The aggregation of amyloid ␤ protein (A␤) is a fundamental pathogenic mechanism leading to the neuronal damage present in Alzheimer disease, and soluble A␤ oligomers are thought to be a major toxic culprit. Thus, better knowledge and specific targeting of the pathways that lead to these noxious species may result in valuable therapeutic strategies. We characterized some effects of the molecular chaperone clusterin, providing new and more detailed evidence of its potential neuroprotective effects. Using a classical thioflavin T assay, we observed a dose-dependent inhibition of the aggregation process. The global analysis of time courses under different conditions demonstrated that clusterin has no effect on the elongation rate but mainly interferes with the nucleation processes (both primary and secondary), reducing the number of nuclei available for further fibril growth. Then, using a recently developed immunoassay based on surface plasmon resonance, we obtained direct evidence of a high-affinity (K D ‫؍‬ 1 nM) interaction of clusterin with biologically relevant A␤ 1-42 oligomers, selectively captured on the sensor chip. Moreover, with the same technology, we observed that substoichiometric concentrations of clusterin prevent oligomer interaction with the antibody 4G8, suggesting that the chaperone shields hydrophobic residues exposed on the oligomeric assemblies. Finally, we found that preincubation with clusterin antagonizes the toxic effects of A␤ 1-42 oligomers, as evaluated in a recently developed in vivo model in Caenorhabditis elegans. These data substantiate the interaction of clusterin with biologically active regions exposed on nuclei/oligomers of A␤ 1-42 , providing a molecular basis for the neuroprotective effects of the chaperone.

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Background: A2V mutation is associated with early onset AD-type dementia in homozygous individuals. Results: A2V mutation leads to a peculiar kinetics of A␤ oligomerization. Conclusion: The A␤ N-terminal region plays an important role in the molecular assembly. Significance: in the homozygous condition the A2V mutation led to aggregation, whereas in the heterozygous state the evolution and kinetics of the aggregation process was hindered.

Human immunodeficiency virus type-1 (HIV-1)-associated neurocognitive disorder (HAND) remains an important neurological manifestation that adversely affects a patient’s quality of life. HIV-1 matrix protein p17 (p17) has been detected in autoptic brain tissue of HAND individuals who presented early with severe AIDS encephalopathy. We hypothesised that the ability of p17 to misfold may result in the generation of toxic assemblies in the brain and may be relevant for HAND pathogenesis. A multidisciplinary integrated approach has been applied to determine the ability of p17 to form soluble amyloidogenic assemblies in vitro. To provide new information into the potential pathogenic role of soluble p17 species in HAND, their toxicological capability was evaluated in vivo. In C. elegans, capable of recognising toxic assemblies of amyloidogenic proteins, p17 induces a specific toxic effect which can be counteracted by tetracyclines, drugs able to hinder the formation of large oligomers and consequently amyloid fibrils. The intrahippocampal injection of p17 in mice reduces their cognitive function and induces behavioral deficiencies. These findings offer a new way of thinking about the possible cause of neurodegeneration in HIV-1-seropositive patients, which engages the ability of p17 to form soluble toxic assemblies.