Suppression of m⁶A reader Ythdf2 promotes hematopoietic stem cell expansion

Area of Science:

• Stem Cell Biology
• Epigenetics
• Hematology

Background:

• Hematopoietic stem cells (HSCs) from human umbilical cord blood (hUCB) are crucial for treating hematological disorders but are limited in quantity.
• Current methods for ex vivo HSC expansion target single molecules, but simultaneous manipulation of multiple targets remains challenging.
• N⁶-methyladenosine (m⁶A) modification influences mRNA stability, impacting stem cell fate, with YTHDF2 identified as a key player in mRNA decay.

Purpose of the Study:

• To investigate the physiological role of YTHDF2 in adult stem cell maintenance.
• To determine the impact of YTHDF2 on the ex vivo expansion of human umbilical cord blood HSCs.
• To elucidate the molecular mechanisms by which YTHDF2 regulates HSC self-renewal and expansion.

Main Methods:

• Conditional knockout of mouse Ythdf2 to assess its function in HSCs.
• Knockdown of human YTHDF2 in hUCB HSCs for ex vivo expansion studies.
• m⁶A RNA sequencing in mouse and human HSCs.
• Limiting dilution transplantation assays to evaluate HSC function.
• Analysis of YTHDF2 targets, including Tal1 mRNA.

Main Results:

• Conditional knockout of Ythdf2 increased functional mouse HSC numbers without inducing malignancies.
• Knockdown of human YTHDF2 resulted in over 10-fold expansion of hUCB HSCs, with increased colony-forming units and secondary transplantation potential.
• m⁶A modification is enriched in self-renewal-related mRNAs, which are targeted for decay by YTHDF2.
• Stabilization of these m⁶A-marked mRNAs in Ythdf2-deficient cells facilitated HSC expansion.
• Knockdown of Tal1 partially rescued the HSC expansion phenotype.

Conclusions:

• YTHDF2 plays a critical role in regulating adult stem cell maintenance.
• YTHDF2 is a key regulator of HSC ex vivo expansion by controlling the stability of multiple mRNAs essential for self-renewal.
• Targeting YTHDF2 offers a promising strategy for enhancing HSC expansion for clinical applications.