APOE4 Copy Number-Dependent Proteomic changes in the Cerebrospinal Fluid

Background: APOE4 has been hypothesized to increase Alzheimer9s disease risk by increasing neuroinflammation, though the specific neuroinflammatory pathways involved are unclear. Objectives: To characterize CSF proteomic changes as a function of APOE4 copy number. Methods: We analyzed targeted proteomic data obtained on ADNI CSF samples using a linear regression model adjusting for age, sex, and APOE4 copy number, and a second linear model also adjusting for AD clinical status. False Discovery Rate (FDR) was used to correct for multiple comparisons. Results: In the first model, increasing APOE4 copy number was associated with significant expression decreases in a CRP peptide (q=0.006), and significant expression increases in peptides from ALDOA, CH3L1 (YKL-40), and FABPH (q<0.05 for each). In the second model (controlling for age, sex, and AD clinical status), increasing APOE4 copy number was associated with significant expression decreases in a CRP peptide (q=0.009). In both models, increased APOE4 copy number was associated with trends towards lower expression of all 24 peptides from all 8 different complement proteins measured here, although none of these differences were statistically significant. The odds of this happening by chance for 24 unrelated peptides would be less than 1 in 16 million. Conclusions: Increasing APOE4 copy number was associated with decreased CSF CRP levels and increased CSF ALDOA, CH3L1 and FABH levels; the CRP decrease remained significant after controlling for AD clinical status. Increased APOE4 copy number may also be associated with decreased CSF complement pathway protein levels, a hypothesis for investigation in future studies.