Preclinical serum alterations and tissue changes in protein and gene expression of early cerebrospinal fluid-validated biomarkers in scrapie.

Identifying reliable biomarkers for prion diseases remains a challenge, particularly for early detection in accessible body fluids. A recent mass spectrometry study on the cerebrospinal fluid proteome identified and validated five proteins significantly dysregulated in the preclinical stage of naturally scrapie-affected sheep. In this study, we quantified these proteins in serum and analysed their distribution and gene expression in the central nervous system, correlating these results with characteristic prion-related neuropathological features. Significantly elevated serum levels of synaptotagmin binding, cytoplasmic RNA interacting protein (SYNCRIP), phospholipase D3 (PLD3) and cathepsin D (CTSD) were detected in preclinical animals, mirroring previous cerebrospinal fluid findings. Central nervous system analyses on these three proteins together with osteopontin (SPP1) and complement component 4 (C4) revealed early and region-specific reduced immunoreactivity alongside upregulated gene expression in scrapie-affected animals, correlating significantly with prion-associated neuropathological features. Together, these findings highlight the potential of SYNCRIP, PLD3 and CTSD as promising minimally invasive biomarkers to diagnose prion diseases from the preclinical stage and provide new insights into the spatiotemporal regulation of the five proteins in the central nervous system throughout the progression of disease. Further research is needed to clarify the peripheral biomarker dynamics in relation to the neurodegenerative pathology.