An Improved Method for Sampling and Quantitative Protein Analytics of Cerebrospinal Fluid of Individual Mice

The mouse is the species most commonly used in preclinical research, but protein analytics of murine cerebrospinal fluid (CSF) remains challenging because of low sample volumes (often <10 microl) and frequent contaminations with blood. We developed an improved CSF sampling method that allows routine collection of larger volumes (20-30 microl) of pure CSF from individual mice, enabling multiple protein analytical assays from a single sample. Based on cell counts and hemoglobin ELISAs, we provide an easy quality control workflow for obtaining cell- and blood-free murine CSF. Through mass spectrometry-based proteomics using an absolutely quantified external standard, we estimated concentrations for hundreds of mouse CSF proteins. While repeated CSF sampling from the same mouse was possible, it induced CSF proteome changes. Applying the improved method, we found that the mouse CSF proteome remains largely stable over time in wild-type mice, but that amyloid pathology in the 5xFAD mouse model of Alzheimer's disease massively changes the CSF proteome. Neurofilament light chain and TREM2, markers of neurodegeneration and activated microglia, respectively, were strongly upregulated and validated using immunoassays. In conclusion, our refined murine CSF collection method overcomes previous limitations, allowing multiple quantitative protein analyses for applications in biomedicine.