Biomedical subjects

Fraser Fellows

Publications and source records attributed to Fraser Fellows.

4 recordsLinked to original sources

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↗

PubMed2002

Successful pregnancy outcome in a patient with severe chylomicronemia due to compound heterozygosity for mutant lipoprotein lipase.

OBJECTIVES: Familial chylomicronemia syndrome is characterized by massive accumulation of plasma chylomicrons, which typically results from an absolute deficiency of lipoprotein lipase (LPL). Chylomicronemia in pregnancy is a rare, but serious clinical problem and can be found in patients with underlying molecular defects in the LPL gene. We report the course and treatment of an 18 yr-old primigravida who had LPL deficiency and hypertriglyceridemia since birth. We also analyzed the molecular basis of her LPL deficiency. DESIGN AND METHODS: The patient's antenatal course was complicated by extreme elevations of plasma triglycerides. Her management included a very low fat diet, pharmacotherapy with gemfibrozil in the third trimester, and intermittent hospitalization with periods of fasting supplemented by IV glucose feeding. We used DNA sequencing to determine whether mutations in LPL were present. RESULTS: At 38 weeks of gestation, labor was induced, and the patient delivered a healthy 2.77 kilogram male. Postnatal triglycerides fell to prenatal levels. DNA sequencing showed that she was a compound heterozygote for mutant LPL: I > T194 and R > H243. CONCLUSIONS: This experience indicates that vigilance is required during pregnancy in patients with familial chylomicronemia due to mutant LPL. Gemfibrozil was used in this patient without apparent adverse effects. Compound heterozygosity for LPL mutations is an important underlying mechanism for LPL deficiency.

Adolescent↗

PubMed2002

Human embryonic-derived hematopoietic repopulating cells require distinct factors to sustain in vivo repopulating function.

OBJECTIVE: We have previously identified a novel circulating embryonic blood cell capable of pluripotent hematopoietic reconstitution, which may serve as a target for in utero stem cell therapy. Based on its unique biological properties and ontogenic origin, we aim to examine the ability to maintain and retrovirally transduce fetal blood (FB) reconstituting cells in ex vivo culture conditions previously optimized for pluripotent hematopoietic repopulating cells derived from later stages of human ontogeny. METHODS: FB cells were evaluated for proliferative potential, progenitor composition, and SCID-repopulating cell (SRC) capacity before and after 3 days of serum free (SF) ex vivo culture using the previously optimized growth factor conditions of SCF, Flt-3L, IL-3, IL-6, and G-CSF (GF Mix), in comparison to cultures using GF Mix + oncostatin M (OSM), or SCF + Flt-3L. We further examined the ability to retrovirally transduce FB-SRC maintained in culture using SCF + Flt-3L alone. RESULTS: Circulating FB-SRC could not be maintained under GF Mix conditions previously shown to sustain CB (cord blood)-SRC. Ex vivo culture with SCF + Flt-3L reduced the proliferation of primitive FB cells lacking lineage commitment markers (Lin(-)), but expanded FB progenitors and sustained FB-SRC compared to culture with GF Mix with and without OSM. Using SCF + Flt-3L, FB-SRC capable of multilineage reconstitution were successfully transduced, suggesting that SCF and Flt-3L are necessary and sufficient for the survival and transduction of human hematopoietic repopulating cells of embryonic origin. CONCLUSION: Our study provides novel insights into the requirements of primitive FB reconstituting cells that are essential for developing in utero stem cell gene therapy protocols, and further illustrates the biological distinctiveness of FB-SRC compared to hematopoietic repopulating cells from other stages of human ontogeny.

Animals↗