RESUMO
In Alzheimer's disease, tau protein undergoes post-translational modifications including hyperphosphorylation and truncation, which promotes two major conformational changes associated with progressive N-terminal folding. Along with the development of the disease, tau ubiquitination was previously shown to emerge in the early and intermediate stages of the disease, which is closely associated with early tau truncation at aspartic acid 421, but not with a subsequently truncated tau molecule at glutamic acid 391. In the same group of cases, using multiple immunolabeling and confocal microscopy, a possible relationship between the ubiquitin-targeting of tau and the progression of conformational changes adopted by the N-terminus of this molecule was further studied. A comparable number of neurofibrillary tangles was found displaying ubiquitin, an early conformation recognized by the Alz-50 antibody, and a phosphorylation. However, a more reduced number of neurofibrillary tangles were immunoreactive to Tau-66 antibody, a late tau conformational change marker. When double-labeling profiles of neurofibrillary tangles were assessed, ubiquitination was clearly demonstrated in tau molecules undergoing early N-terminal folding, but was barely observed in late conformational changes of the N-terminus adopted by tau. The same pattern of colocalization was visualized in neuritic pathology. Overall, these results indicate that a more intact conformation of the N-terminus of tau may facilitate tau ubiquitination, but this modification may not occur in a late truncated and more compressed folding of the N-terminus of the tau molecule.
Assuntos
Doença de Alzheimer/patologia , Encéfalo/patologia , Emaranhados Neurofibrilares/química , Ubiquitinação/fisiologia , Proteínas tau/química , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/metabolismo , Encéfalo/metabolismo , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Emaranhados Neurofibrilares/patologia , Conformação Proteica , Proteínas tau/metabolismoRESUMO
Laminin, an important extracellular matrix component is induced by brain injury and colocalizes with amyloid-beta-peptide (A beta) deposits in Alzheimer brains. We report here that laminin inhibits amyloid fibril formation as determined by thioflavin T fluorescence spectroscopy and electron microscopic examination. The inhibition of amyloid formation by laminin was concentration dependent and was observed at a laminin concentration of 300 nM, corresponding to a laminin/A beta protein molar ratio of 1:800. The potential effect of laminin, may prove important to inhibit A beta fibrillogenesis in vivo, specifically at the level of cerebral blood vessels.
Assuntos
Peptídeos beta-Amiloides/efeitos dos fármacos , Laminina/farmacologia , Peptídeos beta-Amiloides/metabolismo , Peptídeos beta-Amiloides/ultraestrutura , Humanos , Microscopia Eletrônica , Emaranhados Neurofibrilares/químicaRESUMO
1. Neurofibrillary tangles present in Alzheimer's disease and, in a lower proportion, in aged brains are formed mainly by paired helical filaments. The microtubule-associated protein tau is a major structural component of these filaments. In order to increase our understanding of the aberrant behaviour of tau protein leading to its assembly into paired helical filaments, studies were carried out using chemical modifications of brain tau protein. 2. Selective carbamoylation of tau with KCNO resulted in an irreversible modification of lysine residues on tau protein. The capacity of chemically modified tau protein to induce tubulin assembly, under standard in vitro microtubule polymerization conditions, decreased gradually in relation to the increase in concentration of the modifying reagent. 3. Interestingly, carbamoylated tau protein exhibited the capacity to self-assemble into polymeric structures resembling those of paired helical filaments, after incubating the modified protein at concentrations higher than 1.0 mg/ml, at 37 degrees C with KCNO. 4. The nature of polymers obtained from cabamoylated tau protein was analyzed by ultrastructural studies. The data provide new clues toward our understanding of the anomalous interactions of tau in Alzheimer's disease.