Expression of c-Kit receptor tyrosine kinase and effect on beta-cell development in the human fetal pancreas

PAM staining intensity of primary neuroendocrine neoplasms is a potential prognostic biomarker

Neuroendocrine neoplasms (NENs) are rare epithelial tumors with heterogeneous and frequently unpredictable clinical behavior. Available biomarkers are insufficient to guide individual patient prognosis or therapy selection. Peptidylglycine α-amidating monooxygenase (PAM) is an enzyme expressed by neuroendocrine cells that participates in hormone maturation. The objective of this study was to assess the distribution, clinical associations and survival implications of PAM immunoreactivity in primary NENs. Of 109 primary NENs, 7% were PAM-negative, 25% were PAM-low and 68% were PAM-high. Staining intensity was high in small bowel (p = 0.04) and low in stomach (p = 0.004) NENs. PAM staining was lower in higher grade tumors (p < 0.001) and patients who died (p < 0.001) but did not vary by tumor size or stage at surgery. In patients who died, time to death was shorter in patients with reduced PAM immunoreactivity: median times to death were 11.3 (PAM-negative), 29.4 (PAM-low) and 61.7 (PAM-high) months. Lower PAM staining was associated with increased risk of death after adjusting for disease stage [PAM negative, HR = 13.8 (CI: 4.2–45.5)]. PAM immunoreactivity in primary NENs is readily assessable and a potentially useful stage-independent predictor of survival.

Regulation of Energy Metabolism by Receptor Tyrosine Kinase Ligands

Metabolic diseases, such as diabetes, obesity, and fatty liver disease, have now reached epidemic proportions. Receptor tyrosine kinases (RTKs) are a family of cell surface receptors responding to growth factors, hormones, and cytokines to mediate a diverse set of fundamental cellular and metabolic signaling pathways. These ligands signal by endocrine, paracrine, or autocrine means in peripheral organs and in the central nervous system to control cellular and tissue-specific metabolic processes. Interestingly, the expression of many RTKs and their ligands are controlled by changes in metabolic demand, for example, during starvation, feeding, or obesity. In addition, studies of RTKs and their ligands in regulating energy homeostasis have revealed unexpected diversity in the mechanisms of action and their specific metabolic functions. Our current understanding of the molecular, biochemical and genetic control of energy homeostasis by the endocrine RTK ligands insulin, FGF21 and FGF19 are now relatively well understood. In addition to these classical endocrine signals, non-endocrine ligands can govern local energy regulation, and the intriguing crosstalk between the RTK family and the TGFβ receptor family demonstrates a signaling network that diversifies metabolic process between tissues. Thus, there is a need to increase our molecular and mechanistic understanding of signal diversification of RTK actions in metabolic disease. Here we review the known and emerging molecular mechanisms of RTK signaling that regulate systemic glucose and lipid metabolism, as well as highlighting unexpected roles of non-classical RTK ligands that crosstalk with other receptor pathways.

Exenatide regulates pancreatic islet integrity and insulin sensitivity in the nonhuman primate baboon Papio hamadryas

The glucagon-like peptide-1 receptor agonist exenatide improves glycemic control by several and not completely understood mechanisms. Herein, we examined the effects of chronic intravenous exenatide infusion on insulin sensitivity, β cell and α cell function and relative volumes, and islet cell apoptosis and replication in nondiabetic nonhuman primates (baboons). At baseline, baboons received a 2-step hyperglycemic clamp followed by an l-arginine bolus (HC/A). After HC/A, baboons underwent a partial pancreatectomy (tail removal) and received a continuous exenatide (n = 12) or saline (n = 12) infusion for 13 weeks. At the end of treatment, HC/A was repeated, and the remnant pancreas (head-body) was harvested. Insulin sensitivity increased dramatically after exenatide treatment and was accompanied by a decrease in insulin and C-peptide secretion, while the insulin secretion/insulin resistance (disposition) index increased by about 2-fold. β, α, and δ cell relative volumes in exenatide-treated baboons were significantly increased compared with saline-treated controls, primarily as the result of increased islet cell replication. Features of cellular stress and secretory dysfunction were present in islets of saline-treated baboons and absent in islets of exenatide-treated baboons. In conclusion, chronic administration of exenatide exerts proliferative and cytoprotective effects on β, α, and δ cells and produces a robust increase in insulin sensitivity in nonhuman primates.

Long-term c-Kit overexpression in beta cells compromises their function in ageing mice

AIMS/HYPOTHESIS

c-Kit signalling regulates intracellular pathways that enhance beta cell proliferation, insulin secretion and islet vascularisation in mice up to 28 weeks of age and on short-term high-fat diet. However, long-term c-Kit activation in ageing mouse islets has yet to be examined. This study utilises beta cell-specific c-Kit-overexpressing transgenic (c-KitβTg) ageing mice (~60 weeks) to determine the effect of its activation on beta cell dysfunction and insulin secretion.

METHODS

Wild-type and c-KitβTg mice, aged 60 weeks, were examined using metabolic tests to determine glucose tolerance and insulin secretion. Pancreas histology and proteins in isolated islets were examined to determine the expression of beta cell transcription factors, proliferation and intracellular signalling. To determine the role of insulin receptor signalling in ageing c-KitβTg mice, we generated beta cell-specific inducible insulin receptor knockout in ageing c-KitβTg mice (c-KitβTg;βIRKO mice) and examined the ageing mice for glucose tolerance and islet histology.

RESULTS

Ageing c-KitβTg mice progressively developed glucose intolerance, compared with age-matched wild-type littermates, due to impaired insulin secretion. Increased beta cell mass, proliferation and nuclear forkhead box transcription factor O1 (FOXO1) expression and reduced exocytotic protein levels were detected in ageing c-KitβTg mouse islets. Protein analyses of isolated islets showed increased insulin receptor, phosphorylated IRS-1^Ser612 and cleaved poly(ADP-ribose) polymerase levels in ageing c-KitβTg mice. Ageing c-KitβTg mouse islets treated ex vivo with insulin demonstrated reduced Akt phosphorylation, indicating that prolonged c-Kit induced beta cell insulin insensitivity. Ageing c-KitβTg;βIRKO mice displayed improved glucose tolerance and beta cell function compared with ageing c-KitβTg mice.

CONCLUSIONS/INTERPRETATION

These findings indicate that long-term c-Kit overexpression in beta cells has a negative impact on insulin exocytosis and that temporally dependent regulation of c-Kit-insulin receptor signalling is important for optimal beta cell function.

β-Cell Receptor Tyrosine Kinases in Controlling Insulin Secretion and Exocytotic Machinery: c-Kit and Insulin Receptor

Insulin secretion from pancreatic β-cells is initiated through channel-mediated depolarization, cytoskeletal remodeling, and vesicle tethering at the cell membrane, all of which can be regulated through cell surface receptors. Receptor tyrosine kinases (RTKs) promote β-cell development and postnatal signaling to improve β-cell mass and function, yet their activation has also been shown to initiate exocytotic events in β-cells. This review examines the role of RTK signaling in insulin secretion, with a focus on RTKs c-Kit and insulin receptor (IR). Pathways that control insulin release and the potential interplay between c-Kit and IR signaling are discussed, along with clinical implications of RTK therapy on insulin secretion.

Human limbal niche cells are a powerful regenerative source for the prevention of limbal stem cell deficiency in a rabbit model

In this article, human limbal niche cells (LNC) or bone marrow derived mesenchymal stem cells (BMMSC) were used to prevent limbal stem cell deficiency (LSCD) in an alkali burn rabbit model and their results were compared. The epithelial cell defect area, corneal neovascularization, and the print cell cytometry were quantified to grade the severity of LSCD. Three months after the alkali burn, a partial LSCD was observed in the control group (no treatment) indicated by chronic corneal epithelial defects, positive corneal fluorescein staining, neovascularization and goblet cell migration. In contrast, the severity of LSCD in both the LNC and BMMSC transplantation groups was dramatically reduced as shown by smaller epithelial cell defects, decreased fluorescein sodium staining, decreased neovascularization and decreased goblet cell density. Interestingly, the LNC group was shown to more effectively prevent LSCD than the BMMSC group. Further analysis indicated subconjunctivally transplanted LNCs were more powerful than BMMSCs to prevent LSCD, at least partially, due to increased activation of SCF-c-Kit signal. We conclude that LNCs are a more powerful resource than BMMSCs to prevent LSCD in an alkali burn rabbit model, at least partially due to increased activation of SCF signaling.

A New Isolation Method of Human Lacrimal Canaliculus Epithelial Stem Cells by Maintaining Close Association with Their Niche Cells

Purpose: To investigate whether lacrimal canaliculus epithelial stem cells (LCESC) could be isolated and expanded in vitro. Methods: The lacrimal canaliculus epithelium of 6 patients with limbal stem cell deficiency (LSCD) caused by alkali burn or Stevens Johnson Syndrome were examined by lacrimal endoscope. Cadaveric eyelids were fixed and prepared for cross section and stained with HE and antibodies against PCK, Vim, p63α, SCF and c-Kit. Canaliculus tissue was separated under an operating microscope using a lacrimal probe as an indicator and digested with collagenase A. The clusters of epithelial cells with closely associated stroma were further digested with Trypsin/EDTA to obtain single cells for culture on Matrigel-coated plastic plates in MESCM media. The expression of SCF, c-Kit and p63α was determined by immunostaining. The colony-forming efficiency on 3T3 feeder layers was also measured by calculating the percentage of the clone number divided by the total number cells seeded. Results: The epithelial layers of five out of six inferior lacrimal canaliculi and all the six superior lacrimal canaliculi were visually normal in appearance. Five to fifteen layers of the epithelium in the human lacrimal canaliculi were present with a small, tightly compacted basal layer of cells expressing PCK, p63α, SCF and c-Kit. LCESC were isolated by collagenase A and obtained clonal growth in MESCM. The colony-forming efficiency of LCESC holoclones on a 3T3 feeder layer was 3.2%, compared to 1.9% for those of limbal stem cells (LSC). Conclusions: Herein, we first report that LCESCs can be isolated and have stem cell characteristics, similar to those of LSCs. Such a discovery raises a promising substrate resource of stem cells for LSC reconstruction in LSCD patients.

c-Kit Receptor Signaling Regulates Islet Vasculature, β-Cell Survival, and Function In Vivo

The receptor tyrosine kinase c-Kit plays an integral role in maintaining β-cell mass and function. Although c-Kit receptor signaling promotes angiogenesis in multiple cell types, its role in islet vasculature is unknown. This study examines the effects of c-Kit-mediated vascular endothelial growth factor isoform A (VEGF-A) and islet vascularization on β-cell function and survival using in vitro cell culture and in vivo mouse models. In cultured INS-1 cells and primary islets, c-Kit regulates VEGF-A expression via the Akt/mammalian target of rapamycin (mTOR) signaling pathway. Juvenile mice with mutated c-Kit (c-Kit(Wv/+)) showed impaired islet vasculature and β-cell dysfunction, while restoring c-Kit expression in β-cells of c-Kit(Wv/+) mice rescued islet vascular defects through modulation of the Akt/mTOR/VEGF-A pathway, indicating that c-Kit signaling in β-cells is a required regulator for maintaining normal islet vasculature. Furthermore, β-cell-specific c-Kit overexpression (c-KitβTg) in aged mice showed significantly increased islet vasculature and β-cell function, but, when exposed to a long-term high-fat diet, c-Kit signaling in c-KitβTg mice induced substantial vascular remodeling, which resulted in increased islet inflammatory responses and β-cell apoptosis. These results suggest that c-Kit-mediated VEGF-A action in β-cells plays a pivotal role in maintaining islet vascularization and function.

Expression and localisation of c-kit and KITL in the adult human ovary

BACKGROUND

The c-kit/kit ligand (KITL) signalling axis is an essential component of ovarian folliculogenesis in mammals, but little is known about expression and localisation of its key components in the ovaries of reproductive age women. This study aimed to characterise mRNA expression of c-kit and KITL isoforms and the localisation of c-kit and KITL proteins in adult human premenopausal ovaries.

METHODS

This study utilised granulosa cells obtained from the preovulatory follicles of women undergoing assisted reproduction, pieces of ovarian tissue obtained from premenopausal women undergoing gynaecological surgeries and archival paraffin-embedded premenopausal ovarian tissues. Methodology included PCR for gene expression and Western blot or immunohistochemistry for protein expression.

RESULTS

Both c-kit mRNA isoforms, known as GNNK+ and GNNK-, were detected in human ovarian cortex, while KITL protein isoforms (KITL1 and KITL2) were present in ovarian cortex and human granulosa cells. Immunohistochemistry showed expression of KITL and c-kit protein in multiple cell types within follicles throughout development, from primordial follicles to large antral follicles, in addition to atretic follicles. Oocytes of all follicle stages expressed c-kit protein exclusively. Interestingly, unlike animal models, expression of both proteins displayed a less cell-type specific distribution with immunostaining present in granulosa, theca and stromal cells, suggesting that autocrine signalling occurs within the human ovary.

CONCLUSION

The results of this study indicate that c-kit/KITL signalling also occurs in the human ovary, as established in various animal models, and may involve previously unknown autocrine signalling.

A survival Kit for pancreatic beta cells: stem cell factor and c-Kit receptor tyrosine kinase

The interactions between c-Kit and its ligand, stem cell factor (SCF), play an important role in haematopoiesis, pigmentation and gametogenesis. c-Kit is also found in the pancreas, and recent studies have revealed that c-Kit marks a subpopulation of highly proliferative pancreatic endocrine cells that may harbour islet precursors. c-Kit governs and maintains pancreatic endocrine cell maturation and function via multiple signalling pathways. In this review we address the importance of c-Kit signalling within the pancreas, including its profound role in islet morphogenesis, islet vascularisation, and beta cell survival and function. We also discuss the impact of c-Kit signalling in pancreatic disease and the use of c-Kit as a potential target for the development of cell-based and novel drug therapies in the treatment of diabetes.

Clinical and Prognostic Significances of Cytokeratin 19 and KIT Expression in Surgically Resectable Pancreatic Neuroendocrine Tumors

BACKGROUND

Pancreatic neuroendocrine tumors (PanNETs) are malignant endocrine neoplasms that present diverse clinical behaviors. Therefore, identification of biomarkers of PanNETs is important for stratification of the prognosis of PanNET patients. Recently, cytokeratin 19 (CK19) and KIT expression were reported to have prognostic significance in PanNET patients.

METHODS

To identify their prognostic significance, CK19 and KIT protein expression were assessed in 182 surgically resected PanNETs and compared with clinicopathologic factors.

RESULTS

Of 182 PanNETs cases, CK19 and KIT expression was noted in 97 (53.3%) and 16 (8.8%) cases, respectively. PanNET patients with CK19 expression had larger tumors (p=.006), higher World Health Organization (WHO) grade (p=.002) and pT classification (p<.001), increased distant metastasis (p=.004), and lymphovascular (p=.012) and perineural (p=.019) invasion. Similarly, those with KIT expression had larger tumors (p=.030), higher WHO grade (p=.001), advanced pT classification (p<.001), distant metastasis (p=.001), and lymphovascular invasion (p=.014). The 5-year survival rate for PanNET patients with KIT expression was significantly lower (62%) than that of patients without KIT expression (77%, p=.011), as determined by univariate but not by multivariate analyses.

CONCLUSIONS

CK19 and KIT expression correlate with higher metastatic potential and advanced disease stage, and KIT expression is associated with worse survival in PanNET patients.

DAB2IP regulates cancer stem cell phenotypes through modulating stem cell factor receptor and ZEB1

Cancer stem cell (CSC), the primary source of cancer-initiating population, is involved in cancer recurrence and drug-resistant phenotypes. This study demonstrates that the loss of DAB2IP, a novel Ras-GTPase activating protein frequently found in many cancer types, is associated with CSC properties. Mechanistically, DAB2IP is able to suppress stem cell factor receptor (c-kit or CD117) gene expression by interacting with a newly identified silencer in the c-kit gene. Moreover, DAB2IP is able to inhibit c-kit-PI3K-Akt-mTOR signaling pathway that increases c-myc protein to activate ZEB1 gene expression leading to the elevated CSC phenotypes. An inverse correlation between CD117 or ZEB1 and DAB2IP is also found in clinical specimens. Similarly, Elevated expression of ZEB1 and CD117 are found in the prostate basal cell population of DAB2IP knockout mice. Our study reveals that DAB2IP has a critical role in modulating CSC properties via CD117-mediated ZEB1 signaling pathway.

Aldehyde dehydrogenase 1 activity in the developing human pancreas modulates retinoic acid signalling in mediating islet differentiation and survival

AIMS/HYPOTHESIS

Aldehyde dehydrogenase 1 (ALDH1), a human stem-cell marker, is an enzyme responsible for converting retinaldehydes to retinoic acids (RAs) to modulate cell differentiation. However, data on expression levels and functional roles of ALDH1 during human fetal pancreatic development are limited. The focus of this study was to characterise ALDH1 expression patterns and to determine its functional role in islet cell differentiation.

METHODS

The presence of ALDH1 in the human fetal pancreas (8-22 weeks) was characterised by microarray, quantitative RT-PCR, western blotting and immunohistological approaches. Isolated human fetal islet-epithelial cell clusters were treated with ALDH1 inhibitors, retinoic acid receptor (RAR) agonists and ALDH1A1 small interfering (si)RNA.

RESULTS

In the developing human pancreatic cells, high ALDH1 activity frequently co-localised with key stem-cell markers as well as endocrine transcription factors. A high level of ALDH1 was expressed in newly differentiated insulin(+) cells and this decreased as development progressed. Pharmacological inhibition of ALDH1 activity in human fetal islet-epithelial cell clusters resulted in reduced endocrine cell differentiation and increased cell apoptosis, and was reversed with co-treatment of RAR/RXR agonists. Furthermore, siRNA knockdown of ALDH1A1 significantly decreased RAR expression and induced cell apoptosis via suppression of the phosphoinositide 3-kinase (PI3K) pathway and activation of caspase signals.

CONCLUSIONS/INTERPRETATION

Our findings indicate that ALDH1(+) cells represent a pool of endocrine precursors in the developing human pancreas and that ALDH1 activity is required during endocrine cell differentiation. Inhibition of ALDH1-mediated retinoid signalling impairs human fetal islet cell differentiation and survival.

c-Kit immunoexpression delineates a putative endothelial progenitor cell population in developing human lungs

Expression of c-Kit and its ligand, stem cell factor (SCF), in developing human lung tissue was investigated by immunohistochemistry. Twenty-eight human fetal lungs [age range 13 to 38 gestational wk (GW)] and 12 postnatal lungs (age range 1-79 yr) were evaluated. We identified c-Kit(+) cells in the lung mesenchyme as early as 13 GW. These mesenchymal c-Kit(+) cells in the lung did not express mast cell tryptase or α-smooth muscle actin. However, these cells did express CD34, VEGFR2, and Tie-2, indicating their endothelial lineage. Three-dimensional reconstructions of confocal laser scanning images revealed that c-Kit(+) cells displayed a closed-end tube formation that did not contain hematopoietic cells. From the pseudoglandular phase to the canalicular phase, c-Kit(+) cells appeared to continuously proliferate, to connect with central pulmonary vessels, and finally, to develop the lung capillary plexus. The spatial distribution of c-Kit- and SCF-positive cells was also demonstrated, and these cells were shown to be in close association. Our results suggest that c-Kit expression in early fetal lungs marks a progenitor population that is restricted to endothelial lineage. This study also suggests the potential involvement of c-Kit signaling in lung vascular development.

Modulation of c-kit expression in pancreatic adenocarcinoma: a novel stem cell marker responsible for the progression of the disease

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers because of late symptoms and resistance to chemotherapy and radiation therapy. We have investigated the appearance of c-kit, a stem cell marker, in both normal adult pancreatic tissue and in cancerous tissue. Apart from some very pale staining of islets of Langerhans, normal pancreas was devoid of staining with antibodies to c-kit. In contrast, in cancerous tissue that still preserves the overall integrity of the pancreatic tissue, there was a clear labeling in islets of Langerhans, which seemed to be co-localized with insulin containing β cells. In other cases, where the pancreatic tissue was completely deteriorated, intensive labeling was clearly evident in remnants of both the exocrine and the endocrine tissues. The duct cells of the adenocarcinoma were moderately but clearly labeled with antibodies to c-kit. In contrast, in metastasis of PDAC, very intensive labeling of c-kit was evident. The location of KRAS, which is strongly associated with PDAC, was also analyzed at the initial stages of the disease, when islets of Langerhans still preserve their integrity to a large extent. KRAS was found exclusively in islets of Langerhans and overlapped in its location with insulin and c-kit expressing cells. It is suggested that the modulation of the expression of c-kit, visualized by antibodies to the oncogene molecule, may play an important role in the formation and progression of PDAC. The absence of c-kit in normal pancreas and its appearance in PDAC is probably due to a mutational event, which probably allows conversion of the β cells into cancer stem cells (CSC). Co-expression of both c-kit and KRAS, typical markers for CSC with overlapping with insulin in islets of Langerhans, strongly support the notion that β-cells play a central role in the development of PDAC. The use of specific drugs that can attenuate the kinase activity of c-kit or target KRAS expressing cancer cells should be tested in order to attenuate the progression of this lethal disease.

Combined KIT and FGFR2b signaling regulates epithelial progenitor expansion during organogenesis

Organ formation and regeneration require epithelial progenitor expansion to engineer, maintain, and repair the branched tissue architecture. Identifying the mechanisms that control progenitor expansion will inform therapeutic organ (re)generation. Here, we discover that combined KIT and fibroblast growth factor receptor 2b (FGFR2b) signaling specifically increases distal progenitor expansion during salivary gland organogenesis. FGFR2b signaling upregulates the epithelial KIT pathway so that combined KIT/FGFR2b signaling, via separate AKT and mitogen-activated protein kinase (MAPK) pathways, amplifies FGFR2b-dependent transcription. Combined KIT/FGFR2b signaling selectively expands the number of KIT+K14+SOX10+ distal progenitors, and a genetic loss of KIT signaling depletes the distal progenitors but also unexpectedly depletes the K5+ proximal progenitors. This occurs because the distal progenitors produce neurotrophic factors that support gland innervation, which maintains the proximal progenitors. Furthermore, a rare population of KIT+FGFR2b+ cells is present in adult glands, in which KIT signaling also regulates epithelial-neuronal communication during homeostasis. Our findings provide a framework to direct regeneration of branched epithelial organs.

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Combined KIT and FGFR2b signaling amplifies FGFR2b-dependent transcription

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KIT/FGFR2b signaling during organogenesis expands distal KIT+ epithelial progenitors

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Distal progenitors communicate with proximal progenitors via the neuronal niche

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KIT+ progenitors maintain epithelial-neuronal communication during adult homeostasis

A platinum(II) phenylphenanthroimidazole with an extended side-chain exhibits slow dissociation from a c-Kit G-quadruplex motif

A series of three platinum(II) phenanthroimidazoles each containing a protonable side-chain appended from the phenyl moiety through copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) were evaluated for their capacities to bind to human telomere, c-Myc, and c-Kit derived G-quadruplexes. The side-chain has been optimized to enable a multivalent binding mode to G-quadruplex motifs, which would potentially result in selective targeting. Molecular modeling, high-throughput fluorescence intercalator displacement (HT-FID) assays, and surface plasmon resonance (SPR) studies demonstrate that complex 2 exhibits significantly slower dissociation rates compared to platinum phenanthroimidazoles without side-chains and other reported G-quadruplex binders. Complex 2 showed little cytotoxicity in HeLa and A172 cancer cell lines, consistent with the fact that it does not follow a telomere-targeting pathway. Preliminary mRNA analysis shows that 2 specifically interacts with the ckit promoter region. Overall, this study validates 2 as a useful molecular probe for c-Kit related cancer pathways.

Elevated toll-like receptor 3 inhibits pancreatic β-cell proliferation through G1 phase cell cycle arrest

Activation of the innate and acquired immune systems plays an important role in chronic inflammatory diseases and conditions such as obesity, insulin resistance, type 2 diabetes mellitus and atherosclerosis, with additional roles in regulation of cell proliferation and survival. Here, we provide evidence that TLR3 can respond to nutrient signals and induce loss of β-cell mass through induction of G1 cycle arrest. Activation of TLR3 by polyinosinic-polycytidylic acid [poly (I:C)] was shown to trigger the decline of cyclin D1/2 protein levels in pancreatic β-cell lines, which could be reversed by the proteasome inhibitor MG132. P38 was also found to interfere with this degradation which may be associated with G1 cycle arrest. Moreover, inhibitory effects of TLR3 on β-cell growth were supported by gene silencing of TRIF, which could inhibit p38 activity in response to poly (I:C) stimuli. These results support a role for TLR3 in β-cell mass loss in metabolic surplus and raise the possibility that TRIF/p38 signaling may be involved in G1 phase cycle arrest through ubiquitin/proteasome-dependent degradation of cyclin D.

Risk factors and primary prevention trials for type 1 diabetes

Type 1 diabetes mellitus (T1DM) is a chronic autoimmune disease resulting in the designated immune destruction of insulin producing β-cells, usually diagnosed in youth, and associated with important psychological, familial, and social disorders. Once diagnosed, patients need lifelong insulin treatment and will experience multiple disease-associated complications. There is no cure for T1DM currently. The last decade has witnessed great progress in elucidating the causes and treatment of the disease based on numerous researches both in rodent models of spontaneous diabetes and in humans. This article summarises our current understanding of the pathogenesis of T1DM, the roles of the immune system, genes, environment and other factors in the continuing and rapid increase in T1DM incidence at younger ages in humans. In addition, we discuss the strategies for primary and secondary prevention trials of T1DM. The purpose of this review is to provide an overview of this disorder's pathogenesis, risk factors that cause the disease, as well as to bring forward an ideal approach to prevent and cure the disorder.

Downregulation of Fas activity rescues early onset of diabetes in c-Kit(Wv/+) mice

c-Kit and its ligand stem cell factor (SCF) are important for β-cell survival and maturation; meanwhile, interactions between the Fas receptor (Fas) and Fas ligand are capable of triggering β-cell apoptosis. Disruption of c-Kit signaling leads to severe loss of β-cell mass and function with upregulation of Fas expression in c-Kit(Wv/+) mouse islets, suggesting that there is a critical balance between c-Kit and Fas activation in β-cells. In the present study, we investigated the interrelationship between c-Kit and Fas activation that mediates β-cell survival and function. We generated double mutant, c-Kit(Wv/+);Fas(lpr/lpr) (Wv(-/-)), mice to study the physiological and functional role of Fas with respect to β-cell function in c-Kit(Wv/+) mice. Isolated islets from these mice and the INS-1 cell line were used. We observed that islets in c-Kit(Wv/+) mice showed a significant increase in β-cell apoptosis along with upregulated p53 and Fas expression. These results were verified in vitro in INS-1 cells treated with SCF or c-Kit siRNA combined with a p53 inhibitor and Fas siRNA. In vivo, Wv(-/-) mice displayed improved β-cell function, with significantly enhanced insulin secretion and increased β-cell mass and proliferation compared with Wv(+/+) mice. This improvement was associated with downregulation of the Fas-mediated caspase-dependent apoptotic pathway and upregulation of the cFlip/NF-κB pathway. These findings demonstrate that a balance between the c-Kit and Fas signaling pathways is critical in the regulation of β-cell survival and function.

Beta cell dysfunction and insulin resistance

Beta cell dysfunction and insulin resistance are inherently complex with their interrelation for triggering the pathogenesis of diabetes also somewhat undefined. Both pathogenic states induce hyperglycemia and therefore increase insulin demand. Beta cell dysfunction results from inadequate glucose sensing to stimulate insulin secretion therefore elevated glucose concentrations prevail. Persistently elevated glucose concentrations above the physiological range result in the manifestation of hyperglycemia. With systemic insulin resistance, insulin signaling within glucose recipient tissues is defective therefore hyperglycemia perseveres. Beta cell dysfunction supersedes insulin resistance in inducing diabetes. Both pathological states influence each other and presumably synergistically exacerbate diabetes. Preserving beta cell function and insulin signaling in beta cells and insulin signaling in the glucose recipient tissues will maintain glucose homeostasis.

The platelet-derived growth factor (PDGF) family of tyrosine kinase receptors: a Kit to fix the beta cell?

Overexpression of c-Kit has recently been shown to ameliorate beta cell function by increasing the beta cell mass and insulin secretion, thus counteracting the deleterious effects of a high-fat diet on glucose homeostasis. The c-Kit-dependent effects are due to enhanced Akt activity that phosphorylates and inhibits glycogen synthase kinase 3β (GSK3β), thereby increasing the expression of numerous genes that promote insulin production and cell proliferation. Regulating the c-Kit/Akt/GSK3β pathway may provide novel means for improving beta cell function in type 2 diabetes.

Critical role of c-Kit in beta cell function: increased insulin secretion and protection against diabetes in a mouse model

AIMS/HYPOTHESIS

The receptor tyrosine kinase, c-Kit, and its ligand, stem cell factor, control a variety of cellular processes, including pancreatic beta cell survival and differentiation as revealed in c-Kit ( Wv ) mice, which have a point mutation in the c-Kit allele leading to loss of kinase activity and develop diabetes. The present study further investigated the intrinsic role of c-Kit in beta cells, especially the underlying mechanisms that influence beta cell function.

METHODS

We generated a novel transgenic mouse model with c-KIT overexpression specifically in beta cells (c-KitβTg) to further examine the physiological and functional roles of c-Kit in beta cells. Isolated islets from these mice were used to investigate the underlying molecular pathway of c-Kit in beta cells. We also characterised the ability of c-Kit to protect animals from high-fat-diet-induced diabetes, as well as to rescue c-Kit ( Wv ) mice from early onset of diabetes.

RESULTS

c-KitβTg mice exhibited improved beta cell function, with significantly improved insulin secretion, and increased beta cell mass and proliferation in response to high-fat-diet-induced diabetes. c-KitβTg islets exhibited upregulation of: (1) insulin receptor and IRSs; (2) Akt and glycogen synthase kinase 3β phosphorylation; and (3) transcription factors important for islet function. c-KIT overexpression in beta cells also rescued diabetes observed in c-Kit ( Wv ) mice.

CONCLUSIONS/INTERPRETATION

These findings demonstrate that c-Kit plays a direct protective role in beta cells, by regulating glucose metabolism and beta cell function. c-Kit may therefore represent a novel target for treating diabetes.

Inhibition of Gsk3β activity improves β-cell function in c-KitWv/+ male mice

Previous studies have shown that the stem cell marker, c-Kit, is involved in glucose homeostasis. We recently reported that c-Kit(Wv/+) male mice displayed the onset of diabetes at 8 weeks of age; however, the mechanisms by which c-Kit regulates β-cell proliferation and function are unknown. The purpose of this study is to examine if c-Kit(Wv/+) mutation-induced β-cell dysfunction is associated with downregulation of the phospho-Akt/Gsk3β pathway in c-Kit(Wv/+) male mice. Histology and cell signaling were examined in C57BL/6J/Kit(Wv/+) (c-Kit(Wv/+)) and wild-type (c-Kit(+/+)) mice using immunofluorescence and western blotting approaches. The Gsk3β inhibitor, 1-azakenpaullone (1-AKP), was administered to c-Kit(Wv/+) and c-Kit(+/+) mice for 2 weeks, whereby alterations in glucose metabolism were examined and morphometric analyses were performed. A significant reduction in phosphorylated Akt was observed in the islets of c-Kit(Wv/+) mice (P<0.05) along with a decrease in phosphorylated Gsk3β (P<0.05), and cyclin D1 protein level (P<0.01) when compared with c-Kit(+/+) mice. However, c-Kit(Wv/+) mice that received 1-AKP treatment demonstrated normal fasting blood glucose with significantly improved glucose tolerance. 1-AKP-treated c-Kit(Wv/+) mice also showed increased β-catenin, cyclin D1 and Pdx-1 levels in islets, demonstrating that inhibition of Gsk3β activity led to increased β-cell proliferation and insulin secretion. These data suggest that c-Kit(Wv/+) male mice had alterations in the Akt/Gsk3β signaling pathway, which lead to β-cell dysfunction by decreasing Pdx-1 and cyclin D1 levels. Inhibition of Gsk3β could prevent the onset of diabetes by improving glucose tolerance and β-cell function.

Rab27b regulates c-kit expression by controlling the secretion of stem cell factor

Rab27b, a subfamily of Rab27 small GTPases, was originally identified in platelets. However, the role of Rab27b in megakaryocytic lineage cells remains unknown. Here, using a human megakaryoblastic cell line, CMK, we show that Rab27b negatively regulates c-kit-expression. We found that transfection of shRNA-Rab27b into CMK cells led to specific increase in the amount of the receptor-type tyrosine kinase c-kit. To elucidate the molecular mechanisms by which Rab27b regulates c-kit expression, we analyzed the dynamics of c-kit by the stimulation with its ligand, stem cell factor (SCF). We found that cell surface expression of c-kit was promptly reduced and rapidly degraded in both CMK and Rab27b-knockdown CMK cells. Pretreatment with a lysosome inhibitor bafilomycin suppressed the degradation of c-kit, indicating that c-kit expression is controlled by SCF-induced endolysosomal degradation system. We therefore focused on the potential involvement of SCF in Rab27b-mediated effects on c-kit expression levels. We found that autocrine secretion of SCF was downregulated in Rab27b-knockdown cells as compared with parental CMK cells. These results suggest that Rab27b negatively regulates the cell surface expression of c-kit via secretion of SCF and that ligation of SCF leads to the endolysosomal degradation system of c-kit.

Isolation of pancreatic progenitor cells with the surface marker of hematopoietic stem cells

To isolate pancreatic progenitor cells with the surface markers of hematopoietic stem cells, the expression of stem cell antigen (Sca-1) and c-Kit and the coexpression of them with pancreatic duodenal homeobox-1 (PDX-1), neurogenin 3 (Ngn3), and insulin were examined in murine embryonic pancreas. Then different pancreatic cell subpopulations were isolated by magnet-activated cell sorting. Isolated cells were cultured overnight in hanging drops. When cells formed spheres, they were laid on floating filters at the air/medium interface. With this new culture system, pancreatic progenitor cells were induced to differentiate to endocrine and exocrine cells. It was shown that c-Kit and Sca-1 were expressed differently in embryonic pancreas at 12.5, 15.5, and 17.5 days of gestation. The expression of c-Kit and Sca-1 was the highest at 15.5 days of gestation. c-Kit rather than Sca-1 coexpressed with PDX-1, Ngn3, and insulin. Cells differentiated from c-Kit-positive cells contained more insulin-producing cells and secreted more insulin in response to glucose stimulation than that from c-Kit-negative cells. These results suggested that c-Kit could be used to isolate pancreatic progenitor cells and our new culture system permitted pancreatic progenitor cells to differentiate to mature endocrine cells.

Complete meiosis from human induced pluripotent stem cells

Gamete failure-derived infertility affects millions of people worldwide; for many patients, gamete donation by unrelated donors is the only available treatment. Embryonic stem cells (ESCs) can differentiate in vitro into germ-like cells, but they are genetically unrelated to the patient. Using an in vitro protocol that aims at recapitulating development, we have achieved, for the first time, complete differentiation of human induced pluripotent stem cells (hiPSCs) to postmeiotic cells. Unlike previous reports using human ESCs, postmeiotic cells arose without the over-expression of germline related transcription factors. Moreover, we consistently obtained haploid cells from hiPSCs of different origin (keratinocytes and cord blood), produced with a different number of transcription factors, and of both genetic sexes, suggesting the independence of our approach from the epigenetic memory of the reprogrammed somatic cells. Our work brings us closer to the production of personalized human gametes in vitro.

SOX9 regulates endocrine cell differentiation during human fetal pancreas development

The transition of pancreatic progenitor cells to mature endocrine cells is regulated by the sequential activation and interaction of several transcription factors. In mice, the transcription factor Sox9 has been shown to support endocrine cell differentiation. However, the functional role of SOX9 during pancreas development in the human has yet to be determined. The present study was to characterize SOX9 expression during human fetal pancreas development and examine its functional role by transfection with SOX9 siRNA or SOX9 expression vectors. Here we report that SOX9 was most frequently expressed in PDX1(+) cells (60-83%) and least in mature endocrine cells (<1-14%). The proliferation of SOX9(+) cells was significantly higher at 8-10 weeks than at 14-21 weeks (p<0.05) or 20-21 weeks (p<0.01). SOX9 frequently co-localized with FOXA2, NGN3 and transcription factors linked to NGN3 (NKX2.2, NKX6.1, PAX6). siRNA knockdown of SOX9 significantly decreased islet-epithelial cell proliferation, NGN3, NKX6.1, PAX6 and INS mRNA levels and the number of NGN3(+) and insulin(+) cells (p<0.05) while increasing GCG mRNA and glucagon(+) cells (p<0.05). Examination of SOX9 associated signaling pathways revealed a decrease in phospho-Akt (p<0.01), phospho-GSK3β (p<0.01) and cyclin D1 (p<0.01) with a decrease in nuclear β-catenin(+) (p<0.05) cells following SOX9 siRNA knockdown. In contrast, over-expression of SOX9 significantly increased the number of islet cells proliferating, NGN3, NKX6.1, PAX6 and INS mRNA levels, the phospho-Akt/GSK3β cascade and the number of insulin(+) cells. Our results demonstrated that SOX9 is important for the expression of NGN3 and molecular markers of endocrine cell differentiation in the human fetal pancreas.

Circulating concentration of stem cell factor in serum of stimulated IVF patients

Stem cell factor (SCF) plays a major role in haematopoiesis and spermatogenesis, and possibly female fertility. This study investigated the role of changes in SCF concentrations in 74 assisted conception patients. In group 1 (n=74) SCF concentration was assessed in serum and follicular fluid (FF) on the day of follicular puncture (FP) and compared in serum and FF in response to ovarian stimulation between low (n=25), moderate (n=26) and high (n=14) responders. In group 2 (n=30) serum for SCF assessment was collected throughout the menstrual cycle until gestation. SCF concentration related to the number of follicles in serum and in FF decreased from low to moderate and high responders (P<0.001); pregnancy rates were 20.0%, 34.6% and 50.1%, respectively (P=0.05). SCF in serum increased from stimulation days 6-8 to 9-11 and peaked on the day of human chorionic gonadotrophin injection (P=0.03). The SCF concentrations dropped slightly on the day of FP, increased significantly to the day of pregnancy confirmation and reached highest concentration (P=0.02) during gestation. SCF is involved in follicle development and may be a predictor of IVF outcome.

c-Kit and stem cell factor regulate PANC-1 cell differentiation into insulin- and glucagon-producing cells

Recent evidence has shown that stem cell factor (SCF) and its receptor, c-Kit, have an important role in pancreatic islet development by promoting islet cell differentiation and proliferation. In this study, we examined the role of c-Kit and SCF in the differentiation and proliferation of insulin- and glucagon-producing cells using a human pancreatic duct cell line (PANC-1). Our study showed that increased expression of endocrine cell markers (such as insulin and glucagon) and transcription factors (such as PDX-1 and PAX-6) coincided with a decrease in CK19(+) and c-Kit(+) cells (P<0.001) during PANC-1 cell differentiation, determined by immunofluorescence and qRT-PCR. Cells cultured with exogenous SCF showed an increase in insulin(+) (26%) and glucagon(+) (35%) cell differentiation (P<0.01), an increase in cell proliferation (P<0.05) and a decrease in cell apoptosis (P<0.01). siRNA knockdown of c-Kit resulted in a decrease in endocrine cell differentiation with a reduction in PDX-1 and insulin mRNA, as well as the number of cells immunostaining for PDX-1 and insulin. Taken together, these results show that c-Kit/SCF interactions are involved in mediating islet-like cluster formation and islet-like cell differentiation in a human pancreatic duct cell line.

Effect of forkhead box O1 (FOXO1) on beta cell development in the human fetal pancreas

AIMS/HYPOTHESIS

Recent studies have demonstrated that in adult murine beta cells the forkhead box O1 (FOXO1) transcription factor regulates proliferation and stress resistance. However, the role of FOXO1 during pancreatic development remains largely unknown. The present study aimed to characterise the expression of the FOXO1 transcription factor in the early to mid-gestation human fetal pancreas and to understand its role in islet cell development.

METHODS

Human (8-21 week fetal age) pancreases were examined using immunohistological, quantitative RT-PCR and western blotting. Isolated human (18-21 week) fetal islet epithelial cell clusters were treated with insulin or glucose, or transfected with FOXO1 small interfering RNA (siRNA).

RESULTS

Nuclear and cytoplasmic FOXO1 were widely produced during human fetal endocrine pancreatic development, co-localising in cells with the transcription factors pancreatic and duodenal homeobox 1 (PDX-1) and neurogenin 3 (NGN3) as well as cytokeratin 19 (CK19), insulin and glucagon. Treatment with exogenous insulin (50 nmol/l) induced the nuclear exclusion of FOXO1 in both cytokeratin 19 (CK19)(+) (p < 0.01) and insulin(+) cells (p < 0.05) in parallel with increased phospho-Akt (p < 0.05) production. siRNA knockdown of FOXO1 significantly increased the number of NGN3(+) (p < 0.01) and NK6 homeobox 1 (NKX6-1)(+) (p < 0.05) cells in parallel with increases in insulin gene expression (p < 0.03) and C-peptide(+) cells (p < 0.05) and reduced levels of hairy and enhancer of split 1 (HES1) (p < 0.01).

CONCLUSIONS/INTERPRETATION

Our results indicate that FOXO1 may negatively regulate beta cell differentiation in the human fetal pancreas by controlling critical transcription factors, including NGN3 and NKX6-1. These data suggest that the manipulation of FOXO1 levels may be a useful tool for improving cell-based strategies for the treatment of diabetes.

KIT is an independent prognostic marker for pancreatic endocrine tumors: a finding derived from analysis of islet cell differentiation markers

Prediction of the biologic behavior of pancreatic endocrine tumor (PET) without local invasion or metastasis is often difficult. The 2004 World Health Organization (WHO) classification uses size, angioinvasion, mitotic activity, and Ki-67 index as prognostic criteria. Recently, cytokeratin 19 (CK19) was shown to be another prognostic marker, but the mechanism by which CK19 predicts prognosis is unknown. As CK19 is the first cytokeratin expressed in all epithelial cells in fetal pancreas, we sought to test expression of other markers of islet cell differentiation including KIT, Pdx-1, Pax4, and Pax6 in PET and correlation of these markers with clinical behavior. Clinical information and histology was reviewed in 97 PETs. All tumors were classified according to WHO criteria and a tumor, node, and metastases stage system. Immunohistochemistry was performed using antibodies to Ki-67, KIT, CK19, Pdx-1, Pax4, and Pax6. Associations of clinicopathologic and immunohistochemical features with prognosis were evaluated using Cox proportional hazards regression models. WHO and tumor, node, and metastases classifications, mitotic counts and Ki-67 labeling, infiltrative border, necrosis, perineural invasion, extrapancreatic extension, tumor size, and positive CK19 and KIT expression were significantly associated with death from disease in a univariate setting. In multivariate analysis, only WHO criteria and KIT expression were shown to be independent. An immunohistochemical classification system was derived from a combination of KIT and CK19 expression: low risk (KIT-/CK19-), intermediate risk (KIT-/CK19+), and high risk (KIT+/CK19+). Survival, metastases, and recurrence of PET were significantly different among the 3 groups. These results indicate that KIT is a new and independent prognostic marker for PETs. The classification system derived from KIT and CK19 was able to predict clinical behavior of PET.

An appraisal of intermediate filament expression in adult and developing pancreas: vimentin is expressed in alpha cells of rat and mouse embryos

Intermediate filaments are frequently used in studies of developmental biology as markers of cell differentiation. To assess whether they can be useful to identify differentiating pancreatic endocrine cells, we examined the pattern of expression of nestin, cytokeratin 20, and vimentin on acetone-fixed cryosections of rat adult and developing pancreas. We also studied vimentin expression in mouse embryonic pancreas at E19. Cytokeratin 20 was found in all pancreatic epithelial cell lineages during the entire development of the rat gland and in the adult animals. Under our experimental conditions, therefore, cytokeratin 20 is not an exclusive marker of rat duct cells. Nestin was detected exclusively in stromal cells either in the adult or developing rat pancreas. Vimentin was observed within cells located in the primitive ducts of rat pancreas starting from E12.5. Their number rapidly increased, reaching its highest level in newborn animals. Vimentin was also spotted in alpha cells starting from E12.5 but disappeared soon after birth, likely identifying immature or recently differentiated alpha cells. In addition, vimentin was observed in duct and alpha cells of mouse developing pancreas showing that its expression in such cells is not an event restricted to the rat. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Developmental biology of the pancreas: a comprehensive review

Pancreatic development represents a fascinating process in which two morphologically distinct tissue types must derive from one simple epithelium. These two tissue types, exocrine (including acinar cells, centro-acinar cells, and ducts) and endocrine cells serve disparate functions, and have entirely different morphology. In addition, the endocrine tissue must become disconnected from the epithelial lining during its development. The pancreatic development field has exploded in recent years, and numerous published reviews have dealt specifically with only recent findings, or specifically with certain aspects of pancreatic development. Here I wish to present a more comprehensive review of all aspects of pancreatic development, though still there is not a room for discussion of stem cell differentiation to pancreas, nor for discussion of post-natal regeneration phenomena, two important fields closely related to pancreatic development.

c-Kit in early onset of diabetes: a morphological and functional analysis of pancreatic beta-cells in c-KitW-v mutant mice

c-Kit tyrosine receptor kinase, a well-established stem cell marker, is expressed in a variety of tissues including the pancreas. The involvement of c-Kit in fetal rat and human endocrine pancreatic development, survival, and function has been well characterized but primarily using in vitro experimental approaches. Therefore, the aim of the current study was to examine whether deficiency of a functional c-Kit receptor would have physiological and functional implications in vivo. We characterized the c-Kit mutant mouse, c-Kit(W-v/+), to evaluate the in vivo role of c-Kit in beta-cell growth and function. Here we report that male c-Kit(W-v/+) mice, at 8 wk of age, showed high fasting blood glucose levels and impaired glucose tolerance, which was associated with low levels of insulin secretion after glucose stimulation in vivo and in isolated islets. Morphometric analysis revealed that beta-cell mass was significantly reduced (50%) in male c-Kit(W-v/+) mice when compared with controls (c-Kit(+/+)) (P < 0.05). In parallel, a reduction in pancreatic duodenal homeobox-1 and insulin gene expression in whole pancreas as well as isolated islets of c-Kit(W-v/+) male mice was noted along with a decrease in pancreatic insulin content. Furthermore, the reduction in beta-cell mass in male c-Kit(W-v/+) mice was associated with a decrease in beta-cell proliferation. Interestingly, these changes were not observed in female c-Kit(W-v/+) mice until 40 wk of age. Our results clearly demonstrate that the c-Kit receptor is involved in the regulation of glucose metabolism, likely through an important role in beta-cell development and function.