LepR+ Niche Cell-Derived AREG Compromises Hematopoietic Stem Cell Maintenance Under Conditions of DNA Repair Deficiency and Aging

The maintenance of the rare hematopoietic stem cell (HSC) population in the bone marrow (BM) and preservation of their functional properties is supported by a highly specialized microenvironment inside the BM, the HSC niche. However, the crosstalk between extrinsic niche-derived and intrinsic HSC factors controlling hematopoiesis remain elusive. Using three niche-specific conditional knockout mouse models, here we demonstrate that epidermal growth factor (EGF)-like molecule, amphiregulin (AREG) from bone marrow (BM) leptin receptor (LepR⁺) stromal cells is an important factor that mediates the crosstalk between BM niche and HSCs in stem cell maintenance. Mice deficient for the DNA repair gene Brca2 specifically in LepR⁺ cells (LepR-Cre;Brca2^fl/fl) exhibit increased frequencies of total and myeloid-biased HSCs. Furthermore, HSCs from LepR-Cre;Brca2^fl/fl mice show compromised repopulation, increased expansion of donor-derived myeloid-biased HSCs and myeloid output in the transplanted recipients. Brca2-deficient BM LepR⁺ cells exhibit persistent DNA damage-inducible overproduction of stromal AREG. Ex vivo treatment of WT HSCs or systemic treatment of C57BL/6 mice with recombinant AREG impairs repopulation, leading to HSC exhaustion. Conversely, inhibition of AREG by anti-AREG neutralizing antibody or deletion of the Areg gene in LepR-Cre;Brca2^fl/fl mice rescues the HSC defects caused by AREG. Mechanistically, AREG activates the PI3K/AKT/mTOR pathway, promotes HSC cycling and compromises HSC quiescence. Finally, we demonstrate that BM LepR⁺ niche cells from other DNA repair-deficient and aged mice also show persistent DNA damage-associated overexpression of AREG, which exerts similar negative effects on HSC maintenance. We have therefore identified an important niche factor negatively regulating HSCs function under conditions of DNA repair deficiency and aging, and underscored the therapeutic potential of AREG intervention in improving HSC function.