Background: DNA and chromatin modifications are critical mediators in the establishment and maintenance of cell type-specific gene expression patterns that constitute cellular identities. One type of modification, the acetylation and deacetylation of histones, occurs reversibly on lysine ε-NH₃(+) groups of core histones via histone acetyl transferases (HAT) and histone deacetylases (HDAC). Hyperacetylated histones are associated with active chromatin domains, whereas hypoacetylated histones are enriched in non-transcribed loci.
Methods: We analyzed global histone H4 acetylation and HDAC activity levels in mature lineage marker-positive (Lin(+)) and progenitor lineage marker-negative (Lin⁻) hematopoietic cells from murine bone marrow (BM). In addition, we studied the effects of HDAC inhibition on hematopoietic progenitor/stem cell (HPSC) frequencies, cell survival, differentiation and HoxB4 dependence.
Results: We observed that Lin⁻ and Lin(+) cells do not differ in global histone H4 acetylation but in HDAC activity levels. Further, we saw that augmented histone acetylation achieved by transient Trichostatin A (TSA) treatment increased the frequency of cells with HPSC immunophenotype and function in the heterogeneous pool of BM cells. Induction of histone hyperacetylation in differentiated BM cells was detrimental, as evidenced by preferential death of mature BM cells upon HDAC inhibition. Finally, TSA treatment of BM cells from HoxB4(-/-) mice revealed that the HDAC inhibitor-mediated increase in HPSC frequencies was independent of HoxB4.
Conclusions: Overall, these data indicate the potential of chromatin modifications for the regulation of HPSC. Chromatin-modifying agents may provide potential strategies for ex vivo expansion of HPSC.