Machine Learning Analysis of the Orbitofrontal Cortex Transcriptome of Human Opioid Users Identifies Shisa7 as a Translational Target Relevant for Heroin Seeking Leveraging a Male Rat Model.

BACKGROUND

Identifying neurobiological targets predictive of the molecular neuropathophysiological signature of human opioid use disorder (OUD) could expedite new treatments. OUD is characterized by dysregulated cognition and goal-directed behavior mediated by the orbitofrontal cortex (OFC), and next-generation sequencing could provide insights regarding novel targets.

METHODS

Here, we used machine learning to evaluate human postmortem OFC RNA sequencing datasets from heroin users and control participants to identify transcripts that were predictive of heroin use. To determine a causal link to OUD-related behaviors, we examined the effects of overexpressing the top target gene in a translational rat model of heroin seeking and behavioral updating. Additionally, we determined the effects of overexpression on the rat OFC transcriptome compared with that of human heroin users. Co-immunoprecipitation/mass spectrometry (co-IP/MS) from the rat OFC elucidated the protein complex of the novel target.

RESULTS

Our machine learning approach identified SHISA7 as predictive of human heroin users. Shisa7 is understudied but appears to be an auxiliary protein of GABA (gamma-aminobutyric acid A) or AMPA receptors. In rats, Shisa7 expression positively correlated with heroin-seeking behavior. Overexpressing Shisa7 in the OFC augmented heroin seeking and impaired behavioral updating for sucrose-based operant contingency. RNA sequencing of rat OFC revealed gene coexpression networks regulated by Shisa7 overexpression similar to human heroin users. Finally, co-IP/MS showed that heroin influenced Shisa7 binding to glutamatergic and GABAergic receptor subunits. Both gene expression signatures and Shisa7 protein complex emphasized perturbations of neurodegenerative and neuroimmune processes.

CONCLUSIONS

Our findings suggest that OFC Shisa7 is a critical driver of neurobehavioral pathology related to drug-seeking behavior and behavioral updating, thus identifying a potential therapeutic target for OUD.