Investigation into the molecular complexity of alzheimer’s disease: an amyloid-β centered approach
Federica Cioffi is a PhD student in the Nanobiophysics group. Her supervisor is prof.dr. M.M.A.E. Claessens from the faculty of Science and Technology.
Of all the diseases that lead to dementia, Alzheimer’s disease (AD) is the most common, affecting millions of elderly people worldwide. Although a lot of research has been carried out to understand the cellular and molecular events responsible for brain dysfunction and AD pathogenesis, no effective therapy has been identified yet. In the research described in this doctoral thesis we tried to obtain a more detailed understanding of four early hallmarks of AD: Amyloid-beta (Aβ) aggregation, Aβ accumulation, oxidative stress and neuroinflammation.
In chapter 2 and 3 we described in vitro studies aimed at investigating the potential of small molecules to reduce Aβ aggregation or blocking the toxic assemblies forming during the aggregation process. Inhibition of Aβ aggregation is a common strategy that has resulted in the development and testing of several compounds.
Enzymatic removal of soluble Aβ, could provide a mean to maintain brain Aβ homeostasis. Since the Aβ proteolytic cleavage apparatus is hampered in the AD brain, in chapter 4 we investigated the ability of a known Ab degrading enzyme, named Insulin-degrading enzyme (IDE), to cleave Aβ at different aggregation stages. Our findings show that Aβ monomers, either alone in solution or in equilibrium with higher aggregates, are cleaved at multiple sites by IDE. Moreover, we report a new Aβ cleavage site between Met35 and Val36, and show that the resulting Aβ fragments form non-toxic amorphous aggregates that are not or less sensitive for Thioflavin T (ThT) staining
In chapter 5, we reviewed the available literature on molecular mechanisms that drive the contribution of oxidative stress to AD and describe factors that may be causative of oxidative stress in vitro, in vivo and in clinical studies.
The last part, which includes chapters 6 and 7, describes a potential link between neuroinflammation and neurodegeneration in AD. Neuronal loss, observed in AD coincides with neuroinflammation and deposition of Aβ peptide in the brain. We found that Aβ and Interferon-g (IFNg), which plays a major role in inflammation, together potently activate microglia into a pro-inflammatory phenotype and we observed that this resulted into microglial NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome assembly. In response to this, Interleukin-1β (IL-1β) secretion levels were raised, which, in turn, resulted in loss of synchronous firing activity in a rat primary neuronal culture. Moreover, we showed, using biophysical techniques, that IFNg can modulate the aggregation behaviour of Aβ, even though they do not seem to strongly interact.
Summarizing, we have attempted to understand and obtain better insights into the molecular complexity of AD. This thesis highlights the multifactorial and complex character of AD and suggests that a multi-target approach, most likely, will contribute to the development of an effective AD therapy, halting the progression of this devastating disease.