Investigating the Mechanism Of Autoimmune Disease Associated LQTS; anti‐Ro52 IgG Decreases hERG Channel Density

Background The human ether‐a‐go‐go‐related gene (hERG) is the pore forming subunit of Kv11.1, which is responsible for the rapidly activating delayed rectifier potassium current (I Kr ). Reductions to I hERG through mutations or drug interactions can cause LQTS, which predisposes individuals to ventricular arrhythmia's and sudden cardiac death. hERG has been speculated to be involved in autoimmune disease‐associated LQTS, however the mechanism is poorly understood. In 2006, a Japanese group reported an anti‐Ro52 IgG positive patient with LQTS and accompanying torasdes de pointes. The patient's serum was found to reduce the human ether‐a‐go‐related gene (hERG) channel density in a stable cell line. The authors speculated that anti‐Ro52 underwent a cross reaction with hERG, leading the production of anti‐hERG IgG. Here we investigate in detail this proposed mechanism, and provide strong evidence that anti‐Ro52 IgG reduces hERG channel density and current. Methods Human embryonic kidney (HEK 293) cell lines stably expressing the channel of interest were treated with anti‐Ro52 IgG (Sigma, 4 μg/ml) for 24 h, while saline treated cells served as control. Western blot analysis was used to quantify changes in protein expression, and whole cell patch clamp was performed to quantify changes in current. Results We report that anti‐Ro52 IgG reduced hERG channel density and current. This was unique to hERG in that Kv1.5 and EAG channel density and current were not affected by IgG. Replacing the extracellular S5‐pore linker with that of EAGs instilled immunity to IgG treatment. Furthermore, anti‐Ro52 IgG treatment reduced IKr in rat neonatal cardiomyocytes, significantly increased the APD90, but did not affect other native currents. Our data suggest that IgG decreased hERG membrane expression through inducing channel internalization. Digestion of anti‐Ro52 and isolation of the Fab and Fc fragments revealed that the Fc region of IgG is responsible for reducing hERG. Finally, we are currently testing the effects of IgG positive and negative autoimmune patient serum on the QTc interval of rabbits. Conclusion Our findings provide strong evidence that anti‐Ro52 IgG is responsible for autoimmune disease associated‐LQTS, which mechanistically occurs through a reduction of the hERG current due to IgG‐mediated channel internalization. Support or Funding Information Funded by CIHR and Heart and Stroke

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