The challenge of genetic studies in hypertension

A system view and analysis of essential hypertension

OBJECTIVES

The goal of this study was to investigate genes associated with essential hypertension from a system perspective, making use of bioinformatic tools to gain insights that are not evident when focusing at a detail-based resolution.

METHODS

Using various databases (pathways, Genome Wide Association Studies, knockouts etc.), we compiled a set of about 200 genes that play a major role in hypertension and identified the interactions between them. This enabled us to create a protein-protein interaction network graph, from which we identified key elements, based on graph centrality analysis. Enriched gene regulatory elements (transcription factors and microRNAs) were extracted by motif finding techniques and knowledge-based tools.

RESULTS

We found that the network is composed of modules associated with functions such as water retention, endothelial vasoconstriction, sympathetic activity and others. We identified the transcription factor SP1 and the two microRNAs miR27 (a and b) and miR548c-3p that seem to play a major role in regulating the network as they exert their control over several modules and are not restricted to specific functions. We also noticed that genes involved in metabolic diseases (e.g. insulin) are central to the network.

CONCLUSION

We view the blood-pressure regulation mechanism as a system-of-systems, composed of several contributing subsystems and pathways rather than a single module. The system is regulated by distributed elements. Understanding this mode of action can lead to a more precise treatment and drug target discovery. Our analysis suggests that insulin plays a primary role in hypertension, highlighting the tight link between essential hypertension and diseases associated with the metabolic syndrome.

Early inflammatory and metabolic changes in association with AGTR1 polymorphisms in prehypertensive subjects

BACKGROUND

The Seventh Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure in 2003 created a prehypertension category for persons with blood pressures ranging from systolic blood pressure (SBP) of 120-139 mm Hg or diastolic blood pressure (DBP) from 80 to 89 mm Hg, due to increased risk of cardiovascular disease.

METHODS

Our study utilized the University of California-San Diego (UCSD) Twin Hypertension Cohort. We measured comprehensive plasma cholesterol levels and metabolic (glucose, insulin, leptin) and inflammatory markers (interleukin-6 (IL-6), C-reactive protein (CRP), free fatty acids) to determine the differences between normotensive and prehypertensive subjects. Additionally, we determined whether angiotensin II receptor type-1 (AGTR1) polymorphisms, previously associated with hypertension, could predict prehypertension.

RESULTS

A total of 455 white subjects were included in the study (mean age 37.1 years). Prehypertensive subjects were older with greater body mass index (BMI) than the normotensives, and after adjusting for sex and age, had greater plasma glucose, insulin, and IL-6. The common AGTR1 A1166C (rs5186) polymorphism in the 3'-UTR region, particularly the presence of the 1166C allele, which fails to downregulate gene expression, predicted greater likelihood of being in the prehypertension group and higher SBP. A lesser-studied polymorphism in intron-2 of AGTR1 (A/G; rs2276736) was associated with plasma high-density lipoprotein (HDL) and apolipoprotein A-1. In a subgroup analysis of nonobese subjects (N = 405), similar associations were noted.

CONCLUSION

Prehypertensive subjects already exhibit early pathophysiologic changes putting them at risk of future cardiovascular disease, and AGTR1 may also contribute to this increased risk. Further investigation is needed to confirm these findings and the precise molecular mechanisms of action.