3132 – PRODUCTION OF ALARMINS S100A8/A9 BY DNMT3A-MUTANT HEMATOPOIETIC CELLS CAUSES MESENCHYMAL STROMAL CELL SENESCENCE AND SEEDS A PRO-INFLAMMATORY ENVIRONMENT IN CLONAL HEMATOPOIESIS

• Published in: Experimental hematology 2024-08, Vol.137, p.104453, Article 104453
• Main Authors: Mistry, Jayna, Young, Kira, Maestre, Ines Fernandez, Levine, Ross, Trowbridge, Jennifer
• Format: Article
• Language: English
• ISSN: 0301-472X
• DOI: 10.1016/j.exphem.2024.104453

Elevated inflammation is a shared contributor to aging, clonal hematopoiesis (CH) and acute myeloid leukemia (AML). Understanding the cell types and factors that cause elevated inflammation offer potential interventions to reduce the burden of CH and AML in aged populations. Here, we modeled a recurrent CH mutation in the DNA methyltransferase DNMT3A and tested the hypothesis that soluble factors produced by mutant cells remodel the bone marrow (BM) microenvironment to induce a pro-inflammatory state. We found that conditioned media from Dnmt3a-mutant hematopoietic stem and progenitor cells (HSPCs) had elevated levels of S100A8/A9, IL-6 and TNFα. Release and binding of the alarmins S100A8/A9 to PRRs, TLR4, and RAGE is known to result in secretion of IL-6 and TNFα, making S100A8/A9 a strong candidate upstream regulator. We found that treatment of Dnmt3a-mutant HSPCs with the S100A8/A9 inhibitor Tasquinimod reduced their production and secretion of IL-6 and TNFα. To examine the effect of S100A8/A9 on the BM microenvironment, we analyzed single cell RNA-seq data from Dnmt3a-mutant mice and found enrichment of a cellular senescence molecular program in mesenchymal stromal cells (MSCs). Co-culture of Dnmt3a-mutant HSPCs with wild-type MSCs caused senescence of MSCs measured by senescence-associated beta galactosidase (SA-β-gal) and the anti-apoptotic proteins BCL-2 and BCL-xL. Recombinant S100A8/A9 was sufficient to induce SA-β-gal in wild-type MSCs. The addition of Tasquinimod to co-cultures of Dnmt3a-mutant HSPCs and wild-type MSCs blocked the induction of MSC senescence, demonstrating that S100A8/A9 are inducers of MSC senescence. Together, release of the alarmins S100A8/A9 by Dnmt3a-mutant HSPCs act as master regulators to induce low-grade inflammation and remodel the BM microenvironment, and serve as molecular targets to reduce the burden of CH.