Induction Of Myasthenia Gravis By Anti-LRP4 Antibodies

Objective:To explore the pathogenicity of anti-low density lipoprotein receptor-related protein 4 (LRP4) antibody (LRP4Ab) by establishing an experimental autoimmune myasthenia gravis (EAMG) model to determine whether LRP4Ab can damage the structure and function of neuromuscular junction (NMJ) in the LRP4 myasthenia gravis (LRP4-MG).Methods:10 female Balb/c mice were randomly divided into experimental group and control group. Experimental group animals were injected intraperitoneally with a dose of LRP4Ab dissolved in sterile PBS, while control group mice were injected with the pure sterile PBS solution, once a day. After 5 times administration, all animals were executed on the sixth day. Gastrocnemius muscle tissues were used to make the frozen sections. The sections were treated with tetramethylrhodamine-alpha-Bungarotoxin (TR-BTX) and FITC conjugated secondary antibody, and observed under Confocal Laser Scanning Microscope (CLSM), Furthermore, transmission electron microscope (TEM) analysis was performed to investigate NMJ ultrastructural changes in LRP4Ab-injected mice.Results:During the administration procedure, the activity of 40% animals in the experimental group decreased, however it didn’t change in the control group. When the administration programme finished, all animals in the experiment group died, while all were alive in the control group. Both red and green fluorescence were observed under CLSM in the experimental group, indicating that LRP4Ab had bound to the antigen LRP4 in NMJ, which was demonstrated by the binding of TR-BTX to acetylcholine receptor (AChR) located in NMJ. The TEM observation showed that the NMJ were simplified and half-baked, synapse had few shallow junctional folds and rare synaptic vesicles, the postsynaptic membrane were irregular, discontinous and vagues, and the presynaptic membrane only had rare degenerate dispersed axon terminals in experiment group, compared with the normal structure in control group.Conclusion:The LRP4Ab can specifically bind to antigen LRP4 in NMJ, result in postsynaptic membrane structure changes and EAMG clinical symptom, such as muscle fatigue, demonstrating that LRP4Ab are pathogenic to induce MG.