Fibroblast apoptosis precedes cardiomyocyte mass reduction during left ventricular remodeling in hypertensive rats treated with amlodipine

Fibroblasts under pressure: cardiac fibroblast responses to hypertension and antihypertensive therapies

Approximately 50% of Americans have hypertension, which significantly increases the risk of heart failure. In response to increased peripheral resistance in hypertension, intensified mechanical stretch in the myocardium induces cardiomyocyte hypertrophy and fibroblast activation to withstand increased pressure overload. This changes the structure and function of the heart, leading to pathological cardiac remodeling and eventual progression to heart failure. In the presence of hypertensive stimuli, cardiac fibroblasts activate and differentiate to myofibroblast phenotype capable of enhanced extracellular matrix secretion in coordination with other cell types, mainly cardiomyocytes. Both systemic and local renin-angiotensin-aldosterone system activation lead to increased angiotensin II stimulation of fibroblasts. Angiotensin II directly activates fibrotic signaling such as transforming growth factor β/SMAD and mitogen-activated protein kinase (MAPK) signaling to produce extracellular matrix comprised of collagens and matricellular proteins. With the advent of single-cell RNA sequencing techniques, heterogeneity in fibroblast populations has been identified in the left ventricle in models of hypertension and pressure overload. The various clusters of fibroblasts reveal a range of phenotypes and activation states. Select antihypertensive therapies have been shown to be effective in limiting fibrosis, with some having direct actions on cardiac fibroblasts. The present review focuses on the fibroblast-specific changes that occur in response to hypertension and pressure overload, the knowledge gained from single-cell analyses, and the effect of antihypertensive therapies. Understanding the dynamics of hypertensive fibroblast populations and their similarities and differences by sex is crucial for the advent of new targets and personalized medicine.

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.

Amlodipine Ameliorates Ischemia-Induced Neovascularization in Diabetic Rats through Endothelial Progenitor Cell Mobilization

Objectives. We investigated whether amlodipine could improve angiogenic responses in a diabetic rat model of acute myocardial infarction (AMI) through improving bone marrow endothelial progenitor cell (EPC) mobilization, in the same way as angiotensin converting enzyme inhibitors. Methods. After induction of AMI by coronary artery ligation, diabetic rats were randomly assigned to receive perindopril (2 mgkg⁻¹ day⁻¹), amlodipine (2.5 mgkg⁻¹ day⁻¹), or vehicle by gavage (n = 20 per group). Circulating EPC counts before ligation and on days 1, 3, 5, 7, 14, and 28 after AMI were measured in each group. Microvessel density, cardiac function, and cardiac remodeling were assessed 4 weeks after treatment. The signaling pathway related to EPC mobilization was also measured. Results. Circulating EPC count in amlodipine- and perindopril-treated rats peaked at day 7, to an obvious higher level than the control group peak which was reached earlier (at day 5). Rats treated with amlodipine showed improved postischemia neovascularization and cardiac function, together with reduced cardiac remodeling, decreased interstitial fibrosis, and cardiomyocyte apoptosis. Amlodipine treatment also increased cardiac SDF-1/CXCR4 expression and gave rise to activation of VEGF/Akt/eNOS signaling in bone marrow. Conclusions. Amlodipine promotes neovascularization by improving EPC mobilization from bone marrow in diabetic rats after AMI, and activation of VEGF/Akt/eNOS signaling may in part contribute to this.

Does the ADMA/DDAH/NO pathway modulate early regression of left ventricular hypertrophy with esmolol?

Hypertensive left ventricular hypertrophy (LVH) is a maladaptive response to chronic pressure overload and a strong independent risk factor for cardiovascular disease. Regression of LVH is associated with improved prognosis. Regression of LVH with antihypertensive therapy (angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, beta-blockers, calcium channel blockers, and diuretics) has been reported, although only after long-term treatment. Asymmetrical dimethylarginine (ADMA), the most potent endogenous NO synthase inhibitor, is emerging as an important cardiovascular risk factor in patients with arterial hypertension and LVH, and dimethylarginine dimethylaminohydrolase (DDAH) is the mechanism that most frequently leads to accumulation of ADMA (plasma ADMA is cleared in small part by renal excretion, although the bulk of ADMA is degraded by DDAH). Left ventricular mass is strongly modulated by the NO system. As an important inhibitor of the bioavailability of NO, ADMA is an underlying mechanism of LVH. Beta-blockers can induce regression of LVH and reduced plasma ADMA levels. Oxidative stress is increased in patients with LVH, and this in turn increases generation of ADMA. In a previous preclinical study of spontaneously hypertensive rats, we found that short-term treatment (48 h) with esmolol reverses early LVH, increases the bioavailability of NO, and improves antioxidant status in plasma. Therefore, we propose that the ADMA/DDAH/NO pathway could modulate early regression of LVH with esmolol.

Persistent phenotypic shift in cardiac fibroblasts: impact of transient renin angiotensin system inhibition

Fibrotic cardiac remodeling ultimately leads to heart failure - a debilitating and costly condition. Select antihypertensive agents have been effective in reducing or slowing the development of cardiac fibrosis. Moreover, some experimental studies have shown that the reduction in fibrosis induced by these agents persists long after stopping treatment. What has not been as well investigated is whether this transient treatment results in a protection against future fibrotic cardiac remodeling. In the present review, previously published studies are re-examined to assess whether the relative percent increase in collagen deposition over an off-treatment period is attenuated, relative to control, following transient antihypertensive treatment in young or adult rats. Present findings suggest that transient inhibition of the renin angiotensin system (RAS) not only produces a sustained reduction in cardiac fibrosis, but also results in a degree of protection against future collagen deposition. In addition, prior transient RAS inhibition appears to alter the cardiac fibroblast phenotype such that these cells show a muted response to myocardial injury - namely reduced proliferation, chemokine release, and collagen deposition. This review puts forth several potential mechanisms underlying this long-term cardiac protection that is afforded by transient RAS inhibition. Specifically, fibroblast phenotypic change, cardiac fibroblast apoptosis, sustained suppression of the RAS, persistent reduction in left ventricular hypertrophy, and persistent reduction in arterial pressure are each discussed. Identifying the mechanisms ultimately responsible for this change in cardiac fibroblast response to injury, hypertension, and aging may reveal novel targets for therapy.

Egr-1 upregulates Siva-1 expression and induces cardiac fibroblast apoptosis

The early growth response transcription factor Egr-1 controls cell specific responses to proliferation, differentiation and apoptosis. Expression of Egr-1 and downstream transcription is closely controlled and cell specific upregulation induced by processes such as hypoxia and ischemia has been previously linked to multiple aspects of cardiovascular injury. In this study, we showed constitutive expression of Egr-1 in cultured human ventricular cardiac fibroblasts, used adenoviral mediated gene transfer to study the effects of continuous Egr-1 overexpression and studied downstream transcription by Western blotting, immunohistochemistry and siRNA transfection. Apoptosis was assessed by fluorescence microscopy and flow cytometry in the presence of caspase inhibitors. Overexpression of Egr-1 directly induced apoptosis associated with caspase activation in human cardiac fibroblast cultures in vitro assessed by fluorescence microscopy and flow cytometry. Apoptotic induction was associated with a caspase activation associated loss of mitochondrial membrane potential and transient downstream transcriptional up-regulation of the pro-apoptotic gene product Siva-1. Suppression of Siva-1 induction by siRNA partially reversed Egr-1 mediated loss of cell viability. These findings suggest a previously unknown role for Egr-1 and transcriptional regulation of Siva-1 in the control of cardiac accessory cell death.

Resveratrol attenuates left ventricular remodeling in old rats with COPD induced by cigarette smoke exposure and LPS instillation

The objective of this study was to investigate left cardiac damage and the cardioprotective effects of resveratrol in old rats with COPD. Rats 22 months old were divided into three groups: control (CTL), smoking and lipopolysaccharides (SM/LPS), and SM/LPS plus resveratrol (SM/LPS-Res). Cardiac function, pathology, oxidative stress, and apoptosis index were measured. Expression of myocardial SIRT1 was studied by real-time quantitative polymerase chain reaction (PCR) and Western blot detection. The heart weight-body weight ratio (LVW/BW) increased in the SM/LPS group compared with the CTL group. Both the LVW/BW and the area of fibrosis in the SM/LPS-Res group decreased compared with those in the SM/LPS group. 8-OHdG expression increased in cardiac tissue of rats in the SM/LPS group, which could be inhibited by resveratrol. Resveratrol significantly increased the activity of superoxide dismutase (SOD) and reduced the cardiac malonyldialdehyde (MDA) level in the SM/LPS-Res group. There was a significant decrease in the extent of cardiomyocyte apoptosis in the SM/LPS-Res group compared with the SM/LPS group. SIRT1 mRNA increased in the SM/LPS-Res group compared with the SM/LPS group. In conclusion, resveratrol attenuated cardiac oxidative damage and left ventricular remodeling and enhanced the decreased expression of SIRT1 in hearts of old rats with emphysema and thus might be a therapeutic modality for cardiac injury complicated in chronic obstructive pulmonary disease (COPD).

Cardiac hypertrophy during hypercholesterolemia and its amelioration with rosuvastatin and amlodipine

Hypercholesterolemia is a common accompaniment of atherosclerosis and may be associated with cardiac hypertrophy. To define the mechanistic basis of cardiac hypertrophy in hypercholesterolemia, we fed low-density lipoprotein receptor knockout (LDLR KO) mice regular diet or high cholesterol (HC) diet for 26 weeks. There was clear evidence of cardiomyocyte hypertrophy and collagen deposition in the hearts of LDLR KO mice fed with HC diet, confirmed by histopathology (hematoxylin and eosin and Picrosirius staining) and upregulation of genes for brain natriuretic peptide, alpha-tubulin, transforming growth factor beta1, and connective tissue growth factor (CTGF). These changes were independent of change in blood pressure. The hypercholesterolemic mice hearts showed an upregulation of LOX-1, an oxidized low-density lipoprotein receptor, and angiotensin II type 1 receptor (AT1R) at messenger RNA level. In addition, there was a marked upregulation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and nuclear factor kappaB (NF-kappaB) messenger RNA, indicating overexpression of markers of oxidant stress. A separate group of LDLR KO mice were fed HC diet along with a potent 3-hydroxy-3-methylglutarylcoenzyme A reductase inhibitor rosuvastatin or a dihydropyridine calcium channel blocker amlodipine. Administration of rosuvastatin or amlodipine reduced the overexpression of genes for LOX-1 and AT1R and associated NADPH oxidase and NF-kappaB. These phenomena were associated with a marked decrease in cardiomyocyte hypertrophy and collagen deposits in and around the cardiomyocytes. In conclusion, this study provides evidence of cardiac hypertrophy and fibrosis in hypercholesterolemia independent of blood pressure change LOX-1 and AT1R act as possible signals for oxidant stress leading to alterations in cardiac structure during hypercholesterolemia. Most importantly, rosuvastatin and amlodipine ameliorate cardiomyocyte hypertrophy and fibrosis.

Selective reduction of central pulse pressure under angiotensin blockage in SHR: role of the fibronectin-alpha5beta1 integrin complex

BACKGROUND

Meta-analyses of antihypertensive therapy suggest that, independently of blood pressure (BP) level, stroke prevention is influenced mainly by calcium-entry blockers (CEB) and cardiac risk prevention by angiotensin-converting enzyme inhibitors (ACEIs). The possibility that central systolic and pulse pressure (PP) reduction differs between the two drug classes for the same mean BP (MBP) has never been explored. Our aim was to compare carotid PP at the same MBP obtained with the CEB, amlodipine, and the ACEI, trandolapril, in spontaneously hypertensive rats (SHR), and to evaluate the resulting changes of fibronectin (Fn) and its integrin alpha5beta1 receptor on central PP and arterial stiffness.

METHODS

Amlodipine and trandolapril were administered chronically to achieve the same MBP. Carotid arterial systolic BP (SBP) and PP, diameter and incremental elastic modulus (E(inc)) were determined using echo Doppler techniques, and complemented with vascular histomorphometry, and Fn and alpha5beta1-integrin immunolabeling.

RESULTS

Both drugs produced the same MBP, carotid wall thickness, and stress. Trandolapril reduced PP and E(inc) significantly more than amlodipine, while both agents comparably lowered EIIIA-Fn. Total Fn and alpha-subunit were lowered significantly by trandolapril, but unaffected by amlodipine, indicating that ACEI alone contributed to both diminished carotid stiffness and decrease of the Fn-integrin complex.

CONCLUSIONS

Results showed that amlodipine and trandolapril have different effects on carotid mechanical properties for comparable MBP reduction. Changes in Fn-integrin complex not only modify consistently ACEI mechanotransduction but also are associated with selective central PP reduction. Whether this property has consequences on cardiovascular (CV) risk remains to be investigated.