Amyotrophic Lateral Sclerosis Immunoglobulins-G interact with calcium channels?

GONZALEZ, LAURA; VATTINO, LUCAS; KOTLER MÓNICA; REISIN, RICARDO; UCHITEL, OSVALDO

San Diego, California

Congreso; 40th Annual Meeting of the Society for Neuroscience; 2010

Society for Neuroscience

Amyotrophic Lateral Sclerosis (ALS) is an invariably fatal neurodegenerative disease that is characterized by a progressive loss of both superior and inferior motoneurons. The vast majority of ALS cases (90%) belong to a sporadic form whose etiology remains unknown. Several pieces of evidence support autoimmunity as a possible cause of ALS. Furthermore, we recently detected a diminished interaction of ALS antibodies with neuromuscular junction (NMJ) from alpha1A-deficient mice, compared to normal littermates.   The aim of our research was to evaluate the functional implication of suppressing alpha1A expression on ALS-Immunoglobulins G (IgGs) synaptic potentiation, as well as to analyze possible interactions between ALS antibodies and proteins present at the pre-synaptic terminal. We isolated IgGs from ALS sera by affinity chromatography and evaluated their functionality by recording spontaneous NMJ activity in both normal and alpha1A-deficient sv129 adult mice, after incubation with ALS-IgGs for 4h (0.4mg/ml). We also tested them in immunoprecipitation assays followed by western blotting with antibodies specific for pre-synaptic proteins. Diaphragm muscles dissected from wild-type animals and incubated with ALS-IgGs showed an increase in spontaneous synaptic activity compared to the beginning of the experiment (mean 0h: 0.39±0.05 Hz, mean 4h: 27±6 Hz, p<0.001, Mann-Whitney Rank Sum Test, n=9 NMJs). On the other hand, no effects were found in alpha1A-deficient mice, where miniature end-plate potential frequency did not change significantly after incubation time (mean 0h: 0.38±0.04 Hz, mean 4h: 0.31±0.04 Hz, p=0.216, Mann-Whitney Rank Sum Test, n=12 NMJs). However, these synaptic terminals retained their ability to respond to a potassium-induced depolarization by increasing their spontaneous activity. The analysis of synaptosomal proteins immunoprecipitated with ALS antibodies revealed the presence of the alpha1 subunit of the P/Q- and N-type calcium channels. Nevertheless, other synaptic proteins such as Synaptotagmin I, Synaptophysin, Synaptobrevin II and Syntaxin 1A did not interact with disease IgGs as they were not detected in the precipitated fraction. The results described in this research suggest that the sera of some patients contain auto-antibodies that interact either directly or indirectly with P/Q-type calcium channels, and that this interaction is relevant for IgG modulation of NMJ spontaneous activity.