Direct modulation of the bone marrow mesenchymal stromal cell compartment by azacitidine enhances healthy hematopoiesis

Abstract

Key Points• AZA treatment of MSCs in MDS leads to preferential expansion of healthy over malignant hematopoiesis.• AZA regulates key MSC genes crucial for support of hematopoiesis, providing proof of concept for epigenetic therapy of MSCs in MDS. Mesenchymal stromal cells (MSCs) are crucial components of the bone marrow (BM) microenvironment essential for regulating self-renewal, survival, and differentiation of hematopoietic stem/progenitor cells (HSPCs) in the stem cell niche. MSCs are functionally altered in myelodysplastic syndromes (MDS) and exhibit an altered methylome compared with MSCs from healthy controls, thus contributing to disease progression. To determine whether MSCs are amenable to epigenetic therapy and if this affects their function, we examined growth, differentiation, and HSPC-supporting capacity of ex vivo-expanded MSCs from MDS patients in comparison with age-matched healthy controls after direct treatment in vitro with the hypomethylating agent azacitidine (AZA). Strikingly, we find that AZA exerts a direct effect on healthy as well as MDS-derived MSCs such that they favor support of healthy over malignant clonal HSPC expansion in coculture experiments. RNA-sequencing analyses of MSCs identified stromal networks regulated by AZA. Notably, these comprise distinct molecular pathways crucial for HSPC support, foremost extracellular matrix molecules (including collagens) and interferon pathway components. Our study demonstrates that the hypomethylating agent AZA exerts its antileukemic activity in part through a direct effect on the HSPC-supporting BM niche and provides proof of concept for the therapeutic potential of epigenetic treatment of diseased MSCs. In addition, our comprehensive data set of AZA-sensitive gene networks represents a valuable framework to guide future development of targeted epigenetic niche therapy in myeloid malignancies such as MDS and acute myeloid leukemia.

Targeting the Microenvironment in MDS: The Final Frontier

“…Since MDS-MSCs have different methylation patterns compared to their healthy counterparts ( Geyh et al., 2013 ), it begs the question if HMA-induced changes in the BME contribute to the clinical responses observed. To this end, 5-Aza enhances the ability to support normal hematopoiesis in MDS-MSCs, while decreasing their support for MDS HSPCs ( Wenk et al., 2018 ; Poon et al., 2019 ). During disease homeostasis, MDS-induced impairment of MSCs' functions appears reversible by 5-Aza but only up to a certain point in disease progression ( Poon et al., 2019 ).…”

“…5-Aza restored the hematopoiesis-supporting capacity of most primary MDS-MSCs samples derived from low grade MDS but not those from advanced-stage disease ( Poon et al., 2019 ). However, treatment with 5-Aza is capable to enhance hematopoiesis-supporting properties of healthy MSCs as well, suggesting that the effect is not specific to MDS-induced changes ( Wenk et al., 2018 ). It is currently unknown what molecular program induced by azanucleotides rescue MSC function.…”

“…It is currently unknown what molecular program induced by azanucleotides rescue MSC function. RNA-seq data suggests that treatment with 5-Aza optimizes interferon signaling and extracellular matrix homeostasis, including collagen type IV and VI with major implications for HSC anchorage, self-renewal, and differentiation ( Essers et al., 2009 ; Gattazzo et al., 2014 ; Wenk et al., 2018 ). In addition, treatment of MDS-MSCs with 5-Aza reverses aberrant methylation patterns of these cells resulting in rescue of frequently altered signaling pathways such as over activation of betaβ-catenin and the downregulation of HHIP ( Figure 1 ) ( Kobune et al., 2012 ; Bhagat et al., 2017 ).…”

The Bone’s Role in Myeloid Neoplasia

“…Similarly, the hypomethylating agent azacytidine was reported to target stromal niche compartments in addition to its well-known effect on neoplastic hematopoietic cells. Azacytidine-treated MSCs displayed enhanced potential to promote healthy hematopoiesis [ 75 ]. Another study reported comparable effects in an MDS xenograft model [ 76 ].…”

Application of “Primed” Mesenchymal Stromal Cells in Hematopoietic Stem Cell Transplantation: Current Status and Future Prospects

“…Genetic manipulation of feeder layers has been shown to impart better yield of HSCs. Wenk et al [55] showed that 5Azacitidine (5Aza) treatment of MSCs isolated from both, normal and myelodysplastic syndromes marrows resulted in their epigenetic modulation and these 5Aza-modulated MSCs supported the growth of normal HSCs over leukemic HSCs. However, in this study only colony formation assay was used as a read out and in vivo transplantation studies were not done.…”