Modulation Of Neuronal Channels and Receptors in the Brain

National Institute Of Environmental Health Sciences

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Abstract

There have been several major accomplishments within the past fiscal year, with many manuscripts in revision or in preparation. In collaboration with the CARD program of the NIA/NIH, we are studying how viral infections, which have been implicated in neurodegenerative disorders, may alter neuronal function. For this we differentiated human induced pluripotent stem cells (KOLF2.1J) into mature neurons to investigate virus-induced proteomic changes following infection with five neurotropic endemic human viruses: Herpes simplex virus 1 (HSV-1), Human coronavirus 229E (HCoV-229E), Epstein-Barr virus (EBV), Varicella-Zoster virus (VZV), and Influenza A virus (H1N1). Given that these viruses can infect adults and have the potential to cross the placental barrier, their molecular impact on neurons may be relevant across the lifespan. Using mass spectrometry-based proteomics with a customized library for simultaneous detection of human and viral proteins, we confirmed successful infections and identified virus-specific proteomic signatures. Notably, virus-induced protein expression changes converged on key neuronal pathways, including those associated with neurodegeneration. Gene co-expression network analysis identified protein modules correlated with viral proteins. Pathway enrichment analysis of these modules revealed associations with the nervous system, including pathways linked to Alzheimer's and Parkinson's disease. Remarkably, several viral-induced proteomic alterations overlapped with changes observed in postmortem Alzheimer's patient brains, suggesting a mechanistic connection between viral exposure and neurodegenerative disease progression. These findings provide molecular insights into how common viral infections perturb neuronal homeostasis and may contribute to neurodegenerative pathology, highlighting the need to consider endemic viruses as potential environmental risk factors in neurological disorders. A manuscript is currently under revision for submission to a high impact journal. Secondly, cholinergic regulation of hippocampal theta oscillations has long been proposed to be a potential mechanism underlying hippocampus-dependent memory encoding processes. The medial septum plays a central role in generating hippocampal theta oscillations. Optogenetic studies show that medial septal parvalbumin (PV) positive neurons and glutamatergic neurons have the capacity to entrain hippocampal oscillations within the theta range, supporting a potential role in theta frequency generation. However, if and how these septal neuronal subpopulations contribute to the generation of endogenous theta oscillations is not well understood. In this study, we addressed this question by up- or down-regulating septal neuronal subpopulations with Designer Receptors Activated Only by Designer Drugs (DREADDs) in mice during open field exploration. In addition, we selectively knocked out M1 muscarinic acetylcholine receptors (mAChRs), a7 nicotinic AChRs (nAChRs), or NMDA receptor NR1 in these neuronal subpopulations to reveal the neurotransmitter systems involved in theta regulation. We found that activation of either excitatory or inhibitory neurons increased theta power and reduced theta frequency. Inhibition of either population had no significant effects on theta frequency, while inhibition of inhibitory neurons, but not excitatory neurons, reduced theta power. Activation or inhibition of PV neurons up- or down-regulated theta power, respectively, with no significant effects on theta frequency. Knocking out a7 nAChRs, but not M1 mAChRs, in inhibitory or PV neurons largely reduced theta power. Knocking out NR1 in these neurons also partially reduced theta power. These results suggest that medial septal excitatory and inhibitory neurons do not actively regulate endogenous theta frequency under normal condition. Inhibitory neurons, especially PV neurons, do actively regulate theta power, likely through engaging a7 nAChRs and NR1. This work is also currently under revision for submission to a high-impact journal. Thirdly, in collaboration with the Jose Lasalde lab at the University of Puerto Rico, we have been studying how the SARS-CoV-2 spike protein modulates α7 nAChR anti-inflammatory signaling in human macrophages. We found that physiopathological concentrations of SARS‑CoV‑2 spike protein decrease surface α7‑nAChR expression in macrophages, the spike protein promotes the redistribution of α7-nAChRs, and that nicotine pretreatment protects against SARS-CoV-2 spike protein-induced loss of α7-nAChR expression. In understanding how viral components like the spike protein and microbial translocation affect this pathway may offer novel therapeutic targets for mitigating COVID-19-related inflammation. This work is currently being written up for submission to a high-impact journal. Lastly, we have also undertaken a mesoscopic analysis of GABAergic marker expression in acetylcholine neurons in the whole mouse brain in collaboration with colleagues at the NIMH/NIH. These neurons coordinate neural network activity that is required for higher brain functions, and disturbances in cholinergic signaling have been described in many disease including Alzheimer’s Disease. We are particularly interested in a subset of cholinergic neurons that also express for the inhibitory neurotransmitter GABA. We have found that a large subset of cholinergic neurons synthesize GABA and therefore have a partial GABAergic fate. We conclude that GABA co-transmission likely occurs from a small population of cholinergic neurons. A manuscript is currently being prepared.