Impairment of human terminal erythroid differentiation by histone deacetylase 5 deficiency.

Histone deacetylases (HDACs) are a group of enzymes catalyzing the removal of acetyl groups from histone and non-histone proteins. HDACs have been shown to play diverse functions in a wide range of biological processes. However, their roles in mammalian erythropoiesis remain to be fully defined. We show here that of the eleven classic HDAC family members, six of them (HDAC 1,2,3 and HDAC 5,6,7) are expressed in human erythroid cells with HDAC5 most significantly up regulated during terminal erythroid differentiation. Knockdown of HDAC5 by either shRNA or siRNA in human CD34+ cells followed by erythroid cell culture led to increased apoptosis, decreased chromatin condensation, and impaired enucleation of erythroblasts. Biochemical analyses revealed that HDAC5 deficiency resulted in activation of p53 in association with increased acetylation of p53. Furthermore, while acetylation of histone 4 (H4) is decreased during normal terminal erythroid differentiation, HDAC5 deficiency led to increased acetylation of H4 (K12) in late stage erythroblasts. This increased acetylation was accompanied by decreased chromatin condensation, implying a role for H4 (K12) deacetylation in chromatin condensation. ATAC-seq and RNA-seq analyses revealed that HDAC5 knockdown leads to increased chromatin accessibility genome wide and global changes in gene expression. Moreover, pharmacological inhibition of HDAC5 by the inhibitor LMK235 also led to increased H4 acetylation, impaired chromatin condensation and enucleation. Taken together, our findings have uncovered previously unrecognized roles and molecular mechanisms of action for HDAC5 in human erythropoiesis. These results may provide insights into understanding the anemia associated with HDAC inhibitor treatment.