title: Impact of human autoantibodies on β1-adrenergic receptor conformation, activity, and internalization.
abstract: OBJECTIVE
  Autoantibodies against second extracellular loops of β(1)-adrenergic receptors frequent in dilated cardiomyopathy confer myocardial dysfunction presumably via cAMP stimulation. Here, we investigate the autoantibody impact on receptor conformation and function.
  
  
  RESULTS
  IgG was prepared from patients with dilated cardiomyopathy, matched healthy donors (10 each) or commercial IgG preparations (2). IgG binding to β(1)-adrenergic receptor peptides was detected in 5 of 10 patients and 2 of 10 controls. IgG colocalization with the native receptor was detected in 8 of 10 patients and 1 of 10 controls (10 of 10 patients and 7 of 10 controls at >30 mg IgG/L). All IgGs exhibiting receptor colocalization triggered changes in receptor conformation (determined with fluorescent sensors) not stringently correlated to cAMP stimulation, suggesting the induction of more or less active receptor conformations. Receptor-activating IgG was detected in 8 of 10 patients but only 1 of 10 controls. In addition, IgG from 8 of 10 patients and 3 of 10 controls attenuated receptor internalization (measured by total internal reflection fluorescence microscopy). IgG-inducing inactive receptor conformations had no effect on subsequent cAMP stimulation by isoproterenol. IgG-inducing active receptor conformations dampened or augmented subsequent cAMP stimulation by isoproterenol, depending on whether receptor internalization was attenuated or not. Corresponding IgG effects on the basal beating rate and chronotropic isoproterenol response of embryonic human cardiomyocytes were observed.
  
  
  CONCLUSIONS
  (i) Autoantibodies trigger conformation changes in the β(1)-adrenergic receptor molecule. (ii) Some also attenuate receptor internalization. (iii) Combinations thereof increase the basal beating rate of cardiomyocytes and optionally entail dampening of their chronotropic catecholamine responses. (iv) The latter effects seem specific for patient autoantibodies, which also have higher levels.
authors.affiliation: Institute of Clinical Chemistry and Laboratory Diagnostics, University Hospital, Moorenstrasse 5, Düsseldorf 40225,  Germany.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Bornholz
authors.forename: Stefanie
authors.initials: S
authors.lastname: Weidtkamp-Peters
authors.forename: Stephanie
authors.initials: S
authors.lastname: Schmitmeier
authors.forename: Claus A M
authors.initials: CA
authors.lastname: Seidel
authors.forename: Lars R
authors.initials: LR
authors.lastname: Herda
authors.forename: Stephan B
authors.initials: SB
authors.lastname: Felix
authors.forename: Horst
authors.initials: H
authors.lastname: Lemoine
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hescheler
authors.forename: Filomain
authors.initials: F
authors.lastname: Nguemo
authors.forename: Christoph
authors.initials: C
authors.lastname: Schäfer
authors.forename: Morten O
authors.initials: MO
authors.lastname: Christensen
authors.forename: Christian
authors.initials: C
authors.lastname: Mielke
authors.forename: Fritz
authors.initials: F
authors.lastname: Boege
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D001323:Autoantibodies / Q000276:immunology / Q000494:pharmacology*; D002311:Cardiomyopathy, Dilated / Q000276:immunology*; D016022:Case-Control Studies; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010865:Pilot Projects; D011487:Protein Conformation / Q000187:drug effects; D018342:Receptors, Adrenergic, beta-1 / Q000737:chemistry* / Q000276:immunology / Q000502:physiology*
chemical_list: D000318:Adrenergic beta-Agonists; D001323:Autoantibodies; D018342:Receptors, Adrenergic, beta-1; D000242:Cyclic AMP; D007545:Isoproterenol