C3 complement silencing prevents acetylcholine receptor loss and reduces complement activation in the rat passive transfer myasthenia gravis model

Acetylcholine receptor antibody-positive myasthenia gravis (AChR-MG) is a rare autoimmune disease in which AChR autoantibodies trigger complement activation and cause damage to the neuromuscular junction. In this study, the passive transfer myasthenia gravis (PTMG) rat model was used to investigate whether silencing hepatic C3 expression with a triantennary N-acetylgalactosamine (GalNAc)-targeted, C3 small interfering (si)RNA, could prevent neuromuscular damage and disease symptoms in the acute phase of MG. Female Lewis rats were injected subcutaneously with different dosages of C3-siRNA prior to PTMG induction with anti-AChR mAb35. Readout parameters included clinical scoring, muscle strength tests, electromyography, analysis of total muscle AChR and its functional levels, muscle macrophage infiltration, muscle C3 mRNA expression and complement activation at the neuromuscular junction. Two administrations of C3-siRNA (30 mg/kg, 1-week interval) reduced plasma C3 levels below detection limit (> 98% reduction). In PTMG rats, this significantly reduced complement-mediated injury at the neuromuscular junction, as evidenced by reduced membrane attack complex deposition. Treatment also decreased sectional necrosis and macrophage infiltration within the motor endplate region, reduced skeletal muscle C3 mRNA upregulation, partially preserved functional AChR levels, and effectively attenuated the development of muscle weakness, as demonstrated by muscle strength assessments and electromyography findings. Despite near total reduction of plasma C3, low levels of C3 and membrane attack complex were still detectable specifically at the neuromuscular junction. Collectively, these findings highlight the powerful pathogenic effect of C3 in AChR-MG even at very low levels and support the therapeutic potential of hepatic C3 silencing as potential an adjunctive therapeutic strategy for MG.