Research & Initiatives
Function of circular RNAs in reward and motivation
Genetic modifications during transcriptional splicing impart translational consequences on protein expression that can ultimately impact behavior. Such transcriptional events are complex and recent studies have indicated that there is far more regulation that splicing products are capable of than we currently understand. Specifically, circular RNAs (circRNAs) are singled-stranded splice products with closed 5’ and 3’ ends that can act as microRNA sponges, modulate transcriptional events and interfere with RNA splicing and protein polypeptide synthesis. CircRNAs can arise from linear coding mRNA sequences or noncoding RNA. CircRNAs are highly abundant in the brain, conserved from humans to rodents and enriched in neuronal synaptosomes. Thus, circRNAs are poised to contribute to synaptic function in the brain and in turn, the behavioral output that results from synaptic transmission. To begin to determine the contribution of circRNAs to behavioral phenotypes of neuropsychiatric disorders, we are examining circRNA expression in a rodent model of motivation and reward. Reward pathways involving the release of dopamine to cortical and limbic brain areas that regulate emotion, such as the nucleus accumbens and frontal cortex, are known to be altered in many neuropsychiatric disorders, including substance use disorder, schizophrenia, bipolar disorder and major depressive disorder. We utilize use a rodent model of sucrose self-administration to test the hypothesis that reward learning induces modulation of circRNA in the brain and that the continued motivation for rewarding substances can be supported by a unique profile of circRNAs. Completion of this project is expected to uncover novel and critical molecular mechanisms of gene expression regulation that are likely applicable to disciplines beyond the field of neuroscience and inform the science community of general circRNA pathways that function in biological systems.
Delineation of microRNA regulatory pathways
that support fentanyl-seeking behavior
With increased use of fentanyl or fentanyl-analog compounds in the United States, the opioid epidemic has evolved into a ‘fentanyl epidemic.’ Overdose deaths involving these extremely potent mu-opioid receptor (MOR) agonists have increased ~30-40-fold in the last 20 years. Moreover, in 2021, drug overdose deaths in the United States topped 100,000 for the first time ever and more than half of all deaths involved fentanyl or fentanyl analogs. Yet, the brain neuroadaptations induced by fentanyl and fentanyl analog exposure remain poorly described. Additionally, it is not known if the high amount of fentanyl-associated deaths are due to fentanyl being ‘more addictive’ than other opioids, or if fentanyl induces a unique set of neuroadaptations associated with increased opioid seeking. The limited literature describing molecular alterations following fentanyl exposure in comparison with other well-studied opioids such as morphine indicates divergency amongst MOR agonists for neuroadaptations involving microRNA (miRNA) regulation and gene expression. miRNAs inhibit protein translation to modulate gene expression and have recently emerged as critical regulators of drug seeking for many drug classes. miRNAs have additional utility as biomarkers because miRNAs are present in exosomes found in serum of peripheral blood samples. Investigation into the relationship between drug exposure and regulation of brain miRNAs that can also be detected in the periphery can be accomplished
easily with rodent models of self-administration but has yet to be done. In this project, we will use rat opioid self-administration to: 1) examine the acute and long-lasting effects of fentanyl or the ultra-potent analog furanylfentanyl on exosomal blood serum and orbitofrontal cortex (OFC) brain microRNA (miRNA) profiles; 2) compare the fentanyl-induced miRNA profiles to the less potent opioid heroin; 3) correlate fentanyl-induced blood and brain miRNA profiles to opioid seeking behavior at multiple timepoints; and 4) directly compare fentanyl-, furanylfentanyl- and heroin-induced drug seeking behavior at response-equivalent dosages to identify agonist-specific differences in long-lasting drug seeking behavior. This project will provide critical insight into both the immediate and long-lasting molecular consequences of fentanyl and furanylfentanyl exposure on brain neurochemistry and identify miRNA-mediated pathways associated with opioid seeking. Therefore, this study provides an essential opportunity to understand the relationship between blood and brain miRNA expression as an indication of opioid craving. Studies of blood miRNA profiles associated with drug seeking behavior have translational potential, as biomarkers indicative of recovery from substance use or relapse may help to inform patient care or treatment responsiveness.
Harnessing 5-HT2AR-targeting psychedelic compound psilocybin
to reduce opioid seeking and opioid-induced
neuroinflammatory signaling
The therapeutic potential of psychedelic compounds for the relief of perseverative maladaptive symptoms associated with neuropsychiatric disorders has highlighted the utility of compounds such as psilocybin for treatment of substance use disorders. However, the impact of psilocybin treatment on opioid relapse, as well as the molecular mechanism of psilocybin action in the brain, are currently unknown. In published studies, we demonstrated that psilocybin, a serotonin 2a receptor (5-HT2AR) agonist, reduces relapse to the addictive opioid heroin after forced abstinence from heroin self-administration. Psilocybin-mediated reduction of heroin seeking was accompanied by downregulation of the proinflammatory cytokine Il17a in the prefrontal cortex (PFC), a key brain that modulates drug reward that is also sensitive to psilocybin treatment. Transcriptome profiling demonstrated that the IL-17 signaling pathway is enriched in heroin-exposed rats and a single exposure to psilocybin in drug-naïve rats modulates gene pathways that regulate cytokine signaling in the frontal cortex. Furthermore, our published study reported that selective inhibition of PFC IL-17a signaling with a monoclonal antibody is sufficient to reduce heroin seeking following forced abstinence. Because regulation of inflammatory gene expression in the PFC is a consequence of heroin exposure in both OUD subjects, as well as our preclinical heroin SA model, and 5-HT2AR signaling has been shown to have an anti-inflammatory effect in multiple disease models, we hypothesize that psilocybin reduces heroin relapse by promoting anti-inflammatory processes, including downregulation of IL-17a signaling in the PFC. In this project, we seek to further define the extent to which psilocybin and disruption of IL-17a signaling may inhibit heroin seeking behavior by elucidating the molecular mechanism of neuroinflammatory pathways regulated by psilocybin during inhibition of heroin seeking. We are currently evaluating the temporal and dose-dependent efficacy of psilocybin treatment on heroin relapse and heroin-primed reinstatement. We are also examining the contribution of the IL-17a signaling pathway to heroin relapse to determine how IL-17a functions downstream of psilocybin in the brain. Lastly, we are investigating the molecular mechanism of
psilocybin-mediated inhibition of heroin seeking in PFC neuronal, astrocytic, or microglial cells by combining fluorescence-activated cell sorting with RNA sequencing. This project will provide critical insight into the molecular mechanisms of psilocybin in the brain and establish the therapeutic efficacy of psilocybin signaling for the reduction of opioid seeking behavior.
