A genomic-systems biology map for cardiovascular function

Hypothalamic Norepinephrine Concentration and Heart Mass in Hypertensive ISIAH Rats Are Associated with a Genetic Locus on Chromosome 18

The relationship between activation of the sympathetic nervous system and cardiac hypertrophy has long been known. However, the molecular genetic basis of this association is poorly understood. Given the known role of hypothalamic norepinephrine in the activation of the sympathetic nervous system, the aim of the work was to carry out genetic mapping using Quantitative Trait Loci (QTL) analysis and determine the loci associated both with an increase in the concentration of norepinephrine in the hypothalamus and with an increase in heart mass in Inherited Stress-Induced Arterial Hypertension (ISIAH) rats simulating the stress-sensitive form of arterial hypertension. The work describes a genetic locus on chromosome 18, in which there are genes that control the development of cardiac hypertrophy associated with an increase in the concentration of norepinephrine in the hypothalamus, i.e., genes involved in enhanced sympathetic myocardial stimulation. No association of this locus with the blood pressure was found. Taking into consideration previously obtained results, it was concluded that the contribution to the development of heart hypertrophy in the ISIAH rats is controlled by different genetic loci, one of which is associated with the concentration of norepinephrine in the hypothalamus (on chromosome 18) and the other is associated with high blood pressure (on chromosome 1). Nucleotide substitutions that may be involved in the formation or absence of association with blood pressure in different rat strains are discussed.

In silico clinical trials: concepts and early adoptions

Innovations in information and communication technology infuse all branches of science, including life sciences. Nevertheless, healthcare is historically slow in adopting technological innovation, compared with other industrial sectors. In recent years, new approaches in modelling and simulation have started to provide important insights in biomedicine, opening the way for their potential use in the reduction, refinement and partial substitution of both animal and human experimentation. In light of this evidence, the European Parliament and the United States Congress made similar recommendations to their respective regulators to allow wider use of modelling and simulation within the regulatory process. In the context of in silico medicine, the term 'in silico clinical trials' refers to the development of patient-specific models to form virtual cohorts for testing the safety and/or efficacy of new drugs and of new medical devices. Moreover, it could be envisaged that a virtual set of patients could complement a clinical trial (reducing the number of enrolled patients and improving statistical significance), and/or advise clinical decisions. This article will review the current state of in silico clinical trials and outline directions for a full-scale adoption of patient-specific modelling and simulation in the regulatory evaluation of biomedical products. In particular, we will focus on the development of vaccine therapies, which represents, in our opinion, an ideal target for this innovative approach.

Chromosomal Substitution Strategies to Localize Genomic Regions Related to Complex Traits

Chromosomal substitution strategies provide a powerful tool to anonymously reveal the relationship between DNA sequence variants and a normal or disease phenotype of interest. Even in this age of CRISPR-Cas9 genome engineering, the knockdown or overexpression of a gene provides relevant information to our understanding of complex disease only when a close association of an allelic variant with the phenotype has first been established. Limitations of genetic linkage approaches led to the development of more efficient breeding strategies to substitute chromosomal segments from one animal strain into the genetic background of a different strain, enabling a direct comparison of the phenotypes of the strains with variant(s) that differ only at a defined locus. This substitution can be a whole chromosome (consomic), a part of a chromosome (congenic), or as small as only a single or several alleles (subcongenics). In contrast to complete knockout of a specific candidate gene of interest, which simply studies the effects of complete elimination of the gene, the substitution of naturally occurring variants can provide special insights into the functional actions of wild-type alleles. Strategies for production of these inbred strains are reviewed, and a number of examples are used to illustrate the utility of these model systems. Consomic/congenic strains provide a number of experimental advantages in the study of functions of genes and their variants, which are emphasized in this article, such as replication of experimental studies; determination of temporal relationships throughout a life; rigorously controlled experiments in which relations between genotype and phenotype can be tested with the confounding effects of heterogeneous genetic backgrounds, both targeted and multilayered; and "omic" studies performed at many levels of functionality, from molecules to organelles, cells to organs, and organs to organismal behavior across the life span. The application of chromosomal substitution strategies and development of consomic/congenic rat and mouse strains have greatly expanded our knowledge of genomic variants and their phenotypic relationship to physiological functions and to complex diseases such as hypertension and cancer. © 2020 American Physiological Society. Compr Physiol 10:365-388, 2020.

Thioredoxin shapes the C. elegans sensory response to Pseudomonas produced nitric oxide

Nitric oxide (NO) is released into the air by NO-producing organisms; however, it is unclear if animals utilize NO as a sensory cue. We show that C. elegans avoids Pseudomonas aeruginosa (PA14) in part by detecting PA14-produced NO. PA14 mutants deficient for NO production fail to elicit avoidance and NO donors repel worms. PA14 and NO avoidance are mediated by a chemosensory neuron (ASJ) and these responses require receptor guanylate cyclases and cyclic nucleotide gated ion channels. ASJ exhibits calcium increases at both the onset and removal of NO. These NO-evoked ON and OFF calcium transients are affected by a redox sensing protein, TRX-1/thioredoxin. TRX-1’s trans-nitrosylation activity inhibits the ON transient whereas TRX-1’s de-nitrosylation activity promotes the OFF transient. Thus, C. elegans exploits bacterially produced NO as a cue to mediate avoidance and TRX-1 endows ASJ with a bi-phasic response to NO exposure.

Nitric oxide is a colorless gas that contains one nitrogen atom and one oxygen atom. Found at very low levels in the air, this gas is produced by the intense heat of lightning strikes and by combustion engines. Almost all living organisms also produce nitric oxide. In animals, for example, nitric oxide regulates blood pressure and signaling between neurons. However, it was not known if animals could detect nitric oxide in their environment and respond to it.

Caenorhabditis elegans is a worm that has been intensively studied in many fields of biology. Unlike most animals, it cannot make nitric oxide. Yet, living in the soil, C. elegans does come into contact with many microbes that can, including the bacterium Pseudomonas aeruginosa. These bacteria can infect and kill C. elegans, and so the worm typically avoids them. Hao, Yang et al. asked whether C. elegans does so by detecting the nitric oxide that these harmful bacteria release into their environment.

First, worms were added to a petri dish where a small patch of P. aeruginosa was growing. Consistent with previous results, the worms had all moved away from the bacteria after a few hours. The experiments were then repeated with mutant bacteria that cannot produce nitric oxide. The worms were less likely to avoid these mutant bacteria, suggesting that C. elegans does indeed avoid infection by detecting bacterially produced nitric oxide.

Next, using a range of techniques, Hao, Yang et al. showed that C. elegans avoids nitric oxide released into its environment by detecting the gas via a pair of sensory neurons. These neurons require several specific proteins to be able to detect nitric oxide and respond to it. In particular, a protein called Thioredoxin was found to determine the beginning and end of the worm’s sensory response to nitric oxide.

All of these proteins are also found in many other animals, and so it is possible that these findings may be relevant to other species too. Further studies are now needed to confirm whether other organisms can sense nitric oxide from their environment and, if so, how their nervous systems equip them to do this.

Dissecting the genetic components of a quantitative trait locus for blood pressure and renal pathology on rat chromosome 3

BACKGROUND

We have previously confirmed the importance of rat chromosome 3 (RNO3) genetic loci on blood pressure elevation, pulse pressure (PP) variability and renal pathology during salt challenge in the stroke-prone spontaneously hypertensive (SHRSP) rat. The aims of this study were to generate a panel of RNO3 congenic sub-strains to genetically dissect the implicated loci and identify positional candidate genes by microarray expression profiling and analysis of next-generation sequencing data.

METHOD AND RESULTS

A panel of congenic sub-strains were generated containing Wistar-Kyoto (WKY)-introgressed segments of varying size on the SHRSP genetic background, focused within the first 50 Mbp of RNO3. Haemodynamic profiling during salt challenge demonstrated significantly reduced systolic blood pressure, diastolic blood pressure and PP variability in SP.WKYGla3a, SP.WKYGla3c, SP.WKYGla3d and SP.WKYGla3e sub-strains. Only SBP and DBP were significantly reduced during salt challenge in SP.WKYGla3b and SP.WKYGla3f sub-strains, whereas SP.WKYGla3g rats did not differ in haemodynamic response to SHRSP. Those sub-strains demonstrating significantly reduced PP variability during salt challenge also demonstrated significantly reduced renal pathology and proteinuria. Microarray expression profiling prioritized two candidate genes for blood pressure regulation (Dnm1, Tor1b), localized within the common congenic interval shared by SP.WKYGla3d and SP.WKYGla3f strains, and one candidate gene for salt-induced PP variability and renal pathology (Rabgap1), located within the region unique to the SP.WKYGla3d strain. Comparison of next-generation sequencing data identified variants within additional positional genes that are likely to affect protein function.

CONCLUSION

This study has identified distinct intervals on RNO3-containing genes that may be important for blood pressure regulation and renal pathology during salt challenge.

ACE2 and vasoactive peptides: novel players in cardiovascular/renal remodeling and hypertension

The renin-angiotensin system (RAS) is a key component of cardiovascular physiology and homeostasis due to its influence on the regulation of electrolyte balance, blood pressure, vascular tone and cardiovascular remodeling. Deregulation of this system contributes significantly to the pathophysiology of cardiovascular and renal diseases. Numerous studies have generated new perspectives about a noncanonical and protective RAS pathway that counteracts the proliferative and hypertensive effects of the classical angiotensin-converting enzyme (ACE)/angiotensin (Ang) II/angiotensin type 1 receptor (AT1R) axis. The key components of this pathway are ACE2 and its products, Ang-(1-7) and Ang-(1-9). These two vasoactive peptides act through the Mas receptor (MasR) and AT2R, respectively. The ACE2/Ang-(1-7)/MasR and ACE2/Ang-(1-9)/AT2R axes have opposite effects to those of the ACE/Ang II/AT1R axis, such as decreased proliferation and cardiovascular remodeling, increased production of nitric oxide and vasodilation. A novel peptide from the noncanonical pathway, alamandine, was recently identified in rats, mice and humans. This heptapeptide is generated by catalytic action of ACE2 on Ang A or through a decarboxylation reaction on Ang-(1-7). Alamandine produces the same effects as Ang-(1-7), such as vasodilation and prevention of fibrosis, by interacting with Mas-related GPCR, member D (MrgD). In this article, we review the key roles of ACE2 and the vasoactive peptides Ang-(1-7), Ang-(1-9) and alamandine as counter-regulators of the ACE-Ang II axis as well as the biological properties that allow them to regulate blood pressure and cardiovascular and renal remodeling.

Variants in the Atherogenic ALOX5AP, THBD, and KNG1 Genes Potentiate the Risk of Ischemic Stroke via a Genetic Main Effect and Epistatic Interactions in a Chinese Population

BACKGROUND

Ischemic stroke (IS) is a multifactorial disease that displays a strong genetic predisposition. However, the genetic architecture of IS has yet to be fully elucidated. It was hypothesized that epistasis between genes in multiple atherothrombotic pathways may play a vital role in determining the susceptibility to IS. The aim of the present study was to investigate the contributions of the hypothesized genetic factors to IS and the interactions between these genetic factors in a Chinese population.

METHODS

In this study, 351 cases with IS and 417 control subjects from a Chinese population were genotyped for single-nucleotide polymorphisms (SNPs) in 12 genes hypothesized to be involved in atherosclerosis, coagulation, and related pathways. We examined SNP main effects and epistatic interactions between these polymorphic loci.

RESULTS

rs710446 of the KNG1 gene was associated with IS susceptibility based on an additive genetic model (rs710446: P = .012; odds ratio [OR], 1.247; 95% confidence interval [CI], 1.050-1.481) after adjusting for covariates. Furthermore, an epistatic interaction between the ALOX5AP, THBD, and KNG1 gene was also identified in association with stroke susceptibility (P < .001 after 1000 permutations). Based on the chi-squared test, the OR of the high-risk combination of the three-locus model increased the risk of IS by 2.53-fold (95% CI, 1.60-4.01; P < .0001).

CONCLUSIONS

Our findings support the association of the epistatic interactions of ALOX5AP, THBD, and KNG1 and present novel evidence for the main effect of KNG1 gene on IS susceptibility, suggesting a modulation of stroke risk by a genetic main effect and gene-gene interactions.

Effects of p67phox on the mitochondrial oxidative state in the kidney of Dahl salt-sensitive rats: optical fluorescence 3-D cryoimaging

The goal of the present study was to quantify and correlate the contribution of the cytosolic p67(phox) subunit of NADPH oxidase 2 to mitochondrial oxidative stress in the kidneys of the Dahl salt-sensitive (SS) hypertensive rat. Whole kidney redox states were uniquely assessed using a custom-designed optical fluorescence three-dimensional cryoimager to acquire multichannel signals of the intrinsic fluorophores NADH and FAD. SS rats were compared with SS rats in which the cytosolic subunit p67(phox) was rendered functionally inactive by zinc finger nuclease mutation of the gene (SS(p67phox)-null rats). Kidneys of SS rats fed a 0.4% NaCl diet exhibited significantly (P = 0.023) lower tissue redox ratio (NADH/FAD; 1.42 ± 0.06, n = 5) than SS(p67phox)-null rats (1.64 ± 0.07, n = 5), indicating reduced levels of mitochondrial electron transport chain metabolic activity and enhanced oxidative stress in SS rats. When fed a 4.0% salt diet for 21 days, both strains exhibited significantly lower tissue redox ratios (P < 0.001; SS rats: 1.03 ± 0.05, n = 9, vs. SS(p67phox)-null rats: 1.46 ± 0.04, n = 7) than when fed a 0.4% salt, but the ratio was still significantly higher in SS(p67phox) rats at the same salt level as SS rats. These results are consistent with results from previous studies that found elevated medullary interstitial fluid concentrations of superoxide and H2O2 in the medulla of SS rats. We conclude that the p67(phox) subunit of NADPH oxidase 2 plays an important role in the excess production of ROS from mitochondria in the renal medulla of the SS rat.

Refined mapping of a hypertension susceptibility locus on rat chromosome 12

Previously, we found that transferring 6.1 Mb of salt-sensitive (SS) chromosome 12 (13.4-19.5 Mb) onto the consomic SS-12(BN) background significantly elevated mean arterial pressure in response to an 8% NaCl diet (178±7 versus 144±2 mm Hg; P<0.001). Using congenic mapping, we have now narrowed the blood pressure locus by 86% from a 6.1-Mb region containing 133 genes to an 830-kb region (chr12:14.36-15.19 Mb) with 14 genes. Compared with the SS-12(BN) consomic, the 830-kb blood pressure locus was associated with a ∆+15 mm Hg (P<0.01) increase in blood pressure, which coincided with elevated albuminuria (∆+32 mg/d; P<0.001), proteinuria (∆+48 mg/d; P<0.01), protein casting (∆+154%; P<0.05), and renal fibrosis (∆+79%; P<0.05). Of the 14 genes residing in the 830-kb locus, 8 were differentially expressed, and among these, Chst12 (carbohydrate chondroitin 4 sulfotransferase 12) was most consistently downregulated by 2.6- to 4.5-fold (P<0.05) in both the renal medulla and cortex under normotensive and hypertensive conditions. Moreover, whole genome sequence analysis of overlapping blood pressure loci revealed an ≈86-kb region (chr12:14 541 567-14 627 442 bp) containing single-nucleotide variants near Chst12 that are unique to the hypertensive SS strain when compared with the normotensive Brown Norway, Dahl salt-resistant, and Wistar-Kyoto strains. Finally, the 830-kb interval is syntenic to a region on human chromosome 7 that has been genetically linked to blood pressure, suggesting that insight gained from our SS-12(BN) congenic strain may be translated to a better understanding of human hypertension.

MicroRNA-22 and promoter motif polymorphisms at the Chga locus in genetic hypertension: functional and therapeutic implications for gene expression and the pathogenesis of hypertension

Hypertension is a common hereditary syndrome with unclear pathogenesis. Chromogranin A (Chga), which catalyzes formation and cargo storage of regulated secretory granules in neuroendocrine cells, contributes to blood pressure homeostasis centrally and peripherally. Elevated Chga occurs in spontaneously hypertensive rat (SHR) adrenal glands and plasma, but central expression is unexplored. In this report, we measured SHR and Wistar-Kyoto rat (control) Chga expression in central and peripheral nervous systems, and found Chga protein to be decreased in the SHR brainstem, yet increased in the adrenal and the plasma. By re-sequencing, we systematically identified five promoter, two coding and one 3'-untranslated region (3'-UTR) polymorphism at the SHR (versus WKY or BN) Chga locus. Using HXB/BXH recombinant inbred (RI) strain linkage and correlations, we demonstrated genetic determination of Chga expression in SHR, including a cis-quantitative trait loci (QTLs) (i.e. at the Chga locus), and such expression influenced biochemical determinants of blood pressure, including a cascade of catecholamine biosynthetic enzymes, catecholamines themselves and steroids. Luciferase reporter assays demonstrated that the 3'-UTR polymorphism (which disrupts a microRNA miR-22 motif) and promoter polymorphisms altered gene expression consistent with the decline in SHR central Chga expression. Coding region polymorphisms did not account for changes in Chga expression or function. Thus, we hypothesized that the 3'-UTR and promoter mutations lead to dysregulation (diminution) of Chga in brainstem cardiovascular control nuclei, ultimately contributing to the pathogenesis of hypertension in SHR. Accordingly, we demonstrated that in vivo administration of miR-22 antagomir to SHR causes substantial (∼18 mmHg) reductions in blood pressure, opening a novel therapeutic avenue for hypertension.

Altering physiological networks using drugs: steps towards personalized physiology

Background

The rise of personalized medicine has reminded us that each patient must be treated as an individual. One factor in making treatment decisions is the physiological state of each patient, but definitions of relevant states and methods to visualize state-related physiologic changes are scarce. We constructed correlation networks from physiologic data to demonstrate changes associated with pressor use in the intensive care unit.

Methods

We collected 29 physiological variables at one-minute intervals from nineteen trauma patients in the intensive care unit of an academic hospital and grouped each minute of data as receiving or not receiving pressors. For each group we constructed Spearman correlation networks of pairs of physiologic variables. To visualize drug-associated changes we split the networks into three components: an unchanging network, a network of connections with changing correlation sign, and a network of connections only present in one group.

Results

Out of a possible 406 connections between the 29 physiological measures, 64, 39, and 48 were present in each of the three component networks. The static network confirms expected physiological relationships while the network of associations with changed correlation sign suggests putative changes due to the drugs. The network of associations present only with pressors suggests new relationships that could be worthy of study.

Conclusions

We demonstrated that visualizing physiological relationships using correlation networks provides insight into underlying physiologic states while also showing that many of these relationships change when the state is defined by the presence of drugs. This method applied to targeted experiments could change the way critical care patients are monitored and treated.

Interaction between chromosome 2 and 3 regulates pulse pressure in the stroke-prone spontaneously hypertensive rat

In an F2 cross between stroke-prone spontaneously hypertensive (SHRSP) and Wistar Kyoto (WKY) rats, we previously identified blood pressure quantitative trait loci (QTL) on rat chromosome (RNO) 2 and a pulse pressure QTL on RNO3. The aims of this study were to confirm the QTL on RNO3 and to investigate interaction between RNO2 and RNO3 loci through the generation and phenotypic assessment of single RNO3 congenic (SP.WKY(Gla)3a) and bicongenic (SP.WKY(Gla)2a/3a) strains. Hemodynamic profiling, vascular function, and renal histology were examined in these newly generated strains along with the previously reported RNO2 congenic strain (SP.WKY(Gla)2a). Our results demonstrate significant equivalent reduction in systolic, diastolic, and pulse pressure phenotypes in SP.WKY(Gla)3a and SP.WKY(Gla)2a rats, whereas greater reductions were observed with the SP.WKY(Gla)2a/3a bicongenic strain achieving blood pressure levels similar to normotensive WKY rats. Epistasis was observed between pulse pressure QTL on RNO2 and 3 at baseline and during 1% salt challenge. Vascular function and renal pathology studies indicate that QTL on RNO3 are responsible for salt-induced kidney pathology, whereas QTL on RNO2 seem to have greater impact on vascular function. RNO3 congenic and bicongenic strains have confirmed the importance of SHRSP alleles in the RNO3 congenic interval on pulse pressure variability and end-organ damage. These strains will allow interrogation of complex gene-gene and gene-environment interactions contributing to salt-sensitive hypertension and renal pathology in the SHRSP rat.

Challenges and solutions in the development of genomic biomarker panels: a systematic phased approach

In the post-genome era, high throughput gene expression profiling has been successfully used to develop genomic biomarker panels (GBP) that can be integrated into clinical decision making. The development of GBPs in the context of personalized medicine is a scientifically challenging and resource-intense process. It needs to be accomplished in a systematic phased approach to address biological variation related to a clinical phenotype (e.g. disease etiology, gender, etc.) and minimize technical variation (noise). Here we present the methodological aspects of GBP development based on the experience of the Cardiac Allograft Rejection Gene Expression Observation (CARGO) study, a study that lead to the development of a molecular classifier for rejection screening in heart transplant patients.

Differential genetic basis for pre-menopausal and post-menopausal salt-sensitive hypertension

Essential hypertension affects 75% of post-menopausal women in the United States causing greater cardiovascular complications compared with age-matched men and pre-menopausal women. Hormone replacement and current anti-hypertensive therapies do not correct this post-menopausal increased risk suggesting a distinct pathogenic framework. We investigated the hypothesis that distinct genetic determinants might underlie susceptibility to salt sensitive hypertension in pre-menopausal and post-menopausal states. To determine whether distinct genetic loci contribute to post-menopausal salt-sensitive hypertension, we performed a genome-wide scan for quantitative trait loci (QTLs) affecting blood pressure (BP) in 16-month old post-menopausal F2 (Dahl S×R)-intercross female rats characterized for blood pressure by radiotelemetry. Given identical environments and high salt challenge, post-menopausal BP levels were significantly higher than observed in pre-menopausal (post-menopausal versus pre-menopausal SBP, P<0.0001) and ovariectomized (post-menopausal versus ovariectomized SBP, P<0.001) F2-intercross female rats. We detected four significant to highly significant BP-QTLs (BP-pm1 on chromosome 13, LOD 3.78; BP-pm2 on chromosome 11, LOD 2.76; BP-pm3 on chromosome 2, LOD 2.61; BP-pm4 on chromosome 4, LOD 2.50) and two suggestive BP-QTLs (BP-pm5 on chromosome 15, LOD 2.37; BP-f1 on chromosome 5, LOD 1.65), four of which (BP-pm2, BP-pm3, BP-pm4, BP-pm5) were unique to this post-menopausal cohort. These data demonstrate distinct polygenic susceptibility underlying post-menopausal salt-sensitive hypertension providing a pathway towards the identification of mechanism-based therapy for post-menopausal hypertension and ensuing target-organ complications.

Identification of hypertension susceptibility loci on rat chromosome 12

Previous studies have identified multiple blood pressure and renal disease quantitative trait loci located on rat chromosome 12. In the present study, we narrowed blood pressure loci using a series of overlapping Dahl salt-sensitive/Mcwi (SS)-12 Brown Norway (BN) congenic lines. We found that transferring 6.1 Mb of SS chromosome 12 (13.4-19.5 Mb) onto the consomic SS-12BN background significantly elevated blood pressure on 1% NaCl (146±6 versus 127±1 mm Hg; P<0.001) and 8% NaCl diets (178±7 versus 144±2 mm Hg; P<0.001). Compared with the SS-12BN consomic, these animals also had significantly elevated albumin (218±31 versus 104±8 mg/d; P<0.001) and protein excretion (347±41 versus 195±12 mg/d; P<0.001) on a 1% NaCl diet. Elevated blood pressure, albuminuria, and proteinuria coincided with greater renal and cardiac damage, demonstrating that SS allele(s) within the 6.1 Mb congenic interval are associated with strong cardiovascular disease phenotypes. Sequence analysis of the 6.1 Mb congenic region revealed 12 673 single nucleotide polymorphisms between SS and BN rats. Of these polymorphisms, 293 lie within coding regions, and 18 resulted in nonsynonymous changes in conserved genes, of which 5 were predicted to be potentially damaging to protein function. Syntenic regions in human chromosome 7 have also been identified in multiple linkage and association studies of cardiovascular disease, suggesting that genetic variants underlying cardiovascular phenotypes in this congenic strain can likely be translated to a better understanding of human hypertension.

Mapping genetic variants associated with beta-adrenergic responses in inbred mice

β-blockers and β-agonists are primarily used to treat cardiovascular diseases. Inter-individual variability in response to both drug classes is well recognized, yet the identity and relative contribution of the genetic players involved are poorly understood. This work is the first genome-wide association study (GWAS) addressing the values and susceptibility of cardiovascular-related traits to a selective β₁-blocker, Atenolol (ate), and a β-agonist, Isoproterenol (iso). The phenotypic dataset consisted of 27 highly heritable traits, each measured across 22 inbred mouse strains and four pharmacological conditions. The genotypic panel comprised 79922 informative SNPs of the mouse HapMap resource. Associations were mapped by Efficient Mixed Model Association (EMMA), a method that corrects for the population structure and genetic relatedness of the various strains. A total of 205 separate genome-wide scans were analyzed. The most significant hits include three candidate loci related to cardiac and body weight, three loci for electrocardiographic (ECG) values, two loci for the susceptibility of atrial weight index to iso, four loci for the susceptibility of systolic blood pressure (SBP) to perturbations of the β-adrenergic system, and one locus for the responsiveness of QTc (p<10⁻⁸). An additional 60 loci were suggestive for one or the other of the 27 traits, while 46 others were suggestive for one or the other drug effects (p<10⁻⁶). Most hits tagged unexpected regions, yet at least two loci for the susceptibility of SBP to β-adrenergic drugs pointed at members of the hypothalamic-pituitary-thyroid axis. Loci for cardiac-related traits were preferentially enriched in genes expressed in the heart, while 23% of the testable loci were replicated with datasets of the Mouse Phenome Database (MPD). Altogether these data and validation tests indicate that the mapped loci are relevant to the traits and responses studied.

A 4.1-Mb congenic region of Rf-4 contributes to glomerular permeability

The combined transfer of two renal function quantitative trait loci (QTLs), Rf-1 (rat chromosome 1) and Rf-4 (rat chromosome 14), from the Fawn-hooded hypertensive rat onto the August Copenhagen Irish genetic background significantly increases proteinuria and demonstrates an interaction between these QTLs. Because the original Rf-4 congenic region is 61.9 Mbp, it is necessary to reduce this interval to feasibly search for variants responsible for renal susceptibility in this region. Here, we generated a minimal congenic line (Rf-1a+4_a) to identify a 4.1-Mb region of the Rf-4 QTL that significantly contributes to the severity of proteinuria in the Fawn-hooded hypertensive rat. Rf-1a+4_a animals have an increased glomerular permeability to albumin without significant changes in BP, indicating that at least one genetic element in this refined region directly affects renal function. Sequence analysis revealed no variants predicted to damage protein function, implying that regulatory elements are responsible for the Rf-4 phenotype. Multiple human studies, including recent genome-wide association studies, link the homologous human region with susceptibility to renal disease, suggesting that this congenic line is an important model for studying pathways that contribute to the progression of kidney disease.

Systems-based approaches to cardiovascular disease

Common cardiovascular diseases, such as atherosclerosis and congestive heart failure, are exceptionally complex, involving a multitude of environmental and genetic factors that often show nonlinear interactions as well as being highly dependent on sex, age, and even the maternal environment. Although focused, reductionistic approaches have led to progress in elucidating the pathophysiology of cardiovascular diseases, such approaches are poorly powered to address complex interactions. Over the past decade, technological advances have made it possible to interrogate biological systems on a global level, raising hopes that, in combination with computational approaches, it may be possible to more fully address the complexities of cardiovascular diseases. In this Review, we provide an overview of such systems-based approaches to cardiovascular disease and discuss their translational implications.

Strategies and methods to study sex differences in cardiovascular structure and function: a guide for basic scientists

Background

Cardiovascular disease remains the primary cause of death worldwide. In the US, deaths due to cardiovascular disease for women exceed those of men. While cultural and psychosocial factors such as education, economic status, marital status and access to healthcare contribute to sex differences in adverse outcomes, physiological and molecular bases of differences between women and men that contribute to development of cardiovascular disease and response to therapy remain underexplored.

Methods

This article describes concepts, methods and procedures to assist in the design of animal and tissue/cell based studies of sex differences in cardiovascular structure, function and models of disease.

Results

To address knowledge gaps, study designs must incorporate appropriate experimental material including species/strain characteristics, sex and hormonal status. Determining whether a sex difference exists in a trait must take into account the reproductive status and history of the animal including those used for tissue (cell) harvest, such as the presence of gonadal steroids at the time of testing, during development or number of pregnancies. When selecting the type of experimental animal, additional consideration should be given to diet requirements (soy or plant based influencing consumption of phytoestrogen), lifespan, frequency of estrous cycle in females, and ability to investigate developmental or environmental components of disease modulation. Stress imposed by disruption of sleep/wake cycles, patterns of social interaction (or degree of social isolation), or handling may influence adrenal hormones that interact with pathways activated by the sex steroid hormones. Care must be given to selection of hormonal treatment and route of administration.

Conclusions

Accounting for sex in the design and interpretation of studies including pharmacological effects of drugs is essential to increase the foundation of basic knowledge upon which to build translational approaches to prevent, diagnose and treat cardiovascular diseases in humans.

Genetic control of the corticosterone level at rest and under emotional stress in ISIAH rats with inherited stress-induced arterial hypertension

The genetic background of the regulatory systems of the hypothalamic-pituitary-adrenal (HPA) axis in hypertension remains unclear. The inherited stress-induced arterial hypertension (ISIAH) and Wistar Albino Glaxo (WAG) normotensive rats were bred and their F(2) progeny were used in a quantitative trait loci (QTL) analysis to identify genomic regions for plasma basal and stress-induced corticosterone levels, and for absolute and relative adrenal gland weights. The significant loci were found for stress-induced corticosterone on chromosome 9 and for adrenal weight on chromosome 6. The results may help to identify the genes controlling the trait phenotypes in the ISIAH rats characterized by the enhanced responsiveness to stressful stimulation.

Identification of genes and networks driving cardiovascular and metabolic phenotypes in a mouse F2 intercross

To identify the genes and pathways that underlie cardiovascular and metabolic phenotypes we performed an integrated analysis of a mouse C57BL/6JxA/J F2 (B6AF2) cross by relating genome-wide gene expression data from adipose, kidney, and liver tissues to physiological endpoints measured in the population. We have identified a large number of trait QTLs including loci driving variation in cardiac function on chromosomes 2 and 6 and a hotspot for adiposity, energy metabolism, and glucose traits on chromosome 8. Integration of adipose gene expression data identified a core set of genes that drive the chromosome 8 adiposity QTL. This chromosome 8 trans eQTL signature contains genes associated with mitochondrial function and oxidative phosphorylation and maps to a subnetwork with conserved function in humans that was previously implicated in human obesity. In addition, human eSNPs corresponding to orthologous genes from the signature show enrichment for association to type II diabetes in the DIAGRAM cohort, supporting the idea that the chromosome 8 locus perturbs a molecular network that in humans senses variations in DNA and in turn affects metabolic disease risk. We functionally validate predictions from this approach by demonstrating metabolic phenotypes in knockout mice for three genes from the trans eQTL signature, Akr1b8, Emr1, and Rgs2. In addition we show that the transcriptional signatures for knockout of two of these genes, Akr1b8 and Rgs2, map to the F2 network modules associated with the chromosome 8 trans eQTL signature and that these modules are in turn very significantly correlated with adiposity in the F2 population. Overall this study demonstrates how integrating gene expression data with QTL analysis in a network-based framework can aid in the elucidation of the molecular drivers of disease that can be translated from mice to humans.

A wild derived quantitative trait locus on mouse chromosome 2 prevents obesity

Background

The genetic architecture of multifactorial traits such as obesity has been poorly understood. Quantitative trait locus (QTL) analysis is widely used to localize loci affecting multifactorial traits on chromosomal regions. However, large confidence intervals and small phenotypic effects of identified QTLs and closely linked loci are impeding the identification of causative genes that underlie the QTLs. Here we developed five subcongenic mouse strains with overlapping and non-overlapping wild-derived genomic regions from an F2 intercross of a previously developed congenic strain, B6.Cg-Pbwg1, and its genetic background strain, C57BL/6J (B6). The subcongenic strains developed were phenotyped on low-fat standard chow and a high-fat diet to fine-map a previously identified obesity QTL. Microarray analysis was performed with Affymetrix GeneChips to search for candidate genes of the QTL.

Results

The obesity QTL was physically mapped to an 8.8-Mb region of mouse chromosome 2. The wild-derived allele significantly decreased white fat pad weight, body weight and serum levels of glucose and triglyceride. It was also resistant to the high-fat diet. Among 29 genes residing within the 8.8-Mb region, Gpd2, Upp2, Acvr1c, March7 and Rbms1 showed great differential expression in livers and/or gonadal fat pads between B6.Cg-Pbwg1 and B6 mice.

Conclusions

The wild-derived QTL allele prevented obesity in both mice fed a low-fat standard diet and mice fed a high-fat diet. This finding will pave the way for identification of causative genes for obesity. A further understanding of this unique QTL effect at genetic and molecular levels may lead to the discovery of new biological and pathologic pathways associated with obesity.

Vascular responses in aortic rings of a consomic rat panel derived from the Fawn Hooded Hypertensive strain

The present experiments, utilizing the high-throughput vascular protocol of PhysGen (Program for Genomic Applications) characterized the responses of aortic rings to vasoconstrictor (phenylephrine) and vasodilator (acetylcholine, sodium nitroprusside, and reduced tissue bath Po(2)) stimuli in consomic rat strains derived from a cross between the Fawn Hooded Hypertensive rat (FHH/EurMcwi) and the Brown Norway normotensive (BN/NHsdMcwi) rat. The effects of substituting individual BN chromosomes into the FHH genetic background were determined in animals that were maintained on a low-salt (0.4% NaCl) diet or switched to a high-salt (4% NaCl) diet for 3 wk. Sex-specific differences were evaluated in male and female consomic rats on similar dietary salt intake. Multiple chromosomes affected various vascular reactivity phenotypes in the FHH × BN consomic panel, and substantial salt-dependent changes in vascular reactivity and sex-specific differences in aortic reactivity were observed in individual consomic strains. However, compared with earlier studies of consomic rats derived from a cross between the BN rat and the Dahl salt-sensitive (SS) rat, only 3-7% of the vascular phenotypes were affected in a similar manner by substituting specific BN chromosomeschromosomes into the FHH genetic background versus the SS genetic background. The findings of the present study stress the potential value of consomic rat panels in gaining insight into genetic factors influencing vascular reactivity and suggest that the chromosomes that appear to be involved in the determination of aortic ring reactivity in different rodent models of hypertension are highly strain- and sex specific.

Central nervous system serotonin and clustering of hostility, psychosocial, metabolic, and cardiovascular endophenotypes in men

OBJECTIVE

To use measures of cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5HIAA) and genotype of a functional polymorphism of the monoamine oxidase A gene promoter (MAOA-uVNTR) to study the role of central nervous system (CNS) serotonin in clustering of hostility, other psychosocial, metabolic and cardiovascular endophenotypes.

METHODS

In 86 healthy male volunteers, we evaluated CSF levels of the primary serotonin metabolite 5HIAA and MAOA-uVNTR genotype for association with a panel of 29 variables assessing hostility, other psychosocial, metabolic, and cardiovascular endophenotypes.

RESULTS

The correlations of 5HIAA with these endophenotypes in men with more active MAOA-uVNTR alleles were significantly different from those of men with less active alleles for 15 of the 29 endophenotypes. MAOA-uVNTR genotype and CSF 5HIAA interacted to explain 20% and 22% of the variance, respectively, in scores on one factor wherein high scores reflected a less healthy psychosocial profile and a second factor wherein high score reflected increased insulin resistance, body mass index, blood pressure and hostility. In men with less active alleles, higher 5HIAA was associated with more favorable profiles of hostility, other psychosocial, metabolic and cardiovascular endophenotypes; in men with more active alleles, higher 5HIAA was associated with less favorable profiles.

CONCLUSIONS

These findings indicate that, in men, indices of CNS serotonin function influence the expression and clustering of hostility, other psychosocial, metabolic and cardiovascular endophenotypes that have been shown to increase risk of developing cardiovascular disease. The findings are consistent with the hypothesis that increased CNS serotonin is associated with a more favorable psychosocial/metabolic/cardiovascular profile, whereas decreased CNS serotonin function is associated with a less favorable profile.

Mitochondrial polymorphisms in rat genetic models of hypertension

Hypertension is a complex trait that has been studied extensively for genetic contributions of the nuclear genome. We examined mitochondrial genomes of the hypertensive strains: the Dahl Salt-Sensitive (S) rat, the Spontaneously Hypertensive Rat (SHR), and the Albino Surgery (AS) rat, and the relatively normotensive strains: the Dahl Salt-Resistant (R) rat, the Milan Normotensive Strain (MNS), and the Lewis rat (LEW). These strains were used previously for linkage analysis for blood pressure (BP) in our laboratory. The results provide evidence to suggest that variations in the mitochondrial genome do not account for observed differences in blood pressure between the S and R rats. However, variants were detected among the mitochondrial genomes of the various hypertensive strains, S, SHR, and AS, and also among the normotensive strains R, MNS, and LEW. A total of 115, 114, 106, 106, and 16 variations in mtDNA were observed between the comparisons S versus LEW, S versus MNS, S versus SHR, S versus AS, and SHR versus AS, respectively. Among the 13 genes coding for proteins of the electron transport chain, 8 genes had nonsynonymous variations between S, LEW, MNS, SHR, and AS. The lack of any sequence variants between the mitochondrial genomes of S and R rats provides conclusive evidence that divergence in blood pressure between these two inbred strains is exclusively programmed through their nuclear genomes. The variations detected among the various hypertensive strains provides the basis to construct conplastic strains and further evaluate the effects of these variants on hypertension and associated phenotypes.

Ins and outs of systems biology vis-à-vis molecular biology: continuation or clear cut?

The comprehension of living organisms in all their complexity poses a major challenge to the biological sciences. Recently, systems biology has been proposed as a new candidate in the development of such a comprehension. The main objective of this paper is to address what systems biology is and how it is practised. To this end, the basic tools of a systems biological approach are explored and illustrated. In addition, it is questioned whether systems biology 'revolutionizes' molecular biology and 'transcends' its assumed reductionism. The strength of this claim appears to depend on how molecular and systems biology are characterised and on how reductionism is interpreted. Doing credit to molecular biology and to methodological reductionism, it is argued that the distinction between molecular and systems biology is gradual rather than sharp. As such, the classical challenge in biology to manage, interpret and integrate biological data into functional wholes is further intensified by systems biology's use of modelling and bioinformatics, and by its scale enlargement.

Deciphering the molecular basis of venous thromboembolism: where are we and where should we go?

Venous thromboembolism (VTE) is a frequent disease that has a major genetic component of risk. However, known identified genetic risk factors account for <30% of idiopathic (without any environmental origin) VTE cases. This article aims to review the lessons learnt during recent decades in the field of the genetics of VTE, describe the present state-of-art methods and discuss promising themes for finding new susceptibility loci.

The use of network analyses for elucidating mechanisms in cardiovascular disease

Systems biology offers the potential to provide new insights into our understanding of the pathogenesis of complex diseases such as atherosclerosis. It seeks to comprehend the system properties of the non-linear interactions of the multiple biomolecular components that characterize a living organism. An important component of this research approach is identifying the biological networks that connect the differing elements of a system and in the process describe the characteristics that define a shift in equilibrium from a healthy to a diseased state. The utility of this method becomes clear when applied to multifactorial diseases with complex etiologies such as inflammatory-related diseases, herein exemplified by cardiovascular disease. In this study, the application of network theory to systems biology is described in detail and an example is provided using data from a clinical biobank database of carotid endarterectomies from the Karolinska University Hospital (Biobank of Karolinska Endarterectomies, BiKE). Data from 47 microarrays were examined using a combination of Bioconductor modules and the Cytoscape resource with several associated plugins to analyze the transcriptomics data and create a combined gene association and correlation network of atherosclerosis. The methodology and workflow are described in detail, with a total of 43 genes found to be differentially expressed on a gender-specific basis, of which 15 were not directly linked to the sex chromosomes. In particular, the APOC1 gene was 2.1-fold down-regulated in plaques in women relative to men and was selected for further analysis based upon a purported role in cardiovascular disease. The resulting network was identified as a scale-free network that contained specific sub-networks related to immune function and lipid biosynthesis. These sub-networks link atherosclerotic-related genes to other genes that may not have previously known roles in disease etiology and only evidence small alterations, which are challenging to find by statistical and comparison-based methods. A number of Gene Ontology (GO), BioCarta and KEGG pathways involved in the atherosclerotic process were identified in the constructed sub-network, with 19 GO pathways related to APOC1 of which 'phospholipid efflux' evidenced the strongest association. The utility and functionality of network analysis and the different Cytoscape plugins employed are discussed. Lastly, the applications of these methods to cardiovascular disease are discussed with focus on the current limitations and future visions of this emerging field.

Infection in the intensive care unit alters physiological networks

BACKGROUND

Physicians use clinical and physiological data to treat patients every day, and it is essential for treating a patient appropriately. However, medical sources of clinical physiological data are only now starting to find use in bioinformatics research.

RESULTS

We collected 29 types of physiological and clinical data on a minute-by-minute basis from trauma patients in the intensive care unit along with whether they contracted an infection during their stay. Dividing the patients into two groups based on this criterion, we determined that the correlational network amongst pairs of physiological variables changes based on whether the patient contracted an infection.

CONCLUSION

Examining the variable pairs with the largest change in correlation across groups reveals potential changes in the way our treatments affect the patient's physiology and in how our bodies react to physiological insults. These findings highlight the usefulness of physiological informatics and suggest new relationships to study while also validating previously reported relationships.

NOD x 129.H2(g7) backcross delineates 129S1/SvImJ-derived genomic regions modulating type 1 diabetes development in mice

OBJECTIVE

Introduction of genes targeted in 129/Sv embryonic stem (ES) cells into NOD mice brings about linked genes that may modulate type 1 diabetes. Our objective was to identify 129S1/SvJ non-MHC regions contributing type 1 diabetes resistance or susceptibility in backcross to NOD/LtJ.

RESEARCH DESIGN AND METHODS

After congenic transfer of the NOD H2(g7) haplotype onto 129S1/Sv, 310 females were produced by NOD x (NOD x 129.H2(g7))F1 backcross (N2). A genome scan for quantitative trait locus (QTL) affecting clinical diabetes, age of diabetes onset, and insulitis severity was performed using subphenotype characteristics to improve power and resolution for detection of diabetes susceptibility loci.

RESULTS

Thirty-six of 310 (11.6%) N2 females developed type 1 diabetes between 14 and 40 weeks. Significant evidence of linkage for only a single previously reported Idd complex locus (Idd10/17/18, chromosome [Chr] 3) was indicated for clinical diabetes. The quantitative traits of insulitis either alone or combined with age at type 1 diabetes onset were significantly linked to known Idd regions on Chr 1 (Idd5 region), Chr 4 (Idd9 region), Chr 8 (Idd22), Chr 11 (Idd4.3), and proximal Chr 17 (Idd16 region). Significant 129S1/Sv resistance contributions were identified on Chr 1, 15 (two loci), and 19, with suggestive evidence for additional novel 129/Sv resistance QTL on Chr 5 and 17 and susceptibility on Chr 2.

CONCLUSIONS

The 129S1/SvJ genome harbors collections of both known and potentially novel non-MHC Idd loci. Investigators targeting 129/Sv genes mapping within chromosomal regions reported herein or elsewhere in the genome need to exclude potential contributions from linked Idd loci by generating a NOD.129 control strain expressing the nontargeted allele.

Systems biology approaches and pathway tools for investigating cardiovascular disease

Systems biology aims to understand the nonlinear interactions of multiple biomolecular components that characterize a living organism. One important aspect of systems biology approaches is to identify the biological pathways or networks that connect the differing elements of a system, and examine how they evolve with temporal and environmental changes. The utility of this method becomes clear when applied to multifactorial diseases with complex etiologies, such as inflammatory-related diseases, herein exemplified by atherosclerosis. In this paper, the initial studies in this discipline are reviewed and examined within the context of the development of the field. In addition, several different software tools are briefly described and a novel application for the KEGG database suite called KegArray is presented. This tool is designed for mapping the results of high-throughput omics studies, including transcriptomics, proteomics and metabolomics data, onto interactive KEGG metabolic pathways. The utility of KegArray is demonstrated using a combined transcriptomics and lipidomics dataset from a published study designed to examine the potential of cholesterol in the diet to influence the inflammatory component in the development of atherosclerosis. These data were mapped onto the KEGG PATHWAY database, with a low cholesterol diet affecting 60 distinct biochemical pathways and a high cholesterol exposure affecting 76 biochemical pathways. A total of 77 pathways were differentially affected between low and high cholesterol diets. The KEGG pathways "Biosynthesis of unsaturated fatty acids" and "Sphingolipid metabolism" evidenced multiple changes in gene/lipid levels between low and high cholesterol treatment, and are discussed in detail. Taken together, this paper provides a brief introduction to systems biology and the applications of pathway mapping to the study of cardiovascular disease, as well as a summary of available tools. Current limitations and future visions of this emerging field are discussed, with the conclusion that combining knowledge from biological pathways and high-throughput omics data will move clinical medicine one step further to individualize medical diagnosis and treatment.

RGS proteins: identifying new GAPs in the understanding of blood pressure regulation and cardiovascular function

Understanding the mechanisms that underlie BP (blood pressure) variation in humans and animal models may provide important clues for reducing the burden of uncontrolled hypertension in industrialized societies. High BP is often associated with increased signalling via G-protein-coupled receptors. Three members of the RGS (regulator of G-protein signalling) superfamily RGS2, RGS4 and RGS5 have been implicated in the attenuation of G-protein signalling pathways in vascular and cardiac myocytes, as well as cells of the kidney and autonomic nervous system. In the present review, we discuss the current state of knowledge regarding their differential expression and function in cardiovascular tissues, and the likelihood that one or more of these alleles are candidate hypertension genes. Together, findings from the studies described herein suggest that development of methods to modulate the expression and function of RGS proteins may be a possible strategy for the treatment and prevention of hypertension and cardiovascular disease.

Genetically hypertensive Brown Norway congenic rat strains suggest intermediate traits underlying genetic hypertension

AIM

To determine the independent and combined effects of three quantitative trait loci (QTL) for blood pressure in the Genetically Hypertensive (GH/Omr) rat by generating and characterizing single and combined congenic strains that have QTL on rat chromosomes (RNO) 2, 6, and 18 from the GH rat introduced into a hypertension resistant Brown Norway (BN) background.

METHODS

Linkage analysis and QTL identification (genome wide QTL scan) were performed with MapMaker/EXP to build the genetic maps and MapMaker/QTL for linking the phenotypes to the genetic map. The congenic strains were derived using marker-assisted selection strategy from a single male F1 offspring of an intercross between the male GH/Omr and female BN/Elh, followed by 10 generations of selective backcrossing to the female BN progenitor strain. Single congenic strains generated were BN.GH-(D2Rat22-D2Mgh11)/Mcwi (BN.GH2); BN.GH-(D6Mit12-D6Rat15)/Mcwi (BN.GH6); and BN.GH-(D18Rat41-D18Mgh4)/Mcwi (BN.GH18). Blood pressure measurements were obtained either via a catheter placed in the femoral artery or by radiotelemetry. Responses to angiotensin II (ANGII), norepinephrine (NE), and baroreceptor sensitivity were measured in the single congenics.

RESULTS

Transferring one or more QTL from the hypertensive GH into normotensive BN strain was not sufficient to cause hypertension in any of the developed congenic strains. There were no differences between the parental and congenic strains in their response to NE. However, BN.GH18 rats revealed significantly lower baroreceptor sensitivity (beta=-1.25-/+0.17), whereas BN.GH2 (beta=0.66-/+0.09) and BN.GH18 (beta=0.71-/+0.07) had significantly decreased responses to ANGII from those observed in the BN (beta=0.88-/+0.08).

CONCLUSION

The failure to alter blood pressure levels by introducing the hypertensive QTL from the GH into the hypertension resistant BN background suggests that the QTL effects are genome background-dependent in the GH rat. BN.GH2 and BN.GH18 rats reveal significant differences in response to ANGII and impaired baroreflex sensitivity, suggesting that we may have captured a locus responsible for the genetic control of baroreceptor sensitivity, which would be considered an intermediate phenotype of blood pressure.

Blood pressure and heart rate QTL in mice of the B6/D2 lineage: sex differences and environmental influences

A quantitative trait locus (QTL) approach was used to define the genetic architecture underlying variation in systolic blood pressure (SBP) and heart rate (HR), measured indirectly on seven occasions by the tail cuff procedure. The tests were conducted in 395 F(2) adult mice (197 males, 198 females) derived from a cross of the C57BL/6J (B6) and DBA/2J (D2) strains and in 22 BXD recombinant-inbred (RI) strains. Interval mapping of F(2) data for the first 5 days of measurement nominated one statistically significant and one suggestive QTL for SBP on chromosomes (Chr) 4 and 14, respectively, and two statistically significant QTL for HR on Chr 1 (which was specific to female mice) and Chr 5. New suggestive QTL emerged for SBP on Chr 3 (female-specific) and 8 and for HR on Chr 11 for measurements recorded several weeks after mice had undergone stressful blood sampling procedures. The two statistically significant HR QTL were confirmed by analyses of BXD RI strain means. Male and female F(2) mice did not differ in SBP or HR but RI strain analyses showed pronounced strain-by-sex interactions and a negative genetic correlation between the two measures in both sexes. Evidence for a role for mitochondrial DNA was found for both HR and SBP. QTL for HR and SBP may differ in males and females and may be sensitive to different environmental contexts.

Renal medullary 11 beta-hydroxysteroid dehydrogenase type 1 in Dahl salt-sensitive hypertension

The Dahl salt-sensitive rat is a widely used model of human salt-sensitive forms of hypertension. The kidney plays an important role in the pathogenesis of Dahl salt-sensitive hypertension, but the molecular mechanisms involved remain a subject of intensive investigation. Gene expression profiling studies suggested that 11 beta-hydroxysteroid dehydrogenase type 1 might be dysregulated in the renal medulla of Dahl salt-sensitive rats. Additional analysis confirmed that renal medullary expression of 11 beta-hydroxysteroid dehydrogenase type 1 was downregulated by a high-salt diet in SS-13BN rats, a consomic rat strain with reduced blood pressure salt sensitivity, but not in Dahl salt-sensitive rats. 11 beta-Hydroxysteroid dehydrogenase type 1 is known to convert inactive 11-dehydrocorticosterone to active corticosterone. The urinary corticosterone/11-dehydrocorticosterone ratio as well as urinary excretion of corticosterone was higher in Dahl salt-sensitive rats than in SS-13BN rats. Knockdown of renal medullary 11 beta-hydroxysteroid dehydrogenase type 1 with small-interfering RNA attenuated the early phase of salt-induced hypertension in Dahl salt-sensitive rats and reduced urinary excretion of corticosterone. Knockdown of 11 beta-hydroxysteroid dehydrogenase type 1 did not affect blood pressure in SS-13BN rats. Long-term attenuation of salt-induced hypertension was achieved with small hairpin RNA targeting renal medullary 11 beta-hydroxysteroid dehydrogenase type 1. In summary, we have demonstrated that suppression of 11 beta-hydroxysteroid dehydrogenase type 1 expression in the renal medulla attenuates salt-induced hypertension in Dahl salt-sensitive rats.

Pathophysiological, genetic and gene expression features of a novel rodent model of the cardio-metabolic syndrome

BACKGROUND

Complex etiology and pathogenesis of pathophysiological components of the cardio-metabolic syndrome have been demonstrated in humans and animal models.

METHODOLOGY/PRINCIPAL FINDINGS

We have generated extensive physiological, genetic and genome-wide gene expression profiles in a congenic strain of the spontaneously diabetic Goto-Kakizaki (GK) rat containing a large region (110 cM, 170 Mb) of rat chromosome 1 (RNO1), which covers diabetes and obesity quantitative trait loci (QTL), introgressed onto the genetic background of the normoglycaemic Brown Norway (BN) strain. This novel disease model, which by the length of the congenic region closely mirrors the situation of a chromosome substitution strain, exhibits a wide range of abnormalities directly relevant to components of the cardio-metabolic syndrome and diabetes complications, including hyperglycaemia, hyperinsulinaemia, enhanced insulin secretion both in vivo and in vitro, insulin resistance, hypertriglyceridemia and altered pancreatic and renal histological structures. Gene transcription data in kidney, liver, skeletal muscle and white adipose tissue indicate that a disproportionately high number (43-83%) of genes differentially expressed between congenic and BN rats map to the GK genomic interval targeted in the congenic strain, which represents less than 5% of the total length of the rat genome. Genotype analysis of single nucleotide polymorphisms (SNPs) in strains genetically related to the GK highlights clusters of conserved and strain-specific variants in RNO1 that can assist the identification of naturally occurring variants isolated in diabetic and hypertensive strains when different phenotype selection procedures were applied.

CONCLUSIONS

Our results emphasize the importance of rat congenic models for defining the impact of genetic variants in well-characterised QTL regions on in vivo pathophysiological features and cis-/trans- regulation of gene expression. The congenic strain reported here provides a novel and sustainable model for investigating the pathogenesis and genetic basis of risks factors for the cardio-metabolic syndrome.

Chromosome substitution reveals the genetic basis of Dahl salt-sensitive hypertension and renal disease

This study examined the genetic basis of hypertension and renal disease in Dahl SS/Mcwi (Dahl Salt-Sensitive) rats using a complete chromosome substitution panel of consomic rats in which each of the 20 autosomes and the X and Y chromosomes were individually transferred from the Brown Norway (BN) rat onto the Dahl SS/Mcwi genetic background. Male and female rats of each of the two parental and 22 consomic strains (10-12 rats/group) were fed a high-salt (8.0% NaCl) diet for 3 wk. Mean arterial blood pressure rose by 60 mmHg and urinary protein and albumin excretion increased 3- and 20-fold, respectively, in male SS/Mcwi rats compared with BN controls. Substitution of chromosomes 1, 5, 7, 8, 13, or 18 from the BN onto the SS/Mcwi background attenuated the development of hypertension, proteinuria, and albuminuria in male rats. In female rats, substitution of chromosomes 1 and 5 also decreased blood pressure, protein excretion, and albumin excretion. These studies also identified several chromosomes in male (6, 11, Y) and female (4, 6, 11, 19, 20) rats that reduced albuminuria without altering blood pressure. These data indicate that genes contributing to salt-sensitive hypertension are found on multiple chromosomes of the Dahl SS/Mcwi rat. Furthermore, this consomic rat panel provides a stable genetic platform that can facilitate further gene mapping by either linkage studies or the breeding of congenic and subcongenic rats.

Identification of a major locus for islet inflammation and fibrosis in the spontaneously diabetic Torii rat

The pathogenesis of inflammation and fibrosis in the pancreatic islets in diabetes is largely unknown. Spontaneously diabetic Torii (SDT) rats exhibit inflammation and fibrosis in and around the islets during the development of the disease. We investigated genetic factors for diabetes, islet inflammation, and fibrosis in the SDT rat. We produced F1 and F2 rats by intercross between SDT and F344 rats, examined the onset of diabetes, glucose tolerance, and histology of the pancreas, and performed genetic analysis of these traits. We then established a congenic strain carrying the SDT allele at the strongest diabetogenic locus on the F344 genetic background and characterized glucose tolerance and histology of the pancreas. F1 rats showed glucose intolerance and inflammatory changes mainly in the islets. Genetic analysis of diabetes identified a major locus on chromosome 3, designated Dmsdt1, at which a dominantly acting SDT allele was involved. Quantitative trait locus (QTL) analysis of glucose tolerance revealed, in addition to Dmsdt1 [logarithm of odds (LOD) 5.3 near D3Mit12], three other loci, designated Dmsdt2 (LOD 4.2 at D8Rat46), Dmsdt3 (LOD 3.8 near D13Arb5), and Dmsdt4 (LOD 5.8 at D14Arb18). Analysis of a congenic strain for Dmsdt1 indicates that the dominantly acting SDT allele induces islet inflammation and fibrosis. Thus we have found a major locus on chromosome 3 for islet inflammation and fibrosis in the SDT rat. Identification of the genes responsible should provide insight into the pathogenesis of diabetes.

Sympathetic regulation of renal function in stroke-prone spontaneously hypertensive rats congenic for chromosome 1 blood pressure quantitative trait loci

1. Two reciprocal congenic strains, WKYpch1.0 and SHRSPwch1.0, were constructed, respectively, by introgressing the stroke-prone spontaneously hypertensive rat (SHRSP)-derived fragment for the chromosome 1 blood pressure (BP) quantitative trait locus (QTL) into Wistar-Kyoto (WKY) rats and vice versa. 2. Under basal conditions with intact renal sympathetic nerves, the renal noradrenaline content and renal vascular resistance (RVR) were decreased in the order of SHRSP, SHRSPwch1.0, WKYpch1.0 and WKY, exhibiting reciprocal changes in the congenic strains according to the genotype of the chromosome 1 QTL. 3. Renal denervation resulted in significant effects on RVR and the fractional excretion of sodium only in SHRSP and WKYpch1.0, both of which harboured the SHRSP-derived fragment of chromosome 1 QTL. 4. Thus, chromosome 1 QTL may influence both renal sympathetic nervous activity and the regulatory role of the sympathetic nervous system in vascular and tubular functions. The reciprocal congenic strains are thereby unique models that may help in the search for intermediate phenotypes and empower functional deduction of candidate genes.

Medicine. The ultimate model organism

A deeper understanding of disease requires a database of human traits and disease states that is integrated with molecular information.

Renal regional proteomes in young Dahl salt-sensitive rats

We performed an extensive proteomic analysis of the Dahl model of salt-sensitive hypertension. The consomic SS-13(BN) rat, genetically similar to the Dahl salt-sensitive rat, while exhibiting a significant amelioration of salt-induced hypertension, was used as a control. Proteomic analysis, using differential in-gel electrophoresis and mass spectrometry techniques, was performed in the renal cortex and the renal medulla of 6-week-old SS and SS-13(BN) rats before significant differences in blood pressure were developed between the 2 strains of rat. Several dozen proteins were identified as differentially expressed between SS and SS-13(BN) rats fed the 0.4% NaCl diet or switched to the 4% NaCl diet for 3 days (n=4). The identified proteins were involved in cellular functions or structures including signal transduction, energy metabolism, and the cytoskeleton. The proteomic analysis and subsequent Western blotting indicated that heterogeneous nuclear ribonucleoprotein K in the renal medulla was upregulated by the 4% NaCl diet in SS-13(BN) rats but downregulated in SS rats. The level of angiotensinogen mRNA in the renal medulla was regulated in an opposite manner. Silencing of heterogeneous nuclear ribonucleoprotein K resulted in an upregulation of angiotensinogen in cultured human kidney cells. In summary, we identified significant differences in kidney regional proteomic profiles between SS and SS-13(BN) rats and demonstrated a potential role of heterogeneous nuclear ribonucleoprotein K in the regulation of angiotensinogen expression in the renal medulla.

Systematic, genome-wide, sex-specific linkage of cardiovascular traits in French Canadians

The sexual dimorphism of cardiovascular traits, as well as susceptibility to a variety of related diseases, has long been recognized, yet their sex-specific genomic determinants are largely unknown. We systematically assessed the sex-specific heritability and linkage of 539 hemodynamic, metabolic, anthropometric, and humoral traits in 120 French-Canadian families from the Saguenay-Lac-St-Jean region of Quebec, Canada. We performed multipoint linkage analysis using microsatellite markers followed by peak-wide linkage scan based on Affymetrix Human Mapping 50K Array Xba240 single nucleotide polymorphism genotypes in 3 settings, including the entire sample and then separately in men and women. Nearly one half of the traits were age and sex independent, one quarter were both age and sex dependent, and one eighth were exclusively age or sex dependent. Sex-specific phenotypes are most frequent in heart rate and blood pressure categories, whereas sex- and age-independent determinants are predominant among humoral and biochemical parameters. Twenty sex-specific loci passing multiple testing criteria were corroborated by 2-point single nucleotide polymorphism linkage. Several resting systolic blood pressure measurements showed significant genotype-by-sex interaction, eg, male-specific locus at chromosome 12 (male-female logarithm of odds difference: 4.16; interaction P=0.0002), which was undetectable in the entire population, even after adjustment for sex. Detailed interrogation of this locus revealed a 220-kb block overlapping parts of TAO-kinase 3 and SUDS3 genes. In summary, a large number of complex cardiovascular traits display significant sexual dimorphism, for which we have demonstrated genomic determinants at the haplotype level. Many of these would have been missed in a traditional, sex-adjusted setting.

Comparative genomics for detecting human disease genes

Originally, comparative genomics was geared toward defining the synteny of genes between species. As the human genome project accelerated, there was an increase in the number of tools and means to make comparisons culminating in having the genomic sequence for a large number of organisms spanning the evolutionary tree. With this level of resolution and a long history of comparative biology and comparative genetics, it is now possible to use comparative genomics to build or select better animal models and to facilitate gene discovery. Comparative genomics takes advantage of the functional genetic information from other organisms, (vertebrates and invertebrates), to apply it to the study of human physiology and disease. It allows for the identification of genes and regulatory regions, and for acquiring knowledge about gene function. In this chapter, the current state of comparative genomics and the available tools are discussed in the context of developing animal model systems that reflect the clinical picture.

Individual assessment of arteriosclerosis by empiric clinical profiling

Background

Arteriosclerosis is a common cause of chronic morbidity and mortality. Myocardial infarction, stroke or other cardiovascular events identify vulnerable patients who suffer from symptomatic arteriosclerosis. Biomarkers to identify vulnerable patients before cardiovascular events occur are warranted to improve care for affected individuals. We tested how accurately basic clinical data can describe and assess the activity of arteriosclerosis in the individual patient.

Methodology/Principal Findings

269 in-patients who were treated for various conditions at the department of general medicine of an academic tertiary care center were included in a cross-sectional study. Personal history and clinical examination were obtained. When paraclinical tests were performed, the results were added to the dataset. The numerical variables in the clinical examination were statistically compared between patients with proven symptomatic arteriosclerosis (n = 100) and patients who had never experienced cardiovascular events in the past (n = 110). 25 variables were different between these two patient groups and contributed to the disease activity score. The percentile distribution of these variables defined the empiric clinical profile. Anthropometric data, signs of arterial, cardiac and renal disease, systemic inflammation and health economics formed the major categories of the empiric clinical profile that described an individual patient's disease activity. The area under the curve of the receiver operating curve for symptomatic arteriosclerosis was 0.891 (95% CI 0.799-0.983) for the novel disease activity score compared to 0.684 (95% CI 0.600-0.769) for the 10-year risk calculated according to the Framingham score. In patients suffering from symptomatic arteriosclerosis, the disease activity score deteriorated more rapidly after two years of follow-up (from 1.25 to 1.48, P = 0.005) compared to age- and sex-matched individuals free of cardiovascular events (from 1.09 to 1.19, P = 0.125).

Conclusions/Significance

Empiric clinical profiling and the disease activity score that are based on accessible, available and affordable clinical data are valid markers for symptomatic arteriosclerosis.

Multiple blood pressure loci on rat chromosome 13 attenuate development of hypertension in the Dahl S hypertensive rat

Previous studies have indicated that substitution of chromosome 13 of the salt-resistant Brown Norway BN/SsNHsdMcwi (BN) rat into the genomic background of the Dahl salt-sensitive SS/JrHsdMcwi (SS) rat attenuates the development of salt-sensitive hypertension and renal damage. To identify the regions within chromosome 13 that attenuate the development of hypertension during a high-salt diet in the SS rat, we phenotyped a series of overlapping congenic lines covering chromosome 13, generated from an intercross between the consomic SS-13BN rat and the SS rat. Blood pressure was determined in chronically catheterized rats after 2 wk of high-salt diet (8% NaCl) together with microalbuminuria as an index of renal damage. Four discrete regions were identified, ranging in size from 4.5 to 16 Mbp, each of which independently provided significant protection from hypertension during high-salt diet, reducing blood pressure by 20–29 mmHg. Protection was more robust in female than male rats in some of the congenic strains, suggesting a sex interaction with some of the genes determining blood pressure during high-salt diet. Among the 23 congenic strains, several regions overlapped. When three of the “protective” regions were combined onto one broad congenic strain, no summation effect was seen, obtaining the same decrease in blood pressure as with each one independently. We conclude from these studies that there are four regions within chromosome 13 containing genes that interact epistatically and influence arterial pressure.

Fibroblast growth factor 1 gene and hypertension: from the quantitative trait locus to positional analysis

BACKGROUND

The distal portion of the long arm of chromosome 5 is linked to hypertension and contains functional candidate blood pressure-regulating genes.

METHODS AND RESULTS

Tightening the grid of microsatellite markers under this quantitative trait locus in the Silesian Hypertension Study (629 individuals from 207 Polish hypertensive families) provided enhanced support for linkage of this region to blood pressure (maximal Z=3.51, P=0.0002). The fine mapping, comparative genomics, and functional prioritization identified fibroblast growth factor 1 gene (FGF1) as the positional candidate. Linkage disequilibrium mapping based on 51 single nucleotide polymorphisms spanning the locus showed no overlap between 3 independent haploblocks of FGF1 and the adjacent extragenic chromosomal regions. Single and multilocus family-based analysis revealed that genetic variation within FGF1 haploblock 1 was associated with hypertension and identified a common intronic single nucleotide polymorphism, rs152524, as the major driver of this association (P=0.0026). Real-time quantitative polymerase chain reaction and Western blotting analysis of renal tissue obtained from subjects undergoing unilateral nephrectomy showed an increase in both mRNA and protein FGF1 expression in hypertensive patients compared with normotensive controls. Renal immunohistochemistry revealed that FGF1 was expressed exclusively within the glomerular endothelial and mesangial cells.

CONCLUSIONS

Our data demonstrate that genetic variation within FGF1 cosegregates with elevated blood pressure in hypertensive families and that this association is likely to be mediated by upregulation of renal FGF1 expression. The results of our study will need to be replicated in other cohorts.