A Novel Role For Histone Deacetylase 11 (HDAC11) As a Regulator Of Neutrophil Function and Differentiation In Normal and Malignant Hematopoesis

Histone Deacetylase 11 (HDAC11) is the newest member of the HDAC family of enzymes, which we have previously reported to function as a negative regulator of IL-10 expression in macrophages and dendritic cells. Thus far, its role in other hematopoietic cells has not been completely elucidated. We hereby report for the first time a lineage-restricted over-expression of HDAC11 in neutrophils, committed neutrophil precursors and myeloid leukemias exhibiting neutrophilic differentiation demonstrating a novel physiological role of HDAC11 as a negative regulator of neutrophil cytokine production.

Leukocyte subpopulations from murine bone marrow and spleen were flow-sorted and analyzed by qRT-PCR for HDAC11 mRNA, revealing a higher level of mRNA expression on neutrophils and promyelocytes, as compared to monocytes and lymphoid subsets. Similarly, sorted human peripheral blood leukocytes from normal donors, showed higher levels of HDAC11 mRNA in neutrophils, as compared to monocytes. To further investigate the transcriptional activity of HDAC11 in myeloid and lymphoid cells, we utilized a HDAC11 promoter-driven eGFP reporter mice, where eGFP expression indicates HDAC11 transcription (Heintz, N Nat. Rev. Neuroscience 2001). Using multiparametric flow cytometry with lineage-specific markers on this mouse model, we confirmed a marked over-expression of HDAC11 on neutrophils, compared to other subpopulations including monocytes, B-cell, T-cells, NK cells and plasma cells. Furthermore, analysis of bone marrow hematopoietic cells revealed a swift over-expression of HDAC11 at the promyelocyte stage of neutrophil differentiation, with low to undetectable expression in upstream uncommitted common myeloid progenitors and lineage-unrelated monocytic precursors. To study whether this lineage-specific overexpression applies to malignant processes, we studied human cell lines and found overt overexpression of HDAC11 in the acute promyelocytic leukemia cell line NB4, as compared to the myeloblastic cell line Kasumi and two monocyte/macrophage cell lines U937 and THP1. Moreover, in-vitro maturation of the differentiation-inducible myeloid cell line HL60 demonstrated a marked increase in HDAC11 mRNA, paralleling the acquisition of nuclear segmentation characteristic of neutrophil maturation. In order to investigate the physiologic role of HDAC11 overexpression on neutrophils, we utilized a model of germline-HDAC11KO mice. Surprisingly, highly purified neutrophils lacking HDAC11 showed an overt overproduction of TNF-alpha and IL-6 upon stimulation with LPS, as compared to their wild type counterparts.

We hereby report a previously un-described lineage-specific over-expression of HDAC11 in neutrophils and its precursors, which actively functions as a physiological repressor of cytokine production and possibly involved in their regulation. Given the predominance of neutrophils which account for 70% of leukocytes in the peripheral blood, and their pivotal role in the first line of defense, results highlight a novel mechanism for HDAC11, as a key regulator and modulator of neutrophil cytokine production with potential implications for autoimmunity, inflammation, and infection.