Negative social ties, or “hasslers,” are pervasive yet understudied components of social networks that may accelerate biological aging and morbidity. Using ego-centric network data and DNA methylation-based biological aging clocks (i.e., DunedinPACE and age-accelerated GrimAge2) from saliva from a state representative probability sample in Indiana, we examine how negative social ties are associated with accelerated biological aging and a broad range of health outcomes, including inflammation and multimorbidity. Negative relationships are not rare within close relationships, as nearly 30% of individuals report having at least one hassler in their network. These hasslers tend to occupy peripheral network positions and are more likely to be connected through weak, uniplex ties. Importantly, exposure to negative social ties follows patterns of social and health vulnerability, with women, daily smokers, people in poorer health, and those with adverse childhood experiences more likely to report having hasslers in their networks. Having more hasslers is associated with accelerated biological aging in both rate and cumulative burden: Each additional hassler corresponds to approximately 1.5% faster pace of aging and roughly 9 mo older biological age. Moreover, not all hasslers exert the same influence; kin and nonkin hasslers show detrimental associations, whereas spouse hasslers do not. Finally, a greater number of hasslers is associated with multiple adverse health outcomes beyond epigenetic aging. These findings together highlight the critical role of negative social ties in biological aging as chronic stressors and the need for interventions that reduce harmful social exposures to promote healthier aging trajectories.

This insight has major implications for the development of antiaging therapies. First, they suggest that mtDNA integrity is not simply one of the many hallmarks of aging, but rather the foundation upon which others are built. And when that platform is broken, downstream hallmarks such as proteostasis or DNA repair cannot be engaged by typical means. Second, it suggests that interventions that target nutrient-sensing pathways may fail, or even backfire, when applied to organisms or tissues with high levels of mitochondrial damage. Hence, the next generation of geroprotective treatments must be tested in diverse models of aging, including those that combine multiple hallmarks, to better understand the scope and boundaries of their efficacy. Last, the efficacy of those treatments could be amplified by measures that improve the stability of the mitochondrial genome. While a reduction in IGF-1 signaling did not alter the frequency of mutations in WT or Polg^D257A mice, it did slow the pace with which they reached homoplasmy. Thus, although it may not be possible today to reduce mitochondrial mutagenesis in human cells, our data show that it may already be possible to curtail the impact of mtDNA mutations on mammalian health span by slowing their clonal expansion in nondividing cells, the cells that are most sensitive to metabolic dysfunction.

While the precise mechanism by which Pappa influences clonal expansion of mtDNA mutations remains uncertain, several plausible explanations can be proposed. In the absence of cell division (the major driver for homoplasmy in dividing cells), the progression of mtDNA mutations toward homoplasmy is primarily driven by random genetic drift, the rate of mtDNA replication, and mitochondrial quality control. Thus, it is likely that loss of Pappa influences one of these three processes. Loss of Pappa may either reduce the rate of random genetic drift (potentially by changing mitochondrial fusion and fission or the spatial segregation of semi-isolated pockets of mtDNA), reduce the rate of mtDNA replication (less replication lowers the chance that a mutant mtDNA molecule expands enough to reach homoplasmy), or improve mitochondrial quality control by degrading mitochondria with mutant mtDNA molecules. It will be important to distinguish between these possibilities in future work to clear the way for novel interventions aimed at curbing the impact of mtDNA mutations on human health.

Regardless of the mechanism, these findings provide a compelling example of how the interplay between distinct hallmarks of the aging process can fundamentally alter the outcome of otherwise beneficial interventions. They reveal that the efficacy of antiaging strategies such as IGF-1 suppression is not absolute but context dependent. They are contingent on the integrity of underlying systems, including proteostasis and DNA repair. Without an intact mitochondrial genome, these pathways cannot be engaged, indicating that mtDNA integrity is required for these critical antiaging pathways. More broadly, our results underscore the need for a more integrated model of aging, one that considers not only individual pathways but also their interactions, hierarchies, and points of failure. By mapping these interactions, we can better anticipate the limitations of existing interventions and design next-generation therapies that are robust to the complex biology of aged tissues. In this light, strategies that target the expansion of mtDNA mutations, rather than their origin, may offer a powerful new axis for preserving tissue function and extending health span, even when the underlying genomic damage cannot be undone.

Metal ions are indispensable for living organisms, participating in essential physiological processes. However, their dysregulated accumulation can trigger cell death and metal overload. The recent discovery of novel regulated cell death modalities, such as cuproptosis and ferroptosis, has significantly advanced the understanding of metal ions in cell fate and immune regulation. This review systematically elucidates the molecular mechanisms underlying metal ion-induced cell death, encompassing oxidative stress, mitochondrial dysfunction, DNA damage, and epigenetic modifications. It further classifies and discusses the hallmarks of various programmed and non-programmed cell death pathways, emphasizing the pivotal role of metal ions in anti-tumor immunity.

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