Desensitization and Sequestration of Human m2 Muscarinic Acetylcholine Receptors by Autoantibodies from Patients with Chagas' Disease

Abstract

Chronic Chagas' disease is associated with pathologic changes of the cardiovascular, digestive, and autonomic nervous system, culminating in autonomic denervation and congestive heart failure. Previously, circulating autoantibodies that activate signaling by cardiac muscarinic acetylcholine receptors (mAChRs) have been described. However, it remains unclear whether the chagasic IgGs directly interact with the m2 mAChRs (predominant cardiac subtype), and, if so, whether chronic exposure of the mAChRs to such activating IgGs would result in receptor desensitization. Here we performed studies with purified and reconstituted hm2 mAChRs and demonstrate that IgGs from chagasic serum immunoprecipitated the mAChRs in a manner similar to an anti-m2 mAChR monoclonal antibody tested in parallel. The chagasic antibodies did not directly interact with the ligand binding site, because the binding of radiolabeled antagonist was unchanged by the addition of the chagasic IgG. In intact cells stably expressing the hm2 mAChR, the chagasic IgGs, but not normal IgGs, mimicked the ability of the agonist acetylcholine to induce two effects associated with agonist-induced receptor desensitization: a decrease in affinity for agonist binding to m2 mAChR and sequestration of the hm2 mAChRs from the cell surface. The results demonstrate that the chagasic IgGs can directly interact with and desensitize m2 mAChRs and provide support for the hypothesis of autoimmune mechanisms having a role in the pathogenesis of Chagas' cardioneuromyopathy.

Advances in G Protein-Coupled Receptor Allostery: From Function to Structure

“…As mentioned earlier in the example of bias for the CaSR (Makita et al, 2007), autoantibodies can act allosterically to mediate pathophysiology. Other examples where this has been seen include Chagas disease, a parasitic infection by Trypanosoma cruzi that leads to the generation of allosteric antibodies targeting b 1 adrenergic and M 2 mAChRs in the heart (Leiros et al, 1997;Sterin-Borda et al, 1999;Hernandez et al, 2003), and Sjogren syndrome, an autoimmune disorder associated with dysfunction of secretory glands that has been proposed to be mediated, at least in part, by autoantibodies against various mAChR subtypes (Borda et al, 1996). Interestingly, the polycationic human eosinophil major basic protein (MBP), a peptide that constitutes ∼50% of the inflammatory peptides released after infiltration and degranulation of eosinophils (Verbout et al, 2007), has been shown to specifically bind to the M 2 mAChR, potentially in an allosteric fashion (Jacoby et al, 1993).…”

Neurotripanosomiasis americana: aspectos clínicos de un problema básico.

“…Posteriormente, se pueden encontrar múltiples focos inflamatorios en el sistema de conducción, nidos de parásitos dentro del nodo aurículo-ventricular, periganglionitis auricular importante y perineuritis (90). También se han encontrado anticuerpos circulantes contra receptores colinérgicos y adrenérgicos de linfocitos y de miocardio en los pacientes infectados por T. cruzi (91)(92)(93).…”

Presencia de anticuerpos contra neurorreceptores cardiacos de acetilcolina muscarínicos tipo II en pacientes con enfermedad de Chagas e implantación de marcapasos

“…En pacientes con enfermedad de Chagas con cardiopatía crónica y en fase indeterminada, se ha descrito la presencia de anticuerpos circulantes que reconocen los neurorreceptores b -adrenérgicos y colinérgicos muscarínicos cardíacos del tipo II (anti-m2MAChR) que tienen actividad funcional en modelos in vitro e in vivo (5)(6)(7)(8)(9)(10)(11).…”

“…La reactividad de los anticuerpos anti-m2MAChR ha sido descrita contra el tercer dominio intracelular del receptor (12), pero la mayoría de estudios se han centrado en la reactividad dada por el reconocimiento de una secuencia de 25 aminoácidos correspondiente al segundo aro extracelular del m2-MAChR (6,8,11,13) (figura 1). En ensayos in vitro, se ha evaluado la capacidad funcional de este reconocimiento y se ha demostrado que el acople del receptor con los anticuerpos produce una respuesta fisiológica similar a la del ligando natural, dada por la disminución en la fuerza de contracción del tejido cardiaco (14), la variación en los niveles intracelulares de AMPc y GMPc (5,(8)(9)(10), la supresión de corrientes de calcio (15,16) y la pérdida de la sensibilización del receptor (11).…”