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.
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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...