Integrated single-cell and Mendelian randomization analyses identify aging-induced brain endothelial SPARCL1...

Vascular dementia (VaD) is a prevalent age-related neurocognitive disorder characterized by progressive cognitive impairment and a lack of disease-modifying therapies. Although age-related brain endothelial dysfunction has been implicated as a central contributor to the pathogenesis of VaD, the molecular mechanisms underlying this process remain incompletely elucidated.

We employed an integrative analytical framework combining Mendelian randomization (MR) and single-cell RNA sequencing (scRNA-seq). MR analysis was performed using plasma protein quantitative trait loci (pQTLs) and genome-wide association study (GWAS) summary statistics for VaD. Brain endothelial cells (BECs) from young and aged mice underwent scRNA-seq to delineate aging-related transcriptional alterations. Candidate genes originating from MR-derived proteins and endothelial differentially expressed genes (DEGs) were integrated to prioritize high-confidence targets. For validation, human single-nucleus RNA sequencing (snRNA-seq) data from post-mortem brains of VaD patients and non-demented controls were analyzed. External replication was performed using independent pQTL datasets to further corroborate the findings.

MR analysis identified 33 plasma proteins exhibiting significant putative causal associations with VaD risk. Functional enrichment analysis revealed significant enrichment in biological processes including endothelial development, immune activation, and axonal development. scRNA-seq profiling of BECs demonstrated substantial aging-induced transcriptional dysregulation, marked by immune activation, loss of homeostatic endothelial function, and expansion of pro-inflammatory subpopulations. SPARCL1 was identified as a key convergent candidate, demonstrating significant downregulation in aged endothelium and a consistent protective effect in MR analysis. BECs with high SPARCL1 expression maintained a homeostatic transcriptional profile, whereas SPARCL1-low cells exhibited pronounced inflammatory signatures. Importantly, reduced SPARCL1 expression was validated in BECs from post-mortem human brains of VaD patients, and external replication across independent pQTL datasets further corroborated its protective effect against VaD risk.

Our integrative study demonstrates that aging-induced SPARCL1 deficiency in brain endothelial cells causally contributes to VaD pathogenesis. These findings highlight SPARCL1 as a mechanistically grounded and therapeutically promising target for VaD.