| Enzymes that modify epigenetic status provide attractive targets for therapy in various diseases including cardiac hypertrophy, cancer, neurodegenerative diseases, and immune dysfunction. The therapeutic development of epigenetic modulators, however, has been largely limited to direct targeting of the active site of such enzymes. Class IIa histone deacetylases (HDACs) are a group of epigenetic enzymes that depends on interaction with Myocyte Enhancer Factor-2 (MEF2) for their recruitment to specific genomic loci. Targeting this interaction presents a potential alternative approach to inhibiting this class of HDACs by blocking their DNA recruitment. In this paper, we have identified and characterized a group of small molecules that indirectly target class IIa HDACs by binding to MEF2.;The first study explores the molecular interactions between the MEF2 family and the class IIa HDACs. This study revealed that the interfaces between the class IIa HDACs and the MEF2 proteins are sensitive to localized mutations and, therefore, likely targets for inhibition by small molecules. Moreover, we established a mammalian two-hybrid assay that can serve as a screen for small molecule inhibitors of MEF2:HDAC4 interaction.;The second study establishes that the commercially available small molecule, BML-210, which belongs to the pimeloylanilide o-aminoanilide (PAOA) class, is an inhibitor of MEF2:HDAC4 interaction in vitro and in vivo. Specifically, we showed that these small molecules blocked the recruitment of class IIa HDACs to MEF2-targeted genes and enhanced the expression of those targets. Based on structural and functional studies, we synthesized a series of new PAOA compounds, some of which were more potent inhibitors of MEF2:HDAC interaction.;The final study examines the effect of these MEF2:class IIa HDAC inhibitors on learning and memory. In this blind study, we showed that wild type (WT) mice treated with a PAOA molecule displayed enhanced learning and memory compared to mice treated with an inactive PAOA compound. Furthermore, in a similar study, treatment of cultured cortical neurons with PAOA led to a significant decrease in the excitatory synapse number, suggesting, that the effect of PAOA on learning and memory might be through regulating synapse formation. These findings link the inhibition of MEF2:HDAC interaction to MEF2 dependent synaptic morphogenesis, learning and memory.;Collectively, our work describes the first example of sub-class specific HDAC inhibitors (HDACi) that disrupt the protein-protein interaction between the class IIa HDACs and its cofactors. In addition, as evident from the final functional study on the effect of these compounds on synapse formation and memory, the compounds developed here can be used not only as tools to study the MEF2 proteins and class IIa HDACs in vivo but also as leads for drug development. |
