The dynamics of recycled acetylcholine receptors at the neuromuscular junction in vivo

Abstract

At the peripheral neuromuscular junction (NMJ), a significant number of nicotinic acetylcholine receptors (AChRs) recycle back into the postsynaptic membrane after internalization to intermingle with not-yet-internalized 'pre-existing' AChRs. However, the way in which these receptor pools are maintained and regulated at the NMJ in living animals remains unknown. Here, we demonstrate that recycled receptors in functional synapses are removed approximately four times faster than pre-existing receptors, and that most removed recycled receptors are replaced by new recycled ones. In denervated NMJs, the recycling of AChRs is significantly depressed and their removal rate increased, whereas direct muscle stimulation prevents their loss. Furthermore, we show that protein tyrosine phosphatase inhibitors cause the selective accumulation of recycled AChRs in the peri-synaptic membrane without affecting the pre-existing AChR pool. The inhibition of serine/threonine phosphatases, however, has no effect on AChR recycling. These data show that recycled receptors are remarkably dynamic, and suggest a potential role for tyrosine dephosphorylation in the insertion and maintenance of recycled AChRs at the postsynaptic membrane. These findings may provide insights into longterm recycling processes at less accessible synapses in the central nervous system in vivo.

Myosin Va cooperates with PKA RIα to mediate maintenance of the endplate in vivo

“…The high enrichment of AChRs in the postsynapse is regulated by accurate targeting and turnover of this receptor. Vesicular transport is employed for this purpose, using different routes of exocytosis, endocytosis, and recycling (7)(8)(9). We identified myosin Va as the first motor protein involved in AChR trafficking and have found it to facilitate its recycling (4).…”

Molecular Changes at the Post-Synapse and Improved Motor Function Suggest Accelerated Recovery with SARM Treatment in an Androgen-Depleted Animal Model of Nerve Injury

“…The healthy NMJ is constantly turning over as it reforms and modifies. A major component of the NMJ's dynamic nature is the process of AChR removal and addition called acetylcholine receptor turnover [43]. Interplay between acetylcholine receptor density and acetylcholinesterase controls the efficacy of neuromuscular junctions.…”

Cellular trafficking of nicotinic acetylcholine receptors

“…The decrease in halftime appeared to reflect a combination of increased lateral dispersal of synaptic nAChRs and increased internalization. More recent studies using repeated in vivo imaging have provided evidence that nAChRs that are internalized at neuromuscular junctions can be recycled to the cell surface and reincorporated at the synapse [37] ; this recycling apparently requires synaptic activity [37] . It is interesting to note that recycled nAChRs are subsequently removed from the synapse more quickly than newly inserted nAChRs that were not (yet) recycled [37] , suggesting that recycled receptors are somehow tagged or in some way differ from "naive" receptors in their interactions with other proteins.…”

“…Proper recycling of nAChRs to the synapse may require the activity of a protein tyrosine phosphatase [37] . The latter finding appears to be consistent with earlier biochemical studies.…”