Biomedical subjects

Gretchen Darlington

Publications and source records attributed to Gretchen Darlington.

7 recordsLinked to original sources

PubMed2006

Is genomic evaluation feasible in endoscopic studies of Barrett's esophagus? A pilot study.

BACKGROUND: The global gene expression in Barrett's esophagus (BE) in comparison to adjacent or histologically similar tissues has not been extensively studied. OBJECTIVE: To test the feasibility of conducting gene arrays in endoscopically obtained mucosal specimens. DESIGN: Cross-sectional feasibility study. SETTING: The Houston Department of Veterans Affairs Medical Center. PATIENTS: We collected endoscopic biopsies from BE, normal esophagus, antrum, duodenum, and sigmoid colon from 5 patients with BE. RNA was extracted and subjected to cDNA microarrays and gene expression was compared between BE and control tissues. Reverse transcription-PCR was conducted to confirm some of the findings. MAIN OUTCOME MEASUREMENTS: Gene expression profiles in BE tissues and 4 control sites: squamous esophagus, antrum, duodenum, sigmoid colon. RESULTS: On average, 2 biopsies by disposable jumbo biopsy forceps provided approximately 5 microg required for microarrays. From the original number of 22,283 gene probes, 13,805 genes had a quality score of P < .05 and were subjected to further comparison. BE gene expression clustered most closely with that of antrum and least closely with squamous esophagus. Of the 587 genes that had significantly different expression between BE and duodenum, 246 were upregulated and 341 were downregulated in BE. The expression of genes involved in apoptosis, negative regulation of apoptosis, and inflammatory response was significantly lower in BE compared to squamous esophagus. None of the gene groups were significantly overexpressed in BE compared to squamous esophagus or antrum. The reverse transcription-PCR confirmed the results of microarrays. LIMITATIONS: Small sample size. CONCLUSIONS: Microarray-based studies are feasible in endoscopically obtained tissues. Differences in gene expression could identify potential markers and shed light on the pathogenesis of BE.

Aged↗

PubMed2005

Differential mRNA processing in hematopoietic stem cells.

Hematopoietic stem cells (HSCs) maintain tissue homeostasis by rapidly responding to environmental changes. Although this function is well understood, the molecular mechanisms governing this characteristic are largely unknown. We used a sequenced-based strategy to explore the role of both transcriptional and post-transcriptional regulation in HSC biology. We characterized the gene expression differences between HSCs, both quiescent and proliferating, and their differentiated progeny. This analysis revealed a large fraction of sequence tags aligned to intronic sequences, which we showed were derived from unspliced transcripts. A comparison of the biological properties of the observed spliced versus unspliced transcripts in HSCs showed that the unspliced transcripts were enriched in genes involved in DNA binding and RNA processing. In addition, levels of unspliced message decreased in a transcript-specific fashion after HSC activation in vivo. This change in unspliced transcript level coordinated with increases in gene expression of splicing machinery components. Combined, these results suggest that post-transcriptional regulation is important in HSC activation in vivo.

Animals↗

PubMed2005

Gender-specific alterations in gene expression and loss of liver sexual dimorphism in the long-lived Ames dwarf mice.

Genetic mutations that increase lifespan in mice frequently involve alterations in the growth hormone/insulin-like growth factor-I signaling pathway. Although several of the effects of GH on gene expression are known to be sex-dependent, an understanding of the gender-specific vs. gender-independent effects of lifespan-extending mutations of the GH/IGF-I axis is currently lacking. The Ames dwarf mice (prop1(df/df)) are GH, prolactin and thyroid-stimulating hormone deficient and exhibit an increase in mean lifespan of 49% in males and 68% in females. We used oligonucleotide arrays containing over 14,000 genes to study the gender-specific vs. gender-independent effects of the prop1(df) mutation in liver of male and female Ames mice. We identified 381 gender-independent and 110 gender-specific alterations in gene expression produced by the Prop1(df/df) genotype. The gender-specific alterations corresponded to genes with a strong sexual dimorphism in wild-type mice and produced an almost complete loss of sex-specific gene expression in the liver of Ames dwarf mice: out of 123 genes that showed sexual dimorphism in wild-type mice only six maintained a gender difference in mutant mice. However, the Prop1(df/df) genotype did not introduce new sexually dimorphic patterns of gene expression in Ames dwarf mice that were not present in the wild-type animals. The gender-specific alterations accounted for a large fraction of the most significant changes in gene expression in male and female Ames mice livers and affected several metabolic processes, particularly fatty acid metabolism, steroid hormone metabolism, and xenobiotic metabolism.

Animals↗

PubMed2005

Vitamin D receptor Fok1 polymorphisms affect calcium absorption, kinetics, and bone mineralization rates during puberty.

UNLABELLED: Few studies of the VDR polymorphisms have looked at calcium metabolism or long-term effects. We measured bone mineralization and calcium metabolic parameters longitudinally in a group of 99 adolescents. We found a significant relationship between calcium absorption and skeletal calcium accretion and the Fok1, but not other VDR or related, genetic polymorphisms. It seems that the Fok1 polymorphism directly affects bone mineralization during pubertal growth through an effect on calcium absorption. INTRODUCTION: There are few data regarding the relationship between genetic markers for low bone mass and changes in calcium metabolism in childhood or adolescence. We sought to identify the effects of polymorphisms of the vitamin D receptor (VDR) on calcium and bone mineral metabolism in a longitudinal study of pubertal adolescents. MATERIALS AND METHODS: Adolescents (n = 99) received comprehensive stable isotope studies of calcium absorption, bone calcium kinetics, and bone mineralization. Studies were repeated 12 months later. Polymorphisms of putative genetic markers were determined and related to bone mineralization and calcium metabolic finding. Results were analyzed by ANOVA in which changes over time were determined using the initial value as a covariate. RESULTS: Polymorphisms of the Fok1 gene of the VDR were significantly related to calcium absorption (p = 0.008) and whole body BMC (p = 0.03) and BMD (p = 0.006). The Fok1 effect on whole body BMD was significant for those with Ca intake >800 mg/day (p < 0.001), whereas for those with Ca intake < or = 800 mg/day, the Fok1 genotype did not have a significant effect on whole body BMD (p = 0.40). The Fok1 genotype was significantly related to the changes during the year in whole body calcium accretion, with the ff genotype having a 63 +/- 20 mg/day deficit compared with the FF genotype (p = 0.008). CONCLUSIONS: The Fok1 polymorphism of the VDR receptor seems to directly affect bone mineral accretion during pubertal growth through an effect on calcium absorption. The relationship between different genetic polymorphisms and bone mineral metabolism may vary by life stage as well as diet.

Analysis of Variance↗

PubMed2005

A combination of prebiotic short- and long-chain inulin-type fructans enhances calcium absorption and bone mineralization in young adolescents.

BACKGROUND: Short-term studies in adolescents have generally shown an enhancement of calcium absorption by inulin-type fructans (prebiotics). Results have been inconsistent; however, and no studies have been conducted to determine whether this effect persists with long-term use. OBJECTIVE: The objective was to assess the effects on calcium absorption and bone mineral accretion after 8 wk and 1 y of supplementation with an inulin-type fructan. DESIGN: Pubertal adolescents were randomly assigned to receive 8 g/d of a mixed short and long degree of polymerization inulin-type fructan product (fructan group) or maltodextrin placebo (control group). Bone mineral content and bone mineral density were measured before randomization and after 1 y. Calcium absorption was measured with the use of stable isotopes at baseline and 8 wk and 1 y after supplementation. Polymorphisms of the Fok1 vitamin D receptor gene were determined. RESULTS: Calcium absorption was significantly greater in the fructan group than in the control group at 8 wk (difference: 8.5 +/- 1.6%; P < 0.001) and at 1 y (difference: 5.9 +/- 2.8%; P = 0.04). An interaction with Fok1 genotype was present such that subjects with an ff genotype had the least initial response to fructan. After 1 y, the fructan group had a greater increment in both whole-body bone mineral content (difference: 35 +/- 16 g; P = 0.03) and whole-body bone mineral density (difference: 0.015 +/- 0.004 g/cm(2); P = 0.01) than did the control group. CONCLUSION: Daily consumption of a combination of prebiotic short- and long-chain inulin-type fructans significantly increases calcium absorption and enhances bone mineralization during pubertal growth. Effects of dietary factors on calcium absorption may be modulated by genetic factors, including specific vitamin D receptor gene polymorphisms.

Absorption↗

PubMed2004

HIV-1 induces complement factor C3 synthesis in astrocytes and neurons by modulation of promoter activity.

Virus-induced complement expression and activation in the brain is hypothesized to contribute to the process of neurodegeneration in AIDS-associated neurological disorders. Previous experiments have shown that the human immunodeficiency virus (HIV) upregulates the low basal production of complement factor C3 in astrocytes and neurons. Since inhibition of complement synthesis and activation in the brain may represent a putative therapeutic goal to prevent virus-induced damage, we analysed the mechanism of the HIV-induced modulation of C3 expression. Detailed studies using different C3 promoter constructs revealed that HIV activates the synthesis of C3 by stimulation of the promoter. This HIV-induced promoter activation could be measured both in different astrocytic cell lines and in neurons. Deletion constructs of the C3 promoter defined the IL-6/IL-1beta responsive element within the promoter region as a central element for the responsiveness of the C3 promoter towards the influence of HIV. A binding site for the transcription factor C/EBPdelta was identified as important regulatory domain within the IL-6/IL-1beta responsive element, since a point mutation which eliminates the binding capacity of C/EBPdelta to this site also abolishes the induction by HIV-1. Similarly, the viral proteins Nef and gp41 which had also been shown to stimulate the synthesis of C3, exert their effect via the IL-6/IL-1beta responsive element with binding of the transcription factor C/EBPdelta representing the critical step. Our experiments clearly define the mechanism for the induction of complement factors in the HIV-infected brain and reveal a decisive role of the regulator protein C/EBPdelta for the HIV-induced increase in C3 expression.

Astrocytes↗

PubMed2004

Gene expression profile of long-lived Ames dwarf mice and Little mice.

Ames dwarf mice (Prop1df/df) and Little mice (Ghrhrlit/lit) are used as models of delayed aging and show significant increases in lifespan (50% and 25%, respectively) when compared with their wild-type siblings. To gain further insight into the molecular basis for the extended longevity of these mice, we used oligonucleotide microarrays to measure levels of expression of over 14 000 RNA transcripts in liver during normal aging at 3, 6, 12 and 24 months. We found that the Prop1df/df and Ghrhrlit/lit genotypes produce dramatic alterations in gene expression, which are predominantly maintained at all ages. We found 1125 genes to be significantly affected by the Prop1df/df genotype and 1152 genes were significantly affected by the Ghrhrlit/lit genotype; 547 genes were present in both gene lists and showed parallel changes in gene expression, suggesting common mechanisms for the extended longevity in these mutants. Some of the functional gene classes most affected in these mutants included: amino acid metabolism, TCA cycle, mitochondrial electron transport, fatty acid, cholesterol and steroid metabolism, xenobiotic metabolism and oxidant metabolism. We found that the Prop1df/df genotype, and to a minor extent the Ghrhrlit/lit genotype, also produced complex alterations in age-dependent changes in gene expression as compared with wild-type mice. In some cases these alterations reflected a partial delay or deceleration of age-related changes in gene expression as seen in wild-type mice but they also introduced age-related changes that are unique for each of these mutants and not present in wild-type mice.

Aging↗