Biomedical subjects

Rennian Wang

Publications and source records attributed to Rennian Wang.

8 recordsLinked to original sources

PubMed2006

Essential role of Pten in body size determination and pancreatic beta-cell homeostasis in vivo.

PTEN (phosphatase with tensin homology) is a potent negative regulator of phosphoinositide 3-kinase (PI3K)/Akt signaling, an evolutionarily conserved pathway that signals downstream of growth factors, including insulin and insulin-like growth factor 1. In lower organisms, this pathway participates in fuel metabolism and body size regulation and insulin-like proteins are produced primarily by neuronal structures, whereas in mammals, the major source of insulin is the pancreatic beta cells. Recently, rodent insulin transcription was also shown in the brain, particularly the hypothalamus. The specific regulatory elements of the PI3K pathway in these insulin-expressing tissues that contribute to growth and metabolism in higher organisms are unknown. Here, we report PTEN as a critical determinant of body size and glucose metabolism when targeting is driven by the rat insulin promoter in mice. The partial deletion of PTEN in the hypothalamus resulted in significant whole-body growth restriction and increased insulin sensitivity. Efficient PTEN deletion in beta cells led to increased islet mass without compromise of beta-cell function. Parallel enhancement in PI3K signaling was found in PTEN-deficient hypothalamus and beta cells. Together, we have shown that PTEN in insulin-transcribing cells may play an integrative role in regulating growth and metabolism in vivo.

Animals↗

PubMed2005

Stem cell factor/c-Kit interactions regulate human islet-epithelial cluster proliferation and differentiation.

Stem cell factor (SCF), a progenitor cell growth factor, binds to and activates the c-Kit receptor tyrosine kinase, which is critical for early stem cell differentiation in haematopoiesis and gametogenesis. Nothing is known regarding these interactions during islet development in the human fetal pancreas. The present study was to investigate whether an increase in c-Kit receptor activity in isolated human fetal islet-epithelial clusters, by giving exogenous SCF, would promote beta-cell development. In the intact fetal pancreas, SCF and c-Kit were observed co-localizing with cytokeratin 19 in both ductal and newly forming islet cells. Islet cells isolated from 14 to 16 weeks fetal pancreata were cultured with SCF (50 ng/ml) or vehicle for 48 h. We observed an increase in the number of c-Kit-, pancreatic and duodenal homeobox gene 1- (PDX-1-), insulin- and glucagon-expressing cells in the SCF-treated group (PDX-1 and insulin, p < 0.05). PDX-1 and c-Kit mRNA levels were also up-regulated in the SCF group (PDX-1, p < 0.05), with no change in preproinsulin or proglucagon gene expression. Co-localization of insulin with PDX-1 or c-Kit was observed frequently in SCF-treated cultures. A significantly (p < 0.05) greater proliferative capacity of islet-epithelial clusters was found in the SCF group in parallel with increased (p < 0.02) phosphorylation of Akt in a phosphatidylinositol-3 kinase (PI3K)-dependent manner. Our results demonstrate that SCF/c-Kit interactions are likely to be involved in mediating islet cell differentiation and proliferation during human fetal pancreatic development, and that phosphorylated Akt may have a role downstream of SCF/c-Kit signaling.

Cell Differentiation↗

PubMed2005

Role for beta1 integrin and its associated alpha3, alpha5, and alpha6 subunits in development of the human fetal pancreas.

The integrin receptors play a major role in tissue morphogenesis and homeostasis by regulating cell interactions with extracellular matrix proteins. We have examined the expression pattern of integrin subunits in the human fetal pancreas (8-20 weeks fetal age) and the relevance of beta1 integrin function for insulin gene expression and islet cell survival. Its subunits alpha3, alpha5, and alpha6 beta1 integrins are expressed in ductal cells at 8 weeks, before glucagon- and insulin-immunoreactive cells bud off; their levels gradually increase in both ductal cells and islet clusters up to 20 weeks. Colocalization of alpha3, alpha5 and alpha6 beta1 integrins with endocrine cell markers was frequently observed in 8- to 20-week fetal pancreatic cells. When the beta1 integrin receptor was functionally blocked in cultured islet-epithelial clusters with a beta1 immunoneutralizing antibody or following transient beta1 integrin small interfering RNA treatment, there was inhibition of cell adhesion to extracellular matrices, decreased expression of insulin, and increased cell apoptosis. These data offer evidence for dynamic and cell-specific changes in integrin expression during human pancreatic islet neogenesis. They also provide an initial insight into a molecular basis for cell-matrix interactions during islet development and suggest that beta1 integrin plays a vital role in regulating islet cell adhesion, gene expression, and survival.

Apoptosis↗

PubMed2004

Expression of {beta}1 integrin receptors during rat pancreas development--sites and dynamics.

The integrin receptors link to extracellular matrix proteins and exert a dynamic role in development by providing the physical basis for cell adhesion and controlling cell growth. In the present study, we examined changes in the expression of beta1 integrins and its associated alpha-subunits to islet cell development in the rat pancreas. A significant increase in protein expression of integrin alpha3, alpha6, and beta1 was observed from fetal to postnatal life. High mRNA levels of these integrin subunits was detected at embryonic d 18 and dropped significantly after birth with relatively low expression throughout postnatal life. Integrins alpha3, alpha5, alpha6, and beta1 were expressed in a cell-specific manner in the pancreas with high integrin immunoreactivity in duct and islet regions during fetal life, and a progressive increase later into postnatal life. The coexpression with islet and putative islet precursor markers during fetal and postnatal development suggest a role for these integrin subunits in differentiation and maturation of islets. Functional studies in vitro showed that anti-beta1 antibody treatment inhibited islet cell adhesion to extracellular matrices and disrupted islet architecture. Blockade of beta1 integrin receptor and knockdown beta1 mRNA resulted in a decrease in the expression of insulin mRNA and increased islet cell death. These results suggest that progression in islet cell development is accompanied by and dependent upon cell adhesion via beta1 integrin and its respective alpha-subunits and suggest that the beta1 family of integrins may play a critical role in islet cell architecture, development, integrity, and function.

Animals↗

PubMed2004

Expression of stem cell markers and transcription factors during the remodeling of the rat pancreas after duct ligation.

Ligation of the pancreatic duct has been shown to induce islet cell neogenesis from duct cells in the adult rat pancreas. The transcription factors that regulate islet cell neogenesis and the phenotype of putative precursor cells involved in neogenesis are unknown. We, therefore, studied the expression of the transcription factors Pdx1, Pbx1, Meis2, Nkx2.2 and the putative stem cell markers c-Kit and nestin in rat pancreata 3, 5 and 7 days after duct ligation. Immunocytochemical staining revealed a subpopulation of cells in the ligated portion of the pancreas that was positive for the putative stem cell markers c-Kit and nestin. The c-Kit immunoreactivity was upregulated, reaching a peak at day 3, while nestin expression peaked at day 7. The c-Kit-positive cells were located among the duct and islet cells, while nestin-expressing cells were found scattered in the duct epithelium at day 3 and around the ducts at day 7. Both c-Kit- and nestin-positive cells showed high proliferative activity, as determined by BrdU labeling. Pdx1 and Nkx2.2 were found predominantly in the duct cells of the ligated pancreas. There were significant changes in the expression patterns of Pbx1 and Meis2 in the ductular complexes. The findings indicate that the stem cell markers c-Kit and nestin as well as the transcription factors Pdx1 and Nkx2.2 are upregulated in compartments of the pancreas that are involved in islet cell neogenesis after duct ligation.

Animals↗

PubMed2004

Characterization of c-Kit and nestin expression during islet cell development in the prenatal and postnatal rat pancreas.

It has been well documented that there are abundant endocrine progenitor cells in the neonatal pancreas. However, little is known of their relative proportions or even their phenotypes. The aim of this study was to examine the normal distribution and characteristics of putative endocrine precursor cells, identified by c-Kit or nestin expression, within the prenatal and postnatal rat pancreas during islet cell development. Here, we provide evidence of the existence of a subset of ductal, islet, and acinar cells with an immature morphology and high proliferative capacity that expressed c-Kit or nestin. The proportion of islet cells expressing c-Kit or nestin was highest at embryonic day 18 (25 +/- 4% and 28 +/- 6%) and decreased significantly by postnatal day 28 (P < 0.01), 1.3 +/- 0.2% and 5.7 +/- 1%, respectively. The expression of nestin mRNA decreased throughout development, while c-Kit mRNA expression was found to slightly increase in the developing pancreas. Coexpression patterns indicated that c-Kit and nestin form two distinct cell populations in the postnatal pancreas, and infrequently coexpress with other pancreatic cell-specific markers. Furthermore, decreased c-Kit and nestin expression in the islets in postnatal life correlated with an increase in cells immunopositive for Pdx-1 compared with birth (36 +/- 5% vs. 60 +/- 3%, P < 0.01), which accompanied a doubling in the proportion of Glut-2-positive cells (39.4 +/- 4% vs. 68.8 +/- 3%, P < 0.01), both of which are mature beta-cell markers. Taken together, these findings suggest that c-Kit- and nestin-expressing cells represent endocrine precursor cells that undergo marked changes in population dynamics during the transition from prenatal to postnatal pancreatic development in the rat. Characterization of the phenotype, relative abundance and location of these cells within the developing pancreas is an important step toward creating a strategy for isolating stem cell populations and modeling islet cell differentiation in vitro.

Animals↗

PubMed2004

A pentadecapeptide fragment of islet neogenesis-associated protein increases beta-cell mass and reverses diabetes in C57BL/6J mice.

OBJECTIVE: The objective of this study was to demonstrate that islet neogenesis-associated protein (INGAP) peptide, a pentadecapeptide containing the biologically active portion of native INGAP, increases functional beta-cell mass in normal animals and can be used therapeutically to reverse hyperglycemia in streptozotocin-induced diabetes. SUMMARY BACKGROUND DATA: INGAP, a 175 amino acid pancreatic acinar cell protein, has been suggested to be implicated in beta-cell mass expansion. METHODS: In the first part of this study, normoglycemic hamsters were administered either 500 microg INGAP peptide (n = 30) or saline (n = 20) intraperitoneally daily and sacrificed after 10 or 30 days of treatment. Blood glucose and insulin levels were measured, and a histologic and morphometric analysis of the pancreas was performed to determine the effect of INGAP peptide on the endocrine pancreas. In the second part of the study, 6- to 8-week-old C57BL/6J mice (n = 8) were administered multiple low doses of the beta-cell toxin streptozotocin (STZ) inducing insulitis and hyperglycemia. The mice were then injected with INGAP peptide (n = 4) or saline (n = 4) for 39 days and sacrificed at 48 days. Two additional groups of diabetic mice were administered either a peptide composed of a scrambled sequence of amino acids from INGAP peptide (n = 5) or exendin-4 (n = 5), an incretin that has been associated with amelioration of hyperglycemia. RESULTS: Islet cell neogenesis was stimulated in INGAP-treated hamsters by 10 days. At 30 days, the foci of new endocrine cells had the appearance of mature islets. There was a 75% increase in islet number, with normal circulating levels of blood glucose and insulin. Administration of INGAP peptide to diabetic mice reversed the diabetic state in all animals, and this was associated with increased expression of PDX-1 in duct cells and islet cell neogenesis with a reduction of insulitis in the new islets. Diabetic mice treated with exendin-4 or a scrambled INGAP peptide did not revert from hyperglycemia. CONCLUSION: Because there is a deficiency of beta-cell mass in both type-1 and type-2 diabetes, INGAP peptide stimulation of fully functional neoislet differentiation may provide a novel approach for diabetes therapy.

Animals↗

PubMed2004

Phenotypic analysis of c-Kit expression in epithelial monolayers derived from postnatal rat pancreatic islets.

The limitation of available islets for transplantation is a major obstacle for the treatment of diabetes through islet therapy. However, islet monolayers expanded ex vivo may provide a source of progenitor cells and a model to help understand islet development from precursor cell types. The existence of progenitor cells within the islets is highly likely, yet, to date, no fully defined or characterized postnatal stem cell has been isolated, expanded or marked. Our study evaluates the expression of progenitor markers, including the haematopoietic stem cell marker c-Kit, in epithelial monolayers derived from postnatal rat islets through immunofluorescence and RT-PCR, and the ability of precursor-rich monolayers to reform islet-like structures. Islets formed confluent monolayers when cultured on a type I collagen gel which lacked endocrine phenotypes but were positive for cytokeratin 20 and contained an increased proportion of proliferating c-Kit-expressing cells, with the proportion reaching a maximum of 45+/-6% at 8 weeks of culture. Evaluation of transcription factors at the mRNA level revealed constant PDX-1, ngn3 and Pax4 expression, while undifferentiated cell markers, such as Oct4 and alpha-fetoprotein, were also detected frequently after 4 weeks of culture. Changing the extracellular matrix protein to laminin-rich Matrigel, the monolayers re-formed islet-like clusters that secreted insulin in a glucose-responsive fashion. Our data show that islets can be expanded ex vivo to form epithelial monolayers with rich undifferentiating cell populations that are characterized by cells expressing the progenitor markers. These monolayers are capable of extensive proliferation and retain plasticity to form new islet cells, and c-Kit-expressing cells may play an important role in new islet cluster formation.

Animals↗