The mRNA m6A reader YTHDF2 suppresses proinflammatory pathways and sustains hematopoietic stem cell function.

Christopher Mapperley,Dónal O’Carroll,Junho Choe,Ivayla Ivanova,David Wotherspoon,Jozef Durko,Hannah Lawson,Louie N Van De Lagemaat,Joana Campos,Andrea Tavosanis,Kamil R Kranc,Adam J Mead,Richard I Gregory,Daniela S Krause,Jasmin Paris,Alex Von Kriegsheim,Marcos Morgan,Annika Sarapuu,Christian Much

doi:10.1084/jem.20200829

Abstract

The mRNA N6-methyladenosine (m6A) modification has emerged as an essential regulator of normal and malignant hematopoiesis. Inactivation of the m6A mRNA reader YTHDF2, which recognizes m6A-modified transcripts to promote m6A-mRNA degradation, results in hematopoietic stem cell (HSC) expansion and compromises acute myeloid leukemia. Here we investigate the long-term impact of YTHDF2 deletion on HSC maintenance and multilineage hematopoiesis. We demonstrate that Ythdf2-deficient HSCs from young mice fail upon serial transplantation, display increased abundance of multiple m6A-modified inflammation-related transcripts, and chronically activate proinflammatory pathways. Consistent with the detrimental consequences of chronic activation of inflammatory pathways in HSCs, hematopoiesis-specific Ythdf2 deficiency results in a progressive myeloid bias, loss of lymphoid potential, HSC expansion, and failure of aged Ythdf2-deficient HSCs to reconstitute multilineage hematopoiesis. Experimentally induced inflammation increases YTHDF2 expression, and YTHDF2 is required to protect HSCs from this insult. Thus, our study positions YTHDF2 as a repressor of inflammatory pathways in HSCs and highlights the significance of m6A in long-term HSC maintenance.

Highlights

Emerging evidence indicates the importance of the mRNA N6- demonstrated that loss of METTL3, METTL14, or FTO weakens methyladenosine (m6A) modification in hematopoietic stem acute myeloid leukemia (AML) propagation, whereas inacticell (HSC) biology and leukemic transformation (Vu et al, vation of METTL3 and METTL14 has deleterious consequences 2019). m6A is the most abundant internal mRNA modifica- for normal hematopoietic stem cell (HSC) maintenance (Barbieri et al, 2017; Cheng tion, which is cotranscriptionally installed by the “m6A et al, 2019; Li et al, 2017; Vu et al, 2017; Weng et al, 2018). writer” complex, consisting of the METTL3/METTL14 enzy- inactivation of YTHDF2, which recognizes matic core and their regulator WT-associated protein (Frye m6A-modified mRNA to mediate m6A-mRNA degradation (Du et al, 2018)
YTHDF2-deficient HSCs activate proinflammatory pathways and lose their reconstitution capacity upon serial transplantation We have recently demonstrated that hematopoiesis-specific Vav-iCre–mediated deletion of Ythdf2 results in HSC expansion and compromises AML initiation and propagation (Paris et al, 2019)
We used the conditional and reporter Ythdf2fl mouse allele in which exon 2 of Ythdf2 was flanked by loxP sites and GFP was introduced after the start codon of Ythdf2, generating a fully functional GFP-YTHDF2 fusion protein (Ivanova et al, 2017)

Summary

Introduction

Emerging evidence indicates the importance of the mRNA N6- demonstrated that loss of METTL3, METTL14, or FTO weakens methyladenosine (m6A) modification in hematopoietic stem acute myeloid leukemia (AML) propagation, whereas inacticell (HSC) biology and leukemic transformation (Vu et al, vation of METTL3 and METTL14 has deleterious consequences 2019). m6A is the most abundant internal mRNA modifica- for normal HSC maintenance (Barbieri et al, 2017; Cheng tion, which is cotranscriptionally installed by the “m6A et al, 2019; Li et al, 2017; Vu et al, 2017; Weng et al, 2018). writer” complex, consisting of the METTL3/METTL14 enzy- inactivation of YTHDF2, which recognizes matic core and their regulator WT-associated protein (Frye m6A-modified mRNA to mediate m6A-mRNA degradation (Du et al, 2018). The modification can be reversed by m6A de- et al, 2016; Wang et al, 2015), compromises initiation and methylases (FTO and AlkBH5), collectively called “m6A eras- propagation of AML and results in HSC expansion (Li et al, ers.” m6A-modified transcripts are recognized by “m6A 2018; Paris et al, 2019; Wang et al, 2018). 1) and cytoplasmic YTH domain-containing family member nance upon aging remains unknown. We reveal that 1 (YTHDF1), YTHDF2, YTHDF3, and YTHDC2, which execute YTHDF2 functions to down-regulate m6A modified transcripts the outcome of m6A modification by promoting splicing, involved in the inflammatory response and maintains HSC nuclear export, translation, or degradation.

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