Y-chromosome transfer induces changes in blood pressure and blood lipids in SHR

Sex-dependent associations of plasma high-density lipoprotein cholesterol and mortality risk in healthy older men and women: two prospective cohort studies

The relationship between high plasma high-density lipoprotein cholesterol (HDL-C) and cause and mortality are not well established in healthy older people. This study examined the associations between HDL-C levels and mortality in initially healthy older men and women. This analysis included participants from the Aspirin in Reducing Events in the Elderly (ASPREE; n=18,668) trial and a matched cohort from the UK Biobank (UKB; n=62,849 ≥65 years). Cox regression was used to examine hazard ratios between HDL-C categories <1.03 mmol/L, 1.03-1.55 mmol/L (referent category), 1.55-2.07 mmol/L, and >2.07 mmol/L and all-cause, cancer, cardiovascular disease (CVD), and "non-cancer non-CVD" mortality. Genetic contributions were assessed using a polygenic score for HDL-C. Among ASPREE participants (aged 75±5 years), 1836 deaths occurred over a mean follow-up of 6.3±1.8 years. In men, the highest category of HDL-C levels was associated with increased risk of all-cause (HR 1.60, 95% CI 1.26-2.03), cancer (HR 1.37, 95% CI 0.96-2.00), and "non-cancer non-CVD" mortality (HR 2.35, 95% CI 1.41-3.42) but not CVD mortality (HR 1.08, 95% CI 0.60-1.94). The associations were replicated among UKB participants (aged 66.9±1.5 years), including 8739 deaths over a mean follow-up of 12.7±0.8 years. There was a non-linear association between HDL-C levels and all-cause and cause-specific mortality. The association between HDL-C levels and mortality was unrelated to variations in the HDL-C polygenic score. No significant association was found between HDL-C levels and mortality in women. Higher HDL-C levels are associated with increased risk from cancer and "non-cancer non-CVD" mortality in healthy older men but no such relationship was observed in women.

Sex-limited chromosomes and non-reproductive traits

Sex chromosomes are typically viewed as having originated from a pair of autosomes, and differentiated as the sex-limited chromosome (e.g. Y) has degenerated by losing most genes through cessation of recombination. While often thought that degenerated sex-limited chromosomes primarily affect traits involved in sex determination and sex cell production, accumulating evidence suggests they also influence traits not sex-limited or directly involved in reproduction. Here, we provide an overview of the effects of sex-limited chromosomes on non-reproductive traits in XY, ZW or UV sex determination systems, and discuss evolutionary processes maintaining variation at sex-limited chromosomes and molecular mechanisms affecting non-reproductive traits.

Sex differences in the intestinal microbiome: interactions with risk factors for atherosclerosis and cardiovascular disease

Background

There are clearly sex differences in cardiovascular disease. On average, women experience cardiovascular events at an older age, and at any age, women, on average, have less atherosclerotic plaque than men. The role of the human intestinal microbiome in health and disease has garnered significant interest in recent years, and there have been indications of sex differences in the intestinal microbiome. The purpose of this narrative review was to evaluate evidence of sex differences in the interaction between the intestinal microbiome and risk factors for cardiovascular disease. Several studies have demonstrated changes in microbiota composition and metabolic profile as a function of diet, sex hormones, and host metabolism, among other factors. This dysbiosis has consequently been associated with several disease states, including atherosclerosis and cardiovascular disease. In this respect, there is a growing appreciation for the microbiota and its secreted metabolites, including trimethylamine N-oxide (TMAO), derived from intestinal bacterial metabolic pathways involving dietary choline and l-carnitine, as novel risk factors for atherosclerosis and cardiovascular outcomes. Although traditional risk factors for vascular disease have been studied broadly over the years, there exists little research to evaluate interactions of cardiovascular risk factors with a potentially sexually dimorphic intestinal microbiome. This review evaluates the role of sex differences in the composition of the intestinal microbiome, including effects of sex hormones on the microbiome, and the effects of these sex differences on cardiovascular risk factors. Diabetes and obesity exhibit sexual dimorphism, while the data concerning hypertension and dyslipidemia remain inconclusive based on the available literature. In addition, an increased proportion of gram-negative species capable of driving metabolic endotoxemia and a low-grade inflammatory response, as well as decreased numbers of butyrate-producing species, have been observed in relation to traditional vascular risk factors. In this context, circulating SCFAs and TMAO are recognized as key metabolites of the intestinal microbiome that can be readily measured in the blood for the evaluation of metabolic profile.

Conclusion

Novel strategies focused on resolving intestinal dysbiosis as a means to slow progression of atherosclerosis and reduce the risk of cardiovascular disease should be evaluated through a lens of sex differences.

The Y Chromosome: A Complex Locus for Genetic Analyses of Complex Human Traits

The Human Y chromosome (ChrY) has been demonstrated to be a powerful tool for phylogenetics, population genetics, genetic genealogy and forensics. However, the importance of ChrY genetic variation in relation to human complex traits is less clear. In this review, we summarise existing evidence about the inherent complexities of ChrY variation and their use in association studies of human complex traits. We present and discuss the specific particularities of ChrY genetic variation, including Y chromosomal haplogroups, that need to be considered in the design and interpretation of genetic epidemiological studies involving ChrY.

Rat Genome Assemblies, Annotation, and Variant Repository

The first and only published version of the rat reference genome sequence was RGSC3.1, accomplished by the Rat Genome Sequencing Project Consortium. Here we present the history of the community effort in the correction of sequence errors and filling missing gaps in the process of refining and providing researchers with a high-quality rat reference sequence. The genome assembly improvements, addition of different evidence resources over time, such as RNA-Seq data, and software development methodologies had a positive impact on the gene model annotations. Over the years we observed a great increase in the numbers of genes, protein coding sequences, predicted transcripts and transcript features. Before the sequencing of the rat genome was possible, first biochemical and next genomic markers like RAPD, AFLP, RFLP, and SSLP were fundamental in research studies involving cross-breeding between different rat strains, in finding the level of polymorphism, linkage mapping, and phylogeny. Linkage maps provide information on recombination rates, give insight into intra- and interspecies gene rearrangements, and help to identify Mendelian loci and Quantitative Trait Loci (QTL). In the 1990s many reports were published on the construction of rat linkage maps that incorporated increasing numbers of markers and facilitated the localization of disease loci. Current genetic monitoring and linkage mapping relies on single nucleotide polymorphisms (SNPs). The Rat Genome Database collects information on genetic variation from the worldwide community of rat researchers and provides tools for searching and retrieving these data. As of today we show details about almost 605 million variants coming from many studies in our Variant Visualizer tool.

Sexual dimorphism of cardiometabolic dysfunction: Gut microbiome in the play?

BACKGROUND

Sex is one of the most powerful modifiers of disease development. Clear sexual dimorphism exists in cardiometabolic health susceptibility, likely due to differences in sex steroid hormones. Changes in the gut microbiome have been linked with the development of obesity, type 2 diabetes, and atherosclerosis; however, the impact of microbes in sex-biased cardiometabolic disorders remains unclear. The gut microbiome is critical for maintaining a normal estrous cycle, testosterone levels, and reproductive function. Gut microbes modulate the enterohepatic recirculation of estrogens and androgens, affecting local and systemic levels of sex steroid hormones. Gut bacteria can also generate androgens from glucocorticoids.

SCOPE OF REVIEW

This review summarizes current knowledge of the complex interplay between sexual dimorphism in cardiometabolic disease and the gut microbiome.

MAJOR CONCLUSIONS

Emerging evidence suggests the role of gut microbiome as a modifier of disease susceptibility due to sex; however, the impact on cardiometabolic disease in this complex interplay is lacking. Elucidating the role of gut microbiome on sex-biased susceptibility in cardiometabolic disease is of high relevance to public health given its high prevalence and significant financial burden.

Towards Precision Medicine for Hypertension: A Review of Genomic, Epigenomic, and Microbiomic Effects on Blood Pressure in Experimental Rat Models and Humans

Compelling evidence for the inherited nature of essential hypertension has led to extensive research in rats and humans. Rats have served as the primary model for research on the genetics of hypertension resulting in identification of genomic regions that are causally associated with hypertension. In more recent times, genome-wide studies in humans have also begun to improve our understanding of the inheritance of polygenic forms of hypertension. Based on the chronological progression of research into the genetics of hypertension as the "structural backbone," this review catalogs and discusses the rat and human genetic elements mapped and implicated in blood pressure regulation. Furthermore, the knowledge gained from these genetic studies that provide evidence to suggest that much of the genetic influence on hypertension residing within noncoding elements of our DNA and operating through pervasive epistasis or gene-gene interactions is highlighted. Lastly, perspectives on current thinking that the more complex "triad" of the genome, epigenome, and the microbiome operating to influence the inheritance of hypertension, is documented. Overall, the collective knowledge gained from rats and humans is disappointing in the sense that major hypertension-causing genes as targets for clinical management of essential hypertension may not be a clinical reality. On the other hand, the realization that the polygenic nature of hypertension prevents any single locus from being a relevant clinical target for all humans directs future studies on the genetics of hypertension towards an individualized genomic approach.

Genetics of hypertension: an assessment of progress in the spontaneously hypertensive rat

The application of gene mapping methods to uncover the genetic basis of hypertension in the inbred spontaneously hypertensive rat (SHR) began over 25 yr ago. This animal provides a useful model of genetic high blood pressure, and some of its features are described. In particular, it appears to be a polygenic model of disease, and polygenes participate in human hypertension genetic risk. The SHR hypertension alleles were fixed rapidly by selective breeding in just a few generations and so are presumably common genetic variants present in the outbred Wistar strain from which SHR was created. This review provides a background to the origins and genesis of this rat line. It considers its usefulness as a model organism for a common cardiovascular disease. The progress and obstacles facing mapping are considered in depth, as are the emergence and application of other genome-wide genetic discovery approaches that have been applied to investigate this model. Candidate genes, their identification, and the evidence to support their potential role in blood pressure elevation are considered. The review assesses the progress that has arisen from this work has been limited. Consideration is given to some of the factors that have impeded progress, and prospects for advancing understanding of the genetic basis of hypertension in this model are discussed.

The Y chromosome: a blueprint for men's health?

The Y chromosome has long been considered a 'genetic wasteland' on a trajectory to completely disappear from the human genome. The perception of its physiological function was restricted to sex determination and spermatogenesis. These views have been challenged in recent times with the identification of multiple ubiquitously expressed Y-chromosome genes and the discovery of several unexpected associations between the Y chromosome, immune system and complex polygenic traits. The collected evidence suggests that the Y chromosome influences immune and inflammatory responses in men, translating into genetically programmed susceptibility to diseases with a strong immune component. Phylogenetic studies reveal that carriers of a common European lineage of the Y chromosome (haplogroup I) possess increased risk of coronary artery disease. This occurs amidst upregulation of inflammation and suppression of adaptive immunity in this Y lineage, as well as inferior outcomes in human immunodeficiency virus infection. From structural analysis and experimental data, the UTY (Ubiquitously Transcribed Tetratricopeptide Repeat Containing, Y-Linked) gene is emerging as a promising candidate underlying the associations between Y-chromosome variants and the immunity-driven susceptibility to complex disease. This review synthesises the recent structural, experimental and clinical insights into the human Y chromosome in the context of men's susceptibility to disease (with a particular emphasis on cardiovascular disease) and provides an overview of the paradigm shift in the perception of the Y chromosome.

The phenotypic impact of the male-specific region of chromosome-Y in inbred mating: the role of genetic variants and gene duplications in multiple inbred rat strains

Backgound

The male-specific region of chromosome-Y (MSY) contributes to phenotypes outside of testis development and has a high rate of evolution between mammalian species. With a lack of genomic crossover, MSY is one of the few genomic areas under similar variation and evolutionary selection in inbred and outbred animal populations, allowing for an assessment of evolutionary mechanisms to translate between the populations.

Methods

Using next-generation sequencing, MSY consomic strains, molecular characterization, and large-scale phenotyping, we present here regions of MSY that contribute to inbred strain phenotypes.

Results

We have shown that (1) MSY of rat has nine autosomal gene transposition events with strain-specific selection; (2) sequence variants in MSY occur with a 1.98-fold higher number of variants than other chromosomes in seven sequenced rat strains; (3) Sry, the most studied MSY gene, has undergone extensive gene duplications, driving ubiquitous expression not seen in human or mouse; (4) the expression profile of Sry in the rat is driven by the insertion of the Sry2 copy into an intron of the ubiquitously expressed Kdm5d gene in antisense orientation, but due to several loss of function mutations in the Sry2 protein, nuclear localization and transcriptional control are decreased; (5) expression of Sry copies other than Sry2 in the rat overlaps with the expression profile for human SRY; (6) gene duplications and sequence variants (P76T) of Sry can be selected for phenotypes such as high blood pressure and androgen receptor signaling within inbred mating; and most importantly, (7) per chromosome size, MSY contributes to higher strain-specific phenotypic variation relative to all other chromosomes, with 53 phenotypes showing both a male to female and consomic cross significance.

Conclusion

The data presented supports a high probability of MSY genetic variation altering a broad range of inbred rat phenotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0064-z) contains supplementary material, which is available to authorized users.

Chromosome Y genetic variants: impact in animal models and on human disease

Chromosome Y (chrY) variation has been associated with many complex diseases ranging from cancer to cardiovascular disorders. Functional roles of chrY genes outside of testes are suggested by the fact that they are broadly expressed in many other tissues and correspond to regulators of basic cellular functions (such as transcription, translation, and protein stability). However, the unique genetic properties of chrY (including the lack of meiotic crossover and the presence of numerous highly repetitive sequences) have made the identification of causal variants very difficult. Despite the prior lack of reliable sequences and/or data on genetic polymorphisms, earlier studies with animal chrY consomic strains have made it possible to narrow down the phenotypic contributions of chrY. Some of the evidence so far indicates that chrY gene variants associate with regulatory changes in the expression of other autosomal genes, in part via epigenetic effects. In humans, a limited number of studies have shown associations between chrY haplotypes and disease traits. However, recent sequencing efforts have made it possible to greatly increase the identification of genetic variants on chrY, which promises that future association of chrY with disease traits will be further refined. Continuing studies (both in humans and in animal models) will be critical to help explain the many sex-biased disease states in human that are contributed to not only by the classical sex steroid hormones, but also by chrY genetics.

Similarities and differences of X and Y chromosome homologous genes, SRY and SOX3, in regulating the renin-angiotensin system promoters

The renin-angiotensin system (RAS) is subject to sex-specific modulation by hormones and gene products. However, sex differences in the balance between the vasoconstrictor/proliferative ACE/ANG II/AT1 axis, and the vasodilator/antiproliferative ACE2/ANG-(1-7)/MAS axis are poorly known. Data in the rat have suggested the male-specific Y-chromosome gene Sry to contribute to balance between these two axes, but why the testis-determining gene has these functions remains unknown. A combination of in silico genetic/protein comparisons, functional luciferase assays for promoters of the human RAS, and RNA-Seq profiling in rat were used to address if regulation of Sry on the RAS is conserved in the homologous X-chromosome gene, Sox3. Both SRY and SOX3 upregulated the promoter of Angiotensinogen (AGT) and downregulated the promoters of ACE2, AT2, and MAS, likely through overlapping mechanisms. The regulation by both SRY and SOX3 on the MAS promoter indicates a cis regulation through multiple SOX binding sites. The Renin (REN) promoter is upregulated by SRY and downregulated by SOX3, likely through trans and cis mechanisms, respectively. Sry transcripts are found in all analyzed male rat tissues including the kidney, while Sox3 transcripts are found only in the brain and testis, suggesting that the primary tissue for renin production (kidney) can only be regulated by SRY and not SOX3. These results suggest that SRY regulation of the RAS is partially shared with its X-chromosome homolog SOX3, but SRY gained a sex-specific control in the kidney for the rate-limiting step of the RAS, potentially resulting in male-specific blood pressure regulation.

Effect of the Y chromosome on plasma high-density lipoprotein-cholesterol levels in Y-chromosome-consomic mouse strains

Background

Plasma high-density lipoprotein (HDL)-cholesterol level is a clinically important quantitative phenotype that widely varies among inbred mouse strains. Several genes or loci associated with plasma HDL-cholesterol levels have been identified on autosomes and the X chromosome. In contrast, genes or loci on the Y chromosome have not attracted significant attention hitherto. Therefore, we investigated the effects of the Y chromosome on plasma HDL-cholesterol levels in Y- chromosome-consomic (Y-consomic) mouse strains.

Findings

Plasma HDL-cholesterol level data from 16 Y-consomic strains demonstrated that the Y chromosome substitutions significantly altered plasma HDL-cholesterol levels, i.e., variations in the plasma HDL-cholesterol level could be partially explained by Y chromosome genes. We obtained the following results from the genotype data on 30 single nucleotide polymorphisms (SNPs), including nonsynonymous and synonymous SNPs and 9 polymorphisms in Sry: (1) Variation in rs46947134 of Uty was significantly associated with plasma HDL-cholesterol levels. (2) A CAG repeat number polymorphism in Sry was significantly associated with plasma HDL-cholesterol levels. (3) Strains with a certain haplotype of the Mus musculus domesticus-type Y chromosome had significantly lower plasma HDL-cholesterol levels than strains with a certain haplotype of the M. m. musculus-type Y chromosome.

Conclusions

The effect of the Y chromosome on plasma HDL-cholesterol levels was confirmed in the Y-consomic strains. We identified several variants associated with plasma HDL-cholesterol levels. Because the physiological significance of various Y-linked genes remains unclear, the results of this study will provide further insights into the functions of Y-linked genes in lipid metabolism.

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.

Cardiovascular sex differences influencing microvascular exchange

The vital role of the cardiovascular (CV) system is maintenance of body functions via the matching of exchange to tissue metabolic demand. Sex-specific differences in the regulatory mechanisms of CV function and the metabolic requirements of men and women, respectively, have been identified and appreciated. This review focuses on sex differences of parameters influencing exchange at the point of union between blood and tissue, the microvasculature. Microvascular architecture, blood pressure (hydrostatic and oncotic), and vascular permeability, therefore, are discussed in the specific context of sex in health and disorders. It is notable that when sex differences exist, they are generally subtle but significant. In the aggregate, though, they can give rise to profoundly different phenotypes. The postulated mechanisms responsible for sex differences are attributed to genomics, epigenetics, and sex hormones. Depending on specific circumstances, the effect of the combined factors can range from insignificant to lethal. Identifying and understanding key signalling mechanisms bridging genomics/sex hormones and microvascular exchange properties within the scope of this review holds significant promise for sex-specific prevention and treatment of vascular barrier dysfunction.

Dissection of chromosome 18 blood pressure and salt-sensitivity quantitative trait loci in the spontaneously hypertensive rat

Hypertension in humans and experimental models has a strong hereditary basis, but identification of causative genes remains challenging. Quantitative trait loci (QTLs) for hypertension and salt sensitivity have been reported on rat chromosome 18. We set out to genetically isolate and prioritize genes within the salt-sensitivity and hypertension QTLs on the spontaneously hypertensive rat (SHR) chromosome 18 by developing and characterizing a series of congenic strains derived from the SHR and normotensive Brown Norway rat strains. The SHR.BN-D18Rat113/D18Rat82 congenic strain exhibits significantly lower blood pressure and is salt resistant compared with the SHR. Transplantation of kidneys from SHR.BN-D18Rat113/D18Rat82 donors into SHR recipients is sufficient to attenuate increased blood pressure but not salt sensitivity. Derivation of congenic sublines allowed for the separation of salt sensitivity from hypertension QTL regions. Renal expression studies with microarray and Solexa-based sequencing in parental and congenic strains identified 4 differentially expressed genes within the hypertension QTL region, one of which is an unannotated transcript encoding a previously undescribed, small, nonprotein coding RNA. Sequencing selected biological candidate genes within the minimal congenic interval revealed a nonsynonymous variant in SHR transcription factor 4. The minimal congenic interval is syntenic to a region of human chromosome 18 where significant linkage to hypertension was observed in family based linkage studies. These congenic lines provide reagents for identifying causative genes that underlie the chromosome 18 SHR QTLs for hypertension and salt sensitivity. Candidate genes identified in these studies merit further investigation as potentially causative hypertension genes in SHR and human hypertension.

Effects of the Y chromosome on cardiovascular risk factors in Japanese men

Excess cardiovascular risk in men compared with women has been suggested to be partly explained by effects of the Y chromosome. However, inconsistent results have been reported on the Y chromosome's genetic influence on blood pressure and lipid levels. The purpose of the present study was to settle the question whether genetic variants of the Y chromosome influence cardiovascular risk factors using a large epidemiological cohort, the Suita study. Possible influences of the Y chromosome polymorphisms (Y chromosome Alu insertion polymorphism [YAP], M175 and SRY+465) on cardiovascular risk factors were assessed in 974 Japanese men. The frequency of the YAP(+) allele in our study sample was 0.31. The prevalence of hypertension tended to be higher in YAP(+) than in YAP(-) men, and this tendency was found to be stronger among men aged 65 years or older. Men with the YAP(+) genotype had higher levels of high density lipoprotein (HDL) cholesterol compared with those with the YAP(-) genotype, even after adjustment for age, body mass index, and daily ethanol and cigarette consumption (57.0+/-14.6 mg/dL vs. 54.2+/-14.2 mg/dL, nominal p=0.011, adjusted p=0.0062). However, these observed nominal associations disappeared after adjusting for multiple testing (Bonferroni). No association was detected between the YAP genotype and myocardial infarction. Similarly, none of the associations with M175 and SRY+465 attained significance when multiple testing was taken into account. In conclusion, Y chromosome polymorphisms (YAP, M175 and SRY+465) do not appear to be associated with cardiovascular risk factors in Japanese men. Studies using much larger sample sizes and/or additional independent samples will be required for definitive conclusions.

Direct linkage of mitochondrial genome variation to risk factors for type 2 diabetes in conplastic strains

Recently, the relationship of mitochondrial DNA (mtDNA) variants to metabolic risk factors for diabetes and other common diseases has begun to attract increasing attention. However, progress in this area has been limited because (1) the phenotypic effects of variation in the mitochondrial genome are difficult to isolate owing to confounding variation in the nuclear genome, imprinting phenomena, and environmental factors; and (2) few animal models have been available for directly investigating the effects of mtDNA variants on complex metabolic phenotypes in vivo. Substitution of different mitochondrial genomes on the same nuclear genetic background in conplastic strains provides a way to unambiguously isolate effects of the mitochondrial genome on complex traits. Here we show that conplastic strains of rats with identical nuclear genomes but divergent mitochondrial genomes that encode amino acid differences in proteins of oxidative phosphorylation exhibit differences in major metabolic risk factors for type 2 diabetes. These results (1) provide the first direct evidence linking naturally occurring variation in the mitochondrial genome, independent of variation in the nuclear genome and other confounding factors, to inherited variation in known risk factors for type 2 diabetes; and (2) establish that spontaneous variation in the mitochondrial genome per se can promote systemic metabolic disturbances relevant to the pathogenesis of common diseases.

The use of mouse chromosome substitution strains to investigate the genetic regulation of pubertal timing

Identification of genes underlying complex traits such as pubertal timing, is vital to our understanding of fundamental human developmental processes. Animal models can provide an important adjunct to more traditional human investigations. Within this review, we discuss the use and advantages of chromosome substitution strains in the investigation of factors that regulate the timing of the onset of puberty.

Genetic determinants of metabolic syndrome components in the stroke-prone spontaneously hypertensive rat

OBJECTIVE

The metabolic syndrome is a complex multifactorial disease, which results from interactions between genes on multiple chromosomes and environmental factors. Animal models may facilitate genetic analysis of complex phenotypes by allowing complete control of environmental conditions and the ability to produce designer strains.

METHODS

Stroke-prone spontaneously hypertensive (SHRSP) and Wistar-Kyoto (WKY) rat strains were used to construct congenic (SP.WKYGla2a), consomic (SP.WKYGlaYw, WKY.SPGlaYs) and double-introgressed (SP.WKYGla2aYw) strains, which were characterized for metabolic syndrome phenotypes (systolic blood pressure, glucose tolerance and lipid profile) after feeding a 60% fructose diet for 14 days.

RESULTS

The Y consomic strain (SP.WKYGlaYw) demonstrated that the WKY Y chromosome significantly lowered triglyceride levels (3.77 +/- 0.60 versus 9.09 +/- 1.47 mmol/l; P < 0.001) and improved glucose tolerance [area under the curve (AUC): 26.93 +/- 0.81 versus 31.47 +/- 0.89; P < 0.05] compared with SHRSP. The chromosome 2 congenic strain (SP.WKYGla2a) exhibited significantly improved glucose tolerance (AUC: 28.19 +/- 1.17 versus 31.47 +/- 0.89; P < 0.05) and lower systolic blood pressure (161.2 +/- 6.2 versus 179.7 +/- 3.9 mmHg; P < 0.05) compared with SHRSP. 2 x 2 factorial ANOVA identified a significant interaction for glucose metabolism (P = 0.004) in the double-introgressed strain (SP.WKYGla2aYw) between chromosome 2 and Y.

CONCLUSIONS

These results identify novel interacting regions on chromosome 2 and the Y chromosome influencing a cluster of metabolic and cardiovascular phenotypes. Translation to clinical studies will facilitate genetic dissection of human metabolic syndrome.

Salt preference of congenic strains derived from the spontaneously hypertensive rat

Previous studies using reciprocal crosses between the spontaneously hypertensive rat (SHR) and the normotensive Wistar-Kyoto (WKY) strain suggested a role for the Y chromosome in the SHR's exaggerated preference for saline solutions. We have reexamined the role of the Y chromosome in the salt preference of the SHR using a consomic strain derived from SHR and Brown Norway (BN-Lx) progenitors. We also studied congenic lines in which regions of BN-Lx chromosomes 8 and 20 had been introgressed into the SHR genome. Animals were given a choice of water and 0.9% saline to drink over a period of 7 days and their total fluid intake (TFI; water plus saline) and saline preference (proportion of the TFI taken as saline) calculated. SHR bearing the BN-Lx Y chromosome had a significantly reduced saline preference when compared to progenitor SHR. Evidence was also found for the existence of a region on chromosome 8, which influences fluid intake in the SHR. The causative genes involved in these effects however remain to be determined.

Y chromosome polymorphisms in medicine

Ninety-five percent of the length of the human Y chromosome is inherited as a single block in linkage from father to male offspring as a haploid entity. Thus, the Y chromosome represents an invaluable record of all mutations that have occurred along male lineages throughout evolution. For this reason, Y chromosomal DNA variation has been mainly used for investigations on human evolution and for forensic purposes or paternity analysis. Recently, Y chromosomal polymorphisms have been applied in molecular medicine from the perspective of male-specific (spermatogenic failure, testis and prostate cancer) and prevalently male-associated (hypertension, autism) diseases. The absence of recombination on the MSY (male-specific Y) region means that polymorphisms, located in this region, are in tight association with potential functional variations associated with Y-linked phenotypes. Thus, an indirect way to explore if Y chromosome genes are involved in the etiology of a specific disease is the definition of Y chromosome haplogroups in patients versus disease-free and/or the general population. Data on patients with reduced sperm count and prostate cancer indicate that the 'at risk Y haplogroup' may be different in different populations. The situation is rather contradictory for other male-specific or male-associated diseases and further multicenter--possibly multiethnic--studies are needed.

Association between genetic variation in the Y chromosome and hypertension in myocardial infarction patients

A single nucleotide polymorphism (SNP) in chromosome Y has been associated with blood pressure. In men, the risk of suffering from cardiovascular diseases, including coronary artery disease, could be influenced by one or more loci on chromosome Y. We genotyped 208 men who had suffered an early episode of myocardial infarction (MI) (< or =55 years) and 178 healthy control men for two Y-polymorphisms (a HindIII polymorphism in an alphoid satellite in the centromeric non-recombining region and the -2627 T/C in the SRY gene). Frequencies were compared through a chi(2)-test. Frequencies for the two polymorphisms did not differ between patients and controls. The alphoid-HindIII polymorphism was not related to blood pressures in our population (HindIII+: diastolic, 80 +/- 2; systolic, 129 +/- 5. HindIII-: diastolic, 80 +/- 2; systolic, 128 +/- 3). Seventy-six patients (37%) were hypertensives and had a significantly higher frequency of the HindIII+ allele compared to the normotensive patients (46 and 26%, respectively; P = 0.028). According to our data, the alphoid-HindIII polymorphism in chromosome Y was not associated with differences in blood pressure in men from Asturias (Northern Spain). However, the HindIII+ allele increased the risk of suffering an early episode of MI among hypertensives.

Genetic Models in Applied Physiology. HXB/BXH rat recombinant inbred strain platform: a newly enhanced tool for cardiovascular, behavioral, and developmental genetics and genomics

This review deals with the largest set of rat recombinant inbred (RI) strains and summarizes past and recent accomplishments with this platform for genetic mapping and analyses of divergent and complex traits. This strain, derived by crossing the spontaneously hypertensive rat, SHR/Ola, with a Brown Norway congenic, BN-Lx, carrying polydactyly-luxate syndrome, is referred to as HXB/BXH. The RI strain set has been used for linkage and association studies to identify quantitative trait loci for numerous cardiovascular phenotypes, including arterial pressure, stress-elicited heart rate, and pressor response, and metabolic traits, including insulin resistance, dyslipidemia and glucose handling, and left ventricular hypertrophy. The strain's utility has been enhanced with development of a new framework marker-based map and strain distribution patterns of polymorphic markers. Quantitative trait loci for behavioral traits mapped include loci for startle motor response and habituation, anxiety and locomotion traits associated with elevated plus maze, and conditioned taste aversion. The polydactyly-luxate syndrome Lx mutation has allowed the study of alleles important to limb development and malformation phenotypes as well as teratogens. The RI strains have guided development of numerous congenic strains to test locus assignments and to study the effect of genetic background. Although these strains were originally developed to aid in studies of rat genetic hypertension and morphogenetic abnormalities, this rodent platform has been shown to be equally powerful for a wide spectrum of traits and endophenotypes. These strains provide a ready and available vehicle for many physiological and pharmacological studies.

Y is there a risk to being male?

Being male or female can make a vital difference to many important biological functions and can lead to disparities in health. The Y chromosome carries the sex-determining sex reversal Y (SRY) gene and recent studies show that it might also harbor genes that have important biological functions other than sex determination. One such example is the emerging evidence from animal models and humans that supports the presence of cardiovascular genes on the Y chromosome. A significant amount of work remains to identify these genes; however, we report here observations linking the Y chromosome to hypertension, which could explain the higher incidence of cardiovascular disease in males compared with females.

X-linked locus associated with hypertensive renal disease susceptibility in Dahl rats

OBJECTIVE

There is increasing evidence that genetic factors contribute to renal disease susceptibility associated with essential hypertension. To what extent these genetic factors act independently of hypertension susceptibility remains undetermined. The present study was undertaken to assess the potential chromosome X influence on target organ renal disease in the Dahl rat model of salt-sensitive hypertension.

SUBJECTS AND METHODS

Dahl S, Dahl R, F1(RXS), F1(SXR) and F2(RXS) rat male populations were phenotyped for hypertensive renal disease by measuring the percent of incidence of the Grade IV Raij renal pathology score. Six chromosome X markers informative for our (RXS) intercross were analyzed in our F2 rat population (n = 105) for co-segregation with hypertensive renal disease and blood pressure characterized by radiotelemetry.

RESULTS

Comparison of the incidence of renal disease (histologically determined) between F1 reciprocal intercross male progenies reveals a significant chromosome X effect on renal disease [percent incidence of Grade IV Raij renal pathology score in F1 (R female S male) male rats = 2.75 +/- 0.66, and in F1 (S female R male) male rats = 0.67 +/- 0.42; = 0.02]. QTL analysis on an F2(RXS) male population phenotyped for renal disease susceptibility (percent incidence of Grade IV Raij renal pathology score) detects significant linkage to DXRat98 (likelihood ratio statistic = 9.4, P = 0.00223) on chromosome X, corroborating X-linkage of renal disease susceptibility in Dahl rats.

CONCLUSIONS

Our results demonstrate the existence of an X-linked locus associated with hypertensive renal disease susceptibility in Dahl rats. Furthermore, the chromosome X markers tested did not co-segregate with hypertension, indicating that the gene(s) on chromosome X influence renal disease susceptibility independent of blood pressure.

Lack of association between Y chromosome Alu insertion polymorphism and hypertension

There is an inherited paternal predisposition to hypertension. Y chromosome alphoid satellite variation was recently reported to be linked to diastolic blood pressure. To determine whether there is also a Y chromosome marker linked to hypertension, we investigated the prevalence of the Y chromosome Alu insertion polymorphism (YAP) at DYS287 and its association with hypertension in the Aomori population in the northern area of Honshu Island, Japan. YAP was present in 98 of 285 male residents and absent in the rest. The YAP prevalence in the present study would appear to suggest that the present study population represents the general male population in central Japan. Within the study population, there were 110 hypertensive subjects and 104 normotensive subjects. YAP frequency in the hypertensive subjects was not different from that in the normotensive subjects. These results suggest that the YAP is not likely to be a genetic-susceptibility factor for hypertension in the Aomori population.