DEVELOPMENT OF A HIGHLY SENSITIVE TAU IMMUNOASSAY TO MEASURE ENDOGENOUS MURINE TAU IN MOUSE CEREBROSPINAL FLUID

The two pathological hallmarks of Alzheimer’s Disease (AD), amyloid plaques and neurofibrillary tangles, are composed of Aβ42 and tau, respectively. In the cerebrospinal fluid (CSF) of AD patients, the concentration of Aβ42 is reduced while the concentration of Tau is elevated, comparing to those of normal individuals. Notably, recent literature has indicated an age-related increase in endogenous murine Tau with a concomitant decrease in Aβ42 and 40 peptides in the CSF of two APP-overexpressing transgenic mouse models (L. F. Maia et al., 2013, Sci. Transl. Med.5, 194re2). This finding has prompted us to investigate the relationship between CSF endogenous murine Tau and Aβ pathology in the PDAPP transgenic mouse model. In order to detect and quantitate low levels of endogenous murine Tau, a highly sensitive Tau immunoassay was developed. Meso Scale Discovery (MSD) electrochemiluminescence (ECL) immunoassay technology, employing different capture and detection anti-Tau antibodies, was utilized to measure endogenous murine Tau in 5- or 10-fold diluted CSF from wild-type and four to 19 month old PDAPP mice. Brain homogenates and CSF from hTau transgenic and Tau knock-out mice were utilized as positive and negative controls, respectively, to confirm assay specificity. An MSD Tau immunoassay was optimized and validated using recombinant murine Tau to measure endogenous murine Tau in wild-type and PDAPP mouse CSF with a defined lower limit of quantification of 2.8 pg/mL. Tau knock-out mouse CSF and brain homogenate was undetectable in this assay, while hTau transgenic mouse CSF showed significant Tau signal. Preliminary results from an evaluation of CSF from PDAPP mice showed an approximate two-fold, age-dependent increase in Tau that coincided with increasing Aβ pathology. Endogenous murine Tau was measured in mouse CSF utilizing a novel, highly sensitive MSD Tau immunoassay. There was an approximate two-fold increase in Tau CSF in PDAPP mice from four to 12.5 months of age that coincided with increasing Aβ pathology. Ongoing efforts include a longitudinal analysis of CSF Tau from PDAPP mice.