Proteomic Investigation of Murine Neuronal α7-Nicotinic Acetylcholine Receptor Interacting Proteins

Proteome profile of the cerebellum from α7 nicotinic acetylcholine receptor deficient mice

The alpha7 nicotinic acetylcholine receptor (α7 nAChR; CHRNA7) is expressed in the nervous system and in non-neuronal tissues. Within the central nervous system, it is involved in various cognitive and sensory processes such as learning, attention, and memory. It is also expressed in the cerebellum, where its roles are; however, not as well understood as in the other brain regions. To investigate the consequences of absence of CHRNA7 on the cerebellum proteome, we performed a quantitative nano-LC-MS/MS analysis of samples from CHRNA7 knockout (KO) mice and corresponding wild type (WT) controls. Liver, an organ which does not express this receptor, was analyzed, in comparison. While the liver proteome remained relatively unaltered (three proteins more abundant in KOs), 90 more and 20 less abundant proteins were detected in the cerebellum proteome of the KO mice. The gene ontology analysis of the differentially abundant proteins indicates that the absence of CHRNA7 leads to alterations in the glutamatergic system and myelin sheath in the cerebellum. In conclusion, our dataset provides new insights in the role of CHRNA7 in the cerebellum, which may serve as a basis for future in depth-investigations.

Speculation on How RIC-3 and Other Chaperones Facilitate α7 Nicotinic Receptor Folding and Assembly

The process of how multimeric transmembrane proteins fold and assemble in the endoplasmic reticulum is not well understood. The alpha7 nicotinic receptor (α7 nAChR) is a good model for multimeric protein assembly since it has at least two independent and specialized chaperones: Resistance to Inhibitors of Cholinesterase 3 (RIC-3) and Nicotinic Acetylcholine Receptor Regulator (NACHO). Recent cryo-EM and NMR data revealed structural features of α7 nAChRs. A ser-ala-pro (SAP) motif precedes a structurally important but unique "latch" helix in α7 nAChRs. A sampling of α7 sequences suggests the SAP motif is conserved from C. elegans to humans, but the latch sequence is only conserved in vertebrates. How RIC-3 and NACHO facilitate receptor subunits folding into their final pentameric configuration is not known. The artificial intelligence program AlphaFold2 recently predicted structures for NACHO and RIC-3. NACHO is highly conserved in sequence and structure across species, but RIC-3 is not. This review ponders how different intrinsically disordered RIC-3 isoforms from C. elegans to humans interact with α7 nAChR subunits despite having little sequence homology across RIC-3 species. Two models from the literature about how RIC-3 assists α7 nAChR assembly are evaluated considering recent structural information about the receptor and its chaperones.

Drosophila nicotinic acetylcholine receptor subunits and their native interactions with insecticidal peptide toxins

Drosophila nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that represent a target for insecticides. Peptide neurotoxins are known to block nAChRs by binding to their target subunits, however, a better understanding of this mechanism is needed for effective insecticide design. To facilitate the analysis of nAChRs we used a CRISPR/Cas9 strategy to generate null alleles for all ten nAChR subunit genes in a common genetic background. We studied interactions of nAChR subunits with peptide neurotoxins by larval injections and styrene maleic acid lipid particles (SMALPs) pull-down assays. For the null alleles, we determined the effects of α-Bungarotoxin (α-Btx) and ω-Hexatoxin-Hv1a (Hv1a) administration, identifying potential receptor subunits implicated in the binding of these toxins. We employed pull-down assays to confirm α-Btx interactions with the Drosophila α5 (Dα5), Dα6, Dα7 subunits. Finally, we report the localisation of fluorescent tagged endogenous Dα6 during Drosophila CNS development. Taken together, this study elucidates native Drosophila nAChR subunit interactions with insecticidal peptide toxins and provides a resource for the in vivo analysis of insect nAChRs.

Effects of nicotine on DARPP-32 and CaMKII signaling relevant to addiction

Paul Greengard brought to neuroscience the idea of, and evidence for, the role of second messenger systems in neuronal signaling. The fundamental nature of his contributions is evident in the far reach of his work, relevant to various subfields and topics in neuroscience. In this review, we discuss some of Greengard's work from the perspective of nicotinic acetylcholine receptors and their relevance to nicotine addiction. Specifically, we review the roles of dopamine- and cAMP-regulated phospho-protein of 32kDa (DARPP-32) and Ca2+/calmodulin-dependent kinase II (CaMKII) in nicotine-dependent behaviors. For each protein, we discuss the historical context of their discovery and initial characterization, focusing on the extensive biochemical and immunohistochemical work conducted by Greengard and colleagues. We then briefly summarize contemporary understanding of each protein in key intracellular signaling cascades and evidence for the role of each protein with respect to systems and behaviors relevant to nicotine addiction.

[Establishment of a gp120 transgenic mouse model with α7 nAChR knockout]

OBJECTIVE

To construct a HIV-1 gp120 transgenic mouse model (gp120⁺) with α7 nicotinic acetylcholine receptor (α7nAChR) gene knockout.

METHODS

The α7nAChR gene knockout mice (α7R^-/-) were crossed with HIV-1gp120 transgenic mice (gp120⁺) to generate F1 generation mice. We selected the F1 mice with the genotype of α7R^+/-/gp120⁺ to mate to obtain the F2 mice. The genotypes of the F3 mice were identified by PCR, and the protein expressions in the double transgenic animal model was analyzed by immunohistochemistry. BV2 cells were treated with gp120 protein and α7nAChR inhibitor, and the expressions of IL-1β and TNF-α were detected using ELISA.

RESULTS

The results of PCR showed the bands of the expected size in F3 mice. Two F3 mice with successful double gene editing (α7R^-/-/gp120⁺) were obtained, and immunohistochemistry showed that the brain tissue of the mice did not express α7 nAChR but with high gp120 protein expression. In the in vitro cell experiment, treatment with gp120 promoted the secretion of IL-1β and TNF-α in BV2 cells, while inhibition of α7nAChR significantly decreased the expression of IL-1β and TNF-α (P < 0.001).

CONCLUSIONS

By mating gp120 Tg mice with α7R^-/- mice, we obtained gp120 transgenic mice with α7nAChR gene deletion, which serve as a new animal model for exploring the role of α7nAChR in gp120-induced neurotoxicity.