Autoantibodies to Agrin in Myasthenia Gravis Patients

To determine if patients with myasthenia gravis (MG) have antibodies to agrin, a proteoglycan released by motor neurons and is critical for neuromuscular junction (NMJ) formation, we collected serum samples from 93 patients with MG with known status of antibodies to acetylcholine receptor (AChR), muscle specific kinase (MuSK) and lipoprotein-related 4 (LRP4) and samples from control subjects (healthy individuals and individuals with other diseases). Sera were assayed for antibodies to agrin. We found antibodies to agrin in 7 serum samples of MG patients. None of the 25 healthy controls and none of the 55 control neurological patients had agrin antibodies. Two of the four triple negative MG patients (i.e., no detectable AChR, MuSK or LRP4 antibodies, AChR-/MuSK-/LRP4-) had antibodies against agrin. In addition, agrin antibodies were detected in 5 out of 83 AChR+/MuSK-/LRP4- patients but were not found in the 6 patients with MuSK antibodies (AChR-/MuSK+/LRP4-). Sera from MG patients with agrin antibodies were able to recognize recombinant agrin in conditioned media and in transfected HEK293 cells. These sera also inhibited the agrin-induced MuSK phosphorylation and AChR clustering in muscle cells. Together, these observations indicate that agrin is another autoantigen in patients with MG and agrin autoantibodies may be pathogenic through inhibition of agrin/LRP4/MuSK signaling at the NMJ

The cDNA of mouse skeletal muscle transcribe for both isoforms 1 and 2 of acetylcholine receptor alpha subunit

The mRNA isolated front mouse ocular and limb Muscle and human rabdomyosarcoma cell line TE671 was subjected to reverse transcriptase polymerase chain reaction (RT-PCR) using a specific primer pair for the extracellular domain of AChR-alpha subunit that transcribes both for P3A- (isoform 1) and P3A+ (isoform 2). The cDNA synthesized from mRNA by reverse transcription, transcribed both isoforms 1 and 2 from mRNA of mouse limb and ocular Muscle and human rabdomyosarcoma cell line TE671 as evidenced by agarose gel electrophoresis of polymerase chain reaction products. (C) 2005 Elsevier B.V. All rights reserved