Modulation of intracellular Ca2+ via L-type calcium channels in heart cells by the autoantibody directed against the second extracellular loop of the alpha1-adrenoceptors

Calcium Homeostasis, Transporters, and Blockers in Health and Diseases of the Cardiovascular System

Calcium is a highly positively charged ionic species. It regulates all cell types' functions and is an important second messenger that controls and triggers several mechanisms, including membrane stabilization, permeability, contraction, secretion, mitosis, intercellular communications, and in the activation of kinases and gene expression. Therefore, controlling calcium transport and its intracellular homeostasis in physiology leads to the healthy functioning of the biological system. However, abnormal extracellular and intracellular calcium homeostasis leads to cardiovascular, skeletal, immune, secretory diseases, and cancer. Therefore, the pharmacological control of calcium influx directly via calcium channels and exchangers and its outflow via calcium pumps and uptake by the ER/SR are crucial in treating calcium transport remodeling in pathology. Here, we mainly focused on selective calcium transporters and blockers in the cardiovascular system.

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α₁-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α₂-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α₁-AR subtypes (α_1A, α_1B, α_1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.

Basal filopodia and vascular mechanical stress organize fibronectin into pillars bridging the mesoderm-endoderm gap

Cells may exchange information with other cells and tissues by exerting forces on the extracellular matrix (ECM). Fibronectin (FN) is an important ECM component that forms fibrils through cell contacts and creates directionally biased geometry. Here, we demonstrate that FN is deposited as pillars between widely separated germ layers, namely the somitic mesoderm and the endoderm, in quail embryos. Alongside the FN pillars, long filopodia protrude from the basal surfaces of somite epithelial cells. Loss-of-function of Ena/VASP, α5β1-integrins or talin in the somitic cells abolished the FN pillars, indicating that FN pillar formation is dependent on the basal filopodia through these molecules. The basal filopodia and FN pillars are also necessary for proper somite morphogenesis. We identified a new mechanism contributing to FN pillar formation by focusing on cyclic expansion of adjacent dorsal aorta. Maintenance of the directional alignment of the FN pillars depends on pulsatile blood flow through the dorsal aortae. These results suggest that the FN pillars are specifically established through filopodia-mediated and pulsating force-related mechanisms.

Maturing human pluripotent stem cell-derived cardiomyocytes in human engineered cardiac tissues

Engineering functional human cardiac tissue that mimics the native adult morphological and functional phenotype has been a long held objective. In the last 5 years, the field of cardiac tissue engineering has transitioned from cardiac tissues derived from various animal species to the production of the first generation of human engineered cardiac tissues (hECTs), due to recent advances in human stem cell biology. Despite this progress, the hECTs generated to date remain immature relative to the native adult myocardium. In this review, we focus on the maturation challenge in the context of hECTs, the present state of the art, and future perspectives in terms of regenerative medicine, drug discovery, preclinical safety testing and pathophysiological studies.

Enhanced vasoconstriction to α1 adrenoceptor autoantibody in spontaneously hypertensive rats

Autoimmune activities have been implicated in the pathogenesis of hypertension. High levels of autoantibodies against the second extracellular loop of α1-adrenoceptor (α1-AR autoantibody, α1-AA) are found in patients with hypertension, and α1-AA could exert a α1-AR agonist-like vasoconstrictive effect. However, whether the vasoconstrictive effect of α1-AA is enhanced in hypertension is unknown. Using aortic rings of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, we observed the vasoconstrictive responses to α1-AA with phenylephrine (α1-AR agonist) as a positive control drug. Aortic nitrotyrosine levels were also measured by ELISA and immunohistochemistry. The results showed that the aortic constrictive responses to α1-AA and phenylephrine (both 1 nmol L(-1)-10 μmol L(-1)) were greater in SHR than in WKY rats. Endothelial denudation or L-NAME (a non-selective NOS inhibitor) (100 μmol L(-1)) increased α1-AA- or phenylephrine-induced vasoconstrictions both in SHR and WKY. However, selective iNOS inhibitor 1400 W (10 μmol L(-1)) enhanced the α1-AA-induced aortic constriction in WKY, but not in SHR. The aortic nitrotyrosine level was significantly higher in SHR than WKY, as shown by both ELISA and immunohistochemistry. These results indicate that the vasoconstrictive response to α1-AA is enhanced in SHR, and this altered responsiveness is due to endothelial dysfunction and decreased NO bioavailability. The study suggests an important role of α1-AR autoimmunity in the pathogenesis and management of hypertension especially in those harboring high α1-AA levels.

Cardiovascular catecholamine receptors in children: their significance in cardiac disease

Adrenoceptors and dopamine receptors are grouped together under the name 'catecholamine receptors.' Catecholamines and catecholaminergic drugs act on catecholamine receptors located on or near the cardiovascular system. The physiological effects of catecholamine receptor stimulation are only partly understood. The catecholaminergic drugs used in critical care medicine today are not selective, or are, at best, in part selective for the various catecholamine receptor subtypes. Many patients, however, depend on them. A variety of animal models has been developed to unravel catecholamine distribution and function. However, the identification of species heterogeneity makes it imperative to determine catecholamine receptor distribution and function in humans. In addition, age-related alterations in catecholamine receptor distribution and function have been identified in human adults. This might have implications for our understanding of the effect of catecholamines in pediatric patients. This article will focus on the pediatric population and will review currently available in vitro data on the distribution and the function of catecholamine receptors in the cardiovascular system of fetuses and children. Also discussed are relevant young animal models and in vivo hemodynamic effects of cardiotonic drugs acting on the catecholamine receptor in children requiring major cardiac surgery. A better understanding of these topics might provide clues for new, receptor subtype-selective, therapeutic approaches in newborns and children with cardiac disease.

Serum positive for the autoantibody against the β(1)-adrenoceptor from Chinese patients with congestive heart failure decreases I(ss) in mouse cardiac myocytes

Autoantibodies targeting the β₁-adrenergic receptor (AAB-β₁) display agonist-like effects, which may have a pathogenic role in the progression of heart failure. Here, we used the electrophysiological recordings to explore the effects of AAB-β₁-positive serum from Chinese patients with heart failure on the activity of the peak transient outward potassium current (I_to) and the end 50 ms steady-state potassium current (I_ss) in mouse cardiac myocytes. We found that the AAB-β₁-positive serum had no effect on the activity of I_to, but it produced a decrease in the currents of I_ss. A low concentration of positive serum (1/100) had a small inhibitory effect on I_ss. However, positive serum at 1 : 10, 1 : 20, and 1 : 50 significantly decreased I_ss. The concentration-dependence analysis showed that the EC₅₀ of AAB-β₁-positive serum was 1/60.24 and its nH was 2.86. It indicated that the AAB-β₁ could inhibit I_ss in mouse cardiomyocyte in a concentration-dependent manner.

Agonistic antibody to the alpha1-adrenergic receptor mobilizes intracellular calcium and induces phosphorylation of a cardiac 15-kDa protein

Hypertension is a major cause for hypertrophic remodelling of the myocardium. Agonistic autoantibodies to extracellular loops of the alpha(1)-adrenergic receptor (alpha(1)-AR) have been identified in patients with arterial hypertension. However, intracellular reactions elicited by these agonistic antibodies remain elusive. An anti-peptide antibody (anti-alpha(1)) was generated against the second extracellular loop of the alpha(1)-AR that bound to its peptide epitope with high affinity (K (D) approximately 50 nM). We studied anti-alpha(1) effects on intracellular calcium (Ca(i)), a key factor in cellular remodelling, and receptor-mediated cardiac protein phosphorylation. Anti-alpha(1) induced pronounced but transient increases in Ca(i) in CHO cells expressing the human alpha(1)-AR (CHO-alpha(1)) and in neonatal cardiomyocytes. Preincubation experiments failed to demonstrate a tonic effect of anti-alpha(1) on Ca(i). However, preincubation with the antibody attenuated the effect of the alpha(1)-AR antagonist prazosin. In neonatal cardiomyocytes anti-alpha(1) induced a robust phosphorylation of a 15-kDa protein that is involved in alpha(1)-AR signalling. Our data support the notion that elevation of Ca(i) is a general feature of agonistic antibodies' action and constitute an important pathogenic component of hypertension-associated autoantibodies. Furthermore, we suggest that agonistic antibodies to the alpha(1)-AR contribute to hypertrophic remodelling of cardiac myocytes, and that the cardiac 15-kDa protein is a relevant downstream target of their action.

The effects of autoantibodies against the second extracellular loop of alpha(1)-adrenoceptor on vasoconstriction

Recent studies have demonstrated the presence of autoantibodies against alpha(1)-adrenoceptor (alpha(1)-AAB) in the serum of patients with primary hypertension, and that these autoantibodies exert adrenergic-agonist-like effects. However, their role in the development of hypertension remains unclear. The current study determined whether alpha(1)-AAB can cause vascular contraction, and further investigated the cellular receptors that mediate their vasoactivity. Enzyme-linked immunosorbent assay (ELISA) was used to detect alpha(1)-AAB in blood samples collected from 73 patients with primary hypertension and 86 normotensive patients. IgGs were purified from mixed sera from 25 alpha(1)-AAB-positive hypertensive patients and 20 alpha(1)-AAB-negative normotensives, respectively. The vasoconstrictive effect of purified IgG from the sera of either hypertensive or normotensive patients was observed in isolated rat thoracic aorta, coronary artery, renal artery, middle cerebral artery, and mesenteric artery. The effects of alpha(1)-AAB administration on mean arterial blood pressure in vivo were also assessed. The frequency of alpha(1)-AAB presence was considerably higher in patients with primary hypertension than normotensive subjects (34.2 vs. 10.5%, P < 0.01). In isolated thoracic aortic rings, renal artery, middle cerebral artery, and coronary artery segments, alpha(1)-AAB induced vasoconstriction in a concentration-dependent fashion, which can be completely blocked by prazosin, a selective alpha(1)-adrenoceptor antagonist. The mean arterial pressure significantly increased after the administration of alpha(1)-AAB in vivo. Our results demonstrated that the alpha(1)-AAB (which exhibited remarkable effects of vascular contraction in vitro, elevated blood pressure in vivo, and showed no desensitization phenomena) may play a role in both elevating vascular resistance and the development and maintenance of hypertension.

Potential relevance of alpha(1)-adrenergic receptor autoantibodies in refractory hypertension

Background

Agonistic autoantibodies directed at the α₁-adrenergic receptor (α₁-AAB) have been described in patients with hypertension. We implied earlier that α₁-AAB might have a mechanistic role and could represent a therapeutic target.

Methodology/Principal Findings

To pursue the issue, we performed clinical and basic studies. We observed that 41 of 81 patients with refractory hypertension had α₁-AAB; after immunoadsorption blood pressure was significantly reduced in these patients. Rabbits were immunized to generate α₁-adrenergic receptor antibodies (α₁-AB). Patient α₁-AAB and rabbit α₁-AB were purified using affinity chromatography and characterized both by epitope mapping and surface plasmon resonance measurements. Neonatal rat cardiomyocytes, rat vascular smooth muscle cells (VSMC), and Chinese hamster ovary cells transfected with the human α_1A-adrenergic receptor were incubated with patient α₁-AAB and rabbit α₁-AB and the activation of signal transduction pathways was investigated by Western blot, confocal laser scanning microscopy, and gene expression. We found that phospholipase A2 group IIA (PLA2-IIA) and L-type calcium channel (Cacna1c) genes were upregulated in cardiomyocytes and VSMC after stimulation with both purified antibodies. We showed that patient α₁-AAB and rabbit α₁-AB result in protein kinase C alpha activation and transient extracellular-related kinase (EKR1/2) phosphorylation. Finally, we showed that the antibodies exert acute effects on intracellular Ca²⁺ in cardiomyocytes and induce mesentery artery segment contraction.

Conclusions/Significance

Patient α₁-AAB and rabbit α₁-AB can induce signaling pathways important for hypertension and cardiac remodeling. Our data provide evidence for a potential clinical relevance for α₁-AAB in hypertensive patients, and the notion of immunity as a possible cause of hypertension.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the autoimmune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosyl phosphatidyl inositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

Angiotensin II-induced increase of T-type Ca2+ current and decrease of L-type Ca2+ current in heart cells

The effect of angiotensin II (Ang II) on the T- and L-type calcium currents (I(Ca)) in single ventricular heart cells of 18-week-old fetal human and 10-day-old chick embryos was studied using the whole-cell voltage clamp technique. Our results showed that in both, human and chick cardiomyocytes, Ang II (10(-7)M) increased the T-type calcium current and decreased the L-type I(Ca). The effect of Ang II on both types of currents was blocked by the AT1 peptidic antagonist, [Sar1, Ala8] Ang II (2 x 10(-7)M). Protein kinase C activator, phorbol 12,13-dibutyrate, mimicked the effect of Ang II on the T- and L-type calcium currents. These results demonstrate that in fetal human and chick embryo cardiomyocytes Ang II affects the T- and L-type Ca2+ currents differently, and this effect seems to be mediated by the PKC pathway.

Cardiac remodeling after long-term stimulation by antibodies against the alpha1-adrenergic receptor in rats

Although autoantibodies against the alpha1-adrenergic receptor which had been found in hypertensive patients had agonist-like activity as phenylephrine, the effects of these antibodies on cardiac remodeling have not been known. In this paper, the models with agonist-like activity of antibodies to alpha1-adrenergic receptor were made by immunized Wistar rats using synthesized peptides of alpha1A-adrenergic receptor and raised for 1 year, and the excited antibodies against the alpha1-adrenergic receptor which could elevate the free Ca2+ in isolated adult rat cardiomyocytes had been existed throughout the experiments after immunization. In immunized rats, despite that systolic blood pressure (SBP) had no difference with normal control, the hypertrophy of heart and cardiomyocytes was observed, the collagen deposition in heart interstitium increased, and c-jun expression and matrix metalloproteinase (MMP)-2 mRNA expression and activity in heart had increased. The results suggested that antibodies against the alpha1-adrenergic receptor could induce cardiac remodeling and maybe play a particular role in hypertension.