An investigation of genome-wide associations of hypertension with microsatellite markers in the family blood pressure program (FBPP)

A new immune disease: systemic hypertension

Systemic hypertension is the most common medical comorbidity affecting the adult population globally, with multiple associated outcomes including cerebrovascular diseases, cardiovascular diseases, vascular calcification, chronic kidney disease, metabolic syndrome and mortality. Despite advancements in the therapeutic field approximately one in every five adult patients with hypertension is classified as having treatment-resistant hypertension, indicating the need for studies to provide better understanding of the underlying pathophysiology and the need for more therapeutic targets. Recent pre-clinical studies have demonstrated the role of the innate and adaptive immune system including various cell types and cytokines in the pathophysiology of hypertension. Moreover, pre-clinical studies have indicated the potential beneficial effects of immunosuppressant medications in the control of hypertension. Nevertheless, it is unclear whether such pathophysiological mechanisms and therapeutic alternatives are applicable to human subjects, while this area of research is undoubtedly a rapidly growing field.

Hypertension: a new treatment for an old disease? Targeting the immune system

Arterial hypertension represents a serious public health problem, being a major cause of morbidity and mortality worldwide. The availability of many antihypertensive therapeutic strategies still fails to adequately treat around 20% of hypertensive patients, who are considered resistant to conventional treatment. In the pathogenesis of hypertension, immune system mechanisms are activated and both the innate and adaptive immune responses play a crucial role. However, what, when and how the immune system is triggered during hypertension development is still largely undefined. In this context, this review highlights scientific advances in the manipulation of the immune system in order to attenuate hypertension and end-organ damage. Here, we discuss the potential use of immunosuppressants and immunomodulators as pharmacological tools to control the activation of the immune system, by non-specific and specific mechanisms, to treat hypertension and improve end-organ damage. Nevertheless, more clinical trials should be performed with these drugs to establish their therapeutic efficacy, safety and risk-benefit ratio in hypertensive conditions. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Are the innate and adaptive immune systems setting hypertension on fire?

Hypertension is the most common chronic cardiovascular disease and is associated with several pathological states, being an important cause of morbidity and mortality around the world. Low-grade inflammation plays a key role in hypertension and the innate and adaptive immune systems seem to contribute to hypertension development and maintenance. Hypertension is associated with vascular inflammation, increased vascular cytokines levels and infiltration of immune cells in the vasculature, kidneys and heart. However, the mechanisms that trigger inflammation and immune system activation in hypertension are completely unknown. Cells from the innate immune system express pattern recognition receptors (PRR), which detect conserved pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) that induce innate effector mechanisms to produce endogenous signals, such as inflammatory cytokines and chemokines, to alert the host about danger. Additionally, antigen-presenting cells (APC) act as sentinels that are activated by PAMPs and DAMPs to sense the presence of the antigen/neoantigen, which ensues the adaptive immune system activation. In this context, different lymphocyte types are activated and contribute to inflammation and end-organ damage in hypertension. This review will focus on experimental and clinical evidence demonstrating the contribution of the innate and adaptive immune systems to the development of hypertension.

Chronic inflammatory systemic diseases: An evolutionary trade-off between acutely beneficial but chronically harmful programs

It has been recognized that during chronic inflammatory systemic diseases (CIDs) maladaptations of the immune, nervous, endocrine and reproductive system occur. Maladaptation leads to disease sequelae in CIDs. The ultimate reason of disease sequelae in CIDs remained unclear because clinicians do not consider bodily energy trade-offs and evolutionary medicine. We review the evolution of physiological supersystems, fitness consequences of genes involved in CIDs during different life-history stages, environmental factors of CIDs, energy trade-offs during inflammatory episodes and the non-specificity of CIDs. Incorporating bodily energy regulation into evolutionary medicine builds a framework to better understand pathophysiology of CIDs by considering that genes and networks used are positively selected if they serve acute, highly energy-consuming inflammation. It is predicted that genes that protect energy stores are positively selected (as immune memory). This could explain why energy-demanding inflammatory episodes like infectious diseases must be terminated within 3–8 weeks to be adaptive, and otherwise become maladaptive. Considering energy regulation as an evolved adaptive trait explains why many known sequelae of different CIDs must be uniform. These are, e.g. sickness behavior/fatigue/depressive symptoms, sleep disturbance, anorexia, malnutrition, muscle wasting—cachexia, cachectic obesity, insulin resistance with hyperinsulinemia, dyslipidemia, alterations of steroid hormone axes, disturbances of the hypothalamic-pituitary-gonadal (HPG) axis, hypertension, bone loss and hypercoagulability. Considering evolved energy trade-offs helps us to understand how an energy imbalance can lead to the disease sequelae of CIDs. In the future, clinicians must translate this knowledge into early diagnosis and symptomatic treatment in CIDs.

Computation vs. cloning: evaluation of two methods for haplotype determination

Nuclear sequence data, often from multiple loci, are increasingly being employed in analyses of population structure and history, yet there has been relatively little evaluation of methods for accurately and efficiently separating the alleles or haplotypes in heterozygous individuals. We compared the performance of a computational method of haplotype reconstruction and standard cloning methods using a highly variable intron (ornithine decarboxylase, intron 6) in three closely related species of dabbling ducks (genus Anas). Cloned sequences from 32 individuals were compared to results obtained from phase 2.1.1 . phase correctly identified haplotypes in 28 of 30 heterozygous individuals when the underlying model assumed no recombination. Haplotypes of the remaining two individuals were also inferred correctly except for unique polymorphisms, the phase of which was appropriately indicated as uncertain (phase probability = 0.5). For a larger set of 232 individuals, results were essentially identical regardless of the recombination model used and haplotypes for all 30 of the tested heterozygotes were correctly inferred, with the exception of uncertain phase for unique polymorphisms in one individual. In contrast, initial sequences of one clone per sample yielded accurate haplotype determination in only 26 of 30 individuals; polymerase chain reaction (PCR)/cloning errors resulting from misincorporation of individual nucleotides could be recognized and avoided by comparison to direct sequences, but errors due to PCR recombination resulted in incorrect haplotype reconstruction in four individuals. The accuracy of haplotypes reconstructed by phase, even when dealing with a relatively small number of samples and numerous variable sites, suggests broad utility of computational approaches for reducing the cost and improving the efficiency of data collection from nuclear sequence loci.

Blood pressure genetics: time to focus

This review briefly charts the recent history of the genetic study of high blood pressure (BP). After an inconsistent start it was hoped that very large genome-wide association studies (GWAS) might be able to provide some reliable answers. The two largest and most recent GWAS: CHARGE and GlobalBPgen were able to identify, despite some significant inconsistencies, genetic loci that accounted for only about 2% of the genetic factors believed to influence BP. The loci were associated with an estimated effect on BP of 1 mm Hg or less. No doubt many other loci exerting even smaller (<0.5 mm Hg) exist. This review contends that it is time to focus on the loci that can be viewed as confirmed, rather than extending the GWAS searches for less significant genetic influences. It is time to identify the precise deoxyribonucleic acid variants affecting BP, understand their mechanisms of action and think of ways in which such knowledge can be used to prevent and treat high BP in novel, effective, and possibly tailored ways.

Whole-exome sequencing and an iPSC-derived cardiomyocyte model provides a powerful platform for gene discovery in left ventricular hypertrophy

Rationale: Left ventricular hypertrophy (LVH) is a heritable predictor of cardiovascular disease, particularly in blacks. Objective: Determine the feasibility of combining evidence from two distinct but complementary experimental approaches to identify novel genetic predictors of increased LV mass. Methods: Whole-exome sequencing (WES) was conducted in seven African-American sibling trios ascertained on high average familial LV mass indexed to height (LVMHT) using Illumina HiSeq technology. Identified missense or nonsense (MS/NS) mutations were examined for association with LVMHT using linear mixed models adjusted for age, sex, body weight, and familial relationship. To functionally assess WES findings, human induced pluripotent stem cell-derived cardiomyocytes (induced pluripotent stem cell-CM) were stimulated to induce hypertrophy; mRNA sequencing (RNA-seq) was used to determine gene expression differences associated with hypertrophy onset. Statistically significant findings under both experimental approaches identified LVH candidate genes. Candidate genes were further prioritized by seven supportive criteria that included additional association tests (two criteria), regional linkage evidence in the larger HyperGEN cohort (one criterion), and publically available gene and variant based annotations (four criteria). Results: WES reads covered 91% of the target capture region (of size 37.2 MB) with an average coverage of 65×. WES identified 31,426 MS/NS mutations among the 21 individuals. A total of 295 MS/NS variants in 265 genes were associated with LVMHT with q-value <0.25. Of the 265 WES genes, 44 were differentially expressed (P < 0.05) in hypertrophied cells. Among the 44 candidate genes identified, 5, including HLA-B, HTT, MTSS1, SLC5A12, and THBS1, met 3 of 7 supporting criteria. THBS1 encodes an adhesive glycoprotein that promotes matrix preservation in pressure-overload LVH. THBS1 gene expression was 34% higher in hypertrophied cells (P = 0.0003) and a predicted conserved and damaging NS variant in exon 13 (A2099G) was significantly associated with LVHMT (P = 4 × 10⁻⁶). Conclusion: Combining evidence from cutting-edge genetic and cellular experiments can enable identification of novel LVH risk loci.

[Neuroendocrine immunology: new pathogenetic aspects and clinical application]

After two decades of enormous improvements in anti-inflammatory therapy with biologics long-standing disease sequelae in chronic inflammatory diseases (CID) can be recognized, such as fatigue, anorexia/malnutrition, cachectic obesity, insulin resistance, dyslipidemia, changes of steroid hormone axes (e. g. loss of androgens), increased sympathetic nervous tone/decreased parasympathetic nervous tone, inflammation-related anemia and osteopenia. This article demonstrates for the first time in the German language a new theory to explain the pathophysiology of these disease sequelae. It includes concepts from evolutionary medicine and neuroendocrine regulation of energy allocation. The core statement is: the networks of energy regulation and energy allocation have been evolutionarily positively selected for transient inflammatory episodes (not for CIDs due to the negative selection pressure) but long-standing use of these adaptive programs for CID support systemic disease sequelae. These considerations might help to deviate focus from pure anti-inflammatory treatment to adequate diagnosis and therapy of systemic disease sequelae.

Evolutionary medicine and chronic inflammatory state--known and new concepts in pathophysiology

During the last 10 years, a series of exciting observations has led to a new theory of pathophysiology using insights from evolutionary biology and neuroendocrine immunology to understand the sequelae of chronic inflammatory disease. According to this theory, disease sequelae can be explained based on redirection of energy-rich fuels from storage organs to the activated immune system. These disease sequelae are highly diverse and include the following: sickness behavior, anorexia, malnutrition, muscle wasting–cachexia, cachectic obesity, insulin resistance with hyperinsulinemia, dyslipidemia, increase of adipose tissue near inflamed tissue, alterations of steroid hormone axes, elevated sympathetic tone and local sympathetic nerve fiber loss, decreased parasympathetic tone, hypertension, inflammation-related anemia, and osteopenia. Since these disease sequelae can be found in many animal models of chronic inflammatory diseases with mammals (e.g., monkeys, mice, rats, rabbits, etc.), the evolutionary time line goes back at least 70 million years. While the initial version of this theory could explain prominent sequelae of chronic inflammatory disease, it did not however address two features important in the pathogenesis of immune-mediated diseases: the time point when an acute inflammatory disease becomes chronic, and the appearance of hypertension in chronic inflammation. To address these aspects more specifically, a new version of the theory has been developed. This version defines more precisely the moment of transition from acute inflammatory disease to chronic inflammatory disease as a time in which energy stores become empty (complete energy consumption). Depending on the amount of stored energy, this time point can be calculated to be 19–43 days. Second, the revised theory addresses the mechanisms of essential hypertension since, on the basis of water loss, acute inflammatory diseases can stimulate water retention using a positively selected water retention system (identical to the energy provision system). In chronic smoldering inflammation, however, there is no increased water loss. In contrast, there is increased water generation in inflamed tissue and inflammatory cells, and the activation of the water retention system persists. This combination leads to a net increase of the systemic fluid volume, which is hypothesized to be the basis of essential hypertension (prevalence in adults 22–32%).

Five blood pressure loci identified by an updated genome-wide linkage scan: meta-analysis of the Family Blood Pressure Program

BACKGROUND

A preliminary genome-wide linkage analysis of blood pressure in the Family Blood Pressure Program (FBPP) was reported previously. We harnessed the power and ethnic diversity of the final pooled FBPP dataset to identify novel loci for blood pressure thereby enhancing localization of genes containing less common variants with large effects on blood pressure levels and hypertension.

METHODS

We performed one overall and 4 race-specific meta-analyses of genome-wide blood pressure linkage scans using data on 4,226 African-American, 2,154 Asian, 4,229 Caucasian, and 2,435 Mexican-American participants (total N = 13,044). Variance components models were fit to measured (raw) blood pressure levels and two types of antihypertensive medication adjusted blood pressure phenotypes within each of 10 subgroups defined by race and network. A modified Fisher's method was used to combine the P values for each linkage marker across the 10 subgroups.

RESULTS

Five quantitative trait loci (QTLs) were detected on chromosomes 6p22.3, 8q23.1, 20q13.12, 21q21.1, and 21q21.3 based on significant linkage evidence (defined by logarithm of odds (lod) score ≥3) in at least one meta-analysis and lod scores ≥1 in at least 2 subgroups defined by network and race. The chromosome 8q23.1 locus was supported by Asian-, Caucasian-, and Mexican-American-specific meta-analyses.

CONCLUSIONS

The new QTLs reported justify new candidate gene studies. They may help support results from genome-wide association studies (GWAS) that fall in these QTL regions but fail to achieve the genome-wide significance.

The Pharmacogenomics of Anti-Hypertensive Therapy

Hypertension is a major public health problem, but measures to reduce blood pressure and thus cardiovascular risk are complicated by the high prevalence of treatment resistance, despite the availability of multiple drugs. Drug side-effects contribute considerably to suboptimal blood pressure control. Clinicians must often rely on empirical methods to match patients with effective drug treatment. Hypertension pharmacogenomics seeks to find genetic predictors of response to drugs that lower blood pressure and to translate this knowledge into clinical practice. In this review we summarise the current status of hypertension pharmacogenetics from monogenic hypertension to essential hypertension and discuss the issues that need to be considered in a hypertension pharmacogenomic study.

Gene variants of the renin–angiotensin system and hypertension: from a trough of disillusionment to a welcome phase of enlightenment?

There is substantial evidence to suggest that BP (blood pressure) is an inherited trait. The introduction of gene technologies in the late 1980s generated a sharp phase of over-inflated prospects for polygenic traits such as hypertension. Not unexpectedly, the identification of the responsible loci in human populations has nevertheless proved to be a considerable challenge. Common variants of the RAS (renin–angiotensin system) genes, including of ACE (angiotensin-converting enzyme) and AGT (angiotensinogen) were some of the first shown to be associated with BP. Presently, ACE and AGT are the only gene variants with functional relevance, where linkage studies showing relationships with hypertension have been reproduced in some studies and where large population-based and prospective studies have demonstrated these genes to be predictors of hypertension or BP. Nevertheless, a lack of reproducibility in other linkage and association studies has generated scepticism that only a concerted effort to attempt to explain will rectify. Without these explanations, it is unlikely that this knowledge will translate into the clinical arena. In the present review, we show that many of the previous concerns in the field have been addressed, but we also argue that a considerable amount of careful thought is still required to achieve enlightenment with respect to the role of RAS genes in hypertension. We discuss whether the previously identified problems of poor study design have been completely addressed with regards to the impact of ACE and AGT genes on BP. In the context of RAS genes, we also question whether the significance of ‘incomplete penetrance’ through associated environmental, phenotypic or physiological effects has been duly accounted for; whether appropriate consideration has been given to epistatic interactions between genes; and whether future RAS gene studies should consider variation across the gene by evaluating ‘haplotypes’.

Hypertension and genome-wide association studies: combining high fidelity phenotyping and hypercontrols

Among the common complex diseases, hypertension has been particularly unlucky in the recent surge of positive results from genome-wide association studies. We summarize the evidence that would support continuing the effort in the hunt for a genetic basis for hypertension. The problems facing the genetic studies for hypertension are not unique, but phenotypic characterization, heterogeneity and high prevalence make it a special case requiring a more individualized approach. We argue that, even in the presence of a strong environmental component to hypertension risk, the common disease/common variant model is relevant for hypertension and discuss the issues involved in designing a genome-wide association study for hypertension. It is likely that the individual odds ratios for disease variants will be less than 1.3 and, although individually these effect sizes are minor, the combination of even a few such common polymorphisms can have substantial population attributable risks. The identification of hypertension gene variants should provide new insight into the disease susceptibility, progression and severity. This will lead to the identification of potential targets for lifestyle and pharmacological interventions, with the ultimate goal of improving prevention, diagnosis and treatment.

An overview of the genetic dissection of complex traits

Thanks to the recent revolutionary genomic advances such as the International HapMap consortium, resolution of the genetic architecture of common complex traits is beginning to look hopeful. While demonstrating the feasibility of genome-wide association (GWA) studies, the pathbreaking Wellcome Trust Case Control Consortium (WTCCC) study also serves to underscore the critical importance of very large sample sizes and draws attention to potential problems, which need to be addressed as part of the study design. Even the large WTCCC study had vastly inadequate power for several of the associations reported (and confirmed) and, therefore, most of the regions harboring relevant associations may not be identified anytime soon. This chapter provides an overview of some of the key developments in the methodological approaches to genetic dissection of common complex traits. Constrained Bayesian networks are suggested as especially useful for analysis of pathway-based SNPs. Likewise, composite likelihood is suggested as a promising method for modeling complex systems. It discusses the key steps in a study design, with an emphasis on GWA studies. Potential limitations highlighted by the WTCCC GWA study are discussed, including problems associated with massive genotype imputation, analysis of pooled national samples, shared controls, and the critical role of interactions. GWA studies clearly need massive sample sizes that are only possible through genuine collaborations. After all, for common complex traits, the question is not whether we can find some pieces of the puzzle, but how large and what kind of a sample we need to (nearly) solve the genetic puzzle.