Neuronal pentraxin‐2 by Simoa ‐ a potential synaptic biomarker in Alzheimer’s disease

Abstract

AbstractBackgroundSynaptic dysfunction and degeneration are believed to be among the earliest and most reliable indicators of cognitive impairment in neurodegenerative disorders, including Alzheimer’s disease (AD). Discovering and verifying novel biomarkers that can quantify synaptic degeneration and serve as prognostic indicators would be valuable to track cognitive decline in clinical and drug trial settings. By using mass spectrometry, we have studied a panel of 17 synaptic proteins as potential biomarkers for AD and a broad range of neurodegenerative disorders. Of these proteins, neuronal pentraxin‐2 (NPTX2) has shown great promise as a synaptic biomarker, showing a decrease in symptomatic disease. Therefore, we aimed to develop a Single molecule array (Simoa) for NXPT2, a method more suited for routine clinical assessment than mass spectrometry‐based workflows.MethodWe developed an in‐house NPTX2 Simoa assay on the HD‐X platform (Quanterix) with paramagnetic beads coupled with a rabbit monoclonal capture antibody (EPR24020‐38, Abcam) and biotinylated rabbit monoclonal detector antibody (EPR15618, Abcam), both specifically targeting NPTX2. Full‐length recombinant NPTX2 (7816‐NP‐050, Biotechne) was used as the calibrator. Using the assay, we analyzed 55 healthy controls (78.0 (6.5 SD) years) and 54 AD patients (73.5 (7.0 SD) years) using 2 uL cerebrospinal fluid (CSF) in the BioFINDER pilot study. Group comparisons were performed using the Wilcoxon rank sum test and linear models adjusted for age and sex were used to assess associations of NPTX2 protein levels with cognitive function (mini mental status exam (MMSE)) and with neuroimaging, e.g., Aβ‐PET, tau‐PET (temporal ROI, Braak I‐IV) as well as cortical thickness in an AD signature composed of temporal regions in the AD group.ResultCSF NPTX2 concentration was found to be lower in AD compared with controls (p = 0.017, Figure). Lower NPTX2 concentration was associated with greater tau PET SUVR (β(SD) = ‐0.25(0.079), p‐value = 0.0027) and cortical thickness atrophy (β(SD) = 0.075(0.024), p‐value = 0.0034)) but not with amyloid‐β PET SUVR. Lower NPTX2 concentration was also associated with lower MMSE score (β(SD) = 2.62 (0.75), p‐value = 0.0010).ConclusionWe have successfully developed a Simoa assay of a novel CSF biomarker, NPTX2. This semi‐automated method allows for large‐scale evaluation of NPTX2, a leading candidate for synaptic degeneration in neurodegenerative disorders.