Decorin is an early CSF biomarker of Alzheimer’s Aβ amyloidosis

Alzheimer’s disease (AD) is characterized by impaired protein homeostasis leading to amyloid-beta (Aβ) amyloidosis. Here, we show that autophagy is similarly inhibited in AD brains and App knock-in AD mouse models. To determine how pathologies translate to cerebrospinal fluid (CSF), label-free mass spectrometry of mouse CSF was used. This identified autophagy-related extracellular matrix (ECM) protein decorin as significantly and similarly increased in App knock-in mice and cognitively normal human subjects with abnormal CSF-amyloid. Notably, a switch from negative to positive correlation of CSF-decorin and CSF-amyloid occurs in cognitively normal subjects when CSF-amyloid becomes abnormal, indicating an early change in CSF-decorin induced by Aβ amyloidosis. In App knock-in mice increased CSF-decorin correlated with accentuated decorin expression in choroid plexus and decreased interneuronal decorin. Furthermore, decorin activates neuronal autophagy-lysosomal system by enhancing lysosomal degradation. Therefore, decorin is a potential CSF biomarker that reflects ECM and autophagy alterations in early AD Aβ amyloidosis.