Dataset Information

Alzheimer-associated cerebrospinal fluid fragments of neurogranin are generated by Calpain-1 and prolyl endopeptidase.

ABSTRACT: BACKGROUND:Neurogranin (Ng) is a small 7.6 kDa postsynaptic protein that has been detected at elevated concentrations in cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD), both as a full-length molecule and as fragments from its C-terminal half. Ng is involved in postsynaptic calcium (Ca) signal transduction and memory formation via binding to calmodulin in a Ca-dependent manner. The mechanism of Ng secretion from neurons to CSF is currently unknown, but enzymatic cleavage of Ng may be of relevance. Therefore, the aim of the study was to identify the enzymes responsible for the cleavage of Ng, yielding the Ng fragment pattern of C-terminal fragments detectable and increased in CSF of AD patients. METHODS:Fluorigenic quenched FRET probes containing sequences of Ng were utilized to identify Ng cleaving activities among enzymes known to have increased activity in AD and in chromatographically fractionated mouse brain extracts. RESULTS:Human Calpain-1 and prolyl endopeptidase were identified as the candidate enzymes involved in the formation of endogenous Ng peptides present in CSF, cleaving mainly in the central region of Ng, and between amino acids 75_76 in the Ng sequence, respectively. The cleavage by Calpain-1 affects the IQ domain of Ng, which may deactivate or change the function of Ng in Ca2+/calmodulin -dependent signaling for synaptic plasticity. While shorter Ng fragments were readily cleaved in vitro by prolyl endopeptidase, the efficiency of cleavage on larger Ng fragments was much lower. CONCLUSIONS:Calpain-1 and prolyl endopeptidase cleave Ng in the IQ domain and near the C-terminus, respectively, yielding specific fragments of Ng in CSF. These fragments may give clues to the roles of increased activities of these enzymes in the pathophysiology of AD, and provide possible targets for pharmacologic intervention.

SUBMITTER: Becker B

PROVIDER: S-EPMC6116393 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Alzheimer-associated cerebrospinal fluid fragments of neurogranin are generated by Calpain-1 and prolyl endopeptidase.

Becker Bruno B Nazir Faisal Hayat FH Brinkmalm Gunnar G Camporesi Elena E Kvartsberg Hlin H Portelius Erik E Boström Martina M Kalm Marie M Höglund Kina K Olsson Maria M Zetterberg Henrik H Blennow Kaj K

Molecular neurodegeneration 20180829 1

<h4>Background</h4>Neurogranin (Ng) is a small 7.6 kDa postsynaptic protein that has been detected at elevated concentrations in cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD), both as a full-length molecule and as fragments from its C-terminal half. Ng is involved in postsynaptic calcium (Ca) signal transduction and memory formation via binding to calmodulin in a Ca-dependent manner. The mechanism of Ng secretion from neurons to CSF is currently unknown, but enzymatic cleav ...[more]

PMID: 30157938

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Project description:Synaptic dysfunction is linked to cognitive symptoms in Alzheimer's disease. Thus, measurement of synapse proteins in cerebrospinal fluid may be useful biomarkers to monitor synaptic degeneration. Cerebrospinal fluid levels of the postsynaptic protein neurogranin are increased in Alzheimer's disease, including in the predementia stage of the disease. Here, we tested the performance of cerebrospinal fluid neurogranin to predict cognitive decline and brain injury in the Alzheimer's Disease Neuroimaging Initiative study. An in-house immunoassay was used to analyse neurogranin in cerebrospinal fluid samples from a cohort of patients who at recruitment were diagnosed as having Alzheimer's disease with dementia (n = 95) or mild cognitive impairment (n = 173), as well as in cognitively normal subjects (n = 110). Patients with mild cognitive impairment were grouped into those that remained cognitively stable for at least 2 years (stable mild cognitive impairment) and those who progressed to Alzheimer's disease dementia during follow-up (progressive mild cognitive impairment). Correlations were tested between baseline cerebrospinal fluid neurogranin levels and baseline and longitudinal cognitive impairment, brain atrophy and glucose metabolism within each diagnostic group. Cerebrospinal fluid neurogranin was increased in patients with Alzheimer's disease dementia (P < 0.001), progressive mild cognitive impairment (P < 0.001) and stable mild cognitive impairment (P < 0.05) compared with controls, and in Alzheimer's disease dementia (P < 0.01) and progressive mild cognitive impairment (P < 0.05) compared with stable mild cognitive impairment. In the mild cognitive impairment group, high baseline cerebrospinal fluid neurogranin levels predicted cognitive decline as reflected by decreased Mini-Mental State Examination (P < 0.001) and increased Alzheimer's Disease Assessment Scale-cognitive subscale (P < 0.001) scores at clinical follow-up. In addition, high baseline cerebrospinal fluid neurogranin levels in the mild cognitive impairment group correlated with longitudinal reductions in cortical glucose metabolism (P < 0.001) and hippocampal volume (P < 0.001) at clinical follow-up. Furthermore, within the progressive mild cognitive impairment group, elevated cerebrospinal fluid neurogranin levels were associated with accelerated deterioration in Alzheimer's Disease Assessment Scale-cognitive subscale (β = 0.0017, P = 0.01). These data demonstrate that cerebrospinal fluid neurogranin is increased already at the early clinical stage of Alzheimer's disease and predicts cognitive deterioration and disease-associated changes in metabolic and structural biomarkers over time.

Project description:Neurogranin (Ng) is a post-synaptic protein that previously has been shown to be a biomarker for synaptic function when measured in cerebrospinal fluid (CSF). The CSF concentration of Ng is increased in Alzheimer's disease dementia (ADD), and even in the pre-dementia stage. In this prospective study, we used an enzyme-linked immunosorbent assay that quantifies Ng in CSF to test the performance of Ng as a marker of synaptic function. In 915 patients, CSF Ng was evaluated across several different neurodegenerative diseases. Of these 915 patients, 116 had a neuropathologically confirmed definitive diagnosis and the relation between CSF Ng and topographical distribution of different pathologies in the brain was evaluated. CSF Ng was specifically increased in ADD compared to eight other neurodegenerative diseases, including Parkinson's disease (p < 0.0001), frontotemporal dementia (p < 0.0001), and amyotrophic lateral sclerosis (p = 0.0002). Similar results were obtained in neuropathologically confirmed cases. Using a biomarker index to evaluate whether CSF Ng contributed diagnostic information to the core AD CSF biomarkers (amyloid β (Aβ), t-tau, and p-tau), we show that Ng significantly increased the discrimination between AD and several other disorders. Higher CSF Ng levels were positively associated with greater Aβ neuritic plaque (Consortium to Establish a Registry for Alzheimer's Disease (CERAD) neuritic plaque score, p = 0.0002) and tau tangle pathology (Braak neurofibrillary tangles staging, p = 0.0007) scores. In the hippocampus and amygdala, two brain regions heavily affected in ADD with high expression of Ng, CSF Ng was associated with plaque (p = 0.0006 and p < 0.0001), but not with tangle, α-synuclein, or TAR DNA-binding protein 43 loads. These data support that CSF Ng is increased specifically in ADD, that high CSF Ng concentrations likely reflect synaptic dysfunction and that CSF Ng is associated with β-amyloid plaque pathology.

Project description:Widespread implementation of cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease (AD) in clinical settings requires improved accuracy for diagnosis of prodromal disease and for distinguishing AD from non-AD dementias. Novel and promising CSF biomarkers include neurogranin, a marker of synaptic degeneration, and YKL-40, a marker of neuroinflammation.CSF neurogranin and YKL-40 were measured in a cohort of 338 individuals including cognitively healthy controls and patients with stable mild cognitive impairment (sMCI), MCI who later developed AD (MCI-AD), AD dementia, Parkinson's disease dementia (PDD), dementia with Lewy bodies (DLB), vascular dementia (VaD), and frontotemporal dementia (FTD). The diagnostic accuracy of neurogranin and YKL-40 were compared with the core AD biomarkers, β-amyloid (Aβ42 and Aβ40) and tau.Neurogranin levels were increased in AD and decreased in non-AD dementia compared with healthy controls. As a result, AD patients showed considerably higher CSF levels of neurogranin than DLB/PDD, VaD and FTD patients. CSF YKL-40 levels were increased in AD compared with DLB/PDD but not with VaD or FTD. Neither CSF neurogranin nor YKL-40 levels differed significantly between sMCI patients and MCI-AD patients. Both biomarkers correlated positively with CSF Aβ40 and tau. CSF neurogranin and YKL-40 could separate AD dementia from non-AD dementias (neurogranin, area under the curve [AUC] = 0.761; YKL-40, AUC = 0.604; Aβ42/neurogranin, AUC = 0.849; Aβ42/YKL-40, AUC = 0.785), but the diagnostic accuracy was not better compared to CSF Aβ and tau (Aβ42, AUC = 0.755; tau AUC = 0.858; Aβ42/tau, AUC = 0.895; Aβ42/Aβ40, AUC = 0.881). Similar results were obtained when separating sMCI from MCI-AD cases.CSF neurogranin and YKL-40 do not improve the diagnostic accuracy of either prodromal AD or AD dementia when compared to the core CSF AD biomarkers. Nevertheless, the CSF level of neurogranin is selectively increased in AD dementia, whereas YKL-40 is increased in both AD and FTD suggesting that synaptic degeneration and glial activation may be important in these neurodegenerative conditions.

Dataset Information

Alzheimer-associated cerebrospinal fluid fragments of neurogranin are generated by Calpain-1 and prolyl endopeptidase.

Publications

Alzheimer-associated cerebrospinal fluid fragments of neurogranin are generated by Calpain-1 and prolyl endopeptidase.

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