PubMed: 22040696

Title
Chaperoning α7 neuronal nicotinic acetylcholine receptors.
Journal
Biochimica et biophysica acta
Volume
1818
Issue
None
Pages
718-29
Date
2012-03-01
Authors
Barrantes FJ | Vallés AS

Evidence 84d4391e71

AChRs have been linked to many neurodegenerative disorders [13,47–60].

Evidence 2319733475

BDNF can also influence the level of α7 AChRs subunits (Fig. 4) in the hippocampus and other brain regions [160,164,165].

Evidence 5e9ea1d65c

Since α7 AChRs are highly permeable to calcium [198] and increased calcium permeability is required for neuronal migration [199], neurons with less α7 AChRs would fail to migrate to their correct destinations [200] and be activated by acetylcholine.

Evidence 63a286a30f

Furthermore, nicotinic stimulation rapidly induced SNARE-dependent vesicular endocytosis accompanied by receptor internalization [166]. However, the number of surface α7 AChRs was not modified since a SNARE-dependent pro- cess also recruited receptors to the cell surface from internal pools (Fig. 5).

Evidence 650f1c1dd6

Recent studies have also demonstrated the importance of the phos- phatidylinositol 3-kinase (PI3K) pathway downstream of AChRs in pro- tecting neurons from death and up-regulating these receptors [148].

Evidence 35fbeb15f9

During acute in- flammatory processes α7 AChRs attenuate renal failure induced by ische- mia/reperfusion by inhibiting pro-inflammatory cytokine expression, and subsequently decreasing cell apoptosis [180,201].

Evidence a7aee4decd

One of the salient events at early stages of this disease (usually pre- clinical) is the impairment in hippocampus-based episodic memory which can be improved by enhancement of cholinergic transmission [191].

Evidence 8b26589a51

Regulation of receptor subunits by the proteasome, the large pro- tein complex that proteolytically degrades unneeded proteins, has also been demonstrated [113,114].

Evidence 6a89be9029

Furthermore, the proteasome in- directly regulates synaptic transmission mediated by AChRs via regu- lation of RIC-3 [113].

Evidence fde4dc806d

Another important event that associates well with the Alzheimer disease pathology is the aggregation of the β-amyloid peptide [53]. This peptide interacts with α7 AChRs and has been reported to affect the nor- mal functioning of the latter, causing reduced neuronal survival [146,192–194].

Evidence 35d07ef189

α7 AChRs can act at the presynaptic, postsynaptic or perisynaptic levels to facilitate the liberation of neurotransmitters, mediate synaptic transmission, or modulate the connections of different neurons by activating diverse second messenger routes [1,19,23–31].

Evidence 3f43056b45

Additionally, SNARE-dependent trafficking was required for α7 AChRs to be capable of activating the transcription factor cAMP response element-binding protein and attendant gene ex- pression when challenged.

Evidence bd6a8e1958

Reduction of α7 AChRs in the CNS is linked with Alzheimer dis- ease, which has been shown to lead to neuronal loss [53,188–190].

Evidence 1857487bf4

Decreased expression of α7 AChR has also been associated with schizophrenia [51,195–197].

Evidence 8a2d005e42

In adrenal medulla chromaffin cells the tyrosine kinases c-SRC and FYN associate with the α3β4 receptor and are involved in the cholinergic stimulation of catecholamine secretion [141,144,145].

Evidence 39534efc25

Although the mechanisms that regulate phosphorylation of AChRs are still essen- tially unknown, protein tyrosine phosphorylation by the SFKs has been shown to affect peripheral AChRs in various ways, depending on the tis- sue, subunit type and functional role of the receptors involved.

Evidence 11ada65525

In Torpedo electric organ, phosphorylation of AChRs by SFKs causes subtle changes in desensitization kinetics but not in I max , the maximal current flowing through the receptor channel [141–143].

Evidence bcc8b68082

More re- cently, the transmembrane protein resistant to inhibitors of cholines- terase (RIC-3), originally identified in Caenorhabditis elegans, has been classed as a much more selective chaperone of the AChR [71,107–112].

Evidence 2f16547f3d

Co-expression with RIC-3 was shown to be required for AChR ac- tivity in C. elegans body muscles and for enhanced AChR activity in Xenopus oocytes [110,112].

Evidence b8bd304e6a

Interestingly, levels of RIC-3 mRNA are elevat- ed in postmortem brains of individuals with bipolar disorder and schizophrenia [181], and a link has been suggested between defi- cient RIC-3 mediated chaperoning of an AChR subunit and individ- uals with bipolar disorder and psychotic symptoms [181].

Evidence 0c5a35f2c7

In C. elegans, RIC-3 is necessary for synaptic transmission mediated by neuronal AChRs but not by other LGICs [71,77,109].

Evidence 709048b0cf

In contrast, RIC-3 caused a marked inhibition of functional responses with hetero- meric α3β4 and α4β2 AChRs in Xenopus oocytes [109].

Evidence 779ef16698

Osman et al. [122] find that RIC-3 expression increases the total amount of α9 AChR in CL4 cells, supporting the view that RIC-3 regulates AChR trafficking by increasing the number of mature or correctly folded receptor subunits reaching the cell surface.

Evidence e16480057d

It is noteworthy that RIC-3 has been shown to increase α7 AChR heterologous expression both in X. laevis oocytes and in HEK-293, CHO and SHE-P1 mammalian cell lines [66,71,77,107–112,119,125].

Evidence 90bbfd1ecc

Specifically, it has been shown that upon stimulation, α7 AChR activates PI3K via direct association with non-receptor type tyrosine kinase FYN and Janus-activated kinase 2 (JAK2), promoting the survival of neuronal cells (Fig. 3).

Evidence f3fc8ccd80

Reduced expression of the lat- ter protein has been shown to be detrimental to AChR function in C. elegans [113] (See Fig. 2).

Evidence 980eecdd38

Co- expression of RIC-3 with the 5-HT 3 receptor in X. laevis oocytes totally abolishes 5-HT 3 surface expression [108,109].

Evidence 0f6f969a67

There is evidence that AChR folding, assembly and trafficking are influenced by several chaperone proteins, such as the 14-3-3 protein [92,93], BiP [94–96] or calnexin [97–99].

Evidence a18f18b784

Additionally, the pro- lyl isomerase enzyme cyclophilin has been shown to be necessary for efficient folding of the α7 subunit in Xenopus oocytes [85–88].

Evidence 5714b0808a

BDNF regulates development of neuronal structures both in the pe- ripheral and central nervous systems [150–155].

Evidence b031bf44ae

It has acute effects on the synapse, serving as an activity-dependent regulator of synaptic plas- ticity and participating in rapid synaptic transmission [150,151,156–159], in the maturation of GABAergic signaling and in the stabilization of newly formed synapses [151,160–163].

Evidence 091d60373d

Recent studies using dissociated rat hippocampal neurons in culture demonstrated that BDNF increases both surface and internal α7 AChRs pools.

Evidence 45e943e621

Tyrosine phosphorylation of α7 AChR was found to negatively regulate receptor activity in neuroblastoma cells, hippo- campal CA1 interneurons, and supraoptic magnocellular neurons, whereas de-phosphorylation of α7 AChR was found to potentiate ACh-evoked currents in these cells.

Evidence cfb799f0ae

A recent study showed that mutation of amino acids from this region (leucines 335, 336 or 343) to alanine reduced cell-surface expression of α7 AChRs [173].

Evidence f3fa749f7e

Rapsyn is essential for AChR clustering in muscle [100] and has also been detected in non-muscle cells, including neurons of the ciliary ganglia [101,102], fibroblasts [103], myocardial cells, and Leydig cells [104].

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