Autoimmunity against M₂ muscarinic acetylcholine receptor induces myocarditis and leads to a dilated cardiomyopathy‐like phenotype

Abstract

Patients with dilated cardiomyopathy (DCM) often have autoantibodies against cardiac antigens including the M 2 muscarinic acetylcholine receptor (M 2 R). To elucidate the role of autoimmunity against M 2 R in disease development, we induced an immune response against M 2 R by adoptive transfer into Rag2 -/-mice of splenocytes from M 2 R -/-mice immunized with a recombinant M 2 R protein. T lymphocytes transiently infiltrated the heart in recipient mice followed by morphological changes in cardiomyocytes. These mice produced IgG antibodies against M 2 R, which bound to cardiomyocytes in vivo and decreased the amplitude of calcium signals in isolated rat cardiomyocytes in vitro. Recipient mice showed increased heart weights associated with increased intraventricular diameter, decreased systolic function, and increased action potential duration, which are characteristics of DCM. Our results suggest that myocarditis and DCM associated with the presence of anti-M 2 R antibodies are autoimmune diseases with a risk of progressing to the terminal stage. Our mouse model will be useful in the analysis of the molecular mechanisms of disease progression and the development of new therapies for DCM. Keywords IntroductionDilated cardiomyopathy (DCM) causes severe heart failure in young adults including occasional sudden cardiac death. Mutations in genes encoding myocyte structural proteins are found in about 30-40% of DCM, but the etiology of the remaining 60-70% of cases is poorly understood [1][2][3]. Advances in the field of immunology have shed light on the close relationship between immunological disturbances and the progression of heart failure [4][5][6][7]. Adenovirus or enterovirus-specific RNA sequences are often detected in the myocardium of patients with DCM and myocarditis [7][8][9]. Myocardial-reactive antibodies such as those against β 1 adrenergic receptor (β 1 AR), M 2 muscarinic acetylcholine receptor (M 2 R), and cardiac myosin have also been observed in the sera of these patients [10][11][12][13][14]. As a result, it has been hypothesized that prolonged immunological abnormalities after myocarditis, presumably induced by a subclinical viral infection or autoimmunity, could lead to DCM [5,6]. Evidence supporting this hypothesis has accumulated through clinical and experimental studies [15][16][17].For example, immunization of animals with peptides derived from proteins expressed in cardiomyocytes such as β 1 AR [16,17] or cardiac myosin [15] or the transfer of antibodies against cardiac antigens mimics the prolonged immune abnormalities observed after acute myocarditis [18,19]. However, the progression from myocarditis to DCM has not been investigated in detail. The causes of the initial myocardial damage and subsequent cardiac dysfunction along with the subsequent role of autoimmunity in DCM are still unclear.The pathophysiological role of autoantibodies in disease progression has been established in only some autoimmune diseases such as pemphigus vulgaris (PV), involving anti-desmoglein 3 (Dsg3) antibodi...

Mitochondrial Ultrastructural Alterations and Declined M2 Receptor Density Were Involved in Cardiac Dysfunction in Rats after Long Term Treatment with Autoantibodies against M2 Muscarinic Receptor

“…However, the pathophysiological roles of M 2 -AA in the development of DCM need further exploration. In the present model, long-term presence of M 2 -AA can lead to DCM-like morphological changes especially the right ventricular dilation, which is consistent with previous reports [5]. In addition, M 2 -AA can gradually deteriorate cardiac systolic and diastolic function.…”

“…A previous study demonstrated that M 2 -AA could recognize the second extracellular loop of the M 2 muscarinic receptor (M 2 AChR-el2) and stimulate the muscarinic receptor on rats’ heart membrane [4]. Recent studies also indicated that M 2 -AA was responsible for DCM-like morphological changes in mice that were immunized with M 2 receptor for 8 weeks [5]. However, whether long term exposure to M 2 -AA can worsen cardiac function during progression of DCM remains largely unknown.…”

Autoantibodies and Cardiovascular Dysfunction: Cause or Consequence?

“…M 2 R-AAbs extracted from DCM patients induced a significant decrease in Ca 2+ currents [39], negative chronotropic effect in vitro [37] and supraventricular arrhythmia ex vivo [38] which were blocked by M 2 antagonist [38,39] or a synthetic peptide derived from the second extracellular loop of M 2 R [38]. M 2 R-AAbs were also detected along with the induction of DCM-like morphology in the heart of mice receiving adoptive transfer of splenocytes from M 2 R null mice immunized with synthetic M 2 R peptide [40]. In addition, AAbs from these mice induced a significant decrease in Ca 2+ currents in ventricular cardiomyocytes, which was blocked by M 2 R antagonists or synthetic M 2 R peptides [40].…”

“…M 2 R-AAbs were also detected along with the induction of DCM-like morphology in the heart of mice receiving adoptive transfer of splenocytes from M 2 R null mice immunized with synthetic M 2 R peptide [40]. In addition, AAbs from these mice induced a significant decrease in Ca 2+ currents in ventricular cardiomyocytes, which was blocked by M 2 R antagonists or synthetic M 2 R peptides [40]. Clinically the presence of M 2 R-AAbs was strongly and independently associated with the comorbidity of atrial fibrillation [38], and may serve as an independent predictor for the recurrence of atrial fibrillation after catheter ablation [41].…”

An experimental approach to study the function of mitochondria in cardiomyopathy

“…Autoimmunity has been considered as one of major causes for idiopathic DCM (23) , and high titers of autoantibodies (M 2 -AA) against the second extracellular loop of the M 2 muscarinic receptor (M 2 AChR-el2) has been found in serum of patients with idiopathic DCM (24) . Animal models have been established by immunizing rats (25 , 26) or mice (27) with synthetic M 2 AChR-el2 peptide to induce DCM-like morphological changes in the animals’ heart. M 2 AChR-el2-immunized rat heart showed decreased systolic and diastolic function with swollen and damaged mitochondria (26) .…”