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Biomedical subjects

Peter A Doris

Publications and source records attributed to Peter A Doris.

At least 19 recordsLinked to original sources
PubMed2025

Novel insights into the genetic architecture and mechanisms of host/microbiome interactions from a multi-cohort analysis of outbred laboratory rats.

The intestinal microbiome influences health and disease. Its composition is affected by host genetics and environmental exposures. Understanding host genetic effects is critical but challenging in humans, due to the difficulty of detecting, mapping and interpreting them. To address this, we analysed host genetic effects in four cohorts of outbred laboratory rats exposed to distinct but controlled environments. We found that polygenic host genetic effects were consistent across environments. We identified three replicated microbiome-associated loci, one of which involved a sialyltransferase gene and Paraprevotella. We found a similar association in a human cohort, between ST6GAL1 and Paraprevotella, both of which have been linked with immune and infectious diseases. Moreover, we found evidence of indirect genetic effects on microbiome phenotypes, which substantially increased their total genetic variance. Finally, we identified a novel mechanism whereby indirect genetic effects can contribute to "missing heritability".

Journal Article↗
PubMed2006

Sequence variation in the soluble epoxide hydrolase gene and subclinical coronary atherosclerosis: interaction with cigarette smoking.

Soluble epoxide hydrolase (EPHX2) catalyses the degradation of the vasoactive and anti-inflammatory epoxyeicosatrienoic acids and may play a role in the pathophysiology of atherosclerosis. 1337 African-Americans and 1645 Whites from the CARDIA study were genotyped for 22 and 15 EPHX2 single nucleotide polymorphisms (SNPs), respectively, to examine the associations of common EPHX2 haplotypes and genotypes with presence of coronary artery calcified plaque (CAC). The potential influence of cigarette smoking, which increases EPHX2 gene expression, on these associations was also assessed. In African-Americans, a common haplotype uniquely tagged by the R287Q polymorphism was associated with significantly greater risk for CAC (OR=1.7; 95% CI=1.04-3.0). In Whites, a common haplotype uniquely tagged by a polymorphism in Intron 11 of the gene was associated with significantly greater risk for CAC (OR=1.3; 95% CI=1.02-1.6). These haplotype-tagging polymorphisms also showed significant associations with CAC in individual SNP analyses, and these relationships were significantly modified by smoking. This detailed investigation of the association of EPHX2 genetic variation with CAC supports EPHX2's emerging role as a risk factor for atherosclerosis, whose effects are influenced by smoking.

Adolescent↗
PubMed2006

Genomics and epigenomics of hypertension.

Hypertension is the most common risk factor for stroke, heart disease, and end-stage renal disease. Despite significant advances in the characterization of the physiological mechanisms that govern the regulation of blood pressure, the genetic and molecular bases of hypertension remain poorly understood. The completion of the draft sequence of the human genome, and recent advances in the identification and characterization of patterns of sequence variation in human populations, hold the promise that hypertension genomics will offer significant insights into disease pathophysiology and open new avenues for the development of novel therapeutic modalities. However, the emergence of the epigenotype as a major determinant of disease is likely to transform our genome-centric approaches toward more integrative and comprehensive strategies. This review provides an overview of the current progress of and future prospects for the application of genomic and epigenomic sciences to hypertension research.

Epistasis, Genetic↗
PubMed2005

Regulation of adrenocortical cardiotonic steroid production by dopamine and PKA signaling.

There is growing evidence that the adrenal cortex is the source of cardiotonic steroid (CS) regulators of sodium, potassium-ATPase (NKA). The control of adrenocortical production CS may play a critical role in mediating renal and vascular responses involved in arterial hypertension. Dopamine (DA) controls renal NKA by direct regulatory phosphorylation and indirectly by modification of aldosterone release. In the present studies, Y-1 adrenocortical cell cultures which have been shown to produce a cardiotonic steroid indistinguishable from the known vertebrate steroid, marinobufagenin (MBG), were treated with various agents to stimulate or antagonize dopamine signaling pathways. We demonstrate that Y-1 cells express both pharmacological types of dopamine receptor (DA1 and DA2). Treatment of Y-1 cells with DA stimulated MBG production in a dose range similar to that shown to inhibit aldosterone production by the adrenal cortex. Experiments with specific DA1 and DA2 receptor agonists and antagonists were performed and allowed us to attribute the DA stimulatory effect to a DA1 type receptor. The DA stimulatory effect on MBG depended on protein kinase A (PKA) and could be blocked by Rp-cAMPS. Although both basal and forskolin-stimulated progesterone production by Y-1 cells were profoundly inhibited in Y-1 cell lines expressing the dominant negative type I regulatory subunit of PKA, both basal and forskolin-stimulated MBG production were demonstrated in these lines. This evidence suggests a possible role of DA1 signaling through camp-mediated activation of the type II PKA holoenzyme in the adrenal cortex.

Adrenal Cortex↗
PubMed2005

Renal localization, expression, and developmental regulation of P450 4F cytochromes in three substrains of spontaneously hypertensive rats.

Cytochrome P450 4F isoforms have been shown to metabolize arachidonic acid to generate 20-hydroxyeicosatetraenoic acid (20-HETE), a potent eicosanoid that modulates vascular tone and renal tubular function. 20-HETE production in the kidney is implicated in the development of essential hypertension in the spontaneously hypertensive rat (SHR). In this study, we determined CYP4F mRNA localization and distribution in rat liver and kidney by in situ hybridization and real time quantitative PCR. CYP4Fs are regionally distributed in the kidney with CYP4F1, 4F4, and 4F5 being expressed more in the renal cortex than medulla while CYP4F6 shows higher medullary expression. We investigated developmental CYP4F gene expression in three different substrains of SHR. Distinct age-dependent patterns of expression were seen for individual CYP4F isoforms in Wistar-Kyoto (WKY) and three SHR substrains (B2, C, and A3). A steady increase in CYP4F1 expression with age was seen in each of the three substrains which correlate well with increased 20-HETE levels and elevated blood pressure seen in these animals. CYP4F4 expression increased significantly at 8 weeks followed by a precipitous fall in WKY and A3 strains at 12 weeks of age. In strains B2 and C, CYP4F4 levels started declining as early as 8 weeks of age. CYP4F5 and 4F6 levels fluctuated with age in a biphasic manner with a different profile for each sub-strain. Based on the expression profile and catalytic activity, CYP4F1 seems to be the most critical 4F isoform involved in the production of 20-HETE in the SHR kidney.

Animals↗
PubMed2005

The soluble epoxide hydrolase gene harbors sequence variation associated with susceptibility to and protection from incident ischemic stroke.

Stroke is the leading cause of severe disability and the third leading cause of death, accounting for one of every 15 deaths in the USA. We investigated the association of polymorphisms in the soluble epoxide hydrolase gene (EPHX2) with incident ischemic stroke in African-Americans and Whites. Twelve single nucleotide polymorphisms (SNPs) spanning EPHX2 were genotyped in a case-cohort sample of 1336 participants from the Atherosclerosis Risk in Communities (ARIC) study. In each racial group, Cox proportional hazard models were constructed to assess the relationship between incident ischemic stroke and EPHX2 polymorphisms. A score test method was used to investigate the association of common haplotypes of the gene with risk of ischemic stroke. In African-Americans, two common EPHX2 haplotypes with significant and opposing relationships to ischemic stroke risk were identified. In Whites, two common haplotypes showed suggestive indication of an association with ischemic stroke risk but, as in African-Americans, these relationships were in opposite direction. These findings suggest that multiple variants exist within or near the EPHX2 gene, with greatly contrasting relationships to ischemic stroke incidence; some associated with a higher incidence and others with a lower incidence.

Black or African American↗
PubMed2005

Simultaneous expression of apolipoprotein B mRNA editing enzyme and scavenger receptor BI mediated by a therapeutic gene expression system.

Cardiovascular diseases are often accompanied by elevated LDL particles and endothelial dysfunction. We have examined the possibility of concurrently reducing LDL levels and modulating endothelial function using a single helper-dependent adenovirus vector system to simultaneously express the apolipoprotein B mRNA editing enzyme (Apobec1) and the scavenger receptor, class B, type I (SR-BI) genes under the control of separate promoters (designated HD-C2). Apobec1 edits apoB mRNA at nucleotide C-6666 to produce truncated apoB48 and is normally expressed in small intestine only. SR-BI is a receptor for multiple ligands with distinct tissue-specific functions. Expression of Apobec1 in HepG2 cells resulted in apoB mRNA editing, leading to decreased apoB100 abundance (to 6% of control) and the appearance of apoB48. Editing of apoB mRNA in HepG2 cells resulted in decline in apoB mRNA levels of 50%. This was probably the result of nonsense-mediated decay of edited message, since over-expression of Apobec1 increased neither Apobec1 complementary factor (ACF) mRNA nor protein abundance. Over-expression of SR-BI in human endothelial cells activated endothelial nitric oxide synthase (eNOS) activity by phosphorylation of eNOS at residue Ser-1177 in the presence of HDL, leading to increased production of the anti-atherogenic molecule nitric oxide (NO). Taken together, this study demonstrates that using one vector delivery system to express two genes in two different cell types results in the cell-specific beneficial effects of decreasing apoB100 production and increasing eNOS activities. This combined gene expression approach may provide an improved therapeutic strategy by targeting multiple sites in the mechanism of cardiovascular injury.

APOBEC-1 Deaminase↗
PubMed2005

Combined genealogical, mapping, and expression approaches to identify spontaneously hypertensive rat hypertension candidate genes.

Allelic expression in genes has become recognized as a heritable trait by which phenotypes are generated. We have examined gene expression in the rat kidney using genome-wide microarray technology (Affymetrix). Gene expression was determined across 4 rat strains, 3 hypertensive spontaneously hypertensive rat (SHR) substrains (SHR-A3, SHR-B2, and SHR-C), and a normotensive strain (Wistar-Kyoto [WKY]). Expression measurements were made in multiple animals from all strains at 4 time points (4 weeks, 8 weeks, 12 weeks, and 18 weeks of age), covering the prehypertensive period in SHR (4 weeks), and the period of rapidly rising blood pressure (8 and 12 weeks) and of sustained hypertension (18 weeks). Regression analysis revealed a close relationship across all strains during the first 3 time points, after which SHR-A3 became a substantial outlier. SHR-B2 and SHR-C demonstrated a very close relationship in gene expression at all times but also showed increased differences compared with the other strains at 18 weeks of age. We identified genes that were consistently different in expression, comparing all SHR substrains at each time point with WKY. The resulting list of genes was compared with blood pressure quantitative trait loci reported for SHR to refine a number of genes consistently differentially expressed between SHR substrains and WKY, persistently differentially expressed across multiple time points, and located in SHR blood pressure-determinative regions of the genome. Genealogical relationships and SHR substrain intercrosses suggest that genes responsible for heritable hypertension in SHR are shared across SHR substrains. The present approach identifies a number of genes that may influence blood pressure in SHR by virtue of allelic effects on gene expression.

Animals↗
PubMed2005

Single-nucleotide polymorphism genotyping for disease association studies.

The Human Genome Project has led to the discovery of millions of DNA sequence variants in the human genome. The majority of these variants are single-nucleotide polymorphisms (SNPs). Availability of an ultra-high-density SNP map, combined with improvement in genotyping technologies and efficient analytical approaches, opens the possibility of fulfilling the promise of SNP association studies to reveal why some individuals are more susceptible to common chronic diseases such as hypertension and stroke. With millions of SNPs spread throughout the human genome, it is neither practical nor necessary to genotype every single SNP in population samples for association studies. Linkage disequilibrium between sites suggests that it is possible to detect disease association using a relatively sparse collection of SNPs. While the cost associated with assaying a comprehensive set of SNPs is still significant, several technologies show great promise for high-efficiency SNP genotyping. This chapter focuses on two of them: the 5'-nuclease assay and mass spectrometry genotyping.

Base Sequence↗
PubMed2005

The transcribed genome and the heritable basis of essential hypertension.

Gene expression can be now assessed quantitatively and comprehensively. In addition to reflecting the specialized differentiation of the cell or tissue type from which gene expression is sampled, it also manifests patterns determined by inheritance. Thus gene expression is a phenotypic trait, at least when assessed comprehensively. This trait shows familial aggregation and segregation patterns indicative of an inherited contribution. The molecular evolution of genes includes mutations affecting regulatory sequences in the genome that influence gene expression in cis and in trans. Such mutations may increase in frequency in a population either by genetic drift or by selection. Traits of gene expression, acting alone or in concert with other gene expression traits, may generate phenotypes that extend beyond transcript abundance. Indeed, the divergence of species and the traits that distinguish related species appear to rely importantly on inherited divergence in the control of gene expression. Variation in gene expression may contribute to the pathogenesis of a prevalent human disease trait that shows heritability--essential hypertension. Along with other common heritable diseases, hypertension susceptibility arises from the actions of multiple genome sequence variations. The identity of such variation has proven elusive when sought by methods that have been successfully applied to Mendelian diseases. This review explores the potential to uncover hypertension genes by exploiting quantitative variation in the heritable control of gene expression.

Animals↗
PubMed2004

Altered subcellular distribution of Na+,K+-ATPase in proximal tubules in young spontaneously hypertensive rats.

During early development of hypertension, the spontaneously hypertensive rat (SHR) demonstrates increased proximal tubule sodium reabsorption. Our previous observations of reduced Na+,K+-ATPase catalytic alpha1 and gamma subunit transcript abundance in SHR proximal tubule led us to test the hypothesis that increased proximal tubule sodium reabsorption may be attributable to altered subunit protein abundance, post-translational modification, or a shift in subcellular alpha1 and gamma distribution toward the basolateral membrane. We now extend previous gene expression studies by analyzing total cellular alpha1 and gamma protein abundance in proximal tubule from SHR compared with matched Wistar-Kyoto (WKY) controls. We also used sucrose density-gradient centrifugation to isolate basolateral, early, and late endosomal membrane-enriched fractions as well as cell surface biotinylation to test the hypothesis of altered subunit subcellular distribution in the SHR proximal tubule. At 4 weeks of age, significantly greater amounts of alpha1 were present in basolateral membrane-enriched fractions of SHR than WKY (21.1+/-1.8% versus 12.3+/-1.8%; P<0.005), and there was a concomitant reduction of alpha1 in late endosomal membrane-enriched fractions of SHR (63.3+/-2.7% versus 74.8+/-4.3%; P<0.05). This finding was confirmed in cell surface biotinylation studies that showed higher alpha1 (1.45+/-0.1-fold greater; P<0.05) and gamma-subunit (3.48+/-0.7-fold greater; P<0.01) abundance in 4-week-old SHR proximal tubule plasma membrane compared with matched WKY samples. These studies support the hypothesis that development of hypertension in SHR may involve an altered subcellular distribution of proximal tubule Na+,K+-ATPase subunits.

Animals↗
PubMed2004

Polymorphism of the soluble epoxide hydrolase is associated with coronary artery calcification in African-American subjects: The Coronary Artery Risk Development in Young Adults (CARDIA) study.

BACKGROUND: Modulation of endogenous epoxide levels by soluble epoxide hydrolase (sEH) in the endothelium represents an important mechanism in the regulation of cardiovascular function. We examined the relationship between a common, functional polymorphism of the human sEH gene and coronary artery calcification (CAC) in young, largely asymptomatic African-American and non-Hispanic white subjects. METHODS AND RESULTS: Multiple logistic regression and Tobit regression models were used to assess the relationship between the sEH Arg287Gln polymorphism and presence and quantity of CAC. Models adjusting for race (except in race-specific analyses), age, sex, smoking, body mass index, systolic blood pressure, LDL cholesterol, and HDL cholesterol were estimated. Allele and genotype frequency distributions were not significantly different between the 2 ethnic groups (P=0.22; P=0.17, respectively). The Arg287Gln polymorphism of the sEH gene was a significant predictor of CAC status in African-American participants, either alone or after adjusting for other risk factors. African-American subjects with at least 1 copy of the Gln287 allele had a 2-fold greater risk of having CAC compared with those not carrying this allele (95% CI, 1.1 to 2.9; P=0.02). There was no relationship between Arg287Gln polymorphism and the probability of having CAC in white participants (OR, 0.8; 95% CI, 0.5 to 1.3; P=0.49). Inferences from multivariable Tobit regression were similar to those obtained in the logistic regression models, indicating that the Arg287Gln polymorphism was a significant independent predictor of both presence and quantity of CAC in African-American but not white subjects. CONCLUSIONS: These data suggest an intriguing and possibly novel role for sEH in the pathogenesis of atherosclerosis, which deserves additional investigation.

Adolescent↗
PubMed2003

Ouabain- and marinobufagenin-induced proliferation of human umbilical vein smooth muscle cells and a rat vascular smooth muscle cell line, A7r5.

BACKGROUND: We studied the growth-promoting effects of 2 sodium pump-selective cardiotonic steroids, ouabain and marinobufagenin, on cultured cells from vascular smooth muscle (VSMCs) from human umbilical vein and a rat VSMC line, A7r5. METHODS AND RESULTS: Both ouabain and marinobufagenin activated proliferation of these cells in a concentration-dependent manner, reflecting the cardiotonic steroid sensitivity of the specific alpha1 subunit contained within each cell source. The observed effective concentration ranges of both compounds was below that necessary to induce cytoplasmic ion alterations by sodium pump inhibition. CONCLUSIONS: These data indicate that the ouabain-activated proliferative effect previously observed in canine VSMCs occurs in other VSMC sources. This growth effect seems to be initiated by drug interaction with the sodium pump, reflected by the affinity of the steroid for the pump, and is independent of altered transmembrane ionic gradients.

Animals↗
PubMed2003

Gene expression profiling and functional proteomic analysis reveal perturbed kinase-mediated signaling in genetic stroke susceptibility.

The stroke-prone spontaneously hypertensive rat (SHRSP) is a model of heritable hypertension-associated cerebrovascular injury. This study sought to compare SHRSP to the stroke-resistant SHR strain to identify genes and protein pathways whose expression and/or function was significantly altered between the strains prior to the onset of stroke. Cerebral cortex gene expression profiles from male SHRSPs and matched SHRs were examined by Affymetrix microarray analysis. mRNAs encoding the brain-derived neurotrophic factor receptor (TrkB) and multiple kinases of the MAPK/AKT signaling pathways, including JNK2, AKT2, and PI3K, were differentially expressed between SHRSP and SHR. Because these data suggest altered function in pathways involving MAP and AKT kinase activity, we performed Western blot using phosphorylation state-specific antibodies to characterize activity of MAP kinase and PI3K/AKT pathways. Changes in the levels of the phosphorylated forms of these kinases paralleled the changes in transcript levels observed between the strains. Two-dimensional gel electrophoresis and peptide fragment mass fingerprinting were used to identify altered protein substrates of these kinases. Protein profiling of kinase substrates further supported the notion of perturbed kinase-mediated signaling in SHRSP and identified adenylyl cyclase associated protein 2, TOAD-64, propionyl CoA carboxylase, APG-1, and valosin-containing protein as kinase targets whose phosphorylation state is altered between these strains. Altered gene and protein expression patterns in SHRSP are consistent with increased vulnerability of this strain to cerebrovascular injury.

Animals↗
PubMed2003

Ouabain is a potent promoter of growth and activator of ERK1/2 in ouabain-resistant rat renal epithelial cells.

Endogenous cardiotonic steroids (ECS) are putative ligands of the inhibitory binding site of the membrane sodium pump (Na+, K+-ATPase). There is growing evidence that cardiotonic steroids may promote the growth of cardiac and vascular myocytes, including evidence indicating growth stimulation at concentrations in the same range as circulating ECS concentrations. We investigated four parameters to determine whether ouabain, a proposed ECS, promotes growth of immortalized rat proximal tubule epithelial cells: cell count by hemocytometer; metabolic activity as reflected in the mitochondrial conversion of the tetrazolium salt, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, to its formazan product (MA); DNA synthesis reflected as bromodeoxyuridine incorporation (DNA); and mitosis reflected as histone phosphorylation state detected using anti-phosphohistone 3 antibody (HP). Maximum stimulatory responses were observed at 1 nm ouabain (MA, 20.3% increase, p < 0.01; DNA, 28.4% increase, p < 0.001; HP, maximum response at 0.5 h, 50% increase, p < 0.001). We observed that growth stimulation was associated with stimulation of ERK1/2 phosphorylation (ERK-P), and both growth and ERK-P could be blocked by the MEK inhibitor (U0126, 100 nm). Western blot analysis revealed that the only alpha isoform of Na+, K+-ATPase that could be detected in these cultures was the highly ouabain-resistant alpha1 isoform. Measurement of ouabain inhibition of ion transport in these cultures using 86Rb+ uptake revealed the predominance of the expected ouabain-resistant isoform (IC50 = 24 microm) and an additional minor ( approximately 15%) ouabain-sensitive inhibition with IC50 approximately 30 pm. Similar bimodal transport inhibition curves were obtained in freshly dissected rat proximal tubules. These results indicate that renal epithelial cells may be a sensitive target of the ERK1/2-activating and growth-promoting effects of ouabain even in the presence of ouabain-resistant Na+, K+-ATPase.

Animals↗
PubMed2002

Polymorphism in soluble epoxide hydrolase and blood pressure in spontaneously hypertensive rats.

We measured soluble epoxide hydrolase (sEH) renal gene expression in prehypertensive (4 to 5 weeks old) spontaneously hypertensive rats of the Heidelberg SP substrain (SHR [Heid]) and when blood pressure levels entered the hypertensive plateau (17 to 18 weeks old) and compared expression with matched Wistar-Kyoto (WKY [Heid]) rats. Less expression of the gene encoding sEH (EPHX2) was observed in SHR (Heid) than in WKY (Heid). Analysis of sEH protein abundance showed a similar difference. However, no correlation between sEH abundance and blood pressure was observed in the F(2) progeny of a parental strain cross. Measurement of protein abundance in SHR and WKY obtained from Charles River confirmed a recent report that abundance of sEH was greater in SHR (CRiv) than WKY (CRiv) strains. Polymorphisms were detected in EPHX2. Resequencing revealed that 2 alleles of EPHX2 exist in these 4 rat strains, differing by 4 single nucleotide polymorphisms, of which 3 produce nonsynonymous amino acid substitutions. The ancestral allele was shared by SHR (Heid) and WKY (CRiv), and the variant allele was shared by WKY (Heid) and SHR (CRiv). Activity of sEH was greater in animals carrying the variant allele. However, inheritance of this allele was not correlated with blood pressure in the F(2) progeny of a cross between SHR (Heid) and WKY (Heid). These data indicate that sequence variation determining functional alterations in EPHX2 is not likely to contribute to blood pressure levels in SHR.

Animals↗
PubMed2002

Hypertension genetics, single nucleotide polymorphisms, and the common disease:common variant hypothesis.

The investigation of heritable susceptibility to disease is an effort to associate disease phenotype with underlying genotype. Such genotype:phenotype associations have been demonstrated for a large number of monogenetic disorders. The usual strategy has been to use linkage mapping in affected families to identify chromosomal loci from which candidate genes and genotypes can be tested for association with disease. This strategy has not been similarly successful for common heritable disease susceptibilities including hypertension that involve multiple genes and gene-environment interactions. Development of extensive collections of single nucleotide polymorphisms (SNPs) raises the possibility that these SNPs can be used as markers in genome-wide association mapping studies to identify hypertension susceptibility loci. In this approach, large numbers of markers are typed in cases and controls with the expectation that markers interrogating SNPs that are involved in inheritance of disease susceptibility will emerge through their association with this trait in the affected population. Essential hypertension is a common disorder. The term "common" has 2 implications: first, that the disease is prevalent; and, second, that it is widespread. Such frequency and distribution characteristics could arise if the susceptibility alleles for hypertension were prevalent in the founding population of contemporary human beings and became distributed with human global dispersal. This common disease:common variant concept is attractive because it suggests that the genetic heterogeneity underlying hypertension susceptibility could be relatively small. It also allows the possibility that nonrandom association of alleles (linkage disequilibrium, LD) can be used to reduce the number of SNP markers required to identify disease susceptibility alleles because a single marker can act as a surrogate for variation flanking it. The influence of a number of important factors on the detectability of hypertension susceptibility alleles by SNP mapping approaches is not yet fully defined. These factors include the locus and allelic diversity of hypertension, the weaker relationship (compared with Mendelian traits) between genotype and phenotype, the accuracy of high throughput genotyping techniques, the extensive role of nongenetic factors, and the extent and heterogeneous nature of LD across the genome.

Alleles↗