Stiff person syndrome-associated autoantibodies to amphiphysin mediate reduced GABAergic inhibition

Abstract

Synaptic inhibition is a central factor in the fine tuning of neuronal activity in the central nervous system. Symptoms consistent with reduced inhibition such as stiffness, spasms and anxiety occur in paraneoplastic stiff person syndrome with autoantibodies against the intracellular synaptic protein amphiphysin. Here we show that intrathecal application of purified anti-amphiphysin immunoglobulin G antibodies induces stiff person syndrome-like symptoms in rats, including stiffness and muscle spasms. Using in vivo recordings of Hoffmann reflexes and dorsal root potentials, we identified reduced presynaptic GABAergic inhibition as an underlying mechanism. Anti-amphiphysin immunoglobulin G was internalized into neurons by an epitope-specific mechanism and colocalized in vivo with presynaptic vesicular proteins, as shown by stimulation emission depletion microscopy. Neurons from amphiphysin deficient mice that did not internalize the immunoglobulin provided additional evidence of the specificity in antibody uptake. GABAergic synapses appeared more vulnerable than glutamatergic synapses to defective endocytosis induced by anti-amphiphysin immunoglobulin G, as shown by increased clustering of the endocytic protein AP180 and by defective loading of FM 1-43, a styryl dye used to label cell membranes. Incubation of cultured neurons with anti-amphiphysin immunoglobulin G reduced basal and stimulated release of γ-aminobutyric acid substantially more than that of glutamate. By whole-cell patch-clamp analysis of GABAergic inhibitory transmission in hippocampus granule cells we showed a faster, activity-dependent decrease of the amplitude of evoked inhibitory postsynaptic currents in brain slices treated with antibodies against amphiphysin. We suggest that these findings may explain the pathophysiology of the core signs of stiff person syndrome at the molecular level and show that autoantibodies can alter the function of inhibitory synapses in vivo upon binding to an intraneuronal key protein by disturbing vesicular endocytosis.

Synaptic Vesicle-Recycling Machinery Components as Potential Therapeutic Targets

“…Inhibitory GABAergic synapses are more vulnerable than glutamatergic synapses to the impaired clathrin-mediated endocytosis induced by anti-amphiphysin antibodies (Geis et al, 2010;Werner et al, 2016).…”

Measuring Spinal Presynaptic Inhibition in Mice By Dorsal Root Potential Recording <em>In Vivo</em>

“…peripheral inflammation and neuropathic pain 13,14 , as well as abnormal central pain processing 15 , spinal cord injury 16 , and CNS disease with motor hyperexcitability mediated by defective GABAergic transmission 17,18 . Thus, estimating presynaptic inhibition is worthwhile to investigate experimental pathological conditions on the spinal cord level in vivo.…”

Anti-B-Cell Therapies in Autoimmune Neurological Diseases: Rationale and Efficacy Trials

“…Increased B cell and anti-GAD65 IgG+ memory B cell numbers have been reported in SPS [80], and the hallmark of the disease is the presence of autoreactive anti-GAD, antiamphiphysin or antiglycine receptor antibodies [81,82].…”