Search

Characteristically identified as the main component of senile plaques present in patients suffering from Alzheimer's disease, Aβ has been detected in human testis and reproductive fluids, but its effect on spermatozoa has not been addressed. The present study evaluated whether the most toxic and aggregant amyloid precursor protein (APP)-proteolytic product, amyloid-β (Aβ), was capable of affecting sperm functionality. Normozoospermic samples were either exposed to different Aβ doses or to the untreated and scrambled controls for a maximum of 48 h at 37 °C and 5%CO, and motility, viability and mitochondrial status were evaluated. Additionally, tyrosine phosphorylation was analyzed by immunocytochemistry and acrosomal integrity through PSA-FITC. A shorter treatment period was used to monitor prompt Ca responses. Aβ peptide decreased motility before inducing mitochondrial impairment ( p < 0.05; n = 6). Both outcomes became more pronounced with time, reaching their maximal decrease at 48 h, where even 1 μM produced undesirable effects ( p < 0.05; n = 6). Aβ peptide also decreased cell survival ( p < 0.05; n = 6). Furthermore, although no effects on tyrosine phosphorylation were observed ( p > 0.05; n = 6), reduced acrosomal integrity was detected ( p < 0.05; n = 7), which was not correlated with viability loss ( p > 0.05). In parallel, all Aβ concentrations elicited a [Ca] rise but a significant difference was only observed at 20 μM ( p < 0.05; n = 7) and a tendency was obtained with 10 μM ( p = 0.053; n = 7). In conclusion, Aβ peptide oligomers impair sperm function in vitro, although further studies are required to determine the clinical relevance of these findings. [ABSTRACT FROM AUTHOR]

Retention of intracellular secreted APP (isAPP) can be provoked by the neurotoxic peptide Aβ. The latter decreases in the cerebrospinal fluid of Alzheimer's disease (AD) patients, as a consequence of its cerebral accumulation and deposition into senile plaques. Of similar relevance, secreted APP (sAPP) levels can be associated with AD. The studies here presented, reinforce the link between sAPP and Aβ and address putative therapeutic strategies. Laminin and gelsolin are potential candidates; both prevent Aβ fibril formation by complexing with Aβ, thus attenuating its neurotoxicity. We show that preincubation of Aβ with laminin and gelsolin has the effect of rendering it less potent to isAPP accumulation in cortical neurons. This appears to be related to a decrease in F-actin polymerization, whereas Aβ alone induces the polymerization. Further, Aβ decreases gelsolin levels, and the latter is involved in Aβ removal. Our data indicates that Aβ-laminin and Aβ-gelsolin complexes are less neurotoxic and also less potent than fibrillar Aβ at inducing isAPP retention. These results validate the potential of these proteins as therapeutic strategies that prevent the Aβ-induced effects. In hence, given that Aβ decreases the levels of proteins involved in its own clearance, this may contribute to the mechanisms underlying AD pathology. [ABSTRACT FROM AUTHOR]

The intracellular domain of the Alzheimer’s amyloid precursor protein (AICD) has been described as an important player in the transactivation of specific genes. It results from proteolytic processing of the Alzheimer’s amyloid precursor protein (APP), as does the neurotoxic Aβ peptide. Although normally produced in cells, Aβ is typically considered to be a neurotoxic peptide, causing devastating effects. By exposing primary neuronal cultures to relatively low Aβ concentrations, this peptide was shown to affect APP processing. Our findings indicate that APP C-terminal fragments are increased with concomitant reduction in the expression levels of APP itself. AICD nuclear immunoreactivity detected under control conditions was dramatically reduced in response to Aβ exposure. Additionally, intracellular protein levels of Fe65 and GSK3 were also decreased in response to Aβ. APP nuclear signaling is altered by Aβ, affecting not only AICD production but also its nuclear translocation and complex formation with Fe65. In effect, Aβ can trigger a physiological negative feedback mechanism that modulates its own production. [ABSTRACT FROM AUTHOR]

The neurotoxic Abeta peptide is derived by proteolytic processing from the Alzheimer’s amyloid precursor protein (APP), whose short cytoplasmic domain contains several phosphorylatable amino acids. The latter can be phosphorylated ‘in vitro’ and ‘in vivo,’ and in some cases phosphorylation appears to be associated with the disease condition. Using APP-GFP fusion proteins to monitor APP processing, the role of Tyr687 was addressed by mimicking its constitutive phosphorylation (Y687E) and dephosphorylation (Y687F). Contrasting effects on subcellular APP distribution were observed. Y687E-APP-GFP was targeted to the membrane but could not be detected in transferrin containing vesicular structures, and exhibited a concomitant and dramatic decrease in Abeta production. In contrast, Y687F-APP-GFP was endocytosed similarly to wild type APP, but was relatively favoured for beta-secretase cleavage. Overall, Tyr687 appears to be a critical residue determining APP targeting and processing via different pathways, including endocytosis and retrograde transport. Significantly, from a disease perspective, mimicking Tyr687 phosphorylation resulted in a hitherto undescribed inhibition of Abeta production. Our results provide novel insights into the role of direct APP phosphorylation on APP targeting, processing and Abeta production. [ABSTRACT FROM AUTHOR]