Recognition of Alzheimer paired helical filaments by monoclonal neurofilament antibodies is due to crossreaction with tau protein.

Abstract

Neurofibrillary tangles and senile plaques are the principal pathological features of Alzheimer disease. Neurofibrillary tangles and the neurites of senile plaques contain paired helical filaments (PHF) that consist of two 10-nm filaments twisted into a double helix. The precursor proteins of PHIF are not fully known. To identify these precursors, numerous immunochemical studies have been carried out during the past decade. Two apparently conflicting results have been reported. (I) Some, but not all, monoclonal antibodies to neuroframents stained neurofibrillary tangles. (is) Polyclonal antibodies prepared to PHF purified in NaDodSO4 because of their unusual insolubility did not recognize normal proteins, including neurofilaments, on electrophoretic transfer blots of human brain homogenates. These results have been confirmed in several laboratories, including by the use of electron microscopic labeling. Recently, we reported that polyconal PHF antibodies include antibodies to tau proteins, a family of heat-stable microtubule-associated phosphoproteins, and that antibodies to tau stain Alzheimer neurofibrillary tangles. Those monoclonal neuroframent antibodies that recognize tangles are reported to be directed against phosphorylated epitopes. These facts prompted us to reexamine certain neurofilament monoclonal antibodies that stain neurofibrillary tangles. All monoclonal neurofflament antibodies that stain tangles that we examined, including those initially reported, reacted with tau proteins. Our results suggest that these antibodies react with phosphorylated tau proteins in PH1F, not neurofilament proteins, highlighting the problem of using antibodies to phosphorylated protein epitopes in immunochemical studies. Independent evidence for the presence of neurofflament proteins in human paired helical filaments is now required.

p62 Is a Common Component of Cytoplasmic Inclusions in Protein Aggregation Diseases

“…This component had been shown to be recognized by the antibody SMI 31, which binds to phosphoepitopes present on tau protein as well as on neurofilaments in neurofibrillary tangles and Lewy bodies. 14,33 The MB proteins were characterized after tryptic digestion of excised protein spots by MALDI-TOF mass spectrometry (Figure 1). According to the NCBInr database the best hit for peptide masses obtained from tryptic digest of the SMI-31-reactive protein (Figure 1a, spot 4) was the oxidative stress protein A 170 from mouse, which is a homologue to the human p62 ubiquitin-binding protein.…”

Tau protein kinase I is essential for amyloid beta-protein-induced neurotoxicity.

“…Ubiquitin (3,4) and highly phosphorylated tau proteins, members of a family of microtubule-associated phosphoproteins, predominantly compose NFT. The tau proteins form paired helical filaments (PHF), which are found in NFT and degenerative neurites of senile plaques (5)(6)(7). The molecular mechanisms by which these lesions arise are unknown.…”

Tau consists of a set of proteins with repeated C-terminal microtubule-binding domains and variable N-terminal domains.

“…Tau shares epitopes with paired helical filaments, a major constituent of the cytopathological * Corresponding author. neurofibrillary tangles, which are found at autopsy in brains from patients with Alzheimer's disease (14,20, 23,31,42).Although numerous cell biological and biophysical studies of MAP proteins have begun to define the possible roles of these proteins in controlling microtubule assembly and have hinted at a role in mediating interactions with other components, the lack of detailed structural information has limited our understanding. We do not understand whether there are specialized regions of these molecules that act as tubulin receptors, and in the case of tau protein we do not yet understand the basis for the similarities and heterogeneities in that group.…”