Agonistic antibody to the α1-adrenergic receptor mobilizes intracellular calcium and induces phosphorylation of a cardiac 15-kDa protein

Abstract

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.

Agonistic Autoantibodies to the α1‐Adrenergic Receptor and the β2‐Adrenergic Receptor in Alzheimer’s and Vascular Dementia

“…Notably, this patient proved positive for agAAB to α 1 ‐AR but negative for agAAB to the β 2 ‐AR. The patient IgG elicited binding affinities towards the α 1 ‐AR loop1 peptide in the nanomolar range comparable to agAAB specific for the second extracellular loop of the receptor found in patients with refractory hypertension and to an antibody raised in rabbits against the putative receptor epitope [11, 20]. Our data from measurements of Ca i gave evidence for the presence of a α 1 ‐AR‐specific Ca i raising component in the patient IgG preparation.…”

Antibodies to the α1-Adrenergic Receptor Cause Vascular Impairments in Rat Brain as Demonstrated by Magnetic Resonance Angiography

“…In a parallel approach, rats were treated by intravenous injection of an antibody raised against the α 1 -AR peptide. This antibody we previously characterized to be agonistic and to act comparable to α 1 -AR antibodies from hypertensive patients [9], [15]. The intravenously injected α 1 -AR antibody raised in goat disappeared fast from the circulation of the rats.…”

Receptor-activating autoantibodies and disease: preeclampsia and beyond

“…Furthermore, fibrosis was present in the hearts of immunized animals and not controls. Additional studies by Karczewski et al have raised α 1 -AR-AAs by immunizing rats with second loop peptides and have shown that these antibodies stimulate the mobilization of intra-cellular calcium stores [42]. These preclinical studies suggest that α 1 -AR-AAs may contribute to cardiovascular end-organ damage and hypertension.…”