Epigenetic modulation by small molecule compounds for neurodegenerative disorders.

The accumulation of somatic and genetic mutations which altered the structure and coding information of the DNA are the major cause of neurological disorders. However, our recent understanding of molecular mechanisms of 'epigenetic' phenomenon reveals that the modifications of chromatin play a significant role in the development and severity of neurological disorders. These epigenetic processes are dynamic and reversible as compared to genetic ablations which are stable and irreversible. Therefore, targeting these epigenetic processes through small molecule modulators are of great therapeutic potential. To date, large number of small molecule modulators have been discovered which are capable of altering the brain pathology by targeting epigenetic enzymes. In this review, we shall put forward the key studies supporting the role of altered epigenetic processes in neurological disorders with especial emphasis on neurodegenerative disorders. A few small molecule modulators which have been shown to possess promising results in the animal model system of neurological disorders will also be discussed with future perspectives.

Oligomers of human histone chaperone NPM1 alter p300/KAT3B folding to induce autoacetylation.

BACKGROUND: p300 (KAT3B) lysine acetyltransferase activity is modulated under different physiological and pathological contexts through the induction of trans-autoacetylation. This phenomenon is mediated by several factors, mechanisms of which are not fully understood. METHODS: Through acetyltransferase assays using full-length, baculovirus-expressed KATs, the specificity of NPM1-mediated enhancement of p300 autoacetylation was tested. Chaperone assays and tryptophan fluorescence studies were performed to evaluate the NPM1-induced protein folding. The NPM1 oligomer-defective mutant characterization was done by glutaraldehyde-crosslinking. The small-molecule inhibitor of NPM1 oligomerization was used to confirm the absolute requirement of multimeric NPM1 in vivo. Immunohistochemistry analysis of oral cancer patient samples was done to uncover the pathophysiological significance of NPM1-induced p300 autoacetylation. RESULTS: We find that the histone chaperone NPM1 is a specific inducer of p300 autoacetylation. Distinct from its histone chaperone activity, NPM1 is a molecular chaperone of p300. The biophysical experiments suggest that there is a reversible binding between NPM1 and p300 which can modulate p300 acetyltransferase activity. Disruption of NPM1 oligomerization suggests that oligomeric NPM1 is essential for the induction of p300 autoacetylation. Significantly, we observe a concomitant hyper-autoacetylation of p300 with overexpression of NPM1 in oral cancer samples. CONCLUSION: NPM1 can specifically modulate p300 acetyltransferase activity through the enhancement of autoacetylation. The molecular chaperone activity and oligomerization of NPM1 play a pivotal role in this phenomenon. GENERAL SIGNIFICANCE: NPM1 is overexpressed in several solid cancers, the significance of which is unknown. Induction of p300 autoacetylation could be the cause of NPM1-mediated tumorigenicity.

Reinstating plasticity and memory in a tauopathy mouse model with an acetyltransferase activator.

Chromatin acetylation, a critical regulator of synaptic plasticity and memory processes, is thought to be altered in neurodegenerative diseases. Here, we demonstrate that spatial memory and plasticity (LTD, dendritic spine formation) deficits can be restored in a mouse model of tauopathy following treatment with CSP-TTK21, a small-molecule activator of CBP/p300 histone acetyltransferases (HAT). At the transcriptional level, CSP-TTK21 re-established half of the hippocampal transcriptome in learning mice, likely through increased expression of neuronal activity genes and memory enhancers. At the epigenomic level, the hippocampus of tauopathic mice showed a significant decrease in H2B but not H3K27 acetylation levels, both marks co-localizing at TSS and CBP enhancers. Importantly, CSP-TTK21 treatment increased H2B acetylation levels at decreased peaks, CBP enhancers, and TSS, including genes associated with plasticity and neuronal functions, overall providing a 95% rescue of the H2B acetylome in tauopathic mice. This study is the first to provide in vivo proof-of-concept evidence that CBP/p300 HAT activation efficiently reverses epigenetic, transcriptional, synaptic plasticity, and behavioral deficits associated with Alzheimer's disease lesions in mice.

Modulation of neurogenesis by targeting epigenetic enzymes using small molecules: an overview.

Neurogenesis consists of a plethora of complex cellular processes including neural stem cell (NSC) proliferation, migration, maturation or differentiation to neurons, and finally integration into the pre-existing neural circuits in the brain, which are temporally regulated and coordinated sequentially. Mammalian neurogenesis begins during embryonic development and continues in postnatal brain (adult neurogenesis). It is now evident that adult neurogenesis is driven by extracellular and intracellular signaling pathways, where epigenetic modifications like reversible histone acetylation, methylation, as well as DNA methylation play a vital role. Epigenetic regulation of gene expression during neural development is governed mainly by histone acetyltransferases (HATs), histone methyltransferase (HMTs), DNA methyltransferases (DNMTs), and also the enzymes for reversal, like histone deacetylases (HDACs), and many of these have also been shown to be involved in the regulation of adult neurogenesis. The contribution of these epigenetic marks to neurogenesis is increasingly being recognized, through knockout studies and small molecule modulator based studies. These small molecules are directly involved in regeneration and repair of neurons, and not only have applications from a therapeutic point of view, but also provide a tool to study the process of neurogenesis itself. In the present Review, we will focus on small molecules that act predominantly on epigenetic enzymes to enhance neurogenesis and neuroprotection and discuss the mechanism and recent advancements in their synthesis, targeting, and biology.