AbstractSynaptic strength depends on the number of cell-surface neurotransmitter receptors in dynamic equilibrium with intracellular pools. Dysregulation of this homeostatic balance occurs e.g. in myasthenia gravis, an autoimmune disease characterized by a decrease in the number of postsynaptic nicotinic acetylcholine receptors (nAChRs). Monoclonal antibody mAb35 mimics this effect. Here we use STORM nanoscopy to characterize the individual and ensemble dynamics of mAb35-crosslinked receptors in the clonal cell line CHO-K1/A5, which robustly expresses adult muscle-type nAChRs. Antibody labeling of live cells results in 80% receptor immobilization. The remaining mobile fraction exhibits a heterogeneous combination of Brownian and anomalous diffusion. Single-molecule trajectories exhibit a two-state switching behavior between free Brownian walks and anticorrelated walks within confinement areas. The latter act as permeable fences (∼34 nm radius, ∼400 ms lifetime). Dynamic clustering, trapping and immobilization also occur in larger nanocluster zones (120-180 nm radius) with longer lifetimes (11 ± 1 s), in a strongly cholesterol-sensitive manner. Cholesterol depletion increases the size and average duration of the clustering phenomenon; cholesterol enrichment has the opposite effect. The disclosed high proportion of mAb35-crosslinked immobile receptors, together with their anomalous, cholesterol-sensitive diffusion and clustering, provides new insights into the antibody-enhanced antigenic modulation that leads to physiopathological internalization and degradation of receptors in myasthenia.A preliminary version of this work has appeared in the biorXiv repository: https://www.biorxiv.org/content/10.1101/744664v1. The study was not pre-registered.
Single-Molecule Imaging of AMPA and Nicotinic Acetylcholine Receptors in Mammalian Cells