Ferroptosis in aging hematopoietic stem cells and the influence of iron-loaded macrophages

Hematopoietic stem cells (HSCs) are essential for lifelong regeneration of the hematopoietic system, including the production of blood and immune cells. Maintaining functional HSCs during aging is critical for mammalian health, however their functionality declines with age. One intriguing pathway of cell death relevant to this decline is ferroptosis, an iron-dependent process characterized by iron-mediated lipid peroxidation and failure of antioxidant defense systems, ultimately leading to cell death. This study demonstrated that aged HSCs exhibit elevated levels of lipid peroxidation, a hallmark of ferroptosis. Unexpectedly, aged HSCs were less sensitive to iron-induced apoptosis compared to young HSCs, suggesting the presence of protective mechanisms that mitigate ferroptosis in older cells. NUPR1 emerged as a potential key gene involved in protecting HSCs from ferroptosis. We found an increase in NUPR1 protein levels in aged HSCs. Notably, inhibition of NUPR1 rendered aged HSCs more susceptible to iron-induced apoptosis, while young HSCs remained unaffected, indicating that NUPR1 may play a critical role in ferroptosis resistance in aged HSCs. HSCs reside within the bone marrow (BM), where they interact with niche cells, including iron-loaded FABP4+ macrophages, which are a major source of iron and are located in close proximity to HSCs. This study developed a novel isolation and culture method for iron-loaded FABP4+ macrophages, enabling the establishment of a coculture system with lineage-negative cells. Through this coculture, we demonstrated that young macrophages paired with young lineage-negative cells effectively reduced iron-induced apoptosis in HSPCs. Additionally, whole-mount bone staining revealed a spatial association between NUPR1-positive HSCs with iron-loaded FABP4+ macrophages. This suggested a dynamic interplay between ferroptosis regulation, HSC aging, and BM microenvironment dynamics. The novel findings of this study provide significant insights into the mechanisms of ferroptosis in aged HSCs and the role of the BM niche in modulating this process for understanding age-related hematopoietic decline.