Transcriptomic and Epigenomic Investigation of Antidepressant and Non-Hallucinogenic Serotonin Receptor Agonists

PROJECT SUMMARY Roughly 15% and 8% of adults in the United States experience a substance use disorder or major depressive disorder, respectively. The psychedelic class of medicines with agonism at the serotonin 2A receptor has shown promise for treatment of each of these; however, the often concomitant hallucinatory effects diminish their clinical utility, regulatory approval, and widespread adoption. A major question in the psychedelic field is whether the hallucinations can be separated from the antidepressant effects, or if they themselves confer therapeutic effects. The lab of Dr. Olson, a co-sponsor of this proposal, has developed a non-hallucinogenic serotonin receptor agonist, tabernanthalog (TBG), that shows preclinical antidepressant effects. The mechanisms of action of this small molecule are not completely understood. TBG has affinity for multiple receptors and pleiotropic actions within the brain. The availability of hallucinogenic and non-hallucinogenic compounds with shared therapeutic effects enables studies that to address a major question in the field: what are the commonalities and differences in drug-induced cellular and molecular responses between these classes of drugs. I will use paired snRNAseq and snATACseq as well as complementary histology and epignenomics assays to characterize the transcriptomic and epigenomic changes mediated by TBG and a hallucinogenic psychedelic, 5-Methoxy-Dimethyltryptamine (5-MeO-DMT) 24 hours after administration. I will test for cell type specific effects that are shared or differ between drugs and test if cellular responses are correlated with expression of the presumed relevant receptor protein, the serotonin 2a receptor. Specifically, I am focused on the synaptic and plasticity related genes that may drive the persistent therapeutic effects. There have been no reported studies applying these methods to non-hallucinogenic psychedelics, and most previous genetic studies focus on one or a limited set of genes. Finally, using paired snRNA and snATACseq will enable both cell-type specific resolution and linking transcriptomic and epigenetic changes. I will focus on synaptic/plasticity gene loci and attempt to distinguish signaling aspects that are common to both drugs (and thus potentially driving therapeutic effects). Additionally, I will test spatial organization of the responsive cells using RNA-FISH and perform histone CUT&RUN to test for chromatin state changes associated with accessibility and transcriptional regulation. This work will expand understanding of the mechanisms of action and the target cell types of these pleiotropic small molecule psychedelic drugs, and do so with multiomic modalities and systems-biology level of comprehensive analysis not previously attained. This proposal represents a cross-disciplinary effort linking pharmacology and genomics that brings powerful approaches to understanding basic cellular and molecular activities underlying promising psychedelic compounds for the treatment of MDD and other disorders, and these results will have further value towards development of next generation therapeutics.