Funding to date:
The proposed grant will assist in the purchase of an Orbitrap Fusion Tribrid Mass Spectrometer system to
enable the development of a method to assess tau production and clearance rates in humans, animal models,
and in vitro experiments. This cutting edge mass spectrometer system will provide more precise measurements
with the ultra-low abundance of biomolecules of interest than current instruments can quantify. This will allow for
the first time the measuring of tau kinetics enabling evaluation of tau directed therapeutics in animal models, tau
kinetics in humans (e.g. AD), tau isoforms in stem cells and understanding the effects of genetic risk factors
related to tau metabolism. This system will support investigators at Washington University (CAF member Dr.
Holtzman as well as other Washington University investigators) and other CAF members around the country as
opportunities arise. Further, this system will enable plasma amyloid-beta kinetics to be measured. This will
address central issues in amyloid-beta transport from the brain to the blood and also if peripheral kinetics can
indicate brain amyloidosis.
The Stable Isotope Labeling Kinetics (SILK) approach has been adopted both in the academic fields of
neurodegeneration and the commercial sector. The Fusion triple Mass Spectrometry system will enable the
development and application of novel discoveries in amyloid-beta, tau, and related AD proteins in addition to
basic discoveries in the kinetic metabolism of tau in vivo in both humans and animal models. The major limitation
to the adoption and use of SILK is the technological hurdle in accurate mass spectrometry measurement of
labeled biomolecules. The Fusion Tribrid MS system is the only system to demonstrate the capability to quantify
very low abundant labeled biomolecules (attomole quantitation) with very low (<1%) labeling. This resource will
provide accurate, high-throughput mass spectrometry analysis for tau SILK studies.
Compared to brain and CSF Aβ, tau and peripheral Aβ biology and pathophysiology in AD is far less
understood. Importantly, tau levels in CSF correlate more closely with cognitive decline in AD patients than Aβ,
and CSF tau and Aβ are critical biomarkers in precisely predicting the order and magnitude of pathologic
processes in AD. Therefore, we believe that determining the tau metabolism in AD is the next critical step in the
AD research field to improve future clinical trial designs and to develop an early AD detection test. Tau is
predominantly an intracellular protein but recent studies suggest that it is also released into the extracellular
space, where it may be involved in spreading tau pathology to remote brain regions. Many studies have shown
that tau and phosphorylated tau amounts are increased in AD, but the mechanism of tau production or clearance
is not known. Elucidating tau metabolism would greatly enhance our basic knowledge of tau biology as well as
our understanding of the role of tau in AD pathophysiology.