No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of chromosome 17 on features of the metabolic syndrome in the Lyon hypertensive rat
Abstract
The metabolic syndrome (involving obesity, hypertension, dyslipidemia, insulin resistance, and a proinflammatory/prethrombotic state) is a major risk factor for cardiovascular disease. Its incidence continues to rise, in part because of the epidemic increase in obesity. The Lyon hypertensive (LH) rat is a model for hypertension and several other features of the metabolic syndrome, having high body weight, plasma cholesterol, and triglycerides, increased insulin-to-glucose ratio, and salt-sensitive hypertension. Previous genetic studies in LH/Mav rats and a normotensive control (LN/Mav) identified quantitative trait loci (QTLs) on rat chromosome (RNO)17 for multiple features of the metabolic syndrome. To further evaluate the role of RNO17 in the LH rat, we generated a consomic strain (LH-17(BN)) by substituting LH RNO17 with that of the sequenced Brown Norway (BN/NHsdMcwi) rat. Male LH and BN rats and LH-17(BN) rats were characterized for blood pressure and metabolic and morphological parameters. Similar to the protective effect of LN alleles, the LH-17(BN) rat also showed decreased body weight, triglycerides, and blood pressure; however, there was no significant difference in cholesterol or insulin-to-glucose ratio. Therefore, the substitution of the LH chromosome 17 is sufficient to recapitulate some, but not all, of the traits previously mapped to this chromosome. This could be due to the lack of a susceptible LH genome background or due to the introgression of chromosome 17 from another strain. Regardless, this study provides a single-chromosome genetic model for further dissection of blood pressure and morphological and metabolic traits on this chromosome.
... Because of technical considerations, the study of all the consomic strains, as well as the parental strains, was performed simultaneously. Consequently, the parental strains were the same as in our previous study [25] and the framework of the protocol is identical for all the strains, as previously described, with the exception that some biochemical measurements differ among the different consomic strains, as described below. ...
... LH rats were compared to BN rats and the consomic (LH-13 BN and BN-13 LH ) were compared to their respective control (LH and BN rats). Differences were considered statistically significant at p<0.05.Figure 1 shows, as previously described [25], that LH rats exhibit a much larger body weight than BN rats. Interestingly, LH-13 BN rats showed a significantly larger body weight than LH rats, while body weight was lower in BN-13 LH rats than in BN parents. ...
... The substitution of the LH RNO13 markedly reduced plasma triglycerides. Interestingly, in our previous study [25], the replacement of LH RNO17 with that of the BN, also reduced plasma triglycerides to the level observed in BN parents suggesting a strong independent effect of RNO17 on hyperlipidemia or a common pathway with major components on both chromosomes. Taken together, these results allow us to hypothesize that the hypertriglyceridemia observed in LH rats is controlled by loci in at least two chromosomes (RNO17 and RNO13). ...
Hypertension and associated disorders are major risk factors for cardiovascular disease. The Lyon hypertensive rat (LH) is a genetically hypertensive strain that exhibits spontaneous and salt-sensitive hypertension, exaggerated proteinuria, high body weight, hyperlipidemia, and elevated insulin-to-glucose ratio. Previous genetic mapping identified quantitative trait loci (QTLs) influencing blood pressure (BP) on rat chromosome 13 (RNO13) in several models of hypertension.
To study the effects of a single chromosome on the mapped traits, we generated consomic strains by substituting LH RNO13 with that of the normotensive Brown Norway (BN) strain (LH-13BN) and reciprocal consomics by substituting a BN RNO13 with that of LH (BN-13LH). These reciprocal consomic strains, as well as the two parental strains were characterized for BP, metabolic and morphological parameters.
Compared with LH parents, LH-13BN rats showed decreased mean BP (up to -24 mmHg on 2% NaCl in the drinking water), urine proteins and lipids, and increased body weight. Differences between BN-13LH and BN rats were much smaller than those observed between LH-13BN and LH rats, demonstrating the effects of the highly resistant BN genome background. Plasma renin activity was not affected by the substitution of RNO13, despite the significant BP differences.
The present work demonstrates that RNO13 is a determinant of BP, proteinuria, and plasma lipids in the LH rat. The distinct phenotypic differences between the consomic LH-13BN and the LH make it a powerful model to determine genes and pathways leading to these risk factors for cardiovascular and renal disease.
... Generation of congenic strains has been successfully utilized by several groups by introgressing target chromosomal regions from the hypertension-resistant Brown Norway strain onto the SHR genome [51] or from regions of several genetically hypertensive rat chromosomes onto the Brown Norway background [52]. The Lyon investigators have recently constructed reciprocal consomic strains, a variation of congenic strains in which a whole chromosome rather than a chromosomal region is back-crossed [53]. In a recent study, the authors reciprocally backcrossed chromosome 17 in Lyon hypertensive and Brown Norway rats. ...
... Many such alleles may be undetectable when comparing the Lyon hypertensive and Lyon normotensive strains, sharing over 90% gene identity with each other. In the first of their studies, Gilibert et al. [53] used the Brown Norway / Lyon hypertensive reciprocal consomic approach. They found that whereas introgression of chromosome 17 from Brown Norway rats onto Lyon hypertensive rats protected them from hypertension and metabolic abnormalities, introgression of chromosome 17 from Lyon hypertensive rats onto Brown Norway rats was overcome by homeostatic mechanisms in the Brown Norway genome [53]. ...
... In the first of their studies, Gilibert et al. [53] used the Brown Norway / Lyon hypertensive reciprocal consomic approach. They found that whereas introgression of chromosome 17 from Brown Norway rats onto Lyon hypertensive rats protected them from hypertension and metabolic abnormalities, introgression of chromosome 17 from Lyon hypertensive rats onto Brown Norway rats was overcome by homeostatic mechanisms in the Brown Norway genome [53]. ...
Genetic influences contribute upto 30–50% to blood pressure variability in human essential hypertension [1]. Intense efforts have been dedicated to unraveling the role of genes in this disease, following two parallel and interacting tracks. Studies on human populations have mostly focused on the candidate gene linkage approach, associating single nucleotide polymorphic (SNP) markers with the hypertensive phenotype. In spite of some promising observations [2], most attempts to replicate association studies have not been encouraging [3]. There are calls for application of stricter quality criteria for genetic studies, including better definition of phenotype characteristics, increased attention to environmental factors, sharing and combining data resources and more emphasis on whole genome-linkage scans in the context of collaborative multidisciplinary approaches [4–17]. Recently, however, there has been impressive progress in designing studies, understanding the mechanisms of disease and genotyping technology [17].
... The genomes of the LH and LN rat strains have been sequenced (Atanur et al., 2013), and have demonstrated close genetic relatedness and minimal genetic variance (Ma et al., 2014), which lends itself to fine-mapping of causal loci. The importance of LH chromosome 17 (chr17) to their metabolic dysfunction has been demonstrated on multiple occasions, when LH consomic strains produced with either Brown Norway (Gilibert et al., 2008) or LN (Bilusic et al., 2004; chr17 replacement afforded some protection against obesity, dyslipidemia, and hypertension. Independent QTL have been identified for most features of MetS on chr17, including blood pressure, body weight, adiposity, and dyslipidemia (Bilusic et al., 2004;Wang et al., 2015;. ...
... The creation of congenic models allows entire QTL to be substituted into a genomic background, potentially preserving important gene-gene interactions or necessary regulatory context in a way that targeted knockouts or mutations cannot (Clark and Kwitek, 2021). The purpose of this work was to fine-map the proximal end of a previously identified body weight QTL (Bw32; RGD: 1354596) (Bilusic et al., 2004) on chr17 by characterization of a novel congenic rat strain and to identify a putative candidate gene underlying the body weight differences seen in the chr17 consomic rats (Gilibert et al., 2008;. ...
Central obesity is genetically complex, and its exponential increase in the last decades have made it a critical public health issue. The Lyon Hypertensive (LH) rat is a well-characterized hypertensive model that also exhibits spontaneous and profound differences in body weight and adiposity, relative to its metabolically healthy control, the Lyon Normotensive (LN) rat. The mechanisms underlying the body weight differences between these strains are not well-understood, thus a congenic model (LH¹⁷LNa) was developed where a portion of the proximal arm of LN chromosome 17 is introgressed on the LH genomic background to assess the contribution of LN alleles on obesity features. Male and female LH¹⁷LNa rats were studied, but male congenics did not significantly differ from LH in this study. Female LH¹⁷LNa rats exhibited decreases in total body growth, as well as major alterations to their body composition and adiposity. The LH¹⁷LNa female rats also showed decreases in metabolic rate, and a reduction in food intake. The increased adiposity in the female LH¹⁷LNa rats was specific to abdominal white adipose tissue, and this phenomenon was further explained by significant hypertrophy in those adipocytes, with no evidence of adipocyte hyperplasia. Sequencing of the parental strains identified a novel frameshift mutation in the candidate gene Ercc6l2, which is involved in transcription-coupled DNA repair, and is implicated in premature aging. The discovery of the significance of Ercc6l2 in the context of female-specific adipocyte biology could represent a novel role of DNA repair failure syndromes in obesity pathogenesis.
... These studies implicate a single chromosome is sufficient to cause MetS in LH rats. To study the independent role of RNO17 in MetS, a consomic LH-17 BN strain was developed, where only RNO17 from the LH rat was substituted by that of the sequenced BN rat (BN/NHsdMcwi) [20]. This strain was found to have reduced blood pressure, body weight, and plasma triglycerides, confirming the independent role of LH RNO17 in MetS. ...
... Genetic studies in other rat strains have also identified loci for hypertension and other MetS traits on rat chromosome 17 [27][28][29][30][31][32][33]. Previously a consomic rat having a BN chromosome 17 on an LH genome background was generated [20]. That study showed a profile similar to that of the LH-17 LN consomic reported here, with decreased MAP compared to LH parental rats before and after a salt challenge, decreased body weight at 18 weeks of age, as well as decreased plasma triglycerides compared to their respective LH controls. ...
Hypertension is a major risk factor for cardiovascular disease, Type 2 diabetes, and end organ failure, and is often found concomitant with disorders characteristic of the Metabolic Syndrome (MetS), including obesity, dyslipidemia, and insulin resistance. While the associated features often occur together, the pathway(s) or mechanism(s) linking hypertension in MetS are not well understood. Previous work determined that genetic variation on rat chromosome 17 (RNO17) contributes to several MetS-defining traits (including hypertension, obesity, and dyslipidemia) in the Lyon Hypertensive (LH) rat, a genetically determined MetS model. We hypothesized that at least some of the traits on RNO17 are controlled by a single gene with pleiotropic effects. To address this hypothesis, consomic and congenic strains were developed, whereby a defined fragment of RNO17 from the LH rat was substituted with the control Lyon Normotensive (LN) rat, and MetS phenotypes were measured in the resultant progeny. Compared to LH rats, LH-17LN consomic rats have significantly reduced body weight, blood pressure, and lipid profiles. A congenic strain (LH-17LNc), with a substituted fragment at the distal end of RNO17 (17q12.3; 74–97 Mb; rn4 assembly), showed differences from the LH rat in blood pressure and serum total cholesterol and triglycerides. Interestingly, there was no difference in body weight between the LH-17LNc and the parental LH rat. These data indicate that blood pressure and serum lipids are regulated by a gene(s) in the distal congenic interval, and could be due to pleiotropy. The data also indicate that body weight is not determined by the same gene(s) at this locus. Interestingly, only two small haplotypes spanning a total of approximately 0.5 Mb differ between the LH and LN genomes in the congenic interval. Genes in these haplotypes are strong candidate genes for causing dyslipidemia in the LH rat. Overall, MetS, even in a simplified genetic model such as the LH-17LN rat, is likely due to both independent and pleiotropic gene effects.
... [112][113][114] Results of this approach make it clear that the SS phenotype of rats is determined by multiple different genes or by the combination of their effects into a polygenic form of inheritance. An additional contribution of this methodology has been the understanding that components of the SS phenotype (eg, insulin resistance 115 ) or the magnitude of its cardiac 98,116 and renal 99,117-119 target organ damage may be determined by genetic influences distinct from those that control the hypertensive response to salt. ...
The simplest definition of salt sensitivity of blood pressure (SSBP) states that it is a physiological trait present in rodents and other mammals, including humans, by which the blood pressure (BP) of some members of the population exhibits changes parallel to changes in salt intake. In animals, the trait has been inbred such that the salt-sensitive (SS) ones will sustain increases in BP with salt loading and decreases with salt depletion, whereas the salt resistant (SR) ones will not. In humans, the trait is normally distributed; therefore, the distinction between SS and SR members of the population has been made by choosing an arbitrary magnitude of the salt-induced change in BP to define the groups. Regardless of possible causation by abnormalities of sodium handling, the SS phenotype is not usually characterized by alterations in salt balance (eg, impaired natriuresis or expanded plasma volume) but rather by a hypertensive response to maintain it.
In an unselected population, SSBP is a continuous, normally distributed quantitative trait.1 As with any other trait with these characteristics, there is the issue of whether population members with the largest and smallest quantities of the trait represent the randomness of its distribution or are qualitatively different from the population at large. An example of this controversy is the old analyses of the unimodality versus bimodality of BP incidence or prevalence in humans that tried to determine whether hypertension is a distinct entity or simply an extreme of the gaussian distribution of BP.2 The development of the spontaneously hypertensive rat by Japanese investigators3 showing that the trait could be selected by inbreeding made it clear that hypertension had a genetic component. The gaussian distribution of population BP is probably the result of a random mixture of prohypertensive and antihypertensive genes and genetic variants in a …
... Hypertension has genetic and environmental factors in addition to those associated with obesity [4,29,64,65] . Salt sensitive hypertension refers to an increase in blood pressure related to an increase in salt (specifically sodium) intake [6,66,67] . Some workers in this field believe that all hypertension reflects either excessive sodium intake or some form of renal salt sensitivity, but this is admittedly still controversial [63, [68][69][70] . ...
Although it has known for some time that obesity is associated with salt sensitivity and hypertension, recent data suggests that the adipocyte may actually be the proximate cause of this physiological changes. In the following review, the data demonstrating this association as well as the potentially operative pathophysiological mechanisms are reviewed and discussed. Core tip: Hypertension is a growing problem worldwide, and the problem is exacerbated by the growing obesity epidemic. This review looks into the complex relationship between these two diseases, outlining what current literature reports for treatment methods, hypotheses on cause, and potential cross talk between the two. Martin R, Shapiro JI. Role of adipocytes in hypertension. World J Hypertens 2016; 6(2): 66-75 Available from: URL
... 26 The current and previous studies found QTL for multiple MetS traits on RNO17, which were replicated in consomic rat models. 8,34 Therefore, we speculate there may be a gene or genes having pleiotropic effects on the MetS spectrum. In this study, we identified a cisregulated gene on RNO17, RGD1562963, as a putative driver gene regulating multiple downstream genes. ...
-The metabolic syndrome (MetS) is a collection of co-occurring complex disorders including obesity, hypertension, dyslipidemia, and insulin resistance. The Lyon Hypertensive (LH) and Lyon Normotensive (LN) rats are models of MetS sensitivity and resistance, respectively. To identify genetic determinants and mechanisms underlying MetS, an F2 intercross between LH and LN was comprehensively studied.
-Multi-dimensional data were obtained including genotypes of 1536 SNPs, 23 physiological traits and more than 150 billion nucleotides of RNA-seq reads from the livers of F2 intercross offspring and parental rats. Phenotypic and expression QTL were mapped. Application of systems biology methods identified 17 candidate MetS genes. Several putative causal cis-eQTL were identified corresponding with pQTL loci. We found an eQTL hotspot on rat chromosome 17 that is causally associated with multiple MetS-related traits, and found RGD1562963, a gene regulated in cis by this eQTL hotspot, as the most likely eQTL driver gene directly affected by genetic variation between LH and LN rats.
-Our study sheds light on the intricate pathogenesis of MetS and demonstrates that systems biology with high-throughput sequencing is a powerful method to study the etiology of complex genetic diseases.
... The shared lineage between LH and LN strains also resulted in a paucity of informative polymorphic markers between the strains; therefore, the QTL intervals in our previous mapping study were large, and generating congenic and consomic strains by markerassisted selection was a challenge. Consomic strains introgressing the more genetically divergent BN chromosomes 13 or 17 succeeded in recapitulating some of the phenotypesbody weight, triglycerides, and blood pressurethat were identified in the QTL analysis [14,15]. However, the genetic similarity between the Lyon strains presents an opportunity to utilize haplotype mapping to fine-map the loci, if sufficient polymorphic markers could be identified. ...
The metabolic syndrome (MetS), a complex disorder involving hypertension, obesity, dyslipidemia and insulin resistance, is a major risk factor for heart disease, stroke, and diabetes. The Lyon Hypertensive (LH), Lyon Normotensive (LN) and Lyon Low-pressure (LL) rats are inbred strains simultaneously derived from a common outbred Sprague Dawley colony by selection for high, normal, and low blood pressure, respectively. Further studies found that LH is a MetS susceptible strain, while LN is resistant and LL has an intermediate phenotype. Whole genome sequencing determined that, while the strains are phenotypically divergent, they are nearly 98% similar at the nucleotide level. Using the sequence of the three strains, we applied an approach that harnesses the distribution of Observed Strain Differences (OSD), or nucleotide diversity, to distinguish genomic regions of identity-by-descent (IBD) from those with divergent ancestry between the three strains. This information was then used to fine-map QTL identified in a cross between LH and LN rats in order to identify candidate genes causing the phenotypes.
We identified haplotypes that, in total, contain at least 95% of the identifiable polymorphisms between the Lyon strains that are likely of differing ancestral origin. By intersecting the identified haplotype blocks with Quantitative Trait Loci (QTL) previously identified in a cross between LH and LN strains, the candidate QTL regions have been narrowed by 78%. Because the genome sequence has been determined, we were further able to identify putative functional variants in genes that are candidates for causing the QTL.
Whole genome sequence analysis between the LH, LN, and LL strains identified the haplotype structure of these three strains and identified candidate genes with sequence variants predicted to affect gene function. This approach, merged with additional integrative genetics approaches, will likely lead to novel mechanisms underlying complex disease and provide new drug targets and therapies.
... This panel is used as a genetic tool to determine chromosomes that harbor genes involved in complex traits [19], and has been used specifically to identify chromosomes involved in hypertension [20][21][22]. Other panels, such as the Lyon hypertensive (LH) consomic strain (LH-17(BN)) has shown utility for traits involved in metabolic syndrome [23]. The goal of the current study was to employ the use of consomic rats to identify a chromosome or chromosomes that carry a gene(s) that may be responsible for the development of metabolic risk factors after exposure to a high fat/low carbohydrate diet. ...
Background/aims:
Recent studies have highlighted the importance of gene by diet interactions in contributing to risk factors of metabolic syndrome. We used a consomic rat panel, in which a chromosome of the Brown Norway (BN) strain is introgressed onto the background of the Dahl salt-sentitive (SS) strain, to test the hypothesis that these animals will be useful for dissecting gene by diet interactions involved in metabolic syndrome.
Methods:
We placed the parental SS and BN strains on a low-fat/high-carbohydrate (LF) or high-fat/low-carbohydrate (HF) diet for 22 weeks and measured several indices of metabolic syndrome. We then investigated the effect of diet in eight consomic rat strains.
Results:
We show that the HF diet resulted in significantly increased levels of fasting plasma cholesterol and triglycerides in the SS strain, with no effect in the BN. Both strains responded to the HF diet with slight increases in body weight. SSBN8 was the only consomic strain that resembled that of the BN, with low levels of fasting cholesterol and triglycerides even on the HF diet.
Conclusions:
These results indicate that BN chromosome 8 harbors a gene or genes that confer protection against dyslipidemia caused by the HF diet.
... Mutations associated with this gene may result in changes in serotonin transporter function and in fact more the 50 different phenotypic changes have been discovered as a result of genetic variation. [26,32] I425V on chromosome 17 m is found in unrelated families with obsessive compulsive disorder and it leads to faulty transporter function and regulation. [33] The presence of rs-25531 in the same gene of some patients with this variation suggests a genetic'double hit' , resulting in greater biochemical effects and more severe symptoms. ...
Serotonin is a monoamine neurotransmitter that is widely distributed in the body and plays an important role in a variety of psychological and other body functions such as mood, sexual desire and function, appetite, sleep, memory and learning, temperature regulation and social behaviour. This review will assess the use of fluoxetine, one of the most commonly used selective serotonin reuptake inhibitors, as a model for understanding the molecular pharmacology of the serotoninergic system.
Seven serotonin receptor families have been discovered to date. All serotonin receptors, except 5-HT(3), are G-protein coupled, seven transmembrane receptors that activate an intracellular second messenger cascade. The 5-HT(3) receptor is a ligand-gated ion channel. Furthermore, 5-HT(1A) receptors are known as autoreceptors since their stimulation inhibits the release serotonin in nerve terminals. A transporter protein found in the plasma membrane of serotonergic neurones is responsible for the reuptake of this neurotransmitter. Selective serotonin reuptake inhibitors, such as fluoxetine, act primarily at the serotonin transporter protein and have limited, if any, reaction with other neurotransmitter systems. Selective serotonin reuptake inhibitors appear to bind with the serotonin transporter with different rates of occupancy, duration and potency.
The following review focuses on the interaction of serotonin with this membrane transporter in the body and assesses the use of fluoxetine as a reference drug in the understanding of this interaction.
... From these consomic strains, congenic strains can be rapidly generated (Cowley et al. 2004) (Fig. 2, left panel) and have a greater statistical power to detect linkage over traditional F2 crosses (Shao et al. 2010). The feasibility of this approach has been demonstrated by an mapping cardiovascular (Cowley et al. 2001), renal disease (Mattson et al. 2008;Schulz et al. 2010), vascular function (Kunert et al. 2006;Kunert et al. 2010), pulmonary hypertension (Bonnet et al. 2006), respiratory control traits (Dwinell et al. 2005), metabolic syndrome (Gilibert et al. 2008), and tumor susceptibility (Adamovic et al. 2008;Adamovic et al. 2010) in the consomic panels derived from the SS (Dahl salt sensitive) and BN (Brown Norway) strains. For example, hypertension QTLs in these models have recently been reduced to single centimorgan sized regions (Joe et al. 2009;Moreno et al. 2011b). ...
Rat models have been used for many decades to study physiological and pathophysiological mechanisms. Prior to the release of the rat genome and new technologies for targeting gene manipulation, the rat had been the underdog in the genomics era, despite the abundance of physiological data compared to the mouse. The overarching goal of biomedical research is to improve health and advance medical science. Translating human disease gene discovery and validation in the rat, through the use of emerging technologies and integrated tools and databases, is providing power to understand the genetics, environmental influences, and biology of disease. In this review we briefly outline the rat models, bioinformatics tools, and technologies that are changing the landscape of translational research. The strategies used to translate disease traits to genes to function, and, ultimately, to improve human health is discussed. Finally, our perspective on how rat models will continue to positively impact biomedical research is provided.
The rat has been used for a long time as the model of choice in several biomedical disciplines. Numerous inbred strains have been isolated, displaying a wide range of phenotypes and providing many models of human traits and common diseases. Unlike the mouse, the rat was neglected by geneticists. However, most traits and diseases studied in the rat are complex, polygenic, and their analysis requires genetic approaches. Rat genome mapping and genomics were considerably developed in the last two decades, starting, as in the human, with chromosome and cytogenetic mapping based on standard somatic cell hybrids and fluorescence in situ hybridization (FISH). Linkage and radiation hybrid maps were then constructed that included genes, expressed sequences tags (EST), and microsatellite markers and they were integrated with the cytogenetic map. The genome sequences of two rat strains were published in 2004 (BN) and 2010 (spontaneous hypertensive rat, SHR), and thousands of various DNA polymorphisms have been identified. The availability of these resources has stimulated numerous linkage studies in rat crosses and in recombinant inbred strains, leading to the genetic identification of hundreds of quantitative trait loci (QTLs) influencing various traits and demonstrating that the rat is a valuable experimental model, including for geneticists. In addition, high-throughput gene expression profiling and genetical genomics have been applied to the rat, adding a new dimension to disease gene discovery. Several rat genes have now been identified that underlie complex diseases and remarkably, these results have been translated to the human in a significant proportion of cases, leading to the identification of novel human disease susceptibility genes and also suggesting new therapeutic approaches. A major biological limitation of the rat as a model was the lack of totipotent embryonic stem (ES) cells; this limitation was recently removed and targeted knockout rats can now be generated. It can reasonably be predicted that identification of numerous relevant disease genes will be achieved in rat models in a near future and that these results will help in understanding the mechanisms underlying common human diseases, thereby also stimulating the development of new therapies.
The rat has been used for a long time as the model of choice in several biomedical disciplines. Numerous inbred strains have been isolated, displaying a wide range of phenotypes and providing many models of human traits and common diseases. Unlike the mouse, the rat was neglected by geneticists. However, most traits and diseases studied in the rat are complex, polygenic, and their analysis requires genetic approaches. Rat genome mapping and genomics were considerably developed in the last two decades, starting, as in the human, with chromosome and cytogenetic mapping based on standard somatic cell hybrids and fluorescence in situ hybridization (FISH). Linkage and radiation hybrid maps were then constructed that included genes, expressed sequences tags (EST), and microsatellite markers and they were integrated with the cytogenetic map. The genome sequences of two rat strains were published in 2004 (BN) and 2010 (spontaneous hypertensive rat, SHR), and thousands of various DNA polymorphisms have been identified. The availability of these resources has stimulated numerous linkage studies in rat crosses and in recombinant inbred strains, leading to the genetic identification of hundreds of quantitative trait loci (QTLs) influencing various traits and demonstrating that the rat is a valuable experimental model, including for geneticists. In addition, high-throughput gene expression profiling and genetical genomics have been applied to the rat, adding a new dimension to disease gene discovery. Several rat genes have now been identified that underlie complex diseases and remarkably, these results have been translated to the human in a significant proportion of cases, leading to the identification of novel human disease susceptibility genes and also suggesting new therapeutic approaches. A major biological limitation of the rat as a model was the lack of totipotent embryonic stem (ES) cells; this limitation was recently removed and targeted knockout rats can now be generated. It can reasonably be predicted that identification of numerous relevant disease genes will be achieved in rat models in a near future and that these results will help in understanding the mechanisms underlying common human diseases, thereby also stimulating the development of new therapies.
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.
An overview is provided of the advances in plant, animal and human genome studies by summarizing the contents of seven plenary lectures presented at the Plant and Animal Genome (PAG) meeting in January 2010. The area of biology covered was wide and reflected the nature of this fast moving science.
The antihypertensive drug atenolol was found to induce chromosome loss, detected as micronuclei in the peripheral lymphocytes of treated patients. The fundamental question which chromosomes the micronuclei were derived from remains to be answered. Analysis of structural chromosomal aberrations (CAs) and expression of fragile sites (FS) were pursued in this study. They revealed a significantly higher incidence of chromosomal aberrations (chromatid and chromosome breaks) in patients compared with controls, where 10 FS emerged as specific. Also, the band 17q12-21, where known fragile sites have not been reported, was only expressed in atenolol-treated patients. Fluorescence in situ hybridization using chromosome-specific probes revealed the preferential involvement of chromosomes 7, 11, 17 and X in the micronuclei (MN) of patients. The results also suggest a correlation between chromosomal fragility and content of MN, and support the findings for a linkage between hypertension and a locus on chromosome 17.
In previous work, we observed that N/OFQ-induced hyperphagia is greater in DA rats, animals resistant to metabolic syndrome, than in WOKW animals, which are prone to this disease. We attributed this difference to the fact that these two strains have different Cart gene sequences and expression. As a preliminary approach to pursue this hypothesis, the present work focused on Cart gene expression by developing from DA and WOKW rats various congenic animals with exchanges of metabolic syndrome-related QTL's of different chromosomes (3, 5, 10 and 16), and analyzing their N/OFQ-induced (2.1, 4.2, and 8.4nmol/rat) food intake in terms of their CART gene expression and N/OFQ hypothalamic immunostaining. Two groupings emerged, the first, with strains 3a, 3b, and 5a with elevated N/OFQ-induced feeding similar to that of the DA rats, and the second, with strains 16 and 10, with lower feeding, like the WOKW rats. There was a perfect correlation between Cart gene expression and N/OFQ-induced feeding data at 30min for the strains DA, 3a, 3b, 5 in the first group, and 16 and WOKW for the second, but not for strain 10. As expected, the strains with low content of Cart gene expression had elevated N/OFQ-induced feeding, but contrary to expectations, strain 10, with the lowest Cart gene expression, exhibited low N/OFQ-induced feeding, on the order of that of the WOKW rats. A comparable trend was observed with N/OFQ hypothalamic immunostaining. This anomaly may be due to other satiety-related factors involved in N/OFQ-induced feeding.
The "metabolic syndrome" (MetS) is a clustering of components that reflect overnutrition, sedentary lifestyles, and resultant excess adiposity. The MetS includes the clustering of abdominal obesity, insulin resistance, dyslipidemia, and elevated blood pressure and is associated with other comorbidities including the prothrombotic state, proinflammatory state, nonalcoholic fatty liver disease, and reproductive disorders. Because the MetS is a cluster of different conditions, and not a single disease, the development of multiple concurrent definitions has resulted. The prevalence of the MetS is increasing to epidemic proportions not only in the United States and the remainder of the urbanized world but also in developing nations. Most studies show that the MetS is associated with an approximate doubling of cardiovascular disease risk and a 5-fold increased risk for incident type 2 diabetes mellitus. Although it is unclear whether there is a unifying pathophysiological mechanism resulting in the MetS, abdominal adiposity and insulin resistance appear to be central to the MetS and its individual components. Lifestyle modification and weight loss should, therefore, be at the core of treating or preventing the MetS and its components. In addition, there is a general consensus that other cardiac risk factors should be aggressively managed in individuals with the MetS. Finally, in 2008 the MetS is an evolving concept that continues to be data driven and evidence based with revisions forthcoming.
Molecular genetics can be integrated with traditional methods of artificial selection on phenotypes by applying marker-assisted selection (MAS). We derive selection indices that maximize the rate of improvement in quantitative characters under different schemes of MAS combining information on molecular genetic polymorphisms (marker loci) with data on phenotypic variation among individuals (and their relatives). We also analyze statistical limitations on the efficiency of MAS, including the detectability of associations between marker loci and quantitative trait loci, and sampling errors in estimating the weighting coefficients in the selection index. The efficiency of artificial selection can be increased substantially using MAS following hybridization of selected lines. This requires initially scoring genotypes at a few hundred molecular marker loci, as well as phenotypic traits, on a few hundred to a few thousand individuals; the number of marker loci scored can be greatly reduced in later generations. The increase in selection efficiency from the use of marker loci, and the sample sizes necessary to achieve them, depend on the genetic parameters and the selection scheme.
The association of a parental history of diabetes mellitus and hypertension with the multiple metabolic syndrome (MMS) was studied in a population survey of middle-aged adults. The eligible population was drawn from the baseline examination of the Atherosclerosis Risk in Communities Study, a population-based, bi-ethnic, multi-centre cohort study. The MMS was defined as a multivariate, categorical phenotype of co-occurring diabetes, hypertension, and dyslipidaemia. MMS cases (n = 356) were compared to disorder-free control subjects (n = 6797) with respect to their parental history of diabetes and hypertension. MMS cases were more likely to report a history of diabetes in both parents (odds ratio [OR] 4.7, 95 % confidence interval (CI) 1.5-14.7) or a history of hypertension in both parents (OR 1.9, 95 % CI 1.1-3.0) than control subjects, adjusting for BMI, waist-to-hip ratio, age, gender, and ethnicity/centre. A parental history of diabetes and hypertension in both parents was associated with the greatest increase in odds of MMS (OR 8.3, 95 % CI 3.0-22.8). A dose-response relationship between the number of parental disorders (one; two; three to four) and the odds of MMS was observed (OR 1.2, 95 % CI 0.9-1.7; OR 2.0, 95 % CI 1.4-2.8; OR 4.0, 95 % CI 2.5-6.2). Based on the marked associations observed between a parental history of MMS components and the clustering of these metabolic disorders in the offspring generation, we conclude that genetic and/or non-genetic familial influences play a role in the development of the multiple metabolic syndrome.
We report on the development of molecular inversion probe (MIP)
genotyping, an efficient technology for large-scale single nucleotide
polymorphism (SNP) analysis. This technique uses MIPs to produce inverted
sequences, which undergo a unimolecular rearrangement and are then amplified by
PCR using common primers and analyzed using universal sequence tag DNA
microarrays, resulting in highly specific genotyping. With this technology,
multiplex analysis of more than 1,000 probes in a single tube can be done using
standard laboratory equipment. Genotypes are generated with a high call rate
(95%) and high accuracy (>99%) as determined by independent sequencing.
The laboratory rat (Rattus norvegicus) is an indispensable tool in experimental medicine and drug development, having made inestimable contributions to human health. We report here the genome sequence of the Brown Norway (BN) rat strain. The sequence represents a high-quality 'draft' covering over 90% of the genome. The BN rat sequence is the third complete mammalian genome to be deciphered, and three-way comparisons with the human and mouse genomes resolve details of mammalian evolution. This first comprehensive analysis includes genes and proteins and their relation to human disease, repeated sequences, comparative genome-wide studies of mammalian orthologous chromosomal regions and rearrangement breakpoints, reconstruction of ancestral karyotypes and the events leading to existing species, rates of variation, and lineage-specific and lineage-independent evolutionary events such as expansion of gene families, orthology relations and protein evolution.
The complex nature of hypertension makes identifying the pathophysiology and its genetic contributions a challenging task. One powerful approach for the genetic dissection of blood pressure regulation is studying inbred rat models of hypertension, as they provide natural allele variants but reduced heterogeneity (both genetic and etiologic). Furthermore, the detailed physiologic studies to which the rat is amenable allow for the determination of intermediate phenotypes. We have performed a total genome scan in offspring of an F2 intercross between the Lyon hypertensive (LH) and Lyon normotensive rat strains to identify linkage of anthropometric, blood pressure, renal, metabolic, and endocrine phenotypes. Quantitative trait locus (QTL) regions involved in blood pressure regulation, end-stage organ damage, body and organ weight, and lipid metabolism in the LH rat were identified on chromosomes 1, 2, 3, 5, 7, 10, 13, and 17, with 2 phenotypes associated with the metabolic syndrome identified on chromosomes 1 and 17. Regions on chromosomes 2, 13, and 17 were revealed to be important for blood pressure regulation. Regions on chromosome 17 were found to significantly contribute to both metabolic homeostasis and blood pressure regulation; 2 aggregates of a total of 23 QTLs were identified, including several "intermediate phenotypes." These intermediate phenotypes may be used as closer surrogates to the mechanisms leading to hypertension and metabolic dysfunction in the LH rat.
Large-scale genetic studies are highly dependent on efficient and scalable multiplex SNP assays. In this study, we report the development of Molecular Inversion Probe technology with four-color, single array detection, applied to large-scale genotyping of up to 12,000 SNPs per reaction. While generating 38,429 SNP assays using this technology in a population of 30 trios from the Centre d'Etude Polymorphisme Humain family panel as part of the International HapMap project, we established SNP conversion rates of approximately 90% with concordance rates >99.6% and completeness levels >98% for assays multiplexed up to 12,000plex levels. Furthermore, these individual metrics can be "traded off" and, by sacrificing a small fraction of the conversion rate, the accuracy can be increased to very high levels. No loss of performance is seen when scaling from 6,000plex to 12,000plex assays, strongly validating the ability of the technology to suppress cross-reactivity at high multiplex levels. The results of this study demonstrate the suitability of this technology for comprehensive association studies that use targeted SNPs in indirect linkage disequilibrium studies or that directly screen for causative mutations.
The National Cholesterol Education Program’s Adult Treatment Panel III report (ATP III)1 identified the metabolic syndrome as a multiplex risk factor for cardiovascular disease (CVD) that is deserving of more clinical attention. The cardiovascular community has responded with heightened awareness and interest. ATP III criteria for metabolic syndrome differ somewhat from those of other organizations. Consequently, the National Heart, Lung, and Blood Institute, in collaboration with the American Heart Association, convened a conference to examine scientific issues related to definition of the metabolic syndrome. The scientific evidence related to definition was reviewed and considered from several perspectives: (1) major clinical outcomes, (2) metabolic components, (3) pathogenesis, (4) clinical criteria for diagnosis, (5) risk for clinical outcomes, and (6) therapeutic interventions.
ATP III viewed CVD as the primary clinical outcome of metabolic syndrome. Most individuals who develop CVD have multiple risk factors. In 1988, Reaven2 noted that several risk factors (eg, dyslipidemia, hypertension, hyperglycemia) commonly cluster together. This clustering he called Syndrome X , and he recognized it as a multiplex risk factor for CVD. Reaven and subsequently others postulated that insulin resistance underlies Syndrome X (hence the commonly used term insulin resistance syndrome ). Other researchers use the term metabolic syndrome for this clustering of metabolic risk factors. ATP III used this alternative term. It avoids the implication that insulin resistance is the primary or only cause of associated risk factors. Although ATP III identified CVD as the primary clinical outcome of the metabolic syndrome, most people with this syndrome have insulin resistance, which confers increased risk for type 2 diabetes. When diabetes becomes clinically apparent, CVD risk rises sharply. Beyond CVD and type 2 diabetes, individuals with metabolic syndrome seemingly are susceptible to other conditions, notably polycystic ovary syndrome, fatty liver, cholesterol gallstones, asthma, sleep disturbances, and some …
Insulin resistance is the cornerstone for the development of non-insulin-dependent diabetes mellitus (NIDDM). Free fatty acids (FFAs) cause insulin resistance in muscle and liver and increase hepatic gluconeogenesis and lipoprotein production and perhaps decrease hepatic clearance of insulin. It is suggested that the depressing effect of insulin on circulating FFA concentration is dependent on the fraction derived from visceral adipocytes, which have a low responsiveness to the antilipolytic effect of insulin. Elevated secretion of cortisol and/or testosterone induces insulin resistance in muscle. This also seems to be the case for low testosterone concentrations in men. In addition, cortisol increases hepatic gluconeogenesis. Cortisol and testosterone have "permissive" effects on adipose lipolysis and therefore amplify lipolytic stimulation; FFA, cortisol, and testosterone thus have powerful combined effects, resulting in insulin resistance and increased hepatic gluconeogenesis. All these factors promoting insulin resistance are active in abdominal visceral obesity, which is closely associated with insulin resistance, NIDDM, and the "metabolic syndrome." In addition, the endocrine aberrations may provide a cause for visceral fat accumulation, probably due to regional differences in steroid-hormone-receptor density. In addition to the increased activity along the adrenocorticosteroid axis, there also seem to be signs of increased activity from the central sympathetic nervous system. These are the established endocrine consequences of hypothalamic arousal in the defeat and defense reactions. There is some evidence that suggests an increased prevalence of psychosocial stress factors is associated with visceral distribution of body fat. Therefore, it is hypothesized that such factors might provide a background not only to a defense reaction and primary hypertension, suggested previously, but also to a defeat reaction, which contributes to an endocrine aberration leading to metabolic aberrations and visceral fat accumulation, which in turn leads to disease.
Objective: A large population of F2 rats, obtained from a cross between male Lyon hypertensive (LH) rats and female Lyon normotensive (LN) rats, was studied in order to assess the relationship between increased body weight, hyperlipidaemia and high blood pressure which characterize LH rats.
Methods: Mean arterial pressure (MAP) was recorded in male, conscious, freely moving LH, LN, F1 and F2 rats aged 30 weeks. Plasma total cholesterol, high-density lipoprotein-, low-density lipoprotein- and very low-density lipoprotein-cholesterol, phospholipids, triglycerides, insulin and glucose were measured.
Results: In the F2 cohort it was observed that high MAP was a recessive trait that depends on several genes and was unrelated to body weight. The left ventricular weight, corrected for tibia length, was correlated with MAP. Plasma total and high-density lipoprotein-cholesterol and phospholipids concentrations were lower in the F1 rats than in the LN rats, suggesting an overdominance of the LN alleles. In the F2 rats MAP was related to total, high-density lipoprotein- and low-density lipoprotein-cholesterol. Plasma triglycerides, insulin and the insulin: glucose ratio, which were higher in the LH rats than in the LN rats, were also correlated with MAP in the F2 cohort. Using stepwise multiple regression analysis, MAP remained correlated with plasma total cholesterol, insulin and the insulin: glucose ratio, but not with triglycerides.
Conclusions: Hypertension in LH rats is a recessive trait that is independent of body weight. In addition, the cosegregation of blood pressure with plasma cholesterol and, to a lesser degree, with insulin levels, which was observed in the present study provides the first direct evidence that these phenotypes are associated and are not due simply to genetic drift in the Lyon model.
(C) Lippincott-Raven Publishers.
To estimate the prevalence of and the cardiovascular risk associated with the metabolic syndrome using the new definition proposed by the World Health Organization
A total of 4,483 subjects aged 35-70 years participating in a large family study of type 2 diabetes in Finland and Sweden (the Botnia study) were included in the analysis of cardiovascular risk associated with the metabolic syndrome. In subjects who had type 2 diabetes (n = 1,697), impaired fasting glucose (IFG)/impaired glucose tolerance (IGT) (n = 798) or insulin-resistance with normal glucose tolerance (NGT) (n = 1,988), the metabolic syndrome was defined as presence of at least two of the following risk factors: obesity, hypertension, dyslipidemia, or microalbuminuria. Cardiovascular mortality was assessed in 3,606 subjects with a median follow-up of 6.9 years.
In women and men, respectively, the metabolic syndrome was seen in 10 and 15% of subjects with NGT, 42 and 64% of those with IFG/IGT, and 78 and 84% of those with type 2 diabetes. The risk for coronary heart disease and stroke was increased threefold in subjects with the syndrome (P < 0.001). Cardiovascular mortality was markedly increased in subjects with the metabolic syndrome (12.0 vs. 2.2%, P < 0.001). Of the individual components of the metabolic syndrome, microalbuminuria conferred the strongest risk of cardiovascular death (RR 2.80; P = 0.002).
The WHO definition of the metabolic syndrome identifies subjects with increased cardiovascular morbidity and mortality and offers a tool for comparison of results from diferent studies.
Many studies have shown that hyperinsulinemia and/or insulin resistance are related to various metabolic and physiological disorders including hypertension, dyslipidemia, and non-insulin-dependent diabetes mellitus. This syndrome has been termed Syndrome X. An important limitation of previous studies has been that they all have been cross sectional, and thus the presence of insulin resistance could be a consequence of the underlying metabolic disorders rather than its cause. We examined the relationship of fasting insulin concentration (as an indicator of insulin resistance) to the incidence of multiple metabolic abnormalities in the 8-yr follow-up of the cohort enrolled in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease in Mexican Americans and non-Hispanic whites. In univariate analyses, fasting insulin was related to the incidence of the following conditions: hypertension, decreased high-density lipoprotein cholesterol concentration, increased triglyceride concentration, and non-insulin-dependent diabetes mellitus. Hyperinsulinemia was not related to increased low-density lipoprotein or total cholesterol concentration. In multivariate analyses, after adjustment for obesity and body fat distribution, fasting insulin continued to be significantly related to the incidence of decreased high-density lipoprotein cholesterol and increased triglyceride concentrations and to the incidence of non-insulin-dependent diabetes mellitus. Baseline insulin concentrations were higher in subjects who subsequently developed multiple metabolic disorders. These results were not attributable to differences in baseline obesity and were similar in Mexican Americans and non-Hispanic whites. These results support the existence of a metabolic syndrome and the relationship of that syndrome to multiple metabolic disorders by showing that elevations of insulin concentration precede the development of numerous metabolic disorders.
A high salt diet produced increases in SBP, urinary protein excretion (UPE) and renal vascular lesions (RVL) across groups of male and female SHR rats which were allowed to develop moderate or excessive increases in SBP. A highly significant linear relationship between SBP and log-transformed UPE was found when the data from all groups were analyzed together. Males developed high blood-pressure more rapidly, and exhibited more severe RVL and greater UPE than females. Two results prevent the conclusion that the elevated UPE was simply due to the adverse effects of high BP on the kidney. First, the relationship between SBP and UPE across groups could not be demonstrated when regression analyses were performed within individual dietary sub-groups. Secondly, gender differences in UPE were highly significant by analysis of covariance adjusting for individual differences in SBP. The increases in SBP and UPE may be independent consequences of ingestion of a high salt diet.
Patients with hypertension have been shown to be resistant to insulin-stimulated glucose uptake and hyperinsulinemic when compared to matched control groups with normal blood pressure. In addition, insulin resistance and hyperinsulinemia have been demonstrated in rat models of hypertension-including SHR rats and Sprague-Dawley rats fed a fructose-enriched diet. Furthermore, fructose-induced hypertension can be attenuated by experimental interventions which decrease insulin resistance and/or hyperinsulinemia. These observations raise the possibility that insulin resistance and hyperinsulinemia may play a role in blood pressure regulation. Finally, insulin resistance and hyperinsulinemia increase risk of coronary artery decrease in patients with hypertension, both directly, and indirectly by their influence on very low density and high density lipoprotein metabolism.
We report the construction of the first complete genetic linkage map of the laboratory rat. By testing 1171 simple sequence length polymorphisms (SSLPs), we have identified 432 markers that show polymorphisms between the SHR and BN rat strains and mapped them in a single (SHR x BN) F2 intercross. The loci define 21 large linkage groups corresponding to the 21 rat chromosomes, together with a pair of nearby markers on chromosome 9 that are not linked to the rest of the map. Because 99.5% of the markers fall into one of the 21 large linkage groups, the maps appear to cover the vast majority of the rat genome. The availability of the map should facilitate whole genome scans for genes underlying qualitative and quantitative traits relevant to mammalian physiology and pathobiology.
Insulin resistance is part of a metabolic syndrome that also includes non-insulin-dependent diabetes mellitus, dyslipidemia, obesity, and hypertension. It has been hypothesized that insulin resistance represents the primary physiological defect underlying this syndrome. Since insulin resistance is at least partially genetically determined, we hypothesized that genes influencing insulin resistance would have pleiotropic effects on a number of other traits, including triglyceride (TG) and HDL cholesterol levels, body mass index (BMI) and body fat distribution, and blood pressure levels. To investigate this hypothesis, we analyzed data obtained from individuals in 41 families enrolled in the San Antonio Family Heart Study. Statistical methods that take advantage of the relatedness among individuals were used to differentiate between genetic and nongenetic (ie, environmental) contributions to phenotypic variation between traits. Serum levels of fasting and 2-hour insulin (measured in 767 and 743 nondiabetic family members, respectively) were used as a measure of insulin resistance. The genetic correlations were high between insulin levels (both fasting and 2-hour) and each of the following: BMI, HDL level, waist-to-hip ratio, and subscapular-to-triceps ratio, indicating that the same gene, or set of genes, influences each pair of traits. In contrast, the genetic correlations of insulin levels with systolic and diastolic blood pressures were low. We have previously shown that a single diallelic locus accounts for 31% of the phenotypic variation in 2-hour insulin levels in this population. We conducted a bivariate segregation analysis to see if the common genetic effects on insulin and these other traits could be attributable to this single locus. These results indicated a significant effect of the 2-hour insulin locus on fasting insulin levels (P = .02) and BMI (P = .05), with the "high" insulin allele associated with higher levels of fasting insulin but lower levels of BMI. There was no detectable effect of this locus on HDL level, TG level, subscapular-to-triceps ratio, or blood pressure. Overall, these results suggest that a common set of genes influencing insulin levels also influences other insulin resistance syndrome-related traits, although for the most part this pleiotropy is not attributable to the 2-hour insulin level major locus.
To investigate the association of blood pressure with the other major cardiovascular risk factors in a large population of back-cross to Lyon hypertensive (LH) rats.
Mean arterial pressure was recorded in male freely moving Lyon normotensive (LN), LH, F1 and backcross to LH rats aged 30 weeks. Plasma cholesterol, triglycerides, insulin, creatinine, urea, fibrinogen and haematocrit levels, and the insulin: glucose ratio were measured in 31-week-old rats and 24h albuminuria in 6-week-old rats.
Adult LH rats exhibited a significant increase in plasma lipids, insulin, fibrinogen, creatinine, urea and haematocrit levels compared with LN rats. In young LH rats, at an age at which blood pressure is slightly increased, albuminuria was increased to a greater extent than expected from their blood pressure levels. In the adult back-cross to LH rats, only the plasma cholesterol level was associated with blood pressure. Moreover, the plasma cholesterol level was related to fibrinogen and haematocrit levels. Finally, in the same rats, albuminuria developed early in life was positively related to hypercholinesterolaemia measured later in life.
Plasma cholesterol, fibrinogen, haematocrit levels and early albuminuria could act synergistically in the enhancement or the development, or both, of vascular and kidney damage in the LH rat. Most interestingly, the association between plasma cholesterol level and blood pressure indicates that, as in essential hypertension, hypercholesterolaemia is a major phenotype associated with hypertension in the LH rat.
The contribution of genetic and environmental effects to the clustering of metabolic factors contained in insulin-resistance syndrome (IRS) is still unclear. To explore the genetic architecture of IRS, we examined a population of elderly twins from the Swedish Adoption/Twin Study of Aging. A sample of 289 pairs of twins (mean age 65.5 years; range 52-86 years), of whom 140 pairs had been reared apart, was studied. The features contained in the IRS consisted of body-mass index (BMI), insulin resistance, triglycerides, HDL cholesterol, and systolic blood pressure. Intraclass correlations, cross-twin correlations, and model-fitting analyses were used to evaluate the relative importance of genetic and environmental influences for variation in and covariation among the components of the syndrome. All of the five principal metabolic components contained in IRS are more or less influenced by a single latent genetic factor, whereas only three of the components (triglycerides, insulin resistance, and HDL cholesterol) are influenced by a latent individual-specific environmental factor. The genetic factor reflected influences of importance to BMI and insulin resistance and to a lesser degree to triglycerides, HDL cholesterol, and systolic blood pressure, whereas the individual-specific environmental factor reflected influences in common to triglycerides and HDL cholesterol and to a lesser degree to insulin resistance. Systolic blood pressure was related to IRS, albeit weakly, only through genetic effects. In conclusion, IRS appears to be influenced by different sets of genetic and environmental mechanisms. The set of genetic influences in common to all the components may initiate the abnormalities underlying IRS.
Genetically hypertensive rats (LH) of the Lyon strain, compared to their normo-tensive (LN) controls associate, in a unique manner, high blood pressure with increases in body weight and in plasma lipids and insulin/glucose ratio. The present work investigated the development of insulin resistance with age in this model. At the age of 22 and 52 weeks, LH and LN fasted male rats were submitted to an intravenous glucose tolerance test, allowing measurement of the elimination rate of the glucose and the area under the curve of the insulin response. Insulin sensitivity was calculated as the ratio of these two parameters. It was observed that insulin sensitivity coefficient decreased with age in all the animals and that LH rats did not significantly differ from LN controls (from 62.6 +/- 3.3 and 69.1 +/- 4 at 22 weeks to 42.1 +/- 4.4 and 49.5 +/- 12.8 at 52 weeks for LH and LN rats, respectively). It is concluded that 1) elevated plasma insulin/glucose ratio does not mean insulin resistance and 2) hypertension can develop without being associated, even in aged rats, to a true insulin resistance.
The assimilation, storage and use of energy from nutrients constitute a homeostatic system that is essential for life. In vertebrates, the ability to store sufficient quantities of energy-dense triglyceride in adipose tissue allows survival during the frequent periods of food deprivation encountered during evolution. However, the presence of excess adipose tissue can be maladaptive. A complex physiological system has evolved to regulate fuel stores and energy balance at an optimum level. Leptin, a hormone secreted by adipose tissue, and its receptor are integral components of this system. Leptin also signals nutritional status to several other physiological systems and modulates their function. Here we review the role of leptin in the control of body weight and its relevance to the pathogenesis of obesity.
We carried out a total genome screen in the Sabra rat model of hypertension to detect salt-susceptibility genes. We previously reported in male animals the presence of 2 major quantitative trait loci (QTLs) on chromosome 1 that together accounted for most of the difference in the blood pressure (BP) response to salt loading between Sabra hypertension-prone rats (SBH/y) and Sabra hypertension-resistant rats (SBN/y). In females, we reported on 2 major QTLs on chromosomes 1 and 17 that together accounted for only two thirds of the difference in the BP response between the strains. On the basis of phenotypic patterns of inheritance in reciprocal F2 crosses, we proposed a role of the X chromosome. We therefore continued the search for the missing QTL in females that would account for the remaining difference in the BP response between the 2 strains using newly developed microsatellite markers and focusing on chromosome X. We screened an F2 cross, consisting of 371 females and 336 males, using 19 polymorphic chromosome X microsatellite markers. We analyzed the averages of BP by genotype using ANOVA and the individual data using MAPMAKER/QTL. In female F2 progeny, we identified a segment on chromosome X that spans over 33.4 cM and shows significant cosegregation (P<0.001) of 14 microsatellite markers (demarcated by DXRat4 and DXMgh10) with systolic BP after salt loading. This segment has 2 apparent peaks at DXRat4 and DXRat13, with a BP effect of 14 mm Hg for each. Multipoint linkage analysis with a free model detected 3 peaks (logarithm of the odds ratio [LOD] score >4.3) within the same chromosomal segment: One between DXMgh9 and DXMit4 (LOD 4.9; 6.1% of variance), a second between DXMgh12 and DXRat8 (LOD 5.2; 7.2% of variance), and a third between DXRat2 and DXRat4 (LOD 5.8; 7.5% of variance). On the basis of these findings and until congenic strains become available, our working assumption is that within chromosome X, 1 to 3 genetic loci contribute importantly to the BP response of female Sabra rats to salt. In male F2 progeny, we detected no significant cosegregation of any region on chromosome X with the BP response to salt loading. We conclude that in the female rat, salt susceptibility is mediated by 3 to 5 gene loci on chromosomes 1, 17, and X, whereas in the male rat, the X chromosome does not affect the BP response to salt.
Genetic markers throughout the genome can be used to speed up 'recovery' of the recipient genome in the backcrossing phase of the construction of a congenic strain. The prediction of the genomic proportion during backcrossing depends on the assumptions regarding the distribution of chromosome segments, the population structure, the marker spacing and the selection strategy. In this study simulation was used to investigate the rate of recovery of the recipient genome for a mouse, Drosophila and Arabidopsis genome. It was shown that an incorrect assumption of a binomial distribution of chromosome segments, and failing to take account of a reduction in variance in genomic proportion due to selection, can lead to a downward bias of up to two generations in the estimation of the number of generations required for the formation of a congenic strain.
Many valuable animal models of human disease are known and new models are continually being generated in existing inbred strains,. Some disease models are simple mendelian traits, but most have a polygenic basis. The current approach to identifying quantitative trait loci (QTLs) that underlie such traits is to localize them in crosses, construct congenic strains carrying individual QTLs, and finally map and clone the genes. This process is time-consuming and expensive, requiring the genotyping of large crosses and many generations of breeding. Here we describe a different approach in which a panel of chromosome substitution strains (CSSs) is used for QTL mapping. Each of these strains has a single chromosome from the donor strain substituting for the corresponding chromosome in the host strain. We discuss the construction, applications and advantages of CSSs compared with conventional crosses for detecting and analysing QTLs, including those that have weak phenotypic effects.
Genetically hypertensive (LH) rats of the Lyon strain exhibit a blunted pressure-natriuresis function when compared, in acute conditions, with their normotensive (LN) and low blood pressure (LL) controls. The present work was aimed to determine whether LH rats were salt sensitive in chronic conditions. In addition, a protocol was developed to determine the renal function curve in freely moving rats.
Fourteen-week-old rats either untreated or orally treated since weaning with perindopril (3 mg/kg/24 h), an angiotensin-converting enzyme inhibitor, or with valsartan (15 mg/kg/24 h), an angiotensin II subtype 1 receptor antagonist, so as to eliminate the influence of endogenous changes in angiotensin formation were used. Blood pressure (BP) and urinary sodium excretion were measured before, during an oral salt load (2% NaCl in drinking water), and during a two-week aldosterone infusion (50 microg/kg/24 h subcutaneously).
NaCl induced a greater BP increase in untreated LH rats than in LN and LL controls. Perindopril normalized the BP of LH rats but not its elevation during a salt load. Aldosterone slightly increased BP in LH and LL rats either untreated or treated with valsartan. Finally, the combination of telemetric BP measurement with 24-hour urine collection when salt was added to drinking water allowed accurate determination of the slope of the chronic renal function curve in freely moving rats.
The present work demonstrates that LH rats are salt sensitive. This characteristic manifests despite the lack of an active renin-angiotensin system and is not explained by a hypersensitivity to aldosterone.
The present work studied renal medullary blood flow (MBF) and its response to salt load in Lyon hypertensive (LH) rats to
understand the mechanisms underlying the abnormal renal sodium excretion exhibited by LH rats. Experiments were conducted
in uninephrectomized, anesthetized, and volume-expanded 15-week-old male LH and their normotensive (LL) controls. Under standard
diet, LH rats exhibited a blunted pressure diuresis and natriuresis associated with an absence of pressure-induced increase
in MBF compared to LL rats. One week of salt load (2% NaCl as drinking water) induced a significant increase in blood pressure
(BP) in LH (+11 mm Hg) than in LL (+6 mm Hg) rats associated with a decrease in MBF in LH rats only (from 182 ± 25 to 122
± 20 perfusion units, P < .001). Finally, despite the salt load-induced increase in pressure natriuresis, it remained significantly lower in LH than
in LL rats. The results show an alteration in MBF regulation in LH rats and suggest that this abnormality may be involved
in their blunted pressure natriuresis and their enhanced salt sensitivity. Am J Hypertens 2002;15:212–216 © 2002 American
Journal of Hypertension, Ltd.
A consomic rat strain is one in which an entire chromosome is introgressed into the isogenic background of another inbred strain using marker assisted selection. The development and initial physiologic screening of two inbred consomic rat panels on two genetic backgrounds (44 strains) is well underway. The primary uses of consomic strains are: (1) to assign traits and quantitative trait loci (QTL) to chromosomes by surveying the panel of strains with substituted chromosomes; (2) to rapidly develop congenic strains over a narrow region using several approaches described in this review and perform F2 linkage studies to positionally locate QTL in a fixed genetic background. In addition, consomic strains overcome many of the problems encountered with segregating crosses where, even if linkage is found, each individual in the cross is genetically unique and the combination of genes cannot be reproduced or studied in detail. Consomic strains provide greater statistical power to detect linkage than traditional F2 crosses because of their fixed genetic backgrounds, and can produce sufficient numbers of genetically identical rats to validate the relationship between a trait and a particular chromosome. These strains allow studies to be performed in a replicative or longitudinal manner to elucidate in greater detail the sequential changes responsible for the observed phenotypes of these animals, and they enable one to assess the impact of a causal gene region in a genome by allowing comparisons of the effect of replacement of a specific chromosome upon a disease susceptible or resistant genomic background. Consomics can be used to quickly develop multiple chromosome substitution models to investigate gene-gene interactions of complex traits or diseases. Finally, they often provide the best available inbred control strain for particular physiological comparisons with the inbred parental strains. Consomic rat strains are proving to be a unique scientific resource that greatly extends our understanding of genes and complex normal and pathological function.
The National Cholesterol Education Program’s Adult Treatment Panel III report (ATP III)1 identified the metabolic syndrome as a multiplex risk factor for cardiovascular disease (CVD) that is deserving of more clinical attention. The cardiovascular community has responded with heightened awareness and interest. ATP III criteria for metabolic syndrome differ somewhat from those of other organizations. Consequently, the National Heart, Lung, and Blood Institute, in collaboration with the American Heart Association, convened a conference to examine scientific issues related to definition of the metabolic syndrome. The scientific evidence related to definition was reviewed and considered from several perspectives: (1) major clinical outcomes, (2) metabolic components, (3) pathogenesis, (4) clinical criteria for diagnosis, (5) risk for clinical outcomes, and (6) therapeutic interventions.
ATP III viewed CVD as the primary clinical outcome of metabolic syndrome. Most individuals who develop CVD have multiple risk factors. In 1988, Reaven2 noted that several risk factors (eg, dyslipidemia, hypertension, hyperglycemia) commonly cluster together. This clustering he called Syndrome X , and he recognized it as a multiplex risk factor for CVD. Reaven and subsequently others postulated that insulin resistance underlies Syndrome X (hence the commonly used term insulin resistance syndrome ). Other researchers use the term metabolic syndrome for this clustering of metabolic risk factors. ATP III used this alternative term. It avoids the implication that insulin resistance is the primary or only cause of associated risk factors. Although ATP III identified CVD as the primary clinical outcome of the metabolic syndrome, most people with this syndrome have insulin resistance, which confers increased risk for type 2 diabetes. When diabetes becomes clinically apparent, CVD risk rises sharply. Beyond CVD and type 2 diabetes, individuals with metabolic syndrome seemingly are susceptible to other conditions, notably polycystic ovary syndrome, fatty liver, cholesterol gallstones, asthma, sleep disturbances, and some …
The need to translate genes to function has positioned the rat as an invaluable animal model for genomic research. The significant increase in genomic resources in recent years has had an immediate functional application in the rat. Many of the resources for translational research are already in place and are ready to be combined with the years of physiological knowledge accumulated in numerous rat models, which is the subject of this perspective. Based on the successes to date and the research projects under way to further enhance the infrastructure of the rat, we also project where research in the rat will be in the near future. The impact of the rat genome project has just started, but it is an exciting time with tremendous progress.
The postgenome era has provided resources to link disease phenotypes to the genomic sequence, i.e., creating a disease "phenome." Our detailed characterization of the sequenced BN rat strain (BN/NHsdMcwi) provides the first concerted effort in creating a direct link between a sequenced genome and its resulting biology. For the BN sequence to be of broad value to investigators, these measures need to be put into the context of the spectrum of the laboratory rats, so that their physiology can be benchmarked against the sequenced BN. As a major step in generating a comprehensive cardiovascular and pulmonary disease phenome, we measured 281 traits related to diseases of the heart, lung, and blood (http://pga.mcw.edu) in the sequenced BN. We compared these data with those of the same traits measured across multiple genetic backgrounds, both genders, and differing environments. We show that no single strain, inbred or outbred, can be considered a physiological control strain; what is normal depends on what trait is being measured and the strains' genome backgrounds. We find vast differences between the genders, also dependent on genome background. By combining the values across all strains studied, we generated a "population" mean and normal range of values for each of these traits, which are more genetically representative than the measured values in any single inbred or outbred strain. These data provide a baseline for physiological comparison of traits related to cardiovascular, lung, blood, and renal function in the sequenced BN rats relative to the major strains of rats studied in biomedical research.
To assess whether an association between sodium-sensitive hypertension and metabolic syndrome exists; and whether, in patients with metabolic syndrome, the nocturnal fall of blood pressure decreases and salt restriction affects the circadian blood pressure rhythm.
Japanese patients with essential hypertension, who were treated without any antihypertensive agent, were maintained on a high-sodium diet and a low-sodium diet for 1 week each. On the last day of each diet, the 24-h blood pressures were measured. A diagnosis of metabolic syndrome was made according to the International Diabetes Foundation definition
Among the 56 patients with essential hypertension, 15 patients were complicated with metabolic syndrome while 41 patients were not. The nocturnal blood pressure fall was significant in patients without metabolic syndrome, while it was not so in patients with metabolic syndrome. Only in patients with metabolic syndrome was the nocturnal blood pressure fall enhanced by sodium restriction. The prevalence of sodium-sensitive hypertension in patients with metabolic syndrome was significantly higher than in those without metabolic syndrome (70.6 versus 36.0%, respectively; P = 0.017). A multiple logistic regression analysis revealed central obesity to be an independent risk factor for sodium-sensitive hypertension (odds ratio, 1.41; 95% confidence interval, 1.04-1.91).
In patients with essential hypertension, an inter-relationship exists among metabolic syndrome, enhanced sodium sensitivity of the blood pressure and non-dipping. The elevated risk of cardiovascular diseases in patients with metabolic syndrome may be related to sodium-sensitive hypertension and non-dipping.
Leptin and the regulation of body weight in mammals
- J Friedman
Friedman J, Halaas J. Leptin and the regulation of body weight in
mammals. Nature 396: 763–770, 1998.
Analysing complex genetic traits with chromosome substitution strains Genome sequence of the Brown Norway rat yields insights into mammalian evolution
- J Nadeau
- J Singer
- A Matin
- E Lander
Nadeau J, Singer J, Matin A, Lander E. Analysing complex genetic
traits with chromosome substitution strains. Nat Genet 24: 221–225, 2000.
23a.Rat Genome Sequencing Project Consortium. Genome sequence of the
Brown Norway rat yields insights into mammalian evolution. Nature 428:
493–521, 2004.