Extracellular GAPDH promotes Alzheimer disease progression by enhancing amyloid-β aggregation and cytotoxicity

Abstract

Background Neuronal cell death during Alzheimer disease (AD) causes the release of cytosolic proteins, particularly glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which forms highly cytotoxic detergent-insoluble complexes with amyloid-β (Aβ) and promotes neurodegeneration. Methods We detected and quantified the complex formation between Aβ and GAPDH released from brain tissue of patients with AD using ultrafiltration, and fluorescence resonance energy transfer (FRET). To explore the biochemical and structural features of Aβ-GAPDH complexes we employed novel immunoenzyme assays and atomic force microscopy. Lentiviral infection in situ was used to elevate GAPDH in brain tissue of rat and mouse models of AD. The Morris maize water test, MRI, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and lactate dehydrogenase (LDH)-activity assays were used to characterize the effects of Aβ-GAPDH complexes in animal and cellular models of AD. Results Here we report that GAPDH forms stable aggregates with extracellular Aβ. We detected these aggregates in cerebrospinal fluid (CSF) from AD patients at levels directly proportional to the progressive stages of AD. We found that GAPDH forms a covalent bond with Q15 of Aβ that is mediated by transglutaminase (tTG). The Q15A substitution weakens the interaction between Aβ and GAPDH and reduces Aβ-GAPDH cytotoxicity. Lentivirus-driven GAPDH overexpression in two AD animal models increased the level of apoptosis of hippocampal neurons, neuronal degeneration, and cognitive dysfunction. In contrast, in vivo knockdown of GAPDH reversed these pathogenic abnormalities suggesting a pivotal role of GAPDH in Aβ-stimulated neurodegeneration. CSF obtained from animals with enhanced GAPDH expression demonstrated increased cytotoxicity in vitro . Furthermore, RX-624, a specific GAPDH small molecular ligand reduced accumulation of Aβ aggregates and reversed memory deficit in AD transgenic mice. Conclusions Extracellular GAPDH compromises Aβ clearance and accelerates neurodegeneration, thus representing a promising pharmacological target for AD.

Predictors of Cognitive Decline in Healthy Middle-Aged Individuals with Asymptomatic Alzheimer’s Disease

“…SMOC1 (protein for AQALEQAK peptide), which is related to the extracellular matrix and strongly correlated with global AD pathology in brain 63 , has shown the ability to discriminate between AD and non-AD cognitive impairment (specificity for AD) and to predict levels of CSF Aβ42, tTau, and pTau 58 . GAPDH (protein for the YDNSLK peptide) is known to form stable aggregates with extracellular Aβ, and these aggregates have been found to be proportional to the progressive stage of AD 64,65 . These peptides from 8 proteins, each with plausible biological connection to AD pathophysiology, were found to be among the most strongly associated with cognition and were able to discriminate CSF samples from AD patients and Controls with 98% accuracy (Fig.…”

Monitoring GAPDH activity and inhibition with cysteine-reactive chemical probes

“…For example, in the case of Alzheimer's disease, GAPDH binds amyloid-b to form stable neurotoxic aggregates. 15,16 Given the key role of GAPDH in a variety of pathophysiological processes, it is important to have access to methods that allow for rapid interrogation of GAPDH activity within a complex proteome. Current methods for evaluating GAPDH activity involve spectrophotometric assays that monitor NADH levels.…”