Heteromers of amyloid precursor protein in cerebrospinal fluid.

ABSTRACT:

Background

Soluble fragments of the amyloid precursor protein (APP) generated by ?- and ?-secretases, sAPP? and sAPP?, have been postulated as promising new cerebrospinal fluid (CSF) biomarkers for the clinical diagnosis of Alzheimer's disease (AD). However, the capacity of these soluble proteins to assemble has not been explored and could be relevant. Our aim is to characterize possible sAPP oligomers that could contribute to the quantification of sAPP? and sAPP? in CSF by ELISA, as well as to characterize the possible presence of soluble full-length APP (sAPPf).

Results

We employed co-immunoprecipitation, native polyacrylamide gel electrophoresis and ultracentrifugation in sucrose density gradients to characterize sAPP oligomers in CSF. We have characterized the presence of sAPPf in CSF from NDC and AD subjects and demonstrated that all forms, including sAPP? and sAPP?, are capable of assembling into heteromers, which differ from brain APP membrane-dimers. We measured sAPPf, sAPP? and sAPP? by ELISA in CSF samples from AD (n?=?13) and non-disease subjects (NDC, n?=?13) before and after immunoprecipitation with antibodies against the C-terminal APP or against sAPP?. We demonstrated that these sAPP heteromers participate in the quantification of sAPP? and sAPP? by ELISA. Immunoprecipitation with a C-terminal antibody to remove sAPPf reduced by ~30% the determinations of sAPP? and sAPP? by ELISA, whereas immunoprecipitation with an APP? antibody reduced by ~80% the determination of sAPPf and sAPP?.

Conclusions

The presence of sAPPf and sAPP heteromers should be taken into consideration when exploring the levels of sAPP? and sAPP? as potential CSF biomarkers.

SUBMITTER: Cuchillo-Ibanez I 

PROVIDER: S-EPMC4298044 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature