The epigenetic legacy of renin–angiotensin system inhibition in preventing hypertension

This editorial refers to ‘Four-week inhibition of the renin–angiotensin system in spontaneously hypertensive rats results in persistently lower blood pressure with reduced kidney renin and changes in expression of relevant gene networks’, by S.G. Byars et al., https://doi.org/10.1093/cvr/cvae053.

1. Introduction

Hypertension (HTN) is a global health problem affecting around 30% of adults and remains the main contributor to mortality and disability worldwide.¹ HTN is preceded by high-normal blood pressure (BP), previously referred to as pre-HTN. High-normal BP increases the risk of developing HTN and other cardiovascular diseases. Therefore, appropriate management of high-normal BP is very important in cardiovascular prevention.² In about 95% of cases, the pathogenesis of HTN remains unknown and is classified as essential HTN.³ The renin–angiotensin system (RAS) plays an essential role in the pathogenesis of HTN. Pharmacological RAS inhibition attenuates high BP and exerts broad cardiovascular benefits (Figure 1). However, life-long treatment is associated with the accumulation of side effects and poor compliance and can lead to the occurrence of the RAS escape phenomenon associated with a compensatory rise in renin and angiotensin levels.⁴

Figure 1

Effect of early RAS inhibition on renal transcriptome modulation and BP reduction in SHRs. Short-term treatment with ACE-Is or ARBs in young, pre-hypertensive rats initially leads to overactivation of the RAS and increases renin expression. This causes a resetting of the pro-hypertensive transcriptome profile by modulating the expression of miRNA, lncRNA, and mRNA, as well as enhancing the methylation of pro-hypertensive genes. As a result, this leads to persistently lower BP.

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The exciting concept that short-term blockade of RAS using angiotensin receptor blockers (ARBs) or angiotensin-converting enzyme inhibitors (ACE-Is) from age 4 to 8 weeks in the young, spontaneously hypertensive rat (SHR) might prevent the development of HTN was reported more than 30 years ago.⁵ This legacy of early RAS inhibition phenomenon has been attributed to ACE-I or ARBs only but not to other classes of anti-hypertensive drugs.⁶ Increasing understanding of metabolic memory has revived a particular interest in the potential mechanisms of this phenomenon. Indeed, 4-week angiotensin II treatment pre-sensitizes young rats to a more robust high BP development after subsequent L-NAME administration.⁷ Additionally, renal transplantation studies from SHRs after short-term ACE-I treatment showed a reduction of BP in SHR recipients. Although interesting observations have been made regarding the effects of inhibiting RAS on kidneys, the mechanisms of this phenomenon have yet to be explored. Moreover, it is intriguing that while these effects in experimental models are well defined, clinical studies fail to corroborate such profound long-term prevention effects.

Mechanistic insights might illuminate the inconsistencies between observations in experimental models and the absence of comparable effects in clinical studies. Additionally, this understanding could contribute to formulating strategies to prevent the transition from the pre-hypertensive stage to HTN.

In the latest issue of Cardiovascular Research, Byars et al.⁸ aimed to clarify the molecular mechanisms linked to the epigenetic legacy of early RAS inhibition on reduced BP in SHRs, a phenomenon initially described by Harrap. They hypothesize that epigenetic regulation, similar to other cardiovascular conditions, may play an important role in this observation.^9,10 Using next-generation sequencing, the authors comprehensively evaluated mRNA, miRNA, and lncRNA to understand better complex changes in the whole transcriptome related to kidney RAS inhibition. One of the most important findings was related to renin expression regulation, the main enzyme initiating RAS activation. The initial treatment of rats in the pre-hypertensive period resulted in the overexpression of most of the RAS components in the kidney, with a six-fold increase in renin level. However, 6 weeks after stopping the treatment, only renin remained significantly changed, with a ∼23% decline, together with reduced BP. This suggests that 4 weeks of AT1 blockade in the specific lifetime resets the ‘renal hypertensive transcriptome phenotype’ (Figure 1). The study demonstrated that the overexpression of RAS genes, resulting from previous pharmacological inhibition, induces persistent epigenetic modifications. Authors found increased methylation in the promoter region of renin in 20-week-old rats. Finally, the authors also identified 112 genetic renin variants, including three in antisense lncRNA LOC102550525, in SHRs, but not normotensive rats. Next, using weighted correlation network analysis, the authors identified distinct clusters and 43 modules related to the long-term effect of losartan treatment and its associations with BP. This helped identify 13 candidate genes associated with long-term protection against HTN development. Six of them have been confirmed to play a role in CVDs or RAS regulation, while the rest require further investigation. In addition, they identified 45 differentially expressed miRs, with miR-145-3p, which was negatively correlated with nine identified candidates. Within these candidates, the nuclear factor interleukin 3 regulated (Nfil3) caught the authors’ attention because only this gene showed a marked reduction in expression level during and after RAS inhibition treatment. In addition, Nfil3 showed increased methylation and was a hub gene showing co-expression with the greatest number of identified candidate genes. In contrast, B cell lymphoma 6 (Bcl6), which attenuates renal inflammation via inhibition of NF-κB signalling, was significantly upregulated in 20-week-old treated rats. Thus, reduced inflammatory components such as immune cells and pro-inflammatory cytokines may also play a critical role in the genetic legacy of RAS inhibition on BP elevation.

There are several points we have to carefully interpret while addressing this study. Firstly, while authors use a traditional definition of ‘genetic reprogramming’, clearly, most mechanisms are epigenetic and may extend beyond those. Secondly, such ‘reprogramming’ may not necessarily be lifelong, as follow-up for longer than 6 weeks was not verified and is mainly attributed to SHR and SHR SP, characterized by enhanced RAS activity and considered a genetic model of HTN. Although some reports suggest that ARB treatment of Dahl salt-sensitive rats, with a low renin profile, from age 3 to 10 weeks prevented the development of severe salt-induced HTN after the treatment was stopped. It is important to note, however, that despite losartan treatment, animals continued to exhibit relatively elevated BP levels, with tail-cuff measurements approaching 190 mmHg. Nevertheless, this was approximately 30 mmHg lower than the BP in animals treated with a vehicle. This may be relevant as a 10 mmHg reduction in systolic BP (SBP) leads to a 13% reduction in mortality and significantly reduces the risk of major cardiovascular events like coronary heart disease, stroke, and heart failure (17, 27, and 28%, respectively).¹¹

Finally, while the experimental data of Harrap et al. are fascinating, we need to put those in an appropriate clinical context, painting a much less promising landscape. Three attempts were made to verify this innovative approach in humans during the STAR CAST, TROPHY, and DHyPP trials. Nevertheless, a similar treatment of pre-hypertensive or patients with mild HTN did not show any convincing data on long-term BP levels and the prevention of HTN development, despite that some of them reported delayed reoccurrence of HTN or minimal changes in BP levels. On the other hand, animal studies showed improvement in renal haemodynamics, which was not observed in human trials. This may suggest that changes in treatment regimens or better stratification of the patients with a genetic predisposition to develop HTN are needed. Also, humans’ dosage or treatment duration may be insufficient for transcriptome reprogramming observed in SHRs. Furthermore, the pre-hypertensive period in SHRs may not necessarily reflect the populations used during human trials, so intervention was not performed early enough to modulate renal transcriptome before HTN development. Finally, other factors, such as post-translational modifications or inflammation modulation occurring during treatment and not yet explored, may also play a role in this fascinating phenomenon of renal epigenetic legacy in SHRs.

In summary, the current study may identify new pharmacological gene targets for innovative RNA-based treatments aimed at RAS systems, similar to zilebesiran,⁴ which has recently demonstrated significant and sustained BP-lowering effects in patients. This will, however, require a further integrated strategy,¹⁰ including novel genetic approaches in humans.¹²

Funding

R.N. is supported by the Chancellor’s Fellowship at the University of Edinburgh. M.L. is supported by the Italian Society of Arterial Hypertension (SIIA) ‘Giuseppe Schillaci’ scholarship.

Data availability

No new data were generated or analysed in support of this research.

References

Author notes