ApoE and clusterin CSF levels influence associations between APOE genotype and changes in CSF tau, but not CSF Aβ42, levels in non-demented elderly

Apolipoprotein E (APOE) ε4 genotype is associated with increased cerebral amyloid beta (Aβ) deposition in nondemented elderly and suggested to influence ApoE as well as ApoJ (clusterin [Clu]) and ApoA1 expression. We aimed to assess whether APOE affects early Alzheimer's disease pathophysiology via these apolipoproteins. Cerebrospinal fluid (CSF) ApoE, Clu, ApoA1, and CSF amyloid beta1-42 (Aβ42) and tau levels were assessed in 403 individuals with subjective cognitive decline and mild cognitive impairment using enzyme-linked immunosorbent assay. Whether CSF apolipoprotein levels mediated APOEε4 allele frequency effects on CSF Aβ42 and tau in nondemented elderly was investigated using mediation analysis, with age- and gender-adjusted linear regression analyses. CSF ApoE mediated 48% of the association between APOEε4 and CSF tau, whereas Clu and ApoA1 did not. In addition, CSF Clu partially mediated the relation between CSF ApoE and tau (12%). CSF apolipoproteins did not mediate the inverse relation between APOEε4 and CSF Aβ42, despite a strong association between the latter 2 biomarkers. In summary, our findings suggest that ApoE and Clu are involved in Aβ-independent pathways as part of the cascade leading to Alzheimer pathology.