the production of surrogate cells by genetically modifying non-endocrine cells to secrete insulin in response to glucose challenge; (2) the trans-differentiation of non-endocrine stem/progenitor cells or mature cells to glucose-responsive adult tissue; and (3) the regulated differentiation of islet stem/progenitor cells to produce large numbers of mature, functional islets. In recent years, each of these approaches has made impressive advances, leading to the most important question, 'how soon will this new science be available to the patient?' In the present review, we discuss some of the recent advances, focusing primarily on the differentiation of islet stem cells to functional endocrine pancreas that may form the basis for future treatment.

Extracellular matrix distribution and islet morphology in the early postnatal pancreas: anomalies in the non-obese diabetic mouse

Previously, we reported elevated numbers of macrophages in the pancreas of NOD mice, a spontaneous animal model for T1D, during the early postnatal period. Extracellular matrix plays an important role in the tissue trafficking and retention of macrophages as well as in postnatal pancreas development. Therefore, we have examined the expression and distribution of laminin and fibronectin, two major extracellular matrix proteins and their corresponding integrin receptors, in the pre-weaning pancreases of NOD mice and control mouse strains. In addition, we have characterized the pancreas morphology during this period, since the morphology of the pre-weaning pancreas before the onset of lymphocytic peri-insulitis, when the pancreas is still subject to developmental changes, has been poorly documented. We show that laminin labeling is mainly associated with exocrine tissue, whereas fibronectin labeling was mostly localized at the islet-ductal pole, islet periphery and in intralobular septa. Moreover, the protein expression level of fibronectin was increased in NOD pancreases at the early stage of postnatal development, as compared to pancreases of C57BL/6 and BALB/c mouse strains. Interestingly, pancreatic macrophages were essentially found at sites of intense fibronectin labeling. The increased fibronectin content in NOD neonatal pancreas coincided with altered islet morphology, histologically reflected by enlarged and irregular shaped islets and increased percentages of total endocrine area as compared to that of control strains. In conclusion, increased levels of the extracellular matrix protein fibronectin were found in the early postnatal NOD pancreas, and this is associated with an enhanced accumulation of macrophages and altered islet morphology.

Transforming growth factor (TGF)beta, fibroblast growth factor (FGF) and retinoid signalling pathways promote pancreatic exocrine gene expression in mouse embryonic stem cells

Extracellular signalling cues play a major role in the activation of differentiation programmes. Mouse embryonic stem (ES) cells are pluripotent and can differentiate into a wide variety of specialized cells. Recently, protocols designed to induce endocrine pancreatic differentiation in vitro have been designed but little information is currently available concerning the potential of ES cells to differentiate into acinar pancreatic cells. By using conditioned media of cultured foetal pancreatic rudiments, we demonstrate that ES cells can respond in vitro to signalling pathways involved in exocrine development and differentiation. In particular, modulation of the hedgehog, transforming growth factor beta, retinoid, and fibroblast growth factor pathways in ES cell-derived embryoid bodies (EB) resulted in increased levels of transcripts encoding pancreatic transcription factors and cytodifferentiation markers, as demonstrated by RT-PCR. In EB undergoing spontaneous differentiation, expression of the majority of the acinar genes (i.e. amylase, carboxypeptidase A and elastase) was induced after the expression of endocrine genes, as occurs in vivo during development. These data indicate that ES cells can undergo exocrine pancreatic differentiation with a kinetic pattern of expression reminiscent of pancreas development in vivo and that ES cells can be coaxed to express an acinar phenotype by activation of signalling pathways known to play a role in pancreatic development and differentiation.

Cell-specific cytotoxicity of human pancreatic adenocarcinoma cells using rat insulin promoter thymidine kinase-directed gene therapy

The formation of a normal pancreas and the activation of insulin production are, in part, dependent on the expression and activation of the pancreatic duodenal homeobox gene 1 (PDX-1). The expression of PDX-1 also has been detected in various human pancreatic ductal adenocarcinoma (PDA) cell lines. This has made it possible to generate a cancer cell-specific gene expression system to treat human pancreatic cancer. In this study, we have developed a cell-specific cytotoxic model of PDA cells using the expression of herpes simplex virus thymidine kinase (TK) under the control of the rat insulin promoter (RIP-TK). We have shown that the cell-specific cytotoxicity in human PDA cells depends on the presence of PDX-1. Our results also demonstrate that in vivo PDA-specific cytotoxicity can be achieved with RIP-TK using an intraperitoneal liposomal gene delivery method followed by a short period of ganciclovir treatment in severe combined immunodeficient (SCID) mice. Furthermore, PDX-1 protein was found in all six freshly isolated human pancreas cancer specimens and two liver metastasis samples that were group-tested, suggesting the feasibility of using RIP-TK gene therapy in humans. This study may provide an alternative strategy for the future treatment of pancreatic cancer.

Regulated expression of pdx-1 promotes in vitro differentiation of insulin-producing cells from embryonic stem cells

Embryonic stem (ES) cells can differentiate into many cell types. Recent reports have shown that ES cells can differentiate into insulin-producing cells. However, the differentiation is not efficient enough to produce insulin-secreting cells for future therapeutic use. Pdx-1, a homeodomain-containing transcription factor, is a crucial regulator for pancreatic development. We established an ES cell line in which exogenous pdx-1 expression was precisely regulated by the Tet-off system integrated into the ROSA26 locus. Using this cell line, we examined the effect of pdx-1 expression during in vitro differentiation via embryoid body formation. The results showed that pdx-1 expression clearly enhanced the expression of the insulin 2, somatostatin, Kir6.2, glucokinase, neurogenin3, p48, Pax6, PC2, and HNF6 genes in the resulting differentiated cells. Immunohistochemical examination also revealed that insulin was highly produced in most of the differentiated ES cells. Thus, exogenous expression of pdx-1 should provide a promising approach for efficiently producing insulin-secreting cells from human ES cells for future therapeutic use in diabetic patients.

Fundamentals of transcription factors and their impact on pancreatic development and cancer

Transcription factors are proteins that regulate gene expression by modulating the synthesis of messenger RNA. Since this process, known as gene transcription, is often the dominant control point in the production of many proteins, transcription factors are key regulators of numerous cellular functions, including secretion, proliferation, differentiation, and apoptosis. Most transcription factors are also the final effectors of signaling pathways that transduce signals from the cell membrane to the nucleus. Therefore alterations in the activity or expression of some transcription factors have a significant impact on the biology of human cells and may lead to the development of diseases. In this article we review this field of research with a particular emphasis on the role of transcription factors in pancreatic development and cancer.

Specific gene expression and therapy for pancreatic cancer using the cytosine deaminase gene directed by the rat insulin promoter

Suicide gene therapy has been shown to be an effective means of destroying pancreatic cancer cells, but cell-specific delivery of the gene is required to limit host toxicity. The objective of this study is to determine whether the rat insulin promoter (RIP) will permit cell-specific gene delivery and subsequent cell death in human pancreatic cancer cells. The RIP DNA was amplified using polymerase chain reaction (PCR), and the purified fragment was inserted into pCR-Blunt II-TOPO plasmid at the SpeI site, which contains the coding sequence of yeast cytosine deaminase (CD). Transfection assays were carried out using both RIP-lacZ and RIP-CD DNA constructs in two human pancreatic cancer cell lines, PANC-1 and MIA PaCa-2. Reporter assays using X-gal staining were performed, and the in vitro cytotoxicity was examined in RIP-CD-transfected cells treated with 5-flucytosine for 5 days. The expression levels of CD protein in the transfected cells were determined 2 days after transfection by Western blot analysis. The expression levels of insulin promoter factor (IPF-1/PDX-1) in these human pancreatic cell lines, as well as in freshly isolated human pancreatic cancer specimens, were determined using in situ immunohistochemistry analysis. After transfection with RIP-lacZ, only PANC-1 cells, but not MIA PaCa-2 cells, were positive for RIP-lacZ expression, indicating that RIP-directed reporter gene expression occurred only in PANC-1 cells. After transfection with RIP-CD and treatment with 5-flucytosine, PANC-1 cells had a significantly increased cell death rate compared with that of MIA PaCa-2 cells, suggesting that RIP-directed suicide gene expression occurred only in PANC-1 cells. Western blot analysis demonstrated that only PANC-1 cells were able to express the CD protein and that significantly increased levels of PDX-1 were found in PANC-1 but not in Mia PaCa-2 cells. In situ immunohistochemical analysis of both cell lines showed that PDX-1 was only expressed in the nuclei of PANC-1 cells and not in MIA PaCa-2 cells. Furthermore, two freshly isolated human pancreatic cancer specimens had significantly increased levels of PDX-1. The RIP is activated in PANC-1 cells, but not in Mia PaCa-2 cells, and the mechanism of activation is via PDX-1. Pancreatic cancer-specific cytotoxicity can be achieved with the use of RIP-CD and 5-flucytosine treatment in vitro. Significantly increased levels of PDX-1 have been found in human pancreatic cancer specimens. These results suggest that RIP could be used for cell-specific suicide gene therapy to target human pancreatic tumors.

Differentiation and proliferation of endocrine cells in the regenerating rat pancreas after 90% pancreatectomy

The transplantation of pancreatic tissue has been anticipated to serve as a radical treatment for diabetes mellitus. However, the identification of the stem cells, and elucidation of their differential lineage and controlling mechanisms are prerequisites to ensure effective transplantation. We conducted an immunohistochemical study to determine the proliferation and differentiation dynamics of pancreatic endocrine cells in the rat pancreas 1 to 28 days after a 90% pancreatectomy. Regeneration of endocrine cells started immediately after pancreatectomy. The process of regeneration included the proliferation of preexisting islet cells and neogenesis of endocrine cells from epithelial cells of the most peripheral duct. Intercalated ductal cells and centroacinar cells were speculated to be the major sources of neogenesis, from which islet tissue was formed. Glucagon cells were the first endocrine cells differentiated, some of which transformed to insulin cells by a mechanism of non-replication. These results indicate that endocrine stem cells exist among the intercalated ductal and/or centroacinar cells, and these special regions should be utilized in transplantation for the successful treatment of diabetes.

Activin betaB expression in rat experimental goiter and human thyroid tumors

Activins are dimeric proteins of the transforming growth factor beta superfamily, which exhibit multiple functions in gonadal and extragonadal tissues. Expression of activin A, composed of two betaA subunits, has been shown in the thyroid, whereas there has been no study regarding activin B (betaBbetaB) in this gland. In other tissues, such as the gonads, pancreas, and adrenal cortex, expression of both activin betaA and activin betaB has been described. In this study, we detected activin betaB mRNA and protein expression using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in rat experimental goiter and in human thyroid, including multinodular goiter, follicular adenoma, papillary carcinoma, and follicular carcinoma. Activin betaA mRNA and protein expression was also investigated in rat and human thyroid tissue. The expression of both activin betaB and activin betaA was highest in rat methimazole-induced goiter and in human follicular adenoma, and papillary and follicular carcinomas when compared with multinodular goiter and normal thyroid tissue. The increased expression of activin betaB as well as activin betaA, observed in this study, suggests that activin B and activin A may be involved in the proliferative and neoplastic processes of the thyroid.

New analytical method for pancreas and liver regeneration: normalization of streptozotocin-induced hyperglycemia by retrograde injection of insulin producing cells

We established a new analytical system in which functioning cells were transplanted directly into the pancreas and liver. The retrograde transplantation of beta cell line, Min6 cells, into the streptozotocin-diabetic mice normalized plasma glucose and insulin levels. The injected cells were protected from pancreatic enzymes with enzyme inhibitor. Blood glucose decreased gradually over 10 days and the diabetic mice recovered weight at the same time. Intraperitoneal glucose tolerance test showed that the peak of plasma glucose of the transplanted mice was less than half that of the control. The insulin secretion of the transplanted mice was recovered and stimulated 4.6 times from the basal secretion. Histological analyses showed that the pancreas and liver were characterized by Min6 cell clusters dispersed throughout the organs. Min6 cells were detected near the pancreatic or bile ducts. It is suggested that the injected cells obstructed the peripheral ducts where they settled. The weight of pancreas and liver did not differ significantly in either Min6 transplanted or the control mice. The metabolic effects on the weights of these organs appeared the same in both groups. This is the first report that cells transplanted via ducts into the pancreas and liver performed their biological function. Our transplantation model makes possible the in vivo analysis of the regeneration machinery of the pancreas and liver.

Foxa2 controls Pdx1 gene expression in pancreatic beta-cells in vivo

Differentiation of early foregut endoderm into pancreatic endocrine and exocrine cells depends on a cascade of gene activation events controlled by various transcription factors. Prior in vitro analysis has suggested that the forkhead/winged helix transcription factor Foxa2 (formerly HNF-3beta) is a major upstream regulator of Pdx1, a homeobox gene essential for pancreatic development. Pdx1 is also essential for the maintenance of glucose homeostasis, as its human orthologue, IPF-1, is mutated in a subset of patients with early-onset type 2 diabetes (MODY4). To analyze the Foxa2/Pdx1 regulatory cascade during pancreatic beta-cell differentiation, we used conditional gene ablation of Foxa2 in mice. We demonstrated that the deletion of Foxa2 in beta-cell-specific knockout mice results in downregulation of Pdx1 mRNA and subsequent reduction of PDX-1 protein levels in islets. These data represent the first in vivo demonstration that Foxa2 acts upstream of Pdx1 in the differentiated beta-cell.

Pancreatic organogenesis--developmental mechanisms and implications for therapy

The pancreas is a mixed exocrine and endocrine gland that controls many homeostatic functions. The exocrine pancreas produces and secretes digestive enzymes, whereas the endocrine compartment consists of four distinct hormone-producing cell types. Studies that further our knowledge of the basic mechanisms that underlie the formation of the pancreas will be crucial for understanding the development and homeostasis of this organ and of the mechanisms that cause diabetes. This information is also pivotal for any attempt to generate functional insulin-producing beta-cells that are suitable for transplantation.

Combined expression of pancreatic duodenal homeobox 1 and islet factor 1 induces immature enterocytes to produce insulin

Immature rat intestinal stem cells (IEC-6) given the ability to express the transcription factor, pancreatic duodenal homeobox 1 (Pdx-1), yielded YK cells. Although these cells produced multiple enteroendocrine hormones, they did not produce insulin. Exposure of YK cells to 2 nmol/l betacellulin yielded BYK cells that showed the presence of insulin expression in cytoplasm and that secreted insulin into culture media. By examining the mechanism of differentiation in BYK cells, we found that another transcription factor, islet factor 1 (Isl-1) was newly expressed with the disappearance of Pax-6 expression in those cells after exposure to betacellulin. These results indicated that combined expression of Pdx-1 and Isl-1 in IEC-6 cells was required for the production of insulin. In fact, overexpression of both Pdx-1 and Isl-1 in IEC-6 cells (Isl-YK-12, -14, and -15 cells) gave them the ability to express insulin without exposure to betacellulin. Furthermore, implantation of the Isl-YK-14 cells into diabetic rats reduced the animals' plasma glucose levels; glucose levels dropped from 19.4 to 16.9 mmol/l 1 day after the injection of cells. As expected, the plasma insulin concentrations were 2.7 times higher in the diabetic rats injected with Isl-YK-14 cells compared to in controls. In summary, our results indicated that immature intestinal stem cells can differentiate into insulin-producing cells given the ability to express the transcription factors Pdx-1 and Isl-1.

Profound defects in pancreatic beta-cell function in mice with combined heterozygous mutations in Pdx-1, Hnf-1alpha, and Hnf-3beta

Defects in pancreatic beta-cell function contribute to the development of type 2 diabetes, a polygenic disease that is characterized by insulin resistance and compromised insulin secretion. Hepatocyte nuclear factors (HNFs) -1alpha, -3beta, -4alpha, and Pdx-1 contribute in the complex transcriptional circuits within the pancreas that are involved in beta-cell development and function. In mice, a heterozygous mutation in Pdx-1 alone, but not Hnf-1alpha(+/-), Hnf-3beta(+/-), or Hnf-4alpha(+/-), causes impaired glucose-stimulated insulin secretion in mice. To investigate the possible functional relationships between these transcription factors on beta-cell activity in vivo, we generated mice with the following combined heterozygous mutations: Pdx-1(+/-)/Hnf-1alpha(+/-), Pdx-1(+/-)/Hnf-3beta(+/-), Pdx-1(+/-)/Hnf-4alpha(+/-), Hnf-1alpha(+/-)/Hnf-4alpha(+/-), and Hnf-3beta(+/-)/Hnf-4alpha(+/-). The greatest loss in function was in combined heterozygous null alleles of Pdx-1 and Hnf-1alpha (Pdx-1(+/-)/Hnf-1alpha(+/-)), or Pdx-1 and Hnf-3beta (Pdx-1(+/-)/Hnf-3beta(+/-)). Both double mutants develop progressively impaired glucose tolerance and acquire a compromised first- and second-phase insulin secretion profile in response to glucose compared with Pdx-1(+/-) mice alone. The loss in beta-cell function in Pdx-1(+/-)/Hnf-3beta(+/-) mice was associated with decreased expression of Nkx-6.1, glucokinase (Gck), aldolase B (aldo-B), and insulin, whereas Nkx2.2, Nkx-6.1, Glut-2, Gck, aldo-B, the liver isoform of pyruvate kinase, and insulin expression was reduced in Pdx-1(+/-)/Hnf-1alpha(+/-) mice. The islet cell architecture was also abnormal in Pdx-1(+/-)/Hnf-3beta(+/-) and Pdx-1(+/-)/Hnf-1alpha(+/-) mice, with glucagon-expressing cells scattered throughout the islet, a defect that may be connected to decreased E-cadherin expression. Our data suggest that functional interactions between key islet regulatory factors play an important role in maintaining islet architecture and beta-cell function. These studies also established polygenic mouse models for investigating the mechanisms contributing to beta-cell dysfunction in diabetes.

The role of hepatic nuclear factor 1 alpha and PDX-1 in transcriptional regulation of the pdx-1 gene

The PDX-1 homeodomain transcription factor regulates pancreatic development and adult islet beta cell function. Expression of the pdx-1 gene is almost exclusively localized to beta cells within the adult endocrine pancreas. Islet beta cell-selective transcription is controlled by evolutionarily conserved subdomain sequences (termed Areas I (-2839 to -2520 base pairs (bp)), II (-2252 to -2023 bp), and III (-1939 to -1664 bp)) found within the 5'-flanking region of the pdx-1 gene. Areas I and II are independently capable of directing beta cell-selective reporter gene activity in transfection assays, with Area I-mediated stimulation dependent upon binding of hepatic nuclear factor 3 beta (HNF3 beta), a key regulator of islet beta cell function. To identify other transactivators of Area I, highly conserved sequence segments within this subdomain were mutagenized, and their effect on activation was determined. Several of the sensitive sites were found by transcription factor data base analysis to potentially bind endodermally expressed transcription factors, including HNF1 alpha (-2758 to -2746 bp, Segment 2), HNF4 (-2742 to -2730 bp, Segment 4; -2683 to -2671 bp, Segment 7-8), and HNF6 (-2727 to -2715 bp, Segment 5). HNF1 alpha, but not HNF4 and HNF6, binds specifically to Area I sequences in vitro. HNF1 alpha was also shown to specifically activate Area I-driven transcription through Segment 2. In addition, PDX-1 itself was found to stimulate Area I activation. The chromatin immunoprecipitation assay performed with PDX-1 antisera also demonstrated that this factor bound to Area I within the endogenous pdx-1 gene in beta cells. Our results indicate that regulatory factors binding to Area I conserved sequences contribute to the selective transcription pattern of the pdx-1 gene and that control is mediated by endodermal regulators like HNF1 alpha, HNF3 beta, and PDX-1.

Distinct and overlapping functions of insulin and IGF-I receptors

Targeted gene mutations have established distinct, yet overlapping, developmental roles for receptors of the insulin/IGF family. IGF-I receptor mediates IGF-I and IGF-II action on prenatal growth and IGF-I action on postnatal growth. Insulin receptor mediates prenatal growth in response to IGF-II and postnatal metabolism in response to insulin. In rodents, unlike humans, insulin does not participate in embryonic growth until late gestation. The ability of the insulin receptor to act as a bona fide IGF-II-dependent growth promoter is underscored by its rescue of double knockout Igf1r/Igf2r mice. Thus, IGF-II is a true bifunctional ligand that is able to stimulate both insulin and IGF-I receptor signaling, although with different potencies. In contrast, the IGF-II/cation-independent mannose-6-phosphate receptor regulates IGF-II clearance. The growth retardation of mice lacking IGF-I and/or insulin receptors is due to reduced cell number, resulting from decreased proliferation. Evidence from genetically engineered mice does not support the view that insulin and IGF receptors promote cellular differentiation in vivo or that they are required for early embryonic development. The phenotypes of insulin receptor gene mutations in humans and in mice indicate important differences between the developmental roles of insulin and its receptor in the two species.

Expression of the receptor tyrosine kinase KIT in mature beta-cells and in the pancreas in development

In the pancreas, ligands of receptor tyrosine kinases (RTKs) are thought to be implicated in the development and function of the islets of Langerhans, which represent the endocrine part of the pancreas. In a previous study, we randomly screened by reverse transcriptase-polymerase chain reaction for RTKs expressed in the embryonic pancreas. One cDNA fragment that was cloned during this screen corresponded to the KIT receptor. The objective of the present study was to analyze the pattern of Kit expression in the pancreas. We demonstrated that Kit is expressed and functional in terms of signal transduction in the insulin-producing cell line INS-1. Indeed, upon treatment with the KIT ligand (KITL), the extracellular signal-regulated protein kinase was phosphorylated, and the expression of early responsive genes was induced. We also demonstrated that Kit mRNAs are present in fetal and adult rat islets. We next used mice that had integrated the lacZ reporter gene into the Kit locus. In these mice, beta-galactosidase (beta-gal) served as a convenient marker for expression of the endogenous Kit gene. Kit was found to be specifically transcribed in beta-cells (insulin-expressing cells), whereas no expression was found in other endocrine cell types or in the exocrine tissue. Interestingly, not all mature beta-cells expressed Kit, indicating that Kit is a marker of a subpopulation of beta-cells. Finally, by following beta-gal expression in the pancreas during fetal life, we found that at E14.5, Kit is expressed in both insulin- and glucagon-expressing cells present at that stage, and also in a specific cell population present in the epithelium that stained negative for endocrine markers. These data suggest that these Kit-positive/endocrine-negative cells could represent a subpopulation of endocrine cell precursors.

Tissue-specific deletion of Foxa2 in pancreatic beta cells results in hyperinsulinemic hypoglycemia

We have used conditional gene ablation to uncover a dramatic and unpredicted role for the winged-helix transcription factor Foxa2 (formerly HNF-3 beta) in pancreatic beta-cell differentiation and metabolism. Mice that lack Foxa2 specifically in beta cells (Foxa2(loxP/loxP); Ins.Cre mice) are severely hypoglycemic and show dysregulated insulin secretion in response to both glucose and amino acids. This inappropriate hypersecretion of insulin in the face of profound hypoglycemia mimics pathophysiological and molecular aspects of familial hyperinsulinism. We have identified the two subunits of the beta-cell ATP-sensitive K(+) channel (K(ATP)), the most frequently mutated genes linked to familial hyperinsulinism, as novel Foxa2 targets in islets. The Foxa2(loxP/loxP); Ins.Cre mice will serve as a unique model to investigate the regulation of insulin secretion by the beta cell and suggest the human FOXA2 as a candidate gene for familial hyperinsulinism.

Is pancreas development abnormal in the non-obese diabetic mouse, a spontaneous model of type I diabetes?

Despite extensive genetic and immunological research, the complex etiology and pathogenesis of type I diabetes remains unresolved. During the last few years, our attention has been focused on factors such as abnormalities of islet function and/or microenvironment, that could interact with immune partners in the spontaneous model of the disease, the non-obese diabetic (NOD) mouse. Intriguingly, the first anomalies that we noted in NOD mice, compared to control strains, are already present at birth and consist of 1) higher numbers of paradoxically hyperactive beta cells, assessed by in situ preproinsulin II expression; 2) high percentages of immature islets, representing islet neogenesis related to neonatal beta-cell hyperactivity and suggestive of in utero beta-cell stimulation; 3) elevated levels of some types of antigen-presenting cells and FasL+ cells, and 4) abnormalities of extracellular matrix (ECM) protein expression. However, the colocalization in all control mouse strains studied of fibroblast-like cells (anti-TR-7 labeling), some ECM proteins (particularly, fibronectin and collagen I), antigen-presenting cells and a few FasL+ cells at the periphery of islets undergoing neogenesis suggests that remodeling phenomena that normally take place during postnatal pancreas development could be disturbed in NOD mice. These data show that from birth onwards there is an intricate relationship between endocrine and immune events in the NOD mouse. They also suggest that tissue-specific autoimmune reactions could arise from developmental phenomena taking place during fetal life in which ECM-immune cell interaction(s) may play a key role.

Initiation and early patterning of the endoderm

We review the early stages of endoderm formation in the major animal models. In Amphibia maternal molecules are important in initiating endoderm formation. This is followed by successive signaling events that establish and then pattern the endoderm. In other organisms there are differences in endodermal development, particularly in the initial, prephylotypic stages. Later many of the same key families of transcription factors and signaling cassettes are used in all animals, but more work will be needed to establish exact evolutionary homologies.