Dissecting the canonical and non-canonical functions of Tet2 in hematopoietic stem cells and hematologic disorders

Albert Einstein College Of Medicine, Bronx NY

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Abstract

Abstract Myelodysplastic syndrome (MDS) is a clonal hematological disorder. Patients exhibit either marked reductions in blood production, at times precipitating into bone marrow failure, significant dysplasia in the cells produced, or some combination of both. MDS is generally incurable by existing nontransplant therapies. The Ten-eleven translocation 2 (TET2) is a member of the TET family of DNA dioxygenases that regulates genes by promoting DNA demethylation (catalytic activity) and forming complexes with chromatin modifiers (noncatalytic functions). TET2 is one of the most frequently mutated genes in MDS. The role of Tet2 in hematopoietic stem cell homeostasis has largely been studied in knockout mice; however, as these mice lack the entire Tet2 protein, this approach has failed to distinguish the catalytic and noncatalytic requirements of its functions in a physiologically relevant context. In order to delineate the functions of Tet2 in HSCs and their contributions to MDS pathogenesis, we have generated Tet2 catalytically inactive and knockout mice. We have determined that Tet2 catalytic mutant mice exhibit less pronounced hematologic phenotypes than Tet2 KO mice. Moreover, Tet2 catalytic mutant mice developed mainly myeloid disorders while Tet2 KO mice developed both lymphoid and myeloid defects. This has led us to hypothesize that in addition to the canonical roles of Tet2 in DNA demethylation, Tet2 non-catalytic functions significantly contribute to the proper regulation of HSC gene expression programs and homeostasis. We will conduct a comparative epigenomic, transcriptomic and hematologic analyses of Tet2 catalytic mutant and knockout mice at young and old age to establish the non- catalytic requirements of Tet2 in HSC homeostasis and MDS suppression. We propose four aims: (1) to define the contributions of noncatalytic functions of Tet2 to hematopoietic stem cell (HSC) self-renewal and differentiation, (2) to define the non-catalytic functions of human TET2 in a TET2 heterozygote context and in preventing loss-of-TET2-driven MDS, (3) to establish how Tet2 regulates the DNA methylation landscape of hematopoietic stem and progenitor cells (HSPCs) over time in both enzymatic-dependent and -independent manners, and (4) to establish how Tet2 regulates hematopoietic programs in HSPCs non-catalytically by partnering with Sin3a for gene suppression and with Ogt for gene activation. Our findings will have a major impact on the MDS field by defining how the development of hematologic disorders, in particular MDS, is regulated by the catalytic-dependent and -independent functions of Tet2. This will facilitate development of new therapeutics for treatment and management of MDS and other hematologic disorders.