A deep learning-based approach to model anomalous diffusion of membrane proteins: the case of the nicotinic acetylcholine receptor

Fluorescence Studies of Nicotinic Acetylcholine Receptor and Its Associated Lipid Milieu: The Influence of Erwin London's Methodological Approaches

Erwin London dedicated considerable effort to understanding lipid interactions with membrane-resident proteins and how these interactions shaped the formation and maintenance of lipid phases and domains. In this endeavor, he developed ad hoc techniques that greatly contributed to advancements in the field. We have employed and/or modified/extended some of his methodological approaches and applied them to investigate lipid interaction with the nicotinic acetylcholine receptor (nAChR) protein, the paradigm member of the superfamily of rapid pentameric ligand-gated ion channels (pLGIC). Our experimental systems ranged from purified receptor protein reconstituted into synthetic lipid membranes having known effects on receptor function, to cellular systems subjected to modification of their lipid content, e.g., varying cholesterol levels. We have often employed fluorescence techniques, including fluorescence quenching of diphenylhexatriene (DPH) extrinsic fluorescence and of nAChR intrinsic fluorescence by nitroxide spin-labeled phospholipids, DPH anisotropy, excimer formation of pyrene-phosphatidylcholine, and Förster resonance energy transfer (FRET) from the protein moiety to the extrinsic probes Laurdan, DPH, or pyrene-phospholipid to characterize various biophysical properties of lipid-receptor interactions. Some of these strategies are revisited in this review. Special attention is devoted to the anionic phospholipid phosphatidic acid (PA), which stabilizes the functional resting form of the nAChR. The receptor protein was shown to organize its PA-containing immediate microenvironment into microdomains with high lateral packing density and rigidity. PA and cholesterol appear to compete for the same binding sites on the nAChR protein.

Neuronal Menin Overexpression Rescues Learning and Memory Phenotype in CA1-Specific α7 nAChRs KD Mice

The perturbation of nicotinic cholinergic receptors is thought to underlie many neurodegenerative and neuropsychiatric disorders, such as Alzheimer's and schizophrenia. We previously identified that the tumor suppressor gene, MEN1, regulates both the expression and synaptic targeting of α7 nAChRs in the mouse hippocampal neurons in vitro. Here we sought to determine whether the α7 nAChRs gene expression reciprocally regulates the expression of menin, the protein encoded by the MEN1 gene, and if this interplay impacts learning and memory. We demonstrate here that α7 nAChRs knockdown (KD) both in in vitro and in vivo, initially upregulated and then subsequently downregulated menin expression. Exogenous expression of menin using an AAV transduction approach rescued α7 nAChRs KD mediated functional and behavioral deficits specifically in hippocampal (CA1) neurons. These effects involved the modulation of the α7 nAChR subunit expression and functional clustering at the synaptic sites. Our data thus demonstrates a novel and important interplay between the MEN1 gene and the α7 nAChRs in regulating hippocampal-dependent learning and memory.