Autoimmune mechanisms elucidated through muscle acetylcholine receptor structures

Area of Science:

• Structural biology
• Neuroimmunology
• Molecular medicine

Background:

• Skeletal muscle contraction relies on acetylcholine (ACh) binding to nicotinic acetylcholine receptors (AChRs) at the neuromuscular junction.
• Myasthenia gravis (MG) is an autoimmune disorder where autoantibodies target AChRs, impairing neuromuscular transmission and causing muscle weakness.
• Understanding the structural basis of MG pathogenesis is crucial due to variable patient responses to existing therapies.

Purpose of the Study:

• To determine the high-resolution cryo-EM structures of the intact human adult AChR in various functional states.
• To map the epitopes of MG patient-derived autoantibodies and elucidate their pathogenic mechanisms.
• To investigate how these autoantibodies inhibit AChR function at a molecular level.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM) for structural determination.
• Utilizing six monoclonal antibodies derived from MG patients.
• Electrophysiological and binding assays to assess autoantibody effects on AChR function.

Main Results:

• Novel high-resolution cryo-EM structures of the human adult AChR were obtained.
• Distinct antibody epitopes were mapped, revealing diverse pathogenic mechanisms like receptor blockade, internalization, and complement activation.
• Autoantibodies were shown to directly inhibit AChR channel activation through electrophysiological and binding assays.

Conclusions:

• The study provides unprecedented structural insights into the immunopathogenesis of myasthenia gravis.
• Unrecognized antibody epitope diversity and novel modes of AChR inhibition by autoantibodies were uncovered.
• These findings offer a foundation for developing personalized therapeutic strategies for antibody-mediated autoimmune disorders like MG.