Changes in Synaptic Proteins Precede Neurodegeneration Markers in Preclinical Alzheimer's Disease Cerebrospinal Fluid

Mol Cell Proteomics. 2019 Mar;18(3):546-560. doi: 10.1074/mcp.RA118.001290. Epub 2019 Jan 3.


A biomarker of synapse loss, an early event in Alzheimer's disease (AD) pathophysiology that precedes neuronal death and symptom onset, would be a much-needed prognostic biomarker. With direct access to the brain interstitial fluid, the cerebrospinal fluid (CSF) is a potential source of synapse-derived proteins. In this study, we aimed to identify and validate novel CSF biomarkers of synapse loss in AD. Discovery: Combining shotgun proteomics of the CSF with an exhaustive search of the literature and public databases, we identified 251 synaptic proteins, from which we selected 22 for further study. Verification: Twelve proteins were discarded because of poor detection by Selected Reaction Monitoring (SRM). We confirmed the specific expression of 9 of the remaining proteins (Calsynytenin-1, GluR2, GluR4, Neurexin-2A, Neurexin-3A, Neuroligin-2, Syntaxin-1B, Thy-1, Vamp-2) at the human synapse using Array Tomography microscopy and biochemical fractionation methods. Exploration: Using SRM, we monitored these 9 synaptic proteins (20 peptides) in a cohort of CSF from cognitively normal controls and subjects in the pre-clinical and clinical AD stages (n = 80). Compared with controls, peptides from 8 proteins were elevated 1.3 to 1.6-fold (p < 0.04) in prodromal AD patients. Validation: Elevated levels of a GluR4 peptide at the prodromal stage were replicated (1.3-fold, p = 0.04) in an independent cohort (n = 60). Moreover, 7 proteins were reduced at preclinical stage 1 (0.6 to 0.8-fold, p < 0.04), a finding that was replicated (0.7 to 0.8-fold, p < 0.05) for 6 proteins in a third cohort (n = 38). In a cross-cohort meta-analysis, 6 synaptic proteins (Calsyntenin-1, GluR4, Neurexin-2A, Neurexin-3A, Syntaxin-1B and Thy-1) were reduced 0.8-fold (p < 0.05) in preclinical AD, changes that precede clinical symptoms and CSF markers of neurodegeneration. Therefore, these proteins could have clinical value for assessing disease progression, especially in preclinical stages of AD.

Keywords: Alzheimer's disease; Biomarker: Prognostic; Cerebrospinal fluid; Clinical proteomics; Selected reaction monitoring.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Alzheimer Disease / cerebrospinal fluid*
  • Alzheimer Disease / metabolism
  • Autopsy
  • Biomarkers / cerebrospinal fluid*
  • Biomarkers / metabolism
  • Calcium-Binding Proteins / cerebrospinal fluid
  • Calcium-Binding Proteins / metabolism
  • Early Diagnosis
  • Female
  • Humans
  • Male
  • Nerve Tissue Proteins / cerebrospinal fluid
  • Nerve Tissue Proteins / metabolism
  • Prodromal Symptoms
  • Prognosis
  • Proteomics / methods*
  • Receptors, AMPA / metabolism
  • Synapses / metabolism*
  • Syntaxin 1 / cerebrospinal fluid
  • Syntaxin 1 / metabolism
  • Thy-1 Antigens / cerebrospinal fluid
  • Thy-1 Antigens / metabolism


  • Biomarkers
  • CLSTN1 protein, human
  • Calcium-Binding Proteins
  • Nerve Tissue Proteins
  • Receptors, AMPA
  • STX1B protein, human
  • Syntaxin 1
  • Thy-1 Antigens
  • glutamate receptor ionotropic, AMPA 4
  • neurexin IIIalpha