| dc.description.abstracteng | Alzheimer’s disease (AD) is the most common dementia-associated neurodegenerative disorder. It has detrimental social and economic impact not only on patients, but also their family and society as a whole. Current estimations predict a total of 131 million affected with the disease in 2050 (World Alzheimer Report, 2016), increasing socio-economic pressure. To date there is no cure and no efficient treatment against AD available. Appearance and progression of AD depend on the interplay between genetic and environmental risk factors, which is intimately linked with the epigenetic machinery, since it is exactly at the interface between the environment and the genome. With the aim of exploring novel strategies to ameliorate or prevent age- associated dementia, I used 3 complementary approaches that led to the identification of suitable drug- and genetic-based targets.
First, to identify novel drug targets I performed a screening for proteins specifically binding the memory-associated histone mark H4K12ac. I identified ANXA2 as a significant chromatin reader. I could show that ANXA2 not only changes sub-cellular localisation during ageing, but is causally involved in cognitive function. My findings suggest that ANXA2 is a baseline inhibitor of spatial memory function. Since ANXA2 is naturally multifactorial, it is challenging to pinpoint a precise mechanism. However, my data indicates that ANXA2 influences two key aspects relevant to learning and memory: on the one hand it contributes to extracellular matrix dynamics, which has previously been reported to be a regulator of synaptic plasticity. On the other hand, I found evidence that supports a role of ANXA2 in modulating energy metabolism through alternative 5’ usage. Although I did not manipulate ANXA2 in an AD model, my observations suggest that inhibiting it could be a suitable strategy to ameliorate memory impairment in AD.
Second, to test whether previously identified targets could constitute novel treatment strategies against AD, I explored the benefits of two pharmacological compounds (JS28 and anle138b) and a genetic model of HDAC6 deletion (Tau/HDAC6). My findings on HDAC6 depletion show a reversal of the common anxiety phenotype in a mouse model for AD-like tauopathy. This suggests that specific inhibition of HDAC6 could be a suitable treatment strategy specifically aimed at normalising anxiety in AD. This is complemented with other findings reporting a benefit of HDAC6 depletion in AD-like amyloidosis (Govindarajan, Rao et al. 2013). One of the pathological AD mechanisms is the pore formation hypothesis. It states that Aß oligomers pierce through neuronal membranes forming ion-channels and thereby shorting signal transduction and causing cell death. We assessed the efficacy of anle138b as a pore formation inhibitor upon Aß exposure and report highly beneficial effects of the molecule in a recent issue of ”EMBO molecular medicine”. Anle138b reinstated LTP and spatial memory even at late stages of amyloid deposition in the APP/PS1 mouse model for AD-like amyloidosis. We present evidence that anle138b could act through induction of conformational changes to the Aß pore structure and that membrane integrity is reinstated after anle138b treatment both in vitro and in vivo. This supports previous findings that suggested a beneficial function of anle138b in other aggregopathies, including AD-like tauopathy.
Third, I developed a new technical strategy aimed at studying network dynamics. In order to understand complex diseases, such as AD, it is essential to study neurons in the network and go beyond cellular events to systems-level events. I designed and optimised a novel AAV-based vector system to introduce genetic constructs into neuronal subpopulations. I demonstrated the effectiveness of this approach in a proof-of-principle experiment, introducing channelrhodopsin to investigate the influence of low-density activity on neuronal networks. Importantly, this system is highly customisable and could be adapted for a broad range of applications. To complement the channelrhodopsin-driven neuronal network activity, I designed and engineered a new optogenetic stimulator for cell culture (LuCIFR). By combining vector-based subpopulation targeting with FACS sorting, LuCIFR-based stimulation and single-cell sequencing, I established a new technical approach to study network dynamics in subpopulations and individual cells.
In this thesis I explored several molecular pathways involved in cognitive function with an emphasis on therapeutic applications. I identified ANXA2 as a chromatin reader and inhibitor of spatial memory function, contributed to the characterisation of 2 highly novel AD treatment strategies, and developed a new system to decipher neuronal network dynamics. While each of these topics comprises its own field for future investigations, I am positive they will impact neurodegenerative and neurocognitive research and hopefully contribute to future treatments of cognitive impairments and AD.
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