Antagonists to endothelin receptor type B promote apoptosis in human pulmonary arterial smooth muscle cells

Fluorinated perhexiline derivative attenuates vascular proliferation in pulmonary arterial hypertension smooth muscle cells

Increased proliferation and reduced apoptosis of pulmonary artery smooth muscle cells (PASMCs) is recognised as a universal hallmark of pulmonary arterial hypertension (PAH), in part related to the association with reduced pyruvate dehydrogenase (PDH) activity, resulting in decreased oxidative phosphorylation of glucose and increased aerobic glycolysis (Warburg effect). Perhexiline is a well-recognised carnitine palmitoyltransferase-1 (CPT1) inhibitor used in cardiac diseases, which reciprocally increases PDH activity, but is associated with variable pharmacokinetics related to polymorphic variation of the cytochrome P450-2D6 (CYP2D6) enzyme, resulting in the risk of neuro and hepatotoxicity in 'slow metabolisers' unless blood levels are monitored and dose adjusted. We have previously reported that a novel perhexiline fluorinated derivative (FPER-1) has the same therapeutic profile as perhexiline but is not metabolised by CYP2D6, resulting in more predictable pharmacokinetics than the parent drug. We sought to investigate the effects of perhexiline and FPER-1 on PDH flux in PASMCs from patients with PAH. We first confirmed that PAH PASMCs exhibited increased cell proliferation, enhanced phosphorylation of AKTSer473, ERK 1/2Thr202/Tyr204 and PDH-E1αSer293, indicating a Warburg effect when compared to healthy PASMCs. Pre-treatment with perhexiline or FPER-1 significantly attenuated PAH PASMC proliferation in a concentration-dependent manner and suppressed the activation of the AKTSer473 but had no effect on the ERK pathway. Perhexiline and FPER-1 markedly activated PDH (seen as dephosphorylation of PDH-E1αSer293), reduced glycolysis, and upregulated mitochondrial respiration in these PAH PASMCs as detected by Seahorse analysis. However, both perhexiline and FPER-1 did not induce apoptosis as measured by caspase 3/7 activity. We show for the first time that both perhexiline and FPER-1 may represent therapeutic agents for reducing cell proliferation in human PAH PASMCs, by reversing Warburg physiology.

Targeting the microRNA-34a as a Novel Therapeutic Strategy for Cardiovascular Diseases

Cardiovascular diseases (CVDs) are still the main cause of morbidity and mortality worldwide and include a group of disorders varying from vasculature, myocardium, arrhythmias and cardiac development. MicroRNAs (miRs) are endogenous non-coding RNAs with 18–23 nucleotides that regulate gene expression. The miR-34 family, including miR-34a/b/c, plays a vital role in the regulation of myocardial physiology and pathophysiological processes. Recently, miR-34a has been implicated in cardiovascular fibrosis, dysfunction and related cardiovascular disorders as an essential regulator. Interestingly, there is a pivotal link among miR-34a, cardiovascular fibrosis, and Smad4/TGF-β1 signaling. Notably, both loss-of-function and gain-of-function approaches identified the critical roles of miR-34a in cardiovascular apoptosis, autophagy, inflammation, senescence and remodeling by modulating multifunctional signaling pathways. In this article, we focus on the current understanding of miR-34a in biogenesis, its biological effects and its implications for cardiac pathologies including myocardial infarction, heart failure, ischaemia reperfusion injury, cardiomyopathy, atherosclerosis, hypertension and atrial fibrillation. Thus, further understanding of the effects of miR-34a on cardiovascular diseases will aid the development of effective interventions. Targeting for miR-34a has emerged as a potential therapeutic target for cardiovascular dysfunction and related diseases.

Endothelin and the heart in health and diseases

Endothelin-1 (ET-1), a 21-amino acid peptide, was initially identified in 1988 as a potent vasoconstrictor and pressor substance isolated from the culture supernatant of porcine aortic endothelial cells. From human genomic DNA analysis, two other family peptides, ET-2 and ET-3, were found. They showed different effects and distribution, suggesting that each peptide may play separate roles in different organs. In the heart, ET-1 also causes positive inotropic and chronotropic responses and hypertrophic activity of the cardiomyocytes. ETs act via activation of two receptor subtypes, ET_A and ET_B receptors, both of which are coupled to various GTP-binding proteins depending on cell types. Endogenous ET-1 may be involved in progression of various cardiovascular diseases. ET antagonists are currently used clinically in the treatment for patients with pulmonary hypertension, and are considered to have further target diseases as heart failure, cardiac hypertrophy and other cardiac diseases, renal diseases, systemic hypertension, and cerebral vasospasm.

GPCRs in pulmonary arterial hypertension: tipping the balance

Pulmonary arterial hypertension (PAH) is a progressive, fatal disease characterised by increased pulmonary vascular resistance and excessive proliferation of pulmonary artery smooth muscle cells (PASMC). GPCRs, which are attractive pharmacological targets, are important regulators of pulmonary vascular tone and PASMC phenotype. PAH is associated with the altered expression and function of a number of GPCRs in the pulmonary circulation, which leads to the vasoconstriction and proliferation of PASMC and thereby contributes to the imbalance of pulmonary vascular tone associated with PAH; drugs targeting GPCRs are currently used clinically to treat PAH and extensive preclinical work supports the utility of a number of additional GPCRs. Here we review how GPCR expression and function changes with PAH and discuss why GPCRs continue to be relevant drug targets for the disease.

The Glucagon-Like Peptide-1 Receptor Agonist Liraglutide Improves Hypoxia-Induced Pulmonary Hypertension in Mice Partly via Normalization of Reduced ETB Receptor Expression

The glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide is an incretin hormone mimetic used in the treatment of diabetes. However, the effects of liraglutide on pulmonary hypertension (PH) and pulmonary endothelin (ET) system are unknown. Eight-week-old C57BL6/J mice were injected liraglutide or vehicle for 5 weeks. One week after injection, the mice were exposed to either room air (normoxia) or chronic hypoxia (10 % O2) for 4 weeks. The right ventricular systolic pressure (RVSP) was significantly higher in hypoxia + vehicle group than in normoxia + vehicle group. ET-1 mRNA expression in the lungs was comparable among all the groups. ETB mRNA and protein expression in the lungs was significantly lower in hypoxia + vehicle group than in normoxia + vehicle group. The above changes were normalized by liraglutide treatment. The expression of phospho-eNOS and phospho-AMPK proteins in the lungs was significantly higher in hypoxia + liraglutide group than in normoxia + vehicle group. We demonstrated for the first time that liraglutide effectively improved RVSP and RV hypertrophy in hypoxia-induced PH mice by activating eNOS through normalization of impaired ETB pathway and augmentation of AMPK pathway. Therefore, GLP-1R agonists can be promising therapeutic agents for PH.

Role of endothelin-1 and its receptors, ETA and ETB, in the survival of human vascular endothelial cells

Our previous work showed the presence of endothelin-1 (ET-1) receptors, ET_A and ET_B, in human vascular endothelial cells (hVECs). In this study, we wanted to verify whether ET-1 plays a role in the survival of hVECs via the activation of its receptors ET_A and (or) ET_B (ET_AR and ET_BR, respectively). Our results showed that treatment of hVECs with ET-1 prevented apoptosis induced by genistein, an effect that was mimicked by treatment with ET_BR-specific agonist IRL1620. Furthermore, blockade of ET_BR with the selective ET_BR antagonist A-192621 prevented the anti-apoptotic effect of ET-1 in hVECs. However, activation of ET_A receptor alone did not seem to contribute to the anti-apoptotic effect of ET-1. In addition, the anti-apoptotic effect of ET_BR was found to be associated with caspase 3 inhibition and does not depend on the density of this type of receptor. In conclusion, our results showed that ET-1 possesses an anti-apoptotic effect in hVECs and that this effect is mediated, to a great extent, via the activation of ET_BR. This study revealed a new role for ET_BR in the survival of hVECs.

Potential beneficial role for endothelin in scleroderma vasculopathy: inhibition of endothelial apoptosis by type B endothelin-receptor signaling

Objectives

Microvascular endothelial cell (MVEC) apoptosis is considered to be a key event in the pathogenesis of systemic sclerosis (SSc), an increased expression of endothelin-1 (ET1) is also well recognized in the disease. ET1 is thought to exert deleterious effects on the vasculature by virtue of its known vasospastic, proliferative and fibrotic effects, yet ET1 can act as a survival factor for a variety of cells, including MVEC. The aim of this study is to investigate if ET1 signaling protects SSc-MVECs from apoptosis.

Methods

The expression levels of ET1-receptor genes: Endothelin Receptor Type A gene (EDNRA) and Endothelin Receptor Type B gene (EDNRB), and the effects of selective Endothelin Receptor Type A (ETA) antagonists, selective Endothelin Receptor Type B (ETB), and dual ETA/B antagonist in the presence and/or absence of ET1 on control and SSc-MVEC apoptosis were examined.

Results

Significant increase in the expression of ETA and ETB was noted in SSc-MVECs. Growth factors withdrawal (GFW) resulted in a significant apoptosis that was considerably reduced by the addition ET1. The addition of ETA-receptor antagonists did not affect ET1 anti-apoptotic effects, while the nonselective ETA/B or the selective ETB-receptor antagonists blocked the anti-apoptotic effects of ET1. Finally, an upregulation of the proapoptotic gene BAX after GFW was noted that was normalized by the addition of ET1.

Conclusions

The results suggest that ET1 mediates an anti-apoptotic effect through engaging the ETB receptors in MVECs. Therefore, it appears that selective ETA antagonism may have an advantage over the non-selective ET1-receptor antagonists in SSc vasculopathy, particularly in the early stages of the disease when MVEC apoptosis is rampant.