Published online before print December 9, 2008, doi: 10.1161/CIRCGENETICS.108.802652
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Original Articles |
Sex and Age Dimorphism of Myocardial Gene Expression in Nonischemic Human Heart Failure
From the Lillehei Heart Institute, Division of Cardiology (D.R.F., S.L., S.P.P., S.G., J.L.H.), Developmental Biology Center (J.L.H.), University of Minnesota, Minneapolis; Washington Hospital Center (A.B., L.W.M.), Washington DC; University of Pennsylvania (S.H., T.P.C., K.B.M.), Philadelphia; Division of Biostatistics (T.L.B.), School of Public Health, University of Minnesota, Minneapolis; University of Michigan (D.B.D, F.P.), Ann Arbor; and the Department of Anatomy and Histology (S.T., C.R.), University of Sydney, Australia.
Correspondence to Jennifer L. Hall, Division of Cardiology, Lillehei Heart Institute, 312 Church St, Minneapolis, MN 55455. E-mail jlhall{at}umn.edu
Received July 22, 2008; accepted October 14, 2008.
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Abstract |
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Background— We report the first comprehensive analysis of gene expression differences by sex and age in left ventricular samples from 102 patients with dilated cardiomyopathy.
Methods and Results— Gene expression data (HG-U133A gene chip, Affymetrix) were analyzed from 30 females and 72 males from 3 separate centers. More than 1800 genes displayed sexual dimorphism in the heart (adjusted P value <0.05). A significant number of these genes were highly represented in gene ontology pathways involved in ion transport and G-protein-coupled receptor signaling. Localization of these genes revealed enrichment on both the sex chromosomes as well as chromosomes 3, 4, and 14. The second goal of this study was to determine the effect of age on gene expression. Within the female cohort, >140 genes were differentially expressed in the <55 years age group compared with the >55 years age group. These genes were highly represented in gene ontology pathways involved in DNA damage. In contrast, zero genes in the male cohort <55 years met statistical significance when compared with the >55 years age group.
Conclusions— Gene expression in dilated cardiomyopathy displayed evidence of sexual dimorphism similar to other somatic tissues and age dimorphism within the female cohort.
Key Words: aging • genes • heart failure • sex
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Introduction |
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Cardiovascular diseases are the leading cause of death in both men and women.1 There are significant differences in the incidence, etiology, and outcomes of heart failure in men and women, although the causes of these differences are not well understood. Previous reports have established that women are more likely to have nonischemic heart failure than men, a lower 5-year mortality associated with heart failure, and a phenotype of concentric left ventricular hypertrophy and preserved ejection fraction.2 Surprisingly, we still do not understand if there are cellular or biological differences between men and women that may be responsible for these differences in function, remodeling, disease, and mortality. Evidence for sex-based differences in myocardial gene expression in humans has been limited by small sample sizes.3,4 A study testing for sex-based dimorphism in gene expression in the human heart with the power to detect genome-wide significance is a first step toward determining if cellular or biological functions may underlie sex-based differences in phenotype.
In addition to sex, age-related trends in the incidence and prevalence of all cardiovascular diseases have been well established in longitudinal studies.5 An association between age-related trends in cardiovascular disease and age-dependent changes in the expression of genes has not been tested. Identifying genes whose expression levels are modified by age and associated with cardiovascular phenotypes may lead to the identification of new targets for early detection and prevention of cardiovascular disease.
Thus, the goal of this study was to determine the impact of sex and age on gene expression in the failing human heart. The study population included younger male and female subjects (a cutoff of 55 years of age was used as a proxy for premenopausal status in women), which allowed for identification of additional age-specific gene effects between or among the sexes.
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Methods |
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Human Tissue Samples
Human left ventricular myocardium was obtained from 102 patients with idiopathic cardiomyopathy at the time of heart transplant or left ventricular assist device implantation. The study included 72 males (48.2±12.7 years) and 30 females (50.4±11.9 years) from 3 separate cohorts (Temple University, University of Minnesota, University of Michigan; Table 1). In the subsequent analysis, the gender groups were also stratified by age <55 years and
55 years. In women, because menopausal status was not known, this age cutoff was meant to serve as an approximation of premenopause and postmenopause. Total RNA was then extracted from the samples for microarray hybridization assays as described previously.6 In addition, a validation cohort was selected from these samples based on the tissue availability for candidate gene reconfirmation by quantitative real-time polymerase chain reaction (PCR).
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Microarray Analysis
Gene expression arrays from Affymetrix (HG-U133A) were hybridized with the sample RNA as previously described7 to obtain myocardial gene expression profiles of the 102 subjects. After generation of probe cell intensity data (CEL files), all subsequent statistical analysis was performed using R version 2.5.18 with Bioconductor version 2.0 (annotation data from the hgu133a package were built using Entrez gene data as of August 24, 2007 and a Gene Ontology build from February 8, 2007).9 A number of quality control measures were used to assess the quality of each array hybridization as well as institution-to-institution assay variability (there was no prior randomization or systematic control for variability across institutional laboratories). Quality control metrics included overall intensity distribution plots and Affymetrix 3'/5' control probe ratios to identify outlier arrays. In addition, positive and negative controls on the periphery of each array were used to generate "center of intensity" plots, which serve as a metric for hybridization uniformity. Each array was evaluated on the basis of all these quality control measures as a whole, and none were found to be consistently out of specification based on commonly accepted metrics for Affymetrix arrays.10 Using these quality control metrics, we did not find bias of hybridization based on the center in which the arrays were processed. Thus, all 102 samples were entered into the analysis and normalized using the robust multiarray average method. After normalization, probesets were culled for redundancy if there were multiple probesets per gene (each gene may be represented by multiple unique oligonucleotide probesets on the HG-U133 array). First, all probesets without unique Entrez gene identifiers were removed from the analysis. Next, the median expression of each probeset was calculated, and the probeset with the greatest median expression was selected for each gene, in attempt to best capture the true biological expression whereas eliminating variance based on noise at low expression levels. This is a variation on probeset selection methods that have been described elsewhere.11,12
Statistical Analysis
Differential expression between the predefined analysis groups (male and female; <55 and 55 years old) was modeled using the limma linear modeling package in Bioconductor. Contrast matrices were designed as modified analysis of variance comparisons to detect differences between gender and age subgroups as main effects, as well as the interaction between gender and age effects. After fitting the linear model, the empirical Bayesian method was used to calculate test statistics and probability values. Probability values were adjusted for multiple testing using the classical false discovery rate method described by Benjamini and Hochberg.13–15 This method used a controlled false discovery rate (set at 0.05) while adjusting for multiple testing simultaneously across multiple subgroup comparisons of age and gender (further multiplying the number of tests adjusted for by the number of comparisons, for a more conservative global adjustment). Resultant gene sets meeting these criteria for differential expression were ascribed genome-wide significance and were combined with public database annotation data and exported with log2 transformed expression values and fold changes for further heuristic analysis as described later.
Enrichment Analysis
After genes of interest were identified from the subgroup analyses, a recursive (stepwise grouping) approach was used to reanalyze the gene expression data based on functional classification. This method allows for the elucidation of significant gene groups as opposed to a blind probeset-by-probeset approach, thereby allowing for further discovery based on gene set "enrichment." Normalized expression data from the subgroup analyses were analyzed using GOstats, a gene set enrichment analysis package in R based on Gene Ontology classifications. This method tests for overrepresentation of functional groups among the differentially expressed genes (in this case, the GO:Biological Process Ontology).16 Testing for enrichment of individual chromosomes based on the abundance of differentially expressed genes among those represented on the HG-U133A (for those that had chromosomal annotation data) was performed using the Fisher exact test.17
Transcription Factor Binding Sites in Promoters of Candidate Genes
We first converted the ENSEMBL gene identifiers to RefSeq identifiers using ENSEMBL’s biomart tool. Using a previously published, phylogenetic-footprinting approach,7 we compiled a comprehensive database of putative transcription factor binding sites in 1 kb proximal promoters of all human genes with full length transcripts. Briefly, for each gene, we extracted 1 kb of genomic sequence immediately upstream from the transcription start site from UCSC database (www.genome.ucsc.edu). We searched these promoter regions using the 584 transcription factor binding site motifs obtained from the TRANSFAC database v10.2.18 A binding site motif is represented as a "positional weight matrix" (PWM), which is a 4xk matrix for a k bases long binding site and provides, for each of the k positions, the preferences for the 4 nucleotide bases at that position. Matches between TRANSFAC PWMs and promoter regions of cardiac genes were determined using the tool PWMSCAN.19 The criterion for a match was probability value cutoff of 2x10–4, corresponding to an expected frequency of 1 random match in 5 kb. We filtered these matches further using human-mouse genome sequence alignments to focus on promoter regions that showed evolutionary conservation. For each TRANSFAC match, let c be the fraction of binding site bases that were identical between human and mouse. We retained matches such that either probability value 
0.00002 (expected frequency of 1 in 50 kb) or c0.8. These criteria for matching have been evaluated previously and were shown to accurately detect 
65% of experimentally verified binding sites with a low false-positive rate of 1 random match in every 50 kb of genomic sequence searched.19
Estimating Over-Representation of Transcription Factor Binding Sites in a Gene Set
Given two sets of gene promoters, a foreground F (with NF promoters) and a control or background B (with NB promoters), our goal is to identify motifs that are enriched in F relative to B. For a particular transcription factor binding motif M, let MF be the number of foreground promoters that have site for motif M. MB was defined analogously. The quantity (MFxNB)/(MBxNF) represents the enrichment of motif M in F relative to B. We estimated the significance (probability value) of the enrichment using a 1-tailed Fisher exact test. Criteria for calling a family of transcription factor binding motifs enriched in the promoters of differentially expressed genes were based on John Storey’s false discovery rates, computed in R using the probability values as input. In order for a family of transcription factor binding motifs to be selected as enriched, the median q value for PWMs in that family must be <0.10. Male versus Background: In this experiment, male-specific differentially expressed genes were used as the foreground and the nondifferentially expressed genes were used as the background. Female versus Background: Female-specific differentially expressed genes were used as the foreground and the nondifferentially expressed genes were used as the background. We then compared the result from these two analyses to search for transcription factors specifically associated with heart failure in men or women with idiopathic dilated cardiomyopathy.
Quantitative Real-Time PCR
Expression levels of candidate genes were tested using quantitative real-time PCR. Eleven male and 5 female subjects were selected from the initial array analysis. Four candidate genes were selected for validation based on the mean Affymetrix expression levels as well as based on their potential role in the pathogenesis of heart failure. Tropomyosin 3 and myosin light chain 4 encode proteins implicated in the regulation of cardiac contractility,20,21 whereas nitric oxide synthase 1, localized in the sarcoplasmic reticulum of the cardiomyocytes may modulate calcium handling via its association with ryanodine receptor.22 Phosphorylase kinase B is involved in the breakdown of glycogen in the heart.
Primer and probe sets were obtained from optimized TaqMan assays (Applied Biosystems, Foster City, Calif) designed for the ABI 7900HT Fast Real-Time PCR System. Target amplification and detection were performed on samples and controls in the same thermal cycling reaction in replicated fashion, allowing for minimization of experimental variability and calculation of 
Ct based on the corresponding reference control, hypoxanthine guanine phosphoribosyl transferase (ie, TargetCtHPRT).23 All samples were analyzed in duplicate. The results are shown in Supplemental Figure 1. There was a significant correlation between array and RT-PCR relative values for all of the genes except nitric oxide synthase 1. This gene had low expression levels on the array compared to other genes, and suggests that differences between groups at this lower expression level have decreased reliability (Supplemental Figure 1).
Statement of Responsibility
The authors had full access to and take full responsibility for the integrity of the data. All authors have read and agree to the manuscript as written.
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Results |
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Patient Characteristics
The clinical information for the subjects is included in Table 1. The age distribution, ejection fractions, and proportion of inotrope use were not significantly different between the male and the female cohorts. Similarly, the male/female distribution, ejection fractions, and proportion of inotrope use were not significantly different between the <55 years age group versus the >55 years age cohort.
Sex- and Age-Based Differential Expression
The aim of the analysis was to identify the impact of sex and age on gene expression patterns in dilated cardiomyopathy. Using a false discovery rate as described by Benjamini and Hochberg, with a significance level set at 0.05, we found 1837 genes that were differentially expressed between the male and female cohort (for the list of genes see Supplemental Table 1).
Table 2 summarizes the distribution of genes that exhibited differential expression between men and women, stratified by age, at various stringency levels (absolute fold change >1.0, >1.2, >2.0, adjusted probability value <0.05). These genes were further characterized as female-biased or male-biased, based on the predominant expression in females or males respectively. As shown in Table 2, the majority of differences in gene expression are modest in size (<1.2 fold), which is consistent with previously published data.24 Among the differentially expressed genes, there were a significantly larger number of female-biased genes compared with male-biased genes (the greater abundance of >2.0 fold expression in males is largely attributable to Y-linked genes).
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The bottom portion of Table 2 provides a breakdown of differential expression by age within the entire cohort as well as within the male and female cohorts. In this comparison, there is a clear delineation between age-based expression in males and females. Within the male cohort, zero genes met the statistical cutoff for differential expression between the younger and older cohort. In contrast, in the female cohort, 142 genes were differentially expressed in the <55 cohort compared with the >55 group.
The overall comparison to detect interaction between age effects and sex effects did not yield any significant genes when using the specified parameters for genome-wide significance, though there were a number of genes with significant unadjusted probability values (not shown). The agexsex interaction contrast tests for additional deviation in expression ratios that cannot be explained solely by the sum of age and sex differences.
Enrichment Analysis
Evidence for chromosomal enrichment is shown in the Figure. Using the Fisher exact test to compare the frequencies of significant genes on each chromosome against the total number of genes interrogated on each chromosome, chromosomal enrichment in the male versus female comparison was detected. Aside from the sex chromosomes, which segregated as expected, chromosome 4 was found to have more female-biased differential expression, whereas chromosomes 3 and 14 contained more male-biased genes (Figure).
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To better understand the functional categories and the networks represented by the genes whose expression was significantly different between males and females, we used a program based on Gene Ontology biological processes (the GOstats package in Bioconductor for R). Similar categorical groupings were observed when analyzed using another public domain enrichment analysis tool in the DAVID suite as a replication exercise (data not shown).17
Table 3 lists the main functional biological categories of the genes that were significantly different between men and women using Gene Ontology. Both ion transport and G-protein-coupled receptor signaling pathways are included at the P0.001 significance level. These 2 broad categories included some of the genes known to mediate physiological processes in the heart such as G-protein receptor kinases (GRK2 and GRK6), adenosine receptor, chemokine receptor 5, and phosphoinositide-3-kinase as well as sodium and potassium channels (for a full list of the genes within this pathway and all other significant pathways please see Supplemental Table 2).
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In the female over versus <55 years comparison, only the DNA damage response pathway met the statistical significance level of P<0.01 (Table 3 and Supplemental Table 2).
Transcription Factor Binding Site Analysis
For the lists of male-biased and female-biased genes, we compared the frequency of transcription factor bindings sites within the 1 KB promoter regions with the frequencies observed in a background set of 5000 genes, which showed no evidence of differential expression (see Data Supplement for complete lists of male-biased, female biased, and background set). We found that 51 TRANSFAC positional weight matrices were enriched in the promoters of female-biased genes with a false-discovery rate of 0.10, whereas only 2 PWMs were enriched in male promoters (both belong to the E2F family; Supplementary Table 3). These PWMs correspond to the transcription factor families summarized in Table 4. Several transcription factor families previously associated with the pathogenesis of heart failure were identified, including MEF2, GATA, NKX, and FOX.
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Discussion |
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Surprisingly little is known regarding the underlying mechanisms behind sex- and age-related differences in cardiovascular disease. To begin to explore this, we analyzed gene expression profiles in a cohort of 70 men and 32 women with dilated cardiomyopathy. We identified 1837 differentially expressed genes between the sexes. The majority of these genes demonstrated modest absolute fold changes of 1.2 to 2.0 (74.9%). These sexually dimorphic genes showed enrichment on autosomes 3, 4, and 14 as well as the sex chromosomes. A breakdown of these genes into biological processes revealed an overrepresentation of genes involved in ion transport activity and G-protein-coupled receptor signaling pathways. Age-related differences in gene expression were identified in the female cohort (<55 years of age versus >55 years of age). These genes were highly represented in gene ontology pathways involved in DNA damage and signal transduction. In contrast, zero genes in the male cohort <55 years met statistical significance when compared with >55 years group, despite the larger sample size of the male cohort. In conclusion, gene expression in the heart of patients with idiopathic cardiomyopathy displayed evidence of sexual dimorphism similar to other somatic tissues and age dimorphism within the female cohort.
Our findings are in agreement with a recent report on sexually dimorphic genes present in other somatic tissues in mice, such as liver, adipose tissue, muscle, and brain, where >70% of differentially expressed genes were found to display <1.2-fold difference in expression between males and females.25 Greater fold changes (>2.0-fold) were seen in sex-chromosome linked genes as would be expected (Supplemental Table 4). A recent study on a smaller set of human cardiac samples obtained from healthy organ donors reported 16 sexually dimorphic genes that displayed >2-fold differences and nearly all were linked to sex chromosomes.3 Six of these sexually dimorphic genes identified in the hearts of healthy donors were identified in the failing hearts in our cohort (EIF1AY, RPS4Y1, DDX3 years, JARID1D, USP9 years, CYorf14) (Supplemental Table 4). JARID1D is a member of the Jumonji family. Several members of this Jumonji family were recently identified to act as transcriptional repressors and modulators of chromatin.26–30 JARDID1D and JARID1C have been identified as histone demethylases.26 Thus, JARID1D may be an important sex-linked gene that regulates sex-linked changes in gene expression through transcriptional repression or modification of chromatin leading to ultrastructural and functional changes in the heart. Early work showed that mice with a homozygous knockout of the jumonji gene showed abnormal heart development.31 Jumonji has also been shown to repress the transcriptional activities of GATA4 and Nkx2.5.31 Taken together, these findings suggest that X-linked expression of JARID1D may be a critical differentiator underlying sex-related differences in cardiovascular function. X- and Y-linked genes with a priori biological evidence for a role in genetic, molecular, and cellular processes linked to heart structure and function are likely first candidates for targets that lead to differences between men and women.
To increase our understanding of the functional categories highly represented by the genes whose expression was significantly different between men and women, we used an integrative analysis based on GO biological process terms. Two of the major findings of this study are that sexually dimorphic genes are significantly overrepresented in ion transport and G protein coupled receptor signaling pathways.
The sexually dimorphic genes encoding sodium channels such as SCN3B, SCN8A, SCN10A, SCN11A, and SCN3, as well as potassium channels (KCNA2, KCNB2, KCNJ3, KCNJ6, KCNJ14, KCNMB3, KCNMB4, and KCNV1) clustered in the ion transport categories. Preclinical and clinical data suggest a possible role of ion channels in sex-specific cardiovascular phenotypes. For example, female predominance was found in both the acquired and congenital long-QT syndromes.32 In addition, a recent report by Albert et al33 identified an association between functionally significant mutations and rare polymorphisms in SCN5A and sudden cardiac risk in women. In vitro work with human mammary arteries showed that arterial vasorelaxation in response to levosimendan, a calcium sensitizer, and a novel vasodilatory agent that is used in the therapy of heart failure was also quantitatively and qualitatively different in males and females.34 In our analysis, we found that men and women with end-stage heart failure had significantly different expression levels of RNA encoding for sodium and potassium channels. In addition, we identified significant overrepresentation of the transcription factor binding site Nkx2.5 in the female-biased genes. Mutations in Nkx2.5 result in conduction abnormalities.35 Furthermore, many sodium and potassium channel family members harbor Nkx2.5 sites in their promoters. Future work will be needed to explore the biological regulation of these ion channel families and the role and regulation of Nkx.2.5 in male and female preclinical models.
Several transcription factors in addition to Nkx2.5 were identified that were overrepresented in the differentially expressed genes in the female hearts, including factors such as MEF2 and GATA that have been previously associated with heart failure along with novel candidates. Unexpectedly, we detected enrichment of the transcription factor binding site that recognizes Sry (a gene found on the Y chromosome) in the genes differentially expressed in females. Because SRY is only expressed in men, this finding cannot imply an increase in SRY activity in the female failing heart. Instead, it may be a marker of target-genes that are regulated in a different manner in women compared with men via other mechanisms. Alternatively, this finding could be a false-positive association, or it may reflect limitations in the specificity of transcription factor binding motifs in TRANSFAC. For example, the binding motif for Sry (AAACAAA) is similar to that for Sox-9 (GTAAACAATAGA) and a few FOXO transcription factors (TATGTAAACAAACAA). The overexpression of transcription factor binding sites for GATA and MEF are particularly intriguing given their known role in hypertrophy and cardiac remodeling.31,36 The only transcription factor binding site overrepresented in the genes upregulated in the male hearts was E2F. This transcription factor binding site is present in many genes that control cell cycle, gene transcription, and cell death. Future work in the laboratory will be needed to test the mechanistic role of these transcription factors.
The second major pathway identified from a pathways analysis of statistically significant sexually dimorphic genes was G protein coupled receptor signaling. The dimorphic genes from the GPCR functional group included several targets with previously demonstrated roles in ventricular remodeling and function; G-protein receptor kinases (GRK2, GRK6) and phosphoinositide-3-kinase have been reported as critical regulators of inotropic and lusitropic properties of the heart.37 Ablation of the GRK2 (also known as β adrenergic receptor kinase 1) gene was found to cause intrauterine heart failure and death in mice.38 Importantly, increasing evidence for sex-related differences in ventricular remodeling is emerging from different animal models.39–41 Our data provides the basis to further explore the relationship between the observed dimorphism in the signaling pathways and sex-related differences in discrete cardiac phenotypes, such as response to pressure and volume overload or remodeling after myocardial infarction.41
When divided into age groups less than and >55 years of age, zero genes were differentially expressed by age in the male cohort. In contrast, when the female cohort was analyzed separately, >142 genes were significantly different in the age group <55 years compared with >55 years. These genes revealed only one significantly overrepresented functional category, the DNA damage response pathway, with three representative genes including v-abl Abelson murine leukemia viral oncogene homolog 1, GPI anchored molecule like protein, and BRCA1 interacting protein C-terminal helicase 1.
Perspective and Study Limitations
The elucidation of sex-related differences in prognosis and outcomes in chronic heart failure has been limited by the smaller proportion of women enrolled in clinical trials, thus, leading to inconsistent reports about the relationship between sex and survival in heart failure.42–45 The investigators of Candesartan in Heart Failure: Assessment of Reduction in Mortality and Morbidity Program examined the effect of sex on clinical outcomes in 5199 men and 2400 women with heart failure and found that women had lower risk of both fatal and nonfatal cardiovascular outcomes that could not be explained by LVEF or origin of the heart failure,46 thus, suggesting that an alternative explanation should be sought for the observed differential survival. In addition to increasing the number of women in clinical trials and the number of female animals in preclinical studies, we must also continue to test for potential differences at the level of the chromosome as well as mRNA and protein to help define potential mechanisms for differences in clinical trial outcome. Surprisingly, little is known about the role of biology in sex- and age-related differences in cardiovascular disease.47 Uncovering gene expression differences between men and women, and in response to age, will provide new steps toward understanding the interacting cause of disease, prevention of disease, and treatment of disease.
Microarray analyses have been used to identify new candidate genes potentially implicated in cardiovascular disease.4,7 The results of these studies, including our own, suggest that many factors must be considered when examining gene expression in human tissue including different cell types within the tissue, social, diet, and other environmental factors, and the interaction of other on-going biological events in the body including but not limited to inflammation, and metabolic disease. Boheler et al4 identified differences in gene expression based on age and sex in failing and nonfailing hearts in 2003. However, this study was limited in sample size. The analysis presented here represents the largest human cohort analyzed to date for sex- and age-related differences in cardiac gene expression. However, to test or confirm these findings larger better curated databases will need to be developed. These types of analyses will likely be important moving forward as sex-linked cardiovascular traits are mapped to loci.33 A fair amount of heterogeneity existed in the clinical characteristics of the patients. In addition, other pertinent data including all cardiac medications, exact menopausal status of female subjects, and use of hormone replacement therapy were not readily available for most subjects. The use of inotropes was similar in all groups, thus, eliminating many of the known clinical confounders that could be associated with changes in gene expression. However, any of these factors may influence the gene expression profile. Furthermore, such heterogeneity along with a modest sample size (though relatively large for human microarray studies) does not allow for more discrete analysis by variables, such as investigating age as a continuous variable with respect to differential gene expression. In addition to the limitations, it should also be pointed out that an analysis of this scope does permit a robust examination of cell-specific markers. For example, we identified unique leukocyte CD (cluster of differentiation) markers for both T and NK cells present in these hearts (CD3, 896, 160, 172 g, and 247).
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Conclusions |
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In conclusion, we have found substantial evidence for sex and age dimorphisms of cardiac gene expression in nonischemic human heart failure by performing a comprehensive study in a large number of patients. A long-term goal is to link chromosomal information with gene expression and intermediate phenotypic end points in the heart as well as within different cell types within the heart including cardiac myocytes, fibroblasts, vascular smooth muscle cells, and endothelial cells. This will require further observational and clinical trials that will be able to clearly distinguish and identify phenotypes, as well as further cellular and molecular studies that will identify tissue- and disease-specific functions of the pathways involved.
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Acknowledgments |
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Sources of Funding
This work was supported by the National Institutes of Health (AG17022 to K.B.M. and HL092379 to T.P.C. and S.H.) and philanthropic funds from the Lillehei family (J.H.).
Disclosures
L.W.M. is a consultant for Thoratec Corporation. J.H. is a consultant with Catholic Health Care West. The remaining authors report no conflicts. F.P. received research grant support from Thoratec Corporation and Terumo Corporation.
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Footnotes |
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The online-only Data Supplement is available at http://circgenetics.ahajournals.org/cgi/content/full/CIRCGENETICS.108.802652/DC1.
Drs Fermin and Barac contributed equally to this work.
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