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

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.

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.

Sex differences in stroke co-morbidities

Males and females possess distinct biological differences that manifest in diverse risk profiles for acute and chronic diseases. A well-documented example of this is ischemic stroke. It has been demonstrated that older females have greater prevalence of, and worse outcome after, ischemic stroke than do males and younger females. Loss of estrogen after menopause is heavily implicated as a contributing factor for this phenomenon; however, there is mounting evidence to suggest that certain risk factors tend to occur more often in older females, such as hypertension and atrial fibrillation, while others more adversely affect females than they do males, such as diabetes and smoking. Sex-specific risk factors, such as oral contraceptive use and menopause, could also contribute to the discrepancy in stroke prevalence and outcome. Additionally, there is evidence to suggest that females tend to present with more nontraditional symptoms of acute stroke than do males, making it more difficult for clinicians to correctly identify the occurrence of a stroke, which may delay the administration of thrombolytic intervention. Finally, certain sociodemographic factors, such as the fact that females were more likely to live alone prior to stroke, may contribute to poorer recovery in females. This review will explore the various co-morbidities and sociodemographic factors that contribute to the greater prevalence of and poorer outcome after stroke in older females and will highlight the critical need for considering sex as a predisposing biological variable in stroke studies.

Approaching Sex Differences in Cardiovascular Non-Coding RNA Research

Cardiovascular disease (CVD) is the biggest cause of sickness and mortality worldwide in both males and females. Clinical statistics demonstrate clear sex differences in risk, prevalence, mortality rates, and response to treatment for different entities of CVD. The reason for this remains poorly understood. Non-coding RNAs (ncRNAs) are emerging as key mediators and biomarkers of CVD. Similarly, current knowledge on differential regulation, expression, and pathology-associated function of ncRNAs between sexes is minimal. Here, we provide a state-of-the-art overview of what is known on sex differences in ncRNA research in CVD as well as discussing the contributing biological factors to this sex dimorphism including genetic and epigenetic factors and sex hormone regulation of transcription. We then focus on the experimental models of CVD and their use in translational ncRNA research in the cardiovascular field. In particular, we want to highlight the importance of considering sex of the cellular and pre-clinical models in clinical studies in ncRNA research and to carefully consider the appropriate experimental models most applicable to human patient populations. Moreover, we aim to identify sex-specific targets for treatment and diagnosis for the biggest socioeconomic health problem globally.

Y Chromosome, Hypertension and Cardiovascular Disease: Is Inflammation the Answer?

It is now becomingly increasingly evident that the functions of the mammalian Y chromosome are not circumscribed to the induction of male sex. While animal studies have shown variations in the Y are strongly accountable for blood pressure (BP), this is yet to be confirmed in humans. We have recently shown modulation of adaptive immunity to be a significant mechanism underpinning Y-chromosome-dependent differences in BP in consomic strains. This is paralleled by studies in man showing Y chromosome haplogroup is a significant predictor for coronary artery disease through influencing pathways of immunity. Furthermore, recent studies in mice and humans have shown that Y chromosome lineage determines susceptibility to autoimmune disease. Here we review the evidence in animals and humans that Y chromosome lineage influences hypertension and cardiovascular disease risk, with a novel focus on pathways of immunity as a significant pathway involved.

Sex differences in obesity, lipid metabolism, and inflammation-A role for the sex chromosomes?

BACKGROUND

Sex differences in obesity and related diseases are well established. Gonadal hormones are a major determinant of these sex differences. However, sex differences in body size and composition are evident prior to exposure to gonadal hormones, providing evidence for gonadal-independent contributions attributable to the XX or XY sex chromosome complement. Large-scale genetic studies have revealed male/female differences in the genetic architecture of adipose tissue amount and anatomical distribution. However, these studies have typically neglected the X and Y chromosomes.

SCOPE OF THE REVIEW

Here we discuss how the sex chromosome complement may influence obesity, lipid levels, and inflammation. Human sex chromosome anomalies such as Klinefelter syndrome (XXY), as well as mouse models with engineered alterations in sex chromosome complement, support an important role for sex chromosomes in obesity and metabolism. In particular, the Four Core Genotypes mouse model-consisting of XX mice with either ovaries or testes, and XY mice with either ovaries or testes-has revealed an effect of X chromosome dosage on adiposity, hyperlipidemia, and inflammation irrespective of male or female gonads. Mechanisms may include enhanced expression of genes that escape X chromosome inactivation.

MAJOR CONCLUSIONS

Although less well studied than effects of gonadal hormones, sex chromosomes exert independent and interactive effects on adiposity, lipid metabolism, and inflammation. In particular, the presence of two X chromosomes has been associated with increased adiposity and dyslipidemia in mouse models and in XXY men. The enhanced expression of genes that escape X chromosome inactivation may contribute, but more work is required.

Identification of Quantitative Trait Loci That Determine Plasma Total-Cholesterol and Triglyceride Concentrations in DDD/Sgn and C57BL/6J Inbred Mice

DDD/Sgn mice have significantly higher plasma lipid concentrations than C57BL/6J mice. In the present study, we performed quantitative trait loci (QTL) mapping for plasma total-cholesterol (CHO) and triglyceride (TG) concentrations in reciprocal F₂ male intercross populations between the two strains. By single-QTL scans, we identified four significant QTL on chromosomes (Chrs) 1, 5, 17, and 19 for CHO and two significant QTL on Chrs 1 and 12 for TG. By including cross direction as an interactive covariate, we identified separate significant QTL on Chr 17 for CHO but none for TG. When the large phenotypic effect of QTL on Chr 1 was controlled by composite interval mapping, we identified three additional significant QTL on Chrs 3, 4, and 9 for CHO but none for TG. QTL on Chr 19 was a novel QTL for CHO and the allelic effect of this QTL significantly differed between males and females. Whole-exome sequence analysis in DDD/Sgn mice suggested that Apoa2 and Acads were the plausible candidate genes underlying CHO QTL on Chrs 1 and 5, respectively. Thus, we identified a multifactorial basis for plasma lipid concentrations in male mice. These findings will provide insight into the genetic mechanisms of plasma lipid metabolism.

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.

Increased high-density lipoprotein cholesterol levels in mice with XX versus XY sex chromosomes

OBJECTIVE

The molecular mechanisms underlying sex differences in dyslipidemia are poorly understood. We aimed to distinguish genetic and hormonal regulators of sex differences in plasma lipid levels.

APPROACH AND RESULTS

We assessed the role of gonadal hormones and sex chromosome complement on lipid levels using the four core genotypes mouse model (XX females, XX males, XY females, and XY males). In gonadally intact mice fed a chow diet, lipid levels were influenced by both male-female gonadal sex and XX-XY chromosome complement. Gonadectomy of adult mice revealed that the male-female differences are dependent on acute effects of gonadal hormones. In both intact and gonadectomized animals, XX mice had higher HDL cholesterol (HDL-C) levels than XY mice, regardless of male-female sex. Feeding a cholesterol-enriched diet produced distinct patterns of sex differences in lipid levels compared with a chow diet, revealing the interaction of gonadal and chromosomal sex with diet. Notably, under all dietary and gonadal conditions, HDL-C levels were higher in mice with 2 X chromosomes compared with mice with an X and Y chromosome. By generating mice with XX, XY, and XXY chromosome complements, we determined that the presence of 2 X chromosomes, and not the absence of the Y chromosome, influences HDL-C concentration.

CONCLUSIONS

We demonstrate that having 2 X chromosomes versus an X and Y chromosome complement drives sex differences in HDL-C. It is conceivable that increased expression of genes escaping X-inactivation in XX mice regulates downstream processes to establish sexual dimorphism in plasma lipid levels.

Chromosomal assignment of quantitative trait loci influencing baseline circulating total cholesterol level in male laboratory mice: report of a consomic strain survey and comparison with published results

Background

An important risk for atherosclerosis is a low level of HDL cholesterol. Baseline HDL cholesterol is under complex genetic and environmental control. Here we report on results of male mice from a consomic strain survey and the parental inbred strains for baseline circulating total cholesterol concentration, which is almost the same as HDL cholesterol in chow fed mice. The consomic strains have been derived from C57BL/6J (host strain) and A/J (donor strain) inbred lines. The work contributes to the value of the mouse as an animal model for studying the genetic background of differences in baseline circulating total and HDL cholesterol levels.

Results

The consomic strain survey suggested that mouse chromosomes 1, 7, 9, 14, 16, 17, 19, X, and Y contained at least one quantitative trait locus that is involved in baseline circulating total cholesterol concentration. All consomic lines, for which there is evidence that the substituted chromosome contains a quantitative trait locus, increase compared to the host strain baseline circulating total cholesterol concentration. Since there is evidence that ‘body weight’, ‘age at blood sampling’, ‘time of the day blood was collected’, and ‘season’ influence this phenotype, additional statistical analyses (with these variables as covariates) were performed. Now there is only evidence for quantitative trait loci on chromosomes 1, 8, 12, and Y. Taken the present results together with previous consomic strain surveys there is evidence that all mouse chromosomes carry quantitative trait loci that control baseline circulating total cholesterol levels. There was however little agreement between the present consomic strain results and previous sets of data. This might be explained by seasonal effects and differences in methodological variables such as age of the mice, fasting versus non-fasting, percentage of dietary fat, unanesthetized versus anesthetized mice, and the daily light–dark cycle.

Conclusions

The present findings, when compared with previous consomic strain surveys, clearly illustrate the complexity of the genetic-environmental architecture for the regulation of baseline circulating total cholesterol levels in mice. Different data can be obtained from different labs and it underscores that animal geneticists should present as accurate a picture as possible of the laboratory mouse’s environment.