Although acetylcholinesterase (AChE) is primarily a hydrolytic enzyme, metabolising the neurotransmitter acetylcholine in cholinergic synapses, it also has some non-catalytic functions in the brain which are far less well characterised. AChE was shown to be secreted or shed from the neuronal cell surface like several other membrane proteins, such as the amyloid precursor protein (APP). Since AChE does not possess a transmembrane domain, its anchorage in the membrane is established via the Proline Rich Membrane Anchor (PRiMA), a transmembrane protein. Both the subunit oligomerisation and membrane anchor of AChE are shared by a related enzyme, butyrylcholinesterase (BChE), the physiological function of which in the brain is unclear. In this work, we have assayed the relative activities of AChE and BChE in membrane fractions and culture medium of three different neuronal cell lines, namely the neuroblastoma cell lines SH-SY5Y and NB7 and the mouse basal forebrain cell line SN56. In an effort to understand the shedding process of AChE, we have used several pharmacological treatments, which showed that it is likely to be mediated in part by an EDTA- and batimastat-sensitive, but GM6001-insensitive metalloprotease, with the possible additional involvement of a thiol isomerase. Cellular release of AChE by SH-SY5Y is significantly enhanced by the muscarinic acetylcholine receptor (mAChR) agonists carbachol or muscarine, with the effect of carbachol blocked by the mAChR antagonist atropine. AChE has been implicated in the pathogenesis of Alzheimer's disease and it has been shown that it accelerates formation and increases toxicity of amyloid fibrils, which have been closely linked to the pathology of AD. In light of this, greater understanding of AChE and BChE physiology may also benefit AD research.

Article Characterisation of acetylcholinesterase release from neuronal cells

It would be very intersting for many to see a copy of the paper by Hicks et al (2012) added in ResearchGate. Therefore, I have bookmarked it. This is due in part because we have studied AChE release for years, and demostrated that it occurs in almost every species studied, and under a wide variety of physiological and pharmacological stimuli scenario(s). We have also shown that AChE release can precede neurotoxicity and perhaps contribute to chronic degeneration upon acute excitotoxicity (Rodríguez-Ithurralde (RI) et al., 1995, 1996,1997, 1998: please see ResearchGate). We have shown, for instance, that in the mouse spinal cord slice, AChE globular forms, mainly G4, represent more than 90% of the AChE dose-dependently liberated by the ventral horn neurones (RI et al 1995),

As Ulises Ricoy says, "AChE has been implicated in the pathogenesis of Alzheimer's disease and it has been shown that it accelerates formation and increases toxicity of amyloid fibrils" and therefore "greater understanding of AChE and BChE physiology may also benefit AD research." Although AChE appears to play a role in dendrite growth and synapse development and plasticity (Olivera et al. 2003; Mol. Cell. Neurosci 23:96-106) excessive AChE release is able to trigger both glial and microglial reactions that can lead to chronic neurodegeneration (R.I. et al. 1998; J Neurol. Sci. 160: S80-S86).

Article Acetylcholinesterase promotes neurite elongation, synapse fo...

Article Motor neurone acetylcholinesterase release precedes neurotox...

Thank you very much Daniel Rodriguez-Ithurralde, I am working with a colleague at Northern New Mexico College (Dr. David Torres) where we are modeling the Reaction-Diffusion System of AChE in various synaptic geometries.

Article Spectral Element Simulation of Reaction-Diffusion System in ...

Yes Acetycholineesterase ( AChE) is  exclusively bound to the membrane.  

That is very interesting...What about the stability of this bounding to pharmacological action? How much confident can we be about this?   Diffusion can be very rapid and be hard to measure (but it can be perhaps estimated computationally)...

We use partial differential equations (PDEs)  to model the neuromuscular junction (NMJ).  The partial differential equations model the diffusion of the neurotransmitter acetylcholine and the reaction of acetylcholine with acetylcholinesterase.  Equations also model the generation of the Michaelis ligand-substrate complex and its conversion to acylate enzyme followed by the re generation of acetylcholinesterase.

There are many molecular forms of AChE, some of them are soluble. There are soluble molecular forms both intra- AND extracellularly. The soluble globular forms, when released either synaptically or extra-synaptically, they must last in the cleft for some time before they traffic or are degraded. On the other hand, I used to know that at the neuromuscular junction, asymmetrical forms of AChE (mainly A12) are bound to the presynaptic membrane and to the extracellular matrix. With regard to the kinetics aspect, it is important to remember that tight binders to AChE do not behave as Michaelis-Menten equations predict..

 These publications may also be of interest...

Danielle, thank you very much for your contribution to the discussion with these two very interesting articles. It is also of interest to look at Hicks et al 2013.

Article Characterisation of acetylcholinesterase release from neuronal cells

Danielle, I also thank you for your contribution.  "However, the main splice form of AChE in brain lacks a trans- membrane peptide anchor region and is bound to the ‘proline- rich membrane anchor’, PRiMA, in lipid rafts" (Hicks et al., 2010).  "In the central nervous system, acetylcholinesterase (AChE) is present in a tetrameric form that is anchored to membranes via a proline-rich membrane anchor (PRiMA)" (Henderson et al., 2010). 

As Henderson et al. (2010) pointed out, research "on live brain tissue, both in vivo and in vitro, indicate that" "the predominant form of AChE in mammalian brain", i.e., the G4-PRiMA form (Perrier et al., 2003), "can be released from neuronal tissue as a hydrophilic, soluble form upon electrical, pharmacological or behavioral stimulation."  We have shown dose- and calcium-dependent release of the G4 form of AChE upon glutamate receptor stimulation, both from the "in vitro" spinal cord slice and in vivo (Rodríguez-Ithurralde et al., 1995, 1996, 1997, 1998). We found a similarly dose-gradded release (we like release more than "shedding") upon pharmacological stimulation of the hippocampus and many other CNS areas from rodents, birds and anfibia. As Henderson et al. (2010) has proposed "It will therefore be of paramount interest to determine which of these proposed AChE-release mechanisms predominate in the different AChE-rich areas of the brain. If the stimulated shedding mechanism of AChE is demonstrated to occur widely in the central nervous system, this would suggest that the transmembrane protein PRiMA possesses a shedding site that would allow for the regulation of AChE secretion via intracellular second messenger systems."

You can find more points of view related to "New" or "non traditional" roles of AChE en the following question I have made, in the folowing link to RG page: https://www.researchgate.net/post/Can_acetylcholinesterase_AChE_release_contribute_to_neurodegeneration_even_to_Alzheimers_disease_prion_diseases_or_motor_neuron_disease