Related Experiment Videos
Free Heme and Amyloid-β: A Fatal Liaison in Alzheimer's Disease
Elisabeth Chiziane1, Henriette Telemann1, Martin Krueger2
1Institute for Medical Physics and Biophysics, Medical Faculty, Leipzig University, Leipzig, Germany.
Abstract:
While the etiology of Alzheimer's disease (AD) is still unknown, an increased formation of amyloid-β (Aβ) peptide and oxidative processes are major pathological mechanism of the disease. The interaction of Aβ with free heme leads to the formation of peroxidase-active Aβ-heme complexes. However, enzyme-kinetic data and systematic mutational studies are still missing. These aspects were addressed in this study to evaluate the role of Aβ-heme complexes in AD. The enzyme-kinetic measurements showed peroxidase-specific pH- and H2O2-dependencies. In addition, the enzymatic activity of Aβ-heme complexes constantly increased at higher peptide excess. Moreover, the role of the Aβ sequence for the named enzymatic activity was tested, depicting human-specific R5, Y10, and H13 as essential amino acids. Also by studying Y10 as an endogenous peroxidase substrate for Aβ-heme complexes, ratio-specific effects were observed, showing an optimal dityrosine formation at an about 40-fold peptide excess. As dityrosine formation promotes Aβ fibrillation while free heme disturbs protein aggregation, we also investigated the effect of Aβ-heme complex-derived peroxidase activity on the formation of Aβ fibrils. The fluorescence measurements showed a different fibrillation behavior at strong peroxidase activity, leading also to altered fibril morphologies. The latter was detected by electron microscopy. As illustrated by selected in vivo measurements on a mouse model of AD, the disease is also characterized by Aβ-derived microvessel destructions and hemolytic processes. Thus, thrombo-hemorrhagic events are discussed as a source for free heme in brain tissue. In summary, we suggest the formation and enzymatic activity of Aβ-heme complexes as pathological key features of AD.
Insights
Amyloid-beta (Aβ)-heme complexes exhibit peroxidase activity crucial in Alzheimer's disease (AD) pathology. This activity, influenced by specific amino acids and heme levels, promotes Aβ fibrillation and alters fibril morphology, suggesting a key role in AD.
Area of Science:
- Biochemistry
- Neuroscience
- Pathology
Background:
- Alzheimer's disease (AD) etiology remains unknown, but amyloid-beta (Aβ) peptide formation and oxidative stress are key mechanisms.
- Aβ interaction with free heme forms peroxidase-active Aβ-heme complexes, implicated in AD pathogenesis.
- Enzyme-kinetic data and mutational studies of these complexes were lacking.
Purpose of the Study:
- To investigate the enzyme kinetics and mutational effects on Aβ-heme complex activity.
- To evaluate the role of Aβ-heme complex peroxidase activity in Aβ fibrillation and morphology.
- To explore the link between in vivo AD pathology, free heme, and Aβ-heme complex formation.
Main Methods:
- Enzyme-kinetic measurements to determine pH and H2O2 dependencies.
- Systematic mutational studies of Aβ sequence and peptide excess effects.
- Fluorescence spectroscopy and electron microscopy to analyze Aβ fibrillation and morphology.
- In vivo measurements on an AD mouse model.
Main Results:
- Aβ-heme complexes exhibit peroxidase activity with specific pH and H2O2 dependencies.
- Enzymatic activity increases with higher peptide excess, with R5, Y10, and H13 identified as essential amino acids.
- Strong peroxidase activity promotes Aβ fibrillation and alters fibril morphology, with optimal dityrosine formation at ~40-fold peptide excess.
- In vivo studies showed Aβ-derived microvessel destructions and hemolytic processes, suggesting thrombo-hemorrhagic events as a source of free heme.
Conclusions:
- Aβ-heme complexes possess significant peroxidase activity, modulated by peptide concentration and specific amino acid residues.
- This enzymatic activity plays a critical role in promoting Aβ fibrillation and influencing fibril structure.
- The formation and activity of Aβ-heme complexes are proposed as key pathological features in Alzheimer's disease.