Single Nuclei Transcriptome Reveals Perturbed Brain Vascular Molecules in Alzheimer’s Disease

Blood-brain barrier (BBB) dysfunction is well-known in Alzheimer’s disease (AD), but the precise molecular changes contributing to its pathophysiology are unclear. To understand the transcriptional changes in brain vascular cells, we performed single nucleus RNA sequencing (snRNAseq) of temporal cortex tissue in 24 AD and control brains resulting in 79,751 nuclei, 4,604 of which formed three distinct vascular clusters characterized as activated pericytes, endothelia and resting pericytes. We identified differentially expressed genes (DEGs) and their enriched pathways in these clusters and detected the most transcriptional changes within activated pericytes. Using our data and a knowledge-based predictive algorithm, we discovered and prioritized molecular interactions between vascular and astrocyte clusters, the main cell types of the gliovascular unit (GVU) of the BBB. Vascular targets predicted to interact with astrocytic ligands have biological functions in signalling, angiogenesis, amyloid ß metabolism and cytoskeletal structure. Top astrocytic and vascular interacting molecules include both novel and known AD risk genes such as APOE , APP and ECE1 . Our findings provide information on transcriptional changes in predicted vascular-astrocytic partners at the GVU, bringing insights to the molecular mechanisms of BBB breakdown in AD. Graphical Abstract Pericytes (yellow), endothelia (salmon) and astrocytes (purple) that form the gliovascular unit (GVU) at the blood brain barrier (BBB) were interrogated for their differentially expressed genes (DEG) and vascular cell (pericyte or endothelia) to astrocyte interactions using single nucleus RNA sequencing (RNAseq) transcriptome obtained from brains of Alzheimer’s disease (AD) patients and controls. We identified many upregulated (red) or downregulated (blue) DEGs in AD brains in these cell types. These genes have known biological functions in amyloid ß (Aß) clearance, immune modulation, astrogliosis and neuronal death. Novel predicted interactions were identified between vascular cells and astrocytic DEGs. Collectively, our findings highlight the vast transcriptome changes that occur at the GVU and provide mechanistic insights into BBB dysfunction in AD. This figure was created with Biorender.com. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. * Aß : Amyloid ß AD : Alzheimer’s disease BBB : Blood-brain barrier CNS : Central nervous system DEG : Differentially expressed genes ECM : Extracellular matrix FACS : Fluorescence-activated cell sorting FANS : Fluorescence-activated nuclear sorting GO : Gene ontology GVU : Gliovascular unit QC : Quality control RNAseq : RNA sequencing scRNAseq : Single cell RNA sequencing snRNAseq : Single nucleus RNA sequencing TCX : Temporal cortex UMAP : Uniform Manifold Approximation and Projection UMI : Unique molecular identifier [1]: pending:yes