Circulating C-reactive protein influences polygenic risk of inflammatory genes expressed in brain endothelia for Alzheimer's disease.

BACKGROUND

C-reactive protein (CRP) is a key marker of systemic inflammation that affects blood vessel endothelial function, including in the brain. Since endothelial dysfunction is linked to Alzheimer's disease (AD), we investigated whether elevated CRP level interacts with genetic pathways in brain endothelial cells to influence AD risk.

METHODS

Using AD genome-wide association study (GWAS) data, we developed multiple polygenic risk scores (PRSs) including single nucleotide polymorphisms (SNPs) in genes expressed in brain endothelial cells, excluding the APOE region, that are involved in inflammation, synaptic transmission, and other pathways.

RESULTS

Analysis across three independent cohorts revealed that individuals with low inflammatory PRSs (<50%) and elevated blood CRP level were associated with an increased risk of AD; in contrast, those with high inflammatory PRSs (≥50%) did not exhibit this CRP-related AD risk increase. Further examination of individuals with a low inflammatory PRS showed that elevated CRP was associated with lower cerebrospinal fluid (CSF) Aβ42 level and temporal lobe atrophy. Among individuals with a high inflammatory PRS, elevated CRP level was negatively correlated with CSF pTau181 and brain tauopathy, suggesting a potential protective mechanism against tau pathology. Key inflammatory PRS genes, which were impacted by circulating CRP for AD, included APP, IL6ST, and FN1, are involved in amyloid pathology, wound healing, and coagulation.

CONCLUSION

Our findings highlight two distinct genetic-dose dependent backgrounds: "vulnerable" (<50% inflammatory PRS) and "resilient" (≥50% inflammatory PRS), and support a Genome-Internal Environment (G×IE) interaction model, linking peripheral inflammation to AD risk.