ACNP 64th Annual Meeting: Poster Abstracts P292-583

Background:The opioid epidemic is a critical public health crisis, with high overdose and relapse rates in opioid use disorder (OUD) and cooccurrence with major depressive disorder (MDD) in ~36% of cases.While shared genetic risk loci link these disorders, cell type-specific mechanisms in the human brain remain unclear.Emerging evidence implicates inflammatory signaling and synaptic plasticity as dysregulated processes in both OUD and MDD, yet the molecular pathways altered in defined cell populations are understudied.We therefore examined the cell type specific transcriptional and epigenetic signatures associated with OUD, MDD, and co-occurring OUD/MDD (COM) across two brain regions critical to affective processing and motivation.Methods: We generated matched single-nucleus RNA and chromatin accessibility profiles from postmortem subgenual anterior cingulate cortex (sgACC) and nucleus accumbens (NAc) using the 10x Genomics Multiome assay.The cohort included strict diagnostic groups for OUD, MDD, COM, and an unaffected comparison group, with verification that individuals in OUD or MDD groups did not have a lifetime diagnosis of the alternative disorder.A machine-learning workflow (doublet/ambient removal, nucleus-level outlier scoring, cross-modal filters) and standardized metrics (complexity, mitochondrial content, TSS enrichment, FRiP) ensured high-quality data across modalities.Cortical and striatal references facilitated clean, reproducible annotation of excitatory, inhibitory, and glial subpopulations.Differential expression was performed using limma-voom on pseudobulked data within each cell type with covariate control, empirical-Bayes shrinkage, and FDR correction.Chromatin analyses (differential accessibility, peak-2-gene links) nominated candidate regulators.Signal concordance between diagnoses was quantified with RRHO2, while pathway enrichment used Metascape, and UpSet intersections prioritized shared genes for meaningful visualizations.Results: In the sgACC, we found evidence that individuals with OUD+/MDD+ exhibit unique pathology in microglia compared to individuals with only OUD or MDD.Specifically, the OUD+/MDD+ signature had 348 differentially expressed genes (DEGs), 90% of these unique compared to OUD or MDD alone.GSEA revealed that downregulation in synapse-related pathways in microglia is a distinguishing feature of having both disorders (i.e., unique pathology in OUD+/MDD+).Other glial populations were less altered in OUD+/MDD+ compared to controls (85 DEGs in astrocytes, 149 in oligodendrocytes, 79 in OPCs).Notably, threshold-free analyses revealed that, within astrocytes, the upregulated signal in OUD+/MDD+ was driven by OUD rather than MDD.Ongoing efforts are incorporating cell type-specific chromatin accessibility with these transcriptional findings.Analysis in NAc is still ongoing.Conclusions: Across sgACC and NAc, matched single-cell multi-omics delineate robust, cell type-specific alterations linking OUD, MDD, and COM.sgACC exhibits a broad OUD-driven signature with L6-selective COM prominence and distinct pathway signatures; NAc shows MSN-subtype-dependent concordance and a glial shift toward COM/MDD.Signals converge on glial immune/ interferon pathways and neuronal transcriptional-elongation, proteostasis, synaptic-plasticity, and bioenergetic programs.These data provide mechanistic hypotheses and candidate regulators for validation, and motivate sex-aware, precision therapeutic strategies for co-occurring depression and opioid addiction.