Rahul A. Bharadwaj

Major depressive disorder (MDD) involves frontal cortical dysfunction, with emerging evidence implicating gliovascular and immune mechanisms, yet its transcriptional signatures across subregions, cell-types, and molecular layers remain poorly defined. Here, we integrated bulk-tissue RNA-seq data from dlPFC, mPFC, and dACC (n = 286) to identify a conserved core transcriptional profile, anchored in downregulated interneuron markers, and upregulated immune and vascular genes, spatially enriched in leptomeninges and white matter. Concordantly, multiomic factor analysis revealed immune activation, stress-response, and accelerated aging in MDD. Analysis of snRNA-seq data from dlPFC, mPFC, and oFC (863,511 nuclei; n = 204) revealed most pronounced MDD signatures in excitatory neurons, accompanied by coordinated disruption of glucocorticoid receptor machinery across cell-types, including FKBP5 upregulation. Glial, immune, and perivascular populations exhibited signatures of oxidative stress, ECM remodeling, and reduced neuronal support, and greater concordance with bulk-tissue MDD signals than neurons. A global reduction in cell-to-cell communications in MDD revealed a shift from homeostatic neuronal signaling toward endothelial and myelination-associated pathways. Ephrin-Eph signaling was consistently dysregulated, implicating disrupted axonal guidance, synaptic remodeling, and neurovascular integrity. Notably, MDD signatures were shared between MDD-only and PTSD comorbid cases at bulk-tissue analyses, while diverging at single-cell resolution. Together, these findings reframe MDD as a distributed frontal cortex disorder, driven by disrupted neuroglial and neurovascular communication.

The habenula (Hb) is a small epithalamic midline structure critical for reward processing and mood regulation that is implicated in many complex brain disorders, including depression and addiction. The molecular anatomy of the Hb has been well-characterized in model organisms, but little is known about its organization in the human brain, including the transcriptomic and epigenetic signatures of spatially-organized lateral (LHb) and medial (MHb) cell types. Here, we generated a high resolution spatiomolecular map of the human Hb using both multiomic single nucleus sequencing (snMultiome) and spatially-resolved transcriptomics. We measured gene expression and chromatin accessibility across 4 MHb and 5 LHb neuronal cell types as defined by transcriptomic conservation with rodents and zebrafish. We identified cell type-specific molecular specializations related to GABAergic and glutamatergic signaling as well as regulatory relationships between open chromatin regions, transcription factors, and target genes associated with depression and addiction. High resolution spatial transcriptomics identified the anatomical location of heterogeneous LHb subpopulations, including two putative inhibitory populations in the LHb. We further characterized cell-type relationships between Hb neurons and glial subtypes and predicted ligand-receptor interactions between LHb and MHb neurons. Finally, we delineated Hb cell types and spatial domains enriched in genes associated with genetic risk for psychiatric disorders, identifying the strongest enrichment in the MHb. Collectively, the generated data and analyses resolve the spatiomolecular organization of the human Hb and identify molecular-genetic associations with neuropsychiatric disease.

The entorhinal cortex (ERC) is implicated in early progression of Alzheimer’s disease (AD). Here we investigated the impact of established biological risk factors for AD, including APOE genotype (E2 versus E4 alleles), sex, and ancestry, on gene expression in the human ERC. We generated paired spatially-resolved transcriptomics (SRT) and single-nucleus RNA sequencing data (snRNA-seq) in postmortem human ERC tissue from middle aged brain donors with no history of AD. APOE -dependent changes in gene expression predominantly mapped to a transcriptionally-defined oligodendrocyte subtype, which varied substantially with ancestry, and suggested differences in oligodendrocyte differentiation and myelination. Integration of SRT and snRNA-seq data identified a common gene expression signature associated with APOE genotype, which we localized to the same oligodendrocyte subtype and a white matter spatial domain. This suggests that AD risk in ERC may be associated with disrupted oligodendrocyte function, potentially contributing to future neurodegeneration. Lay Summary: Alzheimer’s disease (AD) is a neurodegenerative disorder that accounts for 60-80% dementia cases. Apolipoprotein E ( APOE) genotype is the strongest genetic risk factor for AD, and the entorhinal cortex (ERC) is a brain region implicated in its earliest progression. Our study investigated how APOE genotype impacts gene expression in the ERC. We identified genotype-dependent effects on oligodendrocytes with different transcriptional profiles related to maturation that may help explain how APOE genotype mediates its effects on AD risk.

The locus coeruleus (LC) is a small noradrenergic nucleus in the dorsal pons that sends projections across the brain regulating sleep, arousal, attention, stress responses, and some forms of cognition. LC neurons show pathology in the earliest stages of Alzheimer’s disease (AD), including age-related accumulation of hyperphosphorylated tau (pTau) and accelerated loss of neuromelanin (NM) pigmentation. NM-sensitive neuroimaging of the LC predicts previous cognitive decline, clinical severity, and future AD progression. While these findings suggest that the LC plays an etiologic role in AD, the molecular landscape of the LC prior to clinical manifestation of sporadic AD remains largely uncharacterized. This information is critical for developing interventions that preserve LC integrity and function. We performed spatially-resolved transcriptomics on 85 sections of human postmortem LC from N =33 neurotypical middle-aged donors, balanced for epidemiologic AD risk factors including sex, African or European ancestry, and APOE genotype (carriers of the E4/risk or E2/protective alleles). Comparing across APOE genotypes, we find astrocytic gene expression differences proximal to LC neurons. Associating NM content with local gene expression, we show that higher overall APOE gene expression correlates with reduced NM content and an enrichment of NM-associated genes in aging pathways. Unexpectedly, we find enriched LC expression of cholesterol synthesis genes, alongside evidence for lipid synthesis gene regulatory network activity in NM-containing LC specifically, revealing a potential intersection between intrinsic lipid metabolism in LC neurons, NM, and the role of APOE-mediated lipid biology in AD. Together, these data illuminate the molecular features of the human LC at spatial resolution with unprecedented sampling depth, revealing how AD risk factors and NM content influence resilience and susceptibility of this critical brain nucleus to pathology accumulation and degeneration.

Transcriptome and proteome sequencing of brain tissue homogenate has helped unravel processes underlying schizophrenia (SCZ). However, most studies have lacked granularity at the cell type level and have focused on individual brain regions, rather than examining expression dynamics across multiple regions or illness-relevant circuitries. We used laser capture microdissection to collect excitatory neuron-enriched samples from hippocampal subregions CA1 and presubiculum (SUB), and from dorsolateral prefrontal cortex (DLPFC), a circuit prominently implicated in schizophrenia. Using RNA sequencing and quantitative proteomics, we show significantly superior discrimination of brain regional identity in the transcriptomic (>90% accuracy) and proteomic data (>97% accuracy) compared with gene-level expression data (<70% in bulk). Patients with SCZ show hippocampal-specific differential protein phosphorylation. SCZ risk co-expression gene-sets that replicate across transcript and protein networks are enriched for transmembrane transporters in the DLPFC and CA1 and postsynaptic processes in the SUB. We demonstrate a strong directional connectivity effect of SCZ risk in that excitatory synaptic genes in CA1 unidirectionally predict gene expression in SUB. Finally, parallel CA1 snRNA-seq results suggest that in SCZ excitatory efferents in CA1 are affected by interactions with glia and by downregulation of inhibitory neuropeptide inputs. Our study proposes molecular mechanisms by which hippocampal communication, previously associated with SCZ at the macroscopic level, may be altered at the inter-field and interregional circuit level.

Neuropathological lesions in the brains of individuals affected with neurodegenerative disorders are hypothesized to trigger molecular and cellular processes that disturb homeostasis of local microenvironments. Here, we applied the 10x Genomics Visium Spatial Proteogenomics (Visium-SPG) platform, which measures spatial gene expression coupled with immunofluorescence protein co-detection, in post-mortem human brain tissue from individuals with late-stage Alzheimer’s disease (AD) to investigate changes in spatial gene expression with respect to amyloid-β (Aβ) and hyperphosphorylated tau (pTau) pathology. We identified Aβ-associated transcriptomic signatures in the human inferior temporal cortex (ITC) during late-stage AD, which we further investigated at cellular resolution with combined immunofluorescence and single molecule fluorescent in situ hybridization (smFISH) co-detection technology. We present a workflow for analysis of Visium-SPG data and demonstrate the power of multi-omic profiling to identify spatially-localized changes in molecular dynamics that are linked to pathology in human brain disease. We provide the scientific community with web-based, interactive resources to access the datasets of the spatially resolved AD-related transcriptomes at https://research.libd.org/Visium_SPG_AD/ .

A postmortem human brain collection to study posttraumatic stress disorder (PTSD) is critical for uncovering the molecular mechanisms that contribute to this psychiatric disorder. We describe here the PTSD brain collection at the Lieber Institute for Brain Development in Baltimore, Maryland, consisting of postmortem brain donations acquired between 2012 and 2017. Thus far, 87 brains from individuals meeting DSM‐5 criteria for PTSD were collected after consent was obtained from legal next‐of‐kin, and subsequently clinically characterized for molecular studies. PTSD brain donors had high rates of comorbid diagnoses, including depression (62.1%), substance abuse (74.7%), drug‐related death (69.0%), and suicide completion (17.2%). PTSD cases were subdivided into two categories: combat‐related PTSD (n = 24) and noncombat/domestic PTSD (n = 63). The major differences between the combat‐related and domestic PTSD cohorts were sex, drug‐related death, and the prevalence of bipolar disorder (BPD) comorbidity. The combat‐related group was entirely male, with only one BPD subject (4.2%), and had significantly fewer drug‐related deaths (45.8%) in contrast to the domestic group (31.8% male, 36.5% bipolar, and 77.8% drug‐related deaths). Medical examiners' offices, particularly in areas with higher military populations, are an excellent source for PTSD brain donations of both combat‐related and domestic PTSD.

Posttraumatic stress disorder (PTSD) follows exposure to a traumatic event in susceptible individuals. Recently, genome‐wide association studies have identified a number of genetic sequence variants that are associated with the risk of developing PTSD. To follow up on identifying the molecular mechanisms of these risk variants, we performed genotype to RNA sequencing–derived quantitative expression (whole gene, exon, and exon junction levels) analysis in the dorsolateral prefrontal cortex (DLPFC) of normal postmortem human brains. We further investigated genotype–gene expression associations within the amygdala in a smaller independent RNA sequencing (Genotype‐Tissue Expression [GTEx]) dataset. Our DLPFC analyses identified significant expression quantitative trait loci (eQTL) associations for a “candidate” PTSD risk SNP rs363276 and the expression of two genes: SLC18A2 and PDZD8, where the PTSD risk/minor allele T was associated with significantly lower levels of gene expression for both genes, in the DLPFC. These eQTL associations were independently confirmed in the amygdala from the GTEx database. Rs363276 “T” carriers also showed significantly increased activity in the amygdala during an emotional face‐matching task in healthy volunteers. Taken together, our preliminary findings in normal human brains represent a tractable approach to identify mechanisms by which genetic variants potentially increase an individual's risk for developing PTSD.