Histone deacetylases: From acetylation homeostasis to oncogenic and neurodegenerative disorders.

Histone deacetylases (HDACs) are central regulators of acetylation homeostasis, governing chromatin architecture, transcriptional dynamics, and diverse cellular processes through reversible lysine deacetylation. Dysregulation of HDAC activity disrupts epigenetic balance and is strongly implicated in oncogenic transformation and the progression of neurodegenerative disorders. This chapter provides a comprehensive overview of HDAC biology with a particular emphasis on experimental and analytical methodologies used to investigate their function. We describe the structural and functional diversity of HDAC classes and their roles in multiprotein complexes that regulate gene expression and cellular signaling. A major focus is placed on screening-compatible and mechanistic assays, including fluorometric, colorimetric, radiometric, fluorescence polarization, TR-FRET, AlphaScreen/AlphaLISA, and differential scanning fluorimetry approaches for quantitative measurement of enzymatic activity and inhibitor profiling. In addition, advanced methodologies such as mass spectrometry-based acetylome analysis, chromatin immunoprecipitation sequencing (ChIP-seq), recombinant enzyme assays, and cell-based reporter systems are discussed in the context of functional genomics and drug discovery. The integration of high-throughput screening, structural biology, and multi-omics strategies is highlighted as essential for dissecting HDAC-mediated regulatory networks. Collectively, this chapter serves as a methodological framework for studying HDAC function and developing targeted epigenetic therapies in cancer and neurodegenerative diseases.