Autoantibody against β_1-adrenoceptor induces apoptosis of rat cardiomyocytes in vivo

Objective:By using a rat immunization model,we designed to investigate whether the autoantibody against β1-adrenoceptor(β1-AR) was capable of triggering apoptosis in cardiomyocytes in vivo and,if so,to explore the possible signaling pathway by which the autoantibody may contribute to myocardial apoptosis.Methods:Healthy Wistar rats without the autoantibody against β1-AR were chosen and immunized with the synthetic peptide corresponding to the sequence of second extracellular loop of β1-AR(9 weeks).The titers of the anti-β1-AR autoantibody were detected periodically using ELISA.Apoptosis in the cardiac tissue was assessed by TUNEL technique and agarose gel electrophoresis,the activities of caspase-3,8,9 were also detected by colorimetric assay,and the cardiac function was evaluated periodically.Results:(1)One week after initial immunization,the mean geometric titer of the antibody to β1-AR group was less than 1∶ 10.Subsequently,the mean antibody titer gradually raised to [1∶(1 280±0.07)] after intensified immunization and maintained on this level within 9 weeks.In contrast,the mean antibody titer of control group remained below 1∶ 10 during the whole immunization procedure.(2)TUNEL and agarose gel electrophoresis showed significant cardiomyocyte apoptosis on 3rd,4th,5th weeks after immunization in the β1-AR group,the activities of caspase-3 and caspase-8 were found increased.Cardiac function at 7 to 9 weeks after immunization decreased remarkably.However,no abnormality could be seen in control group.Conclusion:These results demonstrate that the autoantibody could induce cardiomyocyte apoptosis in vivo via death-receptor pathway,and suggest that the autoantibody may be involved in pathogenesis of cardiac dysfunction.