Changes critical to persistent lowering of arterial pressure in spontaneously hypertensive rat occur early in antihypertensive treatment

Transient ACE (Angiotensin-Converting Enzyme) Inhibition Suppresses Future Fibrogenic Capacity and Heterogeneity of Cardiac Fibroblast Subpopulations

Transient ACE (angiotensin-converting enzyme) inhibition in spontaneously hypertensive rats is known to protect against future injury-induced cardiac inflammation, fibrosis, and dysfunction; however, the mechanisms of protection have not been delineated. Here, we used single-cell RNA sequencing to test the hypothesis that transient ACE inhibitor treatment would induce a persistent shift in cardiac fibroblast subpopulations. Adult male spontaneously hypertensive rats (11 weeks old, hypertensive with cardiac hypertrophy) were treated for 2 weeks with an ACE inhibitor, enalapril (30 mg/kg per day, PO), or water (untreated spontaneously hypertensive rats) followed by a 2-week washout period (n=7/group). Cardiac fibroblasts were isolated from the left ventricle and subjected to single-cell RNA sequencing. Nine clusters of fibroblasts were identified, with 98% of cells in clusters 0 to 6. The transient treatment produced significant changes both within and across clusters. Cluster 1 depicted a highly fibrogenic gene profile, with cluster 6 serving as a gateway to cluster 1. Transient ACE inhibition depleted the gateway and expanded cluster 0, which was the least fibrogenic profile. Moreover, within cluster 1 fibroblasts, ACE inhibition reduced expression of individual fibrosis genes (eg, COL1A1, COL3A1, and FN1; all P<1×10-35). Clusters 2 to 5 reflected proliferative, moderately fibrogenic, translationally active, and less inflammatory subsets of fibroblasts, all of which exhibited attenuated fibrogenic gene expression after transient ACE inhibition. In conclusion, transient ACE inhibition shifts cardiac fibroblast subpopulations and degree of activation resulting in an overall reduced fibrogenic phenotype.

RAS inhibition in resident fibroblast biology

Angiotensin II (Ang II) is a primary mediator of profibrotic signaling in the heart and more specifically, the cardiac fibroblast. Ang II-mediated cardiomyocyte hypertrophy in combination with cardiac fibroblast proliferation, activation, and extracellular matrix production compromise cardiac function and increase mortality in humans. Profibrotic actions of Ang II are mediated by increasing production of fibrogenic mediators (e.g. transforming growth factor beta, scleraxis, osteopontin, and periostin), recruitment of immune cells, and via increased reactive oxygen species generation. Drugs that inhibit Ang II production or action, collectively referred to as renin angiotensin system (RAS) inhibitors, are first line therapeutics for heart failure. Moreover, transient RAS inhibition has been found to persistently alter hypertensive cardiac fibroblast responses to injury providing a useful tool to identify novel therapeutic targets. This review summarizes the profibrotic actions of Ang II and the known impact of RAS inhibition on cardiac fibroblast phenotype and cardiac remodeling.

Time course of cardiac inflammation during nitric oxide synthase inhibition in SHR: impact of prior transient ACE inhibition

We have previously demonstrated that angiotensin-converting enzyme (ACE) inhibition with enalapril produces persistent effects that protect against future nitric oxide synthase (NOS) inhibitor (L-arginine methyl ester, L-NAME)-induced cardiac dysfunction and outer wall collagen deposition in spontaneously hypertensive rats (SHR). In the present study, we dissect the cytokine/chemokine release profile during NOS inhibition, its correlation to pathological cardiac remodeling and the impact of transient ACE inhibition on these effects. Adult male SHR were treated with enalapril (E+L) or tap water (C+L) for 2 weeks followed by a 2-week washout period. Rats were then subjected to 0, 3, 7 or 10 days of L-NAME treatment. The temporal response to NOS inhibition was evaluated by measuring arterial pressure, cardiac remodeling and cytokine/chemokine levels. L-NAME equivalently increased blood pressure and myocardial and vascular injury in C+L and E+L rats. However, pulse pressure (PP) was only transiently altered in C+L rats. The levels of several inflammatory mediators were increased during L-NAME treatment. However, interleukin-6 (IL-6) and IL-10 and monocyte chemoattractant protein-1 were uniquely increased in C+L hearts; whereas IL-4 and fractalkine were only elevated in E+L hearts. By days 7 and 10 of L-NAME treatment, there was a significant increase in the cardiac density of macrophages and proliferating cells, respectively only in C+L rats. Although myocardial injury was similar in both treatment groups, PP was not changed and there was a distinct cardiac chemokine/cytokine signature in rats previously treated with enalapril that may be related to the lack of proliferative response and macrophage infiltration in these hearts.

New concepts in endothelin control of sodium balance

1. Endothelin (ET)-1, which was originally found to be secreted by the vascular endothelium, is highly expressed in the kidney, particularly in the renal medulla. 2. Recent studies using genetic models have provided significant breakthroughs in the role of ET-1 in the kidney. For example, ET-1 in the medullary collecting duct physiologically regulates water and salt reabsorption, thereby controlling blood pressure. Surprisingly, to explain the blood pressure regulation both ET(A) and ET(B) receptors are necessary in collecting duct. In fact, we recently revealed that ET(A) receptor stimulation in the renal medulla was natriuretic and diuretic. 3. The expression and secretion of ET-1 in the renal medulla are regulated by multiple mechanisms, such as changes in osmolality, exaggerated renin-angiotensin system activity and hypoxia. The changes in the renal medullary ET system are likely to work as compensatory 'protective' natriuretic factors in response to high sodium exposure in the kidney. 4. In the present review, we focus on recent publications that describe our current knowledge of the functional role of renal medullary ET-1, including the recently characterized actions of ET(A) receptors, the second messenger systems, mechanisms of stimulating ET-1 production and how the ET system is involved in the development of hypertension.

Aldosterone does not contribute to renal p21 expression during the development of angiotensin II-induced hypertension in mice

BACKGROUND

We recently reported that aldosterone-induced cellular senescence via an increase in p21, a cyclin-dependent kinase (CDK) inhibitor, in rat kidney and cultured human proximal tubular cells. In the present study, we investigated the contribution of aldosterone to the renal p21 expression and senescence during the development of angiotensin II (AngII)-induced hypertension.

METHODS

Mice received 1% salt in drinking water and vehicle or AngII, and were divided into five groups: 1, vehicle; 2, AngII; 3, AngII+olmesartan; 4, AngII+eplerenone; and 5, AngII+hydralazine.

RESULTS

Plasma aldosterone levels were increased by AngII infusion. Eplerenone further elevated the plasma aldosterone level, but olmesartan and hydralazine did not. AngII group showed significant increase in blood pressure compared to vehicle. Olmesartan and hydralazine, but not eplerenone, suppressed the AngII-salt hypertension. The increase in urinary protein excretion by AngII-salt was suppressed only by olmesartan. AngII with high salt induced a greater expression of p21 mRNA in the kidney than vehicle. Olmesartan abolished the increase in p21 expression, whereas neither eplerenone nor hydralazine affected it. AngII with high salt did not change the expression of p16, another CDK inhibitor. The mice lacking p21 showed identical changes on blood pressure and albuminuria in response to AngII with high salt compared to wild type.

CONCLUSION

These results suggest that aldosterone does not predominantly contribute to renal p21 expression and senescence during the development of AngII-salt hypertension, and that the increase in p21 in the kidney is not likely involved in the development of hypertension and albuminuria.