Uncovering Tip60's Neural Functions for Neuroepigenetic Therapeutic Modulation in Alzheimer's Disease
Authors:   , Bhatnagar Akanksha , Elefant Felice 
Published: August 2023

Alzheimer's Disease (AD) etiology involves a complex interplay of genetics, age, and environmental factors that influence epigenetic programming mediated neural gene control. Reduced histone acetylation states in the AD brain have since emerged as a widespread hallmark that underlies neural gene repression and cognitive impairment in the AD etiology. In a healthy brain, the antagonistic activities of histone acetyltransferases (HAT) and histone deacetylases (HDAC) that generate or erase acetylation marks on histone proteins, respectively, maintain neural histone acetylation homeostasis necessary for dynamic gene control. However, decreased Tip60 HAT activity and/or increased HDAC2 activity causes chromatin packaging alterations suppressing these critical neuronal genes and blocking cognitive functions under AD pathology. Accordingly, our lab has previously identified a neuroprotective role for Tip60 HAT in AD. Loss of Tip60 protein levels in the brains of our Drosophila AD model and human postmortem AD hippocampus results in reduced acetylation at cognition-associated histone marks with concomitant repression of critical neuroplasticity genes that is reversed by increasing Tip60 levels in the brains of Drosophila AD model. While disruption of Tip60 HAT action in neural gene control is implicated in AD, alternative mechanisms underlying Tip60 function remain unexplored that limits our ability to target Tip60 for therapeutic treatment for AD. Here, we report a novel RNA binding function for Tip60 that allows Tip60 to modulate splicing decisions of its pre-mRNA targets. Importantly, we find that this function is disrupted in Drosophila brains that model AD pathology and may underly altered splicing of these RNA targets that is partially prevented by increasing Tip60 in the fly brain. Further, we find that this Tip60-RNA function is conserved in human hippocampus and disrupted in AD patient hippocampus. Importantly, human orthologs of several Tip60- modulated splicing genes in Drosophila are well characterized aberrantly spliced genes in human AD brains, implicating disruption of Tip60's splicing function in AD pathogenesis. We next tested if pharmacologically enhancing Tip60's HAT function will replicate its AD neuroprotective function observed by genetic overexpression. Using in silico structural modeling, we have designed and synthesized a candidate pool of novel small molecule compounds targeting Tip60's HAT activity. We carried out two different ligand-based virtual screening approaches utilizing either substructure or pharmacophore to find compounds that share structural or functional similarities with a known HAT activator, respectively. Several compounds show specific activation of Tip60 in our in vitro histone acetylation assay and fully rescue locomotor deficits in our Tip60 knockdown model, underscoring their therapeutic effectiveness. Together, our results underscore the neuroprotective role of Tip60 in AD pathology that can be enhanced by our Tip60 specific therapeutic compounds.