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As we age, our ability to maintain healthy blood and a strong immune system gradually declines, largely because hematopoietic stem cells (HSCs), the cells responsible for producing all blood cell types, begin to lose their effectiveness. Normally, HSCs can both self-renew and generate a balanced mix of blood cells, but over time they produce fewer new cells, favor certain cells such as myeloid cells over lymphoid cells, and struggle to support a robust immune response. Accumulated cellular damage, shifts in gene activity, ongoing low-level inflammation, and changes in the bone marrow environment, all appear to contribute to this decline. However, the precise mechanisms by which these diverse stresses converge to weaken HSCs have remained unclear.

Researchers from The University of Tokyo, Japan, and St. Jude Children’s Research Hospital, USA, sought to uncover a mechanism explaining how age-related stresses drive HSC functional deterioration, focusing on the receptor-interacting protein kinase 3 (RIPK3)-mixed lineage kinase like (MLKL) signaling axis—a pathway traditionally associated with necroptosis, or programmed cell death. The study was led by Dr. Masayuki Yamashita, an Assistant Member at St. Jude Children’s Research Hospital, who, at the time of the investigation, was an Assistant Professor at The Institute of Medical Science, The University of Tokyo. The other co-authors include Dr. Atsushi Iwama from The Institute of Medical Science, The University of Tokyo, and Dr. Yuta Yamada from St. Jude Children’s Research Hospital, who was a graduate student at The Institute of Medical Science, The University of Tokyo.

Explaining the motivation behind the study, Dr. Yamashita says, “We discovered an unexpected phenotype in HSCs of MLKL-knockout mice repeatedly treated with 5-fluorouracil, where aging-associated functional changes were markedly attenuated despite no detectable difference in HSC death, prompting us to investigate whether this pathway might induce functional changes beyond cell death.” This observation shifted the research focus toward a non-lethal role of MLKL—a concept later highlighted in their study, published in Volume 17 of the journal Nature Communications on April 6, 2026.

To investigate this, the team employed a combination of genetic mouse models, stress treatments, and functional assays. They used wild-type, MLKL-deficient, and RIPK3-deficient mice, along with specialized reporter mice capable of detecting MLKL activation through a Förster resonance energy transfer-based biosensor. Mice were exposed to stressors mimicking aging, including inflammation, replication stress, and oncogenic stress. HSC function was then assessed primarily through bone marrow transplantation, which measures the ability of stem cells to regenerate the blood system. Complementary analyses included flow cytometry, ex vivo expansion, RNA-seq, assay for transposase-accessible chromatin-seq, high-resolution microscopy, metabolic assays, and mitochondrial analyses, enabling a detailed understanding of how non-lethal MLKL activation impairs HSC function at molecular, cellular, and organelle levels.

Abstract: Nature Communications.

Non-necroptotic MLKL function damages mitochondria and promotes hematopoietic stem cell aging.

https://www.nature.com/articles/s41467-026-71060-4