A human-specific, truncated α7 nicotinic receptor subunit assembles with full-length α7 and forms functional receptors with different stoichiometries

Lasala, Matías; Corradi, Jeremías; Bruzzone, Ariana; Esandi, María del Carmen; Bouzat, Cecilia

doi:10.1074/jbc.ra117.001698

Cited by 30 publications

(37 citation statements)

References 57 publications

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“…Lasala, et al also demonstrated that CHRFAM7A expression alters the assembly of the α7nAChR homopentamer in mammalian BOSC-23 kidney cells [16]. Utilizing a human kidney cell line, they showed that CHRFAM7A expression resulted in heteromeric receptors containing combinations of α7 and CHRFAM7A subunits.…”

Section: Discussionmentioning

confidence: 96%

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CHRFAM7A alters binding to the neuronal alpha-7 nicotinic acetylcholine receptor

Chan

Williams

Cohen

et al. 2019

Neuroscience Letters

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Introduction: CHRFAM7A is a uniquely-human gene that encodes a human-specific variant of the alpha-7 nicotinic acetylcholine receptor (α7nAchR). While the homopentameric α7nAchR consists of 5 equal subunits, previous studies demonstrated that CHRFAM7A expression disrupts the formation of α7nAchR homopentamers. Here we use a rat neuronal cell line expressing CHRFAM7A and a transgenic mouse expressing CHRFAM7A to define the alpha-bungarotoxin (α-BTX) binding in vitro and in vivo. Methods: Rat PC12 cells were stably transfected with human CHRFAM7A. α-BTX, a protein that irreversibly binds the α7nAchR, was utilized to assess the capacity for CHRFAM7A to interfere with α 7AchR subunits using immunohistochemistry and flow cytometry. To evaluate the effects of CHRFAM7A on α7nAchR at the neuromuscular junction in vivo, transgenic mice were engineered to express the uniquely human gene CHRFAM7A under the control of the EF1-α promoter. Using this model, muscle was harvested and CHRFAM7A and CHRNA7 gene expression evaluated by PCR. Binding of α-BTX to the α7nAchR in muscle was compared in sibling-matched wild-type C57 mice by immunostaining the neuromuscular junction using α-BTX and neurofilament antibodies. Results: Expression of CHRFAM7A in transfected, but not vector cells, was confirmed by PCR and by immunoblotting using an antibody we raised to a peptide sequence unique to CHRFAM7A. CHRFAM7A decreased α-BTX binding as detected by immunohistochemistry and flow cytometry. In vivo, α-BTX co-stained with neurofilament at the neuromuscular junction in wildtype mice, however, α-BTX staining was decreased at the neuromuscular junction of CHRFAM7A transgenic mice.

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Section: Discussionmentioning

confidence: 96%

“…Uniquely human CHRFAM7A is a partial duplication and rearrangement of the CHRNA7 gene that encodes the α7nAChR. Previous data suggests that CHRFAM7A expression may alter the structure of the α7nAChR [16]. CHRFAM7A expression is highly variable across individuals suggesting that α7nAChR function may be variable as well [9].…”

Section: Discussionmentioning

confidence: 99%

CHRFAM7A alters binding to the neuronal alpha-7 nicotinic acetylcholine receptor

Chan

Williams

Cohen

et al. 2019

Neuroscience Letters

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“…Allosteric activation of α7 through a transmembrane site has been shown for 4BP-TQS. However, the activity profile is strikingly different to that of ACh, which is not the case of Aβ (Gill et al, 2011; Lasala et al, 2018). Alternatively, Aβ may not occupy the five orthosteric agonist sites but may still be able to induce activation; the remaining sites, subsequently occupied by Carb, may favor activation and desensitization.…”

Section: Discussionmentioning

confidence: 99%

“…The open and closed time histograms obtained from idealization were fitted by the maximum interval likelihood (MIL) function in QuB (Qin et al, 1996, 1997), with a dead time of 0.1 ms. This analysis was performed by sequentially adding an open and/or closed state to a starting C ↔ O model in order to properly fit the corresponding histograms (Fabiani et al, 2018; Lasala et al, 2018). Final models contained five-six closed states and three-four open states for α7 in the presence of ACh plus PNU-120596, five-six closed states and three open states for α7 in the presence of ACh plus NS-1738, or three closed states and one-two open states for α7 in the presence of ACh and absence of PAMs.…”

Section: Methodsmentioning

confidence: 99%

Molecular Modulation of Human α7 Nicotinic Receptor by Amyloid-β Peptides

Lasala

Fabiani

Corradi

et al. 2019

Front. Cell. Neurosci.

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Amyloid β peptide (Aβ) is a key player in the development of Alzheimer’s disease (AD). It is the primary component of senile plaques in AD patients and is also found in soluble forms. Cholinergic activity mediated by α7 nicotinic receptors has been shown to be affected by Aβ soluble forms. To shed light into the molecular mechanism of this effect, we explored the direct actions of oligomeric Aβ1–40 and Aβ1–42 on human α7 by fluorescence spectroscopy and single-channel recordings. Fluorescence measurements using the conformational sensitive probe crystal violet (CrV) revealed that in the presence of Aβ α7 undergoes concentration-dependent conformational changes. Exposure of α7 to 100 pM Aβ changes CrV KD towards that of the desensitized state. However, α7 is still reactive to high carbamylcholine (Carb) concentrations. These observations are compatible with the induction of active/desensitized states as well as of a novel conformational state in the presence of both Aβ and Carb. At 100 nM Aβ, α7 adopts a resting-state-like structure which does not respond to Carb, suggesting stabilization of α7 in a blocked state. In real time, we found that Aβ is capable of eliciting α7 channel activity either in the absence or presence of the positive allosteric modulator (PAM) PNU-120596. Activation by Aβ is favored at picomolar or low nanomolar concentrations and is not detected at micromolar concentrations. At high Aβ concentrations, the mean duration of activation episodes elicited by ACh in the presence of PNU-120596 is significantly reduced, an effect compatible with slow open-channel block. We conclude that Aβ directly affects α7 function by acting as an agonist and a negative modulator. Whereas the capability of low concentrations of Aβ to activate α7 could be beneficial, the reduced α7 activity in the presence of higher Aβ concentrations or its long exposure may contribute to the cholinergic signaling deficit and may be involved in the initiation and development of AD.

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“…The inverted gene is expressed at the RNA level [ 8 ], but protein prediction algorithms suggest that translation is unlikely due to Kozak fragment length [ 7 ]. CHRFAM7A gets incorporated into the α7 nAChR homopentamer based on gene dosage [ 9 , 10 ] and functions as a dominant negative modulator [ 5 , 6 ]. We previously showed that CHRFAM7A decreases α7 nAChR channel open probability and mitigates Aβ 1–42 uptake beyond physiological concentrations [11] .…”

Section: Introductionmentioning

confidence: 99%

CHRFAM7A: A human specific fusion gene, accounts for the translational gap for cholinergic strategies in Alzheimer's disease

et al. 2020

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Background Cholinergic neuronal loss is one of the hallmarks of AD related neurodegeneration; however, preclinical promise of α7 nAChR drugs failed to translate into humans. CHRFAM7A , a uniquely human fusion gene, is a negative regulator of α7 nAChR and was unaccounted for in preclinical models. Methods Molecular methods: Function of CHRFAM7A alleles was studied in vitro in two disease relevant phenotypic readouts: electrophysiology and Aβ uptake. Genome edited human induced pluripotent stem cells (iPSC) were used as a model system with the human context. Double blind pharmacogenetic study: We performed double-blind pharmacogenetic analysis on the effect of AChEI therapy based on CHRFAM7A carrier status in two paradigms: response to drug initiation and DMT effect. Mini Mental Status Examination (MMSE) was used as outcome measure. Change in MMSE score from baseline was compared by 2-tailed T-test. Longitudinal analysis of clinical outcome (MMSE) was performed using a fitted general linear model, based on an assumed autoregressive covariance structure. Model independent variables included age, sex, and medication regimen at the time of the first utilized outcome measure (AChEI alone or AChEI plus memantine), APOE4 carrier status (0, 1 or 2 alleles as categorical variables) and CHRFAM7A genotype. Findings The direct and inverted alleles have distinct phenotypes. Functional CHRFAM7A allele classifies the population as 25% non-carriers and 75% carriers. Induced pluripotent stem cell (iPSC) models α7 nAChR mediated Aβ neurotoxicity. Pharmacological readout translates into both first exposure ( p = 0.037) and disease modifying effect ( p = 0.0048) in two double blind pharmacogenetic studies. Interpretation CHRFAM7A accounts for the translational gap in cholinergic strategies in AD. Clinical trials not accounting for this uniquely human genetic factor may have rejected drug candidates that would benefit 25% of AD. Reanalyses of the completed trials using this pharmacogenetic paradigm may identify effective therapy. Funding:

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A human-specific, truncated α7 nicotinic receptor subunit assembles with full-length α7 and forms functional receptors with different stoichiometries

Cited by 30 publications

References 57 publications

CHRFAM7A alters binding to the neuronal alpha-7 nicotinic acetylcholine receptor

CHRFAM7A alters binding to the neuronal alpha-7 nicotinic acetylcholine receptor

Molecular Modulation of Human α7 Nicotinic Receptor by Amyloid-β Peptides

CHRFAM7A: A human specific fusion gene, accounts for the translational gap for cholinergic strategies in Alzheimer's disease

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