Histone deacetylases (HDACs) modulate the acetylation level of histones to regulate chromatin structure and gene expression. They are considered to be crucial regulators of specific developmental and differentiation processes. Whilst they are primarily involved in the deacetylation of histones, they have also been shown to regulate the acetylation levels of non-histone proteins [].Class IIa histone deacetylases (HDACs4, -5, -6, -7, -9 and -10) modulate the physiology of the human cardiovascular, musculoskeletal, nervous, and immune systems [, [].HDAC4 performs a wide variety of functions, including the regulation of cell growth, survival and proliferation, and the regulation of gene transcription. It has been closely associated with the development of tumours in various tissues. It also induces demethylation of histone proteins, and has been shown to be subject to post-transcriptional modification by multiple methods []. HDAC4 has been reported to regulate chondrocyte hypertrophy and endochondral bone formation, muscle development, and cardiovascular diseases [].HDAC4 is localized to both the nucleus and cytoplasm, and undergoes subcellular shuttling in response to synaptic activity and environmental signals [, ]. It is important for neuronal development and function, and has been implicated in a number of neuronal diseases including brachydactyly mental retardation (BDMR) syndrome, ataxia telangiectasia, and Huntington's disease [].Histone deacetylase 7 (HDAC7) is highly expressed in double-positive thymocytes, suggesting a possible role in thymic T-cell development [, ].
