Enhanced Hematopoietic Stem Cell Function Mediates Immune Regeneration following Sex Steroid Blockade

• Sex steroid ablation (SSA) increases number of hematopoietic stem cells (HSCs)
• SSA enhances reconstitution potential and self-renewal of HSCs
• SSA reverses the age-associated decline in Foxo1 expression by hematopoietic niche
• There is an increase in niche expression of hematopoiesis-associated factors after SSA

SummaryMechanisms underlying age-related defects within lymphoid-lineages remain poorly understood. We previously reported that sex steroid ablation (SSA) induced lymphoid rejuvenation and enhanced recovery from hematopoietic stem cell (HSC) transplantation (HSCT). We herein show that, mechanistically, SSA induces hematopoietic and lymphoid recovery by functionally enhancing both HSC self-renewal and propensity for lymphoid differentiation through intrinsic molecular changes. Our transcriptome analysis revealed further hematopoietic support through rejuvenation of the bone marrow (BM) microenvironment, with upregulation of key hematopoietic factors and master regulatory factors associated with aging such as Foxo1. These studies provide important cellular and molecular insights into understanding how SSA-induced regeneration of the hematopoietic compartment can underpin recovery of the immune system following damaging cytoablative treatments. These findings support a short-term strategy for clinical use of SSA to enhance the production of lymphoid cells and HSC engraftment, leading to improved outcomes in adult patients undergoing HSCT and immune depletion in general.

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