Investigation of the Adolescent Gut Microbiome as a Unique Driver of Protein Expression in Medial Prefrontal Cortex After Opioid Exposure

Adolescence is a time in life when drug use is frequently initiated and use earlier in life is a predicter of problematic use during adulthood. For this reason, adolescence represents a sensitive period for the development of substance use disorder. Adolescents are undergoing many physiological changes at this time, including marked changes in the medial prefrontal cortex (mPFC), a brain region responsible for modulating motivational drive. However, changes in the brain are co-occurring with changes throughout the body. A system that is undergoing marked change during this time that is of particular interest to our group is the gut microbiome, the population of resident bacteria of the intestines that have been shown to exert effects on brain and behavior. The adolescent gut microbiome is also in flux and shifts in the predominant species of bacteria during this time have been linked to systemic inflammation, anxiety-like behavior, and stress responses. There is a growing appreciation for peripheral factors in psychiatric disturbance and our lab has shown that the gut microbiome might contribute to substance use disorder. Our preliminary results demonstrate that adolescent, but not adult, mice with their microbiome depleted with antibiotics demonstrate decreased morphine conditioned place preference after short-term gut microbiome knockdown, suggesting that adolescents are more sensitive to disruption of the gut microbiome. While there are multiple potential mechanisms of gut-brain communication, one of the best studied routes is via the production of metabolites that can cross the blood-brain barrier and affect neuronal and glial function. A number of these microbiome-derived metabolites, such as the short chain fatty acids, are known to have the ability to affect histone post-translational modifications and chromatin conformation. Given the potential of microbially-derived metabolites to alter gene expression via these epigenetic mechanisms, we performed transcriptomic profiling of adolescent and adult mPFC after manipulation of the gut microbiome. Microbiome-depleted adolescent mice treated with morphine showed massive changes in gene expression with more than a ten-fold increase in the number of regulated genes compared to morphine-treated controls with an intact microbiome. Additionally, the adolescent mice also had three-fold the amount of differentially regulated genes compared to microbiome depleted adults given morphine – suggesting that the effects of the microbiome on gene transcription are particularly potent in adolescence. However, at this point it is not known if these effects are purely transcriptional in nature or if there is a similarly large effect on protein levels. Understanding the answer to this question will be critical in dissecting out the nature of how these shifts in the microbiome alter behavioral response in translationally relevant models of substance use disorder. Here I will utilize discovery proteomics analysis in combination with drug self-administration paradigms to better understand changes in global protein expression and to clarify the underlying mechanisms of these important new findings.