Full-length and C-terminal neurogranin in Alzheimer’s disease cerebrospinal fluid analyzed by novel ultrasensitive immunoassays

Abstract

Background Neurogranin (Ng) is a neuron-specific and postsynaptic protein that is abundantly expressed in the brain, particularly in the dendritic spine of the hippocampus and cerebral cortex. The enzymatic cleavage of Ng produces fragments that are released into cerebrospinal (CSF), which have been shown to be elevated in Alzheimer’s disease (AD) patients and predict cognitive decline. Thus, quantification of distinctive cleavage products of Ng could elucidate different features of the disease. Methods In this study, we developed novel ultrasensitive single molecule array (Simoa) assays for measurement of full-length neurogranin (FL-Ng) and C-terminal neurogranin (CT-Ng) fragments in CSF. The Ng Simoa assays were evaluated in CSF samples from AD patients (N = 23), mild cognitive impairment due to AD (MCI-AD) (N = 18), and from neurological controls (N = 26). Results The intra-assay repeatability and inter-assay precision of the novel methods had coefficients of variation below 7% and 14%, respectively. CSF FL-Ng and CSF CT-Ng median concentrations were increased in AD patients (6.02 ng/L, P < 0.00001 and 452 ng/L, P = 0.00001, respectively) and in patients with MCI-AD (5.69 ng/L, P < 0.00001 and 566 ng/L, P < 0.00001) compared to neurological controls (0.644 ng/L and 145 ng/L). The median CSF ratio of CT-Ng/FL-Ng were decreased in AD patients (ratio = 101, P = 0.008) and in patients with MCI-AD (ratio = 115, P = 0.016) compared to neurological controls (ratio = 180). CSF of FL-Ng, CT-Ng, and ratio of CT-Ng/FL-Ng could each significantly differentiate AD patients from controls (FL-Ng, AUC = 0.907; CT-Ng, AUC = 0.913; CT-Ng/FL-Ng, AUC = 0.775) and patients with MCI-AD from controls (FL-Ng, AUC = 0.937; CT-Ng, AUC = 0.963; CT-Ng/FL-Ng, AUC = 0.785). Conclusions Assessments of the FL-Ng and CT-Ng levels in CSF with the novel sensitive immunoassays provide a high separation of AD from controls, even in early phase of the disease. The novel Ng assays are robust and highly sensitive and may be valuable tools to study synaptic alteration in AD, as well as to monitor the effect on synaptic integrity of novel drug candidates in clinical trials.

Alzheimer's Disease Biomarker Analysis Using Targeted Mass Spectrometry

“…Drawing from the knowledge obtained in the initial IP–MS studies, antineurogranin antibodies directed at the C-terminal part of neurogranin have been used to develop immunoassays ( 77 , 83 , 84 ), and the initial findings have been verified in several studies ( 85 ) with neurogranin consistently showing increased levels in CSF of AD patients as compared with controls. Higher levels of CSF neurogranin have been reported in AD compared with MCI ( 78 ).…”

Biofluid Biomarkers of Alzheimer’s Disease: Progress, Problems, and Perspectives

“…The dendritic protein neurogranin (Ng) is a postsynaptic protein associated with protein kinase C. It is found mainly in neurons of the hippocampus and cortex and can bind to calmodulin and regulate long-term potentiation [ 92 ]. Ng is a promising biomarker of AD with high sensitivity and specificity and is associated with AD-specific neurodegeneration and synaptic dysfunction [ 93 ]. CSF Ng is increased in AD associated with CSF t-tau, p-tau181, and Aβ42/Aβ40, and there is no prominent change in Ng in non-AD neurodegeneration.…”

Translocator protein (TSPO) genotype does not change cerebrospinal fluid levels of glial activation, axonal and synaptic damage markers in early Alzheimer’s disease

“…CSF levels of interleukin (IL)-6 and IL-10 measurements are pro and anti inflammatory cytokines, respectively, which are also involved in neuro-inflammation in AD ( Ogunmokun et al, 2021 ). In addition, CSF levels of neurofilament light chain (NfL) and neurogranin reflect axonal and synaptic damage, respectively, which are correlated with AD pathology and longitudinal cognitive decline and brain structural changes ( Mattsson et al, 2016 , Öhrfelt et al, 2020 ).…”