Acetyltransferase activation in Alzheimer's disease – ATACTAD

The ATACTAD project aims at determining how chromatin acetylation is impacted in AD and how such events alter memory functions. It implements a large panel of techniques from molecular biology (protein analyses, gene expression, lentivirus infections, high throughput sequencing allowing high resolution and genome-wide analyses of chromatin structure), cellular biology (electrophysiology, immunohistochemistry) and behavioral analyses (spatial memory). Using 2 animal models relevant of AD (APP and Tau), we will test the ability of a new acetylation modulator molecule, to enhance memory functions and modify pathological features of AD. This is an original strategy based on reactivation of plasticity-related genetic programs through modulation of a chromatin modifying co-activators (CBP/p300 acetyltransferases) to restore memory functions, even when neurodegeneration is in play. Indeed, it acts directly in the nucleus, therefore does not rely on the presence of a specific receptor. We produced the first CBP/p300 HAT activator molecule developed so far, and can, when bound to a carbon nanosphere, cross cellular membranes and modify nuclear chromatin. This molecule pass through the blood brain barrier and can activate histone acetylation in the brain after intraperitoneal injection. Our data show the ability of such molecule to activate adult neurogenesis and long-term spatial memory. We will lead functional and behavioral studies on two AD mouse models presentinf either neurofibrillary tangles or amyloid plaques, and subjected to acute or chronic molceule injections. This study presents an original alternative - and maybe more specific – to current ones developed these last decade that rely on HDAC inhibition.

Our working hypothesis is that chromatin acetylation-related alterations occur during the course of Alzheimer's disease, so that they will disturb neuronal function and plasticity, and more widely, one's memory functions. Our project aims to identify these dysregulations at the epigenetic and genetic levels in transgenic mouse models relevant to AD.
By using chromatin-immunoprecipitation followed by massive parallel sequencing (ChIP-seq), a technique allowing high resolution and genome-wide analyses of chromatin structure, we investigated H2Bac-associated genes during spatial memory formation and their relation to expression level (RNA-seq) in the dorsal hippocampus. Analyses are currently ongoing. We also showed in a mouse model of tauopathy, that global acetylation regulations, particularly that of H2bac, were altered in the dorsal hippocampus and prefrontal cortex, two important brain sub-structures for spatial memory formation and consolidation. Gene expression studies and their correlation with spatial memory-associated genes are ongoing.
We obtained a proof of concept showing that direct pharmacological activation of chromatin acetylating enzymes (CBP/p300 family) favored adult neurogenesis (maturation and differentiation) and improved long-term spatial memory retention in healthy mice. Remarkably, our recent (unpublished) data show that a treatment of Tau mice with a HAT activator molecule restores (spatial) memory functions, at an age at which mice present neurofibrillary tangles (NFTs) and long-term memory is otherwise lost. The precise mechanisms underlying such molecule-induced restoration is currently investigated at the genome-wide (RNA-seq) and cellular (electrophysiology, dendritic spine formation) levels.

In the second half of this project, important findings obtained in the Tau mouse model will be led in an amyloid mouse model. In addition, the influence of the HAT activator treatment when administred chronically will be evaluated for its ability to impact classical AD pathological hallmarks (amyloid plaques, NFTs, inflammation).
Knowledge about the mechanisms of action of HATs activator molecules in the healthy and the pathological brain will open new therapeutic options that should ameliorate the everyday life of AD patients by acting at the symptomatic level (memory improvement, new neuron produciton in the brain). In addition, projet ATACTAD achievement will inform us about the curative potential of these molecule. Another important practical application of such compounds could be to improve regenerative biology with neuronal progenitor in neurodegenerative diseases.

Our data gave rise to a scientific publication in The Journal of Neuroscience, as well as an international application patent. We bring proof of concept of a beneficial effect of HAT activator molecules in the maturation and differentiation of newly-generated neurons and memory functions in healthy adult mice, and further bring evidence of a restoration of long-term spatial memory formation in an AD mouse model.
This project has also contributed to obtain new international contracts with India (Prof. Kundu, Bangalore; CEFIPRA/IFCPAR contract).

Neurodegenerative diseases, above all Alzheimer’s disease (AD), may be accompanied by cognitive deficits that end up in dementia. There is no satisfactory cure for AD. Current symptomatic strategies consist in preserving acetylcholine levels or blocking NMDA receptors. Unfortunately, their benefit is modest and concerns only a subset of patients. The general context of the current proposal is to test a newly developed molecule as a new therapeutic option to mitigate cognitive dysfunctions in AD. This molecule is a histone acetyltransferase (HAT) activator, targeting the CBP/p300 family of enzymes, which are known to play a mandatory role for memory formation and storage. By modulating chromatin histone acetylation, these enzymes are able to impact on specific transcriptional programs and, in the hippocampus, particularly that of memory and plasticity-related genes.

Our proposed strategy is original as it consists in a direct reactivation of memory and plasticity-related transcriptional programs in neurons despite ongoing neurodegeneration. We will use the first HAT activator ever developed, originally produced fom cashewnut shell liquid and modified to specifically target CBP and p300 acetyltransferases in Prof. TK Kundu’s laboratory (JNCASR, Bangalore, India). This molecule is attached to a carbon nanosphere which makes it cell permeant, enabling it to pass through the blood brain barrier, enter the cells and directly target their nucleus (i.e. without requiring membrane-located receptors). We have a series of preliminary data obtained in normal mice, demonstrating that this molecule efficiently acetylates brain histones, improves long term memory formation and activates adult neurogenesis. The patenting (co-inventor ALB) is on progress (IPR section of JNCASR, India, with a 30% participation of the University of Strasbourg).

Our research project has two main aims: 1) establish which chromatin histone acetylation events are affected by the disease and how they relate to memory functions and 2) lead functional and behavioral studies in AD-related mouse models in response to acute and chronic HAT activator treatments. Two AD mouse models have been chosen to explore both sides of AD: an amyloid model, bearing APP/PS1 mutations, and a Tau-expressing model (Thy-Tau22). Importantly, we will also explore these acetylation-dependent regulations in post-mortem brains from AD patients in order to bring insights into the human pathology and check if we can establish some correlates with (dys)regulations found in rodents.

Our working hypothesis is that acetylation regulations important for memory formation may be lost in AD-related neurodegeneration. Evidence found in the literature (APPxPS strain) and our preliminary data (Thy-Tau22 strain) show that the acetylated-histone balance is altered in these two AD-related mouse models, both at the basal level or during memory formation, making them relevant models to lead preclinical tests for acetylation-affecting drugs. The incidence of these treatments will be evaluated at the molecular, cellular and cognitive levels. Furthermore, we also propose to explore whether the HAT activation-based strategy could, after prolonged treatment, impact on the presence of pathological marks of AD (amyloid plaques and tau aggregation). Such knowledge should define new therapeutic targets aimed at re-establishing learning ability and access to long-term memories in diseased patients. This project should also bring important answers as to the mechanisms of action and regulatory pathways of HAT enzymes in the brain.