Summary: As we grow older, the hematopoietic stem cells (HSCs) that generate our blood and support the immune system gradually lose function. That decline weakens immunity and skews blood production toward inflammatory myeloid cells. A new study identifies an unexpected driver of this process: the protein MLKL.
MLKL is best known for executing necroptosis, a form of programmed cell death. The new research reveals a distinct, non-lethal role for MLKL in stem cells: intermittent activation of MLKL damages mitochondria, undermining HSC function and accelerating features of cellular aging without actually killing the cells.
Key findings
- Hallmarks of aging: Stress-triggered MLKL activation suppresses HSC self-renewal and shifts differentiation toward myeloid cells at the expense of lymphoid cells, reducing the capacity for a robust immune response.
- Benefit of MLKL deletion: Removing MLKL preserved HSC regenerative capacity, produced healthier immune cells, and lowered DNA damage in stressed or aged animals.
- Organelle-level mechanism: Rather than acting through large changes in gene expression, MLKL drives aging by post-transcriptional effects on the mitochondria — altering organelle structure and function.
- Mitochondrial protection preserves function: Inactivating MLKL protected mitochondrial health and maintained hematopoietic function, indicating MLKL is a central convergence point for diverse age-related stresses.
Source: University of Tokyo
Overview
Hematopoietic stem cells normally balance self-renewal with production of all blood cell types. With age or repeated stress, HSCs produce fewer new cells, increasingly favor myeloid over lymphoid lineages, and lose the ability to sustain strong immune responses. Accumulated damage, shifts in gene regulation, chronic low-level inflammation, and changes in the bone marrow niche all contribute to this decline, but how these diverse stresses converge on HSC dysfunction has been unclear.
Researchers at The University of Tokyo and St. Jude Children’s Research Hospital investigated how age-related stresses affect HSCs, focusing on the RIPK3–MLKL signaling axis, a pathway classically linked to necroptosis. The team combined genetic mouse models, stress challenges that mimic inflammation, replication stress, and oncogenic stress, and a range of functional and molecular assays to track how MLKL activation affects HSCs.
They used wild-type, MLKL-deficient, and RIPK3-deficient mice and reporter animals that detect MLKL activation. HSC performance was tested primarily by bone marrow transplantation, which measures the cells’ ability to rebuild the blood system. Complementary methods included flow cytometry, ex vivo expansion, RNA sequencing, ATAC-seq for chromatin accessibility, high-resolution microscopy, metabolic assays, and detailed mitochondrial analyses.
The results point to a previously unrecognized, necroptosis-independent role for MLKL in HSC aging. Under stress, MLKL becomes transiently active and localizes to mitochondria. Rather than killing stem cells, this mitochondrial MLKL impairs membrane potential, distorts mitochondrial structure, and reduces energy production. Those organelle-level changes lead to reduced self-renewal, loss of lymphoid differentiation potential, and a myeloid-biased output — all established features of aging HSCs.
Crucially, HSCs lacking MLKL retain regenerative capacity and produce healthier immune lineages, showing lower levels of DNA damage and preserved mitochondrial function even after stress or in aged animals. These improvements occurred with minimal changes in global gene expression or chromatin state, highlighting post-transcriptional, organelle-focused mechanisms rather than large transcriptional rewiring or inflammation-driven effects.
By identifying the RIPK3–MLKL axis as a common route through which diverse stresses impair mitochondria and drive HSC aging, the study provides a unifying mechanism for age-related decline in the blood-forming system. The findings suggest that targeting MLKL or otherwise protecting mitochondria could preserve HSC function and improve outcomes for patients facing chemotherapy, radiation, transplantation, or age-related immune weakening.
Lead author Dr. Masayuki Yamashita notes that the discovery of a non-lethal, stress-responsive role for a necroptosis effector opens new therapeutic possibilities. Future drug strategies might focus on modulating necroptosis signaling or directly safeguarding mitochondrial integrity to keep the blood system “younger” and more resilient.
In summary, the study reveals MLKL as a non-lethal regulator of stem cell aging: it acts as a stress-responsive factor that selectively damages mitochondria and drives functional decline in HSCs. These insights expand our understanding of necroptosis-related proteins and point to new avenues for preserving hematopoietic health with age.
Key Questions Answered
A: In HSCs, MLKL activation is transient and localized. It activates just long enough to damage mitochondria but stops before causing membrane rupture and cell death — producing functional impairment without loss of cell viability.
A: The work identifies MLKL as a clear molecular target. Therapies that block MLKL activation or protect mitochondria may help maintain a more youthful blood system and improve recovery after chemotherapy or other stresses, but clinical translation will require further research.
A: This study focuses on hematopoietic stem cells, but many stem cell types age through mitochondrial dysfunction. The authors suggest that similar non-lethal roles for death pathway proteins may contribute to aging in other tissues, a hypothesis that invites further investigation.
Editorial notes
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was provided by editorial staff.
About this genetics and aging research news
Author: Project Coordination Office
Source: University of Tokyo
Contact: Project Coordination Office – University of Tokyo
Image: Image credited to Neuroscience News
Original Research: Open access.
Paper title: Non-necroptotic MLKL function damages mitochondria and promotes hematopoietic stem cell aging — Yuta Yamada, Jinjing Yang, Akiho Saiki-Tsuchiya, Yuji Watanabe, Shuhei Koide, Shin Murai, Yuriko Sorimachi, Yu Fukuda, Kenta Sumiyama, Hiroshi Sagara, Hiroyasu Nakano, Keiyo Takubo, Atsushi Iwama & Masayuki Yamashita. Nature Communications
DOI: 10.1038/s41467-026-71060-4
Abstract
Non-necroptotic MLKL function damages mitochondria and promotes hematopoietic stem cell aging
Hematopoietic stem cells tolerate diverse stresses but often lose regenerative and lymphoid-producing capacities with age. Dysfunctional HSCs with impaired mitochondria accumulate over time. Multiple stress responses converge on the RIPK3–MLKL axis to induce age-related changes in HSCs. Activated MLKL accumulates in HSC mitochondria, and rather than triggering cell death, it impairs self-renewal and lymphoid differentiation. MLKL-mediated mitochondrial damage and reduced glycolytic flux contribute to functional decline. These results identify the RIPK3–MLKL axis as a key mediator of HSC aging and reveal a necroptosis-independent role for MLKL in mitochondrial damage.